Bio

Academic Appointments


Honors & Awards


  • Honors, University of Chicago (1985)
  • Emil Bogen Award, University of California, Los Angeles (1992)
  • Physician Post-Doctoral Award, Howard Hughes Medical Institute (1997-1999)
  • Esther Ehrman Faculty Scholar Award, Stanford University (2000-2003)
  • Charles Carrington Prize, Stanford University (2002)
  • Clinical Investigator Award, Damon Runyon Foundation (2003-2008)
  • Elected Member, American Society of Clinical Investigation (2005)
  • Translational Research Award, Burroughs Wellcome Trust (2005-2011)
  • Elected Member, Association of American Physicians (2011)

Professional Education


  • MD PhD, UCLA, Medicine/Molecular Biology (1992)
  • BS, University of Chicago, Chemistry (1985)

Research & Scholarship

Current Research and Scholarly Interests


My laboratory investigates how oncogenes initiate and sustain tumorigenesis. I have developed model systems whereby I can conditionally activate oncogenes in normal human and mouse cells in tissue culture or in specific tissues of transgenic mice. In particular using the tetracycline regulatory system, I have generated a conditional model system for MYC-induced tumors. I have shown that cancers caused by the conditional over-expression of the MYC proto-oncogene regress with its inactivation. Thus, even though cancer is a multi-step process, the inactivation of one oncogene can be sufficient to induce tumor regression. Now, I am using these model systems to address three questions:

1. How do oncogenes initiate tumorigenesis?
2. How does oncogene inactivation cause tumor regression?
3. How do tumors escape dependence on oncogenes?

Clinical Trials


  • Phase II Study of Atorvastatin Safety and Antitumor Effects in Non-Hodgkin's Lymphoma Not Recruiting

    The purpose of this study is to: 1. Determine changes in levels of tumor bioactivity upon treatment with atorvastatin. Secondary objective: 2. Determine validity of tumor bioactivity as a biologic endpoint by correlation with clinical response. 3. Determine whether administration of atorvastatin is tolerable and safe in low grade NHL patients. We do not anticipate any significant toxicity since this dose of atorvastatin has been FDA approved for patients with hypercholesterolemia.

    Stanford is currently not accepting patients for this trial. For more information, please contact Alice Fan, 650-736-1285.

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  • Molecular Analysis of Thoracic Malignancies Recruiting

    Primary Objective: To collect detailed clinical information on patients with thoracic malignancies via the electronic medical record and a detailed patient questionnaire, collect blood samples, retrieve paraffin embedded tissue if not collected at Stanford, and perform exploratory molecular analysis of tumor tissues.

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Teaching

2013-14 Courses


Publications

Journal Articles


  • CD271(+) Bone Marrow Mesenchymal Stem Cells May Provide a Niche for Dormant Mycobacterium tuberculosis SCIENCE TRANSLATIONAL MEDICINE Das, B., Kashino, S. S., Pulu, I., Kalita, D., Swami, V., Yeger, H., Felsher, D. W., Campos-Neto, A. 2013; 5 (170)

    Abstract

    Mycobacterium tuberculosis (Mtb) can persist in hostile intracellular microenvironments evading immune cells and drug treatment. However, the protective cellular niches where Mtb persists remain unclear. We report that Mtb may maintain long-term intracellular viability in a human bone marrow (BM)-derived CD271(+)/CD45(-) mesenchymal stem cell (BM-MSC) population in vitro. We also report that Mtb resides in an equivalent population of BM-MSCs in a mouse model of dormant tuberculosis infection. Viable Mtb was detected in CD271(+)/CD45(-) BM-MSCs isolated from individuals who had successfully completed months of anti-Mtb drug treatment. These results suggest that CD271(+) BM-MSCs may provide a long-term protective intracellular niche in the host in which dormant Mtb can reside.

    View details for DOI 10.1126/scitranslmed.3004912

    View details for Web of Science ID 000314343100003

    View details for PubMedID 23363977

  • Twist1 Suppresses Senescence Programs and Thereby Accelerates and Maintains Mutant Kras-Induced Lung Tumorigenesis PLOS GENETICS Tran, P. T., Shroff, E. H., Burns, T. F., Thiyagarajan, S., Das, S. T., Zabuawala, T., Chen, J., Cho, Y., Luong, R., Tamayo, P., Salih, T., Aziz, K., Adam, S. J., Vicent, S., Nielsen, C. H., Withofs, N., Sweet-Cordero, A., Gambhir, S. S., Rudin, C. M., Felsher, D. W. 2012; 8 (5)

    Abstract

    KRAS mutant lung cancers are generally refractory to chemotherapy as well targeted agents. To date, the identification of drugs to therapeutically inhibit K-RAS have been unsuccessful, suggesting that other approaches are required. We demonstrate in both a novel transgenic mutant Kras lung cancer mouse model and in human lung tumors that the inhibition of Twist1 restores a senescence program inducing the loss of a neoplastic phenotype. The Twist1 gene encodes for a transcription factor that is essential during embryogenesis. Twist1 has been suggested to play an important role during tumor progression. However, there is no in vivo evidence that Twist1 plays a role in autochthonous tumorigenesis. Through two novel transgenic mouse models, we show that Twist1 cooperates with Kras(G12D) to markedly accelerate lung tumorigenesis by abrogating cellular senescence programs and promoting the progression from benign adenomas to adenocarcinomas. Moreover, the suppression of Twist1 to physiological levels is sufficient to cause Kras mutant lung tumors to undergo senescence and lose their neoplastic features. Finally, we analyzed more than 500 human tumors to demonstrate that TWIST1 is frequently overexpressed in primary human lung tumors. The suppression of TWIST1 in human lung cancer cells also induced cellular senescence. Hence, TWIST1 is a critical regulator of cellular senescence programs, and the suppression of TWIST1 in human tumors may be an effective example of pro-senescence therapy.

    View details for DOI 10.1371/journal.pgen.1002650

    View details for Web of Science ID 000304864000004

    View details for PubMedID 22654667

  • Immunology in the clinic review series; focus on cancer: multiple roles for the immune system in oncogene addiction CLINICAL AND EXPERIMENTAL IMMUNOLOGY Bachireddy, P., Rakhra, K., Felsher, D. W. 2012; 167 (2): 188-194

    Abstract

    Despite complex genomic and epigenetic abnormalities, many cancers are irrevocably dependent on an initiating oncogenic lesion whose restoration to a normal physiological activation can elicit a dramatic and sudden reversal of their neoplastic properties. This phenomenon of the reversal of tumorigenesis has been described as oncogene addiction. Oncogene addiction had been thought to occur largely through tumour cell-autonomous mechanisms such as proliferative arrest, apoptosis, differentiation and cellular senescence. However, the immune system plays an integral role in almost every aspect of tumorigenesis, including tumour initiation, prevention and progression as well as the response to therapeutics. Here we highlight more recent evidence suggesting that oncogene addiction may be integrally dependent upon host immune-mediated mechanisms, including specific immune effectors and cytokines that regulate tumour cell senescence and tumour-associated angiogenesis. Hence, the host immune system is essential to oncogene addiction.

    View details for DOI 10.1111/j.1365-2249.2011.04514.x

    View details for Web of Science ID 000299037700002

    View details for PubMedID 22235994

  • "Picolog," a Synthetically-Available Bryostatin Analog, Inhibits Growth of MYC-Induced Lymphoma In Vivo ONCOTARGET DeChristopher, B. A., Fan, A. C., Felsher, D. W., Wender, P. A. 2012; 3 (1): 58-66

    Abstract

    Bryostatin 1 is a naturally occurring complex macrolide with potent anti-neoplastic activity. However, its extremely low natural occurrence has impeded clinical advancement. We developed a strategy directed at the design of simplified and synthetically more accessible bryostatin analogs. Our lead analog, "picolog", can be step-economically produced. Picolog, compared to bryostatin, exhibited superior growth inhibition of MYC-induced lymphoma in vitro. A key mechanism of picolog's (and bryostatin's) activity is activation of PKC. A novel nano-immunoassay (NIA) revealed that picolog treatment increased phospho-MEK2 in the PKC pathway. Moreover, the inhibition of PKC abrogated picolog's activity. Finally, picolog was highly potent at 100 micrograms/kg and well tolerated at doses ranging from 100 micrograms/kg to 1 milligram/kg in vivo for the treatment of our aggressive model of MYC-induced lymphoma. We provide the first in vivo validation that the bryostatin analog, picolog, is a potential therapeutic agent for the treatment of cancer and other diseases.

    View details for Web of Science ID 000303914000009

    View details for PubMedID 22308267

  • Lymphomas that recur after MYC suppression continue to exhibit oncogene addiction PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Choi, P. S., van Riggelen, J., Gentles, A. J., Bachireddy, P., Rakhra, K., Adam, S. J., Plevritis, S. K., Felsher, D. W. 2011; 108 (42): 17432-17437

    Abstract

    The suppression of oncogenic levels of MYC is sufficient to induce sustained tumor regression associated with proliferative arrest, differentiation, cellular senescence, and/or apoptosis, a phenomenon known as oncogene addiction. However, after prolonged inactivation of MYC in a conditional transgenic mouse model of E?-tTA/tetO-MYC T-cell acute lymphoblastic leukemia, some of the tumors recur, recapitulating what is frequently observed in human tumors in response to targeted therapies. Here we report that these recurring lymphomas express either transgenic or endogenous Myc, albeit in many cases at levels below those in the original tumor, suggesting that tumors continue to be addicted to MYC. Many of the recurring lymphomas (76%) harbored mutations in the tetracycline transactivator, resulting in expression of the MYC transgene even in the presence of doxycycline. Some of the remaining recurring tumors expressed high levels of endogenous Myc, which was associated with a genomic rearrangement of the endogenous Myc locus or activation of Notch1. By gene expression profiling, we confirmed that the primary and recurring tumors have highly similar transcriptomes. Importantly, shRNA-mediated suppression of the high levels of MYC in recurring tumors elicited both suppression of proliferation and increased apoptosis, confirming that these tumors remain oncogene addicted. These results suggest that tumors induced by MYC remain addicted to overexpression of this oncogene.

    View details for DOI 10.1073/pnas.1107303108

    View details for Web of Science ID 000295975300044

    View details for PubMedID 21969595

  • Survival and Death Signals Can Predict Tumor Response to Therapy After Oncogene Inactivation SCIENCE TRANSLATIONAL MEDICINE Tran, P. T., Bendapudi, P. K., Lin, H. J., Choi, P., Koh, S., Chen, J., Horng, G., Hughes, N. P., Schwartz, L. H., Miller, V. A., Kawashima, T., Kitamura, T., Paik, D., Felsher, D. W. 2011; 3 (103)

    Abstract

    Cancers can exhibit marked tumor regression after oncogene inhibition through a phenomenon called "oncogene addiction." The ability to predict when a tumor will exhibit oncogene addiction would be useful in the development of targeted therapeutics. Oncogene addiction is likely the consequence of many cellular programs. However, we reasoned that many of these inputs may converge on aggregate survival and death signals. To test this, we examined conditional transgenic models of K-ras(G12D)--or MYC-induced lung tumors and lymphoma combined with quantitative imaging and an in situ analysis of biomarkers of proliferation and apoptotic signaling. We then used computational modeling based on ordinary differential equations (ODEs) to show that oncogene addiction could be modeled as differential changes in survival and death intracellular signals. Our mathematical model could be generalized to different imaging methods (computed tomography and bioluminescence imaging), different oncogenes (K-ras(G12D) and MYC), and several tumor types (lung and lymphoma). Our ODE model could predict the differential dynamics of several putative prosurvival and prodeath signaling factors [phosphorylated extracellular signal-regulated kinase 1 and 2, Akt1, Stat3/5 (signal transducer and activator of transcription 3/5), and p38] that contribute to the aggregate survival and death signals after oncogene inactivation. Furthermore, we could predict the influence of specific genetic lesions (p53?/?, Stat3-d358L, and myr-Akt1) on tumor regression after oncogene inactivation. Then, using machine learning based on support vector machine, we applied quantitative imaging methods to human patients to predict both their EGFR genotype and their progression-free survival after treatment with the targeted therapeutic erlotinib. Hence, the consequences of oncogene inactivation can be accurately modeled on the basis of a relatively small number of parameters that may predict when targeted therapeutics will elicit oncogene addiction after oncogene inactivation and hence tumor regression.

    View details for DOI 10.1126/scitranslmed.3002018

    View details for Web of Science ID 000295840000005

    View details for PubMedID 21974937

  • CD4(+) T Cells Contribute to the Remodeling of the Microenvironment Required for Sustained Tumor Regression upon Oncogene Inactivation CANCER CELL Rakhra, K., Bachireddy, P., Zabuawala, T., Zeiser, R., Xu, L., Kopelman, A., Fan, A. C., Yang, Q., Braunstein, L., Crosby, E., Ryeom, S., Felsher, D. W. 2010; 18 (5): 485-498

    Abstract

    Oncogene addiction is thought to occur cell autonomously. Immune effectors are implicated in the initiation and restraint of tumorigenesis, but their role in oncogene inactivation-mediated tumor regression is unclear. Here, we show that an intact immune system, specifically CD4(+) T cells, is required for the induction of cellular senescence, shutdown of angiogenesis, and chemokine expression resulting in sustained tumor regression upon inactivation of the MYC or BCR-ABL oncogenes in mouse models of T cell acute lymphoblastic lymphoma and pro-B cell leukemia, respectively. Moreover, immune effectors knocked out for thrombospondins failed to induce sustained tumor regression. Hence, CD4(+) T cells are required for the remodeling of the tumor microenvironment through the expression of chemokines, such as thrombospondins, in order to elicit oncogene addiction.

    View details for DOI 10.1016/j.ccr.2010.10.002

    View details for Web of Science ID 000284658600013

    View details for PubMedID 21035406

  • The interaction between Myc and Miz1 is required to antagonize TGF beta-dependent autocrine signaling during lymphoma formation and maintenance GENES & DEVELOPMENT van Riggelen, J., Mueller, J., Otto, T., Beuger, V., Yetil, A., Choi, P. S., Kosan, C., Moeroey, T., Felsher, D. W., Eilers, M. 2010; 24 (12): 1281-1294

    Abstract

    The Myc protein suppresses the transcription of several cyclin-dependent kinase inhibitors (CKIs) via binding to Miz1; whether this interaction is important for Myc's ability to induce or maintain tumorigenesis is not known. Here we show that the oncogenic potential of a point mutant of Myc (MycV394D) that is selectively deficient in binding to Miz1 is greatly attenuated. Binding of Myc to Miz1 is continuously required to repress CKI expression and inhibit accumulation of trimethylated histone H3 at Lys 9 (H3K9triMe), a hallmark of cellular senescence, in T-cell lymphomas. Lymphomas that arise express high amounts of transforming growth factor beta-2 (TGFbeta-2) and TGFbeta-3. Upon Myc suppression, TGFbeta signaling is required to induce CKI expression and cellular senescence and suppress tumor recurrence. Binding of Myc to Miz1 is required to antagonize growth suppression and induction of senescence by TGFbeta. We demonstrate that, since lymphomas express high levels of TGFbeta, they are poised to elicit an autocrine program of senescence upon Myc inactivation, demonstrating that TGFbeta is a key factor that establishes oncogene addiction of T-cell lymphomas.

    View details for DOI 10.1101/gad.585710

    View details for Web of Science ID 000278778200008

  • MYC as a regulator of ribosome biogenesis and protein synthesis NATURE REVIEWS CANCER van Riggelen, J., Yetil, A., Felsher, D. W. 2010; 10 (4): 301-309

    Abstract

    MYC regulates the transcription of thousands of genes required to coordinate a range of cellular processes, including those essential for proliferation, growth, differentiation, apoptosis and self-renewal. Recently, MYC has also been shown to serve as a direct regulator of ribosome biogenesis. MYC coordinates protein synthesis through the transcriptional control of RNA and protein components of ribosomes, and of gene products required for the processing of ribosomal RNA, the nuclear export of ribosomal subunits and the initiation of mRNA translation. We discuss how the modulation of ribosome biogenesis by MYC may be essential to its physiological functions as well as its pathological role in tumorigenesis.

    View details for DOI 10.1038/nrc2819

    View details for Web of Science ID 000275932700013

    View details for PubMedID 20332779

  • Nanofluidic proteomic assay for serial analysis of oncoprotein activation in clinical specimens NATURE MEDICINE Fan, A. C., Deb-Basu, D., Orban, M. W., Gotlib, J. R., Natkunam, Y., O'Neill, R., Padua, R., Xu, L., Taketa, D., Shirer, A. E., Beer, S., Yee, A. X., Voehringer, D. W., Felsher, D. W. 2009; 15 (5): 566-571

    Abstract

    Current methods of protein detection are insensitive to detecting subtle changes in oncoprotein activation that underlie key cancer signaling processes. The requirement for large numbers of cells precludes serial tumor sampling for assessing a response to therapeutics. Therefore, we have developed a nanofluidic proteomic immunoassay (NIA) to quantify total and low-abundance protein isoforms in nanoliter volumes. Our method can quantify amounts of MYC oncoprotein and B cell lymphoma protein-2 (BCL2) in Burkitt's and follicular lymphoma; identify changes in activation of extracellular signal-related kinases-1 (ERK1) and ERK2, mitogen-activated kinase-1 (MEK), signal transducer and activator of transcription protein-3 (STAT3) and STAT5, c-Jun N-terminal kinase (JNK) and caspase-3 in imatinib-treated chronic myelogeneous leukemia (CML) cells; measure an unanticipated change in the phosphorylation of an ERK2 isomer in individuals with CML who responded to imatinib; and detect a decrease in STAT3 and STAT5 phosphorylation in individuals with lymphoma who were treated with atorvastatin. Therefore, we have described a new and highly sensitive method for determining oncoprotein expression and phosphorylation in clinical specimens for the development of new therapeutics for cancer.

    View details for DOI 10.1038/nm.1903

    View details for Web of Science ID 000265889300036

    View details for PubMedID 19363496

  • Combined Analysis of Murine and Human Microarrays and ChIP Analysis Reveals Genes Associated with the Ability of MYC To Maintain Tumorigenesis PLOS GENETICS Wu, C., Sahoo, D., Arvanitis, C., Bradon, N., Dill, D. L., Felsher, D. W. 2008; 4 (6)

    Abstract

    The MYC oncogene has been implicated in the regulation of up to thousands of genes involved in many cellular programs including proliferation, growth, differentiation, self-renewal, and apoptosis. MYC is thought to induce cancer through an exaggerated effect on these physiologic programs. Which of these genes are responsible for the ability of MYC to initiate and/or maintain tumorigenesis is not clear. Previously, we have shown that upon brief MYC inactivation, some tumors undergo sustained regression. Here we demonstrate that upon MYC inactivation there are global permanent changes in gene expression detected by microarray analysis. By applying StepMiner analysis, we identified genes whose expression most strongly correlated with the ability of MYC to induce a neoplastic state. Notably, genes were identified that exhibited permanent changes in mRNA expression upon MYC inactivation. Importantly, permanent changes in gene expression could be shown by chromatin immunoprecipitation (ChIP) to be associated with permanent changes in the ability of MYC to bind to the promoter regions. Our list of candidate genes associated with tumor maintenance was further refined by comparing our analysis with other published results to generate a gene signature associated with MYC-induced tumorigenesis in mice. To validate the role of gene signatures associated with MYC in human tumorigenesis, we examined the expression of human homologs in 273 published human lymphoma microarray datasets in Affymetrix U133A format. One large functional group of these genes included the ribosomal structural proteins. In addition, we identified a group of genes involved in a diverse array of cellular functions including: BZW2, H2AFY, SFRS3, NAP1L1, NOLA2, UBE2D2, CCNG1, LIFR, FABP3, and EDG1. Hence, through our analysis of gene expression in murine tumor models and human lymphomas, we have identified a novel gene signature correlated with the ability of MYC to maintain tumorigenesis.

    View details for DOI 10.1371/journal.pgen.1000090

    View details for Web of Science ID 000260410300026

    View details for PubMedID 18535662

  • Cellular senescence is an important mechanism of tumor regression upon c-Myc inactivation PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Wu, C., van Riggelen, J., Yetil, A., Fan, A. C., Bachireddy, P., Felsher, D. W. 2007; 104 (32): 13028-13033

    Abstract

    Oncogene-induced senescence is an important mechanism by which normal cells are restrained from malignant transformation. Here we report that the suppression of the c-Myc (MYC) oncogene induces cellular senescence in diverse tumor types including lymphoma, osteosarcoma, and hepatocellular carcinoma. MYC inactivation was associated with prototypical markers of senescence, including acidic beta-gal staining, induction of p16INK4a, and p15INK4b expression. Moreover, MYC inactivation induced global changes in chromatin structure associated with the marked reduction of histone H4 acetylation and increased histone H3 K9 methylation. Osteosarcomas engineered to be deficient in p16INK4a or Rb exhibited impaired senescence and failed to exhibit sustained tumor regression upon MYC inactivation. Similarly, only after lymphomas were repaired for p53 expression did MYC inactivation induce robust senescence and sustained tumor regression. The pharmacologic inhibition of signaling pathways implicated in oncogene-induced senescence including ATM/ATR and MAPK did not prevent senescence associated with MYC inactivation. Our results suggest that cellular senescence programs remain latently functional, even in established tumors, and can become reactivated, serving as a critical mechanism of oncogene addiction associated with MYC inactivation.

    View details for DOI 10.1073/pnas.0701953104

    View details for Web of Science ID 000248650300015

    View details for PubMedID 17664422

  • Sustained regression of tumors upon MYC inactivation requires p53 or thrombospondin-1 to reverse the angiogenic switch PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Giuriato, S., Ryeom, S., Fan, A. C., Bachireddy, P., Lynch, R. C., Rioth, M. J., van Riggelen, J., Kopelman, A. M., Passegue, E., Tang, F., Folkman, J., Felsher, D. W. 2006; 103 (44): 16266-16271

    Abstract

    The targeted inactivation of oncogenes offers a rational therapeutic approach for the treatment of cancer. However, the therapeutic inactivation of a single oncogene has been associated with tumor recurrence. Therefore, it is necessary to develop strategies to override mechanisms of tumor escape from oncogene dependence. We report here that the targeted inactivation of MYC is sufficient to induce sustained regression of hematopoietic tumors in transgenic mice, except in tumors that had lost p53 function. p53 negative tumors were unable to be completely eliminated, as demonstrated by the kinetics of tumor cell elimination revealed by bioluminescence imaging. Histological examination revealed that upon MYC inactivation, the loss of p53 led to a deficiency in thrombospondin-1 (TSP-1) expression, a potent antiangiogenic protein, and the subsequent inability to shut off angiogenesis. Restoration of p53 expression in these tumors re-established TSP-1 expression. This permitted the suppression of angiogenesis and subsequent sustained tumor regression upon MYC inactivation. Similarly, the restoration of TSP-1 alone in p53 negative tumors resulted in the shut down of angiogenesis and led to sustained tumor regression upon MYC inactivation. Hence, the complete regression of tumor mass driven by inactivation of the MYC oncogene requires the p53-dependent induction of TSP-1 and the shut down of angiogenesis. Notably, overexpression of TSP-1 alone did not influence tumor growth. Therefore, the combined inactivation of oncogenes and angiogenesis may be a more clinically effective treatment of cancer. We conclude that angiogenesis is an essential component of oncogene addiction.

    View details for DOI 10.1073/pnas.0608017103

    View details for Web of Science ID 000241879500038

    View details for PubMedID 17056717

  • Developmental context determines latency of MYC-induced tumorigenesis PLOS BIOLOGY Beer, S., Zetterberg, A., Ihrie, R. A., McTaggart, R. A., Yang, Q. W., Bradon, N., Arvanitis, C., Attardi, L. D., Feng, S., Ruebner, B., Cardiff, R. D., Felsher, D. W. 2004; 2 (11): 1785-1798

    Abstract

    One of the enigmas in tumor biology is that different types of cancers are prevalent in different age groups. One possible explanation is that the ability of a specific oncogene to cause tumorigenesis in a particular cell type depends on epigenetic parameters such as the developmental context. To address this hypothesis, we have used the tetracycline regulatory system to generate transgenic mice in which the expression of a c-MYC human transgene can be conditionally regulated in murine hepatocytes. MYC's ability to induce tumorigenesis was dependent upon developmental context. In embryonic and neonatal mice, MYC overexpression in the liver induced marked cell proliferation and immediate onset of neoplasia. In contrast, in adult mice MYC overexpression induced cell growth and DNA replication without mitotic cell division, and mice succumbed to neoplasia only after a prolonged latency. In adult hepatocytes, MYC activation failed to induce cell division, which was at least in part mediated through the activation of p53. Surprisingly, apoptosis is not a barrier to MYC inducing tumorigenesis. The ability of oncogenes to induce tumorigenesis may be generally restrained by developmentally specific mechanisms. Adult somatic cells have evolved mechanisms to prevent individual oncogenes from initiating cellular growth, DNA replication, and mitotic cellular division alone, thereby preventing any single genetic event from inducing tumorigenesis.

    View details for DOI 10.1371/journal.pbio.0020332

    View details for Web of Science ID 000225160300011

    View details for PubMedID 15455033

  • MYC inactivation uncovers pluripotent differentiation and tumour dormancy in hepatocellular cancer NATURE Shachaf, C. M., Kopelman, A. M., Arvanitis, C., Karlsson, A., Beer, S., Mandl, S., Bachmann, M. H., Borowsky, A. D., Ruebner, B., Cardiff, R. D., Yang, Q. W., BISHOP, J. M., Contag, C. H., Felsher, D. W. 2004; 431 (7012): 1112-1117

    Abstract

    Hepatocellular carcinoma is generally refractory to clinical treatment. Here, we report that inactivation of the MYC oncogene is sufficient to induce sustained regression of invasive liver cancers. MYC inactivation resulted en masse in tumour cells differentiating into hepatocytes and biliary cells forming bile duct structures, and this was associated with rapid loss of expression of the tumour marker alpha-fetoprotein, the increase in expression of liver cell markers cytokeratin 8 and carcinoembryonic antigen, and in some cells the liver stem cell marker cytokeratin 19. Using in vivo bioluminescence imaging we found that many of these tumour cells remained dormant as long as MYC remain inactivated; however, MYC reactivation immediately restored their neoplastic features. Using array comparative genomic hybridization we confirmed that these dormant liver cells and the restored tumour retained the identical molecular signature and hence were clonally derived from the tumour cells. Our results show how oncogene inactivation may reverse tumorigenesis in the most clinically difficult cancers. Oncogene inactivation uncovers the pluripotent capacity of tumours to differentiate into normal cellular lineages and tissue structures, while retaining their latent potential to become cancerous, and hence existing in a state of tumour dormancy.

    View details for DOI 10.1038/nature03043

    View details for Web of Science ID 000224730800044

    View details for PubMedID 15475948

  • Defective double-strand DNA break repair and chromosomal translocations by MYC overexpression PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Karlsson, A., Deb-Basu, D., Cherry, A., Turner, S., Ford, J., Felsher, D. W. 2003; 100 (17): 9974-9979

    Abstract

    DNA repair mechanisms are essential for the maintenance of genomic integrity. Disruption of gene products responsible for DNA repair can result in chromosomal damage. Improperly repaired chromosomal damage can result in the loss of chromosomes or the generation of chromosomal deletions or translocations, which can lead to tumorigenesis. The MYC protooncogene is a transcription factor whose overexpression is frequently associated with human neoplasia. MYC has not been previously implicated in a role in DNA repair. Here we report that the overexpression of MYC disrupts the repair of double-strand DNA breaks, resulting in a several-magnitude increase in chromosomal breaks and translocations. We found that MYC inhibited the repair of gamma irradiation DNA breaks in normal human cells and blocked the repair of a single double-strand break engineered to occur in an immortal cell line. By spectral karyotypic analysis, we found that MYC even within one cell division cycle resulted in a several-magnitude increase in the frequency of chromosomal breaks and translocations in normal human cells. Hence, MYC overexpression may be a previously undescribed example of a dominant mutator that may fuel tumorigenesis by inducing chromosomal damage.

    View details for DOI 10.1073/pnas.1732638100

    View details for Web of Science ID 000184926000064

    View details for PubMedID 12909717

  • Cancer revoked: oncogenes as therapeutic targets NATURE REVIEWS CANCER Felsher, D. W. 2003; 3 (5): 375-380

    Abstract

    Recent findings show that even the brief inactivation of a single oncogene might be sufficient to result in the sustained loss of a neoplastic phenotype. It is therefore possible that the targeted inactivation of oncogenes could be a specific and effective treatment for cancer. So why does oncogene inactivation cause tumour regression and will this be a generally successful approach for the treatment of human neoplasia?

    View details for DOI 10.1038/nrc1070

    View details for Web of Science ID 000183007900016

    View details for PubMedID 12724735

  • Sustained loss of a neoplastic phenotype by brief inactivation of MYC SCIENCE Jain, M., Arvanitis, C., Chu, K., Dewey, W., Leonhardt, E., Trinh, M., Sundberg, C. D., BISHOP, J. M., Felsher, D. W. 2002; 297 (5578): 102-104

    Abstract

    Pharmacological inactivation of oncogenes is being investigated as a possible therapeutic strategy for cancer. One potential drawback is that cessation of such therapy may allow reactivation of the oncogene and tumor regrowth. We used a conditional transgenic mouse model for MYC-induced tumorigenesis to demonstrate that brief inactivation of MYC results in the sustained regression of tumors and the differentiation of osteogenic sarcoma cells into mature osteocytes. Subsequent reactivation of MYC did not restore the cells' malignant properties but instead induced apoptosis. Thus, brief MYC inactivation appears to cause epigenetic changes in tumor cells that render them insensitive to MYC-induced tumorigenesis. These results raise the possibility that transient inactivation of MYC may be an effective therapy for certain cancers.

    View details for Web of Science ID 000176711000043

    View details for PubMedID 12098700

  • BCL-2 inhibition with ABT-737 prolongs survival in an NRAS/BCL-2 mouse model of AML by targeting primitive LSK and progenitor cells. Blood Beurlet, S., Omidvar, N., Gorombei, P., Krief, P., Le Pogam, C., Setterblad, N., de la Grange, P., Leboeuf, C., Janin, A., Noguera, M., Hervatin, F., Sarda-Mantel, L., Konopleva, M., Andreeff, M., Tu, A. W., Fan, A. C., Felsher, D. W., Whetton, A., Pla, M., West, R., Fenaux, P., Chomienne, C., Padua, R. A. 2013; 122 (16): 2864-2876

    Abstract

    Myelodysplastic syndrome (MDS) transforms into an acute myelogenous leukemia (AML) with associated increased bone marrow (BM) blast infiltration. Using a transgenic mouse model, MRP8[NRASD12/hBCL-2], in which the NRAS:BCL-2 complex at the mitochondria induces MDS progressing to AML with dysplastic features, we studied the therapeutic potential of a BCL-2 homology domain 3 mimetic inhibitor, ABT-737. Treatment significantly extended lifespan, increased survival of lethally irradiated secondary recipients transplanted with cells from treated mice compared with cells from untreated mice, with a reduction of BM blasts, Lin-/Sca-1(+)/c-Kit(+), and progenitor populations by increased apoptosis of infiltrating blasts of diseased mice assessed in vivo by technicium-labeled annexin V single photon emission computed tomography and ex vivo by annexin V/7-amino actinomycin D flow cytometry, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, caspase 3 cleavage, and re-localization of the NRAS:BCL-2 complex from mitochondria to plasma membrane. Phosphoprotein analysis showed restoration of wild-type (WT) AKT or protein kinase B, extracellular signal-regulated kinase 1/2 and mitogen-activated protein kinase patterns in spleen cells after treatment, which showed reduced mitochondrial membrane potential. Exon specific gene expression profiling corroborates the reduction of leukemic cells, with an increase in expression of genes coding for stem cell development and maintenance, myeloid differentiation, and apoptosis. Myelodysplastic features persist underscoring targeting of BCL-2-mediated effects on MDS-AML transformation and survival of leukemic cells.

    View details for DOI 10.1182/blood-2012-07-445635

    View details for PubMedID 23943652

  • A c-Myc Activation Sensor-Based High-Throughput Drug Screening Identifies an Antineoplastic Effect of Nitazoxanide. Molecular cancer therapeutics Fan-Minogue, H., Bodapati, S., Solow-Cordero, D., Fan, A., Paulmurugan, R., Massoud, T. F., Felsher, D. W., Gambhir, S. S. 2013; 12 (9): 1896-1905

    Abstract

    Deregulation of c-Myc plays a central role in the tumorigenesis of many human cancers. Yet, the development of drugs regulating c-Myc activity has been challenging. To facilitate the identification of c-Myc inhibitors, we developed a molecular imaging sensor based high throughput-screening (HTS) system. This system uses a cell-based assay to detect c-Myc activation in a HTS format, which is established from a pure clone of a stable breast cancer cell line that constitutively expresses a c-Myc activation sensor. Optimization of the assay performance in the HTS format resulted in uniform and robust signals at the baseline. Using this system, we performed a quantitative HTS against approximately 5,000 existing bioactive compounds from five different libraries. Thirty-nine potential hits were identified, including currently known c-Myc inhibitors. There are a few among the top potent hits that are not known for anti-c-Myc activity. One of these hits is nitazoxanide (NTZ), a thiazolide for treating human protozoal infections. Validation of NTZ in different cancer cell lines revealed a high potency for c-Myc inhibition with IC50 ranging between 10 - 500nM. Oral administration of NTZ in breast cancer xenograft mouse models significantly suppressed tumor growth by inhibition of c-Myc and induction of apoptosis. These findings suggest a potential of NTZ to be repurposed as a new anti-tumor agent for inhibition of c-Myc associated neoplasia. Our work also demonstrated the unique advantage of molecular imaging in accelerating discovery of drugs for c-Myc targeted cancer therapy.

    View details for DOI 10.1158/1535-7163.MCT-12-1243

    View details for PubMedID 23825064

  • A tumor-immune mathematical model of CD4+ T helper cell dependent tumor regression by oncogene inactivation. Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference Nwabugwu, C. I., Rakhra, K., Felsher, D. W., Paik, D. S. 2013; 2013: 4529-4532

    Abstract

    Understanding the complex dynamics between the tumor cells and the host immune system will be key to improved therapeutic strategies against cancer. We propose an ODE-based mathematical model of both the tumor and immune system and how they respond to inactivation of the driving oncogene. Our model supports experimental results showing that cellular senescence of tumor cells is dependent on CD4+ T helper cells, leading to relapse of tumors in immunocompromised hosts.

    View details for DOI 10.1109/EMBC.2013.6610554

    View details for PubMedID 24110741

  • Characterization of MYC-Induced Tumorigenesis by in Situ Lipid Profiling ANALYTICAL CHEMISTRY Perry, R. H., Bellovin, D. I., Shroff, E. H., Ismail, A. I., Zabuawala, T., Felsher, D. W., Zare, R. N. 2013; 85 (9): 4259-4262

    Abstract

    We apply desorption electrospray ionization mass spectrometry imaging (DESI-MSI) to provide an in situ lipidomic profile of genetically modified tissues from a conditional transgenic mouse model of MYC-induced hepatocellular carcinoma (HCC). This unique, label-free approach of combining DESI-MSI with the ability to turn specific genes on and off has led to the discovery of highly specific lipid molecules associated with MYC-induced tumor onset. We are able to distinguish normal from MYC-induced malignant cells. Our approach provides a strategy to define a precise molecular picture at a resolution of about 200 ?m that may be useful in identifying lipid molecules that define how the MYC oncogene initiates and maintains tumorigenesis.

    View details for DOI 10.1021/ac400479j

    View details for Web of Science ID 000318756100008

    View details for PubMedID 23560736

  • Role of MYCN in retinoblastoma LANCET ONCOLOGY Felsher, D. W. 2013; 14 (4): 270-271
  • Noncanonical roles of the immune system in eliciting oncogene addiction. Current opinion in immunology Casey, S. C., Bellovin, D. I., Felsher, D. W. 2013; 25 (2): 246-258

    Abstract

    Cancer is highly complex. The magnitude of this complexity makes it highly surprising that even the brief suppression of an oncogene can sometimes result in rapid and sustained tumor regression, illustrating that cancers can be 'oncogene addicted' [1-10]. The essential implication is that oncogenes may not only fuel the initiation of tumorigenesis, but in some cases must be excessively activated to maintain a neoplastic state [11]. Oncogene suppression acutely restores normal physiological programs that effectively overrides secondary genetic events and a cancer collapses [12,13]. Oncogene addiction is the description of the dramatic and sustained regression of some cancers upon the specific inactivation of a single oncogene [1-13,14(??),15,16(??)], that can occur through tumor intrinsic [1,2,4,12], but also host immune mechanisms [17-23]. Notably, oncogene inactivation elicits a host immune response that involves specific immune effectors and cytokines that facilitate a remodeling of the tumor microenvironment including the shut down of angiogenesis and the induction of cellular senescence of tumor cells [16(??)]. Hence, immune effectors are not only critically involved in tumor prevention, initiation [17-19], and progression [20], but also appear to be essential to tumor regression upon oncogene inactivation [21,22(??),23(??)]. Understanding how the inactivation of an oncogene elicits a systemic signal in the host that prompts a deconstruction of a tumor could have important implications. The combination of oncogene-targeted therapy together with immunomodulatory therapy may be ideal for the development of both robust tumor intrinsic and immunological responses, effectively leading to sustained tumor regression.

    View details for DOI 10.1016/j.coi.2013.02.003

    View details for PubMedID 23571026

  • Generation of a Tetracycline Regulated Mouse Model of MYC-Induced T-Cell Acute Lymphoblastic Leukemia. Methods in molecular biology (Clifton, N.J.) Rakhra, K., Felsher, D. W. 2013; 1012: 221-235

    Abstract

    The tetracycline regulatory system provides a tractable strategy to interrogate the role of oncogenes in the initiation and maintenance of tumorigenesis through both spatial and temporal control of expression. This approach has several potential advantages over conventional methods to generate genetically engineered mouse models. First, continuous constitutive overexpression of an oncogene can be lethal to the host impeding further study. Second, constitutive overexpression fails to model adult onset of disease. Third, constitutive deletion does not permit, whereas conditional overexpression of an oncogene enables the study of the consequences of restoring expression of an oncogene back to endogenous levels. Fourth, the conditional activation of oncogenes enables examination of specific and/or developmental state-specific consequences.Hence, by allowing precise control of when and where a gene is expressed, the tetracycline regulatory system provides an ideal approach for the study of putative oncogenes in both the initiation and maintenance of tumorigenesis. In this protocol, we describe the methods involved in the development of a conditional mouse model of MYC-induced T-cell acute lymphoblastic leukemia.

    View details for DOI 10.1007/978-1-62703-429-6_15

    View details for PubMedID 24006068

  • Tumor dormancy, oncogene addiction, cellular senescence, and self-renewal programs. Advances in experimental medicine and biology Bellovin, D. I., Das, B., Felsher, D. W. 2013; 734: 91-107

    Abstract

    Cancers are frequently addicted to initiating oncogenes that elicit aberrant cellular proliferation, self-renewal, and apoptosis. Restoration of oncogenes to normal physiologic regulation can elicit dramatic reversal of the neoplastic phenotype, including reduced proliferation and increased apoptosis of tumor cells (Science 297(5578):63-64, 2002). In some cases, oncogene inactivation is associated with compete elimination of a tumor. However, in other cases, oncogene inactivation induces a conversion of tumor cells to a dormant state that is associated with cellular differentiation and/or loss of the ability to self-replicate. Importantly, this dormant state is reversible, with tumor cells regaining the ability to self-renew upon oncogene reactivation. Thus, understanding the mechanism of oncogene inactivation-induced dormancy may be crucial for predicting therapeutic outcome of targeted therapy. One important mechanistic insight into tumor dormancy is that oncogene addiction might involve regulation of a decision between self-renewal and cellular senescence. Recent evidence suggests that this decision is regulated by multiple mechanisms that include tumor cell-intrinsic, cell-autonomous mechanisms and host-dependent, tumor cell-non-autonomous programs (Mol Cell 4(2):199-207, 1999; Science 297(5578):102-104, 2002; Nature 431(7012):1112-1117, 2004; Proc Natl Acad Sci U S A 104(32):13028-13033, 2007). In particular, the tumor microenvironment, which is known to be critical during tumor initiation (Cancer Cell 7(5):411-423, 2005; J Clin Invest 121(6):2436-2446, 2011), prevention (Nature 410(6832):1107-1111, 2001), and progression (Cytokine Growth Factor Rev 21(1):3-10, 2010), also appears to dictate when oncogene inactivation elicits the permanent loss of self-renewal through induction of cellular senescence (Nat Rev Clin Oncol 8(3):151-160, 2011; Science 313(5795):1960-1964, 2006; N Engl J Med 351(21):2159-21569, 2004). Thus, oncogene addiction may be best modeled as a consequence of the interplay amongst cell-autonomous and host-dependent programs that define when a therapy will result in tumor dormancy.

    View details for DOI 10.1007/978-1-4614-1445-2_6

    View details for PubMedID 23143977

  • In Vivo Imaging-Based Mathematical Modeling Techniques That Enhance the Understanding of Oncogene Addiction in relation to Tumor Growth COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE Nwabugwu, C., Rakhra, K., Felsher, D., Paik, D. 2013

    Abstract

    The dependence on the overexpression of a single oncogene constitutes an exploitable weakness for molecular targeted therapy. These drugs can produce dramatic tumor regression by targeting the driving oncogene, but relapse often follows. Understanding the complex interactions of the tumor's multifaceted response to oncogene inactivation is key to tumor regression. It has become clear that a collection of cellular responses lead to regression and that immune-mediated steps are vital to preventing relapse. Our integrative mathematical model includes a variety of cellular response mechanisms of tumors to oncogene inactivation. It allows for correct predictions of the time course of events following oncogene inactivation and their impact on tumor burden. A number of aspects of our mathematical model have proven to be necessary for recapitulating our experimental results. These include a number of heterogeneous tumor cell states since cells following different cellular programs have vastly different fates. Stochastic transitions between these states are necessary to capture the effect of escape from oncogene addiction (i.e., resistance). Finally, delay differential equations were used to accurately model the tumor growth kinetics that we have observed. We use this to model oncogene addiction in MYC-induced lymphoma, osteosarcoma, and hepatocellular carcinoma.

    View details for DOI 10.1155/2013/802512

    View details for Web of Science ID 000316905000001

    View details for PubMedID 23573174

  • Regulation of accumulation and function of myeloid derived suppressor cells in different murine models of hepatocellular carcinoma. Journal of hepatology Kapanadze, T., Gamrekelashvili, J., Ma, C., Chan, C., Zhao, F., Hewitt, S., Zender, L., Kapoor, V., Felsher, D. W., Manns, M. P., Korangy, F., Greten, T. F. 2013

    Abstract

    Myeloid derived suppressor cells (MDSC) are immature myeloid cells with immunosuppressive activity. They accumulate in tumor-bearing mice and humans with different types of cancer, including hepatocellular carcinoma (HCC). The aim of this study was to examine the biology of MDSC in murine HCC models and to identify a model, which mimics the human disease.The comparative analysis of MDSC was performed in mice, bearing transplantable, diethylnitrosoamine (DEN)-induced and MYC-expressing HCC at different ages.An accumulation of MDSC was found in mice with HCC irrespectively of the model tested. Transplantable tumors rapidly induced systemic recruitment of MDSC, in contrast to slow-growing DEN-induced or MYC-expressing HCC, where MDSC numbers only increased intra-hepatically in mice with advanced tumors. MDSC derived from mice with subcutaneous tumors were more suppressive than those from mice with DEN-induced HCC. Enhanced expression of genes associated with MDSC generation (GM-CSF, VEGF, IL-6, IL-1 and migration (MCP-1, KC, S100A8, S100A9) was observed in mice with subcutaneous tumors. In contrast, only KC levels increased in mice with DEN-induced HCC. Both KC and GM-CSF over-expression or anti-KC and anti-GM-CSF treatment controlled MDSC frequency in mice with HCC. Finally, the frequency of MDSC decreased upon successful anti-tumor treatment with sorafenib.Our data indicate that MDSC accumulation is a late event during hepatocarcinogenesis and differs significantly depending on the tumor model studied.

    View details for PubMedID 23796475

  • SIRT1 and c-Myc Promote Liver Tumor Cell Survival and Predict Poor Survival of Human Hepatocellular Carcinomas PLOS ONE Jang, K. Y., Noh, S. J., Lehwald, N., Tao, G., Bellovin, D. I., Park, H. S., Moon, W. S., Felsher, D. W., Sylvester, K. G. 2012; 7 (9)

    Abstract

    The increased expression of SIRT1 has recently been identified in numerous human tumors and a possible correlation with c-Myc oncogene has been proposed. However, it remains unclear whether SIRT1 functions as an oncogene or tumor suppressor. We sought to elucidate the role of SIRT1 in liver cancer under the influence of c-Myc and to determine the prognostic significance of SIRT1 and c-Myc expression in human hepatocellular carcinoma. The effect of either over-expression or knock down of SIRT1 on cell proliferation and survival was evaluated in both mouse and human liver cancer cells. Nicotinamide, an inhibitor of SIRT1, was also evaluated for its effects on liver tumorigenesis. The prognostic significance of the immunohistochemical detection of SIRT1 and c-Myc was evaluated in 154 hepatocellular carcinoma patients. SIRT1 and c-Myc regulate each other via a positive feedback loop and act synergistically to promote hepatocellular proliferation in both mice and human liver tumor cells. Tumor growth was significantly inhibited by nicotinamide in vivo and in vitro. In human hepatocellular carcinoma, SIRT1 expression positively correlated with c-Myc, Ki67 and p53 expression, as well as high -fetoprotein level. Moreover, the expression of SIRT1, c-Myc and p53 were independent prognostic indicators of hepatocellular carcinoma. In conclusion, this study demonstrates that SIRT1 expression supports liver tumorigenesis and is closely correlated with oncogenic c-MYC expression. In addition, both SIRT1 and c-Myc may be useful prognostic indicators of hepatocellular carcinoma and SIRT1 targeted therapy may be beneficial in the treatment of hepatocellular carcinoma.

    View details for DOI 10.1371/journal.pone.0045119

    View details for Web of Science ID 000308860100058

    View details for PubMedID 23024800

  • HIF-2 alpha Suppresses p53 to Enhance the Stemness and Regenerative Potential of Human Embryonic Stem Cells STEM CELLS Das, B., Bayat-Mokhtari, R., Tsui, M., Lotfi, S., Tsuchida, R., Felsher, D. W., Yeger, H. 2012; 30 (8): 1685-1695

    Abstract

    Human embryonic stem cells (hESCs) have been reported to exert cytoprotective activity in the area of tissue injury. However, hypoxia/oxidative stress prevailing in the area of injury could activate p53, leading to death and differentiation of hESCs. Here we report that when exposed to hypoxia/oxidative stress, a small fraction of hESCs, namely the SSEA3+/ABCG2+ fraction undergoes a transient state of reprogramming to a low p53 and high hypoxia inducible factor (HIF)-2? state of transcriptional activity. This state can be sustained for a period of 2 weeks and is associated with enhanced transcriptional activity of Oct-4 and Nanog, concomitant with high teratomagenic potential. Conditioned medium obtained from the post-hypoxia SSEA3+/ABCG2+ hESCs showed cytoprotection both in vitro and in vivo. We termed this phenotype as the "enhanced stemness" state. We then demonstrated that the underlying molecular mechanism of this transient phenotype of enhanced stemness involved high Bcl-2, fibroblast growth factor (FGF)-2, and MDM2 expression and an altered state of the p53/MDM2 oscillation system. Specific silencing of HIF-2? and p53 resisted the reprogramming of SSEA3+/ABCG2+ to the enhanced stemness phenotype. Thus, our studies have uncovered a unique transient reprogramming activity in hESCs, the enhanced stemness reprogramming where a highly cytoprotective and undifferentiated state is achieved by transiently suppressing p53 activity. We suggest that this transient reprogramming is a form of stem cell altruism that benefits the surrounding tissues during the process of tissue regeneration.

    View details for DOI 10.1002/stem.1142

    View details for Web of Science ID 000306684900011

    View details for PubMedID 22689594

  • Loss of Dnmt3b function upregulates the tumor modifier Ment and accelerates mouse lymphomagenesis JOURNAL OF CLINICAL INVESTIGATION Hlady, R. A., Novakova, S., Opavska, J., Klinkebiel, D., Peters, S. L., Bies, J., Hannah, J., Iqbal, J., Anderson, K. M., Siebler, H. M., Smith, L. M., Greiner, T. C., Bastola, D., Joshi, S., Lockridge, O., Simpson, M. A., Felsher, D. W., Wagner, K., Chan, W. C., Christman, J. K., Opavsky, R. 2012; 122 (1): 163-177

    Abstract

    DNA methyltransferase 3B (Dnmt3b) belongs to a family of enzymes responsible for methylation of cytosine residues in mammals. DNA methylation contributes to the epigenetic control of gene transcription and is deregulated in virtually all human tumors. To better understand the generation of cancer-specific methylation patterns, we genetically inactivated Dnmt3b in a mouse model of MYC-induced lymphomagenesis. Ablation of Dnmt3b function using a conditional knockout in T cells accelerated lymphomagenesis by increasing cellular proliferation, which suggests that Dnmt3b functions as a tumor suppressor. Global methylation profiling revealed numerous gene promoters as potential targets of Dnmt3b activity, the majority of which were demethylated in Dnmt3b-/- lymphomas, but not in Dnmt3b-/- pretumor thymocytes, implicating Dnmt3b in maintenance of cytosine methylation in cancer. Functional analysis identified the gene Gm128 (which we termed herein methylated in normal thymocytes [Ment]) as a target of Dnmt3b activity. We found that Ment was gradually demethylated and overexpressed during tumor progression in Dnmt3b-/- lymphomas. Similarly, MENT was overexpressed in 67% of human lymphomas, and its transcription inversely correlated with methylation and levels of DNMT3B. Importantly, knockdown of Ment inhibited growth of mouse and human cells, whereas overexpression of Ment provided Dnmt3b+/+ cells with a proliferative advantage. Our findings identify Ment as an enhancer of lymphomagenesis that contributes to the tumor suppressor function of Dnmt3b and suggest it could be a potential target for anticancer therapies.

    View details for DOI 10.1172/JCI57292

    View details for Web of Science ID 000298769400022

    View details for PubMedID 22133874

  • STK38 is a critical upstream regulator of MYC's oncogenic activity in human B-cell lymphoma. Oncogene Bisikirska, B. C., Adam, S. J., Alvarez, M. J., Rajbhandari, P., Cox, R., Lefebvre, C., Wang, K., Rieckhof, G. E., Felsher, D. W., Califano, A. 2012

    Abstract

    The MYC protooncogene is associated with the pathogenesis of most human neoplasia. Conversely, its experimental inactivation elicits oncogene addiction. Besides constituting a formidable therapeutic target, MYC also has an essential function in normal physiology, thus creating the need for context-specific targeting strategies. The analysis of post-translational MYC activity modulation yields novel targets for MYC inactivation. Specifically, following regulatory network analysis in human B-cells, we identify a novel role of the STK38 kinase as a regulator of MYC activity and a candidate target for abrogating tumorigenesis in MYC-addicted lymphoma. We found that STK38 regulates MYC protein stability and turnover in a kinase activity-dependent manner. STK38 kinase inactivation abrogates apoptosis following B-cell receptor activation, whereas its silencing significantly decreases MYC levels and increases apoptosis. Moreover, STK38 knockdown suppresses growth of MYC-addicted tumors in vivo, thus providing a novel viable target for treating these malignancies.Oncogene advance online publication, 26 November 2012; doi:10.1038/onc.2012.543.

    View details for PubMedID 23178486

  • Treatment of higher risk myelodysplastic syndrome patients unresponsive to hypomethylating agents with ON 01910.Na LEUKEMIA RESEARCH Seetharam, M., Fan, A. C., Tran, M., Xu, L., Renschler, J. P., Felsher, D. W., Sridhar, K., Wilhelm, F., Greenberg, P. L. 2012; 36 (1): 98-103

    Abstract

    In a Phase I/II clinical trial, 13 higher risk red blood cell-dependent myelodysplastic syndrome (MDS) patients unresponsive to hypomethylating therapy were treated with the multikinase inhibitor ON 01910.Na. Responses occurred in all morphologic, prognostic risk and cytogenetic subgroups, including four patients with marrow complete responses among eight with stable disease, associated with good drug tolerance. In a subset of patients, a novel nanoscale immunoassay showed substantially decreased AKT2 phosphorylation in CD34+ marrow cells from patients responding to therapy but not those who progressed on therapy. These data demonstrate encouraging efficacy and drug tolerance with ON 01910.Na treatment of higher risk MDS patients.

    View details for DOI 10.1016/j.leukres.2011.08.022

    View details for Web of Science ID 000298149100035

    View details for PubMedID 21924492

  • Cryptococcal osteomyelitis and meningitis in a patient with non-hodgkin's lymphoma treated with PEP-C. BMJ case reports To, C. A., Hsieh, R. W., McClellan, J. S., Howard, W., Fischbein, N. J., Brown, J. M., Felsher, D. W., Fan, A. C. 2012; 2012

    Abstract

    The authors present the first case report of a patient with lymphoma who developed disseminated cryptococcal osteomyelitis and meningitis while being treated with the PEP-C (prednisone, etoposide, procarbazine and cyclophosphamide) chemotherapy regimen. During investigation of fever and new bony lesions, fungal culture from a rib biopsy revealed that the patient had cryptococcal osteomyelitis. Further evaluation demonstrated concurrent cryptococcal meningitis. The patient's disseminated cryptococcal infections completely resolved after a full course of antifungal treatment. Cryptococcal osteomyelitis is itself an extremely rare diagnosis, and the unique presentation with concurrent cryptococcal meningitis in our patient with lymphoma was likely due to his PEP-C treatment. It is well recognised that prolonged intensive chemotherapeutic regimens place patients at risk for atypical infections; yet physicians should recognise that even chronic low-dose therapies can put patients at risk for fungal infections. Physicians should consider fungal infections as part of the infectious investigation of a lymphopaenic patient on PEP-C.

    View details for DOI 10.1136/bcr.08.2011.4578

    View details for PubMedID 22962380

  • High throughput automated chromatin immunoprecipitation as a platform for drug screening and antibody validation LAB ON A CHIP Wu, A. R., Kawahara, T. L., Rapicavoli, N. A., van Riggelen, J., Shroff, E. H., Xu, L., Felsher, D. W., Chang, H. Y., Quake, S. R. 2012; 12 (12): 2190-2198

    Abstract

    Chromatin immunoprecipitation (ChIP) is an assay for interrogating protein-DNA interactions that is increasingly being used for drug target discovery and screening applications. Currently the complexity of the protocol and the amount of hands-on time required for this assay limits its use to low throughput applications; furthermore, variability in antibody quality poses an additional obstacle in scaling up ChIP for large scale screening purposes. To address these challenges, we report HTChIP, an automated microfluidic-based platform for performing high-throughput ChIP screening measurements of 16 different targets simultaneously, with potential for further scale-up. From chromatin to analyzable PCR results only takes one day using HTChIP, as compared to several days up to one week for conventional protocols. HTChIP can also be used to test multiple antibodies and select the best performer for downstream ChIP applications, saving time and reagent costs of unsuccessful ChIP assays as a result of poor antibody quality. We performed a series of characterization assays to demonstrate that HTChIP can rapidly and accurately evaluate the epigenetic states of a cell, and that it is sensitive enough to detect the changes in the epigenetic state induced by a cytokine stimulant over a fine temporal resolution. With these results, we believe that HTChIP can introduce large improvements in routine ChIP, antibody screening, and drug screening efficiency, and further facilitate the use of ChIP as a valuable tool for research and discovery.

    View details for DOI 10.1039/c2lc21290k

    View details for Web of Science ID 000304448700012

    View details for PubMedID 22566096

  • Hypoxia-microRNA-16 downregulation induces VEGF expression in anaplastic lymphoma kinase (ALK)-positive anaplastic large-cell lymphomas LEUKEMIA Dejean, E., Renalier, M. H., Foisseau, M., Agirre, X., Joseph, N., De Paiva, G. R., Al Saati, T., Soulier, J., Desjobert, C., Lamant, L., Prosper, F., Felsher, D. W., Cavaille, J., Prats, H., Delsol, G., Giuriato, S., Meggetto, F. 2011; 25 (12): 1882-1890

    Abstract

    The anaplastic lymphoma kinase (ALK), tyrosine kinase oncogene is implicated in a wide variety of cancers. In this study we used conditional onco-ALK (NPM-ALK and TPM3-ALK) mouse MEF cell lines (ALK+ fibroblasts) and transgenic models (ALK+ B-lymphoma) to investigate the involvement and regulation of angiogenesis in ALK tumor development. First, we observed that ALK expression leads to downregulation of miR-16 and increased Vascular Endothelial Growth Factor (VEGF) levels. Second, we found that modification of miR-16 levels in TPM3-ALK MEF cells greatly affected VEGF levels. Third, we demonstrated that miR-16 directly interacts with VEGF mRNA at the 3'-untranslated region and that the regulation of VEGF by miR-16 occurs at the translational level. Fourth, we showed that expression of both the ALK oncogene and hypoxia-induced factor 1? (HIF1?) is a prerequisite for miR-16 downregulation. Fifth, in vivo, miR-16 gain resulted in reduced angiogenesis and tumor growth. Finally, we highlighted an inverse correlation between the levels of miR-16 and VEGF in human NPM-ALK+ Anaplastic Large Cell Lymphomas (ALCL). Altogether, our results demonstrate, for the first time, the involvement of angiogenesis in ALK+ ALCL and strongly suggest an important role for hypoxia-miR-16 in regulating VEGF translation.

    View details for DOI 10.1038/leu.2011.168

    View details for Web of Science ID 000298405500012

    View details for PubMedID 21778999

  • Functional Interactions between Retinoblastoma and c-MYC in a Mouse Model of Hepatocellular Carcinoma PLOS ONE Saddic, L. A., Wirt, S., Vogel, H., Felsher, D. W., Sage, J. 2011; 6 (5)

    Abstract

    Inactivation of the RB tumor suppressor and activation of the MYC family of oncogenes are frequent events in a large spectrum of human cancers. Loss of RB function and MYC activation are thought to control both overlapping and distinct cellular processes during cell cycle progression. However, how these two major cancer genes functionally interact during tumorigenesis is still unclear. Here, we sought to test whether loss of RB function would affect cancer development in a mouse model of c-MYC-induced hepatocellular carcinoma (HCC), a deadly cancer type in which RB is frequently inactivated and c-MYC often activated. We found that RB inactivation has minimal effects on the cell cycle, cell death, and differentiation features of liver tumors driven by increased levels of c-MYC. However, combined loss of RB and activation of c-MYC led to an increase in polyploidy in mature hepatocytes before the development of tumors. There was a trend for decreased survival in double mutant animals compared to mice developing c-MYC-induced tumors. Thus, loss of RB function does not provide a proliferative advantage to c-MYC-expressing HCC cells but the RB and c-MYC pathways may cooperate to control the polyploidy of mature hepatocytes.

    View details for DOI 10.1371/journal.pone.0019758

    View details for Web of Science ID 000290305600045

    View details for PubMedID 21573126

  • Reactive Oxygen Species Regulate Nucleostemin Oligomerization and Protein Degradation JOURNAL OF BIOLOGICAL CHEMISTRY Huang, M., Whang, P., Chodaparambil, J. V., Pollyea, D. A., Kusler, B., Xu, L., Felsher, D. W., Mitchell, B. S. 2011; 286 (13): 11035-11046

    Abstract

    Nucleostemin (NS) is a nucleolar-nucleoplasmic shuttle protein that regulates cell proliferation, binds p53 and Mdm2, and is highly expressed in tumor cells. We have identified NS as a target of oxidative regulation in transformed hematopoietic cells. NS oligomerization occurs in HL-60 leukemic cells and Raji B lymphoblasts that express high levels of c-Myc and have high intrinsic levels of reactive oxygen species (ROS); reducing agents dissociate NS into monomers and dimers. Exposure of U2OS osteosarcoma cells with low levels of intrinsic ROS to hydrogen peroxide (H(2)O(2)) induces thiol-reversible disulfide bond-mediated oligomerization of NS. Increased exposure to H(2)O(2) impairs NS degradation, immobilizes the protein within the nucleolus, and results in detergent-insoluble NS. The regulation of NS by ROS was validated in a murine lymphoma tumor model in which c-Myc is overexpressed and in CD34+ cells from patients with chronic myelogenous leukemia in blast crisis. In both instances, increased ROS levels were associated with markedly increased expression of NS protein and thiol-reversible oligomerization. Site-directed mutagenesis of critical cysteine-containing regions of nucleostemin altered both its intracellular localization and its stability. MG132, a potent proteasome inhibitor and activator of ROS, markedly decreased degradation and increased nucleolar retention of NS mutants, whereas N-acetyl-L-cysteine largely prevented the effects of MG132. These results indicate that NS is a highly redox-sensitive protein. Increased intracellular ROS levels, such as those that result from oncogenic transformation in hematopoietic malignancies, regulate the ability of NS to oligomerize, prevent its degradation, and may alter its ability to regulate cell proliferation.

    View details for DOI 10.1074/jbc.M110.208470

    View details for Web of Science ID 000288797100015

    View details for PubMedID 21242306

  • MYC Phosphorylation, Activation, and Tumorigenic Potential in Hepatocellular Carcinoma Are Regulated by HMG-CoA Reductase CANCER RESEARCH Cao, Z., Fan-Minogue, H., Bellovin, D. I., Yevtodiyenko, A., Arzeno, J., Yang, Q., Gambhir, S. S., Felsher, D. W. 2011; 71 (6): 2286-2297

    Abstract

    MYC is a potential target for many cancers but is not amenable to existing pharmacologic approaches. Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase) by statins has shown potential efficacy against a number of cancers. Here, we show that inhibition of HMG-CoA reductase by atorvastatin (AT) blocks both MYC phosphorylation and activation, suppressing tumor initiation and growth in vivo in a transgenic model of MYC-induced hepatocellular carcinoma (HCC) as well as in human HCC-derived cell lines. To confirm specificity, we show that the antitumor effects of AT are blocked by cotreatment with the HMG-CoA reductase product mevalonate. Moreover, by using a novel molecular imaging sensor, we confirm that inhibition of HMG-CoA reductase blocks MYC phosphorylation in vivo. Importantly, the introduction of phosphorylation mutants of MYC at Ser62 or Thr58 into tumors blocks their sensitivity to inhibition of HMG-CoA reductase. Finally, we show that inhibition of HMG-CoA reductase suppresses MYC phosphorylation through Rac GTPase. Therefore, HMG-CoA reductase is a critical regulator of MYC phosphorylation, activation, and tumorigenic properties. The inhibition of HMG-CoA reductase may be a useful target for the treatment of MYC-associated HCC as well as other tumors.

    View details for DOI 10.1158/0008-5472.CAN-10-3367

    View details for Web of Science ID 000288381300028

    View details for PubMedID 21262914

  • Definition of an Enhanced Immune Cell Therapy in Mice That Can Target Stem-Like Lymphoma Cells CANCER RESEARCH Contag, C. H., Sikorski, R., Negrin, R. S., Schmidt, T., Fan, A. C., Bachireddy, P., Felsher, D. W., Thorne, S. H. 2010; 70 (23): 9837-9845

    Abstract

    Current treatments of high-grade lymphoma often have curative potential, but unfortunately many patients relapse and develop therapeutic resistance. Thus, there remains a need for novel therapeutics that can target the residual cancer cells whose phenotypes are distinct from the bulk tumor and that are capable of reforming tumors from very few cells. Oncolytic viruses offer an approach to destroy tumors by multiple mechanisms, but they cannot effectively reach residual disease or micrometastases, especially within the lymphatic system. To address these limitations, we have generated immune cells infected with oncolytic viruses as a therapeutic strategy that can combine effective cellular delivery with synergistic tumor killing. In this study, we tested this approach against minimal disease states of lymphomas characterized by the persistence of cancer cells that display stem cell-like properties and resistance to conventional therapies. We found that the immune cells were capable of trafficking to and targeting residual cancer cells. The combination biotherapy used prevented relapse by creating a long-term, disease-free state, with acquired immunity to the tumor functioning as an essential mediator of this effect. Immune components necessary for this acquired immunity were identified. We further demonstrated that the dual biotherapy could be applied before or after conventional therapy. Our approach offers a potentially powerful new way to clear residual cancer cells, showing how restoring immune surveillance is critical for maintenance of a disease-free state.

    View details for DOI 10.1158/0008-5472.CAN-10-2650

    View details for Web of Science ID 000285045900033

    View details for PubMedID 20935221

  • TGF-dependent gene expression shows that senescence correlates with abortive differentiation along several lineages in Myc-induced lymphomas. Cell cycle Mller, J., Samans, B., van Riggelen, J., Fag, G., Peh K N, R., Wei, C., Mller, H., Amati, B., Felsher, D., Eilers, M. 2010; 9 (23): 4622-4626

    Abstract

    Deregulated expression of Myc under the control of an immunoglobulin enhancer induces lymphoma formation in mice. The development of lymphomas is limited by TGF?-dependent senescence and high levels of Myc expression are continuously required to antagonize senescence. The biological processes underlying senescence are not fully resolved. We report here a comprehensive analysis of TGF?-dependent alterations in gene expression when the Myc transgene is switched off. Our data show that Myc-induced target genes are downregulated in a TGF?-independent manner. In contrast, TGF? is required to upregulate a broad spectrum of genes that are characteristic of different T-cell lineages when Myc is turned off. The analysis reveals a significant overlap between these Myc-repressed genes with genes that are targets of polycomb repressive complexes in embryonic stem cells. Therefore, TGF?-dependent senescence is associated with gene expression patterns indicative of abortive cellular differentiation along several lineages.

    View details for PubMedID 21127397

  • TGFbeta-dependent gene expression shows that senescence correlates with abortive differentiation along several lineages in Myc-induced lymphomas CELL CYCLE Mueller, J., Samans, B., van Riggelen, J., Faga, G., Peh, R. K., Wei, C., Mueller, H., Amati, B., Felsher, D., Eilers, M. 2010; 9 (23): 4622-4626
  • PET Imaging of Tumor Neovascularization in a Transgenic Mouse Model with a Novel Cu-64-DOTA-Knottin Peptide CANCER RESEARCH Nielsen, C. H., Kimura, R. H., Withofs, N., Tran, P. T., Miao, Z., Cochran, J. R., Cheng, Z., Felsher, D., Kjaer, A., Willmann, J. K., Gambhir, S. S. 2010; 70 (22): 9022-9030

    Abstract

    Due to the high mortality of lung cancer, there is a critical need to develop diagnostic procedures enabling early detection of the disease while at a curable stage. Targeted molecular imaging builds on the positive attributes of positron emission tomography/computed tomography (PET/CT) to allow for a noninvasive detection and characterization of smaller lung nodules, thus increasing the chances of positive treatment outcome. In this study, we investigate the ability to characterize lung tumors that spontaneously arise in a transgenic mouse model. The tumors are first identified with small animal CT followed by characterization with the use of small animal PET with a novel 64Cu-1,4,7,10-tetra-azacylododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-knottin peptide that targets integrins upregulated during angiogenesis on the tumor associated neovasculature. The imaging results obtained with the knottin peptide are compared with standard 18F-fluorodeoxyglucose (FDG) PET small animal imaging. Lung nodules as small as 3 mm in diameter were successfully identified in the transgenic mice by small animal CT, and both 64Cu-DOTA-knottin 2.5F and FDG were able to differentiate lung nodules from the surrounding tissues. Uptake and retention of the 64Cu-DOTA-knottin 2.5F tracer in the lung tumors combined with a low background in the thorax resulted in a statistically higher tumor to background (normal lung) ratio compared with FDG (6.010.61 versus 4.360.68; P<0.05). Ex vivo biodistribution showed 64Cu-DOTA-knottin 2.5F to have a fast renal clearance combined with low nonspecific accumulation in the thorax. Collectively, these results show 64Cu-DOTA-knottin 2.5F to be a promising candidate for clinical translation for earlier detection and improved characterization of lung cancer.

    View details for DOI 10.1158/0008-5472.CAN-10-1338

    View details for Web of Science ID 000284213300008

    View details for PubMedID 21062977

  • Hypoxia in Models of Lung Cancer: Implications for Targeted Therapeutics CLINICAL CANCER RESEARCH Graves, E. E., Vilalta, M., Cecic, I. K., Erler, J. T., Tran, P. T., Felsher, D., Sayles, L., Sweet-Cordero, A., Le, Q., Giaccia, A. J. 2010; 16 (19): 4843-4852

    Abstract

    To efficiently translate experimental methods from bench to bedside, it is imperative that laboratory models of cancer mimic human disease as closely as possible. In this study, we sought to compare patterns of hypoxia in several standard and emerging mouse models of lung cancer to establish the appropriateness of each for evaluating the role of oxygen in lung cancer progression and therapeutic response.Subcutaneous and orthotopic human A549 lung carcinomas growing in nude mice as well as spontaneous K-ras or Myc-induced lung tumors grown in situ or subcutaneously were studied using fluorodeoxyglucose and fluoroazomycin arabinoside positron emission tomography, and postmortem by immunohistochemical observation of the hypoxia marker pimonidazole. The response of these models to the hypoxia-activated cytotoxin PR-104 was also quantified by the formation of ?H2AX foci in vitro and in vivo. Finally, our findings were compared with oxygen electrode measurements of human lung cancers.Minimal fluoroazomycin arabinoside and pimonidazole accumulation was seen in tumors growing within the lungs, whereas subcutaneous tumors showed substantial trapping of both hypoxia probes. These observations correlated with the response of these tumors to PR-104, and with the reduced incidence of hypoxia in human lung cancers relative to other solid tumor types.These findings suggest that in situ models of lung cancer in mice may be more reflective of the human disease, and encourage judicious selection of preclinical tumor models for the study of hypoxia imaging and antihypoxic cell therapies.

    View details for DOI 10.1158/1078-0432.CCR-10-1206

    View details for Web of Science ID 000282647900017

    View details for PubMedID 20858837

  • Noninvasive molecular imaging of c-Myc activation in living mice PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Fan-Minogue, H., Cao, Z., Paulmurugan, R., Chan, C. T., Massoud, T. F., Felsher, D. W., Gambhir, S. S. 2010; 107 (36): 15892-15897

    Abstract

    The cytoplasmic Myc protein (c-Myc) regulates various human genes and is dysregulated in many human cancers. Phosphorylation mediates the protein activation of c-Myc and is essential for the function of this transcription factor in normal cell behavior and tumor growth. To date, however, the targeting of Myc as a therapeutic approach for cancer treatment has been achieved primarily at the nonprotein level. We have developed a molecular imaging sensor for noninvasive imaging of c-Myc activity in living subjects using a split Firefly luciferase (FL) complementation strategy to detect and quantify the phosphorylation-mediated interaction between glycogen synthase kinase 3beta (GSK3beta) and c-Myc. This sensor system consists of two fusion proteins, GSK 35-433-CFL and NFL-c-Myc, in which specific fragments of GSK3beta and c-Myc are fused with C-terminal and N-terminal fragments of the split FL, respectively. The sensor detects phosphorylation-specific GSK3beta-c-Myc interaction, the imaging signal of which correlates with the steady-state and temporal regulation of c-Myc phosphorylation in cell culture. The sensor also detects inhibition of c-Myc activity via differential pathways, allowing noninvasive monitoring of c-Myc-targeted drug efficacy in intact cells and living mice. Notably, this drug inhibition is detected before changes in tumor size are apparent in mouse xenograft and liver tumor models. This reporter system not only provides an innovative way to investigate the role of functional c-Myc in normal and cancer-related biological processes, but also facilitates c-Myc-targeted drug development by providing a rapid quantitative approach to assessing cancer response to therapy in living subjects.

    View details for DOI 10.1073/pnas.1007443107

    View details for Web of Science ID 000281637800049

    View details for PubMedID 20713710

  • DEVELOPMENT OF A MICRO-COMPUTED TOMOGRAPHY-BASED IMAGE-GUIDED CONFORMAL RADIOTHERAPY SYSTEM FOR SMALL ANIMALS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Zhou, H., Rodriguez, M., van den Haak, F., Nelson, G., Jogani, R., Xu, J., Zhu, X., Xian, Y., Tran, P. T., Felsher, D. W., Keall, P. J., Graves, E. E. 2010; 78 (1): 297-305

    Abstract

    To report on the physical aspects of a system in which radiotherapy functionality was added to a micro-computed tomography (microCT) scanner, to evaluate the accuracy of this instrument, and to and demonstrate the application of this technology for irradiating tumors growing within the lungs of mice.A GE eXplore RS120 microCT scanner was modified by the addition of a two-dimensional subject translation stage and a variable aperture collimator. Quality assurance protocols for these devices, including measurement of translation stage positioning accuracy, collimator aperture accuracy, and collimator alignment with the X-ray beam, were devised. Use of this system for image-guided radiotherapy was assessed by irradiation of a solid water phantom as well as of two mice bearing spontaneous MYC-induced lung tumors. Radiation damage was assessed ex vivo by immunohistochemical detection of gammaH2AX foci.The positioning error of the translation stage was found to be <0.05 mm, whereas after alignment of the collimator with the X-ray axis through adjustment of its displacement and rotation, the collimator aperture error was <0.1 mm measured at isocenter. Computed tomography image-guided treatment of a solid water phantom demonstrated target localization accuracy to within 0.1 mm. Gamma-H2AX foci were detected within irradiated lung tumors in mice, with contralateral lung tissue displaying background staining.Addition of radiotherapy functionality to a microCT scanner is an effective means of introducing image-guided radiation treatments into the preclinical setting. This approach has been shown to facilitate small-animal conformal radiotherapy while leveraging existing technology.

    View details for DOI 10.1016/j.ijrobp.2009.11.008

    View details for Web of Science ID 000281304600041

    View details for PubMedID 20395069

  • Impact of Hydrodynamic Injection and phiC31 Integrase on Tumor Latency in a Mouse Model of MYC-Induced Hepatocellular Carcinoma PLOS ONE Woodard, L. E., Keravala, A., Jung, W. E., Wapinski, O. L., Yang, Q., Felsher, D. W., Calos, M. P. 2010; 5 (6)

    Abstract

    Hydrodynamic injection is an effective method for DNA delivery in mouse liver and is being translated to larger animals for possible clinical use. Similarly, phiC31 integrase has proven effective in mediating long-term gene therapy in mice when delivered by hydrodynamic injection and is being considered for clinical gene therapy applications. However, chromosomal aberrations have been associated with phiC31 integrase expression in tissue culture, leading to questions about safety.To study whether hydrodynamic delivery alone, or in conjunction with delivery of phiC31 integrase for long-term transgene expression, could facilitate tumor formation, we used a transgenic mouse model in which sustained induction of the human C-MYC oncogene in the liver was followed by hydrodynamic injection. Without injection, mice had a median tumor latency of 154 days. With hydrodynamic injection of saline alone, the median tumor latency was significantly reduced, to 105 days. The median tumor latency was similar, 106 days, when a luciferase donor plasmid and backbone plasmid without integrase were administered. In contrast, when active or inactive phiC31 integrase and donor plasmid were supplied to the mouse liver, the median tumor latency was 153 days, similar to mice receiving no injection.Our data suggest that phiC31 integrase does not facilitate tumor formation in this C-MYC transgenic mouse model. However, in groups lacking phiC31 integrase, hydrodynamic injection appeared to contribute to C-MYC-induced hepatocellular carcinoma in adult mice. Although it remains to be seen to what extent these findings may be extrapolated to catheter-mediated hydrodynamic delivery in larger species, they suggest that caution should be used during translation of hydrodynamic injection to clinical applications.

    View details for DOI 10.1371/journal.pone.0011367

    View details for Web of Science ID 000279369900016

    View details for PubMedID 20614008

  • MYC Inactivation Elicits Oncogene Addiction through Both Tumor Cell-Intrinsic and Host-Dependent Mechanisms. Genes & cancer Felsher, D. W. 2010; 1 (6): 597-604

    Abstract

    Tumorigenesis is generally caused by genetic changes that activate oncogenes or inactivate tumor suppressor genes. The targeted inactivation of oncogenes can be associated with tumor regression through the phenomenon of oncogene addiction. One of the most common oncogenic events in human cancer is the activation of the MYC oncogene. The inactivation of MYC may be a general and effective therapy for human cancer. Indeed, it has been experimentally shown that the inactivation of MYC can result in dramatic and sustained tumor regression in lymphoma, leukemia, osteosarcoma, hepatocellular carcinoma, squamous carcinoma, and pancreatic carcinoma through a multitude of mechanisms, including proliferative arrest, terminal differentiation, cellular senescence, induction of apoptosis, and the shutdown of angiogenesis. Cell-autonomous and cell-dependent mechanisms have both been implicated, and recent results suggest a critical role for autocrine factors, including thrombospondin-1 and TGF-?. Hence, targeting the inactivation of MYC appears to elicit oncogene addiction and, thereby, tumor regression through both tumor cell-intrinsic and host-dependent mechanisms.

    View details for DOI 10.1177/1947601910377798

    View details for PubMedID 21037952

  • Conditional TPM3-ALK and NPM-ALK transgenic mice develop reversible ALK-positive early B-cell lymphoma/leukemia BLOOD Giuriato, S., Foisseau, M., Dejean, E., Felsher, D. W., Al Saati, T., Demur, C., Ragab, A., Kruczynski, A., Schiff, C., Delsol, G., Meggetto, F. 2010; 115 (20): 4061-4070

    Abstract

    NPM-ALK (nucleophosmin-anaplastic lymphoma kinase) and TPM3-ALK (nonmuscular tropomyosin 3-anaplastic lymphoma kinase) are oncogenic tyrosine kinases implicated in the pathogenesis of human ALK-positive lymphoma. We report here the development of novel conditional mouse models for ALK-induced lymphomagenesis, with the use of the tetracycline regulatory system under the control of the EmuSRalpha enhancer/promoter. The expression of either oncogene resulted in the arrest of the differentiation of early B cells and lymphomagenesis. We also observed the development of skin keratoacanthoma lesions, probably because of aberrant ALK expression in keratinocytes. The inactivation of the ALK oncogene on doxycycline treatment was sufficient to induce sustained regression of both hematopoietic tumors and skin disease. Importantly, treatment with the specific ALK inhibitor (PF-2341066) also reversed the pathologic states, showing the value of these mouse models for the validation of ALK tyrosine kinase inhibitors. Thus, our results show (1) that NPM-ALK and TPM3-ALK oncogenes are sufficient for lymphoma/leukemia development and required for tumor maintenance, hence validating ALK as potentially effective therapeutic target; and (2) for the first time, in vivo, the equal tumorigenic potential of the NPM-ALK and TPM3-ALK oncogenic tyrosine kinases. Our models offer a new tool to investigate in vivo the molecular mechanisms associated with ALK-induced lymphoproliferative disorders.

    View details for DOI 10.1182/blood-2008-06-163386

    View details for Web of Science ID 000277923600011

    View details for PubMedID 20223922

  • Myc and a Cdk2 senescence switch NATURE CELL BIOLOGY van Riggelen, J., Felsher, D. W. 2010; 12 (1): 7-9

    Abstract

    Cdk2 has been shown to have an unanticipated role in suppressing Myc-induced senescence. This has implications for how c-Myc overcomes failsafe mechanisms to induce tumorigenesis and suggests that the inhibition of Cdk2 may have therapeutic efficacy in the treatment of cancer.

    View details for DOI 10.1038/ncb0110-7

    View details for Web of Science ID 000272973800006

    View details for PubMedID 20027199

  • Low-level shRNA Cytotoxicity Can Contribute to MYC-induced Hepatocellular Carcinoma in Adult Mice MOLECULAR THERAPY Beer, S., Bellovin, D. I., Lee, J. S., Komatsubara, K., Wang, L. S., Koh, H., Boerner, K., Storm, T. A., Davis, C. R., Kay, M. A., Felsher, D. W., Grimm, D. 2010; 18 (1): 161-170

    Abstract

    Short hairpin RNAs (shRNAs) have emerged as a novel therapeutic modality, but there is increasing concern over nonspecific effects in vivo. Here, we used viral vectors to express shRNAs against endogenous p53 in livers of conditional MYC-transgenic mice. As expected, the shRNAs silenced hepatic p53 and accelerated liver tumorigenesis when MYC was concurrently expressed. Surprisingly, various irrelevant control shRNAs similarly induced a rapid onset of tumorigenesis, comparable to carbon tetrachloride (CCl4), a potent carcinogen. We found that even marginal shRNA doses can already trigger histologically detectable hepatoxicity and increased hepatocyte apoptosis. Moreover, we noted that shRNA expression globally dysregulated hepatic microRNA (miRNA) expression, and that shRNA levels and activity further increased in the presence of MYC. In MYC-expressing transgenic mice, the marginal shRNA-induced liver injury sufficed to further stimulate hepatocellular division that was in turn associated with markedly increased expression of the mitotic cyclin B1. Hence, even at low doses, shRNAs can cause low-level hepatoxicity that can facilitate the ability of the MYC oncogene to induce liver tumorigenesis. Our data warrant caution regarding the possible carcinogenic potential of shRNAs when used as clinical agent, particularly in circumstances where tissues are genetically predisposed to cellular transformation and proliferation.

    View details for DOI 10.1038/mt.2009.222

    View details for Web of Science ID 000274447200023

    View details for PubMedID 19844192

  • Cell Cycle Re-Entry and Mitochondrial Defects in Myc-Mediated Hypertrophic Cardiomyopathy and Heart Failure PLOS ONE Lee, H., Chen, Q., Wolfram, J. A., Richardson, S. L., Liner, A., Siedlak, S. L., Zhu, X., Ziats, N. P., Fujioka, H., Felsher, D. W., Castellani, R. J., Valencik, M. L., McDonald, J. A., Hoit, B. D., Lesnefsky, E. J., Smith, M. A. 2009; 4 (9)

    Abstract

    While considerable evidence supports the causal relationship between increases in c-Myc (Myc) and cardiomyopathy as a part of a "fetal re-expression" pattern, the functional role of Myc in mechanisms of cardiomyopathy remains unclear. To address this, we developed a bitransgenic mouse that inducibly expresses Myc under the control of the cardiomyocyte-specific MHC promoter. In adult mice the induction of Myc expression in cardiomyocytes in the heart led to the development of severe hypertrophic cardiomyopathy followed by ventricular dysfunction and ultimately death from congestive heart failure. Mechanistically, following Myc activation, cell cycle markers and other indices of DNA replication were significantly increased suggesting that cell cycle-related events might be a primary mechanism of cardiac dysfunction. Furthermore, pathological alterations at the cellular level included alterations in mitochondrial function with dysregulation of mitochondrial biogenesis and defects in electron transport chain complexes I and III. These data are consistent with the known role of Myc in several different pathways including cell cycle activation, mitochondrial proliferation, and apoptosis, and indicate that Myc activation in cardiomyocytes is an important regulator of downstream pathological sequelae. Moreover, our findings indicate that the induction of Myc in cardiomyocytes is sufficient to cause cardiomyopathy and heart failure, and that sustained induction of Myc, leading to cell cycle re-entry in adult cardiomyocytes, represents a maladaptive response for the mature heart.

    View details for DOI 10.1371/journal.pone.0007172

    View details for Web of Science ID 000270176200013

    View details for PubMedID 19779629

  • SPECT and PET Imaging of EGF Receptors with Site-Specifically Labeled EGF and Dimeric EGF BIOCONJUGATE CHEMISTRY Levashova, Z., Backer, M. V., Horng, G., Felsher, D., Backer, J. M., Blankenberg, F. G. 2009; 20 (4): 742-749

    Abstract

    We describe a new generation of tracers for molecular imaging of the cell surface receptors for epidermal growth factor (EGF). These receptors play a key role in the progression of many tumors and are major drug development targets. Our tracers are based on a recombinant human EGF expressed with a cysteine-containing tag that enables facile site-specific radiolabeling with (99m)Tc for single photon emission computed tomography or site-specific conjugation of (64)Cu PEGylated chelators for positron emission tomography. These tracers retain EGF activities in vitro and display selective and highly specific focal uptake in tumors in vivo. We expect that nuclear imaging of EGF receptors with these tracers will be useful for clinical diagnosis, therapeutic monitoring, and development of new drugs and treatment regimens.

    View details for DOI 10.1021/bc800443w

    View details for Web of Science ID 000265284200013

    View details for PubMedID 19320434

  • Apoptosis-stimulating protein of p53 (ASPP2) heterozygous mice are tumor-prone and have attenuated cellular damage-response thresholds PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Kampa, K. M., Acoba, J. D., Chen, D., Gay, J., Lee, H., Beemer, K., Padiernos, E., Boonmark, N., Zhu, Z., Fan, A. C., Bailey, A. S., Fleming, W. H., Corless, C., Felsher, D. W., Naumovski, L., Lopez, C. D. 2009; 106 (11): 4390-4395

    Abstract

    The expression of ASPP2 (53BP2L), a proapoptotic member of a family of p53-binding proteins, is frequently suppressed in many human cancers. Accumulating evidence suggests that ASPP2 inhibits tumor growth; however, the mechanisms by which ASPP2 suppresses tumor formation remain to be clarified. To study this, we targeted the ASPP2 allele in a mouse by replacing exons 10-17 with a neoR gene. ASPP2(-/-) mice were not viable because of an early embryonic lethal event. Although ASPP2(+/-) mice appeared developmentally normal, they displayed an increased incidence of a variety of spontaneous tumors as they aged. Moreover, gamma-irradiated 6-week-old ASPP2(+/-) mice developed an increased incidence of high-grade T cell lymphomas of thymic origin compared with ASPP2(+/+) mice. Primary thymocytes derived from ASPP2(+/-) mice exhibited an attenuated apoptotic response to gamma-irradiation compared with ASPP2(+/+) thymocytes. Additionally, ASPP2(+/-) primary mouse embryonic fibroblasts demonstrated a defective G(0)/G(1) cell cycle checkpoint after gamma-irradiation. Our results demonstrate that ASPP2 is a haploinsufficient tumor suppressor and, importantly, open new avenues for investigation into the mechanisms by which disruption of ASPP2 pathways could play a role in tumorigenesis and response to therapy.

    View details for DOI 10.1073/pnas.0809080106

    View details for Web of Science ID 000264278800061

    View details for PubMedID 19251665

  • The Neuronal Expression of MYC Causes a Neurodegenerative Phenotype in a Novel Transgenic Mouse AMERICAN JOURNAL OF PATHOLOGY Lee, H., Casadesus, G., Nunomura, A., Zhu, X., Castellani, R. J., Richardson, S. L., Perry, G., Felsher, D. W., Petersen, R. B., Smith, M. A. 2009; 174 (3): 891-897

    Abstract

    Many different proteins associated with the cell cycle, including cyclins, cyclin-dependent kinases, and proto-oncogenes such as c-MYC (MYC), are increased in degenerating neurons. Consequently, an ectopic activation of the cell cycle machinery in neurons has emerged as a potential pathogenic mechanism of neuronal dysfunction and death in many neurodegenerative diseases, including Alzheimer's disease. However, the exact role of cell cycle re-entry during disease pathogenesis is unclear, primarily because of the lack of relevant research models to study the effects of cell cycle re-entry on mature neurons in vivo. To address this issue, we developed a new transgenic mouse model in which forebrain neurons (CaMKII-MYC) can be induced to enter the cell cycle using the physiologically relevant proto-oncogene MYC to drive cell cycle re-entry. We show that such cell cycle re-entry results in neuronal cell death, gliosis, and cognitive deficits. These findings provide compelling evidence that dysregulation of cell cycle re-entry results in neurodegeneration in vivo. Our current findings, coupled with those of previous reports, strengthen the hypothesis that neurodegeneration in Alzheimer's disease, similar to cellular proliferation in cancer, is a disease that results from inappropriate cell cycle control.

    View details for DOI 10.2353/ajpath.2009.080583

    View details for Web of Science ID 000263612600017

    View details for PubMedID 19164506

  • Autochthonous Liver Tumors Induce Systemic T Cell Tolerance Associated with T Cell Receptor Down-Modulation HEPATOLOGY Ney, J. T., Schmidt, T., Kurts, C., Zhou, Q., Eckert, D., Felsher, D. W., Schorle, H., Knolle, P., Tueting, T., Barchet, W., Buettner, R., Limnier, A., Guetgemann, I. 2009; 49 (2): 471-481

    Abstract

    The reason the adaptive immune system fails in advanced liver tumors is largely unclear. To address this question, we have developed a novel murine model that combines c-myc-induced autochthonous tumorigenesis with expression of a cognate antigen, ovalbumin (OVA). When c-myc/OVA transgenic mice were crossed with liver-specific inducer mice, multifocal hepatocellular carcinomas co-expressing OVA developed in a tetracycline-dependent manner with a short latency and 100% penetrance. Transferred OVA-specific T cells, although infiltrating the tumor at high numbers, were hyporesponsive, as evidenced by a lack of in vivo cytotoxicity and interferon gamma production. This allowed the tumor to progress even in the presence of large numbers of antigen-specific T cells and even after vaccination (OVA+CpG-DNA). Interestingly, T cell receptor down-modulation was observed, which may explain antigen-specific hyporesponsiveness. This model is helpful in understanding liver cancer-specific mechanisms of T cell tolerance and dissection of antigen-specific and nonspecific mechanisms of immunotherapies in the preclinical phase.

    View details for DOI 10.1002/hep.22652

    View details for Web of Science ID 000262923300019

    View details for PubMedID 19105207

  • Supramolecular Stacking of Doxorubicin on Carbon Nanotubes for In Vivo Cancer Therapy ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Liu, Z., Fan, A. C., Rakhra, K., Sherlock, S., Goodwin, A., Chen, X., Yang, Q., Felsher, D. W., Dai, H. 2009; 48 (41): 7668-7672

    View details for DOI 10.1002/anie.200902612

    View details for Web of Science ID 000270436900037

    View details for PubMedID 19760685

  • The current STATe of biomarkers to predict the response to anti-angiogenic therapies CANCER BIOLOGY & THERAPY Tran, P. T., Felsher, D. W. 2008; 7 (12): 2004-2006

    View details for Web of Science ID 000262318700024

    View details for PubMedID 19158482

  • F-18 and (18)FDG PET imaging of osteosarcoma to non-invasively monitor in situ changes in cellular proliferation and bone differentiation upon MYC inactivation CANCER BIOLOGY & THERAPY Arvanitis, C., Bendapudi, P. K., Tseng, J. R., Gambhir, S. S., Felsher, D. W. 2008; 7 (12): 1947-1951

    Abstract

    Osteosarcoma is one of the most common pediatric cancers. Accurate imaging of osteosarcoma is important for proper clinical staging of the disease and monitoring of the tumor's response to therapy. The MYC oncogene has been commonly implicated in the pathogenesis of human osteosarcoma. Previously, we have described a conditional transgenic mouse model of MYC-induced osteosarcoma. These tumors are highly invasive and are frequently associated with pulmonary metastases. In our model, upon MYC inactivation osteosarcomas lose their neoplastic properties, undergo proliferative arrest and differentiate into mature bone. We reasoned that we could use our model system to develop noninvasive imaging modalities to interrogate the consequences of MYC inactivation on tumor cell biology in situ. We performed positron emission tomography (PET) combining the use of both (18)F-fluorodeoxyglucose ((18)FDG) and (18)F-flouride ((18)F) to detect metabolic activity and bone mineralization/remodeling. We found that upon MYC inactivation, tumors exhibited a slight reduction in uptake of (18)FDG and a significant increase in the uptake of (18)F along with associated histological changes. Thus, these cells have apparently lost their neoplastic properties based upon both examination of their histology and biologic activity. However, these tumors continue to accumulate (18)FDG at levels significantly elevated compared to normal bone. Therefore, PET can be used to distinguish normal bone cells from tumors that have undergone differentiation upon oncogene inactivation. In addition, we found that (18)F is a highly sensitive tracer for detection of pulmonary metastasis. Collectively, we conclude that combined modality PET/CT imaging incorporating both (18)FDG and (18)F is a highly sensitive means to non-invasively measure osteosarcoma growth and the therapeutic response, as well as to detect tumor cells that have undergone differentiation upon oncogene inactivation.

    View details for Web of Science ID 000262318700015

    View details for PubMedID 18981708

  • A quantitative PCR method to detect blood microRNAs associated with tumorigenesis in transgenic mice MOLECULAR CANCER Fan, A. C., Goldrick, M. M., Ho, J., Liang, Y., Bachireddy, P., Felsher, D. W. 2008; 7

    Abstract

    MicroRNA (miRNA) dysregulation frequently occurs in cancer. Analysis of whole blood miRNA in tumor models has not been widely reported, but could potentially lead to novel assays for early detection and monitoring of cancer. To determine whether miRNAs associated with malignancy could be detected in the peripheral blood, we used real-time reverse transcriptase-PCR to determine miRNA profiles in whole blood obtained from transgenic mice with c-MYC-induced lymphoma, hepatocellular carcinoma and osteosarcoma. The PCR-based assays used in our studies require only 10 nanograms of total RNA, allowing serial mini-profiles (20 - 30 miRNAs) to be carried out on individual animals over time. Blood miRNAs were measured from mice at different stages of MYC-induced lymphomagenesis and regression. Unsupervised hierarchical clustering of the data identified specific miRNA expression profiles that correlated with tumor type and stage. The miRNAs found to be altered in the blood of mice with tumors frequently reverted to normal levels upon tumor regression. Our results suggest that specific changes in blood miRNA can be detected during tumorigenesis and tumor regression.

    View details for DOI 10.1186/1476-4598-7-74

    View details for Web of Science ID 000260393800001

    View details for PubMedID 18826639

  • An efficient and versatile system for acute and chronic modulation of renal tubular function in transgenic mice NATURE MEDICINE Traykova-Brauch, M., Schoenig, K., Greiner, O., Miloud, T., Jauch, A., Bode, M., Felsher, D. W., Glick, A. B., Kwiatkowski, D. J., Bujard, H., Horst, J., Doeberitz, M. v., Niggli, F. K., Kriz, W., Groene, H., Koesters, R. 2008; 14 (9): 979-984

    Abstract

    We describe a transgenic mouse line, Pax8-rtTA, which, under control of the mouse Pax8 promoter, directs high levels of expression of the reverse tetracycline-dependent transactivator (rtTA) to all proximal and distal tubules and the entire collecting duct system of both embryonic and adult kidneys. Using crosses of Pax8-rtTA mice with tetracycline-responsive c-MYC mice, we established a new, inducible model of polycystic kidney disease that can mimic adult onset and that shows progression to renal malignant disease. When targeting the expression of transforming growth factor beta-1 to the kidney, we avoided early lethality by discontinuous treatment and successfully established an inducible model of renal fibrosis. Finally, a conditional knockout of the gene encoding tuberous sclerosis complex-1 was achieved, which resulted in the early outgrowth of giant polycystic kidneys reminiscent of autosomal recessive polycystic kidney disease. These experiments establish Pax8-rtTA mice as a powerful tool for modeling renal diseases in transgenic mice.

    View details for DOI 10.1038/nm.1865

    View details for Web of Science ID 000258988600032

    View details for PubMedID 18724376

  • Tumor dormancy and oncogene addiction APMIS Felsher, D. W. 2008; 116 (7-8): 629-637

    Abstract

    Cancer is caused by genetic changes that activate oncogenes or inactivate tumor suppressor genes. The repair or inactivation of mutant genes may be effective in the treatment of cancer. Indeed, drugs that target oncogenes can be effective in the treatment of cancer. However, it is still unclear why the inactivation of a single cancer-associated gene would ever result in the elimination of tumor cells. In experimental transgenic mouse models the consequences of oncogene inactivation depend upon the genetic and cellular context. In some cases, oncogene inactivation results in the elimination of all or almost all tumor cells through apoptosis by the phenomenon described as oncogene addiction. In other cases, oncogene inactivation predominantly results in the terminal differentiation or cellular senescence of tumor cells. In yet others, oncogene inactivation results in the apparent loss of the neoplastic properties of tumor cells, which now appear and behave like normal cells; however, upon oncogene reactivation at least some of these cells rapidly recover their neoplastic phenotype. Thus, oncogene inactivation can result in a state of tumor dormancy. Hence, understanding when and how oncogene inactivation induces apoptosis, differentiation, and senescence within a tumor will be important when developing effective strategies for the treatment of cancer.

    View details for Web of Science ID 000259037600009

    View details for PubMedID 18834407

  • Genomic and proteomic analysis reveals a threshold level of MYC required for tumor maintenance CANCER RESEARCH Shachaf, C. M., Gentles, A. J., Elchuri, S., Sahoo, D., Soen, Y., Sharpe, O., Perez, O. D., Chang, M., Mitchel, D., Robinson, W. H., Dill, D., Nolan, G. P., Plevritis, S. K., Felsher, D. W. 2008; 68 (13): 5132-5142

    Abstract

    MYC overexpression has been implicated in the pathogenesis of most types of human cancers. MYC is likely to contribute to tumorigenesis by its effects on global gene expression. Previously, we have shown that the loss of MYC overexpression is sufficient to reverse tumorigenesis. Here, we show that there is a precise threshold level of MYC expression required for maintaining the tumor phenotype, whereupon there is a switch from a gene expression program of proliferation to a state of proliferative arrest and apoptosis. Oligonucleotide microarray analysis and quantitative PCR were used to identify changes in expression in 3,921 genes, of which 2,348 were down-regulated and 1,573 were up-regulated. Critical changes in gene expression occurred at or near the MYC threshold, including genes implicated in the regulation of the G(1)-S and G(2)-M cell cycle checkpoints and death receptor/apoptosis signaling. Using two-dimensional protein analysis followed by mass spectrometry, phospho-flow fluorescence-activated cell sorting, and antibody arrays, we also identified changes at the protein level that contributed to MYC-dependent tumor regression. Proteins involved in mRNA translation decreased below threshold levels of MYC. Thus, at the MYC threshold, there is a loss of its ability to maintain tumorigenesis, with associated shifts in gene and protein expression that reestablish cell cycle checkpoints, halt protein translation, and promote apoptosis.

    View details for DOI 10.1158/0008-5472.CAN-07-6192

    View details for Web of Science ID 000257415300024

    View details for PubMedID 18593912

  • Hepatotoxin-Induced Changes in the Adult Murine Liver Promote MYC-Induced Tumorigenesis PLOS ONE Beer, S., Komatsubara, K., Bellovin, D. I., Kurobe, M., Sylvester, K., Felsher, D. W. 2008; 3 (6)

    Abstract

    Overexpression of the human c-MYC (MYC) oncogene is one of the most frequently implicated events in the pathogenesis of hepatocellular carcinoma (HCC). Previously, we have shown in a conditional transgenic mouse model that MYC overexpression is restrained from inducing mitotic cellular division and tumorigenesis in the adult liver; whereas, in marked contrast, MYC induces robust proliferation associated with the very rapid onset of tumorigenesis in embryonic and neonatal mice.Here, we show that non-genotoxic hepatotoxins induce changes in the liver cellular context associated with increased cellular proliferation and enhanced tumorigenesis. Both 5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) and carbon tetrachloride (CCl(4)) cooperate with MYC to greatly accelerate the onset of liver cancer in an adult host to less than 7 days versus a mean latency of onset of over 35 weeks for MYC alone. These hepatotoxin-enhanced liver tumors grossly and histologically resemble embryonic and neonatal liver tumors. Importantly, we found that MYC overexpression is only capable of inducing expression of the mitotic Cyclin B1 in embryonic/neonatal hosts or adult hosts that were treated with either carcinogen.Our results suggest a model whereby oncogenes can remain latently activated, but exposure of the adult liver to hepatotoxins that promote hepatocyte proliferation can rapidly uncover their malignant potential.

    View details for DOI 10.1371/journal.pone.0002493

    View details for Web of Science ID 000263280700056

    View details for PubMedID 18560566

  • Combined Inactivation of MYC and K-Ras Oncogenes Reverses Tumorigenesis in Lung Adenocarcinomas and Lymphomas PLOS ONE Tran, P. T., Fan, A. C., Bendapudi, P. K., Koh, S., Komatsubara, K., Chen, J., Horng, G., Bellovin, D. I., Giuriato, S., Wang, C. S., Whitsett, J. A., Felsher, D. W. 2008; 3 (5)

    Abstract

    Conditional transgenic models have established that tumors require sustained oncogene activation for tumor maintenance, exhibiting the phenomenon known as "oncogene-addiction." However, most cancers are caused by multiple genetic events making it difficult to determine which oncogenes or combination of oncogenes will be the most effective targets for their treatment.To examine how the MYC and K-ras(G12D) oncogenes cooperate for the initiation and maintenance of tumorigenesis, we generated double conditional transgenic tumor models of lung adenocarcinoma and lymphoma. The ability of MYC and K-ras(G12D) to cooperate for tumorigenesis and the ability of the inactivation of these oncogenes to result in tumor regression depended upon the specific tissue context. MYC-, K-ras(G12D)- or MYC/K-ras(G12D)-induced lymphomas exhibited sustained regression upon the inactivation of either or both oncogenes. However, in marked contrast, MYC-induced lung tumors failed to regress completely upon oncogene inactivation; whereas K-ras(G12D)-induced lung tumors regressed completely. Importantly, the combined inactivation of both MYC and K-ras(G12D) resulted more frequently in complete lung tumor regression. To account for the different roles of MYC and K-ras(G12D) in maintenance of lung tumors, we found that the down-stream mediators of K-ras(G12D) signaling, Stat3 and Stat5, are dephosphorylated following conditional K-ras(G12D) but not MYC inactivation. In contrast, Stat3 becomes dephosphorylated in lymphoma cells upon inactivation of MYC and/or K-ras(G12D). Interestingly, MYC-induced lung tumors that failed to regress upon MYC inactivation were found to have persistent Stat3 and Stat5 phosphorylation.Taken together, our findings point to the importance of the K-Ras and associated down-stream Stat effector pathways in the initiation and maintenance of lymphomas and lung tumors. We suggest that combined targeting of oncogenic pathways is more likely to be effective in the treatment of lung cancers and lymphomas.

    View details for DOI 10.1371/journal.pone.0002125

    View details for Web of Science ID 000261642400046

    View details for PubMedID 18461184

  • Oncogene addiction versus oncogene amnesia: Perhaps more than just a bad habit? CANCER RESEARCH Felsher, D. W. 2008; 68 (9): 3081-3086

    Abstract

    Cancer is a multistep process whereby genetic events that result in the activation of proto-oncogenes or the inactivation of tumor suppressor genes usurp physiologic programs mandating relentless proliferation and growth. Experimental evidence surprisingly illustrates that the inactivation of even a single oncogene can be sufficient to induce sustained tumor regression. These observations suggest the hypothesis that tumors become irrevocably addicted to the oncogenes that initiated tumorigenesis. The proposed explanation for this phenomenon is that activated oncogenes result in a signaling state in which the sudden abatement of oncogene activity balances towards proliferative arrest and apoptosis. Indeed, substantial evidence supports this hypothesis. Here, we propose an alternative, although not necessarily mutually exclusive, explanation for how oncogenes initiate and sustain tumorigenesis. We suggest that oncogene activation initiates tumorigenesis precisely because it directly overrides physiologic programs inducing a state of cellular amnesia, not only inducing relentless cellular proliferation, but also bypassing checkpoint mechanisms that are essential for cellular mortality, self-renewal, and genomic integrity. Because no single oncogenic lesion is sufficient to overcome all of these physiologic barriers, oncogenes are restrained from inducing tumorigenesis. Correspondingly, in a tumor that has acquired the complete complement of oncogenic lesions required to overcome all of these safety mechanisms, the inactivation of a single oncogene can restore some of these pathways resulting in proliferative arrest, differentiation, cellular senescence, and/or apoptosis. Thus, oncogenes induce cancer because they induce a cellular state of enforced oncogenic amnesia in which, only upon oncogene inactivation, the tumor becomes aware of its transgression.

    View details for DOI 10.1158/0008-5472.CAN-07-5832

    View details for Web of Science ID 000255602600003

    View details for PubMedID 18451131

  • Reversing cancer from inside and out: oncogene addiction, cellular senescence, and the angiogenic switch. Lymphatic research and biology Felsher, D. W. 2008; 6 (3-4): 149-154

    Abstract

    Cancer is largely caused by genetic events that result in the mutation of oncogenes or tumor suppressor genes, leading to cell autonomous proliferation and growth. The repair of these mutant gene products may be expected to subvert this neoplastic behavior. Indeed, oncogene inactivation can result in the elimination of all or almost all tumor cells by various mechanisms through the phenomena described as oncogene addiction. Recently, we have shown that oncogene addiction occurs through at least two broad classes of mechanisms: tumor cell intrinsic mechanisms of cellular senescence and apoptosis; and tumor cell extrinsic host-dependent mechanisms that include the shut-down of angiogenesis. We have argued that the abatement of oncogenic activity within a cancer cell not only leads to the demise of a tumor from within but also through the instruction of the restoration of the microenvironment.

    View details for DOI 10.1089/lrb.2008.63403

    View details for PubMedID 19093787

  • BCL-2 and mutant NRAS interact physically and functionally in a mouse model of progressive myelodysplasia CANCER RESEARCH Omidvar, N., Kogan, S., Beurlet, S., Pogam, C. I., Janin, A., West, R., Noguera, M., Reboul, M., Soulie, A., Leboeuf, C., Setterblad, N., Felsher, D., Lagasse, E., Mohamedali, A., Thomas, N. S., Fenaux, P., Fontenay, M., Pla, M., Mufti, G. J., Weissman, I., Chomienne, C., Padua, R. A. 2007; 67 (24): 11657-11667

    Abstract

    Myelodysplastic syndromes (MDS) are clonal stem cell hematologic disorders that evolve to acute myeloid leukemia (AML) and thus model multistep leukemogenesis. Activating RAS mutations and overexpression of BCL-2 are prognostic features of MDS/AML transformation. Using NRASD12 and BCL-2, we created two distinct models of MDS and AML, where human (h)BCL-2 is conditionally or constitutively expressed. Our novel transplantable in vivo models show that expression of hBCL-2 in a primitive compartment by mouse mammary tumor virus-long terminal repeat results in a disease resembling human MDS, whereas the myeloid MRP8 promoter induces a disease with characteristics of human AML. Expanded leukemic stem cell (Lin(-)/Sca-1(+)/c-Kit(+)) populations and hBCL-2 in the increased RAS-GTP complex within the expanded Sca-1(+) compartment are described in both MDS/AML-like diseases. Furthermore, the oncogenic compartmentalizations provide the proapoptotic versus antiapoptotic mechanisms, by activating extracellular signal-regulated kinase and AKT signaling, in determination of the neoplastic phenotype. When hBCL-2 is switched off with doxycycline in the MDS mice, partial reversal of the phenotype was observed with persistence of bone marrow blasts and tissue infiltration as RAS recruits endogenous mouse (m)BCL-2 to remain active, thus demonstrating the role of the complex in the disease. This represents the first in vivo progression model of MDS/AML dependent on the formation of a BCL-2:RAS-GTP complex. The colocalization of BCL-2 and RAS in the bone marrow of MDS/AML patients offers targeting either oncogene as a therapeutic strategy.

    View details for DOI 10.1158/0008-5472.CAN-07-0196

    View details for Web of Science ID 000251857900025

    View details for PubMedID 18089795

  • Inhibition of HMGcoA reductase by atorvastatin prevents and reverses MYC-induced lymphomagenesis BLOOD Shachaf, C. M., Perez, O. D., Youssef, S., Fan, A. C., Elchuri, S., Goldstein, M. J., Shirer, A. E., Sharpe, O., Chen, J., Mitchell, D. J., Chang, M., Nolan, G. P., Steinman, L., Felsher, D. W. 2007; 110 (7): 2674-2684

    Abstract

    Statins are a class of drugs that inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMGcoA) reductase, a critical enzyme in the mevalonate pathway. Several reports document that statins may prevent different human cancers. However, whether or not statins can prevent cancer is controversial due to discordant results. One possible explanation for these conflicting conclusions is that only some tumors or specific statins may be effective. Here, we demonstrate in an in vivo transgenic model in which atorvastatin reverses and prevents the onset of MYC-induced lymphomagenesis, but fails to reverse or prevent tumorigenesis in the presence of constitutively activated K-Ras (G12D). Using phosphoprotein fluorescence-activated cell sorter (FACS) analysis, atorvastatin treatment was found to result in the inactivation of the Ras and ERK1/2 signaling pathways associated with the dephosphorylation and inactivation of MYC. Correspondingly, tumors with a constitutively activated K-Ras (G12D) did not exhibit dephosphorylation of ERK1/2 and MYC. Atorvastatin's effects on MYC were specific to the inhibition of HMGcoA reductase, as treatment with mevalonate, the product of HMG-CoA reductase activity, abrogated these effects and inhibited the ability of atorvastatin to reverse or suppress tumorigenesis. Also, RNAi directed at HMGcoA reductase was sufficient to abrogate the neoplastic properties of MYC-induced tumors. Thus, atorvastatin, by inhibiting HMGcoA reductase, induces changes in phosphoprotein signaling that in turn prevent MYC-induced lymphomagenesis.

    View details for DOI 10.1182/blood-2006-09-048033

    View details for Web of Science ID 000249800900069

    View details for PubMedID 17622571

  • Specific tumor suppressor function for E2F2 in Myc-induced T cell lymphomagenesis PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Opavsky, R., Tsai, S., Guimond, M., Arora, A., Opavska, J., Becknell, B., Kaufmann, M., Walton, N. A., Stephens, J. A., Fernandez, S. A., Muthusamy, N., Felsher, D. W., Porcu, P., Caligiuri, M. A., Leone, G. 2007; 104 (39): 15400-15405

    Abstract

    Deregulation of the Myc pathway and deregulation of the Rb pathway are two of the most common abnormalities in human malignancies. Recent in vitro experiments suggest a complex cross-regulatory relationship between Myc and Rb that is mediated through the control of E2F. To evaluate the functional connection between Myc and E2Fs in vivo, we used a bitransgenic mouse model of Myc-induced T cell lymphomagenesis and analyzed tumor progression in mice deficient for E2f1, E2f2, or E2f3. Whereas the targeted inactivation of E2f1 or E2f3 had no significant effect on tumor progression, loss of E2f2 accelerated lymphomagenesis. Interestingly, loss of a single copy of E2f2 also accelerated tumorigenesis, albeit to a lesser extent, suggesting a haploinsufficient function for this locus. The combined ablation of E2f1 or E2f3, along with E2f2, did not further accelerate tumorigenesis. Myc-overexpressing T cells were more resistant to apoptosis in the absence of E2f2, and the reintroduction of E2F2 into these tumor cells resulted in an increase of apoptosis and inhibition of tumorigenesis. These results identify the E2f2 locus as a tumor suppressor through its ability to modulate apoptosis.

    View details for DOI 10.1073/pnas.0706307104

    View details for Web of Science ID 000249806900042

    View details for PubMedID 17881568

  • HIF-dependent antitumorigenic effect of antioxidants in vivo CANCER CELL Gao, P., Zhang, H., Dinavahi, R., Li, F., Xiang, Y., Raman, V., Bhujwalla, Z. M., Felsher, D. W., Cheng, L., Pevsner, J., Lee, L. A., Semenza, G. L., Dang, C. V. 2007; 12 (3): 230-238

    Abstract

    The antitumorigenic activity of antioxidants has been presumed to arise from their ability to squelch DNA damage and genomic instability mediated by reactive oxygen species (ROS). Here, we report that antioxidants inhibited three tumorigenic models in vivo. Inhibition of a MYC-dependent human B lymphoma model was unassociated with genomic instability but was linked to diminished hypoxia-inducible factor (HIF)-1 levels in a prolyl hydroxylase 2 and von Hippel-Lindau protein-dependent manner. Ectopic expression of an oxygen-independent, stabilized HIF-1 mutant rescued lymphoma xenografts from inhibition by two antioxidants: N-acetylcysteine and vitamin C. These findings challenge the paradigm that antioxidants diminish tumorigenesis primarily through decreasing DNA damage and mutations and provide significant support for a key antitumorigenic effect of diminishing HIF levels.

    View details for DOI 10.1016/j.ccr.2007.08.004

    View details for Web of Science ID 000249514500006

    View details for PubMedID 17785204

  • CpG island methylation in a mouse model of lymphoma is driven by the genetic configuration of tumor cells PLOS GENETICS Opavsky, R., Wang, S., Trikha, P., Raval, A., Huang, Y., Wu, Y., Rodriguez, B., Keller, B., Liyanarachchi, S., Wei, G., Davuluri, R. V., Weinstein, M., Felsher, D., Ostrowski, M., Leone, G., Plass, C. 2007; 3 (9): 1757-1769

    Abstract

    Hypermethylation of CpG islands is a common epigenetic alteration associated with cancer. Global patterns of hypermethylation are tumor-type specific and nonrandom. The biological significance and the underlying mechanisms of tumor-specific aberrant promoter methylation remain unclear, but some evidence suggests that this specificity involves differential sequence susceptibilities, the targeting of DNA methylation activity to specific promoter sequences, or the selection of rare DNA methylation events during disease progression. Using restriction landmark genomic scanning on samples derived from tissue culture and in vivo models of T cell lymphomas, we found that MYC overexpression gave rise to a specific signature of CpG island hypermethylation. This signature reflected gene transcription profiles and was detected only in advanced stages of disease. The further inactivation of the Pten, p53, and E2f2 tumor suppressors in MYC-induced lymphomas resulted in distinct and diagnostic CpG island methylation signatures. Our data suggest that tumor-specific DNA methylation in lymphomas arises as a result of the selection of rare DNA methylation events during the course of tumor development. This selection appears to be driven by the genetic configuration of tumor cells, providing experimental evidence for a causal role of DNA hypermethylation in tumor progression and an explanation for the tremendous epigenetic heterogeneity observed in the evolution of human cancers. The ability to predict genome-wide epigenetic silencing based on relatively few genetic alterations will allow for a more complete classification of tumors and understanding of tumor cell biology.

    View details for DOI 10.1371/journal.pgen.0030167

    View details for Web of Science ID 000249767800018

    View details for PubMedID 17907813

  • Development of a conditional bioluminescent transplant model for TPM3-ALK-induced tumorigenesis as a tool to validate ALK-Dependent cancer targeted therapy CANCER BIOLOGY & THERAPY Giuriato, S., Faumont, N., Bousquet, E., Foisseau, M., Bibonne, A., Moreau, M., Saati, T. A., Felsher, D. W., Delsol, G., Meggetto, F. 2007; 6 (8): 1318-1323

    Abstract

    Overexpression and activation of TPM3-ALK tyrosine kinase fusion protein is a causal oncogenic event in the development of Anaplastic Large Cell Lymphoma and Inflammatory Myofibroblastic ALK-positive tumors. Thus, the development of ALK specific tyrosine kinase inhibitors is a current therapeutic challenge. Animal models are essential to assess, in vivo, the efficiency of ALK-oncogene inhibitors and to identify new and/or additional therapeutic targets in the ALK tumorigenesis pathway. Using the tetracycline system to allow conditional and concomitant TPM3-ALK and luciferase expression, we have developed a unique transplant model for bioluminescent TPM3-ALK-induced fibroblastic tumors in athymic nude mice. The reversible TPM3-ALK expression allowed us to demonstrate that this oncogene is essential for the tumor growth and its maintenance. In addition, we showed that this model could be used to precisely assess tumor growth inhibition upon ALK chemical inactivation. As proof of principle, we used the general tyrosine kinase inhibitor herbimycin A to inhibit ALK oncoprotein activity. As expected, herbimycin A treatment reduced tumor growth as assessed both by tumor volume measurement and bioluminescent imaging. We conclude that this transplant model for TPM3-ALK-induced tumors represents a valuable tool not only to accurately and rapidly evaluate in vivo ALK-targeted therapies but also to gain insight into the mechanism of ALK-positive tumor development.

    View details for Web of Science ID 000252666800038

    View details for PubMedID 17660712

  • Enhanced NFATc1 nuclear occupancy causes T cell activation independent of CD28 costimulation JOURNAL OF IMMUNOLOGY Pan, M., Winslow, M. M., Chen, L., Kuo, A., Felsher, D., Crabtree, G. R. 2007; 178 (7): 4315-4321

    Abstract

    TCR signals induce the nuclear localization of NFATc proteins, which are removed from the nucleus after rephosphorylation by glycogen synthase kinase 3 and other kinases. Rapid nuclear export might allow continuous monitoring of receptor occupancy, making the transcriptional response proportional to the duration of TCR/CD28 signaling. To investigate this possibility, we analyzed mice in which T cells express a NFATc1 variant (NFATc1(nuc)) with serine-to-alanine changes at the glycogen synthase kinase 3 phosphorylation sites. NFATc1(nuc) T cells have constitutively nuclear NFATc1, enhanced T cell activation in vivo, and calcineurin-independent proliferation in vitro. NFATc1(nuc) T cells are hypersensitive to TCR/CD3 stimulation, resulting in enhanced proliferation and cytokine production that is independent of CD28 costimulation. These results support the notion that CD28 inhibits nuclear export of NFATc transcription factors. In addition, NFATc1(nuc) destabilizes a positive feedback loop in which NFATc1 activates its own transcription as well as its targets, such as CD40 ligand and Th1/Th2 cytokines.

    View details for Web of Science ID 000245197300038

    View details for PubMedID 17371988

  • Identifying critical signaling molecules for the treatment of cancer. Recent results in cancer research. Fortschritte der Krebsforschung. Progrs dans les recherches sur le cancer Arvanitis, C., Bendapudi, P. K., Bachireddy, P., Felsher, D. W. 2007; 172: 5-24

    View details for PubMedID 17607933

  • Tumor dormancy - Death and resurrection of cancer as seen through transgenic mouse models CELL CYCLE Felsher, D. W. 2006; 5 (16): 1808-1811

    Abstract

    Cancer is caused by genetic changes that activate oncogenes or inactivate tumor suppressor genes. The repair or inactivation of mutant genes may be effective in the treatment of cancer. Drugs that target oncogenes have shown to be effective in the treatment of some cancers. However, it is still unclear why the inactivation of a single cancer associated gene would ever result in the elimination of tumor cells. In experimental transgenic mouse models the consequences of oncogene inactivation depend upon the genetic and cellular context. In some cases, oncogene inactivation results in the elimination of all or almost all tumor cells through apoptosis or terminal differentiation. However, in other cases, oncogene inactivation results in the apparent loss of the neoplastic properties of tumor cells, that now appear and behave like normal cells, however, upon oncogene reactivation rapidly recover their neoplastic phenotype. These observations illustrate that oncogene inactivation can result in a state of tumor dormancy. Understanding when and how oncogene inactivation induces sustained tumor regression will be important towards the development of successful therapeutic strategies for cancer.

    View details for Web of Science ID 000240698600011

    View details for PubMedID 16929172

  • Conditional transgenic models define how MYC initiates and maintains tumorigenesis SEMINARS IN CANCER BIOLOGY Arvanitis, C., Felsher, D. W. 2006; 16 (4): 313-317

    Abstract

    MYC is one of the most commonly overexpressed oncogenes in human cancer. The targeted inactivation of MYC is a possible therapy for neoplasia. Conditional transgenic mouse model systems are tractable methods to precisely dissect how and when the inactivation of MYC might be effective in the treatment for human cancer. From these model systems, several general principles emerge. MYC inactivation stereotypically results in the proliferative arrest, differentiation and/or apoptosis of tumor cells. The specific consequences of MYC inactivation appear to depend both on the type of cancer as well as the constellation of genetic events unique to a given tumor. Tumors can escape from dependence upon MYC by acquiring compensatory genetic events. MYC inactivation can uncover the stem cell properties of tumor cells that differentiate into normal appearing cells. In some cases, these differentiated cells are actually dormant tumor cells that recover their neoplastic properties upon MYC reactivation. In other cases, even brief MYC inactivation is sufficient to induce sustained tumor regression. Insights from conditional transgenic mouse models will be useful in the development of therapies that target MYC for the treatment of cancer.

    View details for DOI 10.1016/j.semcancer.2006.07.012

    View details for Web of Science ID 000241107600008

    View details for PubMedID 16935001

  • c-Myc is an important direct target of Notch1 in T-cell acute lymphoblastic leukemia/lymphoma GENES & DEVELOPMENT Weng, A. P., Millholland, J. M., Yashiro-Ohtani, Y., Arcangeli, M. L., Lau, A., Wai, C., del Bianco, C., Rodriguez, C. G., Sai, H., Tobias, J., Li, Y., Wolfe, M. S., Shachaf, C., Felsher, D., Blacklow, S. C., Pear, W. S., Aster, J. C. 2006; 20 (15): 2096-2109

    Abstract

    Human acute T-cell lymphoblastic leukemias and lymphomas (T-ALL) are commonly associated with gain-of-function mutations in Notch1 that contribute to T-ALL induction and maintenance. Starting from an expression-profiling screen, we identified c-myc as a direct target of Notch1 in Notch-dependent T-ALL cell lines, in which Notch accounts for the majority of c-myc expression. In functional assays, inhibitors of c-myc interfere with the progrowth effects of activated Notch1, and enforced expression of c-myc rescues multiple Notch1-dependent T-ALL cell lines from Notch withdrawal. The existence of a Notch1-c-myc signaling axis was bolstered further by experiments using c-myc-dependent murine T-ALL cells, which are rescued from withdrawal of c-myc by retroviral transduction of activated Notch1. This Notch1-mediated rescue is associated with the up-regulation of endogenous murine c-myc and its downstream transcriptional targets, and the acquisition of sensitivity to Notch pathway inhibitors. Additionally, we show that primary murine thymocytes at the DN3 stage of development depend on ligand-induced Notch signaling to maintain c-myc expression. Together, these data implicate c-myc as a developmentally regulated direct downstream target of Notch1 that contributes to the growth of T-ALL cells.

    View details for DOI 10.1101/gad.1450406

    View details for Web of Science ID 000239504500014

    View details for PubMedID 16847353

  • MYC can induce DNA breaks in vivo and in vitro independent of reactive oxygen species CANCER RESEARCH Ray, S., Atkuri, K. R., Deb-Basu, D., Adler, A. S., Chang, H. Y., Herzenberg, L. A., Felsher, D. W. 2006; 66 (13): 6598-6605

    Abstract

    MYC overexpression is thought to initiate tumorigenesis by inducing cellular proliferation and growth and to be restrained from causing tumorigenesis by inducing cell cycle arrest, cellular senescence, and/or apoptosis. Here we show that MYC can induce DNA breaks both in vitro and in vivo independent of increased production of reactive oxygen species (ROS). We provide an insight into the specific circumstances under which MYC generates ROS in vitro and propose a possible mechanism. We found that MYC induces DNA double-strand breaks (DSBs) independent of ROS production in murine lymphocytes in vivo as well as in normal human foreskin fibroblasts (NHFs) in vitro in normal (10%) serum, as measured by gammaH2AX staining. However, NHFs cultured in vitro in low serum (0.05%) and/or ambient oxygen saturation resulted in ROS-associated oxidative damage and DNA single-strand breaks (SSBs), as measured by Ape-1 staining. In NHFs cultured in low versus normal serum, MYC induced increased expression of CYP2C9, a gene product well known to be associated with ROS production. Specific inhibition of CYP2C9 by small interfering RNA was shown to partially inhibit MYC-induced ROS production. Hence, MYC overexpression can induce ROS and SSBs under some conditions, but generally induces widespread DSBs in vivo and in vitro independent of ROS production.

    View details for DOI 10.1158/0008-5472.CAN-05-3115

    View details for Web of Science ID 000238825800021

    View details for PubMedID 16818632

  • CDK2 is required by MYC to induce apoptosis CELL CYCLE Deb-Basu, D., Aleem, E., Kaldis, P., Felsher, D. W. 2006; 5 (12): 1342-1347

    Abstract

    Depending upon the cellular and physiologic context, the overexpression of the MYC proto-oncogene results in rapid cell growth, proliferation, induction of apoptosis and/or proliferative arrest. What determines the precise consequences upon MYC activation is not clear. We have found that cyclin-dependent kinase 2 (CDK2) is required by MYC to induce apoptosis. MYC-induced apoptosis was suppressed in mouse embryonic fibroblasts (MEF) knocked out for Cdk2 or normal human fibroblasts (NHF) upon expression of the CDK2 inhibitor p27 or treated with RNAi directed at CDK2. Knockout of Cdk2 did not prevent MYC from inducing p53 and Bim. The inhibition of CDK2 did not prevent apoptosis induced by the DNA damaging agent etoposide. Our results surprisingly suggest that CDK2 defines whether MYC induction causes apoptosis.

    View details for Web of Science ID 000238581200019

    View details for PubMedID 16760655

  • MYC can enforce cell cycle transit from G(1) to S and G(2) to S, but not mitotic cellular division, independent of p27-mediated inihibition of Cyclin E/CDK2 CELL CYCLE Deb-Basu, D., Karlsson, A., Li, Q., Dang, C. V., Felsher, D. W. 2006; 5 (12): 1348-1355

    Abstract

    Overexpression of the MYC proto-oncogene exerts protean biological effects that may contribute to its ability to induce tumorigenesis including enforcing cellular growth and proliferation and inducing genomic instability. MYC overexpression may induce genomic damage at least in part by causing inappropriate DNA replication. MYC may induce inappropriate DNA replication through the activation of Cyclin E/CDK2. To address this possibility, the effects of ectopic p27 expression in immortal rat fibroblasts or human breast epithelial cell lines on MYC-induced endo-reduplication was determined. p27 inhibited Cyclin E/CDK2 associated kinase activity, but failed to prevent MYC from inducing transit from G1 to S phase; inhibited at lower but not higher levels of MYC transit from G2 to S and endo-reduplication; however, MYC failed to enforce mitotic cellular division. In addition, MYC was found to induce Cyclin E; and Cyclin E in turn was found to be able to induce endo-reduplication. Hence, MYC appears induce inappropriate cell cycle transit, but not mitotic cellular division independent of p27 mediated inhibition of Cyclin E/Cdk2. Our results have implications for the mechanisms by which MYC overexpression dysregulates cell cycle transit, causes genomic destabilization and is restrained from causing tumorigenesis.

    View details for Web of Science ID 000238581200020

    View details for PubMedID 16760657

  • Lethal cutaneous disease in transgenic mice conditionally expressing type I human T cell leukemia virus tax JOURNAL OF BIOLOGICAL CHEMISTRY Kwon, H., Ogle, L., Benitez, B., Bohuslav, J., Montano, M., Felsher, D. W., Greene, W. C. 2005; 280 (42): 35713-35722

    Abstract

    Type I human T cell leukemia virus (HTLV-I) is etiologically linked with adult T cell leukemia, an aggressive and usually fatal expansion of activated CD4+ T lymphocytes that frequently traffic to skin. T cell transformation induced by HTLV-I involves the action of the 40-kDa viral Tax transactivator protein. Tax both stimulates the HTLV-I long terminal repeat and deregulates the expression of select cellular genes by altering the activity of specific host transcription factors, including cyclic AMP-responsive element-binding protein (CREB)/activating transcription factor, NF-kappaB/Rel, and serum response factor. To study initiating events involved in HTLV-I Tax-induced T cell transformation, we generated "Tet-off" transgenic mice conditionally expressing in a lymphocyte-restricted manner (EmuSR alpha promoter-enhancer) either wild-type Tax or mutant forms of Tax that selectively compromise the NF-kappaB (M22) or CREB/activating transcription factor (M47) activation pathways. Wild-type Tax and M47 Tax-expressing mice, but not M22-Tax expressing mice, developed progressive alopecia, hyperkeratosis, and skin lesions containing profuse activated CD4 T cell infiltrates with evidence of deregulated inflammatory cytokine production. In addition, these animals displayed systemic lymphadenopathy and splenomegaly. These findings suggest that Tax-mediated activation of NF-kappaB plays a key role in the development of this aggressive skin disease that shares several features in common with the skin disease occurring during the preleukemic stage in HTLV-I-infected patients. Of note, this skin disease completely resolved when Tax transgene expression was suppressed by administration of doxycycline, emphasizing the key role played by this viral oncoprotein in the observed pathology.

    View details for DOI 10.1074/jbc.M504848200

    View details for Web of Science ID 000232561200074

    View details for PubMedID 16105841

  • Comparative genomic hybridization on mouse cDNA microarrays and its application to a murine lymphoma model ONCOGENE Sander, S., Bullinger, L., Karlsson, A., Giuriato, S., Hernandez-Boussard, T., Felsher, D. W., Pollack, J. R. 2005; 24 (40): 6101-6107

    Abstract

    Microarray-based formats offer a high-resolution alternative to conventional, chromosome-based comparative genomic hybridization (CGH) methods for assessing DNA copy number alteration (CNA) genome-wide in human cancer. For murine tumors, array CGH should provide even greater advantage, since murine chromosomes are more difficult to individually discern. We report here the adaptation and evaluation of a cDNA microarray-based CGH method for the routine characterization of CNAs in murine tumors, using mouse cDNA microarrays representing approximately 14,000 different genes, thereby providing an average mapping resolution of 109 kb. As a first application, we have characterized CNAs in a set of 10 primary and recurrent lymphomas derived from a Myc-induced murine lymphoma model. In primary lymphomas and more commonly in Myc-independent relapses, we identified a recurrent genomic DNA loss at chromosome 3G3-3H4, and recurrent amplifications at chromosome 3F2.1-3G3 and chromosome 15E1/E2-15F3, the boundaries of which we defined with high resolution. Further, by profiling gene expression using the same microarray platform, we identified within CNAs the relevant subset of candidate cancer genes displaying comparably altered expression, including Mcl1 (myeloid cell leukemia sequence 1), a highly expressed antiapoptotic gene residing within the chr 3 amplicon peak. CGH on mouse cDNA microarrays therefore represents a reliable method for the high-resolution characterization of CNAs in murine tumors, and a powerful approach for elucidating the molecular events in tumor development and progression in murine models.

    View details for DOI 10.1038/sj.onc.1208751

    View details for Web of Science ID 000231718100004

    View details for PubMedID 16007205

  • Conditionally MYC : insights from novel transgenic models CANCER LETTERS Arvanitis, C., Felsher, D. W. 2005; 226 (2): 95-99

    Abstract

    MYC was one of the first oncogenes identified to be associated with chromosomal aberrations and one of the most common oncogenes involved in the pathogenesis of cancer. However, until recently it was not clear if MYC would be a good target for the treatment of cancer. New conditional transgenic models have been used to demonstrate that even the brief inactivation of MYC can reverse tumorigenesis. Here we review results from recent experimental model systems, which demonstrate that the inactivation of MYC may be a specific and effective treatment for many types of cancer.

    View details for DOI 10.1016/j.canlet.2004.10.043

    View details for Web of Science ID 000231161800001

    View details for PubMedID 16039948

  • Suppression of p53 by Notch in lymphomagenesis: Implications for initiation and regression CANCER RESEARCH Beverly, L. J., Felsher, D. W., Capobianco, A. J. 2005; 65 (16): 7159-7168

    Abstract

    Aberrant Notch signaling contributes to more than half of all human T-cell leukemias, and accumulating evidence indicates Notch involvement in other human neoplasms. We developed a tetracycline-inducible mouse model (Top-Notch(ic)) to examine the genetic interactions underlying the development of Notch-induced neoplastic disease. Using this model, we show that Notch suppresses p53 in lymphomagenesis through repression of the ARF-mdm2-p53 tumor surveillance network. Attenuation of Notch expression resulted in a dramatic increase in p53 levels that led to tumor regression by an apoptotic program. This shows that continued Notch activity is required to maintain the disease state. However, all tumors relapsed with rapid kinetics, most of which, by reactivation of Notch expression. Furthermore, by directly inhibiting the mdm2-p53 interaction by using either ionizing radiation or the novel small molecule therapeutic Nutlin, p53 can be activated and cause tumor cell death, even in the presence of sustained Notch activity. Therefore, it is the suppression of p53 that provides the Achilles heel for Notch-induced tumors, as activation of p53 in the presence of Notch signaling drives tumor regression. Our study provides proof-of-principle for the rational targeting of therapeutics against the mdm2-p53 pathway in Notch-induced neoplasms. Furthermore, we propose that suppression of p53 by Notch is a key mechanism underlying the initiation of T-cell lymphoma.

    View details for DOI 10.1158/0008-5472.CAN-05-1664

    View details for Web of Science ID 000231188600020

    View details for PubMedID 16103066

  • Rehabilitation of cancer through oncogene inactivation TRENDS IN MOLECULAR MEDICINE Shachaf, C. M., Felsher, D. W. 2005; 11 (7): 316-321

    Abstract

    The inactivation of the MYC oncogene alone can reverse tumorigenesis. Upon MYC inactivation, tumors stereotypically reverse, undergoing proliferative arrest, cellular differentiation and/or apoptosis. The precise consequences of MYC inactivation appear to depend upon both genetic and epigenetic parameters. In some types of cancer following MYC inactivation, tumor cells become well differentiated and biologically and histologically normal, inducing sustained tumor regression. However, in some cases, these normal-appearing cells are actually dormant tumor cells and upon MYC reactivation they rapidly recover their tumorigenic properties. Future therapies to treat cancer will need to address the possibility that tumor cells can camouflage a normal phenotype following treatment, resting in a dormant, latently cancerous state.

    View details for Web of Science ID 000231084900005

    View details for PubMedID 15955741

  • Getting at MYC through RAS CLINICAL CANCER RESEARCH Bachireddy, P., Bendapudi, P. K., Felsher, D. W. 2005; 11 (12): 4278-4281

    View details for Web of Science ID 000229725900002

    View details for PubMedID 15958607

  • Tumor dormancy and MYC inactivation: Pushing cancer to the brink of normalcy CANCER RESEARCH Shachaf, C. M., Felsher, D. W. 2005; 65 (11): 4471-4474

    Abstract

    Upon MYC inactivation, tumors variously undergo proliferative arrest, cellular differentiation, and apoptosis and in some cases, apparently permanently revoking tumorigenesis. In liver tumor cells, we recently showed that MYC inactivation uncovers stem cell properties and triggers differentiation, but in this case, their neoplastic properties are restorable by MYC reactivation. Thus, whereas oncogene inactivation can push cancer to the brink of normalcy, some cells retain the latent capacity to turn cancerous again, arguing that they may exist in a state of tumor dormancy.

    View details for Web of Science ID 000229407800002

    View details for PubMedID 15930260

  • Putting oncogenes into a developmental context CANCER BIOLOGY & THERAPY Felsher, D. W. 2004; 3 (10): 942-944

    Abstract

    Cancer is largely caused by genomic events that activate oncogenes or inactivate tumor suppressor genes. To date, the mechanisms by which these mutant gene products contribute to tumorigenesis has been studied mostly in experimental model systems that have not been able to interrogate the potential contribution of developmental factors in the etiology of neoplasia. Recently, we employed a conditional transgenic model system to demonstrate that the ability of the MYC oncogene to induce tumorigenesis is influenced by the developmental age of the host. MYC induced in embryonic of neonatal tissues cellular proliferation and the rapid onset of tumorigenesis; whereas MYC activation in adult tissues induces cellular hypertrophy. Thus, differences in the frequency and spectrum of cancers observed in different aged hosts may reflect the influence of developmental context. Cancer may generally be better thought of as a consequence of genetic events that occur in a permissive epigenetic state. Developmental context may be a critical determinant in the pathogenesis of neoplasia.

    View details for Web of Science ID 000227440300012

    View details for PubMedID 15611633

  • The human BCL6 transgene promotes the development of lymphomas in the mouse PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Baron, B. W., Anastasi, J., Montag, A., Huo, D. Z., Baron, R. M., Karrison, T., Thirman, M. J., Subudhi, S. K., Chin, R. K., Felsher, D. W., Fu, Y. X., McKeithan, T. W., Baron, J. M. 2004; 101 (39): 14198-14203

    Abstract

    BCL6, a gene on chromosome 3, band q27, encodes a zinc finger transcriptional repressor that is needed for germinal center formation and has been implicated in the pathogenesis of some human lymphomas when it is mutated or involved in chromosomal rearrangements. To explore further the mechanisms of action of BCL6 in lymphomagenesis, we developed a transgenic mouse model mimicking a common translocation, the t(3, 14)(q27;q32), in human lymphomas. The transgenic mice develop normally and express the transgenic BCL6 protein constitutively in lymphocytes. A small fraction of the animals develop B and T cell lymphomas after a long latency period, but the incidence is dramatically enhanced following administration of N-ethyl-N-nitrosourea, a carcinogen that induces DNA mutations. The N-ethyl-N-nitrosourea-induced lymphomas spread widely, were exclusively T cell, expressed the BCL6 protein, and occurred only in the transgenic mice. Because BCL6 expression has been reported in a number of T cell tumors as well as in the more commonly occurring B cell lymphomas in humans, our transgenic mice provide a model for the study of human lymphomas.

    View details for DOI 10.1073/pnas.0406138101

    View details for Web of Science ID 000224211400043

    View details for PubMedID 15375218

  • The E47 transcription factor negatively regulates CD5 expression during thymocyte development PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yang, Y., Contag, C. H., Felsher, D., Shachaf, C. M., Cao, Y., Herzenberg, L. A., Herzenberg, L. A., Tung, J. W. 2004; 101 (11): 3898-3902

    Abstract

    The expression of CD5 increases progressively as thymocytes mature. We have shown that CD5 expression is controlled by a tissue-specific regulatory promoter located upstream of the CD5 translation start sites. Deletion of this regulatory promoter, which contains three potential transcription factor binding sites (CCAAT, kappa E2, and ets) reduces the promoter activity to basal level. Of these sites, only ets proved essential for CD5 expression in T cell lines. Here, we introduce a role for the E47 transcription factor and the CD5 promoter kappa E2 site in regulating CD5 expression during thymocyte development. Using T cell lines, we show that (i) mutation of the kappa E2 site in the CD5 regulatory promoter results in a significant elevation of CD5 promoter activity; (ii) the E47 transcription factor binds to the kappa E2 site; and (iii) overexpression of E47 inhibits CD5 expression. We then show, in high-dimensional fluorescence-activated cell sorting studies with primary thymocytes at successive developmental stages, that (i) intracellular E47 levels decrease as surface CD5 expression increases; (ii) E47 expression is down-regulated and CD5 expression is correspondingly up-regulated in DN3 thymocytes in RAG-2-deficient mice injected with anti-CD3 to mimic pre-T cell receptor stimulation; and (iii) E47 expression is down-regulated and CD5 expression is up-regulated when double positive thymocytes are stimulated in vitro with anti-CD3. Based on these data, we propose that E47 negatively regulates CD5 expression by interacting with the kappa E2 site in the CD5 regulatory promoter and that decreases in E47 in response to developmental signals are critical to the progressive increase in CD5 expression as thymocytes mature.

    View details for DOI 10.1073/pnas.0308764101

    View details for Web of Science ID 000220314500034

    View details for PubMedID 15001710

  • Reversibility of oncogene-induced cancer CURRENT OPINION IN GENETICS & DEVELOPMENT Felsher, D. W. 2004; 14 (1): 37-42

    Abstract

    Cancer can largely be conceived as a consequence of genomic catastrophes resulting in genetic events that usurp physiologic function of a normal cell. These genetic events mediate their pathologic effects by either activating oncogenes or inactivating tumor-suppressor genes. The targeted repair or inactivation of these damaged gene products may counteract the effects of these genetic events, reversing tumorigenesis and thereby serve as an effective therapy for cancer. However, because they are the result of many genetic events, the inactivation of no single mutant gene product may be sufficient to reverse cancer. Despite this caveat, compelling recent evidence suggests that there are circumstances when even the brief interruption of activation of a single oncogene can be sufficient to reverse tumorigenesis. Understanding how and when oncogene inactivation reverses cancer will be important in both defining the molecular pathogenesis of cancer as well as developing new molecularly based treatments.

    View details for Web of Science ID 000188978200007

    View details for PubMedID 15108803

  • Oncogenes as therapeutic targets SEMINARS IN CANCER BIOLOGY Felsher, D. W. 2004; 14 (1): 1-1
  • Conditional animal models: a strategy to define when oncogenes will be effective targets to treat cancer SEMINARS IN CANCER BIOLOGY Giuriato, S., Rabin, K., Fan, A. C., Shachaf, C. M., Felsher, D. W. 2004; 14 (1): 3-11

    Abstract

    The ability to model cancer in the mouse has provided a robust methodology to dissect the molecular etiology of cancer. These models serve as potentially powerful platforms to preclinically evaluate novel therapeutics. In particular, the recent development of strategies to conditionally induce the or knockout the function of genes in a tissue specific manner has enabled investigators to engineer mice to demonstrate that the targeted inactivation of specific oncogenes can be effective in inducing sustained regression of tumors. Thus, these animal models will be useful to define the specific genes that will be therapeutically useful to target for the treatment of particular human cancers.

    View details for DOI 10.1016/j.semcancer.2003.11.002

    View details for Web of Science ID 000189081200002

    View details for PubMedID 14757531

  • How cancers escape their oncogene habit. Cell cycle Giuriato, S., Felsher, D. W. 2003; 2 (4): 329-332

    Abstract

    Many recent reports demonstrate that at least initially, the inactivation of an oncogene can induce sustained regression of even a highly invasive and genetically complex cancer. However, upon prolonged oncogene inactivation, some cancers ultimately relapse, becoming independent of the very oncogene that initiated the process of tumorigenesis. Understanding the specific mechanisms by which cancers can escape dependence upon a particular oncogene will be critical to anticipate mechanisms by which human cancers will evade therapies that target individual oncogenes. Thereby, more effective strategies will be developed to clinically treat cancer.

    View details for PubMedID 12851484

  • Pharmacological inactivation of MYC for the treatment of cancer DRUG NEWS & PERSPECTIVES Felsher, D. W., Bradon, N. 2003; 16 (6): 370-374

    Abstract

    The overexpression of the MYC proto-oncogene has been implicated in the pathogenesis of most types of human cancer. Recent experimental observations indicate that the inactivation of MYC may be effective in the treatment of neoplasia. Several different strategies have been employed to develop novel drugs that may be effective to target the inactivation of MYC for the treatment of cancer. Some of these strategies are discussed.

    View details for Web of Science ID 000185723900007

    View details for PubMedID 12973448

  • Genomically complex lymphomas undergo sustained tumor regression upon MYC inactivation unless they acquire novel chromosomal translocations BLOOD Karlsson, A., Giuriato, S., Tang, F., Fung-Weier, J., Levan, G., Felsher, D. W. 2003; 101 (7): 2797-2803

    Abstract

    The targeted inactivation of oncogenes may be a specific and effective treatment for cancer. However, because human cancers are the consequence of multiple genetic changes, the inactivation of one oncogene may not be sufficient to cause sustained tumor regression. Moreover, cancers are genomically unstable and may readily compensate for the inactivation of a single oncogene. Here we confirm by spectral karyotypic analysis that MYC-induced hematopoietic tumors are highly genetically complex and genomically unstable. Nevertheless, the inactivation of MYC alone was found to be sufficient to induce sustained tumor regression. After prolonged MYC inactivation, some tumors exhibited a distinct propensity to relapse. When tumors relapsed, they no longer required the overexpression of MYC but instead acquired novel chromosomal translocations. We conclude that even highly genetically complex cancers are reversible on the inactivation of MYC, unless they acquire novel genetic alterations that can sustain a neoplastic phenotype.

    View details for DOI 10.1182/blood-2002-10-3091

    View details for Web of Science ID 000181823600058

    View details for PubMedID 12517816

  • C-Myc is a critical target for C/EBP alpha in granulopoiesis MOLECULAR AND CELLULAR BIOLOGY Johansen, L. M., Iwama, A., Lodie, T. A., Sasaki, K., Felsher, D. W., Golub, T. R., Tenen, D. G. 2001; 21 (11): 3789-3806

    Abstract

    CCAAT/enhancer binding protein alpha (C/EBPalpha) is an integral factor in the granulocytic developmental pathway, as myeloblasts from C/EBPalpha-null mice exhibit an early block in differentiation. Since mice deficient for known C/EBPalpha target genes do not exhibit the same block in granulocyte maturation, we sought to identify additional C/EBPalpha target genes essential for myeloid cell development. To identify such genes, we used both representational difference analysis and oligonucleotide array analysis with RNA derived from a C/EBPalpha-inducible myeloid cell line. From each of these independent screens, we identified c-Myc as a C/EBPalpha negatively regulated gene. We mapped an E2F binding site in the c-Myc promoter as the cis-acting element critical for C/EBPalpha negative regulation. The identification of c-Myc as a C/EBPalpha target gene is intriguing, as it has been previously shown that down-regulation of c-Myc can induce myeloid differentiation. Here we show that stable expression of c-Myc from an exogenous promoter not responsive to C/EBPalpha-mediated down-regulation forces myeloblasts to remain in an undifferentiated state. Therefore, C/EBPalpha negative regulation of c-Myc is critical for allowing early myeloid precursors to enter a differentiation pathway. This is the first report to demonstrate that C/EBPalpha directly affects the level of c-Myc expression and, thus, the decision of myeloid blasts to enter into the granulocytic differentiation pathway.

    View details for Web of Science ID 000168706600017

    View details for PubMedID 11340171

  • Overexpression of MYC causes p53-dependent G(2) arrest of normal fibroblasts PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Felsher, D. W., Zetterberg, A., Zhu, J. Y., Tlsty, T., BISHOP, J. M. 2000; 97 (19): 10544-10548

    Abstract

    Overexpression of the proto-oncogene MYC has been implicated in the genesis of diverse human cancers. One explanation for the role of MYC in tumorigenesis has been that this gene might drive cells inappropriately through the division cycle, leading to the relentless proliferation characteristic of the neoplastic phenotype. Herein, we report that the overexpression of MYC alone cannot sustain the division cycle of normal cells but instead leads to their arrest in G(2). We used an inducible form of the MYC protein to stimulate normal human and rodent fibroblasts. The stimulated cells passed through G(1) and S but arrested in G(2) and frequently became aneuploid, presumably as a result of inappropriate reinitiation of DNA synthesis. Absence of the tumor suppressor gene p53 or its downstream effector p21 reduced the frequency of both G(2) arrest and aneuploidy, apparently by compromising the G(2) checkpoint control. Thus, relaxation of the G(2) checkpoint may be an essential early event in tumorigenesis by MYC. The loss of p53 function seems to be one mechanism by which this relaxation commonly occurs. These findings dramatize how multiple genetic events can collaborate to produce neoplastic cells.

    View details for Web of Science ID 000089341400047

    View details for PubMedID 10962037

  • Reversible tumorigenesis by MYC in hematopoietic lineages MOLECULAR CELL Felsher, D. W., BISHOP, J. M. 1999; 4 (2): 199-207

    Abstract

    The targeted repair of mutant protooncogenes or the inactivation of their gene products may be a specific and effective therapy for human neoplasia. To examine this possibility, we have used the tetracycline regulatory system to generate transgenic mice that conditionally express the MYC protooncogene in hematopoietic cells. Sustained expression of the MYC transgene culminated in the formation of malignant T cell lymphomas and acute myleoid leukemias. The subsequent inactivation of the transgene caused regression of established tumors. Tumor regression was associated with rapid proliferative arrest, differentiation and apoptosis of tumor cells, and resumption of normal host hematopoiesis. We conclude that even though tumorigenesis is a multistep process, remediation of a single genetic lesion may be sufficient to reverse malignancy.

    View details for Web of Science ID 000082387700006

    View details for PubMedID 10488335

  • A NOVEL OCTAMER REGULATORY ELEMENT IN THE V(H)11 LEADER EXON OF B-1 CELLS JOURNAL OF IMMUNOLOGY Goodglick, L., Felsher, D. W., Neshat, M. S., Braun, J. 1995; 154 (9): 4546-4556

    Abstract

    B-1 cells (CD5 B cells) represent an initial fetal wave of B cell lymphopoiesis. B-1 cells have fundamental properties that are unique from conventional B cells, including a restricted Ab repertoire. We investigated the mechanism for the overrepresentation of one such Ig H chain variable-region gene, VH11, by murine B-1 cells. We postulated that a cis-regulatory element contributed to the use of VH11. We observed that the DNA encoding the leader peptide of VH11 was atypically A/T rich and thus was a candidate for nuclear protein binding. By electrophoretic mobility shift analysis, we found that the VH11 leader DNA specifically bound to three protein complexes present in the nucleus of the B-1 cell line AJ9. Of these bands, one was ubiquitous for all cells examined (lymphoid and nonlymphoid); another band was present only in B cells, and the third band was specific for B-1 cells that expressed VH11 or VH12. In addition to its binding properties, the VH11 leader sequence also displayed modest tissue-specific enhancer activity. By DNA footprint analysis, all three protein complexes were found to bind to an octamer motif embedded within the VH11 leader DNA. To identify the octamer-binding proteins, a panel of octamer-specific Abs was used. We found that the ubiquitous band was Oct-1, and the B cell-specific band was Oct-2. The B-1 cell-specific nuclear binding protein was neither Oct-1 nor Oct-2, but may be a novel POU domain protein. We hypothesize that the VH11 leader octamer site may target this gene for preferential rearrangement and/or expression and therefore would be a contributing factor in the increased use of this gene by B-1 cells.

    View details for Web of Science ID A1995QU82500033

    View details for PubMedID 7722308

  • C-MYC, MHCI, AND NK RESISTANCE IN IMMUNODEFICIENCY LYMPHOMAS ANNALS OF THE NEW YORK ACADEMY OF SCIENCES Braun, J., Felsher, D. W., Goodglick, L. A. 1992; 651: 467-469

    View details for Web of Science ID A1992JM21900060

    View details for PubMedID 1599133

  • INDEPENDENT REARRANGEMENT OF IG LAMBDA-GENES IN TISSUE CULTURE-DERIVED MURINE B-CELL LINES INTERNATIONAL IMMUNOLOGY Felsher, D. W., ANDO, D. T., Braun, J. 1991; 3 (7): 711-718

    Abstract

    Rearrangement of the lambda light chain locus is considered a late event in pre-B cell differentiation which occurs after successful heavy chain and unsuccessful kappa light chain rearrangement. However, this view has recently been challenged by the observation of apparently independent lambda rearrangement in certain B cell lines and Ig transgenic populations. In this study we have examined the pattern of Ig rearrangements and expression in several tissue culture-derived murine B cell lines. One pre-B cell line (BDL-1) displayed germline heavy and kappa light chain genes despite the presence of a productive lambda 1 light chain rearrangement. Two other cell lines (DAC-2, BDL-2) had multiple lambda rearrangements despite the presence of productive kappa chain rearrangements. These cell lines provide new precedents for rearrangement of the lambda locus independent of the kappa locus. Their phenotype suggests that accessibility at the different Ig loci may be controlled by a non-sequential mechanism.

    View details for Web of Science ID A1991FX13700013

    View details for PubMedID 1911542

  • A MURINE MODEL FOR B-CELL LYMPHOMAGENESIS IN IMMUNOCOMPROMISED HOSTS - NATURAL-KILLER-CELLS ARE AN IMPORTANT COMPONENT OF HOST-RESISTANCE TO PREMALIGNANT B-CELL LINES CANCER RESEARCH Felsher, D. W., Rhim, S. H., Braun, J. 1990; 50 (21): 7050-7056

    Abstract

    The accompanying paper (D. W. Felsher et al., Cancer Res., 50:7042-7049, 1990) describes a new panel of cloned murine B-cell lines with a premalignant phenotype and in vivo-derived malignant variants. This paper assesses the contribution of immune mediated antitumor mechanisms which might account for host resistance to the tumorigenicity of these cell lines. Conventional T-cell-dependent responses did not appear to be critical to host resistance. In vivo elimination of T-helper cells with anti-L3T4 monoclonal antibody did not reduce host resistance to the tumorigenicity of these cell lines, nor did these cell lines elicit cytotoxic T-cell activity. However, a strong correlation was found between tumorigenicity and host natural killer (NK) activity. In vitro studies demonstrated that the cell lines were as NK sensitive as the prototypical NK target, YAC-1, whereas the malignant variants fully tumorigenic in normal hosts were greater than 20-fold less NK sensitive than were the parent cell lines. In vivo depletion of NK cells with anti-asialo-GM1 in BALB/c strongly diminished host resistance to cell line tumorigenicity, whereas polydeoxyinosinic-deoxycytidilic acid induction of NK cells enhanced host resistance. These findings indicate that NK function is a critical component to host resistance in this system and suggest that endogenous cellular mechanisms which overcome NK sensitivity could be a target for secondary transforming events in B-cell lymphomagenesis. They also raise the unexpected possibility that a non-antigen-dependent (versus immune cytotoxic T-lymphocytes) effector mechanism may be the key deficit promoting B-cell neoplasia in the setting of immunocompromised states.

    View details for Web of Science ID A1990EF20500049

    View details for PubMedID 2208172

  • A MURINE MODEL FOR B-CELL LYMPHOMAGENESIS IN IMMUNOCOMPROMISED HOSTS - C-MYC-REARRANGED B-CELL LINES WITH A PREMALIGNANT PHENOTYPE CANCER RESEARCH Felsher, D. W., DENIS, K. A., Weiss, D., ANDO, D. T., Braun, J. 1990; 50 (21): 7042-7049

    Abstract

    Activation of c-myc or bcl-2 protooncogene is a common event in B-cell lymphomagenesis. Alone, each is insufficient to produce lymphoma, prompting the search for the additional steps required to complete the malignant phenotype. Among the existing systems of murine or human B-cell neoplasia, no commonly occurring complementary oncogenic activation has been found. This study introduces a new series of murine B-cell lines with a phenotype suggesting that such additional events might not involve intrinsic growth control, but instead host immune mechanisms which normally suppress tumorigenicity of premalignant B-cells. Four murine B-cell lines were isolated from the long-term culture of normal lymphoid tissue bearing a premalignant phenotype. (a) Their phenotype resembled naturally occurring lymphoid tumors of immunocompromised hosts with regard to c-myc activation, aberrant or absent immunoglobulin expression, preferential rearrangement of the lambda light chain locus, and a distinctive pattern of tissue invasion and tumor histology. (b) Their tumorigenicity was strictly dependent on host permissiveness correlated with immunodeficient status: C.B-17-scid greater than BALB/c-nu/nu greater than normal BALB/c much greater than other H-2d strains (NZB x NZW F1, NZB, DBA/2). (c) Host passage selected for malignant variants distinguished by a 10(4)-fold increase in tumorigenicity (as judged by limiting cell dose) and by novel tumorigenicity in nonpermissive syngeneic hosts. These features are analogous to properties of human lymphomas arising in immunocompromised states and, to our knowledge, unique among previously reported murine B-cell lines.

    View details for Web of Science ID A1990EF20500048

    View details for PubMedID 2208171

  • A RAPID METHOD FOR THE PURIFICATION OF MONOMERIC AND OR DIMERIC PHOSPHOLIPASES A2 IN CROTALID SNAKE-VENOMS TOXICON WELCHES, W., Felsher, D., LANDSHULZ, W., Maraganore, J. M. 1985; 23 (5): 747-754

    Abstract

    We have developed a simple two-step procedure for the separation of monomeric (14,000 mol. wt) and dimeric (28,000 mol. wt) phospholipases A2 from the venoms of Crotalidae family snakes. All venom phospholipases A2 studied thus far exist as monomers under acidic conditions and are chromatographed as such on a column of G-50 Sephadex (superfine) equilibrated in 5% acetic acid. Separation of dimeric phospholipases A2 from any monomeric enzyme(s) in pools of enzyme thus obtained is achieved by chromatography on a second column of G-50 Sephadex (superfine) identical to the first but developed in 1% ammonium bicarbonate. This method has been applied to an investigation of the prevalence of monomeric and/or dimeric enzymes in venoms of the Crotalidae family. The distribution of monomeric and dimeric phospholipases correlates well with phylogeny. In the more primitive Crotalidae genera, such as Trimeresurus and Agkistrodon, monomeric phospholipases A2 are predominant. In the more highly evolved Crotalus genus, only dimeric enzymes are found.

    View details for Web of Science ID A1985AVE1800004

    View details for PubMedID 4089870

Conference Proceedings


  • Transient excess of MYC activity can elicit genomic instability and tumorigenesis Felsher, D. W., BISHOP, J. M. NATL ACAD SCIENCES. 1999: 3940-3944

    Abstract

    Overexpression of the MYC protooncogene has been implicated in the genesis of diverse human tumors. Tumorigenesis induced by MYC has been attributed to sustained effects on proliferation and differentiation. Here we report that MYC may also contribute to tumorigenesis by destabilizing the cellular genome. A transient excess of MYC activity increased tumorigenicity of Rat1A cells by at least 50-fold. The increase persisted for >30 days after the return of MYC activity to normal levels. The brief surfeit of MYC activity was accompanied by evidence of genomic instability, including karyotypic abnormalities, gene amplification, and hypersensitivity to DNA-damaging agents. MYC also induced genomic destabilization in normal human fibroblasts, although these cells did not become tumorigenic. Stimulation of Rat1A cells with MYC accelerated their passage through G1/S. Moreover, MYC could force normal human fibroblasts to transit G1 and S after treatment with N-(phosphonoacetyl)-L-aspartate (PALA) at concentrations that normally lead to arrest in S phase by checkpoint mechanisms. Instead, the cells subsequently appeared to arrest in G2. We suggest that the accelerated passage through G1 was mutagenic but that the effect of MYC permitted a checkpoint response only after G2 had been reached. Thus, MYC may contribute to tumorigenesis through a dominant mutator effect.

    View details for Web of Science ID 000079507900107

    View details for PubMedID 10097142

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