Bio

Professional Education


  • Doctor of Philosophy, Technische Universitat Munchen (2010)
  • MSc, University of Warsaw, Molecular Biology (2005)
  • BSc, University of Warsaw, Molecular Biology (2003)

Stanford Advisors


Research & Scholarship

Lab Affiliations


Publications

Journal Articles


  • IQGAP1 scaffold-kinase interaction blockade selectively targets RAS-MAP kinase-driven tumors. Nature medicine Jameson, K. L., Mazur, P. K., Zehnder, A. M., Zhang, J., Zarnegar, B., Sage, J., Khavari, P. A. 2013; 19 (5): 626-630

    Abstract

    Upregulation of the ERK1 and ERK2 (ERK1/2) MAP kinase (MAPK) cascade occurs in >30% of cancers, often through mutational activation of receptor tyrosine kinases or other upstream genes, including KRAS and BRAF. Efforts to target endogenous MAPKs are challenged by the fact that these kinases are required for viability in mammals. Additionally, the effectiveness of new inhibitors of mutant BRAF has been diminished by acquired tumor resistance through selection for BRAF-independent mechanisms of ERK1/2 induction. Furthermore, recently identified ERK1/2-inducing mutations in MEK1 and MEK2 (MEK1/2) MAPK genes in melanoma confer resistance to emerging therapeutic MEK inhibitors, underscoring the challenges facing direct kinase inhibition in cancer. MAPK scaffolds, such as IQ motif-containing GTPase activating protein 1 (IQGAP1), assemble pathway kinases to affect signal transmission, and disrupting scaffold function therefore offers an orthogonal approach to MAPK cascade inhibition. Consistent with this, we found a requirement for IQGAP1 in RAS-driven tumorigenesis in mouse and human tissue. In addition, the ERK1/2-binding IQGAP1 WW domain peptide disrupted IQGAP1-ERK1/2 interactions, inhibited RAS- and RAF-driven tumorigenesis, bypassed acquired resistance to the BRAF inhibitor vemurafenib (PLX-4032) and acted as a systemically deliverable therapeutic to significantly increase the lifespan of tumor-bearing mice. Scaffold-kinase interaction blockade acts by a mechanism distinct from direct kinase inhibition and may be a strategy to target overactive oncogenic kinase cascades in cancer.

    View details for DOI 10.1038/nm.3165

    View details for PubMedID 23603816

  • Genetically engineered mouse models of pancreatic cancer: unravelling tumour biology and progressing translational oncology GUT Mazur, P. K., Siveke, J. T. 2012; 61 (10): 1488-1500

    Abstract

    Pancreatic ductal adenocarcinoma (PDAC) remains a devastating disease despite tremendous scientific efforts. Numerous trials have failed to improve the outcome on this deadliest of all major cancers. Potential causes include a still insufficient understanding of key features of this cancer and imperfect preclinical models for identification of active agents and mechanisms of therapeutic responses and resistance. Modern genetically engineered mouse models of PDAC faithfully recapitulate the genetic and biological evolution of human PDAC, thereby providing a potentially powerful tool for addressing tumour biological issues as well as strategies for early detection and assessment of responses to therapeutic interventions. Here, the authors will discuss opportunities and challenges in the application of genetically engineered mouse models for translational approaches in pancreatic cancer and provide a non-exhaustive list of examples with already existing or future clinical relevance.

    View details for DOI 10.1136/gutjnl-2011-300756

    View details for Web of Science ID 000308707300016

    View details for PubMedID 21873467

  • EGF Receptor Is Required for KRAS-Induced Pancreatic Tumorigenesis CANCER CELL Ardito, C. M., Gruener, B. M., Takeuchi, K. K., Lubeseder-Martellato, C., Teichmann, N., Mazur, P. K., DelGiorno, K. E., Carpenter, E. S., Halbrook, C. J., Hall, J. C., Pal, D., Briel, T., Herner, A., Trajkovic-Arsic, M., Sipos, B., Liou, G., Storz, P., Murray, N. R., Threadgill, D. W., Sibilia, M., Washington, M. K., Wilson, C. L., Schmid, R. M., Raines, E. W., Crawford, H. C., Siveke, J. T. 2012; 22 (3): 304-317

    Abstract

    Initiation of pancreatic ductal adenocarcinoma (PDA) is definitively linked to activating mutations in the KRAS oncogene. However, PDA mouse models show that mutant Kras expression early in development gives rise to a normal pancreas, with tumors forming only after a long latency or pancreatitis induction. Here, we show that oncogenic KRAS upregulates endogenous EGFR expression and activation, the latter being dependent on the EGFR ligand sheddase, ADAM17. Genetic ablation or pharmacological inhibition of EGFR or ADAM17 effectively eliminates KRAS-driven tumorigenesis in vivo. Without EGFR activity, active RAS levels are not sufficient to induce robust MEK/ERK activity, a requirement for epithelial transformation.

    View details for DOI 10.1016/j.ccr.2012.07.024

    View details for Web of Science ID 000308735400007

  • MALDI Imaging Mass Spectrometry for In Situ Proteomic Analysis of Preneoplastic Lesions in Pancreatic Cancer PLOS ONE Gruener, B. M., Hahne, H., Mazur, P. K., Trajkovic-Arsic, M., Maier, S., Esposito, I., Kalideris, E., Michalski, C. W., Kleeff, J., Rauser, S., Schmid, R. M., Kuester, B., Walch, A., Siveke, J. T. 2012; 7 (6)
  • Origin of pancreatic ductal adenocarcinoma from atypical flat lesions: a comparative study in transgenic mice and human tissues JOURNAL OF PATHOLOGY Aichler, M., Seiler, C., Tost, M., Siveke, J., Mazur, P. K., Da Silva-Buttkus, P., Bartsch, D. K., Langer, P., Chiblak, S., Duerr, A., Hoefler, H., Kloeppel, G., Mueller-Decker, K., Brielmeier, M., Esposito, I. 2012; 226 (5): 723-734

    Abstract

    Pancreatic ductal adenocarcinoma (PDAC) and its precursor lesions, pancreatic intraepithelial neoplasia (PanIN), display a ductal phenotype. However, there is evidence in genetically defined mouse models for PDAC harbouring a mutated kras under the control of a pancreas-specific promoter that ductal cancer might arise in the centroacinar-acinar region, possibly through a process of acinar-ductal metaplasia (ADM). In order to further elucidate this model of PDAC development, an extensive expression analysis and molecular characterization of the putative and already established (PanIN) precursor lesions were performed in the Kras(G12D/+) ; Ptf1a-Cre(ex1/+) mouse model and in human tissues, focusing on lineage markers, developmental pathways, cell cycle regulators, apomucins, and stromal activation markers. The results of this study show that areas of ADM are very frequent in the murine and human pancreas and represent regions of increased proliferation of cells with precursor potential. Moreover, atypical flat lesions originating in areas of ADM are the most probable precursors of PDAC in the Kras(G12D/+); Ptf1a-Cre(ex1/+) mice and similar lesions were also found in the pancreas of three patients with a strong family history of PDAC. In conclusion, PDAC development in Kras(G12D/+); Ptf1a-Cre(ex1/+) mice starts from ADM and a similar process might also take place in patients with a strong family history of PDAC.

    View details for DOI 10.1002/path.3017

    View details for Web of Science ID 000301178600005

    View details for PubMedID 21984419

  • Expression and Clinicopathological Significance of Notch Signaling and Cell-Fate Genes in Biliary Tract Cancer AMERICAN JOURNAL OF GASTROENTEROLOGY Mazur, P. K., Riener, M., Jochum, W., Kristiansen, G., Weber, A., Schmid, R. M., Siveke, J. T. 2012; 107 (1): 126-132

    Abstract

    Biliary tract cancer (BTC) is a fatal cancer originating from epithelial cells of the intra- and extra-hepatic biliary duct system and the gallbladder. Genes and pathways regulating stem and progenitor cells as well as cell-fate decisions are increasingly recognized in tumorigenesis. We evaluated the expression of Notch1, Notch2, and HES1 (hairy and enhancer of split 1), as well as the biliary cell-fate regulators SOX9 (SRY (sex determining region Y)-box 9) and HNF1? (hepatocyte nuclear factor 1?), in BTC for correlation with clinicopathological parameters.Tissue microarrays including normal bile ducts and 111 BTCs consisting of 17 intrahepatic cholangiocarcinomas, 58 extrahepatic cholangiocarcinomas, and 36 gallbladder carcinomas were analyzed using immunohistochemistry.Lack of cytoplasmic SOX9 expression was associated with a higher tumor grade (P=0.010) and a significantly reduced overall survival (P=0.002; median 6 months vs. 24 months) in univariate survival analysis, whereas lack of nuclear SOX9 expression was associated with a higher tumor stage (P=0.003). Notch pathway members showed high expression in BTC. However, no correlation was found between cytoplasmic or nuclear Notch1, Notch2, and HES1, as well as HNF1? expression, and any of the clinicopathological parameters. In multivariate analysis, cytoplasmic SOX9 expression was an independent prognostic factor for overall survival (P=0.031, relative risk=0.571).We show strong Notch pathway activation and identify SOX9 as a prognostic marker in BTC. These results substantiate diagnostic and therapeutic approaches targeting developmentally active genes and pathways.

    View details for DOI 10.1038/ajg.2011.305

    View details for Web of Science ID 000300573000020

    View details for PubMedID 21931375

  • MALDI imaging mass spectrometry for in situ proteomic analysis of preneoplastic lesions in pancreatic cancer. PloS one Grüner, B. M., Hahne, H., Mazur, P. K., Trajkovic-Arsic, M., Maier, S., Esposito, I., Kalideris, E., Michalski, C. W., Kleeff, J., Rauser, S., Schmid, R. M., Küster, B., Walch, A., Siveke, J. T. 2012; 7 (6)

    Abstract

    The identification of new biomarkers for preneoplastic pancreatic lesions (PanINs, IPMNs) and early pancreatic ductal adenocarcinoma (PDAC) is crucial due to the diseases high mortality rate upon late detection. To address this task we used the novel technique of matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) on genetically engineered mouse models (GEM) of pancreatic cancer. Various GEM were analyzed with MALDI IMS to investigate the peptide/protein-expression pattern of precursor lesions in comparison to normal pancreas and PDAC with cellular resolution. Statistical analysis revealed several discriminative m/z-species between normal and diseased tissue. Intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) could be distinguished from normal pancreatic tissue and PDAC by 26 significant m/z-species. Among these m/z-species, we identified Albumin and Thymosin-beta 4 by liquid chromatography and tandem mass spectrometry (LC-MS/MS), which were further validated by immunohistochemistry, western blot, quantitative RT-PCR and ELISA in both murine and human tissue. Thymosin-beta 4 was found significantly increased in sera of mice with PanIN lesions. Upregulated PanIN expression of Albumin was accompanied by increased expression of liver-restricted genes suggesting a hepatic transdifferentiation program of preneoplastic cells. In conclusion we show that GEM of endogenous PDAC are a suitable model system for MALDI-IMS and subsequent LC-MS/MS analysis, allowing in situ analysis of small precursor lesions and identification of differentially expressed peptides and proteins.

    View details for DOI 10.1371/journal.pone.0039424

    View details for PubMedID 22761793

  • Notch signaling inhibits hepatocellular carcinoma following inactivation of the RB pathway JOURNAL OF EXPERIMENTAL MEDICINE Viatour, P., Ehmer, U., Saddic, L. A., Dorrell, C., Andersen, J. B., Lin, C., Zmoos, A., Mazur, P. K., Schaffer, B. E., Ostermeier, A., Vogel, H., Sylvester, K. G., Thorgeirsson, S. S., Grompe, M., Sage, J. 2011; 208 (10): 1963-1976

    Abstract

    Hepatocellular carcinoma (HCC) is the third cancer killer worldwide with >600,000 deaths every year. Although the major risk factors are known, therapeutic options in patients remain limited in part because of our incomplete understanding of the cellular and molecular mechanisms influencing HCC development. Evidence indicates that the retinoblastoma (RB) pathway is functionally inactivated in most cases of HCC by genetic, epigenetic, and/or viral mechanisms. To investigate the functional relevance of this observation, we inactivated the RB pathway in the liver of adult mice by deleting the three members of the Rb (Rb1) gene family: Rb, p107, and p130. Rb family triple knockout mice develop liver tumors with histopathological features and gene expression profiles similar to human HCC. In this mouse model, cancer initiation is associated with the specific expansion of populations of liver stem/progenitor cells, indicating that the RB pathway may prevent HCC development by maintaining the quiescence of adult liver progenitor cells. In addition, we show that during tumor progression, activation of the Notch pathway via E2F transcription factors serves as a negative feedback mechanism to slow HCC growth. The level of Notch activity is also able to predict survival of HCC patients, suggesting novel means to diagnose and treat HCC.

    View details for DOI 10.1084/jem.20110198

    View details for Web of Science ID 000295318900005

    View details for PubMedID 21875955

  • Early Requirement of Rac1 in a Mouse Model of Pancreatic Cancer GASTROENTEROLOGY Heid, I., Lubeseder-Martellato, C., Sipos, B., Mazur, P. K., Lesina, M., Schmid, R. M., Siveke, J. T. 2011; 141 (2): 719-U436

    Abstract

    Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease without effective chemopreventive or therapeutic approaches. Although the role of oncogenic Kras in initiating development of PDAC is well established, downstream targets of aberrant Ras signaling are poorly understood. Acinar-ductal metaplasia (ADM) appears to be an important prerequisite for development of pancreatic intraepithelial neoplasia (PanIN), a common precursor to PDAC. RAS-related C3 botulinum substrate 1 (Rac1), which controls actin reorganization, can be activated by Ras, is up-regulated in several human cancers, and is required for cerulein-induced morphologic changes in acini. We investigated effects of loss of Rac1 in Kras-induced pancreatic carcinogenesis in mice.Using a Cre/lox approach, we deleted Rac1 from pancreatic progenitor cells in different mouse models of PDAC and in mice with cerulein-induced acute pancreatitis. Acinar epithelial explants of mutant mice were used to investigate the role of Rac1 in vitro.Rac1 expression increased in mouse and human pancreatic tumors, particularly in the stroma. Deletion of Rac1 in Kras(G12D)-induced PDAC in mice reduced formation of ADM, PanIN, and tumors and significantly prolonged survival. Pancreatic epithelial metaplasia was accompanied by apical-basolateral redistribution of F-actin, along with basal expression of Rac1. Acinar epithelial explants that lacked Rac1 or that were incubated with inhibitors of actin polymerization had a reduced ability to undergo ADM in 3-dimensional cultures.In mice, Rac1 is required for early metaplastic changes and neoplasia-associated actin rearrangements in development of pancreatic cancer. Rac1 might be developed as a diagnostic marker or therapeutic target for PDAC.

    View details for DOI 10.1053/j.gastro.2011.04.043

    View details for Web of Science ID 000293523300050

    View details for PubMedID 21684285

  • Identification of Epidermal Pdx1 Expression Discloses Different Roles of Notch1 and Notch2 in Murine Kras(G12D)-Induced Skin Carcinogenesis In Vivo PLOS ONE Mazur, P. K., Gruener, B. M., Nakhai, H., Sipos, B., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Schmid, R. M., Siveke, J. T. 2010; 5 (10)

    Abstract

    The Ras and Notch signaling pathways are frequently activated during development to control many diverse cellular processes and are often dysregulated during tumorigenesis. To study the role of Notch and oncogenic Kras signaling in a progenitor cell population, Pdx1-Cre mice were utilized to generate conditional oncogenic Kras(G12D) mice with ablation of Notch1 and/or Notch2.Surprisingly, mice with activated Kras(G12D) and Notch1 but not Notch2 ablation developed skin papillomas progressing to squamous cell carcinoma providing evidence for Pdx1 expression in the skin. Immunostaining and lineage tracing experiments indicate that PDX1 is present predominantly in the suprabasal layers of the epidermis and rarely in the basal layer. Further analysis of keratinocytes in vitro revealed differentiation-dependent expression of PDX1 in terminally differentiated keratinocytes. PDX1 expression was also increased during wound healing. Further analysis revealed that loss of Notch1 but not Notch2 is critical for skin tumor development. Reasons for this include distinct Notch expression with Notch1 in all layers and Notch2 in the suprabasal layer as well as distinctive p21 and ?-catenin signaling inhibition capabilities.Our results provide strong evidence for epidermal expression of Pdx1 as of yet not identified function. In addition, this finding may be relevant for research using Pdx1-Cre transgenic strains. Additionally, our study confirms distinctive expression and functions of Notch1 and Notch2 in the skin supporting the importance of careful dissection of the contribution of individual Notch receptors.

    View details for DOI 10.1371/journal.pone.0013578

    View details for Web of Science ID 000283419100017

    View details for PubMedID 21042537

  • Notch2 is required for progression of pancreatic intraepithelial neoplasia and development of pancreatic ductal adenocarcinoma PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Mazur, P. K., Einwaechter, H., Lee, M., Sipos, B., Nakhai, H., Rad, R., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Kloeppel, G., Schmid, R. M., Siveke, J. T. 2010; 107 (30): 13438-13443

    Abstract

    Pancreatic cancer is one of the most fatal malignancies lacking effective therapies. Notch signaling is a key regulator of cell fate specification and pancreatic cancer development; however, the role of individual Notch receptors and downstream signaling is largely unknown. Here, we show that Notch2 is predominantly expressed in ductal cells and pancreatic intraepithelial neoplasia (PanIN) lesions. Using genetically engineered mice, we demonstrate the effect of conditional Notch receptor ablation in KrasG12D-driven pancreatic carcinogenesis. Deficiency of Notch2 but not Notch1 stops PanIN progression, prolongs survival, and leads to a phenotypical switch toward anaplastic pancreatic cancer with epithelial-mesenchymal transition. By expression profiling, we identified increased Myc signaling regulated by Notch2 during tumor development, placing Notch2 as a central regulator of PanIN progression and malignant transformation. Our study supports the concept of distinctive roles of individual Notch receptors in cancer development.

    View details for DOI 10.1073/pnas.1002423107

    View details for Web of Science ID 000280602800046

    View details for PubMedID 20624967

  • Conditional ablation of Notch signaling in pancreatic development DEVELOPMENT Nakhai, H., Siveke, J. T., Klein, B., Mendoza-Torres, L., Mazur, P. K., Alguel, H., Radtke, F., Strobl, L., Zimber-Strobl, U., Schmid, R. M. 2008; 135 (16): 2757-2765

    Abstract

    The role of the Notch signaling members Notch1, Notch2 and Rbpj in exocrine pancreatic development is not well defined. We therefore analyzed conditional pancreas-specific Rbpj and combined Notch1/Notch2 knockout mice using Ptf1a(+/Cre(ex1)) mice crossed with floxed Rbpj or Notch1/Notch2 mice. Mice were analyzed at different embryonic stages for pancreatic exocrine and endocrine development. The absence of Rbpj in pancreatic progenitor cells impaired exocrine pancreas development up to embryonic day 18.5 and led to premature differentiation of pancreatic progenitors into endocrine cells. In Rbpj-deficient pancreata, amylase-expressing acini and islets formed during late embryonic and postnatal development, suggesting an essential role of Rbpj in early but not late development. Contrary to this severe phenotype, the concomitant inactivation of Notch1 and Notch2 only moderately disturbed the proliferation of pancreatic epithelial cells during early embryonic development, and did not inhibit pancreatic development. Our results show that, in contrast to Rbpj, Notch1 and Notch2 are not essential for pancreatogenesis. These data favor a Notch-independent role of Rbpj in the development of the exocrine pancreas. Furthermore, our findings suggest that in late stages of pancreatic development exocrine cell differentiation and maintenance are independent of Rbpj.

    View details for DOI 10.1242/dev.013722

    View details for Web of Science ID 000257922600009

    View details for PubMedID 18635610

  • Liver-specific inactivation of Notch2, but not Notch1, compromises intrahepatic bile duct development in mice HEPATOLOGY Geisler, F., Nagl, F., Mazur, P. K., Lee, M., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Schmid, R. M., Siveke, J. T. 2008; 48 (2): 607-616

    Abstract

    The Notch pathway is an evolutionary conserved, intercellular signaling pathway that plays an important role in cell fate specification and the embryonic development of many organs, including the liver. In humans, mutations in the Notch receptor ligand Jagged1 gene result in defective intrahepatic bile duct (IHBD) development in Alagille syndrome. Developmental abnormalities of IHBD in mice doubly heterozygous for Jagged1 and Notch2 mutations propose that interactions of Jagged1 and its receptor Notch2 are crucial for normal IHBD development. Because different cell types in the liver are involved in IHBD development and morphogenesis, the cell-specific role of Notch signaling is not entirely understood. We investigated the effect of combined or single targeted disruption of Notch1 and Notch2 specifically in hepatoblasts and hepatoblast-derived lineage cells on liver development using AlbCre transgenic mice. Hepatocyte differentiation and homeostasis were not impaired in mice after combined deletion of Notch1 and Notch2 (N1N2(F/F)AlbCre). However, we detected irregular ductal plate structures in N1N2(F/F)AlbCre newborns, and further postnatal development of IHBD was severely impaired characterized by disorganized ductular structures accompanied by portal inflammation, portal fibrosis, and foci of hepatocyte feathery degeneration in adulthood. Further characterization of mutant mice with single deletion of Notch1 (N1(F/F)AlbCre) or Notch2 (N2(F/F)AlbCre) showed that Notch2 but not Notch1 is indispensable for normal perinatal and postnatal IHBD development. Further reduction of Notch2 gene dosage in Notch2 conditional/mutant (N2(F/LacZ)AlbCre) animals further enhanced IHBD abnormalities and concomitant liver pathology.Notch2 is required for proper IHBD development and morphogenesis.

    View details for DOI 10.1002/hep.22381

    View details for Web of Science ID 000258247400027

    View details for PubMedID 18666240

  • Notch signaling is required for exocrine regeneration after acute pancreatitis GASTROENTEROLOGY Sivere, J. T., Lubeseder-Martellato, C., Lee, M., Mazur, P. K., Nakhai, H., Radtke, F., Schmid, R. M. 2008; 134 (2): 544-555

    Abstract

    The mechanisms for tissue regeneration and renewal after acute pancreatitis are not well understood but may involve activation of Notch signaling. To study the effect of Notch signaling ablation during acute experimental pancreatitis, we used a chemical and genetic approach to ablate Notch signaling in cerulein-induced pancreatitis in mice.Acute pancreatitis was induced by cerulein treatment in mice treated with the gamma-secretase inhibitor dibenzazepine or in conditional Notch1 knockout mice. Mice were characterized using immunohistologic, biochemical, and molecular methods. To investigate Notch and beta-catenin interaction, acinar 266-6 cells were analyzed using transfection and biochemical assays.Loss of Notch signaling results in impaired regeneration after acute pancreatitis with fewer mature acinar cells in dibenzazepine-treated and Notch1-deficient mice in the regenerative phase 3 days after induction. beta-catenin expression was increased and prolonged during exocrine regeneration. Crosstalk between Notch and beta-catenin-mediated signaling was identified, with Notch1-IC inhibiting beta-catenin-mediated transcriptional activity. This inhibition was dependent on a functional RAM domain.Inhibition of Notch signaling in vivo leads to impaired regeneration of the exocrine pancreas after acute pancreatitis. Our results suggest an interaction of Notch and Wnt signaling in pancreatic acinar cells, providing evidence for a role of these pathways in the regulation of the maturation process of acinar cells.

    View details for DOI 10.1053/j.gastro.2007.11.003

    View details for Web of Science ID 000253032900024

    View details for PubMedID 18242220

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