Sikic Lab In the Division of Oncology

Sikic Lab Research Areas

Multidrug Resistance | Taxane Resistance Mechanisms | Pharmacogenetics


Multidrug Resistance (MDR)

Our overall objective is to study the mechanism of multidrug resistance encoded by the MDR1 gene and its product, P-glycoprotein (P-gp), a transmembrane pump that is responsible for drug efflux and resistance to many natural product chemotherapeutics. Cells enriched with P-gp have altered sensitivities to known anticancer drugs relative to cells that are MDR1-negative, and MDR1 is believed to be significant in the clinical response to anticancer therapies involving doxorubicin, paclitaxel and many other compounds.

In an attempt to overcome this form of resistance, we are currently developing modulators of MDR which inhibit the natural function of P-gp and restore sensitivity to drugs in the laboratory. Clinical trials are on-going to further develop these MDR modulators such as PSC 833 (valspodar, Novartis Corporation). Phase II studies are on-going at the Clinical and Translational Research Unit at Stanford Dxp-imageUniversity Medical Center in leukemias, lymphomas, breast, ovarian and colorectal carcinomas.

Our laboratory has identified a mutation (Chen et al., Journal of Biological Chemistry 272, 1997) in the MDR1 gene which renders the cell line insensitive to MDR modulation. Studies are on-going to generate other MDR1 gene mutations in order to determine the mechanism(s) of resistance to MDR modulation associated with alterations in P-gp structure and function. Since these MDR modulators all bind to P-gp, and most are transport substrates, such mutations will be important in defining clinically relevant structure-activity relationships of P-gp.

We are also investigating other mechanisms in cellular models which contribute to drug resistance in the clinic such as the multidrug resistance-associated protein (mrp), the anti-apoptotic proto-oncogene bcl-2, bcl-xl and alterations in topoisomerase activity in cellular models.

Related Publications

Chen G, Jaffrezou J-P, Fleming WH, Duran GE, and Sikic BI. Prevalence of multidrug resistance related to the activation of the MDR1 gene in human sarcoma mutants derived by single-step doxorubicin selection. Cancer Research 54(18): 4980-7, 1994.

Beketic-Oreskovic L, Duran GE, Chen G, Dumontet C, and Sikic BI. Decreased mutation rate for doxorubicin resistance and suppression of MDR1 gene activation by PSC 833. Journal of the National Cancer Institute 87: 1593-1602, 1995.

Sikic BI, Fisher GA, Lum BL, Halsey J, Beketic-Oreskovic L, and Chen G. Modulation and prevention of multidrug resistance by inhibitors of P-glycoprotein. Cancer Chemotherapy and Pharmacology 40 (Suppl): S13-S19, 1997. [PDF Reprint]

Chen G, Duran GE, Steger KA, Lacayo NJ, Jaffrezou J-P, Dumontet C, and Sikic BI. Multidrug-resistant human sarcoma cells with a mutant P-glycoprotein, altered phenotype, and resistance to cyclosporins. Journal of Biological Chemistry 272: 5974-82, 1997. [PDF Reprint]

Washington CB, Duran GE, Man MC, Sikic BI, and Blaschke TF. Interaction of anti-HIV protease inhibitors with the multidrug transporter P-glycoprotein (P-gp) in human cultured cells. Journal of Acquired Immunne Deficiency Syndrome and Human Retrovirology 19: 203-9, 1998.

Chen GK, Duran GE, Mangili A, Beketic-Oreskovic L, and Sikic BI. MDR1 activation is the predominant resistance mechanism selected by vinblastine in MES-SA cells. British Journal of Cancer 83(7):892-8, 2000. [PDF Reprint]

Chen GK, Lacayo NJ, Duran GE, Cohen D, and Sikic BI. Loss of cyclosporin and azidopine binding are associated with altered ATPase activity by a mutant P-glycoprotein with deleted phe(335). Molecular Pharmacology 57(4):769-77, 2000. [PDF Reprint]

Chen GK, Lacayo NJ, Duran GE, Wang Y, Bangs CD, Rea S, Kovacs M, Cherry AM, Brown JM, and Sikic BI. Preferential expression of a mutant allele of the amplified ABCB1 gene in drug-resistant variants of a human sarcoma. Genes Chromosomes Cancer 34: 372-83, 2002. [PDF Reprint]

Lacayo NJ, Duran GE, and Sikic BI. Modulation of resistance to idarubicin by the cyclosporin PSC 833 (valspodar) in multidrug-resistant cells. Journal of Experimental Therapeutics and Oncology 3: 127-35, 2003. [PDF Reprint]

Taxane Resistance Mechanisms

Our objective is to study mechanisms of cellular resistance to taxanes, paclitaxel (Taxol) and docetaxel (Taxotere). Although the major known mechanism of resistance to these agents is multidrug resistance mediated by MDR1, we hypothesize that the relative expression and composition of tubulin isoforms, the binding targets for these drugs, will differ in resistant cell lines which may alter drug sensitivity.

Preliminary data in paclitaxel resistant variants reveal changes in beta-tubulin expression in some of these cells, and mutations in the predominant isoform (Class I, M40) have been detected in a human ovarian cell line, A2780/1A9 (Giannakakou et al., Journal of Biological Chemistry 272: 17118-17125, 1997). Patients with breast and ovarian cancers and lymphomas are currently undergoing protocol therapies at Stanford with taxanes, and data from the laboratory may implicate the relevance of altered tubulin gene expression in resistant tumors.

We are further pursuing novel mechanisms of resistance to taxanes by the genomic profiling of taxane resistant human ovarian and breast cancer variants using microarray technology in collaboration with the Brown and Botstein laboratories in the Department of Genetics.

Related Publications

Jaffrezou J-P, Dumontet C, Derry WB, Duran GE, Chen G, Tsuchiya E, Wilson L, Jordan MA, and Sikic BI. Novel mechanism of resistance to paclitaxel (Taxol) in human K562 leukemia cells by combined selected with PSC 833. Oncology Research 7: 517-527, 1995.

Jaffrezou J-P, Chen G, Duran GE, Muller C, Bordier C, Laurent G, Sikic BI. Inhibition of lysosomal acid sphingomyelinase by agents which reverse multidrug resistance. Biochimica et Biophysica Acta 1266: 1-8, 1995. [PDF Reprint]

Dumontet C, Duran GE, Steger KA, Beketic-Oreskovic L, and Sikic BI. Resistance mechanisms in human sarcoma mutants derived by single-step exposure to paclitaxel (Taxol). Cancer Research 56: 1091-1097, 1996.

Dumontet C, Duran GE, Steger KA, Murphy G, Sussman H, and Sikic BI. Differential expression of tubulin isotypes during the cell cycle. Cell Motility Cytoskel., 35: 49-58, 1996.

Dumontet C and Sikic BI. Mechanisms of action and resistance to anti-tubulin agents: microtubule dynamics, drug transport and cell death. Journal of Clinical Oncology 17: 1061-1070, 1999. [PDF Reprint]

Sale S, Sung R, Shen P, Yu K, Wang YC, Duran GE, Kim J-H, Fojo T, Oefner PJ, and Sikic BI. Conservation of the class I beta-tubulin in human populations and lack of mutations in lung cancer and paclitaxel-resistant ovarian cancers. Molecular Cancer Therapeutics 1: 215-225, 2002. [PDF Reprint]

Sale S, Oefner PJ and Sikic BI. Re: genetic analysis of the beta-tubulin gene, TUBB, in non-small-cell lung cancer. Journal of the National Cancer Institute 94(10): 776-7, 2002.



We are further pursuing novel mechanisms of resistance to anticancer drugs by the genomic profiling of drug resistant human ovarian and breast cancer cells using microarray technology. Cellular models of resistance to various agents are being developed by step-wise and single step exposure.

Research ImageWe are also screening cancer specimens from patients at diagnosis and after chemotherapy, to identify gene expression patterns that may be important in the disease process as well as in determining response to treatments in the clinic. This project has the potential of identifying new genetic markers that may be useful in the detection and diagnosis of cancers, as well as genes which may be of prognostic significance, particularly with respect to prediction of sensitivity or resistance to therapies.

Projects are underway to profile the gene expression of ovarian cancers, acute leukemias, germ cell cancers, unknown primary cancers, and brain tumors.



Related Publications

Schaner ME, Ross DT, Ciaravino G, Sorlie T, Troyanskaya O, Diehn M, Wang YC, Duran GE, Sikic TL, Caldeira S, Skomedal H, Tu IP, Hernandez-Boussard T, Johnson SW, O'Dwyer PJ, Fero MJ, Kristensen GB , Borresen-Dale AL, Hastie T, Tibshirani R, van de Rijn M, Teng NN, Longacre TA, Botstein D, Brown PO, and Sikic BI. 14: 4376-86, 2003. [PDF Reprint]

Bredel M, Bredel C, and Sikic BI. Genomics-based hypothesis generation: a novel approach to unravelling drug resistance in brain tumours? Lancet Oncology 5: 89-100, 200

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