The ATP-binding cassette (ABC) proteins P-glycoprotein (Pgp; MDR1; encoded by ABCB1), multidrug resistance-associated protein (MRP-1; encoded by ABCC1) and breast cancer resistance protein (BCRP; encoded by ABCG2) are energy-dependent drug efflux pumps associated with multidrug resistance (MDR) in cell lines and with clinical drug resistance in acute myeloid leukemia (AML). Polymorphisms in the genes encoding these MDR proteins have been identified and have also been associated with treatment outcome. MDR has been a focus of recent Cancer and Leukemia Group B (CALGB) AML clinical trials, including CALGB 9621, 9720 and 19808. Response to chemotherapy has varied widely in the presence and absence of MDR modulation, which is aimed at blocking drug efflux and thus sensitizing AML cells to chemotherapy. In studies designed to explain and predict this variation, pre-treatment AML cells were cryopreserved from patients treated on these protocols for measurement of expression and activity of MDR proteins (CALGB 9760). Pre-treatment blasts were also cryopreserved in the CALGB Leukemia Tissue Bank (CALGB 9665) from all treated patients and are available for MDR genotyping studies (CALGB 20501). These CALGB clinical trials, with outcome data on over 1800 treated patients and cryopreserved pretreatment blast samples, represent a gold mine for further discovery related to the role of MDR proteins in drug response. In the proposed study, we plan to use data and samples collected from these large clinical trials to test the hypothesis that polymorphisms in three MDR genes (ABCB1, ABCC1 and ABCG2) contribute to variation in expression level and activity of MDR proteins, and ultimately to treatment response of AML patients. The overall goal of this discovery-based project is to determine the association of variants in MDR genes with clinical outcome and with expression level and activity of MDR proteins in leukemia samples from AML patients enrolled on these large CALGB clinical trials. In particular, we will associate genetic variants discovered in blast cells with clinical drug response and with MDR protein expression and function in the leukemia cells, as genetic variants in leukemic blast cells may differ from variants in germline DNA because of genetic instability of cancers.
The Specific Aims are to: 1. Discover single nucleotide polymorphisms (SNPs) and insertion-deletions in the three MDR genes through re-sequencing in a subset of patient blast samples; 2. Determine the association of common SNPs and haplotypes of the three MDR genes (using tag SNPs identified in Aim 1) with treatment outcome in the clinical studies; and 3. Test the hypothesis that ABCB1, ABCC1 and ABCG2 polymorphisms and haplotypes are associated with Pgp, MRP-1 and BCRP function and expression in pre-treatment blasts from AML patients. The identification of genetic determinants of MDR protein expression and/or function and of AML treatment response will provide important information with potential use in the optimization of AML therapy. Variants in genes that code for multidrug resistance (MDR) proteins have been identified in acute myeloid leukemia (AML) cells and have been implicated in treatment response. Using available outcome data and banked pretreatment AML cells from recent Cancer and Leukemia Group B AML clinical trials, which enrolled over 1800 patients, this project will determine the association of variants in MDR genes with treatment outcome and with expression and activity of MDR proteins in AML cells. The project is expected to provide important information for use in improving AML treatment stratification and outcomes. ? ? ?
