Abstract P4-08-10: Systematic expression analysis of the genes related to drug-resistance in isogenic docetaxel- and adriamycin-resistance breast cancer cell lines.

Background: Docetaxel (Doc) and Adriamycin (Adr) are two of the most effective chemotherapeutic agents in the treatment of breast cancer. However, their efficacy is often limited by the emergence of multidrug resistance (MDR). The purpose of this study was to investigate MDR mechanisms through analyzing systematically the expression changes of genes related to MDR in the induction process of isogenic drug resistant MCF-7 cell lines. Material and Methods: Isogenic resistant sublines selected at 100 and 200nM docetaxel (MCF-7/100nM Doc and MCF-7/200nM Doc) or at 500 and 1500 nM adriamycin (MCF-7/500nM Adr and MCF-7/1500nM) were developed from human breast cancer parental cell line MCF-7/S, by exposing MCF-7/S to gradually increasing concentrations of docetaxel or adriamycin in vitro . Flow cytometry, MTT cytotoxicity assay and cell growth curves were preformed to demonstrate the MDR characteristics developed in sublines. Some key genes on the pathways related to drug resistance (including drug-transporters: MDR1, MRP1 and BCRP; drug metabolizing-enzymes: CYP3A4 and GST pi; target gene: Topo IIα and β-tubulin III; apoptosis genes: Bcl-2 and Bax) were analyzed at RNA and protein expression levels by real time RT-qPCR and western blot, respectively. Results: MCF-7/100nM Doc and MCF-7/200nM Doc was 22- and 37-fold resistant to docetaxel, and 18- and 32-fold to adriamycin, respectively. MCF-7/500nM Adr and MCF-7/1500nM Adr was 61- and 274-fold resistant to adriamycin, and 3- and 12-fold to docetaxel, respectively. Meantime, they also showed cross-resistance to the other anticancer drugs in different degree. Compared to sensitive MCF-7/S, RT-qPCR and Western blot results revealed that the expression of MDR1, MRP1, BCRP, Bcl-2 were elevated in both MCF-7/Doc and MCF-7/Adr, and Topo IIα, Bax were down-regulated in both the sublines, while CYP3A4 and β-tubulin III were increased only in MCF-7/Doc and GST pi was increased only in MCF-7/Adr. Furthermore, these changes above were dose-dependent, i.e. acquirement of MDR is dependent on docetaxel or adriamycin concentrations in breast carcer model resistant MCF-7 cells. Conclusions: The established MCF-7/Doc or MCF-7/Adr has the typical MDR characteristics, which can be used as the models for resistance mechanism study. The acquired process of MCF-7/S resistance to docetaxel or adriamycin is gradual, and is also complicated with the various pathways involved in. There are some common mechanisms as well as drug-special mechanisms between MCF-7/Doc and MCF-7/Adr. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-08-10.