Tamoxifen reverses the multi-drug-resistance of an established human cholangiocarcinoma cell line in combined chemotherapeutics

Our previous study established the human multi-drug-resistant cholangiocarcinoma cell line QBC939/ADM. In this study, we investigate further the ability of tamoxifen (TAM) to reverse drug-resistance to chemotherapeutics using QBC939/ADM cells. Cell growth inhibition was determined by the MTT assay, while cell cycle progression, apoptosis and the intra-cellular concentration of adriamycin (ADM) were all determined by flow cytometry. P-glycoprotein (P-gp) protein and mRNA expression was determined by Western blotting and real-time PCR. Growth inhibition and apoptosis induced by ADM, mitomycin (MMC), or vindesine (VDS) were enhanced after pre-treatment with 5 or 10 μM TAM, while only VDS increased cell numbers in the G₂/M phase. The intra-cellular concentration of ADM rose after pre-treatment with 10 μM TAM, but not 5 μM TAM. Furthermore, real-time PCR and western blot analysis revealed down-regulation of P-gp expression in QBC939/ADM cells after TAM pre-treatment. The enhanced effects of TAM on growth inhibition, apoptosis, and intra-cellular concentration and the down-regulation of P-gp expression were blocked by an anti-P-gp antibody. TAM (10 μM) may reverse the multi-drug-resistance (MDR) of QBC939/ADM and enhance the chemotherapeutic effects on cholangiocarcinoma, by competitively inhibiting over-expressed P-gp.