Docetaxel‐resistant prostate cancer cells become sensitive to gemcitabine due to the upregulation of ABCB1

Abstract Background Docetaxel is the preferred chemotherapeutic agent for hormone‐refractory prostate cancer (PC) patients. However, patients eventually develop docetaxel resistance, and no effective treatment options are available for them. Objective We aimed to establish docetaxel resistance in castration‐resistant prostate cancer (CRPC) cell lines (DU145/TXR, PC‐3/TXR, and CWR22/TXR) and characterized transcriptional changes upon acquiring resistance to the docetaxel. Methods Human PC cells (DU145, PC‐3, CWR22) and all docetaxel‐resistant cells were maintained in Roswell Park Memorial Institute Medium (RPMI) 1640 media supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin. ABCB1 was detected by using both parental and docetaxel‐resistant CRPCs prepared for flow cytometry. For the evaluation of tumor‐suppressive effects under each chemotherapeutic agent, subcutaneous xenografts of DU145 or DU145/TXR were implanted at the mouse flank. Results The P‐glycoprotein‐encoding gene ABCB1 was distinctively upregulated in the resistant cells, and its overexpression played an essential role in docetaxel resistance in CRPC. When tested for the cytotoxicity of gemcitabine, another option for chemotherapy, the docetaxel‐resistant cells were shown to become sensitive to the drug, implying additional phenotypic transformation in the docetaxel‐resistant cells. Studies using xenograft animal models demonstrated that the growth of tumors composed of both docetaxel‐sensitive and docetaxel‐resistant cells was deterred most profoundly when docetaxel and gemcitabine were administered together. Conclusion This study suggests that when a drug develops therapeutic resistance, sensitivity tests could be another option, ultimately providing insight into a novel alternative clinical strategy.