Doxorubicin-resistant variants of human prostate cancer cell lines DU 145,PC-3, PPC-1, and TSU-PR1: characterization of biochemical determinants of antineoplastic drug sensitivity

Intrinsic and acquired antineoplastic drug resistance remain a major proble m for advanced prostate cancer treatment. In order to characterize mechanis ms of antineoplastic drug resistance in human prostate cancer cell lines, r esistant sublines of four of the commonly studied prostate cancer cell line s (DU 145, PC-3, PPC-1, and TSU-PR1) were selected following exposure to in creasing concentrations of doxorubicin (From 10-1000 nM). Sensitivity patte rns of the parent and doxorubicin-resistant sublines to various antineoplas tic drugs, including adriamycin, amsacrine, etoposide, camptothecin, vinbla stine, vincristine, fluorodeoxyuridine, and melphalan, were determined usin g a sulforhudamine B growth inhibition assay. The expression of three well- described antineoplastic drug resistance proteins, P-glycoprotein (P-gp), m ultidrug resistance-associated protein (MRP), and lung resistance protein ( LRP), was assessed using reverse transcriptase-polymerase chain reaction (R T-PCR) assays specific for each of the mRNA species, and using immunocytoch emical staining procedures specific for each of the polypeptides. All four of the doxorubicin-selected prostate cancer cell lines exhibited a multidru g resistance phenotype; administration of verapamil restored doxorubicin se nsitivity for each of the drug resistant sublines. Although significant MDR 1 expression was not detected in any of the parent cell lines before drug e xposure by RT-PCR analysis or by immunocytochemistry, both MDR1 mRNA and P- gp protein were expressed by the TSU-PR1 Adr 1000 subline. In contrast, MRP mRNA and protein were present in each of the prostate cancer cell lines be fore doxorubicin-selection, and an increase in MRP expression appeared to a ccompany the acquisition of drug resistance in DU 145, PC-3, and PPC-1 doxo rubicin-resistant sublines. LRP was variably expressed by each of the paren t and resistant cell lines. These data suggest that drug resistance in huma n prostate cancer may be multifactorial, with MRP and LRP frequently expres sed in prostate cancer cells before antineoplastic drug treatment and P-gp expression occasionally acquired after drug exposure.