Role of the MDR-1-encoded multiple drug resistance phenotype in prostate cancer cell lines.
The treatment of advanced metastatic prostate cancer by hormone manipulation or orchiectomy is frequently followed by the appearance of hormone-insensitive and highly chemoresistant tumor cells. In this study we have investigated the contribution of the P-glycoprotein-mediated drug efflux (multidrug-resistance; MDR) to the cellular resistance of prostate carcinoma-derived cell lines to diverse cytotoxic drugs by detection of P-glycoprotein (P-gp) measurement of P-gp-mediated drug transport and reversal of MDR by chemosensitizers. The in vitro chemosensitivity of three prostate cancer cell lines (PC-3, DU-145 and LNCaP) to doxorubicin was measured in a thymidine incorporation proliferation assay. Growth of the partially hormone-sensitive cell line LNCaP is inhibited by low doses of doxorubicin (IC50:27 ng./ml.), but PC-3 and DU-145 are highly resistant to the drug, with IC50 values of 10 micrograms./ml. and 7.5 micrograms./ml., respectively. The chemosensitivity of the PC-3 and DU-145 cells is increased in response to 1 microM. verapamil, 1 micrograms./ml. cyclosporine A and 2 microM. tamoxifen, which are known to partially reverse the MDR phenotype in other resistant tumors. A verapamil-sensitive drug efflux has been demonstrated for the PC-3 and Du-145, but not for the LNCaP, cell lines, using flow cytometric measurements of the P-gp substrate rhodamine 123 efflux from preloaded cells. In agreement with the functional measurements, the expression of the P-glycoprotein was detected in the PC-3 and Du-145 cell lines in Western blots using the monoclonal C 219 antibody. In conclusion, the chemoresistant and hormone-insensitive PC-3 and Du-145 cell lines express P-gp and exhibit verapamil-sensitive drug efflux, indicative of MDR. However, the low MDR-reversal rates observed in these cell lines in response to chemosensitizers in clinically achievable concentrations (approximately 2- to 3-fold reversal), point to non-MDR-associated cellular mechanisms as dominant factors of chemoresistance in prostate cancer.
Theyer
G
G
Department of Urology, Wilhelminenspital, Vienna, Austria.
Schirmböck
M
M
Thalhammer
T
T
Sherwood
E R
ER
Baumgartner
G
G
Hamilton
G
G
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D002352:Carrier Proteins / Q000096:biosynthesis*; D002455:Cell Division / Q000187:drug effects; D016572:Cyclosporine / Q000494:pharmacology / Q000627:therapeutic use; D004317:Doxorubicin / Q000494:pharmacology / Q000627:therapeutic use; D004351:Drug Resistance; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D010641:Phenotype; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D020112:Rhodamine 123; D012235:Rhodamines / Q000494:pharmacology / Q000627:therapeutic use; D013629:Tamoxifen / Q000494:pharmacology / Q000627:therapeutic use; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology / Q000627:therapeutic use
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D012235:Rhodamines; D013629:Tamoxifen; D020112:Rhodamine 123; D004317:Doxorubicin; D016572:Cyclosporine; D014700:Verapamil