GLUTATHIONE DEPLETION INCREASES THE CYTOTOXICITY OF MELPHALAN TO PC-3, AND ANDROGEN-INSENSITIVE PROSTATE-CANCER CELL-LINE

Prostate cancer that is androgen-insensitive is unresponsive to a wide spectrum of cytotoxic agents, including all of the alkylating agents. Since a major pathway for the detoxification of the alkylating agents is conjugation with glutathione (GSH), GSH depletion has proved to be effective as a technique to restore melphalan sensitivity in melphalan-resistant cancer cell lines. However, the effect of GSH depletion has not been widely studied in tumor cell lines that have not developed resistance due to previous exposure to alkylating agents. Thus, we decided to investigate GSH depletion as a technique to increase melphalan cytotoxicity to PC-3 cells, an androgen-insensitive prostate cancer line. After 2 and 6 h incubation with 0.25 - 5 muM melphalan, virtually no effect was observed on either clonogenic lethality or MTT viability until 5 mum exposures. A 24-h incubation of the cells with 100 muM buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, reduced the GSH content by 70% - 75%. Following GSH depletion, an increase in clonogenic lethality and a decrease in MTT viability occurred after exposure to concentrations as low as 0.25 muM. The dose modification factor ranged from 2.9 after 2 h incubation to 4.5 at 6 h. These results provide support for additional studies in prostate cancer for further investigation of GSH depletion as a technique to induce sensitivity to alkylating agents in this chemotherapy-resistant tumor.