MODULATION OF CISPLATIN SENSITIVITY AND ACCUMULATION BY AMPHOTERICIN-B IN CISPLATIN-RESISTANT HUMAN LUNG-CANCER CELL-LINES

To ascertain whether resistance to cis-diamminedichloroplatinum(II) (cisplatin) could be overcome, we determined the effects of amphotericin B (AmB), an antifungal agent, on cisplatin cytotoxicity, cisplatin-induced DNA interstrand cross-links formation, and cellular accumulation of cisplatin in human lung cancer cell lines, PC-9, PC-14, PC-7, and H69 and their corresponding respective cisplatin-resistant sublines PC-9/CDDP, PC-14/CDDP, PC-7/CDDP, and H69/CDDP in vitro. In PC-9/CDDP but not PC-9 cells, augmentation of cytotoxicity was observed when a nontoxic concentration (10 mug/ml) of AmB was combined with cisplatin, cis-diamine(1,1-cyclobutanedicarboxylato)platinum(II), and cis-diammine(glycolato)platinum(II). Sensitizing effects of AmB of varying magnitudes on cisplatin cytotoxicity also were observed in all the other cell lines except PC-14. AmB-induced increases in cisplatin-induced interstrand cross-links formation were observed, the magnitudes of which corresponded to the magnitudes of AmB-augmented cisplatin cytotoxicity. Increased intracellular cisplatin accumulation was observed in the presence of AmB in all the cells that were sensitized to cisplatin by AmB. Therefore, the increases in cisplatin accumulation were considered to be responsible, at least in part, for the mechanism of the sensitizing effect. Further experiments using other human lung cancer cell lines showed that cells that were more resistant to cisplatin were more sensitized to cisplatin by AmB than cells that were cisplatin-sensitive.