Gene-specific repair of Pt/DNA lesions and induction of apoptosis by the oral platinum drug JM216 in three human ovarian carcinoma cell lines sensitive and resistant to cisplatin

JM216, an oral platinum drug entering into phase III clinical trial, exhibi ted comparable cytotoxicity to cisplatin in three human ovarian carcinoma c ell lines: the sensitive (CH1), acquired resistant (CH1cisR) and intrinsica lly resistant (SKOV-8). Platinum accumulation and binding to DNA were simil ar in each of the three cell lines at equimolar doses, indicating that the resistant cell lines could tolerate higher intracellular platinum levels an d platinum bound to DNA at IC50 concentrations of drug. Comparison with cis platin demonstrated that intracellular platinum levels were marginally high er with JM216, but that platinum binding to DNA was similar for the two dru gs in each of the cell lines. Each of the cell lines exhibited an ability t o repair JM216 induced platinum/DNA lesions in the N-ras gene (gene-specifi c repair) at equitoxic concentrations of drug. However, this occurred to a greater extent in the two resistant cell lines such that by 24 h the CH1cis R and SKOV-3 had removed 72% and 67% respectively compared with approximate ly 32% for the CH1. Reduced gene-specific repair capacity in CH1 cells was also seen following incubation with 25 mu M (or 5 mu M - 2 x IC50) cisplati n, whereas the CH1 cisR and SKOV-9 cell lines were repair proficient. JM216 induced apoptosis in the three cell lines following a 2h incubation with 2 x the IC50 of drug. Fluorescent microscopy of cells stained with propidium iodide showed that the detached cell population displayed typical apoptoti c nuclei. Furthermore, field inversion gel electrophoresis demonstrated the presence of DNA fragments approximately 23-50 kb in size, indicative of ap optosis, in the detached cells. JM216 induced an S phase slow down in each of the three cell lines accompanied by a G2 block in the CH1 pair. Incubati on with this concentration of JM216 also resulted in the induction of p53 i n the CHI and CH1cisR. These studies suggest that the relative sensitivity of the CHI cell line to cisplatin and JM216 is at least partly attributable to a deficiency in gene-specific repair. The oral platinum drug, JM216, ex erts its cytotoxic effects through the induction of apoptosis following a s low-down in S phase in both the sensitive and resistant lines. (C) 1999 Can cer Research Campaign.