Induction of apoptosis in cisplatin-sensitive and -resistant human ovarian cancer cell lines.

In this study, we have assessed the mechanism of cytotoxicity in a series of cisplatin-sensitive and -resistant ovarian carcinoma cells following treatment with equitoxic concentrations of cisplatin. The specific proteolytic degradation and the enzymatic activities of the DNA-dependent protein kinase (DNA-PK) were assessed in the cisplatin-sensitive A2780 cell line and two resistant derivative cell lines, CP70 and C30. Forty-eight h following cisplatin treatment, unattached, apoptotic A2780 cells demonstrated a 20-30% decrease in DNA-PK phosphorylation activity. The resistant CP70 and C30 cell lines showed greater decreases in activity approaching 80 and 90%, respectively. The decreases in kinase activity were attributed to proteolytic degradation of the catalytic subunit of DNA-PK (DNA-PKcs). The extent of degradation mimicked the loss of DNA-PK activity, with the resistant cell lines showing the greatest portion of degraded DNA-PKcs. At the same time point, the ability of the DNA-PK Ku subunits to bind DNA was decreased in apoptotic, unattached cells compared to untreated controls, with the decrease in binding activity being attributed to decreased expression of the Ku subunits. In addition to DNA-PKcs cleavage, specific proteolytic cleavage of the poly(ADP-ribose)polymerase and generation of nucleosome-length DNA ladders was observed in all cell lines following cisplatin treatment. These data suggest that cell death via the accumulation of cisplatin-damaged DNA occurs via apoptosis in both the cisplatin-resistant and -sensitive ovarian cancer cells.