ALTERED EXPRESSION OF GAMMA-GLUTAMYLCYSTEINE SYNTHETASE, METALLOTHIONEIN AND TOPOISOMERASE-I OR TOPOISOMERASE-II DURING ACQUISITION OF DRUG-RESISTANCE TO CISPLATIN IN HUMAN OVARIAN-CANCER CELLS

This study was designed to elucidate the mechanisms of cisplatin (CDDP ) resistance using two human ovarian cancer cell lines, KF and TYK, an d two CDDP-resistant lines, KFr and TYK/R, derived from the former lin es. KFr and TYK/R showed about 3-fold higher resistance to the cytotox ic effects of CDDP than their parental lines. They also showed a signi ficant increase in sensitivity to not only etoposide, but also (+)-(4S )-4, ano[3',4':6,7]inodolizino[1,2-b]quinoline-3,14(4H, 12H)-dione hyd rochloride trihydrate (CPT-11). Cellular CDDP accumulation levels in K Fr and TYK/R were decreased from those of the parental cells. By contr ast, the cellular glutathione (GSH) content in KFr cells was 1.7-fold higher than that in KF, whereas TYK/R cells had a 40% lower content th an TYK cells. Cellular mRNA levels of drug-resistance-related genes, s uch as DNA topoisomerase (topo) I and topo II, glutathione S-transfera se-pi (GST-pi), gamma-glutamylcysteine synthetase (gamma-GCS), and met allothionein (hMT) genes, were compared between drug-sensitive KF or T YK and KFr or TYK/R. KFr cells had 8.5- and 24.7-fold higher mRNA leve ls of gamma-GCS and topo II genes than KF cells while KFr had only a s light increase in GST-pi mRNA level as compared with KF. By contrast, TYK/R cells had 2.9- and 1.7-fold higher hMT and topo I mRNA levels th an TYK cells. Acquisition of CDDP resistance in human ovarian cancer c ells thus appeared to be related mainly to expression of gamma-GCS, to po II and hMT genes, and partly to that of topo I and GST-pi genes, in addition to a decrease in CDDP accumulation.