Altered Expression of γ‐Glutamylcysteine Synthetase, Metallothionein and Topoisomerase I or 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, and two CDDP‐resistant lines, KFr and TYK/R, derived from the former lines. KFr and TYK/R showed about 3‐fold higher resistance to the cytotoxic effects of CDDP than their parental lines. They also showed a significant increase in sensitivity to not only etoposide, but also (+)‐(4S)‐4, ll‐diethyl‐4‐hydroxy‐9‐[(4‐piperidino‐piperidino)carbonyloxy]‐lH‐pyrano[3′,4′:6,7]inodolizino[l,2‐b]quinoline‐3,14(4H, 12H)‐dione hydrochloride trihydrate (CPT‐11). Cellular CDDP accumulation levels in KFr and TYK/R were decreased from those of the parental cells. By contrast, 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 than TYK cells. Cellular mRNA levels of drug‐resistance‐related genes, such as DNA topoisomerase (topo) I and topo II, glutathione S‐transferase‐π (GST‐π;), γ‐glutamylcysteine synthetase (.γ‐GCS), and metallothionein (hMT) genes, were compared between drug‐sensitive KF or TYK and KFr or TYK/R. KFr cells had 8.5‐ and 24.7‐fold higher mRNA levels of γ‐GCS and topo II genes than KF cells while KFr had only a slight increase in GST‐π 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 than TYK cells. Acquisition of CDDP resistance in human ovarian cancer cells thus appeared to be related mainly to expression of γ‐GCS, topo II and hMT genes, and partly to that of topo I and GST‐π genes, in addition to a decrease in CDDP accumulation