INDUCTION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE MESSENGER-RNA BY PLATINUM COMPLEXES IN A HUMAN OVARIAN-CARCINOMA CELL-LINE

Elevation of glutathione (GSH) is widely observed in cellular resistan ce to platinum agents. Our previous studies have shown that sublines o f human ovarian carcinoma cell line A2780, which exhibited low levels of resistance to oxaliplatin, showed elevated steady state levels of m RNA and activity of gamma-glutamyl transpeptidase (gamma-GT, EC 2.3.2. 2), but not of gamma-glutamylcysteine synthetase (gamma-GCS, EC 6.3.2. 2) [El-akawi et al., Cancer Lett. 105:5-14; 1996]. To understand this phenomenon better, we have studied the effect of single exposures of o xaliplatin or cisplatin on the mRNA expression of gamma-GT and gamma-G CS in A2780 cells. The mRNAs of gamma-GT and gamma-GCS were measured b y reverse transcriptase PCR, with quantitation of the PCR product by H PLC; mRNA levels are expressed as ratios to beta-actin mRNA, used as a n endogenous standard. GSH was measured by HPLC. The gamma-GT activity was measured by a colorimetric assay. Single exposures of cells to ox aliplatin induced a time- and concentration-dependent increase in the mRNA of gamma-GT, but not of gamma-GCS. Cisplatin also induced an elev ation in gamma-GT mRNA, but to a lower degree. The gamma-GT enzyme act ivity increased corresponding to the elevation in mRNA expression. The gamma-GT-induced cells showed an increase in cellular GSH when incuba ted in medium containing GSH. The data suggest that a) single, brief e xposures to pharmacologically relevant concentrations of platinum comp lexes induce elevation in mRNA of gamma-GT, b) elevation in gamma-GT m RNA translates into elevated gamma-GT activity and increase in GSH sal vage, and c) the degree of induction of gamma-GT mRNA differs between platinum complexes. Copyright (C) 1996 Elsevier Science Inc.