Role of reactive oxygen species in cis-dichlorodiammineplatinum-induced cytotoxicity on bladder cancer cells

This study was undertaken to investigate the intracellular induction of reactive oxygen species (ROS) by cis-dichlorodiammineplatinum (CDDP) and the augmentation of their cytotoxicity in bladder cancer cells (KU7) by enhancement of ROS generation by the glutathione (GSH) depletors buthionine sulphoximine (BSO) and diethylmaleate (DEM). CDDP-induced cytotoxicity in KU7 cells and its modulation by GSH depletors were determined using spectrophotometric measurement with crystal violet staining. The effects of GSH depletors on intracellular GSH levels were confirmed using the GSH reductase-DTNB recycling method. Intracellular ROS generation induced by CDDP with or without GSH depletors was estimated from the amount of intracellular dichlorofluorescein (DCF), an oxidized product of dichlorofluorescein (DCFH), which was measured with an anchored cell analysis and sorting system. The cytotoxic effects of CDDP (IC50 15.0+/-2.5 mu M) were significantly enhanced by BSO (IC50 9.3+/-2.6 mu M, P<0.01) and DEM (IC50 10.3+/-0.3 mu M, P<0.01). BSO and DEM produced a significant depletion in intracellular GSH levels (9.6+/-0.4 nmol 10(-6) cells, 17.9+/-1.0 nmol 10(-6) cells) compared with the controls (30.5+/-0.6 nmol 10(-6) cells). Intracellular DCF production in KU7 cells treated with CDDP (1.35+/-0.33 mu M) was significantly enhanced by the addition of BSO (4.43+/-0.33 mu M) or DEM (3.12+/-0.22 mu M) at 150 min. These results suggest that ROS may play a substantial role in CDDP-induced cytotoxicity and that GSH depletors augment its cytotoxicity through an enhancement of ROS generation in bladder cancer cells.