Abstract

Tetraplatin (Ormaplatin) has been developed as a second generation platinum complex because of its good antitumor activity against some cisplatin-resistant tumor cell lines. It is currently in clinical trials. Its reduction to diaminocyclohexane (DACH)-dichloroplatinum(II) [DACH-Pt(II)Cl2] or closely similar species is essential for binding to DNA to produce the desired antitumor effects. We have studied the pharmacokinetics of tetraplatin in mice after intraperitoneal administration with the reducing agent glutathione (GSH). The systemic absorption of tetraplatin (5 mg/kg) with GSH (31 mg/kg) was faster than of tetraplatin alone. Peak plasma platinum (Pt) levels of 0.89 and 1.44 micrograms Pt/ml were observed at 15 min and 2 hr after administration of tetraplatin with and without GSH, respectively, and the Pt then decayed biphasically when administered with GSH and monophasically when administered alone. The plasma Pt level was 4-fold lower (0.17 vs. 0.71 micrograms Pt/ml) by 24 hr when tetraplatin was administered with GSH compared with its administration alone. DACH-Pt(II)Cl2 (4.21 mg/kg, ip) gave similar plasma Pt kinetics to that seen with the combination of tetraplatin and GSH. Pt levels in kidney 24 hr after administration of tetraplatin+GSH or of DACH-Pt(II)Cl2 were lower (1.6-fold) than after tetraplatin alone. Plasma and ascitic fluid from tumor-bearing mice demonstrated equivalent abilities to reduce tetraplatin rapidly. However, tetraplatin treatment of intraperitoneal-inoculated L1210/0 (parent) or L1210/DDP (cisplatin-resistant) tumor cells was unaffected by GSH. As GSH lowered systemic tetraplatin exposure in vivo without compromising antitumor activity against peritoneal tumor models, the combination of thiol and tetraplatin may be clinically useful in the treatment of intraperitoneal disseminated cancers.