Inactivation of cis-diamminedichloroplatinum (II) in blood and protection of its toxicity by sodium thiosulfate in rabbits

Summary The mode of inactivation of cis-diamminedichloroplatinum(II) (DDP) in the bloodstream and protection from its toxicity by sodium thiosulfate (STS) were investigated in rabbits.Plasma ultrafiltrate in rabbits given 5 mg/kg DDP IV and various excess molar ratios of STS IV were assayed for the active platinum levels with a new microbiological assay system using an E. coli strain. The active platinum species in the plasma were inactivated completely by coadministration of a 400-fold excess of STS IV. The rabbits were almost completely protected against both BUN increase and body weight loss normally caused by DDP when 400-fold doses of STS were given. Diuretic effects were also observed.Our data provide evidence for the basis of optimum use of STS to protect against DDP toxicity. [6, 9]. This TRC with DDP and STS is now in clinical trial [7, 8], but the precise mode of protective action of STS against DDP toxicity has not been determined.We now present evidence that this protective effect is due to inactivation of biologically active DDP in the bloodstream.Supported by a Grant-in Aid for Cancer Research from the Ministry of Education, Science and Culture, and from the Ministry of Health and Welfare, Japan