Sodium thiosulfate fails to increase the therapeutic index of intravenously administered cis-diamminedichloroplatinum (II) in mice bearing murine and human tumors.

Intravenous (i.v.) administration of sodium thiosulfate reduces the toxicity of cis-diamminedichloroplatinum (II) (CDDP). This effect, which allows the use of increased CDDP doses, has been exploited clinically in the intraperitoneal (i.p.) treatment of intraabdominal tumors. Recently, attempts have been made to treat extraperitoneal tumors by concurrent i.v. administration of CDDP and sodium thiosulfate. We have tested this approach in mice bearing systemic L1210 leukemia, s.c. growing Lewis lung carcinoma, C3H mammary carcinoma, and a human sarcoma growing in athymic nude mice. In all cases the antitumor activity of CDDP was substantially reduced in a manner dependent on the thiosulfate dose. Increased doses of CDDP, permitted by reduced toxicity in the presence of thiosulfate, raised the antitumor activity. However, the latter did not exceed that obtained by much lower doses in the absence of thiosulfate. The present experiments in animal models thus fail to support the clinical use of CDDP given i.v. together with its antidote, sodium thiosulfate.