In vivo protection by the aminothiol WR-2721 against neutron-induced carcinogenesis.

The ability of the compound S-2-(aminopropylamino)ethylphosphorothioic acid, designated WR-2721, to protect against neutron-induced carcinogenesis was investigated. Both sexes of the B6CF1 mouse were injected i.p. with 400 mg/kg of WR-2721 30 min prior to being irradiated by 10 cGy of neutrons. Neoplastic mortality in the groups receiving thiol was either reduced or delayed relative to irradiated mice not given protector. However, the time at which the protective effect of WR-2721 was expressed depended on the sex of the animal. Thiol-related shifts in the time of neoplastic death in females occurred only in the first half of the lifespan. Once a female survived to the mean age at death, no difference in the pattern of mortality could be detected between control and WR-2721-treated mice exposed to neutrons. Irrespective of thiol treatment, the timing of tumour-related death was nearly identical during the first half of life for males exposed to neutrons. In the last half of the lifespan, survival of thiol-protected males was enhanced relative to saline-injected males and even exceeded that observed in the control population.