Studies on a Sulfhydryl Radioprotector of Low Toxicity

Since the discovery of protection of lethally irradiated rats with cysteine by Patt et al. [1] in 1949, many chemicals have been screened for their protective action as reviewed by Thomson [2]. Among them sulfhydryl compounds have been the most extensively investigated, and 2-mercaptoethylamine (cysteamine), S-(2-aminoethyl)isothiouronium (AET) and recently S-2-(3aminopropylamino)ethylphosphorothioic acid (WR-2721) [3], one of the thiophosphate derivatives of cysteamine, have been selected as representative protectors with a high protective activity. Unfortunately, however, they all have a rather high toxicity in their protective doses which prevents their practical application in man.