Radioprotective drugs

Thiol-based compounds remain the most effective radioprotectors known to work in animals and man. The maximum protection factor likely to be achieved with these compounds is 2-3 and indeed such protection has been demonstrated in animals. The maximum protection factors that have been observed in man are much less than this, even using the best drug currently available, WR 2721 (aminopropylaminoethylphosphorothioic acid). Drug toxicity limits the dosage and, therefore, the protection factor that can be achieved. Blocking the SH group generally reduces toxicity and phosphorothioate is one of the best covering functions. Thiol-based compounds probably operate by two mechanisms: chemical repair by the SH group of free-radical damage and induction of tissue hypoxia. Tissue oxygenation is a major determinant of radioprotector drug action. Aminothiols are the most effective radioprotectors, but the exact function of the amino group, or groups, is unclear. Radioprotective action is lost if there are more than three carbon atoms between the latent thiol group and its associated amino group. 28 refs.; 1 figure; 1 table