Analyses of Radioprotective Action and Cytotoxicity of Various Sulfhydryl Compounds in Cultured Mouse L Cells

The radioprotective action and cytotoxicity of various sulfhydryl compounds ; 2-mercaptopropionylglycine (MPG), 2-mercaptopropionylglycine-amide (MPG-amide), 2-mercaptopropionylphenylalanine (MPPA), 2-mercaptopropionylphenylglycine (MPPG), 3-mercaptopropionylglycine (3-MPG), AET, cysteine and cysteamine were compared in irradiated and unirradiated mouse L cells using colony forming ability as a criterion. It was indicated that the sulfhydryl compounds divided into three classes, according to their radioprotective action and toxicity. Most effective radioprotection was obtained by cysteamine and cysteine, followed by AET and MPGamide in that order. Toxicity of these sulfhydryl compounds were generally observed in concentrations in the range of 0.1-2 mM, while they are much less toxic and effectively radioprotective in higher concentration, especially in cysteamine and cysteine. On the other hand, MPG, MPPA, MPPG and 3-MPG were all non-toxic and generally ineffective in protecting irradiated cells, except that MPG in concentrations around 0.02 mM and 15 mM and MPPA and 3-MPG around 15 mM have a slight but significant protective action.