Growth of tumor fragments X-radiated in vitro following pretreatment with cysteine.

Since the discovery of glutathione (16), many workers have demonstrated its occurrence and the significant role of sulfhydryl groups in growing tissues and organisms (13, 17, @4). More recently, the studies of Hellerman et al. (14), Rapkine (@3), and Barron et al. (1, 3) have emphasized the im portance of -SH groups in enzyme systems. Bar ron et al. (1) found that small amounts of x-radia tion readily inhibited the action in vitro of enzymes whose activity was dependent upon the presence of -SH groups, and, after low doses of radiation, the enzymatic activity could be re stored with sulfhydryl compounds such as gluta thione. Ephrati (8) reported that cysteine and other reducing compounds added to culture media lessened the destruction in vitro of x-radiated bacterial toxins. Similarly, it has been shown that sylfhydryl compounds, such as thioglycollic acid and cysteine, as well as other amino acids, added to culture media will protect bacteria from the lethal action of x-rays (10, 15). Patt et al. (@1) and Chapman et a!. (6) found that intravenous injection of cysteine and sub cutaneous injection of glutathione, administered prior to total-body x-radiation, significantly in creased survival of rats and mice. Rats bearing well implanted Walker @56mammary carcinomas were given intravenous injections of cysteine im mediately before exposure to 800 r x-radiation