In vitro antioxidant properties of amifostine (WR-2721, Ethyol)

Purpose: Amifostine (WR-2721), a physphorylated aminothiol pro-drag which i s an analogue of cysteamine, is a selective cytoprotective agent for normal tissues from the toxicities associated with chemotherapy and irradiation. Despite a growing number of reports strongly supporting amifostine's clinic al efficacy, few authors have focused on the biochemical basis of amifostin e's antioxidant activity. Methods: We report on amifostine's free-radical s cavenging activity against superoxide (O-2(.-)), hydroxyl (OH-) and lipoper oxyl radicals in an in vitro model, using pure chemical systems. Amifostine was dephosphorylated to its active metabolite, WR-1065, by adding 10% non- heat-inactivated serum; different amifostine concentrations (1, 10, 50, 100 mu M and 200 mu M) and pH conditions (pH 5, 7.4 and 9) were tested. Result s: Independent of the concentration, amifostine exhibited no major activity against O-2(.-) ions, neither did any pH variations in the experimental mo del provide any scavenger effects of the drug against O-2(.-) radicals. On the other hand, the protective effect of amifostine against OH- radicals wa s confirmed, yielding an EC50 of 255 mu M at pH 7.4 and 230 mu M at pH 5 Fi nally, amifostine exhibited scavenging activity against spontaneous lipoper oxidation, but no apparent antioxidant effect on iron ascorbate-induced lip operoxidation. Conclusions: With this in vitro study, we are able to confir m the scavenging activity of the chemo- and radioprotector amifostine, whos e activity seems to be particularly important from a biological point of vi ew, since it is exerted mainly against highly reactive OH-.