Protective effects of amifostine and its analogues on sulfur mustard toxicity in vitro and in vivo

Sulfur mustard (bis(2-chloroethyl)sulfide, SM) is a highly reactive bifunct ional alkylating agent that forms sulfonium ions in the body. SM alkylates DNA, leading to DNA strand breaks and cell death in a variety of cell types and tissues. Although several approaches have been proposed to challenge t he toxic action(s) of SM, no satisfactory treatment regimen has evolved. Th e synthetic aminothiol amifostine, earlier known as WR-2721 (S-2-(3-amino-p ropylamino)ethyl phosphorothioate), has been extensively used as a chemical radioprotector for the normal tissues in cancer radiotherapy and chemother apy. SM is known as a radiomimetic agent and this prompted us to evaluate t he protective efficacy of amifostine (2.5 mM) and three of its analogues, D RDE-06 (S-2 (3-aminopropylamino) ethyl phenyl sulfide), DRDE-07 (S-2 (2-ami noethylamino) ethyl phenyl sulfide), and DRDE-08 (S-2 (4-aminobutylamino) e thyl phenyl sulfide), against SM toxicity in rat liver slices. Of the four agents tested, a 30-min pretreatment of amifostine and DRDE-07 enhanced the LC50 (a concentration producing 50% leakage of lactate dehydrogenase (LDH) or alanine aminotransferase (ALT)) of SM by 5.9- and 3.3-fold for LDH and 10.2- and 5.5-fold for ALT, respectively. Except DNA fragmentation, both th ese agents significantly attenuated the loss of intracellular K+ and mitoch ondrial integrity (MTT assay), depletion of GSH levels, and histopathology produced by a toxic concentration (80 muM) of SM. However, when amifostine and DRDE-07 were introduced 2 h after SM, no significant protection was obs erved. SM (77.5 or 155 mg/kg) was also applied dermally on female albino mi ce and challenged by 0.20 LD50 (po) of amifostine, DRDE-06, DRDE-07, or DRD E-08 at -30 min, 0 min, or +6 h. Protection was observed only when the agen ts were administered at -30 min or 0 min; posttreatment (+6 h) did not offe r any protection. The magnitude of in vivo protection was in the following order: DRDE-07 greater than or equal to amifostine > DRDE-08 > DRDE-06. Gas chromatographic analysis showed that there was no direct chemical interact ion between SM and the antidotes. The po LD50s of amifostine, DRDE-06, DRDE -07, and DRDE-08 were 1049,1345, 1248, and 951 mg/kg, respectively. Both in vitro and in vivo data indicate promising roles of amifostine and DRDE-07 as prophylactic agents against SM poisoning. (C) 2001 Academic Press.