THIOL WR-1065 AND DISULFIDE WR-33278, 2 METABOLITES OF THE DRUG ETHYOL (WR-2721), PROTECT DNA AGAINST FAST NEUTRON-INDUCED STRAND BREAKAGE

The main metabolites of the cytoprotective drug Ethyol (Amifostine, WR -2721) are the thiol WR-1065 and the disulphide WR-33278 (formed by th e oxidation of WR-1065). Both metabolites are well-known protectors ag ainst DNA damage induced by gamma-rays. Using supercoiled plasmid DNA and restriction fragments we show that they protect efficiently also i n the case of fast neutrons. In anoxic conditions WR-1065 (Z = +2) pro tects by scavenging of OH. and by 'chemical repair' (by H donation fro m its SH function). WR-33278 (Z = +4) protects by scavenging of OH. an d, in the case of the supercoiled plasmid DNA, by reducing the accessi bility of radiolytic attack sites via the induction of packaging of DN A in liquid-crystalline condensates (observed by circular dichroism). Because of this second mechanism, the plasmid DNA is more efficiently protected by WR-33278 than by WR-1065, at concentration ratios > 1 dru g/4 nucleotides. Moreover, using sequencing gel electrophoresis of irr adiated fragments of known sequence, we show that the protection by th e two metabolites is non-homogeneously distributed along the DNA seque nce, with 'hot spots' of protection and with unprotected regions. Base d on presented molecular modelling results we explain the sequence dep endence of radioprotection by structural variations induced by the bin ding of the drugs.