P-226 - An unexpected free radical mechanism for DNA damage by the carcinogenic arylhydroxamic acid via sunlight irradiation

Abstract

The carcinogenicity of N-hydroxy-2-acetamidofluorene (N-OH-AAF), the major genotoxic metabolite of classic model aromatic amine carcinogen 2-acetylaminofluorene (AAF), has been attributed mainly to the formation of DNA adducts via reactive arylnitrenium ion upon further enzymatic activation. Here we show, unexpectedly, that exposure of N-OH-AAF to UV and sunlight irradiation induced the formation of the well-known DNA adducts; but more interestingly, simultaneous oxidative DNA damage was also observed as measured by the formation of DNA single/double strand breaks and 8-oxodG, which were inhibited by the typical •OH scavengers (DMSO and ethanol). ESR secondary radical spin-trapping and fluorescent studies unequivocally confirmed that •OH was generated from N-OH-AAF photolysis. We propose that the highly reactive •OH and amidyl radicals can be readily produced via homolysis N-O in N-OH-AAF by UV and sunlight, which can induce both oxidative DNA damage and formation of DNA adducts. This represents the first report of •OH production and DNA damage via photo-activation of the genotoxic raylhydroxamic acid intermediate, which may provide a new perspective to understand the molecular mechanism for the carcinogenicity of aromatic amines.