UVA light-induced DNA single-strand cleavage by hydroxybenzo[a]pyrenes

UVA light-induced DNA single-strand cleavage by 1-hydroxy, 3-hydroxy, 7-hydroxy, and 9-hydroxybenzo[a]pyrenes (OH-BaPs) and 6-acetoxybenzo[a]pyrene (6-OAc-BaP) was studied. Under experimental conditions, the concentrations of 1-OH, 3-OH, 7-OH, and 9-OH-BaPs and 6-OAc-BaP needed to cause 25% of the supercoiled form I plasmid DNA to become relaxed form II DNA were found to be 0.6, 2.5, 1.0, 1.3, and 1.1 muM, respectively. These concentrations are all smaller than that of BaP, which was 6 muM. These results indicate that on photoirradiation, OH-BaPs are more cytotoxic and/or genotoxic than their parent compound, BaP. Mechanistic studies reveal that singlet oxygen and superoxide free radicals are involved in causing DNA cleavage.