DNA strand cleavage by tumor-inhibiting antibiotic 6-diazo-5-oxo-L-norleucine

A tumor-inhibiting antibiotic, 6-diazo-5-oxo-L-norleucine (DON), caused DNA single-strand breaks. Thus, supercoiled plasmid DNA was transformed into an open circular relaxed form DNA by incubation with DON at pH 7.4. DNA strand cleavage by DON was not inhibited by superoxide dismutase, but inhibited by catalase. The inhibition by catalase may not be due to the destruction of hydrogen peroxide, but to the masking DON by the interaction with the heme moiety of the enzyme. DNA strand cleavage by DON was inhibited by azide, mannitol, ethanol, cysteine and 2-mercaptoethanol, suggesting the involvement of radical species in the cleavage. The cleavage, however, was not suppressed by removal of dissolved oxygen from the reaction mixture, indicating that no oxygen-derived radicals participated in the cleavage. Electron spin resonance spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) elucidated the generation of a carbon-centered radical from DON. Hence, the carbon-centered radical may participate in DNA strand cleavage by DON.