Hydroxyl radical production by free and DNA-bound aminoquinone antibiotics and its role in DNA degradation. Electron spin resonance detection of hydroxyl radicals by spin trapping

Abstract
The reduced antitumor antibiotic mitomycin C in aqueous solution exposed to air gave a 36-line ESR spectrum of the semiquinone identified by computer simulation. Incubation of this radical with the spin trap N-tert-butyl-.alpha.-phenylnitrone (PBN) gave the PBN.cntdot.OH nitroxide radical identified by independent generation. This nitroxide radical was formed from similar treatment of a DNA to which mitomycin C was covalently attached. Incubation of the semiquinone from mitomycin C, mitomycin B or streptonigrin (SN) with catalase or with superoxide dismutase inhibited the generation of OH., implying the intermediacy of H2O2 and .**GRAPHIC**. in its formation. The formation of the spin-trapped nitroxide radical was similarly inhibited by EDTA, suggesting the intermediacy of trace metal ions in the generation of hydroxyl radicals from SN. The results were consistent with the generation by the aminoquinone antibiotics in vivo of OH. already implicated in the degradation of DNA.