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 gives a 36-line electron spin resonance spectrum of the semiquinone identified by computer simulation. Incubation of this radical with the spin trap N-tert-butyl-alpha-phenylnitrone (PBN) gives the PBN.OH nitroxide radical identified by independent generation. This nitroxide radical is also formed from similar treatment of a DNA to which mitomycin C is covalently attached. Incubation of the semiquinone from mitomycin C, mitomycin B, or streptonigrin (SN) with catalase or with superoxide dismutase inhibits the generation of OH, implying the intermediacy of H2O2 and O2 in its formation. The formation of the spin-trapped nitroxide radical is similarly inhibited by EDTA, suggesting the intermediacy of trace metal ions in the generation of hydroxyl radicals from SN. The results are consistent with the generation by the aminoquinone antibiotics in vivo of OH. already implicated in the degradation of DNA.

Spin trapping for hydroxyl in water: a kinetic evaluation of two popular traps

“…5 min) for measurements to be taken. Near to the start of photolysis the chemistry of the system can be described by reactions [3]- [6]. This is because the time scale of this experiment is short compared to that for the unimolecular decay of the spin adducts and spin adduct concentrations are so low that radical-radical reactions do not contribute to the reaction scheme.…”

“…It has also been used to be detected; and (4 the epr parameters of the identify hydroxyl radical production in systems in-spin adducts must be sensitive to the nature of the volving aminoquinone antibiotics (6), bleomycin trapped. and iron(1I) (7), photooxidation of chlorophylls (8), Each of these four criteria has been examined in a and microsomal lipid peroxidation (9).…”

Enhancement of superoxide dismutase activity in cancer cell lines by anticancer drugs.

“…The most probable explanation is that SOD activity may be increased in response to enhanced production of superoxide radicals. Indeed, many anticancer drugs, which have nucleic acids as their principal cell target sites, have been shown to produce superoxide radicals in cancer cells [4,6,21]. However, 5-FU, an inhibitor of metabolism, was found to also enhance SOD activity, though it has been thought to be unable to produce superoxide radicals.…”

Electron paramagnetic resonance characterization and conformation of daunorubicin semiquinone intermediate implicated in anthracycline metabolism, cardiotoxicity, and anticancer action

“…In addition the superoxide anion generated from daunorubicin in microsomal incubations has been spin-trapped (15). The hydroxyl radical generated from quinone antibiotics has also been spin-trapped in epr experiments (16). Moreover we recently provided evidence using kinetic criteria in conjunction with epr spectroscopy for the generation of free hydroxyl radicals from the anthracyclines as well as certain other antibiotics (17).…”