Radiosensitization of Mammalian Cells by Misonidazole and Oxygen: DNA Damage Exposed by Micrococcus luteus Enzymes

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Abstract
The presence of misonidazole [Mz] or O2 enhanced single-strand breaks (SSB) in DNA during irradiation of hypoxic mammalian [Chinese Hamster CHZB2] cells. The dose-modifying factor (DMF) for 15 mM Mz was 3.4, compared to an oxygen enhancement ratio (OER) of 3.5. Another class of DNA damage due to exposure to an M. luteus extract was examined. Radiation-induced M. luteus extract-sensitive sites (MLS) were enhanced by Mz or O2. The DMF for damage from 15 mM Mz was 1.6; the OER was 2.5. The ratio of MLS to SSB was 1.25 under hypoxia, 0.9 in the presence of O2 and 0.6 in the presence of 15 mM Mz under hypoxic conditions. Incubation of mammalian cells with Mz under toxic conditions (37.degree. C, hypoxia) which produce many SSB, produced no detectable lesions sensitive to the M. luteus extract.