Variations in the Spectrum of Lesions Produced in the DNA of Cells from Mouse Tissues after Exposure to γ-rays in Air-breathing or in Artificially Anoxic Animals

Summary

Gamma-ray-induced DNA-protein crosslinks (dpc) are preferentially induced in cultured cells irradiated at very low oxygen tensions (Meyn et al. 1987). Since some cells within mouse tumors may be radiobiologically hypoxic, dpc may also be induced in such cells after irradiation in vivo. To examine this possibility, mice bearing either an FSa or NFSa fibrosarcoma in their hind legs were whole-body irradiated either while breathing atmospheric oxygen or 15 min after cervical dislocation, which induces uniform anoxia. DNA single-strand breaks (ssb) and dpc were then assayed both in tumors and normal tissues by alkaline elution. The level of dpc was inferred from the observed increase in ssb yield after digestion of the cell lysates with proteinase K. In addition, cell suspensions were irradiated in vitro, on ice, exposed to atmospheric oxygen tensions. Few dpc were detected in the DNA from tumor cells irradiated in vitro; however, in cells from both FSa and NFSa tumors irradiated in situ there was a significant level of protein-concealed ssb, and thus of dpc. These data are most likely the result of the relative hypoxia of a proportion of cells from both the FSa and NFSa tumor in the air-breathing animals. Induction of dpc was further enhanced in the DNA from tumor cells irradiated under anoxic conditions. A significant level of dpc was also observed in jejunal and spleen cells irradiated in vivo; however, since a significant level of protein-concealed breaks was also observed in cells irradiated in vitro, oxygenation appears not to be the only parameter capable of modifying the proportion of protein-concealed ssb, and the effects of proteinase K on the DNA elution rate for normal mouse tissues may be complex.