Induction and repair of DNA-DSB induced by heavy ions under hypoxic conditions

The contributions of OH radical-mediated indirect action by heavy ions under hypoxic irradiation condition were investigated by using a radical scavenger (DMSO) CHO cells were irradiated with 290 MeV/n carbon, 490 MeV/n silicon, 500 MeV/n argon, 500 MeV/n iron and 200 MeV/n iron ions over the linear energy transfer (LET) range from 15 keV/μm to 480 keV/μm. The contribution of indirect action to cell killing decreased with increasing LET down from 20% at 480 keV/μm. SCCVII cells were transplanted into the hind legs of C3H mice. The tumors were irradiated with 500 MeV/n iron ions at 200 keV/μm, either hypoxic or oxic. In addition, single-cell suspensions prepared by enzymatically digesting tumors were irradiated under oxic condition. Cell killing under three different conditions was measured by in vivo-in vitro colony formation assay. The survival levels of 10% (D₁₀) were similar values (3.2-3.8 Gy). The radiosensitivity of three conditions after high-LET heavy ion were almost not depending on oxygen density. (author)