Radiosensitivity of Scid Cells Deficient in Repair of DNA Damages Induced by High LET Irradiation

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Scid cells deficient in DNA-PK are highly sensitive to low LET radiations as well as high LET radiations. Hybrid scid cells introduced by a fragment of human chromosome 8 which contains the structural gene of DNA-PK recover radiosensitivity to the level of wild parental cells. In this study, changes in radiosensitivity of scid cells to high LET radiation, heavy ion particles, was investigated in order to elucidate the process how DNA damages induced by LET radiation were repaired.X-rays (200 kV) and carbon ions as heavy ion particles (290MeV/u, 50 keV/μm) for high LET radiation were used. Changes in radiosensitivity by heat treatment in scid cells and hybrid scid cells irradiated with high LET radiation were investigated. Although both cell lines showed radiosensitization when heat treatment was combined, scid cells were more sensitized than scid hybrid cells. This result showed that other DNA repair systems exist in scid cells, which might be heat sensitive.Wortmannin, an inhibitor of phosphorylation to PI3 kinase family, was treated with high LET irradiation. Ratio of radiosensitivity was increased when wortmannin was combined with irradiation in both cell lines. The enhancement ratio of radiosensitivity by applying wortmannin was the same for low and high LET irradiation, and was 2.5-3.1 and 1.3 -1.4 for scid hybrid cells and scid cells respectively.