Radiosensitivity of scid cells for heavy ion particles

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Scid cells deficient in DNA-PK are highly sensitive to low LET radiations. Hybrid 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. Radiosensitivity of scid cells to high LET radiations has not been investigated. In this study radiosensitivity of scid cells to 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) were used. Repair of DNA double strand breaks (DNA-dsb) in hybrid cells irradiated to X-rays showed bi-phasic, but mono-phasic in scid cells. Irradiation to carbon ions showed the same result as X-rays, indicating that repair of DNA-dsb was LET-independent. RBE for carbon ions was analyzed. RBE of scid cells was 1.30, and 1.47 for hybrid cells. The value of radiosensitivity of scid cells subtracted that of hybrid cells indicates damages repaired by DNA-PK, DNA-PK contribution. RBE of DNA-PK contribution was 1.02. These results indicate that lethal DNA damages unrepairable in scid cells and hybrid cells are LET-dependent, and that DNA damages repairable by DNA-PK contribution by LET-independent.