Estimation of Biologic and Molecular Aspects of Heavy Charged Particle Therapy for Cancer Cells

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Carbon ion irradiation has well-balanced dual actions on cancers : efficient doselocalization due to sharp penumbra and distal taill off in dose, and potent biological anticancer effect due to high relative biological effect (RBE). However, biological and molecular mechanisms of carbon ion irradiation have not been clarified. In this study, we focused on the biologic mechanisms of carbon ion irradiation, especially assessing DNA double strand breaks (DSBs) and repair.Cell-killing effect of X-ray and carbon ion irradiation was assessed using a colony-formation assay. The amount of double strand breaks and repair rate was assessed by comat assay. In the comparison of DSBs repair between carbon ion irradiation and X-ray irradiation, the degree of residual DSBs was severe in carbon ion irradiated cells. The expression level of DSB repair associated protein was assessed by Westem blot analysis. Sub-nuclear localization of DNA repair protein Rad51 were immunohistochemically evaluated via epi … More tluorescence microscopy. Rad51 nuclear foci formation was observed after X-ray irradiation and carbon ion irradiation. These nuclear foci in the cells treated with carbon ion were sustained to 24 hours after irradiation, whereas in the cells treated with X-ray irradiation more than half of nuclear foci were disappeared at 24 hours after irradiation. Rad51 antisense oligonucleotides was transfected and irradiated with carbonions. Clonogenic assay after transfection revealed that Rad51 antisense oligonucleotides increased radiosensitivity very little carbon ion irradiation, whereas ti increased about 1.7 fold in X-irradiation. Comet assay was also performed for quantitative analysis of DSB induction and repair. There was no difference of DSB induction and repair rate after carbon ion irradiation in the cells treated with Rad51 antisense oligonucleotides and with control oligos. These results may suggest that carbon-ion-induced DSBs are difficult to be repaired by homologous recombination. Less