Presentation P53-dependent cell-killing effect via bystander effect using carbon-ion microbeams simulating the spot scanning system with pencil beams

鈴木, 雅雄  ,  舟山, 知夫  ,  横田, 裕一郎  ,  鈴木, 芳代  ,  池田, 裕子  ,  坂下, 哲哉  ,  小林, 泰彦  ,  村上, 健

Since 1994, a Phase I/II clinical study and radiotherapy have been carrying out using carbon-ion beams generated with the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences. Now we constructed the new treatment facility for the advanced carbon-ion therapy applying a 3D fast spot scanning system with pencil beams. To identify the biological effects of a spot scanning carbon-ion beams in vitro, we demonstrated cell-killing effect of human tumor cell lines using the spot scanning irradiation of carbon-ion microbeams generated with the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) in Japan Atomic Energy Agency. We irradiated either 4-cell lines with wild-type P53 or 4-cell lines with mutated-type P53 using the TIARA microbeams collimated by 20µm in diameter. We can easily estimate the number of the directly irradiated cells to be 0.01% level of the total cells on the dish using the highly controlled microbeam irradiation system. The percent survival in the cells with wild-type P53 was around 90%, while almost 100% was observed in the cells with mutated-type P53. We can expect the percent survival of 99.99% level when the cell-killing effect was induced in directly irradiated 0.01% cells, assuming no bystander effect. However, the percent in the cells with wild-type P53 was significantly low beyond our expectation. Moreover, the percent returned to 100% when using a specific inhibitor of gap-junction mediated cell-cell communication. The results are consistent with the data using the carbon-ion broad beams with the shielding method at HIMAC, which irradiation was carried out using 4 different protocols; (1) All cells were irradiated; (2) Irradiated and unirradiated cells were pooled in a 1:1 ratio as a single culture; (3) Half of cells were irradiated using beam stopper; and (4) Half of cells were irradiated with a specific inhibitor of gap-junction. Our overall results showed that bystander cell-killing effect was observed in the cells with wild-type P53, but not in the P53-mutated cells. There is clear evidence that the spot scanning irradiation system of carbon ions enables the enhanced cell killing in cells with wild-type P53 gene via gap-junction mediated bystander effect.
15th International Congress of Radiation Research

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