Interaction of heavy-ion microbeam and chemotherapeutic agents in vitro

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It is known that relative biological effectiveness (RBE) of high-LET heavy-ion irradiation is higher than that of low-LET radiation such as X-ray. Monotherapy of charged particles has been applied for several tumors. We investigate the differences between two tumor cell lines with different radiosensitivities in sensitivity to high-LET heavy ion beam and in sensitizing effect and the mechanism of cisplatin and etoposide in combination with heavy-ion beam. Etoposide showed a synergistic effect in combination with carbon beam irradiation in radioresistant NMT-1R cells. However, there was no enhancement effect in radiosensitive NMT-1 cells. On the other hand, cisplatin had no enhancement in both cell lines. There was no differences in the pattern of G2 arrest among Carbon-beam + etoposide, Carbon-beam + cisplatin, and Carbon-beam alone 24 hours after irradiation. The increase in amount of apoptosis and the inhibition of Ku70 protein expression were found in the combination of carbon beam irradiation and etoposide in NMT-1 cells. There were bystander effects after heavy-ion microbeam irradiation.