The effect of heavy-ion beams to mouse malignant melanoma cell line having highly metastatic potential

The aim of this study is to clarify the effect of carbon-ion beams (C-ions) on metastatic potential of melanoma. B16/BL6 cells, a highly metastatic mouse malignant melanoma cell line, were exposed to C-ions or X-rays in vitro. Survival curves showed higher cytotoxic effects of C-ions than X-rays. Additionally, the potentials of migration and invasion were suppressed by C-ions, however those enhanced by X-rays at low dose points compared with controls. Interestingly, the relative biological effectiveness (RBE) of migration and invasion ability was higher than that of cell killing. On the other hand, the cells were implanted in C57BL/6J mice, and tumors were irradiated at the center of 6 cm-SOBP C-ions or γ-rays. C-ions significantly suppressed the tumor growth. The numbers of lung metastatic nodules from local tumors irradiated or non-irradiated decreased with the dose, and C-ions were more effective compared with γ-rays. The metastatic potentials of survived cells in a tumor after irradiation was analyzed, and C-ions showed smaller number of metastasis than γ-rays when the tumor cell survivals were 10%. It might suggest that C-ions inhibit metastasis at radiotherapy compared with the therapy using photons. (author)