Abstract
The aim of this study is to clarify the time and dose dependency of cell cycle in tumor cells exposed to C-ions and X-rays. Six human malignant melanoma cell lines, 92-1, C32TG, Colo679, HMV-I, HMV-II and MeWo were used. Cells were exposed to X-rays or 290 MeV/u C-ions at the center of SOBP. The cell survival after irradiation was obtained using a colony formation method. The 10% survival dose (D10) were estimated from cell survival curves as iso-effect dose, and used for the time dependency analysis. The same physical dose of C-ions and X-rays (1-8Gy) were used for dose dependency analysis. After irradiation, the cells were trypsinized and re-seeded to dishes in appropriate concentration, and cultured in CO2 incubator. Cells were collected at adequate time point (6-204 h after re-seeding), dyed with PI, fixed with Ethanol, and observed by the flow cytometry technique. It was suggested the melanoma cell lines used in this study were arrested in G2/M or G0/G1 phase after C-ions. Cells exposed to X-rays were accumulated in S or G0/G1 phase. Additionally, it was clarify the cells exposed to C-ions still existed in the G2/M phase at a high rate compared to non-irradiation samples 130 hours later. On the other hand, the percentage of cells arrested in G2/M was increased depending on physical dose in C32TG, HMV-I, HMV-II, and MeWo after C-ions irradiation. However the cells were accumulated in G0/G1 in 92-1, and the cell cycle was not changed in Colo679 depending on dose increasing. It has been understood that the behavior at the cell cycle depend on the cell lines, quality of radiation, time course, and irradiation dose. In addition, it was suggested even if the number of cells that dies finally is the same, the process of cell death is quite different between C-ions and X-rays, and it was clarified the transient prolonged G2/M arrest was specific phenomenon induced by heavy-ion beams.
