@article{oai:repo.qst.go.jp:00047072,
 author = {Sato, Katsutoshi and Imai, Takashi and Okayasu, Ryuichi and Shimokawa, Takashi and 佐藤 克俊 and 今井 高志 and 岡安 隆一 and 下川 卓志},
 issue = {4},
 journal = {Radiation research},
 month = {Oct},
 note = {Although it is known that cancer cells can develop radiation resistance after repeated exposures to X rays, the underlying mechanisms and characteristics of this radiation-induced resistance of cancer cells are not well understood. Additionally, it is not known whether cells that develop X-ray resistance also would develop resistance to other types of radiation such as heavy-ions including carbon ions (C-ion). In this study, we established X-ray resistant cancer cell lines by delivering repeated exposures to X rays, and then assessed whether the cells were resistant to carbon ions. The mouse squamous cell carcinoma cell line, NR-S1, was X irradiated six times with 10 Gy, and the X-ray resistant cancer cells named X60 and ten subclones were established. Significant X-ray resistance was induced in four of the subclones (X60, X60-H2, X60-A3 and X60-B12). The X60 cells and all of the subclones were resistant to carbon ions. The correlation analysis between radioresistance and morphological characteristics of these cells showed that X-ray (R = 0.74) and C-ion (R = 0.79) resistance correlated strongly with the number of heterochromatin domains. Moreover, the numbers of γ-H2AX foci remaining in irradiated X60 cells and radioresistant subclones X60-A3 and X60-H2 were lower than in the NR-S1 cells after X-ray or C-ion irradiation, indicating that X60 cells and the radioresistant subclones rapidly repaired the DNA double-strand breaks compared with NR-S1 cells. Our findings suggest that the underlying causal mechanisms of X-ray and C-ion radiation resistance may overlap, and that an increase in heterochromatin domain number may be an indicator of X-ray and C-ion resistance.},
 pages = {408--419},
 title = {Heterochromatin domain number correlates with x-ray and carbon-ion radiation resistance in cancer cells.},
 volume = {182},
 year = {2014}
}