Abstract: Background and purpose: Colorectal cancer is a common tumor of digestive system, radiation therapy is one of the important means of treatment. To explore the mechanism of colorectal cancer cell tolerated to radiation, radioresistant colorectal cancer cell-subline was induced and screened. Methods: Colorectal cancer SW620 cells were repeatedly given individual doses of γ-rays to induce radiation resistance. After monoclonal cells being selected and extensively cultured, the cell subline was named SW620/R. Morphological changes and growth of the cells before and after illumination were observed. Cell proliferation was tested by CCK8 assay. The distribution of cells in different stages of the cell cycle and apoptosis were investigated by flow cytometry. The relative radiosensitivities of tumor cells were assessed by standard colony formation assays. Results: SW620/R cells were established by gradient of increasing radiation dose induction method. SW620/R showed significant morphological changes compared with the parent strain SW620. Proliferation experiments showed SW620/R cell line doubling time was longer than SW620, clonogenic capacity decreased significantly. The resistant cells showed a higher percentage of cells in S phase and didn't appear cell cycle retardation, and the apoptosis rates were also found large differences between two cell lines after irradiation. SW620/R showed lower radiosensitivity by colony-forming assay. Conclusion: Radioresistant colorectal cancer cell subline SW620/R was established and it has lower radiosensitivity than the parental cell line. Two cell lines also have significant differences in proliferation, the rate of colony formation, cell cycle and spontaneous apoptosis (P<0.05).

Key words: Colorectal cancer, Radiation resistance, Cell cycle, Apoptosis