Fractionated Radiation Exposure Enhances DNA Repair Capacity to Amplify Radioresistance of Cancer Cells
Abstract Fractionated radiotherapy is widely used in cancer therapy for its advantages in the preservation of normal tissues, but may amplify radioresistance of cancer cells. To understand whether and how fractionated radiation exposure amplifies radioresistance, HCT-8 human colon cancer cells and MCF-7 human breast cancer cells were received a total dose of 5 Gy X-ray irradiation by a single exposure or fractionated exposures (1 Gy/day for 5 consecutive days), respectively. We then examined the radioresistance of cells. Underwent an additional exposing to 2 Gy, cells received fractionated exposures showed significantly better cell proliferation and clonogenic ability than cells received a single exposure. Compared to the intact cells without radiation exposure, the expression of γ-H2AX, pATM and PARP was significantly enhanced in only these cells received fractionated exposures. However, the expression of cyclin D1 and cyclin E1 was enhanced in only these HCT-8 cells received a single exposure. Otherwise, the expression of SOD1, SOD2 and caspase 3 was not significantly changed in both cells received either a single exposure or fractionated exposures. Fractionated radiation exposure amplifies radioresistance of cancer cells, predominantly by enhancing DNA repair capacity.
