Effects of low priming dose irradiation on cell cycle arrest of HepG2 cells caused by high dose irradiation

Human hepatoma cells hepG2 were irradiated twice by Co γ-rays with a priming dose of 5cGy and 60 a higher dose of 3Gy performed 4h or 8h after the low dose irradiation. Effects of the priming dose irradiation on cell cycle arrest caused by high dose were examined with flow cytometry. Cells in G2/M phase accumulated temporarily after the 5cGyirradiation, and proliferation of tumor cells was promoted significantly by the low dose irradiation. After the 3Gy irradiation, G2 phase arrest occurred, and S phase delayed temporally. In comparison with 3kGy irradiation only, the priming dose delivered 4h prior to the high dose irradiation facilitated accumulation of hepG2 cells in G2/M phase, whereas the priming dose delivered 8h prior to the high dose irradiation helped the cells to overcome G2 arrest. It was concluded that effects of the priming dose treatment on cell cycle arrest caused by high dose irradiation were dependent on time interval between the two irradiations.