Correlation between γ-ray-induced G2 arrest and radioresistance in two human cancer cells

Abstract Purpose: The correlation between radioresistance and γ-ray-induced G 2 arrest was examined in two human cancer cell lines, HeLa (cervical carcinoma) and MeWo (melanoma). Methods and Materials: Cellular radioresistance was examined by a colony formation assay and Hoechst 33342 staining. G 2 arrest induced by γ-rays was examined by flow cytometry, and the accumulation of cyclin B1 and cdc2 proteins was analyzed using Western blotting. Results: HeLa was more resistant (10% survival dose[D10] = 10 Gy) than MeWo (D10 = 4 Gy) to γ-rays. In HeLa, cell cycle analysis showed that G 2 arrest was induced 10 or 24 h after irradiation of 10 or 4 Gy, respectively. In contrast, no clear G 2 arrest in MeWo was observed after irradiation. Western blot analysis showed that cell cycle regulators, cyclin B1 and cdc2, were accumulated in HeLa but not in MeWo. The accumulation of cyclin B1 and cdc2 reached peak levels 24–34 h after irradiation of 10 Gy, and 24 h after irradiation of 4 Gy. In addition, Hoechst staining revealed similar increase in apoptotic bodies with time after irradiation in HeLa and MeWo at isosurvival doses. Conclusion: Radioresistance of these human cancer cells is closely correlated with γ-ray-induced G 2 arrest, and cyclin B1 and cdc2 are possible regulators of G 2 arrest.