ES treatment significantly enhanced radiation-induced cell death in H-520 cells. A) Cell apoptosis observed by Hoechst 33258 staining (×400). H-520 cells treated with medium alone (a), 200 μg/mL ES (b), irradiation (c), and their combination (d) for 72 h. B) Cell death after different treatments was determined by a flow cytometry. The early apoptosis rate of ES-treated H-520 cells was significantly higher than those of un-treated H-520 cells at the radiation dosage of 4Gy. Higher total apoptosis rate of the ES-treated H-520 cells was observed at every radiation dose included in this study. One representative of three identical experiments was shown.