Radiation-induced apoptotic cell death in human gastric epithelial tumour cells; correlation between mitotic death and apoptosis

The mode of cell death in cells undergoing mitotic death after gamma-irradiation was studied in seven human gastric epithelial tumour cell lines and two strains of normal gastric fibroblasts. Apoptotic cells were frequently observed in all tumour lines after irradiation, whereas the two fibroblast strains were quite low in apoptosis frequency. The advent of apoptosis depended on the radiation doses and incubation time. Detailed analysis of one of the carcinoma lines, SH101-P4, revealed that G2-phase arrest was maximum at 12 h postirradiation. The cells began to escape G2 arrest by 24 h. Apoptotic cells began to increase at 12 h postirradiation and became maximal from 72 to 96 h. Apoptosis developed in the G1 phase of the cell cycle subsequent to the irradiation. These results suggest that apoptosis is one of the modes of mitotic death after irradiation.