[Radiation induced apoptosis in cultured human epithelial tumor cells].

The mode of cell death in cells undergoing mitotic death after irradiation was studied in twenty cancer cell lines of human gastrointestinal origin. Apoptotic cells were observed in all cancer cell lines after irradiation, whereas 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. Moreover, the rate of apoptosis of the cells by irradiation did not correlate with p53 gene abnormalities. These results suggest that apoptosis is one of the modes of mitotic death after irradiation.