Sensitivity to heat, radiation, and heat plus radiation of Chinese hamster cells synchronized by mitotic selection, thymidine block or hydroxyurea block

Abstract

1. 1. Chinese hamster V79 cells were synchronized by mitotic selection or by exposure to hydroxyurea, or excess thymidine. Autoradiography showed that each method yielded a high degree of synchrony. 2. 2. The responses to heat and radiation throughout the cell cycle for the three methods of cell synchronization were qualitatively the same. A complementary cell cycle response for heat and radiation treatments was observed. In S-phase, cells were most heat-sensitive and least radiosensitive while in g 1 and G 2-phase the opposite was true. The combined heat and radiation treatments resulted in a synergistic enhancement of radiosensitivity through the cell cycle, which was greatest in S-phase, thus eliminating the cell-cycle variation. 3. 3. These data show that cell-cycle responses to heat and radiation are independent of the method of cell synchronization and provide a rationale for overcoming cell-cycle-dependent problems for cell killing in cancer therapy.