EFFECTS OF HYPERTHERMIA AND X-IRRADIATION ON SISTER CHROMATID EXCHANGE (SCE) FREQUENCY IN CHINESE-HAMSTER OVARY (CHO) CELLS

The BrdUrd labeling method was used to evaluate the effects of hyperthermia, X irradiation and the combined treatment on the incidence of sister chromatid exchange (SCE) in Chinese hamster ovary (CHO) cells. Cells cultures in McCoy's 5A media containing 10 μM 5-bromodeoxyuridine were synchronized after one cell cycle by mitotic shake-off. Early-G1 cells were heated by submerging culture flasks in a 44 ± 0.05°C water bath for periods of 20, 40, and 60 min. By the same method, other cultures were C irradiated at doses of 100, 200, 400, and 600 rad. A third protocol involved combined treatment of 20 min at 44°C followed immediately by one of the above radiation doses. A fourth protocol reversed the sequence of the combined treatment applying X irradiation (200 or 400 rad) followed immediately by hyperthermia. The data showed that hyperthermia and X irradiation both elevated the frequency of SCEs significantly whether applied separately or together. The combined treatment (heat: 20 min at 44°C plus varying X-radiation doses) produced results suggestive of a synergistic interaction. The sequence of the heat and X irradiation did not appear to have a significant effect on the production of SCE.