Effects of Hyperthermia and X Irradiation on Sister Chromatid Exchange (SCE) Frequency in Chinese Hamster Ovary (CHO) Cells

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Abstract
The BrdUrd [bromodeoxyuridine] labeling method was used to evaluate the effects of hyperthermia, X irradiation and the combined treatment [tumor therapy measures] on the incidence of sister chromatid exchange (SCE) in Chinese hamster ovary (CHO) cells. Cells cultured in McCoy''s 5A media containing 10 .mu.M 5-BrdUrd were synchronized after 1 cell cycle by mitotic shake-off. Early-G1 cells were heated by submerging culture flasks in a 44 .+-. 0.05.degree. C water bath for 20, 40 and 60 min. By the same method, other cultures were X irradiated at doses of 100, 200, 400 and 600 rad. A 3rd protocol involved combined treatment of 20 min at 44.degree. C followed immediately by 1 of the above radiation doses. A 4th protocol reversed the sequence of the combined treatment applying X irradiation (200 or 400 rad) followed immediately by hyperthermia. Hyperthermia and X irradiation elevated the frequency of SCE significantly whether applied separately or together. The combined treatment (heat: 20 min at 44.degree. 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.