Effect of hyperthermia at 42 and 45 degrees C on repair of radiation-induced DNA strand breaks in CHO cells.

The effect of hyperthermia on DNA strand break repair was studied in CHO cells. DNA strand breaks were analysed by the alkaline DNA-unwinding technique followed by chromatography on hydroxyapatite. Immediately after irradiation with doses ranging from 2 to 7 Gy, cells were exposed to 42 or 45 degrees C. Heat alone was found to induce DNA strand breaks only at temperatures exceeding 45 degrees C. In comparison to 37 degrees, C, the rate of single-strand break repair was increased by hyperthermia at 42 degrees C, but decreased at 45 degrees C. In contrast hyperthermia at either temperature resulted in a higher number of remaining double-strand breaks 1 hour after irradiation. For the three treatments applied, i.e. X-rays alone or combined with hyperthermia at 42 or 45 degrees C, the relation between cell survival and the number of double-strand breaks measured 1 hour after irradiation could be described by the same function.