Effect of hyperthermia on DNA single-strand breaks induced by bleomycin in Hela cells.

The effect of hyperthermia (43 approximately 45 degrees) on DNA single-strand breaks induced by bleomycin was examined in HeLa cells by the alkaline sucrose gradient sedimentation analysis. When HeLa cells were exposed to a temperature of 43 degrees approximately 45 degrees for 1 hr, only a small number of DNA single-strand breaks than bleomycin treatment at 37 degrees. The DNA strand breaks induced by bleomycin were almost completely repaired by post-treatment incubation of the cells in the control medium at 37 degrees. On the contrary, the repairing capacity of the cells was markedly inhibited by post-treatment incubation at 43 degrees, and this inhibition of cell repair seemed irreversible because no repair was found after an additional incubation of the cells at 37 degrees for 1 hr. These results support the possibility that the mechanism of synergism between the effect of bleomycin and hyperthermia may be related to the inhibition of DNA repair.