Modification of X-ray induced chromosome aberration frequency by pre- and postirradiation hyperthermia of human...

Human peripheral lymphocytes (HPL) were used to study the synergistic effects of hyperthermia and X-irradiation. The effects on the chromosome aberration frequencies of different combinations of heat and radiation exposure at different cell cycle phases were analysed at the first mitosis after irradiation. When unstimulated HPL were heated after irradiation with 2 and 3 Gy, respectively, the chromosomal aberration frequencies were significantly higher than following radiation exposure alone. Heat treatment during different phases of the cell cycle and irradiation during the G2 phase led to an increase in the aberration frequencies when the cells were heat-treated not later than 16 h before radiation. Furthermore we show that the number of breaks increased linearly with the duration of hyperthermia when HPL were heated for periods of 1-15 min at 45 degrees C 32 h before irradiation at 48 h after stimulation. Heat treatment alone during any phase of the cell cycle did not induce chromosome aberrations. The increased aberration frequencies are probably the result of inhibited repair of radiation-induced DNA strand breaks.