Synergistic effect of irradiation and hyperthermia on established cell lines derived from maxillary carcinoma. Report I.

Cultured tumor cells of an established cell line derived from cancer of the head and neck (maxillary and lingual cancer) were irradiated with X-rays (5 or 10 Gy). This treatment inhibited cell proliferation in a dose-dependent way. Cell cycle analysis showed that the ratio of cells in the S phase to the population of viable cells was higher than that in a non-irradiated control group. Thus, the S phase was prolonged by exposure to X-rays. Cell proliferation was also inhibited by 1 h of heat treatment at 43 degrees C. However, movement through the cell cycle was slowed down overall and no cell aggregation in any phase of the cell cycle was found. Proliferation of not only radioresistant but also radiosensitive cells was inhibited by this treatment. Hyperthermia at 43 degrees C for 1 h did not affect cell proliferation, nor did it influence the pattern of cell cycle distribution. However, it caused a decrease in intracellular polyamine amount. The combination of irradiation and hyperthermia caused a stronger inhibition than either treatment alone. The synergistic effect of the two treatments probably arose from the S-phase cells being heat-labile although radioresistant.