Differences in Heat-induced Cell Killing as Determined in Three Mammalian Cell Lines Do Not Correspond with the Extent of Heat Radiosensitization

Three different cell lines, Ehrlich ascites tumour (EAT) cells, HeLa S3 cells and LM mouse fibroblasts, were used to investigate whether or not the extent of heat killing (44°C) and heat radio-sensitization (44°C before 0–6 Gy X-irradiation) are related. Although HeLa cells were the most heat-resistant cell line and showed the least heat radiosensitization, we found that the most heat-sensitive EAT cells (D0, EAT = 8·0 min; D0, LM = 10·0 min; D0 HeLa = 12·5 min) showed less radiosensitization than the more heat-resistant LM fibroblasts (TERHeLa < TEREAT < TERLM). Therefore, it is concluded that the routes leading to heat-induced cell death are not identical to those determining heat radiosensitization. Furthermore the inactivation of DNA polymerase α and β activities by heat seemed not to correlate with heat survival alone but showed a positive relationship to heat radiosensitization. The possibility of these enzymes being a determinant in heat radiosensitization is discussed