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

Summary

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 (TER_HeLa < TER_EAT < TER_LM). 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.