A comparison of the effect of hyperthermia on DNA polymerase in hamster and human glioma cells.

The hyperthermia response of two human glioma cells lines (87MG and 373MG) was compared to the CHO cell line for cell killing and DNA polymerase inactivation. Glioma cells were found to be more thermally resistant than CHO cells over a temperature range of 41-46 degrees C. Inactivation of polymerase alpha and beta by hyperthermia was also more resistant in glioma cells than in CHO cells. The relative order of resistance for both killing and polymerase inactivation was 373MG > 87MG > CHO. While polymerase inactivation correlated with cell killing at high thermal doses, such correlation at low doses was absent; i.e. thermal killing was characterized by survival curves with shoulders while polymerase inactivation was not. Thus at low thermal doses the mechanism of thermal cell killing is probably not related to the degree of polymerase inactivation. Arrhenius analysis of the survival data showed that the inactivation energy for the glioma cells was 133-135 kcal/mol. The inactivation energies of alpha and beta polymerase were also evaluated and were 102-104 and 140-146 kcal/mol, respectively. Further analysis of the temperature-time relationship of hyperthermia treatment resulting in 50% cell kill showed the degree of polymerase beta inactivation to be a good indicator of thermal dose.