Inhibition of Repair of Radiation-induced DNA Damage by Thermal Shock in Chinese Hamster Ovary Cells

Summary

The effect of exposure to elevated temperatures (41–45°C) on the repair of radiation-induced DNA strand breaks was measured in monolayer cultured Chinese hamster ovary (CHO) cells. Prior exposure of cells to temperatures between 43 and 45°C resulted in significant decreases in the rate of repair of DNA damage. Exposure to 45°C for 15 min slowed the rate of DNA repair to 0·17 of the control repair rate. The T_o for inactivation of DNA repair was observed to be 34, 13 and 6 min at 43, 44 and 45°C, respectively. Stepdown-heating (45°C for 15 min followed by repair at 41°C) resulted in greater inhibition of DNA repair (0·11 of the control rate) than was observed after acute heating alone. Repair at 41°C was observed to proceed in unheated cells at a faster rate than at 37°C. An Arrhenius analysis of the inactivation kinetics of DNA repair between 43 and 45°C indicated an activation energy of 140 kcal mol⁻¹ of protein for the inhibition of DNA repair. In general, the results were inconsistent with either a retardation of the DNA repair rate or an increase in unrepaired DNA lesions being responsible for heat-induced radiosensitization.

• hyperthermia
• radiation
• DNA repair