Interaction of Hyperthermia and Radiation in Tolerant and Nontolerant HeLa S3 cells: Role of DNA Polymerase Inactivation

Summary The activities of DNA polymerase α and β were measured in tolerant and nontolerant HeLa S3 suspension cells. The heat-inactivation of the enzymes and their recovery when cells were incubated at 37°C after the heat challenge was compared to the synergistic action of heat and radiation and its disappearance at the level of cell survival. Thermotolerant cells were radiosensitized by heat similarly to nontolerant cells, but the sensitization decreased more rapidly in the tolerant cells when time at 37°C was allowed between the two treatments. For polymerase activities the extent of inactivation, as well as the kinetics of recovery, were similar in tolerant and nontolerant cells. The results show that the activities of DNA polymerase α and β do not always correlate with the extent of heat radiosensitization. It is concluded that heat inactivation of these enzymes may not be taken as a general cause for the synergistic effect of hyperthermia and radiation. As an alternative mechanism, changes in nuclear protein binding due to cellular heating are suggested, since these correlate well with effects observed for radiosensitization under different experimental conditions, including the use of thermotolerant cells.