Inhibition of Repair of Radiation-induced Strand Breaks by Hyperthermia, and Its Relationship to Cell Survival after Hyperthermia Alone

Abstract

Ehrlich ascites cells [mouse] growing in vitro were used to investigate the influence of hyperthermia on the formation and repair of DNA strand breaks after X-irradiation. Different heat pretreatments were given immediately prior to a dose of 6 Gy [gray] of X-rays. When a temperature of 42.degree. C was used, up to 4 h of pretreatment had only a slight inhibitory effect on the repair of DNA strand breaks induced by radiation. At a temperature of 43.degree. C progressively more inhibition was observed with longer treatment times. This was also the case for temperatures of 44.degree. C and 45.degree. C. When the treatment times at 43-45.degree. C were longer, strand breaks in DNA were induced by the hyperthermic treatment alone. Under these conditions almost no repair was found of strand breaks induced by a subsequent radiation dose. The data obtained strongly suggest a correlation between the effect of the hyperthermic treatment alone on cell survival and the kinetics of repair of strand breaks in DNA as induced by radiation. [The combination of hyperthermia and radiation is of considerable current interest for the treatment of cancer.].