Hyperthermia, polyamine depletion, and inhibition of X-ray-induced DNA strand break repair

We have recently demonstrated that HeLa cells that had been depleted of polyamines by treatment with inhibitors of polyamine biosynthesis were deficient in their ability to repair X-ray-induced DNA strand breaks. Since it had previously been demonstrated that hyperthermic shock also inhibited strand break repair following X irradiation and that hyperthermia resulted in a leakage of polyamines from cells, it seemed of interest to examine whether the inhibition of repair by hyperthermia was related to this loss of cellular polyamines. In the present paper it is demonstrated that both polyamine depletion and hyperthermia inhibit strand closure, and that a combined treatment further reduces the rate of repair. In cells not depleted of polyamines, repair is restored to normal levels if hyperthermia treatment is followed by a 4-h incubation at 37 degrees C before X irradiation. In polyamine-depleted cells, this 37 degrees C incubation does not result in a return of repair ability. Polyamine supplementation was not effective in reversing hyperthermia-dependent repair inhibition, and, in fact, restoration of repair in control cells following hyperthermic shock corresponded to a time at which polyamines show a maximum decrease in those cells. These results suggest that the inhibition of repair and the increased radiosensitivity observed in hyperthermically treated cells is not related to polyamine depletion. However, data further suggest that polyamine-depleted cells may have other alterations, perhaps in chromatin, which render them more sensitive to thermal inhibition of repair.