The Modification of Radiation Damage in CHO Cells by Hyperthermia at 40 and 45°C

Low hyperthermia at 40/sup 0/C either before or after X irradiation did not alter the slope of the radiation dose-cell survival curve but reduced the D/sub q/ from 145 to 41 or to 0 rad for a pre- or postirradiation incubation period of 2 hr at 40/sup 0/C, respectively. In contrast, hyperthermia at 45/sup 0/C increased the slope of the radiation survival curve by a factor of 1.7 for a radiation pretreatment of 10 min at 45/sup 0/C, but only by 1.3 for the same treatment immediately after irradiation. The corresponding D/sub q/'s were 262 and 138 rad, respectively. A combination of 45 and 40/sup 0/C hyperthermia (10 min at 45/sup 0/C + 2 hr at 40/sup 0/C + X) resulted in a superposition of the individual effects of 45 or 40/sup 0/C hyperthermia on the radiation survival curve. In addition, the radiation survival curve was shifted downward by a factor of three due to the potentiation of 45/sup 0/C hyperthermia damage by postincubation at 40/sup 0/C. Repair of sublethal radiation damage was completely suppressed during incubation at 40 following hyperthermia at 45/sup 0/C. However, when cells were returned to 37/sup 0/C, even after 6 hr at 40 following 45/supmore » 0/C hyperthermia, the capacity to accumulate and repair sublethal radiation damage was immediately restored. These findings imply that the hyperthermia damage from low or high temperatures interacts differentially with radiation damage. Low hyperthermia at 40/sup 0/C may affect principally the radiation repair system, whereas 45/sup 0/C hyperthermia probably alters the radiation target more severely than the repair system.« less