Recovery of sublethal radiation damage and its inhibition by hyperthermia in normal and transformed mouse cells.

Radiation resistance may be related in part to the capacity of cells to repair radiation damage which can usually be characterized by the survival curve shoulder and split dose recovery. C3H-10T1/2 normal and transformed cells and V79 cells were evaluated for their ability to recover from sublethal radiation damage and for hyperthermia to affect this recovery. The transformed cell line of the 10T1/2 cell system displayed a much larger capacity to recover from radiation damage than did the parental strain. This was also correlated with an enlarged shoulder on the radiation survival curve. When hyperthermia was given, recovery of sublethal radiation damage could be inhibited in both cell lines. This inhibition was dependent on the sequence of hyperthermia treatment and correlated with the removal of the shoulder of the radiation survival curve. In Chinese hamster V79 cells, recovery was much smaller than in the mouse C3H-10T1/2 cell system. In the hamster cells, recovery could also be inhibited by a hyperthermia treatment. In all three cell lines the degree of inhibition was dependent on thermal dose and indicated that very small hyperthermia treatments would not inhibit recovery of sublethal damage but may in fact cause some increase possibly due to increasing the amount of damage available for repair. Thus if hyperthermia doses are sufficiently large, it may be used to overcome sublethal damage repair and may result in therapeutic gain in tumors which have a large capacity for such repair.