Response of human hematopoietic precursor cells (CFUc) to hyperthermia and radiation.

Currently, whole-body and local hyperthermia is being evaluated in clinical studies as a potential method of cancer treatment. Since the hyperthermic sensitivity of normal human bone marrow cells is not known, we have studied the in vitro response of these cells to two anticancer modalities when administered alone or in combination. Cell survival following various treatment schedules was determined by colony formation of bone marrow cells (CFUc) in soft agar suspensions. Within the survival range studied, a thermal tolerant plateau on the cell survival was not observed for temperatures of 42 degrees or less. However, thermotolerance induction could not be ruled out. In addition, when hyperthermia (42.5 degrees for 1 hr) and radiation (100 rads) were sequenced, the human CFUc survival remained the same regardless of whether the radiation was administered before, during, or after the hyperthermic exposure. Under our experimental conditions, we found the human CFUc to be more radiosensitive (D0 = 84 rads) than what has been reported previously. The radiation survival response of human CFUc was similar for cells irradiated either in vitro or in vivo. The possible clinical implications for these data are discussed.