Role of vascular function in response of tumors in vivo to hyperthermia

The response of SCK tumor cells in vivo and in vitro to heat was compared, and the relationship between the kinetics of cell death and vascular function in tumors in vivo after hyperthermia was studied. The number of clonogenic cells in tumors excised immediately after heating was significantly less than that in the in vitro culture treated with the same heat doses. This suggested that the tumor cells in vivo are far more sensitive to direct damage by heat than are the cells in vitro. When the tumors were left in situ after hyperthermia at 43.5 degrees for 30 min, there was a progressive decrease in cell survival until 6 to 12 hr after the heating. The study of intravascular volume using the 51Cr-labeled red blood cell method indicated that severe vascular occlusion occurs in the tumor after hyperthermia. It therefore appeared that delayed cell death in tumors in vivo after hyperthermia resulted from an insufficient supply of oxygen and nutrients and an increase in acidity due to the vascular occlusion. Both the direct damage to tumor cells and the indirect damage to tumor cells as a consequence of vascular occlusion may play important roles in the eradication of tumors by hyperthermia.