Effects of iodoacetamide and x rays on a murine ascites tumor

The radiosensitizing properties of iodoacetamide (IA) have been studied using as end point the proliferative capacity of an ascites tumor (lymphoma, LSA) of the C57BL mouse. When the cells were irradiated in vitro, TD50 assays gave a survival curve with D0 = 120 +- 20 rad and n = 4.0. When cells were irradiated in the presence of 10-3M iodoacetamide (IA), the shoulder of the curve was eliminated, but the slope was not changed. In vivo-in vivo experiments were performed using a 7-day-old tumor. The cells were treated in the donor mice, which were injected ip with 104 cells 7 days before treatment. Survival curves for x rays alone gave D0 = 369 +- 50 rad, with n = 1.70. Irradiation after injection of 0.37 mg of IA eliminated the shoulder and changed the slope (D0 = 243 +- 35 rad). The ratio of the D0's gave a slope ratio of 1.52 +- 0.32, indicating a sensitizing action of the iodoacetamide. Using the potentiating factor (PF), defined as the ratio of the expected to the experimental surviving fraction of the combination, an average PF = 5.61 was obtained. PFs significantly greater than 1.0 indicate a synergistic effect of IA and x rays