THE RADIOSENSITIZING ACTION OF CHLORPROMAZINE

A method for assaying the radioprotective or radiosensitizing effect of various drugs is described. Tumor cells are irradiated in the presence of the drug and changes in their oxygen consumption are subsequently measured in a Warburg apparatus. To carry out the procedure, ascitic fluid from mice bearing Ehrlich ascites sarcoma is centrifuged and the cells are resuspended in Krebs- Ringer solution so that 200 mg of cells are suspended in 1.25 ml. To this is added 1.25 ml of Krebs-Hinger solution containing the drug to be assayed. The cells are then irradiated for 10 min with 80-kv x rays at a rate of 100 r/min, giving a dose of 1000 r. Irradiation is carried out 1 hr after the cells are aspirated from the mice and their respiration is measured 1 hr after irradiation to determine the oxygen consumption for a 1-hr period. In 3 experiments, chlorpromazine at a concentration of 1.5% increased radiosensitivity by 12, 19, and 21%, with a mean of 17%. Another drug, 5801 RP (composition not stated), had only weak radiosensitizing activity (3%). (H.H.D.)