Radiosensitization of Brain Tumor Cells with a Thymidine Analogue (Bromouridine)

T REATMENT of malignant brain tumors has been one of the biggest problems in neurosurgery. If surgical removal is not feasible, two other ways of treatment are available at present, namely, radiation therapy and chemotherapy. Chemotherapy has not yet produced satisfactory results. Radiation therapy is variably effective in some kinds of brain tumor, such as medulloblastoma, ependymoma, pinealoma, and pituitary adenoma. If a way could be found to enhance the radiosensitivity of these and other brain tumors, it would make radiotherapy much more valuable. Many such agents have been examined. 9 Bagshaw 2 classified these agents into four groups according to the mode of action: l) sensitization, 2) augmentation, 3) potentiation, and 4) additivity. We have been greatly interested in one of thymidine analogues that strongly enhances the radiosensitivity of the cells, 19 5-bromo-2'deoxyuridine (bromouridine or BUdR), which belongs to Bagshaw's group 1 (sensitization). In this agent, only the methyl radical of the 5th position of the pyrimidine ring of thymidine is replaced by bromine, as shown below.