Bromodeoxyuridine: a comparison of its photosensitizing and radiosensitizing properties.

The photo- and radiosensitizing properties of bromodeoxyuridine (BUdR) were assessed in vitro using the 9L rat brain tumor cell line. Pretreatment of 9L cells with 10 microM BUdR for 24 hours followed by irradiation with ultraviolet (UV) light resulted in a dose-enhancement ratio of 3.8:1 compared with UV radiation alone. X-radiation of BUdR-pretreated cells produced a dose-enhancement ratio of 1.7:1. Alkaline elution analysis of deoxyribonucleic acid (DNA) from cells treated with BUdR and UV irradiation showed the presence of DNA single-strand breaks and DNA-protein cross-links. Analysis of DNA from cells treated with BUdR and then x-irradiated showed no increase in DNA single-strand breaks compared with cells treated with x-radiation alone; no DNA-protein cross-links could be detected. The possible clinical relevance of these findings is discussed.