Radiosensitization of mammalian cells by diamide.

The effect of diamide on the radiosensitivity of T-cells was investigated under oxic and anoxic conditions. The compound was found to sensitize the cells under both conditions. Under oxic conditions, exposure for 10 min before and during irradiation to 0.1, 0.5 and 1.0 mM diamide produced dose-modifying factors of 0.81, 0.60 and 0.55, respectively. Under anoxic conditions, exposure for 10 min before and during irradiation to 0.5 mM produced a dose-modifying factor of 0.34. When the cells in oxic conditions were exposed for just 20 min before irradiation, the sensitizing effect was smaller, but some sensitization effect was still apparent after a 120 min interval between diamide treatment and irradiation. Diamide also sensitized the cells after irradiation, but this effect was less than when it was present during irradiation. The presence of whole rat-blood in the incubation medium prevented sensitization. No sensitization could be detected in the whole animal. It is proposed that sensitization is due to lack of capacity for repair of radicals by hydrogen transfer and biochemical repair processes.