Binding of Nitroxyls to Radiation-induced DNA-transients in E. Coli K–12 under in Vivo Conditions and Its Relevance for Radiosensitization

Summary

Binding of tritiated 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (³H-TAN) to radiation-induced DNA-transients in E. coli K–12 strain AB 2463 rec⁻A, has been studied under in vivo conditions. In N₂O-saturated cell suspensions 30 per cent higher yield is observed than in N₂. Aerobic bacteria show slight binding ability.

The time-course of the ability of TAN to (a) form complexes with DNA and (b) act as an anoxic cell radiosensitizer has been investigated when TAN is added to the cell suspension at different times before and after irradiation.

When TAN is added before exposure, the yield of TAN-DNA complexing is reduced by only 40 per cent when the contact time is reduced from 10 min to 200 msec. For contact times as short as 200 msec, however, only a minute radiosensitization is observed.

When TAN is added after exposure, there are significant binding yields when mixing occurs within 2 sec after irradiation of the cell suspension. No sensitization at all results, however, even when TAN is added only 200 msec after exposure.

The difference in time-course for binding and sensitization is discussed and a model for the sensitization mechanisms suggested.