Effect of oxygen-radiosensitizer mixtures on the radiation response of Chinese hamster cells, line V.79-753B, in vitro. I. Survival response

The effect of radiosensitizers on the survival of Chinese hamster cells irradiated in the presence of low concentrations of oxygen has been investigated. When the concentrations of oxygen and sensitizer were less than those which would separately produce an enhancement ratio (ER) of 1.9, sensitization was enhanced by the combinations. However, when the concentration of either agent was greater than that required to produce an ER of 1.9, there was no enhanced sensitization in the presence of the mixtures. The nitroxyl TMPN, which does not sensitize in our system, reduced the amount of sensitization produced by oxygen or misonidazole at concentrations that gave an ER of 1.9. When cells were irradiated in the presence of a low concentration of oxygen and 10-4 M of the biradical nitroxyl, Ro.03-6061, there was no change in the slope of the survival curve, but the shoulder removing property of the compound was abolished