Further Observations onin VitroRadiosensitization of Rabbit Erythrocytes by Iodoacetic Acid and Related Substances

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Abstract
A number of compounds more or less related to iodoacetic acid (IAA) have been tested for their radiosensitizing effect on rabbit erythrocytes. As reported previously, red cells irradiated in vitro with x-rays lose the intracellular potassium and haemolyse as a function of radiation dose and, when they have been treated previously with IAA, their radiosensitivity increases up to four times. Bromoacetic acid, iodoacetamide, iodopropionic acid, N-ethylmaleimide, alcaline iodides and molecular iodine all exhibit radiosensitizing ability. The sensitization occurs to the same extent, whether the samples are irradiated under atmospheric oxygen-tension or after flushing with oxygen or nitrogen. For all the halogenated compounds it occurs only if the substance is present in the system at the moment of irradiation. The sensitizing effect appears to be independent of the alkylating ability of tested compounds, and of the inhibition of glycolysis and lowering of ATP-level in red cells. Experiments with iodoacetic acid-1-14C have shown that a significant amount of labelled compound binds to red cells, even after a previous incubation with the inert product. After irradiation with 79 kr of x-rays, the radioactivity bound to the red cells as whole, and to the red-cell membrane, is considerably reduced.