Radiosensitization by Copper Ions, and Consequent Reversal of the Oxygen Effect

Abstract

THE apparently common, action of such various protective compounds as cysteine, glycerol and thiourea¹ suggests, from a chemical standpoint, a common chemical property. Such a property might be the metal chelating ability of compounds containing >N−, >S and >O atoms with unshared electrons². It seemed possible, therefore, that added metals, especially transition metals, might sensitize bacteria if they act in the opposite sense to the known protective compounds. Accordingly, the effect of added cupric salts on bacteria was investigated and the results of the initial work are presented below. Cupric chloride was added to saline (0.067 M) suspensions of Shigella flexneri about 5–10 min before irradiation. The suspensions were irradiated with an electron beam (8 MeV) from the Medical Research Council linear accelerator, dose rate about 20 krads/min, under anoxia and aeration for each concentration of copper salt used. Techniques for gas bubbling and for irradiating suspensions with the 8-MeV electron beam have been described by Alper³. Survival after irradiation was estimated by plating samples after each dose on Difco–salt plates and counting colonies after 15 h at 37° C.