Radiotherapy of Experimental Lung Tumors in the Presence and Absence of a Radioprotective Drug, S-2-(3-aminopropylamino)ethylphosphorothioic Acid (WR-2721)2

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Abstract
The development of a lung tumor-radiotherapy system in the mouse and the improvement of the efficiency of radiotherapy in this system through the use of the radioprotective drug S.2-(3-aminopropylamino) ethylphosphorothioic acid (WR-2721) are described. Tumors were induced by injection of urethan, and the mice were treated with localized γ-rays 6 months later. A clearing-staining procedure with a lower limit of resolution of 0.1 mm in diameter allowed the quantitation of tumor number and size. The tumors were resistant to radiation and required prolonged periods for regression. Injection of the radioprotective drug, just before exposures as high as 3000 rads at 68 rads/minute, offered no protection to the tumors but increased the radiation resistance of the skin and those tissues which determined survival by factors of 1.6–2.1. If the time between injection and the completion of exposurewas between 1 and 2 hours, protection of the tumors was observed, which indicated that the basis of the differential response of the tumor and the normal tissues was not qualitative, but rather depended on a difference between the two types of tissues in the time required to respond to the protective action of the drug.

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