Differential Chemoprotection of Normal and Malignant Tissues

The radioprotective agent, WR-2721 (S-2-[3-aminopropylamino] ethylphosphorothioate), has been tested (or its ability to protect mice against X-ray-induced lethality and against X-ray-induced skin ulceration, and for its ability to protect a transplantable mammary tumor against radiation-induced inhibition of transplantability. Injection of WR-2721 (500 mg/kg) 15 minutes before X-ray exposures increases the dose required to induce 50% lethality within 30 days (LD50/30) by 160–170%, increases the X-ray dose required to induce skin ulceration in 50% of the mice by 140%, but increases the dose required to inhibit tumor transplantability by only 15%. This differential protective activity, even though limited in scope, should be investigated further to assess the potential usefulness of radioprotective agents in radiotherapy.