Chemoprotection against Fractionated Radiation Exposures with WR-2721: Skin Injury

These studies extend the analysis of the potential application of WR-2721 (S-2-(3-aminopropylamino)ethylphosphorothioic acid) to radiation therapy by determining the ability of the drug to protect mice against hair loss induced by multiple exposures to radiation. In the two mouse strains tested, RFM and BALB/c, the relatively low drug dose used (200 mg/kg) protected the mice against hair loss from single exposures by factors of 1.67 and 1.73. The dose necessary to produce a given level of hair loss (ED/sub 50/) increases with increasing number of fractions. The ED/sub 50/ increases as N/sup 0.52/ and N/sup 0.59/ in the two strains of mice when they are not drug-treated, but as N/sup 0.39/ and N/sup 0.50/ in mice that are drug-treated. Thus, the protective effectiveness of WR-2721 decreases with increasing numbers of fractions, but the drug is still able to give a dose-modifying factor of about 1.25 when the total exposure is given as a series of 9 or 10 fractions. WR-2721 appears to offer the possibility of improving the efficiency of radiotherapy under clinical conditions.