Radioprotective activity of ethylcellulose microspheres containing WR 2721, after oral administration.

Ethylcellulose microspheres containing WR 2721 were prepared by the emulsion-solvent evaporation technique. No significant loss or degradation of this phosphorothioate was noted during preparation. Oral administration of these microspheres to mice gave an important lowering of WR 2721 toxicity and an enhancement of its radioprotective activity with a D.R.F. of about 1.7-1.8 over 2-3 h. This action is explained by the protection of WR 2721 from acid hydrolysis and degradation in the gastro-intestinal tract. The adsorption of a fraction of WR 2721 onto the surface of microspheres constitutes an inconvenience. This study confirms the interest of such carriers for providing important sustained radioprotection after oral administration.