Effect of liposome and cyclodextrin entrapment on retardation of glutathione decomposition of nitroimidazolyl sulfones.

A new class of radiosensitizing pharmaceuticals derived from 4-nitro-5-imidazolyl sulfones has its clinical potential compromised by a metabolic reaction with plasma glutathione which leads to a much less active metabolite. Entrapment of two members of the class in three different liposomes, one polymerized liposome, and a beta-cyclodextrin system has shown that this glutathione condensation can be suppressed by a rate factor of nearly 50-fold. Stabilizations of these metabolically labile radiosensitizers appear to relate to their lipid-buffer partition coefficients and to the fluidity of the liposome membrane in which they are entrapped.