Studies on the water-soluble constituents of lichens. III. Changes in antitumor effect caused by modifications of pustulan- and lichenan-type glucans.

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Abstract
Two lichen polysaccharides with antitumor activity, a partially O-acetylated pustulan (GE-3) and a lichenan-type glucan (VR-1-1), isolated from Gyrophora esculenta and Usnea rubescens, respectively, were subjected to various modifications, and the resulting products were tested for noncytotoxic host-mediated antitumor action against mouse sarcoma 180 solid tumor in mice by i.p. administration. Treatment of GE-3 with urea afforded products with the same antitumor effect as the original glucan. Injection of GE-3 or UR-1-1 together with urea also caused no marked decrease in the antitumor activity. On O-carboxymethylation, both glucans yielded products with greatly reduced antitumor activity. Ten lots of the lauroyl derivative with different degrees of substitution were prepared from GE-3. Among them, 3 with lauroyl contents less than 3.3% exhibited strong antitumor activity, while the more highly esterified products were all ineffective. Introduction of carboxymethyl and lauroyl groups into the GE-3 molecule gave a product with moderate antitumor activity. The 10 lots of the lauroyl derivative of GE-3 had no direct antitumor action against Ehrlich ascites carcinoma implanted in mice as determined by the total packed cell volume method.