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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Two lichen polysaccharides with antitumor activity, a partially O-acetylated pustulan (GE-3) and a lichenan-type glucan (UR-1-1), isolated from Gyrophora esculenta MIYOSHI and Usnea rubescens STIRT., respectively, were subjected to various modifications, and the resulting products were tested for noncytotoxic, host-mediated antitumor action against sarcoma 180 solid tumor in mice by intraperitoneal 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, three with lauroyl contents less than 3.3% exhibited strong antitumor activity, while the more highly esterified products were all ineffective. Introduction of both carboxymethyl and lauroyl groups into the GE-3 molecule gave a product with moderate antitumor activity. The ten 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.
1979-09-25