Studies on an antitumor polysaccharide RBS derived from rice bran. II. Preparation and general properties of RON, an active fraction of RBS.

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Abstract
An antitumor polysaccharide RON was obtained by fractionating RBS (a saccharide derived from rice bran) as the non-adsorbed fraction on diethylaminoethyl-Sepharose CL-6B. RON is a dextran-like .alpha.-glucan composed mainly of .alpha.-1,6-glucosidic linkages with a small amount of C-3 branches. Methylation analysis showed that the molar ratio of non reducing terminal: 1,6-linkage: 1,3,6-linkage was 1:25:1.2. Its molecular weight is over 1000 kilodaltons (kDa), the specific rotation is [.alpha.]D20 + 205.degree., it contains almost no protein and no starch, and it contains a small amount of inorganic substances. RON has potent antitumor activities against syngeneic tumors, Meth-A fibrosarcoma and Lewis lung carcinoma not only by intraperitoneal administration but also by oral administration, having optimum doses around 30 mg/kg. It is rare that an .alpha.-glucan such as RON has potent antitumor activities. Therefore, RON could be an interesting material to elucidate the relationship between the structure and antitumor activities of polysaccharides.