Studies on an enzymatically synthesized antitumor polysaccharide SPR-901

An antitumor polysaccharide SPR-901 was found in a fermented broth of a kind of lactic acid bacteria isolated from rice bran. SPR-901 is a high molecular alpha-glucan and its linkages are almost linear alpha-1,6 glucosidic ones with a small amount (ca. 5%) of branches at C-3 positions. It is a highly purified alpha-glucan and it contains no protein and no inorganic salts. SPR-901 showed significant antitumor activities against murine allogeneic and syngeneic tumors by both intraperitoneal and oral administration, and enhanced carbon clearance ability in mice, while it showed no direct cytotoxicities in vitro. The mechanism of antitumor activities of SPR-901 is supposed to be a host-mediated one, and this substance is classified as one of the biological response modifiers. These properties of SPR-901 were identical to those of RON, which was obtained from rice bran, therefore we concluded that these two polysaccharides were the same substance.