The Extraction and Development of Antitumor-Active Polysaccharides from Medicinal Mushrooms in Japan (Review)

It has been known for many years that most mushrooms with known effects against cancer belong to the family Polyporaceae s.l. (Agaricales s.l.). However, the components responsible for such action have not been clearly defined. In Japan, in 1968, a hot water extract from some edible mushrooms belonging to the family Polyporaceae s.l., showed a marked host-mediated antitumor activity. Since then, numerous researchers have isolated active polysaccharides and have identified them to be (1→3)-β-D-glucopyranans with a (1→6)-β-D-glucosyl branch containing protein. Several antitumor polysaccharides, some hetero-β-glucans and their protein complexes, such as xyloglucans and acidic β-glucan containing uronic acid, are insoluble in water. They were, however, isolated from the extracts using large amounts of dilute alkali with Japanese (8 species) and Chinese (5 species) mushrooms. Several trials have been made to enhance activity by chemical modification, such as polyalcohols formed by a mild Smith degradation and the products formed by BH4-reduction after 104-oxidation. Mushroom polysaccharides are considered to be biological response modifiers (BRM), or immunopotentiators, because of their action mechanism. In Japan, three different polysaccharide antitumor agents have been developed from the fruit body, mycelium, and cultured medium, of three mushroom species.