Host-mediated antitumor effect of grifolan NMF-5N, a polysaccharide obtained from Grifola frondosa

The antitumor mechanism of grifolan NMF-5N, a beta-1,3-glucan obtained from mycelia of Grifola frondosa, was examined. Grifolan NMF-5N did not show direct cytocidal effect on cultured tumor cells. However, intraperitoneal injection of grifolan NMF-5N increased the number of peritoneal exudate cells and peritoneal adherent cells which showed cytostatic activity towards syngeneic tumor cells. In an in vivo assay, the administration of carrageenan, an inhibitor of macrophage function, reduced the antitumor activity of grifolan NMF-5N. The delayed-type hypersensitivity reaction was augmented in the grifolan NMF-5N-administered mice. The administration of NMF-5N augmented the induction of cytotoxic T cells but the antitumor activity of grifolan NMF-5N was reduced in athymic nu/nu mice. In addition, the treatment with anti-Thy 1,2 antibody and complement C' of spleen cells taken from mice which showed regression of tumor due to grifolan NMF-5N, reduced the neutralizing effect in Winn assay. These results suggested that grifolan NMF-5N shows antitumor activity via host-mediated mechanisms and both macrophages and T cells play important roles in the mechanisms.