Antitumor activity of cell wall beta-1,3/1,6-glucans from Phytophthora species

From the cell walls of various Phytophthora species (Oomycetes) different water-soluble beta-1,3/1,6-glucans were isolated and characterized. The glucans with relative molecular masses between 13 and 50 kd exhibited varying degrees of branching in the beta-1,3-linked glucan backbone ranging from 14 to 50%. The dose-dependent antitumor activity of the glucans against allogeneic sarcoma-180 was investigated. It could be demonstrated that beta-1,3/1,6-glucans with relative molecular masses below 50 kd can exhibit a prominent antitumor activity (inhibition rate up to 99%), being comparable to that of the high relative molecular mass (450 kd) beta-1,3/1,6-glucans. Biological activity of the glucans could be shown to be correlated with a low degree of branching. The most potent glucan with a degree of branching of 14% also was active against the syngeneic DBA/2-MC.SC-1 fibrosarcoma (inhibition rate up to 90%) and in combination with a suboptimum dose of diethylstilbestrol against Nobel-Nb prostate carcinoma (inhibition rate up to 90%).