PSK as a chemopreventive agent

Abstract

PSK, a protein-bound polysaccharide preparation obtained from cultured mycelia of the CM-101 strain of Coriolus versicolor belonging to basidiomycetes, is a biological response modifier capable of exhibiting diverse biological activities. This agent has been used clinically for the treatment of postoperative cancer patients in Japan by oral use. In this paper, chemopreventive aspects of PSK were reviewed. Oral administration of PSK reduced the incidence of tumor and/or prolonged the survival period in the following chemical carcinogen-induced, radiation-induced, and spontaneously developed animal cancer models: rat gastrointestinal cancer induced by 1,2-dimethylhydrazine; rat hepatoma by 3'-methyl-dimethylaminobenzene; mouse thymic lymphoma by whole-body irradiation; mouse spontaneous mammary tumor; and so on. PSK did not interact and/or inhibit drug-metabolizing enzymes and had no effect on the Ames test. On the other hand, this agent scavenged active oxygen through the induction of manganese superoxide dismutase, prevented the increase in frequency of anticancer agent-induced sister chromatid exchange, and suppressed fetal deformation induced by transplacental injection of teratogen, suggesting an effect on the initiation or promotion process of carcinogenesis. Also, PSK regulated cytokine production and enhanced the antitumor activity of effector cells such as killer T-cells and natural killer cells, suggesting an effect on the growth process after the development of malignant cells. Thus, this agent seems to act at multiple steps during carcinogenesis rather than a particular step. The main mechanism may be an antiteratogenic effect attributed to radical trapping, preventive effects against chromosome injury, and immunomodulative effects attributed to the modulation of cytokine production and effector cell function.(ABSTRACT TRUNCATED AT 250 WORDS)