Polysaccharide-K (Krestin, PSK) is a protein-bound polysaccharide isolated from the mycelium of Trametes versicolor.

Research

PSK is one of the most commonly used medicinal mushroom extracts with a long history as an additive in cancer therapy in Asia, especially in Japan. PSK has adjuvant anti-tumor activity in vitro in various types of cancers, including colorectal, gastric, breast, liver, pancreatic, and lung cancer. Preliminary studies examining PSK include its use in conjunction with chemotherapy for colorectal cancer, non-small cell lung carcinoma, breast cancer, liver cancer, and leukemia.

Chemistry

PSK is a protein polysaccharide consisting of a beta-glucan β-1,4 main chain with β-1,3 and β-1,6 side chains. The approximate molecular weight of PSK is 100,000 Da, and the protein component is reported at the β-1,6 side chain. PSK is isolated from the "CM-101" strain of Trametes versicolor. The analogous compound PSP, is derived from the "COV-1" strain of Trametes versicolor.