Polysaccharide-K (Krestin, PSK) is a protein-bound polysaccharide isolated from the mycelium[1][2]ofTrametes versicolor.
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.[3]
Preliminary studies examining PSK include its use in conjunction with chemotherapy for colorectal cancer,[4][5] non-small cell lung carcinoma,[6] breast cancer,[7] liver cancer,[8] and leukemia.[9]
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.[10] 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.[11]
