Antiproliferative effects of sclerotial polysaccharides from Polyporus rhinocerus cooke (Aphyllophoromycetideae) on different kinds of leukemic cells

Mushroom polysaccharides isolated from fruiting bodies are known for their antitumor activities, whereas those from mushroom sclerotia are not. A hot water- (PR-HW) and a cold alkaline (PR-CA)-soluble polysaccharide isolated from a novel mushroom sclerotium, Polyporus rhinocerus Cooke, were characterized to be a polysaccharide-protein complex and a glucan, respectively. Their in vitro antitumor activities against different leukemic cell lines were investigated. PR-HW demonstrated significant growth inhibition of human acute promyelocytic leukemic cells (HL-60), chronic myelogenous leukemia cells (K562), and human acute monocytic leukemia cells (THP-1) in vitro, whereas PR-CA showed no such inhibition. Flow cytometric analysis has shown that the antiproliferative effect of PR-HW on HL-60 was mediated by cell cycle arrest at the G1 phase, which subsequently led to apoptosis. This suggests that structural differences in PR-HW and PR-CA greatly affects their antitumor activities.