Protein-bound polysaccharide-K reduces colitic tumors and improves survival of inflammatory bowel disease in vivo.

Protein-bound polysaccharide-K (PSK) is a biological response modifier that possesses antitumor effects against various tumors. Although an inflammatory response has been considered to play an important role in the development of colorectal cancer, the anti-inflammatory effect of PSK has yet to be elucidated. An inflammatory bowel disease (IBD)-induced colorectal tumor model with 1.2-dimethyl hydrazine (DMH) and dextran sodium sulfate (DSS) was used to examine the effects of PSK on tumor suppression and survival. Although 90% of the mice that were not treated with PSK developed colitic tumors, oral administration of PSK suppressed tumor formation by less than 30%. Although deaths associated with DSS-induced melena were observed, PSK significantly reduced mortality. In conclusion, the present study showed that PSK not only suppressed colorectal tumor formation in the DMH+DSS-induced IBD model, but also improved the survival rate, indicating that anti-inflammatory activity is one of the mechanisms for the antitumor effects of PSK.