Antitumor and immunomodulatory activity of water-soluble polysaccharide from Inonotus obliquus

► A water-soluble polysaccharide (ISP2a) was purified from Inonotus obliquus. ► ISP2a significantly inhibited the growth of SGC-7901 cells in vivo. ► ISP2a significantly enhanced the lymphocyte proliferation and increased the production of TNF-α. ► ISP2a may indirectly play the role of antitumors activity through improving immunologic function of tumor-bearing mice. The medicinal mushroom Inonotus obliquus has been used as a folk remedy for a long time in Russia and East-European countries to treat gastrointestinal cancer, cardiovascular disease and diabetes. In our study, a water-soluble polysaccharide (ISP2a) was successfully purified from I. obliquus by DEAE-Sepharose CL-6B and Sepharose CL-6B column chromatography. In vivo ISP2a had not only shown antitumor activity, but also could significantly enhance the immune response of tumor-bearing mice. In addition, ISP2a significantly enhanced the lymphocyte proliferation and increased the production of TNF-α. Results of these studies demonstrated that ISP2a had a potential application as natural antitumor agent with immunomodulatory activity.