Branched mannans from the mushroom Cantharellus cibarius enhance the anticancer activity of natural killer cells against human cancers of lung and colon.

Several studies have shown that mushroom polysaccharides enhance the ability of natural killer (NK) cells to recognize cancer cells as foreign and thereby enhance the effectiveness of host immune defence mechanisms. Nevertheless, the use of NK cells in cancer treatment requires finding selective stimulators of their cytotoxicity without disturbing organism homeostasis. Our studies revealed that Cantharellus cibarius polysaccharides present in the CC2a fraction, mainly composed of an O-2 and O-3 branched (1→6)-linked mannan, not only beneficially influenced the viability and proliferation of the human natural killer cells NK92 but also enhanced their anticancer properties against the human lung and colon cancer cells A549 and LS180, and at the same time did not affect the human lung and colon epithelial cells NL20 and CCD841 CoN. Furthermore, the CC2a fraction used alone was also nontoxic to the normal epithelium, while it inhibited the viability of these cancer cells. Nevertheless, the therapeutic potential of NK92 cells was greatly enhanced after coincubation with these polysaccharides and the observed effect was dependent on the CC2a concentrations. The beneficial effect of CC2a on NK92 cells was associated with stimulation of p38 and Erk expression as well as induction of the transcription factor CREB. The discovered beneficial impact of the CC2a fraction on NK92 cells suggested the therapeutic use of the investigated compound especially as an adjuvant. Furthermore, taking into account the abundance of these water soluble mannans in C. cibarius, the results also suggest that an increase in the intake of C. cibarius may promote innate immunity response against cancer through the enhancement of NK cell activity.