Astragalus polysaccharide restores activation of NK cells in radiation therapy of tumors

Astragalus polysaccharide (APS) has been used as an adjuvant in the treatment of malignant tumors, however, most APS trials have been performed with chemotherapy of malignant tumors, the effect and mechanism of APS is unclear in radiotherapy for tumors. In the present study, the hepatocellular carcinoma H22 tumor-bearing mouse model was established. The H22 tumor-bearing mice received radiotherapy combined with APS treatment. Results showed APS could obviously up-regulate the expression of MHC class I chain-related molecule A (MICA) and B (MICB) on tumor cell surface, which is one of the major ligands of activating receptor NKG2D on natural killer cells (NK cells). The binding of MICA/B and NKG2D led to NK cell activation by improving the level of phosphorylated extracellular signal regulated kinase on NK cells. Activated NK cells released more IFN-gamma, Granzyme B and Perforin, promoting the clearance of tumor cells. These results suggested that APS increased the sensitivity of tumors to radiotherapy by activating the extracellular signal regulated kinase pathway of NK cells. APS may be as an efficient adjuvant in radiotherapy of malignant tumors.