Evidence of immunogenic cancer cell death induced by honey-processed Astragalus polysaccharides in vitro and in vivo

Abstract

Honey-processed Astragalus is a dosage form of Radix Astragalus mixed with honey by a traditional Chinese medicine processing method which improves immune activity. This pharmacological activity of honey-processed Astragalus polysaccharide (HP-APS) might be due to structural changes during the honey roasting process. Previously, we have prepared and characterized HP-APS and preliminarily found its anti-inflammatory effects. However, whether the pharmacodynamic activity of HP-APS induces tumor cell apoptosis and the mechanisms responsible for the immunogenic death (ICD) have not been elucidated. Here, A549, MC38 and B16 cells were used to evaluate the cells viability, apoptosis and cell cycles, respectively. Cellular immunogenic cell death-related molecules calreticulin (CRT), Heat Shock Proteins (HSP)70, major histocompatibility complex I (MHC-I), and co-stimulator molecules CD80/CD86 were determined by flow cytometry. The extracellular ATP release was also detected. B16-OVA and MC38-OVA cells were treated with HP-APS and co-cultivated with OT1 mouse of CD3+T cells for assessment of proliferation, in mice model, and the establishment of C57BL/B6 mouse model bearing B16 cells for assessment of HP-APS the regulation of immune activity in vivo. Our results showed that HP-APS has an inhibitory effect on tumor cell proliferation, which induces tumor cell apoptosis, preventing cells-transforming from G1 phase to S phase in cell cycles. Furthermore, HP-APS could effectively increase the expression of HSP70, CRT, MHC-I, CD86, CD80 and ATP release. T cell proliferation index is significantly improved. CD3 cell proliferation in OT1 mice was significantly increased from the 4th generation to the 5th generation. Moreover, the results have also shown that HP-APS could inhibit tumor growth by increasing immune cell infiltration in the tumor tissues. In the mouse melanoma model with HP-APS treatment, the tumor weight and volume were significantly reduced, and the growth of melanoma was inhibited. CD8⁺ T is significantly increased. The ratio of CD4⁺ T and CD8⁺ T cells numbers are also significantly increased in mouse spleen, but it is less than PD-1 alone treatment separately. Altogether, these findings suggest that HP-APS exerts anti-tumor effects, and that its underlying mechanisms might be associated with the expression of immunogenicity cell death related molecules and the immunomodulatory effects of immune cells.

Keywords: Anti-Tumor activity; Honey-processed Astragalus polysaccharide; Immunogenic death; PD-1(programed death-1); T lymphocyte.