The effect and mechanism of astragalus polysaccharides on T cells and macrophages in inhibiting prostate cancer

Background: The impact and underlying mechanisms of astragalus polysaccharide (APS) on prostate cancer, particularly its role in immunomodulation, remain inadequately elucidated. Methods: This study employed the XTT assay for assessing proliferation in prostate cancer cells and macrophages. T cell proliferation was determined using the Carboxyfluorescein diacetate succinimidyl ester labeling assay. APS's effect on T cells and macrophages was scrutinized via flow cytometry, Western blot analysis, ELISA, quantitative PCR and cytokine membrane arrays. The effect of APS on interaction between PD-L1 and PD-1 was investigated by the PD-L1/PD-1 homogeneous assay. Additionally, the impact of conditioned medium from T cells and macrophages on PC-3 cell migration was explored through migration assays. Results: It was observed that APS at concentrations of 1 and 5 mg/mL enhanced the proliferation of CD8⁺ T cells. At a concentration of 5 mg/mL, APS activated both CD4⁺ and CD8⁺ T cells, attenuated PD-L1 expression in prostate cancer cells stimulated with interferon gamma (IFN-γ) or oxaliplatin, and moderately decreased the population of PD-1+ CD4⁺ and PD-1+ CD8⁺ T cells. Furthermore, APS at this concentration impeded the interaction between PD-L1 and PD-1, inhibited the promotion of prostate cancer migration mediated by RAW 264.7 cells, THP-1 cells, CD4⁺ T cells, and CD8⁺ T cells, and initiated apoptosis in prostate cancer cells treated with conditioned medium from APS (5 mg/mL)-treated CD8⁺ T cells, RAW 264.7 cells, or THP-1 cells. Conclusion: The findings indicate a potential role of 5 mg/mL APS in modulating the PD-1/PD-L1 pathway and influencing the immune response, encompassing T cells and macrophages. Consequently, further in vivo research is recommended to assess the efficacy of APS.