Astragaloside IV Enhances Anti-PD-L1 Immunotherapy in Triple-Negative Breast Cancer by Activating the cGAS-STING Pathway.

Astragaloside IV (AS-IV), a natural compound from traditional Chinese medicine, has demonstrated anti-tumor properties. This study aims to explore its potential to enhance anti-mPD-L1 immunotherapy in triple-negative breast cancer (TNBC) by modulating the tumor immune microenvironment. Flow cytometry and immunofluorescence staining analyses were employed to evaluate the influence of AS-IV on cell cycle distribution, apoptosis and DNA damage (phospho-γH2AX staining). The antitumor effects of AS-IV, anti-mPD-L1, or their combination were further investigated using a 4T1 murine breast cancer model. Immune cell infiltration within the tumor tissue was assessed by flow cytometry. AS-IV significantly triggered apoptosis, G0-G1 cell cycle arrest, as well as induced DNA damage and activation of the cGAS-STING pathway in MDA-MB-231 and 4T1 cells. Interestingly, AS-IV notably elevated PD-L1 levels both in two TNBC cells. In vivo experiments indicated that AS-IV treatment notably suppressed tumor growth and triggered tumor cell apoptosis. Meanwhile, AS-IV enhanced anti-tumor efficacy of anti-mPD-L1 on 4T1 murine model, as evidenced by increased infiltration of CD8⁺T cells and elevated secretion of IFN-β, CCL5, and CXCL10. AS-IV remodeled the tumor immune microenvironment and induced PD-L1 upregulation, thereby potentiating the efficacy of anti-mPD-L1 immunotherapy. These findings suggest that AS-IV may serve as a promising immunomodulatory adjuvant in cancer immunotherapy for TNBC.