Vitexin alleviates breast tumor in mice via skewing TAMs toward an iNOS+ profile orchestrating effective CD8+ T cell activation

Tumor-associated macrophages (TAMs) are the most abundant immune cells in the tumor microenvironment (TME) and often induce an immunosuppressed state. Vitexin is an apigenin flavone glycoside found in food and medicinal plants. Vitexin inhibits the growth of many tumors including breast cancer. However, the exact mechanism of the immune response of vitexin in breast cancer growth is not known. In this study, we investigated the potential anti-tumor mechanism of vitexin on regulating TAMs function in vivo and in vitro. An allograft breast tumor mouse model was established by injecting mouse 4T1 cells into female BALB/c mice, and the effect of vitexin on modulating TAMs and CD8+ T cells was assessed. Then, a cell model was used to illustrate the polarization effect of vitexin on the phenotype of macrophages. Finally, an inducible nitric oxide synthase (iNOS) inhibitor, 1400 W, was used to verify the effective target of vitexin. In vivo studies showed that vitexin programs TAMs to an iNOS+ profile and activates CD8+ T cells. In vitro experiments showed that vitexin, together with lipopolysaccharide and interferon-gamma, polarises macrophages to an M1 profile. Mechanistic validation studies showed that the antitumor effect of vitexin was partially attenuated by reduced iNOS expression, but still had an effect on CD8+ T cells in the spleen and blood.