Abstract
The host stimulator of interferon genes (STING) signaling pathway is a major innate immune sensing pathway, and the stimulation of this pathway within antigen-presenting cells shows promise in targeting immune-suppressed tumors. Macrophages resident in tumors exhibit anti-inflammatory properties and enhance tumor growth and development. Polarizing such macrophages towards a pro-inflammatory phenotype is an effective strategy for tumor suppression. In the present study, we observed that the STING pathway was inactivated in breast and lung carcinomas, and a positive correlation existed between STING and macrophage markers in these tumors. We found that vanillic acid (VA) could stimulate the STING/TBK1/IRF3 pathway. VA mediated the production of type I IFN and promoted macrophage polarization into the M1 phenotype; this activity was dependent on STING activation. A direct-contact co-culture model and a transwell co-culture model revealed that macrophages with VA-induced STING activation exhibited anti-proliferative effects on SKBR3 and H1299 cells, although a STING antagonist and M2 macrophage-related cytokines alleviated this anti-proliferative effect. Further investigation indicated that phagocytosis and apoptosis-inducing effects were the major mediators of the anti-tumor effect of VA-treated macrophages. Mechanistically, VA promoted the polarization of macrophages to a M1 phenotype via IL-6R/JAK signaling, resulting in enhanced phagocytosis and apoptosis-induction effects. Additionally, STING activation-induced IFNβ production also participated in the apoptosis mediated by VA-treated macrophage in SKBR3 and H1299 cells. Mouse models with 4 T1 tumors confirmed the anti-tumor properties of VA in vivo and revealed the infiltration of VA-induced cytotoxic T cells into the tumors. These data suggest that VA is an effective agonist of STING and provides a new perspective for cancer immunotherapy.