DNMT inhibition epigenetically restores the cGAS-STING pathway and activates RIG-I/MDA5-MAVS to enhance antitumor immunity.

The cGAS-STING cytosolic DNA-sensing pathway is a key mediator of the innate immune response and plays a crucial role in antitumor immunity. The expression of cGAS and STING is often suppressed in tumor cells, and reduced expression is associated with poor prognosis and inferior response to immunotherapy. In this study we systematically investigated the expression pattern of cGAS-STING pathway in tumors and its correlation with immunotherapy response. We showed that the expression of cGAS and STING was significantly decreased or undetectable in most breast cancer and murine tumor cell lines, while high cGAS and STING expression was associated with increased T cell infiltration, elevated PD-L1 and PD-1 levels, improved immunotherapy response and prolonged survival. In cGAS-STING-deficient MDA-MB-453 cells, DNMT inhibitor decitabine (DAC, 0.05-1 μM) dose-dependently restored the impaired pathway by reversing DNA methylation-mediated silencing. Furthermore, DAC combined with a chemotherapeutic agent cisplatin significantly enhanced the antitumor effect in MDA-MB-453 and MDA-MB-231 cells by activating the cGAS-STING pathway through cytoplasmic DNA accumulation. In addition, DNMT inhibition elevated intracellular dsRNA levels and activated the RIG-I/MDA5-MAVS pathway. These results suggest that DNMT inhibitors can epigenetically reprogram the cGAS-STING pathway, activate the RIG-I/MDA5-MAVS pathway, and in combination with chemotherapeutic agents, synergistically promote antitumor immunity. Together, this study identifies cGAS-STING as a potential predictor of immunotherapy response and highlights a novel therapeutic strategy for restoring innate immune function in cancer. Loss of cGAS-STING signaling in tumors impairs antitumor immunity and correlates with poor immunotherapy response. DNMT inhibition restores cGAS-STING pathway and concurrently activates the RIG-I/MDA5-MAVS signaling, synergistically enhancing immune infiltration and antitumor efficacy.