Identification of a Novel Small Molecule STING Agonist Reshaping the Immunomicroenvironment of Pancreatic Ductal Adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with limited treatment options and poor response to immunotherapy. The immunosuppressive tumor microenvironment, characterized by a dense extracellular matrix, and immunosuppressive cells, plays a crucial role in this resistance. The cGAS-STING pathway, traditionally recognized for antiviral defense, has emerged as a potential target for cancer immunotherapy due to its ability to activate both innate and adaptive immune responses. Methods: A novel small-molecule STING agonist, D166, was synthesized by incorporating deuterium into the structure, leading to improved stability and activation of the STING pathway. The effects of D166 were evaluated using human pancreatic tumor organoids, mouse pancreatic tumor models, and various in vitro and in vivo assays, including flow cytometry, RNA sequencing, ELISA and western blotting. And an organoid-immune cells co-culture system was established for further investigate the effects on immune cells. Results: D166 demonstrated significant anti-tumor activity, effectively activating the cGAS-STING pathway in a time- and dose-dependent manner. D166 inhibited the progression of pancreatic tumor organoids and mouse pancreatic tumors, reshaping the tumor immune microenvironment. The drug enhanced T cell activation, promoted macrophage polarization toward the M1 phenotype, and increased the infiltration of immune cells. Additionally, D166 acted as a sensitizer for anti-PD-1 therapy, significantly improving therapeutic efficacy in combination treatments. Conclusion: D166 is a novel and stable STING agonist that inhibits pancreatic tumor progression by activating the cGAS-STING pathway and remodeling the tumor immune microenvironment. Its combination with anti-PD-1 antibodies offers a promising strategy for overcoming the immunosuppressive barriers in pancreatic cancer, providing new therapeutic insights and directions.