Abstract A146: Novel mRNA-encoded constitutively active STING variant suppressed tumor growth in syngeneic models

Abstract Stimulator of interferon genes (STING) orchestrates the initial immune response against not only pathogens but also cancer. Upon sensing of abnormal cytosolic DNA, the cyclic GMP-AMP synthase (cGAS) generates cyclic GMP-AMP (cGAMP), which binds to and activates STING. This activation triggers downstream signaling through the TBK1/IRF3 and NF-κB pathways, resulting in the production of type I interferons and proinflammatory cytokines, which are key mediators of anti-tumor immunity. However, clinical application of STING agonists has been limited by poor metabolic stability, inefficient cytosolic delivery, and reduced STING expression in various human cancers.To address these challenges, we developed a synthetic mRNA-based therapeutic encoding a constitutively active variant of STING with an optimized CDN-binding domain to enhance signaling potency. STING pathway activation was evaluated using human and murine reporter cell lines (HEK-blue ISG, B16-blue ISG), revealing robust activation of the STING/TBK1/IRF3 pathway by our engineered STING mRNA variants. ELISA assays confirmed elevated IFN-β secretion, and qRT-PCR analysis revealed expression level of inflammatory cytokines downstream of both type I IFN and NF-κB signaling pathways.To assess anti-tumor efficacy in vivo, we conducted syngeneic mouse tumor models. Intravenous administration of our engineered STING mRNA analog significantly suppressed not only tumor growth in MC38 model, but also further inhibited tumor growth LL/2 model, which is considered cold tumor, demonstrating potent immunotherapeutic potential.Our findings demonstrate that an mRNA-encoded constitutively active STING mRNA analog can effectively overcome the limitations of conventional STING agonists and elicit strong anti-tumor immune responses. Citation Format: Ji Hee Lee, Yong Ho Heo, Seung-Hyun Shin, Youngjin Han, Chang Gyu Lim, Hocheol Shin, Jooyun Byun, Daejin Kim, In Young Choi. Novel mRNA-encoded constitutively active STING variant suppressed tumor growth in syngeneic models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr A146.