Abstract LB038: Advancing immunotherapy with the development of a novel STING mRNA analog

Abstract Stimulator of IFN genes (STING), encoded by the STING1 gene, plays a crucial role in initiating immune responses against viral and bacterial pathogens, as well as cancer. Cyclic GMP-AMP synthase (cGAS) detects aberrant cytosolic DNA and produces cyclic GMP-AMP (cGAMP) that binds to and activates STING. Activation of the cGAS-STING pathway induces type I interferon production and NF-κB signaling pathway, leading to the secretion of inflammatory cytokines. These inflammatory cytokines strengthen anti-tumor immunity and contribute to the capacity of immune systems to suppress tumor progression. STING is regulated by various post-translational modifications (PTMs) at different domains, including phosphorylation, ubiquitination, SUMOylation, palmitoylation, alkylation and glycosylation. We engineered an mRNA-based therapeutic encoding a constitutively-active STING variant to activate anti-tumor immune responses. To further enhance the anti-tumor efficacy of the engineered STING variant mRNA, we optimized CDN binding domain associated with STING activity. Using human (HEK-blue ISG) and mouse (B16-blue ISG) reporter cell lines, we evaluated the activation capacity of our different STING mRNA analogs on the STING/TBK1/IRF3 pathway. Increased secretion of IFN-β was confirmed via ELISA, and the expression of inflammatory cytokines downstream of the type I interferon and NF-κB signaling pathways was detected using qRT-PCR. To further validate efficacy, we tested our STING mRNA analog in syngeneic tumor models. Administration of our mRNA analog effectively suppressed tumor growth. Previous approaches utilizing STING agonist as anti-cancer immunotherapies have faced challenges including poor metabolic stability, inefficient cytosolic delivery, and reduced efficacy due to downregulated STING expression in human tumors. Here, we evaluated the anti-cancer potency of an mRNA-encoded constitutively-active STING analog. Our findings propose a novel strategy leveraging mRNA technology to overcome these limitations and robustly trigger STING-mediated anti-tumor immunity. Citation Format: Yong Ho Heo, Youngjin Han, Seung-Hyun Shin, Chang Gyu Lim, Ji Hee Lee, Hocheol Shin, Jooyun Byun, Daejin Kim, In Young Choi. Advancing immunotherapy with the development of a novel STING mRNA analog [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB038.