Abstract 4272: Potent in situ cancer immunotherapy with synthetic human STING-activating cyclic dinucleotides

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Spontaneous tumor-initiated T cell priming is dependent on IFN-β production by tumor-resident dendritic cells. Based on recent observations indicating that IFN-β expression was dependent upon activation of the host STING (Stimulator of Interferon Genes) pathway, we hypothesized that direct engagement of STING through intratumoral administration of specific agonists would result in effective anti-tumor therapy. To this end, we generated novel synthetic cyclic dinucleotide (CDN) derivatives with superior STING-activating and anti-tumor properties. The most potent molecule contains a 2′-5′ and 3′-5′ phosphate bridge that increases its affinity for STING at least 10-fold. Additionally, sulfur atoms at the non-bridging oxygens of the internucleotide phosphate bridge enable both superior STING binding affinity, as well as resistance to host cell phosphodiesterases. Importantly, the lead molecule activates PBMCs from a panel of human donors representing all known STING alleles, including homozygotes for the most refractory allele. Intratumoral injection of the lead CDN molecule induced profound regression of established B16 melanoma tumors, generated substantial systemic immune responses capable of rejecting distant metastases and provided long-lived immunologic memory. Cures in entire cohorts of mice bearing well-established 4T1 mammary and CT26 colon carcinoma models correlated with induction of cytokine-mediated innate and adaptive antigen-specific T cell immunity, both systemically and in the tumor microenvironment. Immune activation and anti-tumor efficacy was lost in mice encoding non-functional STING. In vivo activation of STING with the lead CDN administered by multiple routes demonstrated a high safety and tolerability margin in preclinical toxicology studies. In addition, pharmacokinetic analysis indicates that the lead CDN compound was rapidly cleared from systemic circulation, consistent with pulsatile STING activation and transient systemic cytokine and hematological changes. These results demonstrate that CDNs have high translation potential for treatment strategies to induce activation of the tumor microenvironment, leading to effective tumor-initiated T cell priming and anti-tumor immunity. Citation Format: Laura Hix Glickman, David B. Kanne, Kelsey E. Gauthier, George E. Katibah, Justin J. Leong, Ken Metchette, Thomas W. Dubensky, Sarah M. McWhirter. Potent in situ cancer immunotherapy with synthetic human STING-activating cyclic dinucleotides. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4272. doi:10.1158/1538-7445.AM2015-4272