Background: Agonists of the Stimulator of Interferon Genes (STING) pathway have great potential in cancer immunotherapy. Activation of STING in tumor cells and/or antigen-presenting cells (APCs) can induce type I Interferon production leading to the induction of innate and adaptive immune response. We recently reported the discovery of the cyclic dinucleotide SB 11285 as a potent, first-in-class, STING agonist. Herein, we report that SB 11312, a metabolite of SB 11285, is also a potent antitumor agent in vitro and in vivo.
Methods: (a) Synthesis: SB 11312 was synthesized by solution-phase standard phosphoramidite chemistry. (b) Binding affinity: Differential scanning fluorimetry was used to determine binding affinity of SB 11312 to all STING variants, with 2′3′-cGAMP being used as a positive control. (c) Induction of IRF and NF-KB: THP-1 cells carrying the respective reporter constructs were treated with SB 11312 or controls for 22hrs and induction of IRF and NF-KB was calculated as % fold-change in luminescence compared to vehicle-treated cells. (d) Induction of cytokines: PBMCs and mBMDCs were treated with SB 11312 at different doses, and cell supernatants were analyzed for cytokines by multiplexing assays. (e) In vivo studies: Dose-ranging studies of SB 11312 were performed using i.t. (10 to 100μg, days 1,2,4,6,8), and i.v. (3 to 6mg/kg, days 1,3,5,8) routes in the CT26 syngeneic mouse tumor model. (f) Pharmacodynamic studies: Following i.v. administration of SB 11312 at 3 mg/kg in the CT26 model, flow cytometry and multiplexing assays of blood, spleen and tumor tissues were carried out. Results: (i) SB 11312 demonstrated high binding affinity to human wild-type and STING polymorphic variants, as well as mouse STING. (ii) SB 11312 showed potent induction of (a) STING-dependent IRF and NF-KB signaling induction in wild-type and human STING variants as well as RAW macrophages, (b) secretion of cytokines associated with type I interferon signature in PBMCs and mBMDCs, and (c) interferon stimulated genes (ISGs) in PBMCs, mBMDCs and THP1 cells. In the A20 lymphoma and CT26 colon carcinoma syngeneic mouse models, SB 11312 showed potent antitumor activity when administered by intravenous (i.v.) and intratumoral (i.t.) routes. In PD study, cytokine analysis showed induction of type I interferon signature without significant systemic inflammatory response.
Conclusion: SB 11312, an active metabolite of SB 11285 showed excellent safety and antitumor activity in syngeneic mouse models administered by multiple routes. The mechanism of action of SB 11312 was shown to be STING-dependent that is associated with activation of IRF and NF-KB signaling, induction of type I IFN signature and ISGs. SB 11312 is being advanced for additional studies for application in immuno-oncology.
Citation Format: Sreerupa Challa, Leena Suppiah, Diane Schmidt, Dillon Cleary, Shenghua Zhou, Vishal Nair, Kris Iyer. SB 11312, an active metabolite of SB 11285, is a potent and systemically bioavailable STING agonist [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B88.