Abstract B75: Nanoparticle formulation of the STING agonist SB 11285
Authors: Challa Sreerupa , Suppiah Leena , Cleary Dillon , Sheri Anjaneyulu , Gimi Rayomand , Meher Geeta , Padmanabhan Seetharamaiyer , Shah Sumit , Bhatt Pranav , Tauro Jovita , Iyer Radhakrishnan 
Published: March 2020

Background: Immunotherapy has emerged as a transformative approach for the treatment of cancer. Recent evidence suggests that the activation of Stimulator of Interferon Genes (STING) pathway in immune calls within the tumor microenvironment (TME) can induce the production of Interferons and cytokines that would lead to the induction of innate and adaptive immunity. We have previously disclosed the discovery and development of SB 11285 as a first-in-class synthetic cyclic dinucleotide STING agonist, which has demonstrated potent antitumor activity, when used alone or combined with other antitumor agents, in several syngeneic mouse and rat tumor models when administered by intratumoral, intravenous, or intraperitoneal routes. Presented here is the development of a controlled-release nanoparticle formulation of SB 11285 for subcutaneous administration.

Methods: (a) Nanoparticle formulations of SB 11285. SB 11285-NPs were generated using Polylactic-glycolic acid copolymer (PLGA) using double emulsion and nano-precipitation methods (b) Imaging of nanoparticles: Scanning electron microscopy was performed to visualize and measure size of the nanoparticles. (c) Induction of IRF3 and NF-KB. THP-1 cells and RAW macrophages carrying dual reporter constructs were treated with either SB 11285-NPs or naked SB 11285 for 22hrs and induction of IRF3 and NF-KB was calculated as % fold-change in luminescence compared to vehicle-treated cells. (d) Induction of cytokines: PBMCs were treated with different concentrations of 11285-NPs or naked SB 11285, and cell supernatants were analyzed for IFN-β, TNF-α, and RANTES by ELISA. (e) Dendritic cell maturation assay: PBMCs were differentiated into immature dendritic cells by addition of IL4 and GM-CSF followed by treatment with either SB 11285-NP or naked SB 11285. The maturation of dendritic cells was then evaluated by analyzing expression of CD83 and CD86 by flow cytometry.

Results: PLGA formulations of SB 11285 prepared by double-emulsion method with an entrapment efficiency of 30 to 40% were spherical particles with an average diameter of 800nm. The nanoparticles were stable in aqueous media with minimal release of the entrapped SB 11285. In cell-culture studies, SB 11285-NPs showed potent induction of: (a) STING-dependent IRF3 induction in THP-1 cells (EC50: 3nM) as well as RAW macrophages (EC50: 3nM); (b) secretion of IFN-β (35 pg/ml), TNF-α (800 pg/ml), and RANTES (200 pg/ml), when tested at a low concentration of 112nM; and (c) SB 11285-NPs effectively induced DC maturation that was evident by increase in CD83 and CD86 expression.

Conclusion: PLGA nanoparticles of SB 11285 were successfully prepared with submicron particle size that demonstrated potent expression of STING-dependent Type I IFN and cytokines in immune cells. The nanoparticles also induced maturation of dendritic cells. In vivo evaluation is in progress.

Citation Format: Sreerupa Challa, Leena Suppiah, Dillon Cleary, Anjaneyulu Sheri, Rayomand Gimi, Geeta Meher, Seetharamaiyer Padmanabhan, Sumit Shah, Pranav Bhatt, Jovita Tauro, Radhakrishnan Iyer. Nanoparticle formulation of the STING agonist SB 11285 [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B75.