764 Characterization of RVU-27065 a novel small-molecule STING agonist suitable for systemic administration

Background

STimulator of INterferon Genes (STING) is a key signaling protein involved in activation of the immune system in response to self-DNA. In recent years, STING signaling has been demonstrated to play a major role in activating the antitumor immune response and therefore is considered an attractive drug target in immuno-oncology. The first wave of STING agonists, cyclic-dinucleotide analogues of the internal ligand cGAMP, were developed for local, intratumoral administration. Herein we present the most recent profiling results of our frontrunner molecule RVU-27065, a potent and selective systemic STING agonist with a favorable drug profile.

Methods

Binding to recombinant STING protein was examined using Fluorescence Thermal Shift and Fluorescence Polarisation. Primary activity screen was performed in THP-1 Dual reporter cells. Selectivity was confirmed in THP-1 reporter cells with knocked out STING or expressing STING variants. T cell viability and proliferation was assessed by flow cytometry using activated human T cells. PBMCs were isolated by density gradient from whole blood of healthy donors. Downstream STING pathway activation in cells treated with RVU-27065 was confirmed using Western blot analysis. BALB/c mice were inoculated with EMT6 tumor cells and the compound was administered intravenously followed by regular monitoring of tumor growth. Cured animals were rechallenged by repeated inoculation of EMT6 cells.

Results

RVU-27065 binds and strongly thermostabilizes recombinant STING proteins of all tested species. Binding to the protein results in activation of downstream signalling pathway, confirmed by western blot analysis. The agonist is characterized by selectivity and excellent potency in THP-1 dual reporter cells as well as in human PBMCs and dendritic cells. Short term incubation of RVU-27065 has no impact on T cell viability, activation or proliferation. Furthermore, STING activation with RVU-27065 leads to repolarization of immunosuppressive M2 macrophages into pro-inflammatory M1-like phenotype. In vivo efficacy of RVU-27065 was confirmed, leading to significant tumor growth inhibition and complete tumor regressions in an EMT6 mouse breast cancer syngeneic tumor model.

Conclusions

RVU-27065 is a novel representative of a 3rd generation of Ryvu STING agonists – small-molecule, non-macrocyclic molecules built around a unique chemotype. The compound is characterized by high in vitro potency which translates to efficacy in vivo in preclinical animal models. Drug-like properties, excellent selectivity and a good safety profile make RVU-27065 an attractive candidate for further development for standalone as well as targeted delivery, which holds high potential for improved immunotherapy in cancer patients.

Abstract 4983: Discovery and characterization of next-generation small molecule direct STING agonists

Accumulating evidence highlights an important role of type I interferon response in the immune surveillance mechanisms. IFNβ release by antigen-presenting cells promotes spontaneous anti-tumor CD8+ T cell priming being largely dependent on activation of Stimulator of Interferon Genes (STING). STING agonists promote regression of established tumors and generation of long-term immunologic memory in preclinical animal models. Herein we report the discovery of potent and selective, first-in-class non-nucleotide, non-macrocyclic, small molecule direct STING agonists with molecular weight below 500, structurally unrelated to known cyclic dinucleotide chemotypes with potential for systemic administration. Activation of STING pathway was monitored in THP-1 Dual reporter monocytic cell line as well as peripheral blood mononuclear cells (PBMC) or antigen presenting cells from human and mouse origin. Surface expression of the antigen-presenting cell maturation markers i.e. CD80, CD86, CD83 and HLA-DR was assessed by flow cytometry. Binding affinity was confirmed by three independent assays. RNA sequencing was performed on total RNA isolated from THP-1 cells and PBMC isolated from 2 healthy human donors. Direct binding to both mouse and human STING protein of Selvita agonists have been confirmed in biophysical binding assays (FTS, MST and FP) and by crystallography studies. The compounds have fine-tunable ADME properties with good solubility, permeability and human plasma stability. They selectively activates STING-dependent signaling in both THP-1 reporter assays and in primary cells of human and mouse origin. In addition, RNA sequencing data confirmed selectivity of the Selvita compounds. In vitro functional assays demonstrated their ability to induce cytokine responses (IFNβ, TNFα) in a panel of human peripheral blood mononuclear cell (PBMC), human monocyte derived macrophage (HMDM) and human dendritic cells samples with various STING haplotypes including refractory alleles. Additionally, the compounds efficiently induced cytokine release in mouse bone marrow-derived macrophages and dendritic cells. Pro-inflammatory cytokine profile was accompanied by up-regulation of the maturation markers, i.e. CD80, CD86, CD83 and HLA-DR, on the surface of human antigen presenting cells. These data demonstrate potent, novel, next-generation small molecule STING agonists activating STING-dependent signaling in both mouse and human immune cells to promote potential antitumor immunity. The compounds show good selectivity and in vitro ADME properties enabling further development for systemic administration as a single agent or in combinatory immunotherapies for cancer treatment.

Citation Format: Monika Dobrzańska, Stefan Chmielewski, Magdalena Zawadzka, Jolanta Mazurek, Karolina Gluza, Katarzyna Wójcik-Jaszczyńska, Maciej Kujawa, Grzegorz Topolnicki, Grzegorz Ćwiertnia, Aleksandra Poczkaj, Izabela Dolata, Magdalena Mroczkowska, Agnieszka Gibas, Marcin Leś, Sylwia Sudoł, Adam Radzimierski, Kinga Michalik, Magdalena Sieprawska-Lupa, Katarzyna Banaszak, Katarzyna Wiklik, Federico Malusa, Michał Combik, Karolina Wiatrowska, Agnieszka Adamus, Lukasz Dudek, Jose Alvarez, Charles Fabritius, Anna Rajda, Maciej Rogacki, Faustyna Gajdosz, Peter Littlewood, Luigi Stasi, Krzysztof Brzózka. Discovery and characterization of next-generation small molecule direct STING agonists [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4983.