Abstract 3269: Discovery and characterization of E7766, a novel macrocycle-bridged STING agonist with pan-genotypic and potent antitumor activity through intravesical and intratumoral administration

Introduction: We report discovery and characterization of E7766, a structurally novel STING agonist, as a potential immunotherapy for solid cancers through intratumoral (IT) administration and for Bacillus Calmette-Guerin (BCG) unresponsive non-muscle invasive bladder cancer (NMIBC) through intravesical (VE) administration. Methods: E7766 was designed and synthesized to optimize the potency of binding to dimerized STING proteins of different genetic isoforms. The compound was extensively and comparatively characterized in a variety of biochemical, molecular and cellular, in vivo, ex vivo, and primary human tumor and cellular studies for potency, mechanisms and translational biomarkers. Novel preclinical models to mimic orthotopic NMIBC and deep lesion metastasis were developed, and co-crystalization with recombinant proteins of genetic variations was performed. Results: E7766, a novel Macrocycle-Bridged STING Agonist, showed highly specific and potent agonist activity in both human and mouse STING. In human PBMCs, E7766 demonstrated potent and consistent activity across seven tested human STING genotypes (IC50, 0.15-0.79 μM). By contrast, a reference cyclic dinucleotide STING agonist showed weaker potency and substantial variability across genotypes (IC50, 1.88 μM - >50 μM). Co-crystal structures indicated a structural basis for the superior interactions of E7766 with STING proteins compared with conventional cyclic dinucleotide STING agonists. Intravesical administration of E7766 to a preclinical orthotopic mouse bladder cancer model mimicking the BCG-unresponsive NMIBC demonstrated a dose-dependent and curative activity without serious adverse effects. The anti-tumoral activity was associated with a robust induction of IFNβ, CXCL10 and other downstream effectors of STING pathway inside the bladder cavity. In addition, single IT administration of E7766 to a subcutaneous (SC) tumor in mice bearing dual CT26 tumors in liver and SC lesion cured 90% of animals without recurrence for over 8 months. Those tumor-free animals rejected re-challenge of the same tumor cells in the absence of CD8+ T cells or NK cells, indicating the presence of a highly effective immune memory response following treatment with E7766 independent of either cell population alone. Conclusions: E7766 is a structurally novel and highly potent STING agonist with pan-genotypic activity, demonstrating curative anti-tumoral activity in murine models of BCG-unresponsive NMIBC and of metastatic tumors in deep lesions. Clinical investigation of E7766 is under discussion. Citation Format: Kuan-Chun Huang, Atsushi Endo, Shannon McGrath, Dinesh Chandra, Jiayi Wu, Dae-Shik Kim, Diana Albu, Christy Ingersoll, Karen Tendyke, Kara Loiacono, Thomas Noland, David Verbel, Chi Zhang, Ming-Hong Hao, Mark Matijevic, Vaishali Dixit, Renee R. Hukkanen, Janna Hutz, John Wang, Frank Fang, Xingfeng Bao, Donna Kolber-Simonds, Muzaffar Akram, Nadeem Sarwar. Discovery and characterization of E7766, a novel macrocycle-bridged STING agonist with pan-genotypic and potent antitumor activity through intravesical and intratumoral administration [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 3269.