Abstract 524: The novel STING agonist VB-85247 induces robust durable antitumor immune responses by intravesical administration in a non-muscle invasive bladder cancer model

Abstract

Abstract Introduction: Bacillus Calmette-Guerin (BCG) unresponsive non-muscle invasive bladder cancer (NMIBC) patients are in great need of effective immunotherapies. STING (Stimulator of Interferon Genes) plays a central role in mounting innate and adaptive immune responses to tumor cells. Activation of the STING pathway leads to the induction of inflammatory cytokines (IFN-α/β, TNF-α, IL-6 and CXCL10), maturation and activation of dendritic cells (DC), and induction of anti-tumor T cells. Our group has developed a novel STING agonist, VB-85247. Here we use a murine NMIBC model to report the potent antitumor effect of VB-85247 compared to standard of care BCG and anti-PD1 checkpoint inhibitor therapy currently used in the management of NMIBC. Methods: We developed a mouse model of Non-Muscle Invasive Bladder Cancer (NMIBC) utilizing orthotopically implanted MB49-Luc cells, permitting BLI (Bioluminescence) measurement of tumor growth by In Vivo Imaging Systems (IVIS). Results: VB-85247 was found to bind to mouse STING and all major variants of human STING protein. VB-85247 induced high levels of IFN-β and other cytokines across cells from different species, including primary human bladder epithelial cells. VB-85247 treatment by intravesical instillation in the mouse model of NMIBC resulted in dose dependent tumor regression starting after the first treatment, achieving up to a 100% complete response rate at the 40 µg dose level after 5 weekly treatments. The treatment was well tolerated, eliciting strong and durable anti-tumor immune responses without any mortality. All cured mice rejected a re-challenge with MB49-Luc cells with no further treatment, demonstrating long-lasting anti-tumor immunity. By contrast, BCG treatment in the same model was not efficacious. Combination with anti-PD1 treatment reduced the dose of VB-85247 needed to achieve 100% complete responses to 20 µg, whereas anti-PD1 treatment alone resulted in only 25% complete responses. In addition, a single dose of 40 µg VB-85247 by bladder instillation in the NMIBC model induced systemic immune responses including serum cytokines demonstrating Type I IFN responses plus DC mobilization and activation in the blood, draining lymph nodes, and spleen within 24 hours. Conclusions: The STING agonist VB-85247 was well tolerated and displayed robust efficacy by bladder instillation in a mouse orthotopic tumor model of NMIBC, achieving up to 100% complete responses. All cured mice rejected fresh inoculations of tumor cells with no further treatment, demonstrating induction of immunologic memory. Treatment with BCG was not efficacious in the model. These results suggest the potential utility of the VB-85247 STING agonist in the treatment of BCG unresponsive NMIBC patients. Based on these data, VB-85247 is being advanced to clinical development. Citation Format: Miglena Prabagar, Venu Bommireddy, Rachael Siegel, Haihua Zheng, Lee Pellegrino, Stanley Nawoschik, Albert Uveges, Steven Paget, Ku Lu, Krista Saufler, Axel Metzger, David Diller, Jason Trama, Grant Gallagher, Chia-Yu Huang, Brian McGuinness, James R. Beasley, Michael McQueney, Martin Adelson, Gary L. Schieven, Eli Mordechai, Rukiye-Nazan Eraslan. The novel STING agonist VB-85247 induces robust durable antitumor immune responses by intravesical administration in a non-muscle invasive bladder cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 524.