A new generation of both systemic and targeted CD137 agonists are entering clinical development following agonistic anti-CD137 (4-1BB) antibody development nearly a decade ago. However, each of these molecules rely on biologic agents with potentially suboptimal properties for CD137 agonism due to their relatively large size and long circulating half-lives which may limit their tissue penetration, cause sustained agonism resulting in overstimulation and activation-induced lymphocyte cell death. Fully synthetic constrained bicyclic peptides (Bicycles™) with antibody-like affinities and target selectivity are uniquely suited to circumvent limitations of other targeted CD137 agonistic therapeutics. BT7480 and BCY11864 are tumor targeted immune cell agonists (TICA) designed to deliver a highly potent CD137 agonist to Nectin-4 overexpressing tumors with a flexible dosing schedule maximizing anti-tumor activity while circumventing the need for continuous systemic exposure. The Comparative In Vivo Oncology (CIVO) platform has been developed to enable in situ investigation of multiple microdosed drugs simultaneously in human tumors with safety and feasibility of this platform recently demonstrated in patients with soft tissue sarcomas. CIVO percutaneously injects drug microdoses directly into tumor tissue as trackable columns where tissue can be analyzed after resection for the effect of the drug treatment in the tumor. Here we report on an evaluation of the feasibility of using the CIVO -platform to demonstrate the mechanism of action of our tumor target-dependent CD137 agonist TICAs. Both BT7480 and BCY11864 demonstrate extremely potent Nectin-4-dependent CD137 agonism in primary human PBMC/tumor cell co-culture assays. Systemic administration of BT7480 in Nectin-4 expressing tumors in immunocompetent mice leads to profound reprogramming of the tumor immune microenvironment including a rapid increase in T cell chemotactic cytokine transcripts and macrophage gene signatures followed by an increase in cytotoxic cell gene signature and increase in intratumoral CD8+ T cells. CIVO was used to demonstrate the in vivo mechanism of action of a Nectin-4/CD137 TICA. Micro-injection of BCY11864 into Nectin-4 expressing tumors in immunocompetent mice led to dose dependent induction of immune activation markers in the tumor microenvironment and activation of the tumor resident cytotoxic T cells was evident 24 hours after BCY11864 micro-injection. Akin to our findings with transcriptional profiling of the tumor response to BT7480, BCY11864 activity was shown not to be limited to T cells but also included other CD137 positive cell populations such as myeloid and NK cells. We hypothesize that tumor targeted CD137 agonism may lead to initial myeloid cell response that enhances the cytotoxic T cell recruitment and activation in the tumor tissue.

Citation Format: Johanna Lahdenranta, Stephen J. Blakemore, Kristen Hurov, Marc O. Grenley, Punit Upadhyaya, Carly Campbell, Elizabeth Repash, Eric Haines, Philip E. Brandish, Richard A. Klinghoffer, Nicholas Keen. Microinjection of Nectin-4/CD137 tumor-targeted immune cell agonist (TICA™) activates the local tumor microenvironment [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 1724.