Abstract 5301: Tumor-targeted activation of CD137 using Bicycles: New insights into mechanism of action and discovery of BT7455, a clinical candidate for the treatment of EphA2-expressing cancers

Abstract Introduction: Clinical studies in cancer patients have validated CD137 agonism as an activator of the immune system to enable tumor rejection. We have demonstrated that small, chemically synthetic bicyclic peptides can drive tumor-localized agonism of CD137 and anti-tumor immunity in mouse models. Here, we report the next stage of our work - delving into the mechanism of action of these novel agents and extending our program to serve patients whose tumors express EphA2. Experimental Procedures: MultiOmyx™ hyperplexed immunofluorescence assay was used to evaluate the expression of CD137 and EphA2 in head and neck squamous cell carcinoma samples. Human PBMC/tumor cell co-culture assays were used to assess CD137 Bicycle TICA™ in vitro bioactivity and syngeneic mouse tumor models were used to evaluate CD137 Bicycle TICA anti-tumor activity as mono- or combination therapies. Pharmacodynamic activity was evaluated by transcriptional profiling using NanoString assays or single cell RNA sequencing. Summary of the Data: Studies utilizing a syngeneic mouse model and deep RNA sequencing of tumors from CD137 Bicycle TICA-treated mice implicated intratumoral dendritic cells in addition to T cells as early responders to localized CD137 agonism and potential contributors to the anti-tumor response. Furthermore, a mouse efficacy model demonstrated synergy with checkpoint inhibitor therapy. Multiplex imaging revealed that EphA2 and CD137 are co-expressed in human tumors of high unmet medical need and therefore, using our highly modular Bicycle platform, we discovered BT7455, a Bicycle TICA that engages EphA2 and CD137 with high affinity, resulting in potent EphA2-dependent activity in vitro and robust anti-tumor activity in vivo with intermittent dosing in mouse models. Gene expression profiling of tumors revealed that BT7455 led to increased production of cytokines and chemokines known to drive T cell infiltration, the extent of which differentiated it from both a checkpoint inhibitor and an anti-CD137 monoclonal antibody agonist. BT7455 was well tolerated in preclinical species and liver function tests indicated no evidence of hepatic toxicity. Statement of Conclusions: In summary, we have identified EphA2 as a promising target to pair with a CD137 agonist. In addition to CD8+ T cells, tumor-resident dendritic cells are a likely contributor to anti-tumor immunity following treatment with Bicycle® TICAs, supporting utility for Bicycle® tumor-targeted CD137 agonists in solid tumors beyond those that are highly T cell-infiltrated. We have advanced a clinical development candidate, BT7455, to realize this potential for patients with EphA2-expressing cancers. Citation Format: Johanna Lahdenranta, Kristen Hurov, Heather Cohen, Lia Luus, Cara Bray, Peter Brown, Anna Devlen, Carly Campbell, Matthew Gray, Mike Kelly, Gemma Mudd, Punit Upadhyaya, Sailaja Battula, Kelvin Zhang, Anne-Sophie Dugast, Kevin McDonnell, Phil Brandish, Nicholas Keen. Tumor-targeted activation of CD137 using Bicycles: New insights into mechanism of action and discovery of BT7455, a clinical candidate for the treatment of EphA2-expressing cancers abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5301.