Abstract 1832: EphA2-dependent CD137 agonism and anti-tumor efficacy by BT7455, a Bicycle tumor-targeted immune cell agonist®

Abstract We have developed a new class of modular synthetic drugs, termed Bicycle® tumor-targeted immune cell agonists (Bicycle® TICAs), which are multi-specific molecules composed of constrained bicyclic peptides (Bicycles)1. The first molecule of this class, BT7480, a Nectin-4-dependent CD137 (4-1BB) agonist, entered clinical trials in 2021 in patients with solid tumors associated with Nectin-4 expression. Compelling preclinical data characterizing BT74802 led us to develop a second Bicycle TICA® molecule, BT7455, which is designed to deliver highly potent CD137 agonism to Ephrin receptor A2 (EphA2)-positive cancers. EphA2 is a receptor tyrosine kinase overexpressed in several human cancers and high expression correlates with poor clinical prognosis in certain cancer types3,4. BT7455 pharmacology was assessed in vitro using surface plasmon resonance, receptor occupancy assays, and PBMC/tumor cell co-culture bioactivity assays. BT7455 in vivo activity was evaluated in efficacy studies in syngeneic EphA2-positive mouse tumor models and pharmacodynamic studies using transcriptional profiling of the tumor immune microenvironment. BT7455 engages EphA2 and CD137 with high affinity resulting in potent EphA2-dependent production of interleukin-2 (IL-2) and interferon gamma (IFNγ) in human PBMC/tumor cell co-culture assays. Treatment of MC38 tumor bearing immunocompetent mice with BT7455 using an intermittent dosing regimen led to robust anti-tumor activity, including complete responses. Gene expression profiling of BT7455-treated tumors revealed modulation of the tumor immune microenvironment, including a rapid increase in cytokine expression (both myeloid and T cell origin) and an increase in cytotoxic cell scores. The kinetics and extent of the immune microenvironment modulation differentiated BT7455 from both a checkpoint inhibitor (anti-mouse PD-1) as well as an anti-CD137 agonist antibody (urelumab analogue). To pinpoint the cells responsible for the early bursts of cytokine and chemokine gene expression, we depleted CD8-positive T cells from the mice prior to CD137 Bicycle TICA® treatment. We found that the early increase in gene expression of distinct chemokines was not dependent on CD8-positive T cells. We have now turned to single-cell RNA sequencing of CD137 Bicycle TICA®-treated tumors to further probe the mechanistic underpinning of this novel finding. In summary, BT7455 is a highly potent EphA2-dependent CD137 agonist with optimal target binding, pharmacologic, and pharmacokinetic properties that enable intermittent dosing for curative effect through modulation of the tumor immune microenvironment in syngeneic mouse models. BT7455 is currently being evaluated in IND-enabling studies. 1Upadhyaya P, et al. JITC 2021; 9:e001762. 2Hurov K, et al. JITC 2021; 9:e002883. 3Campbell C, et al. Cancer Res 2020; 80:5300 4Xiao, et al. J Hematol Oncol 2020; 13:114. Citation Format: Lia Luus, Kristen Hurov, Johanna Lahdenranta, Chinmayee Shah, Anna Devlen, Julia Kristensson, Peter Brown, Cara Bray, Heather Cohen, Carly Campbell, Gemma Mudd, Punit Upadhyaya, Kevin McDonnell, Hongmei Xu, Phil Jeffrey, Philip E. Brandish, Nicholas Keen. EphA2-dependent CD137 agonism and anti-tumor efficacy by BT7455, a Bicycle tumor-targeted immune cell agonist® [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1832.