Costimulatory molecules expressed on activated T and NK cells such as 4-1BB (CD137/TNFRSF9) can be leveraged for cancer immunotherapy. Despite compelling preclinical data, 4-1BB agonistic antibodies have been hampered by failure to delineate hepatoxicity from efficacy in the clinic [1,2]. Next generation strategies are focused on bispecific approaches aimed at promoting target-mediated clustering of 4-1BB to limit systemic and liver effects [3,4]. Bicycles® are fully synthetic, constrained bicyclic peptides that have antibody-like affinity and selectivity to their targets. Unlike traditional biologic approaches, the small size (~2 kDa) and tunable pharmacokinetic (PK) parameters of Bicycles enable superior tumor penetration and allow exploration into the relationship between pulsatile dosing and 4-1BB activation while de-risking hepatoxicity concerns due to a differentiated renal elimination mechanism combined with a tumor-localized immune response. We hypothesized that clustering and activation of 4-1BB could be achieved by conjugating a 4-1BB binding Bicycle to a tumor antigen targeting Bicycle. BT7480 is a tumor-targeted immune cell agonist (TICATM) targeting Nectin-4 and agonizing 4-1BB. Nectin-4 (PVRL4) is highly expressed on numerous tumors with unmet medical need, including bladder, pancreatic, breast, ovarian, esophageal, and lung. BT7480 exhibits highly potent 4-1BB agonism in an engineered 4-1BB reporter system that correlates with Nectin-4 surface expression on the co-cultured tumor cells. In addition, BT7480 induces robust production of interleukin-2 (IL-2) and interferon gamma (IFNγ) in primary PBMC/tumor cell co-culture assays. This activity is strictly dependent on the tumor cells expressing Nectin-4 and on the ability of the TICA to bind to both Nectin-4 and 4-1BB. Nectin-4/4-1BB TICAs are also target-specific immune cell stimulators of patient-derived lung tumors with an intact immune microenvironment. Intermittent dosing of BT7480 led to robust anti-tumor efficacy with 22 out of 24 complete responders (CRs) in a MC38 (Nectin-4-expressing) syngeneic mouse model. Importantly, a memory response was established as the CR mice were resistant to re-challenge with MC38 tumors. Additionally, BT7480 led to increased intratumoral T cell infiltration without elevation of liver enzymes in a CT26 (Nectin-4-expressing) syngeneic mouse model. In non-human primates (NHPs), BT7480 exhibits dose linear exposure and is well tolerated up to 10mpk. Further dose-range finding and safety analysis in NHPs is currently ongoing. BT7480 represents a new generation of chemically synthetic tumor antigen targeted 4-1BB agonists. References 1. Segal NH, Logan TF, Hodi FS, et al. Results from an integrated safety analysis of urelumab, an agonist anti-CD137 monoclonal antibody. Clin Cancer Res. 2017;23(8):1929-1936. 2. Chester et al. Immunotherapy targeting 4-1BB: mechanistic rationale, clinical results, and future strategies. Blood 2018;131(1): 49-57. 3. Hinner et al. Tumor-localized costimulatory T-cell engagement by the 4-1BB/HER2 bispecific antibody-anticalin fusion PRS-343. Clin Cancer Res. 2019; 25(19): 5878-5889. 4. Claus C, Ferrara, C, Xu W, et al. Tumor-targeted 4-1BB agonists for combination with T cell bispecific antibodies as off-the-shelf therapy. Sci Transl Med. 2019; 11(496): eaav5989.

Citation Format: Kristen Hurov, Punit Upadhyaya, Johanna Lahdenranta, Jessica Kublin, Jun Ma, Elizabeth Repash, Marianna Kleyman, Julia Kristensson, Liuhong Chen, Eric Haines, Sailaja Battula, Kevin McDonnell, Nicholas Keen. BT7480, a novel fully synthetic tumor-targeted immune cell agonist (TICATM) induces tumor localized 4-1BB agonism [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5552.