The costimulatory immune receptor CD137 (4-1BB/TNFRSF9) has been recognized for its potential as a drug target in cancer alongside checkpoint inhibitors, but this promise has not been realized for patients due to toxicity (principally hepatic toxicity) and limited efficacy of current biologic based therapies [1,2]. Thus, alternative approaches to this important target are warranted. Next generation strategies are focused on bispecific approaches aimed at promoting target-mediated clustering of CD137 to limit systemic and liver toxicities [3-4]. Bicycles® are small, structurally constrained peptides discovered via phage display and optimized using structure-driven design and medicinal chemistry approaches. We have applied this disruptive technology to the problem, identifying CD137 Bicycles and chemically linking these to tumor antigen binding Bicycles to generate multifunctional “bispecific” like molecules that induce tumor antigen dependent, tumor localized agonism of CD137. We termed these Tumor-targeted Immune Cell Agonists (TICAs™). BT7480 is a TICA that was designed to deliver highly potent CD137 agonism to Nectin-4 overexpressing tumor tissue. Nectin-4 is expressed at high levels in bladder, breast, and lung tumors and at low levels in normal tissue and thus is an attractive target for localized immunotherapy. BT7480 binds potently to Nectin-4 expressing cells and engages CD137 expressed on immune cells in trans, leading to robust Nectin-4-dependent CD137 agonism in primary human PBMC/tumor cell co-culture assays. Treatment of Nectin-4 expressing tumors in immunocompetent mice with BT7480 induces complete tumor regressions and subsequent resistance to tumor re-challenge. Using flow cytometry, immunohistochemistry, and transcriptional profiling, we demonstrate that BT7480 treatment leads to profound reprogramming of the tumor immune microenvironment including increased T cell infiltration and upregulation of a cytotoxic cell gene signature. We also observed an increase in the macrophage cell score and interestingly, time course evaluation revealed a unique mechanism of action - rapid activation of myeloid cells (<24h) concomitant with a pulse of chemokine and cytokine secretion peaking at 2-3 days, leading to a dramatic infiltration of cytotoxic T cells on days 4-5. This is distinct from the reported clinical behavior of checkpoint inhibitors. In summary, BT7480 is a novel Nectin-4/CD137 TICA that represents a new generation of chemically synthetic tumor antigen targeted CD137 agonists and the compound is currently in preclinical development. 1. Segal NH, Logan TF, Hodi FS, et al. Clin Cancer Res. 2017;23(8):1929-1936. 2. Chester et al. Blood 2018;131(1): 49-57. 3. Hinner et al. Clin Cancer Res. 2019; 25(19): 5878-5889. 4. Claus C, Ferrara, C, Xu W, et al. Sci Transl Med. 2019; 11(496): eaav5989.

Citation Format: Kristen Hurov, Johanna Lahdenranta, Punit Upadhyaya, Drasti Kanakia, Elizabeth Repash, Fanglei You, Jun Ma, Eric Haines, Heather Cohen, Kevin McDonnell, Philip E. Brandish, Phil Jeffrey, Nicholas Keen. Nectin-4-dependent immune cell stimulation and anti-tumor efficacy by BT7480, a Nectin-4/CD137 Bicycle®tumor-targeted immune cell agonist (TICA™) [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 1728.