LAUSR

Background: CD137 (TNFRSF9, 4-1BB) is a member of the tumor necrosis factor receptor superfamily that functions as a costimulatory molecule of immunocytes and is mainly expressed on the surface of immune cells including activated T and natural killer (NK) cells. Agonists against CD137 have shown promising therapeutic activity in mouse tumor models but have suffered setback in the clinic due to notably hepatotoxicity, or suboptimal agonistic potency. Here, we developed a fully human agonistic anti-CD137 monoclonal IgG4 antibody, ZG033, with an exclusive epitope, to achieve a better efficacy and safety profile for immunotherapy. Methods: The antigen binding specificity and affinity of ZG033 were determined by ELISA, surface plasmon resonance (SPR). X-ray crystallography was conducted to resolve the binding epitopes of the respective binding arms. The activities were determined using cell-based and reporter gene assays. In vivo antitumor activities were evaluated in human 4-1BB transgenic mice bearing with syngeneic tumors, and possible toxicity was evaluated in humanized mice and cynomolgus monkeys. Cytokine release assay was conducted by incubating ZG033 with PBMCs from healthy donors. The pharmacokinetic (PK) behavior of ZG033 were characterized in cynomolgus monkeys. A phase 1 study was initiated to evaluate the safety and preliminary clinical activities of ZG033, as well as the immunogenicity and pharmacokinetics. Results: ZG033 showed high specificity for human CD137 without cross-species reactivity across mouse, rat and exhibited potent CD137 agonist activity dependent on FcγR crosslinking. The binding affinity of ZG033 determined by surface plasmon resonance (SPR) was moderate (KD=10 nM). X-ray crystallography revealed that the Fab of ZG033 binds CD137 at an epitope overlap with the ligand binding interface. ZG033 increased CD137-driven NFκB reporter gene activation and the production of IFN-γ by human T cells in a FcγR-dependent manner. In human CD137 transgenic mice, ZG033 showed robust antitumor activity and induced durable antigen-specific immunological memory that prevented the tumor formation in the rechallenged mice. There were no signs of toxicity in human cytokine release assay which confirmed that ZG033 did not induce pro-inflammatory cytokines in the absence of TCR stimulation. Toxicology data in mice showed that ZG033 was well-tolerated with normal ALT and AST levels. ZG033 was further confirmed to well tolerated up to 180 mg/kg (MTD≥180mg/kg) dose without systemic toxicity in cynomolgus monkeys. Patients with advanced tumors, who are refractory after exhausting available therapies, were enrolled for ZG033 treatment. We will report the results from early dose escalation part of the study. Conclusion: These data demonstrate that ZG033 is an FcγR crosslinking-dependent CD137 agonist that displays a favorable safety profile and has potential in either mono- or combinational immunotherapies. Citation Format: Yang Huang, Liangwei Li, Wenting Liu, Dayan Zhang, Pengfei Zhou, Qing Fang, Weiming Zhou, Fengrong Wang, Guodong Shen, Liansheng Cheng. A novel CD137 agonist exhibits potent antitumor efficacy with a good safety profile [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 1880.