Abstract B123: Mechanism of action of ivonescimab (AK112/SMT112): a first-in-class tetravalent Fc-silent bispecific antibody with dual blockade of PD-1 and VEGF that promotes cooperative biological effects

Abstract Background: Combination treatments using anti-PD-1/PD-L1 antibodies with other VEGF antagonists have shown enhanced clinical antitumor activities1. The expression of PD-1 and VEGF are found to be frequently upregulated and co-expressed in solid tumors. Importantly, VEGF promotes tumor angiogenesis and suppresses antitumor immune response2,3. Consequently, we characterized the mechanism-of-action of a novel first-in-class anti-PD-1/VEGF bispecific antibody, ivonescimab, designed to simultaneously inhibit PD-1-mediated immunosuppression and block tumor angiogenesis in the tumor microenvironment. Methods: Binding activity of ivonescimab to PD-1/VEGF were assessed by ELISA. Blockade of PD-1/VEGF signaling pathways was determined in luciferase reporter cell assays. Ivonescimab-VEGF complex formation was detected by SEC-HPLC. Cooperative binding of ivonescimab-VEGF complex to PD-1 or ivonescimab-PD-1 complex to VEGF was measured by Octet BLI. The enhanced PD-1 blockade bioactivity of ivonescimab with VEGF was evaluated in hPBMC and engineered cell-line co-culture/luciferase-reporter cell assays. Antitumor activity of ivonescimab was investigated in hPBMC-humanized SCID/Beige mice implanted with HCC827 (mEGFR lung adenocarcinoma) or U87MG (glioblastoma). Immuno-safety was assessed by FcγR binding, ADCC, ADCP assays, and reported clinical irAEs. Results: Ivonescimab displayed strong binding activity to human PD-1 and VEGF alone or simultaneously, effectively blocking interactions with ligands and the downstream signaling effects. In presence of VEGF, ivonescimab forms soluble complexes with VEGF dimers, leading to over 10-fold enhanced binding affinity (KD) of ivonescimab to PD-1. The avidity increase was consistent with reduced cell surface PD-1 expression on human T-cell lines, increased potency on blockade of PD-1/PD-L1 signaling and subsequent enhanced T cell activation in-vitro. Likewise, PD-1 binding enhanced ivonescimab binding to VEGF which was associated with enhanced VEGF-signaling blockade. Also, ivonescimab treatment demonstrated statistically significant dose-dependent antitumor response in hPBMC-humanized murine HCC827 and U87MG tumor models. Additionally, ivonescimab enhanced antitumor response in combination with anti-CD47 (AK117) or anti-CD73 (AK119) in mouse models. Finally, ivonescimab contains Fc-silencing mutations abrogating FcγRI/IIIa binding and showed significantly reduced ADCC, ADCP activities and cytokine release in-vitro. Clinically, this is consistent with the safety profile in Phase 1/2 studies of ivonescimab in advanced solid tumors4,5. Conclusions: Ivonescimab is a novel tetravalent anti-PD-1/VEGF bispecific antibody displaying unique cooperative binding to each of its intended targets consistent with increased in-vitro functional bioactivities compared with bevacizumab or PD-1 inhibitors alone. Importantly, the Fc-null IgG1 design resulted in reduced FcgR interactions and minimal ADCC, ADCP activities consistent with its clinical immunosafety profile. Ivonescimab is currently in Ph3 NSCLC trials in the US and EU. Citation Format: Tingting Zhong, Zhaoliang Huang, Xinghua Pang, Chunshan Jin, Xinrong He, Jose G Montoya, Betty Y Chang, Michelle Xia, Baiyong Li, Jing Min. Mechanism of action of ivonescimab (AK112/SMT112): a first-in-class tetravalent Fc-silent bispecific antibody with dual blockade of PD-1 and VEGF that promotes cooperative biological effects [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B123.