Background PD-1/PD-L1 inhibition immunotherapy holds great promise in cancer treatment. Combination treatment using anti-PD-1/PD-L1 agents with other immunotherapeutics brings additional benefits, such as preventing refractory effects towards PD-1/PD-L1 antibodies, and improving anti-tumor activities. Vascular endothelial growth factor (VEGF) is found to be frequently overexpressed in various solid tumors, which not only promotes tumor angiogenesis but also functions to suppress anti-tumor immune response.1, 2 Consequently, a novel anti-PD-1/VEGF bispecific antibody (AK112) was designed to inhibit PD-1-mediated immunosuppression and simultaneously block tumor angiogenesis in the tumor microenvironment (TME). The tetravalent structure of AK112 allows formation of large complexes with dimeric VEGF, resulting in improved avidity to PD-1 and functional activities, which elicits potent anti-tumor efficacy in pre-clinical studies.
Methods The antigen binding activity of AK112 with PD-1 and VEGF were assessed by ELISA, Fortebio and flow cytometry. The formation of AK112-VEGF complexes was detected by size-exclusion high-pressure liquid chromatography (SEC-HPLC). To determine if VEGF could enhance the avidity of AK112 to PD-1, the binding activity of AK112 with PD-1 was evaluated by Fortebio and flow cytometry in the presence of VEGF. The blockade of PD-1/PD-L1 signaling pathway was determined in luciferase reporter cell assay. The PD-1 internalization was determined by flow cytometry. In in-vivo pharmacology studies, the anti-tumor activity of AK112 was investigated in SCID/Beige mice implanted with HCC827 cells.
Results AK112 could specifically bind to human PD-1 and VEGF with high affinity (table 1). Intriguingly, AK112 was found to form soluble complexes with VEGF by SEC-HPLC assay (figure 1). Notably, VEGF efficiently enhanced the binding of AK112 to PD-1 (table 2, figure 2), which led to increased PD-1 internalization (figure 3) and better potency on blockade of PD-1/PD-L1 signaling (figure 4). Moreover, AK112 demonstrated greater anti-tumor efficacy compared to Bevacizumab in mice (figure 5).
Conclusions AK112, a dual-blocking anti-PD-1/VEGF bispecific antibody, shows improved avidity to PD-1 in the presence of VEGF, and displays great anti-tumor efficacy in a mouse tumor model, supporting its clinical development for the treatment of human cancers.
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