Abstract 6026: HX016-9, a novel PD1xVEGF BsAb, as a new candidate treatment of solid tumors

Abstract With the clinical confirmation of the superior efficacy of AK112, a first-in-class (FIC) PD1xVEGF bispecific antibody (BsAb), in the treatment of NSLCL cancers, over the PD1 monoclonal antibody (mAb), as shown in a head-to-head phase III trial, we set out to engineer a novel and potentially best-in-class (BIC) PD1xVEGF BsAb using a unique PD1 (HX008, an approved PD1-mAb) and a novel VEGF (HX006, a mAb with more favor activity over Avastin) mAb sequences. HX016-9 has 2+2 IgG1 symmetric structure which was constructed by grafting the PD1 binding domain of HX008 onto the N-terminus of HX006. HX016-9 binds PD1 recombinant protein with EC50 of 0.13nM (vs. 0.1nM by HX008) and to VEGF recombinant protein with EC50 of 0.097nM (vs. 0.042 by HX006) in ELISA assay. It also binds similarly to the PD1+ cell line as HX008 with slightly reduced affinity. A reporter bioassay for PD1 function demonstrated that HX016-9 has EC50 of 3.2nM (vs. 1.0nM for HX008), while a reporter- bioassay for the VEGF function demonstrated that HX016-9 has EC50 of 12.6nM (vs. 11.4nM for HX006), confirming HX016-9 designed function in vitro. Interestingly, HX016-9 demonstrated enhanced reporter activity (up to 5x) in the presence of VEGF than those without, while in contrast, no enhancement for HX008 in the presence of VEGF, similarly as reported for the FIC molecule previously. This enhancement could possibly be interpreted by the formation of the VEGF-HX016-9 complex, thus it facilitating efficient cis-binding to these PD1+ cells and higher avidity binding. This further implicates the enhanced PD1 blocking by HX-016-9 in these cells when VEGF presents. In the huPD1-C57/B6-based HuGEMM mouse, HX016 was shown to have stronger anti-tumor activity over the HX008 and HX006 in huPD-L1/huVEGF-MC38 CRC syngeneic CRC tumor, which can be attributed to both PD1- and VEGF-targeting. In a xenograft A549 NSCLC tumor in immunocompromised mice, HX016-9 also caused anti-tumor activity that can be attributed to anti-VEGF function. These activities are comparable or superior to those of the FIC molecule, warranting the HX016-9 candidacy to move into IND-enabling evaluation and further clinical development. Citation Format: Hang Ke, Tao Yang, Feiyu Peng, Jialing Li, Cen Chen, Lei Zhang, Stephen Xiong, Faming Zhang, Henry Qixiang Li. HX016-9, a novel PD1xVEGF BsAb, as a new candidate treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6026.