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ZGGS18 is a bifunctional fusion protein targeting both human vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β), which consist of a monoclonal antibody against VEGF and an engineered extracellular domain of TGF-β receptor II (TGF-βRII ECD). In vitro studies show ZGGS18 specifically and simultaneously binding towards various VEGFs and capturing different TGF-β isoforms by trap domains that play a synergistic role to block signaling of VEGF/TGF-β with their receptors. For instance, ZGGS18 inhibits human VEGF121 and 165 induced HUVEC proliferation; ZGGS18 also neutralizes TGF-β1 and -β3 related growth arrest of HT-2 cells. Further studies show that ZGGS18 does not induce ADCC- or CDC-dependent killing tumor cells expressing two soluble targets, suggesting its binding affinities towards Fc-gamma and complement C1q receptors without effector functions. These results support functional depletion of VEGF/TGF-β in tumor microenvironment (TME) by ZGGS18 essentially for its MOA to inhibit tumor growth. A dose-dependent in vivo anti-tumor efficacy of ZGGS18 (1, 3 and 15 mg/kg) has been found in PBMC humanized H460 lung cancer xenograft model. In addition, ZGGS18 has enhanced efficacies to kill tumor growth in MC38 xenograft models when it is combined with anti-PD-1 antibodies (keytruda), support the improvement of TME for I/O reagents by ZGGS18 in cooperation with its role in anti-proliferation and anti-angiogenesis. Toxicity and safety pharmacology studies with weekly repeat doses for four weeks in cynomolgus monkeys indicate that ZGGS18 is well tolerated over the dose range 13, 40 and 120 mg/kg without obviously toxic or adverse effects (NOAEL =120 mg/kg). PK/TK analyses indicate that ZGG18 has a prolonged half-life in plasma, attribute to its human neonatal Fc receptor (FcRn) binding and pH-dependent interaction for mAb recycling. The IND application of ZGGS18 has been approved by both FDA and Chinese NMPA for clinical trials in treatment of advanced tumors as monotherapy and/or in combined with PD-1/PD-L1 based I/O therapies. Citation Format: Ruifeng Liu, Alfonso Suarez, Tyler Liban, Bin Zhang, Tongcheng Dai, Margaret Karow, Jackie Sheng, Zelin Sheng, Binhua Lv, Bing Zhu. ZGGS18, a bispecific drug candidate of anti-VEGF and TGFbeta-trap, inhibiting tumor proliferation and improving tumor microenvironment with I/O therapy [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 2323.