Abstract 2712: Development of GB268, a tri-specific antibody targeting PD-1/CTLA-4/VEGF, with enhanced anti-tumor efficacy and reduced toxicity in pre-clinical studies

Abstract Background: Immunotherapy using immune checkpoint modulators such as anti-PD1/PD-L1 have been widely used in cancer therapy. Combination of checkpoint inhibition using anti-PD1 and anti-CTLA4 has improved therapeutic efficacy but is also accompanied by severe immune related adverse events (irAEs) which limited their clinical use. Bi-specific antibody targeting PD-1/CTLA-4 such as cadonilimab has shown improved clinical benefits with reduced irAEs in cervical cancer. Vascular endothelial growth factor (VEGF) is overexpressed in various solid tumors and anti-VEGF agents inhibit neovascularization and shrink tumor with time. Combined application of bevacizumab and PD-1/PD-L1 blockade displays durable and improved anti-tumor effects. We have recently developed a novel tri-specific antibody GB268, specifically targeting PD-1, CTLA-4 and VEGF with fine-tuned activity & potency for each arm to simultaneously block PD-1/CTLA-4 mediated immune-suppression and VEGF mediated tumor angiogenesis. Methods: GB268 is a hexavalent antibody with symmetrical structure, composed of anti-PD-1 VHH antibody, anti-CTLA-4 VHH antibody, and anti-VEGF conventional antibody. The Fc part is silenced by introducing L234A/L235A mutations. Comprehensive in vitro and in vivo characterization of GB268 have been carried out. Along with in vivo efficacy studies, toxicity has also been evaluated with a murine arthritis model in hPD1/hCTLA4 double-KI mice to assess immune related AEs. Results: GB268 specifically bound to PD-1, VEGF, and CTLA-4 with high affinity and completely blocked PD-1 and VEGF pathways in reporter systems. To reduce the CTLA4 inhibition-induced AEs, the CTLA-4 arm was intentionally designed to only partially block the interaction of CTLA4 to its ligands CD80/CD86, and furthermore, the blockade of CTLA-4 was highly dependent on PD-1 expression. GB268 displayed robust anti-tumor efficacy with attenuated toxicity in murine models. In multiple PBMC-humanized models including A375 melanoma model, HT29 colorectal cancer model, and NCI-H460 NSCLC model, etc., GB268 exhibited significantly better anti-tumor efficacy, compared to PD-1/CTLA-4 bsAb and PD-1/VEGF bsAb, or in the combination of monoclonal antibodies to PD-1, CTLA-4 or VEGF. In arthritis induction model using hPD1/hCTLA4 double KI mice, GB268 had improved tolerance than cadonilimab and at least 20-fold better safety profile than ipilimumab combined with nivolumab. Conclusions: GB268 is a first-in-class anti-PD-1/CTLA-4/VEGF tri-specific antibody with innovative design. Preclinical data demonstrated GB268 is very effective in provoking anti-tumor responses. At the meantime, immune-related AEs is alleviated. Thus, GB268 may emerge as a promising novel therapeutics for cancer treatment. Citation Format: Qinglin Du, Yaxua Lv, Juehua Xu, Fei Peng, Huanhuan Cao, Xueyan Yang, Zhen Qian, Xueqin Li, Yiqi Cao, Qian Ding, Yongcong Tan, Shuhua Han. Development of GB268, a tri-specific antibody targeting PD-1/CTLA-4/VEGF, with enhanced anti-tumor efficacy and reduced toxicity in pre-clinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2712.