Abstract 6939: Tri-specific ADC platform offers potential therapeutic advantage over bi-specific ADC

Abstract Co-expression of EGFR and HER3, along with other tumor-associated antigen (TAA such as c-MET, HER2, B7H3, PD-L1, or others), is frequently observed across diverse human tumors. Targeting more than two TAAs simultaneously presents engineering challenges but offers distinct advantages: increased tumor cell avidity for ADCs, circumvention of antigen-loss-driven resistance, synergistic blockade of cross-talk between signaling pathways, mitigation of tumor heterogeneity, and broadened applicability across cancer types. A tri-specific ADC platform has been developed by combining one arm with both HER3 and EGFR affinities and another arm with affinity for a third TAA. Binding and internalization were assessed in cell lines with varying TAA expression levels to evaluate uptake efficiency. in vitro cytotoxicity was measured via dose-response assays across multiple lines with modest expression of each TAA. in vivo efficacy was tested in murine xenograft models representing diverse target antigen profiles, in comparison with benchmarks Izalonatamab brengitecan (BL-B01D1, EGFR/HER3 bispecific ADC) and an Amivantamab (EGFR/c-MET bispecific mAb )-derived ADC. Our results show that tri-specific ADCs exhibit significantly faster and more efficient internalization than the EGFR/HER3 bispecific ADC, particularly in cells with medium-to-low EGFR and HER3 expression. in vitro, tri-specific ADCs achieved lower IC50 values, indicating enhanced cytotoxic potency across a broad panel of tumor lines. In xenograft models, tri-specific ADCs delivered superior tumor growth inhibition relative to the bispecific benchmark, irrespective of heterogeneous target antigen expression. In conclusion, tri-specific ADCs offer a robust advantage in vitro and in vivo over EGFR/HER3 or c-MET bispecifics by enabling enhanced tumor cell binding, improved internalization, and more effective delivery of cytotoxic agents. This strategy holds promise for broader clinical application in tumors with varied receptor expressions and may address resistance in heterogeneous cancers. Citation Format: Yang Wang, Lixia Cao, Cui Feng, Fangdun Jiang, lixia Gu, Chen Li, Yifan Yang, Qi Zhang, Ming Zhou, Cancan Li, Wei Huang, Bonan Yan, Ziping Wei, Yuhong Zhou, . Tri-specific ADC platform offers potential therapeutic advantage over bi-specific ADC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6939.