The Trispecific Antibody IBI3019 Integrates CDH17-Enhanced EGFR Antagonism with Optimized CD16A Engagement to Elicit Potent Antitumor Activity with Minimal Toxicity.

Potent and sustained inhibition of epidermal growth factor receptor (EGFR) signaling is critical for suppressing colorectal cancer (CRC) growth, yet current EGFR therapies are often limited by incomplete EGFR blockade and on-target/off-tumor toxicities, particularly skin rash. Here, we co-targeted EGFR and cadherin-17 (CDH17) with a bispecific antibody (bsAb), overcoming these limitations by reducing skin-related toxicities and achieving superior tumor growth inhibition compared to EGFR- or c-MET/EGFR-targeting antibodies. Mechanistically, the high-affinity CDH17-binding arm anchored the EGFR/CDH17 bsAb to the tumor cell surface, facilitating rapid engagement of unbound or newly synthesized EGFR. This "anchor and capture" mechanism allowed the EGFR/CDH17 bsAb to achieve superior and more sustained suppression of the EGFR pathway than cetuximab and amivantamab. Further incorporation of an anti-CD16A nanobody transformed the EGFR/CDH17 bsAb into a trispecific natural killer (NK)-cell engager. Extensive format screening revealed that NK cell activation is heavily influenced by the spatial distance between the tumor antigen-binding Fab and the anti-CD16A nanobody, with longer distances impairing the bulky CD45 phosphatase exclusion from the immunological synapse and leading to significantly reduced cytotoxicity. Consequently, the widely adopted Morrison-type antibody consistently underperformed compared to architectures with shorter CD16A-TAA-Fab spacing. The final optimized molecule was IBI3019, a CDH17/EGFR/CD16A trispecific antibody that integrates potent CDH17-enhanced EGFR blockade with optimal architecture for efficient NK cell engagement. It demonstrated superior in vivo efficacy and a good safety profile in cynomolgus monkeys, with no observable skin toxicity. These promising pre-clinical findings warrant the clinical development of IBI3019. .