Preclinical Profile of BYON3521 Predicts an Effective and Safe MET Antibody–Drug Conjugate

MET, the cell-surface receptor for the hepatocyte growth factor/scatter factor, which is widely overexpressed in various solid cancer types, is an attractive target for the development of antibody-based therapeutics. BYON3521 is a novel site-specifically conjugated duocarmycin-based antibody–drug conjugate (ADC), comprising a humanized cysteine-engineered IgG1 monoclonal antibody with low pmol/L binding affinity towards both human and cynomolgus MET. In vitro studies showed that BYON3521 internalizes efficiently upon MET binding and induces both target- and bystander-mediated cell killing. BYON3521 showed good potency and full efficacy in MET-amplified and high MET–expressing cancer cell lines; in moderate and low MET–expressing cancer cell lines good potencies and partial efficacy were observed. In mouse xenograft models, BYON3521 showed significant antitumor activity upon single-dose administration in multiple non-MET–amplified tumor types with low, moderate, and high MET expression, including complete tumor remissions in models with moderate MET expression. In the repeat-dose Good Laboratory Practice (GLP) safety assessment in cynomolgus monkeys, BYON3521 was well tolerated and based on the observed toxicities and their reversibility, the highest non-severely toxic dose was set at 15 mg/kg. A human pharmacokinetics (PK) model was derived from the PK data from the cynomolgus safety assessments, and the minimal efficacious dose in humans is estimated to be in the range of 3 to 4 mg/kg. In all, our nonclinical data suggests that BYON3521 is a safe ADC with potential for clinical benefit in patients. A first-in-human dose-escalation study is currently ongoing to determine the maximum tolerated dose and recommended dose for expansion (NCT05323045).