GPCR Antagonism via Antibody-Mediated Rewiring of Receptor Trafficking and Degradation

G-protein coupled receptors (GPCRs) represent one of the most important yet incompletely targeted classes of therapeutic proteins. Here, we report a novel strategy for functional GPCR antagonism through antibody-mediated endocytosis and lysosomal degradation. Our engineered bispecific antibodies, termed GPCR-TfR1 Targeting Chimeras (GTACs), achieve potent and selective downregulation of various GPCRs, including RXFP1 and CCR6, critical cancer and immune drug targets that are difficult to antagonize with conventional approaches. GTACs led to complete inhibition of receptor activity with over 100-fold greater potency than conventional antibody antagonists. Using four-color imaging, we elucidated the trafficking mechanism of both the target protein and TfR1 in living cells. The GTAC platform enables robust antagonism of signaling across diverse GPCR families and establishes induced endocytosis and lysosomal trafficking as a fundamentally new paradigm for therapeutic GPCR modulation.