Structural basis for direct NGF/TrkA blockade by an analgesic antibody
The NGF/TrkA signaling axis is a central mediator of inflammatory and chronic pain, where injury-induced NGF binds and activates TrkA on nociceptive neurons to drive peripheral sensitization and persistent pain states. Despite its therapeutic promise, targeting this pathway is limited by adverse effects of systemic NGF sequestration such as rapidly progressive osteoarthritis and poor isoform selectivity of Trk kinase inhibitors leading to off-target neurological effects. Targeting the TrkA extracellular domain (TrkAECD) offers a pathway to achieve high isoform selectivity while avoiding these complications. However, the precise structural basis for selective TrkA neutralization remains poorly understood. Monoclonal antibody (mAb) 42F5-15 inhibits TrkA-mediated signaling and increases pain threshold. Here, we report the high-resolution (2.60 [A]) cryo-EM structure of the TrkAECD in complex with the Fab region of the TrkA-neutralizing mAb 42F5-15. Structural analysis reveals that the antibody epitope overlaps the NGF-binding interface, consistent with orthosteric inhibition and distinct from previously proposed allosteric mechanisms. The epitope includes residues conserved in TrkA but divergent in TrkB and TrkC, providing a structural basis for receptor isoform selectivity. Furthermore, we demonstrate in vivo that the mAb 42F5-15 potently mitigates mechanical allodynia and nociceptive sensitization. These findings establish a structural framework for the development of selective extracellular TrkA-targeted therapies for safer, non-opioid chronic pain management.