Structural characterization of nonactive site, TrkA-selective kinase inhibitors

Authors: Su HP1, Rickert K2, Burlein C3, Narayan K3, Bukhtiyarova M3, Hurzy DM4, Stump CA4, Zhang X4, Reid J4, Krasowska-Zoladek A5, Tummala S2, Shipman JM2, Kornienko M2, Lemaire PA3, Krosky D2, Heller A3, Achab A6, Chamberlin C6, Saradjian P6, Sauvagnat B6, Yang X6, Ziebell MR6, Nickbarg E6, Sanders JM4, Bilodeau MT4, Carroll SS3, Lumb KJ2, Soisson SM4, Henze DA5, Cooke AJ4.
Publisher/Year: Proc Natl Acad Sci U S A. 2017 Jan 17; 114 (3): E297-E306
Pub Med ID/Journal ID: PMID: 28039433


Current therapies for chronic pain can have insufficient efficacy and lead to side effects, necessitating research of novel targets against pain. Although originally identified as an oncogene, Tropomyosin-related kinase A (TrkA) is linked to pain and elevated levels of NGF (the ligand for TrkA) are associated with chronic pain. Antibodies that block TrkA interaction with its ligand, NGF, are in clinical trials for pain relief. Here, we describe the identification of TrkA-specific inhibitors and the structural basis for their selectivity over other Trk family kinases. The X-ray structures reveal a binding site outside the kinase active site that uses residues from the kinase domain and the juxtamembrane region. Three modes of binding with the juxtamembrane region are characterized through a series of ligand-bound complexes. The structures indicate a critical pharmacophore on the compounds that leads to the distinct binding modes. The mode of interaction can allow TrkA selectivity over TrkB and TrkC or promiscuous, pan-Trk inhibition. This finding highlights the difficulty in characterizing the structure-activity relationship of a chemical series in the absence of structural information because of substantial differences in the interacting residues. These structures illustrate the flexibility of binding to sequences outside of-but adjacent to-the kinase domain of TrkA. This knowledge allows development of compounds with specificity for TrkA or the family of Trk proteins.