In Pursuit of an Allosteric Human Tropomyosin Kinase A (hTrkA) Inhibitor for Chronic Pain

Pain Signaling by GPCRs and RTKs

Chronic pain is common and debilitating, yet is inadequately treated by current therapies, which can have life-threatening side effects. Treatments targeting G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs), key pain mediators, often fail in clinical trials for unknown reasons. Here, we discuss the recent evidence that GPCRs and RTKs generate sustained signals from multiprotein signaling complexes or signalosomes in intracellular compartments to control chronic pain. We evaluate the evidence that selective antagonism of these intracellular signals provides more efficacious and long-lasting pain relief than antagonism of receptors at the surface of cells. We highlight how the identification of coreceptors and molecular scaffolds that underpin pain signaling by multiple receptors has identified new therapeutic targets for chronic pain, surmounting the redundancy of the pain signaling pathway.

Type II & III inhibitors of tropomyosin receptor kinase (Trk): a 2020-2022 patent update

INTRODUCTION

The Trk family proteins are membrane-bound kinases predominantly expressed in neuronal tissues. Activated by neurotrophins, they regulate critical cellular processes through downstream signaling pathways. Dysregulation of Trk signaling can drive a range of diseases, making the design and study of Trk inhibitors a vital area of research. This review explores recent advances in the development of type II and III Trk inhibitors, with implications for various therapeutic applications.

AREAS COVERED

Patents covering type II and III inhibitors targeting the Trk family are discussed as a complement of the previous review, Type I inhibitors of tropomyosin receptor kinase (Trk): a 2020-2022 patent update. Relevant patents were identified using the Web of Science database, Google, and Google Patents.

EXPERT OPINION

While type II and III Trk inhibitor development has advanced more gradually compared to their type I counterparts, they hold significant promise in overcoming resistance mutations and achieving enhanced subtype selectivity - a critical factor in reducing adverse effects associated with pan-Trk inhibition. Recent interdisciplinary endeavors have marked substantial progress in the design of subtype selective Trk inhibitors, with impressive success heralded by the type III inhibitors. Notably, the emergence of mutant-selective Trk inhibitors introduces an intriguing dimension to the field, offering precise treatment possibilities.

Selective type II TRK inhibitors overcome xDFG mutation mediated acquired resistance to the second-generation inhibitors selitrectinib and repotrectinib

Neurotrophic receptor kinase (NTRK) fusions are actionable oncogenic drivers of multiple pediatric and adult solid tumors, and tropomyosin receptor kinase (TRK) has been considered as an attractive therapeutic target for "pan-cancer" harboring these fusions. Currently, two generations TRK inhibitors have been developed. The representative second-generation inhibitors selitrectinib and repotrectinib were designed to overcome clinic acquired resistance of the first-generation inhibitors larotrectinib or entrectinib resulted from solvent-front and gatekeeper on-target mutations. However, xDFG (TRKAG667C/A/S, homologous TRKCG696C/A/S) and some double mutations still confer resistance to selitrectinib and repotrectinib, and overcoming these resistances represents a major unmet clinical need. In this review, we summarize the acquired resistance mechanism of the first- and second-generation TRK inhibitors, and firstly put forward the emerging selective type II TRK inhibitors to overcome xDFG mutations mediated resistance. Additionally, we concluded our perspectives on new challenges and future directions in this field.

Recent advances in the structural biology of tyrosine kinases

The past few years have seen exciting discoveries in the area of tyrosine kinase structural biology including the first high resolution models of full-length receptor tyrosine kinases and new mechanistic insights into the structural mechanisms of receptor tyrosine kinase activation. Despite being a mature area of research, the application of new technologies continues to advance our understanding. In this article we highlight a selection of recent studies that illustrate the current areas of research interest, focussing in particular on the exciting progress made possible by cryo-electron-microscopy. These new discoveries may herald a wave of new design ideas for therapeutics acting through novel mechanisms.

Recent advances in the discovery of tropomyosin receptor kinases TRKs inhibitors: A mini review

The tropomyosin receptor tyrosine kinases (TRKs) control the cell proliferation mainly in the nervous system and are encoded by NTRK genes. Fusion and mutation of NTRK genes were detected in various types of cancers. Many small molecules TRK inhibitors have been discovered during the last two decades and some of them have entered clinical trials. Moreover, two of these inhibitors; larotrectinib and entrectinib; were approved by FDA for the treatment of TRK-fusion positive solid tumors. However, mutation of TRK enzymes resulted in resistance to both drugs. Therefore, next generation TRK inhibitors were discovered to overcome the acquired drug resistance. Additionally, the off-target and on-target adverse effects on the brain initiated the need for selective TRK subtype inhibitors. Indeed, some molecules were recently reported as selective TRKA or TRKC inhibitors with minimal CNS side effects. The current review highlighted the efforts done during the last three years in the design and discovery of novel TRK inhibitors.

A Shift in Thinking: Cellular Thermal Shift Assay-Enabled Drug Discovery

A decade has passed since the cellular thermal shift assay (CETSA) was introduced to the drug discovery community. Over the years, the method has guided numerous projects by providing insights about, for example, target engagement, lead generation, target identification, lead optimization, and preclinical profiling. With this Microperspective, we intend to highlight recently published applications of CETSA and how the data generated can enable efficient decision-making and prioritization throughout the drug discovery and development value chain.

Identification and structural analysis of a selective tropomyosin receptor kinase C (TRKC) inhibitor

Tropomyosin receptor kinases (TRKs) are a family of TRKA, TRKB and TRKC isoforms. It has been widely reported that TRKs are implicated in a variety of tumors with several Pan-TRK inhibitors currently being used or evaluated in clinical treatment. However, off-target adverse events frequently occur in the clinical use of Pan-TRK inhibitors, which result in poor patient compliance, even drug discontinuation. Although a subtype-selectivity TRK inhibitor may avert the potential off-target adverse events and can act as a more powerful tool compound in the biochemical studies on TRKs, the high sequence similarities of TRKs hinder the development of subtype-selectivity TRK inhibitors. For example, no selective TRKC inhibitor has been reported. Herein, a selective TRKC inhibitor (L13) was disclosed, with potent TRKC inhibitory activity and 107.5-/34.9-fold selectivity over TRKA/B (IC₅₀ TRKA/B/C = 1400 nM, 454 nM, 13 nM, respectively). Extensive molecular dynamics simulations illustrated that key interactions of L13 with the residues and diversely conserved water molecules in the ribose regions of different TRKs may be the structural basis of selectivity. This will provide inspiring insights into the development of subtype-selectivity TRK inhibitors. Moreover, L13 could serve as a tool compound to investigate the distinct biological functions of TRKC and a starting point for further research on drugs specifically targeting TRKC.