Design, Synthesis, and Biological and in silico Evaluation of Novel Indazole-pyridine Hybrids for the Treatment of Breast Cancer.

INTRODUCTION: The prevalence of breast cancer presents a substantial global health concern, underscoring the ongoing need for the development of inventive therapeutic remedies. METHODS: In this investigation, an array of novel indazole-pyridine hybrids (5a-h) have been designed and synthesized to assess their potential as candidates for treating breast cancer. Subsequently, we have conducted biological evaluations to determine their cytotoxic effects on the human MCF-7 breast cancer cell line. Furthermore, in silico analysis was conducted to estimate the inhibition potential of the compounds against TrkA (Tropomyosin receptor kinase A), a specific molecular target associated with breast cancer, through molecular docking. In silico physicochemical and pharmacokinetic predictions were made to assess the compounds' drug-like properties. RESULTS: Compound 5a emerged as the most active compound among the others with GI50 < 10 µg/ml. Besides, compound 5a showed high binding energy (BE -10.7 kcal/mol) against TrkA and was stabilized within the TrkA binding pocket through hydrophobic, H-bonding, and van der Waals interactions. In silico physicochemical and pharmacokinetic prediction studies indicated that compound 5a obeyed both Lipinski's and Veber's rule and displayed a versatile pharmacokinetic profile, implying compound 5a to appear as a viable candidate and that it could be further refined to develop therapeutic agents for potentially treating breast cancer. CONCLUSION: This study offers a promising direction for the advancement of innovative breast cancer treatments, highlighting the effectiveness of indazole-pyridine hybrids as potential anticancer agents. Further optimization and preclinical development are necessary to advance these compounds to clinical trials.

Nerve growth factor promote osteogenic differentiation of dental pulp stem cells through MEK/ERK signalling pathways.

Nerve growth factor (NGF) and its receptor, tropomyosin receptor kinase A (TrkA), are known to play important roles in the immune and nervous system. However, the effects of NGF on the osteogenic differentiation of dental pulp stem cells (DPSCs) remain unclear. This study aimed to investigate the role of NGF on the osteogenic differentiation of DPSCs in vitro and the underlying mechanisms. DPSCs were cultured in osteogenic differentiation medium containing NGF (50 ng/mL) for 7 days. Then osteogenic-related genes and protein markers were analysed using qRT-PCR and Western blot, respectively. Furthermore, addition of NGF inhibitor and small interfering RNA (siRNA) transfection experiments were used to elucidate the molecular signalling pathway responsible for the process. NGF increased osteogenic differentiation of DPSCs significantly compared with DPSCs cultured in an osteogenic-inducing medium. The NGF inhibitor Ro 08-2750 (10 µM) and siRNA-mediated gene silencing of NGF receptor, TrkA and ERK signalling pathways inhibitor U0126 (10 µM) suppressed osteogenic-related genes and protein markers on DPSCs. Furthermore, our data revealed that NGF-upregulated osteogenic differentiation of DPSCs may be associated with the activation of MEK/ERK signalling pathways via TrkA. Collectively, NGF was capable of promoting osteogenic differentiation of DPSCs through MEK/ERK signalling pathways, which may enhance the DPSCs-mediated bone tissue regeneration.

An in silico study of protein-protein interactions and design of novel peptides for TrkA in ameloblastoma.

Ameloblastoma is a benign odontogenic jawbone tumor. The binding of Nerve growth factor (NGF) to receptor tyrosine kinase A (TrkA) promotes cell survival, proliferation, and differentiation via PI3K/AKT and Ras/MAPK signaling. Although the exact cause of ameloblastoma remains unknown, elevated levels of NGF and TrkA expression in ameloblastoma are associated with aggressive tumor behavior and poor patient outcomes. It is previously demonstrated that His 4, Arg 9, and Glu 11 residues of NGF made crucial interactions with the TrkA subunit. The main aim of our present study to develop potential therapeutic strategies by identifying promising peptide candidates. The objectives include starting with a detailed in silico analysis to identify a crucial peptide sequence of NGF that is bound by TrkA, creating a library of novel peptides from the identified peptide sequence through a single-point mutation on interacting residues (His 4, Arg 9, and Glu 11), and selecting the top peptides based on docking score, interactions analysis, and desirable pose analysis. The study ultimately designed a hybrid peptide candidate through the simultaneous and continuous mutation of the top residues, resulting in a peptide that exhibited a more specific interaction with TrkA, blocking the binding site and preventing the interaction between NGF and TrkA.Communicated by Ramaswamy H. Sarma.

Huntingtin-associated protein 1 ameliorates neurological function rehabilitation by facilitating neurite elongation through TrKA-MAPK pathway in mice spinal cord injury.

Aims: Huntingtin-associated protein 1 (HAP1) is a neuronal protein closely associated with microtubules and might facilitate neurological function rehabilitation. This study aimed to investigate the effects of HAP1 on SCI and the underlying mechanisms. Methods: the spinal cord injury (SCI) mouse model was induced by Allen's method. Then recombinant-HAP1 (r-HAP1) was administrated by intrathecal injection, and the BMS, Thermal nociceptive thresholds, tactile nociceptive thresholds, and neurofibrillary regeneration were identified to inspect the therapy outcome. Then NSCs were isolated from mice on embryonic day 14.5 and induced to differentiate into neurons. The efficiency of axon growth was calculated. Signaling pathway array was conducted to examine the signaling pathways in NSCs treated with r-HAP1. Antagonists and activators of TrkA were used to confirm the role of TrkA of HAP1 intervention both in vitro and in vivo. Results: r-HAP1 ameliorates the neurological function rehabilitation after SCI, and benefits the regain of Tuj in injury spinal cord. Also significantly enhances neurite growth during neuronal differentiation of NSCs; Signaling pathway array and Western blot revealed that r-HAP1 significantly activates the phosphorylation of TrkA-MAPK/ERK in NSCs. TrkA selective inhibitor GW441756 blocks r-HAP1 on TrkA-MAPK/ERK signaling pathway and detracts from axonal growth after neuronal differentiation. TrkA selective activator gambogic amide can mimic the function of r-HAP1 by activating the foregoing pathway. ERK activator U-46619 reverses the blocking effect of GW441756 on r-HAP1. Conclusion: HAP1 activates the TrkA-MAPK signaling pathway and is conducive to neurite elongation during NSC neuronal differentiation; by which to improve the prognosis of spinal cord injury in mice.

Unlocking the potential of approved drugs for the allosteric inhibition of tropomyosin-receptor kinase A using molecular docking and molecular dynamics studies.

Tropomyosin-receptor kinase A (TrkA) is the primary isoform among the tropomyosin-receptor kinases that have been associated with human cancer development, contributing to approximately 7.4% of all cancer cases. TrkA represents an attractive target for cancer treatment; however, currently available TrkA inhibitors face limitations in terms of resistance development and potential toxicity. Hence, the objective of this study was to identify new allosteric-approved inhibitors of TrkA that can overcome these challenges and be employed in cancer therapy. To achieve this goal, a screening of 9,923 drugs from the ChEMBL database was conducted to assess their repurposing potential using molecular docking. The top 49 drug candidates, exhibiting the highest docking scores (-11.569 to -7.962 kcal/mol), underwent MM-GBSA calculations to evaluate their binding energies. Delanzomib and tibalosin, the top two drugs with docking scores of -10.643 and -10.184 kcal/mol, respectively, along with MM-GBSA dG bind values of -67.96 and -50.54 kcal/mol, were subjected to 200 ns molecular dynamic simulations, confirming their stable interactions with TrkA. Based on these findings, we recommend further experimental evaluation of delanzomib and tibalosin to determine their potential as allosteric inhibitors of TrkA. These drugs have the potential to provide more effective and less toxic therapeutic alternatives. The approach employed in this study, which involves repurposing drugs through molecular docking and molecular dynamics, serves as a valuable tool for identifying novel drug candidates with distinct therapeutic uses. This methodology can contribute to reducing the attrition rate and expediting the process of drug discovery.

TrkA inhibition alleviates bladder overactivity in cyclophosphamide-induced cystitis by targeting hyperpolarization-activated cyclic nucleotide-gated channels.

Objectives: To investigate the potential of Tropomyosin receptor kinase A (TrkA) for the treatment of interstitial cystitis/ bladder pain syndrome (IC/BPS). Materials and Methods: Sixty-four female rats were randomly assigned to the control and cyclophosphamide (CYP) groups. Quantitative reverse transcription polymerase chain reaction was utilized to detect the mRNA level of TrkA. Western blot analysis was used to measure the protein levels of TNF-α, IL-6, and TrkA. Immunostaining was used to detect the expression of TrkA in bladder sections. Contractility studies and urodynamic measurements were utilized to test the spontaneous contractions of detrusor muscle strips and the global bladder activity, respectively. Results: Rat models of chronic cystitis were successfully established. The mRNA and protein levels of TrkA were significantly increased in the bladders of CYP-treated rats. Also, results of immunohistochemical staining and immunofluorescence staining showed that increased TrkA expression in the CYP group was mainly observed in the urothelium layer and bladder interstitial Cajal-like cells (ICC-LCs) but not in the detrusor smooth muscle cells. The specific inhibitor of TrkA, GW441756 (10 µM), significantly suppressed the robust spontaneous contractions of detrusor muscle strips in the CYP group and alleviated the overall bladder overactivity of CYP-treated rats. However, the inhibitory effects of GW441756 (10 µM) on the spontaneous contractions of detrusor muscle strips and the overall bladder activity were eliminated after pretreatments with the specific blocker of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, ZD7288 (50 µM). Conclusion: Our results suggested that increased TrkA expression during chronic cystitis promotes the development of bladder overactivity by targeting the HCN channels.

Characterization of KRC-108 as a TrkA Kinase Inhibitor with Anti-Tumor Effects.

Tropomyosin receptor kinase A (TrkA) protein is a receptor tyrosine kinase encoded by the NTRK1 gene. TrkA signaling mediates the proliferation, differentiation, and survival of neurons and other cells following stimulation by its ligand, the nerve growth factor. Chromosomal rearrangements of the NTRK1 gene result in the generation of TrkA fusion protein, which is known to cause deregulation of TrkA signaling. Targeting TrkA activity represents a promising strategy for the treatment of cancers that harbor the TrkA fusion protein. In this study, we evaluated the TrkA-inhibitory activity of the benzoxazole compound KRC-108. KRC-108 inhibited TrkA activity in an in vitro kinase assay, and suppressed the growth of KM12C colon cancer cells harboring an NTRK1 gene fusion. KRC-108 treatment induced cell cycle arrest, apoptotic cell death, and autophagy. KRC-108 suppressed the phosphorylation of downstream signaling molecules of TrkA, including Akt, phospholipase Cγ, and ERK1/2. Furthermore, KRC-108 exhibited anti-tumor activity in vivo in a KM12C cell xenograft model. These results indicate that KRC-108 may be a promising therapeutic agent for Trk fusion-positive cancers.

Evaluation of chiral N,N-dimethyl-sphingosine for the interaction between nerve growth factor and tropomyosin receptor kinase A.

Neuropathic pain is an unbearable condition caused by nervous system damage. As distinct acute pain, neuropathic pain is chronic, and it severely influences quality of life. N,N-Dimethyl-d-erythro-sphingosine (DMS), a neuropathic pain inducer, is metabolited de novo from sphingosine. In a recent study, metabolomics showed an increased concentration level of DMS in the spinal cord in mice with neuropathic pain. Nerve growth factor (NGF) is one of the peripheral nervous system targeted pain factors that interact with tropomyosin receptor kinase A (trkA). On the basis of this information, we were interested in the possibility that DMS may induce neuropathic pain-like behavior through an increase of NGF activity. In this study, we showed that DMS can enhance the binding of NGF to trkA, followed by neurite outgrowth of epidermal nerve fibers and phosphorylation of trkA. In addition, a stereoisomer, N,N-dimethyl-l-erythro-sphingosine, did not any show such biological activities. The results suggest that DMS can enhance the binding of NGF to trkA and that its stereochemistry is an essential factor for exhibiting its activity.

Screening of a Small Molecule Compound Library Identifies Potential Drugs that Synergize with PARP Inhibitors against Ovarian Cancer Cells / 中国生物化学与分子生物学报

PARP inhibitors are a new class of drugs that target cancer cells with defective DNA repair. Early trials have shown that PARP inhibitors have achieved satisfactory results, but the mechanism of resistance after drug treatment has not been fully revealed. Therefore, it is necessary to find more targeted drugs in combination with PARP inhibitors to kill tumor cells. In this paper, several potential drugs that can synergistically kill ovarian cancer cells with PARP inhibitors were identified based on the combined drug screening of 379 small molecule compound libraries and PARP inhibitor Niraparib through cell proliferation experiments, colony-formation survival experiments and immunofluorescence staining experiments. The results showed that there are eight small molecule compounds with good combination effects, including two small molecule inhibitors STF-118804 and Disulfiram that have been reported to have combined effects with PARP inhibitors. We selected GW441756, an inhibitor of tropomyosin receptor kinase A (TrKA), to verify a variety of tumor cells and explore the preliminary mechanism. The combined therapeutic effects of the Niraparib and the TrKA inhibitor increased the sensitivity of tumor cells to PARP inhibitors (P < 0. 05). Mechanistically, the number of γH2AX foci in the combined treatment group was significantly increased (P<0. 05), indicating that the TrKA inhibitor hindered the DNA damage repair ability. Moreover, combination therapy significantly reduced the formation of RAD51 foci (P<0. 05), a marker of homologous recombination repair (HRR), suggesting that TrKA inhibitors may inhibit DNA damage repair by inhibiting HRR efficiency. Overall, these results suggest that TrKA inhibitor can be used as a potential drug to kill ovarian cancer cells in combination with PARP inhibitors.

Ultrasound delivery of a TrkA agonist confers neuroprotection to Alzheimer-associated pathologies.

Early degeneration of basal forebrain cholinergic neurons contributes substantially to cognitive decline in Alzheimer's disease. Evidence from preclinical models of neuronal injury and aging support a pivotal role for nerve growth factor (NGF) in neuroprotection, resilience, and cognitive function. However, whether NGF can provide therapeutic benefit in the presence of Alzheimer's disease-related pathologies still unresolved. Perturbations in the NGF signalling system in Alzheimer's disease may render neurons unable to benefit from NGF administration. Additionally, challenges related to brain delivery remain for clinical translation of NGF-based therapies in Alzheimer's disease. To be safe and efficient, NGF-related agents should stimulate the NGF receptor, tropomyosin receptor kinase A (TrkA), avoid activation through the p75 neurotrophin receptor (p75NTR), and be delivered non-invasively to targeted brain areas using real-time monitoring. We addressed these limitations using MRI-guided focused ultrasound (MRIgFUS) to increase blood-brain barrier permeability locally and transiently, allowing an intravenously administered TrkA agonist that does not activate p75NTR, termed D3, to enter targeted brain areas. Here, we report the therapeutic potential of selective TrkA activation in a transgenic mouse model that recapitulates numerous Alzheimer's disease-associated pathologies. Repeated MRIgFUS-mediated delivery of D3 (D3/FUS) improved cognitive function in the TgCRND8 model of Alzheimer's disease. Mechanistically, D3/FUS treatment effectively attenuated cholinergic degeneration and promoted functional recovery. D3/FUS treatment also resulted in widespread reduction of brain amyloid pathology and dystrophic neurites surrounding amyloid plaques. Furthermore, D3/FUS markedly enhanced hippocampal neurogenesis in TgCRND8 mice, implicating TrkA agonism as a novel therapeutic target to promote neurogenesis in the context of Alzheimer's disease-related pathology. Thus, this study provides evidence that selective TrkA agonism confers neuroprotection to effectively counteract Alzheimer's disease-related vulnerability. Recent clinical trials demonstrate that non-invasive blood-brain barrier modulation using MRIgFUS is safe, feasible and reversible in Alzheimer's disease patients. TrkA receptor agonists coupled with MRIgFUS delivery constitute a promising disease-modifying strategy to foster brain health and counteract cognitive decline in Alzheimer's disease.

Discovery of novel TrkA allosteric inhibitors: Structure-based virtual screening, biological evaluation and preliminary SAR studies.

Tropomyosin receptor kinases A (TrkA) is a potential therapeutic target for the treatment of numerous tumor types and chronic pain. However, most of the reported TrkA inhibitors are ATP competitive pan-Trks inhibitors that lack subtype selectivity. A selective TrkA inhibitor may provide valuable therapeutic benefits. Here, we described the discovery of novel TrkA allosteric inhibitors by structure-based virtual screening. A promising hit (D5261, TrkA cell IC50 = 3.32 µM) was selected for further studies. The binding free energy between TrkA and D5261 was calculated. In addition, the preliminary structure-activity relationship (SAR) studies with D5261 were investigated. The results suggest that D5261 can be used as a starting point for development of TrkA allosteric inhibitors.

Reversal of motor-skill transfer impairment by trihexyphenidyl and reduction of dorsolateral striatal cholinergic interneurons in Dyt1 ΔGAG knock-in mice.

DYT-TOR1A or DYT1 early-onset generalized dystonia is an inherited movement disorder characterized by sustained muscle contractions causing twisting, repetitive movements, or abnormal postures. The majority of the DYT1 dystonia patients have a trinucleotide GAG deletion in DYT1/TOR1A. Trihexyphenidyl (THP), an antagonist for excitatory muscarinic acetylcholine receptor M1, is commonly used to treat dystonia. Dyt1 heterozygous ΔGAG knock-in (KI) mice, which have the corresponding mutation, exhibit impaired motor-skill transfer. Here, the effect of THP injection during the treadmill training period on the motor-skill transfer to the accelerated rotarod performance was examined. THP treatment reversed the motor-skill transfer impairment in Dyt1 KI mice. Immunohistochemistry showed that Dyt1 KI mice had a significant reduction of the dorsolateral striatal cholinergic interneurons. In contrast, Western blot analysis showed no significant alteration in the expression levels of the striatal enzymes and transporters involved in the acetylcholine metabolism. The results suggest a functional alteration of the cholinergic system underlying the impairment of motor-skill transfer and the pathogenesis of DYT1 dystonia. Training with THP in a motor task may improve another motor skill performance in DYT1 dystonia.

Role of Mitochondria in Interplay between NGF/TRKA, miR-145 and Possible Therapeutic Strategies for Epithelial Ovarian Cancer.

Ovarian cancer is the most lethal gynecological neoplasm, and epithelial ovarian cancer (EOC) accounts for 90% of ovarian malignancies. The 5-year survival is less than 45%, and, unlike other types of cancer, the proportion of women who die from this disease has not improved in recent decades. Nerve growth factor (NGF) and tropomyosin kinase A (TRKA), its high-affinity receptor, play a crucial role in pathogenesis through cell proliferation, angiogenesis, invasion, and migration. NGF/TRKA increase their expression during the progression of EOC by upregulation of oncogenic proteins as vascular endothelial growth factor (VEGF) and c-Myc. Otherwise, the expression of most oncoproteins is regulated by microRNAs (miRs). Our laboratory group reported that the tumoral effect of NGF/TRKA depends on the regulation of miR-145 levels in EOC. Currently, mitochondria have been proposed as new therapeutic targets to activate the apoptotic pathway in the cancer cell. The mitochondria are involved in a myriad of functions as energy production, redox control, homeostasis of Ca+2, and cell death. We demonstrated that NGF stimulation produces an augment in the Bcl-2/BAX ratio, which supports the anti-apoptotic effects of NGF in EOC cells. The review aimed to discuss the role of mitochondria in the interplay between NGF/TRKA and miR-145 and possible therapeutic strategies that may decrease mortality due to EOC.

Small interfering RNA for cancer treatment: overcoming hurdles in delivery.

In many ways, cancer cells are different from healthy cells. A lot of tactical nano-based drug delivery systems are based on the difference between cancer and healthy cells. Currently, nanotechnology-based delivery systems are the most promising tool to deliver DNA-based products to cancer cells. This review aims to highlight the latest development in the lipids and polymeric nanocarrier for siRNA delivery to the cancer cells. It also provides the necessary information about siRNA development and its mechanism of action. Overall, this review gives us a clear picture of lipid and polymer-based drug delivery systems, which in the future could form the base to translate the basic siRNA biology into siRNA-based cancer therapies.

Increased hippocampal TrkA expression ameliorates cranial radiation­induced neurogenesis impairment and cognitive deficit via PI3K/AKT signaling.

Cognitive deficit is one of the most serious complications of cranial radiotherapy of head and neck cancers. However, the underlying mechanism of this cognitive impairment remains unclear. In the present study, the role of tropomyosin receptor kinase A (TrkA) and its ligand neurotrophin nerve growth factor (NGF) were investigated following whole­brain irradiation (WBI). Young male Sprague­Dawley rats underwent WBI at a single dose of 10 Gy. WBI was determined to result in notable memory decline and substantial neurogenesis impairment in the hippocampus 3 months post­irradiation. Compared with the control group, TrkA protein expression was greater in irradiated rats 1 week after WBI, which then decreased significantly by the 3­month time­point. However, no difference in NGF expression was observed from 1 day to 3 months post­WBI. Overexpression of hippocampal TrkA in rats using adeno­associated virus ameliorated memory decline induced by irradiation. Additionally, upregulating TrkA expression rescued irradiation­induced hippocampal precursor cell proliferation and promoted neurogenesis. PI3K, Akt and ERK1/2 phosphorylation were also revealed to be significantly inhibited by WBI, which was ameliorated by TrkA overexpression. Findings of the present study indicated that the TrkA­dependent signaling pathway may serve a critical role in radiotherapy­induced cognitive deficit and impairments in neurogenesis.

Disturbed Yin-Yang balance: stress increases the susceptibility to primary and recurrent infections of herpes simplex virus type 1.

Herpes simplex virus type 1 (HSV-1), a neurotropic herpes virus, is able to establish a lifelong latent infection in the human host. Following primary replication in mucosal epithelial cells, the virus can enter sensory neurons innervating peripheral tissues via nerve termini. The viral genome is then transported to the nucleus where it can be maintained without producing infectious progeny, and thus latency is established in the cell. Yin-Yang balance is an essential concept in traditional Chinese medicine (TCM) theory. Yin represents stable and inhibitory factors, and Yang represents the active and aggressive factors. When the organism is exposed to stress, especially psychological stress caused by emotional stimulation, the Yin-Yang balance is disturbed and the virus can re-engage in productive replication, resulting in recurrent diseases. Therefore, a better understanding of the stress-induced susceptibility to HSV-1 primary infection and reactivation is needed and will provide helpful insights into the effective control and treatment of HSV-1. Here we reviewed the recent advances in the studies of HSV-1 susceptibility, latency and reactivation. We included mechanisms involved in primary infection and the regulation of latency and described how stress-induced changes increase the susceptibility to primary and recurrent infections.

Targeted viral vector transduction of relaxin-3 neurons in the rat nucleus incertus using a novel cell-type specific promoter.

Modern neuroscience utilizes transgenic techniques extensively to study the activity and function of brain neural networks. A key feature of this approach is its compatibility with molecular methods for selective transgene expression in neuronal circuits of interest. Until now, such targeted transgenic approaches have not been applied to the extensive circuitry involving the neuropeptide, relaxin-3. Pharmacological and gene knock-out studies have revealed relaxin-3 signalling modulates interrelated behaviours and cognitive processes, including stress and anxiety, food and alcohol consumption, and spatial and social memory, highlighting the potential of this system as a therapeutic target. In the present study, we aimed to identify a promoter sequence capable of regulating cell-type specific transgene expression from an adeno-associated viral (AAV) vector in relaxin-3 neurons of the rat nucleus incertus (NI). In parallel to relaxin-3 promoter sequences, we also tested an AAV vector containing promoter elements for the tropomyosin receptor kinase A (TrkA) gene, as TrkA is co-expressed with relaxin-3 in rat NI neurons. Stereotaxic injection of an mCherry-expressing AAV vector revealed widespread non-specific TrkA promoter (880 bp) activity in and adjacent to the NI at 8 weeks post-treatment. In contrast, mCherry expression was successfully restricted to relaxin-3 NI neurons with 98% specificity using a 1736 bp relaxin-3 promoter. In addition to detailed anatomical mapping of NI relaxin-3 networks, illustrated here in association with GABAergic medial septum neurons, this method for targeted transgene delivery offers a versatile tool for ongoing preclinical studies of relaxin-3 circuitry.

Structural basis of the transmembrane domain dimerization and rotation in the activation mechanism of the TRKA receptor by nerve growth factor.

Tropomyosin-receptor kinases (TRKs) are essential for the development of the nervous system. The molecular mechanism of TRKA activation by its ligand nerve growth factor (NGF) is still unsolved. Recent results indicate that at endogenous levels most of TRKA is in a monomer-dimer equilibrium and that the binding of NGF induces an increase of the dimeric and oligomeric forms of this receptor. An unsolved issue is the role of the TRKA transmembrane domain (TMD) in the dimerization of TRKA and the structural details of the TMD in the active dimer receptor. Here, we found that the TRKA-TMD can form dimers, identified the structural determinants of the dimer interface in the active receptor, and validated this interface through site-directed mutagenesis together with functional and cell differentiation studies. Using in vivo cross-linking, we found that the extracellular juxtamembrane region is reordered after ligand binding. Replacement of some residues in the juxtamembrane region with cysteine resulted in ligand-independent active dimers and revealed the preferred dimer interface. Moreover, insertion of leucine residues into the TMD helix induced a ligand-independent TRKA activation, suggesting that a rotation of the TMD dimers underlies NGF-induced TRKA activation. Altogether, our findings indicate that the transmembrane and juxtamembrane regions of TRKA play key roles in its dimerization and activation by NGF.

Nerve growth factor and Tropomyosin receptor kinase A are increased in the gastric mucosa of patients with functional dyspepsia.

BACKGROUND: Nerve growth factor (NGF) and enteric glial cells (EGCs) are associated with visceral hypersensitivity and gastrointestinal motility disorder, which may represent the pathogenesis of functional dyspepsia (FD). This study aimed to investigate the expression of NGF, its high affinity receptor tropomyosin receptor kinase A (TrkA) and the EGC activation marker glial fibrillary acidic protein (GFAP) in the gastric mucosa of patients with FD and the association of these proteins with dyspeptic symptoms. METHODS: Gastric mucosal biopsies taken from 27 FD patients (9 epigastric pain syndrome (EPS) patients, 7 postprandial distress syndrome (PDS) patients and 11 EPS overlap PDS patients) and 26 control subjects were used for analysis. The expression of NGF, TrkA and GFAP was examined, and the association of these proteins with dyspeptic symptoms, including epigastric pain, postprandial fullness, early satiation and epigastric burning, was analysed. RESULTS: The expression levels of NGF, TrkA, and GFAP in the gastric mucosa were significantly higher in the EPS group, the PDS group, and the EPS overlap PDS group than in the healthy control group. There was no significant difference between the FD subgroups. TrkA colocalized with GFAP, which indicated that TrkA was localized to EGCs, and the expression of TrkA in EGCs was significantly higher in the FD group than in the control group. Changes in the expression of NGF, TrkA, and GFAP were positively correlated with epigastric pain, postprandial fullness and early satiation but had no significant relationship with epigastric burning. CONCLUSIONS: The increased expression of gastric NGF, TrkA and GFAP might be involved in FD pathophysiology and symptom perception.

Efficacy and safety of intra-articular injection of tropomyosin receptor kinase A inhibitor in painful knee osteoarthritis: a randomized, double-blind and placebo-controlled study.

OBJECTIVE: This trial evaluated the efficacy and safety of GZ389988A, a tropomyosin receptor kinase A (TrkA) inhibitor, in subjects with painful knee osteoarthritis (OA). METHOD: In this single center, double-blind, placebo-controlled and randomized trial, 104 subjects with moderate-to-severe knee OA pain were enrolled to receive a single intra-articular (IA) injection of either GZ389988A or placebo. Efficacy measures were assessed over 12 weeks and included walking pain (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] A1), overall knee pain, WOMAC A, B, C and total score, Patient Global Impression of Change (PGIC), OMERACT-OARSI responder rate and rescue medication use. Adverse events (AEs) were monitored up to 24 weeks. RESULTS: The primary efficacy endpoint was met with a between-group difference of -7.49 (VAS 0-100) on WOMAC A1 changes over 4 weeks (P < 0.05 favoring GZ389988A). The secondary outcome on WOMAC A1 changes over 12 weeks had a between-group difference of -6.78 (P = 0.064). Among weekly assessments, statistically significant greater improvement in the GZ389988A group was observed in WOMAC A1, overall knee pain and/or WOMAC A at weeks 2-5. Although not statistically significant, improvements over placebo on pain and WOMAC C persisted over 12 weeks. Greater AE incidence was observed in the GZ389988A group including transient and self-limited injection joint inflammatory reactions with a spike of acetaminophen intake within the first week post-injection. CONCLUSION: IA injection of TrkA inhibitor GZ389988A in knee OA subjects reduced pain with a numerically functional gain and an acceptable safety profile. (ClinicalTrials.gov, NCT02845271).