NT-3 contributes to chemotherapy-induced neuropathic pain through TrkC-mediated CCL2 elevation in DRG neurons.

Cancer patients undergoing treatment with antineoplastic drugs often experience chemotherapy-induced neuropathic pain (CINP), and the therapeutic options for managing CINP are limited. Here, we show that systemic paclitaxel administration upregulates the expression of neurotrophin-3 (Nt3) mRNA and NT3 protein in the neurons of dorsal root ganglia (DRG), but not in the spinal cord. Blocking NT3 upregulation attenuates paclitaxel-induced mechanical, heat, and cold nociceptive hypersensitivities and spontaneous pain without altering acute pain and locomotor activity in male and female mice. Conversely, mimicking this increase produces enhanced responses to mechanical, heat, and cold stimuli and spontaneous pain in naive male and female mice. Mechanistically, NT3 triggers tropomyosin receptor kinase C (TrkC) activation and participates in the paclitaxel-induced increases of C-C chemokine ligand 2 (Ccl2) mRNA and CCL2 protein in the DRG. Given that CCL2 is an endogenous initiator of CINP and that Nt3 mRNA co-expresses with TrkC and Ccl2 mRNAs in DRG neurons, NT3 likely contributes to CINP through TrkC-mediated activation of the Ccl2 gene in DRG neurons. NT3 may be thus a potential target for CINP treatment.

Srsf1 and Elavl1 act antagonistically on neuronal fate choice in the developing neocortex by controlling TrkC receptor isoform expression.

The seat of higher-order cognitive abilities in mammals, the neocortex, is a complex structure, organized in several layers. The different subtypes of principal neurons are distributed in precise ratios and at specific positions in these layers and are generated by the same neural progenitor cells (NPCs), steered by a spatially and temporally specified combination of molecular cues that are incompletely understood. Recently, we discovered that an alternatively spliced isoform of the TrkC receptor lacking the kinase domain, TrkC-T1, is a determinant of the corticofugal projection neuron (CFuPN) fate. Here, we show that the finely tuned balance between TrkC-T1 and the better known, kinase domain-containing isoform, TrkC-TK+, is cell type-specific in the developing cortex and established through the antagonistic actions of two RNA-binding proteins, Srsf1 and Elavl1. Moreover, our data show that Srsf1 promotes the CFuPN fate and Elavl1 promotes the callosal projection neuron (CPN) fate in vivo via regulating the distinct ratios of TrkC-T1 to TrkC-TK+. Taken together, we connect spatio-temporal expression of Srsf1 and Elavl1 in the developing neocortex with the regulation of TrkC alternative splicing and transcript stability and neuronal fate choice, thus adding to the mechanistic and functional understanding of alternative splicing in vivo.

Zurletrectinib is a next-generation TRK inhibitor with strong intracranial activity against NTRK fusion-positive tumours with on-target resistance to first-generation agents.

BACKGROUND: While NTRK fusion-positive cancers can be exquisitely sensitive to first-generation TRK inhibitors, resistance inevitably occurs, mediated in many cases by acquired NTRK mutations. Next-generation inhibitors (e.g., selitrectinib, repotrectinib) maintain activity against these TRK mutant tumors; however, there are no next-generation TRK inhibitors approved by the FDA and select trials have stopped treating patients. Thus, the identification of novel, potent and specific next-generation TRK inhibitors is a high priority. METHODS: In silico modeling and in vitro kinase assays were performed on TRK wild type (WT) and TRK mutant kinases. Cell viability and clonogenic assays as well as western blots were performed on human primary and murine engineered NTRK fusion-positive TRK WT and mutant cell models. Finally, zurletrectinib was tested in vivo in human xenografts and murine orthotopic glioma models harboring TRK-resistant mutations. RESULTS: In vitro kinase and in cell-based assays showed that zurletrectinib, while displaying similar potency against TRKA, TRKB, and TRKC WT kinases, was more active than other FDA approved or clinically tested 1st- (larotrectinib) and next-generation (selitrectinib and repotrectinib) TRK inhibitors against most TRK inhibitor resistance mutations (13 out of 18). Similarly, zurletrectinib inhibited tumor growth in vivo in sub-cute xenograft models derived from NTRK fusion-positive cells at a dose 30 times lower when compared to selitrectinib. Computational modeling suggests this stronger activity to be the consequence of augmented binding affinity of zurletrectinib for TRK kinases. When compared to selitrectinib and repotrectinib, zurletrectinib showed increased brain penetration in rats 0.5 and 2 h following a single oral administration. Consistently, zurletrectinib significantly improved the survival of mice harboring orthotopic NTRK fusion-positive, TRK-mutant gliomas (median survival = 41.5, 66.5, and 104 days for selitrectinib, repotrectinib, and zurletrectinib respectively; P < 0.05). CONCLUSION: Our data identifies zurletrectinib as a novel, highly potent next-generation TRK inhibitor with stronger in vivo brain penetration and intracranial activity than other next-generation agents.

Neurotrophin-3 Facilitates Stemness Properties and Associates with Poor Survival in Lung Cancer.

INTRODUCTION: Cancer stem cells (CSCs) shape the tumor microenvironment via neuroendocrine signaling and orchestrate drug resistance and metastasis. Cytokine antibody array demonstrated the upregulation of neurotrophin-3 (NT-3) in lung CSCs. This study aims to dissect the role of NT-3 in lung CSCs during tumor innervation. METHODS: Western blotting, quantitative reverse transcription-PCR, and flow cytometry were used to determine the expression of the NT-3 axis in lung CSCs. NT-3-knockdown and NT-3-overexpressed cells were derived lung CSCs, followed by examining the stemness gene expression, tumorsphere formation, transwell migration and invasion, drug resistance, soft agar colony formation, and in vivo tumorigenicity. Human lung cancer tissue microarray and bioinformatic databases were used to investigate the clinical relevance of NT-3 in lung cancer. RESULTS: NT-3 and its receptor tropomyosin receptor kinase C (TrkC) were augmented in lung tumorspheres. NT-3 silencing (shNT-3) suppressed the migration and anchorage-independent growth of lung cancer cells. Further, shNT-3 abolished the sphere-forming capability, chemo-drug resistance, invasion, and in vivo tumorigenicity of lung tumorspheres with a decreased expression of CSC markers. Conversely, NT-3 overexpression promoted migration and anchorage-independent growth and fueled tumorsphere formation by upregulating the expression of CSC markers. Lung cancer tissue microarray analysis revealed that NT-3 increased in patients with advanced-stage, lymphatic metastasis and positively correlated with Sox2 expression. Bioinformatic databases confirmed a co-expression of NT-3/TrkC-axis and demonstrated that NT-3, NT-3/TrkC, NT-3/Sox2, and NT-3/CD133 worsen the survival of lung cancer patients. CONCLUSION: NT-3 conferred the stemness features in lung cancer during tumor innervation, which suggests that NT-3-targeting is feasible in eradicating lung CSCs.

Neurotrophic tyrosine receptor kinase gene fusions in adult and pediatric patients with solid tumors: a clinicogenomic biobank and record linkage study of expression frequency and patient characteristics from Finland.

BACKGROUND: Neurotrophic tyrosine receptor kinase (NTRK) gene fusions are oncogenic drivers. Using the Auria Biobank in Finland, we aimed to identify and characterize patients with these gene fusions, and describe their clinical and tumor characteristics, treatments received, and outcomes. MATERIAL AND METHODS: We evaluated pediatrics with any solid tumor type and adults with colorectal cancer (CRC), non-small cell lung cancer (NSCLC), sarcoma, or salivary gland cancer. We determined tropomyosin receptor kinase (TRK) protein expression by pan-TRK immunohistochemistry (IHC) staining of tumor samples from the Auria Biobank, scored by a certified pathologist. NTRK gene fusion was confirmed by next generation sequencing (NGS). All 2,059 patients were followed-up starting 1 year before their cancer diagnosis. RESULTS: Frequency of NTRK gene fusion tumors was 3.1% (4/127) in pediatrics, 0.7% (8/1,151) for CRC, 0.3% (1/288) for NSCLC, 0.9% (1/114) for salivary gland cancer, and 0% (0/379) for sarcoma. Among pediatrics there was one case each of fibrosarcoma (TPM3::NTRK1), Ewing's sarcoma (LPPR1::NTRK2), primitive neuroectodermal tumor (DAB2IP::NTRK2), and papillary thyroid carcinoma (RAD51B::NTRK3). Among CRC patients, six harbored tumors with NTRK1 fusions (three fused with TPM3), one harbored a NTRK3::GABRG1 fusion, and the other a NTRK2::FXN/LPPR1 fusion. Microsatellite instability was higher in CRC patients with NTRK gene fusion tumors versus wild-type tumors (50.0% vs. 4.4%). Other detected fusions were SGCZ::NTRK3 (NSCLC) and ETV6::NTRK3 (salivary gland cancer). Four patients (three CRC, one NSCLC) received chemotherapy; one patient (with CRC) received radiotherapy. CONCLUSION: NTRK gene fusions are rare in adult CRC, NSCLC, salivary tumors, sarcoma, and pediatric solid tumors.

A morphological mimic: An NTRK3-rearranged spindle cell neoplasm presenting as a groin mass.

Neurotrophic receptor tyrosine kinase (NTRK)-rearranged spindle cell neoplasms are a recently described group of soft tissue tumors. They commonly present as a painless mass on the extremities of children and young adults. They are characterized microscopically by a heterogeneous spectrum of infiltrative spindle cell proliferations, which can morphologically mimic several other spindle cell neoplasms. Their identification is vital, as they may be amenable to treatment with tyrosine kinase-targeted therapy. This case report describes a rare NTRK3-rearranged spindle cell neoplasm in the groin of a 29-year-old female and provides further clinical and morphological features of this entity.

A TrkB and TrkC partial agonist restores deficits in synaptic function and promotes activity-dependent synaptic and microglial transcriptomic changes in a late-stage Alzheimer's mouse model.

INTRODUCTION: Tropomyosin related kinase B (TrkB) and C (TrkC) receptor signaling promotes synaptic plasticity and interacts with pathways affected by amyloid beta (Aß) toxicity. Upregulating TrkB/C signaling could reduce Alzheimer's disease (AD)-related degenerative signaling, memory loss, and synaptic dysfunction. METHODS: PTX-BD10-2 (BD10-2), a small molecule TrkB/C receptor partial agonist, was orally administered to aged London/Swedish-APP mutant mice (APPL/S) and wild-type controls. Effects on memory and hippocampal long-term potentiation (LTP) were assessed using electrophysiology, behavioral studies, immunoblotting, immunofluorescence staining, and RNA sequencing. RESULTS: In APPL/S mice, BD10-2 treatment improved memory and LTP deficits. This was accompanied by normalized phosphorylation of protein kinase B (Akt), calcium-calmodulin-dependent kinase II (CaMKII), and AMPA-type glutamate receptors containing the subunit GluA1; enhanced activity-dependent recruitment of synaptic proteins; and increased excitatory synapse number. BD10-2 also had potentially favorable effects on LTP-dependent complement pathway and synaptic gene transcription. DISCUSSION: BD10-2 prevented APPL/S/Aß-associated memory and LTP deficits, reduced abnormalities in synapse-related signaling and activity-dependent transcription of synaptic genes, and bolstered transcriptional changes associated with microglial immune response. HIGHLIGHTS: Small molecule modulation of tropomyosin related kinase B (TrkB) and C (TrkC) restores long-term potentiation (LTP) and behavior in an Alzheimer's disease (AD) model. Modulation of TrkB and TrkC regulates synaptic activity-dependent transcription. TrkB and TrkC receptors are candidate targets for translational therapeutics. Electrophysiology combined with transcriptomics elucidates synaptic restoration. LTP identifies neuron and microglia AD-relevant human-mouse co-expression modules.

Pyrazolo[1,5-a]pyrimidine as a Prominent Framework for Tropomyosin Receptor Kinase (Trk) Inhibitors-Synthetic Strategies and SAR Insights.

Tropomyosin receptor kinases (Trks) are transmembrane receptor tyrosine kinases named TrkA, TrkB, and TrkC and encoded by the NTRK1, NTRK2, and NTRK3 genes, respectively. These kinases have attracted significant attention and represent a promising therapeutic target for solid tumor treatment due to their vital role in cellular signaling pathways. First-generation TRK inhibitors, i.e., Larotrectinib sulfate and Entrectinib, received clinical approval in 2018 and 2019, respectively. However, the use of these inhibitors was significantly limited because of the development of resistance due to mutations. Fortunately, the second-generation Trk inhibitor Repotrectinib (TPX-0005) was approved by the FDA in November 2023, while Selitrectinib (Loxo-195) has provided an effective solution to this issue. Another macrocycle-based analog, along with many other TRK inhibitors, is currently in clinical trials. Two of the three marketed drugs for NTRK fusion cancers feature a pyrazolo[1,5-a] pyrimidine nucleus, prompting medicinal chemists to develop numerous novel pyrazolopyrimidine-based molecules to enhance clinical applications. This article focuses on a comprehensive review of chronological synthetic developments and the structure-activity relationships (SAR) of pyrazolo[1,5-a]pyrimidine derivatives as Trk inhibitors. This article will also provide comprehensive knowledge and future directions to the researchers working in the field of medicinal chemistry by facilitating the structural modification of pyrazolo [1,5-a]pyrimidine derivatives to synthesize more effective novel chemotherapeutics as TRK inhibitors.

Selective activation and down-regulation of Trk receptors by neurotrophins in human neurons co-expressing TrkB and TrkC.

In the central nervous system, most neurons co-express TrkB and TrkC, the tyrosine kinase receptors for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3). As NT3 can also activate TrkB, it has been difficult to understand how NT3 and TrkC can exert unique roles in the assembly of neuronal circuits. Using neurons differentiated from human embryonic stem cells expressing both TrkB and TrkC, we compared Trk activation by BDNF and NT3. To avoid the complications resulting from TrkB activation by NT3, we also generated neurons from stem cells engineered to lack TrkB. We found that NT3 activates TrkC at concentrations lower than those of BDNF needed to activate TrkB. Downstream of Trk activation, the changes in gene expression caused by TrkC activation were found to be similar to those resulting from TrkB activation by BDNF, including a number of genes involved in synaptic plasticity. At high NT3 concentrations, receptor selectivity was lost as a result of TrkB activation. In addition, TrkC was down-regulated, as was also the case with TrkB at high BDNF concentrations. By contrast, receptor selectivity as well as reactivation were preserved when neurons were exposed to low neurotrophin concentrations. These results indicate that the selectivity of NT3/TrkC signalling can be explained by the ability of NT3 to activate TrkC at concentrations lower than those needed to activate TrkB. They also suggest that in a therapeutic perspective, the dosage of Trk receptor agonists will need to be taken into account if prolonged receptor activation is to be achieved.

Discovery and characterization of targetable NTRK point mutations in hematologic neoplasms.

Much of what is known about the neurotrophic receptor tyrosine kinase (NTRK) genes in cancer was revealed through identification and characterization of activating Trk fusions across many tumor types. A resurgence of interest in these receptors has emerged owing to the realization that they are promising therapeutic targets. The remarkable efficacy of pan-Trk inhibitors larotrectinib and entrectinib in clinical trials led to their accelerated, tissue-agnostic US Food and Drug Administration (FDA) approval for adult and pediatric patients with Trk-driven solid tumors. Despite our enhanced understanding of Trk biology in solid tumors, the importance of Trk signaling in hematological malignancies is underexplored and warrants further investigation. Herein, we describe mutations in NTRK2 and NTRK3 identified via deep sequencing of 185 patients with hematological malignancies. Ten patients contained a point mutation in NTRK2 or NTRK3; among these, we identified 9 unique point mutations. Of these 9 mutations, 4 were oncogenic (NTRK2A203T, NTRK2R458G, NTRK3E176D, and NTRK3L449F), determined via cytokine-independent cellular assays. Our data demonstrate that these mutations have transformative potential to promote downstream survival signaling and leukemogenesis. Specifically, the 3 mutations located within extracellular (ie, NTRK2A203T and NTRK3E176D) and transmembrane (ie, NTRK3L449F) domains increased receptor dimerization and cell-surface abundance. The fourth mutation, NTRK2R458G, residing in the juxtamembrane domain, activates TrkB via noncanonical mechanisms that may involve altered interactions between the mutant receptor and lipids in the surrounding environment. Importantly, these 4 activating mutations can be clinically targeted using entrectinib. Our findings contribute to ongoing efforts to define the mutational landscape driving hematological malignancies and underscore the utility of FDA-approved Trk inhibitors for patients with aggressive Trk-driven leukemias.

NTRK gene fusions are detected in both secretory and non-secretory breast cancers.

NTRK fusions represent a new biomarker-defined population that can be treated with TRK inhibitors. Although rare, NTRK fusions are detected across a wide range of solid tumors. Previous reports suggest that NTRK fusions are limited to the secretory subtype of breast cancer. Here we examined NTRK fusions in a large real world next-generation sequencing (NGS) dataset and confirmed secretory versus non-secretory status using H&E images. Of 23 NTRK fusion-positive cases, 11 were classified as secretory, 11 as non-secretory, and one as mixed status. The secretory subtype trended younger, was predominantly estrogen receptor (ER)-, had lower tumor mutational burden, and exhibited lower levels of genomic loss of heterozygosity. The non-secretory subtype was enriched for TP53 mutations. The secretory subtype was enriched for ETV6-NTRK3 fusions in 7 of 11 cases, and the non-secretory subtype had NTRK1 fusions in 7 of 11 cases, each with a different fusion partner. Our data suggests NTRK fusions are present in both secretory and non-secretory subtypes, and that comprehensive genomic profiling should be considered across all clinically advanced breast cancers to identify patients that could receive benefit from TRK inhibitors.

TRK Protein Expression in Merkel Cell Carcinoma Is Not Caused by NTRK Fusions.

Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous malignant tumor with neuroendocrine differentiation, with a rapidly growing incidence rate, high risk of recurrence, and aggressive behavior. The available therapeutic options for advanced disease are limited and there is a pressing need for new treatments. Tumors harboring fusions involving one of the neurotrophin receptor tyrosine kinase (NTRK) genes are now actionable with targeted inhibitors. NTRK-fused genes have been identified in neuroendocrine tumors of other sites; thus, a series of 76 MCCs were firstly analyzed with pan-TRK immunohistochemistry and the positive ones with real-time RT-PCR, RNA-based NGS, and FISH to detect the eventual underlying gene fusion. Despite 34 MCCs showing pan-TRK expression, NTRK fusions were not found in any cases. As in other tumors with neural differentiation, TRK expression seems to be physiological and not caused by gene fusions.

GAB1-ABL1 fusions in tumors that have histologic overlap with NTRK-rearranged spindle cell tumors.

Fibroblastic spindle cell tumors are a heterogeneous group of rare soft tissue tumors that are increasingly recognized as associated with a variety of kinase gene fusions. We report two cases of GAB1-ABL1 fusions in spindle cell tumors that histologically overlap with neurotrophic tyrosine receptor kinase (NTRK)-rearranged spindle cell tumors. The first case occurred in a 76-year-old female who had a large deep-seated spindle cell tumor composed of monotonous ovoid to spindle cells in a background of thick stromal collagen bands with prominent hyalinized vessels and inconspicuous mitoses (<1/10 HPF). Immunohistochemical stains showed co-expression of S100 and CD34. A GAB1-ABL1 fusion was detected by whole transcriptome RNA sequencing. The patient had a partial response to imatinib. The second case was previously described as a solitary fibrous tumor, occurring in a 9-year-old female with a cellular spindle cell tumor with patchy CD34 immunoexpression but no expression of S100. Upon clinicopathologic re-review, including anchored multiplex next-generation sequencing, a GAB1-ABL1 fusion was identified. In summary, we report the first two cases of spindle cell tumors with variable expression of CD34 and/or S100, driven by GAB1-ABL1 gene fusions with histologic overlap with NTRK-rearranged spindle cell tumors, suggesting that ABL-fusions may also be oncogenic drivers within this spectrum of tumors. These cases highlight the evolving understanding of fibroblastic spindle cell tumor biology and the utility of sequencing in identifying a targetable alteration.

An unusual fusion gene EML4-ALK in a patient with congenital mesoblastic nephroma.

Congenital mesoblastic nephroma (CMN), the most common renal tumor of infancy, is a mesenchymal neoplasm histologically classified into classic, cellular, or mixed types. Most cellular CMNs harbor a characteristic ETV6-NTRK3 fusion. Here, we report an unusual congenital mesoblastic nephroma presenting in a newborn boy with a novel EML4-ALK gene fusion revealed by Anchored Multiplex RNA Sequencing Assay. The EML4-ALK gene fusion expands the genetic spectrum implicated in the pathogenesis of congenital mesoblastic nephroma, with yet another example of kinase oncogenic activation through chromosomal rearrangement. The methylation profile of the tumor corresponds with infantile fibrosarcoma showing the biological similarity of these two entities.

Gastrointestinal stromal tumors with BRAF gene fusions. A report of two cases showing low or absent KIT expression resulting in diagnostic pitfalls.

Although most gastrointestinal stromal tumors (GISTs) exhibit activating mutations in either KIT or PDGFRA, rare cases have shown to be driven by gene fusions involving kinases, mainly involving NTRK3, and rarely BRAF or FGFR1. BRAF gene rearrangements have been described in only two patients to date, as separate case reports. In addition, BRAF V600E mutation is an uncommon but established oncogenic pathway in GIST. In this report, we describe two new GIST cases harboring novel BRAF fusion genes, arising in two young-adult women (37 and 40 years of age) in the small bowel and distal esophagus, both with a spindle cell phenotype. The small bowel GIST measured 2.8 cm and showed a high cellularity and a mitotic rate of 20/50 HPFs, while the esophageal lesion measured 7 cm and 1/50 HPFs. Immunohistochemically, both tumors showed diffuse reactivity for DOG1, while KIT/CD117 was weakly positive in the small bowel GIST and completely negative in the esophageal tumor. Based on these findings, the latter case was misinterpreted as a low-grade myxoid leiomyosarcoma, as it showed a myxoid stroma, reactivity for SMA and focal positivity for desmin. Archer FusionPlex revealed a fusion between BRAF with either AGAP3 or MKRN1 gene partners. Moreover, MSK-IMPACT DNA targeted sequencing confirmed both fusions but did not identify additional mutations. In one case with available material, the BRAF gene rearrangement was also validated by FISH. The recognition of BRAF fusion-positive GISTs is critical as it may be associated with a low level of KIT expression and may result in diagnostic challenges with significant impact on therapeutic management. The clinical benefit with KIT inhibitors, such as imatinib, remains to be determined.

Prediction of EVT6-NTRK3-Dependent Papillary Thyroid Cancer Using Minor Expression Profile.

Solid tumors resulting from oncogenic stimulation of neurotrophin receptors (TRK) by chimeric proteins are a group of rare tumors of various localization that respond to therapy with targeted drugs entrectinib and larotrectinib. The standard method for detecting chimeric TRK genes in tumor samples today is considered to be next generation sequencing with the determination of the prime structure of the chimeric transcripts. We hypothesized that expression of the chimeric tyrosine kinase proteins in tumors can determine the specific transcriptomic profile of tumor cells. We detected differentially expressed genes allowing distinguishing between TRK-dependent tumors papillary thyroid cancer (TC) from other molecular variants of tumors of this type. Using PCR with reverse transcription (RT-PCR), we identified 7 samples of papillary TC carrying a EVT6-NTRK3 rearrangement (7/215, 3.26%). Using machine learning and the data extracted from TCGA, we developed of a recognition function for predicting the presence of rearrangement in NTRK genes based on the expression of 10 key genes: AUTS2, DTNA, ERBB4, HDAC1, IGF1, KDR, NTRK1, PASK, PPP2R5B, and PRSS1. The recognition function was used to analyze the expression data of the above genes in 7 TRK-dependent and 10 TRK-independent thyroid tumors obtained by RT-PCR. On the test samples from TCGA, the sensitivity was 72.7%, the specificity - 99.6%. On our independent validation samples tested by RT-PCR, sensitivity was 100%, specificity - 70%. We proposed an mRNA profile of ten genes that can classify TC in relation to the presence of driver NTRK-chimeric TRK genes with acceptable sensitivity and specificity.

Implication of TrkC-miR2 in neurotrophin signalling pathway regulation through NGFR transcript targeting.

TrkC and NGFR neurotrophin receptors are associated with cell death, cancer and differentiation. TrkC-miR2, which is located in TrkC gene, is known to regulate Wnt signalling pathway, and its influence on other signalling pathways is under investigation. Here, through RT-qPCR, dual-luciferase assay and Western blotting we reveal that TrkC-miR2 targets NGFR. Overexpression of TrkC-miR2 also affected TrkA, TrkC, NFKB, BCL2 and Akt2 expressions involved in neurotrophin signalling pathway, and elevated survival rate of HEK293t and U87 cells was distinguished by flow cytometry and MTT assay. Consistently, an opposite expression correlation was obtained between TrkC-miR2 and NGFR or TrkC for the duration of NT2 differentiation. Meanwhile, TrkC-miR2 down-regulation attenuated NT2 differentiation into neural-like cells. Overall, here we present in silico and experimental evidence showing TrkC-miR2 as a new controller in regulation of neurotrophin signalling pathway.

Canadian consensus on TRK-inhibitor therapy for NTRK fusion-positive sarcoma.

Malignant sarcomas are rare accounting for <1% of all adult solid malignancies and approximately 11% to 13% of all pediatric malignancies. TRK-inhibitors have demonstrated robust and long-lasting responses in patients with NTRK fusion-positive solid tumors, including sarcoma. Access to these agents in many jurisdictions such as Canada remains limited. We undertook a modified Delphi consensus to articulate and convey the clinical importance of these agents for the Canadian sarcoma community. A systematic search of published and presented literature was conducted to identify clinical trials reporting outcomes on the use of TRK-inhibitors in relapsed/refractory NTRK fusion-positive sarcoma. Three main consensus questions were identified: (a) is there currently an unmet clinical need for systemic therapy options in relapsed/refractory sarcoma? (b) do TRK-inhibitors confer a clinical benefit to patients with NTRK fusion-positive sarcoma? (c) do phase I/II basket trials provide sufficient evidence to justify funding of TRK-inhibitors in NTRK fusion-positive sarcoma? Response rates to the first and second surveys were 57% (n = 30) and 42% (n = 22), respectively. There was strong agreement among the Canadian sarcoma community that there was unmet clinical need for effective systemic therapy options in relapsed/refractory sarcoma, that TRK-inhibitors are a safe and effective treatment option for patients with NTRK fusion-positive sarcoma, and that available phase I/II basket trials provide sufficient evidence to support funding of these agents in relapsed/refractory NTRK fusion-positive sarcoma. TRK-inhibitors are a safe and effective systemic therapy option for patients with relapsed/refractory NTRK fusion-positive sarcoma.

Role of TrkA signaling during tadpole tail regeneration and early embryonic development in Xenopus laevis.

Neurotrophic signaling regulates neural cell behaviors in development and physiology, although its role in regeneration has not been fully investigated. Here, we examined the role of neurotrophic signaling in Xenopus laevis tadpole tail regeneration. After the tadpole tails were amputated, the expression of neurotrophin ligand family genes, especially ngf and bdnf, was up-regulated as regeneration proceeded. Moreover, notochordal expression of the NGF receptor gene TrkA, but not that of other neurotrophin receptor genes TrkB and TrkC, became prominent in the regeneration bud, a structure arising from the tail stump after tail amputation. The regenerated tail length was significantly shortened by the pan-Trk inhibitor K252a or the TrkA inhibitor GW-441756, but not by the TrkB inhibitor ANA-12, suggesting that TrkA signaling is involved in elongation of regenerating tails. Furthermore, during Xenopus laevis embryonic development, TrkA expression was detected in the dorsal mesoderm at the gastrula stage and in the notochord at the neurula stage, and its knockdown led to gastrulation defects with subsequent shortening of the body axis length. These results suggest that Xenopus laevis TrkA signaling, which can act in the mesoderm/notochord, plays a key role in body axis elongation during embryogenesis as well as tail elongation during tadpole regeneration.

Fusion partners of NTRK3 affect subcellular localization of the fusion kinase and cytomorphology of melanocytes.

A subset of Spitz tumors harbor fusions of NTRK3 with ETV6, MYO5A, and MYH9. We evaluated a series of 22 melanocytic tumors in which an NTRK3 fusion was identified as part of the diagnostic workup. Tumors in which NTRK3 was fused to ETV6 occurred in younger patients were predominantly composed of epithelioid melanocytes and were classified by their histopathologic features as Spitz tumors. In contrast, those in which NTRK3 was fused to MYO5A were predominantly composed of spindled melanocytes arrayed in fascicles with neuroid features such as pseudo-Verocay bodies. To further investigate the effects of the fusion kinases ETV6-NTRK3 and MYO5A-NTRK3 in melanocytes, we expressed them in immortalized melanocytes and determined their subcellular localization by immunofluorescence. ETV6-NTRK3 was localized to the nucleus and diffusely within the cytoplasm and caused melanocytes to adopt an epithelioid cytomorphology. In contrast, MYO5A-NTRK3, appeared excluded from the nucleus of melanocytes, was localized to dendrites, and resulted in a highly dendritic cytomorphology. Our findings indicate that ETV6-NTRK3 and MYO5A-NTRK3 have distinct subcellular localizations and effects on cellular morphology.