Neurotrophic Tropomyosin Receptor Kinase Research Articles

Downregulation of TrkC Receptors Increases Dendritic Arborization of Purkinje Cells in the Developing Cerebellum of the Opossum, Monodelphis domestica.

In therian mammals, the cerebellum is one of the late developing structures in the brain. Specifically, the proliferation of cerebellar granule cells occurs after birth, and even in humans, the generation of these cells continues during the first year of life. The main difference between marsupials and eutherians is that the majority of the brain structures in marsupials develop after birth. Herein, we report that in the newborn laboratory opossum (Monodelphis domestica), the cerebellar primordium is distinguishable in Nissl-stained sections. Additionally, bromodeoxyuridine birthdating experiments revealed that the first neurons form the deep cerebellar nuclei (DCN) and Purkinje cells, and are generated within postnatal days (P) 1 and 5. Three weeks after birth, progenitors of granule cells in the external germinal layer (EGL) proliferate, producing granule cells. These progenitor cells persist for a long time, approximately 5 months. Furthermore, to study the effects of neurotrophic tropomyosin receptor kinase C (TrkC) during cerebellar development, cells were obtained from P3 opossums and cultured for 8 days. We found that TrkC downregulation stimulates dendritic branching of Purkinje neurons, which was surprising. The number of dendritic branches was higher in Purkinje cells transfected with the shRNA TrkC plasmid. However, there was no morphological change in the number of dendritic branches of granule cells transfected with either control or shRNA TrkC plasmids. We suggest that inhibition of TrkC activity enables NT3 binding to the neurotrophic receptor p75NTR that promotes dendritic arborization of Purkinje cells. This effect of TrkC receptors on dendritic branching is cell type specific, which could be explained by the strong expression of TrkC in Purkinje cells but not in granule cells. The data indicate a new role for TrkC receptors in Monodelphis opossum.

Spotlight on the treatment of infantile fibrosarcoma in the era of neurotrophic tropomyosin receptor kinase inhibitors: International consensus and remaining controversies

Targeted neurotrophic tropomyosin receptor kinase (TRK) inhibitors offer a highly specific therapeutic option for patients with infantile fibrosarcoma (IFS) carrying the NTRK gene translocation. International recommendations are needed to define the role of TRK inhibitors (TRKI) for infants with IFS. We analysed retrospective data for all published patients with IFS in the European Paediatric Soft tissue sarcoma Study Group and Cooperative Weichteilsarkomstudiengruppe (CWS) experience and developed a consensus strategy with the Children's Oncology Group. Therapies consisted of tumour resection and/or perioperative chemotherapy for extensive tumours. Among the 172 European patients treated, 162 were alive at the end of the follow-up. Sixty-five patients (40% of all survivors) were treated with surgery alone and 64 patients (39%) with surgery combined with chemotherapy. Radiotherapy was delivered to 3% of survivors (five patients). In addition, 28 survivors (17%) exclusively received chemotherapy. Among the 129 patients treated with surgery, 91% had conservative surgery (118 cases). Overall, nine patients died of disease, one from toxicity (6%) and 20 patients (12%) survived with major functional deficits or had mutilating surgery. Overall, conventional conservative strategies before the era of targeted therapy, even in the case of extensive tumours, demonstrate efficacy in IFS, but are associated with acute and some chronic side effects. TRKI have demonstrated very rapid responses in the vast majority of children with IFS with limited acute toxicity. With the current state of our knowledge, both conventional chemotherapy and TRKI should be regarded as options for patients with localised disease at the physician’s and parent's discretion. TRKI should be considered in patients with metastatic disease, and before mutilating surgery when conventional chemotherapy fails. Outside a clinical trial, additional data are needed to resolve the lack of consensus about front-line use of conventional chemotherapy versus TRKI in patients with localised disease.

Entrectinib, a TRK/ROS1 inhibitor with anti-CNS tumor activity: differentiation from other inhibitors in its class due to weak interaction with P-glycoprotein.

BackgroundStudies evaluating the CNS penetration of a novel tyrosine kinase inhibitor, entrectinib, proved challenging, particularly due to discrepancies across earlier experiments regarding P-glycoprotein (P-gp) interaction and brain distribution. To address this question, we used a novel “apical efflux ratio” (AP-ER) model to assess P-gp interaction with entrectinib, crizotinib, and larotrectinib, and compared their brain-penetration properties.MethodsAP-ER was designed to calculate P-gp interaction with the 3 drugs in vitro using P-gp–overexpressing cells. Brain penetration was studied in rat plasma, brain, and cerebrospinal fluid (CSF) samples after intravenous drug infusion. Unbound brain concentrations were estimated through kinetic lipid membrane binding assays and ex vivo experiments, while the antitumor activity of entrectinib was evaluated in a clinically relevant setting using an intracranial tumor mouse model.ResultsEntrectinib showed lower AP-ER (1.1–1.15) than crizotinib and larotrectinib (≥2.8). Despite not reaching steady-state brain exposures in rats after 6 hours, entrectinib presented a more favorable CSF-to-unbound concentration in plasma (CSF/Cu,p) ratio (>0.2) than crizotinib and larotrectinib at steady state (both: CSF/Cu,p ~0.03). In vivo experiments validated the AP-ER approach. Entrectinib treatment resulted in strong tumor inhibition and full survival benefit in the intracranial tumor model at clinically relevant systemic exposures.ConclusionsEntrectinib, unlike crizotinib and larotrectinib, is a weak P-gp substrate that can sustain CNS exposure based on our novel in vitro and in vivo experiments. This is consistent with the observed preclinical and clinical efficacy of entrectinib in neurotrophic tropomyosin receptor kinase (NTRK) and ROS1 fusion-positive CNS tumors and secondary CNS metastases.

OATP1A/1B, CYP3A, ABCB1, and ABCG2 limit oral availability of the NTRK inhibitor larotrectinib, while ABCB1 and ABCG2 also restrict its brain accumulation.

Larotrectinib is a FDA-approved oral small-molecule inhibitor for treatment of neurotrophic tropomyosin receptor kinase fusion-positive cancer. We here investigated the functions of the multidrug efflux transporters ABCB1 and ABCG2, the SLCO1A/1B (OATP1A/1B) uptake transporters, and the multispecific drug-metabolizing enzyme CYP3A in larotrectinib pharmacokinetic behaviour. In vitro, transepithelial drug transport and uptake assays were performed. In vivo, larotrectinib (10 mg·kg-1 ) was administered orally to relevant genetically modified mouse models. Cell medium, plasma samples, and organ homogenates were measured by a sensitive and specific LC-MS/MS larotrectinib assay. In vitro, larotrectinib was avidly transported by human (h) ABCB1 and mouse (m) Abcg2 efficiently by hABCG2 and modestly by hOATP1A2. In vivo, both mAbcb1a/1b and mAbcg2 markedly limited larotrectinib oral availability and brain and testis accumulation (by 2.1-fold, 10.4-fold, and 2.7-fold, respectively), with mAbcb1a/1b playing a more prominent role. mOatp1a/1b also restricted larotrectinib oral availability (by 3.8-fold) and overall tissue exposure, apparently by mediating substantial uptake into the liver, thus likely facilitating hepatobiliary excretion. Additionally, larotrectinib is an excellent substrate of CYP3A, which restricts the oral availability of larotrectinib and hence its tissue exposure. ABCG2 and especially ABCB1 limit the oral availability and brain and testis penetration of larotrectinib, while OATP1A/1B transporters restrict its systemic exposure by mediating hepatic uptake, thus allowing hepatobiliary excretion. CYP3A-mediated metabolism can strongly limit larotrectinib oral availability and hence its tissue concentrations. These insights may be useful in the further clinical development of larotrectinib.

Abstract P3-10-11: Entrectinib in NTRK fusion-positive breast cancer: Integrated analysis of patients enrolled in STARTRK-2, STARTRK-1 and ALKA-372-001

Abstract Background Fusions involving the neurotrophic tropomyosin receptor kinase (NTRK) gene family NTRK1, NTRK2, and NTRK3 lead to the expression of chimeric rearrangements in the TRK tyrosine kinase proteins (TRKA, TRKB, and TRKC, respectively) with constitutively active kinase function. NTRK fusions act as oncogenic drivers, and are potential therapeutic targets across a broad range of tumor types including breast cancer. Entrectinib is a CNS-active, oral, potent inhibitor of TRKA/B/C, ALK and ROS1 designed to cross the blood-brain-barrier. Here we present integrated efficacy data from three trials of entrectinib in NTRK fusion-positive solid tumors focusing on a small cohort of patients with breast cancer, and safety data from the integrated safety population. Methods Patients with locally advanced/metastatic NTRK fusion-positive tumors (with or without baseline CNS disease) confirmed by nucleic acid-based methods were enrolled in three global phase 1/2 entrectinib trials at >150 sites in 15 countries (ALKA-372-001 [EudraCT 2012-000148-88], STARTRK-1 [NCT02097810], STARTRK-2 [NCT02568267]). Disease burden was assessed per blinded independent central review (BICR) using RECIST v1.1 after cycle 1 (4 weeks) then every 8 weeks thereafter. The primary endpoints were objective response rate (ORR) and duration of response (DOR) by BICR. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and safety. Results The total efficacy-evaluable population comprised 54 adult patients with advanced/metastatic NTRK fusion-positive tumors; within this population 10 different tumor types and >19 histopathologies were identified. In the overall integrated analysis population, responses to treatment with entrectinib occurred in all tumor types and included 4 complete responses (7.4%). The ORR by BICR was 57.4% (95% CI 43.2-70.8), and median (95% CI) DOR, PFS, and OS were 10.4 (7.1-not estimable [NE]), 11.2 (8.0-14.9), and 20.9 (14.9-NE) months, respectively. In the cohort of 6 patients with NTRK fusion-positive breast cancer, the median age was 63 years (range 36-67 years). Three patients reported prior systemic therapies (6, 4 and 1 prior therapies). The majority of patients had an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1 (66.7%). Two patients had investigator-assessed CNS metastases at baseline; 1 patient (16.7%) had previously received radiotherapy in the brain 2-6 months prior to treatment with entrectinib. ORR by BICR was 83.3% (95% CI 35.9-99.6); 2 were complete responses, 3 were partial responses, and 1 patient had missing/unevaluable data. Median (95% CI) DOR, PFS, and OS were: 12.9 (4.2- NE), 10.1 (5.1-NE), and NE (5.1-NE) months, respectively. The integrated safety population comprised 355 patients who received ≥1 dose of entrectinib, of which 60.5% of patients had grade 1 or 2 treatment-related adverse events (TRAEs), 27.6% had grade 3, 3.4% had grade 4, and there were no grade 5 TRAEs. The most frequently reported TRAEs were dysgeusia (41.4%), fatigue (27.9%), dizziness (25.4%) and constipation (23.7%). TRAEs led to dose reductions in 27.3%, interruptions in 25.4% and discontinuations in 3.9% of patients. Conclusion In this integrated analysis of global multicenter clinical trials, entrectinib was well tolerated and induced clinically meaningful, durable responses in patients with NTRK fusion-positive breast cancer. Study Sponsor: Ignyta, Inc., a wholly owned subsidiary of F. Hoffmann-La Roche Ltd. Citation Format: Collin Blakely, Christophe Le Tourneau, Janice Lu, Saiama N. Waqar, Xinhui Huang, Bann-mo Day, Brian Simmons, Minal Barve. Entrectinib in NTRK fusion-positive breast cancer: Integrated analysis of patients enrolled in STARTRK-2, STARTRK-1 and ALKA-372-001 [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-10-11.

NTRK Fusions in Central Nervous System Tumors: A Rare, but Worthy Target.

The neurotrophic tropomyosin receptor kinase (NTRK) genes (NTRK1, NTRK2, and NTRK3) code for three transmembrane high-affinity tyrosine-kinase receptors for nerve growth factors (TRK-A, TRK-B, and TRK-C) which are mainly involved in nervous system development. Loss of function alterations in these genes can lead to nervous system development problems; conversely, activating alterations harbor oncogenic potential, promoting cell proliferation/survival and tumorigenesis. Chromosomal rearrangements are the most clinically relevant alterations of pathological NTRK activation, leading to constitutionally active chimeric receptors. NTRK fusions have been detected with extremely variable frequencies in many pediatric and adult cancer types, including central nervous system (CNS) tumors. These alterations can be detected by different laboratory assays (e.g., immunohistochemistry, FISH, sequencing), but each of these approaches has specific advantages and limitations which must be taken into account for an appropriate use in diagnostics or research. Moreover, therapeutic targeting of this molecular marker recently showed extreme efficacy. Considering the overall lack of effective treatments for brain neoplasms, it is expected that detection of NTRK fusions will soon become a mainstay in the diagnostic assessment of CNS tumors, and thus in-depth knowledge regarding this topic is warranted.

Identifying patients with NTRK fusion cancer.

Due to the efficacy of tropomyosin receptor kinase (TRK) inhibitor therapy and the recent Food and Drug Administration approval of larotrectinib, it is now clinically important to accurately and efficiently identify patients with neurotrophic TRK (NTRK) fusion-driven cancer. These oncogenic fusions occur when the kinase domain of NTRK1, NTRK2 or NTRK3 fuse with any of a number of N-terminal partners. NTRK fusions are characteristic of a few rare types of cancer, such as secretory carcinoma of the breast or salivary gland and infantile fibrosarcoma, but they are also infrequently seen in some common cancers, such as melanoma, glioma and carcinomas of the thyroid, lung and colon. There are multiple methods for identifying NTRK fusions, including pan-TRK immunohistochemistry, fluorescence in situ hybridisation and sequencing methods, and the advantages and drawbacks of each are reviewed here. While testing algorithms will obviously depend on availability of various testing modalities and economic considerations for each individual laboratory, we propose triaging specimens based on histology and other molecular findings to most efficiently identify tumours harbouring these treatable oncogenic fusions.

365O - Durability of response with larotrectinib in adult and pediatric patients with TRK fusion cancer

BackgroundGenomic rearrangements involving neurotrophic tropomyosin receptor kinase 1, 2, or 3 (NTRK1/2/3) result in constitutively active tropomyosin receptor kinase (TRK) fusion proteins that are oncogenic drivers in multiple pediatric and adult cancers. Larotrectinib is a selective TRK inhibitor approved by the US Food and Drug Administration in 2018 for the treatment of TRK fusion cancer based on a primary analysis in 55 patients from 3 clinical trials [Drilon et al. NEJM 2018]. Here, we report median duration of response (DOR) data in the primary cohort and updated data in an expanded cohort of 159 patients with TRK fusion cancer treated with larotrectinib, with 153 (55 primary + 98 supplemental) evaluable for efficacy. MethodsPatients with TRK fusion cancer detected by local molecular profiling were treated with larotrectinib across 3 studies (NCT02122913, NCT02637687, NCT02576431). Disease status was assessed by investigators using RECIST 1.1. Data cut-off was February 19, 2019. ResultsIn the primary cohort of 55 patients with a median follow-up of 26 months, the median DOR in 44 patients with complete or partial responses was 35.2 months (95% CI 21.2–not evaluable [NE]), with 17 progression events and 27 responses ongoing (range 1.6–44 months). Median progression-free survival in the primary cohort was 25.8 months (95% CI 9.9–NE), with 27 patients having progressed. In the expanded combined dataset, the most common tumor types included soft tissue sarcoma (n = 36), infantile fibrosarcoma (n = 29), thyroid carcinoma (n = 26), salivary gland carcinoma (n = 21), and lung cancer (n = 12). Median age was 43 years, ranging from < 1 month to 84 years; 33% < 18 years. The overall response rate was 79% (95% CI 72–85), with complete responses in 16%. Adverse events were mostly grade 1–2; 13% of patients had a grade 3–4 event related to larotrectinib. Only one patient discontinued due to an adverse event related to larotrectinib. ConclusionsThese data confirm the marked tissue-agnostic efficacy and long durability of response in patients with TRK fusion cancer treated with larotrectinib. Larotrectinib demonstrated a favorable long-term safety profile. Screening patients for NTRK gene fusions should be considered. Clinical trial identificationNCT02122913, NCT02637687, NCT02576431. Legal entity responsible for the studyBayer. FundingBayer. DisclosureF. Doz: Advisory / Consultancy, Research grant / Funding (self), Travel / Accommodation / Expenses: BMS; Advisory / Consultancy, Research grant / Funding (self): Celgene; Advisory / Consultancy: Bayer; Advisory / Consultancy: Loxo Oncology; Advisory / Consultancy: Servier. L. Mascarenhas: Speaker Bureau / Expert testimony: Bayer. J. Berlin: Research grant / Funding (institution): PsiOxus; Advisory / Consultancy, Research grant / Funding (institution): Bayer; Advisory / Consultancy, Research grant / Funding (institution): EMD Serono; Research grant / Funding (institution): Symphogen; Research grant / Funding (institution): Roche/Genentech; Research grant / Funding (institution): Immunomedics; Research grant / Funding (institution): Novartis; Research grant / Funding (institution): Taiho; Research grant / Funding (institution): AbbVie (pharamcyclics); Research grant / Funding (institution): Boston Biomedical; Research grant / Funding (institution): FivePrime; Research grant / Funding (institution): Loxo; Research grant / Funding (institution): Incyte; Research grant / Funding (institution): Macrogenics; Honoraria (self): Nestle; Advisory / Consultancy: Rafeal; Advisory / Consultancy: Seattle Genetics; Honoraria (self): Eisai; Advisory / Consultancy: Taiho; Advisory / Consultancy: Armo. All other authors have declared no conflicts of interest.

Translating Systems Medicine Into Clinical Practice: Examples From Pulmonary Medicine With Genetic Disorders, Infections, Inflammations, Cancer Genesis, and Treatment Implication of Molecular Alterations in Non-small-cell Lung Cancers and Personalized Medicine.

Non-small-cell lung cancers (NSCLC) represent 85% of all lung cancers, with adenocarcinoma as the most common subtype. Since the 2000's, the discovery of molecular alterations including epidermal growth factor receptor (EGFR) mutations and anaplastic lymphoma kinase (ALK) rearrangements together with the development of specific tyrosine kinase inhibitors (TKIs) has facilitated the development of personalized medicine in the management of this disease. This review focuses on the biology of molecular alterations in NSCLC as well as the diagnostic tools and therapeutic alternatives available for each targetable alteration. Rapid and sensitive methods are essential to detect gene alterations, using tumor tissue biopsies or liquid biopsies. Massive parallel sequencing or Next Generation Sequencing (NGS) allows to simultaneously analyze numerous genes from relatively low amounts of DNA. The detection of oncogenic fusions can be conducted using fluorescence in situ hybridization, reverse-transcription polymerase chain reaction, immunohistochemistry, or NGS. EGFR mutations, ALK and ROS1 rearrangements, MET (MET proto-oncogenereceptor tyrosine kinase), BRAF (B-Raf proto-oncogen serine/threonine kinase), NTRK (neurotrophic tropomyosin receptor kinase), and RET (ret proto-oncogene) alterations are described with their respective TKIs, either already authorized or still in development. We have herein paid particular attention to the mechanisms of resistance to EGFR and ALK-TKI. As a wealth of diagnostic tools and personalized treatments are currently under development, a close collaboration between molecular biologists, pathologists, and oncologists is crucial.

P75 neurotrophin receptor regulates NGF-induced myofibroblast differentiation and collagen synthesis through MRTF-A

Myofibroblasts are characterized by de novo expression of α-smooth muscle actin (α-SMA) and play a key role in tissue repair and remodeling. In addition to TGF-β1, recent studies have shown that nerve growth factor (NGF) has effects on myofibroblast differentiation and collagen synthesis. However, the regulatory mechanism remains poorly defined. NGF effects are mediated by the specific expression of the NGF neurotrophic tropomyosin-receptor kinase A (TrkA) and p75 neurotrophin receptor (p75NTR). Using NIH/3T3 fibroblast cell lines, we examined the induction of myofibroblast differentiation stimulated by NGF. Our findings showed that p75NTR was in keeping with the expression of α-SMA. Herein, we investigated the role of p75NTR in NGF-induced myofibroblast differentiation and collagen synthesis in these cells using lentivirus transfection to overexpress and knock down. Our results showed that p75NTR was preferentially expressed and was sufficient to induce actin cytoskeleton remodeling, which was required for NGF-induced α-SMA expression. Furthermore, NGF induced nuclear translocation of MRTF-A, an effect that was regulated by p75NTR, and required for α-SMA and collagen-I expression in myofibroblasts. Using a novel MRTF-A pathway inhibitor, CCG-203971, we further demonstrated the requirement of MRTF-A nuclear localization and activity in NGF-induced α-SMA expression. In conclusion, we conclude that p75NTR regulates NGF-induced myofibroblast differentiation and collagen synthesis through MRTF-A. Regulation of NGF-p75NTR interactions represents a promising therapy for fibrotic disorders.

Sexual motivation in male rats is modulated by tropomyosin receptor kinase B (TrkB).

The expression of brain derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) are regulated by gonadal hormone signaling and are expressed in brain areas that are important for sexual behaviors. Accordingly, BDNF and TrkB signaling have been shown to be important for the expression of consummatory sexual behaviors. However, the role of TrkB in sexually motivated behaviors remains to be fully elucidated. To this end, male rats were administered either the TrkB antagonist, ANA-12, or a vehicle control prior to sexual motivation testing, which took place on a noncontact version of a partner preference task. Vehicle treated rats, but not rats treated with ANA-12, exhibited a preference for the sexually receptive stimulus female rat relative to the sexually active stimulus male rat, as indicated by the percentage of time and entries in the vicinity of the female throughout the entire 20-min test. In addition, when compared directly with vehicle treated rats, rats treated with ANA-12 exhibited a significant decrease in levels of sexual motivation as indicated by the magnitude of each group's preference for the female during the early stages of testing. Collectively, these results suggest that TrkB plays a role in the sexual preferences and corresponding initial levels of sexual motivation in male rats. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Neurotrophic tropomyosin receptor kinase (NTRK) and nerve growth factor (NGF) are not expressed in Caucasian patients with biliary tract cancers: pooled data from three independent cohorts.

Neuronal signaling has been implicated in the pathophysiology of multiple malignancies. In biliary tract cancers (BTCs), tumor cell expression of nerve growth factor (NGF) and its receptor neurotrophic tropomyosin receptor kinase (NTRK) has been reported in Asian patients and linked to inferior clinical outcome. Furthermore, NTRK fusions have emerged as a promising target in various cancers. Expression patterns of these markers in Caucasian patients remain unknown. In this study, 106 patients with BTCs were included. Immunohistochemistry for pan-NTRK and NGF-beta was performed on > 90 samples of this cohort. Additionally, samples from two independent cohorts, incorporating 254 cases, were used to confirm the findings of the original cohort. While expression of pan-NTRK and NGF-beta was readily detectable in peri-tumoral nerves, these markers were not detectable in malignant epithelial cells in our cohort. In a large cohort of Caucasian patients with BTC, NTRK and NGF-beta were not detectable, underscoring potential differences between Caucasian and Asian patient populations.

The antidepressant effect of 4-hydroxybenzyl alcohol 2-naphthoate through monoaminergic, GABAergic system and BDNF signaling pathway

Gastrodigenin, also known as 4-hydroxybenzyl alcohol (HBA), is one of the main components of Gastrodia elata, which is a perfect lead compound of natural products. In order to get new active compounds, we modified the structure of HBA through esterification with carboxylic acid, and got a series of derivatives in which 4-hydroxybenzyl alcohol 2-naphthoate (NHBA) showed stronger antidepressant activity than HBA. In this paper, we firstly evaluated the antidepressant activity of NHBA by tail suspension test (TST) and forced swimming test (FST). Then, we carried out the biochemical assay and western blot to determine its mechanism. The results displayed that NHBA could increase the content of serotonin, dopamine, norepinephrine, γ-aminobutyric acid, brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) in mice brain. It suggested that NHBA exhibited an antidepressant-like effect through monoaminergic system, GABAergic system and BDNF/TrkB signaling pathways.

Analysis of NTRK Alterations in Pan-Cancer Adult and Pediatric Malignancies: Implications for NTRK-Targeted Therapeutics.

Fusions that involve neurotrophic-tropomyosin receptor kinase (NTRK) genes are known drivers of oncogenesis. Therapies that target these ultra-rare, constitutionally active NTRK fusions have been remarkably effective. Herein, we analyze the prevalence of the full array of NTRK alterations-fusions, mutations, copy number alterations, and increased transcript expression-in diverse adult and pediatric tumor types to understand the landscape of NTRK aberrations in cancer. We assessed 13,467 samples available from The Cancer Genome Atlas (adult tumors) and the St Jude PeCan database (pediatric tumors) for the prevalence of NTRK fusions, as well as associated genomic and transcriptomic co-aberrations in different tumor types. NTRK fusions were observed in 0.31% of adult tumors and in 0.34% of pediatric tumors. The most common gene partners were NTRK3 (0.16% of adult tumors) followed by NTRK1 (0.14% of pediatric tumors). NTRK fusions were found more commonly in pediatric melanoma (11.1% of samples), pediatric glioma (3.97%), and adult thyroid cancers (2.34%). Additional genomic and transcriptomic NTRK alterations- mutation, amplification, and mRNA overexpression-occurred in 14.2% of samples, whereas the frequency of alterations that implicated NTRK ligands and the NTRK co-receptor (p75NTR) ranged from 3.8% to 5.4%. Among 31 adult samples carrying NTRK fusions, co-alterations occurred often and usually involved the downstream phosphoinositide-3-kinase signaling pathway, cell-cycle machinery, other tyrosine-kinase receptors, and mitogen-activated protein kinase signals. Whereas NTRK fusions are exceedingly rare, other NTRK abnormalities affect 14% of patients with cancer. Affecting these alterations has not yet been achievable in cancer. Genomic co-alterations occur frequently with NTRK fusions, but it is not known if co-targeting them can attenuate primary or secondary resistance to NTRK inhibitors.

Primary and Metastatic Melanoma With NTRK Fusions.

A number of oncogenic driver mutations have been identified in melanocytic nevi and melanoma, but translocations also play a role in tumorigenesis and provide potential therapeutic targets for malignant lesions. Various translocations, such as those involving the anaplastic lymphoma kinase (ALK), neurotrophic tropomyosin receptor kinase 1 (NTRK1), and NTRK3 have been reported in spitzoid melanocytic neoplasms leading to kinase-fusion proteins that result in immunohistochemically detectable ALK or NTRK expression. We have previously reported that ALK expression can be found in nonspitzoid primary and metastatic cutaneous melanomas. In this study we report that nonspitzoid metastasizing melanomas of adults may also harbor NTRK fusions and that NTRK expression can be immunohistochemically detected in these tumors. Of 751 melanomas analyzed by next-generation sequencing, 4 metastatic melanomas were identified with NTRK fusions, 3 involving NTRK1, 1 involving NTRK2. They occurred in 3 women and 1 man. Two of the corresponding primary tumors were from the trunk, 1 from an extremity and 1 tumor arose in anal skin. One primary tumor displayed features of superficial spreading melanoma and 3 were nodular melanomas. All tumors were cytologically characterized by the presence of large epithelioid melanocytes. All tumors were immunoreactive with anti-Trk antibody. Next-generation sequencing documented that the NTRK1 fusion partners included TRIM63, DDR2, and GON4L. One tumor harbored an NTRK2-TRAF2 fusion. Thus, our findings document that NTRK kinase fusions can occur in nonspitzoid metastasizing melanomas of adults. The presence of an NTRK family fusion in these tumors may provide a therapeutic opportunity in a small subset of patients with metastatic melanoma.

Foretinib Overcomes Entrectinib Resistance Associated with the NTRK1 G667C Mutation in NTRK1 Fusion–Positive Tumor Cells in a Brain Metastasis Model

Purpose: Rearrangement of the neurotrophic tropomyosin receptor kinase 1 (NTRK1) gene, which encodes tyrosine receptor kinase A (TRK-A), occurs in various cancers, including colon cancer. Although entrectinib is effective in the treatment of central nervous system (CNS) metastases that express NTRK1 fusion proteins, acquired resistance inevitably results in recurrence. The CNS is a sanctuary for targeted drugs; however, the mechanism by which CNS metastases become entrectinib-resistant remains elusive and must be clarified to develop better therapeutics.Experimental Design: The entrectinib-resistant cell line KM12SM-ER was developed by continuous treatment with entrectinib in the brain metastasis-mimicking model inoculated with the entrectinib-sensitive human colon cancer cell line KM12SM, which harbors the TPM3-NTRK1 gene fusion. The mechanism of entrectinib resistance in KM12SM-ER cells was examined by next-generation sequencing. Compounds that overcame entrectinib resistance were screened from a library of 122 kinase inhibitors.Results: KM12SM-ER cells, which showed moderate resistance to entrectinib in vitro, had acquired the G667C mutation in NTRK1 The kinase inhibitor foretinib inhibited TRK-A phosphorylation and the viability of KM12SM-ER cells bearing the NTRK1-G667C mutation in vitro Moreover, foretinib markedly inhibited the progression of entrectinib-refractory KM12SM-ER-derived liver metastases and brain tumors in animal models, predominantly through inhibition of TRK-A phosphorylation.Conclusions: These results suggest that foretinib may be effective in overcoming entrectinib resistance associated with the NTRK1-G667C mutation in NTRK1 fusion-positive tumors in various organs, including the brain, and provide a rationale for clinical trials of foretinib in cancer patients with entrectinib-resistant tumors harboring the NTRK1-G667C mutation, including patients with brain metastases. Clin Cancer Res; 24(10); 2357-69. ©2018 AACR.

The expression of brain-derived neurotrophic factor and tropomyosin receptor kinase B protein in the prefrontal cortex of the post-stroke depression in the rat model

Objective To explore the expression of brain-derived neurotrophic factor(BDNF) and high-affinity receptors tropomyosin receptor kinase B(TrkB) protien in the prefrontal cortex of the post stroke depression in the rats. Methods Focal cerebral ischemic rat models were made with thread embolization method.Post stroke depression rat models were established with comprehensive separately breeding and chronic unpredicted mild stress (CUMS) on this basis.Normal control group, depression group and stroke group were used to compared with PSD group.6 rats were used in each group.Immunohistochemistry for detecting the expression of BDNF and TrkB in the prefrontal was used at 29th day since the CUMS. Results The number of BNDF immunopositive cells in PSD group was the least ((21.00±12.41) per microscope field of vision) than other groups.Whereas there was no statistical difference among groups(P>0.05). The number of TrkB immunopositive cells in the prefrontal cortex in PSD group was the least(20.78±7.20) among three groups, and depreesion group was secondary(21.00±5.61). Stroke group has the most number of immunopositive cells(31.67±7.38) in the prefrontal cortex among four groups.One way ANOVA statistical analysis showed the number of TrkB immunopositive cells decreased significantly in the PSD group and depression group compared with stroke group (P<0.05). Conclusion The downregulation of TrkB immunopositive cells in the prefrontal cortex may be responsible for the pathogenesis of PSD. Key words: Post stroke depression; Prefrontal cortex; Brain derived neurotrophic factor; Tropomyosin receptor kinase B; Protein