Trk Family Research Articles

Structural basis for the transmembrane signaling and antidepressant-induced activation of the receptor tyrosine kinase TrkB.

Neurotrophin receptors of the Trk family are involved in the regulation of brain development and neuroplasticity, and therefore can serve as targets for anti-cancer and stroke-recovery drugs, antidepressants, and many others. The structures of Trk protein domains in various states upon activation need to be elucidated to allow rational drug design. However, little is known about the conformations of the transmembrane and juxtamembrane domains of Trk receptors. In the present study, we employ NMR spectroscopy to solve the structure of the TrkB dimeric transmembrane domain in the lipid environment. We verify the structure using mutagenesis and confirm that the conformation corresponds to the active state of the receptor. Subsequent study of TrkB interaction with the antidepressant drug fluoxetine, and the antipsychotic drug chlorpromazine, provides a clear self-consistent model, describing the mechanism by which fluoxetine activates the receptor by binding to its transmembrane domain.

Positive Allosteric Modulators of Trk Receptors for the Treatment of Alzheimer's Disease.

Neurotrophins are important regulators of neuronal and non-neuronal functions. As such, the neurotrophins and their receptors, the tropomyosin receptor kinase (Trk) family of receptor tyrosine kinases, has attracted intense research interest and their role in multiple diseases including Alzheimer's disease has been described. Attempts to administer neurotrophins to patients have been reported, but the clinical trials have so far have been hampered by side effects or a lack of clear efficacy. Thus, much of the focus during recent years has been on identifying small molecules acting as agonists or positive allosteric modulators (PAMs) of Trk receptors. Two examples of successful discovery and development of PAMs are the TrkA-PAM E2511 and the pan-Trk PAM ACD856. E2511 has been reported to have disease-modifying effects in preclinical models, whereas ACD856 demonstrates both a symptomatic and a disease-modifying effect in preclinical models. Both molecules have reached the stage of clinical development and were reported to be safe and well tolerated in clinical phase 1 studies, albeit with different pharmacokinetic profiles. These two emerging small molecules are interesting examples of possible novel symptomatic and disease-modifying treatments that could complement the existing anti-amyloid monoclonal antibodies for the treatment of Alzheimer's disease. This review aims to present the concept of positive allosteric modulators of the Trk receptors as a novel future treatment option for Alzheimer's disease and other neurodegenerative and cognitive disorders, and the current preclinical and clinical data supporting this new concept. Preclinical data indicate dual mechanisms, not only as cognitive enhancers, but also a tentative neurorestorative function.

The Neurotrophin System in the Postnatal Brain-An Introduction.

Neurotrophins can bind to and signal through specific receptors that belong to the class of the Trk family of tyrosine protein kinase receptors. In addition, they can bind and signal through a low-affinity receptor, termed p75NTR. Neurotrophins play a crucial role in the development, maintenance, and function of the nervous system in vertebrates, but they also have important functions in the mature nervous system. In particular, they are involved in synaptic and neuronal plasticity. Thus, it is not surprisingly that they are involved in learning, memory and cognition and that disturbance in the neurotrophin system can contribute to psychiatric diseases. The neurotrophin system is sensitive to aging and changes in the expression levels correlate with age-related changes in brain functions. Several polymorphisms in genes coding for the different neurotrophins or neurotrophin receptors have been reported. Based on the importance of the neurotrophins for the central nervous system, it is not surprisingly that several of these polymorphisms are associated with psychiatric diseases. In this review, we will shed light on the functions of neurotrophins in the postnatal brain, especially in processes that are involved in synaptic and neuronal plasticity.

CCL19-Positive Lymph Node Stromal Cells Governthe Onset of Inflammatory Arthritis via Tropomyosin Receptor Kinase.

The study objective was to assess the role of CCL19+ lymph node stromal cells of the joint-draining popliteal lymph node (pLN) for the development of arthritis. CCL19+ lymph node stromal cells were spatiotemporally depleted for five days in the pLN before the onset of collagen-induced arthritis (CIA) using Ccl19-Cre × iDTR mice. In addition, therapeutic treatment with recombinant CCL19-immunoglobulin G (IgG), locally injected in the footpad, was used to confirm the results. RNA sequencing of lymph node stromal cells combined with T cell coculture assays using tropomyosin receptor kinase (Trk) family inhibitors together with in vivo local pLN small interfering RNA (siRNA) treatments were used to elucidate the pathway by which CCL19+ lymph node stromal cells initiate the onset of arthritis. Spatiotemporal depletion of CCL19+ lymph node stromal cells prevented disease onset in CIA mice. These inhibitory effects could be mimicked by local CCL19-IgG treatment. The messenger RNA sequencing analyses showed that CCL19+ lymph node stromal cells down-regulated the expression of the tropomyosin receptor kinase A (TrkA) just before disease onset. Blocking TrkA in lymph node stromal cells led to increased T cell proliferation in in vitro coculture assays. Similar effects were observed with the pan-Trk inhibitor larotrectinib in cocultures of lymph node stromal cells of patients with rheumatoid arthritis and T cells. Finally, local pLN treatment with TrkA inhibitor and TrkA siRNA led to exacerbated arthritis scores. CCL19+ lymph node stromal cells are crucially involved in the development of inflammatory arthritis. Therefore, targeting of CCL19+ lymph node stromal cells via TRK could provide a tool to prevent arthritis.

Trk Inhibition Reduces Tumorsphere Formation and Changes Expression of Stemness Markers in SK-ES-1 Ewing Sarcoma Cells

Introduction: Ewing sarcoma (ES) is a highly aggressive type of childhood cancer characterized by a chromosomal translocation resulting in fusions between the gene encoding EWS RNA Binding Protein 1 (EWSR1) and one gene of the ETS family, most frequently FLI-1, resulting in the EWS-FLI1 aberrant transcription factor. ES tumors can contain a subpopulation of cells showing cancer stem cell (CSC) features, which express stemness markers including CD133, OCT4 (Octamer-binding transcription factor 4), and NANOG, and display capacity to form tumorspheres likely enriched in CSCs. Neurotrophin (NT) receptors of the tropomyosin receptor kinase (Trk) family (TrkA, TrkB, and TrkC) may play a role in stimulating ES progression, but their possible role in CSCs remains unknown. Objective: To verify the effect of Trks inhibition on the formation of tumorspheres as well as the gene expression of stem markers. Method: The cells were dissociated and the formation of spheres was induced with supplemented culture medium and the K252a treatment was performed. After RNA extraction, mRNA expression levels of target genes Prom1 (CD133), OCT4 (POU5F1), SOX2, and Musashi-1 (MSI1) were analyzed by qPCR. Results: The pan-Trk inhibitor K252a (100 or 500 mM) hindered tumorsphere formation in human SK-ES-1 ES cell cultures. K252a also reduced mRNA expression of Prom1 (CD133-coding gene) while enhancing expression of OCT4. No changes in mRNA levels of SOX2 or Musashi-1 were observed. Conclusion: These findings provide the first evidence suggesting that Trk activity can influence stemness in ES cells.

The RUNX Family Defines Trk Phenotype and Aggressiveness of Human Neuroblastoma through Regulation of p53 and MYCN.

The Runt-related transcription factor (RUNX) family, which is essential for the differentiation of cells of neural crest origin, also plays a potential role in neuroblastoma tumorigenesis. Consecutive studies in various tumor types have demonstrated that the RUNX family can play either pro-tumorigenic or anti-tumorigenic roles in a context-dependent manner, including in response to chemotherapeutic agents. However, in primary neuroblastomas, RUNX3 acts as a tumor-suppressor, whereas RUNX1 bifunctionally regulates cell proliferation according to the characterized genetic and epigenetic backgrounds, including MYCN oncogenesis. In this review, we first highlight the current knowledge regarding the mechanism through which the RUNX family regulates the neurotrophin receptors known as the tropomyosin-related kinase (Trk) family, which are significantly associated with neuroblastoma aggressiveness. We then focus on the possible involvement of the RUNX family in functional alterations of the p53 family members that execute either tumor-suppressive or dominant-negative functions in neuroblastoma tumorigenesis. By examining the tripartite relationship between the RUNX, Trk, and p53 families, in addition to the oncogene MYCN, we endeavor to elucidate the possible contribution of the RUNX family to neuroblastoma tumorigenesis for a better understanding of potential future molecular-based therapies.

Effects of omega-3 fatty acid supplementation during chronic maternal hypoxiaon behavioral disorders in male rat offspring: the role of Trk family and oxidative stress.

Maternal hypoxia due to a lack of blood flow and insufficient oxygen supply in the brain leads to behavioral disorders in adult offspring. Fish oil includes docosahexaenoic acid (DHA), a significant component of membrane phospholipids of nerve cells, which improved cognition, and memory. Trk family receptors are activated by hypoxic induction factor (HIF), and are involved in the neurotrophin's protective effects at the cellular level. Here we studied the biochemical, and molecular mechanisms of the protective effect of fish oil during the chronic maternal hypoxia model on behavioral responses in male rat offspring. Pregnant female rats were randomly divided into 4 experimental groups: 1) ctr; Control rats were pregnant 2) Hyp; Pregnant female rats received hypoxia from 6 to 15th day of pregnancy, with 10% oxygen intensity, and 90% nitrogen; 3) FO; Pregnant female rats received fish oil (F8020 1ml / day, for ten consecutive days Orally), and 4) FO / Hyp; Pregnant female rats received hypoxia plus fish oil in the same manner. Behavioral parameters were evaluated in 28-day-old male offspring. HIF-1α, TrkB, and P75 gene expression were measured in the offspring's brain. Maternal hypoxia impaired memory performance, and locomotor activity in offspring. Besides, Trk family gene expression, and oxidative stress indicators showed a significant increase in the offspring's brain exposed to maternal hypoxia compared to the control group. Overall, fish oil improved behavioral parameters by inhibiting oxidative stress, and the expression of Trk family receptors.

Intrinsically disordered regions couple the ligand binding and kinase activation of Trk neurotrophin receptors

SummaryReceptor tyrosine kinases (RTKs) are key players in development and several diseases. Understanding the molecular mechanism of RTK activation by its ligand could lead to the design of new RTK inhibitors. How the extracellular domain is coupled to the intracellular kinase domain is a matter of debate. Ligand-induced dimerization and ligand-induced conformational change of pre-formed dimers are two of the most proposed models. Recently we proposed that TrkA, the RTK for nerve growth factor (NGF), is activated by rotation of the transmembrane domain (TMD) pre-formed dimers upon NGF binding. However, one of the unsolved issues is how the ligand binding is conformationally coupled to the TMD rotation if unstructured extracellular juxtamembrane (eJTM) regions separate them. Here we use nuclear magnetic resonance in bicelles and functional studies to demonstrate that eJTM regions from the Trk family are intrinsically disordered and couple the ligand-binding domains and TMDs possibly via the interaction with NGF.

\u03b3-Enolase enhances Trk endosomal trafficking and promotes neurite outgrowth in differentiated SH-SY5Y cells

BackgroundNeurotrophins can activate multiple signalling pathways in neuronal cells through binding to their cognate receptors, leading to neurotrophic processes such as cell survival and differentiation. γ-Enolase has been shown to have a neurotrophic activity that depends on its translocation towards the plasma membrane by the scaffold protein γ1-syntrophin. The association of γ-enolase with its membrane receptor or other binding partners at the plasma membrane remains unknown.MethodsIn the present study, we used immunoprecipitation and immunofluorescence to show that γ-enolase associates with the intracellular domain of the tropomyosin receptor kinase (Trk) family of tyrosine kinase receptors at the plasma membrane of differentiated SH-SY5Y cells.ResultsIn differentiated SH-SY5Y cells with reduced expression of γ1-syntrophin, the association of γ-enolase with the Trk receptor was diminished due to impaired translocation of γ-enolase towards the plasma membrane or impaired Trk activity. Treatment of differentiated SH-SY5Y cells with a γ-Eno peptide that mimics γ-enolase neurotrophic activity promoted Trk receptor internalisation and endosomal trafficking, as defined by reduced levels of Trk in clathrin-coated vesicles and increased levels in late endosomes. In this way, γ-enolase triggers Rap1 activation, which is required for neurotrophic activity of γ-enolase. Additionally, the inhibition of Trk kinase activity by K252a revealed that increased SH-SY5Y cell survival and neurite outgrowth mediated by the γ-Eno peptide through activation of signalling cascade depends on Trk kinase activity.ConclusionsThese data therefore establish the Trk receptor as a binding partner of γ-enolase, whereby Trk endosomal trafficking is promoted by γ-Eno peptide to mediate its neurotrophic signalling.Graphical 2AMQTViHdEDXMx8XQj7RdSVideo abstract

NTRK3-rearranged thyroid carcinoma, clinical and pathologic features

Abstract Introduction/Objective NTRK3 gene encodes a transmembrane protein receptor of the tropomyosin receptor kinase (Trk) family. Gene fusions involving NTRK3 result in a constitutive activation or overexpression of Trk receptor, potentially leading to oncogenesis. NTRK targeted therapies show a promising activity in varied cancer types with NTRK fusions. The aim of this case review is to describe the clinical and pathologic findings of thyroid neoplasm with NTRK3 gene fusions. Methods/Case Report The cytology fine needle aspiration (FNA), molecular testing results and pathology of surgical resections are reviewed in 220 cases of total and hemithyroidectomy from January 2018 to May 2021. Results (if a Case Study enter NA) Three cases with NTRK3 gene fusions are identified by Thyroseq or Afirma GSC from FNA of thyroid nodules with later surgical intervention. No other mutations or gene fusions were identified. Each case had total thyroidectomy. Case 1 is a 41-year-old female with FNA diagnosis of suspicious for papillary thyroid carcinoma (PTC) and ETV6/NTRK3 fusion found by Afirma GSC. Pathology diagnosis is PTC classic type, two tumor nodules 1.1cm and 1.0cm, lymphovascular invasion not identified, three lymph nodes not involved by tumor and pathologic stage pT1b(m) pN0. Case 2 is a 49-year-old female with FNA diagnosis of atypia of undetermined significance and ETV6/NTRK3 fusion detected by Thyroseq. Pathology diagnosis is infiltrative PTC follicular variant, 2.0cm, angioinvasion present, no lymph nodes submitted and pathologic stage pT1b(m) pNX. Case 3 is a 28-year-old female with FNA diagnosis of suspicious for follicular derived neoplasm and NTRK3/RBPMS fusion is detected by Afirma GSC. Pathology diagnosis is infiltrative PTC follicular variant, 1.5cm, 9 of 11 lymph nodes positive for metastatic carcinoma and pathologic stage pT1b pN1b. Conclusion Thyroid neoplasm with NTRK3-rearrangement is rare. Cases 1 and 2 with common ETV6-NTRK3 fusion show PTC classic type and infiltrative PTC follicular variant with angioinvasion. Case 3 with less common NTRK3/RBPMS fusion shows infiltrative PTC follicular variant and significant lymph node involvement. Our limited cases of NTRK3-rearranged thyroid carcinoma demonstrate infiltrative growth, diverse phenotypes, one case with angioinvasion and no lymph nodes submitted and one case with multiple lymph node metastasis. This suggests aggressive behavior of thyroid cancer with NTRK3 gene fusion and patients may benefit from targeted NTRK therapy.

Therapeutic Neuroprotection by an Engineered Neurotrophin that Selectively Activates Tropomyosin Receptor Kinase (Trk) Family Neurotrophin Receptors but Not the p75 Neurotrophin Receptor.

The neurotrophin growth factors bind and activate two types of cell surface receptors: the tropomyosin receptor kinase (Trk) family and p75. TrkA, TrkB, and TrkC are bound preferentially by nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3 (NT3), respectively, to activate neuroprotective signals. The p75 receptors are activated by all neurotrophins, and paradoxically in neurodegenerative disease p75 is upregulated and mediates neurotoxic signals. To test neuroprotection strategies, we engineered NT3 to broadly activate Trk receptors (mutant D) or to reduce p75 binding (mutant RK). We also combined these features in a molecule that activates TrkA, TrkB, and TrkC but has reduced p75 binding (mutant DRK). In neurodegenerative disease mouse models in vivo, the DRK protein is a superior therapeutic agent compared with mutant D, mutant RK, and wild-type neurotrophins and protects a broader range of stressed neurons. This work rationalizes a therapeutic strategy based on the biology of each type of receptor, avoiding activation of p75 toxicity while broadly activating neuroprotection in stressed neuronal populations expressing different Trk receptors. SIGNIFICANCE STATEMENT: The neurotrophins nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3 each can activate a tropomyosin receptor kinase (Trk) A, TrkB, or TrkC receptor, respectively, and all can activate a p75 receptor. Trks and p75 mediate opposite signals. We report the engineering of a protein that activates all Trks, combined with low p75 binding, as an effective therapeutic agent in vivo.

Molecular Basis of Late-Life Depression.

Late-life depression (LLD), compared to depression at a young age, is more likely to have poor prognosis and high risk of progression to dementia. A recent systemic review and meta-analysis of the present antidepressants for LLD showed that the treatment response rate was 48% and the remission rate was only 33.7%, thus implying the need to improve the treatment with other approaches in the future. Recently, agents modulating the glutamatergic system have been tested for mental disorders such as schizophrenia, dementia, and depressive disorder. Ketamine, a noncompetitive NMDA receptor (NMDAR) antagonist, requires more evidence from randomized clinical trials (RCTs) to prove its efficacy and safety in treating LLD. The metabotropic receptors (mGluRs) of the glutamatergic system are family G-protein-coupled receptors, and inhibition of the Group II mGluRs subtypes (mGlu2 and mGlu3) was found to be as effective as ketamine in exerting rapid antidepressant activity in some animal studies. Inflammation has been thought to contribute to depression for a long time. The cytokine levels not only increase with age but also decrease serotonin. Regarding LLD, interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) released in vivo are likely to contribute to the reduced serotonin level. Brain-derived neurotrophic factor (BDNF), a growth factor and a modulator in the tropomyosin receptor kinase (Trk) family of tyrosine kinase receptors, probably declines quantitatively with age. Recent studies suggest that BDNF/TrkB decrement may contribute to learning deficits and memory impairment. In the process of aging, physiological changes in combination with geriatric diseases such as vascular diseases result in poorer prognosis of LLD in comparison with that of young-age depression. Treatments with present antidepressants have been generally unsatisfactory. Novel treatments such as anti-inflammatory agents or NMDAR agonists/antagonists require more studies in LLD. Last but not least, LLD and dementia, which share common pathways and interrelate reciprocally, are a great concern. If it is possible to enhance the treatment of LDD, dementia can be prevented or delated.

Combined kinesin-1 and kinesin-3 activity drives axonal trafficking of TrkB receptors in Rab6 carriers.

SummaryNeurons depend on proper localization of neurotrophic receptors in their distal processes for their function. The Trk family of neurotrophin receptors controls neuronal survival, differentiation, and remodeling and are well known to function as retrograde signal carriers transported from the distal axon toward the cell body. However, the mechanism driving anterograde trafficking of Trk receptors into the axon is not well established. We used microfluidic compartmental devices and inducible secretion assay to systematically investigate the retrograde and anterograde trafficking routes of TrkB receptor along the axon in rat hippocampal neurons. We show that newly synthesized TrkB receptors traffic through the secretory pathway and are directly delivered into axon. We found that these TrkB carriers associate and are regulated by Rab6. Furthermore, the combined activity of kinesin-1 and kinesin-3 is needed for the formation of axon-bound TrkB secretory carriers and their effective entry and processive anterograde transport beyond the proximal axon.

Comparison of tyrosine kinase domain properties for the neurotrophin receptors TrkA and TrkB.

The tropomyosin-related kinase (Trk) family consists of three receptor tyrosine kinases (RTKs) called TrkA, TrkB, and TrkC. These RTKs are regulated by the neurotrophins, a class of secreted growth factors responsible for the development and function of neurons. The Trks share a high degree of homology and utilize overlapping signaling pathways, yet their signaling is associated with starkly different outcomes in certain cancers. For example, in neuroblastoma, TrkA expression and signaling correlates with a favorable prognosis, whereas TrkB is associated with poor prognoses. To begin to understand how activation of the different Trks can lead to such distinct cellular outcomes, we investigated differences in kinase activity and duration of autophosphorylation for the TrkA and TrkB tyrosine kinase domains (TKDs). We find that the TrkA TKD has a catalytic efficiency that is ∼2-fold higher than that of TrkB, and becomes autophosphorylated in vitro more rapidly than the TrkB TKD. Studies with mutated TKD variants suggest that a crystallographic dimer seen in many TrkA (but not TrkB) TKD crystal structures, which involves the kinase-insert domain, may contribute to this enhanced TrkA autophosphorylation. Consistent with previous studies showing that cellular context determines whether TrkB signaling is sustained (promoting differentiation) or transient (promoting proliferation), we also find that TrkB signaling can be made more transient in PC12 cells by suppressing levels of p75NTR. Our findings shed new light on potential differences between TrkA and TrkB signaling, and suggest that subtle differences in signaling dynamics can lead to substantial shifts in the cellular outcome.

602TiP A first-in-human study of NOV1601 (CHC2014), small-molecule inhibitor of TRK family proteins, in adult patients with solid organ malignancies

602TiP A first-in-human study of NOV1601 (CHC2014), small-molecule inhibitor of TRK family proteins, in adult patients with solid organ malignancies

Expression and pharmacological inhibition of TrkB and EGFR in glioblastoma.

A member of the Trk family of neurotrophin receptors, tropomyosin receptor kinase B (TrkB, encoded by the NTRK2 gene) is an increasingly important target in various cancer types, including glioblastoma (GBM). EGFR is among the most frequently altered oncogenes in GBM, and EGFR inhibition has been tested as an experimental therapy. Functional interactions between EGFR and TrkB have been demonstrated. In the present study, we investigated the role of TrkB and EGFR, and their interactions, in GBM.Analyses of NTRK2 and EGFR gene expression from The Cancer Genome Atlas (TCGA) datasets showed an increase in NTRK2 expression in the proneural subtype of GBM, and a strong correlation between NTRK2 and EGFR expression in glioma CpG island methylator phenotype (G-CIMP+) samples. We showed that when TrkB and EGFR inhibitors were combined, the inhibitory effect on A172 human GBM cells was more pronounced than when either inhibitor was given alone. When U87MG GBM cells were xenografted into the flank of nude mice, tumor growth was delayed by treatment with TrkB and EGFR inhibitors, given alone or combined, only at specific time points. Intracranial GBM growth in mice was not significantly affected by drug treatments.Our findings indicate that correlations between NTRK2 and EGFR expression occur in specific GBM subgroups. Also, our results using cultured cells suggest for the first time the potential of combining TrkB and EGFR inhibition for the treatment of GBM.

Abstract 3087: FCN-098, a novel second-generation TRK inhibitor, overcomes TRK resistance mutations in vitro and in vivo

Abstract Tropomyosin receptor kinases (TRK or NTRK) are the transmembrane tyrosine kinases activated by soluble growth factors named neurotrophins (NT). TRK family includes three different members, namely TRKA, TRKB and TRKC. Extracellular recognition of NT to TRK proteins induces receptor dimerization, phosphorylation, and activation of the downstream signal transduction pathways via PI3K, RAS/MAPK/ERK, and PLC-gamma. TRKs are expressed primarily in neuronal tissues and regulate differentiation and survival of neuronal cells. Alteration of TRK pathway caused by gene fusion of TRK is frequently associated with the poor prognosis of a wide range of solid malignancies, such as neuroblastoma, breast cancer, pancreatic cancer, melanoma, thyroid cancer, glioblastoma, colorectal cancer, sarcomas, cholangiocarcinoma, and non-small cell lung cancer. The efficacy of TRK inhibition in TRK fusion-positive cancers has been demonstrated by the high response rate and lasting effect of the first-generation TRK inhibitors larotrectinib and entrectinib. However, acquired resistance mutations of TRK, such as solvent front mutations, gatekeeper mutations and DFG motif mutations, often emerge and abrogate the inhibitory effect of first-generation inhibitors. Thus, developing novel TRK inhibitors that can effectively overcome resistance mutations can provide great clinical benefits to patients. Here we introduce FCN-098, a potent second-generation TRK inhibitor. FCN-098 demonstrated marked kinase inhibition activity against wild-type (WT) and mutant TRK with IC50 at sub-nano or single nanomolar range. FCN-098 significantly and dose-dependently inhibited phosphorylation of TRK and its downstream effector ERK in TRK fusion-positive KM12 human colon cancer cells and BaF3 cells ectopically overexpressing WT or mutant TRK fusions. FCN-098 potently inhibited proliferation of KM12 cells and BaF3 cells overexpressing WT or various mutant TRK fusions while sparing TRK-negative cell lines. Consistent with in vitro results, FCN-098 showed remarkable anti-tumor activity in xenograft models driven by WT or mutant TRK fusions in a dose-dependent manner. In particular, the anti-tumor activity of FCN-098 was superior to another second-generation TRK inhibitor LOXO-195 at the same dose in xenografts driven by TPM3-TRKA G595R or ETV6-TRKC G623R mutation, and exhibited comparable potency to LOXO-195 in LMNA-TRKA G667C-driven xenografts. In non-clinical studies, FCN-098 exhibited excellent pharmacokinetic (PK) and safety properties, demonstrating longer T1/2 in both dogs and rats along with higher Cmax and larger dose-normalized AUC in dogs compared to LOXO-195. Overall, FCN-098 overcomes TRK resistance mutations in vitro and in vivo and exhibits favorable PK and safety profiles. FCN-098 has the potential to become an effective and safe therapeutic choice for a wide range of solid tumors harboring WT or mutant TRK fusions. Citation Format: Shu Lin, Tongshuang Li, Xianlong Wang, Lijun Yang, Zhifang Chen, Yue Rong, Xingdong Zhao, Yanxin Liu, Zongyao Zou, Min Lin, Yuwei Gao, Jiashu Zhou, Weibo Wang. FCN-098, a novel second-generation TRK inhibitor, overcomes TRK resistance mutations in vitro and in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3087.

Bacterial Second Messenger Cyclic di-AMP Modulates the Competence State in Streptococcus pneumoniae.

Streptococcus pneumoniae (the pneumococcus) is a naturally competent organism that causes diseases such as pneumonia, otitis media, and bacteremia. The essential bacterial second messenger cyclic di-AMP (c-di-AMP) is an emerging player in the stress responses of many pathogens. In S. pneumoniae, c-di-AMP is produced by a diadenylate cyclase, CdaA, and cleaved by phosphodiesterases Pde1 and Pde2. c-di-AMP binds a transporter of K+ (Trk) family protein, CabP, which subsequently halts K+ uptake via the transporter TrkH. Recently, it was reported that Pde1 and Pde2 are essential for pneumococcal virulence in mouse models of disease. To elucidate c-di-AMP-mediated transcription that may lead to changes in pathogenesis, we compared the transcriptomes of wild-type (WT) and Δpde1 Δpde2 strains by transcriptome sequencing (RNA-Seq) analysis. Notably, we found that many competence-associated genes are significantly upregulated in the Δpde1 Δpde2 strain compared to the WT. These genes play a role in DNA uptake, recombination, and autolysis. Competence is induced by a quorum-sensing mechanism initiated by the secreted factor competence-stimulating peptide (CSP). Surprisingly, the Δpde1 Δpde2 strain exhibited reduced transformation efficiency compared to WT bacteria, which was c-di-AMP dependent. Transformation efficiency was also directly related to the [K+] in the medium, suggesting a link between c-di-AMP function and the pneumococcal competence state. We found that a strain that possesses a V76G variation in CdaA produced less c-di-AMP and was highly susceptible to CSP. Deletion of cabP and trkH restored the growth of these bacteria in medium with CSP. Overall, our study demonstrates a novel role for c-di-AMP in the competence program of S. pneumoniaeIMPORTANCE Genetic competence in bacteria leads to horizontal gene transfer, which can ultimately affect antibiotic resistance, adaptation to stress conditions, and virulence. While the mechanisms of pneumococcal competence signaling cascades have been well characterized, the molecular mechanism behind competence regulation is not fully understood. The bacterial second messenger c-di-AMP has previously been shown to play a role in bacterial physiology and pathogenesis. In this study, we provide compelling evidence for the interplay between c-di-AMP and the pneumococcal competence state. These findings not only attribute a new biological function to this dinucleotide as a regulator of competence, transformation, and survival under stress conditions in pneumococci but also provide new insights into how pneumococcal competence is modulated.

Abstract 2198: PBI-200: A novel, brain penetrant, next generation pan-TRK kinase inhibitor

Abstract Fusions of NTRK 1, 2 and3 genes encoding the TRK family of receptor tyrosine kinases (TrkA, B and C, respectively) have been reported in 1-3% of all human cancers including lung and breast cancers. NTRK gene fusions are also reported in lung and breast tumors metastatic to the brain as well as in primary brain tumors including glioblastoma (3%), astrocytoma (3%) and pediatric glioma (40%). These gene fusions result in constitutive TRK kinase activity and act as oncogenic drivers of disease. First generation TRK kinase inhibitors have demonstrated clinical proof of concept in patients with tumors bearing NTRK gene fusions. PBI-200 is a novel, selective pan-TRK kinase inhibitor. In biochemical assays it inhibits TrkA, B and C with IC50 values of 0.45, 2.2 and 1.9 nM, respectively. This molecule is highly selective against a panel of 122 other protein kinases tested with the exception of Ros1 (IC50= 31 nM). Importantly, PBI-200 retains potency against resistance mutations reported in patients receiving first generation TRK kinase inhibitors. Biochemical IC50 values are 3.4 nM for the TrkA G595R gatekeeper mutation and 10 nM for the TrkA G667C mutant. PBI-200 potently inhibits proliferation of human tumor cell lines expressing TRK fusions including the KM-12 colorectal cancer cell line (TPM3-NTRK1 fusion; EC50 value = 22 nM) and the MO-91 acute myeloid leukemia cell line (ETV6-NTRK3 fusion; EC50 value = 3.5 nM). It also potently inhibits proliferation of rat BaF3 cells expressing oncogenic NTRK fusions and their resistant variants. In a subcutaneous xenograft model of KM-12 colorectal cancer, PBI-200 induces tumor stasis when dosed intraperitoneally at 15 or 30 mg/kg twice daily (93 and 100% tumor growth inhibition, respectively). The activity of PBI-200 was comparable or superior to that seen with the first generation TRK kinase inhibitors used as comparators in this model. PBI-200 has oral bioavailability in both rat and mouse. Importantly, PBI-200 demonstrates excellent brain penetration in rodent species, with brain/plasma AUC ratios of 3.9 in the mouse and 3.2 in the rat. This is in contrast to the poor brain penetration observed with the first generation TRK kinase inhibitors, larotrectinib and entrectinib.PBI-200 is efficacious in an intracranial KM-12 xenograft model when dosed intraperitoneally or orally, significantly slowing tumor growth and extending survival. Based on the activity of PBI-200 against clinically-relevant resistance mutations and its excellent brain penetration, this molecule has potential to be a next-generation TRK kinase inhibitor especially for primary brain tumors or brain metastatic lesions that harbor a NTRK gene fusion. PBI-200 is currently undergoing further characterization in IND enabling studies. Citation Format: Anthony Regina, Aram Elagoz, Vincent Albert, Jonathan Boudreault, Hong Wang, Marc Ouellet, Nicolas Brunei-Latour, Edith Bellavance, Peter White, Stephane Ciblat, W. Robert Bishop, Kollol Pal. PBI-200: A novel, brain penetrant, next generation pan-TRK kinase inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2198.

Potassium uptake systems of Candida krusei.

Candida krusei is a pathogenic yeast species that is phylogenetically outside both of the well-studied yeast groups, whole genome duplication and CUG. Like all other yeast species, it needs to accumulate high amounts of potassium cations, which are needed for proliferation and many other cell functions. A search in the sequenced genomes of nine C.krusei strains revealed the existence of two highly conserved genes encoding putative potassium uptake systems. Both of them belong to the TRK family, whose members have been found in all the sequenced genomes of species from the Saccharomycetales subclade. Analysis and comparison of the two C.krusei Trk sequences revealed all the typical features of yeast Trk proteins but also an unusual extension of the CkTrk2 hydrophilic N-terminus. The expression of both putative CkTRK genes in Saccharomyces cerevisiae lacking its own potassium importers showed that only CkTrk1 is able to complement the absence of S.cerevisiae's own transporters and provide cells with a sufficient amount of potassium. Interestingly, a portion of the CkTrk1 molecules were localized to the vacuolar membrane. The presence of CkTrk2 had no evident phenotype, due to the fact that this protein was not correctly targeted to the S.cerevisiae plasma membrane. Thus, CkTrk2 is the first studied yeast Trk protein to date that was not properly recognized and targeted to the plasma membrane upon heterologous expression in S.cerevisiae.