Are TrkB receptor agonists the right tool to fulfill the promises for a therapeutic value of the brain-derived neurotrophic factor?

Brain-derived neurotrophic factor signaling via its receptor tro pomyosin receptor kinase B regulates several crucial physiological processes.It has been shown to act in the brain,promoting neuronal survival,growth,and plasticity as well as in the rest of the body where it is involved in regulating for instance aspects of the metabolism.Due to its crucial and very pleiotro pic activity,reduction of brain-derived neurotrophic factor levels and alterations in the brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling have been found to be associated with a wide spectrum of neurological diseases.Howeve r,because of its poor bioavailability and pharmacological properties,brain-derived neurotrophic factor itself has a very low therapeutic value.Moreover,the concomitant binding of exogenous brain-derived neurotrophic factor to the p75 neurotrophin receptor has the potential to elicit several unwanted and deleterious side effects.Therefo re,developing tools and approaches to specifically promote tropomyosin receptor kinase B signaling has become an important goal of translational research.Among the newly developed tools are different categories of tropomyosin receptor kinase B receptor agonist molecules.In this review,we give a comprehensive description of the diffe rent tro pomyosin receptor kinase B receptor agonist drugs developed so far and of the res ults of their application in animal models of several neurological diseases.Moreover,we discuss the main benefits of tropomyosin receptor kinase B receptor agonists,concentrating especially on the new tropomyosin receptor kinase B agonist antibodies.The benefits observed both in vitro and in vivo upon application of tropomyosin receptor kinase B receptor agonist drugs seem to predominantly depend on their general neuroprotective activity and their ability to promote neuronal plasticity.Moreover,tro pomyosin receptor kinase B agonist antibodies have been shown to specifically bind the tropomyosin receptor kinase B receptor and not p75 neurotrophin receptor.Therefore,while,based on the current knowledge,the tropomyosin receptor kinase B receptor agonists do not seem to have the potential to reve rse the disease pathology per se,promoting brainderived neurotrophic factor/tro pomyosin receptor kinase B signaling still has a very high therapeutic relevance.

Light-controlled phosphorylation in the TrkA-Y785 site by photosensitive UAAs activates the MAPK/ERK signaling pathway

Background:This paper aims to establish a light-controlled phosphorylation detection method at the Y785 site of tropomyosin receptor kinase A(TrkA)receptor in mammalian cells by using genetic code expansion technology and detecting the effects of optical activation of this site on the downstream MAPK/ERK pathway.The study is based on the current situation that the regulatory mechanism of TrkA phosphorylation has not been fully elucidated.Methods:Two photosensitive unnatural amino acids,p-azido-L-phenylalanine(AzF)and photo-caged tyrosine(ONB)were introduced into the TrkA-Y785 site by genetic code expansion technology and site-directed mutagenesis.Western blotting and laser confocal imaging were conducted to analyze the effects of this site on activating the MAPK/ERK pathway and nerve cell differentiation before and after photostimulation.Results:Our results supplemented the light-controlled results of the TrkA-Y785 site based on our previous research and verified that Y785 also makes important contributions in regulating the MAPK/ERK pathway.Conclusion:This study demonstrated the significant contributions of the TrkAY785 site in regulating the ERK pathway by precisely controlling the phosphorylation state of a single tyrosine site.

Development of small-molecule tropomyosin receptor kinase(TRK) inhibitors for NTRK fusion cancers

Tropomyosin receptor kinase A,B and C(TRKA,TRKB and TRKC),which are well-known members of the cell surface receptor tyrosine kinase(RTK)family,are encoded by the neurotrophic receptor tyrosine kinase 1,2 and 3(NTRK1,NTRK2 and NTRK3)genes,respectively.TRKs can regulate cell proliferation,differentiation and even apoptosis through the RAS/MAPKs,PI3 K/AKT and PLCγtyrosine kinase fusions;Small-molecule inhibitor;NTRK fusion cancer pathways.Gene fusions involving NTRK act as oncogenic drivers of a broad diversity of adult and pediatric tumors,and TRKs have become promising antitumor targets.Therefore,achieving a comprehensive understanding of TRKs and relevant TRK inhibitors should be urgently pursued for the further development of novel TRK inhibitors for potential clinical applications.This review focuses on summarizing the biological functions of TRKs and NTRK fusion proteins,the development of small-molecule TRK inhibitors with different chemotypes and their activity and selectivity,and the potential therapeutic applications of these inhibitors for future cancer drug discovery efforts.

Neurotrophic factor-based pharmacological approaches in neurological disorders

Aging is a physiological event dependent on multiple pathways that are linked to lifespan and processes leading to cognitive decline.This process represents the major risk factor for aging-related diseases such as Alzheimer’s disease,Parkinson’s disease,and ischemic stroke.The incidence of all these pathologies increases exponentially with age.Research on aging biology has currently focused on elucidating molecular mechanisms leading to the development of those pathologies.Cognitive deficit and neurodegeneration,common features of aging-related pathologies,are related to the alteration of the activity and levels of neurotrophic factors,such as brain-derived neurotrophic factor,nerve growth factor,and glial cell-derived neurotrophic factor.For this reason,treatments that modulate neurotrophin levels have acquired a great deal of interest in preventing neurodegeneration and promoting neural regeneration in several neurological diseases.Those treatments include both the direct administration of neurotrophic factors and the induced expression with viral vectors,neurotrophins’binding with biomaterials or other molecules to increase their bioavailability but also cell-based therapies.Considering neurotrophins’crucial role in aging pathologies,here we discuss the involvement of several neurotrophic factors in the most common brain aging-related diseases and the most recent therapeutic approaches that provide direct and sustained neurotrophic support.

Neuroprotective effects of exogenous brain-derived neurotrophic factor on amyloid-beta 1-40-induced retinal degeneration

Amyloid-beta(Aβ)-related alterations,similar to those found in the brains of patients with Alzheimer's disease,have been observed in the retina of patients with glaucoma.Decreased levels of brain-derived neurotrophic factor(BDNF)are believed to be associated with the neurotoxic effects of Aβpeptide.To investigate the mechanism underlying the neuroprotective effects of BDNF on Aβ_(1-40)-induced retinal injury in Sprague-Dawley rats,we treated rats by intravitreal administration of phosphate-buffered saline(control),Aβ_(1-40)(5 nM),or Aβ_(1-40)(5 nM)combined with BDNF(1μg/mL).We found that intravitreal administration of Aβ_(1-40)induced retinal ganglion cell apoptosis.Fluoro-Gold staining showed a significantly lower number of retinal ganglion cells in the Aβ_(1-40)group than in the control and BDNF groups.In the Aβ_(1-40)group,low number of RGCs was associated with increased caspase-3 expression and reduced TrkB and ERK1/2 expression.BDNF abolished Aβ_(1-40)-induced increase in the expression of caspase-3 at the gene and protein levels in the retina and upregulated TrkB and ERK1/2 expression.These findings suggest that treatment with BDNF prevents RGC apoptosis induced by Aβ_(1-40)by activating the BDNF-TrkB signaling pathway in rats.

Therapeutic potential of brain-derived neurotrophic factor(BDNF)and a small molecular mimics of BDNF for traumatic brain injury

Traumatic brain injury（TBI） is a major health problem worldwide.Following primary mechanical insults,a cascade of secondary injuries often leads to further neural tissue loss.Thus far there is no cure to rescue the damaged neural tissue.Current therapeutic strategies primarily target the secondary injuries focusing on neuroprotection and neuroregeneration.The neurotrophin brain-derived neurotrophic factor（BDNF） has significant effect in both aspects,promoting neuronal survival,synaptic plasticity and neurogenesis.Recently,the flavonoid 7,8-dihydroxyflavone（7,8-DHF）,a small Trk B agonist that mimics BDNF function,has shown similar effects as BDNF in promoting neuronal survival and regeneration following TBI.Compared to BDNF,7,8-DHF has a longer half-life and much smaller molecular size,capable of penetrating the blood-brain barrier,which makes it possible for non-invasive clinical application.In this review,we summarize functions of the BDNF/Trk B signaling pathway and studies examining the potential of BDNF and 7,8-DHF as a therapy for TBI.

An NT-3-releasing bioscaffold supports the formation of TrkC-modified neural stem cell-derived neural network tissue with efficacy in repairing spinal cord injury

The mechanism underlying neurogenesis during embryonic spinal cord development involves a specific ligand/receptor interaction,which may be help guide neuroengineering to boost stem cell-based neural regeneration for the structural and functional repair of spinal cord injury.Herein,we hypothesized that supplying spinal cord defects with an exogenous neural network in the NT-3/fibroin-coated gelatin sponge(NF-GS)scaffold might improve tissue repair efficacy.To test this,we engineered tropomyosin receptor kinase C(TrkC)-modified neural stem cell(NSC)-derived neural network tissue with robust viability within an NF-GS scaffold.When NSCs were genetically modified to overexpress TrkC,the NT-3 receptor,a functional neuronal population dominated the neural network tissue.The pro-regenerative niche allowed the long-term survival and phenotypic maintenance of the donor neural network tissue for up to 8 weeks in the injured spinal cord.Additionally,host nerve fibers regenerated into the graft,making synaptic connections with the donor neurons.Accordingly,motor function recovery was significantly improved in rats with spinal cord injury(SCI)that received TrkC-modified NSC-derived neural network tissue transplantation.Together,the results suggested that transplantation of the neural network tissue formed in the 3D bioactive scaffold may represent a valuable approach to study and develop therapies for SCI.

Opportunities and challenges in developing tissue-agnostic anti-cancer drugs

The rapid advances in the understanding of oncogenic process and the maturation of affordable precision diagnostic tools have enabled the development of targeted therapeutic agents,such as those targeting BCR-ABL,epithelial growth factor receptor L858R,EML4-anaplastic lymphoma kinase,and BRAF V600E,to treat cancers that harbor specific molecular alterations.Traditionally,each targeted drug has been developed for a particular tumor type where such alteration is most frequently found.Recently,the widespread adoption of next generation sequencing has led to an increase in the identification of rare and ultra-rare alterations,and,in some cases,the same rare alterations are found across multiple tumor types.The rarity of these alterations makes clinical trials traditionally designed for specific tumor types infeasible.As a result,tissue-agnostic trials have been developed to study the efficacy of these treatments and increase patient access.This review summarizes current successful cases of tissue-agnostic development,such as drugs targeting tropomyosin receptor kinase fusions,and proposes the next wave of potential tissue-agnostic targets,including fusions of ROS1,anaplastic lymphoma kinase,fibroblast growth factor receptor,and rearranged during transfection.In addition,the advantages and the challenges of such approach are discussed in the context of clinical development and approval.