Inhibition of DYRK1A proteolysis modifies its kinase specificity and rescues Alzheimer phenotype in APP/PS1 mice

Discovering a novel dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) inhibitor and its impact on tau phosphorylation and amyloid-β formation

Dual-specificity tyrosine-regulated kinase 1 A (DYRK1A) is crucial in neurogenesis, synaptogenesis, and neuronal functions. Its dysregulation is linked to neurodegenerative disorders like Down syndrome and Alzheimer's disease. Although the development of DYRK1A inhibitors has significantly advanced in recent years, the selectivity of these drugs remains a critical challenge, potentially impeding further progress. In this study, we utilised structure-based virtual screening (SBVS) from NCI library to discover novel DYRK1A inhibitors. The top-ranked compounds were then validated through enzymatic assays to assess their efficacy towards DYRK1A. Among them, NSC361563 emerged as a potent and selective DYRK1A inhibitor. It was shown to decrease tau phosphorylation at multiple sites, thereby enhancing tubulin stability. Moreover, NSC361563 diminished the formation of amyloid β and offered neuroprotective benefits against amyloid β-induced toxicity. Our research highlights the critical role of selective DYRK1A inhibitors in treating neurodegenerative diseases and presents a promising starting point for the development of targeted therapies.

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

Design, synthesis, and biological evaluation of some 2-(3-oxo-5,6-diphenyl-1,2,4-triazin-2(3H)-yl)-N-phenylacetamide hybrids as MTDLs for Alzheimer's disease therapy

Inspite of established symptomatic relief drug targets, a multi targeting approach is highly in demand to cure Alzheimer's disease (AD). Simultaneous inhibition of cholinesterase (ChE), β secretase-1 (BACE-1) and Dyrk1A could be promising in complete cure of AD. A series of 18 diaryl triazine based molecular hybrids were successfully designed, synthesized, and tested for their hChE, hBACE-1, Dyrk1A and Aβ aggregation inhibitory potentials. Compounds S-11 and S-12 were the representative molecules amongst the series with multi-targeted inhibitory effects. Compound S-12 showed hAChE inhibition (IC50 value = 0.486 ± 0.047 μM), BACE-1 inhibition (IC50 value = 0.542 ± 0.099 μM) along with good anti-Aβ aggregation effects in thioflavin-T assay. Only compound S-02 of the series has shown Dyrk1A inhibition (IC50 value = 2.000 ± 0.360 μM). Compound S-12 has also demonstrated no neurotoxic liabilities against SH-SY5Y as compared to donepezil. The in vivo behavioral studies of the compound S-12 in the scopolamine- and Aβ-induced animal models also demonstrated attanuation of learning and memory functions in rats models having AD-like characteristics. The ex vivo studies, on the rat hippocampal brain demonstrated reduction in certain biochemical markers of the AD brain with a significant increase in ACh level. The Western blot and Immunohistochemistry further revealed lower tau, APP and BACE-1 molecular levels. The drosophilla AD model also revealed improved eyephenotype after treatment with compound S-12. The molecular docking studies of the compounds suggested that compound S-12 was interacting with the ChE-PAS & CAS residues and catalytic dyad residues of the BACE-1 enzymes. The 100 ns molecular dynamics simulation studies of the ligand-protein complexed with hAChE and hBACE-1 also suggested stable ligand-protein confirmation throughout the simulation run.

Truncated Dyrk1A aggravates neuronal apoptosis by inhibiting ASF-mediated Bcl-x exon 2b inclusion

AIM

Aggravated neuronal loss, caused mainly by neuronal apoptosis, is observed in the brain of patients with Alzheimer's disease (AD) and animal models of AD. A truncated form of Dual-specific and tyrosine phosphorylation-regulated protein kinase 1A (Dyrk1A) plays a vital role in AD pathogenesis. Downregulation of anti-apoptotic Bcl-xL is tightly correlated with neuronal loss in AD. However, the molecular regulation of neuronal apoptosis and Bcl-x expression by Dyrk1A in AD remains largely elusive. Here, we aimed to explore the role and molecular mechanism of Dyrk1A in apoptosis.

METHODS

Cell Counting Kit-8 (CCK8), flow cytometry, and TdT-mediated dUTP Nick-End Labeling (TUNEL) were used to check apoptosis. The cells, transfected with Dyrk1A or/and ASF with Bcl-x minigene, were used to assay Bcl-x expression by RT-PCR and Western blots. Co-immunoprecipitation, autoradiography, and immunofluorescence were conducted to check the interaction of ASF and Dyrk1A. Gene set enrichment analysis (GSEA) of apoptosis-related genes was performed in mice overexpressing Dyrk1A (TgDyrk1A) and AD model 5xFAD mice.

RESULTS

Dyrk1A promoted Bcl-xS expression and apoptosis. Splicing factor ASF promoted Bcl-x exon 2b inclusion, leading to increased Bcl-xL expression. Dyrk1A suppressed ASF-mediated Bcl-x exon 2b inclusion via phosphorylation. The C-terminus deletion of Dyrk1A facilitated its binding and kinase activity to ASF. Moreover, Dyrk1a1-483 further suppressed the ASF-mediated Bcl-x exon 2b inclusion and aggravated apoptosis. The truncated Dyrk1A, increased Bcl-xS, and enrichment of apoptosis-related genes was observed in the brain of 5xFAD mice.

CONCLUSIONS

We speculate that increased Dyrk1A and truncated Dyrk1A may aggravate neuronal apoptosis by decreasing the ratio of Bcl-xL/Bcl-xS via phosphorylating ASF in AD.

Molecular and Therapeutic Targets for Amyloid-beta Plaques in Alzheimer's Disease: A Review Study

Alzheimer's disease (AD) is characterized by progressive loss of cognition and a gradual decrease in memory. Although AD is considered the most persistent form of dementia and a global concern, no complete cure or agents that can completely halt the progression of AD have been found. In the past years, significant progress has been made in understanding the cellular and molecular changes associated with AD, and numerous drug targets have been identified for the development of drugs for this disease. Amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFT) are the major attributes of AD. Symptomatic relief is the only possible treatment available at present and a disease-modifying drug is of utmost importance. The development of drugs that can inhibit different targets responsible for the formation of plaques is a potential area in AD research. This review is not a complete list of all possible targets for AD but serves to highlight the targets related to Aβ pathology and pathways concerned with the formation of Aβ fragments. This shall serve as a prospect in the identification of Aβ plaque inhibitors and pave the strategies for newer drug treatments. Nevertheless, substantial research is done in this area but to bridle, the clinical difficulty remains a concern.

Leucettinib-21, a DYRK1A Kinase Inhibitor as Clinical Drug Candidate for Alzheimer's Disease and Down Syndrome

Alzheimer's disease (AD) and Down syndrome (DS) share a common therapeutic target, the dual-specificity, tyrosine phosphorylation activated kinase 1A (DYRK1A). Abnormally active DYRK1A is responsible for cognitive disorders (memory, learning, spatial localization) observed in both conditions. In DS, DYRK1A is overexpressed due to the presence of the DYRK1A gene on chromosome 21. In AD, calcium-activated calpains cleave full-length DYRK1A (FL-DYRK1A) into a more stable and more active, low molecular weight, kinase (LMW-DYRK1A). Genetic and pharmacological experiments carried out with animal models of AD and DS strongly support the idea that pharmacological inhibitors of DYRK1A might be able to correct memory/learning disorders in people with AD and DS. Starting from a marine sponge natural product, Leucettamine B, Perha Pharmaceuticals has optimized, through classical medicinal chemistry, and extensively characterized a small molecule drug candidate, Leucettinib-21. Regulatory preclinical safety studies in rats and minipigs have been completed and formulation of Leucettinib-21 has been optimized as immediate-release tablets. Leucettinib-21 is now undergoing a phase 1 clinical trial (120 participants, including 12 adults with DS and 12 patients with AD). The therapeutic potential of DYRK1A inhibitors in AD and DS is presented.

Chemical, Biochemical, Cellular, and Physiological Characterization of Leucettinib-21, a Down Syndrome and Alzheimer's Disease Drug Candidate

Leucettinibs are substituted 2-aminoimidazolin-4-ones (inspired by the marine sponge natural product Leucettamine B) developed as pharmacological inhibitors of DYRK1A (dual-specificity, tyrosine phosphorylation-regulated kinase 1A), a therapeutic target for indications such as Down syndrome and Alzheimer's disease. Leucettinib-21 was selected as a drug candidate following extensive structure/activity studies and multiparametric evaluations. We here report its physicochemical properties (X-ray powder diffraction, differential scanning calorimetry, stability, solubility, crystal structure) and drug-like profile. Leucettinib-21's selectivity (analyzed by radiometric, fluorescence, interaction, thermal shift, residence time assays) reveals DYRK1A as the first target but also some "off-targets" which may contribute to the drug's biological effects. Leucettinib-21 was cocrystallized with CLK1 and modeled in the DYRK1A structure. Leucettinib-21 inhibits DYRK1A in cells (demonstrated by direct catalytic activity and phosphorylation levels of Thr286-cyclin D1 or Thr212-Tau). Leucettinib-21 corrects memory disorders in the Down syndrome mouse model Ts65Dn and is now entering safety/tolerance phase 1 clinical trials.

Leucettinibs, a Class of DYRK/CLK Kinase Inhibitors Inspired by the Marine Sponge Natural Product Leucettamine B

Dual-specificity, tyrosine phosphorylation-regulated kinases (DYRKs) and cdc2-like kinases (CLKs) recently attracted attention due to their central involvement in various pathologies. We here describe a family of DYRK/CLK inhibitors derived from Leucettines and the marine natural product Leucettamine B. Forty-five N2-functionalized 2-aminoimidazolin-4-ones bearing a fused [6 + 5]-heteroarylmethylene were synthesized. Benzothiazol-6-ylmethylene was selected as the most potent residue among 15 different heteroarylmethylenes. 186 N2-substituted 2-aminoimidazolin-4-ones bearing a benzothiazol-6-ylmethylene, collectively named Leucettinibs, were synthesized and extensively characterized. Subnanomolar IC50 (0.5-20 nM on DYRK1A) inhibitors were identified and one Leucettinib was modeled in DYRK1A and co-crystallized with CLK1 and the weaker inhibited off-target CSNK2A1. Kinase-inactive isomers of Leucettinibs (>3-10 μM on DYRK1A), named iso-Leucettinibs, were synthesized and characterized as suitable negative control compounds for functional experiments. Leucettinibs, but not iso-Leucettinibs, inhibit the phosphorylation of DYRK1A substrates in cells. Leucettinibs provide new research tools and potential leads for further optimization toward therapeutic drug candidates.

DYRK1A inhibitors leucettines and TGF-β inhibitor additively stimulate insulin production in beta cells, organoids, and isolated mouse islets

The decreased β-cell mass and impaired β-cell functionality are the primary causes of diabetes mellitus (DM). Nevertheless, the underlying molecular mechanisms by which β-cell growth and function are controlled are not fully understood. In this work, we show that leucettines, known to be DYRK1A kinase inhibitors, can improve glucose-stimulated insulin secretion (GSIS) in rodent β-cells and isolated islets, as well as in hiPSC-derived β-cells islets. We confirm that DYRK1A is expressed in murine insulinoma cells MIN6. In addition, we found that treatment with selected leucettines stimulates proliferation of β-cells and promotes MIN6 cell cycle progression to the G2/M phase. This effect is also confirmed by increased levels of cyclin D1, which is highly responsive to proliferative signals. Among other leucettines, leucettine L43 had a negligible impact on β-cell proliferation, but markedly impair GSIS. However, leucettine L41, in combination with LY364947, a, a potent and selective TGF-β type-I receptor, significantly promotes GSIS in various cellular diabetic models, including MIN6 and INS1E cells in 2D and 3D culture, iPSC-derived β-cell islets derived from iPSC, and isolated mouse islets, by increased insulin secretion and decreased glucagon level. Our findings confirm an important role of DYRK1A inhibitors as modulators of β-cells function and suggested a new potential target for antidiabetic therapy. Moreover, we show in detail that leucettine derivatives represent promising antidiabetic agents and are worth further evaluation, especially in vivo.

Comparative Efficacy and Selectivity of Pharmacological Inhibitors of DYRK and CLK Protein Kinases

Dual-specificity, tyrosine phosphorylation-regulated kinases (DYRKs) and cdc2-like kinases (CLKs) play a large variety of cellular functions and are involved in several diseases (cognitive disorders, diabetes, cancers, etc.). There is, thus, growing interest in pharmacological inhibitors as chemical probes and potential drug candidates. This study presents an unbiased evaluation of the kinase inhibitory activity of a library of 56 reported DYRK/CLK inhibitors on the basis of comparative, side-by-side, catalytic activity assays on a panel of 12 recombinant human kinases, enzyme kinetics (residence time and K_d), in-cell inhibition of Thr-212-Tau phosphorylation, and cytotoxicity. The 26 most active inhibitors were modeled in the crystal structure of DYRK1A. The results show a rather large diversity of potencies and selectivities among the reported inhibitors and emphasize the difficulties to avoid "off-targets" in this area of the kinome. The use of a panel of DYRKs/CLKs inhibitors is suggested to analyze the functions of these kinases in cellular processes.

Development of Novel Fluorinated Polyphenols as Selective Inhibitors of DYRK1A/B Kinase for Treatment of Neuroinflammatory Diseases including Parkinson's Disease

Natural polyphenol derivatives such as those found in green tea have been known for a long time for their useful therapeutic activity. Starting from EGCG, we have discovered a new fluorinated polyphenol derivative (1c) characterized by improved inhibitory activity against DYRK1A/B enzymes and by considerably improved bioavailability and selectivity. DYRK1A is an enzyme that has been implicated as an important drug target in various therapeutic areas, including neurological disorders (Down syndrome and Alzheimer's disease), oncology, and type 2 diabetes (pancreatic β-cell expansion). Systematic structure-activity relationship (SAR) on trans-GCG led to the discovery that the introduction of a fluoro atom in the D ring and methylation of the hydroxy group from para to the fluoro atom provide a molecule (1c) with more desirable drug-like properties. Owing to its good ADMET properties, compound 1c showed excellent activity in two in vivo models, namely the lipopolysaccharide (LPS)-induced inflammation model and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model for Parkinson's disease.

Inhibition of CDK4/6 regulates AD pathology, neuroinflammation and cognitive function through DYRK1A/STAT3 signaling

Repurposing approved drugs is an emerging therapeutic development strategy for Alzheimer's disease (AD). The CDK4/6 inhibitor abemaciclib mesylate is an FDA-approved drug for breast cancer treatment. However, whether abemaciclib mesylate affects Aβ/tau pathology, neuroinflammation, and Aβ/LPS-mediated cognitive impairment is unknown. In this study, we investigated the effects of abemaciclib mesylate on cognitive function and Aβ/tau pathology and found that abemaciclib mesylate improved spatial and recognition memory by regulating the dendritic spine number and neuroinflammatory responses in 5xFAD mice, an Aβ-overexpressing model of AD. Abemaciclib mesylate also inhibited Aβ accumulation by enhancing the activity and protein levels of the Aβ-degrading enzyme neprilysin and the α-secretase ADAM17 and decreasing the protein level of the γ-secretase PS-1 in young and aged 5xFAD mice. Importantly, abemaciclib mesylate suppressed tau phosphorylation in 5xFAD mice and tau-overexpressing PS19 mice by reducing DYRK1A and/or p-GSK3β levels. In wild-type (WT) mice injected with lipopolysaccharide (LPS), abemaciclib mesylate rescued spatial and recognition memory and restored dendritic spine number. In addition, abemaciclib mesylate downregulated LPS-induced microglial/astrocytic activation and proinflammatory cytokine levels in WT mice. In BV2 microglial cells and primary astrocytes, abemaciclib mesylate suppressed LPS-mediated proinflammatory cytokine levels by downregulating AKT/STAT3 signaling. Taken together, our results support repurposing the anticancer drug, CDK4/6 inhibitor abemaciclib mesylate as a multitarget therapeutic for AD pathologies.

Function and Inhibition of DYRK1A: emerging roles of treating multiple human diseases

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is an evolutionarily conserved protein kinase and the most studied member of the Dual-specificity tyrosine-regulated kinase (DYRK) family. It has been shown that it participates in the development of plenty of diseases, and both the low or high expression of DYRK1A protein could lead to disorder. Thus, DYRK1A is recognized as a key target for the therapy for these diseases, and the studies on natural or synthetic DYRK1A inhibitors have become more and more popular. Here, we provide a comprehensive review for DYRK1A from the structure and function of DYRK1A, the roles of DYRK1A in various types of diseases, including diabetes mellitus, neurodegenerative diseases, and kinds of cancers, and the studies of its natural and synthetic inhibitors.

Type 2 Diabetes Mellitus and Alzheimer's Disease: Shared Molecular Mechanisms and Potential Common Therapeutic Targets

The global prevalence of diabetes mellitus and Alzheimer's disease is increasing alarmingly with the aging of the population. Numerous epidemiological data suggest that there is a strong association between type 2 diabetes and an increased risk of dementia. These diseases are both degenerative and progressive and share common risk factors. The amyloid cascade plays a key role in the pathophysiology of Alzheimer's disease. The accumulation of amyloid beta peptides gradually leads to the hyperphosphorylation of tau proteins, which then form neurofibrillary tangles, resulting in neurodegeneration and cerebral atrophy. In Alzheimer's disease, apart from these processes, the alteration of glucose metabolism and insulin signaling in the brain seems to induce early neuronal loss and the impairment of synaptic plasticity, years before the clinical manifestation of the disease. The large amount of evidence on the existence of insulin resistance in the brain during Alzheimer's disease has led to the description of this disease as "type 3 diabetes". Available animal models have been valuable in the understanding of the relationships between type 2 diabetes and Alzheimer's disease, but to date, the mechanistical links are poorly understood. In this non-exhaustive review, we describe the main molecular mechanisms that may link these two diseases, with an emphasis on impaired insulin and IGF-1 signaling. We also focus on GSK3β and DYRK1A, markers of Alzheimer's disease, which are also closely associated with pancreatic β-cell dysfunction and type 2 diabetes, and thus may represent common therapeutic targets for both diseases.

DYRK1A and Activity-Dependent Neuroprotective Protein Comparative Diagnosis Interest in Cerebrospinal Fluid and Plasma in the Context of Alzheimer-Related Cognitive Impairment in Down Syndrome Patients

Down syndrome (DS) is a complex genetic condition due to an additional copy of human chromosome 21, which results in the deregulation of many genes. In addition to the intellectual disability associated with DS, adults with DS also have an ultrahigh risk of developing early onset Alzheimer's disease dementia. DYRK1A, a proline-directed serine/threonine kinase, whose gene is located on chromosome 21, has recently emerged as a promising plasma biomarker in patients with sporadic Alzheimer's disease (AD). The protein DYRK1A is truncated in symptomatic AD, the increased truncated form being associated with a decrease in the level of full-length form. Activity-dependent neuroprotective protein (ADNP), a key protein for the brain development, has been demonstrated to be a useful marker for symptomatic AD and disease progression. In this study, we evaluated DYRK1A and ADNP in CSF and plasma of adults with DS and explored the relationship between these proteins. We used mice models to evaluate the effect of DYRK1A overexpression on ADNP levels and then performed a dual-center cross-sectional human study in adults with DS in Barcelona (Spain) and Paris (France). Both cohorts included adults with DS at different stages of the continuum of AD: asymptomatic AD (aDS), prodromal AD (pDS), and AD dementia (dDS). Non-trisomic controls and patients with sporadic AD dementia were included for comparison. Full-form levels of DYRK1A were decreased in plasma and CSF in adults with DS and symptomatic AD (pDS and dDS) compared to aDS, and in patients with sporadic AD compared to controls. On the contrary, the truncated form of DYRK1A was found to increase both in CSF and plasma in adults with DS and symptomatic AD and in patients with sporadic AD with respect to aDS and controls. ADNP levels showed a more complex structure. ADNP levels increased in aDS groups vs. controls, in agreement with the increase in levels found in the brains of mice overexpressing DYRK1A. However, symptomatic individuals had lower levels than aDS individuals. Our results show that the comparison between full-length and truncated-form levels of DYRK1A coupled with ADNP levels could be used in trials targeting pathophysiological mechanisms of dementia in individuals with DS.

Catechins as a Potential Dietary Supplementation in Prevention of Comorbidities Linked with Down Syndrome

Plant-derived polyphenols flavonoids are increasingly being recognized for their medicinal potential. These bioactive compounds derived from plants are gaining more interest in ameliorating adverse health risks because of their low toxicity and few side effects. Among them, therapeutic approaches demonstrated the efficacy of catechins, a major group of flavonoids, in reverting several aspects of Down syndrome, the most common genomic disorder that causes intellectual disability. Down syndrome is characterized by increased incidence of developing Alzheimer's disease, obesity, and subsequent metabolic disorders. In this focused review, we examine the main effects of catechins on comorbidities linked with Down syndrome. We also provide evidence of catechin effects on DYRK1A, a dosage-sensitive gene encoding a protein kinase involved in brain defects and metabolic disease associated with Down syndrome.

Discovery of novel 6-hydroxybenzothiazole urea derivatives as dual Dyrk1A/α-synuclein aggregation inhibitors with neuroprotective effects

A role of Dyrk1A in the progression of Down syndrome-related Alzheimer's disease (AD) is well supported. However, the involvement of Dyrk1A in the pathogenesis of Parkinson's disease (PD) was much less studied, and it is not clear whether it would be promising to test Dyrk1A inhibitors in relevant PD models. Herein, we modified our previously published 1-(6-hydroxybenzo[d]thiazol-2-yl)-3-phenylurea scaffold of Dyrk1A inhibitors to obtain a new series of analogues with higher selectivity for Dyrk1A on the one hand, but also with a novel, additional activity as inhibitors of α-synuclein (α-syn) aggregation, a major pathogenic hallmark of PD. The phenyl acetamide derivative b27 displayed the highest potency against Dyrk1A with an IC50 of 20 nM and high selectivity over closely related kinases. Furthermore, b27 was shown to successfully target intracellular Dyrk1A and to inhibit SF3B1 phosphorylation in HeLa cells with an IC50 of 690 nM. In addition, two compounds among the Dyrk1A inhibitors, b1 and b20, also suppressed the aggregation of α-synuclein (α-syn) oligomers (with IC50 values of 10.5 μM and 7.8 μM, respectively). Both compounds but not the Dyrk1A reference inhibitor harmine protected SH-SY5Y neuroblastoma cells against α-syn-induced cytotoxicity, with b20 exhibiting a higher neuroprotective effect. Compound b1 and harmine were more efficient in protecting SH-SY5Y cells against 6-hydroxydopamine-induced cell death, an effect that was previously correlated to Dyrk1A inactivation in cells but not yet verified using chemical inhibitors. The presented dual inhibitors exhibited a novel activity profile encouraging for further testing in neurodegenerative disease models.

Structure-Activity Relationship in the Leucettine Family of Kinase Inhibitors

The protein kinase DYRK1A is involved in Alzheimer's disease, Down syndrome, diabetes, viral infections, and leukemia. Leucettines, a family of 2-aminoimidazolin-4-ones derived from the marine sponge alkaloid Leucettamine B, have been developed as pharmacological inhibitors of DYRKs (dual specificity, tyrosine phosphorylation regulated kinases) and CLKs (cdc2-like kinases). We report here on the synthesis and structure-activity relationship (SAR) of 68 Leucettines. Leucettines were tested on 11 purified kinases and in 5 cellular assays: (1) CLK1 pre-mRNA splicing, (2) Threonine-212-Tau phosphorylation, (3) glutamate-induced cell death, (4) autophagy and (5) antagonism of ligand-activated cannabinoid receptor CB1. The Leucettine SAR observed for DYRK1A is essentially identical for CLK1, CLK4, DYRK1B, and DYRK2. DYRK3 and CLK3 are less sensitive to Leucettines. In contrast, the cellular SAR highlights correlations between inhibition of specific kinase targets and some but not all cellular effects. Leucettines deserve further development as potential therapeutics against various diseases on the basis of their molecular targets and cellular effects.

Dyrk1a from Gene Function in Development and Physiology to Dosage Correction across Life Span in Down Syndrome

Down syndrome is the main cause of intellectual disabilities with a large set of comorbidities from developmental origins but also that appeared across life span. Investigation of the genetic overdosage found in Down syndrome, due to the trisomy of human chromosome 21, has pointed to one main driver gene, the Dual-specificity tyrosine-regulated kinase 1A (Dyrk1a). Dyrk1a is a murine homolog of the drosophila minibrain gene. It has been found to be involved in many biological processes during development and in adulthood. Further analysis showed its haploinsufficiency in mental retardation disease 7 and its involvement in Alzheimer's disease. DYRK1A plays a role in major developmental steps of brain development, controlling the proliferation of neural progenitors, the migration of neurons, their dendritogenesis and the function of the synapse. Several strategies targeting the overdosage of DYRK1A in DS with specific kinase inhibitors have showed promising evidence that DS cognitive conditions can be alleviated. Nevertheless, providing conditions for proper temporal treatment and to tackle the neurodevelopmental and the neurodegenerative aspects of DS across life span is still an open question.

Diabetic Kinome Inhibitors-A New Opportunity for β-Cells Restoration

Diabetes, and several diseases related to diabetes, including cancer, cardiovascular diseases and neurological disorders, represent one of the major ongoing threats to human life, becoming a true pandemic of the 21st century. Current treatment strategies for diabetes mainly involve promoting β-cell differentiation, and one of the most widely studied targets for β-cell regeneration is DYRK1A kinase, a member of the DYRK family. DYRK1A has been characterized as a key regulator of cell growth, differentiation, and signal transduction in various organisms, while further roles and substrates are the subjects of extensive investigation. The targets of interest in this review are implicated in the regulation of β-cells through DYRK1A inhibition-through driving their transition from highly inefficient and death-prone populations into efficient and sufficient precursors of islet regeneration. Increasing evidence for the role of DYRK1A in diabetes progression and β-cell proliferation expands the potential for pharmaceutical applications of DYRK1A inhibitors. The variety of new compounds and binding modes, determined by crystal structure and in vitro studies, may lead to new strategies for diabetes treatment. This review provides recent insights into the initial self-activation of DYRK1A by tyrosine autophosphorylation. Moreover, the importance of developing novel DYRK1A inhibitors and their implications for the treatment of diabetes are thoroughly discussed. The evolving understanding of DYRK kinase structure and function and emerging high-throughput screening technologies have been described. As a final point of this work, we intend to promote the term "diabetic kinome" as part of scientific terminology to emphasize the role of the synergistic action of multiple kinases in governing the molecular processes that underlie this particular group of diseases.

A novel inhibitor rescues cerebellar defects in a zebrafish model of Down syndrome-associated kinase Dyrk1A overexpression

The highly conserved dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) plays crucial roles during central nervous system development and homeostasis. Furthermore, its hyperactivity is considered responsible for some neurological defects in individuals with Down syndrome. We set out to establish a zebrafish model expressing human Dyrk1A that could be further used to characterize the interaction between Dyrk1A and neurological phenotypes. First, we revealed the prominent expression of dyrk1a homologs in cerebellar neurons in the zebrafish larval and adult brains. Overexpression of human dyrk1a in postmitotic cerebellar Purkinje neurons resulted in a structural misorganization of the Purkinje cells in cerebellar hemispheres and a compaction of this cell population. This impaired Purkinje cell organization was progressive, leading to an age-dependent dispersal of Purkinje neurons throughout the cerebellar molecular layer with larval swim deficits resulting in miscoordination of swimming and reduced exploratory behavior in aged adults. We also found that the structural misorganization of the larval Purkinje cell layer could be rescued by pharmacological treatment with Dyrk1A inhibitors. We further reveal the in vivo efficiency of a novel selective Dyrk1A inhibitor, KuFal194. These findings demonstrate that the zebrafish is a well-suited vertebrate organism to genetically model severe neurological diseases with single cell type specificity. Such models can be used to relate molecular malfunction to cellular deficits, impaired tissue formation, and organismal behavior and can also be used for pharmacological compound testing and validation.

Dual-Specificity, Tyrosine Phosphorylation-Regulated Kinases (DYRKs) and cdc2-Like Kinases (CLKs) in Human Disease, an Overview

Dual-specificity tyrosine phosphorylation-regulated kinases (DYRK1A, 1B, 2-4) and cdc2-like kinases (CLK1-4) belong to the CMGC group of serine/threonine kinases. These protein kinases are involved in multiple cellular functions, including intracellular signaling, mRNA splicing, chromatin transcription, DNA damage repair, cell survival, cell cycle control, differentiation, homocysteine/methionine/folate regulation, body temperature regulation, endocytosis, neuronal development, synaptic plasticity, etc. Abnormal expression and/or activity of some of these kinases, DYRK1A in particular, is seen in many human nervous system diseases, such as cognitive deficits associated with Down syndrome, Alzheimer's disease and related diseases, tauopathies, dementia, Pick's disease, Parkinson's disease and other neurodegenerative diseases, Phelan-McDermid syndrome, autism, and CDKL5 deficiency disorder. DYRKs and CLKs are also involved in diabetes, abnormal folate/methionine metabolism, osteoarthritis, several solid cancers (glioblastoma, breast, and pancreatic cancers) and leukemias (acute lymphoblastic leukemia, acute megakaryoblastic leukemia), viral infections (influenza, HIV-1, HCMV, HCV, CMV, HPV), as well as infections caused by unicellular parasites (Leishmania, Trypanosoma, Plasmodium). This variety of pathological implications calls for (1) a better understanding of the regulations and substrates of DYRKs and CLKs and (2) the development of potent and selective inhibitors of these kinases and their evaluation as therapeutic drugs. This article briefly reviews the current knowledge about DYRK/CLK kinases and their implications in human disease.

Epigallocatechin-3-gallate inhibits the growth of three-dimensional in vitro models of neuroblastoma cell SH-SY5Y

The aim of the study is to investigate the potential of using three-dimensional (3D) in vitro neuroblastoma models to mimic the neuroblastoma microenvironment by testing a potential therapeutic compound—the natural extract epigallocatechin-3-gallate (EGCG), and to further elucidate the roles of DYRK1A in the growth and differentiation of neuroblastoma tissue. In vitro models based on a classic neuroblastoma cell line SH-SY5Y were employed, including 3D models with extracellular matrix and co-cultured with vascular endothelial cells. Cell viability was tested using AlamarBlue and Resazurin assay. The growth and differentiation of in vitro models of SH-SY5Y were analysed based on microscopy images obtained from immunofluorescence or real-time imaging. Protein expression level was investigated using immunoblotting analysis. The two-dimensional (2D) in vitro model implies the cytotoxicity and DYRK1A inhibition effect of EGCG and shows the induction of neuronal differentiation marker TuJ1. 3D in vitro models suggest that EGCG treatment compromised the growth of SH-SY5Y multicellular 3D spheroids and the viability of SH-SY5Y cultured in 3D Matrigel matrix. In addition, co-culture of SH-SY5Y with human vascular umbilical vein endothelial cells implied the inhibitory effects by EGCG in a vascularised microenvironment. In this study, novel 3D in vitro models of neuroblastoma were established in the application of testing a potential anti-cancer candidate compound EGCG. In pursuit of the goals of the 3Rs (replacement, reduction and refinement), the usage of these 3D in vitro models has the potential to reduce and eventually replace current animal models used in neuroblastoma research. The DYRK1A inhibiting nature of EGCG, together with the facts that EGCG inhibits the growth and induces the differentiation of neuroblastoma in vitro models, suggests an oncogene role of DRYK1A.

DYRK1A: a down syndrome-related dual protein kinase with a versatile role in tumorigenesis

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a dual kinase that can phosphorylate its own activation loop on tyrosine residue and phosphorylate its substrates on threonine and serine residues. It is the most studied member of DYRK kinases, because its gene maps to human chromosome 21 within the Down syndrome critical region (DSCR). DYRK1A overexpression was found to be responsible for the phenotypic features observed in Down syndrome such as mental retardation, early onset neurodegenerative, and developmental heart defects. Besides its dual activity in phosphorylation, DYRK1A carries the characteristic of duality in tumorigenesis. Many studies indicate its possible role as a tumor suppressor gene; however, others prove its pro-oncogenic activity. In this review, we will focus on its multifaceted role in tumorigenesis by explaining its participation in some cancer hallmarks pathways such as proliferative signaling, transcription, stress, DNA damage repair, apoptosis, and angiogenesis, and finally, we will discuss targeting DYRK1A as a potential strategy for management of cancer and neurodegenerative disorders.

The novel DYRK1A inhibitor KVN93 regulates cognitive function, amyloid-beta pathology, and neuroinflammation

Regulating amyloid beta (Aβ) pathology and neuroinflammatory responses holds promise for the treatment of Alzheimer's disease (AD) and other neurodegenerative and/or neuroinflammation-related diseases. In this study, the effects of KVN93, an inhibitor of dual-specificity tyrosine phosphorylation-regulated kinase-1A (DYRK1A), on cognitive function and Aβ plaque levels and the underlying mechanism of action were evaluated in 5x FAD mice (a mouse model of AD). KVN93 treatment significantly improved long-term memory by enhancing dendritic synaptic function. In addition, KVN93 significantly reduced Aβ plaque levels in 5x FAD mice by regulating levels of the Aβ degradation enzymes neprilysin (NEP) and insulin-degrading enzyme (IDE). Moreover, Aβ-induced microglial and astrocyte activation were significantly suppressed in the KVN-treated 5xFAD mice. KVN93 altered neuroinflammation induced by LPS in microglial cells but not primary astrocytes by regulating TLR4/AKT/STAT3 signaling, and in wild-type mice injected with LPS, KVN93 treatment reduced microglial and astrocyte activation. Overall, these results suggest that the novel DYRK1A inhibitor KVN93 is a potential therapeutic drug for regulating cognitive/synaptic function, Aβ plaque load, and neuroinflammatory responses in the brain.

Bifenthrin insecticide promotes oxidative stress and increases inflammatory mediators in human neuroblastoma cells through NF-kappaB pathway

The extensive application of bifenthrin (BF) insecticide in agriculture has raised serious concerns with regard to increased risks of developing neurodegenerative diseases. Recently, our group showed that BF exposure in rodent models induced oxidative stress and inflammation markers in various regions of the brain (frontal cortex, striatum and hippocampus) and this was associated with behavioral changes. This study aimed to confirm such inflammatory and oxidative stress in an in vitro cell culture model of SK-N-SH human neuroblastoma cells. Markers of oxidative stress (ROS, NO, MDA, H₂O₂), antioxidant enzyme activities (CAT, GPx, SOD) and inflammatory response (TNF-α, IL-6, PGE₂) were analyzed in SK-N-SH cells after 24 h of exposure to different concentrations of BF (1-20 μM). Protein synthesis and mRNA expression of the enzymes implicated in the synthesis of PGE₂ were also measured (COX-2, mPGES-1) as well as nuclear factor κappaB (NF-κBp65) and antioxidant nuclear erythroid-2 like factor-2 (Nrf-2). Cell viability was analyzed by MTT-tetrazolio (MTT) and lactate dehydrogenase (LDH) assays. Exposure of SK-N-SH cells to BF resulted in a concentration-dependent reduction in the number of viable cells (reduction of MTT and increase in LDH activity). There was also a BF concentration-dependent increase in oxidative stress markers (ROS release, NO, MDA and H₂O₂) and decrease in the activity of antioxidant enzymes (CAT and GPx activities). There was further a concentration-dependent increase in pro-inflammatory cytokines (TNF-α and IL-6) and inflammatory mediator PGE₂, increase in protein synthesis and mRNA expression of inflammatory markers (COX-2, mPGES-1 and NF-κBp65) and decrease in protein synthesis and mRNA expression of antioxidant Nrf-2. Our data shows that BF induces various oxidative stress and inflammatory markers in SK-N-SH human neuroblastoma cells as well as the activation of NF-κBp65 signaling pathway. This is in line with prior results in brain regions of rodents exposed in vivo to BF showing increased oxidative stress in response to BF exposure, occurring in pro-inflammatory conditions and likely activating programmed cell death.

[b]-Annulated Halogen-Substituted Indoles as Potential DYRK1A Inhibitors

Since hyperactivity of the protein kinase DYRK1A is linked to several neurodegenerative disorders, DYRK1A inhibitors have been suggested as potential therapeutics for Down syndrome and Alzheimer's disease. Most published inhibitors to date suffer from low selectivity against related kinases or from unfavorable physicochemical properties. In order to identify DYRK1A inhibitors with improved properties, a series of new chemicals based on [b]-annulated halogenated indoles were designed, synthesized, and evaluated for biological activity. Analysis of crystal structures revealed a typical type-I binding mode of the new inhibitor 4-chlorocyclohepta[b]indol-10(5H)-one in DYRK1A, exploiting mainly shape complementarity for tight binding. Conversion of the DYRK1A inhibitor 8-chloro-1,2,3,9-tetrahydro-4H-carbazol-4-one into a corresponding Mannich base hydrochloride improved the aqueous solubility but abrogated kinase inhibitory activity.

GLUT12 Expression in Brain of Mouse Models of Alzheimer's Disease

The brain depends on glucose as a source of energy. This implies the presence of glucose transporters, being GLUT1 and GLUT3 the most relevant. Expression of GLUT12 is found in mouse and human brain at low levels. We previously demonstrated GLUT12 upregulation in the frontal cortex of aged subjects that was even higher in aged Alzheimer's disease (AD) patients. However, the cause and the mechanism through which this increase occurs are still unknown. Here, we aimed to investigate whether the upregulation of GLUT12 in AD is related with aging or Aβ deposition in comparison with GLUT1, GLUT3, and GLUT4. In the frontal cortex of two amyloidogenic mouse models (Tg2576 and APP/PS1) GLUT12 levels were increased. Contrary, expression of GLUT1 and GLUT3 were decreased, while GLUT4 did not change. In aged mice and the senescence-accelerated model SAMP8, GLUT12 and GLUT4 were upregulated in comparison with young animals. GLUT1 and GLUT3 did not show significant changes with age. The effect of β-amyloid (Aβ) deposition was also evaluated in Aβ peptide i.c.v. injected mice. In the hippocampus, GLUT12 expression increased whereas GLUT4 was not modified. Consistent with the results in the amyloidogenic models, GLUT3 and GLUT1 were downregulated. In summary, Aβ increases GLUT12 protein expression in the brain pointing out a central role of the transporter in AD pathology and opening new perspectives for the treatment of this neurodegenerative disease.

Hypothesis and Theory: Circulating Alzheimer's-Related Biomarkers in Type 2 Diabetes. Insight From the Goto-Kakizaki Rat

Epidemiological data suggest an increased risk of developing Alzheimer's disease (AD) in individuals with type 2 diabetes (T2D). AD is anatomically associated with an early progressive accumulation of Aβ leading to a gradual Tau hyperphosphorylation, which constitute the main characteristics of damaged brain in AD. Apart from these processes, mounting evidence suggests that specific features of diabetes, namely impaired glucose metabolism and insulin signaling in the brain, play a key role in AD. Moreover, several studies report a potential role of Aβ and Tau in peripheral tissues such as pancreatic β cells. Thus, it appears that several biological pathways associated with diabetes overlap with AD. The link between peripheral insulin resistance and brain insulin resistance with concomitant cognitive impairment may also potentially be mediated by a liver/pancreatic/brain axis, through the excessive trafficking of neurotoxic molecules across the blood-brain barrier. Insulin resistance incites inflammation and pro-inflammatory cytokine activation modulates the homocysteine cycle in T2D patients. Elevated plasma homocysteine level is a risk factor for AD pathology and is also closely associated with metabolic syndrome. We previously demonstrated a strong association between homocysteine metabolism and insulin via cystathionine beta synthase (CBS) activity, the enzyme implicated in the first step of the trans-sulfuration pathway, in Goto-Kakizaki (GK) rats, a spontaneous model of T2D, with close similarities with human T2D. CBS activity is also correlated with DYRK1A, a serine/threonine kinase regulating brain-derived neurotrophic factor (BDNF) levels, and Tau phosphorylation, which are implicated in a wide range of disease such as T2D and AD. We hypothesized that DYRK1A, BDNF, and Tau, could be among molecular factors linking T2D to AD. In this focused review, we briefly examine the main mechanisms linking AD to T2D and provide the first evidence that certain circulating AD biomarkers are found in diabetic GK rats. We propose that the spontaneous model of T2D in GK rat could be a suitable model to investigate molecular mechanisms linking T2D to AD.