10-iodo-11H-indolo[3,2-c]quinoline-6-carboxylic acids are selective inhibitors of DYRK1A

The indole motif is essential for the antitrypanosomal activity of N5-substituted paullones

Severe infections with potentially fatal outcomes are caused by parasites from the genera Trypanosoma and Leishmania (class Kinetoplastea). The diseases affect people of remote areas in the tropics and subtropics with limited access to adequate health care. Besides insufficient diagnostics, treatment options are limited, with tenuous developments in recent years. Therefore, new antitrypanosomal antiinfectives are required to fight these maladies. In the presented approach, new compounds were developed and tested on the target trypanothione synthetase (TryS). This enzyme is crucial to the kinetoplastids' unique trypanothione-based thiol redox metabolism and thus for pathogen survival. Preceding studies have shown that N5-substituted paullones display antitrypanosomal activity as well as TryS inhibition. Herein, this compound class was further examined regarding the structure-activity relationships (SAR). Diverse benzazepinone derivatives were designed and tested in cell-based assays on bloodstream Trypanosoma brucei brucei (T. b. brucei) and intracellular amastigotes of Leishmania infantum (L. infantum) as well as in enzyme-based assays on L. infantum TryS (LiTryS) and T. b. brucei TryS (TbTryS). While an exchange of just the substituent in the 9-position of paullones led to potent inhibitors on LiTryS and T. b. brucei parasites, new compounds lacking the indole moiety showed a total loss of activity in both assays. Conclusively, the indole as part of the paullone structure is pivotal for keeping the TryS inhibitory and antitrypanosomal activity of this substance class.

Anticancer Activity and Molecular Targets of Piper cernuum Substances in Oral Squamous Cell Carcinoma Models

Oral squamous cell carcinoma (OSCC) is a worldwide public health problem, with high morbidity and mortality rates. The development of new drugs to treat OSCC is paramount. Piper plant species have shown many biological activities. In the present study, we show that dichloromethane partition of Piper cernuum (PCLd) is nontoxic in chronic treatment in mice, reduces the amount of atypia in tongues of chemically induced OSCC, and significantly increases animal survival. To identify the main active compounds, chromatographic purification of PCLd was performed, where fractions 09.07 and 14.05 were the most active and selective. These fractions promoted cell death by apoptosis characterized by phosphatidyl serine exposition, DNA fragmentation, and activation of effector caspase-3/7 and were nonhemolytic. LC-DAD-MS/MS analysis did not propose matching spectra for the 09.07 fraction, suggesting compounds not yet known. However, aporphine alkaloids were annotated in fraction 14.05, which are being described for the first time in P. cernuum and corroborate the observed cytotoxic activity. Putative molecular targets were determined for these alkaloids, in silico, where the androgen receptor (AR), CHK1, CK2, DYRK1A, EHMT2, LXRβ, and VEGFR2 were the most relevant. The results obtained from P. cernuum fractions point to promising compounds as new preclinical anticancer candidates.

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.

An Effective Synthesis of Previously Unknown 7-Aryl Substituted Paullones

A straightforward three-step procedure affording a wide range of novel 7-aryl substituted paullone derivatives was developed. This scaffold is structurally similar to 2-(1H-indol-3-yl)acetamides-promising antitumor agents-hence, could be useful for the development of a new class of anticancer drugs.

An overview of cdc2-like kinase 1 (Clk1) inhibitors and their therapeutic indications

Over the past decade, Clk1 has been identified as a promising target for the treatment of various diseases, in which deregulated alternative splicing plays a role. First small molecules targeting Clk1 are in clinical trials for the treatment of solid cancer, where variants of oncogenic proteins derived from alternative splicing promote tumor progression. Since many infectious pathogens hi-jack the host cell's splicing machinery to ensure efficient replication, further indications in this area are under investigation, such as Influenza A, HIV-1 virus, and Trypanosoma infections, and more will likely be discovered in the future. In addition, Clk1 was found to contribute to the progression of Alzheimer's disease through causing an imbalance of tau splicing products. Interestingly, homozygous Clk1 knockout mice showed a rather mild phenotype, opposed to what might be expected in view of the profound role of Clk1 in alternative splicing. A major drawback of most Clk1 inhibitors is their insufficient selectivity; in particular, Dyrk kinases and haspin were frequently identified as off-targets, besides the other Clk isoforms. Only few inhibitors were shown to be selective over Dyrk1A and haspin, whereas no Clk1 inhibitor so far achieved selectivity over the Clk4 isoform. In this review, we carefully compiled all Clk1 inhibitors from the scientific literature and summarized their structure-activity relationships (SAR). In addition, we critically discuss the available selectivity data and describe the inhibitor's efficacy in cellular models, if reported. Thus, we provide a comprehensive overview on the current state of Clk1 drug discovery and highlight the most promising chemotypes.

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.

Condition-Dependent Selective Synthesis of Indolo[1,2-c]quinazolines and Indolo[3,2-c]quinolines from 2-(1H-Indol-2-yl)anilines and Sulfoxonium Ylides

In this paper, a selective synthesis of indolo[1,2-c]quinazolines and indolo[3,2-c]quinolines through the cascade reactions of 2-(1H-indol-2-yl)anilines with sulfoxonium ylides is presented. The formation of products involves the generation of a carbene species from sulfoxonium ylide and its N-H bond insertion reaction with 2-(1H-indol-2-yl)aniline followed by deoxygenative imine formation, intramolecular N- or C- nucleophilic addition and deoxygenative aromatization. This switchable synthesis was condition-dependent. In the presence of K₂CO₃ in CH₃CN, the reaction mainly furnished indolo[1,2-c]quinazolines. In the presence of HOAc in dioxane, it selectively afforded indolo[3,2-c]quinolines. In addition, direct C-H/N-H functionalization of the products obtained provides a convenient and direct access to polycyclic heteroaromatic compounds. These novel protocols have advantages such as readily accessible substrates, easily tunable selectivity, good compatibility with diverse functional groups, and the use of air as a cost-free and sustainable oxidant.

A critical update on the strategies towards small molecule inhibitors targeting Serine/arginine-rich (SR) proteins and Serine/arginine-rich proteins related kinases in alternative splicing

>90% of genes in the human body undergo alternative splicing (AS) after transcription, which enriches protein species and regulates protein levels. However, there is growing evidence that various genetic isoforms resulting from dysregulated alternative splicing are prevalent in various types of cancers. Dysregulated alternative splicing leads to cancer generation and maintenance of cancer properties such as proliferation differentiation, apoptosis inhibition, invasion metastasis, and angiogenesis. Serine/arginine-rich proteins and SR protein-associated kinases mediate splice site recognition and splice complex assembly during variable splicing. Based on the impact of dysregulated alternative splicing on disease onset and progression, the search for small molecule inhibitors targeting alternative splicing is imminent. In this review, we discuss the structure and specific biological functions of SR proteins and describe the regulation of SR protein function by SR protein related kinases meticulously, which are closely related to the occurrence and development of various types of cancers. On this basis, we summarize the reported small molecule inhibitors targeting SR proteins and SR protein related kinases from the perspective of medicinal chemistry. We mainly categorize small molecule inhibitors from four aspects, including targeting SR proteins, targeting Serine/arginine-rich protein-specific kinases (SRPKs), targeting Cdc2-like kinases (CLKs) and targeting dual-specificity tyrosine-regulated kinases (DYRKs), in terms of structure, inhibition target, specific mechanism of action, biological activity, and applicable diseases. With this review, we are expected to provide a timely summary of recent advances in alternative splicing regulated by kinases and a preliminary introduction to relevant small molecule inhibitors.

Differential maturation and chaperone dependence of the paralogous protein kinases DYRK1A and DYRK1B

The HSP90/CDC37 chaperone system not only assists the maturation of many protein kinases but also maintains their structural integrity after folding. The interaction of mature kinases with the HSP90/CDC37 complex is governed by the conformational stability of the catalytic domain, while the initial folding of the protein kinase domain is mechanistically less well characterized. DYRK1A (Dual-specificity tyrosine (Y)-phosphorylation Regulated protein Kinase 1A) and DYRK1B are closely related protein kinases with discordant HSP90 client status. DYRK kinases stoichiometrically autophosphorylate on a tyrosine residue immediately after folding, which served us as a traceable marker of successful maturation. In the present study, we used bacterial expression systems to compare the capacity of autonomous maturation of DYRK1A and DYRK1B in the absence of eukaryotic cofactors or chaperones. Under these conditions, autophosphorylation of human DYRK1B was severely compromised when compared with DYRK1A or DYRK1B orthologs from zebrafish and Xenopus. Maturation of human DYRK1B could be restored by bacterial expression at lower temperatures, suggesting that folding was not absolutely dependent on eukaryotic chaperones. The differential folding properties of DYRK1A and DYRK1B were largely due to divergent sequences of the C-terminal lobes of the catalytic domain. Furthermore, the mature kinase domain of DYRK1B featured lower thermal stability than that of DYRK1A when exposed to heat challenge in vitro or in living cells. In summary, our study enhances the mechanistic understanding of the differential thermodynamic properties of two closely related protein kinases during initial folding and as mature kinases.

Novel and Potential Small Molecule Scaffolds as DYRK1A Inhibitors by Integrated Molecular Docking-Based Virtual Screening and Dynamics Simulation Study

The dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a novel, promising and emerging biological target for therapeutic intervention in neurodegenerative diseases, especially in Alzheimer's disease (AD). The molMall database, comprising rare, diverse and unique compounds, was explored for molecular docking-based virtual screening against the DYRK1A protein, in order to find out potential inhibitors. Ligands exhibiting hydrogen bond interactions with key amino acid residues such as Ile165, Lys188 (catalytic), Glu239 (gk+1), Leu241 (gk+3), Ser242, Asn244, and Asp307, of the target protein, were considered potential ligands. Hydrogen bond interactions with Leu241 (gk+3) were considered key determinants for the selection. High scoring structures were also docked by Glide XP docking in the active sites of twelve DYRK1A related protein kinases, viz. DYRK1B, DYRK2, CDK5/p25, CK1, CLK1, CLK3, GSK3β, MAPK2, MAPK10, PIM1, PKA, and PKCα, in order to find selective DYRK1A inhibitors. MM/GBSA binding free energies of selected ligand-protein complexes were also calculated in order to remove false positive hits. Physicochemical and pharmacokinetic properties of the selected six hit ligands were also computed and related with the proposed limits for orally active CNS drugs. The computational toxicity webserver ProTox-II was used to predict the toxicity profile of selected six hits (molmall IDs 9539, 11352, 15938, 19037, 21830 and 21878). The selected six docked ligand-protein systems were exposed to 100 ns molecular dynamics (MD) simulations to validate their mechanism of interactions and stability in the ATP pocket of human DYRK1A kinase. All six ligands were found to be stable in the ATP binding pocket of DYRK1A kinase.

DYRK1A inhibitors for disease therapy: Current status and perspectives

Dual-specificity tyrosine phosphorylation-regulated kinase 1 A (DYRK1A) is a conserved protein kinase that plays essential roles in various biological processes. It is located in the region q22.2 of chromosome 21, which is involved in the pathogenesis of Down syndrome (DS). Moreover, DYRK1A has been shown to promote the accumulation of amyloid beta (Aβ) peptides leading to gradual Tau hyperphosphorylation, which contributes to neurodegeneration. Additionally, alterations in the DRK1A expression are also associated with cancer and diabetes. Recent years have witnessed an explosive increase in the development of DYRK1A inhibitors. A variety of novel DYRK1A inhibitors have been reported as potential treatments for human diseases. In this review, the latest therapeutic potential of DYRK1A for different diseases and the novel DYRK1A inhibitors discoveries are summarized, guiding future inhibitor development and structural optimization.

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.

Recent advances in chemistry and therapeutic potential of functionalized quinoline motifs – a review

Quinoline, which consists of benzene fused with N-heterocyclic pyridine, has received considerable attention as a core template in drug design because of its broad spectrum of bioactivity. This review aims to present the recent advances in chemistry, medicinal potential and pharmacological applications of quinoline motifs to unveil their substantial efficacies for future drug development. Essential information in all the current and available literature used was accessed and retrieved using different search engines and databases, including Scopus, ISI Web of Knowledge, Google and PUBMED. Numerous derivatives of the bioactive quinolines have been harnessed via expeditious synthetic approaches, as highlighted herein. This review reveals that quinoline is an indisputable pharmacophore due to its tremendous benefits in medicinal chemistry research and other valuable areas of human endeavour. The recent in vivo and in vitro screening reported by scientists is highlighted herein, which may pave the way for novel drug development. Owing to the array of information available and highlighted herein on the medicinal potential of quinoline and its functionalized derivatives, a new window of opportunity may be opened to medicinal chemists to access more biomolecular quinolines for future drug development.

Quinoline, which consists of benzene fused with N-heterocyclic pyridine, has received considerable attention as a core template in drug design because of its broad spectrum of bioactivity.

Disruption of DYRK1A-induced hyperphosphorylation of amyloid-beta and tau protein in Alzheimer's disease: An integrative molecular modeling approach

Alzheimer's disease (AD) is a neurological disorder caused by the abnormal accumulation of hyperphosphorylated proteins. Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a dual phosphorylation enzyme which phosphorylates the amyloid-β (Aβ) and neurofibrillary tangles (NFTs). A high throughput virtual screening approach was applied to screen a library of 98,071 compounds against DYRK1A using different programs including AutoDock Vina, Smina, and idock. Based on the binding affinities, we selected 330 compounds for absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis. Various pharmacokinetics parameters were predicted using the admetSAR server, and based on the pharmacokinetics results, 14 compounds were selected for cross-docking analysis using AutoDock. Cross-docking analysis revealed four compounds, namely, ZINC3843365 (-11.07 kcal/mol^-1), ZINC2123081 (-10.93 kcal/mol^-1), ZINC5220992 (-10.63 kcal/mol^-1), and ZINC68569602 (-10.35 kcal/mol^-1), which had the highest negative affinity scores compared to the 10 other molecules analyzed. Density functional theory (DFT) analysis was conducted for all the four top-ranked compounds. The molecular interaction stability of these four compounds with DYRK1A has been evaluated using molecular dynamics (MD) simulations on 100 nanoseconds followed by principal component analysis (PCA) and binding free energy calculations. The Gibbs free energy landscape analysis suggested the metastable state and folding pattern of selected docking complexes. Based on the present study outcome, we propose four antagonists, viz., ZINC3843365, ZINC2123081, ZINC5220992, and ZINC68569602 as potential inhibitors against DYRK1A and to reduce the amyloid-β and neurofibrillary tangle burden. These screened molecules can be further investigated using a number of in vitro and in vivo experiments.

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.

Discovery of Hydroxybenzothiazole Urea Compounds as Multitargeted Agents Suppressing Major Cytotoxic Mechanisms in Neurodegenerative Diseases

Multiple factors are causally responsible and/or contribute to the progression of Alzheimer's and Parkinson's diseases. The protein kinase Dyrk1A was identified as a promising target as it phosphorylates tau protein, α-synuclein, and parkin. The first goal of our study was to optimize our previously identified Dyrk1A inhibitors of the 6-hydroxy benzothiazole urea chemotype in terms of potency and selectivity. Our efforts led to the development of the 3-fluorobenzyl amide derivative 16b, which displayed the highest potency against Dyrk1A (IC₅₀ = 9.4 nM). In general, the diversification of the benzylamide moiety led to an enhanced selectivity over the most homologous isoform, Dyrk1B, which was a meaningful indicator, as the high selectivity could be confirmed in an extended selectivity profiling of 3b and 16b. Eventually, we identified the novel phenethyl amide derivative 24b as a triple inhibitor of Dyrk1A kinase activity (IC₅₀ = 119 nM) and the aggregation of tau and α-syn oligomers. We provide evidence that the novel combination of selective Dyrk1A inhibition and suppression of tau and α-syn aggregations of our new lead compound confers efficacy in several established cellular models of neurotoxic mechanisms relevant to neurodegenerative diseases, including α-syn- and 6-hydroxydopamine-induced cytotoxicities.

Aristolactam BIII, a naturally derived DYRK1A inhibitor, rescues Down syndrome-related phenotypes

BACKGROUND

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a significant pathogenic factor in Down syndrome (DS), wherein DYRK1A is overexpressed by 1.5-fold because of trisomy of human chromosome 21. Thus, DYRK1A inhibition is considered a therapeutic strategy to modify the disease.

PURPOSE

This study aims to identify a novel DYRK1A inhibitor and validate its therapeutic potential in DS-related pathological conditions.

STUDY DESIGN

In order to identify a novel DYRK1A inhibitor, we carried out two-step screening: a structure-based virtual screening of > 300,000 chemical library (first step) and cell-based nuclear factor of activated T-cells (NFAT)-response element (RE) promoter assay (second step). Primary hits were evaluated for their DYRK1A inhibitory activity using in vitro kinase assay and Tau phosphorylation in mammalian cells. Confirmed hit was further evaluated in pathological conditions including DYRK1A-overexpressing fibroblasts, flies, and mice.

RESULTS

We identified aristolactam BIII, a natural product derived from herbal plants, as a novel DYRK1A inhibitor. It potently inhibited the kinase activity of DYRK1A in vitro (IC₅₀ = 9.67 nM) and effectively suppressed DYRK1A-mediated hyperphosphorylation of Tau in mammalian cells. Aristolactam BIII rescued the proliferative defects of DYRK1A transgenic (TG) mouse-derived fibroblasts and neurological and phenotypic defects of DS-like Drosophila models. Oral administration of aristolactam BIII acutely suppressed Tau hyperphosphorylation in the brain of DYRK1A TG mice. In the open field test, aristolactam BIII significantly ameliorated the exploratory behavioral deficit of DYRK1A TG mice.

CONCLUSION

Our work revealed that aristolactam BIII as a novel DYRK1A inhibitor rescues DS phenotypes in cells and in vivo and suggested its therapeutic potential for the treatment of DYRK1A-related diseases.

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

Development of Cdc2-like Kinase 2 Inhibitors: Achievements and Future Directions

Cdc2-like kinases (CLKs; CLK1-4) are associated with various neurodegenerative disorders, metabolic regulation, and viral infection and have been recognized as potential drug targets. Human CLK2 has received increasing attention as a regulator that phosphorylates serine- and arginine-rich (SR) proteins and subsequently modulates the alternative splicing of precursor mRNA (pre-mRNA), which is an attractive target for degenerative disease and cancer. Numerous CLK2 inhibitors have been identified, with several molecules currently in clinical development. The first CLK2 inhibitor Lorecivivint (compound 1) has recently entered phase 3 clinical trials. However, highly selective CLK2 inhibitors are rarely reported. This Perspective summarizes the biological roles and therapeutic potential of CLK2 along with progress on the development of CLK2 inhibitors and discusses the achievements and future prospects of CLK2 inhibitors for therapeutic applications.

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.

Fragment-Derived Selective Inhibitors of Dual-Specificity Kinases DYRK1A and DYRK1B

The serine/threonine kinase DYRK1A has been implicated in regulation of a variety of cellular processes associated with cancer progression, including cell cycle control, DNA damage repair, protection from apoptosis, cell differentiation, and metastasis. In addition, elevated-level DYRK1A activity has been associated with increased severity of symptoms in Down's syndrome. A selective inhibitor of DYRK1A could therefore be of therapeutic benefit. We have used fragment and structure-based discovery methods to identify a highly selective, well-tolerated, brain-penetrant DYRK1A inhibitor which showed in vivo activity in a tumor model. The inhibitor provides a useful tool compound for further exploration of the effect of DYRK1A inhibition in models of disease.

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.

Structure-Guided Discovery of Potent and Selective DYRK1A Inhibitors

The kinase DYRK1A is an attractive target for drug discovery programs due to its implication in multiple diseases. Through a fragment screen, we identified a simple biaryl compound that is bound to the DYRK1A ATP site with very high efficiency, although with limited selectivity. Structure-guided optimization cycles enabled us to convert this fragment hit into potent and selective DYRK1A inhibitors. Exploiting the structural differences in DYRK1A and its close homologue DYRK2, we were able to fine-tune the selectivity of our inhibitors. Our best compounds potently inhibited DYRK1A in the cell culture and in vivo and demonstrated drug-like properties. The inhibition of DYRK1A in vivo translated into dose-dependent tumor growth inhibition in a model of ovarian carcinoma.

Cu(OTf)2-Catalyzed Intramolecular Radical Cascade Reactions for the Diversity-Oriented Synthesis of Quinoline-Annulated Polyheterocyclic Frameworks

Compound libraries with high levels of structural diversity and novelty could cover underexploited chemical space and thus have been highly pursued in drug discovery. Herein, we report the first Cu(OTf)₂-catalyzed intramolecular radical cascade reactions that enable the diversity-oriented synthesis of quinoline-annulated polyheterocyclic compounds (7 unique scaffolds, 66 examples) in an efficient manner. This work demonstrates an alternative route to access the natural product- and druglike compound collection with high levels of structural diversity and novelty.

Diverse synthesis of pyrrolo/indolo[3,2-c]coumarins as isolamellarin-A scaffolds: a brief update

This review presents a different synthetic approach of pyrrolo/indolo[3,2-c]coumarins via classical reactions including metal-catalyzed and green reaction protocols.

4-Chloro-3-formylcoumarin as a multifaceted building block for the development of various bio-active substituted and fused coumarin heterocycles: a brief review

This review presents the diverse synthesis of 3,4-substituted coumarins and 5-, 6- and 7-membered ring fused coumarins using 4-chloro-3-formylcoumarin as the precursor via classical reactions including metal-catalyzed and green reaction protocols.

Emerging roles of DYRK2 in cancer

Over the last decade, the CMGC kinase DYRK2 has been reported as a tumor suppressor across various cancers triggering major antitumor and proapoptotic signals in breast, colon, liver, ovary, brain, and lung cancers, with lower DYRK2 expression correlated with poorer prognosis in patients. Contrary to this, various medicinal chemistry studies reported robust antiproliferative properties of DYRK2 inhibitors, whereas unbiased 'omics' and genome-wide association study-based studies identified DYRK2 as a highly overexpressed kinase in various patient tumor samples. A major paradigm shift occurred in the last 4 years when DYRK2 was found to regulate proteostasis in cancer via a two-pronged mechanism. DYRK2 phosphorylated and activated the 26S proteasome to enhance degradation of misfolded/tumor-suppressor proteins while also promoting the nuclear stability and transcriptional activity of its substrate, heat-shock factor 1 triggering protein folding. Together, DYRK2 regulates proteostasis and promotes protumorigenic survival for specific cancers. Indeed, potent and selective small-molecule inhibitors of DYRK2 exhibit in vitro and in vivo anti-tumor activity in triple-negative breast cancer and myeloma models. However, with conflicting and contradictory reports across different cancers, the overarching role of DYRK2 remains enigmatic. Specific cancer (sub)types coupled to spatiotemporal interactions with substrates could decide the procancer or anticancer role of DYRK2. The current review aims to provide a balanced and critical appreciation of the literature to date, highlighting top substrates such as p53, c-Myc, c-Jun, heat-shock factor 1, proteasome, or NOTCH1, to discuss DYRK2 inhibitors available to the scientific community and to shed light on this duality of protumorigenic and antitumorigenic roles of DYRK2.

A review: Biologically active 3,4-heterocycle-fused coumarins

The combination of heterocycles offers a new opportunity to create novel multicyclic compounds having improved biological activity. Coumarins are ubiquitous natural heterocycle widely adopted in the design of various biologically active compounds. Fusing different heterocycles with coumarin ring is one of the interesting approaches to generating novel hybrid molecules having highlighted biological activities. In the efforts to develop heterocyclic-fused coumarins, a wide range of 3,4-heterocycle-fused coumarins have been introduced bearing outstanding biological activity. The effect of heterocycles annulation at 3,4-positions of coumarin ring on the biological activity of the target structures were discussed. This review focuses on the important progress of 3,4-heterocycle-fused coumarins providing better insight for medicinal chemists on the design and preparation of biologically active heterocycle-fused coumarins with a significant therapeutic effect in the future.

A Chemical Probe for Dark Kinase STK17B Derives Its Potency and High Selectivity through a Unique P-Loop Conformation

STK17B is a member of the death-associated protein kinase family and has been genetically linked to the development of diverse diseases. However, the role of STK17B in normal and disease pathology is poorly defined. Here, we present the discovery of thieno[3,2-d] pyrimidine SGC-STK17B-1 (11s), a high-quality chemical probe for this understudied "dark" kinase. 11s is an ATP-competitive inhibitor that showed remarkable selectivity over other kinases including the closely related STK17A. X-ray crystallography of 11s and related thieno[3,2-d]pyrimidines bound to STK17B revealed a unique P-loop conformation characterized by a salt bridge between R41 and the carboxylic acid of the inhibitor. Molecular dynamic simulations of STK17B revealed the flexibility of the P-loop and a wide range of R41 conformations available to the apo-protein. The isomeric thieno[2,3-d]pyrimidine SGC-STK17B-1N (19g) was identified as a negative control compound. The >100-fold lower activity of 19g on STK17B was attributed to the reduced basicity of its pyrimidine N1.

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.

Small Molecule Inhibitors of DYRK1A Identified by Computational and Experimental Approaches

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a protein kinase with diverse functions in cell regulation. Abnormal expression and activity of DYRK1A contribute to numerous human malignancies, Down syndrome, and Alzheimer's disease. Notably, DYRK1A has been proposed as a potential therapeutic target for the treatment of diabetes because of its key role in pancreatic β-cell proliferation. Consequently, DYRK1A is an attractive drug target for a variety of diseases. Here, we report the identification of several DYRK1A inhibitors using our in-house topological water network-based approach. All inhibitors were further verified by in vitro assay.

A Dual Inhibitor of DYRK1A and GSK3β for β-Cell Proliferation: Aminopyrazine Derivative GNF4877

Loss of β-cell mass and function can lead to insufficient insulin levels and ultimately to hyperglycemia and diabetes mellitus. The mainstream treatment approach involves regulation of insulin levels; however, approaches intended to increase β-cell mass are less developed. Promoting β-cell proliferation with low-molecular-weight inhibitors of dual-specificity tyrosine-regulated kinase 1A (DYRK1A) offers the potential to treat diabetes with oral therapies by restoring β-cell mass, insulin content and glycemic control. GNF4877, a potent dual inhibitor of DYRK1A and glycogen synthase kinase 3β (GSK3β) was previously reported to induce primary human β-cell proliferation in vitro and in vivo. Herein, we describe the lead optimization that lead to the identification of GNF4877 from an aminopyrazine hit identified in a phenotypic high-throughput screening campaign measuring β-cell proliferation.

Isolation and synthesis of cryptosanguinolentine (isocryptolepine), a naturally-occurring bioactive indoloquinoline alkaloid

Cryptosanguinolentine (isocryptolepine) is one of the minor naturally-occurring monomeric indoloquinoline alkaloids, isolated from the West African climbing shrub Cryptolepis sanguinolenta. The natural product displays such a simple and unique skeleton, which chemists became interested in well before it was found in Nature. Because of its structure and biological activity, the natural product has been targeted for synthesis on numerous occasions, employing a wide range of different strategies. Hence, discussed here are aspects related to the isolation of isocryptolepine, as well as the various approaches toward its total synthesis.

Structure-Activity Relationships and Biological Evaluation of 7-Substituted Harmine Analogs for Human β-Cell Proliferation

Recently, we have shown that harmine induces β-cell proliferation both in vitro and in vivo, mediated via the DYRK1A-NFAT pathway. We explore structure-activity relationships of the 7-position of harmine for both DYRK1A kinase inhibition and β-cell proliferation based on our related previous structure-activity relationship studies of harmine in the context of diabetes and β-cell specific targeting strategies. 33 harmine analogs of the 7-position substituent were synthesized and evaluated for biological activity. Two novel inhibitors were identified which showed DYRK1A inhibition and human β-cell proliferation capability. The DYRK1A inhibitor, compound 1-2b, induced β-cell proliferation half that of harmine at three times higher concentration. From these studies we can draw the inference that 7-position modification is limited for further harmine optimization focused on β-cell proliferation and cell-specific targeting approach for diabetes therapeutics.

Synthesis and Biological Validation of a Harmine-Based, Central Nervous System (CNS)-Avoidant, Selective, Human β-Cell Regenerative Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase A (DYRK1A) Inhibitor

Recently, our group identified that harmine is able to induce β-cell proliferation both in vitro and in vivo, mediated via the DYRK1A-NFAT pathway. Since, harmine suffers from a lack of selectivity, both against other kinases and CNS off-targets, we therefore sought to expand structure-activity relationships for harmine's DYRK1A activity, to enhance selectivity for off-targets while retaining human β-cell proliferation activity. We carried out optimization of the 9-N-position of harmine to synthesize 29 harmine-based analogs. Several novel inhibitors showed excellent DYRK1A inhibition and human β-cell proliferation capability. An optimized DYRK1A inhibitor, 2-2c, was identified as a novel, efficacious in vivo lead candidate. 2-2c also demonstrates improved selectivity for kinases and CNS off-targets, as well as in vivo efficacy for β-cell proliferation and regeneration at lower doses than harmine. Collectively, these findings demonstrate that 2-2c is a much improved in vivo lead candidate as compared to harmine for the treatment of diabetes.

Selective DYRK1A Inhibitor for the Treatment of Type 1 Diabetes: Discovery of 6-Azaindole Derivative GNF2133

Autoimmune deficiency and destruction in either β-cell mass or function can cause insufficient insulin levels and, as a result, hyperglycemia and diabetes. Thus, promoting β-cell proliferation could be one approach toward diabetes intervention. In this report we describe the discovery of a potent and selective DYRK1A inhibitor GNF2133, which was identified through optimization of a 6-azaindole screening hit. In vitro, GNF2133 is able to proliferate both rodent and human β-cells. In vivo, GNF2133 demonstrated significant dose-dependent glucose disposal capacity and insulin secretion in response to glucose-potentiated arginine-induced insulin secretion (GPAIS) challenge in rat insulin promoter and diphtheria toxin A (RIP-DTA) mice. The work described here provides new avenues to disease altering therapeutic interventions in the treatment of type 1 diabetes (T1D).

Fragment-to-Lead Medicinal Chemistry Publications in 2018

This Perspective, the fourth in an annual series, summarizes fragment-to-lead (F2L) success stories published during 2018. Topics such as target class, screening methods, physicochemical properties, and ligand efficiency are discussed for the 2018 examples as well as for the combined 111 F2L examples covering 2015-2018. While the overall properties of fragments and leads have remained constant, a number of new trends are noted, for example, broadening of target class coverage and application of FBDD to covalent inhibitors. Moreover, several studies make use of fragment hits that were previously described in the literature, illustrating that fragments are versatile starting points that can be optimized to structurally diverse leads. By focusing on success stories, the hope is that this Perspective will identify and inform best practices in fragment-based drug discovery.

[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.

Discovery of the First in Vivo Active Inhibitors of the Soluble Epoxide Hydrolase Phosphatase Domain

The emerging pharmacological target soluble epoxide hydrolase (sEH) is a bifunctional enzyme exhibiting two different catalytic activities that are located in two distinct domains. Although the physiological role of the C-terminal hydrolase domain is well-investigated, little is known about its phosphatase activity, located in the N-terminal phosphatase domain of sEH (sEH-P). Herein we report the discovery and optimization of the first inhibitor of human and rat sEH-P that is applicable in vivo. X-ray structure analysis of the sEH phosphatase domain complexed with an inhibitor provides insights in the molecular basis of small-molecule sEH-P inhibition and helps to rationalize the structure-activity relationships. 4-(4-(3,4-Dichlorophenyl)-5-phenyloxazol-2-yl)butanoic acid (22b, SWE101) has an excellent pharmacokinetic and pharmacodynamic profile in rats and enables the investigation of the physiological and pathophysiological role of sEH-P in vivo.

Design, synthesis and biological evaluation of 2-(3,4-dimethoxyphenyl)-6 (1,2,3,6-tetrahydropyridin-4-yl)imidazo[1,2-a]pyridine analogues as antiproliferative agents

Two series of forty five novel 2-(3,4-dimethoxyphenyl)-6-(1,2,3,6-tetrahydropyridin-4-yl) imidazo[1,2-a]pyridine analogues (IPA 1-22, IPS 1-22 and IP-NH) have been designed, synthesized and structures confirmed by ¹H NMR, ¹³C NMR, mass spectrometry. Furthermore, single crystal was developed for IPS-13. All the final derived conjugates were evaluated for their in vitro antiproliferative activity against a panel of diverse cancer cell lines viz., A549 (lung cancer), HeLa (cervical cancer), B16F10 (melanoma) and found to show potent anticancer activity on the tested cell lines. Many of them showed the IC₅₀ values in the range 2.0-20.0 µM. The most active compounds (IPA 5,6,8,9,12,16,17,19 and IPS 7,8,9,22) from IPA and IPS series were screened to determine their cytotoxicity on HEK-293 (human embryonic kidney) normal cell line and were found to be nontoxic to normal human cells. The molecular interactions of the derivatised conjugates were also supported by molecular docking simulations. These derivatives may serve as lead structures for development of novel potential anticancer drug candidates.