Selective inhibition of the kinase DYRK1A by targeting its folding process

Temperature vaulting: A method for screening of slow- and tight-binding inhibitors that selectively target kinases in their non-native state

A polypeptide folds into its protein tertiary structure in the native state through a folding intermediate in the non-native state. The transition between these states is thermodynamically driven. A folding intermediate of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) autophosphorylates intramolecularly, whereas DYRK1A in the native state no longer catalyzes this reaction. The alteration in substrate specificity suggests a conformational transition of DYRK1A during its folding process. Consistent with this hypothesis, we identified FINDY (1), which inhibits the intramolecular autophosphorylation but not the intermolecular phosphorylation, suggesting that DYRK1A in the non-native state possesses an alternative inhibitor-binding site. Meanwhile, it remains an issue that the methods for approaching the alternative binding site require an intricate assay tailored to the individual target. Here we show a method, designated as "temperature vaulting," for inhibitor screening that targets the non-native state. Transient heating of recombinant DYRK1A protein drove the reversible transition between the native state and the non-native state targeted by FINDY (1). At physiological temperature, FINDY (1) slowly bound to the DYRK1A protein. These results indicate that transient heating accelerates the slow-binding process by assisting the protein to overcome the high-energy barrier leading to the target non-native state. The energy barrier also slowed down the dissociation, resulting in tight binding between DYRK1A and FINDY (1). Structure-activity relationship revealed that both the methoxy group and the alkyne moiety underlie the selectivity of FINDY (1) toward DYRK1A in the non-native state. Furthermore, this study suggests that the dissociation rate underlies the inhibition selectivity of FINDY (1) between DYRK1A and its family kinase DYRK1B. This method could leverage conventional assays to identify slow- and tight-binding inhibitors.

Computational advances in discovering cryptic pockets for drug discovery

A number of promising therapeutic target proteins have been considered "undruggable" due to the lack of well-defined ligandable pockets. Substantial research in protein dynamics has elucidated the existence of "cryptic" pockets that only exist transiently and become favorable for binding in the presence of a ligand. These pockets provide an avenue to target challenging proteins, inspiring the development of multiple computational methods. This review highlights established cryptic pocket modeling approaches like mixed solvent molecular dynamics and recent applications of enhanced sampling and AI-based methods in therapeutically relevant proteins.

Mechanochemical Palladium-Catalyzed Cross-Coupling of Thianthrenium Salts and Arylboronic Acids

Cross-coupling reactions are indispensable for the construction of complex molecular scaffolds. In this work, we developed a sustainable methodology for the cross-coupling reaction of arene thianthrenium salts with aryl boronic acids, which can be effectively realized under mechanochemical conditions. Liquid-assisted grinding (LAG) enabled fast and high-yielding synthesis of a range of biaryls via Pd/RuPhos-catalyzed cross-coupling. The transformation works under ambient temperature and on air. Environmentally friendly solvent 2-methyltetrahydrofurane (Me-THF) was used as a LAG additive. Moreover, the major by-product of the cross-coupling reaction, thianthrene, can be recovered and reused.

Identification, biological evaluation, and crystallographic analysis of coumestrol as a novel dual-specificity tyrosine-phosphorylation-regulated kinase 1A inhibitor

Alzheimer's disease (AD) is an irreversible neurodegenerative disease, with tau pathology caused by abnormally activated dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) being one of the culprits. Coumestrol, a phytoestrogen and natural antioxidant found in various plants, has been reported to alleviate AD, but the underlying mechanism remains unclear. We confirmed coumestrol as a novel DYRK1A inhibitor through enzyme-based assays, X-ray crystallography, and cell line experiments. Coumestrol exhibited minimal cytotoxicity at concentrations up to 100 μM in cell types such as N2A and SH-SY5Y and reduced DYRK1A-induced phosphorylated tau protein levels by >50 % at 60 μM. In the tau protein phosphorylation and microtubule assembly assay, coumestrol at 30 μM reduced phosphorylated tau by >50 % and restored the microtubule assembly process. Coumestrol also significantly reduced amyloid-β (Aβ)-induced oxidative stress in microglia at 1 μM. In zebrafish larvae co-overexpressing DYRK1A and tau, coumestrol mitigated neuronal damage and protected motor function at 48 h-postfertilization. Our results suggest that coumestrol has potential therapeutic effects in AD by inhibiting DYRK1A, lowering p-Tau levels, restoring microtubule assembly, and protecting microglia cells from Aβ-induced cell death, providing new insights into the development of coumestrol as a potential AD treatment.

Dissecting the role of SMN multimerization in its dissociation from the Cajal body using harmine as a tool compound

Survival motor neuron protein (SMN), which is linked to spinal muscular atrophy, is a key component of the Gemin complex, which is essential for the assembly of small nuclear RNA-protein complexes (snRNPs). After initial snRNP assembly in the cytoplasm, both snRNPs and SMN migrate to the nucleus and associate with Cajal bodies, where final snRNP maturation occurs. It is assumed that SMN must be free from the Cajal bodies for continuous snRNP biogenesis. Previous observation of the SMN granules docked in the Cajal bodies suggests the existence of a separation mechanism. However, the precise processes that regulate the spatial separation of SMN complexes from Cajal bodies remain unclear. Here, we have employed a super-resolution microscope alongside the β-carboline alkaloid harmine, which disrupts the Cajal body in a reversible manner. Upon removal of harmine, SMN and Coilin first appear as small interconnected condensates. The SMN condensates mature into spheroidal structures encircled by Coilin, eventually segregating into distinct condensates. Expression of a multimerization-deficient SMN mutant leads to enlarged, atypical Cajal bodies in which SMN is unable to segregate into separate condensates. These findings underscore the importance of multimerization in facilitating the segregation of SMN from Coilin within Cajal bodies.

The TRAF3-DYRK1A-RAD54L2 complex maintains ACE2 expression to promote SARS-CoV-2 infection

Angiotensin converting enzyme 2 (ACE2), the host receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, is differentially expressed in a wide variety of tissues and cell types. The expression of ACE2 is under tight regulation, but the mechanisms regulating ACE2 expression have not yet been well defined. Through a genome-wide CRISPR knockout screen, we discovered that host factors TRAF3, DYRK1A, and RAD54L2 (TDR) form a complex to regulate the expression of ACE2. Knockout of TRAF3, DYRK1A, or RAD54L2 reduces the mRNA levels of ACE2 and inhibits the cellular entry of SARS-CoV-2. On the other hand, SARS-CoV-2 continuously evolves by genetic mutations for the adaption to the host. We have identified mutations in spike (S) (P1079T) and nucleocapsid (N) (S194L) that enhance the replication of SARS-CoV-2 in cells that express ACE2 at a low level. Our results have revealed the mechanisms for the transcriptional regulation of ACE2 and the adaption of SARS-CoV-2.

IMPORTANCE

The expression of ACE2 is essential for the entry of SARS-CoV-2 into host cells. We identify a new complex-the TDR complex-that acts to maintain the abundance of ACE2 in host cells. The identification and characterization of the TDR complex provide new targets for the development of therapeutics against SARS-CoV-2 infection. By analysis of SARS-CoV-2 virus replicating in cells expressing low levels of ACE2, we identified mutations in spike (P1079T) and nucleocapsid (S194L) that overcome the restriction of limited ACE2. Functional analysis of these key amino acids in S and N extends our knowledge of the impact of SARS-CoV-2 variants on virus infection and transmission.

Synthesis of alkynyl sulfides via base-promoted nucleophilic ring-opening of α-bromostyrene sulfonium salt

An efficient method for the synthesis of alkynyl sulfides via a C(sp3)-S bond cleavage of α-bromostyrene sulfonium salts has been developed. This base-promoted nucleophilic ring-opening pathway allows the preparation of diverse alkynyl sulfide compounds using tetramethylene sulfoxide as the sulfur source. The reaction proceeds with good functional group tolerance and could be applied to the late-stage functionalization of bioactive molecules and drugs. Furthermore, the synthetic utility of this method was demonstrated by a one-pot synthesis, scale-up reaction and further modification of various alkynyl sulfide products.

Identification of selective dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) inhibitors and their effects on tau and microtubule

The overexpression of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), commonly observed in neurodegenerative diseases like Alzheimer's disease (AD) and Down syndrome (DS), can induce the formation of neurofibrillary tangles (NFTs) and amyloid plaques. Hence, designing a selective DYRK1A inhibitor would result in a promising small molecule for treating neurodegenerative diseases. Developing selective inhibitors for DYRK1A has been a difficult challenge due to the highly preserved ATP-binding site of protein kinases. In this study, we employed a structure-based virtual screening (SBVS) campaign targeting DYRK1A from a database containing 1.6 million compounds. Enzymatic assays were utilized to verify inhibitory properties, confirming that Y020-3945 and Y020-3957 showed inhibitory activity towards DYRK1A. In particular, the compounds exhibited high selectivity for DYRK1A over a panel of 120 kinases, reduced the phosphorylation of tau, and reversed the tubulin polymerization for microtubule stability. Additionally, treatment with the compounds significantly reduced the secretion of inflammatory cytokines IL-6 and TNF-α activated by DYRK1A-assisted NFTs and Aβ oligomers. These identified inhibitors possess promising therapeutic potential for conditions associated with DYRK1A in neurodegenerative diseases. The results showed that Y020-3945 and Y020-3957 demonstrated structural novelty compared to known DYRK1A inhibitors, making them a valuable addition to developing potential treatments for neurodegenerative diseases.

DnaK promotes autophosphorylation of DYRK1A and its family kinases in Escherichia coli-based cell-free protein expression

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is one of the drug target kinases involved in neurological disorders. DYRK1A phosphorylates substrate proteins related to disease progression in an intermolecular manner. Meanwhile, DYRK1A intramolecularly phosphorylates its own residues on key segments during folding process, which is required for its activation and stabilization. To reproduce the autophosphorylation in vitro, DYRK1A was expressed in Escherichia coli-based cell-free protein synthesis system. Although this system was useful for investigating autophosphorylation of serine residue at position 97 (Ser97) in DYRK1A, only a small fraction of the synthesized protein was successfully autophosphorylated. In this study, we found that the addition of DnaK, a bacterial HSP70 chaperone, to cell-free expression of DYRK1A promoted its Ser97 autophosphorylation. Structure prediction with AlphaFold2 indicates that Ser97 forms a hydrogen bond within an α-helix structure, indicating a possibility that DnaK unfolds the α-helix and maintains the structure around Ser97 in a conformation susceptible to phosphorylation. In addition, DnaK promoted phosphorylation of DYRK1B and HIPK2, but not DYRK2 and DYRK4, suggesting a sequence selectivity in the action of DnaK. This study provides a facile method for promoting autophosphorylation of DYRK family kinases in cell-free protein expression.

Discovery of Potent, Selective, and Orally Bioavailable DYRK2 Inhibitors for the Treatment of Prostate Cancer

Prostate cancer (PCa) seriously threatens male health, and targeting dual-specificity tyrosine phosphorylation-regulated kinase 2 (DYRK2) has been verified to reduce PCa burden, while the research progress on the DYRK2 inhibitors was relatively slow. In this work, we discovered DYRK2 inhibitor 12 (IC50 = 9681 nM) through virtual screening. Subsequently, we performed systematic structural optimization to obtain 54 (IC50 = 14 nM). Compound 54 exhibited high selectivity among 215 kinases and significantly suppressed the proliferation and metastasis of PCa cells in vitro. Moreover, compound 54 displayed high safety, favorable bioavailability, and potent tumor growth inhibitory activity in vivo, which could be used as a potential candidate in the discovery of novel anti-PCa drugs.

A Pan-Respiratory Antiviral Chemotype Targeting a Host Multi-Protein Complex

We present a novel small molecule antiviral chemotype that was identified by an unconventional cell-free protein synthesis and assembly-based phenotypic screen for modulation of viral capsid assembly. Activity of PAV-431, a representative compound from the series, has been validated against infectious virus in multiple cell culture models for all six families of viruses causing most respiratory disease in humans. In animals this chemotype has been demonstrated efficacious for Porcine Epidemic Diarrhea Virus (a coronavirus) and Respiratory Syncytial Virus (a paramyxovirus). PAV-431 is shown to bind to the protein 14-3-3, a known allosteric modulator. However, it only appears to target the small subset of 14-3-3 which is present in a dynamic multi-protein complex whose components include proteins implicated in viral lifecycles and in innate immunity. The composition of this target multi-protein complex appears to be modified upon viral infection and largely restored by PAV-431 treatment. Our findings suggest a new paradigm for understanding, and drugging, the host-virus interface, which leads to a new clinical therapeutic strategy for treatment of respiratory viral disease.

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.

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.

pSNAP: Proteome-wide analysis of elongating nascent polypeptide chains

Cellular global translation is often measured using ribosome profiling or quantitative mass spectrometry, but these methods do not provide direct information at the level of elongating nascent polypeptide chains (NPCs) and associated co-translational events. Here, we describe pSNAP, a method for proteome-wide profiling of NPCs by affinity enrichment of puromycin- and stable isotope-labeled polypeptides. pSNAP does not require ribosome purification and/or chemical labeling, and captures bona fide NPCs that characteristically exhibit protein N-terminus-biased positions. We applied pSNAP to evaluate the effect of silmitasertib, a potential molecular therapy for cancer, and revealed acute translational repression through casein kinase II and mTOR pathways. We also characterized modifications on NPCs and demonstrated that the combination of different types of modifications, such as acetylation and phosphorylation in the N-terminal region of histone H1.5, can modulate interactions with ribosome-associated factors. Thus, pSNAP provides a framework for dissecting co-translational regulations on a proteome-wide scale.

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Nascent polypeptidome analysis with a simplified protocol

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Quantification of acute changes in nascent polypeptides induced by external stimuli

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Profiling and characterization of chemical modifications on nascent polypeptides

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.

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.

Identification and analysis of a selective DYRK1A inhibitor

The dysregulation of DYRK1A is implicated in many diseases such as cancer, diabetes, and neurodegenerative diseases. Alzheimer's disease is one of the most common neurodegenerative disease and has elevated interest in DYRK1A research. Overexpression of DYRK1A has been linked to the formation of tau aggregates. Currently, an effective therapeutic treatment that targets DYRK1A is lacking. A specific small-molecule inhibitor would further our understanding of the physiological role of DYRK1A in neurodegenerative diseases and could be presented as a possible therapeutic option. In this study, we identified pharmacological interactions within the DYRK1A active site and performed a structure-based virtual screening approach to identify a selective small-molecule inhibitor. Several compounds were selected in silico for enzymatic and cellular assays, yielding a novel inhibitor. A structure-activity relationship analysis was performed to identify areas of interactions for the compounds selected in this study. When tested in vitro, reduction of DYRK1A dependent phosphorylation of tau was observed for active compounds. The active compounds also improved tau turbidity, suggesting that these compounds could alleviate aberrant tau aggregation. Testing the active compound against a panel of kinases across the kinome revealed greater selectivity towards DYRK1A. Our study demonstrates a serviceable protocol that identified a novel and selective DYRK1A inhibitor with potential for further study in tau-related pathologies.

What Features of Ligands Are Relevant to the Opening of Cryptic Pockets in Drug Targets?

Small-molecule drug design aims to identify inhibitors that can specifically bind to a functionally important region on the target, i.e., an active site of an enzyme. Identification of potential binding pockets is typically based on static three-dimensional structures. However, small molecules may induce and select a dynamic binding pocket that is not visible in the apo protein, which presents a well-recognized challenge for structure-based drug discovery. Here, we assessed whether it is possible to identify features in molecules, which we refer to as inducers, that can induce the opening of cryptic pockets. The volume change between apo and bound protein conformations was used as a metric to differentiate chemical features in inducers vs. non-inducers. Based on the dataset of holo–apo pairs, classification models were built to determine an optimum threshold. The model analysis suggested that inducers preferred to be more hydrophobic and aromatic. The impact of sulfur was ambiguous, while phosphorus and halogen atoms were overrepresented in inducers. The fragment analysis showed that small changes in the structures of molecules can strongly affect the potential to induce a cryptic pocket. This analysis and developed model can be used to design inducers that can potentially open cryptic pockets for undruggable proteins.

Structure-activity relationship for the folding intermediate-selective inhibition of DYRK1A

DYRK1A phosphorylates proteins involved in neurological disorders in an intermolecular manner. Meanwhile, during the protein folding process of DYRK1A, a transitional folding intermediate catalyzes the intramolecular autophosphorylation required for the "one-off" inceptive activation and stabilization. In our previous study, a small molecule termed FINDY (1) was identified, which inhibits the folding intermediate-catalyzed intramolecular autophosphorylation of DYRK1A but not the folded state-catalyzed intermolecular phosphorylation. However, the structural features of FINDY (1) responsible for this intermediate-selective inhibition remain elusive. In this study, structural derivatives of FINDY (1) were designed and synthesized according to its predicted binding mode in the ATP pocket of DYRK1A. Quantitative structure-activity relationship (QSAR) of the derivatives revealed that the selectivity against the folding intermediate is determined by steric hindrance between the bulky hydrophobic moiety of the derivatives and the entrance to the pocket. In addition, a potent derivative 3 was identified, which inhibited the folding intermediate more strongly than FINDY (1); it was designated as dp-FINDY. Although dp-FINDY (3) did not inhibit the folded state, as well as FINDY (1), it inhibited the intramolecular autophosphorylation of DYRK1A in an in vitro cell-free protein synthesis assay. Furthermore, dp-FINDY (3) destabilized endogenous DYRK1A in HEK293 cells. This study provides structural insights into the folding intermediate-selective inhibition of DYRK1A and expands the chemical options for the design of a kinase inhibitor.

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.

GSK-3β, FYN, and DYRK1A: Master Regulators in Neurodegenerative Pathways

Protein kinases (PKs) have been recognized as central nervous system (CNS)-disease-relevant targets due to their master regulatory role in different signal transduction cascades in the neuroscience space. Among them, GSK-3β, FYN, and DYRK1A play a crucial role in the neurodegeneration context, and the deregulation of all three PKs has been linked to different CNS disorders with unmet medical needs, including Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal lobar degeneration (FTLD), and several neuromuscular disorders. The multifactorial nature of these diseases, along with the failure of many advanced CNS clinical trials, and the lengthy approval process of a novel CNS drug have strongly limited the CNS drug discovery. However, in the near-decade from 2010 to 2020, several computer-assisted drug design strategies have been combined with synthetic efforts to develop potent and selective GSK-3β, FYN, and DYRK1A inhibitors as disease-modifying agents. In this review, we described both structural and functional aspects of GSK-3β, FYN, and DYRK1A and their involvement and crosstalk in different CNS pathological signaling pathways. Moreover, we outlined attractive medicinal chemistry approaches including multi-target drug design strategies applied to overcome some limitations of known PKs inhibitors and discover improved modulators with suitable blood-brain barrier (BBB) permeability and drug-like properties.

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 human isogenic iPSC-derived cell line panel identifies major regulators of aberrant astrocyte proliferation in Down syndrome

Astrocytes exert adverse effects on the brains of individuals with Down syndrome (DS). Although a neurogenic-to-gliogenic shift in the fate-specification step has been reported, the mechanisms and key regulators underlying the accelerated proliferation of astrocyte precursor cells (APCs) in DS remain elusive. Here, we established a human isogenic cell line panel based on DS-specific induced pluripotent stem cells, the XIST-mediated transcriptional silencing system in trisomic chromosome 21, and genome/chromosome-editing technologies to eliminate phenotypic fluctuations caused by genetic variation. The transcriptional responses of genes observed upon XIST induction and/or downregulation are not uniform, and only a small subset of genes show a characteristic expression pattern, which is consistent with the proliferative phenotypes of DS APCs. Comparative analysis and experimental verification using gene modification reveal dose-dependent proliferation-promoting activity of DYRK1A and PIGP on DS APCs. Our collection of human isogenic cell lines provides a comprehensive set of cellular models for further DS investigations.

Keiji Kawatani et al. developed a panel of Down syndrome (DS) isogenic astrocytes derived from iPSCs to observe the consequence of DS on astrocyte precursor proliferation, differentiation, and gene expression. Their results suggest a dose-dependent effect of DYRK1A and PIGP on DS-derived astrocyte precursor proliferation, and represent a valuable resource and cellular model for future DS research.

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.

S1PR3-G12-biased agonist ALESIA targets cancer metabolism and promotes glucose starvation

Metabolic activities are altered in cancer cells compared with those in normal cells, and the cancer-specific pathway becomes a potential therapeutic target. Higher cellular glucose consumption, which leads to lower glucose levels, is a hallmark of cancer cells. In an objective screening for chemicals that induce cell death under low-glucose conditions, we discovered a compound, denoted as ALESIA (Anticancer Ligand Enhancing Starvation-induced Apoptosis). By our shedding assay of transforming growth factor α in HEK293A cells, ALESIA was determined to act as a sphingosine-1-phosphate receptor 3-G₁₂-biased agonist that promotes nitric oxide production and oxidative stress. The oxidative stress triggered by ALESIA resulted in the exhaustion of glucose, cellular NADPH deficiency, and then cancer cell death. Intraperitoneal administration of ALESIA improved the survival of mice with peritoneally disseminated rhabdomyosarcoma, indicating its potential as a new type of anticancer drug for glucose starvation therapy.

Druggable Transient Pockets in Protein Kinases

Drug discovery using small molecule inhibitors is reaching a stalemate due to low selectivity, adverse off-target effects and inevitable failures in clinical trials. Conventional chemical screening methods may miss potent small molecules because of their use of simple but outdated kits composed of recombinant enzyme proteins. Non-canonical inhibitors targeting a hidden pocket in a protein have received considerable research attention. Kii and colleagues identified an inhibitor targeting a transient pocket in the kinase DYRK1A during its folding process and termed it FINDY. FINDY exhibits a unique inhibitory profile; that is, FINDY does not inhibit the fully folded form of DYRK1A, indicating that the FINDY-binding pocket is hidden in the folded form. This intriguing pocket opens during the folding process and then closes upon completion of folding. In this review, we discuss previously established kinase inhibitors and their inhibitory mechanisms in comparison with FINDY. We also compare the inhibitory mechanisms with the growing concept of “cryptic inhibitor-binding sites.” These sites are buried on the inhibitor-unbound surface but become apparent when the inhibitor is bound. In addition, an alternative method based on cell-free protein synthesis of protein kinases may allow the discovery of small molecules that occupy these mysterious binding sites. Transitional folding intermediates would become alternative targets in drug discovery, enabling the efficient development of potent kinase inhibitors.

Protein phosphatase PPM1B inhibits DYRK1A kinase through dephosphorylation of pS258 and reduces toxic tau aggregation

Down syndrome (DS) is mainly caused by an extra copy of chromosome 21 (trisomy 21), and patients display a variety of developmental symptoms, including characteristic facial features, physical growth delay, intellectual disability, and neurodegeneration (i.e., Alzheimer's disease; AD). One of the pathological hallmarks of AD is insoluble deposits of neurofibrillary tangles (NFTs) that consist of hyperphosphorylated tau. The human DYRK1A gene is mapped to chromosome 21, and the protein is associated with the formation of inclusion bodies in AD. For example, DYRK1A directly phosphorylates multiple serine and threonine residues of tau, including Thr212. However, the mechanism underpinning DYRK1A involvement in Trisomy 21-related pathological tau aggregation remains unknown. Here, we explored a novel regulatory mechanism of DYRK1A and subsequent tau pathology through a phosphatase. Using LC-MS/MS technology, we analyzed multiple DYRK1A-binding proteins, including PPM1B, a member of the PP2C family of Ser/Thr protein phosphatases, in HEK293 cells. We found that PPM1B dephosphorylates DYRK1A at Ser258, contributing to the inhibition of DYRK1A activity. Moreover, PPM1B-mediated dephosphorylation of DYRK1A reduced tau phosphorylation at Thr212, leading to inhibition of toxic tau oligomerization and aggregation. In conclusion, our study demonstrates that DYRK1A autophosphorylates Ser258, the dephosphorylation target of PPM1B, and PPM1B negatively regulates DYRK1A activity. This finding also suggests that PPM1B reduces the toxic formation of phospho-tau protein via DYRK1A modulation, possibly providing a novel cellular protective mechanism to regulate toxic tau-mediated neuropathology in AD of DS.

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.

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.

Updating dual-specificity tyrosine-phosphorylation-regulated kinase 2 (DYRK2): molecular basis, functions and role in diseases

Members of the dual-specificity tyrosine-regulated kinase (DYRKs) subfamily possess a distinctive capacity to phosphorylate tyrosine, serine, and threonine residues. Among the DYRK class II members, DYRK2 is considered a unique protein due to its role in disease. According to the post-transcriptional and post-translational modifications, DYRK2 expression greatly differs among human tissues. Regarding its mechanism of action, this kinase performs direct phosphorylation on its substrates or acts as a priming kinase, enabling subsequent substrate phosphorylation by GSK3β. Moreover, DYRK2 acts as a scaffold for the EDVP E3 ligase complex during the G2/M phase of cell cycle. DYRK2 functions such as cell survival, cell development, cell differentiation, proteasome regulation, and microtubules were studied in complete detail in this review. We have also gathered available information from different bioinformatic resources to show DYRK2 interactome, normal and tumoral tissue expression, and recurrent cancer mutations. Then, here we present an innovative approach to clarify DYRK2 functionality and importance. DYRK2 roles in diseases have been studied in detail, highlighting this kinase as a key protein in cancer development. First, DYRK2 regulation of c-Jun, c-Myc, Rpt3, TERT, and katanin p60 reveals the implication of this kinase in cell-cycle-mediated cancer development. Additionally, depletion of this kinase correlated with reduced apoptosis, with consequences on cancer patient response to chemotherapy. Other functions like cancer stem cell formation and epithelial-mesenchymal transition regulation are also controlled by DYRK2. Furthermore, the pharmacological modulation of this protein by different inhibitors (harmine, curcumine, LDN192960, and ID-8) has enabled to clarify DYRK2 functionality.

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.

Photoredox-Mediated Synthesis of Functionalized Sulfoxides from Terminal Alkynes

A photoredox-mediated protocol for the synthesis of α-alkoxy-β-ketosulfoxides and α,β-dialkoxysulfoxides using alkynes, thiol, and alcohols is reported. This work presents a rare single-step synthesis of α-substituted sulfoxides, involving tandem introduction of a thiol and alcohol as a key enabling advancement. Furthermore, the method can be easily employed to access vinyl sulfoxides and β-ketosulfoxides.

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.

Monovalent protein-degraders - Insights and future perspectives

The therapeutic potential of interfering with dysregulated proteins by inducing its selective degradation has been pursued using different mechanisms. In the present article, we review representative examples of monovalent protein-degraders that, contrary to the proteolysis targeting chimeras, achieve target degradation without displaying recognition motifs for the recruitment of E3 ubiquitin ligases. We also highlight new technologies and assays that may brought to bear on the discovery of common elements that could predict and enable the selective degradation of pathogenic targets by monovalent protein-degraders. The successful application of these methods would pave the way to the advancement of new drugs with unique efficacy and tolerability properties.

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).

[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.

Impaired development of neocortical circuits contributes to the neurological alterations in DYRK1A haploinsufficiency syndrome

Autism spectrum disorders are early onset neurodevelopmental disorders characterized by deficits in social communication and restricted repetitive behaviors, yet they are quite heterogeneous in terms of their genetic basis and phenotypic manifestations. Recently, de novo pathogenic mutations in DYRK1A, a chromosome 21 gene associated to neuropathological traits of Down syndrome, have been identified in patients presenting a recognizable syndrome included in the autism spectrum. These mutations produce DYRK1A kinases with partial or complete absence of the catalytic domain, or they represent missense mutations located within this domain. Here, we undertook an extensive biochemical characterization of the DYRK1A missense mutations reported to date and show that most of them, but not all, result in enzymatically dead DYRK1A proteins. We also show that haploinsufficient Dyrk1a+/- mutant mice mirror the neurological traits associated with the human pathology, such as defective social interactions, stereotypic behaviors and epileptic activity. These mutant mice present altered proportions of excitatory and inhibitory neocortical neurons and synapses. Moreover, we provide evidence that alterations in the production of cortical excitatory neurons are contributing to these defects. Indeed, by the end of the neurogenic period, the expression of developmental regulated genes involved in neuron differentiation and/or activity is altered. Therefore, our data indicate that altered neocortical neurogenesis could critically affect the formation of cortical circuits, thereby contributing to the neuropathological changes in DYRK1A haploinsufficiency syndrome.

DYRK1A and cognition: A lifelong relationship

The dosage of the serine threonine kinase DYRK1A is critical in the central nervous system (CNS) during development and aging. This review analyzes the functions of this kinase by considering its interacting partners and pathways. The role of DYRK1A in controlling the differentiation of prenatal newly formed neurons is presented separately from its role at the pre- and post-synaptic levels in the adult CNS; its effects on synaptic plasticity are also discussed. Because this kinase is positioned at the crossroads of many important processes, genetic dosage errors in this protein produce devastating effects arising from DYRK1A deficiency, such as in MRD7, an autism spectrum disorder, or from DYRK1A excess, such as in Down syndrome. Effects of these errors have been shown in various animal models including Drosophila, zebrafish, and mice. Dysregulation of DYRK1A levels also occurs in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Finally, this review describes inhibitors that have been assessed in vivo. Accurate targeting of DYRK1A levels in the brain, with either inhibitors or activators, is a future research challenge.

Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase 1A (DYRK1A) Inhibitors as Potential Therapeutics

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a member of an evolutionarily conserved family of protein kinases that belongs to the CMGC group of kinases. DYRK1A, encoded by a gene located in the human chromosome 21q22.2 region, has attracted attention due to its association with both neuropathological phenotypes and cancer susceptibility in patients with Down syndrome (DS). Inhibition of DYRK1A attenuates cognitive dysfunctions in animal models for both DS and Alzheimer's disease (AD). Furthermore, DYRK1A has been studied as a potential cancer therapeutic target because of its role in the regulation of cell cycle progression by affecting both tumor suppressors and oncogenes. Consequently, selective synthetic inhibitors have been developed to determine the role of DYRK1A in various human diseases. Our perspective includes a comprehensive review of potent and selective DYRK1A inhibitors and their forthcoming therapeutic applications.

DYRK1A kinase inhibition with emphasis on neurodegeneration: A comprehensive evolution story-cum-perspective

Alzheimer, the fourth leading cause of death embodies a key responsible event including formation of β-amyloid protein clustering to amyloid plaque on blood vessels. The origin of above events is Amyloid precursor protein (APP) which is an integral membrane protein known for its function in synapses formation. Modern research had proposed that the over expression of DYRK1A (Dual specificity tyrosine phosphorylation regulated kinase1A, a family of protein kinases, positioned within the Down's syndrome critical region (DSCR) on human chromosome 21causes phosphorylation of APP protein resulting in its cleavage to Aβ 40, 42 and tau proteins (regulated by beta and gamma secretase) which plays critical role in early onset of Alzheimer's disease (AD) detected in Down's syndrome (DS), leading to permanent functional and structural deformities which results ultimately into neuro-degeneration and neuronal death. Therefore, DYRK1A emerges as a potential target for prevention of neuro-degeneration and hence Alzheimer. Presently, the treatment methods for Down's syndrome, as well as Alzheimer's disease are extremely biased and represent a major deficiency for therapeutic necessities. We hereby, focus our review on the current status of the research and contributions in the development of DYRK1A inhibitors.

Development of Kinase-Selective, Harmine-Based DYRK1A Inhibitors that Induce Pancreatic Human β-Cell Proliferation

DYRK1A has been implicated as an important drug target in various therapeutic areas, including neurological disorders and oncology. DYRK1A has more recently been shown to be involved in pathways regulating human β-cell proliferation, thus making it a potential therapeutic target for both Type 1 and Type 2 diabetes. Our group, using a high-throughput phenotypic screen, identified harmine that is able to induce β-cell proliferation both in vitro and in vivo. Since harmine has suboptimal kinase selectivity, we sought to expand structure-activity relationships for harmine's DYRK1A activity, to enhance selectivity, while retaining human β-cell proliferation capability. We carried out the optimization of the 1-position of harmine and synthesized 15 harmine analogues. Six compounds showed excellent DYRK1A inhibition with IC50 in the range of 49.5-264 nM. Two compounds, 2-2 and 2-8, exhibited excellent human β-cell proliferation at doses of 3-30 μM, and compound 2-2 showed improved kinase selectivity as compared to harmine.