Identification of Glycogen Synthase Kinase-3 Inhibitors with a Selective Sting for Glycogen Synthase Kinase-3α

Therapeutic implications of glycogen synthase kinase-3β in Alzheimer's disease: a novel therapeutic target

Alzheimer's disease (AD) is an extremely popular neurodegenerative condition associated with dementia, responsible for around 70% of the cases. There are presently 50 million people living with dementia in the world, but this number is anticipated to increase to 152 million by 2050, posing a substantial socioeconomic encumbrance. Despite extensive research, the precise mechanisms that cause AD remain unidentified, and currently, no therapy is available. Numerous signalling paths related to AD neuropathology, including glycogen synthase kinase 3-β (GSK-3β), have been investigated as potential targets for the treatment of AD in current years.GSK-3β is a proline-directed serine/threonine kinase that is linked to a variety of biological activities, comprising glycogen metabolism to gene transcription. GSK-3β is also involved in the pathophysiology of sporadic as well as familial types of AD, which has led to the development of the GSK3 theory of AD. GSK-3β is a critical performer in the pathology of AD because dysregulation of this kinase affects all the main symbols of the disease such as amyloid formation, tau phosphorylation, neurogenesis and synaptic and memory function. The current review highlights present-day knowledge of GSK-3β-related neurobiology, focusing on its role in AD pathogenesis signalling pathways. It also explores the possibility of targeting GSK-3β for the management of AD and offers an overview of the present research work in preclinical and clinical studies to produce GSK-3β inhibitors.

Insights on effects of Wnt pathway modulation on insulin signaling and glucose homeostasis for the treatment of type 2 diabetes mellitus: Wnt activation or Wnt inhibition?

Type 2 diabetes mellitus (T2DM) is a major worldwide chronic disease and can lead to serious diabetic complications. Despite the availability of many anti-diabetic agents in the market, they are unable to meet the long-term treatment goals. Also, they cause many side effects which justify the need for novel class of anti-diabetic drugs with newer mechanism of action. Wnt signaling is one of such novel target pathways which can be explored for metabolic disorders. Many key components of the Wnt signaling are involved in the regulation of glucose homeostasis. Polymorphism in the Transcription factor 7-like 2 (TCF7L2) gene, and mutations in the LRP5 (LDL Receptor Related Protein 5) gene lead to disturbed glucose metabolism and obesity. Despite of several years of research in this field, there is no concrete proof of concept available on whether Wnt activation or Wnt inhibition is the beneficial approach for the treatment of T2DM. Here, we have summarized the conclusions of relevant published research studies to give structured insights into possibilities to explore Wnt modulation as a novel target pathway for the treatment of T2DM. The review also highlights the present challenges and future opportunities towards the development of anti-diabetic small molecules targeting the Wnt signaling pathway.

New insights into glycogen synthase kinase-3: A common target for neurodegenerative diseases

Glycogen synthase kinase 3 (GSK-3) is a highly conserved protein serine/threonine kinase that plays a central role in a wide variety of cellular processes to coordinate catabolic and anabolic pathways and regulate cell growth and fate. There is increasing evidence showing that abnormal glycogen synthase kinase 3 (GSK-3) is associated with the pathogenesis and progression of many disorders, such as cancer, diabetes, psychiatric diseases, and neurodegenerative diseases. In this review, we summarize recent findings about the regulatory role of GSK-3 in the occurrence and development of multiple neurodegenerative diseases, mainly focusing on Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The aim of this study is to provide new insight into the shared working mechanism of GSK-3 as a therapeutic target of multiple neurodegenerative diseases.

Designing Functionally Substituted Pyridine-Carbohydrazides for Potent Antibacterial and Devouring Antifungal Effect on Multidrug Resistant (MDR) Strains

The emergence of multidrug-resistant (MDR) pathogens and the gradual depletion of available antibiotics have exacerbated the need for novel antimicrobial agents with minimal toxicity. Herein, we report functionally substituted pyridine carbohydrazide with remarkable antimicrobial effect on multi-drug resistant strains. In the series, compound 6 had potent activity against four MDR strains of Candida spp., with minimum inhibitory concentration (MIC) values being in the range of 16-24 µg/mL and percentage inhibition up to 92.57%, which was exceptional when compared to broad-spectrum antifungal drug fluconazole (MIC = 20 µg/mL, 81.88% inhibition). Substitution of the octyl chain in 6 with a shorter butyl chain resulted in a significant anti-bacterial effect of 4 against Pseudomonas aeruginosa (ATCC 27853), the MIC value being 2-fold superior to the standard combination of ampicillin/cloxacillin. Time-kill kinetics assays were used to discern the efficacy and pharmacodynamics of the potent compounds. Further, hemolysis tests confirmed that both compounds had better safety profiles than the standard drugs. Besides, molecular docking simulations were used to further explore their mode of interaction with target proteins. Overall results suggest that these compounds have the potential to become promising antimicrobial drugs against MDR strains.

Recent Applications of the Multicomponent Synthesis for Bioactive Pyrazole Derivatives

Pyrazole and its derivatives are considered a privileged N-heterocycle with immense therapeutic potential. Over the last few decades, the pot, atom, and step economy (PASE) synthesis of pyrazole derivatives by multicomponent reactions (MCRs) has gained increasing popularity in pharmaceutical and medicinal chemistry. The present review summarizes the recent developments of multicomponent reactions for the synthesis of biologically active molecules containing the pyrazole moiety. Particularly, it covers the articles published from 2015 to date related to antibacterial, anticancer, antifungal, antioxidant, α-glucosidase and α-amylase inhibitory, anti-inflammatory, antimycobacterial, antimalarial, and miscellaneous activities of pyrazole derivatives obtained exclusively via an MCR. The reported analytical and activity data, plausible synthetic mechanisms, and molecular docking simulations are organized in concise tables, schemes, and figures to facilitate comparison and underscore the key points of this review. We hope that this review will be helpful in the quest for developing more biologically active molecules and marketed drugs containing the pyrazole moiety.

Glycogen Synthase Kinase-3 Inhibitors: Preclinical and Clinical Focus on CNS-A Decade Onward

The protein kinase, GSK-3, participates in diverse biological processes and is now recognized a promising drug discovery target in treating multiple pathological conditions. Over the last decade, a range of newly developed GSK-3 inhibitors of diverse chemotypes and inhibition modes has been developed. Even more conspicuous is the dramatic increase in the indications that were tested from mood and behavior disorders, autism and cognitive disabilities, to neurodegeneration, brain injury and pain. Indeed, clinical and pre-clinical studies were largely expanded uncovering new mechanisms and novel insights into the contribution of GSK-3 to neurodegeneration and central nerve system (CNS)-related disorders. In this review we summarize new developments in the field and describe the use of GSK-3 inhibitors in the variety of CNS disorders. This remarkable volume of information being generated undoubtedly reflects the great interest, as well as the intense hope, in developing potent and safe GSK-3 inhibitors in clinical practice.

Non-redundant activity of GSK-3α and GSK-3β in T cell-mediated tumor rejection

Glycogen synthase kinase-3 (GSK-3) is a positive regulator of PD-1 expression in CD8+ T cells and GSK-3 inhibition enhances T cell function and is effective in the control of tumor growth. GSK-3 has two co-expressed isoforms, GSK-3α and GSK-3β. Using conditional gene targeting, we demonstrate that both isoforms contribute to T cell function to different degrees. Gsk3b-/- mice suppressed tumor growth to the same degree as Gsk3a/b-/- mice, whereas Gsk3a-/- mice behaved similarly to wild-type, revealing an important role for GSK-3β in regulating T cell-mediated anti-tumor immunity. The individual GSK-3α and β isoforms have differential effects on PD-1, IFNγ, and granzyme B expression and operate in synergy to control PD-1 expression and the infiltration of tumors with CD4 and CD8 T cells. Our data reveal a complex interplay of the GSK-3 isoforms in the control of tumor immunity and highlight non-redundant activity of GSK-3 isoforms in T cells, with implications for immunotherapy.

Mechanisms and Therapeutic Implications of GSK-3 in Treating Neurodegeneration

Neurodegenerative disorders are spreading worldwide and are one of the greatest threats to public health. There is currently no adequate therapy for these disorders, and therefore there is an urgent need to accelerate the discovery and development of effective treatments. Although neurodegenerative disorders are broad ranging and highly complex, they may share overlapping mechanisms, and thus potentially manifest common targets for therapeutic interventions. Glycogen synthase kinase-3 (GSK-3) is now acknowledged to be a central player in regulating mood behavior, cognitive functions, and neuron viability. Indeed, many targets controlled by GSK-3 are critically involved in progressing neuron deterioration and disease pathogenesis. In this review, we focus on three pathways that represent prominent mechanisms linking GSK-3 with neurodegenerative disorders: cytoskeleton organization, the mammalian target of rapamycin (mTOR)/autophagy axis, and mitochondria. We also consider the challenges and opportunities in the development of GSK-3 inhibitors for treating neurodegeneration.

Design and synthesis of 3-(4-pyridyl)-5-(4-sulfamido-phenyl)-1,2,4-oxadiazole derivatives as novel GSK-3β inhibitors and evaluation of their potential as multifunctional anti-Alzheimer agents

Pleiotropic intervention has prominent advantages for complex pathomechanisms, such as Alzheimer's disease (AD). In this study, a series of novel 3-(4-pyridyl)-5-(4- sulfamido-phenyl)-1,2,4-oxadiazole derivatives were designed and synthesized following the multitarget-directed ligand-based strategy. All compounds were evaluated for glycogen synthase kinase 3β (GSK-3β) inhibition and antineuroinflammatory and neuroprotective activities. Given that abnormal glucose metabolism plays an important role in AD occurrence and development, the effects of all compounds on glucose consumption in HepG2 cells was evaluated. Compounds 5e and 10b showed good dual potency in GSK-3β inhibition (IC50: 5e = 1.52 μM, 10b = 0.19 μM) and antineuroinflammatory potency (IC50: 5e = 0.47 ± 0.64 μM, 10b = 6.94 ± 2.33 μM). The effect of compound 10b on glucose consumption was higher than that of positive drug metformin. These compounds exerted a certain neuroprotective effect. Compound 10b dramatically reduced Aβ-induced Tau hyperphosphorylation, thus inhibiting GSK-3β at the cellular level. Notably, compounds 5e and 10b exhibited good inhibitory effects on the formation of intracellular reactive oxygen species (ROS). Moreover, these compounds displayed proper blood-brain barrier permeability and lacked neurotoxicity up to 50 μM concentration. Finally, in vivo experiments revealed that compound 10b improved cognitive impairment in scopolamine-induced mouse models. Results indicated that compound 10b deserves further study as a multifunctional lead compound.

GSK3α: An Important Paralog in Neurodegenerative Disorders and Cancer

The biological activity of the enzyme glycogen synthase kinase-3 (GSK3) is fulfilled by two paralogs named GSK3α and GSK3β, which possess both redundancy and specific functions. The upregulated activity of these proteins is linked to the development of disorders such as neurodegenerative disorders (ND) and cancer. Although various chemical inhibitors of these enzymes restore the brain functions in models of ND such as Alzheimer’s disease (AD), and reduce the proliferation and survival of cancer cells, the particular contribution of each paralog to these effects remains unclear as these molecules downregulate the activity of both paralogs with a similar efficacy. Moreover, given that GSK3 paralogs phosphorylate more than 100 substrates, the simultaneous inhibition of both enzymes has detrimental effects during long-term inhibition. Although the GSK3β kinase function has usually been taken as the global GSK3 activity, in the last few years, a growing interest in the study of GSK3α has emerged because several studies have recognized it as the main GSK3 paralog involved in a variety of diseases. This review summarizes the current biological evidence on the role of GSK3α in AD and various types of cancer. We also provide a discussion on some strategies that may lead to the design of the paralog-specific inhibition of GSK3α.

Identification of a new series of flavopiridol-like structures as kinase inhibitors with high cytotoxic potency

In this work, unique flavopiridol analogs bearing thiosugars, amino acids and heterocyclic moieties tethered to the flavopiridol via thioether and amine bonds mainly on its C ring have been prepared. The analogs bearing thioether-benzimidazoles as substituents have demonstrated high cytotoxic activity in vitro against up to seven cancer cell lines. Their cytotoxic effects are comparable to those of flavopiridol. The most active compound 13c resulting from a structure-activity relationship (SAR) study and in silico docking showed the best antiproliferative activity and was more efficient than the reference compound. In addition, compound 13c showed significant nanomolar inhibition against CDK9, CDK10, and GSK3β protein kinases.

Exploiting an Asp-Glu "switch" in glycogen synthase kinase 3 to design paralog-selective inhibitors for use in acute myeloid leukemia

Glycogen synthase kinase 3 (GSK3), a key regulatory kinase in the wingless-type MMTV integration site family (WNT) pathway, is a therapeutic target of interest in many diseases. Although dual GSK3α/β inhibitors have entered clinical trials, none has successfully translated to clinical application. Mechanism-based toxicities, driven in part by the inhibition of both GSK3 paralogs and subsequent β-catenin stabilization, are a concern in the translation of this target class because mutations and overexpression of β-catenin are associated with many cancers. Knockdown of GSK3α or GSK3β individually does not increase β-catenin and offers a conceptual resolution to targeting GSK3: paralog-selective inhibition. However, inadequate chemical tools exist. The design of selective adenosine triphosphate (ATP)-competitive inhibitors poses a drug discovery challenge due to the high homology (95% identity and 100% similarity) in this binding domain. Taking advantage of an Asp¹³³→Glu¹⁹⁶ "switch" in their kinase hinge, we present a rational design strategy toward the discovery of paralog-selective GSK3 inhibitors. These GSK3α- and GSK3β-selective inhibitors provide insights into GSK3 targeting in acute myeloid leukemia (AML), where GSK3α was identified as a therapeutic target using genetic approaches. The GSK3α-selective compound BRD0705 inhibits kinase function and does not stabilize β-catenin, mitigating potential neoplastic concerns. BRD0705 induces myeloid differentiation and impairs colony formation in AML cells, with no apparent effect on normal hematopoietic cells. Moreover, BRD0705 impairs leukemia initiation and prolongs survival in AML mouse models. These studies demonstrate feasibility of paralog-selective GSK3α inhibition, offering a promising therapeutic approach in AML.

Discovery of novel glycogen synthase kinase-3α inhibitors: Structure-based virtual screening, preliminary SAR and biological evaluation for treatment of acute myeloid leukemia

Glycogen synthase kinase 3α (GSK-3α) plays a constitutive role in various physiological processes and has been proved to be a therapeutic target for acute myeloid leukemia (AML). In this paper, by means of computer-aided drug design, we discovered a novel chemical series of GSK-3α inhibitors with an IC₅₀ value of 0.033-2.804 μM. The preliminary structure-activity relationship was concluded and, notably, the most potent and isoform-selective compound G28_14 was identified with IC₅₀ values of 33 nM and 218 nM against GSK-3α and -3β, respectively, exhibiting a nearly ten-fold isoform-selectivity. Further cell viability assays and colony formation assays revealed that G28_14 suppressed cell survival by impairing cell proliferation by up to 90% in two AML cell lines. Moreover, surface marker expression analysis demonstrated that G28_14 induced terminal differentiation with a high level of CD11b, CD11c, and CD14. Western immunoblotting showed that G28_14 isoform-selectively inhibited the phosphorylation of GSK-3α in-cell without activating Wnt/β-catenin signaling. In addition, to elucidate its structure-activity relationship, the binding mode of this chemical series was proposed using molecular docking and molecular dynamics simulations. Taken together, this chemical series is worth developing as differentiation therapies for the treatment of AML.

Off-target based drug repurposing opportunities for tivantinib in acute myeloid leukemia

GSK3α has been identified as a new target in the treatment of acute myeloid leukemia (AML). However, most GSK3 inhibitors lack specificity for GSK3α over GSK3β and other kinases. We have previously shown in lung cancer cells that GSK3α and to a lesser extent GSK3β are inhibited by the advanced clinical candidate tivantinib (ARQ197), which was designed as a MET inhibitor. Thus, we hypothesized that tivantinib would be an effective therapy for the treatment of AML. Here, we show that tivantinib has potent anticancer activity across several AML cell lines and primary patient cells. Tivantinib strongly induced apoptosis, differentiation and G2/M cell cycle arrest and caused less undesirable stabilization of β-catenin compared to the pan-GSK3 inhibitor LiCl. Subsequent drug combination studies identified the BCL-2 inhibitor ABT-199 to synergize with tivantinib while cytarabine combination with tivantinib was antagonistic. Interestingly, the addition of ABT-199 to tivantinib completely abrogated tivantinib induced β-catenin stabilization. Tivantinib alone, or in combination with ABT-199, downregulated anti-apoptotic MCL-1 and BCL-XL levels, which likely contribute to the observed synergy. Importantly, tivantinib as single agent or in combination with ABT-199 significantly inhibited the colony forming capacity of primary patient AML bone marrow mononuclear cells. In summary, tivantinib is a novel GSK3α/β inhibitor that potently kills AML cells and tivantinib single agent or combination therapy with ABT-199 may represent attractive new therapeutic opportunities for AML.

Synthesis of benzimidazole-linked-1,3,4-oxadiazole carboxamides as GSK-3β inhibitors with in vivo antidepressant activity

Recent findings of potential implications of glycogen synthase kinase-3β (GSK-3β) dysfunction in psychiatric disorders like depression, have increased focus for development of GSK-3β inhibitors with possible anti-depressant activity. Keeping this in view, we synthesized a series of benzimidazole-linked-1,3,4-oxadiazole carboxamides and evaluated them for in vitro GSK-3β inhibition. Active compounds were investigated for in vivo antidepressant activity in Wistar rats. Docking studies of active compounds have also been performed. Among nineteen compounds synthesized, compounds 7a, 7r, 7j, and 7d exhibited significant potency against GSK-3β in sub-micromolar range with IC₅₀ values of 0.13 μM, 0.14 μM, 0.20 μM, 0.22 μM respectively and significantly reduced immobility time (antidepressant-like activity) in rats compared to control group. Docking study showed key interactions of these compounds with GSK-3β. These compounds may thus serve as valuable candidates for subsequent development of effective drugs against depression and related disorders.

Multifaceted Roles of GSK-3 in Cancer and Autophagy-Related Diseases

GSK-3 is a ubiquitously expressed serine/threonine kinase existing as GSK-3α and GSK-3β isoforms, both active under basal conditions and inactivated upon phosphorylation by different upstream kinases. Initially discovered as a regulator of glycogen synthesis, GSK-3 is also involved in several signaling pathways controlling many different key functions. Here, we discuss recent advances regarding (i) GSK-3 structure, function, regulation, and involvement in several cancers, including hepatocarcinoma, cholangiocarcinoma, breast cancer, prostate cancer, leukemia, and melanoma (active GSK-3 has been shown to induce apoptosis in some cases or inhibit apoptosis in other cases and to induce cancer progression or inhibit tumor cell proliferation, suggesting that different GSK-3 modulators may address different specific targets); (ii) GSK-3 involvement in autophagy modulation, reviewing signaling pathways involved in neurodegenerative and liver diseases; (iii) GSK-3 role in oxidative stress and autophagic cell death, focusing on liver injury; (iv) GSK-3 as a possible therapeutic target of natural substances and synthetic inhibitors in many diseases; and (v) GSK-3 role as modulator of mammalian aging, related to metabolic alterations characterizing senescent cells and age-related diseases. Studies summarized here underline the GSK-3 multifaceted role and indicate such kinase as a molecular target in different pathologies, including diseases associated with autophagy dysregulation.

Glycogen synthase kinase-3 and its inhibitors: Potential target for various therapeutic conditions

Glycogen Synthase Kinase-3 (GSK-3) is a serine/threonine kinase which is ubiquitously expressed and is regarded as a regulator for various cellular events and signalling pathways. It exists in two isoforms, GSK-3α and GSK-3β and can phosphorylate a wide range of substrates. Aberrancy in the GSK-3 activity can lead to various diseases like Alzheimer's, diabetes, cancer, neurodegeneration etc., rendering it an attractive target to develop potent and specific inhibitors. The present review focuses on the recent developments in the area of GSK-3 inhibitors and also enlightens its therapeutic applicability in various disease conditions.

Effects of mutations in Wnt/β-catenin, hedgehog, Notch and PI3K pathways on GSK-3 activity-Diverse effects on cell growth, metabolism and cancer

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that participates in an array of critical cellular processes. GSK-3 was first characterized as an enzyme that phosphorylated and inactivated glycogen synthase. However, subsequent studies have revealed that this moon-lighting protein is involved in numerous signaling pathways that regulate not only metabolism but also have roles in: apoptosis, cell cycle progression, cell renewal, differentiation, embryogenesis, migration, regulation of gene transcription, stem cell biology and survival. In this review, we will discuss the roles that GSK-3 plays in various diseases as well as how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTOR, Ras/Raf/MEK/ERK, Wnt/beta-catenin, hedgehog, Notch and TP53. Mutations that occur in these and other pathways can alter the effects that natural GSK-3 activity has on regulating these signaling circuits that can lead to cancer as well as other diseases. The novel roles that microRNAs play in regulation of the effects of GSK-3 will also be evaluated. Targeting GSK-3 and these other pathways may improve therapy and overcome therapeutic resistance.

Inhibitors of Glycogen Synthase Kinase 3 with Exquisite Kinome-Wide Selectivity and Their Functional Effects

The mood stabilizer lithium, the first-line treatment for bipolar disorder, is hypothesized to exert its effects through direct inhibition of glycogen synthase kinase 3 (GSK3) and indirectly by increasing GSK3's inhibitory serine phosphorylation. GSK3 comprises two highly similar paralogs, GSK3α and GSK3β, which are key regulatory kinases in the canonical Wnt pathway. GSK3 stands as a nodal target within this pathway and is an attractive therapeutic target for multiple indications. Despite being an active field of research for the past 20 years, many GSK3 inhibitors demonstrate either poor to moderate selectivity versus the broader human kinome or physicochemical properties unsuitable for use in in vitro systems or in vivo models. A nonconventional analysis of data from a GSK3β inhibitor high-throughput screening campaign, which excluded known GSK3 inhibitor chemotypes, led to the discovery of a novel pyrazolo-tetrahydroquinolinone scaffold with unparalleled kinome-wide selectivity for the GSK3 kinases. Taking advantage of an uncommon tridentate interaction with the hinge region of GSK3, we developed highly selective and potent GSK3 inhibitors, BRD1652 and BRD0209, which demonstrated in vivo efficacy in a dopaminergic signaling paradigm modeling mood-related disorders. These new chemical probes open the way for exclusive analyses of the function of GSK3 kinases in multiple signaling pathways involved in many prevalent disorders.

Design, synthesis and biological evaluation of 5-benzylidene-2-iminothiazolidin-4-ones as selective GSK-3β inhibitors

In this work, iminothiazolidin-4-one derivatives were explored as selective GSK-3β inhibitors. Molecular docking analysis was carried to design a series of compounds, which were synthesized using substituted thiourea, 2-bromoacetophenones and benzaldehydes. Out of the twenty five compounds synthesized during this work, the in vitro evaluation against GSK-3 led to the identification of nine compounds with activity in lower nano-molar range (2-85 nM). Further, in vitro evaluation against CDK-2 showed five compounds to be selective towards GSK-3.

Synthesis of benzimidazole-based 1,3,4-oxadiazole-1,2,3-triazole conjugates as glycogen synthase kinase-3β inhibitors with antidepressant activity in in vivo models

Synthesized benzimidazole based 1,3,4-oxadiazole-1,2,3-triazole conjugates were found to inhibit GSK-3β activityin vitroand exhibit antidepressant-like activity inin vivostudies.

Molecular dynamics simulation studies of GSK-3β ATP competitive inhibitors: understanding the factors contributing to selectivity

Glycogen synthase kinase-3 is a constitutively acting, multifunctional serine threonine kinase, the role of which has been implicated in several physiological pathways and has emerged as a promising target for the treatment of type-II diabetes and Alzheimer's disease. In order to provide a detailed understanding of the origin of selectivity determinants of ATP competitive inhibitors, molecular dynamics simulations in combination with MM-PBSA binding energy calculations were performed using crystal structures of GSK-3β and CDK-2 in complex with 12 ATP competitive inhibitors. Analysis of energy contributions indicate that electrostatic interaction energy dictates the selectivity of ATP competitive inhibitors against CDK-2. Key interactions as well as residues that potentially make a major contribution to the binding free energy were identified at the ATP binding site. This analysis stresses the need for the inhibitors to interact with Lys85, Thr138, and Arg141 in the binding site of GSK-3β to show selectivity. The residue-wise energy decomposition analysis further suggested the additional role of Gln185 in determining the selectivity of maleimides. The results obtained in this study can be utilized to design new selective GSK-3 ATP competitive inhibitors.

Evaluation of Improved Glycogen Synthase Kinase-3α Inhibitors in Models of Acute Myeloid Leukemia

The challenge for glycogen synthase kinase-3 (GSK-3) inhibitor design lies in achieving high selectivity for one isoform over the other. The therapy of certain diseases, such as acute myeloid leukemia (AML), may require α-isoform specific targeting. The scorpion shaped GSK-3 inhibitors developed by our group achieved the highest GSK-3α selectivity reported so far but suffered from insufficient aqueous solubility. This work presents the solubility-driven optimization of our isoform-selective inhibitors using a scorpion shaped lead. Among 15 novel compounds, compound 27 showed high activity against GSK-3α/β with the highest GSK-3α selectivity reported to date. Compound 27 was profiled for bioavailability and toxicity in a zebrafish embryo phenotype assay. Selective GSK-3α targeting in AML cell lines was achieved with compound 27, resulting in a strong differentiation phenotype and colony formation impairment, confirming the potential of GSK-3α inhibition in AML therapy.

Pivotal role of glycogen synthase kinase-3: A therapeutic target for Alzheimer's disease

Neurodegenerative diseases are among the most challenging diseases with poorly known mechanism of cause and paucity of complete cure. Out of all the neurodegenerative diseases, Alzheimer's disease is the most devastating and loosening of thinking and judging ability disease that occurs in the old age people. Many hypotheses came forth in order to explain its causes. In this review, we have enlightened Glycogen Synthase Kinase-3 which has been considered as a concrete cause for Alzheimer's disease. Plaques and Tangles (abnormal structures) are the basic suspects in damaging and killing of nerve cells wherein Glycogen Synthase Kinase-3 has a key role in the formation of these fatal accumulations. Various Glycogen Synthase Kinase-3 inhibitors have been reported to reduce the amount of amyloid-beta as well as the tau hyperphosphorylation in both neuronal and nonneuronal cells. Additionally, Glycogen Synthase Kinase-3 inhibitors have been reported to enhance the adult hippocampal neurogenesis in vivo as well as in vitro. Keeping the chemotype of the reported Glycogen Synthase Kinase-3 inhibitors in consideration, they may be grouped into natural inhibitors, inorganic metal ions, organo-synthetic, and peptide like inhibitors. On the basis of their mode of binding to the constituent enzyme, they may also be grouped as ATP, nonATP, and allosteric binding sites competitive inhibitors. ATP competitive inhibitors were known earlier inhibitors but they lack efficient selectivity. This led to find the new ways for the enzyme inhibition.

Structural Plasticity of Dendritic Spines Requires GSK3α and GSK3β

Although memories appear to be elusive phenomena, they are stored in the network of physical connections between neurons. Dendritic spines, which are actin-rich dendritic protrusions, serve as the contact points between networked neurons. The spines’ shape contributes to the strength of signal transmission. To acquire and store information, dendritic spines must remain plastic, i.e., able to respond to signals, by changing their shape. We asked whether glycogen synthase kinase (GSK) 3α and GSK3β, which are implicated in diseases with neuropsychiatric symptoms, such as Alzheimer's disease, bipolar disease and schizophrenia, play a role in a spine structural plasticity. We used Latrunculin B, an actin polymerization inhibitor, and chemically induced Long-Term Depression to trigger fast spine shape remodeling in cultured hippocampal neurons. Spine shrinkage induced by either stimulus required GSK3α activity. GSK3β activity was only important for spine structural changes after treatment with Latrunculin B. Our results indicate that GSK3α is an essential component for short-term spine structural plasticity. This specific function should be considered in future studies of neurodegenerative diseases and neuropsychiatric conditions that originate from suboptimal levels of GSK3α/β activity.

A screen for transcription factor targets of glycogen synthase kinase-3 highlights an inverse correlation of NFκB and androgen receptor signaling in prostate cancer

Expression of Glycogen Synthase Kinase-3 (GSK-3) is elevated in prostate cancer and its inhibition reduces prostate cancer cell proliferation, in part by reducing androgen receptor (AR) signaling. However, GSK-3 inhibition can also activate signals that promote cell proliferation and survival, which may preclude the use of GSK-3 inhibitors in the clinic. To identify such signals in prostate cancer, we screened for changes in transcription factor target DNA binding activity in GSK-3-silenced cells. Among the alterations was a reduction in AR DNA target binding, as predicted from previous studies, and an increase in NFκB DNA target binding. Consistent with the latter, gene silencing of GSK-3 or inhibition using the GSK-3 inhibitor CHIR99021 increased basal NFκB transcriptional activity. Activation of NFκB was accompanied by an increase in the level of the NFκB family member RelB. Conversely, silencing RelB reduced activation of NFκB by CHIR99021. Furthermore, the reduction of prostate cancer cell proliferation by CHIR99021 was potentiated by inhibition of NFκB signaling using the IKK inhibitor PS1145. Finally, stratification of human prostate tumor gene expression data for GSK3 revealed an inverse correlation between NFκB-dependent and androgen-dependent gene expression, consistent with the results from the transcription factor target DNA binding screen. In addition, there was a correlation between expression of androgen-repressed NFκB target genes and reduced survival of patients with metastatic prostate cancer. These findings highlight an association between GSK-3/AR and NFκB signaling and its potential clinical importance in metastatic prostate cancer.

Glycogen synthase kinase-3 (GSK3): regulation, actions, and diseases

Glycogen synthase kinase-3 (GSK3) may be the busiest kinase in most cells, with over 100 known substrates to deal with. How does GSK3 maintain control to selectively phosphorylate each substrate, and why was it evolutionarily favorable for GSK3 to assume such a large responsibility? GSK3 must be particularly adaptable for incorporating new substrates into its repertoire, and we discuss the distinct properties of GSK3 that may contribute to its capacity to fulfill its roles in multiple signaling pathways. The mechanisms regulating GSK3 (predominantly post-translational modifications, substrate priming, cellular trafficking, protein complexes) have been reviewed previously, so here we focus on newly identified complexities in these mechanisms, how each of these regulatory mechanism contributes to the ability of GSK3 to select which substrates to phosphorylate, and how these mechanisms may have contributed to its adaptability as new substrates evolved. The current understanding of the mechanisms regulating GSK3 is reviewed, as are emerging topics in the actions of GSK3, particularly its interactions with receptors and receptor-coupled signal transduction events, and differential actions and regulation of the two GSK3 isoforms, GSK3α and GSK3β. Another remarkable characteristic of GSK3 is its involvement in many prevalent disorders, including psychiatric and neurological diseases, inflammatory diseases, cancer, and others. We address the feasibility of targeting GSK3 therapeutically, and provide an update of its involvement in the etiology and treatment of several disorders.

Indolinone based LRRK2 kinase inhibitors with a key hydrogen bond

The most prevalent leucine-rich repeat kinase 2 (LRRK2) mutation G2019S is associated with Parkinson's disease (PD). It enhances kinase activity and has been identified in both familial and sporadic cases. Kinase activity was reported to be required for LRRK2 mutants to exert their toxic effects. Hence LRRK2 kinase inhibition may be a promising therapeutic target for PD. Here we report on the discovery and characterization of indolinone based LRRK2 inhibitors. Indolinone 15b, the most potent and selective inhibitor of the present series, is characterized by an IC50 of 15nM against wild-type LRRK2 and 10nM against the LRRK2 G2019S mutant, respectively. Compound 15b was further evaluated in a kinase panel including 46 human protein kinases and in a zebrafish embryo phenotype assay, which enabled toxicity determination in whole organisms.

GSK3 alpha and beta are new functionally relevant targets of tivantinib in lung cancer cells

Tivantinib has been described as a potent and highly selective inhibitor of the receptor tyrosine kinase c-MET and is currently in advanced clinical development for several cancers including non-small cell lung cancer (NSCLC). However, recent studies suggest that tivantinib's anticancer properties are unrelated to c-MET inhibition. Consistently, in determining tivantinib's activity profile in a broad panel of NSCLC cell lines, we found that, in contrast to several more potent c-MET inhibitors, tivantinib reduces cell viability across most of these cell lines. Applying an unbiased, mass-spectrometry-based, chemical proteomics approach, we identified glycogen synthase kinase 3 (GSK3) alpha and beta as novel tivantinib targets. Subsequent validation showed that tivantinib displayed higher potency for GSK3α than for GSK3β and that pharmacological inhibition or simultaneous siRNA-mediated loss of GSK3α and GSK3β caused apoptosis. In summary, GSK3α and GSK3β are new kinase targets of tivantinib that play an important role in its cellular mechanism-of-action in NSCLC.

Design, synthesis, and biological evaluation of 1-phenylpyrazolo[3,4-e]pyrrolo[3,4-g]indolizine-4,6(1H,5H)-diones as new glycogen synthase kinase-3β inhibitors

Compound 5 was selected from our in-house library as a suitable starting point for the rational design of new GSK-3β inhibitors. MC/FEP calculations of 5 led to the identification of a structural class of new GSK-3β inhibitors. Compound 18 inhibited GSK-3β with an IC50 of 0.24 μM and inhibited tau phosphorylation in a cell-based assay. It proved to be a selective inhibitor of GSK-3 against a panel of 17 kinases and showed >10-fold selectivity against CDK2. Calculated physicochemical properties and Volsurf predictions suggested that compound 18 has the potential to diffuse passively across the blood-brain barrier.

Docking and quantitative structure-activity relationship of oxadiazole derivates as inhibitors of GSK3β

The binding modes of 42 oxadiazole derivates inside glycogen synthase kinase 3 beta (GSK3β were determined using docking experiments; thus, the preferred active conformations of these inhibitors are proposed. We found that these compounds adopt a scorpion-shaped conformation and they accept a hydrogen bond (HB) from the residue Val135 of the GSK3β ATP-binding site hinge region. In addition, quantitative structure-activity relationship (QSAR) models were constructed to explain the trend of the GSK3β inhibitory activities for the studied compounds. In a first approach, three-dimensional (3D) vectors were calculated using docking conformations and, by using multiple-linear regression, we assessed that GETAWAY vectors were able to describe the reported biological activities. In other QSAR approach, SMILES-based optimal descriptors were calculated. The best model included three-SMILES elements SSSβ leading to the identification of key molecular features that contribute to a high GSK3β inhibitory activity.

Ligand based approach to L-type calcium channel by imidazo[2,1-b]thiazole-1,4-dihydropyridines: from heart activity to brain affinity

The synthesis, characterization, and functional in vitro assay in cardiac and smooth muscle (vascular and nonvascular) of a series of 4-imidazo[2,1-b]thiazole-1,4-dihydropyridines are reported. To define the calcium blocker nature of the imidazo[2,1-b]thiazole-1,4-DHPs and their selectivity on Cav1.2 and Cav1.3 isoforms, we performed binding studies on guinea pig atrial and ventricular membranes on intact cells expressing the cloned Cav1.2a subunit and on rat brain cortex. To get major insights into the reasons for the affinity for Cav1.2 and/or Cav1.3, molecular modeling studies were also undertaken. Some physicochemical and pharmacokinetic properties of selected compounds were calculated and compared. All the biological data collected and reported herein allowed us to rationalize the structure-activity relationship of the 4-imidazo[2,1-b]thiazole-1,4-DHPs and to identify which of these enhanced the activity at the central level.

Design, synthesis and biological evaluation of trimethine cyanine dyes as fluorescent probes for the detection of tau fibrils in Alzheimer's disease brain and olfactory epithelium

Shedding light on grey matter: Fluorescent trimethine cyanines were evaluated as imaging probes for neurofibrillary tangles in post-mortem brain sections of Alzheimer's disease patients. These probes bind to neurofibrillary tangles with high contrast and selectivity over amyloid β plaques.

Structure-based optimization of oxadiazole-based GSK-3 inhibitors

Inhibition of glycogen synthase kinase-3 (GSK-3) induces neuroprotective effects, e.g. decreases β-amyloid production and reduces tau hyperphosphorylation, which are both associated with Alzheimer's disease (AD). The two isoforms of GSK-3 in mammalians are GSK-3α and β, which share 98% homology in their catalytic domains. We investigated GSK-3 inhibitors based on 2 different scaffolds in order to elucidate the demands of the ATP-binding pocket [1]. Particularly, the oxadiazole scaffold provided potent and selective GSK-3 inhibitors. For example, the most potent inhibitor of the present series, the acetamide 26d, is characterized by an IC50 of 2 nM for GSK-3α and 17 nM for GSK-3β. In addition, the benzodioxane 8g showed up to 27-fold selectivity for GSK-3α over GSK-3β, with an IC50 of 35 nM for GSK-3α. Two GSK-3 inhibitors were further profiled for efficacy and toxicity in the wild-type (wt) zebrafish embryo assay to evaluate simultaneously permeability and safety.