PROTAC-Induced Glycogen Synthase Kinase 3β Degradation as a Potential Therapeutic Strategy for Alzheimer's Disease

Glycogen synthase kinase 3β (GSK-3β) is a serine/threonine kinase and an attractive therapeutic target for Alzheimer's disease. Based on proteolysis-targeting chimera (PROTAC) technology, a small set of novel GSK-3β degraders was designed and synthesized by linking two different GSK-3β inhibitors, SB-216763 and tideglusib, to pomalidomide, as E3 recruiting element, through linkers of different lengths. Compound 1 emerged as the most effective PROTAC being nontoxic up to 20 μM to neuronal cells and already able to degrade GSK-3β starting from 0.5 μM in a dose-dependent manner. PROTAC 1 significantly reduced the neurotoxicity induced by Aβ_25-35 peptide and CuSO₄ in SH-SY5Y cells in a dose-dependent manner. Based on its encouraging features, PROTAC 1 may serve as a starting point to develop new GSK-3β degraders as potential therapeutic agents.

Integrated analytical approaches for the characterization of Spirulina and Chlorella microalgae

Microalgae are well-known for their content of bioactive molecules such as pigments, proteins, fatty acids, polysaccharides, vitamins and antioxidants, all of which are of great interest in the preparation of a wide range of products such as food, cosmetics and nutraceuticals. The purpose of this project was the analytical characterization of commercial dry microalgal biomass: four samples of Chlorella and five of Spirulina were analysed in order to highlight their content in terms of micro/macro nutrients. The research was oriented towards the development and validation of accurate, fast and reproducible methods for the nutritional assessment of algal biomasses, aiming to provide a guiding methodology. The lipid profiles of algal matrixes were analysed for the content of saturated, unsaturated and polyunsaturated fatty acids. The process was divided into two phases: firstly, the extraction and determination of the total lipids and pigment content; secondly, the trans-esterification of the extracted lipid-pigment portion in order to analyse fatty acid methyl esters (FAMEs) with a GC-MS method. A fingerprinting of MUFAs and PUFAs was obtained regarding microalgae species. The determination of total carotenoids and chlorophylls content in the lipid extracts was evaluated through a fast UV-Vis spectrophotometric analysis, which was validated by a new HPLC-DAD analysis. Furthermore, the total antioxidant activity of each lipid extract was determined along with the determination of the microalgae protein content. Then, with the aid of the principal component analysis (PCA) plots, the two microalgae were clustered in terms of their micro/macro nutrients, for differentiating their properties. Spirulina, resulting to have a greater antioxidant activity, supposedly due to a higher content in pigments and higher protein concentration, could be suggested for an appropriate diet for sporting people. Chlorella, instead, showed a more balanced profile of PUFAs and MUFAs and its use could be suggested for cosmetics and vegan diets. This paper puts forward an overall analytical approach, sustained by a multivariate analysis, for emphasising content differences and activity of two different microalgae strains, in order to underline specific claims for each class, addressed to defined final users.

Multi-target neuroprotective effects of herbal medicines for Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease is the most common form of dementia, but its treatment options remain few and ineffective. To find new therapeutic strategies, natural products have gained interest due to their neuroprotective potential, being able to target different pathological hallmarks associated with this disorder. Several plant species are traditionally used due to their empirical neuroprotective effects and it is worth to explore their mechanism of action.

AIM OF THE STUDY

This study intended to explore the neuroprotective potential of seven traditional medicinal plants, namely Scutellaria baicalensis, Ginkgo biloba, Hypericum perforatum, Curcuma longa, Lavandula angustifolia, Trigonella foenum-graecum and Rosmarinus officinalis. The safety assessment with reference to pesticides residues was also aimed.

MATERIALS AND METHODS

Decoctions prepared from these species were chemically characterized by HPLC-DAD and screened for their ability to scavenge four different free radicals (DPPH^•, ABTS^•+, O₂^•‒ and ^•NO) and to inhibit enzymes related to neurodegeneration (cholinesterases and glycogen synthase kinase-3β). Cell viability through MTT assay was also evaluated in two different brain cell lines, namely non-tumorigenic D3 human brain endothelial cells (hCMEC/D3) and NSC-34 motor neurons. Furthermore, and using GC, 21 pesticides residues were screened.

RESULTS

Regarding chemical composition, chromatographic analysis revealed the presence of several flavonoids, phenolic acids, curcuminoids, phenolic diterpenoids, one alkaloid and one naphthodianthrone in the seven decoctions. All extracts were able to scavenge free radicals and were moderate glycogen synthase kinase-3β inhibitors; however, they displayed weak to moderate acetylcholinesterase and butyrylcholinesterase inhibition. G. biloba and L. angustifolia decoctions were the less cytotoxic to hCMEC/D3 and NSC-34 cell lines. No pesticides residues were detected.

CONCLUSIONS

The results extend the knowledge on the potential use of plant extracts to combat multifactorial disorders, giving new insights into therapeutic avenues for Alzheimer's disease.

(±)-: Pentatarget-Directed Ligand combining Cholinesterase, Monoamine Oxidase, and Glycogen Synthase Kinase 3β Inhibition with Calcium Channel Antagonism and Antiaggregating Properties for Alzheimer's Disease

Multitarget-directed ligands (MTDLs) are considered a promising therapeutic strategy to address the multifactorial nature of Alzheimer's disease (AD). Novel MTDLs have been designed as inhibitors of human acetylcholinesterases/butyrylcholinesterases, monoamine oxidase A/B, and glycogen synthase kinase 3β and as calcium channel antagonists via the Biginelli multicomponent reaction. Among these MTDLs, (±)-BIGI-3h was identified as a promising new hit compound showing in vitro balanced activities toward the aforementioned recognized AD targets. Additional in vitro studies demonstrated antioxidant effects and brain penetration, along with the ability to inhibit the aggregation of both τ protein and β-amyloid peptide. The in vivo studies have shown that (±)-BIGI-3h (10 mg/kg intraperitoneally) significantly reduces scopolamine-induced cognitive deficits.

Discovery of a Potent Dual Inhibitor of Acetylcholinesterase and Butyrylcholinesterase with Antioxidant Activity that Alleviates Alzheimer-like Pathology in Old APP/PS1 Mice

The combination of the scaffolds of the cholinesterase inhibitor huprine Y and the antioxidant capsaicin results in compounds with nanomolar potencies toward human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) that retain or improve the antioxidant properties of capsaicin. Crystal structures of their complexes with AChE and BChE revealed the molecular basis for their high potency. Brain penetration was confirmed by biodistribution studies in C57BL6 mice, with one compound (5i) displaying better brain/plasma ratio than donepezil. Chronic treatment of 10 month-old APP/PS1 mice with 5i (2 mg/kg, i.p., 3 times per week, 4 weeks) rescued learning and memory impairments, as measured by three different behavioral tests, delayed the Alzheimer-like pathology progression, as suggested by a significantly reduced Aβ42/Aβ40 ratio in the hippocampus, improved basal synaptic efficacy, and significantly reduced hippocampal oxidative stress and neuroinflammation. Compound 5i emerges as an interesting anti-Alzheimer lead with beneficial effects on cognitive symptoms and on some underlying disease mechanisms.

Glycogen Synthase Kinase 3β: A New Gold Rush in Anti-Alzheimer's Disease Multitarget Drug Discovery?

Alzheimer’s disease (AD), like other multifactorial diseases, is the result of a systemic breakdown of different physiological networks. As result, several lines of evidence suggest that it could be more efficiently tackled by molecules directed toward different dysregulated biochemical targets or pathways. In this context, the selection of targets to which the new molecules will be directed is crucial. For years, the design of such multitarget-directed ligands (MTDLs) has been based on the selection of main targets involved in the “cholinergic” and the “β-amyloid” hypothesis. Recently, there have been some reports on MTDLs targeting the glycogen synthase kinase 3β (GSK-3β) enzyme, due to its appealing properties. Indeed, this enzyme is involved in tau hyperphosphorylation, controls a multitude of CNS-specific signaling pathways, and establishes strict connections with several factors implicated in AD pathogenesis. In the present Miniperspective, we will discuss the reasons behind the development of GSK-3β-directed MTDLs and highlight some of the recent efforts to obtain these new classes of MTDLs as potential disease-modifying agents.

Centrally Active Multitarget Anti-Alzheimer Agents Derived from the Antioxidant Lead CR-6

Oxidative stress is a major pathogenic factor in Alzheimer's disease, but it should not be tackled alone rather together with other key targets to derive effective treatments. The combination of the scaffold of the polar antioxidant lead 7-methoxy-2,2-dimethylchroman-6-ol (CR-6) with that of the lipophilic cholinesterase inhibitor 6-chlorotacrine results in compounds with favorable brain permeability and multiple activities in vitro (acetylcholinesterase, butyrylcholinesterase, β-site amyloid precursor protein (APP) cleaving enzyme-1 (BACE-1), and Aβ42 and tau aggregation inhibition). In in vivo studies on wild-type and APP/presenilin 1 (PS1) mice, two selected compounds were well tolerated and led to positive trends, albeit statistically nonsignificant in some cases, on memory performance, amyloid pathology (reduced amyloid burden and potentiated non-amyloidogenic APP processing), and oxidative stress (reduced cortical oxidized proteins and increased antioxidant enzymes superoxide dismutase 2 (SOD2), catalase, glutathione peroxidase 1 (GPX1), and heme oxygenase 1 (Hmox1) and transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2)). These compounds emerge as interesting brain-permeable multitarget compounds, with a potential as anti-Alzheimer agents beyond that of the original lead CR-6.

Functionalized aromatic esters of the Amaryllidaceae alkaloid haemanthamine and their in vitro and in silico biological activity connected to Alzheimer's disease

A novel series of aromatic esters (1a-1m) related to the Amaryllidaceae alkaloid (AA) haemanthamine were designed, synthesized and tested in vitro with particular emphasis on the treatment of neurodegenerative diseases. Some of the synthesized compounds revealed promising acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory profile. Significant human AChE (hAChE) inhibition was demonstrated by 11-O-(3-nitrobenzoyl)haemanthamine (1j) with IC₅₀value of 4.0 ± 0.3 µM. The strongest human BuChE (hBuChE) inhibition generated 1-O-(2-methoxybenzoyl)haemanthamine (1g) with IC₅₀ value 3.3 ± 0.4 µM. Moreover, 11-O-(2-chlorbenzoyl)haemanthamine (1m) was able to inhibit both enzymes in dose-dependent manner. The mode of hAChE and hBuChE inhibition was minutely inspected using enzyme kinetic analysis in tandem with in silico experiments, the latter elucidating crucial interaction in 1j-, 1m-hAChE and 1g-, 1m-hBuChE complexes. The blood-brain barrier (BBB) permeability was investigated applying the parallel artificial membrane permeation assay (PAMPA) to predict the CNS availability of the compounds.

Pyridinylimidazoles as GSK3β Inhibitors: The Impact of Tautomerism on Compound Activity via Water Networks

Glycogen synthase kinase-3β (GSK3β) is involved in many pathological conditions and represents an attractive drug target. We previously reported dual GSK3β/p38α mitogen-activated protein kinase inhibitors and identified N-(4-(4-(4-fluorophenyl)-2-methyl-1H-imidazol-5-yl)pyridin-2-yl)cyclopropanecarboxamide (1) as a potent dual inhibitor of both target kinases. In this study, we aimed to design selective GSK3β inhibitors based on our pyridinylimidazole scaffold. Our efforts resulted in several novel and potent GSK3β inhibitors with IC₅₀ values in the low nanomolar range. 5-(2-(Cyclopropanecarboxamido)pyridin-4-yl)-4-cyclopropyl-1H-imidazole-2-carboxamide (6g) displayed very good kinase selectivity as well as metabolical stability and inhibited GSK3β activity in neuronal SH-SY5Y cells. Interestingly, we observed the importance of the 2-methylimidazole's tautomeric state for the compound activity. Finally, we reveal how this crucial tautomerism effect is surmounted by imidazole-2-carboxamides, which are able to stabilize the binding via enhanced water network interactions, regardless of their tautomeric state.

Correction to "Discovery of the First-in-Class GSK-3β/HDAC Dual Inhibitor as Disease-Modifying Agent To Combat Alzheimer's Disease"

[This corrects the article DOI: 10.1021/acsmedchemlett.8b00507.].

Amaryllidaceae alkaloids from Narcissus pseudonarcissus L. cv. Dutch Master as potential drugs in treatment of Alzheimer's disease

Twenty-one known Amaryllidaceae alkaloids of various structural types and one undescribed alkaloid, named narcimatuline, have been isolated from fresh bulbs of Narcissus pseudonarcissus L. cv. Dutch Master. The chemical structures were elucidated by combination of MS, HRMS, 1D and 2D NMR spectroscopic techniques, and by comparison with literature data. Narcimatuline amalgamates two basic scaffolds of Amaryllidaceae alkaloids in its core, namely galanthamine and galanthindole. All isolated compounds were evaluated for their in vitro acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), prolyl oligopeptidase (POP), and glycogen synthase kinase-3β (GSK-3β) inhibitory activities. The most interesting biological profile was demonstrated by newly isolated alkaloid narcimatuline.

Investigating in Vitro Amyloid Peptide 1-42 Aggregation: Impact of Higher Molecular Weight Stable Adducts

The self-assembly of amyloid peptides (Aβ), in particular Aβ_1-42, into oligomers and fibrils is one of the main pathological events related to Alzheimer's disease. Recent studies have demonstrated the ability of carbon monoxide-releasing molecules (CORMs) to protect neurons and astrocytes from Aβ_1-42 toxicity. In fact, CORMs are able to carry and release controlled levels of CO and are known to exert a wide range of anti-inflammatory and anti-apoptotic activities at physiologically relevant concentrations. In order to investigate the direct effects of CORMs on Aβ_1-42, we studied the reactivity of CORM-2 and CORM-3 with Aβ_1-42 in vitro and the potential inhibition of its aggregation by mass spectrometry (MS), as well as fluorescence and circular dichroism spectroscopies. The application of an electrospray ionization-MS (ESI-MS) method allowed the detection of stable Aβ_1-42/CORMs adducts, involving the addition of the Ru(CO)₂ portion of CORMs at histidine residues on the Aβ_1-42 skeleton. Moreover, CORMs showed anti-aggregating properties through formation of stable adducts with Aβ_1-42 as demonstrated by a thioflavin T fluorescence assay and MS analysis. As further proof, comparison of the CD spectra of Aβ_1-42 recorded in the absence and in the presence of CORM-3 at a 1:1 molar ratio showed the ability of CORM-3 to stabilize the peptide in its soluble, unordered conformation, thereby preventing its misfolding and aggregation. This multi-methodological investigation revealed novel interactions between Aβ_1-42 and CORMs, contributing new insights into the proposed neuroprotective mechanisms mediated by CORMs and disclosing a new strategy to divert amyloid aggregation and toxicity.

A novel class of multitarget anti-Alzheimer benzohomoadamantane‒chlorotacrine hybrids modulating cholinesterases and glutamate NMDA receptors

The development of multitarget compounds against multifactorial diseases, such as Alzheimer's disease, is an area of very intensive research, due to the expected superior therapeutic efficacy that should arise from the simultaneous modulation of several key targets of the complex pathological network. Here we describe the synthesis and multitarget biological profiling of a new class of compounds designed by molecular hybridization of an NMDA receptor antagonist fluorobenzohomoadamantanamine with the potent acetylcholinesterase (AChE) inhibitor 6-chlorotacrine, using two different linker lengths and linkage positions, to preserve or not the memantine-like polycyclic unsubstituted primary amine. The best hybrids exhibit greater potencies than parent compounds against AChE (IC₅₀ 0.33 nM in the best case, 44-fold increased potency over 6-chlorotacrine), butyrylcholinesterase (IC₅₀ 21 nM in the best case, 24-fold increased potency over 6-chlorotacrine), and NMDA receptors (IC₅₀ 0.89 μM in the best case, 2-fold increased potency over the parent benzohomoadamantanamine and memantine), which suggests an additive effect of both pharmacophoric moieties in the interaction with the primary targets. Moreover, most of these compounds have been predicted to be brain permeable. This set of biological properties makes them promising leads for further anti-Alzheimer drug development.

Histone Deacetylase Inhibitors as Multitarget Ligands: New Players in Alzheimer's Disease Drug Discovery?

Histone deacetylase inhibitors (HDACIs) are responsible for controlling gene expression by modulating the acetylation status of histone proteins. Furthermore, they modulate the activity of cytoplasmic non-histone proteins. Due to the involvement of HDACs in neurodevelopment, memory formation, and cognitive processes, HDACIs have been suggested as innovative agents for the treatment of neurodegenerative disorders such as Alzheimer's disease (AD). Given their mechanisms of action and the complex nature of AD, HDACIs have been proposed for the design of novel multitarget ligands (MTLs). To this aim, the fragment responsible for HDAC inhibition has been coupled with other structures that are able to provide additional biological actions, such as antioxidant activity or the inhibition of phosphodiesterase 5, transglutaminase 2, and glycogen synthase kinase 3β. Herein we discuss recent efforts to design HDACI-based MTLs as potential disease-modifying entities.

Derivatives of the β-Crinane Amaryllidaceae Alkaloid Haemanthamine as Multi-Target Directed Ligands for Alzheimer's Disease

Twelve derivatives 1a–1m of the β-crinane-type alkaloid haemanthamine were developed. All the semisynthetic derivatives were studied for their inhibitory potential against both acetylcholinesterase and butyrylcholinesterase. In addition, glycogen synthase kinase 3β (GSK-3β) inhibition potency was evaluated in the active derivatives. In order to reveal the availability of the drugs to the CNS, we elucidated the potential of selected derivatives to penetrate through the blood-brain barrier (BBB). Two compounds, namely 11-O-(2-methylbenzoyl)-haemanthamine (1j) and 11-O-(4-nitrobenzoyl)-haemanthamine (1m), revealed the most intriguing profile, both being acetylcholinesterase (hAChE) inhibitors on a micromolar scale, with GSK-3β inhibition properties, and predicted permeation through the BBB. In vitro data were further corroborated by detailed inspection of the compounds’ plausible binding modes in the active sites of hAChE and hBuChE, which led us to provide the structural determinants responsible for the activity towards these enzymes.

Discovery of the First-in-Class GSK-3β/HDAC Dual Inhibitor as Disease-Modifying Agent To Combat Alzheimer's Disease

Several evidence pointed out the role of epigenetics in Alzheimer's disease (AD) revealing strictly relationships between epigenetic and "classical" AD targets. Based on the reported connection among histone deacetylases (HDACs) and glycogen synthase kinase 3β (GSK-3β), herein we present the discovery and the biochemical characterization of the first-in-class hit compound able to exert promising anti-AD effects by modulating the targeted proteins in the low micromolar range of concentration. Compound 11 induces an increase in histone acetylation and a reduction of tau phosphorylation. It is nontoxic and protective against H₂O₂ and 6-OHDA stimuli in SH-SY5Y and in CGN cell lines, respectively. Moreover, it promotes neurogenesis and displays immunomodulatory effects. Compound 11 shows no lethality in a wt-zebrafish model (<100 μM) and high water solubility.

A patent review of butyrylcholinesterase inhibitors and reactivators 2010-2017

INTRODUCTION

Butyrylcholinesterase (BuChE) has obtained a renewed interest as therapeutic target in Alzheimer's disease (AD), when changes in BuChE activity and expression along disease progression were highlighted as well as correlation between BuChE levels and cognitive function.

AREAS COVERED

During the last eight years, fourteen patents on BuChE inhibitors (BuChEI) have been submitted. Only three of them relate to BuChE selective inhibitors, while four of them focus on multitarget inhibitors which address different key pathological factors other than BuChE. Two patents report on non-selective acetylcholinesterase (AChE)/BuChE inhibitors, while four patents deal with natural compounds and their derivatives. One patent relates to antitoxic agents to treat exposure to ChEI pesticides and nerve agents.

EXPERT OPINION

Increasing evidence supports BuChE as a more beneficial target in moderate-to-severe forms of AD in comparison to the well-known AChE. However, hitting a single pathological target is likely not sufficient to halt the disease progression. Therefore, patented BuChE inhibitors with a multifunctional profile may open new therapeutic avenues, since the additional activities could reinforce the therapeutic effects. Unfortunately, in vivo studies are limited and key parameters, such as ADMET data, are missing. This lack of information makes difficult to forecast the development of patented BuChEIs into effective drug candidates.

Development and validation of an LC-ESI-MS/MS method for the quantification of D-84, reboxetine and citalopram for their use in MS Binding Assays addressing the monoamine transporters hDAT, hSERT and hNET

MS Binding Assays represent a label-free alternative to radioligand binding assays. In this study, we present an LC-ESI-MS/MS method for the quantification of (R,R)-4-(2-benzhydryloxyethyl)-1-(4-fluorobenzyl)piperidin-3-ol [(R,R)-D-84, (R,R)-1], (S,S)-reboxetine [(S,S)-2], and (S)-citalopram [(S)-3] employed as highly selective nonlabeled reporter ligands in MS Binding Assays addressing the dopamine [DAT, (R,R)-D-84], norepinephrine [NET, (S,S)-reboxetine] and serotonin transporter [SERT, (S)-citalopram], respectively. The developed LC-ESI-MS/MS method uses a pentafluorphenyl stationary phase in combination with a mobile phase composed of acetonitrile and ammonium formate buffer for chromatography and a triple quadrupole mass spectrometer in the multiple reaction monitoring mode for mass spectrometric detection. Quantification is based on deuterated derivatives of all three analytes serving as internal standards. The established LC-ESI-MS/MS method enables fast, robust, selective and highly sensitive quantification of all three reporter ligands in a single chromatographic run. The method was validated according to the Center for Drug Evaluation and Research (CDER) guideline for bioanalytical method validation regarding selectivity, accuracy, precision, calibration curve and sensitivity. Finally, filtration-based MS Binding Assays were performed for all three monoamine transporters based on this LC-ESI-MS/MS quantification method as read out. The affinities determined in saturation experiments for (R,R)-D-84 toward hDAT, for (S,S)-reboxetine toward hNET, and for (S)-citalopram toward hSERT, respectively, were in good accordance with results from literature, clearly demonstrating that the established MS Binding Assays have the potential to be an efficient alternative to radioligand binding assays widely used for this purpose so far.

Amaryllidaceae Alkaloids as Potential Glycogen Synthase Kinase-3β Inhibitors

Glycogen synthase kinase-3β (GSK-3β) is a multifunctional serine/threonine protein kinase that was originally identified as an enzyme involved in the control of glycogen metabolism. It plays a key role in diverse physiological processes including metabolism, the cell cycle, and gene expression by regulating a wide variety of well-known substances like glycogen synthase, tau-protein, and β-catenin. Recent studies have identified GSK-3β as a potential therapeutic target in Alzheimer´s disease, bipolar disorder, stroke, more than 15 types of cancer, and diabetes. GSK-3β is one of the most attractive targets for medicinal chemists in the discovery, design, and synthesis of new selective potent inhibitors. In the current study, twenty-eight Amaryllidaceae alkaloids of various structural types were studied for their potency to inhibit GSK-3β. Promising results have been demonstrated by alkaloids of the homolycorine-{9-O-demethylhomolycorine (IC₅₀ = 30.00 ± 0.71 µM), masonine (IC₅₀ = 27.81 ± 0.01 μM)}, and lycorine-types {caranine (IC₅₀ = 30.75 ± 0.04 μM)}.

Simultaneous Multiple MS Binding Assays for the Dopamine, Norepinephrine, and Serotonin Transporters

In this work, we present label-free, mass-spectrometry-based binding assays (MS Binding Assays), targeting the human dopamine, norepinephrine, and serotonin transporters (hDAT, hNET, and hSERT) in simultaneous binding experiments. Using a validated LC-ESI-MS/MS method for quantification of the selective dopamine transporter inhibitor (R,R)-4-(2-benzhydryloxyethyl)-1-(4-fluorobenzyl)piperidin-3-ol ((R,R)-D-84), the selective norepinephrine transporter inhibitor (S,S)-reboxetine, and the selective serotonin reuptake inhibitor (S)-citalopram, binding affinities at the three monoamine transporters could be characterized simultaneously in a single binding experiment. The performed simultaneous saturation and competition experiments yielded results that are in good accordance with those determined in MS Binding Assays addressing the monoamine transporters individually. The results obtained from this study underscore the potential of MS Binding Assays for simultaneous affinity determination at different targets, which is difficult to accomplish with conventional radioligand binding assays.

Designing Dual Transglutaminase 2/Histone Deacetylase Inhibitors Effective at Halting Neuronal Death

In recent years there has been a clear consensus that neurodegenerative conditions can be better treated through concurrent modulation of different targets. Herein we report that combined inhibition of transglutaminase 2 (TG2) and histone deacetylases (HDACs) synergistically protects against toxic stimuli mediated by glutamate. Based on these findings, we designed and synthesized a series of novel dual TG2-HDAC binding agents. Compound 3 [(E)-N-hydroxy-5-(3-(4-(3-oxo-3-(pyridin-3-yl)prop-1-en-1-yl)phenyl)thioureido)pentanamide] emerged as the most interesting of the series, being able to inhibit TG2 and HDACs both in vitro (TG2 IC₅₀ =13.3±1.5 μm, HDAC1 IC₅₀ =3.38±0.14 μm, HDAC6 IC₅₀ =4.10±0.13 μm) and in cell-based assays. Furthermore, compound 3 does not exert any toxic effects in cortical neurons up to 50 μm and protects neurons against toxic insults induced by glutamate (5 mm) with an EC₅₀ value of 3.7±0.5 μm.

Hydroxy-substituted trans-cinnamoyl derivatives as multifunctional tools in the context of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial pathology that requires multifaceted agents able to address its peculiar nature. In recent years, a plethora of proteins and biochemical pathways has been proposed as possible targets to counteract neurotoxicity. Although the complex scenario is not completely elucidated, close relationships are emerging among some of these actors. In particular, increasing evidence has shown that aggregation of amyloid beta (Aβ), glycogen synthase kinase 3β (GSK-3β) and oxidative stress are strictly interconnected and their concomitant modulation may have a positive and synergic effect in contrasting AD-related impairments. We designed compound 3 which demonstrated the ability to inhibit both GSK-3β (IC₅₀ = 24.36 ± 0.01 μM) and Aβ₄₂ self-aggregation (IC₅₀ = 9.0 ± 1.4 μM), to chelate copper (II) and to act as exceptionally strong radical scavenger (k_inh = 6.8 ± 0.5 · 10⁵ M^-1s^-1) even in phosphate buffer at pH 7.4 (k_inh = 3.2 ± 0.5 · 10⁵ M^-1s^-1). Importantly, compound 3 showed high-predicted blood-brain barrier permeability, did not exert any significant cytotoxic effects in immature cortical neurons up to 50 μM and showed neuroprotective properties at micromolar concentration against toxic insult induced by glutamate.

Naturally Inspired Molecules as Multifunctional Agents for Alzheimer's Disease Treatment

Alzheimer’s disease (AD) has been defined as a multi-factorial disorder resulting from a complex array of networked cellular and molecular mechanisms. In particular, elevated levels of Aβ protein and its aggregation products in the presence of metal ions proved to be highly neurotoxic and therapeutic strategies aimed at preventing Aβ generation and oxidative stress may represent an effective approach for AD treatment. A recent paradigm for the treatment of complex diseases such as AD suggests the employment of multifunctional compounds, single chemical entities capable of simultaneously modulating different targets involved in the pathology. In this paper, the “pharmacophores combination” strategy was applied, connecting the main scaffold of the BACE-1 ligand 1 to that of the chalcone 2, as metal chelating pharmacophore, to obtain a small library of compounds. Conjugate 5 emerged as the most interesting derivative, proving to inhibit BACE-1 with low-micromolar potency, and showing neuroprotective effects. In particular, 5 proved to be able to protect from metal-associated oxidative stress by hampering intracellular Cu²⁺-induced ROS formation without any direct neurotoxic effect.

Versatility of the Curcumin Scaffold: Discovery of Potent and Balanced Dual BACE-1 and GSK-3β Inhibitors

The multitarget approach has gained increasing acceptance as a useful tool to address complex and multifactorial maladies such as Alzheimer's disease (AD). The concurrent inhibition of the validated AD targets β-secretase (BACE-1) and glycogen synthase kinase-3β (GSK-3β) by attacking both β-amyloid and tau protein cascades has been identified as a promising AD therapeutic strategy. In our study, curcumin was identified as a lead compound for the simultaneous inhibition of both targets; therefore, synthetic efforts were dedicated to obtaining a small library of novel curcumin-based analogues, and a number of potent and balanced dual-target inhibitors were obtained. In particular, 2, 6, and 7 emerged as promising drug candidates endowed with neuroprotective potential and brain permeability. Notably, for some new compounds the symmetrical diketo and the β-keto-enol tautomeric forms were purposely isolated and tested in vitro, allowing us to gain insight into the key requirements for BACE-1 and GSK-3β inhibition.

Novel Tacrine-Benzofuran Hybrids as Potent Multitarget-Directed Ligands for the Treatment of Alzheimer's Disease: Design, Synthesis, Biological Evaluation, and X-ray Crystallography

Twenty-six new tacrine-benzofuran hybrids were designed, synthesized, and evaluated in vitro on key molecular targets for Alzheimer's disease. Most hybrids exhibited good inhibitory activities on cholinesterases and β-amyloid self-aggregation. Selected compounds displayed significant inhibition of human β-secretase-1 (hBACE-1). Among the 26 hybrids, 2e showed the most interesting profile as a subnanomolar selective inhibitor of human acetylcholinesterase (hAChE) (IC50 = 0.86 nM) and a good inhibitor of both β-amyloid aggregation (hAChE- and self-induced, 61.3% and 58.4%, respectively) and hBACE-1 activity (IC50 = 1.35 μM). Kinetic studies showed that 2e acted as a slow, tight-binding, mixed-type inhibitor, while X-ray crystallographic studies highlighted the ability of 2e to induce large-scale structural changes in the active-site gorge of Torpedo californica AChE (TcAChE), with significant implications for structure-based drug design. In vivo studies confirmed that 2e significantly ameliorates performances of scopolamine-treated ICR mice. Finally, 2e administration did not exhibit significant hepatotoxicity.

3,4-Dihydro-1,3,5-triazin-2(1H)-ones as the First Dual BACE-1/GSK-3β Fragment Hits against Alzheimer's Disease

One of the main obstacles toward the discovery of effective anti-Alzheimer drugs is the multifactorial nature of its etiopathology. Therefore, the use of multitarget-directed ligands has emerged as particularly suitable. Such ligands, able to modulate different neurodegenerative pathways, for example, amyloid and tau cascades, as well as cognitive and neurogenic functions, are fostered to come. In this respect, we report herein on the first class of BACE-1/GSK-3β dual inhibitors based on a 3,4-dihydro-1,3,5-triazin-2(1H)-one skeleton, whose hit compound 1 showed interesting properties in a preliminary investigation. Notably, compound 2, endowed with well-balanced potencies against the two isolated enzymes (IC50 of 16 and 7 μM against BACE-1 and GSK-3β, respectively), displayed effective neuroprotective and neurogenic activities and no neurotoxicity in cell-based assays. It also showed good brain permeability in a pharmacokinetic assessment in mice. Overall, triazinone derivatives, thanks to the simultaneous modulation of multiple points of the diseased network, might emerge as suitable candidates to be tested in in vivo Alzheimer's disease models.

Multitarget drug discovery for Alzheimer's disease: triazinones as BACE-1 and GSK-3β inhibitors

Cumulative evidence strongly supports that the amyloid and tau hypotheses are not mutually exclusive, but concomitantly contribute to neurodegeneration in Alzheimer's disease (AD). Thus, the development of multitarget drugs which are involved in both pathways might represent a promising therapeutic strategy. Accordingly, reported here in is the discovery of 6-amino-4-phenyl-3,4-dihydro-1,3,5-triazin-2(1H)-ones as the first class of molecules able to simultaneously modulate BACE-1 and GSK-3β. Notably, one triazinone showed well-balanced in vitro potencies against the two enzymes (IC50 of (18.03±0.01) μM and (14.67±0.78) μM for BACE-1 and GSK-3β, respectively). In cell-based assays, it displayed effective neuroprotective and neurogenic activities and no neurotoxicity. It also showed good brain permeability in a preliminary pharmacokinetic assessment in mice. Overall, triazinones might represent a promising starting point towards high quality lead compounds with an AD-modifying potential.

Reprint of: Liquid chromatographic enzymatic studies with on-line Beta-secretase immobilized enzyme reactor and 4-(4-dimethylaminophenylazo) benzoic acid/5-[(2-aminoethyl) amino] naphthalene-1-sulfonic acid peptide as fluorogenic substrate

High throughput screening (HTS) techniques are required for the fast hit inhibitors selection in the early discovery process. However, in Beta-secretase (BACE1) inhibitors screening campaign, the most frequently used methoxycoumarin based peptide substrate (M-2420) is not widely applicable when aromatic or heterocycle compounds of natural source show auto-fluorescence interferences. Here, in order to overcome these drawbacks, we propose the use of a highly selective 4-(4-dimethylaminophenylazo)benzoic acid/5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (DABCYL/1,5-EDANS) based peptide substrate (Substrate IV), whose cleavage product is devoid of spectroscopic interference. HrBACE1-IMER was prepared and characterized in terms of units of immobilised hrBACE1. BACE1 catalyzed Substrate IV cleavage was on-line kinetically characterized in terms of KM and vmax, in a classical Michaelis and Menten study. The on-line kinetic constants were found consistent with those obtained with the in solution fluorescence resonance energy transfer (FRET) standard method. In order to further validate the use of Substrate IV for inhibition studies, the inhibitory potency of the well-known BACE1 peptide InhibitorIV (IC₅₀: 0.19 ± 0.02 μM) and of the natural compound Uleine (IC₅₀: 0.57 ± 0.05) were determined in the optimized on-line hrBACE1-IMER. The IC₅₀ values on the hrBACE1-IMER system were found in agreement with that obtained by the conventional methods confirming the applicability of Substrate IV for on-line BACE1 kinetic and inhibition studies.

Liquid chromatographic enzymatic studies with on-line Beta-secretase immobilized enzyme reactor and 4-(4-dimethylaminophenylazo) benzoic acid/5-[(2-aminoethyl) amino] naphthalene-1-sulfonic acid peptide as fluorogenic substrate

High throughput screening (HTS) techniques are required for the fast hit inhibitors selection in the early discovery process. However, in Beta-secretase (BACE1) inhibitors screening campaign, the most frequently used methoxycoumarin based peptide substrate (M-2420) is not widely applicable when aromatic or heterocycle compounds of natural source show auto-fluorescence interferences. Here, in order to overcome these drawbacks, we propose the use of a highly selective 4-(4-dimethylaminophenylazo)benzoic acid/5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (DABCYL/1,5-EDANS) based peptide substrate (Substrate IV), whose cleavage product is devoid of spectroscopic interference. HrBACE1-IMER was prepared and characterized in terms of units of immobilised hrBACE1. BACE1 catalyzed Substrate IV cleavage was on-line kinetically characterized in terms of KM and vmax, in a classical Michaelis and Menten study. The on-line kinetic constants were found consistent with those obtained with the in solution fluorescence resonance energy transfer (FRET) standard method. In order to further validate the use of Substrate IV for inhibition studies, the inhibitory potency of the well-known BACE1 peptide InhibitorIV (IC50: 0.19±0.02μM) and of the natural compound Uleine (IC50: 0.57±0.05) were determined in the optimized on-line hrBACE1-IMER. The IC50 values on the hrBACE1-IMER system were found in agreement with that obtained by the conventional methods confirming the applicability of Substrate IV for on-line BACE1 kinetic and inhibition studies.

Amyloid β-peptide 25-35 self-assembly and its inhibition: a model undecapeptide system to gain atomistic and secondary structure details of the Alzheimer's disease process and treatment

Combined results of theoretical molecular dynamic simulations and in vitro spectroscopic (circular dichroism and fluorescence) studies are presented, providing the atomistic and secondary structure details of the process by which a selected small molecule may destabilize the β-sheet ordered "amyloid" oligomers formed by the model undecapeptide of amyloid β-peptide 25-35 [Aβ(25-35)]. Aβ(25-35) was chosen because it is the shortest fragment capable of forming large β-sheet fibrils and retaining the toxicity of the full length Aβ(1-40/42) peptides. The conformational transition, that leads to the formation of β-sheet fibrils from soluble unordered structures, was found to depend on the environmental conditions, whereas the presence of myricetin destabilizes the self-assembly and antagonizes this conformational shift. In parallel, we analyzed several molecular dynamics trajectories describing the evolution of five monomer fragments, without inhibitor as well as in the presence of myricetin. Other well-known inhibitors (curcumin and (-)-tetracycline), found to be stronger and weaker Aβ(1-42) aggregation inhibitors, respectively, were also studied. The combined in vitro and theoretical studies of the Aβ(25-35) self-assembly and its inhibition contribute to understanding the mechanism of action of well-known inhibitors and the peptide amino acid residues involved in the interaction leading to a rational drug design of more potent new molecules able to antagonize the self-assembly process.

Protein flexibility in virtual screening: the BACE-1 case study

Simulating protein flexibility is a major issue in the docking-based drug-design process for which a single methodological solution does not exist. In our search of new anti-Alzheimer ligands, we were faced with the challenge of including receptor plasticity in a virtual screening campaign aimed at finding new β-secretase inhibitors. To this aim, we incorporated protein flexibility in our simulations by using an ensemble of static X-ray enzyme structures to screen the National Cancer Institute database. A unified description of the protein motion was also generated by computing and combining a set of grid maps using an energy weighting scheme. Such a description was used in an energy-weighted virtual screening experiment on the same molecular database. Assessment of the enrichment factors from these two virtual screening approaches demonstrated comparable predictive powers, with the energy-weighted method being faster than the ensemble method. The in vitro evaluation demonstrated that out of the 32 tested ligands, 17 featured the predicted enzyme inhibiting property. Such an impressive success rate (53.1%) demonstrates the enhanced power of the two methodologies and suggests that energy-weighted virtual screening is a more than valid alternative to ensemble virtual screening given its reduced computational demands and comparable performance.

Structural characterization of recombinant therapeutic proteins by circular dichroism

Most of the protein therapeutics are now produced by recombinant DNA technology. The advantages of recombinant proteins are related to their higher specificity and to their safety as exposure to animal or human diseases. However, several problems are still present in development of recombinant proteins as therapeutics, such as low bioavailability, short serum half-life, and immune response. Their successful application hinges on the protein stereochemical stability, and on the folding and the tendency to aggregate induced by purification steps and storage. All these aspects determine the failure of many potential protein therapies, and limitations in the development of the formulation. The application of multiple analytical techniques is important in order to obtain a detailed product profile and to understand how manufacturing can influence product structure and activity. Surely the protein conformation is a key aspect to be assessed, because a specific conformation is often essential for the biological function of the protein. Thus, there is a growing need to perform structural studies under the conditions in which the proteins operate, and to monitor the structural changes of the protein. Circular dichroism has been increasingly recognised as a valuable and reliable technique to get this information. In particular, examples will be here reported on the use of circular dichroism spectroscopy in the structural characterization of free and formulated recombinant proteins, looking at the prediction of the secondary structure, propensity to conformational changes, stability, and tendency to aggregate.

Human recombinant beta-secretase immobilized enzyme reactor for fast hits' selection and characterization from a virtual screening library

In the present work, a human recombinant BACE1 immobilized enzyme reactor (hrBACE1-IMER) has been applied for the sensitive fast screening of 38 compounds selected through a virtual screening approach. HrBACE1-IMER was inserted into a liquid chromatograph coupled with a fluorescent detector. A fluorogenic peptide substrate (M-2420), containing the β-secretase site of the Swedish mutation of APP, was injected and cleaved in the on-line HPLC-hrBACE1-IMER system, giving rise to the fluorescent product. The compounds of the library were tested for their ability to inhibit BACE1 in the immobilized format and to reduce the area related to the chromatographic peak of the fluorescent enzymatic product. The results were validated in solution by using two different FRET methods. Due to the efficient virtual screening methodology, more than fifty percent of the selected compounds showed a measurable inhibitory activity. One of the most active compound (a bis-indanone derivative) was characterized in terms of IC(50) and K(i) determination on the hrBACE1-IMER. Thus, the hrBACE1-IMER has been confirmed as a valid tool for the throughput screening of different chemical entities with potency lower than 30μM for the fast hits' selection and for mode of action determination.