A Prospective Repurposing of Dantrolene as a Multitarget Agent for Alzheimer's Disease

Benzimidazole-derived carbohydrazones as dual monoamine oxidases and acetylcholinesterase inhibitors: design, synthesis, and evaluation

A series of novel benzimidazole-derived carbohydrazones was designed, synthesized and evaluated for their dual inhibition potential against monoamine oxidases (MAOs) and acetylcholinesterase (AChE) using multitarget-directed ligand approach (MTDL). The investigated compounds have exhibited moderate to excellent in vitro MAOs/AChE inhibitory activity at micromolar to nanomolar concentrations. Compound 12, 2-(1H-Benzo[d]imidazol-1-yl)-N'-[1-(4-hydroxyphenyl) ethylidene]acetohydrazide has emerged as a lead dual MAO-AChE inhibitor by exhibiting superior multi-target activity profile against MAO-A (IC50 = 0.067 ± 0.018 µM), MAO-B (IC50 = 0.029 ± 0.005 µM) and AChE (IC50 = 1.37 ± 0.026 µM). SAR studies suggest that the site A (hydrophobic ring) and site C (semicarbazone linker) modifications attempted on the semicarbazone-based MTDL resulted in a significant enhancement in the MAO-A/B inhibitory potential and a drastic decrease in the AChE inhibitory activity. Further, molecular docking and dynamics simulation experiments disclosed the possible molecular interactions of inhibitors inside the active site of respective enzymes. Also, computational prediction of drug-likeness and ADME parameters of test compounds revealed their drug-like characteristics.Communicated by Ramaswamy H. Sarma.

Novel 6-hydroxybenzothiazol-2-carboxamides as potent and selective monoamine oxidase B inhibitors endowed with neuroprotective activity

In neurodegenerative diseases, using a single molecule that can exert multiple effects to modify the disease may have superior activity over the classical "one molecule-one target" approach. Herein, we describe the discovery of 6-hydroxybenzothiazol-2-carboxamides as highly potent and selective MAO-B inhibitors. Variation of the amide substituent led to several potent compounds having diverse side chains with cyclohexylamide 40 displaying the highest potency towards MAO-B (IC50 = 11 nM). To discover new compounds with extended efficacy against neurotoxic mechanisms in neurodegenerative diseases, MAO-B inhibitors were screened against PHF6, R3 tau, cellular tau and α-synuclein (α-syn) aggregation. We identified the phenethylamide 30 as a multipotent inhibitor of MAO-B (IC50 = 41 nM) and α-syn and tau aggregation. It showed no cytotoxic effects on SH-SY5Y neuroblastoma cells, while also providing neuroprotection against toxicities induced by α-syn and tau. The evaluation of key physicochemical and in vitro-ADME properties revealed a great potential as drug-like small molecules with multitarget neuroprotective activity.

Optimization of CHARMM force field parameters for ryanodine receptor inhibitory drug dantrolene using FFTK and FFParam

CONTEXT

Ryanodine receptors (RyRs) are large intracellular ligand-gated calcium release ion channels. Mutations in human RyR1 in combination with a volatile anesthetic or muscle relaxant are known to cause leaky RyRs resulting in malignant hyperthermia (MH). This has long been primarily treated with the RyR inhibitory drug dantrolene. Alternatives to dantrolene as a RyR inhibitor may be found through computer-aided drug design. Additionally, molecular dynamics (MD) studies of dantrolene interacting with RyRs may reveal its full mechanism of action. The availability of accurate force field parameters is important for the success of both.

METHODS

In this study, force field parameters for dantrolene were obtained from the CHARMM General Force Field (CGenFF) program and optimized using the force field toolkit (FFTK) and FFParam programs. The obtained parameters were then validated by a comparison between calculated and experimental IR spectra and normal mode analysis, among other techniques.

AI molecular property prediction for Parkinson's Disease reveals potential repurposing drug candidates based on the increase of the expression of PINK1

BACKGROUND AND OBJECTIVE

Parkinson's Disease (PD), a common neurodegenerative disorder and one of the major current challenges in neuroscience and pharmacology, may potentially be tackled by the modern AI techniques employed in drug discovery based on molecular property prediction. The aim of our study was to explore the application of a machine learning setup for the identification of the best potential drug candidates among FDA approved drugs, based on their predicted PINK1 expression-enhancing activity.

METHODS

Our study relies on supervised machine learning paradigm exploiting in vitro data and utilizing the scaffold splits methodology in order to assess model's capability to extract molecular patterns and generalize from them to new, unseen molecular representations. Models' predictions are combined in a meta-ensemble setup for finding new pharmacotherapies based on the predicted expression of PINK1.

RESULTS

The proposed machine learning setup can be used for discovering new drugs for PD based on the predicted increase of expression of PINK1. Our study identified nitazoxanide as well as representatives of imidazolidines, trifluoromethylbenzenes, anilides, nitriles, stilbenes and steroid esters as the best potential drug candidates for PD with PINK1 expression-enhancing activity on or inside the cell's mitochondria.

CONCLUSIONS

The applied methodology allows to reveal new potential drug candidates against PD. Next to novel indications, it allows also to confirm the utility of already known antiparkinson drugs, in the new context of PINK1 expression, and indicates the potential for simultaneous utilization of different mechanisms of action.

RyR2 inhibition with dantrolene is antiarrhythmic, prevents further pathological remodeling, and improves cardiac function in chronic ischemic heart disease

Diastolic Ca2+ leak due to cardiac ryanodine receptor (RyR2) hyperactivity has been widely documented in chronic ischemic heart disease (CIHD) and may contribute to ventricular tachycardia (VT) risk and progressive left-ventricular (LV) remodeling. Here we test the hypothesis that targeting RyR2 hyperactivity can suppress VT inducibility and progressive heart failure in CIHD by the RyR2 inhibitor dantrolene. METHODS AND RESULTS: CIHD was induced in C57BL/6 J mice by left coronary artery ligation. Four weeks later, mice were randomized to either acute or chronic (6 weeks via implanted osmotic pump) treatment with dantrolene or vehicle. VT inducibility was assessed by programmed stimulation in vivo and in isolated hearts. Electrical substrate remodeling was assessed by optical mapping. Ca2+ sparks and spontaneous Ca2+ releases were measured in isolated cardiomyocytes. Cardiac remodeling was quantified by histology and qRT-PCR. Cardiac function and contractility were measured using echocardiography. Compared to vehicle, acute dantrolene treatment reduced VT inducibility. Optical mapping demonstrated reentrant VT prevention by dantrolene, which normalized the shortened refractory period (VERP) and prolonged action potential duration (APD), preventing APD alternans. In single CIHD cardiomyocytes, dantrolene normalized RyR2 hyperactivity and prevented spontaneous intracellular Ca2+ release. Chronic dantrolene treatment not only reduced VT inducibility but also reduced peri-infarct fibrosis and prevented further progression of LV dysfunction in CIHD mice. CONCLUSIONS: RyR2 hyperactivity plays a mechanistic role for VT risk, post-infarct remodeling, and contractile dysfunction in CIHD mice. Our data provide proof of concept for the anti-arrhythmic and anti-remodeling efficacy of dantrolene in CIHD.

Thioxanthenone-based derivatives as multitarget therapeutic leads for Alzheimer's disease

A set of twenty-five thioxanthene-9-one and xanthene-9-one derivatives, that were previously shown to inhibit cholinesterases (ChEs) and amyloid β (Aβ₄₀) aggregation, were evaluated for the inhibition of tau protein aggregation. All compounds exhibited a good activity, and eight of them (5-8, 10, 14, 15 and 20) shared comparable low micromolar inhibitory potency versus Aβ₄₀ aggregation and human acetylcholinesterase (AChE), while inhibiting human butyrylcholinesterase (BChE) even at submicromolar concentration. Compound 20 showed outstanding biological data, inhibiting tau protein and Aβ₄₀ aggregation with IC₅₀ = 1.8 and 1.3 μM, respectively. Moreover, at 0.1-10 μM it also exhibited neuroprotective activity against tau toxicity induced by okadoic acid in human neuroblastoma SH-SY5Y cells, that was comparable to that of estradiol and PD38. In preliminary toxicity studies, these interesting results for compound 20 are somewhat conflicting with a narrow safety window. However, compound 10, although endowed with a little lower potency for tau and Aβ aggregation inhibition additionally demonstrated good inhibition of ChEs and rather low cytotoxicity. Compound 4 is also worth of note for its high potency as hBChE inhibitor (IC₅₀ = 7 nM) and for the three order of magnitude selectivity versus hAChE. Molecular modelling studies were performed to explain the different behavior of compounds 4 and 20 towards hBChE. The observed balance of the inhibitory potencies versus the relevant targets indicates the thioxanthene-9-one derivatives as potential MTDLs for AD therapy, provided that the safety window will be improved by further structural variations, currently under investigation.

The Mycotoxin Patulin Inhibits the Mitochondrial Carnitine/Acylcarnitine Carrier (SLC25A20) by Interaction with Cys136 Implications for Human Health

The effect of mycotoxin patulin (4-hydroxy-4H-furo [3,2c] pyran-2 [6H] -one) on the mitochondrial carnitine/acylcarnitine carrier (CAC, SLC25A20) was investigated. Transport function was measured as [³H]-carnitine_ex/carnitine_in antiport in proteoliposomes reconstituted with the native protein extracted from rat liver mitochondria or with the recombinant CAC over-expressed in E. coli. Patulin (PAT) inhibited both the mitochondrial native and recombinant transporters. The inhibition was not reversed by physiological and sulfhydryl-reducing reagents, such as glutathione (GSH) or dithioerythritol (DTE). The IC₅₀ derived from the dose-response analysis indicated that PAT inhibition was in the range of 50 µM both on the native and on rat and human recombinant protein. The kinetics process revealed a competitive type of inhibition. A substrate protection experiment confirmed that the interaction of PAT with the protein occurred within a protein region, including the substrate-binding area. The mechanism of inhibition was identified using the site-directed mutagenesis of CAC. No inhibition was observed on Cys mutants in which only the C136 residue was mutated. Mass spectrometry studies and in silico molecular modeling analysis corroborated the outcomes derived from the biochemical assays.

Lithium Provides Broad Therapeutic Benefits in an Alzheimer's Disease Mouse Model

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with a progressive loss of cognitive function. Currently, no effective treatment regimen is available. Lithium, a mood stabilizer for bipolar disorder, exerts broad neuroprotective and neurotrophic actions and improves cognitive function.

OBJECTIVE

The study investigated if lithium stabilizes Ca2+ signaling abnormalities in hippocampal neurons and subsequently normalize downstream effects on AD neuropathology and synaptic plasticity in young AD mice.

METHODS

Four-month-old 3xTg-AD mice were treated with a LiCl diet chow for 30 days. At the end of the lithium treatment, a combination of two-photon Ca2+ imaging, electrophysiology, and immunohistochemistry assays were used to assess the effects of the LiCl treatment on inositol trisphosphate receptor (IP3R)-dependent endoplasmic reticulum (ER) Ca2+ and voltage-gated Ca2+ channel (VGCC)-mediated Ca2+ signaling in CA1 neurons, neuronal nitric oxide synthase (nNOS) and hyperphosphorylated tau (p-tau) levels and synaptic plasticity in the hippocampus and overlying cortex from 3xTg-ADmice.

RESULTS

Thirty-day LiCl treatment reduced aberrant IP3R-dependent ER Ca2+ and VGCC-mediated Ca2+ signaling in CA1 pyramidal neurons from 3xTg-AD mice and restored neuronal nitric oxide synthase (nNOS) and hyperphosphorylated tau (p-tau) levels to control levels in the hippocampal subfields and overlying cortex. The LiCl treatment enhanced post-tetanic potentiation (PTP), a form of short-term plasticity in the hippocampus.

CONCLUSION

The study found that lithium exerts therapeutic effects across several AD-associated early neuronal signaling abnormalities including aberrant Ca2+ signaling, nNOS, and p-tau formation and enhances short-term synaptic plasticity. Lithium could serve as an effective treatment or co-therapeutic for AD.

Synthesis of Isomeric 3-Benzazecines Decorated with Endocyclic Allene Moiety and Exocyclic Conjugated Double Bond and Evaluation of Their Anticholinesterase Activity

Transformations of 1-methoxymethylethynyl substituted isoquinolines triggered by terminal alkynes in alcohols were studied and new 3-benzazecine-containing compounds synthesized, such as 6-methoxymethyl-3-benzazecines incorporating an endocyclic C6–C8 allene fragment and the -ylidene derivatives 6-methoxymethylene-3-benzazecines. The reaction mechanisms were investigated and a preliminary in vitro screening of their potential inhibitory activities against human acetyl- and butyrylcholinesterases (AChE and BChE) and monoamine oxidases A and B (MAO-A and MAO-B) showed that the allene compounds were more potent than the corresponding -ylidene ones as selective AChE inhibitors. Among the allenes, 3e (R³ = CH₂OMe) was found to be a competitive AChE inhibitor with a low micromolar inhibition constant value (K_i = 4.9 μM), equipotent with the corresponding 6-phenyl derivative 3n (R³ = Ph, K_i = 4.5 μM), but 90-fold more water-soluble.

Synthesis and Biological Evaluation of Dantrolene-Like Hydrazide and Hydrazone Analogues as Multitarget Agents for Neurodegenerative Diseases

Dantrolene, a drug used for the management of malignant hyperthermia, had been recently evaluated for prospective repurposing as multitarget agent for neurodegenerative syndromes, including Alzheimer's disease (AD). Herein, twenty-one dantrolene-like hydrazide and hydrazone analogues were synthesized with the aim of exploring structure-activity relationships (SARs) for the inhibition of human monoamine oxidases (MAOs) and acetylcholinesterase (AChE), two well-established target enzymes for anti-AD drugs. With few exceptions, the newly synthesized compounds exhibited selectivity toward MAO B over either MAO A or AChE, with the secondary aldimine 9 and phenylhydrazone 20 attaining IC50 values of 0.68 and 0.81 μM, respectively. While no general SAR trend was observed with lipophilicity descriptors, a molecular simplification strategy allowed the main pharmacophore features to be identified, which are responsible for the inhibitory activity toward MAO B. Finally, further in vitro investigations revealed cell protection from oxidative insult and activation of carnitine/acylcarnitine carrier as concomitant biological activities responsible for neuroprotection by hits 9 and 20 and other promising compounds in the examined series.

Transcriptome-wide association study of treatment-resistant depression and depression subtypes for drug repurposing

Major depressive disorder (MDD) is the single largest contributor to global disability and up to 20-30% of patients do not respond to at least two antidepressants (treatment-resistant depression, TRD). This study leveraged imputed gene expression in TRD to perform a drug repurposing analysis. Among those with MDD, we defined TRD as having at least two antidepressant switches according to primary care records in UK Biobank (UKB). We performed a transcriptome-wide association study (TWAS) of TRD (n = 2165) vs healthy controls (n = 11,188) using FUSION and gene expression levels from 21 tissues. We identified compounds with opposite gene expression signatures (ConnectivityMap data) compared to our TWAS results using the Kolmogorov-Smirnov test, Spearman and Pearson correlation. As symptom patterns are routinely assessed in clinical practice and could be used to provide targeted treatments, we identified MDD subtypes associated with TRD in UKB and analysed them using the same pipeline described for TRD. Anxious MDD (n = 14,954) and MDD with weight gain (n = 4697) were associated with TRD. In the TWAS, two genes were significantly dysregulated (TMEM106B and ATP2A1 for anxious and weight gain MDD, respectively). A muscarinic receptor antagonist was identified as top candidate for repurposing in TRD; inhibition of heat shock protein 90 was the main mechanism of action identified for anxious MDD, while modulators of metabolism such as troglitazone showed promising results for MDD with weight gain. This was the first TWAS of TRD and associated MDD subtypes. Our results shed light on possible pharmacological approaches in individuals with difficult-to-treat depression.

Limiting RyR2 open time prevents Alzheimer's disease-related deficits in the 3xTG-AD mouse model

Increasing evidence suggests that Alzheimer's disease (AD) progression is driven by a vicious cycle of soluble β-amyloid (Aβ)-induced neuronal hyperactivity. Thus, breaking this vicious cycle by suppressing neuronal hyperactivity may represent a logical approach to stopping AD progression. In support of this, we have recently shown that genetically and pharmacologically limiting ryanodine receptor 2 (RyR2) open time prevented neuronal hyperactivity, memory impairment, dendritic spine loss, and neuronal cell death in a rapid, early onset AD mouse model (5xFAD). Here, we assessed the impact of limiting RyR2 open time on AD-related deficits in a relatively late occurring, slow developing AD mouse model (3xTG-AD) that bears more resemblance (compared to 5xFAD) to that of human AD. Using behavioral tests, long-term potentiation recordings, and Golgi and Nissl staining, we found that the RyR2-E4872Q mutation, which markedly shortens the open duration of the RyR2 channel, prevented learning and memory impairment, defective long-term potentiation, dendritic spine loss, and neuronal cell death in the 3xTG-AD mice. Furthermore, pharmacologically shortening the RyR2 open time with R-carvedilol rescued these AD-related deficits in 3xTG mice. Therefore, limiting RyR2 open time may offer a promising, neuronal hyperactivity-targeted anti-AD strategy.

The Mitochondrial Carnitine Acyl-carnitine Carrier (SLC25A20): Molecular Mechanisms of Transport, Role in Redox Sensing and Interaction with Drugs

The SLC25A20 transporter, also known as carnitine acyl-carnitine carrier (CAC), catalyzes the transport of short, medium and long carbon chain acyl-carnitines across the mitochondrial inner membrane in exchange for carnitine. The 30-year story of the protein responsible for this function started with its purification from rat liver mitochondria. Even though its 3D structure is not yet available, CAC is one of the most deeply characterized transport proteins of the inner mitochondrial membrane. Other than functional, kinetic and mechanistic data, post-translational modifications regulating the transport activity of CAC have been revealed. CAC interactions with drugs or xenobiotics relevant to human health and toxicology and the response of the carrier function to dietary compounds have been discovered. Exploiting combined approaches of site-directed mutagenesis with chemical targeting and bioinformatics, a large set of data on structure/function relationships have been obtained, giving novel information on the molecular mechanism of the transport catalyzed by this protein.

Synthesis of 8-phenyl substituted 3-benzazecines with allene moiety, their thermal rearrangement and evaluation as acetylcholinesterase inhibitors

Various 4'-R-substituted phenyl azacyclic allenes were synthesized in good yields, and their thermal transformations were studied. For the first time, the obtained rearrangement products-new N-bridged cyclopenta[a]indenes, and the corresponding parent allenes were evaluated as potential inhibitors of acetyl- and butyrylcholinesterase. Among the tested compounds, the allene derivative 2g proved to competitively inhibit human AChE with inhibition constant value (K_i) in the low micromolar range.

Multitarget Biological Profiling of New Naphthoquinone and Anthraquinone-Based Derivatives for the Treatment of Alzheimer's Disease

Two series of naphthoquinone and anthraquinone derivatives decorated with an aromatic/heteroaromatic chain have been synthesized and evaluated as potential promiscuous agents capable of targeting different factors playing a key role in Alzheimer’s disease (AD) pathogenesis. On the basis of the in vitro biological profiling, most of them exhibited a significant ability to inhibit amyloid aggregation, PHF6 tau sequence aggregation, acetylcholinesterase (AChE), and monoamine oxidase (MAO) B. In particular, naphthoquinone 2 resulted as one of the best performing multitarget-directed ligand (MTDL) experiencing a high potency profile in inhibiting β-amyloid (Aβ₄₀) aggregation (IC₅₀ = 3.2 μM), PHF6 tau fragment (91% at 10 μM), AChE enzyme (IC₅₀ = 9.2 μM) jointly with a remarkable inhibitory activity against MAO B (IC₅₀ = 7.7 nM). Molecular modeling studies explained the structure–activity relationship (SAR) around the binding modes of representative compound 2 in complex with hMAO B and hAChE enzymes, revealing inhibitor/protein key contacts and the likely molecular rationale for enzyme selectivity. Compound 2 was also demonstrated to be a strong inhibitor of Aβ₄₂ aggregation, with potency comparable to quercetin. Accordingly, atomic force microscopy (AFM) revealed that the most promising naphthoquinones 2 and 5 and anthraquinones 11 and 12 were able to impair Aβ₄₂ fibrillation, deconstructing the morphologies of its fibrillar aggregates. Moreover, the same compounds exerted a moderate neuroprotective effect against Aβ₄₂ toxicity in primary cultures of cerebellar granule cells. Therefore, our findings demonstrate that these molecules may represent valuable chemotypes toward the development of promising candidates for AD therapy.

Away from Flatness: Unprecedented Nitrogen-Bridged Cyclopenta[a]indene Derivatives as Novel Anti-Alzheimer Multitarget Agents

Nature-inspired, bridged polycyclic molecules share low similarity with currently available drugs, containing preferentially planar and/or achiral moieties. This "Escape from Flatland" scenario, aimed at exploring pharmacological properties of atypical molecular scaffolds, finds interest in synthetic routes leading to tridimensional-shaped molecules. Herein we report on the synthesis of N-bridged cyclopenta[a]indene derivatives, achieved through microwave-assisted thermal rearrangement of allene 3-benzazecines with high diastereoselectivity. The biological evaluation disclosed selective inhibition of human acetylcholinesterase or butyrylcholinesterase, depending on the substitution around the molecular core, which was rationalized by means of docking simulations. The most potent BChE inhibitor 31 was effective in neuroprotection from glutamatergic excitotoxicity and displayed low intrinsic cytotoxicity and good brain penetration. Overall, compound 31 and its close congeners 34 and 35 acted as multitarget agents addressing different biological events involved in neurodegeneration, particularly in the progression of Alzheimer's disease.

First Synthesis of Racemic Trans Propargylamino-Donepezil, a Pleiotrope Agent Able to Both Inhibit AChE and MAO-B, with Potential Interest against Alzheimer's Disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease towards which pleiotropic approach using Multi-Target Directed Ligands is nowadays recognized as probably convenient. Among the numerous targets which are today validated against AD, acetylcholinesterase (ACh) and Monoamine Oxidase-B (MAO-B) appear as particularly convincing, especially if displayed by a sole agent such as ladostigil, currently in clinical trial in AD. Considering these results, we wanted to take benefit of the structural analogy lying in donepezil (DPZ) and rasagiline, two indane derivatives marketed as AChE and MAO-B inhibitors, respectively, and to propose the synthesis and the preliminary in vitro biological characterization of a structural compromise between these two compounds, we called propargylaminodonepezil (PADPZ). The synthesis of racemic trans PADPZ was achieved and its biological evaluation established its inhibitory activities towards both (h)AChE (IC₅₀ = 0.4 µM) and (h)MAO-B (IC₅₀ = 6.4 µM).

Pharmacophore Modeling and 3D-QSAR Study of Indole and Isatin Derivatives as Antiamyloidogenic Agents Targeting Alzheimer's Disease

Thirty-six novel indole-containing compounds, mainly 3-(2-phenylhydrazono) isatins and structurally related 1H-indole-3-carbaldehyde derivatives, were synthesized and assayed as inhibitors of beta amyloid (Aβ) aggregation, a hallmark of pathophysiology of Alzheimer’s disease. The newly synthesized molecules spanned their IC₅₀ values from sub- to two-digit micromolar range, bearing further information into structure-activity relationships. Some of the new compounds showed interesting multitarget activity, by inhibiting monoamine oxidases A and B. A cell-based assay in tau overexpressing bacterial cells disclosed a promising additional activity of some derivatives against tau aggregation. The accumulated data of either about ninety published and thirty-six newly synthesized molecules were used to generate a pharmacophore hypothesis of antiamyloidogenic activity exerted in a wide range of potencies, satisfactorily discriminating the ‘active’ compounds from the ‘inactive’ (poorly active) ones. An atom-based 3D-QSAR model was also derived for about 80% of ‘active’ compounds, i.e., those achieving finite IC₅₀ values lower than 100 μM. The 3D-QSAR model (encompassing 4 PLS factors), featuring acceptable predictive statistics either in the training set (n = 45, q² = 0.596) and in the external test set (n = 14, r²_ext = 0.695), usefully complemented the pharmacophore model by identifying the physicochemical features mainly correlated with the Aβ anti-aggregating potency of the indole and isatin derivatives studied herein.