Recent development of multifunctional agents as potential drug candidates for the treatment of Alzheimer's disease

Novel Multitarget-Directed Ligands Aiming at Symptoms and Causes of Alzheimer's Disease

Alzheimer's disease (AD) is a major public health problem, which is due to its increasing prevalence and lack of effective therapy or diagnostics. The complexity of the AD pathomechanism requires complex treatment, e.g. multifunctional ligands targeting both the causes and symptoms of the disease. Here, we present new multitarget-directed ligands combining pharmacophore fragments that provide a blockade of serotonin 5-HT₆ receptors, acetyl/butyrylcholinesterase inhibition, and amyloid β antiaggregation activity. Compound 12 has displayed balanced activity as an antagonist of 5-HT₆ receptors ( K_i = 18 nM) and noncompetitive inhibitor of cholinesterases (IC_{50 hAChE} = 14 nM, IC_{50 eqBuChE} = 22 nM). In further in vitro studies, compound 12 has shown amyloid β antiaggregation activity (IC₅₀ = 1.27 μM) and ability to permeate through the blood-brain barrier. The presented findings may provide an excellent starting point for further studies and facilitate efforts to develop new effective anti-AD therapy.

Computer-Aided Multi-Target Management of Emergent Alzheimer's Disease

Alzheimer's disease (AD) represents an enormous global health burden in terms of human suffering and economic cost. AD management requires a shift from the prevailing paradigm targeting pathogenesis to design and develop effective drugs with adequate success in clinical trials. Therefore, it is of interest to report a review on amyloid beta (Aβ) effects and other multi-targets including cholinesterase, NFTs, tau protein and TNF associated with brain cell death to be neuro-protective from AD. It should be noted that these molecules have been generated either by target-based or phenotypic methods. Hence, the use of recent advancements in nanomedicine and other natural compounds screening tools as a feasible alternative for circumventing specific liabilities is realized. We review recent developments in the design and identification of neuro-degenerative compounds against AD generated using current advancements in computational multi-target modeling algorithms reflected by theragnosis (combination of diagnostic tests and therapy) concern.

Discovery of novel dual acetylcholinesterase inhibitors with antifibrillogenic activity related to Alzheimer's disease

AIM

Alzheimer's disease is a progressive and neurodegenerative disorder of the CNS, affecting elderly people. The current pharmacological approach is based on the improvement of cholinergic neurotransmission by inhibiting acetylcholinesterase (AChE) with AChE inhibitors. The disease is also characterized by the accelerated accumulation of β-amyloid plaques around neurons. Furthermore, in vitro studies revealed that AChE can induce β-amyloid peptide (Aβ) aggregation.

METHODOLOGY

Computer-aided molecular design by virtual screening was here employed to discover novel potential AChE inhibitors, with antifibrillogenic properties, in other words, inhibiting Aβ aggregation.

RESULTS

Compounds 1, 4 and 6 showed interesting AChE inhibition. In addition, they particularly inhibit Aβ aggregation in vitro, indicating to be promising novel anti-Alzheimer agents.

90 years of monoamine oxidase: some progress and some confusion

It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted.

Multifunctional properties of novel tacrine congeners: cholinesterase inhibition and cytotoxic activity

This review describes the synthesis of a wide range of novel tetrahydroacridine derivatives (tiocyanates, selenocyanates, ureas, selenoureas, thioureas, isothioureas, disulfides, diselenides and several tacrine homo- and hetro-hybrids). These tacrine congeners exhibit significant anticholinesterase and cytotoxic properties and may therefore be of considerable potential for the development of new drugs for the treatment of Alzheimer's disease.

7-Deoxy-trans-dihydronarciclasine Reduces β-Amyloid and Ameliorates Memory Impairment in a Transgenic Model of Alzheimer's Disease

The critical pathological feature of Alzheimer's disease (AD) is the accumulation of β-amyloid (Aβ), the main constituent of amyloid plaques. β-amyloid precursor protein (APP) undergoes amyloidogenic cleavage by β- and γ-secretase generating Aβ at endosomes or non-amyloidogenic processing by α-secretase precluding the production of Aβ at the plasma membrane. Recently, several natural products have been widely researched on the prevention of Aβ accumulation for AD treatment. We previously reported that Lycoris chejuensis K. Tae et S. Ko (CJ), which originated from Jeju Island in Korea, improved the disrupted memory functions and reduced Aβ production in vivo. Here, we further explored the effect of its active component, 7-deoxy-trans-dihydronarciclasine (coded as E144), on Aβ generation and the underlying mechanism. Our results showed that E144 reduced the level of APP, especially its mature form, in HeLa cells overexpressing human APP with the Swedish mutation. Concomitantly, E144 decreased the levels of Aβ, sAPPβ, sAPPα, and C-terminal fragment. In addition, administration of E144 normalized the behavioral deficits in Tg2576 mice, an APP transgenic mouse model of AD. E144 also decreased the Aβ and APP levels in the cerebral cortex of Tg2576 mice. Thus, we propose that E144 could be a potential drug candidate for an anti-amyloid disease-modifying AD therapy.

Have there been improvements in Alzheimer's disease drug discovery over the past 5 years?

INTRODUCTION

Alzheimer's disease (AD) is the most important neurodegenerative disorder with a global cost worldwide of over $700 billion. Pharmacological treatment accounts for 10-20% of direct costs; no new drugs have been approved during the past 15 years; and the available medications are not cost-effective. Areas covered: A massive scrutiny of AD-related PubMed publications (ps)(2013-2017) identified 42,053ps of which 8,380 (19.60%) were associated with AD treatments. The most prevalent pharmacological categories included neurotransmitter enhancers (11.38%), multi-target drugs (2.45%), anti-Amyloid agents (13.30%), anti-Tau agents (2.03%), natural products and derivatives (25.58%), novel drugs (8.13%), novel targets (5.66%), other (old) drugs (11.77%), anti-inflammatory drugs (1.20%), neuroprotective peptides (1.25%), stem cell therapy (1.85%), nanocarriers/nanotherapeutics (1.52%), and others (<1% each). Expert opinion: Unsuccessful outcomes in AD therapeutics are attributed to pathogenic misconceptions, erratic procedures in drug development and inappropriate regulations. Recommendations for the future are as follows: (i) the reconsideration of dominant pathogenic theories, (ii) the identification of reliable biomarkers, (iii) the redefinition of diagnostic criteria, (iv) new guidelines for disease management, (v) the reorientation of drug discovery programs, (vi) the updating of regulatory requirements, (vii) the introduction of pharmacogenomics in drug development and personalized treatments, and (viii) the implementation of preventive programs.

Synthesis, molecular modeling, and biological evaluation of 4-[5-aryl-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl] benzenesulfonamides toward acetylcholinesterase, carbonic anhydrase I and II enzymes

In this study, 4-[5-aryl-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl] benzenesulfonamides were synthesized, and inhibition effects on AChE, hCA I, and hCA II were evaluated. Ki values of the compounds toward hCA I were in the range of 24.2 ± 4.6-49.8 ± 12.8 nm, while they were in the range of 37.3 ± 9.0-65.3 ± 16.7 nm toward hCA II. Ki values of the acetazolamide were 282.1 ± 19.7 nm and 103.60 ± 27.6 nm toward both isoenzymes, respectively. The compounds inhibited AChE with Ki in the range of 22.7 ± 10.3-109.1 ± 27.0 nm, whereas the tacrine had Ki value of 66.5 ± 13.8 nm. Electronic structure calculations at M06-L/6-31 + G(d,p)//AM1 level and molecular docking studies were also performed to enlighten inhibition mechanism and to support experimental findings. Results obtained from calculations of molecular properties showed that the compounds obey drug-likeness properties. The experimental and computational findings obtained in this study might be useful in the design of novel inhibitors against hCA I, hCA II, and AChE.

Gene-gene interactions among coding genes of iron-homeostasis proteins and APOE-alleles in cognitive impairment diseases

Cognitive impairments of different aetiology share alterations in iron and lipid homeostasis with mutual relationships. Since iron and cholesterol accumulation impact on neurodegenerative disease, the associated gene variants are appealing candidate targets for risk and disease progression assessment. In this light, we explored the role of common single nucleotide polymorphisms (SNPs) in the main iron homeostasis genes and in the main lipoprotein transporter gene (APOE) in a cohort of 765 patients with dementia of different origin: Alzheimer’s disease (AD) n = 276; vascular dementia (VaD), n = 255; mild cognitive impairment (MCI), n = 234; and in normal controls (n = 1086). In details, four genes of iron homeostasis (Hemochromatosis (HFE: C282Y, H63D), Ferroportin (FPN1: -8CG), Hepcidin (HAMP: -582AG), Transferrin (TF: P570S)), and the three major alleles of APOE (APOE2, APOE3, APOE4) were analyzed to explore causative interactions and synergies. In single analysis, HFE 282Y allele yielded a 3-fold risk reduction in the whole cohort of patients (P<0.0001), confirmed in AD and VaD, reaching a 5-fold risk reduction in MCI (P = 0.0019). The other iron SNPs slightly associated with risk reduction whereas APOE4 allele resulted in increased risk, reaching more than 7-fold increased risk in AD homozygotes (P = 0.001), confirmed to a lower extent in VaD and MCI (P = 0.038 and P = 0.013 respectively) as well as in the whole group (P<0.0001). Comparisons of Mini Mental State Examination (MMSE) among AD showed appreciable lowering in APOE4 carriers (P = 0.038), confirmed in the whole cohort of patients (P = 0.018). In interaction analysis, the HFE 282Y allele completely extinguished the APOE4 allele associated risk. Conversely, the coexistence in patients of a substantial number of iron SNPs accrued the APOE4 detrimental effect on MMSE. Overall, the analysis highlighted how a specific iron-allele burden, defined as different combinations of iron gene variants, might have different effects on cognitive impairment and might modulate the effects of established genetic risk factors such as APOE4. Our results suggest that established genetic risk factors might be affected by specific genetic backgrounds, making patients differently suited to manage iron accumulation adding new genetic insights in neurodegeneration. The recently recognized interconnections between iron and lipids, suggest that these pathways might share more than expected. We therefore extended to additional iron gene variants the newly proposed influencing mechanisms that HFE gene has on cholesterol metabolism. Our results have a strong translational potential promoting new pharmacogenetics studies on therapeutic target identification aimed at optimally tuning brain iron levels.

MH84 improves mitochondrial dysfunction in a mouse model of early Alzheimer's disease

BACKGROUND

Current approved drugs for Alzheimer's disease (AD) only attenuate symptoms, but do not cure the disease. The pirinixic acid derivate MH84 has been characterized as a dual gamma-secretase/proliferator activated receptor gamma (PPARγ) modulator in vitro. Pharmacokinetic studies in mice showed that MH84 is bioavailable after oral administration and reaches the brain. We recently demonstrated that MH84 improved mitochondrial dysfunction in a cellular model of AD. In the present study, we extended the pharmacological characterization of MH84 to 3-month-old Thy-1 AβPPSL mice (harboring the Swedish and London mutation in human amyloid precursor protein (APP)) which are characterized by enhanced AβPP processing and cerebral mitochondrial dysfunction, representing a mouse model of early AD.

METHODS

Three-month-old Thy-1 AβPPSL mice received 12 mg/kg b.w. MH84 by oral gavage once a day for 21 days. Mitochondrial respiration was analyzed in isolated brain mitochondria, and mitochondrial membrane potential and ATP levels were determined in dissociated brain cells. Citrate synthase (CS) activity was determined in brain tissues and MitoTracker Green fluorescence was measured in HEK293-AβPPwt and HEK293-AβPPsw cells. Soluble Aβ1-40 and Aβ1-42 levels were determined using ELISA. Western blot analysis and qRT-PCR were used to measure protein and mRNA levels, respectively.

RESULTS

MH84 reduced cerebral levels of the β-secretase-related C99 peptide and of Aβ40 levels. Mitochondrial dysfunction was ameliorated by restoring complex IV (cytochrome-c oxidase) respiration, mitochondrial membrane potential, and levels of ATP. Induction of PPARγ coactivator-1α (PGC-1α) mRNA and protein expression was identified as a possible mode of action that leads to increased mitochondrial mass as indicated by enhanced CS activity, OXPHOS levels, and MitoTracker Green fluorescence.

CONCLUSIONS

MH84 modulates β-secretase processing of APP and improves mitochondrial dysfunction by a PGC-1α-dependent mechanism. Thus, MH84 seems to be a new promising therapeutic agent with approved in-vivo activity for the treatment of AD.

Synthesis and activity towards Alzheimer's disease in vitro: Tacrine, phenolic acid and ligustrazine hybrids

A series of novel tacrine-phenolic acid dihybrids and tacrine-phenolic acid-ligustrazine trihybrids were synthesized, characterized and screened as novel potential anti-Alzheimer drug candidates. These compounds showed potent inhibition activity towards cholinesterases (ChEs), among of them, 9i was the most potent one towards acetylcholinesterase (eeAChE, IC₅₀ = 3.9 nM; hAChE, IC₅₀ = 65.2 nM). 9i could also effectively block β-amyloid (Aβ) self-aggregation with an inhibition ratio of 47% at 20 μM. In addition, its strong anti-oxidation activity could protect PC12 cells from CoCl₂-damage in the experimental condition while no neurotoxicity. Furthermore, its hepatotoxicity was lower than tacrine in vitro and in vivo. Kinetic and molecular modeling studies revealed that 9i worked in a mixed-type way, could interact simultaneously with catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Therefore, 9i was a promising multifunctional candidate for the treatment of AD.

Effect of the Cycle Size and Spacer Structure in Tacrine and its Cyclopentyl Homologue Conjugates with 5-(4-trifluoromethyl-phenylamino)-1,2,4-thiadiazole on the Spectrum of their Biological Activity

The conjugates of tacrine and its cyclopentyl analogue with 5-(4-trifluoromethyl-phenylamino)-1,2,4-thiadiazole, combined with two different spacers, pentylaminopropane and pentylaminopropene, were synthesized. Their esterase profile, the ability to displace propidium from the peripheral anionic site (PAS) of acetylcholinesterase (AChE) and antioxidant activity in the ABTS test were investigated. The compounds obtained effectively inhibit cholinesterases with a predominant effect on butyrylcholinesterase, displace propidium from the PAS of Electrophorus electricus AChE (EeAChE) and exhibit a high radical-scavenging capacity. It is shown that, depending on the spacer structure, particulary, the presence of a propenamine or propanamine fragment, the spectrum of biological activity of the conjugates changes.

Time Trends in the Prevalence of Neurocognitive Disorders and Cognitive Impairment in the United States: The Effects of Disease Severity and Improved Ascertainment

BACKGROUND

Trends in the prevalence of cognitive impairment (CI) based on cognitive assessment instruments are often inconsistent with those of neurocognitive disorders (ND) based on Medicare claims records.

OBJECTIVE

We hypothesized that improved ascertainment and resulting decrease in disease severity at the time of diagnosis are responsible for this phenomenon.

METHODS

Using Medicare data linked to the Health and Retirement Study (1992-2012), we performed a joint analysis of trends in CI and ND to test our hypothesis.

RESULTS

We identified two major contributors to the divergent directions in CI and ND trends: reductions in disease severity explained more than 60% of the differences between CI and ND prevalence over the study period; the remaining 40% was explained by a decrease in the fraction of undiagnosed individuals.

DISCUSSION

Improvements in the diagnoses of ND diseases were a major contributor to reported trends in ND and CI. Recent forecasts of CI and ND trends in the U.S. may be overly pessimistic.

Changing Paradigm from one Target one Ligand Towards Multi-target Directed Ligand Design for Key Drug Targets of Alzheimer Disease: An Important Role of In Silico Methods in Multi-target Directed Ligands Design

Alzheimer disease (AD) is now considered as a multifactorial neurodegenerative disorder and rapidly increasing to an alarming situation and causing higher death rate. One target one ligand hypothesis does not provide complete solution of AD due to multifactorial nature of the disease and one target one drug fails to provide better treatment against AD. Moreover, currently available treatments are limited and most of the upcoming treatments under clinical trials are based on modulating single target. So, the current AD drug discovery research is shifting towards a new approach for a better solution that simultaneously modulates more than one targets in the neurodegenerative cascade. This can be achieved by network pharmacology, multi-modal therapies, multifaceted, and/or the more recently proposed term "multi-targeted designed drugs". Drug discovery project is a tedious, costly and long-term project. Moreover, multi-target AD drug discovery added extra challenges such as the good binding affinity of ligands for multiple targets, optimal ADME/T properties, no/less off-target side effect and crossing of the blood-brain barrier. These hurdles may be addressed by insilico methods for an efficient solution in less time and cost as computational methods successfully applied to single target drug discovery project. Here, we are summarizing some of the most prominent and computationally explored single targets against AD and further, we discussed a successful example of dual or multiple inhibitors for same targets. Moreover, we focused on ligand and structure-based computational approach to design MTDL against AD. However, it is not an easy task to balance dual activity in a single molecule but computational approach such as virtual screening docking, QSAR, simulation and free energy is useful in future MTDLs drug discovery alone or in combination with a fragment-based method. However, rational and logical implementations of computational drug designing methods are capable of assisting AD drug discovery and play an important role in optimizing multi-target drug discovery.

Multifunctional Analogs of Kynurenic Acid for the Treatment of Alzheimer's Disease: Synthesis, Pharmacology, and Molecular Modeling Studies

We report the synthesis and pharmacological investigation of analogs of the endogenous molecule kynurenic acid (KYNA) as multifunctional agents for the treatment of Alzheimer's disease (AD). Synthesized KYNA analogs were tested for their N-methyl-d-aspartate (NMDA) receptor binding, mGluR5 binding and function, acetylcholinesterase (AChE) inhibition, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, interference with the amyloid β peptide (Aβ) fibrillation process, and protection against Aβ-induced toxicity in transgenic Caenorhabditis elegans strain GMC101 expressing full-length Aβ₄₂. Molecular modeling studies were also performed to predict the binding modes of most active compounds with NMDAR, mGluR5, and Aβ₄₂. Among the synthesized analogs, 3c, 5b, and 5c emerged as multifunctional compounds that act via multiple anti-AD mechanisms including AChE inhibition, free radical scavenging, NMDA receptor binding, mGluR5 binding, inhibition of Aβ₄₂ fibril formation, and disassembly of preformed Aβ₄₂ fibrils. Interestingly, 5c showed protection against Aβ₄₂-induced toxicity in transgenic C. elegans strain GMC101. Moreover, 5b and 5c displayed high permeability in an MDR1-MDCKII cell-based model of the blood-brain barrier (BBB). Compound 3b emerged with specific activity as a micromolar AChE inhibitor, however it had low permeability in the BBB model. This study highlights the opportunities that exist to develop analogs of endogenous molecules from the kynurenine pathway for therapeutic uses.

A Trishistidine Pseudopeptide with Ability to Remove Both CuΙ and CuΙΙ from the Amyloid-β Peptide and to Stop the Associated ROS Formation

The pseudopeptide L, derived from a nitrilotriacetic acid scaffold and functionalized with three histidine moieties, is reminiscent of the amino acid side chains encountered in the Alzheimer's peptide (Aβ). Its synthesis and coordination properties for CuΙ and CuΙΙ are described. L efficiently complex CuΙΙ in a square-planar geometry involving three imidazole nitrogen atoms and an amidate-Cu bond. By contrast, CuΙ is coordinated in a tetrahedral environment. The redox behavior is irreversible and follows an ECEC mechanism in accordance with the very different environments of the two redox states of the Cu center. This is in line with the observed resistance of the CuΙ complex to oxidation by oxygen and the CuΙΙ complex reduction by ascorbate. The affinities of L for CuΙΙ and CuΙ at physiological pH are larger than that reported for the Aβ peptide. Therefore, due to its peculiar Cu coordination properties, the ligand L is able to target both redox states of Cu, redox silence them and prevent reactive oxygen species production by the CuAβ complex. Because reactive oxygen species contribute to the oxidative stress, a key issue in Alzheimer's disease, this ligand thus represents a new strategy in the long route of finding molecular concepts for fighting Alzheimer's disease.

Novel tetrahydroacridine derivatives with iodobenzoic acid moiety as multifunctional acetylcholinesterase inhibitors

New synthesized series of 9-amino-1,2,3,4-tetrahydroacridine derivatives with iodobenzoic acid moiety were studied for their inhibitory activity toward cholinesterase and against β-amyloid aggregation. All novel molecules 3a-3i interacted with both cholinesterases-acetylcholinesterase and butyrylcholinesterase-delivered nanomolar IC₅₀ values. The structure-activity relationship showed that N-butyl moiety derivatives are stronger inhibitors toward AChE and BuChE than N-ethyl and N-propyl moieties compounds. The most potent compound toward acetylcholinesterase was inhibitor 3f (IC₅₀  = 31.2 nm), and it was more active than reference drug, tacrine (IC₅₀  = 100.2 nm). Compound 3f showed strong inhibition of butyrylcholinesterase (IC₅₀  = 8.0 nm), also higher than tacrine (IC₅₀  = 16.3 nm). In the kinetic studies, compound 3f revealed mixed type of acetylcholinesterase inhibition. The computer modeling was carried out. The most active compound 3f was confirmed as peripheral anionic site inhibitor of acetylcholinesterase. Moreover, molecule 3f inhibited β-amyloid aggregation (at the concentration 10 μm-24.96% of inhibition, 25 μm-72%, 50 μm-78.44%, and 100 μm-84.92%). Therefore, among all examined, compound 3f is the most promising molecule for further, more detailed research of novel multifunctional agents in the therapy of Alzheimer's disease.

Alzheimer Disease: Clues from traditional and complementary medicine

Despite modern medicine's incredible innovation and resulting accumulation of valuable knowledge, many of the world's most problematic diseases such as Alzheimer Disease (AD) still lack effective cures and treatments. Western medicine has revealed many genetic, cellular, and molecular processes that characterize AD such as protein aggregation and inflammation. As the need for novel and effective treatments increases, researchers have turned towards traditional medicine as a resource. Modern, evidence based research examining traditional and complementary remedies for AD has generated promising results within the last decade. Animal based products inhibiting cellular toxicity, anti-inflammatory nutraceuticals such as omega-3 fatty acids, and plant based compounds derived from herbal medicine demonstrate viability as neuroprotective treatments and possible application in developing pharmaceuticals. Analysis of antioxidant, anti-inflammatory, and neuroprotective phytochemicals used in various traditional medicines around the world reveal potential to ameliorate and prevent the devastating neurodegeneration observed in AD.

Discovery of novel isoflavone derivatives as AChE/BuChE dual-targeted inhibitors: synthesis, biological evaluation and molecular modelling

AChE and BuChE are druggable targets for the discovery of anti-Alzheimer’s disease drugs, while dual-inhibition of these two targets seems to be more effective. In this study, we synthesised a series of novel isoflavone derivatives based on our hit compound G from in silico high-throughput screening and then tested their activities by in vitro AChE and BuChE bioassays. Most of the isoflavone derivatives displayed moderate inhibition against both AChE and BuChE. Among them, compound 16 was identified as a potent AChE/BuChE dual-targeted inhibitor (IC₅₀: 4.60 μM for AChE; 5.92 μM for BuChE). Molecular modelling study indicated compound 16 may possess better pharmacokinetic properties, e.g. absorption, blood–brain barrier penetration and CYP2D6 binding. Taken together, our study has identified compound 16 as an excellent lead compound for the treatment of Alzheimer’s disease.

Advances toward multifunctional cholinesterase and β-amyloid aggregation inhibitors

The emergence of a multitarget design approach in the development of new potential anti-Alzheimer's disease agents has resulted in the discovery of many multifunctional compounds focusing on various targets. Among them the largest group comprises inhibitors of both cholinesterases, with additional anti-β-amyloid aggregation activity. This review describes recent advances in this research area and presents the most interesting compounds reported over a 2-year span (2015-2016). The majority of hybrids possess heterodimeric structures obtained by linking structurally active fragments interacting with different targets. Multipotent cholinesterase inhibitors with β-amyloid antiaggregating activity may additionally possess antioxidative, neuroprotective or metal-chelating properties or less common features such as anti-β-secretase or τ-antiaggregation activity.

Synthesis, Crystal Structure and Biological Evaluation of Novel 2-Phenylthiazole Derivatives as Multi-Targeting Agents to Treat Alzheimer's Disease

Three novel 2-phenylthiazole derivatives were synthesised and characterised by spectroscopic techniques. The structure of the synthesised compounds was unambiguously confirmed by a single-crystal X-ray diffraction analysis of ethyl 2-(4-{[5-(4-benzylpiperidin-1-yl)pentyl]oxy}phenyl)thiazole-4-carboxylate. All of the compounds presented good cholinesterase-inhibition activities and ethyl 2-(4-{[5-(4-benzylpiperidin-1-yl)pentyl]oxy}phenyl)thiazole-4-carboxylate showed the best acetylcholinesterase-inhibition and butyrylcholinesterase-inhibition abilities with IC50 values of 5.19 μM and 5.83 μM. The docking study demonstrated that it could interact with both the catalytic active site (CAS) and the peripheral anionic site (PAS) of acetylcholinesterase and could chelate with metal ions like Cu2+ and Zn2+.

Dual/multitargeted xanthone derivatives for Alzheimer's disease: where do we stand?

To date, the current therapy for Alzheimer's disease (AD) based on acetylcholinesterase inhibitors is only symptomatic, being its efficacy limited. Hence, the recent research has been focused in the development of different pharmacological approaches. Here we discuss the potential of xanthone derivatives as new anti-Alzheimer agents. The interference of xanthone derivatives with acetylcholinesterase and other molecular targets and cellular mechanisms associated with AD have been recently systematically reported. Therefore, we report xanthones with anticholinesterase, monoamine oxidase and amyloid β aggregation inhibitory activities as well as antioxidant properties, emphasizing xanthone derivatives with dual/multitarget activity as potential agents to treat AD. We also propose the structural features for these activities that may guide the design of new, more effective xanthone derivatives. [Formula: see text].

Monoterpenes as a renewable source of biologically active compounds

Monoterpenes and their derivatives play an important role in the creation of new biologically active compounds including drugs. The review focuses on the data on various types of biological activity exhibited by monoterpenes and their derivatives, including analgesic, anti-inflammatory, anticonvulsant, antidepressant, anti-Alzheimer, anti-Parkinsonian, antiviral, and antibacterial (anti-tuberculosis) effects. Searching for novel potential drugs among monoterpene derivatives shows great promise for treating various pathologies. Special attention is paid to the effect of absolute configuration of monoterpenes and monoterpenoids on their activity.

Focused design of polypharmacophoric neuroprotective compounds: Conjugates of γ-carbolines with carbazole derivatives and tetrahydrocarbazole

Alzheimer’s disease has a complex multifactorial nature; therefore, a promising approach for the development of efficient therapeutic agents is the concept of multitarget drugs, which affect several biological targets involved in the pathogenesis of the disease. We developed a synthetic algorithm for conjugating several pharmacophoric ligands acting on the key stages of pathogenesis of several neurodegenerative diseases and synthesized hybrid structures combining the γ-carboline fragment of Dimebon with carbazole and tetrahydrocarbazole moieties. Using the complex primary screening system the structures have been revealed that combine the high inhibitory activity and selectivity towards butyrylcholinesterase with the radical-scavenging activity and the ability to potentiate tubulin polymerization to microtubules with a normal structure and/or prevent mitochondrial permeability transition. The lead compound was identified for future optimization and development of new multi-target drugs against neurodegenerative diseases combining the cognitive-stimulating and neuroprotective potentials.

Novel Tacrine-Scutellarin Hybrids as Multipotent Anti-Alzheimer's Agents: Design, Synthesis and Biological Evaluation

A novel series of 6-chlorotacrine-scutellarin hybrids was designed, synthesized and the biological activity as potential anti-Alzheimer's agents was assessed. Their inhibitory activity towards human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE), antioxidant activity, ability to cross the blood-brain barrier (BBB) and hepatotoxic profile were evaluated in vitro. Among these compounds, hybrid K1383, bearing two methylene tether between two basic scaffolds, was found to be very potent hAChE inhibitor (IC50 = 1.63 nM). Unfortunately, none of the hybrids displayed any antioxidant activity (EC50 ≥ 500 μM). Preliminary data also suggests a comparable hepatotoxic profile with 6-Cl-THA (established on a HepG2 cell line). Kinetic studies performed on hAChE with the most active compound in the study, K1383, pointed out to a mixed, non-competitive enzyme inhibition. These findings were further corroborated by docking studies.

Multitarget drug design strategy in Alzheimer's disease: focus on cholinergic transmission and amyloid-β aggregation

Aim: Alzheimer pathogenesis has been associated with a network of processes working simultaneously and synergistically. Over time, much interest has been focused on cholinergic transmission and its mutual interconnections with other active players of the disease. Besides the cholinesterase mainstay, the multifaceted interplay between nicotinic receptors and amyloid is actually considered to have a central role in neuroprotection. Thus, the multitarget drug-design strategy has emerged as a chance to face the disease network. Methods: By exploiting the multitarget approach, hybrid compounds have been synthesized and studied in vitro and in silico toward selected targets of the cholinergic and amyloidogenic pathways. Results: The new molecules were able to target the cholinergic system, by joining direct nicotinic receptor stimulation to acetylcholinesterase inhibition, and to inhibit amyloid-β aggregation. Conclusion: The compounds emerged as a suitable starting point for a further optimization process.

AlzhCPI: A knowledge base for predicting chemical-protein interactions towards Alzheimer's disease

Alzheimer's disease (AD) is a complicated progressive neurodegeneration disorder. To confront AD, scientists are searching for multi-target-directed ligands (MTDLs) to delay disease progression. The in silico prediction of chemical-protein interactions (CPI) can accelerate target identification and drug discovery. Previously, we developed 100 binary classifiers to predict the CPI for 25 key targets against AD using the multi-target quantitative structure-activity relationship (mt-QSAR) method. In this investigation, we aimed to apply the mt-QSAR method to enlarge the model library to predict CPI towards AD. Another 104 binary classifiers were further constructed to predict the CPI for 26 preclinical AD targets based on the naive Bayesian (NB) and recursive partitioning (RP) algorithms. The internal 5-fold cross-validation and external test set validation were applied to evaluate the performance of the training sets and test set, respectively. The area under the receiver operating characteristic curve (ROC) for the test sets ranged from 0.629 to 1.0, with an average of 0.903. In addition, we developed a web server named AlzhCPI to integrate the comprehensive information of approximately 204 binary classifiers, which has potential applications in network pharmacology and drug repositioning. AlzhCPI is available online at http://rcidm.org/AlzhCPI/index.html. To illustrate the applicability of AlzhCPI, the developed system was employed for the systems pharmacology-based investigation of shichangpu against AD to enhance the understanding of the mechanisms of action of shichangpu from a holistic perspective.

Protective Roles of Monsonia angustifolia and Its Active Compounds in Experimental Models of Alzheimer's Disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is characterized by the accumulation of neurotoxic β-amyloid (Aβ) peptides, which consequently affects cognitive decline and memory impairment. Current research on AD treatment is actively focusing on the prevention of neurotoxic Aβ peptide accumulation. Monsonia angustifolia is reported to be consumed as an indigenous vegetable in Tanzania. In this study, we investigated the effect of the ethanol (EtOH) extract of M. angustifolia dried ground material on Aβ production and spatial learning ability as protection against AD. The formation of Aβ peptides was significantly reduced in HeLa cells stably transfected with the Swedish mutant form of β-amyloid precursor protein (APPsw) after treatment with a 60% EtOH extract of M. angustifolia. We next examined the cognitive-improving effects of the EtOH extract in vivo. Tg2576 mice were treated with extract for 6 months and subjected to Morris water maze and novel object recognition tests. The results showed that the 60% EtOH extract of M. angustifolia significantly ameliorated behavioral deficits of the AD transgenic mice and reduced the level of insoluble Aβ42 in the cerebral cortex and hippocampus. We further found that the 60% EtOH extract was effective for memory function recovery after shorter treatment (4 months). In addition, we isolated and identified several single compounds, justicidin A, 5-methoxyjusticidin A, chinensinaphthol, retrochinensinaphthol methyl ether, and suchilactone, from M. angustifolia and tested these compounds. Among them, justicidin A potently decreased the formation of Aβ in APPsw-transfected cells. These data suggest that the 60% EtOH extract of M. angustifolia has the potential to be developed as a treatment of AD. Furthermore, justicidin A may contribute, at least partially, to the Aβ alteration observed with the extract treatment.

Application of Strep-Tactin XT for affinity purification of Twin-Strep-tagged CB2, a G protein-coupled cannabinoid receptor

Human cannabinoid receptor CB2 belongs to the class A of G protein-coupled receptor (GPCR). CB2 is predominantly expressed in membranes of cells of immune origin and is implicated in regulation of metabolic pathways of inflammation, neurodegenerative disorders and pain sensing. High resolution structural studies of CB2 require milligram quantities of purified, structurally intact protein. While we previously reported on the methodology for expression of the recombinant CB2 and its stabilization in a functional state, here we describe an efficient protocol for purification of this protein using the Twin-Strep-tag/Strep-Tactin XT system. To improve the affinity of interaction of the recombinant CB2 with the resin, the double repeat of the Strep-tag (a sequence of eight amino acids WSHPQFEK), named the Twin-Strep-tag was attached either to the N- or C-terminus of CB2 via a short linker, and the recombinant protein was expressed in cytoplasmic membranes of E. coli as a fusion with the N-terminal maltose binding protein (MBP). The CB2 was isolated at high purity from dilute solutions containing high concentrations of detergents, glycerol and salts, by capturing onto the Strep-Tactin XT resin, and was eluted from the resin under mild conditions upon addition of biotin. Surface plasmon resonance studies performed on the purified protein demonstrate the high affinity of interaction between the Twin-Strep-tag fused to the CB2 and Strep-Tactin XT with an estimated Kd in the low nanomolar range. The affinity of binding did not vary significantly in response to the position of the tag at either N- or C-termini of the fusion. The binding capacity of the resin was several-fold higher for the tag located at the N-terminus of the protein as opposed to the C-terminus- or middle of the fusion. The variation in the length of the linker between the double repeats of the Strep-tag from 6 to 12 amino acid residues did not significantly affect the binding. The novel purification protocol reported here enables efficient isolation of a recombinant GPCR expressed at low titers in host cells. This procedure is suitable for preparation of milligram quantities of stable isotope-labelled receptor for high-resolution NMR studies.

Design, synthesis and evaluation of 2-arylethenyl-N-methylquinolinium derivatives as effective multifunctional agents for Alzheimer's disease treatment

A series of 2-arylethenyl-N-methylquinolinium derivatives were designed and synthesized based on our previous research of 2-arylethenylquinoline analogues as multifunctional agents for the treatment of Alzheimer's disease (AD) (Eur. J. Med. Chem. 2015, 89, 349-361). The results of in vitro biological activity evaluation, including β-amyloid (Aβ) aggregation inhibition, cholinesterase inhibition, and antioxidant activity, showed that introduction of N-methyl in quinoline ring significantly improved the anti-AD potential of compounds. The optimal compound, compound a12, dramatically attenuated the cell death of glutamate-induced HT22 cells by preventing the generation of ROS and increasing the level of GSH. Most importantly, intragastric administration of a12•HAc was well tolerated at doses up to 2000 mg/kg and could traverse blood-brain barrier.

Novel multitarget-directed tacrine derivatives as potential candidates for the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is complex and progressive; it has not only threatened the health of elderly people, but also burdened the whole social medical and health system. The available therapy for AD is limited and the efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the design and development of efficacious and safe anti-AD agents has become a hotspot in the field of pharmaceutical research. Due to the multifactorial etiology of AD, the multitarget-directed ligands (MTDLs) approach is promising in search for new drugs for AD. Tacrine, which is the first acetylcholinesterase (AChE) inhibitor, has been selected as the ideal active fragment because of its simple structure, clear activity, and its superiority in the structural modification, thus it could be introduced into the overall molecular skeletons of the multi-target-directed anti-AD agents. In this review, we have summarized the recent advances (2012 to the present) in the chemical modification of tacrine, which could provide the reference for the further study of novel multi-target-directed tacrine derivatives to treat AD.

Green synthesis of novel spiro-indenoquinoxaline derivatives and their cholinesterases inhibition activity

A convenient synthesis of substituted spiroindenoquinoxalines at mild and green conditions was developed. Multicomponent reaction of substituted phenylene diamines, ninhydrin, malononitrile and N,N'-substituted-2-nitroethene-1,1-diamines produced the target compounds. Twelve new spiroindenoquinoxalines were obtained, and their ability in inhibition of acetyl and butyrylcholinesterases were investigated both in vitro and in silico. All compounds showed moderate level activity against both acetyl and butyrylcholinesterases.