Structure−Activity Relationships of Acetylcholinesterase Noncovalent Inhibitors Based on a Polyamine Backbone. 4. Further Investigation on the Inner Spacer

Blood-Brain Barrier Permeable and NO-Releasing Multifunctional Nanoparticles for Alzheimer's Disease Treatment: Targeting NO/cGMP/CREB Signaling Pathways

The development of novel therapeutic strategies for combating Alzheimer's disease (AD) is challenging but imperative. Multifunctional nanoparticles are promising tools for regulating complex pathological dysfunctions for AD treatment. Herein, we constructed multifunctional nanoparticles consisting of regadenoson (Reg), nitric oxide (NO) donor, and YC-1 in a single molecular entity that can spontaneously self-assemble into nanoparticles and load donepezil to yield Reg-nanoparticles (Reg-NPs). The Reg moiety enabled the Reg-NPs to effectively regulate tight junction-associated proteins in the blood-brain barrier, thus facilitating the permeation of donepezil through the barrier and its accumulation in the brain. Moreover, the released NO and YC-1 activated the NO/cGMP/CREB signaling pathway by stimulating soluble guanylyl cyclase and inhibiting phosphodiesterase activity, which finally reduced cytotoxicity induced by aggregated Aβ in the neurons and was beneficial for synaptic plasticity and memory formation.

Synthesis and in vitro evaluation of naphthalimide-benzimidazole conjugates as potential antitumor agents

A series of novel naphthalimide-benzimidazoles was designed and synthesized for the first time and studied for their effect on antiproliferative activity. Some of these compounds possessed good antitumor activity towards the tested cancer cell lines. Noticeably, (diethylamino)ethyl 15 and (dimethylamino)ethyl 23 derivatives displayed superior antiproliferative activity towards human cancer cell lines with MG_MID GI50 values of 1.43 and 1.83 μM, respectively. Preliminary investigation revealed that compounds 15 and 23 might bind with ct-DNA through the intercalation mode which is responsible for potent bioactivity. Moreover, transportation behaviour indicated that these molecules could efficiently bind to and be carried by bovine albumin, and the hydrogen bonding and hydrophobic interactions played important roles in interaction with serum albumin.

Protein-Protein Interactions and Aggregation Inhibitors in Alzheimer's Disease

BACKGROUND

Alzheimer's Disease (AD), a multifaceted disorder, involves complex pathophysiology and plethora of protein-protein interactions. Thus such interactions can be exploited to develop anti-AD drugs.

OBJECTIVE

The interaction of dynamin-related protein 1, cellular prion protein, phosphoprotein phosphatase 2A and Mint 2 with amyloid β, etc., studied recently, may have critical role in progression of the disease. Our objective has been to review such studies and their implications in design and development of drugs against the Alzheimer's disease.

METHODS

Such studies have been reviewed and critically assessed.

RESULTS

Review has led to show how such studies are useful to develop anti-AD drugs.

CONCLUSION

There are several PPIs which are current topics of research including Drp1, Aβ interactions with various targets including PrPC, Fyn kinase, NMDAR and mGluR5 and interaction of Mint2 with PDZ domain, etc., and thus have potential role in neurodegeneration and AD. Finally, the multi-targeted approach in AD may be fruitful and opens a new vista for identification and targeting of PPIs in various cellular pathways to find a cure for the disease.

Design and development of novel N-(pyrimidin-2-yl)-1,3,4-oxadiazole hybrids to treat cognitive dysfunctions

Novel hybrids bearing a 2-aminopyrimidine (2-AP) moiety linked to substituted 1,3,4-oxadiazoles were designed, synthesized and biologically evaluated. Among the developed compounds, 28 noncompetitively inhibited human acetylcholinesterase (hAChE; pIC₅₀ = 6.52; Ki = 0.17 µM) and showed potential in vitro antioxidant activity (60.0%) when evaluated using the Ellman's and DPPH assays, respectively. Compound 28 competitively displaced propidium iodide (PI) from the peripheral anionic site (PAS) of hAChE (17.6%) and showed high blood-brain barrier (BBB) permeability, as observed in the PAMPA-BBB assay. Additionally, compound 28 inhibited hAChE-induced Aβ aggregation in a concentration-dependent manner according to the thioflavin T assay and was devoid of neurotoxic liability towards SH-SY5Y cell lines, as demonstrated by the MTT assay. The behavioral studies of compound 28 in mice showed a significant reversal of scopolamine-induced amnesia, as observed in Y-maze and passive avoidance tests. Furthermore, compound 28 exhibited significant AChE inhibition in the brain in ex vivo studies. An evaluation of oxidative stress biomarkers revealed the antioxidant potential of 28. Moreover, in silico molecular docking and dynamics simulation studies were used as a computational tool to evaluate the interactions of compound 28 with the active site residues of hAChE.

Design, Synthesis and Evaluation of Novel Tacrine-Ferulic Acid Hybrids as Multifunctional Drug Candidates against Alzheimer's Disease

Five novel tacrine-ferulic acid hybrid compounds (8a-e) were synthesized and their structures were identified on the basis of a detailed spectroscopic analysis. The activities of inhibiting acetyl cholinesterase (AChE) and butyryl cholinesterase (BuChE), reducing self-induced β-amyloid (Aβ) aggregation and chelating Cu²⁺ were evaluated in vitro. Among them, 8c and 8d displayed the higher selectivity in inhibiting AChE over BuChE. Moreover, 8d also showed dramatic inhibition of self-Aβ aggregation, activity of chelating Cu²⁺ and activity against Aβ-induced neurotoxicity in Neuro-2A cells.

Development of 3D-QSAR Model for Acetylcholinesterase Inhibitors Using a Combination of Fingerprint, Molecular Docking, and Structure-Based Pharmacophore Approaches

Acetylcholinesterase (AChE), a serine hydrolase vital for regulating the neurotransmitter acetylcholine in animals, has been used as a target for drugs and pesticides. With the increasing availability of AChE crystal structures, with or without ligands bound, structure-based approaches have been successfully applied to AChE inhibitors (AChEIs). The major limitation of these approaches has been the small applicability domain due to the lack of structural diversity in the training set. In this study, we developed a 3 dimensional quantitative structure-activity relationship (3D-QSAR) for inhibitory activity of 89 reversible and irreversible AChEIs including drugs and insecticides. A 3D-fingerprint descriptor encoding protein-ligand interactions was developed using molecular docking and structure-based pharmacophore to rationalize the structural requirements responsible for the activity of these compounds. The obtained 3D-QSAR model exhibited high correlation value (R(2) = 0.93) and low mean absolute error (MAE = 0.32 log units) for the training set (n = 63). The model was predictive across a range of structures as shown by the leave-one-out cross-validated correlation coefficient (Q(2) = 0.89) and external validation results (n = 26, R(2) = 0.89, and MAE = 0.38 log units). The model revealed that the compounds with high inhibition potency had proper conformation in the active site gorge and interacted with key amino acid residues, in particular Trp84 and Phe330 at the catalytic anionic site, Trp279 at the peripheral anionic site, and Gly118, Gly119, and Ala201 at the oxyanion hole. The resulting universal 3D-QSAR model provides insight into the multiple molecular interactions determining AChEI potency that may guide future chemical design and regulation of toxic AChEIs.

(-)-Meptazinol-melatonin hybrids as novel dual inhibitors of cholinesterases and amyloid-β aggregation with high antioxidant potency for Alzheimer's therapy

The multifactorial pathogenesis of Alzheimer's disease (AD) implicates that multi-target-directed ligands (MTDLs) intervention may represent a promising therapy for AD. Amyloid-β (Aβ) aggregation and oxidative stress, two prominent neuropathological hallmarks in patients, play crucial roles in the neurotoxic cascade of this disease. In the present study, a series of novel (-)-meptazinol-melatonin hybrids were designed, synthesized and biologically characterized as potential MTDLs against AD. Among them, hybrids 7-7c displayed higher dual inhibitory potency toward cholinesterases (ChEs) and better oxygen radical absorbance capacity (ORAC) than the parental drugs. Furthermore, compound 7c could effectively inhibit Aβ self-aggregation, showed favorable safety and the blood-brain barrier (BBB) permeability. Therefore, 7c may serve as a valuable candidate that is worthy of further investigations in the treatment of AD.

Design, synthesis and evaluation of genistein-polyamine conjugates as multi-functional anti-Alzheimer agents

A series of genistein-polyamine conjugates (4a–4h) were designed, synthesized and evaluated as multi-functional anti-Alzheimer agents. The results showed that these compounds had significant cholinesterases (ChEs) inhibitory activity. Compound 4b exhibited the strongest inhibition to acetylcholinesterase (AChE) with an IC₅₀ value of 2.75 μmol/L, which was better than that of rivastigmine (5.60 μmol/L). Lineweaver–Burk plot and molecular modeling study showed that compound 4b targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Besides, compound 4b showed potent metal-chelating ability. In addition, it was found that 4a–4h did not affect HepG-2 cell viability at the concentration of 10 μmol/L.

Design, synthesis and evaluation of tacrine-flurbiprofen-nitrate trihybrids as novel anti-Alzheimer's disease agents

To search for multifunctional anti-Alzheimer's disease (AD) agents with good safety, the previously synthesized tacrine-flurbiprofen hybrids 1a and 1b were modified into tacrine-flurbiprofen-nitrate trihybrids 3a-h. These compounds displayed comparable or higher cholinesterase inhibitory activity relative to the bivalent hybrids. Compound 3a was the most potent, which released moderate NO, exerted blood vessel relaxative activity, and showed significant Aβ inhibitory effects whereas tacrine and flurbiprofen did not exhibit any Aβ inhibitory activity at the same dose. In addition, 3a was active in improving memory impairment in vivo. More importantly, the hepatotoxicity study showed that 3a was much safer than tacrine, suggesting it might be a promising anti-AD agent for further investigation.

A ROS-mediated lysosomal-mitochondrial pathway is induced by a novel Amonafide analogue, 7c, in human Hela cervix carcinoma cells

In this study, a novel naphthalimide derivative 7c was designed which is topo II inhibiting though owning weak DNA binders. It was shown that 7c could induce cancer cells apoptosis and have less cytotoxicity in normal human cell. Further investigations on Hela cells revealed that 7c could also induce ROS generation, lysosome rupture as well as cathepsin B release. Subsequent mitochondrial damages including mitochondrial membrane permeabilization and the release of cytochrome c were also found in 7c when treating with Hela cells. According to our data, 7c may act as a lead compound for potential anticancer drugs. The idea of naphthalimides modification may also provide a novel strategy for naphthalimides design.

Molecular docking and receptor-specific 3D-QSAR studies of acetylcholinesterase inhibitors

The reversible inhibition of acetylcholinesterase (AChE) has become a promising target for the treatment of Alzheimer's disease (AD) which is mainly associated with low in vivo levels of acetylcholine (ACh). The availability of AChE crystal structures with and without a ligand triggered the effort to find a structure-based design of acetylcholinesterase inhibitors (AChEIs) for AD. The major problem observed with the structure-based design was the feeble robustness of the scoring functions toward the correlation of docking scores with inhibitory potencies of known ligands. This prompted us to develop new prediction models using the stepwise regression analysis based on consensus of different docking and their scoring methods (GOLD, LigandFit, and GLIDE). In the present investigation, a dataset of 91 molecules belonging to 9 different structural classes of heterocyclic compounds with an activity range of 0.008 to 281,000 nM was considered for docking studies and development of AChE-specific 3D-QSAR models. The model (M1) developed using consensus of docking scores of scoring functions viz. Glide score, Gold score, Chem score, ASP score, PMF score, and DOCK score was found to be the best (R(2) = 0.938, Q(2) = 0.925, R(pred)(2) = 0.919, R(2)m((overall)) = 0.936) compared to other consensus models. Docking studies revealed that the molecules with proper alignment in the active site gorge and the ability to interact with all the crucial amino acid residues, in particular by forming π-π stacking interactions with Trp84 at the catalytic anionic site (CAS) and Trp279 at peripheral anionic site (PAS), showed augmented potencies with consequent improvement in patient cognition and reduced the formation of senile plaques associated with AD. Further, the descriptors that signify the association of the ligands with the receptor as well as ADME properties of the ligands were also analyzed by means of the set of ligands that have been pre-positioned with respect to a receptor after docking analysis and considered as independent variables to generate a linear model (M3 and M4) using a stepwise multiple linear regression method to get additional insight into the physicochemical requirements for effective binding of ligands with AChE as well as for prediction of AChE inhibition. The developed AChE-specific prediction models (M1-M4) satisfactorily reflect the structure-activity relationship of the existing AChEIs and have all the potential to facilitate the process of design and development of new potent AChEIs.

Application of conformational clustering in protein-ligand docking

Protein-Ligand docking is a powerful technique routinely employed in structure-based drug design. Despite many reported success stories, docking is not always able to provide an accurate and easily interpretable prediction of the structure of the bound complex formed by a small organic molecule and a pharmacologically relevant target. Cluster analysis can represent a versatile and readily available postprocessing tool to be employed in combination with protein-ligand docking to simplify the evaluation of the results and help to overcome present limitations of docking protocols.

Synthesis, biological evaluation, and molecular modeling of donepezil and N-[(5-(benzyloxy)-1-methyl-1H-indol-2-yl)methyl]-N-methylprop-2-yn-1-amine hybrids as new multipotent cholinesterase/monoamine oxidase inhibitors for the treatment of Alzheimer's disease

A new family of multitarget molecules able to interact with acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), as well as with monoamino oxidase (MAO) A and B, has been synthesized. Novel compounds (3-9) have been designed using a conjunctive approach that combines the benzylpiperidine moiety of the AChE inhibitor donepezil (1) and the indolyl propargylamino moiety of the MAO inhibitor N-[(5-benzyloxy-1-methyl-1H-indol-2-yl)methyl]-N-methylprop-2-yn-1-amine (2), connected through an oligomethylene linker. The most promising hybrid (5) is a potent inhibitor of both MAO-A (IC50=5.2±1.1 nM) and MAO-B (IC50=43±8.0 nM) and is a moderately potent inhibitor of AChE (IC50=0.35±0.01 μM) and BuChE (IC50=0.46±0.06 μM). Moreover, molecular modeling and kinetic studies support the dual binding site to AChE, which explains the inhibitory effect exerted on Aβ aggregation. Overall, the results suggest that the new compounds are promising multitarget drug candidates with potential impact for Alzheimer's disease therapy.

Exploiting the lipoic acid structure in the search for novel multitarget ligands against Alzheimer's disease

Lipoic acid (LA) is a natural antioxidant. Its structure was previously combined with that of the acetylcholinesterase inhibitor tacrine to give lipocrine (1), a lead compound multitargeted against Alzheimer's disease (AD). Herein, we further explore LA as a privileged structure for developing multimodal compounds to investigate AD. First, we studied the effect of LA chirality by evaluating the cholinesterase profile of 1's enantiomers. Then, a new series of LA hybrids was designed and synthesized by combining racemic LA with motifs of other known anticholinesterase agents (rivastigmine and memoquin). This afforded 4, which represents a step forward in the search for balanced anticholinesterase and antioxidant capacities.

Synthetic polyamines as potential amine oxidase inhibitors: a preliminary study

In the last few decades, medicinal chemists have carried out extensive research on synthetic polyamines for use as anticancer drugs and multitarget-directed ligands in neurodegenerative diseases. The aim of this study was to evaluate the effect of some synthetic polyamines as inhibitors of two new potential targets, human semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) and monoamine oxidases B (MAO B), enzymes involved in various multi-factorial diseases such as Alzheimer's disease. N,N'-Dibenzyl-dodecane-1,12-diamine (Bis-Bza-Diado), a newly synthesised compound, and ELP 12, a muscarinic cholinergic M(2) receptor antagonist, were found to behave as reversible and mixed non-competitive inhibitors of both amine oxidases (dissociation constants of about 100 μM). ELP 12 was found to be more selective for SSAO/VAP-1. Combining kinetic and structural approaches, the binding mode of ELP 12 to SSAO/VAP-1 was investigated. ELP 12 may bind at the entrance of the active site channel by ionic interactions with ASP446 and/or ASP180; one end of the polyamine may be accommodated inside the channel, reaching the TPQ cofactor area. The binding of ELP 12 induces rearrangement of the secondary structure of the enzyme and impedes substrate entry and/or product release and catalysis. These structural data reveal that the entrance and the first part of the SSAO/VAP-1 channel may be considered as a new target area, or a "secondary binding site", for modulators of human SSAO/VAP-1 activity. These results indicate ELP 12 and Bis-Bza-Diado as new "skeletons" for the development of novel SSAO/VAP-1 and MAO B inhibitors.

Recent advances in the multitarget-directed ligands approach for the treatment of Alzheimer's disease

With 27 million cases worldwide documented in 2006, Alzheimer's disease (AD) constitutes an overwhelming health, social, economic, and political problem to nations. Unless a new medicine capable to delay disease progression is found, the number of cases will reach 107 million in 2050. So far, the therapeutic paradigm one-compound-one-target has failed. This could be due to the multiple pathogenic mechanisms involved in AD including amyloid β (Aβ) aggregation to form plaques, τ hyperphosphorylation to disrupt microtubule to form neurofibrillary tangles, calcium imbalance, enhanced oxidative stress, impaired mitochondrial function, apoptotic neuronal death, and deterioration of synaptic transmission, particularly at cholinergic neurons. Approximately 100 compounds are presently been investigated directed to single targets, namely inhibitors of β and γ secretase, vaccines or antibodies that clear Aβ, metal chelators to inhibit Aβ aggregation, blockers of glycogen synthase kinase 3β, enhancers of mitochondrial function, antioxidants, modulators of calcium-permeable channels such as voltage-dependent calcium channels, N-methyl-D-aspartate receptors for glutamate, or enhancers of cholinergic neurotransmission such as inhibitors of acetylcholinesterase or butyrylcholinesterase. In view of this complex pathogenic mechanisms, and the successful treatment of chronic diseases such as HIV or cancer, with multiple drugs having complementary mechanisms of action, the concern is growing that AD could better be treated with a single compound targeting two or more of the pathogenic mechanisms leading to neuronal death. This review summarizes the current therapeutic strategies based on the paradigm one-compound-various targets to treat AD. A treatment that delays disease onset and/or progression by 5 years could halve the number of people requiring institutionalization and/or dying from AD. 

The discovery of potential acetylcholinesterase inhibitors: a combination of pharmacophore modeling, virtual screening, and molecular docking studies

BACKGROUND

Alzheimer's disease (AD) is the most common cause of dementia characterized by progressive cognitive impairment in the elderly people. The most dramatic abnormalities are those of the cholinergic system. Acetylcholinesterase (AChE) plays a key role in the regulation of the cholinergic system, and hence, inhibition of AChE has emerged as one of the most promising strategies for the treatment of AD.

METHODS

In this study, we suggest a workflow for the identification and prioritization of potential compounds targeted against AChE. In order to elucidate the essential structural features for AChE, three-dimensional pharmacophore models were constructed using Discovery Studio 2.5.5 (DS 2.5.5) program based on a set of known AChE inhibitors.

RESULTS

The best five-features pharmacophore model, which includes one hydrogen bond donor and four hydrophobic features, was generated from a training set of 62 compounds that yielded a correlation coefficient of R = 0.851 and a high prediction of fit values for a set of 26 test molecules with a correlation of R² = 0.830. Our pharmacophore model also has a high Güner-Henry score and enrichment factor. Virtual screening performed on the NCI database obtained new inhibitors which have the potential to inhibit AChE and to protect neurons from Aβ toxicity. The hit compounds were subsequently subjected to molecular docking and evaluated by consensus scoring function, which resulted in 9 compounds with high pharmacophore fit values and predicted biological activity scores. These compounds showed interactions with important residues at the active site.

CONCLUSIONS

The information gained from this study may assist in the discovery of potential AChE inhibitors that are highly selective for its dual binding sites.

A new class of naphthalimide-based antitumor agents that inhibit topoisomerase II and induce lysosomal membrane permeabilization and apoptosis

Based on the advantages of multitarget drugs for cancer treatment, a new class of naphthalimides was designed, synthesized, and proved to inhibit topoisomerase II (topo II), induced lysosomal membrane permeabilization (LMP), and ultimately caused apoptosis and cell death. The majority of compounds 7a-d and 8a-d potently inhibited the growth of the five tested cancer cell lines with IC(50) values ranging from 2 to 10 microM and are more active than amonafide, a naphthalimide that was in phase III clinical trials. These compounds were tested for their interactions with DNA and their cell-free topo II inhibition activities, which demonstrated these compounds were weak DNA binders but modest topo II inhibitors. Furthermore, compounds 7b-d were found to notably induce LMP and exhibited better antiproliferative activity compared with their single-target analogues. All of the newly synthesized compounds were demonstrated to efficiently induce apoptosis via a mitochondrial pathway. Accordingly, a new paradigm was suggested for the design of novel multitarget anticancer drugs.