Multi-Target Directed Drugs: A Modern Approach for Design of New Drugs 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.

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.

Melatonin as a versatile molecule to design novel multitarget hybrids against neurodegeneration

Melatonin is an indoleamine produced mainly in the pineal gland. The natural decline of melatonin levels with aging strongly contributes to the development of neurodegenerative disorders. Pleiotropic actions displayed by melatonin prevent several processes involved in neurodegeneration such as neuroinflammation, oxidative stress, excitotoxicity and/or apoptosis. This review focuses on a number of melatonin hybrids resulting from the juxtaposition of tacrine, berberine, tamoxifen, curcumin, N,N-dibenzyl(N-methyl)amine, among others, with potential therapeutic effects for the treatment of neurodegenerative diseases.

Novel conjugates of aminoadamantanes with carbazole derivatives as potential multitarget agents for AD treatment

A new group of compounds, promising for the design of original multitarget therapeutic agents for treating neurodegenerative diseases, based on conjugates of aminoadamantane and carbazole derivatives was synthesized and investigated. Compounds of these series were found to interact with a group of targets that play an important role in the development of this type of diseases. First of all, these compounds selectively inhibit butyrylcholinesterase, block NMDA receptors containing NR2B subunits while maintaining the properties of MK-801 binding site blockers, exert microtubules stabilizing properties, and possess the ability to protect nerve cells from death at the calcium overload conditions. The leading compound C-2h has been shown the most promising effects on all analyzed parameters. Thus, these compounds can be regarded as promising candidates for the design of multi-target disease-modifying drugs for treatment of AD and/or similar neuropathologies.

Novel Triazole-Piperazine Hybrid Molecules Induce Apoptosis via Activation of the Mitochondrial Pathway and Exhibit Antitumor Efficacy in Osteosarcoma Xenograft Nude Mice Model

Mitochondria impart a crucial role in the regulation of programmed cell death and reactive oxygen species (ROS) generation, besides serving as a primary energy source. Mitochondria appeared as an important target for the therapy of cancer due to their significant contribution to cell survival and death. Here, we report the design and synthesis of a novel series of triazole-piperazine hybrids as potent anticancer agents. MCS-5 emerged as an excellent anticancer agent which showed better anticancer activity than the standard drug doxorubicin in in vitro and in vivo studies. MCS-5 displayed an IC₅₀ value of 1.92 μM and induced apoptosis in Cal72 (human osteosarcoma cell line) cells by targeting the mitochondrial pathway. This compound arrested the G2/M phase of the cell cycle and induced ROS production and mitochondrial potential collapse in Cal72 cells. MCS-5 displayed excellent anticancer activity in the Cal72 xenograft nude mice model, where it significantly reduced tumor progression, leading to enhanced life span in treated animals compared to control and doxorubicin treated animals without exerting noticeable toxicity. In addition, a 2DG optical probe guided study clearly evoked that MCS-5 remarkably reduced tumor metastasis in the Cal72 xenograft nude mice model. These results indicate that MCS-5 appeared as a novel chemical entity which is endowed with excellent in vitro as well as in vivo anticancer activity and may contribute significantly to the management of cancer in the future.

Computational polypharmacology: a new paradigm for drug discovery

INTRODUCTION

Over the past couple of years, the cost of drug development has sharply increased along with the high rate of clinical trial failures. Such increase in expenses is partially due to the inability of the "one drug - one target" approach to predict drug side effects and toxicities. To tackle this issue, an alternative approach, known as polypharmacology, is being adopted to study small molecule interactions with multiple targets. Apart from developing more potent and effective drugs, this approach allows for studies of off-target activities and the facilitation of drug repositioning. Although exhaustive polypharmacology studies in-vitro or in-vivo are not practical, computational methods of predicting unknown targets or side effects are being developed. Areas covered: This article describes various computational approaches that have been developed to study polypharmacology profiles of small molecules. It also provides a brief description of the algorithms used in these state-of-the-art methods. Expert opinion: Recent success in computational prediction of multi-targeting drugs has established polypharmacology as a promising alternative approach to tackle some of the daunting complications in drug discovery. This will not only help discover more effective agents, but also present tremendous opportunities to study novel target pharmacology and facilitate drug repositioning efforts in the pharmaceutical industry.

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.

Tacrine, Trolox and Tryptoline as Lead Compounds for the Design and Synthesis of Multi-target Agents for Alzheimer's Disease Therapy

The versatile biological activities of tacrine, trolox and β-carboline derivatives make them promising lead structures for the development of multifunctional Alzheimer’s disease (AD) agents. Based on the topology of the active site of cholinesterases and other target proteins involved in the pathogenesis of AD, we have designed and synthesized tacrine-trolox and tacrine-tryptoline hybrids with various linker chain lengths. The hybrids containing the trolox moiety (8a-8d) showed moderate to high TcAChE inhibition (IC₅₀: 17.37 - 2200 nM), eqBuChE inhibition (IC₅₀: 3.16 – 128.82 nM) and free radical scavenging activities (IC₅₀: 11.48 – 49.23 µM). The hybrids with longer linker chain lengths in general showed better ChE inhibitory activity. As expected, free radical scavenging activities were not significantly affected by varying linker chain lengths. The hybrid compound containing the tryptoline moiety linked with a 7 carbon spacer to tacrine (14) displayed the best AChE and BuChE inhibitory activity (IC₅₀ = 17.37 and 3.16 nM). Docking experiments exhibited that compounds 8d and 14 were able to bind to both the CAS and PAS of TcAChE and eqBuChE, suggesting that they will be able to inhibit ChE induced Aβ aggregation. Novel multi-target agents that exhibit good ChE inhibition (8d and 14) and anti-oxidant (8d) activity were identified as suitable candidates for further investigation.

Xanthone and Flavone Derivatives as Dual Agents with Acetylcholinesterase Inhibition and Antioxidant Activity as Potential Anti-Alzheimer Agents

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disorder that is associated with the elderly. The current therapy that is used to treat AD is based mainly on the administration of acetylcholinesterase (AChE) inhibitors. Due to their low efficacy there is a considerable need for other therapeutic strategies. Considering that the malfunctions of different, but interconnected, biochemical complex pathways play an important role in the pathogenesis of this disease, a promising therapy may consist in administration of drugs that act on more than a target on biochemical scenery of AD. In this work, the synthesis and evaluation of xanthone and flavone derivatives as antioxidants with AChE inhibitory activity were accomplished. Among the obtained compounds, Mannich bases3and14showed capacity to inhibit AChE and antioxidant property, exerting dual activity. Moreover, for the most promising AChE inhibitors, docking studies on the target have been performed aiming to predict the binding mechanism. The results presented here may help to identify new xanthone and flavone derivatives as dual anti-Alzheimer agents with AChE inhibitory and antioxidant activities.

Arylidene indanone scaffold: medicinal chemistry and structure–activity relationship view

Arylidene indanone (AI) scaffolds are considered as the rigid cousins of chalcones, incorporating the α,β-unsaturated ketone system of chalcones forming a cyclic 5 membered ring.

AChE Inhibition-based Multi-target-directed Ligands, a Novel Pharmacological Approach for the Symptomatic and Disease-modifying Therapy of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in elder people, characterised by a progressive decline in memory as a result of an impairment of cholinergic neurotransmission. To date acetylcholinesterase inhibitors (AChEIs) have become the most prescribed drugs for the symptomatic treatment of mild to moderate AD. However, the traditional “one molecule-one target” paradigm is not sufficient and appropriate to yield the desired therapeutic efficacy since multiple factors, such as amyloid-β (Aβ) deposits, neuroinflammation, oxidative stress, and decreased levels of acetylcholine (ACh) have been thought to play significant roles in the AD pathogenesis. New generation of multi-target drugs is earnestly demanded not only for ameliorating symptoms but also for modifying the disease. Herein, we delineated the catalytic and non-catalytic functions of AChE, and summarized the works of our group and others in research and development of novel AChEI-based multi-target-directed ligands (MTDLs), such as dual binding site AChEIs and multi-target AChEIs inhibiting Aβ aggregation, regulating Aβ procession, antagonizing platelet-activating factor (PAF) receptor, scavenging oxygen radical, chelating metal ions, inhibiting monoamine oxidase B (MAO-B), blocking N-methyl-D-aspartic acid (NMDA) receptor and others.

Synthesis and anticholinesterase activity of new substituted benzo[d]oxazole-based derivatives

A series of novel benzo[d]oxazole derivatives (6a-n) have been synthesized and biologically evaluated as potential inhibitors of acetylcholinesterases (AChE) and butyrylcholinesterase (BChE). The chemical structures of all final compounds were confirmed by spectroscopic methods. In vitro studies showed that most of the synthesized compounds are potent acetylcholinesterase and butyrylcholinesterase inhibitors. Among them, compounds 6a and 6j strongly inhibited AChE and BChE activities with IC₅₀ values of 1.03-1.35 and 6.6-8.1 μm, respectively. Docking studies also provided the binding modes of action and identified hydrophobic pi forces as the main interaction.

Monoaminergic and Histaminergic Strategies and Treatments in Brain Diseases

The monoaminergic systems are the target of several drugs for the treatment of mood, motor and cognitive disorders as well as neurological conditions. In most cases, advances have occurred through serendipity, except for Parkinson's disease where the pathophysiology led almost immediately to the introduction of dopamine restoring agents. Extensive neuropharmacological studies first showed that the primary target of antipsychotics, antidepressants, and anxiolytic drugs were specific components of the monoaminergic systems. Later, some dramatic side effects associated with older medicines were shown to disappear with new chemical compounds targeting the origin of the therapeutic benefit more specifically. The increased knowledge regarding the function and interaction of the monoaminergic systems in the brain resulting from in vivo neurochemical and neurophysiological studies indicated new monoaminergic targets that could achieve the efficacy of the older medicines with fewer side-effects. Yet, this accumulated knowledge regarding monoamines did not produce valuable strategies for diseases where no monoaminergic drug has been shown to be effective. Here, we emphasize the new therapeutic and monoaminergic-based strategies for the treatment of psychiatric diseases. We will consider three main groups of diseases, based on the evidence of monoamines involvement (schizophrenia, depression, obesity), the identification of monoamines in the diseases processes (Parkinson's disease, addiction) and the prospect of the involvement of monoaminergic mechanisms (epilepsy, Alzheimer's disease, stroke). In most cases, the clinically available monoaminergic drugs induce widespread modifications of amine tone or excitability through neurobiological networks and exemplify the overlap between therapeutic approaches to psychiatric and neurological conditions. More recent developments that have resulted in improved drug specificity and responses will be discussed in this review.

Molecular Signaling Mechanisms of Natural and Synthetic Retinoids for Inhibition of Pathogenesis in Alzheimer's Disease

Retinoids, which are vitamin A derivatives, interact through retinoic acid receptors (RARs) and retinoid X receptors (RXRs) and have profound effects on several physiological and pathological processes in the brain. The presence of retinoic acid signaling is extensively detected in the adult central nervous system, including the amygdala, cortex, hypothalamus, hippocampus, and other brain areas. Retinoids are primarily involved in neural patterning, differentiation, and axon outgrowth. Retinoids also play a key role in the preservation of the differentiated state of adult neurons. Impairment in retinoic acid signaling can result in neurodegeneration and progression of Alzheimer's disease (AD). Recent studies demonstrated severe deficiencies in spatial learning and memory in mice during retinoic acid (vitamin A) deprivation indicating its significance in preserving memory function. Defective cholinergic neurotransmission plays an important role in cognitive deficits in AD. All-trans retinoic acid is known to enhance the expression and activity of choline acetyltransferase in neuronal cell lines. Activation of RAR and RXR is also known to impede the pathogenesis of AD in mice by inhibiting accumulation of amyloids. In addition, retinoids have been shown to inhibit the expression of chemokines and pro-inflammatory cytokines in microglia and astrocytes, which are activated in AD. In this review article, we have described the chemistry and molecular signaling mechanisms of natural and synthetic retinoids and current understandings of their therapeutic potentials in prevention of AD pathology.

The Antioxidant Additive Approach for Alzheimer's Disease Therapy: New Ferulic (Lipoic) Acid Plus Melatonin Modified Tacrines as Cholinesterases Inhibitors, Direct Antioxidants, and Nuclear Factor (Erythroid-Derived 2)-Like 2 Activators

Novel multifunctional tacrines for Alzheimer's disease were obtained by Ugi-reaction between ferulic (or lipoic acid), a melatonin-like isocyanide, formaldehyde, and tacrine derivatives, according to the antioxidant additive approach in order to modulate the oxidative stress as therapeutic strategy. Compound 5c has been identified as a promising permeable agent showing excellent antioxidant properties, strong cholinesterase inhibitory activity, less hepatotoxicity than tacrine, and the best neuroprotective capacity, being able to significantly activate the Nrf2 transcriptional pathway.

Synthesis and antitumor activity of selenium-containing quinone-based triazoles possessing two redox centres, and their mechanistic insights

Selenium-containing quinone-based 1,2,3-triazoles were synthesized using click chemistry, the copper catalyzed azide-alkyne 1,3-dipolar cycloaddition, and evaluated against six types of cancer cell lines: HL-60 (human promyelocytic leukemia cells), HCT-116 (human colon carcinoma cells), PC3 (human prostate cells), SF295 (human glioblastoma cells), MDA-MB-435 (melanoma cells) and OVCAR-8 (human ovarian carcinoma cells). Some compounds showed IC50 values < 0.3 μM. The cytotoxic potential of the quinones evaluated was also assayed using non-tumor cells, exemplified by peripheral blood mononuclear (PBMC), V79 and L929 cells. Mechanistic role for

NAD(P)H

Quinone Oxidoreductase 1 (NQO1) was also elucidated. These compounds could provide promising new lead derivatives for more potent anticancer drug development and delivery, and represent one of the most active classes of lapachones reported.

Synthesis and evaluation of 4-hydroxyl aurone derivatives as multifunctional agents for the treatment of Alzheimer's disease

A series of 4-hydroxyl aurone derivatives were designed synthesized and evaluated as potential multifunctional agents for the treatment of Alzheimer's disease. The results demonstrated that most of the derivatives exhibited good multifunctional properties. Among them, compound 14e displayed good inhibitory activities of self- and Cu(2+)-induced Aβ1-42 aggregation with 99.2% and 84.0% at 25μM, respectively, and high antioxidant activity with a value 1.90-fold of Trolox. In addition, 14e also showed remarkable inhibitory activities of both monoamine oxidase A and B with IC50 values of 0.271μM and 0.393μM, respectively. However the 6-methoxyl aurones 15a-c revealed excellent selectivity toward MAO-B. Furthermore, the representative compounds 14e and 15b displayed good metal-chelating abilities and blood-brain barrier (BBB) permeabilities in vitro.

Synthesis, Molecular Modelling and Biological Evaluation of Novel Heterodimeric, Multiple Ligands Targeting Cholinesterases and Amyloid Beta

Cholinesterases and amyloid beta are one of the major biological targets in the search for a new and efficacious treatment of Alzheimer's disease. The study describes synthesis and pharmacological evaluation of new compounds designed as dual binding site acetylcholinesterase inhibitors. Among the synthesized compounds, two deserve special attention--compounds 42 and 13. The former is a saccharin derivative and the most potent and selective acetylcholinesterase inhibitor (EeAChE IC50 = 70 nM). Isoindoline-1,3-dione derivative 13 displays balanced inhibitory potency against acetyl- and butyrylcholinesterase (BuChE) (EeAChE IC50 = 0.76 μM, EqBuChE IC50 = 0.618 μM), and it inhibits amyloid beta aggregation (35.8% at 10 μM). Kinetic studies show that the developed compounds act as mixed or non-competitive acetylcholinesterase inhibitors. According to molecular modelling studies, they are able to interact with both catalytic and peripheral active sites of the acetylcholinesterase. Their ability to cross the blood-brain barrier (BBB) was confirmed in vitro in the parallel artificial membrane permeability BBB assay. These compounds can be used as a solid starting point for further development of novel multifunctional ligands as potential anti-Alzheimer's agents.

Sulforaphane exerts its anti-inflammatory effect against amyloid-β peptide via STAT-1 dephosphorylation and activation of Nrf2/HO-1 cascade in human THP-1 macrophages

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide, accounting for most cases of dementia in elderly individuals, and effective therapies are still lacking. This study was designed to investigate the anti-inflammatory properties of sulforaphane against Aβ1-42 monomers in human THP-1 microglia-like cells. The results showed that sulforaphane preferentially inhibited cathepsin B- and caspase-1-dependent NLRP3 inflammasome activation induced by mostly Aβ1-42 monomers, an effect that potently reduced excessive secretion of the proinflammatory cytokine interleukin-1β (IL-1β). Subsequent mechanistic studies revealed that sulforaphane mitigated the activation of signal transducer and activator of transcription-1 induced by Aβ1-42 monomers. Sulforaphane also increased nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation, which was followed by upregulation of heme-oxygenase 1 (HO-1). The anti-inflammatory effect of sulforaphane on Aβ1-42-induced IL-1β production was diminished by small interfering RNA-mediated knockdown of Nrf2 or HO-1. Moreover, sulforaphane significantly attenuated the levels of microRNA-146a, which is selectively upregulated in the temporal cortex and hippocampus of AD brains. The aforementioned effects of sulforaphane were replicated by the tyrosine kinase inhibitor, herbimycin A, and Nrf2 activator. These results indicate that signal transducer and activator of transcription-1 dephosphorylation, HO-1 and its upstream effector, Nrf2, play a pivotal role in triggering an anti-inflammatory signaling cascade of sulforaphane that results in decreases of IL-1β release and microRNA-146a production in Aβ1-42-stimulated human microglia-like cells. These findings suggest that the phytochemical sulforaphane has a potential application in AD therapeutics.

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

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

Multi-target pharmacology: possibilities and limitations of the "skeleton key approach" from a medicinal chemist perspective

Multi-target drugs have raised considerable interest in the last decade owing to their advantages in the treatment of complex diseases and health conditions linked to drug resistance issues. Prospective drug repositioning to treat comorbid conditions is an additional, overlooked application of multi-target ligands. While medicinal chemists usually rely on some version of the lock and key paradigm to design novel therapeutics, modern pharmacology recognizes that the mid- and long-term effects of a given drug on a biological system may depend not only on the specific ligand-target recognition events but also on the influence of the repeated administration of a drug on the cell gene signature. The design of multi-target agents usually imposes challenging restrictions on the topology or flexibility of the candidate drugs, which are briefly discussed in the present article. Finally, computational strategies to approach the identification of novel multi-target agents are overviewed.

Structure-based development of nitroxoline derivatives as potential multifunctional anti-Alzheimer agents

Tremendous efforts have been dedicated to the development of effective therapeutics against Alzheimer's disease, which represents the most common debilitating neurodegenerative disease. Multifunctional agents are molecules designed to have simultaneous effects on different pathological processes. Such compounds represent an emerging strategy for the development of effective treatments against Alzheimer's disease. Here, we report on the synthesis and biological evaluation of a series of nitroxoline-based analogs that were designed by merging the scaffold of 8-hydroxyquinoline with that of a known selective butyrylcholinesterase inhibitor that has promising anti-Alzheimer properties. Most strikingly, compound 8g inhibits self-induced aggregation of the amyloid beta peptide (Aβ1-42), inhibits with sub-micromolar potency butyrylcholinesterase (IC50=215 nM), and also selectively complexes Cu(2+). Our study thus designates this compound as a promising multifunctional agent for therapeutic treatment of Alzheimer's disease. The crystal structure of human butyrylcholinesterase in complex with compound 8g is also solved, which suggests ways to further optimize compounds featuring the 8-hydroxyquinoline scaffold.