Dual-Acting Cholinesterase-Human Cannabinoid Receptor 2 Ligands Show Pronounced Neuroprotection in Vitro and Overadditive and Disease-Modifying Neuroprotective Effects in Vivo

A systematic review of novel cannabinoids and their targets: Insights into the significance of structure in activity

To provide a comprehensive framework of the current information on the potency and efficacy of interaction between phyto- and synthetic cannabinoids and their respective receptors, an electronic search of the PubMed, Scopus, and EMBASE literature was performed. Experimental studies included reports of mechanistic data providing affinity, efficacy, and half-maximal effective concentration (EC50). Among the 108 included studies, 174 structures, and 16 targets were extracted. The most frequent ligands belonged to the miscellaneous category with 40.2% followed by phytocannabinoid-similar, indole-similar, and pyrrole-similar structures with an abundance of 17.8%, 16.6%, and 12% respectively. 64.8% of structures acted as agonists, 17.1 % appeared as inverse agonists, 10.8% as antagonists, and 7.2% of structures were reported with antagonist/inverse agonist properties. Our outcomes identify the affinity, EC50, and efficacy of the interactions between cannabinoids and their corresponding receptors and the subsequent response, evaluated in the available evidence. Considering structures' significance and very important effects of on the activities, the obtained results also provide clues to drug repurposing.

Patent review of cannabinoid receptor type 2 (CB2R) modulators (2016-present)

INTRODUCTION

Cannabinoid receptor type 2 (CB2R), predominantly expressed in immune tissues, is believed to play a crucial role within the body's protective mechanisms. Its modulation holds immense therapeutic promise for addressing a wide spectrum of dysbiotic conditions, including cardiovascular, gastrointestinal, liver, kidney, neurodegenerative, psychiatric, bone, skin, and autoimmune diseases, as well as lung disorders, cancer, and pain management.

AREAS COVERED

This review is an account of patents from 2016 up to 2023 which describes novel CB2R ligands, therapeutic applications, synthesis, as well as formulations of CB2R modulators.

EXPERT OPINION

The patents cover a vast, structurally diverse chemical space. The focus of CB2R ligand development has shifted from unselective dual-cannabinoid receptor type 1 (CB1R) and 2 agonists toward agonists with high selectivity over CB1R, particularly for indications associated with inflammation and tissue injury. Currently, there are at least eight CB2R agonists and one antagonist in active clinical development. A better understanding of the endocannabinoid system (ECS) and in particular of CB2R pharmacology is required to unlock the receptor's full therapeutic potential.

New insights into butyrylcholinesterase: Pharmaceutical applications, selective inhibitors and multitarget-directed ligands

Butyrylcholinesterase (BChE), also known as pseudocholinesterase and serum cholinesterase, is an isoenzyme of acetylcholinesterase (AChE). It mediates the degradation of acetylcholine, especially under pathological conditions. Proverbial pharmacological applications of BChE, its mutants and modulators consist of combating Alzheimer's disease (AD), influencing multiple sclerosis (MS), addressing cocaine addiction, detoxifying organophosphorus poisoning and reflecting the progression or prognosis of some diseases. Of interest, recent reports have shed light on the relationship between BChE and lipid metabolism. It has also been proved that BChE is going to increase abnormally as a compensator for AChE in the middle and late stages of AD, and BChE inhibitors can alleviate cognitive disorders and positively influence some pathological features in AD model animals, foreboding favorable prospects and potential applications. Herein, the selective BChE inhibitors and BChE-related multitarget-directed ligands published in the last three years were briefly summarized, along with the currently known pharmacological applications of BChE, aiming to grasp the latest research directions. Thereinto, some emerging strategies for designing BChE inhibitors are intriguing, and the modulators based on target combination of histone deacetylase and BChE against AD is unprecedented. Furthermore, the involvement of BChE in the hydrolysis of ghrelin, the inhibition of low-density lipoprotein (LDL) uptake, and the down-regulation of LDL receptor (LDLR) expression suggests its potential to influence lipid metabolism disorders. This compelling prospect likely stimulates further exploration in this promising research direction.

Benzimidazole and Benzoxazole Derivatives Against Alzheimer's Disease

Benzimidazole and benzoxazole derivatives are included in the category of medical drugs in a wide range of areas such as anticancer, anticoagulant, antihypertensive, anti- inflammatory, antimicrobial, antiparasitic, antiviral, antioxidant, immunomodulators, proton pump inhibitors, hormone modulators, etc. Many researchers have focused on synthesizing more effective benzimidazole and benzoxazole derivatives for screening various biological activities. In addition, there are benzimidazole and benzoxazole rings as bioisosteres of aromatic rings found in drugs used in the treatment of Alzheimer's disease. Because of the diverse activity of the benzimidazole and benzoxazole rings and bioisosteres marketed as drugs for Alzheimer Diseases, designed compounds containing these rings are likely to be effective against Alzheimer's disease. In this study, the effectiveness of compounds containing benzimidazole and benzoxazole rings against Alzheimer's disease will be examined.

Novel Dual-Acting Hybrids Targeting Type-2 Cannabinoid Receptors and Cholinesterase Activity Show Neuroprotective Effects In Vitro and Amelioration of Cognitive Impairment In Vivo

Alzheimer's disease (AD) is a neurodegenerative form of dementia characterized by the loss of synapses and a progressive decline in cognitive abilities. Among current treatments for AD, acetylcholinesterase (AChE) inhibitors have efficacy limited to symptom relief, with significant side effects and poor compliance. Pharmacological agents that modulate the activity of type-2 cannabinoid receptors (CB2R) of the endocannabinoid system by activating or blocking them have also been shown to be effective against neuroinflammation. Herein, we describe the design, synthesis, and pharmacological effects in vitro and in vivo of dual-acting compounds that inhibit AChE and butyrylcholinesterase (BChE) and target CB2R. Within the investigated series, compound 4g proved to be the most promising. It achieved IC50 values in the low micromolar to submicromolar range against both human cholinesterase isoforms while antagonizing CB2R with Ki of 31 nM. Interestingly, 4g showed neuroprotective effects on the SH-SY5Y cell line thanks to its ability to prevent oxidative stress-induced cell toxicity and reverse scopolamine-induced amnesia in the Y-maze forced alternation test in vivo.

A Novel Hybrid of Telmisartan and Borneol Ameliorates Neuroinflammation and White Matter Injury in Ischemic Stroke Through ATF3/CH25H Axis

Cerebral ischemic stroke causes substantial white matter injury, which is further aggravated by neuroinflammation mediated by microglia/astrocytes. Given the anti-neuroinflammatory action of telmisartan and the enhancing blood-brain barrier (BBB) permeability potential of resuscitation-inducing aromatic herbs, 13 hybrids (3a-m) of telmisartan (or its simplified analogues) with resuscitation-inducing aromatic agents were designed, synthesized, and biologically evaluated. Among them, the optimal compound 3a (the ester hybrid of telmisartan and (+)-borneol) potently inhibited neuroinflammation mediated by microglia/astrocytes and ameliorated ischemic stroke. Particularly, 3a significantly conferred protection for white matter integrity after cerebral ischemic stroke via decreasing abnormally dephosphorylated neurofilament protein, upregulating myelin basic protein, and attenuating oligodendrocyte damage. Further RNA-sequencing data revealed that 3a upregulated expression of transcriptional regulator ATF3 to reduce the expression of CH25H, prevented proinflammatory state of lipid-droplet-accumulating microglia/astrocytes to limit excessive inflammation, and eventually protected neighboring oligodendrocytes to prevent white matter injury. Taken with the desirable pharmacokinetics behavior and improved brain distribution, 3a may be a feasible therapeutic agent for ischemic stroke and other neurological disorders with white matter injury.

Visible-Light Photoswitchable Benzimidazole Azo-Arenes as β-Arrestin2-Biased Selective Cannabinoid 2 Receptor Agonists

The cannabinoid 2 receptor (CB2 R) has high therapeutic potential for multiple pathogenic processes, such as neuroinflammation. Pathway-selective ligands are needed to overcome the lack of clinical success and to elucidate correlations between pathways and their respective therapeutic effects. Herein, we report the design and synthesis of a photoswitchable scaffold based on the privileged structure of benzimidazole and its application as a functionally selective CB2 R "efficacy-switch". Benzimidazole azo-arenes offer huge potential for the broad extension of photopharmacology to a wide range of optically addressable biological targets. We used this scaffold to develop compound 10 d, a "trans-on" agonist, which serves as a molecular probe to study the β-arrestin2 (βarr2) pathway at CB2 R. βΑrr2 bias was observed in CB2 R internalization and βarr2 recruitment, while no activation occurred when looking at Gα16 or mini-Gαi . Overall, compound 10 d is the first light-dependent functionally selective agonist to investigate the complex mechanisms of CB2 R-βarr2 dependent endocytosis.

Bridging the Binding Sites 2.0: Photoswitchable Dualsteric Ligands for the Cannabinoid 2 Receptor

The cannabinoid receptor 2 (CB2R) has high, unexploited therapeutic potential in several central nervous system disorders due to its involvement in neuroinflammatory processes and pathologies like neurodegeneration. Dualsteric/bitopic ligands are currently developed to achieve receptor subtype selectivity and biased signaling. To obtain a molecular tool compound with photoswitchable potential dualsteric properties, we applied two different approaches to link a positive allosteric modulator with an orthosteric agonist via a photochromic unit. We characterized the photophysical properties of all compounds and determined efficacy in internalization, calcium mobilization, and BRET studies. We report the first potentially dualsteric photoswitchable ligand for studying molecular mechanisms of CB2R-associated pathologies. Compound 17-para is a submicromolar "cis-on" agonist with >10-fold higher potency compared to its trans photoisomer and allows high spatiotemporal control of CB2R activation.

Dual-Acting Small Molecules: Subtype-Selective Cannabinoid Receptor 2 Agonist/Butyrylcholinesterase Inhibitor Hybrids Show Neuroprotection in an Alzheimer's Disease Mouse Model

We present the synthesis and characterization of merged human butyrylcholinesterase (hBChE) inhibitor/cannabinoid receptor 2 (hCB₂R) ligands for the treatment of neurodegeneration. In total, 15 benzimidazole carbamates were synthesized and tested for their inhibition of human cholinesterases, also with regard to their pseudoirreversible binding mode and affinity toward both cannabinoid receptors in radioligand binding studies. After evaluation in a calcium mobilization assay as well as a β-arrestin 2 (βarr2) recruitment assay, two compounds with balanced activities on both targets were tested for their immunomodulatory effect on microglia activation and regarding their pharmacokinetic properties and blood-brain barrier penetration. Compound 15d, containing a dimethyl carbamate motif, was further evaluated in vivo, showing prevention of Aβ_25-35-induced learning impairments in a pharmacological mouse model of Alzheimer's disease for both short- and long-term memory responses. Additional combination studies proved a synergic effect of BChE inhibition and CB₂R activation in vivo.

Discovery of 4-(1,2,4-Oxadiazol-5-yl)azepan-2-one Derivatives as a New Class of Cannabinoid Type 2 Receptor Agonists for the Treatment of Inflammatory Pain

Selectively targeting the cannabinoid receptor CB2 is an attractive therapeutic strategy for the treatment of inflammatory pain without psychiatric side effects mediated by the cannabinoid receptor CB1. Herein, we report the discovery of 4-(1,2,4-oxadiazol-5-yl)azepan-2-one derivatives as a new class of CB2 agonists. Systematic structure-activity relationship investigations resulted in the identification of the most potent compound 25r. This compound displayed high selectivity for CB2 against CB1 (CB2 EC₅₀ = 21.0 nM, E_max = 87%, CB1 EC₅₀ > 30 μM, ratio CB1/CB2 > 1428) with favorable pharmacokinetic properties. Especially, 25r demonstrated significant efficacy in the analgesic model of rodent inflammatory pain. All the results suggest that compound 25r could serve as a lead compound for treating inflammatory pain and deserves further in-depth studies.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

SAR investigation and optimization of benzimidazole-based derivatives as antimicrobial agents against Gram-negative bacteria

Antibiotic-resistant bacteria represent a serious threat to modern medicine and human life. Only a minority of antibacterial agents are active against Gram-negative bacteria. Hence, the development of novel antimicrobial agents will always be a vital need. In an effort to discover new therapeutics against Gram-negative bacteria, we previously reported a structure-activity-relationship (SAR) study on 1,2-disubstituted benzimidazole derivatives. Compound III showed a potent activity against tolC-mutant Escherichia coli with an MIC value of 2 μg/mL, representing a promising lead for further optimization. Building upon this study, herein, 49 novel benzimidazole compounds were synthesized to investigate their antibacterial activity against Gram-negative bacteria. Our design focused on three main goals, to address the low permeability of our compounds and improve their cellular accumulation, to expand the SAR study to the unexplored ring C, and to optimize the lead compound (III) by modification of the methanesulfonamide moiety. Compounds (25a-d, 25f-h, 25k, 25l, 25p, 25r, 25s, and 26b) exhibited potent activity against tolC-mutant E. coli with MIC values ranging from 0.125 to 4 μg/mL, with compound 25d displaying the highest potency among the tested compounds with an MIC value of 0.125 μg/mL. As its predecessor, III, compound 25d exhibited an excellent safety profile without any significant cytotoxicity to mammalian cells. Time-kill kinetics assay indicated that 25d exhibited a bacteriostatic activity and significantly reduced E. coli JW55031 burden as compared to DMSO. Additionally, combination of 25d with colistin partially restored its antibacterial activity against Gram-negative bacterial strains (MIC values ranging from 4 to 16 μg/mL against E. coli BW25113, K. pneumoniae, A. baumannii, and P. aeruginosa). Furthermore, formulation of III and 25d as lipidic nanoparticles (nanocapsules) resulted in moderate enhancement of their antibacterial activity against Gram-negative bacterial strains (A. Baumannii, N. gonorrhoeae) and compound 25d demonstrated superior activity to the lead compound III. These findings establish compound 25d as a promising candidate for treatment of Gram-negative bacterial infections and emphasize the potential of nano-formulations in overcoming poor cellular accumulation in Gram-negative bacteria where further optimization and investigation are warranted to improve the potency and broaden the spectrum of our compounds.

Cannabidiol repairs behavioral and brain disturbances in a model of fetal alcohol spectrum disorder

Fetal alcohol spectrum disorder (FASD) includes neuropsychiatric disturbances related to gestational and lactational ethanol exposure. Available treatments are minimal and do not modulate ethanol-induced damage. Developing animal models simulating FASD is essential for understanding the underlying brain alterations and searching for efficient therapeutic approaches. The main goal of this study was to evaluate the effects of early and chronic cannabidiol (CBD) administration on offspring exposed to an animal model of FASD. Ethanol gavage (3 g/kg/12 h, p.o.) was administered to C57BL/6 J female mice, with a previous history of alcohol consumption, between gestational day 7 and postnatal day 21. On the weaning day, pups were separated by sex, and CBD administration began (30 mg/kg/day, i.p.). After 4-6 weeks of treatment, behavioral and neurobiological changes were analyzed. Mice exposed to the animal model of FASD showed higher anxiogenic and depressive-like behaviors and cognitive impairment that were evaluated through several experimental tests. These behaviors were accompanied by alterations in the gene, cellular and metabolomic targets. CBD administration normalized FASD model-induced emotional and cognitive disturbances, gene expression, and cellular changes with sex-dependent differences. CBD modulates the metabolomic changes detected in the hippocampus and prefrontal cortex. Interestingly, no changes were found in mitochondria or the oxidative status of the cells. These results suggest that the early and repeated administration of CBD modulated the long-lasting behavioral, gene and protein alterations induced by the FASD model, encouraging the possibility of performing clinical trials to evaluate the effects of CBD in children affected with FASD.

In silico and in vitro studies confirm Ondansetron as a novel acetylcholinesterase and butyrylcholinesterase inhibitor

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is growing rapidly among the elderly population around the world. Studies show that a lack of acetylcholine and butyrylcholine due to the overexpression of enzymes Acetylcholinesterase (AChE) and Butyrylcholinesterase (BChE) may lead to reduced communication between neuron cells. As a result, seeking novel inhibitors targeting these enzymes might be vital for the future treatment of AD. Ondansetron is used to prevent nausea and vomiting caused by chemotherapy or radiation treatments and is herein shown to be a potent inhibitor of cholinesterase. Comparison is made between Ondansetron and FDA-approved cholinesterase inhibitors Rivastigmine and Tacrine. Molecular docking demonstrates that interactions between the studied ligand and aromatic residues in the peripheral region of the active site are important in binding. Molecular dynamics simulations and binding pose metadynamics show that Ondansetron is highly potent against both enzymes and far better than Rivastigmine. Inhibitor activities evaluated by in vitro studies confirm that the drug inhibits AChE and BChE by non-competitive and mixed inhibition, respectively, with IC₅₀ values 33 µM (AChE) and 2.5 µM (BChE). Based on the findings, we propose that Ondansetron may have therapeutic applications in inhibiting cholinesterase, especially for BChE.

Current Pharmacotherapy and Multi-Target Approaches for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by decreased synaptic transmission and cerebral atrophy with appearance of amyloid plaques and neurofibrillary tangles. Cognitive, functional, and behavioral alterations are commonly associated with the disease. Different pathophysiological pathways of AD have been proposed, some of which interact and influence one another. Current treatment for AD mainly involves the use of therapeutic agents to alleviate the symptoms in AD patients. The conventional single-target treatment approaches do not often cause the desired effect in the disease due to its multifactorial origin. Thus, multi-target strategies have since been undertaken, which aim to simultaneously target multiple targets involved in the development of AD. In this review, we provide an overview of the pathogenesis of AD and the current drug therapies for the disease. Additionally, rationales of the multi-target approaches and examples of multi-target drugs with pharmacological actions against AD are also discussed.

Evaluation of cannabinoid type 2 receptor expression and pyridine-based radiotracers in brains from a mouse model of Alzheimer’s disease

Neuroinflammation plays an important role in the pathophysiology of Alzheimer’s disease. The cannabinoid type 2 receptor (CB2R) is an emerging target for neuroinflammation and therapeutics of Alzheimer’s disease. Here, we aim to assess the alterations in brain CB2R levels and evaluate novel CB2R imaging tracers in the arcAß mouse model of Alzheimer’s disease amyloidosis. Immunohistochemical staining for amyloid-ß deposits (6E10), microgliosis (anti-Iba1 and anti-CD68 antibodies), astrocytes (GFAP) and the anti-CB2R antibody was performed on brain slices from 17-month-old arcAß mice. Autoradiography using the CB2R imaging probes [18F]RoSMA-18-d6, [11C]RSR-056, and [11C]RS-028 and mRNA analysis were performed in brain tissue from arcAß and non-transgenic littermate (NTL) mice at 6, 17, and 24 months of age. Specific increased CB2R immunofluorescence intensities on the increased number of GFAP-positive astrocytes and Iba1-positive microglia were detected in the hippocampus and cortex of 17-month-old arcAß mice compared to NTL mice. CB2R immunofluorescence was higher in glial cells inside 6E10-positive amyloid-ß deposits than peri-plaque glial cells, which showed low background immunofluorescence in the hippocampus and cortex of 17-month-old arcAß mice. Ex vivo autoradiography showed that the specific binding of [18F]RoSMA-18-d6 and [11C]RSR-056 was comparable in arcAß and NTL mice at 6, 17, and 24 months of age. The level of Cnr2 mRNA expression in the brain was not significantly different between arcAß and NTL mice at 6, 17, or 24 months of age. In conclusion, we demonstrated pronounced specific increases in microglial and astroglial CB2R expression levels in a mouse model of AD-related cerebral amyloidosis, emphasizing CB2R as a suitable target for imaging neuroinflammation.

Novel benzimidazole-based pseudo-irreversible butyrylcholinesterase inhibitors with neuroprotective activity in an Alzheimer's disease mouse model

As levels of acetylcholinesterase (AChE) decrease while levels of butyrylcholinesterase (BChE) increase in later stages of Alzheimer's disease (AD), BChE stands out as a promising target for treatment of AD. Therefore, several benzimidazole-carbamates were designed based on docking studies to inhibit BChE selectively over AChE, while retaining a reasonable solubility. Synthesized molecules exhibit IC50 values from 2.4 μM down to 3.7 nM with an overall highly hBChE-selective profile of the designed compound class. After evaluation of potential neurotoxicity, the most promising compound was further investigated in vivo. Compound 11d attenuates Aβ25-35-induced learning impairments in both spontaneous alternation and passive avoidance responses at a very low dosage of 0.03 mg kg-1, proving selective BChE inhibition to lead to effective neuroprotectivity in AD.

N-linoleyltyrosine exerts neuroprotective effects in APP/PS1 transgenic mice via cannabinoid receptor-mediated autophagy

Anandamide (AEA) analogs show fair effects in counteracting the deterioration of Alzheimer's disease (AD). Our previous studies demonstrated that AEA analog-N-linoleyltyrosine (NITyr) exerted significant activities. In our current research, the role and mechanisms of NITyr were assessed in APP/PS1 mice mimicking the AD model. NITyr improved motor coordination in the rotarod test (RRT) and ameliorated spatial memory in the Morris water maze (MWM) but did not increase spontaneous locomotor activity in the open field test (OFT). In addition, NITyr protected neurons against β-amyloid (Aβ) injury via hematoxylin-eosin (HE) and Nissl staining. Moreover, the related biochemical indexes showed that NITyr reduced the levels of Aβ40 and Aβ42 in the hippocampus but did not affect the expression of p-APP and β-secretase 1 (BACE1). Furthermore, the autophagy inhibitor 3-methyladenine (3 MA) attenuated the effect of NITyr on animal behaviors and neurons. Meanwhile, NITyr upregulated the expression levels of LC3-II and Beclin-1, which were weakened by AM630 (an antagonist of CB2 receptor and a weak partial agonist of CB1 receptors). AM630 also weakened the role of NITyr in animal behaviors. Thus, NITyr improved behavioral impairment and neural loss by inducing autophagy mainly mediated by the CB2 receptor, and weakly mediated by the CB1 receptor.

A ratiometric near-infrared fluorescent probe based on a novel reactive cyanine platform for mitochondrial pH detection

A near-infrared reactive cyanine platform (probe A) was prepared by condensation of 9-chloro-1,2,3,4-tetrahydro-10-methyl-acridinium iodide with Fisher's aldehyde. A near-infrared fluorescent probe (probe B) was prepared by modifying a reactive chlorine atom of probe A with tert-butyl(2-aminoethyl)carbamate through a substitution reaction. The deprotection of the Boc group of probe B was achieved under an acidic condition, affording an amine-functionalized cyanine dye (probe C). A near-infrared ratiometric fluorescent probe (probe D) for mitochondrial pH detection was synthesized by conjugating a FRET coumarin donor to a FRET cyanine acceptor (probe C) through an amide bond connection. Probe A shows low fluorescence of 2% due to an electron-withdrawing chlorine atom, while probes B-D display high fluorescence quantum yields of 60%, 32%, and 35% in aqueous solutions containing 10% ethanol, respectively. Probes B-D show strong fluorescence with push-pull molecular structures in neutral and basic pH conditions. However, protonation of the probe's second amine at the 9-position under acidic condition disrupts the push-pull feature of the probes, resulting in fluorescence quenching of the new cyanine fluorophores. The probes can selectively stain mitochondria, while probe D was employed to detect pH changes in HeLa cells and Drosophila melanogaster first-instar larvae.

Selective Pseudo-irreversible Butyrylcholinesterase Inhibitors Transferring Antioxidant Moieties to the Enzyme Show Pronounced Neuroprotective Efficacy In Vitro and In Vivo in an Alzheimer's Disease Mouse Model

A series of multitarget-directed ligands (MTDLs) was designed by functionalizing a pseudo-irreversible butyrylcholinesterase (BChE) inhibitor. The obtained hybrids were investigated in vitro regarding their hBChE and hAChE inhibition, their enzyme kinetics, and their antioxidant physicochemical properties (DPPH, ORAC, metal chelating). In addition, in vitro assays were applied to investigate antioxidant effects using murine hippocampal HT22 cells and immunomodulatory effects on the murine microglial N9 cell line. The MTDLs retained their antioxidative properties compared to the parent antioxidant-moieties in vitro and the inhibition of hBChE was maintained in the submicromolar range. Representative compounds were tested in a pharmacological Alzheimer's disease (AD) mouse model and demonstrated very high efficacy at doses as low as 0.1 mg/kg. The most promising compound was also tested in BChE^-/- mice and showed reduced efficacy. In vivo neuroprotection by BChE inhibition can be effectively enhanced by incorporation of structurally diverse antioxidant moieties.

Potential and Limits of Cannabinoids in Alzheimer's Disease Therapy

Simple Summary

This review was aimed at exploring the potentiality of drugging the endocannabinoid system as a therapeutic option for Alzheimer’s disease (AD). Recent discoveries have demonstrated how the modulation of cannabinoid receptor 1 (CB1) and receptor 2 (CB2) can exert neuroprotective effects without the recreational and pharmacological properties of Cannabis sativa. Thus, this review explores the potential of cannabinoids in AD, also highlighting their limitations in perspective to point out the need for further research on cannabinoids in AD therapy.

Abstract

Alzheimer’s disease (AD) is a detrimental brain disorder characterized by a gradual cognitive decline and neuronal deterioration. To date, the treatments available are effective only in the early stage of the disease. The AD etiology has not been completely revealed, and investigating new pathological mechanisms is essential for developing effective and safe drugs. The recreational and pharmacological properties of marijuana are known for centuries, but only recently the scientific community started to investigate the potential use of cannabinoids in AD therapy—sometimes with contradictory outcomes. Since the endocannabinoid system (ECS) is highly expressed in the hippocampus and cortex, cannabis use/abuse has often been associated with memory and learning dysfunction in vulnerable individuals. However, the latest findings in AD rodent models have shown promising effects of cannabinoids in reducing amyloid plaque deposition and stimulating hippocampal neurogenesis. Beneficial effects on several dementia-related symptoms have also been reported in clinical trials after cannabinoid treatments. Accordingly, future studies should address identifying the correct therapeutic dosage and timing of treatment from the perspective of using cannabinoids in AD therapy. The present paper aims to summarize the potential and limitations of cannabinoids as therapeutics for AD, focusing on recent pre-clinical and clinical evidence.

Multidirectional in vitro and in cellulo studies as a tool for identification of multi-target-directed ligands aiming at symptoms and causes of Alzheimer's disease

Effective therapy of Alzheimer's disease (AD) requires treatment with a combination of drugs that modulate various pathomechanisms contributing to the disease. In our research, we have focused on the development of multi-target-directed ligands - 5-HT₆ receptor antagonists and cholinesterase inhibitors - with disease-modifying properties. We have performed extended in vitro (FRET assay) and in cellulo (Escherichia coli model of protein aggregation) studies on their β-secretase, tau, and amyloid β aggregation inhibitory activity. Within these multifunctional ligands, we have identified compound 17 with inhibitory potency against tau and amyloid β aggregation in in cellulo assay of 59% and 56% at 10 µM, respectively, hBACE IC₅₀=4 µM, h5TH6 K _i=94 nM, hAChE IC₅₀=26 nM, and eqBuChE IC₅₀=5 nM. This study led to the development of multifunctional ligands with a broad range of biological activities crucial not only for the symptomatic but also for the disease-modifying treatment of AD.

Azobioisosteres of Curcumin with Pronounced Activity against Amyloid Aggregation, Intracellular Oxidative Stress, and Neuroinflammation

Many (poly-)phenolic natural products, for example, curcumin and taxifolin, have been studied for their activity against specific hallmarks of neurodegeneration, such as amyloid-β 42 (Aβ42) aggregation and neuroinflammation. Due to their drawbacks, arising from poor pharmacokinetics, rapid metabolism, and even instability in aqueous medium, the biological activity of azobenzene compounds carrying a pharmacophoric catechol group, which have been designed as bioisoteres of curcumin has been examined. Molecular simulations reveal the ability of these compounds to form a hydrophobic cluster with Aβ42, which adopts different folds, affecting the propensity to populate fibril-like conformations. Furthermore, the curcumin bioisosteres exceeded the parent compound in activity against Aβ42 aggregation inhibition, glutamate-induced intracellular oxidative stress in HT22 cells, and neuroinflammation in microglial BV-2 cells. The most active compound prevented apoptosis of HT22 cells at a concentration of 2.5 μm (83 % cell survival), whereas curcumin only showed very low protection at 10 μm (21 % cell survival).

Discovery of multifunctional anti-Alzheimer's agents with a unique mechanism of action including inhibition of the enzyme butyrylcholinesterase and γ-aminobutyric acid transporters

Looking for an effective anti-Alzheimer's agent is very challenging; however, a multifunctional ligand strategy may be a promising solution for the treatment of this complex disease. We herein present the design, synthesis and biological evaluation of novel hydroxyethylamine derivatives displaying unique, multiple properties that have not been previously reported. The original mechanism of action combines inhibitory activity against disease-modifying targets: β-secretase enzyme (BACE1) and amyloid β (Aβ) aggregation, along with an effect on targets associated with symptom relief - inhibition of butyrylcholinesterase (BuChE) and γ-aminobutyric acid transporters (GATs). Among the obtained molecules, compound 36 exhibited the most balanced and broad activity profile (eeAChE IC₅₀ = 2.86 μM; eqBuChE IC₅₀ = 60 nM; hBuChE IC₅₀ = 20 nM; hBACE1 IC₅₀ = 5.9 μM; inhibition of Aβ aggregation = 57.9% at 10 μM; mGAT1 IC₅₀ = 10.96 μM; and mGAT2 IC₅₀ = 19.05 μM). Moreover, we also identified 31 as the most potent mGAT4 and hGAT3 inhibitor (IC₅₀ = 5.01 μM and IC₅₀ = 2.95 μM, respectively), with high selectivity over other subtypes. Compounds 36 and 31 represent new anti-Alzheimer agents that can ameliorate cognitive decline and modify the progress of disease.

Melatonin- and Ferulic Acid-Based HDAC6 Selective Inhibitors Exhibit Pronounced Immunomodulatory Effects In Vitro and Neuroprotective Effects in a Pharmacological Alzheimer's Disease Mouse Model

The structures of melatonin and ferulic acid were merged into tertiary amide-based histone deacetylase 6 (HDAC6) inhibitors to develop multi-target-directed inhibitors for neurodegenerative diseases to incorporate antioxidant effects without losing affinity and selectivity at HDAC6. Structure-activity relationships led to compound 10b as a hybrid molecule showing pronounced and selective inhibition of HDAC6 (IC50 = 30.7 nM, > 25-fold selectivity over other subtypes). This compound shows comparable DPPH radical scavenging ability to ferulic acid, comparable ORAC value to melatonin and comparable Cu²⁺ chelating ability to EDTA. It also lacks neurotoxicity on HT-22 cells, exhibits a pronounced immunomodulatory effect, and is active in vivo showing significantly higher efficacy in an AD mouse model to prevent both Aβ25-35-induced spatial working and long-term memory dysfunction at lower dose (0.3 mg/kg) compared to positive control HDAC6 inhibitor ACY1215 and an equimolar mixture of the three entities ACY1215, melatonin and ferulic acid, suggesting potentially disease-modifying properties.

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

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

Structure and therapeutic uses of butyrylcholinesterase: Application in detoxification, Alzheimer's disease, and fat metabolism

Structural information of butyrylcholinesterase (BChE) and its variants associated with several diseases are discussed here. Pure human BChE has been proved safe and effective in treating organophosphorus (OPs) poisoning and has completed Phase 1 and 2 pharmacokinetic (PK) and safety studies. The introduction of specific mutations into native BChE to endow it a self-reactivating property has gained much progress in producing effective OPs hydrolases. The hydrolysis ability of native BChE on cocaine has been confirmed but was blocked to clinical application due to poor PK properties. Several BChE mutants with elevated cocaine hydrolysis activity were published, some of which have shown safety and efficiency in treating cocaine addiction of human. The increased level of BChE in progressed Alzheimer's disease patients made it a promising target to elevate acetylcholine level and attenuate cognitive status. A variety of selective BChE inhibitors with high inhibitory activity published in recent years are reviewed here. BChE could influence the weight and insulin secretion and resistance of BChE knockout (KO) mice through hydrolyzing ghrelin. The BChE-ghrelin pathway could also regulate aggressive behaviors of BChE-KO mice.

Cannabinoid Receptor Subtype 2 (CB2R) in a Multitarget Approach: Perspective of an Innovative Strategy in Cancer and Neurodegeneration

The cannabinoid receptor subtype 2 (CB2R) represents an interesting and new therapeutic target for its involvement in the first steps of neurodegeneration as well as in cancer onset and progression. Several studies, focused on different types of tumors, report a promising anticancer activity induced by CB2R agonists due to their ability to reduce inflammation and cell proliferation. Moreover, in neuroinflammation, the stimulation of CB2R, overexpressed in microglial cells, exerts beneficial effects in neurodegenerative disorders. With the aim to overcome current treatment limitations, new drugs can be developed by specifically modulating, together with CB2R, other targets involved in such multifactorial disorders. Building on successful case studies of already developed multitarget strategies involving CB2R, in this Perspective we aim at prompting the scientific community to consider new promising target associations involving HDACs (histone deacetylases) and σ receptors by employing modern approaches based on molecular hybridization, computational polypharmacology, and machine learning algorithms.

Recent advances in multitarget-directed ligands targeting G-protein-coupled receptors

Mounting evidence indicates that single-target drugs might be inadequate to achieve satisfactory therapeutic effects on complex diseases. Recently, increasing attention has been paid to developing drugs that can manipulate multiple targets to generate beneficial effects through potential synergy. G-protein-coupled receptors (GPCRs) become desirable targets for developing multitarget-directed ligands (MTDLs) because of their crucial roles in the pathophysiology of various human diseases and the accessibility of druggable sites at the cell surface. Herein, we review the most recent advances in the development of GPCR-targeted MTDLs in treating complex diseases, and discuss their potential therapeutic strategies to reveal current trends and shed insights into the utility of GPCR-targeted MTDLs for future drug design and development.

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

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

Sterubin: Enantioresolution and Configurational Stability, Enantiomeric Purity in Nature, and Neuroprotective Activity in Vitro and in Vivo

Alzheimer's disease (AD) is a neurological disorder with still no preventive or curative treatment. Flavonoids are phytochemicals with potential therapeutic value. Previous studies described the flavanone sterubin isolated from the Californian plant Eriodictyon californicum as a potent neuroprotectant in several in vitro assays. Herein, the resolution of synthetic racemic sterubin (1) into its two enantiomers, (R)-1 and (S)-1, is described, which has been performed on a chiral chromatographic phase, and their stereochemical assignment online by HPLC-ECD coupling. (R)-1 and (S)-1 showed comparable neuroprotection in vitro with no significant differences. While the pure stereoisomers were configurationally stable in methanol, fast racemization was observed in the presence of culture medium. We also established the occurrence of extracted sterubin as its pure (S)-enantiomer. Moreover, the activity of sterubin (1) was investigated for the first time in vivo, in an AD mouse model. Sterubin (1) showed a significant positive impact on short- and long-term memory at low dosages.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-6

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials that is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules [...].