Development and crystallography-aided SAR studies of multifunctional BuChE inhibitors and 5-HT6R antagonists with β-amyloid anti-aggregation properties

The lack of an effective treatment makes Alzheimer's disease a serious healthcare problem and a challenge for medicinal chemists. Herein we report interdisciplinary research on novel multifunctional ligands targeting proteins and processes involved in the development of the disease: BuChE, 5-HT₆ receptors and β-amyloid aggregation. Structure-activity relationship analyses supported by crystallography and docking studies led to the identification of a fused-type multifunctional ligand 50, with remarkable and balanced potencies against BuChE (IC₅₀ = 90 nM) and 5-HT₆R (K_i = 4.8 nM), and inhibitory activity against Aβ aggregation (53% at 10 μM). In in vitro ADME-Tox and in vivo pharmacokinetic studies compound 50 showed good stability in the mouse liver microsomes, favourable safety profile and brain permeability with the brain to plasma ratio of 6.79 after p.o. administration in mice, thus being a promising candidate for in vivo pharmacology studies and a solid foundation for further research on effective anti-AD therapies.

Discovery of 1-(phenylsulfonyl)-1H-indole-based multifunctional ligands targeting cholinesterases and 5-HT6 receptor with anti-aggregation properties against amyloid-beta and tau

Multifunctional ligands as an essential variant of polypharmacology are promising candidates for the treatment of multi-factorial diseases like Alzheimer's disease. Based on clinical evidence and following the paradigm of multifunctional ligands we have rationally designed and synthesized a series of compounds targeting processes involved in the development of the disease. The biological evaluation led to the discovery of two compounds with favorable pharmacological characteristics and ADMET profile. Compounds 17 and 35 are 5-HT₆R antagonists (K_i = 13 nM and K_i = 15 nM respectively) and cholinesterase inhibitors with distinct mechanisms of enzyme inhibition. Compound 17, a tacrine derivative is a reversible inhibitor of acetyl- and butyrylcholinesterase (IC₅₀ = 8 nM and IC₅₀ = 24 nM respectively), while compound 35 with rivastigmine-derived phenyl N-ethyl-N-methylcarbamate fragment is a selective, pseudo-irreversible inhibitor of butyrylcholinesterase (IC₅₀ = 455 nM). Both compounds inhibit aggregation of amyloid β in vitro (75% for compound 17 and 68% for 35 at 10 μM) moreover, compound 35 is a potent tau aggregation inhibitor in cellulo (79%). In ADMET in vitro studies both compounds showed acceptable metabolic stability on mouse liver microsomes (28% and 60% for compound 17 and 35 respectively), no or little effect on CYP3A4 and 2D6 up to a concentration of 10 μM and lack of toxicity on HepG2 cell line (IC₅₀ values of 80 and 21 μM, for 17 and 35 respectively). Based on the pharmacological characteristics and favorable pharmacokinetic properties, we propose compounds 17 and 35 as an excellent starting point for further optimization and in-depth biological studies.

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.

1-Benzylpyrrolidine-3-amine-based BuChE inhibitors with anti-aggregating, antioxidant and metal-chelating properties as multifunctional agents against Alzheimer's disease

Complex pathomechanism of Alzheimer's disease (AD) prompts researchers to develop multifunctional molecules in order to find effective therapy against AD. We designed and synthesized novel multifunctional ligands for which we assessed their activities towards butyrylcholinesterase, beta secretase, amyloid beta (Aβ) and tau protein aggregation as well as antioxidant and metal-chelating properties. All compounds showed dual anti-aggregating properties towards Aβ and tau protein in the in cellulo assay in Escherichia coli. Of particular interest are compounds 24b and 25b, which efficiently inhibit aggregation of Aβ and tau protein at 10 μM (24b: 45% for Aβ, 53% for tau; 25b: 49% for Aβ, 54% for tau). They display free radical scavenging capacity and antioxidant activity in ABTS and FRAP assays, respectively, and selectively chelate copper ions. Compounds 24b and 25b are also the most potent inhibitors of BuChE with IC₅₀ of 2.39 μM and 1.94 μM, respectively. Promising in vitro activities of the presented multifunctional ligands as well as their original scaffold are a very interesting starting point for further research towards effective anti-AD treatment.

Design, Synthesis, and Biological Evaluation of 1-Benzylamino-2-hydroxyalkyl Derivatives as New Potential Disease-Modifying Multifunctional Anti-Alzheimer's Agents

The multitarget approach is a promising paradigm in drug discovery, potentially leading to new treatment options for complex disorders, such as Alzheimer's disease. Herein, we present the discovery of a unique series of 1-benzylamino-2-hydroxyalkyl derivatives combining inhibitory activity against butyrylcholinesterase, β-secretase, β-amyloid, and tau protein aggregation, all related to mechanisms which underpin Alzheimer's disease. Notably, diphenylpropylamine derivative 10 showed balanced activity against both disease-modifying targets, inhibition of β-secretase (IC_{50  hBACE-1} = 41.60 μM), inhibition of amyloid β aggregation (IC_50 Aβ = 3.09 μM), inhibition of tau aggregation (55% at 10 μM); as well as against symptomatic targets, butyrylcholinesterase inhibition (IC_{50  hBuChE} = 7.22 μM). It might represent an encouraging starting point for development of multifunctional disease-modifying anti-Alzheimer's agents.

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

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

Design, synthesis and biological evaluation of new phthalimide and saccharin derivatives with alicyclic amines targeting cholinesterases, beta-secretase and amyloid beta aggregation

The complexity of Alzheimer's disease (AD) calls for search of multifunctional compounds as potential candidates for effective therapy. A series of phthalimide and saccharin derivatives linked by different alicyclic fragments (piperazine, hexahydropyrimidine, 3-aminopyrrolidine or 3-aminopiperidine) with phenylalkyl moieties attached have been designed, synthesized, and evaluated as multifunctional anti-AD agents with cholinesterase, β-secretase and β-amyloid inhibitory activities. In vitro studies showed that the majority of saccharin derivatives with piperazine moiety and one phthalimide derivative with 3-aminopiperidine fragment exhibited inhibitory potency toward acetylcholinesterase (AChE) with EeAChE IC₅₀ values ranging from 0.83 μM to 19.18 μM. The target compounds displayed inhibition of human β-secretase-1 (hBACE1) ranging from 26.71% to 61.42% at 50 μM concentration. Among these compounds, two multifunctional agents (26, [2-(2-(4-benzylpiperazin-1-yl)ethyl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide] and 52, 2-(2-(3-(3,5-difluorobenzylamino)piperidin-1-yl)ethyl)isoindoline-1,3-dione) have been identified. Compound 26 exhibited the highest inhibitory potency against EeAChE (IC₅₀ = 0.83 μM) and inhibitory activity against hBACE1 (33.61% at 50 μM). Compound 52 is a selective AChE inhibitor (IC_{50 AChE} = 6.47 μM) with BACE1 inhibitory activity (26.3% at 50 μM) and it displays the most significant Aβ anti-aggregating properties among all the obtained compounds (39% at 10 μM). Kinetic and molecular modeling studies indicate that 26 may act as non-competitive AChE inhibitor able to interact with both catalytic and peripheral active site of the enzyme.

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.

[Multifunctional ligands--a new approach in the search for drugs against multi-factorial diseases]

Selective drugs directed at a single biological target often prove ineffective in the treatment of diseases with a complex pathomechanism, e.g. Alzheimer's disease (AD). This situation prompts researchers to design multi-target-directed ligands (MTDLs), capable of interacting with a number of selected biological targets. The paper outlines the concept of the multi-target-directed ligand design and examples of its use in the search of a cure for AD. In the knowledge-based approach for designing MTDLs, selective ligands of different targets are combined in one molecule. In the screening-based approach, libraries of compounds are screened against selected targets, which allows one to find molecules with a desirable pharmacological profile. It is also possible to obtain multifunctional ligands by performing optimization of a drug with known side activity and transforming it into the main activity, with a simultaneous decrease or complete removal of the original activity. The type of biological targets and applied MTDL design strategy affect the physicochemical and pharmacokinetic properties of the resulting molecules. AD is a multifactorial neurodegenerative disease of the central nervous system associated with the formation of neurofibrillary tangles within neurons, formed by the hyperphosphorylated τ proteins, and extracellular β-amyloid deposits (senile plaques). Current AD therapy comprises symptomatic drugs that enhance cholinergic neurotransmission or inhibit glutamate receptors. The literature provides numerous examples of compounds which proved in in vitro tests to be multifunctional ligands. Most of them are derivatives of cholinesterase-inhibiting drugs, also capable of inhibiting the aggregation of Aβ and showing neuroprotective effects in Aβ-induced cytotoxicity assays.