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Alzheimer’s disease (AD) is a neurodegenerative disorder which is characterized by β-amyloid (Aβ) aggregation, τ-hyperphosphorylation, and loss of cholinergic neurons. The other important hallmarks of AD are oxidative stress, metal dyshomeostasis, inflammation, and cell cycle dysregulation. Multiple therapeutic targets may be proposed for the development of anti-AD drugs, and the “one drug–multiple targets” strategy is of current interest. Tacrine (THA) was the first clinically approved cholinesterase (ChE) inhibitor, which was withdrawn due to high hepatotoxicity. However, its high potency in ChE inhibition, low molecular weight, and simple structure make THA a promising scaffold for developing multi-target agents. In this review, we summarized THA-based hybrids published from 2006 to 2022, thus providing an overview of strategies that have been used in drug design and approaches that have resulted in significant cognitive improvements and reduced hepatotoxicity.

The incorporation of selenium into tacrine derivatives has been explored as a novel strategy to enhance therapeutic efficacy while minimizing toxicity in the treatment of neurodegenerative diseases such as Alzheimer’s. This study utilized computational and experimental approaches, including Density Functional Theory (DFT), molecular docking, pharmacokinetic profiling, and toxicological predictions, to evaluate the potential of these derivatives. The selenium-modified compounds demonstrated improved electronic properties, such as narrower HOMO–LUMO gaps and optimized electronegativity, resulting in enhanced stability and reactivity. Pharmacokinetic analyses revealed favorable absorption, distribution, and blood–brain barrier penetration, while toxicological assessments indicated reduced hepatotoxicity and skin sensitization risks compared to tacrine. Molecular docking and dynamic simulations highlighted strong and stable interactions of the derivatives with critical enzymes, including acetylcholinesterase (AChE) and beta-secretases (BACE1 and BACE2). Compounds 12 and 13, in particular, emerged as the most promising candidates due to their superior stability and binding affinity. These findings underscore the potential of selenium-modified tacrine derivatives as safer and more effective therapeutic agents for Alzheimer’s disease, warranting further experimental validation.

Pursuing the widespread interest on multi-target drugs to combat Alzheimer´s disease (AD), a new series of hybrids was designed and developed based on the repositioning of the well-known acetylcholinesterase (AChE) inhibitor, tacrine (TAC), by its coupling to benzofuran (BF) derivatives. The BF framework aims to endow the conjugate molecules with ability for inhibition of AChE (bimodal way) and of amyloid-beta peptide aggregation, besides providing metal (Fe, Cu) chelating ability and concomitant extra anti-oxidant activity, for the hybrids with hydroxyl substitution. The new TAC-BF conjugates showed very good activity for AChE inhibition (sub-micromolar range) and good capacity for the inhibition of self- and Cu-mediated Aβ aggregation, with dependence on the linker size and substituent groups of each main moiety. Neuroprotective effects were also found for the compounds through viability assays of neuroblastoma cells, after Aβ 1-42 induced toxicity. Structure-activity relationship analysis provides insights on the best structural parameters, to take in consideration for future studies in view of potential applications in AD therapy. Design, synthesis and evaluation of new tacrine-benzofuran hybrids as multitargeting anti- Alzheimer's disease agents; high AChE inhibition associated with other relevant properties; structure-activity relationship analysis

Alzheimer’s is the leading factor behind dementia, producing steady impairments in memory, cognitive reasoning, behavioral, and social interactions. This scientific study investigates thirty-two phenoxy tacrine (PhO-THA) derivatives through an integrated computational modeling to identify potential therapeutic candidates. 3D-QSAR models were developed using comparative molecular similarity indices analysis and comparative molecular field analysis, which were subjected to rigorous internal and external validation to establish a robust quantitative relationship between molecular interaction fields and cytotoxic activities. Based on these validated structural insights, fourteen new compounds (D1-D14) were designed. Comprehensive molecular docking and molecular dynamics (MD) simulations, coupled with ADME-Tox profiling, were used to evaluate their pharmacological potential. Our results highlight four specific compounds (D9-D12) that exhibit favorable pharmacokinetic properties and a high safety profile, making them promising candidates for future drug development. D9 was selected for MD simulations due to its lower cytotoxic activity (pIC 50 of 3.50), which is comparable to the reference THA drug (pIC 50 of 3.52). The results demonstrated exceptional thermodynamic stability for D9 upon complexation with the NMDA receptor (PDB ID: 5EWJ) over a 100 ns simulation time.

A series of previously synthesized conjugates of tacrine and salicylamide was extended by varying the structure of the salicylamide fragment and using salicylic aldehyde to synthesize salicylimine derivatives. The hybrids exhibited broad-spectrum biological activity. All new conjugates were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. The structure of the salicylamide moiety exerted little effect on anticholinesterase activity, but AChE inhibition increased with spacer elongation. The most active conjugates were salicylimine derivatives: IC50 values of the lead compound 10c were 0.0826 µM (AChE) and 0.0156 µM (BChE), with weak inhibition of the off-target carboxylesterase. The hybrids were mixed-type reversible inhibitors of both cholinesterases and displayed dual binding to the catalytic and peripheral anionic sites of AChE in molecular docking, which, along with experimental results on propidium iodide displacement, suggested their potential to block AChE-induced β-amyloid aggregation. All conjugates inhibited Aβ42 self-aggregation in the thioflavin test, and inhibition increased with spacer elongation. Salicylimine 10c and salicylamide 5c with (CH2)8 spacers were the lead compounds for inhibiting Aβ42 self-aggregation, which was corroborated by molecular docking to Aβ42. ABTS•+-scavenging activity was highest for salicylamides 5a–c, intermediate for salicylimines 10a–c, low for F-containing salicylamides 7, and non-existent for methoxybenzoylamides 6 and difluoromethoxybenzoylamides 8. In the FRAP antioxidant (AO) assay, the test compounds displayed little or no activity. Quantum chemical analysis and molecular dynamics (MD) simulations with QM/MM potentials explained the AO structure–activity relationships. All conjugates were effective chelators of Cu2+, Fe2+, and Zn2+, with molar compound/metal (Cu2+) ratios of 2:1 (5b) and ~1:1 (10b). Conjugates exerted comparable or lower cytotoxicity than tacrine on mouse hepatocytes and had favorable predicted intestinal absorption and blood-brain barrier permeability. The overall results indicate that the synthesized conjugates are promising new multifunctional agents for the potential treatment of AD.

Alzheimer’s disease (AD) is a complex neurodegenerative disease that can lead to the loss of cognitive function. The progression of AD is regulated by multiple signaling pathways and their associated targets. Therefore, multitarget strategies theoretically have greater potential for treating AD. In this work, a series of new hybrids were designed and synthesized by the hybridization of tacrine (4, AChE: IC50 = 0.223 μM) with pyrimidone compound 5 (GSK-3β: IC50 = 3 μM) using the cysteamine or cystamine group as the connector. The biological evaluation results demonstrated that most of the compounds exhibited moderate to good inhibitory activities against acetylcholinesterase (AChE) and glycogen synthase kinase 3β (GSK-3β). The optimal compound 18a possessed potent dual AChE/GSK-3β inhibition (AChE: IC50 = 0.047 ± 0.002 μM, GSK-3β: IC50 = 0.930 ± 0.080 μM). Further molecular docking and enzymatic kinetic studies revealed that this compound could occupy both the catalytic anionic site and the peripheral anionic site of AChE. The results also showed a lack of toxicity to SH-SY5Y neuroblastoma cells at concentrations of up to 25 μM. Collectively, this work explored the structure–activity relationships of novel tetrahydroacridin hybrids with sulfur-inserted linkers, providing a reference for the further research and development of new multitarget anti-AD drugs.

A new series of tacrine–coumarin hybrids (compounds 15a–18b) linked by 1,2,3-triazole had been designed and synthesized as multifunctional ligands for the treatment of Alzheimer’s disease (AD). The inhibitory effects of the synthesized compounds on AChE and BuChE, their ability to inhibit Aβ aggregation, and their MAO inhibitory activities were evaluated. In vitro studies showed that some of the hybrids (compounds 17a–18b) exhibited significant abilities to inhibit both AChE and BuChE, self-induced Aβ aggregation, and MAO-B. In particular, compound 17d showed a well-balanced inhibitory profile against AChE and BuChE (IC50 = 0.080 ± 0.007 μM for AChE, IC50 = 0.044 ± 0.004 μM for BuChE), self-induced Aβ aggregation (58.4% ± 2.1% at 20 μM), and MAO-B (IC50 = 0.18 ± 0.01 μM), suggesting that 17d might be an excellent multifunctional agent for AD treatment. In addition, compounds 15a and 15b were identified as selective inhibitors of BuChE at micromolar concentrations.

A549 human lung carcinoma cell lines were treated with a series of new drugs with both tacrine and coumarin pharmacophores (derivatives 1a–2c) in order to test the compounds’ ability to inhibit both cancer cell growth and topoisomerase I and II activity. The ability of human topoisomerase I (hTOPI) and II to relax supercoiled plasmid DNA in the presence of various concentrations of the tacrine-coumarin hybrid molecules was studied with agarose gel electrophoresis. The biological activities of the derivatives were studied using MTT assays, clonogenic assays, cell cycle analysis and quantification of cell number and viability. The content and localization of the derivatives in the cells were analysed using flow cytometry and confocal microscopy. All of the studied compounds were found to have inhibited topoisomerase I activity completely. The effect of the tacrine-coumarin hybrid compounds on cancer cells is likely to be dependent on the length of the chain between the tacrine and coumarin moieties (1c, 1d = tacrine-(CH2)8–9-coumarin). The most active of the tested compounds, derivatives 1c and 1d, both display longer chains.

In this work, we designed, synthesised and biologically investigated a novel series of 14 N- and O-phosphorylated tacrine derivatives as potential anti-Alzheimer's disease agents. In the reaction of 9-chlorotacrine and corresponding diamines/aminoalkylalcohol we obtained diamino and aminoalkylhydroxy tacrine derivatives. Next, the compounds were acid to give final products 6-13 and 16-21 that were characterised by 1 H, 13  C, 31  P NMR and MS. The results of the docking studies revealed that the designed phosphorus hybrids, in theory can bind to AChE and BChE. All compounds exhibited significantly lower AutoDock Vina scores compared to tacrine. The inhibitory potency evaluation was performed using the Ellman's method. The most inhibitory activity against AChE exhibited compound 8 with an IC 50 value of 6.11 nM and against BChE 13 with an IC 50 value of 1.97 nM and they were 6- and 12-fold potent than tacrine. Compound 19 showed the lack of hepatocytotoxicity in MTT assay.

A novel series of multifunctional tacrine–quinoline hybrids were designed, synthesized, and evaluated as potential anti-Alzheimer’s agents. These compounds incorporate tacrine for cholinesterase’s inhibition and 8-hydroxyquinoline for metal chelation. Piperazine was selected as a linker to provide conformational flexibility and to create favorable cation–π interactions with residues in the mid-gorge region of AChE, enhancing dual-site binding with AChE to inhibit Aβ aggregation. In vitro studies demonstrated submicromolar inhibitory activity toward both AChE and BuChE, particularly for compounds 16e (IC50 = 0.10 μM for AChE, 0.043 μM for BuChE) and 16h (IC50 = 0.21 μM for AChE, 0.10 μM for BuChE). These compounds also exhibited potent inhibition of self-induced Aβ1–42 aggregation (16e: 80.5% ± 4.4%, 16h: 93.2% ± 3.9% at 20 μM). Kinetic analyses revealed mixed-type inhibition, suggesting dual binding to both CAS and PAS of AChE. UV–vis spectrometry confirmed the chelation of Cu2+ and Zn2+ ions by the 8-hydroxyquinoline moiety. These findings highlight the tacrine–quinoline scaffold as a promising platform for the discovery of a multitarget-directed anti-AD drug.