Design, Synthesis, and Evaluation of Novel Ferulic Acid Derivatives as Multi-Target-Directed Ligands for the Treatment of Alzheimer's Disease

Design, synthesis and biological evaluation of novel naturally-inspired multifunctional molecules for the management of Alzheimer's disease

In our overall goal to overcome the limitations associated with natural products for the management of Alzheimer's disease and to develop in-vivo active multifunctional cholinergic inhibitors, we embarked on the development of ferulic acid analogs. A systematic SAR study to improve upon the cholinesterase inhibition of ferulic acid with analogs that also had lower logP was carried out. Enzyme inhibition and kinetic studies identified compound 7a as a lead molecule with preferential acetylcholinesterase inhibition (AChE IC₅₀ = 5.74 ± 0.13 μM; BChE IC₅₀ = 14.05 ± 0.10 μM) compared to the parent molecule ferulic acid (% inhibition of AChE and BChE at 20 μM, 15.19 ± 0.59 and 19.73 ± 0.91, respectively). Molecular docking and dynamics studies revealed that 7a fits well into the active sites of AChE and BChE, forming stable and strong interactions with key residues Asp74, Trp286, and Tyr337 in AChE and with Tyr128, Trp231, Leu286, Ala328, Phe329, and Tyr341 in BChE. Compound 7a was found to be an efficacious antioxidant in a DPPH assay (IC₅₀ = 57.35 ± 0.27 μM), and it also was able to chelate iron. Data from atomic force microscopy images demonstrated that 7a was able to modulate aggregation of amyloid β_1-42. Upon oral administration, 7a exhibited promising in-vivo activity in the scopolamine-induced AD animal model and was able to improve spatial memory in cognitive deficit mice in the Y-maze model. Analog 7a could effectively reverse the increased levels of AChE and BChE in scopolamine-treated animals and exhibited potent ex-vivo antioxidant properties. These findings suggest that 7a can act as a lead molecule for the development of naturally-inspired multifunctional molecules for the management of Alzheimer's and other neurodegenerative disorders.

The development of advanced structural framework as multi-target-directed ligands for the treatment of Alzheimer's disease

In this work, we have developed a novel series of multi-target-directed ligands to address low levels of acetylcholine (ACh), oxidative stress, metal ion dysregulation, and the misfolded proteins. Novel apigenin-donepezil derivatives, naringenin-donepezil derivatives, genistein-donepezil derivatives and chalcone-donepezil derivatives have been synthesized, in vitro results showed that TM-4 was a reversible and potent huAChE (IC₅₀ = 0.36 μM) and huBChE (IC₅₀ = 15.3 μM) inhibitor, and showed potent antioxidant activity (ORAC = 1.2 eq). TM-4 could significantly inhibit self-induced Aβ_1-42 aggregation (IC₅₀ = 3.7 μM). TM-4 was also an ideal neuroprotectant, potential metal chelation agent, and it could inhibit and disaggregate huAChE-induced and Cu²⁺-induced Aβ aggregation. Moreover, TM-4 could activate UPS degradation pathway in HT22 cells and induce autophagy on U87 cells to clear abnormal proteins associated with AD. More importantly, TM-4 could cross BBB in vitro assay. In addition, in vivo assay revealed that TM-4 exhibited remarkable dyskinesia recovery rate and response efficiency on AlCl₃-induced zebrafish AD model, and TM-4 indicated surprising protective effect on Aβ_1-40-induced vascular injury. TM-4 presented precognitive effect on scopolamine-induced memory impairment. And the regulation of multi-targets for TM-4 were further conformed through transcriptome sequencing. More interesting, the blood, urine and feces metabolism in rat and rat/human liver microsome metabolism towards TM-4 were also investigated. Overall, TM-4 is a promising multi-function candidate for the development of drugs to Alzheimer's disease.

Tacrine-Hydrogen Sulfide Donor Hybrid Ameliorates Cognitive Impairment in the Aluminum Chloride Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by progressive loss of memory and cognitive function, and is associated with the deficiency of synaptic acetylcholine, as well as chronic neuroinflmmation. Tacrine, a potent acetylcholinesterase (AChE) inhibitor, was previously a prescribed clinical therapeutic agent for AD, but it was recently withdrawn because it caused widespread hepatotoxicity. Hydrogen sulfide (H₂S) has neuroprotective, hepatoprotective, and anti-inflammatory effects. In this study, we synthesized a new compound, a tacrine-H₂S donor hybrid (THS) by introducing H₂S-releasing moieties (ACS81) to tacrine. Subsequently, pharmacological and biological evaluations of THS were conducted in the aluminum trichloride (AlCl₃)-induced AD mice model. We found that THS (15 mmol/kg) improved cognitive and locomotor activity in AD mice in the step-through test and open field test, respectively. THS showed strong AChE inhibitory activity in the serum and hippocampus of AD mice and induced increased hippocampal H₂S levels. Furthermore, THS reduced mRNA expression of the proinflammatory cytokines, TNF-α, IL-6, and IL-1β and increased synapse-associated proteins (synaptophysin and postsynaptic density protein 95) in the hippocampus of AD mice. Importantly, THS, unlike tacrine, did not increase liver transaminases (alanine transaminase and aspartate transaminase) or proinflammatory cytokines, indicating THS is much safer than tacrine. Therefore, the multifunctional effects of this new hybrid compound of tacrine and H₂S indicate it is a promising compound for further research into the treatment of AD.

The development of 2-acetylphenol-donepezil hybrids as multifunctional agents for the treatment of Alzheimer's disease

A series of 2-acetylphenol-donepezil hybrids was designed and synthesized based on multi-target-directed ligands strategy. The biological activities were evaluated by AChE/BChE inhibition and MAO-A/MAO-B inhibition. The results revealed that the tertiary amines and methylene chain length significantly affected the eeAChE inhibitory potency, in particular, compound TM-14 showed the best eeAChE inhibitory activity with IC₅₀ value of 2.9 μM, in addition, both kinetic analysis of AChE inhibition and docking study displayed that TM-14 could simultaneously bind to the catalytic active site and peripheral anionic site of AChE. Moreover, compound TM-14 was a selective metal chelator and could form 1:1 TM-14-Cu²⁺ complex. The structure-active-relationship also indicated that the O-alkylamine fragment remarkably decreased hMAO-B inhibitory activity, compound TM-2 exhibited potent hMAO-B inhibitory activity (IC₅₀ = 6.8 μM), which was supported by the molecular docking study. More interestingly, compounds TM-14 and TM-2 could cross the blood-brain barrier in vitro. Therefore, the structure-active-relationship of 2-acetylphenol-donepezil hybrids could encourage the development of multifunction agents with selective AChE inhibition or selective MAO-B inhibition for the treatment of Alzheimer's disease.