Development of bivalent compounds as potential neuroprotectants for Alzheimer’s disease

In our efforts to further investigate the impact of the spacer and membrane anchor to the neuroprotective activities, a series of bivalent compounds that contain cholesterol and extended spacers were designed, synthesized and biologically characterized. Our results support previous studies that incorporation of a piperazine ring into the spacer significantly improved the protective potency of bivalent compounds in MC65 cell model. Spacer length beyond 21 atoms does not add further benefits with 21MO being the most potent one with an EC₅₀ of 81.86 ± 11.91 nM. Our results also demonstrated that bivalent compound 21MO suppressed the production of mitochondria reactive oxygen species. Furthermore, our results confirmed that both of the spacer and membrane anchor moiety are essential to metal binding. Collectively, the results provide further evidence and information to guide optimization of such bivalent compounds as potential neuroprotectants for Alzheimer’s disease.     

Design and development of novel p-aminobenzoic acid derivatives as potential cholinesterase inhibitors for the treatment of Alzheimer’s disease

Based on the quantitative structure-activity relationship (QSAR), some novel p-aminobenzoic acid derivatives as promising cholinesterase enzyme inhibitors were designed, synthesized, characterized and evaluated to enhance learning and memory. The in vitro enzyme kinetic study of the synthesized compounds revealed the type of inhibition on the respective acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. The in vivo studies of the synthesized compounds exhibited significant reversal of cognitive deficits in the animal models of amnesia as compared to standard drug donepezil. Further, the ex vivo studies in the specific brain regions like the hippocampus, hypothalamus, and prefrontal cortex regions also exhibited AChE inhibition comparable to standard donepezil. The in silico molecular docking and dynamics simulations studies of the most potent compound 22 revealed the consensual interactions at the active site pocket of the AChE.     

Synthesis of carbon-11-labeled CK1 inhibitors as new potential PET radiotracers for imaging of Alzheimer’s disease

The reference standards methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate (5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-methoxybenzamide (5c), and their corresponding desmethylated precursors 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoic acid (6a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-hydroxybenzamide (6b), were synthesized from 5-amino-2,2-difluoro-1,3-benzodioxole and 3-substituted benzoic acids in 5 and 6 steps with 33% and 11%, 30% and 7% overall chemical yield, respectively. Carbon-11-labeled casein kinase 1 (CK1) inhibitors, [¹¹C]methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate ([¹¹C]5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-[¹¹C]methoxybenzamide ([¹¹C]5c), were prepared from their O-desmethylated precursor 6a or 6b with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–45% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.     

Novel tacrine-related drugs as potential candidates for the treatment of Alzheimer’s disease

A summary of the recently published efforts on tacrine derivatives as a renewed potential therapeutic approach for the treatment of Alzheimer’s disease is presented.     

Pyridoxine-resveratrol hybrids Mannich base derivatives as novel dual inhibitors of AChE and MAO-B with antioxidant and metal-chelating properties for the treatment of Alzheimer’s disease

A series of pyridoxine-resveratrol hybrids Mannich base derivatives as multifunctional agents have been designed, synthesized and evaluated for cholinesterase (ChE) and monoamine oxidase (MAO) inhibitory activity. To further explore the multifunctional properties of the new derivatives, their antioxidant activities and metal-chelating properties were also tested. The results showed that most of these compounds could selectively inhibit acetylcholinesterase (AChE) and MAO-B. Among them, compounds 7d and 8b exhibited the highest potency for AChE inhibition with IC₅₀ values of 2.11 μM and 1.56 μM, respectively, and compound 7e exhibited the highest MAO-B inhibition with an IC₅₀ value of 2.68 μM. The inhibition kinetic analysis revealed that compound 7d showed a mixed-type inhibition, binding simultaneously to the CAS and PAS of AChE. Molecular modeling study was also performed to investigate the binding mode of these hybrids with MAO-B. In addition, all target compounds displayed good antioxidant and metal-chelating properties. Taken together, these preliminary findings can be a new starting point for further development of multifunctional agents for Alzheimer’s disease.     

Evaluation of nicotine and cotinine analogs as potential neuroprotective agents for Alzheimer’s disease

The currently available therapies for Alzheimer’s disease (AD) and related forms of dementia are limited by modest efficacy, adverse side effects, and the fact that they do not prevent the relentless progression of the illness. The purpose of the studies described here was to investigate the neuroprotective effects of the nicotine metabolite cotinine as well as a small series of cotinine and nicotine analogs (including stereoisomers) and to compare their effects to the four clinically prescribed AD therapies.     

Novel multitarget-directed tacrine derivatives as potential candidates for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is complex and progressive; it has not only threatened the health of elderly people, but also burdened the whole social medical and health system. The available therapy for AD is limited and the efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the design and development of efficacious and safe anti-AD agents has become a hotspot in the field of pharmaceutical research. Due to the multifactorial etiology of AD, the multitarget-directed ligands (MTDLs) approach is promising in search for new drugs for AD. Tacrine, which is the first acetylcholinesterase (AChE) inhibitor, has been selected as the ideal active fragment because of its simple structure, clear activity, and its superiority in the structural modification, thus it could be introduced into the overall molecular skeletons of the multi-target-directed anti-AD agents. In this review, we have summarized the recent advances (2012 to the present) in the chemical modification of tacrine, which could provide the reference for the further study of novel multi-target-directed tacrine derivatives to treat AD.     

Lead optimization studies towards the discovery of novel carbamates as potent AChE inhibitors for the potential treatment of Alzheimer’s disease

The optimization of our previous lead compound 1 (AChE IC₅₀ = 3.31 μM) through synthesis and pharmacology of a series of novel carbamates is reported. The synthesized compounds were evaluated against mouse brain AChE enzyme using the colorimetric method described by Ellman et al. The three compounds 6a (IC₅₀ = 2.57 μM), 6b (IC₅₀ = 0.70 μM) and 6i (IC₅₀ = 2.56 μM) exhibited potent in vitro AChE inhibitory activities comparable to the drug rivastigmine (IC₅₀ = 1.11 μM). Among them, the compound 6b has been selected as possible optimized lead for further neuropharmacological studies. In addition, the AChE–carbamate Michaelis complexes of these potent compounds including rivastigmine and ganstigmine have been modeled using covalent docking protocol of GOLD and important direct/indirect interactions contributing to stabilization of the AChE–carbamate Michaelis complexes have been investigated.     

Development of pyrazole and spiropyrazoline analogs as multifunctional agents for treatment of Alzheimer’s disease

Cholinergic hypothesis of Alzheimer’s disease has been advocated as an essential tool in the last couple of decades for the drug development. Here in, we report de novo fragment growing strategy for the design of novel 3,5-diarylpyrazoles and hit optimization of spiropyrazoline derivatives as acetyl cholinesterase inhibitors. Both type of scaffolds numbering forty compounds were synthesized and evaluated for their potencies against AChE, BuChE and PAMPA. Introduction of lipophilic cyclohexane ring in 3,5-diarylpyrazole analogs led to spiropyrazoline derivatives, which facilitated and improved the potencies. Compound 44 (AChE = 1.937 ± 0.066 µM; BuChE = 1.166 ± 0.088 µM; hAChE = 1.758 ± 0.095 µM; P_e = 9.491 ± 0.34 × 10⁻⁶ cm s¹) showed positive results, which on further optimization led to the development of compound 67 (AChE = 0.464 ± 0.166 µM; BuChE = 0.754 ± 0.121 µM; hAChE = 0.472 ± 0.042 µM; P_e = 13.92 ± 0.022 × 10⁻⁶ cm s¹). Compounds 44 and 67 produced significant displacement of propidium iodide from the peripheral anionic site (PAS) of AChE. They were found to be safer to MC65 cells and decreased metal induced Aβ_1-42 aggregation. Further, in-vivo behavioral studies, on scopolamine induced amnesia model, the compounds resulted in better percentage spontaneous alternation scores and were safe, had no influence on locomotion in tested animal groups at dose of 3 mg/kg. Early pharmacokinetic assessment of optimized hit molecules was supportive for further drug development.     

Design,synthesis and evaluation of flavonoid derivatives as potential multifunctional acetylcholinesterase inhibitors against Alzheimer’s disease

A new series of flavonoid derivatives were designed, synthesized and evaluated as potential multifunctional AChE inhibitors against Alzheimer’s disease. Most of them exhibited potent AChE inhibitory activity, high selectivity for AChE over BuChE, and moderate to good inhibitory potency toward Aβ aggregation. Specifically, compound 12c was the strongest AChE inhibitor, being 20-fold more potent than galanthamine and twofold more potent than tacrine, and it also had ability to inhibit Aβ aggregation (close to the reference compound) and to function as a metal chelator. Molecular modeling and enzyme kinetic study revealed that it targeted both the catalytic active site and the peripheral anionic site of AChE. Consequently, this class of compounds deserved to be thoroughly and systematically studied for the treatment of Alzheimer’s disease.     

Identification of abelson tyrosine kinase inhibitors as potential therapeutics for Alzheimer’s disease using multiple e-pharmacophore modeling and molecular dynamics

Efforts to combat Alzheimer’s disease are focused predominantly on inhibiting the activity of the enzyme(s) that have been identified to be responsible for the production of the amyloid-forming peptide. However, the inherent complexity associated with the network of pathways leading to the disease may involve additional targets for designing effective therapies. Recent experimental findings have identified abelson tyrosine kinase, a non-receptor kinase as a new target for Alzheimer’s. In this work, we employed energy optimized multiple pharmacophore modeling strategy from multiple c-Abl structures bound with ligands in the inactive ATP binding conformation (DFG-out). Virtual screening followed by docking of molecules from ChemBridge resulted in the identification of 10 best scoring molecules. MD simulations of the top three complexes revealed that Compound A, C are the most stable complexes with the most persistent protein–ligand interactions consistent with the calculated binding affinities for the top three compounds. Given the implied role of c-Abl not only in AD but in Parkinson’s disease, the identified compounds may serve as leads for effective neurotherapeutics.     

A predictive microarray-based biomarker for early detection of Alzheimer’s disease intended for clinical diagnostic application

Abstract

Objective: Microarray-based signatures for clinical application are often plagued by processing variability or batch effects that compromise the robustness of the test performance.

Methods: A splice variant array-based signature for early detection of Alzheimer’s disease (AD) was developed using 315 AD or normal subjects processed in three disparate microarray batches.

Results: A modified top scoring pair classifier using the signature, is robust to batch effects and outperforms other common classifiers, with sensitivity and specificity of 88.3% (95% CI:81.2%, 93.4%) and 88.9% (95% CI:65.3%, 98.6%), respectively, on an independent cohort.

Conclusions: This splice-variant array-based signature shows promise for clinical diagnostic use in AD.     

Synthesis and evaluation of novel benzothiazole derivatives based on the bithiophene structure as potential radiotracers for β-amyloid plaques in Alzheimer’s disease

In this study, six novel benzothiazole derivatives based on the bithiophene structure were developed as potential β-amyloid probes. In vitro binding studies using Aβ aggregates showed that all of them demonstrated high binding affinities with K_i values ranged from 0.11 to 4.64 nM. In vitro fluorescent staining results showed that these compounds can intensely stained Aβ plaques within brain sections of APP/PS1 transgenic mice, animal model for AD. Two radioiodinated compounds [¹²⁵I]-2-(5′-iodo-2,2′-bithiophen-5-yl)-6-methoxybenzo[d]thiazole [¹²⁵I]10 and [¹²⁵I]-2-(2,2′-bithiophen-5-yl)-6-iodobenzo[d]thiazole [¹²⁵I]13 were successfully prepared through an iododestannylation reaction. Furthermore, in vitro autoradiography of the AD model mice brain sections showed that both [¹²⁵I]10 and [¹²⁵I]13 labeled the Aβ plaques specifically with low background. In vivo biodistribution studies in normal mice indicated that [¹²⁵I]13 exhibited high brain uptake (3.42% ID/g at 2 min) and rapid clearance from the brain (0.53% ID/g at 60 min), while [¹²⁵I]10 showed lower brain uptake (0.87% ID/g at 2 min). In conclusion, these preliminary results of this study suggest that the novel radioiodinated benzothiazole derivative [¹²⁵I]13 may be a candidate as an in vivo imaging agent for detecting β-amyloid plaques in the brain of AD patients.     

Coumarin-dithiocarbamate hybrids as novel multitarget AChE and MAO-B inhibitors against Alzheimer’s disease: Design,synthesis and biological evaluation

A series of new coumarin-dithiocarbamate hybrids were designed and synthesized as multitarget agents for the treatment of Alzheimer’s disease. Most of them showed potent and clearly selective inhibition towards AChE and MAO-B. Among these compounds, compound 8f demonstrated the most potent inhibition to AChE with IC₅₀ values of 0.0068 μM and 0.0089 μM for eeAChE and hAChE, respectively. Compound 8g was identified as the most potent inhibitor to hMAO-B, and it is also a good and balanced inhibitor to both hAChE and hMAO-B (0.114 µM for hAChE; 0.101 µM for hMAO-B). Kinetic and molecular modeling studies revealed that 8g was a dual binding site inhibitor for AChE and a competitive inhibitor for MAO-B. Further studies indicated that 8g could penetrate the BBB and exhibit no toxicity on SH-SY5Y neuroblastoma cells. More importantly, 8g did not display any acute toxicity in mice at doses up to 2500 mg/kg and could reverse the cognitive dysfunction of scopolamine-induced AD mice. Overall, these results highlighted 8g as a potential multitarget agent for AD treatment and offered a starting point for design of new multitarget AChE/MAO-B inhibitors based on dithiocarbamate scaffold.     

sFRP-mediated Wnt sequestration as a potential therapeutic target for Alzheimer’s disease

The extracellular ligand, Wnt, and its receptors are involved in sign al transduction and play an important role in axis formation and neural development. In neurodegenerative disorders such as Alzheimer’s disease (AD), a decrease of the intracellular Wnt effector, β-catenin, has been linked to amyloid-β-peptide-induced neurotoxicity. Despite this knowledge, targeting Wnt inhibitors as potential biomarkers has not been explored, and harnessing Wnt activators as therapeutic candidates remains largely not investigated. A wide acting family of Wnt mediators, secreted frizzled-related proteins (sFRPs), has not been probed so far as molecular indicators of disease occurrence and progression of Alzheimer’s. Unlike the effect of the Dickkopf (DKK) family of Wnt antagonists on AD, the sFRP molecules have a more pleiotropic impact on the Wnt signaling cascade and probably have a far-reaching involvement in neurodegeneration. The role of sFRPs has been poorly described in AD, and in this review, we analyze the present status of the role of sFRPs on neurodegeneration, their likely involvement, and potential implications in treatment modalities of AD. This information would provide valuable clues for the development of potential therapeutic targets for aberrant neurodegenerative disorders.     

[11C]Dimebon,radiosynthesis and lipophilicity of a new potential PET agent for imaging of Alzheimer’s disease and Huntington’s disease

[¹¹C]Dimebon (2-[¹¹C]methyl-8-methyl-5-(2-(6-methylpyridin-3-yl)ethyl)-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole), a new potential PET agent for imaging of Alzheimer’s disease and Huntington’s disease, was prepared by N-[¹¹C]methylation of desmethyl-Domebon precursor with [¹¹C]CH₃OTf and purified with a semi-preparative HPLC method in 30–40% decay corrected radiochemical yield and 222–296 GBq/μmol specific activity at EOB. The measured lipophilicity coefficient (Log P) value of [¹¹C]Dimebon was 2.53.     

Oxazolopyridines and thiazolopyridines as monoamine oxidase B inhibitors for the treatment of Parkinson’s disease

In Parkinson’s disease, the motor impairments are mainly caused by the death of dopaminergic neurons. Among the enzymes which are involved in the biosynthesis and catabolism of dopamine, monoamine oxidase B (MAO-B) has been a therapeutic target of Parkinson’s disease. However, due to the undesirable adverse effects, development of alternative MAO-B inhibitors with greater optimal therapeutic potential towards Parkinson’s disease is urgently required. In this study, we designed and synthesized the oxazolopyridine and thiazolopyridine derivatives, and biologically evaluated their inhibitory activities against MAO-B. Structure–activity relationship study revealed that the piperidino group was the best choice for the R¹ amino substituent to the oxazolopyridine core structure and the activities of the oxazolopyridines with various phenyl rings were between 267.1 and 889.5 nM in IC₅₀ values. Interestingly, by replacement of the core structure from oxazolopyrine to thiazolopyridine, the activities were significantly improved and the compound 1n with the thiazolopyridine core structure showed the most potent activity with the IC₅₀ value of 26.5 nM. Molecular docking study showed that van der Waals interaction in the human MAO-B active site could explain the enhanced inhibitory activities of thiazolopyridine derivatives.