Development Of Multitarget-directed Ligands Research Articles

Piperazine-2-carboxylic acid derivatives as MTDLs anti-Alzheimer agents: Anticholinesterase activity, mechanistic aspect, and molecular modeling studies

Development of Multitarget-Directed Ligands (MTDLs) is a promising approach to combat the complex etiologies of Alzheimer's disease (AD). Herein we report the design, synthesis, and characterization of a new series of 1,4-bisbenzylpiperazine-2-carboxylic acid derivatives 3-5(a-g), 7a-f, 8a-s, and their piperazine-2-yl-1,3,4-oxadiazole analogs 6a-g. In vitro inhibitory effect against Electrophorus electricus acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) from Equine serum was evaluated using modified Ellman’s method, considering donepezil and tacrine as reference drugs. Lineweaver–Burk plot analysis of the results proved competitive inhibition of AChE and BChE with Ki values, in low micromolar range. The free carboxylic acid series 4a-g showed enhanced selectivity for AChE. Hence, 4c, 1,4-bis (4-chlorobenzyl)-piperazinyl-2-carboxylic acid), was the most active member of this series (Ki (AChE) = 10.18 ± 1.00 µM) with clear selectivity for AChE (SI ∼ 17.90). However, the hydroxamic acids 7a-f and carboxamides 8a-s congeners were more potent and selective inhibitors of BChE (SI ∼ 5.38 – 21862.5). Extraordinarily, 1,4-bis (2-chlorobenzyl)-piperazinyl-2-hydroxamic acid 7b showed promising inhibitory activity against BChE enzyme (Ki = 1.6 ± 0.08 nM, SI = 21862.5), that was significantly superior to that elicited by donepezil (Ki = 12.5 ± 2.6 µM) and tacrine (Ki = 17.3 ± 2.3 nM). Cytotoxicity assessment of 4c and 7b, on human neuroblastoma (SH-SY5Y) cell lines, revealed lower toxicity than staurosporine and was nearly comparable to that of donepezil. Molecular docking and molecular dynamics simulation afforded unblemished insights into the structure–activity relationships for AChE and BChE inhibition. The results showed stable binding with fair H-bonding, hydrophobic and/or ionic interactions to the catalytic and peripheral anionic sites of the enzymes. In silico predicted ADME and physicochemical properties of conjugates showed good CNS bioavailability and safety parameters. In this regard, compound (7b) might be considered as a promising inhibitor of BChE with an innovative donepezil-based anti-Alzheimer activity. Further assessments of the most potent AChE and BChE inhibitors as potential MTDLs anti-Alzheimer’s agents are under investigation with our research group and will be published later.

Rational Multitargeted Drug Design Strategy from the Perspective of a Medicinal Chemist.

The development of multitarget-directed ligands (MTDLs) has become a widely focused research topic, but rational design remains as an enormous challenge. This paper reviews and discusses the design strategy of incorporating the second activity into an existing single-active ligand. If the binding sites of both targets share similar endogenous substrates, MTDLs can be designed by merging two lead compounds with similar functional groups. If the binding sites are large or adjacent to the solution, two key pharmacophores can be fused directly. If the binding regions are small and deep inside the proteins, the linked-pharmacophore strategy might be the only way. The added pharmacophores of second targets should not affect the binding mode of the original ones. Moreover, the inhibitory activities of the two targets need to be adjusted to achieve an optimal ratio.

Recent Multi-target Approaches on the Development of Anti- Alzheimer's Agents Integrating Metal Chelation Activity.

Alzheimer´s disease (AD) is the most common and severe age-dependent neurodegenerative disorder worldwide. Notwithstanding the large amount of research dedicated to both the elucidation of this pathology and the development of an effective drug, the multifaceted nature and complexity of the disease are certainly a rationale for the absence of cure so far. Currently available drugs are used, mainly to compensate the decline of the neurotransmitter acetylcholine by acetylcholinesterase (AChE) inhibition, though they only provide temporary symptomatic benefits and cannot stop AD progression. Although the multiple factors that contribute to trigger AD onset and progression are not yet fully understood, several pathological features and underneath pathways have been recognized to contribute to its pathology, such as metal dyshomeostasis, protein misfolding, oxidative stress and neurotransmitter deficiencies, some of them being interconnected. Thus, there is widespread recent interest in the development of multitarget-directed ligands (MTDLs) for simultaneous interaction with several pathological targets of AD. In this review, a selection of the most recent reports (2016-up to present) on metal chelators of MTDLs with multifunctionalities is presented. These compounds enable the hitting of several AD targets or pathways, such as modulation of specific biometal ions (e.g., Cu, Fe, Zn) and of protein misfolding (β-amyloid and tau protein), anti-oxidant activity and AChE inhibition. The properties found for these hybrids are discussed in comparison with the original reference compounds, some MTDLs being outlined as leading compounds for pursuing future studies in view of efficient potential applications in AD therapy.

Indoloquinoxaline derivatives as promising multi-functional anti-Alzheimer agents

To confront a disease like Alzheimer’s disease having complex pathogenesis, development of multitarget-directed ligands has emerged as a promising drug discovery approach. In our endeavor towards the development of multitarget-directed ligands for Alzheimer’s disease, a series of indoloquinoxaline derivatives were designed and synthesized. In vitro cholinesterase inhibition studies revealed that all the synthesized compounds exhibited moderate to good cholinesterase inhibitory activity. 6-(6-(Piperidin-1-yl)hexyl)-6H-indolo[2,3-b]quinoxaline 9f was identified as the most potent and selective BuChE inhibitor (IC50 = 0.96 µM, selectivity index = 0.17) that possessed 2 fold higher BuChE inhibitory activity compared to the commercially approved reference drug donepezil (IC50 = 1.87 µM). Moreover, compound 9f is also endowed with self-induced Aβ1-42 aggregation inhibitory activity (51.24% inhibition at 50 μM concentration). Some of the compounds of the series also displayed moderate anti-oxidant activity. To perceive a putative binding mode of the compound 9f, molecular docking studies were carried out, and the results pointed out significant interactions of compound 9f with the enzymes in the binding sites of cholinesterases as well as Aβ1-42. Additionally, compound 9f exhibited favorable in silico ADMET properties. Put together these findings project compound 9f as a potential multitarget-directed ligand in the direction of developing novel anti-AD drugs. Communicated by Ramaswamy H. Sarma

Rational design of new multitarget histamine H3 receptor ligands as potential candidates for treatment of Alzheimer's disease.

Design and development of multitarget-directed ligands (MTDLs) has become a very important approach in the search of new therapies for Alzheimer's disease (AD). In our present research, a number of xanthone derivatives were first designed using a pharmacophore model for histamine H3 receptor (H3R) antagonists/inverse agonists, and virtual docking was then performed for the enzyme acetylcholinesterase. Next, 23 compounds were synthesised and evaluated invitro for human H3R (hH3R) affinity and inhibitory activity on cholinesterases. Most of the target compounds showed hH3R affinities in nanomolar range and exhibited cholinesterase inhibitory activity with IC50 values in submicromolar range. Furthermore, the inhibitory effects of monoamine oxidases (MAO) A and B were investigated. The results showed low micromolar and selective human MAO B (hMAO B) inhibition. Two azepane derivatives, namely 23 (2-(5-(azepan-1-yl)pentyloxy)-9H-xanthen-9-one) and 25 (2-(5-(azepan-1-yl)pentyloxy)-7-chloro-9H-xanthen-9-one), were especially very promising and showed high affinity for hH3R (Ki=170nM and 100nM respectively) and high inhibitory activity for acetylcholinesterase (IC50=180nM and 136nM respectively). Moreover, these compounds showed moderate inhibitory activity for butyrylcholinesterase (IC50=880nM and 394nM respectively) and hMAO B (IC50=775nM and 897nM respectively). Furthermore, molecular docking studies were performed for hH3R, human cholinesterases and hMAO B to describe the mode of interactions with these biological targets. Next, the two most promising compounds 23 and 25 were selected for invivo studies. The results showed significant memory-enhancing effect of compound 23 in dizocilpine-induced amnesia in rats in two tests: step-through inhibitory avoidance paradigm (SIAP) and transfer latency paradigm time (TLPT). In addition, favourable analgesic effects of compound 23 were observed in neuropathic pain models. Therefore, compound 23 is a particularly promising structure for further design of new MTDLs for AD.

Design of novel monoamine oxidase-B inhibitors based on piperine scaffold: Structure-activity-toxicity, drug-likeness and efflux transport studies

Piperine has been associated with neuroprotective effects and monoamine oxidase (MAO) inhibition, thus being an attractive scaffold to develop new antiparkinsonian agents. Accordingly, we prepared a small library of piperine derivatives and screened the inhibitory activities towards human MAO isoforms (hMAO-A and hMAO-B). Structure-activity relationship (SAR) studies pointed out that the combination of α-cyano and benzyl ester groups increased both potency and selectivity towards hMAO-B. Kinetic experiments with compounds 7, 10 and 15 indicated a competitive hMAO-B inhibition mechanism. Compounds 15 and 16, at 10 μM, caused a small but significant decrease in P-gp efflux activity in Caco-2 cells. Compound 15 stands out as the most potent piperine-based hMAO-B inhibitor (IC50 = 47.4 nM), displaying favourable drug-like properties and a broad safety window. Compound 15 is thus a suitable candidate for lead optimization and the development of multitarget-directed ligands.

The chemistry toolbox of multitarget-directed ligands for Alzheimer's disease

The discovery and development of multitarget-directed ligands (MTDLs) is a promising strategy to find new therapeutic solutions for neurodegenerative diseases (NDs), in particular for Alzheimer's disease (AD).Currently approved drugs for the clinical management of AD are based on a single-target strategy and focus on restoring neurotransmitter homeostasis. Finding disease-modifying therapies AD and other NDs remains an urgent unmet clinical need.The growing consensus that AD is a multifactorial disease, with several interconnected and deregulated pathological pathways, boosted an intensive research in the design of MTDLs. Due to this scientific boom, the knowledge behind the development of MTDLs remains diffuse and lacks balanced guidelines. To rationalize the large amount of data obtained in this field, we herein revise the progress made over the last 5 years on the development of MTDLs inspired by drugs approved for AD. Due to their putative therapeutic benefit in AD, MTDLs based on MAO-B inhibitors will also be discussed in this review.

Preparation of 4-Flexible Amino-2-Arylethenyl-Quinoline Derivatives as Multi-target Agents for the Treatment of Alzheimer's Disease.

Alzheimer’s disease (AD) is a complex and multifactorial neurodegenerative disorder of aged people. The development of multitarget-directed ligands (MTDLs) to act as multifunctional agents to treat this disease is the mainstream of current research. As a continuation of our previous studies, a series of 4-flexible amino-2-arylethenylquinoline derivatives as multi-target agents was efficiently synthesized and evaluated for the treatment of AD. Among these synthesized derivatives, some compounds exhibited strong self-induced Aβ1–42 aggregation inhibition and antioxidant activity. The structure-activity relationship was summarized, which confirmed that the introduction of a flexible amino group featuring a N,N-dimethylaminoalkylamino moiety at the 4-position increased the Aβ1–42 aggregation inhibition activity, with an inhibition ratio of 95.3% at 20 μM concentration. Compound 6b1, the optimal compound, was able to selectively chelate copper (II), and inhibit Cu2+-induced Aβ aggregation effectively. It also could disassemble the self-induced Aβ1–42 aggregation fibrils with a ratio of 64.3% at 20 μM concentration. Moreover, compound 6b1 showed low toxicity and a good neuroprotective effect against Aβ1–42-induced toxicity in SH-SY5Y cells. Furthermore, the step-down passive avoidance test indicated compound 6b1 significantly reversed scopolamine-induced memory deficit in mice. Taken together, these results suggested that compound 6b1 was a promising multi-target compound worthy of further study for AD.