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Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Yeong KY, Berdigaliyev N, Chang Y

ACS Chem Neurosci, 2020 12 16;11(24):4073-4091.
PMID: 33280374 DOI: 10.1021/acschemneuro.0c00696

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.
Fulltext Ethyl 2-[5-(4-fluoro-phen-yl)pyridin-3-yl]-1-[3-(2-oxopyrrolidin-1-yl)prop-yl]-1H-benzimidazole-5-carboxyl-ate

Yeong KY, Ali MA, Choon TS, Rosli MM, Razak IA

Acta Crystallogr Sect E Struct Rep Online, 2013;69(Pt 7):o1013-4.
PMID: 24046597 DOI: 10.1107/S1600536813014177

In the title compound, C28H27FN4O3·H2O, the benzimidazole ring system is essentially planar with a maximum deviation of 0.028 (1) Å. It makes dihedral angles of 47.59 (5) and 60.31 (5)°, respectively, with the pyridine and benzene rings, which make a dihedral angle of 22.58 (6)° with each other. The pyrrolidine ring shows an envelope conformation with one of the methyl-ene C atoms as the flap. In the crystal, the components are connected into a tape along the b-axis direction through O-H⋯O and O-H⋯N hydrogen bonds and a π-π inter-action between the pyridine and benzene rings [centroid-centroid distance of 3.685 (8) Å]. The tapes are further linked into layers parallel to the ab plane by C-H⋯O and C-H⋯F inter-actions.
Fulltext Ethyl 2-[4-(di-methyl-amino)-phen-yl]-1-phenyl-1H-benzimidazole-5-carboxyl-ate

Yeong KY, Ali MA, Choon TS, Rosli MM, Razak IA

Acta Crystallogr Sect E Struct Rep Online, 2013 Jun 1;69(Pt 6):o886.
PMID: 23795062 DOI: 10.1107/S1600536813012440

In the title compound, C24H23N3O2, the benzimidazole ring system makes dihedral angles of 7.28 (5) and 67.17 (5)°, respectively, with the planes of the benzene and phenyl rings, which in turn make a dihedral angle of 69.77 (6)°. In the crystal, mol-ecules are connected by C-H⋯N and C-H⋯O inter-actions, forming a layer parallel to the bc plane. A π-π inter-action, with a centroid-centroid distance of 3.656 (1) Å, is observed in the layer.
Method validation in quantitative analysis of phase I and phase II metabolites of mitragynine in human urine using liquid chromatography-tandem mass spectrometry

Lee MJ, Ramanathan S, Mansor SM, Yeong KY, Tan SC

Anal Biochem, 2018 02 15;543:146-161.
PMID: 29248503 DOI: 10.1016/j.ab.2017.12.021

A method using solid phase extraction and liquid chromatography-tandem mass spectrometry to quantitatively detect mitragynine, 16-carboxy mitragynine, and 9-O-demethyl mitragynine in human urine samples was developed and validated. The relevant metabolites were identified using multiple reaction monitoring in positive ionization mode using nalorphine as an internal standard. The method was validated for accuracy, precision, recovery, linearity, and lower limit of quantitation. The intra- and inter-day accuracy and precision were found in the range of 83.6-117.5% with coefficient of variation less than 13%. The percentage of recovery for mitragynine, 16-carboxy mitragynine, and 9-O-demethyl mitragynine was within the range of 80.1-118.9%. The lower limit of quantification was 1 ng/mL for mitragynine, 2 ng/mL for 16-carboxy mitragynine, and 50 ng/mL for 9-O-demethyl mitragynine. The developed method was reproducible, high precision and accuracy with good linearity and recovery for mitragynine, 16-carboxy mitragynine, and 9-O-demethyl mitragynine in human urine.
In silico studies, synthesis and pharmacological evaluation to explore multi-targeted approach for imidazole analogues as potential cholinesterase inhibitors with neuroprotective role for Alzheimer's disease

Gurjar AS, Darekar MN, Yeong KY, Ooi L

Bioorg Med Chem, 2018 05 01;26(8):1511-1522.
PMID: 29429576 DOI: 10.1016/j.bmc.2018.01.029

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with multiple factors associated with its pathogenesis. Our strategy against AD involves design of multi-targeted 2-substituted-4,5-diphenyl-1H-imidazole analogues which can interact and inhibit AChE, thereby, increasing the synaptic availability of ACh, inhibit BuChE, relieve induced oxidative stress and confer a neuroprotective role. Molecular docking was employed to study interactions within the AChE active site. In silico ADME study was performed to estimate pharmacokinetic parameters. Based on computational studies, some analogues were synthesized and subjected to pharmacological evaluation involving antioxidant activity, toxicity and memory model studies in animals followed by detailed mechanistic in vitro cholinesterase inhibition study. Amongst the series, analogue 13 and 20 are the most promising multi-targeted candidates which can potentially increase memory, decrease free radical levels and protect neurons against cognitive deficit.
Ethyl nitrobenzoate: A novel scaffold for cholinesterase inhibition

Yeong KY, Liew WL, Murugaiyah V, Ang CW, Osman H, Tan SC

Bioorg Chem, 2017 02;70:27-33.
PMID: 27863748 DOI: 10.1016/j.bioorg.2016.11.005

A series of novel cholinesterase inhibitors containing nitrobenzoate core structure were synthesized by a facile and efficient method. The structure of the novel compounds were fully characterized and confirmed by analytical as well as spectroscopic methods. Compound indicated as 2f was found to possess the best cholinesterase inhibitory activities of all the evaluated compounds. Results suggest that 2f is a selective acetylcholinesterase inhibitor, although it also inhibits butyrylcholinesterase at higher concentration. Kinetics inhibition result suggest that 2f is a mixed-mode inhibitor of acetylcholinesterase. In addition, it was found to have low cytotoxicity. Molecular docking on compound 2f was carried out to rationalize the observed in vitro enzymatic assay results. Most importantly, the potential of nitrobenzoate derivatives as cholinesterase inhibitor was shown through this study. In summary, we discovered nitrobenzoates as a new scaffold that may eventually yield useful compounds in treatment of Alzheimer's disease.
Discovery of gamma-mangostin from Garcinia mangostana as a potent and selective natural SIRT2 inhibitor

Yeong KY, Khaw KY, Takahashi Y, Itoh Y, Murugaiyah V, Suzuki T

Bioorg Chem, 2020 01;94:103403.
PMID: 31711765 DOI: 10.1016/j.bioorg.2019.103403

Studies have suggested that sirtuin inhibition may have beneficial effects on several age-related diseases such as neurodegenerative disorders and cancer. Garcinia mangostana is a well-known tropical plant found mostly in South East Asia with several positive health effects. Some of its phytochemicals such as α-mangostin was found to be able to modulate sirtuin activity in mice and was implicated with inflammation, diabetes and obesity. However, comprehensive studies on sirtuin activity by the prenylated xanthones extracted from Garcinia mangostana have yet to be reported. The present study led to the discovery and identification of γ-mangostin as a potent and selective SIRT2 inhibitor. It was demonstrated that γ-mangostin was able to increase the α-tubulin acetylation in MDA-MD-231 and MCF-7 breast cancer cells. It was also found to possess potent antiproliferative activity against both cell lines. In addition, it was able to induce neurite outgrowth in the N2a cells.
Fulltext Shaping the future of antiviral Treatment: Spotlight on Nucleobase-Containing drugs and their revolutionary impact

Wong XK, Ng CS, Yeong KY

Bioorg Chem, 2024 Mar;144:107150.
PMID: 38309002 DOI: 10.1016/j.bioorg.2024.107150

Nucleobases serve as essential molecular frameworks present in both natural and synthetic compounds that exhibit notable antiviral activity. Through molecular modifications, novel nucleobase-containing drugs (NCDs) have been developed, exhibiting enhanced antiviral activity against a wide range of viruses, including the recently emerged SARS‑CoV‑2. This article provides a detailed examination of the significant advancements in NCDs from 2015 till current, encompassing various aspects concerning their mechanisms of action, pharmacology and antiviral properties. Additionally, the article discusses antiviral prodrugs relevant to the scope of this review. It fills in the knowledge gap by examining the structure-activity relationship and trend of NCDs as therapeutics against a diverse range of viral diseases, either as approved drugs, clinical candidates or as early-stage development prospects. Moreover, the article highlights on the status of this field of study and addresses the prevailing limitations encountered.
Scopolamine, a Toxin-Induced Experimental Model, Used for Research in Alzheimer's Disease

Chen WN, Yeong KY

CNS Neurol Disord Drug Targets, 2020;19(2):85-93.
PMID: 32056532 DOI: 10.2174/1871527319666200214104331

Scopolamine as a drug is often used to treat motion sickness. Derivatives of scopolamine have also found applications as antispasmodic drugs among others. In neuroscience-related research, it is often used to induce cognitive disorders in experimental models as it readily permeates the bloodbrain barrier. In the context of Alzheimer's disease, its effects include causing cholinergic dysfunction and increasing amyloid-β deposition, both of which are hallmarks of the disease. Hence, the application of scopolamine in Alzheimer's disease research is proven pivotal but seldom discussed. In this review, the relationship between scopolamine and Alzheimer's disease will be delineated through an overall effect of scopolamine administration and its specific mechanisms of action, discussing mainly its influences on cholinergic function and amyloid cascade. The validity of scopolamine as a model of cognitive impairment or neurotoxin model will also be discussed in terms of advantages and limitations with future insights.
Benzimidazoles in Drug Discovery: A Patent Review

Law CSW, Yeong KY

ChemMedChem, 2021 06 17;16(12):1861-1877.
PMID: 33646618 DOI: 10.1002/cmdc.202100004

Benzimidazole is a heterocyclic ring system that has been widely studied in the pharmaceutical field. For the past decade, numerous benzimidazole derivatives have been synthesized and evaluated for their wide range of pharmacological activities, which are beneficial for drug development. This article presents the biological effects of benzimidazole derivatives in each invention from 2015 to 2020. Two patent databases, Google Patents and Lens, were used to locate relevant granted patent applications. Specifically, this review delineates the role of patented benzimidazoles from a disease-centric perspective and examines the mechanisms of action of these compounds in related diseases. Most of the benzimidazoles have shown good activities against various target proteins. Whilst several of them have progressed into clinical trials, most patents presented novel therapeutic approaches for respective target diseases. Hence, their potential in being developed into clinical drugs are also discussed.
A Patent Review on the Current Developments of Benzoxazoles in Drug Discovery

Wong XK, Yeong KY

ChemMedChem, 2021 11 05;16(21):3237-3262.
PMID: 34289258 DOI: 10.1002/cmdc.202100370

The benzoxazole moiety is widely found in various natural compounds, which are often found to be biologically active. Due to its versatile biological properties, benzoxazole has been incorporated as an essential pharmacophore and substructure in many medicinal compounds. In the past years, numerous benzoxazole derivatives have been synthesised and evaluated for their biological potential. The wide range in therapeutic potential of benzoxazole derivatives is related to the favourable interactions of the benzoxazole moiety with different protein targets. Herein we review the biological activities of benzoxazole derivatives patented within the past six years. Using the Lens database, granted patents issued from 2015 to 2020 were retrieved. The patented benzoxazole derivatives demonstrated excellent activity against various protein targets and diseases, with some reaching clinical trial stage. Pharmacological and medicinal aspects of patented benzoxazole derivatives are discussed. The recent development and drawbacks are also reviewed.
Contrasting sirtuin and poly(ADP-ribose)polymerase activities of selected 2,4,6-trisubstituted benzimidazoles

Yeong KY, Tan SC, Mai CW, Leong CO, Chung FF, Lee YK, et al.

Chem Biol Drug Des, 2018 01;91(1):213-219.
PMID: 28719017 DOI: 10.1111/cbdd.13072

Both sirtuin and poly(ADP-ribose)polymerase (PARP) family of enzymes utilize NAD+ as co-substrate. Inhibitors of sirtuins and PARPs are important tools in drug discovery as they are reported to be linked to multiple diseases such as cancer. New potent sirtuin inhibitors (2,4,6-trisubstituted benzimidazole) were discovered from reported PARP inhibitor scaffold. Interestingly, the synthesized compounds have contrasting sirtuin and PARP-1 inhibitory activities. We showed that modification on benzimidazoles may alter their selectivity toward sirtuin or PARP-1 enzymes. This offers an opportunity for further discovery and development of new promising sirtuin inhibitors. Molecular docking studies were carried out to aid the rationalization of these observations. Preliminary antiproliferative studies of selected compounds against nasopharyngeal cancer cells also showed relatively promising results.
Synthesis, Molecular Docking, and Biological Evaluation of Benzimidazole Derivatives as Selective Butyrylcholinesterase Inhibitors

Ha ZY, Ong HC, Oo CW, Yeong KY

Curr Alzheimer Res, 2020;17(13):1177-1185.
PMID: 33602088 DOI: 10.2174/1567205018666210218151228

BACKGROUND: Benzimidazole is an interesting pharmacophore which has been extensively studied in medicinal chemistry due to its high affinity towards various enzymes and receptors. Its derivatives have been previously shown to possess a wide range of biological activities including anthelmintic, antihypertensive, antiulcer, as well as anticholinesterase activity.
OBJECTIVE: The objective of this study is to search for more potent benzimidazole-based cholinesterase inhibitors, through the modification of the 1- and 2-positions of the benzimidazole core.
METHODS: Synthesis of compounds were carried out via a 4-step reaction scheme following a previously reported protocol. Structure-activity relationship of the compounds are established through in vitro cholinesterase assays and in silico docking studies. Furthermore, cytotoxicity and blood brain barrier (BBB) permeability of the compounds were also investigated.
RESULTS: Among the synthesised compounds, three of them (5IIa, 5IIb, and 5IIc) exhibited potent selective butyrylcholinesterase inhibition at low micromolar level. The compounds did not show any significant cytotoxicity when tested against a panel of human cell lines. Moreover, the most active compound, 5IIc, was highly permeable across the blood brain barrier.
CONCLUSION: In total 10 benzimidazole derivatives were synthesized and screened for their AChE and BuChE inhibitory activities. Lead compound 5Iic, represents a valuable compound for further development as potential AD therapeutics.
Natural Sirtuin Modulators in Drug Discovery: A Review (2010 -2020)

Chang Y, Yeong KY

Curr Med Chem, 2021 Mar 29.
PMID: 33781187 DOI: 10.2174/0929867328666210329124415

There have been intense research interests in sirtuins since the establishment of their regulatory roles in a myriad of pathological processes. In the last two decades, much research efforts have been dedicated to the development of sirtuin modulators. Although synthetic sirtuin modulators are the focus, natural modulators remain an integral part to be further explored in this area as they are found to possess therapeutic potential in various diseases including cancers, neurodegenerative diseases, and metabolic disorders. Owing to the importance of this cluster of compounds, this review gives a current stand on the naturally occurring sirtuin modulators, , associated molecular mechanisms and their therapeutic benefits.. Furthermore, comprehensive data mining resulted in detailed statistical data analyses pertaining to the development trend of sirtuin modulators from 2010-2020. Lastly, the challenges and future prospect of natural sirtuin modulators in drug discovery will also be discussed.
Repurposing Antihypertensive Drugs for the Management of Alzheimer's Disease

Law CSW, Yeong KY

Curr Med Chem, 2021;28(9):1716-1730.
PMID: 32164502 DOI: 10.2174/0929867327666200312114223

Alzheimer's disease (AD) is a neurodegenerative disorder that has affected millions of people worldwide. However, currently, there is no treatment to cure the disease. The AD drugs available in the market only manage the disease symptomatically and the effects are usually short-term. Thus, there is a need to look at alternatives AD therapies. This literature review aims to shed some light on the potential of repurposing antihypertensives to treat AD. Mid-life hypertension has not only been recognised as a risk factor for AD, but its relation with AD has also been well established. Hence, antihypertensives were postulated to be beneficial in managing AD. Four classes of antihypertensives, as well as their potential limitations and prospects in being utilised as AD therapeutics, were discussed in this review.
From Nucleic Acids to Drug Discovery: Nucleobases as Emerging Templates for Drug Candidates

Wong XK, Yeong KY

Curr Med Chem, 2021 Oct 27;28(34):7076-7121.
PMID: 33588718 DOI: 10.2174/0929867328666210215113828

Nucleobases represent key structural motifs in biologically active molecules, including synthetic and natural products. Molecular modifications made on nucleobases or their isolation from natural sources are being widely investigated for the development of drugs with improved potency for the treatment of different diseases, such as cancer, as well as viral and bacterial infections. This review article focuses on the nucleobase analogue drug developments of the past 20 years (2000-2020). Various pharmacological and medicinal aspects of nucleobases and their analogues are discussed. The current state and limitations are also highlighted.
Fulltext Potential Roles of α-amylase in Alzheimer's Disease: Biomarker and Drug Target

Chen WN, Tang KS, Yeong KY

Curr Neuropharmacol, 2022;20(8):1554-1563.
PMID: 34951390 DOI: 10.2174/1570159X20666211223124715

Alzheimer's disease (AD), the most common form of dementia, is pathologically characterized by the deposition of amyloid-β plaques and the formation of neurofibrillary tangles. In a neurodegenerative brain, glucose metabolism is also impaired and considered as one of the key features in AD patients. The impairment causes a reduction in glucose transporters and the uptake of glucose as well as alterations in the specific activity of glycolytic enzymes. Recently, it has been reported that α-amylase, a polysaccharide-degrading enzyme, is present in the human brain. The enzyme is known to be associated with various diseases such as type 2 diabetes mellitus and hyperamylasaemia. With this information at hand, we hypothesize that α-amylase could have a vital role in the demented brains of AD patients. This review aims to shed insight into the possible link between the expression levels of α-amylase and AD. Lastly, we also cover the diverse role of amylase inhibitors and how they could serve as a therapeutic agent to manage or stop AD progression.
Fulltext Linking Diabetes to Alzheimer's Disease: Potential Roles of Glucose Metabolism and Alpha-Glucosidase

Wee AS, Nhu TD, Khaw KY, Tang KS, Yeong KY

Curr Neuropharmacol, 2023;21(10):2036-2048.
PMID: 36372924 DOI: 10.2174/1570159X21999221111102343

Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) are more prevalent with ageing and cause a substantial global socio-economic burden. The biology of these two conditions is well elaborated, but whether AD and type 2 DM arise from coincidental roots in ageing or are linked by pathophysiological mechanisms remains unclear. Research findings involving animal models have identified mechanisms shared by both AD and type 2 DM. Deposition of β-amyloid peptides and formation of intracellular neurofibrillary tangles are pathological hallmarks of AD. Type 2 DM, on the other hand, is a metabolic disorder characterised by hyperglycaemia and insulin resistance. Several studies show that improving type 2 DM can delay or prevent the development of AD, and hence, prevention and control of type 2 DM may reduce the risk of AD later in life. Alpha-glucosidase is an enzyme that is commonly associated with hyperglycaemia in type 2 DM. However, it is uncertain if this enzyme may play a role in the progression of AD. This review explores the experimental evidence that depicts the relationship between dysregulation of glucose metabolism and AD. We also delineate the links between alpha-glucosidase and AD and the potential role of alpha-glucosidase inhibitors in treating AD.
Butyrylcholinesterase: A Multifaceted Pharmacological Target and Tool

Ha ZY, Mathew S, Yeong KY

Curr Protein Pept Sci, 2020;21(1):99-109.
PMID: 31702488 DOI: 10.2174/1389203720666191107094949

Butyrylcholinesterase is a serine hydrolase that catalyzes the hydrolysis of esters in the body. Unlike its sister enzyme acetylcholinesterase, butyrylcholinesterase has a broad substrate scope and lower acetylcholine catalytic efficiency. The difference in tissue distribution and inhibitor sensitivity also points to its involvement external to cholinergic neurotransmission. Initial studies on butyrylcholinesterase showed that the inhibition of the enzyme led to the increment of brain acetylcholine levels. Further gene knockout studies suggested its involvement in the regulation of amyloid-beta, a brain pathogenic protein. Thus, it is an interesting target for neurological disorders such as Alzheimer's disease. The substrate scope of butyrylcholinesterase was recently found to include cocaine, as well as ghrelin, the "hunger hormone". These findings led to the development of recombinant butyrylcholinesterase mutants and viral gene therapy to combat cocaine addiction, along with in-depth studies on the significance of butyrylcholinesterase in obesity. It is observed that the pharmacological impact of butyrylcholinesterase increased in tandem with each reported finding. Not only is the enzyme now considered an important pharmacological target, it is also becoming an important tool to study the biological pathways in various diseases. Here, we review and summarize the biochemical properties of butyrylcholinesterase and its roles, as a cholinergic neurotransmitter, in various diseases, particularly neurodegenerative disorders.
Monitoring of heavy metal pollution in urban and rural environments across Pakistan using House crows (Corvus splendens) as bioindicator

Iqbal F, Ayub Q, Wilson R, Song BK, Talei A, Yeong KY, et al.

Environ Monit Assess, 2021 Mar 30;193(4):237.
PMID: 33783594 DOI: 10.1007/s10661-021-08966-7

A widely distributed urban bird, the house crow (Corvus splendens), was used to assess bioavailable heavy metals in urban and rural environments across Pakistan. Bioaccumulation of arsenic (As), zinc (Zn), lead (Pb), cadmium (Cd), nickel (Ni), iron (Fe), manganese (Mn), chromium (Cr), and copper (Cu) was investigated in wing feathers of 96 crows collected from eight locations and categorized into four groups pertaining to their geographical and environmental similarities. Results revealed that the concentrations of Pb, Ni, Mn, Cu, and Cr were positively correlated and varied significantly among the four groups. Zn, Fe, Cr, and Cu regarded as industrial outputs, were observed in birds both in industrialized cities and in adjoining rural agricultural areas irrigated through the Indus Basin Irrigation System. Birds in both urban regions accrued Pb more than the metal toxicity thresholds for birds. The house crow was ranked in the middle on the metal accumulation levels in feathers between highly accumulating raptor and piscivore and less contaminated insectivore and granivore species in the studied areas,. This study suggests that the house crow is an efficient bioindicator and supports the feasibility of using feathers to discriminate the local pollution differences among terrestrial environments having different levels and kinds of anthropogenic activities.

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