Design, selection, and characterization of thioflavin-based intercalation compounds with metal chelating properties for application in Alzheimer's disease

Targeting Biometals in Alzheimer's Disease with Metal Chelating Agents Including Coumarin Derivatives

Numerous physiological processes happening in the human body, including cerebral development and function, require the participation of biometal ions such as iron, copper, and zinc. Their dyshomeostasis may, however, contribute to the onset of Alzheimer's disease (AD) and potentially other neurodegenerative diseases. Chelation of biometal ions is therefore a therapeutic strategy against AD. This review provides a survey of natural and synthetic chelating agents that are or could potentially be used to target the metal hypothesis of AD. Since metal dyshomeostasis is not the only pathological aspect of AD, and the nature of this disorder is very complex and multifactiorial, the most efficient therapeutics should target as many neurotoxic factors as possible. Various coumarin derivatives match this description and apart from being able to chelate metal ions, they exhibit the capacity to inhibit cholinesterases (ChEs) and monoamine oxidase B (MAO-B) while also possessing antioxidant, anti-inflammatory, and numerous other beneficial effects. Compounds based on the coumarin scaffold therefore represent a desirable class of anti-AD therapeutics.

Power of Dopamine: Multifunctional Compound Assisted Conversion of the Most Risk Factor into Therapeutics of Alzheimer's Disease

In Alzheimer's disease (AD), reactive oxygen species (ROS) plays a crucial role, which is produced from molecular oxygen with extracellular deposited amyloid-β (Aβ) aggregates through the reduction of a Cu2+ ion. In the presence of a small amount of redox-active Cu2+ ion, ROS is produced by the Aβ-Cu2+ complex as Aβ peptide alone is unable to generate excess ROS. Therefore, Cu2+ ion chelators are considered promising therapeutics against AD. Here, we have designed and synthesized a series of Schiff base derivatives (SB) based on 2-hydroxy aromatic aldehyde derivatives and dopamine. These SB compounds contain one copper chelating core, which captures the Cu2+ ions from the Aβ-Cu2+ complex. Thereby, it inhibits copper-induced amyloid aggregation as well as amyloid self-aggregation. It also inhibits copper-catalyzed ROS production through sequestering of Cu2+ ions. The uniqueness of our designed ligands has the dual property of dopamine, which not only acts as a ROS scavenger but also chelates the copper ion. The crystallographic analysis proves the power of the dopamine unit. Therefore, dual exploration of dopamine core can be considered as potential therapeutics for future AD treatment.

Targeting misfolding and aggregation of the amyloid-β peptide and mutant p53 protein using multifunctional molecules

Biomolecule misfolding and aggregation play a major role in human disease, spanning from neurodegeneration to cancer. Inhibition of these processes is of considerable interest, and due to the multifactorial nature of these diseases, the development of drugs that act on multiple pathways simultaneously is a promising approach. This Feature Article focuses on the development of multifunctional molecules designed to inhibit the misfolding and aggregation of the amyloid-β (Aβ) peptide in Alzheimer's disease (AD), and the mutant p53 protein in cancer. While for the former, the goal is to accelerate the removal of the Aβ peptide and associated aggregates, for the latter, the goal is reactivation via stabilization of the active folded form of mutant p53 protein and/or aggregation inhibition. Due to the similar aggregation pathway of the Aβ peptide and mutant p53 protein, a common therapeutic approach may be applicable.

Latest advances in dual inhibitors of acetylcholinesterase and monoamine oxidase B against Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain disease characterised by progressive memory loss and cognition impairment, ultimately leading to death. There are three FDA-approved acetylcholinesterase inhibitors (donepezil, rivastigmine, and galantamine, AChEIs) for the symptomatic treatment of AD. Monoamine oxidase B (MAO-B) has been considered to contribute to pathologies of AD. Therefore, we reviewed the dual inhibitors of acetylcholinesterase (AChE) and MAO-B developed in the last five years. In this review, these dual-target inhibitors were classified into six groups according to the basic parent structure, including chalcone, coumarin, chromone, benzo-fused five-membered ring, imine and hydrazine, and other scaffolds. Their design strategies, structure-activity relationships (SARs), and molecular docking studies with AChE and MAO-B were analysed and discussed, giving valuable insights for the subsequent development of AChE and MAO-B dual inhibitors. Challenges in the development of balanced and potent AChE and MAO-B dual inhibitors were noted, and corresponding solutions were provided.

Interaction studies of oxindole-derivatives with β-amyloid peptides inhibiting its aggregation induced by metal ions

Some hydrazones and Schiff bases derived from isatin, an endogenous oxindole formed in the metabolism of tryptophan, were obtained to investigate their effects on in vitro aggregation of β-amyloid peptides (Aβ), macromolecules implicated in Alzheimer's disease. Some hydrazone ligands, prepared by condensation reactions of isatin with hydrazine derivatives, showed a large affinity binding to the synthetic peptides Aβ, particularly to Aβ1-16. Measurements by NMR spectroscopy indicated that those interactions occur mainly at the metal binding site of the peptide, involving His6, His13, and His14 residues, and that hydrazone E-diastereoisomer interacts preferentially with the amyloid peptides. Experimental results were consistent with simulations using a docking approach, where it is demonstrated that the amino acid residues Glu3, His6, His13, and His14 are those that mostly interact with the ligands. Further, these oxindole-derived ligands can efficiently chelate copper(II) and zinc(II) ions, forming moderate stable [ML] 1:1 species. The corresponding formation constants were determined by UV/Vis spectroscopy, by titrations of the ligands with increasing amounts of metal salts, and the obtained log K values were in the range 2.74 to 5.11. Both properties, good affinity for amyloid peptides, and reasonably good capacity of chelating biometal ions, like copper and zinc, can explain the efficient inhibition of Aβ fragments aggregation, as shown by experiments carried out with the oxindole derivatives in the presence of metal ions.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Early Aggregation of Amyloid-β(1-42) Studied by Fluorescence Correlation Spectroscopy

Alzheimer's disease (AD) is a progressive neurodegenerative disease affecting cognitive and memory abilities and is believed to be linked to the formation and accumulation of neurotoxic aggregates of the Amyloid-β peptide (Aβ). In particular, it is the formation of soluble pre-fibrillar oligomers within the early stage of Aβ aggregation which is thought to represent a key step in the development of AD, thus underlining the interest in characterizing the aggregation process and the nature of these aggregates. In this context, fluorescence correlation spectroscopy (FCS) has emerged as a valuable alternative for the study of these systems in solution. Indeed, the use of FCS to study terminally labelled Aβ provides a means to detect changes in the size and concentration of initially monomeric Aβ samples by monitoring these fluorescently labelled species freely diffusing in solution with single-molecule resolution. Herein, we show how to employ FCS to study the early aggregation process of Aβ(1-42) and how this can be used to estimate the critical concentration for oligomer formation and to characterize the aggregates formed.

Drug discovery and amyotrophic lateral sclerosis: Emerging challenges and therapeutic opportunities

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of upper and lower motor neurons (MNs) leading to paralysis and, ultimately, death by respiratory failure 3-5 years after diagnosis. Edaravone and Riluzole, the only drugs currently approved for ALS treatment, only provide mild symptomatic relief to patients. Extraordinary progress in understanding the biology of ALS provided new grounds for drug discovery. Over the last two decades, mitochondria and oxidative stress (OS), iron metabolism and ferroptosis, and the major regulators of hypoxia and inflammation - HIF and NF-κB - emerged as promising targets for ALS therapeutic intervention. In this review, we focused our attention on these targets to outline and discuss current advances in ALS drug development. Based on the challenges and the roadblocks, we believe that the rational design of multi-target ligands able to modulate the complex network of events behind the disease can provide effective therapies in a foreseeable future.

Tailoring the AIE Chromogen 2-(2-Hydroxyphenyl)benzothiazole for Use in Enzyme-Triggered Molecular Brachytherapy

A targeted strategy for treating cancer is antibody-directed enzyme prodrug therapy, where the enzyme attached to the antibody causes conversion of an inactive small-molecule prodrug into an active drug. A limitation may be the diffusion of the active drug away from the antibody target site. A related strategy with radiotherapeutics entails enzymatically promoted conversion of a soluble to insoluble radiotherapeutic agent, thereby immobilizing the latter at the target site. Such a molecular brachytherapy has been scarcely investigated. In distinct research, the advent of molecular designs for aggregation-induced emission (AIE) suggests translational use in molecular brachytherapy. Here, several 2-(2-hydroxyphenyl)benzothiazole substrates that readily aggregate in aqueous solution (and afford AIE) were elaborated in this regard. In particular, (1) the 2-(2-hydroxyphenyl) unit was derivatized to bear a pegylated phosphodiester that imparts water solubility yet undergoes enzymatic cleavage, and (2) a p-phenol unit was attached to the benzo moiety to provide a reactive site for final-step iodination (here examined with natural abundance iodide). The pegylated phosphodiester-iodinated benzothiazole undergoes conversion from aqueous-soluble to aqueous-insoluble upon treatment with a phosphatase or phosphodiesterase. The aggregation is essential to molecular brachytherapy, whereas the induced emission of AIE is not essential but provides a convenient basis for research development. Altogether, 21 compounds were synthesized (18 new, 3 known via new routes). Taken together, blending biomedical strategies of enzyme prodrug therapy with materials chemistry concerning substances that undergo AIE may comprise a step forward on the long road toward molecular brachytherapy.

Novel Rivastigmine Derivatives as Promising Multi-Target Compounds for Potential Treatment of Alzheimer’s Disease

Alzheimer’s disease (AD) is the most serious and prevalent neurodegenerative disorder still without cure. Since its aetiology is diverse, recent research on anti-AD drugs has been focused on multi-target compounds. In this work, seven novel hybrids (RIV–BIM) conjugating the active moiety of the drug rivastigmine (RIV) with 2 isomeric hydroxyphenylbenzimidazole (BIM) units were developed and studied. While RIV assures the inhibition of cholinesterases, BIM provides further appropriate properties, such as inhibition of amyloid β-peptide (Aβ) aggregation, antioxidation and metal chelation. The evaluated biological properties of these hybrids included antioxidant activity; inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and Aβ₄₂ aggregation; as well as promotion of cell viability and neuroprotection. All the compounds are better inhibitors of AChE than rivastigmine (IC₅₀ = 32.1 µM), but compounds of series 5 are better inhibitors of BChE (IC₅₀ = 0.9−1.7 µM) than those of series 4. Series 5 also showed good capacity to inhibit self- (42.1−58.7%) and Cu(II)-induced (40.3−60.8%) Aβ aggregation and also to narrow (22.4−42.6%) amyloid fibrils, the relevant compounds being 5b and 5d. Some of these compounds can also prevent the toxicity induced in SH-SY5Y cells by Aβ₄₂ and oxidative stress. Therefore, RIV–BIM hybrids seem to be potential drug candidates for AD with multi-target abilities.

α-Lipoic Acid Has the Potential to Normalize Copper Metabolism, Which Is Dysregulated in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is an age-dependent progressive neurodegenerative disorder and the most common cause of dementia. The treatment and prevention of AD present immense yet unmet needs. One of the hallmarks of AD is the formation of extracellular amyloid plaques in the brain, composed of amyloid-β (Aβ) peptides. Besides major amyloid-targeting approach there is the necessity to focus also on alternative therapeutic strategies. One factor contributing to the development of AD is dysregulated copper metabolism, reflected in the intracellular copper deficit and excess of extracellular copper.

OBJECTIVE

In the current study, we follow the widely accepted hypothesis that the normalization of copper metabolism leads to the prevention or slowing of the disease and search for new copper-regulating ligands.

METHODS

We used cell culture, ICP MS, and Drosophila melanogaster models of AD.

RESULTS

We demonstrate that the natural intracellular copper chelator, α-lipoic acid (LA) translocates copper from extracellular to intracellular space in an SH-SY5Y-based neuronal cell model and is thus suitable to alleviate the intracellular copper deficit characteristic of AD neurons. Furthermore, we show that supplementation with LA protects the Drosophila melanogaster models of AD from developing AD phenotype by improving locomotor activity of fruit fly with overexpression of human Aβ with Iowa mutation in the fly brain. In addition, LA slightly weakens copper-induced smooth eye phenotype when amyloid-β protein precursor (AβPP) and beta-site AβPP cleaving enzyme 1 (BACE1) are overexpressed in eye photoreceptor cells.

CONCLUSION

Collectively, these results provide evidence that LA has the potential to normalize copper metabolism in AD.

Metals and Metal-Nanoparticles in Human Pathologies: From Exposure to Therapy

An increasing number of pathologies correlates with both toxic and essential metal ions dyshomeostasis. Next to known genetic disorders (e.g., Wilson's Disease and β-Thalassemia) other pathological states such as neurodegeneration and diabetes are characterized by an imbalance of essential metal ions. Metal ions can enter the human body from the surrounding environment in the form of free metal ions or metal-nanoparticles, and successively translocate to different tissues, where they are accumulated and develop distinct pathologies. There are no characteristic symptoms of metal intoxication, and the exact diagnosis is still difficult. In this review, we present metal-related pathologies with the most common onsets, biomarkers of metal intoxication, and proper techniques of metal qualitative and quantitative analysis. We discuss the possible role of drugs with metal-chelating ability in metal dyshomeostasis, and present recent advances in therapies of metal-related diseases.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Impact of Cu(II) and Al(III) on the conformational landscape of amyloidβ1-42

Metal ions have been found to play an important role in the formation of extracellular β-amyloid plaques, a major hallmark of Alzheimer's disease. In the present study, the conformational landscape of Aβ42 with Al(iii) and Cu(ii) has been explored using Gaussian accelerated molecular dynamics. Both metals reduce the flexibility of the peptide and entail a higher structural organization, although to different degrees. As a general trend, Cu(ii) binding leads to an increased α-helix content and to the formation of two α-helices that tend to organize in a U-shape. By contrast, most Al(iii) complexes induce a decrease in helical content, leading to more extended structures that favor the appearance of transitory β-strands.

Computational Design of Copper Ligands with Controlled Metal Chelating, Pharmacokinetics, and Redox Properties for Alzheimer's Disease

BACKGROUND

Redox active metal cations, such as Cu2 +, have been related to induce amyloid plaques formation and oxidative stress, which are two of the key events in the development of Alzheimer's disease (AD) and others metal promoted neurodegenerative diseases. In these oxidative events, standard reduction potential (SRP) is an important property especially relevant in the reactive oxygen species formation.

OBJECTIVE

The SRP is not usually considered for the selection of drug candidates in anti-AD treatments. In this work, we present a computational protocol for the selection of multifunctional ligands with suitable metal chelating, pharmacokinetics, and redox properties.

METHODS

The filtering process is based on quantum chemical calculations and the use of in silico tools. Calculations of SRP were performed by using the M06-2X density functional and the isodesmic approach. Then, a virtual screening technique (VS) was used for similar structure search.

RESULTS

Protocol application allowed the assessment of chelating, drug likeness, and redox properties of copper ligands. Those molecules showing the best features were selected as molecular scaffolds for a VS procedure in order to obtain related compounds. After applying this process, we present a list of candidates with suitable properties to prevent the redox reactions mediated by copper(II) ion.

CONCLUSION

The protocol incorporates SRP in the filtering stage and can be effectively used to obtain a set of potential drug candidates for AD treatments.

Longitudinal Functional Study of Murine Aging: A Resource for Future Study Designs

Aging is characterized by systemic declines in tissue and organ functions. Interventions that slow these declines represent promising therapeutics to protect against age-related disease and improve the quality of life. In this study, several interventions associated with lifespan extension in invertebrates or improvement of age-related disease were tested in mouse models to determine if they were effective in slowing tissue aging in a broad spectrum of functional assays. Benzoxazole, which extends the lifespan of Caenorhabditis elegans, slowed age-related femoral bone loss in mice. Rates of change were established for clinically significant parameters in untreated mice, including kyphosis, blood glucose, body composition, activity, metabolic measures, and detailed parameters of skeletal aging in bone. These findings have implications for the study of preclinical physiological aging and therapies targeting aging. Finally, an online application was created that includes the calculated rates of change and that enables power and variance to be calculated for many clinically important metrics of aging with an emphasis on bone. This resource will help in future study designs employing novel interventions in aging mice. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

The Influence of Ca2+ and Zn2+ on the Amyloid Fibril Formation by β-Casein

BACKGROUND

The amyloid fibril formation in different tissues or organs is related to amyloidosis. The Ca2+, Zn2+ and heparan sulfate (HS) are important elements and compositions in human body, which play a key role in regulating various physiological activities. Recently, there are increasing evidence suggest that they are closely linked to the amyloid fibril formation.

OBJECTIVE

The effect of Ca2+ and Zn2+ on the amyloid fibril formation by β-casein was investigated in the absence and presence of HS, which was significantly to explore the relationship between the concentration changes of Ca2+ and Zn2+ and amyloid fibril formation.

METHODS

In this work, the influence of Ca2+ and Zn2+ on the β-casein fibril formation in the absence and presence of HS was investigated by various methods of Thioflavin T fluorescence assay, transmission electron microscopy and intrinsic fluorescence measure.

RESULTS

The results demonstrated that Ca2+ and Zn2+ promoted the β-casein fibril formation. The effect of Ca2+ was greater than that of Zn2+. Meanwhile, the both metal ions had stronger effects when β-casein was incubated with HS together. In addition, it was also observed that the microenvironment of β-casein was changed because the intrinsic fluorescence peaks were red-shifted on the influence of Ca2+ and Zn2+.

CONCLUSION

Ca2+ and Zn2+ were capable of promoting the β-casein fibril formation in the both absence and presence of HS. This work set up the foundation for further researching of the amyloidosis pathogenesis and provided new insight for us to understand relationship between the inflammation and amyloidosis.

Multifunctional compounds for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia, and the prevalence of this currently untreatable disease is expected to rise in step with increased global life expectancy. AD is a multifaceted disorder commonly characterized by extracellular amyloid–beta (Aβ) aggregates, oxidative stress, metal ion dysregulation, and intracellular neurofibrillary tangles. This review will focus on medicinal inorganic chemistry strategies to target AD, with a focus on the Aβ peptide and its relation to metal ion dysregulation and oxidative stress. Multifunctional compounds designed to target multiple disease processes have emerged as promising therapeutic options, and recent reports detailing multifunctional metal-binding compounds, as well as discrete metal complexes, will be discussed.

Ruthenium(ii) p-cymene complexes of pyridine-2-carboxaldehyde and 2-amino benzothiazole-based ligands: cytoselective and in vitro live cell imaging agents

A new class of DNA targeting, highly cytoselective, luminescent Ru(ii)–arene complexes was developed.

Donepezil-based hybrids as multifunctional anti-Alzheimer's disease chelating agents: Effect of positional isomerization

The intricate and multifactorial nature of Alzheimer's disease (AD) requires the development of compounds able to hit different pathophysiological targets, such as cholinergic dysfunction, deposits of amyloid beta (Aβ) peptide and metal dyshomeostasis. In order to continue the search for new anti-AD drugs, a design strategy was once more followed based on repositioning donepezil (DNP) drug, by ortho-attaching a benzylpiperidine mimetic of DNP moiety to a hydroxyphenyl-benzimidazole (BIM) chelating unit (compound 1). Herein, compound 1 and a positional isomer 2 are compared in terms of their potential multiple properties: both present good acetylcholinesterase (AChE) inhibition (low μmolar range) and are moderate/good inhibitors of Aβ self- and Cu-mediated aggregation, the inhibition process being mainly due to ligand intercalation between the β-sheets of the fibrils; compound 1 has a higher chelating capacity towards Cu²⁺ and Zn²⁺ (pCu = 14.3, pZn = 6.4, pH 7.4, C_L/C_M = 10, C_M = 10^-6 M) than 2 (pCu = 10.7, pZn = 6.3), attributed to its ability to establish a tridentate (N,O,O) coordination to the metal ion. Both compounds are eligible as drug candidates for oral administration but compound 1 shows improved neuroprotective role by completely preventing Aβ-induced cell toxicity.

Direct Oxygenation of C-H Bonds through Photoredox and Palladium Catalysis

This report presents the oxygenation of C-H bonds via the merger of photocatalysis and Pd catalysis. Herein, we describe the utilization of a photocatalyst to oxidize an organopalladium(II) intermediate to high-valent Pd^III or Pd^IV intermediates, which promotes the formation of C-O bonds. The demonstrated method works efficiently with various directing groups, such as oxime ether and benzothiazole. The applicability of this direct C-O bond formation method is shown by synthesizing several metal complexes of 2-(benzo[d]thiazol-2-yl)phenol that can be used in organic light-emitting diodes and pharmaceuticals.

Twisted Schiff-base macrocycle showing excited-state intramolecular proton-transfer (ESIPT): assembly and sensing properties

A Schiff-base macrocyclic host showing ESIPT-based AIEE and nanoparticle assembly.

Aryldiazoquinoline based multifunctional small molecules for modulating Aβ42aggregation and cholinesterase activity related to Alzheimer's disease

Novel series of aryldiazoquinoline multifunctional molecules controls amyloid formation and neuro-protective role by inhibiting esterase enzymes.

Engineering of an archaeal phosphodiesterase to trigger aggregation-induced emission (AIE) of synthetic substrates

Aggregation-induced emission (AIE) probes that can be triggered by enzymatic activity are valuable for applications across the life sciences.

Recent Developments in Metal-Based Drugs and Chelating Agents for Neurodegenerative Diseases Treatments

The brain has a unique biological complexity and is responsible for important functions in the human body, such as the command of cognitive and motor functions. Disruptive disorders that affect this organ, e.g. neurodegenerative diseases (NDDs), can lead to permanent damage, impairing the patients' quality of life and even causing death. In spite of their clinical diversity, these NDDs share common characteristics, such as the accumulation of specific proteins in the cells, the compromise of the metal ion homeostasis in the brain, among others. Despite considerable advances in understanding the mechanisms of these diseases and advances in the development of treatments, these disorders remain uncured. Considering the diversity of mechanisms that act in NDDs, a wide range of compounds have been developed to act by different means. Thus, promising compounds with contrasting properties, such as chelating agents and metal-based drugs have been proposed to act on different molecular targets as well as to contribute to the same goal, which is the treatment of NDDs. This review seeks to discuss the different roles and recent developments of metal-based drugs, such as metal complexes and metal chelating agents as a proposal for the treatment of NDDs.

Novel dual-action prodrug triggers apoptosis in glioblastoma cells by releasing a glutathione quencher and lysine-specific histone demethylase 1A inhibitor

Targeting epigenetic mechanisms has shown promise against several cancers but has so far been unsuccessful against glioblastoma (GBM). Altered histone 3 lysine 4 methylation and increased lysine‐specific histone demethylase 1A (LSD1) expression in GBM tumours nonetheless suggest that epigenetic mechanisms are involved in GBM. We engineered a dual‐action prodrug, which is activated by the high hydrogen peroxide levels associated with GBM cells. This quinone methide phenylaminecyclopropane prodrug releases the LSD1 inhibitor 2‐phenylcyclopropylamine with the glutathione scavenger para‐quinone methide to trigger apoptosis in GBM cells. Quinone methide phenylaminocyclopropane impaired GBM cell behaviours in two‐dimensional and three‐dimensional assays, and triggered cell apoptosis in several primary and immortal GBM cell cultures. These results support our double‐hit hypothesis of potentially targeting LSD1 and quenching glutathione, in order to impair and kill GBM cells but not healthy astrocytes. Our data suggest this strategy is effective at selectively targeting GBM and potentially other types of cancers.

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Luminescent bis(benzo[d]thiazolyl)quinoxaline: facile synthesis, nucleic acid and protein BSA interaction, live-cell imaging, biopharmaceutical research and cancer theranostic application

A series of quinoxaline-2-hydroxyphenylbenzothiazole scaffolds were synthesized and characterized using NMR, UV, fluorescence spectroscopy and LCMS. These newly synthesized compounds were found to be cytotoxic in human epithelioid cervix carcinoma (HeLa) and human colon cancer cell lines (Caco-2). Selectivity of the compounds 7e and 7g are more than 9 fold higher in Caco-2 cells with respect to the normal cell line HEK-293. The most fluorescent compound 7e has displayed high cytoselectivity, significant cellular uptake in HeLa cells and strong binding efficacy with DNA and BSA. The most potent compound 7g has primarily classified as BCS class 4 and BDDCS class 4.

A series of luminescent bis(benzo[d]thiazolyl)quinoxalines have been synthesized and their fluorescence properties, anticancer potency, DNA and BSA interactions, cellular uptake, and metabolic stabilities are investigated.

Dual-Aptamer-Conjugated Molecular Modulator for Detecting Bioactive Metal Ions and Inhibiting Metal-Mediated Protein Aggregation

Bioactive metal ions play important roles in both physiological and pathological processes. Developing biosensing probes for bioactive metal ion detection can contribute to fields including disease diagnosis and therapy and studying the mechanisms of biological activities. In this work, we designed a dual-aptamer-conjugated molecular modulator that can detect Zn²⁺ and further inhibit Zn²⁺-induced amyloid β (Aβ) aggregation. The molecular modulator is able to selectively target Aβ species and block Zn²⁺ due to the specific recognition capability of aptamers. With the binding of Zn²⁺, the fluorescence signal of this molecular modulator is restored, thus allowing for Zn²⁺ detection. More importantly, this molecular modulator can inhibit the generation of Zn²⁺-triggered Aβ aggregates due to the trapping of Zn²⁺ around Aβ species. Circular dichroism measurements reveal that the dual-aptamer-conjugated molecular modulator prevents the conformational transition of the Aβ monomer from a random coil to a β-sheet. Furthermore, after treating with the molecular modulator, no Aβ aggregate is observed in the Aβ solution with added Zn²⁺, demonstrating that Aβ aggregation is successfully inhibited by this molecular modulator. Our approach provides a promising tool for detecting bioactive metal ions and studying the molecular mechanisms behind life activities.

Modulating Conformation of Aβ-Peptide: An Effective Way to Prevent Protein-Misfolding Disease

Alzheimer's disease (AD) is a typical protein-misfolding disease. Aggregation of amyloid β-peptide (Aβ) plays a key role in the etiology of AD. The misfolding of Aβ results in the formation of β-sheet-rich aggregates and damages the function of neurons. A modified polyoxometalate (POM), [CoL(H₂O)]₂[CoL]₂[HAs^VMo^V₆Mo^VI₆O₄₀] [CAM, L = 2-(1 H-pyrazol-3-yl)pyridine], was designed to disaggregate the Aβ aggregates, where L acts as an Aβ-targeting group and POM as a conformational modulator. X-ray crystallography shows that CAM is composed of a ε-Keggin unit and four coordination units. CAM can disaggregate the β-sheet-rich fibrils and metal-induced or self-aggregated Aβ aggregates, and it further inhibits the production of ROS; as a result, it can protect the neurons from synaptic toxicity induced by Zn²⁺- or Cu²⁺-Aβ aggregates or Aβ self-aggregation. The mechanism of disaggregation involves a transformation of Aβ conformation from β-sheet to other conformers. The nature of the process is an interference of the β-sheet conformation by CAM via hydrogen bonding. CAM specifically interacts with Aβ aggregates but does not disturb the cerebral metal homeostasis and enzymatic systems. Molecular simulation suggests that the appropriate size of CAM and the cavity of β-sheets facilitate the interaction between CAM and Aβ aggregates; additionally, the H-bonding-favored amino acid residues in the cavity provide a precondition for the interaction. Moreover, CAM is lipophilic and capable of penetrating the blood-brain barrier, and it is metabolizable without causing an untoward effect to mice at high dosages. In view of the significant inhibitory effect on the Aβ aggregation and related neurotoxicity, CAM represents a new type of leading compounds with a distinctive mechanism of action for the treatment of Alzheimer' disease. The conception of this study may be applied to other protein-misfolding diseases caused by conformational changes.

Bifunctionality of Iminodiacetic Acid-Modified Lysozyme on Inhibiting Zn2+-Mediated Amyloid β-Protein Aggregation

Aggregation of amyloid β-proteins (Aβ) mediated by metal ions such as Zn²⁺ has been suggested to be implicated in the progression of Alzheimer's disease (AD). Hence, development of bifunctional agents capable of inhibiting Aβ aggregation and modulating metal-Aβ species is an effective strategy for the treatment of AD. In this work, we modified iminodiacetic acid (IDA) onto human lysozyme (hLys) surface to create an inhibitor of Zn²⁺-mediated Aβ aggregation and cytotoxicity. The IDA-modified hLys (IDA-hLys) retained the stability and biocompatibility of native hLys. Extensive biophysical and biological analyses indicated that IDA-hLys significantly attenuated Zn²⁺-mediated Aβ aggregation and cytotoxicity due to its strong binding affinity for Zn²⁺, whereas native hLys showed little effect. Stopped-flow fluorescence spectroscopy showed that IDA-hLys could protect Aβ from Zn²⁺-induced aggregation and rapidly depolymerize Zn²⁺-Aβ aggregates. The research indicates that IDA-hLys is a bifunctional agent capable of inhibiting Aβ fibrillization and modulating Zn²⁺-mediated Aβ aggregation and cytotoxicity as a strong Zn²⁺ chelator.