Development of dual targeting inhibitors against aggregations of amyloid-β and tau protein

Cross-talk between amyloid beta peptides and tau proteins in Co-aggregation investigating with the combination of coarse-grained and all-atom simulations

The synergistic roles of amyloid beta (Aβ) peptides and tau proteins in the pathogenesis of Alzheimer's disease (AD) have garnered increasing attention. However, the mechanisms underlying their interactions and co-assembly remain largely unknown. Due to the rapid aggregation properties of Aβ and tau, current experimental methods face challenges in observing these interactions. In this study, we conducted coarse-grained (CG) simulations in conjunction with all-atom (AA) simulations to explore the initial stages of self-assembly of Aβ monomers in both the presence and absence of tau. The comparative results demonstrate that tau enhances the aggregation of Aβ and competes with Aβ for binding to fibrils. A gradual growth model is proposed to describe the initial co-aggregation process, wherein two specific domains of tau, R2 and R3, preferentially interact with Aβ to form dimers or trimers through electrostatic forces. Key regions have also been identified that facilitate binding with Aβ. These findings provide valuable structural and dynamic insights into the interaction between Aβ and tau, as well as the initial aggregation process, which could aid in elucidating the pathology of AD and in the development of novel therapeutic strategies for the disease.

Innovative pathological network-based multitarget approaches for Alzheimer's disease treatment

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and is a major health threat globally. Its prevalence is forecasted to exponentially increase during the next 30 years due to the global aging population. Currently, approved drugs are merely symptomatic, being ineffective in delaying or blocking the relentless disease advance. Intensive AD research describes this disease as a highly complex multifactorial disease. Disclosure of novel pathological pathways and their interconnections has had a major impact on medicinal chemistry drug development for AD over the last two decades. The complex network of pathological events involved in the onset of the disease has prompted the development of multitarget drugs. These chemical entities combine pharmacological activities toward two or more drug targets of interest. These multitarget-directed ligands are proposed to modify different nodes in the pathological network aiming to delay or even stop disease progression. Here, we review the multitarget drug development strategy for AD during the last decade.

Protein aggregation and neurodegenerative disease: Structural outlook for the novel therapeutics

Before the controversial approval of humanized monoclonal antibody lecanemab, which binds to the soluble amyloid-β protofibrils, all the treatments available earlier, for Alzheimer's disease (AD) were symptomatic. The researchers are still struggling to find a breakthrough in AD therapeutic medicine, which is partially attributable to lack in understanding of the structural information associated with the intrinsically disordered proteins and amyloids. One of the major challenges in this area of research is to understand the structural diversity of intrinsically disordered proteins under in vitro conditions. Therefore, in this review, we have summarized the in vitro applications of biophysical methods, which are aimed to shed some light on the heterogeneity, pathogenicity, structures and mechanisms of the intrinsically disordered protein aggregates associated with proteinopathies including AD. This review will also rationalize some of the strategies in modulating disease-relevant pathogenic protein entities by small molecules using structural biology approaches and biophysical characterization. We have also highlighted tools and techniques to simulate the in vivo conditions for native and cytotoxic tau/amyloids assemblies, urge new chemical approaches to replicate tau/amyloids assemblies similar to those in vivo conditions, in addition to designing novel potential drugs.

Photosensitizers with aggregation-induced far-red/near-infrared emission for versatile visualization and broad-spectrum photodynamic killing of pathogenic microbes

The exploration of photosensitizers with aggregation-induced emission (AIE PSs) for efficient visualization and broad-spectrum photodynamic killing of pathogenic microbes is a significant task. Herein, two far-red/near-infrared AIE-active PSs (TBTPy and TBTCy) were attained to show efficient Type I and Type II ROS generation, benefiting from the efficient ISC processes. The attained AIE PSs, especially TBTPy with bright emission, showed advantages in discriminating G⁺ bacteria over G^- bacteria, and distinguishing dead E. coli from lived one. Both TBTPy and TBTCy have the capacity of broad-spectrum photodynamic killing of pathogenic microbes in vitro with considerable safety for mammalian cells. Antimicrobial mechanism is found to be changing osmotic pressure of cytoplasm in E. coli, causing cell deformation and destruction of S. aureus and C. albicans. In vivo anti-infection experiment demonstrated AIE PSs can accelerate the healing process of the burned wounds on rats infected by methicillin-resistant S. aureus (MRSA) or E. coli, indicating their potential to treat tertiary burns in clinical application. Therefore, the attained AIE PSs hold great promise as antimicrobial candidates in infective therapeutic application.

Thioxanthenone-based derivatives as multitarget therapeutic leads for Alzheimer's disease

A set of twenty-five thioxanthene-9-one and xanthene-9-one derivatives, that were previously shown to inhibit cholinesterases (ChEs) and amyloid β (Aβ₄₀) aggregation, were evaluated for the inhibition of tau protein aggregation. All compounds exhibited a good activity, and eight of them (5-8, 10, 14, 15 and 20) shared comparable low micromolar inhibitory potency versus Aβ₄₀ aggregation and human acetylcholinesterase (AChE), while inhibiting human butyrylcholinesterase (BChE) even at submicromolar concentration. Compound 20 showed outstanding biological data, inhibiting tau protein and Aβ₄₀ aggregation with IC₅₀ = 1.8 and 1.3 μM, respectively. Moreover, at 0.1-10 μM it also exhibited neuroprotective activity against tau toxicity induced by okadoic acid in human neuroblastoma SH-SY5Y cells, that was comparable to that of estradiol and PD38. In preliminary toxicity studies, these interesting results for compound 20 are somewhat conflicting with a narrow safety window. However, compound 10, although endowed with a little lower potency for tau and Aβ aggregation inhibition additionally demonstrated good inhibition of ChEs and rather low cytotoxicity. Compound 4 is also worth of note for its high potency as hBChE inhibitor (IC₅₀ = 7 nM) and for the three order of magnitude selectivity versus hAChE. Molecular modelling studies were performed to explain the different behavior of compounds 4 and 20 towards hBChE. The observed balance of the inhibitory potencies versus the relevant targets indicates the thioxanthene-9-one derivatives as potential MTDLs for AD therapy, provided that the safety window will be improved by further structural variations, currently under investigation.

Joint Computational/Cell-Based Approach for Screening Inhibitors of Tau Oligomerization: A Proof-of-Concept Study

BACKGROUND

Tau assembly produces soluble oligomers and insoluble neurofibrillary tangles, which are neurotoxic to the brain and associated with Alzheimer's and Parkinson's diseases. Therefore, preventing tau aggregation is a promising therapy for those neurodegenerative disorders.

OBJECTIVE

The aim of this study was to develop a joint computational/cell-based oligomerization protocol for screening inhibitors of tau assembly.

METHODS

Virtual oligomerization inhibition (VOI) experiment using molecular dynamics simulation was performed to screen potential oligomerization inhibitors of PHF6 hexapeptide. Tau seeding assay, which is directly related to the outcome of therapeutic intervention, was carried out to confirm a ligand's ability in inhibiting tau assembly formation.

RESULTS

Our protocol was tested on two known compounds, EGCG and Blarcamesine. EGCG inhibited both the aggregation of PHF6 peptide in VOI and tau assembly in tau seeding assay, while Blarcamesine was not a good inhibitor at the two tasks. We also pointed out that good binding affinity to tau aggregates is needed, but not sufficient for a ligand to become a good inhibitor of tau oligomerization.

CONCLUSION

VOI goes beyond traditional computational inhibitor screening of amyloid aggregation by directly examining the inhibitory ability of a ligand to tau oligomerization. Comparing with the traditional biochemical assays, tau seeding activities in cells is a better indicator for the outcome of a therapeutic intervention. Our hybrid protocol has been successfully validated. It can effectively and efficiently identify the inhibitors of amyloid oligomerization/aggregation processes, thus, facilitate to the drug development of tau-related neurodegenerative diseases.

Revisiting the grammar of Tau aggregation and pathology formation: how new insights from brain pathology are shaping how we study and target Tauopathies

Converging evidence continues to point towards Tau aggregation and pathology formation as central events in the pathogenesis of Alzheimer's disease and other Tauopathies. Despite significant advances in understanding the morphological and structural properties of Tau fibrils, many fundamental questions remain about what causes Tau to aggregate in the first place. The exact roles of cofactors, Tau post-translational modifications, and Tau interactome in regulating Tau aggregation, pathology formation, and toxicity remain unknown. Recent studies have put the spotlight on the wide gap between the complexity of Tau structures, aggregation, and pathology formation in the brain and the simplicity of experimental approaches used for modeling these processes in research laboratories. Embracing and deconstructing this complexity is an essential first step to understanding the role of Tau in health and disease. To help deconstruct this complexity and understand its implication for the development of effective Tau targeting diagnostics and therapies, we firstly review how our understanding of Tau aggregation and pathology formation has evolved over the past few decades. Secondly, we present an analysis of new findings and insights from recent studies illustrating the biochemical, structural, and functional heterogeneity of Tau aggregates. Thirdly, we discuss the importance of adopting new experimental approaches that embrace the complexity of Tau aggregation and pathology as an important first step towards developing mechanism- and structure-based therapies that account for the pathological and clinical heterogeneity of Alzheimer's disease and Tauopathies. We believe that this is essential to develop effective diagnostics and therapies to treat these devastating diseases.

Chemoinformatics Analyses of Tau Ligands Reveal Key Molecular Requirements for the Identification of Potential Drug Candidates against Tauopathies

Tau is a highly soluble protein mainly localized at a cytoplasmic level in the neuronal cells, which plays a crucial role in the regulation of microtubule dynamic stability. Recent studies have demonstrated that several factors, such as hyperphosphorylation or alterations of Tau metabolism, may contribute to the pathological accumulation of protein aggregates, which can result in neuronal death and the onset of a number of neurological disorders called Tauopathies. At present, there are no available therapeutic remedies able to reduce Tau aggregation, nor are there any structural clues or guidelines for the rational identification of compounds preventing the accumulation of protein aggregates. To help identify the structural properties required for anti-Tau aggregation activity, we performed extensive chemoinformatics analyses on a dataset of Tau ligands reported in ChEMBL. The performed analyses allowed us to identify a set of molecular properties that are in common between known active ligands. Moreover, extensive analyses of the fragment composition of reported ligands led to the identification of chemical moieties and fragment combinations prevalent in the more active compounds. Interestingly, many of these fragments were arranged in recurring frameworks, some of which were clearly present in compounds currently under clinical investigation. This work represents the first in-depth chemoinformatics study of the molecular properties, constituting fragments and similarity profiles, of known Tau aggregation inhibitors. The datasets of compounds employed for the analyses, the identified molecular fragments and their combinations are made publicly available as supplementary material.

Amyloid-β and tau aggregation dual-inhibitors: A synthetic and structure-activity relationship focused review

Alzheimer's disease (AD) is one of the most common types of dementia, especially in elderly, with an increasing number of people suffering from this disease worldwide. There are no available disease-modifying therapies and only four drugs are approved for the relief of symptoms. Currently, the therapeutic approach used for AD treatment is based on single target drugs, which are not capable to stop its progression. To address this issue, multi-target compounds, combining two or more pharmacophores in a single molecular entity, have gained increasing interest to deal with the multiple factors related to AD. The exact cause of AD is not yet completely disclosed, and several hallmarks have been associated to this neurodegenerative disease. Even though, the accumulation of both amyloid-β plaques (Aβ) and neurofibrillary tangles (NFTs) are fully accepted as the main AD hallmarks, being object of lots of research for early-stage diagnosis and pharmacological therapy. In this context, this review summarizes the state-of-the-art in the field of dual-target inhibitors of both Aβ and tau aggregation simultaneously, including the design and synthetic strategy of the dual-target compounds, as well as a brief structure-activity relationships (SAR) analysis.

Small molecule therapeutics for tauopathy in Alzheimer's disease: Walking on the path of most resistance

Alzheimer's disease (AD) is the most common form of dementia characterized by presence of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of tau protein. Currently there are close to 50 million people living with dementia and this figure is expected to increase to 75 million by 2030 putting a huge burden on the economy due to the health care cost. Considering the effects on quality of life of patients and the increasing burden on the economy, there is an enormous need of new disease modifying therapies to tackle this disease. The current therapies are dominated by only symptomatic treatments including cholinesterase inhibitors and N-methyl-D-aspartate receptor blockers but no disease modifying treatments exist so far. After several failed attempts to develop drugs against amyloidopathy, tau targeting approaches have been in the main focus of drug development against AD. After an overview of the tauopathy in AD, this review summarizes recent findings on the development of small molecules as therapeutics targeting tau modification, aggregation, and degradation, and tau-oriented multi-target directed ligands. Overall, this work aims to provide a comprehensive and critical overview of small molecules which are being explored as a lead candidate for discovering drugs against tauopathy in AD.

Perspectives for New and More Efficient Multifunctional Ligands for Alzheimer's Disease Therapy

Despite tremendous research efforts at every level, globally, there is still a lack of effective drugs for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease are not yet clearly understood. This review analyses the relevance of multiple ligands in drug discovery for AD as a versatile toolbox for a polypharmacological approach to AD. Herein, we highlight major targets associated with AD, ranging from acetylcholine esterase (AChE), beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1), glycogen synthase kinase 3 beta (GSK-3β), N-methyl-d-aspartate (NMDA) receptor, monoamine oxidases (MAOs), metal ions in the brain, 5-hydroxytryptamine (5-HT) receptors, the third subtype of histamine receptor (H3 receptor), to phosphodiesterases (PDEs), along with a summary of their respective relationship to the disease network. In addition, a multitarget strategy for AD is presented, based on reported milestones in this area and the recent progress that has been achieved with multitargeted-directed ligands (MTDLs). Finally, the latest publications referencing the enlarged panel of new biological targets for AD related to the microglia are highlighted. However, the question of how to find meaningful combinations of targets for an MTDLs approach remains unanswered.

Investigation into the influence of an acrylic acid acceptor in organic D-π-A sensitizers against phototoxicity

Photodynamic therapy (PDT) is a non-invasive, selective, and cost-effective cancer therapy. We previously reported that thiophene-based organic D-π-A sensitizers consist of an electron-donating (D) moiety, a π-conjugated bridge (π) moiety, and an electron-accepting (A) moiety, and are readily accessible and stable templates for photosensitizers that could be used in PDT. In addition, acrylic acid acceptor-containing photosensitizers exert a high level of phototoxicity. This study was an investigation into 1) the possibility of increasing phototoxicity by introducing another carboxyl group or by replacing a carboxyl group with a pyridinium group, and 2) the importance of an alkene in the acrylic acid acceptor for phototoxicity. A review of the design, synthesis, and evaluation of sensitizers revealed that neither dicarboxylic acid nor pyridinium photosensitizers enhance phototoxicity. An evaluation of a photosensitizer without an alkene in the acrylic acid moiety revealed that the alkene was not indispensable in the pursuit of phototoxicity. The obtained results provided new insight into the design of ideal D-π-A photosensitizers for PDT.

Tau Protein Aggregation in Alzheimer's Disease: Recent Advances in the Development of Novel Therapeutic Agents

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Major research in Alzheimer’s disease (AD) related to disease-modifying agents is concentrated on pharmacological approaches related to diagnostic markers, neurofibrillary tangles and amyloid plaques. Although most studies focus on anti-amyloid strategies, investigations on tau protein have produced significant advances in the modulation of the pathophysiology of several neurodegenerative diseases. Since the discovery of phenothiazines as tau protein aggregation inhibitors (TAGIs), many additional small molecule inhibitors have been discovered and characterized in biological model systems, which exert their interaction effects by covalent and noncovalent means. In this paper, we summarize the latest advances in the discovery and development of tau aggregation inhibitors using a specialized approach in their chemical classes. The design of new TAGIs and their encouraging use in in vivo and clinical trials support their potential therapeutic use in AD.

Design, synthesis, and evaluation of azo D-π-A dyes as photothermal agents

Thirteen readily accessible azo D-π-A dyes, intended for use as photothermal agents, were synthesized using only a few steps. Absorption wavelengths were readily tuned by changing the building blocks, and 6 of these dyes exhibited NIR absorption that would be useful for biomedical applications. Unexpected suppression of an N-C single bond rotation that neighbors the azo bond was observed in the case of 5 dyes. Photothermal conversion efficiency measurements revealed a significant effect of the D moiety in these synthesized azo D-π-A dyes, but neither the π moiety nor the A moiety showed an obvious influence. The obtained results offer valuable information for the design of high-performance azo D-π-A dyes that have utility as photothermal agents.

Advancement of multi-target drug discoveries and promising applications in the field of Alzheimer's disease

Complex diseases (e.g., Alzheimer's disease) or infectious diseases are usually caused by complicated and varied factors, including environmental and genetic factors. Multi-target (polypharmacology) drugs have been suggested and have emerged as powerful and promising alternative paradigms in modern medicinal chemistry for the development of versatile chemotherapeutic agents to solve these medical challenges. The multifunctional agents capable of modulating multiple biological targets simultaneously display great advantages of higher efficacy, improved safety profile, and simpler administration compared to single-targeted agents. Therefore, multifunctional agents would certainly open novel avenues to rationally design the next generation of more effective but less toxic therapeutic agents. Herein, the authors review the recent progress made in the discovery and design processes of selective multi-targeted agents, especially the successful application of multi-target drugs for the treatment of Alzheimer's disease.

Repurposing nitrocatechols: 5-Nitro-α-cyanocarboxamide derivatives of caffeic acid and caffeic acid phenethyl ester effectively inhibit aggregation of tau-derived hexapeptide AcPHF6

Polyphenols like caffeic acid and its phenethyl ester have been associated with potent anti-aggregating activity. Accordingly, we screened a library of polyphenols and synthetic derivatives thereof for their capacity to inhibit tau-aggregation using a thioflavin T-based fluorescence method. Our results show that the nitrocatechol scaffold is required for a significant anti-aggregating activity, which is enhanced by introducing bulky substituents at the side chain. A remarkable increase in activity was observed for α-cyanocarboxamide derivatives 26-27. Molecular docking studies showed that the amide bond provides superior conformational stability in the steric zipper assembly of tau, which drives the increase in activity. We also found that derivatives 24-27 were potent chelators of copper(II) - a property of pharmacological significance in abnormal protein aggregation. These small molecules can provide promising leads to develop new drugs for tauopathies and AD. These findings open a new window on the repurposing of nitrocatechols beyond their established role as catechol-O-methyltransferase inhibitors.

Elucidating the mode of action for thiophene-based organic D-π-A sensitizers for use in photodynamic therapy

Photodynamic therapy (PDT) is a non-invasive, selective, and cost-effective cancer therapy. The development of readily accessible templates that allow rapid structural modification for further improvement of PDT remains important. We previously reported thiophene-based organic D-π-A sensitizers consisted of an electron-donating (D) moiety, a π-conjugated bridge (π) moiety, and an electron-accepting (A) moiety as valuable templates for a photosensitizer that can be used in PDT. Our preliminary structure-activity relationship study revealed that the structure of the A moiety significantly influences its phototoxicity. In this study, we evaluated the photoabsorptive, cellular uptake, and photo-oxidizing abilities of D-π-A sensitizers that contained different A moieties. The level of phototoxicity of the D-π-A sensitizers was rationalized by considering those three abilities. In addition, we observed the ability of amphiphilic sensitizers containing either a carboxylic acid or an amide in an A moiety to form aggregates that penetrate cells mainly via endocytosis.

Fullerenemalonates inhibit amyloid beta aggregation, in vitro and in silico evaluation

The onset of Alzheimer's disease (AD) is associated with the presence of neurofibrillary pathology such as amyloid β (Aβ) plaques. Different therapeutic strategies have focused on the inhibition of Aβ aggregate formation; these pathological structures lead to neuronal disorder and cognitive impairment. Fullerene C60 has demonstrated the ability to interact and prevent Aβ fibril development; however, its low solubility and toxicity to cells remain significant problems. In this study, we synthesized, characterized and compared diethyl fullerenemalonates and the corresponding sodium salts, adducts of C60 bearing 1 to 3 diethyl malonyl and disodium malonyl substituents to evaluate the potential inhibitory effect on the aggregation of Aβ42 and their biocompatibility. The dose-dependent inhibitory effect of fullerenes on Aβ42 aggregation was studied using a thioflavin T fluorescent assay, and the IC50 value demonstrated a low range of fullerene concentration for inhibition, as confirmed by electron microscopy. The exposure of neuroblastoma to fullerenemalonates showed low toxicity, primarily in the presence of the sodium salt-adducts. An isomeric mixture of bisadducts, trisadducts and a C 3-symetrical trisadduct demonstrated the highest efficacy among the tests. In silico calculations were performed to complement the experimental data, obtaining a deeper understanding of the Aβ inhibitory mechanism; indicating that C 3-symetrical trisadduct interacts mainly with 1D to 16K residues of Aβ42 peptide. These data suggest that fullerenemalonates require specific substituents designed as sodium salt molecules to inhibit Aβ fibrillization and perform with low toxicity. These are promising molecules for developing future therapies involving Aβ aggregates in diseases such as AD and other types of dementia.

The design, synthesis, and evaluation of organic dithienopyrrole-based D-π-A dyes for use as sensitizers in photodynamic therapy

Dithienopyrrole-based organic dyes that combine an electron-donating moiety (D), a π-conjugated bridge moiety (π), and an electron-accepting moiety (A) were designed and synthesized in short steps by previously developed one-pot Suzuki-Miyaura coupling approach. Absorption wavelengths of the dyes were readily tuned by altering the D and A moieties. The use of a strongly electron-withdrawing cyanopyridone acceptor enabled NIR absorption. A synthesized sensitizer, 2j, exerted potent phototoxicity mainly via a Type I mechanism in cells. A nitrogen atom in the dithienopyrrole ring serves as a connecting point for the introduction of functional building blocks that can improve the properties of sensitizers, which makes this D-π-A sensitizer a valuable template for the further development of sensitizers.

Design, Synthesis, and Biological Evaluation of 1-Benzylamino-2-hydroxyalkyl Derivatives as New Potential Disease-Modifying Multifunctional Anti-Alzheimer's Agents

The multitarget approach is a promising paradigm in drug discovery, potentially leading to new treatment options for complex disorders, such as Alzheimer's disease. Herein, we present the discovery of a unique series of 1-benzylamino-2-hydroxyalkyl derivatives combining inhibitory activity against butyrylcholinesterase, β-secretase, β-amyloid, and tau protein aggregation, all related to mechanisms which underpin Alzheimer's disease. Notably, diphenylpropylamine derivative 10 showed balanced activity against both disease-modifying targets, inhibition of β-secretase (IC_{50  hBACE-1} = 41.60 μM), inhibition of amyloid β aggregation (IC_50 Aβ = 3.09 μM), inhibition of tau aggregation (55% at 10 μM); as well as against symptomatic targets, butyrylcholinesterase inhibition (IC_{50  hBuChE} = 7.22 μM). It might represent an encouraging starting point for development of multifunctional disease-modifying anti-Alzheimer's agents.

Effect of saturation in phospholipid/fatty acid monolayers on interaction with amyloid β peptide

The effect of the saturation of fatty acid (FA) in 1,2-dimyristoyl-sn-glycero-3-phosphocoline (DMPC)/FA membrane on the interaction between lipid membrane and amyloid β monomer was investigated by using the Langmuir monolayer technique. The surface pressure (Π)-mean molecular area (A) isotherms and fluorescent measurements reveal that DMPC and octadecanoic acid (stearic acid, SA) molecules were somewhat miscible in the mixed membrane, which was maintained to homogeneous gel phase by enhance of the intermolecular hydrophobic interactions because of the all trans acyl chains. On the other hand, DMPC and 9Z,12Z-octadecadienoic acid (linoleic acid, LA) molecules were considered to be well miscible in the mixed membrane, where the membrane partially transferred from gel phase to liquid-crystalline phase. The Π-A isotherms of the monolayers on amyloid β-peptide (Aβ) solution indicated that Aβ monomers tend to be inserted into the saturated acyl chain region of monolayers at low surface pressure and that the Aβ monomers were then extruded from the monolayer at higher surface pressure. It was observed that behaviors of Aβ monomers at higher surface pressure depended on membrane microstructures. In the DMPC/SA monolayers, Aβ aggregated and then was extruded from monolayers at about 20 mN m^-1 of surface pressure irrespective of the SA proportion. On the other hand, in the DMPC/LA monolayers, Aβ, which favors to interact with DMPC, is dispersed in the monolayer even at high surface pressure because DMPC and LA molecules were well miscible in the monolayer.

Underlying mechanisms and chemical/biochemical therapeutic approaches to ameliorate protein misfolding neurodegenerative diseases

Protein misfolding and inclusion body formations are common events in neurodegenerative diseases characterized by deposition of misfolded proteins inside or outside of neurons, and are commonly referred to as "protein misfolding neurodegenerative diseases" (PMNDs). These phenotypically diverse but biochemically similar aggregates suggest a highly conserved molecular mechanism of pathogenesis. These challenges are magnified by presence of mutations that render individual proteins subject to misfolding and/or aggregation. Cell proteostasis network and molecular chaperoning are maintaining cell proteome to preserve the protein folding, refolding, oligomerization, or disaggregation, and play formidable tasks to maintain the health of organism in the face of developmental changes, environmental insults, and rigors of aging. Maintenance of cell proteome requires the orchestration of major pathways of the cellular proteostasis network (heat shock response (HSR) in the cytosol and the unfolded protein response (UPR) in the endoplasmic reticulum). Proteostasis responses culminate in transcriptional and post-transcriptional programs that up-regulate the homeostatic mechanisms. Proteostasis is strongly influenced by the general properties of individual proteins for folding, misfolding, and aggregation. We examine a growing body of evidence establishing that when cellular proteostasis goes awry, it can be reestablished by deliberate chemical and biological interventions. We first try to introduce some new chemical approaches to prevent the misfolding or aggregation of specific proteins via direct binding interactions. We then start with approaches that employ chemicals or biological agents to enhance the general capacity of the proteostasis network. We finish with evidence that synergy is achieved with the combination of mechanistically distinct approaches to reestablish organ proteostasis. © 2016 BioFactors, 43(6):737-759, 2017.

Tau protein aggregation in Alzheimer's disease: An attractive target for the development of novel therapeutic agents

Alzheimer's Disease (AD) is a neurodegenerative brain disorder in which many biological dysfunctions are involved. Among them, two main types of lesions were discovered and widely studied: the amyloid plaques and the neurofibrillary tangles (NFTs). These two lesions are caused by the dysfunction and the accumulation of two proteins which are, respectively, the beta-amyloid peptide and the tau protein. The process that leads these two proteins to aggregate is complex and is the subject of current studies. After a brief description of the aggregation mechanisms, we will provide an overview of new therapeutic agents targeting the different dysfunctions and toxic species found during aggregation.

X-Ray Structural Study of Amyloid-Like Fibrils of Tau Peptides Bound to Small-Molecule Ligands

Atomic structures of Tau involved in Alzheimer's disease complexed with small molecule binders are the first step to define the Tau pharmacophore, leading the way to a structure-based design of improved diagnostics and therapeutics. Yet the partially disordered and polymorphic nature of Tau hinders structural analyses. Fortunately, short segments from amyloid proteins, which exhibit similar biophysical properties to the full-length proteins, also form fibrils and oligomers, and their atomic structures can be determined using X-ray microcrystallography. Such structures were successfully used to design amyloid inhibitors. This chapter describes experimental procedures used to determine crystal structures of Tau peptide segments in complex with small-molecule binders.

Binding of ACE-inhibitors to in vitro and patient-derived amyloid-β fibril models

Currently, no drugs exist that can prevent or reverse Alzheimer's disease, a neurodegenerative disease associated with the presence, in the brain, of plaques that are composed of β-amyloid (Aβ) peptides. Recent studies suggest that angiotensin-converting enzyme (ACE) inhibitors, a set of drugs used to treat hypertension, may inhibit amyloid formation in vitro. In the present study, we investigate through computer simulations the binding of ACE inhibitors to patient-derived Aβ fibrils and contrast it with that of ACE inhibitors binding to in vitro generated fibrils. The binding affinities of the ACE inhibitors are compared with that of Congo red, a dye that is used to identify amyloid structures and that is known to be a weak inhibitor of Aβ aggregation. We find that ACE inhibitors have a lower binding affinity to the patient-derived fibrils than to in vitro generated ones. For patient-derived fibrils, their binding affinities are even lower than that of Congo red. Our observations raise doubts on the hypothesis that these drugs inhibit fibril formation in Alzheimer patients by interacting directly with the amyloids.

Multitarget strategies in Alzheimer's disease: benefits and challenges on the road to therapeutics

Alzheimer's disease is a multifactorial syndrome, for which effective cures are urgently needed. Seeking for enhanced therapeutic efficacy, multitarget drugs have been increasingly sought after over the last decades. They offer the attractive prospect of tackling intricate network effects, but with the benefits of a single-molecule therapy. Herein, we highlight relevant progress in the field, focusing on acetylcholinesterase inhibition and amyloid pathways as two pivotal features in multitarget design strategies. We also discuss the intertwined relationship between selected molecular targets and give a brief glimpse into the power of multitarget agents as pharmacological probes of Alzheimer's disease molecular mechanisms.

3,4-Dihydro-1,3,5-triazin-2(1H)-ones as the First Dual BACE-1/GSK-3β Fragment Hits against Alzheimer's Disease

One of the main obstacles toward the discovery of effective anti-Alzheimer drugs is the multifactorial nature of its etiopathology. Therefore, the use of multitarget-directed ligands has emerged as particularly suitable. Such ligands, able to modulate different neurodegenerative pathways, for example, amyloid and tau cascades, as well as cognitive and neurogenic functions, are fostered to come. In this respect, we report herein on the first class of BACE-1/GSK-3β dual inhibitors based on a 3,4-dihydro-1,3,5-triazin-2(1H)-one skeleton, whose hit compound 1 showed interesting properties in a preliminary investigation. Notably, compound 2, endowed with well-balanced potencies against the two isolated enzymes (IC50 of 16 and 7 μM against BACE-1 and GSK-3β, respectively), displayed effective neuroprotective and neurogenic activities and no neurotoxicity in cell-based assays. It also showed good brain permeability in a pharmacokinetic assessment in mice. Overall, triazinone derivatives, thanks to the simultaneous modulation of multiple points of the diseased network, might emerge as suitable candidates to be tested in in vivo Alzheimer's disease models.

Function and toxicity of amyloid beta and recent therapeutic interventions targeting amyloid beta in Alzheimer's disease

Our Feature Article details the physiological role of amyloid beta (Aβ), elaborates its toxic effects and outlines therapeutic molecules designed in the last two years targeting different aspects of Aβ for preventing AD.

Elucidation of the structure-property relationship of p-type organic semiconductors through rapid library construction via a one-pot, Suzuki-Miyaura coupling reaction

The elucidation of the structure-property relationship is an important issue in the development of organic electronics. Combinatorial synthesis and the evaluation of systematically modified compounds is a powerful tool in the work of elucidating structure-property relationships. In this manuscript, D-π-A structure, 32 p-type organic semiconductors were rapidly synthesized via a one-pot, Suzuki-Miyaura coupling with subsequent Knoevenagel condensation. Evaluation of the solubility and photovoltaic properties of the prepared compounds revealed that the measured solubility was strongly correlated with the solubility parameter (SP), as reported by Fedors. In addition, the SPs were correlated with the Jsc of thin-film organic solar cells prepared using synthesized compounds. Among the evaluated photovoltaic properties of the solar cells, Jsc and Voc had strong correlations with the photoconversion efficiency (PCE).