Anle138b: a novel oligomer modulator for disease-modifying therapy of neurodegenerative diseases such as prion and Parkinson's disease

An update on multiple system atrophy

PURPOSE OF REVIEW

Multiple system atrophy (MSA) is a rapidly progressive synucleinopathy characterized by autonomic failure, parkinsonism, and cerebellar ataxia. Here, we provide an update on α-synuclein's role in MSA pathophysiology and review the new Movement Disorders Society (MDS) diagnostic criteria and the utility of α-synuclein-based biomarkers. We also highlight ongoing efforts toward clinical trial readiness and review potential disease-modifying therapies undergoing clinical trials.

RECENT FINDINGS

A role of urinary tract infections in triggering α-synuclein aggregation and contribution of genes implicated in oligodendroglial development have been suggested in the MSA pathophysiology. The clinically probable MSA category of the new diagnostic criteria shows improved accuracy in early disease stages. Predictors of phenoconversion from pure autonomic failure to MSA are now better defined. Alpha-synuclein strains in CSF and serum, phosphorylated α-synuclein deposits in the skin, and brain α-synuclein pathology visualized using PET ligand [18F]ACI-12589 are emerging as valuable diagnostic tools. Clinical trials in MSA investigate drugs targeting α-synuclein aggregation or preventing α-synuclein expression, along with stem cell and gene therapies to halt disease progression.

SUMMARY

New MSA diagnostic criteria and α-synuclein-based biomarkers may enhance diagnostic accuracy while promising therapies are in development to address disease progression.

Novel 4-triazole phenyl amide (4-TPA) molecules: Potent promoters of α-synuclein fibril disassembly

Parkinson's disease profoundly compromises patients' daily lives, and the disassembly of α-synuclein aggregates, a primary pathological factor, represents a promising therapeutic approach. In this study, we conducted a systematic screening and optimization process to identify the novel scaffold B37, a 4-triazolyl-phenylamine derivative, exhibiting a potent disassembly activity of 1.1 μM against α-synuclein preformed fibrils. Notably, B37 demonstrated significant neuroprotective effects, ameliorated autophagic dysfunction induced by preformed fibrils, mitigated oxidative stress, and restored the co-localization of preformed fibrils with lysosomes. Transmission electron microscopy corroborated its in vitro disassembly function. Pharmacokinetic profiling revealed favorable parameters with a receptible blood-brain barrier permeability. B37 emerges as a promising lead compound for further optimization, aiming to develop a highly effective agent targeting the disassembly of α-synuclein aggregates to treat neurodegenerative diseases like Parkinson's disease.

Interfering with aggregated α-synuclein in advanced melanoma leads to a major upregulation of MHC class II proteins

Melanoma is the most serious and deadly form of skin cancer and with progression to advanced melanoma, the intrinsically disordered protein α-synuclein is upregulated to high levels. While toxic to dopaminergic neurons in Parkinson's disease, α-synuclein is highly beneficial for primary and metastatic melanoma cells. To gain detailed insights into this exact opposite role of α-synuclein in advanced melanoma, we performed proteomic studies of high-level α-synuclein-expressing human melanoma cell lines that were treated with the diphenyl-pyrazole small-molecule compound anle138b, which binds to and interferes with the oligomeric structure of α-synuclein. We also performed proteomic and transcriptomic studies of human melanoma xenografts that were treated systemically with the anle138b compound. The results reveal that interfering with oligomerized α-synuclein in the melanoma cells in these tumor xenografts led to a substantial upregulation and expression of major histocompatibility complex proteins, which are pertinent to enhancing anti-melanoma immune responses.

Modulating α-synuclein propagation and decomposition: Implications in Parkinson's disease therapy

α-Synuclein (α-Syn) is closely related to the pathogenesis of Parkinson's disease (PD). Under pathological conditions, the conformation of α-syn changes and different forms of α-syn lead to neurotoxicity. According to Braak stages, α-syn can propagate in different brain regions, inducing neurodegeneration and corresponding clinical manifestations through abnormal aggregation of Lewy bodies (LBs) and lewy axons in different types of neurons in PD. So far, PD lacks early diagnosis biomarkers, and treatments are mainly targeted at some clinical symptoms. There is no effective therapy to delay the progression of PD. This review first summarized the role of α-syn in physiological and pathological states, and the relationship between α-syn and PD. Then, we focused on the origin, secretion, aggregation, propagation and degradation of α-syn as well as the important regulatory factors in these processes systematically. Finally, we reviewed some potential drug candidates for alleviating the abnormal aggregation of α-syn in order to provide valuable targets for the treatment of PD to cope with the occurrence and progression of this disease.

Combination of Styrylbenzoazole Compound and Hydroxypropyl Methylcellulose Enhances Therapeutic Effect in Prion-Infected Mice

Prion diseases are fatal transmissible neurodegenerative disorders. Tremendous efforts have been made for prion diseases; however, no effective treatment is available. Several anti-prion compounds have a preference for which prion strains or prion-infected animal models to target. Styrylbenzoazole compound called cpd-B is effective in RML prion-infected mice but less so in 263K prion-infected mice, whereas hydroxypropyl methylcellulose is effective in 263K prion-infected mice but less so in RML prion-infected mice. In the present study, we developed a combination therapy of cpd-B and hydroxypropyl methylcellulose expecting synergistic effects in both RML prion-infected mice and 263K prion-infected mice. A single subcutaneous administration of this combination had substantially a synergistic effect in RML prion-infected mice but had no additive effect in 263K prion-infected mice. These results showed that the effect of cpd-B was enhanced by hydroxypropyl methylcellulose. The complementary nature of the two compounds in efficacy against prion strains, chemical properties, pharmacokinetics, and physical properties appears to have contributed to the effective combination therapy. Our results pave the way for the strategy of new anti-prion agents.

Advancing Parkinson's Disease Diagnostics: The Potential of Arylpyrazolethiazole Derivatives for Imaging α-Synuclein Aggregates

The development of positron emission tomography (PET) tracers capable of detecting α-synuclein (α-syn) aggregates in vivo would represent a breakthrough for advancing the understanding and enabling the early diagnosis of Parkinson's disease and related disorders. It also holds the potential to assess the efficacy of therapeutic interventions. However, this remains challenging due to different structures of α-syn aggregates, the need for selectivity over other structurally similar amyloid proteins, like amyloid-β (Aβ), which frequently coexist with α-syn pathology, and the low abundance of the target in the brain that requires the development of a high-affinity ligand. To develop a successful PET tracer for the central nervous system (CNS), stringent criteria in terms of polarity and molecular size must also be considered, as the tracer must penetrate the blood-brain barrier and have low nonspecific binding to brain tissue. Here, we report a series of arylpyrazolethiazole (APT) derivatives, rationally designed from a structure-activity relationship study centered on existing ligands for α-syn fibrils, with a particular focus on the selectivity toward α-syn fibrils and control of physicochemical properties suitable for a CNS PET tracer. In vitro competition binding assays performed against [3H]MODAG-001 using recombinant α-syn and Aβ1-42 fibrils revealed APT-13 with an inhibition constant of 27.8 ± 9.7 nM and a selectivity of more than 3.3 fold over Aβ. Radiolabeled [11C]APT-13 demonstrated excellent brain penetration in healthy mice with a peak standardized uptake value of 1.94 ± 0.29 and fast washout from the brain (t 1/2 = 9 ± 1 min). This study highlights the potential of APT-13 as a lead compound for developing PET tracers to detect α-syn aggregates in vivo.

Pharmacological inhibition of α-synuclein aggregation within liquid condensates

Aggregated forms of α-synuclein constitute the major component of Lewy bodies, the proteinaceous aggregates characteristic of Parkinson's disease. Emerging evidence suggests that α-synuclein aggregation may occur within liquid condensates formed through phase separation. This mechanism of aggregation creates new challenges and opportunities for drug discovery for Parkinson's disease, which is otherwise still incurable. Here we show that the condensation-driven aggregation pathway of α-synuclein can be inhibited using small molecules. We report that the aminosterol claramine stabilizes α-synuclein condensates and inhibits α-synuclein aggregation within the condensates both in vitro and in a Caenorhabditis elegans model of Parkinson's disease. By using a chemical kinetics approach, we show that the mechanism of action of claramine is to inhibit primary nucleation within the condensates. These results illustrate a possible therapeutic route based on the inhibition of protein aggregation within condensates, a phenomenon likely to be relevant in other neurodegenerative disorders.

LETC inhibits α-Syn aggregation and ameliorates motor deficiencies in the L62 mouse model of synucleinopathy

Alpha-Synuclein (α-Syn) aggregation is a pathological feature of synucleinopathies, neurodegenerative disorders that include Parkinson's disease (PD). Here, we explored the efficacy of N,N,N',N'-tetraethyl-10H-phenothiazine-3,7-diamine dihydrochloride (LETC), a protein aggregation inhibitor, on α-Syn aggregation. In both cellular models and transgenic mice, α-Syn aggregation was achieved by the overexpression of full-length human α-Syn fused with a signal sequence peptide. α-Syn accumulated in transfected DH60.21 neuroblastoma cells and α-Syn aggregation was inhibited by LETC with an EC50 of 0.066 ± 0.047 μM. Full-length human α-Syn overexpressing Line 62 (L62) mice accumulated neuronal α-Syn that was associated with a decreased motor performance in the open field and automated home cage. LETC, administered orally for 6 weeks at 10 mg/kg significantly decreased α-Syn-positive neurons in multiple brain regions and this resulted in a rescue of movement deficits in the open field in these mice. LETC however, did not improve activity deficits of L62 mice in the home cage environment. The results suggest that LETC may provide a potential disease modification therapy in synucleinopathies through the inhibition of α-Syn aggregation.

Anti-alpha synuclein and anti-tau immunotherapies: Can a cocktail approach work?

The hypothesis that neurodegenerative diseases are proteinopathies due to toxic effect of different underlying proteins, such as amyloid-beta and 3+4R-tau in Alzheimer's disease (AD) and alpha-synuclein in Parkinson's disease (PD), while still controversial is supported by several studies in the literature. This has led to conduct clinical trials attempting to reduce the load of these allegedly toxic proteins by immunotherapy, mostly but not solely based on antibodies against these proteins. Already completed clinical trials have ranged from initially negative results to recently partial positive outcomes, specifically for anti-amyloid antibodies in AD but also albeit to lesser degree for anti-synuclein antibodies in PD. Currently, there are several ongoing clinical trials in degenerative parkinsonisms with anti-synuclein approaches in PD and multiple system atrophy (MSA), as well as with anti-tau antibodies in 4R-tauopathies such as progressive supranuclear palsy (PSP). While it can be argued that expectations that part of these clinical trials will be positive can be hope or hype, it is reasonable to consider the future possibility of "cocktail" combination of different antibodies after the available experimental evidence of cross-talk between these proteins and neuropathological evidence of coexistence of these proteinopathies more frequently than expected by chance. Moreover, such "cocktail" approaches are widespread and accepted common practice in other fields such as oncology, and the complexity of neurodegenerative parkinsonisms makes reasonable the option for testing and eventually applying such combined approaches, should these prove useful separately, in the setting of patients with evidence of underlying concomitant proteinopathies, for example through biomarkers.

Multiple system atrophy: an update and emerging directions of biomarkers and clinical trials

Multiple system atrophy is a rare, debilitating, adult-onset neurodegenerative disorder that manifests clinically as a diverse combination of parkinsonism, cerebellar ataxia, and autonomic dysfunction. It is pathologically characterized by oligodendroglial cytoplasmic inclusions containing abnormally aggregated α-synuclein. According to the updated Movement Disorder Society diagnostic criteria for multiple system atrophy, the diagnosis of clinically established multiple system atrophy requires the manifestation of autonomic dysfunction in combination with poorly levo-dopa responsive parkinsonism and/or cerebellar syndrome. Although symptomatic management of multiple system atrophy can substantially improve quality of life, therapeutic benefits are often limited, ephemeral, and they fail to modify the disease progression and eradicate underlying causes. Consequently, effective breakthrough treatments that target the causes of disease are needed. Numerous preclinical and clinical studies are currently focusing on a set of hallmarks of neurodegenerative diseases to slow or halt the progression of multiple system atrophy: pathological protein aggregation, synaptic dysfunction, aberrant proteostasis, neuronal inflammation, and neuronal cell death. Meanwhile, specific biomarkers and measurements with higher specificity and sensitivity are being developed for the diagnosis of multiple system atrophy, particularly for early detection of the disease. More intriguingly, a growing number of new disease-modifying candidates, which can be used to design multi-targeted, personalized treatment in patients, are being investigated, notwithstanding the failure of most previous attempts.

Unraveling brain diseases: The promise of brain-on-a-chip models

Brain disorders, encompassing a wide spectrum of neurological and psychiatric conditions, present a formidable challenge in modern medicine. Despite decades of research, the intricate complexity of the human brain still eludes comprehensive understanding, impeding the development of effective treatments. Recent advancements in microfluidics and tissue engineering have led to the development of innovative platforms known as "Brain-on-a-Chip" (BoC) i.e., advanced in vitro systems that aim to replicate the microenvironment of the brain with the highest possible fidelity. This technology offers a promising test-bed for studying brain disorders at the cellular and network levels, providing insights into disease mechanisms, drug screening, and, in perspective, the development of personalized therapeutic strategies. In this review, we provide an overview of the BoC models developed over the years to model and understand the onset and progression of some of the most severe neurological disorders in terms of incidence and debilitation (stroke, Parkinson's, Alzheimer's, and epilepsy). We also report some of the cutting-edge therapeutic approaches whose effects were evaluated by means of these technologies. Finally, we discuss potential challenges, and future perspectives of the BoC models.

Discovery of potent inhibitors of α-synuclein aggregation using structure-based iterative learning

Machine learning methods hold the promise to reduce the costs and the failure rates of conventional drug discovery pipelines. This issue is especially pressing for neurodegenerative diseases, where the development of disease-modifying drugs has been particularly challenging. To address this problem, we describe here a machine learning approach to identify small molecule inhibitors of α-synuclein aggregation, a process implicated in Parkinson's disease and other synucleinopathies. Because the proliferation of α-synuclein aggregates takes place through autocatalytic secondary nucleation, we aim to identify compounds that bind the catalytic sites on the surface of the aggregates. To achieve this goal, we use structure-based machine learning in an iterative manner to first identify and then progressively optimize secondary nucleation inhibitors. Our results demonstrate that this approach leads to the facile identification of compounds two orders of magnitude more potent than previously reported ones.

Targeted protein degradation in CNS disorders: a promising route to novel therapeutics?

Targeted protein degradation (TPD) is a rapidly expanding field, with various PROTACs (proteolysis-targeting chimeras) in clinical trials and molecular glues such as immunomodulatory imide drugs (IMiDs) already well established in the treatment of certain blood cancers. Many current approaches are focused on oncology targets, leaving numerous potential applications underexplored. Targeting proteins for degradation offers a novel therapeutic route for targets whose inhibition remains challenging, such as protein aggregates in neurodegenerative diseases. This mini review focuses on the prospect of utilizing TPD for neurodegenerative disease targets, particularly PROTAC and molecular glue formats and opportunities for novel CNS E3 ligases. Some key challenges of utilizing such modalities including molecular design of degrader molecules, drug delivery and blood brain barrier penetrance will be discussed.

Anti-prion drugs do not improve survival in novel knock-in models of inherited prion disease

Prion diseases uniquely manifest in three distinct forms: inherited, sporadic, and infectious. Wild-type prions are responsible for the sporadic and infectious versions, while mutant prions cause inherited variants like fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD). Although some drugs can prolong prion incubation times up to four-fold in rodent models of infectious prion diseases, no effective treatments for FFI and fCJD have been found. In this study, we evaluated the efficacy of various anti-prion drugs on newly-developed knock-in mouse models for FFI and fCJD. These models express bank vole prion protein (PrP) with the pathogenic D178N and E200K mutations. We applied various drug regimens known to be highly effective against wild-type prions in vivo as well as a brain-penetrant compound that inhibits mutant PrPSc propagation in vitro. None of the regimens tested (Anle138b, IND24, Anle138b + IND24, cellulose ether, and PSCMA) significantly extended disease-free survival or prevented mutant PrPSc accumulation in either knock-in mouse model, despite their ability to induce strain adaptation of mutant prions. Our results show that anti-prion drugs originally developed to treat infectious prion diseases do not necessarily work for inherited prion diseases, and that the recombinant sPMCA is not a reliable platform for identifying compounds that target mutant prions. This work underscores the need to develop therapies and validate screening assays specifically for mutant prions, as well as anti-prion strategies that are not strain-dependent.

Molecular docking analysis of α-Synuclein aggregation with Anle138b

α-Synuclein aggregation into toxic oligomeric species is central to Parkinson's disease pathogenesis. Anle138b is a recently identified inhibitor of α-synuclein oligomerization showing promise in preclinical studies. This study employed computational approaches to elucidate Anle138b's mechanism of oligomer-specific action. The inhibitory potential of Anle138b against α-synuclein oligomers was evaluated by performing molecular docking studies using AutoDock Tools, followed by their binding pocket analysis. Further, protein-protein docking studies were performed using Hex8.0 to validate the aggregation inhibitory potential of Anle138b. Molecular docking revealed increasing binding affinity of Anle138b against higher order α-synuclein oligomers (dimer to decamer). Anle138b occupied oligomeric cavity and interacted with residues Thr54, Gly73, Val74 and Thr75 across several oligomers. Protein-protein docking showed that Anle138b interferes with α-synuclein decamer formation. These results highlight the oligomer-directed inhibitory mechanism of Anle138b, without hindering the monomeric forms and provide molecular insights to advance its therapeutic development for Parkinson's and related synucleinopathies.

In situ single-molecule investigations of the impacts of biochemical perturbations on conformational intermediates of monomeric α-synuclein

α-Synuclein aggregation is a common trait in synucleinopathies, including Parkinson's disease. Being an unstructured protein, α-synuclein exists in several distinct conformational intermediates, contributing to both its function and pathogenesis. However, the regulation of these monomer conformations by biochemical factors and potential drugs has remained elusive. In this study, we devised an in situ single-molecule manipulation approach to pinpoint kinetically stable conformational intermediates of monomeric α-synuclein and explore the effects of various biochemical factors and drugs. We uncovered a partially folded conformation located in the non-amyloid-β component (NAC) region of monomeric α-synuclein, which is regulated by a preNAC region. This conformational intermediate is sensitive to biochemical perturbations and small-molecule drugs that influencing α-synuclein's aggregation tendency. Our findings reveal that this partially folded intermediate may play a role in α-synuclein aggregation, offering fresh perspectives for potential treatments aimed at the initial stage of higher-order α-synuclein aggregation. The single-molecule approach developed here can be broadly applied to the study of disease-related intrinsically disordered proteins.

Discovery of small molecule benzothiazole and indole derivatives tackling tau 2N4R and α-synuclein fibrils

Tau and α-synuclein aggregates are the main histopathological hallmarks present in Alzheimer's disease (AD), Parkinson's disease (PD), and other neurodegenerative disorders. Intraneuronal hyperphosphorylated tau accumulation is significantly connected to the degree of cognitive impairment in AD patients. In particular, the longest 2N4R tau isoform has a propensity to rapidly form oligomers and mature fibrils. On the other hand, misfolding of α-synuclein (α-syn) is the characteristic feature in PD and dementia with Lewy bodies (DLB). There is a strong crosstalk between the two prone-to-aggregation proteins as they coprecipitated in some brains of AD, PD, and DLB patients. Simultaneous targeting of both proteinaceous oligomers and aggregates is still challenging. Here, we rationally designed and synthesized benzothiazole- and indole-based compounds using the structural hybridization strategy between the benzothiazole N744 cyanine dye and the diphenyl pyrazole Anle138b that showed anti-aggregation activity towards 2N4R tau and α-syn, respectively. The anti-aggregation effect of the prepared compounds was monitored using the thioflavin-T (ThT) fluorescence assay, while transmission electron microscopy (TEM) was employed to detect fibrils upon the completion of a time-course study with the ThT assay. Moreover, the photo-induced crosslinking of unmodified protein (PICUP) assay was used to determine the formation of oligomers. Specifically, compounds 46 and 48 demonstrated the highest anti-aggregation activity by decreasing the ThT fluorescence to 4.0 and 14.8%, respectively, against α-syn. Although no noticeable effect on 2N4R tau oligomers, 46 showed promising anti-oligomer activity against α-syn. Both compounds induced a significantly high anti-aggregation effect against the two protein fibrils as visualized by TEM. Moreover, compound 48 remarkably inhibited α-syn inclusion and cell confluence using M17D cells. Collectively, compounds 46 and 48 could serve as a basic structure for further optimization to develop clinically active AD and PD disease-modifying agents.

Perspective Strategies for Interventions in Parkinsonism: Remedying the Neglected Role of TPPP

Neurological disorders such as Parkinsonism cause serious socio-economic problems as there are, at present, only therapies that treat their symptoms. The well-established hallmark alpha-synuclein (SYN) is enriched in the inclusion bodies characteristic of Parkinsonism. We discovered a prominent partner of SYN, termed Tubulin Polymerization Promoting Protein (TPPP), which has important physiological and pathological activities such as the regulation of the microtubule network and the promotion of SYN aggregation. The role of TPPP in Parkinsonism is often neglected in research, which we here attempt to remedy. In the normal brain, SYN and TPPP are expressed endogenously in neurons and oligodendrocytes, respectively, whilst, at an early stage of Parkinsonism, soluble hetero-associations of these proteins are found in both cell types. The cell-to-cell transmission of these proteins, which is central to disease progression, provides a unique situation for specific drug targeting. Different strategies for intervention and for the discovery of biomarkers include (i) interface targeting of the SYN-TPPP hetero-complex; (ii) proteolytic degradation of SYN and/or TPPP using the PROTAC technology; and (iii) depletion of the proteins by miRNA technology. We also discuss the potential roles of SYN and TPPP in the phenotype stabilization of neurons and oligodendrocytes.

Using Generative Modeling to Endow with Potency Initially Inert Compounds with Good Bioavailability and Low Toxicity

In the early stages of drug development, large chemical libraries are typically screened to identify compounds of promising potency against the chosen targets. Often, however, the resulting hit compounds tend to have poor drug metabolism and pharmacokinetics (DMPK), with negative developability features that may be difficult to eliminate. Therefore, starting the drug discovery process with a "null library", compounds that have highly desirable DMPK properties but no potency against the chosen targets, could be advantageous. Here, we explore the opportunities offered by machine learning to realize this strategy in the case of the inhibition of α-synuclein aggregation, a process associated with Parkinson's disease. We apply MolDQN, a generative machine learning method, to build an inhibitory activity against α-synuclein aggregation into an initial inactive compound with good DMPK properties. Our results illustrate how generative modeling can be used to endow initially inert compounds with desirable developability properties.

GV-971 attenuates α-Synuclein aggregation and related pathology

RATIONALE

Synucleinopathies, including Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), share a distinct pathological feature, that is, a widespread accumulation of α-synuclein (α-syn) in the brain. There is a significant clinical unmet need for disease-modifying treatments for synucleinopathies. Recently, a seaweed-derived mixture of oligosaccharides sodium oligomannate, GV-971, was approved for Phase 2 clinical trials for PD. This study aimed to further evaluate the therapeutic effects of GV-971 on synucleinopathies using cellular and animal models and explore its associated molecular mechanisms.

METHODS

α-Syn aggregation was assessed, in vitro and ex vivo, by ThT assay. A dopaminergic neuron cell line, Prnp-SNCAA53T mice, and brain slices from PD and DLB patients were used to determine the efficacy of GV-971 in ameliorating α-syn pathology. Measurements of motor functions, including pole, cylinder, and rotarod tests, were conducted on Prnp-SNCAA53T mice 4 weeks after intragastric administration of GV-971 (200 mg day-1  kg-1 ).

RESULTS

GV-971 effectively prevented α-syn aggregation and even disassembled pre-aggregated α-syn fibrils, in vitro and ex vivo. In addition, GV-971 was able to rescue α-syn-induced neuronal damage and reduced release of extracellular vesicles (EVs), likely via modulating Alix expression. In the Prnp-SNCAA53T mouse model, when treated at the age of 5 months, GV-971 significantly decreased α-syn deposition in the cortex, midbrain, and cerebellum regions, along with ameliorating the motor dysfunctions.

CONCLUSIONS

Our results indicate that GV-971, when administered at a relatively early stage of the disease process, significantly reduced α-syn accumulation and aggregation in Prnp-SNCAA53T mice. Furthermore, GV-971 corrected α-syn-induced inhibition of EVs release in neurons, contributing to neuronal protection. Future studies are needed to further assess GV-971 as a promising disease-modifying therapy for PD and other synucleinopathies.

Navigating α-Synuclein Aggregation Inhibition: Methods, Mechanisms, and Molecular Targets

Parkinson's disease is a yet incurable, age-related neurodegenerative disorder characterized by the aggregation of small neuronal protein α-synuclein into amyloid fibrils. Inhibition of this process is a prospective strategy for developing a disease-modifying treatment. We overview here small molecule, peptide, and protein inhibitors of α-synuclein fibrillization reported to date. Special attention was paid to the specificity of inhibitors and critical analysis of their action mechanisms. Namely, the importance of oxidation of polyphenols and cross-linking of α-synuclein into inhibitory dimers was highlighted. We also compared strategies of targeting monomeric, oligomeric, and fibrillar α-synuclein species, thoroughly discussed the strong and weak sides of different approaches to testing the inhibitors.

Multiplexed Digital Characterization of Misfolded Protein Oligomers via Solid-State Nanopores

Misfolded protein oligomers are of central importance in both the diagnosis and treatment of Alzheimer's and Parkinson's diseases. However, accurate high-throughput methods to detect and quantify oligomer populations are still needed. We present here a single-molecule approach for the detection and quantification of oligomeric species. The approach is based on the use of solid-state nanopores and multiplexed DNA barcoding to identify and characterize oligomers from multiple samples. We study α-synuclein oligomers in the presence of several small-molecule inhibitors of α-synuclein aggregation as an illustration of the potential applicability of this method to the development of diagnostic and therapeutic methods for Parkinson's disease.

Targeted protein modification as a paradigm shift in drug discovery

Targeted Protein Modification (TPM) is an umbrella term encompassing numerous tools and approaches that use bifunctional agents to induce a desired modification over the POI. The most well-known TPM mechanism is PROTAC-directed protein ubiquitination. PROTAC-based targeted degradation offers several advantages over conventional small-molecule inhibitors, has shifted the drug discovery paradigm, and is acquiring increasing interest as over ten PROTACs have entered clinical trials in the past few years. Targeting the protein of interest for proteasomal degradation by PROTACS was the pioneer of various toolboxes for selective protein degradation. Nowadays, the ever-increasing number of tools and strategies for modulating and modifying the POI has expanded far beyond protein degradation, which phosphorylation and de-phosphorylation of the protein of interest, targeted acetylation, and selective modification of protein O-GlcNAcylation are among them. These novel strategies have opened new avenues for achieving more precise outcomes while remaining feasible and minimizing side effects. This field, however, is still in its infancy and has a long way to precede widespread use and translation into clinical practice. Herein, we investigate the pros and cons of these novel strategies by exploring the latest advancements in this field. Ultimately, we briefly discuss the emerging potential applications of these innovations in cancer therapy, neurodegeneration, viral infections, and autoimmune and inflammatory diseases.

Lysosome and related protein degradation technologies

Recently, targeted protein degradation technologies based on lysosomal pathways have been developed. Lysosome-based targeted protein degradation technology has a broad range of substrates and the potential to degrade intracellular and extracellular proteins, protein aggregates, damaged organelles and non-protein molecules. Thus, they hold great promise for drug R&D. This study has focused on the biogenesis of lysosomes, their basic functions, lysosome-associated diseases and targeted protein degradation technologies through the lysosomal pathway. In addition, we thoroughly examine the potential applications and limitations of this technology and engage in insightful discussions on potential avenues for future research. Our primary objective is to foster preclinical research on this technology and facilitate its successful clinical implementation.

Genome-wide CRISPR-Cas9 Knockout Screening Reveals a TSPAN3-mediated Endo-lysosome Pathway Regulating the Degradation of α-Synuclein Oligomers

Misfolding and aggregation of α-Synuclein (α-Syn), which are hallmark pathological features of neurodegenerative diseases such as Parkinson's disease (PD) and dementia with Lewy Bodies, continue to be significant areas of research. Among the diverse forms of α-Syn - monomer, oligomer, and fibril, the oligomer is considered the most toxic. However, the mechanisms governing α-Syn oligomerization are not yet fully understood. In this study, we utilized genome-wide CRISPR/Cas9 loss-of-function screening in human HEK293 cells to identify negative regulators of α-Syn oligomerization. We found that tetraspanin 3 (TSPAN3), a presumptive four-pass transmembrane protein, but not its homolog TSPAN7, significantly modulates α-Syn oligomer levels. TSPAN3 was observed to interact with α-Syn oligomers, regulate the amount of α-Syn oligomers on the cell membrane, and promote their degradation via the clathrin-AP2 mediated endo-lysosome pathway. Our findings highlight TSPAN3 as a potential regulator of α-Syn oligomers, presenting a promising target for future PD prevention and treatment strategies.

Lewy Body Dementia: An Overview of Promising Therapeutics

PURPOSE OF REVIEW

Lewy body dementia (LBD) encompasses dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). This article will emphasize potential disease-modifying therapies as well as investigative symptomatic treatments for non-motor symptoms including cognitive impairment and psychosis that can present a tremendous burden to patients with LBD and their caregivers.

RECENT FINDINGS

We review 11 prospective disease-modifying therapies (DMT) including four with phase 2 data (neflamapimod, nilotinib, bosutinib, and E2027); four with some limited data in symptomatic populations including phase 1, open-label, registry, or cohort data (vodabatinib, ambroxol, clenbuterol, and terazosin); and three with phase 1 data in healthy populations (Anle138b, fosgonimeton, and CT1812). We also appraise four symptomatic therapies for cognitive impairment, but due to safety and efficacy concerns, only NYX-458 remains under active investigation. Of symptomatic therapies for psychosis recently investigated, pimavanserin shows promise in LBD, but studies of nelotanserin have been suspended. Although the discovery of novel symptomatic and disease-modifying therapeutics remains a significant challenge, recently published and upcoming trials signify promising strides toward that aim.

Targeted protein degradation for the treatment of Parkinson's disease: Advances and future perspective

Parkinson's disease (PD) is a progressive disorder that belongs to a class of neurodegenerative disorders (NDs) called Synucleinopathies. It has characterized by the misfolding and aggregation of a-synuclein. Our understanding of PD continues to evolve, and so does our approach to treatment. including therapies aimed at delaying pathology, quitting neuronal loss, and shortening the course of the disease by selectively targeting essential proteins suspected to play a role in PD pathogenesis. One emerging approach that is generating significant interest is Targeted Protein Degradation (TPD). TPD is an innovative method that allows us to specifically break down certain proteins using specially designed molecules or peptides, like PROteolysis-TArgeting-Chimera (PROTACs). This approach holds great promise, particularly in the context of NDs. In this review, we will briefly explain PD and its pathogenesis, followed by discussing protein degradation systems and TPD strategy in PD by reviewing synthesized small molecules and peptides. Finally, future perspectives and challenges in the field are discussed.

Anti-prion drugs do not improve survival in knock-in models of inherited prion disease

Prion diseases uniquely manifest in three distinct forms: inherited, sporadic, and infectious. Wild-type prions are responsible for the sporadic and infectious versions, while mutant prions cause inherited variants like fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD). Although some drugs can prolong prion incubation times up to four-fold in rodent models of infectious prion diseases, no effective treatments for FFI and fCJD have been found. In this study, we evaluated the efficacy of various anti-prion drugs on newly-developed knock-in mouse models for FFI and fCJD. These models express bank vole prion protein (PrP) with the pathogenic D178N and E200K mutations. We applied various drug regimens known to be highly effective against wild-type prions in vivo as well as a brain-penetrant compound that inhibits mutant PrP Sc propagation in vitro . None of the regimens tested (Anle138b, IND24, Anle138b + IND24, cellulose ether, and PSCMA) significantly extended disease-free survival or prevented mutant PrP Sc accumulation in either knock-in mouse model, despite their ability to induce strain adaptation of mutant prions. Paradoxically, the combination of Anle138b and IND24 appeared to accelerate disease by 16% and 26% in kiBVI E200K and kiBVI D178N mice, respectively, and accelerated the aggregation of mutant PrP molecules in vitro . Our results show that anti-prion drugs originally developed to treat infectious prion diseases do not necessarily work for inherited prion diseases, and that the recombinant sPMCA is not a reliable platform for identifying compounds that target mutant prions. This work underscores the need to develop therapies and validate screening assays specifically for mutant prions.

Secondary Processes Dominate the Quiescent, Spontaneous Aggregation of α-Synuclein at Physiological pH with Sodium Salts

The accurate recapitulation in an in vitro assay of the aggregation process of α-synuclein in Parkinson's disease has been a significant challenge. As α-synuclein does not aggregate spontaneously in most currently used in vitro assays, primary nucleation is triggered by the presence of surfaces such as lipid membranes or interfaces created by shaking, to achieve aggregation on accessible time scales. In addition, secondary nucleation is typically only observed by lowering the pH below 5.8. Here we investigated assay conditions that enables spontaneous primary nucleation and secondary nucleation at pH 7.4. Using 400 mM sodium phosphate, we observed quiescent spontaneous aggregation of α-synuclein and established that this aggregation is dominated by secondary processes. Furthermore, the presence of potassium ions enhanced the reproducibility of quiescent α-synuclein aggregation. This work provides a framework for the study of spontaneous α-synuclein aggregation at physiological pH.

Advances in understanding the function of alpha-synuclein: implications for Parkinson's disease

The critical role of alpha-synuclein in Parkinson's disease represents a pivotal discovery. Some progress has been made over recent years in identifying disease-modifying therapies for Parkinson's disease that target alpha-synuclein. However, these treatments have not yet shown clear efficacy in slowing the progression of this disease. Several explanations exist for this issue. The pathogenesis of Parkinson's disease is complex and not yet fully clarified and the heterogeneity of the disease, with diverse genetic susceptibility and risk factors and different clinical courses, adds further complexity. Thus, a deep understanding of alpha-synuclein physiological and pathophysiological functions is crucial. In this review, we first describe the cellular and animal models developed over recent years to study the physiological and pathological roles of this protein, including transgenic techniques, use of viral vectors and intracerebral injections of alpha-synuclein fibrils. We then provide evidence that these tools are crucial for modelling Parkinson's disease pathogenesis, causing protein misfolding and aggregation, synaptic dysfunction, brain plasticity impairment and cell-to-cell spreading of alpha-synuclein species. In particular, we focus on the possibility of dissecting the pre- and postsynaptic effects of alpha-synuclein in both physiological and pathological conditions. Finally, we show how vulnerability of specific neuronal cell types may facilitate systemic dysfunctions leading to multiple network alterations. These functional alterations underlie diverse motor and non-motor manifestations of Parkinson's disease that occur before overt neurodegeneration. However, we now understand that therapeutic targeting of alpha-synuclein in Parkinson's disease patients requires caution, since this protein exerts important physiological synaptic functions. Moreover, the interactions of alpha-synuclein with other molecules may induce synergistic detrimental effects. Thus, targeting only alpha-synuclein might not be enough. Combined therapies should be considered in the future.

Optimization of a small molecule inhibitor of secondary nucleation in α-synuclein aggregation

Parkinson's disease is characterised by the deposition in the brain of amyloid aggregates of α-synuclein. The surfaces of these amyloid aggregates can catalyse the formation of new aggregates, giving rise to a positive feedback mechanism responsible for the rapid proliferation of α-synuclein deposits. We report a procedure to enhance the potency of a small molecule to inhibit the aggregate proliferation process using a combination of in silico and in vitro methods. The optimized small molecule shows potency already at a compound:protein stoichiometry of 1:20. These results illustrate a strategy to accelerate the optimisation of small molecules against α-synuclein aggregation by targeting secondary nucleation.

Development of an α-synuclein positron emission tomography tracer for imaging synucleinopathies

Synucleinopathies are characterized by the accumulation of α-synuclein (α-Syn) aggregates in the brain. Positron emission tomography (PET) imaging of synucleinopathies requires radiopharmaceuticals that selectively bind α-Syn deposits. We report the identification of a brain permeable and rapid washout PET tracer [18F]-F0502B, which shows high binding affinity for α-Syn, but not for Aβ or Tau fibrils, and preferential binding to α-Syn aggregates in the brain sections. Employing several cycles of counter screenings with in vitro fibrils, intraneuronal aggregates, and neurodegenerative disease brain sections from several mice models and human subjects, [18F]-F0502B images α-Syn deposits in the brains of mouse and non-human primate PD models. We further determined the atomic structure of the α-Syn fibril-F0502B complex by cryo-EM and revealed parallel diagonal stacking of F0502B on the fibril surface through an intense noncovalent bonding network via inter-ligand interactions. Therefore, [18F]-F0502B is a promising lead compound for imaging aggregated α-Syn in synucleinopathies.

Experimental models of gut-first Parkinson's disease: A systematic review

BACKGROUND

There is strong support from studies in humans and in animal models that Parkinson's disease (PD) may begin in the gut. This brings about a unique opportunity for researchers in the field of neurogastroenterology to contribute to advancing the field and making contributions that could lead to the ability to diagnose and treat PD in the premotor stages. Lack of familiarity with some of the aspects of the experimental approaches used in these studies may present a barrier for neurogastroenterology researchers to enter the field. Much remains to be understood about intestinal-specific components of gut-first PD pathogenesis and the field would benefit from contributions of enteric and central nervous system neuroscientists.

PURPOSE

To address these issues, we have conducted a systematic review of the two most frequently used experimental models of gut-first PD: transneuronal propagation of α-synuclein preformed fibrils and oral exposure to environmental toxins. We have reviewed the details of these studies and present methodological considerations for the use of these models. Our aim is that this review will serve as a framework and useful reference for neuroscientists, gastroenterologists, and neurologists interested in applying their expertise to advancing our understanding of gut-first PD.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Disrupting pathologic phase transitions in neurodegeneration

Solid-like protein deposits found in aged and diseased human brains have revealed a relationship between insoluble protein accumulations and the resulting deficits in neurologic function. Clinically diverse neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis, exhibit unique and disease-specific biochemical protein signatures and abnormal protein depositions that often correlate with disease pathogenesis. Recent evidence indicates that many pathologic proteins assemble into liquid-like protein phases through the highly coordinated process of liquid-liquid phase separation. Over the last decade, biomolecular phase transitions have emerged as a fundamental mechanism of cellular organization. Liquid-like condensates organize functionally related biomolecules within the cell, and many neuropathology-associated proteins reside within these dynamic structures. Thus, examining biomolecular phase transitions enhances our understanding of the molecular mechanisms mediating toxicity across diverse neurodegenerative diseases. This Review explores the known mechanisms contributing to aberrant protein phase transitions in neurodegenerative diseases, focusing on tau and TDP-43 proteinopathies and outlining potential therapeutic strategies to regulate these pathologic events.

Are Therapies That Target α-Synuclein Effective at Halting Parkinson's Disease Progression? A Systematic Review

There are currently no pharmacological treatments available that completely halt or reverse the progression of Parkinson's Disease (PD). Hence, there is an unmet need for neuroprotective therapies. Lewy bodies are a neuropathological hallmark of PD and contain aggregated α-synuclein (α-syn) which is thought to be neurotoxic and therefore a suitable target for therapeutic interventions. To investigate this further, a systematic review was undertaken to evaluate whether anti-α-syn therapies are effective at preventing PD progression in preclinical in vivo models of PD and via current human clinical trials. An electronic literature search was performed using MEDLINE and EMBASE (Ovid), PubMed, the Web of Science Core Collection, and Cochrane databases to collate clinical evidence that investigated the targeting of α-syn. Novel preclinical anti-α-syn therapeutics provided a significant reduction of α-syn aggregations. Biochemical and immunohistochemical analysis of rodent brain tissue demonstrated that treatments reduced α-syn-associated pathology and rescued dopaminergic neuronal loss. Some of the clinical studies did not provide endpoints since they had not yet been completed or were terminated before completion. Completed clinical trials displayed significant tolerability and efficacy at reducing α-syn in patients with PD with minimal adverse effects. Collectively, this review highlights the capacity of anti-α-syn therapies to reduce the accumulation of α-syn in both preclinical and clinical trials. Hence, there is potential and optimism to target α-syn with further clinical trials to restrict dopaminergic neuronal loss and PD progression and/or provide prophylactic protection to avoid the onset of α-syn-induced PD.

Discovery of Small-Molecule Degraders for Alpha-Synuclein Aggregates

Alpha-synuclein (αSyn) species, especially the oligomers and fibers, are associated with multiple neurodegenerative diseases and cannot be directly targeted under the conventional pharmacological paradigm. Proteolysis-targeting chimera technology confers degradation of various "undruggable" targets; however, hardly any small-molecule degrader for αSyn aggregates has been reported yet. Herein, by using the probe molecule sery308 as a warhead, a series of small-molecule degraders for αSyn aggregates were designed and synthesized. Their degradation effects on αSyn aggregates were evaluated on a modified pre-formed fibril-seeding cell model. Compound 2b exhibited the highest degradation efficiency (DC₅₀ = 7.51 ± 0.53 μM) with high selectivity. Mechanistic exploration revealed that both proteasomal and lysosomal pathways were involved in this kind of degradation. Moreover, the therapeutic effects of 2b were tested on SH-SY5Y (human neuroblastoma cell line) cells and Caenorhabditis elegans. Our results provided a new class of small-molecule candidates against synucleinopathies and broadened the substrate spectrum of PROTAC-based degraders.

Neurodegeneration and inflammation crosstalk: Therapeutic targets and perspectives

Glia, which was formerly considered to exist just to connect neurons, now plays a key function in a wide range of physiological events, including formation of memory, learning, neuroplasticity, synaptic plasticity, energy consumption, and homeostasis of ions. Glial cells regulate the brain's immune responses and confers nutritional and structural aid to neurons, making them an important player in a broad range of neurological disorders. Alzheimer's, ALS, Parkinson's, frontotemporal dementia (FTD), and epilepsy are a few of the neurodegenerative diseases that have been linked to microglia and astroglia cells, in particular. Synapse growth is aided by glial cell activity, and this activity has an effect on neuronal signalling. Each glial malfunction in diverse neurodegenerative diseases is distinct, and we will discuss its significance in the progression of the illness, as well as its potential for future treatment.

Design, Synthesis and Biological Evaluation of α-Synuclein Proteolysis-Targeting Chimeras

α-Synuclein aggregation under pathological conditions is one of the causes of related neurodegenerative diseases. PROTACs (proteolysis targeting chimeras) are bifunctional small molecules that induce a post-translational erasure of proteins via the ubiquitination of target proteins by E3 ubiquitin ligase and subsequent proteasomal degradation. However, few research studies have been conducted for targeted protein degradation of α-synuclein aggregates. In this article, we have designed and synthesized a series of small-molecule degraders 1-9 based on a known α-synuclein aggregation inhibitor sery384. In silico docking studies of sery384 with α-synuclein aggregates were accomplished to ensure that the compounds bound to α-synuclein aggregates specifically. The protein level of α-synuclein aggregates was determined to evaluate the degradation efficiency of PROTAC molecules on α-synuclein aggregates in vitro. The results show that compound 5 had the most significant degradation effect, with DC₅₀ of 5.049 μM, and could induce the degradation of α-synuclein aggregates in a time- and dose-dependent manner in vitro. Furthermore, compound 5 could inhibit the elevation of the ROS level caused by overexpression and aggregation of α-synuclein and protect H293T cells from α-synuclein toxicity. Conclusively, our results provide a new class of small-molecule degraders and an experimental basis for the treatment of α-synuclein related neurodegenerative diseases.

Synthesis and Preliminary Characterization of Putative Anle138b-Centered PROTACs against α-Synuclein Aggregation

The search for disease-modifying agents targeted against Parkinson's disease led us to rationally design a small array of six Anle138b-centered PROTACs, 7a,b, 8a,b and 9a,b, targeting αSynuclein (αSyn) aggregates for binding, polyubiquitination by the E3 ligase Cereblon (CRBN), and proteasomal degradation. Lenalidomide and thalidomide were used as CRBN ligands and coupled with amino- and azido Anle138b derivatives through flexible linkers and coupling reactions (amidation, 'click' chemistry). Four Anle138b-PROTACs, 8a,b and 9a,b, were characterized against in vitro αSyn aggregation, monitoring them in a Thioflavin T (ThT) fluorescence assay and in dopaminergic neurons derived from a set of isogenic pluripotent stem cell (iPSC) lines with SNCA multiplications. Native and seeded αSyn aggregation was determined with a new biosensor, and a partial correlation between αSyn aggregation, cellular dysfunctions, and neuronal survival was obtained. Anle138b-PROTAC 8a was characterized as the most promising αSyn aggregation inhibitor/degradation inducer, with potential usefulness against synucleinopathies and cancer.

The Structural Combination of SIL and MODAG Scaffolds Fails to Enhance Binding to α-Synuclein but Reveals Promising Affinity to Amyloid β

A technique to image α-synuclein (αSYN) fibrils in vivo is an unmet scientific and clinical need that would represent a transformative tool in the understanding, diagnosis, and treatment of various neurodegenerative diseases. Several classes of compounds have shown promising results as potential PET tracers, but no candidate has yet exhibited the affinity and selectivity required to reach clinical application. We hypothesized that the application of the rational drug design technique of molecular hybridization to two promising lead scaffolds could enhance the binding to αSYN up to the fulfillment of those requirements. By combining the structures of SIL and MODAG tracers, we developed a library of diarylpyrazoles (DAPs). In vitro evaluation through competition assays against [³H]SIL26 and [³H]MODAG-001 showed the novel hybrid scaffold to have preferential binding affinity for amyloid β (Aβ) over αSYN fibrils. A ring-opening modification on the phenothiazine building block to produce analogs with increased three-dimensional flexibility did not result in an improved αSYN binding but a complete loss of competition, as well as a significant reduction in Aβ affinity. The combination of the phenothiazine and the 3,5-diphenylpyrazole scaffolds into DAP hybrids did not generate an enhanced αSYN PET tracer lead compound. Instead, these efforts identified a scaffold for promising Aβ ligands that may be relevant to the treatment and monitoring of Alzheimer's disease (AD).

Anle138b interaction in α-synuclein aggregates by dynamic nuclear polarization NMR

Small molecules that bind to oligomeric protein species such as membrane proteins and fibrils are of clinical interest for development of therapeutics and diagnostics. Definition of the binding site at atomic resolution via NMR is often challenging due to low binding stoichiometry of the small molecule. For fibrils and aggregation intermediates grown in the presence of lipids, we report atomic-resolution contacts to the small molecule at sub nm distance via solid-state NMR using dynamic nuclear polarization (DNP) and orthogonally labelled samples of the protein and the small molecule. We apply this approach to α-synuclein (αS) aggregates in complex with the small molecule anle138b, which is a clinical drug candidate for disease modifying therapy. The small central pyrazole moiety of anle138b is detected in close proximity to the protein backbone and differences in the contacts between fibrils and early intermediates are observed. For intermediate species, the 100 K condition for DNP helps to preserve the aggregation state, while for both fibrils and oligomers, the DNP enhancement is essential to obtain sufficient sensitivity.

Small molecule-based fluorescent probes for the detection of α-Synuclein aggregation states

The formation of aggregates due to protein misfolding is encountered in various neurodegenerative diseases. α-Synuclein (α-Syn) aggregation is linked to Parkinson's disease (PD). It is one of the most prevalent neurodegenerative disorders after Alzheimer's disease. Aggregation of α-Syn is associated with Lewy body formation and degeneration of the dopaminergic neurons in the brain. These are the pathological hallmarks of PD progression. α-Syn aggregates in a multi-step process. The native unstructured α-Syn monomers combine to form oligomers, followed by amyloid fibrils, and finally Lewy bodies. Recent evidence suggests that α-Syn oligomerization and fibrils formation play major roles in PD development. α-Syn oligomeric species is the main contributor to neurotoxicity. Therefore, the detection of α-Syn oligomers and fibrils has drawn significant attention for potential diagnostic and therapeutic development. In this regard, the fluorescence strategy has become the most popular approach for following the protein aggregation process. Thioflavin T (ThT) is the most frequently used probe for monitoring amyloid kinetics. Unfortunately, it suffers from several significant drawbacks including the inability to detect neurotoxic oligomers. Researchers developed several small molecule-based advanced fluorescent probes compared to ThT for the detection/monitoring of α-Syn aggregates states. These are summarized here.

A review of the current research on in vivo and in vitro detection for alpha-synuclein: a biomarker of Parkinson's disease

Parkinson's disease is a health-threatening neurodegenerative disease of the elderly with clinical manifestations of motor and non-motor deficits such as tremor palsy and loss of smell. Alpha-synuclein (α-Syn) is the pathological basis of PD, it can abnormally aggregate into insoluble forms such as oligomers, fibrils, and plaques, causing degeneration of nigrostriatal dopaminergic neurons in the substantia nigra in the patient's brain and the formation of Lewy bodies (LBs) and Lewy neuritis (LN) inclusions. As a result, achieving α-Syn aggregate detection in the early stages of PD can effectively stop or delay the progression of the disease. In this paper, we provide a brief overview and analysis of the molecular structures and α-Syn in vivo and in vitro detection methods, such as mass spectrometry, antigen-antibody recognition, electrochemical sensors, and imaging techniques, intending to provide more technological support for detecting α-Syn early in the disease and intervening in the progression of Parkinson's disease.

A single protective polymorphism in the prion protein blocks cross-species prion replication in cultured cells

The bank vole (BV) prion protein (PrP) can function as a universal acceptor of prions. However, the molecular details of BVPrP's promiscuity for replicating a diverse range of prion strains remain obscure. To develop a cultured cell paradigm capable of interrogating the unique properties of BVPrP, we generated monoclonal lines of CAD5 cells lacking endogenous PrP but stably expressing either hamster (Ha), mouse (Mo), or BVPrP (M109 or I109 polymorphic variants) and then challenged them with various strains of mouse or hamster prions. Cells expressing BVPrP were susceptible to both mouse and hamster prions, whereas cells expressing MoPrP or HaPrP could only be infected with species-matched prions. Propagation of mouse and hamster prions in cells expressing BVPrP resulted in strain adaptation in several instances, as evidenced by alterations in conformational stability, glycosylation, susceptibility to anti-prion small molecules, and the inability of BVPrP-adapted mouse prion strains to infect cells expressing MoPrP. Interestingly, cells expressing BVPrP containing the G127V prion gene variant, identified in individuals resistant to kuru, were unable to become infected with prions. Moreover, the G127V polymorphic variant impeded the spontaneous aggregation of recombinant BVPrP. These results demonstrate that BVPrP can facilitate cross-species prion replication in cultured cells and that a single amino acid change can override the prion-permissive nature of BVPrP. This cellular paradigm will be useful for dissecting the molecular features of BVPrP that allow it to function as a universal prion acceptor.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.

Exploration and Exploitation Approaches Based on Generative Machine Learning to Identify Potent Small Molecule Inhibitors of α-Synuclein Secondary Nucleation

The high attrition rate in drug discovery pipelines is an especially pressing issue for Parkinson's disease, for which no disease-modifying drugs have yet been approved. Numerous clinical trials targeting α-synuclein aggregation have failed, at least in part due to the challenges in identifying potent compounds in preclinical investigations. To address this problem, we present a machine learning approach that combines generative modeling and reinforcement learning to identify small molecules that perturb the kinetics of aggregation in a manner that reduces the production of oligomeric species. Training data were obtained by an assay reporting on the degree of inhibition of secondary nucleation, which is the most important mechanism of α-synuclein oligomer production. This approach resulted in the identification of small molecules with high potency against secondary nucleation.

One-Pot Radiosynthesis of [18F]Anle138b—5-(3-Bromophenyl)-3-(6-[18F]fluorobenzo[d][1,3]dioxol-5-yl)-1H-pyrazole—A Potential PET Radiotracer Targeting α-Synuclein Aggregates

Availability of PET imaging radiotracers targeting α-synuclein aggregates is important for early diagnosis of Parkinson’s disease and related α-synucleinopathies, as well as for the development of new therapeutics. Derived from a pyrazole backbone, 11C-labelled derivatives of anle138b (3-(1,3-benzodioxol-5-yl)-5-(3-bromophenyl)-1H-pyrazole)—an inhibitor of α-synuclein and prion protein oligomerization—are currently in active development as the candidates for PET imaging α-syn aggregates. This work outlines the synthesis of a radiotracer based on the original structure of anle138b, labelled with fluorine-18 isotope, eminently suitable for PET imaging due to half-life and decay energy characteristics (97% β+ decay, 109.7 min half-life, and 635 keV positron energy). A three-step radiosynthesis was developed starting from 6-[18F]fluoropiperonal (6-[18F]FP) that was prepared using (piperonyl)(phenyl)iodonium bromide as a labelling precursor. The obtained 6-[18F]FP was used directly in the condensation reaction with tosylhydrazide followed by 1,3-cycloaddition of the intermediate with 3′-bromophenylacetylene eliminating any midway without any intermediate purifications. This one-pot approach allowed the complete synthesis of [18F]anle138b within 105 min with RCY of 15 ± 3% (n = 3) and Am in the range of 32–78 GBq/µmol. The [18F]fluoride processing and synthesis were performed in a custom-built semi-automated module, but the method can be implemented in all the modern automated platforms. While there is definitely space for further optimization, the procedure developed is well suited for preclinical studies of this novel radiotracer in animal models and/or cell cultures.

Novel repertoire of tau biosensors to monitor pathological tau transformation and seeding activity in living cells

Aggregates of the tau protein are a well-known hallmark of several neurodegenerative diseases, collectively referred to as tauopathies, including frontal temporal dementia and Alzheimer's disease (AD). Monitoring the transformation process of tau from physiological monomers into pathological oligomers or aggregates in a high-throughput, quantitative manner and in a cellular context is still a major challenge in the field. Identifying molecules able to interfere with those processes is of high therapeutic interest. Here, we developed a series of inter- and intramolecular tau biosensors based on the highly sensitive Nanoluciferase (Nluc) binary technology (NanoBiT) able to monitor the pathological conformational change and self-interaction of tau in living cells. Our repertoire of tau biosensors reliably reports i. molecular proximity of physiological full-length tau at microtubules; ii. changes in tau conformation and self-interaction associated with tau phosphorylation, as well as iii. tau interaction induced by seeds of recombinant tau or from mouse brain lysates of a mouse model of tau pathology. By comparing biosensors comprising different tau forms (i.e. full-length or short fragments, wild-type, or the disease-associated tau(P301L) variant) further insights into the tau transformation process are obtained. Proof-of-concept data for the high-throughput suitability and identification of molecules interfering with the pathological tau transformation processes are presented. This novel repertoire of tau biosensors is aimed to boost the disclosure of molecular mechanisms underlying pathological tau transformation in living cells and to discover new drug candidates for tau-related neurodegenerative diseases.

Mechanism of action deconvolution of the small-molecule pathological tau aggregation inhibitor Anle138b

BACKGROUND

A key histopathological hallmark of Alzheimer's disease (AD) is the presence of neurofibrillary tangles of aggregated microtubule-associated protein tau in neurons. Anle138b is a small molecule which has previously shown efficacy in mice in reducing tau aggregates and rescuing AD disease phenotypes.

METHODS

In this work, we employed bioinformatics analysis-including pathway enrichment and causal reasoning-of an in vitro tauopathy model. The model consisted of cultured rat cortical neurons either unseeded or seeded with tau aggregates derived from human AD patients, both of which were treated with Anle138b to generate hypotheses for its mode of action. In parallel, we used a collection of human target prediction models to predict direct targets of Anle138b based on its chemical structure.

RESULTS

Combining the different approaches, we found evidence supporting the hypothesis that the action of Anle138b involves several processes which are key to AD progression, including cholesterol homeostasis and neuroinflammation. On the pathway level, we found significantly enriched pathways related to these two processes including those entitled "Superpathway of cholesterol biosynthesis" and "Granulocyte adhesion and diapedesis". With causal reasoning, we inferred differential activity of SREBF1/2 (involved in cholesterol regulation) and mediators of the inflammatory response such as NFKB1 and RELA. Notably, our findings were also observed in Anle138b-treated unseeded neurons, meaning that the inferred processes are independent of tau pathology and thus represent the direct action of the compound in the cellular system. Through structure-based ligand-target prediction, we predicted the intracellular cholesterol carrier NPC1 as well as NF-κB subunits as potential targets of Anle138b, with structurally similar compounds in the model training set known to target the same proteins.

CONCLUSIONS

This study has generated feasible hypotheses for the potential mechanism of action of Anle138b, which will enable the development of future molecular interventions aiming to reduce tau pathology in AD patients.