Safety, tolerability and pharmacokinetics of the oligomer modulator anle138b with exposure levels sufficient for therapeutic efficacy in a murine Parkinson model: A randomised, double-blind, placebo-controlled phase 1a trial

New therapies on the horizon: Targeted protein degradation in neuroscience

This minireview explores the burgeoning field of targeted protein degradation (TPD) and its promising applications in neuroscience and clinical development. TPD offers innovative strategies for modulating protein levels, presenting a paradigm shift in small-molecule drug discovery and therapeutic interventions. Importantly, small-molecule protein degraders specifically target and remove pathogenic proteins from central nervous system cells without the drug delivery challenges of genomic and antibody-based modalities. Here, we review recent advancements in TPD technologies, highlight proteolysis targeting chimera (PROTAC) protein degrader molecules with proximity-induced degradation event-driven and iterative pharmacology, provide applications in neuroscience research, and discuss the high potential for translation of TPD into clinical settings.

A Peptide Strategy for Inhibiting Different Protein Aggregation Pathways

Protein aggregation correlates with many human diseases. Protein aggregates differ in structure and shape. Strategies to develop effective aggregation inhibitors that reach the clinic failed so far. Here, we developed a family of peptides targeting early aggregation stages for both amorphous and fibrillar aggregates of proteins unrelated in sequence and structure. They act on dynamic precursors before mechanistic differentiation takes place. Using peptide arrays, we first identified peptides inhibiting the amorphous aggregation of a molten globular, aggregation-prone mutant of the Axin tumor suppressor. Optimization revealed that the peptides activity did not depend on their sequences but rather on their molecular determinants: a composition of 20-30 % flexible, 30-40 % aliphatic and 20-30 % aromatic residues, a hydrophobicity/hydrophilicity ratio close to 1, and an even distribution of residues of different nature throughout the sequence. The peptides also suppressed fibrillation of Tau, a disordered protein that forms amyloids in Alzheimer's disease, and slowed down that of Huntingtin Exon1, an amyloidogenic protein in Huntington's disease, both entirely unrelated to Axin. Our compounds thus target early stages of different aggregation mechanisms, inhibiting both amorphous and amyloid aggregation. Such cross-mechanistic, multi-targeting aggregation inhibitors may be lead compounds for developing drug candidates against various protein aggregation diseases.

The PM20D1-NADA pathway protects against Parkinson's disease

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra and the accumulation of α-synuclein (α-Syn) aggregates. However, the molecular mechanisms regulating α-Syn aggregation and neuronal degeneration remain poorly understood. The peptidase M20 domain containing 1 (PM20D1) gene lies within the PARK16 locus genetically linked to PD. Single nucleotide polymorphisms regulating PM20D1 expression are associated with changed risk of PD. Dopamine (DA) metabolism and DA metabolites have been reported to regulate α-Syn pathology. Here we report that PM20D1 catalyzes the conversion of DA to N-arachidonoyl dopamine (NADA), which interacts with α-Syn and inhibits its aggregation. Simultaneously, NADA competes with α-Syn fibrils to regulate TRPV4-mediated calcium influx and downstream phosphatases, thus alleviating α-Syn phosphorylation. The expression of PM20D1 decreases during aging. Overexpression of PM20D1 or the administration of NADA in a mouse model of synucleinopathy alleviated α-Syn pathology, dopaminergic neurodegeneration, and motor impairments. These observations support the protective effect of the PM20D1-NADA pathway against the progression of α-Syn pathology in PD.

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.

Pharmacokinetics and Enterohepatic Circulation of 2-(Quinoline-8-carboxamido)benzoic Acid (2-QBA) in Mice

The quinoline alkaloid 2-(quinoline-8-carboxamido)benzoic acid (2-QBA), which is isolated from Aspergillus sp. SCSIO06786, a deep sea-derived fungus, has been suggested as a therapeutic candidate for the treatment of Parkinson's disease. We developed an analytical method for 2-QBA using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) in mouse plasma, in which a protein precipitation method for the sample preparation of 2-QBA in mouse plasma was used due to its simplicity and good extraction recovery rates (80.49-97.56%). The linearity of the calibration standard sample, inter- and intraday precision and accuracy, and stability of three quality control samples were suitable based on the assessment criteria and the lower limit of quantification (LLOQ) of the 2-QBA was 1 ng/mL. A pharmacokinetic study of 2-QBA was performed in mice divided into oral (2.0, 5.0, and 15 mg/kg) and intravenous (0.5 and 1.0 mg/kg) administration groups. The absolute oral bioavailability (BA) range of 2-QBA was calculated as 68.3-83.7%. Secondary peaks were observed at approximately 4-8 h after the oral administration of 2-QBA at all doses. The elimination half-life of the orally administered 2-QBA was significantly longer than that of the intravenous 2-QBA. In addition, glucuronide metabolites of 2-QBA were identified. They were transformed into 2-QBA using the β-glucuronidase treatment. Furthermore, the 2-QBA was readily absorbed from the jejunum to lower ileum. Taken together, the secondary peaks could be explained by the enterohepatic circulation of 2-QBA. In conclusion, the reabsorption of orally administered 2-QBA could contribute to the high oral BA of 2-QBA and could be beneficial for the efficacy of 2-QBA. Moreover, the simple and validated analytical method for 2-QBA using LC-MS/MS was applied to the pharmacokinetic study and BA assessments of 2-QBA in mice and would be helpful for subsequent pharmacokinetic studies, as well as for evaluations of the toxicokinetics and pharmacokinetic-pharmacodynamic correlation of 2-QBA to assess its potential as a drug.

Evaluation of the Effect of β-Wrapin AS69 in a Mouse Model Based on Alpha-Synuclein Overexpression

Aggregation of the protein α-Synuclein (αSyn) is a hallmark of Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple systems atrophy, and alleviating the extent of αSyn pathology is an attractive strategy against neurodegeneration. The engineered binding protein β-wrapin AS69 binds monomeric αSyn. AS69 reduces primary and secondary nucleation as well as fibril elongation in vitro. It also mitigates aSyn pathology in a mouse model based on intrastriatal injection of aSyn pre-formed fibrils (PFFs). Since the PFF-based model does not represent all aspects of PD, we tested here whether AS69 can reduce neurodegeneration resulting from αSyn overexpression. Human A53T-αSyn was overexpressed in the mouse Substantia nigra (SN) by using recombinant adeno-associated viral vector (rAAV). AS69 was also expressed by rAAV transduction. Behavioral tests and immunofluorescence staining were used as outcomes. Transduction with rAAV-αSyn resulted in αSyn pathology as reported by phospho-αSyn staining and caused degeneration of dopaminergic neurons in the SN. The co-expression of rAAV-AS69 did not reduce αSyn pathology or the degeneration of dopaminergic neurons. We conclude that αSyn monomer binding by rAAV-AS69 was insufficient to protect from aSyn pathology resulting from αSyn overexpression.

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.

Nonintuitive Immunogenicity and Plasticity of Alpha-Synuclein Conformers: A Paradigm for Smart Delivery of Neuro-Immunotherapeutics

Despite the extensive research successes and continuous developments in modern medicine in terms of diagnosis, prevention, and treatment, the lack of clinically useful disease-modifying drugs or immunotherapeutic agents that can successfully treat or prevent neurodegenerative diseases is an ongoing challenge. To date, only one of the 244 drugs in clinical trials for the treatment of neurodegenerative diseases has been approved in the past decade, indicating a failure rate of 99.6%. In corollary, the approved monoclonal antibody did not demonstrate significant cognitive benefits. Thus, the prevalence of neurodegenerative diseases is increasing rapidly. Therefore, there is an urgent need for creative approaches to identifying and testing biomarkers for better diagnosis, prevention, and disease-modifying strategies for the treatment of neurodegenerative diseases. Overexpression of the endogenous α-synuclein has been identified as the driving force for the formation of the pathogenic α-synuclein (α-Syn) conformers, resulting in neuroinflammation, hypersensitivity, endogenous homeostatic responses, oxidative dysfunction, and degeneration of dopaminergic neurons in Parkinson's disease (PD). However, the conformational plasticity of α-Syn proffers that a certain level of α-Syn is essential for the survival of neurons. Thus, it exerts both neuroprotective and neurotoxic (regulatory) functions on neighboring neuronal cells. Furthermore, the aberrant metastable α-Syn conformers may be subtle and difficult to detect but may trigger cellular and molecular events including immune responses. It is well documented in literature that the misfolded α-Syn and its conformers that are released into the extracellular space from damaged or dead neurons trigger the innate and adaptive immune responses in PD. Thus, in this review, we discuss the nonintuitive plasticity and immunogenicity of the α-Syn conformers in the brain immune cells and their physiological and pathological consequences on the neuroimmune responses including neuroinflammation, homeostatic remodeling, and cell-specific interactions that promote neuroprotection in PD. We also critically reviewed the novel strategies for immunotherapeutic delivery interventions in PD pathogenesis including immunotherapeutic targets and potential nanoparticle-based smart drug delivery systems. It is envisioned that a greater understanding of the nonintuitive immunogenicity of aberrant α-Syn conformers in the brain's microenvironment would provide a platform for identifying valid therapeutic targets and developing smart brain delivery systems for clinically effective disease-modifying immunotherapeutics that can aid in the prevention and treatment of PD in the future.

Common genetic risk for Parkinson's disease and dysfunction of the endo-lysosomal system

Parkinson's disease is a progressive neurological disorder, characterized by prominent movement dysfunction. The past two decades have seen a rapid expansion of our understanding of the genetic basis of Parkinson's, initially through the identification of monogenic forms and, more recently, through genome-wide association studies identifying common risk variants. Intriguingly, a number of cellular pathways have emerged from these analysis as playing central roles in the aetiopathogenesis of Parkinson's. In this review, the impact of data deriving from genome-wide analyses for Parkinson's upon our functional understanding of the disease will be examined, with a particular focus on examples of endo-lysosomal and mitochondrial dysfunction. The challenges of moving from a genetic to a functional understanding of common risk variants for Parkinson's will be discussed, with a final consideration of the current state of the genetic architecture of the disorder. This article is part of a discussion meeting issue 'Understanding the endo-lysosomal network in neurodegeneration'.

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.

Recent Advances in Clinical Trials in Multiple System Atrophy

PURPOSE OF REVIEW

This review summarizes previous and ongoing neuroprotection trials in multiple system atrophy (MSA), a rare and fatal neurodegenerative disease characterized by parkinsonism, cerebellar, and autonomic dysfunction. It also describes the preclinical therapeutic pipeline and provides some considerations relevant to successfully conducting clinical trials in MSA, i.e., diagnosis, endpoints, and trial design.

RECENT FINDINGS

Over 30 compounds have been tested in clinical trials in MSA. While this illustrates a strong treatment pipeline, only two have reached their primary endpoint. Ongoing clinical trials primarily focus on targeting α-synuclein, the neuropathological hallmark of MSA being α-synuclein-bearing glial cytoplasmic inclusions. The mostly negative trial outcomes highlight the importance of better understanding underlying disease mechanisms and improving preclinical models. Together with efforts to refine clinical measurement tools, innovative statistical methods, and developments in biomarker research, this will enhance the design of future neuroprotection trials in MSA and the likelihood of positive outcomes.

Insights into the management of Lewy body dementia: a scoping review

Lewy body dementia (LBD) is situated at the convergence of neurodegenerative disorders, posing an intricate and diverse clinical dilemma. The accumulation of abnormal protein in the brain, namely, the Lewy body causes disturbances in typical neural functioning, leading to a range of cognitive, motor, and mental symptoms that have a substantial influence on the overall well-being and quality of life of affected individuals. There is no definitive cure for the disease; however, several nonpharmacological and pharmacological modalities have been tried with questionable efficacies. The aim of this study is to figure out the role of different interventional strategies in the disease. Donepezil, rivastigmine, memantine, and galantamine were the commonly used drugs for LBD. Together with that, levodopa, antipsychotics, armodafinil, piracetam, and traditional medications like yokukansan were also used, when indicated. Talking about nonpharmacological measures, exercise, physical therapy, multicomponent therapy, occupational therapy, psychobehavioral modification, transcranial stimulation, and deep brain stimulation have been used with variable efficacies. Talking about recent advances in the treatment of LBD, various disease-modifying therapies like ambroxol, neflamapimod, irsenontrine, nilotinib, bosutinib, vodobatinib, clenbuterol, terazosin, elayta, fosgonimeton, and anle138b are emerging out. However, there drugs are still in the different phases of clinical trials and are not commonly used in clinical practice. With the different pharmacological and nonpharmacological modalities we have for treatment of LBD, all of them offer symptomatic relief only. Being a degenerative disease, definite cure of the disease can only be possible with regenerative measures.

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.

Therapeutic advances in neuroinfectious diseases

There have been several major advances in therapeutic options for the treatment of neurological infections over the past two decades. These advances encompass both the development of new antimicrobial therapies and the repurposing of existing agents for new indications. In addition, advances in our understanding of the host immune response have allowed for the development of new immunomodulatory strategies in the treatment of neurological infections. This review focuses on the key advances in the treatment of neurological infections, including viral, bacterial, fungal, and prion diseases, with a particular focus on immunomodulatory treatment options. This review also highlights the process by which clinicians can request access to therapeutic agents on a compassionate or emergency basis when they may not be commercially available. While many therapeutic advances have been achieved in the past several years, there remains a pressing need for the continued development of additional therapeutic agents in the treatment of neurological infections.

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.

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.

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.

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.

Parkinson's disease therapy: what lies ahead?

The worldwide prevalence of Parkinson's disease (PD) has been constantly increasing in the last decades. With rising life expectancy, a longer disease duration in PD patients is observed, further increasing the need and socioeconomic importance of adequate PD treatment. Today, PD is exclusively treated symptomatically, mainly by dopaminergic stimulation, while efforts to modify disease progression could not yet be translated to the clinics. New formulations of approved drugs and treatment options of motor fluctuations in advanced stages accompanied by telehealth monitoring have improved PD patients care. In addition, continuous improvement in the understanding of PD disease mechanisms resulted in the identification of new pharmacological targets. Applying novel trial designs, targeting of pre-symptomatic disease stages, and the acknowledgment of PD heterogeneity raise hopes to overcome past failures in the development of drugs for disease modification. In this review, we address these recent developments and venture a glimpse into the future of PD therapy in the years to come.

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.

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.

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.

Genetic modifiers of synucleinopathies-lessons from experimental models

α-Synuclein is a pleiotropic protein underlying a group of progressive neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies. Together, these are known as synucleinopathies. Like all neurological diseases, understanding of disease mechanisms is hampered by the lack of access to biopsy tissues, precluding a real-time view of disease progression in the human body. This has driven researchers to devise various experimental models ranging from yeast to flies to human brain organoids, aiming to recapitulate aspects of synucleinopathies. Studies of these models have uncovered numerous genetic modifiers of α-synuclein, most of which are evolutionarily conserved. This review discusses what we have learned about disease mechanisms from these modifiers, and ways in which the study of modifiers have supported ongoing efforts to engineer disease-modifying interventions for synucleinopathies.

Development of Small Molecules Targeting α-Synuclein Aggregation: A Promising Strategy to Treat Parkinson's Disease

Parkinson's disease, the second most common neurodegenerative disorder worldwide, is characterized by the accumulation of protein deposits in the dopaminergic neurons. These deposits are primarily composed of aggregated forms of α-Synuclein (α-Syn). Despite the extensive research on this disease, only symptomatic treatments are currently available. However, in recent years, several compounds, mainly of an aromatic character, targeting α-Syn self-assembly and amyloid formation have been identified. These compounds, discovered by different approaches, are chemically diverse and exhibit a plethora of mechanisms of action. This work aims to provide a historical overview of the physiopathology and molecular aspects associated with Parkinson's disease and the current trends in small compound development to target α-Syn aggregation. Although these molecules are still under development, they constitute an important step toward discovering effective anti-aggregational therapies for Parkinson's disease.

Who Ever Said It Would Be Easy? Reflecting on Two Clinical Trials Targeting α-Synuclein

Two recent, high-profile manuscripts reported negative results with two parallel approaches of passive immunization targeting α-synuclein in a population of patients with early Parkinson's disease (PD). These phase II studies failed to show a bona fide disease-modifying neuroprotective effect on PD progression, despite the evidence that these antibodies effectively bind native α-synuclein in human serum. Here, we discuss the possible reasons that could help explain the lack of clinical efficacy. In particular, we highlight (1) the wealth of evidence supporting the notion of α-synuclein as a valid therapeutic target; (2) the lack of evidence of target engagement in the aforementioned studies, especially of the elusive oligomeric species, the likely culprits in disease pathogenesis and/or its propagation; (3) the limitations, especially in terms of timing passive immunization, of preclinical models, where the same α-synuclein antibodies succeeded in mitigating disease manifestations; (4) the consideration of possibly intervening at an even earlier stage of disease in future trials; and (5) the multitude of strategies beyond passive immunization that could be used to combat α-synuclein-mediated neurodegeneration, if in the end the current approach is not fruitful. Overall, our perception is that converging developments in the field, among them novel bioassays and biomarkers, improved cellular and animal models and objective measurements of motor activities integrated into clinical trials, if further optimized, will gradually move the momentum of the field forward. This, to better test the concept of whether α-synuclein-targeting therapies can indeed deliver the "holy grail" of neuroprotection to the benefit of the PD community. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Therapeutic Trial of anle138b in Mouse Models of Genetic Prion Disease

Phenotypic screening has yielded small-molecule inhibitors of prion replication that are effective in vivo against certain prion strains but not others. Here, we sought to test the small molecule anle138b in multiple mouse models of prion disease. In mice inoculated with the RML strain of prions, anle138b doubled survival and durably suppressed astrogliosis measured by live-animal bioluminescence imaging. In knock-in mouse models of the D178N and E200K mutations that cause genetic prion disease, however, we were unable to identify a clear, quantifiable disease endpoint against which to measure therapeutic efficacy. Among untreated animals, the mutations did not impact overall survival, and bioluminescence remained low out to >20 months of age. Vacuolization and PrP deposition were observed in some brain regions in a subset of mutant animals but appeared to be unable to carry the weight of a primary endpoint in a therapeutic study. We conclude that not all animal models of prion disease are suited to well-powered therapeutic efficacy studies, and care should be taken in choosing the models that will support drug development programs. IMPORTANCE There is an urgent need to develop drugs for prion disease, a currently untreatable neurodegenerative disease. In this effort, there is a debate over which animal models can best support a drug development program. While the study of prion disease benefits from excellent animal models because prions naturally afflict many different mammals, different models have different capabilities and limitations. Here, we conducted a therapeutic efficacy study of the drug candidate anle138b in mouse models with two of the most common mutations that cause genetic prion disease. In a more typical model where prions are injected directly into the brain, we found anle138b to be effective. In the genetic models, however, the animals never reached a clear, measurable point of disease onset. We conclude that not all prion disease animal models are ideally suited to drug efficacy studies, and well-defined, quantitative disease metrics should be a priority.

In Silico Study of the Interactions of Anle138b Isomer, an Inhibitor of Amyloid Aggregation, with Partner Proteins

Herein, we aimed to highlight current "gaps" in the understanding of the potential interactions between the Anle138b isomer ligand, a promising agent for clinical research, and the intrinsically disordered alpha-synuclein protein. The presence of extensive unstructured areas in alpha-synuclein determines its existence in the cell of partner proteins, including the cyclophilin A chaperone, which prevents the aggregation of alpha-synuclein molecules that are destructive to cell life. Using flexible and cascaded molecular docking techniques, we aimed to expand our understanding of the molecular architecture of the protein complex between alpha-synuclein, cyclophilin A and the Anle138b isomer ligand. We demonstrated the possibility of intricate complex formation under cellular conditions and revealed that the main interactions that stabilize the complex are hydrophobic and involve hydrogen.

Lysophospholipids: A Potential Drug Candidates for Neurodegenerative Disorders

Neurodegenerative diseases (NDs) commonly present misfolded and aggregated proteins. Considerable research has been performed to unearth the molecular processes underpinning this pathological aggregation and develop therapeutic strategies targeting NDs. Fibrillary deposits of α-synuclein (α-Syn), a highly conserved and thermostable protein, are a critical feature in the development of NDs such as Alzheimer's disease (AD), Lewy body disease (LBD), Parkinson's disease (PD), and multiple system atrophy (MSA). Inhibition of α-Syn aggregation can thus serve as a potential approach for therapeutic intervention. Recently, the degradation of target proteins by small molecules has emerged as a new therapeutic modality, gaining the hotspot in pharmaceutical research. Additionally, interest is growing in the use of food-derived bioactive compounds as intervention agents against NDs via functional foods and dietary supplements. According to reports, dietary bioactive phospholipids may have cognition-enhancing and neuroprotective effects, owing to their abilities to influence cognition and mental health in vivo and in vitro. However, the mechanisms by which lipids may prevent the pathological aggregation of α-Syn warrant further clarification. Here, we review evidence for the potential mechanisms underlying this effect, with a particular focus on how porcine liver decomposition product (PLDP)-derived lysophospholipids (LPLs) may inhibit α-Syn aggregation.

The genetic background of Parkinson's disease and novel therapeutic targets

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. The median age of disease onset is around 60 years. From a genetic point of view, PD is basically considered a sporadic, idiopathic disease, however, hereditary components can be detected in 5-10% of patients. Expanding data are available regarding the targeted molecular therapy of the disease.

AREAS COVERED

The aim of this current review article is to provide brief clinical and molecular insight into three important genetic forms (LRRK2, SNCA, GBA) of hereditary PD subtypes and to present the human clinical trials in relation to these forms of the disease.

EXPERT OPINION

These small hereditary subgroups are crucially important in drug development, because the general trend is that clinical trials that treat PD patients as a large group, without any separation, do not meet expectations. As a result, no long term conclusions can currently be drawn regarding the effectiveness of the molecules tested in these phase 1 and 2 studies. Further precise studies are needed in the near future.

The clinical drug candidate anle138b binds in a cavity of lipidic α-synuclein fibrils

Aggregation of amyloidogenic proteins is a characteristic of multiple neurodegenerative diseases. Atomic resolution of small molecule binding to such pathological protein aggregates is of interest for the development of therapeutics and diagnostics. Here we investigate the interaction between α-synuclein fibrils and anle138b, a clinical drug candidate for disease modifying therapy in neurodegeneration and a promising scaffold for positron emission tomography tracer design. We used nuclear magnetic resonance spectroscopy and the cryogenic electron microscopy structure of α-synuclein fibrils grown in the presence of lipids to locate anle138b within a cavity formed between two β-strands. We explored and quantified multiple binding modes of the compound in detail using molecular dynamics simulations. Our results reveal stable polar interactions between anle138b and backbone moieties inside the tubular cavity of the fibrils. Such cavities are common in other fibril structures as well.