Parkinson's Disease Drug Therapies in the Clinical Trial Pipeline: 2020

Waiting for PARIS-A Biological Target in Search of a Drug

A recent breakthrough paper published in Science Translational Medicine has provided compelling evidence that inhibition of Parkin Interacting Substrate (PARIS) may offer clinical researchers an important new therapeutic approach since it shows considerable promise as an important biological target potentially capable of pharmaceutical intervention to slow long term neurodegeneration in patients with Parkinson’s disease (PD). We present several PD-relevant perspectives on this paper that were not discussed in that otherwise entirely scientific narrative. We also outline the some of the work leading up to it, including the massive drug screen that proved necessary to discover a clinically suitable inhibitor of PARIS (Farnesol), as well as relevant PD research within the wider drug class, issues surrounding its future formulation, and next steps in translating this new knowledge into the clinic to evaluate possible long-term PD patient benefits.

Are ion channels potential therapeutic targets for Parkinson's disease?

Parkinson's disease (PD) is primarily associated with the progressive neurodegeneration of the dopaminergic neurons in the substantia nigra region of the brain. The resulting motor symptoms are managed with the help of dopamine replacement therapies. However, these therapeutics do not prevent the neurodegeneration underlying the disease and therefore lose their effectiveness in managing disease symptoms over time. Thus, there is an urgent need to develop newer therapeutics for the benefit of patients. The release of dopamine and the firing activity of substantia nigra neurons is regulated by several ion channels that act in concert. Dysregulations of these channels cause the aberrant movement of various ions in the intracellular milieu. This eventually leads to disruption of intracellular signalling cascades, alterations in cellular homeostasis, and bioenergetic deficits. Therefore, ion channels play a central role in driving the high vulnerability of dopaminergic neurons to degenerate during PD. Targeting ion channels offers an attractive mechanistic strategy to combat the process of neurodegeneration. In this review, we highlight the evidence pointing to the role of various ion channels in driving the PD processes. In addition, we also discuss the various drugs or compounds that target the ion channels and have shown neuroprotective potential in the in-vitro and in-vivo models of PD. We also discuss the current clinical status of various drugs targeting the ion channels in the context of PD.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

A novel multi-target strategy to attenuate the progression of Parkinson's disease by diamine hybrid AGE/ALE inhibitor

Instead of a conventional 'one-drug-one-target approach', this article presents a novel multi-target approach with a concept of trapping simultaneously as many detrimental factors as possible involved in the progression of Parkinson's disease. These factors include reactive carbonyl species, reactive oxygen species, Fe^3+/Cu²⁺ and ortho-quinones (o-quinone), in particular. Different from the known multi-target strategies for Parkinson's disease, it is a sort of 'vacuum cleaning' strategy. The new agent consists of reactive carbonyl species scavenging moiety and reactive oxygen species scavenging and metal chelating moiety linked by a spacer. Provided that the capacity of scavenging o-quinones is demonstrated, this type of agent can further broaden its potential therapeutic profile. In order to support this new hypothetical approach, a number of simple in vitro experiments are proposed.

A High-Throughput Chemical Screen in DJ-1β Mutant Flies Identifies Zaprinast as a Potential Parkinson's Disease Treatment

Dopamine replacement represents the standard therapy for Parkinson's disease (PD), a common, chronic, and incurable neurological disorder; however, this approach only treats the symptoms of this devastating disease. In the search for novel disease-modifying therapies that target other relevant molecular and cellular mechanisms, Drosophila has emerged as a valuable tool to study neurodegenerative diseases due to the presence of a complex central nervous system, the blood-brain barrier, and a similar neurotransmitter profile to humans. Human PD-related genes also display conservation in flies; DJ-1β is the fly ortholog of DJ-1, a gene for which mutations prompt early-onset recessive PD. Interestingly, flies mutant for DJ-1β exhibit PD-related phenotypes, including motor defects, high oxidative stress (OS) levels and metabolic alterations. To identify novel therapies for PD, we performed an in vivo high-throughput screening assay using DJ-1β mutant flies and compounds from the Prestwick® chemical library. Drugs that improved motor performance in DJ-1ß mutant flies were validated in DJ-1-deficient human neural-like cells, revealing that zaprinast displayed the most significant ability to suppress OS-induced cell death. Zaprinast inhibits phosphodiesterases and activates GPR35, an orphan G-protein-coupled receptor not previously associated with PD. We found that zaprinast exerts its beneficial effect in both fly and human PD models through several disease-modifying mechanisms, including reduced OS levels, attenuated apoptosis, increased mitochondrial viability, and enhanced glycolysis. Therefore, our results support zaprinast as a potential therapeutic for PD in future clinical trials.

A Practical Approach to Early-Onset Parkinsonism

Early-onset parkinsonism (EO parkinsonism), defined as subjects with disease onset before the age of 40 or 50 years, can be the main clinical presentation of a variety of conditions that are important to differentiate. Although rarer than classical late-onset Parkinson’s disease (PD) and not infrequently overlapping with forms of juvenile onset PD, a correct diagnosis of the specific cause of EO parkinsonism is critical for offering appropriate counseling to patients, for family and work planning, and to select the most appropriate symptomatic or etiopathogenic treatments. Clinical features, radiological and laboratory findings are crucial for guiding the differential diagnosis. Here we summarize the most important conditions associated with primary and secondary EO parkinsonism. We also proposed a practical approach based on the current literature and expert opinion to help movement disorders specialists and neurologists navigate this complex and challenging landscape.

Seeking progress in disease modification in Parkinson disease

OBJECTIVE

Disease modification in Parkinson disease (PD) has remained an elusive goal, in spite of large investments over several decades. Following a large meeting of experts, this review article discusses the state of the science, possible reasons for past PD trials' failures to demonstrate disease-modifying benefit, and potential solutions.

METHODS

The National Institute of Neurological Disorders and Stroke (NINDS) convened a meeting including leaders in the field and representatives of key stakeholder groups to discuss drug therapy with the goal of disease modification in PD.

RESULTS

Important lessons can be learned from previous attempts, as well as from other fields. The selection process for therapeutic targets and agents differs among various organizations committed to therapeutic development. The areas identified as critical to target in future research include the development of relevant biomarkers, refinements of the targeted patient populations, considerations of novel trial designs, and improving collaborations between all stakeholders.

CONCLUSIONS

We identify potential barriers to progress in disease modification for Parkinson's and propose a set of research priorities that may improve the likelihood of success.

Parkinson's Disease Drug Therapies in the Clinical Trial Pipeline: 2021 Update

Background:

Despite the COVID-19 pandemic, there has been considerable activity in the clinical development of novel and improved drug-based therapies for the neurodegenerative condition of Parkinson’s disease (PD) during 2020. The agents that were investigated can be divided into “symptomatic” (alleviating the features of the condition) and “disease modifying” (attempting to address the underlying biology of PD) treatments, ST and DMT respectively, with further categorisation possible based on mechanism of action and class of therapy.

Objective:

Our goal in this report was to provide an overview of the pharmacological therapies –both ST and DMT - in clinical trials for PD during 2020–2021, with the aim of creating greater awareness and involvement in the clinical trial process. We also hope to stimulate collaboration amongst commercial and academic researchers as well as between the research and patient communities.

Methods:

We conducted a review of clinical trials of drug therapies for PD using trial data obtained from the ClinicalTrials.gov and World Health Organisation (WHO) registries, and performed a breakdown analysis of studies that were active as of February 18th 2021. We also assessed active drug development projects that had completed one clinical phase but were yet to start the next.

Results:

We identified 142 trials on ClinicalTrials.gov and 14 studies on the WHO registries that met our analysis criteria. Of these 156 trials, 91 were ST and 65 were DMT, Of the 145 trials registered on ClinicalTrials.gov in our 2020 analysis, 45 fell off the list and 42 were added. Despite this change, the balance of ST to DMT; the distribution across phases; the profile of therapeutic categories; and the proportion of repurposed therapies (33.5%); all remained very similar. There are only two DMTs in phase 3, and we identified 33 in-between-phase projects.

Conclusions:

Despite the effects of the coronavirus pandemic, investment and effort in clinical trials for PD appears to remain strong. There has been little change in the profile of the clinical trial landscape even though, over the past year, there has been considerable change to the content of the list.

The Impact of SNCA Variations and Its Product Alpha-Synuclein on Non-Motor Features of Parkinson's Disease

Parkinson’s disease (PD) is a common and progressive neurodegenerative disease, caused by the loss of dopaminergic neurons in the substantia nigra pars compacta in the midbrain, which is clinically characterized by a constellation of motor and non-motor manifestations. The latter include hyposmia, constipation, depression, pain and, in later stages, cognitive decline and dysautonomia. The main pathological features of PD are neuronal loss and consequent accumulation of Lewy bodies (LB) in the surviving neurons. Alpha-synuclein (α-syn) is the main component of LB, and α-syn aggregation and accumulation perpetuate neuronal degeneration. Mutations in the α-syn gene (SNCA) were the first genetic cause of PD to be identified. Generally, patients carrying SNCA mutations present early-onset parkinsonism with severe and early non-motor symptoms, including cognitive decline. Several SNCA polymorphisms were also identified, and some of them showed association with non-motor manifestations. The functional role of these polymorphisms is only partially understood. In this review we explore the contribution of SNCA and its product, α-syn, in predisposing to the non-motor manifestations of PD.

The Prion-Like Spreading of Alpha-Synuclein in Parkinson's Disease: Update on Models and Hypotheses

The pathological aggregation of the presynaptic protein α-synuclein (α-syn) and propagation through synaptically coupled neuroanatomical tracts is increasingly thought to underlie the pathophysiological progression of Parkinson's disease (PD) and related synucleinopathies. Although the precise molecular mechanisms responsible for the spreading of pathological α-syn accumulation in the CNS are not fully understood, growing evidence suggests that de novo α-syn misfolding and/or neuronal internalization of aggregated α-syn facilitates conformational templating of endogenous α-syn monomers in a mechanism reminiscent of prions. A refined understanding of the biochemical and cellular factors mediating the pathological neuron-to-neuron propagation of misfolded α-syn will potentially elucidate the etiology of PD and unravel novel targets for therapeutic intervention. Here, we discuss recent developments on the hypothesis regarding trans-synaptic propagation of α-syn pathology in the context of neuronal vulnerability and highlight the potential utility of novel experimental models of synucleinopathies.

Review of medicine utilization for Parkinson's disease management: the Bulgarian perspective

Background: Parkinson’s disease (PD), which occurs in 1% of the population, is the second most common neurodegenerative disorder. Despite the broad spectrum of PD manifestations and high disease prevalence, there are insufficient data on medicine utilization and prescription strategies. The purpose of the current study was to analyze published data concerning treatment approaches and to compare them with Bulgarian therapeutic practice.

Design and methods: We conducted a systematic review of the PubMed and Google Scholar databases, and we calculated medicine utilization in Bulgaria during 2018 and 2019 using the WHO methodology.

Results: The literature search identified a total of 311 publications, but only 12 met the inclusion criteria. Eleven studies pointed out that levodopa-containing medicine are the most frequently used, followed by dopamine agonists. The highest rate was found for levodopa-containing products and decarboxylase inhibitor (1.06 and 1.33 DDD/1000 inh/day), followed by anticholinergic Biperiden (0.494 and 0.455 DDD/1000 inh/day) during 2018 and 2019 in Bulgaria.

Conclusion: Overall, the treatment approaches used in the last decade comply with guideline recommendations, despite variations in levodopa and dopamine agonist utilization. Even though new medicines have been approved for PD management, levodopa- containing products are still most often prescribed and used worldwide.

Present and Future of Parkinson's Disease in Spain: PARKINSON-2030 Delphi Project

Parkinson's disease (PD) is a chronic progressive and irreversible disease and the second most common neurodegenerative disease worldwide. In Spain, it affects around 120.000-150.000 individuals, and its prevalence is estimated to increase in the future. PD has a great impact on patients' and caregivers' lives and also entails a substantial socioeconomic burden. The aim of the present study was to examine the current situation and the 10-year PD forecast for Spain in order to optimize and design future management strategies. This study was performed using the modified Delphi method to try to obtain a consensus among a panel of movement disorders experts. According to the panel, future PD management will improve diagnostic capacity and follow-up, it will include multidisciplinary teams, and innovative treatments will be developed. The expansion of new technologies and studies on biomarkers will have an impact on future PD management, leading to more accurate diagnoses, prognoses, and individualized therapies. However, the socio-economic impact of the disease will continue to be significant by 2030, especially for patients in advanced stages. This study highlighted the unmet needs in diagnosis and treatment and how crucial it is to establish recommendations for future diagnostic and therapeutic management of PD.

Progress towards therapies for disease modification in Parkinson's disease

The development of interventions to slow or halt the progression of Parkinson's disease remains a priority for patients and researchers alike. To date, no agents have been shown to have unequivocal evidence of disease-modifying effects in Parkinson's disease. The absence of disease-modifying treatments might relate not only to inadequate approaches for the selection of therapeutic candidates but also to insufficient attention to detail in clinical trial design. Better understanding of Parkinson's disease pathogenesis associated with advances in laboratory models, the use of objective biomarkers of disease progression and target engagement, and a focus on agents known to be safe for human use, alongside the use of precision medicine approaches, should together greatly increase the likelihood for successful identification of disease-modifying treatments for Parkinson's disease.

Modulation of the Interactions Between α-Synuclein and Lipid Membranes by Post-translational Modifications

Parkinson's disease is characterised by the presence in brain tissue of aberrant inclusions known as Lewy bodies and Lewy neurites, which are deposits composed by α-synuclein and a variety of other cellular components, including in particular lipid membranes. The dysregulation of the balance between lipid homeostasis and α-synuclein homeostasis is therefore likely to be closely involved in the onset and progression of Parkinson's disease and related synucleinopathies. As our understanding of this balance is increasing, we describe recent advances in the characterisation of the role of post-translational modifications in modulating the interactions of α-synuclein with lipid membranes. We then discuss the impact of these advances on the development of novel diagnostic and therapeutic tools for synucleinopathies.

Reappraisal of metabolic dysfunction in neurodegeneration: Focus on mitochondrial function and calcium signaling

The cellular and molecular mechanisms that drive neurodegeneration remain poorly defined. Recent clinical trial failures, difficult diagnosis, uncertain etiology, and lack of curative therapies prompted us to re-examine other hypotheses of neurodegenerative pathogenesis. Recent reports establish that mitochondrial and calcium dysregulation occur early in many neurodegenerative diseases (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and others. However, causal molecular evidence of mitochondrial and metabolic contributions to pathogenesis remains insufficient. Here we summarize the data supporting the hypothesis that mitochondrial and metabolic dysfunction result from diverse etiologies of neuropathology. We provide a current and comprehensive review of the literature and interpret that defective mitochondrial metabolism is upstream and primary to protein aggregation and other dogmatic hypotheses of NDDs. Finally, we identify gaps in knowledge and propose therapeutic modulation of mCa2+ exchange and mitochondrial function to alleviate metabolic impairments and treat NDDs.

Domain-Independent Inhibition of CBP/p300 Attenuates α-Synuclein Aggregation

Neurodegenerative diseases are associated with failed proteostasis and accumulation of insoluble protein aggregates that compromise neuronal function and survival. In Parkinson's disease, a major pathological finding is Lewy bodies and neurites that are mainly composed of phosphorylated and aggregated α-synuclein and fragments of organelle membranes. Here, we analyzed a series of selective inhibitors acting on multidomain proteins CBP and p300 that contain both lysine acetyltransferase and bromodomains and are responsible for the recognition and enzymatic modification of lysine residues. By using high-affinity inhibitors, A-485, GNE-049, and SGC-CBP30, we explored the role of two closely related proteins, CBP and p300, as promising targets for selective attenuation of α-synuclein aggregation. Our data show that selective CBP/p300 inhibitors may alter the course of pathological α-synuclein accumulation in primary mouse embryonic dopaminergic neurons. Hence, drug-like CBP/p300 inhibitors provide an effective approach for the development of high-affinity drug candidates preventing α-synuclein aggregation via systemic administration.

Parkinson disease-associated cognitive impairment

Parkinson disease (PD) is the second most common neurodegenerative disorder, affecting >1% of the population ≥65 years of age and with a prevalence set to double by 2030. In addition to the defining motor symptoms of PD, multiple non-motor symptoms occur; among them, cognitive impairment is common and can potentially occur at any disease stage. Cognitive decline is usually slow and insidious, but rapid in some cases. Recently, the focus has been on the early cognitive changes, where executive and visuospatial impairments are typical and can be accompanied by memory impairment, increasing the risk for early progression to dementia. Other risk factors for early progression to dementia include visual hallucinations, older age and biomarker changes such as cortical atrophy, as well as Alzheimer-type changes on functional imaging and in cerebrospinal fluid, and slowing and frequency variation on EEG. However, the mechanisms underlying cognitive decline in PD remain largely unclear. Cortical involvement of Lewy body and Alzheimer-type pathologies are key features, but multiple mechanisms are likely involved. Cholinesterase inhibition is the only high-level evidence-based treatment available, but other pharmacological and non-pharmacological strategies are being tested. Challenges include the identification of disease-modifying therapies as well as finding biomarkers to better predict cognitive decline and identify patients at high risk for early and rapid cognitive impairment.

Bringing Advanced Therapies for Parkinson's Disease to the Clinic: The Scientist's Perspective

After many years of preclinical development, cell and gene therapies have advanced from research tools in the lab to clinical-grade products for patients, and today they constitute more than a quarter of all new Phase I clinical trials for Parkinson’s disease. Whereas efficacy has been convincingly proven for many of these products in preclinical models, the field is now entering a new phase where the functionality and safety of these products will need to stand the test in clinical trials. If successful, these new products can have the potential to provide patients with a one-time administered treatment which may alleviate them from daily symptomatic dopaminergic medication.

Role of Liver Growth Factor (LGF) in Parkinson's Disease: Molecular Insights and Therapeutic Opportunities

Parkinson's disease is the most common neurodegenerative movement disorder with unclear etiology and only symptomatic treatment to date. Toward the development of novel disease-modifying agents, neurotrophic factors represent a reasonable and promising therapeutic approach. However, despite the robust preclinical evidence, clinical trials using glial-derived neurotrophic factor (GDNF) and neurturin have been unsuccessful. In this direction, the therapeutic potential of other trophic factors in PD and the elucidation of the underlying molecular mechanisms are of paramount importance. The liver growth factor (LGF) is an albumin-bilirubin complex acting as a hepatic mitogen, which also exerts regenerative effects on several extrahepatic tissues including the brain. Accumulating evidence suggests that intracerebral and peripheral administration of LGF can enhance the outgrowth of nigrostriatal dopaminergic axonal terminals; promote the survival, migration, and differentiation of neuronal stem cells; and partially protect against dopaminergic neuronal loss in the substantia nigra of PD animal models. In most studies, these effects are accompanied by improved motor behavior of the animals. Potential underlying mechanisms involve transient microglial activation, TNF-α upregulation, and activation of the extracellular signal-regulated kinases 1/2 (ERK1/2) and of the transcription factor cyclic AMP response-element binding protein (CREB), along with anti-inflammatory and antioxidant pathways. Herein, we summarize recent preclinical evidence on the potential role of LGF in PD pathogenesis, aiming to shed more light on the underlying molecular mechanisms and reveal novel therapeutic opportunities for this debilitating disease.

Small molecule therapeutics for neuroinflammation-mediated neurodegenerative disorders

Chronically activated microglia and the resulting cascade of neuroinflammatory mechanisms have been postulated to play a critical role in neurodegenerative disorders. Microglia are the main component of the brain's innate immune system and become activated by infection, injury, misfolded proteins or a multitude of other stimuli. Activated microglia release pro-inflammatory and cytotoxic factors that can damage neurons and transform astrocytes to become toxic to neurons as well. Therapeutic approaches aiming to modulate microglia activation may be beneficial to mitigate the progression of inflammatory-mediated neurodegenerative diseases. In this literature review, we provide an overview of recent progress on key microglia targets and discovery of small molecule compounds advancing in clinical trials to minimize neuroinflammation.

Green Tea Epigallocatechin-3-gallate (EGCG) Targeting Protein Misfolding in Drug Discovery for Neurodegenerative Diseases

The potential to treat neurodegenerative diseases (NDs) of the major bioactive compound of green tea, epigallocatechin-3-gallate (EGCG), is well documented. Numerous findings now suggest that EGCG targets protein misfolding and aggregation, a common cause and pathological mechanism in many NDs. Several studies have shown that EGCG interacts with misfolded proteins such as amyloid beta-peptide (Aβ), linked to Alzheimer's disease (AD), and α-synuclein, linked to Parkinson's disease (PD). To date, NDs constitute a serious public health problem, causing a financial burden for health care systems worldwide. Although current treatments provide symptomatic relief, they do not stop or even slow the progression of these devastating disorders. Therefore, there is an urgent need to develop effective drugs for these incurable ailments. It is expected that targeting protein misfolding can serve as a therapeutic strategy for many NDs since protein misfolding is a common cause of neurodegeneration. In this context, EGCG may offer great potential opportunities in drug discovery for NDs. Therefore, this review critically discusses the role of EGCG in NDs drug discovery and provides updated information on the scientific evidence that EGCG can potentially be used to treat many of these fatal brain disorders.

The promise of crowdfunding to finance R&D of novel diagnostics and therapeutics for incurable diseases

The level of funding available for research and development (R&D) of diagnostics (D) and therapeutics (T) for incurable diseases varies and is not associated with the extent of their disease burden. Crowdfunding is a promising way to increase funding for R&D of D&T for underfunded incurable diseases, such as Alzheimer's and Parkinson's disease, which has not been exploited to its full capacity. Investing into efforts to educate patients and researchers about its prospective is a worthwhile endeavor, which could lead to the generation of substantial new capital to finance the development of novel therapeutics for these diseases.

Bringing Advanced Therapies for Parkinson's Disease to the Clinic: The Patient's Perspective

There is an urgent unmet need in the Parkinson’s disease community—advanced therapies to modify the inevitable decline that occurs in those affected by this progressive neurodegenerative disease for which there is no cure. This will require collaboration from all stakeholders and central to those partnerships are patients themselves. But participation in clinical trials and clinical use of advanced therapies have their own risk profile above and beyond standard therapeutics as evidenced by past invasive procedures. Therefore, it is of utmost importance that clear, evidence-based information about these potential treatments be clearly communicated by those exploring their use to ensure safe and informed participation from the patient community. Likewise, patients must weigh the benefits of these treatments their limitations and risks in order to truly give informed consent to participate in bringing these treatments to the clinic. Here we explore these issues from the patient perspective.

Challenges in the diagnosis of Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease and its prevalence has been projected to double over the next 30 years. An accurate diagnosis of Parkinson's disease remains challenging and the characterisation of the earliest stages of the disease is ongoing. Recent developments over the past 5 years include the validation of clinical diagnostic criteria, the introduction and testing of research criteria for prodromal Parkinson's disease, and the identification of genetic subtypes and a growing number of genetic variants associated with risk of Parkinson's disease. Substantial progress has been made in the development of diagnostic biomarkers, and genetic and imaging tests are already part of routine protocols in clinical practice, while novel tissue and fluid markers are under investigation. Parkinson's disease is evolving from a clinical to a biomarker-supported diagnostic entity, for which earlier identification is possible, different subtypes with diverse prognosis are recognised, and novel disease-modifying treatments are in development.

Treatment Options for Motor and Non-Motor Symptoms of Parkinson's Disease

Parkinson’s disease (PD) usually presents in older adults and typically has both motor and non-motor dysfunctions. PD is a progressive neurodegenerative disorder resulting from dopaminergic neuronal cell loss in the mid-brain substantia nigra pars compacta region. Outlined here is an integrative medicine and health strategy that highlights five treatment options for people with Parkinson’s (PwP): rehabilitate, therapy, restorative, maintenance, and surgery. Rehabilitating begins following the diagnosis and throughout any additional treatment processes, especially vis-à-vis consulting with physical, occupational, and/or speech pathology therapist(s). Therapy uses daily administration of either the dopamine precursor levodopa (with carbidopa) or a dopamine agonist, compounds that preserve residual dopamine, and other specific motor/non-motor-related compounds. Restorative uses strenuous aerobic exercise programs that can be neuroprotective. Maintenance uses complementary and alternative medicine substances that potentially support and protect the brain microenvironment. Finally, surgery, including deep brain stimulation, is pursued when PwP fail to respond positively to other treatment options. There is currently no cure for PD. In conclusion, the best strategy for treating PD is to hope to slow disorder progression and strive to achieve stability with neuroprotection. The ultimate goal of any management program is to improve the quality-of-life for a person with Parkinson’s disease.

The Cellular Prion Protein-ROCK Connection: Contribution to Neuronal Homeostasis and Neurodegenerative Diseases

Amyloid-based neurodegenerative diseases such as prion, Alzheimer's, and Parkinson's diseases have distinct etiologies and clinical manifestations, but they share common pathological events. These diseases are caused by abnormally folded proteins (pathogenic prions PrP^Sc in prion diseases, β-amyloids/Aβ and Tau in Alzheimer's disease, α-synuclein in Parkinson's disease) that display β-sheet-enriched structures, propagate and accumulate in the nervous central system, and trigger neuronal death. In prion diseases, PrP^Sc-induced corruption of the physiological functions exerted by normal cellular prion proteins (PrP^C) present at the cell surface of neurons is at the root of neuronal death. For a decade, PrP^C emerges as a common cell surface receptor for other amyloids such as Aβ and α-synuclein, which relays, at least in part, their toxicity. In lipid-rafts of the plasma membrane, PrP^C exerts a signaling function and controls a set of effectors involved in neuronal homeostasis, among which are the RhoA-associated coiled-coil containing kinases (ROCKs). Here we review (i) how PrP^C controls ROCKs, (ii) how PrP^C-ROCK coupling contributes to neuronal homeostasis, and (iii) how the deregulation of the PrP^C-ROCK connection in amyloid-based neurodegenerative diseases triggers a loss of neuronal polarity, affects neurotransmitter-associated functions, contributes to the endoplasmic reticulum stress cascade, renders diseased neurons highly sensitive to neuroinflammation, and amplifies the production of neurotoxic amyloids.

Recent Developments in New Therapeutic Agents against Alzheimer and Parkinson Diseases: In-Silico Approaches

Neurodegenerative diseases (ND), including Alzheimer's (AD) and Parkinson's Disease (PD), are becoming increasingly more common and are recognized as a social problem in modern societies. These disorders are characterized by a progressive neurodegeneration and are considered one of the main causes of disability and mortality worldwide. Currently, there is no existing cure for AD nor PD and the clinically used drugs aim only at symptomatic relief, and are not capable of stopping neurodegeneration. Over the last years, several drug candidates reached clinical trials phases, but they were suspended, mainly because of the unsatisfactory pharmacological benefits. Recently, the number of compounds developed using in silico approaches has been increasing at a promising rate, mainly evaluating the affinity for several macromolecular targets and applying filters to exclude compounds with potentially unfavorable pharmacokinetics. Thus, in this review, an overview of the current therapeutics in use for these two ND, the main targets in drug development, and the primary studies published in the last five years that used in silico approaches to design novel drug candidates for AD and PD treatment will be presented. In addition, future perspectives for the treatment of these ND will also be briefly discussed.

Probiotics for Parkinson's disease: Current evidence and future directions

The gut-brain axis is a hot topic in Parkinson's disease (PD). It has been postulated that gut pathogens and dysbiosis can contribute to peripheral inflammatory states or trigger downstream metabolic effects that exacerbate the neurodegenerative process in PD. Several preclinical and clinical studies have demonstrated disrupted intestinal permeability, intestinal inflammation, altered gut microbiome, and reduced fecal short-chain fatty acids in PD. In this regard, microbial-directed therapies such as probiotics are emerging as potential therapeutic options. Probiotic supplementation is postulated to confer a variety of health benefits due to the diverse functions of these live microorganisms, including inhibition of pathogen colonization, modulation/"normalization" of the microbiome and/or its function, immunomodulatory effects (e.g. reducing inflammation), and improved host epithelial barrier function. Interestingly, several PD animal model studies have demonstrated the potential neuroprotective effects of probiotics in reducing dopaminergic neuronal degeneration. Notably, two randomized placebo-controlled trials have provided class I evidence for probiotics as a treatment for constipation in PD. However, the effects of probiotics on other PD aspects, such as motor disability and cognitive function, and its long-term efficacy (including effects on PD drug absorption in the gut) have not been investigated adequately. Further targeted animal and human studies are also warranted to understand the mechanisms of actions of probiotics in PD and to tailor probiotic therapy based on individual host profiles to improve patient outcomes in this disabling disorder.

Targeting for Success: Demonstrating Proof-of-Concept with Mechanistic Early Phase Clinical Pharmacology Studies for Disease-Modification in Neurodegenerative Disorders

The clinical failure rate for disease-modifying treatments (DMTs) that slow or stop disease progression has been nearly 100% for the major neurodegenerative disorders (NDDs), with many compounds failing in expensive and time-consuming phase 2 and 3 trials for lack of efficacy. Here, we critically review the use of pharmacological and mechanistic biomarkers in early phase clinical trials of DMTs in NDDs, and propose a roadmap for providing early proof-of-concept to increase R&D productivity in this field of high unmet medical need. A literature search was performed on published early phase clinical trials aimed at the evaluation of NDD DMT compounds using MESH terms in PubMed. Publications were selected that reported an early phase clinical trial with NDD DMT compounds between 2010 and November 2020. Attention was given to the reported use of pharmacodynamic (mechanistic and physiological response) biomarkers. A total of 121 early phase clinical trials were identified, of which 89 trials (74%) incorporated one or multiple pharmacodynamic biomarkers. However, only 65 trials (54%) used mechanistic (target occupancy or activation) biomarkers to demonstrate target engagement in humans. The most important categories of early phase mechanistic and response biomarkers are discussed and a roadmap for incorporation of a robust biomarker strategy for early phase NDD DMT clinical trials is proposed. As our understanding of NDDs is improving, there is a rise in potentially disease-modifying treatments being brought to the clinic. Further increasing the rational use of mechanistic biomarkers in early phase trials for these (targeted) therapies can increase R&D productivity with a quick win/fast fail approach in an area that has seen a nearly 100% failure rate to date.

LRRK2 Kinase Activity Does Not Alter Cell-Autonomous Tau Pathology Development in Primary Neurons

BACKGROUND

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD) and are also associated with genetic risk in idiopathic PD. Mutations in LRRK2, including the most common p.G2019S lead to elevated kinase activity, making LRRK2 kinase inhibitors prime targets for therapeutic development. However, the role of LRRK2 kinase activity in PD pathogenesis has remained unclear. While essentially all LRRK2-PD patients exhibit dopaminergic neuron loss, many of these patients do not have α-synuclein Lewy bodies in their brains. So, what is the neuropathological substrate of LRRK2-PD? Tau has emerged as a possible candidate due to the presence of tau pathology in the majority of LRRK2 mutation carriers and reports of hyperphosphorylated tau in LRRK2 animal models.

OBJECTIVE

In the current study, we aim to address whether a mutation in LRRK2 changes the cell-autonomous seeding of tau pathology in primary neurons. We also aim to assess whether LRRK2 kinase inhibitors are able to modulate tau pathology.

METHODS/RESULTS

Treatment of primary neurons with LRRK2 kinase inhibitors leads to prolonged kinase inhibition but does not alter tau pathology induction. The lack of an effect of LRRK2 kinase activity was further confirmed in primary neurons expressing LRRK2G2019S and with two different forms of pathogenic tau. In no case was there more than a minor change in tau pathology induction.

CONCLUSION

Together, our results indicate that LRRK2 kinase activity is not playing a major role in the induction of tau pathology in individual neurons. Understanding the impact of LRRK2 kinase inhibitors on pathology generation is important as kinase inhibitors move forward in clinical trials.

Utilizing Xenogeneic Cells As a Therapeutic Agent for Treating Diseases

The utilization of biologically produced cells to treat diseases is a revolutionary invention in modern medicine after chemically synthesized small molecule drugs and biochemically made protein drugs. Cells are basic units of life with diverse functions in mature and developing organs, which biological properties could be utilized as a promising therapeutic approach for currently intractable and incurable diseases. Xenogeneic cell therapy utilizing animal cells other than human for medicinal purpose has been studied as a new way of treating diseases. Xenogeneic cell therapy is considered as a potential regenerative approach to fulfill current unmet medical needs because xenogeneic cells could be isolated from different animal organs and expanded ex vivo as well as maintain the characteristics of original organs, providing a versatile and plenty cell source for cell-based therapeutics beside autologous and allogeneic sources. The swine species is considered the most suitable source because of the similarity with humans in size and physiology of many organs in addition to the economic and ethical reasons plus the possibility of genetic modification. This review discusses the old proposed uses of xenogeneic cells such as xenogeneic pancreatic islet cells, hepatocytes and neuronal cells as a living drug for the treatment of degenerative and organ failure diseases. Novel applications of xenogeneic mesenchymal stroma cells and urothelial cells are also discussed. There are formidable immunological barriers toward successful cellular xenotransplantation in clinic despite major progress in the development of novel immunosuppression regimens and genetically multimodified donor pigs. However, immunological barriers could be turn into immune boosters by using xenogeneic cells of specific tissue types as a novel immunotherapeutic agent to elicit bystander antitumor immunity due to rejection immune responses. Xenogeneic cells have the potential to become a safe and efficacious option for intractable diseases and hard-to-treat cancers, adding a new class of cellular medicine in our drug armamentarium.

Arbutin effectively ameliorates the symptoms of Parkinson's disease: the role of adenosine receptors and cyclic adenosine monophosphate

An antagonistic communication exists between adenosinergic and dopaminergic signaling in the basal ganglia, which suggests that the suppression of adenosine A_2A receptors-cyclic adenosine monophosphate pathway may be able to restore the disrupted dopamine transmission that results in motor symptoms in Parkinson’s disease (PD). Arbutin is a natural glycoside that possesses antioxidant, anti-inflammatory, and neuroprotective properties. The purpose of this study was to investigate whether arbutin could ameliorate the symptoms of PD and to examine the underlying mechanism. In this study, Swiss albino mouse models of PD were established by the intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine for 4 successive days, with the concurrent intraperitoneal administration of arbutin (50 and 100 mg/kg) for 7 days. The results showed that arbutin significantly reduced lipid peroxidation, total nitrite levels, and inflammation in the substantia nigra and striatum of PD mouse models. In addition, arbutin decreased the activity of endogenous antioxidants, reduced the levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and γ-aminobutyric acid, and minimized neurodegeneration in the striatum. Arbutin also reduced the abnormal performance of PD mouse models in the open field test, bar test, pole test, and rotarod test. The therapeutic efficacy of arbutin was similar to that of madopar. The intraperitoneal injection of the A_2AR agonist CGS21680 (0.5 mg/kg) attenuated the therapeutic effects of arbutin, whereas the intraperitoneal injection of forskolin (3 mg/kg) enhanced arbutin-mediated improvements. These findings suggest that arbutin can improve the performance of PD mouse models by inhibiting the function of the A_2AR and enhancing the effects of cyclic adenosine monophosphate. This study was approved by the Institutional Animal Ethics Committee (1616/PO/Re/S/12/CPCSEA) on November 17, 2019 (approval No. IAEC/2019/010).

Therapeutic Strategies to Reduce the Toxicity of Misfolded Protein Oligomers

The aberrant aggregation of proteins is implicated in the onset and pathogenesis of a wide range of neurodegenerative disorders, including Alzheimer’s and Parkinson’s diseases. Mounting evidence indicates that misfolded protein oligomers produced as intermediates in the aggregation process are potent neurotoxic agents in these diseases. Because of the transient and heterogeneous nature of these elusive aggregates, however, it has proven challenging to develop therapeutics that can effectively target them. Here, we review approaches aimed at reducing oligomer toxicity, including (1) modulating the oligomer populations (e.g., by altering the kinetics of aggregation by inhibiting, enhancing, or redirecting the process), (2) modulating the oligomer properties (e.g., through the size–hydrophobicity–toxicity relationship), (3) modulating the oligomer interactions (e.g., by protecting cell membranes by displacing oligomers), and (4) reducing oligomer toxicity by potentiating the protein homeostasis system. We analyze examples of these complementary approaches, which may lead to the development of compounds capable of preventing or treating neurodegenerative disorders associated with protein aggregation.

Seven Solutions for Neuroprotection in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra and accumulation of iron and alpha-synuclein; it follows a characteristic pattern throughout the nervous system. Despite decades of successful preclinical neuroprotective studies, no drug has then shown efficacy in clinical trials. Considering this dilemma, we have reviewed and organized solutions of varying importance that can be exclusive or additive, and we outline approaches to help generate successful development of neuroprotective drugs for PD: (1) select patients in which the targeted mechanism is involved in the pathological process associated with the monitoring of target engagement, (2) combine treatments that target multiple pathways, (3) establish earliest interventions and develop better prodromal biomarkers, (4) adopt rigorous methodology and specific disease-relevant designs for disease-modifying clinical trials, (5) customize drug with better brain biodistribution, (6) prioritize repurposed drugs as a first line approach, and (7) adapt preclinical models to the targeted mechanisms with translational biomarkers to increase their predictive value. © 2020 International Parkinson and Movement Disorder Society.

The Emerging Role of the Lysosome in Parkinson's Disease

Lysosomal function has a central role in maintaining neuronal homeostasis, and, accordingly, lysosomal dysfunction has been linked to neurodegeneration and particularly to Parkinson’s disease (PD). Lysosomes are the converging step where the substrates delivered by autophagy and endocytosis are degraded in order to recycle their primary components to rebuild new macromolecules. Genetic studies have revealed the important link between the lysosomal function and PD; several of the autosomal dominant and recessive genes associated with PD as well as several genetic risk factors encode for lysosomal, autophagic, and endosomal proteins. Mutations in these PD-associated genes can cause lysosomal dysfunction, and since α-synuclein degradation is mostly lysosomal-dependent, among other consequences, lysosomal impairment can affect α-synuclein turnover, contributing to increase its intracellular levels and therefore promoting its accumulation and aggregation. Recent studies have also highlighted the bidirectional link between Parkinson’s disease and lysosomal storage diseases (LSD); evidence includes the presence of α-synuclein inclusions in the brain regions of patients with LSD and the identification of several lysosomal genes involved in LSD as genetic risk factors to develop PD.

Approaches to Disease Modification for Parkinson's Disease: Clinical Trials and Lessons Learned

Despite many clinical trials over the last three decades, the goal of demonstrating that a treatment slows the progression of Parkinson's disease (PD) remains elusive. Research advances have shed new insight into cellular pathways contributing to PD pathogenesis and offer increasingly compelling therapeutic targets. Here we review recent and ongoing clinical trials employing novel strategies toward disease modification, including those targeting alpha-synuclein and those repurposing drugs approved for other indications. Active and passive immunotherapy approaches are being studied with the goal to modify the spread of alpha-synuclein pathology in the brain. Classes of currently available drugs that have been proposed to have potential disease-modifying effects for PD include calcium channel blockers, antioxidants, anti-inflammatory agents, iron-chelating agents, glucagon-like peptide 1 agonists, and cAbl tyrosine kinase inhibitors. The mechanistic diversity of these treatments offers hope, but to date, results from these trials have been disappointing. Nevertheless, they provide useful lessons in guiding future therapeutic development.