A randomized, placebo-controlled trial of memantine for functional disability in amyotrophic lateral sclerosis

Current therapy in amyotrophic lateral sclerosis (ALS): A review on past and future therapeutic strategies

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects the first and second motoneurons (MNs), associated with muscle weakness, paralysis and finally death. The exact etiology of the disease still remains unclear. Currently, efforts to develop novel ALS treatments which target specific pathomechanisms are being studied. The mechanisms of ALS pathogenesis involve multiple factors, such as protein aggregation, glutamate excitotoxicity, oxidative stress, mitochondrial dysfunction, apoptosis, inflammation etc. Unfortunately, to date, there are only two FDA-approved drugs for ALS, riluzole and edavarone, without curative treatment for ALS. Herein, we give an overview of the many pathways and review the recent discovery and preclinical characterization of neuroprotective compounds. Meanwhile, drug combination and other therapeutic approaches are also reviewed. In the last part, we analyze the reasons of clinical failure and propose perspective on the treatment of ALS in the future.

Neurophysiological and imaging biomarkers of lower motor neuron dysfunction in motor neuron diseases/amyotrophic lateral sclerosis: IFCN handbook chapter

This chapter discusses comprehensive neurophysiological biomarkers utilised in motor neuron disease (MND) and, in particular, its commonest form, amyotrophic lateral sclerosis (ALS). These encompass the conventional techniques including nerve conduction studies (NCS), needle and high-density surface electromyography (EMG) and H-reflex studies as well as novel techniques. In the last two decades, new methods of assessing the loss of motor units in a muscle have been developed, that are more convenient than earlier methods of motor unit number estimation (MUNE),and may use either electrical stimulation (e.g. MScanFit MUNE) or voluntary activation (MUNIX). Electrical impedance myography (EIM) is another novel approach for the evaluation that relies upon the application and measurement of high-frequency, low-intensity electrical current. Nerve excitability techniques (NET) also provide insights into the function of an axon and reflect the changes in resting membrane potential, ion channel dysfunction and the structural integrity of the axon and myelin sheath. Furthermore, imaging ultrasound techniques as well as magnetic resonance imaging are capable of detecting the constituents of morphological changes in the nerve and muscle. The chapter provides a critical description of the ability of each technique to provide neurophysiological insight into the complex pathophysiology of MND/ALS. However, it is important to recognise the strengths and limitations of each approach in order to clarify utility. These neurophysiological biomarkers have demonstrated reliability, specificity and provide additional information to validate and assess lower motor neuron dysfunction. Their use has expanded the knowledge about MND/ALS and enhanced our understanding of the relationship between motor units, axons, reflexes and other neural circuits in relation to clinical features of patients with MND/ALS at different stages of the disease. Taken together, the ultimate goal is to aid early diagnosis, distinguish potential disease mimics, monitor and stage disease progression, quantify response to treatment and develop potential therapeutic interventions.

Animal Models of FUS-Proteinopathy: A Systematic Review

Mutations that disrupt the function of the DNA/RNA-binding protein FUS could cause amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases. One of the key features in ALS pathogenesis is the formation of insoluble protein aggregates containing aberrant isoforms of the FUS protein in the cytoplasm of upper and lower motor neurons. Reproduction of human pathology in animal models is the main tool for studying FUS-associated pathology and searching for potential therapeutic agents for ALS treatment. In this review, we provide a systematic analysis of the role of FUS protein in ALS pathogenesis and an overview of the results of modelling FUS-proteinopathy in animals.

Therapeutic targeting of ALS pathways: Refocusing an incomplete picture

Numerous potential amyotrophic lateral sclerosis (ALS)-relevant pathways have been hypothesized and studied preclinically, with subsequent translation to clinical trial. However, few successes have been observed with only modest effects. Along with an improved but incomplete understanding of ALS as a neurodegenerative disease is the evolution of more sophisticated and diverse in vitro and in vivo preclinical modeling platforms, as well as clinical trial designs. We highlight proposed pathological pathways that have been major therapeutic targets for investigational compounds. It is likely that the failures of so many of these therapeutic compounds may not have occurred because of lack of efficacy but rather because of a lack of preclinical modeling that would help define an appropriate disease pathway, as well as a failure to establish target engagement. These challenges are compounded by shortcomings in clinical trial design, including lack of biomarkers that could predict clinical success and studies that are underpowered. Although research investments have provided abundant insights into new ALS-relevant pathways, most have not yet been developed more fully to result in clinical study. In this review, we detail some of the important, well-established pathways, the therapeutics targeting them, and the subsequent clinical design. With an understanding of some of the shortcomings in translational efforts over the last three decades of ALS investigation, we propose that scientists and clinicians may choose to revisit some of these therapeutic pathways reviewed here with an eye toward improving preclinical modeling, biomarker development, and the investment in more sophisticated clinical trial designs.

A comprehensive review of protein misfolding disorders, underlying mechanism, clinical diagnosis, and therapeutic strategies

INTRODUCTION

Proteins are the most common biological macromolecules in living system and are building blocks of life. They are extremely dynamic in structure and functions. Due to several modifications, proteins undergo misfolding, leading to aggregation and thereby developing neurodegenerative and systemic diseases. Understanding the pathology of these diseases and the techniques used to diagnose them is therefore crucial for their effective management . There are several techniques, currently being in use to diagnose them and those will be discussed in this review.

AIM/OBJECTIVES

Current review aims to discuss an overview of protein aggregation and the underlying mechanisms linked to neurodegeneration and systemic diseases. Also, the review highlights protein misfolding disorders, their clinical diagnosis, and treatment strategies.

METHODOLOGY

Literature related to neurodegenerative and systemic diseases was explored through PubMed, Google Scholar, Scopus, and Medline databases. The keywords used for literature survey and analysis are protein aggregation, neurodegenerative disorders, Alzheimer's disease, Parkinson's disease, systemic diseases, protein aggregation mechanisms, etc. DISCUSSION /CONCLUSION: This review summarises the pathogenesis of neurodegenerative and systemic disorders caused by protein misfolding and aggregation. The clinical diagnosis and therapeutic strategies adopted for the management of these diseases are also discussed to aid in a better understanding of protein misfolding disorders. Many significant concerns about the role, characteristics, and consequences of protein aggregates in neurodegenerative and systemic diseases are not clearly understood to date. Regardless of technological advancements, there are still great difficulties in the management and cure of these diseases. Therefore, for better understanding, diagnosis, and treatment of neurodegenerative and systemic diseases, more studies to identify novel drugs that may aid in their treatment and management are required.

The Disruption of NMDAR/TRPM4 Death Signaling with TwinF Interface Inhibitors: A New Pharmacological Principle for Neuroprotection

With the discovery that the acquisition of toxic features by extrasynaptic NMDA receptors (NMDARs) involves their physical interaction with the non-selective cation channel, TRPM4, it has become possible to develop a new pharmacological principle for neuroprotection, namely the disruption of the NMDAR/TRPM4 death signaling complex. This can be accomplished through the expression of the TwinF domain, a 57-amino-acid-long stretch of TRPM4 that mediates its interaction with NMDARs, but also using small molecule TwinF interface (TI) inhibitors, also known as NMDAR/TRPM4 interaction interface inhibitors. Both TwinF and small molecule TI inhibitors detoxify extrasynaptic NMDARs without interfering with synaptic NMDARs, which serve important physiological functions in the brain. As the toxic signaling of extrasynaptic NMDARs contributes to a wide range of neurodegenerative conditions, TI inhibitors may offer therapeutic options for currently untreatable human neurodegenerative diseases including Amyotrophic Lateral Sclerosis, Alzheimer's disease, and Huntington's disease.

Roles of Aging, Circular RNAs, and RNA Editing in the Pathogenesis of Amyotrophic Lateral Sclerosis: Potential Biomarkers and Therapeutic Targets

Amyotrophic lateral sclerosis (ALS) is an incurable motor neuron disease caused by upper and lower motor neuron death. Despite advances in our understanding of ALS pathogenesis, effective treatment for this fatal disease remains elusive. As aging is a major risk factor for ALS, age-related molecular changes may provide clues for the development of new therapeutic strategies. Dysregulation of age-dependent RNA metabolism plays a pivotal role in the pathogenesis of ALS. In addition, failure of RNA editing at the glutamine/arginine (Q/R) site of GluA2 mRNA causes excitotoxicity due to excessive Ca²⁺ influx through Ca²⁺-permeable α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, which is recognized as an underlying mechanism of motor neuron death in ALS. Circular RNAs (circRNAs), a circular form of cognate RNA generated by back-splicing, are abundant in the brain and accumulate with age. Hence, they are assumed to play a role in neurodegeneration. Emerging evidence has demonstrated that age-related dysregulation of RNA editing and changes in circRNA expression are involved in ALS pathogenesis. Herein, we review the potential associations between age-dependent changes in circRNAs and RNA editing, and discuss the possibility of developing new therapies and biomarkers for ALS based on age-related changes in circRNAs and dysregulation of RNA editing.

Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation

Amyotrophic lateral sclerosis (ALS) is a devastating disease caused by degeneration of motor neurons. As with all major neurodegenerative disorders, development of disease-modifying therapies has proven challenging for multiple reasons. Nevertheless, ALS is one of the few neurodegenerative diseases for which disease-modifying therapies are approved. Significant discoveries and advances have been made in ALS preclinical models, genetics, pathology, biomarkers, imaging and clinical readouts over the last 10-15 years. At the same time, novel therapeutic paradigms are being applied in areas of high unmet medical need, including neurodegenerative disorders. These developments have evolved our knowledge base, allowing identification of targeted candidate therapies for ALS with diverse mechanisms of action. In this Review, we discuss how this advanced knowledge, aligned with new approaches, can enable effective translation of therapeutic agents from preclinical studies through to clinical benefit for patients with ALS. We anticipate that this approach in ALS will also positively impact the field of drug discovery for neurodegenerative disorders more broadly.

Emerging clinical investigational drugs for the treatment of amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder caused by motoneuron death with a median survival time of 3-5 years since disease onset. There are no effective treatments to date. However, a variety of innovative investigational drugs and biological-based therapies are under clinical development.

AREAS COVERED

This review provides an overview of the clinical investigational small molecules as well as a brief summary of the biological-based therapies that are currently undergoing clinical trials for the treatment of ALS. All the data were obtained from ClinicalTrials.gov (registered through November 1).

EXPERT OPINION

Drug discovery for ALS is an active and evolving field, where many investigational clinical drugs are in different trials. There are several mechanisms of action supporting all these new therapies, although proteostasis is gaining stage. Probably, small orally bioavailable molecules able to recover functional TDP-43 homeostasis may have solid chances to modify ALS progression.

Systematic, comprehensive, evidence-based approach to identify neuroprotective interventions for motor neuron disease: using systematic reviews to inform expert consensus

OBJECTIVES

Motor neuron disease (MND) is an incurable progressive neurodegenerative disease with limited treatment options. There is a pressing need for innovation in identifying therapies to take to clinical trial. Here, we detail a systematic and structured evidence-based approach to inform consensus decision making to select the first two drugs for evaluation in Motor Neuron Disease-Systematic Multi-arm Adaptive Randomised Trial (MND-SMART: NCT04302870), an adaptive platform trial. We aim to identify and prioritise candidate drugs which have the best available evidence for efficacy, acceptable safety profiles and are feasible for evaluation within the trial protocol.

METHODS

We conducted a two-stage systematic review to identify potential neuroprotective interventions. First, we reviewed clinical studies in MND, Alzheimer's disease, Huntington's disease, Parkinson's disease and multiple sclerosis, identifying drugs described in at least one MND publication or publications in two or more other diseases. We scored and ranked drugs using a metric evaluating safety, efficacy, study size and study quality. In stage two, we reviewed efficacy of drugs in MND animal models, multicellular eukaryotic models and human induced pluripotent stem cell (iPSC) studies. An expert panel reviewed candidate drugs over two shortlisting rounds and a final selection round, considering the systematic review findings, late breaking evidence, mechanistic plausibility, safety, tolerability and feasibility of evaluation in MND-SMART.

RESULTS

From the clinical review, we identified 595 interventions. 66 drugs met our drug/disease logic. Of these, 22 drugs with supportive clinical and preclinical evidence were shortlisted at round 1. Seven drugs proceeded to round 2. The panel reached a consensus to evaluate memantine and trazodone as the first two arms of MND-SMART.

DISCUSSION

For future drug selection, we will incorporate automation tools, text-mining and machine learning techniques to the systematic reviews and consider data generated from other domains, including high-throughput phenotypic screening of human iPSCs.

New developments and opportunities in drugs being trialed for amyotrophic lateral sclerosis from 2020 to 2022

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that primarily affects motor neurons in the brain and spinal cord. In the recent past, there have been just two drugs approved for treatment, riluzole and edaravone, which only prolong survival by a few months. However, there are many novel experimental drugs in development. In this review, we summarize 53 new drugs that have been evaluated in clinical trials from 2020 to 2022, which we have classified into eight mechanistic groups (anti-apoptotic, anti-inflammatory, anti-excitotoxicity, regulated integrated stress response, neurotrophic factors and neuroprotection, anti-aggregation, gene therapy and other). Six were tested in phase 1 studies, 31 were in phase 2 studies, three failed in phase 3 studies and stopped further development, and the remaining 13 drugs were being tested in phase 3 studies, including methylcobalamin, masitinib, MN-166, verdiperstat, memantine, AMX0035, trazodone, CNM-Au8, pridopidine, SLS-005, IONN363, tofersen, and reldesemtiv. Among them, five drugs, including methylcobalamin, masitinib, AMX0035, CNM-Au8, and tofersen, have shown potent therapeutic effects in clinical trials. Recently, AMX0035 has been the third medicine approved by the FDA for the treatment of ALS after riluzole and edaravone.

Motor Neuron Disease Systematic Multi-Arm Adaptive Randomised Trial (MND-SMART): a multi-arm, multi-stage, adaptive, platform, phase III randomised, double-blind, placebo-controlled trial of repurposed drugs in motor neuron disease

INTRODUCTION

Motor neuron disease (MND) is a rapidly fatal neurodegenerative disease. Despite decades of research and clinical trials there remains no cure and only one globally approved drug, riluzole, which prolongs survival by 2-3 months. Recent improved mechanistic understanding of MND heralds a new translational era with many potential targets being identified that are ripe for clinical trials. Motor Neuron Disease Systematic Multi-Arm Adaptive Randomised Trial (MND-SMART) aims to evaluate the efficacy of drugs efficiently and definitively in a multi-arm, multi-stage, adaptive trial. The first two drugs selected for evaluation in MND-SMART are trazodone and memantine.

METHODS AND ANALYSIS

Initially, up to 531 participants (177/arm) will be randomised 1:1:1 to oral liquid trazodone, memantine and placebo. The coprimary outcome measures are the Amyotrophic Lateral Sclerosis Functional Rating Scale Revised (ALSFRS-R) and survival. Comparisons will be conducted in four stages. The decision to continue randomising to arms after each stage will be made by the Trial Steering Committee who receive recommendations from the Independent Data Monitoring Committee. The primary analysis of ALSFRS-R will be conducted when 150 participants/arm, excluding long survivors, have completed 18 months of treatment; if positive the survival effect will be inferentially analysed when 113 deaths have been observed in the placebo group. The trial design ensures that other promising drugs can be added for evaluation in planned trial adaptations. Using this novel trial design reduces time, cost and number of participants required to definitively (phase III) evaluate drugs and reduces exposure of participants to potentially ineffective treatments.

ETHICS AND DISSEMINATION

MND-SMART was approved by the West of Scotland Research Ethics Committee on 2 October 2019. (REC reference: 19/WS/0123) Results of the study will be submitted for publication in a peer-reviewed journal and a summary provided to participants.

TRIAL REGISTRATION NUMBERS

European Clinical Trials Registry (2019-000099-41); NCT04302870.

The landscape of neurophysiological outcome measures in ALS interventional trials: A systematic review

OBJECTIVE

We collated all interventional clinical trials in amyotrophic lateral sclerosis (ALS), which utilised at least one neurophysiological technique as a primary or secondary outcome measure. By identifying the strengths and limitations of these studies, we aim to guide study design in future trials.

METHODS

We conducted and reported this systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Eight databases were searched from inception. In total, 703 studies were retrieved for screening and eligibility assessment.

RESULTS

Dating back to 1986, 32 eligible interventional clinical trials were identified, recruiting a median of 30 patients per completed trial. The most widely employed neurophysiological techniques were electromyography, motor unit number estimation (including motor unit number index), neurophysiological index and transcranial magnetic stimulation (including resting motor threshold and short-interval intracortical inhibition). Almost 40% of trials reported a positive outcome with respect to at least one neurophysiological measure. The interventions targeted either ion channels, immune mechanisms or neuronal metabolic pathways.

CONCLUSIONS

Neurophysiology offers many promising biomarkers that can be utilised as outcome measures in interventional clinical trials in ALS. When selecting the most appropriate technique, key considerations include methodological standardisation, target engagement and logistical burden.

SIGNIFICANCE

Future trial design in ALS would benefit from a standardised, updated and easily accessible repository of neurophysiological outcome measures.

Comprehensive Research on Past and Future Therapeutic Strategies Devoted to Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly debilitating fatal neurodegenerative disorder, causing muscle atrophy and weakness, which leads to paralysis and eventual death. ALS has a multifaceted nature affected by many pathological mechanisms, including oxidative stress (also via protein aggregation), mitochondrial dysfunction, glutamate-induced excitotoxicity, apoptosis, neuroinflammation, axonal degeneration, skeletal muscle deterioration and viruses. This complexity is a major obstacle in defeating ALS. At present, riluzole and edaravone are the only drugs that have passed clinical trials for the treatment of ALS, notwithstanding that they showed modest benefits in a limited population of ALS. A dextromethorphan hydrobromide and quinidine sulfate combination was also approved to treat pseudobulbar affect (PBA) in the course of ALS. Globally, there is a struggle to prevent or alleviate the symptoms of this neurodegenerative disease, including implementation of antisense oligonucleotides (ASOs), induced pluripotent stem cells (iPSCs), CRISPR-9/Cas technique, non-invasive brain stimulation (NIBS) or ALS-on-a-chip technology. Additionally, researchers have synthesized and screened new compounds to be effective in ALS beyond the drug repurposing strategy. Despite all these efforts, ALS treatment is largely limited to palliative care, and there is a strong need for new therapeutics to be developed. This review focuses on and discusses which therapeutic strategies have been followed so far and what can be done in the future for the treatment of ALS.

Mouse Nerve Growth Factor Injection and Progression Rate in Patients With Amyotrophic Lateral Sclerosis: An Observational Study

Objectives

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal disease with no curative treatment up to now. This study aims to analyze ALS progression of patients treated with mouse nerve growth factor (mNGF), as well as the effects, side effects, and adverse events of the therapy.

Materials and Methods

A retrospective, observational study was performed including 94 patients with ALS from July 2020 to July 2021. Thirty-two of them were treated with at least one course of mNGF on a regular riluzole use, and the rest 62 were treated with riluzole only. The declining rates of body mass index (BMI) and ALS Functional Rating Scale-Revised (ALSFRS-R) scores were compared between the two groups to indicate ALS progression.

Results

No significant differences in ALS progression indicated by the declining rates of BMI and ALSFRS-R score were observed between the two cohorts. ALS progression before and after the first treatment course of mNGF also showed no discernible difference. However, we noticed a moderate 62.7 and 25.1% reduction in the declining rate of BMI and ALSFRS-R motor subscore when comparing mNGF + riluzole treatment to riluzole only. The mNGF treatment was overall safe and well-tolerated, and a rare case of diarrhea was reported after mNGF injection.

Conclusions

Our study revealed that mNGF treatment was overall safe and well-tolerated in patients of ALS. Application of mNGF combined with regular riluzole treatment had no significant clinical effects on delaying ALS progression. Prospective cohort studies and randomized clinical trials based on larger cohorts and longer follow-up times are needed to make a more convincing conclusion.

RNA Editing: A New Therapeutic Target in Amyotrophic Lateral Sclerosis and Other Neurological Diseases

The conversion of adenosine to inosine in RNA editing (A-to-I RNA editing) is recognized as a critical post-transcriptional modification of RNA by adenosine deaminases acting on RNAs (ADARs). A-to-I RNA editing occurs predominantly in mammalian and human central nervous systems and can alter the function of translated proteins, including neurotransmitter receptors and ion channels; therefore, the role of dysregulated RNA editing in the pathogenesis of neurological diseases has been speculated. Specifically, the failure of A-to-I RNA editing at the glutamine/arginine (Q/R) site of the GluA2 subunit causes excessive permeability of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors to Ca²⁺, inducing fatal status epilepticus and the neurodegeneration of motor neurons in mice. Therefore, an RNA editing deficiency at the Q/R site in GluA2 due to the downregulation of ADAR2 in the motor neurons of sporadic amyotrophic lateral sclerosis (ALS) patients suggests that Ca²⁺-permeable AMPA receptors and the dysregulation of RNA editing are suitable therapeutic targets for ALS. Gene therapy has recently emerged as a new therapeutic opportunity for many heretofore incurable diseases, and RNA editing dysregulation can be a target for gene therapy; therefore, we reviewed neurological diseases associated with dysregulated RNA editing and a new therapeutic approach targeting dysregulated RNA editing, especially one that is effective in ALS.

Pathophysiology and Treatment of Non-motor Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is a progressive and fatal neurodegenerative disease typically presenting with bulbar or limb weakness. There is increasing evidence that amyotrophic lateral sclerosis is a multisystem disease with early and frequent impacts on cognition, behaviour, sleep, pain and fatigue. Dysfunction of normal physiological and metabolic processes also appears common. Evidence from pre-symptomatic studies and large epidemiological cohorts examining risk factors for the future development of amyotrophic lateral sclerosis have reported a high prevalence of changes in behaviour and mental health before the emergence of motor weakness. This suggests that changes beyond the motor system are underway at an early stage with dysfunction across brain networks regulating a variety of cognitive, behavioural and other homeostatic processes. The full impact of non-motor dysfunction continues to be established but there is now sufficient evidence that the presence of non-motor symptoms impacts overall survival in amyotrophic lateral sclerosis, and with up to 80% reporting non-motor symptoms, there is an urgent need to develop more robust therapeutic approaches. This review provides a contemporary overview of the pathobiology of non-motor dysfunction, offering readers a practical approach with regard to assessment and management. We review the current evidence for pharmacological and non-pharmacological treatment of non-motor dysfunction in amyotrophic lateral sclerosis and highlight the need to further integrate non-motor dysfunction as an important outcome measure for future clinical trial design.

Improving clinical trial outcomes in amyotrophic lateral sclerosis

Individuals who are diagnosed with amyotrophic lateral sclerosis (ALS) today face the same historically intransigent problem that has existed since the initial description of the disease in the 1860s - a lack of effective therapies. In part, the development of new treatments has been hampered by an imperfect understanding of the biological processes that trigger ALS and promote disease progression. Advances in our understanding of these biological processes, including the causative genetic mutations, and of the influence of environmental factors have deepened our appreciation of disease pathophysiology. The consequent identification of pathogenic targets means that the introduction of effective therapies is becoming a realistic prospect. Progress in precision medicine, including genetically targeted therapies, will undoubtedly change the natural history of ALS. The evolution of clinical trial designs combined with improved methods for patient stratification will facilitate the translation of novel therapies into the clinic. In addition, the refinement of emerging biomarkers of therapeutic benefits is critical to the streamlining of care for individuals. In this Review, we synthesize these developments in ALS and discuss the further developments and refinements needed to accelerate the introduction of effective therapeutic approaches.

Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of largely unknown pathophysiology, characterized by the progressive loss of motoneurons (MNs). We review data showing that in presymptomatic ALS mice, MNs display reduced intrinsic excitability and impaired level of excitatory inputs. The loss of repetitive firing specifically affects the large MNs innervating fast contracting muscle fibers, which are the most vulnerable MNs in ALS. Interventions that aimed at restoring either the intrinsic excitability or the synaptic excitation result in a decrease of disease markers in MNs and delayed neuromuscular junction denervation. We then focus on trans‐spinal direct current stimulation (tsDCS), a noninvasive tool, since it modulates the activity of spinal neurons and networks. Effects of tsDCS depend on the polarity of applied current. Recent work shows that anodal tsDCS induces long‐lasting enhancement of MN excitability and synaptic excitation of spinal MNs. Moreover, we show preliminary results indicating that anodal tsDCS enhances the excitatory synaptic inputs to MNs in ALS mice. In conclusion, we suggest that chronic application of anodal tsDCS might be useful as a complementary method in the management of ALS patients.

Copper-ATSM as a Treatment for ALS: Support from Mutant SOD1 Models and Beyond

The blood-brain barrier permeant, copper-containing compound, CuII(atsm), has successfully progressed from fundamental research outcomes in the laboratory through to phase 2/3 clinical assessment in patients with the highly aggressive and fatal neurodegenerative condition of amyotrophic lateral sclerosis (ALS). The most compelling outcomes to date to indicate potential for disease-modification have come from pre-clinical studies utilising mouse models that involve transgenic expression of mutated superoxide dismutase 1 (SOD1). Mutant SOD1 mice provide a very robust mammalian model of ALS with high validity, but mutations in SOD1 account for only a small percentage of ALS cases in the clinic, with the preponderant amount of cases being sporadic and of unknown aetiology. As per other putative drugs for ALS developed and tested primarily in mutant SOD1 mice, this raises important questions about the pertinence of CuII(atsm) to broader clinical translation. This review highlights some of the challenges associated with the clinical translation of new treatment options for ALS. It then provides a brief account of pre-clinical outcomes for CuII(atsm) in SOD1 mouse models of ALS, followed by an outline of additional studies which report positive outcomes for CuII(atsm) when assessed in cell and mouse models of neurodegeneration which do not involve mutant SOD1. Clinical evidence for CuII(atsm) selectively targeting affected regions of the CNS in patients is also presented. Overall, this review summarises the existing evidence which indicates why clinical relevance of CuII(atsm) likely extends beyond the context of cases of ALS caused by mutant SOD1.

Median Nerve-Neurophysiological Index Correlates With the Survival of Patients With Amyotrophic Lateral Sclerosis

Objective: This study aims to explore the association between median nerve-neurophysiological index (NI) and survival of patients with amyotrophic lateral sclerosis (ALS).

Methods: A retrospective case series with a prospective follow-up study was performed in 238 patients with ALS. Their clinical profiles and NI were recorded. Kaplan-Meier curves and Cox regression were adopted to perform survival analysis.

Results: The median survival time of all ALS cases was 33.0 months. Multivariate analysis showed that older age of onset, shorter diagnostic delay, higher ΔALSFRS-R, and faster progression {NI ≤ 2.15; hazard ratio [HR] = 1.543 [95% confidence interval (CI), 1.136–2.094]} were associated with short survival. NI was correlated with ALSFRS-R at baseline (r_s = 0.3153; p < 0.0001) and ALSFRS-R at different time points of follow-up (r_s = 0.5127; p < 0.0001). The higher NI slope of decline (> 0.25) showed shorter survival compared with the lower group (≤ 0.25; 34.0 vs. 52.0 months; p = 0.0003). A predictive model was constructed based on the age of onset, diagnostic delay, median nerve NI, and ΔALSFRS-R. The higher predictive score (> 14) showed significantly shorter survival compared with the lower group (≤ 14; HR = 3.907, 95% CI, 2.857–5.342).

Conclusion: Median nerve NI and its slope of decline were predictive of survival of ALS.

A systematic review of neuropsychiatric and cognitive assessments used in clinical trials for amyotrophic lateral sclerosis

Background

Up to 50% of people with amyotrophic lateral sclerosis (ALS) experience cognitive dysfunction, whilst depression and anxiety are reported in up to 44% and 33%, respectively. These symptoms impact on quality of life, and are associated with a poorer prognosis. Historically, outcomes in clinical trials have focused on the effect of candidate drugs on physical functioning.

Methods

We reviewed the past 25 years of clinical trials of investigative medicinal products in people with ALS, since the licensing of riluzole, and extracted data on frequency and type of assessment for neuropsychiatric symptoms and cognitive impairment. Trial registry databases, including WHO International Trials Registry, European Clinical Trials Register, clinicaltrials.gov, and PubMed, were systematically searched for Phase II, III or IV trials registered, completed or published between 01/01/1994 and 31/10/2019. No language restrictions were applied. Outcome measures, exclusion criteria and assessment tool used were extracted.

Results

216 trials, investigating 26,326 people with ALS, were reviewed. 35% assessed neuropsychiatric symptoms, and 22% assessed cognition, as Exclusion Criteria or Outcome Measures. 3% (n = 6) of trials assessed neuropsychiatric symptoms as a Secondary Outcome Measure, and 4% (n = 8) assessed cognition as Outcome Measures; only one trial included assessments for both cognition and neuropsychiatric symptoms as Outcome Measures. Three ALS-specific assessments were used in six trials.

Conclusions

Trials for people with ALS have neglected the importance of neuropsychiatric symptoms and cognitive impairment. Evaluation of these extra-motor features is essential to understanding the impact of candidate drugs on all symptoms of ALS.

PROPSERO registration

CRD42020175612.

Electronic supplementary material

The online version of this article (10.1007/s00415-020-10203-z) contains supplementary material, which is available to authorized users.

The clinical trial landscape in amyotrophic lateral sclerosis-Past, present, and future

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease marked by progressive loss of muscle function. It is the most common adult-onset form of motor neuron disease, affecting about 16 000 people in the United States alone. The average survival is about 3 years. Only two interventional drugs, the antiglutamatergic small-molecule riluzole and the more recent antioxidant edaravone, have been approved for the treatment of ALS to date. Therapeutic strategies under investigation in clinical trials cover a range of different modalities and targets, and more than 70 different drugs have been tested in the clinic to date. Here, we summarize and classify interventional therapeutic strategies based on their molecular targets and phenotypic effects. We also discuss possible reasons for the failure of clinical trials in ALS and highlight emerging preclinical strategies that could provide a breakthrough in the battle against this relentless disease.

Divergence, Convergence, and Therapeutic Implications: A Cell Biology Perspective of C9ORF72-ALS/FTD

Ever since a GGGGCC hexanucleotide repeat expansion mutation in C9ORF72 was identified as the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), three competing but nonexclusive hypotheses to explain how this mutation causes diseases have been proposed and are still under debate. Recent studies in the field have tried to understand how the repeat expansion disrupts cellular physiology, which has suggested interesting convergence of these hypotheses on downstream, functional defects in cells, such as nucleocytoplasmic transport disruption, membrane-less organelle defects, and DNA damage. These studies have not only provided an integrated view of the disease mechanism but also revealed novel cell biology implicated in neurodegeneration. Furthermore, some of the discoveries have given rise to new ideas for therapeutic development. Here, we review the research progress on cellular pathophysiology of C9ORF72-mediated ALS and FTD and its therapeutic implication. We suggest that the repeat expansion drives pathogenesis through a combination of downstream defects, of which some can be therapeutic targets.

Emerging Drugs for the Treatment of Amyotrophic Lateral Sclerosis: A Focus on Recent Phase 2 Trials

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease involving both upper and lower motor neurons and resulting in increasing disability and death 3-5 years after onset of symptoms. Over 40 large clinical trials for ALS have been negative, except for Riluzole that offers a modest survival benefit, and Edaravone that modestly reduces disease progression in patients with specific characteristics. Thus, the discovery of efficient disease modifying therapy is an urgent need.

AREAS COVERED

Although the cause of ALS remains unclear, many studies have demonstrated that neuroinflammation, proteinopathies, glutamate-induced excitotoxicity, microglial activation, oxidative stress, and mitochondrial dysfunction may play a key role in the pathogenesis. This review highlights recent discoveries relating to these diverse mechanisms and their implications for the development of therapy. Ongoing phase 2 clinical trials aimed to interfere with these pathophysiological mechanisms are discussed.

EXPERT OPINION

This review describes the challenges that the discovery of an efficient drug therapy faces and how these issues may be addressed. With the continuous advances coming from basic research, we provided possible suggestions that may be considered to improve performance of clinical trials and turn ALS research into a 'fertile ground' for drug development for this devastating disease.

ALS Genetics, Mechanisms, and Therapeutics: Where Are We Now?

The scientific landscape surrounding amyotrophic lateral sclerosis (ALS) continues to shift as the number of genes associated with the disease risk and pathogenesis, and the cellular processes involved, continues to grow. Despite decades of intense research and over 50 potentially causative or disease-modifying genes identified, etiology remains unexplained and treatment options remain limited for the majority of ALS patients. Various factors have contributed to the slow progress in understanding and developing therapeutics for this disease. Here, we review the genetic basis of ALS, highlighting factors that have contributed to the elusiveness of genetic heritability. The most commonly mutated ALS-linked genes are reviewed with an emphasis on disease-causing mechanisms. The cellular processes involved in ALS pathogenesis are discussed, with evidence implicating their involvement in ALS summarized. Past and present therapeutic strategies and the benefits and limitations of the model systems available to ALS researchers are discussed with future directions for research that may lead to effective treatment strategies outlined.

Safety and tolerability of Triumeq in amyotrophic lateral sclerosis: the Lighthouse trial

Background: Neuroinflammation and human endogenous retroviruses (HERV) are thought to have a role in the pathophysiology of amyotrophic lateral sclerosis (ALS). Therapy directed against endogenous retroviruses has demonstrated positive effects during in vitro and biomarker studies. Consequently, the present study was undertaken to assess the safety and tolerability of long-term antiretroviral therapy (ART), Triumeq (abacavir, lamivudine, and dolutegravir) exposure in patients with ALS, and efficacy against biomarkers of disease progression. Methods: Patients were observed during a 10-week lead-in period before receiving Triumeq treatment for 24 weeks at four specialist ALS centers. The primary outcomes were safety and tolerability. Secondary outcomes included HERV-K expression levels, urinary p75ECD levels, neurophysiological parameters, and clinical indicators. The ENCALS prediction model was applied to provide an estimate of the cohort survival. The trial was registered (NCT02868580). Findings: 40 patients with ALS received Triumeq and 35 (88%) completed treatment. There were no drug-related serious adverse events; one patient was withdrawn from the study due to a drug-associated increase in liver enzymes. A favorable response on HERV-K expression levels was observed, accompanied by a decline in ALSFRS-R progression rate of 21.8% (95% CI -4.8%-48.6%) and the amount of urinary p75ECD measured. One patient died five months after stopping treatment, while five were expected to have died during the treatment period (interquartile range 2-8). Interpretation: Long-term Triumeq exposure was safe and well tolerated in this cohort. There was suggestive indication for a possible biological response in some pharmacodynamic and clinical biomarkers. A larger international phase 3 trial will be deployed to assess the effect of Triumeq on overall survival and disease progression. Funding: Funding was provided by the FightMND Foundation; MND Research Institute of Australia; MND Association, United Kingdom, and GSK. ViiV Healthcare provided the Triumeq.

Molecular Mechanisms of TDP-43 Misfolding and Pathology in Amyotrophic Lateral Sclerosis

TAR DNA binding protein 43 (TDP-43) is a versatile RNA/DNA binding protein involved in RNA-related metabolism. Hyper-phosphorylated and ubiquitinated TDP-43 deposits act as inclusion bodies in the brain and spinal cord of patients with the motor neuron diseases: amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). While the majority of ALS cases (90-95%) are sporadic (sALS), among familial ALS cases 5-10% involve the inheritance of mutations in the TARDBP gene and the remaining (90-95%) are due to mutations in other genes such as: C9ORF72, SOD1, FUS, and NEK1 etc. Strikingly however, the majority of sporadic ALS patients (up to 97%) also contain the TDP-43 protein deposited in the neuronal inclusions, which suggests of its pivotal role in the ALS pathology. Thus, unraveling the molecular mechanisms of the TDP-43 pathology seems central to the ALS therapeutics, hence, we comprehensively review the current understanding of the TDP-43's pathology in ALS. We discuss the roles of TDP-43's mutations, its cytoplasmic mis-localization and aberrant post-translational modifications in ALS. Also, we evaluate TDP-43's amyloid-like in vitro aggregation, its physiological vs. pathological oligomerization in vivo, liquid-liquid phase separation (LLPS), and potential prion-like propagation propensity of the TDP-43 inclusions. Finally, we describe the various evolving TDP-43-induced toxicity mechanisms, such as the impairment of endocytosis and mitotoxicity etc. and also discuss the emerging strategies toward TDP-43 disaggregation and ALS therapeutics.

Metabolomics Biomarkers: A Strategy Toward Therapeutics Improvement in ALS

Biomarkers research in amyotrophic lateral sclerosis (ALS) holds the promise of improving ALS diagnosis, follow-up of patients, and clinical trials outcomes. Metabolomics have a big impact on biomarkers identification. In this mini-review, we provide the main findings of metabolomics studies in ALS and discuss the most relevant therapeutics attempts that targeted some prominent alterations found in ALS, like glutamate excitotoxicity, oxidative stress, alterations in energetic metabolism, and creatinine levels. Metabolomics studies have reported putative diagnosis or prognosis biomarkers, but discrepancies among these studies did not allow validation of metabolic biomarkers for clinical use in ALS. In this context, we wonder whether metabolomics knowledge could improve ALS therapeutics. As metabolomics identify specific metabolic pathways modified by disease progression and/or treatment, we support that adjuvant or combined treatment should be used to rescue these pathways, creating a new perspective for ALS treatment. Some ongoing clinical trials are already trying to target these pathways. As clinical trials in ALS have been disappointing and considering the heterogeneity of the disease presentation, we support the application of a pharmacometabolomic approach to evaluate the individual response to drug treatments and their side effects, enabling the development of personalized treatments for ALS. We suggest that the best strategy to apply metabolomics for ALS therapeutics progress is to establish a metabolic signature for ALS patients in order to improve the knowledge of patient metabotypes, to choose the most adequate pharmacological treatment, and to follow the drug response and side effects, based on metabolomics biomarkers.

High-throughput drug screens for amyotrophic lateral sclerosis drug discovery

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a rapid adult-onset neurodegenerative disorder characterised by the progressive loss of upper and lower motor neurons. Current treatment options are limited for ALS, with very modest effects on survival. Therefore, there is a unmet need for novel therapeutics to treat ALS. Areas covered: This review highlights the many diverse high-throughput screening platforms that have been implemented in ALS drug discovery. The authors discuss cell free assays including in silico and protein interaction models. The review also covers classical in vitro cell studies and new cell technologies, such as patient derived cell lines. Finally, the review looks at novel in vivo models and their use in high-throughput ALS drug discovery Expert opinion: Greater use of patient-derived in vitro cell models and development of better animal models of ALS will improve translation of lead compounds into clinic. Furthermore, AI technology is being developed to digest and interpret obtained data and to make 'hidden knowledge' usable to researchers. As a result, AI will improve target selection for high-throughput drug screening (HTDS) and aid lead compound optimisation. Furthermore, with greater genetic characterisation of ALS patients recruited to clinical trials, AI may help identify responsive genetic subtypes of patients from clinical trials.

Motoneuron Disease: Clinical

ALS is a neurodegenerative disease in which the primary symptoms result in progressive neuromuscular weakness. Recent studies have highlighted that there is significant heterogeneity with regard to anatomical and temporal disease progression. Importantly, more recent advances in genetics have revealed new causative genes to the disease. New efforts have focused on the development of biomarkers that could aid in diagnosis, prognosis, and serve as pharmacodynamics markers. Although traditional pharmaceuticals continue to undergo trials for ALS, new therapeutic strategies including stem cell transplantation studies, gene therapies, and antisense therapies targeting some of the familial forms of ALS are gaining momentum.

Increasing the efficiency of clinical trials in neurodegenerative disorders using group sequential trial designs

OBJECTIVES

Clinical trials in neurodegenerative disorders are facing high futility rates and rising development costs. We aim to review and exemplify the value of group sequential trial designs (i.e., designs with one or more prospectively planned interim analyses) within the field of amyotrophic lateral sclerosis.

STUDY DESIGN AND SETTING

We reviewed the literature to identify sequentially conducted trials. Subsequently, we reanalyzed the dexpramipexole trial (EMPOWER), a classically designed and conducted trial involving 942 participants, by sequentially monitoring the functional questionnaire and survival endpoint. Finally, we simulated the performance of the sequential methodology under different treatment effects.

RESULTS

Only six (12%) randomized, placebo-controlled trials incorporated stopping rules for both futility and superiority. Despite its high enrollment rate, sequential reanalysis of the EMPOWER study reduced the total trial duration with 140 days (23.4%, 95% confidence interval [CI] 13.2-34.4%), the number of follow-ups with 2,688 visits (23.6%, 95% CI 11.3-38.6%), and the total drug exposure time with 73,377 days (20.6%, 95% CI 9.8-35.9%). The functional questionnaire considerably increased the heterogeneity in the test statistics, which may negatively affect sequential monitoring.

CONCLUSION

Group sequential trials can result in important reductions in the trial duration, which could make clinical trials more ethical by reducing the patients' exposure to noneffective treatments or by limiting their time on placebo.

Synaptic dysfunction and altered excitability in C9ORF72 ALS/FTD

Amyotrophic lateral sclerosis (ALS) is characterized by a progressive degeneration of upper and lower motor neurons, resulting in fatal paralysis due to denervation of the muscle. Due to genetic, pathological and symptomatic overlap, ALS is now considered a spectrum disease together with frontotemporal dementia (FTD), the second most common cause of dementia in individuals under the age of 65. Interestingly, in both diseases, there is a large prevalence of RNA binding proteins (RBPs) that are mutated and considered disease-causing, or whose dysfunction contribute to disease pathogenesis. The most common shared genetic mutation in ALS/FTD is a hexanucleuotide repeat expansion within intron 1 of C9ORF72 (C9). Three potentially overlapping, putative toxic mechanisms have been proposed: loss of function due to haploinsufficient expression of the C9ORF72 mRNA, gain of function of the repeat RNA aggregates, or RNA foci, and repeat-associated non-ATG-initiated translation (RAN) of the repeat RNA into toxic dipeptide repeats (DPRs). Regardless of the causative mechanism, disease symptoms are ultimately caused by a failure of neurotransmission in three regions: the brain, the spinal cord, and the neuromuscular junction. Here, we review C9 ALS/FTD-associated synaptic dysfunction and aberrant neuronal excitability in these three key regions, focusing on changes in morphology and synapse formation, excitability, and excitotoxicity in patients, animal models, and in vitro models. We compare these deficits to those seen in other forms of ALS and FTD in search of shared pathways, and discuss the potential targeting of synaptic dysfunctions for therapeutic intervention in ALS and FTD patients.

Classics in Chemical Neuroscience: Memantine

Memantine was the first breakthrough medication for the treatment of moderate to severe Alzheimer's disease (AD) patients and represents a fundamentally new mechanism of action (moderate-affinity, uncompetitive, voltage-dependent, N-methyl-d-aspartate (NMDA) receptor antagonist that exhibits fast on/off kinetics) to modulate glutamatergic dysfunction. Since its approval by the FDA in 2003, memantine, alone and in combination with donepezil, has improved patient outcomes in terms of cognition, behavioral disturbances, daily functioning, and delaying time to institutionalization. In this review, we will highlight the historical significance of memantine to AD (and other neuropsychiatric disorders) as well as provide an overview of the synthesis, pharmacology, and drug metabolism of this unique NMDA uncompetitive antagonist that clearly secures its place among the Classics in Chemical Neuroscience.

Blood-Brain Barrier Driven Pharmacoresistance in Amyotrophic Lateral Sclerosis and Challenges for Effective Drug Therapies

The blood-brain barrier (BBB) is essential for proper neuronal function, homeostasis, and protection of the central nervous system (CNS) microenvironment from blood-borne pathogens and neurotoxins. The BBB is also an impediment for CNS penetration of drugs. In some neurologic conditions, such as epilepsy and brain tumors, overexpression of P-glycoprotein, an efflux transporter whose physiological function is to expel catabolites and xenobiotics from the CNS into the blood stream, has been reported. Recent studies reported that overexpression of P-glycoprotein and increase in its activity at the BBB drives a progressive resistance to CNS penetration and persistence of riluzole, the only drug approved thus far for treatment of amyotrophic lateral sclerosis (ALS), rapidly progressive and mostly fatal neurologic disease. This review will discuss the impact of transporter-mediated pharmacoresistance for ALS drug therapy and the potential therapeutic strategies to improve the outcome of ALS clinical trials and efficacy of current and future drug treatments.

ALS Clinical Trials Review: 20 Years of Failure. Are We Any Closer to Registering a New Treatment?

Amyotrophic lateral sclerosis (ALS) is a devastating condition with an estimated mortality of 30,000 patients a year worldwide. The median reported survival time since onset ranges from 24 to 48 months. Riluzole is the only currently approved mildly efficacious treatment. Riluzole received marketing authorization in 1995 in the USA and in 1996 in Europe. In the years that followed, over 60 molecules have been investigated as a possible treatment for ALS. Despite significant research efforts, the overwhelming majority of human clinical trials (CTs) have failed to demonstrate clinical efficacy. In the past year, oral masitinib and intravenous edaravone have emerged as promising new therapeutics with claimed efficacy in CTs in ALS patients. Given their advanced phase of clinical development one may consider these drugs as the most likely near-term additions to the therapeutic arsenal available for patients with ALS. In terms of patient inclusion, CT with masitinib recruited a wider, more representative, less restrictive patient population in comparison to the only successful edaravone CT (edaravone eligibility criteria represents only 18% of masitinib study patients). The present manuscript reviews >50 CTs conducted in the last 20 years since riluzole was first approved. A special emphasis is put on the analysis of existing evidence in support of the clinical efficacy of edaravone and masitinib and the possible implications of an eventual marketing authorisation in the treatment of ALS.

Drugs in clinical development for the treatment of amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a fatal motor neuron progressive disorder for which no treatment exists to date. However, there are other investigational drugs and therapies currently under clinical development may offer hope in the near future. Areas covered: We have reviewed all the ALS ongoing clinical trials (until November 2016) and collected in Clinicaltrials.gov or EudraCT. We have described them in a comprehensive way and have grouped them in the following sections: biomarkers, biological therapies, cell therapy, drug repurposing and new drugs. Expert opinion: Despite multiple obstacles that explain the absence of effective drugs for the treatment of ALS, joint efforts among patient's associations, public and private sectors have fueled innovative research in this field, resulting in several compounds that are in the late stages of clinical trials. Drug repositioning is also playing an important role, having achieved the approval of some orphan drug applications, in late phases of clinical development. Endaravone has been recently approved in Japan and is pending in USA.

Integrated molecular landscape of amyotrophic lateral sclerosis provides insights into disease etiology

Amyotrophic lateral sclerosis (ALS) is a severe, progressive and ultimately fatal motor neuron disease caused by a combination of genetic and environmental factors, but its underlying mechanisms are largely unknown. To gain insight into the etiology of ALS, we here conducted genetic network and literature analyses of the top-ranked findings from six genome-wide association studies of sporadic ALS (involving 3589 cases and 8577 controls) as well as genes implicated in ALS etiology through other evidence, including familial ALS candidate gene association studies. We integrated these findings into a molecular landscape of ALS that allowed the identification of three main processes that interact with each other and are crucial to maintain axonal functionality, especially of the long axons of motor neurons, i.e. (1) Rho-GTPase signaling; (2) signaling involving the three regulatory molecules estradiol, folate, and methionine; and (3) ribonucleoprotein granule functioning and axonal transport. Interestingly, estradiol signaling is functionally involved in all three cascades and as such an important mediator of the molecular ALS landscape. Furthermore, epidemiological findings together with an analysis of possible gender effects in our own cohort of sporadic ALS patients indicated that estradiol may be a protective factor, especially for bulbar-onset ALS. Taken together, our molecular landscape of ALS suggests that abnormalities within three interconnected molecular processes involved in the functioning and maintenance of motor neuron axons are important in the etiology of ALS. Moreover, estradiol appears to be an important modulator of the ALS landscape, providing important clues for the development of novel disease-modifying treatments.

Assessment of Motor Units in Neuromuscular Disease

The motor unit comprises the anterior horn cell, its axon, and the muscle fibers that it innervates. Although the true number of motor units is unknown, the number of motor units appears to vary greatly between different muscles and between different individuals. Assessment of the number and function of motor units is needed in diseases of the anterior horn cell and other motor nerve disorders. Amyotrophic lateral sclerosis is the most important disease of anterior horn cells. The need for an effective biomarker for assessing disease progression and for use in clinical trials in amyotrophic lateral sclerosis has stimulated the study of methods to measure the number of motor units. Since 1970 a number of different methods, including the incremental, F-wave, multipoint, and statistical methods, have been developed but none has achieved widespread applicability. Two methods (MUNIX and the multipoint incremental method) are in current use across multiple centres and are discussed in detail in this review, together with other recently published methods. Imaging with magnetic resonance and ultrasound is increasingly being applied to this area. Motor unit number estimates have also been applied to other neuromuscular diseases such as spinal muscular atrophy, compression neuropathies, and prior poliomyelitis. The need for an objective measure for the assessment of motor units remains tantalizingly close but unfulfilled in 2016.

Potential new complication in drug therapy development for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by motor neuron degeneration in the brain and spinal cord. Treatment development for ALS is complicated by complex underlying disease factors. Areas covered: Numerous tested drug compounds have shown no benefits in ALS patients, although effective in animal models. Discrepant results of pre-clinical animal studies and clinical trials for ALS have primarily been attributed to limitations of ALS animal models for drug-screening studies and methodological inconsistencies in human trials. Current status of pre-clinical and clinical trials in ALS is summarized. Specific blood-CNS barrier damage in ALS patients, as a novel potential reason for the clinical failures in drug therapies, is discussed. Expert commentary: Pathological perivascular collagen IV accumulation, one unique characteristic of barrier damage in ALS patients, could be hindering transport of therapeutics to the CNS. Restoration of B-CNS-B integrity would foster delivery of therapeutics to the CNS.

Altered Metabolic Homeostasis in Amyotrophic Lateral Sclerosis: Mechanisms of Energy Imbalance and Contribution to Disease Progression

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the death of motor neurones, which leads to paralysis and death in an average of 3 years following diagnosis. The cause of ALS is unknown, but there is substantial evidence that metabolic factors, including nutritional state and body weight, affect disease progression and survival. This review provides an overview of the characteristics of metabolic dysregulation in ALS focusing on mechanisms that lead to disrupted energy supply (at a whole-body and cellular level) and altered energy expenditure. We discuss how a decrease in energy supply occurs in parallel with an increase in energy demand and leads to a state of chronic energy deficit which has a negative impact on disease outcome in ALS. We conclude by presenting potential and tested strategies to compensate for, or correct this energy imbalance, and speculate on promising areas for further research.

Amyotrophic Lateral Sclerosis, 2016: existing therapies and the ongoing search for neuroprotection

INTRODUCTION

Amyotrophic lateral sclerosis (ALS), one in a family of age-related neurodegenerative disorders, is marked by predominantly cryptogenic causes, partially elucidated pathophysiology, and elusive treatments. The challenges of ALS are illustrated by two decades of negative drug trials.

AREAS COVERED

In this article, we lay out the current understanding of disease genesis and physiology in relation to drug development in ALS, stressing important accomplishments and gaps in knowledge. We briefly consider clinical ALS, the ongoing search for biomarkers, and the latest in trial design, highlighting major recent and ongoing clinical trials; and we discuss, in a concluding section on future directions, the prion-protein hypothesis of neurodegeneration and what steps can be taken to end the drought that has characterized drug discovery in ALS.

EXPERT OPINION

Age-related neurodegenerative disorders are fast becoming major public health problems for the world's aging populations. Several agents offer promise in the near-term, but drug development is hampered by an interrelated cycle of obstacles surrounding etiological, physiological, and biomarkers discovery. It is time for the type of government-funded, public-supported offensive on neurodegenerative disease that has been effective in other fields.

Why is ALS so Difficult to Treat?

Amyotrophic lateral sclerosis (ALS) is proving intractable. Difficulties in pre-clinical studies contribute in small measure to this futility, but the chief reason for failure is an inadequate understanding of disease pathogenesis. Many acquired and inherited processes have been advanced as potential causes of ALS but, while they may predispose to disease, it seems increasingly likely that none leads directly to ALS. Rather, two recent overlapping considerations, both involving aberrant protein homeostasis, may provide a better explanation for a common disease phenotype and a common terminal pathogenesis. If so, therapeutic approaches will need to be altered and carefully nuanced, since protein homeostasis is essential and highly conserved. Nonetheless, these considerations provide new optimism in a difficult disease which has hitherto defied treatment.

A randomized trial of mexiletine in ALS: Safety and effects on muscle cramps and progression

OBJECTIVE

To determine the safety and tolerability of mexiletine in a phase II double-blind randomized controlled trial of sporadic amyotrophic lateral sclerosis (SALS).

METHODS

Sixty participants with SALS from 10 centers were randomized 1:1:1 to placebo, mexiletine 300 mg/d, or mexiletine 900 mg/d and followed for 12 weeks. The primary endpoints were safety and tolerability. Secondary endpoints were pharmacokinetic study from plasma and CSF, ALS Functional Rating Scale-Revised (ALSFRS-R) score, slow vital capacity (SVC), and muscle cramp frequency and severity.

RESULTS

The only serious adverse event among active arm participants was one episode of imbalance. Thirty-two percent of participants receiving 900 mg of mexiletine discontinued study drug vs 5% on placebo (p = 0.026). Pharmacokinetic study demonstrated a peak plasma concentration 2 hours postdose and strong correlation between plasma and CSF (p < 0.001). Rates of decline of ALSFRS-R and SVC did not differ from placebo. Analysis of all randomized patients demonstrated significant reductions of muscle cramp frequency (300 mg: rate = 31% of placebo, p = 0.047; 900 mg: 16% of placebo, p = 0.002) and cramp intensity (300 mg: mean = 45% of placebo, p = 0.08; 900 mg: 25% of placebo, p = 0.005).

CONCLUSIONS

Mexiletine was safe at both doses and well-tolerated at 300 mg/d but adverse effects at 900 mg/d led to a high rate of discontinuation. Mexiletine treatment resulted in large dose-dependent reductions in muscle cramp frequency and severity. No effect on rate of progression was detected, but clinically important differences could not be excluded in this small and short-duration study.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that mexiletine is safe when given daily to patients with amyotrophic lateral sclerosis at 300 and 900 mg and well-tolerated at the lower dose.

Intraspinal stem cell transplantation for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder in which the loss of upper and lower motor neurons produces progressive weakness and eventually death. In the decades since the approval of riluzole, the only US Food and Drug Administration-approved medication to moderately slow progression of ALS, no new therapeutics have arisen to alter the course of the disease. This is partly due to our incomplete understanding of the complex pathogenesis of motor neuron degeneration. Stem cells have emerged as an attractive option in treating ALS, because they come armed with equally complex cellular machinery and may modulate the local microenvironment in many ways to rescue diseased motor neurons. Various stem cell types are being evaluated in preclinical and early clinical applications; here, we review the preclinical strategies and advances supporting the recent clinical translation of neural progenitor cell therapy for ALS. Specifically, we focus on the use of spinal cord neural progenitor cells and the pipeline starting from preclinical studies to the designs of phase I and IIa clinical trials involving direct intraspinal transplantation in humans.