Reviews

Improving clinical trial outcomes in amyotrophic lateral sclerosis

Matthew C. Kiernan 1,2 ✉ , Steve Vucic3, Kevin Talbot 4, Christopher J. McDermott 5,6, Orla Hardiman7,8, Jeremy M. Shefner 9, Ammar Al-Chalabi 10, William Huynh 1,2, Merit Cudkowicz11,12, Paul Talman 13, Leonard H. Van den Berg14, Thanuja Dharmadasa 4, Paul Wicks 15, Claire Reilly 16 and Martin R. Turner 4 Abstract | 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.

Neurodegeneration and dementia pose a major public owing to a lack of proven biomarkers and clinical trial health challenge worldwide owing to their devastating outcome measures10. Progress in this era of potential impact on quality of life and the tremendous burden therapeutic advance, in which an unparalleled num- they place on health-care systems1,2. The number of ber of disease-modifying therapies are ready to be tri- adults with a diagnosis of neurodegenerative disease alled or implemented into clinical practice, requires the across the globe is set to increase dramatically in the establishment of stronger collaborative networks across coming decades — the ageing population harbours a clinical and translational neuroscience domains. potential epidemic of functional disability, pain and In this Review, we first appraise the current status loss of independence3–5. Among the neurodegenerative of the ALS field from a basic neuroscience perspective disorders, amyotrophic lateral sclerosis (ALS) is the most with respect to recent molecular discoveries and then rapidly fatal6 — the typical time from symptom onset to discuss progress in the development of therapeutics, death is 2–3 years7,8. including biomarkers, drug repurposing strategies and Research in the past 25 years has improved our high-throughput drug screening. We critically analyse understanding of the pathophysiology of ALS, but the molecular technology and the emergence of genetic and translation of this knowledge into effective treatments cellular therapies for patients currently living with ALS. has been disappointing — even today, most patients Finally, we consider new trial designs that are facilitated with ALS do not have the opportunity to participate in by advances in patient-reported outcome measures. clinical trials9. Previously unrecognized bottlenecks in the translational process have been revealed, including Deconstructing ALS a lack of large-scale research infrastructure and of the Clinical identification of ALS starts with the confirma-

✉e-mail: matthew.kiernan@ coordination necessary to initiate trials. In addition, tion of upper and lower motor neuron abnormalities sydney.edu.au inherent disease characteristics, such as disease hetero­ that involve the brain, spinal regions and the peripheral 11 https://doi.org/10.1038/ geneity, make a one-size-fits-all solution unwork­ neuromuscular system . Typical clinical presentations s41582-020-00434-z able and long durations of clinical trials are necessary include bulbar-onset ALS with speech and swallowing

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Key points ALS are commonly grouped according to whether they alter proteostasis, RNA function or the cytoskeleton20–22. • The development of effective treatments for amyotrophic lateral sclerosis (ALS) has By contrast, sporadic ALS presents in individuals been limited by a lack of comprehensive understanding of the biological processes without a family history of the disease. Family aggre- that trigger the disease and promote progression. gation studies have identified overlap between sporadic • Causative genetic mutations have been identified, many of which are linked to RNA ALS and other neurodegenerative or developmental dis- function and metabolism. orders, suggesting that variants in some susceptibility • Disease heterogeneity suggests that a precision medicine paradigm incorporating genes increase the overall risk of brain and mind dis- extensive phenotypic and genotypic information will be required to realize effective orders within families23,24, similar to findings in famil- therapy and improve the outcomes for individual patients with ALS. ial ALS25 that are consistent with genetic pleiotropy26. • The repurposing of drugs with established safety profiles from their use in other Attempts to determine the genetic basis of sporadic ALS human diseases is a new approach to therapeutic discovery in ALS. have produced limited success, supporting the concept • Enhanced clinical trial designs, including multi-arm, multi-stage platform trials, that of ALS as a common disease associated with multiple incorporate biomarkers of treatment responses will accelerate drug discovery and increase trial participation. rare variants. The pathophysiological basis of ALS is typically • Improved patient stratification and patient-reported outcome measures, including home assessments, will improve the reliability and sensitivity of trial endpoints. thought to involve glutamate-induced excitotoxicity, structural abnormalities of mitochondria, autophagy, neuroinflammation and disruption of axonal transport problems and limb-onset ALS that initially manifests mechanisms1,2 (Fig. 1). Non-neuronal cells, including with arm or leg weakness, followed by progressive astrocytes and microglia, also play a role in neurodegen- paralysis7,8,12. Other, less common presentations include eration in ALS via the secretion of neurotoxic mediators isolated type 2 respiratory failure, weight loss, cramps, and the modulation of glutamate receptor expression27,28. fasciculations in the absence of muscle weakness, emo- TAR DNA-binding protein 43 (TDP43) is thought to be tional lability and cognitive abnormalities13,14. The pathogenic in ALS. This protein is a major component of altered function of upper motor neurons leads to spas- the ubiquitylated cytoplasmic protein aggregates that are ticity and brisk deep reflexes8 and symptoms of lower present in most cases of sporadic and familial ALS. The motor neuron abnormalities include fasciculations, observation that mutations in highly conserved regions muscle wasting and weakness15–17. Given that there of the TARDBP gene are not evident in controls and seg- are no specific radiological or serological markers of regate with the disease29 provides further evidence for ALS, the diagnosis is established on the basis of clinical the pathogenicity of TDP43. features as ratified by consensus criteria11. Approximately 15% of ALS cases are familial, Development of therapeutics with a Mendelian pattern of inheritance and a high Precision approaches and biomarkers penetrance18,19. Mutations of C9orf72, SOD1, TARDBP, In light of the clinical heterogeneity of ALS, the involve- FUS, ANG and OPTN can produce typical ALS pheno- ment of the upper and lower motor neuron systems, and types (Table 1). Many of these mutations affect proteins the underlying molecular complexity that determines that are involved in gene expression and regulation via disease expression, the concept of therapy that is tai- the regulation of transcription, microRNA processing, lored to an individual’s genetic signature has started to RNA maturation and splicing. The mutations linked to emerge (Fig. 2). An example of how this approach could be beneficial has come from post hoc analysis of three 30 Author addresses trials of lithium for ALS , which showed that patients experienced different effects of the therapy according 1Brain and Mind Centre, University of Sydney, Sydney, New South Wales, Australia. to their UNC13A genotype. For patients with ALS who 2 Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, New South were homozygous for a specific variant in UNC13A, Wales, Australia. lithium had a positive disease-modifying effect despite 3Sydney Medical School Westmead, University of Sydney, Sydney, New South Wales, the overall negative results of trials. Among individuals Australia. 4Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK. with the UNC13A variant, the probability of survival at 5Sheffield Institute for Translational Neuroscience, University of Sheffield, Sheffield, UK. 12 months was 28% higher among those who received 6NIHR Sheffield Biomedical Research Centre, Sheffield, UK. lithium than among those who received placebo. 7Academic Neurology Unit, Trinity Biomedical Sciences Institute, Trinity College Dublin, The understanding of individual differences in res­ Dublin, Ireland. ponse to a trial therapy, particularly in a longitudinal man- 8National Neuroscience Centre, Beaumont Hospital, Dublin, Ireland. ner to assess progression, requires reliable biomarkers. 9Department of Neurology, Barrow Neurological Institute, University of Arizona College Several candidate biomarkers for ALS have emerged, of Medicine Phoenix, Creighton University, Phoenix, AZ, USA. including biofluid, neurophysiological and neuroimag- 10 King’s College London, Maurice Wohl Clinical Neuroscience Institute, Department ing measures30–34 that indicate various aspects of disease, of Basic and Clinical Neuroscience, London, UK. from network-level dysfunction to structural changes 11Massachusetts General Hospital, Boston, MA, USA. 12Harvard Medical School, Boston, MA, USA. and basic cellular processes. Most of these markers indi- 13Neurosciences Department, Barwon Health District, Melbourne, Victoria, Australia. cate the loss of either the upper or lower motor neuron 14Department of Neurology, UMC Utrecht Brain Center, University Medical Center systems but rarely of both. However, their clinical utility Utrecht, Utrecht, Netherlands. and ability to enable patient stratification are variable. 15Wicks Digital Health, Lichfield, United Kingdom. A consistent diagnostic biomarker for ALS is cortical 16The Motor Neurone Disease Association of New Zealand, Auckland, New Zealand. hyperexcitability measured with transcranial magnetic

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Table 1 | Genes known to be associated with ALS Proportion of cases associated with genea Gene Protein product Protein function Locus Familial Sporadic ALS ALS C9orf72 Chromosome 9 open reading frame 72 Nucleotide factor 9p21–22 20–50% 10% SOD1 Superoxide dismutase 1 Superoxide dismutase 21q22.1 10–20% 2% TARDBP TDP43 RNA-binding protein q36 5% <1% FUS Fused in sarcoma protein RNA-binding protein 16p11.2 5% <1% MAT3 Matrin 3 RNA-binding protein 5q31.2 <1% <1% HNRNPA1 Heterogeneous nuclear RNA-binding protein 12q13.1 <1% <1% ribonucleoprotein A1 OPTN Optineurin Mediator of apoptosis, inflammation and 10p15–p14 4% <1% vasoconstriction, cellular morphogenesis, membrane trafficking, vesicle trafficking, transcription activation UBQLN2 Ubiquilin 2 Ubiquitination and protein degradation Xp11.23–Xp13.1 <1% <1% SQSTM1 Sequestosome 1 Autophagosome cargo protein, targets 5q35.3 <1% <1% proteins for autophagy TBK1 Serine/threonine-protein kinase TBK1 Phosphorylation of nuclear factor-κB, 12q14.2 <1% <1% regulation of cell proliferation, apoptosis and glucose metabolism, promotion of autophagy via the ubiquitylation pathway VCP Transitional endoplasmic reticulum Ubiquitin segregase 9p13.3 2% <1% ATPase DCTN1 Dynactin subunit 1 Mediator of organelle transport, spindle 2p13 1% <1% formation and axonogenesis ANG Angiogenin Ribonuclease 14q11 <1% <1% PFN1 Profilin 1 Actin-binding protein 17p13.2 <1% <1% CHCHD10 Coiled-coil-helix-coiled-coil-helix Maintenance of cristae morphology in 22q11.23 <1% <1% domain-containing protein 10 mitochondria, oxidative phosphorylation TUBA4A Tubulin α4A chain Microtubule formation, maintenance 2q36.1 <1% <1% of cytoskeleton and structure of cells ALS, amyotrophic lateral sclerosis; TDP43, TAR DNA-binding protein 43. aThe proportion of ALS cases associated with each genetic mutation varies depending on the population studied13,18–22.

stimulation35. Whether the measurement of cortical assays have increased in sensitivity to offer a simple, excitability can contribute to prognostic stratification non-invasive measure41. Measurement of serum NfL is less clear — the pharmacodynamic sensitivity of this has been applied in trials of the latest therapies for mul- measure has only been investigated with riluzole, the tiple sclerosis42. In the context of monitoring treatment only established disease-modifying drug for ALS36,37. responses in trials of therapies for ALS, failure of serum Structural changes in ALS can also be observed with NfL levels to decrease during treatment could enable MRI, which has revealed widespread involvement of decisions regarding the efficacy of potential therapeutic cerebral white matter tracts and grey matter. However, agents to be made earlier. In a multi-arm, multi-stage the sensitivity of these measures to longitudinal change (MAMS) platform trial structure (see Enhanced trial is inconsistent even at the group level and functional design, below), patients could subsequently switch to changes are even more difficult to quantify38. Emerging a new trial agent. techniques that combine neuroimaging with functional The development of biomarkers for use in trials in neurophysiological approaches, such as quantitative ALS is further complicated by the possibility that ALS electroencephalography, evoked responses and source results from a cascade of multiple pathways. For this analyses, could capture a true systems-level signature reason, multidrug trials will be needed to tackle dif- for ALS39. ferent aspects of the disease. In such multidrug trials, The most promising biofluid marker of ALS is neuro­ specific biomarkers are needed for each of the targeted filament in the cerebrospinal fluid (CSF) and blood, mechanisms to enable the contributions of individual levels of which correlate with the rate of disease pro- therapies to be assessed as advocated by the Airlie House gression and are most strongly associated with the guidelines10 (See Patient-reported outcomes, below). involvement of the upper motor neuron system40,41. Biomarkers are also needed to enable the testing of pre- CSF and serum levels of the neurofilament light chain ventive strategies for at-risk individuals, but biomarkers (NfL) correlate tightly with one another and serum associated with the symptomatic phase of the disease

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Compartments of the nervous system Anatomical and physiological networks Molecular pathways

Glutamate

Motor cortex Glutamate excitotoxicity 1

Ionotropic glutamate receptors Ca2+ Na+

Upper motor neuron 9 Release of Microglia pro-inflammatory cytokines Mitochondrial dysfunction Ca2+-dependent enzymatic ↑Ca2+ pathways Na+–K+ pump Astrocyte dysfunction TDP43 FUS 2K+ 7 2 aggregates Neuronal 3Na+ death 10 ↑Na+ Ion channel EAAT2 C9orf72, TARDBP, FUS and SOD1 Oxidative dysfunction Glutamate stress mutations + excitotoxicity Na 3 Defects in K+ nucleo- Mutant SOD1 cytoplasmic trafficking 4 8 5 Ca2+ 6 Na+ Lower Defects in Defects in RNA protein folding processing and Reversal motor Schwann cells 11 + 2+ and degradation protein synthesis of Na – Ca neuron SOD1 exchanger Schwann aggregates cell defects

Dysfunction of axonal transport Ca+ systems

Accumulated Neuromuscular neurofilament junction Muscle

Fig. 1 | The pathophysiology of ALS. Amyotrophic lateral sclerosis (ALS) nucleocytoplasmic trafficking associated with neuronal degeneration preferentially involves the descending corticospinal motor neurons that (step 5). Mutant SOD1 enzymes increase oxidative stress, induce synapse with spinal motor neurons and project to skeletal muscles via the mitochondrial dysfunction, form intracellular aggregates, and adversely neuromuscular junction. The processes of neurodegeneration in affect neurofilament and axonal transport processes (step 6). Mutations in amyotrophic lateral sclerosis involve a complex array of molecular and TARDBP, FUS and C9orf72 can result in the formation of intracellular genetic pathways. Glutamate-induced excitotoxicity can result from the aggregates of their protein products (step 7), leading to increased oxidative overactivation of ionotropic glutamate receptors that allow excessive influx stress, mitochondrial dysfunction, defects in axonal transport and, of Na+ and Ca2+ ions (step 1) and ultimately neurodegeneration through consequently, in neuronal death. Defects in protein folding and degradation the activation of Ca2+-dependent enzymatic pathways. Glutamate also lead to protein aggregates (step 8). The activation of microglia excitotoxicity also generates free radicals, which further contribute to promotes the secretion of pro-inflammatory cytokines and neurotoxic the process of neurodegeneration via oxidative stress. Na+–K+ pump substances, such as glutamate, which promote neuroinflammation and dysfunction (step 2) disrupts the resting membrane potential and leads to neuronal death (step 9). Reduced expression and activity of the astrocytic secondary effects of altered intracellular Na+ levels. Ion channel dysfunction glutamate transporter excitatory amino acid transporter 2 (EAAT2) (step 10) (step 3) also leads to altered intracellular Na+ levels. Altered Na+ levels result is associated with motor neuron degeneration owing to glutamate toxicity. in the reversal of the Na+–Ca2+ exchanger (step 4), thereby increasing the Accumulation of mutant SOD1 protein in Schwann cells (step 11) are intracellular Ca2+ levels that can cause neuronal toxicity. Defects in RNA thought to mediate synaptic denervation, which precedes the onset of processing, RNA metabolism and protein synthesis lead to defects in anterior horn cell degeneration.

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might not be useful in this context. Currently, the identi- into neuronal and glial cell lines46. This phenotypic fication of individuals who are at risk of developing ALS approach provides a rich source of neurons and glial cells can only be done by screening individuals from families that are derived from patients with ALS and that retain that carry highly penetrant mutations. However, some the key pathophysiological properties of the disease. data suggest that predictive biomarkers do exist. A study These properties enable the rapid, ex vivo screening of of individuals who carried an intronic GGGGCC expan- drugs relevant to an individual’s phenotype. The use sion in C9orf72 showed that expansion-derived dipep- of existing drugs that modulate established pathophysio- tides were present in cerebrospinal fluid and peripheral logical mechanisms in ALS has already identified several blood mononuclear cells many decades before symp- therapeutic candidates47 (Table 2). The most promising tom onset43. Similarly, a large primary care cohort study of these candidates from a clinical trial perspective are identified novel metabolic markers, including altera- discussed below. tions in carbohydrate, lipid and apolipoprotein profiles, that were associated with an increased risk of ALS in Edaravone. One candidate for repurposing in ALS later life44. is edaravone, which was initially discovered as a free- radical scavenger and potent antioxidant in the treat- Drug repurposing ment of acute ischaemic stroke in Japan48. A phase III Alongside efforts to discover new disease-modifying clinical trial of edaravone in Japanese patients with ALS therapies for ALS, drug repurposing is also being inves- showed that the drug slowed disease progression in this tigated to rapidly identify effective therapies in ALS. cohort49. Based on this finding, edaravone was approved The repurposing of existing drugs enables the rapid for the treatment of ALS by the FDA in 2017. However, assessment of drug efficacy in phase II trials owing to a subsequent multicentre study of edaravone in patients the established safety profiles of these drugs. In addi- with ALS in Italy did not have a positive outcome50 and tion, advances in cell reprogramming are revolutioniz- therefore regulatory approval of edaravone for ALS in ing drug repurposing strategies in ALS. Human somatic Europe is likely to require additional evidence for its cells, including skin fibroblasts, can be reprogrammed efficacy, including evidence of long-term benefits for into induced pluripotent stem cells45, which can then be survival and of efficacy in cohorts of patients with ALS differentiated into neural progenitor cells and ultimately outside Japan49,51.

One-size-fits-all medicine Stratified medicine Precision medicine Brain • Demographics cognition • Clinical phenotype • Medical records • Molecular • Exogenous factors Spine subpopulation • Pharmacogenetics Peripheral nerve

Endophenotype

Biomarker

Individualized diagnosis

Single treatment Individualized treatment

Adverse No benefit Benefit Benefit Benefit Benefit events

Fig. 2 | Model of precision medicine for ALS. A one-size-fits-all approach (left) in amyotrophic lateral sclerosis (ALS) leads to the use of a single treatment in heterogeneous populations. In this scenario, some patients benefit from therapy but others do not. Stratified medicine (centre) improves on the one-size-fits-all approach by enabling patients to be separated into more homogeneous groups based on demographics, clinical phenotype and molecular subtypes of ALS. However, advances in knowledge and technology are enabling a transition to a precision medicine paradigm (right) in ALS. Precision medicine incorporates individual phenotypic and genotypic data to guide individualized therapy. In this scenario, all patients can benefit from treatment.

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Table 2 | Repurposed drugs in clinical development for ALS Repurposed drug Existing use Targeted pathogenic ALS trial identifier Primary outcome Outcome mechanism measures Tauroursodeoxycholic Familial amyloid Endoplasmic NCT03488524 ALSFRS-R Reduction acid polyneuropathy reticulum stress, in functional (transthyretin) mitochondrial decline137 dysfunction NCT03127514 Survival Prolonged69 Mexiletine Cardiac arrhythmia Neuronal NCT01811355 Daily cramp frequency Significant hyperexcitability reduction in cramp frequency and severity138 NCT02781454 Change in resting Pending motor threshold NCT01849770 Safety Safe139 Ezogabine Epilepsy Neuronal NCT02450552 Change in short-interval Pending hyperexcitability intracortical inhibition as measured by transcranial magnetic stimulation Dimethyl fumarate Relapsing–remitting Neuroinflammation, ACTRN12618000534280 ALSFRS-R Pending multiple sclerosis upregulation of

Treg cells IL-2 Metastatic melanoma, Neuroinflammation, NCT02059759 Change in number Pending

metastatic renal cancer cytokine signalling, of Treg cells upregulation of NCT03039673 Survival Pending Treg cells Edaravone Acute stroke Oxidative stress NCT01492686 ALSFRS-R Significant slowing of disease progression vs placeboa,140 Dolutegravir, abacavir HIV infection HERVK expression NCT02868580 Safety Safe120 and lamivudine (Triumeq) Ibudilast (MN-166) Chronic obstructive Neuroinflammation NCT02238626 Safety and tolerability Pending pulmonary disease and microglial activation NCT02714036 Safety and tolerability Pending Tamoxifen Breast cancer Neuroinflammation, NCT02166944 ALSFRS-R Not significant141 proteostasis NCT00214110 Muscle strength Pending NCT01257581 ALSFRS-R No significant effect142 Memantine Advanced stages of Glutamate NCT01020331 ALSFRS-R No significant Alzheimer disease excitotoxicity effect143 NCT02118727 ALSFRS-R Pending NCT00409721 ALSFRS-R, FVC, muscle Pending strength, cognitive function NCT00353665 ALSFRS-R No significant effect144 Perampanel Partial-onset seizures Glutamate NCT03019419 ALSFRS-R Pending excitotoxicity (AMPA-receptor NCT03377309 Safety Pending mediated) NCT03793868 Motor threshold Pending NCT03020797 Safety Pending Rasagiline Parkinson disease Oxidative stress NCT01786603 ALSFRS-R No significant and apoptosis effect72 NCT01232738 ALSFRS-R No significant effect145 NCT01879241 Survival No significant effect146

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Table 2 (cont.) | Repurposed drugs in clinical development for ALS Repurposed drug Existing use Targeted pathogenic ALS trial identifier Primary outcome Outcome mechanism measures Masitinib Mastocytosis, severe Neuroinflammation NCT02588677 ALSFRS-R Significant slowing asthma (microglia) in functional decline64 NCT03127267 ALSFRS-R Pending Methylcobalamin Vitamin B12 deficiency Glutamate NCT03548311 ALSFRS-R No significant excitotoxicity effect128 Cu(II)ATSM PET ligand Copper deficiency NCT02870634 Safety Pending Arimoclomol Insulin resistance, Impaired proteostasis NCT00244244 Safety Safe82 complications of NCT00706147 Time to death, Safe, no significant diabetes mellitus tracheostomy or effect on permanent assisted outcomes147 ventilation NCT03491462 Combined assessment Pending of function and survival NCT03836716 Safety Pending

ALS, amyotrophic lateral sclerosis; ALSFRS-R, ALS Functional Rating Scale – Revised; Cu(II)ATSM, diacetyl-bis(4-methyl-3-thiosemicarbazonato) copper(II); a FVC, forced vital capacity; HERVK, human endogenous retrovirus type K; Treg cell, regulatory T cell. In a select group of patients with ALS.

Ezogabine. Neuronal hyperexcitability is an important the importance of neuroinflammation as a treatment pathophysiological mechanism in ALS52 and the antiepi­ target in ALS64. leptic agent ezogabine is a potent K+ channel activator that induces membrane hyperpolarization53 and therefore AMX0035. AMX0035 is a combination of sodium pheny­ reduces neuronal excitability. Consequently, ezogabine lbutyrate and tauroursodeoxycholic acid. These agents has potential for repurposing in ALS and has been inves- have been used individually in the treatment of vari- tigated in this context. In an induced pluripotent stem ous disorders — sodium phenylbutyrate for urea cycle cell model of ALS, ezogabine reduced neuronal hyper­ disorders65 and tauroursodeoxycholic acid for familial excitability and increased motor neuron survival54. On this amyloid polyneuropathy, cholelithiasis and cholestatic basis, a clinical trial has been initiated to assess the efficacy liver disease66. In combination, they act synergistically of ezogabine on central and peripheral nerve excitability to prevent neuronal death and oxidative, bioenergetic in ALS — results are expected in late 2020 (ref.55). and metabolic stress67 and could therefore be beneficial in ALS. A trial to evaluate the efficacy of AMX0035 in Immunomodulatory therapies. Neuroinflammatory 137 people with ALS has been completed68. Treatment pathways have been implicated in the pathophysiology of with this combination therapy resulted in a significant ALS and immunomodulatory therapies are under inves- 25% slowing of disease progression over 6 months68. tigation for repurposing in ALS. Two of these agents — Secondary outcomes of vital capacity and quantitative

dimethyl fumarate and IL-2 — target regulatory T (Treg) strength trended in a positive direction. When the rand-

cell function. Treg cells have neuroprotective effects via omized controlled study was combined with a period of the suppression of toxic neuroinflammation in the CNS56 open-label access, survival was also improved in patients

and autologous infusion of expanded Treg cells in a small who originally received placebo: overall, random assign- cohort of patients with ALS slowed disease progression57. ment to receive AMX0035 conferred a 6.5-month survival Dimethyl fumarate, which is approved for the treatment advantage compared with random assignment to receive 69 of relapsing–remitting multiple sclerosis, increases Treg cell placebo . Separately, the antioxidant effects of taurour- numbers and function58 and could therefore be beneficial sodeoxycholic acid alone in ALS are being assessed in a in ALS. A phase II clinical trial is currently under way to European consortium trial (TUDCA-ALS)70. assess the efficacy of dimethyl fumarate in this context59.

IL-2 is a cytokine that is important for Treg cell develop- Rasagiline. Rasagiline is a monoamine oxidase B inhib- ment and homeostasis60 and recombinant analogues of itor used for the treatment of Parkinson disease, but IL-2 are used in the treatment of cancers. Currently, two a study in the SOD1 mouse model of ALS indicated a trials in Europe are in progress to assess the effects of benefit of rasagiline in this context71. However, two sub- IL-2 in ALS61,62. Results from one of these studies — the sequent trials of rasagiline in patients with ALS did not IMODALS study — showed that low-dose IL-2 was well demonstrate its efficacy71–73 (although post hoc analysis tolerated and immunologically effective in ALS63. identified a possible effect in patients with rapid disease Microglia are another potential neuroinflammatory progression) suggesting that, overall, repurposing of this target in ALS. Masitinib, which was originally developed drug will not be a useful strategy in ALS. This lack of as a therapy for cancer, is a tyrosine kinase inhibitor that translation from the SOD1 mouse model to humans with inhibits microglial activation. In a phase II–III trial in ALS could be a result of differences in pathophysiology. patients with ALS, masitinib as an add-on therapy to For instance, in SOD1 mice, the loss of motor neurons riluzole slowed disease progression50, underscoring and associated weakness progresses over a short period

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of time74, whereas symptoms in humans do not emerge could have a role in the onset and progression of ALS; for decades, apparently triggered by a multi-step process therefore, the translational relevance remains unclear. that has not yet been replicated in animal models75–80. Genetic and cellular therapy Arimoclomol. Arimoclomol is a co-inducer of heat shock The success of targeted therapies for spinal muscu- proteins that is under investigation for therapeutic use lar atrophy — antisense oligonucleotides (ASOs) or in insulin resistance. Preclinical data suggest that arimo­ small molecules and τηε use of viral vectors for gene clomol could be beneficial in ALS, as it reduced misaggre- replacement — has demonstrated the power of genetic gated proteins in ALS models and in models of lysosomal therapy91. Genetic mutations are present in ~15% of storage diseases81. The safety and tolerability of arimo- patients with ALS, but the multiplicity of mutation types clomol has been established in patients with ALS82 and that cause ALS, including missense mutations, repeat larger trials are now being conducted to assess its effi- expansions and loss-of-function mutations, means that cacy; whether translational difficulties similar to those a variety of gene therapy approaches would be needed encountered with rasagiline arise remains to be seen. to target all the causal mutations. In addition, although many causal mutations are associated with the toxicity High-throughput drug screening of the mutant protein and therefore reducing the expres- High-throughput drug screening (HTDS) methodo­ sion of the toxic protein seems a logical approach, many logies represent an alternative to drug repurposing strate­ different mutations have been identified in single genes, gies for the identification of effective therapeutic agents making it difficult to design ASOs to selectively target in ALS. The main advantage of HTDS is the ability to the mutant allele. Furthermore, the safe inactivation of identify novel compounds that exert unexpected effects gene expression with ASOs is likely to be impossible in on the pathogenic mechanisms of ALS. Advances in some cases; for example, the inactivation of TARDBP computational techniques and artificial intelligence have would be lethal owing to the physiological function of led to the development of powerful platforms that enable TDP43 in splicing and the contribution of the protein the screening of millions of compounds and hundreds of to other pathways that are critical for cellular survival92. thousands of cell assays83. In ALS, in silico approaches have predominantly Antisense oligonucleotides. Evidence from mouse been used to screen millions of drugs for predicted studies suggests that knockdown of the SOD1 protein effects such as receptor binding or protein stabilization. is tolerated without severe phenotypic consequences. Drug-focused and disease-focused databases and online Whether this tolerance would be maintained over dec- tools that associate drugs with disease mechanisms are ades, particularly in the context of human ageing, is being developed and are likely to result in additional ther- unknown, but these findings have encouraged the devel- apeutic breakthroughs for ALS83. However, the increase opment of ASO therapy directed against wild-type and in potential therapies that these platforms are expected mutant SOD1 (ref.93). Initial reports suggest that such an to identify could lead to bottlenecks if large numbers of approach is well tolerated and could be effective. Results drugs subsequently need to be tested in patients. of the phase I–II trial of the ASO tofersen, which medi- Engineering tools that simulate developmental sys- ates the degradation of SOD1 mRNA, were published tems, such as cell-based in silico HTDS approaches, are in 2020 and confirmed that the treatment reduced CSF increasingly being used in ALS drug discovery, largely concentrations of SOD1 protein in patients with ALS94. driven by advances in computational and cell repro- Separate studies in two patients with ALS with SOD1 gramming technologies. Many cell-based HTDS stud- mutations have raised the possibility that intrathecal ies have been undertaken to identify compounds that delivery of an adeno-associated virus that encodes a exert anti-glutamatergic activity84, downregulate mutant microRNA that targets SOD1 could be a potential ther- SOD1 transcription85, reduce TDP43 protein levels and apy in these patients95. To maximize the benefits of these aggregation86, reduce oxidative stress87, and improve ASO therapies, various routes of administration have motor neuron survival88. Several promising drug can- been considered, from systemic intravenous adminis- didates have been identified in these studies but none tration to intraparenchymal brain delivery, although have yet been translated into effective therapies for ALS. intrathecal delivery has been used most frequently to Cell-free in silico HTDS strategies have also been date. Commonly observed lumbar puncture-related used in ALS drug discovery to identify drugs that mod- adverse events could be mitigated in the future through ulate protein interactions and misfolding. This cell-free the development of specialized nanotechnology drug approach has identified drugs that inhibit TDP43 protein delivery systems96. misfolding and aggregation but whether these drugs are In ALS caused by C9orf72 mutations, ASOs against beneficial in ALS remains to be determined89. Similarly, apparently toxic RNA species that arise from the hexa- the disruption of molecular pathways, including inter- nucleotide repeat expansion are currently in early phase actions between mutant SOD1 protein and proteins that clinical trials. Preclinical research suggests that RNA trigger motor neuron death via the resident endoplas- repeats can be successfully targeted in this way with- mic reticulum protein Derlin 1, could represent a fur- out downregulating the C9orf72 protein, which could ther therapeutic option90. However, a critical limitation contribute to toxicity independently of the RNA97. of cell-free HTDS approaches is that biological interac- The efficiency of ASOs is currently limited by a tions are assessed outside of the cellular environment failure to traverse the blood–brain barrier, a generic and in the absence of other pathogenic processes that problem that will need to be solved for all forms of

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precision-based molecular therapies in ALS. However, a single agent is tested in a homogeneous population, ASOs are also limited by complexities in intracellu- with a null hypothesis that treatment with this agent is lar processing that limit their direct engagement with no better than standard care. Such trials are costly and mRNA species. Advances in the development of chemi- inefficient given that only a small proportion of treat- cal modifications that increase the stability of ASOs and ments make it from initial testing to the commercial their ability to penetrate cells will result in a new gener- market — the FDA reports that just 8% of treatments ation of ASOs that could be delivered via the systemic tested in a phase I trial make it to market102. This sequen- circulation98. tial approach has been used in more than 40 clinical tri- als of potential disease-modifying therapies for ALS. The Gene editing. Besides the use of ASOs, genome editing approach limits the speed with which treatments for ALS could form the basis of another gene-based therapy for can be evaluated owing to the finite capacity of trial net- ALS. Rapid advances in genome editing have greatly works in terms of personnel and infrastructure, the lim- advanced the cellular modelling of ALS but also raise ited number of patients with ALS who are eligible, and the possibility that precise targeting of genetic mutations limited financial resources, especially for academic-led with systems such as CRISPR–Cas9 could be possible clinical trials. In addition, inherent problems exist in this in vivo; such gene editing could effectively prevent approach, such as patient heterogeneity and long trial ALS from developing. A key requirement for such an durations, even when the ALS Functional Rating Scale approach is the ability to safely target constructs to the is used as the primary outcome measure. nervous system, thereby avoiding off-target effects. The inefficiencies in the current approach to ALS However, the use of gene editing in ALS poses similar clinical trials become more evident when considering challenges as the use of ASOs as many of the muta- the time commitment and expense required for staff tions in genes commonly linked to ALS are unique to recruitment, deployment and training, contract negoti- the individual; therefore, a bespoke approach would be ations, regulatory approvals, monitoring arrangements, required that also avoids the inactivation of the normal and infrastructure; these costs must be reconstituted gene copy. Gene editing is a rapidly advancing field and anew for each trial102. After trial completion, staff move the technical challenges in developing genome editing elsewhere, skills are lost and approvals lapse. A further as a therapy for diseases such as ALS are gradually being inefficiency, and perhaps the most problematic from addressed — studies are moving from cell and rodent a patient perspective, is the fact that each study has a models into larger animals, including dogs99. separate placebo arm. Such an approach is costly and is a major disincentive for patients to participate in a Cellular therapy. Expectations in most therapeutic trials clinical trial, particularly as their disease is terminal. in ALS are limited to slowing or arresting disease pro- Indeed, patients with ALS are known to be particularly gression, but patients understandably place a high value motivated to participate in trials and report being less on the search for treatments that could restore function. dissuaded by the possibility of adverse effects and pri- Whether targeting the cause of ALS will influence dis- vacy and confidentiality issues than are people with ease progression in symptomatic individuals remains other diseases103. However, as their disease progresses, unclear; if this is not the case, then gene therapy that patients with ALS face increasing challenges, including targets causal genes would be pointless in these people. the logistics of attending clinic appointments104. So-called regenerative medicine approaches, in which various forms of stem cells or neural progenitor cells are Advanced trial design used, are more plausibly based around the notion that Interest is increasing in methods that maintain the rig- transplanted cells could provide trophic support to slow our of randomized controlled trials while maximizing the disease process and raise hopes for restorative ther- their efficiency, reducing costs and providing answers apy for people already living with ALS. However, given regarding efficacy. One approach that is gaining trac- the immense complexity of the functional networks tion is the use of a master protocol for the simultaneous required to produce voluntary movement and the fact evaluation of multiple compounds105,106 (Fig. 3). With a that these networks are produced via a complex develop- master protocol, a common system is used for patient mental programme that is inactivated in adulthood, the selection, logistics, templates and data management. restoration of function with cellular therapy is currently This approach can incorporate precision genotyping and a theoretical rather than practical option. Several early molecular markers and can be implemented in different phase research programmes are under way to explore the trial designs, including basket trials (in which the thera- potential of transplantation of neural progenitors into peutic target is a specific genetic mutation) and MAMS the spinal cord, but results of small-scale tolerability and platform trials107. Such designs have been successfully safety studies have not yet provided any clear evidence used in cancer, HIV and some neurological diseases such of disease-modifying effects100. as multiple sclerosis107–109. In a MAMS trial with a sequential design, the sam- Improving trial design ple size is not fixed in advance and data are sequentially Challenges with traditional trials analysed, with pre-determined futility or superiority In ALS, as in other neurodegenerative diseases, the analyses built in, which enable treatment arms to be dis- mainstay of clinical research has been the randomized continued owing to a lack of efficacy or to graduate to controlled trial in which the effects of a therapeutic can- the next phase of study (Fig. 3). Consequently, adaptive, didate are compared with those of a placebo101. Typically, seamless phase II–III designs can be used to reduce the

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Master protocol • Patient selection, logistics and data management • Outcome measures • Biomarkers

Random Treatment 1 assignment to treatment or placebo Placebo 1

Random assignment to Treatment 2 treatment or Placebo 2 Random placebo Eligible assignment patient to sub-study Random assignment to Treatment 3 treatment or placebo Placebo 3

Random Treatment 4 assignment to treatment or placebo Placebo 4 Pooled placebo

A B Time Fig. 3 | MAMS adaptive platform trial design. In this multi-arm, multi-stage (MAMS) platform trial, eligible patients are randomly assigned to one of four sub-studies and subsequently randomly assigned to receive active treatment or placebo. A master protocol determines patient selection criteria, logistics, outcome measures, biomarkers and data management in all four sub-studies. Genotype and molecular markers can also be collected systematically. The platform consists of five arms (treatments 1–4 and a pooled placebo arm). Pre-planned interim analyses are built into the design at points A and B. At point A, treatment 2 is found to have a favourable efficacy signal, so the arm seamlessly moves into phase III and more patients are recruited into that arm (thicker arrow). At the same point, futility criteria are met with treatment 3 and this arm is dropped (cross). New arms can be added over time such as treatment 4 here.

delays that are usually encountered after an early prom- their own challenges, including highly complex Bayesian ising signal in a phase II trial. Typically, criteria for the statistical analyses and the fact that several small analysis of accumulating data are pre-planned and, if a sub-studies being conducted in parallel can increase the favourable signal is detected in one sub-study, recruit- rate of false positive findings106,107. Additional challenges ment into that arm is increased to provide phase III effi- of platform trials include their large-scale, long-term cacy data for regulatory approval. As data accumulate, nature, the associated costs of managing and execut- response-adaptive randomization can be used to allocate ing the trial, the need to build organizations or frame- more patients to a treatment arm that is showing more works that can operate these trials perpetually, and the promise than others and to reduce random assignment need for an independent data monitoring committee106. to arms with inferior outcomes. Regulatory authorities are open to discussing such These approaches work well in diseases for which approaches: the FDA has published its guidance for readouts are robust, for example, tumour load in can- adaptive platform master protocol designs and the EMA cer or white matter lesion burden on MRI in multiple has established a taskforce to explore the issue110. sclerosis. Such a robust biomarker does not yet exist for In addition to the trial platform, the complex patho- ALS and therefore adaptive decisions will be limited by physiological mechanisms in ALS and the involvement of existing metrics such as ALS Functional Rating Scale — multiple pathways mean that the clinical benefits might Revised (ALSFRS-R) scores and survival. However, not be apparent with a single drug. The use of a multi‐ a further advantage of the MAMS platform is that patients drug regimen could enable the detection of a more uni- can be randomly assigned to a particular sub-study for versal treatment effect by simultaneously addressing mul- which genetic or other molecular data predicts a favour- tiple disease mechanisms. However, designing trials that able response and can be automatically excluded from test multiple drugs remains complex and determining the sub-studies for which they are not suitable. This possibil- mechanisms of action of a synergistic combination of ity promotes personalized stratification in a biologically therapeutics would logically require a factorial design111. heterogeneous disease. The advantages of a master protocol platform design Patient stratification include efficiencies in terms of cost (fixed costs shared In the context of disease heterogeneity in ALS, the strat- across a number of trials), time and infrastructure that ification of patients as an inclusion criterion for clinical enable more patients to participate in clinical trials. trials is becoming an important consideration when However, these designs are not a panacea and they bring determining the efficacy of a compound. A lead-in phase

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during which patients are monitored before being ran- because ALS is a continuously evolving process and domly assigned to receive a treatment (typically after treatments might need to be administered at precise time patient inclusion but before initiation of therapy) might points in the disease course to be beneficial — staging provide a more accurate indication of disease pro- provides information about this timing. The benefits of gression in individuals and thereby enable the assess- staging were shown in a post hoc analysis of the orig- ment of investigational drug efficacy112–114. In addition, inal riluzole trial data; specifically, post hoc analysis patient stratification can be based on clinical parameters, showed that riluzole has a beneficial effect late in the genetics, disease stage and disease trajectory. disease course121–123. No information was available in The purpose of pre-selection criteria for trial entry the original trial data about patients in the very early is to facilitate the use of tailored treatments. In ALS, stages of disease and therefore the post hoc analysis could pre-selection is a technique that is still in its infancy not examine whether there was an effect early in the and remains largely confined to selection on this basis disease. A subsequent analysis of data from the Pooled of genetic causes. However, some studies suggest that Resource Open-Access ALS Clinical Trials (PRO-ACT) modifier genes, such as those that affect prognosis, can database, which includes patients in the early stages of the also be used as enrolment criteria20 and specific clinical disease, confirmed the original finding and showed that features, such as respiratory, nutritional or emotional riluzole also has an effect in the early stages of ALS121. symptoms, have been used for pre-selection115,116. For The two main staging systems currently under con- example, patients with respiratory impairment have been sideration in ALS are the King’s Clinical Staging system the focus of trials of enhancers of troponin C (which and the Milano–Torino Staging (MiToS) system124. The activates muscle contraction) to improve diaphragmatic King’s system includes five stages based on disease bur- function117. Pre-selection is also an obvious approach for den, assessed according to the muscle groups that are clinical trials of nutritional interventions and approaches clinically involved, and incorporates feeding difficulties to saliva control, which have so far only been tested in and respiratory failure123; stage 1 is symptom onset and exploratory studies. For example, dextromethorphan– stage 5 is death. The MiToS system involves six stages quinidine is beneficial for emotional lability in ALS, (0–5) based on functional ability assessed with the which occurs in a subset of patients, often in associa- ALSFRS-R; stage 0 is defined as normal function and tion with bulbar impairment. Anecdotal patient reports stage 5 is death. The MiToS stage at diagnosis correlates also suggest that dextromethorphan–quinidine might with survival at 18 months122. The two staging systems be useful for improving bulbar function and a phase II are complementary — the King’s system has a higher trial has indicated benefits on all aspects of self-reported resolution in early disease to mid-disease, when clinical bulbar function, including speech, swallowing and or disease burden is increasing, and the MiToS system salivation118. has a higher resolution in late disease, when functional Stratification at the time of recruitment also ena- involvement has developed. Cognitive change, which is bles patients to be matched according to their likely a feature of ALS, is not accounted for in either the King’s clinical course. Ideally, the rate of disease progression or MiToS systems115,125. However, use of the Edinburgh for an individual would be established at the initial Cognitive and Behavioural ALS Screen (ECAS) tool has clinic visit and classified as fast, medium or slow119. demonstrated that increasing impairment in executive However, the clinical course remains heterogeneous function and behavioural changes correlate with later and unpredictable and, therefore, attempts to homo­ King’s stages126 and a cognitive protocol is likely to form genize cohorts on the basis of likely disease course at part of future staging systems. trial entry lead to restrictive inclusion criteria for most trials. The ENCALS Prediction model, published in Patient-reported outcomes 2018, is based on data from over 11,000 patients with The requirement for participants in clinical trials to ALS in population-based registers and has improved the make episodic visits to study centres so that progres- accuracy of personalized prediction of clinical decline sion of their disease can be measured imposes sub- and survival8. The model is based on eight factors: age, stantial restrictions on the conduct of clinical trials. El Escorial classification, site of onset, vital capacity, First, it limits participation to patients who live close genetic status for C9orf72 expansion, diagnostic delay, enough to a study centre to attend mandatory visits cognitive status and functional score. In the context of on a monthly or bimonthly schedule. In an analysis of clinical trial enrolment, the model generates a person- the reasons for poor adherence in ALS clinical trials, alized prediction of survival for each patient and ena- travel difficulties and caregiver burden were contribut­ bles the inclusion of those in whom an effect of the trial ing factors to the withdrawal of 27% of patients who treatment is most likely (for example, minimizing the withdrew their consent127. Second, the requirement number of patients with very slow or very rapid disease for visits to study centres means that substantial vari- progression). The use of the model as an inclusion cri- ability is seen in outcome measures that are commonly terion could enable up to 80% of patients to participate used in phase II and III trials128; some of this variability in trials while minimizing the impact of disease vari- might be due to true fluctuations in patient status and ance. This model was recently used in ALS in a phase II some due to measurement error. Both of these issues clinical trial of dolutegravir, abacavir and lamivudine could be addressed if data could be collected through (Triumeq)120. more frequent assessment of patients because it would Another emerging approach to stratification for clin- reduce variability by increasing the sampling frequency; ical trials in ALS is disease staging. Staging is important however, this would be possible only if undertaken in

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patients’ homes. Other aspects of trial participation, such study, patient views on the experience were assessed with as safety assessments and drug dispensing, could also an online questionnaire. The results of this study will be accommodated at patients’ homes, thereby enabling be used to determine whether home assessments are a the participation of patients who have previously been viable strategy for clinical trials in ALS and the extent deemed inaccessible129. to which frequent sampling improves the reliability and The value of self-reported outcomes has previously sensitivity of a range of trial endpoints. been studied through the use of the PatientsLikeMe In another study, published in 2019, a hybrid design website, where patients directly entered their symp- was used in which a traditional in-clinic trial was com- toms and the data were subsequently analysed130. Such bined with a ‘virtual’ study to test the nutritional sup- patient-reported outcomes are valuable as they are plement lunasin134, which was previously identified cost-effective, can be implemented from a distance, can as a candidate for ALS therapy135. Fifty participants provide comprehensive assessments and can capture an enrolled at one centre for the 12-month, open-label element of personal well-being that is not captured with study. Historical controls were used rather than a con- other approaches131. The limitations of self-reported trol group. The self-reported ALSFRS-R scores closely outcomes include a lack of objectivity and unfamiliarity agreed with confirmatory clinical assessment (Lin’s with the use of digital platforms that are necessary for concordance correlation coefficient, 0.94–0.99). The this approach to be successfully implemented. study produced no evidence that lunasin can lead to The assessment of patients at home with the “ALS reversal”136, but lessons learned from this hybrid ALSFRS-R has frequently been performed in clinical virtual trial could provide ideas for ways to reduce the trials and in clinical practice, usually via a telephone burden on participants by enabling clinical study visits assessment by a trained evaluator132. Furthermore, to be reduced. the reliability of an online tool for assessment with the Given that each trial is unique, the 2019 Airlie House ALSFRS-R that requires no evaluator assistance has been Clinical Trial guidelines recommend that patients and established — values were close to those from assess- caregivers are included in trial design groups to mini- ments in the clinic133. The self-reporting of ALSFRS-R mize the trial burden and ensure that recruitment and scores was done via secure online portals and this retention strategies will be successful10. These guidelines approach was reliable and quick. were developed to accelerate progress in ALS, from In an ongoing study, the results of which are not yet preclinical research through to trial design and statis- available129, the evaluation of ALS trial endpoints at tical approaches, and to advocate the incorporation home was extended to include novel endpoints as well of biomarkers in all future trials and the development of as commonly used endpoints. In that study, patients were home-based outcome measures10. Such measures are recruited via online tools, diagnosis was confirmed from included in large genetic and biomarker studies in which medical records and consent was obtained from patients the goal is to enrol more than 1,000 patients with ALS through an interactive webinar. Tools for endpoint and assess phenotypic information in the clinic and at measurement were sent to patients and demonstration home (ANSWER ALS, TARGET ALS and ALS Therapy and training in the use of these tools was conducted online. Development Institute). Home-based outcome meas- These tools included an activity band, a spirometer, ures are also becoming increasingly relevant for patients a handgrip metre, a personal electrical impedance myo­ with ALS who have substantial disease-related disability, graphy device and a voice evaluation tool that included particularly in the context of a shift towards telemedicine an app for most smartphones. ALSFRS-R scores were owing to the COVID-19 pandemic. assessed and recorded via a secure website. Once trained, participants were asked to perform all assessments — Conclusions and future directions except the ALSFRS-R — every day for 3 months and ALS is a complex neurodegenerative disorder mediated then twice weekly for an additional 6 months. Overall, by interactions between genetic, epigenetic and envi- 114 patients and 30 healthy controls were recruited from ronmental factors, with multiple steps probably being 40 states in the USA. At 3 months and at the end of the required to trigger disease onset. Consequently, effec- tive treatment strategies might require the use of novel compounds acting synergistically, potentially in dif- Box 1 | Priority strategies to improve clinical trial outcomes in ALS ferent phases of the disease. Advances in clinical trials • Facilitate the translation of genetic and cellular therapies into the clinic seem critical to accelerate the translation of such novel • Develop effective high-throughput screening and incorporate drug repurposing therapies into the clinic; novel trial designs are needed strategies to enable the assessment of multiple compounds with • Refinement of clinical biomarkers and integration of biomarker discovery and a common placebo group and to better determine tar- validation in all trials get engagement and the effect on disease trajectory • Develop platforms for initial testing in small patient cohorts to identify a biological (Box 1). The implementation of these approaches for signal using biomarkers the assessment of current and future treatment strat- • Develop patient stratification pathways that better reflect clinical populations egies in ALS could shorten trial durations and reduce • Increase the use of self-reported patient outcomes, thereby reducing costs and costs and burden on patients, thereby providing hope streamlining outcomes for investigators and patients that effective therapies can be rapidly translated into • Widen the use of multi-arm, multi-stage platform trials the ALS clinic. ALS, amyotrophic lateral sclerosis. Published online 18 December 2020

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Acknowledgements funding from Ada Health, AstraZeneca, Baillie Gifford, Bold Peer review information This manuscript was prepared by members of ForeFront, Health, Camoni, Compass Pathways, Coronna, EIT, Happify, Nature Reviews Neurology thanks M. de Carvalho, C. a large collaborative research group dedicated to the study HealthUnlocked, Inbeeo, Kheiron Medical, Sano Genetics, Lunetta, S. Petri and the other, anonymous, reviewer(s) for of neurodegenerative diseases and funded by the National Self Care Catalysts, The Learning Corp, The Wellcome Trust, their contribution to the peer review of this work. Health and Medical Research Council of Australia Program VeraSci and Woebot. M.R.T. is supported by the Motor Publisher’s note Grant (#1132524), a Dementia Research Team Grant Neurone Disease Association. Springer Nature remains neutral with regard to jurisdictional (#1095127) and a Partnership Project (1153439). M.C.K. is claims in published maps and institutional affiliations. supported by an NHMRC Practitioner Fellowship (1156093). Author contributions J.M.S. receives funding from ALS Finding a Cure Foundation. M.C.K. researched data for the article. M.C.K. and S.V. made A.A.-C. is supported through the United Kingdom Medical substantial contributions to discussion of the content. M.C.K., Related links Research Council (MR/R024804/1) under the aegis of JPND S.V., K.T., C.J.M., O.H., J.M.S., A.A.-C. and M.R.T. contributed ALs Therapy Development institute: www.als.net (www.jpnd.eu), the Motor Neurone Disease Association, and to the writing of the article. All authors reviewed and edited ANsweR ALs: www.answerals.org the National Institute for Health Research (NIHR) Biomedical the manuscript before submission. PatientsLikeMe: www.patientslikeme.com Research Centre at South London and Maudsley NHS TARGeT ALs: www.targetals.org Foundation Trust and King’s College London. P.W. is Competing interests employed by Wicks Digital Health, which has received The authors declare no competing interests. © Springer Nature Limited 2020

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