Current and emerging treatment strategies for Duchenne muscular dystrophy

Discovery of Quinazoline and Quinoline-Based Small Molecules as Utrophin Upregulators via AhR Antagonism for the Treatment of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal muscle-wasting disease caused by the absence of a dystrophin protein. Elevating utrophin, a dystrophin paralogue, offers an alternative therapeutic strategy for treating DMD, irrespective of the mutation type. Herein, we report the design and synthesis of novel quinazoline and quinoline-based small molecules as potent utrophin modulators screened via high throughput In-Cell ELISA in C2C12 cells. Remarkably, lead molecule SG-02, identified from a library of 70 molecules, upregulates utrophin 2.7-fold at 800 nM in a dose-dependent manner, marking the highest upregulation within the nanomolar range. SG-02's efficacy was further validated through DMD patient-derived cells, demonstrating a significant 2.3-fold utrophin expression. Mechanistically, SG-02 functions as an AhR antagonist, with excellent binding affinity (Kd = 41.68 nM). SG-02 also enhances myogenesis, as indicated by an increased MyHC expression. ADME evaluation supports SG-02's oral bioavailability. Overall, SG-02 holds promise for addressing the global DMD population.

Duchenne muscular dystrophy: promising early-stage clinical trials to watch

INTRODUCTION

Current therapies are unable to cure Duchenne muscular dystrophy (DMD), a severe and common form of muscular dystrophy, and instead aim to delay disease progression. Several treatments currently in phase I trials could increase the number of therapeutic options available to patients.

AREAS COVERED

This review aims to provide an overview of current treatments undergoing or having recently undergone early-stage trials. Several exon-skipping and gene therapy approaches are currently being investigated at the clinical stage to address an unmet need for DMD treatments. This article also covers Phase I trials from the last 5 years that involve inhibitors, small molecules, a purified synthetic flavanol, a cell-based therapy, and repurposed cardiac or tumor medications.

EXPERT OPINION

With antisense oligonucleotide (AON) treatments making up the majority of conditionally approved DMD therapies, most of the clinical trials occurring within the last 5 years have also evaluated exon-skipping AONs. The approval of Elevidys, a micro-dystrophin therapy, is reflected in a recent trend toward gene transfer therapies in phase I DMD clinical trials, but their safety and efficacy are being established in this phase of development. Other Phase I clinical-stage approaches are diverse, but have a range in efficacy, safety, and endpoint measures.

Mutational spectrum and phenotypic variability of Duchenne muscular dystrophy and related disorders in a Bangladeshi population

Duchenne muscular dystrophy (DMD) is a severe rare neuromuscular disorder caused by mutations in the X-linked dystrophin gene. Several mutations have been identified, yet the full mutational spectrum, and their phenotypic consequences, will require genotyping across different populations. To this end, we undertook the first detailed genotype and phenotype characterization of DMD in the Bangladeshi population. We investigated the rare mutational and phenotypic spectrum of the DMD gene in 36 DMD-suspected Bangladeshi participants using an economically affordable diagnostic strategy involving initial screening for exonic deletions in the DMD gene via multiplex PCR, followed by testing PCR-negative patients for mutations using whole exome sequencing. The deletion mapping identified two critical DMD gene hotspot regions (near proximal and distal ends, spanning exons 8-17 and exons 45-53, respectively) that comprised 95% (21/22) of the deletions for this population cohort. From our exome analysis, we detected two novel pathogenic hemizygous mutations in exons 21 and 42 of the DMD gene, and novel pathogenic recessive and loss of function variants in four additional genes: SGCD, DYSF, COL6A3, and DOK7. Our phenotypic analysis showed that DMD suspected participants presented diverse phenotypes according to the location of the mutation and which gene was impacted. Our study provides ethnicity specific new insights into both clinical and genetic aspects of DMD.

Anti-RANKL Therapy Prevents Glucocorticoid-Induced Bone Loss and Promotes Muscle Function in a Mouse Model of Duchenne Muscular Dystrophy

Bisphosphonates prevent bone loss in glucocorticoid (GC)-treated boys with Duchenne muscular dystrophy (DMD) and are recommended as standard of care. Targeting receptor activator of nuclear factor kappa-B ligand (RANKL) may have advantages in DMD by ameliorating dystrophic skeletal muscle function in addition to their bone anti-resorptive properties. However, the potential effects of anti-RANKL treatment upon discontinuation in GC-induced animal models of DMD are unknown and need further investigation prior to exploration in the clinical research setting. In the first study, the effects of anti-RANKL and deflazacort (DFZ) on dystrophic skeletal muscle function and bone microstructure were assessed in mdx mice treated with DFZ or anti-RANKL, or both for 8 weeks. Anti-RANKL and DFZ improved grip force performance of mdx mice but an additive effect was not noted. However, anti-RANKL but not DFZ improved ex vivo contractile properties of dystrophic muscles. This functional improvement was associated with a reduction in muscle damage and fibrosis, and inflammatory cell number. Anti-RANKL treatment, with or without DFZ, also improved trabecular bone structure of mdx mice. In a second study, intravenous zoledronate (Zol) administration (1 or 2 doses) following 2 months of discontinuation of anti-RANKL treatment was mostly required to record an improvement in bone microarchitecture and biomechanical properties in DFZ-treated mdx mice. In conclusion, the ability of anti-RANKL therapy to restore muscle function has profound implications for DMD patients as it offers the possibility of improving skeletal muscle function without the steroid-related skeletal side effects.

Sleep apnoea and hypoventilation in patients with five major types of muscular dystrophy

BACKGROUND

The characteristics of and relationship between sleep apnoea and hypoventilation in patients with muscular dystrophy (MD) remain to be fully understood.

METHODS

We analysed 104 in-laboratory sleep studies of 73 patients with MD with five common types (DMD-Duchenne, Becker MD, CMD-congenital, LGMD-limb-girdle and DM-myotonic dystrophy). We used generalised estimating equations to examine differences among these types for outcomes.

RESULTS

Patients in all five types had high risk of sleep apnoea with 53 of the 73 patients (73%) meeting the diagnostic criteria in at least one study. Patients with DM had higher risk of sleep apnoea compared with patients with LGMD (OR=5.15, 95% CI 1.47 to 18.0; p=0.003). Forty-three per cent of patients had hypoventilation with observed prevalence higher in CMD (67%), DMD (48%) and DM (44%). Hypoventilation and sleep apnoea were associated in those patients (unadjusted OR=2.75, 95% CI 1.15 to 6.60; p=0.03), but the association weakened after adjustment (OR=2.32, 95% CI 0.92 to 5.81; p=0.08). In-sleep average heart rate was about 10 beats/min higher in patients with CMD and DMD compared with patients with DM (p=0.0006 and p=0.02, respectively, adjusted for multiple testing).

CONCLUSION

Sleep-disordered breathing is common in patients with MD but each type has its unique features. Hypoventilation was only weakly associated with sleep apnoea; thus, high clinical suspicion is needed for diagnosing hypoventilation. Identifying the window when respiratory muscle weakness begins to cause hypoventilation is important for patients with MD; it enables early intervention with non-invasive ventilation-a therapy that should both lengthen the expected life of these patients and improve its quality.Cite Now.

Clinical potential of microdystrophin as a surrogate endpoint

Accelerated approval based on a likely surrogate endpoint can be life-changing for patients suffering from a rare progressive disease with unmet medical need, as it substantially hastens access to potentially lifesaving therapies. In one such example, antisense morpholinos were approved to treat Duchenne muscular dystrophy (DMD) based on measurement of shortened dystrophin in skeletal muscle biopsies as a surrogate biomarker. New, promising therapeutics for DMD include AAV gene therapy to restore another form of dystrophin termed mini- or microdystrophin. AAV-microdystrophins are currently in clinical trials but have yet to be accepted by regulatory agencies as reasonably likely surrogate endpoints. To evaluate microdystrophin expression as a reasonably likely surrogate endpoint for DMD, this review highlights dystrophin biology in the context of functional and clinical benefit to support the argument that microdystrophin proteins have a high probability of providing clinical benefit based on their rational design. Unlike exon-skipping based strategies, the approach of rational design allows for functional capabilities (i.e. quality) of the protein to be maximized with every patient receiving the same optimized microdystrophin. Therefore, the presence of rationally designed microdystrophin in a muscle biopsy is likely to predict clinical benefit and is consequently a strong candidate for a surrogate endpoint analysis to support accelerated approval.

A pilot study of newborn screening for Duchenne muscular dystrophy in Guangzhou

Background

To estimate the overall situation of Duchenne muscular dystrophy (DMD) screening in newborns in Guangzhou, China.

Method

A total of 62553 newborns including 44268 males and 18285 females were screened for DMD by measuring muscle specific creatine kinase isoform (CK-MM) concentrations using the GSP® Neonatal CK-MM kit based on time-resolved immunofluorescence. We recalled positive cases and recollected dried blood spots (DBS) for retest of CK-MM. The newborns with retest positive result were recalled again for serum creatine kinase (CK) and multiplex ligation-dependent probe amplification (MLPA) test. Whole exon sequencing was performed when MLPA test was negative.

Results

Four males were diagnosed with DMD. The incidence of males was 1/11067. No DMD patient was found in female. There were significant differences of CK-MM concentration between male and female newborns. Among gestational age (GA), birth weight (BW) and age at sampling, linear regression analysis showed that CK-MM concentration was much more closely correlated with GA and age at sampling.

Conclusions

CK-MM concentration is affected by gender, GA, BW and age at sampling. The efficiency of DMD screening might be improved by adjusting a multitier cut-off value according to GA and age at sampling. DMD newborn screening should be male priority.

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A total of 62553 newborns including 44268 males and 18285 females were screened for DMD in Guangzhou.

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Four males were diagnosed with DMD. The incidence of males was 1/11067. No DMD patient found in female.

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DMD newborn screening should be male priority.

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The efficiency of DMD screening might be improved by adjusting a multitier cut-off value according to GA and age at sampling.

The Hidden Disease: Delayed Diagnosis in Duchenne Muscular Dystrophy and Co-Occurring Conditions

OBJECTIVE

Early diagnosis of Duchenne muscular dystrophy (DMD) is important for timely intervention to prolong function and preserve quality of life. The prevalence of various neurocognitive disorders is known to be higher in patients with DMD than the general population. In this study, we highlight cases of delayed DMD diagnosis that resulted from misattribution of early motor symptoms to co-occurring neurocognitive conditions. We also investigate the difference in age at DMD diagnosis in the setting of specific co-occurring neurocognitive conditions.

METHOD

In this study, we reviewed 40 consecutive patients seen at a Certified Duchenne Care Center, excluding siblings of already-diagnosed patients. We highlight cases of significant delay in DMD diagnosis in the setting of co-occurring neurocognitive diagnoses. We also investigate the association of autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), intellectual disability, and speech/language delay on age of DMD diagnosis.

RESULTS

The prevalence of co-occurring neurocognitive diagnoses was 73.1% in patients diagnosed at or after age 5 years vs. 35.7% in those diagnosed before age 5 years. The average age of DMD diagnosis was 6.6 years in patients with any co-occurring neurocognitive diagnoses and 4.9 years in patients without ( p = 0.09). Individual analysis of ASD and ADHD showed significant differences. A greater number of co-occurring conditions were associated with an increased age at DMD diagnosis ( R2 = 0.87, p < 0.001).

CONCLUSION

The data suggest an association between the presence of co-occurring neurocognitive conditions and a later age of DMD diagnosis. One cost-effective diagnostic step that can be implemented by all pediatric practitioners is testing serum creatinine kinase (CK) in any child with motor delays or hypotonia, even in the context of other behavioral or cognitive disabilities.

Implications of notch signaling in duchenne muscular dystrophy

This review focuses upon the implications of the Notch signaling pathway in muscular dystrophies, particularly Duchenne muscular dystrophy (DMD): a pervasive and catastrophic condition concerned with skeletal muscle degeneration. Prior work has defined the pathogenesis of DMD, and several therapeutic approaches have been undertaken in order to regenerate skeletal muscle tissue and ameliorate the phenotype. There is presently no cure for DMD, but a promising avenue for novel therapies is inducing muscle regeneration via satellite cells (muscle stem cells). One specific target using this approach is the Notch signaling pathway. The canonical Notch signaling pathway has been well-characterized and it ultimately governs cell fate decision, cell proliferation, and induction of differentiation. Additionally, inhibition of the Notch signaling pathway has been directly implicated in the deficits seen with muscular dystrophies. Here, we explore the connection between the Notch signaling pathway and DMD, as well as how Notch signaling may be targeted to improve the muscle degeneration seen in muscular dystrophies.

Control of backbone chemistry and chirality boost oligonucleotide splice switching activity

Although recent regulatory approval of splice-switching oligonucleotides (SSOs) for the treatment of neuromuscular disease such as Duchenne muscular dystrophy has been an advance for the splice-switching field, current SSO chemistries have shown limited clinical benefit due to poor pharmacology. To overcome limitations of existing technologies, we engineered chimeric stereopure oligonucleotides with phosphorothioate (PS) and phosphoryl guanidine-containing (PN) backbones. We demonstrate that these chimeric stereopure oligonucleotides have markedly improved pharmacology and efficacy compared with PS-modified oligonucleotides, preventing premature death and improving median survival from 49 days to at least 280 days in a dystrophic mouse model with an aggressive phenotype. These data demonstrate that chemical optimization alone can profoundly impact oligonucleotide pharmacology and highlight the potential for continued innovation around the oligonucleotide backbone. More specifically, we conclude that chimeric stereopure oligonucleotides are a promising splice-switching modality with potential for the treatment of neuromuscular and other genetic diseases impacting difficult to reach tissues such as the skeletal muscle and heart.

Effects of Low-Intensity and Long-Term Aerobic Exercise on the Psoas Muscle of mdx Mice: An Experimental Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a muscle disease characterized by the absence of the protein dystrophin, which causes a loss of sarcolemma integrity, determining recurrent muscle injuries, decrease in muscle function, and progressive degeneration. Currently, there is a need for therapeutic treatments to improve the quality of life of DMD patients. Here, we investigated the effects of a low-intensity aerobic training (37 sessions) on satellite cells, peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α protein (PGC-1α), and different types of fibers of the psoas muscle from mdx mice (DMD experimental model). Wildtype and mdx mice were randomly divided into sedentary and trained groups (n = 24). Trained animals were subjected to 37 sessions of low-intensity running on a motorized treadmill. Subsequently, the psoas muscle was excised and analyzed by immunofluorescence for dystrophin, satellite cells, myosin heavy chain (MHC), and PGC-1α content. The minimal Feret’s diameters of the fibers were measured, and light microscopy was applied to observe general morphological features of the muscles. The training (37 sessions) improved morphological features in muscles from mdx mice and caused an increase in the number of quiescent/activated satellite cells. It also increased the content of PGC-1α in the mdx group. We concluded that low-intensity aerobic exercise (37 sessions) was able to reverse deleterious changes determined by DMD.

Muscle histological changes in a large cohort of patients affected with Becker muscular dystrophy

Becker muscular dystrophy (BMD) is a severe X-linked muscle disease. Age of onset, clinical variability, speed of progression and affected tissues display wide variability, making a clinical trial design for drug development very complex. The histopathological changes in skeletal muscle tissue are central to the pathogenesis, but they have not been thoroughly elucidated yet. Here we analysed muscle biopsies from a large cohort of BMD patients, focusing our attention on the histopathological muscle parameters, as fibrosis, fatty replacement, fibre cross sectional area, necrosis, regenerating fibres, splitting fibres, internalized nuclei and dystrophy evaluation. We correlated histological parameters with both demographic features and clinical functional evaluations. The most interesting results of our study are the accurate quantification of fibroadipose tissue replacement and the identification of some histopathological aspects that well correlate with clinical performances. Through correlation analysis, we divided our patients into three clusters with well-defined histological and clinical features. In conclusion, this is the first study that analyses in detail the histological characteristics of muscle biopsies in a large cohort of BMD patients, correlating them to a functional impairment. The collection of these data help to better understand the histopathological progression of the disease and can be useful to validate any pharmacological trial in which the modification of muscle biopsy is utilized as outcome measure.

Prediagnosis pathway benchmarking audit in patients with Duchenne muscular dystrophy

OBJECTIVE

To describe age and time at key stages in the Duchenne muscular dystrophy (DMD) prediagnosis pathway at selected centres to identify opportunities for service improvement.

DESIGN

A multicentre retrospective national audit.

SETTING

Nine tertiary neuromuscular centres across the UK and Ireland. A prior single-centre UK audit of 20 patients with no DMD family history provided benchmark criteria.

PATIENTS

Patients with a definitive diagnosis of DMD documented within 3 years prior to December 2018 (n=122).

MAIN OUTCOME MEASURES

Mean age (months) at four key stages in the DMD diagnostic pathway and mean time (months) of presentational and diagnostic delay, and time from first reported symptoms to definitive diagnosis. Type of symptoms was also recorded.

RESULTS

Overall, mean age at definitive diagnosis, age at first engagement with healthcare professional (HCP) and age at first reported symptoms were 53.9±29.7, 49.9±28.9 and 36.4±26.8 months, respectively. The presentational delay and time to diagnosis were 21.1 (±21.1) and 4.6 (±7.9) months, respectively. The mean time from first reported symptoms to definitive diagnosis was 24.2±20.9. The percentages of patients with motor and/or non-motor symptoms recorded were 88% (n=106/121) and 47% (n=57/121), respectively.

CONCLUSIONS

Majority of data mirrored the benchmark audit. However, while the time to diagnosis was shorter, a presentational delay was observed. Failure to recognise early symptoms of DMD could be a contributing factor and represents an unmet need in the diagnosis pathway. Methods determining how to improve this need to be explored.

Pharmacological Profile of Viltolarsen for the Treatment of Duchenne Muscular Dystrophy: A Japanese Experience

Duchenne muscular dystrophy (DMD) is a fatal, X-linked recessive disorder characterized by progressive muscle loss and cardiorespiratory complications. Mutations in the DMD gene that eliminate the production of dystrophin protein are the underlying causes of DMD. Viltolarsen is a drug of phosphorodiamidate morpholino oligomer (PMO) chemistry, designed to skip exon 53 of the DMD gene. It aims to produce truncated but partially functional dystrophin in DMD patients and restore muscle function. Based on a preclinical study showing the ability of antisense PMOs targeting the DMD gene to improve muscle function in a large animal model, viltolarsen was developed by Nippon Shinyaku and the National Center of Neurology and Psychiatry in Japan. Following clinical trials conducted in Japan, Canada, and the United States showing significant improvements in muscle function, viltolarsen was approved for medical use in Japan in March 2020 and the United States in August 2020, respectively. Viltolarsen is a mutation-specific drug and will work for 8% of the persons with DMD who carry mutations amenable to exon 53 skipping. This review summarizes the pharmacological profile of viltolarsen, important clinical trials, and challenges, focusing on the contribution of Japanese patients and researchers in its development.

The impact of genotype on outcomes in individuals with Duchenne muscular dystrophy: A systematic review

Duchenne muscular dystrophy (DMD) is associated with progressive muscle weakness, loss of ambulation (LOA), and early mortality. In this review we have synthesized published data on the clinical course of DMD by genotype. Using a systematic search implemented in Medline and Embase, 53 articles were identified that describe the clinical course of DMD, with pathogenic variants categorizable by exon skip or stop-codon readthrough amenability and outcomes presented by age. Outcomes described included those related to ambulatory, cardiac, pulmonary, or cognitive function. Estimates of the mean (95% confidence interval) age at LOA ranged from 9.1 (8.7-9.6) years among 90 patients amenable to skipping exon 53 to 11.5 (9.5-13.5) years among three patients amenable to skipping exon 8. Although function worsened with age, the impact of genotype was less clear for other outcomes (eg, forced vital capacity and left ventricular ejection fraction). Understanding the distribution of pathogenic variants is important for studies in DMD, as this research suggests major differences in the natural history of disease. In addition, specific details of the use of key medications, including corticosteroids, antisense oligonucleotides, and cardiac medications, should be reported.

Ataluren delays loss of ambulation and respiratory decline in nonsense mutation Duchenne muscular dystrophy patients

Aim: We investigated the effect of ataluren plus standard of care (SoC) on age at loss of ambulation (LoA) and respiratory decline in patients with nonsense mutation Duchenne muscular dystrophy (nmDMD) versus patients with DMD on SoC alone. Patients & methods: Study 019 was a long-term Phase III study of ataluren safety in nmDMD patients with a history of ataluren exposure. Propensity score matching identified Study 019 and CINRG DNHS patients similar in disease progression predictors. Results & conclusion: Ataluren plus SoC was associated with a 2.2-year delay in age at LoA (p = 0.0006), and a 3.0-year delay in decline of predicted forced vital capacity to <60% in nonambulatory patients (p = 0.0004), versus SoC. Ataluren plus SoC delays disease progression and benefits ambulatory and nonambulatory patients with nmDMD. ClinicalTrials.gov: NCT01557400.

Long-Term Safety and Efficacy Data of Golodirsen in Ambulatory Patients with Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A First-in-human, Multicenter, Two-Part, Open-Label, Phase 1/2 Trial

The aim of this Phase 1/2, 2-part, multicenter trial was to report clinical safety and efficacy of long-term golodirsen treatment among ambulatory patients with exon 53 skip-amenable Duchenne muscular dystrophy (DMD). Part 1 was a 12-week, randomized, double-blind, placebo-controlled, dose-titration study followed by 9-week safety review. Part 2 was a 168-week, open-label evaluation of golodirsen 30 mg/kg. Part 1 primary endpoint was safety. Part 2 primary endpoints were dystrophin protein expression and 6-minute walk test (6MWT); secondary endpoints were percent predicted forced vital capacity (FVC%p) and safety. Post hoc ambulation analyses used mutation-matched external natural history controls. All patients from Part 1 (golodirsen, n = 8; placebo, n = 4) plus 13 additional patients entered Part 2; 23 completed the study. Adverse events were generally mild, nonserious, and unrelated to golodirsen, with no safety-related discontinuations or deaths. Golodirsen increased dystrophin protein (16.0-fold; P < 0.001) and exon skipping (28.9-fold; P < 0.001). At 3 years, 6MWT change from baseline was −99.0 m for golodirsen-treated patients versus −181.4 m for external controls (P = 0.067), and loss of ambulation occurred in 9% versus 26% (P = 0.21). FVC%p declined 8.4% over 3 years in golodirsen-treated patients, comparing favorably with literature-reported rates. This study provides evidence for golodirsen biologic activity and long-term safety in a declining DMD population and suggests functional benefit versus external controls. Clinical Trial Registration number: NCT02310906.

First Regulatory Qualification of a Novel Digital Endpoint in Duchenne Muscular Dystrophy: A Multi-Stakeholder Perspective on the Impact for Patients and for Drug Development in Neuromuscular Diseases

Background

Functional outcome measures used to assess efficacy in clinical trials of investigational treatments for rare neuromuscular diseases like Duchenne muscular dystrophy (DMD) are performance-based tasks completed by the patient during hospital visits. These are prone to bias and may not reflect motor abilities in real-world settings. Digital tools, such as wearable devices and other remote sensors, provide the opportunity for continuous, objective, and sensitive measurements of functional ability during daily life. Maintaining ambulation is of key importance to individuals with DMD. Stride velocity 95th centile (SV95C) is the first wearable acquired digital endpoint to receive qualification from the European Medicines Agency (EMA) to quantify the ambulation ability of ambulant DMD patients aged ≥5 years in drug therapeutic studies; it is also currently under review for the US Food and Drug Administration (FDA) qualification.

Summary

Focusing on SV95C as a key example, we describe perspectives of multiple stakeholders on the promise of novel digital endpoints in neuromuscular disease drug development.

Human muscle production in vitro from pluripotent stem cells: Basic and clinical applications

Human pluripotent stem cells (PSCs), which have the capacity to self-renew and differentiate into multiple cell types, offer tremendous therapeutic potential and invaluable flexibility as research tools. Recently, remarkable progress has been made in directing myogenic differentiation of human PSCs. The differentiation strategies, which were inspired by our knowledge of myogenesis in vivo, have provided an important platform for the study of human muscle development and modeling of muscular diseases, as well as a promising source of cells for cell therapy to treat muscular dystrophies. In this review, we summarize the current state of skeletal muscle generation from human PSCs, including transgene-based and transgene-free differentiation protocols, and 3D muscle tissue production through bioengineering approaches. We also highlight their basic and clinical applications, which facilitate the study of human muscle biology and deliver new hope for muscular disease treatment.

De novo revertant fiber formation and therapy testing in a 3D culture model of Duchenne muscular dystrophy skeletal muscle

The biological basis of Duchenne muscular dystrophy (DMD) pathology is only partially characterized and there are still few disease-modifying therapies available, therein underlying the value of strategies to model and study DMD. Dystrophin, the causative gene of DMD, is responsible for linking the cytoskeleton of muscle fibers to the extracellular matrix beyond the sarcolemma. We posited that disease-associated phenotypes not yet captured by two-dimensional culture methods would arise by generating multinucleated muscle cells within a three-dimensional (3D) extracellular matrix environment. Herein we report methods to produce 3D human skeletal muscle microtissues (hMMTs) using clonal, immortalized myoblast lines established from healthy and DMD donors. We also established protocols to evaluate immortalized hMMT self-organization and myotube maturation, as well as calcium handling, force generation, membrane stability (i.e., creatine kinase activity and Evans blue dye permeability) and contractile apparatus organization following electrical-stimulation. In examining hMMTs generated with a cell line wherein the dystrophin gene possessed a duplication of exon 2, we observed rare dystrophin-positive myotubes, which were not seen in 2D cultures. Further, we show that treating DMD hMMTs with a β1-integrin activating antibody, improves contractile apparatus maturation and stability. Hence, immortalized myoblast-derived DMD hMMTs offer a pre-clinical system with which to investigate the potential of duplicated exon skipping strategies and those that protect muscle cells from contraction-induced injury. STATEMENT OF SIGNIFICANCE: Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder that is caused by mutation of the dystrophin gene. The biological basis of DMD pathology is only partially characterized and there is no cure for this fatal disease. Here we report a method to produce 3D human skeletal muscle microtissues (hMMTs) using immortalized human DMD and healthy myoblasts. Morphological and functional assessment revealed DMD-associated pathophysiology including impaired calcium handling and de novo formation of dystrophin-positive revertant muscle cells in immortalized DMD hMMTs harbouring an exon 2 duplication, a feature of many DMD patients that has not been recapitulated in culture prior to this report. We further demonstrate that this "DMD in a dish" system can be used as a pre-clinical assay to test a putative DMD therapeutic and study the mechanism of action.

Current Pharmacological Strategies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-linked neuromuscular disorder caused by the absence of dystrophin protein, which is essential for muscle fiber integrity. Loss of dystrophin protein leads to recurrent myofiber damage, chronic inflammation, progressive fibrosis, and dysfunction of muscle stem cells. There is still no cure for DMD so far and the standard of care is principally limited to symptom relief through glucocorticoids treatments. Current therapeutic strategies could be divided into two lines. Dystrophin-targeted therapeutic strategies that aim at restoring the expression and/or function of dystrophin, including gene-based, cell-based and protein replacement therapies. The other line of therapeutic strategies aims to improve muscle function and quality by targeting the downstream pathological changes, including inflammation, fibrosis, and muscle atrophy. This review introduces the important developments in these two lines of strategies, especially those that have entered the clinical phase and/or have great potential for clinical translation. The rationale and efficacy of each agent in pre-clinical or clinical studies are presented. Furthermore, a meta-analysis of gene profiling in DMD patients has been performed to understand the molecular mechanisms of DMD.

Comparison of Long-term Ambulatory Function in Patients with Duchenne Muscular Dystrophy Treated with Eteplirsen and Matched Natural History Controls

Background:

Duchenne muscular dystrophy (DMD) is a rare, X-linked, fatal, degenerative neuromuscular disease caused by DMD gene mutations. A relationship between exon skipping and dystrophin production in exon 51-amenable patients treated with eteplirsen (EXONDYS 51^®) is established. Once-weekly eteplirsen significantly increased dystrophin, with slower decline in ambulatory function compared to baseline. Long-term treatment with eteplirsen leads to accumulation of dystrophin over time and observed functional benefits in patients with DMD.

Objective:

Compare long-term ambulatory function in eteplirsen-treated patients versus controls.

Methods:

Study 201/202 included 12 eteplirsen-treated patients assessed twice/year for ambulatory function over 4 years. Ambulatory evaluations (6-minute walk test [6MWT], loss of ambulation, and North Star Ambulatory Assessment [NSAA]) were compared with matched controls from Italian Telethon and Leuven registries.

Results:

At Years 3 and 4, eteplirsen-treated patients demonstrated markedly greater mean 6MWT than controls (difference in change from baseline of 132 m [95%CI (29, 235), p = 0.015] at Year 3 and 159 m [95%CI (66, 253), p = 0.002] at Year 4). At Year 4, a significantly greater proportion of eteplirsen-treated patients were still ambulant versus controls (10/12 vs 3/11; p = 0.020). At Year 3, eteplirsen-treated patients demonstrated milder NSAA decline versus controls (difference in change from baseline of 2.6, 95%CI [-6, 11]), however, the difference was not statistically significant; Year 4 control NSAA data were not available.

Conclusion:

In this retrospective matched control study, eteplirsen treatment resulted in attenuation of ambulatory decline over a 4-year observation period, supporting long-term benefit in patients with DMD.

DMD/BMD prenatal diagnosis and treatment expectation in a single centre in China for 15 years

Objective

DMD/BMD prenatal diagnosis for 931 foetuses.

Background

DMD is the most common fatal X-linked recessive muscular disease. There is no effective clinical treatment method at present. Accurate gene diagnosis and prenatal diagnosis technology are important ways for early detection, early prevention and early treatment.

Methods

A total of 931 prenatal diagnoses were performed for pregnant women with a definite family history of DMD or a history of DMD childbirth between 2005 and 2019. This report may be considered the largest DMD prenatal diagnosis report in a single centre worldwide. Multiple ligation-dependent probe amplification (MLPA) and next-generation sequencing were used in combination. Techniques and short tandem repeat (STR) linkage analysis were used to determine the location of the DMD gene mutation in the pregnant woman and then to detect the DMD gene in the foetuses.

Results

There were 872 families in our study. Among all 931 foetuses, 20.73% (193/931) were males expected to develop DMD and 16.33% (152/931) were female carriers. In addition, gonadal mosaicism was observed in 5 mothers, and gene recombination was identified in three foetuses. The results of the prenatal diagnosis were consistent with the results of the CPK analysis, and the results of the prenatal diagnosis were 100% accurate.

Conclusions

MLPA and Sanger sequencing, when combined with STR linkage analyses, can provide an accurate and rapid prenatal diagnosis. Due to the high de novo rate, prenatal diagnosis and genetic counselling should be given great attention.

Safety, tolerability, and pharmacokinetics of casimersen in patients with Duchenne muscular dystrophy amenable to exon 45 skipping: A randomized, double-blind, placebo-controlled, dose-titration trial

INTRODUCTION/AIMS

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene resulting in the absence of dystrophin. Casimersen is a phosphorodiamidate morpholino oligomer designed to bypass frameshift DMD mutations and produce internally truncated, yet functional, dystrophin protein in patients amenable to exon 45 skipping. Our primary study objective was to evaluate safety and tolerability of casimersen; the secondary objective was to characterize the plasma pharmacokinetics.

METHODS

This multicenter, phase 1/2 trial enrolled 12 participants (aged 7-21 years, who had limited ambulation or were nonambulatory) and comprised a 12-week, double-blind dose titration, then an open-label extension for up to 132 weeks. During dose titration, participants were randomized 2:1 to weekly casimersen infusions at escalating doses of 4, 10, 20, and 30 mg/kg (≥2 weeks per dose), or placebo.

RESULTS

Participants received casimersen for a mean 139.6 weeks. Treatment-emergent adverse events (TEAEs) occurred in all casimersen- and placebo-treated participants and were mostly mild (over 91.4%) and unrelated to casimersen or its dose. There were no deaths, dose reductions, abnormalities in laboratory parameters or vital signs, or casimersen-related serious AEs. Casimersen plasma concentration increased with dose and declined similarly for all dose levels over 24 hours postinfusion. All pharmacokinetic parameters were similar at weeks 7 and 60.

DISCUSSION

Casimersen was well tolerated in participants with DMD amenable to exon 45 skipping. Most TEAEs were mild, nonserious, and unrelated to casimersen. Plasma exposure was dose proportional with no suggestion of plasma accumulation. These results support further studies of casimersen in this population.

A novel DMD intronic alteration: a potentially disease-causing variant of an intermediate muscular dystrophy phenotype

Pathogenic germline variants in DMD gene, which encodes the well-known cytoskeletal protein named dystrophin, are associated with a wide range of dystrophinopathies disorders, such as Duchenne muscular dystrophy (DMD, severe form), Becker muscular dystrophy (BMD, mild form) and intermediate muscular dystrophy (IMD). Muscle biopsy, immunohistochemistry, molecular (multiplex ligation-dependent probe amplification (MLPA)/next-generation sequencing (NGS) and Sanger methods) and in silico analyses were performed in order to identify alterations in DMD gene and protein in a patient with a clinical manifestation and with high creatine kinase levels. Herein, we described a previously unreported intronic variant in DMD and reduced dystrophin staining in the muscle biopsy. This novel DMD variant allele, c.9649+4A>T that was located in a splice donor site within intron 66. Sanger sequencing analysis from maternal DNA showed the presence of both variant c.9649+4A>T and wild-type (WT) DMD alleles. Different computational tools suggested that this nucleotide change might affect splicing through a WT donor site disruption, occurring in an evolutionarily conserved region. Indeed, we observed that this novel variant, could explain the reduced dystrophin protein levels and discontinuous sarcolemmal staining in muscle biopsy, which suggests that c.9649+4A>T allele may be re-classified as pathogenic in the future. Our data show that the c.9649+4A>T intronic sequence variant in the DMD gene may be associated with an IMD phenotype and our findings reinforce the importance of a more precise diagnosis combining muscle biopsy, molecular techniques and comprehensive in silico approaches in the clinical cases with negative results for conventional genetic analysis.

In vitro metabolism, reaction phenotyping, enzyme kinetics, CYP inhibition and induction potential of ataluren

Ataluren promotes ribosomal readthrough of premature termination codons in mRNA which result from nonsense mutations. In vitro studies were performed to characterize the metabolism and enzyme kinetics of ataluren and its interaction potential with CYP enzymes. Incubation of [¹⁴C]‐ataluren with human liver microsomes indicated that the major metabolic pathway for ataluren is via direct glucuronidation and that the drug is not metabolized via cytochrome P450 (CYP). Glucuronidation was also observed in the incubation in human intestinal and kidney microsomes, but not in human pulmonary microsomes. UGT1A9 was found to be the major uridine diphosphate glucuronosyltransferase (UGT) responsible for ataluren glucuronidation in the liver and kidney microsomes. Enzyme kinetic analysis of the formation of ataluren acyl glucuronide, performed in human liver, kidney, and intestinal microsomes and recombinant human UGT1A9, found that increasing bovine serum albumin (BSA) levels enhanced the glucuronidation Michaelis‐Menten constant (K_m) and ataluren protein binding but had a minimal effect on maximum velocity (V_max) of glucuronidation. Due to the decreased unbound Michaelis‐Menten constant (K_m,u), the ataluren unbound intrinsic clearance (CL_int,u) increased for all experimental systems and BSA concentrations. Human kidney microsomes were about 3.7‐fold more active than human liver microsomes, in terms of CL_int,u/mg protein, indicating that the kidney is also a key organ for the metabolism and disposition of ataluren in humans. Ataluren showed no or little potential to inhibit or induce most of the CYP enzymes.

A single NGS-based assay covering the entire genomic sequence of the DMD gene facilitates diagnostic and newborn screening confirmatory testing

Molecular diagnosis for Duchenne and Becker muscular dystrophies (DMD/BMD) involves a two-tiered approach for detection of deletions/duplications using MLPA or array CGH, followed by sequencing of coding and flanking intronic regions to detect sequence variants, which is time-consuming and expensive. We have developed a comprehensive next-generation sequencing (NGS)-based single-step assay to sequence the entire 2.2 Mb of the DMD gene to detect all copy number and sequence variants in both index males and carrier females. Assay validation was 100% concordant with other methodologies. A total of 772 samples have been tested, of which 62% (N = 480) were index cases with a clinical suspicion of DMD. Carrier testing females account for 38% (N = 292). Molecular diagnosis was confirmed in 86% (N = 413) of the index cases. Intragenic deletions and duplications (single-exon or multi-exon) were detected in 60% (N = 247) and 14% (N = 58) of the index cases, respectively. Full-sequence analysis of the entire gene allows for detection of deep intronic pathogenic variants and accurate breakpoint detection of CNVs involving similar exons, which could have an impact on the outcome of clinical trials. This comprehensive assay is highly sensitive for diagnostic testing for DMD and is also suitable for confirmatory testing for newborn screening for DMD.

Assessing Dysferlinopathy Patients Over Three Years With a New Motor Scale

OBJECTIVE

Dysferlinopathy is a muscular dystrophy with a highly variable clinical presentation and currently unpredictable progression. This variability and unpredictability presents difficulties for prognostication and clinical trial design. The Jain Clinical Outcomes Study of Dysferlinopathy aims to establish the validity of the North Star Assessment for Limb Girdle Type Muscular Dystrophies (NSAD) scale and identify factors that influence the rate of disease progression using NSAD.

METHODS

We collected a longitudinal series of functional assessments from 187 patients with dysferlinopathy over 3 years. Rasch analysis was used to develop the NSAD, a motor performance scale suitable for ambulant and nonambulant patients. Generalized estimating equations were used to evaluate the impact of patient factors on outcome trajectories.

RESULTS

The NSAD detected significant change in clinical progression over 1 year. The steepest functional decline occurred during the first 10 years after symptom onset, with more rapid decline noted in patients who developed symptoms at a younger age (p = 0.04). The most rapidly deteriorating group over the study was patients 3 to 8 years post symptom onset at baseline.

INTERPRETATION

The NSAD is the first validated limb girdle specific scale of motor performance, suitable for use in clinical practice and clinical trials. Longitudinal analysis showed it may be possible to identify patient factors associated with greater functional decline both across the disease course and in the short-term for clinical trial preparation. Through further work and validation in this cohort, we anticipate that a disease model incorporating functional performance will allow for more accurate prognosis for patients with dysferlinopathy. ANN NEUROL 2021;89:967-978.

Effects of Bisphosphonates on Osteoporosis Induced by Duchenne Muscular Dystrophy: A Prospective Study

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a severe X-linked progressive neuromuscular disease that brings a significantly increased risk of osteoporosis and bone fractures. We prospectively evaluated the effects of oral and intravenous bisphosphonates on the bones of children with DMD.

METHODS

This study included a total of 52 children with DMD. They were divided into zoledronic acid (ZOL), alendronate (ALN), and control groups according to bone mineral density (BMD) and history of fragility fractures. For 2 years, all patients took calcium, vitamin D, and calcitriol. Meanwhile, 17 patients received infusions of ZOL, and 18 patients received ALN. BMD, serum levels of alkaline phosphatase (ALP) and the cross-linked C-telopeptide of type I collagen (β-CTX) were evaluated.

RESULTS

After 24 months of treatment, the percentage changes in lumbar spine BMD were 23.2 ± 9.7% and 23.6 ± 8.8% in the ZOL and ALN groups (all P<.01 vs. baseline). The increases did not differ between the ZOL and ALN groups, but were significantly larger than those of the control group (P<.01). Serum β-CTX and ALP levels, respectively, were decreased by 44.4 ± 18.0% and 31.9 ± 26.7% in the ZOL group and by 36.0 ± 20.3% and 25.8 ± 14.4% in the ALN group (all P<.01 vs. baseline).

CONCLUSION

Zoledronic acid and alendronate had similar protective effects to increase bone mineral density and reduce bone resorption in children with DMD, which were superior to treatment of calcium, vitamin D, and calcitriol.

ABBREVIATIONS

25OHD = 25 hydroxyvitamin D; ALN = alendro-nate; ALP = alkaline phosphatase; ALT = alanine aminotransferase; BMD = bone mineral density; BP = bisphosphonate; Ca = calcium; β-CTX = cross-linked C-telopeptide of type I collagen; DMD = Duchenne muscular dystrophy; FN = femoral neck; GC = glucocorticoid; LS = lumbar spine; ZOL = zoledronic acid.

Combined Cell Therapy in the Treatment of Neurological Disorders

Cell therapy of neurological diseases is gaining momentum. Various types of stem/progenitor cells and their derivatives have shown positive therapeutic results in animal models of neurological disorders and in clinical trials. Each tested cell type proved to have its advantages and flaws and unique cellular and molecular mechanism of action, prompting the idea to test combined transplantation of two or more types of cells (combined cell therapy). This review summarizes the results of combined cell therapy of neurological pathologies reported up to this point. The number of papers describing experimental studies or clinical trials addressing this subject is still limited. However, its successful application to the treatment of neurological pathologies including stroke, spinal cord injury, neurodegenerative diseases, Duchenne muscular dystrophy, and retinal degeneration has been reported in both experimental and clinical studies. The advantages of combined cell therapy can be realized by simple summation of beneficial effects of different cells. Alternatively, one kind of cells can support the survival and functioning of the other by enhancing the formation of optimum environment or immunomodulation. No significant adverse events were reported. Combined cell therapy is a promising approach for the treatment of neurological disorders, but further research needs to be conducted.

Duchenne muscular dystrophy (DMD) cardiomyocyte-secreted exosomes promote the pathogenesis of DMD-associated cardiomyopathy

Cardiomyopathy is a leading cause of early mortality in Duchenne muscular dystrophy (DMD). There is a need to gain a better understanding of the molecular pathogenesis for the development effective therapies. Exosomes (exo) are secreted vesicles and exert effects via their RNA, lipid and protein cargo. The role of exosomes in disease pathology is unknown. Exosomes derived from stem cells have demonstrated cardioprotection in the murine DMD heart. However, it is unknown how the disease status of the donor cell type influences exosome function. Here, we sought to determine the phenotypic responses of DMD cardiomyocytes (DMD-iCMs) after long-term exposure to DMD cardiac exosomes (DMD-exo). DMD-iCMs were vulnerable to stress, evidenced by production of reactive oxygen species, the mitochondrial membrane potential and cell death levels. Long-term exposure to non-affected exosomes (N-exo) was protective. By contrast, long-term exposure to DMD-exo was not protective, and the response to stress improved with inhibition of DMD-exo secretion in vitro and in vivo The microRNA (miR) cargo, but not exosome surface peptides, was implicated in the pathological effects of DMD-exo. Exosomal surface profiling revealed N-exo peptides associated with PI3K-Akt signaling. Transcriptomic profiling identified unique changes with exposure to either N- or DMD-exo. Furthermore, DMD-exo miR cargo regulated injurious pathways, including p53 and TGF-beta. The findings reveal changes in exosomal cargo between healthy and diseased states, resulting in adverse outcomes. Here, DMD-exo contained miR changes, which promoted the vulnerability of DMD-iCMs to stress. Identification of these molecular changes in exosome cargo and effectual phenotypes might shed new light on processes underlying DMD cardiomyopathy.This article has an associated First Person interview with the first author of the paper.

The Impact of Treatment-Related Internet Health Information Seeking on Patient Compliance

Background: Patients are increasingly using technology to seek health information, particularly on treatments. Treatment-related internet health information-seeking behavior may have impact on patients' trust in their physicians and the patient-physician relationship. Therefore, understanding the impacts of treatment-related internet health information-seeking behavior on patient-physician relationship, especially patient compliance, from the perspective of trust is important. Methods: The established research model has two independent variables (emerging and mature treatment-related internet health information seeking), two mediators (cognition- and affect-based trust), and one dependent variable (patient compliance). All variables were measured using previously validated multiple-item scales. We collected data through a web-based questionnaire survey in China and obtained 336 valid responses. The questionnaire validity rate was 89.6% (336/375), and reliability and validity were acceptable. Finally, we used confirmatory factor analysis and structural equation modeling to test the hypotheses and develop the research model. Results: Cognition- and affect-based trust had a direct positive impact on patient compliance. Cognition-based trust had a direct positive impact on affect-based trust. Mature treatment-related internet health information seeking had a significant positive impact on patient compliance through patients' cognition- and affect-based trust in their physicians. However, the emerging treatment-related internet health information seeking indicated a nonsignificant impact on patients' cognition- and affect-based trust in their physicians. Conclusions: Providing patients with access to treatment-related internet health information will not have a negative impact on the patient-physician relationship. Instead, encouraging patients to seek treatment-related health information online can improve patient compliance. Physicians can also learn much about health information related to emerging treatments to enhance their professionalism and reliability.

An allosteric site on MKP5 reveals a strategy for small-molecule inhibition

The mitogen-activated protein kinase (MAPK) phosphatases (MKPs) have been considered "undruggable," but their position as regulators of the MAPKs makes them promising therapeutic targets. MKP5 has been suggested as a potential target for the treatment of dystrophic muscle disease. Here, we identified an inhibitor of MKP5 using a p38α MAPK-derived, phosphopeptide-based small-molecule screen. We solved the structure of MKP5 in complex with this inhibitor, which revealed a previously undescribed allosteric binding pocket. Binding of the inhibitor to this pocket collapsed the MKP5 active site and was predicted to limit MAPK binding. Treatment with the inhibitor recapitulated the phenotype of MKP5 deficiency, resulting in activation of p38 MAPK and JNK. We demonstrated that MKP5 was required for TGF-β1 signaling in muscle and that the inhibitor blocked TGF-β1-mediated Smad2 phosphorylation. TGF-β1 pathway antagonism has been proposed for the treatment of dystrophic muscle disease. Thus, allosteric inhibition of MKP5 represents a therapeutic strategy against dystrophic muscle disease.

Induced Pluripotent Stem Cells: Hope in the Treatment of Diseases, including Muscular Dystrophies

Induced pluripotent stem (iPS) cells are laboratory-produced cells that combine the biological advantages of somatic adult and stem cells for cell-based therapy. The reprogramming of cells, such as fibroblasts, to an embryonic stem cell-like state is done by the ectopic expression of transcription factors responsible for generating embryonic stem cell properties. These primary factors are octamer-binding transcription factor 4 (Oct3/4), sex-determining region Y-box 2 (Sox2), Krüppel-like factor 4 (Klf4), and the proto-oncogene protein homolog of avian myelocytomatosis (c-Myc). The somatic cells can be easily obtained from the patient who will be subjected to cellular therapy and be reprogrammed to acquire the necessary high plasticity of embryonic stem cells. These cells have no ethical limitations involved, as in the case of embryonic stem cells, and display minimal immunological rejection risks after transplant. Currently, several clinical trials are in progress, most of them in phase I or II. Still, some inherent risks, such as chromosomal instability, insertional tumors, and teratoma formation, must be overcome to reach full clinical translation. However, with the clinical trials and extensive basic research studying the biology of these cells, a promising future for human cell-based therapies using iPS cells seems to be increasingly clear and close.

Cardiac Involvement in Dystrophin-Deficient Females: Current Understanding and Implications for the Treatment of Dystrophinopathies

Duchenne muscular dystrophy (DMD) is a fatal X-linked recessive condition caused primarily by out-of-frame mutations in the dystrophin gene. In males, DMD presents with progressive body-wide muscle deterioration, culminating in death as a result of cardiac or respiratory failure. A milder form of DMD exists, called Becker muscular dystrophy (BMD), which is typically caused by in-frame dystrophin gene mutations. It should be emphasized that DMD and BMD are not exclusive to males, as some female dystrophin mutation carriers do present with similar symptoms, generally at reduced levels of severity. Cardiac involvement in particular is a pressing concern among manifesting females, as it may develop into serious heart failure or could predispose them to certain risks during pregnancy or daily life activities. It is known that about 8% of carriers present with dilated cardiomyopathy, though it may vary from 0% to 16.7%, depending on if the carrier is classified as having DMD or BMD. Understanding the genetic and molecular mechanisms underlying cardiac manifestations in dystrophin-deficient females is therefore of critical importance. In this article, we review available information from the literature on this subject, as well as discuss the implications of female carrier studies on the development of therapies aiming to increase dystrophin levels in the heart.

Prognostic factors for changes in the timed 4-stair climb in patients with Duchenne muscular dystrophy, and implications for measuring drug efficacy: A multi-institutional collaboration

The timed 4-stair climb (4SC) assessment has been used to measure function in Duchenne muscular dystrophy (DMD) practice and research. We sought to identify prognostic factors for changes in 4SC, assess their consistency across data sources, and the extent to which prognostic scores could be useful in DMD clinical trial design and analysis. Data from patients with DMD in the placebo arm of a phase 3 trial (Tadalafil DMD trial) and two real-world sources (Universitaire Ziekenhuizen, Leuven, Belgium [Leuven] and Cincinnati Children's Hospital Medical Center [CCHMC]) were analyzed. One-year changes in 4SC completion time and velocity (stairs/second) were analyzed. Prognostic models included age, height, weight, steroid use, and multiple timed function tests and were developed using multivariable regression, separately in each data source. Simulations were used to quantify impacts on trial sample size requirements. Data on 1-year changes in 4SC were available from the Tadalafil DMD trial (n = 92) Leuven (n = 67), and CCHMC (n = 212). Models incorporating multiple timed function tests, height, and weight significantly improved prognostic accuracy for 1-year change in 4SC (R²: 29%-36% for 4SC velocity, and 29%-34% for 4SC time) compared to models including only age, baseline 4SC and steroid duration (R²:8%-17% for 4SC velocity and 2%-13% for 4SC time). Measures of walking and rising ability contributed important prognostic information for changes in 4SC. In a randomized trial with equal allocation to treatment and placebo, adjustment for such a prognostic score would enable detection (at 80% power) of a treatment effect of 0.25 stairs/second with 100–120 patients, compared to 170–190 patients without prognostic score adjustment. Combining measures of ambulatory function doubled prognostic accuracy for 1-year changes in 4SC completion time and velocity. Randomized clinical trials incorporating a validated prognostic score could reduce sample size requirements by approximately 40%. Knowledge of important prognostic factors can also inform adjusted comparisons to external controls.

Lack of miR-378 attenuates muscular dystrophy in mdx mice

The severity of Duchenne muscular dystrophy (DMD), an incurable disease caused by the lack of dystrophin, might be modulated by different factors, including miRNAs. Among them, miR-378 is considered of high importance for muscle biology, but intriguingly, its role in DMD and its murine model (mdx mice) has not been thoroughly addressed so far. Here, we demonstrate that dystrophic mice additionally globally lacking miR-378 (double-KO [dKO] animals) exhibited better physical performance and improved absolute muscle force compared with mdx mice. Accordingly, markers of muscle damage in serum were significantly decreased in dKO mice, accompanied by diminished inflammation, fibrosis, and reduced abundance of regenerating fibers within muscles. The lack of miR-378 also normalized the aggravated fusion of dystrophin-deficient muscle satellite cells (mSCs). RNA sequencing of gastrocnemius muscle transcriptome revealed fibroblast growth factor 1 (Fgf1) as one of the most significantly downregulated genes in mice devoid of miR-378, indicating FGF1 as one of the mediators of changes driven by the lack of miR-378. In conclusion, we suggest that targeting miR-378 has the potential to ameliorate DMD pathology.

Advance genome editing technologies in the treatment of human diseases: CRISPR therapy (Review)

Genome editing techniques are considered to be one of the most challenging yet efficient tools for assisting therapeutic approaches. Several studies have focused on the development of novel methods to improve the efficiency of gene editing, as well as minimise their off-target effects. Clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (Cas9) is a tool that has revolutionised genome editing technologies. New applications of CRISPR/Cas9 in a broad range of diseases have demonstrated its efficiency and have been used in ex vivo models of somatic and pluripotent stem cells, as well as in in vivo animal models, and may eventually be used to correct defective genes. The focus of the present review was the recent applications of CRISPR/Cas9 and its contribution to the treatment of challenging human diseases, such as various types of cancer, neurodegenerative diseases and a broad spectrum of other disorders. CRISPR technology is a novel method for disease treatment, enhancing the effectiveness of drugs and improving the development of personalised medicine.

Expectations and anxieties of Duchenne muscular dystrophy patients and their families during the first-in-human clinical trial of NS-065/NCNP-01

Duchenne muscular dystrophy (DMD) is a recessive X-linked genetic disease caused by a mutation in the dystrophin gene. The new drug NS-065/NCNP-01 utilizing exon-skipping therapy targeting specific deletions has been used in a first-in-human trial for the treatment of DMD. We surveyed 10 pairs of DMD participants and their parents within this clinical trial via an iPad survey form and through interviews regarding their understanding of the trial, expectations, anxieties, and reasons for participating in the trial. Approximately half of the participants actively decided to participate of their own volition, and none considered quitting the trial. This indicates that participants participated more positively in this clinical trial than previously expected. However, some potential concerns were also revealed, with one being that the desire to please those around them might be more important to the DMD participants than the effects of the drug. Another issue is the possibility of biased information originating from the study subjects' parents; while seven out of 10 of the parents told their children that the study drug might work, only four of these parents also explained that it might not work. Only two study participants received an explanation concerning the drug's side effects from their parents. This result implies that caution should be taken when family expectations are high, and there is a possibility that subjects will be given biased information from their parents.

Comparative proteomic analyses of Duchenne muscular dystrophy and Becker muscular dystrophy muscles: changes contributing to preserve muscle function in Becker muscular dystrophy patients

BACKGROUND

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are characterized by muscle wasting leading to loss of ambulation in the first or third decade, respectively. In DMD, the lack of dystrophin hampers connections between intracellular cytoskeleton and cell membrane leading to repeated cycles of necrosis and regeneration associated with inflammation and loss of muscle ordered structure. BMD has a similar muscle phenotype but milder. Here, we address the question whether proteins at variance in BMD compared with DMD contribute to the milder phenotype in BMD, thus identifying a specific signature to be targeted for DMD treatment.

METHODS

Proteins extracted from skeletal muscle from DMD/BMD patients and young healthy subjects were either reduced and solubilized prior two-dimensional difference in gel electrophoresis/mass spectrometry differential analysis or tryptic digested prior label-free liquid chromatography with tandem mass spectrometry. Statistical analyses of proteins and peptides were performed by DeCyder and Perseus software and protein validation and verification by immunoblotting.

RESULTS

Proteomic results indicate minor changes in the extracellular matrix (ECM) protein composition in BMD muscles with retention of mechanotransduction signalling, reduced changes in cytoskeletal and contractile proteins. Conversely, in DMD patients, increased levels of several ECM cytoskeletal and contractile proteins were observed whereas some proteins of fast fibres and of Z-disc decreased. Detyrosinated alpha-tubulin was unchanged in BMD and increased in DMD although neuronal nitric oxide synthase was unchanged in BMD and greatly reduced in DMD. Metabolically, the tissue is characterized by a decrement of anaerobic metabolism both in DMD and BMD compared with controls, with increased levels of the glycogen metabolic pathway in BMD. Oxidative metabolism is severely compromised in DMD with impairment of malate shuttle; conversely, it is active in BMD supporting the tricarboxylic acid cycle and respiratory chain. Adipogenesis characterizes DMD, whereas proteins involved in fatty acids beta-oxidation are increased in BMD. Proteins involved in protein/amino acid metabolism, cell development, calcium handling, endoplasmic reticulum/sarcoplasmic reticulum stress response, and inflammation/immune response were increased in DMD. Both disorders are characterized by the impairment of N-linked protein glycosylation in the endoplasmic reticulum. Authophagy was decreased in DMD whereas it was retained in BMD.

CONCLUSIONS

The mechanosensing and metabolic disruption are central nodes of DMD/BMD phenotypes. The ECM proteome composition and the metabolic rewiring in BMD lead to preservation of energy levels supporting autophagy and cell renewal, thus promoting the retention of muscle function. Conversely, DMD patients are characterized by extracellular and cytoskeletal protein dysregulation and by metabolic restriction at the level of α-ketoglutarate leading to shortage of glutamate-derived molecules that over time triggers lipogenesis and lipotoxicity.

CRISPR-Generated Animal Models of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal X-linked recessive neuromuscular disorder most commonly caused by mutations disrupting the reading frame of the dystrophin (DMD) gene. DMD codes for dystrophin, which is critical for maintaining the integrity of muscle cell membranes. Without dystrophin, muscle cells receive heightened mechanical stress, becoming more susceptible to damage. An active body of research continues to explore therapeutic treatments for DMD as well as to further our understanding of the disease. These efforts rely on having reliable animal models that accurately recapitulate disease presentation in humans. While current animal models of DMD have served this purpose well to some extent, each has its own limitations. To help overcome this, clustered regularly interspaced short palindromic repeat (CRISPR)-based technology has been extremely useful in creating novel animal models for DMD. This review focuses on animal models developed for DMD that have been created using CRISPR, their advantages and disadvantages as well as their applications in the DMD field.

Increased dystrophin production with golodirsen in patients with Duchenne muscular dystrophy

Objective

To report safety, pharmacokinetics, exon 53 skipping, and dystrophin expression in golodirsen-treated patients with Duchenne muscular dystrophy (DMD) amenable to exon 53 skipping.

Methods

Part 1 was a randomized, double-blind, placebo-controlled, 12-week dose titration of once-weekly golodirsen; part 2 is an ongoing, open-label evaluation. Safety and pharmacokinetics were primary and secondary objectives of part 1. Primary biological outcome measures of part 2 were blinded exon skipping and dystrophin protein production on muscle biopsies (baseline, week 48) evaluated, respectively, using reverse transcription PCR and Western blot and immunohistochemistry.

Results

Twelve patients were randomized to receive golodirsen (n = 8) or placebo (n = 4) in part 1. All from part 1 plus 13 additional patients received 30 mg/kg golodirsen in part 2. Safety findings were consistent with those previously observed in pediatric patients with DMD. Most of the study drug was excreted within 4 hours following administration. A significant increase in exon 53 skipping was associated with ∼16-fold increase over baseline in dystrophin protein expression at week 48, with a mean percent normal dystrophin protein standard of 1.019% (range, 0.09%–4.30%). Sarcolemmal localization of dystrophin was demonstrated by significantly increased dystrophin-positive fibers (week 48, p < 0.001) and a positive correlation (Spearman r = 0.663; p < 0.001) with dystrophin protein change from baseline, measured by Western blot and immunohistochemistry.

Conclusion

Golodirsen was well-tolerated; muscle biopsies from golodirsen-treated patients showed increased exon 53 skipping, dystrophin production, and correct dystrophin sarcolemmal localization.

Clinicaltrials.gov identifier

NCT02310906.

Classification of evidence

This study provides Class I evidence that golodirsen is safe and Class IV evidence that it induces exon skipping and novel dystrophin as confirmed by 3 different assays.

The Genetic Landscape of Dystrophin Mutations in Italy: A Nationwide Study

Dystrophinopathies are inherited diseases caused by mutations in the dystrophin (DMD) gene for which testing is mandatory for genetic diagnosis, reproductive choices and eligibility for personalized trials. We genotyped the DMD gene in our Italian cohort of 1902 patients (BMD n = 740, 39%; DMD n =1162, 61%) within a nationwide study involving 11 diagnostic centers in a 10-year window (2008–2017). In DMD patients, we found deletions in 57%, duplications in 11% and small mutations in 32%. In BMD, we found deletions in 78%, duplications in 9% and small mutations in 13%. In BMD, there are a higher number of deletions, and small mutations are more frequent than duplications. Among small mutations that are generally frequent in both phenotypes, 44% of DMD and 36% of BMD are nonsense, thus, eligible for stop codon read-through therapy; 63% of all out-of-frame deletions are eligible for single exon skipping. Patients were also assigned to Italian regions and showed interesting regional differences in mutation distribution. The full genetic characterization in this large, nationwide cohort has allowed us to draw several correlations between DMD/BMD genotype landscapes and mutation frequency, mutation types, mutation locations along the gene, exon/intron architecture, and relevant protein domain, with effects on population genetic characteristics and new personalized therapies.

Multiple poloxamers increase plasma membrane repair capacity in muscle and nonmuscle cells

Various previous studies established that the amphiphilic tri-block copolymer known as poloxamer 188 (P188) or Pluronic-F68 can stabilize the plasma membrane following a variety of injuries to multiple mammalian cell types. This characteristic led to proposals for the use of P188 as a therapeutic treatment for various disease states, including muscular dystrophy. Previous studies suggest that P188 increases plasma membrane integrity by resealing plasma membrane disruptions through its affinity for the hydrophobic lipid chains on the lipid bilayer. P188 is one of a large family of copolymers that share the same basic tri-block structure consisting of a middle hydrophobic propylene oxide segment flanked by two hydrophilic ethylene oxide moieties [poly(ethylene oxide)80-poly(propylene oxide)27-poly(ethylene oxide)80]. Despite the similarities of P188 to the other poloxamers in this chemical family, there has been little investigation into the membrane-resealing properties of these other poloxamers. In this study we assessed the resealing properties of poloxamers P181, P124, P182, P234, P108, P407, and P338 on human embryonic kidney 293 (HEK293) cells and isolated muscle from the mdx mouse model of Duchenne muscular dystrophy. Cell membrane injuries from glass bead wounding and multiphoton laser injury show that the majority of poloxamers in our panel improved the plasma membrane resealing of both HEK293 cells and dystrophic muscle fibers. These findings indicate that many tri-block copolymers share characteristics that can increase plasma membrane resealing and that identification of these shared characteristics could help guide design of future therapeutic approaches.

In Vivo Myoblasts Tracking Using the Sodium Iodide Symporter Gene Expression in Dogs

Stem cell-based therapies are a promising approach for the treatment of degenerative muscular diseases; however, clinical trials have shown inconclusive and even disappointing results so far. Noninvasive cell monitoring by medicine imaging could improve the understanding of the survival and biodistribution of cells following injection. In this study, we assessed the canine sodium iodide symporter (cNIS) reporter gene as an imaging tool to track by single-photon emission computed tomography (SPECT/CT) transduced canine myoblasts after intramuscular (IM) administrations in dogs. cNIS-expressing cells kept their myogenic capacities and showed strong ^{99 m}Tc-pertechnetate (^{99 m}TcO₄⁻) uptake efficiency both in vitro and in vivo. cNIS expression allowed visualization of cells by SPECT/CT along time: 4 h, 48 h, 7 days, and 30 days after IM injection; biopsies collected 30 days post administration showed myofiber’s membranes expressing cNIS. This study demonstrates that NIS can be used as a reporter to track cells in vivo in the skeletal muscle of large animals. Our results set a proof of concept of the benefits NIS-tracking tool may bring to the already challenging cell-based therapies arena in myopathies and pave the way to a more efficient translation to the clinical setting from more accurate pre-clinical results.