Tamoxifen in Duchenne muscular dystrophy (TAMDMD): study protocol for a multicenter, randomized, placebo-controlled, double-blind phase 3 trial

Targeted genetic therapies for inherited disorders that affect both cardiac and skeletal muscle

Skeletal myopathies and ataxias with secondary cardiac involvement are complex, progressive and debilitating conditions. As life expectancy increases across these conditions, cardiac involvement often becomes more prominent. This highlights the need for targeted therapies that address these evolving cardiac pathologies. Musculopathies by and large lack cures that directly target the genetic basis of the diseases; however, as our understanding of the genetic causes of these conditions has evolved, it has become tractable to develop targeted therapies using biologics, to design precision approaches to target the primary genetic causes of these varied diseases. Using the examples of Duchenne muscular dystrophy, Friedreich ataxia and Pompe disease, we discuss how the genetic causes of such diseases derail diverse homeostatic, energetic and signalling pathways, which span multiple cellular systems in varied tissues across the body. We outline existing therapeutics and treatments in the context of emerging novel genetic approaches. We discuss the hurdles that the field must overcome to deliver targeted therapies across the many tissue types affected in primary myopathies.

Beneficial immune-modulatory effects of the N-163 strain of Aureobasidium pullulans-produced 1,3-1,6 Beta glucans in Duchenne muscular dystrophy: Results of an open-label, prospective, exploratory case-control clinical study

Background

This exploratory case-control study is to evaluate the effects of supplementation of Aureobasidium pullulans-N-163 strain produced 1,3-1,- 6 beta glucan in young patients with Duchenne muscular dystrophy (DMD).

Methods

Twenty-seven male subjects aged 5-19 years with DMD were included, nine in the control arm and 18 in the treatment arm to receive N-163 beta glucan along with conventional therapies for 45 days. While performing the analysis, steroid usage was also taken into consideration, those not administered steroids (Steroid -ve) (Control, n = 5; treatment, n = 9), those administered steroids (Steroid +ve) (Control, n = 4; treatment, n = 9).

Results

IL-6 showed a significant decrease in the treatment groups, especially the N-163 Steroid -ve group. IL-13 decreased in both treatment groups and TGF-β levels showed a significant decrease in the treatment groups, especially the N-163 Steroid -ve group, (p < 0.05). Dystrophin levels increased by up to 32% in the treatment groups compared to the control. Medical research council (MRC) grading showed slight improvement in muscle strength improvement in 12 out of 18 patients (67%) in the treatment group and four out of nine (44%) subjects in the control group.

Conclusion

Supplementation with the N-163 beta glucan food supplement produced beneficial effects: a significant decrease in inflammation and fibrosis markers, increase in serum dystrophin and slight improvement in muscle strength in DMD subjects over 45 days, thus making this a potential adjunct treatment for DMD after validation.

Trial registration

The study was registered in Clinical trials registry of India, CTRI/2021/05/033346. Registered on 5th May, 2021.

Rasch analysis of the 32-item motor function measure in ambulant patients with Duchenne muscular dystrophy

OBJECTIVE

This study analyzed the 32-item Motor Function Measure in a cohort of ambulatory patients with Duchenne muscular dystrophy using Rasch measurement methods.

DESIGN

This is a psychometric study.

SETTING

Rehabilitation centre of a large public children's hospital in Shenzhen, China.

PARTICIPANTS

Data from 176 genetically confirmed ambulant patients with Duchenne muscular dystrophy (mean age 7.3 years, SD 2.3 years, range 3.1-13.1 years) were analyzed.

RESULTS

Rasch analyses supported the Motor Function Measure domain D1 as a reliable (person reliability  =  0.88, person separation index  =  2.71) and valid (acceptable targeting, little misfit, minimal category disordering) measure in ambulant patients with Duchenne muscular dystrophy. Remodelling the domain D1 by collapsing item 25 from 4 to 3 response categories addressed the problematic disordered thresholds, resulting in a rebuilt domain D1 with enhanced measurement properties. However, findings for domains D2 and D3 did not fulfil most Rasch model expectations. There were disordered thresholds for most items in domains D2 and D3, with low reliability coefficients, item mistargeting and misfit, and large ceiling effects.

CONCLUSION

Rasch analyses confirmed that the Motor Function Measure domain D1 was reliable and valid and provided a unidimensional measure for motor function in ambulant Duchenne muscular dystrophy patients. Accuracy of measurement had been enhanced through remodelling, and a rebuilt domain D1 with category collapsing for item 25 was proposed. The analysis revealed multiple limitations of the domains D2 and D3 that certain essential psychometrics were poorly met and, therefore, should be used with caution in this patient group.

A state-of-the-art review of tamoxifen as a potential therapeutic for duchenne muscular dystrophy

Introduction: This systematic review analyzes the state-of-art repurposing of the drug tamoxifen (TAM) in the treatment of Duchenne Muscular Dystrophy (DMD), including its mechanism of action, toxicological findings, and past and ongoing clinical trials. A parallel aim of this work was to explore whether evidence exists to support further funding of investigation on TAM treatment for DMD patients with a pivotal trial in young patients. Bringing evidence and answering the scientific question of whether this treatment could improve the quality-of-life of DMD patients is needed to establish guidelines and accelerate access to promising therapies for DMD patients. Methods: The search was conducted in January 2022 utilizing PubMed. All MeSH terms for "Duchenne Muscular Dystrophy" and "tamoxifen" were used. The inclusion and exclusion criteria were defined according to the PICOS framework. Results: The included publications all explored the use of TAM with promising outcomes in muscular strength recovery and a decrease in pathology biomarkers. Two reviews recognize TAM as a potential treatment for DMD patients and state that drug repurposing plays a crucial role in the quest for a drug candidate to treat this rare disease. Conclusion: According to available data, TAM shows promise as a treatment for DMD, both pharmacologically and clinically. However, published data to date are insufficient to definitively conclude the beneficial effect of TAM on quality-of-life and ultimately survival, particularly in the youngest patients diagnosed with DMD.

Identifying obstacles hindering the conduct of academic-sponsored trials for drug repurposing on rare-diseases: an analysis of six use cases

Background

Academic-sponsored trials for rare diseases face many challenges; the present paper identifies hurdles in the set-up of six multinational clinical trials for drug repurposing, as use cases.

Methods

Six academic-sponsored multinational trials aiming to generate knowledge on rare diseases drug repurposing were used as examples to identify problems in their set-up. Coordinating investigators leading these trials provided feedback on hurdles linked to study, country, and site set up, on the basis of pre-identified categories established through the analysis of previous peer-reviewed publications.

Results

Administrative burden and lack of harmonization for trial-site agreements were deemed as a major hurdle. Other main identified obstacles included the following: (1) complexity and restriction on the use of public funding, especially in a multinational set up, (2) drug supply, including procurement tendering rules and country-specific requirements for drug stability, and (3) lack of harmonization on regulatory requirements to get trial approvals.

Conclusion

A better knowledge of the non-commercial clinical research landscape and its challenges and requirements is needed to make drugs—especially those with less commercial gain—accessible to rare diseases patients. Better information about existing resources like research infrastructures, clinical research programs, and counseling mechanisms is needed to support and guide clinicians through the many challenges associated to the set-up of academic-sponsored multinational trials.

Ambulatory Duchenne muscular dystrophy children: cross-sectional correlation between function, quantitative muscle ultrasound and MRI

Duchenne muscular dystrophy (DMD) is a progressive genetic muscle disease. Quantitative muscle ultrasound (US), muscle MRI, and functional tools are important to delineate characteristics of muscle involvement. We aimed to establish correlations between clinical/functional and above-named imaging tools respecting their diagnostic and prognostic role in DMD children. A cross-sectional retrospective study of 27 steroid-naive, ambulant male children/adolescents with genetically-confirmed DMD (mean age, 8.8 ± 3.3 years). Functional performance was assessed using motor function measure (MFM) which assess standing/transfer (D1), proximal (D2) and distal (D3) motor function, and six-minute walk test (6MWT). Imaging evaluation included quantitative muscle MRI which measured muscle fat content in a specific location of right rectus femoris by mDixon sequence. Quantitative muscle US measured right rectus femoris muscle brightness in standardized US image as an indicator of muscle fat content. We found a highly significant positive correlation between the mean MFM total score and 6MWT (R = 0.537, p = 0.007), and a highly significant negative correlation between fat content by muscle US and MFM total score (R = -0.603, p = 0.006) and its D1 subscore (R =-0.712, p = 0.001), and a significant negative correlation between fat content by US and 6MWT (R = -0.529, p = 0.02), and a significant positive correlation between muscle fat content by mDixon MRI and patient's age (R = 0.617, p = 0.01). Quantitative muscle US correlates significantly with clinical/functional assessment tools as MFM and 6MWT, and augments their role in disease-tracking of DMD. Quantitative muscle US has the potential to act as a substitute to functional assessment tools.

Tamoxifen treatment ameliorates contractile dysfunction of Duchenne muscular dystrophy stem cell-derived cardiomyocytes on bioengineered substrates

Duchenne muscular dystrophy (DMD) is a progressive genetic myopathy that leads to heart failure from dilated cardiomyopathy by early adulthood. Recent evidence suggests that tamoxifen, a selective estrogen receptor modulator widely used to treat breast cancer, ameliorates DMD cardiomyopathy. However, the mechanism of action of 4-hydroxytamoxifen, the active metabolite of tamoxifen, on cardiomyocyte function remains unclear. To examine the effects of chronic 4-hydroxytamoxifen treatment, we used state-of-the-art human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and a bioengineered platform to model DMD. We assessed the beating rate and beating velocity of iPSC-CMs in monolayers and as single cells on micropatterns that promote a physiological cardiomyocyte morphology. We found that 4-hydroxytamoxifen treatment of DMD iPSC-CMs decreased beating rate, increased beating velocity, and ameliorated calcium-handling deficits, leading to prolonged viability. Our study highlights the utility of a bioengineered iPSC-CM platform for drug testing and underscores the potential of repurposing tamoxifen as a therapy for DMD cardiomyopathy.

Antioxidants to prevent respiratory decline in people with Duchenne muscular dystrophy and progressive respiratory decline

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterised by progressive muscle weakness beginning in early childhood. Respiratory failure and weak cough develop in all patients as a consequence of muscle weakness leading to a risk of atelectasis, pneumonia, or the need for ventilatory support. There is no curative treatment for DMD. Corticosteroids are the only pharmacological intervention proven to delay the onset and progression of muscle weakness and thus respiratory decline in DMD. Antioxidant treatment has been proposed to try to reduce muscle weakness in general, and respiratory decline in particular.  OBJECTIVES: To assess the effects of antioxidant agents on preventing respiratory decline in people with Duchenne muscular dystrophy during the respiratory decline phase of the condition.  SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, and two trials registers to 23 March 2021, together with reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs that met our inclusion criteria. We included male patients with a diagnosis of DMD who had respiratory decline evidenced by a forced vital capacity (FVC%) less than 80% but greater than 30% of predicted values, receiving any antioxidant agent compared with other therapies for the management of DMD or placebo.  DATA COLLECTION AND ANALYSIS: Two review authors screened studies for eligibility, assessed risk of bias of studies, and extracted data. We used standard methods expected by Cochrane. We assessed the certainty of the evidence using the GRADE approach. The primary outcomes were FVC and hospitalisation due to respiratory infections. Secondary outcomes were quality of life, adverse events, change in muscle function, forced expiratory volume in the first second (FEV1), and peak expiratory flow (PEF).  MAIN RESULTS: We included one study with 66 participants who were not co-treated with corticosteroids, which was the only study to contribute data to our main analysis. We also included a study that enrolled 255 participants treated with corticosteroids, which was only available as a press release without numerical results. The studies were parallel-group RCTs that assessed the effect of idebenone on respiratory function compared to placebo. The trial that contributed numerical data included patients with a mean (standard deviation) age of 14.3 (2.7) years at the time of inclusion, with a documented diagnosis of DMD or severe dystrophinopathy with clinical features consistent with typical DMD. The overall risk of bias across most outcomes was similar and judged as 'low'.  Idebenone may result in a slightly less of a decline in FVC from baseline to one year compared to placebo (mean difference (MD) 3.28%, 95% confidence interval (CI) -0.41 to 6.97; 64 participants; low-certainty evidence), and probably has little or no effect on change in quality of life (MD -3.80, 95% CI -10.09 to 2.49; 63 participants; moderate-certainty evidence) (Pediatric Quality of Life Inventory (PedsQL), range 0 to 100, 0 = worst, 100 = best quality of life). As a related but secondary outcome, idebenone may result in less of a decline from baseline in FEV1 (MD 8.28%, 95% CI 0.89 to 15.67; 53 participants) and PEF (MD 6.27%, 95% CI 0.61 to 11.93; 1 trial, 64 participants) compared to placebo. Idebenone was associated with fewer serious adverse events (RR 0.42, 95% CI 0.09 to 2.04; 66 participants; low-certainty evidence) and little to no difference in non-serious adverse events (RR 1.00, 95% CI 0.88 to 1.13; 66 participants; low-certainty evidence) compared to placebo. Idebenone may result in little to no difference in change in arm muscle function (MD -2.45 N, 95% CI -8.60 to 3.70 for elbow flexors and MD -1.06 N, 95% CI -6.77 to 4.65 for elbow extensors; both 52 participants) compared to placebo. We found no studies evaluating the outcome hospitalisation due to respiratory infection.  The second trial, involving 255 participants, for which data were available only as a press release without numerical data, was prematurely discontinued due to futility after an interim efficacy analysis based on FVC. There were no safety concerns. The certainty of the evidence was low for most outcomes due to imprecision and publication bias (the lack of a full report of the larger trial, which was prematurely terminated).

AUTHORS' CONCLUSIONS

Idebenone is the only antioxidant agent tested in RCTs for preventing respiratory decline in people with DMD for which evidence was available for assessment. Idebenone may result in slightly less of a decline in FVC and less of a decline in FEV1 and PEF, but probably has little to no measurable effect on change in quality of life. Idebenone is associated with fewer serious adverse events than placebo. Idebenone may result in little to no difference in change in muscle function. Discontinuation due to the futility of the SIDEROS trial and its expanded access programmes may indicate that idebenone research in this condition is no longer needed, but we await the trial data. Further research is needed to establish the effect of different antioxidant agents on preventing respiratory decline in people with DMD during the respiratory decline phase of the condition.

Antioxidants to prevent respiratory decline in people with Duchenne muscular dystrophy and progressive respiratory decline

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterised by progressive muscle weakness beginning in early childhood. Respiratory failure and weak cough develop in all patients as a consequence of muscle weakness leading to a risk of atelectasis, pneumonia, or the need for ventilatory support. There is no curative treatment for DMD. Corticosteroids are the only pharmacological intervention proven to delay the onset and progression of muscle weakness and thus respiratory decline in DMD. Antioxidant treatment has been proposed to try to reduce muscle weakness in general, and respiratory decline in particular.  OBJECTIVES: To assess the effects of antioxidant agents on preventing respiratory decline in people with Duchenne muscular dystrophy during the respiratory decline phase of the condition.  SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, and two trials registers to 23 March 2021, together with reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs that met our inclusion criteria. We included male patients with a diagnosis of DMD who had respiratory decline evidenced by a forced vital capacity (FVC%) less than 80% but greater than 30% of predicted values, receiving any antioxidant agent compared with other therapies for the management of DMD or placebo.  DATA COLLECTION AND ANALYSIS: Two review authors screened studies for eligibility, assessed risk of bias of studies, and extracted data. We used standard methods expected by Cochrane. We assessed the certainty of the evidence using the GRADE approach. The primary outcomes were FVC and hospitalisation due to respiratory infections. Secondary outcomes were quality of life, adverse events, change in muscle function, forced expiratory volume in the first second (FEV1), and peak expiratory flow (PEF).  MAIN RESULTS: We included one study with 66 participants who were not co-treated with corticosteroids, which was the only study to contribute data to our main analysis. We also included a study that enrolled 255 participants treated with corticosteroids, which was only available as a press release without numerical results. The studies were parallel-group RCTs that assessed the effect of idebenone on respiratory function compared to placebo. The trial that contributed numerical data included patients with a mean (standard deviation) age of 14.3 (2.7) years at the time of inclusion, with a documented diagnosis of DMD or severe dystrophinopathy with clinical features consistent with typical DMD. The overall risk of bias across most outcomes was similar and judged as 'low'.  Idebenone may result in a slightly less of a decline in FVC from baseline to one year compared to placebo (mean difference (MD) 3.28%, 95% confidence interval (CI) -0.41 to 6.97; 64 participants; low-certainty evidence), and probably has little or no effect on change in quality of life (MD -3.80, 95% CI -10.09 to 2.49; 63 participants; moderate-certainty evidence) (Pediatric Quality of Life Inventory (PedsQL), range 0 to 100, 0 = worst, 100 = best quality of life). As a related but secondary outcome, idebenone may result in less of a decline from baseline in FEV1 (MD 8.28%, 95% CI 0.89 to 15.67; 53 participants) and PEF (MD 6.27%, 95% CI 0.61 to 11.93; 1 trial, 64 participants) compared to placebo. Idebenone was associated with fewer serious adverse events (RR 0.42, 95% CI 0.09 to 2.04; 66 participants; low-certainty evidence) and little to no difference in non-serious adverse events (RR 1.00, 95% CI 0.88 to 1.13; 66 participants; low-certainty evidence) compared to placebo. Idebenone may result in little to no difference in change in arm muscle function (MD -2.45 N, 95% CI -8.60 to 3.70 for elbow flexors and MD -1.06 N, 95% CI -6.77 to 4.65 for elbow extensors; both 52 participants) compared to placebo. We found no studies evaluating the outcome hospitalisation due to respiratory infection.  The second trial, involving 255 participants, for which data were available only as a press release without numerical data, was prematurely discontinued due to futility after an interim efficacy analysis based on FVC. There were no safety concerns. The certainty of the evidence was low for most outcomes due to imprecision and publication bias (the lack of a full report of the larger trial, which was prematurely terminated).

AUTHORS' CONCLUSIONS

Idebenone is the only antioxidant agent tested in RCTs for preventing respiratory decline in people with DMD for which evidence was available for assessment. Idebenone may result in slightly less of a decline in FVC and less of a decline in FEV1 and PEF, but probably has little to no measurable effect on change in quality of life. Idebenone is associated with fewer serious adverse events than placebo. Idebenone may result in little to no difference in change in muscle function. Discontinuation due to the futility of the SIDEROS trial and its expanded access programmes may indicate that idebenone research in this condition is no longer needed, but we await the trial data. Further research is needed to establish the effect of different antioxidant agents on preventing respiratory decline in people with DMD during the respiratory decline phase of the condition.

Molecular and cellular basis of genetically inherited skeletal muscle disorders

Neuromuscular disorders comprise a diverse group of human inborn diseases that arise from defects in the structure and/or function of the muscle tissue - encompassing the muscle cells (myofibres) themselves and their extracellular matrix - or muscle fibre innervation. Since the identification in 1987 of the first genetic lesion associated with a neuromuscular disorder - mutations in dystrophin as an underlying cause of Duchenne muscular dystrophy - the field has made tremendous progress in understanding the genetic basis of these diseases, with pathogenic variants in more than 500 genes now identified as underlying causes of neuromuscular disorders. The subset of neuromuscular disorders that affect skeletal muscle are referred to as myopathies or muscular dystrophies, and are due to variants in genes encoding muscle proteins. Many of these proteins provide structural stability to the myofibres or function in regulating sarcolemmal integrity, whereas others are involved in protein turnover, intracellular trafficking, calcium handling and electrical excitability - processes that ensure myofibre resistance to stress and their primary activity in muscle contraction. In this Review, we discuss how defects in muscle proteins give rise to muscle dysfunction, and ultimately to disease, with a focus on pathologies that are most common, best understood and that provide the most insight into muscle biology.

Common Pathogenic Mechanisms in Centronuclear and Myotubular Myopathies and Latest Treatment Advances

Centronuclear myopathies (CNM) are rare congenital disorders characterized by muscle weakness and structural defects including fiber hypotrophy and organelle mispositioning. The main CNM forms are caused by mutations in: the MTM1 gene encoding the phosphoinositide phosphatase myotubularin (myotubular myopathy), the DNM2 gene encoding the mechanoenzyme dynamin 2, the BIN1 gene encoding the membrane curvature sensing amphiphysin 2, and the RYR1 gene encoding the skeletal muscle calcium release channel/ryanodine receptor. MTM1, BIN1, and DNM2 proteins are involved in membrane remodeling and trafficking, while RyR1 directly regulates excitation-contraction coupling (ECC). Several CNM animal models have been generated or identified, which confirm shared pathological anomalies in T-tubule remodeling, ECC, organelle mispositioning, protein homeostasis, neuromuscular junction, and muscle regeneration. Dynamin 2 plays a crucial role in CNM physiopathology and has been validated as a common therapeutic target for three CNM forms. Indeed, the promising results in preclinical models set up the basis for ongoing clinical trials. Another two clinical trials to treat myotubular myopathy by MTM1 gene therapy or tamoxifen repurposing are also ongoing. Here, we review the contribution of the different CNM models to understanding physiopathology and therapy development with a focus on the commonly dysregulated pathways and current therapeutic targets.

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.

Catalpol counteracts the pathology in a mouse model of Duchenne muscular dystrophy by inhibiting the TGF-β1/TAK1 signaling pathway

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by a mutation in the gene encoding the dystrophin protein. Catalpol is an iridoid glycoside found in Chinese herbs with anti-inflammatory, anti-oxidant, anti-apoptotic, and hypoglycemic activities that can protect against muscle wasting. In the present study we investigated the effects of catalpol on DMD. Aged Dystrophin-deficient (mdx) mice (12 months old) were treated with catalpol (100, 200 mg·kg-1·d-1, ig) for 6 weeks. At the end of the experiment, the mice were sacrificed, and gastrocnemius (GAS), tibialis anterior (TA), extensor digitorum longus (EDL), soleus (SOL) muscles were collected. We found that catalpol administration dose-dependently increased stride length and decreased stride width in Gait test. Wire grip test showed that the time of wire grip and grip strength were increased. We found that catalpol administration dose-dependently alleviated skeletal muscle damage, evidenced by reduced plasma CK and LDH activity as well as increased the weight of skeletal muscles. Catalpol administration had no effect on dystrophin expression, but exerted anti-inflammatory effects. Furthermore, catalpol administration dose-dependently decreased tibialis anterior (TA) muscle fibrosis, and inhibited the expression of TGF-β1, TAK1 and α-SMA. In primary myoblasts from mdx mice, knockdown of TAK1 abolished the inhibitory effects of catalpol on the expression levels of TGF-β1 and α-SMA. In conclusion, catalpol can restore skeletal muscle strength and alleviate skeletal muscle damage in aged mdx mice, thus may provide a novel therapy for DMD. Catalpol attenuates muscle fibrosis by inhibiting the TGF-β1/TAK1 signaling pathway.

Safety and clinical outcome of tamoxifen in Duchenne Muscular Dystrophy

Patients having Duchenne Muscular Dystrophy (DMD) are currently being treated with corticosteroids, which slow down disease progression at the expense of serious adverse effects. Tamoxifen is a pro-drug some of whose metabolites interact with the nuclear estrogen receptor, leading to anti-fibrotic and muscle-protective effects as has been demonstrated in a murine model of DMD. Here we report the results from a monocentric single arm prospective study in 13 ambulant boys aged 6-14 years with genetically confirmed DMD, aimed to assess the safety of tamoxifen and its impact on disease progression. Boys were treated for up to 3 years with 20 mg/day of oral tamoxifen, in addition to their ongoing corticosteroid treatment. For 8 of these patients, outcome was compared to an age- and performance-matched 12-month natural history dataset. The primary end point was the 6-minute walk test. Secondary end points were the NorthStar assessment, timed function tests, pulmonary function, the biomarker creatine phosphokinase and adverse effects. No adverse effects were noticed other than mild gynecomastia in 4 boys. Tamoxifen-treated patients retained motor and respiratory function, compared with a significant deterioration of age-matched historical control patients receiving corticosteroids only. These encouraging findings warrant a larger clinical trial to substantiate the use of tamoxifen in Duchenne Muscular Dystrophy.

Drug Safety in Translational Paediatric Research: Practical Points to Consider for Paediatric Safety Profiling and Protocol Development: A Scoping Review

Translational paediatric drug development includes the exchange between basic, clinical and population-based research to improve the health of children. This includes the assessment of treatment related risks and their management. The objectives of this scoping review were to search and summarise the literature for practical guidance on how to establish a paediatric safety specification and its integration into a paediatric protocol. PubMed, Embase, Web of Science, and websites of regulatory authorities and learned societies were searched (up to 31 December 2020). Retrieved citations were screened and full texts reviewed where applicable. A total of 3480 publications were retrieved. No article was identified providing practical guidance. An introduction to the practical aspects of paediatric safety profiling and protocol development is provided by combining health authority and learned society guidelines with the specifics of paediatric research. The paediatric safety specification informs paediatric protocol development by, for example, highlighting the need for a pharmacokinetic study prior to a paediatric trial. It also informs safety related protocol sections such as exclusion criteria, safety monitoring and risk management. In conclusion, safety related protocol sections require an understanding of the paediatric safety specification. Safety data from carefully planned paediatric research provide valuable information for children, parents and healthcare providers.

Advances in Treatments in Muscular Dystrophies and Motor Neuron Disorders

Increased understanding of disease pathophysiology and advances in gene therapies and drug technologies are revolutionizing treatment of muscular dystrophies and motor neuron disorders (MNDs). New drugs have been approved for Duchenne muscular dystrophy, spinal muscular atrophy, and amyotrophic lateral sclerosis. For other diseases, new targets have been identified, and new therapies are in clinical trials. The impact of such therapies will be fully understood only in the next decades. Cost burden and accessibility are major challenges in the wide application of new drugs. This article reviews advances in gene therapies, newly approved drugs, and therapeutic promises in muscular dystrophies and MNDs.

Recent advances of glucocorticoids in the treatment of Duchenne muscular dystrophy (Review)

Duchenne muscular dystrophy (DMD) is the most common degenerative neuromuscular disease. The incidence of DMD in live births is 1/3,600-1/6,000. Although glucocorticoid-dependent medication is the mainstay treatment option for DMD, a standard treatment regimen has yet to be determined. The present review discusses the literature on the timing, methods and courses of glucocorticoid treatment for DMD. The review highlights the importance of the immediate commencement of glucocorticoid treatment following the diagnosis of DMD, with weekend-only administration being advantageous. Adherence to long-term single-glucocorticoid therapy can delay the loss of ambulation ability, and the side effects of the treatment are controllable. However, the standard medication for patients of different ages and stages of disease development, and the use of combination therapy require further investigation.

Molecular correction of Duchenne muscular dystrophy by splice modulation and gene editing

Duchenne muscular dystrophy (DMD) is a currently incurable X-linked neuromuscular disorder, characterized by progressive muscle wasting and premature death, typically as a consequence of cardiac failure. DMD-causing mutations in the dystrophin gene are highly diverse, meaning that the development of a universally-applicable therapy to treat all patients is very challenging. The leading therapeutic strategy for DMD is antisense oligonucleotide-mediated splice modulation, whereby one or more specific exons are excluded from the mature dystrophin mRNA in order to correct the translation reading frame. Indeed, three exon skipping oligonucleotides have received FDA approval for use in DMD patients. Second-generation exon skipping drugs (i.e. peptide-antisense oligonucleotide conjugates) exhibit enhanced potency, and also induce dystrophin restoration in the heart. Similarly, multiple additional antisense oligonucleotide drugs targeting various exons are in clinical development in order to treat a greater proportion of DMD patient mutations. Relatively recent advances in the field of genome engineering (specifically, the development of the CRISPR/Cas system) have provided multiple promising therapeutic approaches for the RNA-directed genetic correction of DMD, including exon excision, exon reframing via the introduction of insertion/deletion mutations, disruption of splice signals to promote exon skipping, and the templated correction of point mutations by seamless homology directed repair or base editing technology. Potential limitations to the clinical translation of the splice modulation and gene editing approaches are discussed, including drug delivery, the importance of uniform dystrophin expression in corrected myofibres, safety issues (e.g. renal toxicity, viral vector immunogenicity, and off-target gene editing), and the high cost of therapy.

Developing DMD therapeutics: a review of the effectiveness of small molecules, stop-codon readthrough, dystrophin gene replacement, and exon-skipping therapies

INTRODUCTION

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin (DMD) gene. Most patients die from respiratory failure or cardiomyopathy. There are significant unmet needs for treatments for DMD as the standard of care is principally limited to symptom relief through treatments including steroids.

AREAS COVERED

This review summarizes safety and efficacy in promising areas of DMD therapeutics - small molecules, stop codon readthrough, gene replacement, and exon skipping - under clinical examination from 2015-2020 as demonstrated in the NIH Clinical Trials and PubMed search engines.

EXPERT OPINION

Currently, steroids persist as the most accessible medicine for DMD. Stop-codon readthrough, gene replacement, and exon-skipping therapies all aim to restore dystrophin expression. Of these strategies, gene replacement therapy has recently gained momentum while exon-skipping retains great traction. The  FDA approval of three exon-skipping antisense oligonucleotides illustrate this regulatory momentum, though the effectiveness and sequence design of eteplirsen remain controversial. Cell-penetrating peptides promise to more efficaciously treat DMD-related cardiomyopathy.The recent success of antisense therapies, however, poses major regulatory challenges. To fully realize the benefits of exon-skipping, including cocktail oligonucleotide-mediated multiple exon-skipping and oligonucleotide drugs for very rare mutations, regulatory challenges need to be addressed in coordination with scientific advances.

Anti-Inflammatory and General Glucocorticoid Physiology in Skeletal Muscles Affected by Duchenne Muscular Dystrophy: Exploration of Steroid-Sparing Agents

In Duchenne muscular dystrophy (DMD), the activation of proinflammatory and metabolic cellular pathways in skeletal muscle cells is an inherent characteristic. Synthetic glucocorticoid intake counteracts the majority of these mechanisms. However, glucocorticoids induce burdensome secondary effects, including hypertension, arrhythmias, hyperglycemia, osteoporosis, weight gain, growth delay, skin thinning, cushingoid appearance, and tissue-specific glucocorticoid resistance. Hence, lowering the glucocorticoid dosage could be beneficial for DMD patients. A more profound insight into the major cellular pathways that are stabilized after synthetic glucocorticoid administration in DMD is needed when searching for the molecules able to achieve similar pathway stabilization. This review provides a concise overview of the major anti-inflammatory pathways, as well as the metabolic effects of glucocorticoids in the skeletal muscle affected in DMD. The known drugs able to stabilize these pathways, and which could potentially be combined with glucocorticoid therapy as steroid-sparing agents, are described. This could create new opportunities for testing in DMD animal models and/or clinical trials, possibly leading to smaller glucocorticoids dosage regimens for DMD patients.