Interventions for muscular dystrophy: molecular medicines entering the clinic

Reliable and versatile immortal muscle cell models from healthy and myotonic dystrophy type 1 primary human myoblasts

Primary human skeletal muscle cells (hSkMCs) are invaluable tools for deciphering the basic molecular mechanisms of muscle-related biological processes and pathological alterations. Nevertheless, their use is quite restricted due to poor availability, short life span and variable purity of the cells during in vitro culture. Here, we evaluate a recently published method of hSkMCs immortalization, relying on ectopic expression of cyclin D1 (CCND1), cyclin-dependent kinase 4 (CDK4) and telomerase (TERT) in myoblasts from healthy donors (n=3) and myotonic dystrophy type 1 (DM1) patients (n=2). The efficacy to maintain the myogenic and non-transformed phenotype, as well as the main pathogenetic hallmarks of DM1, has been assessed. Combined expression of the three genes i) maintained the CD56(NCAM)-positive myoblast population and differentiation potential; ii) preserved the non-transformed phenotype and iii) maintained the CTG repeat length, amount of nuclear foci and aberrant alternative splicing in immortal muscle cells. Moreover, immortal hSkMCs displayed attractive additional features such as structural maturation of sarcomeres, persistence of Pax7-positive cells during differentiation and complete disappearance of nuclear foci following (CAG)7 antisense oligonucleotide (ASO) treatment. Overall, the CCND1, CDK4 and TERT immortalization yields versatile, reliable and extremely useful human muscle cell models to investigate the basic molecular features of human muscle cell biology, to elucidate the molecular pathogenetic mechanisms and to test new therapeutic approaches for DM1 in vitro.

Cellular Therapies for Muscular Dystrophies: Frustrations and Clinical Successes

Cell-based therapy for muscular dystrophies was initiated in humans after promising results obtained in murine models. Early trials failed to show substantial clinical benefit, sending researchers back to the bench, which led to the discovery of many hurdles as well as many new venues to optimize this therapeutic strategy. In this review we summarize progress in preclinical cell therapy approaches, with a special emphasis on human cells potentially attractive for human clinical trials. Future perspectives for cell therapy in skeletal muscle are discussed, including the perspective of combined therapeutic approaches.

Comparative mass spectrometric and immunoassay-based proteome analysis in serum of Duchenne muscular dystrophy patients

PURPOSE

Duchenne muscular dystrophy (DMD) is a severe and fatal neuromuscular disease. With the current developments on novel therapeutic strategies for DMD, the need to carefully monitor disease progression or regression upon treatment using molecular markers has become urgent.

EXPERIMENTAL DESIGN

2D LC protein fractionation was performed on patient serum samples, followed by LC-MS/MS-based identifications with label-free quantifications.

RESULTS

Protein signatures were compared between patients and healthy (child and adult) controls and between ambulant and nonambulant patients. Various myofibrillar proteins demonstrated differences between DMD patients and controls, likely due to leakiness and breakdown of muscle fibers. Previously reported biomarkers, such as muscle-derived titin, myosin, and carbonic anhydrase I (CA1), were verified. MS-based results were compared with ELISA for vitamin D binding protein (GC), fibulin-1 (FBLN1), gelsolin (GSN), and carbonic anhydrase 1 (CA1).

CONCLUSIONS AND CLINICAL RELEVANCE

The combined results of MS- and ELISA-based quantifications indicated more studies are needed to validate this serum protein signature for DMD patients. With these data promising candidate biomarkers have been identified for a rare genetic disease using serum proteome analysis.

Invited review: Stem cells and muscle diseases: advances in cell therapy strategies

Despite considerable progress to increase our understanding of muscle genetics, pathophysiology, molecular and cellular partners involved in muscular dystrophies and muscle ageing, there is still a crucial need for effective treatments to counteract muscle degeneration and muscle wasting in such conditions. This review focuses on cell-based therapy for muscle diseases. We give an overview of the different parameters that have to be taken into account in such a therapeutic strategy, including the influence of muscle ageing, cell proliferation and migration capacities, as well as the translation of preclinical results in rodent into human clinical approaches. We describe recent advances in different types of human myogenic stem cells, with a particular emphasis on myoblasts but also on other candidate cells described so far [CD133+ cells, aldehyde dehydrogenase-positive cells (ALDH+), muscle-derived stem cells (MuStem), embryonic stem cells (ES) and induced pluripotent stem cells (iPS)]. Finally, we provide an update of ongoing clinical trials using cell therapy strategies.

The TREAT-NMD advisory committee for therapeutics (TACT): an innovative de-risking model to foster orphan drug development

Despite multiple publications on potential therapies for neuromuscular diseases (NMD) in cell and animal models only a handful reach clinical trials. The ability to prioritise drug development according to objective criteria is particularly critical in rare diseases with large unmet needs and a limited numbers of patients who can be enrolled into clinical trials. TREAT-NMD Advisory Committee for Therapeutics (TACT) was established to provide independent and objective guidance on the preclinical and development pathway of potential therapies (whether novel or repurposed) for NMD.

We present our experience in the establishment and operation of the TACT. TACT provides a unique resource of recognized experts from multiple disciplines. The goal of each TACT review is to help the sponsor to position the candidate compound along a realistic and well-informed plan to clinical trials, and eventual registration. The reviews and subsequent recommendations are focused on generating meaningful and rigorous data that can enable clear go/no-go decisions and facilitate longer term funding or partnering opportunities. The review process thereby acts to comment on viability, de-risking the process of proceeding on a development programme.

To date TACT has held 10 review meeting and reviewed 29 program applications in several rare neuromuscular diseases: Of the 29 programs reviewed, 19 were from industry and 10 were from academia; 15 were for novel compounds and 14 were for repurposed drugs; 16 were small molecules and 13 were biologics; 14 were preclinical stage applications and 15 were clinical stage applications. 3 had received Orphan drug designation from European Medicines Agency and 3 from Food and Drug Administration. A number of recurrent themes emerged over the course of the reviews and we found that applicants frequently require advice and education on issues concerned with preclinical standard operating procedures, interactions with regulatory agencies, formulation, repurposing, clinical trial design, manufacturing and ethics.

Over the 5 years since its establishment TACT has amassed a body of experience that can be extrapolated to other groups of rare diseases to improve the community’s chances of successfully bringing new rare disease drugs to registration and ultimately to market.

RD-Connect: an integrated platform connecting databases, registries, biobanks and clinical bioinformatics for rare disease research

Research into rare diseases is typically fragmented by data type and disease. Individual efforts often have poor interoperability and do not systematically connect data across clinical phenotype, genomic data, biomaterial availability, and research/trial data sets. Such data must be linked at both an individual-patient and whole-cohort level to enable researchers to gain a complete view of their disease and patient population of interest. Data access and authorization procedures are required to allow researchers in multiple institutions to securely compare results and gain new insights. Funded by the European Union's Seventh Framework Programme under the International Rare Diseases Research Consortium (IRDiRC), RD-Connect is a global infrastructure project initiated in November 2012 that links genomic data with registries, biobanks, and clinical bioinformatics tools to produce a central research resource for rare diseases.

Autonomic, locomotor and cardiac abnormalities in a mouse model of muscular dystrophy: targeting the renin-angiotensin system

New Findings What is the topic of this review? This symposium report summarizes autonomic, cardiac and skeletal muscle abnormalities in sarcoglycan-δ-deficient mice (Sgcd-/-), a mouse model of limb girdle muscular dystrophy, with emphasis on the roles of autonomic dysregulation and activation of the renin-angiotensin system at a young age. What advances does it highlight? The contributions of the autonomic nervous system and the renin-angiotensin system to the pathogenesis of muscular dystrophy are highlighted. Results demonstrate that autonomic dysregulation precedes and predicts later development of cardiac dysfunction in Sgcd-/- mice and that treatment of young Sgcd-/- mice with the angiotensin type 1 receptor antagonist losartan or with angiotensin-(1-7) abrogates the autonomic dysregulation, attenuates skeletal muscle pathology and increases spontaneous locomotor activity. Muscular dystrophies are a heterogeneous group of genetic muscle diseases characterized by muscle weakness and atrophy. Mutations in sarcoglycans and other subunits of the dystrophin-glycoprotein complex cause muscular dystrophy and dilated cardiomyopathy in animals and humans. Aberrant autonomic signalling is recognized in a variety of neuromuscular disorders. We hypothesized that activation of the renin-angiotensin system contributes to skeletal muscle and autonomic dysfunction in mice deficient in the sarcoglycan-δ (Sgcd) gene at a young age and that this early autonomic dysfunction contributes to the later development of left ventricular (LV) dysfunction and increased mortality. We demonstrated that young Sgcd-/- mice exhibit histopathological features of skeletal muscle dystrophy, decreased locomotor activity and severe autonomic dysregulation, but normal LV function. Autonomic regulation continued to deteriorate in Sgcd-/- mice with age and was accompanied by LV dysfunction and dilated cardiomyopathy at older ages. Autonomic dysregulation at a young age predicted later development of LV dysfunction and higher mortality in Sgcd-/- mice. Treatment of Sgcd-/- mice with the angiotensin type 1 receptor blocker losartan for 8-9 weeks, beginning at 3 weeks of age, decreased fibrosis and oxidative stress in skeletal muscle, increased locomotor activity and prevented autonomic dysfunction. Chronic infusion of the counter-regulatory peptide angiotensin-(1-7) resulted in similar protection. We conclude that activation of the renin-angiotensin system, at a young age, contributes to skeletal muscle and autonomic dysfunction in muscular dystrophy. We speculate that the latter is mediated via abnormal sensory nerve and/or cytokine signalling from dystrophic skeletal muscle to the brain and contributes to age-related LV dysfunction, dilated cardiomyopathy, arrhythmias and premature death. Therefore, correcting the early autonomic dysregulation and renin-angiotensin system activation may provide a novel therapeutic approach in muscular dystrophy.

Zebrafish models flex their muscles to shed light on muscular dystrophies

Muscular dystrophies are a group of genetic disorders that specifically affect skeletal muscle and are characterized by progressive muscle degeneration and weakening. To develop therapies and treatments for these diseases, a better understanding of the molecular basis of muscular dystrophies is required. Thus, identification of causative genes mutated in specific disorders and the study of relevant animal models are imperative. Zebrafish genetic models of human muscle disorders often closely resemble disease pathogenesis, and the optical clarity of zebrafish embryos and larvae enables visualization of dynamic molecular processes in vivo. As an adjunct tool, morpholino studies provide insight into the molecular function of genes and allow rapid assessment of candidate genes for human muscular dystrophies. This unique set of attributes makes the zebrafish model system particularly valuable for the study of muscle diseases. This review discusses how recent research using zebrafish has shed light on the pathological basis of muscular dystrophies, with particular focus on the muscle cell membrane and the linkage between the myofibre cytoskeleton and the extracellular matrix.

Treatment of facioscapulohumeral muscular dystrophy with Denosumab

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is the 3(rd) most common form of muscular dystrophy. Effective treatments for any of the muscular dystrophies have yet to be realized. This report describes such a treatment.

CASE REPORT

A 66 year old female was diagnosed with osteoporosis. She had been diagnosed with FSHD muscular dystrophy a number of years previously by both genetic and clinical studies. Following a 2 year course with Forteo for osteoporosis, she was given an injection of Denosumab (Prolia) to maintain her bone density. By 24 hours, she exhibited increased strength and a dramatic reduction of her dystrophic symptoms e.g. she could walk unassisted in high heels. She was able to accomplish other things that had not been possible for a number of years. After approximately 5 weeks she gradually lost the newfound strength with a complete loss by about 6 weeks. A second injection of Denosumab resulted in the same effect, i.e. reversal of symptoms and increased functionality. A number of measurements and videos were taken to establish the beneficial effects of Prolia for future studies. This was repeated with a 3(rd) and 4(th) injection in order to establish the unequivocal beneficial effects on muscular dystrophy.

CONCLUSIONS

Further studies will be required to establish Denosumab as a major "front line" treatment for this disease and possibly other muscular dystrophies.

Pathophysiology of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a clinically and genetically heterogeneous disorder of heart muscle that is associated with ventricular arrhythmias and risk of sudden cardiac death, particularly in the young and athletes. Mutations in five genes that encode major components of the desmosomes, namely junction plakoglobin, desmoplakin, plakophilin-2, desmoglein-2, and desmocollin-2, have been identified in approximately half of affected probands. AC is, therefore, commonly considered a 'desmosomal' disease. No single test is sufficiently specific to establish a diagnosis of AC. The diagnostic criteria for AC were revised in 2010 to improve sensitivity, but maintain specificity. Quantitative parameters were introduced and identification of a pathogenic mutation in a first-degree relative has become a major diagnostic criterion. Caution in the interpretation of screening results is highly recommended because a 'pathogenic' mutation is difficult to define. Experimental data confirm that this genetically determined cardiomyopathy develops after birth because of progressive myocardial dystrophy, and is initiated by cardiomyocyte necrosis; cellular and animal models are necessary to gain insight into the cascade of underlying molecular events. Crosstalk from the desmosome to the nucleus, gap junctions, and ion channels is under investigation, to move from symptomatic to targeted therapy, with the ultimate aim to stop disease onset and progression.

Quantitative assessment of skeletal muscle degeneration in patients with myotonic dystrophy type 1 using MRI

PURPOSE

To identify MRI biomarkers that could be used to follow disease progression and therapeutic efficacy in one individual muscle in patients with myotonic dystrophy type 1 (DM1).

MATERIALS AND METHODS

Lower limb MRI and maximal ankle dorsiflexor strength assessment, using a hand-held dynamometer, were performed in 19 DM1 patients and 6 control subjects. The volume of residual muscle tissue of Tibialis Anterior (TA) muscle was chosen as an index for muscle atrophy, and the T2-relaxation-time of the residual muscle tissue was measured to evaluate edema-like lesions. The fat-to-water ratio was assessed using three-point Dixon images to quantify fat infiltration in the entire muscle.

RESULTS

The intra-observer variability of MRI indices (∼5.2% for the residual muscle tissue volume and 2.5% for the fat-to-water ratio) was lower than that of the dorsiflexor torque measurement (∼11.5%). A high correlation (r = 0.91) was found between maximal ankle dorsiflexor strength and residual TA muscle tissue volume in DM1 patients. Increases in the fat-to-water ratio and T2-relaxation-time were associated with a decrease in maximal ankle dorsiflexor strength.

CONCLUSION

MRI appears as a noninvasive method which can be used to follow disease progression and therapeutic efficacy.

Progress in therapy for Duchenne muscular dystrophy

Duchenne muscular dystrophy is a devastating muscular dystrophy of childhood. Mutations in the dystrophin gene destroy the link between the internal muscle filaments and the extracellular matrix, resulting in severe muscle weakness and progressive muscle wasting. There is currently no cure and, whilst palliative treatment has improved, affected boys are normally confined to a wheelchair by 12 years of age and die from respiratory or cardiac complications in their twenties or thirties. Therapies currently being developed include mutation-specific treatments, DNA- and cell-based therapies, and drugs which aim to modulate cellular pathways or gene expression. This review aims to provide an overview of the different therapeutic approaches aimed at reconstructing the dystrophin-associated protein complex, including restoration of dystrophin expression and upregulation of the functional homologue, utrophin.

Improvement of cardiac contractile function by peptide-based inhibition of NF-κB in the utrophin/dystrophin-deficient murine model of muscular dystrophy

Background

Duchenne muscular dystrophy (DMD) is an inherited and progressive disease causing striated muscle deterioration. Patients in their twenties generally die from either respiratory or cardiac failure. In order to improve the lifespan and quality of life of DMD patients, it is important to prevent or reverse the progressive loss of contractile function of the heart. Recent studies by our labs have shown that the peptide NBD (Nemo Binding Domain), targeted at blunting Nuclear Factor κB (NF-κB) signaling, reduces inflammation, enhances myofiber regeneration, and improves contractile deficits in the diaphragm in dystrophin-deficient mdx mice.

Methods

To assess whether cardiac function in addition to diaphragm function can be improved, we investigated physiological and histological parameters of cardiac muscle in mice deficient for both dystrophin and its homolog utrophin (double knockout = dko) mice treated with NBD peptide. These dko mice show classic pathophysiological hallmarks of heart failure, including myocyte degeneration, an impaired force-frequency response and a severely blunted β-adrenergic response. Cardiac contractile function at baseline and frequencies and pre-loads throughout the in vivo range as well as β-adrenergic reserve was measured in isolated cardiac muscle preparations. In addition, we studied histopathological and inflammatory markers in these mice.

Results

At baseline conditions, active force development in cardiac muscles from NBD treated dko mice was more than double that of vehicle-treated dko mice. NBD treatment also significantly improved frequency-dependent behavior of the muscles. The increase in force in NBD-treated dko muscles to β-adrenergic stimulation was robustly restored compared to vehicle-treated mice. However, histological features, including collagen content and inflammatory markers were not significantly different between NBD-treated and vehicle-treated dko mice.

Conclusions

We conclude that NBD can significantly improve cardiac contractile dysfunction in the dko mouse model of DMD and may thus provide a novel therapeutic treatment for heart failure.

Current advances in cell therapy strategies for muscular dystrophies

INTRODUCTION

Muscular dystrophies are a heterogeneous group of genetic diseases characterized by muscle weakness, wasting and degeneration. Cell therapy consists of delivering myogenic precursor cells to damaged tissue for the complementation of missing proteins and/or the regeneration of new muscle fibres.

AREAS COVERED

We focus on human candidate cells described so far (myoblasts, mesoangioblasts, pericytes, myoendothelial cells, CD133(+) cells, aldehyde-dehydrogenase-positive cells, mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells), gene-based strategies developed to modify cells prior to injection, animal models (dystrophic and/or immunodeficient) used for pre-clinical studies, and clinical trials that have been performed using cell therapy strategies. The approaches are reviewed in terms of feasibility, hurdles, potential solutions and/or research areas from where the solution may come and potential application in terms of types of dystrophies and targets.

EXPERT OPINION

Cell therapy for muscular dystrophies should be put in the context of which dystrophy or muscle group is targeted, what tools are available at hand, but even more importantly what can cell therapy bring as compared with and/or in combination with other therapeutic strategies. The solution will probably be the right dosage of these combinations adapted to each dystrophy, or even to each type of mutation within a dystrophy.

Proinflammatory signals and the loss of lymphatic vessel hyaluronan receptor-1 (LYVE-1) in the early pathogenesis of laminin alpha2-deficient skeletal muscle

Congenital muscular dystrophy type 1A, a severe neuromuscular disease characterized by early-onset muscle weakness and degeneration, is caused by insufficient levels of laminin α2 (LAMA2) in the basal lamina surrounding muscle fibers and other cells. A better understanding of the molecular mechanisms leading to muscle loss is needed to develop therapeutic interventions for this disease. Here, the authors show that inflammation is an early feature of pathogenesis in Lama2-deficient mouse muscle, indicated by elevated expression of tenascin C in the endomysium around muscle fibers, infiltration of macrophages, and induction of the inflammatory cytokines tumor necrosis factor α (TNFα) and IL-1β. In addition, the expression of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), a specific marker for lymphatic vessel endothelial cells, is dramatically reduced early in Lama2-deficient muscle pathogenesis. LYVE-1 expression, which is inhibited by TNFα, is also decreased in muscles undergoing degeneration due to dystrophin deficiency and cardiotoxin damage. LYVE-1 expression thus provides a useful biomarker to monitor the onset of muscle pathogenesis, likely serving as an indicator of inflammatory signals present in muscles. Together, the data show that inflammatory pathways are activated in the earliest stages of Lama2-deficient disease progression and could play a role in early muscle degeneration.

Novel compounds for the treatment of Duchenne muscular dystrophy: emerging therapeutic agents

The identification of dystrophin and the causative role of mutations in this gene in Duchenne and Becker muscular dystrophies (D/BMD) was expected to lead to timely development of effective therapies. Despite over 20 years of research, corticosteroids remain the only available pharmacological treatment for DMD, although significant benefits and extended life have resulted from advances in the clinical care and management of DMD individuals. Effective treatment of DMD will require dystrophin restitution in skeletal, cardiac, and smooth muscles and nonmuscle tissues; however, modulation of muscle loss and regeneration has the potential to play an important role in altering the natural history of DMD, particularly in combination with other treatments. Emerging biological, molecular, and small molecule therapeutics are showing promise in ameliorating this devastating disease, and it is anticipated that regulatory environments will need to display some flexibility in order to accommodate the new treatment paradigms.