Duchenne muscular dystrophy (DMD) is a severe, progressive, and ultimately fatal disease of skeletal muscle wasting, respiratory insufficiency, and cardiomyopathy. The identification of the dystrophin gene as central to DMD pathogenesis has led to the understanding of the muscle membrane and the proteins involved in membrane stability as the focal point of the disease. The lessons learned from decades of research in human genetics, biochemistry, and physiology have culminated in establishing the myriad functionalities of dystrophin in striated muscle biology. Here, we review the pathophysiological basis of DMD and discuss recent progress toward the development of therapeutic strategies for DMD that are currently close to or are in human clinical trials. The first section of the review focuses on DMD and the mechanisms contributing to membrane instability, inflammation, and fibrosis. The second section discusses therapeutic strategies currently used to treat DMD. This includes a focus on outlining the strengths and limitations of approaches directed at correcting the genetic defect through dystrophin gene replacement, modification, repair, and/or a range of dystrophin-independent approaches. The final section highlights the different therapeutic strategies for DMD currently in clinical trials.

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Duchenne muscular dystrophy: disease mechanism and therapeutic strategies

Duchenne muscular dystrophy (DMD) is a severe, progressive, and incurable X-linked disorder caused by mutations in the dystrophin gene. Patients with DMD have an absence of functional dystrophin protein, which results in chronic damage of muscle fibers during contraction, thus leading to deterioration of muscle quality and loss of muscle mass over time. Although there is currently no cure for DMD, improvements in treatment care and management could delay disease progression and improve quality of life, thereby prolonging life expectancy for these patients. Furthermore, active research efforts are ongoing to develop therapeutic strategies that target dystrophin deficiency, such as gene replacement therapies, exon skipping, and readthrough therapy, as well as strategies that target secondary pathology of DMD, such as novel anti-inflammatory compounds, myostatin inhibitors, and cardioprotective compounds. Furthermore, longitudinal modeling approaches have been used to characterize the progression of MRI and functional endpoints for predictive purposes to inform Go/No Go decisions in drug development. This review showcases approved drugs or drug candidates along their development paths and also provides information on primary endpoints and enrollment size of Ph2/3 and Ph3 trials in the DMD space.

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Drug development progress in duchenne muscular dystrophy

Duchenne muscular dystrophy is an X-linked disease caused by the absence of functional dystrophin in the muscle cells. Major advances have led to the development of gene therapies, tools that induce exon skipping, and other therapeutic approaches, including treatments targeting molecular pathways downstream of the absence of functional dystrophin. However, glucocorticoids remain the only treatment unequivocally shown to slow disease progression, despite the adverse effects associated with their long-term use. Besides glucocorticoids, which are standard care, five compounds have received regulatory approval in some but not all jurisdictions, with further efficacy results being awaited. Several compounds with promising results in early-phase clinical trials have not met their efficacy endpoints in late-phase trials, but the clinical development of many other compounds is ongoing. The current landscape is complicated by the number of compounds in various stages of development, their various mechanisms of action, and their genotype-specific applicability. The difficulties of clinical development that arise from both the rarity and variability of Duchenne muscular dystrophy might be overcome in the future by use of sensitive biomarkers, natural history data, and ameliorated trial designs.

Emerging therapies for Duchenne muscular dystrophy

Abstract Duchenne Muscular Dystrophy (DMD) is a lethal disease caused by mutations in dystrophin encoding gene, causing progressive degeneration of cardiac, respiratory, and skeletal muscles leading to premature death due to cardiac and respiratory failure. Currently, there is no cure for DMD. Therefore, novel therapeutic approaches are needed for DMD patients. We have previously reported functional improvements which correlated with increased dystrophin expression following administration of dystrophin expressing chimeric (DEC) cells of myoblast origin to the mdx mouse models of DMD. In the current study, we confirmed dose-dependent protective effect of human DEC therapy created from myoblasts of normal and DMD-affected donors, on restoration of dystrophin expression and amelioration of cardiac, respiratory, and skeletal muscle function at 180 days after systemic-intraosseous DEC administration to mdx/scid mouse model of DMD. Functional improvements included maintenance of ejection fraction and fractional shortening levels on echocardiography, reduced enhanced pause and expiration time on plethysmography and improved grip strength and maximum stretch induced contraction of skeletal muscles. Improved function was associated with amelioration of mdx muscle pathology revealed by reduced muscle fibrosis, reduced inflammation and improved muscle morphology confirmed by reduced number of centrally nucleated fibers and normalization of muscle fiber diameters. Our findings confirm the long-term systemic effect of DEC therapy in the most severely affected by DMD organs including heart, diaphragm, and long skeletal muscles. These encouraging preclinical data introduces human DEC as a novel therapeutic modality of Advanced Therapy Medicinal Product (ATMP) with the potential to improve or halt the progression of DMD and enhance quality of life of DMD patients. Graphical Abstract Human DEC as a novel therapeutic modality with the potential to improve or halt progression of the DMD disease and enhance quality of life of DMD patients. Graphical abstract represents manufacturing process of the human DEC therapy for the future clinical applications. 1. We report the long-term efficacy of human DEC therapy resulting in increased dystrophin expression and reduced mdx muscle pathology after systemic-intraosseous administration of human Dystrophin Expressing Chimeric (DEC) Cells to the mdx/scid mouse model of DMD. 2. Systemic administration of human DEC therapy resulted in amelioration of cardiac, respiratory and skeletal muscle function as confirmed by echocardiography, plethysmography and standard muscle strength tests respectively. 3. We introduce human DEC as a novel Advanced Therapy Medicinal Product (ATMP) for future clinical application in DMD patients. 

/pdf/long-term-protective-effect-of-human-dystrophin-expressing-151ihf76.pdf

Long-Term Protective Effect of Human Dystrophin Expressing Chimeric (DEC) Cell Therapy on Amelioration of Function of Cardiac, Respiratory and Skeletal Muscles in Duchenne Muscular Dystrophy

MicroRNAs (miRNAs) are epigenetic regulators that can target and inhibit translation of multiple mRNAs within a given cell type. As such, a number of different pathways and networks may be modulated as a result. In fact, miRNAs are known to regulate many cellular processes including differentiation, proliferation, inflammation, and metabolism. This review focuses on the miR‐181 family and provides information from the published literature on the role of miR‐181 homologs in regulating a range of activities in different cell types and tissues. Of note, we have not included details on miR‐181 expression and function in the context of cancer since this is a broad topic area requiring independent review. Instead, we have focused on describing the function and mechanism of miR‐181 family members on differentiation toward a number of cell lineages in various non‐neoplastic conditions (e.g., immune/hematopoietic cells, osteoblasts, osteoclasts, chondrocytes, adipocytes). We have also provided information on how modulation of miR‐181 homologs can have positive effects on disease states such as cardiac abnormalities, pulmonary arterial hypertension, thrombosis, osteoarthritis, and vascular inflammation. In this context, we have used some examples of FDA‐approved drugs that modulate miR‐181 expression. We conclude by discussing some common mechanisms by which miR‐181 homologs appear to regulate a number of different cellular processes and how targeting specific miR‐181 family members may lead to attractive therapeutic approaches to treat a number of human disease or repair conditions, including those associated with the aging process.

The miR‐181 family: Wide‐ranging pathophysiological effects on cell fate and function

BACKGROUND
Cardiosphere-derived cells (CDCs) ameliorate skeletal and cardiac muscle deterioration in experimental models of Duchenne muscular dystrophy. The HOPE-2 trial examined the safety and efficacy of sequential intravenous infusions of human allogeneic CDCs in late-stage Duchenne muscular dystrophy.


METHODS
In this multicentre, randomised, double-blind, placebo-controlled, phase 2 trial, patients with Duchenne muscular dystrophy, aged 10 years or older with moderate upper limb impairment, were enrolled at seven centres in the USA. Patients were randomly assigned (1:1) using stratified permuted blocks to receive CAP-1002 (1·5 × 108 CDCs) or placebo intravenously every 3 months for a total of four infusions. Clinicians, caregivers, patients, and clinical operations personnel were fully masked to treatment groups. The primary outcome was the change in mid-level elbow Performance of Upper Limb version 1.2 (PUL 1.2) score at 12 months, assessed in the intention-to-treat population. Safety was assessed in all individuals who received an investigational product. This trial is registered with ClinicalTrials.gov, NCT03406780.


FINDINGS
Between March 1, 2018, and March 31, 2020, 26 male patients with Duchenne muscular dystrophy were enrolled, of whom eight were randomly assigned to the CAP-1002 group and 12 to the placebo group (six were not randomised due to screening failure). In patients who had a post-treatment PUL 1.2 assessment (eight in the CAP-1002 group and 11 in the placebo group), the mean 12-month change from baseline in mid-level elbow PUL1.2 favoured CAP-1002 over placebo (percentile difference 36·2, 95% CI 12·7-59·7; difference of 2·6 points; p=0·014). Infusion-related hypersensitivity reactions without long-term sequelae were observed in three patients, with one patient discontinuing therapy due to a severe allergic reaction. No other major adverse reactions were noted, and no deaths occurred.


INTERPRETATION
CAP-1002 cell therapy appears to be safe and effective in reducing deterioration of upper limb function in patients with late-stage Duchenne muscular dystrophy. Various measures of cardiac function and structure were also improved in the CAP-1002 group compared with the placebo group. Longer-term extension studies are needed to confirm the therapeutic durability and safety of CAP-1002 beyond 12 months for the treatment of skeletal myopathy and cardiomyopathy in Duchenne muscular dystrophy.


FUNDING
Capricor Therapeutics.

Repeated intravenous cardiosphere-derived cell therapy in late-stage Duchenne muscular dystrophy (HOPE-2): a multicentre, randomised, double-blind, placebo-controlled, phase 2 trial

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Repeated intravenous cardiosphere-derived cell therapy in late-stage Duchenne muscular dystrophy (HOPE-2): a multicentre, randomised, double-blind, placebo-controlled, phase 2 trial