Update on Standard Operating Procedures in Preclinical Research for DMD and SMA Report of TREAT-NMD Alliance Workshop, Schiphol Airport, 26 April 2015, The Netherlands

Pharmacological Therapies of Spinal Muscular Atrophy: A Narrative Review of Preclinical, Clinical-Experimental, and Real-World Evidence

Spinal muscular atrophy (SMA) is a rare neuromuscular disease, with an estimated incidence of about 1 in 10,000 live births. To date, three orphan drugs have been approved for the treatment of SMA: nusinersen, onasemnogene abeparvovec, and risdiplam. The aim of this narrative review was to provide an overview of the pre- and post-marketing evidence on the pharmacological treatments approved for the treatment of SMA by identifying preclinical and clinical studies registered in clinicaltrials.gov and in the EU PAS register from their inception until the 4 January 2023. The preclinical evidence on the drugs approved for SMA allowed a significant acceleration in the experimental phase of these drugs. However, since these drugs had been authorized through accelerated programs, the conduction of post-marketing studies was requested as a condition of their marketing approval to better understand their risk-benefit profiles in real-world settings. As of the 4 January 2023, a total of 69 post-marketing studies concerning the three orphan drugs approved for SMA were identified in clinicaltrials.gov (N = 65; 94.2%) and in the EU PAS register (N = 4; 5.8%). Currently, ongoing studies are primarily aimed at providing evidence concerning the risk-benefit profile of the three drugs in specific populations that were not included in the pivotal trials and to investigate the long-term safety and clinical benefits of these drugs. Real-world data sources collecting information regarding the natural history of the disease and post-marketing surveillance of the available therapies are increasingly becoming essential for generating real-world evidence on this rare disease and its orphan drugs.

On the use of D2.B10-Dmdmdx/J (D2.mdx) Versus C57BL/10ScSn-Dmdmdx/J (mdx) Mouse Models for Preclinical Studies on Duchenne Muscular Dystrophy: A Cautionary Note from Members of the TREAT-NMD Advisory Committee on Therapeutics

The C57BL/10ScSn-Dmdmdx/J (mdx) mouse model has been used by researchers for decades as a model to study pathology of and develop therapies for Duchenne muscular dystrophy. However, the model is relatively mildly affected compared to the human situation. Recently, the D2.B10-Dmdmdx/J (D2.mdx) mouse model was suggested as a more severely affected and therefore better alternative. While the pathology of this model is indeed more pronounced early in life, it is not progressive, and increasing evidence suggest that it actually partially resolves with age. As such, caution is needed when using this model. However, as preclinical experts of the TREAT-NMD advisory committee for therapeutics (TACT), we frequently encounter study designs that underestimate this caveat. We here provide context for how to best use the two models for preclinical studies at the current stage of knowledge.

The First Report of Iranian Registry of Patients with Spinal Muscular Atrophy

BACKGROUND

Insufficient amounts of survival motor neuron protein is leading to one of the most disabling neuromuscular diseases, spinal muscular atrophy (SMA). Before the current study, the detailed characteristics of Iranian patients with SMA had not been determined.

OBJECTIVE

To describe the key demographic, clinical, and genetic characteristics of patients with SMA registered in the Iranian Registry of SMA (IRSMA).

METHODS

IRSMA has been established since 2018, and the demographic, clinical, and genetic characteristics of patients with SMA were recorded according to the methods of treat neuromuscular disease (TREAT-NMD) project.

RESULTS

By October 1, 2022, 781 patients with 5q SMA were registered. Of them, 164 patients died, the majority of them had SMA type 1 and died during the first 20 months of life. The median survival of patients with type 1 SMA was 23 months. The consanguinity rate in 617 alive patients was 52.4%, while merely 24.8% of them had a positive family history. The most common type of SMA in live patients was type 3. Morbidities were defined as having scoliosis (44.1%), wheelchair dependency (36.8%), tube feeding (8.1%), and requiring mechanical ventilation (9.9%). Most of the registered patients had a homozygous deletion of SMN1, while the frequency of patients with higher copy numbers of SMN2, was less in more severe types of the disease. Earlier onset of the disease was significantly seen in patients with lower copy numbers of SMN2. The neuronal apoptosis inhibitory protein (NAIP) gene deletion was associated with a higher incidence of more severe types of SMA, higher dependency on ventilators, tube feeding, and earlier onset of the disease.

CONCLUSIONS

The IRSMA is the first established Iranian nationwide registry of patients with SMA. Using this registry, decision-makers, researchers, and practitioners can precisely understand the epidemiology, characteristics, and genetics of patients with SMA in Iran.

Navigating regulatory pathways for translation of biologic cartilage repair products

Long-term clinical repair of articular cartilage remains elusive despite advances in cartilage tissue engineering. Only one cartilage repair therapy classified as a "cellular and gene therapy product" has obtained Food and Drug Administration (FDA) approval within the past decade although more than 200 large animal cartilage repair studies were published. Here, we identify the challenges impeding translation of strategies and technologies for cell-based cartilage repair, such as the disconnect between university funding and regulatory requirements. Understanding the barriers to translation and developing solutions to address them will be critical for advancing cell therapy products for cartilage repair to clinical use.

The predictive value of models of neuromuscular disorders to potentiate clinical translation

Neuromuscular disorders (NMDs) are a heterogenous group of rare inherited diseases that compromise the function of peripheral nerves and/or muscles. With limited treatment options available, there is a growing need to design effective preclinical studies that can lead to greater success in clinical trials for novel therapeutics. Here, I discuss recent advances in modelling NMDs to improve preclinical studies as well as two articles from this issue that work in parallel to enable a deeper understanding of a particularly rare NMD, known as X-linked myotubular myopathy.

Co-Administration of Simvastatin Does Not Potentiate the Benefit of Gene Therapy in the mdx Mouse Model for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most common and cureless muscle pediatric genetic disease, which is caused by the lack or the drastically reduced expression of dystrophin. Experimental therapeutic approaches for DMD have been mainly focused in recent years on attempts to restore the expression of dystrophin. While significant progress was achieved, the therapeutic benefit of treated patients is still unsatisfactory. Efficiency in gene therapy for DMD is hampered not only by incompletely resolved technical issues, but likely also due to the progressive nature of DMD. It is indeed suspected that some of the secondary pathologies, which are evolving over time in DMD patients, are not fully corrected by the restoration of dystrophin expression. We recently identified perturbations of the mevalonate pathway and of cholesterol metabolism in DMD patients. Taking advantage of the mdx model for DMD, we then demonstrated that some of these perturbations are improved by treatment with the cholesterol-lowering drug, simvastatin. In the present investigation, we tested whether the combination of the restoration of dystrophin expression with simvastatin treatment could have an additive beneficial effect in the mdx model. We confirmed the positive effects of microdystrophin, and of simvastatin, when administrated separately, but detected no additive effect by their combination. Thus, the present study does not support an additive beneficial effect by combining dystrophin restoration with a metabolic normalization by simvastatin.

Resolvin-D2 targets myogenic cells and improves muscle regeneration in Duchenne muscular dystrophy

Lack of dystrophin causes muscle degeneration, which is exacerbated by chronic inflammation and reduced regenerative capacity of muscle stem cells in Duchenne Muscular Dystrophy (DMD). To date, glucocorticoids remain the gold standard for the treatment of DMD. These drugs are able to slow down the progression of the disease and increase lifespan by dampening the chronic and excessive inflammatory process; however, they also have numerous harmful side effects that hamper their therapeutic potential. Here, we investigated Resolvin-D2 as a new therapeutic alternative having the potential to target multiple key features contributing to the disease progression. Our in vitro findings showed that Resolvin-D2 promotes the switch of macrophages toward their anti-inflammatory phenotype and increases their secretion of pro-myogenic factors. Moreover, Resolvin-D2 directly targets myogenic cells and promotes their differentiation and the expansion of the pool of myogenic progenitor cells leading to increased myogenesis. These effects are ablated when the receptor Gpr18 is knocked-out, knocked-down, or blocked by the pharmacological antagonist O-1918. Using different mouse models of DMD, we showed that Resolvin-D2 targets both inflammation and myogenesis leading to enhanced muscle function compared to glucocorticoids. Overall, this preclinical study has identified a new therapeutic approach that is more potent than the gold-standard treatment for DMD.

Safety issues and harmful pharmacological interactions of nutritional supplements in Duchenne muscular dystrophy: considerations for Standard of Care and emerging virus outbreaks

At the moment, little treatment options are available for Duchenne muscular dystrophy (DMD). The absence of the dystrophin protein leads to a complex cascade of pathogenic events in myofibres, including chronic inflammation and oxidative stress as well as altered metabolism. The attention towards dietary supplements in DMD is rapidly increasing, with the aim to counteract pathology-related alteration in nutrient intake, the consequences of catabolic distress or to enhance the immunological response of patients as nowadays for the COVID-19 pandemic emergency. By definition, supplements do not exert therapeutic actions, although a great confusion may arise in daily life by the improper distinction between supplements and therapeutic compounds. For most supplements, little research has been done and little evidence is available concerning their effects in DMD as well as their preventing actions against infections. Often these are not prescribed by clinicians and patients/caregivers do not discuss the use with their clinical team. Then, little is known about the real extent of supplement use in DMD patients. It is mistakenly assumed that, since compounds are of natural origin, if a supplement is not effective, it will also do no harm. However, supplements can have serious side effects and also have harmful interactions, in terms of reducing efficacy or leading to toxicity, with other therapies. It is therefore pivotal to shed light on this unclear scenario for the sake of patients. This review discusses the supplements mostly used by DMD patients, focusing on their potential toxicity, due to a variety of mechanisms including pharmacodynamic or pharmacokinetic interactions and contaminations, as well as on reports of adverse events. This overview underlines the need for caution in uncontrolled use of dietary supplements in fragile populations such as DMD patients. A culture of appropriate use has to be implemented between clinicians and patients' groups.

Duchenne muscular dystrophy animal models for high-throughput drug discovery and precision medicine

Introduction: Duchenne muscular dystrophy (DMD) is an X-linked handicapping disease due to the loss of an essential muscle protein dystrophin. Dystrophin-null animals have been extensively used to study disease mechanisms and to develop experimental therapeutics. Despite decades of research, however, treatment options for DMD remain very limited.Areas covered: High-throughput high-content screening and precision medicine offer exciting new opportunities. Here, the authors review animal models that are suitable for these studies.Expert opinion: Nonmammalian models (worm, fruit fly, and zebrafish) are particularly attractive for cost-effective large-scale drug screening. Several promising lead compounds have been discovered using these models. Precision medicine for DMD aims at developing mutation-specific therapies such as exon-skipping and genome editing. To meet these needs, models with patient-like mutations have been established in different species. Models that harbor hotspot mutations are very attractive because the drugs developed in these models can bring mutation-specific therapies to a large population of patients. Humanized hDMD mice carry the entire human dystrophin gene in the mouse genome. Reagents developed in the hDMD mouse-based models are directly translatable to human patients.

A new era in the management of Duchenne muscular dystrophy

The management of Duchenne muscular dystrophy (DMD) has changed considerably over the last few decades. Standards of care have recently been updated, based on systematic reviews of the literature and structured, case-based consensus discussions of experts. Besides addressing muscular function, these recommendations cover most areas of organ involvement and psychosocial issues. Studies employing animal models investigating basic disease mechanisms have increased considerably. Development of valid functional outcome measures enabled high-evidence, clinical trials in males with DMD. Stop codon readthrough with ataluren has revealed some effect in patients with moderate disability and has been approved for males with suitable mutations who are still ambulant. Exon 51 skipping with eteplirsen demonstrated a structural and functional effect in a small group of patients and received restricted approval in the USA. Further trials investigating a broad range of mechanisms are underway. However, much more work is needed to develop more active treatments that stop disease progression. Likewise, the distribution of complex and expensive therapies to underprivileged patients and those in poorer regions must be improved. WHAT THIS PAPER ADDS: Updated standards of care covering most clinical aspects of Duchenne muscular dystrophy (DMD) are available. Adequately controlled clinical trials have allowed initial approval of disease-modifying drugs for small groups of patients. Scientific, economic, and political efforts are needed to make effective therapies available more quickly. Effective therapies should be made available more quickly to patients in low-income regions.