Safety, Tolerability, and Efficacy of Viltolarsen in Boys With Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A Phase 2 Randomized Clinical Trial

Gene-based therapies for neuromuscular disorders

Neuromuscular diseases (NMD) include a broad group of medical conditions with both acquired and genetic causes. In recent years, important advances have been made in the treatment of genetically caused NMD, and most of these advances are due to the implementation of therapies aimed at gene regulation. Among these therapies, gene replacement, small interfering RNA (siRNA), and antisense antinucleotides are the most promising approaches. More importantly, some of these therapies have already gained regulatory approval or are in the final stages of approval. The review focuses on motor neuron diseases, neuropathies, and Duchenne muscular dystrophy, summarizing the most recent developments in gene-based therapies for these conditions.

Long-Term Comparative Efficacy and Safety of Risdiplam and Nusinersen in Children with Type 1 Spinal Muscular Atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is a severe genetic neuromuscular disease characterized by a loss of motor neurons and progressive muscle weakness. Children with untreated type 1 SMA never sit independently and require increasing levels of ventilatory support as the disease progresses. Without intervention, and lacking ventilatory support, death typically occurs before the age of 2 years. There are currently no head-to-head trials comparing available treatments in SMA. Indirect treatment comparisons are therefore needed to provide information on the relative efficacy and safety of SMA treatments for healthcare decision-making.

METHODS

The long-term efficacy and safety of risdiplam versus nusinersen in children with type 1 SMA was evaluated using indirect treatment comparison methodology to adjust for differences between population baseline characteristics, to reduce any potential bias in the comparative analysis. An unanchored matching-adjusted indirect comparison was conducted using risdiplam data from 58 children in FIREFISH (NCT02913482) and published aggregate nusinersen data from 81 children obtained from the ENDEAR (NCT02193074) and SHINE (NCT02594124) clinical trials with at least 36 months of follow-up.

RESULTS

Children with type 1 SMA treated with risdiplam had a 78% reduction in the rate of death, an 81% reduction in the rate of death or permanent ventilation, and a 57% reduction in the rate of serious adverse events compared with children treated with nusinersen. Children treated with risdiplam also had a 45% higher rate of achieving a Hammersmith Infant Neurological Examination, Module 2 motor milestone response and a 186% higher rate of achieving a ≥ 4-point improvement in Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders compared with children treated with nusinersen.

CONCLUSION

Long-term data supported risdiplam as a superior alternative to nusinersen in children with type 1 SMA. Video abstract available for this article. Video abstract (MP4 184542 KB).

Molecular mechanisms and therapeutic strategies for neuromuscular diseases

Neuromuscular diseases encompass a heterogeneous array of disorders characterized by varying onset ages, clinical presentations, severity, and progression. While these conditions can stem from acquired or inherited causes, this review specifically focuses on disorders arising from genetic abnormalities, excluding metabolic conditions. The pathogenic defect may primarily affect the anterior horn cells, the axonal or myelin component of peripheral nerves, the neuromuscular junction, or skeletal and/or cardiac muscles. While inherited neuromuscular disorders have been historically deemed not treatable, the advent of gene-based and molecular therapies is reshaping the treatment landscape for this group of condition. With the caveat that many products still fail to translate the positive results obtained in pre-clinical models to humans, both the technological development (e.g., implementation of tissue-specific vectors) as well as advances on the knowledge of pathogenetic mechanisms form a collective foundation for potentially curative approaches to these debilitating conditions. This review delineates the current panorama of therapies targeting the most prevalent forms of inherited neuromuscular diseases, emphasizing approved treatments and those already undergoing human testing, offering insights into the state-of-the-art interventions.

Empowerment of genetic information by women at-risk of being carriers of Duchenne and Becker muscular dystrophies

The emergence of therapies acting on specific molecular targets for Duchenne and Becker muscular dystrophies (DBMD) led to expanded access of diagnostic DMD analysis. However, it is unclear how much of these advances have also improved healthcare and access to genetic testing for women at-risk of being carriers. This study evaluates the process of genetic counseling and empowerment of genetic information by women from DBMD families. We carried out a cross-sectional study between February and June 2022 in Brazil. The online survey with items regarding sociodemographic data; family history; access to health services; reproductive decisions; and the Genomic Outcome Scale was answered by 123 women recruited from a rare diseases reference service and a nationwide patient advocacy group. Genetic counseling was reported by 77/123 (62.6%) of women and 53.7% reported having performed genetic analysis of DMD. Although the majority knew about the risks for carriers of developing heart disease and muscle weakness, only 35% of potential carriers have had cardiac studies performed at least once in their lives. Country region, type of kinship, number of affected males in the family, age, notion of genetic risk, education level, and participation in advocacy groups were the main factors associated with adequate healthcare access to women and empowerment of genetic information. Education to health professionals and policies to expand access to carrier genetic testing, whether public policies or regulation of pharmaceutical companies' diagnostic programs, is paramount to improve the care of families with DBMD in Brazil.

CRISPR-Based Gene Editing Techniques in Pediatric Neurological Disorders

The emergence of gene editing technologies offers a unique opportunity to develop mutation-specific treatments for pediatric neurological disorders. Gene editing systems can potentially alter disease trajectory by correcting dysfunctional mutations or therapeutically altering gene expression. Clustered regularly interspaced short palindromic repeats (CRISPR)-based approaches are attractive gene therapy platforms to personalize treatments because of their specificity, ease of design, versatility, and cost. However, many such approaches remain in the early stages of development, with ongoing efforts to optimize editing efficiency, minimize unintended off-target effects, and mitigate pathologic immune responses. Given the rapid evolution of CRISPR-based therapies, it is prudent for the clinically based child neurologist to have a conceptual understanding of what such therapies may entail, including both benefits and risks and how such therapies may be clinically applied. In this review, we describe the fundamentals of CRISPR-based therapies, discuss the opportunities and challenges that have arisen, and highlight preclinical work in several pediatric neurological diseases.

State of Gene Therapy for Monogenic Cardiovascular Diseases

Over the past 2 decades, significant efforts have been made to advance gene therapy into clinical practice. Although successful examples exist in other fields, gene therapy for the treatment of monogenic cardiovascular diseases lags behind. In this review, we (1) highlight a brief history of gene therapy, (2) distinguish between gene silencing, gene replacement, and gene editing technologies, (3) discuss vector modalities used in the field with a special focus on adeno-associated viruses, (4) provide examples of gene therapy approaches in cardiomyopathies, channelopathies, and familial hypercholesterolemia, and (5) present current challenges and limitations in the gene therapy field.

Evolving Role of Viltolarsen for Treatment of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is one of the most prevalent X-linked inherited neuromuscular disorders, with an estimated incidence between 1 in 3500 and 5000 live male births. The median life expectancy at birth is around 30 years due to a rapid and severe disease progression. Currently, there is no cure for DMD, and the standard of care is mainly palliative therapy and glucocorticoids to mitigate symptoms and improve quality of life. Recent advances in phosphorodiamidate morpholino antisense oligonucleotide (PMO) technology has proven optimistic in providing a disease-modifying therapy rather than a palliative treatment option through correcting the primary genetic defect of DMD by exon skipping. However, as a result of the high variance in mutations of the dystrophin gene causing DMD, it has been challenging to tailor an effective therapy in most patients. Viltolarsen is effective in 8% of patients and accurately skips exon 53, reestablishing the reading frame and producing a functional form of dystrophin and milder disease phenotype. Results of recently concluded preclinical and clinical trials show significantly increased dystrophin protein expression, no severe adverse effects, and stabilization of motor function. In summary, viltolarsen has provided hope for those working toward giving patients a safe and viable treatment option for managing DMD. This review summarizes an overview of the presentation, pathophysiology, genetics, and current treatment guidelines of DMD, pharmacological profile of viltolarsen, and a summary of the safety and efficacy with additional insights using recent clinical trial data.

Nucleic Acid Therapeutics: Successes, Milestones, and Upcoming Innovation

Nucleic acid-based therapies have become the third major drug class after small molecules and antibodies. The role of nucleic acid-based therapies has been strengthened by recent regulatory approvals and tremendous clinical success. In this review, we look at the major obstacles that have hindered the field, the historical milestones that have been achieved, and what is yet to be resolved and anticipated soon. This review provides a view of the key innovations that are expanding nucleic acid capabilities, setting the stage for the future of nucleic acid therapeutics.

Assembling the RNA therapeutics toolbox

From the approval of COVID-19 mRNA vaccines to the 2023 Nobel Prize awarded for nucleoside base modifications, RNA therapeutics have entered the spotlight and are transforming drug development. While the term "RNA therapeutics" has been used in various contexts, this review focuses on treatments that utilize RNA as a component or target RNA for therapeutic effects. We summarize the latest advances in RNA-targeting tools and RNA-based technologies, including but not limited to mRNA, antisense oligos, siRNAs, small molecules and RNA editors. We focus on the mechanisms of current FDA-approved therapeutics but also provide a discussion on the upcoming workforces. The clinical utility of RNA-based therapeutics is enabled not only by the advances in RNA technologies but in conjunction with the significant improvements in chemical modifications and delivery platforms, which are also briefly discussed in the review. We summarize the latest RNA therapeutics based on their mechanisms and therapeutic effects, which include expressing proteins for vaccination and protein replacement therapies, degrading deleterious RNA, modulating transcription and translation efficiency, targeting noncoding RNAs, binding and modulating protein activity and editing RNA sequences and modifications. This review emphasizes the concept of an RNA therapeutic toolbox, pinpointing the readers to all the tools available for their desired research and clinical goals. As the field advances, the catalog of RNA therapeutic tools continues to grow, further allowing researchers to combine appropriate RNA technologies with suitable chemical modifications and delivery platforms to develop therapeutics tailored to their specific clinical challenges.

Mitochondria and Reactive Oxygen Species: The Therapeutic Balance of Powers for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic progressive muscle-wasting disorder that leads to rapid loss of mobility and premature death. The absence of functional dystrophin in DMD patients reduces sarcolemma stiffness and increases contraction damage, triggering a cascade of events leading to muscle cell degeneration, chronic inflammation, and deposition of fibrotic and adipose tissue. Efforts in the last decade have led to the clinical approval of novel drugs for DMD that aim to restore dystrophin function. However, combination therapies able to restore dystrophin expression and target the myriad of cellular events found impaired in dystrophic muscle are desirable. Muscles are higher energy consumers susceptible to mitochondrial defects. Mitochondria generate a significant source of reactive oxygen species (ROS), and they are, in turn, sensitive to proper redox balance. In both DMD patients and animal models there is compelling evidence that mitochondrial impairments have a key role in the failure of energy homeostasis. Here, we highlighted the main aspects of mitochondrial dysfunction and oxidative stress in DMD and discussed the recent findings linked to mitochondria/ROS-targeted molecules as a therapeutic approach. In this respect, dual targeting of both mitochondria and redox homeostasis emerges as a potential clinical option in DMD.

The Clinical Development of Taldefgrobep Alfa: An Anti-Myostatin Adnectin for the Treatment of Duchenne Muscular Dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a genetic muscle disorder that manifests during early childhood and is ultimately fatal. Recently approved treatments targeting the genetic cause of DMD are limited to specific subpopulations of patients, highlighting the need for therapies with wider applications. Pharmacologic inhibition of myostatin, an endogenous inhibitor of muscle growth produced almost exclusively in skeletal muscle, has been shown to increase muscle mass in several species, including humans. Taldefgrobep alfa is an anti-myostatin recombinant protein engineered to bind to and block myostatin signaling. Preclinical studies of taldefgrobep alfa demonstrated significant decreases in myostatin and increased lower limb volume in three animal species, including dystrophic mice.

METHODS

This manuscript reports the cumulative data from three separate clinical trials of taldefgrobep alfa in DMD: a phase 1 study in healthy adult volunteers (NCT02145234), and two randomized, double-blind, placebo-controlled studies in ambulatory boys with DMD-a phase 1b/2 trial assessing safety (NCT02515669) and a phase 2/3 trial including the North Star Ambulatory Assessment (NSAA) as the primary endpoint (NCT03039686).

RESULTS

In healthy adult volunteers, taldefgrobep alfa was generally well tolerated and resulted in a significant increase in thigh muscle volume. Treatment with taldefgrobep alfa was associated with robust dose-dependent suppression of free myostatin. In the phase 1b/2 trial, myostatin suppression was associated with a positive effect on lean body mass, though effects on muscle mass were modest. The phase 2/3 trial found that the effects of treatment did not meet the primary endpoint pre-specified futility analysis threshold (change from baseline of ≥ 1.5 points on the NSAA total score).

CONCLUSIONS

The futility analysis demonstrated that taldefgrobep alfa did not result in functional change for boys with DMD. The program was subsequently terminated in 2019. Overall, there were no safety concerns, and no patients were withdrawn from treatment as a result of treatment-related adverse events or serious adverse events.

TRIAL REGISTRATION

NCT02145234, NCT02515669, NCT03039686.

Gene therapy for monogenic disorders: challenges, strategies, and perspectives

Monogenic disorders refer to a group of human diseases caused by mutations in single genes. While disease-modifying therapies have offered some relief from symptoms and delayed progression for some monogenic diseases, most of these diseases still lack effective treatments. In recent decades, gene therapy has emerged as a promising therapeutic strategy for genetic disorders. Researchers have developed various gene manipulation tools and gene delivery systems to treat monogenic diseases. Despite this progress, concerns about inefficient delivery, persistent expression, immunogenicity, toxicity, capacity limitation, genomic integration, and limited tissue specificity still need to be addressed. This review gives an overview of commonly used gene therapy and delivery tools, along with the challenges they face and potential strategies to counter them.

Genetic testing in adults with neurologic disorders: indications, approach, and clinical impacts

The role of genetic testing in neurologic clinical practice has increased dramatically in recent years, driven by research on genetic causes of neurologic disease and increased availability of genetic sequencing technology. Genetic testing is now indicated for adults with a wide range of common neurologic conditions. The potential clinical impacts of a genetic diagnosis are also rapidly expanding, with a growing list of gene-specific treatments and clinical trials, in addition to important implications for prognosis, surveillance, family planning, and diagnostic closure. The goals of this review are to provide practical guidance for clinicians about the role of genetics in their practice and to provide the neuroscience research community with a broad survey of current progress in this field. We aim to answer three questions for the neurologist in practice: Which of my patients need genetic testing? What testing should I order? And how will genetic testing help my patient? We focus on common neurologic disorders and presentations to the neurology clinic. For each condition, we review the most current guidelines and evidence regarding indications for genetic testing, expected diagnostic yield, and recommended testing approach. We also focus on clinical impacts of genetic diagnoses, highlighting a number of gene-specific therapies recently approved for clinical use, and a rapidly expanding landscape of gene-specific clinical trials, many using novel nucleotide-based therapeutic modalities like antisense oligonucleotides and gene transfer. We anticipate that more widespread use of genetic testing will help advance therapeutic development and improve the care, and outcomes, of patients with neurologic conditions.

RNA therapeutics history and future perspectives

Ribonucleic acid (RNA) therapeutics have significantly used RNA-based drugs to the prevention and treatment of diseases as effective messenger RNA-based vaccines in response to the COVID-19 pandemic. The RNA therapeutics with five classes including antisense oligonucleotide, small interfering RNA, microRNA, APTAMER and messenger RNAs are being quickly developed to treat various human diseases as neurological disease, cardiovascular disease, genetic and rare disease, cancer disease, coronavirus disease… which cannot be treated by other conventional drugs as small molecule-based drugs and antibodies. Therefore, the discovery of these RNA therapeutics created a new avenue for treatment of various human diseases. This chapter demonstrates the history of important discoveries in RNA biology and their impact on key developments in RNA therapeutics as well as the advantages of RNA therapeutics; RNA therapeutics describes the action mechanisms and examples of RNA-based drugs approved for treatment of various disease; and RNA therapeutics discusses delivery methods for RNA therapeutics to target organs and cells. In conclusion, this chapter is designed to offer an updated important development and advance of RNA therapeutics for the prevention and treatment of various human diseases.

How Can Proteomics Help to Elucidate the Pathophysiological Crosstalk in Muscular Dystrophy and Associated Multi-System Dysfunction?

This perspective article is concerned with the question of how proteomics, which is a core technique of systems biology that is deeply embedded in the multi-omics field of modern bioresearch, can help us better understand the molecular pathogenesis of complex diseases. As an illustrative example of a monogenetic disorder that primarily affects the neuromuscular system but is characterized by a plethora of multi-system pathophysiological alterations, the muscle-wasting disease Duchenne muscular dystrophy was examined. Recent achievements in the field of dystrophinopathy research are described with special reference to the proteome-wide complexity of neuromuscular changes and body-wide alterations/adaptations. Based on a description of the current applications of top-down versus bottom-up proteomic approaches and their technical challenges, future systems biological approaches are outlined. The envisaged holistic and integromic bioanalysis would encompass the integration of diverse omics-type studies including inter- and intra-proteomics as the core disciplines for systematic protein evaluations, with sophisticated biomolecular analyses, including physiology, molecular biology, biochemistry and histochemistry. Integrated proteomic findings promise to be instrumental in improving our detailed knowledge of pathogenic mechanisms and multi-system dysfunction, widening the available biomarker signature of dystrophinopathy for improved diagnostic/prognostic procedures, and advancing the identification of novel therapeutic targets to treat Duchenne muscular dystrophy.

Increase in Full-Length Dystrophin by Exon Skipping in Duchenne Muscular Dystrophy Patients with Single Exon Duplications: An Open-label Study

Single exon duplications account for disease in a minority of Duchenne muscular dystrophy patients. Exon skipping in these patients has the potential to be highly therapeutic through restoration of full-length dystrophin expression. We conducted a 48-week open label study of casimersen and golodirsen in 3 subjects with an exon 45 or 53 duplication. Two subjects (aged 18 and 23 years) were non-ambulatory at baseline. Upper limb, pulmonary, and cardiac function appeared stable in the 2 subjects in whom they could be evaluated. Dystrophin expression increased from 0.94 % ±0.59% (mean±SD) of normal to 5.1% ±2.9% by western blot. Percent dystrophin positive fibers also rose from 14% ±17% at baseline to 50% ±42% . Our results provide initial evidence that the use of exon-skipping drugs may increase dystrophin levels in patients with single-exon duplications.

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum of Disease

Background

Duchenne muscular dystrophy (DMD) and related dystrophinopathies are neuromuscular conditions with great unmet medical needs that require the development of effective medical treatments.

Objective

To aid sponsors in clinical development of drugs and therapeutic biological products for treating DMD across the disease spectrum by integrating advancements, patient registries, natural history studies, and more into a comprehensive guidance.

Methods

This guidance emerged from collaboration between the FDA, the Duchenne community, and industry stakeholders. It entailed a structured approach, involving multiple committees and boards. From its inception in 2014, the guidance underwent revisions incorporating insights from gene therapy studies, cardiac function research, and innovative clinical trial designs.

Results

The guidance provides a deeper understanding of DMD and its variants, focusing on patient engagement, diagnostic criteria, natural history, biomarkers, and clinical trials. It underscores patient-focused drug development, the significance of dystrophin as a biomarker, and the pivotal role of magnetic resonance imaging in assessing disease progression. Additionally, the guidance addresses cardiomyopathy's prominence in DMD and the burgeoning field of gene therapy.

Conclusions

The updated guidance offers a comprehensive understanding of DMD, emphasizing patient-centric approaches, innovative trial designs, and the importance of biomarkers. The focus on cardiomyopathy and gene therapy signifies the evolving realm of DMD research. It acts as a crucial roadmap for sponsors, potentially leading to improved treatments for DMD.

Evaluation of Chemically Modified Nucleic Acid Analogues for Splice Switching Application

In recent years, several splice switching antisense oligonucleotide (ASO)-based therapeutics have gained significant interest, and several candidates received approval for clinical use for treating rare diseases, in particular, Duchenne muscular dystrophy and spinal muscular atrophy. These ASOs are fully modified; in other words, they are composed of chemically modified nucleic acid analogues instead of natural RNA oligomers. This has significantly improved drug-like properties of these ASOs in terms of efficacy, stability, pharmacokinetics, and safety. Although chemical modifications of oligonucleotides have been discussed previously for numerous applications including nucleic acid aptamers, small interfering RNA, DNAzyme, and ASO, to the best of our knowledge, none of them have solely focused on the analogues that have been utilized for splice switching applications. To this end, we present here a comprehensive review of different modified nucleic acid analogues that have been explored for developing splice switching ASOs. In addition to the antisense chemistry, we also endeavor to provide a brief historical overview of the approved spice switching ASO drugs, including a list of drugs that have entered human clinical trials. We hope this work will inspire further investigations into expanding the potential of novel nucleic acid analogues for constructing splice switching ASOs.

Persistence of exon 2 skipping and dystrophin expression at 18 months after U7snRNA-mediated therapy in the Dup2 mouse model

Duchenne muscular dystrophy (DMD) is a progressive X-linked disease caused by mutations in the DMD gene that prevent the expression of a functional dystrophin protein. Exon duplications represent 6%-11% of mutations, and duplications of exon 2 (Dup2) are the most common (∼11%) of duplication mutations. An exon-skipping strategy for Dup2 mutations presents a large therapeutic window. Skipping one exon copy results in full-length dystrophin expression, whereas skipping of both copies (Del2) activates an internal ribosomal entry site (IRES) in exon 5, inducing the expression of a highly functional truncated dystrophin isoform. We have previously confirmed the therapeutic efficacy of AAV9.U7snRNA-mediated skipping in the Dup2 mouse model and showed the absence of off-target splicing effects and lack of toxicity in mice and nonhuman primates. Here, we report long-term dystrophin expression data following the treatment of 3-month-old Dup2 mice with the scAAV9.U7.ACCA vector. Significant exon 2 skipping and robust dystrophin expression in the muscles and hearts of treated mice persist at 18 months after treatment, along with the partial rescue of muscle function. These data extend our previous findings and show that scAAV9.U7.ACCA provides long-term protection by restoring the disrupted dystrophin reading frame in the context of exon 2 duplications.

Exon 44 skipping in Duchenne muscular dystrophy: NS-089/NCNP-02, a dual-targeting antisense oligonucleotide

Exon-skipping therapy mediated by antisense oligonucleotides is expected to provide a therapeutic option for Duchenne muscular dystrophy. Antisense oligonucleotides for exon skipping reported so far target a single continuous sequence in or around the target exon. In the present study, we investigated antisense oligonucleotides for exon 44 skipping (applicable to approximately 6% of all Duchenne muscular dystrophy patients) to improve activity by using a novel antisense oligonucleotide design incorporating two connected sequences. Phosphorodiamidate morpholino oligomers targeting two separate sequences in exon 44 were created to target two splicing regulators in exon 44 simultaneously, and their exon 44 skipping was measured. NS-089/NCNP-02 showed the highest skipping activity among the oligomers. NS-089/NCNP-02 also induced exon 44 skipping and dystrophin protein expression in cells from a Duchenne muscular dystrophy patient to whom exon 44 skipping is applicable. We also assessed the in vivo activity of NS-089/NCNP-02 by intravenous administration to cynomolgus monkeys. NS-089/NCNP-02 induced exon 44 skipping in skeletal and cardiac muscle of cynomolgus monkeys. In conclusion, NS-089/NCNP-02, an antisense oligonucleotide with a novel connected-sequence design, showed highly efficient exon skipping both in vitro and in vivo.

Networking to Optimize Dmd exon 53 Skipping in the Brain of mdx52 Mouse Model

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene that disrupt the open reading frame and thus prevent production of functional dystrophin proteins. Recent advances in DMD treatment, notably exon skipping and AAV gene therapy, have achieved some success aimed at alleviating the symptoms related to progressive muscle damage. However, they do not address the brain comorbidities associated with DMD, which remains a critical aspect of the disease. The mdx52 mouse model recapitulates one of the most frequent genetic pathogenic variants associated with brain involvement in DMD. Deletion of exon 52 impedes expression of two brain dystrophins, Dp427 and Dp140, expressed from distinct promoters. Interestingly, this mutation is eligible for exon skipping strategies aimed at excluding exon 51 or 53 from dystrophin mRNA. We previously showed that exon 51 skipping can restore partial expression of internally deleted yet functional Dp427 in the brain following intracerebroventricular (ICV) injection of antisense oligonucleotides (ASO). This was associated with a partial improvement of anxiety traits, unconditioned fear response, and Pavlovian fear learning and memory in the mdx52 mouse model. In the present study, we investigated in the same mouse model the skipping of exon 53 in order to restore expression of both Dp427 and Dp140. However, in contrast to exon 51, we found that exon 53 skipping was particularly difficult in mdx52 mice and a combination of multiple ASOs had to be used simultaneously to reach substantial levels of exon 53 skipping, regardless of their chemistry (tcDNA, PMO, or 2'MOE). Following ICV injection of a combination of ASO sequences, we measured up to 25% of exon 53 skipping in the hippocampus of treated mdx52 mice, but this did not elicit significant protein restoration. These findings indicate that skipping mouse dystrophin exon 53 is challenging. As such, it has not yet been possible to answer the pertinent question whether rescuing both Dp427 and Dp140 in the brain is imperative to more optimal treatment of neurological aspects of dystrophinopathy.

Challenges of Assessing Exon 53 Skipping of the Human DMD Transcript with Locked Nucleic Acid-Modified Antisense Oligonucleotides in a Mouse Model for Duchenne Muscular Dystrophy

Antisense oligonucleotide (AON)-mediated exon skipping is a promising therapeutic approach for Duchenne muscular dystrophy (DMD) patients to restore dystrophin expression by reframing the disrupted open reading frame of the DMD transcript. However, the treatment efficacy of the already conditionally approved AONs remains low. Aiming to optimize AON efficiency, we assessed exon 53 skipping of the DMD transcript with different chemically modified AONs, all with a phosphorothioate backbone: 2'-O-methyl (2'OMe), locked nucleic acid (LNA)-2'OMe, 2'-fluoro (FRNA), LNA-FRNA, αLNA-FRNA, and FANA-LNA-FRNA. Efficient exon 53 skipping was observed with the FRNA, LNA-FRNA, and LNA-2'OMe AONs in human control myoblast cultures. Weekly subcutaneous injections (50 mg/kg AON) for a duration of 6 weeks were well tolerated by hDMDdel52/mdx males. Treatment with the LNA-FRNA and LNA-2'OMe AONs resulted in pronounced exon 53 skip levels in skeletal muscles and heart up to 90%, but no dystrophin restoration was observed. This discrepancy was mainly ascribed to the strong binding nature of LNA modifications to RNA, thereby interfering with the amplification of the unskipped product resulting in artificial overamplification of the exon 53 skip product. Our study highlights that treatment effect on RNA and protein level should both be considered when assessing AON efficiency.

Sleep in pediatric neuromuscular disorders

Sleep disordered breathing (SDB) is prevalent among children with neuromuscular disorders (NMD). The combination of respiratory muscle weakness, altered drive, and chest wall distortion due to scoliosis make sleep a stressful state in this population. Symptomatology can range from absent to snoring, nocturnal awakenings, morning headaches, and excessive daytime sleepiness. Sequelae of untreated SDB includes cardiovascular effects, metabolic derangements, and neurocognitive concerns which can be compounded by those innate to the NMD. The clinician should have a low threshold for obtaining polysomnography and recognize the nuances of individual disorders due to disproportionately impacted muscle groups such as hypoventilation in ambulating patients from diaphragm weakness. Non-invasive or invasive ventilation are the mainstay of treatment. In this review we explore the diagnosis and treatment of SDB in children with various NMD.

Assessment of Motor Unit Potentials Duration as the Biomarker of DT-DEC01 Cell Therapy Efficacy in Duchenne Muscular Dystrophy Patients up to 12 Months After Systemic-Intraosseous Administration

Duchenne muscular dystrophy (DMD) is a lethal X-linked disease caused by mutations in the dystrophin gene, leading to muscle degeneration and wasting. Electromyography (EMG) is an objective electrophysiological biomarker of muscle fiber function in muscular dystrophies. A novel, DT-DEC01 therapy, consisting of Dystrophin Expressing Chimeric (DEC) cells created by fusing allogeneic myoblasts from normal donors with autologous myoblasts from DMD-affected patients, was assessed for safety and preliminary efficacy in boys of age 6-15 years old (n = 3). Assessments included EMG testing of selected muscles of upper (deltoideus, biceps brachii) and lower (rectus femoris and gastrocnemius) extremities at the screening visit and at 3, 6, and 12 months following systemic-intraosseous administration of a single low dose of DT-DEC01 therapy (Bioethics Committee approval no. 46/2019). No immunosuppression was administered. Safety of DT-DEC01 was confirmed by the lack of therapy-related Adverse Events or Serious Adverse Events up to 22 months following DT-DEC01 administration. EMG of selected muscles of both, ambulatory and non-ambulatory patients confirmed preliminary efficacy of DT-DEC01 therapy by an increase in motor unit potentials (MUP) duration, amplitudes, and polyphasic MUPs at 12 months. This study confirmed EMG as a reliable and objective biomarker of functional assessment in DMD patients after intraosseous administration of the novel DT-DEC01 therapy.

Antisense oligonucleotides: a novel Frontier in pharmacological strategy

Antisense oligonucleotides (ASOs) are short single stranded synthetic RNA or DNA molecules, whereas double-stranded RNA nucleotide sequences are called small interfering RNA (siRNA). ASOs bind to complementary nucleic acid sequences impacting the associated functions of the targeted nucleic acids. They represent an emerging class of drugs that, through a revolutionary mechanism of action, aim to directly regulate disease-causing genes and their variants, providing an alternative tool to traditional "protein-specific" therapies. The majority of the ASOs are designed to treat orphan genetic disorders that in most of the cases are seriously disabling and still lacking an adequate therapy. In order to translate ASOs into clinical success, constant technological advances have been instrumental in overcoming several pharmacological, toxicological and formulation limitations. Accordingly, chemical structures have been recently implemented and new bio-conjugation and nanocarriers formulation strategies explored. The aim of this work is to offer an overview of the antisense technology with a comparative analysis of the oligonucleotides approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA).

Therapeutic approaches for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a monogenic muscle-wasting disorder and a priority candidate for molecular and cellular therapeutics. Although rare, it is the most common inherited myopathy affecting children and so has been the focus of intense research activity. It is caused by mutations that disrupt production of the dystrophin protein, and a plethora of drug development approaches are under way that aim to restore dystrophin function, including exon skipping, stop codon readthrough, gene replacement, cell therapy and gene editing. These efforts have led to the clinical approval of four exon skipping antisense oligonucleotides, one stop codon readthrough drug and one gene therapy product, with other approvals likely soon. Here, we discuss the latest therapeutic strategies that are under development and being deployed to treat DMD. Lessons from these drug development programmes are likely to have a major impact on the DMD field, but also on molecular and cellular medicine more generally. Thus, DMD is a pioneer disease at the forefront of future drug discovery efforts, with these experimental treatments paving the way for therapies using similar mechanisms of action being developed for other genetic diseases.

269th ENMC international workshop: 10 years of clinical trials in Duchenne muscular dystrophy - What have we learned? 9-11 December 2022, Hoofddorp, The Netherlands

There are multiple avenues for therapeutic development in Duchenne muscular dystrophy (DMD), which are highlighted in the first section of this report for the "10 years of Clinical trials in DMD - What have we learned?" workshop. This report then provides an overview of the presentations made at the workshop grouped into the following core themes: trial outcomes, disease heterogeneity, meaningfulness of outcomes and the utility of real-world data in trials. Finally, we present the consensus that was achieved at the workshop on the learning points from 10 years of clinical trials in DMD, and possible action points from these. This includes further work in expanding the scope and range of trial outcomes and assessing the efficacy of new trial structures for DMD. We also highlight several points which should be addressed during future interactions with regulators, such as clinical meaningfulness and the use of real-world data.

Cellular pathogenesis of Duchenne muscular dystrophy: progressive myofibre degeneration, chronic inflammation, reactive myofibrosis and satellite cell dysfunction

Duchenne muscular dystrophy is a highly progressive muscle wasting disease of early childhood and characterized by complex pathophysiological and histopathological changes in the voluntary contractile system, including myonecrosis, chronic inflammation, fat substitution and reactive myofibrosis. The continued loss of functional myofibres and replacement with non-contractile cells, as well as extensive tissue scarring and decline in tissue elasticity, leads to severe skeletal muscle weakness. In addition, dystrophic muscles exhibit a greatly diminished regenerative capacity to counteract the ongoing process of fibre degeneration. In normal muscle tissues, an abundant stem cell pool consisting of satellite cells that are localized between the sarcolemma and basal lamina, provides a rich source for the production of activated myogenic progenitor cells that are involved in efficient myofibre repair and tissue regeneration. Interestingly, the self-renewal of satellite cells for maintaining an essential pool of stem cells in matured skeletal muscles is increased in dystrophin-deficient fibres. However, satellite cell hyperplasia does not result in efficient recovery of dystrophic muscles due to impaired asymmetric cell divisions. The lack of expression of the full-length dystrophin isoform Dp427-M, which is due to primary defects in the DMD gene,  appears to affect key regulators of satellite cell polarity causing a reduced differentiation of myogenic progenitors, which are essential for myofibre regeneration. This review outlines the complexity of dystrophinopathy and describes the importance of the pathophysiological role of satellite cell dysfunction. A brief discussion of the bioanalytical usefulness of single cell proteomics for future studies of satellite cell biology is provided.

Prediction of Human Pharmacokinetics of Phosphorodiamidate Morpholino Oligonucleotides in Duchenne Muscular Dystrophy Patients Using Viltolarsen

Several modified antisense oligonucleotides (ASOs) have recently been approved for clinical use. Some are phosphorodiamidate morpholino oligomers (PMOs), which, unlike other nucleic acids, are not negatively charged. Thus, PMOs differ from other ASOs in their pharmacokinetic (PK) properties. Drugs with a PMO backbone have been administered to Duchenne muscular dystrophy pediatric patients; however, appropriate methodologies are not currently available to predict their human PK from nonclinical data. In this study, we used viltolarsen as a representative PMO to investigate the applicability of the allometric scaling approach to human PK prediction. We first summarized the nonclinical and clinical PK data for viltolarsen as showing high total clearance, low serum protein binding, metabolic resistance, and urinary excretion as the unchanged drug in both animals and humans. We then investigate the PK of viltolarsen in mice, rats, cynomolgus monkeys, and dogs and used the results, with body weight, to extrapolate to humans by several methods. The estimate of human total clearance obtained from cynomolgus monkeys was the best, and body weight may be the key factor in accurately predicting human total clearance. In contrast, all of the well-known prediction methods for the volume of distribution at steady state gave underestimates. However, the human PK profiles predicted from the PK parameters in cynomolgus monkeys fit the observed human plasma concentrations well. These results are expected to contribute to the further development of PMOs. SIGNIFICANCE STATEMENT: We investigated how to predict the human PK of phosphorodiamidate morpholino oligomers from nonclinical data. The estimates of human PK parameters and profiles determined from cynomolgus monkeys by an allometric scaling approach were the most suitable, and the cynomolgus monkey body weight may be the key factor in accurately predicting human total clearance.

Evolving Therapeutic Options for the Treatment of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. It is caused by mutations in the DMD gene, leading to reduced or absent expression of the dystrophin protein. Clinically, this results in loss of ambulation, cardiomyopathy, respiratory failure, and eventually death. In the past decades, the use of corticosteroids has slowed down the disease progression. More recently, the development of genetically mediated therapies has emerged as the most promising treatment for DMD. These strategies include exon skipping with antisense oligonucleotides, gene replacement therapy with adeno-associated virus, and gene editing with CRISPR (clustered regularly interspaced short palindromic repeats) technology. In this review, we highlight the most up-to-date therapeutic progresses in the field, with emphasis on past and recent experiences, as well as the latest clinical results of DMD micro-dystrophin gene therapy. Additionally, we discuss the lessons learned along the way and the challenges encountered, all of which have helped advance the field, with the potential to finally alleviate such a devastating disease.

Expression and function of four AAV-based constructs for dystrophin restoration in the mdx mouse model of Duchenne muscular dystrophy

Robust expression of shortened, functional dystrophin provided impetus to develop adeno-associated virus (AAV)-based constructs for clinical application. Because several cassettes are being tested in clinical trials, this study compared the efficacies of four shortened dystrophin-promoter combinations with implications for outcomes in clinical trials: MHCK7 or MCK promoter with a shortened dystrophin transgene containing the N-terminus and spectrin repeats R1, R2, R3 and R24 (rAAVrh74.MHCK7.micro-dystrophin and rAAVrh74.MCK.micro-dystrophin, respectively); shortened dystrophin construct containing the neuronal nitric oxide (nNOS) binding site (rAAVrh74.MHCK7.DV.mini-dystrophin); and shortened dystrophin containing the C-terminus (rAAVrh74.MHCK7.micro-dystrophin.Cterm). Functional and histological benefit were examined at 4 weeks following intramuscular delivery in mdx mice. rAAVrh74.MHCK7.micro-dystrophin provided the most robust transgene expression and significantly increased specific force output in the tibialis anterior muscle. Muscle environment was normalized (i.e. reductions in central nucleation), indicating functional and histological advantages of rAAVrh74.MHCK7.micro-dystrophin. Thus, promoter choice and transgene design are critical for optimal dystrophin expression/distribution for maximal functional improvement.

Deletion of miR-146a enhances therapeutic protein restoration in model of dystrophin exon skipping

Duchenne muscular dystrophy (DMD) is a progressive muscle disease caused by the absence of dystrophin protein. One current DMD therapeutic strategy, exon skipping, produces a truncated dystrophin isoform using phosphorodiamidate morpholino oligomers (PMOs). However, the potential of exon skipping therapeutics has not been fully realized as increases in dystrophin protein have been minimal in clinical trials. Here, we investigate how miR-146a-5p, which is highly elevated in dystrophic muscle, impacts dystrophin protein levels. We find inflammation strongly induces miR-146a in dystrophic, but not wild-type myotubes. Bioinformatics analysis reveals that the dystrophin 3'UTR harbors a miR-146a binding site, and subsequent luciferase assays demonstrate miR-146a binding inhibits dystrophin translation. In dystrophin-null mdx52 mice, co-injection of miR-146a reduces dystrophin restoration by an exon 51 skipping PMO. To directly investigate how miR-146a impacts therapeutic dystrophin rescue, we generated mdx52 with body-wide miR-146a deletion (146aX). Administration of an exon skipping PMO via intramuscular or intravenous injection markedly increases dystrophin protein levels in 146aX versus mdx52 muscles; skipped dystrophin transcript levels are unchanged, suggesting a post-transcriptional mechanism-of-action. Together, these data show that miR-146a expression opposes therapeutic dystrophin restoration, suggesting miR-146a inhibition warrants further research as a potential DMD exon skipping co-therapy.

Systemic deletion of DMD exon 51 rescues clinically severe Duchenne muscular dystrophy in a pig model lacking DMD exon 52

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease caused by mutations in the DMD gene, leading to complete absence of dystrophin and progressive degeneration of skeletal musculature and myocardium. In DMD patients and in a corresponding pig model with a deletion of DMD exon 52 (DMDΔ52), expression of an internally shortened dystrophin can be achieved by skipping of DMD exon 51 to reframe the transcript. To predict the best possible outcome of this strategy, we generated DMDΔ51-52 pigs, additionally representing a model for Becker muscular dystrophy (BMD). DMDΔ51-52 skeletal muscle and myocardium samples stained positive for dystrophin and did not show the characteristic dystrophic alterations observed in DMDΔ52 pigs. Western blot analysis confirmed the presence of dystrophin in the skeletal muscle and myocardium of DMDΔ51-52 pigs and its absence in DMDΔ52 pigs. The proteome profile of skeletal muscle, which showed a large number of abundance alterations in DMDΔ52 vs. wild-type (WT) samples, was normalized in DMDΔ51-52 samples. Cardiac function at age 3.5 mo was significantly reduced in DMDΔ52 pigs (mean left ventricular ejection fraction 58.8% vs. 70.3% in WT) but completely rescued in DMDΔ51-52 pigs (72.3%), in line with normalization of the myocardial proteome profile. Our findings indicate that ubiquitous deletion of DMD exon 51 in DMDΔ52 pigs largely rescues the rapidly progressing, severe muscular dystrophy and the reduced cardiac function of this model. Long-term follow-up studies of DMDΔ51-52 pigs will show if they develop symptoms of the milder BMD.

Cardiac therapies for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating disease that results in life-limiting complications such as loss of skeletal muscle function as well as respiratory and cardiac complications. Advanced therapeutics in pulmonary care have significantly reduced respiratory complication-related mortality, making cardiomyopathy the main determinant factor of survival. While there are multiple therapies such as the use of anti-inflammatory drugs, physical therapy, and ventilatory assistance targeted toward delaying the disease progression in DMD, a cure remains elusive. In the last decade, several therapeutic approaches have been developed to improve patient survival. These include small molecule-based therapy, micro-dystrophin gene delivery, CRISPR-mediated gene editing, nonsense readthrough, exon skipping, and cardiosphere-derived cell therapy. Associated with the specific benefits of each of these approaches are their individual risks and limitations. The variability in the genetic aberrations leading to DMD also limits the widespread use of these therapies. While numerous approaches have been explored to treat DMD pathophysiology, only a handful have successfully advanced through the preclinical stages. In this review, we summarize the currently approved as well as the most promising therapeutics undergoing clinical trials aimed toward treating DMD with a focus on its cardiac manifestations.

Gene therapy for Duchenne muscular dystrophy: an update on the latest clinical developments

INTRODUCTION

Duchenne muscular dystrophy (DMD) is one of the most severe and devastating neuromuscular hereditary diseases with a male newborn incidence of 20 000 cases each year. The disease caused by mutations (exon deletions, nonsense mutations, intra-exonic insertions or deletions, exon duplications, splice site defects, and deep intronic mutations) in the DMD gene, progressively leads to muscle wasting and loss of ambulation. This situation is painful for both patients and their families, calling for an emergent need for effective treatments.

AREAS COVERED

In this review, the authors describe the state of the gene therapy approach in clinical trials for DMD. This therapeutics included gene replacement, gene substitution, RNA-based therapeutics, readthrough mutation, and the CRISPR approach.

EXPERT OPINION

Only a few drug candidates have yet been granted conditional approval for the treatment of DMD. Most of these therapies have only a modest capability to restore the dystrophin or improve muscle function, suggesting an important unmet need in the development of DMD therapeutics. Complementary genes and cellular therapeutics need to be explored to both restore dystrophin, improve muscle function, and efficiently reconstitute the muscle fibers in the advanced stage of the disease.

Viltolarsen: a treatment option for Duchenne muscular dystrophy patients who are amenable to exon 53 skipping therapy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a progressive genetic disease leading to muscular weakness. DMD is caused by mutations of the dystrophin gene on the X chromosome that is responsible for production of dystrophin protein. Dystrophin contributes to structural support in muscle cells and mutations result in dystrophin protein deficiency which causes muscle damage and the associated clinical presentation. Exon skipping medications, including the exon 53 targeting viltolarsen, are the first agents with the ability to partially restore dystrophin protein.

AREAS COVERED

Herein, the authors profile viltolarsen for the DMD patients who are amenable to exon 53 skipping therapy and provide their expert perspectives on this subject.

EXPERT OPINION

Current findings suggest that viltolarsen could play a role in the current and possible future treatment of DMD. Viltolarsen seems to be safe and restores dystrophin protein to around 6% of the normal level. Due to orphan drug status, after the completion of the phase 2 clinical trial, viltolarsen was granted accelerated approval in Japan and in the US. A phase 3 trial is currently in progress and needs to earn full approval. Although a multidisciplinary approach continues to be critical, the addition of exon skipping agents like viltolarsen may improve the quality of patients' lives. However, data on the long-term safety and efficacy of this medication are not yet available due to its recent accelerated approval.

Duchenne muscular dystrophy: disease mechanism and therapeutic strategies

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.

Duchenne muscular dystrophy: pathogenesis and promising therapies

Duchenne muscular dystrophy (DMD) is a severe, progressive, muscle-wasting disease, characterized by progressive deterioration of skeletal muscle that causes rapid loss of mobility. The failure in respiratory and cardiac muscles is the underlying cause of premature death in most patients with DMD. Mutations in the gene encoding dystrophin result in dystrophin deficiency, which is the underlying pathogenesis of DMD. Dystrophin-deficient myocytes are dysfunctional and vulnerable to injury, triggering a series of subsequent pathological changes. In this review, we detail the molecular mechanism of DMD, dystrophin deficiency-induced muscle cell damage (oxidative stress injury, dysregulated calcium homeostasis, and sarcolemma instability) and other cell damage and dysfunction (neuromuscular junction impairment and abnormal differentiation of muscle satellite). We also describe aberrant function of other cells and impaired muscle regeneration due to deterioration of the muscle microenvironment, and dystrophin deficiency-induced multiple organ dysfunction, while summarizing the recent advances in the treatment of DMD.

Pamrevlumab, a Fully Human Monoclonal Antibody Targeting Connective Tissue Growth Factor, for Non-Ambulatory Patients with Duchenne Muscular Dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a neuromuscular disease stemming from dystrophin gene mutations. Lack of dystrophin leads to progressive muscle damage and replacement of muscle with fibrotic and adipose tissue. Pamrevlumab (FG-3019), a fully human monoclonal antibody that binds to connective tissue growth factor (CTGF), is in Phase III development for treatment of DMD and other diseases.

METHODS

MISSION (Study 079; NCT02606136) was an open-label, Phase II, single-arm trial of pamrevlumab in 21 non-ambulatory patients with DMD (aged≥12 years, receiving corticosteroids) who received 35-mg/kg intravenous infusions every 2 weeks for 2 years. The primary endpoint was change from baseline in percent predicted forced vital capacity (ppFVC). Secondary endpoints included other pulmonary function tests, upper limb function and strength assessments, and changes in upper arm fat and fibrosis scores on magnetic resonance imaging.

RESULTS

Fifteen patients completed the trial. Annual change from baseline (SE) in ppFVC was -4.2 (0.7) (95% CI -5.5, -2.8). Rate of decline in ppFVC in pamrevlumab-treated patients was slower than observed in historical published trials of non-ambulatory patients. MISSION participants experienced slower-than-anticipated muscle function declines compared with natural history and historical published trials of non-ambulatory patients with DMD. Pamrevlumab was well-tolerated. Treatment-emergent adverse events were mild to moderate, and none led to study discontinuation.

CONCLUSIONS

nti-CTGF therapy with pamrevlumab represents a potential treatment for DMD. The lack of internal control group limits the results.

Upper Limb Changes in DMD Patients Amenable to Skipping Exons 44, 45, 51 and 53: A 24-Month Study

INTRODUCTION

The Performance of Upper Limb version 2.0 (PUL 2.0) is increasingly used in Duchenne Muscular Dystrophy (DMD) to study longitudinal functional changes of motor upper limb function in ambulant and non-ambulant patients. The aim of this study was to evaluate changes in upper limb functions in patients carrying mutations amenable to skipping exons 44, 45, 51 and 53.

METHODS

All DMD patients were assessed using the PUL 2.0 for at least 2 years, focusing on 24-month paired visits in those with mutations eligible for skipping exons 44, 45, 51 and 53.

RESULTS

285 paired assessments were available. The mean total PUL 2.0 12-month change was -0.67 (2.80), -1.15 (3.98), -1.46 (3.37) and -1.95 (4.04) in patients carrying mutations amenable to skipping exon 44, 45, 51 and 53, respectively. The mean total PUL 2.0 24-month change was -1.47 (3.73), -2.78 (5.86), -2.95 (4.56) and -4.53 (6.13) in patients amenable to skipping exon 44, 45, 51 and 53, respectively. The difference in PUL 2.0 mean changes among the type of exon skip class for the total score was not significant at 12 months but was significant at 24 months for the total score (p < 0.001), the shoulder (p = 0.01) and the elbow domain (p < 0.001), with patients amenable to skipping exon 44 having smaller changes compared to those amenable to skipping exon 53. There was no difference within ambulant or non-ambulant cohorts when subdivided by exon skip class for the total and subdomains score (p > 0.05).

CONCLUSIONS

Our results expand the information on upper limb function changes detected by the PUL 2.0 in a relatively large group of DMD patients with distinct exon-skipping classes. This information can be of help when designing clinical trials or in the interpretation of the real world data including non-ambulant patients.

Long-term favorable prognosis in late onset dominant distal titinopathy: Tibial muscular dystrophy

BACKGROUND AND PURPOSE

Tibial muscular dystrophy (TMD) is a dominant late onset distal titinopathy. It was first described in Finnish patients 3 decades ago. TMD patients with several other TTN mutations occur in many European populations. In this retrospective study, we were able to obtain longitudinal follow-up data of the disease progression over 15 years in 137 TMD patients.

METHODS

We retrieved clinical data retrospectively from three examinations spanning a period of 15 years. The data were analyzed in R. Frequencies, percentages, and median values were used to describe data. Probability values were determined with the chi-squared test.

RESULTS

In the cohort, the first symptoms were walking difficulties (97.8%) and weakness in distal lower limbs (98.5%). The progression of the weakness in distal lower limbs was moderate, and in the proximal lower limbs and proximal upper limbs it was mild. The distal upper limbs were not affected. Magnetic resonance imaging results indicated fatty degeneration preferentially in lower leg anterior muscles, gluteus minimus, and hamstring muscles. Serum creatine kinase values in the cohort were mostly normal (40.7%) or mildly elevated (53.7%). The data suggest that 50% of patients need walking aids by the age of 88 years.

CONCLUSIONS

Despite individual variability of severity, the overall disability due to walking difficulties and upper limb weakness remained moderate even at very advanced ages, and cardiomyopathy did not develop due to the titin defect alone. The acquired results promote the correct identification of TMD, and the obtained trajectories of disease evolution can be used as natural history data for any therapeutic intervention.

Efficacy and Safety of Viltolarsen in Boys With Duchenne Muscular Dystrophy: Results From the Phase 2, Open-Label, 4-Year Extension Study

Background: Duchenne muscular dystrophy (DMD) is caused by DMD gene mutations, resulting in absence of functional dystrophin protein. Viltolarsen, an exon 53 skipping therapy, significantly increased dystrophin levels in patients with DMD. Presented here are completed study results of >4 years of functional outcomes in viltolarsen-treated patients compared to a historical control group (Cooperative International Neuromuscular Research Group Duchenne Natural History Study [CINRG DNHS]). Objective: To evaluate the efficacy and safety of viltolarsen for an additional 192 weeks in boys with DMD. Methods: This phase 2, open-label, 192-week long-term extension (LTE) study (NCT03167255) evaluated the efficacy and safety of viltolarsen in participants aged 4 to <10 years at baseline with DMD amenable to exon 53 skipping. All 16 participants from the initial 24-week study enrolled into this LTE. Timed function tests were compared to the CINRG DNHS group. All participants received glucocorticoid treatment. The primary efficacy outcome was time to stand from supine (TTSTAND). Secondary efficacy outcomes included additional timed function tests. Safety was continuously assessed. Results: For the primary efficacy outcome (TTSTAND), viltolarsen-treated patients showed stabilization of motor function over the first two years and significant slowing of disease progression over the following two years compared with the CINRG DNHS control group which declined. Viltolarsen was well tolerated, with most reported treatment-emergent adverse events being mild or moderate. No participants discontinued drug during the study. Conclusions: Based on the results of this 4-year LTE, viltolarsen can be an important treatment strategy for DMD patients amenable to exon 53 skipping.

Duchenne muscular dystrophy: Current treatment and emerging exon skipping and gene therapy approach

Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder that causes debilitating muscle weakness and atrophy due to a loss of the dystrophin protein. Patients with DMD are commonly diagnosed at about 3-5 years of age and progressively decline until complications of the disease often result in death at about 20 years of age. While there is no current cure for DMD, several treatment options focus on improving the quality of life and slowing progression of symptoms associated with the disease. The current treatment for DMD is glucocorticoids and physical therapy. Respiratory therapy, cardiac management, bone health maintenance, orthopedic interventions, and dietary considerations are also utilized in managing DMD patients. Emerging therapeutic approaches include gene transfer therapy, using adeno-associated virus (AAV) vectors, and exon skipping agents. Both approaches have been shown to be relatively safe, with few significant side effects. Even though exon skipping agents produce a smaller dystrophin protein, they effectively preserve a significant portion of its function. Exon skipping agents have clinical advantages over traditional therapies, such as corticosteroids, because they slow the progression of DMD in addition to relieving symptoms. This review discusses the pathogenesis of DMD and explores the current treatment options as well as new and emerging therapies.

Delivery challenges for CRISPR-Cas9 genome editing for Duchenne muscular dystrophy

Duchene muscular dystrophy (DMD) is an X-linked neuromuscular disorder that affects about one in every 5000 live male births. DMD is caused by mutations in the gene that codes for dystrophin, which is required for muscle membrane stabilization. The loss of functional dystrophin causes muscle degradation that leads to weakness, loss of ambulation, cardiac and respiratory complications, and eventually, premature death. Therapies to treat DMD have advanced in the past decade, with treatments in clinical trials and four exon-skipping drugs receiving conditional Food and Drug Administration approval. However, to date, no treatment has provided long-term correction. Gene editing has emerged as a promising approach to treating DMD. There is a wide range of tools, including meganucleases, zinc finger nucleases, transcription activator-like effector nucleases, and, most notably, RNA-guided enzymes from the bacterial adaptive immune system clustered regularly interspaced short palindromic repeats (CRISPR). Although challenges in using CRISPR for gene therapy in humans still abound, including safety and efficiency of delivery, the future for CRISPR gene editing for DMD is promising. This review will summarize the progress in CRISPR gene editing for DMD including key summaries of current approaches, delivery methodologies, and the challenges that gene editing still faces as well as prospective solutions.

Channeling of New Neuropsychiatric Drugs-Impact on Safety and Effectiveness Studies

This study aimed to examine differential prescribing due to channeling and propensity score non-overlap over time in new versus established treatments for common neurological conditions. We conducted cross-sectional analyses on a national sample of US commercially insured adults using 2005-2019 data. We compared new users of recently approved versus established medications for management of diabetic peripheral neuropathy (pregabalin versus gabapentin), Parkinson disease psychosis (pimavanserin versus quetiapine), and epilepsy (brivaracetam versus levetiracetam). Within these drug pairs, we compared demographic, clinical, and healthcare utilization characteristics of recipients of each drug. In addition, we fit yearly propensity score models for each condition and assessed propensity score non-overlap over time. For all three drug pairs, users of the more recently approved medications more frequently had prior treatment (pregabalin = 73.9%, gabapentin = 38.7%; pimavanserin = 41.1%, quetiapine = 14.0%; brivaracetam = 93.4%, levetiracetam = 32.1%). Propensity score non-overlap and its resulting sample loss after trimming were the greatest in the first year that the more recently approved medication was available (diabetic peripheral neuropathy, 12.4% non-overlap; Parkinson disease psychosis, 6.1%; epilepsy, 43.2%) and subsequently improved. Newer neuropsychiatric therapies appear to be channeled to individuals with refractory disease or intolerance to other treatments, leading to potential confounding and biased comparative effectiveness and safety study findings when compared to established treatments. Propensity score non-overlap should be reported in comparative studies that include newer medications. When studies comparing newer and established treatments are critically needed as soon as new treatments enter the market, investigators should recognize the potential for channeling bias and implement methodological approaches like those demonstrated in this study to understand and improve this issue in such studies.

Whole-genome sequence of Macaca fascicularis: liver tissue

OBJECTIVES

Thrombocytopenia is a condition that causes a low amount of blood platelets. Platelets are blood cells that play an essential role in blood coagulation. Therefore, thrombocytopenia can put the patient at risk for mild to severe bleeding. Thrombocytopenia is caused by a decrease in platelet production in the bone marrow or by a drug or immune system problem when production is normal. In particular, in some ASO-induced thrombocytopenia, the mechanism is not clear. Therefore, whole genome sequencing (WGS) was performed to discover genetic differences that affect thrombocytopenia and individual susceptibility to drugs between normal and reduced platelet monkeys despite administering the same ASO.

DATA DESCRIPTION

Three antisense oligonucleotide (ASO) substances were injected into the subcutaneous tissue of monkeys for 12 weeks in two experiments. The monkeys were classified into three groups: monkeys with thrombocytopenia, monkeys without thrombocytopenia, and control monkeys not treated with ASO substances. Whole genome sequencing data was generated using liver tissues of monkeys. These data will be useful for identifying genetic differences that affect thrombocytopenia and drug sensitivity.

Antisense oligonucleotides to therapeutically target SARS-CoV-2 infection

Although the COVID-19 pandemic began over three years ago, the virus responsible for the disease, SARS-CoV-2, continues to infect people across the globe. As such, there remains a critical need for development of novel therapeutics against SARS-CoV-2. One technology that has remained relatively unexplored in COVID-19 is the use of antisense oligonucleotides (ASOs)-short single-stranded nucleic acids that bind to target RNA transcripts to modulate their expression. In this study, ASOs targeted against the SARS-CoV-2 genome and host entry factors, ACE2 and TMPRSS2, were designed and tested for their ability to inhibit cellular infection by SARS-CoV-2. Using our previously developed SARS-CoV-2 bioassay platform, we screened 180 total ASOs targeting various regions of the SARS-CoV-2 genome and validated several ASOs that potently blocked SARS-CoV-2 infection in vitro. Notably, select ASOs retained activity against both the WA1 and B.1.1.7 (commonly known as alpha) variants. Screening of ACE2 and TMPRSS2 ASOs showed that targeting of ACE2 also potently prevented infection by the WA1 and B.1.1.7 SARS-CoV-2 viruses in the tested cell lines. Combined with the demonstrated success of ASOs in other disease indications, these results support further research into the development of ASOs targeting SARS-CoV-2 and host entry factors as potential COVID-19 therapeutics.

A longitudinal study of creatine kinase and creatinine levels in Duchenne muscular dystrophy

INTRODUCTION/AIMS

Management of Duchenne muscular dystrophy (DMD) has entered an era featuring novel treatments. Trackable noninvasive biomarkers could improve disease progression monitoring and drug effect detection. Our aim in this study was to measure changes in selected noninvasive biomarkers and assess their relationship to age and motor function.

METHODS

We retrospectively studied 555 patients with DMD who had at least 12 months of treatment of glucocorticoids and were not enrolled in trials of potential disease-modifying therapies. We extracted biomarker data of serum creatine kinase (CK), serum creatinine (Cr), urine Cr, and urine Cr/urine osmolality (osm), as well as functional data for age at loss of ambulation and Functional Motor Scale (FMS) values from patients' clinical records. Data were analyzed using linear mixed-model analyses.

RESULTS

CK, serum Cr, urine Cr, and urine Cr/urine osm all decreased with declining motor function. CK consistently decreased and FMS score consistently worsened with age without clear inflection points. There was an increased odds ratio for LOA with lower values of CK, serum Cr, urine Cr, and urine Cr/urine osm, most notably for urine Cr.

DISCUSSION

Although individual biomarker values are challenging to directly apply clinically, our study has demonstrated that trends over time may complement functional measures in the assessment of individuals with DMD. Future studies could elucidate predictive utility of these biomarkers in assessing motor function changes in DMD.