Open-Label Evaluation of Eteplirsen in Patients with Duchenne Muscular Dystrophy Amenable to Exon 51 Skipping: PROMOVI 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.

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.

The complex landscape of DMD mutations: moving towards personalized medicine

Duchenne muscular dystrophy (DMD) is a severe genetic disorder characterized by progressive muscle degeneration, with respiratory and cardiac complications, caused by mutations in the DMD gene, encoding the protein dystrophin. Various DMD mutations result in different phenotypes and disease severity. Understanding genotype/phenotype correlations is essential to optimize clinical care, as mutation-specific therapies and innovative therapeutic approaches are becoming available. Disease modifier genes, trans-active variants influencing disease severity and phenotypic expressivity, may modulate the response to therapy, and become new therapeutic targets. Uncovering more disease modifier genes via extensive genomic mapping studies offers the potential to fine-tune prognostic assessments for individuals with DMD. This review provides insights into genotype/phenotype correlations and the influence of modifier genes in DMD.

Characteristics of Patients Receiving Novel Muscular Dystrophy Drugs in Trials vs Routine Care

Importance

The US Food and Drug Administration approved eteplirsen for Duchenne muscular dystrophy (DMD) in 2016 based on a controversial pivotal study that demonstrated a limited effect on the surrogate measure of dystrophin production. Other DMD treatments in the same class followed.

Objective

To assess how patients receiving novel DMD treatments in postapproval clinical settings compare with patients in the clinical trials.

Design, Setting, and Participants

This cross-sectional study collected data on patients who initiated 1 of 4 novel DMD treatments (eteplirsen, golodirsen, viltolarsen, and casimersen) using national claims databases of commercially insured (Merative MarketScan and Optum's Clinformatics Data Mart Database [CDM]) and Medicaid patients between September 19, 2016, and March 31, 2022. Patients were followed for 1 year after the date of first use of any novel DMD treatment. In addition, patients in pivotal DMD drug trials were identified for comparison.

Exposures

Age, sex, race and ethnicity, region, and DMD stage of patients receiving novel DMD treatment.

Main Outcome and Measures

The main outcome was health care costs and drug discontinuation as measured using descriptive statistics.

Results

A total of 223 routine care patients initiating novel DMD drugs (58 in MarketScan, 35 in CDM, and 130 in Medicaid) were identified. Among the 106 patients in the pivotal trials, the mean (SD) age was 8.5 (2.0) years (range, 4.0-13.0 years), which was younger than the mean age of patients in routine care (MarketScan: 13.7 [7.0] years [range, 1.8-33.3 years; P < .001]; CDM: 11.9 [5.7] years [range, 0.6-23.6 years; P < .001]; Medicaid: 13.4 [6.5] years [range, 1.8-46.1 years; P < .001]). The proportion of female patients identified in postapproval clinical settings was 2.9% (n = 1) in CDM (vs 34 male patients [97.1%]) and 1.5% (n = 2) in Medicaid (vs 128 male patients [98.5%]), which was not different from the pivotal trials. While nearly all patients in the pivotal trials had DMD disease stage 1 or 2 when initiating the DMD treatments (103 [97.2%]), in the postapproval clinical setting, slightly more than one-third of patients were in disease stage 3 or 4 (MarketScan, 17 [36.2%; P < .001]; CDM, 13 [41.9%; P < .001]; Medicaid, 54 [47.0%; P < .001]). The payer's cost for novel DMD treatments varied across the databases, with a mean (SD) of $634 764 ($607 101) in MarketScan, $482 749 ($582 350) in CDM, and $384 023 ($1 165 730) in Medicaid. Approximately one-third of routine care patients discontinued the treatments after approximately 7 months (mean [SD], 6.1 [4.4], 6.9 [3.9], and 7.2 [4.3] months in MarketScan, CDM, and Medicaid, respectively).

Conclusions and Relevance

These findings raise questions about the translation of DMD drug trial findings to routine care settings, with patients in routine care discontinuing the treatment within 1 year and payers incurring substantial expenses for these medications. More data are needed on whether these high costs are accompanied by corresponding clinical benefits.

Duchenne muscular dystrophy treatment with lentiviral vector containing mini-dystrophin gene in vivo

Duchenne muscular dystrophy (DMD) is an incurable X-linked recessive genetic disease caused by mutations in the dystrophin gene. Many researchers aim to restore truncated dystrophin via viral vectors. However, the low packaging capacity and immunogenicity of vectors have hampered their clinical application. Herein, we constructed four lentiviral vectors with truncated and sequence-optimized dystrophin genes driven by muscle-specific promoters. The four lentiviral vectors stably expressed mini-dystrophin in C2C12 muscle cells in vitro. To estimate the treatment effect in vivo, we transferred the lentiviral vectors into neonatal C57BL/10ScSn-Dmdmdx mice through local injection. The levels of modified dystrophin expression increased, and their distribution was also restored in treated mice. At the same time, they exhibited the restoration of pull force and a decrease in the number of mononuclear cells. The remissions lasted 3-6 months in vivo. Moreover, no integration sites of vectors were distributed into the oncogenes. In summary, this study preliminarily demonstrated the feasibility and safety of lentiviral vectors with mini-dystrophin for DMD gene therapy and provided a new strategy to restore truncated dystrophin.

Post-transcriptional Regulation of Gene Expression via Unproductive Splicing

Unproductive splicing is a mechanism of post-transcriptional gene expression control in which premature stop codons are inserted into protein-coding transcripts as a result of regulated alternative splicing, leading to their degradation via the nonsense-mediated decay pathway. This mechanism is especially characteristic of RNA-binding proteins, which regulate each other's expression levels and those of other genes in multiple auto- and cross-regulatory loops. Deregulation of unproductive splicing is a cause of serious human diseases, including cancers, and is increasingly being considered as a prominent therapeutic target. This review discusses the types of unproductive splicing events, the mechanisms of auto- and cross-regulation, nonsense-mediated decay escape, and problems in identifying unproductive splice isoforms. It also provides examples of deregulation of unproductive splicing in human diseases and discusses therapeutic strategies for its correction using antisense oligonucleotides and small molecules.

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.

A qualitative study to understand the Duchenne muscular dystrophy experience from the parent/patient perspective

BACKGROUND

Duchenne muscular dystrophy (DMD) is a rare, severe, fatal neuromuscular disease characterized by progressive atrophy and muscle weakness, resulting in loss of ambulation, decreased upper body function, and impaired cardiorespiratory function. This study aimed to generate qualitative evidence to describe the primary symptoms and impacts of DMD in ambulatory and non-ambulatory patients as reported by patient/caregiver dyads. Information was also gathered on expectations for future DMD treatments.

METHODS

Forty-six dyads (caregiver and patients with DMD aged 4 to 22 years) participated in 60-min semi-structured video interviews. Interview transcripts were analyzed using thematic analysis. Differences in experiences with DMD by ambulation status were examined.

RESULTS

Mean ages of ambulatory (n = 28) and non-ambulatory participants (n = 18) were 8.7 and 11.3 years, respectively, with an average age of diagnosis of 3.7 years (SD = 2.3). The primary symptoms reported by both groups were lack of strength (ambulatory: n = 28, 100.0%; non-ambulatory: n = 17, 94.4%) and fatigue (ambulatory: n = 24, 85.7%; non-ambulatory: n = 14, 77.8%). Physical function was the domain that was most impacted by DMD, with participants describing progressive decline of physical function due to loss of physical strength as the primary defining feature of the disease across all stages of ambulatory ability. For those who maintained ambulatory ability at the time of the interview, physical function impacts described impaired mobility (e.g., climbing stairs: n = 16, 57.1%; running: n = 13, 46.4%), impaired upper body function, in particular fine motor skills like holding a pen/pencil or buttoning clothes (n = 17, 60.7%), problem with transfers (e.g., getting off the floor: n = 10, 35.7%), and activities of daily living (ADLs; n = 15, 53.6%). For non-ambulatory participants, the functional impacts most frequently described were problems with transfers (e.g., getting in/out of bed: n = 13, 72.2%; getting in/out of chair or position in bed: both n = 10, 55.6%), impaired upper body function (reaching: n = 14, 77.8%), and ADLs (n = 15, 83.3%). Meaningful treatment goals differed by ambulatory status; for ambulatory participants, goals included maintaining current functioning (n = 20, 71.4%), improving muscle strength (n = 7, 25.9%), and reducing fatigue (n = 6, 22.2%). For non-ambulatory participants, these included increased upper body strength (n = 8, 42.1%) and greater independence in ADLs (n = 6, 31.6%). A preliminary conceptual model was developed to illustrate the primary symptoms and physical function impacts of DMD and capture their relationship to disease progression.

CONCLUSION

This study contributes to the limited qualitative literature by characterizing impacts of physical limitations and symptoms of DMD on disease progression and thus providing insights into the lived experience with DMD. Differences in treatment goals were also identified based on ambulatory status. Taken together, these findings can help inform patient-centered measurement strategies for evaluating outcomes in DMD clinical research.

Myopathologic trajectory in Duchenne muscular dystrophy (DMD) reveals lack of regeneration due to senescence in satellite cells

Duchenne muscular dystrophy (DMD) is a devastating X-linked muscular disease, caused by mutations in the DMD gene encoding Dystrophin and affecting 1:5000 boys worldwide. Lack of Dystrophin leads to progressive muscle wasting and degeneration resulting in cardiorespiratory failure. Despite the absence of a definitive cure, innovative therapeutic avenues are emerging. Myopathologic studies are important to further understand the biological mechanisms of the disease and to identify histopathologic benchmarks for clinical evaluations. We conducted a myopathologic analysis on twenty-four muscle biopsies from DMD patients, with particular emphasis on regeneration, fibro-adipogenic progenitors and muscle stem cells behavior. We describe an increase in content of fibro-adipogenic progenitors, central orchestrators of fibrotic progression and lipid deposition, concurrently with a decline in muscle regenerative capacity. This regenerative impairment strongly correlates with compromised activation and expansion of muscle stem cells. Furthermore, our study uncovers an early acquisition of a senescence phenotype by DMD-afflicted muscle stem cells. Here we describe the myopathologic trajectory intrinsic to DMD and establish muscle stem cell senescence as a pivotal readout for future therapeutic interventions.

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.

The endosomal escape vehicle platform enhances delivery of oligonucleotides in preclinical models of neuromuscular disorders

Biological therapeutic agents are highly targeted and potent but limited in their ability to reach intracellular targets. These limitations often necessitate high therapeutic doses and can be associated with less-than-optimal therapeutic activity. One promising solution for therapeutic agent delivery is use of cell-penetrating peptides. Canonical cell-penetrating peptides, however, are limited by low efficiencies of cellular uptake and endosomal escape, minimal proteolytic stability, and toxicity. To overcome these limitations, we designed a family of proprietary cyclic cell-penetrating peptides that form the core of our endosomal escape vehicle technology capable of delivering therapeutic agent-conjugated cargo intracellularly. We demonstrated the therapeutic potential of this endosomal escape vehicle platform in preclinical models of muscular dystrophy with distinct disease etiology. An endosomal escape vehicle-conjugated, splice-modulating oligonucleotide restored dystrophin protein expression in striated muscles in the mdx mouse, a model for Duchenne muscular dystrophy. Furthermore, another endosomal escape vehicle-conjugated, sterically blocking oligonucleotide led to knockdown of aberrant transcript expression levels in facioscapulohumeral muscular dystrophy patient-derived skeletal muscle cells. These findings suggest a significant therapeutic potential of our endosomal escape vehicle conjugated oligonucleotides for targeted upregulation and downregulation of gene expression in neuromuscular diseases, with possible broader application of this platform for delivery of intracellular biological agents.

Antisense Therapy for Infectious Diseases

Infectious diseases, particularly Tuberculosis (TB) caused by Mycobacterium tuberculosis, pose a significant global health challenge, with 1.6 million reported deaths in 2021, making it the most fatal disease caused by a single infectious agent. The rise of drug-resistant infectious diseases adds to the urgency of finding effective and safe intervention therapies. Antisense therapy uses antisense oligonucleotides (ASOs) that are short, chemically modified, single-stranded deoxyribonucleotide molecules complementary to their mRNA target. Due to their designed target specificity and inhibition of a disease-causing gene at the mRNA level, antisense therapy has gained interest as a potential therapeutic approach. This type of therapy is currently utilized in numerous diseases, such as cancer and genetic disorders. Currently, there are limited but steadily increasing studies available that report on the use of ASOs as treatment for infectious diseases. This review explores the sustainability of FDA-approved and preclinically tested ASOs as a treatment for infectious diseases and the adaptability of ASOs for chemical modifications resulting in reduced side effects with improved drug delivery; thus, highlighting the potential therapeutic uses of ASOs for treating infectious diseases.

Assessing the value of delandistrogene moxeparvovec (SRP-9001) gene therapy in patients with Duchenne muscular dystrophy in the United States

Background: Delandistrogene moxeparvovec (SRP-9001) is an investigational gene therapy that may delay progression of Duchenne muscular dystrophy (DMD), a severe, rare neuromuscular disease caused by DMD gene mutations. Early cost-effectiveness analyses are important to help contextualize the value of gene therapies for reimbursement decision making. Objective: To determine the potential value of delandistrogene moxeparvovec using a cost-effectiveness analysis. Study design: A simulation calculated lifetime costs and equal value of life years gained (evLYG). Inputs included extrapolated clinical trial results and published utilities/costs. As a market price for delandistrogene moxeparvovec has not been established, threshold analyses established maximum treatment costs as they align with value, including varying willingness-to-pay up to $500,000, accounting for severity/rarity. Setting: USA, healthcare system perspective Patients: Boys with DMD Intervention: Delandistrogene moxeparvovec plus standard of care (SoC; corticosteroids) versus SoC alone Main outcome measure: Maximum treatment costs at a given willingness-to-pay threshold Results: Delandistrogene moxeparvovec added 10.30 discounted (26.40 undiscounted) evLYs. The maximum treatment cost was approximately $5 M, assuming $500,000/evLYG. Varying the benefit discount rate to account for the single administration increased the estimated value to #$5M, assuming $500,000/evLYG. Conclusion: In this early economic model, delandistrogene moxeparvovec increases evLYs versus SoC and begins to inform its potential value from a healthcare perspective.

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.

[Molecular therapies: present and future in neuromuscular diseases]

BACKGROUND

The possibilities in the field of molecular therapies of neuromuscular diseases have rapidly developed in recent years. First compounds are already available in clinical practice and numerous other substances are in advanced phases of clinical trials. This article gives an exemplary overview of the current state of clinical research in molecular therapies of neuromuscular diseases. It also gives a view into the near future of the clinical application, including the challenges.

DISCUSSION

Using Duchenne muscular dystrophy (DMD) and myotubular myopathy as examples, the principles of gene addition in monogenetic skeletal muscle diseases, which are already manifested in childhood are described. In addition to initial successes, the challenges and setbacks hindering the approval and regular clinical application of further compounds are demonstrated. Furthermore, the state of current clinical research in Becker-Kiener muscular dystrophy (BMD) and the numerous forms of limb-girdle muscular dystrophy (LGMD) are summarized. Numerous new therapeutic approaches and a corresponding outlook are also shown for facioscapulohumeral muscular dystrophy (FSHD), Pompe disease, and myotonic dystrophy.

CONCLUSION

Clinical research in the field of molecular therapy of neuromuscular diseases is one of the pacesetters of modern precision medicine; however, challenges need to be seen, jointly addressed and overcome in the future.

DNAzymes: Expanding the Potential of Nucleic Acid Therapeutics

Nucleic acids drugs have been proven in the clinic as a powerful modality to treat inherited and acquired diseases. However, key challenges including drug stability, renal clearance, cellular uptake, and movement across biological barriers (foremost the blood-brain barrier) limit the translation and clinical efficacy of nucleic acid-based therapies, both systemically and in the central nervous system. In this study we provide an overview of an emerging class of nucleic acid therapeutic, called DNAzymes. In particular, we review the use of chemical modifications and carrier molecules for the stabilization and/or delivery of DNAzymes in cell and animal models. Although this review focuses on DNAzymes, the strategies described are broadly applicable to most nucleic acid technologies. This review should serve as a general guide for selecting chemical modifications to improve the therapeutic performance of DNAzymes.

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.

Pathophysiology and Management of Fatigue in Neuromuscular Diseases

Fatigue is a major determinant of quality of life and motor function in patients affected by several neuromuscular diseases, each of them characterized by a peculiar physiopathology and the involvement of numerous interplaying factors. This narrative review aims to provide an overview on the pathophysiology of fatigue at a biochemical and molecular level with regard to muscular dystrophies, metabolic myopathies, and primary mitochondrial disorders with a focus on mitochondrial myopathies and spinal muscular atrophy, which, although fulfilling the definition of rare diseases, as a group represent a representative ensemble of neuromuscular disorders that the neurologist may encounter in clinical practice. The current use of clinical and instrumental tools for fatigue assessment, and their significance, is discussed. A summary of therapeutic approaches to address fatigue, encompassing pharmacological treatment and physical exercise, is also overviewed.

Safety, tolerability and pharmacokinetics of eteplirsen in young boys aged 6–48 months with Duchenne muscular dystrophy amenable to exon 51 skipping

Eteplirsen is FDA-approved for the treatment of Duchenne muscular dystrophy (DMD) in exon 51 skip-amenable patients. Previous studies in boys > 4 years of age indicate eteplirsen is well tolerated and attenuates pulmonary and ambulatory decline compared with matched natural history cohorts. Here the safety, tolerability and pharmacokinetics of eteplirsen in boys aged 6-48 months is evaluated. In this open-label, multicenter, dose-escalation study (NCT03218995), boys with a confirmed mutation of the DMD gene amenable to exon 51 skipping (Cohort 1: aged 24-48 months, n = 9; Cohort 2: aged 6 to < 24 months, n = 6) received ascending doses (2, 4, 10, 20, 30 mg/kg) of once-weekly eteplirsen intravenously over 10 weeks, continuing at 30 mg/kg up to 96 weeks. Endpoints included safety (primary) and pharmacokinetics (secondary). All 15 participants completed the study. Eteplirsen was well tolerated with no treatment-related discontinuations, deaths or evidence of kidney toxicity. Most treatment-emergent adverse events were mild; most common were pyrexia, cough, nasopharyngitis, vomiting, and diarrhea. Eteplirsen pharmacokinetics were consistent between both cohorts and with previous clinical experience in boys with DMD > 4 years of age. These data support the safety and tolerability of eteplirsen at the approved 30-mg/kg dose in boys as young as 6 months old.

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.

Next steps for the optimization of exon therapy for Duchenne muscular dystrophy

INTRODUCTION

It is established that the exon-skipping approach can restore dystrophin in Duchenne muscular dystrophy (DMD) patients. However, dystrophin restoration levels are low, and the field is evolving to provide solutions for improved exon skipping. DMD is a neuromuscular disorder associated with chronic muscle tissue loss attributed to the lack of dystrophin, which causes muscle inflammation, fibrosis formation, and impaired regeneration. Currently, four antisense oligonucleotides (AONs) based on phosphorodiamidate morpholino oligomer (PMO) chemistry are approved by US Food and Drug Administration for exon skipping therapy of eligible DMD patients.

AREAS COVERED

This review describes a preclinical and clinical experience with approved and newly developed AONs for DMD, outlines efforts that have been done to enhance AON efficiency, reviews challenges of clinical trials, and summarizes the current state of the exon skipping approach in the DMD field.

EXPERT OPINION

The exon skipping approach for DMD is under development, and several chemical modifications with improved properties are under (pre)-clinical investigation. Despite existing advantages of these modifications, their safety and effectiveness have to be examined in clinical trials, which are planned or ongoing. Furthermore, we propose clinical settings using natural history controls to facilitate studying the functional effect of the therapy.

miRNAs: The Road from Bench to Bedside

miRNAs are small noncoding RNAs that control gene expression at the posttranscriptional level. It has been recognised that miRNA dysregulation reflects the state and function of cells and tissues, contributing to their dysfunction. The identification of hundreds of extracellular miRNAs in biological fluids has underscored their potential in the field of biomarker research. In addition, the therapeutic potential of miRNAs is receiving increasing attention in numerous conditions. On the other hand, many operative problems including stability, delivery systems, and bioavailability, still need to be solved. In this dynamic field, biopharmaceutical companies are increasingly engaged, and ongoing clinical trials point to anti-miR and miR-mimic molecules as an innovative class of molecules for upcoming therapeutic applications. This article aims to provide a comprehensive overview of current knowledge on several pending issues and new opportunities offered by miRNAs in the treatment of diseases and as early diagnostic tools in next-generation medicine.

Respiratory phenotypes of neuromuscular diseases: A challenging issue for pediatricians

Neuromuscular disease (NMDs) encompass a heterogeneous group of genetic disorders, with respiratory problems of variable intensity and progression described at any pediatric age, from infancy to adolescence, and they are largely associated with significant lifelong morbidity and high mortality. Restriction of breathing, impaired gas exchange, decline of lung function and sleep disordered breathing progressively develop because of muscular weakness and culminate in respiratory failure. Depending on the disease progression, airways manifestations can take weeks to months or even years to evolve, thus depicting two major respiratory phenotypes, characterized by rapid or slow progression to respiratory failure. Assessing type and age at onset of airways problems and their evolution over time can support pediatricians in the diagnostic assessment of NMD. In addition, knowing the characteristics of patients' respiratory phenotype can increase the level of awareness among neonatologists, geneticists, neurologists, pulmonologists, nutritionists, and chest therapists, supporting them in the challenging task of the multidisciplinary medical care of patients. In this review we examine the issues related to the pediatric respiratory phenotypes of NMD and present a novel algorithm that can act as a guide for the diagnostic agenda and the key preventive or therapeutic interventions of airways manifestations. With prolonged survival of children with NMD, the advent of neuromuscular respiratory medicine, including accurate assessment of the respiratory phenotype, will help physicians to determine patients' prognoses and to design studies for the evaluation of new therapies.

Gene therapy review: Duchenne muscular dystrophy case study

Gene therapy, i.e., any therapeutic approach involving the use of genetic material as a drug and more largely altering the transcription or translation of one or more genes, covers a wide range of innovative methods for treating diseases, including neurological disorders. Although they share common principles, the numerous gene therapy approaches differ greatly in their mechanisms of action. They also differ in their maturity for some are already used in clinical practice while others have never been used in humans. The aim of this review is to present the whole range of gene therapy techniques through the example of Duchenne muscular dystrophy (DMD). DMD is a severe myopathy caused by mutations in the dystrophin gene leading to the lack of functional dystrophin protein. It is a disease known to all neurologists and in which almost all gene therapy methods were applied. Here we discuss the mechanisms of gene transfer techniques with or without viral vectors, DNA editing with or without matrix repair and those acting at the RNA level (RNA editing, exon skipping and STOP-codon readthrough). For each method, we present the results obtained in DMD with a particular focus on clinical data. This review aims also to outline the advantages, limitations and risks of gene therapy related to the approach used.

G-rich motifs within phosphorothioate-based antisense oligonucleotides (ASOs) drive activation of FXN expression through indirect effects

Friedreich's ataxia is an incurable disease caused by frataxin (FXN) protein deficiency, which is mostly induced by GAA repeat expansion in intron 1 of the FXN gene. Here, we identified antisense oligonucleotides (ASOs), complementary to two regions within the first intron of FXN pre-mRNA, which could increase FXN mRNA by ∼2-fold in patient fibroblasts. The increase in FXN mRNA was confirmed by the identification of multiple overlapping FXN-activating ASOs at each region, two independent RNA quantification assays, and normalization by multiple housekeeping genes. Experiments on cells with the ASO-binding sites deleted indicate that the ASO-induced FXN activation was driven by indirect effects. RNA sequencing analyses showed that the two ASOs induced similar transcriptome-wide changes, which did not resemble the transcriptome of wild-type cells. This RNA-seq analysis did not identify directly base-paired off-target genes shared across ASOs. Mismatch studies identified two guanosine-rich motifs (CCGG and G4) within the ASOs that were required for FXN activation. The phosphorodiamidate morpholino oligomer analogs of our ASOs did not activate FXN, pointing to a PS-backbone-mediated effect. Our study demonstrates the importance of multiple, detailed control experiments and target validation in oligonucleotide studies employing novel mechanisms such as gene activation.

The Dystrophinopathies

PURPOSE OF REVIEW

This article reviews the history, epidemiology, genetics, clinical presentation, multidisciplinary management, and established and emerging therapies for the dystrophinopathies.

RECENT FINDINGS

The multidisciplinary care of individuals with dystrophinopathies continues to improve in many ways, including early surveillance and implementation of respiratory, cardiac, and orthopedic health management. The era of genetic therapeutics has altered the treatment landscape in neuromuscular disorders, including the dystrophinopathies.

SUMMARY

The dystrophinopathies are a spectrum of X-linked genetic disorders characterized by childhood-onset progressive weakness and variable cardiac and cognitive involvement. Corticosteroids are the mainstay of therapy to slow disease progression. Additional strategies for disease amelioration and dystrophin restoration, including gene replacement therapy, are under investigation.

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

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

Perspectives on the advances in the pharmacotherapeutic management of Duchenne muscular dystrophy

INTRODUCTION

: Duchenne muscular dystrophy (DMD) is a progressive genetic disease characterized by muscular weakness with a global prevalence of 7.1 cases per 100,000 males. DMD is caused by mutations of the dystrophin gene on the X chromosome which is responsible for dystrophin protein production. Dystrophin is a cytoskeletal protein that contributes to structural support in muscle cells. DMD mutations result in dystrophin protein deficiency which leads to muscle damage and the associated clinical presentation.

AREAS COVERED

: Corticosteroids such as prednisone and deflazacort are routinely given to patients to treat inflammation, but their use is limited by the occurrence of side effects and a lack of standardized prescribing. Exon-skipping medications are emerging as treatment options for a small portion of DMD patients even though efficacy is uncertain. Many new therapeutics are under development that target inflammation, fibrosis, and dystrophin replacement.

EXPERT OPINION

: Because of side effects associated with corticosteroid use, there is need for better alternatives to the standard of care. Excessive cost is a barrier to patients receiving medications that have yet to have established efficacy. Additional therapies have the potential to help patients with DMD, although most are several years away from approval for patient use.

Drug development progress in duchenne muscular dystrophy

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.

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

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.

Dysregulation and therapeutic targeting of RNA splicing in cancer

High-throughput sequencing and functional characterization of the cancer transcriptome have uncovered cancer-specific dysregulation of RNA splicing across a variety of cancers. Alterations in the cancer genome and dysregulation of RNA splicing factors lead to missplicing, splicing alteration-dependent gene expression and, in some cases, generation of novel splicing-derived proteins. Here, we review recent advances in our understanding of aberrant splicing in cancer pathogenesis and present strategies to harness cancer-specific aberrant splicing for therapeutic intent.

Application of Droplet Digital PCR Technology in Muscular Dystrophies Research

Although they are considered rare disorders, muscular dystrophies have a strong impact on people’s health. Increased disease severity with age, frequently accompanied by the loss of ability to walk in some people, and the lack of treatment, have directed the researchers towards the development of more effective therapeutic strategies aimed to improve the quality of life and life expectancy, slow down the progression, and delay the onset or convert a severe phenotype into a milder one. Improved understanding of the complex pathology of these diseases together with the tremendous advances in molecular biology technologies has led to personalized therapeutic procedures. Different approaches that are currently under extensive investigation require more efficient, sensitive, and less invasive methods. Due to its remarkable analytical sensitivity, droplet digital PCR has become a promising tool for accurate measurement of biomarkers that monitor disease progression and quantification of various therapeutic efficiency and can be considered a tool for non-invasive prenatal diagnosis and newborn screening. Here, we summarize the recent applications of droplet digital PCR in muscular dystrophy research and discuss the factors that should be considered to get the best performance with this technology.

Recent Advances in RNA Therapy and Its Carriers to Treat the Single-Gene Neurological Disorders

The development of new sequencing technologies in the post-genomic era has accelerated the identification of causative mutations of several single gene disorders. Advances in cell and animal models provide insights into the underlining pathogenesis, which facilitates the development and maturation of new treatment strategies. The progress in biochemistry and molecular biology has established a new class of therapeutics—the short RNAs and expressible long RNAs. The sequences of therapeutic RNAs can be optimized to enhance their stability and translatability with reduced immunogenicity. The chemically-modified RNAs can also increase their stability during intracellular trafficking. In addition, the development of safe and high efficiency carriers that preserves the integrity of therapeutic RNA molecules also accelerates the transition of RNA therapeutics into the clinic. For example, for diseases that are caused by genetic defects in a specific protein, an effective approach termed “protein replacement therapy” can provide treatment through the delivery of modified translatable mRNAs. Short interference RNAs can also be used to treat diseases caused by gain of function mutations or restore the splicing aberration defects. Here we review the applications of newly developed RNA-based therapeutics and its delivery and discuss the clinical evidence supporting the potential of RNA-based therapy in single-gene neurological disorders.

Long-Term Safety and Efficacy Data of Golodirsen in Ambulatory Patients with Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A First-in-human, Multicenter, Two-Part, Open-Label, Phase 1/2 Trial

The aim of this Phase 1/2, 2-part, multicenter trial was to report clinical safety and efficacy of long-term golodirsen treatment among ambulatory patients with exon 53 skip-amenable Duchenne muscular dystrophy (DMD). Part 1 was a 12-week, randomized, double-blind, placebo-controlled, dose-titration study followed by 9-week safety review. Part 2 was a 168-week, open-label evaluation of golodirsen 30 mg/kg. Part 1 primary endpoint was safety. Part 2 primary endpoints were dystrophin protein expression and 6-minute walk test (6MWT); secondary endpoints were percent predicted forced vital capacity (FVC%p) and safety. Post hoc ambulation analyses used mutation-matched external natural history controls. All patients from Part 1 (golodirsen, n = 8; placebo, n = 4) plus 13 additional patients entered Part 2; 23 completed the study. Adverse events were generally mild, nonserious, and unrelated to golodirsen, with no safety-related discontinuations or deaths. Golodirsen increased dystrophin protein (16.0-fold; P < 0.001) and exon skipping (28.9-fold; P < 0.001). At 3 years, 6MWT change from baseline was −99.0 m for golodirsen-treated patients versus −181.4 m for external controls (P = 0.067), and loss of ambulation occurred in 9% versus 26% (P = 0.21). FVC%p declined 8.4% over 3 years in golodirsen-treated patients, comparing favorably with literature-reported rates. This study provides evidence for golodirsen biologic activity and long-term safety in a declining DMD population and suggests functional benefit versus external controls. Clinical Trial Registration number: NCT02310906.

Scaffold biomaterials and nano-based therapeutic strategies for skeletal muscle regeneration

Skeletal muscle is integral to the functioning of the human body. Several pathological conditions, such as trauma (primary lesion) or genetic diseases such as Duchenne muscular dystrophy (DMD), can affect and impair its functions or exceed its regeneration capacity. Tissue engineering (TE) based on natural, synthetic and hybrid biomaterials provides a robust platform for developing scaffolds that promote skeletal muscle regeneration, strength recovery, vascularization and innervation. Recent 3D-cell printing technology and the use of nanocarriers for the release of drugs, peptides and antisense oligonucleotides support unique therapeutic alternatives. Here, the authors present recent advances in scaffold biomaterials and nano-based therapeutic strategies for skeletal muscle regeneration and perspectives for future endeavors.

Non-Invasive Respiratory Assessment in Duchenne Muscular Dystrophy: From Clinical Research to Outcome Measures

Ventilatory failure, due to the progressive wasting of respiratory muscles, is the main cause of death in patients with Duchenne muscular dystrophy (DMD). Reliable measures of lung function and respiratory muscle action are important to monitor disease progression, to identify early signs of ventilatory insufficiency and to plan individual respiratory management. Moreover, the current development of novel gene-modifying and pharmacological therapies highlighted the urgent need of respiratory outcomes to quantify the effects of these therapies. Pulmonary function tests represent the standard of care for lung function evaluation in DMD, but provide a global evaluation of respiratory involvement, which results from the interaction between different respiratory muscles. Currently, research studies have focused on finding novel outcome measures able to describe the behavior of individual respiratory muscles. This review overviews the measures currently identified in clinical research to follow the progressive respiratory decline in patients with DMD, from a global assessment to an individual structure–function muscle characterization. We aim to discuss their strengths and limitations, in relation to their current development and suitability as outcome measures for use in a clinical setting and as in upcoming drug trials in DMD.

Comparison of Long-term Ambulatory Function in Patients with Duchenne Muscular Dystrophy Treated with Eteplirsen and Matched Natural History Controls

Background:

Duchenne muscular dystrophy (DMD) is a rare, X-linked, fatal, degenerative neuromuscular disease caused by DMD gene mutations. A relationship between exon skipping and dystrophin production in exon 51-amenable patients treated with eteplirsen (EXONDYS 51^®) is established. Once-weekly eteplirsen significantly increased dystrophin, with slower decline in ambulatory function compared to baseline. Long-term treatment with eteplirsen leads to accumulation of dystrophin over time and observed functional benefits in patients with DMD.

Objective:

Compare long-term ambulatory function in eteplirsen-treated patients versus controls.

Methods:

Study 201/202 included 12 eteplirsen-treated patients assessed twice/year for ambulatory function over 4 years. Ambulatory evaluations (6-minute walk test [6MWT], loss of ambulation, and North Star Ambulatory Assessment [NSAA]) were compared with matched controls from Italian Telethon and Leuven registries.

Results:

At Years 3 and 4, eteplirsen-treated patients demonstrated markedly greater mean 6MWT than controls (difference in change from baseline of 132 m [95%CI (29, 235), p = 0.015] at Year 3 and 159 m [95%CI (66, 253), p = 0.002] at Year 4). At Year 4, a significantly greater proportion of eteplirsen-treated patients were still ambulant versus controls (10/12 vs 3/11; p = 0.020). At Year 3, eteplirsen-treated patients demonstrated milder NSAA decline versus controls (difference in change from baseline of 2.6, 95%CI [-6, 11]), however, the difference was not statistically significant; Year 4 control NSAA data were not available.

Conclusion:

In this retrospective matched control study, eteplirsen treatment resulted in attenuation of ambulatory decline over a 4-year observation period, supporting long-term benefit in patients with DMD.