Recent Trends in Antisense Therapies for Duchenne Muscular Dystrophy

Design and screening of novel endosomal escape compounds that enhance functional delivery of oligonucleotides in vitro

Antisense oligonucleotides (ASOs), including splice-switching oligonucleotides (SSOs), are promising therapeutic approaches for targeting genetic defects. ASOs act in the nucleus and the cytosol to cleave mRNAs via the RNaseH1 mechanism (e.g., gapmers), while SSOs alter transcript splicing to restore or inhibit protein function. RNA interference (RNAi) is another approach to down-regulate gene expression via the RISC complex. However, a major challenge is the effective delivery of these nucleic acid-based therapeutics. Recent developments focus on enhancing cellular uptake and endosomal release, including the use of small-molecule endosomal escape enhancers (EEEs) such as chloroquine. Here, we disclose a next generation of EEEs, which efficiently enhance SSOs and gapmers in vitro activity. We identify proton sponge-mediated endosomal leakage as a mechanism of action and observe, by Gene Ontology analysis on bulk RNA sequencing, that EEE treatment increased gene expression of markers associated with vesicle organization. Additionally, using primary human hepatocytes, we demonstrate that EEEs enhance small interfering RNA (siRNA) activity. Unconjugated siRNA reached similar levels of mRNA knockdown to the observed GalNAc-conjugated siRNA. Substantial GalNAc conjugated siRNA enhancement was also observed when used together with EEE. Our results indicate that these EEEs constitute a promising strategy to enhance the activity of multimodal oligonucleotide therapeutics.

No more nonsense: evaluating poison exons as therapeutic targets in neurodevelopmental disorders

Alternative splicing of pre-mRNA generates multiple transcripts from a single gene, contributing to transcriptomic diversity. Alternative splicing can result in inclusion of poison exons (PEs), which contain a premature stop codons (PTC) that target transcripts for nonsense-mediated decay (NMD). PE-containing transcripts are prevalent in the brain, where they can play roles in fine-tuning mRNA and protein levels. Antisense, or splice-switching, oligonucleotides (ASOs/SSOs) are used to target PEs to reduce their inclusion and treat neurodevelopmental disorders. ASOs/SSOs address the genetic causes of disease and are precision therapies that can provide a cure rather than only address disease symptoms. This review explores the role of PEs in the brain, therapeutic targeting of PEs, and current challenges in our understanding of PEs.

Is dystrophin immunogenicity a barrier to advancing gene therapy for Duchenne muscular dystrophy?

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder that leads to severe disability and premature death in young men. As DMD is caused by the absence of dystrophin, therapeutic development has focused on strategies to restore dystrophin expression. These include readthrough of premature stop codons, exon skipping to restore the reading frame, and gene therapy. The first two methods are mutation-specific, benefiting only subsets of patients, whereas gene therapy could treat all individuals with DMD. Immunogenicity of dystrophin may challenge these efforts. The immune system can recognize dystrophin as a neo-antigen, just as it can recognize newly arising antigens present on mutated cells. An in-depth evaluation of anti-dystrophin immune response as a factor affecting the treatment effectiveness is needed. Key questions include the underlying mechanisms of immunity induction by antigenic epitopes of the re-expressed dystrophin, the impact of such responses on the therapeutic efficacy, and the role of patient-specific risk factors, such as preimmunization due to revertant fibres, chronic muscle inflammation, pre-existing T lymphocytes reactive to dystrophin, which avoided deletion in dystrophic thymus, or antigen cross-reactivity. Patients' immune status assessment before treatment may help mitigating anti-dystrophin responses. Exploring potential therapeutic strategies to enhance treatment outcomes is also essential: Since DMD can be diagnosed at birth, early dystrophin re-expression could prevent damage and also potentially induce neonatal tolerance. In older patients, carefully managed immunosuppression and tolerogenic protocols could pave the way for more successful dystrophin replacement therapies.

Inhibiting EZH2 complements steroid effects in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating X-linked disorder caused by dystrophin gene mutations. Despite recent advances in understanding the disease etiology and applying emerging treatment methodologies, glucocorticoid derivatives remain the only general therapeutic option that can slow disease development. However, the precise molecular mechanism of glucocorticoid action remains unclear, and there is still need for additional remedies to complement the treatment. Here, using single-nucleus RNA sequencing and spatial transcriptome analyses of human and mouse muscles, we investigated pathogenic features in patients with DMD and palliative effects of glucocorticoids. Our approach further illuminated the importance of proliferating satellite cells and revealed increased activity of a signal transduction pathway involving EZH2 in the patient cells. Subsequent administration of EZH2 inhibitors to Dmd mutant mice resulted in improved muscle phenotype through maintaining the immune-suppressing effect but overriding the muscle weakness and fibrogenic effects exerted by glucocorticoids. Our analysis reveals pathogenic mechanisms that can be readily targeted by extant therapeutic options for DMD.

A peptide conjugate enables systemic injection of the morpholino inducer and more durable induction of T3H38 ribozyme-controlled AAV transgene in mice

Genetic switches that allow for precise control over transgene expression timing or levels may improve the safety and expand the use of adeno-associated viral (AAV) vector-based gene therapy technologies. We previously engineered an efficient RNA switch system that comprises a novel self-cleaving ribozyme (T3H38) and an octaguanidine dendrimer-conjugated morpholino oligonucleotide (v-M8) complementary to the ribozyme. This switch system can be used to efficiently regulate AAV-delivered transgenes with an up to 200-fold regulatory range in mice. However, this switch system has a relatively short induction half-life and only works well when v-M8 was locally but not systemically administered, representing two key limitations of the system. To address these issues, here, we tested replacing the octa-guanidine dendrimer in the v-M8 morpholino oligo with a cell-penetrating peptide (CPP). Two CPP-conjugated morpholino oligos (B-M8 and B-MSP-M8) were synthesized and compared with v-M8 for the induction of T3H38-regulated AAV-luciferase in mice. One of the CPP-conjugated oligos (B-MSP-M8) not only showed significantly improved induction half-life over that of v-M8, but also enabled efficient induction of AAV transgene expression when the oligo was systemically administered. This study improves in vivo performance and broadens the utility of the T3H38 ribozyme-based RNA switch system in gene therapy applications.

Quantitative Structure-Property Relationship Modeling with the Prediction of Physicochemical Properties of Some Novel Duchenne Muscular Dystrophy Drugs

Duchenne muscular dystrophy is a critical, progressively worsening, and ultimately deadly illness characterized by the deterioration of skeletal muscles, respiratory failure, and heart disease. The pharmaceutical industries are persistently innovating drug design processes to address the rise of infections and effectively treat emerging syndromes or genetically based disorders with the help of quantitative structure-property relationship models. These models are mathematical tools that correlate molecular structures with their physicochemical properties through structural characteristics. Different models can be generated based on the various structural features of the compounds, and topological indices are one such significant structural feature generated from the molecular graph and are key tools used in these models. This study focuses on creating quantitative structure-property relationship models using degree-based topological indices, which are highly effective in quantitative structure-property relationship analysis to explore the diverse physicochemical properties of Duchenne muscular dystrophy drugs with the prediction of properties of a recently approved drug givinostat. Furthermore, the drug discovery and development activities can be accelerated using the developed models to forecast the possible productiveness of novel Duchenne muscular dystrophy treatment drugs.

A Manual for Genome and Transcriptome Engineering

Genome and transcriptome engineering have emerged as powerful tools in modern biotechnology, driving advancements in precision medicine and novel therapeutics. In this review, we provide a comprehensive overview of the current methodologies, applications, and future directions in genome and transcriptome engineering. Through this, we aim to provide a guide for tool selection, critically analyzing the strengths, weaknesses, and best use cases of these tools to provide context on their suitability for various applications. We explore standard and recent developments in genome engineering, such as base editors and prime editing, and provide insight into tool selection for change of function (knockout, deletion, insertion, substitution) and change of expression (repression, activation) contexts. Advancements in transcriptome engineering are also explored, focusing on established technologies like antisense oligonucleotides (ASOs) and RNA interference (RNAi), as well as recent developments such as CRISPR-Cas13 and adenosine deaminases acting on RNA (ADAR). This review offers a comparison of different approaches to achieve similar biological goals, and consideration of high-throughput applications that enable the probing of a variety of targets. This review elucidates the transformative impact of genome and transcriptome engineering on biological research and clinical applications that will pave the way for future innovations in the field.

Oligonucleotide therapeutics in sports? An antidoping perspective

Within the last two decades, the European Medicines Agency and the US Food and Drug Administration have approved several gene therapies. One category is oligonucleotide therapeutics, which allow for the regulation of the expression of target genes. Besides already approved therapeutics, there are several preclinical and clinical trials ongoing. The World Anti-Doping Agency prohibits the use of "nucleic acids or nucleic acid analogs that may alter genome sequences and/or alter gene expression by any mechanism" as a nonspecified method at all times. Hence, the administration of nucleic acids or analogs by athletes would cause an Anti-Doping Rule Violation. Herein, we discuss types of oligonucleotide therapeutics, their potential to be misused in sports, and considerations to sample preparation and mass spectrometric approaches with regard to antidoping analysis.

Inhibition of SARS-CoV-2 growth in the lungs of mice by a peptide-conjugated morpholino oligomer targeting viral RNA

Further development of direct-acting antiviral agents against human SARS-CoV-2 infections remains a public health priority. Here, we report that an antisense peptide-conjugated morpholino oligomer (PPMO) named 5'END-2, targeting a highly conserved sequence in the 5' UTR of SARS-CoV-2 genomic RNA, potently suppressed SARS-CoV-2 growth in vitro and in vivo. In HeLa-ACE 2 cells, 5'END-2 produced IC50 values of between 40 nM and 1.15 μM in challenges using six genetically disparate strains of SARS-CoV-2, including JN.1. In vivo, using K18-hACE2 mice and the WA-1/2020 virus isolate, two doses of 5'END-2 at 10 mg/kg, administered intranasally on the day before and the day after infection, produced approximately 1.4 log10 virus titer reduction in lung tissue at 3 days post-infection. Under a similar dosing schedule, intratracheal administration of 1.0-2.0 mg/kg 5'END-2 produced over 3.5 log10 virus growth suppression in mouse lungs. Electrophoretic mobility shift assays characterized specific binding of 5'END-2 to its complementary target RNA. Furthermore, using reporter constructs containing SARS-CoV-2 5' UTR leader sequence, in an in-cell system, we observed that 5'END-2 could interfere with translation in a sequence-specific manner. The results demonstrate that direct pulmonary delivery of 5'END-2 PPMO is a promising antiviral strategy against SARS-CoV-2 infections and warrants further development.

Systemic Treatment of Body-Wide Duchenne Muscular Dystrophy Symptoms

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease that leads to premature death due to the loss of dystrophin. Current strategies predominantly focus on the therapeutic treatment of affected skeletal muscle tissue. However, certain results point to the fact that with successful treatment of skeletal muscle, DMD-exposed latent phenotypes in tissues, such as cardiac and smooth muscle, might lead to adverse effects and even death. Likewise, it is now clear that the absence of dystrophin affects the function of the nervous system, and that this phenotype is more pronounced when shorter dystrophins are absent, in addition to the full-length dystrophin that is present predominantly in the muscle. Here, I focus on the systemic aspects of DMD, highlighting the ubiquitous expression of the dystrophin gene in human tissues. Furthermore, I describe therapeutic strategies that have been tested in the clinic and point to unresolved questions regarding the function of distinct dystrophin isoforms, and the possibility of current therapeutic strategies to tackle phenotypes that relate to their absence.

Peptide-based therapeutics targeting genetic disorders

Genetic disorders (GDs) are challenging to treat owing to a lack of optimal treatment regimens and intricate and often difficult-to-understand underlying biological processes. Limited therapeutic approaches, which mostly provide symptomatic relief, are available. To date, a limited number of peptide-based drugs for the treatment of GDs are available, and several candidates are under clinical study. This review provides mechanistic insights into GDs and potential target areas where peptide-based drugs are beneficial. In addition, it emphasizes the usefulness of peptides as carriers for gene delivery, biomarkers for mutation detection and peptide-based vaccines for treating GDs.

Identification of disease-specific extracellular vesicle-associated plasma protein biomarkers for Duchenne Muscular Dystrophy and Facioscapulohumeral Muscular Dystrophy

Objective

Reliable, circulating biomarkers for Duchenne, Becker and facioscapulohumeral muscular dystrophies (DBMD and FSHD) remain unvalidated. Here, we investigated the plasma extracellular vesicle (EV) proteome to identify disease-specific biomarkers that could accelerate therapy approvals.

Methods

We extracted EVs from the plasma of DBMD and FSHD patients and healthy controls using size-exclusion chromatography, conducted mass spectrometry on the extracted EV proteins, and performed comparative analysis to identify disease-specific biomarkers. We correlated the levels of these biomarkers with clinical outcome measures and confounding factors.

Results

The muscle-associated proteins PYGM, MYOM3, FLNC, MYH2 and TTN were exclusively present in DBMD EVs. PYGM, MYOM3, and TTN negatively correlated with age. PYGM and MYOM3 levels were elevated in patients without cardiomyopathy, and PYGM levels were specifically elevated in ambulatory DMD patients. On the other hand, female FSHD patients displayed significantly higher MBL2 and lower GPLD1 levels. However, male FSHD patients exhibited higher C9 and lower C4BPB levels. Additionally, desmosome proteins JUP and DSP were uniquely found in FSHD males. MBL2 positively correlated with age and C4BPB negatively correlated with FSHD severity in male patients.

Interpretation

Our findings underscore the sensitivity of analyzing circulating EV content to identify disease-specific protein biomarkers for DBMD and FSHD. Our results also emphasize the potential of EV-based biomarker discovery as a promising approach to monitor disease progression as well as effectiveness of therapies in muscular dystrophy, potentially contributing to their approval. Further research with larger cohorts is needed to validate these biomarkers and explore their clinical implications.

Nucleic acid drugs: recent progress and future perspectives

High efficacy, selectivity and cellular targeting of therapeutic agents has been an active area of investigation for decades. Currently, most clinically approved therapeutics are small molecules or protein/antibody biologics. Targeted action of small molecule drugs remains a challenge in medicine. In addition, many diseases are considered 'undruggable' using standard biomacromolecules. Many of these challenges however, can be addressed using nucleic therapeutics. Nucleic acid drugs (NADs) are a new generation of gene-editing modalities characterized by their high efficiency and rapid development, which have become an active research topic in new drug development field. However, many factors, including their low stability, short half-life, high immunogenicity, tissue targeting, cellular uptake, and endosomal escape, hamper the delivery and clinical application of NADs. Scientists have used chemical modification techniques to improve the physicochemical properties of NADs. In contrast, modified NADs typically require carriers to enter target cells and reach specific intracellular locations. Multiple delivery approaches have been developed to effectively improve intracellular delivery and the in vivo bioavailability of NADs. Several NADs have entered the clinical trial recently, and some have been approved for therapeutic use in different fields. This review summarizes NADs development and evolution and introduces NADs classifications and general delivery strategies, highlighting their success in clinical applications. Additionally, this review discusses the limitations and potential future applications of NADs as gene therapy candidates.

[Advances and Challenges in Microdystrophin gene therapy for Duchenne Muscular Dystrophy: progress and future directions]

Duchenne muscular dystrophy (DMD) is a severe degenerative genetic muscle disease affecting mainly young boys, characterized by a significant alteration or absence of dystrophin expression. Significant strides have been made in comprehending and treating DMD, particularly with the recent approval of the first gene therapy using a recombinant adeno-associated vector (rAAV) to deliver a shortened form of dystrophin (microdystrophin). Nevertheless, major challenges remain in improving therapeutic outcomes. The use of rAAV vectors is hindered by major limitations, notably the risks of immunotoxicity and hepatotoxicity, linked to high-dose administration. Additionally, microdystrophin exhibits inherent functional limitations and immunological risks. This article examines these challenges and explores the avenues for enhancing gene therapy for DMD.

Structure-Activity Relationship of Antibody-Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody-Phosphorodiamidate Morpholino Oligomer Conjugates for Drug Development

Antibody-oligonucleotide conjugates (AOCs) are promising treatments for Duchenne muscular dystrophy (DMD). They work via induction of exon skipping and restoration of dystrophin protein in skeletal and heart muscles. The structure-activity relationships (SARs) of AOCs comprising antibody-phosphorodiamidate morpholino oligomers (PMOs) depend on several aspects of their component parts. We evaluate the SAR of antimouse transferrin receptor 1 antibody (αmTfR1)-PMO conjugates: cleavable and noncleavable linkers, linker location on the PMO, and the impact of drug-to-antibody ratios (DARs) on plasma pharmacokinetics (PK), oligonucleotide delivery to tissues, and exon skipping. AOCs containing a stable linker with a DAR9.7 were the most effective PMO delivery vehicles in preclinical studies. We demonstrate that αmTfR1-PMO conjugates induce dystrophin protein restoration in the skeletal and heart muscles of mdx mice. Our results show that αmTfR1-PMO conjugates are a potentially effective approach for the treatment of DMD.

Neuromuscular Disorders in Pediatric Respiratory Disease

Respiratory sequelae are a frequent cause of morbidity and mortality in children with NMD. Impaired cough strength and resulting airway clearance as well as sleep disordered breathing are the two main categories of respiratory sequelae. Routine clinical evaluation and diagnostic testing by pulmonologists is an important pillar of the multidisciplinary care required for children with NMD. Regular surveillance for respiratory disease and timely implementation of treatment including pulmonary clearance techniques as well as ventilation can prevent respiratory related morbidity including hospital admissions and improve survival. Additionally, novel disease modifying therapies for some NMDs are now available which has significantly improved the clinical trajectories of patients resulting in a paradigm shift in clinical care. Pulmonologists are 'learning' the new natural history for these diseases and adjusting clinical management accordingly.

Gene therapy for ultrarare diseases: a geneticist's perspective

Gene therapy has made considerable strides in recent years. More than 4000 protein-coding genes have been implicated in more than 6000 genetic diseases; next-generation sequencing has dramatically revolutionized the diagnosis of genetic diseases. Most genetic diseases are considered very rare or ultrarare, defined here as having fewer than 1:100,000 cases, but only one of the 12 approved gene therapies (excluding RNA therapies) targets an ultrarare disease. This article explores three gene supplementation therapy approaches suitable for various rare genetic diseases: lentiviral vector-modified autologous CD34+ hematopoietic stem cell transplantation, systemic delivery of adeno-associated virus (AAV) vectors to the liver, and local AAV delivery to the cerebrospinal fluid and brain. Together with RNA therapies, we propose a potential business model for these gene therapies.

Comprehensive review of adverse reactions and toxicology in ASO-based therapies for Duchenne Muscular Dystrophy: From FDA-approved drugs to peptide-conjugated ASO

Duchenne Muscular Dystrophy (DMD) is a devastating X-linked genetic disorder characterized by progressive muscle degeneration due to mutations in the dystrophin gene. This results in the absence or dysfunction of the dystrophin protein, leading to muscle weakness, loss of ambulation, respiratory issues, and cardiac complications, often leading to premature death. Recently, antisense oligonucleotide (ASO)-mediated exon skipping has emerged as a promising therapeutic strategy for DMD. Notably, the FDA has conditionally approved four ASO therapies for DMD, with numerous others in various stages of clinical development, indicating the growing interest and potential in this field. To enhance ASO-based therapies, researchers have explored the novel concept of conjugating peptides to the phosphorodiamidate morpholino backbone (PMO) of ASOs, leading to the development of peptide-conjugated PMOs (PPMOs). These PPMOs have demonstrated significantly improved pharmacokinetic profiles, potentially augmenting their therapeutic effectiveness. Despite the optimism surrounding ASOs and PPMOs, concerns persist regarding their efficacy and safety. To comprehensively evaluate these therapies, it is imperative to expand patient populations in clinical trials and conduct thorough investigations into the associated risks. This article provides a comprehensive review and discussion of the available data pertaining to adverse reactions and toxicology associated with FDA-approved ASO drugs for DMD. Furthermore, it offers insights into the emerging category of peptide-conjugated ASO drugs those are clinical and preclinical trials, shedding light on their potential benefits and challenges.

Antisense therapy: a potential breakthrough in the treatment of neurodegenerative diseases

Neurodegenerative diseases are a group of disorders characterized by the progressive degeneration of neurons in the central or peripheral nervous system. Currently, there is no cure for neurodegenerative diseases and this means a heavy burden for patients and the health system worldwide. Therefore, it is necessary to find new therapeutic approaches, and antisense therapies offer this possibility, having the great advantage of not modifying cellular genome and potentially being safer. Many preclinical and clinical studies aim to test the safety and effectiveness of antisense therapies in the treatment of neurodegenerative diseases. The objective of this review is to summarize the recent advances in the development of these new technologies to treat the most common neurodegenerative diseases, with a focus on those antisense therapies that have already received the approval of the U.S. Food and Drug Administration.

Defining clinical endpoints in limb girdle muscular dystrophy: a GRASP-LGMD study

BACKGROUND

The Limb Girdle Muscular Dystrophies (LGMDs) are characterized by progressive weakness of the shoulder and hip girdle muscles as a result of over 30 different genetic mutations. This study is designed to develop clinical outcome assessments across the group of disorders.

METHODS/DESIGN

The primary goal of this study is to evaluate the utility of a set of outcome measures on a wide range of LGMD phenotypes and ability levels to determine if it would be possible to use similar outcomes between individuals with different phenotypes. We will perform a multi-center, 12-month study of 188 LGMD patients within the established Genetic Resolution and Assessments Solving Phenotypes in LGMD (GRASP-LGMD) Research Consortium, which is comprised of 11 sites in the United States and 2 sites in Europe. Enrolled patients will be clinically affected and have mutations in CAPN3 (LGMDR1), ANO5 (LGMDR12), DYSF (LGMDR2), DNAJB6 (LGMDD1), SGCA (LGMDR3), SGCB (LGMDR4), SGCD (LGMDR6), or SGCG (LGMDR5, or FKRP-related (LGMDR9).

DISCUSSION

To the best of our knowledge, this will be the largest consortium organized to prospectively validate clinical outcome assessments (COAs) in LGMD at its completion. These assessments will help clinical trial readiness by identifying reliable, valid, and responsive outcome measures as well as providing data driven clinical trial decision making for future clinical trials on therapeutic agents for LGMD. The results of this study will permit more efficient clinical trial design. All relevant data will be made available for investigators or companies involved in LGMD therapeutic development upon conclusion of this study as applicable.

TRIAL REGISTRATION

Clinicaltrials.gov NCT03981289; Date of registration: 6/10/2019.

Duchenne muscular dystrophy: promising early-stage clinical trials to watch

INTRODUCTION

Current therapies are unable to cure Duchenne muscular dystrophy (DMD), a severe and common form of muscular dystrophy, and instead aim to delay disease progression. Several treatments currently in phase I trials could increase the number of therapeutic options available to patients.

AREAS COVERED

This review aims to provide an overview of current treatments undergoing or having recently undergone early-stage trials. Several exon-skipping and gene therapy approaches are currently being investigated at the clinical stage to address an unmet need for DMD treatments. This article also covers Phase I trials from the last 5 years that involve inhibitors, small molecules, a purified synthetic flavanol, a cell-based therapy, and repurposed cardiac or tumor medications.

EXPERT OPINION

With antisense oligonucleotide (AON) treatments making up the majority of conditionally approved DMD therapies, most of the clinical trials occurring within the last 5 years have also evaluated exon-skipping AONs. The approval of Elevidys, a micro-dystrophin therapy, is reflected in a recent trend toward gene transfer therapies in phase I DMD clinical trials, but their safety and efficacy are being established in this phase of development. Other Phase I clinical-stage approaches are diverse, but have a range in efficacy, safety, and endpoint measures.

Targeting RNA with synthetic oligonucleotides: Clinical success invites new challenges

Synthetic antisense oligonucleotides (ASOs) and duplex RNAs (dsRNAs) are an increasingly successful strategy for drug development. After a slow start, the pace of success has accelerated since the approval of Spinraza (nusinersen) in 2016 with several drug approvals. These accomplishments have been achieved even though oligonucleotides are large, negatively charged, and have little resemblance to traditional small-molecule drugs-a remarkable achievement of basic and applied science. The goal of this review is to summarize the foundation underlying recent progress and describe ongoing research programs that may increase the scope and impact of oligonucleotide therapeutics.

Precision medicine using whole genome sequencing identifies a novel dystrophin (DMD) variant for X-linked muscular dystrophy in a cat

BACKGROUND

Muscular dystrophies (MDs) are a large, heterogeneous group of degenerative muscle diseases. X-linked dystrophin-deficient MD in cats is the first genetically characterized cat model for a human disease and a few novel forms have been identified.

HYPOTHESIS/OBJECTIVES

Muscular dystrophy was suspected in a young male domestic shorthair cat. Clinical, molecular, and genetic techniques could provide a definitive diagnosis.

ANIMALS

A 1-year-old male domestic shorthair cat presented for progressive difficulty walking, macroglossia and dysphagia beginning at 6 months of age. The tongue was thickened, protruded with constant ptyalism, and thickening and rigidity of the neck and shoulders were observed.

METHODS

A complete neurological examination, baseline laboratory evaluation and biopsies of the trapezius muscle were performed with owner consent. Indirect immunofluorescence staining of muscle cryosections was performed using several monoclonal and polyclonal antibodies against dystrophy-associated proteins. DNA was isolated for genomic analyses by whole genome sequencing and comparison to DNA variants in the 99 Lives Cat Genome Sequencing dataset.

RESULTS AND CLINICAL IMPORTANCE

Aspartate aminotransferase (687 IU/L) and creatine kinase (24 830 IU/L) activities were increased and mild hypokalemia (3.7 mmol/L) was present. Biopsy samples from the trapezius muscle confirmed a degenerative and regenerative myopathy and protein alterations identified by immunohistochemistry resulted in a diagnosis of a in dystrophin-deficient form of X-linked MD. A stop gain variant (c.4849C>T; p.Gln1617Ter) dystrophin was identified by genome sequencing. Precision/genomic medicine efforts for the domestic cat and in veterinary medicine support disease variant and animal model discovery and provide opportunities for targeted treatments for companion animals.

Defining Clinical Endpoints in Limb Girdle Muscular Dystrophy: A GRASP-LGMD study

Background

The Limb Girdle Muscular Dystrophies (LGMDs) are characterized by progressive weakness of the shoulder and hip girdle muscles as a result of over 30 different genetic mutations. This study is designed to develop clinical outcome assessments across the group of disorders.

Methods/design

The primary goal of this study is to evaluate the utility of a set of outcome measures on a wide range of LGMD phenotypes and ability levels to determine if it would be possible to use similar outcomes between individuals with different phenotypes. We will perform a multi-center, 12-month study of 188 LGMD patients within the established Genetic Resolution and Assessments Solving Phenotypes in LGMD (GRASP-LGMD) Research Consortium, which is comprised of 11 sites in the United States and 2 sites in Europe. Enrolled patients will be clinically affected and have mutations in CAPN3 (LGMDR1), ANO5 (LGMDR12), DYSF (LGMDR2), DNAJB6 (LGMDD1), SGCA (LGMDR3), SGCB (LGMDR4), SGCD (LGMDR6), or SGCG (LGMDR5, or FKRP-related (LGMDR9).

Discussion

To the best of our knowledge, this will be the largest consortium organized to prospectively validate clinical outcome assessments (COAs) in LGMD at its completion. These assessments will help clinical trial readiness by identifying reliable, valid, and responsive outcome measures as well as providing data driven clinical trial decision making for future clinical trials on therapeutic agents for LGMD. The results of this study will permit more efficient clinical trial design. All relevant data will be made available for investigators or companies involved in LGMD therapeutic development upon conclusion of this study as applicable.

Trial registration

clinicaltrials.gov NCT03981289; Date of registration: 6/10/2019.

CRISPR-Cas9 correction in the DMD mouse model is accompanied by upregulation of Dp71f protein

Duchenne muscular dystrophy (DMD) is a severe hereditary disease caused by a deficiency in the dystrophin protein. The most frequent types of disease-causing mutations in the DMD gene are frameshift deletions of one or more exons. Precision genome editing systems such as CRISPR-Cas9 have shown potential to restore open reading frames in numerous animal studies. Here, we applied an AAV-CRISPR double-cut strategy to correct a mutation in the DMD mouse model with exon 8-34 deletion, encompassing the N-terminal actin-binding domain. We report successful excision of the 100-kb genomic sequence, which includes exons 6 and 7, and partial improvement in cardiorespiratory function. While corrected mRNA was abundant in muscle tissues, only a low level of truncated dystrophin was produced, possibly because of protein instability. Furthermore, CRISPR-Cas9-mediated genome editing upregulated the Dp71f dystrophin isoform on the sarcolemma. Given the previously reported Dp71-associated muscle pathology, our results question the applicability of genome editing strategies for some DMD patients with N-terminal mutations. The safety and efficacy of CRISPR-Cas9 constructs require rigorous investigation in patient-specific animal models.

Development and electronic health record validation of an algorithm for identifying patients with Duchenne muscular dystrophy in US administrative claims

BACKGROUND: Muscular dystrophies (MDs) comprise a heterogenous group of genetically inherited conditions characterized by progressive muscle weakness and increasing disability. The lack of separate diagnosis codes for Duchenne MD (DMD) and Becker MD, 2 of the most common forms of MD, has limited the conduct of DMD-specific real-world studies. OBJECTIVE: To develop and validate administrative claims-based algorithms for identifying patients with DMD and capturing their nonambulatory and ventilation-dependent status. METHODS: This was a retrospective cohort study using the statistically deidentified Optum Market Clarity Database (including patient claims linked with electronic health records [EHRs] data) to develop and validate the following algorithms: DMD diagnosis, nonambulatory status, and ventilation-dependent status. The initial study sample consisted of US patients in the database who had a diagnosis code for Duchenne/Becker MD (DBMD) between October 1, 2018, and September 30, 2020, who were male, aged 40 years or younger on their first DBMD diagnosis, and met continuous enrollment and 1-day minimal clinical activities requirement in a 12-month measurement period between October 1, 2017, and September 30, 2020. The algorithms, developed by a cross-functional team of DMD specialists (including patient advocates), were based on administrative claims data with International Classification of Diseases, Tenth Revision, Clinical Modifications coding, using information of diagnosis codes for DBMD, sex, age, treatment, and disease severity (eg, evidence of ambulation assistance/support and/or evidence of ventilation support or dependence). Patients who met each algorithm and had EHR notes available were then validated against structured fields and unstructured provider notes from their own linked EHR to confirm patients' DMD diagnoses, nonambulatory status, and ventilation-dependent status. Algorithm performance was assessed by positive predictive value with 95% CIs. RESULTS: A total of 1,300 patients were included in the initial study sample. Of these, EHR were available and reviewed for 303 patients. The mean age of the 303 patients was 14.8 years, with 61.7% being non-Hispanic White. A majority had a Charlson comorbidity index score of 0 (59.4%) or 1-2 (27.7%). Positive predictive value (95% CI) was 91.6% (85.8%-95.6%) for the DMD diagnosis algorithm, 88.4% (80.2%-94.1%) for the nonambulatory status algorithm, and 77.8% (62.9%-88.8%) for the ventilation-dependent status algorithm. CONCLUSIONS: This work provides the means to more accurately identify patients with DMD from administrative claims data without a specific diagnosis code. The algorithms validated in this study can be applied to assess treatment effectiveness and other outcomes among patients with DMD treated in clinical practice. DISCLOSURES: This study was funded by Pfizer, which contracted with Optum to perform the study and provide medical writing assistance. Ms Schrader reports being an employee of Parent Project Muscular Dystrophy. Mr Posner reports being an employee and stockholder of Pfizer and receiving support from Pfizer for attending conferences not related to this manuscript. Dr Dorling reports being an employee and stockholder of Pfizer at the time the study was conducted and is a current employee of Chiesi USA, Inc. Ms Senerchia reports being an employee of Optum and owning stock in Pfizer and UnitedHealth Group, the parent company of Optum. Dr Chen reports being an employee and stockholder of Pfizer. Ms Beaverson reports being an employee of Pfizer and owning stock in Pfizer and Amicus Therapeutics. Dr Seare reports being an employee of Optum at the time the study was conducted. Dr Garnier and Ms Merla report being employees of Pfizer. Ms Walker reports being an employee of Optum. Dr Alvir reports being an employee and stockholder of Pfizer. Dr Mahn reports being an employee and stockholder of Pfizer. Dr Zhang reports being an employee of Optum. Ms Landis reports being an employee of Optum. Ms Buikema reports being an employee of Optum and holding stock in UnitedHealth Group, the parent company of Optum.

Expression of SRP-9001 dystrophin and stabilization of motor function up to 2 years post-treatment with delandistrogene moxeparvovec gene therapy in individuals with Duchenne muscular dystrophy

Introduction: Delandistrogene moxeparvovec (SRP-9001) is an investigational gene transfer therapy designed for targeted expression of SRP-9001 dystrophin protein, a shortened dystrophin retaining key functional domains of the wild-type protein. Methods: This Phase 2, double-blind, two-part (48 weeks per part) crossover study (SRP-9001-102 [Study 102]; NCT03769116) evaluated delandistrogene moxeparvovec in patients, aged ≥4 to <8 years with Duchenne muscular dystrophy. Primary endpoints (Part 1) were change from baseline (CFBL) in SRP-9001 dystrophin expression (Week 12), by Western blot, and in North Star Ambulatory Assessment (NSAA) score (Week 48). Safety assessments included treatment-related adverse events (TRAEs). Patients were randomized and stratified by age to placebo (n = 21) or delandistrogene moxeparvovec (n = 20) and crossed over for Part 2. Results: SRP-9001 dystrophin expression was achieved in all patients: mean CFBL to Week 12 was 23.82% and 39.64% normal in Parts 1 and 2, respectively. In Part 1, CFBL to Week 48 in NSAA score (least-squares mean, LSM [standard error]) was +1.7 (0.6) with treatment versus +0.9 (0.6) for placebo; p = 0.37. Disparity in baseline motor function between groups likely confounded these results. In 4- to 5-year-olds with matched baseline motor function, CFBL to Week 48 in NSAA scores was significantly different (+2.5 points; p = 0.0172), but not significantly different in 6-to-7-year-olds with imbalanced baseline motor function (-0.7 points; p = 0.5384). For patients treated with delandistrogene moxeparvovec in Part 2, CFBL to Week 48 in NSAA score was +1.3 (2.7), whereas for those treated in Part 1, NSAA scores were maintained. As all patients in Part 2 were exposed to treatment, results were compared with a propensity-score-weighted external control (EC) cohort. The LSM difference in NSAA score between the Part 2 treated group and EC cohort was statistically significant (+2.0 points; p = 0.0009). The most common TRAEs were vomiting, decreased appetite, and nausea. Most occurred within the first 90 days and all resolved. Discussion: Results indicate robust expression of SRP-9001 dystrophin and overall stabilization in NSAA up to 2 years post-treatment. Differences in NSAA between groups in Part 1 were not significant for the overall population, likely because cohorts were stratified only by age, and other critical prognostic factors were not well matched at baseline.