Journal of Neuromuscular Diseases - Volume 8, issue s2

Article Type: Other

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S301-S301, 2021

Authors: Elangkovan, Nertiyan | Dickson, George

Article Type: Review Article

Abstract: Duchenne muscular dystrophy (DMD) is an X-linked, muscle wasting disease that affects 1 in 5000 males. Affected individuals become wheelchair bound by the age of twelve and eventually die in their third decade due to respiratory and cardiac complications. The disease is caused by mutations in the DMD gene that codes for dystrophin. Dystrophin is a structural protein that maintains the integrity of muscle fibres and protects them from contraction-induced damage. The absence of dystrophin compromises the stability and function of the muscle fibres, eventually leading to muscle degeneration. So far, there is no effective treatment for deteriorating muscle …function in DMD patients. A promising approach for treating this life-threatening disease is gene transfer to restore dystrophin expression using a safe, non-pathogenic viral vector called adeno-associated viral (AAV) vector. Whilst microdystrophin gene transfer using AAV vectors shows extremely impressive therapeutic success so far in large animal models of DMD, translating this advanced therapy medicinal product from bench to bedside still offers scope for many optimization steps. In this paper, the authors review the current progress of AAV-microdystrophin gene therapy for DMD and other treatment strategies that may apply to a subset of DMD patients depending on the mutations they carry. Show more

Keywords: Gene therapy, duchenne, muscular dystrophy, dystrophin, microdystrophin, adeno-associated virus, antisense, exon skipping

DOI: 10.3233/JND-210678

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S303-S316, 2021

Authors: Morgan, Jennifer | Muntoni, Francesco

Article Type: Review Article

Abstract: Adult skeletal muscle is a relatively stable tissue, as the multinucleated muscle fibres contain post-mitotic myonuclei. During early postnatal life, muscle growth occurs by the addition of skeletal muscle stem cells (satellite cells) or their progeny to growing muscle fibres. In Duchenne muscular dystrophy, which we shall use as an example of muscular dystrophies, the muscle fibres lack dystrophin and undergo necrosis. Satellite-cell mediated regeneration occurs, to repair and replace the necrotic muscle fibres, but as the regenerated muscle fibres still lack dystrophin, they undergo further cycles of degeneration and regeneration. AAV gene therapy is a promising approach for …treating Duchenne muscular dystrophy. But for a single dose of, for example, AAV coding for microdystrophin, to be effective, the treated myonuclei must persist, produce sufficient dystrophin and a sufficient number of nuclei must be targeted. This latter point is crucial as AAV vector remains episomal and does not replicate in dividing cells. Here, we describe and compare the growth of skeletal muscle in rodents and in humans and discuss the evidence that myofibre necrosis and regeneration leads to the loss of viral genomes within skeletal muscle. In addition, muscle growth is expected to lead to the dilution of the transduced nuclei especially in case of very early intervention, but it is not clear if growth could result in insufficient dystrophin to prevent muscle fibre breakdown. This should be the focus of future studies. Show more

Keywords: Skeletal muscle growth, satellite cells, myonuclei, adeno-associated virus, Duchenne muscular dystrophy, gene therapy

DOI: 10.3233/JND-210683

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S317-S324, 2021

Authors: Li, Ning | Parkes, Joanna E. | Spathis, Rita | Morales, Melissa | Mcdonald, John | Kendra, Ryan M. | Ott, Emily M. | Brown, Kristy J. | Lawlor, Michael W. | Nagaraju, Kanneboyina

Article Type: Research Article

Abstract: Background: AAV-based gene therapy is an attractive approach to treat Duchenne muscular dystrophy (DMD) patients. Although the long-term consequences of a gene therapy approach for DMD are unknown, there is evidence in both DMD patients and animal models that dystrophin replacement by gene therapy leads to an anti-dystrophin immune response that is likely to limit the long-term use of these therapeutic strategies. Objective: Our objective is to test whether the anti-dystrophin immune response is affected by immunomodulatory drugs in mdx mice after rAAV gene therapy. Methods: mdx mice were treated with …rAAV microdystrophin alone or in combination with immunomodulatory drugs. Dystrophin expression in skeletal muscle was assessed by mass spectrometry. Immune responses were assessed by immunophenotyping, western blot for anti-dystrophin antibodies and flow cytometry assays for antigen-specific T-cell cytokine expression. The impact on muscle was measured by grip strength assessment, in vivo torque, optical imaging for inflammation and H&E staining of sections to assess muscle damage. Results: We found that AAV-9-microdystrophin gene therapy induced expression of microdystrophin, anti-dystrophin antibodies, and T-cell cytokine responses. Immunomodulatory treatments, rituximab and VBP6 completely abrogated the anti-dystrophin antibody response. Prednisolone, CTLA4-Ig, and eplerenone showed variable efficacy in blocking the anti-dystrophin immune response. In contrast, none of the drugs completely abrogated the antigen specific IFN-γ response. AAV-microdystrophin treatment significantly reduced inflammation in both forelimbs and hindlimbs, and the addition of prednisolone and VBP6 further reduced muscle inflammation. Treatment with immunomodulatory drugs, except eplerenone, enhanced the beneficial effects of AAV-microdystrophin therapy in terms of force generation. Conclusions: Our data suggest that AAV-microdystrophin treatment results in anti-dystrophin antibody and T-cell responses, and immunomodulatory treatments have variable efficacy on these responses. Show more

Keywords: Gene therapy, microdystrophin, immune response, adeno associated virus, anti-dystrophin antibodies, immunomodulatory treatments

DOI: 10.3233/JND-210706

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S325-S340, 2021

Article Type: Other

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S341-S341, 2021

Authors: Takeda, Shin’ichi | Clemens, Paula R. | Hoffman, Eric P.

Article Type: Review Article

Abstract: Duchenne muscular dystrophy (DMD) is a devastating, rare disease. While clinically described in the 19th century, the genetic foundation of DMD was not discovered until more than 100 years later. This genetic understanding opened the door to the development of genetic treatments for DMD. Over the course of the last 30 years, the research that supports this development has moved into the realm of clinical trials and regulatory drug approvals. Exon skipping to therapeutically restore the frame of an out-of-frame dystrophin mutation has taken center stage in drug development for DMD. The research reviewed here focuses on the clinical …development of exon skipping for the treatment of DMD. In addition to the generation of clinical treatments that are being used for patient care, this research sets the stage for future therapeutic development with a focus on increasing efficacy while providing safety and addressing the multi-systemic aspects of DMD. Show more

DOI: 10.3233/JND-210682

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S343-S358, 2021

Authors: Lu, Qi Long

Article Type: Review Article

Abstract: This review recollects my initial research focus on revertant fibers (expressing dystrophin in the background of frame-shifting mutation) in Duchenne muscular dystrophy (DMD) muscles in Professor Terrence Partridge’s Muscle Cell Biology Laboratory in MRC Clinical Research Science Center, Harmmersmith Hospital, London, UK. Our data indicated that revertant fibers are most likely resulted from epigenetic random events which skip exon(s) flanking the mutated exon, leading to the restoration of the reading frame. Some of these events establish themselves as relatively permanent skipping patterns, a mechanism similar to multiple transcript species established in various cell types. With this hypothesis, antisense oligonucleotide-mediated exon …skipping is likely to have a great chance to achieve restoration of therapeutic levels of dystrophin in DMD muscles. This leads to our first reports of local and systemic efficacy of antisense oligonucleotide-mediated exon skipping for DMD treatment. The experience under Terry’s mentorship shaped my thinking and led me to explore another revertant feature in the dystroglycanopathy caused by mutations in the Fukutin Related Protein (FKRP) gene which functions as a glycosyltransferase. Mutant FKRPs retain partial function and produce a fraction of normal to no detectable levels of laminin-binding α -dystroglycan (matriglycan) in most of the muscle fibers. Reversion to near normal levels of matriglycan expression in muscles with FKRP mutations depends on muscle regeneration and in muscles of neonate mice, suggesting that changes in metabolism and gene expression could be sufficient to compensate for the reduced function of mutant FKRP genes even those associated with severe congenital muscular dystrophy (CMD). This is now supported by our successful demonstration that supply of FKRP mutant mice with ribitol, a precursor for substrate of FKRP, is sufficient to restore the levels of matriglycan with therapeutic significance. Our data overall suggest that rare events of reversion in muscular dystrophy, and likely other diseases could provide unique insight for mechanisms and therapeutic exploitation. Show more

DOI: 10.3233/JND-210692

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S359-S367, 2021

Authors: Benny Klimek, Margaret E. | Vila, Maria Candida | Edwards, Katie | Boehler, Jessica | Novak, James | Zhang, Aiping | Van der Meulen, Jack | Tatum, Kathleen | Quinn, James | Fiorillo, Alyson | Burki, Umar | Straub, Volker | Lu, Qi Long | Hathout, Yetrib | van Den Anker, John | Partridge, Terence A. | Morales, Melissa | Hoffman, Eric | Nagaraju, Kanneboyina

Article Type: Research Article

Abstract: Background: Phosphorodiamidate morpholino oligomer (PMO)-mediated exon skipping is currently used in clinical development to treat Duchenne muscular dystrophy (DMD), with four exon-skipping drugs achieving regulatory approval. Exon skipping elicits a truncated, but semi-functional dystrophin protein, similar to the truncated dystrophin expressed in patients with Becker Muscular dystrophy (BMD) where the disease phenotype is less severe than DMD. Despite promising results in both dystrophic animal models and DMD boys, restoration of dystrophin by exon skipping is highly variable, leading to contradictory functional outcomes in clinical trials. Objective: To develop optimal PMO dosing protocols that result in increased dystrophin and …improved outcome measures in preclinical models of DMD. Methods: Tested effectiveness of multiple chronic, high dose PMO regimens using biochemical, histological, molecular, and imaging techniques in mdx mice. Results: A chronic, monthly regimen of high dose PMO increased dystrophin rescue in mdx mice and improved specific force in the extensor digitorum longus (EDL) muscle. However, monthly high dose PMO administration still results in variable dystrophin expression localized throughout various muscles. Conclusions: High dose monthly PMO administration restores dystrophin expression and increases muscle force; however, the variability of dystrophin expression at both the inter-and intramuscular level remains. Additional strategies to optimize PMO uptake including increased dosing frequencies or combination treatments with other yet-to-be-defined therapies may be necessary to achieve uniform dystrophin restoration and increases in muscle function. Show more

Keywords: KeywordsMorpholinos, dystrophin quantitation, specific force of muscle, dystrophin deficiency

DOI: 10.3233/JND-210701

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S369-S381, 2021

Authors: Novak, James S. | Spathis, Rita | Dang, Utkarsh J. | Fiorillo, Alyson A. | Hindupur, Ravi | Tully, Christopher B. | Mázala, Davi A.G. | Canessa, Emily | Brown, Kristy J. | Partridge, Terence A. | Hathout, Yetrib | Nagaraju, Kanneboyina

Article Type: Research Article

Abstract: Recently, the Food and Drug Administration granted accelerated approvals for four exon skipping therapies –Eteplirsen, Golodirsen, Viltolarsen, and Casimersen –for Duchenne Muscular Dystrophy (DMD). However, these treatments have only demonstrated variable and largely sub-therapeutic levels of restored dystrophin protein in DMD patients, limiting their clinical impact. To better understand variable protein expression and the behavior of truncated dystrophin protein in vivo , we assessed turnover dynamics of restored dystrophin and dystrophin glycoprotein complex (DGC) proteins in mdx mice after exon skipping therapy, compared to those dynamics in wild type mice, using a targeted, highly-reproducible and sensitive, in vivo …stable isotope labeling mass spectrometry approach in multiple muscle tissues. Through statistical modeling, we found that restored dystrophin protein exhibited altered stability and slower turnover in treated mdx muscle compared with that in wild type muscle (∼44 d vs. ∼24 d, respectively). Assessment of mRNA transcript stability (quantitative real-time PCR, droplet digital PCR) and dystrophin protein expression (capillary gel electrophoresis, immunofluorescence) support our dystrophin protein turnover measurements and modeling. Further, we assessed pathology-induced muscle fiber turnover through bromodeoxyuridine (BrdU) labeling to model dystrophin and DGC protein turnover in the context of persistent fiber degeneration. Our findings reveal sequestration of restored dystrophin protein after exon skipping therapy in mdx muscle leading to a significant extension of its half-life compared to the dynamics of full-length dystrophin in normal muscle. In contrast, DGC proteins show constant turnover attributable to myofiber degeneration and dysregulation of the extracellular matrix (ECM) in dystrophic muscle. Based on our results, we demonstrate the use of targeted mass spectrometry to evaluate the suitability and functionality of restored dystrophin isoforms in the context of disease and propose its use to optimize alternative gene correction strategies in development for DMD. Show more

Keywords: Duchenne muscular dystrophy, dystrophin, dystrophin-associated glycoprotein complex, mass spectrometry, stable isotope, antisense oligonucleotides, exon skipping, gene therapy

DOI: 10.3233/JND-210696

Citation: Journal of Neuromuscular Diseases, vol. 8, no. s2, pp. S383-S402, 2021