Sarepta Therapeutics, Inc. (NASDAQ: SRPT), a developer of innovative RNA-based therapeutics, today announced a new online resource center, called Let’s Skip Ahead, for families affected by Duchenne muscular dystrophy (DMD) and their healthcare providers.
Skipping multiple exons at the same time, by using a combination of antisense oligonucleotides, offers the potential to treat a significant number of Duchenne patients. This would address one of the major limitations of current antisense therapy, in that the approach is “personalizedâ€ù and designed to skip a single exon.
Specifically, exons 45 to 55 cover the main mutation “hotspotâ€ù of the DMD gene and this area is thought to harbor mutations that are present in more than half of Duchenne patients.
Individuals with this specific 45-55 deletion show almost asymptomatic skeletal muscle involvement or exceptionally mild clinical symptoms and it is this observation that has spurred interest in developing strategies for multi-exon skipping.
This review (http://www.hindawi.com/journals/bmri/2013/402369/), by leading researchers in the field of multiexon skipping, highlights novel findings from a DMD mouse model utilizing systemic multiexon skipping targeting exons 45–55.
The authors highlight the hurdles and limitations impeding the clinical translation of this approach and provide a perspective on the opportunity for exon 45–55 skipping in DMD patients.
Title: Development of Multiexon Skipping Antisense Oligonucleotide Therapy for Duchenne Muscular Dystrophy.
Ref. BioMed Research International, Volume 2013 (2013), http://dx.doi.org/10.1155/2013/402369
Authors: Yoshitsugu Aoki, Toshifumi Yokota, and Matthew J. A. Wood
Skeletal muscles have been shown to display sporadic dystrophin-positive revertant fibers, both in animal models of DMD as well as in Duchenne patients. These dystrophin-positive fibers arise from spontaneous exon skipping events (alternative splicing of the mRNA) and lead to the production of an in-frame truncated dystrophin protein. The revertant events are thought to arise within a subset of muscle precursor cells which proliferate in response to the ongoing muscle degeneration and the expansion the clusters of revertant fibers is known to be dependent on active muscle regeneration.
The mechanisms by which revertant fibers arise and expand are not understood, and in the present study,
Toshifumi Yokoto et al. (Echigoya Y, Lee J, Rodrigues M, Nagata T, Tanihata J, et al. (2013) Mutation Types and Aging Differently Affect Revertant Fiber Expansion in Dystrophic Mdx and Mdx52 Mice. PLoS ONE 8(7): e69194. doi:10.1371/journal.pone.0069194) examined the effects of two types of mutation (mdx mice containing a nonsense mutation in exon 23 and mdx52 mice containing deletion mutation of exon 52) and aging on revertant fibers expansion and muscle regeneration. Their results demonstrate that revertant fiber expansion and muscle regeneration is influenced by both ageing and the specific type of mutation.
The translation of preclinical drug discover to clinical development has historically suffered a high attrition rate resulting in the majority of clinical studies failing in Phase I and Phase II clinical trials. The reasons for this are as varied and complex as the disease we aim to treat. To combat this, improvements are simultaneously needed in multiple areas; both preclinical and clinical as well as understanding the limitations of certain preclinical models as they relate to human disease. A recent paper by Kimmelman et al. (http://www.plosmedicine.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pmed.1001489&representation=PDF) examines guidelines for in vivo experiments in animals in order to help improve the fidelity of preclinical studies. The researchers identified preclinical guidelines that met their predefined eligibility criteria, and offered 55 different recommendations for the design and execution of preclinical in vivo animal studies.
A recent paper from Gersbach et al. (Molecular Therapy, 4th June, 2013) entitled “Reading Frame Correction by Targeted Genome Editing Restores Dystrophin Expression in Cells From Duchenne Muscular Dystrophy Patientsâ€ù highlights the recent advances in approaches to correct genetic mutations in patient derived cells using an engineered nuclease.
The purpose of the study is to see whether PRO045 is safe and effective to use as medication for Duchenne Muscular Dystrophy (DMD) patients with a mutation around location 45 in the DNA for the dystrophin protein.
Evidence-based therapeutics in Duchenne muscular dystrophy
(DMD) has been limited to corticosteroids for the past 30 years. There have been a host of other therapeutic interventions studied in mice, canines and more recently humans, but they are yet to show effectiveness in clinical trials. Newer genetic approaches are in early stages of clinical trials.
A team of the New York Stem Cell Foundation (NYSCF) Research Institute have recently developed a new way to generate induced pluripotent stem (iPS) cell lines from human fibroblasts, acquired […]
DMD nonsense and frameshift mutations lead to severe Duchenne muscular dystrophy while in-frame mutations lead to milder Becker muscular dystrophy. Exceptions are found in 10% of cases and the production of alternatively spliced transcripts is considered a key modifier of disease severity. Several exonic mutations have been shown to induce exon-skipping, while splice site mutations result in exon-skipping or activation of cryptic splice sites. However, factors determining the splicing pathway are still unclear. Point mutations provide valuable information regarding the regulation of pre-mRNA splicing and elements defining exon identity in the DMD gene. Here we provide a comprehensive analysis of 98 point mutations related to clinical phenotype and their effect on muscle mRNA and dystrophin expression. Aberrant splicing was found in 27 mutations due to alteration of splice sites or splicing regulatory elements. Bioinformatics analysis was performed to test the ability of the available algorithms to predict consequences on mRNA and to investigate the major factors that determine the splicing pathway in mutations affecting splicing signals. Our findings suggest that the splicing pathway is highly dependent on the interplay between splice site strength and density of regulatory elements.
