Antisense-induced exon skipping for duplications in Duchenne muscular dystrophy

<p>Abstract</p> <p>Background</p> <p>Antisense-mediated exon skipping is currently one of the most promising therapeutic approaches for Duchenne muscular dystrophy (DMD). Using antisense oligonucleotides (AONs) targeting specific exons the DMD reading frame is restored and partially functional dystrophins are produced. Following proof of concept in cultured muscle cells from patients with various deletions and point mutations, we now focus on single and multiple exon duplications. These mutations are in principle ideal targets for this approach since the specific skipping of duplicated exons would generate original, full-length transcripts.</p> <p>Methods</p> <p>Cultured muscle cells from DMD patients carrying duplications were transfected with AONs targeting the duplicated exons, and the dystrophin RNA and protein were analyzed.</p> <p>Results</p> <p>For two brothers with an exon 44 duplication, skipping was, even at suboptimal transfection conditions, so efficient that both exons 44 were skipped, thus generating, once more, an out-of-frame transcript. In such cases, one may resort to multi-exon skipping to restore the reading frame, as is shown here by inducing skipping of exon 43 and both exons 44. By contrast, in cells from a patient with an exon 45 duplication we were able to induce single exon 45 skipping, which allowed restoration of wild type dystrophin. The correction of a larger duplication (involving exons 52 to 62), by combinations of AONs targeting the outer exons, appeared problematic due to inefficient skipping and mistargeting of original instead of duplicated exons.</p> <p>Conclusion</p> <p>The correction of DMD duplications by exon skipping depends on the specific exons targeted. Its options vary from the ideal one, restoring for the first time the true, wild type dystrophin, to requiring more 'classical' skipping strategies, while the correction of multi-exon deletions may need the design of tailored approaches.</p

The future of exon skipping for Duchenne muscular dystrophy

Antisense oligonucleotide (ASO)-mediated exon skipping can restore the open reading frame of dystrophin transcripts for Duchenne muscular dystrophy (DMD) patients. This allows production of internally deleted dystrophin proteins as found in the later onset, less severely progressive Becker muscular dystrophy. At present, ASOs that induce exon skipping and dystrophin restoration are approved for the treatment of DMD by the regulatory agencies of the United States and Japan. However, approval was based on restoration of very small amounts of dystrophin and the approved ASOs apply to only a subset of patients. This expert perspective evaluates ways to improve ASO efficiency that are currently in or close to clinical trials, as well as ways to improve applicability of this mutation-specific approach.Functional Genomics of Muscle, Nerve and Brain Disorder

Vertaalslagen van fundamenteel naar toegepast onderzoek

Oratie uitgesproken door Prof.dr. A. Aartsma-Rus bij de aanvaarding van het ambt van hoogleraar in de Humane Genetica, i.h.b. de Translationele Genetica aan de Universiteit Leiden op vrijdag 17 juni 2016Oratie uitgesproken door Prof.dr. A. Aartsma-Rus bij de aanvaarding van het ambt van hoogleraar in de Humane Genetica, i.h.b. de Translationele Genetica aan de Universiteit Leiden op vrijdag 17 juni 201

FDA Approval of Nusinersen for Spinal Muscular Atrophy Makes 2016 the Year of Splice Modulating Oligonucleotides

Functional Genomics of Muscle, Nerve and Brain Disorder

'Developments in reading frame restoring therapy developments for Duchenne Muscular Dystrophy'

ABSTRACTIntroduction: Exon skipping compounds restoring the dystrophin transcript reading frame havereceived regulatory approval for Duchenne muscular dystrophy (DMD). Recently, focus shifted todeveloping compounds to skip additional exons, improving delivery to skeletal muscle, and to genomeediting, to restore the reading frame on DNA level.Areas covered: We outline developments for reading frame restoring approaches, challenges ofmutation specificity, and optimizing delivery. Also, we highlight ongoing efforts to better detect exonskipping therapeutic effects in clinical trials. Searches on relevant terms were performed, focusing onrecent publications (Expert opinion: Currently, 3 AONS are approved. Whether dystrophin levels are sufficient to slowdowndisease progression needs to be confirmed. Enhancing AON uptake by muscles is currently underinvestigation. Gene editing is an alternative, but one that involves practical and ethical concerns. Giventhe field’s momentum, we believe the efficiency of frame-restoring approaches will improve.Functional Genomics of Muscle, Nerve and Brain Disorder

Antisense PMO Found in Dystrophic Dog Model Was Effective in Cells from Exon 7-Deleted DMD Patient

BACKGROUND: Antisense oligonucleotide-induced exon skipping is a promising approach for treatment of Duchenne muscular dystrophy (DMD). We have systemically administered an antisense phosphorodiamidate morpholino oligomer (PMO) targeting dystrophin exons 6 and 8 to a dog with canine X-linked muscular dystrophy in Japan (CXMD(J)) lacking exon 7 and achieved recovery of dystrophin in skeletal muscle. To date, however, antisense chemical compounds used in DMD animal models have not been directly applied to a DMD patient having the same type of exon deletion. We recently identified a DMD patient with an exon 7 deletion and tried direct translation of the antisense PMO used in dog models to the DMD patient's cells. METHODOLOGY/PRINCIPAL FINDINGS: We converted fibroblasts of CXMD(J) and the DMD patient to myotubes by FACS-aided MyoD transduction. Antisense PMOs targeting identical regions of dog and human dystrophin exons 6 and 8 were designed. These antisense PMOs were mixed and administered as a cocktail to either dog or human cells in vitro. In the CXMD(J) and human DMD cells, we observed a similar efficacy of skipping of exons 6 and 8 and a similar extent of dystrophin protein recovery. The accompanying skipping of exon 9, which did not alter the reading frame, was different between cells of these two species. CONCLUSION/SIGNIFICANCE: Antisense PMOs, the effectiveness of which has been demonstrated in a dog model, achieved multi-exon skipping of dystrophin gene on the FACS-aided MyoD-transduced fibroblasts from an exon 7-deleted DMD patient, suggesting the feasibility of systemic multi-exon skipping in humans

Guidance in social and ethical issues related to clinical, diagnostic care and novel therapies for hereditary neuromuscular rare diseases

Drug trials in children engage with many ethical issues, from drug-related safety concerns to communication with patients and parents, and recruitment and informed consent procedures. This paper addresses the field of neuromuscular disorders where the possibility of genetic, mutation-specific treatments, has added new complexity. Not only must trial design address issues of equity of access, but researchers must also think through the implications of adopting a personalised medicine approach, which requires a precise molecular diagnosis, in addition to other implications of developing orphan drugs. It is against this background of change and complexity that the Project Ethics Council (PEC) was established within the TREAT-NMD EU Network of Excellence. The PEC is a high level advisory group that draws upon the expertise of its interdisciplinary membership which includes clinicians, lawyers, scientists, parents, representatives of patient organisations, social scientists and ethicists. In this paper we describe the establishment and terms of reference of the PEC, give an indication of the range and depth of its work and provide some analysis of the kinds of complex questions encountered. The paper describes how the PEC has responded to substantive ethical issues raised within the TREAT-NMD consortium and how it has provided a wider resource for any concerned parent, patient, or clinician to ask a question of ethical concern. Issues raised range from science related ethical issues, issues related to hereditary neuromuscular diseases and the new therapeutic approaches and questions concerning patients rights in the context of patient registries and bio-banks. We conclude by recommending the PEC as a model for similar research contexts in rare diseases

Targeted Skipping of Human Dystrophin Exons in Transgenic Mouse Model Systemically for Antisense Drug Development

Antisense therapy has recently been demonstrated with great potential for targeted exon skipping and restoration of dystrophin production in cultured muscle cells and in muscles of Duchenne Muscular Dystrophy (DMD) patients. Therapeutic values of exon skipping critically depend on efficacy of the drugs, antisense oligomers (AOs). However, no animal model has been established to test AO targeting human dystrophin exon in vivo systemically. In this study, we applied Vivo-Morpholino to the hDMD/mdx mouse, a transgenic model carrying the full-length human dystrophin gene with mdx background, and achieved for the first time more than 70% efficiency of targeted human dystrophin exon skipping in vivo systemically. We also established a GFP-reporter myoblast culture to screen AOs targeting human dystrophin exon 50. Antisense efficiency for most AOs is consistent between the reporter cells, human myoblasts and in the hDMD/mdx mice in vivo. However, variation in efficiency was also clearly observed. A combination of in vitro cell culture and a Vivo-Morpholino based evaluation in vivo systemically in the hDMD/mdx mice therefore may represent a prudent approach for selecting AO drug and to meet the regulatory requirement

The role of patient involvement when developing therapies

The drug development process is a long and arduous one, especially for rare diseases. Patient and patient representatives can and should be involved in this process from an early stage, since they have the perspective of living with a disease on a daily basis and can best identify which symptoms are the largest burden and which benefits would be more important to them. In this perspective, we outline how patients can be involved optimally in drug development. We outline success factors such as finding the right partners, bilateral education, having realistic expectations, and an open and honest dialog with all stakeholders.Functional Genomics of Muscle, Nerve and Brain Disorder