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Abstract
Objective To describe the quantification of novel dystrophin production in patients with Duchenne muscular dystrophy (DMD) after long-term treatment with eteplirsen.
Methods Clinical study 202 was an observational, open-label extension of the randomized, controlled study 201 assessing the safety and efficacy of eteplirsen in patients with DMD with a confirmed mutation in the DMD gene amenable to correction by skipping of exon 51. Patients received once-weekly IV doses of eteplirsen 30 or 50 mg/kg. Upper extremity muscle biopsy samples were collected at combined study week 180, blinded, and assessed for dystrophin-related content by Western blot, Bioquant software measurement of dystrophin-associated immunofluorescence intensity, and percent dystrophin-positive fibers (PDPF). Results were contrasted with matched untreated biopsies from patients with DMD. Reverse transcription PCR followed by Sanger sequencing of newly formed slice junctions was used to confirm the mechanism of action of eteplirsen.
Results Reverse transcription PCR analysis and sequencing of the newly formed splice junction confirmed that 100% of treated patients displayed the expected skipped exon 51 sequence. In treated patients vs untreated controls, Western blot analysis of dystrophin content demonstrated an 11.6-fold increase (p = 0.007), and PDPF analysis demonstrated a 7.4-fold increase (p < 0.001). The PDPF findings were confirmed in a re-examination of the sample (15.5-fold increase, p < 0.001). Dystrophin immunofluorescence intensity was 2.4-fold greater in treated patients than in untreated controls (p < 0.001).
Conclusion Taken together, the 4 assays, each based on unique evaluation mechanisms, provided evidence of eteplirsen muscle cell penetration, exon skipping, and induction of novel dystrophin expression.
Classification of evidence This study provides Class II evidence of the muscle cell penetration, exon skipping, and induction of novel dystrophin expression by eteplirsen, as confirmed by 4 assays.
Glossary
- BMD=
- Becker muscular dystrophy;
- DMD=
- Duchenne muscular dystrophy;
- NCH=
- Nationwide Children's Hospital;
- PDPF=
- percent dystrophin-positive fibers;
- PROMOVI=
- An Open-Label, Multi-Center Study With a Concurrent Untreated Control Arm to Evaluate the Efficacy and Safety of Eteplirsen in Duchenne Muscular Dystrophy;
- RT-PCR=
- reverse transcription PCR;
- 6MWT=
- 6-minute walk test
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Class of Evidence: NPub.org/coe
Editorial Page 1091
- Received October 13, 2017.
- Accepted in final form March 15, 2018.
- © 2018 American Academy of Neurology
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