Phase 2a study of ataluren-mediated dystrophin production in patients with nonsense mutation Duchenne muscular dystrophy

Richard S Finkel, Kevin M Flanigan, Brenda Wong, Carsten Bönnemann, Jacinda Sampson, H Lee Sweeney, Allen Reha, Valerie J Northcutt, Gary Elfring, Jay Barth, Stuart W Peltz, Richard S Finkel, Kevin M Flanigan, Brenda Wong, Carsten Bönnemann, Jacinda Sampson, H Lee Sweeney, Allen Reha, Valerie J Northcutt, Gary Elfring, Jay Barth, Stuart W Peltz

Abstract

Background: Approximately 13% of boys with Duchenne muscular dystrophy (DMD) have a nonsense mutation in the dystrophin gene, resulting in a premature stop codon in the corresponding mRNA and failure to generate a functional protein. Ataluren (PTC124) enables ribosomal readthrough of premature stop codons, leading to production of full-length, functional proteins.

Methods: This Phase 2a open-label, sequential dose-ranging trial recruited 38 boys with nonsense mutation DMD. The first cohort (n = 6) received ataluren three times per day at morning, midday, and evening doses of 4, 4, and 8 mg/kg; the second cohort (n = 20) was dosed at 10, 10, 20 mg/kg; and the third cohort (n = 12) was dosed at 20, 20, 40 mg/kg. Treatment duration was 28 days. Change in full-length dystrophin expression, as assessed by immunostaining in pre- and post-treatment muscle biopsy specimens, was the primary endpoint.

Findings: Twenty three of 38 (61%) subjects demonstrated increases in post-treatment dystrophin expression in a quantitative analysis assessing the ratio of dystrophin/spectrin. A qualitative analysis also showed positive changes in dystrophin expression. Expression was not associated with nonsense mutation type or exon location. Ataluren trough plasma concentrations active in the mdx mouse model were consistently achieved at the mid- and high- dose levels in participants. Ataluren was generally well tolerated.

Interpretation: Ataluren showed activity and safety in this short-term study, supporting evaluation of ataluren 10, 10, 20 mg/kg and 20, 20, 40 mg/kg in a Phase 2b, double-blind, long-term study in nonsense mutation DMD.

Trial registration: ClinicalTrials.gov NCT00264888.

Conflict of interest statement

Competing Interests: AR, VJN, GE, JB, and SWP are employees of PTC Therapeutics, Inc. and hold financial interests in the company. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials. The following authors work on this study resulted in institutional compensation as a grant awarded to PTC Therapeutics: BW, KMF, RSF, HLS, CB, and JS, PTC employee authors and the PTC Study Group. BW was compensated for travel to meetings for the study. BW and KMF received a consulting fee or honorarium associated with this study. CB’s institution, the Children’s Hospital of Philadelphia, received a consulting fee or honorarium for laboratory supplies and technician time. Regarding financial activities conducted outside of the study presented in this manuscript, the following authors have received compensation for consultancy, or grant for their institution: KMF, RSF, HLS, and JS. HLS also received from various entities, compensation not associated with the submitted work for board membership, royalties, various travel accommodations and meeting expenses. All other authors do not have a relationship with a commercial entity that has an interest in the subject of this manuscript other than the study sponsor.

Figures

Figure 1. CONSORT Flow Diagram.
Figure 1. CONSORT Flow Diagram.
Figure 2. In Vivo Dystrophin Expression by…
Figure 2. In Vivo Dystrophin Expression by Immunofluorescence in Extensor Digitorum Brevis Muscle: Example of a Responder Subject.
Figure 3. Percentage Change From Pretreatment in…
Figure 3. Percentage Change From Pretreatment in Dystrophin:Spectrin Ratio.
Figure 4. Serum Creatine Kinase Concentrations.
Figure 4. Serum Creatine Kinase Concentrations.
Serum CK levels at baseline (mean of screening and Day 1 pretreatment), end-of-treatment (Day 28), and follow-up (Day 56). P-values obtained from paired t-tests. Abbreviations: CK = creatine kinase, EOT = end of treatment, nmDMD = nonsense mutation Duchenne muscular dystrophy, SEM = standard error of the mean.
Figure 5. Ataluren Plasma Concentrations Over Time.
Figure 5. Ataluren Plasma Concentrations Over Time.
Blood samples were collected pre-dose and at 1, 2, 3, and 4 hours after the morning dose; pre-dose and at 1, 2, 3, and 4 hours after the midday dose; and pre-dose and at 1, 2, 3, 4, and 12 hours after the evening dose. Ataluren plasma concentrations were derived from a validated bioanalytical method. Abbreviations: SE = standard error.
Figure 6. Dose-Normalized Day 27 AUC 0–24…
Figure 6. Dose-Normalized Day 27 AUC0–24 Ataluren Values by Concomitant Corticosteroid Use (All Dose Levels). Note:
Subject 001–012 in the 20, 20, 40 mg/kg dose group was receiving prednisolone, a metabolite of prednisone. This subject is included in the prednisone group above. Abbreviation: AUC0–24 = area under the plasma concentration-time curve from 0 to 24 hours.

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