Long-Term Efficacy, Safety, and Pharmacokinetics of Drisapersen in Duchenne Muscular Dystrophy: Results from an Open-Label Extension Study

Abstract

Background: Drisapersen induces exon 51 skipping during dystrophin pre-mRNA splicing and allows synthesis of partially functional dystrophin in Duchenne muscular dystrophy (DMD) patients with amenable mutations.

Methods: This 188-week open-label extension of the dose-escalation study assessed the long-term efficacy, safety, and pharmacokinetics of drisapersen (PRO051/GSK2402968), 6 mg/kg subcutaneously, in 12 DMD subjects. Dosing was once weekly for 72 weeks. All subjects had a planned treatment interruption (weeks 73-80), followed by intermittent dosing (weeks 81-188).

Results: Subjects received a median (range) total dose of 5.93 (5.10 to 6.02) mg/kg drisapersen. After 177 weeks (last efficacy assessment), median (mean [SD]) six-minute walk distance (6MWD) improved by 8 (-24.5 [161]) meters for the 10 subjects able to complete the 6MWD at baseline (mean age [SD]: 9.5 [1.9] years). These statistics include 2 subjects unable to complete the test at later visits and who scored "zero". When only the 8 ambulant subjects at week 177 were taken into account, a median (mean [SD]) increase of 64 (33 [121]) meters in 6MWD was observed. Of 7 subjects walking ≥330 m at extension baseline, 5 walked farther at week 177. Of 3 subjects walking <330 m, 2 lost ambulation, while 1 declined overall but walked farther at some visits. Over the 188 weeks, the most common adverse events were injection-site reactions, raised urinary α1-microglobulin and proteinuria. Dystrophin expression was detected in all muscle biopsies obtained at week 68 or 72.

Conclusion: Drisapersen was generally well tolerated over 188 weeks. Possible renal effects, thrombocytopenia and injection-site reactions warrant continued monitoring. Improvements in the 6MWD at 12 weeks were sustained after 3.4 years of dosing for most patients. For a small, uncontrolled study, the outcomes are encouraging, as natural history studies would anticipate a decline of over 100 meters over a 3-year period in a comparable cohort.

Trial registration: ClinicalTrials.gov NCT01910649.

Fig 1. Patient flow diagram.

^aExcluding planned washout and off-drug periods.

Fig 2. Change from extension study baseline in 6MWD, by visit over 177 weeks.

Data shown are for all subjects who completed the test at the extension study baseline. One subject (Subject 3) was non-ambulant at study entry and did not participate in any 6MWD tests, while another subject (Subject 4) was unable to complete the 6MWD test at the extension study baseline. Data for both of these subjects are not shown here. Subjects 1, 2, 5, 6, 7, 9, and 12 walked ≥330 m at extension study baseline; subjects 8, 10, and 11 walked <330 m at extension study baseline. 6MWD: six-minute walk distance.

Fig 3. α₁-Microglobulin levels over 177 weeks.

Subjects 1, 2, 5, 6, 7, 9, and 12 walked ≥330 m at extension study baseline; subjects 3, 4, 8 10, and 11 walked <330 m at extension study baseline. Grey shading is representative of off-treatment periods.

Fig 4. Individual drisapersen trough concentrations from weeks 72 to 184.

Subject 5 had an additional treatment break from weeks 101 to 128 inclusive. Subjects 1, 2, 5, 6, 7, 9, and 12 walked ≥330 m at extension study baseline; subjects 3, 4, 8 10, and 11 walked <330 m at extension study baseline. Grey shading is representative of off-treatment periods.

Fig 5. Comparison of change from baseline in 6MWD from drisapersen-treated subjects with natural history data.

The continuous line includes all patients from the drisapersen cohort or natural history cohort for which the 6MWD was available, whereas the dashed line shows the same cohorts but excludes patients that lost ambulation during follow-up. ^†Natural history data provided by Professor Eugenio Mercuri (Catholic University Policlinico Gemelli, Rome, Italy) 6MWD: six-minute walk distance.