AAV gene therapy for Duchenne muscular dystrophy: the EMBARK phase 3 randomized trial.

Duchenne muscular dystrophy (DMD) is a rare, X-linked neuromuscular disease caused by pathogenic variants in the DMD gene that result in the absence of functional dystrophin, beginning at birth and leading to progressive impaired motor function, loss of ambulation and life-threatening cardiorespiratory complications. Delandistrogene moxeparvovec, an adeno-associated rh74-viral vector-based gene therapy, addresses absent functional dystrophin in DMD. Here the phase 3 EMBARK study aimed to assess the efficacy and safety of delandistrogene moxeparvovec in patients with DMD. Ambulatory males with DMD, ≥4 years to <8 years of age, were randomized and stratified by age group and North Star Ambulatory Assessment (NSAA) score to single-administration intravenous delandistrogene moxeparvovec (1.33 × 1014 vector genomes per kilogram; n = 63) or placebo (n = 62). At week 52, the primary endpoint, change from baseline in NSAA score, was not met (least squares mean 2.57 (delandistrogene moxeparvovec) versus 1.92 (placebo) points; between-group difference, 0.65; 95% confidence interval (CI), -0.45, 1.74; P = 0.2441). Secondary efficacy endpoints included mean micro-dystrophin expression at week 12: 34.29% (treated) versus 0.00% (placebo). Other secondary efficacy endpoints at week 52 (between-group differences (95% CI)) included: Time to Rise (-0.64 (-1.06, -0.23)), 10-meter Walk/Run (-0.42 (-0.71, -0.13)), stride velocity 95th centile (0.10 (0.00, 0.19)), 100-meter Walk/Run (-3.29 (-8.28, 1.70)), time to ascend 4 steps (-0.36 (-0.71, -0.01)), PROMIS Mobility and Upper Extremity (0.05 (-0.08, 0.19); -0.04 (-0.24, 0.17)) and number of NSAA skills gained/improved (0.19 (-0.67, 1.06)). In total, 674 adverse events were recorded with delandistrogene moxeparvovec and 514 with placebo. There were no deaths, discontinuations or clinically significant complement-mediated adverse events; 7 patients (11.1%) experienced 10 treatment-related serious adverse events. Delandistrogene moxeparvovec did not lead to a significant improvement in NSAA score at week 52. Some of the secondary endpoints numerically favored treatment, although no statistical significance can be claimed. Safety was manageable and consistent with previous delandistrogene moxeparvovec trials. ClinicalTrials.gov: NCT05096221.

Practical Considerations for Delandistrogene Moxeparvovec Gene Therapy in Patients With Duchenne Muscular Dystrophy.

BACKGROUND: Delandistrogene moxeparvovec is a gene transfer therapy approved in the United States, United Arab Emirates, and Qatar for the treatment of ambulatory patients aged four through five years with a confirmed Duchenne muscular dystrophy (DMD)-causing mutation in the DMD gene. This therapy was developed to address the underlying cause of DMD through targeted skeletal, respiratory, and cardiac muscle expression of delandistrogene moxeparvovec micro-dystrophin, an engineered, functional dystrophin protein. METHODS: Drawing on clinical trial experience from Study 101 (NCT03375164), Study 102 (NCT03769116), and ENDEAVOR (Study 103; NCT04626674), we outline practical considerations for delandistrogene moxeparvovec treatment. RESULTS: Before infusion, the following are recommended: (1) screen for anti-adeno-associated virus rhesus isolate serotype 74 total binding antibody titers <1:400; (2) assess liver function, platelet count, and troponin-I; (3) ensure patients are up to date with vaccinations and avoid vaccine coadministration with infusion; (4) administer additional corticosteroids starting one day preinfusion (for patients already on corticosteroids); and (5) postpone dosing patients with any infection or acute liver disease until event resolution. Postinfusion, the following are recommended: (1) monitor liver function weekly (three months postinfusion) and, if indicated, continue until results are unremarkable; (2) monitor troponin-I levels weekly (first month postinfusion, continuing if indicated); (3) obtain platelet counts weekly (two weeks postinfusion), continuing if indicated; and (4) maintain the corticosteroid regimen for at least 60 days postinfusion, unless earlier tapering is indicated. CONCLUSIONS: Although the clinical safety profile of delandistrogene moxeparvovec has been consistent, monitorable, and manageable, these practical considerations may mitigate potential risks in a real-world clinical practice setting.

Long-term safety and functional outcomes of delandistrogene moxeparvovec gene therapy in patients with Duchenne muscular dystrophy: A phase 1/2a nonrandomized trial.

INTRODUCTION/AIMS: Delandistrogene moxeparvovec is indicated in the United States for the treatment of ambulatory pediatric patients aged 4 through 5 years with Duchenne muscular dystrophy (DMD) with a confirmed mutation in the DMD gene. Long-term delandistrogene moxeparvovec microdystrophin protein (a shortened dystrophin that retains key functional domains of the wild-type protein) expression may positively alter disease progression in patients with DMD. We evaluated long-term safety and functional outcomes of delandistrogene moxeparvovec in patients with DMD. METHODS: An open-label, phase 1/2a, nonrandomized controlled trial (Study 101; NCT03375164) enrolled ambulatory males, ≥4 to <8 years old, with DMD. Patients received a single intravenous infusion (2.0 × 1014 vg/kg by supercoiled quantitative polymerase chain reaction) of delandistrogene moxeparvovec and prednisone (1 mg/kg/day) 1 day before to 30 days after treatment. The primary endpoint was safety. Functional outcomes were change from baseline in North Star Ambulatory Assessment (NSAA) and timed function tests. RESULTS: Four patients (mean age, 5.1 years) were enrolled. There were 18 treatment-related adverse events; all occurred within 70 days posttreatment and resolved. Mean NSAA total score increased from 20.5 to 27.5, baseline to year 4, with a mean (standard deviation) change of +7.0 (2.9). Post hoc analysis demonstrated a statistically significant and clinically meaningful 9-point difference in NSAA score, relative to a propensity-score-weighted external control cohort (least-squares mean [standard error] = 9.4 [3.4]; P = .0125). DISCUSSION: Gene transfer therapy with delandistrogene moxeparvovec treatment is well tolerated, with a favorable safety profile. Functional improvements are sustained through 4 years, suggesting delandistrogene moxeparvovec may positively alter disease progression.

Delandistrogene Moxeparvovec Gene Therapy in Ambulatory Patients (Aged ≥4 to <8 Years) with Duchenne Muscular Dystrophy: 1-Year Interim Results from Study SRP-9001-103 (ENDEAVOR).

OBJECTIVE: Delandistrogene moxeparvovec is approved in the USA for the treatment of ambulatory patients (4-5 years) with Duchenne muscular dystrophy. ENDEAVOR (SRP-9001-103; NCT04626674) is a single-arm, open-label study to evaluate delandistrogene moxeparvovec micro-dystrophin expression, safety, and functional outcomes following administration of commercial process delandistrogene moxeparvovec. METHODS: In cohort 1 of ENDEAVOR (N = 20), eligible ambulatory males, aged ≥4 to <8 years, received a single intravenous infusion of delandistrogene moxeparvovec (1.33 × 1014 vg/kg). The primary endpoint was change from baseline (CFBL) to week 12 in delandistrogene moxeparvovec micro-dystrophin by western blot. Additional endpoints evaluated included: safety; vector genome copies; CFBL to week 12 in muscle fiber-localized micro-dystrophin by immunofluorescence; and functional assessments, including North Star Ambulatory Assessment, with comparison with a propensity score-weighted external natural history control. RESULTS: The 1-year safety profile of commercial process delandistrogene moxeparvovec in ENDEAVOR was consistent with safety data reported in other delandistrogene moxeparvovec trials (NCT03375164 and NCT03769116). Delandistrogene moxeparvovec micro-dystrophin expression was robust, with sarcolemmal localization at week 12; mean (SD) CFBL in western blot, 54.2% (42.6); p < 0.0001. At 1 year, patients demonstrated stabilized or improved North Star Ambulatory Assessment total scores; mean (SD) CFBL, +4.0 (3.5). Treatment versus a propensity score-weighted external natural history control demonstrated a statistically significant difference in least squares mean (standard error) CFBL in North Star Ambulatory Assessment, +3.2 (0.6) points; p < 0.0001. INTERPRETATION: Results confirm efficient transduction of muscle by delandistrogene moxeparvovec. One-year post-treatment, delandistrogene moxeparvovec was well tolerated, and demonstrated stabilized or improved motor function, suggesting a clinical benefit for patients with Duchenne muscular dystrophy. ANN NEUROL 2023;94:955-968.