A study of sevasemten (EDG-5506) in Becker muscular dystrophy (known as CANYON) and pivotal cohort (known as GRAND CANYON). The EDG-5506-201 CANYON study was expanded to include an additional 120 adult participants in a cohort called GRAND CANYON, that is a multicenter, randomized, double-blind, placebo-controlled study to evaluate the safety and efficacy of sevasemten in adults with Becker.

CANYON and GRAND CANYON are fully enrolled.

The EDG-5506-201 protocol was amended to include an additional cohort thus consists of two parts.

Part 1: CANYON is a double-blind, randomized, placebo-controlled design to investigate the effect of sevasemten on the safety, pharmacokinetics, biomarkers, and functional measures. Approximately 32 adults and 18 adolescents with Becker muscular dystrophy are planned to enroll in this study. This study will have up to a 4-week Screening period, a 12-month Treatment period, followed by a 4-week follow-up period.

Approximately 32 adult participants will randomize to Cohort 1 or Cohort 2 in a 1:1 ratio then each cohort will further randomize to sevasemten or placebo in a 3:1 ratio.

Approximately 9 adolescent participants will enroll in Cohort 4 and randomize in a 2:1 ratio to sevasemten or placebo. Cohort 5 will randomize an additional 9 participants in a 2:1 ratio to either sevasemten or placebo after Cohort 4.

CANYON is now fully enrolled.

Part 2: GRAND CANYON or Cohort 6 is a double-blind, randomized, placebo-controlled design to investigate the safety and efficacy of sevasemten in adults with Becker muscular dystrophy after 18 months of treatment. Approximately 120 adults with Becker muscular dystrophy are planned to enroll in this study. This study will have up to a 4-week Screening period, an 18-month Treatment period, followed by a 4-week follow-up period.

Approximately 120 adult participants will be randomized in Cohort 6 in a 2:1 ratio either to sevasemten or placebo.

The CANYON Study including the adolescent cohorts are fully enrolled.

GRAND CANYON eligibility is listed below.

Key Inclusion Criteria:

1. Adults (aged 18 to 50 years, inclusive) with a documented dystrophin mutation and phenotype consistent with Becker muscular dystrophy, and history of being ambulatory beyond 16 years of age without steroids; history of being ambulatory beyond 18 years of age with steroids.
2. Able to complete the 100-meter timed test in < 200 seconds with or without use of mobility aid devices.
3. Able to perform the North Star Ambulatory Assessment scale and achieve a score of 5 to 32, inclusive.

Key Exclusion Criteria:

1. Medical history or clinically significant physical examination/laboratory result that, in the opinion of the investigator, would render the participant unsuitable for the study. This includes contraindications to magnetic resonance imaging such as non-compatible implanted medical devices or severe claustrophobia.
2. Cardiac echocardiogram ejection fraction < 40%
3. Forced vital capacity predicted <60% or using daytime ventilatory support
4. Receipt of oral corticosteroids for the treatment of BMD in the previous 6 months.
5. Receipt of an investigational drug within 30 days or 5 half-lives (whichever is longer) of the screening visit in the present study.