Interpreting Long-Term MESA Data of Sevasemten to Treat Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) remains a progressive neuromuscular disorder with no approved disease-modifying therapies, characterized by gradual functional decline over time. Natural history data suggest that once decline begins, patients experience steady worsening in mobility and independence, highlighting a significant unmet clinical need.

At the 2026 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference, held March 8-11 in Orlando, Florida, investigators presented long-term data from the MESA open-label extension study evaluating sevasemten (Edgewise Therapeutics), an investigational fast skeletal myosin inhibitor designed to reduce contraction-induced muscle damage. Over multiple years of follow-up, findings suggested stabilization of functional outcomes, contrasting with expected declines observed in untreated populations.

In a conversation with NeurologyLive®, Joanne Donovan, MD, PhD, chief medical officer at Edgewise Therapeutics, provided context on the findings and their significance. Donovan, a neurologist and staff physician, detailed the clinical relevance of sustained North Star Ambulatory Assessment (NSAA) stabilization, how these findings compare with natural history trajectories, and what clinicians should anticipate from the ongoing pivotal GRAND CANYON trial.

NeurologyLive: Can you summarize the key long-term findings from the MESA study, particularly the observed stabilization in NSAA scores over 3.5 years?

Joanne Donovan, MD, PhD: Yes, these are exciting results observed with sevasemten, our novel fast skeletal myosin inhibitor designed to protect against contraction-induced muscle damage.

The main finding in MESA, an open-label extension (OLE) trial in Becker muscular dystrophy, is participants on sevasemten experienced stabilization of their disease – as measured by the NSAA score – for up to 3.5 years. Over the course of several years, we observed a divergence in NSAA function scores in the sevasemten-treated population versus what is predicted in Becker natural history.

Based on their individual baseline characteristics, the sevasemten participants who joined MESA from our Phase 1 ARCH trial showed a +0.1 improvement over 3.5 years (vs. a predicted -5.3 pt decline). The sevasemten participants who joined MESA from our Phase 2 CANYON study showed a +0.1 improvement over 2 years (vs. a predicted -2.9 decline). And, importantly, after 3+ years of treatment with sevasemten in this OLE, we continue to observe a favorable safety profile.

Stabilization in Becker is truly a remarkable finding as it is in stark contrast to what is observed in untreated Becker populations where individuals experience a predictable functional decline over time.

The data show a notable divergence from expected natural history decline in Becker muscular dystrophy. How clinically meaningful is this stabilization in the context of typical disease progression?

The MESA data show a difference in NSAA score which is a validated tool used in clinical practice to measure function. It is important to translate these measurements from the clinic to a real-world setting. Just a 1-point NSAA decline could translate into a man with Becker requiring daily assistance stepping up a curb, standing up from a chair, or getting up after a fall. Imagine a 35-year-old man with Becker where his disease robs him this independence.

Given that MESA is an open-label extension, how should clinicians interpret these findings in terms of durability and potential bias compared with controlled data?

MESA provides us extensive sevasemten data, over 3.5 years, including a consistent efficacy and safety profile. It is rare to have this significant of an exposure profile on an investigational agent at this stage in a clinical program.

Last year we presented our placebo-controlled Phase 2 CANYON data which showed a reduction in biomarkers of muscle damage (CK) with a trend in functional stability vs. placebo over 12 months. Our fully enrolled 18-month, placebo-controlled global pivotal cohort, GRAND CANYON, data are anticipated end of 2026.

Can you explain the mechanistic rationale of sevasemten, a fast skeletal myosin inhibitor, and how this approach may differ from other investigational strategies in muscular dystrophy?

Sevasemten is a novel, oral fast-skeletal myosin inhibitor designed to protect against contraction-induced muscle damage while preserving function. This muscle-focused approach is notable in comparison to the available muscular dystrophy therapies where approaches like gene therapy, gene editing, exon-skipping, or RNA knockdown are commonly used.

Sevasemten has the potential to become a disease-modifying therapy for Becker muscular dystrophy, where there are currently no approved treatments.

With the pivotal GRAND CANYON study expected to read out later this year, what key endpoints or signals should clinicians be watching for to better understand the therapy’s potential role in practice?

The GRAND CANYON pivotal cohort is an 18-month study of sevasemten in adults with Becker. The primary endpoint is change in NSAA score with the study statically powered at over 98% for observing a ~1.7 NSAA point difference in the treated vs. placebo population. Several additional endpoints will be measured including timed function tests, biomarkers of muscle damage, MRI, patient reported outcomes, and safety.

If approved, how might sevasemten fit into the clinical management of Becker muscular dystrophy, particularly given the current lack of disease-modifying treatment options?

The prospect of a therapy specifically designed for this disease, with the potential of halting functional decline, is very encouraging to the entire Becker community. Sevasemten is an oral small molecule designed to be taken as a fixed dose once daily, which should provide an ease of administration.

Provided our pivotal GRAND CANYON data are positive at the end of 2026, we anticipate filing our regulatory applications in 2027 with the goal of commercializing sevasemten globally.

Transcript edited for clarity. Click here for more MDA 2026 coverage.