Satellos Bioscience (MSCL) Study update summary

Regulatory strategy and primary endpoint

• Following FDA Type C feedback, BASECAMP amended its protocol to replace dynamometry with 12-week MRI-measured vastus lateralis fat fraction as the primary efficacy endpoint; safety and tolerability are also assessed.

• FDA feedback supports fat fraction as a potential surrogate reasonably likely to predict clinical benefit; discussions covered its supporting evidence and correlation with clinical function, with no concerns raised about study size or conduct.

• Stabilization or reduction versus placebo, alongside clinical endpoints and the totality of evidence, may support a potential accelerated approval pathway; further data and regulatory review remain necessary.

BASECAMP design and readout

• Global, randomized, double-blind, placebo-controlled Phase 2 study of 53 ambulatory boys aged 7–9 at 17 sites in 7 countries; 12 weeks of two-dose forazapadin versus placebo, followed by 36 weeks of forazapadin for all participants.

• Q1 2027 topline is expected to include the 12-week fat-fraction comparison across all randomized participants, safety, tolerability and available secondary measures; a subset has six-month supportive data at the cut.

• Secondary and exploratory measures include function, dynamometry, physical activity, strength, biomarkers, muscle quality and biopsy Regenerative Index.

• MRI uses a standardized Dixon protocol across sites, central blinded reading and water-signal control; functional assessments include stride velocity, time to rise, four-stair climb and dynamometry.

Clinical rationale and prior evidence

• Fat fraction quantifies muscle composition and rises with DMD progression; higher levels are associated with functional decline and earlier loss of ambulation. In boys near 10% vastus lateralis fat fraction, progression may be ~10% annually, with individual variability.

• TRAILHEAD interim data from 4 adults showed mean biceps brachii fat fraction fell 3.7 percentage points, from 49.7% to 46.0% at Day 140; reported findings also included increased total effort, stable strength and lower creatine kinase.

• TRAILHEAD was a small open-label study not designed to establish efficacy; its findings provide preliminary support for evaluating fat fraction alongside function in BASECAMP.