Solid Biosciences Advances SGT-003 DMD Gene Therapy with FDA Alignment, Reports No Liver Toxicity

Solid Biosciences has secured alignment with the FDA on a registration pathway for its Duchenne muscular dystrophy gene therapy candidate SGT-003 and intends to seek accelerated approval, running a double-blind, placebo-controlled DMD study outside the U.S. with "time to rise" as the primary endpoint and an approximately 18-month assessment. The company expects first pediatric dosing within roughly 90 days.

The company has dosed 36 patients to date in its ongoing open-label INSPIRE DUCHENNE Phase I/II clinical trial, which has enrolled 40 patients, and reports no observed drug-induced liver injury, myocarditis, atypical hemolytic uremic syndrome (aHUS), or thrombotic microangiopathy (TMA) so far. The company emphasized it had not reviewed functional data from the open-label cohort, which could help the company and FDA jointly determine appropriate statistical plans and the use of natural history or external controls.

The planned double-blind, placebo-controlled study will be conducted in Europe, Australia, and Canada. The FDA reviewed the design, suggested changes including to secondary endpoints, and indicated the trial was reasonable. The first patient was originally expected to be dosed the following week, but that patient was ill and would not be dosed; the company was scheduling the next patient.

SGT-003 uses an engineered capsid designated SLB101 with RGD peptides intended to bind integrin receptors upregulated in skeletal and cardiac muscle. The capsid clears rapidly from blood in human subjects, with approximately 90% clearance by day four. The capsid reached human cardiomyocytes and expressed about 20 times greater than AAV9. Animal findings suggested liver "retargeting," and in humans the company was tracking liver enzymes (ALT/AST) and GGT, which did not show the spikes seen with other approaches.

The construct aims to preserve flexibility in a shortened dystrophin protein and includes features intended to support nNOS creation. The company discussed nitric oxide's role in coronary perfusion and potential impacts on oxidative stress, fibrosis, and inflammation, and also mentioned incorporating alpha-syntrophin and caveolin-4 with a rationale related to ERK phosphorylation in the heart.

Solid's manufacturing process yields approximately a 75% full-to-empty capsid ratio. The company argued that a higher fraction of full capsids could support expression and reduce the need to increase vector genomes per kilogram, which could otherwise place pressure on complement and the liver. SGT-003 uses a revised steroid regimen starting on day −3.

The company described its approach as designed to improve upon first-generation DMD gene therapy approaches, contrasting its current regimen—described as using only steroids—with other approaches that can involve higher rates of liver injury, hospitalizations, cardiomyopathy, and the use of additional immunomodulatory or complement-related therapies.

In Friedreich's ataxia, Solid dosed its first patient with a dual-route approach using MRI-guided dentate nucleus plus IV administration and reported only a transient headache at approximately 40 days, noting anecdotal signals of benefit. The company plans to dose 3–6 FA patients this year and expects topline data from the first three in the second half of 2026.

The company has roughly 120 employees and describes itself as a precision genetic medicine company, with an emphasis on gene therapies. Beyond SGT-003 for DMD and the dual-vector program for FA, the company highlighted a program for catecholaminergic polymorphic ventricular tachycardia (CPVT) and referenced additional work in dilated cardiomyopathy (TNNT2). The company has built a capsid library and broader delivery platform.