Sarepta Therapeutics, Inc. shared the first clinical results from two of its siRNA programs for neuromuscular diseases. Early results from Phase 1/2 ascending dose studies of SRP-1001 for facioscapulohumeral muscular dystrophy type 1 (FSHD1) and SRP-1003 for myotonic dystrophy type 1 (DM1) demonstrated dose-dependent muscle exposure, early biomarker effects, and favorable tolerability, reinforcing scientific confidence in the potential for differentiated benefits of the avß6 integrin-targeted delivery platform. The Company has generated proof-of-concept data which found that after a single dose, both SRP-1001 and SRP-1003 support reduction, or knockdown, of the target protein or mRNA.
In both studies, the majority of adverse events were mild to moderate and were not dose dependent. For rare, genetic diseases, such as FSHD and DM1, which are caused by overexpression of mutant proteins or toxic mRNA, RNA-targeted therapies hold significant promise but have been limited by rapid degradation of drug before it reaches the intended cells. SRP-1001 and SRP-1003 are each designed with an optimized siRNA chemistry and a proprietary, avß6 integrin-targeted ligand, intended to enable the siRNA to enter the cell and penetrate muscle tissue.
Through this targeted delivery approach, these investigational treatments aim to overcome some of the delivery and safety challenges of other approaches. Preliminary clinical data show consistent dose-dependent increases in plasma and muscle drug exposures across clinical and nonclinical studies and suggest that the avß6 integrin-targeting ligand mediates robust siRNA muscle delivery, which is hypothesized will ultimately enable higher dosing and translate into clinical efficacy for patients with FSHD1 and DM1. The Company will host an investor call on March 25, 2026, at 8:30 a.m. Eastern time to discuss the data in greater detail.
The event will be webcast live under the investor relations section of Sarepta's website and following the event a replay will be archived there for one year. Interested parties participating by phone will need to register using an online form. After registering for dial-in details, all phone participants will receive an auto-generated e-mail containing a link to the dial-in number along with a personal PIN number to use to access the event by phone.
Facioscapulohumeral muscular dystrophy (FSHD) is a rare genetic disease that causes progressive weakness of skeletal muscles. The disease typically affects muscles of the face, shoulder girdle, upper limbs, abdomen, pelvis, and legs, although the pattern and severity of muscle involvement vary widely among individuals. FSHD is caused by abnormal activation of the DUX4 gene on chromosome 4, leading to production of the DUX4 protein, which is toxic to muscle cells and drives muscle degeneration.
There is currently no cure for FSHD, and no disease modifying treatments are available. Approximately 16,000 individuals in the United States are diagnosed with FSHD. SRP-1001 is an investigational siRNA treatment designed to reduce, or knock down, the production of DUX4 protein in skeletal muscle in patients living with FSHD1.
Study 1001-101 is combined Phase 1/2, single ascending dose (SAD)/multiple ascending dose (MAD), randomized, placebo-controlled trial in participants with FSHD1 aged 16 through 70. Myotonic dystrophy type 1 (DM1) is the most common form of adult-onset muscular dystrophy and is caused by a repeat expansion in the DMPK gene. DM1 is a progressive, multisystem disorder that affects skeletal and smooth muscle, as well as the heart, respiratory system, eye, endocrine, gastrointestinal, and central nervous systems. The disease is commonly associated with muscle weakness, daytime sleepiness, breathing difficulties, and cardiac conduction abnormalities.
There is currently no cure for DM1, and no disease modifying treatments are available. Approximately 40,000 individuals in the United States are diagnosed with DM1. SRP-1003 is an investigational siRNA treatment for DM1 and is designed to target and knockdown, or silence, the DMPK mRNA in target cells.
Study SRP-1003-101 is a first-in-human, Phase 1/2, SAD/MAD, randomized, placebo-controlled clinical trial being conducted in individuals with DM1 aged 18 to 65. Sarepta?s next-generation siRNA platform is focused on chronically administered therapies for neurodegenerative and pulmonary diseases and includes the following investigational treatments: SRP-1001 for Facioscapulohumeral muscular dystrophy (FSHD), SRP-1002 for Idiopathic Pulmonary Fibrosis (IPF), SRP-1003 for Myotonic dystrophy type 1 (DM1), SRP-1004 for Spinocerebellar ataxia type 2 (SCA2), SRP-1005 for Huntington?s disease (HD). Sarepta is advancing these programs, as well as preclinical programs for Spinocerebellar ataxia type 1 (SCA1) and Spinocerebellar ataxia type 3 (SCA3) and additional discovery targets in muscle or central nervous system disorders, under an exclusive license with Arrowhead Pharmaceuticals.
