PepGen's DM1 Therapy Achieves Record 53.7% Splicing Correction in Phase 1 Trial
Key Insights
PepGen's PGN-EDODM1 demonstrated a mean splicing correction of 53.7% at 15 mg/kg dose in DM1 (search) patients, representing the highest splicing correction ever reported in this patient population.
All six patients (100%) receiving the 15 mg/kg dose showed improved splicing correction, with the therapy demonstrating greater than dose-proportional increases across all tested doses.
The treatment was generally well-tolerated with no serious adverse events, while PepGen's stock surged 121.8% following the announcement of these breakthrough results.
PepGen Inc. announced breakthrough clinical data from its FREEDOM-DM1 (search) Phase 1 trial, demonstrating unprecedented splicing correction in patients with myotonic dystrophy type 1 (search) (DM1). The 15 mg/kg dose cohort of PGN-EDODM1 achieved a mean splicing correction of 53.7%, substantially higher than any previously reported splicing correction in DM1 patients.
The results represent a significant advancement in treating DM1 (search), a genetic disorder characterized by muscle weakness and wasting that affects approximately 40,000 patients in the United States. Since mis-splicing is the underlying cause of DM1, these high levels of correction could potentially reverse the molecular defects and produce functional improvements in multiple outcome measures.
Dose-Dependent Efficacy Demonstrated
The FREEDOM-DM1 (search) single ascending dose study revealed compelling dose-response relationships across all tested cohorts. PepGen previously reported mean splicing correction of 12.3% at 5 mg/kg and 29.1% at 10 mg/kg, demonstrating greater than dose-proportional increases in splicing correction as doses escalated to the 15 mg/kg level.
"We are delighted to report that the FREEDOM clinical study achieved all of its key objectives, including unprecedented splicing correction following a single dose of PGN-EDODM1 at 15 mg/kg," said Dr. Paul Streck, Executive Vice President of Research and Development at PepGen. "Since mis-splicing is the underlying cause of DM1 (search), we believe high levels of splicing correction have the potential to reverse the underlying molecular defects, and produce functional improvements in multiple outcome measures, including myotonia and muscle weakness, in repeat dose studies."
All six patients (100%) receiving the 15 mg/kg dose showed improved splicing correction, as measured by a 22-gene panel at 28 days post-dosing. Additionally, greater than dose-proportional increases in muscle tissue concentrations of PGN-EDODM1 were observed across all three dose cohorts at Day 28.
Safety Profile Supports Continued Development
PGN-EDODM1 demonstrated a favorable safety profile at the highest tested dose. The therapy was generally well-tolerated at 15 mg/kg, with no serious treatment-related adverse events reported. All treatment-related adverse events were mild or moderate in severity, transient, and with the exception of one patient who received oral over-the-counter antihistamines, did not require intervention.
The safety data showed no electrolyte-related adverse events, including an absence of hypomagnesemia. All renal biomarker-related adverse events were asymptomatic, transient (approximately 48 hours), and resolved without intervention. One patient experienced a transient and reversible kidney biomarker elevation that qualified as a dose-limiting toxicity per study protocol but was classified as mild and resolved without intervention, with the patient remaining in the study.
Market Response and Future Development
The clinical results triggered a dramatic market response, with PepGen's stock jumping 121.8% from $2.66 to $5.90, bringing the company's market capitalization to $192.86 million. This surge reflects investor confidence in the therapeutic potential of PGN-EDODM1 for addressing a significant unmet medical need.
James McArthur, PepGen's President and Chief Executive Officer, emphasized the significance of the universal response rate: "We are excited to report that 100% of patients in the 15 mg/kg cohort of our FREEDOM trial showed improved splicing correction following treatment. We look forward to reporting data from the first cohort of FREEDOM2, our multiple ascending dose study currently underway, in the first quarter of 2026."
Enhanced Delivery Technology Platform
PGN-EDODM1 utilizes PepGen's proprietary Enhanced Delivery Oligonucleotide (EDO) technology to deliver a therapeutic oligonucleotide designed to restore normal splicing function of MBNL1 (search), a key RNA splicing protein. The therapy addresses the deleterious effects of cytosine-uracil-guanine (CUG) repeat expansion in dystrophia myotonic protein kinase (DMPK (search)) transcripts by binding to pathogenic CUG trinucleotide repeat expansions and disrupting their binding with MBNL1.
This approach offers potential advantages over oligonucleotide modalities that rely on knockdown or degradation of DMPK (search) transcripts, as it allows the transcripts to continue their normal cellular function while liberating MBNL1 (search) to correct downstream mis-splicing events. The U.S. Food and Drug Administration has granted PGN-EDODM1 both Orphan Drug and Fast Track Designations for DM1 (search) treatment.
Clinical Program Advancement
PepGen is conducting the FREEDOM-DM1 (search) multinational, randomized, double-blind, placebo-controlled Phase 1 single ascending dose study, enrolling 24 adult participants with DM1 across the United States, United Kingdom, and Canada. The company anticipates reporting results from the FREEDOM2-DM1 multiple ascending dose study 5 mg/kg cohort in the first quarter of 2026, with dosing of the 10 mg/kg cohort also expected to begin in Q1 2026.
The competitive landscape includes Avidity Biosciences (search)' del-desiran, currently in Phase III trials, with GlobalData predicting sales of $1.31 billion in 2031 compared to $283 million projected for PGN-EDODM1. However, the unprecedented splicing correction achieved by PGN-EDODM1 positions it as a potentially transformative therapy for the estimated 130,000 DM1 (search) patients globally.