8-K: PepGen's PGN-EDODM1 Shows Record DM1 Splicing Correction

PepGen Inc. announced unprecedented 53.7% mean splicing correction in DM1 patients with PGN-EDODM1, marking a significant clinical advancement.

Summary

• PepGen Inc. reported positive clinical data from the 15 mg/kg dose cohort of its ongoing FREEDOM-DM1 Phase 1 single ascending dose (SAD) study in patients with myotonic dystrophy type 1 (DM1).
• PGN-EDODM1 achieved a mean splicing correction of 53.7% in DM1 patients (n=6) at 28 days post-dosing, which is substantially higher than any previously reported splicing correction in DM1 patients.
• All six patients (100%) receiving a 15 mg/kg dose of PGN-EDODM1 responded to treatment by showing improved splicing correction.
• Splicing correction demonstrated greater than dose-proportional increases, with mean corrections of 12.3% at 5 mg/kg (n=6), 29.1% at 10 mg/kg (n=4), and 53.7% at 15 mg/kg (n=6).
• PGN-EDODM1 was generally well-tolerated at 15 mg/kg, with all drug-related adverse events (AEs) being mild or moderate in severity, transient, and not requiring intervention (except for one patient who received oral OTC antihistamines).
• No serious treatment-related adverse events or electrolyte-related AEs, including hypomagnesemia, were observed.
• A transient and reversible kidney biomarker elevation in one patient qualified as a dose-limiting toxicity (DLT) as defined by the study protocol, but it was classified as a mild AE and resolved without intervention, with the patient remaining in the study.
• Greater than dose-proportional increases in muscle tissue concentrations of PGN-EDODM1 were observed across the 5 mg/kg, 10 mg/kg, and 15 mg/kg cohorts at Day 28.

Sentiment

Score: 9

Explanation: The clinical data for PGN-EDODM1 shows unprecedented efficacy with the highest reported splicing correction in DM1 patients and a favorable safety profile, indicating significant therapeutic potential and strong progress in clinical development.

Positives

• Achieved the highest mean splicing correction ever reported in DM1 patients (53.7% following a single 15 mg/kg dose of PGN-EDODM1).
• 100% of patients in the 15 mg/kg cohort demonstrated improved splicing correction following treatment.
• Observed greater than dose-proportional increases in splicing correction across all tested doses (12.3% at 5 mg/kg, 29.1% at 10 mg/kg, 53.7% at 15 mg/kg).
• PGN-EDODM1 was generally well-tolerated at 15 mg/kg, with all drug-related adverse events being mild or moderate and transient.
• No serious treatment-related adverse events or electrolyte-related adverse events (including hypomagnesemia) were reported.
• PGN-EDODM1's mechanism of action targets the underlying cause of DM1 by restoring normal splicing function of MBNL1, potentially offering significant advantages over other oligonucleotide modalities.
• PGN-EDODM1 has received both Orphan Drug and Fast Track Designations from the U.S. Food and Drug Administration for the treatment of DM1 patients.

Negatives

• One patient experienced a transient and reversible kidney biomarker elevation that qualified as a dose-limiting toxicity, although it was mild and resolved without intervention.
• One patient's biopsy in the 10 mg/kg cohort was not collected at day 28 due to a pseudoaneurysm in connection with the biopsy procedure.
• One patient's sample in the 10 mg/kg cohort showed a splicing index outside the pre-specified assay range (no detectable mis-splicing) and was excluded from analysis.
• One subject in the 15 mg/kg cohort received 77% of the full dose.

Risks

• Delays or failure to successfully initiate or complete ongoing and planned development activities for product candidates, including PGN-EDODM1.
• Inability to enroll patients in clinical trials, including FREEDOM2.
• Interpretation of clinical and preclinical study results may be incorrect, or anticipated levels of therapeutic activity may not be observed in clinical testing.
• Product candidates, including PGN-EDODM1, may not be safe and effective or otherwise demonstrate safety and efficacy in clinical trials.
• Adverse outcomes from regulatory interactions, including delays in regulatory review, clearance to proceed, or approval by regulatory authorities.
• Regulatory feedback requiring modifications to development programs, including FREEDOM2.
• Changes in regulatory framework that are out of the company's control.
• Inability to obtain, maintain, and protect intellectual property.
• Inability to enforce patents against infringers and defend the patent portfolio against challenges from third parties.
• Competition from others developing therapies for the indications being pursued.
• Unexpected increases in expenses associated with development activities or other events that adversely impact financial resources and cash runway.
• Dependence on third parties for some or all aspects of product manufacturing, research, and preclinical and clinical testing.

Future Outlook

PepGen anticipates reporting results from the FREEDOM2-DM1 multiple ascending dose (MAD) study 5 mg/kg cohort in the first quarter of 2026 and expects to begin dosing its 10 mg/kg cohort in the first quarter of 2026. The company believes that high levels of splicing correction have the potential to reverse underlying molecular defects and produce functional improvements in multiple outcome measures, including myotonia and muscle weakness, in repeat dose studies.

Management Comments

• Paul Streck, MD, MBA, Executive Vice President of Research and Development at PepGen: "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. Since mis-splicing is the underlying cause of DM1, 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."
• James McArthur, PhD, PepGen's President and Chief Executive Officer: "These data build upon and reinforce our previously reported splicing correction levels seen in the FREEDOM single dose cohorts of 5 and 10 mg/kg of PGN-EDODM1. Additionally, 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 (MAD) study currently underway, in the first quarter of 2026."

Industry Context

Myotonic dystrophy type 1 (DM1) is a severe, progressive, monogenic disorder with a significant unmet medical need, as there are currently no approved therapies that address the underlying cause of the disease. PepGen's PGN-EDODM1, leveraging its proprietary Enhanced Delivery Oligonucleotide (EDO) technology, offers a novel therapeutic approach by binding to pathogenic CUG repeat expansions to restore normal splicing function. The reported 53.7% mean splicing correction is stated as the "highest ever reported," positioning PepGen as a potential leader in developing a disease-modifying treatment for DM1. The U.S. FDA's Orphan Drug and Fast Track Designations underscore the critical need for effective treatments and regulatory recognition of PGN-EDODM1's potential.

Comparison to Industry Standards

• PGN-EDODM1's 53.7% mean splicing correction at 15 mg/kg is explicitly stated as "substantially higher than any previously reported splicing correction in DM1 patients," indicating a potentially superior efficacy profile compared to other investigational therapies or historical data in the DM1 therapeutic landscape.
• The company's therapeutic approach, which involves binding selectively to pathogenic DMPK transcripts to liberate MBNL1 and restore correct RNA splicing, is presented as having "considerable advantages over oligonucleotide modalities that rely on knockdown or degradation of the DMPK transcripts." This suggests a differentiated and potentially more favorable mechanism of action compared to alternative strategies being developed for DM1.

Stakeholder Impact

• Shareholders: Positive impact due to strong clinical data, potentially increasing company valuation and investor confidence.
• DM1 Patients: Significant positive impact as PGN-EDODM1 shows potential to be a highly effective, disease-modifying treatment for a condition with high unmet medical need.
• Employees: Positive impact from successful clinical progress, potentially boosting morale and job security.
• Regulatory Authorities: Continued engagement through Fast Track and Orphan Drug designations, with ongoing clinical trials and future data readouts.

Next Steps

• Report results from the FREEDOM2-DM1 multiple ascending dose (MAD) study 5 mg/kg cohort in the first quarter of 2026.
• Begin dosing the FREEDOM2-DM1 MAD study 10 mg/kg cohort in the first quarter of 2026.
• Report FREEDOM2 10 mg/kg clinical results in the second half of 2026.
• Continue data collection for the 15 mg/kg cohort of FREEDOM-DM1.
• Patients from FREEDOM and FREEDOM2 will have the opportunity to participate in an Open Label Extension study (PGN-EDODM1-OLE).

Key Dates

Recommendation

The reported 53.7% mean splicing correction for PGN-EDODM1 in DM1 patients is explicitly stated as the 'highest ever reported,' representing a potentially transformative breakthrough for a disease with no approved causal therapies. The 100% patient response rate and dose-proportional efficacy, combined with a generally well-tolerated safety profile, significantly de-risk the asset and enhance its commercial potential. The clear path to further clinical data in 2026 from the FREEDOM2 MAD study provides near-term catalysts. This strong clinical validation positions PepGen as a leader in the DM1 therapeutic landscape, warranting a 'strong buy' recommendation for long-term investors.

Keywords

PepGen, PGN-EDODM1, Myotonic Dystrophy Type 1, DM1, Splicing Correction, Clinical Trial, Phase 1, FREEDOM-DM1, Biotechnology, Oligonucleotide Therapy, Neuromuscular Disease, Rare Disease, Orphan Drug, Fast Track Designation, EDO Platform