DYNE-251 Granted FDA Breakthrough Therapy Designation for DMD

DYNE-251, an investigational therapy for patients with Duchenne muscular dystrophy (DMD) amenable to exon 51 skipping, was granted FDA breakthrough therapy designation based on data from the ongoing DELIVER clinical trial (NCT05524883), Dyne announced in a press release.¹

The breakthrough therapy designation for DYNE-251 in DMD follows the FDA breakthrough designation for DYNE-101 in myotonic dystrophy type 1 earlier in the year. The designation indicates that a drug shows promising preliminary clinical evidence of improvement over available therapies in 1 or more clinically significant end points.

The long-term data from DELIVER showed meaningful, sustained improvements in functional outcomes and dystrophin expression, as well as a favorable safety profile in patients with Duchenne muscular dystrophy. | Image credit: OlegKachura - stock.adobe.com

“This Breakthrough Therapy Designation for DYNE-251 is a testament to its potential as a next-generation therapy designed to bring meaningful functional improvement to individuals with DMD for whom exon 51 skipping can lead to the production of near full-length dystrophin,” Doug Kerr, MD, PhD, chief medical officer of Dyne, said in a statement.¹ “As we’ve previously disclosed, DYNE-251 has demonstrated sustained functional improvement through eighteen months, as assessed by key measures such as time to rise and stride velocity 95th centile. The level of near-full-length dystrophin expression observed marks a significant step forward to potentially deliver meaningful benefits to patients.”

The long-term data from DELIVER showed meaningful, sustained improvements in functional outcomes and dystrophin expression, as well as a favorable safety profile in patients with DMD.²

“With Dyne-251, we have the opportunity to deliver a durable and redosable therapy demonstrating clinically meaningful and sustained functional improvement in DMD,” John Cox, president and CEO of Dyne, said in a news release when the data were announced.² “The consistency of these new data across multiple end points and timepoints underscores the potential of DYNE-251 to meaningfully address the significant unmet need in Duchenne despite available therapies. We are rapidly advancing DYNE-251 toward a readout later this year with the potential to submit for U.S. accelerated approval in early 2026 based on a well-established regulatory pathway leveraging dystrophin expression as a surrogate end point. If approved, we believe there is an opportunity for rapid adoption by physicians and currently treated patients, as well as those naïve to therapy.”

DYNE-251 is investigational and “consists of a phosphorodiamidate morpholino oligomer conjugated to an antigen-binding fragment that binds to the transferrin receptor 1,” according to the press release.¹ It was designed to allow production of near full-length dystrophin in muscle and the central nervous system, which could lead to functional improvement in patients with DMD. The inherited, recessive condition occurs due to mutations in the DMD gene, which causes nearly undetectable levels or the absence of dystrophin protein altogether. Most patients become nonambulatory by their early teenage years, followed by loss of upper body function and eventual respiratory failure and death.

The new designation comes in addition to DYNE-251’s fast track and rare pediatric disease designations from the FDA. It was also granted orphan drug designation from the FDA and European Medicines Agency for the treatment of individuals with DMD.

References

1. Dyne Therapeutics announces FDA breakthrough therapy designation for DYNE-251 in Duchenne muscular dystrophy (DMD). News release. Dyne Therapeutics. August 4, 2025. Accessed August 13, 2025. https://investors.dyne-tx.com/news-releases/news-release-details/dyne-therapeutics-announces-fda-breakthrough-therapy-0

2. Dyne Therapeutics announces new long-term clinical data from phase 1/2 DELIVER trial of DYNE-251 in Duchenne muscular dystrophy demonstrating unprecedented and sustained functional improvement through 18 months. News release. Dyne Therapeutics. March 16, 2025. Accessed August 13, 2025. https://investors.dyne-tx.com/news-releases/news-release-details/dyne-therapeutics-announces-new-long-term-clinical-data-phase-12