Avidity Biosciences, Inc. today shared that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy designation to del-zota (AOC 1044) for the treatment of Duchenne in individuals amenable to exon 44 skipping.
Del-zota is currently being assessed in the Phase 2 EXPLORE44 Open-Label Extension (EXPLORE44-OLE
) trial and is the first of multiple exon skipping therapies the company is developing for Duchenne. The therapy is designed to deliver phosphorodiamidate morpholino oligomers (PMOs) to skeletal muscle and heart tissue to specifically skip exon 44 of the dystrophin gene and enable production of near-full length dystrophin.
According to Avidity, in the completed Phase 1/2 EXPLORE44® trial, del-zota demonstrated statistically significant increases in exon skipping, a substantial increase in dystrophin production, a significant and sustained reduction in creatine kinase levels to near normal, and consistent favorable safety and tolerability. The company plans to present topline and functional data from the ongoing Phase 2 EXPLORE44-OLE trial in the fourth quarter of 2025, and is on track to submit a Biologics License Applications (BLA) at the end of 2025.
Breakthrough Therapy designation is utilized by the FDA to help speed up the development and review of treatments for serious conditions like Duchenne. It’s granted when early clinical data suggests that a therapy may offer meaningful improvement over existing options on key measures of effectiveness. In addition to receiving Breakthrough Therapy designation, del-zota has previously been granted Orphan designation by the FDA and the European Medicines Agency (EMA) and Rare Pediatric Disease and Fast Track designations by the FDA for the treatment of Duchenne in individuals amenable to exon 44 skipping.
PPMD is pleased to see del-zota recognized with Breakthrough Therapy designation and encouraged by the progress of Avidity’s exon 44 program. We are optimistic about what this may mean for the community and look forward to continued updates from Avidity in the months ahead.
Read Avidity’s press release here.
Read Avidity’s community letter:
July 23, 2025
Dear Advocacy Partner,
We are pleased to share that the U.S. Food and Drug Administration (FDA) granted delpacibart zotadirsen (abbreviated as del-zota) Breakthrough Therapy designation for the treatment of people living with Duchenne muscular dystrophy amenable to exon 44 skipping (DMD44).
We understand that there has been significant news in the DMD community over the past week, and we share your sense of urgency and desire to bring therapies to the DMD community as quickly as possible.
Our expected timelines for development and potential approval of del-zota remain unchanged, and we remain on track for a planned Biologics License Application (BLA) submission at year end 2025.
Breakthrough Therapy designation is granted by FDA to expedite the development and review of drugs for serious or life-threatening conditions. To achieve Breakthrough Therapy designation, there must be preliminary clinical evidence that demonstrates the drug may have a substantial improvement on at least one clinically significant endpoint over currently available therapies.
We want to thank the entire DMD community for your time, commitment and continued contributions to the development of del-zota. In particular, we are so grateful to the participants in the EXPLORE44® and EXPLORE44-OLETM studies, their families, the investigators and their teams. Your participation in the EXPLORE44 program generated the data that support this designation as well as the data needed to advance del-zota to the next stage of development.
This designation from the FDA further reinforces the significant potential of del-zota to address the underlying cause of DMD44 and underscores the unmet need in the DMD community. Del-zota is currently an investigational product. It has not been approved by the FDA or any other regulatory authority for commercial use, and the safety and efficacy of del-zota have not been established.
You can view our full press release announcing today’s DMD44 news here: Avidity Biosciences Receives FDA Breakthrough Therapy Designation for Delpacibart Zotadirsen (del-zota) for the Treatment of DMD in People with Mutations Amenable to Exon 44 Skipping
We encourage you to contact your doctor if you have any questions about del-zota or the EXPLORE44 and EXPLORE44-OLE trials.
Sincerely,
The Avidity Team
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