The Food and Drug Administration (FDA) has accepted for Priority Review the New Drug Application (NDA) for casimersen (SRP-4045; Sarepta Therapeutics) for the treatment of Duchenne muscular dystrophy (DMD) in patients who have genetic mutations that are amenable to skipping exon 45 of the Duchenne gene.

Casimersen is a phosphorodiamidate morpholino oligomer that works by binding to exon 45 of dystrophin pre-mRNA, resulting in exclusion of this exon during mRNA processing. Exon skipping allows for the production of an internally truncated but functional dystrophin protein.

The NDA submission is supported by data from the ongoing multicenter, double-blind, placebo-controlled phase 3 ESSENCE study that evaluated the efficacy and safety of casimersen and golodirsen in DMD patients amenable to skipping exons 45 or 53, respectively. Interim analysis demonstrated that treatment with casimersen led to a statistically significant increase in dystrophin production from baseline to week 48.

A Prescription Drug User Fee Act (PDUFA) target action date of February 25, 2021 has been set for this application. The Company has also received a conditional approval of Amondys 45 as the brand name for casimersen.

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“The FDA’s acceptance of our NDA for casimersen is an important step toward our goal of rapidly bringing therapies to patients living with Duchenne muscular dystrophy,” said Doug Ingram, President and CEO, Sarepta Therapeutics. “If it is approved, casimersen, our third exon-skipping medicine in our PMO RNA-based platform, will offer treatment to the 8% of Duchenne patients who are amenable to exon 45 skipping.”

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Sarepta Therapeutics announces FDA acceptance of casimersen (SRP-4045) New Drug Application for patients with Duchenne muscular dystrophy amenable to skipping exon 45. Accessed August 25, 2020.