Question: Describe mechanism of action of Eteplirsen?

Context:
Eteplirsen (Exondys 51) is an antisense oligonucleotide designed to induce exon 51 skipping that is developed by Sarepta Therapeutics. Intravenous eteplirsen has received accelerated approval from the US FDA for the treatment of Duchenne muscular dystrophy (DMD) in patients with a confirmed mutation of the DMD gene amenable to exon 51 skipping.
The first AON (eteplirsen) has recently received accelerated approval by the Food and Drug Administration in the US.
Currently, the most promising potential drugs are the exon-skipping agents eteplirsen and drisapersen.
OBJECTIVE: In prior open-label studies, eteplirsen, a phosphorodiamidate morpholino oligomer, enabled dystrophin production in Duchenne muscular dystrophy (DMD) with genetic mutations amenable to skipping exon 51.
We also assessed the effect of dystrophin restoration on the expression of the five dystromirs in serum of DMD patients treated systemically for 12 weeks with antisense oligomer eteplirsen that induces skipping of exon 51 in the dystrophin gene. 
Exon skipping quantification by quantitative reverse-transcription polymerase chain reaction in Duchenne muscular dystrophy patients treated with the antisense oligomer eteplirsen.
We previously conducted a proof of principle; dose escalation study in Duchenne muscular dystrophy (DMD) patients using the morpholino splice-switching oligonucleotide AVI-4658 (eteplirsen) that induces skipping of dystrophin exon 51 in patients with relevant deletions, restores the open reading frame and induces dystrophin protein expression after intramuscular (i.m.) injection. 
To continue evaluation of the long-term efficacy and safety of eteplirsen, a phosphorodiamidate morpholino oligomer designed to skip DMD exon 51 in patients with Duchenne muscular dystrophy (DMD).
In prior open-label studies, eteplirsen, a phosphorodiamidate morpholino oligomer, enabled dystrophin production in Duchenne muscular dystrophy (DMD) with genetic mutations amenable to skipping exon 51.
The present study used a double-blind placebo-controlled protocol to test eteplirsen's ability to induce dystrophin production and improve distance walked on the 6-minute walk test (6MWT).DMD boys aged 7 to 13 years, with confirmed deletions correctable by skipping exon 51 and ability to walk 200 to 400 m on 6 MWT, were randomized to weekly intravenous infusions of 30 or 50 mg/kg/wk eteplirsen or placebo for 24 weeks (n = 4/group).
Here we describe the development of a Taqman quantitative (q)RT-PCR assay to quantify exon skipping and highlight its use to determine the levels of exon skipping in DMD patients treated intramuscularly with a morpholino AO to skip exon 51, eteplirsen (AVI-4658).
The subset of patients amenable to exon 51 skipping showed a more severe disease course than those amenable to any exon skipping.Over 3 years of follow-up, eteplirsen-treated patients showed a slower rate of decline in ambulation assessed by 6MWT compared to untreated matched HC.<CopyrightInformation>© 2016 The Authors.
We previously conducted a proof of principle; dose escalation study in Duchenne muscular dystrophy (DMD) patients using the morpholino splice-switching oligonucleotide AVI-4658 (eteplirsen) that induces skipping of dystrophin exon 51 in patients with relevant deletions, restores the open reading frame and induces dystrophin protein expression after intramuscular (i.m.) injection.

Answer: Eteplirsen (Exondys 51) is an antisense oligonucleotide designed to induce exon 51 skipping. Eteplirsen is approved for the treatment of Duchenne muscular dystrophy (DMD) in patients with a confirmed mutation of the DMD gene amenable to exon 51 skipping.