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Sarepta will seek accelerated approval for 2nd Duchenne muscular dystrophy drug

John Boal for The Boston Globe/File

Sarepta Therapeutics will file an application with the Food and Drug Administration by the end of 2018 seeking accelerated approval for its second drug to treat Duchenne muscular dystrophy, a rare, inherited, muscle-wasting disease.

The Cambridge biotech company said Monday that the decision to seek a rapid approval of its drug, called golodirsen, was made after receiving a report last week that summarized a meeting with FDA officials held in February.

The meeting, sought by Sarepta to seek regulatory guidance on golodirsen, could have been treacherous. In attendance on the FDA side were clinical reviewers who vehemently disagreed with the agency’s top-level decision in late 2016 to approve Exondys 51, Sarepta’s first drug to treat Duchenne muscular dystrophy.

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Among those once-angry FDA officials: Ellis Unger, director of the Office of Drug Evaluation, who had called Exondys 51 an “elegant placebo” that should never have been approved.

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But there was no residual hostility or hard feelings, including from Unger, during the February meeting, just a willingness to reestablish a collaborative relationship with the company, said Sarepta’s CEO, Doug Ingram.

“What we encountered were FDA people who were professional, productive, and helpful. They gave us straightforward, unequivocal guidance,” said Ingram, who spoke with STAT Sunday night. “In exchange, I gave them my personal commitment that Sarepta will let golodirsen live or die by the data. We’d be fully transparent, and we’d be thoughtful about how we communicated with the agency and the public.”

At the top of the list for Sarepta was confirmation from the FDA that accelerated approval for golodirsen could be obtained if the company submits convincing data showing the drug is capable of producing significantly larger quantities of dystrophin, a muscle protein normally missing in DMD patients.

Sarepta believes it has those dystrophin data in hand for golodirsen from a small clinical trial conducted last year, although only the FDA makes the call that the data are sufficient.

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“Obviously, whether golodirsen will obtain accelerated approval is a review decision that will come after the submission and review of our new drug application,” Ingram said.

The company intends to start submitting the golodirsen-related dystrophin data to the FDA soon, but the full application won’t be complete until a long-term safety study in animals is finished in the fourth quarter. Sarepta’s goal is to reach a point where the FDA is ready to make an approval decision on golodirsen by the summer of 2018.

Golodirsen is designed to treat patients whose DMD is caused by an error in the DNA sequence known as exon 53. The drug, administered via monthly infusions, works by skipping over that mutation and producing dystrophin. Approximately 8 percent of the 5,000 DMD patients in the United States carry the exon 53 error.

Sarepta’s first DMD drug, Exondys 51, works in much the same way, but for the 13 percent of patients whose DMD is caused by an error in the DNA sequence known as exon 51. Sarepta charges an average of $300,000 a year for Exondys 51, but because dose is based on the patient’s weight, the list price for some can top $750,000 a year.

Exondys 51 sales totaled $155 million in 2017. Sarepta has forecast Exondys 51 sales this year in the range of $295 million to $305 million.

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Even if Sarepta secures accelerated approval for golodirsen based on its ability to generate dystrophin, the company will still need to correlate that biomarker with real clinical outcomes in patients, such as improved walking ability.

‘I gave them [FDA] my personal commit-ment that Sarepta will let golodirsen live or die by the data.’

To get that evidence, Sarepta is enrolling DMD patients with mutations in exons 45 and 53 into a phase 3 clinical trial called ESSENCE, which is designed to measure dystrophin production and improvements in clinical outcomes by comparing golodirsen against a placebo.

The ESSENCE study is almost fully enrolled. Ingram said he promised the FDA that accelerated approval of golodirsen will not get in the way of the study being completed.

Adam Feuerstein can be reached at adam.feuerstein@statnews.com.