Sarepta Therapeutics plans to submit eteplirsen NDA for treatment of Duchenne muscular dystrophy

Apr 21 2014

Sarepta Therapeutics, Inc. (NASDAQ:SRPT), a developer of innovative RNA-based therapeutics, today announced it plans to submit a New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) by the end of 2014 for the approval of eteplirsen for the treatment of Duchenne muscular dystrophy (DMD). Eteplirsen is Sarepta's lead exon-skipping drug candidate in development for the treatment of patients with DMD who have a genotype amenable to skipping of exon 51.

The plan to submit an NDA for eteplirsen by the end of 2014 is based on a guidance letter from the Agency that proposed a strategy regarding the submission of an NDA for eteplirsen under a potential Accelerated Approval pathway and served as the final meeting minutes for four meetings that took place between November, 2013 and March, 2014. The Agency stated that "with additional data to support the efficacy and safety of eteplirsen for the treatment of DMD, an NDA should be fileable," and outlined examples of additional data and analysis that, if positive, will be important to enhance the acceptability of an NDA filing by addressing areas of ongoing concern in the existing dataset. Additionally, the Agency provided clear guidance on an open-label, historically controlled confirmatory study of eteplirsen, as well as initial guidance on a placebo-controlled study of one or more follow-on DMD drug candidates, which, like the open-label study, could also be considered an acceptable confirmatory study to verify the clinical benefit of eteplirsen in the event of an accelerated approval.

"As we announce our plan to submit an eteplirsen NDA by the end of 2014, we are very pleased with the detailed guidance that the FDA has provided us on a potential eteplirsen approval pathway and their support of a historically controlled eteplirsen confirmatory study," said Chris Garabedian, president and chief executive officer of Sarepta Therapeutics. "We also appreciate that the FDA shares our urgency in dosing a broader base of eteplirsen patients and has encouraged us to begin the clinical program with our follow-on exon-skipping drugs as soon as possible."

Based on the Agency's guidance, Sarepta plans to initiate several additional clinical studies with eteplirsen later this year in exon-51 amenable genotypes. These studies will include a clinical trial with predefined efficacy endpoints for ambulatory patients between the ages of 7 to 16 years who can walk a minimum distance, and two additional clinical trials that will evaluate safety and biomarkers in DMD patients younger than 7 years and DMD patients who have advanced in their disease progression to a point they cannot walk a minimum distance or have become non-ambulant. Additionally, Sarepta plans to initiate a placebo-controlled study with one or more of its follow-on DMD exon-skipping drug candidates by the end of the year.

"We are excited to have guidance from the FDA that allows us to move quickly into additional clinical trials with eteplirsen to confirm our current understanding of eteplirsen's safety profile, its effect on dystrophin production, and its impact on clinical outcomes in DMD patients," said Edward Kaye, M.D., senior vice president and chief medical officer of Sarepta Therapeutics. "We are particularly pleased that the FDA shares our interest in accelerating the clinical development of our follow-on exon-skipping drugs and we expect to initiate enrollment in this trial later this year."

Sarepta plans to immediately take steps to initiate the additional eteplirsen clinical studies with the goal of beginning dosing in the confirmatory study in the third quarter, with dosing in the additional trials (i.e., younger and more advanced DMD patients) to begin later this year. Once available, detailed study eligibility criteria and clinical site information will be posted on www.ClinicalTrials.gov and Let's Skip Ahead, an online resource center from Sarepta for the DMD community available at www.SkipAhead.com.

Excerpts from the FDA's letter on an NDA filing included:

"…with additional data to support the efficacy and safety of eteplirsen for the treatment of DMD, described below, an NDA should be fileable (assuming other aspects of the submitted application meet applicable standards). As we are sure you appreciate, however, our willingness to consider an application for filing cannot be taken to suggest the outcome of our review. We also note that if the application is filed, you should expect public discussion of the NDA at an Advisory Committee meeting."

The FDA outlined two potential pathways to accelerated approval:

"1. The clinical data from Study 201/202 [Phase IIb clinical trial program] on 6-minute walk could be considered a finding on an intermediate clinical endpoint that could have the potential to support accelerated approval."

Related to this first pathway to Accelerated Approval, the Agency stated that they have "significant concerns regarding our ability to draw valid conclusions based on the Study 201/202 data with respect to walking performance and other data," and identified areas relating to the interpretation of the existing data set that will be addressed as part of an NDA review once the NDA is filed.

"2. We have discussed the possibility of using a number of modalities to quantify dystrophin in muscle biopsies, and discussed how these biomarkers might be used as a surrogate endpoint(s) to support accelerated approval."

In evaluating this pathway, the FDA expressed concerns about methodological problems in the assessments of dystrophin and, "remain skeptical about the persuasiveness of the (dystrophin) data" and, as a result, the Agency is "uncertain whether the existing dystrophin biomarker data will be persuasive enough to serve as a surrogate endpoint that is reasonably likely to predict clinical benefit." However, the Agency further states that if they "were to find the biomarker data to be adequate upon detailed review, however, they would have the potential to support accelerated approval." To that end, the Agency proposed "a collaborative effort in which we will work to better understand the methods and analyses used for the existing biomarker data," and "also work together on methods for the collection of additional data that could be more reliable."

Furthermore, the Agency suggested that "another approach to demonstrating an effect of eteplirsen on dystrophin protein production would be to obtain a fourth muscle biopsy in patients who are continuing in Study 202," which could serve to enhance the acceptability of an NDA filing and accelerated approval.

Under either potential application of the Accelerated Approval pathway, the FDA's letter included comments expressing both a desire for more eteplirsen safety and efficacy data and a willingness to consider supplemental data in an NDA filing or during an NDA review (following the NDA filing) from the ongoing Study 202 and early safety and biomarker data from a confirmatory eteplirsen study. The Agency also encouraged Sarepta to collect safety and biomarker data with eteplirsen in a broader population of patients, including DMD patients who were younger, older and non-ambulant, and previously treated with drisapersen.

Additional excerpts from the FDA's letter on the eteplirsen and follow-on exon-skipping drug confirmatory studies:

"…any accelerated approval [of eteplirsen] would necessitate confirmatory studies to verify the clinical benefit. Confirmatory studies should be underway at the time of approval."

The FDA outlined two approaches for confirmatory trials and urged Sarepta to "initiate both of these trials as soon as possible."

"1. A historically-controlled trial might be acceptable to confirm clinical benefit following accelerated approval."

"2. A randomized, placebo-controlled trial of another PMO [phosphorodiamidate morpholino oligomer] with a similar mechanism of action, directed at a different exon (e.g., SRP-4053 or SRP-4045), with a demonstration of a correlation between dystrophin production and definitive clinical benefit on 6-minute walk or another measure, could provide confirmatory evidence of eteplirsen's clinical benefit if approval were based on a surrogate endpoint."

SOURCE Sarepta Therapeutics, Inc.