Prosensa Provides Update On Drisapersen

Leiden, The Netherlands, May 1, 2014 (GLOBE NEWSWIRE) -- Prosensa Holding N.V. (NASDAQ: RNA) the Dutchbiopharmaceutical company focusing on rare diseases with a highunmet medical need, yesterday provided the data analysis of itssecond open-label extension study (DEMAND IV/DMD114349) ofdrisapersen in boys with Duchenne Muscular Dystrophy (DMD)during the 66 th American Academy of Neurology (AAN)Annual Meeting in Philadelphia, PA. The Company also provided anupdate on the drisapersen clinical program earlier this week in aletter sent to patient group representatives and clinicalinvestigators and will present a corporate update during aninvestor briefing on May 1 (webcast here).

Following positive feedback from patients andinvestigators regarding the willingness and desire of patients togo back on drisapersen and encouraging analyses of its clinicaltrial data, Prosensa has confirmed that it will re-dose an initialcohort of boys in the third quarter of 2014.  The Company hasmade significant progress in the transition of the program from itsformer partner, GSK, and expects to communicate on a regulatorypath forward for drisapersen before the end of June.

In a poster and presentation on Wednesday, April30 at the AAN, Dr. Nathalie Goemans, Head of the NeuromuscularReference Center for Children at the University Hospitals Leuven(UHL) in Belgium and one of the key investigators in variousdrisapersen studies confirmed the earlier preliminary analysis ofthe results of DEMAND IV/DMD114349, which include data from 96weeks of continuous drisapersen treatment.

"We see very positive signs of the ability ofdrisapersen to improve the walking ability of boys with DMD. Inthis extension study, patients who entered the study with a lessadvanced stage of the disease either improved or experienced lessdecline in mobility with two-year continuous drisapersen therapy,and these data suggest a treatment difference from those initiallyon placebo," reported Dr. Goemans. 

The poster (online here) included detailed data up to Week48 (total of 96 weeks of treatment) from the second open-labelextension study of drisapersen in 113 boys with DMD (DEMAND IV),who had previously completed a 48-week, double-blind,placebo-controlled treatment phase in one of two feeder studies(DEMAND II/DMD114117 and DEMAND III/DMD114044).  In the sixminute walk test (6MWT), boys from the DEMAND II study declined byonly 5 meters over 96 weeks on continuous drisapersen (6mg/kg/week)compared with 57 meters in boys who had placebo/delayed treatment.Furthermore, boys of 7 years or younger in DEMAND IV improved fromtheir baseline 6MWT by 8 meters with continuous drisapersentreatment compared with a 29 meter decline for patients in theplacebo/delayed treatment arm. The extension study was designed tomonitor the long-term safety and efficacy of drisapersen over thecourse of two years at more than 50 sites in 24 countries.

"These data support our hypothesis that treatingearlier in the disease and treating for a longer duration confers atreatment benefit for boys with DMD. Early intervention is apotentially crucial component to improving disease outcome," saidDr. Giles Campion, Chief Medical Officer of Prosensa.

In a letter to all participating investigatorsand patient groups sent earlier this week, Prosensa confirmed it ison track with its re-dosing plans, which will take a stagedapproach. Dr. Nathalie Goemans (UHL, Belgium) and Dr. CraigMcDonald (UC Davis, Sacramento, USA), who will be participating atan investor briefing on May 1, will be amongst investigatorsworking with Prosensa to undertake re-dosing protocols withdrisapersen. The first wave of re-dosing in the third quarter willfocus on sites in North America and Europe. Patients in NorthAmerica will be re-dosed under existing extension protocols andpatients in Europe will either participate in a new treatmentprotocol or via an appropriate expanded access program. "We realizethat this has been an incredibly difficult period for the boys andtheir families as they eagerly await any updates. We are workingwith all key stakeholders as diligently and quickly as possible toprovide access to drisapersen and to determine a path forward"confirmed Dr. Campion.

"Prosensa is dedicated to enabling long termpatient access to drisapersen and its follow-on products as noveltreatments for DMD. We are determined to accomplish this as soon aspossible, as we know time is not on patients' side" said HansSchikan, Prosensa's Chief Executive Officer. "We have beenfollowing the recent communication in the DMD community and areencouraged by the apparent regulatory flexibility and positivityshown with respect to potential pathways for investigationalproducts for the treatment of DMD, especially given the very urgentand unmet medical need of boys with this debilitating andlife-shortening disease. We are heartened by the FDA's commitmentto DMD and its willingness to work closely with all keystakeholders, and to consider amenable approaches to expedite theavailability of treatment options for DMD."

About drisapersen and the clinicaldevelopment program

Drisapersen, (previously GSK2402968/PRO051), anantisense oligonucleotide which induces exon skipping of exon 51,is currently in-late stage development for DMD. Drisapersen hasorphan drug status in the EU, US, Australia and Japan. In June2013, drisapersen was granted Breakthrough Therapy designation bythe US Food and Drug Administration.

The overall drisapersen clinical programcomprises three double-blind, placebo-controlled studies (DEMANDII, DEMAND V and DEMAND III) and two long term open-label extensionstudies (DMD114673 and DEMAND IV).

About DMD

Duchenne Muscular Dystrophy (DMD) is a severelydebilitating childhood neuromuscular disease that affects up to 1in 3,500 live male births. This rare disease is caused by mutationsin the dystrophin gene, resulting in the absence or defect of thedystrophin protein. Patients suffer from progressive loss of musclefunction, often making them wheelchair bound before the age of 12.Respiratory and cardiac muscle can also be affected by the disease.Few patients survive the age of 30.

About exon skipping

The dystrophin gene is the largest gene in thebody, consisting of 79 exons. Exons are small sequences of geneticcode which lead to the manufacture of sections of protein. In DMD,when certain exons are mutated/deleted, the RNA cannot read thegenetic code past the fault. This prevents the rest of the exonsbeing read, resulting in a non-functional dystrophin protein andthe severe symptoms of DMD.

RNA-based therapeutics, specifically antisenseoligonucleotides inducing exon skipping, are currently indevelopment for DMD. This technology uses synthetic antisenseoligonucleotides to skip an exon next to a deletion and therebycorrect the reading frame, enabling the production of a noveldystrophin protein. Up to 13% of boys with DMD have dystrophin genemutation/deletions amenable to an exon 51 skip.

About Prosensa Holding N.V.

Prosensa (NASDAQ: RNA) is a Dutch biotechnology company engagedin the discovery and development of RNA-modulating therapeutics forthe treatment of genetic disorders. Its primary focus is on rareneuromuscular and neurodegenerative disorders with a large unmetmedical need, including Duchenne muscular dystrophy, myotonicdystrophy and Huntington's disease.

www.prosensa.com

Forward Looking Statements

This press release contains certainforward-looking statements.  All statements, other thanstatements of historical facts, contained in this press release,including statements regarding our strategy, future operations,future financial position, future revenues, projected costs,prospects, plans and objectives of management, are forward-lookingstatements. The words "anticipate," "believe," "estimate,""expect," "intend," "may," "plan," "predict," "project," "target,""potential," "will," "would," "could," "should," "continue," andsimilar expressions are intended to identify forward-lookingstatements, although not all forward-looking statements containthese identifying words. Forward-looking statements in this pressrelease include statements around our exon -skipping drugcandidates. Actual results may differ materially from thoseprojected or implied in such forward-looking statements.  Suchforward-looking information involves risks and uncertainties thatcould significantly affect expected results.  These risks anduncertainties are discussed in the Company's SEC filings,including, but not limited to, the Company's Form 6-K containingthis press release and certain sections of the Company's annualreport on Form 20-F. In addition, any forward-looking statementsrepresent our views only as of today and should not be relied uponas representing our views as of any subsequent date. While we mayelect to update these forward-looking statements at some point inthe future, we specifically disclaim any obligation to do so, evenif our views change.
CONTACT: Prosensa Holding N.V.         Celia Economides, Senior Director IR & Corporate Communications         Phone: +1 917 941 9059         Email: c.economides@prosensa.nl

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