Muscular Dystrophy WA hails US approval of eterplirsen


Professors Sue Fletcher and Steve Wilton have spent more than 20 years developing a new drug that fights muscular dystrophy.
Professors Sue Fletcher and Steve Wilton have spent more than 20 years developing a new drug that fights muscular dystrophy.

MUSCULAR Dystrophy WA has hailed the US approval of new drug eterplirsen as the first glimmer of real hope for treating the disease.

The average life expectancy for a child born with Duchenne muscular dystrophy (DMD) – the most common form of the genetic disorder – is 27 years.

Murdoch University professor Steve Wilton and colleague Sue Fletcher have dedicated nearly that much time to fighting the disease.

On Monday, their life work was vindicated when the US Food and Drug Administration (FDA) rubber-stamped eterplirsen, the first approved treatment for DMD.

Affecting one in 3500 newborn boys, DMD is caused by a spelling error in the gene responsible for producing dystrophin, a protein that protects muscle cells from damage.

The disease is much less common in girls but the symptoms are the same; gradual muscle deterioration that usually leaves patients in a wheelchair by the time they are 11 years old before progressing to the breathing apparatus and heart.

Prof Wilton is now the director of the WA Neuroscience Research Institute but his first exposure to DMD came as a senior research scientist developing rapid screening for DMD-causing mutations.

In 1994, he came up with a theoretical treatment – a genetic patch or “white-out” correcting the spelling error – and two years later while attending a conference on molecular genetics he realised how it could be applied to DMD.

Twenty years on, and after a trip to the US to argue eterplirsen’s case at an FDA advisory committee in April, Prof Wilton was at his Applecross home when he received a phone call from long-time colleague Prof Fletcher.

“I’d just been on my computer trying to look for news on eterplirsen when Sue rang and said the drug had been approved,” he said.

“I didn’t doubt her but I couldn’t find anything on the web and started panicking; until I checked the shares of the company that owns eterplirsen and saw they’d jumped from $24 to $54.

“Then it was a combination of relief, thinking thank God it’s happened and why did it take so long?”

The FDA’s hesitance stemmed from eterplirsen’s relatively small initial clinical trial; just 12 boys were given the drug but all of them displayed increased dystrophin levels and 10 are still walking five years after starting treatment.

“The trial was designed for kids who were ‘close to the edge of the cliff’ in terms of losing the ability to walk and the drug does take some time to build up the protein to clinically relevant amounts,” Prof Wilton said.

“If the two boys who stopped walking early in the trial had received the drug when they were younger, I believe they’d still be walking today.”

Eterplirsen is now available for prescription in the US and Profs Wilton and Fletcher are turning their attention to adapting the drug to treat different spelling errors that cause DMD.

“Eterplirsen’s name has been changed to Exondys 51, which reflects the spelling error it treats,” Prof Wilton said.

“One in 10 boys with DMD have that particular genetic mutation, which is the most common.

“We’ve got two new drugs in clinical trials named Exondys 53 and Exondys 45 that target different disease-causing mutations and we have many more ready to go.”

It will be some time before the drug is approved for use in Australia by the Therapeutic Goods Administration but a Muscular Dystrophy WA spokeswoman said getting the green light from the FDA was an exciting step in the right direction.

“It’s finally the recognition (eterplirsen) deserves and we couldn’t be prouder of Steve and Sue’s achievement and dedication,” she said.

“At this stage we cannot say when this drug will be available for our local community, but what we can say is that through the approval from the FDA, we know the drug is deemed to work and it is safe to use.

“Steve and Sue were both made Honorary Life Members of our organisation in 2013 to recognise their dedication to research but also the personal interest they take in building and fostering genuine relationships with the WA muscular dystrophy community.”