Exon skipping trial results released
In a press release GlaxoSmithKline and Prosensa have said that the results of the phase 3 exon skipping trial for Duchenne muscular dystrophy are disappointing. Preliminary results show that at the end of the 48 week trial, treated boys were unable to walk any further in six minutes than boys receiving a placebo.
The trial tested drisapersen – a molecular patch designed to skip exon 51 of the dystrophin gene – which could potentially treat 13 percent of boys with Duchenne MD. A total of 186 boys from 20 countries around the world (not Australia) participated in the trial. About two thirds of the boys received a weekly injection of drisapersen under the skin for 48 weeks, and the rest received a placebo. Neither the participants nor the clinicians conducting the trial knew who was receiving the real drug.
The main way to measure the success of the treatment was to measure the distance the boys could walk in six minutes. Other measures were also included such as a run and stair climb test. Unfortunately the treated boys performed no better at any of these tests than those receiving placebo. A detailed analysis of all of the data will now be done to fully understand why this potential treatment did not deliver the results so many had hoped for.
This is devastating news for boys with Duchenne MD and their families but there is still hope for the future. Exon skipping is still an exciting and promising approach to treat Duchenne MD – clinical trials have shown that it can restore production of the dystrophin protein that is missing in the muscles of boys with Duchenne MD. Exon skipping therefore has the remarkable potential to treat the underlying cause of the condition. However, in this trial of drisapersen perhaps not enough dystrophin was produced in the right places to have a positive effect on mobility.
Other formulations of exon skipping drugs are being developed; in particular Sarepta Therapeutics is trialing exon skipping drugs with a different chemical composition. Their exon 51 skipping drug – called eteplirsen – recently produced promising results in a phase 2 trial. Experts have commented that the phase 2 trial results for eteplirsen are more convincing than the results that were obtained in the phase 2 trial of drisapersen.
There are other promising therapeutic approaches being developed for Duchenne MD besides exon skipping. This is important because on average only one in five drugs that enter clinical trial prove to be safe and effective. You can read a summary of these other approaches in the Duchenne MD factsheet.
MDA Executive Director, Boris M Struk said “While unfortunately this trial did not yield any tangible results, it is very encouraging to see so many scientists around the globe dedicating their lives to helping to find a treatment for this condition. Our scientists here in Australia at the National Muscular Dystrophy Research Centre (NMDRC) are amongst the best in the world and are also continually working towards finding a timely solution. So while we may be initially disappointed in these results we have to think to the future and know that it is only through trials like these that a breakthrough can occur.”
- Read the press release
- Clinical trials: Your questions answered
- What is exon skipping and how does it work?
- Read about the results of the phase 2 drisapersen trial
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