What happened

After management reported interim phase 2 results for ezutromid that suggest it may offer hope to Duchenne muscular dystrophy (DMD) patients, shares in Summit Therapeutics Plc (SMMT) rallied 12.9% Thursday.

So what

DMD is a rare muscle-wasting disease caused by the inadequate production of dystrophin, a key protein necessary for building and maintaining muscle.

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Currently, the only approved drug for DMD is Exondys 51, an exon-skipping drug that bypasses a mutation to help restore some dystrophin production. Exondys 51, which is marketed by Sarepta Therapeutics (SRPT 0.51%) can only help about 13% of DMD patients, yet it's already selling at a $228 million annualized pace after only five quarters on the market.

Unlike Exondys 51, ezutromid attempts to slow disease progression by targeting utrophin, rather than dystrophin. Utrophin is a protein that performs a similar role to dystrophin in muscle development and repair. However, as muscle fibers mature, utrophin switches off and dystrophin takes over. Summit Therapeutics' hopes that ezutromid's ability to keep utrophin from being shut off in DMD patients can prevent damage caused by inadequate dystrophin production, potentially addressing all DMD patients, rather than only a small subset of patients.

On Thursday, Summit Therapeutics revealed 24-week interim data from its 48-week study that's encouraging. Specifically, it was able to measure a statistically significant and meaningful reduction in muscle damage as measured by a biomarker and an increase in mean utrophin protein intensity levels of 7%.

Now what

A combination of reduced muscle damage and increased utrophin levels offers evidence that ezutromid may help delay the progress of this disease. Management plans to conduct a pivotal study soon that may enable an accelerated or conditional approval in the U.S. and Europe.

If additional data at the 48-week mark confirms ezotromid's efficacy, it will be great news for patients and Summit Therapeutics. It will also be good news for Sarepta Therapeutics because Sarepta obtained certain ex-U.S. licensing rights to ezotromid in 2016. Specifically, it licensed rights in Europe and certain other abroad markets in exchange for $40 million up front, plus up to $522 million in milestones and royalties ranging from a low to high teens percentage of net sales in its licensed territory.

Given the significant sales that Sarepta is already generating by addressing a fairly limited segment of the DMD market, the potential for Summit Therapeutics drug is significant. As a result, investors will want to keep close tabs on the company  in the third quarter, when the full 48-week data is anticipated.