This Slide Paints Grim Picture of Glaxo, Prosensa's DMD Drug

MONTEREY, Calif. ( TheStreet) -- The slide above depicts the failure of GlaxoSmithKline ( GSK) and Prosensa's ( RNA) drisapersen to improve the walking ability of boys with Duchenne muscular dystrophy. The companies announced the disappointing results from the drisapersen trial on Sept. 20 but detailed data were presented Saturday at the World Muscle Society meeting.

What you're looking at in the slide above is pretty much the worst-case scenario for drisapersen. Sarepta Therapeutics ( SRPT) no longer has to be concerned with competition from Glaxo and Prosensa, regardless of whether FDA approves eteplirsen quickly or asks for a pre-approval phase III study.

The two curves represent the six-minute walk distance of the DMD boys over the 48 weeks of the drisapersen phase III study. Look how the green line -- the boys treated with drisapersen -- slopes down immediately. At 12 weeks, the first assessment after randomization, the drisapersen boys are already losing the ability to walk. There isn't a hint of drisapersen efficacy, nothing to suggest the drug can even stabilize the DMD boys.

The boys on placebo (the blue line) are also losing the ability to walk at almost the same rate. At weeks 12 and 24, the drisapersen boys are only walking 5 meters more than the placebo boys.

At week 36, the difference between the two groups of patients is less than 2 meters.

Note the two curves in this slide are offset so you can see them better. Without the offset, the blue and green lines would sit almost exactly on top of each other.

Between weeks 36 and 48, the rate of walking decline for the placebo boys accelerates a little bit so the difference in the six-minute walk test at week 48 grows to 10 meters. That's the largest difference observed in the study but it's hardly a positive for Glaxo and Prosensa because at no point during the study do the drisapersen boys improve or even stabilize.

Here is the conclusion slide from the phase III presentation:

The drisapersen phase III study presented Saturday look a lot different from results of the drisapersen phase II study presented last April.

Glaxo and Prosensa are conducting more analysis of the phase III study, looking at different subgroups of patients to figure out what went wrong and see if drisapersen can be salvaged. The outcome of these analyses should be completed by the end of the year.

At this point, the chance of a drisapersen comeback seems low.

Sarepta shares have jumped from $36 to $53 since the drisapersen failure. The heightened risk FDA asks for a pre-approval phase III study of eteplirsen has been eclipsed by the disappearance of a major competitor.

Speaking of eteplirsen, the 96-week data on six-minute walk from Sarepta's phase II were also presented this weekend at the World Muscle Society meeting. Here's what those data look like graphically:

-- Reported by Adam Feuerstein in Boston.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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