Ultragenyx under pressure as seizure drug fails phase 2 test

Ultragenyx is still hopeful for a positive outcome in a larger movement disorder trial due in a few weeks.

Shares in Ultragenyx Pharmaceutical weakened after a midpipeline drug candidate missed its targets in a trial for a rare genetic disorder, leaving it with fingers crossed for a study of another drug due to report in the coming weeks.

The phase 2 trial involved patients with glucose transporter type 1 deficiency syndrome (G1DS), a genetic defect in glucose metabolism which is linked to epileptic seizures and movement impairment. Ultragenyx's drug—called triheptanoin (UX007)—was able to cut the seizure rate by around 13% compared to placebo in the trial after eight weeks' treatment, but that wasn't enough to reach statistical significance.

Cue the modest sell-off in shares, but analysts at Leerink have been quick to suggest that the reaction is a tad overblown. In fact, they say it represents a buying opportunity ahead of the read-out of a phase 3 trial of Ultragenyx's lead drug KRN23 for the rare bone disease X-linked hypophosphatemia (XLH), due in the first half of this year, which they reckon is a lower-risk program.

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"Unlike the G1DS program, we previously highlighted our optimism surrounding the XLH program including consistently positive data in both pediatric and adult patients, as well as the breakthrough therapy designation … and the expectation of a regulatory filing in 2H17," said Leerink. KRN23 has already been submitted for XLH in Europe, and a verdict should be forthcoming before the end of the year.

Drilling down into the phase 2 UX007 data, 2013 Fierce 15 company Ultragenyx said that while it failed on the top-line measure, its drug was able to cut absence seizures—a brief loss and recovery of consciousness—which Ultragenyx CEO Emil Kakkis, M.D., Ph.D., said pointed to a "clinically meaningful effect."

The company has previously billed the seizure trial as an add-on to a larger assessment of UX007 in G1DS patients with movement disorders, which could provide results next year. For now, it's saying it will "continue to evaluate our plans in the seizure indication."

Overall, the effect of the drug was "lackluster" and "disappointing," said Leerink, and they don't share the company's optimism on the absence seizure data. Nevertheless, they still have hopes for the G1DS movement disorder study, pointing out that an earlier trial showed a "robust reduction" in intermittent symptoms such as muscle spasms.

Ultragenyx already has phase 2 data in hand from a small trial of UX007 in long-chain fatty acid oxidation disorders which showed a significant reduction in both the frequency and duration of major clinical events, including hospitalizations, and is working on the design of a phase 3 trial.

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