Raptor jumps as its Huntington's hopeful slows the loss of muscle control

Raptor Pharmaceutical's ($RPTP) investigational Huntington's disease drug helped delay the progression of the brain-deteriorating disorder in a subset of patients, the company said, news that sent the biotech's shares soaring despite some lingering concerns with the data.

In a 96-patient Phase II/III study, Raptor's RP103 slowed the loss of muscle of control in Huntington's patients compared to placebo, according to the company, but the drug's effect only reached statistical significance in those not concurrently taking a treatment for involuntary movements. Looking at 18 months of data from the planned three-year study, Raptor said RP103 delayed the progress of spasms and uncontrollable movements by just 32% across all patients, but it did so by a clinically valid 58% in the 66 subjects not taking Lundbeck's Xenazine.

Raptor's spin is that the full analysis "showed a positive trend" toward the trial's primary endpoint, and that was good enough for investors, as the company's shares leapt as much as 30% in premarket trading Thursday. And that positive trend could help Raptor win FDA approval and get its second product to market, Chief Medical Officer Dr. Patrice Rioux said, following the rare-disease drug Procysbi.

"We are thrilled to build on these results and will engage regulatory agencies to discuss the most efficient means to advance this program to potential approval," Rioux said in a statement. "These results not only support the safety and efficacy of Raptor's RP103 in Huntington's disease, but also the rationale for testing the use of RP103 in other indications such as [nonalcoholic fatty liver disease], Leigh syndrome and mitochondrial diseases."

Raptor allowed the patients in the positive subset to stay on their drug regimens because of the long duration of the study, the company said, and, in addition to Xenazine, some were taking antidepressants. On the safety side, the most common adverse events were nausea, vomiting, abdominal pain, constipation and bad breath, according to Raptor.

- read the statement