Isis hits Ph3 endpoint but shares slide on liver worries

Researchers for Genzyme (GENZ) and Isis Pharmaceuticals (ISIS) trumpeted the success of their cholesterol drug mipomersen in a late-stage trial, but investors heard a sour note when the side affects were discussed. Isis shares dropped 20 percent as analysts sounded off on their concerns about the drug's impact on the liver.

Mipomersen was successful in hitting the primary endpoint in the trial, which enrolled 124 patients with a rare genetic disorder characterized by a high level of cholesterol. Their bad cholesterol dropped 28 percent in patients with heterozygous familial hypercholesterolemia.

But the patients also suffered a spike in liver enzymes, a classic red flag for any clinical trial. Isis executives said that the spike wasn't unexpected in this type of trial and may even have been inflated somewhat because of the particularly close attention that was paid to the biomarker. Some analysts, though, weren't easily mollified by the explanation.

"We continue to see significant risk for mipomersen beyond the ultra-niche indication... and see little probability of significant sales until at least an outcomes trial is completed in the middle part of this decade," said Morgan Stanley's Steven Harr. Quite a few investors agreed.

- check out Isis' press release
- read the story from Dow Jones