Alnylam Hemophilia Drug Shows Early Success Among Hard-to-Treat

  • Interim data presented at San Diego blood disease conference
  • Majority of patients haven’t bled since starting the drug

Alnylam Pharmaceuticals Inc.’s experimental hemophilia drug helped control bleeding among hard-to-treat patients in an early-stage trial, suggesting it may compete with an expected blockbuster from Roche Holding AG if further tests succeed.

Fifty-six percent of patients on Alnylam’s drug, called fitusiran, haven’t bled since starting therapy, according to interim data the company presented Saturday at the American Society of Hematology meeting in San Diego. The 16 hemophilia patients in the study had inhibitors, immune proteins that interfere with the most common type of drug used to treat the bleeding disorder.

“These patients typically have higher morbidity, higher mortality and it really is at the pinnacle of the problems that can emerge in people living with hemophilia,” Chief Executive Officer John Maraganore said by phone, calling the results “very promising.”

Roche is running a late-stage trial of its own drug, called emicizumab, that’s designed to repress bleeding among some hemophilia patients with inhibitors. The drug has shown it can reduce the number of times patients bleed, but investors have been concerned about four cases of blood clots reported last month among those who took emicizumab in combination with existing drugs, called bypassing agents, that are typically used when patients are resistant to more common therapies. In Alnylam’s smaller study there were no such complications in patients who took a bypassing agent as well as fitusiran, Maraganore said.

Bleed Rate

“These results are at least as good as what’s been presented for emicizumab,” Maraganore said. The company will start a late-stage study of fitusiran next year, he said.

Hemophilia drugs are evaluated according to median bleed rate, the midpoint number of bleeding events per patient in a given group. Before entering Alnylam’s study, the median bleed rate over a year for the group was 31; in the early results from the trial, it was zero.

Three of the 16 patients had higher-than-normal liver enzyme levels, an early sign of possible damage, though all of them also have had the liver disease hepatitis C. The raised levels were reversible and didn’t cause symptoms, Alnylam said.

RNA Interference

Alnylam’s drugs use a technology called RNA interference that inhibits cellular messages involved in making protein. A small number of patients in a trial of an Alnylam drug being developed with Medicines Co. to reduce cholesterol levels also showed elevated liver enzymes.

Alnylam plunged in October after reporting that, in a study of a rare protein disease, more patient who were taking the company’s drug died than among those on placebo. The company is still investigating, Maraganore said, and hopes to have some answers later this month.

“There’s no obvious immediate ‘aha’ type of thing,” he said. There may have been a difference in the severity of existing disease between patients taking the drug and those on placebo, he said, though that’s uncertain.

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