WEDNESDAY, July 24, 2013 (HealthDay News) -- Yet another experimental drug has failed to help those who have Alzheimer's disease.
The drug, called semagacestat, was designed to block an enzyme called gamma secretase that makes beta amyloid, a sticky protein that clogs the brains of patients with the memory-robbing disease.
Animal studies and early human trials had suggested that the drug did what it was designed to do, but in a test of the medication in more than 1,500 patients with mild to moderate Alzheimer's, those taking semagacestat actually declined faster on thinking tests than those who took a dummy pill.
And those on the drug experienced more serious side effects, including skin cancers and infections.
The study results were published in the July 25 issue of The New England Journal of Medicine.
"You've got a very clear look at some not good results here," said study author Dr. Rachelle Doody, a neurologist with the Baylor College of Medicine in Houston.
Semagacestat is just the latest in a string of medications being tested for Alzheimer's that have faltered in late-stage clinical trials, and it is the second drug in its class to be shelved because it didn't work.
Last November, Bristol-Meyers Squibb announced that it was pulling the plug on its gamma secretase inhibitor, avagacestat.
"It clearly leads to the conclusion that targeting gamma secretase as a way to reduce amyloid simply doesn't work," said Steven Ferris, director of the Alzheimer's Disease Center at NYU's Langone Medical Center in New York City. "It doesn't appear that this is a promising target for treatment."
Researchers hope that studying why drugs like this fail may help drug manufacturers learn from their mistakes and pave the way for future successes.
Eli Lilly stopped the trial early, in 2010, after preliminary analysis of the data suggested safety problems with the medication.
The company then turned over all its study data to the Alzheimer's Disease Cooperative Study, a project of the U.S. National Institutes of Health, for independent analysis.
"In the Alzheimer's field, that's unprecedented," Doody said. "There's never been an industry group that's turned over their data and said, 'We're giving up our rights to publish the data.'"
Doody said Lilly deserves a lot of credit for its efforts to get unbiased information to the public.
"Those on the drug did worse, and that's a very important thing to get out to the public," she said.
For more on drugs in development to treat Alzheimer's disease, visit the Alzheimer's Association.