Studies show mixed success in Alzheimer's fight

All affect message-carrying chemicals in the brain called neurotransmitters. The Medivation drug would offer a different approach. "It's a unique mechanism," Doody said by telephone.

TARGETING PLAQUE

A study by Dr. Clive Holmes of Moorgreen Hospital in Southampton in Britain, involved six-year follow-up of AN1792. The vaccine was one of the first attempts to to reverse formation of plaques in the brain associated with Alzheimer's.

Studies in mice showed immunization against a protein called amyloid beta helped remove plaques, but a study in humans was halted early because some patients developed severe brain inflammation.

Holmes and colleagues followed 80 patients who had been in the study. Tests showed no signs it had any effect on cognitive function. They also did autopsies on eight people who died. "In some cases there was a virtually complete removal of plaques," Holmes said in an e-mail.

But seven out of the eight, including those with virtually complete plaque removal, had severe end-stage dementia before death. "It strongly suggests that plaques are not sufficient on their own to account for disease progression," Holmes said.

Dr. Peter St George-Hyslop of the University of Cambridge said in a commentary, "This study will undoubtedly evoke concern that anti-amyloid therapies will be ineffectual, and that two decades of experimental work supporting their development were spent barking up the wrong tree."

While not a cure, he said the approach may still slow progression of the disease.

Elan and Wyeth now have hopes for bapineuzumab, an antibody drug that fights beta amyloid plaques, in late-stage clinical trials after success in some patients in a smaller study. Alzheimer's affects 26 million people worldwide. (Editing by Maggie Fox and Jackie Frank)