Studies show mixed success in Alzheimer's fight

By Julie Steenhuysen

CHICAGO, July 17 (Reuters) - A new drug showed promise at treating Alzheimer's disease, but an experimental vaccine that cleared brain-clogging plaques failed to improve memory or help patients live longer, researchers said on Thursday.

One of two studies, conducted in Russia and published in the journal Lancet, showed Medivation Inc's (MDVN.O) drug Dimebon, first approved in Russia as an antihistamine, improved thinking processes and ability to function in patients with mild to moderate Alzheimer's disease.

A second showed that an experimental vaccine by Elan Corp (ELN.I) and Wyeth WYE.N known as AN1792 may have removed signature plaques from patients' brains, but they all developed severe dementia anyway.

Dimebon helped keep Alzheimer's from progressing for more than a year. "It's a strong signal," said Dr. Rachelle Doody of Baylor College of Medicine in Houston.

Doody said the drug helped improve five measures of memory and function.

It is not yet clear how the drug works, but Doody said it appears to protect the energy powerhouses in cells known as mitochondria, which are often destroyed in neurodegenerative diseases.

Medivation, which helped design the study, earlier this month said Dimebon significantly improved cognitive function in patients with Huntington's disease, which causes uncontrolled movement and loss of thinking ability.

If proven to work in a larger study, the drug could add to a limited pool of approved drugs, which include Eisai (4523.T) and Pfizer's (PFE.N) Aricept, Forest Laboratories' FRX.N Namenda, Novartis' (NOVN.VX) Exelon and Johnson & Johnson's (JNJ.N) Razadyne.