CHICAGO (Reuters) - Despite some recent dramatic failures, Alzheimer's disease researchers say they have never been more encouraged by the wealth of promising new treatments being studied for the brain-wasting disease.
"Twenty years ago we were at zero," said Dr. Steven DeKosky of the University of Pittsburgh, who has been studying the problem of addressing Alzheimer's for three decades.
DeKosky led one of three panels focused on new therapies featured this week at the International Conference on Alzheimer's Disease in Chicago.
There is no cure for Alzheimer's, the most common form of dementia, and current drugs merely delay symptoms a bit.
While the most advanced drugs have focused on removing clumps of beta amyloid protein that forms plaques in the brain, researchers got their first look at therapies to address the toxic tangles caused by an abnormal build-up of the protein tau.
One, a nasal spray made by Allon Therapeutics Inc, improved some measures of memory in patients with mild cognitive impairment, a precursor to Alzheimer's, researchers reported this week. They said findings from the three-month study were strong enough for a longer, larger study.
Another, called Rember, is a refined version of an older drug used to treat urinary tract infections called methylthioninium chloride or methylene blue.
Researchers said the drug significantly improved key measures of thinking and memory in some people with moderate Alzheimer's disease for more than a year and a half.
TARGETING THE TANGLE
"We now show for the first time it is possible to halt the progression of Alzheimer's disease by targeting the tangle," Claude Wischik, of the University of Aberdeen in Scotland and chairman of TauRX Therapeutics in Singapore, told the meeting.
Wischik said he thinks the compound keeps the tau protein from forming tangles inside brain cells and eventually from bursting them open.
"I can't make any statements about safety and efficacy," he added.
Another promising drug is Medivation Inc's Dimebon, developed in Russia as an antihistamine. An 18-month study of 183 patients done in that country showed it was safe and produced a persistent benefit.
How Dimebon works is not clear. Researchers said it may help protect mitochondria, the energy powerhouses of cells.
"It has many effects as opposed to having one single effect," said Dr. Scott Turner, the incoming director of the Memory Disorders Program at Georgetown University Medical Center in Washington.
Turner said more studies will be needed to show whether Dimebon offers an advance over current treatments.
New attempts at targeting beta amyloid include a drug called PBT2 from Prana Biotechnology Ltd, which aims to keep beta amyloid from interacting with copper and zinc in the brain, a process involved in plaque formation.
In another new approach, Baxter International Inc said an intravenous therapy of antibodies derived from human plasma called Gammagard helped preserve and in some cases improve cognitive function in a nine-month study.
"We're fascinated by the mechanism, but we know nothing about whether it will be useful long-term," DeKosky said of the study.
This path of attempting to alter the course of Alzheimer's by attacking beta amyloid has been littered with disappointments.
Last August, a drug by Canadian biotech Bellus Health , formerly known as Neurochem Inc, failed to show a benefit in a study of more than 1,000 patients.
Last month, Flurizan, also known as tarenflurbil, failed to help patients in a pivotal clinical test, dealing a blow to its backers Myriad Genetics and Lundbeck .
This week, shares of Elan and Wyeth plunged on news of a weaker-than-hoped-for response in a mid-stage study of its new antibody therapy bapineuzumab. Researchers are still hopeful this drug, or one like it, will work.
"There are lots of curve balls in this research and we are not having an easy time," said Marcelle Morrison-Bogorad, director of Alzheimer's research at the National Institute on Aging.
Meanwhile, the need for effective therapies is pressing.
An estimated 5.2 million people in the United States have Alzheimer's, according to the Alzheimer's Association, and 26 million globally -- a number projected to grow to 106 million by 2050. (Editing by Maggie Fox and Xavier Briand)