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Dr. Gary Landreth in the new Alzheimer's lab in the Robins Health Center at Case Western Reserve University in Cleveland, Ohio.

David Ahntholz

A drug currently used to fight cancer may also double as a powerful weapon against Alzheimer's disease – a dramatic finding giving hope where little has existed.

In a landmark study, U.S. researchers gave bexarotene to mice whose brains were clogged with deposits of amyloid-beta plaque – a potentially harmful protein associated with Alzheimer's disease.

After just several days of treatment, 75 per cent of the plaque was cleared from the mouse brains and the rodents experienced a personality transformation. They showed improvements in memory, cognitive abilities, and social behaviour, as well as their sense of smell, according to the findings published Friday Feb. 10 in the journal Science.

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"The remarkable thing is how efficient this drug is at removing amyloid from the brain," said the senior researcher, Gary Landreth, at Case Western Reserve University School of Medicine in Cleveland.

Everyone's brain produces some amyloid for normal functioning. In healthy individuals, excess levels are routinely removed with the aid of a protein called ApoE. But in people prone to Alzheimer's, amyloid plaque builds up between nerve cells, eventually leading to interference in memory and other mental processes.

The researchers believe bexarotene activates a gene that increases the production of ApoE which, in turn, starts rapidly removing the amyloid deposits.

"What we are doing is stimulating the normal mechanism by which amyloid is cleared from the brain. So we are just revving up Mother Nature, " explained one of the researchers, Paige Cramer, a doctoral student at the university.

Bexarotene seems to provide a ray of hope in a field of research marked by setbacks and failure. There are no known treatments that can halt the mind-robbing disease.

Even so, Dr. Landreth insisted it's far too soon to consider bexarotene a breakthrough.

"I would like to say loudly and clearly," he warned, "we have to be cautious about extrapolating to whether this is going to work in humans."

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The genetically engineered mice used in the experiment don't develop the human variant of Alzheimer's. And, in particular, Alzheimer's in humans also involves another protein, called tau, that sometimes forms fibrous tangles, which are linked to the death of brain cells.

That means bexarotene may be able to rid the human brain of amyloid deposits, but a patient's symptoms might not improve significantly if tau remains a problem.

The researchers are already making plans for further studies.

Large-scale human trials could start fairly soon because it has already been demonstrated that patients can tolerate the drug – a key consideration for any new or experimental medication.

"We know it is safe in people because it has been in use for 10 years," said Ms. Cramer. "Some of the hoops have already been jumped for us."

Bexarotene, also known by the brand name of Targretin, is primarily used to treat a type of non-Hodgkin's lymphoma of the skin called cutaneous T-cell lymphoma.

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