WASHINGTON: A widely available cancer drug has shown remarkable success in reversing Alzheimer's disease in mice, raising hope of a breakthrough against incurable dementia in humans, US researchers said Thursday.

Mice treated with the drug, known as bexarotene, became rapidly smarter and the plaque in their brains that was causing their Alzheimer's started to disappear within hours, said the research in the journal Science.

“We were shocked and amazed,” lead author Gary Landreth of the Department of Neurosciences at Case Western Reserve University School of Medicine in Ohio told AFP.

“Things like this had never, ever been seen before,” he said. The drug works by boosting levels of a protein, Apolipoprotein E (ApoE), that helps clear amyloid plaque buildup in the brain, a key hallmark of Alzheimer's disease.

“Think of this as a garbage disposal,” Landreth said.

“When we are young and healthy, all of us can basically get rid of this (amyloid) and degrade it and grind it into small bits and it gets cleared.

“Many of us will be unable to do this as efficiently as we age. And this is associated with mental decline or cognitive impairment.”Six hours after mice got the drug, soluble amyloid levels fell by 25 per cent, ultimately reaching 75 per cent reductions. The effect lasted up to three days, said the study.

Soon after taking the drug, mice performed better on tests of mental ability and showed improved responses to odors.

Unlike normal mice, Alzheimer's mice will not usually build nests if given tissue paper in their cage, as if they have forgotten to associate paper with the opportunity to nest. But 72 hours after treatment, the Alzheimer's mice began to build nests again.

“They are not great nests but they are nests nonetheless,” added Landreth, suggesting that if the drug can be shown to work in humans it might be best targeted to people in the early stages of the disease.

Clinical trials in people should begin soon and produce early results in the next year, researchers said. Bexarotene was initially made by US-based Ligand Pharmaceuticals under the brand name Targretin.

It gained orphan drug status in the United States, approval by the US Food and Drug Administration, in 1999 as a treatment for cutaneous T-cell lymphoma, a rare cancer.

The Japanese pharmaceutical giant Eisai bought the worldwide rights for it in 2006. Bexarotene is now available in 26 countries in Europe, North America and South America.