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Following the announcement last year of a highly touted cancer drug which successfully cured Alzheimer's in mice, four separate teams of scientists have now said they were unable to replicate the drug.

Alzheimer's disease is the most common type of dementia - a persistently degenerative loss of cognitive function. Memory, language, judgment, reasoning, planning, and behavior and personality are affected as vital sectors of the brain deteriorate.

"We wanted to repeat the study to see if we could build on it, and we couldn't," said David Borchelt, a professor of neuroscience at the University of Florida, noting that "it was important to publish the fact."

"Maybe there should be some caution going forward in regard to patients," he added.

The high profile February 2012 study in the journal Science found that mice treated with bexarotene became rapidly smarter and the plaque in their brains that was causing Alzheimer's started to disappear within hours. Bexarotene, tradenamed Targretin, is an oral antineoplastic agent specifically designated - by the US Food and Drug Administration (FDA) - for cutaneous T-cell lymphoma, and used as an off-label treatment for lung cancer, breast cancer, and Kaposi's sarcoma (KS).

The study touted that Targretin cured a form of Alzheimer's in a rat model - eliminating the hallmark plaque, clumps of protein known as beta-amyloid, associated with the disease. The study said the mice seemed to recover some cognitive ability. Since then, Targretin was being seen as a possible miracle drug. However, critics argued the effectiveness of the drug on humans, the potential side-effects, and the exorbitant expense of the medication likely not to be covered by insurance - projected to cost patients $14,000 a year.

"It was our expectation other people would be able to repeat this," said Gary Landreth, a neuroscientist at Case Western Reserve University School of Medicine in Cleveland, Ohio.  "Turns out that wasn't the case, and we fundamentally don't understand that." He suggests that the other groups might have used different drug preparations that altered the concentration of bexarotene in the brain or even changed its biological activity.