A new drug against Alzheimer's disease, developed by British researchers, has shown promise in tests on a handful of patients.

A team at the University College London found the small molecule drug caused the disappearance of a protein called SAP, thought to be involved in the disease, from the brains of five Alzheimer's patients who took it for three months.

The results were published in the journal Proceedings of the National Academy of Science.

Britain's Alzheimer's Research Trust, which helped fund the research, said the results with the drug, CPHPC, were cause for "cautious optimism," but it was too soon to know for sure if removing SAP from the brain would provide clinical benefit.

Larger scale clinical studies are now planned.

"New treatments for Alzheimer's disease are desperately needed, and it's possible that this small molecule could be a future candidate," said Trust Chief Executive Rebecca Wood.

Given the world's aging population and the lack of an effective treatment, new medicines for Alzheimer's are seen as a major untapped opportunity for the pharmaceutical industry.

The field, however, is littered with past failures.

Among the furthest advanced experimental drugs for Azheimer's is bapineuzumab from Elan and Wyeth — now being acquired by Pfizer — which produced disappointing clinical trial results last summer.