A drug used to treat leukaemia has been shown to improve cognitive function and physical movement in patients with Parkinson's disease.
The small clinical trial of 12 people found that the drug 'nilotinib' encouraged significant changes in toxic proteins found in the brains of those with the disease.
Participants who received the drug were found to have more efficient cognitive function.
One individual who was confined to a wheelchair was able to walk again, while three participants who could not talk were able to hold conversations.
Fernando Pagan, one of the researchers involved in the study, said: "To my knowledge, this study represents the first time a therapy appears to reverse - to a greater or lesser degree depending on stage of disease - cognitive and motor decline in patients with these neurodegenerative disorders."
Parkinson’s disease is a condition in which parts of the brain become progressively damaged over many years. The three main symptoms are: tremors, slow movement, and stiff, inflexible muscles.
'Nilotinib' works by helping to clear toxic proteins found in the brain, which are associated with the disease.
Alan Hoffman, a retired professor at Georgia State University, was diagnosed with Parkinson's in 1997. He participated in the latest 'nilotinib' trials.
"Before the 'nilotinib', I did almost nothing around the house," he said. "Now, I empty the garbage, unload the dishwasher, load the washer and the dryer, set the table, even take responsibility for grilling."
Hoffman said he fell eight times in the three weeks prior to enrolling in the study, but only fell once during six months on the study. His speech has improved, as has his thinking.
"My wife says it's life-changing for her and for my children and grandchildren," Hoffman said. "To say that 'nilotinib' has made a change in our lives is a huge understatement."
Hoffman, alongside the other 10 Parkinson's patients, was given an escalating daily dose of 'nilotinib' (between 150 and 300mg) over a period of six months.
Out of the 11 people participating in the study, 10 of them exhibited meaningful clinical improvements.
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"Study participants with earlier stage disease responded best, as did those diagnosed with Lewy body dementia, often described as a combination of Parkinson's and Alzheimer's diseases," said Pagan.
But he said it is now "critical" to conduct larger studies before scientists can determine the drug's true impact.
The study's primary objective was to test safety. Researchers said that use of 'nilotinib', in doses much smaller than are used to treat cancer (which is up to 800 mg daily), was well tolerated with no serious side effects.
'Nilotinib' was first discovered as a potential Parkinson's treatment by Dr Charbel Moussa from Georgetown University Medical Centre in Washington DC.