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It did appear "relatively safe" among the dozen patients studied, said Dr. Charbel Moussa, the senior researcher on the work.
One patient had to withdraw from the study because of heart complications. But the drug was "well tolerated" in the remaining patients, according to Moussa, an assistant professor of neurology at Georgetown University Medical Center, in Washington, D.C.
Plus, he said, there were hints of benefit.
The researchers found signs that the drug boosted the brain's production of dopamine, a chemical that helps regulate movement. It also appeared to reduce certain "toxic proteins" that build up in the brains of people with Parkinson's.
On top of that, the patients typically showed some improvement in both physical symptoms and problems with memory and thinking, the findings showed.
"I think this is a very promising beginning," Moussa said.
But he also emphasized how much remains to be seen.
"We have to be very cautious about the safety profile of this drug in Parkinson's patients," Moussa said. "We also need to clarify the symptom areas that it may benefit, [and] how and when should this drug be used."
That cautious tone was echoed by James Beck, vice president of scientific affairs for the Parkinson's Disease Foundation.
"It's still the early days," said Beck, who wasn't involved in the research.
He pointed to a number of issues that make it difficult to know how nilotinib could fit into Parkinson's treatment, if at all.
And since the study was designed only as an early "proof of concept," it lacked the rigors that are used in later-stage trials: There was no comparison group given a placebo (inactive treatment), Beck said, and all of the study patients (and researchers) knew they were on the drug.
Moussa acknowledged those limitations. He said his team is planning two trials that will put nilotinib to a tougher test -- where patients will be randomly assigned to take either the drug or a placebo.
One study, Moussa said, will include patients with moderate-stage Parkinson's. The other will focus on people with mild to moderate Alzheimer's disease -- since there is evidence the drug could affect dementia symptoms.
Nearly one million Americans and up to 10 million people worldwide have Parkinson's, according to the Parkinson's Disease Foundation.
It is a chronic, progressive movement disorder that causes tremors, stiffness in the limbs, slowed movement and problems with balance and coordination. Most people also have symptoms that are unrelated to movement, according to the foundation. For some, those include memory issues, fuzzy thinking or even full-blown dementia.
No one is sure exactly what causes Parkinson's, but it involves the death of certain brain cells -- including ones that produce dopamine, which help regulate movement.
For the past 50 years, the mainstay of Parkinson's treatment has been levodopa, a drug that boosts brain dopamine levels.
"But what we've all been waiting for," Beck said, "is a treatment that can actually alter the course of Parkinson's."
According to Moussa, nilotinib "gets more to the roots" of Parkinson's.
Lab research has shown that small amounts of nilotinib can reach the brain, and help cells shed toxic proteins without killing the cell itself, Moussa said.
"The drug acts like a switch," he explained. "It turns on the 'garbage disposal mechanism' in the cell, so it can get rid of toxic proteins."
For the current study, Moussa's team had 12 patients take low doses of nilotinib every day for six months. One patient had to withdraw after one month because he had a heart attack.
Nilotinib carries a boxed warning about potentially risky changes in heart rhythm. That's a concern, Beck said, because Parkinson's patients are generally older and often have other conditions that can raise their risk of heart problems.
He also said the improvements in patients' symptoms are "difficult to interpret."
The improvements happened quickly -- within a month, Beck pointed out. That, he said, suggests a "symptomatic benefit" only, due to higher dopamine levels, rather than any shift in the course of the disease.
With nilotinib already on the market, some patients and doctors might be tempted to try it without more evidence, Moussa acknowledged. But he cautioned against that.
"We should not rush to conclusions," he said.
The study was supported by government and philanthropic funds. Moussa is listed as an inventor on a Georgetown University patent application related to the use of tyrosine kinase inhibitors for treating Parkinson's and other neurodegenerative diseases.
The findings are published in the July 11 issue of the Journal of the Parkinson's Disease.
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