NBC News - An experimental drug to treat Parkinson's disease damaged the lungs of monkeys, and it almost certainly would do the same to people, researchers reported Wednesday.

It's unusual for medical journals to report on drugs that fail, but most do fail before they are ever tested in humans. This report, published in the journal Science Translational Medicine, illustrates the pitfalls of drug development.

The vast, scientific plain that potential drugs must survive before reaching human trials is dubbed the "Valley of Death" — and this once-promising drug has likely fallen into it. The National Institutes of Health estimates that as many as 90 percent of experimental drugs never make it to testing in humans.

Reina Fuji of drugmaker Genentech Inc. and colleagues were testing a drug that interferes with a compound called leucine-rich repeat kinase 2 (LRRK2). Mutations in the gene that produces LRRK2 have been linked with Parkinson's disease. The mutations appear to cause overproduction of LRRK2.

The idea was to make a drug that reduces overproduction of LRRK2. It looked good in mice. But when it was tested in monkeys, the drug damaged their lungs.

That might make for "a critical safety liability" for human patients, they concluded.

http://www.nbcnews.com/health/health-news/potential-parkinsons-drug-too-toxic-use-n300241