In a study, "Rapid Selection of Cyclic Peptides that Reducealpha-Synuclein Toxicity in Yeast and Animal Models," published online inmid-July by Nature Chemical Biology, theNINDS-funded researchers showed that they can save yeast cells from the toxiceffects of a protein implicated in Parkinson's disease by stimulating thoseyeast cells to make very small proteins called cyclic peptides. Two of thecyclic peptides had a protective effect on the yeast cells and on neurons in ananimal model of Parkinson's disease.
"This biological approach to compound development opens upan entirely new direction for drug discovery, not only for Parkinson's disease,but theoretically for any disease where key aspects of the pathology can bereproduced in yeast," says Dr. Margaret Sutherland, a program director atNINDS. "A key step for the future will be to identify the cellular pathwaysthat are affected by these cyclic peptides."
The findings comes out of work at the lab of Dr. SusanLindquist, Ph.D., a professor of biology at the Massachusetts Institute ofTechnology (MIT), a member of the Whitehead Institute for Biomedical Research,and a Howard Hughes Medical Institute investigator. Lindquist is also aninvestigator at the Massachusetts General Hospital/MIT Morris K. Udall Centerfor Excellence in Parkinson's Research, one of 14 centers funded by NINDS todevelop treatment breakthroughs for Parkinson's disease.
Dr. Joshua Kritzer, a chemist and postdoctoral fellow inLindquist's lab, designed and executed the cyclic peptide strategy and, as heputs it, "We are making the yeast do a ton of work for us. They make thecompounds and then they tell us which ones are functional."
Out of a library of 50 million cyclic peptides, only twosaved the yeast from alpha-synuclein toxicity, the researchers note. Looking atthe Parkinson's work specifically, Kritzer notes that he and colleagues exposedyeast cells to short snippets of DNA that the cells can absorb and use to makecyclic peptides. Then, they turned on the genetic switch that causes the cellsto produce toxic levels of alpha-synuclein. If the yeast made cyclic peptidesthat suppressed alpha-synuclein toxicity, they lived; if not, they died.
As the NINDS notes, this simple assay allowed for thetesting of millions of cyclic peptides (CPs) simultaneously in millions ofyeast cells. The process is, therefore, "extremely rapid and much lessexpensive compared to other techniques used to screen large number of chemicalswith an eye toward new drugs," notes the NINDS.
As the researchers wrote in their paper, "Hits can berapidly identified using selections or screens that sort millions of CPs in asingle day without expensive robotics. In selections using our yeastsynucleinopathy model, we isolated two hits from an original pool of 5 millionafter only a single round of selection. Although more rounds of selection werenot required for selections in the synucleinopathy model, we note that multiplerounds of selection could be performed by pooling colonies and amplifying theirplasmids en masse."
"Our technique, which capitalizes on a long line ofinvestigation in my lab, will lead to a whole new way to obtain small moleculetools useful for improving our understanding of disease mechanisms and fordeveloping new therapies," says Lindquist, noting that her lab and others havemodeled many human diseases in yeast and in other kinds of cells.
The findings are exciting, notes the NINDS, because of thelack of treatment options for Parkinson's disease. A synthetic precursor ofdopamine called L-DOPA, or drugs that mimic dopamine's action, can providesymptomatic relief from Parkinson's disease, but these drugs lose much of theireffectiveness in later stages of the disease. Moreover, there is currently noway to substantially slow the progression of Parkinson's disease.
What remains unknown, however, is why the cyclic peptidesseem to be protective. They found that the cyclic peptides do not affect asystem of transport inside cells known as vesicle trafficking. This came as asurprise, given that alpha-synuclein and other proteins that have beenimplicated in human Parkinson's disease are believed to play a role in vesicletrafficking. However, the researchers observed that the two peptides share astructure that may hold clues to their targets.The researchers are conducting further experiments toexplore how cyclic peptides prevent cell death. They are also adapting their systemfor making cyclic peptides so that it can be used in other cell types(including human cells) and other diseases.