Scientists at Johns Hopkins, New York University and Mount Sinai School of Medicine in New York have found a way to block the action of specific enzymes with a pivotal role in triggering certain autoimmune diseases such as rheumatoid arthritis.
Their research, described in last month’s Nature Structural Biology, explains how a blockading molecule, called a bisubstrate analog, effectively prevents protein kinase enzymes from docking with other molecules in the body — in short, from working. “The bisubstrate analogs are extremely potent in inhibiting reactions,” says Philip A. Cole, M.D., Ph.D., who led the research.
The researchers designed the bisubstrate analog using an improved understanding of how protein kinases normally work at the molecular level. They liken their work to the science that produced the protease inhibiting drugs that tipped the disease scales from fatal to chronic for many AIDS sufferers. “We don’t have a drug for patients yet, but this is still a real advance in the field,” Cole adds.
Protein kinases are widespread in the body. “About 2 percent of our genes code for protein kinases,” says Cole. The enzymes help ferry a small, reactive cluster of atoms containing phosphorus — called a phosphoryl group — to cell proteins. Once thought to be a mere housekeeping procedure, this transfer, researchers now know, is crucial to cells. Once a protein gains a phosphoryl group, Cole says, the protein changes, becoming a key player in cell reactions that prompt growth and reproduction.
Experiments show that too much of a particular kinase can lead to tumors, and that autoimmune diseases such as arthritis and other inflammatory conditions probably involve kinases that are too efficient or overactive. “Finding a way to inhibit them is probably a very good idea,” Cole adds. “Our work may be particularly helpful in developing therapies for cancers,” says Cole, “which can stem from mutations in genes that regulate kinases.”
Unlike other approaches to block protein kinases, the researchers say, the new technique works both on the molecules that donate the phosphoryl groups and on the protein molecules that accept them. Their bisubstrate analog simultaneously attaches to both molecules, crowding out protein kinases.
Most important, Cole says, is that their approach targets specific protein kinases. “There are probably several thousand different kinases with roles in different disease pathways. The biggest problem has been singling out specific ones to inhibit,” he says. Minor tinkering with bisubstrate analogs may produce a wide variety of the molecular red herrings, each designed to counteract a specific protein kinase.
Cole’s team now plans versions of the analogs that can persist long enough in the human body to be useful therapy.