Many human diseases—including cancer—are caused by protein malfunctions. Those malfunctions, in turn, are caused by damaged DNA that gets translated into the damaged proteins. While many clinicians and scientists are trying to treat those diseases by fixing the DNA, Ron Raines is taking a different approach—he’s looking to replace the proteins directly.
“Our strategy is to do gene therapy without the genes,” explains Raines, a professor of biochemistry. “We want to skip the genes and go right to the proteins.”
The strategy is intriguing, but there’s a problem. Proteins have a hard time getting into cells where they would do their work. The lipid bilayer of a cell membrane serves as a barrier that keeps the inside of the cell in and the outside out. That membrane stops potential intruders—including uninvited proteins—from entering.
Raines and his team have found a way around this in what amounts to a kind of biochemical calling card. They can attach “decorations,” using what is called an ester bond, to the protein to change its characteristics. The ester bonds link the protein to a “moiety,” a molecule that gives the protein a desired attribute or function.
“Moieties could encourage cell entry, which is one of our major goals,” says Raines. “But moieties could also enhance the movement of the protein in an animal body. Or they could be agents that target the protein, for example, to cancer cells specifically.”
Modifying proteins to give them these attributes has been done using other approaches, but those changes are permanent and can cause problems. The modified protein might not function normally, or the immune system might see the protein as foreign and mount an attack.
Raines’ strategy avoids these problems by using reversible modifications. Because the moieties are added using ester bonds, they are removed once inside a target cell. Naturally occurring enzymes in the cell—called esterases—sever the ester bonds and break off the moieties. What’s left is the normal protein without any decorations. That protein can then do its job.
“We don’t have the problem of damaging the function of the protein or of an immune response because what we ultimately deliver will be the wild-type protein, the protein as it’s naturally found in cells,” explains Raines.
The strategy is promising, and the Wisconsin Alumni Research Foundation (WARF) already has patent applications for it on file. Raines’ lab is now working to make adding the decorations as straightforward and user-friendly as possible. That way, scientists and clinicians could add a moiety of their choosing and get the protein to perform its desired function.
Raines sees innumerable possibilities.
“We’re very excited about this because it has a lot of potential,” he says. “We can now decorate proteins reversibly with pretty much any molecule you can imagine. We are exploring the possibilities to try to bring something closer to the clinic.”