Keeping It Clear: Improving the Outlook for Heart Patients

Mark Kester doesn't have to look far for an example of the relevance of his research. He can point to the world's most famous heart patient.

red drawing of heart and circulatory system

In November 2000, U.S. vice president Dick Cheney, a veteran of four heart attacks and one bypass surgery, underwent balloon angioplasty to clear a plaque-clogged artery near his heart. A slim catheter tipped with a latex balloon was inserted in the femoral artery in Cheney's groin. Fitted over the catheter was a stainless-steel stent—a wire-mesh cylinder resembling the spring from a ballpoint pen. The device was threaded into the proper position, as determined by x-rays. Once in place, the balloon was inflated, forcing the artery open and at the same time expanding the stent and locking it into place. Then the balloon was deflated and removed, the stent remaining as permanent scaffolding.

All went well until four months later, when Cheney complained to his cardiologist of burning in his chest, a sign that the artery was closing down again. The doctors call it restenosis.

"It's not plaque re-accumulating," says Kester, professor of pharmacology at Penn State's Hershey Medical Center. "It's smooth muscle cells, pushing through the damaged arterial wall. They've been activated, they're angry, and they're responding to having this metal or this balloon pushed against them." He picks up a poster with drawings of normal and narrowed arteries in cross-section. "These cells divide out of control, and the only place they have to go is into the lumen, the opening that carries the blood."

Since it was first performed in 1977 by a German surgeon named Andreas Gruentzig, balloon angioplasty has become an immensely popular procedure. About a million coronary angioplasties are done in the U.S. each year, and another 500,000 elsewhere in the world. In most of those cases, the procedure saves patients from a far more serious step: open-chest surgery and heart bypass. But for 20 to 30 percent of angioplasty patients, including Cheney, restenosis is severe enough that a second procedure is required after only six months.

"So again this group has the risk of complications that goes along with the procedure, not to mention the trauma," Kester says. "These are patients who were sent home 24 hours after balloon angioplasty—it's basically an outpatient procedure now—and told that if they change their lifestyle, watch what they eat, they're going to be fine. They're thinking, 'I beat a heart attack.' Then this happens. That's the kind of trauma I'm talking about."

A lot of medical effort has been expended trying to prevent restenosis. Various drugs have been tried—mostly anti-inflammatories and platelet inhibitors—but none have been very effective. The mesh stent, standard procedure in about 90 percent of cases, cuts down substantially on the rate of closure from scarring and other causes, but stents may actually stimulate the proliferation of smooth muscle cells, Kester says. The most promising approach so far has been radiation, which involves sending a tiny string of irradiated beads, via catheter, to the stent site for a fixed period of time. But radiation "is a drastic therapy. It kills everything," Kester says. And the long-term side-effects are not known.

"A therapy effective against restenosis has been kind of the holy grail of cardiovascular pharmacology," Kester says. Now, in what is literally a byproduct of his explorations into basic cell signaling, Kester may have found the prize.

Signaling is the process by which information is relayed from a cell's surface to its nucleus: crucial instructions for growth, proliferation, and death. A chemical messenger, in the form of a hormone or other protein, is dispatched by the initiating cell to finds its way to the surface of the cell that is its chosen target. There it docks with a specific receptor—a protein or complex that responds to it like a lock to the proper key. Once activated, the receptor releases other proteins inside the cell, kicking off the "cascade" of reactions that ultimately delivers the message to the cell's command center.

These cascades, or pathways, can be anywhere from fairly simple to extremely complex. But what makes understanding cell-signaling really interesting, Kester says, is that the individual pathways interact and overlap.

"You can think of it like a New York City subway map, with 47 trains intersecting at multiple stations," Kester says.

He shifts analogies. "There's always a yin and yang in a cell, never just one mechanism. There are always multiple pathways telling the cell to grow, and multiple pathways telling it to stop growing. It's the cross-talk between pro and con pathways that determines the cell's ultimate fate."

For the last ten years, Kester has been focused on tapping into the cross-talk inside smooth muscle cells. "We've looked especially at the role played by second messengers," he says. Second messengers are exactly what they sound like: proteins released inside the cell after the first messenger makes contact. They are relay runners, a way to get the signal through the cell wall, which is otherwise impermeable. Recently, however, researchers have found that wall itself, in addition to providing a barrier, plays a role in communication. Specifically, lipids, the fatty, water-resistant molecules that make up a major structural component of the membrane, are involved in signaling.

"Our major hypothesis was that lipids are not inert, they are bioactive," Kester says. "They break down, and in the process they create by-products." One of these by-products, a molecule called ceramide, turns out to contain powerful information regarding cell growth. "Ceramide can bind to and interact with certain proteins within a smooth muscle cell," Kester says. When it does, it suspends the cell's growth. Ceramide is a second messenger.

Intrigued, Kester spent the next several years working out the details of the ceramide pathway using cell cultures. ("I am now the world expert on how ceramide can stop smooth-muscle-cell growth on cells growing on plastic," he says, with a quick smile.) It works, he found, by binding to precise targets in the cell which inactivate certain critical proteins that are a link in the pro-growth response. If these proteins don't turn on, the signal can't get through. The "start dividing" message never gets to the nucleus.

Once he had conquered the biochemistry, Kester started to scout around for ways that his discovery could be, as he puts it, "kicked up a notch, and applied to the human condition." Not surprising for a pharmacologist, an expert in metabolic processes and drug interactions. Even so, moving from basic science to possible clinical application was moving into new territory, taking time and effort away from the work he knew (and knew he could get funding for), and putting it into something that was far from a sure bet.

"It requires a leap of faith," Kester acknowledges. "But Penn State allowed me to take the risk. They encouraged me to explore the clinical possibilities."

One that jumped out right away was restenosis. "It's basically a complication of wound-healing," Kester explains. The arterial wall is made up of a thin layer of endothelial cells backed by a thick weave of smooth muscle cells whose strength and flexibility give the vessel its definition. During angioplasty, the press of the expanding balloon stretches and injures the endothelial lining. The endothelial cells respond by secreting substances that promote repair. Where a stent is placed, these cells actually "grow around and through the stent and re-endothelialize it," Kester says: they make it part of the wall.

The problem is, the repair-promoting substances also activate the smooth muscle cells behind the endothelium. These cells, too, begin to grow and proliferate. Soon, they migrate through the remodeling endothelium and into the lumen. In rabbits, Kester has observed, within four weeks the artery is completely closed.

"What is needed is something that would stop those smooth muscle cells from growing, while still allowing the endothelium to heal," he says. It seemed a perfect spot for ceramide.

Kester figured from the start that the substance would have to be delivered directly. "Most of the drugs that had been tried for preventing restenosis had been given orally," he says. "They didn't target the damaged area." But if you could put the medicine directly on the balloon—better yet, on the stent—you could get the ceramide right to the angioplasty site. A stent coated with a slow-release, cell-permeable form of ceramide could deliver the drug over a period of weeks.

"There are other companies trying to develop applications using coated stents," Kester says. "Some of the major pharmaceutical companies are working on this. But none of them are using ceramide. They're using anti-rejection drugs, or anti-cancer drugs." As with radiation, the effect is both more drastic—the cells involved are killed—and less discriminating, impacting epithelial cells as well as smooth muscle cells.

Ceramide works more like a designer drug: it targets smooth muscle cells, but lets epithelial cells alone. Importantly, however, ceramide is not a drug, Kester stresses: "It's a product of your metabolism. Your body recognizes it as self, not an organically synthesized molecule." And ceramide's action is relatively gentle: while it halts smooth muscle cells in the no-growth state, it does not kill them.

Kester went to Penn State's Intellectual Property Office with his idea, and papers were filed for a provisional patent. Then IPO director Ron Huss and assistant vice president for technology transfer Gary Weber started looking for a licensing partner, a company that would be willing to invest money in development in exchange for rights to market a product if Kester's idea comes to fruition.

Kester, meanwhile, went back to the lab. With funding from the W.W. Smith Charitable Trust, a Pennsylvania-based foundation that supports emerging clinical technologies, he began the long and unfamiliar process of testing the effects of ceramide in a series of animal models.

To do so, he first had to put together both a scientific team and a clinical one. For the first, Kester recruited Lakshman Sandirasegarane and Jong Yun, both assistant professors of pharmacology; technician Roger Charles and Ph.D. student Nicole Bourbon; and Steve Levison and Ray Rothstein from the department of neuroscience and anatomy. On the clinical side he had radiologist Peter Waybill, cardiologist Mark Kozak, and veterinary surgeon Ronald Wilson.

For the first set of experiments, Kester and his team coated balloon catheters with a cell-permeable form of ceramide and then performed angioplasties on rabbit carotid arteries. Two weeks after the procedure they compared ceramide-treated arteries against those that had been stretched without application of the lipid.

The results were dramatic. In quantitative terms, restenosis in ceramide-treated arteries was decreased by over 90 percent. "It's rare these days to see in vivo results match in vitro results so well," says Jong Yun. The findings were published in the cardiology journal Circulation Research in September 2000.

There's now a patent pending on Kester's device, and after a number of companies expressed interest, Weber says, the idea has now been licensed. But there's a lot that remains to be done before a ceramide-coated stent might become an option for cardiac patients. The first step, Kester says, is more animal trials. "This time we'll try it with rabbits fed a high-cholesterol diet," to see if it works as well in plaque-filled arteries as in healthy ones. "Then, we'll move up to pigs." Human trials, he says, are a year or two away.

Another task will be to perfect the coating and delivery process. "An advantage of the balloon is that it pushes the cell-permeable ceramide into the cells in adequate dosages to be effective," Kester says. "One thing we're working on now is learning how long from the time of the original trauma ceramide should remain bioactive. You don't want it to go on forever—after healing you want the ceramide to go away."

Nor is there anything like a guarantee that Kester's laboratory results will translate to clinical success. "Many of these therapies don't work out," he says flatly. "The human body is a lot more complicated than animal models, with redundancy and compensatory mechanisms built in. We still have a lot to learn.

"Even though we're very excited," in other words, "it's still preliminary," he says. But the potential benefit, both human and commercial, is huge. That's why Kester's work was mentioned-along with the Penn State artificial heart-when Pennsylvania governor Tom Ridge visited Hershey Medical Center in April to promote his Life Sciences Greenhouse initiative. The "greenhouse" plan would use some $90 million of the state's anticipated share of national tobacco settlement proceeds to create centers for commercializing new discoveries in the life sciences.

Being singled out as a "poster boy" for technology transfer, as Kester puts it, is okay with him. "I think this kind of transitional research is the future.

"There's a lot that has to happen before a discovery becomes a product," he explains. "Refinement, scale-up, clinical trials…. Getting FDA approval for this device will take years.

"I've been able to do it all thus far in my lab, with the help of a lot of dedicated people. But having a reliable infrastructure in place could make it happen a lot quicker."

Mark Kester, Ph.D., is professor of pharmacology in the College of Medicine, Hershey Medical Center, 500 University Drive, Box 850, Hershey, PA 17033; 717-531-8964; mxk38@psu.edu. The work reported above was supported by grants from the W.W. Smith Charitable Trust and from the National Institutes of Health.

Last Updated January 01, 2002