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[DewDiligence]

Abbott Progresses on Dissolving Stent

http://www.businessweek.com/technology/content/oct2008/tc20081013_902359.htm

›October 14, 2008
By John Carey

The best stent may be one that disappears, according to new data presented at a meeting of cardiologists in Washington, D.C., on Oct. 13.

For years, surgeons have used small mesh tubes called stents to prop open narrow arteries. Such stents, made by Boston Scientific (BSX), Johnson & Johnson (JNJ), and Guidant, acquired by Abbott Laboratories (ABT) in 2006, have become a huge business, racking up more than $5 billion in sales per year.

But stents are not a perfect device. After a bare metal stent is inserted in a damaged vessel, new layers of cells grow over the metal as part of the healing process. That's a good thing. Problems come, however, when the healing is too vigorous, and the resulting layer of cells is too thick. The vessel narrows again, causing symptoms like chest pain. About 20% to 30% of patients who get such bare stents eventually have this problem, called restenosis.

To tackle this problem, scientists and companies developed stents impregnated with drugs designed to slow the healing process, keeping the vessels clear longer. This class of stent quickly captured more than 90% of the market after being introduced in 2003. But it isn't without problems either. "Delaying healing is a double-edged sword," explains Dr. Remu Virmani, head of the nonprofit CVPath Institute in Maryland. In some cases, the site of the stent remains an unhealed wound. That can lead to a deadly clot. As a result, many cardiologists now recommend that patients who have received these stents must take blood-thinning drugs, like Plavix, which is marketed by Bristol-Myers Squibb (BMY) and Sanofi-Aventis (SNY). Plus, having a metal stent implanted in an artery makes it difficult to image the blood vessel using an MRI because the metal gets in the way.

A Bit Like Bioabsorbing Sutures

In the meantime, however, researchers have been working on another approach to stents. What if the device itself was made of a material that eventually dissolves, like bioabsorbing sutures? That way, the stent could prop open a damaged artery long enough to help it to heal. But once the job is done, it would disappear completely, leaving nothing behind. "Philosophically, why have a permanent implant if a temporary one can do the job?" asks Dr. John Ormiston of the Auckland City Hospital in New Zealand. Think of a cast for a broken arm. You wouldn't leave it on after the arm is healed.

Boston Scientific, Biotronik in Germany, Guidant, and others have been working on an absorbable stent. It hasn't been easy. Some prototypes dissolved too quickly. Others haven't been successful holding the arteries open. But now, Abbott is reporting some success with a small clinical trial conducted at sites in New Zealand and Europe. Thirty patients received the company's experimental dissolvable stent and have been followed for two years. The company presented the data at the Transcatheter Cardiovascular Therapeutics meeting in Washington.

With the exception of one patient who had a mild heart attack early on, the trial has been very encouraging, principal investigator Ormiston says. "We've learned it is safe and effective," he says. "It's all pretty amazing."

Normal blood vessels expand and contract in response to various stimuli. That can't happen after metal stents have been implanted. But in the bioabsorbable stent trial, the vessels appeared to return to normal. "We found that the vessel can expand and contract," Ormiston says. "The artery is more normal. That's a good thing. It means there's less chance of thrombosis [i.e. clotting]."

Up Next: An 80-Patient Trial

Ormiston and representatives from Abbott say they are proceeding slowly and cautiously with the new device. They've learned, for instance, that it needs to be improved. The original device shrank a bit after implanting. The next trial, which will include 80 patients, will use a somewhat stronger version of the stent.

Researchers not affiliated with the trials warn that these are early days for bioabsorbable stents. "It's an interesting concept, and theoretically it could reduce the risk of late-stage thrombosis," says Dr. Steven Nissen, chairman of the department of cardiovascular medicine at Cleveland Clinic. "But to find out, we'll need a really big study."

Abbott and Ormiston are hopeful the next studies will show that the device will deliver on the promise. "We have to be cautious," Ormiston says. "But I think it…could be a huge step forward for patients."‹