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NEW INTERVENTIONAL TREATMENT MAY PROVIDE LONG-SOUGHT ANSWER TO PREVENT BLOOD VESSELS FROM RE-CLOGGING

San Francisco -- Taxol (Tm)-coated stents are showing promise as a possible solution to the stubborn problem of restenosis, the re-clogging of blood vessels, which is the most common cause of failure in angioplasty, researchers announced here today at the 23rd Annual Meeting of the Society of Cardiovascular & Interventional Radiology (SCVIR).

Researchers at the National Institutes of Health (NIH), the University of British Columbia Hospital in Vancouver and St. Guy's Hospital, London, have found they can prevent tissue growth using stents, which are tiny metal cylinders that act as scaffolding to hold open blood vessels. The stents are coated with a slow-release form of Taxol, a chemotherapeutic drug originally developed to treat ovarian, breast and other cancers.

"We have had success implanting Taxol-coated stents in people with esophageal cancer, so we know that humans can tolerate slow release of the drug," said researcher Lindsay Machan, M.D., head of angiography and interventional radiology, University of British Columbia Hospital. "We're confident it will be beneficial in human blood vessels, as well."

Researchers at the University of British Columbia Hospital and the NIH have separately conducted a number of animal studies that found Taxol consistently effective in preventing blood vessels from re-clogging, a very common medical problem. Clinical studies to test the therapy in humans are planned shortly at both institutions.

After angioplasty to open clogged blood vessels, restenosis develops 30 percent to 50 percent of the time in coronary, pelvic and thigh arteries, and more often in arteries below the knees. Doctors then need to do either another angioplasty, place a stent, or do bypass surgery, which is a major procedure. Roughly 750,000 angioplasties are performed in the United States each year; another 75,000 are performed in Canada.

The early studies have been promising. In one University of British Columbia Hospital study, researchers applied three variations of Taxol directly to the damaged neck arteries of 60 rats; 10 control rats with damaged carotid arteries were not treated. All 10 of the control rats developed significant scarring in the artery, while none receiving Taxol developed scarring. Early results show Taxol-coated stents implanted in the iliac arteries of pigs beneficial in preventing restenosis as well.

"Although it is too early to say definitively, this could be huge," said Dr. Machan. "We believe this is the most significant potential answer to this problem."

NIH researchers have had success applying Taxol directly to the carotid artery of rats and Taxol-coated stents in the iliac (pelvic) artery of rabbits. Early NIH results indicate Taxol-coated stents implanted in the coronary arteries of pigs also prevents restenosis.

To implant a stent in a clogged blood vessel in an angioplasty procedure, an interventional radiologist makes a quarter-inch skin nick, typically in the groin or neck, and, under imaging guidance, advances a catheter, or tube, through the blood vessel to the site of the blockage. Typically, a tiny balloon is inflated to stretch open the blood vessel, and the stent is then deployed and left behind to keep the vessel open.

While angioplasty is generally preferred over the more invasive bypass surgery, the procedure itself can cause a subsequent narrowing of the vessel and growth of scar-like tissue inside the vessel that re-clogs the opening.

Stents are commonly implanted to counteract the narrowing of blood vessels, but they don't prevent the benign tissue growth. The researchers are hopeful Taxol will be the answer to that problem.

Derived from the bark of the Pacific yew tree and now partially synthesized, Taxol is used in chemotherapy to treat metastatic breast and ovarian cancer in far greater amounts than that used to coat stents. It might eventually be developed for use in site-specific chemotherapy, notes Dr, Machan.

"Taxol is like aspirin we're finding more uses for it other than what was originally intended," said Dr. Machan.

The clogging of blood vessels, called atherosclerosis, is a gradual process in which cholesterol and scar tissue build up inside the artery, forming plaque. Depending on the site of the atherosclerosis, the condition can cause a heart attack, stroke or peripheral vascular disease. Factors that contribute to the disease include smoking, high blood pressure, diabetes, high cholesterol, a family history of heart or vascular disease, or being overweight.

For years, doctors have been searching for a way to prevent restenosis. Researchers also are studying the effects of radiation on restenosis.

"It may turn out the radiation treatment works out for one area of the body, Taxol for another," said Dr. Machan.

In the University of British Columbia Hospital/St. Guy's Hospital study of patients with esophageal cancer, none of the 10 patients who received Taxol-coated stents experienced significant tumor growth into the esophagus after 6 months; 3 of 11 who received uncoated stents experienced significant tumor ingrowth. Although the treatment is not a cure, it provides relief for end-stage esophageal cancer patients who usually have difficulty eating and swallowing.

For the procedure, an interventional radiologist uses x-ray imaging to guide the Taxol-coated stent down the throat to the esophagus, where it expands to the size of the esophagus and props it open. Taxol on the coated stent is released slowly to inhibit the growth of blood vessels that feed the tumor, limiting tumor growth. Implanting the stents in the esophagus provided evidence that humans can tolerate the slow-release Taxol, said Dr. Machan.

Co-authors of a paper on Taxol usage to prevent restenosis in rats and pigs being presented by Dr. Machan are Pierre Signore, Ph.D., Peter Bromley, M.D. and Bill Hunter, M.D.

Co-authors of a paper on esophageal Taxol-stenting being presented by Dr. Machan are Mark Cowling, M.D., Andy Adam, M.B., Nicholas Maynard, M.B. and Richard Mason, M.B.

An estimated 1,700 physicians are attending the annual scientific meeting in San Francisco, of SCVIR, a professional society of more than 3,000 members based in Fairfax, Va., for physicians who specialize in minimally invasive interventional procedures.

An interventional radiologist is a physician who has special training to diagnose and treat illness using miniature tools and imaging guidance. Typically, the interventional radiologist performs procedures through very small incisions in the skin, about the size of a pencil tip. Interventional radiology treatments are generally easier for the patient than surgery because they involve smaller incisions, less pain and shorter hospital stays. # # #