Novel Gene Therapy to Clear Blood Clots in Leg Arteries

Stanford researchers have devised a novel approach for delivering a clot-busting gene to blocked leg arteries in animals, effectively restoring blood flow to the damaged vessels, according to a new study presented at the 24th scientific meeting of the Society of Cardiovascular and Interventional Radiology.

The researchers inserted the gene for human tPA (tissue plasminogen activator) into a healthy leg vein in rabbits. The vein began pumping out large quantities of tPA, and then was used as a bypass for an adjacent artery constricted by a blood clot. The procedure reduced clotting by 75% and restored normal blood flow in the legs of treated rabbits, said Michael Kuo, MD, a radiology resident at Stanford University Medical Center and the first author of the study.

Creating Super Veins

“We’re taking a vein and making it into a super structure that is resistant to clots, which are the number one killers in this country,” said Dr. Kuo, who presented the study.

Dr. Kuo said the technique could benefit the millions of patients with peripheral vascular disease. As many as 5% of men and 2.5% of women in the United States 60 years or older have symptoms of peripheral vascular disease.

A current treatment for peripheral vascular disease involves injecting tPA-like clot-busting drugs into the patient’s bloodstream. However, one major drawback of this generalized treatment is that it can induce serious bleeding in the body. This new therapy would sidestep that problem by delivering the gene directly to the site of the blockage.

“Because it’s locally delivered, bleeding is virtually nonexistent,” said Dr. Kuo.

The new technique also has the potential to greatly improve the results of coronary artery bypass surgeries, which often fail as a result of arterial clotting. The artery is particularly prone to clotting within a month of surgery; 10 years after surgery, half of all bypass grafts fail as a result of accelerated plaque build-up that is believed to be related to clotting, he said.

“With our new therapy, we’re technically able to get rid of both the short- and long-term problems,” said Dr. Kuo.

Surgeons could easily adapt the technique to coronary bypass procedures. Theoretically, all they would have to do is inject the tPA gene into the patient’s saphenous vein before removing it from the thigh. The procedure would then follow its standard course, with doctors sewing this clot-resistant super vessel into the patient’s chest to channel blood past the diseased artery, said Dr. Kuo.

The researchers now are moving toward testing the gene in humans.

Animal Study Protocol

In their initial study, the researchers applied the new therapy in rabbits with blocked leg arteries. Two groups of animals served as controls, receiving either a simple saline solution or a different gene. The researchers used an adenovirus to serve as a delivery vehicle for the tPA gene. They inserted the gene into a disabled form of the virus and then injected this newly engineered virus into the femoral vein in the animals’ legs. The veins then began turning out large quantities of tPA.

The researchers applied the therapy in healthy veins because these vessels would be more likely to integrate the gene, said Dr. Kuo. In arteries that are affected by clotting, the plaque forms a barrier to tPA, making it difficult to deliver the gene. The new clot-resistant veins were then transplanted to the site of the diseased arteries. In animals that did not receive the tPA gene, the clot blocked more than 60% of the artery. In the treated animals, the clotting was reduced to 15% of the artery, enough to keep blood flow completely clear, said Dr. Kuo.

The treatment appears to alter the vein so that it becomes more like an artery, capable of handling more circulatory pressure. These super veins are much less likely to fail in the long run, he said.

Dr. Kuo’s colleagues in the study were Michael Dake, MD, associate professor of radiology at Stanford and the principal investigator; Jacob M. Waugh, MD, a research fellow in interventional radiology at Stanford; EserYuksel, MD, clinical professor of plastic surgery at Baylor College of Medicine; and Adam Weinfeld, a medical student at Baylor College of Medicine.

The study was supported by Stanford with no outside funding.