Tiny Bubbles in My Veins?
June 6, 2000 -- It's not exactly what Don Ho envisioned when he sang
"Tiny Bubbles": Floating tiny bubbles to the heart and other organs via
the circulatory system, then using ultrasound technology to pop them once they
reach their destination so they can deliver drug or gene therapy right to the
Smaller than red blood cells -- so there is no risk of them blocking blood
vessels -- the bubbles would be injected into a vein. Once they arrive at the
desired location, they would be popped, or imploded, by ultrasound waves. This
implosion would enable the drug or gene to enter the cells.
A researcher who has helped to develop the so-called microbubble technique,
Evan Unger, MD, of the University of Arizona and president of ImaRx
Therapeutics, presented his findings at an Acoustical Society of America
meeting in Atlanta. Microbubbles already are being used for medical diagnosis,
but not for therapy. In fact, Unger's company developed microbubble diagnostic
tools that were subsequently sold to Du Pont. Now his firm, along with some
others, is focusing on using the bubbles for treatments.
Unger tells WebMD the technique is a promising avenue to site-specific drug
delivery or gene therapy. The basic idea is that by targeting the ultrasound
onto a tumor, for example, the drug attacking the tumor can be much more
And microbubbles aren't just for drugs. In a study in rats, published in
Circulation: Journal of the American Heart Association, researchers used
the technique to deliver genes to the heart.
"It is possible to use ultrasound-mediated microbubble destruction to
deliver genes and other small [agents that are active in the body] directly to
the heart," says study author Paul A. Grayburn, MD. "This method is
noninvasive and could avoid the systemic side effects of medications that are
administered by conventional methods, oral or IV."
Researchers also are studying delivery of genes using a virus, but this is
problematic because the infection is delivered not only to the target organ but
to other tissues as well. In hopes of achieving organ-specific gene delivery,
Grayburn and colleagues introduced a test gene into microbubbles and injected
them into the veins of laboratory rats. Then, using ultrasound, they burst the
bubbles once they reached the heart. The virus then attached and expressed the
gene into the heart muscle, without infecting surrounding tissues.
The heart is not the only organ that could benefit from this "tiny
bubble" technology, Grayburn tells WebMD. "Theoretically, this
technique could be used to treat any kind of disease in an organ or tissue that
is accessible by ultrasound. It should work best for treatments that only
require gene expression for a limited time period, because the body is very
efficient at recognizing and eliminating foreign DNA," says Grayburn, a
professor of internal medicine at the University of Texas Southwestern Medical
Center in Dallas and chief of cardiology at Dallas VA Medical Center.