DELIVERING GENES AND DRUGS WITH ULTRASOUND-ACTIVATED BUBBLES. At this week's meeting of the Acoustical Society of America, Evan Unger of the University of Arizona and ImaRx Therapeutics in Tucson (520-770-1259, eunger@imarx.com) presented several new uses for ultrasound contrast agents, micron-sized bubbles that are injected into the bloodstream for medical ultrasound purposes. Traditionally used to enhance ultrasound images of the heart, because they reflect sound so well, the bubbles can now dissolve blood clots and potentially deliver genes and drugs to targeted parts of the body. Introducing the microbubbles into a rabbit's blood vessel, and aiming ultrasound at it, Unger and his coworkers dissolved a blood clot, by causing the bubbles to pop in that location and sweep away the clot in small pieces. In addition, Unger and his colleagues have attached drugs and genes to the microbubbles in several ways. Introducing gene-containing microbubbles into an animal and aiming ultrasound at its heart, the researchers observed significant quantities in the heart of CAT, the protein expressed by the gene.
In traditional gene therapy, the gene is delivered via a modified virus, which may cause serious allergic reactions in some cases. But ultrasound-activated microbubbles may provide a safer alternative, and a more effective one, since the application of ultrasound even without the bubbles seems to enhance the introduction of genes and drugs into cells in many cases. Even without the bubbles, Unger showed that ultrasound enabled the tumor-suppressing drug interleukin-12 to be taken up in 10-1000 times greater amounts in mice. Unger speculated that the microbubbles might someday be used in outpatient heart exams, first to detect plaque, then to dissolve the plaque if it is present. While promising, these applications all require further testing and development.
