Ultrasound boosts drug delivery to tumors. (Biomedicine: From Chicago, at the 87th annual meeting of the Radiological Society of North America).

A beam of ultrasound can make the blood vessels that infiltrate cancerous growths leakier than normal, a process that might be used to increase the dose of anticancer drugs reaching tumors from the bloodstream.

Physicians already use ultrasound to identify tumors in the liver and to guide biopsy procedures, says Jonathan B. Kruskal of Beth Israel Deaconess Medical Center in Boston. Meanwhile, cardiology research has hinted that ultrasound might make blood vessels more permeable.

So Kruskal and his colleagues injected human liver cancer cells into 14 mice and waited 8 days for liver tumors to grow. Then, the researchers injected microbeads containing the fluorescent molecule doxyrubicin into a large blood vessel feeding the liver in each mouse. An hour and a half later, the team directed a burst of ultrasound at one lobe of each animal's liver. As a final step, the researchers looked for fluorescence in lobes that had received ultrasound and lobes that hadn't.

Among the mice, there were 56 tumors in parts of the liver that got ultrasound and 64 in parts that didn't. The tumors that received the ultrasound fluoresced twice as brightly as the tumors that weren't exposed to ultrasound, Kruskal reports. The ultrasound seems to increase delivery of the microbeads to the tumor and to increase the percentage of spheres that release doxyrubicin, he says.

This technology theoretically would enable doctors to give lower doses of an anticancer drug to a patient--thus reducing side effects--while still delivering effective doses to tumors, Kruskal says. The Boston researchers don't know yet whether such drug delivery might help an animal survive longer than they do with conventional methods.

Side effects from the ultrasound itself appear unlikely. "Nothing suggests there is any significant increase in permeability in nontumor tissues," says Kruskal. In fact, the same frequency of ultrasound he used in the tests is already used widely for various medical procedures, Kruskal says. --D.C.