

Flying across the blood-brain barrier with microbubbles


Brain of an activist
The brain is very good at keeping things out. That's both a good and a bad thing. Department of Psychology, Cornell University

The blood-brain barrier refers to a protective sheath of endothelial cells that wraps around the blood vessels in our brains, keeping damaging substances away from our precious gray matter. The trouble is, the BBB can also keep out valuable life-saving drugs like chemotherapy compounds that destroy tumors.

To overcome the stubborn nature of the BBB and sneak chemotherapy drugs around tumors, Kullervo Hynynen, a medical physicist at Tornoto's Sunnybrook Research Institute, plans to use a novel approach: microbubbles.

These tiny structures are about the size of a red blood cell and consist of a core of gas surrounded by a shell of surfactants, lipids, proteins, polymers, or a combination of all four, according to a paper written by Shashank Sirsi and Mark Borden from Columbia University's Department of Chemical Engineering. They have been used for years to increase contrast in medical tests like echocardiograms and ultrasounds and have the unique property of oscillating when beamed with ultrasonic waves.

Hynynen's plan is to work with a team of doctors to inject 10 brain-cancer patients with chemotherapy drugs, followed by microbubbles. He'll then beam the microbubbles with high-frequency ultrasound which will cause them to expand and contract approximately 200,000 times per second, according to a report in New Scientist. This should force the endothelial cells apart, allowing the tumor-destroying compounds to enter the brain and attack the tumor at nine different points. The tumors will then be removed and analyzed to see if there are more chemo drugs in the areas in which they were hit by the ultrasonic waves.

In addition to using this technique to fight brain cancer, Hynynen believes it could also allow a more effective treatment of Alzheimer's disease by delivering antibodies to the brain that fight the disease-causing protein plaques. "We think trials of these antibodies in humans failed because researchers haven't managed to get a high enough dose into the brain," he told New Scientist. "So we hope to try these drugs in humans in the future, maybe as soon as a year, depending on how well this first trial goes."