Riding a Wave of Sound
One way to get drugs through the blood-brain barrier: smuggle them across using sound waves.
The blood-brain barrier, a name given to the tightly packed vascular cells in the brain’s capillaries, keeps the central nervous system remarkably free of most pathogens. But that defense is a major challenge for delivering drugs that treat brain disorders. One reason glioblastoma, an aggressive brain cancer, is so lethal is that treatments can’t get across the barrier to reach tumors.
A growing number of researchers see promise in focused ultrasound (FUS), a technique that uses sound waves to cause a targeted breach. During the past year, the first trials of FUS for patients with Alzheimer’s disease have taken place, with encouraging results that suggest the technology may be safe and technically feasible for other hard-to-treat brain diseases, as well.
Sounds in the ultrasound range have a frequency higher than 20kHz, which is the limit of most human hearing. In the 1930s and 1940s, researchers realized that these quickly oscillating waves could be focused on a fixed point to create an intense heat, a discovery that was first tested therapeutically in 1954 as a non-surgical alternative to lobotomies. The technology was tested by directing sound waves into the brain.
The idea of using focused ultrasound to breach the blood-brain barrier has been around for decades, but the challenge has been to keep the disruption temporary and not cause permanent damage. Some investigations have looked at a powerful form of FUS, high-frequency focused ultrasound (HiFU), which can burn away cells and is currently used to destroy tumors and reduce painful bone metastases from cancer.
A study on rabbits published in 2001 led the way to a new method of using lower-frequency focused ultrasound, guided by MRI, to temporarily open the capillary walls. It was the first nondestructive approach to opening the blood-brain barrier, and laid the groundwork for new experimental ways to help targeted chemotherapies, beneficial viruses, stem cells and nanoparticles get past the barrier to the brain, though studies to date have been almost exclusively in animals.
Read more at Proto magazine, here.
Image: Proto