A brain tumor patient was treated with an innovative technique that allows to deliver drugs to the brain via bloodstream. The chemotherapy agent was able to breach the blood-brain barrier thanks to the co-injection of gas bubbles and the application of ultrasound waves to the skull. Changes in the size of the bubbles in the bloodstream opened temporary holes in the barrier. The study, by researchers at Sunnybrook Health Sciences Centre in Toronto, was announced by the Focused Ultrasound Foundation.
The blood-brain barrier is a protective layer of tightly packed cells that line the blood vessels in the brain to avoid damaging molecules access to the neuronal tissue. While it prevents toxins from entering the brain, the barrier is also an obstacle for drug delivery to treat Parkinson´s, Alzheimer´s and other brain diseases. Alternative options exist, but present serious limitations. Direct injection of drugs in the brain can cause infection or permanent damage. Manitol administration into the bloodstream opens up the barrier, but it is non-selective and affects blood pressure.
Treating brain cancer with ultrasounds and gas bubbles
The research team at Sunnybrook decided to start a pilot study to treat brain tumor patients with an ultrasound-based, non-invasive technique. In the focused ultrasound technique, several beams of ultrasound are directed to a convergent point, where they exert their effects, which vary depeding on the tissue and the ultrasound parameters. Ultrasound beams don´t affect the regions they pass through, so the target can be deep inside a tissue. Kullervo Hynynen, PhD and Todd Mainprize, MD directed the first ever use of focused ultrasound to deliver a chemotherapy agent to the brain of a patient. Doxorubicin and tiny gas bubbles where injected into the bloodstream. Then, focused ultrasound was directed to specific brain areas, causing the bubbles to vibrate and expand, temporarily opening small holes between the cells that form the blood-brain barrier. This allowed the drug to enter the selected brain regions. An MRI scan confirmed that the barrier had been open. Eventually, the team extracted the tumor and is now analyzing the concentration of drug that penetrated the tissue.
The success of this trial opens the door to using focused ultrasound to treat other neurological conditions. Nanoparticles, viral vectors or antibodies could be delivered to the brain non-invasively.