Chemotherapy Drugs Broke the Blood-Brain Barrier for the First Time

Astronomers once thought that the asteroid belt, the ring of floating space junk that separates Mars from Jupiter, would be difficult for spacecraft to traverse. But on July 16, 1972, Pioneer 10 hurtled past the barrier, opening the path to outer solar system exploration for the first time.

The blood-brain barrier, a highly selective film of cells that stops dangerous neurotoxins and life-saving cancer drugs alike from entering the brain, just had its Pioneer 10 moment.

For the first time, doctors at Toronto's Sunnybrook hospital used ultrasound waves to successfully deliver chemotherapy drugs directly to the affected part of the brain through the blood-brain barrier in an experimental surgery.

If the technique is determined to be safe and replicable, doctors will soon be sending drugs to treat diseases that affect the brain straight to where they'll be most effective, instead of applying a big dose to the body and hoping it works.

"By using a focused ultrasound technique, you can apply chemotherapy directly to a lesion," Allison Bethune, Sunnybrooke's clinical research coordinator for neurosurgery, told me over the phone. "With traditional chemotherapy, you have to apply a large dose that wreaks havoc on the body. This opens the doors to more treatments for other diseases with a similar technique."

Alzheimer's and Parkinson's would be two neurodegenerative diseases that could be treated in the future with drugs that are moved through the blood-brain barrier with ultrasound, Bethune added.

Here's how it worked: the Toronto doctors first introduced medication and tiny "microbubbles" of air to the bloodstream, and then used focused ultrasound waves to force the bubbles to expand and contract in targeted areas of the brain. This expansion and contraction briefly created little tears in the mesh of cells that make up the blood-brain barrier so medication could pass through.

The blood-brain barrier only lets through a limited number of things like water and amino acids, and scientists have been trying to figure out ways to open up or otherwise "trick" the barrier into letting drugs through for some time now. Some suggestions so far have included magnetic nanoparticles and stealthy "Trojan" molecules that disguise antibodies as proteins.

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These approaches are still decades away from being clinically useful, and established methods like like a direct injection are extremely invasive. Using ultrasound is a lot easier on patients than inserting a catheter into the skull, which is the alternative approach to getting drugs into the brain.

Without a good way to bypass through the barrier in very specific locations, medicating the brain is extremely dangerous for patients, Bethune said, and bypassing the blood-brain barrier mitigates this risk.

"If you just give a general dose, you could do a lot of damage in the patient that is treated," Bethune said. "Depending on which side of the brain you're working on, you could risk impairing their speech permanently or leave them paralyzed. You have to be very careful and targeted."

Even though the surgery was an apparent success, there still needs to be some follow-up with the patient and further testing to make sure that the technique really works and is safe. Over the next one or two years, the team at Sunnybrooke hopes to perform the surgery on five to 10 more brave patients willing to undergo the experimental procedure.

The successful surgery is no doubt a first step down a very long road, but one that, at least, we are finally marching down. Decades from now, if the science pans out, nanobots could enter our blood streams and deliver smart drugs to our brains once we let them through by firing ultrasound waves at our heads.