Magnets can be used for much more than attaching a photo to your fridge – someday they may be used to treat brain cancer.
Scientists have been able to guide microscopic magnetic particles coated with an anti-cancer drug to brain tumors brains in rats. The researchers, who are from the Chang-Gung University College of Medicine and Memorial Hospital in Taiwan, reported their results in the August 10 in Proceedings of the National Academy of Sciences.
“Magnet-targeted therapy could potentially be an exciting new way tool to fight cancer,” said Allan David, an assistant professor of pharmacy at University of Michigan, who was not involved in the study. “However, this method is still far from being used to treat humans with brain cancer.”
While nano-based treatments have generally shown promise in animals it has been difficult to devise a treatment for humans that does not damage healthy tissue. In addition, nanoparticles — though so small that up to 100,000 of them side by side would equal the width of a human hair — can still be too large to cross the brain’s protective shield (known as the blood-brain barrier).
The blood-brain barrier, a tightly packed network of small blood vessels, typically protects the brain from invading pathogens. In people with brain tumors, this barrier develops some holes, allowing more things to get through.
“However, even with these gaps in the blood-brain barrier, typically a very low quantity of drug-coated nanoparticles — about 0.1 percent — actually make it to the tumor,” said David. “This means large quantities of the particles are circulating through other parts of the brain or the rest of the body, and may be toxic.”
Previous research has shown that a magnetic pulse from an ultrasound can disrupt the blood-brain barrier for several hours, potentially creating more avenues for drugs to find tumors.
That is exactly what Kuo-Chen Wei and his colleagues from Chang-Gung University decided to try. They injected rats with nanoparticles specially designed to have magnetic properties, and temporarily disrupted the rats’ blood-brain barrier using an ultrasound. The researchers then used a magnet to guide these nanoparticles to the specific tumor sites.
During the 7-day treatment period, tumor size increased by 100 percent in the 11 rats treated with both ultrasound and the targeted magnet, while the tumor grew more than 300 percent in 12 untreated rats. The combination treatment permitted the most drug-coated nanoparticles to accumulate around tumors in the brain. Overall, the rats treated with the combination therapy survived 30 days (66 percent longer) than the untreated rats who survived 18 days.
“The numbers here are not terribly impressive,” said David. “We would ideally want to see a decrease in tumor size in the rats, not just that the tumor grew more slowly.”
J?rg Kreuter, a professor at Johann Wolfgang Goethe-University in Germany, who focuses on nanoparticle therapies, said previous studies using nanoparticles without a magnet have shown more promise. In 2008, Kreuter injected nanoparticles coated with an anti-cancer drug into rats and found that the animals not only lived longer but 20 to 40 percent of them experienced complete tumor remission.
Kreuter, who was not involved in the current research, also points out that using an ultrasound to disrupt the blood-brain barrier “is a big concern.” This could expose the brain to toxic molecules, he said.
The study coauthor Pin-Yuan Chen said that, “We did not observe any obvious side effect in these rats in 40 days after treatment. However, the long-term side effects need to be evaluated further.”
