Any parent fretting about the fever of a child knows that temperatures a few degrees above normal can kill. But cancer researchers have now found a way to cure high temperatures. In a new study, a team found that injecting mice with tiny magnets and start up the heat eliminated tumors in animal body, without apparent side effects.
The idea of killing the cancer with heat is not new. Researchers know that, like normal cells, cancer cells start to die when the mercury rises above 43˚C. The trick is how to kill the cancer without damaging the cells of the body. A promising idea, known as magnetic hyperthermia, involves injecting "nanoparticles" essentially tiny microscopic bits of iron oxide or other compounds in tumors to make them magnetic. The patient is placed in a magnetic field that changes direction thousands of times per second. Magnetic nanoparticles are excited by the applied field and start to get hot, heating and potentially destroy the tissue surrounding cancer. Because the healthy tissue is not altered by the magnetic field, it does not heat and are not damaged.
But the therapy has not yet made its way to the clinic, with only one trial reported in humans (with limited success). This is largely because conventional nanoparticles interact weakly with the applied field, so a large dose quite is required to generate sufficient heat to damage the tumor. Although nanoparticles are not particularly toxic in large quantities, they can trigger the body's immune system to attack, causing allergic reactions.
Nanoscientist Cheon Jinwoo of Yonsei University in Seoul and colleagues set out to create a nanoparticle that would get hotter than traditional nanoparticle so not much would need to be injected into the body. They nanoparticles in two layers, each containing a core of a magnetic mineral within an envelope of another. Due to an interaction between the two esoteric mineral, called exchange coupling, these nanoparticles "core-shell" interacted more strongly with the magnetic field to traditional nanoparticles and released 10 times more heat. This means that we would need to give only 10% of the initial dose for patients to achieve the same degree of hyperthermia with conventional nanoparticles.
The team tested the technique on three mice whose abdomens had been grafted with human brain cancer cells. The researchers injected tumors with core-shell nanoparticles and placed mice in a coil of wire (see illustration). They are focused on an alternating current in the coil, creating a magnetic alternating field. While researchers are not able to measure the exact temperature inside tumors, their estimates range between 43˚ and 48C. After 10 minutes, the team removed the mouse from the coil and monitoring of tumors for the next 4 weeks.
All traces of cancer have disappeared from the mice without apparent side effects, the team reported online June 26 in Nature Nanotechnology . For comparison, another group of mice were treated instead with a single dose of doxorubicin, a traditional anticancer drug. Although initially shrunk some tumors, they pushed to four times their original size at the end of the trial. The heat treatment after injection of traditional nanoparticles of iron oxide had no significant effect on the tumors.
Nanoengineer Naomi Halas of Rice University in Houston, Texas, is impressed. "This group has solved the key impasse that has stopped the development of magnetic nanotherapies, that is, the poor response of the nanoparticle to the applied magnetic field," she said. "I am so happy that many of these types of hyperthermic therapies based on nanoparticles are developed to increase the arsenal of weapons against cancer."
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