Magnets capture cancer cells

Seek and destroy: Magnetic nanoparticles (above, red) coated with cancer-targeting peptides can seek out and glom on to cancer cells like the one shown above. The peptides were designed to bind with a molecule found on the surface of ovarian-cancer cells. Researchers hope to use the nanoparticles to filter cancer cells from the abdominal fluid of patients with ovarian cancer, perhaps preventing metastasis. Credit: J. Am. Chem. Soc. Copyright 2008 American Chemical Society

Magnetic nanoparticles coated with a specialized targeting molecule were able to latch on to cancer cells in mice and drag them out of the body. The results are described in a study published online this month in the Journal of the American Chemical Society. The study's authors, researchers at Georgia Institute of Technology, hope that the new technique will one day provide a way to test for--and potentially even treat--metastatic ovarian cancer.

"It's a fairly novel approach, to use magnetic particles in vivo to try to sequester cancer cells," says Michael King, an associate professor of biomedical engineering at Cornell University, who was not involved in the study.

With ovarian cancer, metastasis occurs when cells slough off the primary tumor and float free in the abdominal cavity. If researchers could use the magnetic nanoparticles to trap drifting cancer cells and pull them out of the abdominal fluid, they could predict and perhaps prevent metastasis. Although the nanoparticles were tested inside the bodies of mice, the authors envision an external device that would remove a patient's abdominal fluid, magnetically filter out the cancer cells, and then return the fluid to the body. After surgery to remove the primary tumor, a patient would undergo the treatment to remove any straggling cancer cells. The researchers are currently developing such a filter and testing it on abdominal fluid from human cancer patients.

"It's possible that the particles may not ever have to go into the patient's body," says John McDonald, chief scientific officer of the Ovarian Cancer Institute at Georgia Tech and a senior author of the paper. "That would be preferable, because then you don't have to worry about any potential toxicity."

The particles, which are just 10 nanometers or less in diameter, have cobalt-spiked magnetite at their core. Most of the time they are not magnetic, but when a magnet is present, they become strongly attracted to it. On the surface of the particles is a peptide--a small, proteinlike molecule--designed to attach to a marker that protrudes from most ovarian cancer cells.

To test the new technology, the researchers injected first cancer cells and then the magnetic nanoparticles into the abdominal cavities of mice. The cancer cells were tagged with a green fluorescent marker, and the nanoparticles with a red one. When the team brought a magnet near each mouse's belly, a concentrated area of green and red glow appeared just under the skin, indicating that the nanoparticles had latched on to the cancer cells and dragged them toward the magnet.