To assure that only diseased cells were destroyed in the experiment, the scientists had to find a way to selectively deliver carbon nanotubes into cancer cells and not into healthy ones. Dai and his co-workers achieved this by performing a bit of biochemical trickery. Unlike normal cells, the surface of a cancer cell contains numerous receptors for a vitamin known as folate. The researchers decided to coat the nanotubes with folate molecules, which would only be attracted to diseased cells with folate receptors.
The experiment worked as predicted. Most of the folate-coated nanotubes ended up inside cancer cells, bypassing the normal cells--like Trojan horses crossing the enemy line. Once the nanotubes were planted inside, the researchers shined the near-infrared laser on the cancer cells, which soon heated up and died.
"Folate is just an experimental model that we used," Dai says. "In reality, there are more interesting ways we can do this. For example, we can attach an antibody to a carbon nanotube to target a particular kind of cancer cell."
One example is lymphoma, or cancer of the lymphatic system. Like many cancers, lymphoma cells have well-defined surface receptors that recognize unique antibodies. When attached to a carbon nanotube, the antibody would play the role of a Trojan horse. Dai and Dean Felsher, a lymphoma researcher in the Stanford School of Medicine, have begun a collaboration using laboratory mice with lymphoma. The researchers want to determine if shining near-infrared light on the animal's skin will destroy lymphatic tumors, while leaving normal cells intact.
"It's a really interesting idea," says Felsher, an assistant professor of medicine and of pathology. "For a long time people have thought about ways to target cancer cells, and this is a very promising technique."
Researchers at Rice University recently conducted a similar experiment on mice with cancerous tumors. Instead of carbon nanotubes, t