TUESDAY, Nov. 4, 2003 (HealthDayNews) -- New experiments in the science of the super-small suggest that nanoshells coated with gold and placed into cancerous tumors will kill only malignant cells when external near-infrared light is applied.
The nanoshells used in these experiments are microscopic silica beads, according to the report in this week's issue of the Proceedings of the National Academy of Sciences.
A gold coating is used because it absorbs energy turning it into heat, and can also carry biological markers that direct the nanoshells to their target tissues.
Nanotechnology is the study of finding practical uses of minuscule items, and in medicine it is how to insert those items in a body in a way to heal. Researchers study at the level of a nanometer, which is so small it would take 80,000 of them to equal the diameter of a human hair.
The research team speculated that when near-infrared light -- a type of low-energy radiation that does not affect living cells -- was applied to the nanoshells, they would become hot enough to kill the tumor cells, but the tissue outside the tumor would be unaffected.
"We can use nanoshells as a localized heat source in tissues to heat the cells to 55 degrees Celsius [131 degrees Fahrenheit] to induce cell death," says co-researcher Naomi Halas, a professor of electrical and computer engineering and a professor of chemistry at Rice University.
The researchers tested their technique on human breast cancer cells and on cancerous tumors grown on mice. In each case, the combination of nanoshells and near-infrared light caused irreversible heat damage to tumor cells while leaving surrounding tissue unharmed.
These nanoparticles can be used to induce cell death in specific areas, while leaving the surrounding tissue unharmed and at normal temperatures, Halas explains.
Halas suspects that this nanoshell technology can be used to replace or supplement chemotherapy and surgery.
"The nice thing about nanoshells is that you can attach antibodies or proteins to their surfaces to target specific tissue types or specific cells the way chemotherapy does. But the advantage is that unlike chemotherapy, nanoshells are benign, so there would be very few side effects," she says.
In ongoing studies, the researchers are finding that after serving their purpose, nanoshells are eliminated from the body.
Halas' team is also looking at several mechanisms that can be used to mark the nanoshells so they reach their intended tissue targets when injected into the body.
"This is a very interesting piece of work on the use of near-infrared-absorbing nanoshells for photothermal treatment of cancer, " says Shuming Nie, director of cancer nanotechnology and an associate professor of biomedical engineering and chemistry at Emory University.
Nie notes the key finding in the paper is that when heat is applied, the temperature increases enough to induce cell death.
However, "it is unclear whether these large nanoshell particles. . . could be selectively delivered to small metastasized tumors upon systemic injection, a very different process from direct tumoral injection," Nie adds.