Tiny gold shells that absorb certain types of radiation may become a new weapon in the ongoing battle against cancer.
Called nanoshells, the golden balls have a bit of mica in their center and can be designed to absorb radiation at various frequencies.
A group of Texas researchers injected the nanoshells - so small it would take 5,000 of them to reach the size of a poppy seed - into tumors in mice. They then exposed the tumors to near infrared radiation, heating them enough to kill the cancer but without injuring nearby normal tissue.
Their results are reported in this week's online issue of Proceedings of the National Academy of Sciences.
Nanoshells should work in most soft tissue tumors but would be most effective on cancers that can't be removed surgically because they're in an awkward location, such as in the brain, the researchers said.
"Nanoshells can be directly injected," said Jennifer L. West of Rice University, "or, our most recent study shows that you can inject nanoshells intravenously and they will accumulate in tumor sites because the blood vessels in tumors are leakier than elsewhere in the body."
West said patients could be treated in two ways.
"Near infrared light can be applied from outside of the body for most applications, but if necessary, fiber optics can be run through catheters," said West, who led the team from Rice and the University of Texas M.D. Anderson Cancer Center.
Near infrared light is a type of low-energy radiation not absorbed by living tissues. However, the nanoshells can be designed to absorb this light, which heats them up.
Andrei Laszlo of the Washington University School of Medicine in St. Louis said that although the method is a novel approach for removing tumors, it "will require a considerable amount of further work" to overcome the problem of directing the nanoshells to the specific tumor sites.
The Texas researchers first experimented with cultured human breast cancer cells in a solution containing nanoshells and then turned to tumors in mice.
In both cases, temperatures inside the tumors reached levels high enough to damage cells within 4 to 6 minutes, killing the tumors but leaving surrounding tissue unharmed.
The researchers will monitor the long-term health of the treated mice.
West said a company called Nanospectra Biosciences has licensed the technology and plans to do studies in people, which could occur within 12 to 18 months.
By Randolph E. Schmid