Imagine being treated for cancer with a couple of visits to your doctor. He simply gives you an injection and then a couple of weeks later runs infrared light over your body to activate cancer-killing agents and excise the tumor. Sound like a Ray Bradbury novel? Don’t tell Naomi Halas that. She is the Stanley C. Moore professor of electrical and computer engineering and professor of chemistry at Rice University, and she has more than imagined it-she’s been developing the process since 1997, when she invented miniscule particles with huge therapeutic potential. She calls them nanoshells.Nanoshells are microscopic concentric spheres with silica cores and gold shells. Gold gives Halas the thermal and optical response her treatment process requires, and the body generates no antibodies against it. By varying the size of the silica core and the thickness of the gold, Halas found she could “tune” the nanoshells to absorb light of different wavelengths. “For cancer treatment,” she says, “infrared proved best because it penetrates the body the furthest.”
In experiments, nanoshells are injected into an animal’s bloodstream, where “targeting” agents applied to them seek out and attach to the surface receptors of cancerous cells. Illumination with infrared light “raises the cells’ temperature to 55 degrees Celsius” and burns away the tumor, she says.
Halas is focusing her research on breast cancer. She hopes nanoshells will prove a viable alternative to chemotherapy, which kills both healthy and diseased cells, resulting in side effects like fatigue and hair loss. Nanoshells, by contrast, kill only cancer cells.
Nanoshells are just one of several intriguing cancer diagnosis and treatment options that nanotechnology is making possible. Miqin Zhang, a materials scientist at the University of Washington in Seattle, is using her own brand of nanoparticles to noninvasively diagnose and treat brain tumors. She calls her creations “smart superparamagnetic nanoparticle conjugates.” When injected into the bloodstream, these particles target tumors’ cell receptors with agents known as ligands.
Zhang’s nanoparticles are made from iron oxide, which becomes especially magnetic when placed in a magnetic field such as those used for magnetic resonance imaging. The particles therefore enhance the signal that tumors emit during an MRI, making them easier to locate at earlier stages of development. But nanoparticles must circulate long enough to locate tumor cells. Zhang found in early trials that they were quickly attacked and neutralized by antibodies called microphages. So she modified them with a polymer coating that resists microphages. Once the nanoparticles find tumors, they release an attached drug called methotrexate, which kills the cell.
The nanoparticles, which are less than 20 nanometers in diameter, must remain separate from another to do their job. “Aggregated nanoparticles become toxic to healthy tissue,” Zhang explains. The particles’ small size and their ability to permeate tissue let them pass through what’s known as the blood-brain barrier and reach brain tumors. Zhang says this is key because “98 percent of cancer drugs cannot do that.”