Cooking Tumors

Cancer researchers have long sought a “magic bullet” that selectively targets tumor cells for destruction. In an attempt to enlist nanotechnology in that search, a Rice University spinoff, Nanospectra Biosciences, has developed gold-coated glass nanoparticles capable of invading a tumor and – when heated remotely – killing it.

The dimensions of the particles are the key to their effectiveness. Nanospectra’s particles measure 150 nanometers in diameter, which the company believes is the ideal size to permit passage through tumors’ characteristically leaky blood vessels. The particles should thus accumulate in tumors more than in other tissues. When near-infrared light is directed at the tumor site, either from outside the body or from a light probe inserted into the body, the particles absorb the light and heat up. As a result, the tumors get hotter than surrounding tissue and die.

In the company’s first published study, tumors in mice injected with the nanoparticles disappeared six days after the light treatment, while tumors in control-group mice grew quickly. While near-infrared light has been used as an imaging tool, “the novelty is the use of near infrared to heat tissue,” says John Frangioni, an assistant professor of medicine and radiology at Harvard Medical School who’s applying nanotechnology to cancer surgery.

In theory, the technology could be useful for the eradication of any solid tumor, such as those typical of breast, prostate, and lung cancer, says Donald Payne, Nanospectra’s president. “We think we’re a great adjunct to chemotherapy and radiation. We would be a much less toxic tool in the physician’s toolbox.”

The three-year-old company says it will seek its first round of venture capital this fall and hopes to soon begin more formal animal studies to convince the U.S. Food and Drug Administration to let it test its technology on humans. Nanospectra probably faces several more years of testing, since the application of nanotechnology to the treatment of cancer is new, not well studied, and likely to be highly scrutinized by regulatory authorities.

The first studies will focus on the safety and effectiveness of the injected particles. Most of the particles don’t go to the tumor and are instead filtered out by the liver, says Jennifer West, the company’s scientific cofounder and a bioengineering professor at Rice University. That could be a problem for the liver, says Frangioni. “The toxicity of gold remains unknown. Recent data at meetings suggest gold may be more toxic than we first believed,” he says.

Company researchers say that in early cell and animal studies, they haven’t yet seen any harmful effects from their particles. But the possible dangers of injecting people with nanoparticles are a general concern among some researchers and activist groups, who are calling for further study.

Other challenges loom. Tumor leakiness will vary from one tumor to the next, says Gregory Lanza, a professor of medicine at Washington University. The company will likely have to look into methods for more precisely targeting malignant cells, such as tagging the particles with proteins that selectively bind to cancer cells, says Oleg Salata, a nanomaterials researcher at the University of Oxford in England. But if Nanospectra can meet these challenges, it could usher in a fundamentally new class of therapeutics and help bring nanotechnology into the doctor’s office.