Top left: Transmission electron micrograph of gold-silica nanoshells (Auroshells, Nanospectra Biosciences, Inc). Bottom left: Scanning electron micrograph shows how the nanoshells are deposited close to the tumor microvasculature. Right: Magnetic resonance temperature imaging of the tumors during irradiation with an 808-nm laser at low power (4 W/cm2) demonstrates a striking difference in heating between the control and nanoshell-treated animals.
Tiny gold nanoshells—known for their surface plasmonic properties—may someday help guide cancer-seeking heat therapy to its target.
Nanoshells, developed by Naomi J. Halas of Rice University, are tiny spheres coated with gold. They can be designed to strongly absorb certain frequencies of near-infrared radiation. When inserted into a tumor and heated, they can kill cancer cells without damaging surrounding tissue, according to R. Jason Stafford, a scientist at the University of Texas M.D. Anderson Cancer Center in Houston.
Stafford is part of a team that transferred thermal ablation technology from mice to dogs, which make more relevant test animals because they are closer in size to humans. He spoke at a recent meeting of the American Association of Physicists in Medicine (AAPM) in Houston.
Stafford and his colleagues, including Rice bioengineer Jennifer L. West, have been studying the use of nanoshells in cancer therapy for five years (Proc. Natl. Acad. Sci. USA 100, 13549). The group’s technique uses light from an 808-nm diode laser, which is close to the plasmon resonance frequency of the roughly 100-nm-diameter particles.
Researchers get the nanoshells into position by simply injecting them intravenously into a subject. The particles find their way through the body and concentrate themselves around the tumor’s blood supply. A laser probe heats the spheres and cancer tissue to 60° C—which coagulates the tumor cells’ proteins enough to kill them. “It’s a bloodless sort of surgery,” Stafford said.
Originally the nanoshells contained silica cores, but that dielectric material was difficult for clinicians to see inside an animal, according to Stafford. Another M.D. Anderson researcher, Chun Li, developed nanoshells with an iron oxide core that show up on magnetic resonance (MR) images taken during thermal ablation therapy.
Scientists at the University of Texas at San Antonio have begun human trials with the nanoshell-assisted therapy, Stafford said. At the AAPM meeting, Stafford also reported on an MR-guidance system for laser-induced thermal therapy (LITT) without the use of nanoshells. Visualase Inc. of Houston developed an LITT system that employs a thin fiber-optic probe to selectively destroy unhealthy cells by guiding light from a 980-nm diode laser to solid tumors. The MR imaging allows the administering physician to choose the correct dosage of light.
Stafford tested the system in dogs with tumors, and the device has gained approval for human use from the FDA. Both projects are being submitted to journals.