Nanotechnology-Based Strategy Aims at Noninvasive Cancer Therapy

HOUSTON, Nov. 2 -- Carbon nanotubes embedded in tumors and then heated externally by radiofrequency energy achieved total tumor necrosis in preclinical studies, investigators here reported.
Action Points
Explain to interested patients that research involving microscopic technology has shown promise in animals as a noninvasive approach to treating cancer.
Point out that the approach has not been tested in humans and might not be for several years.
The heated nanotubes initially destroyed cancer cells in vitro and then obliterated tumors in a rabbit model of liver cancer, Steven A. Curley, M.D., of the University of Texas M. D. Anderson Cancer Center, and colleagues, reported online in advance of the December issue of Cancer.
The approach suggested a potential noninvasive means to treat tumors virtually anywhere in the body, said the investigators. The treatment damaged some healthy tissue adjacent to tumors, but investigators found encouragement in the overall results of the study.
"These are promising, even exciting, preclinical results in this liver cancer model," said Dr. Curley. "Our next step is to look at ways to more precisely target the nanotubes so they attach to, and are taken up by, cancer cells while avoiding normal tissue."
Dr. Curley estimated that clinical studies are at least three or four years away.
Radiofrequency ablation of tumors, as currently practiced, has several drawbacks--the need to insert needles directly into tumors; incomplete tumor destruction in as many as 40% of cases; nonspecific treatment resulting in damage to healthy tissue; and complications of thermal injury in 10% of patients. As a consequence, the therapy is used for only a few malignancies, including liver, kidney, breast, lung, and bone.
Radiofrequency energy fields have excellent tissue penetration, the authors noted. Theoretically, the process could be used for noninvasive treatment of tumors located anywhere in the body.
Single-walled carbon nanotubes also have considerable potential in cancer therapy, the authors continued. The nanotubes can be used to deliver a variety of diagnostic and therapeutic agents.
"Given the unique electrical and chemical properties of [single-walled carbon nanotubes], we hypothesized that exposure to a focused external radiofrequency field would lead to significant heat release by the [nanotubes] allowing them to serve directly as an anticancer agent," they said.
The initial studies involved human liver cancer cells, to which the water-soluble nanotubes were added. After incorporation of the nanotubes, the cells were exposed for one to two minutes to an 800-watt external radiofrequency field.
The radiofrequency energy resulted in efficient heating of the aqueous suspensions of nanotubes and concentration-dependent destruction in vitro of the human cancer cells.
In the second phase of investigation, the researchers injected the nanotubes directly into tumors. That was followed immediately by external RF field treatment. At 48 hours all of the nanotube-containing tumors demonstrated complete necrosis. In contrast, control tumors with nanotube or radiofrequency exposure (but not both) remained viable.
Dr. Curley said targeting nanotubes to cancer cells is the major obstacle in advancing the therapy. Investigators are examining the ability of monoclonal antibodies, peptides, and other potential delivery vehicles to target the nanotubes more specifically.
The authors reported no disclosures. The study was supported by the American Association for Cancer Research, the National Aeronautics and Space Administration, the National Science Foundation, and the Fulbright Foundation.Primary source: CancerSource reference: Gannon CJ, et al. "Carbon nanotube-enhanced thermal destruction of cancer cells in a non-invasive radiofrequency field." Cancer 2007;110:epub.