Gold nanoshells are among the most promising new nanoscale therapeutics being developed to kill tumors, acting as antennas that turn light energy into heat that cooks cancer to death. Now, a multi-institutional research team has shown that polymer-coated gold nanorods one-up their spherical counterparts, with a single dose completely destroying all tumors in a nonhuman animal model of human cancer.
Reporting its work in the journal Cancer Research, a research team headed by Sangeeta N. Bhatia, M.D., Ph.D., Massachusetts Institute of Technology, and Michael J. Sailor, Ph.D., University of California, San Diego, described its development of gold nanorods, coated with polyethylene glycol, which set a new record for the time they remain circulating in the bloodstream. This long-circulation half-life of approximately 17 hours affords the nanorods the opportunity to accumulate in tumors, thanks to the leaky blood vessels that surround malignancies. Both Dr. Bhatia and Dr. Sailor are members of the National Cancer Institute's Alliance for Nanotechnology in Cancer.
Gold nanoparticles can absorb different frequencies of light, depending on their shape. The rod-shaped particles developed for this study absorb near-infrared light, which heats the nanorods but passes harmlessly through human tissue. In the current work, tumors in mice that received an intravenous injection of nanorods plus near-infrared laser treatment disappeared within 15 days. Those mice survived for 3 months, with no evidence of recurrence, until the end of the study, whereas mice that received no treatment or only the nanorods or laser died within weeks.
During a single exposure to a near-infrared laser, the nanorods heat up to 70° C, hot enough to kill tumor cells. Additionally, heating them to a lower temperature weakens tumor cells enough to enhance the effectiveness of existing chemotherapy treatments, raising the possibility of using the nanorods as a supplement to those treatments. The nanorods also could be used to kill tumor cells left behind after surgery. The investigators note that the nanorods can be more than 1,000 times more precise than a surgeon's scalpel, so potentially they could remove residual cells the surgeon cannot get at.
Another useful characteristic of the gold nanorods is that they are very efficient at absorbing x-rays, providing a sensitivity boost to x-ray imaging methods such as computerized tomography scanning. The investigators took advantage of this property, using x-rays to create a detailed three-dimensional map of where the nanorods accumulated in the tumor-bearing animals. They then used this map to calculate the optimal irradiation protocol to maximize the tumor-killing effect and minimize damage to healthy tissue.