The noninvasive cancer treatment uses a combination of harmless, near-infrared light and benign, gold nanoshells to destroy tumors with heat. The treatment does not affect healthy tissue.
"We are extremely encouraged by the results of these first animal tests," said Jennifer West, professor of bioengineering and chemical engineering. "These results confirm that nanoshells are effective agents for the photothermal treatment of in vivo tumors."
Results of the study are published in the June 25 issue of the journal Cancer Letters.
Invented in the 1990s by Naomi Halas at Rice, nanoshells are about 20 times smaller than a red blood cell. The multilayered nanoshells consist of a silica core covered by a thin gold shell. The size, shape and composition of nanoshells give them unique optical properties. By varying the size of the core and the thickness of the gold shell, researchers can tailor a nanoshell to respond to a specific wavelength of light.
The photothermal cancer treatment uses nanoshells that are tuned to respond to near-infrared light. Located just outside the visible spectrum, near-infrared light passes harmlessly through soft tissue. In the treatment, nanoshells convert this light into heat that destroys nearby tumor cells. The heating is very localized and does not affect healthy tissue adjacent to the tumor.
The animal trial involved 25 mice with tumors ranging in size from 3-5.5 millimeters. The mice were divided into three groups. The first group was given no treatment. The second received saline injections, followed by three minutes exposure to near-infrared laser light. The final group received nanoshell injections and laser treatments.
The blood vessels inside tumors develop poorly, allowing small particles like nanoshells to leak out and accumulate inside tumors. In the test, researchers injected nanoshells into the mice, waited six hours to give the nanoshells time to accumulate in the tumors and then applied a 5 millimeter wide laser on the skin above each tumor.
Surface temperature measurements taken on the skin above the tumors during the laser treatments showed a marked increase that averaged about 46 degrees Fahrenheit for the nanoshells group. There was no measurable temperature increase at the site of laser treatments in the saline group. Likewise, sections of laser-treated skin located apart from the tumor sites in the nanoshells group also showed no increase in temperature, indicating that the nanoshells had accumulated as expected within the tumors.
All signs of tumors disappeared in the nanoshells group within 10 days. These mice remained cancer-free after treatment.
Tumors in the other two test groups continued to grow rapidly. All mice in these groups were euthanized when the tumors reached 10 millimeters in size. The mean survival time of the mice receiving no treatment was 10.1 days; the mean survival time for the group receiving saline injections and laser treatments was 12.5 days.
"The results of these first animal studies are very promising, and while we don't yet have a target date for our first human trial, our entire team is working hard to make this treatment available to cancer patients as soon as possible," said Halas, the Stanley C. Moore Professor in Electrical and Computer Engineering and professor of chemistry. "We have licensed the technology to the Houston-based firm Nanospectra Biosciences Inc., which will obtain the necessary approvals and funding for human trials."
This research was funded by the National Science Foundation under both an STTR grant to Nanospectra Biosciences and a National Nanotechnology Initiative grant to Rice's Center for Biological and Environmental Nanotechnology.