Marie Freebody, email@example.com
ATLANTA – A five-year grant totaling
more than $2.3 million will enable researchers at Emory University and Georgia Institute
of Technology to explore the effectiveness of plasmonic photothermal therapy (PPTT).
The award, from the National Cancer Institute’s Cancer Nanotechnology
Platform Partnerships program, will allow the researchers to join forces to tackle
head and neck cancers. They hope to optimize the efficacy of the technique to kill
off cancerous cells that develop in the soft tissue of the mouth and throat.
PPTT is a therapeutic strategy in which photon energy is converted
into heat to damage and destroy cancer cells. It has had some success in treating
cancer in the past few decades and offers important advantages over conventional
therapies: Because it is a minimally invasive approach, it overcomes the severe
infection problems commonly encountered after surgery. It also avoids the side effects
and drug-resistance issues of chemotherapy by circumventing the use of free-form
In their study, titled “Toxicity and efficacy of gold nanoparticle
photothermal cancer therapy,” the researchers plan to expose mice to near-IR
radiation (808 nm) using a diode laser. The intensity will be set to 1, 2, 5 and
10 W/cm2 for 5, 10 and 20 min.
The mice will be injected with gold nanoparticles, which, according
to Dr. Dong Moon Shin, show great potential for photothermal cancer therapy. Shin,
who heads up the Emory University contingent, is a professor of hematology, medical
oncology and otolaryngology, and director of the Winship Cancer Chemoprevention
program at the university.
Dr. Dong Moon Shin describes the merits of gold nanoparticles for
photothermal cancer therapy.
“Plasmonic gold nanoparticles are very promising for biomedical
applications because of their strongly enhanced radiative – e.g., absorption
and scattering – and nonradiative photothermal properties due to surface plasmon
resonance – the coherent collective oscillation of the free electrons in the
metal upon the excitation of resonant incident light,” he said.
The challenge is that there is limited knowledge regarding several
features of this new generation of gold nanoparticles, he said. These include their
biodistribution, long-term fate, toxicity, tumor affinity and how these properties
are influenced by factors such as the particle aspect ratio, surface coating and
the addition of tumor-targeting ligands.
In the past, light-absorbing dye molecules have been used in photothermal
therapy studies with some success. But the group hopes to prove that nanoparticles
are much more effective.
These images depict normal healthy cells (HaCaT) and cancerous cells
(HSC-3 and HOC-313). In the top row (a), gold nanorods are applied to normal cells
and cancerous cells. The gold attaches more to the cancerous cells than to normal
healthy cells. In the bottom row (b), near-IR laser application of PPTT kills the
cancerous cells (highlighted by trypan blue staining) but not the normal healthy
cells. Images courtesy of Emory University and Georgia Institute of Technology.
“Nanoparticles absorb light 105-6 times more strongly than
most strongly light-absorbing dye molecules,” Shin explained. “The absorbed
light is converted into heat rapidly – on the picosecond time scale –
and efficiently via nonradiative processes including electron-electron and electron-photon
The result is that, when gold nanoparticles are targeted to cancer
cells, irradiation with an optical laser will induce massive heat that can destroy
the surrounding cells. In addition, gold nanoparticles overcome the photobleaching
problems of dye molecules, making the method robust enough for clinical applications.
By the end of four years, Shin hopes to have optimized the PPTT
method and extended the preclinical toxicology studies of the best gold nanoparticles
from mice to rats. By the end of the fifth year, he hopes to determine the nontoxic
dose and toxicology of the best gold nanoparticles to be used in humans.