Cancer institute invests $2.3 million in plasmonic photothermal therapy study

Marie Freebody, marie.freebody@photonics.com

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 anticancer drugs.

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 10^5-6 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 interactions.”

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.