Plasmonic Nanoheaters Enable Photothermal Cancer Therapy

In vitro and in vivo studies have positively correlated the heat generation of plasmonic nanoparticles with their potential as cancer-killing agents.

Using a single-particle and positron emission tomography (PET)-based platform, researchers from the University of Copenhagen quantified the photothermal efficiency of near-infrared (NIR) -resonant silica-gold nanoshells (AuNSs) and benchmarked this against the heating of colloidal spherical, solid gold nanoparticles (AuNPs). The researchers reported that both in vitro and in vivo (with live mice as subjects), the heat generation of the resonant AuNSs performed better than nonresonant AuNPs.

The images show PET scans of a mouse with a large tumor (by the white arrow). The tumor was treated with nanoparticles, which were injected directly into the tumor and then flashed with near-infrared laser light. The light heated the nanoparticles, damaging or killing the cancer cells (red arrows). Courtesy of Kamilla Nørregaard and Jesper Tranekjær Jørgensen/Panum Inst.

The treatment involved direct injection of 80- to 150-nm nanoparticles into the cancerous cells, which were then irradiated with an NIR laser, causing the particles to heat up. The result was damage to or death of the cancer cells. The team reported 150-nm AuNSs particles were most effective.

In contrast to conventional radiation therapy, NIR laser light causes no burn damage to the tissue it passes through. Just an hour after the treatment, the researcher said they could already directly see with PET scans that the cancer cells had been killed; the effect continued for at least two days after the treatment.

This drawing shows a mouse with a cancerous tumor on its hind leg. The nanoparticles were injected directly into the tumor, which was then flashed with near-infrared laser light. The light penetrated through the tissue well and caused no burn damage. Courtesy of Kamilla Nørregaard/Panum Inst.

"Now we have proven that the method works. In the longer term, we would like the method to work by injecting the nanoparticles into the bloodstream, where they end up in the tumors that may have metastasized,” said researcher Lene Oddershede. "With the PET scans, we can see where the tumors are and irridate them with lasers, while also effectively assessing how well the treatment has worked shortly after the irradiation. In addition, we will coat the particles with chemotherapy, which is released by the heat and which will also help kill the cancer cells.”

The research was published in Scientific Reports (doi: 10.1038/srep30076).