Near-infrared photoablation with nanoshells restricts damage to malignant tissue

Focusing near-infrared light on nanoparticle absorbers injected into solid tumors in mice kills malignant tissue but does not harm surrounding normal tissue, investigators report in the October 28th issue of the Proceedings of the National Academy of Sciences.

Thermal ablation therapy is considered a minimally invasive alternative to surgical resection of solid tumors, Dr. Jennifer L. West, at Rice University in Houston, Texas, and colleagues note. However, nonspecific heating can destroy normal tissue adjacent to malignant tissue.Near-infrared light (NIR) readily penetrates but is not absorbed by normal tissue. To take advantage of this property, Dr. West’s group constructed metal “nanoshells” with strong absorption in the NIR, consisting of 110-nm silica particles surrounded by a 10-nm layer of gold colloid. They coated these nanoshells to prevent aggregation and promote permeability and retention at the tumor site. When breast epithelial carcinoma cells were incubated with nanoshells and irradiated with NIR, cells within the laser spot were destroyed, with irreversible damage to cell membrane barriers. To examine efficacy in vivo, the investigators injected nanoshells into 1-cm diameter subcutaneous tumors in mice. Treatment with a low-power diode laser for 4 to 6 minutes raised temperatures in the tumors by about 37 degrees centigrade. Pathologic examination revealed irreversible thermal destruction, confined to the tumor volume, with tissue coagulation, cell shrinkage and loss of nuclear staining.Exposure to either nanoshells or NIR light alone had no effect on cell viability in vitro or in vivo.Dr. West’s team points out that “nanoshells may also be conjugated with antibodies targeting surface oncoproteins overexpressed within the tumor to promote cell internalization, further accumulation, and more selective thermal damage of the tumor.”(Source: Proc Natl Acad Sci USA 2003;100:13549-13554: Reuters Health: November 3, 2003: Oncolink)