University of Texas scientists have created a technique that utilizes gold nanoparticles to increase the efficiency of photothermal ablation when treating melanoma. During photothermal ablation, infrared light is used to burn suspected tumor tissue, but often the healthy stuff gets cooked too. Now, by injecting highly light absorbing gold nanoparticles that have a high affinity for tumors, the efficiency and specificity of photothermal ablation is increased.
From the University of Texas M. D. Anderson Cancer Center:
With hollow gold nanospheres inside melanoma cells, photothermal ablation destroyed tumors in mice with a laser light dose that was 12 percent of the dose required when the nanospheres aren’t applied, Li [Chun Li, Ph.D., professor in M. D. Anderson’s Department of Experimental Diagnostic Imaging] and colleagues report. Such a low dose is more likely to spare surrounding tissue.
Injected, untargeted nanoparticles accumulate in tumors because they are so small that they fit through the larger pores of abnormal blood vessels that nourish cancer, Li said. This “passive targeting” delivers a low dose of nanoparticles and concentrates them near the cell’s vasculature.
The researchers packaged hollow, spherical gold nanospheres with a peptide – a small compound composed of amino acids – that binds to the melanocortin type 1 receptor, which is overly abundant in melanoma cells. They first treated melanoma cells in culture and later injected both targeted and untargeted nanospheres into mice with melanoma, then applied near-infrared light.
Fluorescent tagging of the targeted nanospheres showed that they were embedded in cultured melanoma cells, while hollow gold nanospheres without the targeting peptide were not. The targeted nanospheres were actively drawn into the cells through the cell membrane.
When the researchers beamed near-infrared light onto treated cultures, most cells with targeted nanospheres died, and almost all of those left were irreparably damaged. Only a small fraction of cells treated with untargeted nanospheres died. Cells treated only with near-infrared light or only with the nanospheres were undamaged.
Most of the targeted nanospheres in the treated mice gathered in the tumor, with smaller amounts found in the liver and spleen. Most of the untargeted nanospheres gathered in the spleen, then in the liver and then the tumor, demonstrating the selectivity and importance of targeting.
In another group of mice, near-infrared light beamed into tumors with targeted nanospheres destroyed 66 percent of the tumors, but only destroyed 7.9 percent of tumors treated with untargeted nanospheres.
The researchers used F-18-labeled glucose to monitor tumor activity by observing how much glucose it metabolized. This action “lights up” the tumor for positron emission tomography (PET) imaging. Tumors treated with targeted shells largely went dark.
Press release: Targeted Nanospheres Find, Penetrate, then Fuel Burning of Melanoma
Image: Gold nanoparticles from an unrelated project. Credit Annie Cavanagh, Wellcome Images