Scientists at The University of Texas M. D. Anderson Cancer Center have announced that they have been successful in equipping hollow gold nanospheres with a targeting peptide in such a manner that they find melanoma cells, penetrate them deeply, and then cook the tumour when bathed with near-infrared light.
"Active targeting of nanoparticles to tumors is the holy grail of therapeutic nanotechnology for cancer. We're getting closer to that goal," said senior author Dr. Chun Li, professor in M. D. Anderson's Department of Experimental Diagnostic Imaging.
The researcher revealed that upon being heated with lasers, the actively targeted hollow gold nanospheres did eight times more damage to melanoma tumours in mice than did the same nanospheres that gathered less directly in the tumours.
They claim that their study, involving experiments in lab as well as on mouse models, shows the first in vivo active targeting of gold nanostructures to tumours in conjunction with photothermal ablation, a minimally invasive treatment that uses heat generated through absorption of light to destroy target tissue.
They say that tumours are burnt with near-infrared light, which penetrates deeper into tissue than visible or ultraviolet light.
Highlighting the fact that photothermal ablation is used to treat some cancers by embedding optical fibres inside tumours to deliver near-infrared light, Li said that it could be greatly improved when a light-absorbing material is applied to the tumour.
Photothermal ablation has been explored for melanoma, but because it also hits healthy tissue, dose duration and volume have been limited.
The researchers said that during their experiments, hollow gold nanospheres inside melanoma cells enabled photothermal ablation destroy tumours in mice with a laser light dose that was 12 percent of the dose required when the nanospheres aren't applied.
Li says that such a low dose is more likely to spare surrounding tissue.
The researcher has revealed that upon being injected into the body, untargeted nanoparticles accumulate in tumours because they are so small that they fit through the larger pores of abnormal blood vessels that nourish cancer.
This "passive targeting" delivers a low dose of nanoparticles and concentrates them near the cell's vasculature, Li adds.
The scientific team packaged hollow gold nanospheres with a peptide 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.
Using fluorescent tagging of the targeted nanospheres enabled them to see that they were embedded in cultured melanoma cells, while hollow gold nanospheres without the targeting peptide were not.
Dr. Jin Zhang, professor in the University of California-Santa Cruz Department of Chemistry and developer of the hollow nanospheres, said that the targeted nanospheres have a number of advantages.
Their size - small even for nanoparticles at 40-50 nanometers in diameter - and spherical shape allow for greater uptake and cellular penetration.
They have strong, but narrow and tunable ability to absorb light across the visible and near-infrared spectrum, making them unique from other metal nanoparticles.
Li pointed out that the hollow spheres are pure gold, which has a long history of safe medical use with few side-effects.
The study report has been published in the journal Clinical Cancer Research.