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Gold nanospheres search out and ‘cook’ cancer cells

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March 23, 2009

Partial view of a gold nanosphere magnified by a factor of one billion. The darker ring sh...

Partial view of a gold nanosphere magnified by a factor of one billion. The darker ring shows the 'wall' of the nanosphere. (Image: Adam Schwartzberg, Ph.D.; Jin Zhang, Ph.D.)

March 24, 2009 A minimally invasive therapy that could help fight cancer may be on its way with the development of the first hollow gold nanospheres that actively search for and burn tumors. Researchers believe the new technique could prove particularly effective against malignant Melanoma, a deadly form of skin cancer responsible for around 48,000 deaths worldwide each year... and numbers are growing.

The nanospheres are equipped with a special targeting peptide, a protein fragment which draws them directly to melanoma cells while avoiding healthy skin cells. The nanospheres collect deep inside the cancer cell and heat up when exposed to near-infrared light, effectively cooking the tumor. Studies with mice have shown that nanospheres with the targeting peptide did eight times more damage to skin tumors than nanospheres without.

However, it’s not only the peptide that has the researchers excited: the hollow gold structure, or "nanoshell", is also important as it absorbs infrared light far more effectively than solid gold.

“This technique is very promising and exciting,” explains study co-author Jin Zhang, Ph.D., a professor of chemistry and biochemistry at the University of California in Santa Cruz. “It’s basically like putting a cancer cell in hot water and boiling it to death. The more heat the metal nanospheres generate, the better.”

The use of light and heat to burn tumors - photothermal or photoablation therapy (PAT) – is already used as a treatment, however it can destroy healthy skin cells so its duration and intensity must be carefully controlled. Applying a light absorbing material such as metal nanoparticles to the tumor can enhance the effectiveness of PAT but many materials used, including solid gold nanospheres, have limited light absorption capacity and poor penetration into cancer cells.

By contrast, the hollow gold spherical nanospheres - each about 1/50,000th the width of a single human hair – can more effectively pass through the cell membrane. Zhang says that gold is also safer and has fewer side effects in the body than other metal nanoparticles.

The next step will be trials of the nanospheres in humans although extensive preclinical toxicity studies will need to be conducted first. Clinical use may still a long way off, but with similar techniques in cancer-fighting nanomedicine under development elsewhere we can expect to hear a great deal more about this new branch of medicine.

Karen Sprey

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