Golden nanobullets to knock out cancer
Scientists in the U.S. say they have devised a new "magic-bullet" technique that may quickly destroy cancers without surgery and still leave the surrounding tissue unscathed.
The bullets are tiny gold-coated silica particles, known as nanoshells, that can be injected into a cancer then heated with a special light, says a team led by Dr Jennifer West of Rice University, in Houston, in a report today in the journal Proceedings of the National Academy of Science.
"Temperatures inside the tumours reached levels high enough to damage cells within four to six minutes, killing the tumours but leaving surrounding tissue unharmed," the journal said in a media statement.
The researchers suggest that if their preliminary results prove to be correct, the technique could be ideal for killing off cancers that are small and embedded in vital tissue, such as the brain.
The nanoshells are so minuscule - about 120 nanometres in, or 1,500 times smaller than the thickness of a human hair - that they can be readily taken up by cells, the scientists showed, in a series of experiments aimed at developing the technique.
The gold coating on the shells is not only benign in the body - as gold tooth fillings are - but by adjusting its thickness in relation to the silica core, the researchers were able to "tune" the nanoshells to receive a specific type of light in the near-infrared range.
Like gold, near-infrared light does not harm living tissue, but when the two reacted with each other the gold heated up to an average 37° C, enough to fatally injure the cells to which the nanoshells had bound.
After incubating cultured human breast cancer cells in a solution containing nanoshells, the researchers exposed the incubated cells along with control cells to a near-infrared light source. The incubated cells showed signs of irreversible heat damage and cell death, while the control cells remained undamaged.
The scientists then injected nanoshells into tumours growing on mice and then exposed the animals to low doses of near-infrared light. Within minutes, the cancer cells were zapped by the generated heat.
The researchers note that conventional surgery is an effective therapy for well-defined primary tumours in accessible, non-vital tissues. Alternative treatments - such as laser and ultrasound - are available for treating small, poorly defined cancers embedded in vital tissues, however most methods are either invasive or do not discriminate well between healthy and cancerous cells.
Other researchers have experimented with treatments that rely on injected dyes that absorb near-infrared light, but West and colleagues have shown that nanoshells are potentially far more effective. They calculate that nanoshells are over a million times more likely than a dye molecule to be hit by a light particle and heat up.
Another advantage of nanoshells over dyes is that biochemists can create coatings for them that 'stealth' them to the body's immune system, the researchers point out.
Nanoshells could also be used to deliver biologically active molecules - such as drug treatments - to specific sites before being activated by an external energy source, such as light, radio or sound waves.