Cancer therapy: Tiny gold particles just one five thousandth of the thickness of a human hair could become the next big thing in cancer therapy. They are being used like Trojan horses to infiltrate cells and carry in toxins that cause tumours to commit suicide.
These "magic golden bullets" were described yesterday in a session at the ongoing British Association Festival of Science in Norwich. "We are trying to use these particles to get inside the cell," stated Prof David Russell of the University of East Anglia.
The gold particles are incredibly small, measuring from about two to 16 billionths of a metre across. The small vial pictured here is about seven centimetres tall but contains no less than two million golden bullets, Prof Russell stated.
The nanoparticles are readily taken up into cells and are used to piggy-back substances like chemicals and proteins in through the cell membrane. "We can coat them with a material that gives them function."
Gold is useful for this purpose because it is very stable and doesn't affect tissues or cell chemistry. Using a precious metal is not expensive in this case given the nanoparticles are so small, he adds. "We are dealing with such small particles they represent a minute quantity of gold." He has tested them in vitro using human white blood cells and a cervical cancer cell line. The technology can be used to study what happens inside normal cells and also to kill cancer cells from the inside.
White blood cells, macrophages, defend against infection, engulfing bacteria and trapping them in tiny structures called phagosomes inside the cell. Once captured the macrophage uses nitric oxide to destroy the bacteria.
"We want to get inside the phagosome and take measurements of the nitric oxide," Prof Russell stated. No other technology other than the golden bullets has yet achieved this, he added.
In this case he coats the nanoparticles with a protein that also carries a fluorescent tag. The protein reacts with nitric oxide and in so doing increases the intensity of fluorescent light emitted. This allows the researchers to gauge the levels of nitric oxide.
The use of the golden bullets as Trojan horses to kill cancer cells is particularly exciting, he stated. The approach is based on photodynamic therapy, the use of ordinary red light to activate toxic chemicals delivered to the cell.
In this case the gold nanoparticles are coated with photosensitisers, chemicals that react with light to cause cell damage. Only the cancer cells take up the coated nanoparticles, Prof Russell said. "The photosensitiser has a particular affinity for tumour cells." When the tissues are exposed to red light the chemical activates and damages the tumour cell, causing it to die off. They key is the use of second generation photosensitisers that are 100 times better at killing the cells, he added. This means much smaller amounts of the chemical would be needed to destroy a tumour while having little or no effect on healthy cells. The approach may be useful in treating a variety of cancers including of the lung, skin and bladder.
"Can we cure some cancers? It looks promising," he stated.
