By Branwen Morgan

Norwich



Each gold particle is just 16 billionths of a metre across

UK researchers are employing tiny gold "nanoparticles", 1/5000th the thickness of a human hair, to deliver the chemical compound directly into cancer cells, tearing them apart instantly.

The common dye found in blue jeans and ballpoint pens is called phthalocyanine and is a light-activated, or photosensitive, agent with cell-destroying properties.

This has been known for at least 15 years but, until now, scientists have not been able to successfully deliver it into cells; hence there's no harm in wearing blue jeans.

The University of East Anglia (UEA) team used the gold particles as "trojan horses". Their small size enables them to easily enter cells, and the phthalocyanine is taken up along with them.

When pulsed with laser light, the compound produces a highly reactive form of oxygen which causes the cancer cells to commit suicide.

Cancer cells are too greedy for their own good

Dr David Russell

"We have shown using nanotechnology that we can get phthalocyanine into the cancer cells where it binds and, on activation, causes substantial cell death," he told the British Association's Science Festival.

Red 'trigger'

Healthy cells will also internalise the drug-coated nanoparticles, but unlike cancer cells they will excrete the phthalocyanine.

"Cancer cells are too greedy for their own good," said Dr Russell. "They are growing so fast that they take in and retain everything - not just nutrients needed for growth."

Nanoparticles guide the dye into cancer cells

Of these all are water soluble and are used largely to treat skin cancer as they naturally accumulate in the surface of the skin where they are more easily activated by light.

For some reason, phthalocyanine does not get into the skin - making it more suitable for treating solid tumours within the body. "Best of all," added Dr Russell, "this compound is optimised for activation by red light and produces far more of the deadly oxygen than the currently available photodynamic therapies.

"In addition, because it doesn't go into the skin there is no need for the patient to stay out of the sun which can trigger side-effects with the other drugs."

No escape

Traditional cancer chemotherapies rely on the patient being able to process the drug. In some people, their genetic differences mean this does not happen and for others, their cells become resistant to the effects of the drug.

Photodynamic therapy bypasses this issue because it does not rely on the body to activate the drug - rather a pulse of, rather ordinary, red light.

Dr Mark Wainwright, a senior lecturer in medicinal chemistry at the Liverpool John Moores University says that an improved drug design such as this should have significant advantages over the currently available photosensitive agents.

He adds: "Red light can only travel through 5-6mm tissue, but activating the nanoparticles in tumours inside the body, such as in the gut, could be done by using a fibre optic cable to shine the laser on the cancer target."

So far, Dr Russell's research, recently published in Photochemical and Photobiological Sciences, has only been conducted on human cervical cells in the laboratory.

But his team's collaborators in Italy have just begun testing the approach in animal models of cancer.

If all goes to plan, phthalocyanine nanoparticles could be available for human trials within five years and will be administered either by injection into the bloodstream or directly into a tumour.