Gold “nano-bullets” could seek and destroy inoperable human cancers, suggest new studies by US scientists.
The tiny silica particles are plated with gold and heat up when near infrared light (NIR) is shone on them. This kills the cancer cells. Tests on human breast cancers, both in the test tube and in tumours in mice, were highly successful, the researchers report in the Proceedings of the National Academy of Sciences.
“The nanoshells are designed to absorb near infrared light and convert that light to heat,” explains Jennifer West, who led the study at Rice University, Houston, Texas. This is possible because the body’s normal tissues are “essentially transparent” to NIR.
West says the potential benefits of the treatment should be that, unlike other cancer treatments such as surgery, it would be non-invasive. Both NIR and the nanoshells are completely harmless by themselves, she says.
“We believe that we should also be able to treat very small metastases, not detected yet,” West told New Scientist. More recent, unpublished work by the group, has shown that the gold bullets can be injected into the blood stream and find their way to cancer cells in mice.
“These results are promising, particularly for tumours that cannot be treated by surgery,” says Emma Knight, at Cancer Research UK. “However, the studies are at a very early stage.”
The Rice University team created nanoparticles from a non-conducting core of silica with a diameter of 110 nanometres and a 10 nm thick metal shell. Gold was used because it is biologically inert.
When the nanoshells were added to human breast cancer cells in the test tube, and then exposed to both NIR, 100 per cent were killed, says West. “And we saw no changes in cell viability with just nanoshells or just the laser – it’s a true on/off situation.”
The team also injected the nanoshells directly into the tumours of living mice and applied NIR. The tumours were destroyed within days.
Warming the tumour cells to only about 55°C is enough to kill them, because it changes the permeability of the cell membrane. “Leakiness is what causes the cell to die,” West explains. “Cells normally have to have a very tightly controlled barrier between the inside of the cells and the fluid surrounding them. If you disrupt that, you create huge pores which lets everything across, significantly changing the composition of the fluid inside – it ends up very toxic.”
Right on target
The team has now engineered the nanoshells to specifically target tumour cells. In a recent study, submitted to Cancer Letters, they injected mice with nanoshells attached to an antibody that only binds to cancer cells. She says the tumours were “completely destroyed” and 150 days later the mice were alive and well with no tumour growth.