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Nano-superstructures may bring safer chemo

DNA building blocks DNA could be used to link nanoparticle sub-units to create "superstructures" that effectively and safely deliver cancer drugs to tumours, say researchers.

Professor Warren Chan, from the University of Toronto, and colleagues, report their findings today in the journal Nature Nanotechnology.

"If you can target the drugs right into the tumour site you will have less side effects and kill specifically the tumour cells," says Chan.

Chemotherapy involves the use of drugs to kill tumours, but can also kill healthy cells.

Scientists have been working on using nanoparticles of gold, silver and cadmium to deliver drugs directly to tumours.

However, after the drug has been delivered the nanoparticles are not cleared from the system.

Instead, they are taken up by macrophages and accumulate in the body.

"They could be potentially toxic because you're basically accumulating metal in your system," says Chan.

The problem, he says, is that in order for a particle to be effectively delivered into a tumour, it needs to be between 10 and 100 nanometres.

But in order for it to be eliminated from the body so that it doesn't have long-term toxicity, it has to be smaller than 6 nanometres, says Chan.

"So that's a conundrum," he says.

"The question for us is how do you run a nanoparticle delivery system that can have optimal sizes for targeting the tumour, but that can also be broken apart?"

DNA 'glue'

Chan and colleagues built short fragments of DNA, which they used to "glue" small nanoparticle subunits together into a larger "nanoparticle superstructure".

"It's kind of like they're Lego blocks," says Chan.

Filling the nanoparticles with fluorescent chemicals, the researchers tracked what happened when the superstructure was injected into a lab mouse with a tumour.

Chan and colleagues found the superstructure successfully entered the tumour. Macrophages then broke it down to the original subunits, which was confirmed when the researchers measured the metal content of urine from the lab mice.

The researchers now had a way of building nanoparticle structures that would break down and be excreted by the body once they had delivered drugs to their target.

Chan says while the findings are "a good first step" it could be another five to 10 years before the superstructures reach the clinical testing phase.

The next step, he says, is to test whether the superstructures can successfully deliver a chemotherapy drug.