Attack of the nanoparticles

MIT scientists have developed nanoparticles that, when pulsed with an electromagnetic field, release drugs to attack tumours. The development could lead to the improved diagnosis and targeted treatment of cancer.

The team of reserchers, led by Sangeeta Bhatia from MIT's Department of Electrical Engineering and Computer Science, had previously developed injectable nanoparticles that can flow through the bloodstream, find a home in a tumour and then clump together. The tumour can then be visualised through Magnetic Resonance Imaging (MRI).

The team then realised that they could tether drugs to the nanoparticles using strands of DNA, a classical heat sensitive material. Because the nanoparticles are superparamagnetic, when they are exposed to a low-frequency electromagnetic field, they radiate heat that breaks the tethers and releases the drugs.

The waves in the magnetic field have frequencies between 350 and 400kHz - the same range as radio waves, which pass harmlessly through the body and heat only the nanoparticles.

One advantage of a DNA tether is that its melting point is tunable. Longer strands and differently coded strands require different amounts of heat to break. This heat-sensitive tuneability makes it possible for a single particle to simultaneously carry many different types of cargo, each of which can be released at different times or in various combinations by applying different frequencies or durations of electromagnetic pulses.

To test the particles, the researchers implanted mice with a tumour-like gel saturated with nanoparticles. They then placed the implanted mouse into the well of a cup-shaped electrical coil and activated the magnetic pulse. The results confirmed that without the pulse, the tethers remained unbroken. With the pulse, the tethers broke and released the drugs into the surrounding tissue.

However, work remains to be done before such therapies become viable in the clinic. To heat the region, for example, a critical mass of injected particles must clump together inside the tumour. The team is still working to make intravenously injected particles clump effectively enough to achieve this critical mass.

'Our overall goal is to create multifunctional nanoparticles that home to a tumour, accumulate, and provide customisable remotely activated drug delivery right at the site of the disease,' said Bhatia.

Here, dark gray nanoparticles carry different drug payloads (one red, one green). A remotely generated five-minute pulse of a low-energy electromagnetic field releases the green drug but not the red. A five-minute pulse of a higher-energy electromagnetic field releases the red drug, which had been tethered using a DNA strand twice as long as the green tether, as measured in base pairs