Magnetic nanoparticles are being developed as a highly selective cancer treatment, heating tumour cells to death while leaving surrounding healthy tissue unscathed.

Iron oxide nanoparticles that heat up in response to an alternating magnetic field offer a promising approach to cancer therapy - scientists are already running clinical trials to combine the treatment, known as magnetic field hyperthermia (MFH), with traditional chemotherapy. Now chemists in Taiwan are looking to develop a new generation of more effective nanoparticles, while an Indian group has discovered just how MFH kills cells.

Yuh-Jiuan Lin at the Industrial Technology Research Institute (ITRI) in Hsinchu, Taiwan, and colleagues are investigating new nanoparticles that, when injected into a tumour, heat up faster in a magnetic field. Lin doped the iron oxide nanoparticles with gadolinium, an element already used in the magnetic resonance imaging (MRI) procedures used by doctors to look at tumours inside the body.

'The better the particles heat up the less you need to use,' said Philip Drake, a member of the ITRI team. 'We'd like to inject as little as possible to minimise any side effects. Magnetic nanoparticles have already been accepted for use in MRI, but for MFH we need to inject about 100 times the current FDA-approved dose.'

Cells exposed to nanoparticles (second row) and a magnetic field (second and fourth columns) display disrupted cytoskeletons

Dhirendra Bahadur, of the Indian Institute of Technology Bombay in Mumbai, stressed the technique's inherent selectivity. 'Heat can be applied locally to cause fewer side effects,' he said. And oxygen-poor tumour cells are more heat-sensitive than healthy cells anyway, he added.

Bahadur's team has used immunofluorescence microscopy to examine cancer cells after MFH treatment, which showed the cells' underlying cytoskeleton had been 'significantly disrupted.' Until this study, the mechanism by which the method killed cells was unknown. 

Both Drake and Bahadur see developing nanoparticles that specifically target cancer cells as the key challenge facing MFH. 'Our intention is to conjugate these nanoparticles with specific ligands or antibodies to make them site-specific,' said Bahadur.

'The use of basic hyperthermia combined with chemotherapy could happen very fast - maybe five years for certain cases,' said Drake. 'Hyperthermia as I'd like to see it, with particles that can actively seek out cancer cells, would be more like 25 years!'

James Mitchell Crow