The precise delivery of drugs to specific cells during cancer therapy reduces harmful side effects and increases the chances of successful treatment. When developing new drug-delivery platforms it is therefore essential to be able to make biocompatible carriers for the drugs and also to monitor the uptake of the drugs by the target cells in a non-invasive way.

Miqin Zhang and colleagues at the University of Washington in the US have recently shown that this can be done by attaching the anti-cancer drug methotrexate to superparamagnetic iron oxide nanoparticles with poly(ethylene glycol) links and then monitoring the uptake by magnetic resonance imaging. The action of enzymes on the linker layer releases the drug inside the target cells.

Magnetic resonance images of cells containing the nanoparticle showed enhanced contrast, thus confirming the uptake of iron. Successful implementation of this approach will enable doctors to monitor the action of drugs on tumours during the diagnosis and treatment of cancer in real time.