Credit: © 2010 NAS

One of the main challenges in treating tumours is that they are difficult to target. Nanoparticle carriers are promising delivery vehicles that improve the retention of diagnostic or therapeutic agents within the tumours, but unfortunately they also slow down their initial uptake. Perrault and Chan from the University of Toronto have now sidestepped this issue to improve tumour imaging1.

A passive approach can be used when utilizing nanoparticles to target tumours whereby, without engineering their 'active' binding, they naturally accumulate in the tumours because of their size through what is known as the 'enhanced permeability and retention effect'. This passive approach, however, requires a long circulation time in the body, which is not suitable when contrast agents are attached. Perrault and Chan have avoided this problem by in vivo assembly of the agent and particle directly at the tumour site, combining the high accumulation of the nanoparticles in the tumour, with its rapid uptake of the contrast agent.

In studies on mice, the researchers first injected passive gold nanoparticles bearing a biotin anchor, and these accumulate in tumours within 24 hours. A fluorescent contrast agent bearing streptavidin, which binds strongly with biotin, was then injected. The agent thus rapidly attaches to the surface of the nanoparticles and remains within the tumours. The uptake of contrast agent was shown to be eight times faster, and the resulting diagnostic sensitivity for tumour imaging three times higher, than with passively injected molecules. This approach is also promising for the delivery of other molecules to tumours, such as therapeutic compounds.