Cancer-detecting nanoparticles

28 May 2008

Chemists in the US have created nanoparticles which can locate tumour cells

Scientists at Brown University, Rhode Island, US have created the smallest magnetic nanoparticle to date which can be used to highlight a tumour during a magnetic resonance imaging (MRI) scan.

Magnetic nanoparticles can be especially helpful in locating cancerous cell clusters during MRI scans. The nanoparticles ‘seek out' tumour cells and attach themselves toi them, greatly aiding the MRI's detection capability.

The results have been published online this week in the Journal of the American Chemical Society. Brown graduates Jin Xie, Chenjie Xu and Sheng Peng collaborated on the research, along with Professor Xiaoyuan Chen and his associates from Stanford University.

The team created peptide-coated iron oxide nanoparticles billionths of a metre in size, injecting the particles into mice to test their ability to locate a brain tumour cell. Sun and his collaborators concentrated specifically on the nanoparticle's size and the thickness of the peptide coating, which ensures the nanoparticle attaches to the tumour cell.

Size is key as the nanoparticle must be small enough to navigate through the bloodstream and reach the diseased area: Bigger particles tend to block the circulatory system. Sun's team developed a nanoparticle around 8.4 nanometers in overall diameter - some six times smaller than the size of particles currently used in medicine.

"We wanted to make it very small, so the body's immune system won't recognise it," Sun explained. "That way, you let more particles interact with and attach to the tumour cell."

Nanoparticles are important in MRI detection because they enhance what scientists refer to as the "contrast" between the background, such as water molecules in the body, and a solid mass, such as a tumour.

The coating, while integral to the nanoparticles' attachment to the tumour cell, also is crucial to establishing the "signal-to-noise" ratio that a MRI uses. The thinner the coating, the stronger the emitted signal and vice versa.

The team outfitted their nanoparticles with a two-nanometer thick peptide coating, 10 times thinner than the coating available in popular MRI contrast agents such as Feridex. It's easier for the MRI to "see" the stronger signal and to hone in on the signal's source.

Another important feature of the team's work is discovering that the RGD peptide coating binds almost seamlessly to the specific tumour cell used in the experiment. The team plans to test the particle's ability to bind with other tumour cells in further animal experiments.