Scientists at Brown University have developed the smallest iron oxide nanoparticles, to be used as MRI imaging contrast agents, capable of locating and attaching specifically to tumor cells.
The team created peptide-coated iron oxide nanoparticles — particles billionths of a meter in size. The researchers injected the particles into mice and tested their ability to locate a brain tumor cell called U87MG. Sun [Shouheng Sun, Brown University chemist –ed.] and his collaborators concentrated specifically on the nanoparticle’s size and the thickness of the peptide coating, which ensures the nanoparticle attaches to the tumor cell.
Size is important because the trick is to create a nanoparticle that is small enough to navigate through the bloodstream and reach the diseased area. Bigger particles tend to stack up, creating the circulatory system’s version of a traffic jam. Sun’s team developed a nanoparticle that is about 8.4 nanometers in overall diameter — some six times smaller than the size of particles currently used in medicine.
The coating, while integral to the nanoparticles’ attachment to the tumor 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. Sun’s 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. Sun’s nanoparticles are like having a 50,000-watt radio transmitter versus a 150-watt station; it’s easier for the MRI to "hear" 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 U87MG tumor cell. The team plans to test the particle’s ability to bind with other tumor cells in further animal experiments.
Press release: Brown Chemists Create Cancer-Detecting Nanoparticles
Image caption: The illustration (top) shows how a RGD peptide-coated iron oxide nanoparticle binds with an integrin-rich tumor cell. At bottom left is a MRI of a mouse with the implanted U87MG tumor (red circle). At bottom right is an optical image that reveals iron oxide nanoparticles (blue) amassed in the tumor area (pink). Credit: Jin Xie, Brown University