A new nanoparticle contrast agent gives a clearer picture of a mouse's brain tumor in both MRI and optical images (left column) than is possible without the agent (right column). The tumor is located in the cerebellum. Credit: Cancer Research

Researchers at the University of Washington, Seattle have made the first imaging nanoparticle that can cross the blood-brain barrier. The nanoparticle, which specifically targets tumor cells, might help surgeons better pinpoint the boundaries of brain tumors.

The blood vessels that serve the brain are much more selective about what gets through than those feeding the rest of the body's organs. This helps protect the brain from infection, but it also makes it difficult to get drugs and image-contrast agents inside the brain. The barrier can be temporarily broached using drugs, but at the risk of infection. This has made it difficult to apply recent developments in the field of molecular imaging, which uses targeted nanoparticles to light up tumor cells, to the brain. Targeted imaging could be particularly useful for imaging brain tumors, since these tend to be very invasive, infiltrating the surrounding brain tissue, making it difficult to remove them without damaging surrounding tissues, leading to cognitive problems.

The Seattle researchers developed a nanoparticle that is visible on magnetic resonance imaging scans and under the near-infrared light used by surgical microscopes. They tuned the particle's properties--size, fat content, and electrical charge--so that it could cross the blood-brain barrier. It's made up of an iron-oxide sphere coated with a fluorescent protein and a protein that's targeted to tumor cells. When administered through a blood vessel to mice carrying brain tumors, the nanoparticle, which is described this week in the journal Cancer Research, improved contrast in brain imaging scans.