Nanoparticles could mark spots for surgery.

When a tumor starts spreading, cancer cells begin showing up in nearby lymph nodes. That's why cancer surgeons often remove and examine nodes as they plan treatments.

A new panicle studded with gadolinium ions may soon help surgeons extract only those nodes most likely to harbor cancer, say its developers. Doctors would inject the spherical, nanoscale particles into a tumor and then track them using magnetic resonance imaging (MRI), says Hisataka Kobayashi of the National Cancer Institute in Bethesda, Md.

Dubbed G6, the multilayered spherical particles are made up largely of nitrogen-rich chemical groups built into structures known as dendrimers. The researchers then coated the dendrimers with more than 200 gadolinium ions housed within cages of nitrogen and oxygen atoms. The ions are apparent in MRI scans. Physicians already use the gadolinium complexes by themselves to identify potentially cancerous lymph nodes, but these tend to spread so readily that they migrate to tissues that aren't likely to contain cancer.

The G6 particles, which are just over 10 nanometers in diameter, circumvent that problem. They're small enough to migrate rapidly through lymphatic vessels, mimicking how cancer cells might spread from a tumor to lymph nodes, yet large enough to stay inside the vessels and nodes.

Kobayashi and his colleagues experimented in mice with spheres of different sizes before settling on G6 as the version to pursue in human studies. They describe their new diagnostic dendrimers in the May 5 Journal of the National Cancer Institute.--B.H.