Rusty particles spot tumors

Enzymes that can flip the magnetic properties of iron oxidenanoparticles could provide oncologists with a way to image tumorsalmost as quickly and easily as radiologists view broken bones withX-rays. Sangeeta Bhatia in Boston, Massachusetts and colleagues at theHarvard-MIT Division of Health Sciences and Technology have found thatthe aggregation properties of Fe3O4 nanoparticlescan be used as a novel imaging agent in magnetic resonance imaging. Theycoated one half of a sample of the nanoparticles with the protein biotinand the other with neutravidin. They then added peptide-attached PEG asa protecting group to the proteins to prevent them sticking togetherspontaneously. The peptide anchor is cleaved only by the action of atumor-specific enzyme, matrix metalloproteinase-2 (MMP-2). Thenanoparticles can thus float freely until they reach a tumor, MMP-2 thencleaves off the protecting groups, leaving the biotin and neutravidinfree to bond. Once this occurs the nanoparticles form significantclusters visible to MRI, allowing a precise picture of the tumor's shapeto be obtained.