Receptor-mediated Uptake of an Enzyme-activated Mri Contrast Agent

In recent report (Nature Biotechnology 2000, 16:321-325) we presented a new approach for obtaining high resolution in vivo images of gene expression using magnetic resonance imaging (MRI). We prepared MRI contrast agents in which the access of water to the fust coordination sphere of a chelated paramagnetic ion is blocked with a galactopyranose residue that can he cleaved by beta-galactosidase, the product of a common marker gene. Following cleavage, the block is removed and the agent becomes active. Here, we present evidence that the contrast agent is taken up by cells through the asialoglycoprotein receptor.