Metabolic biotinylation of cell surface receptors for in vivo imaging

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Abstract
We have developed a versatile, potent technique for imaging cells in culture and in vivo by expressing a metabolically biotinylated cell-surface receptor and visualizing it with labeled streptavidin moieties. The recombinant reporter protein, which incorporates a biotin acceptor peptide (BAP) between an N-terminal signal sequence and a transmembrane domain, (BAP-TM) was efficiently biotinylated by endogenous biotin ligase in mammalian cells with the biotin displayed on the cell surface. Tumors expressing the BAP-TM have high sensitivity for magnetic resonance and fluorescence tomographic imaging in vivo after intravascular injection of streptavidin conjugated to magnetic nanoparticles or fluorochromes, respectively. Moreover, streptavidin–horseradish peroxidase conjugates in conjunction with a peroxidase-sensitive gadolinium agent further increased and prolonged the magnetic resonance signal. This BAP-TM allows noninvasive real-time imaging of any cell type transduced to express this reporter protein in culture or in vivo. *Note: In the version of this article originally published, reference 12 was incorrect. The correct reference 12 is Querol, M., Chen, J.W., Weissleder, R. & Bogdanov, A. Jr. DTPA-bis-amide based MR sensor agents for peroxidase imaging. Org. Lett. 17, 1719–1722 (2005). This error has been corrected in the PDF version of the article.