Article

1001. Metabolic Biotinylation of Cell Surface Receptors for In Vivo Imaging

Center for Molecular Imaging Research, Massachusetts General Hospital-East, Building 149, 13th Street, Charlestown, Massachusetts 02129, USA.
Nature Methods (Impact Factor: 25.95). 06/2006; 3(5):391-6. DOI: 10.1038/nmeth875
Source: PubMed

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.

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Available from: Jan Grimm, Sep 26, 2014
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    • "Indirect MRI labeling involves genetic manipulations and enables the cell to use either endogenous or exogenous substrates. Methods of indirect MRI labeling include: (1) genes encoding cell surface receptors/ligands are expressed in the cell to bind MRI probes that have been functionalized with streptavidin or transferrin 62, 63; (2) an HSV thymidine kinase is introduced in the cell to trap thymidine analogues that are detectable by CEST MRI 64; (3) iron-binding proteins (e.g., ferritin) are expressed in the cell to capture endogenous irons, which can produce paramagnetic contrast signals 65, 66; and (4) proteins rich in amide protons (e.g., lysine-rich protein, LRP) are produced in the cell and can be readily detected by CEST MRI 67. To address the concern of intracellular stability of the LRP gene, a newer MRI reporter gene based on human protamine‑1 (hPRM1) has been developed 68. "
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    • "The AP tag may also be replaced with the biotin acceptor domain from Propionibacterium shermanii 1.3S- transcarboxylase (PSTCD), which is recognized and biotinylated by an endogenous biotin ligase in mammalian cells. A displayed protein containing PSTCD may be directly labeled with streptavidin conjugated to magnetic nanoparticles or fluorophores (Tannous et al. 2006). "
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    • "Since then, four main categories of MRI reporter genes have emerged. They involve increasing endogenous accumulation of iron 68-70, exploiting cell surface interactions 71, 72, harnessing enzymatic reactions 67, 73, 74, or employing chemical exchange saturation transfer (CEST) 75, 76. "
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