(13)C MR reporter probe system using dynamic nuclear polarization.

Reporter-based cell detection and localization in vivo may become an important imaging tool with the emergence of cellular therapy. With the strong signal enhancement provided by dynamic nuclear polarization, an NMR-based reporter probe system utilizing specific enzyme expression and activity can potentially provide stable, high-resolution visualization of the cells of interest noninvasively. In this work, a proof-of-concept (13) C MR reporter system, using the aminoacylase-1 reporter gene (Acy-1) and prepolarized [1-(13) C]N-acetyl-L-methionine as the paired substrate, was developed. Using a 3-T MR scanner, the feasibility of detecting and imaging de-acetylation of the prepolarized (13) C-labeled substrate by the aminoacylase-1 enzyme was demonstrated with purified protein in solution by dynamic (13) C MRS and two-dimensional MRSI experiments. The potential to perform targeted MRI of cells using this system was also demonstrated by (13) C MR measurement of aminoacylase-1 activity in HEK 293 cells transfected with the Acy-1 gene. The de-acetylation of the substrate was not observed in control cells.