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Abstract

An antisense MR contrast agent and its nonsense counterpart, conjugated to a peptide nucleic acid and a cell penetrating peptide were synthesized capable of
targeting cellular mRNA. Intracellular uptake in non-targeted 3T3 fibroblasts was confirmed by fluorescence and MR studies. The intracellular relaxation rate R1,cell increased significantly already at a labeling concentration of 0.5 μM, thus contrast enhancement was also detectable. An in vitro binding assay provided first evidence of a higher specificity of the antisense contrast agent. These results demonstrate its potential to be used as a targeted contrast agent for tracking mRNA transcription in cells by MRI.