1Department of Radiology, Johns Hopkins University, Baltimore, MD, United States; 2Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, United States
The Drosophila melanogaster 2-deoxynucleoside kinase (Dm-dNK) enzyme phosphorylates a wide range of nucleoside analogs, including the fluorescent nucleoside pyrrolo-2-deoxycytidine (pyrrolo-dC). We show here that the NH proton of the pyrrolo-dC generates high CEST contrast when a saturation pulse is applied at 5.8ppm from the water protons. The formation of the pyrrolo-dC monophosphate by recombinant Dm-dNK resulted in accumulation of the probe selectively in the cytoplasm of Dm-dNK-expressing cells since its negative charge prevents cellular export. Hence, pyrrolo-dC can be used for monitoring the reporter gene Dm-dNK expression with CEST MRI.