REPORTER GENE MRI AGENTS FOR QUANTITATIVE DETECTION OF GLYCOSIDE HYDROLASE ENZYMES

Imaging agents for the non-invasive in vivo detection of enzyme activity in preclinical and clinical settings could have fundamental implications in the field of drug discovery. In particular, reporter gene technologies have been employed to monitor gene expression levels, track cells to study biological development or cell transplantation therapy, and monitor gene therapy. Reporter gene imaging has primarily used optical imaging and radionuclide imaging modalities, but these modalities have limitations such as a shallow depth of view for optical imaging, the use of ionizing radiation for radionuclide imaging, and poor spatial resolution for both imaging modalities. Magnetic resonance imaging (MRI) has also been used for reporter gene imaging, but current MRI methods are notoriously insensitive for this application. Herein we report the design and synthesis of new diamagnetic MRI agents that quantitatively detect β-galactosidase and β-glucuronidase activities by measuring changes in chemical exchange saturation transfer (CEST). Based on a modular approach, we incorporated the enzymes’ respective substrates to a salicylate moiety with a chromogenic spacer via a carbamate linkage. This furnished highly selective diamagnetic CEST agents that detected and quantified enzyme activities of glycoside hydrolase enzymes. Michaelis-Menten enzyme kinetics studies were performed by monitoring catalyCEST MRI signals, which were validated with UV-vis assays.