Highly Adaptable 15N-Molecular Tags for Development of Novel Hyperpolarized Molecular Imaging Probes

Abstract

Hyperpolarized magnetic resonance spectroscopic imaging (HP-MRSI) enables non-invasive visualization of metabolism and physiological activities in real-time. Hyperpolarized agents developed to date are primarily 13C-labeled metabolites with short polarization lifetimes of less than a minute, limiting the imaging assay to fast metabolic pathways. To expand on the applications of HP-MRSI, we proposed the use of a versatile 15N-molecular tagging strategy. This dissertation reports our exploration and application of highly adaptable 15N-molecular handles for development of hyperpolarized molecular imaging probes. Towards this goal, we have investigated 15N2-diazirines and 15N3-azides as biocompatible HP tags with long polarization lifetimes. Several 15N-tagged biological molecules were prepared, including amino acid, glucose, and drug molecules. Hyperpolarization with a d-DNP method demonstrated high signal enhancements (over 400,000-fold) and long 15N relaxation lifetimes (T1) of average 3–4 minutes in aqueous solutions, which warrants a long MR imaging window. Moreover, we have rationally designed and synthesized novel 15N-labeled reaction-based probes for sensing hydrogen peroxide (H2O2) and nitric oxide (NO) as biomarkers for oxidative stress. We were able to observe the 15N-signal from our 15N-labeled H2O2 sensing probe in vivo using an animal model, which presents exciting progress in the field. Additionally, we explored various molecular probe designs to pursue the most practical 15N-labeled gamma-glutamyl transferase (GGT) sensor. These reaction-based redox and enzyme sensing probes showed favorable hyperpolarization and bioimaging properties. Our work on innovative de novo chemical probes highlights the unprecedented HP-MRSI applications for imaging disease biomarkers.