Development of (15N)2-Diazirine-Tagged Molecular Probes for Hyperpolarized Magnetic Resonance Imaging of Cancer Biomarkers

Abstract

Hyperpolarized magnetic resonance imaging (HP-MRI) is a non-invasive imaging modality that allows for direct and real-time monitoring of metabolism in vivo with high soft-tissue contrast and spatial resolution. HP-MRI has transformed cancer imaging by targeting important biomarkers related to aberrant glucose utilization in cancer cells. However, many cancers exhibit metabolic reprogramming toward glutamine dependence. Given the central role of glutaminolysis in tumor growth and proliferation, imaging of glutamine metabolism offers an opportunity to complement existing diagnostic strategies. Current HP MRI probes for glutaminolysis suffer from short windows of detection (T1= 30-40 s) which highlights the necessity for molecular probes with long-lasting signals to better investigate biochemical processes.This dissertation reports the synthesis and characterization of probes that utilize (15N)2-diazirine tags as long-lasting signaling units for direct monitoring of glutamine metabolism as well as related disease biomarkers. Herein we disclose the design and synthesis of highly functionalized diazirine-tagged glutamine probes 4-(15N)2-DT-Gln and 3-(15N)2-DT-Gln that target glutaminase. Initial investigations of these probes highlight the long imaging window afforded by (15N)2-diazirine tags, while also revealing practical limitations associated with its incorporation into amino-acid backbones. Additionally, we disclose the rational design, synthesis and evaluation of a successful probe, (15N)2-DT-GG-PA, utilized in in vitro and in vivo imaging of γ-glutamyl transferase (GGT), a cancer biomarker that is metabolically related to glutamine utilization. Overall, this work highlights synthetic challenges in installation of (15N)2-diazirine tags and represents the first successful in vivo example of a hyperpolarized (HP) nitrogen-15 MRI probe that utilizes such tags, highlighting the potential of this strategy for developing new HP probes for in vivo metabolic imaging.