Development and Application of CatalyCEST MRI Contrast Agents for the Study of Enzyme Activities in Tumor Models

Abstract

The in vivo detection of enzyme activity is a significant biomarker in tumorigenesis. Assessment of enzyme activity relative to enzyme concentration can serve as quite an accurate measurement of several disease states. Chemical Exchange Saturation Transfer (CEST) MRI is a non-invasive imaging technique that can be used to evaluate enzyme activity. Compared to other contrast agents CEST MRI agents have a slower chemical exchange rate and thus have greater specificity for detecting the intended biomarker. Chapter 1 provides an overview of the advances made in the field of molecular imaging for detection of cancer biomarkers. The molecular mechanism of each technique is explained with specific examples and advantages as well as disadvantages of each technique. Chapter 2 investigates the specific example of detection of an enzyme, γ-glutamyl transferase (GGT) in ovarian cancer tumor models using a catalyCEST MRI contrast agent. This chapter discusses the step-by step evaluation of the non-metallic contrast agent, from synthesis to evaluation of its catalytic efficiency with Michaelis Menten kinetics studies and finally in vivo GGT detection in ovarian tumor models of OVCAR-8 and OVCAR-3. Chapter 3 investigates the enzyme, Kallikrein-6 and its detection in HCT116 colon cancer tumor model. In addition to enzyme detection, enzyme inhibition using Antithrombin III inhibitor has also been explored within in vitro media and in vivo HCT116 tumor model. Chapter 4 introduces the catalyCEST agent for detection of sulfatase enzyme. This chapter discusses the synthesis of this agent and its ability to detect sulfatase in bacterial cell suspension and mammalian cell suspension. These examples portray catalyCEST MRI as a platform technology for enzyme activity detection. Finally in Chapter 5 future ideas have been proposed to improve the in vivo detection and broaden the applications of catalyCEST MRI in the field of enzyme studies.