Metabolic imaging using hyperpolarized (HP) 13C and 15N substrates offers the potential to monitor intermediary metabolism in tissues throughout the human body. HP-[1-13C]pyruvate is the molecule most widely used in HP studies, but there are several other TCA cycle intermediates that meet the requirements of a good metabolic imaging candidate probe. In this TR&D Project we propose to develop new 13C- and 15N-enriched compounds as reporters of tissue physiology and metabolism. We will apply these hyperpolarized sensors to measure important physiological parameters at sensitivity levels never before achieved by MRI. One of the main thrusts of this proposal is to develop HP-13C labeled mono-esters of TCA cycle intermediates to image whole-body glucose production because this could potentially have an enormous impact on development of new drugs to control glucose levels in type 2 diabetic patient populations. Thus, Aim 1 will focus on the design, synthesis and DNP hyperpolarization of monoesters of 13C-labeled TCA cycle intermediates such as [4-13C]oxaloacetate-1-ethyl ester, [4-13C]malate-1-ethyl ester, and [1-13C]-2-ketoglutarate-4-ethyl ester. The 13C-enriched carbon in these molecules should display long T1 values and these derivatives should enter hepatocytes quickly via mono-carboxylate transporters and hydrolyze to their respective dicarboxylate intermediates. 15N is another attractive nucleus for the design of HP-probes but its potential for metabolic imaging has largely remained unexplored.
In Aim 2 novel 15N- labeled molecular design platforms are proposed that will yield HP-15N-agents for imaging pH and free Zn2+-levels in zinc-rich tissues.. Considering the fact that HP-[1-13C]pyruvate is the most popular molecule of choice for metabolic MR imaging, in Aim 3, a practical chemical approach will be developed to produce gram quantities of HP-[1-13C]pyruvate by starting with an ester of pyruvate and para-H2. If we are successful, this would make HP-[1-13C]pyruvate more widely available to MRI clinics across the country for molecular imaging of cancer and other metabolic diseases. The overarching goal of this core project is to develop and implement novel hyperpolarized agents in vivo to image important biomarkers and metabolic pathways in type 2 diabetes, cancer and other diseases.
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