There is currently no non-invasive method to quantify beta-cell mass in humans. Continued existence of this gap represents an important problem because it potentially limits health care of patients with diabetes, with pancreas transplants, and leaves in place an unmet need for an imaging tool not only for mechanistic studies which evaluate the pathogenesis of this disease, but also as an outcome tool for new pharmacologic interventions. The long-term goal is to develop imaging methods, based on novel probes, for non-invasive assessment of beta cell mass (BCM) and function. Within the pancreas the glucagon-like peptide-1 receptor (GLP-1R) is uniquely expressed in the islets. The objective in this application is to develop and test a novel class of radiotracers for positron emission tomography (PET) imaging of beta cell mass based on analogues of GLP-1. The central hypothesis is GLP-1 based PET probes can be used to monitor BCM change with clinically acceptable specificity, accuracy, and reproducibility. This hypothesis has been formulated on the basis of preliminary data derived from successful development of a bicyclic GLP-1 analog for beta cell specific imaging in mice. The rationale for the proposed research is that development of these probes and the attendant imaging method has the potential to translate into better health care of patients with diabetes, currently 8% of the US population, and patients with pancreas or islet cell transplants, and insulinomas. Guided by strong preliminary data, the hypothesis will be tested by pursuing three specific aims:
Aim 1 : To synthesize, characterize, and evaluate NOTA-(EM2198)n. Multimers of EM2198 on a novel class of bifunctional chelator scaffolds together with the PET isotope, 68Ga will enhance the sensitivity and specificity of imaging. The scaffold precursors and EM2198 conjugates will be synthesized by existing methods. The biological behavior will be evaluated using cell lines, freshly isolated rat/pig islets, and mouse models;
Aim 2 : To determine the accuracy and reproducibility of PET-CT imaging of BCM in a clinically relevant model, namely Ossabaw minipigs. Mini-pigs have genetic, anatomical, and physiological similarities to humans. The Ossabaw miniature pigs develop type 2 diabetes when placed on an atherogenic diet. PET measures of 68Ga-NOTA-EM2198 uptake will be correlated with the gold standard of pathology assay of porcine pancreas.
Aim 3 : To longitudinally monitor the dynamic BCM change in T2D Ossabaw swine and assess the potential toxic effect of the longitudinal imaging procedure. Serial PET-CT imaging will be performed on lean and diabetic Ossabaw swine before the onset and during the progression of T2D. Imaging and clinical outcomes will be correlated. The potential risk of this longitudinal imaging technique and radiation dosimetry will be determined. Upon the successful completion of this project, we expect to have a safe imaging technique available for further clinical evaluation.
The proposed research is relevant to public health because the development of novel imaging probes to noninvasively monitor pancreatic beta cell mass (BCM) is ultimately expected to impact health care of patients with diabetes, a global epidemic. Thus, the proposed research is relevant to the part of NIH's mission that pertains to seeking fundamental knowledge that will reduce the burdens of illness.
