There is an unmet need in clinical diabetes research to directly and non-invasively measure the insulin reserves of the pancreas. We propose to develop imaging agents that will allow visualization and quantitative measurement of the insulin content using PET or SPECT imaging. When combined with measurements of insulin resistance, insulin secretion response, and tissue glucose consumption, such a method will enable the comprehensive assessment of an individual's metabolic condition. This will be a useful tool in the hands of researchers for elucidating the mechanism of diabetes development. It will also provide a meaningful method for monitoring existing therapeutic interventions, for quantitative evaluation of new drug therapies (especially regenerative therapy or those treatments purported to have 2-cell protective effects), and an effective means of stratifying an already enormous population of individuals at risk for developing type 2 diabetes. Theoretical feasibility studies grounded in previously published data have indicated that our molecular target has the potential to be a good biomarker for the amount of insulin available in the pancreas. Our goal is to verify this prediction experimentally. For this we need to develop an assay which would allow us to test binding of prospective imaging agents to the target in biological context in vitro: pancreatic tissue and islets. In this proposal, we plan to optimize the properties of known small molecule ligands to our target for high affinity, low plasma protein binding and an appropriate balance between solubility and membrane penetration capability. These ligands will be radiolabeled and used to develop the cell- and tissue-based assays necessary for the first phase of target validation. Further work will be aimed at in vivo target validation studies using the ligands identified at this phase as potential imaging agents.
The broad goal of the proposed research is to develop imaging agents that will allow visualization and quantitative measurement of the insulin reserves of the pancreas using PET or SPECT imaging. Such a test will facilitate faster development of drugs, better choice of therapies, and will also allow diagnosis and earlier intervention, which has the potential to decrease the incidence of the disease by 30-50%. We have identified a new target for this purpose and propose to develop the necessary assays and ligands for in vitro target validation.