MASSACHUSETTS GENERAL HOSPITAL, THE
Diabetes mellitus is characterized by the selective destruction of insulin-producing beta- cells, which leads to a deficiency in insulin secretion and as a result, to hyperglycemia. As islet transplantation becomes an acceptable clinical modality for restoring normoglycemia in Type 1 diabetic patients, there is a critical need for non-invasive imaging assessment of the fate of islet grafts because of significant graft loss after the procedure. At the same time, the potential of gene therapy utilizing RNA interference holds promise for silencing harmful genes and improving islet graft resistance to damaging factors after transplantation. In this application we propose for the first time to combine therapy and in vivo imaging and synthesize and test a novel gene therapy imaging probes that in addition to its silencing properties can also serve as an imaging contrast agent capable of detecting and following the fate of islet grafts in vivo after transplantation. This proposal is based on a previously developed in vivo magnetic resonance imaging (MRI) approach to assess the fate of islet grafts (1; 2; 4). The therapeutic part of this proposal is based on our prior experience in synthesizing dual- purpose probes for siRNA transfer to cancer cells with subsequent in vivo imaging of tumors (3). Here we propose to synthesize and test a multifunctional siRNA-imaging probe consisting of magnetic nanoparticles covalently linked to an siRNA molecule(s) specific for model or therapeutic targets. As siRNA targets we propose to use molecules responsible for potential graft damage. Specifically, we will target 2-2microglobulin (to prevent possible immune attack), the apoptotic proteins caspase 3, caspase 8 and Fas. Since nanoparticles are taken up by islet cells with high efficiency, no toxicity and no specificity, we expect that siRNA therapy will protect a to-be transplanted graft from autoimmune attack and allogeneic rejection. Therefore, the overall goal of this proposal is two fold: first, we propose to genetically manipulate pancreatic islets with the purpose to reduce their susceptibility to damaging factors after transplantation, and second, to monitor in vivo their survival after transplantation in diabetic animals using magnetic resonance imaging. The novel "two-in-one" siRNA-imaging probe capable of delivering genetic and contrast imaging material to the islets will be used to achieve these goals. PUBLIC HEALTH RELEVANCE The biggest challenge in pancreatic islet transplantation as it becoming an accepted clinical procedure to treat patients with Type 1 Diabetes is significant graft loss after the procedure. This proposal will combine therapy based on silencing certain genes responsible for islet death and in vivo imaging to monitor transplanted grafts. We propose to synthesize and test a novel gene therapy imaging probes that in addition to its silencing properties can also serve as an imaging contrast agent capable of detecting and following the fate of islet grafts in vivo after transplantation.