Somatostatin receptors and autoimmune-mediated diabetes.

Somatostatin (SST) peptide is produced by various SST-secreting cells throughout the body and acts as a neurotransmitter or paracrine/autocrine regulator in response to ions, nutrients, peptides hormones and neurotransmitters. SST is also widely distributed in the periphery to regulate the inflammatory and immune cells in response to hormones, growth factors, cytokines and other secretive molecules. SST peptides are considered the most important physiologic regulator of the islet cell, gastrointestinal cell and immune cell functions, and the importance of SST production levels has been implicated in several diseases including diabetes. The expression of SST receptors has also been found in T lymphocytes and primary immunologic organs. Interaction of SST and its receptors is also involved in T-cell proliferation and thymocyte selection. SSTR gene-ablated mice developed diabetes with morphologic, physiologic and immunologic alterations in the endocrine pancreas. Increased levels of mononuclear cell infiltration of the islets are associated with the increased levels of antigen-presenting cells located in the islets and peripancreatic lymph nodes. Increased levels of SST were also found in antigen-presenting cells and are associated with a significant increase of CD8 expression levels on CD4(+)/CD8(+) immature thymocytes. These findings highlight the crucial role of this neuroendocrine peptide and its receptors in regulating autoimmune functions.

Cell-specific cytotoxicity of human pancreatic adenocarcinoma cells using rat insulin promoter thymidine kinase-directed gene therapy.

The formation of a normal pancreas and the activation of insulin production are, in part, dependent on the expression and activation of the pancreatic duodenal homeobox gene 1 (PDX-1). The expression of PDX-1 also has been detected in various human pancreatic ductal adenocarcinoma (PDA) cell lines. This has made it possible to generate a cancer cell-specific gene expression system to treat human pancreatic cancer. In this study, we have developed a cell-specific cytotoxic model of PDA cells using the expression of herpes simplex virus thymidine kinase (TK) under the control of the rat insulin promoter (RIP-TK). We have shown that the cell-specific cytotoxicity in human PDA cells depends on the presence of PDX-1. Our results also demonstrate that in vivo PDA-specific cytotoxicity can be achieved with RIP-TK using an intraperitoneal liposomal gene delivery method followed by a short period of ganciclovir treatment in severe combined immunodeficient (SCID) mice. Furthermore, PDX-1 protein was found in all six freshly isolated human pancreas cancer specimens and two liver metastasis samples that were group-tested, suggesting the feasibility of using RIP-TK gene therapy in humans. This study may provide an alternative strategy for the future treatment of pancreatic cancer.