guanylyl-imidodiphosphate and Pancreatic-Neoplasms

Pancreatic cancer is the fourth most common cancer-related mortality in the United States, and the ninth most common cause of death from cancer worldwide. The opioid growth factor (OGF), [Met5]-enkephalin, inhibits the growth of human pancreatic adenocarcinoma in vitro and in vivo, and acts in a receptor-mediated fashion. Ligand binding assays using PANC-1 human pancreatic tumor cells and [3H]-[Met5]-enkephalin were performed to identify and characterize the receptor responsible for the growth-regulatory effects of OGF in pancreatic cancer. Specific and saturable binding was detected, and a Scatchard analysis revealed that the data were consistent for a single binding site with a binding affinity of 1.2+/-0.3 nM and a binding capacity of 36.4+/-4.1 fmol/mg protein. Subcellular fractionation studies showed that binding was restricted to the nuclear fraction. Competition experiments revealed that cold [Met5]-enkephalin was the most effective ligand at displacing [3H]-[Met5]-enkephalin; ligands for mu, delta, and kappa opioid receptors exhibited little or no competition. Binding was detected in 3 other human pancreatic tumor cell lines. Receptor number in xenografts of Capan-1 was decreased 8.6-fold compared to the same cells grown in tissue culture. Binding to radiolabeled [Met5]-enkephalin was detected in pancreatic cancers obtained from surgical resections. Binding capacity, but not binding affinity, was 7.1-fold greater in normal pancreatic tissues than in pancreatic neoplasia. The function, pharmacological and biochemical characteristics, distribution, and subcellular location of OGF binding in human pancreatic cancer were consistent with the OGF receptor (OGFr). In addition, human pancreatic cancer appears to have a low number of receptors for OGF, having the net effect of diminishing control of cellular replicative events.

Topics: Adenocarcinoma; Animals; Binding Sites; Binding, Competitive; Cell Fractionation; Culture Media, Serum-Free; Enkephalin, Methionine; Guanylyl Imidodiphosphate; Humans; Hydrogen-Ion Concentration; Mice; Mice, Nude; Narcotics; Nuclear Proteins; Pancreatic Neoplasms; Protein Binding; Receptors, Opioid; Transplantation, Heterologous; Tumor Cells, Cultured

Inhibitory G proteins (Gi) play an important role in cell proliferation. In order to characterize Gi proteins in RINm5F (RIN) cells, we first established RIN cells in cell culture. Immunoblot analysis was performed on extracted G proteins using Western blot techniques and a Gi-specific antibody. We identified three prominent bands consistent with three distinct inhibitory alpha subunits of membrane-bound G protein (Gi) in RIN cells. In contrast, we identified only one prominent distinct inhibitory alpha subunit of G protein in an equal quantity of membrane-protein in our control (normal rat pancreas). In several cell types, Gi is known to mediate the inhibitory action of somatostatin on intracellular cyclic AMP (cAMP) accumulation. Therefore, we studied the action of the long-acting analogue of somatostatin, octreotide (SMS), on basal and 3-isobutyl-1-methylxanthine-stimulated cAMP accumulation in RIN cells. SMS did not inhibit cAMP accumulation or tritiated thymidine incorporation into DNA (TTID) in RIN cells. However, when treatment with SMS is supplemented with the nonhydrolyzable analogue of guanine nucleotide, Gpp(NH)p (Gpp), which is known to dissociate G proteins into its constitutive subunits, then SMS+Gpp induced an inhibitory action and significantly reduced cAMP accumulation and TTID. These data are consistent with the concept of qualitatively and functionally altered inhibitory G protein expression in the insulin-producing, islet cell (RINm5F) rat insulinoma tumor cell line. Further study of human tumors will lead to new insights into the clinical implications of G protein-mediated signal transduction in insulinoma.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Cyclic AMP; DNA, Neoplasm; Drug Combinations; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Insulinoma; Octreotide; Pancreas; Pancreatic Neoplasms; Rats; Tumor Cells, Cultured

The existence of a single or of multiple populations of glibenclamide binding sites is a subject of controversy. In the present study, radioligand binding techniques were employed to determine whether multiple populations of [3H]glibenclamide binding sites exist in pancreatic tumor (insulinoma) cells. Additional studies were performed to further characterize the binding of [3H]glibenclamide to insulinoma and cardiac membranes. [3H]Glibenclamide bound to high (0.1 nM) and low (240 nM) affinity binding sites in insulinoma membranes. The physiological relevance of multiple populations of sites is unknown. The binding of glibenclamide to insulinoma and cardiac membranes was altered by guanine nucleotides and not adenine nucleotides. This suggests glibenclamide binding can be modulated by G-proteins. Glibenclamide binding was also modulated by divalent cations. The divalent cations, Ca2+ and Zn2+, stimulated specific glibenclamide binding to cardiac and insulinoma membranes, while Mg2+ and Mn2+ enhanced cardiac binding only. Moreover, the lowering of pH from 7.4 to 6.5 was found to enhance specific glibenclamide binding. Interestingly, the magnitude of this effect was much larger in cardiac membranes. The specific nature of the regulation of glibenclamide binding by guanine nucleotides, divalent cations and pH remains to be explored.

Topics: Animals; Cations, Divalent; Dogs; Female; Glyburide; Guanosine 5'-O-(3-Thiotriphosphate); Guanylyl Imidodiphosphate; Hydrogen-Ion Concentration; In Vitro Techniques; Insulinoma; Male; Membranes; Myocardium; Nucleotides; Pancreatic Neoplasms; Potassium Channels; Rats; Receptors, Drug; Trypsin; Tumor Cells, Cultured