guanosine-diphosphate and Pancreatic-Neoplasms

Since taxol (NSC 125975) and tiazofurin (NSC 286193) attack at two different sites in microtubular synthetic processes, we tested the rationale that the two drugs might be synergistic in human ovarian (OVCAR-5), pancreatic (PANC-1) and lung carcinoma (H-125) cells and in rat hepatoma 3924A cells. In human OVCAR-5, PANC-1, H-125 and rat 3924A cells, for taxol the anti-proliferative IC50 was 0.05, 0.06, 0.03 and 0.04 microM, respectively; for tiazofurin IC50 = 8.3, 2.3, 1.8 and 6.9 microM. Thus, the concentrations for taxol required for IC50 for inhibiting cell proliferation were 166-, 38-, 60- and 173-fold lower than those for tiazofurin. Taxol and tiazofurin proved synergistic in all four cell lines tested. The synergism of taxol with tiazofurin should have implications in the clinical treatment of human solid tumors with particular relevance to ovarian, pancreatic, lung and hepatocellular carcinomas.

Topics: Animals; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Carcinoma; Carcinoma, Adenosquamous; Cell Division; Drug Screening Assays, Antitumor; Drug Synergism; Female; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Liver Neoplasms, Experimental; Lung Neoplasms; Ovarian Neoplasms; Paclitaxel; Pancreatic Neoplasms; Rats; Ribavirin; Spindle Apparatus; Tumor Cells, Cultured

Glucagon-like peptide-1 (7-36)amide (GLP-1 (7-36)amide) represents a physiologically important incretin in mammals including man. Receptors for GLP-1 (7-36)amide have been described in RINm5F cells. We have solubilized active GLP-1(7-36)amide receptors from RINm5F cell membranes utilizing the detergents octyl-beta-glucoside and CHAPS; Triton X-100 and Lubrol PX were ineffective. Binding of radiolabeled GLP-1(7-36)amide to the solubilized receptor was inhibited concentration-dependently by addition of unlabeled peptide. Scatchard analysis of binding data revealed a single class of binding sites with Kd = 0.26 +/- 0.03 nM and Bmax = 65.4 +/- 21.24 fmol/mg of protein for the membrane-bound receptor and Kd = 22.54 +/- 4.42 microM and Bmax = 3.9 +/- 0.79 pmol/mg of protein for the solubilized receptor. The binding of the radiolabel to the solubilized receptor was dependent both on the concentrations of mono- and divalent cations and the protein/detergent ratio in the incubation buffer. The membrane bound receptor is sensitive to guanine-nucleotides, however neither GTP-gamma-S nor GDP-beta-S affected binding of labeled peptide to solubilized receptor. These data indicate that the solubilized receptor may have lost association with its G-protein. In conclusion, the here presented protocol allows solubilization of the GLP-1(7-36)amide receptor in a functional state, and opens up the possibility for further molecular characterization of the receptor protein.

Topics: Animals; Cations; Detergents; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucagon-Like Peptides; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Insulinoma; Pancreatic Neoplasms; Peptide Fragments; Peptides; Protein Binding; Rats; Receptors, Cell Surface; Receptors, Glucagon; Solubility; Thionucleotides; Tumor Cells, Cultured

The growth-inhibiting peptide hormone somatostatin stimulates phosphotyrosine phosphatase activity in the human pancreatic cell line MIA PaCa-2. This hormonal activation was mediated by a pertussis toxin-sensitive guanosine 5'-triphosphate-binding protein (G protein) in the membranes of these cells. Activation of this G protein by somatostatin stimulated the dephosphorylation of exogenous epidermal growth factor receptor prepared from A-431 cells in vitro. This pathway may mediate the antineoplastic action of somatostatin in these cells and in human tumors and could represent a general mechanism of G protein coupling that is utilized by normal cells in the hormonal control of cell growth.

Topics: Adenosine Triphosphate; Carcinoma, Squamous Cell; Cell Line; Cell Membrane; Dose-Response Relationship, Drug; Enzyme Activation; ErbB Receptors; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Humans; Kinetics; Pancreatic Neoplasms; Peptides; Pertussis Toxin; Phosphorylation; Protein Kinases; Protein Tyrosine Phosphatases; Somatostatin; Thionucleotides; Virulence Factors, Bordetella