Neurotensin interacts with carbachol, secretin, and caerulein in the stimulation of the exocrine pancreas of the rat in vitro

In the present investigation the effect of neurotensin on pancreatic secretion of isolated pancreatic lobules from the rat was examined. We found a dose- and time-dependent stimulation of amylase release beginning with a concentration of 10(-9) M neurotensin. This response was potentiated by the cholinergic agonist carbachol, the gastrointestinal peptide secretin, and the CCK analogue caerulein. As we found neurotensin-immunoreactive nerves within the pancreas and as neurotensin-like immunoreactivity is present in the circulation (found previously), neurotensin may well be a further peptide taking part in the regulation of exocrine pancreatic secretion either as a hormone or a neurotransmitter. Neurotensin would then cooperate with cholinergic mechanisms, secretin, and CCK.     

Dose-response comparisons of canine plasma gastroenteropancreatic hormone responses to bombesin and the porcine gastrin-releasing peptide (GRP)

This study compares the potencies of the porcine gastrin-releasing peptide (pGRP) and bombesin, in causing elevations of canine plasma gastroenteropancreatic (GEP) levels. In the dose range 0-600 pmol . kg-1 . h-1, infusion of both peptides resulted in obvious dose-related elevations of plasma levels of gastrin, pancreatic polypeptide, enteroglucagon, immunoreactive pancreatic glucagon, and insulin. In this dose range, no significant difference in potency between the two peptides in elevating plasma levels of the above hormones was observed. The results of this study, demonstrating equimolar potency of pGRP and bombesin, are in contrast to previous studies reporting that pGRP was less potent than bombesin in causing certain bioactivities in the rat following intracranial administration of the two peptides.     

Influence ofl-thyroxine,l-triiodothyronine,thyroid stimulating hormone,or estradiol on the cell kinetics of cultured mammary cancer cells

Summary We describe the in vitro influence of 3,5,3′-triiodo-l-thyronine (T₃),l-thyroxine (T₄), a thyroid-stimulating hormone (TSH), and/or estradiol (E₂: chosen as the control of the methodology) on the cell kinetics (cell distribution in the S+G₂+M phases) of mouse MXT and human MCF-7 mammary cancer cells. Experiments were performed by means of a cell image processor, analyzing MCF-7 or MXT cells that had been grown on glass cover slips and whose nuclei had been stained by the Feulgen reaction, which is selective and quantitative (stoichiometric) with respect to DNA. We show that T₃, T₄, and TSH at 0.01 μM dramatically stimulate the cell kinetics of the MXT mouse and the MCF-7 human mammary cancer cell lines. Indeed, the three hormones bring about a significant transient increase in the S+G₂+M fraction as does E₂. Furthermore, our data indicate that E₂ and TSH are antagonistic with regards to MXT or MCF-7 cell kinetics. This work is supported by grants awarded by the IRSIA and the Fonds de la Recherche Scientifique Médicale (FRSM, Belgium).     

Biomechanical interactions of cancer cells with the microvasculature during metastasis

Metastasis is a major, life-threatening complication of cancer. The bloodstream is the most important disseminative route for cancer cells liberated from their parent tumors. Single circulating cancer cells are arrested in the microvasculature, where the vast majority are killed by rapid or slow processes, and the relatively few survivors grow into micrometastases. We review the underlying causes of one type of rapid cancer cell death in the microcirculation, namely, that caused by biomechanical interactions of cancer cells with microvessel walls, which may result in cell surface membrane expansion and lethal rupture. These lethal interactions appear to be important rate-regulators in hematogenous metastasis, and to dictate some aspects of metastatic patterns. Although these are not the only interactions involving cancer cells, in contrast to others involving cellular and humoral defense mechanisms, they have received comparatively little attention.     

Cyproheptadine metabolites inhibit proinsulin and insulin biosynthesis and insulin release in isolated rat pancreatic islets

The contribution of drug metabolites to cyproheptadine (CPH)-induced alterations in endocrine pancreatic -cells was investigated by examining the inhibitory activity of CPH and its biotransformation products, desmethylcyproheptadine (DMCPH), CPH-epoxide and DMCPH-epoxide, on hormone biosynthesis and secretion in pancreatic islets isolated from 50-day-old rats. Measurement of (pro)insulin (proinsulin and insulin) synthesis using incorporation of ³H-leucine showed that DMCPH-epoxide, DMCPH and CPH-epoxide were 22, 10 and 4 times, respectively, more potent than CPH in inhibiting hormone synthesis. The biosynthesis of (pro)insulin was also inhibited by CPH and DMCPH-epoxide in islets isolated from 21-day-old rat fetuses. The inhibitory action of CPH and its metabolites was apparently specific for (pro)insulin, and the synthesis of other islet proteins was not affected. Other experiments showed the metabolites of CPH were active in inhibiting glucose-stimulated insulin secretion but were less potent than the parent drug in producing this effect. CPH and its structurally related metabolites, therefore, have differential inhibitory activities on insulin synthesis and release. The observation that CPH metabolites have higher potency than CPH to inhibit (pro)insulin synthesis, when considered with published reports on the disposition of the drug in rats, indicate that CPH metabolites, particularly DMCPH-epoxide, are primarily responsible for the insulin depletion observed when the parent compound is given to fetal and adult animals.Abbreviations CPH cyproheptadine - CPH-epoxide cyproheptadine-10-11-epoxide - DMCPH desmethylcyproheptadine - DMCPH-epoxide desmethylcyproheptadine-10,11-epoxide - HPLC high-performance liquid chromatography - KBB Krebs biocarbonate buffer Recipient of a Society of Toxicology Predoctoral Research Fellowship.Present address: Department of Biochemistry, The University of Hong Kong, Hong Kong.     

Ras interaction with the GTPase-activating protein (GAP)

Biologically active forms of Ras complexed to GTP can bind to the GTPase-activating protein (GAP), which has been implicated as possible target of Ras in mammalian cells. In order to study the structural features of Ras required for this interaction, we have evaluated a series of mutant ras proteins for the ability to bind GAP and a series of Ras peptides for the ability to interfere with this interaction. Point mutations in the putative effector region of Ras (residues 32-40) that inhibit biological activity also impair Ras binding to GAP. An apparent exception is the Thr to Ser substitution at residue 35; [Ser-35]Ras binds to GAP as effectively as wild-type Ras even though this mutant is biologically weak in both mammalian and S. cerevisiae cells. In vitro, [Ser-35]Ras can also efficiently stimulate the S. cerevisiae target of Ras, adenylyl cyclase, indicating that other factors may influence Ras/protein interactions in vivo. Peptides having Ras residues 17-44 and 17-32 competed with the binding of Ras to E. coli-expressed GAP with IC50 values of 2.4 and 0.9 microM, respectively, whereas Ras peptide 17-26 was without effect up to 400 microM. A related peptide from the yeast GTP-binding protein YPT1 analogous to Ras peptide 17-32 competed with an IC50 value of 19 microM even though the YPT1 protein itself is unable to bind to GAP. These results suggest that determinants within Ras peptide 17-32 may be important for Ras binding to GAP.     

Characterization of differentiated syrian golden hamster pancreatic duct cells maintained in extended monolayer culture

Summary Epithelial cells isolated from fragments of hamster pancreas interlobular ducts were freed of fibroblast contamination by plating them on air-dried collagen, maintaining them in serum-free Dulbecco's modified Eagle's (DME):F12 medium suppleneted with growth factors, and selecting fibroblast-free aggregates of duct cells with cloning cylinders. Duct epithelial cells plated on rat type I collagen gel and maintained in DME:F12 supplemented with Nu Serum IV, bovine pituitary extract, epidermal growth factor, 3,3′, 5-triodothyronine, dexamethasone, and insulin, transferrin, selenium, and linoleic acid conjugated to bovine serum albumin (ITS⁺), showed optimal growth as monolayers with a doubling time of about 20 h and were propagated for as long as 26 wk. Early passage cells consisted of cuboidal cells with microvilli on their apical surface, complex basolateral membranes, numerous elongated mitochondria, and both free and membrane-bound ribosomes. Cell grown as monolayers for 3 mo. were more flattened and contained fewer apical microvilli, mitochondria, and profiles of rough surfaced endoplasmic reticulum; in addition, there were numerous autophagic vacuoles. Functional characteristics of differentiated pancreatic duct cells which were maintained during extended monolayer culture included intracellular levels of carbonic anhydrase and their capacity to generate cyclic AMP (cAMP) after stimulation by 1×10⁻⁶ M secretin. From 5 to 7 wk in culture, levels of carbonic anhydrase remained stable but after 25 to 26 wk decreased by 1.9-fold. At 5 to 7 wk of culture, cyclic AMP increased 8.7-fold over basal levels after secretin stimulation. Although pancreatic duct cells cultured for 25 to 26 wk showed lower basal levels of cAMP, they were still capable of generating significant levels of cAMP after exposure to serretin with a 7.0-fold increase, indicating that secretin receptors and the adenyl cyclase system were both present and functional. These experiments document that pancreatic duct monolayer cultures can be maintained in a differentiated state for up to 6 mo. and suggest that this culture system may be useful for in vitro physiologic and pathologic studies. This research was supported by grant CA34051 from the National Cancer Institute, Bethesda, MD.     

Normal human colon cells suppress malignancy when fused with colon cancer cells

Summary Normal human colon mucosa cells and cells obtained from histologically normal tissues near that cancer were fused with human colon cancer cells. Resultant hybrid populations of normal and malignant cell fusions behaved as nonmalignant cells in culture, were unable to grow in soft agar, did not express tumor-associated antigens, and were nontumorigenic in nude mice. Autofusion of the cancer cell population led to a phenotype intermediate between normal and malignant cells. That is, the cultures had a much lower plating efficiency in soft agar, and the tumors had a longer latency and slower growth rate in nude mice. This is the first cell culture system to demonstrate that normal epithelial cells can suppress malignancy of their autologous cancer cells, and is a prelude to more extensive studies of genetic events involved in malignant conversion of human colonic epithelium. This study was supported by The University of Texas Health Science Center at San Antonio Center for Human Cell Biotechnology and a graduate student stipend (T. J.) from the Department of Cellular and Structural Biology.     

Effects of interleukin-12 on in vitro culture with interleukin-2 of regional lymph node lymphocytes from lung cancer patients

 In the present study, we carried out a functional analysis of regional lymph node lymphocytes (RLNL) from patients with lung cancer after in vitro activation by interleukin-2 (IL-2) and interleukin-12 (IL-12). IL-12 (100 U/ml) enhanced both the proliferation and cytotoxic activity of RLNL in a culture with low doses of IL-2 (5 – 10 JRU/ml). After comparing an RLNL culture with a low dose of IL-2 alone, a higher proportion of CD8⁺ cells and CD56⁺ cells and a lower proportion of CD4⁺ cells were found in the culture with both IL-12 and a low dose of IL-2. Such a combination of the cytokines effectively activated RLNL in terms of the expression of IL-2 receptors. In the culture condition of IL-12 and a low dose of IL-2, a synergistic effect was observed in the production of such cytokines as interferon γ, tumor necrosis factor α (TNFα), and TNFβ, as well as in tumor cytotoxicity. However, the addition of IL-12 inhibited the cytotoxicity of RLNL in the culture with a high dose of IL-2 (100 JRU/ml). This inhibition is considered to be partially due to the endogenous production of TNFα by lymphocytes, because the neutralization of TNFα bioactivity partially restored the cytotoxic activities of RLNL. Furthermore, in the presence of hydrocortisone, IL-12 synergistically enhanced the cytotoxic activity of RLNL cultured with a high dose of IL-2. These results provide useful information about the improvement of adoptive immunotherapy against cancer using RLNL. Received: 2 February 1996 / Accepted: 30 July 1996     

Characterisation of the anti-bladder-cancer monoclonal antibody BLCA-8: Identification of its antigen as a neutral glycolipid

A monoclonal antibody, BLCA-8, was raised against the human bladder cancer cell line, UCRU-BL-17CL. By flow cytometry and immunoperoxidase staining, this antibody was found to possess high specificity for bladder tumours, some reactivity with fetal tissues, and no reactivity with normal bladder, or any normal or malignant tissue. This high specificity and the stability of the antigen to the urinary environment suggest that BLCA-8 may have potential for use as an anti-bladder-cancer therapeutic agent. By thin-layer chromatography and autoradiography, BLCA-8 was found to bind four components within the neutral lipid fraction of a bladder cancer cell line, UCRU-BL-17/23. These components hadR _F values of 0.22, 0.16/0.15 (doublet), 0.12 and 0.08, and migrated below globoside, indicating the presence of more than four sugars. By enzyme-linked immunosorbant assay and thin-layer chromatography it was found that the binding of BLCA-8 to the lipid extract was increased by both mild alkaline hydrolysis and enzymatic treatments, indicating that adjacent phospholipids and glycolipids interfere with the accessibility of the antibody-binding site. Full biochemical characterisation of the BLCA-8 antigen is currently underway.