monensin and Adenocarcinoma

We and others have shown that the copper transporters ATP7A and ATP7B play a role in cellular resistance to cis-diaminedichloroplatinum (II) (CDDP). In this study, we found that ATP7A transfection of Chinese hamster ovary cells (CHO-K1) and fibroblasts isolated from Menkes disease patients enhanced resistance not only to CDDP but also to various anticancer drugs, such as vincristine, paclitaxel, 7-ethyl-10-hydroxy-camptothecin (SN-38), etoposide, doxorubicin, mitoxantron, and 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11). ATP7A preferentially localized doxorubicin fluorescence to the Golgi apparatus in contrast to the more intense nuclear staining of doxorubicin in the parental cells. Brefeldin A partially and monensin completely altered the distribution of doxorubicin to the nuclei in the ATP7A-expressing cells. ATP7A expression also enhanced the efflux rates of doxorubicin and SN-38 from cells and increased the uptake of SN-38 in membrane vesicles. These findings strongly suggested that ATP7A confers multidrug resistance to the cells by compartmentalizing drugs in the Golgi apparatus and by enhancing efflux of these drugs, and the trans-Golgi network has an important role of ATP7A-related drug resistance. ATP7A was expressed in 8 of 34 (23.5%) clinical colon cancer specimens but not in the adjacent normal epithelium. Using the histoculture drug response assay that is useful for the prediction of drug sensitivity of clinical cancers, ATP7A-expressing colon cancer cells were significantly more resistant to SN-38 than ATP7A-negative cells. Thus, ATP7A confers resistance to various anticancer agents on cancer cells and might be a good index of drug resistance in clinical colon cancers.

Topics: Adenocarcinoma; Adenosine Triphosphatases; Animals; Antineoplastic Agents, Phytogenic; Brefeldin A; Camptothecin; Cation Transport Proteins; Cell Membrane; CHO Cells; Cisplatin; Colonic Neoplasms; Copper; Copper-Transporting ATPases; Cricetinae; Cricetulus; Doxorubicin; Drug Interactions; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Golgi Apparatus; Humans; Irinotecan; Monensin; Transfection

Previously, we showed that monensin, Na+ ionophore, potently inhibited the growth of acute myelogenous leukemia and lymphoma cells. Here, we demonstrate that monensin inhibited the proliferation of solid tumor cells with IC50 of about 2.5 micro M. Monensin induced a G1 or a G2-M phase arrest in these cells. When we examined the effects of this drug on SNU-C1 cells, monensin decreased the levels of CDK2, CDK4, CDK6, cyclin D1 and cyclin A proteins. While p27 was increased by monensin, p21 was not. In addition, monensin markedly enhanced the binding of p27 with CDK2, CDK4 and CDK6. Furthermore, the activities of CDK2-, CDK4- and CDK6-associated kinase were reduced in association with hypophosphorylation of Rb protein. Monensin also induced apoptosis in solid tumor cells. Apoptotic process of SNU-C1 cells was associated with the changes of Bax, caspase-3 and mitochondria transmembrane potential (deltapsim). Taken together, these results demonstrated for the first time that monensin inhibited the growth of solid tumor cells, especially SNU-C1 cells, via cell cycle arrest and apoptosis.

Topics: Adenocarcinoma; Apoptosis; bcl-2-Associated X Protein; Breast Neoplasms; Caspase 3; Caspases; CDC2-CDC28 Kinases; Cell Cycle; Cell Cycle Proteins; Cell Division; Colonic Neoplasms; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 6; Cyclin-Dependent Kinase Inhibitor p27; Cyclin-Dependent Kinases; Drug Screening Assays, Antitumor; Female; HeLa Cells; Humans; Inhibitory Concentration 50; Intracellular Membranes; Ionophores; Membrane Potentials; Mitochondria; Monensin; Neoplasm Proteins; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Retinoblastoma Protein; Sodium; Tumor Cells, Cultured; Tumor Suppressor Proteins; Uterine Cervical Neoplasms

The uptake kinetics of alpha-linolenic acid (18:3(n - 3)), an essential fatty acid, were investigated in the human intestinal cell line Caco-2. Four clones (PD10, PF11, PD7 and TC7) from the heterogeneous parental Caco-2 cells population were used. After a screening step using isolated cells, the TC7 clone was selected for the study of alpha-linolenic acid uptake. [1-(14)C]linolenic acid dissolved in 10 mM taurocholate was presented to the microvillus plasma membrane (apical side) of TC7 differentiated cells, grown on a semi-permeable polycarbonate membrane. The results show that the initial rate of uptake is not a linear function of the 18:3(n- 3) monomer concentration in the incubation medium. In the monomer concentration range studied (0.2 to 36 microM) apical uptake was saturable and followed Michaelis-Menten kinetics (V(max) = 15.4 +/- 0.6 nmol/mg protein per min, K(m) = 14.3 +/- 1.3 microM). In addition, it was temperature- and energy-dependent but was apparently unaffected by the sodium gradient and intracellular metabolic fate of 18:3(n - 3). Excess of unlabeled saturated or unsaturated long chain fatty acids (C16 to C22) led to a 27-68% reduction of [1-(14)C]linolenic acid uptake. Likewise basolateral uptake was saturable (V(max) = 4.9 +/- 0.7 nmol/mg protein per min, K(m) = 8.7 +/- 2.9 microM). These facts argue in favour of the existence in these human intestinal cells of a carrier-mediated transport system for alpha-linolenic acid and probably other long chain fatty acids as well.

Topics: Adenocarcinoma; alpha-Linolenic Acid; Antimetabolites; Caco-2 Cells; Carbon Radioisotopes; Cell Division; Clone Cells; Colonic Neoplasms; Deoxyglucose; Enzyme Inhibitors; Fatty Acids; Glucose; Humans; Intestinal Mucosa; Intestines; Ionophores; Kinetics; Lipids; Monensin; Oligomycins; Osmolar Concentration; Serine Endopeptidases; Substrate Specificity; Temperature; Time Factors

We have shown previously [McCool, Forstner and Forstner (1994) Biochem. J. 302, 111-118] using pulse-chase labelling of mucin with [3H]threonine that LS180 colonic tumour cells synthesize and secrete MUC2 without the addition of secretagogues. Treatment of the LS180 cells with monensin to disrupt Golgi function was also found to inhibit baseline secretion almost completely. In this paper we show that addition of nocodazole to inhibit microtubule assembly reduced baseline secretion by 53% over a 6 h chase period. In contrast, cytochalasin D did not affect the rate of unstimulated mucin synthesis or secretion, suggesting that baseline secretion is not influenced by disruption of actin microfilaments. In addition, regulated mucin secretion by LS180 cells was studied in response to carbachol, phorbol 12-myristate 13-acetate and A23187. Mucin released in response to secretagogues behaved identically on SDS/PAGE to that secreted under baseline conditions. T84 cells and the B6 subclone of the HT29 cell line responded in a similar manner to LS180 cells and secreted high-molecular-mass mucin which included MUC2 and behaved like LS180 mucin on SDS/PAGE. Neither monensin nor nocodazole significantly affected secretagogue-stimulated mucin secretion. Since these compounds inhibited secretion of labelled mucin under baseline conditions, mucin released by secretagogues must have come from a separate, unlabelled mucin pool in stored granules. Cytochalasin D, on the other hand, caused the release of small amounts of stored mucin, suggesting that actin microfilaments participate in regulated exocytosis. Thus two kinds of mucin secretion occur in LS180 cells. Unregulated secretion depends upon continuous transport of mucin granules from Golgi vesicles to the cell surface and does not utilize stored mucin, whereas regulated secretion involves the release of mucin from storage granules and is not affected by microtubule or Golgi disruption.

Topics: Adenocarcinoma; Biomarkers, Tumor; Calcimycin; Carbachol; Cell Size; Colchicine; Colonic Neoplasms; Cytochalasin D; Cytoplasmic Granules; Golgi Apparatus; Humans; Microscopy, Electron; Monensin; Mucin-2; Mucins; Neoplasm Proteins; Nocodazole; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

Cholera toxin (CT) consists of a pentameric B subunit which binds to ganglioside GM1 on the cell surface and an A subunit which activates adenylylcyclase. The latter process involves the reduction of A to the A1 peptide which ADP-ribosylates the stimulatory G protein, Gs of adenylylcyclase. There is a distinct lag phase between toxin binding and activation of adenylylcyclase. Little is known about the events during this lag including where A1 is generated and how it gains access to Gs on the cytoplasmic side of the plasma membrane. We explored the effects of several inhibitors of intracellular trafficking on the response of human SK-N-MC neurotumor and Caco-2 intestinal tumor cells to CT. Whereas chloroquine or monensin had little or no effect on CT stimulation of cyclic AMP accumulation, brefeldin A (BFA) totally inhibited the response to CT in a time- and dose-dependent and reversible manner. BFA was effective when added at the same time as CT and had an IC50 of 30 ng/ml. BFA did not alter cell surface GM1 as cells treated with BFA for 30 min bound as much 125I-CT as control cells. Furthermore, BFA inhibited CT stimulation of GM1-treated rat glioma C6 cells. BFA treatment did not affect beta-adrenergic agonist stimulation of cyclic AMP. In addition, adenylylcyclase was activated by A1 peptide and NAD+ to the same extent in membranes from control and BFA-treated cells, or when BFA was added directly to the assay. Whereas control cells generated small amounts of A1 from bound CT with time, no A1 was detected in BFA-treated cells. BFA treatment did not prevent the internalization of CT but did inhibit its degradation. BFA is known to disrupt the organization of the Golgi complex, resulting in inhibition of protein transport from the endoplasmic reticulum and redistribution of Golgi enzymes to the endoplasmic reticulum. BFA also prevents the formation of non-clathrin-coated vesicles from Golgi membranes and thus vesicular transport between Golgi cisternae. We confirmed that BFA caused the morphological disruption of the Golgi apparatus in Caco-2 cells. The data support a role for a functional Golgi apparatus with its associated vesicular routing in CT action.

Topics: Adenocarcinoma; Adenylyl Cyclases; Animals; Biological Transport; Brefeldin A; Cell Line; Chloroquine; Cholera Toxin; Colonic Neoplasms; Cyclic AMP; Cyclopentanes; Enzyme Activation; Glioma; Golgi Apparatus; Humans; Isoproterenol; Kinetics; Monensin; Mycotoxins; Rats; Time Factors; Tumor Cells, Cultured

A method was elaborated for high-yield 125I-trap labeling of rat colon carcinoma cells using conjugates of dichlorotriazine aminofluorescein and bovine serum albumin substituted with either N-acetylgalactosamine or N-acetylglucosamine as vehicles. Fluorescence microscopy revealed that the ligands accumulated in perinuclear vesicles that were probably lysosomes. Monensin inhibited accumulation by 40%, signifying receptor-mediated endocytosis. Competition experiments revealed that the same receptor(s) mediated endocytosis of the two neoglycoproteins. Accumulation of label was greatly enhanced in the absence of serum, resulting in a labeling efficiency of at least 15 cpm/cell, with no sign of toxic effects. At least 75% of the initially accumulated radioactivity resided in the cells 4 days after labeling. After that the loss of radioactivity was linear with time and stabilized at 1.1%/day for at least 2 weeks. Injection of labeled carcinoma cells i.v. into syngeneic rats revealed a very rapid clearance from the circulation. Isolation of the liver cells 24 h later revealed that a great proportion of the administered cells or their remnants had been engulfed by sinusoidal Kupffer and endothelial cells; the parenchymal cells contained a smaller proportion of label. In conclusion, we have developed a technique of labeling colon carcinoma cells with 125I and fluorescein utilizing specific lectin-like receptors for endocytosis. Since the label is trapped intralysosomally, it will also label Kupffer cells and other members of the reticuloendothelial system after internalization. These features make the procedure well suited for studies on the fate of the colon carcinoma cells after administration in vivo. Since the label is trapped intralysosomally for an extended length of time, parameters such as the formation of metastasis and elimination by phagocytosis can readily be determined.

Topics: Acetylgalactosamine; Acetylglucosamine; Adenocarcinoma; Animals; Colonic Neoplasms; Endocytosis; Fluorescein-5-isothiocyanate; Fluoresceins; Iodine Radioisotopes; Liver; Male; Microscopy, Fluorescence; Monensin; Neoplastic Cells, Circulating; Rats; Rats, Inbred Strains; Sensitivity and Specificity; Serum Albumin, Bovine

The role of CFTR in lysosome acidification was examined in CFPAC-1 pancreatic adenocarcinoma cells with the delta F508 mutation that were transduced with a retroviral vector (PLJ-CFPAC) or with the normal CFTR gene (CFTR-CFPAC). Steady-state lysosomal pHi in intact cells was lower in PLJ-CFPAC cells than CFTR-CFPAC cells (3.55 vs 3.80) and was not affected by cAMP or forskolin. Initial rates of ATP-dependent acidification of isolated lysosomes and steady-state ATP-dependent pHi were similar in both cell lines over a range of chloride concentrations and were not altered when cells were exposed to cAMP or to forskolin prior to preparation of lysosomes. These observations suggest that CFTR plays no role in acidification of lysosomes, possibly due to limited permeability of lysosomal membranes to chloride.

Topics: Adenocarcinoma; Adenosine Triphosphate; Bucladesine; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Line; Colforsin; Cyclic AMP; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Dextrans; Fluorescein-5-isothiocyanate; Fluorescent Dyes; Hydrogen-Ion Concentration; Kinetics; Lysosomes; Membrane Proteins; Monensin; Mutation; Pancreatic Neoplasms; Spectrometry, Fluorescence

Treatment for 48 h of differentiated, confluent Caco-2 cells with 2.5 10(-5) M forskolin or 10(-6) M monensin, which produces a significant decrease of the de novo biosynthesis of sucrase-isomaltase, does not change quantitatively the de novo biosynthesis of dipeptidylpeptidase IV. Western blot analysis and silver nitrate staining indicate that neither drug induces any modification in the steady state expression of these two brush border hydrolases. Northern blot analysis shows that the level of dipeptidylpeptidase IV mRNA does not change in treated as compared to control Caco-2 cells. In contrast, forskolin and monensin dramatically decrease the level of sucrase-isomaltase mRNA. These observations suggest a separate regulation of biosynthesis for sucrase-isomaltase and dipeptidylpeptidase IV in intestinal cells. The mechanisms responsible for such a difference are discussed. Among them, the role of glucose metabolism, which is perturbed by both drugs, appears to be of crucial importance.

Topics: Adenocarcinoma; Antibodies, Monoclonal; Blotting, Northern; Blotting, Western; Colforsin; Colonic Neoplasms; Cyclic AMP; Dipeptidyl Peptidase 4; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Glucose; Humans; Monensin; RNA, Messenger; Sucrase-Isomaltase Complex; Tumor Cells, Cultured

Dimethylsulfoxide (DMSO) modulates the tumorigenicity and other characteristics of some malignant cell lines in vitro. We have investigated DMSO effects on cell proliferation and glycosaminoglycan (GAG) synthesis in rat prostate adenocarcinoma (PAIII) cells in culture. DMSO inhibited cell proliferation and GAG synthesis and shedding. Cells that survived the initial exposure to 2.5% DMSO could be propagated in this concentration of the agent and were designated PAIII-DMSO resistant (PAIII-DMSOr). PAIII-DMSOr cells showed reversible indications of increased differentiation such as decreased growth rate and saturation density. Although the PAIII-DMSOr cells were grown in 2.5% DMSO, they had normal or elevated GAG content. The major GAG of both PAIII and PAIII-DMSOr cells was undersulfated heparan sulfate. Verapamil, a calcium channel blocker that reverses drug resistance in tumor cells, stimulated the growth of PAIII-DMSOr cells in the presence of 2.5% DMSO, but was inhibitory in the absence of DMSO. Growth of PAIII cells was inhibited by the differentiating agents sodium butyrate and retinoic acid and by the ionophore monensin. Interestingly, growth of PAIII-DMSOr cells in the presence of 2.5% DMSO was largely unaffected by sodium butyrate or retinoic acid. The results suggest that (1) PAIII-DMSOr cells arise from the induction of a compensation mechanism to DMSO effects in a preexisting population of cells: (2) there is a correlation between GAG synthesis and cell proliferation; and (3) further study of the verapamil effect may help elucidate the mechanism of the DMSO-induced differentiation of cancer cells.

Topics: Adenocarcinoma; Animals; Antineoplastic Agents; Cell Division; Dimethyl Sulfoxide; Drug Resistance; Electrophoresis, Cellulose Acetate; Glycosaminoglycans; In Vitro Techniques; Male; Monensin; Prostatic Neoplasms; Rats; Tumor Cells, Cultured; Verapamil

The intracellular flow and fate of two fluorescently labeled sphingolipids, 6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]hexanoyl glucosyl sphingosine (C6-NBD-glucosylceramide) and C6-NBD-sphingomyelin, was examined in the human colon adenocarcinoma cell line HT29. After their insertion into the plasma membrane at low temperature and subsequent warming of the cells to 37 degrees C, both sphingolipid analogues were internalized by endocytosis, but their intracellular site of destination differed. After 30 min of internalization, C6-NBD-glucosylceramide was localized in the Golgi apparatus, as demonstrated by colocalization with fluorescently labeled ceramide, a Golgi complex marker, and by showing that monensin-induced disruption of the Golgi structure was paralleled by a similar perturbation of the fluorescence distribution. By contrast, C6-NBD-sphingomyelin does not colocalize with the tagged ceramide. Rather, a colocalization with ricin, which is internalized by endocytosis and predominantly reaches the lysosomes, was observed, indicating that the site of delivery of this lipid is restricted to endosomal/lysosomal compartments. Also, in monensin-treated cells no change in the distribution of fluorescence was observed. Thus, these results demonstrate that (sphingo)lipid sorting can occur in the endocytic pathway. Interestingly, the observed sorting phenomenon was specific for glucosylceramide, when compared to other glycolipids, while only undifferentiated HT29 cells displayed the different routing of the two lipids. In differentiated HT29 cells the internalization pathway of sphingomyelin and glucosylceramide was indistinguishable from that of transferrin.

Topics: Adenocarcinoma; Cell Line; Cell Membrane; Ceramides; Colonic Neoplasms; Endocytosis; Glucosylceramides; Golgi Apparatus; Humans; Lysosomes; Microscopy, Fluorescence; Monensin; Ricin; Sphingolipids; Sphingomyelins

Intracavitary administration of immunotoxins may play a role in the control of malignant effusions. Selection of immunotoxins for this form of therapy is based on their prior evaluation in preclinical studies. Monoclonal antibodies (mAb) 454A12 (antitransferrin receptor), and 260F9 are directed against antigens which are present on tumor cells in pleural and peritoneal effusions of patients with adenocarcinoma of the breast and ovary. In the present study, immunotoxins derived by conjugating these mAb to recombinant ricin A (rRA) were shown to be cytotoxic to human ovarian adenocarcinoma HEY cells in vitro and in vivo. In the in vitro assay 454A12-rRA and 260F9-rRA were 1000-fold and 10-fold, respectively, more cytotoxic than free rRa against HEY cells, and both immunotoxins were potentiated approximately 1000-fold by monensin. For in vivo studies HEY cells were injected i.p. into nude mice at a challenge dose (3 x 10(5) cells) which produced carcinomatosis with ascites, leading to death 30 days following injection. Administration of 454A12-rRA i.p. following the challenge dose resulted in a complete cure, whereas administration of 260 F9-rRA with monensin significantly prolonged survival. The greater cytotoxicity of 454A12-rRA than 260F9-rRA against HEY cells could be accounted for by the greater number of binding sites and higher internalization rate for 454A12-rRA and mAb 454A12 than 260F9-rRA and mAb 260F9, respectively. These results suggest a potential role for 454A12-rRA and 260F9-rRA plus monensin in the intracavitary therapy of malignant effusions associated with carcinoma of breast and ovary. In the case of 260F9-rRA, this represents the first preliminary indication of the suitability of this immunotoxin for intracavitary therapy of malignancies.

Topics: Adenocarcinoma; Animals; Antibodies, Monoclonal; Female; Humans; Immunotoxins; Injections, Intraperitoneal; Mice; Mice, Inbred BALB C; Mice, Nude; Monensin; Neoplasm Transplantation; Ovarian Neoplasms; Ricin; Transplantation, Heterologous; Tumor Cells, Cultured

A fraction of intestinal alkaline phosphatase (IAP) is secreted into blood. To study this process, enzyme secretion was examined in a fetal (IRD-98) and a differentiated (Caco-2) intestinal cell line. Tissue-unspecific alkaline phosphatase (AP) activity in the IRD-98 cells increased 20-fold after addition of 1.5 mM sodium butyrate and 40 mM NaCl, but no AP activity was secreted into the medium. In contrast, newly synthesized IAP in Caco-2 cells was secreted into the medium. AP secretion increased with time and was inhibited by monensin. Medium AP was still partially bound to membranes as assessed by Triton X-114 phase separation and could be released by the addition of serum. Analysis by sodium dodecyl sulfate polyacrylamide gels and by isoelectric focussing showed that secreted AP gave a pattern similar to that of the AP released from membranes by phospholipase D treatment. When Caco-2 cells were grown on filters, AP activity was found in both basolateral (75%) and luminal (25%) media. These data demonstrate that the secretion of a particulate AP with extracellular release from the membrane can account for the appearance of the intestinal isozyme in both the serum and the lumen.

Topics: Adenocarcinoma; Alkaline Phosphatase; Animals; Butyrates; Butyric Acid; Cell Differentiation; Cell Line; Colonic Neoplasms; Duodenum; Electrophoresis, Polyacrylamide Gel; Humans; Ileum; Intestines; Isoelectric Focusing; Microvilli; Monensin; Phosphatidylinositol Diacylglycerol-Lyase; Phospholipase D; Phosphoric Diester Hydrolases; Rats; Sodium Chloride; Tumor Cells, Cultured

ASGP-1, the major cell surface sialomucin of the 13762 ascites rat mammary adenocarcinoma, is at least 0.5% of the total ascites cell protein and has sulfate on 20% of its O-linked oligosaccharide chains. We have used this system to investigate the O-glycosylation pathway in these cells and to determine the temporal relationship between sulfation and sialylation. The two major sulfated oligosaccharides (S-1 and S-2) were isolated as their oligosaccharitols by alkaline borohydride elimination, anion exchange HPLC, and ion-suppression HPLC. From structural analyses S-1 is proposed to be a branched, sulfated trisaccharide -O4S-GlcNAc beta 1,6-(Gal beta 1,3)-GalNAc and S-2 its sialylated derivative -O4S-GlcNAc beta 1,6-(NeuAc alpha 2,3-Gal beta 1,3)-GalNac. Pulse labeling with sulfate indicated that sulfation occurred primarily on a form of ASGP-1 intermediate in size between immature and mature sialomucin. Pulse-chase analyses showed that the intermediate could be chased into mature ASGP-1. The concomitant conversion of S-1 into S-2 had a half-time of less than 5 min. Monensin treatment of the tumor cells led to a 95% inhibition of sulfation with the accumulation of unsulfated trisaccharide GlcNAc beta 1,6-(Gal beta 1,3)-GalNAc and sialylated derivative GlcNAc beta 1,6-(NeuAc alpha 2,3-Gal beta 1,3)-GalNAc. These data suggest that sulfation of ASGP-1 is an intermediate synthetic step, which competes with beta-1,4-galactosylation for the trisaccharide intermediate and thus occurs in the same compartment as beta-1,4-galactosylation. Moreover, sulfation precedes sialylation, but the two are rapidly successive kinetic events in the oligosaccharide assembly of ASGP-1.

Topics: Adenocarcinoma; Animals; Chromatography, Ion Exchange; Kinetics; Mammary Neoplasms, Experimental; Monensin; Mucins; Oligosaccharides; Rats; Sialomucins; Sulfuric Acids; Tumor Cells, Cultured

The sensitivity of three human colon adenocarcinoma cell lines (LoVo, LS174T, and SW1116) and a human pancreatic adenocarcinoma cell line (Hs766T) to a recombinant ricin A chain-antitransferrin receptor immunotoxin was studied. In addition, the carboxylic ionophore monensin was used in conjunction with the immunotoxin to determine the possibility of increased cytotoxicity without loss of specificity. The immunotoxin, 454A12-rRTA, is composed of the monoclonal antibody 454A12 directed against transferrin receptor and of ricin A chain, which was produced by recombinant DNA techniques. In 18 h dose-response cytotoxicity assays, the median inhibitory dose (ID50) against LoVo, LS174T, and SW1116 was found to be 3 X 10(-10), 3.6 X 10(-11), and 3.6 X 10(-10) M, respectively; in the same assay, the ID50 for Hs766T was found to be 4 X 10(-10) M. In the presence of monensin, the ID50 for the adenocarcinoma cell lines was reduced 9-fold, 28-fold, and 5-fold, respectively. In cytotoxic kinetic assays, 50% of control protein inhibition was reached in immunotoxin-treated LS174T cells 12-fold faster in the presence of monensin than in its absence. Immunotoxin-treated LoVo cells reached 50% inhibition of control protein synthesis fivefold faster in the presence of monensin than in its absence. Furthermore, no toxicity of immunotoxin or potentiation by monensin was observed in either a control cell line (Swiss albino mouse 3T6) treated with specific immunotoxin or with a control immunotoxin assay. These results show the in vitro specificity and selectivity of 454A12-rRTA immunotoxin for human gastrointestinal and pancreatic cancer cell lines.

Topics: Adenocarcinoma; Antibodies, Monoclonal; Colonic Neoplasms; Drug Synergism; Humans; Immunotoxins; Monensin; Pancreatic Neoplasms; Receptors, Transferrin; Recombinant Proteins; Ricin; Tumor Cells, Cultured

HT29 cells originating from a human colon adenocarcinoma, spread very rapidly after seeding on their own extracellular matrix (ECM). Preincubation of cells with the inhibitor of protein glycosylation tunicamycin (TM) or with the ionophore monensin substantially suppressed cell spreading in serum-free medium without affecting cell adhesion to ECM. Addition of the drugs after cell attachment and spreading inhibited cell growth. TM-treated cells remained viable after 6 days of exposure to 2 micrograms ml-1 of TM and resumed their normal growth rate and shape after removing the drug from the medium. On the contrary, monensin inhibition of cell growth was not reversible: after 3 days, cells detached from the ECM and were unable to exclude Trypan Blue. At the ultrastructural level, a swollen Golgi apparatus with numerous vacuoles was observed after treatment for 2 h in either TM or monensin-preincubated cells. These results suggest that TM and monensin interfere with the insertion and, or, function of one or more cell surface glycoproteins, possibly interacting with cytoskeleton and involved in cell spreading and growth.

Topics: Adenocarcinoma; Cell Adhesion; Cell Line; Colonic Neoplasms; Furans; Glucosamine; Humans; Microscopy, Electron; Monensin; Tunicamycin