New aspects of siglec binding specificities, including the significance of fucosylation and of the sialyl-Tn epitope. Sialic acid-binding immunoglobulin superfamily lectins.
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The siglecs (sialic acid-binding immunoglobulin superfamily lectins) are immunoglobulin superfamily members recognizing sialylated ligands. Most prior studies of siglec specificities focused on alpha2-3- and alpha2-6-sialyllactos(amin)es and on one or two of the siglecs at a time. Here, we explore several new aspects of specificities of the first six reported siglecs, using sialylated glycans presented in multivalent form, on synthetic polyacrylamide backbones, or on mucin polypeptides. First, we report that binding of siglec-1 (sialoadhesin), siglec-3 (CD33), siglec-4a (myelin-associated glycoprotein), and siglec-5 to alpha2-3 sialyllactosamine is affected markedly by the presence of an alpha1-3-linked fucose. Thus, while siglecs may not interfere with selectin-mediated recognition, fucosylation could negatively regulate siglec binding. Second, in contrast to earlier studies, we find that siglec-3 prefers alpha2-6-sialyllactose. Third, siglec-5 binds alpha2-8-linked sialic acid, making it the siglec least specific for linkage recognition. Fourth, siglecs-2 (CD22), -3, -5, and -6 (obesity-binding protein 1) showed significant binding to sialyl-Tn (Neu5Acalpha2-6-GalNAc), a tumor marker associated with poor prognosis. Fifth, siglec-6 is an exception among siglecs in not requiring the glycerol side chain of sialic acid for recognition. Sixth, all siglecs require the carboxyl group of sialic acid for binding. Finally, the presentation of the sialyl-Tn epitope and/or more extended structures that include this motif may be important for optimal recognition by the siglecs. This was concluded from studies using ovine, bovine, and porcine submaxillary mucins and Chinese hamster ovary cells transfected with ST6GalNAc-I and/or the mucin polypeptide MUC1. (+info)
Effects of Thomsen-Friedenreich antigen-specific peptide P-30 on beta-galactoside-mediated homotypic aggregation and adhesion to the endothelium of MDA-MB-435 human breast carcinoma cells.
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Both the ability of malignant cells to form multicellular aggregates via homotypic or heterotypic aggregation and their adhesion to the endothelium are important if not critical during early stages of cancer metastasis. The tumor-associated carbohydrate Thomsen-Friedenreich antigen (T antigen) and beta-galactoside binding lectins (galectins) have been implicated in tumor cell adhesion and tissue invasion. In this study, we demonstrate the involvement of T antigen in both homotypic aggregation of MDA-MB-435 human breast carcinoma cells and their adhesion to the endothelium. The T antigen-specific peptide P-30 (HGRFILPWWYAFSPS) selected from a bacteriophage display library was able to inhibit spontaneous homotypic aggregation of MDA-MB-435 cells up to 74% in a dose-dependent manner. Because T antigen has beta-galactose as a terminal sugar, the expression profile of beta-galactoside-binding lectins (galectins) in MDA-MB-435 cells was studied. Our data indicated the abundant expression of [35S]methionine/cysteine-labeled galectin-1 and galectin-3 in this cell line, which suggested possible interactions between galectins and T antigen. As revealed by laser confocal microscopy, both galectin-1 and galectin-3 also participate in the adhesion of the MDA-MB-435 cells to the endothelium. We observed the clustering of galectin-3 on endothelial cells at the sites of the contact with tumor cells, consistent with its possible interaction with T antigen on cancer cells The galectin-1 signal, however, strongly accumulated at the sites of cell-cell contacts predominantly on tumor cells. The T antigen-specific P-30 significantly (50%) inhibited this adhesion, which indicated that T antigen participates in the adhesion of MDA-MB-435 breast cancer cells to the endothelium. The ability of synthetic P-30 to inhibit both the spontaneous homotypic aggregation of MDA-MB-435 cells and their adhesion to the endothelium (>70 and 50%, respectively) suggests its potential functional significance for antiadhesive therapy of cancer metastasis. (+info)
Phase I trial of the anti-Lewis Y drug immunoconjugate BR96-doxorubicin in patients with lewis Y-expressing epithelial tumors.
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PURPOSE: We conducted a phase I clinical trial of BR96-Doxorubicin (BR96-Dox), a chimeric anti-Lewis Y (Le(Y)) monoclonal antibody conjugated to doxorubicin, in patients whose tumors expressed the Le(Y) antigen. The study aimed to determine the toxicity, maximum-tolerated dose, pharmacokinetics, and immunogenicity of BR96-Dox. PATIENTS AND METHODS: This was a phase I dose escalation study. BR96-Dox was initially administered alone as a 2-hour infusion every 3 weeks. The occurrence of gastrointestinal (GI) toxicity necessitated the administration of BR96-Dox as a continuous infusion over 24 hours and use of antiemetics and antigastritis premedication. Patients experiencing severe GI toxicity underwent GI endoscopy. All patients underwent restaging after two cycles. RESULTS: A total of 66 patients predominantly with metastatic colon and breast cancer were enrolled onto the study. The most common side effects were GI toxicity, fever, and elevation of pancreatic lipase. At higher doses, BR96-Dox was associated with nausea, vomiting, and endoscopically documented exudative gastritis of the upper GI tract, which was dose-limiting at a maximum dose of 875 mg/m(2) (doxorubicin equivalent, 25 mg/m(2)) administered every 3 weeks. Toxicity was reversible and generally of short duration. Premedication with the antiemetic Kytril (granisetron hydrochloride; SmithKline Beecham, Philadelphia, PA), the antacid omeprazole, and dexamethasone was most effective in ameliorating GI toxicity. A dose of 700 mg/m(2) BR96-Dox (doxorubicin equivalent, 19 mg/m(2)) every 3 weeks was determined to be the optimal phase II dose when administered with antiemetic and antigastritis prophylaxis. BR96-Dox deposition on tumor tissue was documented immunohistochemically and by confocal microscopy. At the 550-mg/m(2) dose, the half-life (mean +/- SD) of BR96 and doxorubicin was 300 +/- 95 hours and 43 +/- 4 hours, respectively. BR96-Dox elicited a weak immune response in 37% of patients. Objective clinical responses were seen in two patients. CONCLUSION: BR96-Dox provides a unique strategy to deliver doxorubicin to Le(Y)-expressing tumor and was well tolerated at doses of 700 mg/m(2) every 3 weeks. BR96-Dox was not associated with the typical side-effect profile of native doxorubicin and can potentially deliver high doses of doxorubicin to antigen-expressing tumors. A phase II study in doxorubicin-sensitive tumors is warranted. (+info)
The beta 1,3-galactosyltransferase beta 3GalT-V is a stage-specific embryonic antigen-3 (SSEA-3) synthase.
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We have previously reported the molecular cloning of beta1, 3-galactosyltransferase-V (beta3GalT-V), which catalyzes the transfer of Gal to GlcNAc-based acceptors with a preference for the core3 O-linked glycan GlcNAc(beta1,3)GalNAc structure. Further characterization indicated that the recombinant beta3GalT-V enzyme expressed in Sf9 insect cells also utilized the glycolipid Lc3Cer as an efficient acceptor. Surprisingly, we also found that beta3GalT-V catalyzes the transfer of Gal to the terminal GalNAc unit of the globoside Gb4, thereby synthesizing the glycolipid Gb5, also known as the stage-specific embryonic antigen-3 (SSEA-3). The SSEA-3 synthase activity of beta3GalT-V was confirmed in vivo by stable expression of the human beta3GalT-V gene in F9 mouse teratocarcinoma cells, as detected with the monoclonal antibody MC-631 by flow cytometry analysis and immunostaining of extracted glycolipids. The biological relation between SSEA-3 formation and beta3GalT-V was further documented by showing that F9 cells treated with the differentiation-inducing agent retinoic acid induced the expression of both the SSEA-3 epitope and the endogenous mouse beta3GalT-V gene. This study represents the first example of a glycosyltransferase, which utilizes two kinds of sugar acceptor substrates without requiring any additional modifier molecule. (+info)
Clinical outcome of breast and ovarian cancer patients treated with high-dose chemotherapy, autologous stem cell rescue and THERATOPE STn-KLH cancer vaccine.
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The purpose of this study was to evaluate the toxicity and potential efficacy of administering the THERATOPE STn-KLH cancer vaccine to ovarian and breast cancer patients after an autologous stem cell transplant. Forty patients (11 high-risk stage II/III breast cancer, 22 stage IV breast cancer, and seven stage III/IV ovarian cancer patients) were treated with high-dose chemotherapy followed by autologous/syngeneic stem cell rescue and vaccination with THERATOPE STn-KLH (Sialyl-Tn-KLH with Detox-B Stable Emulsion). Each patient was scheduled to receive a total of five vaccinations beginning on days 30-151 after stem cell infusion. The vaccine was well tolerated. Induration and erythema at the site of injection were the most common side-effects. When one compares the outcome of patients vaccinated with 66 breast and ovarian cancer patients who were not, following risk-adjustment analysis, vaccinated patients appeared more likely to survive (P = 0.07) and less likely to relapse (P = 0. 10). Vaccinated patients with the greatest specific lytic activity against STn+OVCAR tumor cells relative to nonspecific killing of Daudi cells tended to remain in remission longer than patients who displayed less specific immune activity (P = 0.057). We conclude that the THERATOPE STn-KLH cancer vaccine is well tolerated in breast and ovarian cancer patients after autologous transplant and, while not statistically significant, the trends in data support the concept that THERATOPE vaccine may decrease the risk for relapse and death and thus warrants further study. Bone Marrow Transplantation (2000) 25, 1233-1241. (+info)
The Fc-region of a new class of intact bispecific antibody mediates activation of accessory cells and NK cells and induces direct phagocytosis of tumour cells.
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Bispecific antibodies (bsAb) are considered as promising tools for the elimination of disseminated tumour cells in a minimal residual disease situation. The bsAb-mediated recruitment of an immune effector cell in close vicinity of a tumour cell is thought to induce an antitumoural immune response. However, classical bispecific molecules activate only a single class of immune effector cell that may not yield optimal immune responses. We therefore constructed an intact bispecific antibody, BiUII (anti-CD3 x anti-EpCAM), that not only recognizes tumour cells and T lymphocytes with its two binding arms, but also binds and activates Fcgamma-receptor positive accessory cells through its Fc-region. We have demonstrated recently that activated accessory cells contribute to the bsAb-induced antitumoural activity. We now analyse this stimulation in more detail and demonstrate here the BiUII-induced upregulation of activation markers like CD83 and CD95 on accessory cells and the induction of neopterin and biopterin synthesis. Experiments with pure cell subpopulations revealed binding of BiUII to CD64+ accessory cells and CD16+ NK cells, but not to CD32+ B lymphocytes. We provide further evidence for the importance of the Fc-region in that this bispecific molecule stimulates Fcgamma-R-positive accessory cells to eliminate tumour cells in vitro by direct phagocytosis. (+info)
Enrichment and localization of ganglioside G(D3) and caveolin-1 in shed tumor cell membrane vesicles.
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Tumor cell ganglioside shedding has been implicated in the process of tumor formation. Previously, we identified three forms of tumor ganglioside shedding: micelles, monomers and membrane vesicles. Here, we have explored the membrane vesicle form of ganglioside shedding, using a newly identified human ovarian carcinoma cell line, CABA I. These cells synthesize and express a spectrum of gangliosides, including the disialoganglioside, G(D3). Immunostaining using the monoclonal antibody R24 confirmed G(D3) expression and its presence in the plasma membrane of these cells. Cellular gangliosides were detected in the culture supernatant by HPTLC autoradiography, confirming an active shedding rate of 3% of cellular gangliosides/24 h. CABA I cell membranes also express caveolin-1, a characteristic protein marker for caveolae, which was detected by flow cytometric analysis and by Western blotting in both the cell membranes and the isolated membrane vesicles. To further define the expression of G(D3) and caveolin-1, we used immunogold electron microscopy. This revealed localization of G(D3) in small clusters in the plasma membrane as well as enrichment and localization of ganglioside G(D3) and caveolin-1 in shed membrane vesicles, with 58-78% of vesicles carrying both G(D3) and caveolin-1. Together, these results suggest that membrane vesicle shedding originates in plasma membrane domains enriched in gangliosides and caveolin-1. (+info)
Characterization of the rabbit homolog of human MUC1 glycoprotein isolated from bladder by affinity chromatography on immobilized jacalin.
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The urinary bladder is lined by transitional epithelium, the glycocalyx on the luminal surface has interesting properties and is implicated in protective functions. Glycoconjugates are major components of the glycocalyx, but their biochemical nature is not well understood. Previous studies on rabbit bladder indicated the presence of significant levels of sialoglycoproteins compared to glycosaminoglycans in the epithelium. In this study, rabbit explant cultures were radiolabeled by precursor sugars or amino acids and a major lectin-reactive glycoprotein of rabbit bladder mucosa was isolated by affinity chromatography on jacalin-agarose. The radiolabeled glycoprotein was purified to homogeneity by a second cycle on the lectin column, followed by gel filtration and density gradient centrifugation. The average molecular mass of the glycoprotein was estimated to be 245 kDa and 210 kDa by gel filtration and SDS-PAGE, respectively. Its buoyant density was 1.40 g/ml, suggesting a carbohydrate content of approximately 50%. The percent distribution of glucosamine-derived tritium label in sialic acid, galactosamine, and glucosamine was 30, 52, and 18, respectively. The glycoprotein consisted entirely of small sialylated and neutral oligosaccharides O-glycosidically linked to serine and threonine residues. The same glycoprotein could be immunoprecipitated with an antibody against the carboxy terminal 17 amino acid peptide of human MUC1 mucin glycoprotein. This suggests that this mucin glycoprotein is the rabbit homolog of MUC1 glycoprotein, which has been previously established to be a component of human bladder urothelium and has been purified from human urine and biochemically characterized. (+info)