Glycosaminoglycan mediated differentiation in stem cells

Includes bibliographical references.Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005."February 2005." Vita.(cont.) Such therapeutic approaches require an understanding of the mechanisms regulating stem cell differentiation. The second part of this thesis investigates the role of HSGAGs in embryonic stem cell differentiation into endothelial cells. Differentiation of stem cells was accompanied by increases in the transcript levels of key HSGAG-biosynthetic enzymes, and the quantity of cell surface HSGAGs. Differentiation into endothelial cells was inhibited by ablation of the HSGAG-biosynthetic machinery by chlorate treatment, or by the enzymatic degradation of the HSGAGs. Exogenous addition of heparin to chlorate-treated cells partially restored differentiation into endothelial cells. These effects were mirrored in phospho-ERK levels, suggesting the involvement of the MAPK pathway. These results suggest that stem cell differentiation can be regulated by modulating the HSGAG moiety and this opens up new treatment modalities for cancer therapy and regenerative medicine.The new paradigm is that cancers may originate from stem cells, and that terminal differentiation of stem cells is a possible treatment for cancers. Understanding the origin of cancers requires elucidation of factors causing genetic rearrangements. The first part of this thesis explores the effects of NO on homologous recombination in embryonic stem cells. Using terminal differentiation of stem cells as a therapy for cancer necessitates an understanding of factors governing their differentiation. The second part of this thesis explores the effects of heparan sulfate glycosaminoglycans (HSGAGs) on stem cell differentiation. Inflammation is increasingly recognized as an important risk factor for cancer. During inflammation, macrophages secrete NO, which reacts with superoxide or oxygen to produce ONOO⁻ or N₂O₃, respectively. Although ONOO⁻ and N₂O₃ are potent DNA damaging agents, little was known about the ability of these agents to induce homologous recombination in mammalian cells. Homologous recombination events are a significant source of mutations that are likely to contribute to initiation and progression of some cancers. In the first part of this thesis, the recombinogenic potential of ONOO⁻ and N₂O₃ was characterized by sister chromatid exchanges, chromosomal direct repeat substrate and interplasmid recombination assays. Our results show that on a per lesion basis, ONOO⁻ -induced oxidative base lesions and single strand breaks are more recombinogenic than N₂O₃-induced base deamination products. These results are in accordance with the model that ONOO⁻ -induced recombination may contribute to inflammation-induced cancer. Directed differentiation of stem cells holds an immense potential for regenerative medicine as well as cancer therapy.by Tanyel Kiziltepe.Ph.D

Inhibition of weak-affinity epitope-IgE interactions prevents mast cell degranulation

Development of specific inhibitors of allergy has had limited success, in part, owing to a lack of experimental models that reflect the complexity of allergen-IgE interactions. We designed a heterotetravalent allergen (HtTA) system, which reflects epitope heterogeneity, polyclonal response and number of immunodominant epitopes observed in natural allergens, thereby providing a physiologically relevant experimental model to study mast cell degranulation. The HtTA design revealed the importance of weak-affinity epitopes in allergy, particularly when presented with high-affinity epitopes. The effect of selective inhibition of weak-affinity epitope-IgE interactions was investigated with heterobivalent inhibitors (HBIs) designed to simultaneously target the antigen- and nucleotide-binding sites on the IgE Fab. HBI demonstrated enhanced avidity for the target IgE and was a potent inhibitor of degranulation in vitro and in vivo. These results demonstrate that partial inhibition of allergen-IgE interactions was sufficient to prevent mast cell degranulation, thus establishing the therapeutic potential of the HBI design

Glycome and Transcriptome Regulation of Vasculogenesis

Background— Therapeutic vasculogenesis is an emerging concept that can potentially be harnessed for the management of ischemic pathologies. The present study elucidates the potential coregulation of vasculogenesis by the heparan sulfate glycosaminoglycan–rich cell-surface glycome and the transcriptome. Methods and Results— Differentiation of embryonic stem cells into endothelial cells in an in vitro embryoid body is paralleled by an amplification of heparan sulfate glycosaminoglycan sulfation, which correlates with the levels of the enzyme N-deacetylase/N-sulfotransferase 1 (NDST1). Small hairpin RNA–mediated knockdown of NDST1 or modification of heparan sulfate glycosaminoglycans in embryonic stem cells with heparinases or sodium chlorate inhibited differentiation of embryonic stem cells into endothelial cells. This was translated to an in vivo zebrafish embryo model, in which the genetic knockdown of NDST1 resulted in impaired vascularization characterized by a concentration-dependent decrease in intersegmental vessel lumen and a large tail-vessel configuration, which could be rescued by use of exogenous sulfated heparan sulfate glycosaminoglycans. To explore the cross talk between the glycome and the transcriptome during vasculogenesis, we identified by microarray and then validated wild-type and NDST1 knockdown–associated gene-expression patterns in zebrafish embryos. Temporal analysis at 3 developmental stages critical for vasculogenesis revealed a cascade of pathways that may mediate glycocalyx regulation of vasculogenesis. These pathways were intimately connected to cell signaling, cell survival, and cell fate determination. Specifically, we demonstrated that forkhead box O3A/5 proteins and insulin-like growth factor were key downstream signals in this process. Conclusions— The present study for the first time implicates interplay between the glycome and the transcriptome during vasculogenesis, revealing the possibility of harnessing specific cellular glyco-microenvironments for therapeutic vascularization

Covalent Heterobivalent Inhibitor Design for Inhibition of IgE-Dependent Penicillin Allergy in a Murine Model

Drug allergies occur when hapten-like drug metabolites conjugated to serum proteins, through their interactions with specific immunoglobulin E (IgE), trigger allergic reactions that can be life-threatening. A molecule termed covalent heterobivalent inhibitor (cHBI) was designed to specifically target drug-hapten specific IgE to prevent it from binding drug-haptenated serum proteins. cHBI binds the two independent sites on a drug-hapten specific antibody and covalently conjugates only to the specific IgE, permanently inhibiting it. The cHBI design was evaluated via ELISA to measure cHBI-IgE binding, degranulation assays of rat basophil leukemia (RBL) cells for in vitro efficacy, and mouse models of ear swelling and systemic anaphylaxis responses for in vivo efficacy. The cHBI design was evaluated using two seperate models: one specific to inhibit penicillin G reactive IgE, and another to inhibit IgE specific to a model compound, dansyl. We show that cHBI conjugated specifically to its target antibody and inhibited degranulation in cellular degranulation assays using RBL cells. Furthermore, cHBIs demonstrated in vivo inhibition of allergic responses in both murine models. We establish the cHBI design to be a versatile platform for inhibiting hapten/IgE interactions, which can potentially be applied to inhibit IgE mediated allergic reactions to any drug/small molecule allergy

Retraction: Fatty acid synthase is a novel therapeutic target in multiple myeloma

This study investigated the biological significance of the inhibition of fatty acid synthase (FAS) in multiple myeloma (MM) using the small molecule inhibitor Cerulenin. Cerulenin triggered growth inhibition in both MM cell lines and MM patient cells, and overcame the survival and growth advantages conferred by interleukin-6, insulin-like growth factor-1, and bone marrow stromal cells. It induced apoptosis in MM cell lines with only modest activation of caspase -8, -9, -3 and PARP; moreover, the pan-caspase inhibitor Z-VAD-FMK did not inhibit Cerulenin-induced apoptosis and cell death. In addition, treatment of MM cells with Cerulenin primarily up-regulated apoptosis-inducing factor/endonuclease G, mediators of caspase-independent apoptosis. Importantly, Cerulenin induced endoplasmic reticulum stress response via up-regulation of the Grp78/IRE1α/JNK pathway. Although the C-Jun-NH2-terminal kinase (JNK) inhibitor SP600215 blocked Cerulenin-induced cytotoxicity, it did not inhibit apoptosis and caspase cleavage. Furthermore, Cerulenin showed synergistic cytotoxic effects with various agents including Bortezomib, Melphalan and Doxorubicin. Our results therefore indicate that inhibition of FAS by Cerulenin primarily triggered caspase-independent apoptosis and JNK-dependent cytotoxicity in MM cells. This report demonstrated that inhibition of FAS has anti-tumour activity against MM cells, suggesting that it represents a novel therapeutic target in MM

Designer covalent heterobivalent inhibitors prevent IgE-dependent responses to peanut allergen

Allergies are a result of allergen proteins cross-linking allergen-specific IgE (sIgE) on the surface of mast cells and basophils. The diversity and complexity of allergen epitopes, and high-affinity of the sIgE-allergen interaction have impaired the development of allergen-specific inhibitors of allergic responses. This study presents a design of food allergen-specific sIgE inhibitors named covalent heterobivalent inhibitors (cHBIs) that selectively form covalent bonds to only sIgEs, thereby permanently inhibiting them. Using screening reagents termed nanoallergens, we identified two immunodominant epitopes in peanuts that were common in a population of 16 allergic patients. Two cHBIs designed to inhibit only these two epitopes completely abrogated the allergic response in 14 of the 16 patients in an in vitro assay and inhibited basophil activation in an allergic patient ex vivo analysis. The efficacy of the cHBI design has valuable clinical implications for many allergen-specific responses and more broadly for any antibody-based disease

The monoclonal antibody nBT062 conjugated to maytansinoids has potent and selective cytotoxicity against CD138 positive multiple myeloma cells _in vitro_ and _in vivo_

CD138 (Syndecan1) is highly expressed on multiple myeloma (MM) cells. In this study, we examined the anti-MM effect of murine/human chimeric CD138-specific monoclonal antibody (mAb) nBT062 conjugated with highly cytotoxic maytansinoid derivatives _in vitro_ and _in vivo_. These agents significantly inhibited growth of CD138-positive MM cell lines and primary tumor cells from MM patients, without cytotoxicity against peripheral blood mononuclear cells from healthy volunteers. In MM cells, they induced G2/M cell cycle arrest followed by apoptosis associated with cleavage of PARP and caspase-3, -8 and -9. Non-conjugated nBT062 completely blocked cytotoxicity induced by nBT062-maytansinoid conjugate, confirming that binding is required for inducing cytotoxicity. Moreover, nBT062-maytansinoid conjugates blocked adhesion of MM cells to bone marrow stromal cells (BMSCs). Co-culture of MM cells with BMSCs, which protects against dexamethasone-induced death, had no impact on the cytotoxicity of the immunoconjugates. Importantly, nBT062-SPDB-DM4 and nBT062-SPP-DM1 significantly inhibited MM tumor growth _in vivo_ in both human multiple myeloma xenograft mouse models and in SCID-human bone grafts (SCID-hu mouse model). These studies provide the preclinical framework supporting evaluation of nBT062-maytansinoid derivatives in clinical trials to improve patient outcome in MM

Synthetic Allergen Design Reveals The Significance of Moderate Affinity Epitopes in Mast Cell Degranulation

This study describes the design of a well-defined homotetravalent synthetic allergen (HTA) system to investigate the effect of hapten–IgE interactions on mast cell degranulation. A library of DNP variants with varying affinities for IgEDNP was generated (Kd from 8.1 nM to 9.2 μM), and 8 HTAs spanning this range were synthesized via conjugation of each DNP variant to the tetravalent scaffold. HTAs with hapten Kd < 235 nM stimulated degranulation following a bell-shaped dose response curve with maximum response occurring near the hapten Kd. HTAs with hapten Kd ≥ 235 nM failed to stimulate degranulation. To mimic physiological conditions, the percent of allergen specific IgE on cell surface was varied, and maximum degranulation occurred at 25% IgEDNP. These results demonstrated that moderate hapten–IgE affinities are sufficient to trigger mast cell degranulation. Moreover, this study established the HTA design as a well-defined, controllable, and physiologically relevant experimental system to elucidate the mast cell degranulation mechanism

Oriented Surface Immobilization of Antibodies at the Conserved Nucleotide Binding Site for Enhanced Antigen Detection

The conserved nucleotide binding site (NBS), found on the Fab variable domain of all antibody isotypes, remains a not-so-widely known and unutilized site. Here, we describe a UV photo-cross-linking method (UV-NBS) that utilizes the NBS for oriented immobilization of antibodies onto surfaces, such that the antigen binding activity remains unaffected. Indole-3-butyric acid (IBA) has an affinity for the NBS with a <i>K</i>_d ranging from 1 to 8 μM for different antibody isotypes and can be covalently photo-cross-linked to the antibody at the NBS upon exposure to UV light. Using the UV-NBS method, antibody was successfully immobilized on synthetic surfaces displaying IBA via UV photo-cross-linking at the NBS. An optimal UV exposure of 2 J/cm² yielded significant antibody immobilization on the surface with maximal relative antibody activity per immobilized antibody without any detectable damage to antigen binding activity. Comparison of the UV-NBS method with two other commonly used methods, ε-NH₃⁺ conjugation and physical adsorption, demonstrated that the UV-NBS method yields surfaces with significantly enhanced antigen detection efficiency, higher relative antibody activity, and improved antigen detection sensitivity. Taken together, the UV-NBS method provides a practical, site-specific surface immobilization method, with significant implications in the development of a large array of platforms with diverse sensor and diagnostic applications