Control of glial number: purification from mammalian brain extracts of an inhibitor of astrocyte division

Structural analysis of brain ganglioside acetylation patterns in mice with altered ganglioside biosynthesis

Gangliosides are sialylated membrane glycosphingolipids especially abundant in mammalian brain tissue. Sialic acid O-acetylation is one of the most common structural modifications of gangliosides which considerably influences their chemical properties. In this study, gangliosides extracted from brain tissue of mice with altered ganglioside biosynthesis (St8sia1 null and B4galnt1 null mice) were structurally characterized and their acetylation pattern was analyzed. Extracted native and alkali-treated gangliosides were resolved by high performance thin layer chromatography. Ganglioside mixtures as well as separated individual ganglioside fractions were further analyzed by tandem mass spectrometry. Several O-acetylated brain ganglioside species were found in knockout mice, not present in the wild-type mice. To the best of our knowledge this is the first report on the presence of O-acetylated GD1a in St8sia1 null mice and O-acetylated GM3 species in B4galnt1 null mice. In addition, much higher diversity of abnormally accumulated brain ganglioside species regarding the structure of ceramide portion was observed in knockout versus wild-type mice. Obtained findings indicate that the diversity of brain ganglioside structures as well as acetylation patterns in mice with altered ganglioside biosynthesis, is even higher than previously reported. Further investigation is needed in order to explore the effects of acetylation on ganglioside interactions with other molecules and consequently the physiological role of acetylated ganglioside species.

Specific synthesis of neurostatin and gangliosides O-acetylated in the outer sialic acids using a sialate transferase

Gangliosides are sialic acid containing glycosphingolipids, commonly found on the outer leaflet of the plasma membrane. O-acetylation of sialic acid hydroxyl groups is one of the most common modifications in gangliosides. Studies on the biological activity of O-acetylated gangliosides have been limited by their scarcity in nature. This comparatively small change in ganglioside structure causes major changes in their physiological properties. When the ganglioside GD1b was O-acetylated in the outer sialic acid, it became the potent inhibitor of astroblast and astrocytoma proliferation called Neurostatin. Although various chemical and enzymatic methods to O-acetylate commercial gangliosides have been described, O-acetylation was nonspecific and produced many side-products that reduced the yield. An enzyme with O-acetyltransferase activity (SOAT) has been previously cloned from the bacteria Campylobacter jejuni. This enzyme catalyzed the acetylation of oligosaccharide-bound sialic acid, with high specificity for terminal alpha-2,8-linked residues. Using this enzyme and commercial gangliosides as starting material, we have specifically O-acetylated the gangliosides' outer sialic acids, to produce the corresponding gangliosides specifically O-acetylated in the sialic acid bound in alpha-2,3 and alpha-2,8 residues. We demonstrate here that O-acetylation occurred specifically in the C-9 position of the sialic acid. In summary, we present a new method of specific O-acetylation of ganglioside sialic acids that permits the large scale preparation of these modified glycosphingolipids, facilitating both, the study of their mechanism of antitumoral action and their use as therapeutic drugs for treating glioblastoma multiform (GBM) patients.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Glioma growth inhibition by neurostatin and O-But GD1b

In spite of their low incidence, central nervous system tumors have elevated morbidity and mortality, being responsible for 2.3% of total cancer deaths. The ganglioside O-acetylated GD1b (O-Ac GD1b; neurostatin), present in the mammalian brain, and the semi-synthetic O-butyrylated GD1b (O-But GD1b) are potent glioma proliferation inhibitors, appearing as possible candidates for the treatment of nervous system tumors. Tumoral cell division inhibitory activity in culture correlated with growth inhibition of glioma xenotransplants in Foxn1(nu) nude mice and intracranial glioma allotransplants. Both O-Ac GD1b and O-But GD1b inhibited in vivo cell proliferation, induced cell cycle arrest, and potentiated immune cell response to the tumor. Furthermore, the increased stability of the butyrylated compound (O-But GD1b) enhanced its activity with respect to the acetylated ganglioside (neurostatin). These results are the first report of the antitumoral activity of neurostatin and a neurostatin-like compound in vivo and indicate that semi-synthetic O-acetylated and O-butyrylated gangliosides are potent antitumoral compounds that should be considered in strategies for brain tumor treatment.

Design and synthesis of glycoside inhibitors of glioma and melanoma growth

An N-acetylglucosaminide derivative with a pentaerythritol substituent at position C-6 was previously synthesized and shown to inhibit neural tumor growth. Now, we report the preparation of a series of new synthetic compounds introducing systematic changes in the nature, polarity, and size of the sugar substituents. The antimitotic activity of the new compounds was tested on cultured rat (C6) and human (U-373) glioma lines and on a human melanoma line (A-375). The antimitotic and antitumoral activity of the new compounds on glioma cell lines increased up to 2 orders of magnitude with respect to the parent compound or was abolished, permitting a detailed structure-function analysis of the new antitumorals. One of the glycosides inhibited melanoma division with an ID50 below the micromolar range.

Human gliosarcoma-associated ganglioside composition is complex and distinctive as evidenced by high-performance mass spectrometric determination and structural characterization

Gangliosides (GGs), involved in malignant alteration and tumor progression/invasiveness, are considered as tumor biomarkers or therapeutic targets. Here, we describe the first systematic GG composition characterization in human gliosarcoma versus normal brain tissue using our recently developed mass spectrometry (MS) methods, based on nano-electrospray (nano-ESI), Fourier-transform ion cyclotron resonance (FT-ICR), and chip nano-ESI quadrupole time-of-flight (QTOF), complemented by thin-layer chromatographic (TLC) analysis and quantification. Combined MS enabled detection and structural assignment of 73 distinct GG species: many more than reported so far for investigated gliomas. Apart from the 7.4-times lower total GG content, gliosarcoma contained all major brain-associated species, however, in very altered proportions, exhibiting a highly distinctive pattern: GD3 (48.9%)>GD1a/nLD1>GD2/GT3>GM3>GT1b>GM2>GM1a/GM1b/nLM1>LM1>GD1b>GQ1b. MS also revealed abundant O-Ac-GD3; its sequencing provided structural evidence to postulate a novel O-Ac-GD3 isomer O-acetylated at the inner Neu5Ac-residue, previously not structurally confirmed. The high sensitivity and mass accuracy permitted the assignment of unusual minor species: GM4, Hex-HexNAc-nLM1, Gal-GD1, Fuc-GT1, GalNAc-GT1, O-Ac-GM3, di- O-Ac-GD3O-Ac-GD3, and O-Ac-GT3, not previously reported as glioma-associated. The gliosarcoma-expressed GA2 might represent a marker distinguishing astrocytic from oligodendroglial tumors. This is, to our knowledge, so far the most complete GG composition characterization of certain glioma, which demonstrates that our MS-based approach could provide essential structural information relevant to glycosphingolipid role(s) in brain tumor biology, differential diagnosis/prognosis and novel treatment concepts.

Galectin-1: a bifunctional regulator of cellular proliferation

Galectin-1 has demonstrated a diverse range of activities in relation to cell survival and proliferation. In different circumstances, it acts as a mitogen, as an inhibitor of cell proliferation, and as a promoter of cellular apoptosis. Many of these activities, particularly the mitogenic and apoptotic responses, follow from the interaction of galectin-1 with cell-surface beta-galactoside ligands, but there is increasing evidence for protein-protein interactions involving galectin-1, and for a beta-galactoside-independent cytostatic mechanism. The bifunctional nature of galectin-1, in conjunction with other experimental variables, makes it difficult to assess the overall outcomes and significance of the growth-regulatory actions in many previous investigations. There is thus a need for well-defined experimental cross-correlation of observations, for which specific loss-of-function galectin-1 mutants will be invaluable. Unsurprisingly, in view of this background, the interpretation of the actions of galectin-1 in developmental situations, both normal and neoplastic, is often very complex.

Inhibiting human astrocytoma growth: structure-activity relationships in neurostatin related glycolipids

Neurostatin, a mammalian brain inhibitor of division of astroblast and astrocytoma cells, was characterized as the disialoganglioside GD1b, 9-O-acetylated on the outer sialic acid residue (Galbeta1-->3GalNAcbeta1-->4(9-O-Ac-NeuAcalpha2-->8NeuAcalpha2-->3)Galbeta1-->4Glcbeta1-->1'-ceramide). Using semisynthetic approaches, we prepared and tested different gangliosides O-acetylated in the sialic acid and compared them to non-O-acetylated partners as inhibitors of U-373 glioma cells. Athough the O-acetylation of the sialic acid was the most important molecular feature for the antiproliferative activity of O-acetylated gangliosides, monosaccharide links Galbeta1--> 3GalNAcbeta1 and NeuAcalpha2-->8NeuAcalpha2 enhanced the inhibitory activity.

Negative regulation of neuroblastoma cell growth by carbohydrate-dependent surface binding of galectin-1 and functional divergence from galectin-3

The cell density-dependent growth inhibition of human SK-N-MC neuroblastoma cells is initiated by increased ganglioside sialidase activity leading to elevated cell surface presentation of ganglioside GM1, a ligand of galectin-1. We herein show that the extent of the cell surface expression of the galectin coincides with marked increases of the sialidase activity. Reverse transcriptase-polymerase chain reaction analysis excludes a regulation at the transcriptional level. Exposure of cells to purified galectin-1 reveals its carbohydrate-dependent activity to reduce cell proliferation. Assays to detect DNA fragmentation biochemically and cytometrically and to block caspases render it unlikely that galectin-1 acts as a classical proapoptotic factor on these cells. Because the chimeric galectin-3 shares binding sites and binding parameters with galectin-1 for these cells, we tested whether this galectin will elicit the same response as the homodimeric cross-linking galectin-1. Evidently, galectin-3 fails to affect cell growth by itself but interferes with galectin-1 upon coincubation. Its proteolytically truncated variant, the C-terminal lectin domain with impaired capacity to form aggregates when surface bound, has only weak binding properties. Thus, the way in which the galectin-1 interacts topologically with an apparently common set of ligands relative to galectin-3 is crucial for eliciting post-binding events. We conclude that galectin-1 is a probable effector in the sialidase-dependent growth control in this system. Moreover, the experiments with galectin-3 reveal functional divergence, most probably based on different topologies of presentation of homologous carbohydrate-binding sites.

Isolation and purification of an epidermal growth factor receptor-related inhibitor of cell growth from cultured rat astrocytes

Astrocytes rarely undergo mitotic cell division in the developed adult. However, following injury to the central nervous system (CNS), astrocytes undergo rapid cell division and reactive astrocytes encapsulate exposed areas of the CNS producing a glial scar. Studies indicate the existence of a family of epidermal growth factor receptor (EGFr) related glycosidic mitogen inhibitors with growth inhibiting properties for astrocytes. Here, for the first time, we describe the isolation of such a factor from cultured rat astrocytes by ion-exchange and immunoaffinity chromatography. The isolated factor is glycosidic in nature, cross reacts with the anti-EGFr monoclonal antibody Clone 29.1, and inhibits the growth of primary astrocytes and N2a neuroblastoma cells in vitro.

Purification and structure of neurostatin, an inhibitor of astrocyte division of mammalian brain

Neurostatin was originally described as an inhibitor of astroblast and astrocytoma division present in rat brain extracts and immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens. It was purified recently from mammalian brain extracts and characterized as a glycosphingolipid, but its precise structure remained unknown. Neurostatin has now been purified to apparent homogeneity from ganglioside extracts of rat, bovine, and porcine brain. It is cytostatic for astroblasts, C6 glioma cells, and various human astrocytomas grades III and IV, with IC(50) values ranging from 250 to 450 nM, but does not affect the division of primary or transformed fibroblasts up to concentrations >4 microM. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of purified pig neurostatin showed a molecular ion of 1, 905 Da and ions of 1,863 and 1,934 Da, compatible with a disialoganglioside. Mono- and bidimensional NMR spectra, together with biochemical studies, suggest that neurostatin may be the 9-O-monoacetyl ester of GD1b.