Characterization of a human melanoma-associated ganglioside antigen defined by a monoclonal antibody, 4.2

Growing impact of sialic acid-containing glycans in future drug discovery

In nature, almost all cells are covered with a complex array of glycan chain namely sialic acids or nuraminic acids, a negatively charged nine carbon sugars which is considered for their great therapeutic importance since long back. Owing to its presence at the terminal end of lipid bilayer (commonly known as terminal sugars), the well-defined sialosides or sialoconjugates have served pivotal role on the cell surfaces and thus, the sialic acid-containing glycans can modulate and mediate a number of imperative cellular interactions. Understanding of the sialo-protein interaction and their roles in vertebrates in regard of normal physiology, pathological variance, and evolution has indeed a noteworthy journey in medicine. In this tutorial review, we present a concise overview about the structure, linkages in chemical diversity, biological significance followed by chemical and enzymatic modification/synthesis of sialic acid containing glycans. A more focus is attempted about the recent advances, opportunity, and more over growing impact of sialosides and sialoconjugates in future drug discovery and development.

The terminal sialic acid of stage-specific embryonic antigen-4 has a crucial role in binding to a cancer-targeting antibody

Cancer remains a leading cause of morbidity and mortality worldwide, requiring ongoing development of targeted therapeutics such as monoclonal antibodies. Carbohydrates on embryonic cells are often highly expressed in cancer and are therefore attractive targets for antibodies. Stage-specific embryonic antigen-4 (SSEA-4) is one such glycolipid target expressed in many cancers, including breast and ovarian carcinomas. Here, we defined the structural basis for recognition of SSEA-4 by a novel monospecific chimeric antibody (ch28/11). Five X-ray structures of ch28/11 Fab complexes with the SSEA-4 glycan headgroup, determined at 1.5-2.7 Å resolutions, displayed highly similar three-dimensional structures indicating a stable binding mode. The structures also revealed that by adopting a horseshoe-shaped conformation in a deep groove, the glycan headgroup likely sits flat against the membrane to allow the antibody to interact with SSEA-4 on cancer cells. Moreover, we found that the terminal sialic acid of SSEA-4 plays a dominant role in dictating the exquisite specificity of the ch28/11 antibody. This observation was further supported by molecular dynamics simulations of the ch28/11-glycan complex, which show that SSEA-4 is stabilized by its terminal sialic acid, unlike SSEA-3, which lacks this sialic acid modification. These high-resolution views of how a glycolipid interacts with an antibody may help to advance a new class of cancer-targeting immunotherapy.

Glycan-directed CAR-T cells

Cancer immunotherapy is rapidly advancing in the treatment of a variety of hematopoietic cancers, including pediatric acute lymphoblastic leukemia and diffuse large B cell lymphoma, with chimeric antigen receptor (CAR)-T cells. CARs are genetically encoded artificial T cell receptors that combine the antigen specificity of an antibody with the machinery of T cell activation. However, implementation of CAR technology in the treatment of solid tumors has been progressing much slower. Solid tumors are characterized by a number of challenges that need to be overcome, including cellular heterogeneity, immunosuppressive tumor microenvironment (TME), and, in particular, few known cancer-specific targets. Post-translational modifications that differentially occur in malignant cells generate valid cell surface, cancer-specific targets for CAR-T cells. We previously demonstrated that CAR-T cells targeting an aberrant O-glycosylation of MUC1, a common cancer marker associated with changes in cell adhesion, tumor growth and poor prognosis, could control malignant growth in mouse models. Here, we discuss the field of glycan-directed CAR-T cells and review the different classes of antibodies specific for glycan-targeting, including the generation of high affinity O-glycopeptide antibodies. Finally, we discuss historic and recently investigated glycan targets for CAR-T cells and provide our perspective on how targeting the tumor glycoproteome and/or glycome will improve CAR-T immunotherapy.

Immunization of A4galt-deficient mice with glycosphingolipids from renal cell cancers resulted in the generation of anti-sulfoglycolipid monoclonal antibodies

In this study, we immunized Gb3/CD77 synthase gene (A4galt) knockout (KO) mice with glycosphingolipids (GSLs) extracted from 3 renal cell cancer (RCC) cell lines to raise monoclonal antibodies (mAbs) reactive with globo-series GSLs specifically expressed in RCCs. Although a number of mAbs reactive with globo-series GSLs were generated, they reacted with both RCC cell lines and normal kidney cells. When we analyzed recognized antigens by mAbs that were specifically reactive with RCC, but not with normal kidney cells at least on the cell surface, many of them turned out to be reactive with sulfoglycolipids. Eight out of 11 RCC-specific mAbs were reactive with SM2 alone, and the other 3 mAbs were more broadly reactive with sulfated glycolipids, i.e. SM3 and SM4 as well as SM2. In the immunohistochemistry, these anti-sulfoglycolipids mAbs showed RCC-specific reaction, with no or minimal reaction with adjacent normal tissues. Thus, immunization of A4galt KO mice with RCC-derived GSLs resulted in the generation of anti sulfated GSL mAbs, and these mAbs may be applicable for the therapeutics for RCC patients.

UVB-irradiated keratinocytes induce melanoma-associated ganglioside GD3 synthase gene in melanocytes via secretion of tumor necrosis factor α and interleukin 6

Although expression of gangliosides and their synthetic enzyme genes in malignant melanomas has been well studied, that in normal melanocytes has been scarcely analyzed. In particular, changes in expression levels of glycosyltransferase genes responsible for ganglioside synthesis during evolution of melanomas from melanocytes are very important to understand roles of gangliosides in melanomas. Here, expression of glycosyltransferase genes related to the ganglioside synthesis was analyzed using RNAs from cultured melanocytes and melanoma cell lines. Quantitative RT-PCR revealed that melanomas expressed high levels of mRNA of GD3 synthase and GM2/GD2 synthase genes and low levels of GM1/GD1b synthase genes compared with melanocytes. As a representative exogenous stimulation, effects of ultraviolet B (UVB) on the expression levels of 3 major ganglioside synthase genes in melanocytes were analyzed. Although direct UVB irradiation of melanocytes caused no marked changes, culture supernatants of UVB-irradiated keratinocytes (HaCaT cells) induced definite up-regulation of GD3 synthase and GM2/GD2 synthase genes. Detailed examination of the supernatants revealed that inflammatory cytokines such as TNFα and IL-6 enhanced GD3 synthase gene expression. These results suggest that inflammatory cytokines secreted from UVB-irradiated keratinocytes induced melanoma-associated ganglioside synthase genes, proposing roles of skin microenvironment in the promotion of melanoma-like ganglioside profiles in melanocytes.

Chemoenzymatic synthesis of GD3 oligosaccharides and other disialyl glycans containing natural and non-natural sialic acids

In order to understand the biological importance of naturally occurring sialic acid variations on disialyl structures in nature, we developed an efficient two-step multienzyme approach for the synthesis of a series of GD3 ganglioside oligosaccharides and other disialyl glycans containing a terminal Siaalpha2-8Sia component with different natural and non-natural sialic acids. In the first step, alpha2-3- or alpha2-6-linked monosialylated oligosaccharides were obtained using a one-pot three-enzyme approach. These compounds were then used as acceptors for the alpha2-8-sialyltransferase activity of a recombinant truncated multifunctional Campylobacter jejuni sialyltransferase CstII mutant, CstIIDelta32(I53S), to produce disialyl oligosaccharides. The alpha2-8-sialyltransferase activity of CstIIDelta32(I53S) has promiscuous donor substrate specificity and can tolerate various substitutions at C-5 or C-9 of the sialic acid in CMP-sialic acid, while its acceptor substrate specificity is relatively restricted. The terminal sialic acid residues in the acceptable monosialylated oligosaccharide acceptors are restricted to Neu5Ac, Neu5Gc, KDN, and some of their C-9-modified forms but not their C-5 derivatives. The disialyl oligosaccharides obtained are valuable probes for their biological studies.

The repertoire of glycan determinants in the human glycome

The number of glycan determinants that comprise the human glycome is not known. This uncertainty arises from limited knowledge of the total number of distinct glycans and glycan structures in the human glycome, as well as limited information about the glycan determinants recognized by glycan-binding proteins (GBPs), which include lectins, receptors, toxins, microbial adhesins, antibodies, and enzymes. Available evidence indicates that GBP binding sites may accommodate glycan determinants made up of 2 to 6 linear monosaccharides, together with their potential side chains containing other sugars and modifications, such as sulfation, phosphorylation, and acetylation. Glycosaminoglycans, including heparin and heparan sulfate, comprise repeating disaccharide motifs, where a linear sequence of 5 to 6 monosaccharides may be required for recognition. Based on our current knowledge of the composition of the glycome and the size of GBP binding sites, glycoproteins and glycolipids may contain approximately 3000 glycan determinants with an additional approximately 4000 theoretical pentasaccharide sequences in glycosaminoglycans. These numbers provide an achievable target for new chemical and/or enzymatic syntheses, and raise new challenges for defining the total glycome and the determinants recognized by GBPs.

Atomic-resolution conformational analysis of the GM3 ganglioside in a lipid bilayer and its implications for ganglioside-protein recognition at membrane surfaces

Eukaryotic cells depend on external surface markers, such as gangliosides, to recognize and bind various other molecules as part of normal growth and maturation. The localization of gangliosides in the outer leaflet of the plasma membrane, also make them targets for pathogens trying to invade the host cells. Since ganglioside-mediated interactions are critical to both beneficial and pathological processes, much effort has been directed at determining the 3D structures of their carbohydrate head groups; however, technical difficulties have generally prevented the characterization of the head group in intact membrane-bound gangliosides. Determining the 3D structure and presentation of gangliosides at the surface of membranes is important in understanding how cells interact with their local environment. Here, we employ all-atom explicit solvent molecular dynamics (MD) simulations, using the GLYCAM06 force field, to model the conformation and dynamics of ganglioside G(M3) (alpha-Neu5Ac-(2-3)-beta-Gal-(1-4)-beta-Glc-ceramide) in a DMPC lipid bilayer. By comparison with MD simulations of the carbohydrate head-group fragment of G(M3) alone, it was possible to quantify and characterize the extent of changes in head-group presentation and dynamics associated with membrane anchoring. The accuracy of data from the MD simulations was determined by comparison to NMR and crystallographic data for the head group in solution and for G(M3) in membrane-mimicking environments. The experimentally consistent model of G(M3), in a lipid bilayer, was then used to model the recognition of G(M3) at the cell surface by known protein receptors.

Ganglioside signatures of primary and nodal metastatic melanoma cell lines from the same patient

The primary cutaneous melanoma initially migrates to the regional lymph nodes (LNs). Human melanoma overexpresses gangliosides, the sialylglycosphingolipids. The ganglioside signatures may differ between primary and LN melanomas owing to the differences in the tumor microenvironments. The melanoma cells obtained from the primary and LN of the same patient might be useful to evaluate the above hypothesis. For this purpose, the cryopreserved cell lines from a primary cutaneous melanoma (IGR-39) and its nodal metastasis (IGR-37) from the same patient were used. We have also compared the ganglioside signatures of freshly obtained melanoma cells from primary, LN and organ metastases from different patients. Gangliosides were extracted, purified and identified by resorcinol and specific murine monoclonal antibodies. Comparison of the primary cell line with the nodal metastatic line obtained from the same patient distinctly showed the following features: (i) an increased production of gangliosides, (ii) O-acetylation of GM2 and GD3, (iii) an increased and altered O-acetylation of GD2 and (iv) possibly de-N-acetylation of GD3. These findings suggest that the nodal microenvironment might favor activation of O-acetyl-transferases capable of O-acetylating both alpha2, 3 and alpha2, 8 sialic acids of gangliosides. Supporting this, the primary melanoma cells obtained from different patients, showed no O-acetylation of GD3 or GD2. The cell line from groin LN showed the presence of O-acetyl (O-Ac)GD3. The cell lines from thyroid, spleen and jejunum expressed O-AcGD2. In all metastatic melanoma cell lines GD1a is more prevalent than GD3, suggesting that GD1a may be a major melanoma-ganglioside.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Glycoimmunomics of human cancer: current concepts and future perspectives

Future strategies for the treatment of human cancer require a full appreciation of the intracellular and extracellular changes that accompany neoplastic transformation. The changes may involve a variety of micro- and macro-molecules, including, but not restricted to, peptides, proteins (with sugar and/or lipid moieties), oligosaccharides, glycolipids (neutral or acidic, e.g., gangliosides), ceramides, fatty acids and other lipids. Although several therapeutic approaches have been well developed in recent years, most of the reported studies focus on proteins and peptides. Glycoantigens and lipoantigens have been neglected. Elucidation of the profiles and properties of all molecules associated with tumor progression is required to develop a successful strategy to treat human cancer. This review describes the unique immunomics of tumor-associated glycoantigens and explains why the field of glycoimmunomics may yield clinically important biomarkers and treatments for the management of human cancer.

Gangliosides of organ-confined versus metastatic androgen-receptor-negative prostate cancer

Prior development of a unique androgen-receptor (AR)-negative cell line (HH870) from organ-confined (T2b) human prostate cancer (CaP) enabled comparison of the gangliosides associated with normal and neoplastic prostate epithelial cells, organ-confined versus metastatic (DU 145, PC-3), and AR-negative versus AR-positive CaP cell lines. Resorcinol-HCl and specific monoclonal antibodies were used to characterize gangliosides on 2D-chromatograms, and to visualize them on the cell surface with confocal-fluorescence microscopy. AR-negative cells expressed GM1b, GM2, GD2, GD1a, and GM3. GM1a, GD1b, and GT1b were undetectable. GM1b and GD1a were more prominent in AR-negative than in AR-positive cells. PC-3 and HH870 cells were unique in the expression of O-acetylGD2 (O-AcGD2) and two alpha2,3-sialidase-resistant, alkali-susceptible GMR17-reactive gangliosides. Expression of GD1a, GM1b, doublets of GD3, GD2, and O-AcGD2, and the presence of an additional alkali-labile-14.G2a-reactive ganglioside, two alkali-susceptible, and three alkali-resistant GMR17-reactive gangliosides makes HH870 a potential component of a polyvalent-vaccine for active-specific immunotherapy of CaP.

Bioengineering of Surface GD3 Ganglioside for Immunotargeting Human Melanoma Cells

N-Propionyl, N-butyryl (N-Bu), and N-benzoyl mannosamine, as precursors of sialic acid biosynthesis, were incubated with human melanoma SK-MEL-28 cells and resulted in the replacement of N-acetyl groups on the cell surface sialic acid residues, including those associated with GD3. Meanwhile, vaccines containing GD3 and modified GD3 tetrasaccharide-keyhole limpet hemocyanin conjugates were synthesized, and BALB/c mice were immunized with them together with monophosphoryl lipid A adjuvant. The GD3Bu-keyhole limpet hemocyanin conjugate raised the highest IgG titers without any cross-reactivity to unmodified GD3. Expression of GD3Bu epitopes on the surface of SK-MEL-28 cells was confirmed in vitro and in vivo by the binding of a polyclonal antiserum and monoclonal antibody (mAb) 2A, both of which specifically recognize GD3Bu, and by mass spectroscopic analysis of glycolipids extracted from cells. Following expression of GD3Bu on the surface of SK-MEL-28 cells, the cells could be lysed by mAb 2A and GD3Bu antiserum in the presence of complement. Although less effective in the control of existing large size tumors ( approximately 10 mm inner diameter) on BALB/c nu/nu mice, mAb 2A in combination with ManNBu effectively protected mice from SK-MEL-28 tumor grafting. This approach may provide a method to augment the immunogenicity of sialylated human antigens and to avoid generating an autoimmune response to them at same time.

Gangliosides as therapeutic targets for cancer

Gangliosides, sialic acid-containing glycosphingolipids, have engendered great interest for more than 20 years in the search for target molecules of relevance for tumour growth and formation of metastases and as potential targets for immunotherapy. These molecules show large quantitative and structural variability, which is related to cell type and developmental stage. Their potential role in the formation of tumour metastases was suggested from data supporting that they are involved in cell growth regulation and in cell-cell and cell-matrix adhesion. Moreover, gangliosides are expressed on the cell surface and thereby are accessible for antibodies or other ganglioside-binding molecules to induce cell death, inhibit cell growth and/or inhibit formation of tumour metastasis. All tumours exhibit aberrant ganglioside expression. This includes overexpression of normal ganglioside constituents, which appears to be common among various tumours, and expression of gangliosides not found in normal adult tissue but often found during fetal development. The ganglioside composition of melanoma cells has been found to correlate with their metastatic potential and also to be selectively expressed in cells of a tumour mass and invading tumour cells. Passive immunotherapy using murine or murine/human chimeric monoclonal antiganglioside antibodies in their native form or combined with various effector molecules has been investigated. However, the vaccination strategy using native or structurally modified tumour-associated gangliosides in combination with adjuvants is currently the dominant method in clinical trials. The outcomes reported so far vary between type of tumour and treatment strategies. However, we believe that targeting gangliosides is as promising as any other immune therapeutic strategy, and basic research as well as clinical trials utilising new aspects is encouraged.

Paraneoplastic retinopathies and optic neuropathies

Unusual neuro-ophthalmologic symptoms and signs that go unexplained should warrant a thorough investigation for paraneoplastic syndromes. Although these syndromes are rare, these clinical manifestations can herald an unsuspected, underlying malignancy that could be treated early and aggressively. This point underscores the importance of distinguishing and understanding the various, sometimes subtle, presentations of ocular paraneoplastic syndromes. Outlined in this review article are diagnostic features useful in differentiating cancer-associated retinopathy, melanoma-associated retinopathy, and paraneoplastic optic neuropathy. These must also be distinguished from non-cancer-related eye disorders that may clinically resemble cancer-associated retinopathy. The associated antibodies and histopathology of each syndrome are presented to help in the understanding of these autoimmune phenomena. Treatment outcomes from reported cases are summarized, and some potential novel immunotherapies are also discussed.

Synthesis of ganglioside GD3 and its comparison with bovine GD3 with regard to oligodendrocyte apoptosis mitochondrial damage

2,3-Dehydroneuraminic acid derivative 5 was transformed in five efficient steps into sialyl donor 2, which has a phenylthio group on the beta-side of the 3-position for anchimeric assistance and a diethyl phosphite residue as leaving group at the anomeric carbon. The known GM3 intermediate 10 was transformed into the 4b,4c,8c-O-unprotected acceptor 3, which was then allowed to react with 2 by using TMSOTf as catalyst and acetonitrile as solvent to afford the desired tetrasaccharide 12, which has an alpha(2-8)-linkage between two neuraminic acid residues. Removal of the phenylthio group gave intermediate 13, which was transformed into O-tetraosyl trichloroacetimidate 16 as glycosyl donor. Application of the azidosphingosine glycosylation procedure furnished GD3 (1) in high overall yield. Comparison of synthetic GD3 with bovine-brain-derived GD3 showed that there were similar effects in GD3-triggered uncoupling of mitochondrial respiration and in induction of apoptosis in oligodendrocytes.

Tumor-associated carbohydrate antigens defining tumor malignancy: basis for development of anti-cancer vaccines

Tumors expressing a high level of certain types of tumor-associated carbohydrate antigens (TACAs) exhibit greater metastasis and progression than those expressing low level of TACAs, as reflected in decreased patient survival rate. Well-documented examples of such TACAs are: (i) H/Le(y)/Le(a) in primary non-small cell lung carcinoma; (ii) sialyl-Le(x) (SLe(x)) and sialyl-Le(a) (SLe(a)) in various types of cancer; (iii) Tn and sialyl-Tn in colorectal, lung, breast, and many other cancers; (iv) GM2, GD2, and GD3 gangliosides in neuroectodermal tumors (melanoma and neuroblastoma); (v) globo-H in breast, ovarian, and prostate cancer; (vi) disialylgalactosylgloboside in renal cell carcinoma. Some glycosylations and TACAs suppress invasiveness and metastatic potential. Well-documented examples are: (i) blood group A antigen in primary lung carcinoma; (ii) bisecting beta1 --> 4GlcNAc of N-linked structure in melanoma and other cancers; (iii) galactosylgloboside (GalGb4) in seminoma. The biochemical mechanisms by which the above glycosylation changes promote or suppress tumor metastasis and invasion are mostly unknown. A few exceptional cases in which we have some knowledge are: (i) SLe(x) and SLe(a) function as E-selectin epitopes promoting tumor cell interaction with endothelial cells; (ii) some tumor cells interact through binding of TACA to specific proteins other than selectin, or to specific carbohydrate expressed on endothelial cells or other target cells (carbohydrate-carbohydrate interaction); (iii) functional modification of adhesive receptor (integrin, cadherin, CD44) by glycosylation. So far, a few successful cases of anti-cancer vaccine in clinical trials have been reported, employing TACAs whose expression enhances malignancy. Examples are STn for suppression of breast cancer, GM2 and GD3 for melanoma, and globo-H for prostate cancer. Vaccine development canbe extended using other TACAs, with the following criteria for success: (i) the antigen is expressed highly on tumor cells; (ii) high antibody production depending on two factors: (a) clustering of antigen used in vaccine; (b) choice of appropriate carrier protein or lipid; (iii) high T cell response depending on choice of appropriate carrier protein or lipid; (iv) expression of the same antigen in normal epithelial tissues (e.g., renal, intestinal, colorectal) may not pose a major obstacle, i.e., these tissues are not damaged during immune response. Idiotypic anti-carbohydrate antibodies that mimic the surface profile of carbohydrate antigens, when administered to patients, elicit anti-carbohydrate antibody response, thus providing an effect similar to that of TACAs for suppression of tumor progression. An extension of this idea is the use of peptide mimetics of TACAs, based on phage display random peptide library. Although examples are so far highly limited, use of such "mimotopes" as immunogens may overcome the weak immunogenicity of TACAs in general.

Targeting of T lymphocytes to melanoma cells through chimeric anti-GD3 immunoglobulin T-cell receptors

Immunoglobulin T-cell receptors (IgTCRs) combine the specificity of antibodies with the potency of cellular killing by grafting antibody recognition domains onto TCR signaling chains. IgTCR-modified T cells are thus redirected to kill tumor cells based on their expression of intact antigen on cell surfaces, bypassing the normal mechanism of activation through TCR-peptide-major histocompatibility complex (MHC) recognition. Melanoma is one of the most immunoresponsive of human cancers and has served as a prototype for the development of a number of immunotherapies. The target antigen for this study is the ganglioside GD3, which is highly expressed on metastatic melanoma with only minor immunologic cross-reaction with normal tissues. To determine an optimal configuration for therapy, four combinations of IgTCRs were prepared and studied: sFv-epsilon, sFv-zeta, Fab-epsilon, Fab-zeta. These were expressed on the surface of human T cells by retroviral transduction. IgTCR successfully redirected T-cell effectors in an MHC-unrestricted manner, in this case against a non-T-dependent antigen, with specific binding, activation, and cytotoxicity against GD3+ melanoma cells. Soluble GD3 in concentrations up to 100 microg/ml did not interfere with recognition and binding of membrane-bound antigen. Based on the outcomes of these structural and functional tests, the sFv-zeta construct was selected for clinical development. These results demonstrate key features that emphasize the potential of anti-GD3 IgTCR-modified autologous T cells for melanoma therapies.

Alteration of ganglioside composition by stable transfection with antisense vectors against GD3-synthase gene expression

Gangliosides are ubiquitous components of mammalian cells. Their expression is frequently altered in many tumor types. We previously showed that alteration of the ganglioside composition often resulted in changes in cellular morphology and differentiation of cultured cells. In this study, we targeted sialyltransferase gene expression by the antisense knockdown experiment, and the results showed that inhibition of the expression of gangliosides GD3 and O-acetylated GD3 (OAc-GD3) in the neuroblastoma F-11 cells greatly reduced the tumor growth in nude mice. The sense and antisense vectors containing either a 5' end fragment or the entire sequence of the cDNA coding for GD3-synthase were prepared and used in separate experiments to transfect the F-11 cells which express high levels of gangliosides GD3 and OAc-GD3. Single clones were isolated and expanded. Both the activity of the GD3-synthase and the concentrations of GD3 and OAc-GD3 in the antisense-transfected cells were dramatically decreased as a result of transfection with the antisense expression vectors. Further characterization of the antisense-transfected cells showed reduced rates of cell growth and neurite formation and changes in cellular morphology. When the cells were inoculated in athymic nude mice, the tumor growth rate was remarkably suppressed although the tumor incidence was not affected by the altered ganglioside composition. These results indicate that the tumor-associated ganglioside(s) is(are) involved in regulation of tumor growth, probably through the stimulation of angiogenesis of the tumor.

Characterization of human IgG1 monoclonal antibody against gangliosides expressed on tumor cells

A human IgG1.k monoclonal antibody (MAb) designated GMA1 was developed by fusing pooled lymph node lymphocytes from cancer patients with the human lymphoblastoid cell line, SHFP-1. The GMA1 MAb reacted with several melanoma and neuroblastoma cell lines. Normal tissue derived from human brain and tumor-cell lines derived from colon, ovary, and breast were not reactive. FACS analysis performed using live cells demonstrated that the antibody recognizes a cell-surface antigen. Enzyme immunoassay (EIA) and thin layer chromatography (TLC) immunostaining with purified gangliosides indicated that the antibody has specificity for the major tumor associated gangliosides GD3, GM3, and GD2. GMA1 heavy and light chain genes were isolated by RT-PCR and a recombinant derivative of this human antibody was expressed in Chinese hamster ovary (CHO) cells. High-level antibody synthesis and secretion was achieved using a vector designed to maximize expression. FACS analysis and TLC immunostaining indicated recombinant GMA1 reacted with human tumor cell lines and gangliosides GD3, GM3, GD2 in a manner similar to the antibody produced by the hybridoma cell line, demonstrating that the specificity of the antibody was not altered during molecular cloning.

Detection of medulloblastoma and astrocytoma-associated ganglioside GD3 in cerebrospinal fluid

Shedding of gangliosides by tumor cells may enhance tumor development. We recently showed that cells of the human brain tumor, medulloblastoma, shed gangliosides in vitro and have therefore examined ganglioside shedding by pediatric brain tumors into the cerebrospinal fluid (CSF). GD3, a major ganglioside in medulloblastoma and astrocytoma, was the target for detection in the CSF by immunostaining using the monoclonal antibody R24 and enhanced chemiluminescence detection. Mean CSF GD3 levels in patients with medulloblastomas (n = 9) and astrocytomas (n = 10) were significantly higher than those of controls (mean +/- SD 44.7 +/- 8.4 versus 18.2 +/- 1.9 pmol/ml, n = 20, P < 0.0002). Mass spectrometric analysis showed that tumor-derived ganglioside GD3 contained heterogeneous ceramide structures and, interestingly, the ceramide subspecies with shorter fatty acyl chains were selectively shed. The elevated CSF GD3 concentrations in patients with medulloblastoma and astrocytoma support the concept that ganglioside shedding, which may have significant biological consequences, is characteristic of human brain tumors.

C-myc oncogene expression in human melanoma and its relationship with tumour antigenicity

Melanoma produces specific tumour antigens which are capable of eliciting an immune response. However, this tumour evades the immune system, in part, by downregulation of class I HLA antigens on the cell surface, which are required for T cell recognition. It has been suggested that the oncogene c-myc may have a role in effecting this change in vitro, however, the relationship between oncoprotein level and tumour antigenicity has not been established in human tumours. This study measured c-myc oncoprotein in 94 melanoma specimens (46 primary tumours and 48 regional metastases) using flow cytometry and evaluated class I HLA expression with immunohistochemistry. C-myc expression was found in 91 tumours (96%) with higher expression in metastases than primary melanomas (P<0.005). Class I HLA expression was found to show great variation although metastases showed less antigenicity than primary tumours (P<0.01). Analysis of the relationship between these two parameters revealed a highly significant correlation in both primary (P<0.01) and metastatic disease (P<0.01), with high oncoprotein being associated with down regulation of cell surface antigens. Knowledge of the control of tumour antigenicity is likely to provide an objective platform for the development of new strategies for immunotherapy.

Generation of human monoclonal antibodies against ganglioside antigens and their applications in the diagnosis and therapy of cancer

Different approaches to generating human monoclonal antibodies (MAbs) against tumor-associated ganglioside antigens have been carried out in several laboratories. A specific goal addressed by our laboratory is to produce human MAbs to several ganglioside antigens of relevance as therapeutic targets, such as the GM2, GD2, GD3 and GM3 gangliosides in melanoma. In vitro immunization of human B lymphocytes from normal donors was performed using liposomes containing gangliosides as the immunizing antigen combined with either complete tetanus toxoid or a synthetic peptide corresponding to a T helper epitope to stimulate in vitro immunization. Specific human anti-ganglioside antibodies were obtained, indicating that the antibody response found in vitro was antigen-driven. To overcome the widely reported problems concerning stability of immunoglobulin production by the antibody-secreting cell lines, a method of positive selection using GM3-coated magnetic beads has been developed in order to rescue unstable clones. Development of new methods to reproducibly generate ganglioside-specific human MAbs will amplify the possibilities for diagnostic and therapeutic applications.

Possible involvement of tumour cell membrane gangliosides in platelet-tumour cell interactions

The possible correlation(s) between platelet proaggregating activity, and sialic acid content and ganglioside expression of six human colorectal tumour cell lines (CBS, GEO, HT-29, WiDr, MIP and DLD-1) was evaluated. The three cell lines (HT-29, WiDr and DLD-1) capable of inducing remarkable in vitro platelet aggregation, had significantly higher amounts of lipid-bound sialic acid than those cell lines characterised by a lower platelet proaggregating activity (GEO, CBS and MIP). High performance thin-layer chromatography demonstrated the presence of one band comigrating with GM3 in all cell lines, while GD1a and GT1b comigrating gangliosides were present only in HT-29, WiDr and DLD-1 cells. Finally, an increased platelet pro-aggregating activity of GEO and CBS cell lines was observed after the incorporation of exogenous gangliosides. The present data support the hypothesis that lipid-bound sialic acid may be involved in platelet-tumour cell interactions.

Autoantibodies against ganglioside GM3 represent a portion of anti-lymphocyte antibodies in AIDS patients

In this study we analysed the relationship between anti-lymphocytic ganglioside antibodies and anti-lymphocyte antibodies in AIDS patients. Anti-lymphocytic ganglioside antibodies were detected by thin layer chromatography (TLC) immunostaining; three colour flow cytometry was used to analyse circulating antibodies against different lymphocyte subsets. Anti-lymphocytic ganglioside antibodies were detected in 23 out of 49 AIDS patients sera (46.9%). All positive sera reacted selectively with the GM3 comigrating band from AIDS lymphocytes. Twenty two out of the 23 anti-lymphocytic GM3 positive sera also had antibodies against CD4+T cells, versus 17/26 anti-GM3 negative. Furthermore, patients with lymphocytic GM3 antibodies showed a significantly higher antibody reactivity against CD4+ T cells than patients in which these antibodies were not detected. The absorption tests revealed that preincubation of positive sera with GM3 was followed by a decrease in the reaction with target lymphocytes. These findings suggest that anti-GM3 antibodies are a portion, but not the majority, of antibodies reacting with CD4+ T cells.

A rapid method for the preparation of ganglioside Glac2 (GD3)

A method is described for the preparation of ganglioside Glac2 [(II3(NeuAc)2-LacCer, GD3] from cream of bovine milk using liquid-phase extraction with methanol or ethanol followed by anion exchange chromatography. The method is rapid and inexpensive; 1 kg cream, centrifuged from 14-15 L of bovine milk, yields approximately 70 mg of pure ganglioside Glac2. The sialic acid constituent of ganglioside Glac2 isolated from bovine milk cream consists solely of the N-acetylneuraminic acid derivative. The major components of its ceramide consist of octadecasphing-4-enine and the 22:0 (behenic acid) and 23:0 fatty acids.

Factors affecting the fine specificity and sensitivity of serum antiganglioside antibodies in ELISA

The major problem associated with ELISA of serum antiganglioside antibodies is the high background values (absorbancy of sera added to wells without ganglioside), which interfere with the accurate assessment of the fine specificity and sensitivity of these antibodies. This investigation identifies factors elevating the background values and/or decreasing the fine specificity, and describes strategies to minimize their influence. Using sera of neuropathy and melanoma patients, we found that highest background values were observed with the polystyrene 'tissue culture' microtiter plates; of the various 'non-tissue culture' microtiter plates tested, the lowest background values (> 0.060) were observed with Costar-3590 (H), Immunolon-3, Immunolon-1, Falcon-3915 (in increasing order). Background artifact of polystyrene microtest plates was significantly reduced by gamma irradiation (at 40 kRad) and/or use of detergent Tween-20 (0.1%) in the washing step. Even after controlling the background values, the fine specificity, namely, the ability of the antibody to distinguish between the target epitope of an antigen and epitopes of related antigens (when moles of antigen/well is constant) varied with different microtiter plates. Using sera with high affinity and specificity for GM2, GD3 or GM3, we observed that Immunolon-1, Immunolon-3 and particularly Falcon-3915 were superior for assessing the abilities of the antibodies to distinguish closely related epitopes found on other gangliosides. The reactivity of antiganglioside antibodies was more consistent after detergent treatment. The reactivity of antibodies to GD3 is significantly enhanced after treatment with Tween-20, but that of antibodies reacting to GM1 and GM2 is reduced. Fine specificity of the antiglycolipid antibodies was resolved better by coating glycolipids in mol/well rather than by weight/well. Based on these results, a protocol for a sensitive and reproducible ELISA for serum antiganglioside antibodies is recommended. The protocol takes into consideration the suitability of polystyrene plates, coating based on the number of molecules, pertinency of the solvent for coating, use of human serum albumin for blocking, dilution and washing steps and use of 0.1% Tween-20 to further minimize the background absorbancy.

Reactivity of chagasic sera with crude and highly purified glycosphingolipid fractions from Trypanosoma cruzi epimastigotes

The reactivities of sera from patients with Chagas disease or from T. cruzi-immunized rabbits with two different lipid preparations of T. cruzi were assessed using epimastigote antigens. Serum reactivities were determined using a quantitative enzyme-linked immunosorbent assay (ELISA). Antigen 1 represents the lower phase obtained from crude lipid extract after Folch partition (LCL). Antigen 2 is a highly purified glycosphingolipid fraction (GSL). The LCL antigen discriminated quite well the reactivities of Chagasic patients' sera and sera from healthy individuals, as well as between the serum from a T. cruzi-immunized rabbit (TIRS) and normal rabbit serum (NRS). A strong reactivity with GSL was obtained with TIRS. Reactivity with GSL was also obtained with human Chagasic sera. Compared to a group of normal individuals, the reactions of antibodies directed against lipid antigens were considerably increased in sera of patients with Chagas disease. Chagasic sera did not differentiate between glycolipids with terminal beta-glucosyl or beta-galactosyl non-reducing units. They discriminated, however, glucosylceramides with differences in the ceramide structure. To determine the specificity of Chagasic sera, antibodies isolated on LCL-immunosorbent (LCL-Ch Abs) as well as on laminin-immunosorbent (Lam-Ch Abs) were tested against laminin and LCL antigens. We found that Lam-Ch Abs reacted with murine laminin, whereas the reaction was negative with LCL. In contrast, the LCL-Ch Abs reacted either with LCL antigens or with laminin. The reactivity with laminin was strong in comparison with LCL.(ABSTRACT TRUNCATED AT 250 WORDS)

A synthetic approach to polysialogangliosides containing alpha-sialyl-(2-->8)-sialic acid: total synthesis of ganglioside GD3

A stereocontrolled, facile total synthesis of ganglioside GD3 is described as an example of a proposed systematic approach to the preparation of gangliosides containing an alpha-sialyl-(2-->8)-sialic acid unit alpha-glycosidically linked to O-3 of a D-galactose residue in their oligosaccharide chains. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-, 3-O-benzoyl-, or 3-O-benzyl-beta-D-galactopyrano-sides, or 2-(trimethylsilyl)ethyl 2,3,6,2',6'-penta-O-benzyl-beta-lactoside (7), with methyl [phenyl 5- acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D- glycero-alpha-D-galacto-2-nonulopyranosylono-1',9 lactone)- 4,7-di-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto-2-nonulopyrano sid] onate (3), using N-iodosuccinimide-trifluoromethanesulfonic acid as a promoter, gave the corresponding alpha glycosides 8 (32%), 13 (33%), 14 (48%), and 17 (31%), respectively. The glycosyl donor 3 was prepared from O-(5-acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosy lonic acid)-(2-->8)-5-acetamido-3,5- dideoxy-D-glycero-D-galacto-2-nonulopyranosonic acid by treatment with Amberlite IR-120 (H+) in methanol, O-acetylation, and subsequent replacement of the anomeric acetoxy group with phenylthio. Compound 8 was converted into the methyl beta-thioglycoside via O-benzoylation, replacement of the 2-(trimethylsilyl)ethyl group by acetyl, and introduction of the methylthio group by reaction with methylthiotrimethylsilane. Compound 17 was converted, via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the alpha-trichloroacetimidate, which was coupled with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol to give the beta-glycoside. This glycoside was easily transformed, via selective reduction of the azido group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester and lactone functions, into ganglioside GD3.

A mouse/human chimeric anti-(ganglioside GD3) antibody with enhanced antitumor activities

Ganglioside GD3, which is one of the major gangliosides expressed on the cell surface of human tumors of neuroectodermal origin has been focused on as a target molecule for passive immunotherapy. We have cloned the cDNA encoding the immunoglobulin light and heavy chains of an anti-GD3 monoclonal antibody KM641 (murine IgG3, kappa), and constructed the chimeric genes by linking the cDNA fragments of the murine light and heavy variable regions to cDNA fragments of the human kappa and gamma 1 constant regions, respectively. The transfer of these cDNA constructs into SP2/0 mouse myeloma cells resulted in the production of the chimeric antibody, designated KM871, that retained specific binding activity to GD3. Indirect immunofluorescence revealed the same staining pattern for chimeric KM871 and the mouse counterpart KM641 on GD3-expressing melanoma cells. When human serum and human peripheral blood mononuclear cells were used as effectors in complement-mediated cytotoxicity and antibody-dependent cell-mediated cytotoxicity respectively, the chimeric KM871 was more effective in killing GD3-expressing tumor cells than was the mouse counterpart KM641. Intravenous injection of chimeric KM871 markedly suppressed tumor growth in nude mice. The chimeric KM871, having enhanced antitumor activities and less immunogenicity than the mouse counterpart, would be a useful agent for passive immunotherapy of human cancer.

Colony-stimulating factor enhancement of myeloid effector cell cytotoxicity towards neuroectodermal tumour cells

We conducted experiments to determine the optimal conditions for colony-stimulating factor-enhanced neutrophil- and mononuclear phagocyte-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) using monoclonal antibodies to disialogangliosides expressed on neuroectodermal tumour target cells. Neutrophil ADCC was most effective at effector:target ratios of 100:1, with maximal cytotoxic responses to melanoma target cells generated by 3 h. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) were the most potent stimulators of neutrophil ADCC, and enhanced ADCC activity was inhibited in the presence of antibody to Fc receptor type II (FcRII). GM-CSF and macrophage colony-stimulating factor (M-CSF) treatment of freshly isolated monocytes inhibited antibody-independent cytotoxicity but enhanced antibody-dependent responses. After 3 d in culture with CSF, 3-10-fold enhancement of ADCC against melanoma target cells was observed at effector:target cell ratios of 10:1. Greatest stimulation of macrophage ADCC was obtained when GM-CSF, M-CSF or interleukin 3 (IL-3) were used in conjunction with a secondary stimulus. Although gamma interferon (gamma-IFN) did not augment the cytotoxic capability of GM-CSF- and IL-3-stimulated macrophages, prominent cytotoxic enhancement was seen when M-CSF-stimulated macrophages were exposed to gamma-IFN. A chimaeric mouse/human monoclonal antibody was found to be equivalent in activity to the murine antibody in neutrophil ADCC; however, in macrophage ADCC assays with submaximal effector cell stimulation, the chimaeric antibody was associated with a two-fold greater response. These studies indicate that under specific conditions, CSFs capable of increasing the number and functional activity of mature myeloid effector cells enhance antibody-dependent cytotoxicity to neuroectodermal tumour target cells.

Monoclonal antibodies in cancer detection and therapy

Anticancer antibodies have had a long history in the management of cancer, with major applications having been shown in the immunohistochemistry and immunoassay of tumor-associated antigen markers. With the advent of hybridoma-derived monoclonal antibodies, attempts to use these more reproducible reagents in vivo for cancer detection and therapy have intensified. Radiolabeled monoclonal antibodies appear to be gaining a role in the management of cancer by means of imaging methods to detect sites of increased radioactivity, and several products have been developed and tested clinically. In the area of radioimmunotherapy, a number of problems still need to be solved, including low tumor uptake of the radioimmunoconjugate, dose-limiting myelotoxicity, and the induction of an immune response to repeated doses of murine (foreign) immunoglobulins. Similar problems exist for toxin and drug immunoconjugates, but these also fail to benefit from the "bystander" effect of the ionizing radiation delivered with radioimmunoconjugates, and plant and bacterial toxin molecules appear to have additional immunogenicity that restricts repeated injections. Despite these limitations, recombinant engineering and other chemical approaches are making progress in developing second-generation immunoconjugates that may be more efficacious and less immunogenic as cancer-selective therapeutics. Although nonconjugated, "naked", murine monoclonal antibodies have shown limited success in the therapy of human neoplasms, human and "humanized" forms may be more effective, particularly in lymphatic tumors. Some evidence also suggests that anti-idiotype antibodies (antiantibodies) may serve as surrogate antigens in cancer vaccines. Thus, a number of promising immunologic approaches for cancer diagnosis, detection, and therapy have made important progress in recent years.

Antitumor effects of a novel monoclonal antibody with high binding affinity to ganglioside GD3

Ganglioside GD3, which is one of the major gangliosides expressed on the cell surface human tumors of neuroectodermal origin, has been studied as a target molecule for passive immunotherapy. We established ten kinds of anti-GD3 monoclonal antibodies (mAb) of the mouse IgG3 subclass by immunization with purified GD3 and melanoma cells. One of the established mAb, KM641, showed major reactivity with GD3 and minor reactivity with GQ1b out of 11 common gangliosides in an enzyme-linked immunosorbent assay. Immunostaining of gangliosides, separated on thin-layer chromatography plates, using KM641 revealed that most of the melanoma cell lines contained immunoreactive GD3 and GD3-lactone at a high level, but only the adrenal gland and the urinary bladder out of 21 human normal tissues had immunoreactive GD3. In immunofluorescence, KM641 bound to a variety of living tumor cell lines especially melanoma cells, including some cell lines to which another anti-GD3 mAb R24, established previously, failed to bind. High-affinity binding of KM641 to a tumor cell line was quantified by Scatchard analysis (Kd = 1.9 x 10(-8) M). KM641 exerted tumor-killing activity in the presence of effector cells or complement against melanoma cells expressing GD3 at a high level. Not only natural killer cells but also polymorphonuclear cells were effective as the effector cells in antibody-dependent cellular cytotoxicity. Intravenous injection of KM641 markedly suppressed the tumor growth of a slightly positive cell line, C24.22 (7.2 x 10(5) binding sites/cell), as well as a very GD3-positive cell line, G361 (1.9 x 10(7) binding sites/cell), inoculated intradermally in nude mice. KM641, characterized by a high binding affinity for GD3, has the potential to be a useful agent for passive immunotherapy of human cancer.

Immunorecognition of different ganglioside epitopes on human normal and melanoma tissues

There is increasing evidence that cell-surface gangliosides play a role in tumor growth, progression and metastases. In order to determine the frequency of ganglioside GD3 in patients with metastatic malignant melanoma for further therapeutic trials, GD3 ganglioside expression was determined in 119 tissue samples. Of these melanomas, 93% (111/119) were R-24-positive, which indicates the value of this diagnostic marker for melanoma. To study the structural epitopes of gangliosides, 10 ganglioside antibodies with defined specificities and affinities were tested on over 100 fresh-frozen tissue specimens of human normal and melanoma tissues. All the antibodies tested recognize the ganglioside GD3, but vary in their cross-reactivity with other gangliosides. According to their epitope specificity, they can be divided into 5 groups. For example, the antibodies Z-21 and A-4 react like the previously established MAb R-24 with gangliosides GD3 and GQlb, and one MAb (Q-4) detects all gangliosides containing 2 connected sialic acids (GD3, GD2, GDlb, GTlb, GQlb). Specificity on TLC does not always correlate with specificity to melanoma tissues and vice-versa. For example, MAb A-4, which recognizes only GD3 and GQlb on TLC, shows no specific reactivity on tissues. Furthermore, antibodies with the same ganglioside specificity do not have the same staining pattern on human tissues. For example, MAb Z-21, which is directed against the same gangliosides as MAb R-24 on TLC, does not cross-react with as many neuroectodermal tissues as MAb R-24. Because of their distinct properties, some of these antibodies may be even more useful for immunodiagnosis and immunotherapy of malignant melanoma than MAb R-24.

Antibody responses to ganglio-series gangliosides in different strains of inbred mice

We studied antibody responses after immunization with ganglio-series gangliosides against 10 strains of inbred mice, including Balb/c, C57BL/6, A/J, C3H/HeN, C3H/HeJ, CBA/N, AKR/N, NZB/N, DBA/2 and nu/nu Balb/c. Twelve gangliosides having NeuAc as their sialic acid moiety (GM4, GM3, GM2, GM1, GD3, O-Ac-GD3, GD2, GD1a, GD1b, GT1a, GT1b and GQ1b), four gangliosides having NeuGc (GM3, GM2, GM1 and GD3) and four asialo-gangliosides (GA4, GA3, GA2 and GA1) were injected intravenously adsorbed to Salmonella minnesota. The antibody titers of the mice sera were determined by an enzyme-linked immunosorbent assay and an immune adherence assay. Antibody responses were found to depend not only on the ganglioside used as an immunogen but also on the mouse strain. Gangliosides having a trisaccharide sequence (NeuAc alpha 2----8NeuAc alpha 2----3Gal-) such as GD3, GD2, GD1b, GT1a and GQ1b, in particular O-Ac-GD3, induced high-titer antibody responses, whereas those having a disaccharide sequence (NeuAc alpha 2----3Gal-) such as GM4, GM3, GM2, GM1, GD1a and GT1b induced low-titer antibody responses. On the other hand, gangliosides with NeuGc developed minimum titers. In contrast, asialogangliosides induced much higher responses than the corresponding gangliosides. The differences in ceramide portions of these gangliosides did not appear to be involved in inducing antibody responses. Mice could be divided into three groups according to the magnitude of their antibody responses: Group 1, those that produce the highest antibody responses (C3H/HeN and A/J); Group 2, those that demonstrate moderate antibody titers (Balb/c, C57BL/6, DBA/2 and nu/nu Balb/c); and Group 3, those that make minimum responses (AKR/N, C3H/HeJ, CBA/N and NZB/N). The pattern of reactivity to the various gangliosides was similar in all the strains tested.