Generation of monoclonal antibodies specific for ganglioside lactones: evidence of the expression of lactone on human melanoma cells

Biology of GD2 ganglioside: implications for cancer immunotherapy

Part of the broader glycosphingolipid family, gangliosides are composed of a ceramide bound to a sialic acid-containing glycan chain, and locate at the plasma membrane. Gangliosides are produced through sequential steps of glycosylation and sialylation. This diversity of composition is reflected in differences in expression patterns and functions of the various gangliosides. Ganglioside GD2 designates different subspecies following a basic structure containing three carbohydrate residues and two sialic acids. GD2 expression, usually restrained to limited tissues, is frequently altered in various neuroectoderm-derived cancers. While GD2 is of evident interest, its glycolipid nature has rendered research challenging. Physiological GD2 expression has been linked to developmental processes. Passing this stage, varying levels of GD2, physiologically expressed mainly in the central nervous system, affect composition and formation of membrane microdomains involved in surface receptor signaling. Overexpressed in cancer, GD2 has been shown to enhance cell survival and invasion. Furthermore, binding of antibodies leads to immune-independent cell death mechanisms. In addition, GD2 contributes to T-cell dysfunction, and functions as an immune checkpoint. Given the cancer-associated functions, GD2 has been a source of interest for immunotherapy. As a potential biomarker, methods are being developed to quantify GD2 from patients' samples. In addition, various therapeutic strategies are tested. Based on initial success with antibodies, derivates such as bispecific antibodies and immunocytokines have been developed, engaging patient immune system. Cytotoxic effectors or payloads may be redirected based on anti-GD2 antibodies. Finally, vaccines can be used to mount an immune response in patients. We review here the pertinent biological information on GD2 which may be of use for optimizing current immunotherapeutic strategies.

Recent Advance in Tumor-associated Carbohydrate Antigens (TACAs)-based Antitumor Vaccines

Cancer cells can be distinguished from normal cells by displaying aberrant levels and types of carbohydrate structures on their surfaces. These carbohydrate structures are known as tumor-associated carbohydrate antigens (TACAs). TACAs were considered as promising targets for the design of anticancer vaccines. Unfortunately, carbohydrates alone can only evoke poor immunogenicity because they are unable to induce T-cell-dependent immune responses, which is critical for cancer therapy. Moreover, immunotolerance and immunosuppression are easily induced by using natural occurring TACAs as antigens due to their endogenous property. This review summarizes the recent strategies to overcome these obstacles: (1) covalently coupling TACAs to proper carriers to improve immunogenicity, including clustered or multivalent conjugate vaccines, (2) coupling TACAs to T-cell peptide epitopes or the built-in adjuvant to form multicomponent glycoconjugate vaccines, and (3) developing vaccines based on chemically modified TACAs, which is combined with metabolic engineering of cancer cells.

Multivalent presentation of a hydrolytically stable GM(3) lactone mimetic as modulator of melanoma cells motility and adhesion

A hydrolytically stable mimetic of the tumour antigen GM(3) lactone is used to decorate multivalent scaffolds. Two of them positively interfere on melanoma cell adhesion, migration and resistance to apoptosis (anoikis). Notably, their ability to hamper melanoma-cells adhesion and reduce the metastatic potential is enhanced when the two scaffolds, presenting a different shape, are used in combination.

Recent Development in Carbohydrate Based Anti-cancer Vaccines

The development of carbohydrate based anti-cancer vaccines is of high current interests. Herein, the latest development in this exciting field is reviewed. After a general introduction about tumor associated carbohydrate antigens and immune responses, the review is focused on the various strategies that have been developed to enhance the immunogenecity of these antigens. The results from animal studies and clinical trials are presented.

High-performance CE: an effective method to study lactonization of alpha2,8-linked oligosialic acid

A sensitive and efficient method using high-performance CE (HPCE) and neuraminidase hydrolysis was developed to study the lactonization and hydrolysis of alpha2,8-pentasialic acid. Eleven lactone species of pentasialic acid formed in glacial acetic acid were detected and classified into three groups based on the number of carboxylic acids: monolactones with four carboxylic acids, dilactones with three carboxylic acids, and trilactones with two carboxylic acids. These lactones eluted between the original pentamer (with five carboxylic acids) and the fully lactonized species (with one carboxylic acid) in HPCE. Eight of the isomers were identified by hydrolysis with neuraminodase. Results obtained from previous reports and from this study together reveal a general rule for predicting the subtle difference in the acidity of each carboxylic acid in oligosialic acids: the closer the carboxylic acid is to the nonreducing end, the more acidic it is. Therefore, the elution order of lactone isomers having the same number of carboxylic groups can be predicted from the position of the free carboxylic groups in pentasialic acid. We used this principle and the results of hydrolysis with neuraminidase to identify hexamer lactone isomers separated by HPCE.

Molecular cloning and characterization of galactosylceramide expression factor-1 (GEF-1)

A rat brain cDNA clone has been isolated using a eukaryotic cell transient expression system with anti-galactosylceramide (GalCer) monoclonal antibody (MAb), that induces GalCer expression in COS-7 cells. The protein was designated as GalCer expression factor-1 (GEF-1). The deduced amino acid sequences revealed a strikingly high homology to a mouse hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), but no homology to UDP-galactose: ceramide galactosyltransferase. COS-7 cells transfected with the cDNA clone showed dramatic morphological changes and cell growth suppression. Overexpression of GEF-1 in MDCK (MDCK/GEF-1) cells showed GalCer-derived sulfatide expression as well as morphological changes, but not cell growth suppression. The enzyme activity and the mRNA level of CGT increased significantly in MDCK/GEF-1 cells compared with control cells. Taking these results together, it is suggested that GEF-1 may play an important role in regulating GalCer and sulfatide expression in the epithelial cells as well as in the brain.

Inhibition of EGF-mediated receptor activity and cell proliferation by HK1-ceramide, a stable analog of the ganglioside GM3-lactone

Gangliosides have been described as modulators of growth factor receptor activity and subsequent cellular function. Due to the lower-pH environment found in tumor cells, ganglosides are thought to be formed (at least to some extent) into their lactone forms. The aim of the study was to analyze the mode of action of the lactone of the ganglioside GM3 on epidermal growth factor (EGF) signaling in human ovarial epidermoid carcinoma A431 cells and cell growth in human oral epidermoid carcinoma KB cells by applying the GM3 lactone analog HK1-ceramide 2, which is stable under hydrolytic conditions. Specific inhibition of EGF-dependent receptor tyrosine phosphorylation was observed by HK1-ceramide 2 at 25 microM, whereas GM3 showed a comparable inhibition at eightfold higher concentrations. In cells exposed to low pH, where GM3 is thought to form its lactone to a higher extent, addition of GM3 showed no further inhibitory effect on EGF-dependent receptor phosphorylation. Similarly to GM3, HK1-ceramide 2 does not affect binding of (125)I-EGF to the cell surface receptor. EGF-dependent growth of KB cells was also found to be inhibited by HK1-ceramide 2 at much lower concentrations compared to GM3. In conclusion, our results indicate that the GM3 lactone analog HK1-ceramide 2 is a specific inhibitor of EGF receptor function and is more potent in reducing EGF-dependent tyrosine phosphorylation of the receptor in A431 cells and in inhibiting EGF-dependent growth of KB cells compared to GM3.

Synthesis of GD3-lactam: a potential ligand for the development of an anti-melanoma vaccine

The novel sialyl donor methyl (ethyl 4,7,8,9-tetra-O-acetyl-5-N,N-diacetylamino-3,5-dideoxy-2-thio-3-thiophenyl-D-erythro-beta-L-gluco-non-2-ulopyranosid)onate was used for glycosylation of a lactosyl acceptor to give the GM3-trisaccharide derivative in 83% yield. Introduction of an azido group at C-9" of the GM3-trisaccharide derivative, transformation into a glycosyl acceptor, and sialylation with the above mentioned novel sialyl donor gave a GD3-trisaccharide in 50% yield. Reduction of the azido group gave the corresponding amine, which underwent spontaneous lactamization to the GD3-[1"'-9"]-lactam in an overall yield of 86%. Removal of protecting groups of over five steps, followed by per-O-acetylation gave an acetylated GD3-[1"'-9"]-lactam TMSEt glycoside in 27% overall yield. The acetylated GD3-[1"'-9"]-lactam TMSEt glycoside is suitable for glycosylation of linker-arms and the resulting linker-glycosides are planned to be coupled to carrier proteins, thus providing immunogens for trial vaccinations against malignant melanoma.

Induction of antibodies against GD3 ganglioside in melanoma patients by vaccination with GD3-lactone-KLH conjugate plus immunological adjuvant QS-21

The gangliosides GD3, GD2 and GM2 are expressed on the cell surface of malignant melanomas, GD3 being the most abundant. We have shown that immunization of melanoma patients with GM2 adherent to Bacillus Calmette-Guerin (GM2/BCG) induced an IgM antibody response. Vaccines containing GM2-keyhole limpet hemocyanin (KLH) conjugate and the immunological adjuvant QS-21 induced a higher titer IgM response and consistent IgG antibodies. Patients with antibodies against GM2 survived longer than patients without antibody. On the other hand, our previous trials with GD3/BCG, GD3 derivatives including GD3-lactone (GD3-L)/BCG failed to induce antibodies against GD3. In our continuing efforts to induce antibody against GD3, we have immunized groups of 6 melanoma patients with GD3-KLH or GD3-L-KLH conjugates containing 30 microg of ganglioside plus 100 microg of QS-21 at 0, 1, 2, 3, 7 and 19 weeks. Prior to vaccination, no serological reactivity against GD3 or GD3-L was detected. After immunization, IgM and IgG antibodies were detected against both GD3 and GD3-L in the GD3-L group exclusively. The GD3-L-KLH vaccine induced IgM titers against GD3-L of 1:40-1/1,280 in all patients and IgG titers of 1/160-1/1,280 in 4 patients. These antibodies also strongly cross-reacted with GD3. ELISA reactivity was confirmed by immune thin-layer chromatography on GD3 and melanoma extracts. Sera obtained from 4 of these 6 patients showed cell surface reactivity by FACS and from 2 showed strong cell surface reactivity by immune adherence (IA) assay and complement lysis against the GD3 positive cell line SK-Mel-28.

Structural characterization of gangliosides isolated from mullet milt using electrospray ionization-tandem mass spectrometry

Electrospray ionization (ESI) coupled with tandem mass spectrometry has been used in conjunction with microwave-mediated saponification, periodate oxidation, and clostridial sialidase hydrolysis to enable detailed structural characterization of gangliosides and their derivatives present in mullet milt. The gangliosides extracted from mullet milt were determined to be GM3, GM3 lactone, GM3 methyl ester, and 9-O-acetyl GM3. For the major ganglioside GM3 and all GM3 derivatives, the ceramide composition was revealed to be C18:1/C16:0. GM3 with a C18:0/C16:0 ceramide was also found as a minor ganglioside. Both the ganglioside intramolecular ester and the ganglioside methyl ester (lacking carboxylic acid groups) showed dominant chloride attachment peaks (M + Cl)- in negative ion ESI-MS in addition to low intensity peaks corresponding to (M-H)-. GM3 and O-acetyl GM3 bearing carboxylic acid functions showed only (M-H)-. In positive ion ESI, GM3 and O-acetyl GM3 revealed (M + 2Na-H)+ peaks in addition to (M + Na)+, indicating free exchange of the carboxylic acid proton with a sodium cation, while the ganglioside intramolecular ester and ganglioside methyl ester with no acidic protons yielded only (M + Na)+. The strategy of employing ESI-MS to detect products of established wet chemical reactions represents a general approach for elucidation of ganglioside structural details.

Acid-catalyzed lactonization of alpha2,8-linked oligo/polysialic acids studied by high performance anion-exchange chromatography

Recent studies from many laboratories revealed remarkable structural, distributional, and functional diversities of oligo/polysialic acids (OSA/PSA) that exist in organisms ranging from bacteria to man. These diversities are further complicated by the fact that OSA/PSA spontaneously form lactones under even mildly acidic conditions. By using high performance anion-exchange chromatography (HPAEC) with nitrate eluents, we found that lactonization of alpha2,8-linked OSA/PSA (oligo/poly-Neu5Ac, oligo/poly-Neu5Gc and oligo/poly-KDN) proceeds readily, and the lactonization process displays three discrete stages. The initial stage is characterized by limited lactonization occurring between two internal sialic acid residues, reflected by a regular pattern of lactone peaks interdigitated with non-lactonized peaks on HPAEC. In the middle stage, multiple lactonized species are formed from a molecule with a given degree of polymerization (DP), in which the maximum number of lactone rings formed equals DP minus 2. At the final stage, completely lactonized species become the major components, resulting in drastic changes in the physicochemical properties of the sample. Interestingly, the smallest lactonizable OSA are tetramer, trimer, and dimer at the initial, middle, and final stages, respectively. At any of the stages, OSA/PSA of higher DP lactonize more rapidly, but all the lactone rings rapidly open up when exposed to mild alkali. Lactonized OSA/PSA are resistant to both enzyme- and acid-catalyzed glycosidic bond cleavage. The latter fact was utilized to obtain more high DP oligo/poly(alpha2,8-Neu5Gc) chains from a polysialoglycoprotein. Our results should be useful in preparation, storage, and analysis of OSA/PSA. Possible biological significance and bioengineering potentials of lactonization are discussed.

Generation and characterization of mouse monoclonal antibodies specific for N-linked neutral oligosaccharides of glycoproteins

We generated four monoclonal antibodies (MAbs) specific for asparagine-linked neutral oligosaccharides of glycoproteins by immunizing mice with neoglycolipids, which were derived from glycoproteins by conjugation to phosphatidylethanolamine dipalmitoyl. The binding specificity of these MAbs was determined by an enzyme-linked immunosorbent assay and immunostaining on thin-layer chromatography. The four MAbs designated OMB3, OMB4, OMR5, and OMR6 reacted strongly with the neoglycolipids, Gal beta1-4GlcNAc beta1-2Man alpha1-6(Gal beta1-4GlcNAc beta1-2Man alpha1-3)Man beta1-4GlcNAc-PD, GlcNAc beta1-2Man alpha1-6(GlcNAc beta1-2Man alpha1-3)(GlcNAc beta1-4)Man beta1-4GlcNAc beta1-4GlcNAc-PD, Man alpha1-6Man beta1-4GlcNAc beta1-4(Fuc alpha1-6)GlcNAc-PD, and Man alpha1-3Man beta1-4GlcNAc-PD, respectively, that were used as immunogens. All of these MAbs exhibited a high binding specificity. The epitopes of the MAbs OMB3 and OMB4 were suggested to be nonreducing terminal trisaccharides, Gal beta1-4GlcNAc beta1-2Man-, and nonreducing beta-GlcNAc residues, respectively. MAbs OMR5 and OMR6 showed a highly restricted binding specificity, reacting only with the immunizing neoglycolipids. Subsequently, MAbs OMB3 and OMB4 were shown to react strongly with asialo-alpha1-acid-glycoprotein and asialo-agalacto-alpha1-acid-glycoprotein, respectively, by Western blotting. Furthermore, it was shown that these MAbs reacted specifically with the epitope on Chinese hamster ovary cells by an immunofluorescence technique. MAb OMB4 was also shown to detect the accumulated oligosaccharides with nonreducing terminal beta-GlcNAc residues as granular inclusions in the cultured fibroblasts from a classical Sandhoff disease patient.

An immunohistochemical technique with a series of monoclonal antibodies to gangliosides: their differential distribution in the rat cerebellum

Gangliosides, sialic acid-containing glycosphingolipids, are normal membrane constituents and are highly expressed in the vertebral central nervous system. Owing to their topological localization on the outer surface of neural plasma membranes and their unique chemical structure, gangliosides have been implicated in a variety of phenomena. It was, however, difficult to study the localization of gangliosides in the central nervous system because of the lack of useful probes for gangliosides. We recently established an improved method for the generation of mouse MAbs to gangliosides by immunizing C3H/HeN mice with purified gangliosides. Using this method, we succeeded in generating a large number of the MAbs specific for gangliosides. These MAbs enabled us to determine the localization of gangliosides in the rat brain. We previously described the differential distribution patterns of gangliosides in the brain regions by an immunohistochemical technique with MAbs. In the present paper, we describe an immunofluorescence technique for the detection of ganglioside distribution in the postnatal rat cerebellar cortex in detail. The principles of immunohistochemistry have been described in several review articles.

Immunocytochemical analysis of gangliosides in rat primary cerebellar cultures using specific monoclonal antibodies

We studied the expression of ganglioside antigens in primary cultures of rat cerebellum using an immunocytochemical technique with mouse monoclonal antibodies (MAbs) specific for various gangliosides. Twelve MAbs that specifically recognize each ganglioside were used. Our study revealed that there is a cell type-specific expression of ganglioside antigens in the primary cultures. A number of b-series gangliosides were detected in the granule cells, whereas a-series gangliosides were not intensely expressed. GD1b was detected in the granule cells. GD2 appeared to be present in a subset of the granule cells or a type of small neurons. GD3 was associated not only with the granule cells, but also with both astrocytes and oligodendrocytes. An O-Ac-disialoganglioside, which was suggested to be O-Ac-LD1, was restrictedly detected in Purkinje cells. The other gangliosides were not detected clearly in these cells. These results suggest that several gangliosides may be useful markers for identifying cells in primary cultures of the rat cerebellum; particularly b-series gangliosides such as GD2 and GD1b for the granule cells and O-Ac-LD1 for Purkinje cells.

Approaches to augmenting the immunogenicity of melanoma gangliosides: from whole melanoma cells to ganglioside-KLH conjugate vaccines

Gangliosides are neuraminic acid containing glycosphingolipids that are anchored into the lipid bilayer of the plasma membrane by their lipophilic ceramide moiety. They are overexpressed on tissues of neuroectodermal origin, particularly in tumors such as melanomas, sarcomas, neuroblastomas and astrocytomas. With the ganglioside-KLH plus immunological adjuvant QS-21 conjugate vaccine, GM2 and GD2 have been shown to be consistently immunogenic, inducing cytotoxic IgM antibodies in most patients. The immunogenicity of other gangliosides also expressed on melanoma cells such as 9-0-acetyl GD3 and GD3 lactone is currently being tested with this conjugate vaccine approach. From the initiation of our adjuvant vaccine trials in 1975 to the present, the immunogenicity of ganglioside vaccines has increased significantly as vaccine development has progressed. For instance, GM2 antibody responses increased from low titer IgM antibodies induced in occasional patients after whole cell vaccines, to moderate titer IgM antibodies in 86% of patients after GM2/BCG vaccines, to higher titer IgM antibodies in 100% of patients treated with the GM2-KLH plus QS-21 vaccine. These antibodies are capable of mediating complement mediated cytotoxicity of GM2 expressing melanoma cells in the majority of patients and such antibodies, whether naturally produced or vaccine induced, have been associated with a significantly improved disease-free and overall survival. An initial double-blind randomized trial in AJCC Stage III melanoma patients comparing GM2/BCG with BCG alone, demonstrated a 14% improvement in disease-free interval at 4 years and an 11% improvement in overall survival, though neither result achieved statistical significance. Based on these encouraging clinical results and the clearly improved immunogenicity of the GM2-KLH plus QS-21 vaccine compared to the previous GM2/BCG vaccine, the following two large clinical trials are anticipated to begin in 1995-1996. The GM2-KLH plus QS-21 vaccine will be tested in the intergroup setting by ECOG in 450 patients with AJCC Stage II or III melanoma who are free of disease after surgery. Also to be tested in a multicenter trial is a GM2-KLH plus GD2-KLH plus QS-21 vaccine in patients with high risk AJCC Stage II-IV sarcoma after surgical excision of all known disease.