Studies of a ganglioside fraction extracted from human malignant melanoma

Ganglioside GM2, highly expressed in the MIA PaCa-2 pancreatic ductal adenocarcinoma cell line, is correlated with growth, invasion, and advanced stage

Gangliosides, a group of glycosphingolipids, are known to be cell surface markers and functional factors in several cancers. However, the association between gangliosides and pancreatic ductal adenocarcinoma (PDAC) has not been well elucidated. In this study, we examined the expression and roles of ganglioside GM2 in PDAC. GM2+ cells showed a higher growth rate than GM2− cells in the adherent condition. When GM2– and GM2+ cells were cultured three-dimensionally, almost all cells in the spheres expressed GM2, including cancer stem cell (CSC)-like cells. A glycolipid synthesis inhibitor reduced GM2 expression and TGF-β1 signaling in these CSC-like cells, presumably by inhibiting the interaction between GM2 and TGFβ RII and suppressing invasion. Furthermore, suppression of GM2 expression by MAPK inhibition also reduced TGF-β1 signaling and suppressed invasion. GM2+ cells formed larger subcutaneous tumors at a high incidence in nude mice than did GM2– cells. In PDAC cases, GM2 expression was significantly associated with younger age, larger tumor size, advanced stage and higher histological grade. These findings suggest that GM2 could be used as a novel diagnostic and therapeutic target for PDAC.

Detection of Naturally Occurring Human Antibodies Against Gangliosides by ELISA

Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Natural antibodies against gangliosides have been detected not only in cancer patients but also in healthy donors. The presence of these antibodies can be used as diagnostic or prognostic factor. However, these responses are difficult to detect because anti-ganglioside antibodies are usually of IgM isotype and low affinity. Enzyme Linked Immunosorbent Assay (ELISA) is an immunoassay based on the specific binding of antibodies to antigens bound to a solid phase. These antigens can be glycolipids like gangliosides. An enzyme linked to the last reactant allows the detection of specific binding through the development of color after the addition of a suitable substrate. ELISA combines the specificity of antibodies with the sensitivity of enzyme reactions. The ELISA method described herein can be used to detect antibody responses against gangliosides not only related to cancer but also to autoimmune diseases and infections, both in healthy donors, and patients, untreated or receiving specific immunotherapy.

Anti-ganglioside anti-idiotypic vaccination: more than molecular mimicry

Surgery, chemotherapy, and radiation therapy are standard modalities for cancer treatment, but the effectiveness of these treatments has reached a plateau. Thus, other strategies are being explored to combine with the current treatment paradigms in order to reach better clinical results. One of these approaches is the active immunotherapy based on the induction of anti-tumor responses by anti-idiotypic vaccination. This approach arose from Jerne’s idiotypic network theory, which postulates that B lymphocytes forms a functional network, with a role in the establishment of the immune repertoires, in the regulation of natural antibody production and even in the establishment of natural tolerance. Due to the large potential diversity of the immunoglobulin variable regions, the idiotypes repertoire can mimic the universe of self and foreign epitopes, even those of non-protein nature, like gangliosides. Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Although any idiotype could be able to mimic any antigen, only those related to antigens involved in functions relevant for organism homeostasis, and that in consequence has been fixed by evolution, would be able not only to mimic, but also to activate the idiotypic cascades related with the nominal antigen. The present review updates the results, failures and hopes, obtained with ganglioside mimicking anti-idiotypic antibodies and presents evidences of the existence of a natural response against gangliosides, suggesting that these glycolipids could be idiotypically relevant antigens.

Genetically engineered humanized anti-ganglioside GM2 antibody against multiple organ metastasis produced by GM2-expressing small-cell lung cancer cells

Small-cell lung cancer (SCLC) grows rapidly and metastasizes to multiple organs. We examined the antimetastatic effects of the humanized anti-ganglioside GM2 (GM2) antibodies, BIW-8962 and KM8927, compared with the chimeric antibody KM966, in a SCID mouse model of multiple organ metastases induced by GM2-expressing SCLC cells. BIW-8962 and KM8927 induced higher antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity than KM966 against the GM2-expressing SCLC cell line SBC-3 in vitro. These humanized antibodies inhibited the production of multiple organ metastases, increased the number of apoptotic cells, and prolonged the survival of the SCID mice. Histological analyses using clinical specimens showed that SCLC cells expressed GM2. These findings suggest that humanized anti-GM2 antibodies could be therapeutically useful for controlling multiple organ metastases of GM2-expressing SCLC.

O-acetylation of GD3 prevents its apoptotic effect and promotes survival of lymphoblasts in childhood acute lymphoblastic leukaemia

We have previously demonstrated induction of O-acetylated sialoglycoproteins on lymphoblasts of childhood acute lymphoblastic leukaemia (ALL). These molecules promote survival of lymphoblasts by preventing apoptosis. Although O-acetylated sialoglycoproteins are over expressed, the status of O-acetylation of gangliosides and their role in lymphoblasts survival remains to be explored in ALL patients. Here, we have observed enhanced levels of 9-O-acetylated GD3 (9-O-AcGD3) in the lymphoblasts of patients and leukaemic cell line versus disialoganglioside GD3 in comparison to the normal cells. Localization of GD3 and 9-O-AcGD3 on mitochondria of patient's lymphoblasts has been demonstrated by immuno-electron microscopy. The exogenous administration of GD3-induced apoptosis in lymphoblasts as evident from the nuclear fragmentation and sub G0/G1 apoptotic peak. In contrast, 9-O-AcGD3 failed to induce such apoptosis. We further explored the mitochondria-dependent pathway triggered during GD3-induced apoptosis in lymphoblasts. GD3 caused a time-dependent depolarization of mitochondrial membrane potential, release of cytochrome c and 7.4- and 8-fold increased in caspase 9 and caspase 3 activity respectively. However, under identical conditions, an equimolar concentration of 9-O-AcGD3 failed to induce similar effects. Interestingly, 9-O-AcGD3 protected the lymphoblasts from GD3-induced apoptosis when administered in equimolar concentrations simultaneously. In situ de-O-acetylation of 9-O-AcGD3 with sodium salicylate restores the GD3-responsiveness to apoptotic signals. Although both GD3 and 9-O-acetyl GD3 localize to mitochondria, these two structurally related molecules may play different roles in ALL-disease biology. Taken together, our results suggest that O-acetylation of GD3, like that of O-acetylated sialoglycoproteins, might be a general strategy adopted by leukaemic blasts towards survival in ALL.

Genetic mechanisms for the synthesis of fucosyl GM1 in small cell lung cancer cell lines

Fucosyl GM1 has been reported to be specifically expressed in small cell lung cancer (SCLC) cells. However, the genetic basis for the synthesis of fucosyl GM1 has not been investigated. We analyzed the glycosyltransferases responsible for the synthesis of fucosyl GM1 in SCLC cell lines. In four SCLC cell lines expressing fucosyl GM1, both FUT1 and FUT2 mRNAs were detected, indicating that either one or both of alpha1,2-fucosyltransferases may be involved in the expression of fucosyl GM1. However, three of these four lines contained function-loss mutations in the FUT2 coding region, suggesting that FUT1 is mainly involved in the alpha1,2-fucosylation of GM1. The expression levels of the GM1 synthase gene showed no correlation with those of fucosyl GM1, whereas the co-transfection of GM1 synthase cDNA with FUT1 or FUT2 into SK-LC-17 clearly enhanced the neo-expression of fucosyl GM1, indicating its essential role. In contrast, the co-transfection of GD3 synthase cDNA reduced the expression levels of fucosyl GM1 with FUT1 or FUT2. Consequently, FUT1 seems to mainly contribute to the expression of fucosyl GM1, although both FUT1 and FUT2 are capable of generating the antigen. These results should promote the functional analysis of fucosyl GM1 leading to the development of novel therapies for SCLC.

9-O-acetyl GD3 protects tumor cells from apoptosis

The ganglioside GD3 (Neu5Ac alpha8Neu5Ac alpha3Gal beta4GlcCer) is an intracellular lipid messenger that induces apoptosis by targeting mitochondria in various cell types. GD3 can also promote apoptosis when externally added to cells. Previous studies showed that the proapoptotic effects of GD3 can be counteracted by 9-O-acetylation. To determine whether 9-O-acetyl GD3 (acGD3) has a general antiapoptotic potential, the apoptosis-sensitive Jurkat cell line and an apoptosis-sensitive variant of the cell line Molt-4 were preincubated with micromolar concentrations of acGD3 and then treated with inducers of apoptosis. A reduced apoptotic index and an increased cell viability were observed. On the other hand, when the Jurkat cells were treated with GD3 for extended periods of time, a population was selected that was resistant to apoptosis induction by N-acetyl sphingosine as well as by the anti-leukemic drug daunorubicin. Comparative analysis of gangliosides revealed the formation of acGD3 in the resistant Jurkat cells that was not found in the apoptosis-sensitive cells. Conversely, exposing the acGD3 positive and apoptosis-resistant cell line Molt-4 to the O-deacetylating activity of salicylate resulted in a complete disappearance of acGD3 and an enhanced sensitivity to N-acetyl sphingosine-mediated apoptosis. Formation of acGD3 might thus represent a new mechanism how tumor cells can escape apoptosis.

Metastatic melanoma secreted IL-10 down-regulates CD1 molecules on dendritic cells in metastatic tumor lesions

CD1 molecules are expressed by antigen-presenting cells such as dendritic cells and mediate primary immune responses to lipids and glycolipids which have been shown to be expressed by various tumors. Glycolipids are expressed by melanoma cells but, despite their immunogenicity, no efficient spontaneous immune responses are elicited. As IL-10 has previously been shown to down-regulate CD1a on dendritic cells and is known to be expressed by various melanoma cell lines, we investigated if melanoma-derived IL-10 could down-regulate CD1 molecule expression on dendritic cells as a possible way to circumvent immune recognition. We found that CD1a, CD1b, CD1c, and CD1d were significantly down-regulated on dendritic cells in metastatic (n = 10) but not in primary melanoma lesions (n = 10). We further detected significantly higher IL-10 protein levels in metastatic than in primary melanomas. Moreover, supernatants from metastatic melanomas were significantly more effective in down-regulating CD1 molecules on dendritic cells than supernatants from primary melanoma cultures. This effect was blocked using a neutralizing IL-10 antibody in a dose dependent manner. Our findings suggest that metastatic but not primary melanomas can down-regulate CD1 molecules on infiltrating dendritic cells by secreting IL-10 which may represent a novel way to escape the immune response directed against the tumor.

Suppression of lung metastasis of mouse Lewis lung cancer P29 with transfection of the ganglioside GM2/GD2 synthase gene

Ganglioside functions in tumor metastasis were analyzed by carbohydrate remodeling of a mouse Lewis lung cancer (subline P29) by introducing beta1,4GalNAc-T cDNA. Although P29 was originally a low-metastatic subline in the s.c. injection system, it showed high potential in lung metastasis when i.v.-injected via the tail vein. Two lines of GM(2)(+) transfectants showed markedly reduced metastatic potential to the lung compared to 2 control lines. However, cell proliferation rates and expression levels of various cell adhesion molecules, e.g., integrin family members, SLe(x) and CD44, were essentially unchanged after transfection of the cDNA. Then, cell adhesion to fibronectin-coated dishes was examined, showing that GM(2) (+) transfectants attached to the plates much more slowly than controls, suggesting functional modulation of integrins with newly expressed GM(2). Phosphorylation of the FAK located at downstream of integrin molecules was markedly reduced in GM(2)(+) transfectants, suggesting that GM(2) suppressed cell adhesion signals via fibronectin-integrin interaction.

A parallel approach to the discovery of carrier delivery vehicles to enhance antigen immunogenicity

As part of an ongoing effort to generate human and murine monoclonal antibodies against poorly immunogenic tumor-associated antigens we have merged the rapidly expanding disciplines of parallel polymer synthesis and controlled-release technology with immunology to produce a rapid and generic approach to improve the immunogenicity of carrier-bound antigens. The process involves three stages: An array of cross-linked hydrogel materials containing a carrier protein (at various concentrations) is prepared in parallel in one step. The array is then screened in mice to determine the most effective hydrogel at enhancing the immunogenicity of the encapsulated versus nonencapsulated carrier. Finally, the most efficient hydrogel is prepared containing the critical carrier-antigen conjugate and is used for immunization protocols. The strategy was successful for the BSA-glycoconjugate of the tumor-associated antigen GM3 analogue 4. When encapsulated within the hydrogel array member most efficient at elevating BSA immunogenicity, the BSA-4 glycoconjugate was significantly more immunogenic that when administered as a free antigen.

High-dose interferon alfa-2b does not diminish antibody response to GM2 vaccination in patients with resected melanoma: results of the Multicenter Eastern Cooperative Oncology Group Phase II Trial E2696

PURPOSE

High-dose interferon alfa-2b (IFNalpha2b) is the only established adjuvant therapy of resectable high-risk melanoma. GM2-KLH/QS-21 (GMK) is a chemically defined vaccine that is one of the best developed of a range of vaccine candidates for melanoma. A single-institution phase III trial conducted at Memorial Hospital served as the impetus for an intergroup adjuvant E1694/S9512/C509801 trial, which recently completed enrollment of 880 patients. To build on the apparent benefit of IFNalpha2b in resectable high-risk American Joint Committee on Cancer (AJCC) stage IIB or III melanoma, this phase II study was designed to evaluate the combination of GMK and IFNalpha2b. The E2696 trial was undertaken to evaluate the toxicity and other effects of the established adjuvant high-dose IFNalpha2b regimen in relation to immune responses to GMK and to evaluate the potential clinical and immunologic effects of the combined therapies.

PATIENTS AND METHODS

This trial enrolled 107 patients with resectable high- or very high-risk melanoma (AJCC stages IIB, III, and IV).

RESULTS

The results demonstrate that IFNalpha2b does not significantly inhibit immunoglobulin M or G serologic responses to the vaccine and that the combination of high-dose IFNalpha2b and GMK is well tolerated in this patient population.

CONCLUSION

Cox analysis of the results of the combination with IFNalpha2b show improvement in the relapse-free survival of patients with very high-risk melanoma (including those with resectable M1 disease).

Inhibition of highly metastatic FBJ-LL cell migration by ganglioside GD1a highly expressed in poorly metastatic FBJ-S1 cells

For clarification of the functions of gangliosides on tumor metastasis, examination was made of the ganglioside patterns of poorly metastatic FBJ-S1 and highly metastatic FBJ-LL cells. FBJ-S1 cells expressed GM3 and GD1a, whereas FBJ-LL cells expressed GM3 and slightly expressed GD1a. The capacity for FBJ-LL cells to migrate was ten times that of FBJ-S1 cells, but decreased by a half by pretreatment with GD1a. GD1b or GT1b had the same effect as GD1a, and synthetic sialyl compounds to a lesser extent, suggesting that gangliosides contain more than two sialyl residues to inhibit the migration of FBJ-LL cells.

Quantitation of the density of cell surface carbohydrate antigens on cancer cells with a sensitive cell-suspension ELISA

The density of carbohydrate epitopes on the surface of tumor cells is a governing factor for immune recognition and antibody-mediated targeting of tumor-associated carbohydrate antigens in cancer immunotherapy. A sensitive cell-suspension ELISA (cs-ELISA) is developed for quantitation of the functionally exposed carbohydrate epitopes on the cell surface. The factors affecting the measurement of tumor-cell surface glycoconjugates are evaluated using three human melanoma cell lines before and after exposure to various cell preservation treatments. The results of cs-ELISA are compared with the quantitative profile obtained by biochemical and flow cytometry assays. Cs-ELISA measures the density of the functionally exposed specific sugar epitopes on the surface of tumor cells, even in the presence of other similar carbohydrate antigens, provided that the monoclonal antibodies to carbohydrate epitopes are monospecific and sensitive, and that the cells are viable and present in optimal density. Of the three melanoma cell lines, M10-v and M101 expressed disialolactosyl residues of GD3 at concentrations of 5-6 pmol/10(6) cells and 2-3 pmol/10(6) cells, respectively. In both cell lines, the cell-surface GD2 was less than 1.0 pmol/10(6) cells. M24 melanoma cells expressed trace quantities (< 0.1 pmol/10(6) cells) of GD3 and GD2. Trypsinization of M10-v and M101 cells significantly reduced the cell-surface expression of GD3, suggesting GD3 loss, but increased the expression of GD2, suggesting crypticity of membrane-bound GD2. Cs-ELISA results showed that cryopreservation with 10% DMSO and irradiation at 15 krad decreased melanoma cell viability and ganglioside expression for M10-v but not M101 and M24. Formalinization did not affect cs-ELISA measurement of cell-surface carbohydrates. Cs-ELISA was used to monitor the quantity of incorporation of exogenous GD3 onto the surface of GD3-deficient M24 cells. Cs-ELISA for assessment of density of cell surface carbohydrate epitopes may be useful to characterize different types of tumors, to develop carbohydrate-based whole cell vaccines from tumor biopsies, to monitor the effects of cell preservation treatments commonly used in a whole cell vaccine preparation, and to evaluate the incorporation of a particular glycolipid (antigen or adjuvant) into glycolipid-deficient cells that are useful for carbohydrate-based active specific immunotherapy.

Humoral immune response in disease-free advanced melanoma patients after vaccination with melanoma-associated gangliosides. EORTC Cooperative Melanoma Group

Several studies have shown that melanoma-associated gangliosides are immunogenic in melanoma patients and that antibodies against them have a favorable prognostic effect. Our study aims at characterizing the humoral immune response in disease-free, advanced melanoma patients vaccinated with a total ganglioside fraction extracted from pooled metastases of human melanoma, containing as major gangliosides GM3 and GD3, and as minor ones GM2 and GD2. Prior to vaccination, all patients were made disease-free by surgical removal of skin, lymph-node or other distant metastases. Repeated vaccinations were carried out intradermally with gangliosides either in the native form in buffered solution, or in the form of liposomes. Serum samples were collected at regular intervals and assayed by ELISA for the presence of specific IgG and IgM antiganglioside antibodies. Selected samples were tested by immunostaining on thin-layer plates to specify the ganglioside species involved in the reactivity. Out of 32 evaluable patients, 17 presented a significant increase in antibody titer, mostly of the IgG isotype, which was maximal between 2 and 4 months after starting injections of gangliosides, and gradually disappeared within 1 year. No significant difference could be seen between the group of 20 patients treated with native gangliosides and the group of 12 vaccinated with the gangliosides in liposomes. All gangliosides seemed to be immunogenic, but GM2 and GD2 were somewhat more reactive. The disease-free intervals for the patients who showed an antibody response to the treatment were significantly higher (p less than 0001) than those of the non-responding group, as compared by the Kaplan-Meier method.

Antibody response to immunization with ganglioside GD3 and GD3 congeners (lactones, amide and gangliosidol) in patients with malignant melanoma

GD3 is the ganglioside most abundantly expressed on the cell surface of human melanoma, and treatment with a murine MAb recognizing GD3 has induced major responses in a small proportion of patients with melanoma. We have therefore attempted to induce production of GD3 antibodies in melanoma patients by active immunization. We found, however, that vaccination with GD3-expressing melanoma cells or purified GD3 does not result in antibody production. We describe here attempts to overcome the poor immunogenicity of GD3 in patients with melanoma by chemical modification. GD3 lactones, GD3 amide and GD3 gangliosidol were synthesized, and the humoral immune response to these derivatives was analyzed. Immunization of melanoma patients with these GD3 derivatives resulted in production of IgM antibodies and, in the case of GD3 amide, also of IgG antibodies. The antibodies to the GD3 derivatives did not cross-react with GD3. This is in contrast to observations in the mouse, where GD3 lactone I induced antibodies that showed cross-reactivity with GD3. Thus, the human immune response was specifically directed toward the modified epitope, rather than to the native structure.

Glycolipid modulation of membrane adhesion

A novel test of carbohydrate-mediated adhesion has been developed. At the tips of two syringes, large spherical model membranes have been made from phosphatidylcholine and varying amounts of mixed brain gangliosides dissolved in n-decane. The apposition of two such membranes resulted in adhesion, not fusion, as judged by the absence of fluorescence mixing in the junction with NBD-phosphatidylethanolamine in one membrane and perylene in the other. Adhesion was observed without gangliosides. The rate of formation of the adhesion area ("rate" of adhesion) was unchanged from 0 to 0.8 mol% gangliosides. A slightly lower but constant rate was observed within the physiological range from 2 to 10 mol%. Adhesion was frequently blocked at 11 to 15 mol% gangliosides. The rate of adhesion with pure gangliosides increased with the number of sialic acid residues: GT greater than GD1a greater than GM1. These results are interpreted in terms of a sialic acid-dependent segregation of gangliosides into the adhesion zone.

Immunogenicity of melanoma-associated gangliosides in cancer patients

The immunogenicity of gangliosides found on human melanoma cells was determined from sera of 26 melanoma patients who were immunized every 1-4 weeks for 4 months with tumor-cell vaccine (TCV) prepared from cultured melanoma cells. Total lipid-bound sialic acid in the gangliosides isolated from TCV was 0.38 mumol/10(8) cells, and was distributed as follows: 44.8% to GM3, 44.2% to GD3, 5.6% to GM2, and 4.6% to GD2. Sera were tested at monthly intervals for antibodies to each ganglioside by ELISA with purified gangliosides as the antigen source. The immunologic specificity of the antibody was confirmed by absorption tests. None of the 26 patients had detectable anti-GM3, anti-GD3, or anti-GD2 antibodies before immunization, although anti-GM2 antibody was detected in 3 patients. After immunization, 2 patients developed IgM anti-GD2, 10 developed IgM anti-GM2, and 2 developed IgG anti-GM2 antibodies. No patient developed detectable anti-GM3 or anti-GD3 antibodies. These results indicate that both GD2 and GM2 expressed on human melanoma cells are immunogenic in humans, although GM2 appears to be more immunogenic. The other two gangliosides, GM3 and GD3, are present in human sera and in human normal tissues, and thus immunologic tolerance may have been established against these gangliosides. Alternatively, circulating GM3 and GD3 may have neutralized anti-GM3 and anti-GD3 antibodies, if any were induced by TCV immunization.

Lipid composition of human malignant melanoma tumors at various levels of malignant growth

The lipid pattern of thirteen human melanoma tumors from various tissues were investigated. In seven of the tumors, an estimate was given about the proportion of malignant melanocytes to the total cell population, and a reverse correlation was determined between the proportion of malignant cells in these tumors and their neutral lipid content. The phospholipids did not show any modification, nor did the cholesterol in the cancerous tissues. The ganglioside pattern was found to be similar in all analyzed samples, with GM3, GM2 and GD3 as major components, although no correlation was found between the malignant level and the ganglioside content of the tumors.