Carbohydrate vaccines that induce antibodies against cancer. 1. Rationale

Recent advances on smart glycoconjugate vaccines in infections and cancer

Vaccination is one of the greatest achievements in biomedical research preventing death and morbidity in many infectious diseases through the induction of pathogen-specific humoral and cellular immune responses. Currently, no effective vaccines are available for pathogens with a highly variable antigenic load, such as the human immunodeficiency virus or to induce cellular T-cell immunity in the fight against cancer. The recent SARS-CoV-2 outbreak has reinforced the relevance of designing smart therapeutic vaccine modalities to ensure public health. Indeed, academic and private companies have ongoing joint efforts to develop novel vaccine prototypes for this virus. Many pathogens are covered by a dense glycan-coat, which form an attractive target for vaccine development. Moreover, many tumor types are characterized by altered glycosylation profiles that are known as "tumor-associated carbohydrate antigens". Unfortunately, glycans do not provoke a vigorous immune response and generally serve as T-cell-independent antigens, not eliciting protective immunoglobulin G responses nor inducing immunological memory. A close and continuous crosstalk between glycochemists and glycoimmunologists is essential for the successful development of efficient immune modulators. It is clear that this is a key point for the discovery of novel approaches, which could significantly improve our understanding of the immune system. In this review, we discuss the latest advancements in development of vaccines against glycan epitopes to gain selective immune responses and to provide an overview on the role of different immunogenic constructs in improving glycovaccine efficacy.

Chemical synthesis and immunological evaluation of entirely carbohydrate conjugate Globo H-PS A1

An anticancer, entirely carbohydrate conjugate, Globo H-polysaccharide A1 (Globo H-PS A1), was chemically prepared and immunologically evaluated in C57BL/6 mice. Tumor associated carbohydrate antigen Globo H hexasaccharide was synthesized in an overall 7.8% yield employing a convergent [3 + 3] strategy that revealed an anomeric aminooxy group used for conjugation to oxidized PS A1 via an oxime linkage. Globo H-PS A1, formulated with adjuvants monophosphoryl lipid A and TiterMax® Gold. After immunization an antigen specific immune response was observed in ELISA with anti-Globo H IgG/IgM antibodies. Specificity of the corresponding antibodies was determined by FACS showing cell surface binding to Globo H-positive cancer cell lines MCF-7 and OVCAR-5. The anti-Globo H antibodies also exhibited complement-dependent cellular cytotoxicity against MCF-7 and OVCAR-5 cells.

Monosialoganglioside GM1 reduces toxicity of Ptx and increase anti-metastasic effect in a murine mammary cancer model

Having demonstrated the ability of monosialoganglioside GM1 micelles as oncology drug transporter, this work focuses on evaluating its application in an in vivo system, studying the toxicity and antitumoral effect of GM1-Ptx micellar formulation. The maximum tolerated dose (MTD) obtained after intravenous administration of GM1-Ptx in mice was 55 mg/kg and the 50% lethal dose (LD50) was 70 mg/kg. This value is higher than those described for the commercial formulations TAXOL and ABRAXANE, with LD50 of 30 and 45 mg/kg respectively. The antitumor activity, mortality and incidence of metastasis were studied on a murine model of mammary gland cancer. The GM1-Ptx formulation was administered i.v. at different doses for 9 weeks using empty GM1 micelles and saline as treatment controls. Once the treatments were completed, biochemical markers were quantified and histological tissue tests were performed. The most promising results were obtained with the treatment at a dose of 15 mg/kg/twice a week, condition in which a longer survival and significant reduction in the incidence of animals with metastasis, since only one 25% of the mice showed presence of pulmonary micro metastases.

Synthetic carbohydrate-based vaccines: challenges and opportunities

Glycoconjugate vaccines based on bacterial capsular polysaccharides (CPS) have been extremely successful in preventing bacterial infections. The glycan antigens for the preparation of CPS based glycoconjugate vaccines are mainly obtained from bacterial fermentation, the quality and length of glycans are always inconsistent. Such kind of situation make the CMC of glycoconjugate vaccines are difficult to well control. Thanks to the advantage of synthetic methods for carbohydrates syntheses. The well controlled glycan antigens are more easily to obtain, and them are conjugated to carrier protein to from the so-call homogeneous fully synthetic glycoconjugate vaccines. Several fully glycoconjugate vaccines are in different phases of clinical trial for bacteria or cancers. The review will introduce the recent development of fully synthetic glycoconjugate vaccine.

Human MUC1 Mucin: A Multifaceted Glycoprotein

Human MUC1 mucin, a membrane-bound glycoprotein, is a major component of the ductal cell surface of normal glandular cells. MUC1 is overexpressed and aberrantly glycosylated in carcinoma cells. The role MUC1 plays in cancer progression represents two sides of one coin: on the one hand, loss of polarity and overexpression of MUC1 in cancer cells interferes with cell adhesion and shields the tumor cell from immune recognition by the cellular arm of the immune system, thus favoring metastases; on the other hand, MUC1, in essence a self-antigen, is displaced and altered in malignancy and induces immune responses. Tumor-associated MUC1 has short carbohydrate sidechains and exposed epitopes on its peptide core; it gains access to the circulation and comes into contact with the immune system provoking humoral and cellular immune responses. Natural antibodies to MUC1 present in the circulation of cancer patients may be beneficial to the patient by restricting tumor growth and dissemination: early stage breast cancer patients with a humoral response to MUC1 have a better disease-specific survival. Several MUC1 peptide vaccines, differing in vectors, carrier proteins and adjuvants, have been tested in phase I clinical trials. They are capable of inducing predominantly humoral responses to the antigen, but evidence that these immune responses may be effective against the tumor in humans is still scarce.

Common antigens between hydatid cyst and cancers

Background:

Different research groups reported a negative correlation between cancers and parasitical infections. As an example, the prevalence of a hydatid cyst among patients with cancer was significantly lower than its prevalence among normal population. Tn antigens exist both in cancer and hydatid cyst. This common antigen may be involved in the effect of parasite on cancer growth. So in this work, common antigens between hydatid cyst and cancers have been investigated.

Materials and Methods:

Different hydatid cyst antigens including hydatid fluid, laminated and germinal layer antigens, and excretory secretory antigens of protoscolices were run in SDS PAGE and transferred to NCP paper. In western immunoblotting, those antigens were probed with sera of patients with different cancer and also sera of non-cancer patients. Also, cross reaction among excretory secretory products of cancer cells and antisera raised against different hydatid cyst antigen was investigated.

Results:

In western immunoblotting, antisera raised against laminated and germinal layers of hydatid cyst reacted with excretory secretory products of cancer cells. Also, a reaction was detected between hydatid cyst antigens and sera of patients with some cancers.

Conclusion:

Results of this work emphasize existence of common antigens between hydatid cyst and cancers. More investigation about these common antigens is recommended.

Lipopeptide-Coated Iron Oxide Nanoparticles as Potential Glycoconjugate-Based Synthetic Anticancer Vaccines

Although iron oxide magnetic nanoparticles (NPs) have been widely utilized in molecular imaging and drug delivery studies, they have not been evaluated as carriers for glycoconjugate-based anticancer vaccines. Tumor-associated carbohydrate antigens (TACAs) are attractive targets for the development of anticancer vaccines. Due to the weak immunogenicity of these antigens, it is highly challenging to elicit strong anti-TACA immune responses. With their high biocompatibilities and large surface areas, magnetic NPs were synthesized for TACA delivery. The magnetic NPs were coated with phospholipid-functionalized TACA glycopeptides through hydrophobic-hydrophobic interactions without the need for any covalent linkages. Multiple copies of glycopeptides were presented on NPs, potentially leading to enhanced interactions with antibody-secreting B cells through multivalent binding. Mice immunized with the NPs generated strong antibody responses, and the glycopeptide structures important for high antibody titers were identified. The antibodies produced were capable of recognizing both mouse and human tumor cells expressing the glycopeptide, resulting in tumor cell death through complement-mediated cytotoxicities. These results demonstrate that magnetic NPs can be a new and simple platform for multivalently displaying TACA and boosting anti-TACA immune responses without the need for a typical protein carrier.

Anti-cancer properties of gastropodan hemocyanins in murine model of colon carcinoma

BACKGROUND

Various immunotherapeutic approaches have been used for the treatment of cancer. A number of natural compounds are designed to repair, stimulate, or enhance the immune system response. Among them are the hemocyanins (Hcs) - extracellular copper proteins isolated from different arthropod and mollusc species. Hcs are oxygen transporter molecules and normally are freely dissolved in the hemolymph of these animals. Hemocyanins are very promising class of anti-cancer therapeutics due to their immunogenic properties and the absence of toxicity or side effects. KLH (Megathura crenulata hemocyanin) is the most studied molecule of this group setting a standard for natural carrier protein for small molecules and has been used in anti-tumor clinical trials.

RESULTS

The Hcs isolated from marine snail Rapana thomasiana (RtH) and the terrestrial snail Helix pomatia (HpH) express strong in vivo anti-cancer and anti-proliferative effects in the developed by us murine model of colon carcinoma. The immunization with RtH and HpH prolonged the survival of treated animals, improve humoral anti-cancer response and moderate the manifestation of C-26 carcinoma symptoms as tumor growth, splenomegaly and lung metastasis appearance.

CONCLUSION

Hemocyanins are used so far for therapy of superficial bladder cancer and murine melanoma models. Our findings demonstrate a potential anti-cancer effect of hemocyanins on a murine model of colon carcinoma suggesting their use for immunotherapy of different types of cancer.

Tumor-Associated Glycans and Immune Surveillance

Changes in cell surface glycosylation are a hallmark of the transition from normal to inflamed and neoplastic tissue. Tumor-associated carbohydrate antigens (TACAs) challenge our understanding of immune tolerance, while functioning as immune targets that bridge innate immune surveillance and adaptive antitumor immunity in clinical applications. T-cells, being a part of the adaptive immune response, are the most popular component of the immune system considered for targeting tumor cells. However, for TACAs, T-cells take a back seat to antibodies and natural killer cells as first-line innate defense mechanisms. Here, we briefly highlight the rationale associated with the relative importance of the immune surveillance machinery that might be applicable for developing therapeutics.

A new generation of carbohydrate-based therapeutics: recombinant mucin-type fusion proteins as versatile inhibitors of protein-carbohydrate interactions

Cell surface carbohydrates are essential for a multitude of biomedically important interactions that take place at the cell surface. Carbohydrate-binding proteins are, therefore, significant targets for the development of carbohydrate-based inhibitors. Due to their multivalent character, monovalent low-molecular-weight sugar homologues or analogues are usually poor inhibitors of these interactions. Recent advances in organic and chemoenzymatic synthesis of carbohydrates will undoubtedly increase the pace by which new multivalent carbohydrate-based drugs are developed. Knowledge gained on the glycosyltransferases that are involved in glycan biosynthesis can be used to engineer host cells for recombinant production of proteins with tailored glycan substitution. In particular, recombinant mucin-type proteins can serve as natural scaffolds for multivalent presentation of therapeutic carbohydrate determinants.

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.

Naturally occurring antibodies directed against carbohydrate tumor antigens

Healthy persons carry within their pool of circulating antibodies immunoglobulins preferentially of IgM isotype, which are directed against a variety of tumor-associated antigens. In closer scrutiny of their nature, some of these antibodies could be defined as naturally occurring antibodies due to the germline configuration of the variable immunoglobulin region. The majority of these immunoglobulins recognize carbohydrate antigens which can be classified as oncofetal antigens. Many of these IgM antibodies present in the peripheral blood circulation can bind to tumor cells and of these a minor portion are also able to destroy tumor cells by several mechanisms, as for instance complement-mediated cytolysis or apoptosis. It was postulated that anti-carbohydrate antibodies are part of an anti-tumor immune response, while their presence in the peripheral blood of healthy donors is still waiting for a plausible explanation. It may be that recognition of defined epitopes, including carbohydrate sequences, by naturally occurring antibodies constitutes the humoral arm of an anti-tumor immune response as part of the often postulated tumor surveillance. The cytotoxic capacity of these antibodies inspired several research groups and pharmaceutical companies to design novel strategies of immunoglobulin-based anti-tumor immunotherapy.

Immunoreactivity of the 14F7 Mab Raised against N-Glycolyl GM3 Ganglioside in Epithelial Malignant Tumors from Digestive System

The limited expression of N-Glycolyl GM3 (NeuGcGM3) ganglioside in human normal tissues, as well as its presence in melanoma and breast carcinoma using 14F7 Mab (anti-NeuGcGM3), has been previously reported. In this work we evaluated for the first time the 14F7 Mab immunorecognition in some digestive system tumors. Immunohistochemical assays were made with 14F7, followed by anti-mouse biotinylated antibody and ABC/HRP system in normal and pathological human tissues were made. No immunoreaction was evidenced in normal tissues. The reactivity of 14F7 was detected in all adenocarcinomas of the stomach (12/12), colon (12/12), and pancreas (11/11). A finely granular immunorecognition in esophageal tumors (5/15), epidermoid carcinoma of the rectum (5/7), and basaloid carcinoma (4/5) of the latter as well as in hepatocellular carcinoma (13/14) was also observed. Our results are in agreement with the assumption that NeuGcGM3 ganglioside may be considered as target for passive and active immunotherapy in digestive system malignancies expressing this molecule.

Synthetic carbohydrate-based anticancer vaccines: the Memorial Sloan-Kettering experience

Malignantly transformed cells can express aberrant cell surface glycosylation patterns, which serve to distinguish them from normal cells. This phenotype provides an opportunity for the development of carbohydrate-based vaccines for cancer immunotherapy. Synthetic carbohydrate-based vaccines, properly introduced through vaccination of a subject with a suitable construct, should be recognized by the immune system. Antibodies induced against these carbohydrate antigens could then participate in the eradication of carbohydrate-displaying tumor cells. Advances in carbohydrate synthetic capabilities have allowed us to efficiently prepare a range of complex, synthetic anticancer vaccine candidates. We describe herein the progression of our longstanding carbohydrate-based anticancer vaccine program, which is now at the threshold of clinical evaluation in several contexts. Our carbohydrate-based anticancer vaccine program has evolved through a number of stages: monomeric vaccines, monomeric clustered vaccines, unimolecular multi-antigenic vaccines and dual-acting vaccines. This account will focus on our recently developed unimolecular multi-antigenic constructs and potential dual-acting constructs, which contain clusters of both carbohydrate and peptide epitopes.

A new model for the presentation of tumor-associated antigens and the quest for an anticancer vaccine: a solution to the synthesis challenge via ring-closing metathesis

Fully synthetic, carbohydrate-based antitumor vaccine candidates have been synthesized in highly clustered modes. Multiple copies of tumor-associated carbohydrate antigens, Tn and STn, were assembled on a single cyclic peptide scaffold in a highly convergent manner. Ring-closing metathesis-mediated incorporation of an internal cross-linker was also demonstrated. In particular, this rigidified cross-linked construct would enhance a cluster-recognizing antibody response by retaining an appropriate distance between glycans attached to the peptide platform. Details of the design and synthesis of highly clustered antigens are described herein.

Synthetic and immunological studies of 5'-N-phenylacetyl sTn to develop carbohydrate-based cancer vaccines and to explore the impacts of linkage between carbohydrate antigens and carrier proteins

5'- N-Phenylacetyl sTn (sTnNPhAc), an unnatural derivative of sTn antigen expressed by many tumors, and its alpha-linked protein conjugates were prepared and investigated to explore glycoconjugate cancer vaccines. sTnNPhAcalpha-KLH elicited a robust T cell dependent immunity. The antiserum derived from sTnNPhAcalpha- or sTnNPhAcbeta-KLH-inoculated mice was similarly reactive to sTnNPhAcalpha and sTnNPhAcbeta but showed very little reactivity to sTn, NeuNPhAcalpha(2,3)GalNAc--a regioisomer of sTnNPhAc, isolated phenylacetyl group, and the linker employed to conjugate sTnNPhAc and carrier protein. It was concluded that the sTnNPhAc-elicited immunity was specific for the whole antigen rather than the phenylacetyl group or other partial structures of sTnNPhAc and that the reducing end configuration or linkage of sTnNPhAc did not affect its immunological identity. It was also concluded that a new linker designed to conjugate carbohydrates and proteins did not provoke any immune reaction and that the linker, as well as the associated new and convenient coupling strategy, can be safely used for the development of glycoconjugate vaccines.

Specificity in cancer immunotherapy

From the earliest days in the field of tumor immunology three questions have been asked: do cancer cells express tumor-specific antigens, does the immune system recognize these antigens and if so, what is their biochemical nature? We now know that truly tumor-specific antigens exist, that they are caused by somatic mutations, and that these antigens can induce both humoral and cell-mediated immune responses. Because tumor-specific antigens are exclusively expressed by the cancer cell and are often crucial for tumorigenicity, they are ideal targets for anti-cancer immunotherapy. Nevertheless, the antigens that are targeted today by anti-tumor immunotherapy are not tumor-specific antigens, but antigens that are normal molecules also expressed by normal tissues (so-called "tumor-associated" antigens). If tumor-specific antigens exist and are ideal targets for immunotherapy, why are they not being targeted? In this review, we summarize current knowledge of tumor-specific antigens: their identification, immunological relevance and clinical use. We discuss novel tumor-specific epitopes and propose new approaches that could improve the success of cancer immunotherapy, especially for the treatment of solid tumors.

Cytotoxic natural antibodies against human tumours: an option for anti-cancer immunotherapy?

Healthy individuals may contain in their peripheral blood antibodies which are able to destroy human tumour cells mediated either by complement-dependent cytotoxicity or by apoptosis. The largest proportion of these antibodies is of IgM isotype and directed against distinct tumour associated carbohydrate epitopes. Although the origin of these antibodies is not clear they seem to belong to the class of natural antibodies because they are not affinity matured and are encoded by distinct germ-line restricted gene families. It is most likely that this class of natural antibodies has in vivo an anti-tumour protective effect which may contribute to so-called tumour surveillance. On the other hand malignant tumour cells exert mechanisms to counteract such an antibody attack. These comprise soluble factors as well as cell surface expressed membrane complement regulatory proteins (mCRP). Further studies are needed to elucidate molecular mechanisms leading to either tumour destruction induced by natural antibodies or to overcome the protective strategies of the tumour against antibody attack.

Harnessing the immune system for ovarian cancer therapy

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemo-resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. Many questions remain as optimal strategies are developed, which include: (i) What is the best antigen form (e.g. peptides, proteins or tumor lysates)? (ii) What are the appropriate adjuvants? (iii) Are mono-valent or multi-valent vaccines likely to be more effective? (iv) What is the optimal frequency and duration of vaccination? (v) How should antigen-specific responses be monitored? and (vi) How should the anti-cancer response be maintained? In this review, we explore representative examples of immune strategies under investigation for patients with ovarian carcinoma which illustrate many of these issues. Basic principles generic to all these immunotherapeutic approaches will also be discussed.

Pilot study of a heptavalent vaccine-keyhole limpet hemocyanin conjugate plus QS21 in patients with epithelial ovarian, fallopian tube, or peritoneal cancer

PURPOSE

To characterize the safety and immunogenicity of a heptavalent antigen-keyhole limpet hemocyanin (KLH) plus QS21 vaccine construct in patients with epithelial ovarian, fallopian tube, or peritoneal cancer in second or greater complete clinical remission.

EXPERIMENTAL DESIGN

Eleven patients in this pilot trial received a heptavalent vaccine s.c. containing GM2 (10 microg), Globo-H (10 microg), Lewis Y (10 microg), Tn(c) (3 microg), STn(c) (3 microg), TF(c) (3 microg), and Tn-MUC1 (3 microg) individually conjugated to KLH and mixed with adjuvant QS21(100 microg). Vaccinations were administered at weeks 1, 2, 3, 7, and 15. Periodic blood and urine samples were obtained to monitor safety (complete blood count, comprehensive panel, amylase, thyroid-stimulating hormone, and urinalysis) and antibody production (ELISA, fluorescence-activated cell sorting, and complement-dependent cytotoxicity).

RESULTS

Eleven patients were included in the safety analysis; 9 of 11 patients remained on study for at least 2 weeks past fourth vaccination and were included in the immunologic analysis (two withdrew, disease progression). The vaccine was well tolerated. Self-limited and mild fatigue (maximum grade 2 in two patients), fever, myalgia, and localized injection site reactions were most frequent. No clinically relevant hematologic abnormalities were noted. No clinical or laboratory evidence of autoimmunity was seen. Serologic responses by ELISA were largely IgM against each antigen with the exception of Tn-MUC1 where both IgM and IgG responses were induced. Antibody responses were generally undetectable before immunization. After immunization, median IgM titers were as follows: Tn-MUC1, 1:640 (IgG 1:80); Tn, 1:160; TF, 1:640; Globo-H, 1:40; and STn, 1:80. Only one response was seen against Lewis Y; two were against GM2. Eight of nine patients developed responses against at least three antigens. Antibody titers peaked at weeks 4 to 8 in all patients. Fluorescence-activated cell sorting and complement-dependent cytotoxicity analysis showed substantially increased reactivity against MCF7 cells in seven of nine patients, with some increase seen in all patients.

CONCLUSIONS

This heptavalent-KLH conjugate plus QS21 vaccine safely induced antibody responses against five of seven antigens. Investigation in an adequately powered efficacy trial is warranted.

Immunologic approaches to ovarian cancer treatment

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemotherapy resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. The role of immune surveillance in improving outcome has been supported by the correlation of increased survival with the presence or absence of tumor-infiltrating lymphocytes in a given patient. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. As optimal strategies are being developed, many questions remain. Some of the questions are as follows: What is the best antigen form (eg, peptides, proteins, or tumor lysates)? What are the appropriate adjuvants? Are monovalent or multivalent vaccines likely to be more effective? What is the optimal frequency and duration of vaccination? How should antigen-specific responses be monitored? How should the anticancer response be maintained? In this review, we will explore representative examples of immune strategies under investigation for patients with ovarian carcinoma that illustrate many of these issues. We will review ongoing phase III studies for patients in first clinical remission. Basic principles generic to all these immunotherapeutic approaches will be discussed in the hopes of yielding the most promising results as the field continues to evolve.

Improving the antigenicity of sTn antigen by modification of its sialic acid residue for development of glycoconjugate cancer vaccines

Sialyl Tn (sTn) antigen is a sialylated disaccharide abundantly expressed by many tumors. To search for effective cancer immunotherapies based on sTn antigen, we designed and synthesized a series of unnatural N-acyl derivatives of sTn and studied their immunological properties. For this purpose, an efficient method was developed to synthesize the natural and unnatural forms of sTn antigen and their protein conjugates. The resultant glycoconjugates were used to immunize C57BL/6 mice, and the immune response was assessed by enzyme-linked immunosorbent assay (ELISA). Whereas the keyhole limpet hemocyanin (KLH) conjugate of sTn elicited low levels of IgM antibodies, the KLH conjugates of N-iso-butanoyl sTn and N-phenylacetyl sTn, especially the latter, induced high titers of antigen-specific IgG antibodies, showing a T-cell-dependent response that is critical for the antitumor activity. The results suggest that the modified forms of sTn, especially N-phenylacetyl sTn, have improved antigenicity and promising immunological properties for use as cancer vaccines.

Induction of immune responses against glycosphingolipid antigens: comparison of antibody responses in mice immunized with antigen associated with liposomes prepared from various phospholipids

The immune responses of mice against glycosphingolipid (GSL) antigens and the effect of the phospholipid composition of liposomes on the immunogenicity in mice of liposome-associated GSL antigens were examined. The immunization with GSL antigen alone was unable to induce any detectable anti-GSL antibody responses. On the other hand, the immune responses against GSL antigens were detected after immunization with liposomes composed of dipalmitoylphosphatidylcholine (DPPC) (0.5 micromol), cholesterol (Chol) (0.5 micromol), Salmonella minnesota R595 lipopolysaccharides (LPS) (10 microg) and GSL (0.05 micromol) (DPPC-liposome). However, the administration with liposome composed of dimyristoylphosphatidylcholine (DMPC) (0.5 micromol), Chol (0.5 micromol), S. minnesota R595 LPS (10 microg) and GSL (0.05 micromol) and with liposomes composed of distearylphosphatidylcholine (DSPC) (0.5 micromol), Chol (0.5 micromol), and S. minnesota R595 LPS (10 microg) and GSL (0.05 micromol) was ineffective for the induction of the immune responses against GSL antigens. These results suggest that DPPC-liposome would serve effectively as a delivery vehicle for inducing immune responses against GSL antigen.

Chemical and Chemoenzymatic Synthesis of S-Linked Ganglioside Analogues and Their Protein Conjugates for Use as Immunogens

Analogues of the tumor-associated gangliosides GM(3) and GM(2) containing terminal S-linked neuraminic acid residues and an amino terminated, truncated ceramide homologue have been synthesized and conjugated to a protein. The synthesis involved coupling of a S-linked sialyl alpha(2-->3) galactose disaccharide with a glucosyl sphingosine analogue, followed by elaboration and deprotection to give amino-terminated glycosyl ceramide 1. Glycosyltransferase-catalyzed extension of the trisaccharide 1 provided access to the modified GM(2) tetrasaccharide 2 or sulphur-containing GD(3) analogue 30. Owing to their potentially enhanced resistance to endogenous exo-glycoside hydrolases and their inherent non-self character, carbohydrate antigens containing non-reducing terminal thioglycosidic linkages may be more immunogenic than O-linked antigens and may stimulate the production of antibodies capable of recognizing naturally occurring oligosaccharides. Our initial results suggest that in fact these antigens are viable immunogens and furthermore, that immune sera cross reacts with O-gangliosides in the context of a heterologous glycoprotein conjugate.

Chemoenzymatic synthesis of GM3and GM2gangliosides containing a truncated ceramide functionalized for glycoconjugate synthesis and solid phase applications

Analogues of GM3 and GM2 gangliosides were chemoenzymatically synthesized on a multifunctional ceramide-type tether designed to facilitate diverse strategies for glycoconjugate synthesis. The truncated ceramide aglycon maintains the stereogenic centres of natural ceramide while avoiding extensive hydrophobicity that can hamper synthesis and purification of the glycolipids. Tetanus toxoid and BSA glycoconjugates of these two gangliosides were prepared for immunization of mice, and for solid phase assays to screen for ganglioside-specific antibodies. Inhibition experiments showed that antibodies generated by tetanus toxoid conjugates of GM3 and GM2 exhibited specificity for the carbohydrate epitope and the stereogenic centres of the ceramide.

Organic synthesis in pursuit of immunology: large-scale synthesis of peracetylated GM2 glycosylamino acid for preparation of a multiantigenic prostate cancer vaccine

We describe herein the stereo-controlled, large-scale synthesis of peracetylated GM2 glycosylamino acid. Key features of the synthesis include a newly modified [1+3] coupling reaction and an olefin cross-metathesis-hydrogenation sequence. The GM2 glycosylamino acid is now ready for incorporation into a hexavalent prostate cancer vaccine construct.

Effect of anti-ganglioside antibody in experimental Trypanosoma brucei infection in mice

The effect of antibody against ganglioside antigen on Trypanosoma brucei parasites was examined in vitro and in vivo using anti-ganglioside GM1 (AGM-1) monoclonal antibody. The antibody showed complement-dependent cytotoxicity against T. brucei with mouse complement. Furthermore, mice given AGM-1 were challenged intraperitoneally with T. brucei. Although all non-treated control mice died within six days after infection, all of AGM-1-injected mice had survived by six days post-infection. These data suggest that antibody against ganglioside antigen on T. brucei has potential in protection against T. brucei infection.

Thomsen-Friedenreich (T) antigen expression increases sensitivity of natural killer cell lysis of cancer cells

In this study, we demonstrate a correlation between T antigen expression on a panel of human carcinoma cell lines and their sensitivity to porcine NK cell lysis. Specifically, the more T antigen is expressed, the more sensitive the cancer cells are to porcine NK cell lysis. Furthermore, this correlation also exists for these cells and their ability to induce tumors in vivo. In this porcine animal model, the less T antigen is expressed, the more prolific the tumor growth in vivo and vice versa. Using the human colorectal adenocarcinoma cell line SW-48, we used limiting dilution to clone 2 populations of cells, one expressing high and the other low levels of T antigen, clones 143 and 111, respectively. In these cloned cells, the clone that expressed more T antigen was more NK-sensitive in vitro and weakly induced tumor growth in vivo. Inversely, the clone that expressed less T antigen clone was more NK-resistant in vitro and grew more prolific tumors in vivo. Using soluble T antigen in a competitive inhibition assay, there was a decrease in porcine NK cell killing of the T antigen+ human cell line Colo 320HSR. Taken together, these findings suggest a novel role for T antigen in the NK cell recognition of cancer cells, specifically as markers for NK sensitivity in carcinoma cell lines. The significance of T antigens as targets for NK cell-mediated lysis is novel and identifies NK cell-T antigen interactions as potentially significant in the immunotherapy of cancer and its associated metastases.

Prospects for total synthesis: a vision for a totally synthetic vaccine targeting epithelial tumors

Vaccines derived from totally synthetic carbohydrate antigens have been shown to elicit an immune response in both preclinical and clinical settings. The vaccines have been proven safe when administered in human clinical trials and are also competent at inducing antibodies that react with aberrant cells expressing the corresponding carbohydrate antigen. The most well studied vaccines have hitherto focused on single carbohydrate antigens, notwithstanding the known heterogeneity of transformed cells. Advances in synthetic organic chemistry have enabled the preparation and subsequent investigation of vaccines that contain several different tumor-associated carbohydrate antigens in a single molecule. These unimolecular constructs could, in principle, serve as superior mimics of cell surface antigens and hence, as multifaceted cancer vaccines. We report here the synthesis of a pentameric vaccine targeting a specific cancer. The new vaccine contains prostate tumor-associated antigens, Tn, TF, STn, Lewis(y), and Globo-H. To reach our goal, antigen-containing amino acid monomers were assembled in a linear fashion to form a glycopeptide containing the five distinct carbohydrate antigen units. The attachment of a linker to the glycopeptide followed by an extraordinary global deprotection and subsequent conjugation to two different immunogenic carriers, keyhole limpet hemocyanin and N-alpha-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-L-cysteine, resulted in the vaccine constructs. The results described herein indicate that complex unimolecular multivalent vaccines can be efficiently produced in the laboratory. These fully synthetic vaccines have the potential to stimulate a multifaceted immune response against prostate cancer.

Tissue and serum MUC1 mucin detection in breast cancer patients

Tumor MUC1 expression as well as levels of MUC1, MUC1 circulating immune complexes (MUC1-CIC) and free antibodies against MUC1 (IgG and IgM-MUC1) were evaluated in 70 breast cancer patients with different stages of disease. Controls included: 135 serum samples from healthy women, normal mammary tissue samples (n = 7) and benign breast disease specimens (n = 6). In all assays, pre- and post-vaccination serum samples from breast cancer patients belonging to a vaccination protocol developed at the Memorial Sloan Kettering Cancer Center (New York, USA) were included as controls. Serum MUC1 was measured through Cancer Associated Serum Antigen test and CA15-3 test. Employing ELISA, MUC1-CIC-IgG/M were measured with either C595 or SM3 monoclonal antibodies (MAb) as catchers and also free antibodies against MUC1 (IgG and IgM) using 100mer peptide as catcher. Employing multivariate statistical analysis, results were correlated with age, tumor type, stage of disease and grade of differentiation. By quantitative immunohistochemistry using three anti-MUC1 core protein MAbs (C595, HMFG2 and SM3), tumor MUC1 was detected in 60/70 (86%) breast cancer specimens which reacted with at least one of these MAbs. High MUCI serum levels were detected in 14/67 (21%); IgG and IgM anti-MUC1 antibodies were found elevated in 32 and 14%, respectively, while IgG-MUC1-CIC-measured with C595 in 42% and IgM-MUC1-CIC in 54%; finally, SM3 was positive in 43 and 18%, respectively. Results of these studies demonstrate that in a group of breast cancer patients, MUC1 was detected both in tissue specimens as well as free in serum samples; furthermore, MUC1 can also circulate complexed with IgG and IgM antibodies; thus an accurate measurement should include free and complexed forms. On the other hand, immunohistochemical studies on breast cancer tissues may contribute to reveal different MUC1 glycoforms.

Immunotherapy of advanced breast cancer with a heterophilic ganglioside (NeuGcGM3) cancer vaccine

PURPOSE

A heterophilic ganglioside cancer vaccine was developed by combining NeuGcGM3 with the outer membrane protein complex of Neisseria meningitidis to form very small size proteoliposomes (VSSP). A phase I clinical trial was performed to determine safety and immunogenicity of this vaccine.

PATIENTS AND METHODS

Stage III to IV breast cancer patients received up to 15 (200 micro g) doses of the vaccine by intramuscular injection. The first five doses (induction phase) were given at 2-week intervals, with the remaining treatment (maintenance) administered on a monthly basis.

RESULTS

Twenty-one patients, 11 of whom had metastatic disease, were included. Main toxicities included erythema and induration at the injection site, sometimes associated with mild pain, and low-grade fever (World Health Organization grades 1 and 2). All treated patients who completed the induction phase developed anti-NeuGcGM3 antibody titers between 1:1,280 and 1:164,000 immunoglobulin G (IgG), and 1:640 and 1:164,000 IgM. Noteworthy specific IgA antibodies were induced by vaccination in all stage III patients and in three stage IV patients. Serum antibody levels were higher in the stage III patients, with the larger increases observed after week 32. The antiganglioside IgG subclasses were mainly IgG1 and IgG3. Hyperimmune sera increased complement-mediated cytotoxicity versus P3X63 myeloma cells and a marked IgG differential reactivity against human mammary ductal carcinoma samples.

CONCLUSION

NeuGcGM3/VSSP/Montanide ISA 51 is an unusual immunogenic ganglioside vaccine and also seems to be safe in this small trial. Immunologic surrogates of activity indicate that this reagent warrants further investigation.

Better survival of Helicobacter pylori infected patients with early gastric cancer is related to a higher level of Thomsen-Friedenreich antigen-specific antibodies

The survival of patients with histologically verified gastric carcinoma at stage I (n = 44) and stage II (n = 43) was analysed by the Kaplan-Meier method depending on H. pylori serological status and a level of IgG and IgM antibody to tumor-associated Thomson-Friedenreich antigen (T Ag). In cancer patients at stage I, significantly better survival for H. pylori seropositive patients was observed compared to H. pylori seronegative patients (median SE survival time: 60.0 +/- 3.8 mths and 37.0 +/- 7.8 mths, respectively; P < 0.0004, log-rank test). Patients with higher level of T Ag-specific IgG antibody (strong responders) showed significantly and dramatically better (P < 0.00001) survival rate than weak responders. However, an association of better survival with a higher level of anti-T antibody level was limited to the H. pylori seropositive patients exclusively (P < 0.00001) with no difference for H. pylori seronegative group of patients. The level of IgM anti-T Ag antibody was not significantly related to the survival of patients at both stages of the disease, though better survival was noted in H. pylori seropositive IgM strong responders at approximately 40-60 months of observation. Statistically insignificant associations between survival and H. pylori status or anti-T antibody levels were also observed in a group of gastric cancer patients at stage II. In summary, the survival of patients with early gastric cancer (stage I) is significantly better in H. pylori seropositive patients, and this phenomenon may be in part explained by up-regulation of T Ag-specific IgG immune response in H. pylori infected individuals.

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.

Toxicity of a GM3 cancer vaccine in Macaca fascicularis monkey: a 12-month study

GM3 is a ganglioside that has been biochemically identified as dominating the cell surface of several human tumours, but is also found on human normal cells at much lower density. Since GM3 is widely distributed in essentially all types of animal cells, there is a conflict with the concepts of tumour-associated antigen, immunogen, and toxicity. We have designed a GM3-based cancer vaccine for the treatment of human breast and melanoma tumours. Prior to the Phase I clinical trial, we carried out a 12-month dose repeated toxicity study in five male Macaca fascicularis monkeys. Four male monkeys were treated with placebo in a similar way. During the study, no differences were observed between control and treated monkeys related to daily clinical observations (other than local damage) including rectal temperature, blood pressure, respiratory and cardiac rates, weight gain, biochemical and hematological parameters (with the exception of transitory pathological changes), and anti-DNA and anti-nuclear antibodies, although treated monkeys consistently developed both IgM- and IgG-specific anti-GM3 antibodies. Sixty per cent of treated monkeys developed moderate local reactions at the injection site, which disappeared without sequels. We concluded that this GM3 cancer vaccine overcame in monkeys the natural tolerance to GM3 ganglioside evidenced by a strong immune response, while the local reactions elicited-were transitory without apparent important systemic toxicity effects.

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.

Use of surrogate antigens as vaccines against cancer

Tumor cells may evade immune surveillance by possessing polysaccharides or carbohydrates on their surface. This evasive strategy is effective because glycans are poorly immunogenic and fail to elicit immunological memory responses due to an absence of T-cell processing. Induction of an immune response to cell surface carbohydrate antigens is considered as an important strategy to fight cancer. As carbohydrates per se are poor immunogens, alternative approaches are being evaluated to induce functional cross-reactive responses. We are focusing on the use of peptide mimotopes of tumor-associated carbohydrate antigens to challenge cancer, as we would manipulate the immune system to establish protective immunity based on carbohydrate cross-reactive humoral and cellular responses.

A rat model to study the role of STn antigen in colon cancer

Expression of the mucin-associated sialyl-Tn (STn) antigen has been associated with a decreased survival in patients with colorectal, gastric, and ovarian cancer. To better understand the role of STn antigen in tumor biology, we developed STn(+) (called LP) and STn(-) (called LN) clonal cell lines from a parental metastatic rat colon carcinoma cell line (LMCR). Both derivative cell lines exhibited identical proliferation rates in vitro. LP cells strongly expressed STn antigen both in vitro and in vivo, and were poorly tumorigenic when given to syngeneic rats. LN cells did not express STn antigen in vitro, but as in vivo tumors these cells rapidly acquired STn expression, readily formed tumors, and were highly lethal. When rats were given an otherwise lethal inoculum of i.p. LN cells, pre-immunization with synthetic STn antigen conjugated to keyhole limpet hemocyanin (STn-KLH) resulted in a 60% survival rate. When LN cells were injected subcutaneously in the presence of STn-KLH-sensitized lymphocytes, tumor growth was decreased. Distribution of STn antigen in normal organs of host rats is quite similar to that of humans. This model mimics human disease and should facilitate studies of mucin-associated antigens in tumor biology and the development of immunotherapeutic agents based on mucin-related antigens.

Antibody-dependent cell-mediated cytotoxicity can be induced by MUC1 peptide vaccination of breast cancer patients

Human polymorphic epithelial mucin (PEM, MUC1) is a high molecular weight transmembrane glycoprotein expressed on the apical cell surface of glandular epithelium and is over-expressed and hypo-glycosylated in adenocarcinomas. The extracellular part of the molecule consists mainly of a variable number of 20 amino acid repeats that contain cryptic epitopes exposed in malignancy. The objective of our study was to determine whether humanized MUC1 MAbs and Abs induced by vaccination of breast cancer patients with MUC1 peptides can effect an antibody-dependent cell-mediated cytotoxicity (ADCC). An in vitro assay has been set up in which the breast tumor cell line ZR-75-1 is used as target and PBMC of healthy donors as effector cells. Different target and effector cells, as well as various MUC1 MAbs were tested to optimize the efficacy of the in vitro assay. The humanized MAb HuHMFG-1, which recognizes the PDTR sequence in the MUC1 tandem repeat, induced a strong cell-mediated cytotoxicity. Nine MUC1-expressing tumor cell lines, including 3 bone marrow-derived cell lines, as well as 2 MUC1-transfected cell lines were susceptible to different extent to MUC1 Ab-dependent killing. Large variations in the killing capacity of PBMC from healthy donors were found. The NK cells were the essential effector cells for the MUC1 Ab-dependent killing. Plasma samples with induced high levels of MUC1 Ab were obtained from breast cancer patients repeatedly immunized with a KLH-conjugated 33-mer or 106-mer MUC1 tandem repeat. Pre- and post-vaccinated plasma samples of these patients were compared in the ADCC assay and it could be clearly demonstrated that the induced MUC1 Abs can effect tumor cell killing. MUC1 Ab-dependent cell-mediated tumor cell killing may occur in vivo and the ADCC assay can be applied to monitor MUC1 vaccination trials.

A purified GM3 ganglioside conjugated vaccine induces specific, adjuvant-dependent and non-transient antitumour activity against B16 mouse melanoma in vitro and in vivo

The presence of substantial amounts of GM3 ganglioside on human melanomas and other tumours, together with its peculiar biological properties, makes this glycolipid a unique target for cancer immunotherapy. B16 mouse melanoma expresses GM3 and constitutes an appropriate model for the development of novel GM3-based vaccines. Recently, we hydrophobically incorporated purified GM3 into the outer membrane protein complex from Neisseria meningitidis to form very small size proteoliposomes (GM3/VSSP). We have examined the antitumour properties of GM3/VSSP vaccine and compared it with GM3 incorporated in very low density serum lipoproteins (GM3/VLDL). Immunization with four doses of GM3/VSSP vaccine (120 microg of ganglioside) plus Freund's adjuvant or Montanide ISA 51 significantly increased the overall survival of mice inoculated in the subcutis with 103 B16-F1 cells, whereas the GM3/VLDL immunogen was ineffective. The non-transient character of tumour protection was confirmed in animals surviving the first challenge and re-inoculated with 5 x 103 cells. GM3/VSSP vaccine also reduced the subcutaneous growth of highly aggressive B16-F10 cells. The importance of ganglioside structure in the tumour-protective effect of GM3/VSSP vaccine was confirmed using GM3 containing N-glycolylneuraminic acid, a ganglioside absent in melanoma cells. Immunostaining and enzyme-linked immunosorbent assay (ELISA) experiments showed a high specificity of immune sera against GM3 and the presence of all four IgG subclasses, with a preponderance of IgG2b and IgG3. In addition, a strong anti-B16 complement-mediated cytotoxicity was induced by vaccination with GM3/VSSP. The present data indicate the molecular specificity of GM3/VSSP vaccine as well as the adjuvant-dependent and non-transient character of tumour protection in the B16 mouse model. These findings suggest that an appropriate GM3 vaccine may be capable of inducing prolonged tumour protection in melanoma patients.