Neuraminidase-mediated augmentation of in vitro immune response of patients with solid tumors

Insights into the Role of Sialylation in Cancer Metastasis, Immunity, and Therapeutic Opportunity

Sialylation is an enzymatic process that covalently attaches sialic acids to glycoproteins and glycolipids and terminates them by creating sialic acid-containing glycans (sialoglycans). Sialoglycans, usually located in the outmost layers of cells, play crucial biological roles, notably in tumor transformation, growth, metastasis, and immune evasion. Thus, a deeper comprehension of sialylation in cancer will help to facilitate the development of innovative cancer therapies. Cancer sialylation-related articles have consistently increased over the last four years. The primary subjects of these studies are sialylation, cancer, immunotherapy, and metastasis. Tumor cells activate endothelial cells and metastasize to distant organs in part by the interactions of abnormally sialylated integrins with selectins. Furthermore, cancer sialylation masks tumor antigenic epitopes and induces an immunosuppressive environment, allowing cancer cells to escape immune monitoring. Cytotoxic T lymphocytes develop different recognition epitopes for glycosylated and nonglycosylated peptides. Therefore, targeting tumor-derived sialoglycans is a promising approach to cancer treatments for limiting the dissemination of tumor cells, revealing immunogenic tumor antigens, and boosting anti-cancer immunity. Exploring the exact tumor sialoglycans may facilitate the identification of new glycan targets, paving the way for the development of customized cancer treatments.

Sweet escape: sialic acids in tumor immune evasion

Sialic acids represent a family of sugar molecules derived from neuraminic acid that frequently terminate glycan chains and contribute to many biological processes. Already five decades ago, aberrantly high expression of sialic acids has been proposed to protect cancer cells from recognition and eradication by the immune system. Today, increased understanding at the molecular level demonstrates the broad immunomodulatory capacity of tumor-derived sialic acids that is, at least in part, mediated through interactions with immunoinhibitory Siglec receptors. Here we will review current studies from a sialic acid sugar perspective showing that tumor-derived sialic acids disable major killing mechanisms of effector immune cells, trigger production of immune suppressive cytokines and dampen activation of antigen-presenting cells and subsequent induction of anti-tumor immune responses. Furthermore, strategies to modulate sialic acid expression in cancer cells to improve cancer immunotherapy will be discussed.

Plasma sialic acid in patients with prostate cancer

Serum sialic acid (N-acetylneuraminic acid) was evaluated as a tumour marker for prostate cancer and compared with serum prostate specific antigen (PSA). The records of 35 patients suffering from prostate cancer (9 with bone metastases) were analysed and compared with those of 21 healthy individuals. Total serum sialic acid was significantly elevated among the cancer patients. Levels in patients with distant metastases were significantly higher than in those with locally restricted disease and normal individuals, whereas no such difference was seen between the latter 2 groups. A direct association between serum sialic acid and tumour T category and grade could not be established. The difference between the cancer and the control groups was reflected more significantly by PSA. As sialic acid lacks tumour specificity, it is not helpful in screening for prostate cancer, yet might contribute towards the early detection of tumour progression and metastases during both therapy and follow-up.

A critical analysis of the use of sialic acid determination in the diagnosis of malignancy

The measurement of serum sialic acid in sera from individuals with leukemia, breast, gastrointestinal, lung and bladder cancers, brucellosis and manic depression is described. The serum sialic acid levels were also examined in mice bearing Landschutz ascites tumours. The presence of sialic acid-enriched glycopeptides in serum was shown. The results indicate that while sialic acid may be significantly elevated in sera of some tumour-bearing individuals, it is not solely tumour-derived. Its application as a tumour marker is limited and requires critical analysis.

Axillary versus peripheral blood levels of sialic acid, ferritin, and CEA in patients with breast cancer

Serum levels of total sialic acid, carcinoembryonic antigen (CEA), ferritin, lactate dehydrogenase, and creatine phosphokinase were measured both in tumor drainage blood (axillary vein) and in peripheral blood obtained from 121 breast cancer patients during surgery. No significant differences between mean values in peripheral and tumor draining blood, between cancer patients and healthy controls, or between patients with or without axillary lymph node metastases were found for any of the markers. Both ferritin and CEA levels were higher in axillary and peripheral blood from patients with central breast cancer versus other sites but the difference was significant only for CEA (p less than 0.05). CEA levels were significantly higher (p less than 0.01) in patients with greater than 2 cm diameter carcinomas versus T1 stage patients in axillary but not in peripheral blood. When the cephalic vein was clamped before the axillary sample was taken, ferritin showed a significant increase (p less than 0.05). We conclude that measurement of sialic acid, CEA, and ferritin in axillary venous blood in breast cancer patients is not of clinical benefit, although further data are needed to clarify whether other advantages can be derived.

Controlled clinical trial of adjuvant immunotherapy with BCG and neuraminidase-treated autologous tumour cells in large bowel cancer

A controlled, randomised clinical trial of immunotherapy was performed in 301 patients with stage B or C colorectal cancer. The immunotherapy treatment consisted of 18 vaccinations over a 2 year period following surgery with a combination of BCG given by scarification plus subcutaneous injection of Vibrio cholera neuraminidase (VCN)-modified autologous tumour cells. Five year follow-up has now been completed in all patients. The immunotherapy did not alter either the disease-free interval or the overall survival of patients in comparison with a control group of patients not receiving immunotherapy.

Melbourne trial of adjuvant immunotherapy in operable large bowel cancer

A controlled randomized clinical trial was undertaken to assess the ability of combined non-specific and specific immunotherapy to alter the disease-free interval and overall survival of patients with Stage B or C large bowel cancer. The immunotherapy consisted of a 2 year programme of vaccinations with BCG and neuraminidase-treated autologous tumour cells. Three hundred and one patients entered the trial. At 5 years of follow-up there is no evidence that this form of immunotherapy can alter either the disease-free interval or survival in this group of patients.

Diagnosis of head and neck carcinomas by means of immunological tumour markers (Beta-2-microglobulin, immunoglobulin E, ferritin, N-acetyl-neuraminic acid, phosphohexose-isomerase)

In a great number of patients with squamous cell cancer of the head and neck, tumour markers in the serum were determined before any therapy, in order to evaluate their possible usefulness as parameters for monitoring therapy as well as for early detection of cancer. Patients with primary tumours (n = 101) were distributed to groups TI-II and TIII-IV according to the UICC classification 1978, and investigated together with a group of recurrences (n = 105). 50 age-matched healthy individuals served as controls. Substances investigated were beta 2-Microglobulin (beta 2-M), Immunoglobulin E (IgE), Ferritin, N-Acetyl-Neuraminic Acid (sialic acid; NANA), Phosphohexose-Isomerase (PHI). Not only were the mean values of the groups compared with each other, but also the percentages of the respective groups displaying increases above the upper norm limit (95. percentile) were calculated. Critical evaluation of the results led to the conclusion that in particular IgE, NANA and--with some reservations--ferritin should be further investigated as biological serum markers in serial determination with special regard to their possible relevance for cancer treatment.

Sialic acid, sialyltransferase and neuraminidase levels in maternal plasma, urine and lymphocytes during pregnancy and post-partum period--a longitudinal study in women

The total sialic (N-acetylneuraminic acid) levels were serially determined in maternal plasma, urine and lymphocytes during human pregnancy and post-partum period. The enzymes, sialyltransferase and neuraminidase, were also examined in the plasma samples. The sialic acid content of plasma and urine (expressed in terms of the creatinine content in urine) was elevated during pregnancy and increased with advancing gestation (P less than 0.001). A few days (0-6) prior to parturition there was a significant (P less than 0.01) fall in the plasma sialic acid levels, which subsequently increased again in the post-partum period (1-14 days), reaching values even greater than that observed during pregnancy. On the other hand, there was no decrease in the urinary sialic acid levels before delivery, and the post-partum values in urine, though higher than the values obtained in non-pregnant women, were not significantly greater than the levels observed during pregnancy. The sialic acid levels in lymphocytes were not altered during pregnancy. There was also no statistically significant change in serum sialyltransferase activity at any stage of pregnancy or post-partum period, while neuraminidase was not detectable in any of the plasma samples. The results are discussed with reference to the role of circulating sialic acid during pregnancy.

Macrophage-mediated tumor cytotoxicity: role of macrophage surface sialic acid

Cell surface sialic acid levels were compared for monocytes and macrophages obtained from normal volunteers and breast cancer patients. Equal quantities of sialic acid were found on the monocytes obtained from normal volunteers and breast cancer patients. Approximately 60% more cell surface sialic acid was found on the macrophages from breast cancer patients than was found on the macrophages from normal volunteers. In order to determine whether cell surface sialic acid had any effect on macrophage-mediated cytotoxicity, macrophages were pretreated with neuraminidase (NANAse) prior to co-cultivation with tumor cells. The normal macrophages, after neuraminidase treatment, no longer retained their ability to kill tumor cells. However, when macrophages from breast cancer patients were treated with NANAse, no difference was observed in the ability of untreated and NANAse treated macrophages to kill tumor cells.

Transitional mucosa and survival in human colorectal cancer

The mucosa in 100 segments of colon and rectum resected for cancer were examined using light microscopy and histochemical techniques. The extent of abnormal or transitional mucosa was defined for each case. Transitional mucosa was present in 93 of 95 adenocarcinomas and one malignant melanoma. The average total length of transitional change was 3.4 cm the maximum length was 19.5 cm. An inverse correlation was observed between the survival and the length of transitional mucosa around locally invasive (Dukes' B) carcinomas (P = 0.005). This may be related to increased amounts of sialic acid in transitional mucosa and the ability of sialic acid to depress tumor immunogenicity. The raised levels of sialic acids in transitional mucosa may have practical value in assessment of prognosis in colorectal cancer.

Serum sialic acid and CEA concentrations in human breast cancer

The concentration of bound sialic acid in the sera of 56 normal subjects and 65 subjects with breast cancer was measured, in order to determine (1) whether serum sialic acid concentrations are raised in breast cancer and (2) whether the concentration of sialic acid in serum reflects tumour stage. The amount of sialic acid in serum was compared to serum carcinoembryonic antigen (CEA) values. Urinary hydroxyproline and serum alkaline phosphatase concentrations were used as indicators of bone and liver involvement. Erythrocyte sedimentation rate (ESR) was also measured. Significantly elevated serum sialic acid concentrations were found in breast cancer, and showed correlation with tumour stage. Serum sialic acid values did not correlate with CEA values. The results suggest that measurement of serum sialic acid concentrations may be of adjunctive value in assessing tumour stage.

Serological studies of seromucoids from normal subjects and patients with malignant and non-malignant diseases

During investigations of serum from patients with carcinoma, elevated levels of two proteins were observed. The larger (MW approximately 44,000) was identified as (alpha-acid glycoprotein. The smaller MW approximately 20,000) has not yet been identified. Further investigation of alpha-acid-glycoprotein-containing seromucoid showed that many red blood cell and tissue antigens were present, for example, I, i, P1, Tja (P+P+Pk), H, A, B, Lea, Leb1, M and N. Differences in antigen content between normal serum and serum from carcinoma patients could be demonstrated quantitatively and qualitatively. Seromucoid preparations from patients with Hodgkin's lymphoma inhibited phytohaemagglutinin-induced lymphocyte transformation more often than seromucoid preparations from normal subjects.

Serum sialic acid elevations in malignant melanoma patients

Elevated membrane sialic acid (n-acetyl neuraminic acid) concentration may be a general phenomenon associated with malignant or transformed cells. In this study, sera from 30 normal persons and 25 melanoma patients were examined to determine first, if serum sialic acid elevations were associated with malignant melanoma, and second, if there was a relationship between tumor burden and serum sialic acid level. Significantly elevated sialic acid concentrations were found in the melanoma patients (p less than 0.005), and levels tended to be greater in those with a large tumor burden (p less than 0.05). Thus, increased serum sialic acid could prove to be a valuable clinical monitor of change in tumor burden as a result of therapy or change due to recurrence of disease following treatment.

Immunobiology of primary intracranial tumors. Part 3: Microcytotoxicity assays of specific immune responses of brain tumor patients

Fifty-six in vitro microcytotoxicity assays were conducted on 30 patients with intracranial tumors at various times during the postoperative course. Significant specific cellular cytotoxic responses were found in nine of 56 assays, humoral cytotoxic responses in nine of 54 assays, and host effector cell-dependent, antibody-dependent cytotoxic responses in four of 28 assays. Variables that might influence the occurrence of cytotoxicity were studied, and the relationship of these findings to other immune parameters was discussed.

Correlations among serum protein-bound carbohydrates, serum glycoproteins, lymphocyte reactivity, and tumors burden in cancer patients

Levels of glycoprotein-associated carbohydrates (neutral hexoses, hexosamine, sialic acid and fucose) were determined in the serum of patients with either local, regional or metastatic cancer, patients clinically cured of cancer, and controls (smokers and nonsmokers). Total protein-bound carbohydrates were compared with levels of 17 normal serum glycoproteins, carcinoembryonic antigen (CEA), and with lymphocyte reactivity to phytohemagglutin (PHA). Tumor burden was directly related to protein-bound carbohydrate levels in patient groups. Levels of bound carbohydrates reflect the sum of all the changes in serum glycoproteins, but primarily changes in the acute-phase proteins (alpha 1-acid glycoprotein, alpha 1-antitrypsin, haptoglobin, ceruloplasmin) found in the alpha-globulin fraction of serum. Increases in protein-bound carbohydrates in tumor-bearers were not related to increases in CEA. Increased levels of the acute-phase proteins occurred in individuals with depressed in vitro lymphocyte reactivity to PHA. A significant positive correlation was found between lymphocyte reactivity and level of alpha 2HS-glycoprotein. The results suggest that serum protein-bound carbohydrates or glycoproteins may be of adjunctive value is assessing tumor burden and immune reactivity in cancer patients.

Neuraminidase and tumor immunotherapy

Preliminary results of first clinical studies with the enzyme neuraminidase call attention to a new kind of cancer treatment. This promising approach to tumor immunotherapy was entered into the clinical phase as a consequence of successful experimental studies in tumor-bearing mice, rats and dogs. In this review, the presently known and essential results of experimental and clinical studies on tumor immunotherapy by means of neuraminidase are presented as well as some necessary and critical considerations in this context. Moreover, out of a broad variety of results of biochemical and biological in vitro studies, it was attempted to select the more essential knowledge which could contribute to a better understanding of the still rather unclear in vivo mode of action of the enzyme neuraminidase. In a first brief paragraph (1.0), the biochemically characteristic data of the enzyme neuraminidase is presented. In the second section (2.0), the basic knowledge about the effects of neuraminidase on cell behavior is rather amply contained. Here, on the one hand, the biophysical and biochemical alterations are mentioned, the so-called ""unmasking'' effects are reconsidered and, on the other hand, the effects on the immunologically responding cell are discussed. In a third section (3.0), the diverse findings from animal experiments using neuraminidase-treated tumor cells are confronted, whereby tumor transplantation experiments and tumor therapy experiments are dealt with separately. The last section (4.0) reports about the first clinical studies with neuraminidase-treated autologous as well as homologous tumor cells, which partly brought about rather surprising and astonishing success. On the basis of recent findings by the study group of the authors, the more prior and sometimes discrepant results of various groups are critically considered. The problems of alteration of antigenicity and of other properties of cells through splitting off membrane-bound neuraminic acid, the facts of adjuvanticity of neuraminidase itself, the relation of successful therapy to dose dependency as well as the relation of undesirable methods for tumor mass reduction to the immunological responsiveness of the tumor bearer were especially looked into.

The effects of neuraminidase on concanavalin A agglutination of erythrocytes: evidence for adsorption of neuraminidase to erythrocyte membrane

Neuraminidase-treated human erythrocytes, but not untreated erythrocytes, were agglutinated by concanavalin A. The degree of concanavalin A agglutinability was not directly related to sialic acid removal by neuraminidase. While maximal sialic acid release was obtained with 5 units neuraminidase/2 x10(9) erythrocytes, maximal concanavalin A agglutination was only obtained after exposure to 20 units neuramindase. Binding of 3H-concanavalin A by erythrocytes was 10-fold higher with rabbit compared to human red cells. Neuraminidase treatment of human erythrocytes caused a relative increase in 3H-concanavalin binding, but the absolute amount was still 10-fold less than that bound to rabbit erythrocytes. Specific adherence of neuraminidase to Con A-Agarose could not be demonstrated. There was no evidence for contamination of the neuraminidase preparation with proteases using a sensitive assay. These studies suggest that neuraminidase absorbs to erythrocytes by a mechanism other than removal of sialic acid.

Humoral reactions in syngeneic hosts against tumor cell surface incomplete saccharide moieties

Components on the surface of MM2 ascites mammary carcinoma cells induce agglutination factors in the serum of syngeneic host C3H/He mice, and bind the factors in vitro. These components have been classified into three groups: MM2-specific substances, mammary tumor virus (MTV)-associated substances and tumor-associated embryonic materials. The substances contained saccharide moieties and their terminal sugar residues were essential for the binding of the serum factors. These terminal saccharides were exposed during cell proliferation,but masked in stationary cells, at least partly, due to elongation of the saccahride moieits. The terminal structures of these polysaccharide moities of growing and stationary cells were studied by semiquantitative tumor cell agglutination using the agglutinating activities against MM2 cells of MM2-regressor serum and of FMA/R- and Ehrlich-regressor sera which had partial cross-agglutination activities. Agglutination by phytohemagglutinins, inhibition of the agglutination by saccharides or with isolated cell surface components and treatment of the cells with glycosidases were also used for this purpose.

CEA levels in head and neck cancer

Serum carcinoembryonic antigen (CEA) levels were determined for 439 patients with squamous carcinoma of the head and neck region, 154 healthy smokers, and 122 nonsmokers. Among nonsmokers 95% of the CEA levels did not exceed 5 ng/ml, but among smokers this discriminatory level was 7 ng/ml. Among tumor-bearing patients 36% of the CEA levels exceeded 5 ng/ml but only 17% exceeded 7 ng/ml. Both the incidence and magnitude of CEA elevations correlated with clinical stage of tumor; however, excluding patients with clinically apparent advanced malignancies, the incidence and magnitude of elevations were similar among tumor-bearing patients, tumor-free treated patients, and smokers. Although not predictive of ultimate survival, elevated preoperative CEA levels declined to the range of normals after resection. Similarly, during palliative irradiation for incurable tumors, CEA levels declined with regression of tumor. Irradiation did not nonspecifically elevate CEA levels. The data indicate that in patients with head and neck squamous carcinomas CEA level is not likely to contribute to a determination of prognosis after therapy; however, serial determinations may have adjunctive value in monitoring tumor response.

Lymphocyte stimulation by autologous tumor cells in the presence of serum from the same patient or from healthy donors

Lymphocyte blastogenesis induced by autologous tumor biopsy cells, by allogeneic lymphocytes and by PHA, was performed in the presence of autologous or allogeneic serum collected from normal blood donors. In 13 of the 15 cases lymphocyte stimulation by autologous tumor cells was inhibited in the presence of autologous serum. In contrast, autologous serum somewhat enhanced the blastogenic effect of PHA and allogeneic lymphocytes.

Immunologic approach to cancer therapy

The resistance that many cancer patients show to the progress of their disease, attested to by well documented cases of spontaneous regressions as in neuroblastoma, hypernephroma, choriocarcinoma and malignant melanoma, and the long-term dormancy of multiple metastases seen particularly after removal of a primary mass, can be explained only by host defense mechanisms. Attemps at immunotherapy over the years are reviewed and new directions are presented.