O-linked mucin-type glycoproteins in normal and malignant colon mucosa: lack of T-antigen expression and accumulation of Tn and sialosyl-Tn antigens in carcinomas

Human milk oligosaccharide 2'-fucosyllactose protects against high-fat diet-induced obesity by changing intestinal mucus production, composition and degradation linked to changes in gut microbiota and faecal proteome profiles in mice

OBJECTIVE

To decipher the mechanisms by which the major human milk oligosaccharide (HMO), 2'-fucosyllactose (2'FL), can affect body weight and fat mass gain on high-fat diet (HFD) feeding in mice. We wanted to elucidate whether 2'FL metabolic effects are linked with changes in intestinal mucus production and secretion, mucin glycosylation and degradation, as well as with the modulation of the gut microbiota, faecal proteome and endocannabinoid (eCB) system.

RESULTS

2'FL supplementation reduced HFD-induced obesity and glucose intolerance. These effects were accompanied by several changes in the intestinal mucus layer, including mucus production and composition, and gene expression of secreted and transmembrane mucins, glycosyltransferases and genes involved in mucus secretion. In addition, 2'FL increased bacterial glycosyl hydrolases involved in mucin glycan degradation. These changes were linked to a significant increase and predominance of bacterial genera Akkermansia and Bacteroides, different faecal proteome profile (with an upregulation of proteins involved in carbon, amino acids and fat metabolism and a downregulation of proteins involved in protein digestion and absorption) and, finally, to changes in the eCB system. We also investigated faecal proteomes from lean and obese humans and found similar changes observed comparing lean and obese mice.

CONCLUSION

Our results show that the HMO 2'FL influences host metabolism by modulating the mucus layer, gut microbiota and eCB system and propose the mucus layer as a new potential target for the prevention of obesity and related disorders.

Tn as a potential predictor for regional lymph node metastasis in T1 colorectal cancer

BACKGROUND

Approximately 10 percent of T1 colorectal cancer (CRC) has lymph node metastasis. In this study, we aimed to determine possible predictors for nodal involvement in order to aid selection of appropriate patients for organ-preserving strategies.

METHODS

We retrospectively reviewed CRC patients underwent radical surgery from January 2009 to December 2016, with final pathology report disclosed as T1 lesion. The paraffin-embedded samples were achieved for glycosylated proteins expression analysis by immunohistochemistry.

RESULTS

Totally, 111 CRC patients with T1 lesion were enrolled in this study. Of these patients, seventeen patients had nodal metastases, with the lymph node positive rate of 15.3%. Semiquantitative analysis of immunohistochemical results indicated that mean value of Tn protein expression in T1 CRC specimens was significantly different between patients with and without lymph node metastasis (63.6 vs. 27.4; p = 0.018).

CONCLUSIONS

Our data shown that Tn expression may be applied as a molecular predictor for regional lymph node metastasis in T1 CRC. Moreover, the organ-preserving strategy could be improved by proper classification of patients. The mechanism involved in expression of Tn glycosylation protein and CRC metastasis need further investigation.

O-GlcNAcylation: A Crucial Regulator in Cancer-Associated Biological Events

O-GlcNAcylation, a recently discovered post-translational modification of proteins, plays a crucial role in regulating protein structure and function, and is closely associated with multiple diseases. Research has shown that O-GlcNAcylation is abnormally upregulated in most cancers, promoting disease progression. To elucidate the roles of O-GlcNAcylation in cancer, this review summarizes various cancer-associated biological events regulated by O-GlcNAcylation and the corresponding signaling pathways. This work may provide insights for future studies on the function or underlying mechanisms of O-GlcNAcylation in cancer.

Identification of the Glycan Binding Profile of Human and Rodent Plasmodium Sporozoites

The transmission of Plasmodium spp. sporozoites to the mammalian host is the first step in the initiation of the mosquito-borne disease known as malaria. The exact route of transmission from the bloodstream to the liver is still not clearly elucidated, and identification of the host glycan structures bound by the sporozoites may inform as to which host cells are involved. Here, we provide a comprehensive analysis of the glycan structures that sporozoites from the human pathogen, P. falciparum, and the rodent pathogen, P. yoelii, recognize and bind. Glycan array analysis was used to profile the glycans bound by the sporozoites, and the binding affinities of these sporozoite-glycan interactions were then determined by surface plasmon resonance. Data showed that the different Plasmodium spp. bind different classes of glycans. P. falciparum was observed to bind to glycans with terminal N-acetylgalactosamine (GalNAc) or Galactose (Gal) linked to a GalNAc, and the highest-affinity observed was with the GalNAc monosaccharide (12.5 nM). P. yoelii bound glycosaminoglycans, mannosyl glycans, Gal linked to N-acetylglucosamine structures, and the αGal epitope. The highest-affinity interaction for P. yoelii was with the αGal epitope (31.4 nM). This is the first study to identify the key host glycan structures recognized by human and rodent Plasmodium spp. sporozoites. An understanding of how Plasmodium sporozoites interact with the specific glycan structures identified here may provide further insight into this infectious disease that could help direct the design of an effective therapeutic.

Tn Antigen Expression Defines an Immune Cold Subset of Mismatch-Repair Deficient Colorectal Cancer

Colorectal cancer (CRC) cells often express Tn antigen, a tumor-associated truncated immature O-glycan (GalNAcα-O-Ser/Thr) that can promote tumor progression. Immunotherapies against Tn antigen have been developed and are being evaluated in clinical trials. Tn antigen can also be considered a novel immune checkpoint that induces immunosuppressive signaling through glycan-biding lectins to lead effector T cell apoptosis. We evaluated the correlation of Tn antigen expression by immunohistochemistry with mismatch-repair (MMR) status, tumor-infiltrating lymphocytes, tumor cell PD-L1 expression, and clinicopathological characteristics in 507 CRC patients. Although 91.9% of CRCs showed negative or weak Tn antigen staining (Tn-negative/weak), we identified a small subset of CRCs (8.1%) that displayed particularly intense and diffuse distribution of Tn antigen immunoreactivity (Tn-strong) that closely related to deficient MMR (dMMR). Moreover, 40 dMMR CRCs were stratified into 24 Tn-negative/weak dMMR tumors (60.0%) exhibiting dense CD8+ lymphocyte infiltrate concomitant with a high rate of PD-L1 positivity, and 16 Tn-strong dMMR tumors (40.0%) that demonstrated CD8+ T cell exclusion and a lack of PD-L1 expression, which was comparable to those of proficient MMR. Our finding suggests that the immune cold subset of patients with Tn-strong dMMR CRC may be effectively treated with immune checkpoint blockade therapy or cellular immunotherapy targeting Tn antigen.

Shigella flexneri Targets Human Colonic Goblet Cells by O Antigen Binding to Sialyl-Tn and Tn Antigens via Glycan-Glycan Interactions

Shigella flexneri targets colonic cells in humans to initiate invasive infection processes that lead to dysentery, and direct interactions between their lipopolysaccharide O antigens and blood group A related glycans are involved in the cell adherence interactions. Here, we show that treatment with Tn and sialyl-Tn glycans, monoclonal antibodies and lectins reactive to Tn/sialyl-Tn, and luteolin (a Tn antigen synthesis inhibitor) all significantly inhibited S. flexneri adherence and invasion of cells in vitro. Surface plasmon resonance analysis showed that lipopolysaccharide O antigen had a high affinity interaction with Tn/sialyl-Tn. Immunofluorescence probing of human colon tissue with antibodies detected expression of Tn/sialyl-Tn by MUC2 producing goblet cells (GCs), and S. flexneri incubated with human colon tissue colocalized with GCs. Our findings demonstrate that S. flexneri targets GCs in the human colonic crypts via glycan-glycan interactions, establishing new insight into the infection process in humans.

Tn and Sialyl-Tn antigens in canine gastric tissues

Malignant transformation is often associated with abnormal protein glycosylation expressed, amongst others, by the accumulation of simple mucin-type carbohydrates namely Tn and Sialyl-Tn (STn) antigens. These are usually limited in normal tissues and their increased expression has been associated with cancer progression and poor prognosis. This study aims to evaluate the role of Tn and STn antigens in the neoplastic transformation of the canine gastric mucosa and to correlate their putative immunoexpression alterations with some pathological features. Tn and STn antigens expression were immunohistochemically evaluated in canine normal gastric mucosa (n = 3), gastric polyps (n = 9) and gastric carcinomas (n = 25), neoplastic emboli (n = 12) and metastases (n = 8). In normal gastric mucosa, Tn antigen was detected in the gastric epithelial cells, while STn antigen was absent. Similarly, all gastric polyps expressed Tn antigen, but none displayed STn antigen immunostaining. In carcinomas, Tn antigen was expressed in 96% of the cases and STn antigen in 68% of the neoplasms. STn antigen was significantly higher in carcinomas compared with normal mucosa (P < .05). No correlation was found between each antigen and the different subtypes of tumours according to WHO classification, tumour differentiation, lymph vascular invasion or metastasis. All neoplastic emboli expressed both antigens, and the expression score was similar or higher than that displayed by the neoplastic cells of the primary tumour. The high prevalence of STn antigen in gastric carcinomas compared with normal mucosa highlights the cancer-associated nature of this antigen. Our results link STn antigen expression to neoplastic transformation and suggest that it may be a useful marker of gastric cancer progression in dogs.

Aberrant O-glycosylation contributes to tumorigenesis in human colorectal cancer

Aberrant O‐glycosylation is frequently observed in colorectal cancer (CRC) patients, but it is unclear if it contributes intrinsically to tumorigenesis. Here, we investigated the biological consequences of aberrant O‐glycosylation in CRC. We first detected the expression profile of Tn antigen in a serial of human CRC tissues and then explored the genetic and biosynthetic mechanisms. Moreover, we used a human CRC cell line (LS174T), which express Tn antigen, to assess whether aberrant O‐glycosylation can directly promote oncogenic properties. It showed that Tn antigen was detected in around 86% human primary and metastatic CRC tissues. Bio‐functional investigations showed that T‐synthase and Cosmc were both impaired in cancer tissues. A further analysis detected an occurrence of hypermethylation of Cosmc gene, which possibly caused its loss‐of‐function and a consequent inactive T‐synthase. Transfection of LS174T cells with WT Cosmc restored mature O‐glycosylation, which subsequently down‐regulated cancer cell proliferation, migration and apoptotic‐resistant ability. Significantly, the expression of MUC2, a heavily O‐glycosylated glycoprotein that plays an essential role in intestinal function, was uniformly reduced in human CRC tissues as well as in LS174T cells. These data suggest that aberrant O‐glycosylation contributes to the development of CRC through direct induction of oncogenic properties in cancer cells.

N-(2-Hydroxypropyl)methacrylamide Copolymer-9-Aminocamptothecin Conjugate: Colon-Specific Drug Delivery in Rats

An N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugate containing 9-aminocamptothecin (9-AC) boundvia a spacer containing an aromatic azo bond and leucylalanine (P-Azo-Leu-Ala-9-AC) was synthesized. The in vivo pharmacokinetic profile after oral administration was examined in rats and comparedto free 9-AC. The aromatic azo bond of P-Azo-Leu-Ala-9-AC was stable in stomach and small intestine; the delivery of a large amount of intact conjugate to the colon was achieved. In the colon, the azoreductase activity first cleaved the azo bond followed by peptidase catalyzed cleavage of the leucylalanyl drug derivative resulting in the release of free 9-AC. However, the release rate from the conjugate was not fast enough to achieve high colon concentrations of free 9-AC. The results of the study suggest design features for the second generation of conjugates, including the use of a side-chain with a higher cleavage rate in the colon, combined with the incorporation of bioadhesion technology, to increase colon transit time.

Mucins and associated glycan signatures in colon adenoma-carcinoma sequence: Prospective pathological implication(s) for early diagnosis of colon cancer

Development of biomarkers that detect early stage resectable premalignant lesions of colon can provide critical aid in the prevention of colorectal cancer. Recent lines of evidence suggest the utility of mucin expression to predict malignant transformation of colon pre-neoplastic lesions. In this study, we investigated the combined expression of multiple mucins and mucin-associated glycans during the adenoma-carcinoma sequence of colon cancer progression. Further, we evaluated their applicability as markers for differentiating adenomas/adenocarcinomas from hyperplastic polyps. Immunohistochemical analyses performed on colon disease tissue microarrays revealed downregulation of MUC2 and MUC4 expression (p < 0.0001) while MUC1 and MUC5AC expressions were upregulated (p = 0.01) during adenoma-adenocarcinoma progression. Expression of MUC17 was downregulated in inflamed tissues compared to normal tissues, but its increased expression differentiated adenomas (p = 0.0028) and adenocarcinomas (p = 0.025) from inflammation. Glycan epitope-Tn/STn on MUC1 showed higher expression in hyperplastic polyps (p = 0.023), adenomas (p = 0.042) and adenocarcinomas (p = 0.0096) compared to normal tissues. Multivariate regression analyses indicated that a combination of MUC2, MUC5AC, and MUC17 could effectively discriminate adenoma-adenocarcinoma from hyperplastic polyps. Altogether, a combined analysis of altered mucins and mucin-associated glycans is a useful approach to distinguish premalignant/malignant lesions of colon from benign polyps.

The Cosmc connection to the Tn antigen in cancer

The Tn antigen is a tumor-associated carbohydrate antigen that is not normally expressed in peripheral tissues or blood cells. Expression of this antigen, which is found in a majority of human carcinomas of all types, arises from a blockage in the normal O-glycosylation pathway in which glycans are extended from the common precursor GalNAcα1-O-Ser/Thr (Tn antigen). This precursor is generated in the Golgi apparatus on newly synthesized glycoproteins by a family of polypeptide α-N-acetylgalactosaminyltransferases (ppGalNAcTs) and then extended to the common core 1 O-glycan Galβ1-3GalNAcα1-O-Ser/Thr (T antigen) by a single enzyme termed the T-synthase (core 1 β3-galactosyltransferase or C1GalT). Formation of the active form of the T-synthase requires a unique molecular chaperone termed Cosmc, encoded by Cosmc on the X-chromosome (Xq24 in humans, Xc3 in mice). Cosmc resides in the endoplasmic reticulum (ER) and prevents misfolding, aggregation, and proteasome-dependent degradation of newly synthesized T-synthase. Loss of expression of active T-synthase or Cosmc can lead to expression of the Tn antigen, along with its sialylated version Sialyl Tn antigen as observed in several cancers. Both genetic and epigenetic pathways, in addition to potential metabolic regulation, can result in abnormal expression of the Tn antigen. Engineered expression of the Tn antigen by disruption of either C1GalT (T-syn) or Cosmc in mice is associated with a tremendous range of pathologies and engineered expression of the Tn antigen in mouse embryos leads to embryonic death. Studies indicate that many membrane glycoproteins expressing the Tn antigen and/or truncated O-glycans may be dysfunctional, due to degradation and/or misfolding. Thus, expression of normal O-glycans is associated with health and homeostasis whereas truncation of O-glycans, e.g. the Tn and/or Sialyl Tn antigens is associated with cancer and other pathologies.

Tn and sialyl-Tn antigens, aberrant O-glycomics as human disease markers

In many different human disorders, the cellular glycome is altered. An interesting but poorly understood alteration occurs in the mucin-type O-glycome, in which there is aberrant expression of the truncated O-glycans Tn (GalNAcα1-Ser/Thr) and its sialylated version sialyl-Tn (STn) (Neu5Acα2,6GalNAcα1-Ser/Thr). Both Tn and STn are tumor-associated carbohydrate antigens and tumor biomarkers, since they are not expressed normally and appear early in tumorigenesis. Moreover, their expression is strongly associated with poor prognosis and tumor metastasis. The Tn and STn antigens are also expressed in other human diseases and disorders, such as Tn syndrome and IgA nephropathy. The major pathological mechanism for expression of the Tn and STn antigens is compromised T-synthase activity, resulting from alteration of the X-linked gene that encodes for Cosmc, a molecular chaperone specifically required for the correct folding of T-synthase to form active enzyme. This review will summarize our current understanding of the Tn and STn antigens in terms of their biochemistry and role in pathology.

Essence of affinity and specificity of peanut agglutinin-immobilized fluorescent nanospheres with surface poly(N-vinylacetamide) chains for colorectal cancer

We have designed a novel colonoscopic imaging agent that is composed of submicron-sized fluorescent polystyrene nanospheres with two functional groups - peanut agglutinin (PNA) and poly(N-vinylaceamide) (PNVA) - on their surfaces. PNA is a targeting moiety that binds to β-d-galactosyl-(1-3)-N-acetyl-d-galactosamine (Gal-β(1-3)GalNAc), which is the terminal sugar of the Thomsen-Friedenreich antigen that is specifically expressed on the mucosal side of colorectal cancer cells; it is anchored on the nanosphere surface via a poly(methacrylic) acid (PMAA) linker. PNVA is immobilized to enhance the specificity of PNA by reducing nonspecific interactions between the imaging agent and normal tissues. The essential nature of both functional groups was evaluated through in vivo experiments using PNA-free and PNVA-free nanospheres. The imaging agent recognized specifically tumors on the cecal mucosa of immune-deficient mice in which human colorectal cancer cells had been implanted; however, the recognition capability disappeared when PNA was replaced with wheat germ agglutinin, which has no affinity for Gal-β(1-3)GalNAc. PNA-free nanospheres with exclusively surface PNVA chains rarely adhered to the cecal mucosa of normal mice that did not undergo the cancer cell implantation. In contrast, there were strong nonspecific interactions between normal tissues and PNA-free nanospheres with exclusively surface PMAA chains. In vivo data proved that PNA and PNVA were essential for biorecognition for tumor tissues and a reduction of nonspecific interactions with normal tissues, respectively.

A potential of peanut agglutinin-immobilized fluorescent nanospheres as a safe candidate of diagnostic drugs for colonoscopy

We designed peanut agglutinin (PNA)-immobilized fluorescent nanospheres as a non-absorbable endoscopic imaging agent capable of being administered intracolonically. Following our previous researches with evidence that the imaging agent recognized small-sized colorectal tumors on the mucosal surface with high affinity and specificity in animal experiments, a potential of this nanoprobe as a drug candidate was evaluated from a safety perspective. The imaging agent detects colorectal tumors through recognition of the tumor-specific antigen by PNA immobilized on the nanosphere surface, and the detection is made via the fluorescent signal derived from coumarin 6 encapsulated into the nanosphere core. The stability studies revealed that the high activity of PNA was maintained and there was no significant leakage of coumarin 6 after intracolonic administration of the imaging agent. Cytotoxicity studies indicated that no local damage to the large intestinal membrane was induced by the imaging agent. Further, in vitro and in vivo permeation studies demonstrated that there was no significant permeation of the imaging agent through the monolayer of cultured cells and that the imaging agent administered locally to the luminal side of the large intestine was almost completely recovered from the administration site. Therefore, we concluded that the imaging agent is a safe and stable probe which remains in the large intestine without systemic exposure.

Immunohistochemical examination of anti-STn monoclonal antibodies LLU9B4, B72.3, and B35.2 for their potential use as tumor markers

PURPOSE

Several investigators, including ourselves, have demonstrated by immunohistochemistry that in malignancy of colon, the tumor cells or cells adjacent to the tumor become reactive with anti-STn monoclonal antibodies, while in normal individuals the colonic cells do not react with anti-STn monoclonal antibodies. In the present study, an anti-STn monoclonal antibody LLU9B4 was generated in the laboratory by immunization of mice with STn extracted from LS174T, along with commercially available B72.3 and B35.5 anti-STn monoclonal antibodies for their sensitivity in staining colon cancer sections.

RESULT

The results showed that 83.3% stained positive with 9B4 and 66.6% with B72.3, and there was no staining with B35.5 monoclonal antibody. The positive staining was mainly in the cells adjacent to colon cancer. It was also observed that the staining with LLU9B4 was much more pronounced than with B72.3.

CONCLUSION

Our study indicates that these antibodies may at least be more sensitive and specific for colon cancers than the current standard of care, FOBT.

Lewis x is highly expressed in normal tissues: a comparative immunohistochemical study and literature revision

An immunohistochemical analysis was employed to determine the expression of carbohydrate antigens associated to mucins in normal epithelia. Tissue samples were obtained as biopsies from normal breast (18), colon (35) and oral cavity mucosa (8). The following carbohydrate epitopes were studied: sialyl-Lewis x, Lewis x, Lewis y, Tn hapten, sialyl-Tn and Thomsen-Friedenreich antigen. Mucins were also studied employing antibodies against MUC1, MUC2, MUC4, MUC5AC, MUC6 and also normal colonic glycolipid. Statistical analysis was performed and Kendall correlations were obtained. Lewis x showed an apical pattern mainly at plasma membrane, although cytoplasmic staining was also found in most samples. TF, Tn and sTn haptens were detected in few specimens, while sLewis x was found in oral mucosa and breast tissue. Also, normal breast expressed MUC1 at a high percentage, whereas MUC4 was observed in a small number of samples. Colon specimens mainly expressed MUC2 and MUC1, while most oral mucosa samples expressed MUC4 and MUC1. A positive correlation between MUC1VNTR and TF epitope (r=0.396) was found in breast samples, while in colon specimens MUC2 and colonic glycolipid versus Lewis x were statistically significantly correlated (r=0.28 and r=0.29, respectively). As a conclusion, a defined carbohydrate epitope expression is not exclusive of normal tissue or a determined localization, and it is possible to assume that different glycoproteins and glycolipids may be carriers of carbohydrate antigens depending on the tissue localization considered.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.

The immunoexpression of Tn, sialyl-Tn and T antigens in chronic active gastritis in relation to Helicobacter pylori infection

The simple mucin-type carbohydrate antigens Tn, sialyl-Tn and T represent the mucin core oligosaccharide structures that are produced in the initial steps of mucin biosynthetic pathway. Utilising monoclonal antibodies anti-Tn antigen, anti-sialyl-Tn antigen and anti-T antigen, we have investigated the expression of the simple mucin-type carbohydrate antigens in 47 biopsy specimens of antral mucosa with chronic active gastritis, 25 of which had Helicobacter pylori infection. The Tn immunoreactivity, localised at the supranuclear region of surface and glandular mucous cells, was observed in all samples, independently from H. pylori status. The sialyl-Tn antigen, mainly localised in the cytoplasm of glandular mucous cells and in goblet cells vacuoles, was seen in 56% of the cases with H. pylori infection and in 41% of the cases in the H. pylori-negative group. In addition, the T antigen was found in the cytoplasm of surface and glandular mucous cells in 16% of the H. pylori-positive group, whereas the percentage of positive cases was reduced to 5% in H. pylori-negative patients, with an exclusive localisation in the cytoplasm of glandular mucous cells; after neuraminidase treatment, the percentage of T antigen-positive cases was increased to 28% in H. pylori-positive cases and to 27% in negative cases. No significant relationships between H. pylori infection and Tn, sialyl-Tn or T antigen immunoexpression were encountered in our cases. Therefore, we maintain that the inflammatory infiltrate may itself play an important role in the expression of simple mucin-type carbohydrate antigens in chronic active antral gastritis.

Altered GalNAc-alpha-2,6-sialylation compartments for mucin-associated sialyl-Tn antigen in colorectal adenoma and adenocarcinoma

Sialyl-Tn (STn), a mucin-associated disaccharide antigen carried by apomucins such as MUC2, plays an important role in tumor biology. However, little is known about the subcellular localization and compartments involved in STn synthesis. In this study we used immunoelectron microscopy to localize STn and MUC2 apomucin in human colorectal tissues. MUC2 apomucin was localized predominantly in the rough endoplasmic reticulum (RER) in normal colorectal mucosa (n=6), colorectal adenoma (n=8), and colorectal adenocarcinoma (n=10). STn, recognized by monoclonal antibody TKH2, was not readily detectable in normal colorectal mucosa but becomes manifest in both trans-Golgi apparatus and mucin droplets in colorectal adenoma. In colorectal adenocarcinoma, STn was localized not only in late but also in early Golgi compartments, and particularly in some RER lumens. Furthermore, electron microscopic in situ hybridization revealed that gold particles representing MUC2 mRNA are primarily localized over the RER. Our findings indicate that in colorectal adenoma STn sialylation takes place in the trans-Golgi apparatus, whereas in colorectal cancer STn sialylation occurs in all the Golgi compartments and in the RER.

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.

Sialyltransferases in cancer

It has long been known that cancer cells often express more heavily sialylated glycans on their surface and that this feature sometimes correlates with invasion. It is now well established that specific sialylated structures, such as the Thomsen-Friedenreich-related antigens, the sialyl Lewis antigens, the sialyl alpha2-6 lactosaminyl structure, the polysialic acid or some gangliosides, can mediate cellular interactions and are altered in cancer cells. This review summarizes the current knowledge on the cancer-associated alterations in sialyltransferase expression which are often at the basis of the deranged expression of sialylated structures.

Biorecognizable HPMA copolymer-drug conjugates for colon-specific delivery of 9-aminocamptothecin

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates for colon-specific delivery of 9-aminocamptothecin (9-AC) were designed. They hold 9-AC bound via spacers containing amino acid residues and aromatic azo bonds. In vitro release profiles of 9-AC from HPMA copolymer conjugates were evaluated under artificial conditions that simulated large intestinal azoreductase and peptidase activities. The studies indicated that the azo bond was reduced first, followed by the release of unmodified 9-AC from the 9-AC containing fragment by peptidases. Release profiles depended on the chemical structure of the peptide part of the spacer. Conjugates containing leucylalanine showed high colon-specific release of 9-AC when compared to alanine containing conjugates. It appears that the studied conjugates are suitable as colon-specific drug delivery systems.

Potential of lectin-N-(2-hydroxypropyl)methacrylamide copolymer-drug conjugates for the treatment of pre-cancerous conditions

N-(2-Hydroxypropyl)methacrylamide (HPMA)-lectin (wheat germ agglutinin (WGA), peanut agglutinin (PNA)) drug conjugates for treatment of the pre-cancerous conditions ulcerative colitis and Barrett's esophagus are being developed. Cell-surface glycoproteins that are altered in disease and development bind lectins. PNA binds alpha-lactose and the Thomsen-Friedenreich (TF) antigen, a disease- and development-associated glycoprotein. PNA incorporation in conjugates may allow for preferential delivery to diseased over healthy tissues. Conjugates were prepared by attaching lectins to HPMA copolymers via an amide linkage. Frontal affinity chromatography was used to measure dissociation constants (K(d)) of free and conjugated lectins. Animal models of colitis (DSS, TNBS/EtOH) were developed. Human biopsy specimens were obtained. Free and HPMA copolymer-conjugated FITC-labeled lectin and anti-TF antigen antibody binding patterns were examined in normal neonatal, adult and diseased rodent tissues and normal and diseased human tissues. K(d) values of free and conjugated lectins were similar ( approximately 10(-5) M(-1)). Free and conjugated lectins had comparable binding patterns. In health, strong WGA binding was seen in goblet cells; PNA binding was minimal, occurring only in the supranuclear goblet cell region. In disease, WGA binding was not altered, but PNA binding was increased in both human and rodent tissues; entire goblets bound the lectin. Anti-TF antigen antibody binding was minimal, but did overlap with PNA binding patterns both in normal and diseased tissues. Conjugation of lectins to HPMA copolymers does not affect binding affinity. Alterations in glycoprotein structures in development and disease resulted in modified lectin binding patterns. In development and disease, the PNA binding seen was to the TF antigen and other lactose-containing glycoproteins. The results suggest that site-specific delivery of therapeutic agents such as cyclosporin A (CsA) for ulcerative colitis and mesochlorin e(6) for Barrett's esophagus may be achieved. P(HPMA)-lectin-CsA conjugates have been prepared and preliminary in vivo studies are underway.

Altered mucin expression in the gastrointestinal tract: a review

Early studies of changes in mucin expression in disorders of the gastrointestinal tract focused on alterations in the carbohydrate chain. This review briefly considers the various mechanisms by which such alterations may come about: (a) normal variation, (b) sialic acid alterations, (c) defective assembly of carbohydrate side-chains, (d) changed expression of core proteins and (e) epithelial metaplasia. The availability of monoclonal antibodies to mucin core proteins adds a new dimension to mucin histochemistry. It is now possible to offer explanations for traditional mucin histochemical findings on the basis of lineage-specific patterns of mucin core protein expression. Changes in core protein expression are described in inflammatory, metaplastic and neoplastic disorders of the gastrointestinal tract. The possibility that mucin change could be important in the aetiology of some diseases such as ulcerative colitis and H. pylori gastritis is considered. It is more probable, however, that changes in mucin expression are secondary to reprogramming of cellular differentiation and altered cell turnover. As such they may serve as markers to explain pathogenesis and provide novel diagnostic and prognostic information.

Biorecognition of HPMA copolymer-lectin conjugates as an indicator of differentiation of cell-surface glycoproteins in development, maturation, and diseases of human and rodent gastrointestinal tissues

Lectins are proteins that bind glycoproteins; binding patterns are altered with changes in glycoprotein expression accompanying maturation or disease. Binding of two lectins, wheat germ agglutinin (WGA) and peanut agglutinin (PNA), in human and rodent colon were previously examined. Normal tissue showed intense WGA binding; PNA binding was minimal. Diseased tissues showed increased PNA binding. We hypothesized that N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-lectin-drug conjugates could deliver therapeutic agents to diseased tissues by targeting colonic glycoproteins. We examined biorecognition of free and HPMA copolymer-conjugated WGA and PNA and anti-Thomsen-Friedenreich (TF) antigen antibody binding in normal neonatal, adult, and diseased rodent tissues, human specimens of inflammation, and Barrett's esophagus. Neonatal WGA binding was comparable to the adult, with additional luminal columnar cell binding. PNA binding was more prevalent; luminal columnar cell binding existed during the first 2.5 weeks of life. WGA binding was strong in both normal and diseased adult tissues; a slight decrease was noted in disease. PNA binding was minimal in normal tissues; increases were seen in disease. Anti-TF antigen antibody studies showed that PNA did not bind to the antigen. The results suggest that HPMA copolymer-lectin-drug conjugates may provide site-specific treatment of conditions such as colitis and Barrett's esophagus.

Pathways of O-glycan biosynthesis in cancer cells

Glycoproteins with O-glycosidically linked carbohydrate chains of complex structures and functions are found in secretions and on the cell surfaces of cancer cells. The structures of O-glycans are often unusual or abnormal in cancer, and greatly contribute to the phenotype and biology of cancer cells. Some of the mechanisms of changes in O-glycosylation pathways have been determined in cancer model systems. However, O-glycan biosynthesis is a complex process that is still poorly understood. The glycosyltransferases and sulfotransferases that synthesize O-glycans appear to exist as families of related enzymes of which individual members are expressed in a tissue- and growth-specific fashion. Studies of their regulation in cancer may reveal the connection between cancerous transformation and glycosylation which may help to understand and control the abnormal biology of tumor cells. Cancer diagnosis may be based on the appearance of certain glycosylated epitopes, and therapeutic avenues have been designed to attack cancer cells via their glycans.

Comparison of glycoprotein expression between ovarian and colon adenocarcinomas

OBJECTIVE

Tumor-associated antigens may be expressed as surface glycoproteins. These molecules undergo qualitative and quantitative modifications during cell differentiation and malignant transformation. During malignant transformation, incomplete glycosylation is common, and certain glycosylation pathways are preferred. These antigens might help distinguish between ovarian and colonic adenocarcinomas in the primary and metastatic lesions. Different cytokeratins have been proposed as relatively organ-specific antigens.

DESIGN

We used monoclonal antibodies against T1, Tn, sialosyl-Tn, B72.3, CA125, carcinoembryonic antigen, and cytokeratins 7 and 20 to detect tumor-associated glycoproteins and keratin proteins in ovarian and colonic carcinomas.

RESULTS

CA125, carcinoembryonic antigen, and cytokeratins 7 and 20 can distinguish between colonic and serous or endometrioid adenocarcinomas of the ovary in both primary and metastatic lesions. Mucinous ovarian adenocarcinomas differed in that they express carcinoembryonic antigen and cytokeratins 7 and 20 and weakly express CA125. The other glycoprotein antigens were equally expressed by ovarian and colonic adenocarcinomas and therefore were of no use in distinguishing between these 2 entities.

CONCLUSION

A panel of monoclonal antibodies against cytokeratins 7 and 20 antigens, CA125, and carcinoembryonic antigen is useful in differentiating serous and endometrioid adenocarcinomas of the ovary from colonic adenocarcinomas. Mucinous ovarian adenocarcinomas cannot be distinguished from colonic adenocarcinomas using immunohistochemistry.

Differential expression of the cancer associated antigens T (Thomsen-Friedenreich) and Tn to the skin in primary and metastatic carcinomas

AIM

To study the immunohistochemical expression of the Thomsen-Friedenreich antigen (T) and its precursor, Tn, in the skin in various cancers.

METHODS

T and Tn antigens were studied with monoclonal antibodies in 91 primary premalignant and malignant lesions, 13 cases of Paget's disease, and 26 carcinomas metastatic to the skin. The material had been collected over a 10 year period, formalin fixed, and paraffin embedded. Diagnoses had been made after examination of standard histological sections, supplemented when needed by appropriate immunohistochemical staining.

RESULTS

21% and 29% of the primary cutaneous premalignant and malignant epithelial tumours expressed the Tn and T antigens, respectively. By contrast, 81% of metastatic carcinomas to the skin were Tn positive, while only 23% of them expressed the T antigen. All cases of Paget's disease were Tn positive but only 15% of them expressed the T antigen. The 21 nonepithelial tumours (including melanomas) were as a rule unreactive.

CONCLUSIONS

The accumulation of the precursor (Tn) antigen in tumours metastasising to the skin highlights the incomplete glycosylation of carbohydrate antigens occurring in these tumours. The predominant Tn versus T antigen expression appears to be a useful immunohistochemical feature which may aid in the differentiation of primary cutaneous carcinomas from metastatic tumours.

Enzymatic basis for sialyl-Tn expression in human colon cancer cells

Sialyl-Tn antigen (SAalpha2-6 GalNAc alpha-Ser/Thr) is expressed as a cancer-associated antigen on the surface of cancer cells and its expression correlates with a poor prognosis in patients with colorectal and other adenocarcinomas. To understand the enzymatic basis of sialyl-Tn (STn) antigen expression, we used two clonal cell lines, LSB and LSC, derived from LS174T human colonic cancer cells. LSC cells express only the truncated carbohydrate antigen Tn (GalNAc alpha-Ser/Thr) and sialyl-Tn on their mucin molecules, whereas LSB cells express elongated oligosaccharide chains. Both cell lines demonstrated similar activities of glycosyltransferases involved in the biosynthesis of elongated and terminal structures of complex O-glycans. However, LSC cells were unable to synthesize core 1 (Gal beta1-3GalNAc-) because the ubiquitous enzyme activity of UDP-Gal:GalNAc-R beta3-Gal-transferase (core 1 beta3-Gal-transferase) was lacking. Core 1 beta3-Gal-transferase could not be reactivated in LSC cells by treatment with sodium butyrate or by in vivo growth of LSC cells in nude mice. In contrast, LSB cells were able to synthesize and process core 1 and core 2 (GlcNAc beta1-6 (Gal beta1-3) GalNAc-). LSC cells represent the first example of a non-hematopoietic cell line which lacks core 1 beta3-Gal-transferase activity. The lack of core 1 beta3-Gal-transferase in LSC cells explains why they are incapable of forming the common mucin O-glycan core structures and are committed to synthesizing the short Tn and STn oligosaccharides. These findings suggest that the activity of core 1 beta3-Gal-transferase is an important determinant of the STn phenotype of colon cancer cells.

Invasion potential and N-acetylgalactosamine expression in a human melanoma model

Reactivity of the N-acetylgalactosamine-binding Helix pomatia agglutinin (HPA) in tumours has been associated with poor prognosis and metastasis development. In our LOX/FEMX-I human melanoma model, the binding of HPA correlates with experimental lung metastasis formation in athymic nude mice. In the present study, the metastatic potential of 2 human melanoma cell lines (LOX and FEMX-I) was assessed in relation to carbohydrate and invasive phenotype. Immunocytological and invasion assays highlighted significant differences between these 2 cell lines. Immuno-cytochemical analysis confirmed the widespread expression of HPA-binding glycoconjugates on LOX but not FEMX-I cells. One of these HPA-binding glycoconjugates, the Tn antigen, was expressed highly on the surface of LOX cells but only weakly in the cytoplasm of FEMX-I cells. The sialyl Tn antigen was expressed in FEMX-I but not in LOX cells. There was no difference between the cell lines in adhesion/rate of trapping in athymic nude mouse lung tissues. In Matrigel invasion assays, LOX cells demonstrated an invasion potential more than 6 times greater than that observed with FEMX-I cells. Matrigel invasion of LOX cells was inhibited after incubation with HPA (89%) compared to controls with HPA and GalNAc blocking sugar or without HPA (p < 0.0005 at 5 df). In contrast, there was no inhibitory effect with the anti-Tn antibody IE3. Invasion of FEMX-I cells was not affected by the lectin and the IE3 antibody. Immuno-cytochemical analysis revealed expression of the terminal galactose- and polylactosamine-binding lectin galectin 3 (Mac-2) in these melanoma cell lines. Expression of both the lectin and its receptor may be a contributory feature in the pulmonary invasion of LOX melanoma cells. Overall, our findings suggest that HPA-binding glycoconjugates other than the alphaGalNAc-O-Ser/Thr of the Tn antigen may be important in the extracellular matrix invasion of LOX melanoma cells.

Development and characterization of an antibody directed to an alpha-N-acetyl-D-galactosamine glycosylated MUC2 peptide

In an attempt to raise anti-Tn antibodies, an alpha-N-acetyl-D-galactosamine glycosylated peptide based on the tandem repeat of the intestinal mucin MUC2 was used as an immunogen. The MUC2 peptide (PTTTPISTTTMVTPTPTPTC) was glycosylated in vitro using concentrated alpha-N-acetylgalactosaminyltransferases activity from porcine submaxillary glands which resulted in the incorporation of 8-9 mol of Ga/NAc. Rabbits and mice developed specific anti-MUC2-GalNAc glycopeptide antibodies and no detectable anti-Tn antibodies. Anti-glycopeptide antibodies did not show reactivity with the unglycosylated MUC2 peptide or with other GalNAc glycosylated peptides. A mouse monoclonal antibody (PMH1) representative of the observed immune response was generated and its immunohistological reactivity analysed in normal tissues. PMH1 reacted similarly to other anti-MUC2 peptide antibodies. However, in some cells the staining was not restricted to the supranuclear area but extended to the entire cytoplasm. In addition, PMH1 reacted with purified colonic mucin by Western blot analysis suggesting that PMH1 reacted with some glycoforms of MUC2. The present work presents a useful approach for development of anti-mucin antibodies directed to different glycoforms of individual mucins.

Peanut ingestion increases rectal proliferation in individuals with mucosal expression of peanut lectin receptor

BACKGROUND & AIMS

The Thomsen-Friedenreich blood group antigen (galactose beta 1,3-N-acetyl galactosamine alpha-) acts as an oncofetal antigen in the colonic epithelium, with low expression in normal adult epithelia but increasing to fetal levels of expression in hyperplasia or malignancy. Peanut lectin is one of the commonest dietary lectins that binds this antigen. The aim of this study was to determine whether peanut ingestion can alter rectal epithelial proliferation.

METHODS

Thirty-six patients with normal colonic mucosa consumed 100 g of peanuts each day for 5 days. Rectal mitotic index was measured before and after ingestion, and changes in proliferation were correlated with immunohistochemical detection of lectin receptor expression by colonocytes and fecal lectin activity as measured by hemagglutination assay.

RESULTS

Peanut ingestion caused a 41% increase in rectal mucosal proliferation in individuals with macroscopically normal mucosa who express TF antigen in their rectal mucosae (10 of 36 patients studied). The proliferative response correlated with fecal hemagglutinating activity, and peanut lectin could be shown immunohistochemically within the rectal mucosa.

CONCLUSIONS

The common expression of galactose beta 1,3-N-acetyl galactosamine alpha- by hyperplastic and neoplastic epithelia may therefore be functionally important because it allows interaction with mitogenic dietary lectins. This could be an important mechanism for the association between diet and colorectal cancer.

The prognostic significance of sialyl-Tn antigen in women treated with breast carcinoma treated with adjuvant chemotherapy

BACKGROUND

Sialyl-Tn (STn) represents an aberrantly glycosylated mucin epitope that is expressed in breast carcinoma and other adenocarcinomas and is an important factor in the development of novel immunotherapeutic approaches. The primary aim of the current study was to investigate the influence of STn expression on the prognoses of patients with breast carcinoma.

METHODS

A cohort of 207 women diagnosed with invasive breast carcinoma who were treated with anthracycline-containing adjuvant chemotherapy and were enrolled in a randomized clinical trial were studied. Expression of STn was determined by an immunohistochemical procedure in which the B72.3 monoclonal antibody was used. Kaplan-Meier and Cox proportional regression survival analyses were used to compare low STn and high STn patients.

RESULTS

Forty-eight (23%) of the 207 specimens demonstrated high STn staining (>25% cells were immunoreactive). During a median follow-up of 5 years, high STn patients had worse disease free survival than low STn patients (55% vs. 74%, respectively; P = 0.03). High STn expression was significantly associated with age (P = 0.04) but not with other conventional prognostic markers. In multivariate analysis using the Cox regression model, high STn emerged as an independent prognostic indicator for disease free survival (hazard ratio [HR], 2.02; 95% confidence interval [CI], 1.09-3.73) and for overall survival (HR, 2.16; 95% CI, 0.95-4.92).

CONCLUSIONS

The results of this study suggest that STn may be a valuable marker for identifying women at high risk of developing recurrent breast carcinoma who may be candidates for trials investigating new therapies in combination with standard adjuvant therapy.

Different expressions of sialyl Tn antigen between polypoid and flat-type early colorectal cancers

PURPOSE

Sialyl Tn (STn) antigen is a cancer-associated carbohydrate antigen expressed in cancers of the digestive tract. We compared the proportion of specimens of flat-type colorectal cancers expressing STn with that of polypoid cancers, by examining the immunohistochemical reactivity of STn in various morphologic types of early and advanced colorectal cancers.

METHODS

A total of 111 biopsies from the colorectal area were examined for STn expression, including 11 adenomas, 58 early cancers, and 42 advanced cancers. Each section was stained immunohistochemically for STn antigen. In each section, we examined STn expression in the cancer area, adjacent mucosa, and normal epithelium.

RESULTS

STn expression was detected in 90.9 percent of adenomas, 36.2 percent of early cancers (T1), 64.3 percent of advanced cancers (>T1), and 52 percent of mucosa adjacent to cancer. The morphology of cancer tissue did not influence the number of specimens exhibiting STn antigen expression in mucosa adjacent to cancer cells. STn antigen was rarely expressed in flat or depressed-type early cancers (T1; 7.1 percent), and the expression was higher in moderately than in well-differentiated adenocarcinomas. In advanced cancers (>T1), a similar proportion of protruding and small ulcerative cancers expressed STn.

CONCLUSION

Our results suggest that the low expression of STn antigen in flat-type cancers may be the result of different mechanisms of cellular transformation during carcinogenesis from the usual adenoma-carcinoma sequence in colorectal neoplasms.