Analysis of the protein and glycan parts of CA125 antigen from human amniotic fluid

Lectin-based biosensors as analytical tools for clinical oncology

The review focus on the use of lectin-based biosensors in the oncology field, and ponders the potentialities of using these devices as analytical tools to monitor the levels of cancer glycobiomarkers in biological fluids, helping in the diagnosis, prognosis and treatment assessment. Several examples of lectin-based biosensors directed for cancer biomarkers are described and discussed, and their potential application in the clinic is considered, taking into account their analytical features, advantages and performance in sample analysis. Technical and practical aspects in the construction process, which are specific for lectin biosensors, are debated, as well as the requirements in sample collection and processing, and biosensor validation. Today's challenges for real implementation of these devices in the clinic are presented, along with the future trends in the field.

Nano-sized CA125 antigen glycocamouflage: Mucin - Extracellular vesicles alliance to watch?

Mucin 16 (MUC16) is a transmembrane type mucin and its released extracellular portion is designated as CA125 antigen. It is considered to be part of a supramolecular glycoprotein complex having a complicated epitope map and extreme structural heterogeneity. Starting from the initial transmembrane localization of MUC16/CA125 antigen and its alternative routes of release by shedding or putative secretion, CA125 antigen from human amniotic fluid soluble and extracellular vesicles (EVs)-containing fractions were characterized aiming at the possible glycosylation-associated mode of distribution as a factor contributing to the reported conflicting structural data. Ultracentrifugation, sucrose density gradient centrifugation, ion-exchange chromatography and TEM were used for analysis. The results indicated that the smeared abundantly glycosylated high molecular mass CA125-immunoreactive species, which follow the wheat germ agglutinin-binding pattern, were shared across amniotic fluid soluble and particulate fractions. A lower molecular mass glycoprotein-like CA125-immunoreactive species which follows the peanut agglutinin-binding pattern and was specifically associated with the EVs-enriched fraction was observed. CA125 presentation in the particulate amniotic fluid fraction was found to be shaped by a complex interactome partially involving lactose-sensitive galectin-3 binding. The MUC16 - EVs alliance as well as heterogeneous mucin/macromolecular complexes, at membranes or extracellularly, may represent cryptic pools of distinct CA125 species.

Focused Glycomic Profiling With an Integrated Microfluidic Lectin Barcode System

Protein glycosylation is one of the key processes that play essential roles in biological functions and dysfunctions. However, progress in glycomics has considerably lagged behind genomics and proteomics, due in part to the enormous challenges associated with the analysis of glycans. Here we present a new integrated and automated microfluidic lectin barcode platform to substantially improve the performance of lectin array for focused glycomic profiling. The chip design and flow control were optimized to promote the lectin-glycan binding kinetics and the speed of lectin microarrays. Moreover, we established an on-chip lectin assay which employs a very simple blocking method to effectively suppress the undesired background due to lectin binding of antibodies. Using this technology, we demonstrated focused differential profiling of tissue-specific glycosylation changes of a biomarker, the CA125 protein purified from ovarian cancer cell lines, and different tissues from ovarian cancer patients in a fast, reproducible, and high-throughput fashion. Highly sensitive CA125 detection was also demonstrated with a detection limit much lower than the clinical cutoff value for cancer diagnosis. This microfluidic platform holds the potential to integrate with sample preparation functions to construct a fully integrated "sample-to-answer" microsystem for focused differential glycomic analysis. Thus, our technology should present a powerful tool in support of rapid advance in glycobiology and glycobiomarker development.

Integrated Microfluidic Lectin Barcode Platform for High-Performance Focused Glycomic Profiling

Protein glycosylation is one of the key processes that play essential roles in biological functions and dysfunctions. However, progress in glycomics has considerably lagged behind genomics and proteomics, due in part to the enormous challenges in analysis of glycans. Here we present a new integrated and automated microfluidic lectin barcode platform to substantially improve the performance of lectin array for focused glycomic profiling. The chip design and flow control were optimized to promote the lectin-glycan binding kinetics and speed of lectin microarray. Moreover, we established an on-chip lectin assay which employs a very simple blocking method to effectively suppress the undesired background due to lectin binding of antibodies. Using this technology, we demonstrated focused differential profiling of tissue-specific glycosylation changes of a biomarker, CA125 protein purified from ovarian cancer cell line and different tissues from ovarian cancer patients in a fast, reproducible, and high-throughput fashion. Highly sensitive CA125 detection was also demonstrated with a detection limit much lower than the clinical cutoff value for cancer diagnosis. This microfluidic platform holds the potential to integrate with sample preparation functions to construct a fully integrated "sample-to-answer" microsystem for focused differential glycomic analysis. Thus, our technology should present a powerful tool in support of rapid advance in glycobiology and glyco-biomarker development.

CA-125 of fetal origin can act as a ligand for dendritic cell-specific ICAM-3-grabbing non-integrin

CA-125 (coelomic epithelium-related antigen) forms the extracellular portion of transmembrane mucin 16 (MUC16). It is shed after proteolytic degradation. Due to structural heterogeneity, CA-125 ligand capacity and biological roles are not yet understood. In this study, we assessed CA-125 as a ligand for dendritic cell-specific ICAM-3-grabbing non-integrin (DC-SIGN), which is a C-type lectin showing specificity for mannosylated and fucosylated structures. It plays a role as a pattern recognition molecule for viral and bacterial glycans or as an adhesion receptor. We probed a human DC-SIGN-Fc chimera with CA-125 of fetal or cancer origin using solid- or fluid-phase binding and inhibition assays. The results showed that DC-SIGN binds to CA-125 of fetal origin and that this interaction is carbohydrate-dependent. By contrast, cancer-derived CA-125 displayed negligible binding. Inhibition assays indicated differences in the potency of CA-125 to interfere with DC-SIGN binding to pathogen-related glycoconjugates, such as mannan and Helicobacter pylori antigens. The differences in ligand properties between CA-125 of fetal and cancer origin may be due to specificities of glycosylation. This might influence various functions of dendritic cells based on their subset diversity and maturation-related functional capacity.

Exploring the glycosylation of serum CA125

Ovarian cancer is the most lethal gynaecologic cancer affecting women. The most widely used biomarker for ovarian cancer, CA125, lacks sensitivity and specificity. Here, we explored differences in glycosylation of CA125 between serum from patients with ovarian cancer and healthy controls. We found differences between CA125 N-glycans from patient sera compared to controls. These include increases in core-fucosylated bi-antennary monosialylated glycans, as well as decreases in mostly bisecting bi-antennary and non-fucosylated glycans in patients compared to controls. Measurement of the glycosylated state of CA125 may therefore provide a more specific biomarker for patients with ovarian cancer.

Deciphering the molecular nature of ovarian cancer biomarker CA125

The ovarian cancer biomarker CA125 has been extensively investigated over the last 30 years. The knowledge about the exact molecular nature of this protein, however, remains fragmented. This review provides an overview of the structural research regarding CA125, and presents an orthogonal verification method to confirm the identity of this molecule. The need for independent identification of CA125 is exemplified by several reports where mutually exclusive data concerning the existence of isoforms and the glycan moieties is presented. Mass spectrometry can overcome the pitfalls of a single detection/identification method such as antibody probing. Independent verification of CA125 identity in characterization studies will help establish a refined model of its molecular structure that will promote the development of new approaches for diagnosis, prognosis and therapy of ovarian cancer.

Methods for identification of CA125 from ovarian cancer ascites by high resolution mass spectrometry

CA125 is the most widely used tumour marker in ovarian cancer with unsatisfactory sensitivity and specificity especially at early stage. It is quantified by antibody-based immunoassays; however different molecular weight isoforms have been described in the literature which have never been validated by mass spectrometry, potentially affecting the diagnostic accuracy and clinical reliability of the test. In this study, CA125 was detected by Western blot and its identity confirmed by mass spectrometry. Two-dimensional (2D) gel electrophoresis in combination with mass spectrometry revealed that positive Western blot signals up to 500 kDa are most likely false-positive interactions of M11-like and OC125-like antibodies. Fibronectin, identified as one of these false-positive interaction partners, increased the reading for CA125 in a first generation ELISA significantly (p = 0.02). The existence of low-molecular weight isoforms of CA125 is therefore questionable and is most likely reflecting cross-reactivity of the antibodies with other proteins. This would explain the conflicting reports on the molecular structure of CA125 and also the inconsistency of CA125 levels by different ELISAs. Our results are also the first steps towards a mass spectrometric assay for CA125 quantification, which would improve sensitivity and reliability.

Biochemical and morphological differences between CA125 isolated from healthy women and patients with epithelial ovarian cancer from Tunisian population

Analysis of the structure of CA125 is essential for determining the physiological role of this significant tumor antigen. The objectives of this study were: (1) to identify the characteristics of the CA125 isolated from healthy and patient women with epithelial ovarian cancer; and (2) to determine the ferning structure of this antigen. The cancer-derived CA125 antigen (cCA125) purified by gel filtration and affinity chromatography (Concanavalin A) was run on SDS-PAGE and examined using light microscopy and compared with healthy-derived CA125 antigen (hCA125). Both purified antigen cCA125 and hCA125 showed a high molecular mass (> 2,000 kDa) with high mannose glycans. The ferning patterns related to cCA125 and hCA125 revealed distinct differences in the patterns of arborescence. The ferning morphology of cCA125 antigen was denser than that of hCA125 antigen making an obvious difference between cCA125 and hCA125, with respect to length, branching and distribution of crystals. The current study provides the first evidence for a potential functional link between CA125 and its structure which, in the light of a comparison between cCA125 and hCA125, might proof to be of significant biomedical importance in the future.

Identification of pregnancy-associated CA125-reactive protein as a carbohydrate-binding immunoglobulin G

Cancer antigen 125 (CA125), also referred to as mucin 16, is expressed under both normal and pathological conditions and the complexity of its structure indicates multifunctionality, i.e. both the protein and carbohydrate parts may be involved in diverse interactions at different levels of cell and tissue organization. Its biological role is not understood, but involvement in immune response modulation and influence on cell adhesion have been speculated. This study aimed at isolation and characterization of endogenous ligands for CA125 as an initial step in gaining insight into its activity. A CA125-reactive fraction was separated from human placental extract by affinity chromatography. The isolated preparation was characterized by SDS-PAGE, immunoblotting, peptide mass fingerprinting and binding assay. The CA125-reactive fraction from placental extract was identified as carbohydrate-binding IgG. The glycan composition of inhibitors of carbohydrate-binding pointed to sialic acid as one determinant for recognition but indicated that sialylation was not alone and that glycotopes containing galactose, N-acetylgalactosamine and N-acetylglucosamine were also important. CA125-reactive IgG could be selectively enriched using fetuin as the ligand and represents a distinct IgG subfraction differing from abundant natural carbohydrate-binding antibodies. Taking advantage of the particular properties of ligands for CA125 may have biomedical potential for use as biological modifiers or delivery agents and have an impact beyond pregnancy, since many immunoregulatory molecular pathways are common to embryonic development and malignant transformation.

Glycans as a Target in the Detection of Reproductive Tract Cancers

The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is highly recognized. In this review we summarized literature data on the alteration of glycans in cancer, especially glycoforms of tumor markers of reproductive tract cancers: prostate-specific antigen (PSA) and cancer antigen 125 (CA125). We aimed to highlight the diagnostic potential and relevance of glycan microheterogeneity and to present some novel methods for cancer detection. A computerized search of articles published up to 2007 was performed through the PubMed database. Search terms utilized included prostate/ovarian cancer glycosylation, prostate/ovarian cancer detection, PSA/CA125 glycosylation. Additional sources were identified through cross-referencing and researching in available biomedical books. The comparative studies of sugar chain structures of the PSA and CA125 indicated specific structural alterations associated with malignant transformation, in relation to glycan branching, sialylation and fucosylation. These glycan modifications should be better in distinguishing between benign and malignant conditions than the measurement of marker concentrations alone, which is widely used in practice. Cancer-associated changes in the glycosylation could yield more sensitive and discriminative diagnostic tests for reproductive tract cancer detection, i.e. for improvement of the clinical utility of known tumor markers or the discovery of new ones.