Identification and Confirmation of Differentially Expressed Fucosylated Glycoproteins in the Serum of Ovarian Cancer Patients Using a Lectin Array and LC-MS/MS

In order to discover potential glycoprotein biomarkers in ovarian cancer, we applied a lectin array and Exactag labeling based quantitative glycoproteomics approach. A lectin array strategy was used to detect overall lectin-specific glycosylation changes in serum proteins from patients with ovarian cancer and those with benign conditions. Lectins, which showed significant differential response for fucosylation, were used to extract glycoproteins that had been labeled using isobaric chemical tags. The glycoproteins were then identified and quantified by LC-MS/MS, and five glycoproteins were found to be differentially expressed in the serum of ovarian cancer patients compared to benign diseases. The differentially expressed glycoproteins were further confirmed by lectin-ELISA and ELISA assay. Corticosteroid-binding globulin (CBG), serum amyloid p component (SAP), complement factor B (CFAB), and histidine-rich glycoprotein (HRG) were identified as potential markers for differentiating ovarian cancer from benign diseases or healthy controls. A combination of CBG and HRG (AUC = 0.825) showed comparable performance to CA125 (AUC = 0.829) in differentiating early stage ovarian cancer from healthy controls. The combination of CBG, SAP, and CA125 showed improved performance for distinguishing stage III ovarian cancer from benign diseases compared to CA125 alone. The ability of CBG, SAP, HRG, and CFAB to differentiate the serum of ovarian cancer patients from that of controls was tested using an independent set of samples. Our findings suggest that glycoprotein modifications may be a means to identify novel diagnostic markers for detection of ovarian cancer.     

Glycoproteomic analyses of ovarian cancer cell lines and sera from ovarian cancer patients show distinct glycosylation changes in individual proteins

Ovarian cancer is difficult to diagnose in women because symptoms of the disease are often not noticed until the disease has progressed to an advanced untreatable stage. Although a serum test, CA125, is currently available to assist with monitoring treatment of ovarian cancer, this test lacks the necessary specificity and sensitivity for early detection. Therefore, better biomarkers of ovarian cancer are needed. A glycoprotein analysis approach was undertaken using high resolution Fourier transform ion cyclotron resonance mass spectrometry to analyze glycosylated proteins present in the conditioned media of ovarian cancer cell lines and in sera obtained from ovarian cancer patients and normal controls. In this study, glycosylated proteins were separated by gel electrophoresis, and individual glycoproteins were selected for glycosylation analysis and protein identification. The attached glycans from each protein were released and profiled by mass spectrometry. Glycosylation of a mucin protein and a large glycosylated protein isolated from the ES2 ovarian cancer cell line was determined to consist of mostly O-linked glycans. Four prominent glycoproteins of approximate 517, 370, 250, 163 kDa from serum samples were identified as two forms of apolipoprotein B-100, fibronectin, and immunoglobulin A1, respectively. Mass spectrometric analysis of glycans isolated from apolipoprotein B-100 (517 kD) showed the presence of small, specific O-linked oligosaccharides. In contrast, analysis of fibronectin (250 kD) and immunoglobulin A1 (163 kD) produced N-linked glycan fragments in forms that were sufficiently different from the glycans obtained from the corresponding protein band present in the normal serum samples. This study shows that not only a single protein but several are aberrantly glycosylated, and those abnormal glycosylation changes can be detected and may ultimately serve as glycan biomarkers for ovarian cancer.     

Evaluation of the serum N-linked glycome for the diagnosis of cancer and chronic inflammation

The identification of serum biomarkers has lead to improvements in the detection and diagnosis of cancer, and combinations of these biomarkers have increased further their sensitivity and specificity. Glycosylation is the most common PTM of secreted proteins and the identification of novel serum glyco-biomarkers has become a topic of increasing interest because the glycan processing pathways are frequently disturbed in cancer cells. A future goal is to combine current biomarkers with glyco-biomarkers to yield further improvements. Well characterised N-glycosylation changes in the serum glycome of cancer patients include changes in the levels of tri- and tetra-antennary glycan structures, sialyl Lewis X epitopes and agalactosylated bi-antennary glycans. Several of these glycosylated markers have been linked to chronic inflammatory diseases, promoting questions about the links between inflammation and cancer. In this review, the glycoproteins which display these glycan epitopes, the glycosyl transferases which can generate them, their potential functions and their use as biomarkers are evaluated.     

Annotation of a serum N-glycan library for rapid identification of structures

Glycosylation is one of the most common post-translational modifications of proteins and has been shown to change with various pathological states including cancer. Global glycan profiling of human serum based on mass spectrometry has already led to several promising markers for diseases. The changes in glycan structure can result in altered monosaccharide composition as well as in the linkages between the monosaccharides. High-throughput glycan structural elucidation is not possible because of the lack of a glycan template to expedite identification. In an effort toward rapid profiling and identification of glycans, we have constructed a library of structures for the serum glycome to aid in the rapid identification of serum glycans. N-Glycans from human serum glycoproteins are used as a standard and compiled into a library with exact structure (composition and linkage), liquid chromatography retention time, and accurate mass. Development of the library relies on highly reproducible nanoLC-MS retention times. Tandem MS and exoglycosidase digestions were used for structural elucidation. The library currently contains over 300 entries with 50 structures completely elucidated and over 60 partially elucidated structures. This database is steadily growing and will be used to rapidly identify glycans in unknown biological samples.     

Glycomic/glycoproteomic analysis by liquid chromatography/mass spectrometry: analysis of glycan structural alteration in cells

The alteration of glycosyltransferase expression and the subsequent changes in oligosaccharide structures are reported in several diseases. The analysis of glycan structural alteration in glycoproteins is becoming increasingly important in the discovery of therapies and diagnostic markers. In this study, we propose a strategy for glycomic/glycoproteomic analysis based on oligosaccharide profiling by LC/MS followed by proteomic approaches, including 2-DE and 2-D lectin blot. As a model of aberrant cells, we used Chinese hamster ovary cells transfected with N-acetylglucosaminyltransferase III (GnT-III), which catalyzes the addition of a bisecting N-acetylglucosamine (GlcNAc) to beta-mannose of the mannosyl core of N-linked oligosaccharides. LC/MS equipped with a graphitized carbon column (GCC) enabled us to elucidate the structural alteration induced by the GnT-III expression. Using 2-D lectin blot followed by LC/MS/MS, the protein carrying an extra N-acetylhexosamine in cells transfected with GnT-III was successfully identified as integrin alpha3. Thus, oligosaccharide profiling by GCC-LC/MS followed by proteomic methods can be a powerful tool for glycomic/glycoproteomic analysis.     

A serum glycomics approach to breast cancer biomarkers

Because the glycosylation of proteins is known to change in tumor cells during the development of breast cancer, a glycomics approach is used here to find relevant biomarkers of breast cancer. These glycosylation changes are known to correlate with increasing tumor burden and poor prognosis. Current antibody-based immunochemical tests for cancer biomarkers of ovarian (CA125), breast (CA27.29 or CA15-3), pancreatic, gastric, colonic, and carcinoma (CA19-9) target highly glycosylated mucin proteins. However, these tests lack the specificity and sensitivity for use in early detection. This glycomics approach to find glycan biomarkers of breast cancer involves chemically cleaving oligosaccharides (glycans) from glycosylated proteins that are shed or secreted by breast cancer tumor cell lines. The resulting free glycan species are analyzed by MALDI-FT-ICR MS. Further structural analysis of the glycans can be performed in FTMS through the use of tandem mass spectrometry with infrared multiphoton dissociation. Glycan profiles were generated for each cell line and compared. These methods were then used to analyze sera obtained from a mouse model of breast cancer and a small number of serum samples obtained from human patients diagnosed with breast cancer or patients with no known history of breast cancer. In addition to the glycosylation changes detected in mice as mouse mammary tumors developed, glycosylation profiles were found to be sufficiently different to distinguish patients with cancer from those without. Although the small number of patient samples analyzed so far is inadequate to make any legitimate claims at this time, these promising but very preliminary results suggest that glycan profiles may contain distinct glycan biomarkers that may correspond to glycan "signatures of cancer."     

Identification of unique glycoisoforms of vitamin D-binding protein and haptoglobin as biomarker candidates in hepatocarcinogenesis of STAM mice

Hepatocellular carcinoma (HCC) is the major subtype of primary liver cancer, and is typically diagnosed late in its course. Considering the limitations and the reluctance of patients to undergo a liver biopsy, a reliable, noninvasive diagnostic marker that predicts and assesses the treatment and prognosis of HCC is needed. With recent technological advances of mass spectrometry, glycomics is gathering momentum and holds substantial potential to discover new glycan markers in cancer research. Here, to discover specific glycan markers for the early diagnosis of HCC, we analyzed the glycan profiles of gel-separated serum proteins of progressive liver disease model mice. By focused protein glycomics of 12 gel-separated glycoproteins using sera from the mouse models, we revealed the entire profile of glycans in each major serum protein. We found that the levels of trisialylated triantennary glycans of haptoglobin and vitamin D-binding protein increased significantly as the disease progressed, while the alteration in these protein levels were modest. Furthermore, these glycan increases were not observed in age-matched control mice. In conclusion, our approach has identified specific glycan marker candidates for the early diagnosis of HCC.     

Plasma glycoprotein profiling for colorectal cancer biomarker identification by lectin glycoarray and lectin blot

Colorectal cancer (CRC) remains a major worldwide cause of cancer-related morbidity and mortality largely due to the insidious onset of the disease. The current clinical procedures utilized for disease diagnosis are invasive, unpleasant, and inconvenient; hence, the need for simple blood tests that could be used for the early detection of CRC. In this work, we have developed methods for glycoproteomics analysis to identify plasma markers with utility to assist in the detection of colorectal cancer (CRC). Following immunodepletion of the most abundant plasma proteins, the plasma N -linked glycoproteins were enriched using lectin affinity chromatography and subsequently further separated by nonporous silica reversed-phase (NPS-RP)-HPLC. Individual RP-HPLC fractions were printed on nitrocellulose coated slides which were then probed with lectins to determine glycan patterns in plasma samples from 9 normal, 5 adenoma, and 6 colorectal cancer patients. Statistical tools, including principal component analysis, hierarchical clustering, and Z-statistics analysis, were employed to identify distinctive glycosylation patterns. Patients diagnosed with colorectal cancer or adenomas were shown to have dramatically higher levels of sialylation and fucosylation as compared to normal controls. Plasma glycoproteins with aberrant glycosylation were identified by nano-LC-MS/MS, while a lectin blotting methodology was used to validate proteins with significantly altered glycosylation as a function of cancer progression. The potential markers identified in this study for diagnosis to distinguish colorectal cancer from adenoma and normal include elevated sialylation and fucosylation in complement C3, histidine-rich glycoprotein, and kininogen-1. These potential markers of colorectal cancer were subsequently validated by lectin blotting in an independent set of plasma samples obtained from 10 CRC patients, 10 patients with adenomas, and 10 normal subjects. These results demonstrate the utility of this strategy for the identification of N -linked glycan patterns as potential markers of CRC in human plasma, and may have the utility to distinguish different disease states.     

Comparative serum glycoproteomics using lectin selected sialic acid glycoproteins with mass spectrometric analysis: application to pancreatic cancer serum

A strategy is developed in this study for identifying sialylated glycoprotein markers in human cancer serum. This method consists of three steps: lectin affinity selection, a liquid separation and characterization of the glycoprotein markers using mass spectrometry. In this work, we use three different lectins (Wheat Germ Agglutinin, (WGA) Elderberry lectin,(SNA), Maackia amurensis lectin, (MAL)) to extract sialylated glycoproteins from normal and cancer serum. Twelve highly abundant proteins are depleted from the serum using an IgY-12 antibody column. The use of the different lectin columns allows one to monitor the distribution of alpha(2,3) and alpha(2,6) linkage type sialylation in cancer serum vs that in normal samples. Extracted glycoproteins are fractionated using NPS-RP-HPLC followed by SDS-PAGE. Target glycoproteins are characterized further using mass spectrometry to elucidate the carbohydrate structure and glycosylation site. We applied this approach to the analysis of sialylated glycoproteins in pancreatic cancer serum. Approximately 130 sialylated glycoproteins are identified using microLC-MS/MS. Sialylated plasma protease C1 inhibitor is identified to be down-regulated in cancer serum. Changes in glycosylation sites in cancer serum are also observed by glycopeptide mapping using microLC-ESI-TOF-MS where the N83 glycosylation of alpha1-antitrypsin is down regulated. In addition, the glycan structures of the altered proteins are assigned using MALDI-QIT-MS. This strategy offers the ability to quantitatively analyze changes in glycoprotein abundance and detect the extent of glycosylation alteration as well as the carbohydrate structure that correlate with cancer.     

Proteomic Profiling of a Mouse Model for Ovarian Granulosa Cell Tumor Identifies VCP as a Highly Sensitive Serum Tumor Marker in Several Human Cancers

The initial aim of this study was to identify novel serum diagnostic markers for the human ovarian granulosa cell tumor (GCT), a tumor that represents up to 5% of all ovarian cancers. To circumvent the paucity of human tissues available for analyses, we used the Ctnnb1(tm1Mmt/+);Pten(tm1Hwu/tmiHwu);Amhr2(tm3(cre)Bhr/+) transgenic mouse model, which features the constitutive activation of CTNNB1 signaling combined with the loss of Pten in granulosa cells and develops GCTs that mimic aggressive forms of the human disease. Proteomic profiling by mass spectrometry showed that vinculin, enolase 1, several heat shock proteins, and valosin containing protein (VCP) were more abundantly secreted by cultured mouse GCT cells compared to primary cultured GC. Among these proteins, only VCP was present in significantly increased levels in the preoperative serum of GCT cancer patients compared to normal subjects. To determine the specificity of VCP, serum levels were also measured in ovarian carcinoma, non-Hodgkin's lymphoma and breast, colon, pancreatic, lung, and prostate cancer patients. Increased serum VCP levels were observed in the majority of cancer cases, with the exception of patients with lung or prostate cancer. Moreover, serum VCP levels were increased in some GCT, ovarian carcinoma, breast cancer, and colon cancer patients who did not otherwise display increased levels of widely used serum tumor markers for their cancer type (e.g. inhibin A, inhibin B, CA125, CEA, or CA15.3). These results demonstrate the potential use of VCP as highly sensitive serum marker for GCT as well as several other human cancers.     

Wisteria floribunda agglutinin positive glycobiomarkers: a unique lectin as a serum biomarker probe in various diseases

Introduction: Serum proteins are generally glycosylated and solubilized, and are thus present as glycoproteins. The glycan structure of glycoproteins reflects cell differentiation status; glycan structures generated by diseased cells are distinguishable from those produced by healthy cells. Proteins may therefore serve as markers of tissues that secrete them. Several strategies for the identification of novel serum biomarkers using a combination of glycoscience-based technologies have been recently proposed. The selection of lectins for use as probes for identification of altered glycan structures represents a critical step.

Areas covered: This review describes the identification of Wisteria floribunda agglutinin (WFA) as a probe that recognizes the altered glycan structure of glycoproteins secreted by diseased cells. WFA may be employed as a probe for several diseases, e.g., liver fibrosis, liver cirrhosis, prostate cancer, ovarian cancer, and IgA nephropathy. The advantage of employing WFA as a serum biomarker probe is that only very small amounts of WFA-positive glycoproteins are present in serum; therefore, WFA background in serum is very low.

Expert commentary: Based on the findings to date, several WFA-positive serum biomarkers may be measured without pre-purification of target glycoproteins, indicating their utility as serum biomarkers in patients with various diseases.     

On the analysis of glycomics mass spectrometry data via the regularized area under the ROC curve

Background  

Novel molecular and statistical methods are in rising demand for disease diagnosis and prognosis with the help of recent advanced biotechnology. High-resolution mass spectrometry (MS) is one of those biotechnologies that are highly promising to improve health outcome. Previous literatures have identified some proteomics biomarkers that can distinguish healthy patients from cancer patients using MS data. In this paper, an MS study is demonstrated which uses glycomics to identify ovarian cancer. Glycomics is the study of glycans and glycoproteins. The glycans on the proteins may deviate between a cancer cell and a normal cell and may be visible in the blood. High-resolution MS has been applied to measure relative abundances of potential glycan biomarkers in human serum. Multiple potential glycan biomarkers are measured in MS spectra. With the objection of maximizing the empirical area under the ROC curve (AUC), an analysis method was considered which combines potential glycan biomarkers for the diagnosis of cancer.     

A strategy to reveal potential glycan markers from serum glycoproteins associated with breast cancer progression

Aberrant glycosylation on glycoproteins that are either presented on the surface or secreted by cancer cells is a potential source of disease biomarkers and provides insights into disease pathogenesis. N-Glycans of the total serum glycoproteins from advanced breast cancer patients and healthy individuals were sequenced by HPLC with fluorescence detection coupled with exoglycosidase digestions and mass spectrometry. We observed a significant increase in a trisialylated triantennary glycan containing alpha1,3-linked fucose which forms part of the sialyl Lewis x epitope. Following digestion of the total glycan pool with a combination of sialidase and beta-galactosidase, we segregated and quantified a digestion product, a monogalactosylated triantennary structure containing alpha1,3-linked fucose. We compared breast cancer patients and controls and detected a 2-fold increase in this glycan marker in patients. In 10 patients monitored longitudinally, we showed a positive correlation between this glycan marker and disease progression and also demonstrated its potential as a better indicator of metastasis compared to the currently used biomarkers, CA 15-3 and carcinoembryonic antigen (CEA). A pilot glycoproteomic study of advanced breast cancer serum highlighted acute-phase proteins alpha1-acid glycoprotein, alpha1-antichymotrypsin, and haptoglobin beta-chain as contributors to the increase in the glycan marker which, when quantified from each of these proteins, marked the onset of metastasis in advance of the CA 15-3 marker. These preliminary findings suggest that specific glycans and glycoforms of proteins may be candidates for improved markers in the monitoring of breast cancer progression.     

N-linked glycosylation profiling of pancreatic cancer serum using capillary liquid phase separation coupled with mass spectrometric analysis

Glycoproteins play important roles in various biological processes including intracellular transport, cell recognition, and cell-cell interactions. The change of the cellular glycosylation profile may have profound effects on cellular homeostasis and malignancy. Therefore, we have developed a sensitive screening approach for the comprehensive analysis of N-glycans and glycosylation sites on human serum proteins. Using this approach, N-linked glycopeptides were extracted by double lectin affinity chromatography. The glycans were enzymatically cleaved from the peptides and then profiled using capillary hydrophilic interaction liquid chromatography coupled online with ESI-TOF MS. The structures of the separated glycans were determined by MALDI quadrupole ion-trap TOF mass spectrometry in both positive and negative modes. The glycosylation sites were elucidated by sequencing of PNGase F modified glycopeptides using nanoRP-LC-ESI-MS/MS. Alterations of glycosylation were analyzed by comparing oligosaccharide expression of serum glycoproteins at different disease stages. The efficiency of this method was demonstrated by the analysis of pancreatic cancer serum compared to normal serum. Ninety-two individual glycosylation sites and 202 glycan peaks with 105 unique carbohydrate structures were identified from approximately 25 mug glycopeptides. Forty-four oligosaccharides were found to be distinct in the pancreatic cancer serum. Increased branching of N-linked oligosaccharides and increased fucosylation and sialylation were observed in samples from patients with pancreatic cancer. The methodology described in this study may elucidate novel, cancer-specific oligosaccharides and glycosylation sites, some of which may have utility as useful biomarkers of cancer.     

Evaluation of proteomics-identified CCL18 and CXCL1 as circulating tumor markers for differential diagnosis between ovarian carcinomas and benign pelvic masses

A lack of sensitive and specific tumor markers for early diagnosis and treatment is a major cause for the high mortality rate of ovarian cancer. The purpose of this study was to identify potential proteomics-based biomarkers useful for the differential diagnosis between ovarian cancer and benign pelvic masses. Serum samples from 41 patients with ovarian cancer, 32 patients with benign pelvic masses, and 41 healthy female blood donors were examined, and proteomic profiling of the samples was assessed by surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectroscopy (MS). A confirmatory study was also conducted with serum specimens from 58 patients with ovarian carcinoma, 37 patients with benign pelvic masses, and 48 healthy women. A classification tree was established using Biomarker Pattern Software. Six differentially expressed proteins (APP, CA 125, CCL18, CXCL1, IL-8, and ITIH4) were separated by high-performance liquid chromatography and identified by matrix-assisted laser desorption/ionization (MALDI)-MS/MS and database searches. Two of the proteins overexpressed in ovarian cancer patients, chemokine CC2 motif ligand 18 (CCL18) and chemokine CXC motif ligand 1 (CXCL1), were automatically selected in a multivariate predictive model. These two protein biomarkers were then validated and evaluated by enzyme-linked immunosorbent assay (ELISA) in 535 serum specimens (130 ovarian cancer, 64 benign ovarian masses, 36 lung cancer, 60 gastric cancer, 55 nasopharyngeal carcinoma, 48 hepatocellular carcinoma, and 142 healthy women). The combined use of CCL18 and CXCL1 as biomarkers for ovarian cancer had a sensitivity of 92% and a specificity of 97%. The multivariate ELISA analysis of the two putative markers in combination with CA 125 resulted in a sensitivity of 99% for healthy women and 94% for benign pelvic masses, and a specificity of 92% for both groups; these values were significantly higher than those obtained with CA 125 alone (p and lt;0.05). We conclude that serum CCL18 and CXCL1 are potentially useful as novel circulating tumor markers for the differential diagnosis between ovarian cancer and benign ovarian masses.     

The pattern of glycosyl- and sulfotransferase activities in cancer cell lines: a predictor of individual cancer-associated distinct carbohydrate structures for the structural identification of signature glycans

Carbohydrate chains of cancer glycoprotein antigens contain major outer changes dictated by tissue-specific regulation of glycosyltransferase genes, the availability of sugar nucleotides, and competition between enzymes for acceptor intermediates during glycan elongation. However, it is evident from recent studies with recombinant mucin probes that the final glycosylation profiles of mucin glycoproteins are mainly determined by the cellular repertoire of glycosyltransferases. Hence, we examined various cancer cell lines for the levels of fucosyl-, beta-galactosyl, beta-N-acetylgalactosaminyl-, sialyl-, and sulfotransferase activities that generate the outer ends of the oligosaccharide chains. We have identified glycosyltransferases activities at the levels that would give rise to O-glycan chains as reported by others in breast cancer cell lines, T47D, ZR75-1, MCF-7, and MDA-MB-231. Most breast cancer cells express Gal-3-O-sulfotransferase specific for T-hapten Gal beta1-->3GalNAc alpha-, whereas the enzyme from colon cancer cells exhibits a vast preference for the Gal beta1,4GlcNAc terminal unit in O-glycans. We also studied ovarian cancer cells SW626 and PA-1 and hepatic cancer cells HepG2. Our studies show that alpha1,2-L-fucosyl-T, alpha(2,3) sialyl-T, and 3-O-Sulfo-T capable of acting on the mucin core 2 tetrasaccharide, Gal beta1,4GlcNAc beta1,6(Gal beta1,3)GalNAc alpha-, can also act on the Globo H antigen backbone, Gal beta1,3GalNAc beta1,3Gal alpha-, suggesting the existence of unique carbohydrate moieties in certain cancer-associated glycolipids. Briefly, our study indicates the following: (i) 3'-Sulfo-T-hapten has an apparent relationship to the tumorigenic potential of breast cancer cells; (ii) the 3'-sulfo Lewis(x), the 3-O-sulfo-Globo unit, and the 3-fucosylchitobiose core could be uniquely associated with colon cancer cells; (iii) synthesis of a polylactosamine chain and T-hapten are favorable in ovarian cancer cells due to negligible sialyltransferase activities; and (iv) a 6'-sialyl LacNAc unit and 3'-sialyl T-hapten appear to be prevalent structures in hepatic cancer cell glycans. Thus, it is apparent that different cancer cells are expressing unique glycan epitopes, which could be novel targets for cancer diagnosis and treatment.     

Cancer stem cell marker glycosylation: Nature,function and significance

Glycans are essential for the maintenance of normal biological function, with alterations in glycan expression being a hallmark of cancer. Cancer stem cells (CSCs) are a subset of cells within a tumour capable of self-renewal, cellular differentiation and resistances to conventional therapies. As is the case with stem cells, marker proteins present on the cell surface are frequently used to identify and enrich CSCs, with the expression of these markers statistical correlating with the likelihood of cancer recurrence and overall patient survival. As such CSC markers are of high clinical relevance. The majority of markers currently used to identify CSC populations are glycoproteins, and although the diverse biological roles for many of these markers are known, the nature and function of the glycan moiety on these glycoproteins remains to be fully elucidated. This mini-review summarises our current knowledge regarding the types and extent of CSC marker glycosylation, and the various roles that these glycans play in CSC biology, including in mediating cell adhesion, metastasis, evading apoptosis, tear shear resistance, tumour growth, maintaining pluripotency, self-renewal, trafficking, maintaining stability, maintaining enzymatic activity and aiding epithelial mesenchymal transitioning. Given that CSCs markers have multiple diverse biological functions, and are potentially of significant diagnostic and therapeutic benefit the search for new markers that are uniquely expressed on CSCs is vital to selectively target/identify this subset of cancer cells. As such we have also outlined how high-throughput lectin microarrays can be used to successfully profile the glycosylation status of CSC and to identify glyco-markers unique to CSCs.     

Comparative profiling of serum glycoproteome by sequential purification of glycoproteins and 2-nitrobenzensulfenyl (NBS) stable isotope labeling: a new approach for the novel biomarker discovery for cancer

The recent progress in various proteomic technologies allows us to screen serum biomarker including carbohydrate antigens. However, only a limited number of proteins could be detected by current conventional methods such as shotgun proteomics, primarily because of the enormous concentration distribution of serum proteins and peptides. To circumvent this difficulty and isolate potential cancer-specific biomarkers for diagnosis and treatment, we established a new screening system consisting of the sequential steps of (1) immunodepletion of 6 high-abundance proteins, (2) targeted enrichment of glycoproteins by lectin column chromatography, and (3) the quantitative proteome analysis using 12C6- or 13C6-NBS (2-nitrobenzenesulfenyl) stable isotope labeling followed by MALDI-QIT-TOF mass spectrometric analysis. Through this systematic analysis for five serum samples derived from patients with lung adenocarcinoma, we identified as candidate biomarkers 34 serum glycoproteins that revealed significant difference in alpha1,6-fucosylation level between lung cancer and healthy control, clearly demonstrating that the carbohydrate-focused proteomics could allow for the detection of serum components with cancer-specific features. In addition, we developed a more simplified and practical technique, mass spectrometry-based glycan structure analysis and lectin blotting, in order to validate glycan structure of candidate biomarkers that could be applicable in clinical use. Our new glycoproteomic strategy will provide highly sensitive and quantitative profiling of specific glycan structures on multiple proteins, which should be useful for serum biomarker discovery.     

Integrated Proteomic Analysis of Human Cancer Cells and Plasma from Tumor Bearing Mice for Ovarian Cancer Biomarker Discovery

Background

The complexity of the human plasma proteome represents a substantial challenge for biomarker discovery. Proteomic analysis of genetically engineered mouse models of cancer and isolated cancer cells and cell lines provide alternative methods for identification of potential cancer markers that would be detectable in human blood using sensitive assays. The goal of this work is to evaluate the utility of an integrative strategy using these two approaches for biomarker discovery.

Methodology/Principal Findings

We investigated a strategy that combined quantitative plasma proteomics of an ovarian cancer mouse model with analysis of proteins secreted or shed by human ovarian cancer cells. Of 106 plasma proteins identified with increased levels in tumor bearing mice, 58 were also secreted or shed from ovarian cancer cells. The remainder consisted primarily of host-response proteins. Of 25 proteins identified in the study that were assayed, 8 mostly secreted proteins common to mouse plasma and human cancer cells were significantly upregulated in a set of plasmas from ovarian cancer patients. Five of the eight proteins were confirmed to be upregulated in a second independent set of ovarian cancer plasmas, including in early stage disease.

Conclusions/Significance

Integrated proteomic analysis of cancer mouse models and human cancer cell populations provides an effective approach to identify potential circulating protein biomarkers.