Glycoprofiling of cancer biomarkers: Label-free electrochemical lectin-based biosensors

Linking aberrant glycosylation of plasma glycoproteins with progression of myelodysplastic syndromes: a study based on plasmonic biosensor and lectin array

Aberrant glycosylation of glycoproteins has been linked with various pathologies. Therefore, understanding the relationship between aberrant glycosylation patterns and the onset and progression of the disease is an important research goal that may provide insights into cancer diagnosis and new therapy development. In this study, we use a surface plasmon resonance imaging biosensor and a lectin array to investigate aberrant glycosylation patterns associated with oncohematological disease-myelodysplastic syndromes (MDS). In particular, we detected the interaction between the lectins and glycoproteins present in the blood plasma of patients (three MDS subgroups with different risks of progression to acute myeloid leukemia (AML) and AML patients) and healthy controls. The interaction with lectins from Aleuria aurantia (AAL) and Erythrina cristagalli was more pronounced for plasma samples of the MDS and AML patients, and there was a significant difference between the sensor response to the interaction of AAL with blood plasma from low and medium-risk MDS patients and healthy controls. Our data also suggest that progression from MDS to AML is accompanied by sialylation of glycoproteins and increased levels of truncated O-glycans and that the number of lectins that allow discriminating different stages of disease increases as the disease progresses.

Glycan-Based Electrochemical Biosensors: Promising Tools for the Detection of Infectious Diseases and Cancer Biomarkers

Glycan-based electrochemical biosensors are emerging as analytical tools for determining multiple molecular targets relevant to diagnosing infectious diseases and detecting cancer biomarkers. These biosensors allow for the detection of target analytes at ultra-low concentrations, which is mandatory for early disease diagnosis. Nanostructure-decorated platforms have been demonstrated to enhance the analytical performance of electrochemical biosensors. In addition, glycans anchored to electrode platforms as bioreceptors exhibit high specificity toward biomarker detection. Both attributes offer a synergy that allows ultrasensitive detection of molecular targets of clinical interest. In this context, we review recent advances in electrochemical glycobiosensors for detecting infectious diseases and cancer biomarkers focused on colorectal cancer. We also describe general aspects of structural glycobiology, definitions, and classification of electrochemical biosensors and discuss relevant works on electrochemical glycobiosensors in the last ten years. Finally, we summarize the advances in electrochemical glycobiosensors and comment on some challenges and limitations needed to advance toward real clinical applications of these devices.

Cleaning of LTCC, PEN, and PCB Au electrodes towards reliable electrochemical measurements

Surface cleaning of the working electrode has a key role in improved electrochemical and physicochemical properties of the biosensors. Herein, chemical oxidation in piranha, chemical cleaning in potassium hydroxide-hydrogen peroxide, combined (electro-) chemical alkaline treatment, and potential cycling in sulfuric acid were applied to gold finish electrode surfaces deposited onto three different substrates; low temperature co-fired ceramics (LTCC), polyethylene naphthalate (PEN), and polyimide (PI), using three different deposition technologies; screen printing, inkjet printing, and electroplating (printed circuit board technology, PCB) accordingly. The effects of the (electro-) chemical treatments on the gold content and electrochemical responses of LTCC, PEN, and PCB applicable for aptamer-based sensors are discussed. In order to assess the gold surface and to compare the efficiency of the respective cleaning procedures; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were employed. LTCC sensors electrochemically cycled in sulfuric acid resulted in the most gold content on the electrode surface, the lowest peak potential difference, and the highest charge transfer ability. While, for PEN, the highest elemental gold and the lowest peak-to-peak separation were achieved by a combined (electro-) chemical alkaline treatment. Gold content and electrochemical characteristics on the PCB surface with extremely thin gold layer could be slightly optimized with the chemical cleaning in KOH + H₂O₂. The proposed cleaning procedures might be generally applied to various kinds of Au electrodes fabricated with the same conditions comparable with those are introduced in this study.

Lectins applied to diagnosis and treatment of prostate cancer and benign hyperplasia: A review

Environmental factors, as well as genetic factors, contribute to the increase in prostate cancer cases (PCa), the second leading cause of cancer death in men. This fact calls for the development of more reliable, quick and low-cost early detection tests to distinguish between malignant and benign cases. Abnormal cell glycosylation pattern is a promising PCa marker for this purpose. Proteins, such as lectins can decode the information contained in the glycosylation patterns. Several studies have reported on applications of plant lectins as diagnostic tools for PCa considering the ability to differentiate it from benign cases. In addition, they can be used to detect, separate and differentiate the glycosylation patterns of cells or proteins present in serum, urine and semen. Herein, we present an overview of these studies, showing the lectins that map glycans differentially expressed in PCa, as well as benign hyperplasia (BPH). We further review their applications in biosensors, histochemical tests, immunoassays, chromatography, arrays and, finally, their therapeutic potential. This is the first study to review vegetable lectins applied specifically to PCa.

Integrated workflow for urinary prostate specific antigen N-glycosylation analysis using sdAb partitioning and downstream capillary electrophoresis separation

Prostate cancer represents the second highest malignancy rate in men in all cancer diagnoses worldwide. The development and progression of prostate cancer is not completely understood yet at molecular level, but it has been reported that changes in the N-glycosylation of prostate-specific antigen (PSA) occur during tumor genesis. In this paper we report on the development and implementation of a high-throughput capillary electrophoresis based glycan analysis workflow for urinary PSA analysis. The technology utilizes selective, high yield single domain antibody based PSA capture, followed by preconcentration and capillary electrophoresis coupled with laser-induced fluorescence detection, resulting in high resolution N-glycan profiles. Urinary PSA glycan profiles were compared to a commercially available PSA standard revealing differences in their α2,3- and α2,6-sialylated isomers, proving the excellent selectivity of the suggested workflow. This is important as sialylation classification plays an important role in the differentiation between indolent, significant and aggressive forms of prostate cancer.

Detection of Carrageenan in Meat Products Using Lectin Histochemistry

Carrageenan is a polysaccharide that is widely used in the food industry. Due to its water holding capacity, there is a higher risk of adulteration for economic reasons related to it. A verifiable method for detecting carrageenan is still missing in the food inspection sector. The detection of carrageenan in meat products is not well described. Our study describes lectin histochemistry as a novel approach for carrageenan detection. Within this study, the detection of carrageenan in meat products by lectin histochemistry is validated. Lectins of Arachis hypogaea (PNA) and Bandeiraea simlicifolia (BSA), specific for galactose units of carrageenan, were used. The samples included model meat products (ground chicken-meat products) and meat products from retail markets (chicken and pork hams, sausages, salami, and dried sausages). The limit of determination (LoD) of this method was set at 0.01 g kg^-1. The method sensitivity for lectin PNA reached 1, and, for lectin BSA, it reached 0.96. Method specificity for lectin PNA was 1, and, for lectin BSA, it was 1.33. Cross-reactivity with other hydrocolloids tested was not confirmed. The results confirm that lectin histochemistry is suitable for detecting carrageenan in meat products.

Lectin and Liquid Chromatography-Based Methods for Immunoglobulin (G) Glycosylation Analysis

Immunoglobulin (Ig) glycosylation has been shown to dramatically affect its structure and effector functions. Ig glycosylation changes have been associated with different diseases and show a promising biomarker potential for diagnosis and prognosis of disease advancement. On the other hand, therapeutic biomolecules based on structural and functional features of Igs demand stringent quality control during the production process to ensure their safety and efficacy. Liquid chromatography (LC) and lectin-based methods are routinely used in Ig glycosylation analysis complementary to other analytical methods, e.g., mass spectrometry and capillary electrophoresis. This chapter covers analytical approaches based on LC and lectins used in low- and high-throughput N- and O-glycosylation analysis of Igs, with the focus on immunoglobulin G (IgG) applications. General principles and practical examples of the most often used LC methods for Ig purification are described, together with typical workflows for N- and O-glycan analysis on the level of free glycans, glycopeptides, subunits, or intact Igs. Lectin chromatography is a historical approach for the analysis of lectin-carbohydrate interactions and glycoprotein purification but is still being used as a valuable tool in Igs purification and glycan analysis. On the other hand, lectin microarrays have found their application in the rapid screening of glycan profiles on intact proteins.

Use of the ReCIVA device in breath sampling of patients with acute breathlessness: a feasibility study

Introduction

Investigating acute multifactorial undifferentiated breathlessness and understanding the driving inflammatory processes can be technically challenging in both adults and children. Being able to validate noninvasive methods such as breath analysis would be a huge clinical advance. The ReCIVA® device allows breath samples to be collected directly onto sorbent tubes at the bedside for analysis of exhaled volatile organic compounds (eVOCs). We aimed to assess the feasibility of using this device in acutely breathless patients.

Methods

Adults hospitalised with acute breathlessness and children aged 5–16 years with acute asthma or chronic stable asthma, as well as healthy adult and child volunteers, were recruited. Breath samples were collected onto sorbent tubes using the ReCIVA® device and sent for analysis by means of two-dimensional gas chromatography-mass spectrometry (GCxGC-MS). The NASA Task Load Index (NASA-TLX) was used to assess the perceived task workload of undertaking sampling from the patient's perspective.

Results

Data were available for 65 adults and 61 children recruited. In total, 98.4% of adults and 75.4% of children were able to provide the full target breath sample using the ReCIVA® device. NASA-TLX measurements were available in the adult population with mean values of 3.37 for effort, 2.34 for frustration, 3.8 for mental demand, 2.8 for performance, 3.9 for physical demand and 2.8 for temporal demand.

Discussion

This feasibility study demonstrates it is possible and acceptable to collect breath samples from both adults and children at the bedside for breathomics analysis using the ReCIVA® device.

It is feasible to collect breath samples for breath analysis at the bedside using the ReCIVA device in acutely breathless adults and childrenhttps://bit.ly/2ZTonWo

Nanoparticle enhanced optical biosensing technologies for Prostate Specific Antigen biomarker detection

Prostate Cancer (PCa) is one of the deadliest forms of Cancer among men. Early screening process for PCa is primarily conducted with the help of a FDA approved biomarker known as Prostate Specific Antigen (PSA). The PSA-based screening is challenged with the inability to differentiate between the cancerous PSA and Benign Prostatic Hyperplasia (BPH), resulting in high rates of false-positives. Optical techniques such as optical absorbance, scattering, surface plasmon resonance (SPR), and fluorescence have been extensively employed for Cancer diagnostic applications. One of the most important diagnostic applications involves utilization of nanoparticles (NPs) for highly specific, sensitive, rapid, multiplexed, and high performance Cancer detection and quantification. The incorporation of NPs with these optical biosensing techniques allow realization of low cost, point-of-care, highly sensitive, and specific early cancer detection technologies, especially for PCa. In this work, the current state-of-the-art, challenges, and efforts made by the researchers for realization of low cost, point-of-care (POC), highly sensitive, and specific NP enhanced optical biosensing technologies for PCa detection using PSA biomarker are discussed and analyzed.

130 years of Plant Lectin Research

Lectins are proteins with diverse molecular structures that share the ability to recognize and bind specifically and reversibly to carbohydrate structures without changing the carbohydrate moiety. The history of lectins started with the discovery of ricin about 130 years ago but since then our understanding of lectins has dramatically changed. Over the years the research focus was shifted from 'the characterization of carbohydrate-binding proteins' to 'understanding the biological function of lectins'. Nowadays plant lectins attract a lot of attention especially because of their potential for crop improvement and biomedical research, as well as their application as tools in glycobiology. The present review aims to give an overview of plant lectins and their applications, and how the field evolved in the last decades.

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

Carbohydrate-independent antibiofilm effect of Bothrops jararacussu lectin BJcuL on Staphylococcus aureus

The antivirulence approach to fighting biofilm-based infections caused by Staphylococcus aureus is a promising therapy that has been studied extensively. Here, we compare the antibiofilm activity of a purified lectin from Bothrops jararacussu venom (BJcuL) and commercial lectins obtained from Triticum vulgaris (Wheat Germ Agglutinin, WGA), Bandeiraea simplicifolia BS-II, and Maclura pomifera. Only WGA had antibiofilm activity, although no effect was seen on pre-formed biofilms. The pre-incubation of WGA and BJcuL with their preferential sugars inhibited the biological activity of WGA, but not that of BJcuL, suggesting that biofilm disruption does not involve carbohydrate-recognition domains (CRDs). Quantitative real-time PCR showed that BJcuL promotes modulation of expression of S. aureus genes involved in biofilm formation. Light microscopy revealed cocci and small cell clusters after biofilm formation in the presence of BJcuL, showing that the lectin treatment was unable to completely disrupt biofilm structure. Exposing the free cells to 50 times the minimum inhibitory concentration of gentamicin or ciprofloxacin did not prevent biofilm reestablishment, although inhibition was stronger than in the control (no lectin). This disruption of the biofilm architecture can expose the bacterial cell and may facilitate clearance by the immune system.

Evaluation of In-Flow Magnetoresistive Chip Cell-Counter as a Diagnostic Tool

Inexpensive simple medical devices allowing fast and reliable counting of whole cells are of interest for diagnosis and treatment monitoring. Magnetic-based labs on a chip are one of the possibilities currently studied to address this issue. Giant magnetoresistance (GMR) sensors offer both great sensitivity and device integrability with microfluidics and electronics. When used on a dynamic system, GMR-based biochips are able to detect magnetically labeled individual cells. In this article, a rigorous evaluation of the main characteristics of this magnetic medical device (specificity, sensitivity, time of use and variability) are presented and compared to those of both an ELISA test and a conventional flow cytometer, using an eukaryotic malignant cell line model in physiological conditions (NS1 murine cells in phosphate buffer saline). We describe a proof of specificity of a GMR sensor detection of magnetically labeled cells. The limit of detection of the actual system was shown to be similar to the ELISA one and 10 times higher than the cytometer one.

'Clickable lectins': bioorthogonal reactive handles facilitate the directed conjugation of lectins in a modular fashion

Lectins are carbohydrate-binding proteins with specificity for their target ligands. They play diverse roles in cellular recognition and signalling processes, as well as in infections and cancer metastasis. Owing to their specificity, lectins find application in biotechnology and medicine, e.g. for blood group typing, purification of glycoproteins or lipids and as markers that target cancer cells. For some applications, lectins are immobilized on a solid support, or they are conjugated with other molecules. Classical protein conjugation reactions at nucleophilic amino acids such as cysteine or lysine are often non-selective, and the site of conjugation is difficult to pre-define. Random conjugation, however, can interfere with protein function. Therefore, we sought to equip lectins with a unique reactive handle, which can be conjugated with other molecules in a pre-defined manner. We site-specifically introduced non-canonical amino acids carrying bioorthogonal reactive groups into several lectins. As a proof of principle, we conjugated these 'clickable lectins' with small molecules. Furthermore, we conjugated lectins with different ligand specificities with one another to produce superlectins. The 'clickable lectins' might be useful for any process where lectins shall be conjugated with another module in a selective, pre-defined and site-specific manner.

Lectin-based lateral flow assay: proof-of-concept

Lateral flow assays (LFAs) enable the simple and rapid detection and quantification of analytes and is popular for point-of-care (PoC), point-of-use and outdoor testing applications. LFAs typically depend on antibody or nucleic acid based recognition. We present the innovative concept of a LFA using lectins in the role of the biorecognition element. Lectins are a special kind of glycan-binding protein and the lectin-based LFA herein described was developed for the determination of the glycosylation of free prostate specific antigen (PSA). PSA is routinely used as a biomarker of prostate cancer (PCa) and the glycosylation status of PSA is a more specific marker of disease progress than only the PSA level. Using the lectin-based LFA we were able to detect α-2,6 sialic acid present in fPSA using Sambucus nigra (SNA) lectin. As a negative control, we employed Maackia amurensis lectin II (MAA II) which specifically binds α-2,3 sialic acid. The novel approach presented here can be applied to a wide range of biomarkers that have a significant impact on clinical diagnosis and prognosis, providing an alternative to standard lectin-based assays. The assay uses commercial components and is easily performed by applying a sample to the sampling pad on the lectin-based LFA strip, with results obtained within 10 minutes.

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.

Developments in Point-of-Care Diagnostic Technology for Cancer Detection

Cancer is the cause of death for one in seven individuals worldwide. It is widely acknowledged that screening and early diagnosis are of vital importance for improving the likelihood of recovery. However, given the costly, time-consuming, and invasive nature of the many methods currently in use, patients often do not take advantage of the services available to them. Consequently, many researchers are exploring the possibility of developing fast, reliable, and non-invasive diagnostic tools that can be used directly or by local physicians at the point-of-care. Herein, we look at the use of established biomarkers in cancer therapy and investigate emerging biomarkers exhibiting future potential. The incorporation of these biomarkers into point-of-care devices could potentially reduce the strain currently experienced by screening programs in hospitals and healthcare systems. Results derived from point-of-care tests should be accurate, sensitive, and generated rapidly to assist in the selection of the best course of treatment for optimal patient care. Essentially, point-of-care diagnostics should enhance the well-being of patients and lead to a reduction in cancer-related deaths.

Lectins: an effective tool for screening of potential cancer biomarkers

In recent years, the use of lectins for screening of potential biomarkers has gained increased importance in cancer research, given the development in glycobiology that highlights altered structural changes of glycans in cancer associated processes. Lectins, having the properties of recognizing specific carbohydrate moieties of glycoconjugates, have become an effective tool for detection of new cancer biomarkers in complex bodily fluids and tissues. The specificity of lectins provides an added advantage of selecting peptides that are differently glycosylated and aberrantly expressed in cancer patients, many of which are not possibly detected using conventional methods because of their low abundance in bodily fluids. When coupled with mass spectrometry, research utilizing lectins, which are mainly from plants and fungi, has led to identification of numerous potential cancer biomarkers that may be used in the future. This article reviews lectin-based methods that are commonly adopted in cancer biomarker discovery research.

Full-length antibodies versus single-chain antibody fragments for a selective impedimetric lectin-based glycoprofiling of prostate specific antigen

The main aim of the research was to design a functional impedimetric biosensor able to glycoprofile prostate specific antigen (PSA), a biomarker for prostate cancer (PCa), with high specificity using lectins as glycan recognising proteins. Traditionally, full-length antibody is immobilised on the biosensor interface for specific capture of PSA with subsequent glycoprofiling of PSA by addition of lectins. Since full-length antibodies contain glycans in the Fc domain, particular attention has to be paid to suppress direct binding of lectins to immobilised full-length antibodies, which would compromise accurate glycoprofiling. This issue is addressed here using a recombinant single-chain antibody fragments (scAb), which do not contain any carbohydrate moiety. Surface plasmon resonance was applied to prove negligible interaction of lectins with immobilised scAb fragments, while substantial binding of lectins to full length antibodies was observed. Eight different biosensor designs were tested for their ability to detect PSA. The biosensor device based on scAb fragments covalently immobilised on the gold electrode surface, patterned by a mixed SAM using standard amine coupling chemistry, proved to be the most sensitive. The scAb fragment-based biosensor exhibited sensitivity of 15.9 ± 0.8% decade^-1 (R² = 0.991 with an average RSD of 4.9%), while the full antibody-based biosensor offered sensitivity towards PSA of 4.2 ± 0.1% decade^-1 (R² = 0.999 with an average RSD of 4.8%). Moreover, the selectivity of the scAb-based biosensor was tested using a kallikrein 2 protein, a protein structurally similar to PSA, and the results indicated high selectivity for PSA detection.

Plant Lectins as Medical Tools against Digestive System Cancers

Digestive system cancers-those of the esophagus, stomach, small intestine, colon-rectum, liver, and pancreas-are highly related to genetics and lifestyle. Most are considered highly mortal due to the frequency of late diagnosis, usually in advanced stages, caused by the absence of symptoms or masked by other pathologies. Different tools are being investigated in the search of a more precise diagnosis and treatment. Plant lectins have been studied because of their ability to recognize and bind to carbohydrates, exerting a variety of biological activities on animal cells, including anticancer activities. The present report integrates existing information on the activity of plant lectins on various types of digestive system cancers, and surveys the current state of research into their properties for diagnosis and selective treatment.

Glycan and lectin biosensors

A short description about the importance of glycan biorecognition in physiological (blood cell type) and pathological processes (infections by human and avian influenza viruses) is provided in this review. Glycans are described as much better information storage media, compared to proteins or DNA, due to the extensive variability of glycan structures. Techniques able to detect an exact glycan structure are briefly discussed with the main focus on the application of lectins (glycan-recognising proteins) in the specific analysis of glycans still attached to proteins or cells/viruses. Optical, electrochemical, piezoelectric and micromechanical biosensors with immobilised lectins or glycans able to detect a wide range of analytes including whole cells/viruses are also discussed.

Selective adsorption of carbohydrates and glycoproteins via molecularly imprinted hydrogels: application to visible detection by a boronic acid monomer

Molecularly imprinted PEG-based hydrogels were prepared for carbohydrates and glycoproteins. Visible detection of fructose was achieved by the gels.

Electrochemical Impedance Spectroscopy Study of Concanavalin A Binding to Self-Assembled Monolayers of Mannosides on Gold Wire Electrodes

The interactions of the lectin Concanavalin A (Con A) with self-assembled monolayers (SAMs) of thiolated mono-, di-, and tri-mannosides were studied on the surface of gold wires using electrochemical impedance spectroscopy (EIS). The SAMs of mannosides were prepared either pure or along with thiolated triethylene glycol (TEG) at different molar ratios (1:1, 1:2, 1:4, 1:9, and 1:19) to better understand and optimize the interaction conditions. The charge-transfer resistance of the [Fe(CN)₆]^3-/^4- redox probe was compared before and after the interaction at different concentrations of Con A to determine the equilibrium dissociation constant (K_d) and limit of detection (LOD). Values of K_d were found in the nanomolar range showing multivalent interactions between mannosides and Con A, and LOD was found ranging from 4-13 nM depending on the type of mannoside SAM used. Analysis using the Hill equation suggests negative cooperativity in the binding behavior. Peanut agglutinin was used as a negative control, and cyclic voltammetry was used to further support the experiments. We have found that neither the pure nor the widely dispersed monolayers of mannosides provide the conditions for optimal binding of Con A. The binding of Con A to these SAMs is sensitive to the molar ratio of the mannoside used to prepare the SAM and to the structure of the mannoside. A simple cleaning method has also been shown to regenerate the used gold wire electrodes. The results from these experiments contribute to the development of simple, cheap, selective, and sensitive EIS-based bioassays, especially for lectin-carbohydrate interactions.

Graphene oxide-based electrochemical label-free detection of glycoproteins down to aM level using a lectin biosensor

A label-free ultrasensitive impedimetric biosensor with lectin immobilised on graphene oxide (GO) for the detection of glycoproteins from 1 aM is shown here. This is the first time a functional lectin biosensor with lectin directly immobilised on a graphene-based interface without any polymer modifier has been described. The study also shows that hydrophilic oxidative debris present on GO has a beneficial effect on the sensitivity of (8.46 ± 0.20)% per decade for the lectin biosensor compared to the sensitivity of (4.52 ± 0.23)% per decade for the lectin biosensor built up from GO with the oxidative debris washed out.

Sweet characterisation of prostate specific antigen using electrochemical lectin-based immunosensor assay and MALDI TOF/TOF analysis: Focus on sialic acid

The construction of a sensitive electrochemical lectin-based immunosensor for detection of a prostate specific antigen (PSA) is shown here. Three lectins with different carbohydrate specificities were used in this study to glycoprofile PSA, which is the most common biomarker for prostate cancer (PCa) diagnosis. The biosensor showed presence of α-L-fucose and α-(2,6)-linked terminal sialic acid within PSA´s glycan with high abundance, while only traces of α-(2,3)-linked terminal sialic acid were found. MALDI TOF/TOF mass spectrometry was applied to validate results obtained by the biosensor with a focus on determination of a type of sialic acid linkage by two methods. The first direct comparison of electrochemical immunosensor assay employing lectins for PSA glycoprofiling with mass spectrometric techniques is provided here and both methods show significant agreement. Thus, electrochemical lectin-based immunosensor has potential to be applied for prostate cancer diagnosis.

DNA aptamer-based sandwich microfluidic assays for dual quantification and multi-glycan profiling of cancer biomarkers

Two novel sandwich-based immunoassays for prostate cancer (PCa) diagnosis are reported, in which the primary antibody for capture is replaced by a DNA aptamer. The assays, which can be performed in parallel, were developed in a microfluidic device and tested for the detection of free Prostate Specific Antigen (fPSA). A secondary antibody (Aptamer-Antibody Assay) or a lectin (Aptamer-Lectin Assay) is used to quantify, by chemiluminescence, both the amount of fPSA and its glycosylation levels. The use of aptamers enables a more reliable, selective and controlled sensing of the analyte. The dual approach provides sensitive detection of fPSA along with selective fPSA glycoprofiling, which is of significant importance in the diagnosis and prognosis of PCa, as tumor progression is associated with changes in fPSA glycosylation. With these approaches, we can potentially detect 0.5 ng/mL of fPSA and 3 ng/mL of glycosylated fPSA using Sambucus nigra (SNA) lectin, both within the relevant clinical range. The approach can be applied to a wide range of biomarkers, thus providing a good alternative to standard antibody-based immunoassays with significant impact in medical diagnosis and prognosis.

Sensitive detection and glycoprofiling of a prostate specific antigen using impedimetric assays

This study presents a proof-of-concept for the development of an impedimetric biosensor for ultra-sensitive glycoprofiling of prostate specific antigen (PSA). The biosensor exhibits three unique characteristics: (1) analysis of PSA with limit of detection (LOD) down to 4 aM; (2) analysis of the glycan part of PSA with LOD down to 4 aM level and; (3) both assays (i.e., PSA quantification and PSA glycoprofiling) can be performed on the same interface due to label-free analysis.

Cancer serum biomarkers based on aberrant post-translational modifications of glycoproteins: Clinical value and discovery strategies

Due to the increase in life expectancy in the last decades, as well as changes in lifestyle, cancer has become one of the most common diseases both in developed and developing countries. Early detection remains the most promising approach to improve long-term survival of cancer patients and this may be achieved by efficient screening of biomarkers in biological fluids. Great efforts have been made to identify specific alterations during oncogenesis. Changes at the cellular glycosylation profiles are among such alterations. The "glycosylation machinery" of cells is affected by malignant transformation due to the altered expression of glycogens, leading to changes in glycan biosynthesis and diversity. Alterations in the post-translational modifications of proteins that occur in cancer result in the expression of antigenically distinct glycoproteins. Therefore, these aberrant and cancer-specific glycoproteins and the autoantibodies that are produced in response to their presence constitute targets for cancer biomarkers' search. Different strategies have been implemented for the discovery of cancer glycobiomarkers and are herein reviewed, along with their potentialities and limitations. Practical issues related with serum analysis are also addressed, as well as the challenges that this area faces in the near future.