Recombinant antibody piezoimmunosensors for the detection of cytochrome P450 1B1

Rapid-format recombinant antibody-based methods for the diagnosis of Clostridioides difficile infection: Recent advances and perspectives

Clostridioides difficile, the most common cause of nosocomial diarrhea, has been continuously reported as a worldwide problem in healthcare settings. Additionally, the emergence of hypervirulent strains of C. difficile has always been a critical concern and led to continuous efforts to develop more accurate diagnostic methods for detection of this recalcitrant pathogen. Currently, the diagnosis of C. difficile infection (CDI) is based on clinical manifestations and laboratory tests for detecting the bacterium and/or its toxins, which exhibit varied sensitivity and specificity. In this regard, development of rapid diagnostic techniques based on antibodies has demonstrated promising results in both research and clinical environments. Recently, application of recombinant antibody (rAb) technologies like phage display has provided a faster and more cost-effective approach for antibody production. The application of rAbs for developing ultrasensitive diagnostic tools ranging from immunoassays to immunosensors, has allowed the researchers to introduce new platforms with high sensitivity and specificity. Additionally, DNA encoding antibodies are directly accessible in these approaches, which enables the application of antibody engineering to increase their sensitivity and specificity. Here, we review the latest studies about the antibody-based ultrasensitive diagnostic platforms for detection of C. difficile bacteria, with an emphasis on rAb technologies.

Ribosome display for the rapid generation of high-affinity Zika-neutralizing single-chain antibodies

Background

Zika virus (ZIKV) is an emerging pathogen with no approved therapeutics and only limited diagnostics available. To address this gap, six mouse single-chain antibodies (scFvs) to ZIKV envelope (E) protein were isolated rapidly and efficiently from a ribosome-displayed antibody library constructed from the spleens of five immunized mice.

Methodology/Results

In this report, we have generated a panel of mouse scFvs to ZIKV E protein using ribosome display. The six scFvs demonstrated no cross-reactivity with DENV2 NGC envelope protein, suggesting specificity for ZIKV E protein. These scFvs showed differences in their affinity: two (scFv45-3, scFv63-1) of them were dominant after four rounds of panning, and showed higher affinity (an apparent Kd values from 19 to 27 nM) than the other four (scFv5-1, scFv7-2, scFv38-1, and scFv51-2). All six scFvs showed ZIKV-neutralizing activity in the plaque reduction neutralization test (PRNT) assay and their neutralizing activity was positively correlated with their affinities.

Conclusions/Significance

The scFvs (45–3 and 63–1) with highest affinity may have dual utility as diagnostics capable of recognizing ZIKV E subtypes and may be further developed to treat ZIKV infection. Our approach has the added advantage of generating Fc receptor-deficient antibodies, minimizing concern of antibody-dependent enhancement (ADE) of infection.

Characterization of Self-Assembled Monolayers of Peptide Mimotopes of CD20 Antigen and Their Binding with Rituximab

CD20, expressed in greater than 90% of B-lymphocytic lymphomas, is a target for antibody therapy. Rituximab is a chimeric therapeutic monoclonal antibody (mAb) against the protein CD20, allowing it to destroy B cells and to treat lymphoma, leukemia, transplant rejection, and autoimmune disorder. In this work, the binding of rituximab to self-assembled monolayers (SAMs) of peptide mimotopes of CD20 antigen was systematically characterized. Four peptide mimotopes of CD 20 antigen were selected from the literature and redesigned to allow their SAM immobilizations on gold electrodes through a peptide linker with cysteine. The bindings of these peptides with rituximab and control mAbs (trastuzumab and bevacizumab) were characterized by quartz crystal microbalance (QCM). Among the four peptide mimotopes initially selected, the peptide designated as CN-14 (CGSGSGSWPRWLEN) was the most selective and sensitive for rituximab binding. The CN-14 SAM was further characterized by ellipsometry and atomic force microscopy. The thickness of the CN-14 SAM film was approximately 32 Å, and the CN-14 SAM is suggested to be stabilized by a salt bridge of Arg-10 and Glu-13 between CN-14 peptides. The CN-14 salt bridge was evaluated by a series of modifications to the CN-14 peptide sequence and characterized by QCM. The CN-14 amide variant produced a better affinity to rituximab than CN-14 without a significant impact on selectivity. As the pKa of the Glu residue of CN-14 increased, the affinity of the SAM to rituximab increased, whereas the selectivity decreased. This was attributed to the weakening of the salt bridge between the CN-14 Arg-10 and Glu-13 at higher pKa values for Glu-13. Our study shows that peptide mimotopes have potential benefits in sensor applications, as the peptide-peptide interactions in the SAMs can be manipulated by the addition of functional groups to the peptide to influence the binding of target proteins.

Quartz-Crystal Microbalance (QCM) for Public Health: An Overview of Its Applications

Nanobiotechnologies, from the convergence of nanotechnology and molecular biology and postgenomics medicine, play a major role in the field of public health. This overview summarizes the potentiality of piezoelectric sensors, and in particular, of quartz-crystal microbalance (QCM), a physical nanogram-sensitive device. QCM enables the rapid, real time, on-site detection of pathogens with an enormous burden in public health, such as influenza and other respiratory viruses, hepatitis B virus (HBV), and drug-resistant bacteria, among others. Further, it allows to detect food allergens, food-borne pathogens, such as Escherichia coli and Salmonella typhimurium, and food chemical contaminants, as well as water-borne microorganisms and environmental contaminants. Moreover, QCM holds promises in early cancer detection and screening of new antiblastic drugs. Applications for monitoring biohazards, for assuring homeland security, and preventing bioterrorism are also discussed.

A theophylline quartz crystal microbalance biosensor based on recognition of RNA aptamer and amplification of signal

A quartz crystal microbalance (QCM) biosensor for theophylline was developed by recognition of RNA aptamer and gold nanoparticle amplification technique. Firstly, a designed small single-stranded RNA, RNA1, was immobilized onto the QCM electrode through a thiol linker. Then, the complementary stranded RNA2, which can combine with RNA1 to form a double-stranded RNA with a recognition unit of theophylline, could be self-assembled on the QCM electrode surface through a hybrid reaction in the presence of theophylline. The recognition process could cause a frequency change of QCM to give the signal related to theophylline. When RNA2 was tethered to gold nanoparticles, the signal could be amplified to further enhance the sensitivity of the designed sensor. Under the optimal conditions, the QCM-based biosensor showed excellent sensitivity (limit of detection, 8.2 nM) and specificity with a dissociation constant of Kd = 5.26 × 10(-7) M. The sensor can be used to quantitatively detect theophylline in serum, suggesting that it can be applied in complex biological samples.

Real time analysis of binding between Rituximab (anti-CD20 antibody) and B lymphoma cells

CD20, expressed on greater than 90% of B-lymphocytic lymphomas, is an attractive target for antibody therapy. Rituximab is a chimeric murine/human-engineered monoclonal antibody which can selectively deplete CD20-expressing cells in peripheral blood and lymphoid tissues. The immobilization of B-lymphoblast-like Burkitt's lymphoma Raji cells on the quartz crystal microbalance (QCM) gold electrode surface using arginine-glycine-aspartic acid (RGD) tripeptide was electrochemically confirmed. The real-time processes of attachment of Raji cells on the gold electrode and the subsequent binding of Rituximab to the cells were studied using a QCM biosensor. The interaction between Rituximab and Raji cells led to the increased resonant frequency shifts (Δf0) in the studied antibody concentration range from 5 to 250 μg mL(-1) following the Langmuir adsorption model. From these observations, the apparent binding constant between a single-layer of Rituximab and Raji cells was calculated to be 1.6 × 10(6) M(-1). Control experiments using other therapeutic antibodies (i.e., Trastuzumab and Bevacizumab) and different cells (i.e., T cells and endothelial cells) proved the specific interaction between Rituximab and B cells. The effects of Ca(2+) and Mn(2+) ions on the Rituximab-Raji cell interaction were also studied providing the enhanced QCM signals, in particular with Ca(2+), further indicating that CD20 is a calcium ion channel that can transport these metal ions into the cells and accelerate the cell lysis induced by Rituximab. Thus, the real time capability of QCM and its simplicity of operation are shown to be highly suitable for multipurpose studies on living cells including cell-immobilization, cytotoxicity of drugs, and the cell action mechanisms.

Targeted multiplex imaging mass spectrometry with single chain fragment variable (scfv) recombinant antibodies

Recombinant scfv antibodies specific for CYP1A1 and CYP1B1 P450 enzymes were combined with targeted imaging mass spectrometry to simultaneously detect the P450 enzymes present in archived, paraffin-embedded, human breast cancer tissue sections. By using CYP1A1 and CYP1B1 specific scfv, each coupled to a unique reporter molecule (i.e., a mass tag) it was possible to simultaneously detect multiple antigens within a single tissue sample with high sensitivity and specificity using mass spectrometry. The capability of imaging multiple antigens at the same time is a significant advance that overcomes technical barriers encountered when using present day approaches to develop assays that can simultaneously detect more than a single antigen in the same tissue sample.

Characterization of the native and denatured herceptin by enzyme linked immunosorbent assay and quartz crystal microbalance using a high-affinity single chain fragment variable recombinant antibody

Herceptin/Trastuzumab is a humanized IgG1κ light chain antibody used to treat some forms of breast cancer. A phage-displayed recombinant antibody library was used to obtain a single chain fragment variable (scFv, designated 2B4) to a linear synthetic peptide representing Herceptin's heavy chain CDR3. Enzyme linked immunosorbent assays (ELISAs) and piezoimmunosensor/quartz crystal microbalance (QCM) assays were used to characterize 2B4-binding activity to both native and heat denatured Herceptin. The 2B4 scFv specifically bound to heat denatured Herceptin in a concentration dependent manner over a wide (35-220.5 nM) dynamic range. Herceptin denatures and forms significant amounts of aggregates when heated. UV-vis characterization confirms that Herceptin forms aggregates as the temperature used to heat Herceptin increases. QCM affinity assay shows that binding stoichiometry between 2B4 scFv and Herceptin follows a 1:2 relationship proving that 2B4 scFv binds strongly to the dimers of heat denatured Herceptin aggregates and exhibits an affinity constant of 7.17 × 10(13) M(-2). The 2B4-based QCM assay was more sensitive than the corresponding ELISA. Combining QCM with ELISA can be used to more fully characterize nonspecific binding events in assays. The potential theoretical and clinical implications of these results and the advantages of the use of QCM to characterize human therapeutic antibodies in samples are also discussed.

Detection of biomarkers using recombinant antibodies coupled to nanostructured platforms

The utility of biomarker detection in tomorrow's personalized health care field will mean early and accurate diagnosis of many types of human physiological conditions and diseases. In the search for biomarkers, recombinant affinity reagents can be generated to candidate proteins or post-translational modifications that differ qualitatively or quantitatively between normal and diseased tissues. The use of display technologies, such as phage-display, allows for manageable selection and optimization of affinity reagents for use in biomarker detection. Here we review the use of recombinant antibody fragments, such as scFvs and Fabs, which can be affinity-selected from phage-display libraries, to bind with both high specificity and affinity to biomarkers of cancer, such as Human Epidermal growth factor Receptor 2 (HER2) and Carcinoembryonic antigen (CEA). We discuss how these recombinant antibodies can be fabricated into nanostructures, such as carbon nanotubes, nanowires, and quantum dots, for the purpose of enhancing detection of biomarkers at low concentrations (pg/mL) within complex mixtures such as serum or tissue extracts. Other sensing technologies, which take advantage of 'Surface Enhanced Raman Scattering' (gold nanoshells), frequency changes in piezoelectric crystals (quartz crystal microbalance), or electrical current generation and sensing during electrochemical reactions (electrochemical detection), can effectively provide multiplexed platforms for detection of cancer and injury biomarkers. Such devices may soon replace the traditional time consuming ELISAs and Western blots, and deliver rapid, point-of-care diagnostics to market.

Recombinant antibodies and their use in biosensors

Inexpensive, noninvasive immunoassays can be used to quickly detect disease in humans. Immunoassay sensitivity and specificity are decidedly dependent upon high-affinity, antigen-specific antibodies. Antibodies are produced biologically. As such, antibody quality and suitability for use in immunoassays cannot be readily determined or controlled by human intervention. However, the process through which high-quality antibodies can be obtained has been shortened and streamlined by use of genetic engineering and recombinant antibody techniques. Antibodies that traditionally take several months or more to produce when animals are used can now be developed in a few weeks as recombinant antibodies produced in bacteria, yeast, or other cell types. Typically most immunoassays use two or more antibodies or antibody fragments to detect antigens that are indicators of disease. However, a label-free biosensor, for example, a quartz-crystal microbalance (QCM) needs one antibody only. As such, the cost and time needed to design and develop an immunoassay can be substantially reduced if recombinant antibodies and biosensors are used rather than traditional antibody and assay (e.g. enzyme-linked immunosorbant assay, ELISA) methods. Unlike traditional antibodies, recombinant antibodies can be genetically engineered to self-assemble on biosensor surfaces, at high density, and correctly oriented to enhance antigen-binding activity and to increase assay sensitivity, specificity, and stability. Additionally, biosensor surface chemistry and physical and electronic properties can be modified to further increase immunoassay performance above and beyond that obtained by use of traditional methods. This review describes some of the techniques investigators have used to develop highly specific and sensitive, recombinant antibody-based biosensors for detection of antigens in simple or complex biological samples.

Immobilization of a human epidermal growth factor receptor 2 mimotope-derived synthetic peptide on Au and its potential application for detection of herceptin in human serum by quartz crystal microbalance

Therapeutic antibodies are antigenically similar to human antibodies and are difficult to detect in assays of human serum samples without the use of the therapeutic antibody's complementary antigen. Herein for the first time, we established a platform to detect Herceptin in solutions by using a small (<2.2 kDa), inexpensive, highly stable human epidermal growth factor receptor (HER2) mimotope-derived synthetic peptide immobilized on the surface of a Au quartz electrode. We used the HER2 mimotope as a substitute for the HER2 receptor protein in piezoimmunosensor or quartz crystal microbalance (QCM) assays to detect Herceptin in human serum. We demonstrated that assay sensitivity was dependent upon the amino acids used to tether and link the peptide to the sensor surface and the buffers used to carry out the assays. The detection limit of the piezoimmunosensor assay was 0.038 nM with a linear operating range of 0.038-0.859 nM. Little nonspecific binding to other therapeutic antibodies (Avastin and Rituxan) was observed. Levels of Herceptin in serum samples obtained from treated patients, as ascertained using the synthetic peptide-based QCM assay, were typical for those treated with Herceptin. The findings of this study are significant in that low-cost synthetic peptides could be used in a QCM assay, in lieu of native or recombinant antigens or capture antibodies, to rapidly detect a therapeutic antibody in human serum. The results suggested that a synthetic peptide bearing a particular functional sequence could be applied for developing a new generation of affinity-based immunosensors to detect a broad range of clinical biomarkers.

Affinity chromatography as a tool for antibody purification

The global antibody market has grown exponentially due to increasing applications in research, diagnostics and therapy. Antibodies are present in complex matrices (e.g. serum, milk, egg yolk, fermentation broth or plant-derived extracts). This has led to the need for development of novel platforms for purification of large quantities of antibody with defined clinical and performance requirements. However, the choice of method is strictly limited by the manufacturing cost and the quality of the end product required. Affinity chromatography is one of the most extensively used methods for antibody purification, due to its high selectivity and rapidity. Its effectiveness is largely based on the binding characteristics of the required antibody and the ligand used for antibody capture. The approaches used for antibody purification are critically examined with the aim of providing the reader with the principles and practical insights required to understand the intricacies of the procedures. Affinity support matrices and ligands for affinity chromatography are discussed, including their relevant underlying principles of use, their potential value and their performance in purifying different types of antibodies, along with a list of commercially available alternatives. Furthermore, the principal factors influencing purification procedures at various stages are highlighted. Practical considerations for development and/or optimizations of efficient antibody-purification protocols are suggested.

Lipoic acid glyco-conjugates, a new class of agents for controlling nonspecific adsorption of blood serum at biointerfaces for biosensor and biomedical applications

The carbohydrate-derived lipoic acid derivatives were studied as protein and cell resistant biomaterials. Six types of carbohydrates were examined for their abilities to reduce nonspecific adsorption of human serum and Hela cell using quartz crystal microbalance. Our data suggested that the structures of carbohydrates play an important role in resisting nonspecific binding. Specifically, the resistance was found to increase in the order lipoic fucose < lipoic mannose < lipoic N-acetyl glucosamine < lipoic glucose < lipoic sialic acid < lipoic galactose, where lipoic galactose derivative resisted most nonspecific adsorption. Furthermore, the combination of lipoic galactose and BSA was the most effective in reducing the adsorption of even undiluted human serum and the attachment of Hela cells while allowing specific binding. Several control experiments have demonstrated that the resistant-ability of mixed lipoic galactose and BSA was comparable to the best known system for decreasing nonspecific adsorption.

Organization of cytochrome P450 enzymes involved in sex steroid synthesis: PROTEIN-PROTEIN INTERACTIONS IN LIPID MEMBRANES

Mounting evidence underscores the importance of protein-protein interactions in the functional regulation of drug-metabolizing P450s, but few studies have been conducted in membrane environments, and none have examined P450s catalyzing sex steroid synthesis. Here we report specific protein-protein interactions for full-length, human, wild type steroidogenic cytochrome P450 (P450, CYP) enzymes: 17alpha-hydroxylase/17,20-lyase (P450c17, CYP17) and aromatase (P450arom, CYP19), as well as their electron donor NADPH-cytochrome P450 oxidoreductase (CPR). Fluorescence resonance energy transfer (FRET)(3) in live cells, coupled with quartz crystal microbalance (QCM), and atomic force microscopy (AFM) studies on phosphatidyl choline +/- cholesterol (mammalian) biomimetic membranes were used to investigate steroidogenic P450 interactions. The FRET results in living cells demonstrated that both P450c17 and P450arom homodimerize but do not heterodimerize, although they each heterodimerize with CPR. The lack of heteroassociation between P450c17 and P450arom was confirmed by QCM, wherein neither enzyme bound a membrane saturated with the other. In contrast, the CPR bound readily to either P450c17- or P450arom-saturated surfaces. Interestingly, N-terminally modified P450arom was stably incorporated and gave similar results to the wild type, although saturation was achieved with much less protein, suggesting that the putative transmembrane domain is not required for membrane association but for orientation. In fact, all of the proteins were remarkably stable in the membrane, such that high resolution AFM images were obtained, further supporting the formation of P450c17, P450arom, and CPR homodimers and oligomers in lipid bilayers. This unique combination of in vivo and in vitro studies has provided strong evidence for homodimerization and perhaps some higher order interactions for both P450c17 and P450arom.

Antibody Fragments as Probe in Biosensor Development

Today's proteomic analyses are generating increasing numbers of biomarkers, making it essential to possess highly specific probes able to recognize those targets. Antibodies are considered to be the first choice as molecular recognition units due to their target specificity and affinity, which make them excellent probes in biosensor development. However several problems such as difficult directional immobilization, unstable behavior, loss of specificity and steric hindrance, may arise from using these large molecules. Luckily, protein engineering techniques offer designed antibody formats suitable for biomarker analysis. Minimization strategies of antibodies into Fab fragments, scFv or even single-domain antibody fragments like VH, VL or VHHs are reviewed. Not only the size of the probe but also other issues like choice of immobilization tag, type of solid support and probe stability are of critical importance in assay development for biosensing. In this respect, multiple approaches to specifically orient and couple antibody fragments in a generic one-step procedure directly on a biosensor substrate are discussed.