Monitoring an antibody affinity chromatography with a label-free optical biosensor technique

Comparison of methods for quantitative biomolecular interaction analysis

In order to perform good kinetic experiments, not only the experimental conditions have to be optimized, but the evaluation procedure as well. The focus of this work is the in-depth comparison of different approaches and algorithms to determine kinetic rate constants for biomolecular interaction analysis (BIA). The different algorithms are applied not only to flawless simulated data, but also to real-world measurements. We compare five mathematical approaches for the evaluation of binding curves following pseudo-first-order kinetics with different noise levels. In addition, reflectometric interference spectroscopy (RIfS) measurements of two antibodies are evaluated to determine their binding kinetics. The advantages and disadvantages of the individual approach will be investigated and discussed in detail. In summary, we will raise awareness on how to evaluate and judge results from BIA by using different approaches rather than having to rely on “black box” closed (commercial) software packages.

Process Analytical Approach towards Quality Controlled Process Automation for the Downstream of Protein Mixtures by Inline Concentration Measurements Based on Ultraviolet/Visible Light (UV/VIS) Spectral Analysis

Downstream of pharmaceutical proteins, such as monoclonal antibodies, is mainly done by chromatography, where concentration determination of coeluting components presents a major problem. Inline concentration measurements (ICM) by Ultraviolet/Visible light (UV/VIS)-spectral data analysis provide a label-free and noninvasive approach to significantly speed up the analysis and process time. Here, two different approaches are presented. For a test mixture of three proteins, a fast and easily calibrated method based on the non-negative least-squares algorithm is shown, which reduces the calibration effort compared to a partial least-squares approach. The accuracy of ICM for analytical separations of three proteins on an ion exchange column is over 99%, compared to less than 85% for classical peak area evaluation. The power of the partial least squares algorithm (PLS) is shown by measuring the concentrations of Immunoglobulin G (IgG) monomer and dimer under a worst-case scenario of completely overlapping peaks. Here, the faster SIMPLS algorithm is used in comparison to the nonlinear iterative partial least squares (NIPALS) algorithm. Both approaches provide concentrations as well as purities in real-time, enabling live-pooling decisions based on product quality. This is one important step towards advanced process automation of chromatographic processes. Analysis time is less than 100 ms and only one program is used for all the necessary communications and calculations.

A tool for selective inline quantification of co-eluting proteins in chromatography using spectral analysis and partial least squares regression

Selective quantification of co-eluting proteins in chromatography is usually performed by offline analytics. This is time-consuming and can lead to late detection of irregularities in chromatography processes. To overcome this analytical bottleneck, a methodology for selective protein quantification in multicomponent mixtures by means of spectral data and partial least squares regression was presented in two previous studies. In this paper, a powerful integration of software and chromatography hardware will be introduced that enables the applicability of this methodology for a selective inline quantification of co-eluting proteins in chromatography. A specific setup consisting of a conventional liquid chromatography system, a diode array detector, and a software interface to Matlab® was developed. The established tool for selective inline quantification was successfully applied for a peak deconvolution of a co-eluting ternary protein mixture consisting of lysozyme, ribonuclease A, and cytochrome c on SP Sepharose FF. Compared to common offline analytics based on collected fractions, no loss of information regarding the retention volumes and peak flanks was observed. A comparison between the mass balances of both analytical methods showed, that the inline quantification tool can be applied for a rapid determination of pool yields. Finally, the achieved inline peak deconvolution was successfully applied to make product purity-based real-time pooling decisions. This makes the established tool for selective inline quantification a valuable approach for inline monitoring and control of chromatographic purification steps and just in time reaction on process irregularities.

Strategies for label-free optical detection

A large number of methods using direct detection with label-free systems are known. They compete with the well-introduced fluorescence-based methods. However, recent applications take advantage of label-free detection in protein-protein interactions, high-throughput screening, and high-content screening. These new applications require new strategies for biosensors. It becomes more and more obvious that neither the transduction principle nor the recognition elements for the biomolecular interaction process alone determine the quality of the biosensor. Accordingly, the biosensor system has to be considered as a whole. This chapter focuses on strategies to optimize the detection platform and the biomolecular recognition layer. It concentrates on direct detection methods, with special focus on optical transduction. Since even this restriction still leaves a large number of methods, only microrefractometric and microreflectometric methods using planar transducers have been selected for a detailed description and a listing of applications. However, since many review articles on the physical principles exist, the description is kept short. Other methods are just mentioned in brief and for comparison. The outlook and the applications demonstrate the future perspectives of direct optical detection in bioanalytics.

Diet-derived polyphenol metabolite enterolactone is a tissue-specific estrogen receptor activator

Numerous dietary compounds can modify gene expression by binding to the members of the nuclear receptor superfamily of transcription factors. For example, dietary polyphenols, such as soy isoflavones genistein and daidzein, modulate the activity of the estrogen receptors (ERs)-alpha and ERbeta. An additional class of dietary polyphenols that modulate cellular signaling pathways are lignans, compounds that are common constituents of Western diets. In this study, we show that a metabolite of dietary lignans, enterolactone, at physiological concentrations, activates ER-mediated transcription in vitro with preference for ERalpha. The effects of enterolactone are mediated by the ER ligand binding domain and are susceptible to antiestrogen treatment. Furthermore, the affinity of enterolactone toward ERalpha, measured by a novel ligand binding assay, is augmented in cell culture conditions. Moreover, our results demonstrate for the first time that enterolactone has estrogenic activity in vivo. In transgenic estrogen-sensitive reporter mice, enterolactone induces tissue-specific estrogen-responsive reporter gene expression as well as promotes uterine stromal edema and expression of estrogen-responsive endogenous genes (CyclinD1 and Ki67). Taken together, our data show that enterolactone is a selective ER agonist inducing ER-mediated transcription both in vitro in different cell lines and in vivo in the mouse uterus.

A new approach for producing polyclonal antibodies using impure antigens

A new convenient approach has been designed to produce polyclonal antibodies (PcAb). The approach is based on the principle of the immunoglobulin (Ig) class switch in the immune response. We produced six different antibodies (Ab) against calcineurin A subunit (CNA). CNA, His-tagged calcineurin A subunit (His-CNA), single chain calcineurin (CNB-CNA) and single chain calcineurin-calmodulin complex (CaM-CNB-CNA) were expressed in Escherichia coli (E. coli) BL21 strain, and they were used to immunize male BALB/c mice. These Ab were examined by enzyme-linked immunosorbent assay (ELISA) and western blot analysis. The results clearly demonstrated that the specificity of the Ab produced by different protein samples was much higher than that of the Ab produced by a single sample. We used CNA, CaM-CNB-CNA and His-CNA to immunize mice in turn and obtained monospecific PcAb against CNA fortunately by our new approach. Remarkably, our approach not only offered a simple and general alternative to other methods for producing PcAb described previously, but also disclosed a novel process of immunization that could be used to produce monoclonal antibodies (mAb).

A label-free continuous total-internal-reflection-fluorescence-based immunosensor

In this study, we continuously monitored, second-by-second, concentration changes of two different carbohydrates (maltose and panose) by using monoclonal antibodies in an optical immunosensor based on total internal reflection fluorescence. Earlier studies have demonstrated that these antibodies increase their intrinsic tryptophan fluorescence upon binding of carbohydrate antigens. Using the four immobilized monoclonal antibodies with low affinities (K(d)>10(-6)M), fast kinetics (k(off)>1s(-1)), and high reversibility gave opportunities for developing a continuous immunosensor without any need for regeneration. Since intrinsic fluorescence was used, no extrinsic labeling was necessary. Sensitivity was in the range of 1-5 microM for panose, and 10-15 microM for maltose and the loss of intensity was as low as 3.5% per hour during measurements. Calculations of DeltaH degrees and DeltaS degrees from the temperature dependence of K(d) indicated an enthalpic driven antigen-antibody binding event that is diminished upon antibody immobilization. We feel certain that weakly interacting antibodies can be used in future applications for continuous monitoring where there is a need to achieve instantaneous information on the concentration of an analyte.

Label-free characterization of cell adhesion using reflectometric interference spectroscopy (RIfS)

Reflectometric interference spectroscopy (RIfS) is a label-free, time-resolved technique for detecting interactions of molecules immobilized on a surface with ligands in solution. Here we show that RIfS also permits the detection of the adhesion of tissue culture cells to a functionalized surface in a flow system. Interactions of T cells with other leukocytes or epithelial cells of blood vessels are crucial steps in the regulating immune response and inflammatory reactions. Jurkat T cell leukemia cells rapidly attached to a transducer functionalized with a monoclonal antibody directed against the T cell receptor (TCR)/CD3 complex, followed by activation-dependent cell spreading. RIfS curves were obtained for the Jurkat derivative JCaM 1.6 (which lacks the key signaling protein Lck), cells preincubated with cytochalasin D (an inhibitor of actin polymerization), and for surfaces functionalized with an antibody directed against the coreceptor CD28. These curves differed with respect to the maximum signal and the initial slope of the increase in optical thickness. The testing of chemical inhibitors, cell surface molecules and gene products relevant to a key event in T cell immunity illustrates the potential of label-free techniques for the analysis of activation-dependent cell-surface contacts.