Determination of binding constants by ultrafast affinity extraction: Theoretical and experimental studies of optimum conditions for analysis

High-performance chromatographic immunoassay utilizing a biotin-streptavidin platform for activity-based analysis of therapeutic monoclonal antibodies

There has been rapid growth in the use of monoclonal antibodies (mAbs) as biopharmaceuticals over the last twenty years. This has led to the need for new analytical methods that can rapidly and specifically measure or characterize mAbs for research, development and quality control, including means for the assessment of a therapeutic mAb's biological activity. High-performance immunoaffinity chromatography (HPIAC) was examined in this report as an approach for such work, in which the interactions between an antibody and its antigen were used for the selective isolation and analysis of one of these components. This report describes the utilization of a biotin-streptavidin platform in HPIAC and with affinity microcolumns that were used together in a chromatographic immunoassay for the analysis of a therapeutic mAb. Various components of this method were characterized and optimized to provide a method that was reusable and that could provide results within 7 min. The final assay could measure down to 0.03 mg/mL mAb (1.5 μg) for a 50 μL sample injection. The assay precision was ±0.7-1.3 % based on peak area measurements and ± 1.0-2.4 % using peak heights. The method was then evaluated for its use with typical samples encountered for a therapeutic mAb during its development and processing. Each microcolumn in this assay could be used for more than 350-400 sample application/elution cycles. The extension of this platform and approach to other applications was also considered.

Determination of the binding constants and ionic mobilities of diquat complexes with randomly sulfated cyclodextrins by affinity capillary electrophoresis

The enantiomers of diquats (DQs), a new class of functional organic molecules, were recently separated by capillary electrophoresis (CE) with high resolution up to 11.4 within 5-7 min using randomly sulfated α-, β-, and γ-cyclodextrins (CDs) as chiral selectors. These results indicated strong interactions between dicationic diquats and multiply negatively charged sulfated CDs (S-CDs). However, the binding strength of these interactions was not quantified. For that reason, in this study, affinity CE was applied for the determination of the binding constants and ionic mobilities of the complexes of DQ P- and M-enantiomers with CD chiral selectors in an aqueous medium. The non-covalent interactions of 10 pairs of DQ enantiomers with the above CDs were investigated in a background electrolyte (BGE) composed of 22 mM NaOH, 35 mM H3PO4, pH 2.5, and 0.0-1.0 mM concentrations of CDs. The average apparent binding constant and the average actual ionic mobility of the DQ-CD complexes were determined by nonlinear regression analysis of the dependence of the effective mobility of DQ enantiomers on the concentration of CDs in the BGE. The complexes were found to be relatively strong with the averaged apparent binding constants in the range 13 600-547 400 L/mol.

A chromatographic method for determining the interaction between a drug and two target proteins by fabricating a dual-heterogeneous surface

Characterization of the drug-target interactions is pivotal throughout the whole procedure of drug development. Most of the current assays, particularly, chromatographic methods lack the capacity to reveal drug adsorption on the muti-target surface. To this end, we derived a reliable and workable mathematical equation for revealing drug bindings to dual targets on the heterogeneous surface starting from the mass balance equation. The derivatization relied on the correlation of drug injection amounts with their retention factors. Experimental validation was performed by determining the binding parameters of three canonical drugs on a heterogeneous surface, which was fabricated by fusing angiotensin receptor type I and type II receptors (AT1R and AT2R) at the terminuses of circularly permuted HaloTag (cpHaloTag) and immobilizing the whole fusion protein onto 6-bromohexanoic acid modified silica gel. We proved that immobilized AT1R-cpHalo-AT2R maintained the original ligand- and antibody-binding activities of the two receptors in three weeks. The association constants of valsartan, candesartan, and telmisartan to AT1R were (6.26±0.14) × 105, (9.66±0.71) × 105, and (3.17±0.03) × 105 L/mol. In the same column, their association constants to AT2R were (1.25±0.04) × 104, (2.30±0.08) × 104, and (8.51±0.06) × 103 L/mol. The patterns of the association constants to AT1R/AT2R (candesartan>valsartan>telmisartan) were in good line with the data by performing nonlinear chromatography on control columns containing immobilized AT1R or AT2R alone. This provided proof of the fact that the derivatization allowed the determination of drug bindings on the heterogeneous surface with the utilization of a single series of injections and linear regression. We reasoned that is simple enough to model the bindings of drug adsorption on commercially available adsorbents in fundamental or industrial fields, thus having the potential to become a universal method for analyzing the bindings of a drug to the heterogeneous surface containing multiple targets.