Intact and middle-down CIEF of commercial therapeutic monoclonal antibody products under non-denaturing conditions

An Imaged Capillary Isoelectric Focusing Separation of the Linear and Cyclic Variants of a Mimotope of the Cancer-Related CD20 Antigen-Validation and Statistical Evaluation

Imaged capillary isoelectric focusing was successfully applied for separating an in-house synthesized closely related peptide pair, that is, a linear 12-mer (Rp5-L) and its cyclic 15-mer variant (Rp5-C). Rp5-L represents a mimotope, that is, an epitope mimicking peptide, of the CD20 antigen, which is over-expressed in B-cell-related tumors. Peptide identity-including the successful disulfide bond formation in Rp5-C-was confirmed with matrix-assisted laser desorption ionization-time of flight mass spectrometry. The purity of synthesized products was determined by a reversed-phase high-performance liquid chromatographic method with ultraviolet detection. The apparent isoelectric point (pI) of cyclic Rp5-C and Rp5-L was 5.99 and 6.47, respectively. An appropriate combination of carrier ampholytes allowed for their baseline separation with an analysis time of <20 min. Method validation was done for the synthesized peptides and three flanking pI markers covering, for example, repeatability and intermediate precision. Calibrations on different days resulted in identical slopes for Rp5-L and Rp5-C, respectively, as statistically confirmed by Welch's t-test and pooled t-test over 8 days. The calibration data of mimotopes and pI markers were evaluated for outliers, normality, homoscedasticity, and autocorrelation with complementary statistical procedures, which identified an otherwise unnoticed outlier for a pI marker. The linearity of calibration for Rp5-L, Rp5-C, and the pI markers was tested with Mandel's fitting test and lack-of-fit test. For Rp5-L and Rp5-C, the calculated limits of detection and limits of quantification were ≤0.31 and ≤0.96 µmol/L, respectively.

Development of a novel, high-throughput imaged capillary isoelectric focusing-Western method to characterize charge heterogeneity of monoclonal antibody heavy and light chains

Charge heterogeneity is one of the commonly monitored quality attributes in biotherapeutics. It can impact the stability, efficacy, and safety of products, but it can also affect the pharmacokinetics, binding affinity, and overall biological activity of the molecules. Given the substantial size and complexity of antibodies, subtle variations or specific modifications that result in charge heterogeneity might be concealed when mAbs are analyzed under native conditions. Two-dimensional gel electrophoresis has traditionally been used to characterize antibody heavy chain (HC) and light chain (LC) charge variants. The procedures, however, are laborious, and the method is only qualitative. ChromiCE was developed as an alternative approach to provide quantitative analysis, but the method is also labor intensive, requiring separation of the HC and LC by chromatography before imaged capillary isoelectric focusing (iCIEF) analysis. We thus developed a novel, automated high-throughput iCIEF-Western method to directly quantify the HC and LC charge variants with high sensitivity under denatured and reduced conditions. The HC and LC charge variants are selectively characterized using detection antibodies specific to the HC or LC. In addition, the reduced, denatured iCIEF-Western method allows for the analysis of up to 96 samples overnight, offering good precision and high throughput with minimal analyst hands-on time. Further, the developed method can be applied in different aspects of drug development, such as comparability, release or stability testing given its ability to provide identity, as well as qualitative and quantitative comparative analysis.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Peptide mapping of proteins by capillary electromigration methods

This review article provides a wide overview of important developments and applications of capillary electromigration methods in the area of peptide mapping of proteins in the period 1997-mid-2022, including review articles on this topic. It deals with all major aspects of peptide mapping by capillary electromigration methods: i) precleavage sample preparation involving purification, preconcentration, denaturation, reduction and alkylation of protein(s) to be analyzed, ii) generation of peptide fragments by off-line or on-line enzymatic and/or chemical cleavage of protein(s), iii) postcleavage preparation of the generated peptide mixture for capillary electromigration separation, iv) separation of the complex peptide mixtures by one-, two- and multidimensional capillary electromigration methods coupled with mass spectrometry detection, and v) a large application of peptide mapping for variable purposes, such as qualitative analysis of monoclonal antibodies and other protein biopharmaceuticals, monitoring of posttranslational modifications, determination of primary structure and investigation of function of proteins in biochemical and clinical research, characterization of proteins of variable origin as well as for protein and peptide identification in proteomic and peptidomic studies.

Knowing more from less: miniaturization of ligand-binding assays and electrophoresis as new paradigms for at-line monitoring and control of mammalian cell bioprocesses

Monitoring technologies for Process Analytical Technology (PAT) in mammalian cell cultures are often focusing on the same hand full parameters although a deeper knowledge and control of a larger panel of culture components would highly benefit process optimization, control and robustness. This short review highlights key advances in microfluidic affinity assays and microchip capillary electrophoresis (MCE). Aiming at the miniaturization and integration of PAT, these can detect at-line a variety of metabolites, proteins and Critical Quality Attributes (CQA's) in a bioprocess. Furthermore, discrete analytical components, which can potentially support the translation of increasingly mature microfluidic technologies towards this novel application, are also presented as a comprehensive toolbox ranging from sample preparation to signal acquisition.