Peak identification in capillary isoelectric focusing using the concept of relative peak position as determined by two isoelectric point markers

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.

Optimization of the Imaged cIEF Method for Monitoring the Charge Heterogeneity of Antibody-Maytansine Conjugate

The aim of this study was to develop a whole-column imaging-detection capillary isoelectric focusing (icIEF) method for the analytical characterization of charge heterogeneity of a novel humanized anti-EphA2 antibody conjugated to a maytansine derivative. In addition to focusing time, sample composition was optimized: pH range, percent of carrier ampholytes, conjugated antibody concentration, and urea concentration. A good separation of charge isoforms was obtained with 4% carrier ampholytes of a large (3-10) and narrow pH range (8-10.5) (1 : 1 ratio), conjugated antibody concentration (0.3-1 mg/ml) with a good linearity (R²: 0.9905), 2 M of urea concentration, and 12 minute for focusing. The optimized icIEF method demonstrated a good interday repeatability with RSD values: <1% (pI), <8% (% peak area), and 7% (total peak areas). The optimized icIEF was useful as an analytical characterization tool to assess the charged isoform profile of a discovery batch of the studied maytansinoid-antibody conjugate in comparison to its naked antibody. It exhibited a large pI range (7.5-9.0), while its naked antibody showed a narrow pI range (8.9-9.0). In the discovery batch of maytansinoid-antibody conjugate, 2% of charge isoforms had the same pI as the pI of naked antibody isoforms.

Sixteen capillary electrophoresis applications for viral vaccine analysis

A broad range of CE applications from our organization is reviewed to give a flavor of the use of CE within the field of vaccine analyses. Applicability of CE for viral vaccine characterization, and release and stability testing of seasonal influenza virosomal vaccines, universal subunit influenza vaccines, Sabin inactivated polio vaccines (sIPV), and adenovirus vector vaccines were demonstrated. Diverse CZE, CE-SDS, CGE, and cIEF methods were developed, validated, and applied for virus, protein, posttranslational modifications, DNA, and excipient concentration determinations, as well as for the integrity and composition verifications, and identity testing (e.g., CZE for intact virus particles, CE-SDS application for hemagglutinin quantification and influenza strain identification, chloride or bromide determination in process samples). Results were supported by other methods such as RP-HPLC, dynamic light scattering (DLS), and zeta potential measurements. Overall, 16 CE methods are presented that were developed and applied, comprising six adenovirus methods, five viral protein methods, and methods for antibodies determination of glycans, host cell-DNA, excipient chloride, and process impurity bromide. These methods were applied to support in-process control, release, stability, process- and product characterization and development, and critical reagent testing. Thirteen methods were validated. Intact virus particles were analyzed at concentrations as low as 0.8 pmol/L. Overall, CE took viral vaccine testing beyond what was previously possible, improved process and product understanding, and, in total, safety, efficacy, and quality.

Analysis of Monoclonal Antibodies by Capillary Electrophoresis: Sample Preparation, Separation, and Detection

Therapeutic monoclonal antibodies (mAbs) are dominating the biopharmaceutical field due to the fact of their high specificity in the treatment of diverse diseases. Nevertheless, mAbs are very complex glycoproteins exhibiting several macro- and microheterogeneities that may affect their safety, quality, and efficacy. This complexity is very challenging for mAbs development, formulation, and quality control. To tackle the quality issue, a combination of multiple analytical approaches is necessary. In this perspective, capillary electrophoresis has gained considerable interest over the last decade due to the fact of its complementary features to chromatographic approaches. This review provides an overview of the strategies of mAbs and derivatives analysis by capillary electrophoresis hyphenated to ultraviolet, fluorescence, and mass spectrometry detection. The main sample preparation approaches used for mAb analytical characterization (i.e., intact, middle-up/down, and bottom-up) are detailed. The different electrophoretic modes used as well as integrated analysis approaches (sample preparation and separation) are critically discussed.

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

A two‐step CIEF with chemical mobilization was developed for charge profiling of the therapeutic mAb rituximab under non‐denaturing separation conditions. CIEF of the intact mAb was combined with a middle‐down approach analyzing Fc/2 and F(ab´)₂ fragments after digest with a commercial cysteine protease (IdeS). CIEF methods were optimized separately for the intact mAb and its fragments due to their divergent pIs. Best resolution was achieved by combining Pharmalyte (PL) 8–10.5 with PL 3–10 for variants of intact rituximab and of F(ab´)₂ fragments, respectively, whereas PL 6.7–7.7 in combination with PL 3–10 was used for Fc/2 variants. Charge heterogeneity in Fc/2 dominates over F(ab´)₂. In addition, a copy product of rituximab, and adalimumab were analyzed. Both mAbs contain additional alkaline C‐terminal lysine variants as confirmed by digest with carboxypeptidase B. The optimized CIEF methods for intact mAb and Fc/2 were tested for their potential as platform approaches for these mAbs. The CIEF method for Fc/2 was slightly adapted in this process. The pI values for major intact mAb variants were determined by adjacent pI markers resulting in 9.29 (rituximab) and 8.42 (adalimumab). In total, seven to eight charge variants could be distinguished for intact adalimumab and rituximab, respectively.

Determination of glycation levels in Erwinia chrysanthemi asparaginase drug product by liquid chromatography - mass spectrometry

Erwinase (Erwinia chrysanthemi L-asparaginase) Drug Product (DP) is a freeze-dried formulation with a three-year shelf life at 2-8 ^°C, and an established safety, stability and efficacy profile over the more than three decades of clinical use. Seven Erwinase® DP batches, released over a 7-year period, were screened by reversed-phase liquid chromatography coupled to time-of-flight mass spectrometry for glycation levels. This modification is a known and natural consequence of exposure of Erwinase Drug Product to glucose excipients in stabilizing formulations. Although glycation is detected in current release and stability methods, glycation, including the conditions under which this reaction occurs, has not been previously characterised in detail. We have found that glycation levels of different DP lots generally correlated with age, when they were stored at low temperature. This suggests that the glycation reaction continues over time within the Drug Product formulation in the lyophilised state, even under low temperature (+2-8 °C) conditions. We were also able to examine glycation levels of one DP lot, Lot D, held under long term stability at 3 different temperatures over a 5-year period. The 2 samples held at -20 °C and -80 °C, were glycated to levels of 12% and 17%, respectively. However, the DP Lot D sample held at +2-8 ^oC in this time period was found to be glycated to a level of 35.6%, with multiple glycations of individual subunits observed. For analytical reference materials, it is important to keep parameters such as glycation levels as constant as possible, to avoid a 'moving target' with respect to comparisons with release and stability testing. These data suggest that storage of DP as reference standards at a lower temperature (e.g., -20 °C) can significantly reduce levels of glycation over the longer time periods required for analytical reference standards.

A proof-of-concept analysis of carbohydrate-deficient transferrin by imaged capillary isoelectric focusing and in-capillary immunodetection

Carbohydrate-deficient transferrin (CDT) is a reliable biomarker for chronic alcohol abuse. We developed a method for CDT analysis by capillary isoelectric focusing, followed by immunodetection directly in the capillary, in an automated fashion and on a single platform (Peggy Sue™; ProteinSimple, CA, USA). Transferrin glycoforms in serum samples, including disialo-transferrin, were separated and their apparent isoelectric points and relative percentages were determined. The relative CDT values (percent of total transferrin) matched expected values for both healthy and alcoholic samples. Because the method leveraged the sensitivity of an immunoassay, CDT was measured when serum samples were diluted up to 1200-fold, reducing the volume of serum required. Finally, the process is fully automated, with up to 96 samples analyzed per batch.

Gradient-free determination of isoelectric points of proteins on chip

The isoelectric point (pI) of a protein is a key characteristic that influences its overall electrostatic behaviour. The majority of conventional methods for the determination of the isoelectric point of a molecule rely on the use of spatial gradients in pH, although significant practical challenges are associated with such techniques, notably the difficulty in generating a stable and well controlled pH gradient. Here, we introduce a gradient-free approach, exploiting a microfluidic platform which allows us to perform rapid pH change on chip and probe the electrophoretic mobility of species in a controlled field. In particular, in this approach, the pH of the electrolyte solution is modulated in time rather than in space, as in the case for conventional determinations of the isoelectric point. To demonstrate the general approachability of this platform, we have measured the isoelectric points of representative set of seven proteins, bovine serum albumin, β-lactoglobulin, ribonuclease A, ovalbumin, human transferrin, ubiquitin and myoglobin in microlitre sample volumes. The ability to conduct measurements in free solution thus provides the basis for the rapid determination of isoelectric points of proteins under a wide variety of solution conditions and in small volumes.

Capillary isoelectric focusing after sample enrichment with immunoaffinity chromatography in a single capillary

For accurate micro-scale quantification of a specific protein in biological fluids, immunoaffinity chromatography (IAC) and isoelectric focusing (IEF) were combined in a single fused-silica capillary. The inner wall of the capillary was coated with an anti-E-tag antibody at the inlet side to form an IAC column, and polydimethylacrylamide, a neutral polymer, at the outlet side to form the capillary for IEF. After loading a sample, the whole capillary was filled with a carrier ampholyte solution. An anode solution, an acid, was then introduced to fill only the IAC column segment. Focusing was started with a pressure that balances with the electroosmotic flow produced in the acidified IAC column. Fluorescence-labeled recombinant Fab with an E-tag spiked at 16 pM to 10 nM in 50% serum was separated and detected with high precision. The coupling principle allows rapid and high-resolution IEF analysis of a protein in a biological sample without any loss of the immunoaffinity captured protein.

SpeB proteolysis with imaged capillary isoelectric focusing for the characterization of domain-specific charge heterogeneities of reference and biosimilar Rituximab

The charge variations of therapeutic monoclonal antibody reveal important information of the post-translational modifications that may potentially impact the potency and safety of pharmaceutical products, especially during the evaluation of biosimilarity of therapeutic proteins. In this work, a novel SpeB-based proteolysis strategy coupling with imaged capillary isoelectric focusing was developed for the determination of domain-specific charge heterogeneities of innovator and generic Rituximab drug products from United States, European and Indian markets. It was observed that innovator Rituximab from the United States and Europe share highly similar peak distributions and charge heterogeneities with 26.2-26.6% Fc/2, 28.9-29.3% LC and 44.4-44.5% Fd peak areas detected, respectively, while multiple basic variations of Fc/2 and less acidic LC and Fd species were found from generic Rituximab from India with 20.9% Fc/2, 32.3% LC and 46.9% Fd peak areas detected. It was also demonstrated that structural changes caused by Carboxypeptidase B treatment and deamidation study at pH extremes could be sensitively captured with the established method, with the results further indicating that the generic product's basic variations of Fc/2 were un-cleaved Lysine residues, while the lack of certain acidic peaks on LC and Fd probably was due to the lower level of deamidation. This new strategy could become a useful tool to reveal domain-specific charge heterogeneities profiles of a variety of therapeutic monoclonal antibodies in regulated environments.

Charge variants in IgG1: Isolation, characterization, in vitro binding properties and pharmacokinetics in rats

Antibody charge variants have gained considerable attention in the biotechnology industry due to their potential influence on stability and biological activity. Subtle differences in the relative proportions of charge variants are often observed during routine biomanufacture or process changes and pose a challenge to demonstrating product comparability. To gain further insights into the impact on biological activity and pharmacokinetics (PK) of monoclonal antibody (mAb) charge heterogeneity, we isolated the major charge forms of a recombinant humanized IgG1 and compared their in vitro properties and in vivo PK. The mAb starting material had a pI range of 8.7-9.1 and was composed of about 20% acidic variants, 12% basic variants, and 68% main peak. Cation exchange displacement chromatography was used to isolate the acidic, basic, and main peak fractions for animal studies. Detailed analyses were performed on the isolated fractions to identify specific chemical modification contributing to the charge differences, and were also characterized for purity and in vitro potency prior to being administered either subcutaneously (SC) or intravenously (IV) in rats. All isolated materials had similar potency and rat FcRn binding relative to the starting material. Following IV or SC administration (10 mg/kg) in rats, no difference in serum PK was observed, indicating that physiochemical modifications and pI differences among charge variants were not sufficient to result in PK changes. Thus, these results provided meaningful information for the comparative evaluation of charge-related heterogeneity of mAbs, and suggested that charge variants of IgGs do not affect the in vitro potency, FcRn binding affinity, or the PK properties in rats.

Recent developments in CE and CEC of peptides

The article brings a comprehensive survey of recent developments and applications of high-performance capillary electromigration methods, zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography, to analysis, preparation, and physicochemical characterization of peptides. New approaches to the theoretical description and experimental verification of electromigration behavior of peptides and to methodology of their separations, such as sample preparation, adsorption suppression, and detection, are presented. Novel developments in individual CE and CEC modes are shown and several types of their applications to peptide analysis are presented: conventional qualitative and quantitative analysis, purity control, determination in biomatrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid and sequence analysis, and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of CE and CEC techniques to provide important physicochemical characteristics of peptides are demonstrated.

Profiling recombinant major birch pollen allergen Bet v 1a and carbamylated variants with CZE and CIEF

A preparation of recombinant birch pollen allergen of Betula verrucosa isoform 1a (Bet v 1a) containing chemically modified (carbamylated) variants has been analyzed by CZE and CIEF. In CZE, employing a 100 mmol/L MES buffer at pH 6.50, with 0.4 mmol/L tetraethylenepentamine (TEPA) added, allowed for the resolution of 17 protein fractions. The CIEF profiling of the allergen preparation required a combination of a wide-pH-range carrier ampholyte (CA) of pH 3-10 with two narrow-range CAs of pH 5-6 and 5-7. For CIEF, 91 mmol/L of glycine at pH 2.12 and 20 mmol/L of CHES at pH 10.00 were applied as anolyte and catholyte, respectively. The generated pH gradient was nonlinear with a flat slope for pH 4-6, thus providing an improved resolution. In CIEF, up to 18 protein fractions were distinguished as well. The pI of the target allergen Bet v 1a was 4.9 as determined by means of two pI marker compounds flanking the allergen. Relative purity of the target allergen within the preparation containing carbamylated variants was in accordance for both separation systems and varied between 40.7 and 42.8%.