Evaluation of capillary zone electrophoresis for charge heterogeneity testing of monoclonal antibodies

Microfluidic capillary electrophoresis - mass spectrometry for rapid charge-variant and glycoform assessment of monoclonal antibody biosimilar candidates

Early-stage cell line screening is a vital step in developing biosimilars of therapeutic monoclonal antibodies (mAbs). While the quality of the manufactured antibodies is commonly assessed by charge-based separation methods employing UV absorbance detection, these methods lack the ability to identify resolved mAb variants. We evaluated the performance of microfluidic capillary electrophoresis coupled to mass spectrometry (MCE-MS) as a rapid tool for profiling mAb biosimilar candidates from clonal cell lines. A representative originator sample was used to develop the MCE-MS method. The addition of dimethylsulfoxide (DMSO) to the background electrolyte yielded up to 60-fold enhancement of the protein MS signal. The resulting electropherograms consistently provided resolution of mAb charge variants within 10 min. Deconvoluted mass spectra facilitated the identification of basic variants such as C-terminal lysine and proline amidation, while the acidic variants could be assigned to deamidated forms. The MCE-MS method also allowed the identification of 18 different glycoforms in biosimilar samples. To mimic early-stage cell line selection, samples from five clonal cell lines that all expressed the same biosimilar candidate mAb were compared to their originator mAb. Based on the similarity observed in charge variants and glycoform profiles acquired by MCE-MS, the most promising candidate could be selected. The MCE-MS method demonstrated good overall reproducibility, as confirmed by a transferability study involving two separate laboratories. This study highlights the efficacy of the MCE-MS method for rapid proteoform screening of clonal cell line samples, underscoring its potential significance as an analytical tool in biosimilar process development.

Getting the Best out of Capillary Electrophoresis and Capillary Electrophoresis-Mass Spectrometry by Quantifying Sources of Peak Broadening for Proteins Using Polyelectrolyte Multilayer Coated Fused Silica Capillaries

Capillary electrophoresis (CE) has emerged as a relevant technique for protein and biopharmaceutical analysis, as it combines high separation efficiency, sensitivity, and versatility. The use of capillary coatings, including successive multiple ionic-polymer layers (SMILs), reduces interactions between analytes and the capillary, further improving the CE performance. Nevertheless, separations done on SMIL coatings rarely surpass 500 × 103 plates/m. To obtain the best out of the CE, it is interesting to have a detailed look at the sources of peak dispersion. Separations of a mix of model proteins were performed on (poly(diallyldimethylammonium chloride)/poly(styrenesulfonate))2.5-coated capillaries at different electrical field strengths, leading to plate height H against migration velocity u plots that enabled a quantitative analysis of each contribution. Using this model, capillary lengths and injected volumes were systematically varied. For the first time, the contribution of sample electrophoretic heterogeneity to the total peak dispersion was deciphered for model proteins and a monoclonal antibody. Dispersion due to electromigration was seen to have an impact on plate heights in the case of triangular peaks of small molecules but not for proteins under the present conditions. UV and mass spectrometry detections were compared on the same capillary, providing valuable information on the impact of the detection type on separation efficiency. Close to 1 million plates/m were reached in the best conditions.

Sensitive and rapid analysis of plasmid DNA topology isoforms by capillary gel electrophoresis with laser induced fluorescence in uncoated capillary

The work describes the use of SYBR Gold to improve the detection sensitivity of plasmid DNA topoisomers by capillary gel electrophoresis with laser induced fluorescence in an uncoated capillary. The impact of different dyes, including ethidium bromide, SYBR Green and SYBR Gold, was compared based on detection and separation of DNA plasmid topoisomers. Use of SYBR Gold enabled improvement of detection sensitivity by 15-fold while maintaining good separation resolution of the different topoisomers. The baseline dropped with the use SYBR Gold but was overcome by the employment of a capillary with longer ineffective length (40 vs. 20 cm). Separation resolution and reproducibility were impacted by the concentration of SYBR Gold and hydroxypropyl methylcellulose. With the use of a short capillary (10 cm effective length and 50 cm total length), fast separations of supercoiled, linear, open circular, and other isoforms were accomplished within 8 min. Appropriate capillary cleaning with 0.1 M sodium hydroxide/0.1 M hydrochloric acid and capillary storage with 0.1 M hydrochloric acid ensured good separation reproducibility of 217 runs during an extended period of use.

Identity verification of monoclonal antibodies by triple injection capillary zone electrophoresis

This paper presents an approach based on triple injection capillary zone electrophoresis for identification of monoclonal antibodies. The analyte to be identified is injected between two zones of a known reference. The distances between the reference zones (plug I and III) and the target zone (plug II) are adjusted by partial electrophoresis of the first and second injection plugs. The full migration time of the target analyte is calculated from the observed migration time by considering the migration times of the reference in the first and third injection plugs. The relative migration time, that is, the ratio between the full migration time of the analyte and the migration time of the reference in the third injection plug provides the basis for identification. Here, eight monoclonal antibodies, including a pair of biosimilars, were used interchangeably as both analyte and reference to investigate potential of the method. The relative migration time for a preliminary positive identification were found to vary between 0.994 and 1.006 (1.000 ± 0.006, p = 95%). Beside the relative migration time, isoform distribution, peak profiles, and early migrating peaks, originating from components in the pharmaceutical formulations, were successfully used to verify the identity of all tested monoclonal antibodies.

Modeling the behavior of monoclonal antibodies on hydrophobic interaction chromatography resins

Monoclonal antibodies (mAbs) require a high level of purity for regulatory approval and safe administration. High-molecular weight (HMW) species are a common impurity associated with mAb therapies. Hydrophobic interaction chromatography (HIC) resins are often used to remove these HMW impurities. Determination of a suitable HIC resin can be a time and resource-intensive process. In this study, we modeled the chromatographic behavior of seven mAbs across 13 HIC resins using measurements of surface hydrophobicity, surface charge, and thermal stability for mAbs, and hydrophobicity and zeta-potential for HIC resins with high fit quality (adjusted R2 > 0.80). We identified zeta-potential as a novel key modeling parameter. When using these models to select a HIC resin for HMW clearance of a test mAb, we were able to achieve 60% HMW clearance and 89% recovery. These models can be used to expedite the downstream process development for mAbs in an industry setting.

An interlaboratory capillary zone electrophoresis-UV study of various monoclonal antibodies, instruments, and ε-aminocaproic acid lots

Capillary zone electrophoresis ultraviolet (CZE-UV) has become increasingly popular for the charge heterogeneity determination of mAbs and vaccines. The ε-aminocaproic acid (eACA) CZE-UV method has been used as a rapid platform method. However, in the last years, several issues have been observed, for example, loss in electrophoretic resolution or baseline drifts. Evaluating the role of eACA on the reported issues, various laboratories were requested to provide their routinely used eACA CZE-UV methods, and background electrolyte compositions. Although every laboratory claimed to use the He et al. eACA CZE-UV method, most methods actually deviate from He's. Subsequently, a detailed interlaboratory study was designed wherein two commercially available mAbs (Waters' Mass Check Standard mAb [pI 7] and NISTmAb [pI 9]) were provided to each laboratory, along with two detailed eACA CZE-UV protocols for a short-end, high-speed, and a long-end, high-resolution method. Ten laboratories participated each using their own instruments, and commodities, showing excellence method performance (relative standard deviations [RSDs] of percent time-corrected main peak areas from 0.2% to 1.9%, and RSDs of migration times from 0.7% to 1.8% [n = 50 per laboratory], analysis times in some cases as short as 2.5 min). This study clarified that eACA is not the main reason for the abovementioned variations.

Two-Dimensional Capillary Zone Electrophoresis-Mass Spectrometry: Intact mAb Charge Variant Separation Followed by Peptide Level Analysis Using In-Capillary Digestion

Characterization of charge heterogeneity is an essential pillar for pharmaceutical development and quality control of therapeutic monoclonal antibodies (mAbs). The highly selective and commonly applied capillary zone electrophoresis (CZE) method containing high amounts of ε-aminocaproic acid (EACA) provides a detailed and robust charge heterogeneity profile of intact mAb variants. Nevertheless, the exact location of protein modifications within these charge profiles remains ambiguous. Electrospray ionization mass spectrometry (ESI-MS) is a promising tool for this purpose; however, EACA is incompatible with electrospray. In this context, we present a two-dimensional CZE-CZE-MS system to combine efficient charge variant separation of intact mAbs with subsequent peptide analysis after in-capillary digestion of selected charge variants. The first dimension is based on a generic CZE(EACA) method in a fused silica capillary. In the second dimension, a neutral-coated capillary is used for in-capillary reduction and digestion with Tris(2-carboxyethyl)phosphine (TCEP) and pepsin, followed by CZE separation and MS/MS-characterization of the resulting peptides. The setup is demonstrated using stressed and nonstressed mAbs where peaks of basic, main, and acidic variants were transferred in a heart-cut fashion, digested, and characterized on the peptide level. Sequence coverages of more than 90% were obtained for heavy chain (HC) and light chain (LC) for four different mAbs, including low-abundance variants (<2% of the main peak). Frequently observed modifications (deamidation, oxidation, etc.) could be detected and localized. This study demonstrates a proof-of-concept for identification and localization of protein modifications from CZE charge heterogeneity profiles and, in this way, is expected to support the development and quality control testing of protein pharmaceuticals.

Analysis of Denosumab by a Validated CZE Method and Determination of Sialic Acids by the RP-HPLC Method

A capillary zone electrophoresis (CZE) method was developed and validated to quantitate the monoclonal antibody denosumab (DmAb) and its charge variants in pharmaceutical products, demonstrating excellent precision, linearity and accuracy. Separations were obtained with migration times of 11.3 min for DmAb and the calibration curve was linear in the range of 0.95-20 mg/mL. The analytical comparability of seven batches of Prolia® showed mean differences of the estimated content/potencies of 1.87% lower, and 0.84 and 1.21% higher compared with the size-exclusion and reversed-phase liquid chromatography (SE-HPLC and RP-HPLC) methods and the osteoclast antiproliferative bioassay, respectively, with non-significant differences (P > 0.05). An RP-HPLC method with fluorescence detection (RP-HPLC-F), performed on a Kinetex® EVO C18 column (5 μm, 100 Å, 250 mm × 4.6 mm), was optimized to determine the levels of sialic acids of DmAb biomolecules, giving mean concentrations of 0.16 and 0.17 μg N-acetylneuraminic acid/mg DmAb for Prolia® and Xgeva® pharmaceutical products, respectively. The results demonstrated the capability of each one of the methods, and their use in combination constitutes a strategy to monitor instability, thereby assuring the quality and the batch-to-batch consistency of the biotechnology-derived medicine.

Method development for quantitative monitoring of monoclonal antibodies in upstream cell-culture process samples with limited sample preparation - An evaluation of various capillary coatings

Monoclonal antibodies (mAbs) have become an important class of biopharmaceuticals used for the treatment of various diseases. Their quantification during the manufacturing process is important. In this work, a capillary zone electrophoresis (CZE) method was developed for the monitoring of the mAb concentration during cell-culture processes. CZE method development rules are outlined, particularly discussing various capillary coatings, such as a neutral covalent polyvinyl alcohol coating, a dynamic successive multiple ionic-polymer coating, and dynamic coatings using background electrolyte additives such as triethanolamine (T-EthA) and triethylamine. The dynamic T-EthA coating resulted in most stable electro-osmotic flows and most efficient peak shapes. The method is validated over the range 0.1-10 mg/ml, with a linear range of 0.08-1.3 mg/ml and an extended range of 1-10 mg/ml by diluting samples in the latter concentration range 10-fold in water. The intraday precision and accuracy were 2%-12% and 88%-107%, respectively, and inter-day precision and accuracy were 4%-9% and 93%-104%, respectively. The precision and accuracy of the lowest concentration level (0.08 mg/ml) were slightly worse and still well in scope for monitoring purposes. The presented method proved applicable for analysing in-process cell-culture samples from different cell-culture processes and is possibly well suited as platform method.

Evaluation of an icIEF-MS system for comparable charge variant analysis of biotherapeutics with rapid peak identification by mass spectrometry

Protein therapeutics are usually produced in heterogeneous forms during bioproduction and bioprocessing. Heterogeneity results from post‐translational modifications that can yield charge variants and require characterization throughout product development and manufacturing. Isoelectric focusing (IEF) with UV detection is one of the most common methods to evaluate protein charge heterogeneity in the biopharmaceutical industry. To identify charge variant peaks, a new imaged microfluidic chip‐based isoelectric focusing (icIEF) system coupled directly to mass spectrometry was recently reported. Bridging is required to demonstrate comparability between existing and new technology. As such, here we demonstrate the comparability of the pI value measurement and relative charge species distributions between the icIEF‐MS system and the control data from a frequently utilized methodology in the biopharmaceutical industry for several blinded development‐phase biopharmaceutical monoclonal antibodies across a wide pI range of 7.3–9.0. Hyphenation of the icIEF system with mass spectrometry enabled direct and detailed structural determination of a test molecule, with masses suggesting acidic and basic shifts are caused by sialic acid additions and the presence of unprocessed lysine residues. In addition, MS analysis further identified several low‐abundance glycoforms. The icIEF‐MS system provides sample quantification, characterization, and identification of mAb proteoforms without sacrificing icIEF quantification comparability or speed.

Coupling Anion Exchange Chromatography with Native Mass Spectrometry for Charge Heterogeneity Characterization of Monoclonal Antibodies

Despite the recent success of coupling anion exchange chromatography with native mass spectrometry (AEX-MS) to study anionic proteins, the utility of AEX-MS methods in therapeutic monoclonal antibody (mAb) characterization has been limited. In this work, we developed and optimized a salt gradient-based AEX-MS method and explored its utility in charge variant analysis of therapeutic mAbs. We demonstrated that, although the developed AEX-MS method is less useful for IgG1 molecules that have higher isoelectric points (pIs), it is an attractive alternative for charge variant analysis of IgG4 molecules. By elevating the column temperature and lowering the mAb pI through PNGase F-mediated deglycosylation, the chromatographical resolution from AEX separation can be significantly improved. We also demonstrated that, after PNGase F and IdeS digestion, the AEX-MS method exhibited excellent resolving power for multiple attributes in the IgG4 Fc region, including unprocessed C-terminal Lys, N-glycosylation occupancy, and several conserved Fc deamidations, making it ideally suited for multiple attribute monitoring (MAM). Through fractionation and peptide mapping analysis, we also demonstrated that the developed AEX-MS method can provide site-specific and isoform-resolved separation of Fc deamidation products, allowing rapid and artifact-free quantitation of these modifications without performing bottom-up analysis.

Analytical Similarity Assessment of Biosimilars: Global Regulatory Landscape, Recent Studies and Major Advancements in Orthogonal Platforms

Biopharmaceuticals are one of the fastest-growing sectors in the biotechnology industry. Within the umbrella of biopharmaceuticals, the biosimilar segment is expanding with currently over 200 approved biosimilars, globally. The key step towards achieving a successful biosimilar approval is to establish analytical and clinical biosimilarity with the innovator. The objective of an analytical biosimilarity study is to demonstrate a highly similar profile with respect to variations in critical quality attributes (CQAs) of the biosimilar product, and these variations must lie within the range set by the innovator. This comprises a detailed comparative structural and functional characterization using appropriate, validated analytical methods to fingerprint the molecule and helps reduce the economic burden towards regulatory requirement of extensive preclinical/clinical similarity data, thus making biotechnological drugs more affordable. In the last decade, biosimilar manufacturing and associated regulations have become more established, leading to numerous approvals. Biosimilarity assessment exercises conducted towards approval are also published more frequently in the public domain. Consequently, some technical advancements in analytical sciences have also percolated to applications in analytical biosimilarity assessment. Keeping this in mind, this review aims at providing a holistic view of progresses in biosimilar analysis and approval. In this review, we have summarized the major developments in the global regulatory landscape with respect to biosimilar approvals and also catalogued biosimilarity assessment studies for recombinant DNA products available in the public domain. We have also covered recent advancements in analytical methods, orthogonal techniques, and platforms for biosimilar characterization, since 2015. The review specifically aims to serve as a comprehensive catalog for published biosimilarity assessment studies with details on analytical platform used and critical quality attributes (CQAs) covered for multiple biotherapeutic products. Through this compilation, the emergent evolution of techniques with respect to each CQA has also been charted and discussed. Lastly, the information resource of published biosimilarity assessment studies, created during literature search is anticipated to serve as a helpful reference for biopharmaceutical scientists and biosimilar developers.

An improved capillary isoelectric focusing-mass spectrometry method for high-resolution characterization of monoclonal antibody charge variants

Routine and high-resolution characterization of monoclonal antibody (mAb) charge variants is vital for controlling mAb quality as therapeutics. Capillary isoelectric focusing-mass spectrometry (cIEF-MS) has emerged as a powerful tool for characterizing mAb charge variants because it can achieve high-resolution separation and highly sensitive detection of proteins. It provides much better identification of charge variants than the traditionally used cIEF-UV method. However, further improvement of cIEF-MS regarding stability and separation resolution is needed. Here, we improved the stability and enhanced separation resolution of automated cIEF-MS by bettering the quality of capillary neutral coating, reducing catholyte pH to 10 for cIEF-MS for the first time, and systematically optimizing the cIEF separation conditions. The improved cIEF-MS method was applied to characterize charge variants of three previously well characterized mAbs (NISTmAb, cetuximab, trastuzumab) and one tool mAb (mAb1). The charge variants of the studied mAbs were well resolved, and the majority of post-translational modifications (PTMs) found in those mAbs agreed with the literature. cIEF-MS analyses of mAb1 were capable of discovering ten charge variants with various interesting PTMs, such as PGK amidation, incomplete C-terminal lysine clipping, glycosylation, and deamination. cIEF-MS was successfully used for accurately determining the isoelectric points (pIs) of mAb1 charge variants via analyzing the pI markers and spiking in a standard protein (cytochrome c) to samples for migration time normalization, which is beneficial for evaluating pI-related pharmacokinetic properties. Our cIEF-MS agreed with and, in some cases (i.e., cetuximab and mAb1), outperformed cIEF-UV for detecting mAb charge variants.

CE-MS for Proteomics and Intact Protein Analysis

This chapter aims to explore various parameters involved in achieving high-end capillary electrophoresis hyphenated to mass spectrometry (CE-MS) analysis of proteins, peptides, and their posttranslational modifications. The structure of the topics discussed in this book chapter is conveniently mapped on the scheme of the CE-MS system itself, starting from sample preconcentration and injection techniques and finishing with mass analyzer considerations. After going through the technical considerations, a variety of relevant applications for this analytical approach are presented, including posttranslational modifications analysis, clinical biomarker discovery, and its growing use in the biotechnological industry.

Applications of capillary electrophoresis for biopharmaceutical product characterization

Capillary electrophoresis (CE), after being introduced several decades ago, has carved out a niche for itself in the field of analytical characterization of biopharmaceutical products. It does not only offer fast separation, high resolution in miniaturized format, but equally importantly represents an orthogonal separation mechanism to high-performance liquid chromatography. Therefore, it is not surprising that CE-based methods can be found in all major pharmacopoeias and are recommended for the analysis of biopharmaceutical products during process development, characterization, quality control, and release testing. Different separation formats of CE, such as capillary gel electrophoresis, capillary isoelectric focusing, and capillary zone electrophoresis are widely used for size and charge heterogeneity characterization as well as purity and stability testing of therapeutic proteins. Hyphenation of CE with MS is emerging as a promising bioanalytical tool to assess the primary structure of therapeutic proteins along with any impurities. In this review, we confer the latest developments in capillary electrophoresis, used for the characterization of critical quality attributes of biopharmaceutical products covering the past 6 years (2015-2021). Monoclonal antibodies, due to their significant share in the market, have been given prioritized coverage.

Recent biopharmaceutical applications of capillary electrophoresis methods on recombinant DNA technology-based products

Biopharmaceuticals (recombinant technology-based products, vaccines, whole blood and blood components, gene therapy, cells, tissues, etc.,) are described as biological medical products produced from various living sources such as human, microbial, animal, and so on by manufacturing, extraction, or semi-synthesis. They are complex molecules having high molecular weights. For their safety and efficacy, their structural, clinical, physicochemical, and chemical features must be carefully controlled, and they must be well characterized by analytical techniques before the approval of the final product. Capillary electrophoresis (CE) having versatile modes can provide valuable safety and efficacy information, such as amino acid sequence, size variants (low and high molecular weight variants), charged variants (acidic and basic impurities), aggregates, N-linked glycosylation, and O-linked glycosylation. There are numerous applications of CE in the literature. In this review, the most significant and recent studies on the analysis of recombinant DNA technology-based products using different CE modes in the last ten years have been overviewed. It was seen that the researches mostly focus on the analysis of mAbs and IgG. In addition, in recent years, researchers have started to prefer CE combined mass spectrometry (MS) techniques to provide a more detailed characterization for protein and peptide fragments.

Methionine oxidation of proteins analyzed by affinity capillary electrophoresis in presence of silver(I) and gold(III) ions

Oxidative damage of biopharmaceuticals during manufacturing and storage is a key concern throughout pharmaceutical development. However, few simple and robust analytical methods are available for the determination of oxidation sites. Here, the potential of affinity capillary electrophoresis (ACE) in the separation of proteins with oxidized methionine (Met) residues is shown. Silver(I) and gold(I) ions have the attribute to selectively form complexes with thioethers over sulfoxides. The addition of these ions to the BGE leads to a selective complexation of Met residues and, thus, to a change of charge allowing separation of species according to the different oxidation states of Met. The mechanisms of these interactions are discussed and binding constants for peptides containing Met with silver(I) are calculated. Additionally, the proposed method can be used as an indicator of oxidative stress in large proteins. The presented technique is easily accessible, economical, and has rapid analysis times, adding new approaches to the analytical toolbox of Met sulfoxide detection.

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.

Isolation and characterization of charge variants of infliximab biosimilar HS626

Charge variants are the most commonly observed sources of heterogeneity in the routine manufacturing of monoclonal antibodies. To gain further insight into the structural foundation of charge heterogeneity and its influence on biological functions, an infliximab biosimilar HS626 from a biopharmaceutical facility was isolated by semipreparative cation exchange chromatography (CEX) to obtain fractions of acidic and basic charge variants and determine the main species. It was assessed again by CEX to ensure purities. Through a series of structural and physicochemical characterizations, we concluded that the acidic variants were caused by fragments, Met oxidation, Asn deamidation, higher levels of sialylation and galactosylation of N-linked glycans, and less high mannose. The basic variants resulted mainly from aggregates, fragments, and Met oxidation. Through further analysis of antigen binding affinity, cell death inhibitory activity, ADCC, and CDC, as well as FcRn, FcγRIIIa, and C1q affinity, we demonstrated that the charge heterogeneity did not affect biological functions. This research enhances the understanding of charge variants, which are usually effective components that should not be intentionally reduced unless biological functions are affected.

Application of affinity capillary electrophoresis for charge heterogeneity profiling of biopharmaceuticals

Charge heterogeneity profiling is important for the quality control (QC) of biopharmaceuticals. Because of the increasing complexity of these therapeutic entities [1], the development of alternative analytical techniques is needed. In this work, flow-through partial-filling affinity capillary electrophoresis (FTPFACE) has been established as a method for the analysis of a mixture of two similar monoclonal antibodies (mAbs). The addition of a specific ligand results in the complexation of one mAb in the co-formulation, thus changing its migration time in the electric field. This allows the characterization of the charged variants of the non-shifted mAb without interferences. Adsorption of proteins to the inner capillary wall has been circumvented by rinsing with guanidine hydrochloride before each injection. The presented FTPFACE approach requires only very small amounts of ligands and provides complete comparability with a standard CZE of a single mAb.

Comparative charge-based separation study with various capillary electrophoresis (CE) modes and cation exchange chromatography (CEX) for the analysis of monoclonal antibodies

Charge heterogeneity is an important critical quality attribute for the analysis of monoclonal antibodies (mAbs). For this, (imaged) capillary isoelectric focusing ((i)cIEF), ion exchange chromatography (IEC) and, recently, capillary zone electrophoresis (CZE) are the predominantly used techniques. In order to investigate which one is most suitable to answer a specific analytical question, here, the four aforementioned separation techniques were systematically evaluated using NISTmAb and Infliximab as test molecules. The performance parameters (precision, separation efficiency, linearity and sensitivity) were determined under comparable conditions. Moreover, important aspects for daily routine such as speed and ease of use were considered. Each technique has its own pros and cons. The (i)cIEF methodology is distinguished by its excellent separation efficiency. In addition, the native fluorescence mode in icIEF is a good tool to analyze small sample amounts (LOQ: 2.8 mg/l for Infliximab). Nevertheless, high performance liquid chromatography (HPLC) still has superior precision. CZE, and also micellar electrokinetic chromatography (MEKC), have emerged as further interesting alternatives. For all techniques, variations connected to the sample preparation strongly influence precision. Looking at the relative standard deviation (RSD) values of the relative peak areas, all techniques provide acceptable performance (RSD: 0.6-1.6%).

Intact monoclonal antibodies separation and analysis by sheathless capillary electrophoresis-mass spectrometry

Capillary electrophoresis-mass spectrometry coupling is a growing technique in biopharmaceutics characterization. Assessment of monoclonal antibodies is well known at middle-up and bottom-up levels to obtain information about the sequence, post-translational modifications and degradation products. Intact protein analysis is an actual challenge to be closer to the real protein structure. At this level, actual techniques are time consuming or cumbersome processes. In this work, a 20 minutes separation method has been developed to optimize characterization of intact monoclonal antibodies. Thus, separation has been done on a positively charged coated capillary with optimized volatile background electrolyte and sample buffer. Three world-wide health authorities approved monoclonal antibodies have been used to set up a rapid and ease of use method. Intact trastuzumab, rituximab and palivizumab isoforms have been partially separated with this method in less than 20 minutes under denaturing conditions. For each monoclonal antibody, 2X-glycosylated and 1X-glycosylated structures have been identified and separated. Concerning basic and acidic variants, potential aspartic acid isomerization modification and asparagine deamidation have been observed. Accurate mass determination for high-mass molecular species remains a challenge, but the progress in intact monoclonal antibodies separation appears very promising for biopharmaceutics characterization.

Advances in capillary electrophoresis for the life sciences

Capillary electrophoresis (CE) played an important role in developments in the life sciences. The technique is nowadays used for the analysis of both large and small molecules in applications where it performs better than or is complementary to liquid chromatographic techniques. In this review, principles of different electromigration techniques, especially capillary isoelectric focusing (CIEF), capillary gel (CGE) and capillary zone electrophoresis (CZE), are described and recent developments in instrumentation, with an emphasis on mass spectrometry (MS) coupling and microchip CE, are discussed. The role of CE in the life sciences is shown with applications in which it had a high impact over the past few decades. In this context, current practice for the characterization of biopharmaceuticals (therapeutic proteins) is shown with CIEF, CGE and CZE using different detection techniques, including MS. Subsequently, the application of CGE and CZE, in combination with laser induced fluorescence detection and CZE-MS are demonstrated for the analysis of protein-released glycans in the characterization of biopharmaceuticals and glycan biomarker discovery in biological samples. Special attention is paid to developments in capillary coatings and derivatization strategies for glycans. Finally, routine CE analysis in clinical chemistry and latest developments in metabolomics approaches for the profiling of small molecules in biological samples are discussed. The large number of CE applications published for these topics in recent years clearly demonstrates the established role of CE in life sciences.

Separation of two microbial transglutaminase isomers from Streptomyces mobaraensis using pH-mediated cation exchange chromatography and their characterization

Microbial transglutaminase (MTGase) derived from Streptomyces mobaraensis has been widely used in the food, biotechnology and medicine fields. The lot-to-lot consistency and product stability of MTGase must be ensured. The structure and charge variants of MTGase can influence its bioactivity. In this study, MTGase isomers (MTG I1 and MTG I2) were found during the separation of MTGase by pH-mediated cation-exchange chromatography. MTG I1 and MTG I2 had the same molecular weight and N-terminal amino acid sequences, but they showed charge heterogeneity. The affinity of MTG I2 for substrates was higher than that of MTG I1, and the thermal stability and the acid-base tolerance of MTG I1 were significantly higher than that of MTG I2. Therefore, the ratio of MTG I1/MTG I2 was positively correlated with the stability of MTGase. The buffer pH and the ionic strength of the eluent had significant effects on the separation of MTG I1 and MTG I2, and the elution gradient steepness and column load showed little effect on the separation of the MTG I1 and MTG I2 peaks. We built a stable and repeatable separation method for MTG I1 and MTG I2. MTG I1 could transform into MTG I2, but MTG I2 was unable to transform into MTG I1, making the transformation of MTG I1 to MTG I2 was irreversible. When MTG I2 was removed from the MTGase, a portion of the MTG I1 could transform into MTG I2. Therefore, one way to increase the stability of MTGase was to reduce the transformation of MTG I1 to MTG I2.

Two-dimensional capillary electrophoresis-mass spectrometry (CE-CE-MS): coupling MS-interfering capillary electromigration methods with mass spectrometry

Electromigration separation techniques often demand certain compounds in the electrolyte to achieve the required selectivity and efficiency. These compounds, including the electrolyte itself, ampholytes, polymeric compounds for sieving, complexing agents, tensides, etc. are often non-volatile. Thus, interference with the electrospray ionization process is a common issue, impeding direct coupling of such electrolyte systems to mass spectrometry. Still, several options exist to obtain mass spectra after separation, including offline fractionation, alternative ionization, dilution, or the change to volatile constituents. In the first part of this article, these methods are discussed. However, all of these options are a compromise of separation performance and sensitivity of mass spectrometric detection. Two-dimensional capillary electrophoresis-mass spectrometry (CE-CE-MS) systems represent a promising alternative to the aforementioned challenges, as they allow the use of existing methods with best separation performance in combination with sensitive mass characterization. In this context, the second part of this article is dedicated to the advantages, limitations, and applications of this approach. Finally, an outlook towards future developments is given.

Qualification of NISTmAb charge heterogeneity control assays

The NISTmAb is a monoclonal antibody Reference Material from the National Institute of Standards and Technology; it is a class-representative IgG1κ intended serve as a pre-competitive platform for harmonization and technology development in the biopharmaceutical industry. The publication series of which this paper is a part describes NIST's overall control strategy to ensure NISTmAb quality and availability over its lifecycle. In this paper, the development and qualification of methods for monitoring NISTmAb charge heterogeneity are described. Capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF) assays were optimized and evaluated as candidate assays for NISTmAb quality control. CIEF was found to be suitable as a structural characterization assay yielding information on the apparent pI of the NISTmAb. CZE was found to be better suited for routine monitoring of NISTmAb charge heterogeneity and was qualified for this purpose. This paper is intended to provide relevant details of NIST's charge heterogeneity control strategy to facilitate implementation of the NISTmAb as a test molecule in the end user's laboratory. Graphical Abstract Representative capillary zone electropherogram of the NIST monoclonal antibody (NISTmAb). The NISTmAb is a publicly available research tool intended to facilitate advancement of biopharmaceutical analytics.

Optimization of capillary zone electrophoresis for charge heterogeneity testing of biopharmaceuticals using enhanced method development principles

CZE is a well-established technique for charge heterogeneity testing of biopharmaceuticals. It is based on the differences between the ratios of net charge and hydrodynamic radius. In an extensive intercompany study, it was recently shown that CZE is very robust and can be easily implemented in labs that did not perform it before. However, individual characteristics of some examined proteins resulted in suboptimal resolution. Therefore, enhanced method development principles were applied here to investigate possibilities for further method optimization. For this purpose, a high number of different method parameters was evaluated with the aim to improve CZE separation. For the relevant parameters, design of experiments (DoE) models were generated and optimized in several ways for different sets of responses like resolution, peak width and number of peaks. In spite of product specific DoE optimization it was found that the resulting combination of optimized parameters did result in significant improvement of separation for 13 out of 16 different antibodies and other molecule formats. These results clearly demonstrate generic applicability of the optimized CZE method. Adaptation to individual molecular properties may sometimes still be required in order to achieve optimal separation but the set screws discussed in this study [mainly pH, identity of the polymer additive (HPC versus HPMC) and the concentrations of additives like acetonitrile, butanolamine and TETA] are expected to significantly reduce the effort for specific optimization.

Molecular and functional analysis of monoclonal antibodies in support of biologics development

Monoclonal antibody (mAb)-based therapeutics are playing an increasingly important role in the treatment or prevention of many important diseases such as cancers, autoimmune disorders, and infectious diseases. Multi-domain mAbs are far more complex than small molecule drugs with intrinsic heterogeneities. The critical quality attributes of a given mAb, including structure, post-translational modifications, and functions at biomolecular and cellular levels, need to be defined and profiled in details during the developmental phases of a biologics. These critical quality attributes, outlined in this review, serve an important database for defining the drug properties during commercial production phase as well as post licensure life cycle management. Specially, the molecular characterization, functional assessment, and effector function analysis of mAbs, are reviewed with respect to the critical parameters and the methods used for obtaining them. The three groups of analytical methods are three essential and integral facets making up the whole analytical package for a mAb-based drug. Such a package is critically important for the licensure and the post-licensure life cycle management of a therapeutic or prophylactic biologics. In addition, the basic principles on the evaluation of biosimilar mAbs were discussed briefly based on the recommendations by the World Health Organization.

Method development and qualification of capillary zone electrophoresis for investigation of therapeutic monoclonal antibody quality

Capillary electrophoresis techniques are widely used in the analytical biotechnology. Different electrophoretic techniques are very adequate tools to monitor size-and charge heterogenities of protein drugs. Method descriptions and development studies of capillary zone electrophoresis (CZE) have been described in literature. Most of them are performed based on the classical one-factor-at-time (OFAT) approach. In this study a very simple method development approach is described for capillary zone electrophoresis: a "two-phase-four-step" approach is introduced which allows a rapid, iterative method development process and can be a good platform for CZE method. In every step the current analytical target profile and an appropriate control strategy were established to monitor the current stage of development. A very good platform was established to investigate intact and digested protein samples. Commercially available monoclonal antibody was chosen as model protein for the method development study. The CZE method was qualificated after the development process and the results were presented. The analytical system stability was represented by the calculated RSD% value of area percentage and migration time of the selected peaks (<0.8% and <5%) during the intermediate precision investigation.

Cutting-edge capillary electrophoresis characterization of monoclonal antibodies and related products

Out of all categories, monoclonal antibodies (mAbs), biosimilar, antibody-drug conjugates (ADCs) and Fc-fusion proteins attract the most interest due to their strong therapeutic potency and specificity. Because of their intrinsic complexity due to a large number of micro-heterogeneities, there is a crucial need of analytical methods to provide comprehensive in-depth characterization of these molecules. CE presents some obvious benefits as high resolution separation and miniaturized format to be widely applied to the analysis of biopharmaceuticals. CE is an effective method for the separation of proteins at different levels. capillary gel electrophoresis (CGE), capillary isoelectric focusing (cIEF) and capillary zone electrophoresis (CZE) have been particularly relevant for the characterization of size and charge variants of intact and reduced mAbs, while CE-MS appears to be a promising analytical tool to assess the primary structure of mAbs and related products. This review will be dedicated to detail the current and state-of-the-art CE-based methods for the characterization of mAbs and related products.

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.

Development of a capillary zone electrophoresis method for dose determination in a tetravalent dengue vaccine candidate

Dengue is known to cause morbidity and mortality worldwide and currently there is neither available specific therapeutics to treat nor a vaccine to prevent this disease. Although efforts are being made, development of a vaccine against this disease remains challenging. Hawaii Biotech Inc developed a recombinant subunit envelope protein-based vaccine against all four serotypes produced in Drosophila S2 cells which were transferred over to Merck in 2010. Each subunit of the four dengue serotypes contains the N-terminal 80% of the amino acids comprising the envelope protein (DEN-80E). A Phase 1 study using only monovalent DEN1-80E was done by Hawaii Biotech Inc and most recently, a Phase 1 clinical trial of the tetravalent DEN-80E formulation (V180) was conducted. Here, we report the development of a dose assay for the tetravalent dengue vaccine-containing subunit protein of DEN1-80E, DEN2-80E, DEN3-80E, and DEN4-80E using various separation methods such as HPLC and CE. Based on the results of the comparison, the CZE separation was chosen as the most suitable method to perform the dose assay for the tetravalent dengue vaccine.