Characterization of cation exchanger stationary phases applied for the separations of therapeutic monoclonal antibodies

What is the role of current mass spectrometry in pharmaceutical analysis?

The role of mass spectrometry (MS) has become more important in most application domains in recent years. Pharmaceutical analysis is specific due to its stringent regulation procedures, the need for good laboratory/manufacturing practices, and a large number of routine quality control analyses to be carried out. The role of MS is, therefore, very different throughout the whole drug development cycle. While it dominates within the drug discovery and development phase, in routine quality control, the role of MS is minor and indispensable only for selected applications. Moreover, its role is very different in the case of analysis of small molecule pharmaceuticals and biopharmaceuticals. Our review explains the role of current MS in the analysis of both small-molecule chemical drugs and biopharmaceuticals. Important features of MS-based technologies being implemented, method requirements, and related challenges are discussed. The differences in analytical procedures for small molecule pharmaceuticals and biopharmaceuticals are pointed out. While a single method or a small set of methods is usually sufficient for quality control in the case of small molecule pharmaceuticals and MS is often not indispensable, a large panel of methods including extensive use of MS must be used for quality control of biopharmaceuticals. Finally, expected development and future trends are outlined.

Cation exchange chromatography on a monodisperse 3 µm particle enables extensive analytical similarity assessment of biosimilars

Biosimilarity assessment requires extensive characterization and comparability exercises to investigate product quality attributes of an originator product and its potential biosimilar(s) and to highlight any differences between them. Performing a thorough comparison allows a shortened approval path, which also eliminates lengthy and expensive clinical trials, ensuring comparable product quality and efficacy but at lower drug prices. The wide variety of analytical methods available for biosimilar assessment ranges from biological to analytical assays, each providing orthogonal information to fully characterize biosimilar candidates. Intact native mass spectrometry (MS) has been shown to be an excellent tool for detection and monitoring of important quality attributes such as N-glycosylation, deamidation, sequence truncation and higher order structures. When combined with efficient upfront separation methods, simplification of the proteoform heterogeneity and associated complexity prior to MS analysis can be achieved. Native mass spectrometry can provide robust and accurate results within short analysis times and requires minimal sample preparation. In this study we report the use of a monodisperse strong cation exchange chromatography phase hyphenated with Orbitrap mass spectrometry (SCX-MS) to compare the best-selling biopharmaceutical product Humira® with 7 commercially approved biosimilar products. SCX-MS analysis allowed for the identification of previously described as well as so far unreported proteoforms and their relative quantitation across all samples, revealing differences in N-glycosylation and lysine truncation, as well as unique features for some products such as sialylation and N-terminal clipping. SCX-MS analysis, powered by a highly efficient separation column, enabled deep and efficient analytical comparison of biosimilar products.

Yields and product comparison between Escherichia coli BL21 and W3110 in industrially relevant conditions: anti-c-Met scFv as a case study

INTRODUCTION

In the biopharmaceutical industry, Escherichia coli is one of the preferred expression hosts for large-scale production of therapeutic proteins. Although increasing the product yield is important, product quality is a major factor in this industry because greatest productivity does not always correspond with the highest quality of the produced protein. While some post-translational modifications, such as disulphide bonds, are required to achieve the biologically active conformation, others may have a negative impact on the product's activity, effectiveness, and/or safety. Therefore, they are classified as product associated impurities, and they represent a crucial quality parameter for regulatory authorities.

RESULTS

In this study, fermentation conditions of two widely employed industrial E. coli strains, BL21 and W3110 are compared for recombinant protein production of a single-chain variable fragment (scFv) in an industrial setting. We found that the BL21 strain produces more soluble scFv than the W3110 strain, even though W3110 produces more recombinant protein in total. A quality assessment on the scFv recovered from the supernatant was then performed. Unexpectedly, even when our scFv is correctly disulphide bonded and cleaved from its signal peptide in both strains, the protein shows charge heterogeneity with up to seven distinguishable variants on cation exchange chromatography. Biophysical characterization confirmed the presence of altered conformations of the two main charged variants.

CONCLUSIONS

The findings indicated that BL21 is more productive for this specific scFv than W3110. When assessing product quality, a distinctive profile of the protein was found which was independent of the E. coli strain. This suggests that alterations are present in the recovered product although the exact nature of them could not be determined. This similarity between the two strains' generated products also serves as a sign of their interchangeability. This study encourages the development of innovative, fast, and inexpensive techniques for the detection of heterogeneity while also provoking a debate about whether intact mass spectrometry-based analysis of the protein of interest is sufficient to detect heterogeneity in a product.

Structural and Functional Analysis of CEX Fractions Collected from a Novel Avastin® Biosimilar Candidate and Its Innovator: A Comparative Study

Avastin^® is a humanized recombinant monoclonal antibody used to treat cancer by targeting VEGF-A to inhibit angiogenesis. SIMAB054, an Avastin^® biosimilar candidate developed in this study, showed a different charge variant profile than its innovator. Thus, it is fractionated into acidic, main, and basic isoforms and collected physically by Cation Exchange Chromatography (CEX) for a comprehensive structural and functional analysis. The innovator product, fractionated into the same species and collected by the same method, is used as a reference for comparative analysis. Ultra-Performance Liquid Chromatography (UPLC) ESI-QToF was used to analyze the modifications leading to charge heterogeneities at intact protein and peptide levels. The C-terminal lysine clipping and glycosylation profiles of the samples were monitored by intact mAb analysis. The post-translational modifications, including oxidation, deamidation, and N-terminal pyroglutamic acid formation, were determined by peptide mapping analysis in the selected signal peptides. The relative binding affinities of the fractionated charge isoforms against the antigen, VEGF-A, and the neonatal receptor, FcRn, were revealed by Surface Plasmon Resonance (SPR) studies. The results show that all CEX fractions from the innovator product and the SIMAB054 shared the same structural variants, albeit in different ratios. Common glycoforms and post-translational modifications were the same, but at different percentages for some samples. The dissimilarities were mostly originating from the presence of extra C-term Lysin residues, which are prone to enzymatic degradation in the body, and thus they were previously assessed as clinically irrelevant. Another critical finding was the presence of different glyco proteoforms in different charge species, such as increased galactosylation in the acidic and afucosylation in the basic species. SPR characterization of the isolated charge variants further confirmed that basic species found in the CEX analyses of the biosimilar candidate were also present in the innovator product, although at lower amounts. The charge variants’ in vitro antigen- and neonatal receptor-binding activities varied amongst the samples, which could be further investigated in vivo with a larger sample set to reveal the impact on the pharmacokinetics of drug candidates. Minor structural differences may explain antigen-binding differences in the isolated charge variants, which is a key parameter in a comparability exercise. Consequently, such a biosimilar candidate may not comply with high regulatory standards unless the binding differences observed are justified and demonstrated not to have any clinical impact.

Characterization and Value Assignment of a Monoclonal Antibody Reference Material, NMIJ RM 6208a, AIST-MAB

Monoclonal antibodies have been established as the largest product class of biopharmaceuticals. Since extensive characterization is required for development and quality control of monoclonal antibody, a widely available reference material (RM) is needed. Herein, a humanized IgG1κ monoclonal antibody reference material, RM 6208-a, AIST-MAB, was established by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). The monoclonal antibody solution was produced as a pharmaceutical grade using a Chinese hamster ovary-derived cell line. The assigned indicative value represents the concentration of the antibody with a heterotetrameric structure including oligomeric forms, determined by an amino acid analysis using isotope dilution mass spectrometry, and their homogeneity and stability were assessed. In addition to antibody concentration, various physicochemical properties, including peptide mapping data, charge variants, and aggregates, were examined. This RM is intended for use in validation of analytical procedures and instruments such as a system suitability test for quantification of antibody. It is also intended for comparing and evaluating the results of antibody analyses across analytical methods and analytical laboratories such as inter-laboratory comparison. Both the material and the set of data from our study provide a tool for an accurate and reliable characterization of product quality attributes of monoclonal antibodies in biopharmaceutical and metrology communities.

Hyphenation of strong cation exchange chromatography to native mass spectrometry for high throughput online characterization of charge heterogeneity of therapeutic monoclonal antibodies

Characterization of charge heterogeneity in monoclonal antibodies (mAbs) is needed during developability assessment and downstream development of drug candidates. Charge heterogeneity can come from post-translational modifications like deamidation, isomerization, and sialylation. Elucidation of charge variants with mass spectrometry (MS) has historically been challenging. Due to the nonvolatility and high ionic strength of conventional buffer systems, labor-intensive offline fractionation followed by MS analysis is routinely used. Here, we describe an alternative strategy that directly couples strong cation exchange (SCX) chromatography to high-resolution Orbitrap MS for online native MS analysis (SCX-MS). A combined pH and salt gradient was used for universal separation of mAbs from a wide range of pI values (6.38 ~ 9.2), including infliximab (Remicade®, chimeric IgG1/kappa), NISTmab (humanized IgG1/kappa) and trastuzumab (Herceptin®, humanized IgG1/kappa), without tailoring of chromatographic profiles. Liquid chromatography and MS parameters were optimized to achieve high-quality spectra and enhanced detection of low abundant species under high flow rate conditions. Genedata Expressionist, a vendor agnostic software, was used for data processing. This integrated strategy allows unbiased characterization of numerous charge variant species and low molecular weight fragments (<0.05%) without post-column flow splitting. The application was further expanded with middle-up approaches for subdomain analysis, which demonstrated the versatility of the strategy for analysis of various construct types. With our analysis of mAbs during developability assessment and forced degradation studies, which aimed at assessing potential critical quality attributes in antibody drug molecules, we provide, for the first time, direct visualization of molecular alterations of mAbs at intact level. Furthermore, strong correlation was observed between this novel MS approach and analysis by capillary isoelectric focusing.

Fractionated charge variants of biosimilars: A review of separation methods, structural and functional analysis

The similarity between originator and biosimilar monoclonal antibody candidates are rigorously assessed based on primary, secondary, tertiary, quaternary structures, and biological functions. Minor differences in such parameters may alter target-binding, potency, efficacy, or half-life of the molecule. The charge heterogeneity analysis is a prerequisite for all biotherapeutics. Monoclonal antibodies are prone to enzymatic or non-enzymatic structural modifications during or after the production processes, leading to the formation of fragments or aggregates, various glycoforms, oxidized, deamidated, and other degraded residues, reduced Fab region binding activity or altered FcR binding activity. Therefore, the charge variant profiles of the monoclonal antibodies must be regularly and thoroughly evaluated. Comparative structural and functional analysis of physically separated or fractioned charged variants of monoclonal antibodies has gained significant attention in the last few years. The fraction-based charge variant analysis has proved very useful for the biosimilar candidates comprising of unexpected charge isoforms. In this report, the key methods for the physical separation of monoclonal antibody charge variants, structural and functional analyses by liquid chromatography-mass spectrometry, and surface plasmon resonance techniques were reviewed.

Global characterization of modifications to the charge isomers of IgG antibody

Posttranslational modifications of antibody products affect their stability, charge distribution, and drug activity and are thus a critical quality attribute. The comprehensive mapping of antibody modifications and different charge isomers (CIs) is of utmost importance, but is challenging. We intended to quantitatively characterize the posttranslational modification status of CIs of antibody drugs and explore the impact of posttranslational modifications on charge heterogeneity. The CIs of antibodies were fractionated by strong cation exchange chromatography and verified by capillary isoelectric focusing-whole column imaging detection, followed by stepwise structural characterization at three levels. First, the differences between CIs were explored at the intact protein level using a top-down mass spectrometry approach; this showed differences in glycoforms and deamidation status. Second, at the peptide level, common modifications of oxidation, deamidation, and glycosylation were identified. Peptide mapping showed nonuniform deamidation and glycoform distribution among CIs. In total, 10 N-glycoforms were detected by peptide mapping. Finally, an in-depth analysis of glycan variants of CIs was performed through the detection of enriched glycopeptides. Qualitative and quantitative analyses demonstrated the dynamics of 24 N-glycoforms. The results revealed that sialic acid modification is a critical factor accounting for charge heterogeneity, which is otherwise missed in peptide mapping and intact molecular weight analyses. This study demonstrated the importance of the comprehensive analyses of antibody CIs and provides a reference method for the quality control of biopharmaceutical analysis.

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A stepwise investigation on the diversity and dynamics of modifications of antibody charge isomers (CIs) was performed.

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The results from SCX-HPLC and cIEF-WCID supported each other.

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In-depth analysis on glycan variants of CIs was achieved by analyzing the enriched glycopeptides.

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Sialic acid and deamidation modifications were critical factors for the charge heterogeneity.

Comparative Elucidation of Cetuximab Heterogeneity on the Intact Protein Level by Cation Exchange Chromatography and Capillary Electrophoresis Coupled to Mass Spectrometry

Charge sensitive separation methods such as ion exchange chromatography (CEX) and capillary electrophoresis (CE) have recently been coupled to mass spectrometry to facilitate high resolution profiling of proteoforms present within the charge variant profile of complex biopharmaceuticals. Here we apply pH gradient cation exchange chromatography and microfluidic capillary electrophoresis using the ZipChip platform for comparative characterization of the monoclonal antibody Cetuximab. Cetuximab harbors four glycans per molecule, two on each heavy chain, of which the Fab glycans have been reported to be complex and multiply sialylated. The presence of these extra glycosylation sites in the variable region of the molecule causes significant charge variant and glycan heterogeneity, which makes comprehensive analysis on the intact protein level challenging. Both pH gradient CEX-MS and CE-MS were found to be powerful for the separation of Cetuximab charge variants with eight major peaks being baseline resolved using both separation platforms. Informative native-like mass spectra were collected for each charge variant peak using both platforms that facilitated deconvolution and further analysis. The total proteoform coverage was exceptionally high with >100 isoforms identified and relatively quantified with CEX-MS, in case of CE-MS the proteoform coverage was >200. A deep insight into the heterogeneity of Cetuximab was unveiled, the high level of sensitivity achievable enables the implementation of the presented technologies even at early stages of the biopharmaceutical development platform, such as in developability assessment, process development and also for monitoring process consistency.

Practical considerations on the particle size and permeability of ion-exchange columns applied to biopharmaceutical separations

The goal of this study was to better understand the possibilities and limitations of modern cation exchange chromatography (CEX) columns for the separation of protein biopharmaceuticals (typically mAbs and related products). Several commercial and research columns consisting of a non-porous polymeric core particle with a thin hydrophilic coating and grafted ion-exchanger sulfonate groups, were compared. The impact of particle size, porosity and packing pressure on the separation of therapeutic proteins was evaluated in a systematic way. First, it was shown that the porosity of modern CEX columns depends on the applied conditions, and lower apparent porosity as well as increased column pressures were observed when using low ionic strength mobile phase (less than 0.01 M NaCl), due to swelling. Column pressure seemed to be dependent on the 1/d_p³ to 1/d_p⁵ relationships with particle size, depending on whether 0.3 M NaCl or pure water was used as mobile phase, respectively. Using 5 cm long columns packed with 2 or 2.5 µm particles could easily result in higher than 1000 bar pressure drops when the mobile phase ionic strength is low. Therefore, it is recommended that particle size not be decreased to below 2.5 µm so that technologies can remain compatible with the current state of ultra-high pressure (UHPLC) instrumentation. This recommendation is underscored by the fact that a decrease in particle size does not produce improved separations, since the particles are non-porous (no intra-particle diffusion nor resistance to mass transfer) and that large solutes follow an on-off (bind and elute) type retention mechanism. The only advantage of CEX columns packed with small particles is that they can provide more specific surface area per unit length of column, and thus facilitate higher throughput methods. In conclusion, it appears that there is no need to further decrease the particle size in CEX since decreasing their particle size may result in more drawbacks than benefits.

Current possibilities of liquid chromatography for the characterization of antibody-drug conjugates

Antibody Drug Conjugates (ADCs) are innovative biopharmaceuticals gaining increasing attention over the last two decades. The concept of ADCs lead to new therapy approaches in numerous oncological indications as well in infectious diseases. Currently, around 60 CECs are in clinical trials indicating the expanding importance of this class of protein therapeutics. ADCs show unprecedented intrinsic heterogeneity and address new quality attributes which have to be assessed. Liquid chromatography is one of the most frequently used analytical method for the characterization of ADCs. This review summarizes recent results in the chromatographic characterization of ADCs and supposed to provide a general overview on the possibilities and limitations of current approaches for the evaluation of drug load distribution, determination of average drug to antibody ratio (DAR_av), and for the analysis of process/storage related impurities. Hydrophobic interaction chromatography (HIC), reversed phase liquid chromatography (RPLC), size exclusion chromatography (SEC) and multidimensional separations are discussed focusing on the analysis of marketed ADCs. Fundamentals and aspects of method development are illustrated with applications for each technique. Future perspectives in hydrophilic interaction chromatography (HILIC), HIC, SEC and ion exchange chromatography (IEX) are also discussed.

Orthogonal liquid chromatography-mass spectrometry methods for the comprehensive characterization of therapeutic glycoproteins, from released glycans to intact protein level

Proteins are increasingly used as therapeutics. Their characterization is challenging due to their size and inherent heterogeneity notably caused by post-translational modifications, among which glycosylation is probably the most prominent. The glycosylation profile of therapeutic proteins must therefore be thoroughly analyzed. Here, we illustrate how the use of a combination of various cutting-edge LC or LC/MS(/MS) methods, and operating at different levels of analysis allows the comprehensive characterization of both the N- and O-glycosylations of therapeutic proteins without the need for other approaches (capillary electrophoresis, MALDI-TOF). This workflow does not call for the use of highly specialized/custom hardware and software nor an extensive knowledge of glycan analysis. Most notably, we present the point of view of a contract research organization, with the constraints associated to the work in a regulated environment (GxP). Two salient points of this work are i) the use of mixed-mode chromatography as a fast and straightforward mean of profiling N-glycans sialylation as well as an orthogonal method to separate N-glycans co-eluting in the HILIC mode; and ii) the use of widepore HILIC/MS to analyze challenging N/O-glycosylation profiles at both the peptide and subunit levels. A particular attention was given to the sample preparations in terms of duration, specificity, versatility, and robustness, as well as the ease of data processing.

Mixed-mode reversed phase/positively charged repulsion chromatography for intact protein separation

A mixed-mode reversed phase/positively charged repulsion stationary phase C8PN composed of octyl and amino group has been developed for separation of intact protein. Before the separation of proteins, a set of probe compounds were employed to evaluate the chromatographic properties of C8PN, demonstrating typical reversed phase/positively charged repulsion interaction on this stationary phase as estimated. Then the new C8PN stationary phase was used to separate a standard protein mixture on the reversed phase mode. Compared with a commercial C4 stationary phase, it showed different selectivity for some proteins. In order to better understand the properties of C8PN, the effect of acetonitrile content was investigated based on retention equation. Higher values of the equation parameters on C8PN demonstrated that the protein retentions were more sensitive to the change of acetonitrile content. Besides, the influences of buffer salt additives on the protein retentions were also studied. The retention factors of the proteins got larger with the increase of buffer salt concentration, which confirmed the positively charged repulsion interaction on the column. Finally, the C8PN was further applied to separate oxidized- and reduced- forms of Recombinant Human Growth Hormone. Our study indicated the advantages and application potential of mixed-mode reversed phase/positively charged repulsion stationary phase for intact protein separation.

Microheterogeneity of therapeutic monoclonal antibodies is governed by changes in the surface charge of the protein

It has previously been shown for individual antibodies, that the microheterogenity pattern can have a significant impact on various key characteristics of the product. The aim of this study to get a more generalized understanding of the importance of microheterogeneity. For that purpose, the charge variant pattern of various different commercially available therapeutic mAb products was compared using Cation-Exchange Chromatography with linear pH gradient antigen affinity, Fc-receptor affinity, antibody dependent cellular cytotoxicity (ADCC) and conformational stability. For three of the investigated antibodies, the basic charge variants showed a stronger binding affinity towards FcγRIIIa as well as an increased ADCC response. Differences in the conformational stability of antibody charge variants and the corresponding reference samples could not be detected by differential scanning calorimetry. The different biological properties of the mAb variants are therefore governed by changes in the surface charge of the protein and not by an altered structure. This can help to identify aspects of microheterogeneity that are critical for product quality and can lead to further improvements in the development and production of therapeutic antibody products.

Antibody-drug conjugate characterization by chromatographic and electrophoretic techniques

Due to the inherent structure complexity and component heterogeneity of antibody drug conjugates (ADCs), separation technologies play a critical role in their characterization. In this review, we focus on chromatographic and electrophoretic approaches used to characterize ADCs with respect to drug-to-antibody ratio, drug distribution and conjugation sites, free small molecule drugs, charge variants, aggregates and fragments, etc. Chromatographic techniques including reversed-phase, ion exchange, size exclusion, hydrophobic interaction, two-dimensional liquid chromatography, and gas chromatography as well as capillary electrophoretic techniques including capillary electrophoresis sodium dodecyl sulfate, capillary zone electrophoresis and capillary isoelectric focusing are reviewed for their applications in the characterization of ADCs.