Characterization of the Acidic Species of a Monoclonal Antibody Using Weak Cation Exchange Chromatography and LC-MS

Offline Coupling of Hydrophobic Interaction Chromatography-Capillary Zone Electrophoresis for Monitoring Charge-Based Heterogeneity of Recombinant Monoclonal Antibodies

A holistic understanding of the charge heterogeneity in monoclonal antibodies (mAbs) is paramount for ensuring acceptable product quality. Hence, biotherapeutic manufacturers are expected to thoroughly characterize their products via advanced analytical techniques. Recently, two-dimensional liquid chromatography (2DLC) methods have gained popularity for resolving complex charged species. Capillary electrophoresis (CE) is regarded as a sensitive and faster tool for charged species estimation in biotherapeutics. In this study, we aim to combine the separation power of chromatographic and electrophoretic tools (liquid chromatography [LC]-CE) so as to achieve maximum resolution of mAb charge variants. Hydrophobic interaction chromatography (HIC) has been used as the preferred LC mode with CE for achieving successful separation of both charge and hydrophobic variants for two of the mAbs (trastuzumab and rituximab). The standalone HIC and capillary zone electrophoresis (CZE) methods separated 4 hydrophobic variants and 7 charge variants for each mAb, whereas the 2DLC method separated 10 and 11 variants for mAbs A and B. On the other hand, the HIC-CZE-UV method resolved 29 variants in mAb A and 23 variants in mAb B. The reproducibility of the HIC-CZE-UV method was demonstrated by % change in values of retention time (RT) and peak area as <5% (mAb A), <3% (mAb B), and <12% (for both mAbs), respectively. Thus, the utility of the proposed LC-CE method for characterization of mAb charge variants has been displayed.

Characterization of the Charge Heterogeneity of a Monoclonal Antibody That Binds to Both Cation Exchange and Anion Exchange Columns under the Same Binding Conditions

Therapeutic antibodies play an important role in the public healthcare system to treat patients with a variety of diseases. Protein characterization using an array of analytical tools provides in-depth information for drug quality, safety, efficacy, and the further understanding of the molecule. A therapeutic antibody candidate MAB1 exhibits unique binding properties to both cation and anion exchange columns at neutral pH. This uniqueness disrupts standard purification processes and necessitates adjustments in manufacturing. This study identifies that the charge heterogeneity of MAB1 is primarily due to the N-terminal cyclization of glutamine to pyroglutamine and, to a lesser extent, succinimide intermediate, deamidation, and C-terminal lysine. Using three approaches, i.e., deferential chemical labeling, H/D exchange, and molecular modeling, the binding to anion exchange resins is attributed to negatively charged patches on the antibody's surface, involving specific carboxylic acid residues. The methodologies shown here can be extended to study protein binding orientation in column chromatography.

LAP: Liability Antibody Profiler by sequence & structural mapping of natural and therapeutic antibodies

Antibody-based therapeutics must not undergo chemical modifications that would impair their efficacy or hinder their developability. A commonly used technique to de-risk lead biotherapeutic candidates annotates chemical liability motifs on their sequence. By analyzing sequences from all major sources of data (therapeutics, patents, GenBank, literature, and next-generation sequencing outputs), we find that almost all antibodies contain an average of 3-4 such liability motifs in their paratopes, irrespective of the source dataset. This is in line with the common wisdom that liability motif annotation is over-predictive. Therefore, we have compiled three computational flags to prioritize liability motifs for removal from lead drug candidates: 1. germline, to reflect naturally occurring motifs, 2. therapeutic, reflecting chemical liability motifs found in therapeutic antibodies, and 3. surface, indicative of structural accessibility for chemical modification. We show that these flags annotate approximately 60% of liability motifs as benign, that is, the flagged liabilities have a smaller probability of undergoing degradation as benchmarked on two experimental datasets covering deamidation, isomerization, and oxidation. We combined the liability detection and flags into a tool called Liability Antibody Profiler (LAP), publicly available at lap.naturalantibody.com. We anticipate that LAP will save time and effort in de-risking therapeutic molecules.

Small conformational changes in IgG1 detected as acidic charge variants by cation exchange chromatography

Fully characterizing the post-translational modifications present in charge variants of therapeutic monoclonal antibodies (mAbs), particularly acidic variants, is challenging and remains an open area of investigation. In this study, to test the possibility that chromatographically separated acidic fractions of therapeutic mAbs contain conformational variants, we undertook a mAb refolding approach using as a case study an IgG1 that contains many unidentified acidic peaks with few post-translational modifications, and examined whether different acidic peak fractions could be generated corresponding to these variants. The IgG1 drug substance was denatured by guanidine hydrochloride, without a reducing agent present, and gradually refolded by stepwise dialysis against arginine hydrochloride used as an aggregation suppressor. Each acidic chromatographic peak originally contained in the IgG1 drug substance was markedly increased by this stepwise refolding process, indicating that these acidic variants are conformational variants. However, no conformational changes were detected by small-angle X-ray scattering experiments for the whole IgG1, indicating that the conformational changes are minor. Chromatographic, thermal and fluorescence analyses suggested that the conformational changes are a localized denaturation effect centred around the aromatic amino acid regions. This study provides new insights into the characterization of acidic variants that are currently not fully understood.

In-Depth Characterization of Acidic Variants Induced by Metal-Catalyzed Oxidation in a Recombinant Monoclonal Antibody

Characterization of antibody charge heterogeneity is an important task for antibody drug development. Recently, a correlation between acidic charge heterogeneity and metal-catalyzed oxidation has been observed for antibody drugs. However, to date, the acidic variants induced by metal-catalyzed oxidation have not been elucidated. In addition, it is challenging to satisfactorily explain the induced acidic charge heterogeneity, as the existing analytical workflows, which relied on either untargeted or targeted peptide mapping analysis, could lead to incomplete identification of the acidic variants. In this work, we present a new characterization workflow by combining untargeted and targeted analyses to thoroughly identify and characterize the induced acidic variants in a highly oxidized IgG1 antibody. As a part of this workflow, a tryptic peptide mapping method was also developed for accurate determination of the relative extent of site-specific carbonylation, where a new hydrazone reduction procedure was established to minimize under-quantitation artifacts caused by incomplete reduction of hydrazones during sample preparation. In summary, we identified 28 site-specific oxidation products, which are located on 26 residues and of 11 different modification types, as the sources of the induced acidic charge heterogeneity. Many of the oxidation products were reported for the first time in antibody drugs. More importantly, this study provides new insights to understanding acidic charge heterogeneity of antibody drugs in the biotechnology industry. Additionally, the characterization workflow presented in this study can be applied as a platform approach in the biotechnology industry to better address the need for in-depth characterization of antibody charge variants.

Risk-Based Control Strategies of Recombinant Monoclonal Antibody Charge Variants

Since the first approval of the anti-CD3 recombinant monoclonal antibody (mAb), muromonab-CD3, a mouse antibody for the prevention of transplant rejection, by the US Food and Drug Administration (FDA) in 1986, mAb therapeutics have become increasingly important to medical care. A wealth of information about mAbs regarding their structure, stability, post-translation modifications, and the relationship between modification and function has been reported. Yet, substantial resources are still required throughout development and commercialization to have appropriate control strategies to maintain consistent product quality, safety, and efficacy. A typical feature of mAbs is charge heterogeneity, which stems from a variety of modifications, including modifications that are common to many mAbs or unique to a specific molecule or process. Charge heterogeneity is highly sensitive to process changes and thus a good indicator of a robust process. It is a high-risk quality attribute that could potentially fail the specification and comparability required for batch disposition. Failure to meet product specifications or comparability can substantially affect clinical development timelines. To mitigate these risks, the general rule is to maintain a comparable charge profile when process changes are inevitably introduced during development and even after commercialization. Otherwise, new peaks or varied levels of acidic and basic species must be justified based on scientific knowledge and clinical experience for a specific molecule. Here, we summarize the current understanding of mAb charge variants and outline risk-based control strategies to support process development and ultimately commercialization.

Multiattribute Monitoring of Charge-Based Heterogeneity of Recombinant Monoclonal Antibodies Using 2D HIC-WCX-MS

Charged heterogeneity of monoclonal antibody (mAb) products is regarded as a critical quality attribute (CQA) depending on its impact on the safety and efficacy profile of the product. Hence, manufacturers are expected to perform a comprehensive characterization of the charge heterogeneity to ensure that the manufactured product meets its specifications. Further, monitoring is also expected during the product lifecycle to demonstrate consistency in product quality. However, conventional analytical methods for characterization of hydrophobic and charge variants are nonvolatile salt-based and require manual fraction collection and desalting steps before analysis through mass spectrometry can be performed. In the present study, a workflow of a two-dimensional liquid chromatography method using mass spectrometry (MS)-compatible buffers coupled with native mass spectrometry was performed to characterize hydrophobic variants in the first dimension and charge variants in the second dimension without any need for manual fractionation. This novel two-dimensional (2D) hydrophobic interaction chromatography (HIC)-weak cation-exchange chromatography (WCX)-MS workflow identified 10 variants in mAb A, out of which 2 variants are exclusive to the 2D orthogonal method. Similarly, for mAb B, a total of 11 variants are identified, including 5 variants exclusive to the 2D orthogonal workflow. When compared to stand-alone, HIC resolved only 4 variants for both mAbs and WCX resolved 7 variants for mAb A and 6 variants for mAb B. In addition, the proposed method allows direct characterization of hydrophobic/charge variant peaks through native mass spectrometry in a single-run workflow.

A systematic assessment of structural heterogeneity and IgG/IgE-binding of ovalbumin

Ovalbumin (OVA), one of the major allergens in hen egg, exhibits extensive structural heterogeneity due to a range of post-translational modifications (PTMs). However, analyzing the structural heterogeneity of native OVA is challenging, and the relationship between heterogeneity and IgG/IgE-binding of OVA remains unclear. In this work, ion exchange chromatography (IXC) with salt gradient elution and on-line detection by native electrospray ionization mass spectrometry (ESI MS) was used to assess the structural heterogeneity of OVA, while inhibition-ELISA was used to assess the IgG/IgE binding characteristics of OVA. Over 130 different OVA proteoforms (including glycan-free species and 32 pairs of isobaric species) were identified. Proteoforms with acetylation, phosphorylation, oxidation and succinimide modifications had reduced IgG/IgE binding capacities, whereas those with few structural modifications had higher IgG/IgE binding capacities. OVA isoforms with a sialic acid-containing glycan modification had the highest IgG/IgE binding capacity. Our results demonstrate that on-line native IXC/MS with salt gradient elution can be used for rapid assessment of the structural heterogeneity of proteins. An improved understanding of the relationship between IgG/IgE binding capacity and OVA structure provides a basis for developing biotechnology or food processing methods for reducing protein allergenicity reduction.

Monoclonal antibody charge variant characterization by fully automated four-dimensional liquid chromatography-mass spectrometry

Fully automated characterization of monoclonal antibody (mAb) charge variants using four-dimensional liquid chromatography-mass spectrometry (4D-LC-MS) is reported and illustrated. Charge variants resolved by cation-exchange chromatography (CEX) using a salt- or pH-gradient are collected in loops installed on a multiple heart-cutting valve and consequently subjected to online desalting, denaturation, reduction and trypsin digestion prior to LC-MS based peptide mapping. This innovation which substantially reduces turnaround time, sample manipulation, loss and artefacts and increases information gathering, is described in great technical detail, and applied to characterize the charge heterogeneity associated with three therapeutic mAbs. Sequence coverages > 95% are obtained for major and minor charge variants (> 1.0%). Post-translational modifications (PTMs) and modification sites are readily revealed in a repeatable manner including unstable succinimide intermediates which are not maintained when performing classical in-solution overnight digestion of offline collected CEX peaks.

Identification, characterization and control of a sequence variant in monoclonal antibody drug product: a case study

Sequence variants (SV) in protein bio therapeutics can be categorized as unwanted impurities and may raise serious concerns in efficacy and safety of the product. Early detection of specific sequence modifications, that can result in altered physicochemical and or biological properties, is therefore desirable in product manufacturing. Because of their low abundance, and finite resolving power of conventional analytical techniques, they are often overlooked in early drug development. Here, we present a case study where trace amount of a sequence variant is identified in a monoclonal antibody (mAb) based therapeutic protein by LC-MS/MS and the structural and functional features of the SV containing mAb is assessed using appropriate analytical techniques. Further, a very sensitive selected reaction monitoring (SRM) technique is developed to quantify the SV which revealed both prominent and inconspicuous nature of the variant in process chromatography. We present the extensive characterization of a sequence variant in protein biopharmaceutical and first report on control of sequence variants to < 0.05% in final drug product by utilizing SRM based mass spectrometry method during the purification steps.

Inter-laboratory study to evaluate the performance of automated online characterization of antibody charge variants by multi-dimensional LC-MS/MS

An international study was conducted to evaluate the performance and reliability of an online multi-dimensional (mD)-LC-MS/MS approach for the characterization of antibody charge variants. The characterization of antibody charge variants is traditionally performed by time-consuming, offline isolation of charge variant fractions by ion exchange chromatography (IEC) that are subsequently subjected individually to LC-MS/MS peptide mapping. This newly developed mD-LC-MS/MS approach enables automated and rapid characterization of charge variants using much lower sample requirements. This online workflow includes sample reduction, digestion, peptide mapping, and subsequent mass spectrometric analysis within a single, fully-automated procedure. The benefits of using online mD-LC-MS/MS for variant characterization include fewer handling steps, a more than 10-fold reduction in required sample amount, reduced sample hold time as well as a shortening of the overall turnaround time from weeks to few days compared to standard offline procedures. In this site-to-site comparison study, we evaluated the online peptide mapping data collected from charge variants of trastuzumab (Herceptin®) across three international laboratories. The purpose of this study was to compare the overall performance of the online mD-LC-MS/MS approach for antibody charge variant characterization, with all participating sites employing different mD-LC-MS/MS setups (e.g., instrument vendors, modules, columns, CDS software). The high sequence coverage (95%-97%) obtained in each laboratory, enabled a reproducible generation of tryptic peptides and the comparison of values of the charge variants. Results obtained at all three participating sites were in good agreement, highlighting the reliability and performance of this approach, and correspond with data gained by the standard offline procedure. Overall, our results underscore of the benefit mD-LC-MS/MS technology for therapeutic antibody characterization, confirming its potential to become an important tool in the toolbox of protein characterization scientists.

C-terminal lysine clipping of IgG1: impact on binding to human FcγRIIIa and neonatal Fc receptors

Monoclonal antibodies (mAbs) display numerous structural attributes, some of them may impact their safety and/or efficacy profiles. C-terminal lysine clipping is a common phenomenon occurring during the bioproduction of mAbs and leads to variable amounts of final process-related charge variants. If Fc-glycosylation has been by far the most documented critical quality attribute (CQA), the potential impacts of mAb C-terminal lysine content is far less reported, particularly on the ability of these basic variants to bind human Fc receptors. To address this question, three charge variant species having zero (K0), one (K1) and two (K2) C-terminal lysine(s) were isolated with high purity from an in-house human IgG1 by preparative strong-cation exchange (SCX) chromatography. A comprehensive biophysical characterization of these three fractions was undertaken, demonstrating their high similarity in terms of structural homogeneity, with a particular attention paid on their respective N-glycosylation profiles. The binding affinity of the fractions to human FcγRIIIa-Val¹⁷⁶ was assessed both by affinity chromatography and surface plasmon resonance (SPR), and to human neonatal Fc receptor (FcRn) by affinity chromatography. Results demonstrate that the three charge variants did not show any significant binding difference for the two tested human Fc receptors, translating certainly to comparable biological properties. As a consequence, C-terminal lysine clipping of the present therapeutic IgG1 should not impact both FcRn-dependent pharmacokinetic profiles and FcγRIIIa-driven cytotoxic activities. The methods used in this study can be widely applied to other IgG1 to define criticality of the C-terminal lysine clipping as a CQA.

Identification of critical chemical modifications and paratope mapping by size exclusion chromatography of stressed antibody-target complexes

Therapeutic proteins including antibodies and Fc-fusion proteins undergo a large number of chemical modifications during cell culture, purification, storage and in human circulation. They are also exposed to harsh conditions during stress studies, including elevated temperature, extremes of pH, forced oxidation, physiological pH, UV light to assess the possible degradation pathways and suitability of methods for detecting them. Some of these modifications are located on residues in binding regions, leading to loss of binding and potency and classified as critical quality attributes. Currently, criticality of modifications is assessed by a laborious process of collecting antibody fractions from the soft chromatography techniques ion exchange and hydrophobic interaction chromatography and characterizing the fractions one-by-one for potency and chemical modifications. Here, we describe a method for large-scale, parallel identification of all critical chemical modifications in one experiment. In the first step, the antibody is stressed by one or several stress methods. It is then mixed with target protein and separated by size-exclusion chromatography (SEC) on bound antibody-target complex and unbound antibody. Peptide mapping of fractions and statistical analysis are performed to identify modifications on amino acid residues that affect binding. To identify the modifications leading to slight decreases in binding, competitive SEC of antibody and antigen mixtures was developed and described in a companion study by Shi et al, where target protein is provided at lower level, below the stoichiometry. The newly described method was successfully correlated to crystallography for assessing criticality of chemical modifications and paratope mapping. It is more sensitive to low-level modifications, better streamlined and platform ready.

Use of novel cystine analogs to decrease oxidative stress and control product quality

Continuous improvements of cell culture media are required in order to ensure high yield and product quality. However, some components can be instable and lead to detrimental effects on bioprocess performances. l-cysteine is an essential amino acid commonly used in cell culture media. Despite its beneficial effect on recombinant protein production, in some cases, this component can be responsible for product microheterogeneity. In this context, alternative components have to be found in order to reduce product variants while maintaining high productivity. In this study, we have assessed the performance of different cysteine and cystine analogs : N-acetyl-cysteine, s-sulfocysteine, N,N'-diacetyl-l-cystine and the N,N'-diacetyl-l-cystine dimethylester (DACDM). Replacement of cysteine by cystine analogs, and especially DACDM, has shown positive impact on charge variants level and recombinant protein coloration level. Moreover, this molecule contributed to the increase of the intracellular glutathione pool, which suggests a close relationship with the oxidative stress regulation.

Cysteine in cell culture media induces acidic IgG1 species by disrupting the disulfide bond network

A high degree of charge heterogeneity is an unfavorable phenomenon commonly observed for therapeutic monoclonal antibodies (mAbs). Removal of these impurities during manufacturing often comes at the cost of impaired step yields. A wide spectrum of posttranslational and chemical modifications is known to modify mAb charge. However, a deeper understanding of underlying mechanisms triggering charged species would be beneficial for the control of mAb charge variants during bioprocessing. In this study, a comprehensive analytical investigation was carried out to define the root causes and mechanisms inducing acidic variants of an immunoglobulin G1‐derived mAb. Characterization of differently charged species by liquid chromatography–mass spectrometry revealed the reduction of disulfide bonds in acidic variants, which is followed by cysteinylation and glutathionylation of cysteines. Importantly, biophysical stability and integrity of the mAb are not affected. By in vitro incubation of the mAb with the reducing agent cysteine, disulfide bond degradation was directly linked to an increase of numerous acidic species. Modifying the concentrations of cysteine during the fermentation of various mAbs illustrated that redox potential is a critical aspect to consider during bioprocess development with respect to charge variant control.

Physicochemical stability study of MYL-1401O, a biosimilar of trastuzumab, following a transient temperature excursion

INTRODUCTION

The extended stability of the trastuzumab biosimilar Ogivri™ (MYL-1401O; trastuzumab-dkst) was studied under different storage conditions, including following reconstitution of the lyophilized powder (21 mg/mL) but undiluted and stored in vials at 4°C; after dilution at two concentrations (0.8 and 2.4 mg/mL) in polyolefin bags and stored at 4°C; and following a three-day thermal excursion to 25°C.

METHODS

Several methods were utilized to assess the physical and chemical stability of the drug under different storage conditions.

RESULTS

At all storage conditions tested, there was no change in the tertiary structure of MYL-1401O as assessed by second-derivative ultraviolet and fluorescence-derived spectral analysis, and no evidence of oligomer formation or fragmentation was observed as assessed by gel exclusion chromatography and dynamic light scattering, confirmed by assessment of quinary structures using size-exclusion chromatography. Ion-exchange chromatography showed no significant changes in the distribution of ionic variants, particularly deamidations. Thermal denaturation curves indicated no destabilization of the three-dimensional structure after 90 days at 4°C or after thermal excursion for 72 h at 25°C.

CONCLUSION

The trastuzumab biosimilar MYL-1401O maintained its physical and chemical stability for at least 90 days at 4°C or after thermal excursion to 25°C, supporting the safe use of MYL-1401O in several real-world settings, including advanced preparation for administration or when a break in the cold cycle occurs.

Performance Comparison of a Laterally-Fed Membrane Chromatography (LFMC) Device with a Commercial Resin Packed Column

The use of conventional membrane adsorbers such as radial flow devices is largely restricted to flow-through applications, such as virus and endotoxin removal, as they fail to give acceptable resolution in bind-and-elute separations. Laterally-fed membrane chromatography or LFMC devices have been specifically developed to combine high-speed with high-resolution. In this study, an LFMC device containing a stack of strong cation exchange membranes was compared with an equivalent resin packed column. Preliminary characterization experiments showed that the LFMC device had a significantly greater number of theoretical plates per metre than the column. These devices were used to separate a ternary model protein mixture consisting of ovalbumin, conalbumin and lysozyme. The resolution obtained with the LFMC device was better than that obtained with the column. For instance, the LFMC device could resolve lysozyme dimer from lysozyme monomer, which was not possible using the column. In addition, the LFMC device could be operated at lower pressure and at significantly higher flow rates. The devices were then compared based on an application case study, i.e., preparative separation of monoclonal antibody charge variants. The LFMC device gave significantly better separation of these variants than the column.

Macro- and Micro-Heterogeneity of Natural and Recombinant IgG Antibodies

Recombinant monoclonal antibodies (mAbs) intended for therapeutic usage are required to be thoroughly characterized, which has promoted an extensive effort towards the understanding of the structures and heterogeneity of this major class of molecules. Batch consistency and comparability are highly relevant to the successful pharmaceutical development of mAbs and related products. Small structural modifications that contribute to molecule variants (or proteoforms) differing in size, charge or hydrophobicity have been identified. These modifications may impact (or not) the stability, pharmacokinetics, and efficacy of mAbs. The presence of the same type of modifications as found in endogenous immunoglobulin G (IgG) can substantially lower the safety risks of mAbs. The knowledge of modifications is also critical to the ranking of critical quality attributes (CQAs) of the drug and define the Quality Target Product Profile (QTPP). This review provides a summary of the current understanding of post-translational and physico-chemical modifications identified in recombinant mAbs and endogenous IgGs at physiological conditions.

Modulating cell culture oxidative stress reduces protein glycation and acidic charge variant formation

Controlling acidic charge variants is critical for an industrial bioprocess due to the potential impact on therapeutic efficacy and safety. Achieving a consistent charge variant profile at manufacturing scale remains challenging and may require substantial resources to investigate effective control strategies. This is partially due to incomplete understanding of the underlying causes for charge variant formation during the cell culture process. To address this gap, we examined the effects of four process input factors (temperature, iron concentration, feed media age, and antioxidant (rosmarinic acid) concentration) on charge variant profile. These factors were found to affect the charge profile by modulating the cell culture oxidative state. Process conditions with higher acidic peaks corresponded to elevated supernatant peroxide concentration, intracellular reactive oxygen species (ROS) levels, or both. Changes in glycation level were the primary cause of the charge heterogeneity, and for the first time, supernatant peroxide was found to positively correlate with glycation levels. Based on these findings, a novel mathematical model was developed to demonstrate that the rate of acidic species formation was exponentially proportional to the concentrations of supernatant peroxide and protein product. This work provides critical insights into charge variant formation during the cell culture process and highlights the importance of modulating of cell culture oxidative stress for charge variant control.

Structure, heterogeneity and developability assessment of therapeutic antibodies

Increasing attention has been paid to developability assessment with the understanding that thorough evaluation of monoclonal antibody lead candidates at an early stage can avoid delays during late-stage development. The concept of developability is based on the knowledge gained from the successful development of approximately 80 marketed antibody and Fc-fusion protein drug products and from the lessons learned from many failed development programs over the last three decades. Here, we reviewed antibody quality attributes that are critical to development and traditional and state-of-the-art analytical methods to monitor those attributes. Based on our collective experiences, a practical workflow is proposed as a best practice for developability assessment including in silico evaluation, extended characterization and forced degradation using appropriate analytical methods that allow characterization with limited material consumption and fast turnaround time.

Comprehensive characterisation of the heterogeneity of adalimumab via charge variant analysis hyphenated on-line to native high resolution Orbitrap mass spectrometry

Charge variant analysis is a widely used tool to monitor changes in product quality during the manufacturing process of monoclonal antibodies (mAbs). Although it is a powerful technique for revealing mAb heterogeneity, an unexpected outcome, for example the appearance of previously undetected isoforms, requires further, time-consuming analysis. The process of identifying these unknowns can also result in unwanted changes to the molecule that are not attributable to the manufacturing process. To overcome this, we recently reported a method combining highly selective cation exchange chromatography-based charge variant analysis with on-line mass spectrometric (MS) detection. We further explored and adapted the chromatographic buffer system to expand the application range. Moreover, we observed no salt adducts on the native protein, also supported by the optimal choice of MS parameters, resulting in increased data quality and mass accuracy. Here, we demonstrate the utility of this improved method by performing an in-depth analysis of adalimumab before and after forced degradation. By combining molecular mass and retention time information, we were able to identify multiple modifications on adalimumab, including lysine truncation, glycation, deamidation, succinimide formation, isomerisation, N-terminal aspartic acid loss or C-terminal proline amidation and fragmentation along with the N-glycan distribution of each of these identified proteoforms. Host cell protein (HCP) analysis was performed using liquid chromatography-mass spectrometry that verified the presence of the protease Cathepsin L. Based on the presence of trace HCPs with catalytic activity, it can be questioned if fragmentation is solely driven by spontaneous hydrolysis or possibly also by enzymatic degradation.

LC/MS at the whole protein level: Studies of biomolecular structure and interactions using native LC/MS and cross-path reactive chromatography (XP-RC) MS

Interfacing liquid chromatography (LC) with electrospray ionization (ESI) to enable on-line MS detection had been initially implemented using reversed phase LC, which in the past three decades remained the default type of chromatography used for LC/MS and LC/MS/MS studies of protein structure. In contrast, the advantages of other types of LC as front-ends for ESI MS, particularly those that allow biopolymer higher order structure to be preserved throughout the separation process, enjoyed relatively little appreciation until recently. However, the past few years witnessed a dramatic surge of interest in the so-called "native" (with "non-denaturing" being perhaps a more appropriate adjective) LC/MS and LC/MS/MS analyses within the bioanalytical and biophysical communities. This review focuses on recent advances in this field, with an emphasis on size exclusion and ion exchange chromatography as front-end platforms for protein characterization by LC/MS. Also discussed are the benefits provided by the integration of chemical reactions in the native LC/MS analyses, including both ion chemistry in the gas phase (e.g., limited charge reduction for characterization of highly heterogeneous biopolymers) and solution-phase reactions (using the recently introduced technique cross-path reactive chromatography).

Characterization of recombinant monoclonal antibody variants detected by hydrophobic interaction chromatography and imaged capillary isoelectric focusing electrophoresis

In-depth characterization of the commonly observed variants is critical to the successful development of recombinant monoclonal antibody therapeutics. Multiple peaks of a recombinant monoclonal antibody were observed when analyzed by hydrophobic interaction chromatography and imaged capillary isoelectric focusing. The potential modification causing the heterogeneity was localized to F(ab')2 region by analyzing the antibody after IdeS digestion using hydrophobic interaction chromatography. LC-MS analysis identified asparagine deamidation as the root cause of the observed multiple variants. While the isoelectric focusing method is expected to separate deamidated species, the similar profile observed in hydrophobic interaction chromatography indicates that the single site deamidation caused differences in hydrophobicity. Forced degradation demonstrated that the susceptible asparagine residue is highly exposed, which is expected as it is located in the light chain complementarity determining region. Deamidation of this single site decreased the mAb binding affinity to its specific antigen.

Qualitative and quantitative characterization of protein biotherapeutics with liquid chromatography mass spectrometry

In the last decade, the advancement of liquid chromatography mass spectrometry (LC/MS) techniques has enabled their broad application in protein characterization, both quantitatively and qualitatively. Owing to certain important merits of LC/MS techniques (e.g., high selectivity, flexibility, and rapid method development), LC/MS assays are often deemed as preferable alternatives to conventional methods (e.g., ligand-binding assays) for the analysis of protein biotherapeutics. At the discovery and development stages, LC/MS is generally employed for two purposes absolute quantification of protein biotherapeutics in biological samples and qualitative characterization of proteins. For absolute quantification of a target protein in bio-matrices, recent work has led to improvements in the efficiency of LC/MS method development, sample treatment, enrichment and digestion, and high-performance low-flow-LC separation. These advances have enhanced analytical sensitivity, specificity, and robustness. As to qualitative analysis, a range of techniques have been developed to characterize intramolecular disulfide bonds, glycosylation, charge variants, primary sequence heterogeneity, and the drug-to-antibody ratio of antibody drug conjugate (ADC), which has enabled a refined ability to assess product quality. In this review, we will focus on the discussion of technical challenges and strategies of LC/MS-based quantification and characterization of biotherapeutics, with the emphasis on the analysis of antibody-based biotherapeutics such as monoclonal antibodies (mAbs) and ADCs. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 36:734-754, 2017.

Forced degradation of recombinant monoclonal antibodies: A practical guide

Forced degradation studies have become integral to the development of recombinant monoclonal antibody therapeutics by serving a variety of objectives from early stage manufacturability evaluation to supporting comparability assessments both pre- and post- marketing approval. This review summarizes the regulatory guidance scattered throughout different documents to highlight the expectations from various agencies such as the Food and Drug Administration and European Medicines Agency. The various purposes for forced degradation studies, commonly used conditions and the major degradation pathways under each condition are also discussed.

Rapid and improved characterization of therapeutic antibodies and antibody related products using IdeS digestion and subunit analysis

Antibody subunits LC, Fd and Fc/2, generated by IdeS digestion has been applied in analytical methodologies to characterize antibody quality attributes such as glycosylation, oxidation, deamidation, and identity.