Characterization of Recombinant Monoclonal Antibody Charge Variants Using OFFGEL Fractionation, Weak Anion Exchange Chromatography, and Mass Spectrometry

Isolation and characterization of rabies monoclonal antibody charge variants

Current postexposure prophylaxis of rabies includes vaccines, human rabies immunoglobulin (RIG), equine RIG, and recombinant monoclonal antibodies (mAb). In the manufacturing of rabies recombinant mAb, charge variants are the most common source of heterogeneity. Charge variants of rabies mAb were isolated by salt gradient cation exchange chromatography (CEX) to separate acidic and basic and main charge variants. Separated variants were further extensively characterized using orthogonal analytical techniques, which include secondary and tertiary structure determination by far and near ultraviolet circular dichroism spectroscopy. Charge and size heterogeneity were evaluated using CEX, isoelectric focusing (IEF), capillary-IEF, size exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blotting. Antigen binding affinity was assessed by enzyme linked immuno-sorbent assay and rapid florescence foci inhibition test. Results from structural and physicochemical characterizations concluded that charge variants are formed due to posttranslational modification demonstrating that the charge heterogeneity, these charge variants did neither show any considerable physicochemical change nor affect its biological function. This study shows that charge variants are effective components of mAb and there is no need of deliberate removal, until biological functions of rabies mAb will get affected.

Identification of Surfactant Impact on a Monoclonal Antibody Characterization via HPLC-Separation Based and Biophysical Methods

PURPOSE OR OBJECTIVE

Surfactants, including polysorbates and poloxamers, play a crucial role in the formulation of therapeutic proteins by acting as solubilizing and stabilizing agents. They help prevent protein aggregation and adsorption, thereby enhancing the stability of drug substance and products., However, it is important to note that utilizing high concentrations of surfactants in protein formulations can present significant analytical challenges, which can ultimately affect the product characterization.

METHODS

In our study, we specifically investigated the impact of elevated surfactant concentrations on the characterization of monoclonal antibodies. We employed various analytical techniques including size-exclusion chromatography (SEC), capillary electrophoresis (CE-SDS), a cell based functional assay, and biophysical characterization.

RESULTS

The findings of our study indicate that higher levels of Polysorbate 80 (PS-80) have adverse effects on the measured purity, biological activity, and biophysical characterization of biologic samples. Specifically, the elevated levels of PS-80 cause analytical interferences, which can significantly impact the accuracy and reliability of analytical studies.

CONCLUSIONS

Our study results highlight a significant risk in analytical investigations, especially in studies involving the isolation and characterization of impurities. It is important to be cautious of surfactant concentrations, as they can become more concentrated during common sample manipulations like buffer exchange. Indeed, the research presented in this work emphasizes the necessity to evaluate the impact on analytical assays when there are substantial alternations in the matrix composition. By doing so, valuable insights can be gained regarding potential challenges associated with assay development and characterization of biologics with complex formulations.

An Online Two-Dimensional Approach to Characterizing the Charge-Based Heterogeneity of Recombinant Monoclonal Antibodies Using a 2D-CEX-AEX-MS Workflow

Assessment of product quality attributes such as charge heterogeneity is an upmost requisite for the release of a monoclonal antibody (mAb). Analytical techniques, such as cation-exchange chromatography (CEX), accomplish this, causing the mAb to separate into acidic, main species, and basic variants. Here, an online volatile-salt-containing two-dimensional liquid chromatography (2D-LC) method coupled with mass spectrometry (MS) was performed to characterize the charge heterogeneity of mAbs using CEX chromatography in the first dimension (D1) and anion-exchange chromatography (AEX) in the second dimension (D2). The main peak of the CEX profile of D1 was transferred through a 2D heart-cut method to D2 for further analysis by the AEX-MS method. In the CEX method, mAb A showed 10 distinct variants, while the AEX method resulted in eight variants. However, a total of 13 variants were successfully resolved for mAb A in the 2D method. Similarly, mAb B exhibited seven variants in the CEX method and four variants in the AEX method, but the 2D-LC method revealed a total of nine variants for mAb B. Likewise, mAb C displayed seven variants in CEX and seven variants in AEX, whereas the 2D-LC method unveiled a total of 11 variants for mAb C. Additionally, native MS analysis revealed that the resolved charge variants were identified as amidation, oxidation, and isomerization of Asp variants in the main peak, which were not resolved in stand-alone methods. The present study demonstrates how 2D-LC can assist in identifying minor variations in charge distribution or conformation of mAb variants that would otherwise not be picked up by a single analytical method alone.

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.

Challenges and Strategies for a Thorough Characterization of Antibody Acidic Charge Variants

Heterogeneity of therapeutic Monoclonal antibody (mAb) drugs are due to protein variants generated during the manufacturing process. These protein variants can be critical quality attributes (CQAs) depending on their potential impact on drug safety and/or efficacy. To identify CQAs and ensure the drug product qualities, a thorough characterization is required but challenging due to the complex structure of biotherapeutics. Past characterization studies for basic and acidic variants revealed that full characterizations were limited to the basic charge variants, while the quantitative measurements of acidic variants left gaps. Consequently, the characterization and quantitation of acidic variants are more challenging. A case study of a therapeutic mAb1 accounted for two-thirds of the enriched acidic variants in the initial characterization study. This led to additional investigations, closing the quantification gaps of mAb1 acidic variants. This work demonstrates that a well-designed study with the right choices of analytical methods can play a key role in characterization studies. Thus, the updated strategies for more complete antibody charge variant characterization are recommended.

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.

A Charge Variant of Bevacizumab Offers Enhanced FcRn-Dependent Pharmacokinetic Half-Life and Efficacy

BACKGROUND

Lysine variants of monoclonal antibodies (mAbs) result from incomplete clipping of the C-terminal lysine residues of the heavy chain. Although the structure of the lysine variants has been determined for several mAb products, a detailed study that investigates the impact of lysine charge variants on PK/PD and preclinical safety is yet to be published.

OBJECTIVE

An in-depth investigation of the impact of C- terminal lysine clipping of mAbs on safety and efficacy for bevacizumab charge variants.

METHOD

Charge variant isolation using semi-preparative chromatography is followed by a comparative analysis of FcRn binding, pharmacokinetics, and pharmacodynamics in relevant animal models.

RESULTS

K1 variant exhibited improved FcRn binding affinity (4-fold), half-life (1.3-fold), and anti-tumor activity (1.3-fold) as compared to the K0 (main) product. However, the K2 variant, even though exhibited higher FcRn affinity (2-fold), displayed lower half-life (1.6-fold) and anti-tumor activity at medium and low doses. Differential proteomic analysis revealed that seven pathways (such as glycolysis, gluconeogenesis, carbon metabolism, synthesis of amino acids) were significantly enriched. Higher efficacy of the K1 variant is likely due to higher bioavailability of the drug, leading to complete downregulation of the pathways that facilitate catering of the energy requirements of the proliferating tumor cells. On the contrary, the K2 variant exhibits a shorter half-life, resulting only in partial reduction in the metabolic/energy requirements of the growing tumor cells.

CONCLUSION

Overall, we conclude that the mAb half-life, dosage, and efficacy of a biotherapeutic product are significantly impacted by the charge variant profile of a biotherapeutic product.

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.

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.

Antibody capture process based on magnetic beads from very high cell density suspension

Cell clarification represents a major challenge for the intensification through very high cell density in the production of biopharmaceuticals such as monoclonal antibodies (mAbs). The present report proposes a solution to this challenge in a streamlined process where cell clarification and mAb capture are performed in a single step using magnetic beads coupled with protein A. Capture of mAb from non-clarified CHO cell suspension showed promising results; however, it has not been demonstrated that it can handle the challenge of very high cell density as observed in intensified fed-batch cultures. The performances of magnetic bead-based mAb capture on non-clarified cell suspension from intensified fed-batch culture were studied. Capture from a culture at density larger than 100 × 10⁶ cells/ml provided an adsorption efficiency of 99% and an overall yield of 93% with a logarithmic host cell protein (HCP) clearance of ≈2-3 and a resulting HCP concentration ≤≈5 ppm. These results show that direct capture from very high cell density cell suspension is possible without prior processing. This technology, which brings significant benefits in terms of operational cost reduction and performance improvements such as low HCP, can be a powerful tool alleviating the challenge of process intensification.

Characterization of therapeutic proteins by cation exchange chromatography-mass spectrometry and top-down analysis

Recently, cation exchange chromatography (CEX) using aqueous volatile buffers was directly coupled with mass spectrometry (MS) and applied for intact analysis of therapeutic proteins and antibodies. In our study, chemical modifications responsible for charge variants were identified by CEX-UV-MS for a monoclonal antibody (mAb), a bispecific antibody, and an Fc-fusion protein. We also report post-CEX column addition of organic solvent and acid followed by mixing at elevated temperatures, which unfolded proteins, increased ion intensity (sensitivity) and facilitated top-down analysis. mAb stressed by hydrogen peroxide oxidation was used as a model system, which produced additional CEX peaks. The on-line CEX-UV-MS top-down analysis produced gas-phase fragments containing one or two methionine residues. Oxidation of some methionine residues contributed to earlier (acidic), some to later (basic) eluting peaks, while oxidation of other residues did not change CEX elution. The abundance of the oxidized and non-oxidized fragment ions also allowed estimation of the oxidation percentage of different methionine residues in stressed mAb. CEX-UV-MS measurement revealed a new intact antibody proteoform at 5% that eluted as a basic peak and included paired modifications: high-mannose glycosylation and remaining C-terminal lysine residue (M5/M5 + K). This finding was confirmed by peptide mapping and on-column disulfide reduction coupled with reversed-phase liquid chromatography – top-down MS analysis of the collected basic peak. Overall, our results demonstrate the utility of the on-line method in providing site-specific structural information of charge modifications without fraction collection and laborious peptide mapping.

LC-MS based case-by-case analysis of the impact of acidic and basic charge variants of bevacizumab on stability and biological activity

The present study investigates the impact of charge variants on bevacizumab's structure, stability, and biological activity. Five basic and one acidic charge variants were separated using semi-preparative cation exchange chromatography using linear pH gradient elution with purity > 85%. Based on the commercial biosimilar product's composition, two basic variants, one acidic and the main bevacizumab product, were chosen for further investigation. Intact mass analysis and tryptic peptide mapping established the basic variants' identity as those originating from an incomplete clipping of either one or both C-terminal lysine residues in the heavy chain of bevacizumab. Based on peptide mapping data, the acidic variant formation was attributed to deamidation of asparagine residue (N84), oxidation of M258, and preservation of C-terminal lysine residue, located on the heavy chain of bevacizumab. None of the observed charge heterogeneities in bevacizumab were due to differences in glycosylation among the variants. The basic (lysine) variants exhibited similar structural, functional, and stability profiles as the bevacizumab main product. But it was also noted that both the variants did not improve bevacizumab's therapeutic utility when pooled in different proportions with the main product. The acidic variant was found to have an equivalent secondary structure with subtle differences in the tertiary structure. The conformational difference also translated into a ~ 62% decrease in biological activity. Based on these data, it can be concluded that different charge variants behave differently with respect to their structure and bioactivity. Hence, biopharmaceutical manufacturers need to incorporate this understanding into their process and product development guidelines to maintain consistency in product quality.

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.

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.

Identification and quantitation of hinge cysteinylation on endogenous IgG2 antibodies from human serum

Cysteinylation is a post-translational modification (PTM) that occurs when a cysteine residue on a protein forms a disulfide bond with a terminal cysteine molecule. This PTM has been found in the hinge region of several recombinant therapeutic IgG2 antibodies, but the impact of cysteinylation on the safety and immunogenicity of therapeutics remains unclear. In this study, we characterized recombinant and endogenous IgG2 antibodies to quantify their levels of hinge cysteinylation, if present. To the best of our knowledge, this is the first study to identify and quantify hinge cysteinylation in endogenous IgG2 antibodies from healthy human serum. We used anti-IgG2 immunopurification of human serum to specifically enrich for endogenous IgG2 antibodies, and then subjected the resulting samples to Lys-C peptide mapping coupled with targeted mass spectrometry techniques. Using this analytical workflow, we found that all healthy human serum samples tested (N = 10) contained quantifiable levels of hinge cysteinylation (0.8 ± 0.3%) in their endogenous human IgG2s (IgG2-A isoform). These findings demonstrate that hinge cysteinylation in therapeutic IgG2s, at least up to a certain level, is well tolerated in humans and pose minimal safety or immunogenicity risks.

Recent progress in the analysis of protein deamidation using mass spectrometry

Deamidation is a nonenzymatic and spontaneous posttranslational modification (PTM) that introduces changes in both structure and charge of proteins, strongly associated with aging proteome instability and degenerative diseases. Deamidation is also a common PTM occurring in biopharmaceutical proteins, representing a major cause of degradation. Therefore, characterization of deamidation alongside its inter-related modifications, isomerization and racemization, is critically important to understand their roles in protein stability and diseases. Mass spectrometry (MS) has become an indispensable tool in site-specific identification of PTMs for proteomics and structural studies. In this review, we focus on the recent advances of MS analysis in protein deamidation. In particular, we provide an update on sample preparation, chromatographic separation, and MS technologies at multi-level scales, for accurate and reliable characterization of protein deamidation in both simple and complex biological samples, yielding important new insight on how deamidation together with isomerization and racemization occurs. These technological progresses will lead to a better understanding of how deamidation contributes to the pathology of aging and other degenerative diseases and the development of biopharmaceutical drugs.

Development of a Gold Nanoparticle-Functionalized Surface Plasmon Resonance Assay for the Sensitive Detection of Monoclonal Antibodies and Its Application in Pharmacokinetics

As a prominent human therapeutic, therapeutic monoclonal antibodies (mAbs) have attracted increasing attention in the past decade due to their high-targeting specificity, low toxicity, and prolonged efficacy. Systematic pharmacokinetic analysis of mAbs not only largely facilitates the understanding of their biologic functions but also promotes the development of therapeutic drug discovery, early clinical trial implementation, and therapeutic monitoring. However, the extremely complex nature of biomatrices and the especially low dosages of mAbs make their detection in biomatrices and further pharmacokinetic analysis highly challenging. Therefore, a method capable of reliably, quickly, and sensitively quantifying mAbs in biomatrices is urgently needed. In this work, we developed and evaluated an gold nanoparticle-functionalized surface plasmon resonance assay for cetuximab (C225) detection and pharmacokinetic analysis in rhesus monkeys. Combining its advantages of label-free pretreatment and amplified signal response, the lower limit of quantitation of C225 in monkey serum was reduced to 0.0125 μg/ml, and the linear range had an order of magnitude comparable to that of an ELISA-based method. Furthermore, the pharmacokinetics of C225 in rhesus monkeys was studied after intravenous infusions of single doses at 7.5, 24, and 75 mg/kg. The concentration of C225 in monkey serum was detectable after dosing for 720 hours. We believe that this new strategy will be applicable as a general protocol for mAb quantification, pharmacokinetic characteristic determination, and toxicokinetic analysis during drug development.

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.

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.

Identification and quantification of product-related quality attributes in bio-therapeutic monoclonal antibody via a simple, and robust cation-exchange HPLC method compatible with direct online detection of UV and native ESI-QTOF-MS analysis

Modern analytical ion-exchange chromatography is one of the conventional tools used for assessment of product-related quality attributes in bio-therapeutic monoclonal antibodies (mAbs). Here, we present an approach to resolve, identify, and quantify product-related substances of therapeutic mAb at its intact molecular level by cation exchange (CIEX) HPLC coupled directly to electrospray ionization - quadrupole time of flight mass spectrometry (ESI-QTOF-MS). This method utilizes pH gradient elution mode comprised of ammonium formate buffer components, and a weak cation exchange column as stationary phase. Furthermore, ion-mobility mass spectrometry (IM-MS) provided additional insights on its higher order structure. Also, orthogonal assays such as conventional CIEX-HPLC, high resolution capillary isoelectric focusing, peptide mapping, spectroscopic, and fluorescence methods were used considerably to support the findings. Additionally, an in vitro assay was included to assess the associated impact on Fc mediated function. Overall, the developed method with simultaneous detection of UV peak area percentage at 280 nm and native ESI-MS is found to be a rapid and robust analytical tool for direct assessment of structural and purity attributes, process optimization, product development, and to decipher the relevant role of micro-variants on quality, stability, and clinical outcomes.

Characterization of recombinant monoclonal antibody charge variants using WCX chromatography, icIEF and LC-MS/MS

Charge heterogeneity is an important aspect of research into the development of monoclonal antibody drugs. In the present study, charge variants were separated into four fractions using weak cation exchange chromatography and were thoroughly analyzed using liquid chromatography-mass spectrometry at multiple levels. Molecular weight analysis of intact antibody and subunits confirmed the presence of heavy-chain leader sequences, light-chain leader sequences, dehydration, and cysteinylation. Peptide mapping of the fractions using different enzymes further localized the modified sites. Modified proportions identified at peptide level were compared with the purity detected by imaged capillary isoelectric focusing, the results showed that basic variant 1 consisted of cysteinylation and dehydration of asparagine, and basic variant 2 fully accounted for the N-terminal leader sequence of the heavy chain. About 14.8% of the acidic variant can be explained by N-terminal leader sequences in the light chain, and 18% of the acidic variant was demonstrated to be deamidation of asparagine in the heavy chain. There was approximately 54.2% of the acidic variant still cannot be explained. It was hypothesized that those acidic variants that have not yet been identified are an ensemble of molecules with slight molecular weight differences or the same molecular weight but different structures.

Recent advancements, challenges, and practical considerations in the mass spectrometry-based analytics of protein biotherapeutics: A viewpoint from the biosimilar industry

The extensive analytical characterization of protein biotherapeutics, especially of biosimilars, is a critical part of the product development and registration. High-resolution mass spectrometry became the primary analytical tool used for the structural characterization of biotherapeutics. Its high instrumental sensitivity and methodological versatility made it possible to use this technique to characterize both the primary and higher-order structure of these proteins. However, even by using high-end instrumentation, analysts face several challenges with regard to how to cope with industrial and regulatory requirements, that is, how to obtain accurate and reliable analytical data in a time- and cost-efficient way. New sample preparation approaches, measurement techniques and data evaluation strategies are available to meet those requirements. The practical considerations of these methods are discussed in the present review article focusing on hot topics, such as reliable and efficient sequencing strategies, minimization of artefact formation during sample preparation, quantitative peptide mapping, the potential of multi-attribute methodology, the increasing role of mass spectrometry in higher-order structure characterization and the challenges of MS-based identification of host cell proteins. On the basis of the opportunities in new instrumental techniques, methodological advancements and software-driven data evaluation approaches, for the future one can envision an even wider application area for mass spectrometry in the biopharmaceutical industry.

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.

Analytical comparability study of recombinant monoclonal antibody therapeutics

Process changes are inevitable in the life cycle of recombinant monoclonal antibody therapeutics. Products made using pre- and post-change processes are required to be comparable as demonstrated by comparability studies to qualify for continuous development and commercial supply. Establishment of comparability is a systematic process of gathering and evaluating data based on scientific understanding and clinical experience of the relationship between product quality attributes and their impact on safety and efficacy. This review summarizes the current understanding of various modifications of recombinant monoclonal antibodies. It further outlines the critical steps in designing and executing successful comparability studies to support process changes at different stages of a product's lifecycle.

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.

Two-Dimensional Isoelectric Focusing OFFGEL, Micro-Fluidic Lab-on-Chip Electrophoresis and FTIR for Assessment of Long-Term Stability of rhG-CSF Formulation

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) has been increasingly recognized from among one of the most abundant families of biosimilars. Upon long-term storage, the rhG-CSF is subject to subtle chemical modifications that rapidly occur and, in particular, produce deaminated variants with divergent charge. Indeed, changes in charge from glutamine deamination may alter the way rhG-SCF will refold and the structure of resulting molecule. To assess this charge heterogeneity, 2-D gel electrophoresis has limited application. Recent micro-fluidic- based technical advances offer a great alternative method to better control liquid volumes on a minute scale. Here, we used IEF OFFGEL-lab-on-chip electrophoresis for 2-D separation of the rhG-CSF peptides according to their isoelectric point (pI) and molecular weight (kDa). We used an rhG-CSF commercial therapeutic formulation, kept refrigerated 24 months after expiry. The samples were analyzed for particulate matter and charge variants. Subsequently, the secondary structure was assessed by FTIR spectroscopy and residual biological activity was recorded. Interestingly, we showed an additional band in the acidic gel area above and below the most intense protein band (fractions 10, 11, and 12 at 22.84s). This observation reveals the presence of the rhG-CSF variant charges without any additional high molecular weight impurity or biological activity decrease. We conclude that after two years of storage, the rhG-CSF solution maintained its native secondary structure with little -sheet deviation, as reflected in the 1622 cm-1 and 1695 cm-1. These data demonstrated that a combined strategy is a more suitable and accurate analytical assessment of the rhG-CSF and recombinant protein-based biosimilars.

Identification and quantification of signal peptide variants in an IgG1 monoclonal antibody produced in mammalian cell lines

Sequence variants of a monoclonal antibody resulting from incomplete processing of signal peptide were identified and characterized using multiple mass spectrometry platforms and reverse phase chromatography. Detection and quantification of these variants by three LC/MS platforms were assessed. Quantification was also performed by mass spectrometric analysis of the subunits of the antibody generated by reduction and IdeS proteolysis. Peptide mapping with LC/MS/MS detection was used to quantify and confirm the identities of signal peptide sequence variants. Although quantification of the signal peptide variants thru mass spectrometry approaches is system dependent, our data revealed the results are close to the values determined by chromatographic separation with UV detection. Each of the methods have proven effective in demonstrating the consistency of signal peptide variants levels across the manufacture history of the antibody.

Main Quality Attributes of Monoclonal Antibodies and Effect of Cell Culture Components

The culture media optimization is an inevitable part of upstream process development in therapeutic monoclonal antibodies (mAbs) production. The quality by design (QbD) approach defines the assured quality of the final product through the development stage. An important step in QbD is determination of the main quality attributes. During the media optimization, some of the main quality attributes such as glycosylation pattern, charge variants, aggregates, and low-molecular-weight species, could be significantly altered. Here, we provide an overview of how cell culture medium components affects the main quality attributes of the mAbs. Knowing the relationship between the culture media components and the main quality attributes could be successfully utilized for a rational optimization of mammalian cell culture media for industrial mAbs production.