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

LC-MS Characterization and Stability Assessment Elucidate Correlation Between Charge Variant Composition and Degradation of Monoclonal Antibody Therapeutics

Aggregation stability of monoclonal antibody (mAb) therapeutics is influenced by many critical quality attributes (CQA) such as charge and hydrophobic variants in addition to environmental factors. In this study, correlation between charge heterogeneity and stability of mAbs for bevacizumab and trastuzumab has been investigated under a variety of stresses including thermal stress at 40 °C, thermal stress at 55 °C, shaking (mechanical), and low pH. Size- and charge-based heterogeneities were monitored using analytical size exclusion chromatography (SEC) and cation exchange chromatography (CEX), respectively, while dynamic light scattering was used to assess changes in hydrodynamic size. CEX analysis revealed an increase in cumulative acidic content for all variants of both mAbs post-stress treatment attributed to increased deamidation. Higher charge heterogeneity was observed in variants eluting close to the main peak than the ones eluting further away (25-fold and 42-fold increase in acidic content for main and B1 of bevacizumab and 19-fold for main of trastuzumab, respectively, under thermal stress; 50-fold increase in acidic for main and B1 of bevacizumab and 10% rise in basic content of main of trastuzumab under pH stress). Conversely, variants eluting far away from main exhibit greater aggregation as compared to close-eluting ones. Aggregation kinetics of variants followed different order for the different stresses for both mAbs (2nd order for thermal and pH stresses and 0th order for shaking stress). Half-life of terminal charge variants of both mAbs was 2- to 8-fold less than main indicating increased degradation propensity.

Demonstration of Physicochemical and Functional Similarity of Biosimilar Adalimumab-aqvh to Adalimumab

BACKGROUND

Adalimumab-aqvh/CHS-1420 (YUSIMRYTM) (hereafter referred to as adalimumab-aqvh) was recently approved by the US Food and Drug Administration as a biosimilar for adalimumab.

OBJECTIVE

The current study was conducted to investigate the analytical similarity of adalimumab-aqvh and the reference product, adalimumab.

METHODS

The structural, functional, and stability attributes of adalimumab-aqvh and adalimumab were compared using state-of-the-art assays. The primary structure, disulfide structure, glycan profile, secondary and tertiary structures, molar mass, size variants, free thiol, charge variants, hydrophobic variants, post-translational modifications, subvisible particles, host cell proteins, and protein concentration were investigated. The functional similarity between adalimumab-aqvh and adalimumab was demonstrated by comparing fragment antigen-binding (Fab)-associated and fragment crystallizable (Fc)-associated biological activities. The stability of adalimumab-aqvh and of adalimumab was compared through forced degradation.

RESULTS

The structural attributes of adalimumab-aqvh were identical to those of adalimumab or met the similarity criteria, with a few exceptions. Adalimumab-aqvh and adalimumab exhibited comparable stability profiles and functional activities. Any observed differences in the physiochemical attributes did not impact the conclusion of similarity because they did not influence any functional activities related to the adalimumab mechanism of action.

CONCLUSION

The structural, functional, and stability data provide convincing evidence of biosimilarity between adalimumab-aqvh and the reference product, adalimumab.

Long term culturing of CHO cells: phenotypic drift and quality attributes of the expressed monoclonal antibody

OBJECTIVE

Establishing cell lines with enhanced protein production requires a deep understanding of the cellular dynamics and cell line stability. The aim of the study is to investigate the impact of long term culturing (LTC) on cell morphology and altered cellular functions possibly leading to phenotypic drift, impacting product yield and quality. Study highlights the orthogonal cellular and analytical assay toolbox to define cell line stability for optimal culture performance and product quality.

METHODS

We investigated recombinant monoclonal antibody (mAb) expressing CHO cells for 60 passages or 180 generations and assessed the cell growth characteristics and morphology by confocal and scanning electron microscopy. Quality attributes of expressed mAb is accessed by performing charge variants, glycan, and host cell protein analysis.

RESULTS

We observed a 1.65-fold increase in viable cell population and 1.3-fold increase in cell specific growth rate. A 2.5-fold decrease in antibody titer and abatement of actin filament indicate cellular phenotypic drift. Mitochondrial membrane potential (∆ΨM) signified cell health and metabolic activity during LTC. Host cell protein production is reduced by 1.8-fold. Charge heterogeneity was perturbed with 12.5% and 43% reduction in abundance of acidic and basic charge variants respectively. Glycan profile indicated a decline in fucosylation with 17% increase in galactosylated species as compared with early passaged cells.

CONCLUSION

LTC impinges on cellular phenotype as well as the quality of the expressed antibody, suggesting a defined subculturing limit to retain stable protein expression and cell morphology to achieve consistent product quality. Study signifies the changes in cellular and metabolic markers, suggesting cellular and analytical toolbox which could play a significant role in defining cell characteristics and ensured product quality.

Extending the performance of FcRn and FcγRIIIa affinity liquid chromatography for protein biopharmaceuticals

Affinity liquid chromatography using FcRn and FcγRIIIa columns can provide important information on the drug effector functions and the unique PK/PD properties of therapeutic mAbs. In this study, we propose a unique strategy to improve the performance of affinity chromatography by applying pH-gradient programs that incorporate multi-isocratic and negative gradient segments. These alternative gradient programs are known to greatly improve the separation of large solutes that follow a "bind-and-elute" type retention behavior. First, judicious optimization of the mobile phase compositions was performed to obtain a linear pH response. Then, with the developed strategy using multi-isocratic analysis conditions, the FcRn affinity separation selectivity for the analysis of oxidized mAb species was greatly improved. Furthermore, the introduction of negative gradient segments after each eluted peak improved the resolution between multiple glycosylated mAb species on the FcγRIIIa column. Therefore, this work provides a new strategy to improve the performance of affinity chromatography with mAb species, and could assist in the development of more accurate binding assays for important critical quality attributes related to FcRn and FcγRIIIa binding.

Observation of Heavy-Chain C-Terminal Amidation in Human Endogenous IgG

Therapeutic IgG mAbs expressed from Chinese hamster ovary (CHO) cells are known to contain three C-terminal variants in their heavy chains, namely, the unprocessed C-terminal lysine, the processed C-terminal lysine, and C-terminal amidation. Although the presence of C-terminal amidation in CHO-expressed IgGs is well studied, the biological impact of the variant on the safety and efficacy of biotherapeutics has not been well understood. To further our biological understanding of C-terminal amidation, we analyzed a series of IgG samples, including both endogenous human IgGs as well as recombinant IgGs of different subclasses expressed from both CHO and murine cell lines, for their heavy-chain C-terminal variants by LC-MS/MS based peptide mapping. The results demonstrate that heavy-chain C-terminal amidation is a common variant occurring in IgG of all four subclasses (IgG1, IgG2, IgG3 and IgG4). The variant is generally present in recombinant IgG mAbs expressed from CHO cell lines but not in IgG mAbs expressed from murine cell lines, whereas the IgGs expressed from murine cell lines contain a much larger amount of unprocessed C-terminal lysine. Additionally, a significant amount of heavy-chain C-terminal amidation is observed in endogenous human IgGs, indicating that small amount of the variant present in therapeutic IgGs does not pose a safety concern.

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.

Structural identification and absolute quantification of monoclonal antibodies in suspected counterfeits using capillary electrophoresis and liquid chromatography-tandem mass spectrometry

Monoclonal antibodies (mAbs) represent a major category of biopharmaceutical products which due to their success as therapeutics have recently experienced the emergence of mAbs originating from different types of trafficking. We report the development of an analytical strategy which enables the structural identification of mAbs in addition to comprehensive characterization and quantification in samples in potentially counterfeit samples. The strategy is based on the concomitant use of capillary zone electrophoresis analysis (CZE-UV), size exclusion chromatography coupled to multi-angle light scattering (SEC-MALS) and liquid chromatography hyphenated to tandem mass spectrometry (LC-MS/MS). This analytical strategy was applied to the investigation of different samples having unknown origins seized by the authorities, and potentially incorporating an IgG 4 or an IgG 1. The results achieved from the different techniques demonstrated to provide orthogonal and complementary information regarding the nature and the structure of the different mAbs. Therefore, they allowed to conclude unequivocally on the identification of the mAbs in the potentially counterfeit samples. Finally, a LC-MS/MS quantification method was developed which specificity was to incorporate a different mAbs labeled with stable isotopes as internal standard. The LC-MS/MS quantification method was validated and thus demonstrated the possibility to use common peptides with the considered IgG in order to achieve limit of quantification as low as 41.4 nM. The quantification method was used to estimate the concentration in the investigated samples using a single type of internal standard and experimental conditions, even in the case of mAbs with no stable isotope labeled homologues available.

Simultaneous Monitoring of Monoclonal Antibody Variants by Strong Cation-Exchange Chromatography Hyphenated to Mass Spectrometry to Assess Quality Attributes of Rituximab-Based Biotherapeutics

Different manufacturing processes and storage conditions of biotherapeutics can lead to a significant variability in drug products arising from chemical and enzymatic post-translational modifications (PTMs), resulting in the co-existence of a plethora of proteoforms with different physicochemical properties. To unravel the heterogeneity of these proteoforms, novel approaches employing strong cation-exchange (SCX) high-performance liquid chromatography (HPLC) hyphenated to mass spectrometry (MS) using a pH gradient of volatile salts have been developed in recent years. Here, we apply an established SCX-HPLC-MS method to characterize and compare two rituximab-based biotherapeutics, the originator MabThera® and its Indian copy product Reditux™. The study assessed molecular differences between the two drug products in terms of C-terminal lysine variants, glycosylation patterns, and other basic and acidic variants. Overall, MabThera® and Reditux™ displayed differences at the molecular level. MabThera® showed a higher degree of galactosylated and sialylated glycoforms, while Reditux™ showed increased levels of oligomannose and afucosylated glycoforms. Moreover, the two drug products showed differences in terms of basic variants such as C-terminal lysine and N-terminal truncation, present in Reditux™ but not in MabThera®. This study demonstrates the capability of this fast SCX-HPLC-MS approach to compare different drug products and simultaneously assess some of their quality attributes.