Assessing analytical methods to monitor isoAsp formation in monoclonal antibodies

In-Depth Characterization for Methionine Oxidization in Complementary Domain Region by Hydrophobic Interaction Chromatography

The oxidation of the complementarity-determining region (CDR) in monoclonal antibodies (mAbs) is a critical quality attribute that can affect the clinical efficacy and safety of recombinant mAb therapeutics. In this study, a robust hydrophobic interaction chromatography (HIC) method was developed to quantify and characterize CDR oxidation variants in mAb-A by using a Proteomix Butyl-NP5 column. The HIC analysis revealed oxidation variants that eluted earlier than the main species with weaker hydrophobicity. It was found that Met105 in the CDR was more susceptible to oxidation. Additionally, it was noted that the oxidation of Met105 on a single heavy chain resulted in elution at a distinct position compared to the oxidation on two heavy chains. This observation led to the fractionation and enrichment of the oxidized variants for further evaluation of their biofunction. The study also demonstrated that the oxidation of Met105 did not impact the antigen-binding capacity but significantly reduced the PD-1/PD-L1 blockade activity of mAb-A. The HIC method, which was employed to quantify CDR oxidation, underwent validation and was subsequently utilized for stability studies as well as for assessing the similarity between mAb-A and its reference product.

Impact of Excipient Extraction and Buffer Exchange on Recombinant Monoclonal Antibody Stability

The foundation of a biosimilar manufacturer's regulatory filing is the demonstration of analytical and functional similarity between the biosimilar product and the pertinent originator product. The excipients in the formulation may interfere with characterization using typical analytical and functional techniques during this biosimilarity exercise. Consequently, the producers of biosimilar products resort to buffer exchange to isolate the biotherapeutic protein from the drug product formulation. However, the impact that this isolation has on the product stability is not completely known. This study aims to elucidate the extent to which mAb isolation via ultrafiltration-diafiltration-based buffer exchange impacts mAb stability. It has been demonstrated that repeated extraction cycles do result in significant changes in higher-order structure (red-shift of 5.0 nm in fluorescence maxima of buffer exchanged samples) of the mAb and also an increase in formation of basic variants from 19.1 to 26.7% and from 32.3 to 36.9% in extracted innovator and biosimilar Tmab samples, respectively. It was also observed that under certain conditions of tertiary structure disruptions, Tmab could be restabilized depending on formulation composition. Thus, mAb isolation through extraction with buffer exchange impacts the product stability. Based on the observations reported in this paper, we recommend that biosimilar manufacturers take into consideration these effects of excipients on protein stability when performing biosimilarity assessments.

LC-MS Approach to Decipher a Light Chain Chromatographic Peak Splitting of a Monoclonal Antibody

PURPOSE

Monoclonal antibodies (mAbs), like other protein therapeutics, are prone to various forms of degradation, some of which are difficult to distinguish from the native form yet may alter potency. A generalizable LC-MS approach was developed to enable quantitative analysis of isoAsp. In-depth understanding of product quality attributes (PQAs) enables optimization of the manufacturing process, better formulation selection, and decreases risk associated with product handling in the clinic or during shipment.

METHODS

Reversed-phase chromatographic peak splitting was observed when a mAb was exposed to elevated temperatures. Multiple LC-MS based methods were applied to identify the reason for peak splitting. The approach involved the use of complementary HPLC columns, multiple enzymatic digestions and different MS/MS ion dissociation methods. In addition, mAb potency was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The split peaks had identical masses, and the root cause of the peak splitting was identified as isomerization of an aspartic acid located in the complementarity-determining region (CDR) of the light chain. And the early eluting and late eluting peaks were collected and performed enzymatic digestion to confirm the isoAsp enrichment in the early eluting peak. In addition, decreased potency was observed in the same heat-stressed sample, and the increased isoAsp levels in the CDR correlate well with a decrease of potency.

CONCLUSION

Liquid chromatography-mass spectrometry (LC-MS) has been utilized extensively to assess PQAs of biological therapeutics. In this study, a generalizable LC-MS-based approach was developed to enable identification and quantitation of the isoAsp-containing peptides.

Differentiation of Aspartic and Isoaspartic Acid Using 193 nm Ultraviolet Photodissociation Mass Spectrometry

Spontaneous conversion of aspartic acid (Asp) to isoaspartic acid (isoAsp) is a ubiquitous modification that influences the structure and function of proteins. This modification of Asp impacts the stability of biotherapeutics and has been linked to the development of neurodegenerative diseases. We explored the use of 193 nm ultraviolet photodissociation (UVPD) to distinguish Asp and isoAsp in the protonated and deprotonated peptides. The differences in the relative abundances of several fragment ions uniquely generated by UVPD were used to differentiate isomeric peptide standards containing Asp or isoAsp. These fragment ions result from the cleavage of bonds N-terminal to Asp/isoAsp residues in addition to the side-chain losses from Asp/isoAsp or the losses of COOH, CO2, CO, or H2O from y-ions. Fragmentation of Asp-containing tryptic peptides using UVPD resulted in more enhanced w/w + 1/y - 1/x ions, while isoAsp-containing peptides yielded more enhanced y - 18/y - 45/y - 46 ions. UVPD was also used to identify an isomerized peptide from a tryptic digest of a monoclonal antibody. Moreover, UVPD of a protonated nontryptic peptide resulted in more enhanced y ions N- and C-terminal to isoAsp and differences in b/y ion ratios that were used to identify the isoAsp peptide.

Pertuzumab Charge Variant Analysis and Complementarity-Determining Region Stability Assessment to Deamidation

Pertuzumab is a monoclonal antibody used for the treatment of HER2-positive breast cancer in combination with trastuzumab. Charge variants of trastuzumab have been extensively described in the literature; however, little is known about the charge heterogeneity of pertuzumab. Here, changes in the ion-exchange profile of pertuzumab were evaluated by pH gradient cation-exchange chromatography after stressing it for up to 3 weeks at physiological and elevated pH and 37 °C. Isolated charge variants arising under stress conditions were characterized by peptide mapping. The results of peptide mapping showed that deamidation in the Fc domain and N-terminal pyroglutamate formation in the heavy chain are the main contributors to charge heterogeneity. The heavy chain CDR2, which is the only CDR containing asparagine residues, was quite resistant to deamidation under stress conditions according to peptide mapping results. Using surface plasmon resonance, it was shown that the affinity of pertuzumab for the HER2 target receptor does not change under stress conditions. Peptide mapping analysis of clinical samples showed an average of 2-3% deamidation in the heavy chain CDR2, 20-25% deamidation in the Fc domain, and 10-15% N-terminal pyroglutamate formation in the heavy chain. These findings suggest that in vitro stress studies are able to predict in vivo modifications.

Developability assessment at early-stage discovery to enable development of antibody-derived therapeutics

Developability refers to the likelihood that an antibody candidate will become a manufacturable, safe and efficacious drug. Although the safety and efficacy of a drug candidate will be well considered by sponsors and regulatory agencies, developability in the narrow sense can be defined as the likelihood that an antibody candidate will go smoothly through the chemistry, manufacturing and control (CMC) process at a reasonable cost and within a reasonable timeline. Developability in this sense is the focus of this review. To lower the risk that an antibody candidate with poor developability will move to the CMC stage, the candidate's developability-related properties should be screened, assessed and optimized as early as possible. Assessment of developability at the early discovery stage should be performed in a rapid and high-throughput manner while consuming small amounts of testing materials. In addition to monoclonal antibodies, bispecific antibodies, multispecific antibodies and antibody-drug conjugates, as the derivatives of monoclonal antibodies, should also be assessed for developability. Moreover, we propose that the criterion of developability is relative: expected clinical indication, and the dosage and administration route of the antibody could affect this criterion. We also recommend a general screening process during the early discovery stage of antibody-derived therapeutics. With the advance of artificial intelligence-aided prediction of protein structures and features, computational tools can be used to predict, screen and optimize the developability of antibody candidates and greatly reduce the risk of moving a suboptimal candidate to the development stage.

High-Resolution Demultiplexing (HRdm) Ion Mobility Spectrometry-Mass Spectrometry for Aspartic and Isoaspartic Acid Determination and Screening

Isomeric peptide analyses are an analytical challenge of great importance to therapeutic monoclonal antibody and other biotherapeutic product development workflows. Aspartic acid (Asp, D) to isoaspartic acid (isoAsp, isoD) isomerization is a critical quality attribute (CQA) that requires careful control, monitoring, and quantitation during the drug discovery and production processes. While the formation of isoAsp has been implicated in a variety of disease states such as autoimmune diseases and several types of cancer, it is also understood that the formation of isoAsp results in a structural change impacting efficacy, potency, and immunogenic properties, all of which are undesirable. Currently, lengthy ultrahigh-performance liquid chromatography (UPLC) separations are coupled with MS for CQA analyses; however, these measurements often take over an hour and drastically limit analysis throughput. In this manuscript, drift tube ion mobility spectrometry-mass spectrometry (DTIMS-MS) and both a standard and high-resolution demultiplexing approach were utilized to study eight isomeric Asp and isoAsp peptide pairs. While the limited resolving power associated with the standard DTIMS analysis only separated three of the eight pairs, the application of HRdm distinguished seven of the eight and was only unable to separate DL and isoDL. The rapid high-throughput HRdm DTIMS-MS method was also interfaced with both flow injection and an automated solid phase extraction system to present the first application of HRdm for isoAsp and Asp assessment and demonstrate screening capabilities for isomeric peptides in complex samples, resulting in a workflow highly suitable for biopharmaceutical research needs.

Establishment of a highly precise multi-attribute method for the characterization and quality control of therapeutic monoclonal antibodies

The multi-attribute method (MAM) has garnered attention as a new quality control method of therapeutic monoclonal antibodies (mAbs). MAM analysis allows multiple relative quantifications of several structural attributes of therapeutic mAbs; however, some issues remain to be addressed in its procedures especially for sample preparation. The goal of this study was to optimize the sample preparation method for MAM analysis of mAbs. Using a model mAb, we compared five sample preparation methods based on sequence coverage, peptide redundancy, missed cleavage and chemical deamidation. It was found that low pH buffer and short digestion time reduced artificial deamidation. The desalting process after carboxymethylation was essential to obtaining high sequence coverage by a short digestion time. The generation of missed cleavage peptides was also improved by using a trypsin/lysyl endopeptidase (Lys-C) mixture. Next, we evaluated the usefulness of our method as a part of MAM analysis. Finally, 17 glycopeptides, 2 deamidated peptides and N- and C-terminal peptides of the heavy chain were successfully monitored with acceptable mass accuracy and coefficient of variation (CV, %) of the relative peak area. On the other hand, 4 oxidated peptides indicated the unavoidable slightly higher inter-assay CV (%) of the peak area ratio due to the instability in the MS sample solution. Collectively, we demonstrated that our method was applicable as an easy and reliable sample preparation method for MAM analysis, and the variation in the relative peak area could be influenced by the modification type rather than by the amount of each peptide.

Unequivocal Identification of Aspartic Acid and isoAspartic Acid by MALDI-TOF/TOF: From Peptide Standards to a Therapeutic Antibody

Aspartic acid (Asp) to isoaspartic acid (isoAsp) isomerization in therapeutic monoclonal antibodies (mAbs) and other biotherapeutics is a critical quality attribute (CQA) that requires careful control and monitoring during the drug discovery and production processes. The unwanted formation of isoAsp within biotherapeutics and resultant structural changes in the peptide backbone may negatively impact the efficacy, potency, and safety of the molecule or become immunogenic, especially if the isomerization occurs within the mAb complementarity determining region (CDR). Herein we describe a MALDI-TOF/TOF mass spectrometry method that affords unequivocal identification of the presence and the exact position of the isoAsp residue(s) in peptide standards ranging in size from a tripeptide to a docosapeptide (22 residues). In general, the peptide bond immediately N-terminal to the isoAsp residue is more susceptible to MALDI-TOF/TOF fragmentation than its unmodified counterpart. In some of the peptides evaluated in this study, fragmentation of the peptide bond C-terminal to the isoAsp residue (the aspartate effect) is also enhanced when compared to the control. Relative quantification by MALDI-TOF/TOF of this chemical modification is dependent upon a successful reversed-phase HPLC (rpHPLC) separation of the control and modified peptides. This method has also been validated on a therapeutic mAb that contains a well-documented isoAsp residue in the heavy chain CDR3 after forced degradation. Moreover, we also demonstrate that higher energy C-trap dissociation of only the singly charged species, and not the multiply charged form, of the isoAsp containing peptide, separated by rpHPLC, results in LC-MS/MS fragmentation that is highly consistent to that of MALDI-TOF/TOF.

Assessing and Improving Protein Sample Quality

One essential prerequisite of any experiment involving a purified protein, such as interaction studies or structural and biophysical characterization, is to work with a "good-quality" sample in order to ensure reproducibility and reliability of the data. Here, we define a "good-quality" sample as a protein preparation that fulfills three criteria: (1) the preparation contains a protein that is pure and soluble and exhibits structural and functional integrity, (2) the protein must be structurally homogeneous, and (3) the preparation must be reproducible. To ensure effective quality control (QC) of all these parameters, we suggest to follow a simple workflow involving the use of gel electrophoresis, light scattering, and spectroscopic experiments. We describe the techniques used in every step of this workflow and provide easy-to-use standard protocols for each step.

Investigation of anomalous charge variant profile reveals discrete pH-dependent conformations and conformation-dependent charge states within the CDR3 loop of a therapeutic mAb

During the development of a therapeutic monoclonal antibody (mAb-1), the charge variant profile obtained by pH-gradient cation exchange chromatography (CEX) contained two main peaks, each of which exhibited a unique intrinsic fluorescence profile and demonstrated inter-convertibility upon reinjection of isolated peak fractions. Domain analysis of mAb-1 by CEX and liquid chromatography-mass spectrometry indicated that the antigen-binding fragment chromatographed as two separate peaks that had identical mass. Surface plasmon resonance binding analysis to antigen demonstrated comparable kinetics/affinity between these fractionated peaks and unfractionated starting material. Subsequent molecular modeling studies revealed that the relatively long and flexible complementarity-determining region 3 (CDR3) loop on the heavy chain could adopt two discrete pH-dependent conformations: an “open” conformation at neutral pH where the HC-CDR3 is largely solvent exposed, and a “closed” conformation at lower pH where the solvent exposure of a neighboring tryptophan in the light chain is reduced and two aspartic acid residues near the ends of the HC-CDR3 loop have atypical pKa values. The pH-dependent equilibrium between “open” and “closed” conformations of the HC-CDR3, and its proposed role in the anomalous charge variant profile of mAb-1, were supported by further CEX and hydrophobic interaction chromatography studies. This work is an example of how pH-dependent conformational changes and conformation-dependent changes to net charge can unexpectedly contribute to perceived instability and require thorough analytical, biophysical, and functional characterization during biopharmaceutical drug product development.

Detecting aspartate isomerization and backbone cleavage after aspartate in intact proteins by NMR spectroscopy

The monitoring of non-enzymatic post-translational modifications (PTMs) in therapeutic proteins is important to ensure drug safety and efficacy. Together with methionine and asparagine, aspartic acid (Asp) is very sensitive to spontaneous alterations. In particular, Asp residues can undergo isomerization and peptide-bond hydrolysis, especially when embedded in sequence motifs that are prone to succinimide formation or when followed by proline (Pro). As Asp and isoAsp have the same mass, and the Asp-Pro peptide-bond cleavage may lead to an unspecific mass difference of + 18 Da under native conditions or in the case of disulfide-bridged cleavage products, it is challenging to directly detect and characterize such modifications by mass spectrometry (MS). Here we propose a 2D NMR-based approach for the unambiguous identification of isoAsp and the products of Asp-Pro peptide-bond cleavage, namely N-terminal Pro and C-terminal Asp, and demonstrate its applicability to proteins including a therapeutic monoclonal antibody (mAb). To choose the ideal pH conditions under which the NMR signals of isoAsp and C-terminal Asp are distinct from other random coil signals, we determined the pK_a values of isoAsp and C-terminal Asp in short peptides. The characteristic ¹H-¹³C chemical shift correlations of isoAsp, N-terminal Pro and C-terminal Asp under standardized conditions were used to identify these PTMs in lysozyme and in the therapeutic mAb rituximab (MabThera) upon prolonged storage under acidic conditions (pH 4-5) and 40 °C. The results show that the application of our 2D NMR-based protocol is straightforward and allows detecting chemical changes of proteins that may be otherwise unnoticed with other analytical methods.

Analysis of NIST Monoclonal Antibody Reference Material Glycosylation Using the LC-MS/MS-Based Glycoproteomic Approach

Protein-based therapeutics such as mAbs have become emerging drugs in modern medicine. Most of the approved therapeutic proteins are glycoproteins. Glycosylation is an essential critical quality attribute (CQA) due to the influence that glycoforms have on the safety, efficacy, and pharmacokinetics/pharmacodynamics (PK/PD) of biotherapeutics. Here, we applied an LC-MS/MS-based glycoproteomics approach to characterize Fc glycans of an NISTmAb reference material (RM) 8671 (sample B) and a β-1,4-galactosidase-treated NISTmAb (sample A). Overall, 48 glycan compositions were identified and quantified. The glycan structure with the highest abundance was FA2, with a relative abundance of 52% in sample A and 38% in sample B. Over 50% of the identified glycans presented at levels smaller than 0.1%. Important glycan attributes were further derived using the quantitative results. The galactosylation level of modified NISTmAb was found to decrease by ∼10% when compared to the galactosylation level of NISTmAb. There was no significant difference between the two samples in the levels of sialylation, fucosylation, and high mannose. Moreover, unglycosylated peptides were also observed at a level of 1-2%.

Structure-Function Assessment and High-Throughput Quantification of Site-Specific Aspartate Isomerization in Monoclonal Antibody Using a Novel Analytical Tool Kit

Isomerization of surface-exposed aspartic acid (Asp) in the complementarity-determining regions of therapeutic proteins could potentially impact their target binding affinity because of the sensitive location, and often requires complex analytical tactics to understand its effect on structure-function and stability. Inaccurate quantitation of Asp-isomerized variants, especially the succinimide intermediate, presents major challenge in understanding Asp degradation kinetics, its stability, and consequently establishing a robust control strategy. As a practical solution to this problem, a comprehensive analytical tool kit has been developed, which provides a solution to fully characterize and accurately quantify the Asp-related product variants. The toolkit offers a combination of 2 steps, an ion-exchange chromatography method to separate and enrich the isomerized variants in the folded structure for structure-function evaluation and a novel focused peptide mapping method to quantify the individual complementarity-determining region isomerization components including the unmodified Asp, succinimide, and isoaspartate. This novel procedure allowed an accurate quantification of each Asp-related variant and a comprehensive assessment of the functional impact of Asp isomerization, which ultimately helped to establish an appropriate control strategy for this critical quality attribute.

A post-translational modification of human Norovirus capsid protein attenuates glycan binding

Attachment of human noroviruses to histo blood group antigens (HBGAs) is essential for infection, but how this binding event promotes the infection of host cells is unknown. Here, we employ protein NMR experiments supported by mass spectrometry and crystallography to study HBGA binding to the P-domain of a prevalent virus strain (GII.4). We report a highly selective transformation of asparagine 373, located in an antigenic loop adjoining the HBGA binding site, into an iso-aspartate residue. This spontaneous post-translational modification (PTM) proceeds with an estimated half-life of a few days at physiological temperatures, independent of the presence of HBGAs but dramatically affecting HBGA recognition. Sequence conservation and the surface-exposed position of this PTM suggest an important role in infection and immune recognition for many norovirus strains.

Attachment of human noroviruses to histo blood group antigens (HBGAs) is essential for infection. Here the authors report that an asparagine residue located near the HBGA-attachment site can convert into an iso-aspartate residue through spontaneous deamidation and influence HBGA recognition.

Expression vector-derived heterogeneity in a therapeutic IgG4 monoclonal antibody

While characterizing a therapeutic IgG4 monoclonal antibody (mAb), we observed a variant with a mass 1177 Da larger than the predominant mAb form that could not be ascribed to previously described modifications. Through successive rounds of experimentation, we localized the mass addition to the C-terminus of the heavy chain (HC). During this process we observed that when the mAb was broken down into separate domains, the Fc and the 1177 Da-modified Fc could be chromatographically separated. Separation allowed collection of native and modified Fc fractions for LC/MS peptide mapping. A unique peptide present in the modified fraction was de novo sequenced and demonstrated to be a modified form of the HC C-terminus lacking two native residues (GK) and gaining twelve additional non-native residues (EAEAASASELFQ). Aware of other mAb variants with genetic origins, we sought to understand whether this modification too had a genetic basis. In silico translation of the expression vector encoding the mAb demonstrated that a normally non-coding section of nucleotides in the + 1 reading frame relative to the HC C-terminal coding region could have led to a transcript with the non-native C-terminal extension. Two potential mechanisms for how this nucleotide sequence might have fused to the native HC coding region and led to expression of the extension product are presented.

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.

Sequence and Solution Effects on the Prevalence of d-Isomers Produced by Deamidation

Deamidation of asparagine is a spontaneous and irreversible post-translational modification associated with a growing list of human diseases. While pervasive, deamidation is often overlooked because it represents a relatively minor chemical change. Structural and functional characterization of this modification is complicated because deamidation of asparagine yields four isomeric forms of Asp. Herein, radical directed dissociation (RDD), in conjunction with mass spectrometry, is used to identify and quantify all four isomers in a series of model peptides that were subjected to various deamidation conditions. Although primary sequence significantly influences the rate of deamidation, it has little impact on the relative proportions of the product isomers. Furthermore, the addition of ammonia can be used to increase the rate of deamidation without significantly perturbing isomer populations. Conversely, external factors such as buffer conditions and temperature alter product distributions but exhibit less dramatic effects on the deamidation rate. Strikingly, the common laboratory and biologically significant bicarbonate buffer is found to strongly promote racemization, yielding increased amounts of d-Asp and d-isoAsp. These outcomes following deamidation have broad implications in human aging and should be considered during the development of protein-based therapeutics.

N+1 Engineering of an Aspartate Isomerization Hotspot in the Complementarity-Determining Region of a Monoclonal Antibody

Aspartate (Asp) isomerization is a common degradation pathway and a potential critical quality attribute that needs to be well characterized during the optimization and development of therapeutic antibodies. A putative Asp-serine (Ser) isomerization motif was identified in the complementarity-determining region of a humanized monoclonal antibody and shown to be a developability risk using accelerated stability analyses. To address this issue, we explored different antibody engineering strategies. Direct engineering of the Asp residue resulted in a greater than 5× loss of antigen-binding affinity and bioactivity, indicating a critical role for this residue. In contrast, rational engineering of the Ser residue at the n+1 position had a negligible impact on antigen binding affinity and bioactivity compared with the parent molecule. Furthermore, the n+1 engineering strategy effectively eliminated Asp isomerization as determined by accelerated stability analysis. This outcome affirms that the rate of Asp isomerization is strongly dependent on the identity of the n+1 residue. This report highlights a systematic antibody engineering strategy for mitigating an Asp isomerization developability risk during lead optimization.

SpeB proteolysis with imaged capillary isoelectric focusing for the characterization of domain-specific charge heterogeneities of reference and biosimilar Rituximab

The charge variations of therapeutic monoclonal antibody reveal important information of the post-translational modifications that may potentially impact the potency and safety of pharmaceutical products, especially during the evaluation of biosimilarity of therapeutic proteins. In this work, a novel SpeB-based proteolysis strategy coupling with imaged capillary isoelectric focusing was developed for the determination of domain-specific charge heterogeneities of innovator and generic Rituximab drug products from United States, European and Indian markets. It was observed that innovator Rituximab from the United States and Europe share highly similar peak distributions and charge heterogeneities with 26.2-26.6% Fc/2, 28.9-29.3% LC and 44.4-44.5% Fd peak areas detected, respectively, while multiple basic variations of Fc/2 and less acidic LC and Fd species were found from generic Rituximab from India with 20.9% Fc/2, 32.3% LC and 46.9% Fd peak areas detected. It was also demonstrated that structural changes caused by Carboxypeptidase B treatment and deamidation study at pH extremes could be sensitively captured with the established method, with the results further indicating that the generic product's basic variations of Fc/2 were un-cleaved Lysine residues, while the lack of certain acidic peaks on LC and Fd probably was due to the lower level of deamidation. This new strategy could become a useful tool to reveal domain-specific charge heterogeneities profiles of a variety of therapeutic monoclonal antibodies in regulated environments.

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.