Comparison of SEC and CE-SDS methods for monitoring hinge fragmentation in IgG1 monoclonal antibodies

Identification and Activity Study of an Impurity Band Observed in the nrSDS-PAGE of Aflibercept

BACKGROUND

Aflibercept is a biopharmaceutical targeting vascular endothelial growth factor (VEGF) that has shown promise in the treatment of neovascular age-related macular degeneration (nAMD) and diabetic macular edema (DME) in adults. Quality control studies of aflibercept employing non-reduced SDS-PAGE (nrSDS-PAGE) have shown that a significant variant band (IM1) is consistently present below the main band. Considering the quality control strategy of biopharmaceuticals, structural elucidation and functional studies are required.

METHODS

In this study, the variant bands in nrSDS-PAGE were collected through electroelution and identified by peptide mass fingerprinting based on liquid chromatography-tandem MS (LC-MS/MS). This variant was expressed using knob-into-hole (KIH) design transient transfection for the detection of ligand affinity, binding activity and biological activity.

RESULTS

The variant band was formed by C-terminal truncation at position N99 of one chain in the aflibercept homodimer. Then, this variant was successfully expressed using KIH design transient transfection. The ligand affinity of the IM1 truncated variant was reduced by 18-fold, and neither binding activity nor biological activity were detected.

CONCLUSIONS

The efficacy of aflibercept is influenced by the loss of biological activity of the variant. Therefore, this study supports the development of a quality control strategy for aflibercept.

Leveraging high-throughput analytics and automation to rapidly develop high-concentration mAb formulations: integrated excipient compatibility and viscosity screening

BACKGROUND

Formulation screening is essential to experimentally balance stability and viscosity in high-concentration mAb formulations. We developed a high-throughput approach with automated sample preparation and analytical workflows to enable the integrated assessment of excipient compatibility and viscosity of mAb formulations.

METHODS

Ninety-six formulations of a trastuzumab biosimilar were screened by combining 8 types of excipient modifiers with 4 types of buffers across a pH range of 4.5 to 7.5. Key stability risks, including high molecular weight (HMW) aggregation and fragmentation, were thoroughly assessed along with viscosity at high concentrations. Additionally, several biophysical parameters were evaluated for their ability to predict stability or viscosity outcomes. Multiple linear regression was applied to fit the data and identify key factors.

RESULTS

The optimal pH range for the trastuzumab biosimilar was found to be 5.0 to 6.5, based on opposing pH dependencies for stability and viscosity. Buffer type had a minor effect on viscosity and fragmentation but played a significant role in influencing HMW aggregates, with Na-acetate and histidine-HCl being the best candidates. The impact of excipient modifiers on viscosity, HMW, and fragmentation depended on both pH and buffer type, showing strong interactions among factors. Arginine-HCl and lysine-HCl effectively lowered viscosity of the trastuzumab biosimilar at pH levels above 6.0, while glycine formulations were more effective at reducing viscosity below pH 6.0. Histidine-HCl, arginine-HCl, and lysine-HCl lowered the risk of HMW aggregation, whereas formulations containing Na-phosphate or NaCl showed higher HMW aggregation. Formulations with arginine-HCl, lysine-HCl, and NaCl demonstrated a rapid increase in fragmentation at pH levels below 5.0, while Na-aspartate formulations showed increased fragmentation at pH levels above 6.5.

CONCLUSION

Hence, it is important to optimize the levels of each chosen excipient in the formulation study to balance their benefits against potential incompatibilities. This study serves as a foundation for identifying high-concentration antibody formulations using a high-throughput approach, where minimal materials are required, and optimized formulation design spaces can be quickly identified.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Catechins prevent monoclonal antibody fragmentation during production via fed-batch culture of Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells are widely used for the industrial production of therapeutic monoclonal antibodies (mAbs). To meet the increasing market demands, high productivity, and quality are required in cell culture. One of the critical attributes of mAbs, from a safety perspective, is mAb fragmentation. However, methods for preventing mAbs fragmentation in CHO cell culture are limited. In this study, we observed that the antibody fragment content increased with increasing titers in fed-batch cultures for all three cell lines expressing recombinant antibodies. Adding copper sulfate to the culture medium further increased the fragment content, suggesting the involvement of reactive oxygen species (ROS) in the fragmentation process. Though antioxidants may be helpful to scavenge ROS, several antioxidants are reported to decrease the productivity of CHO cells. Among the antioxidants examined, we observed that the addition of catechin or (-)-epigallocatechin gallate to the culture medium prevented fragmentation content by about 20% and increased viable cell density and titer by 30% and 10%, respectively. Thus, the addition of catechins or compounds of equivalent function would be beneficial for manufacturing therapeutic mAbs with a balance between high titers and good quality.

Effects of process intensification on homogeneity of an IgG1:κ monoclonal antibody during perfusion culture

The pharmaceutical industry employs various strategies to improve cell productivity. These strategies include process intensification, culture media improvement, clonal selection, media supplementation and genetic engineering of cells. However, improved cell productivity has inherent risk of impacting product quality attributes (PQA). PQAs may affect the products' efficacy via stability, bioavailability, or in vivo bioactivity. Variations in manufacturing process may introduce heterogeneity in the products by altering the type and extent of N-glycosylation, which is a PQA of therapeutic proteins. We investigated the effect of different cell densities representing increasing process intensification in a perfusion cell culture on the production of an IgG1-κ monoclonal antibody from a CHO-K1 cell line. This antibody is glycosylated both on light chain and heavy chain. Our results showed that the contents of glycosylation of IgG1-κ mAb increased in G0F and fucosylated type glycans as a group, whereas sialylated type glycans decreased, for the mAb whole protein. Overall, significant differences were observed in amounts of G0F, G1F, G0, G2FS1, and G2FS2 type glycans across all process intensification levels. G2FS2 and G2 type N-glycans were predominantly quantifiable from light chain rather than heavy chain. It may be concluded that there is a potential impact to product quality attributes of therapeutic proteins during process intensification via perfusion cell culture that needs to be assessed. Since during perfusion cell culture the product is collected throughout the duration of the process, lot allocation needs careful attention to process parameters, as PQAs are affected by the critical process parameters (CPPs). KEY POINTS: • Molecular integrity may suffer with increasing process intensity. • Galactosylated and sialylated N-glycans may decrease. • Perfusion culture appears to maintain protein charge structure.

Application of Raman spectroscopy during pharmaceutical process development for determination of critical quality attributes in Protein A chromatography

Raman spectroscopy is considered a Process Analytical Technology (PAT) tool in biopharmaceutical downstream processes. In the past decade, researchers have shown Raman spectroscopy's feasibility in determining Critical Quality Attributes (CQAs) in bioprocessing. This study verifies the feasibility of implementing a Raman-based PAT tool in Protein A chromatography as a CQA monitoring technique, for the purpose of accelerating process development and achieving real-time release in manufacturing. A system connecting Raman to a Tecan liquid handling station enables high-throughput model calibration. One calibration experiment collects Raman spectra of 183 samples with 8 CQAs within 25 h. After applying Butterworth high-pass filters and k-nearest neighbor (KNN) regression for model training, the model showed high predictive accuracy for fragments (Q2 = 0.965) and strong predictability for target protein concentration, aggregates, as well as charge variants (Q2≥ 0.922). The model's robustness was confirmed by varying the elution pH, load density, and residence time using 19 external validation preparative Protein A chromatography runs. The model can deliver elution profiles of multiple CQAs within a set point ± 0.3 pH range. The CQA readouts were presented as continuous chromatograms with a resolution of every 28 s for enhanced process understanding. In external validation datasets, the model maintained strong predictability especially for target protein concentration (Q2 = 0.956) and basic charge variants (Q2 = 0.943), except for overpredicted HCP (Q2 = 0.539). This study demonstrates a rapid, effective method for implementing Raman spectroscopy for in-line CQA monitoring in process development and biomanufacturing, eliminating the need for labor-intensive sample pooling and handling.

GB12-09, a bispecific antibody targeting IL4Rα and IL31Rα for atopic dermatitis therapy

Atopic dermatitis (AD) is a chronic inflammatory skin condition characterized by dysregulated immune responses. The key mediators of AD pathogenesis are T helper 2 (TH2) cells and TH2 cytokines. Targeting interleukin 4 (IL4), IL13 or IL31 has become a pivotal focus in both research and clinical treatments for AD. However, the need remains pressing for the development of a more effective and safer therapy, as the current approaches often yield low response rates and adverse effects. In response to this challenge, we have engineered a immunoglobulin G-single-chain fragment variable (scFv) format bispecific antibody (Ab) designed to concurrently target IL4R and IL31R. Our innovative design involved sequence optimization of VL-VH and the introduction of disulfide bond (VH44-VL100) within the IL31Rα Ab scFv region to stabilize the scFv structure. Our bispecific Ab efficiently inhibited the IL4/IL13/IL31 signaling pathways in vitro and reduced serum immunoglobulin E and IL31 levels in vivo. Consequently, this intervention led to improved inflammation profiles and notable amelioration of AD symptoms. This research highlighted a novel approach to AD therapy by employing bispecific Ab targeting IL4Rα and IL31Rα with potent efficacy.

Using enhanced development tools offered by analytical Quality by Design to support switching of a quality control method

Quality by Design (QbD) principles play an increasingly important role in the pharmaceutical industry. Here, we used an analytical QbD (AQbD) approach to develop a capillary electrophoresis sodium dodecyl sulfate under reducing conditions (rCE-SDS), with the aim of replacing SDS-polyacrylamide gel electrophoresis (SDS-PAGE) as release and stability test method for a commercialized monoclonal antibody product. Method development started with defining analytical method performance requirements as part of an analytical target profile, followed by a systematic risk assessment of method input parameters and their relation to defined method outputs. Based on this, design of experiments studies were performed to identify a method operable design region (MODR). The MODR could be leveraged to improve method robustness. In a bridging study, it was demonstrated that the rCE-SDS method is more sensitive than the legacy SDS-PAGE method, and a conversion factor could be established to compensate for an off-set due to the higher sensitivity, without losing the correlation to the historical data acquired with the former method. Overall, systematic application of analytical Quality by Design principles for designing and developing a new analytical method helped to elucidate the complex dependency of method outputs on its input parameters. The link of the method to product quality attributes and the definition of method performance requirements were found to be most relevant for derisking the analytical method switch, regarding impact on the control strategy.

Monitoring of low-molecular-weight protein aggregation by CE-SDS as a complementary method to SE-HPLC

Capillary electrophoresis with sodium dodecyl sulfate (CE-SDS) has long been proven to have excellent performance in the analysis and characterization of therapeutic proteins. However, it is rarely used for the detection of low-molecular-weight proteins or peptides. Our research has proved the ability of CE-SDS to characterize the purity of low-molecular-weight proteins (i.e., <10 kDa) and even polypeptides. In this article, insulin glargine was used as a model protein, and CE-SDS was used to analyze the samples damaged by heating and light exposure. The monomers, dimers, and trimers of insulin glargine were effectively separated, and the results of the mass spectrometry also confirmed the existence of two kinds of insulin aggregates. For comparison, the size-exclusion high-performance liquid chromatography (SE-HPLC) only showed a single aggregate peak. In addition, the denaturation conditions caused only the covalent aggregates to appear in the CE-SDS analysis. These advantages also make CE-SDS an excellent supplementary technology to the traditional SE-HPLC, providing biopharmaceutical analysts with more information.

Anti-TGF-β/PD-L1 bispecific antibody promotes T cell infiltration and exhibits enhanced antitumor activity in triple-negative breast cancer

BACKGROUND

Agents blocking programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) have been approved for triple-negative breast cancer (TNBC). However, the response rate of anti-PD-1/PD-L1 is still unsatisfactory, partly due to immunosuppressive factors such as transforming growth factor-beta (TGF-β). In our previous pilot study, the bispecific antibody targeting TGF-β and murine PD-L1 (termed YM101) showed potent antitumor effect. In this work, we constructed a bispecific antibody targeting TGF-β and human PD-L1 (termed BiTP) and explored the antitumor effect of BiTP in TNBC.

METHODS

BiTP was developed using Check-BODY^TM bispecific platform. The binding affinity of BiTP was measured by surface plasmon resonance, ELISA, and flow cytometry. The bioactivity was assessed by Smad and NFAT luciferase reporter assays, immunofluorescence, western blotting, and superantigen stimulation assays. The antitumor activity of BiTP was explored in humanized epithelial-mesenchymal transition-6-hPDL1 and 4T1-hPDL1 murine TNBC models. Immunohistochemical staining, flow cytometry, and bulk RNA-seq were used to investigate the effect of BiTP on immune cell infiltration.

RESULTS

BiTP exhibited high binding affinity to dual targets. In vitro experiments verified that BiTP effectively counteracted TGF-β-Smad and PD-L1-PD-1-NFAT signaling. In vivo animal experiments demonstrated that BiTP had superior antitumor activity relative to anti-PD-L1 and anti-TGF-β monotherapy. Mechanistically, BiTP decreased collagen deposition, enhanced CD8⁺ T cell penetration, and increased tumor-infiltrating lymphocytes. This improved tumor microenvironment contributed to the potent antitumor activity of BiTP.

CONCLUSION

BiTP retains parent antibodies' binding affinity and bioactivity, with superior antitumor activity to parent antibodies in TNBC. Our data suggest that BiTP might be a promising agent for TNBC treatment.

Monoclonal Antibody Sequence Variants Disguised as Fragments: Identification, Characterization, and Their Removal by Purification Process Optimization

During early stage development of a therapeutic IgG1 monoclonal antibody, high levels of low molecular weight (LMW) peaks were observed by high performance size-exclusion chromatography and capillary electrophoresis. Further characterization of the LMW peak enriched HPSEC fractions using reversed phase liquid chromatography coupled to mass spectrometry showed these LMW species were 47 kDa and 50 kDa in size. However, the measured masses could not be matched to any fragments resulting from peptide bond hydrolysis. To identify these unknown LMW species, molecular characterization methods were employed, including high-throughput sequencing of RNA. Transcriptomic analysis revealed the LMW species were generated by mis-splicing events in the heavy chain transcript, which produced truncated heavy chain products that assembled with the light chain to mimic the appearance of fragments identified by routine purity assays. In an effort to improve product quality, an optimized purification process was developed. Characterization of the process intermediates confirmed removal of both LMW species by the optimized process. Our study demonstrates that deep-dive analytical characterization of biotherapeutics is critical to ensure product quality and inform process development. Transcriptomic analysis tools can help identify the cause of unknown species, and plays a key role in product and process characterization.

Identification of a CE-SDS shoulder peak as disulfide-linked fragments from common CH2 cleavages in IgGs and IgG-like bispecific antibodies

Fragmentation is a well-characterized degradation pathway of therapeutic antibodies and is usually monitored by capillary electrophoresis–sodium dodecyl sulfate (CE-SDS). Although fragments due to cleavage in C_H2 domains linked by intrachain disulfide bonds are common and can be detected by reduced reversed-phase – liquid chromatography mass spectrometry (RP-LCMS) and reduced CE-SDS methods, their separation in nonreduced CE-SDS (nrCE-SDS) has not been reported but speculated as comigrating with intact IgG. A shoulder peak in nrCE-SDS was observed in the stability samples of an IgG-like bispecific antibody and was determined to be mainly caused by fragments from clipping at the C-terminus of leucine (L)306 or L309 (EU numbering) in the C_H2 domain of both heavy chains (HCs) and, to a lesser degree, at the C-terminus of L182 in the C_H1 domain of the knob HC. Subunit LCMS analysis verified that the crystallizable fragment contained variants with one or multiple mass additions of ~18 Da due to clipping. Further investigation revealed that C_H2 clippings at L306 and L309 were largely due to proteolytic activity, and cleavages were present at various levels in all in-house IgG1 and IgG4 molecules studied. Our study shows that C_H2 domain cleavages, with complementary fragments still linked by intrachain disulfide, can be electrophoretically resolved as a front shoulder of the main peak in nrCE-SDS. Given the high occurrence of C_H2 cleavages in antibodies, these findings will have broad applicability and could help manufacturers of therapeutic antibodies in process improvement, product characterization, investigations, formulation stability, and stability comparability studies.

Shedding light on both ends: An update on analytical approaches for N- and C-terminomics

Though proteases were long regarded as nonspecific degradative enzymes, over time, it was recognized that they also hydrolyze peptide bonds very specifically with a limited substrate pool. This irreversible posttranslational modification modulates the fate and activity of many proteins, making proteolytic processing a master switch in the regulation of e.g., the immune system, apoptosis and cancer progression. N- and C-terminomics, the identification of protein termini, has become indispensable in elucidating protease substrates and therefore protease function. Further, terminomics has the potential to identify yet unknown proteoforms, e.g. formed by alternative splicing or the recently discovered alternative ORFs. Different strategies and workflows have been developed that achieve higher sensitivity, a greater depth of coverage or higher throughput. In this review, we summarize recent developments in both N- and C-terminomics and include the potential of top-down proteomics which inherently delivers information on both ends of analytes in a single analysis.

Recent biopharmaceutical applications of capillary electrophoresis methods on recombinant DNA technology-based products

Biopharmaceuticals (recombinant technology-based products, vaccines, whole blood and blood components, gene therapy, cells, tissues, etc.,) are described as biological medical products produced from various living sources such as human, microbial, animal, and so on by manufacturing, extraction, or semi-synthesis. They are complex molecules having high molecular weights. For their safety and efficacy, their structural, clinical, physicochemical, and chemical features must be carefully controlled, and they must be well characterized by analytical techniques before the approval of the final product. Capillary electrophoresis (CE) having versatile modes can provide valuable safety and efficacy information, such as amino acid sequence, size variants (low and high molecular weight variants), charged variants (acidic and basic impurities), aggregates, N-linked glycosylation, and O-linked glycosylation. There are numerous applications of CE in the literature. In this review, the most significant and recent studies on the analysis of recombinant DNA technology-based products using different CE modes in the last ten years have been overviewed. It was seen that the researches mostly focus on the analysis of mAbs and IgG. In addition, in recent years, researchers have started to prefer CE combined mass spectrometry (MS) techniques to provide a more detailed characterization for protein and peptide fragments.

Antibody disulfide bond reduction and recovery during biopharmaceutical process development-A review

Antibody disulfide bond reduction has been a challenging issue in monoclonal antibody manufacturing. It could lead to a decrease of product purity and failure to meet the targeted product profile and/or specifications. More importantly, disulfide bond reduction could also impact drug safety and efficacy. Scientists across the industry have been examining the root causes and developing mitigation strategies to address the challenge. In recent years, with the development of high titer mammalian cell culture processes to meet the rapidly growing demand for antibody biopharmaceuticals, disulfide bond reduction has been observed more frequently. Thus, it is necessary to continue evolving the disulfide reduction mitigation strategies and developing novel approaches to maintain high product quality. Additionally, in recent years as more complex molecules (such as bispecific and trispecific antibodies) emerge, the molecular heterogeneity due to incomplete formation of the interchain disulfide bonds becomes a more imperative challenging issue. Given the disulfide reduction challenges that biotech industry is facing, in this review, we provide a comprehensive scientific summary of the root cause analysis of disulfide reduction during process development of antibody therapeutics, mitigation strategies and its potential remediated recovery based on published papers. First, this paper intends to highlight different aspects of the root cause for disulfide reduction. Secondly, to provide a broader understanding of the disulfide bond reduction in downstream process, this paper discusses disulfide bond reduction impact on product stability, associated analytical methods for disulfide bond reduction detection and characterization, process control strategies as well as their manufacturing implementation. In addition, brief perspectives on the development of future mitigation strategies are also reviewed, including platform alignment, mitigation strategy application for the emerging new modalities such as bispecific and trispecific antibodies as well as using machine learning to identify molecule susceptibility of disulfide bond reduction. The data in this review are originated from the published papers.

The construction, expression, and enhanced anti-tumor activity of YM101: a bispecific antibody simultaneously targeting TGF-β and PD-L1

Background

Therapeutic antibodies targeting programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis induce potent and durable anti-tumor responses in multiple types of cancers. However, only a subset of patients benefits from anti-PD-1/PD-L1 therapies. As a negative regulator of anti-tumor immunity, TGF-β impairs the efficacy of anti-PD-1/PD-L1 and induces drug resistance. Developing a novel treatment strategy to simultaneously block PD-1/PD-L1 and TGF-β would be valuable to enhance the effect of anti-PD-1/PD-L1 and relieve drug resistance.

Methods

Based on the Check-BODY™ technology platform, we developed an anti-TGF-β/PD-L1 bispecific antibody YM101. The bioactivity of the anti-TGF-β moiety was determined by Smad-luciferase reporter assay, transwell assay, western blotting, CCK-8, and flow cytometry. The bioactivity of the anti-PD-L1 moiety was measured by T cell activation assays. EMT-6, CT26, and 3LL tumor models were used to investigate the anti-tumor activity of YM101 in vivo. RNA-seq, immunohistochemical staining, and flow cytometry were utilized to analyze the effect of YM101 on the tumor microenvironment.

Results

YM101 could bind to TGF-β and PD-L1 specifically. In vitro experiments showed that YM101 effectively counteracted the biological effects of TGF-β and PD-1/PD-L1 pathway, including activating Smad signaling, inducing epithelial-mesenchymal transition, and immunosuppression. Besides, in vivo experiments indicated the anti-tumor activity of YM101 was superior to anti-TGF-β and anti-PD-L1 monotherapies. Mechanistically, YM101 promoted the formation of ‘hot tumor’: increasing the numbers of tumor infiltrating lymphocytes and dendritic cells, elevating the ratio of M1/M2, and enhancing cytokine production in T cells. This normalized tumor immune microenvironment and enhanced anti-tumor immune response might contribute to the robust anti-tumor effect of YM101.

Conclusion

Our results demonstrated that YM101 could simultaneously block TGF-β and PD-L1 pathways and had a superior anti-tumor effect compared to the monotherapies.

Capillary Electrophoresis-Sodium Dodecyl Sulfate with Laser-Induced Fluorescence Detection as a Highly Sensitive and Quality Control-Friendly Method for Monitoring Adeno-Associated Virus Capsid Protein Purity

The capsid protein purity of adeno-associated virus (AAV) is considered a critical quality attribute of AAV-based gene therapy products. However, the analytical methods currently available to monitor the viral capsid proteins, which are present in extremely low concentrations, have limited sensitivity and robustness, thus limiting their general applicability. As a result, there is an urgent need to develop robust separation methods with highly sensitive detection. In this article, we describe the first denaturation and fluorescence labeling procedure for AAV capsid proteins using the pyrylium dye Chromeo™ P503, enabling the establishment of the first capillary electrophoresis-sodium dodecyl sulfate (CE-SDS) method combined with laser-induced fluorescence (LIF) detection for AAV. Upon optimization using a quality-by-design approach, the newly developed method features a simple and robust one-step sample preparation workflow resulting in consistently labeled and denatured viral protein samples, which can subsequently be separated and quantified by CE-LIF. The method has been validated to be accurate and precise with a linear range of 50-150% of the nominal concentration of 2.0 × 10¹¹ vector genomes per mL (vg/mL). The detection limit and quantitation limit were established to be 8.0 × 10⁷ vg/mL (∼0.8 ng/mL) and 4.2 × 10⁸ vg/mL (∼4 ng/mL), respectively, representing the highest sensitivity achieved for AAV capsid protein quantitation reported to date and a linear dynamic range of 8.0 × 10⁷-3.0 × 10¹¹ vg/mL. A comparison of the CE-SDS LIF method with existing methods, such as CE-SDS ultraviolet and sodium dodecyl sulfate-polyacrylamide gel electrophoresis with SYPRO Ruby stain, indicated that the new method has superior resolution and a significant increase in signal intensity. Capsid protein purity analysis of multiple AAV serotypes, including AAV5, scAAVrh10, AAV2, and AAV6, has been demonstrated for the first time using the same method, indicating the newly developed AAV labeling procedure and CE-LIF analysis could serve as a Quality Control-friendly platform and best-in-class analytical method for the control of AAV capsid protein purity.

Analysis of Monoclonal Antibodies by Capillary Electrophoresis: Sample Preparation, Separation, and Detection

Therapeutic monoclonal antibodies (mAbs) are dominating the biopharmaceutical field due to the fact of their high specificity in the treatment of diverse diseases. Nevertheless, mAbs are very complex glycoproteins exhibiting several macro- and microheterogeneities that may affect their safety, quality, and efficacy. This complexity is very challenging for mAbs development, formulation, and quality control. To tackle the quality issue, a combination of multiple analytical approaches is necessary. In this perspective, capillary electrophoresis has gained considerable interest over the last decade due to the fact of its complementary features to chromatographic approaches. This review provides an overview of the strategies of mAbs and derivatives analysis by capillary electrophoresis hyphenated to ultraviolet, fluorescence, and mass spectrometry detection. The main sample preparation approaches used for mAb analytical characterization (i.e., intact, middle-up/down, and bottom-up) are detailed. The different electrophoretic modes used as well as integrated analysis approaches (sample preparation and separation) are critically discussed.

Formation of an Unprecedented Impurity during CE-SDS Analysis of a Recombinant Protein

PURPOSES

The main purposes of this article are to describe an unprecedented phenomenon in which significant amount of a shoulder peak impurity was observed during normal non-reducing capillary electrophoresis-sodium dodecyl sulfate (CE-SDS) analysis of a recombinant fusion protein X, and to evaluate the root cause for this phenomenon.

METHODS

A series of experiments were conducted to study the nature of this degradation. Effects of iodoacetamide (IAM), heating temperature, duration, and SDS on the formation of this specific impurity were evaluated using a variety of characterization techniques.

RESULTS

The formation of the impurity as observed in CE-SDS was actually due to alkylation of lysine and serine residues with IAM, as confirmed by peptide mapping and LC-MS/MS, which increased the molecular weight and therefore decreased the electrophoretic mobility. The amount of impurity was also strongly dependent on sample preparation conditions including the presence or absence of SDS.

CONCLUSIONS

Our study clearly suggested that even though IAM has been used extensively as an alkylation reagent in the traditional non-reducing CE-SDS analysis of monoclonal antibodies and other proteins, alkylation with IAM could potentially lead to additional impurity peak, and therefore complicating analysis. Therefore, before performing CE-SDS and other analyses, the effects of sample preparation procedures on analytical results must be evaluated. For protein X, IAM should be excluded for CE-SDS analysis.

Hydrophobic interaction chromatography (HIC) method development and characterization of resolved drug-load variants in site-specifically conjugated pyrrolobenzodiazepine dimer-based antibody drug conjugates (PBD-ADCs)

Antibody drug conjugates (ADCs) are heterogeneous biopharmaceutical products that demand extensive characterization to ensure batch consistency, safety, and efficacy. Hydrophobic interaction chromatography (HIC) is the state-of-the-art analytical tool to monitor conjugation-related critical quality attributes (CQAs) e.g. drug-load distribution and Drug-to-Antibody Ratio (DAR). For the next generation site-specific PBD-ADCs (PBD: pyrrolobenzodiazepine dimer), denaturing RP-HPLC (reverse-phase high-performance chromatography) is the current method to determine average DAR. In this manuscript, we have utilized native HIC for the first time to understand conjugation related CQAs in PBD-ADCs. In terms of the method development, the type of stationary phase and salt, coupled with reduction of the reactive imine in the PBD drug-linker to an amine form in the sample preparation, have played a key role in achieving the best HIC resolution for the drug-load variants. The established HIC conditions resolved DAR 0, DAR 1, and two DAR 2 peaks for PBD-ADCs. Extended characterization of the DAR 2 peaks confirmed that they have retained characteristically distinct antibody Fc N-glycan distributions (Fc = Fragment crystallization region). Therefore, the results support that the HIC conditions established for PBD-ADCs is valuable in not only determining DAR values but also other important attributes including native drug-load distribution and unique DAR 2 conformations existed as a result of the N-glycan heterogeneity.

Specific and high-resolution identification of monoclonal antibody fragments detected by capillary electrophoresis-sodium dodecyl sulfate using reversed-phase HPLC with top-down mass spectrometry analysis

In recent years, capillary electrophoresis-sodium dodecyl sulfate (cSDS) has been widely used for high resolution separation and quantification of the fragments and aggregates of monoclonal antibodies (mAbs) to ensure the quality of mAb therapeutics. However, identification of the low-molecular-weight (LMW) and high-molecular-weight (HMW) species detected in cSDS electropherograms has been based primarily on the approximate MWs calculated from standard curves using known MW standards and correlations with fragments and aggregates identified by other methods. It is not easy to collect sufficient amounts of H/LMW species from cSDS for analysis by orthogonal methods and the direct coupling of cSDS with mass spectrometry (MS) is very difficult due to interference from SDS. In this study, we describe the precise identification of H/LMW species detected by cSDS using reversed-phase high performance liquid chromatography (RP-HPLC) coupled with top-down tandem MS analysis. The H/LMW species were first identified by on-line RP-HPLC MS analysis and the RP-HPLC fractions were then analyzed by cSDS to connect the identified H/LMW species with the peaks in the cSDS electropherogram. With this method, 58 unique H/LMW species were identified from an immunoglobulin G1 (IgG1) mAb. The identified fragments ranged from 10 kDa single chain fragments to 130 kDa triple chain fragments, including some with post-translational modifications. This is the first study to clearly identify the antibody fragments, including the exact clipping sites, observed in cSDS electropherograms. The methodology and results presented here should be applicable to most other IgG1 mAbs.

Characterization of a Novel Bispecific Antibody With Improved Conformational and Chemical Stability

Bispecific antibodies containing single-chain variable fragment (scFv) appended to immunoglobulins G offer unique development challenges. Here, we describe the stability of a novel bispecific format, BiS5, where the scFv is tethered to the C_H3 domain. BiS5 showed an improved conformational and chemical stability compared with that of BiS4 in which the scFv is appended in the hinge region between the F_ab and F_c. By switching the location of the scFv from hinge region to the C_H3, there was an improved stabilization of C_H2 and scFv domains. Interestingly, no noticeable impact was observed on the conformational stability of C_H3 and F_ab domains. BiS4 and BiS5 showed different aggregation and fragmentation rates under accelerated temperature stress conditions. BiS4 showed higher fragmentation rates compared with BiS5 likely owing to fragmentation in the linker region on either side of the scFv while BiS5 is more resistant toward fragmentation owing to tethering of scFv to the C_H3 domain at its N and C terminus. In conclusion, the location of scFv affects both aggregation and fragmentation kinetics. These insights into the molecular structure and correlations with their physical and chemical stability will help formulation development of these novel bispecific antibodies.

Discovery and characterization of CHO host cell protease-induced fragmentation of a recombinant monoclonal antibody during production process development

Monoclonal antibody (mAb) fragmentation is a widespread issue of protein stability that needs to be carefully monitored for critical mAb quality control during the production process development. This study describes here the discovery and characterization of CHO host cell protease-induced fragmentation of a therapeutic mAb-X in the formulation samples from an early production process. The fragmentation was observed in the sodium dodecyl sulfate capillary electrophoresis (CE-SDS) analysis of mAb-X formulation samples incubated at elevated temperature. Size exclusion liquid chromatography (SEC-HPLC) was used to analyze and collect these cleaved fragments derived from mAb-X. Reversed phase liquid chromatography mass spectrometry (RP-LC-MS) and tandem mass (MS/MS) analysis demonstrated that the fragment was generated mainly due to the hinge region cleavage of mAb-X. The fragmentation rate was characterized in the mAb-X formulation samples at pH from 4.0 to 6.0 using CE-SDS and SDS-PAGE analysis. The percentage of the main fragment increased dramatically from 2.8% to 31.2% as pH decreased from 6.0 to 4.0 at 40 °C for 28 days, which indicated the fragmentation was highly pH-dependent. The SDS-PAGE analysis further verified the pH-dependent property of the framentation of mAb-X. Moreover, the fragmentation was characterized in the presence and absence of pepstatin A, an inhibitor of acidic proteases. Significant inhibition of mAb-X fragmentation was observed with the addition of pepstatin A to mAb-X formulation samples. These results suggested residual acidic host cell protease(s) in the formulation samples from an early production process caused the fragmentation of mAb-X. To prove evidence, we developed an optimized protein A chromatography to enhance the residual host cell protease(s) removal capability of mAb-X purification process and consequently eliminate the above described cleaved fragment of mAb-X, which further supported the hypothesis that the fragmentation of mAb-X was catalyzed by the residual host cell protease(s) in the formulation samples from the early production process. This case study reiterated that residual host cell protease is a critical quality attribute (CQA) that should be carefully controlled and evaluated to guarantee successful manufacture processes for mAb products.

Engineering the hinge region of human IgG1 Fc-fused bispecific antibodies to improve fragmentation resistance

Fc domain fusion can improve the therapeutic effects of relatively small biological molecules such as peptides, cytokines, and antibody fragments. Fc fusion proteins can also be used to enhance the cytotoxic effects of small bispecific antibodies (bsAbs). However, fragmentation of Fc fusion proteins, which mainly occurs around the hinge regions during production, storage, and circulation in the blood, is a major issue. In this study, we first investigated the mechanisms of fragmentation around the hinge region during storage using Fc-fused bsAbs with specificity for epidermal growth factor receptor and CD3 as a model. The fragmentation peaks generated by gel filtration analysis indicated that both contaminating proteases and dissolved active oxygen should be considered causes of fragmentation. We designed and constructed variants by introducing a point mutation into the upper hinge region, which reduced the cleavage caused by dissolved active oxygen, and shortened the hinge region to restrict access of proteases. These hinge modifications improved fragmentation resistance and did not affect the biological activity of the bsAbs in vitro. We confirmed the versatility of the hinge modifications using another Fc-fused bsAb. Our results show that hinge modifications to the Fc fusion protein, especially the introduction of a point mutation into the upper hinge region, can reduce fragmentation substantially, and these modifications can be used to improve the fragmentation resistance of other recombinant Fc fusion proteins.

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.