Glycation of antibodies: Modification, methods and potential effects on biological functions

Development of a platform method for rapid detection and characterization of domain-specific post-translational modifications in bispecific antibodies

Charge heterogeneity is inherent to all therapeutic antibodies and arises from post-translational modifications (PTMs) and/or protein degradation events that may occur during manufacturing. Among therapeutic antibodies, the bispecific antibody (bsAb) containing two unique Fab arms directed against two different targets presents an additional layer of complexity to the charge profile. In the context of a bsAb, a single domain-specific PTM within one of the Fab domains may be sufficient to compromise target binding and could potentially impact the stability, safety, potency, and efficacy of the drug product. Therefore, characterization and routine monitoring of domain-specific modifications is critical to ensure the quality of therapeutic bispecific antibody products. We developed a Digestion-assisted imaged Capillary isoElectric focusing (DiCE) method to detect and quantitate domain-specific charge variants of therapeutic bispecific antibodies (bsAbs). The method involves enzymatic digestion using immunoglobulin G (IgG)-degrading enzyme of S. pyogenes (IdeS) to generate F(ab)2 and Fc fragments, followed by imaged capillary isoelectric focusing (icIEF) under reduced, denaturing conditions to separate the light chains (LCs) from the Fd domains. Our results suggest that DiCE is a highly sensitive method that is capable of quantitating domain-specific PTMs of a bsAb. In one case study, DiCE was used to quantitate unprocessed C-terminal lysine and site-specific glycation of Lys98 in the complementarity-determining region (CDR) of a bsAb that could not be accurately quantitated using conventional, platform-based charge variant analysis, such as intact icIEF. Quantitation of these PTMs by DiCE was comparable to results from peptide mapping, demonstrating that DiCE is a valuable orthogonal method for ensuring product quality. This method may also have potential applications for characterizing fusion proteins, antibody-drug conjugates, and co-formulated antibody cocktails.

Rapid Mass Spectrometry-Based Multiattribute Method for Glycation Analysis with Integrated Afucosylation Detection Capability

The multiattribute method (MAM) has emerged as a powerful tool for simultaneously screening multiple product quality attributes of therapeutic antibodies. One such potential critical quality attribute (CQA) is glycation, a common modification that can impact the heterogeneity, functional activity, and immunogenicity of therapeutic antibodies. However, current methods for monitoring glycation levels in MAM are rare and not sufficiently rapid and accurate. In this study, an improved mass spectrometry (MS)-based MAM was developed to simultaneously monitor glycation and other quality attributes including afucosylation. The method was evaluated using two therapeutic antibodies with different glycosylation site numbers. Treatment with IdeS, Endo F2, and dithiothreitol generated three distinct subunits, and the glycation results obtained were similar to those treated with PNGase F, which is routinely used to release glycans; the sample processing time was greatly reduced while providing additional quality attribute information. The MS-based MAM was also employed to assess the glycation progression following forced glycation in various buffer solutions. A significant increase in oxidation was observed when forced glycation was conducted in an ammonium bicarbonate buffer solution, and a total of 23 potential glycation sites and 4 significantly oxidized sites were identified. Notably, we found that ammonium bicarbonate was found to specifically stimulate oxidation, while glycation had a synergistic effect on oxidation. These findings establish this study as a novel methodology for achieving a technologically advanced platform and concept that enhances the efficacy of product development and quality control, characterized by its broad-spectrum, rapid, and accurate nature.

Identification of heavily glycated proteoforms by hydrophilic-interaction liquid chromatography and native size-exclusion chromatography - High-resolution mass spectrometry

BACKGROUND

The non-enzymatic glycation of proteins and their advanced glycation end products (AGEs) are associated with protein transformations such as in the development of diseases and biopharmaceutical storage. The characterization of heavily glycated proteins at the intact level is of high interest as it allows to describe co-occurring protein modifications. However, the high heterogeneity of glycated protein makes this process challenging, and novel methods are required to accomplish this.

RESULTS

In this study, we investigated two novel LC-HRMS methods to study glycated reference proteins at the intact protein level: low-flow hydrophilic-interaction liquid chromatography (HILIC) and native size-exclusion chromatography (SEC). Model proteins were exposed to conditions that favored extensive glycation and the formation of AGEs. After glycation, complicated MS spectra were observed, along with a sharply reduced signal response, possibly due to protein denaturation and the formation of aggregates. When using HILIC-MS, the glycated forms of the proteins could be resolved based on the number of reducing monosaccharides. Moreover, some positional glycated isomers were separated. The SEC-MS method under non-denaturing conditions provided insights into glycated aggregates but offered only a limited separation of glycated species based on molar mass. Overall, more than 25 different types of species were observed in both methods, differing in molar mass by 14-162 Da. 19 of these species have not been previously reported.

SIGNIFICANCE

The proposed strategies show great potential to characterize highly glycated intact proteins from native and denaturing perspectives and provide new opportunities for fast clinical diagnoses and investigating glycation-related diseases.

Driving towards digital biomanufacturing by CHO genome-scale models

Genome-scale metabolic models (GEMs) of Chinese hamster ovary (CHO) cells are valuable for gaining mechanistic understanding of mammalian cell metabolism and cultures. We provide a comprehensive overview of past and present developments of CHO-GEMs and in silico methods within the flux balance analysis (FBA) framework, focusing on their practical utility in rational cell line development and bioprocess improvements. There are many opportunities for further augmenting the model coverage and establishing integrative models that account for different cellular processes and data for future applications. With supportive collaborative efforts by the research community, we envisage that CHO-GEMs will be crucial for the increasingly digitized and dynamically controlled bioprocessing pipelines, especially because they can be successfully deployed in conjunction with artificial intelligence (AI) and systems engineering algorithms.

Non-enzymatic glycation and aggregation of camel immunoglobulins induce breast cancer cell proliferation

Glycation of biomolecules results in the formation of advanced glycation end products (AGEs). Immunoglobulin G (IgG) has been implicated in the progression of various diseases, including diabetes and cancer. This study purified three IgG subclasses (IgG1, IgG2, and IgG3) from Camelus dromedarius colostrum using ammonium sulfate fractionation and chromatographic procedures. SDS-PAGE was performed to confirm the purity and molecular weight of the IgG subclasses. Several biochemical and biophysical techniques were employed to study the effect of glycation on camel IgG using methylglyoxal (MGO), a dicarbonyl sugar. Early glycation measurement showed an increase in the fructosamine content by ~four-fold in IgG2, ~two-fold in IgG3, and a slight rise in IgG1. AGEs were observed in all classes of IgGs with maximum hyperchromicity (96.6%) in IgG2. Furthermore, glycation-induced oxidation of IgGs led to an increase in carbonyl content and loss of -SH groups. Among subclass, IgG2 showed the highest (39.7%) increase in carbonyl content accompanied by 82.5% decrease in -SH groups. Far UV-CD analysis illustrated perturbation of β-sheet structure during glycation reaction with MGO. Moreover, glycation of IgG proceeds to various conformational states like aggregation and increased hydrophobicity. In addition, the cytotoxicity assay (MTT) illustrated the proliferation of breast cancer cells (MCF-7) with IgG2 treatment.

Non-Genomic Hallmarks of Aging-The Review

Aging is a natural, gradual, and inevitable process associated with a series of changes at the molecular, cellular, and tissue levels that can lead to an increased risk of many diseases, including cancer. The most significant changes at the genomic level (DNA damage, telomere shortening, epigenetic changes) and non-genomic changes are referred to as hallmarks of aging. The hallmarks of aging and cancer are intertwined. Many studies have focused on genomic hallmarks, but non-genomic hallmarks are also important and may additionally cause genomic damage and increase the expression of genomic hallmarks. Understanding the non-genomic hallmarks of aging and cancer, and how they are intertwined, may lead to the development of approaches that could influence these hallmarks and thus function not only to slow aging but also to prevent cancer. In this review, we focus on non-genomic changes. We discuss cell senescence, disruption of proteostasis, deregualation of nutrient sensing, dysregulation of immune system function, intercellular communication, mitochondrial dysfunction, stem cell exhaustion and dysbiosis.

Expanding the Analytical Toolbox: Developing New Lys-C Peptide Mapping Methods with Minimized Assay-Induced Artifacts to Fully Characterize Antibodies

Peptide mapping is an important tool used to confirm that the correct sequence has been expressed for a protein and to evaluate protein post-translational modifications (PTMs) that may arise during the production, processing, or storage of protein drugs. Our new orally administered drug (Ab-1), a single-domain antibody, is highly stable and resistant to proteolysis. Analysis via the commonly used tryptic mapping method did not generate sufficient sequence coverage. Alternative methods were needed to study the Ab-1 drug substance (75 mg/mL) and drug product (3 mg/mL). To meet these analytical needs, we developed two new peptide mapping methods using lysyl endopeptidase (Lys-C) digestion. These newly developed protein digestion protocols do not require desalting/buffer-exchange steps, thereby reducing sample preparation time and improving method robustness. Additionally, the protein digestion is performed under neutral pH with methionine acting as a scavenger to minimize artifacts, such as deamidation and oxidation, which are induced during sample preparation. Further, the method for low-concentration samples performs comparably to the method for high-concentration samples. Both methods provide 100% sequence coverage for Ab-1, and, therefore, enable comprehensive characterization for its product quality attribute (PQA) assessment. Both methods can be used to study other antibody formats.

A comprehensive review on glycation and its potential application to reduce food allergenicity

Food allergens are a major concern for individuals who are susceptible to food allergies and may experience various health issues due to allergens in their food. Most allergenic foods are subjected to heat treatment before being consumed. However, thermal processing and prolonged storage can cause glycation reactions to occur in food. The glycation reaction is a common processing method requiring no special chemicals or equipment. It may affect the allergenicity of proteins by altering the structure of the epitope, revealing hidden epitopes, concealing linear epitopes, or creating new ones. Changes in food allergenicity following glycation processing depend on several factors, including the allergen's characteristics, processing parameters, and matrix, and are therefore hard to predict. This review examines how glycation reactions affect the allergenicity of different allergen groups in allergenic foods.

An assessment of the impact of Raman based glucose feedback control on CHO cell bioreactor process development

Process analytical technology (PAT) tools such as Raman Spectroscopy have become established tools for real time measurement of CHO cell bioreactor process variables and are aligned with the QbD approach to manufacturing. These tools can have a significant impact on process development if adopted early, creating an end-to-end PAT/QbD focused process. This study assessed the impact of Raman based feedback control on early and late phase development bioreactors by using a Raman based PLS model and PAT management system to control glucose in two CHO cell line bioreactor processes. The impact was then compared to bioreactor processes which used manual bolus fed methods for glucose feed delivery. Process improvements were observed in terms of overall bioreactor health, product output and product quality. Raman controlled batches for Cell Line 1 showed a reduction in glycation of 43.4% and 57.9%, respectively. Cell Line 2 batches with Raman based feedback control showed an improved growth profile with higher VCD and viability and a resulting 25% increase in overall product titer with an improved glycation profile. The results presented here demonstrate that Raman spectroscopy can be used in both early and late-stage process development and design for consistent and controlled glucose feed delivery.

Re-mining serum proteomics data reveals extensive post-translational modifications upon Zika and dengue infection

Zika virus (ZIKV) and dengue virus (DENV) are two closely related flaviviruses with similar symptoms. However, due to the implications of ZIKV infections for pregnancy outcomes, understanding differences in their molecular impact on the host is of high interest. Viral infections change the host proteome, including post-translational modifications. As modifications are diverse and of low abundance, they typically require additional sample processing which is not feasible for large cohort studies. Therefore, we tested the potential of next-generation proteomics data in its ability to prioritize specific modifications for later analysis. We re-mined published mass spectra from 122 serum samples from ZIKV and DENV patients for the presence of phosphorylated, methylated, oxidized, glycosylated/glycated, sulfated, and carboxylated peptides. We identified 246 modified peptides with significantly differential abundance in ZIKV and DENV patients. Amongst these, methionine-oxidized peptides from apolipoproteins and glycosylated peptides from immunoglobulin proteins were more abundant in ZIKV patient serum and generate hypotheses on the potential roles of the modification in the infection. The results demonstrate how data-independent acquisition techniques can help prioritize future analyses of peptide modifications.

Evaluating the effect of glycation on lipase activity using boronate affinity chromatography and mass spectrometry

Protein glycation may occur naturally when reducing sugars and proteins coexist, which is often the case for industrial enzymes. The impact of post-translational modifications on enzyme performance (e.g., stability or function) is often not predictable, highlighting the importance of having appropriate analytical methodologies to monitor the influence of glycation on performance. Here, a boronate affinity chromatography method was developed to enrich glycated species followed by mass spectrometry for structural characterization and activity assays for functional assessment. This approach was applied to a (temperature-stressed) lipase used for food applications revealing that storage at -20 °C and 4 °C resulted in minor glycation (below 9%), whereas storage at 25 °C led to a higher glycation level with up to four sugars per lipase molecule. Remarkably, activity measurements revealed that glycation did not reduce lipase activity or stability. Altogether, this novel strategy is a helpful extension to the current analytical toolbox supporting development of enzyme products.

Protein glycation in diabetes mellitus

Diabetes mellitus is the ninth leading cause of mortality worldwide. It is a complex disease that manifests as chronic hyperglycemia. Glucose exposure causes biochemical changes at the proteome level as reflected in accumulation of glycated proteins. A prominent example is hemoglobin A1c (HbA1c), a glycated protein widely accepted as a diabetic indicator. Another emerging biomarker is glycated albumin which has demonstrated utility in situations where HbA1c cannot be used. Other proteins undergo glycation as well thus impacting cellular function, transport and immune response. Accordingly, these glycated counterparts may serve as predictors for diabetic complications and thus warrant further inquiry. Fortunately, modern proteomics has provided unique analytic capability to enable improved and more comprehensive exploration of glycating agents and glycated proteins. This review broadly covers topics from epidemiology of diabetes to modern analytical tools such as mass spectrometry to facilitate a better understanding of diabetes pathophysiology. This serves as an attempt to connect clinically relevant questions with findings of recent proteomic studies to suggest future avenues of diabetes research.

Assessment of the effect of glycation on the allergenicity of sesame proteins

Sesame allergy is a growing concern worldwide. In this study, sesame proteins was glycated with glucose, galactose, lactose and sucrose respectively, and the allergenicity of different glycated sesame proteins were assessed by a comprehensive strategy, including simulated gastrointestinal digestion in vitro, a BALB/c mice model, a rat basophilic leukemia (RBL)-2H3 cell degranulation model and a serological experiment. Firstly, simulated gastrointestinal digestion in vitro showed that glycated sesame proteins were more easily to digest than raw sesame. Subsequently, the allergenicity of sesame proteins was assessed in vivo by detecting the allergic indexes of mice, and results showed that the levels of total immunoglobulin E (IgE) and histamine were reduced in glycated sesame proteins treated mice. Meanwhile, the Th2 cytokines (IL-4, IL-5, and IL-13) were downregulated significantly, demonstrating that sesame allergy was relieved in glycated sesame treated mice. Thirdly, the RBL-2H3 cell degranulation model results showed that the release of β-hexosaminidase and histamine were decreased to different degrees in glycated sesame proteins treated groups. Notably, the monosaccharide glycated sesame proteins exhibited lower allergenicity both in vivo and in vitro. Furthermore, the study also analyzed the structure alteration of sesame proteins, and the results showed that the secondary structure of glycated sesame proteins were changed (the content of α-helix and β-sheet were reduced), and the tertiary structure of sesame proteins after glycation modification was also changed (microenvironment around aromatic amino acids was altered). Besides, the surface hydrophobicity of glycated sesame proteins was also reduced except sucrose glycated sesame proteins. In conclusion, this study demonstrated that glycation reduced the allergenicity of sesame proteins effectively, especially glycation with monosaccharides, and the allergenicity reduction might be related to structural changes. The results will provide a new reference for developing hypoallergenic sesame products.

FcγRIIIA affinity chromatography complements conventional functional characterization of rituximab

Analytical and functional characterization of batches of biologics/biosimilar products are imperative towards qualifying them for pre-clinical and clinical investigations. Several orthogonal strategies are employed to characterize the functional attributes of these drugs. However, the use of conventional techniques for online monitoring of functional attributes is not feasible. Liquid chromatography is one of the crucial unit operations during the downstream processing of biopharmaceuticals. In this work, we have demonstrated the utility of FcγRIIIA affinity chromatography as an independent quantitative functional characterization tool. FcγRIIIA affinity chromatography aided in sequential elution of Rituximab glycoform mixtures, based on varying levels of galactosylation, and thereby the affinity for the receptor protein. The predominant glycans present in the three Rituximab glycoform mixture peaks were G0F, G1F, and G2F, respectively. Dissociation rate constants were derived from the chromatographic elution profiles by the peak profiling method, for the control and glucose stress conditions. The glucose stress conditions did not result in unfavorable binding kinetics of Rituximab and FcγRIIIA. The dissociation rate constants of the glycoform mixture 2, predominantly consisting of G1F, were similar to the dissociation rate constants obtained by surface plasmon resonance. Moreover, the glycosylation profiles obtained from chromatographic estimation can be corroborated with the ADCC activity. However, the ex vivo ADCC reporter assay indicated that there was an increase in the effector activity with increasing glucose stress. Thus, FcγRIIIA affinity chromatography permitted three independent assessments via a single analysis. Such approaches can be utilized as potential process analytical technology (PAT) tools in the biosimilar development process.

Characterization of light chain c-terminal extension sequence variant in one bispecific antibody

Protein modifications such as post-translational modifications (PTMs) and sequence variants (SVs) occur frequently during protein biosynthesis and have received great attention by biopharma industry and regulatory agencies. In this study, an aberrant peak near light chain (LC) was observed in the non-reduced capillary electrophoresis sodium dodecyl sulfate (nrCE-SDS) electrophoretogram during cell line development of one bispecific antibody (BsAb) product, and the detected mass was about 944 Da higher than LC. The corresponding peak was then enriched by denaturing size-exclusion chromatography (SEC-HPLC) and further characterized by nrCE-SDS and peptide mapping analyses. De novo mass spectra/mass spectra (MS/MS) analysis revealed that the aberrant peak was LC related sequence variant, with the truncated C-terminal sequence “SFNR” (“GEC”deleted) linked with downstream SV40 promotor sequence “EAEAASASELFQ”. The unusual sequence was further confirmed by comparing with the direct synthetic peptide “SFNREAEAASASELFQ”. It was demonstrated by mRNA sequencing of the cell pool that the sequence variant was caused by aberrant splicing at the transcription step. The prepared product containing this extension variant maintained well-folded structure and good functional properties though the LC/Heavy chain (HC) inter-chain disulfide was not formed. Several control strategies to mitigate the risk of this LC related sequence variant were also proposed.

Characterization of outcomes of amino acid modifications using a combinatorial approach to reveal physical and structural perturbations: A case study using trastuzumab biosimilar

Biopharmaceuticals, such as monoclonal antibodies, are considered as life-saving drugs for autoimmune diseases, cancer and infectious diseases. However, biotherapeutics tend to undergo chemical degradation during various stages of manufacturing. The conditions of chemical degradation, along with the physical degradation pathways, have a direct influence on the overall stability, safety and efficacy of these therapeutics. While site-specific chemical changes have been well-explored and investigated using various analytical approaches, the resulting conformational and structural changes have not been much studied. Thus, we explored various biophysical techniques for assessing the influence of three representatives forced degradation conditions viz. oxidation, deamidation, and glycation, in a model therapeutic trastuzumab biosimilar. The site-specific modifications caused by these stress conditions were analysed using high resolution mass spectrometry. While their thermodynamic and conformational consequences were investigated by using differential scanning colorimetry (Nano-DSC), circular dichroism (CD) spectroscopy, analytical ultracentrifugation (AUC), and dynamic light scattering (DLS). The investigated stress conditions resulted in reduced thermodynamic stability of mAb, as confirmed using Nano-DSC. Secondary structure analysis performed with CD spectroscopy indicated detectable structural alterations in the beta sheets of stressed samples. DLS and SV-AUC studies demonstrated an enhanced level of aggregation and fragmentation in presence of all stress conditions. Thus, the biophysical analytical toolkits, when used simultaneously, could offer deeper insights into the subtle conformational changes that result from site-specific chemical modifications in mAbs. Hence, these analytical approaches may serve as significant additions to the battery of techniques used for forced degradation analysis of biopharmaceuticals.

Proteins in human body fluids contain in vivo antigen analog of the melibiose-derived glycation product: MAGE

Melibiose-derived AGE (MAGE) is an advanced glycation end-product formed in vitro in anhydrous conditions on proteins and protein-free amino acids during glycation with melibiose. Our previous studies revealed the presence of MAGE antigen in the human body and tissues of several other species, including muscles, fat, extracellular matrix, and blood. MAGE is also antigenic and induces generation of anti-MAGE antibody. The aim of this paper was to identify the proteins modified by MAGE present in human body fluids, such as serum, plasma, and peritoneal fluids. The protein-bound MAGE formed in vivo has been isolated from human blood using affinity chromatography on the resin with an immobilized anti-MAGE monoclonal antibody. Using mass spectrometry and immunochemistry it has been established that MAGE epitope is present on several human blood proteins including serum albumin, IgG, and IgA. In serum of diabetic patients, mainly the albumin and IgG were modified by MAGE, while in healthy subjects IgG and IgA carried this modification, suggesting the novel AGE can impact protein structure, contribute to auto-immunogenicity, and affect function of immunoglobulins. Some proteins in peritoneal fluid from cancer patients modified with MAGE were also observed and it indicates a potential role of MAGE in cancer.

Low pKa of Lys promotes glycation at one complementarity-determining region of a bispecific antibody

Protein glycation is a common, normally innocuous, post-translational modification in therapeutic monoclonal antibodies. However, when glycation occurs on complementarity-determining regions (CDRs) of a therapeutic monoclonal antibody, its biological activities (e.g., potency) may be impacted. Here, we present a comprehensive approach to understanding the mechanism of protein glycation using a bispecific antibody. Cation exchange chromatography and liquid chromatography-mass spectrometry were used to characterize glycation at a lysine residue within a heavy chain (HC) CDR (HC-CDR3-Lys98) of a bispecific antibody. Thermodynamic analysis revealed that this reaction is reversible and can occur under physiological conditions with an apparent affinity of 8-10 mM for a glucose binding to HC-CDR3-Lys98. Results from kinetic analysis demonstrated that this reaction follows Arrhenius behavior in the temperature range of 5°C-45°C and can be well predicted in vitro and in a non-human primate. In addition, this glycation reaction was found to be driven by an unusually low pK_a on the ε-amino group of HC-CDR3-Lys98. Van't Hoff analysis and homology modeling suggested that this reaction is enthalpically driven, with this lysine residue surrounded by a microenvironment with low polarity. This study provides, to our knowledge, new insights toward a mechanistic understanding of protein glycation and strategies to mitigate the impact of protein glycation during pharmaceutical development.

Native Liquid Chromatography and Mass Spectrometry to Structurally and Functionally Characterize Endo-Xylanase Proteoforms

Xylanases are of great value in various industries, including paper, food, and biorefinery. Due to their biotechnological production, these enzymes can contain a variety of post-translational modifications, which may have a profound effect on protein function. Understanding the structure–function relationship can guide the development of products with optimal performance. We have developed a workflow for the structural and functional characterization of an endo-1,4-β-xylanase (ENDO-I) produced by Aspergillus niger with and without applying thermal stress. This workflow relies on orthogonal native separation techniques to resolve proteoforms. Mass spectrometry and activity assays of separated proteoforms permitted the establishment of structure–function relationships. The separation conditions were focus on balancing efficient separation and protein functionality. We employed size exclusion chromatography (SEC) to separate ENDO-I from other co-expressed proteins. Charge variants were investigated with ion exchange chromatography (IEX) and revealed the presence of low abundant glycated variants in the temperature-stressed material. To obtain better insights into the effect on glycation on function, we enriched for these species using boronate affinity chromatography (BAC). The activity measurements showed lower activity of glycated species compared to the non-modified enzyme. Altogether, this workflow allowed in-depth structural and functional characterization of ENDO-I proteoforms.

In silico prediction of post-translational modifications in therapeutic antibodies

Monoclonal antibodies are susceptible to chemical and enzymatic modifications during manufacturing, storage, and shipping. Deamidation, isomerization, and oxidation can compromise the potency, efficacy, and safety of therapeutic antibodies. Recently, in silico tools have been used to identify liable residues and engineer antibodies with better chemical stability. Computational approaches for predicting deamidation, isomerization, oxidation, glycation, carbonylation, sulfation, and hydroxylation are reviewed here. Although liable motifs have been used to improve the chemical stability of antibodies, the accuracy of in silico predictions can be improved using machine learning and molecular dynamic simulations. In addition, there are opportunities to improve predictions for specific stress conditions, develop in silico prediction of novel modifications in antibodies, and predict the impact of modifications on physical stability and antigen-binding.

Quality similarity-driven development of biosimilar monoclonal antibodies

The number of approved and marketed biosimilar monoclonal antibodies has been increasing steeply in recent years in regulated markets. In contrast to small molecular generic drugs, structure and variant profile of biosimilar mAbs are not identical with those of the reference medicinal product. Biosimilarity is proven by using the "totality of evidence" approach, and it forms the basis of the approval process of biosimilars in regulated markets. This process includes a comprehensive quality similarity exercise. This step involves the evaluation of all physico-chemical and biological-functional characteristics. The present paper evaluates the analytical similarity approaches taken through the evaluation of quality attributes of recently approved biosimilar mAbs.

Raman based chemometric model development for glycation and glycosylation real time monitoring in a manufacturing scale CHO cell bioreactor process

The Quality by Design (QbD) approach to the production of therapeutic monoclonal antibodies (mAbs) emphasizes an understanding of the production process ensuring product quality is maintained throughout. Current methods for measuring critical quality attributes (CQAs) such as glycation and glycosylation are time and resource intensive, often, only tested offline once per batch process. Process analytical technology (PAT) tools such as Raman spectroscopy combined with chemometric modeling can provide real time measurements process variables and are aligned with the QbD approach. This study utilizes these tools to build partial least squares (PLS) regression models to provide real time monitoring of glycation and glycosylation profiles. In total, seven cell line specific chemometric PLS models; % mono-glycated, % non-glycated, % G0F-GlcNac, % G0, % G0F, % G1F, and % G2F were considered. PLS models were initially developed using small scale data to verify the capability of Raman to measure these CQAs effectively. Accurate PLS model predictions were observed at small scale (5 L). At manufacturing scale (2000 L) some glycosylation models showed higher error, indicating that scale may be a key consideration in glycosylation profile PLS model development. Model robustness was then considered by supplementing models with a single batch of manufacturing scale data. This data addition had a significant impact on the predictive capability of each model, with an improvement of 77.5% in the case of the G2F. The finalized models show the capability of Raman as a PAT tool to deliver real time monitoring of glycation and glycosylation profiles at manufacturing scale.

Fast analysis of antibody-derived therapeutics by automated multidimensional liquid chromatography - Mass spectrometry

Characterization of post-translational modifications (PTMs) of therapeutic antibodies is commonly performed by bottom-up approaches, involving sample preparation and peptide analysis by liquid chromatography-mass spectrometry (LC-MS). Conventional sample preparation requires extensive hands-on time and can increase the risk of inducing artificial modifications as many off-line steps - denaturation, disulfide-reduction, alkylation and tryptic digestion - are performed. In this study, we developed an on-line multidimensional (mD)-LC-MS bottom-up approach for fast sample preparation and analysis of (formulated) monoclonal antibodies and antibody-derived therapeutics. This approach allows on-column reduction, tryptic digestion and subsequent peptide analysis by RP-MS. Optimization of the 1D -and 2D flow and temperature improved the trapping of small polar peptides during on-line peptide mapping analysis. These adaptations increased the sequence coverage (95-98% versus 86-94% for off-line approaches) and allowed identification of various PTMs (i.e. deamidation of asparagine, methionine oxidation and lysine glycation) within a single analysis. This workflow enables a fast (<2 h) characterization of antibody heterogeneities within a single run and a low amount of protein (10 μg). Importantly, the new mD-LC-MS bottom-up method was able to detect the polar, fast-eluting peptides: Fc oxidation at Hc-Met-252 and the Fc N-glycosylation at Hc-Asn-297, which can be challenging using mD-LC-MS. Moreover, the method showed good comparability across the different measurements (RSD of retention time in the range of 0.2-1.8% for polar peptides). The LC system was controlled by only a standard commercial software package which makes implementation for fast characterization of quality attributes relatively easy.

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.

Role of Advanced Glycation End-Products and Other Ligands for AGE Receptors in Thyroid Cancer Progression

To date, thyroid cancers (TCs) remain a clinical challenge owing to their heterogeneous nature. The etiopathology of TCs is associated not only with genetic mutations or chromosomal rearrangements, but also non-genetic factors, such as oxidative-, nitrosative-, and carbonyl stress-related alterations in tumor environment. These factors, through leading to the activation of intracellular signaling pathways, induce tumor tissue proliferation. Interestingly, the incidence of TCs is often coexistent with various simultaneous mutations. Advanced glycation end-products (AGEs), their precursors and receptors (RAGEs), and other ligands for RAGEs are reported to have significant influence on carcinogenesis and TCs progression, inducing gene mutations, disturbances in histone methylation, and disorders in important carcinogenesis-related pathways, such as PI₃K/AKT/NF-kB, p21/MEK/MPAK, or JAK/STAT, RAS/ERK/p53, which induce synthesis of interleukins, growth factors, and cytokines, thus influencing metastasis, angiogenesis, and cancer proliferation. Precursors of AGE (such as methylglyoxal (MG)) and selected ligands for RAGEs: AS1004, AS1008, and HMGB1 may, in the future, become potential targets for TCs treatment, as low MG concentration is associated with less aggressive anaplastic thyroid cancer, whereas the administration of anti-RAGE antibodies inhibits the progression of papillary thyroid cancer and anaplastic thyroid cancer. This review is aimed at collecting the information on the role of compounds, engaged in glycation process, in the pathogenesis of TCs. Moreover, the utility of these compounds in the diagnosis and treatment of TCs is thoroughly discussed. Understanding the mechanism of action of these compounds on TCs pathogenesis and progression may potentially be the grounds for the development of new treatment strategies, aiming at quality-of-life improvements.

Formulation Considerations for Autologous T Cell Drug Products

Genetically modified autologous T cells have become an established immunotherapy in the fight against cancer. The manufacture of chimeric antigen receptor (CAR) and αβ-T cell receptor (TCR) transduced T cells poses unique challenges, including the formulation, cryopreservation and fill-finish steps, which are the focus of this review. With an increasing number of marketing approvals for CAR-T cell therapies, comparison of their formulation design and presentation for administration can be made. These differences will be discussed alongside the emergence of automated formulation and fill-finish processes, the formulation design space, Monte Carlo simulation applied to risk analysis, primary container selection, freezing profiles and thaw and the use of dimethyl sulfoxide and alternative solvents/excipients as cryopreservation agents. The review will conclude with a discussion of the pharmaceutical solutions required to meet the simplification of manufacture and flexibility in dosage form for clinical treatment.

Orthogonal Comparison of Analytical Methods by Theoretical Reconstruction from Bottom-up Assay Data

In the never-ending endeavor to produce stable and efficacious protein therapeutics, biopharmaceutical companies often employ numerous analytical techniques to characterize and quantify a drug candidate's stability. Mass spectrometry, due to the information-rich data it produces, is commonly used in its numerous configurations to ascertain chemical and structural stability. At issue is the comparison of the various configurations utilized, that is, comparing bottom-up methods such as proteolytic digest followed by reversed phase LC-MS with intact LC-MS methods. Similar issues also arise when using capillary isoelectric focusing to see how charge variants change over time, that is, monitoring the progression of charge altering modifications like deamidation. To this end, site-specific degradations as quantified from bottom-up methods like peptide mapping can be used to build reconstructions of both theoretical intact mass spectra as well as theoretical electropherograms. The result can then be superimposed over the experimental data to qualitatively, and perhaps quantitatively, evaluate differences. In theory, if both experimental bottom-up data and intact data are accurate, the theoretical reconstruction produced from the bottom-up data should perfectly overlay with that of the experimental data. Valuable secondary information can also be ascertained from reconstructions, such as whether modifications are stochastic, as well as a detailed view of all possible combinations of modifications and their quantities used in the reconstruction. This comparison is also useful in determining unknown mass differences in deconvoluted intact protein spectra that may be a result of multiple modifications in combination. The comparison of data from alternate sources provides a holistic and more comprehensive view of the molecule under study.

The Different Colors of mAbs in Solution

The color of a therapeutic monoclonal antibody solution is a critical quality attribute. Consistency of color is typically assessed at time of release and during stability studies against preset criteria for late stage clinical and commercial products. A therapeutic protein solution's color may be determined by visual inspection or by more quantitative methods as per the different geographical area compendia. The nature and intensity of the color of a therapeutic protein solution is typically determined relative to calibrated standards. This review covers the analytical methodologies used for determining the color of a protein solution and presents an overview of protein variants and impurities known to contribute to colored recombinant therapeutic protein solutions.

Quantification of Antibody Persistence for Cell Surface Protein Labeling

Introduction

Antibodies are an essential research tool for labeling surface proteins but can potentially influence the behavior of proteins and cells to which they bind. Because of this, researchers and clinicians are interested in the persistence of these antibodies, particularly for live-cell applications. We developed an easily adoptable method for researchers to characterize antibody removal timelines for any cell-antibody combination, with the benefit of studying broad, hypothesized mechanisms of antibody removal.

Methods

We developed a method using four experimental conditions to elucidate the contributions of possible factors influencing antibody removal: cell proliferation, internalization, permanent dissociation, and environmental perturbation. This method was tested on adipose-derived stem cells and a human lung fibroblast cell line with anti-CD44, CD90, and CD105 antibodies. The persistence of the primary antibody was probed using a fluorescent secondary antibody daily over 10 days. Relative contributions by the antibody removal mechanisms were quantified based on differences between the four culture conditions.

Results

Greater than 90% of each antibody tested was no longer present on the surface of the two cell types after 5 days, with removal observed in as little as 1 day post-labeling. Anti-CD90 antibody was primarily removed by environmental perturbation, anti-CD105 antibody by internalization, and anti-CD44 antibody by a combination of all four factors.

Conclusions

Antibody removal mechanism depended on the specific antibody tested, while removal timelines for the same antibody depended more on cell type. This method should be broadly relevant to researchers interested in quantifying an initial timeframe for uninhibited use of antibody-labeled cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00670-3.

Using continuous chromatography methodology to achieve high-productivity and high-purity enrichment of charge variants for analytical characterization

Charge variants of biological products, such as monoclonal antibodies (mAbs), often play an important role in stability and biological activity. Characterization of these charge variants is challenging, however, primarily due to the lack of both efficient and effective isolation methods. In this work, we present a novel use of an established, high productivity continuous chromatography method, known as multi-column counter-current solvent gradient purification (MCSGP), to create an enriched product that can be better utilized for analytical characterization. We demonstrate the principle of this separation method and compare it to traditional batch HPLC (high performance liquid chromatography) or FPLC (fast protein liquid chromatography) methods, using the isolation of charge variants of different mAbs as a case study. In a majority of cases, we are able to show that the MCSGP method is able to provide enhanced purity and quantity of samples when compared to traditional fractionation methods, using the same separation conditions. In one such case, a sample prepared by MCSGP methodology achieved 95% purity in 10 hours of processing time, while those prepared by FPLC and HPLC achieved purities of 78% and 87% in 48 and 300 hours of processing time, respectively. We further evaluate charge variant enrichment strategies using both salt and pH gradients on cation exchange chromatography (CEX) and anion exchange chromatography (AEX) resins, to provide more effective separation and less sample processing following enrichment. As a result, we find that we are able to utilize different gradients to change the enrichment capabilities of certain charged species. Lastly, we summarize the identified mAb charge variants used in this work, and highlight benefits to analytical characterization of charge variants enriched with the continuous chromatography method. The method adds a new option for charge variant enrichment and facilitates analytical characterization of charge variants.

Biosimilar or Not: Physicochemical and Biological Characterization of MabThera and Its Two Biosimilar Candidates

The development of therapeutic biosimilar antibodies has become an important driving force of the modern biopharmaceutical industry. In this study, physiochemical characteristics (amino acid sequence, intact/subunit molecular weight, isoelectric point, post-translation modification, and disulfide linkage pattern), purity (charge variants, high and low molecular weight variants), antigen binding activity, Fc receptor binding affinity and Fc-effector function (CDC and ADCC) were analyzed by using an extensive set of state-of-the-art and orthogonal analytical technologies to provide a comprehensive characterization of the innovative product rituximab and two biosimilar candidates. The similarity study showed that biosimilar candidate 1 (BC1) and the reference product (RP) MabThera had an identical protein amino acid sequences and highly similar primary structures along with similar purity, heterogeneity profiles, antigen binding activity, Fc receptor binding affinity, and Fc-effector functions. Biosimilar candidate 2 (BC2), which had an amino acid replacement at a constant region, a different N-glycosylation profiling, and purity, was not analytically similar to RP. Although BC2 showed improvement such as an increased level of afucose, another IgG1 allotype, and similar biological activities, it was not recommended to be applied as a biosimilar compound in drug registration because the biosimilar manufacturer must first show that its primary structure was identical to that of RP. Our physicochemical characterizations and bioassay comparability study provided a deepened understanding of the structure-function relationship of quality attributes.

Identification of critical chemical modifications by size exclusion chromatography of stressed antibody-target complexes with competitive binding

Chemical modifications (attributes) in the binding regions of stressed therapeutic proteins may affect binding to target and efficacy of therapeutic proteins. The method presented here describes the criticality assessment of therapeutic antibody modifications by size-exclusion chromatography (SEC) of competitive binding between a stressed antibody and its target, human epidermal growth factor receptor-2 (HER2), followed by SEC fractionation and peptide mapping characterization of bound and unbound antibodies. When stressed antibody and its target were mixed at a stoichiometric molar ratio of 1:2, only antibody-receptor complex eluted from SEC, indicating that binding was not decreased to break the complex. When a smaller amount of the receptor was provided (1:1), the antibody species with modifications reducing binding eluted as unbound from SEC, while the antibody-receptor complex eluted as the bound fraction. Peptide mapping revealed ratios of modifications between unbound and bound fractions. Statistical analysis after triplicate measurements (n = 3) indicated that heavy chain (HC) D102 isomerization and light chain (LC) N30 deamidation were four-fold higher in unbound fraction with high statistical significance. Although HC N55 deamidation and M107 oxidation were also abundant, they were not statistically different between unbound and bound. Our findings agree with previously published potency measurements of collected CEX fractions and the crystal structure of antibody and HER2. Overall, competitive SEC of stressed antibody-receptor mixture followed by peptide mapping is a useful tool in revealing critical residues and modifications involved in the antibody-target binding, even if they elute as a complex from SEC when mixed at 1:2 stoichiometric ratio.

Microdroplet Ultrafast Reactions Speed Antibody Characterization

Recently, microdroplet reactions have aroused much interest because the microdroplet provides a unique medium where organic reactions could be accelerated by a factor of 10³ or more. However, microdroplet reactions of proteins have been rarely studied. We report the occurrence of multiple-step reactions of a large protein, specifically, the digestion, reduction, and deglycosylation of an intact antibody, which can take place in microseconds with high reaction yields in aqueous microdroplets at room temperature. As a result, fast structural characterization of a monoclonal antibody, essential for assessing its quality as a therapeutic drug, can be enabled. We found that the IgG1 antibody can be digested completely by the IdeS protease in aqueous microdroplets in 250 microseconds, a 7.5 million-fold improvement in speed in comparison to traditional digestion in bulk solution (>30 min). Strikingly, inclusion of the reductant tris(2-carboxyethyl)phosphine in the spray solution caused simultaneous antibody digestion and disulfide bond reduction. Digested and reduced antibody fragments were either collected or analyzed online by mass spectrometry. Further addition of PNGase F glycosylase into the spray solution led to antibody deglycosylation, thereby producing reduced and deglycosylated fragments of analytical importance. In addition, glycated fragments of IgG1 derived from glucose modification were identified rapidly with this ultrafast digestion/reduction technique. We suggest that microdroplets can serve as powerful microreactors for both exploring large-molecule reactions and speeding their structural analyses.

Comprehensive Assessment of Protein and Excipient Stability in Biopharmaceutical Formulations Using 1H NMR Spectroscopy

Biopharmaceutical proteins are important drug therapies in the treatment of a range of diseases. Proteins, such as antibodies (Abs) and peptides, are prone to chemical and physical degradation, particularly at the high concentrations currently sought for subcutaneous injections, and so formulation conditions, including buffers and excipients, must be optimized to minimize such instabilities. Therefore, both the protein and small molecule content of biopharmaceutical formulations and their stability are critical to a treatment's success. However, assessing all aspects of protein and small molecule stability currently requires a large number of analytical techniques, most of which involve sample dilution or other manipulations which may themselves distort sample behavior. Here, we demonstrate the application of 1H nuclear magnetic resonance (NMR) spectroscopy to study both protein and small molecule content and stability in situ in high-concentration (100 mg/mL) Ab formulations. We show that protein degradation (aggregation or fragmentation) can be detected as changes in 1D 1H NMR signal intensity, while apparent relaxation rates are specifically sensitive to Ab fragmentation. Simultaneously, relaxation-filtered spectra reveal the presence and degradation of small molecule components such as excipients, as well as changes in general solution properties, such as pH. 1H NMR spectroscopy can thus provide a holistic overview of biopharmaceutical formulation content and stability, providing a preliminary characterization of degradation and acting as a triaging step to guide further analytical techniques.

Integration of liquid chromatography mass spectrometry with a heavy peptide response curve accurately measures unprocessed C-terminal lysine during peptide mapping analysis of therapeutic antibodies in a single run

Therapeutic monoclonal and bispecific antibodies are susceptible to modification after protein biosynthesis. These post-translational modifications (PTMs) not only contribute to mass and charge heterogeneity, but they can also negatively impact the molecule's activity, half-life, and immunogenicity. Therefore, identification and quantification of PTMs are critical to ensure the safety and efficacy of an antibody therapeutic as well as demonstrate product consistency and process control. Unprocessed C-terminal lysine on the heavy chain (HC) is a prevalent modification that contributes to this charge heterogeneity in antibodies. Peptide mapping through liquid chromatography tandem mass spectrometry (LC-MS²) enjoys higher selectivity and sensitivity for measuring this PTM relative to global PTM methods, but differences in the ionization efficiencies of the unprocessed C-terminal K peptide and the truncated C-terminal K peptide result in its overestimation. Consequently, large discrepancies in this PTM's measured abundance may exist between different characterization assays used in regulatory filings, which can be further compounded by large variability when multiple mass spectrometers are used to quantify C-terminal K during a therapeutic's lifespan. In this study, we propose a simple new method to quantify unprocessed C-terminal K in antibodies in a single LC-MS² run that incorporates heavy isotopic standards for both the unprocessed and truncated C-terminal K peptide to build a response curve and correct for the disparity in ionization efficiency between these two different peptide sequences. The approach was evaluated across two different Orbitrap-based mass spectrometers using multiple monoclonal and bispecific therapeutic antibodies, resulting in accurate (<10% error, as determined with peptide standards) and precise C-terminal K quantification during peptide mapping analysis.

Detailed Structure and Pathophysiological Roles of the IgA-Albumin Complex in Multiple Myeloma

Immunoglobulin A (IgA)-albumin complexes may be associated with pathophysiology of multiple myeloma, although the etiology is not clear. Detailed structural analyses of these protein-protein complexes may contribute to our understanding of the pathophysiology of this disease. We analyzed the structure of the IgA-albumin complex using various electrophoresis, mass spectrometry, and in silico techniques. The data based on the electrophoresis and mass spectrometry showed that IgA in the sera of patients was dimeric, linked via the J chain. Only dimeric IgA can bind to albumin molecules leading to IgA-albumin complexes, although both monomeric and dimeric forms of IgA were present in the sera. Molecular interaction analyses in silico implied that dimeric IgA and albumin interacted not only via disulfide bond formation, but also via noncovalent bonds. Disulfide bonds were predicted between Cys34 of albumin and Cys311 of IgA, resulting in an oxidized form of albumin. Furthermore, complex formation prolongs the half-life of IgA molecules in the IgA-albumin complex, leading to excessive glycation of IgA molecules and affects the accumulation of IgA in serum. These findings may demonstrate why complications such as hyperviscosity syndrome occur more often in patients with IgA dimer producing multiple myeloma.

Quantification of glycated IgG in CHO supernatants: A practical approach

Post-translational, nonenzymatic glycation of monoclonal antibodies (mAbs) in the presence of reducing sugars (in bioprocesses) is a widely known phenomenon, which affects protein heterogeneity and potentially has an impact on quality, safety, and efficacy of the end product. Quantification of individual glycation levels is compulsory for each mAb therapeutically applied in humans. We therefore propose an analytical method for monitoring glycation levels of mAb products during the bioprocess. This is a useful tool for process-design considerations, especially concerning glucose-feed strategies and temperature as major driving factors of protein glycation. In this study, boronate affinity chromatography (BAC) was optimized for determination of the glycation level of mAbs in supernatants. In fact, the complex matrix found in supernatants is an underlying obstacle to use BAC, but with a simple clean-up step, we found that the elution profile could be significantly improved so that qualitative and quantitative determination could be reached. Complementary analytical methods confirmed the performance quality, including the correctness and specificity of the results. For quantitative determination of mAb glycation in supernatants, we established a calibration procedure for the retained mAb peak, identified as glycated antibody monomers. For this approach, an available fully characterized mAb standard, Humira®, was successfully applied, and continuous monitoring of mAbs across three repetitive fed-batch processes was finally performed. With this practical, novel approach, an insight was obtained into glycation levels during bioprocessing, in conjunction with glucose levels and product titer over time, facilitating efficient process development and batch-consistency monitoring.

Monitoring glycation levels of a bispecific monoclonal antibody at subunit level by ultrahigh-resolution MALDI FT-ICR mass spectrometry

Bispecific monoclonal antibodies (BsAbs) are engineered proteins with multiple functionalities and properties. The "bi-specificity" of these complex biopharmaceuticals is a key characteristic for the development of novel and more effective therapeutic strategies. The high structural complexity of BsAbs poses a challenge to the analytical methods needed for their characterization. Modifications of the BsAb structure, resulting from enzymatic and non-enzymatic processes, further complicate the analysis. An important example of the latter type of modification is glycation, which can occur in the manufacturing process, during storage in the formulation or in vivo after application of the drug. Glycation affects the structure, function, and stability of monoclonal antibodies, and consequently, a detailed analysis of glycation levels is required. Mass spectrometry (MS) plays a key role in the structural characterization of monoclonal antibodies and top-down, middle-up and middle-down MS approaches are increasingly used for the analysis of modifications. Here, we apply a novel middle-up strategy, based on IdeS digestion and matrix-assisted laser desorption ionization (MALDI) Fourier transform ion cyclotron resonance (FT-ICR) MS, to analyze all six different BsAb subunits in a single high-resolution mass spectrum, namely two light chains, two half fragment crystallizable regions and two Fd' regions, thus avoiding upfront chromatography. This method was used to monitor glycation changes during a 168 h forced-glycation experiment. In addition, hot spot glycation sites were localized using top-down and middle-down MALDI-in-source decay FT-ICR MS, which provided complementary information compared to standard bottom-up MS.

Micro-Heterogeneity of Antibody Molecules

Therapeutic monoclonal antibodies (mAbs) are mostly of the IgG class and constitute highly efficacious biopharmaceuticals for a wide range of clinical indications. Full-length IgG mAbs are large proteins that are subject to multiple posttranslational modifications (PTMs) during biosynthesis, purification, or storage, resulting in micro-heterogeneity. The production of recombinant mAbs in nonhuman cell lines may result in loss of structural fidelity and the generation of variants having altered stability, biological activities, and/or immunogenic potential. Additionally, even fully human therapeutic mAbs are of unique specificity, by design, and, consequently, of unique structure; therefore, structural elements may be recognized as non-self by individuals within an outbred human population to provoke an anti-therapeutic/anti-drug antibody (ATA/ADA) response. Consequently, regulatory authorities require that the structure of a potential mAb drug product is comprehensively characterized employing state-of-the-art orthogonal analytical technologies; the PTM profile may define a set of critical quality attributes (CQAs) for the drug product that must be maintained, employing quality by design parameters, throughout the lifetime of the drug. Glycosylation of IgG-Fc, at Asn297 on each heavy chain, is an established CQA since its presence and fine structure can have a profound impact on efficacy and safety. The glycoform profile of serum-derived IgG is highly heterogeneous while mAbs produced in mammalian cells in vitro is less heterogeneous and can be "orchestrated" depending on the cell line employed and the culture conditions adopted. Thus, the gross structure and PTM profile of a given mAb, established for the drug substance gaining regulatory approval, have to be maintained for the lifespan of the drug. This review outlines our current understanding of common PTMs detected in mAbs and endogenous IgG and the relationship between a variant's structural attribute and its impact on clinical performance.

An Electrochemical Chip to Monitor In Vitro Glycation of Proteins and Screening of Antiglycation Potential of Drugs

Hyperglycemia and the production of advanced glycation end products (AGEs) are the primary factors for the development of chronic complications in diabetes. The level of protein glycation is proportional to the glucose concentration and represents mean glycemia. In this study, we present an electrochemical chip-based method for in vitro glycation monitoring and the efficacy evaluation of an antiglycation compound. An electrochemical chip consisting of five microchambers and embedded microelectrodes was designed for parallel measurements of capacitance signals from multiple solutions at different concentrations. The feasibility of glycation monitoring was then investigated by measuring the capacitance signal at 0.13 MHz with bovine serum albumin and gelatin samples in the presence of various glucose concentrations over 28 days. A significant change in the capacitance due to protein glycation was observed through measurements conducted within 30 s and 21 days of incubation. Finally, we demonstrated that the chip-based capacitance measurement can be utilized for the selection of an antiglycation compound by supplementing the protein solution and hyperglycemic concentration of glucose with an inhibitory concentration of the standard antiglycation agent aspirin. The lack of a significant change in the capacitance over 28 days proved that aspirin is capable of inhibiting protein glycation. Thus, a strong relationship exists between glycation and capacitance, suggesting the application of an electrochemical chip for evaluating glycation and novel antiglycation agents.

A Simple Strategy to Eliminate Hexosylation Bias in the Relative Quantification of N-Glycosylation in Biopharmaceuticals

N‐glycosylation may affect the safety and efficacy of biopharmaceuticals and is thus monitored during manufacturing. Mass spectrometry of the intact protein is increasingly used to reveal co‐existing glycosylation variants. However, quantification of N‐glycoforms via this approach may be biased by single hexose residues as introduced by glycation or O‐glycosylation. Herein, we describe a simple strategy to reveal actual N‐glycoform abundances of therapeutic antibodies, involving experimental determination of glycation levels followed by computational elimination of the “hexosylation bias”. We show that actual N‐glycoform abundances may significantly deviate from initially determined values. Indeed, glycation may even obscure considerable differences in N‐glycosylation patterns of drug product batches. Our observations may thus have implications for biopharmaceutical quality control. Moreover, we solve an instance of the problem of isobaricity, which is fundamental to mass spectrometry.

Interlaboratory Study for Characterizing Monoclonal Antibodies by Top-Down and Middle-Down Mass Spectrometry

The Consortium for Top-Down Proteomics (www.topdownproteomics.org) launched the present study to assess the current state of top-down mass spectrometry (TD MS) and middle-down mass spectrometry (MD MS) for characterizing monoclonal antibody (mAb) primary structures, including their modifications. To meet the needs of the rapidly growing therapeutic antibody market, it is important to develop analytical strategies to characterize the heterogeneity of a therapeutic product's primary structure accurately and reproducibly. The major objective of the present study is to determine whether current TD/MD MS technologies and protocols can add value to the more commonly employed bottom-up (BU) approaches with regard to confirming protein integrity, sequencing variable domains, avoiding artifacts, and revealing modifications and their locations. We also aim to gather information on the common TD/MD MS methods and practices in the field. A panel of three mAbs was selected and centrally provided to 20 laboratories worldwide for the analysis: Sigma mAb standard (SiLuLite), NIST mAb standard, and the therapeutic mAb Herceptin (trastuzumab). Various MS instrument platforms and ion dissociation techniques were employed. The present study confirms that TD/MD MS tools are available in laboratories worldwide and provide complementary information to the BU approach that can be crucial for comprehensive mAb characterization. The current limitations, as well as possible solutions to overcome them, are also outlined. A primary limitation revealed by the results of the present study is that the expert knowledge in both experiment and data analysis is indispensable to practice TD/MD MS.

Non-enzymatic covalent modifications: a new link between metabolism and epigenetics

Epigenetic modifications, including those on DNA and histones, have been shown to regulate cellular metabolism by controlling expression of enzymes involved in the corresponding metabolic pathways. In turn, metabolic flux influences epigenetic regulation by affecting the biosynthetic balance of enzyme cofactors or donors for certain chromatin modifications. Recently, non-enzymatic covalent modifications (NECMs) by chemically reactive metabolites have been reported to manipulate chromatin architecture and gene transcription through multiple mechanisms. Here, we summarize these recent advances in the identification and characterization of NECMs on nucleic acids, histones, and transcription factors, providing an additional mechanistic link between metabolism and epigenetics.