Etanercept is a highly glycosylated therapeutic Fc-fusion protein that contains multiple N- and O-glycosylation sites. An in-depth characterization of the glycosylation of etanercept was carried out using liquid chromatography/mass spectrometry (LC/MS) methods in a systematic approach in which we analyzed the N- and O-linked glycans and located the occupied O-glycosylation sites. Etanercept was first treated with peptide N-glycosidase F to release the N-glycans. The N-glycan pool was labeled with a 2-aminobenzamide (2-AB) fluorescence tag and separated using ultraperformance liquid chromatography-hydrophilic interaction liquid chromatography (UPLC-HILIC). Preliminary structures were assigned using Glycobase. These assignments, which included monosaccharide sequence and linkage information, were confirmed by exoglycosidase array digestions of aliquots of the N-glycan pool. The removal of the N-glycans from etanercept facilitated the selective characterization of O-glycopeptides and enabled the O-glycans to be identified. These were predominantly of the core 1 subtype (HexHexNAc O-structure) attached to Ser/Thr residues. α2→3,6,8,9 sialidase was used to remove the sialic acid residues on the O-glycans allowing the use of an automated LC/MS(E) protocol to identify the O-glycopeptides. Electron-transfer dissociation (ETD) was then used to pinpoint the 12 occupied O-glycosylation sites. The determination of N- and O-glycans and O-glycosylation sites in etanercept provides a basis for future studies addressing the biological importance of specific protein glycosylations in the production of safe and efficacious biotherapeutics.

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The multi-attribute method (MAM) is a liquid chromatography–mass spectrometry based method that is used to directly characterize and monitor many product quality attributes and impurities on biotherapeutics, most commonly at the peptide level. It utilizes high-resolution accurate mass spectral data which are analyzed in an automated fashion. MAM is a promising approach that is intended to replace or supplement several conventional assays with a single LC-MS analysis and can be implemented in a Current Good Manufacturing Practice environment. MAM provides accurate site-specific quantitation information on targeted attributes and the nontargeted new peak detection function allows to detect new peaks as impurities, modifications, or sequence variants when comparing to a reference sample. The high resolution MAM workflow was applied here for three independent case studies. First, to monitor the behavior of monoclonal antibody product quality attributes over the course of a 12-day cell culture experiment providing an insight into the behavior and dynamics of product attributes throughout the process. Second, the workflow was applied to test the purity and identity of a product through analysis of samples spiked with host cell proteins. Third, through the comparison of a drug product and a biosimilar with known sequence variants. The three case studies presented here, clearly demonstrate the robustness and accuracy of the MAM workflow that implies suitability for deployment in the regulated environment.

Accurate, reproducible, and fast quantification of N-glycans is crucial not only for the development and quality control of modern glycosylated biopharmaceuticals, but also in clinical biomarker discovery. Several methods exist for fluorescent labeling of N-glycans and subsequent chromatographic separation and quantification. However, the methods can be complex, lengthy, and expensive. Here we report an automated ultrafiltration-based N-glycoanalytical workflow combined with a glycan labeling strategy that is based on the reaction of glycosylamines with fluorescent carbamate. The entire protocol is quick, simple, and cost-effective and requires less than 1 μg of protein per sample. As many as 768 affinity purified IgG glycoprotein samples can be prepared in a single run with a liquid handling platform.

Peptide mapping analysis is a regulatory expectation to verify the primary structure of a recombinant product sequence and to monitor post-translational modifications (PTMs). Although proteolytic digestion has been used for decades, it remains a labour-intensive procedure that can be challenging to accurately reproduce. Here, we describe a fast and reproducible protocol for protease digestion that is automated using immobilised trypsin on magnetic beads, which has been incorporated into an optimised peptide mapping workflow to show method transferability across laboratories. The complete workflow has the potential for use within a multi-attribute method (MAM) approach in drug development, production and QC laboratories. The sample preparation workflow is simple, ideally suited to inexperienced operators and has been extensively studied to show global applicability and robustness for mAbs by performing sample digestion and LC-MS analysis at four independent sites in Europe. LC-MS/MS along with database searching was used to characterise the protein and determine relevant product quality attributes (PQAs) for further testing. A list of relevant critical quality attributes (CQAs) was then established by creating a peptide workbook containing the specific mass-to-charge (m/z) ratios of the modified and unmodified peptides of the selected CQAs, to be monitored in a subsequent test using LC-MS analysis. Data is provided that shows robust digestion efficiency and low levels of protocol induced PTMs.

The NISTmAb is a monoclonal antibody Reference Material from the National Institute of Standards and Technology; it is a class-representative IgG1κ intended to serve as a pre-competitive platform for harmonization and technology development in the biopharmaceutical industry. The publication series of which this paper is a part describes NIST's overall control strategy to ensure NISTmAb quality and availability over its lifecycle. In this paper, the development of a control strategy for monitoring NISTmAb size heterogeneity is described. Optimization and qualification of size heterogeneity measurement spanning a broad size range are described, including capillary electrophoresis-sodium dodecyl sulfate (CE-SDS), size exclusion chromatography (SEC), dynamic light scattering (DLS), and flow imaging analysis. This paper is intended to provide relevant details of NIST's size heteroge-neity control strategy to facilitate implementation of the NISTmAb as a test molecule in the end user's laboratory.

Capillary electrophoresis (CE) offers excellent efficiency and orthogonality to liquid chromatographic (LC) separations for oligosaccharide structural analysis. Combination of CE with high resolution mass spectrometry (MS) for glycan analysis remains a challenging task due to the MS incompatibility of background electrolyte buffers and additives commonly used in offline CE separations. Here, a novel method is presented for the analysis of 2-aminobenzoic acid (2-AA) labelled glycans by capillary electrophoresis coupled to mass spectrometry (CE-MS). To ensure maximum resolution and excellent precision without the requirement for excessive analysis times, CE separation conditions including the concentration and pH of the background electrolyte, the effect of applied pressure on the capillary inlet and the capillary length were evaluated. Using readily available C stable isotopologues of 2-AA, the developed method can be applied for quantitative glycan profiling in a twoplex manner based on the generation of extracted ion electropherograms (EIE) for C 'light' and C 'heavy' 2-AA labelled glycan isotope clusters. The twoplex quantitative CE-MS glycan analysis platform is ideally suited for comparability assessment of biopharmaceuticals, such as monoclonal antibodies, for differential glycomic analysis of clinical material for potential biomarker discovery or for quantitative microheterogeneity analysis of different glycosylation sites within a glycoprotein. Additionally, due to the low injection volume requirements of CE, subsequent LC-MS analysis of the same sample can be performed facilitating the use of orthogonal separation techniques for structural elucidation or verification of quantitative performance.

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