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Liquid chromatography-mass spectrometry (LC-MS) is an information rich analytical tool that can provide fast, robust and sensitive characterization of protein therapeutics for quality assurance and structural comparison. Herein, structural characterization of two anti-CD20 monoclonal antibodies obtained from two different sources was performed using a middle-down LC-MS strategy to determine if they can be analytically differentiated. Through the use of a specific enzymatic digestion method using IdeS with subsequent LC-MS analysis, we show that the anti-CD20 monoclonal antibody that has been approved by the FDA can be partially characterized and differentiated analytically from an Indian sourced product that lacks FDA approval. In comparison to the FDA-approved product, differential modifications to both the N- and C-termini result in increased charge heterogeneity for the Indian product. In addition, significant differences in the intensities of the observed glycoforms between the two antibodies were detected. While this study assesses only one lot of each of a FDA approved drug product and the Indian sourced drug product, the observed differences may represent process specific fingerprints that could be useful for surveillance purposes. [ABSTRACT FROM AUTHOR]

The application of multiplexed isobaric tandem mass tag (TMT) labeling and an LTQ Orbitrap XL ETD (electron transfer dissociation) hybrid mass spectrometer as a direct approach for qualitative and quantitative characterization of glycoproteins is reported. Bovine fetuin was used as a model glycoprotein in this study. For online liquid chromatography-mass spectrometry (LC-MS) analysis, high-resolution, mass accurate full scan MS spectra were acquired in the Orbitrap mass analyzer followed by data-dependent tandem mass spectrometry (MS/MS) with alternating collision-induced dissociation (CID), ETD, and higher-energy collisional dissociation (HCD) scans. An additional in-source dissociation scan was used as a highly sensitive and selective detection method for eluting glycosylated peptides. By alternatively using three different dissociation methods, 23 glycoforms from all 5 corresponding glycopeptides were identified from a trypsin digest of bovine fetuin. With ETD, labile glycans were retained without any signs of carbohydrate cleavage with concurrent fragmentation of the peptide backbone. Glycosylation sites were clearly localized from the ETD fragmentation data. Glycan structure elucidation was accomplished using CID. The CID experiments generated fragment ions predominantly from cleavage of glycosidic bonds without breaking the peptide bond. Novel to this method, the TMT labeling protocol was modified and adapted for higher labeling efficiency, and a TriVersa NanoMate was used to reinfuse samples to improve ETD and HCD spectra of glycopeptides. Quantification with TMT was verified based on the HCD spectra from multiple nonglycopeptides and glycopeptides. This method can be used as a qualitative and quantitative technique for direct characterization of glycoproteins and has applicability for detection of counterfeit glycoprotein drug products. [ABSTRACT FROM AUTHOR]