ABSTRACT
Liquid chromatography mass spectrometry (LC-MS) peptide mapping can be a versatile technique for characterizing protein glycosylation sites without the need to remove the attached glycans as in conventional oligosaccharide mapping methods. In this way, both N-linked and O-linked sites of glycosylation can each be directly identified, characterized, and quantified by LC-MS as intact glycopeptides in a single experiment. LC-MS peptide mapping of the individual glycosylation sites avoids many of the limitations of preparing and analyzing an entire pool of released N-linked oligosaccharides from all sites mixed together. In this study, LC interfaced to a linear ion trap mass spectrometer (ESI-LIT-MS) were used to characterize the glycosylation of a recombinant IgG1 monoclonal antibody and a CTLA4-Ig fusion protein with multiple sites of N-and O-glycosylation. Samples were reduced, S-carboxyamidomethylated, and cleaved with either trypsin or endoproteinase Asp-N. Enhanced detection for minor IgG1 glycoforms (â¼0.1 to 1.0 mol% level) was obtained by LC-MS of the longer 32-residue Asp-N glycopeptide (4+ protonated ion) compared to the 9-residue tryptic glycopeptide (2+ ion). LC-MS peptide mapping was run according to a general procedure: (1) Locate N-linked and/or O-linked sites of glycosylation by selected-ion-monitoring of carbohydrate oxonium fragment ions generated by ESI in-source collision-induced dissociation (CID), i.e. 204, 366, and 292 Da marker ions for HexNAc, HexNAc-Hex, and NeuAc, respectively; (2) Characterize oligosaccharides at each site via MS and MSMS. Use selected ion currents (SIC) to estimate relative amounts of each glycoform; and (3) Measure the percentage of site-occupancy by searching for any corresponding nonglycosylated peptide.
Subject(s)
Antibodies, Monoclonal/chemistry , CTLA-4 Antigen/chemistry , Glycopeptides/chemistry , Immunoglobulin G/chemistry , Peptide Mapping/methods , Recombinant Fusion Proteins/chemistry , Amino Acid Sequence , Antibodies, Monoclonal/metabolism , CTLA-4 Antigen/metabolism , Carbohydrate Conformation , Catalytic Domain , Chromatography, High Pressure Liquid , Glycopeptides/metabolism , Glycosylation , Humans , Immunoglobulin G/metabolism , Mass Spectrometry , Models, Molecular , Molecular Sequence Data , Peptide Fragments/chemistry , Peptide Fragments/metabolism , Recombinant Fusion Proteins/metabolism , TrypsinABSTRACT
In this paper, we discuss an improved high-performance liquid chromatography (HPLC) method for the quantitation of polysorbate 80 (polyoxyethylenesorbitan monooleate), a commonly used stabilizing excipient in therapeutic drug solutions. This method is performed by quantitation of oleic acid, a hydrolysis product of polysorbate 80. Using base hydrolysis, polysorbate 80 releases the oleic acid at a 1:1 molar ratio. The oleic acid can then be separated from other polysorbate 80 hydrolysis products and matrices using reversed phase HPLC. The oleic acid is monitored without derivatization using the absorbance at 195 nm. The method was validated and also shown to be accurate for the quantitation of polysorbate 80 in a high protein concentration monoclonal antibody drug product. For the measured polysorbate 80 concentrations, the repeatability was less than 6.2% relative standard deviation of the mean (% RSD) with the day-to-day intermediate precision being less than 8.2% RSD. The accuracy of the oleic acid quantitation averaged 94-109% in different IgG(1) and IgG(4) drug solutions with variable polysorbate 80 concentrations. In this study, polyoxyethylene, a by-product of the polysorbate 80 hydrolysis was also identified. This peak was not identified by previous methods and also increased proportionally to the polysorbate 80 concentration. We have developed and qualified a method which uses common equipment found in most laboratories and is usable over a range of monoclonal antibody subclasses and protein concentrations.
