Unambiguous Characterization of N-Glycans of Monoclonal Antibody Cetuximab by Integration of LC-MS/MS and 1H NMR Spectroscopy
2014
Wiegandt, Alena | Meyer, Bernd
Monoclonal antibodies are most rapidly emerging as therapeutic drugs for the treatment of cancer and of various other diseases such as autoimmunity or inflammation. Recently, it was found that nonhuman glycosylation of recombinant antibodies can cause tremendous problems for some patients. Therefore, unambiguous assignment of the glycosylation pattern of therapeutic antibodies is of high importance for assessment of human compatibility. Here we present results from a broad and detailed N-glycan analysis of the therapeutic antibody cetuximab by LC-MS/MS analyses tightly integrated with ¹H NMR to obtain unambiguous structures. Thirty-seven N-glycan compositions were identified by LC-MS(/MS). Subsequently, ten abundant structures were structurally characterized by applying the recently introduced method called three-dimensional cross correlation (3DCC). It was possible to extract NMR spectra of pure N-glycans that were heavily overlapping in a chromatographic separation by mathematically dissecting the NMR spectra obtained from chromatographic fractions. Even mass isobaric structures that differ only in the branching position of one monosaccharide unit were distinguished and characterized. We also developed an improvement of the 3DCC method by introducing singular value decomposition (SVD) for processing of the data. The smallest amount of the N-glycan characterized by 3DCC was approximately 400 pmol (836 ng). Among the ten unambiguously identified glycans, six N-glycans, representing 24% of all detected glycans, possess the immunogenic α-1,3-Gal epitope and/or N-glycolylneuraminic acid. These results illustrate the importance of integrated use of LC-MS(/MS) and ¹H NMR for the glycome analysis of biopharmaceuticals in research, development, and quality control.
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