Biosimilarity and advanced structural characterization of monoclonal antibodies charge variants using capillary zone electrophoresis and mass spectrometry.

Monoclonal antibodies (mAbs) structural complexity arises from their macromolecular nature and their propensity to undergo post-translational modifications (PTM), potentially leading to the formation of charge variants. Capillary zone electrophoresis (CZE) showed to be particularly relevant for their analysis, however the selectivity provided by CZE separation is not completely elucidated. In this work, CZE-UV analysis was used to characterize charge variants for biosimilars products corresponding to infliximab. Results demonstrated the possibility to identify faint variations between the different products showing its applicability to contribute to mAbs biosimilarity assessment. Enzymatic treatment allowed to attribute the origin of infliximab charge variants. CZE-UV analysis of pembrolizumab showed that none of the five charge variants separated were originating from C-terminal lysine residues and/or N-glycans. To enable further identification, an analytical strategy was developed to achieve CZE-UV fraction collection and enrichment of mAb charge variants followed by systematic offline characterization in CE coupled to tandem mass spectrometry (MS/MS). CE-MS/MS experiments allowed the identification of different types of PTMs such as N-terminal pyroglutamic acid formation and asparagine deamidation for charge variant fractions correlated with decreased mobility. In addition, for the first time succinimide intermediate formation could be successfully characterized using CE-MS/MS data, which could be correlated to increased mobility. Thus, the CZE-UV separation resulted from the synergistic effect of several simultaneous PTMs affecting the apparent mobilities of the charge variants. As a consequence, experiments illustrated the relevance and potential of intact mAbs analysis using CZE-UV to provide an overview of the structural diversity of therapeutic mAbs.