SpeB proteolysis with imaged capillary isoelectric focusing for the characterization of domain-specific charge heterogeneities of reference and biosimilar Rituximab

Abstract The charge variations of therapeutic monoclonal antibody reveal important information of the post-translational modifications that may potentially impact the potency and safety of pharmaceutical products, especially during the evaluation of biosimilarity of therapeutic proteins. In this work, a novel SpeB-based proteolysis strategy coupling with imaged capillary isoelectric focusing was developed for the determination of domain-specific charge heterogeneities of innovator and generic Rituximab drug products from United States, European and Indian markets. It was observed that innovator Rituximab from the United States and Europe share highly similar peak distributions and charge heterogeneities with 26.2–26.6% Fc/2, 28.9–29.3% LC and 44.4–44.5% Fd peak areas detected, respectively, while multiple basic variations of Fc/2 and less acidic LC and Fd species were found from generic Rituximab from India with 20.9% Fc/2, 32.3% LC and 46.9% Fd peak areas detected. It was also demonstrated that structural changes caused by Carboxypeptidase B treatment and deamidation study at pH extremes could be sensitively captured with the established method, with the results further indicating that the generic product’s basic variations of Fc/2 were un-cleaved Lysine residues, while the lack of certain acidic peaks on LC and Fd probably was due to the lower level of deamidation. This new strategy could become a useful tool to reveal domain-specific charge heterogeneities profiles of a variety of therapeutic monoclonal antibodies in regulated environments.