Ion Mobility-Mass Spectrometry Reveals the Structures and Stabilities of Biotherapeutic Antibody Aggregates

Stability is a key critical quality attribute monitored throughout the development of monoclonal antibody (mAb) therapeutics. Minor changes in their higher order structure (HOS) caused by stress or environment may alter mAb aggregation, immunogenicity, and efficacy. In addition, the structures of the resulting mAb aggregates are largely unknown, as are their dependencies on conditions under which they are created. In this report, we investigate the HOS of mAb monomers and dimers under a variety of forced degradation conditions with ion mobility-mass spectrometry (IM-MS) and collision-induced unfolding (CIU) technologies. We evaluate two model IgG1 antibodies that differ significantly only in their complementarity-determinant regions: IgG1 alpha and IgG1 beta. Our data covering both heat- and pH-based forced degradation conditions, aquired on two different IM-MS platforms, show that these mAbs undergo global HOS changes at both monomer and dimer levels upon degradation, but shifts in collision cross section (CCS) differ under pH or heat degradation conditions. In addition, the level of CCS change detected is different between IgG1 alpha and IgG1 beta, suggesting that differences in the CDR drive differential responses to degradation that influence the antibody HOS. Dramatically different CIU fingerprints are obtained for IgG1 alpha and IgG1 beta monomers and dimers for both degradation conditions. Finally, we constructed a series of computational models of mAb dimers for comparison with experimental CCS values and found evidence for a compact, overlapped dimer structure under native and heat degradation conditions, possibly adopting an inverted or nonoverlapped quaternary structure when produced through pH degredation. We conclude by discussing the potential impact of our findings on ongoing biotherapeutic discovery and development efforts.