Utility of High Resolution NMR Methods to Probe the Impact of Chemical Modifications on Higher Order Structure of Monoclonal Antibodies in Relation to Antigen Binding.

PURPOSE: An understanding of higher order structure (HOS) of monoclonal antibodies (mAbs) could be critical to predicting its function. Amongst the various factors that can potentially affect HOS of mAbs, chemical modifications that are routinely encountered during production and long-term storage are of significant interest. METHODS: To this end, two Pfizer mAbs were subjected to forced deamidation stress for a period of eight weeks. Samples were aliquoted at various time points and high resolution accurate mass liquid chromatography-mass spectrometry (LC-MS/MS) was performed using low-artifact trypsin digestion (LATD) peptide mapping to identify and quantify chemical modifications. 2D backbone amide and sidechain methyl NMR spectra were acquired to gauge the effect of HOS changes upon chemical modification. Differential scanning calorimetry was also performed to assess the effect of thermal stability of mAbs upon modification. Finally, functional studies via target-binding based ELISA were performed to connect HOS changes to any loss of potency. RESULTS: The extent of deamidation in the mAb domains were quantified by LC-MS/MS. The HOS changes as obtained from 2D NMR were mostly localized around the affected sites leaving the overall structure relatively unchanged. The antigen-antibody binding of the mAbs, in spite of deamidation in the Fab region, remains unchanged. CONCLUSION: This case study provides an integrated approach of relating chemical modifications in mAb domains with possible changes in HOS. This can be potentially used to assess a possible loss of potency within the structure-function paradigm of proteins in an orthogonal manner.

Probing Conformational Diversity of Fc Domains in Aggregation-Prone Monoclonal Antibodies.

PURPOSE: Fc domains are an integral component of monoclonal antibodies (mAbs) and Fc-based fusion proteins. Engineering mutations in the Fc domain is a common approach to achieve desired effector function and clinical efficacy of therapeutic mAbs. It remains debatable, however, whether molecular engineering either by changing glycosylation patterns or by amino acid mutation in Fc domain could impact the higher order structure of Fc domain potentially leading to increased aggregation propensities in mAbs. METHODS: Here, we use NMR fingerprinting analysis of Fc domains, generated from selected Pfizer mAbs with similar glycosylation patterns, to address this question. Specifically, we use high resolution 2D [13C-1H] NMR spectra of Fc fragments, which fingerprints methyl sidechain bearing residues, to probe the correlation of higher order structure with the storage stability of mAbs. Thermal calorimetric studies were also performed to assess the stability of mAb fragments. RESULTS: Unlike NMR fingerprinting, thermal melting temperature as obtained from calorimetric studies for the intact mAbs and fragments (Fc and Fab), did not reveal any correlation with the aggregation propensities of mAbs. Despite >97% sequence homology, NMR data suggests that higher order structure of Fc domains could be dynamic and may result in unique conformation(s) in solution. CONCLUSION: The overall glycosylation pattern of these mAbs being similar, these conformation(s) could be linked to the inherent plasticity of the Fc domain, and may act as early transients to the overall aggregation of mAbs.

Impact of Buffers on Colloidal Property and Aggregation Propensities of a Bispecific Antibody.

Bispecific antibodies represent a promising avenue whereby 2 different binding specificities of a single-chain antibody can be grafted into a common Fc fragment to generate one antibody-like molecule. Despite the promising efficacy of such modalities, they may lack manufacturability because of stability and aggregation issues. Herein, we performed a systematic buffer screening for an aggregation-prone therapeutic bispecific antibody (BsAb) during early stage development. To this end, various buffers (histidine, glutamate, acetate, and arginine) and buffer combinations, including arginine and glutamate (Arg + Glu), were evaluated for their stabilizing effects on BsAb. Specifically, we identified an equimolar combination of histidine and glutamate (His + Glu at pH 5.0) buffer that showed enhanced colloidal stability as measured by dynamic light scattering interaction parameter (kD). This implies a role of net protein-protein interaction in mediating aggregation propensity of the protein. Two-dimensional nuclear magnetic resonance and multiangle light scattering experiments suggest the formation of a reversible dimer as a potential precursor to overall aggregation process. Furthermore, 1D nuclear magnetic resonance studies suggest a unique mode of interaction of histidine with BsAb that can be modulated by other buffer components or ionic strength.