Investigation of anomalous charge variant profile reveals discrete pH-dependent conformations and conformation-dependent charge states within the CDR3 loop of a therapeutic mAb. Issue 1 (1st January 2020)

• Record Type: Journal Article
• Authors: Lan, Wenkui; Valente, Joseph J.; Ilott, Andrew; Chennamsetty, Naresh; Liu, Zhihua; Rizzo, Joseph M.; Yamniuk, Aaron P.; Qiu, Difei; Shackman, Holly M.; Bolgar, Mark S.
• Is Part Of: MAbs. Volume 12:Issue 1(2020)
• Publication Date: 2020-01-01
• Subjects: pH-dependent conformation -- charge heterogeneity -- conformational equilibrium -- HC-CDR3 -- therapeutic monoclonal antibody -- cation exchange chromatography -- hydrophobic interaction chromatography -- surface plasmon resonance; Monoclonal antibodies -- Therapeutic use -- Periodicals; Monoclonal antibodies -- Periodicals; Antibodies, Monoclonal -- Periodicals; 616.0798
• DOI: 10.1080/19420862.2020.1763138
• Languages: English
• ISSNs: 1942-0862

Abstract

ABSTRACT: During the development of a therapeutic monoclonal antibody (mAb-1), the charge variant profile obtained by pH-gradient cation exchange chromatography (CEX) contained two main peaks, each of which exhibited a unique intrinsic fluorescence profile and demonstrated inter-convertibility upon reinjection of isolated peak fractions. Domain analysis of mAb-1 by CEX and liquid chromatography-mass spectrometry indicated that the antigen-binding fragment chromatographed as two separate peaks that had identical mass. Surface plasmon resonance binding analysis to antigen demonstrated comparable kinetics/affinity between these fractionated peaks and unfractionated starting material. Subsequent molecular modeling studies revealed that the relatively long and flexible complementarity-determining region 3 (CDR3) loop on the heavy chain could adopt two discrete pH-dependent conformations: an "open" conformation at neutral pH where the HC-CDR3 is largely solvent exposed, and a "closed" conformation at lower pH where the solvent exposure of a neighboring tryptophan in the light chain is reduced and two aspartic acid residues near the ends of the HC-CDR3 loop have atypical pKa values. The pH-dependent equilibrium between "open" and "closed" conformations of the HC-CDR3, and its proposed role in the anomalous charge variant profile of mAb-1, were supported by further CEX and hydrophobic interaction chromatography studies. This work is an example of how pH-dependent conformational changes and conformation-dependent changes to net charge can unexpectedly contribute to perceived instability and require thorough analytical, biophysical, and functional characterization during biopharmaceutical drug product development.