Viscosities and Protein Interactions of Bispecific Antibodies and Their Monospecific Mixtures

Solution viscosities (η) and protein-protein interactions (PPI) of three monoclonal antibodies (mAb-A, mAb-B, mAb-C), two bispecific antibodies (BsAb-A/B, BsAb-A/C), and two 1:1 binary mixtures (mAb-A + mAb-B and mAb-A + mAb-C) were measured. mAb-A and mAb-C have similar isoelectric point (pI) values but significantly different η versus protein concentration ( c₂) profiles. The viscosity of the mAb-A + mAb-C mixture followed an Arrhenius mixing rule and was identical to viscosity of the bispecific BsAb-A/C. In contrast, mAb-A and mAb-B had similar η versus c₂ profiles, but the Arrhenius mixing rule failed to predict the higher viscosities of their mixtures. The viscosity of the bispecific BsAb-A/B followed the 1:1 mAb-A + mAb-B mixture at all concentrations. The nature of the interactions for mAb-A, mAb-B, the BsAb-A/B bispecific, and the 1:1 mAb-A + mAb-B mixture were characterized by static and dynamic light scattering (SLS and DLS). mAb-A and mAb-B exhibited net-attractive and -repulsive electrostatic interactions, respectively. The bispecific antibody (BsAb-A/B) had short-ranged attractive interactions, suggesting that the increase in viscosity for this molecule and the mAb-A + mAb-B mixture was due to cross-interactions between Fab regions. At high and low ionic strengths and protein concentrations, the Rayleigh scattering profile, the collective diffusion coefficient, and viscosity for the mixture closely followed that for the bispecific antibody. These results highlight the possible anomalous viscosity increases of bispecific antibodies constructed from relatively low-viscosity mAbs but demonstrates a potentially fruitful approach of using mAb mixtures to predict the viscosity of candidate bispecific constructs.