Charge and Interaction Analysis for Predicting Antibody Formulation Stability

Net surface charge may be characterized readily by means of electrophoretic light scattering, implemented in the Möbius as massively-parallel phase-analysis light scattering (MP-PALS), combined with simultaneous dynamic light scattering (DLS) for hydrodynamic radius. In some cases (high charge, moderate concentration) the net charge is sufficient to predict aggregation propensity. However, when the charge is relatively weak, additional information is necessary.

The overall magnitude of non-specific interactions at moderate protein concentrations is described well by the diffusion interaction parameter, kD. This quantity is measured via the concentration dependence of the diffusion coefficient, also determined by DLS. Since it can be plumbed to an autosampler, the Möbius facilitates automated kD measurement in parallel with charge determination.

This application note presents an example of combined measurements of net charge and kD in order to understand the difference between two formulations with different stability behavior. Even though they have approximately the same net charge, its value is relatively low and so stability is dominated by the secondary effects of asymmetric charge distributions and hydrophobic residues.