Determining Charge and Diffusion Interaction Parameter

Wyatt Technology Corporation has published the results of a new study outlining the simultaneous measurement of protein charge and diffusion interaction parameter (kD) to determine the colloidal stability of two formulations with different long-term stability behavior. Traditionally, these two properties are measured independently in laborious experiments requiring manual sample preparation and loading. The Möbius® from Wyatt Technology uses massively-parallel phase-analysis light scattering (MP-PALS) in conjunction with an autosampler to automate this combined measurement. The Möbius is therefore an ideal tool for protein characterization and is unique in its ability to provide a complete picture of factors affecting a protein’s stability. To obtain a copy of the application note, please click here.

Characterization of net charge as well as the overall non-specific self-interactions of biotherapeutics proteins is essential in assessing their aggregation propensity. These colloidal stability measurements are often used in the course of formulation to screen out poorly behaved buffer conditions. Both charge and kD are important parameters to indicate colloidal stability, since charge alone may not provide a complete picture: molecules can have a favorable net charge though be de-stabilized by localized factors such as charge asymmetry and hydrophobic residues. This study showcases the unique ability of the Wyatt Möbius to combine the measurement of charge and kD of monoclonal antibodies in parallel.

Two antibodies were characterized in the study: one was known to be stable under a variety of stress conditions and the second had poor stability. Their measured net charge values indicated that both would exhibit ‘Incipient Instability’, i.e. factors beyond net charge would determine the ultimate stability levels at high concentrations or in buffers of moderate/high ionic strength. However, the kD values correlated quite clearly with overall stability, with a negative value indicative of tendency of a protein to form aggregates. The measurement of kD therefore adds valuable information about the ultimate solution behavior of the antibodies used in the experiment while the charge determination helps interpret the sources of colloidal instability.

Geofrey Wyatt, President of Wyatt Technology highlighted the benefits of the simultaneous measurement of charge and kD, “The simultaneous, fully automated measurement of both variables in a single experiment, reduces the time and resources required to ensure that formulations are suitable for further development for therapeutic applications. The Möbius is truly unique in its capability to provide reliable, reproducible and non-destructive electrophoretic mobility measurements of fragile biomolecules and we believe that this capability will dramatically improve the level of confidence researchers can have in their assessment of the stability of any given protein.”