Highly concentrated therapeutic monoclonal antibody (mAb) solutions are desired for subcutaneous delivery in patients. However, at these high concentrations, protein-protein interactions (PPI) including local, short-range attractions may cause prohibitively high viscosities and poor storage stability. The understanding of this behavior has been limited by the lack of characterization techniques that are applicable at these extreme conditions. Here, we determine the effects of pH and co-solute on the strength and geometry of short-range anisotropic attractions for both a mAb and a polyclonal bovine IgG by comparing static light scattering (SLS) and small angle x-ray scattering (SAXS) data to those computed in molecular dynamics simulations. The simulations utilize 12-bead models exhibiting a van der Waals attraction and additional short-ranged attractions between specific beads and quantify the distribution of reversible clusters in solution. Since our model captures key features of the protein shape, it can describe the experimental SAXS scattering profiles for solutions of 10-200 mg/mL protein with only a small (&lt;1 k<sub>B</sub>T) variation in the model’s attraction strength. The apparent molecular weights calculated from SLS show reduced net attractions with the addition of NaCl and arginine. Structure factors (S(q)) from SAXS for mAb solutions with added NaCl exhibit an upturn at low q, which our modeling reveals is due to the formation of large reversible oligomers resulting from strong anisotropic attractions in the Fab and Fc regions. For the bovine IgG, reducing the pH below the pI or adding NaCl weaken short-range anisotropic attractions, but not enough to remove large reversible oligomers that raise viscosity. In contrast, for arginine added at pH 5.5, the scattering for both proteins can be approximated by a uniform attraction model exhibiting only monomers and dimers. The cluster size distributions are used to improve the understanding and prediction of experimental viscosities using an empirical viscosity model. The ability to discriminate between different interaction geometries and identify the presence of oligomers has great utility in designing and formulating low viscosity, stable mAb solutions.

Protein-protein interactions and self association in antibody solutions via static light scattering, small angle X-ray scattering, and coarse-grained molecular dynamics simulations

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.