Improving Viscosity and Stability of a Highly Concentrated Monoclonal Antibody Solution with Concentrated Proline

Purpose To explain the effects of the osmolyte proline on the protein-protein interactions (PPI), viscosity and stability of highly concentrated antibody solutions in contrast to other neutral osmolytes. Methods The viscosity of ~225 mg/mL mAb solutions was measured with proline, glycine and trehalose as a function of pH and co-solute concentration up to 1.3 M. The stability was assessed via turbidity as well as size exclusion chromatography after 4 weeks storage at 40°C. The PPI strength was assessed qualitatively via the high concentration diffusion rate by dynamic light scattering. Results Increasing proline significantly reduced the mAb viscosity and increased the colloidal stability at pH 6, but not at pH 5 further from the mAb pI. In contrast, glycine and trehalose did not improve the viscosity nor stability. The normalized diffusion coefficient at high concentration, which is inversely proportional to the attractive PPI strength, increased with proline concentration but decreased with increasing glycine. Conclusions Proline demonstrated greater efficacy for improving mAb viscosity and stability in contrast to glycine and trehalose due to its amphipathic structure and partial charge on the pyrrolidine side chain. These properties likely allow proline to screen the attractive electrostatic and hydrophobic interactions that promote self-association and high viscosities. Binary proline-histidine formulations also demonstrated greater viscosity reduction effects than histidine alone at the same total co-solute concentration, while maintaining a lower total solution osmolarity.