Assessing the impact of viscosity lowering excipient on liquid-liquid phase separation for high concentration...

With continued interest in high concentration monoclonal antibody drug products to meet subcutaneous administration requirements, there is heightened attention on balancing protein-protein interactions, solution properties and overcoming instabilities such as increased in viscosity, particle formation, loss in potency, and aggregation of drug products. L-arginine hydrochloride is a commonly used viscosity reducing excipient used to influence protein-protein interactions of high concentration of mAbs. Contrary to literature, we observed that slight modifications to L-arginine hydrochloride concentrations in model drug product formulations can result in liquid-liquid phase separation if excipient and pH conditions are not well tightly controlled. We utilized a biophysical toolkit to assess the potentials of liquid-liquid phase separation (LLPS) that informs the limits of excipient and pH levels using structural- and molecular interaction-based assessments. While liquid-liquid phase separation observed in this study is reversible and does not impact inherent protein folding and structure, we demonstrated that increased ionic content in the formulations can significantly alter the balance of osmolarity toward the occurrence of LLPS. The aim of this work is to demonstrate the diversity of the toolbox used to evaluate the observed LLPS and the decision-making for optimization of formulation development.