Phosphatidylcholine-Polysorbate 20-Based Mixed Micelles: A New Option to Prevent Protein Aggregation?

Background/Objectives: Surfactants are commonly used to protect proteins from denaturation and particle formation, thereby ensuring the long-term stability of biopharmaceuticals. Polysorbates (PS) 20 and 80 are the most widely used surfactants in the pharmaceutical industry. However, alternative excipients such as poloxamers are currently under investigation. In this study, mixed micelles (MMs) composed of phospholipids (PL) and polysorbate 20 (PS20) were explored as a novel stabilisation strategy, aiming to reduce the PS content in protein formulations by partial substitution with PL. Despite their favourable properties, including thermodynamic stability and small particle size, MMs have seen limited application, and no reports exist on their use for stabilising antibody solutions. Results: In a first step, PS20/PL ratios were identified, which are advantageous to form stable MM solutions, followed by an optimization of the formulation process by introducing a second heating step using the direct dispersion method. Successful MM formation was confirmed via transmission and dynamic light scattering analyses at total surfactant concentrations of up to 20 mg·mL^-1 and 50 mg·mL^-1, with PL contents of 50% and up to 40%, respectively. These surfactant concentrations of up to 20 mg·mL^-1 and 50 mg·mL^-1 are substantially higher than the surfactant concentrations that are typically used in final biopharmaceutical formulations (0.01-2 mg·mL^-1). Consequently, the mixed micellar system enables operation even at concentrations substantially above practical formulation limits. In the ensuing study, the stabilizing potential of the PL/PS20 micellar system was appraised through agitation studies. Methods: In these studies, bovine serum albumin was employed as a model protein, while a monoclonal antibody was used as a candidate therapeutic molecule. Stability was assessed through visual inspection, turbidity measurements, particle analysis, and size-exclusion chromatography. Conclusions: A protective effect comparable to that of PS20 alone was observed for both model proteins, demonstrating for the first time that MMs can effectively stabilise biologics.