Effect of silicone oil on the structure, stability, and aggregation of a therapeutic antibody

Silicone oil is commonly used as a coating in prefilled syringes of protein therapeutics to facilitate the smooth operation of the syringe plunger. The presence of silicone oil droplets in formulations has often been associated with increased aggregation of proteins, which is undesirable for protein-based therapeutics. To ensure the safety and efficacy of protein therapeutics, it is essential to understand the mechanism of adsorption of proteins to silicone oil and subsequent structural transitions leading to aggregation. We have used a model protein dupilumab (commercially known as DUPIXENT®) that is marketed in a prefilled syringe coated with an emulsion of dimethicone silicone oil. The binding interactions between protein and silicone oil were characterized using isothermal titration calorimetry (ITC). The structural and stability changes in the protein were characterized using circular dichroism, intrinsic protein fluorescence, and nuclear magnetic resonance (NMR) spectroscopy. Front-face fluorescence was used to obtain the fluorescence spectra from turbid samples containing silicone oil emulsions. Silicone oil droplets and protein aggregates were characterized with flow imaging techniques and dynamic light scattering (DLS). ITC results revealed a weak binding interaction between silicone oil and dupilumab with a millimolar affinity mediated by hydrophobic interactions. Tryptophan fluorescence, near-UV CD, and 2D ¹³C-¹H NMR spectroscopy indicated no effect of silicone oil on the structure and conformational stability of the protein. However, silicone oil accelerated protein aggregation under thermal stress conditions, potentially due to a decrease in colloidal stability or partial unfolding of the protein adsorbed to silicone oil droplets.