Excipient effects on humanized monoclonal antibody interactions with silicone oil emulsion

Silicone oil is a lubricant used for plunger depression in prefilled glass syringes. Many therapeutic protein products are stored in prefilled syringes and may be exposed to the silicone oil-water interface for up to 18-24 months. At the present, our understanding of how proteins interact with this interface remains poorly understood. In this work, the interaction of three humanized monoclonal antibodies (humAbs) with silicone oil emulsion was assessed in presence of sodium chloride, sucrose, TweenRTM 20, TweenRTM 80, and poloxamer 188. It was found that the amount of humAb adsorbed was antibody- and excipient-dependent. Once adsorbed, the tryptophan exposure to solvent resembled that of unfolded protein and was independent of the identity of different excipients present in the formulation buffer. Protein aggregation was not detected in solution. But, colloidal destabilization of silicone oil emulsion resulting from protein adsorption lowered the activation energy barrier to flocculation thereby enabling heterogeneous aggregates comprised of protein-coated silicone oil microdroplets to form. The size of these flocs was dependent on the solution ionic strength. Flocculation occurred in the presence of all excipients examined except in the presence of surfactant. In formulations containing surfactant, there was competition between humAb and surfactant molecules for adsorption sites at the silicone oil-water interface. The results suggest that the kinetics of humAb displacement from the silicone oil interface was surfactant-dependent. Whether the mechanism of this replacement involved the formation of protein-surfactant complex remains uncertain.