Characterization of Protein Aggregates, Silicone Oil Droplets, and Protein-Silicone Interactions Using Imaging Flow Cytometry.

Protein therapeutic exposure to siliconized surfaces during manufacturing and storage has potential to induce protein aggregation or generate protein-silicone complexes that are potentially immunogenic. Consequently, assessing the stability and safety of protein therapeutics requires discrimination of protein and silicone oil particles and evaluation of protein-silicone oil interactions. Industry-established methods are challenged to distinguish protein aggregates from silicone oil droplets for particles smaller than 5 μm. In addition, emerging techniques for accessing particles in the sub-5 μm range are limited by low sampling volumes, narrow size ranges, complications such as clogging, and an inability to evaluate protein-silicone interactions. In this study, imaging flow cytometry was evaluated as a new method for discrimination of protein aggregates and silicone oil droplets, as well as for quantification of protein-silicone interactions. A simple and fast fluorescence labeling protocol using low concentrations of extrinsic dyes was developed. The results demonstrate that imaging flow cytometry can be used to discriminate fluorescently labeled protein aggregates and silicone oil droplets with greater than 95% accuracy, regardless of size, and protein-silicone oil interactions can be assessed qualitatively through inspection of image data or quantitatively using features extracted from the image data.