Differential scanning fluorescence approach using a fluorescent molecular rotor to detect thermostability of proteins in surfactant-containing formulations

Abstract

A differential scanning fluorimetry (DSF) based high-throughput screening assay with the fluorescent molecular rotor CCVJ (9-(2-carboxy-2-cyanovinyl)julolidine) was developed. CCVJ is mainly sensitive to viscosity and less to polarity in comparison to polarity-sensitive dyes like SYPRO Orange, which was commonly used in DSF measurements. Therefore DSF with CCVJ is a suitable approach for high-throughput screening and stability testing of surfactant-containing protein formulations. Due to the different detection principles of CCVJ and SYPRO Orange, the midpoint of the fluorescence curve of CCVJ, defined as temperature of aggregation (Tagg), was obtained at a higher temperature than the midpoint of the SYPRO Orange fluorescence curve, defined as temperature of hydrophobic exposure (Th). Granulocyte colony stimulating factor (G-CSF) was used as model protein for all measurements. Commonly used surfactants in therapeutic protein formulations (polysorbate 20, polysorbate 80 and poloxamer 188) were investigated by DSF with CCVJ and SYPRO Orange. The fluorescence properties of CCVJ were minimally affected by investigated surfactants at concentrations typically used in pharmaceutical protein formulations. SYPRO Orange however, showed high background fluorescence as it also interacts with hydrophobic groups of surfactants. CCVJ was also capable of detecting thermally induced aggregation in the commercial polysorbate 80-containing product Neupogen(®).