Differential scanning fluorimetry: rapid screening of formulations that promote the stability of reference preparations.

When formulating a biopharmaceutical protein, its stability in the liquid state is critical. In addition, when preparing biological reference materials the stability, both when lyophilised and after reconstitution, needs to be determined. In order to optimise the stability in aqueous conditions (as indicated by Tmelt or denaturation point) the impact of different excipient choices should be evaluated. Micro differential scanning calorimetry is a well established method for these applications but can be time consuming even when an autosampler is used. Differential scanning fluorimetry (DSF) is a novel technique which measures the fluorescence of a dye when bound to the hydrophobic regions of a denatured protein. We have investigated these techniques for their suitability using alpha-1-protease inhibitor (A1PI) as a model system and found similar trends in terms of the impact of different excipients by both methods. DSF is a promising method and has advantages in terms of speed and quantities of biological material required and can be performed using a PCR instrument.