A critical evaluation of microcalorimetry as a predictive tool for long term stability of liquid protein...

Microcalorimetry is frequently used as a high throughput predictive method in order to screen different formulations for their storage stability. However, the predictive power of measuring unfolding temperatures (Tm), although studied for the stability of proteins under stress, has not been investigated systematically for long term stability of pharmaceutical proteins yet. In this study, the microcalorimetric Tm is evaluated as a predictive tool for long term stability of 24 liquid formulations of Granulocyte Colony Stimulating Factor. Those were tested with respect to the effect of different buffer salts in different concentrations, different pH values, and the effect of two excipients: polysorbate 80 and hydroxy propyl-β-Cyclodextrin. Formulations were first ranked based on the measured Tm. The same formulations were then ranked based on a long term stability study at 2-8 °C for a period of up to 24 months. For this study, standard analytical methods were used to assess both physical and chemical stabilities of the formulations on long term. Microcalorimetric Tm based ranking was then compared with the long term stability ranking. Determining Tm turned out to be a successful predictive tool to select good formulations and exclude bad ones with an acceptable low degree of error. In particular, physical long term stability at a storage temperature of 2-8 °C was better predicted by just measuring Tm than by conducting stress studies at elevated temperatures.