Extrapolating differential scanning calorimetry data for monoclonal antibodies to low temperatures

For irreversible denaturation transitions such as those exhibited by monoclonal antibodies, differential scanning calorimetry provides the denaturation temperature, T_m, the rate of denaturation at T_m, and the activation energy at T_m. These three quantities are essential but not sufficient for an accurate extrapolation of the rate of denaturation to temperatures of 25 °C and below. We have observed that the activation energy is not constant but temperature dependent due to the existence of an activation heat capacity, C_p,a. It is shown in this paper that a model that incorporates C_p,a is able to account for previous observations like, for example, that increasing the T_m does not always improve the stability at low temperatures; that some antibodies exhibit lower stabilities at 5 °C than at 25 °C; or that low temperature stabilities do not follow the rank order derived from T_m values. Most importantly, the activation heat capacity model is able to reproduce time dependent stabilities measured by size exclusion chromatography at low temperatures.