Stability of Freeze-Dried Protein Formulations: Contributions of Ice Nucleation Temperature and Residence Time in the Freeze-Concentrate

Controlling ice nucleation, at a fixed higher temperature, results in larger ice crystals, which can reduce the ice/freeze-concentrate interface area where proteins can adsorb and partially unfold. Moreover, limited work has been done to address any effects on short-term stability due to a slow ramp or long isothermal hold after the ice nucleation step. The objective was to evaluate the effect of the ice nucleation temperature and residence time in the freeze-concentrate on in-process or storage stability of representative proteins, human IgG, and recombinant human serum albumin. The results suggest a higher ice nucleation temperature can minimize aggregation of protein pharmaceuticals, which are labile at ice/aqueous interface. Apart from the ice nucleation step, the present study identified the residence time in the freeze-concentrate as the critical factor that influences protein stability post ice nucleation. At a temperature where enough mobility exists (i.e., above Tg' of the formulation), the long residence time in the freeze-concentrate can result in significant protein aggregation during the process. In addition to stability, the findings revealed that not only the ice nucleation temperature but also the thermal history of the formulation post ice nucleation defines the surface area of ice and the porous structure of the freeze-dried cake.