Understanding the Role of Excipients in the Stability of Biological Macromolecules

The cold chain is currently a well-established but expensive technology used for the storage and transportation of vaccines and medicines, ensuring they remain at the low temperatures needed to maintain efficacy. To reduce dependence on the cold chain, we investigated the performance of various excipients in enhancing the thermal stability of biologics, including proteins and viruses. Specifically, we used hydrophobic exposure temperature (HET) to accurately capture the transition between the folded and unfolded states of proteins, utilizing a dynamic equilibrium heating system. We characterized the HETs of various model proteins, in the presence of different concentrations of sugars, sugar alcohols, and amino acids. Our data showed that disaccharides generally outperformed sugar alcohols in increasing the HETs of proteins, while lysine and glutamate were stabilizing regardless of protein net charge. Interestingly, arginine was destabilizing across all proteins. Our goal is to understand how the molecular features of excipients and how they interact with water affect stability, and to use studies of proteins to predict formulations for viruses with the goal of developing a design rule for selecting excipients to enhance the thermal stability of biologics in general.