Protein Stability, Solubility and Solute Interactions
Developing a protein drug manufacturing process to obtain high purity and yield at a reasonable cost requires an understanding of protein biophysics. Processes causing instability in the protein may lead to irreversible denaturation including changes in secondary or higher-order structures and the formation of aggregates. Denaturation may destroy the activity of the drug and has the potential to cause adverse side effects. Understanding the physical forces involved in causing denaturation will help the process development scientist design purification schemes that not only remove denatured protein, but also minimize the stresses that can lead to the formation of denatured protein impurities. Most purification unit operations must be designed to keep protein in solution, although some operations may selectively precipitate the protein for purification reasons or long-term storage (e.g. ammonium sulfate induced precipitate.) Solubility and stability will be a function of protein-excipient interactions. Appropriate use of these interactions can improve yield and stability during purification processes, while formulation optimization can utilize these interactions for long-term storage of protein drugs. To understand how to use process variables to stabilize native protein structure, one must understand the mechanisms by which a protein adopts a folded conformation in solution. These mechanisms may be separated into thermodynamic and kinetic contributions to protein stability. Proteins can degrade through a number of mechanisms including surface-induced denaturation, temperature induced denaturation, freeze-thaw denaturation, and non-optimal excipient conditions. Excipient interactions can affect the stability, solubility, and retentate concentration of excipients. Manufacturing processes can be optimized through an understanding of protein degradation pathways and how excipients interact with proteins.
Note: This chapter was originally published in the first edition of this study, in its entirety.
About the Authors
Brent S. Kendrick, Ph.D.
Research Scientist, Process Development Analytical Sciences Department, Amgen
Dr. Kendrick is a Research Scientist in the Process Development Analytical Sciences Department of Amgen, Inc in the area of biophysical and biochemical characterization of proteins, and an adjunct faculty member at the University of Colorado. He is the author of over 20 professional papers and book chapters that reflect his research interests in the areas of protein degradation pathways, protein formulation, and analysis techniques. Dr. Kendrick received a B.S. degree in Aerospace Engineering in 1988 and a Ph.D. degree in Pharmaceutical Sciences in 1997. He was a Surface Warfare Officer in the United States Navy from 1988 to 1992.