Editorial pubs.acs.org/molecularpharmaceutics
Advances in Biophysical and Bioanalytical Protein Characterization
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charge, charge distribution, protein concentration, hydrodynamic radius, and hydration on key performance attributes of protein stability such as viscosity, solubility, and aggregation. Systematic and higher resolution analyses capable of decoupling chemical and structural contributions are expected to provide new insights and are already under development. Most of the analytical techniques used in pharmaceutical protein analysis provide general information about the entire protein and lack site-specific information. Techniques that provide a higher resolution view of exactly what is altered within the protein as a function of solution conditions and/or chemical changes are now being used to gain improved understanding of degradation mechanisms. The two main tools include nuclear magnetic resonance spectroscopy and mass spectrometry. Hydrogen−deuterium exchange experiments and analysis of chemical composition and conformational changes in proteins can be obtained from these studies and are providing new insights into mechanisms of both physical and chemical instability. Several studies utilizing these techniques to assess chemical and kinetic aspects of mechanism are presented, and they demonstrate that specific changes occur within proteins at particular residues that correlate with overall stability. New advances in analytical methods have enabled generation of stable protein formulations and further are improving our ability to identify fundamental parameters that influence conformational and colloidal behaviors of proteins. Studies presented in this issue demonstrate fundamental chemical properties of the protein and the formulation synergize to influence protein stability, and understanding the molecular basis of protein stability in a formulation puts forth the possibility of rational design.
ver the past few years, emphasis in drug development has shifted substantially from small organic compounds toward macromolecules, particularly monoclonal antibodies (mAbs), to take advantage of their greatly improved target specificity and binding affinity. With approximately 25 mAbbased drugs now on the market and a couple hundred more in the pipeline, protein stability and methods to characterize and predict stability are of major interest to pharmaceutical scientists and formulation experts. In addition, antibodies and enzymes are often key components of assays and diagnostics, whose accuracy depends on protein integrity. The increased complexity of protein molecules as well as the manufacturing and purification processes to which they are exposed makes them susceptible to chemical and physical degradation, which can lead to diminished efficacy and safety. As such, enormous effort has been put into identifying stable conditions and formulating protein-based products. Access to a diverse and increasingly rich set of analytical tools underlies the success of this pursuit and is providing a path toward the possibility of rational design. This special issue presents research innovations and approaches that are advancing understanding of protein stability. Two reviews and nine original research articles are included. A review of high-throughput screening approaches summarizes the state of the art in protein characterization. It describes how biophysical and spectroscopic methods are used to quickly survey a broad range of sample conditions and empirically guide formulation design. A separate review describes current understanding of structural transitions in amyloidogenic peptides and the implications of these findings. Original research articles in this issue are focused on understanding how different chemical properties and attributes of the protein and/or the environment in which the protein resides affect physicochemical stability of the protein. Preventing degradation of protein drugs is important to retain activity but also because aggregates can promote immune reactions. Many protein formulations are lyophilized to improve stability and must be reconstituted for use, but liquid formulations are becoming increasingly common. In solution physical stability is better at low protein concentration, but high concentration (>50 mg/mL) formulations are sought because they provide additional and improved delivery options that increase compliance, convenience, and patient comfort. Achievement of stable high-concentration formulations demands a better understanding of the fundamental parameters that determine protein stability. Physical instability can take several forms, and selfassociation may manifest in viscosity differences for one formulation and aggregation for another. Identification of specific factors that dictate each outcome is required to accelerate identification of and ultimately predict formulation conditions. Individual articles in this issue address aspects of chemical, conformational, and/or colloidal stability, many with respect to fundamental solution parameters such as pH and ionic strength. These investigations probe the importance of © 2012 American Chemical Society
Jennifer S. Laurence,* Guest Editor
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Department of Pharmaceutical Chemistry, University of Kansas, MRB, 2030 Becker Drive, Lawrence, Kansas 66047, United States
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
ACKNOWLEDGMENTS The Biotechnology section of ACS has grown and attracted an increasingly strong core of academic and industrial scientists in this field, and their work inspired the idea for this special issue. I thank Dr. Gordon Amidon for devoting an issue to highlight some of the innovations and approaches advancing understanding of protein stability, the numerous colleagues who participated in conversations and contributed and/or reviewed manuscripts, and K. Barrett and K. Ziegler for their administrative support. Special Issue: Advances in Biophysical and Bioanalytical Protein Characterization Published: April 2, 2012 695
dx.doi.org/10.1021/mp300105p | Mol. Pharmaceutics 2012, 9, 695−695
