STUDIES ON THE CONFORMATIONAL STABILITY, DYNAMICS AND VISCOSITY OF IMMUNOGLOBULINS

Abstract

Proteins, such as immunoglobulins, are inherently dynamic molecules with unique biological functions. The intra- and intermolecular interactions that govern the dynamic nature and function of immunoglobulins may also influence their stability. A molecular understanding of interrelationship between dynamics, function and conformational stability of immunoglobulins, both in solution and in presence of co-solutes, can be important for their pharmaceutical development. In addition, it is important to understand the differences in any such correlations between closely related immunoglobulins. Furthermore, molecular interactions in immunoglobulins can be unique at low and high concentrations, which necessitate newer complementary approaches to investigate such complex systems. Therefore, a better understanding of interactions that govern protein structure, dynamics and conformational stability at low and high concentrations and in presence of excipients should aid in designing, optimizing and developing rational formulation conditions for protein based therapeutics. A variety of experimental methods sensitive to structure, dynamics and conformational stability of proteins in solution were employed in these studies. External perturbations such a change in pH, ionic strength and temperature were used to probe the response of proteins, both at low and high concentrations. Different monoclonal antibodies within IgG1 isotype were used to investigate interrelationships between protein dynamics and conformational stability in absence and presence of co-solutes. In addition, an ultraviolet spectroscopy based approach was developed to understand interactions modulating solution viscosity in high concentration immunoglobulin solutions. These studies provide evidence that immunoglobulins belonging to the same IgG1 subtype can have notable differences in their conformational stability, dynamics, aggregation propensity, hydration properties and their response to co-solutes. In addition, alterations in protein dynamics (at a global protein level and in local regions with differences in solvent exposures) by stabilizing or destabilizing excipients were found to modulate the conformational stability of a monoclonal antibody. Furthermore, it was determined that potential interactions and factors modulating solution viscosity at high protein concentrations may also result in changes in their extinction coefficients. The work presented in this dissertation provides evidence that factors modulating protein dynamics and those governing intra- and intermolecular interactions can influence the conformational stability, aggregation and viscosity of proteins in solution.