B.S., University of Colorado (1983)
Ph.D. University of California, Berkeley (1987)
Stabilization and Formulation of Therapeutic Proteins- Converting Molecules into Drugs:
Protein-based pharmaceuticals are the fastest-growing class of new drugs. They not only offer promise for treatments to address major health challenges such as cancer, but also a wealth of new engineering problems to solve. Chemical engineers have long been proficient at producing products that meet exacting specifications for chemical purity, but therapeutic proteins now bring additional challenges: these products must not only be highly chemically pure, but also conformationally pure, and must remain so after manufacturing through the drug’s entire shelf-life and delivery to patients. For economic viability, therapeutic protein formulations typically require a shelf life of 18-24 months. Over the course of this time the protein must retain adequate chemical and conformational purity. Meeting the stringent requirements for chemical and conformational stability during shelf life is a daunting task. Most of the common chemical degradation products (especially hydrolysis and oxidation byproducts) are significantly thermodynamically favored versus the desired native state of the protein. Furthermore, the properly folded native state of most proteins is only marginally more stable (the free energy of unfolding, ΔGunf, is about 20-60 kJ/mol) than the unfolded state, and appears to be unstable under most conditions with respect to aggregated forms of the protein.
To slow degradation sufficiently to allow proteins to be used as therapeutic agents, proteins must be placed in a formulation that confers suitable stability against physical and chemical degradation. In addition to stabilizing the pharmaceutically-active protein ingredients, formulation components, or excipients, also must be compatible with their intended use. For example, a formulation intended for parenteral use (e.g., subcutaneous injection) must be sterile, non-toxic and exhibit acceptable viscosity and tonicity. Although these requirements place limits on the types and concentrations of excipients that practically can be used, there are still far too many possible sets of formulations to allow a purely empirical screening approach to be used. The approach that our group takes is to explore fundamental mechanisms of processes that result in degradation and instability of therapeutic proteins. In particular, we use a number of spectroscopic techniques (e.g., FTIR, EPR, NMR, 2D-UV, LALLS, fluorescence spectroscopies) and physical techniques (e.g., analytical ultracentrifugation, titration microcalorimetry, field flow fractionation, mass spectrometry) to understand how solution variables (such as concentration and type of excipients, protein type and concentration, solution ionic strength) and process variables (e.g., agitation) interact to stabilize or destabilize proteins.
Immunogenicity of Protein Therapeutics:
Therapeutic proteins are susceptible to aggregation in response to a wide variety of stresses encountered during their manufacture, storage and delivery to patients. In turn, aggregates of therapeutic proteins may compromise their safety and efficacy. The primary safety concern is that aggregates in therapeutic protein products may induce immune responses, which can have consequences ranging from reduction of product efficacy to patient fatality. Currently it is not well-known what characteristics of protein aggregates are responsible for immunogenicity. We are working to understand how nano- and microparticulate contaminants (including protein aggregates and exogenous microparticles resulting from processing) affect the immune response to therapeutic proteins. In these studies, we rely on physical and spectroscopic methods to characterize aggregate size and structure, and then test how animal models (usually naïve or transgenic mice) respond to parenteral administration of the aggregates.
A related area is our studies of protein-based vaccines. Vaccines offer tremendous benefit to human health, but creation of vaccine formulations that provoke a reliable, protective immune response in a formulation with adequate shelf life is a serious challenge. We are studying the stability of protein structure when adsorbed to relevant surfaces such as the aluminum phosphate salt microparticles that are currently used as adjuvants to enhance immune response.