Impact of Fill-Finish Process on Protein Formulation in the Absence of Stabilizing Agents
University of Kansas
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Optimization of the fill-finish process for a biotherapeutic is imperative for the highest quality drug product. Chemical and physical degradation must be fully characterized as an enzyme progresses towards commercialization to design a fully optimized process. To avoid degradation and/or sensitivity to the filling process of an enzyme, pharmaceutical scientists utilize stabilizing excipients as tools to mitigate known chemical or structural weaknesses; however, little work has been published on process-related stabilization techniques when the route of administration dictates the exclusion of key stabilizing excipients. The goal of this thesis is to provide guidance in selecting key factors impacting enzyme stability in fill-finish processes in the absence of excipients. The effect of shear stress applied to an enzyme solution was studied in the presence of various interfacial phenomenon between solution and surface of air, stainless steel and tubings commonly used in manufacturing. Although interfacial interactions and aggregation pathways are considered to be enzyme-specific, this work will allow researchers to focus on key conditions affecting stability of proteins in this process. Factors studied here include exposure of the formulation to shear stress from several models with increasing interfacial complexity. The most simplistic model applied a specific shear stress through a microfluidic chip, exposing the enzyme solution to high levels of shear for a short period of time. A cone and plate rotational rheometer was used to study shear applied to an enzyme solution for up to ten minutes with the addition of an air-water interface. Lastly, a recirculation model was employed to study the interaction with tubing surfaces and the shear stresses caused by peristaltic pumping over time. Several analytical assays were employed to understand destabilization caused by these stress models, and were extended to lead to an overall understanding of the impact of various process-related stresses. An enzyme solution exhibits the most dramatic change when exposed to the peristaltic recirculation pumping model, with the most significantly destabilizing factor being the use of a thermoplastic elastomer tubing surface. The other shear stress models did not produce trends in measured responses, indicating that the associated levels of stress with these models are below the amount necessary to irreversibly alter stability. Methods to measure and characterize aggregation for the recirculation models across a large dynamic range showed dramatic changes with increasing exposure time, resulting in increased aggregate populations over the length of pumping time. The flow imaging data captured high levels of particles shed from the tubing material in the 1-100 µm size-range. These particles could act as heterogeneous nucleation sites, and could explain the increase in aggregation in enzyme solution with these tubing types. The presence of unique multimeric soluble enzyme aggregates was observed in the thermoplastic elastomer tubings, indicating not only that they are deleterious in terms of colloidal stability, but presumably they are formed via different pathways. Silicone tubings performed to a higher standard in recirculation models than thermoplastic tubings. Silicone tubings produced a very low amount of subvisible particulate shedding, undetectable multimeric aggregate species, and a better overall visual appearance after recirculation for up to four hours. In summary, notable enzyme solution instability was not related to the stress of shear in a flow field alone, but rather the use of an incompatible tubing material in the fill-finish process.
- Pharmaceutical Chemistry Dissertations and Theses 
- Theses 
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