Interfacial Stress in the Development of Biologics: Fundamental Understanding, Current Practice, and Future Perspective.

Biologic products encounter various types of interfacial stress during development, manufacturing, and clinical administration. When proteins come in contact with vapor-liquid, solid-liquid, and liquid-liquid surfaces, these interfaces can significantly impact the protein drug product quality attributes, including formation of visible particles, subvisible particles, or soluble aggregates, or changes in target protein concentration due to adsorption of the molecule to various interfaces. Protein aggregation at interfaces is often accompanied by changes in conformation, as proteins modify their higher order structure in response to interfacial stresses such as hydrophobicity, charge, and mechanical stress. Formation of aggregates may elicit immunogenicity concerns; therefore, it is important to minimize opportunities for aggregation by performing a systematic evaluation of interfacial stress throughout the product development cycle and to develop appropriate mitigation strategies. The purpose of this white paper is to provide an understanding of protein interfacial stability, explore methods to understand interfacial behavior of proteins, then describe current industry approaches to address interfacial stability concerns. Specifically, we will discuss interfacial stresses to which proteins are exposed from drug substance manufacture through clinical administration, as well as the analytical techniques used to evaluate the resulting impact on the stability of the protein. A high-level mechanistic understanding of the relationship between interfacial stress and aggregation will be introduced, as well as some novel techniques for measuring and better understanding the interfacial behavior of proteins. Finally, some best practices in the evaluation and minimization of interfacial stress will be recommended.

Mechanistic failure mode investigation and resolution of parvovirus retentive filters.

Virus retentive filters are a key product safety measure for biopharmaceuticals. A simplistic perception is that they function solely based on a size-based particle removal mechanism of mechanical sieving and retention of particles based on their hydrodynamic size. Recent observations have revealed a more nuanced picture, indicating that changes in viral particle retention can result from process pressure and/or flow interruptions. In this study, a mechanistic investigation was performed to help identify a potential mechanism leading to the reported reduced particle retention in small virus filters. Permeate flow rate or permeate driving force were varied and analyzed for their impact on particle retention in three commercially available small virus retentive filters. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:959-970, 2016.

Effect of protein and solution properties on the Donnan effect during the ultrafiltration of proteins.

Formulation of protein biopharmaceuticals as highly concentrated liquids can improve the drug substance storage and supply chain, improve the target product profile, and allow greater flexibility in dosing methods. The Donnan effect can cause a large offset in pH from the target value established with the diafiltration buffer during the concentration and diafiltration of charged proteins with ultrafiltration membranes. For neutral formulations, the pH will typically increase above the diafiltration buffer pH for basic monoclonal antibodies and decline below the diafiltration buffer pH for acidic Fc-fusion proteins. In this study, new equations for the Donnan effect during the diafiltration and concentration of proteins in solutions containing monovalent and divalent ions were derived. The new Donnan models obey mass conservation laws, account for the buffering capacity of proteins, and account for protein-ion binding. Data for the pH offsets of an Fc-fusion protein and a monoclonal antibody were predicted in both monovalent and divalent buffers using these equations. To compensate for the pH offset caused by the Donnan effect, diafiltration buffers with pH and excipient values offset from the ultrafiltrate pool specifications can be used. The Donnan offset observed during the concentration of an acidic Fc-fusion protein was mitigated by operating at low temperature. It is important to account for the Donnan effect during preformulation studies. The excipients levels in an ultrafiltration pool may differ from the levels in a protein solution obtained by adding buffers into concentrated protein solutions due to the Donnan effect.

Achieving high mass-throughput of therapeutic proteins through parvovirus retentive filters.

Parvovirus retentive filters that assure removal of viruses and virus-like particles during the production of therapeutic proteins significantly contribute to total manufacturing costs. Operational approaches that can increase throughput and reduce filtration area would result in a significant cost savings. A combination of methods was used to achieve high throughputs of an antibody or therapeutic protein solution through three parvovirus retentive filters. These methods included evaluation of diatomaceous earth or size-based prefilters, the addition of additives, and the optimization of protein concentration, temperature, buffer composition, and solution pH. An optimum temperature of 35°C was found for maximizing throughput through the Virosart CPV and Viresolve Pro filters. Mass-throughput values of 7.3, 26.4, and 76.2 kg/m(2) were achieved through the Asahi Planova 20N, Virosart CPV, and Viresolve Pro filters, respectively, in 4 h of processing. Mass-throughput values of 73, 137, and 192 kg/m(2) were achieved through a Millipore Viresolve Pro filter in 4.0, 8.8, and 22.1 h of processing, respectively, during a single experiment. However, large-scale parvovirus filtration operations are typically controlled to limit volumetric throughput to below the level achieved during small-scale virus spiking experiments. The virus spike may cause significant filter plugging, limiting throughput. Therefore newer parvovirus filter spiking strategies should be adopted that may lead to more representative viral clearance data and higher utilization of large-scale filter capacity.