Tavakoli-Keshe, R; (2014) Quantifying the impact of the physical environment during processing and storage of biopharmaceuticals. Doctoral thesis , UCL (University College London).

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Abstract

As more complex biotherapeutics are produced, the numbers of antibodies exhibiting aggregation phenomenon has increased greatly. It is therefore of growing importance to understand the products and origin of these phenomena and to be able to select candidates that show the greatest stability. The purpose of this work was to assess different methods for determining protein stability and the aspects of stability they measure, analysing the different aggregate species produced to offer a platform solution when dealing with different aggregate phenomenon during process development. The effect of reversible self association (RSA) on the purification of a product was evaluated and shown to only critically effect the operation of viral filtration steps in a typical bioprocess through blockage of filter pores. A custom made, rotating disc, interfacial shear device was evaluated along with thermal, spectroscopic and molecular modelling methods for their ability to determine the relative stabilities of antibodies to aggregation. A capillary interfacial shear device with 10 fold reduced volume was designed and tested, showing comparability of monomer loss in the capillary with the coefficient of monomer decay in the disc device. This surface related damage was further studied by comparison to thermal methods with a range of known modifications to IgG structures, using modelling techniques to indicate aspects of protein structure key to loss of stability. The interfacial shear device provides an orthogonal measurement related to modification of exposed protein residues whereas thermal techniques trend with intramolecular stability. It was also concluded that for full characterisation of an aggregate profile SE-HPLC, Nanosight and Microflow Imaging should be used to enable capture of the entire size range of aggregate species from 10nm to 100μm. The work highlights the future prominence of molecular modelling techniques as part of a fully integrated aggregate mitigating solution to determine aggregation hot spots.

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