Freeze drying formulation using microscale and design of experiment approaches: a case study using granulocyte colony-stimulating factor

Investigation of the Solid-State Interactions in Lyophilized Human G-CSF Using Hydrogen-Deuterium Exchange Mass Spectrometry

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) previously elucidated the interactions between excipients and proteins for liquid granulocyte colony stimulating factor (G-CSF) formulations, confirming predictions made using computational structure docking. More recently, solid-state HDX mass spectrometry (ssHDX-MS) was developed for proteins in the lyophilized state. Deuterium uptake in ssHDX-MS has been shown for various proteins, including monoclonal antibodies, to be highly correlated with storage stability, as measured by protein aggregation and chemical degradation. As G-CSF is known to lose activity through aggregation upon lyophilization, we applied the ssHDX-MS method with peptide mapping to four different lyophilized formulations of G-CSF to compare the impact of three excipients on local structure and exchange dynamics. HDX at 22 °C was confirmed to correlate well with the monomer content remaining after lyophilization and storage at -20 °C, with sucrose providing the greatest protection, and then phenylalanine, mannitol, and no excipient leading to progressively less protection. Storage at 45 °C led to little difference in final monomer content among the formulations, and so there was no discernible relationship with total deuterium uptake on ssHDX. Incubation at 45 °C may have led to a structural conformation and/or aggregation mechanism no longer probed by HDX at 22 °C. Such a conformational change was observed previously at 37 °C for liquid-formulated G-CSF using NMR. Peptide mapping revealed that tolerance to lyophilization and -20 °C storage was linked to increased stability in the small helix, loop AB, helix C, and loop CD. LC-MS HDX and NMR had previously linked loop AB and loop CD to the formation of a native-like state (N*) prior to aggregation in liquid formulations, suggesting a similar structural basis for G-CSF aggregation in the liquid and solid states.

Lyophilization to enable distribution of ChAdOx1 and ChAdOx2 adenovirus-vectored vaccines without refrigeration

Distribution of vaccines which require refrigerated or frozen storage can be challenging and expensive. The adenovirus vector platform has been widely used for COVID-19 vaccines while several further candidate vaccines using the platform are in clinical development. In current liquid formulations, adenoviruses require distribution at 2-8 °C. The development of formulations suitable for ambient temperature distribution would be advantageous. Previous peer-reviewed reports of adenovirus lyophilization are relatively limited. Here, we report the development of a formulation and process for lyophilization of simian adenovirus-vectored vaccines based on the ChAdOx1 platform. We describe the iterative selection of excipients using a design of experiments approach, and iterative cycle improvement to achieve both preservation of potency and satisfactory cake appearance. The resulting method achieved in-process infectivity titre loss of around 50%. After drying, there was negligible further loss over a month at 30 °C. Around 30% of the predrying infectivity remained after a month at 45 °C. This performance is likely to be suitable for 'last leg' distribution at ambient temperature. This work may also facilitate the development of other product presentations using dried simian adenovirus-vectored vaccines.

Protein Engineering and HDX Identify Structural Regions of G-CSF Critical to Its Stability and Aggregation

The protein engineering and formulation of therapeutic proteins for prolonged shelf-life remain a major challenge in the biopharmaceutical industry. Understanding the influence of mutations and formulations on the protein structure and dynamics could lead to more predictive approaches to their improvement. Previous intrinsic fluorescence analysis of the chemically denatured granulocyte colony-stimulating factor (G-CSF) suggested that loop AB could subtly reorganize to form an aggregation-prone intermediate state. Hydrogen deuterium exchange mass spectrometry (HDX-MS) has also revealed that excipient binding increased the thermal unfolding transition midpoint (T_m) by stabilizing loop AB. Here, we have combined protein engineering with biophysical analyses and HDX-MS to reveal that increased exchange in a core region of the G-CSF comprising loop AB (ABI, a small helix, ABII) and loop CD packed onto helix B and the beginning of loop BC leads to a decrease in T_m and higher aggregation rates. Furthermore, some mutations can increase the population of the aggregation-prone conformation within the native ensemble, as measured by the greater local exchange within this core region.

HDX and In Silico Docking Reveal that Excipients Stabilize G-CSF via a Combination of Preferential Exclusion and Specific Hotspot Interactions

Assuring the stability of therapeutic proteins is a major challenge in the biopharmaceutical industry, and a better molecular understanding of the mechanisms through which formulations influence their stability is an ongoing priority. While the preferential exclusion effects of excipients are well known, the additional presence and impact of specific protein-excipient interactions have proven to be more elusive to identify and characterize. We have taken a combined approach of in silico molecular docking and hydrogen deuterium exchange-mass spectrometry (HDX-MS) to characterize the interactions between granulocyte colony-stimulating factor (G-CSF), and some common excipients. These interactions were related to their influence on the thermal-melting temperatures (T_m) for the nonreversible unfolding of G-CSF in liquid formulations. The residue-level interaction sites predicted in silico correlated well with those identified experimentally and highlighted the potential impact of specific excipient interactions on the T_m of G-CSF.

Protein freeze concentration and micro-segregation analysed in a temperature-controlled freeze container

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Freeze concentration of bovine serum albumin studied in a laboratory freeze container.

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Protein micro-segregation visualized by confocal laser scanning microscopy.

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Freezing protocol affected protein freeze concentration.

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Spatial heterogeneities created by freeze concentration.

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Micro-segregation was affected by freezing parameters.

To examine effects of varied freezing conditions on the development of spatial heterogeneity in the frozen protein solution, macroscopic freeze concentration and micro-segregation of bovine serum albumin (BSA) were investigated in a temperature-controlled 200-ml freeze container. Freezing to −40 °C promoted formation of protein concentration gradients (69–114 μg ml⁻¹) in frozen samples taken from 12 different freezer positions, whereby slow freezing in 4 h or longer facilitated the evolution of strong spatial heterogeneities and caused local concentration increases by 1.15-fold relative to the initial protein concentration (100 μg ml⁻¹). To visualize protein micro-segregation during phase separation, BSA was conjugated with fluorescein isothiocyanate and confocal laser scanning fluorescence microscopy was used to localize and size the freeze-concentrated protein regions. Slow freezing resulted in distinctly fewer and larger protein domains in the frozen bulk than fast freezing. Surface stress on the protein during freezing would therefore be minimized at low cooling rates; microscopic freeze concentration would however be highest under these conditions, potentially favoring protein aggregation.

Proteins behaving badly: emerging technologies in profiling biopharmaceutical aggregation

Over recent decades biotechnology has made significant advances owing to the emergence of powerful biochemical and biophysical instrumentation. The development of such technologies has enabled high-throughput assessment of compounds, the implementation of recombinant DNA technology, and large-scale manufacture of monoclonal antibodies. Such innovations have ultimately resulted in the current experienced biopharmaceutical stronghold in the therapeutic market. Yet aggregate prediction and profiling remains a challenge in the formulation of biopharmaceuticals due to artifacts associated with each analytical method. We review some emerging trends and novel technologies that offer a promising potential for accurately predicting and profiling protein aggregation at various stages of biopharmaceutical product design.