The ReFOLD assay for protein formulation studies and prediction of protein aggregation during long-term storage

Synergistic effect of cyclodextrins and electrolytes at high concentrations on protein aggregation inhibition

The stabilization of protein therapeutics against aggregation is crucial for maintaining their efficacy and safety. This study investigated the synergistic effects of cyclodextrins (CDs) and electrolytes at high concentrations on the stabilization of immunoglobulin G (IgG), insulin, and adeno-associated virus (AAV) vectors. The effects of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) combined with various electrolytes were evaluated using human plasma-derived IgG as a model protein. The HP-β-CD and L(+)-arginine hydrochloride combination synergistically increased the onset temperature of protein aggregation and inhibited the formation of soluble and insoluble aggregates during long-term storage. Notably, this synergistic effect was not observed when sucrose was used instead of HP-β-CD. Similar synergistic effects were observed with insulin and AAV vectors. The findings suggest that the stabilization mechanism could potentially involve enhanced interactions between HP-β-CD and IgG, preventing protein-protein interactions. However, the combination did not synergistically improve the solubility of free aromatic amino acids, including tyrosine and tryptophan. This study highlights the potential of using the combination of CDs and electrolytes as a promising formulation strategy for stabilizing complex protein therapeutics. Further studies are needed to elucidate the underlying mechanisms and generalize the approach to other proteins with varying physicochemical properties.

QTY code designed antibodies for aggregation prevention: A structural bioinformatic and computational study

Therapeutic monoclonal antibodies are the most rapidly growing class of molecular medicine, and they are beneficial to the treatment of a broad spectrum of human diseases. However, the aggregation of antibodies during the process of manufacture, distribution, and storage poses significant challenges, potentially compromising efficacy and inducing adverse immune responses. We previously conceived a QTY (glutamine, threonine, tyrosine) code, a simple tool for enhancing protein water-solubility by systematically pairwise replacing hydrophobic residues L (leucine), V (valine)/I (isoleucine), and F (phenylalanine). The QTY code offers a promising alternative to traditional methods of controlling aggregation in integral transmembrane proteins. In this study, we designed variants of four antibodies applying the QTY code, changing only the β-sheets. Through the structure-based aggregation analysis, we found that these QTY antibody variants demonstrated significantly decreased aggregation propensity compared to their wild-type counter parts. Our results of molecular dynamics simulations showed that the design by QTY code is capable of maintaining the antigen-binding affinity and structural stability. Our structural informatic and computational study suggests that the QTY code offers a significant potential in mitigating antibody aggregation.

Microwave-Assisted Freeze-Drying: Impact of Microwave Radiation on the Quality of High-Concentration Antibody Formulations

Microwave-assisted freeze-drying (MFD) offers significant time savings compared to conventional freeze-drying (CFD). While a few studies have investigated the stability of biopharmaceuticals with low protein concentrations after MFD and storage, the impact of MFD on high-concentration monoclonal antibody (mAb) formulations remains unclear. In this study, we systematically examined the effect of protein concentration in MFD and assessed protein stability following MFD, CFD, and subsequent storage using seven protein formulations with various stabilizers and concentrations. We demonstrated that microwaves directly interact with the active pharmaceutical ingredient (API), leading to decreased physical stability, specifically aggregation, in high-concentration antibody formulations. Furthermore, typically used sugar:protein ratios from CFD were insufficient for stabilizing mAbs when applying microwaves. We identified the intermediate drying phase as the most critical for particle formation, and cooling the samples provided some protection for the mAb. Our findings suggest that MFD technology may not be universally applicable to formulations well tested in CFD and could be particularly beneficial for formulations with low API concentrations requiring substantial amounts of glass-forming excipients, such as vaccines and RNA-based products.

Accelerated Production of Biopharmaceuticals via Microwave-Assisted Freeze-Drying (MFD)

Recently, attention has been drawn to microwave-assisted freeze-drying (MFD), as it drastically reduces the typically long drying times of biopharmaceuticals in conventional freeze-drying (CFD). Nevertheless, previously described prototype machines lack important attributes such as in-chamber freezing and stoppering, not allowing for the performance of representative vial freeze-drying processes. In this study, we present a new technical MFD setup, designed with GMP processes in mind. It is based on a standard lyophilizer equipped with flat semiconductor microwave modules. The idea was to enable the retrofitting of standard freeze-dryers with a microwave option, which would reduce the hurdles of implementation. We aimed to collect process data with respect to the speed, settings, and controllability of the MFD processes. Moreover, we studied the performance of six monoclonal antibody (mAb) formulations in terms of quality after drying and stability after storage for 6 months. We found drying processes to be drastically shortened and well controllable and observed no signs of plasma discharge. The characterization of the lyophilizates revealed an elegant cake appearance and remarkably good stability in the mAb after MFD. Furthermore, overall storage stability was good, even when residual moisture was increased due to high concentrations of glass-forming excipients. A direct comparison of stability data following MFD and CFD demonstrated similar stability profiles. We conclude that the new machine design is highly advantageous, enabling the fast-drying of excipient-dominated, low-concentrated mAb formulations in compliance with modern manufacturing technology.

Approaches to expand the conventional toolbox for discovery and selection of antibodies with drug-like physicochemical properties

Antibody drugs should exhibit not only high-binding affinity for their target antigens but also favorable physicochemical drug-like properties. Such drug-like biophysical properties are essential for the successful development of antibody drug products. The traditional approaches used in antibody drug development require significant experimentation to produce, optimize, and characterize many candidates. Therefore, it is attractive to integrate new methods that can optimize the process of selecting antibodies with both desired target-binding and drug-like biophysical properties. Here, we summarize a selection of techniques that can complement the conventional toolbox used to de-risk antibody drug development. These techniques can be integrated at different stages of the antibody development process to reduce the frequency of physicochemical liabilities in antibody libraries during initial discovery and to co-optimize multiple antibody features during early-stage antibody engineering and affinity maturation. Moreover, we highlight biophysical and computational approaches that can be used to predict physical degradation pathways relevant for long-term storage and in-use stability to reduce the need for extensive experimentation.

Hydroxylpropyl-β-cyclodextrin as Potential Excipient to Prevent Stress-Induced Aggregation in Liquid Protein Formulations

Due to the growing demand for patient-friendly subcutaneous dosage forms, the ability to increasing protein solubility and stability in formulations to deliver on the required high protein concentrations is crucial. A common approach to ensure protein solubility and stability in high concentration protein formulations is the addition of excipients such as sugars, amino acids, surfactants, approved by the Food and Drug Administration. In a best-case scenario, these excipients fulfil multiple demands simultaneously, such as increasing long-term stability of the formulation, reducing protein adsorption on surfaces/interfaces, and stabilizing the protein against thermal or mechanical stress. 2-Hydroxylpropyl-β-cyclodextrin (derivative of β-cyclodextrin) holds this potential, but has not yet been sufficiently investigated for use in protein formulations. Within this work, we have systematically investigated the relevant molecular interactions to identify the potential of Kleptose^®HPB (2-hydroxylpropyl-β-cyclodextrin from Roquette Freres, Lestrem, France) as “multirole” excipient within liquid protein formulations. Based on our results three factors determine the influence of Kleptose^®HPB on protein formulation stability: (1) concentration of Kleptose^®HPB, (2) protein type and protein concentration, and (3) quality of the protein formulation. Our results not only contribute to the understanding of the relevant interactions but also enable the target-oriented use of Kleptose^®HPB within formulation design.

Self-Interactions of Two Monoclonal Antibodies: Small-Angle X-ray Scattering, Light Scattering, and Coarse-Grained Modeling

Using light scattering (LS), small-angle X-ray scattering (SAXS), and coarse-grained Monte Carlo (MC) simulations, we studied the self-interactions of two monoclonal antibodies (mAbs), PPI03 and PPI13. With LS measurements, we obtained the osmotic second virial coefficient, B₂₂, and the molecular weight, M_w, of the two mAbs, while with SAXS measurements, we studied the mAbs' self-interaction behavior in the high protein concentration regime up to 125 g/L. Through SAXS-derived coarse-grained representations of the mAbs, we performed MC simulations with either a one-protein or a two-protein model to predict B₂₂. By comparing simulation and experimental results, we validated our models and obtained insights into the mAbs' self-interaction properties, highlighting the role of both ion binding and charged patches on the mAb surfaces. Our models provide useful information about mAbs' self-interaction properties and can assist the screening of conditions driving to colloidal stability.

Application of ultraviolet, visible, and infrared light imaging in protein-based biopharmaceutical formulation characterization and development studies

Imaging is increasingly more utilized as analytical technology in biopharmaceutical formulation research, with applications ranging from subvisible particle characterization to thermal stability screening and residual moisture analysis. This review offers a comprehensive overview of analytical imaging for scientists active in biopharmaceutical formulation research and development, where it presents the unique information provided by the ultraviolet (UV), visible (Vis), and infrared (IR) sections in the electromagnetic spectrum. The main body of this review consists of an outline of UV, Vis, and IR imaging techniques for several (bio)physical properties that are commonly determined during protein-based biopharmaceutical formulation characterization and development studies. The review concludes with a future perspective of applied imaging within the field of biopharmaceutical formulation research.

Protein analysis and stability: Overcoming trial-and-error by grouping according to physicochemical properties

Today proteins are possibly the most important class of substances. Yet new tasks for proteins are still often solved by trial-and-error approaches. However, in some areas these euphemistically called "screening approaches" are not suitable. E.g. stability tests just take too long and therefore require a more strategic, target-orientated concept. This concept is available by grouping proteins according to their physicochemical properties and then pulling out the right drawer for new tasks. These properties include size, then charge and hydrophobicity as well as their patchinesses, and the degree of order. In addition, solubility, the content of (free) enthalpy, aromatic-amino-acid- and α/β-frequency as well as helix capping, and corresponding patchiness, the number of specific motifs and domains as well as the typical concentration range can be helpful to discriminate between different groups of proteins. Analyzing correlations will reduce the necessary amount of parameters and additional ones, which may be still undiscovered at the present time, can be identified looking at protein subgroups with similar physicochemical properties which still behave heterogeneously. Step-by-step the methodology will be improved. Possibly protein stability will be the driver of this process, but all other areas such as production, purification and analytics including sample pre-treatment and the choice of appropriate separation conditions for e.g. chromatography and electrophoresis will profit from a rational strategy.

Combining Unfolding Reversibility Studies and Molecular Dynamics Simulations to Select Aggregation-Resistant Antibodies

The efficient development of new therapeutic antibodies relies on developability assessment with biophysical and computational methods to find molecules with drug-like properties such as resistance to aggregation. Despite the many novel approaches to select well-behaved proteins, antibody aggregation during storage is still challenging to predict. For this reason, there is a high demand for methods that can identify aggregation-resistant antibodies. Here, we show that three straightforward techniques can select the aggregation-resistant antibodies from a dataset with 13 molecules. The ReFOLD assay provided information about the ability of the antibodies to refold to monomers after unfolding with chemical denaturants. Modulated scanning fluorimetry (MSF) yielded the temperatures that start causing irreversible unfolding of the proteins. Aggregation was the main reason for poor unfolding reversibility in both ReFOLD and MSF experiments. We therefore performed temperature ramps in molecular dynamics (MD) simulations to obtain partially unfolded antibody domains in silico and used CamSol to assess their aggregation potential. We compared the information from ReFOLD, MSF, and MD to size-exclusion chromatography (SEC) data that shows whether the antibodies aggregated during storage at 4, 25, and 40 °C. Contrary to the aggregation-prone molecules, the antibodies that were resistant to aggregation during storage at 40 °C shared three common features: (i) higher tendency to refold to monomers after unfolding with chemical denaturants, (ii) higher onset temperature of nonreversible unfolding, and (iii) unfolding of regions containing aggregation-prone sequences at higher temperatures in MD simulations.

Room Temperature Intrinsic Emission Ratio of BSA Correlates With Percent Aggregates During Long-Term Storage

Successful formulation development hinges on the ability to screen and identify excipients that stabilize drug products during long-term storage. Biophysical and accelerated stability studies are used to screen for excipients that stabilize protein drug products. However, these studies are not always predictive of aggregation during long-term storage. In this study, we used multivariate experimentation to compare the effectiveness of intrinsic fluorescence and size exclusion chromatography accelerated stability parameters to predict excipients that stabilized bovine serum albumin (BSA) against aggregation on long-term storage at 4 °C. Emission intensity ratio (IR_330/350) data was more sensitive than emission maxima (λ_max) or intensity measurements in identifying significant factors and interactions. We observed the expected inverse correlation between the mid-points of fluorescence thermal transitions (T_ms) and insoluble aggregates at 4 and 40 °C. However, there were positive correlations between T_ms and % aggregates at 4 °C, indicating that if T_m was used as a predictive tool, it would select formulations that promoted soluble aggregates on long-term storage. Ambient temperature IR_330/350 measurements identified excipients that reduced BSA soluble aggregates on long-term storage. The results show ambient temperature emission ratio measurements can be useful for protein formulation development.

Storage stability of soy protein isolate powders containing soluble protein aggregates formed at varying pH

Soy protein is wildly used in food industry due to its high nutritional value and good functionalities. However, the poor storage stability of commercial soy protein products has puzzled both the producers and the users for a long time. The current study assessed the changes in protein solubility, aggregation, oxidation, and conformation of soy protein isolate (SPI) with various soluble aggregates formed at different pH values (pH 5-8) during storage. During storage, SPI samples showed a reduced protein solubility (p < .05), an increased protein oxidation (p < .05), and an attenuated conformational enthalpy (∆H). SPI with a higher pH produced more disulfide-mediated aggregates at the expense of sulfhydryl groups and experienced greater losses of protein tertiary structure and a faster reduction in solubility. Yet, all samples nearly shared similar rising trend during 8-week storage, which indicated the production of protein carbonyls was insensitive to pH. Soluble aggregates present in fresh SPI samples appeared to induce instability of SPI during storage. These findings suggested SPI prepared at pH 6 was in favor of its storage stability, and soluble aggregates presented in fresh samples should be paid more attention for further study of storage stability kinetics.

The uniqueness of flow in probing the aggregation behavior of clinically relevant antibodies

The development of therapeutic monoclonal antibodies (mAbs) can be hindered by their tendency to aggregate throughout their lifetime, which can illicit immunogenic responses and render mAb manufacturing unfeasible. Consequently, there is a need to identify mAbs with desirable thermodynamic stability, solubility, and lack of self-association. These behaviors are assessed using an array of in silico and in vitro assays, as no single assay can predict aggregation and developability. We have developed an extensional and shear flow device (EFD), which subjects proteins to defined hydrodynamic forces which mimic those experienced in bioprocessing. Here, we utilize the EFD to explore the aggregation propensity of 33 IgG1 mAbs, whose variable domains are derived from clinical antibodies. Using submilligram quantities of material per replicate, wide-ranging EFD-induced aggregation (9-81% protein in pellet) was observed for these mAbs, highlighting the EFD as a sensitive method to assess aggregation propensity. By comparing the EFD-induced aggregation data to those obtained previously from 12 other biophysical assays, we show that the EFD provides distinct information compared with current measures of adverse biophysical behavior. Assessing a candidate's liability to hydrodynamic force thus adds novel insight into the rational selection of developable mAbs that complements other assays.

Binding of excipients is a poor predictor for aggregation kinetics of biopharmaceutical proteins

One of the major challenges in formulation development of biopharmaceuticals is improving long-term storage stability, which is often achieved by addition of excipients to the final formulation. Finding the optimal excipient for a given protein is usually done using a trial-and-error approach, due to the lack of general understanding of how excipients work for a particular protein. Previously, preferential interactions (binding or exclusion) of excipients with proteins were postulated as a mechanism explaining diversity in the stabilisation effects. Weak preferential binding is however difficult to quantify experimentally, and the question remains whether the formulation process should seek excipients which preferentially bind with proteins, or not. Here, we apply solution NMR spectroscopy to comprehensively evaluate protein-excipient interactions between therapeutically relevant proteins and commonly used excipients. Additionally, we evaluate the effect of excipients on thermal and colloidal protein stability, on aggregation kinetics and protein storage stability at elevated temperatures. We show that there is a weak negative correlation between the strength of protein-excipient interactions and effect on enhancing protein thermal stability. We found that the overall protein-excipient binding per se can be a poor criterion for choosing excipients enhancing formulation stability. Experiments on a diverse set of excipients and test proteins reveal that while excipients affect all of the different aspects of protein stability, the effects are very much protein specific, and care must be taken to avoid apparent generalisations if a smaller dataset is being used.

Relationship of PEG-induced precipitation with protein-protein interactions and aggregation rates of high concentration mAb formulations at 5 °C

Native protein-protein interactions can play an important role in determining the tendency of monoclonal antibodies (mAbs) to aggregate under storage conditions. In this context, phase separation of mAb solutions induced by the addition of neutral polymers such as poly(ethylene glycol) (PEG) represents a simple method to assess the tendency of proteins to self-associate in the native state. Here, we investigated their relationships between PEG-induced phase separation, protein-protein interactions and long-term aggregation rate of several formulations of four mAbs at 100 mg/mL and 5 °C over 12 weeks of storage. We observed that the location of the phase boundary correlated well with the osmotic second virial coefficient B₂₂ determined in absence of the polymer, indicating that for our solutions PEG primarily leads to depletion forces between protein molecules, which are additive to protein-protein interactions. However, limited correlation between aggregation rate at 5 °C and phase behavior was observed across different mAbs, pH values and ionic strengths, indicating that colloidal stability is not the only determinant of aggregation even at such low temperature and high protein concentration. Our results contribute to the growing realization that aggregation propensity in the context of antibody developability is a complex feature, which depends on a variety of biophysical properties rather than one single parameter.