Protein aggregation and its inhibition in biopharmaceutics

Characterization of Protein Aggregation Using Hydrogel-Encapsulated nIR Fluorescent Nanoparticle Sensors

The monitoring of biopharmaceutical critical quality attributes in-process, at both the process development and manufacturing stages, is necessary for the implementation of process analytical technology and quality-by-design principles. Among these attributes, it is important to monitor and control protein aggregation during the manufacturing of biological therapeutics to prevent adverse immunogenic responses and minimize negative impacts on drug deliverability. In this work, we explore hydrogel-encapsulated, label-free fluorescent nanosensors for the characterization of protein aggregation. A mathematical model is used to describe the diffusion and binding of a series of stressed pharmaceutical samples to such sensors, describing their dynamic response. We use mathematical modeling to map the influence of hydrogel properties on the separation performance, given the composition of UV-stressed IgG₁ samples. Using this modified model, the compositions of light-stressed IgG₁ samples were fit to experimental data and correlated with size-exclusion chromatography data. The results demonstrate the ability to detect the presence of high-molecular-weight protein species at a concentration as low as 1%. This work represents a significant step toward the development and deployment of rapid process analytical technologies for biopharmaceutical characterization.

Armoring the Interface with Surfactants to Prevent the Adsorption of Monoclonal Antibodies

The pharmaceutical industry uses surface-active agents (excipients) in protein drug formulations to prevent the aggregation, denaturation, and unwanted immunological response of therapeutic drugs in solution as well as at the air/water interface. However, the mechanism of adsorption, desorption, and aggregation of proteins at the interface in the presence of excipients remains poorly understood. The objective of this work is to explore the molecular-scale competitive adsorption process between surfactant-based excipients and two monoclonal antibody (mAb) proteins, mAb-1 and mAb-2. We use pendant bubble tensiometry to measure the ensemble average adsorption dynamics of mAbs with and without the excipient. The surface tension measurements allow us to quantify the rate at which the molecules "race" to the interface in single-component and mixed systems. These results define the phase space, where coadsorption of both mAbs and excipients occurs onto the air/water interface. In parallel, we use X-ray reflectivity (XR) measurements to understand the molecular-scale dynamics of competitive adsorption, revealing the surface-adsorbed amounts of the antibody and excipient. XR has revealed that at a sufficiently high surface concentration of the excipient, mAb adsorption to the surface and subsurface domains was inhibited. In addition, despite the fact that both mAbs adsorb via a similar mechanistic pathway and with similar dynamics, a key finding is that the competition for the interface directly correlates with the surface activity of the two mAbs, resulting in a fivefold difference in the concentration of the excipient needed to displace the antibody.

Optimization of the interaction of graphene quantum dots with lipase for biological applications

Graphene quantum dots (GQDs) are known as emerging sub-10 nm nanoparticles (NPs), which are in fact few-layered pieces of graphene, capable of emitting blue fluorescence, when exposed to 360 nm UV light. Understanding the details of the interaction between GQDs and lipase can serve as a critical step for improving the biological outcome of GQD-derived drug-delivery and diagnosis systems. The interaction occurs in the form of surface adsorption, which can subsequently influence the physicochemical properties of both the NP and the protein. Hence, a systematic approach was taken here to optimize the GQDs' synthesis conditions in order to achieve the highest possible quantum yield (QY). Furthermore, to understands the influence of the interaction of GQDs and lipase, on both the activity of lipase and the emission intensity of GQDs, various incubation conditions were tested to achieve optimized conditions over central composite design algorithm by Design-Expert®, using response surface methodology. The results show that the GQDs fabricated by thermal decomposition of citric acid at 160°C, with a heating duration of 55 min, obtain almost three times higher QY than the highest values reported previously. The best enzymatic activity after the formation of the hard corona, as well as the highest fluorescent emission, were achieved at GQD-to-enzyme ratios within the rage of 23-25%, at temperatures between 41 and 42°C, for 6-8 min. In the aforementioned condition, the enzyme retains 91-95% of its activity and the NP preserves about 80-82% of its fluorescence intensity after incubation.

The role of the medium in the effective-sphere interpretation of holographic particle characterization data

The in-line hologram of a micrometer-scale colloidal sphere can be analyzed with the Lorenz-Mie theory of light scattering to obtain precise measurements of the sphere's diameter and refractive index. The same technique also can be used to characterize porous and irregularly shaped colloidal particles provided that the extracted parameters are interpreted with effective-medium theory to represent the properties of an equivalent effective sphere. Here, we demonstrate that the effective-sphere model consistently accounts for changes in the refractive index of the medium as it fills the pores of porous particles and therefore yields quantitative information about such particles' structure and composition. In addition to the sample-averaged porosity, holographic perfusion porosimetry gauges the polydispersity of the porosity. We demonstrate these capabilities through measurements on mesoporous spheres, fractal protein aggregates and irregular nanoparticle agglomerates, all of which are noteworthy for their industrial significance.

Application of machine learning to predict monomer retention of therapeutic proteins after long term storage

An important aspect of initial developability assessments as well formulation development and selection of therapeutic proteins is the evaluation of data obtained under accelerated stress condition, i.e. at elevated temperatures. We propose the application of artificial neural networks (ANNs) to predict long term stability in real storage condition from accelerated stability studies and other high-throughput biophysical properties e.g. the first apparent temperature of unfolding (T_m). Our models have been trained on therapeutic relevant proteins, including monoclonal antibodies, in various pharmaceutically relevant formulations. Further, we developed network architectures with good prediction power using the least amount of input features, i.e. experimental effort to train the network. This provides an empiric means to highlight the most important parameters in the prediction of real-time protein stability. Further, several models were developed by a different validation means (i.e. leave-one-protein-out cross-validation) to test the robustness and the limitations of our approach. Finally, we apply surrogate machine learning algorithms (e.g. linear regression) to build trust in the ANNs decision making procedure and to highlight the connection between the leading inputs and the outputs.

Amyloid formation of bovine insulin is retarded in moderately acidic pH and by addition of short-chain alcohols

Protein aggregation and amyloid formation are associated with multiple human diseases, but are also a problem in protein production. Understanding how aggregation can be modulated is therefore of importance in both medical and industrial contexts. We have used bovine insulin as a model protein to explore how amyloid formation is affected by buffer pH and by the addition of short-chain alcohols. We find that bovine insulin forms amyloid fibrils, albeit with different rates and resulting fibril morphologies, across a wide pH range (2–7). At pH 4.0, bovine insulin displayed relatively low aggregation propensity in combination with high solubility; this condition was therefore chosen as basis for further exploration of how bovine insulin’s native state can be stabilized in the presence of short-chain alcohols that are relevant because of their common use as eluents in industrial-scale chromatography purification. We found that ethanol and isopropanol are efficient modulators of bovine insulin aggregation, providing a three to four times retardation of the aggregation kinetics at 30–35% (vol/vol) concentration; we attribute this to the formation of oligomers, which we detected by AFM. We discuss this effect in terms of reduced solvent polarity and show, by circular dichroism recordings, that a concomitant change in α-helical packing of the insulin monomer occurs in ethanol. Our results extend current knowledge of how insulin aggregates, and may, although bovine insulin serves as a simplistic model, provide insights into how buffers and additives can be fine-tuned in industrial production of proteins in general and pharmaceutical insulin in particular.

Functional zwitterionic biomaterials for administration of insulin

This review summarizes the structures and biomedical applications of zwitterionic biomaterials in the administration of insulin.

Preparation and Characterization of β-glucosidase Films for Stabilization and Handling in Dry Configurations

BACKGROUND

Although the stability of proteins is of significance to maintain protein function for therapeutical applications, this remains a challenge. Herein, a general method of preserving protein stability and function was developed using gelatin films.

METHODS

Enzymes immobilized onto films composed of gelatin and Ethylene Glycol (EG) were developed to study their ability to stabilize proteins. As a model functional protein, β-glucosidase was selected. The tensile properties, microstructure, and crystallization behavior of the gelatin films were assessed.

RESULTS

Our results indicated that film configurations can preserve the activity of β-glucosidase under rigorous conditions (75% relative humidity and 37°C for 47 days). In both control films and films containing 1.8 % β-glucosidase, tensile strength increased with increased EG content, whilst the elongation at break increased initially, then decreased over time. The presence of β-glucosidase had a negligible influence on tensile strength and elongation at break. Scanning electron-microscopy (SEM) revealed that with increasing EG content or decreasing enzyme concentrations, a denser microstructure was observed.

CONCLUSION

In conclusion, the dry film is a promising candidate to maintain protein stabilization and handling. The configuration is convenient and cheap, and thus applicable to protein storage and transportation processes in the future.

Effect of Stabilizers on Encapsulation Efficiency and Release Behavior of Exenatide-Loaded PLGA Microsphere Prepared by the W/O/W Solvent Evaporation Method

The aim of this study was to investigate the effects of various stabilizers on the encapsulation efficiency and release of exenatide-loaded PLGA (poly(lactic-co-glycolic acid)) microspheres prepared by the water-in-oil-in-water (W/O/W) solvent evaporation (SE) method. It was shown that the stabilizers affected exenatide stability in aqueous solutions, at water/dichloromethane interfaces, on PLGA surfaces, or during freeze-thawing and freeze-drying procedures. Sucrose predominantly reduces instability generated during freeze-thawing and freeze-drying. Phenylalanine prevents the destabilization at the water-dichloromethane (DCM) interface through decreased adsorption. Poloxamer 188 enhances stability in aqueous solutions and prevents adsorption to PLGA. Proline and lysine decrease adsorption on PLGA surfaces. Fourier transform infra-red spectroscopy (FT-IR) was used to find the molecular interaction of additives with exenatide or PLGA. Additives used in stability assessments were then added stepwise into the inner or outer water phase of the W/O/W double emulsion, and exenatide-loaded microspheres were prepared using the solvent evaporation method. The effect of each stabilizer on the encapsulation efficiency and release behavior of microspheres correlated well with the stability assessment results, except for the negative effect of poloxamer 188. Particle size analysis using laser diffractometry, scanning electron microscopy (SEM), water vapor sorption analysis, differential scanning calorimetry (DSC), and circular dichroism (CD) spectroscopy were also employed to characterize the prepared exenatide-loaded PLGA microsphere. This study demonstrated that an adequate formulation can be obtained by the study about the effect of stabilizers on peptide stability at the preformulation step. In addition, it can help to overcome various problems that can cause the destabilization of a peptide during the microsphere-manufacturing process and sustained drug release.

Apparent protein cloud point temperature determination using a low volume high-throughput cryogenic device in combination with automated imaging

Short-term parameters correlating to long-term protein stability, such as the protein cloud point temperature (T_cloud), are of interest to improve efficiency during protein product development. Such efficiency is reached if short-term parameters are obtained in a low volume and high-throughput (HT) manner. This study presents a low volume HT detection method for (sub-zero) T_cloud determination of lysozyme, as such an experimental method is not available yet. The setup consists of a cryogenic device with an automated imaging system. Measurement reproducibility (median absolute deviation of 0.2 °C) and literature-based parameter validation (Pearson correlation coefficient of 0.996) were shown by a robustness and validation study. The subsequent case study demonstrated a partial correlation between the obtained apparent T_cloud parameter and long-term protein stability as a function of lysozyme concentration, ion type, ionic strength, and freeze/thaw stress. The presented experimental setup demonstrates its ability to advance short-term strategies for efficient protein formulation development.

A phase diagram-based toolbox to assess the impact of freeze/thaw ramps on the phase behavior of proteins

The influence of process parameters during freeze/thaw (FT) operations is essential for the preservation of the protein stability/activity during production and storage processes in the biopharmaceutical industry. Process parameters, such as FT ramps, the final storage time and temperature, affect the occurring FT stress onto the target protein in different ways. FT stress includes cold denaturation, freeze concentration, and ice crystal formation which can result in protein aggregation. To visualize the impact of variations in FT ramps, descriptors such as solubility, phase behavior and crystal morphology were evaluated. The phase diagram-based toolbox in combination with an HTS-compatible cryo-device allowed the identification of suitable ramping schemes during FT operations. It could be clearly shown that rapid operations are needed above the glass transition temperature of the target protein to circumvent precipitation during FT cycles. Finally, a stability index is introduced which allows ranking of the systems investigated.

Improved adsorption reactions, kinetics and stability for model and therapeutic proteins immobilised on affinity resins

Protein adsorption on solid state media is important for the industrial affinity chromatography of biotherapeutics and for preparing materials for self-interaction chromatography where fundamental protein solution thermodynamic properties are measured. The adsorption of three model proteins (lysozyme, catalase and BSA) and two antibodies (a monoclonal and a polyclonal antibody) have been investigated on commercial affinity chromatography media with different surface functionalities (Formyl, Tresyl and Amino). Both the extent of protein immobilised (mg protein/ml media) and the reaction kinetics are reported for a range of reaction conditions, including pH, differing buffers as well as the presence of secondary reactants (glutaraldehyde, sodium cyanoborohydride, EDC and NHS). Compared to the reaction conditions recommended by manufacturers as well as those reported in previous published work, significant increases in the extent of protein immobilisation and reaction kinetics are reported here. The addition of glutaraldehyde or sodium cyanoborohydride was found to be especially effective even when not directly needed for the adsorption to happen. For mAb and pIgG, immobilisation levels of 50 and 31 mg of protein/ml of resin respectively were achieved, which are 100% or more than previously reported. Enhanced levels were achieved for lysozyme of 120 mg/ml with very rapid reaction kinetics (< 1 h) with sodium cyanoborohydride. It can be concluded that specific chromatography resins with Tresyl activated support offered enhanced levels of protein immobilisation due to their ability to react to form amine or thio-ether linkages with proteins. Additionally, glutaraldehyde can result in higher immobilisation levels whilst it can also accelerate immobilisation reaction kinetics.

Isotonic concentrations of excipients control the dimerization rate of a therapeutic immunoglobulin G1 antibody during refrigerated storage based on their rank order of native-state interaction

Inert co-solutes, or excipients, are often included in protein biologic formulations to adjust the tonicity of liquid dosage forms intended for subcutaneous delivery. Despite the low concentration of their use, many of these excipients alter protein-protein interactions such as dimerization and aggregation rates of high concentration monoclonal antibody (mAb) therapeutics to varying extents during long-term refrigerated clinical storage, challenging the formulation scientist to make informed excipient selections at the earliest stages of development when protein supply and time are often limited. The objectives of this study were to better understand how isotonic concentrations of excipients influence the dimerization rates of a model mAb stored at refrigerated and room temperatures and explore protein sparing biophysical methods capable of predicting this dependence. Despite their prevalence of use in the biopharmaceutical industry, methods for assessing conformational stability such differential scanning calorimetry and isothermal equilibrium unfolding showed little predictive power and we highlight some of the assumptions and technical challenges of their use with mAbs. Conversely, measures of colloidal stability of the native-state such as preferential interaction coefficients measured by vapor pressure osmometry and solubility assessed by polyethylene-glycol induced precipitation correlated reasonably well with the mAb dimerization data and are most consistent with the excipients tested minimizing dimerization by interacting favorably with the residues comprising the protein-protein association interface.

Temperature-induced aggregation behavior in bovine pancreas trypsin solutions

In this study, we investigate the effect of temperature treatment on Bovine Pancreas Trypsin (BPT) in aqueous solutions using dynamic, static and electrophoretic light scattering, fluorescence spectroscopy and circular dichroism. Static and dynamic light scattering at various solution conditions i.e. different salt content and pH, reveals that BPT aggregation is enhanced as temperature increases in a non-reversible manner. At acidic pH protein monomers are the dominant population over aggregates of globules, nevertheless the two populations co-exist at neutral and basic pH. The surface charge of the aggregates is intensified by aggregation and it is dominated by the negative residues of the protein at all pH conditions. Protein unfolding upon thermal treatment is probed by variation of the fluorescence spectrum which is caused by the exposure of tryptophan to the aqueous environment. The exposure of the hydrophobic interior of BPT upon heating may be considered as the reason of aggregation at the molecular level. Τhis study provides information that can be useful for utilizing thermal treatment protocols of BPT towards manufacturing protein-based nano formulated drugs.

Predicting High-Concentration Interactions of Monoclonal Antibody Solutions: Comparison of Theoretical Approaches for Strongly Attractive Versus Repulsive Conditions

Nonspecific protein-protein interactions of a monoclonal antibody were quantified experimentally using light scattering from low to high protein concentrations (c₂) and compared with prior work for a different antibody that yielded qualitatively different behavior. The c₂ dependence of the excess Rayleigh ratio (R^ex) provided the osmotic second virial coefficient (B₂₂) at low c₂ and the static structure factor (S_q=0) at high c₂, as a function of solution pH, total ionic strength (TIS), and sucrose concentration. Net repulsive interactions were observed at pH 5, with weaker repulsions at higher TIS. Conversely, attractive electrostatic interactions were observed at pH 6.5, with weaker attractions at higher TIS. Refined coarse-grained models were used to fit model parameters using experimental B₂₂ versus TIS data. The parameters were used to predict high-c₂ R^ex values via Monte Carlo simulations and separately with Mayer-sampling calculations of higher-order virial coefficients. For both methods, predictions for repulsive to mildly attractive conditions were quantitatively accurate. However, only qualitatively accurate predictions were practical for strongly attractive conditions. An alternative, higher resolution model was used to show semiquantitatively and quantitatively accurate predictions of strong electrostatic attractions at low c₂ and low ionic strength.

Aggregate Forms of Recombinant Human Erythropoietin With Different Charge Profile Substantially Impact Biological Activities

Recombinant human erythropoietin (rHuEPO) as a glycoprotein growth factor has been considered a biological drug for treatment of anemic patients with chronic renal failure or who receive cancer chemotherapy. Biological activity and circulation time are 2 parameters that are important to achieve EPO's efficacy. Previous efforts for increasing EPO's efficacy have focused on glycosylation modification via adding more sialic acid antenna and generates more negative charged protein. Evidences cleared that EPO's activity increased by numbers of N-glycan moieties with presence of sialic acids at their terminus. Correlation between bioactivity and glycosylation with terminal sialylation is theoretically achieved using the calculation of the amount of charge profile of the EPO variants called "I-number." Here, we studied and compared the relationship between bioactivities of different EPOs that contained various I-numbers and the effect of their secondary and tertiary protein structures on measured in vivo efficacy. Eight recombinant EPOs batches were produced under the same condition. I-numbers found out by EPO's charge profiles determination using capillary electrophoresis and activities were studied upon erythroid precursor cell stimulation in mice. Analyzing the bioactivity, I-number, and structural studies revealed that in spite of I-number, conformational changes in protein structure and presence of aggregated species impact bioactivity substantially.

Detection and Sizing of Submicron Particles in Biologics With Interferometric Scattering Microscopy

We demonstrate the application of interferometric scattering microscopy (IFS) for characterizing submicron particles in stir-stressed monoclonal antibody. IFS uses a layered silicon sensor and modified optical microscope to rapidly visualize and determine the particle size distribution (PSD) of submicron particles based on their scattering intensity, which is directly proportional to particle mass. Limits for particle size and optimal solution concentration were established for IFS characterization of submicron particles. We critically compare IFS data with dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) and find IFS is superior to NTA and DLS for determining the realistic shape of the number-based PSD, whereas NTA and DLS provide superior information about absolute particle size. Together, IFS, NTA, and DLS provide complementary information on submicron particles and enable quantitative characterization of the PSD of submicron aggregates. Finally, we explore quantifying particle size with IFS by developing a calibration curve for particle scattering intensity based on correlative scanning electron microscopy imaging. We found that only a subset of isotropic-shaped particles followed the expected proportionality between IFS intensity and particle mass. Overall, this study demonstrates IFS is a simple approach for detecting and quantifying submicron aggregate PSD in protein-based therapeutics.

Surface patches on recombinant erythropoietin predict protein solubility: engineering proteins to minimise aggregation

BACKGROUND

Protein solubility characteristics are important determinants of success for recombinant proteins in relation to expression, purification, storage and administration. Escherichia coli offers a cost-efficient expression system. An important limitation, whether for biophysical studies or industrial-scale production, is the formation of insoluble protein aggregates in the cytoplasm. Several strategies have been implemented to improve soluble expression, ranging from modification of culture conditions to inclusion of solubility-enhancing tags.

RESULTS

Surface patch analysis has been applied to predict amino acid changes that can alter the solubility of expressed recombinant human erythropoietin (rHuEPO) in E. coli, a factor that has importance for both yield and subsequent downstream processing of recombinant proteins. A set of rHuEPO proteins (rHuEPO E13K, F48D, R150D, and F48D/R150D) was designed (from the framework of wild-type protein, rHuEPO WT, via amino acid mutations) that varied in terms of positively-charged patches. A variant predicted to promote aggregation (rHuEPO E13K) decreased solubility significantly compared to rHuEPO WT. In contrast, variants predicted to diminish aggregation (rHuEPO F48D, R150D, and F48D/R150D) increased solubility up to 60% in relation to rHuEPO WT.

CONCLUSIONS

These findings are discussed in the wider context of biophysical calculations applied to the family of EPO orthologues, yielding a diverse range of calculated values. It is suggested that combining such calculations with naturally-occurring sequence variation, and 3D model generation, could lead to a valuable tool for protein solubility design.

Controlling and quantifying the stability of amino acid-based cargo within polymeric delivery systems

In recent years, the rapid growth and availability of protein and peptide therapeutics has not only expanded the boundaries of modern science but has also revolutionized the practice of medicine today. The potential of such therapies, however, is greatly limited by the innate instabilities of proteins and peptides, which is further magnified during therapeutic formulation processing, transport, storage, and administration. In this paper, we will consider the unique stability challenges associated with protein/peptide polymeric delivery systems from an engineering approach oriented towards the quantification and modification of amino acid-based cargo stability. While a number of methods have been developed for the purposes of quantifying factors affecting protein and peptide stability, current measurement techniques remain largely limited in scope in regard to polymeric drug delivery systems. This paper will primarily describe the influence of water content, pH, and temperature on protein and peptide stability within polymer-based delivery systems. Moreover, we will review current instrumentation used to quantify factors affecting protein/peptide stability with respect to water content, pH, and temperature. Lastly, we will outline several recommendations to help guide future research efforts to develop methods more specific to quantifying protein/peptide stability within polymer-based delivery systems.

Laser irradiation affects the biological identity and cellular uptake of plasmonic nanoparticles

The biological identity of nanoparticles (NPs) is defined by a protein layer formed on their surface, called protein corona (PC), once they meet the biological milieu. Any change in the PC composition may influence the biological fate of NPs. The PC composition is strongly dependent on several parameters including the physicochemical properties of NPs, and biological and environmental factors. As one of the main features of plasmonic NPs is their capacity to induce local heating by laser irradiation, we hypothesized that laser irradiation may change the biological identity of NPs and therefore alter their biological fate. To test this hypothesis, here we investigated the effects of either simultaneous or sequential laser irradiation on the conformations of a few proteins selected from two main categories of plasma proteins (i.e. human serum albumin and human fibrinogen) on the surfaces of gold nanorods (AuNRs). The outcomes revealed a significant role of laser irradiation on conformational changes of fibrinogen compared to albumin. Moreover, the effects of plasmonic heating - at various times - on the achieved corona composition from interactions of AuNRs and human plasma with various concentrations were monitored. Consequently, the cellular uptake of the corona coated AuNRs was measured in two cell types: malignant (MCF-7) and normal (MCF-10A) breast cell lines. The results demonstrated a substantial reduction in the cellular uptake of AuNRs in response to an increase in the laser irradiation time, especially in MCF-10A. Our results may pave the way for a mechanistic understanding of the biological identity of plasmonic NPs which in turn can help their safe and efficient clinical translations.

Quantitation of low concentrations of polysorbates 80 in protein formulations by Coomassie brilliant blue

Polysorbate 80, as pharmaceutical excipient and virus inactivating agent, is commonly used in the protein pharmaceutical industry. In this study, a method has been developed for the determination of low concentration of Polysorbate 80 in the presence of high concentration proteins (≤100 mg/ml) and excipients. This colorimetric method is based on the interaction of Polysorbate 80 and Coomassie brilliant blue, and suitable for quantitation of Polysorbate 80 in the range of 10-100 μg/ml. Dozens or hundreds of samples can be quantified simultaneously by using microplate. Besides Polysorbate 80, this method can also be used to determine other types of surfactants in protein solutions, such as Polysorbate 20, Triton X-100, NP40, SDS, Benzalkonium chloride/bromide and PEG4000.

Peripheral cyclic β-amino acids balance the stability and edge-protection of β-sandwiches

Engineering water-soluble stand-alone β-sandwich mimetics is a current challenge because of the difficulties associated with tailoring long-range interactions. In this work, single cis-(1R,2S)-2-aminocyclohexanecarboxylic acid mutations were introduced into the edge strands of the eight-stranded β-sandwich mimetic structures from the betabellin family. Temperature-dependent NMR and CD measurements, together with thermodynamic analyses, demonstrated that the modified peripheral strands exhibited an irregular and partially disordered structure but were able to exert sufficient shielding on the hydrophobic core to retain the predominantly β-sandwich structure. Although the frustrated interactions decreased the free energy of unfolding, the temperature of the maximum stabilities increased to or remained at physiologically relevant temperatures. We found that the irregular peripheral strands were able to prevent edge-to-edge association and fibril formation in the aggregation-prone model. These findings establish a β-sandwich stabilization and aggregation inhibition approach, which does not interfere with the pillars of the peptide bond or change the net charge of the peptide.

Effect of additives on liquid droplet of protein-polyelectrolyte complex for high-concentration formulations

Liquid droplets of protein-polyelectrolyte complexes (PPCs) have been developed as a new candidate for stabilization and concentration of protein drugs. However, it remains unclear whether additives affect the precipitation and redissolution yields of PPCs. In the present study, we investigated the PPC formation of human immunoglobulin G (IgG) and poly-L-glutamic acid (polyE) in the presence of various additives that have diverse effects, such as protein stabilization. Alcohols, including ethanol, successfully increased the PPC precipitation yield to over 90%, and the PPCs formed were completely redissolved at physiological ionic strength. However, poly(ethylene glycol), sugars, and amino acids did not improve the precipitation and redissolution yields of PPCs over those observed when no additives were included. Circular dichroism spectrometry showed that the secondary structure of polyE as well as electrostatic interactions play important roles in increasing the PPC precipitation yield when ethanol is used as an additive. The maximum concentration of IgG reached 100 mg/ml with the use of ethanol, which was 15% higher efficiency of the protein yield after precipitation and redissolution than that in the absence of additives. Thus, the addition of a small amount of ethanol is effective for the concentration and stabilization of precipitated PPCs containing IgG formulations.

Isothermal Analysis of ThermoFluor Data can readily provide Quantitative Binding Affinities

Differential scanning fluorimetry (DSF), also known as ThermoFluor or Thermal Shift Assay, has become a commonly-used approach for detecting protein-ligand interactions, particularly in the context of fragment screening. Upon binding to a folded protein, most ligands stabilize the protein; thus, observing an increase in the temperature at which the protein unfolds as a function of ligand concentration can serve as evidence of a direct interaction. While experimental protocols for this assay are well-developed, it is not straightforward to extract binding constants from the resulting data. Because of this, DSF is often used to probe for an interaction, but not to quantify the corresponding binding constant (Kd). Here, we propose a new approach for analyzing DSF data. Using unfolding curves at varying ligand concentrations, our "isothermal" approach collects from these the fraction of protein that is folded at a single temperature (chosen to be temperature near the unfolding transition). This greatly simplifies the subsequent analysis, because it circumvents the complicating temperature dependence of the binding constant; the resulting constant-temperature system can then be described as a pair of coupled equilibria (protein folding/unfolding and ligand binding/unbinding). The temperature at which the binding constants are determined can also be tuned, by adding chemical denaturants that shift the protein unfolding temperature. We demonstrate the application of this isothermal analysis using experimental data for maltose binding protein binding to maltose, and for two carbonic anhydrase isoforms binding to each of four inhibitors. To facilitate adoption of this new approach, we provide a free and easy-to-use Python program that analyzes thermal unfolding data and implements the isothermal approach described herein ( https://sourceforge.net/projects/dsf-fitting ).

An Expanded Conformation of an Antibody Fab Region by X-Ray Scattering, Molecular Dynamics, and smFRET Identifies an Aggregation Mechanism

Protein aggregation is the underlying cause of many diseases, and also limits the usefulness of many natural and engineered proteins in biotechnology. Better mechanistic understanding and characterization of aggregation-prone states is needed to guide protein engineering, formulation, and drug-targeting strategies that prevent aggregation. While several final aggregated states-notably amyloids-have been characterized structurally, very little is known about the native structural conformers that initiate aggregation. We used a novel combination of small-angle x-ray scattering (SAXS), atomistic molecular dynamic simulations, single-molecule Förster resonance energy transfer, and aggregation-prone region predictions, to characterize structural changes in a native humanized Fab A33 antibody fragment, that correlated with the experimental aggregation kinetics. SAXS revealed increases in the native state radius of gyration, R_g, of 2.2% to 4.1%, at pH 5.5 and below, concomitant with accelerated aggregation. In a cutting-edge approach, we fitted the SAXS data to full MD simulations from the same conditions and located the conformational changes in the native state to the constant domain of the light chain (C_L). This C_L displacement was independently confirmed using single-molecule Förster resonance energy transfer measurements with two dual-labeled Fabs. These conformational changes were also found to increase the solvent exposure of a predicted APR, suggesting a likely mechanism through which they promote aggregation. Our findings provide a means by which aggregation-prone conformational states can be readily determined experimentally, and thus potentially used to guide protein engineering, or ligand binding strategies, with the aim of stabilizing the protein against aggregation.

Preparation-free method can enable rapid surfactant screening during industrial processing of influenza vaccines

Triton X-100 (TX-100) is the most common surfactant used to split viruses during the production of influenza split-virus vaccines. It is a mild surfactant not known to denature the viral proteins; this property makes TX-100 useful for maintaining antigen conformational structure, and, as an added benefit, for partially stabilizing vaccine formulations against protein aggregation. Despite its benefits, TX-100 needs to be filtered out after virus splitting has been achieved, due to its toxicity in large quantities. Accordingly, residual TX-100 presence in vaccine formulations has implications for both formulation stability and safety, necessitating both accurate screening during processing to guide decision-making about filtration repeats and accurate quantitation in the final product. Accurate HPLC-based methods are used successfully for the latter but their use for routine screening during processing is far from ideal because they often require extensive sample preparation and are fairly slow, complicated and costly. Here, "deconstruction" of UV-Vis absorption spectra into components corresponding to different absorbing "species" is demonstrated as a novel and viable method for routine TX-100 screening in vaccine samples from different industrial processing steps. This method is fairly accurate and, more importantly, preparation-free, rapid, simple/user-friendly and comparatively inexpensive. It is evaluated in depth in terms of applicability conditions, limitations and potential for high-throughput adaptation as well as generalization to other complex biopharmaceutical formulations.

Test models for the evaluation of immunogenicity of protein aggregates

Protein aggregates have been discussed for a long time as a potential risk factor for immunogenicity in patients. Meanwhile, many research groups have investigated the immunogenicity of differently produced aggregates using in vitro or in vivo models. Despite all knowledge gained in these studies still little is known about the mechanisms of immunogenicity and the kind of protein aggregates bearing the greatest risk for immunogenicity. The choice of a suitable test model regarding the predictability of immunogenicity of protein aggregates in humans plays a major role and influences results and conclusions substantially. In this review we will provide an overview of the test models recently used for the evaluation of immunogenicity of protein aggregates; we will discuss advantages and drawbacks regarding their usability and predictive power for immunogenicity in humans.