A rapid method to monitor structural perturbations of high-concentrated therapeutic antibody solutions using Intrinsic Tryptophan Fluorescence Emission spectroscopy

Drug product development of therapeutic antibody formulations is still dictated by the risk of protein particle formation during processing or storage, which can lead to loss of potency and potential immunogenic reactions. Since structural perturbations are the main driver for irreversible protein aggregation, the conformational integrity of antibodies should be closely monitored. The present study evaluated the applicability of a plate reader-based high throughput method for Intrinsic Tryptophan Fluorescence Emission (ITFE) spectroscopy to detect protein aggregation due to protein unfolding in high-concentrated therapeutic antibody samples. The impact of fluorophore concentration on the ITFE signal in microplate readers was investigated by analysis of dilution series of two therapeutic antibodies and pure tryptophan. At low antibody concentrations (< 5 mg/mL, equivalent to 0.8 mM tryptophan), the low inner filter effect suggests a quasi-linear relationship between antibody concentration and ITFE intensity. In contrast, the constant ITFE intensity at high protein concentrations (> 40 mg/mL, equivalent to 6.1 mM tryptophan) indicate that ITFE spectroscopy measurements of IgG1 antibodies are feasible in therapeutically relevant concentrations (up to 223 mg/mL). Furthermore, the capability of the method to detect low levels of unfolding (around 1 %) was confirmed by limit of detection (LOD) determination with temperature-stressed antibody samples as degradation standards. Change of fluorescence intensity at the maximum (ΔIaM) was identified as sensitive descriptor for protein degradation, providing the lowest LOD values. The results demonstrate that ITFE spectroscopy performed in a microplate reader is a valuable tool for high-throughput monitoring of protein degradation in therapeutic antibody formulations.

Optimization of Flow Imaging Microscopy Setting Using Spherical Beads with Optical Properties Similar to Those of Biopharmaceuticals

Flow imaging microscopy (FIM) is widely used to characterize biopharmaceutical subvisible particles (SVPs). The segmentation threshold, which defines the boundary between the particle and the background based on pixel intensity, should be properly set for accurate SVP quantification. However, segmentation thresholds are often subjectively and empirically set, potentially leading to variations in measurements across instruments and operators. In the present study, we developed an objective method to optimize the FIM segmentation threshold using poly(methyl methacrylate) (PMMA) beads with a refractive index similar to that of biomolecules. Among several candidate particles that were evaluated, 2.5-µm PMMA beads were the most reliable in size and number, suggesting that the PMMA bead size analyzed by FIM could objectively be used to determine the segmentation threshold for SVP measurements. The PMMA bead concentrations measured by FIM were highly consistent with the indicative concentrations, whereas the PMMA bead size analyzed by FIM decreased with increasing segmentation threshold. The optimal segmentation threshold where the analyzed size was closest to the indicative size differed between an instrument with a black-and-white camera and that with a color camera. Inter-instrument differences in SVP concentrations in acid-stressed recombinant adeno-associated virus (AAV) and protein aggregates were successfully minimized by setting an optimized segmentation threshold specific to the instrument. These results reveal that PMMA beads can aid in determining a more appropriate segmentation threshold to evaluate biopharmaceutical SVPs using FIM.

The Strengths of Total Holographic Video Microscopy in Detecting Sub-Visible Protein Particles in Biopharmaceuticals: A Comparison to Flow Imaging and Resonant Mass Measurement

Determination of subvisible particle (SVP) content in biopharmaceuticals is a prerequisite to ensure the quality of liquid biopharmaceutical products. Here, we present a comparison of the recently introduced holographic video microscopy (total holographic characterization, THC) with two orthogonal and well-established analytical technologies: micro flow imaging (MFI) and resonant mass measurement (RMM). The capabilities of the THC were investigated under conditions commonly applied in drug product development. Three different antibody products were used at different concentrations and formulations to cover a wide range of realistic use-cases. The comparison was particularly focused on protein aggregates to investigate the applicability of THC to this critical class of particles in drug product development. Protein concentrations up to 100 mg/ml were investigated covering a broad range of viscosity and refractive indices, both important parameters in particle detection. The comparison reveals that THC is highly sensitive to detect protein aggregates in a size range from 0.5 µm to 10 µm. THC shows a significant superiority to FI and RMM in detecting heterogenous protein aggregates which often appear as transparent and porous particles. Additionally, THC needs very small sample amount of about 30 µl and short measurement times, making it applicable for early development stages and high-throughput approaches. These results show that THC is a valuable supplement to the existing particle characterization method portfolio in drug product development.

Particles in Biopharmaceutical Formulations, Part 2: An Update on Analytical Techniques and Applications for Therapeutic Proteins, Viruses, Vaccines and Cells

Particles in biopharmaceutical formulations remain a hot topic in drug product development. With new product classes emerging it is crucial to discriminate particulate active pharmaceutical ingredients from particulate impurities. Technical improvements, new analytical developments and emerging tools (e.g., machine learning tools) increase the amount of information generated for particles. For a proper interpretation and judgment of the generated data a thorough understanding of the measurement principle, suitable application fields and potential limitations and pitfalls is required. Our review provides a comprehensive overview of novel particle analysis techniques emerging in the last decade for particulate impurities in therapeutic protein formulations (protein-related, excipient-related and primary packaging material-related), as well as particulate biopharmaceutical formulations (virus particles, virus-like particles, lipid nanoparticles and cell-based medicinal products). In addition, we review the literature on applications, describe specific analytical approaches and illustrate advantages and drawbacks of currently available techniques for particulate biopharmaceutical formulations.

Development challenges of high concentration monoclonal antibody formulations

High concentration monoclonal antibody drug products represent a special segment of biopharmaceuticals. In contrast to other monoclonal antibody products, high concentration monoclonal antibodies are injected subcutaneously helping increase patient compliance and reduce the number of hospital patient visits. It is important to note that a high protein concentration (≥50 mg/mL) poses a challenge from a product development perspective. Colloidal properties, physical and chemical protein stability should be considered during formulation, primary packaging and manufacturing process development as well as optimization of other dosage form-related parameters. The aim of such development work is to obtain a drug product capable of maintaining appropriate protein structure throughout its shelf-life and ensure proper and accurate dosage upon administration.

Physicochemical analysis and biological characterization of FKB327 as a biosimilar to adalimumab

FKB327 was approved by the European Medicines Agency as a biosimilar to European-authorized adalimumab (Humira® ; AbbVie Inc). Adalimumab is a monoclonal antibody, binding and inhibiting tumor necrosis factor (TNF)-α with use indicated for several immune-mediated, chronic, and inflammatory disorders. The approval is based on high similarity in the physicochemical properties between FKB327 and adalimumab. The objective of this study is to assess the biological similarity, with regard to Fab- and Fc-associated functions, and describe the relationship between physicochemical and biological characterization and functional activity. State-of-the-art orthogonal techniques were implemented to assess the structure and function of FKB327. Peptide mapping with liquid chromatography and mass spectrometry, capillary electrophoresis-sodium dodecyl sulfate, ultraviolet circular dichroism, size-exclusion high-performance liquid chromatography (HPLC), and cation exchange HPLC were the techniques used to assess structure. Functional activity was assessed with enzyme-linked immunosorbent assay, surface plasmon resonance, and cell-based assays. The polypeptide sequence of FKB327 was identical to that of adalimumab. FKB327 also was demonstrated to have a similar secondary and tertiary structure to adalimumab. Posttranslational heterogeneities, along with size and charge variants, were not clinically meaningful. FKB327 binds to TNF-α, FcγR, the neonatal Fc receptor, and C1q, and induces apoptosis, antibody-dependent cellular cytotoxicity, and complement-dependent cytotoxicity. The binding and activity of FKB327 were similar to that of adalimumab. FKB327 shares similar structure and activity with adalimumab. Based on characterization of physicochemical and biological properties, FKB327 is expected to have a similar safety, immunogenicity, and efficacy profile to adalimumab.

A comparison of background membrane imaging versus flow technologies for subvisible particle analysis of biologics

A recently developed high-throughput background membrane imaging (BMI) technique, the HORIZON, was assessed for its ability to quantify subvisible particulate (SVP) generated during protein therapeutic development. The HORIZON platform method was optimized and compared to three well-characterized SVP counting techniques: light obscuration, micro-flow imaging (MFI), and FlowCam®. A head-to-head comparison was performed for precision, linearity, SVP concentration, and morphological output of BMI compared to the other three techniques using two unique enzymes under investigation. We found that dilution requirements for BMI are protein-specific, and membrane coverage is the critical instrument parameter to monitor for dilution suitability. The precision of BMI ranked similarly to all other techniques. Analysis of the same sample dilution, run in triplicate, across all four techniques indicated the BMI technique provides SVP concentrations that are comparable with the flow imaging techniques. Morphological information from BMI was generally less practical when compared with flow microscopy. The major drawback of BMI was that the current software indiscriminately clips large particles, potentially resulting in a misrepresentation of SVP size distribution. Despite this phenomenon, the concentration and size data generated corresponds well with current flow imaging techniques while decreasing time, cost, and sample requirements for SVP quantification.

Separation, Characterization and Discriminant Analysis of Subvisible Particles in Biologics Formulations

Background:

The presence of subvisible particles (SVPs) in parenteral formulations of biologics is a major challenge in the development of therapeutic protein formulations. Distinction between proteinaceous and non-proteinaceous SVPs is vital in monitoring formulation stability.

Methods:

The current compendial method based on light obscuration (LO) has limitations in the analysis of translucent/low refractive index particles. A number of attempts have been made to develop an unambiguous method to characterize SVPs, albeit with limited success.

Results:

Herein, we describe a robust method that characterizes and distinguishes both potentially proteinaceous and non-proteinaceous SVPs in protein formulations using Microflow imaging (MFI) in conjunction with the MVAS software (MFI View Analysis Suite), developed by ProteinSimple. The method utilizes two Intensity parameters and a morphological filter that successfully distinguishes proteinaceous SVPs from non-proteinaceous SVPs and mixed aggregates.

Conclusion:

he MFI generated raw data of a protein sample is processed through Lumetics LINK software that applies an in-house developed filter to separate proteinaceous from the rest of the particulates.

19F Dark-State Exchange Saturation Transfer NMR Reveals Reversible Formation of Protein-Specific Large Clusters in High-Concentration Protein Mixtures

Proteins frequently exist as high-concentration mixtures, both in biological environments and increasingly in biopharmaceutical co-formulations. Such crowded conditions promote protein-protein interactions, potentially leading to formation of protein clusters, aggregation, and phase separation. Characterizing these interactions and processes in situ in high-concentration mixtures is challenging due to the complexity and heterogeneity of such systems. Here we demonstrate the application of the dark-state exchange saturation transfer (DEST) NMR technique to a mixture of two differentially 19F-labeled 145 kDa monoclonal antibodies (mAbs) to assess reversible temperature-dependent formation of small and large protein-specific clusters at concentrations up to 400 mg/mL. 19F DEST allowed quantitative protein-specific characterization of the cluster populations and sizes for both mAbs in the mixture under a range of conditions. Additives such as arginine glutamate and NaCl also had protein-specific effects on the dark-state populations and cluster characteristics. Notably, both mAbs appear to largely exist as separate self-associated clusters, which mechanistically respond differently to changes in solution conditions. We show that for mixtures of differentially 19F-labeled proteins DEST NMR can characterize clustering in a protein-specific manner, offering unique tracking of clustering pathways and a means to understand and control them.

Protein Adsorption and Layer Formation at the Stainless Steel-Solution Interface Mediates Shear-Induced Particle Formation for an IgG1 Monoclonal Antibody

Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can result in the production of unwanted subvisible protein particles (SVPs). In this work, surface-mediated SVP formation was investigated. Specifically, the effects of different solid interface materials, interfacial shear rates, and protein concentrations on SVP formation were measured for the National Institute of Standards and Technology monoclonal antibody (NISTmAb), a reference IgG1 monoclonal antibody (mAb). A stainless steel rotary piston pump was used to identify formulation and process parameters that affect aggregation, and a flow cell (alumina or stainless steel interface) was used to further investigate the effect of different interface materials and/or interfacial shear rates. SVP particles produced were monitored using flow microscopy or flow cytometry. Neutron reflectometry and a quartz crystal microbalance with dissipation monitoring were used to characterize adsorption and properties of NISTmAb at the stainless steel interface. Pump/shear cell experiments showed that the NISTmAb concentration and interface material had a significant effect on SVP formation, while the effects of interfacial shear rate and passage number were less important. At the higher NISTmAb concentrations, the adsorbed protein became structurally altered at the stainless steel interface. The primary adsorbed layer remained largely undisturbed during flow, suggesting that SVP formation at high NISTmAb concentration was caused by the disruption of patches and/or secondary interactions.

Measurement of Average Aggregate Density by Sedimentation and Brownian Motion Analysis

The spatially averaged density of protein aggregates is an important parameter that can be used to relate size distributions measured by orthogonal methods, to characterize protein particles, and perhaps to estimate the amount of protein in aggregate form in a sample. We obtained a series of images of protein aggregates exhibiting Brownian diffusion while settling under the influence of gravity in a sealed capillary. The aggregates were formed by stir-stressing a monoclonal antibody (NISTmAb). Image processing yielded particle tracks, which were then examined to determine settling velocity and hydrodynamic diameter down to 1 μm based on mean square displacement analysis. Measurements on polystyrene calibration microspheres ranging in size from 1 to 5 μm showed that the mean square displacement diameter had improved accuracy over the diameter derived from imaged particle area, suggesting a future method for correcting size distributions based on imaging. Stokes' law was used to estimate the density of each particle. It was found that the aggregates were highly porous with density decreasing from 1.080 to 1.028 g/cm³ as the size increased from 1.37 to 4.9 μm.

Polymethacrylate Coated Electrospun PHB Fibers as a Functionalized Platform for Bio-Diagnostics: Confirmation Analysis on the Presence of Immobilized IgG Antibodies against Dengue Virus

In this article, a combination of far field electrospinning (FFES) and free-radical polymerization has been used to create a unique platform for protein immobilization via the physical attachment of biomolecules to the surface of the fiber mats. The large specific surface area of the fibers with its tailored chemistry provides a desirable platform for effective analyte-surface interaction. The detailed analysis of protein immobilization on a newly developed bio-receptive surface plays a vital role to gauge its advantages in bio-diagnostic applications. We relied on scanning electron microscopy (SEM), diameter range analysis, and X-ray photoelectron spectroscopy (XPS), along with thermal gravimetric analysis (TGA), water-in-air contact angle analysis (WCA), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) to study our developed platforms and to provide valuable information regarding the presence of biomolecular entities on the surface. Detailed analyses of the fiber mats before and after antibody immobilization have shown obvious changes on the surface of the bioreceptive surface including: (i) an additional peak corresponding to the presence of an antibody in TGA analysis; (ii) extra FTIR peaks corresponding to the presence of antibodies on the coated fiber platforms; and (iii) a clear alteration in surface roughness recorded by AFM analysis. Confirmation analyses on protein immobilization are of great importance as they underlay substantial grounds for various biosensing applications.

Immunogenicity of protein aggregates of a monoclonal antibody generated by forced shaking stress with siliconized and nonsiliconized syringes in BALB/c mice

OBJECTIVE

In this study, we aimed to investigate the immunogenicity of protein aggregates of monoclonal antibodies (mAbs), generated by forced shaking stress with siliconized and nonsiliconized syringes in a mouse model.

METHODS

Samples were filled in siliconized and nonsiliconized syringes with shaking and headspace air. Characterization studies were performed using high-performance size-exclusion chromatography, nanoparticle tracking analysis, flow cytometry, micro-flow imaging and resonant mass measurement. The samples (10 or 100 μg) were subcutaneously injected into BALB/c mice for 21 days, and the anti-drug antibody (ADA) concentrations were monitored.

KEY FINDINGS

In samples shaken with siliconized syringes [SO (+)], large amounts of submicron and subvisible protein aggregates were formed by interactions with silicone oil droplets. The characteristics of protein aggregates differed between the mAb solution and shaken samples, which strongly indicates that silicone oil accelerates protein aggregation. When administered at low doses, the ADA concentration in all samples increased with repeated injections, and SO (+) induced the highest immunogenicity. However, when administered at high doses, ADA concentration decreased following prolonged repeated administration for tolerance.

CONCLUSIONS

These results indicated that mAb protein aggregation induced immunogenicity in mice, and SO (+) induced higher immunogenicity than samples shaken with nonsiliconized syringe.

Variability in Flow-Imaging Microscopy Measurements and Considerations for Biopharmaceutical Development

Flow-imaging microscopy is widely used in the biopharmaceutical industry to characterize populations of subvisible (1-100 μm) particles due to high sensitivity and the ability to discriminate different particle morphologies. The present work provides a comprehensive assessment of the capabilities of flow-imaging microscopy by exploring the impacts of a variety of factors on the observed variability of these measurements. A novel graphical presentation is proposed to facilitate both determination of expected levels and detection of potential atypical results. Data collected across different products and container-closure systems illustrate that a substantial amount of historical experience is typically required to adequately define the expected levels of subvisible particles for any specific system. It is also shown, however, that an appropriate level of control can be demonstrated without the need to pool large numbers of containers or perform replicate measurements.

Influence of particle shedding from silicone tubing on antibody stability

Objectives

Peristaltic pumps are increasingly employed during fill & finish operations of a biopharmaceutical drug, due to sensitivity of many biological products to rotary piston pump-related stresses. Yet, possibly also unit operations using peristaltic pumps may shed particulates into the final product due to abrasion from the employed tubing. It was the aim of this study to elucidate the potential influence of particles shed from peristaltic pump tubing on the stability of a drug product.

Methods

Spiking solutions containing shed silicone particles were prepared via peristaltic pumping of placebo under recirculating conditions and subsequently characterized. Two formulated antibodies were spiked with two realistic, but worst-case levels of particles and a 6-month accelerated stability study with storage at 2–8, 25 and 40°C were conducted.

Key findings

Regarding the formation of aggregates and fragments, both mAbs degraded at their typically expected rates and no additional impact of spiked particles was observed. No changes were discerned however in turbidity, subvisible and visible particle assessments. Flow imaging data for one of the mAb formulations with spiked particles suggested limited colloidal stability of shed particles as indicated by a similar increase in spiked placebo.

Conclusions

Shed silicone particles from peristaltic pump tubing are assumed to not impair drug product stability.

Interfacial dilatational deformation accelerates particle formation in monoclonal antibody solutions

Protein molecules are amphiphilic moieties that spontaneously adsorb at the air/solution (A/S) interface to lower the surface energy. Previous studies have shown that hydrodynamic disruptions to these A/S interfaces can result in the formation of protein aggregates that are of concern to the pharmaceutical industry. Interfacial hydrodynamic stresses encountered by protein therapeutic solutions under typical manufacturing, filling, and shipping conditions will impact protein stability, prompting a need to characterize the contribution of basic fluid kinematics to monoclonal antibody (mAb) destabilization. We demonstrate that dilatational surface deformations are more important to antibody stability when compared to constant-area shear of the A/S interface. We have constructed a dilatational interfacial rheometer that utilizes simultaneous pressure and bubble shape measurements to study the mechanical stability of mAbs under interfacial aging. It has a distinct advantage over methods utilizing the Young-Laplace equation, which incorrectly describes viscoelastic interfaces. We provide visual evidence of particle ejection from dilatated A/S interfaces and spectroscopic data of ejected mAb particles. These rheological studies frame a molecular understanding of the protein-protein interactions at the complex-fluid interface.

Evaluation of Microflow Digital Imaging Particle Analysis for Sub-Visible Particles Formulated with an Opaque Vaccine Adjuvant

Microflow digital imaging (MDI) has become a widely accepted method for assessing sub-visible particles in pharmaceutical formulations however, to date; no data have been presented on the utility of this methodology when formulations include opaque vaccine adjuvants. This study evaluates the ability of MDI to assess sub-visible particles under these conditions. A Fluid Imaging Technologies Inc. FlowCAM^® instrument was used to assess a number of sub-visible particle types in solution with increasing concentrations of AddaVax^™, a nanoscale squalene-based adjuvant. With the objective (10X) used and the limitations of the sensor resolution, the instrument was incapable of distinguishing between sub-visible particles and AddaVax^™ droplets at particle sizes less than 5 μm. The instrument was capable of imaging all particle types assessed (polystyrene beads, borosilicate glass, cellulose, polyethylene protein aggregate mimics, and lysozyme protein aggregates) at sizes greater than 5 μm in concentrations of AddaVax^™ up to 50% (vol:vol). Reduced edge gradients and a decrease in measured particle sizes were noted as adjuvant concentrations increased. No significant changes in particle counts were observed for polystyrene particle standards and lysozyme protein aggregates, however significant reductions in particle counts were observed for borosilicate (80% of original) and cellulose (92% of original) particles. This reduction in particle counts may be due to the opaque adjuvant masking translucent particles present in borosilicate and cellulose samples. Although the results suggest that the utility of MDI for assessing sub-visible particles in high concentrations of adjuvant may be highly dependent on particle morphology, we believe that further investigation of this methodology to assess sub-visible particles in challenging formulations is warranted.

Particulate Matter in Injectable Drugs: Evaluation of Risks to Patients

One of the fundamental principles guiding the pharmaceutical quality of parenteral products is to prevent injecting contaminants from microbiological, chemical or physical sources. It is just as difficult to ensure the absence of chemical and particulate contaminants in injectable products as it is to weigh up the microbiological risk. The problem of particulate matter is mainly related to the preparing and administrating of injectable drugs rather than through the contamination of marketed products. Particulate contamination also arises

Structural Changes and Aggregation Mechanisms for Anti-Streptavidin IgG1 at Elevated Concentration

Non-native protein aggregation may occur during manufacturing and storage of protein therapeutics, and this may decrease drug efficacy or jeopardize patient safety. From a regulatory perspective, changes in higher order structure due to aggregation are of particular interest but can be difficult to monitor directly at elevated protein concentrations. The present report focuses on non-native aggregation of antistreptavidin (AS) IgG1 at 30 mg/mL under solution conditions that prior work at dilute concentrations (e.g., 1 mg/mL) indicated would result in different aggregation mechanisms. Time-dependent aggregation and structural changes were monitored in situ with dynamic light scattering, small-angle neutron scattering, and Raman scattering and ex situ with far-UV circular dichroism and second-derivative UV spectroscopy. The effects of adding 0.15 M (∼5 w/w %) sucrose were also assessed. The addition of sucrose decreased monomer loss rates but did not change protein-protein interactions, aggregation mechanism(s), or aggregate structure and morphology. Consistent with prior results, altering the pD or salt concentration had the primary effect of changing the aggregation mechanism. Overall, the results provide a comparison of aggregate structure and morphology created via different growth mechanisms using orthogonal techniques and show that the techniques agree at least qualitatively. Interestingly, AS-IgG1 aggregates created at pD 5.3 with no added salt formed the smallest aggregates but had the largest structural changes compared to other solution conditions. The observation that the larger aggregates were also those with less structural perturbation compared to folded AS-IgG1 might be expected to extend to other proteins if the same strong electrostatic repulsions that mediate aggregate growth also mediate structural changes of the constituent proteins within aggregates.

Protein comparability assessments and potential applicability of high throughput biophysical methods and data visualization tools to compare physical stability profiles

In this review, some of the challenges and opportunities encountered during protein comparability assessments are summarized with an emphasis on developing new analytical approaches to better monitor higher-order protein structures. Several case studies are presented using high throughput biophysical methods to collect protein physical stability data as function of temperature, agitation, ionic strength and/or solution pH. These large data sets were then used to construct empirical phase diagrams (EPDs), radar charts, and comparative signature diagrams (CSDs) for data visualization and structural comparisons between the different proteins. Protein samples with different sizes, post-translational modifications, and inherent stability are presented: acidic fibroblast growth factor (FGF-1) mutants, different glycoforms of an IgG1 mAb prepared by deglycosylation, as well as comparisons of different formulations of an IgG1 mAb and granulocyte colony stimulating factor (GCSF). Using this approach, differences in structural integrity and conformational stability profiles were detected under stress conditions that could not be resolved by using the same techniques under ambient conditions (i.e., no stress). Thus, an evaluation of conformational stability differences may serve as an effective surrogate to monitor differences in higher-order structure between protein samples. These case studies are discussed in the context of potential utility in protein comparability studies.

Structural characterization of IgG1 mAb aggregates and particles generated under various stress conditions

IgG1 mAb solutions were prepared with and without sodium chloride and subjected to different environmental stresses. Formation of aggregates and particles of varying size was monitored by a combination of size-exclusion chromatography, Nanoparticle Tracking Analysis, Micro-flow Imaging (MFI), turbidity, and visual assessments. Stirring and heating induced the highest concentration of particles. In general, the presence of NaCl enhanced this effect. The morphology of the particles formed from mAb samples exposed to different stresses was analyzed from transmission electron microscopy and MFI images. Shaking samples without NaCl generated the most fibrillar particles, whereas stirring created largely spherical particles. The composition of the particles was evaluated for covalent cross-linking by SDS-PAGE, overall secondary structure by FTIR microscopy, and surface apolarity by extrinsic fluorescence spectroscopy. Freeze-thaw and shaking led to particles containing protein with native-like secondary structure. Heating and stirring produced IgG1-containing aggregates and particles with some non-native disulfide cross-links, varying levels of intermolecular beta sheet content, and increased surface hydrophobicity. These results highlight the importance of evaluating protein particle morphology and composition, in addition to particle number and size distributions, to better understand the effect of solution conditions and environmental stresses on the formation of protein particles in mAb solutions.

Studies of the aggregation of RNase Sa

Thirty-eight mutants of RNase Sa (ribonuclease from Streptomyces aureofaciens) were examined for their structure, thermal sensitivity, and tendency to aggregate. Although a biphasic correlation was seen between the effect of temperature on structure and the free energy of transfer changes in many of the mutants, little correlation was seen between the time at which aggregation is initiated or the rate of aggregation and the thermal sensitivity of the mutants. It is hypothesized that the nature of contacts between protein molecules in the associated (aggregated) phase rather than structural changes dominates the aggregation process for these series of mutants.

High-throughput biophysical analysis of protein therapeutics to examine interrelationships between aggregate formation and conformational stability

Stabilization and formulation of therapeutic proteins against physical instability, both structural alterations and aggregation, is particularly challenging not only due to each protein's unique physicochemical characteristics but also their susceptibility to the surrounding milieu (pH, ionic strength, excipients, etc.) as well as various environmental stresses (temperature, agitation, lyophilization, etc.). The use of high-throughput techniques can significantly aid in the evaluation of stabilizing solution conditions by permitting a more rapid evaluation of a large matrix of possible combinations. In this mini-review, we discuss both key physical degradation pathways observed for protein-based drugs and the utility of various high-throughput biophysical techniques to aid in protein formulation development to minimize their occurrence. We then focus on four illustrative case studies with therapeutic protein candidates of varying sizes, shapes and physicochemical properties to explore different analytical challenges in monitoring protein physical instability. These include an IgG2 monoclonal antibody, an albumin-fusion protein, a recombinant pentameric plasma glycoprotein, and an antibody fragment (Fab). Future challenges and opportunities to improve and apply high-throughput approaches to protein formulation development are also discussed.

Radar chart array analysis to visualize effects of formulation variables on IgG1 particle formation as measured by multiple analytical techniques

This study presents a novel method to visualize protein aggregate and particle formation data to rapidly evaluate the effect of solution and stress conditions on the physical stability of an immunoglobulin G (IgG) 1 monoclonal antibody (mAb). Radar chart arrays were designed so that hundreds of microflow digital imaging (MFI) solution measurements, evaluating different mAb formulations under varying stresses, could be presented in a single figure with minimal loss of data resolution. These MFI radar charts show measured changes in subvisible particle number, size, and morphology distribution as a change in the shape of polygons. Radar charts were also created to visualize mAb aggregate and particle formation across a wide size range by combining data sets from size-exclusion chromatography, Archimedes resonant mass measurements, and MFI. We found that the environmental/mechanical stress condition (e.g., heat vs. agitation) was the most important factor in influencing the particle size and morphology distribution with this IgG1 mAb. Additionally, the presence of NaCl exhibited a pH and stress-dependent behavior resulting in promotion or inhibition mAb particle formation. This data visualization technique provides a comprehensive analysis of the aggregation tendencies of this IgG1 mAb in different formulations with varying stresses as measured by different analytical techniques.

Flow imaging microscopy for protein particle analysis--a comparative evaluation of four different analytical instruments

Flow imaging microscopy was introduced as a technique for protein particle analysis a few years ago and has strongly gained in importance ever since. The aim of the present study was a comparative evaluation of four of the most relevant flow imaging microscopy systems for biopharmaceuticals on the market: Micro-Flow Imaging (MFI)4100, MFI5200, Flow Cytometer And Microscope (FlowCAM) VS1, and FlowCAM PV. Polystyrene standards, particles generated from therapeutic monoclonal antibodies, and silicone oil droplets were analyzed by all systems. The performance was critically assessed regarding quantification, characterization, image quality, differentiation of protein particles and silicone oil droplets, and handling of the systems. The FlowCAM systems, especially the FlowCAM VS1, showed high-resolution images. The FlowCAM PV system provided the most precise quantification of particles of therapeutic monoclonal antibodies, also under impaired optical conditions by an increased refractive index of the formulation. Furthermore, the most accurate differentiation of protein particles and silicone oil droplets could be achieved with this instrument. The MFI systems provided excellent size and count accuracy (evaluated with polystyrene standards) especially the MFI5200 system. This instrument also showed very good performance for protein particles, also in case of an increased refractive index of the formulation. Both MFI systems were easier to use and appeared more standardized regarding measurement and data analysis as compared to the FlowCAM systems. Our study shows that the selection of the appropriate flow imaging microscopy system depends strongly on the main output parameters of interest and it is recommended to decide based on the intended application.

Size fractionation of microscopic protein aggregates using a preparative fluorescence-activated cell sorter

Protein aggregation, which takes place both in vivo and in vitro, is an important degradative pathway for all proteins. Protein aggregates have distinct physicochemical and biological properties that are important to study and characterize from the perspective of both fundamental and applied sciences. The size of protein aggregates varies across a huge range, spanning several orders of magnitude. Currently, protein aggregates larger than hundreds of nanometers in diameter are impossible to physically fractionate. Here, we present a new method to fractionate microscopic proteinaceous particles using preparative fluorescence-activated cell sorting technology.