Protein Adsorption, Desorption, and Aggregation Mediated by Solid-Liquid Interfaces

An experimentally validated cavitation inception model for spring-driven autoinjectors

Cavitation, the formation and collapse of vapor-filled bubbles, poses a problem in spring-driven autoinjectors (AIs). It occurs when the syringe accelerates abruptly during activation, causing pressure fluctuations within the liquid. These bubbles expand and then collapse, generating shock waves that can harm both the device and the drug molecules. This issue stems from the syringe's sudden acceleration when the driving rod hits the plunger. To better understand cavitation in AIs, we explore how design factors like drive spring force, air gap size, and fluid viscosity affect its likelihood and severity. We use a dynamic model for spring-driven autoinjectors to predict and analyze the factors contributing to cavitation initiation and severity. This model predicts the motion of AI components, such as the displacement and velocity of the syringe barrel, and allows us to investigate pressure wave propagation and the subsequent dynamics of cavitation under various operating conditions. We investigated different air gap heights (from 1 to 4 mm), drive spring forces (from 8 to 30 N), and drug solution viscosities (from 1 to 18 cp) to assess cavitation inception based on operational parameters. Results reveal that AI dynamics and cavitation onset and severity strongly depend upon AI operating parameters, namely drive spring force and air gap height. The maximum syringe acceleration increases with spring stiffness and decreases with air gap height; increases in air gap height prolong the time interval of syringe acceleration but diminish the maximum syringe acceleration. From actuation to injection, air gap pressure peaks twice, first due to impact with the rod/plunger and secondly due to the deacceleration event upon injection. The maximum air gap pressure increases with spring stiffness and decreases with air gap height. Results show that maximum cavitation bubble radii and collapse-driven extension rates occur with higher driver spring forces, smaller air gap heights, and less viscous solutions. A cavitation criterion is developed for cavitation in autoinjectors that concludes that cavitation in autoinjectors depends on the peak syringe acceleration.

Molecular Dynamics Study of Protein Aggregation at Moving Interfaces

Repeated compression and dilation of a protein film adsorbed to an interface lead to aggregation and entry of film fragments into the bulk. This is a major mechanism for protein aggregate formation in drug products upon mechanical stress, such as shaking or pumping. To gain a better understanding of these events, we developed a molecular dynamics (MD) setup, which would, in a later stage, allow for in silico formulation optimization. In contrast to previous approaches, the molecules of our model protein human growth hormone displayed realistic shapes, surfaces, and interactions with each other and the interface. This enabled quantitative assessment of protein cluster formation. Simulation outcomes aligned with experimental data on subvisible particles and turbidity, thereby validating the model. Computational and experimental results indicated that compression speed does not affect the aggregation behavior of preformed protein films but rather their regeneration. Protein clusters that formed during compression disassembled upon relaxation, suggesting that the particles originate from a partly compressed state. Desorption studies via steered MD revealed that proteins from compressed systems are more likely to detach as clusters, implying that compression effects at the interface translate into aggregates present in the bulk solution. With the possibility of studying the impact of different variables upon compression and dilation at the interface on a molecular level, our model contributes to the understanding of the mechanisms of protein aggregation at moving interfaces. It also enables further studies to change formulation parameters, interfaces, or proteins.

Shear stress as a driver of degradation for protein-based therapeutics: More accomplice than culprit

Protein degradation is a major concern for protein-based therapeutics. It may alter the biological activity of the product and raise the potential for undesirable effects on the patients. Among the numerous drivers of protein degradation, shear stress has been the focus around which much work has revolved since the 1970s. In the pharmaceutical realm, the product is often processed through several unit operations, which include mixing, pumping, filtration, filling, and atomization. Nonetheless, the drug might be exposed to significant shear stresses, which might cooperatively contribute to product degradation, together with interfacial stress. This review presents fundamentals of shear stress about protein structure, followed by an overview of the drivers of product degradation. The impact of shear stress on protein stability in different unit operations is then presented, and recommendations for limiting the adverse effects on the biopharmaceutical formulations are outlined. Finally, several devices used to explore the effects of shear stress are discussed.

Antibodies Adsorbed to the Air-Water Interface Form Soft Glasses

When monoclonal antibodies are exposed to an air-water interface, they form aggregates, which negatively impacts their performance. Until now, the detection and characterization of interfacial aggregation have been difficult. Here, we exploit the mechanical response imparted by interfacial adsorption by measuring the interfacial shear rheology of a model antibody, anti-streptavidin immunoglobulin-1 (AS-IgG1), at the air-water interface. Strong viscoelastic layers of AS-IgG1 form when the protein is adsorbed from the bulk solution. Creep experiments correlate the compliance of the interfacial protein layer with the subphase solution pH and bulk concentration. These, along with oscillatory strain amplitude and frequency sweeps, show that the viscoelastic behavior of the adsorbed layers is that of a soft glass with interfacial shear moduli on the order of 10-3 Pa m. Shifting the creep compliance curves under different applied stresses forms master curves consistent with stress-time superposition of soft interfacial glasses. The interfacial rheology results are discussed in the context of the interface-mediated aggregation of AS-IgG1.

Enhanced Thermal Stability and Reduced Aggregation in an Antibody Fab Fragment at Elevated Concentrations

The aggregation of protein therapeutics such as antibodies remains a major challenge in the biopharmaceutical industry. The present study aimed to characterize the impact of the protein concentration on the mechanisms and potential pathways for aggregation, using the antibody Fab fragment A33 as the model protein. Aggregation kinetics were determined for 0.05 to 100 mg/mL Fab A33, at 65 °C. A surprising trend was observed whereby increasing the concentration decreased the relative aggregation rate, ln(v) (% day^-1), from 8.5 at 0.05 mg/mL to 4.4 at 100 mg/mL. The absolute aggregation rate (mol L^-1 h^-1) increased with the concentration following a rate order of approximately 1 up to a concentration of 25 mg/mL. Above this concentration, there was a transition to an apparently negative rate order of -1.1 up to 100 mg/mL. Several potential mechanisms were examined as possible explanations. A greater apparent conformational stability at 100 mg/mL was observed from an increase in the thermal transition midpoint (T_m) by 7-9 °C, relative to those at 1-4 mg/mL. The associated change in unfolding entropy (△S_vh) also increased by 14-18% at 25-100 mg/mL, relative to those at 1-4 mg/mL, indicating reduced conformational flexibility in the native ensemble. Addition of Tween or the crowding agents Ficoll and dextran, showed that neither surface adsorption, diffusion limitations nor simple volume crowding affected the aggregation rate. Fitting of kinetic data to a wide range of mechanistic models implied a reversible two-state conformational switch mechanism from aggregation-prone monomers (N*) into non-aggregating native forms (N) at higher concentrations. k_D measurements from DLS data also suggested a weak self-attraction while remaining colloidally stable, consistent with macromolecular self-crowding within weakly associated reversible oligomers. Such a model is also consistent with compaction of the native ensemble observed through changes in T_m and △S_vh.

Protein Self-Assembly at the Liquid-Surface Interface. Surface-Mediated Aggregation Catalysis

Protein self-assembly into aggregates of various morphologies is a ubiquitous phenomenon in physical chemistry and biophysics. The critical role of amyloid assemblies in the development of diseases, neurodegenerative diseases especially, highlights the importance of understanding the mechanistic picture of the self-assembly process. The translation of this knowledge to the development of efficient preventions and treatments for diseases requires designing experiments at conditions mimicking those in vivo. This Perspective reviews data satisfying two major requirements: membrane environment and physiologically low concentrations of proteins. Recent progress in experiments and computational modeling resulted in a novel model for the amyloid aggregation process at the membrane-liquid interface. The self-assembly under such conditions has a number of critical features, further understanding of which can lead to the development of efficient preventive means and treatments for Alzheimer's and other devastating neurodegenerative disorders.

Relationship between aggregation of therapeutic proteins and agitation parameters: Acceleration and frequency

An increase in protein aggregates during transportation should be suppressed in therapeutic protein products because the aggregates have a potential risk of immunogenicity. In this study, three protein solutions in vials were exposed to tri-axial vibration with various combinations of frequency and acceleration using a transportation test system to investigate the relationship between low g-force stresses and protein aggregate generation. The number concentration of micron aggregates detected by flow imaging analysis increased markedly when the acceleration and frequency of agitation were within a specific range, in other words, above a threshold. This threshold was common among the three protein solutions. The suppression of micron aggregate formation by adding a surfactant suggested that agitation above the threshold increased micron aggregates mainly via interface-mediated routes. Notably, agitation, including agitation below the threshold, accelerated spontaneous oligomerization (nanometer aggregate generation) of proteins in bulk solution even in the presence of the surfactant. Studies of stability against mechanical stresses (e.g., a random vibration test to simulate actual shipment, with a time-compressed setting by increasing acceleration) need to be performed and discussed with careful consideration of the threshold for generating micron aggregates.

Influence of Nonspecific Interactions on Protein Associations: Implications for Biochemistry In Vivo

The cellular interior is composed of a variety of microenvironments defined by distinct local compositions and composition-dependent intermolecular interactions. We review the various types of nonspecific interactions between proteins and between proteins and other macromolecules and supramolecular structures that influence the state of association and functional properties of a given protein existing within a particular microenvironment at a particular point in time. The present state of knowledge is summarized, and suggestions for fruitful directions of research are offered. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Modeling cavitation bubble dynamics in an autoinjector and its implications on drug molecules

The collapse of cavitation bubbles induced by abrupt acceleration of the syringe in an autoinjector device can lead to protein aggregation. The details of bubble dynamics are investigated using an axisymmetric, three-dimensional simulation with passive tracers to illustrate the transport of protein molecules. When a bubble near the syringe wall collapses, protein molecules are concentrated in the re-entrant jet, pushed towards the syringe wall, and then spread across the wall, potentially leading to protein adsorption on the syringe wall and aggregation. This phenomenon is more prominent for bubbles positioned closer to the bottom wall, growing to a larger maximum radius. The bubble's maximum radius decreases with the bubble's distance from the syringe wall and air gap pressure, and increases with an increase in liquid column height and nucleus size. The strain rate induced by the bubble collapse is not large enough to unfold the proteins. When the re-entrant jet impacts the bubble surface or syringe wall, the bubble breaks up, generating smaller bubbles with high surface concentration of protein molecules, potentially inducing aggregation in the bulk. The bubble dynamics are influenced by dimensionless distance of the nucleus from the wall, normalized by maximum bubble radius (γ). The re-entrant jet velocity increases with γ, while the maximum liquid pressure, typically 100∼1000 bar, first decreases and then increases with γ. For a cloud of cavitation bubbles, i.e., closely clustered bubbles, coalescence of bubbles can occur, leading to a higher peak pressure at collapse.

Minimizing Oxidation of Freeze-Dried Monoclonal Antibodies in Polymeric Vials Using a Smart Packaging Approach

Primary containers made of cyclic olefin polymer (COP) have recently gained attention since they may overcome several risks and shortcomings of glass containers as they exhibit a high break resistance, biocompatibility, and homogeneous heat transfer during lyophilization. On the downside, COP is more permeable for gases, which can lead to an ingress of oxygen into the container over time. Since oxidation is an important degradation pathway for monoclonal antibodies (mAbs), the continuous migration of oxygen into drug product containers should be avoided overall. To date, no long-term stability studies regarding lyophilizates in polymer vials have been published, potentially because of the unbearable gas permeability. In this study, we demonstrate that after lyophilization in COP vials and storage of these vials in aluminum pouches together with combined oxygen and moisture absorbers (“smart packaging”), oxidation of two lyophilized therapeutic antibodies was as low as in glass vials due to the deoxygenated environment in the pouch. Nevertheless, active removal of oxygen from the primary container below the initial level over time during storage in such “smart” secondary packaging was not achieved. Furthermore, residual moisture was controlled. Overall, the smart packaging reveals a promising approach for long-term stability of biopharmaceuticals; in addition to COP’s known benefits, stable, low oxygen and moisture levels as well as the protection from light and cushioning against mechanical shock by the secondary packaging preserve the sensitive products very well.

Influence of Protein Adsorption on Aggregation in Prefilled Syringes

Protein aggregate formation in prefilled syringes (PFSs) can be influenced by protein adsorption and desorption at the solid-liquid interface. Although inhibition of protein adsorption on the PFS surface can lead to a decrease in the amount of aggregation, the mechanism underlying protein adsorption-mediated aggregation in PFSs is unclear. This study investigated protein aggregation caused by protein adsorption on silicone oil-free PFS surfaces [borosilicate glass (GLS) and cycloolefin polymer (COP)] and the factors affecting the protein adsorption on the PFS surfaces. The adsorbed proteins formed multilayered structures that consisted of two distinct types of layers: proteins adsorbed on the surface of the material and proteins adsorbed on top of the proteins on the surface. A pH-dependent electrostatic interaction was the dominant force for protein adsorption on the GLS surface, while hydrophobic effects were dominant for protein adsorption on the COP surface. When the repulsion force between proteins was weak, protein adsorption on the adsorbed protein layer was increased for both materials and as a result, protein aggregation increased. Therefore, a formulation with high colloidal stability can minimize protein adsorption on the COP surface, leading to reduced protein aggregation.

The viability of SARS-CoV-2 on solid surfaces

The COVID-19 pandemic had a major impact on life in 2020 and 2021. One method of transmission occurs when the causative virus, SARS-CoV-2, contaminates solids. Understanding and controlling the interaction with solids is thus potentially important for limiting the spread of the disease. We review work that describes the prevalence of the virus on common objects, the longevity of the virus on solids, and surface coatings that are designed to inactivate the virus. Engineered coatings have already succeeded in producing a large reduction in viral infectivity from surfaces. We also review work describing inactivation on facemasks and clothing and discuss probable mechanisms of inactivation of the virus at surfaces.

Adsorbed protein film on pump surfaces leads to particle formation during fill-finish manufacturing

During fill-finish manufacturing, therapeutic proteins may aggregate or form subvisible particles in response to the physical stresses encountered within filling pumps. Understanding and quantitating this risk is important since filling may be the last unit operation before the patient receives their dose. We studied particle formation from lab-scale to manufacturing-scale using sensitive and robust protein formulations. Filling experiments with a ceramic rotary piston pump were integrated with a rinse-stripping method to investigate the relationship between protein adsorption and particle formation. For a sensitive protein, multilayer film formation on the piston surface correlated with high levels of subvisible particles in solution. For a robust protein formulation, adsorption and subvisible particle formation were minimal. These results support an aggregation mechanism that is initiated by adsorption to pump surfaces and propagated by mechanical and/or hydrodynamic disruption of the film. The elemental analysis confirmed that ceramic wear debris remained at trace levels and did not contribute appreciably to protein aggregation.

The role of surfaces on amyloid formation

Interfaces can strongly accelerate or inhibit protein aggregation, destabilizing proteins that are stable in solution or, conversely, stabilizing proteins that are aggregation-prone. Although this behaviour is well-known, our understanding of the molecular mechanisms underlying surface-induced protein aggregation is still largely incomplete. A major challenge is represented by the high number of physico-chemical parameters involved, which are highly specific to the considered combination of protein, surface properties, and solution conditions. The key aspect determining the role of interfaces is the relative propensity of the protein to aggregate at the surface with respect to bulk. In this review, we discuss the multiple molecular determinants that regulate this balance. We summarize current experimental techniques aimed at characterizing protein aggregation at interfaces, and highlight the need to complement experimental analysis with theoretical modelling. In particular, we illustrate how chemical kinetic analysis can be combined with experimental methods to provide insights into the molecular mechanisms underlying surface-induced protein aggregation, under both stagnant and agitation conditions. We summarize recent progress in the study of important amyloids systems, focusing on selected relevant interfaces.

A Rapid, Small-Volume Approach to Evaluate Protein Aggregation at Air-Water Interfaces

Non-native protein aggregation is a common concern for biopharmaceuticals. A given protein may aggregate through a variety of mechanisms that depend on solution and physico-chemical stress conditions. A thorough evaluation of aggregation behavior for a protein under all conditions of interest is necessary to ensure drug safety and efficacy. This work introduces a rapid, small-volume approach to evaluate protein aggregation propensity upon exposure to air-water interfaces (AWI). A microtensiometer apparatus is used to aerate a small volume of a protein solution with microbubbles for short periods of time (≤10 s). Sub-visible particles that form are captured and analyzed using backgrounded membrane imaging. This allows one to capture all particles in the solution while being sample sparing. The surface-mediated aggregation of two model monoclonal antibodies (MAbs) and a globular protein (aCgn) was tested as a function of pH and temperature. Temperature had a negligible effect under the rapid interface turnover time scales with this technique. Electrostatic protein-protein interactions, mediated by pH changes, were more influential for particle formation via AWI. Nonionic surfactants substantially reduced particle formation for all MAb solutions, but not aCgn. The results are contrasted with expectations when exposing samples to much larger air-water interfacial stress.

M. Brito R. Structure and Aggregation Mechanisms in Amyloids

The aggregation of a polypeptide chain into amyloid fibrils and their accumulation and deposition into insoluble plaques and intracellular inclusions is the hallmark of several misfolding diseases known as amyloidoses. Alzheimer′s, Parkinson′s and Huntington’s diseases are some of the approximately 50 amyloid diseases described to date. The identification and characterization of the molecular species critical for amyloid formation and disease development have been the focus of intense scrutiny. Methods such as X-ray and electron diffraction, solid-state nuclear magnetic resonance spectroscopy (ssNMR) and cryo-electron microscopy (cryo-EM) have been extensively used and they have contributed to shed a new light onto the structure of amyloid, revealing a multiplicity of polymorphic structures that generally fit the cross-β amyloid motif. The development of rational therapeutic approaches against these debilitating and increasingly frequent misfolding diseases requires a thorough understanding of the molecular mechanisms underlying the amyloid cascade. Here, we review the current knowledge on amyloid fibril formation for several proteins and peptides from a kinetic and thermodynamic point of view, the structure of the molecular species involved in the amyloidogenic process, and the origin of their cytotoxicity.

The Impact of the Metal Interface on the Stability and Quality of a Therapeutic Fusion Protein

Subvisible particle formation, which occurs after the sterile filtration step of the fill/finish process, is a challenge that may occur during the development of biotherapeutics with complex molecular structures. Here, we show that a stainless steel pump head from a rotary piston pump produces more protein aggregates, past the limit of the acceptable quality range for subvisible particle counts, in comparison to a ceramic pump head. The quartz crystal microbalance was used to quantify the primary layer, proteins irreversibly adsorbed at the solid-liquid interface, and the secondary diffuse gel-like layer interacting on top of the primary layer. The results showed that the mass of protein irreversibly adsorbed onto stainless steel sensors is greater than on an aluminum oxide surface (ceramic pump mimic). This suggests that the amount of adsorbed protein plays a role in surface-induced protein aggregation at the solid-liquid interface.

Surfaces Affect Screening Reliability in Formulation Development of Biologics

PURPOSE

The ability to predict an antibody's propensity for aggregation is particularly important during product development to ensure the quality and safety of therapeutic antibodies. We demonstrate the role of container surfaces on the aggregation process of three mAbs under elevated temperature and long-term storage conditions in the absence of mechanical stress.

METHODS

A systematic study of aggregation is performed for different proteins, vial material, storage temperature, and presence of surfactant. We use size exclusion chromatography and micro-flow imaging to determine the bulk concentration of aggregates, which we combine with optical and atomic force microscopy of vial surfaces to determine the effect of solid-liquid interfaces on the bulk aggregate concentration under different conditions.

RESULTS

We show that protein particles under elevated temperature conditions adhere to the vial surfaces, causing a substantial underestimation of aggregation propensity as determined by common methods used in development of biologics. Under actual long-term storage conditions at 5°C, aggregate particles do not adhere to the surface, causing an increase in bulk concentration of particles, which cannot be predicted from elevated temperature screening tests by common methods alone. We also identify specific protein - surface interactions which promote oligomer formation in the nanometre range.

CONCLUSIONS

Special care should be taken when interpreting size exclusion and particle count data from stability studies if different temperatures and vial types are involved. We propose a novel combination of methods to characterise vial surfaces and bulk solution for a full understanding of protein aggregation processes in a sample.

In Pursuit of Zero 2.0: Recent Developments in Nonfouling Polymer Brushes for Immunoassays

"Nonfouling" polymer brush surfaces can greatly improve the performance of in vitro diagnostic (IVD) assays due to the reduction of nonspecific protein adsorption and consequent improvement of signal-to-noise ratios. The development of synthetic polymer brush architectures that suppress adventitious protein adsorption is reviewed, and their integration into surface plasmon resonance and fluorescent sandwich immunoassay formats is discussed. Also, highlighted is a novel, self-contained immunoassay platform (the D4 assay) that transforms time-consuming laboratory-based assays into a user-friendly and point-of-care format with a sensitivity and specificity comparable or better than standard enzyme-linked immunosorbent assay (ELISA) directly from unprocessed samples. These advancements clearly demonstrate the utility of nonfouling polymer brushes as a substrate for ultrasensitive and robust diagnostic assays that may be suitable for clinical testing, in field and laboratory settings.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Micro- and Nanotopography Sensitive Bacterial Attachment Mechanisms: A Review

Bacterial attachment to material surfaces can lead to the development of biofilms that cause severe economic and health problems. The outcome of bacterial attachment is determined by a combination of bacterial sensing of material surfaces by the cell and the physicochemical factors in the near-surface environment. This paper offers a systematic review of the effects of surface topography on a range of antifouling mechanisms, with a focus on how topographical scale, from micro- to nanoscale, may influence bacterial sensing of and attachment to material surfaces. A good understanding of these mechanisms can facilitate the development of antifouling surfaces based on surface topography, with applications in various sectors of human life and activity including healthcare, food, and water treatment.

Coadsorption of a Monoclonal Antibody and Nonionic Surfactant at the SiO2/Water Interface

During the formulation of therapeutic monoclonal antibodies (mAbs), nonionic surfactants are commonly added to attenuate structural rearrangement caused by adsorption/desorption at interfaces during processing, shipping, and storage. We examined the adsorption of a mAb (COE-3) at the SiO₂/water interface in the presence of pentaethylene glycol monododecyl ether (C₁₂E₅), polysorbate 80 (PS80-20EO), and a polysorbate 80 analogue with seven ethoxylates (PS80-7EO). Spectroscopic ellipsometry was used to follow COE-3 dynamic adsorption, and neutron reflection was used to determine interfacial structure and composition. Neither PS80-20EO nor C₁₂E₅ had a notable affinity for COE-3 or the interface under the conditions studied and thus did not prevent COE-3 adsorption. In contrast, PS80-7EO did coadsorb but did not influence the dynamic process or the equilibrated amount of absorbed COE-3. Near equilibration, COE-3 underwent structural rearrangement and PS80-7EO started to bind the COE-3 interfacial layer and subsequently formed a well-defined surfactant bilayer via self-assembly. The resultant interfacial layer comprised an inner mAb layer of about 70 Å thickness and an outer surfactant layer of a further 70 Å, with distinct transitional regions across the mAb-surfactant and surfactant-bulk water boundaries. Once formed, such interfacial layers were very robust and worked to prevent further mAb adsorption, desorption, and structural rearrangement. Such robust interfacial layers could be anticipated to exist for formulated mAbs stored in type II glass vials; further research is required to understand the behavior of these layers for siliconized glass syringes.

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.

Sweeping of Adsorbed Therapeutic Protein on Prefillable Syringes Promotes Micron Aggregate Generation

This study evaluated how differences in the surface properties of prefillable syringe barrels and in-solution sampling methods affect micron aggregates and protein adsorption levels. Three syringe types (glass barrel with silicone oil coating [GLS/SO+], glass barrel without silicone oil coating [GLS/SO-], and cyclo-olefin polymer [COP] barrel syringes) were tested with 3 therapeutic proteins (adalimumab, etanercept, and infliximab) using 2 sampling methods (aspiration or ejection). After quiescent incubation, solutions sampled by aspiration exhibited no significant change in micron aggregate concentration in any syringes, whereas those sampled by ejection exhibited increased micron aggregates in both GLS syringe types. Micron aggregate concentration in ejected solutions generally increased with increasing density of adsorbed proteins. Notably, COP syringes contained the lowest micron aggregate concentrations, which were independent of the sampling method. Correspondingly, the adsorbed protein density on COP syringes was the lowest at 1-2 mg/m², which was much less compared with that on GLS syringes and was calculated to be equivalent to only 1-2 protein layers, as visually confirmed by high-speed atomic force microscopy. These data indicate that low-adsorption prefillable syringes should be used for therapeutic proteins because protein aggregate concentration in the ejected solution is elevated by increased protein adsorption to the syringe surface.

Interfacial Adsorption of Monoclonal Antibody COE-3 at the Solid/Water Interface

Spectroscopic ellipsometry (SE) and neutron reflection (NR) data for the adsorption of a monoclonal antibody (mAb, termed COE-3, pI 8.44) at the bare SiO₂/water interface are compared here to the simulations based on Derjaguin-Landau-Verwey-Overbeek theory. COE-3 adsorption was characterized by an initial rapid increase in the surface-adsorbed amount (Γ) followed by a plateau. Only the initial rate of the increase in Γ was strongly correlated with the bulk concentration (0.002-0.2 mg/mL), with Γ at the plateau being about 2.2 mg/m² (pH 5.5). Simulations captured COE-3 adsorption at equilibrium most accurately, the point at which the outgoing flux of molecules within the adsorbed plane matched the adsorption flux. Increasing the buffer pH from 5.5 to 9 increased Γ at equilibrium to ∼3 mg/m² (0.02 mg/mL COE-3), revealing a dominant role for lateral repulsion between adsorbed mAb molecules. In contrast, increasing the buffer ionic strength (pH 6) reduced Γ, which was captured by simulations accounting for electrostatic screening by ions, in addition to mAb/SiO₂ attractive forces and lateral repulsion. NR data at the same bulk concentrations corroborated the SE data, albeit with slightly higher Γ due to longer adsorption times for data acquisition; for example, at pH 9, Γ was 3.6 mg/m² (0.02 mg/mL COE-3), equivalent to a relatively high volume fraction of 0.5. An adsorbed monolayer with a thickness of 50-52 Å was consistently determined by NR, corresponding to the short axial lengths of fragment antigen-binding and fragment crystallization and implying minimal structural perturbation. Thus, the simulations enabled a mechanistic interpretation of the experimental data of mAb adsorption at the SiO₂/water interface.

Neutron Reflection Study of Surface Adsorption of Fc, Fab, and the Whole mAb

Characterizing the influence of fragment crystallization (Fc) and antigen-binding fragment (Fab) on monoclonal antibody (mAb) adsorption at the air/water interface is an important step to understanding liquid mAb drug product stability during manufacture, shipping, and storage. Here, neutron reflection is used to study the air/water adsorption of a mAb and its Fc and Fab fragments. By varying the isotopic contrast, the adsorbed amount, thickness, orientation, and immersion of the adsorbed layers could be determined unambiguously. While Fc adsorption reached saturation within the hour, its surface adsorbed amount showed little variation with bulk concentration. In contrast, Fab adsorption was slower and the adsorbed amount was concentration dependent. The much higher Fc adsorption, as compared to Fab, was linked to its lower surface charge. Time and concentration dependence of mAb adsorption was dominated by Fab behavior, although both Fab and Fc behaviors contributed to the amount of mAb adsorbed. Changing the pH from 5.5 to 8.8 did not much perturb the adsorbed amount of Fc, Fab, or mAb. However, a small decrease in adsorption was observed for the Fc over pH 8-8.8 and vice versa for the Fab and mAb, consistent with a dominant Fab behavior. As bulk concentration increased from 5 to 50 ppm, the thicknesses of the Fc layers were almost constant at 40 Å, while Fab and mAb layers increased from 45 to 50 Å. These results imply that the adsorbed mAb, Fc, and Fab all retained their globular structures and were oriented with their short axial lengths perpendicular to the interface.

Neutron reflectivity measurement of protein A-antibody complex at the solid-liquid interface

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The orientation of IgG4 adsorbed at the solid-liquid interface was probed.

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A chromatography resin was mimicked by attaching protein A to a silica surface.

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Neutron reflectivity was used to measure protein A and adsorbed IgG structures.

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Protein A-modified silica was blocked with either BSA or PEG before IgG adsorption.

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Adsorbed IgG extended up to 230 Å from the surface, depending on blocking strategy.

Chromatography is a ubiquitous unit operation in the purification of biopharmaceuticals yet few studies have addressed the biophysical characterisation of proteins at the solution-resin interface. Chromatography and other adsorption and desorption processes have been shown to induce protein aggregation which is undesirable in biopharmaceutical products. In order to advance understanding of how adsorption processes might impact protein stability, neutron reflectivity was used to characterise the structure of adsorbed immunoglobulin G (IgG) on model surfaces. In the first model system, IgG was adsorbed directly to silica and demonstrated a side-on orientation with high surface contact. A maximum dimension of 60 Å in the surface normal direction and high density surface coverage were observed under pH 4.1 conditions. In chromatography buffers, pH was found to influence IgG packing density and orientation at the solid-liquid interface. In the second model system, which was designed to mimic an affinity chromatography surface, protein A was attached to a silica surface to produce a configuration representative of a porous glass chromatography resin. Interfacial structure was probed during sequential stages from ligand attachment, through to IgG binding and elution. Adsorbed IgG structures extended up to 250 Å away from the surface and showed dependence on surface blocking strategies. The data was suggestive of two IgG molecules bound to protein A with a somewhat skewed orientation and close proximity to the silica surface. The findings provide insight into the orientation of adsorbed antibody structures under conditions encountered during chromatographic separations.

Lipidation Effect on Surface Adsorption and Associated Fibrillation of the Model Protein Insulin

Lipidation of proteins is used in the pharmaceutical field to increase the therapeutic efficacy of proteins. In this study, we investigate the effect of a 14-carbon fatty acid modification on the adsorption behavior of human insulin to a hydrophobic solid surface and the subsequent fibrillation development under highly acidic conditions and elevated temperature by comparing to the fibrillation of human insulin. At these stressed conditions, the lipid modification accelerates the rate of fibrillation in bulk solution. With the use of several complementary surface-sensitive techniques, including quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and neutron reflectivity (NR), we show that there are two levels of structurally different protein organization at a hydrophobic surface for both human insulin and the lipidated analogue: a dense protein layer formed within minutes on the surface and a diffuse outer layer of fibrillar structures which took hours to form. The two layers may only be weakly connected, and proteins from both layers are able to desorb from the surface. The lipid modification increases the protein surface coverage and the thickness of both layer organizations. Upon lipidation not only the fibrillation extent but also the morphology of the fibrillar structures changes from fibril clusters on the surface to a more homogeneous network of fibrils covering the entire hydrophobic surface.

Posttranslational Modifications and the Immunogenicity of Biotherapeutics

Whilst the amino acid sequence of a protein is determined by its gene sequence, the final structure and function are determined by posttranslational modifications (PTMs), including quality control (QC) in the endoplasmic reticulum (ER) and during passage through the Golgi apparatus. These processes are species and cell specific and challenge the biopharmaceutical industry when developing a production platform for the generation of recombinant biologic therapeutics. Proteins and glycoproteins are also subject to chemical modifications (CMs) both in vivo and in vitro. The individual is naturally tolerant to molecular forms of self-molecules but nonself variants can provoke an immune response with the generation of anti-drug antibodies (ADA); aggregated forms can exhibit enhanced immunogenicity and QC procedures are developed to avoid or remove them. Monoclonal antibody therapeutics (mAbs) are a special case because their purpose is to bind the target, with the formation of immune complexes (ICs), a particular form of aggregate. Such ICs may be removed by phagocytic cells that have antigen presenting capacity. These considerations may frustrate the possibility of ameliorating the immunogenicity of mAbs by rigorous exclusion of aggregates from drug product. Alternate strategies for inducing immunosuppression or tolerance are discussed.

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.