Notorious but not understood: How liquid-air interfacial stress triggers protein aggregation

Impact of pneumatic tube transportation on the aggregation of monoclonal antibodies in clinical practice

Postproduction handling and in-hospital transportation of antibody drugs cause mechanical stress, including interfacial and shear stress, that can induce antibody unfolding and aggregation. The handling practices differ significantly between hospitals and the impact on protein stability is unknown. For example, the mechanical stress caused by transport via pneumatic tube systems (PTS) on therapeutic antibody aggregation is a potential safety and quality gap. The aim of this study was to investigate whether mechanical stress and PTS transportation in a hospital cause aggregation of five commonly used antibody drugs diluted in infusion bags. Orthogonal analytical methods showed that the handling and PTS transportation in this hospital did not cause aggregation of the investigated mAbs. The absence of aggregation could be explained by the reduction of interfacial stress due to headspace removal from the infusion bags and a mechanical sensor indicated that there was also only a moderate amount of mechanical stress caused by transportation with this particular PTS. Although this case study focuses on five antibody drugs and the practices in one hospital, the work demonstrates how to evaluate whether other handling and transportation practices cause significant mechanical stress that could compromise the quality and safety of antibody drugs.

Aggregation of therapeutic monoclonal antibodies due to thermal and air/liquid interfacial agitation stress: Occurrence, stability assessment strategies, aggregation mechanism, influencing factors, and ways to enhance stability

Therapeutic proteins, such as monoclonal antibodies (mAbs) are known to undergo stability related issues during various stages of product life cycle resulting in the formation of aggregates and fragments. Aggregates of mAb might result in reduced therapeutic activity and could cause various adverse immunogenic responses. Sample containing mAb undergo aggregation due to various types of stress factors, and there is always a continuous interest among researchers and manufacturers to determine the effect of different factors on the stability of mAb. Thermal stress and air/liquid interfacial agitation stress are among two of the common stress factors to which samples containing mAb are exposed to during various stages. Initial part of this review articles aims to provide a generalized understanding of aggregation of mAb such as size ranges of aggregates, aggregate types, stress factors, analytical techniques, permissible aggregate limits, and stability assessment methods. This article further aims to explain different aspects associated with aggregation of mAb in liquid samples due to thermal and air/liquid interfacial agitation stress. Under each stress category, the occurrence of stress during product life cycle, type of aggregates formed, mechanism of aggregation, strategies used by various researchers to expose mAb containing samples to stress, different factors affecting aggregation, fate of aggregates in human body fluids, and strategies used to enhance mAb stability has been explained in detail. The authors hope that this article provides a detailed understanding about stability of mAb due to thermal and air/liquid interfacial stress with relevance to product life cycle from manufacturing to administration into patients.

Particle formation in response to different protein formulations and containers: Insights from machine learning analysis of particle images

Subvisible particle count is a biotherapeutics stability indicator widely used by pharmaceutical industries. A variety of stresses that biotherapeutics are exposed to during development can impact particle morphology. By classifying particle morphological differences, stresses that have been applied to monoclonal antibodies (mAbs) can be identified. This study aims to evaluate common biotherapeutic drug storage and shipment conditions that are known to impact protein aggregation. Two different studies were conducted to capture particle images using micro-flow imaging and to classify particles using a convolutional neural network. The first study evaluated particles produced in response to agitation, heat, and freeze-thaw stresses in one mAb formulated in five different formulations. The second study evaluated particles from two common drug containers, a high-density polyethylene bottle and a glass vial, in six mAbs exposed solely to agitation stress. An extension of this study was also conducted to evaluate the impact of sequential stress exposure compared to exposure to one stress alone, on particle morphology. Overall, the convolutional neural network was able to classify particles belonging to a particular formulation or container. These studies indicate that storage and shipping stresses can impact particle morphology according to formulation composition and mAb.

Reconsidering freeze-induced protein aggregation: Air bubbles as the root cause of ice-water interface stress

Freeze-induced stress causing aggregation of proteins has typically been primarily attributed to the ice-water interface. However, we hypothesize that the underlying observed and perceived detrimental effect of ice is, to some extent, attributed to air bubbles expelled from ice crystal lattices or to nanobubbles existing prior to freezing. The reduction of dissolved air was achieved via a deaeration process by placing samples in a reduced pressure chamber, while the reduction of nanobubbles was achieved by filtering samples via a syringe filter. The results showed that the reduction of both dissolved air molecules and stable colloidal nanobubbles in a bovine IgG solution prior to freezing led to a significant decrease in aggregation after thawing compared to untreated samples (∼6,000 vs. ∼ 40,000 particles/mL at a freezing rate of 100 K/s, respectively). The deaeration-filtration treatment works additively with cryoprotectants such as trehalose, further reducing the freeze-induced aggregation of IgG. The results also demonstrated that air-water interfacial aggregation of IgG in bulk liquid samples is a time-dependent process. The number of IgG subvisible particles increased with time and temperature, suggesting that random collisions of denatured molecules promoted the formation of aggregates with spherical morphology. In contrast, the IgG subvisible count after freeze-thawing had already reached its nominal value, suggesting a time-independent process where denatured protein molecules were compressed between ice crystals into filament-like aggregates. In summary, the findings shift the current paradigm from ice crystals being the main destabilizing factor during freezing to air bubbles, although the two are intertwined. From a translational aspect, this study underscores the value of deaeration-filtration as an essential supplemental process that can be applied in addition to formulation approaches such as the use of cryoprotectants to further reduce freezing stress on proteins and increase their stability.

Mitigation Strategies against Antibody Aggregation Induced by Oleic Acid in Liquid Formulations

Polysorbates 20 and 80 (PS20 and PS80) are commonly used in the formulations of biologics to protect against interfacial stresses. However, these surfactants can degrade over time, releasing free fatty acids, which assemble into solid particles or liquid droplets. Here, we apply a droplet microfluidic platform to analyze the interactions between antibodies and oleic acid, the primary free fatty acid resulting from the hydrolysis of PS80. We show that antibodies adsorb within seconds to the polar oleic acid-water interface, forming a viscoelastic protein layer that leads to particle formation upon mechanical rupture. By testing two different monoclonal antibodies of pharmaceutical origin, we show that the propensity to form a rigid viscoelastic layer is protein-specific. We further demonstrate that intact PS80 is effective in preventing antibody adsorption at the oleic acid-water interface only at low antibody concentrations and low pH, where oleic acid is fully protonated. Importantly, introduction of the amino acid l-arginine prevents the formation of the interfacial layer and protein particles even at high antibody concentrations (180 mg mL-1). Overall, our findings indicate that oleic acid droplets in antibody formulations can lead to the formation of protein particles via an interface-mediated mechanism. Depending on the conditions, intact PS80 alone might not be sufficient to protect against antibody aggregation. Additional mitigation strategies include the optimization of protein physicochemical properties, pH, and the addition of arginine.

Lyso-phosphatidylcholine as an interfacial stabilizer for parenteral monoclonal antibody formulations

Therapeutic proteins suffer from physical and chemical instability in aqueous solution. Polysorbates and poloxamers are often added for protection against interfacial stress to prevent protein aggregation and particle formation. Previous studies have revealed that the hydrolysis and oxidation of polysorbates in parenteral formulations can lead to the formation of free fatty acid particles, insufficient long-term stabilization, and protein oxidation. Poloxamers, on the other hand, are considered to be less effective against protein aggregation. Here we investigated two lyso-phosphatidylcholines (LPCs) as potential alternative surfactants for protein formulations, focusing on their physicochemical behavior and their ability to protect against the formation of monoclonal antibody particles during mechanical stress. The hemolytic activity of LPC was tested in varying ratios of plasma and buffer mixtures. LPC effectively stabilized mAb formulations when shaken at concentrations several orders of magnitude below the onset of hemolysis, indicating that the potential for erythrocyte damage by LPC is non-critical. LPC formulations subjected to mechanical stress through peristaltic pumping exhibited comparable protein particle formation to those containing polysorbate 80 or poloxamer 188. Profile analysis tensiometry and dilatational rheology indicated that the stabilizing effect likely arises from the formation of a viscoelastic film at approximately the CMC. Data gathered from concentration-gradient multi-angle light scattering and isothermal titration calorimetry support this finding. Surfactant desorption was evaluated through sub-phase exchange experiments. While LPCs readily desorbed from the interface, resorption occurred rapidly enough in the bulk solution to prevent protein adsorption. Overall, LPCs behave similarly to polysorbate with respect to interfacial stabilization and show promise as a potential substitute for polysorbate in parenteral protein formulations.

Utilizing a hydrophobic primary container surface to reduce the formation of subvisible particles in monoclonal antibody solution caused by fluid shear

The exposure of protein molecules to interfaces may cause protein aggregation and particle formation in protein formulations, especially hydrophobic interfaces, which may promote protein aggregation in solution. In this study, we found that modification of the surface properties by application of a hydrophobic Octadecyltrichlorosilane (OTS) could reduce the generation of protein aggregates and particles in protein solution induced by fluid shear. A stable protein adsorption layer was formed at the hydrophobic interface through the strong hydrophobic interaction between the protein and hydrophobic surface, which could prevent the aggregated protein from falling off into the bulk solution to form subvisible particles and insoluble protein aggregates. In addition, human complement enzyme linked immunosorbent assay results showed that the particles that were generated in the OTS-coated container did not activate human complement which indicated the OTS-coated container could be used as primary containers for certain types of monoclonal antibody formulation.

Correlating Differences in the Surface Activity to Interface-Induced Particle Formation in Different Protein Modalities: IgG mAb Versus Fc-Fusion Protein

The propensity of protein-based biologics to form protein particles during bioprocessing can be related to their interfacial properties. In this study, we compare the surface activity and interfacial film properties of two structurally different biologics, an IgG and Fc-fusion, in the absence and presence of interfacial dilatational stresses, and correlate these differences to their tendency to form interface-induced protein particles. Our results show that interface-induced particle formation is protein-dependent, with the Fc-fusion demonstrating greater interfacial stability. This observation can be correlated with faster adsorption kinetics of the Fc-fusion protein, and formation of a less incompressible film at the air-liquid interface. The addition of polysorbate 80 (PS80), commonly added to mitigate protein particle formation, led to a surfactant-dominant interface for quiescent conditions and coadsorption of protein and surfactant for the Fc-fusion when exposed to interfacial stress. On the other hand, for the IgG molecule, the surface always remained surfactant dominant. Image analysis demonstrated that PS80 was more effective in mitigating particle formation for the IgG than Fc-fusion. This suggests that a surfactant-dominant interface is necessary to prevent interface-induced protein particle formation. Further, while PS80 is effective in mitigating particle formation in the IgG formulation, it may not be the best choice for other protein modalities.

Pharmaceutical proteins at the interfaces and the role of albumin

A critical measure of the quality of pharmaceutical proteins is the preservation of native conformations of the active pharmaceutical ingredients. Denaturation of the active proteins in any step before administration into patients could lead to loss of potency and/or aggregation, which is associated with an increased risk of immunogenicity of the products. Interfacial stress enhances protein instability as their adsorption to the air-liquid and liquid-solid interfaces are implicated in the formation of denatured proteins and aggregates. While excipients in protein formulations have been employed to reduce the risk of aggregation, the roles of albumin as a stabilizer have not been reviewed from practical and theoretical standpoints. The amphiphilic nature of albumin makes it accumulate at the interfaces. In this review, we aim to bridge the knowledge gap between interfacial instability and the influence of albumin as a surface-active excipient in the context of reducing the immunogenicity risk of protein formulations.

Understanding the Impact of Combined Hydrodynamic Shear and Interfacial Dilatational Stress, on Interface-Mediated Particle Formation for Monoclonal Antibody Formulations

During biomanufacturing, several unit operations expose solutions of biologics to multiple stresses, such as hydrodynamic shear forces due to fluid flow and interfacial dilatational stresses due to mechanical agitation or bubble collapse. When these stresses individually act on proteins adsorbed to interfaces, it results in an increase in protein particles in the bulk solution, a phenomenon referred to as interface-induced protein particle formation. However, an understanding of the dominant cause, when multiple stresses are acting simultaneously or sequentially, on interface-induced protein particle formation is limited. In this work, we established a unique set-up using a peristaltic pump and a Langmuir-Pockels trough to study the impact of hydrodynamic shear stress due to pumping and interfacial dilatational stress, on protein particle formation. Our experimental results together demonstrate that for protein solutions subjected to various combinations of stress (i.e., interfacial and hydrodynamic stress in different sequences), surface pressure values during adsorption and when subjected to compression/dilatational stresses, showed no change, suggesting that the interfacial properties of the protein film are not impacted by pumping. The concentration of protein particles is an order of magnitude higher when interfacial dilatational stress is applied at the air-liquid interface, compared to solutions that are only subjected to pumping. Furthermore, the order in which these stresses are applied, have a significant impact on the concentration of protein particles measured in the bulk solution. Together, these studies conclude that for biologics exposed to multiple stresses throughout bioprocessing and manufacturing, exposure to air-liquid interfacial dilatational stress is the predominant mechanism impacting protein particle formation at the interface and in the bulk solution.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Study of Monoclonal Antibody Aggregation at the Air-Liquid Interface under Flow by ATR-FTIR Spectroscopic Imaging

Throughout bioprocessing, transportation, and storage, therapeutic monoclonal antibodies (mAbs) experience stress conditions that may cause protein unfolding and/or chemical modifications. Such structural changes may lead to the formation of aggregates, which reduce mAb potency and may cause harmful immunogenic responses in patients. Therefore, aggregates need to be detected and removed or ideally prevented from forming. Air-liquid interfaces, which arise during various stages of bioprocessing, are one of the stress factors causing mAb aggregation. In this study, the behavior of an immunoglobulin G (IgG) at the air-liquid interface was investigated under flow using macro attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging. This chemically specific imaging technique allows observation of adsorption of IgG to the air-liquid interface and detection of associated secondary structural changes. Chemical images revealed that IgG rapidly accumulated around an injected air bubble under flow at 45 °C; however, no such increase was observed at 25 °C. Analysis of the second derivative spectra of IgG at the air-liquid interface revealed changes in the protein secondary structure associated with increased intermolecular β-sheet content, indicative of aggregated IgG. The addition of 0.01% w/v polysorbate 80 (PS80) reduced the amount of IgG at the air-liquid interface in a static setup at 30 °C; however, this protective effect was lost at 45 °C. These results suggest that the presence of air-liquid interfaces under flow may be detrimental to mAb stability at elevated temperatures and demonstrate the power of ATR-FTIR spectroscopic imaging for studying the structural integrity of mAbs under bioprocessing conditions.

Using Passive Microrheology to Measure the Evolution of the Rheological Properties of NIST mAb Formulations during Adsorption to the Air-Water Interface

The development of novel protein-based therapeutics, such as monoclonal antibodies (mAbs), is often limited due to challenges associated with maintaining the stability of these formulations during manufacturing, storage, and clinical administration. An undesirable consequence of the instability of protein therapeutics is the formation of protein particles. MAbs can adsorb to interfaces and have the potential to undergo partial unfolding as well as to form viscoelastic gels. Further, the viscoelastic properties may be correlated with their aggregation potential. In this work, a passive microrheology technique was used to correlate the evolution of surface adsorption with the evolution of surface rheology of the National Institute of Standards and Technology (NIST) mAb reference material (NIST mAb) and interface-induced subvisible protein particle formation. The evolution of the surface adsorption and interfacial shear rheological properties of the NIST mAb was recorded in four formulation conditions: two different buffers (histidine vs phosphate-buffered saline) and two different pHs (6.0 and 7.6). Our results together demonstrate the existence of multiple stages for both surface adsorption and surface rheology, characterized by an induction period that appears to be purely viscous, followed by a sharp increase in protein molecules at the interface when the film rheology is viscoelastic and ultimately a slowdown in the surface adsorption that corresponds to the formation of solid-like or glassy films at the interface. When the transitions between the different stages occurred, they were dependent on the buffer/pH of the formulations. The onset of these transitions can also be correlated to the number of protein particles formed at the interface. Finally, the addition of polysorbate 80, an FDA-approved surfactant used to mitigate protein particle formation, led to the interface being surfactant-dominated, and the resulting interface remained purely viscous.

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.

Correlating Surface Activity with Interface-Induced Aggregation in a High-Concentration mAb Solution

Interface-induced aggregation resulting in protein particle formation is an issue during the manufacturing and storage of protein-based therapeutics. High-concentration formulations of therapeutic proteins are even more prone to protein particle formation due to increased protein-protein interactions. However, the dependence of interface-induced protein particle formation on bulk protein concentration is not understood. Furthermore, the formation of protein particles is often mitigated by the addition of polysorbate-based surfactants. However, the details of surfactant-protein interactions that prevent protein particle formation at high concentrations remain unclear. In this work, a tensiometer technique was used to evaluate the surface pressure of an industrially relevant mAb at different bulk concentrations, and in the absence and presence of a polysorbate-based surfactant, polysorbate 20 (PS20). The adsorption kinetics was correlated with subvisible protein particle formation at the air-water interface and in the bulk protein solution using a microflow imaging technique. Our results showed that, in the absence of any surfactant, the number of subvisible particles in the bulk protein solutions increased linearly with mAb concentration, while the number of protein particles measured at the interface showed a logarithmic dependence on bulk protein concentration. In the presence of surfactants above the critical micelle concentration (CMC), our results for low-concentration mAb solutions (10 mg/mL) showed an interface that is surfactant-dominated, and particle characterization results showed that the addition of the surfactant led to reduced particle formation. In contrast, for the highest concentration (170 mg/mL), coadsorption of proteins and surfactants was observed at the air-water interface, even for surfactant formulations above CMC and the surfactant did not mitigate subvisible particle formation. Our results taken together provide evidence that the ratio between the surfactant and mAb molecules is an important consideration when formulating high-concentration mAb therapeutics to prevent unwanted aggregation.

Combined Effect of Shaking Orbit and Vial Orientation on the Agitation-Induced Aggregation of Proteins

Orbital shaking in a glass vial is a commonly used forced degradation test to evaluate protein propensity for agitation-induced aggregation. Vial shaking in horizontal orientation has been widely recommended to maximize the air-liquid interface area while ensuring solution contact with the stopper. We evaluated the impact of shaking orbit diameter and frequency, and glass vial orientation (horizontal versus vertical) on the aggregation of three proteins prepared in surfactant-free formulation buffers. As soon as an orbit-specific frequency threshold was reached, an increase in turbidity was observed for the three proteins in vertical orientation only when using a 3 mm agitation orbit, and in horizontal orientation only when using a 30 mm agitation orbit. Orthogonal analyses confirmed turbidity was linked to protein aggregation. The most turbid samples had a visually more homogeneous appearance in vertical than in horizontal orientation, in line with the predicted dispersion of air and liquid phases obtained from computational fluid dynamics agitation simulations. Both shaking orbits were used to assess the performance of nonionic surfactants. We show that the propensity of a protein to aggregate in a vial agitated in horizontal or vertical orientation depends on the shaking orbit, and confirm that Brij® 58 and FM1000 prevent proteins from agitation-induced aggregation at lower concentrations than polysorbate 80.

The Effects of Excipients on Freeze-dried Monoclonal Antibody Formulation Degradation and Sub-Visible Particle Formation during Shaking

PURPOSES

We previously reported an unexpected phenomenon that shaking stress could cause more protein degradation in freeze-dried monoclonal antibody (mAb) formulations than liquid ones (J Pharm Sci, 2022, 2134). The main purposes of the present study were to investigate the effects of shaking stress on protein degradation and sub-visible particle (SbVP) formation in freeze-dried mAb formulations, and to analyze the factors influencing protein degradation during production and transportation.

METHODS

The aggregation behavior of mAb-X formulations during production and transportation was simulated by shaking at a rate of 300 rpm at 25°C for 24 h. The contents of particles and monomers were analyzed by micro-flow imaging, dynamic light scattering, size exclusion chromatography, and ultraviolet - visible (UV-Vis) spectroscopy to compare the protective effects of excipients on the aggregation of mAb-X.

RESULTS

Shaking stress could cause protein degradation in freeze-dried mAb-X formulations, while surfactant, appropriate pH, polyol mannitol, and high protein concentration could impact SbVP generation. Water content had little effect on freeze-dried protein degradation during shaking, as far as the water content was controlled in the acceptable range as recommended by mainstream pharmacopoeias (i.e., less than 3%).

CONCLUSIONS

Shaking stress can reduce the physical stability of freeze-dried mAb formulations, and the addition of surfactants, polyol mannitol, and a high protein concentration have protective effects against the degradation of model mAb formulations induced by shaking stress. The experimental results provide new insight for the development of freeze-dried mAb formulations.

Solid-Solid Interfacial Contact of Tubing Walls Drives Therapeutic Protein Aggregation During Peristaltic Pumping

Peristaltic pumping during bioprocessing can cause therapeutic protein loss and aggregation during use. Due to the complexity of this apparatus, root-cause mechanisms behind protein loss have been long sought. We have developed new methodologies isolating various peristaltic pump mechanisms to determine their effect on monomer loss. Closed-loops of peristaltic tubing were used to investigate the effects of peristaltic pump parameters on temperature and monomer loss, whilst two mechanism isolation methodologies are used to isolate occlusion and lateral expansion-relaxation of peristaltic tubing. Heat generated during peristaltic pumping can cause heat-induced monomer loss and the extent of heat gain is dependent on pump speed and tubing type. Peristaltic pump speed was inversely related to the rate of monomer loss whereby reducing speed 2.0-fold increased loss rates by 2.0- to 5.0-fold. Occlusion is a parameter that describes the amount of tubing compression during pumping. Varying this to start the contacting of inner tubing walls is a threshold that caused an immediate 20-30% additional monomer loss and turbidity increase. During occlusion, expansion-relaxation of solid-liquid interfaces and solid-solid interface contact of tubing walls can occur simultaneously. Using two mechanisms isolation methods, the latter mechanism was found to be most destructive and a function of solid-solid contact area, where increasing the contact area 2.0-fold increased monomer loss by 1.6-fold. We establish that a form of solid-solid contact mechanism whereby the contact solid interfaces disrupt adsorbed protein films is the root-cause behind monomer loss and protein aggregation during peristaltic pumping.

Exploring a role for flow-induced aggregation assays in platform formulation optimisation for antibody-based proteins

The development time of therapeutic monoclonal antibodies (mAbs) has been shortened by formulation platforms and the assessment of 'protein stability' using 'developability' assays. A range of assays are used to measure stability to a variety of stresses, including forces induced by hydrodynamic flow. We have previously developed a low-volume Extensional Flow Device (EFD) which subjects proteins to defined fluid flow fields in the presence of glass interfaces and used it to identify robust candidate sequences. Here, we study the aggregation of mAbs and Fc-fusion proteins using the EFD and orbital shaking under different formulations, investigating the relationship between these assays and evaluating their potential in formulation optimisation. EFD experiments identified the least aggregation-prone molecule using a fraction of the material and time involved in traditional screening. We also show that the EFD can differentiate between different formulations and that protective formulations containing polysorbate 80 stabilised poorly developable Fc-fusion proteins against EFD-induced aggregation up to two-fold. Our work highlights common platform formulation additives that affect the extent of aggregation under EFD-stress, as well as identifying factors that modulate the underlying aggregation mechanism. Together, our data could aid the choice of platform formulations early in development for next-generation therapeutics including fusion proteins.

Mechanism of Protein-PDMS Visible Particles Formation in Liquid Vial Monoclonal Antibody Formulation

Visible particles (VPs) formation in liquid monoclonal antibody formulations is a critical quality issue. Formulations that include poloxamer 188 (PX188) as a surfactant are prone to the formation of VPs comprising aggregated complexes of protein and polydimethylsiloxane (PDMS; silicone oil) derived from primary containers. However, the mechanisms through which these VPs form are complicated and remain to be fully elucidated. This study demonstrates for the first time the dominant spot and pathway of protein-PDMS VP formation in a particular liquid vial formulation. Specifically, when a vial sealed with a PDMS-coated stopper is stored in an upright position under conditions whereby the antibody solution has become well-adhered to the stopper and an air phase exists in the vicinity, protein-PDMS aggregates form on the stopper and are then desorbed into the drug solution to be detected as VPs. Here, we evaluated the effects of several factors on VP formation: adhesion of the drug solution to the stopper, storage orientation, silicone coating on the stopper, vial material, and hydrophobicity of PX188. Remarkably, we found that changing any one of the factors could significantly affect VP formation. Our findings are instructive for better understanding the mechanisms of VP formation in vial products and can provide strategies for VP mitigation in biotherapeutics.

Steps toward nebulization in-use studies to understand the stability of new biological entities

The need for novel biological drugs against respiratory diseases has been highlighted during the Coronavirus (COVID-19) pandemic. The use of inhalation presents challenges to drug product stability, which is especially true for delivery using nebulizers (jet versus mesh technologies). The late-stage process of drug development in the pharmaceutical industry requires the investigation of in-use stability. In-use studies generate data that are guided by the requirements of regulatory authorities for inclusion in the clinical trial application dossier. In this review, I introduce the initial aspects of in-use stability studies during the development of an aerosol formulation to deliver biologics with a nebulizer. Lessons learned from this experience can guide future development and planning for formulation, analytics, material compatibility, nebulization process, and clinical trial preparations.

Surface-Induced Protein Aggregation and Particle Formation in Biologics: Current Understanding of Mechanisms, Detection and Mitigation Strategies

Protein stability against aggregation is a major quality concern for the production of safe and effective biopharmaceuticals. Amongst the different drivers of protein aggregation, increasing evidence indicates that interactions between proteins and interfaces represent a major risk factor for the formation of protein aggregates in aqueous solutions. Potentially harmful surfaces relevant to biologics manufacturing and storage include air-water and silicone oil-water interfaces as well as materials from different processing units, storage containers, and delivery devices. The impact of some of these surfaces, for instance originating from impurities, can be difficult to predict and control. Moreover, aggregate formation may additionally be complicated by the simultaneous presence of interfacial, hydrodynamic and mechanical stresses, whose contributions may be difficult to deconvolute. As a consequence, it remains difficult to identify the key chemical and physical determinants and define appropriate analytical methods to monitor and predict protein instability at these interfaces. In this review, we first discuss the main mechanisms of surface-induced protein aggregation. We then review the types of contact materials identified as potentially harmful or detected as potential triggers of proteinaceous particle formation in formulations and discuss proposed mitigation strategies. Finally, we present current methods to probe surface-induced instabilities, which represent a starting point towards assays that can be implemented in early-stage screening and formulation development of biologics.

A proteome scale study reveals how plastic surfaces and agitation promote protein aggregation

Protein aggregation in biotherapeutics can reduce their activity and effectiveness. It may also promote immune reactions responsible for severe adverse effects. The impact of plastic materials on protein destabilization is not totally understood. Here, we propose to deconvolve the effects of material surface, air/liquid interface, and agitation to decipher their respective role in protein destabilization and aggregation. We analyzed the effect of polypropylene, TEFLON, glass and LOBIND surfaces on the stability of purified proteins (bovine serum albumin, hemoglobin and α-synuclein) and on a cell extract composed of 6000 soluble proteins during agitation (P = 0.1-1.2 W/kg). Proteomic analysis revealed that chaperonins, intrinsically disordered proteins and ribosomes were more sensitive to the combined effects of material surfaces and agitation while small metabolic oligomers could be protected in the same conditions. Protein loss observations coupled to Raman microscopy, dynamic light scattering and proteomic allowed us to propose a mechanistic model of protein destabilization by plastics. Our results suggest that protein loss is not primarily due to the nucleation of small aggregates in solution, but to the destabilization of proteins exposed to material surfaces and their subsequent aggregation at the sheared air/liquid interface, an effect that cannot be prevented by using LOBIND tubes. A guidance can be established on how to minimize these adverse effects. Remove one of the components of this combined stress - material, air (even partially), or agitation - and proteins will be preserved.

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

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

End-to-End Approach to Surfactant Selection, Risk Mitigation, and Control Strategies for Protein-Based Therapeutics

A survey performed by the AAPS Drug Product Handling community revealed a general, mostly consensus, approach to the strategy for the selection of surfactant type and level for biopharmaceutical products. Discussing and building on the survey results, this article describes the common approach for surfactant selection and control strategy for protein-based therapeutics and focuses on key studies, common issues, mitigations, and rationale. Where relevant, each section is prefaced by survey responses from the 22 anonymized respondents. The article format consists of an overview of surfactant stabilization, followed by a strategy for the selection of surfactant level, and then discussions regarding risk identification, mitigation, and control strategy. Since surfactants that are commonly used in biologic formulations are known to undergo various forms of degradation, an effective control strategy for the chosen surfactant focuses on understanding and controlling the design space of the surfactant material attributes to ensure that the desired material quality is used consistently in DS/DP manufacturing. The material attributes of a surfactant added in the final DP formulation can influence DP performance (e.g., protein stability). Mitigation strategies are described that encompass risks from host cell proteins (HCP), DS/DP manufacturing processes, long-term storage, as well as during in-use conditions.

Exploring the Protein Stabilizing Capability of Surfactants Against Agitation Stress and the Underlying Mechanisms

The application of surfactants in liquid protein formulation is a common practice to protect proteins from liquid-air interface-induced protein aggregation. Typically, Polysorbate 20 or 80 are used, but degradation of these surfactants can result in particle formation and/or protein degradation. The purpose of the current study was to directly compare three alternative protein stabilizing molecules - Poloxamer 188, hydroxypropyl-cyclodextrin and a trehalose-based surfactant - to Polysorbate 80 for their capacities to reduce agitation-induced protein aggregation and particle formation; and furthermore, investigate their underlying protein stabilizing mechanisms. To this end, a small-volume, rapid agitation stress approach was used to quantify the molecules' abilities to stabilize two model proteins. This assay was presented to be a powerful tool to screen the protein stabilizing capability of surfactants using minimum of material and time. SEC, turbidity measurements and particle analysis showed an efficient protein stabilization of all tested surfactants as well as cyclodextrin. STD-NMR and dynamic surface tension measurements indicated the competitive surface adsorption to be the main protein stabilizing mechanism of the three surfactants tested. It might also play a role to some extent in the protein stabilization by HPβCD. However, additional mechanisms might also contribute to protein stabilization leaving room for further investigations.

Machine Learning Analysis Provides Insight into Mechanisms of Protein Particle Formation Inside Containers During Mechanical Agitation

Container choice can influence particle generation within protein formulations. Incompatibility between proteins and containers can manifest as increased particle concentrations, shifts in particle size distributions and changes in particle morphology distributions. In this study, flow imaging microscopy (FIM) combined with machine learning-based goodness-of-fit hypothesis testing algorithms were used in accelerated stability studies to investigate the impact of containers on particle formation. Containers in four major container categories subdivided into eleven container types were filled with monoclonal antibody formulations and agitated with and without headspace, producing subvisible particles. Digital images of the particles were recorded using flow imaging microscopy and analyzed with machine learning algorithms. Particle morphology distributions depended on container category and type, revealing differences that would not have been obvious by analysis of particle concentrations or container surface characteristics alone. Additionally, the algorithm was used to compare morphologies of particles generated in containers against those generated using isolated stresses at air-liquid and container-air-liquid interfaces. These comparisons showed that the morphology distributions of particles formed during agitation most closely resemble distributions that result from exposure of proteins to moving triple interface lines at points where container-air-liquid interfaces intersect. The approach described here can be used to identify dominant causes of particle generation due to protein-container interactions.

Reaching the breaking point: Effect of tubing characteristics on protein particle formation during peristaltic pumping

Peristaltic pumping has been identified as a cause for protein particle formation during manufacturing of biopharmaceuticals. To give advice on tubing selection, we evaluated the physicochemical parameters and the propensity for tubing and protein particle formation using a monoclonal antibody (mAb) for five different tubings. After pumping, particle levels originating from tubing and protein differed substantially between the tubing types. An overall low shedding of tubing particles by wear was linked to low surface roughness and high abrasion resistance. The formation of mAb particles upon pumping was dependent on the tubing hardness and surface chemistry. Defined stretching of tubing filled with mAb solution revealed that aggregation increased with higher strain beyond the breaking point of the protein film adsorbed to the tubing wall. This is in line with the decrease in protein particle concentration with increasing tubing hardness. Furthermore, material composition influenced particle formation propensity. Faster adsorption to materials with higher hydrophobicity is suspected to lead to a higher protein film renewal rate resulting in higher protein particle counts. Overall, silicone tubing with high hardness led to least protein particles during peristaltic pumping. Results from this study emphasize the need of proper tubing selection to minimize protein particle generation upon pumping.

Differential Surface Adsorption Phenomena for Conventional and Novel Surfactants Correlates with Changes in Interfacial mAb Stabilization

Protein adsorption on surfaces can result in loss of drug product stability and efficacy during the production, storage, and administration of protein-based therapeutics. Surface-active agents (excipients) are typically added in protein formulations to prevent undesired interactions of proteins on surfaces and protein particle formation/aggregation in solution. The objective of this work is to understand the molecular-level competitive adsorption mechanism between the monoclonal antibody (mAb) and a commercially used excipient, polysorbate 80 (PS80), and a novel excipient, N-myristoyl phenylalanine-N-polyetheramine diamide (FM1000). The relative rate of adsorption of PS80 and FM1000 was studied by pendant bubble tensiometry. We find that FM1000 saturates the interface faster than PS80. Additionally, the surface-adsorbed amounts from X-ray reflectivity (XRR) measurements show that FM1000 blocks a larger percentage of interfacial area than PS80, indicating that a lower bulk FM1000 surface concentration is sufficient to prevent protein adsorption onto the air/water interface. XRR models reveal that with an increase in mAb concentration (0.5-2.5 mg/mL: IV based formulations), an increased amount of PS80 concentration (below critical micelle concentration, CMC) is required, whereas a fixed value of FM1000 concentration (above its relatively lower CMC) is sufficient to inhibit mAb adsorption, preventing mAb from co-existing with surfactants on the surface layer. With this observation, we show that the CMC of the surfactant is not the critical factor to indicate its ability to inhibit protein adsorption, especially for chemically different surfactants, PS80 and FM1000. Additionally, interface-induced aggregation studies indicate that at minimum surfactant concentration levels in protein formulations, fewer protein particles form in the presence of FM1000. Our results provide a mechanistic link between the adsorption of mAbs at the air/water interface and the aggregation induced by agitation in the presence of surfactants.

Insulin aggregation starts at dynamic triple interfaces, originating from solution agitation

The consequences of agitation on protein stability are particularly relevant to therapeutic proteins. However, the precise contribution of the different effects induced by agitation in pathways leading to protein denaturation and aggregation at interfaces is not entirely understood. In particular, the contribution of a moving triple line, induced by the sweeping of a solution meniscus on a container wall upon agitation, has only been rarely assessed. In this article, we therefore designed experimental setups to analyze how mixing, shear stress, and dynamic triple interfaces influence insulin aggregation in physiological conditions. This has been achieved by controlling agitation speed, shear stress, and the extension of triple interfaces in order to shed light on the contribution of different agitation-induced effects on insulin aggregation in physiological conditions. We demonstrate that strong agitation is necessary for the onset of insulin aggregation, while the growth of the aggregates is sustained even under weak agitation. Kinetic insulin aggregation studies in conditions of intermittent wetting show that the aggregation rate correlates with the amount of dynamic triple interfaces that the proteins are exposed to. Finally, we demonstrate that the triple line, where the protein solution, the air, and a hydrophobic surface meet constitutes a preferential early aggregation site.

A Mechanistic Understanding of Monoclonal Antibody Interfacial Protection by Hydrolytically Degraded Polysorbate 20 and 80 under IV Bag Conditions

PURPOSE

Polysorbates (PS) contain polyoxyethylene (POE) sorbitan/isosorbide fatty acid esters that can partially hydrolyze over time in liquid drug products to generate degradants and a remaining intact PS fraction with a modified ester distribution. The degradants are composed of free fatty acids (FFAs) --primarily lauric acid for PS20 and oleic acid for PS80-- and POE head groups. We previously demonstrated that under IV bag agitation conditions, mAb1 (a surface-active IgG4) aggregation increased with increasing amounts of degradants for PS20 but not for PS80. The purpose of this work is to understand the mechanism behind this observation.

METHODS

The surface tension of the remaining intact PS fraction without degradants was modeled and compared with that of enzymatically degraded PS solutions. Next, mAb1 aggregation in saline was measured in the presence of laurate and oleate salts during static storage. Lastly, colloidal and conformational stability of mAb1 in the presence of these salts was investigated through differential scanning fluorimetry and dynamic light scattering under IV bag solution conditions.

RESULTS

The surface tension was primarily influenced by FFAs rather than the modified ester distribution of the remaining intact PS. MAb1 bulk aggregation increased in the presence of laurate but not oleate salts. Both salt types increased the melting temperature of mAb1 indicating FFA-mAb1 interactions. However, only laurate salt increased mAb1 self-association potentially explaining the higher aggregation propensity in its presence.

CONCLUSION

Our results help explain the observed differences between hydrolytically degraded PS20 and PS80 in affecting mAb1 aggregation under IV bag agitation conditions.

Proteins on the rack: Mechanistic studies on protein particle formation during peristaltic pumping

Peristaltic pumping can cause protein particle formation. The expected causes were unfolding by heat in the pump head, oxidative stress by cavitation generated during roller movement, interfacial adsorption to the tubing wall and mechanical stress by stretching of the tubing itself. The pump head reached 28°C during experiments stayed well below the onset of the melting point of the proteins. Thus, heat may only be a relevant root cause for proteins containing domains with very low unfolding temperature. Analysis by terephthalic acid dosimetry and protein oxidation via RP-HPLC ruled out major induction of reactive hydroxyl radicals by pumping, indicating that cavitation does not play a significant role in particle generation. Addition of surfactants suppresses protein adsorption to the tubing wall and drastically reduced protein particle formation. This indicates that interfacial protein adsorption is a key element. Repeated stretching of tubing filled with protein solution led to the formation of protein particles, demonstrating that expansion and compression of the protein film on the tubing surface is the second key component for particle formation. Thus, protein particle generation during peristaltic pumping originates from the formation of a protein film on the tubing surface which gets stretched and compressed, leading to film fragments entering the bulk solution. This interplay of protein film formation and its rupture has been also observed at liquid/liquid or liquid/air interfaces.

Characterization of Grinding-Induced Subvisible Particles and Free Radicals in a Freeze-Dried Monoclonal Antibody Formulation

PURPOSES

The primary objectives of this study were to investigate the degradation mechanisms of freeze-dried monoclonal antibody (mAb) formulations under mechanical grinding, assess the sensitivity and suitability of various particle analysis techniques, analyze the structure of the collected subvisible particles (SbVPs), and analyze the antioxidant mechanism of methionine (Met) under degradation process to gain a thorough understanding of the phenomenon.

METHODS

The freeze-dried mAb-X formulations underwent grinding, and the resultant SbVPs were characterized through visual inspection, flow imaging microscopy, dynamic light scattering, ultraviolet-visible spectroscopy, and size-exclusion high-performance liquid chromatography. We further evaluated the effect of different temperatures and the free radical scavenger Met on SbVP formation. The produced free radicals were detected using electron paramagnetic resonance, and Met S-oxide formation was detected using liquid chromatography-mass spectrometry. In addition, we analyzed the obtained SbVPs using capillary electrophoresis sodium dodecyl sulfate and Fourier transform infrared spectroscopy.

RESULTS

Grinding leads to SbVP formation under high temperature and free radical formation. Free radicals produced during grinding require the participation of a macromolecule. Met could then bind to the produced free radicals, thus partially protecting mAb-X from degradation while itself undergoing oxidation to form Met(O). Sensitivity differences between different particle analysis techniques were evaluated, and the obtained SbVPs showed significant changes in secondary structure and the formation of covalent aggregates and fragments.

CONCLUSIONS

Met plays the role of an antioxidant in protecting macromolecules by quenching the free radicals produced during grinding. To thoroughly characterize SbVPs, multiple and orthogonal particle analysis techniques should be used, and if necessary, SbVPs should be processed by enrichment to accurately analyze primary and high order structures.

Positive response to surfactants on the interfacial behavior and aggregation stability of Fab fragments from yolk immunoglobulin

The antigen binding fragment (Fab) is pepsin-digested product from egg yolk immunoglobulin (IgY), which shows lower immunogenicity and higher antibacterial activity. However, it limited the application of Fab due to the spontaneous adsorption and aggregation at the air-liquid interface. The present work is to investigate the effect of surfactants polysorbate 20 (PS20), poloxamer 188 (P188), and polyethylene glycol (PEG) on the aggregation stability of Fab of IgY. The results confirmed the positive role of surfactants in improving Fab stability. PS20 could effectively prevent the generation of Fab aggregates (DLS and light-obscuration analysis). It could also distinctly increase the internal hydrophobicity level, fortify the surface charge by altering the molecular conformational characteristics of Fab. The results of CLSM and surface tension demonstrated that P188 and PEG were co-adsorbed with Fab at the air-liquid interface and inhibited the formation of aggregation. PS20 competitively adsorbed in the gap between Fab molecules to inhibit the formation of aggregates. These findings would give an in-depth understanding of protein aggregation behavior influenced by surfactants and provide a theoretical basis for the development of functional food based on Fab active fragments.

Evaluating the combined impact of temperature and application of interfacial dilatational stresses on surface-mediated protein particle formation in monoclonal antibody formulations

Formation of submicron and subvisible protein particles (0.1-100 μm) present a major obstacle during processing and storage of therapeutic proteins. While protein aggregation resulting in particle formation is well-understood in bulk solution, the mechanisms of aggregation due to interfacial stresses is less understood. Particularly, in this study, we focus on understanding the combined effect of temperature and application of interfacial dilatational stresses, on interface-induced protein particle formation, using two industrially relevant monoclonal antibodies (mAbs). The surface activity of Molecule C (MC) and Molecule B (MB) were measured at room temperature (RT) and 4°C in the absence and presence of interfacial dilatation stress using a Langmuir trough. These results were correlated with Micro-flow imaging (MFI) to characterize formation of subvisible protein particles at the interface and in the bulk solution. Our results show that the surface activity for both proteins is temperature dependent. However, the extent of the impact of temperature on the mechanical properties of the monomolecular protein films when subjected to dilatational stresses is protein dependent. Protein particle analysis provided evidence that protein particles formed in bulk solution originate at the interface and are dependent on both application of thermal stresses and interfacial dilatational stresses. In the absence of any interfacial stresses, more and larger protein particles were formed at the interface at RT than at 4°C. When mAb formulations are subjected to interfacial dilatational stresses, protein particle formation in bulk solution was found to be temperature dependent. Together our results validate that mAb solutions maintained at 4°C can lower the surface activity of proteins and reduce their tendency to form interface-induced protein particles both in the absence and presence of interfacial dilatational stresses.

Fatty Acids Can Induce the Formation of Proteinaceous Particles in Monoclonal Antibody Formulations

The presence of subvisible or visible particles in mAb formulations can pose significant challenges to pharmaceutical development as it can lead to reduced shelf life, batch rejection, and recalls. Among all type of particles, proteinaceous particles are the most concerning due to their potential role in immunogenicity. Nevertheless, the underlying mechanism for protein particle formation remains poorly understood. Past research highlighted the importance of interfaces and mechanical agitation in causing protein particle formation. Current research suggests that fatty acids, as impurities present in excipients or as a result of polysorbate degradation, can also induce protein assembly and promote particle formation. In this work, we assessed oleic and lauric acid for their impact on particle formation as each represents the main hydrolysis product of PS80 or PS20, respectively. It was found that co-existence of either fatty acids with 10 mg/mL mAb A can cause protein particles, with a similar morphology to those observed previously in mAb formulations. FTIR spectra showed that the particles are proteinaceous, heterogeneous in its composition, but contain corresponding fatty acids. Interestingly, it was found that oleic acid is significantly more effective in causing protein particles than lauric acid in these experiments. This suggests that PS20 containing formulations might have a lower likelihood to have protein particles compared to PS80 containing mAb formulations if hydrolysis of polysorbate were to occur. Lastly, the presence of 0.01% polysorbate in the mAb A formulation was able to fully mitigate the effect of fatty acids and reduce the protein particles significantly, suggesting a potential mechanism where interfacial action is involved. The present study can help to understand the root cause for protein particles in a mAb formulation where fatty acids are introduced because of polysorbate hydrolysis. With further work, it will help to shed light into product control strategy as well as design approaches for robust mAb products.

Long-term stability predictions of therapeutic monoclonal antibodies in solution using Arrhenius-based kinetics

Long-term stability of monoclonal antibodies to be used as biologics is a key aspect in their development. Therefore, its possible early prediction from accelerated stability studies is of major interest, despite currently being regarded as not sufficiently robust. In this work, using a combination of accelerated stability studies (up to 6 months) and first order degradation kinetic model, we are able to predict the long-term stability (up to 3 years) of multiple monoclonal antibody formulations. More specifically, we can robustly predict the long-term stability behaviour of a protein at the intended storage condition (5 °C), based on up to six months of data obtained for multiple quality attributes from different temperatures, usually from intended (5 °C), accelerated (25 °C) and stress conditions (40 °C). We have performed stability studies and evaluated the stability data of several mAbs including IgG1, IgG2, and fusion proteins, and validated our model by overlaying the 95% prediction interval and experimental stability data from up to 36 months. We demonstrated improved robustness, speed and accuracy of kinetic long-term stability prediction as compared to classical linear extrapolation used today, which justifies long-term stability prediction and shelf-life extrapolation for some biologics such as monoclonal antibodies. This work aims to contribute towards further development and refinement of the regulatory landscape that could steer toward allowing extrapolation for biologics during the developmental phase, clinical phase, and also in marketing authorisation applications, as already established today for small molecules.

Miniaturized Forced Degradation of Therapeutic Proteins and ADCs by Agitation-Induced Aggregation Using Orbital Shaking of Microplates

Microplate-based formulation screening is a powerful approach to identify stabilizing excipients for therapeutic proteins while reducing material requirements. However, this approach is sometimes not representative of studies conducted in relevant container closures. The present study aimed to identify critical parameters for a microplate-based orbital shaking method to screen biotherapeutic formulations by agitation-induced aggregation. For this purpose, an in-depth methodological study was conducted using different shakers, microplates, and plate seals. Aggregation was monitored by size exclusion chromatography, turbidity, and backgrounded membrane imaging. Both shaker quality and liquid-seal contact had substantial impacts on aggregation during shaking and resulted in non-uniform sample treatment when parameters were not suitably selected. The well volume to fill volume ratio (V_well/V_fill) was identified as an useful parameter for achieving comparable aggregation levels between different microplate formats. An optimized method (2400 rpm [a_c 95 m/s²], V_fill 60-100 µL [V_well/V_fill 6-3.6], 24 h, RT, heat-sealed) allowed for uniform sample treatment independent of surface tension and good agreement with vial shaking results. This study provides valuable guidance for miniaturization of shaking stress studies in biopharmaceutical drug development, facilitating method transfer and comparability between laboratories.

Rapid aggregation of therapeutic monoclonal antibodies by bubbling induced air/liquid interfacial and agitation stress at different conditions

Degradation of therapeutic monoclonal antibodies (mAb) due to interfacial agitation through air bubbling was investigated. Samples containing mAb in phosphate buffered saline were subjected to rapid bubbling by using a peristaltic pump at an air flow rate of 11.5 mL/min. Samples were analyzed by visual observation, UV-Vis, fluorescence, circular dichroism and infrared spectroscopy, size-exclusion chromatography (SEC), dynamic light scattering, microscopy, and cell-based activity assays. The stressed samples showed increasing turbidity with bubbling time, with mAb1 showing a protein loss of 53% in the supernatant at the latest time point (240 min), indicating formation of sub-visible and visible aggregates. Aggregate rich samples exhibited altered secondary structure and higher hydrophobicity with 40% reduction in activity. The supernatants of the stressed samples showed unchanged secondary and tertiary structure without the presence of any oligomers in SEC. Furthermore, the impact of various factors that could affect aggregation was investigated and it was found that the extent of aggregation was affected by protein concentration, sample volume, presence of surfactants, temperature, air flow rate, and presence of silicone oil. In conclusion, exposure to air/liquid interfacial stress through bubbling into liquid mAb samples effectively generated sub-visible and visible aggregates, making air bubbling an attractive approach for interfacial stress degradation studies of mAbs.

An accelerated surface-mediated stress assay of antibody instability for developability studies

High physical stability is required for the development of monoclonal antibodies (mAbs) into successful therapeutic products. Developability assays are used to predict physical stability issues such as high viscosity and poor conformational stability, but protein aggregation remains a challenging property to predict. Among different types of stresses, air–water and solid–liquid interfaces are well known to potentially trigger protein instability and induce aggregation. Yet, in contrast to the increasing number of developability assays to evaluate bulk properties, there is still a lack of experimental methods to evaluate antibody stability against interfaces. Here, we investigate the potential of a hydrophobic nanoparticle surface-mediated stress assay to assess the stability of mAbs during the early stages of development. We evaluate this surface-mediated accelerated stability assay on a rationally designed library of 14 variants of a humanized IgG4, featuring a broad span of solubility values and other developability properties. The assay could identify variants characterized by high instability against agitation in the presence of air–water interfaces. Remarkably, for the set of investigated molecules, we observe strong correlations between the extent of aggregation induced by the surface-mediated stress assay and other developability properties of the molecules, such as aggregation upon storage at 45°C, self-association (evaluated by affinity-capture self-interaction nanoparticle spectroscopy) and nonspecific interactions (estimated by cross-interaction chromatography, stand-up monolayer chromatography (SMAC), SMAC*). This highly controlled surface-mediated stress assay has the potential to complement and increase the ability of the current set of screening techniques to assess protein aggregation and developability potential of mAbs during the early stages of drug development.

Abbreviations:AC-SINS: Affinity-Capture Self-Interaction Nanoparticle Spectroscopy; AMS: Ammonium sulfate precipitation; ANS: 1-anilinonaphtalene-8-sulfonate; CIC: Cross-interaction chromatography; DLS: Dynamic light scattering; HIC: Hydrophobic interaction chromatography; HNSSA: Hydrophobic nanoparticles surface-stress assay; mAb: Monoclonal antibody; NP: Nanoparticle; SEC: Size exclusion chromatography; SMAC: Stand-up monolayer chromatography; WT: Wild type

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.

Reversible Photoisomerization in Thin Surface Films from Azo-Functionalized Guanosine Derivatives

Two novel azo-functionalized guanosine derivatives were synthesized, and their photoisomerization process was investigated in molecular monolayers at the air-water interface and in the Langmuir-Blodgett (LB) films on solid substrates. Measurements of surface pressure vs area isotherms, surface potential measurements, UV-visible (vis) absorption spectroscopy, Brewster angle microscopy (BAM), and atomic force microscopy (AFM) were performed. Despite not having a typical amphiphilic molecular structure, the derivatives formed stable films on the water surface. They could also undergo repeated photoisomerization in all of the investigated thin-film configurations. The observations suggest that in the films at the air-water interface, the molecules first exhibit a conformational change, and then they reorient to an energetically more favored orientation. In the LB films transferred onto solid substrates, the isomerization process occurs on a similar time scale as in solution. However, the isomerization efficiency is about an order of magnitude lower than that in solution. Our results show that DNA nucleobases functionalized with azobenzene moieties are suitable candidates for the fabrication of photoactive two-dimensional (2D) materials that can provide all beneficial functionalities of DNA-based compounds.

Hydrolytic polysorbate 20 degradation - Sensitive detection of free fatty acids in biopharmaceuticals via UPLC-QDa analytics with isolator column

The enzymatic hydrolysis of polysorbates, e.g. induced by specific host cell proteins in biologics, is a known risk factor regarding the potential particle formation in the product over time. One of the root causes for this observation is an increase in free fatty acids (FA) within the formulation, which indicates the need for convenient monitoring of FA release. This study presents a novel UPLC-QDa based method to evaluate the content of the FAs esterified to polysorbate 20 (PS20) after hydrolysis. The presented method is label-free, i.e. independent of elaborate fluorophore-labeling and able to directly measure the ionized FAs. Furthermore, the method allows the determination of released FAs as percentage of ester bond hydrolysis and as absolute concentration expressed in ng/mL. Additionally, we describe for the first time in FA analytics the application of an isolator column, to remove trace levels of FAs present in the eluents to improve the sensitivity of the method. Lastly, the capabilities of the newly developed method are proven in case studies with three different monoclonal antibodies, which display characteristic FA release patterns in PS20-containing formulations. In summary, we developed a reliable, sensitive method for FA quantification in biologics, which could also be used as a predictive tool, considering FA solubility, regarding the formation of particles.

Powder suspensions in non-aqueous vehicles for delivery of therapeutic proteins

Formulating biopharmaceuticals is a challenging task due to their complex and sensitive nature. Protein drugs are typically marketed either as an aqueous solution or as a lyophilizate. Usually aqueous solutions are preferred as neither drying nor reconstitution are required. But it may be unfeasible if the protein features low stability. An interesting alternative to avoid at least reconstitution are protein powder suspensions in non-aqueous vehicles. Such formulations combine the ready-to-use approach with the high protein stability in the solid state. Additionally, protein powder suspensions offer a potentially lower viscosity compared to aqueous solutions at high protein concentrations. Besides injection, other application routes might also benefit from the protein powder approach such as topical or inhalational delivery. Protein powders, which can be dispersed in the non-aqueous suspension vehicle, are usually prepared by spray-drying or freeze-drying with an additional milling step, but other techniques have also been described in literature. An ideal powder preparation technique results in minimum protein damage and yields particle sizes in the lower micrometre range and homogeneous particle size distribution enabling subcutaneous or intramuscular injection through hypodermic needles. As suspension vehicles traditional non-aqueous injectable liquids, such as plant oils, may be selected. But they show an inherent high viscosity, which can lead to unacceptable glide forces during injection. Furthermore, the vehicle should provide high product stability with respect to protein integrity and suspension resuspendability. This review will describe how proteins can be formulated as protein powder suspensions in non-aqueous vehicles for subcutaneous injection including potential vehicles, protein powder preparation techniques, protein and suspension physical stability, as well as the use in the field of high concentration protein formulations.