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

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

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

High-Throughput Fluorometric Assay For Quantifying Polysorbate In Biopharmaceutical Products Using Micelle Activated Fluorescence Probe N-Phenyl-1-Naphthylamine

PURPOSE

Polysorbates are among the most used surfactants in biopharmaceutical products containing proteins. Our work aims to develop a high-throughput fluorometric assay to further diversify the analytical toolbox for quantification of PSs.

METHOD

The assay leverages the micelle activated fluorescence signal from N-Phenyl-1-Naphthylamine (NPN). The development and optimization of assay parameters were guided by the pre-defined analytical target profile. Furthermore, NMR was used to probe the interaction between protein, PS80 and NPN in the measurement system and understand protein interference.

RESULTS

All assay parameters including excitation and emission wavelengths, standard curve, NPN concentration, and incubation time have been optimized and adapted to a microplate format, making it compatible with automated solutions that will be pursued in the near future to drive consistency and efficiency in our workflows. The specificity, accuracy, and precision of the assay have been demonstrated through a case study. Furthermore, NMR results provided additional insight into the change of the interaction dynamics between PS80 and NPN as the protein concentration increases. The results indicate minimal interaction between the protein and PS80 at lower concentration. However, when the concentration exceeds 75 mg/mL, there is a significant interaction between the protein and PS-80 micelle and monomer.

CONCLUSION

A high-throughput fluorometric assay has been developed for quantification of polysorbates in biopharmaceutical samples including in-process samples, drug substance and drug product. The assay reported herein could serve as a powerful analytical tool for polysorbate quantification and control, complementing the widely used liquid chromatography with charged aerosol detection method.

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.'

Engineering Core/Ligands Interfacial Anchors of Nanoparticles for Efficiently Inhibiting Both Aβ and Amylin Fibrillization

Accurate construction of artificial nano-chaperones' structure is crucial for precise regulation of protein conformational transformation, facilitating effective treatment of proteopathy. However, how the ligand-anchors of nano-chaperones affect the spatial conformational changes in proteins remains unclear, limiting the development of efficient nano-chaperones. In this study, three types of gold nanoparticles (AuNPs) with different core/ligands interface anchor structures (Au─NH─R, Au─S─R, and Au─C≡C─R, R = benzoic acid) are synthesized as an ideal model to investigate the effect of interfacial anchors on Aβ and amylin fibrillization. Computational results revealed that the distinct interfacial anchors imparted diverse distributions of electrostatic potential on the nanointerface and core/ligands bond strength of AuNPs, leading to differential interactions with amyloid peptides. Experimental results demonstrated that all three types of AuNPs exhibit site-specific inhibitory effects on Aβ40 fibrillization due to preferential binding. For amylin, amino-anchored AuNPs demonstrate strong adsorption to multiple sites on amylin and effectively inhibit fibrillization. Conversely, thiol- and alkyne-anchored AuNPs adsorb at the head region of amylin, promoting folding and fibrillization. This study not only provided molecular insights into how core/ligands interfacial anchors of nanomaterials induce spatial conformational changes in amyloid peptides but also offered guidance for precisely engineering artificial-chaperones' nanointerfaces to regulate the conformational transformation of proteins.

Microfluidic Stress Device to Decouple the Synergistic Effect of Shear and Interfaces on Antibody Aggregation

Protein denaturation and aggregation resulting from the effects of interfacial stress, often enhanced by flow and shear stress, pose significant challenges in the production of therapeutic proteins and monoclonal antibodies. The influence of flow on protein stability is closely intertwined with interfacial effects. In this study, we have developed a microfluidic device capable of exposing low volume (< 320 µL) protein solutions to highly uniform shear. To disentangle the synergistic impact of flow and interfaces on protein aggregation, we fabricated two devices composed of different materials, namely poly(methyl methacrylate) (PMMA) and stainless steel. Upon application of shear, we observed formation of protein particles in the micron-size range. Notably, The number of particles generated in the steel devices was ∼ 3.5 fold lower than in the PMMA device, hinting at an interface-mediated effect. With increasing the protein concentration from 1 to 50 mg/mL we observed a saturation in the amount of aggregates, further confirming the key role of solid-liquid interfaces in inducing particle formation. Introduction of non-ionic surfactants prevented protein aggregation, even at the highest tested protein concentration and low surfactant concentrations of 0.05 mg/mL. Overall, our findings corroborate the synergistic impact of shear and interface effects on protein aggregation. The device developed in this study offers a small-scale platform for assessing the stability of antibody formulations throughout various stages of the development and manufacturing process.

Dual Functionality of Poloxamer 188 in Freeze-Dried Protein Formulations: A Stabilizer in Frozen Solutions and a Bulking Agent in Lyophiles

Poloxamer 188 (P188) was hypothesized to be a dual functional excipient, (i) a stabilizer in frozen solution to prevent ice-surface-induced protein destabilization and (ii) a bulking agent to provide elegant lyophiles. Based on X-ray diffractometry and differential scanning calorimetry, sucrose, in a concentration-dependent manner, inhibited P188 crystallization during freeze-drying, while trehalose had no such effect. The recovery of lactate dehydrogenase (LDH), the model protein, was evaluated after reconstitution. While low LDH recovery (∼60%) was observed in the lyophiles prepared with P188, the addition of sugar improved the activity recovery to >85%. The secondary structure of LDH in the freeze-dried samples was assessed using infrared spectroscopy, and only moderate structural changes were observed in the lyophiles formulated with P188 and sugar. Thus, P188 can be a promising dual functional excipient in freeze-dried protein formulations. However, P188 alone does not function as a lyoprotectant and needs to be used in combination with a sugar.

Agitation-Induced Aggregation of Lysine- And Interchain Cysteine-Linked Antibody-Drug Conjugates

Drug conjugation to an antibody can affect its stability, which depends on factors such as the conjugation technique used, drug-linker properties, and stress encountered. This study focused on the effects of agitation stress on the physical stability of two lysine (ADC-K) and two interchain cysteine (ADC-C) conjugates of an IgG1 monoclonal antibody (mAb) linked to either ∼4 MMAE or DM1 payloads. During agitation, all antibody-drug conjugates (ADCs) exhibited higher aggregation than the mAb, which was dependent on the conjugation technique (aggregation of ADC-Ks > ADC-Cs) and drug-linker (aggregation of ADCs with MMAE > ADCs with DM1). The aggregation propensities correlated well with higher self-interaction, hydrophobicity, and surface activity of ADCs relative to the mAb. The intermediate reduced mAb (mAb-SH) showed even higher aggregation than the final product ADC-Cs. However, blocking mAb-SH's free thiols with N-ethylmaleimide (NEM) strongly reduced its aggregation, suggesting that free thiols should be minimized in cysteine ADCs. Further, this study demonstrates that a low-volume surface tension method can be used for estimating agitation-induced aggregation of ADCs in early development phases. Identifying liabilities to agitation stress and their relationship to biophysical properties may help optimize ADC stability.

Protein Compartments Modulate Fibrillar Self-Assembly

A notable feature of complex cellular environments is protein-rich compartments that are formed via liquid-liquid phase separation. Recent studies have shown that these biomolecular condensates can play both promoting and inhibitory roles in fibrillar protein self-assembly, a process that is linked to Alzheimer's, Parkinson's, Huntington's, and various prion diseases. Yet, the exact regulatory role of these condensates in protein aggregation remains unknown. By employing microfluidics to create artificial protein compartments, the self-assembly behavior of the fibrillar protein lysozyme within them can be characterized. It is observed that the volumetric parameters of protein-rich compartments can change the kinetics of protein self-assembly. Depending on the change in compartment parameters, the lysozyme fibrillation process either accelerated or decelerated. Furthermore, the results confirm that the volumetric parameters govern not only the nucleation and growth phases of the fibrillar aggregates but also affect the crosstalk between the protein-rich and protein-poor phases. The appearance of phase-separated compartments in the vicinity of natively folded protein complexes triggers their abrupt percolation into the compartments' core and further accelerates protein aggregation. Overall, the results of the study shed more light on the complex behavior and functions of protein-rich phases and, importantly, on their interaction with the surrounding environment.

Design of a Reciprocal Injection Device for Stability Studies of Parenteral Biological Drug Products

Formulation screening, essential for assessing the impact of physical, chemical, and mechanical stresses on protein stability, plays a critical role in biologics drug product development. This research introduces a Reciprocal Injection Device (RID) designed to accelerate formulation screening by probing protein stability under intensified stress conditions within prefilled syringes. This versatile device is designed to accommodate a broad spectrum of injection parameters and diverse syringe dimensions. A commercial drug product was employed as a model monoclonal antibody formulation. Our findings effectively highlight the efficacy of the RID in assessing concentration-dependent protein stability. This device exhibits significant potential to amplify the influences of interfacial interactions, such as those with buffer salts, excipients, air, metals, and silicone oils, commonly found in combination drug products, and to evaluate the protein stability under varied stresses.

"Negative" Impact: The Role of Payload Charge in the Physicochemical Stability of Auristatin Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) tend to be less stable than their parent antibodies, which is often attributed to the hydrophobic nature of their drug payloads. This study investigated how the payload charge affects ADC stability by comparing two interchain cysteine ADCs that had matched drug-to-antibody ratios and identical linkers but differently charged auristatin payloads, vcMMAE (neutral) and vcMMAF (negative). Both ADCs exhibited higher aggregation than their parent antibody under shaking stress and thermal stress conditions. However, conjugation with vcMMAF increased the aggregation rates to a greater extent than conjugation with uncharged but more hydrophobic vcMMAE. Consistent with the payload logD values, ADC-vcMMAE showed the greatest increase in hydrophobicity but minor changes in charge compared with the parent antibody, as indicated by hydrophobic interaction chromatography and capillary electrophoresis data. In contrast, ADC-vcMMAF showed a decrease in net charge and isoelectric point along with an increase in charge heterogeneity. This charge alteration likely contributed to a reduced electrostatic repulsion and increased surface activity in ADC-vcMMAF, thus affecting its aggregation propensity. These findings suggest that not only the hydrophobicity of the payload, but also its charge should be considered as a critical factor affecting the stability of ADCs.

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.

Monitoring polysorbate 80 degradation in protein solutions using Total Holographic Characterization

The degradation of polysorbate surfactants can limit the shelf life of biologic pharmaceutical products. Polysorbate is susceptible to degradation via either oxidation or hydrolysis pathways which releases free fatty acids (FFA) and other complex polymers. Degradants from Polysorbate 80 (PS80) can form particles and impact drug product quality. PS80 degradation products appear at low concentrations, and their refractive indexes are similar to that of the buffer, making them very challenging to detect. Furthermore, aggregates of FFA are similar in size and refractive index to protein aggregates adding complexity to characterizing these particles in protein solutions. Total Holographic Characterization (THC) is used in this work to characterize FFA particles of oleic acid and linoleic acid, the two most common degradation products of PS80. We demonstrate that the characteristic THC profile of the FFA oleic acid emulsion droplets can be used to monitor the degradation of PS80. THC can detect oleic acid at a concentration down to less than 100 ng/mL. Using the characteristic THC signal of oleic acid as a marker, the degradation of PS80 in protein solutions can be monitored quantitatively even in the presence of other contaminants of the same size, including silicone oil emulsion droplets and protein aggregates.

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.

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.

Identification of nonvolatile organic compounds (NVOCs) in biopharmaceuticals through non-target analysis and quantification using complexation-precipitation extraction

Single-use systems in biopharmaceutical manufacturing can potentially release chemical constituents (leachables) into drug products. Prior to conducting toxicological risk assessments, it is crucial to establish the qualitative and quantitative methods for these leachables. In this study, we conducted a comprehensive screening and structure elucidation of 23 leachables (nonvolatile organic compounds, NVOCs) in two antibody drugs using multiple (self-built and public) databases and mass spectral simulation. We identified 7 compounds that have not been previously reported in medical or medicinal extractables and leachables. The confidence levels for identified compounds were classified based on analytical standards, literature references, and fragment assignments. Most of the identified leachables were found to be plasticizers, antioxidants, slip agents or polymer degradants. Polysorbate (namely Tween) is commonly used as an excipient for protein stabilization in biopharmaceutical formulations, but its ionization in liquid chromatography-electrospray ionization mass spectrometry can interfere with compound quantification. To address this, we employed a complexation-precipitation extraction method to reduce polysorbate content and quantify the analytes. The developed quantitative method for target NVOCs demonstrated high sensitivity (limit of quantification: 20 or 50 μg/L), accuracy (recoveries: 77.2 to 109.5 %) and precision (RSD ≤ 8.2 %). Overall, this established method will facilitate the evaluation of NVOC safety in drug products.

Stabilization challenges and aggregation in protein-based therapeutics in the pharmaceutical industry

Protein-based therapeutics have revolutionized the pharmaceutical industry and become vital components in the development of future therapeutics. They offer several advantages over traditional small molecule drugs, including high affinity, potency and specificity, while demonstrating low toxicity and minimal adverse effects. However, the development and manufacturing processes of protein-based therapeutics presents challenges related to protein folding, purification, stability and immunogenicity that should be addressed. These proteins, like other biological molecules, are prone to chemical and physical instabilities. The stability of protein-based drugs throughout the entire manufacturing, storage and delivery process is essential. The occurrence of structural instability resulting from misfolding, unfolding, and modifications, as well as aggregation, poses a significant risk to the efficacy of these drugs, overshadowing their promising attributes. Gaining insight into structural alterations caused by aggregation and their impact on immunogenicity is vital for the advancement and refinement of protein therapeutics. Hence, in this review, we have discussed some features of protein aggregation during production, formulation and storage as well as stabilization strategies in protein engineering and computational methods to prevent aggregation.

Transportation of mAb Dosing Solution in Intravenous Bag: Impact of Manual, Vehicle, and Pneumatic Tube System Transportation Methods on Product Quality

Monoclonal antibody (mAb) products for intravenous (IV) administration generally require aseptic compounding with a commercial diluent within a pharmacy. The prepared dosing solution in the IV bag may be transported to the dosing location via manual, vehicular, pneumatic tube system (PTS), or a combination of these methods. In this study, the type and level of physical stresses associated with these three methods and their product quality impact for relatively sensitive and stable mAbs were assessed. Vibration was found to be the main stress associated with manual and vehicle transportation methods, although this was at a relatively low level (<1 GRMS/Root-Mean-Square Acceleration). Shock and drop events, at relatively low levels, were also observed with these methods. PTS transportation showed substantially more intense shock, vibration, and drop stresses and the measured levels were up to 91 G/force of acceleration or deceleration, 3.7 GRMS and 39 G, respectively. Using a foam padding insert for PTS transportation reduced the shock level considerably (91 G to 59 G). Transportation of mAb dosing solutions in IV bags via different methods including PTS transportation variables caused a small increase in the subvisible particle counts and there was no change in submicrometer particle distribution. No visible particles and no significant change to soluble aggregate levels were observed after transportation. Strategies such as removal of IV bag headspace prior to transport and in-line filtration poststress reduced the subvisible particles counts. All tested transportation conditions showed negligible impact on other product quality attributes tested. Removal of IV bag headspace prior to PTS transport prevented formation of micro air bubbles and foaming compared to the unaltered IV bag. This study shows examples where manual, vehicle, and PTS transport methods did not significantly impact product quality, and provides evidence that mAb products that are appropriately stabilized in the dosing solution (e.g., with a surfactant) can be transported via a PTS.

Comparison of the Protective Effect of Polysorbates, Poloxamer and Brij on Antibody Stability Against Different Interfaces

Therapeutic proteins and antibodies are exposed to a variety of interfaces during their lifecycle, which can compromise their stability. Formulations, including surfactants, must be carefully optimized to improve interfacial stability against all types of surfaces. Here we apply a nanoparticle-based approach to evaluate the instability of four antibody drugs against different solid-liquid interfaces characterized by different degrees of hydrophobicity. We considered a model hydrophobic material as well as cycloolefin-copolymer (COC) and cellulose, which represent some of the common solid-liquid interfaces encountered during drug production, storage, and delivery. We assess the protective effect of polysorbate 20, polysorbate 80, Poloxamer 188 and Brij 35 in our assay and in a traditional agitation study. While all nonionic surfactants stabilize antibodies against the air-water interface, none of them can protect against hydrophilic charged cellulose. Polysorbates and Brij increase antibody stability in the presence of COC and the model hydrophobic interface, although to a lesser extent compared to the air-water interface, while Poloxamer 188 has a negligible stabilizing effect against these interfaces. These results highlight the challenge of fully protecting antibodies against all types of solid-liquid interfaces with traditional surfactants. In this context, our high-throughput nanoparticle-based approach can complement traditional shaking assays and assist in formulation design to ensure protein stability not only at air-water interfaces, but also at relevant solid-liquid interfaces encountered during the product lifecycle.

Interaction of βL- and γ-Crystallin with Phospholipid Membrane Using Atomic Force Microscopy

Highly concentrated lens proteins, mostly β- and γ-crystallin, are responsible for maintaining the structure and refractivity of the eye lens. However, with aging and cataract formation, β- and γ-crystallin are associated with the lens membrane or other lens proteins forming high-molecular-weight proteins, which further associate with the lens membrane, leading to light scattering and cataract development. The mechanism by which β- and γ-crystallin are associated with the lens membrane is unknown. This work aims to study the interaction of β- and γ-crystallin with the phospholipid membrane with and without cholesterol (Chol) with the overall goal of understanding the role of phospholipid and Chol in β- and γ-crystallin association with the membrane. Small unilamellar vesicles made of Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (Chol/POPC) membranes with varying Chol content were prepared using the rapid solvent exchange method followed by probe tip sonication and then dispensed on freshly cleaved mica disk to prepare a supported lipid membrane. The βL- and γ-crystallin from the cortex of the bovine lens was used to investigate the time-dependent association of βL- and γ-crystallin with the membrane by obtaining the topographical images using atomic force microscopy. Our study showed that βL-crystallin formed semi-transmembrane defects, whereas γ-crystallin formed transmembrane defects on the phospholipid membrane. The size of semi-transmembrane defects increases significantly with incubation time when βL-crystallin interacts with the membrane. In contrast, no significant increase in transmembrane defect size was observed in the case of γ-crystallin. Our result shows that Chol inhibits the formation of membrane defects when βL- and γ-crystallin interact with the Chol/POPC membrane, where the degree of inhibition depends upon the amount of Chol content in the membrane. At a Chol/POPC mixing ratio of 0.3, membrane defects were observed when both βL- and γ-crystallin interacted with the membrane. However, at a Chol/POPC mixing ratio of 1, no association of γ-crystallin with the membrane was observed, which resulted in a defect-free membrane, and the severity of the membrane defect was decreased when βL-crystallin interacted with the membrane. The semi-transmembrane or transmembrane defects formed by the interaction of βL- and γ-crystallin on phospholipid membrane might be responsible for light scattering and cataract formation. However, Chol suppressed the formation of such defects in the membrane, likely maintaining lens membrane homeostasis and protecting against cataract formation.

Monitoring of low-molecular-weight protein aggregation by CE-SDS as a complementary method to SE-HPLC

Capillary electrophoresis with sodium dodecyl sulfate (CE-SDS) has long been proven to have excellent performance in the analysis and characterization of therapeutic proteins. However, it is rarely used for the detection of low-molecular-weight proteins or peptides. Our research has proved the ability of CE-SDS to characterize the purity of low-molecular-weight proteins (i.e., <10 kDa) and even polypeptides. In this article, insulin glargine was used as a model protein, and CE-SDS was used to analyze the samples damaged by heating and light exposure. The monomers, dimers, and trimers of insulin glargine were effectively separated, and the results of the mass spectrometry also confirmed the existence of two kinds of insulin aggregates. For comparison, the size-exclusion high-performance liquid chromatography (SE-HPLC) only showed a single aggregate peak. In addition, the denaturation conditions caused only the covalent aggregates to appear in the CE-SDS analysis. These advantages also make CE-SDS an excellent supplementary technology to the traditional SE-HPLC, providing biopharmaceutical analysts with more information.

Real-Time Assessment of the Size Changes of Individual Sub-Visible Protein Particles under Buffer Variations: A Microfluidic Study

Protein particles in biological drugs can significantly impact drug efficacy and carry the risk of adverse effects. Despite advancements, the understanding and control of particle formation in biopharmaceutical manufacturing remain incomplete. Therefore, further investigation into protein particles is warranted, especially considering that novel formats of biological drugs may be more susceptible to aggregation and particle formation than conventional monoclonal antibodies. In this study, we introduce a microfluidic approach for the real-time analysis of individual sub-visible protein particles during buffer exchange. We find that the modulation of intermolecular forces, achieved by changing the buffer pH or urea concentration, leads to the reversible swelling and shrinkage of particles by up to 50%, which is a consequence of altered intermolecular distances. Additionally, we identify a discrepancy in the biophysical behavior of protein particles compared to monomeric protein. This finding highlights the limited predictive power of commonly applied biophysical characterization methods for particle formation in early formulation development. Moreover, the observed particle swelling may be associated with manufacturing deviations, such as filter clogging. These results highlight the importance of studying individual particles to gain a comprehensive insight into particle behavior and the impact of formulation variations in the biopharmaceutical industry.

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.