The effect of arginine glutamate on the stability of monoclonal antibodies in solution

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.

Synergistic effect of cyclodextrins and electrolytes at high concentrations on protein aggregation inhibition

The stabilization of protein therapeutics against aggregation is crucial for maintaining their efficacy and safety. This study investigated the synergistic effects of cyclodextrins (CDs) and electrolytes at high concentrations on the stabilization of immunoglobulin G (IgG), insulin, and adeno-associated virus (AAV) vectors. The effects of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) combined with various electrolytes were evaluated using human plasma-derived IgG as a model protein. The HP-β-CD and L(+)-arginine hydrochloride combination synergistically increased the onset temperature of protein aggregation and inhibited the formation of soluble and insoluble aggregates during long-term storage. Notably, this synergistic effect was not observed when sucrose was used instead of HP-β-CD. Similar synergistic effects were observed with insulin and AAV vectors. The findings suggest that the stabilization mechanism could potentially involve enhanced interactions between HP-β-CD and IgG, preventing protein-protein interactions. However, the combination did not synergistically improve the solubility of free aromatic amino acids, including tyrosine and tryptophan. This study highlights the potential of using the combination of CDs and electrolytes as a promising formulation strategy for stabilizing complex protein therapeutics. Further studies are needed to elucidate the underlying mechanisms and generalize the approach to other proteins with varying physicochemical properties.

Phenylalanine as an effective stabilizer and aggregation inhibitor of Bacillus amyloliquefaciens alpha-amylase

Aromatic compounds are known anti-amyloid aggregates. Their effect on amorphous aggregates of proteins is, however, less studied. We chose aromatic amino acids Trp, Tyr, and Phe, as well as another known stabilizer (i.e. Arg), as potential compatible solvents to be tested on Bacillus amyloliquefaciens alpha-amylase (BAA). Among these additives, Phe was the only one to be effective on the thermal inactivation and amorphous aggregation of BAA, while preserving its intrinsic activity. A concentration of 50 mM Phe was used to test its potential in counteracting the deleterious effect of BAA amorphous aggregates in vivo. After 21 days of daily subcutaneous injections of the native enzyme to mice, amorphous aggregates of BAA, as well as aggregates produced in presence of 50 mM Phe, the tissues located at the site of injection were studied histologically. Amorphous aggregates caused an increase in macrophages and lipid droplets. Serum levels of IL6 and TNF-α were also accordingly elevated and indicative of an inflammation state. Aggregates also resulted into increased levels of glucose, triglycerides and cholesterol, as well as liver enzymes SGOT and SGPT. On the other hand, the presence of Phe prevented this exacerbated inflammatory state and the subsequent impairment of biochemical parameters. In conclusion, Phe is an interesting compound for both stabilizing proteins and counteracting the pathological effect of amorphous aggregates.

Understanding the Specific Implications of Amino Acids in the Antibody Development

As the demand for immunotherapy to treat and manage cancers, infectious diseases and other disorders grows, a comprehensive understanding of amino acids and their intricate role in antibody engineering has become a prime requirement. Naturally produced antibodies may not have the most suitable amino acids at the complementarity determining regions (CDR) and framework regions, for therapeutic purposes. Therefore, to enhance the binding affinity and therapeutic properties of an antibody, the specific impact of certain amino acids on the antibody's architecture must be thoroughly studied. In antibody engineering, it is crucial to identify the key amino acid residues that significantly contribute to improving antibody properties. Therapeutic antibodies with higher binding affinity and improved functionality can be achieved through modifications or substitutions with highly suitable amino acid residues. Here, we have indicated the frequency of amino acids and their association with the binding free energy in CDRs. The review also analyzes the experimental outcome of two studies that reveal the frequency of amino acids in CDRs and provides their significant correlation between the outcomes. Additionally, it discusses the various bond interactions within the antibody structure and antigen binding. A detailed understanding of these amino acid properties should assist in the analysis of antibody sequences and structures needed for designing and enhancing the overall performance of therapeutic antibodies.

Effects of arginine in therapeutic protein formulations: a decade review and perspectives

Arginine (Arg) is a natural amino acid with an acceptable safety profile and a unique chemical structure. Arg and its salts are highly effective in enhancing protein refolding and solubilization, suppressing protein-protein interaction and aggregation and reducing viscosity of high concentration protein formulations. Arg and its salts have been used in research and 20 approved protein injectables. This review summarizes the effects of Arg as an excipient in therapeutic protein formulations with the focus on its physicochemical properties, safety, applications in approved protein products, beneficial and detrimental effects in liquid and lyophilized protein formulations when combined with different counterions and mechanism on protein stabilization and destabilization. The decade literature review indicates that the benefits of Arg overweigh its risks when it is used appropriately. It is recommended to add Arg along with glutamate as a counterion to high concentration protein formulations on top of sugars or polyols to counterbalance the negative effects of Arg hydrochloride. The use of Arg as a viscosity reducer and protein stabilizer in high concentration formulations will be the inevitable future trend of the biopharmaceutical industry for subcutaneous administration.

An Intercompany Perspective on Practical Experiences of Predicting, Optimizing and Analyzing High Concentration Biologic Therapeutic Formulations

Developing high-dose biologic drugs for subcutaneous injection often requires high-concentration formulations and optimizing viscosity, solubility, and stability while overcoming analytical, manufacturing, and administration challenges. To understand industry approaches for developing high-concentration formulations, the Formulation Workstream of the BioPhorum Development Group, an industry-wide consortium, conducted an inter-company collaborative exercise which included several surveys. This collaboration provided an industry perspective, experience, and insight into the practicalities for developing high-concentration biologics. To understand solubility and viscosity, companies desire predictive tools, but experience indicates that these are not reliable and experimental strategies are best. Similarly, most companies prefer accelerated and stress stability studies to in-silico or biophysical-based prediction methods to assess aggregation. In addition, optimization of primary container-closure and devices are pursued to mitigate challenges associated with high viscosity of the formulation. Formulation strategies including excipient selection and application of studies at low concentration to high-concentration formulations are reported. Finally, analytical approaches to high concentration formulations are presented. The survey suggests that although prediction of viscosity, solubility, and long-term stability is desirable, the outcome can be inconsistent and molecule dependent. Significant experimental studies are required to confirm robust product definition as modeling at low protein concentrations will not necessarily extrapolate to high concentration formulations.

Analytical Workflows to Unlock Predictive Power in Biotherapeutic Developability

PURPOSE

Forming accurate data models that assist the design of developability assays is one area that requires a deep and practical understanding of the problem domain. We aim to incorporate expert knowledge into the model building process by creating new metrics from instrument data and by guiding the choice of input parameters and Machine Learning (ML) techniques.

METHODS

We generated datasets from the biophysical characterisation of 5 monoclonal antibodies (mAbs). We explored combinations of techniques and parameters to uncover the ones that better describe specific molecular liabilities, such as conformational and colloidal instability. We also employed ML algorithms to predict metrics from the dataset.

RESULTS

We found that the combination of Differential Scanning Calorimetry (DSC) and Light Scattering thermal ramps enabled us to identify domain-specific aggregation in mAbs that would be otherwise overlooked by common developability workflows. We also found that the response to different salt concentrations provided information about colloidal stability in agreement with charge distribution models. Finally, we predicted DSC transition temperatures from the dataset, and used the order of importance of different metrics to increase the explainability of the model.

CONCLUSIONS

The new analytical workflows enabled a better description of molecular behaviour and uncovered links between structural properties and molecular liabilities. In the future this new understanding will be coupled with ML algorithms to unlock their predictive power during developability assessment.

Amino acid-mPEGs: Promising excipients to stabilize human growth hormone against aggregation

Objectives

Today, the non-covalent PEGylation methods of protein pharmaceuticals attract more attention and possess several advantages over the covalent approach. In the present study, Amino Acid-mPEGs (aa-mPEGs) were synthesized, and the human Growth Hormone (hGH) stability profile was assessed in their presence and absence.

Materials and Methods

aa-mPEGs were synthesized with different amino acids (Trp, Glu, Arg, Cys, and Leu) and molecular weights of polymers (2 and 5 KDa). The aa-mPEGs were analyzed with different methods. The physical and structural stabilities of hGH were analyzed by SEC and CD spectroscopy methods. Physical stability was assayed at different temperatures within certain intervals. Molecular dynamics (MD) simulation was used to realize the possible mode of interaction between protein and aa-mPEGs. The cell-based method was used to evaluate the cytotoxicity.

Results

HNMR and FTIR spectroscopy indicated that aa-mPEGs were successfully synthesized. hGH as a control group is known to be stable at 4 ^°C; a pronounced change in monomer degradation is observed when stored at 25 ^°C and 37 ^°C. hGH:Glu-mPEG 2 kDa with a molar ratio of 1:1 to the protein solution can significantly increase the physical stability. The CD spectroscopy method showed that the secondary structure of the protein was preserved during storage. aa-mPEGs did not show any cytotoxicity activities. The results of MD simulations were in line with experimental results.

Conclusion

This paper showed that aa-mPEGs are potent excipients in decreasing the aggregation of hGH. Glu-mPEG exhibited the best-stabilizing properties in a harsh environment among other aa-mPEGs.

Effective blocking of neuropilin-1activity using oligoclonal nanobodies targeting different epitopes

Neuropilin-1 (NRP-1) is a non-tyrosine kinase receptor and when overexpressed, leads to angiogenesis. High expression of NRP-1 has been observed in various cancers. Unique characteristic of nanobodies (small size, high affinity and stability, and ease production) make them potential therapeutic tools. Oligoclonal nanobodies which detect multiple functional epitopes on the target antigen could be potential tools for inhibition of cancer resistance problems due to escape variant of tumor cells. In this study, oligoclonal anti-NRP-1 nanobodies were selected from camel immune library and their binding activities as well as in vitro functionality were evaluated. Anti-NRP-1 nanobodies were expressed in an Escherichia coli host, and purified using nickel affinity chromatography. The effect of each individual and oligoclonal nanobodies on human endothelial cells were evaluated by MTT, Tube formation, and migration assay as well. Results showed that oligoclonal anti-NRP-1 nanobodies detected different epitopes of NRP-1 antigen and inhibited in vitro angiogenesis of human endothelial cells better than each individual nanobody. Results indicate promising oligoclonal anti-NRP-1 nanobodies for inhibition of angiogenesis.

Role of Arginine Salts in Preventing Freezing-induced Increase in Subvisible Particles in Protein Formulations

While arginine hydrochloride (ArgHCl) has emerged as a potential stabilizer of protein drugs in liquid formulations the purpose of this manuscript was to evaluate its stabilization potential in frozen solutions. The phase behavior of frozen AgHCl solutions was investigated by differential scanning calorimetry and low temperature powder X-ray diffractometry. The aggregation of β-galactosidase was evaluated following freeze-thaw cycling in ArgHCl solutions with and without mannitol. ArgHCl (5% w/v) was retained amorphous in frozen aqueous solutions and effectively inhibited protein aggregation even after 5 freeze-thaw cycles. Annealing frozen arginine solution (5% w/v) containing mannitol (10% w/v) induced mannitol crystallization which in turn facilitated crystallization of ArgHCl. The stabilizing effect of ArgHCl was completely lost in the presence of mannitol. Use of alternate arginine salts (aspartate, glutamate, and acetate) allowed selective crystallization of mannitol while the arginine was retained amorphous and stabilized the protein.

Live-cell imaging to analyze intracellular aggregation of recombinant IgG in CHO cells

Recombinant immunoglobulin G (IgG) aggregates are formed during their production. However, the process underlying intracellular/extracellular aggregation in cell culture conditions is not well understood, and no effective method exists to assess IgG aggregates. Here, we establish an approach to detect intracellular aggregates using AF.2A1, a small artificial protein that binds to non-native IgG conformers and aggregates. Fluorescent-labeled AF.2A1 is prepared via conjugation and transfected into antibody-producing Chinese hamster ovary (CHO) cells. Micrographic images show intracellular IgG aggregates in CHO cells. The relative amount of intracellular aggregates (versus total intracellular IgG) differed depending on the type of additives used during cell culture. Interestingly, the relative amount of intracellular aggregates moderately correlates with that of in vitro extracellular IgG aggregates, suggesting they are secreted. This method will allow the investigation of antibody aggregation in cells, and may guide the production of therapeutic antibodies with high yield/quality.

Stability of a high-concentration monoclonal antibody solution produced by liquid-liquid phase separation

Subcutaneous injection of a low volume (<2 mL) high concentration (>100 mg/mL) formulation is an attractive administration strategy for monoclonal antibodies (mAbs) and other biopharmaceutical proteins. Using concentrated solutions may also be beneficial at various stages of bioprocessing. However, concentrating proteins by conventional techniques, such as ultrafiltration, can be time consuming and challenging. Isolation of the dense fraction produced by macroscopic liquid–liquid phase separation (LLPS) has been suggested as a means to produce high-concentration solutions, but practicality of this method, and the stability of the resulting protein solution have not previously been demonstrated. In this proof-of-concept study, we demonstrate that LLPS can be used to concentrate a mAb solution to >170 mg/mL. We show that the structure of the mAb is not altered by LLPS, and unperturbed mAb is recoverable following dilution of the dense fraction, as judged by ¹H nuclear magnetic resonance spectroscopy. Finally, we show that the physical properties and stability of a model high concentration protein formulation obtained from the dense fraction can be improved, for example through the addition of the excipient arginine·glutamate. This results in a stable high-concentration protein formulation with reduced viscosity and no further macroscopic LLPS. Concentrating mAb solutions by LLPS represents a simple and effective technique to progress toward producing high-concentration protein formulations for bioprocessing or administration.

Abbreviations

Arginine·glutamate (Arg·Glu), Carr-Purcell-Meiboom-Gill (CPMG), critical temperature (T_C), high-performance size-exclusion chromatography (HPSEC), liquid–liquid phase separation (LLPS), monoclonal antibody (mAb), nuclear magnetic resonance (NMR), transverse relaxation rate (R₂)

Prediction of Drug Stability Using Deep Learning Approach: Case Study of Esomeprazole 40 mg Freeze-Dried Powder for Solution

A critical step in the production of Esomeprazole powder for solution is a period between the filling process and lyophilization, where all vials, partially closed, are completely exposed to environmental influences. Excessive instability reflects in pH value variations caused by oxygen's impact. In order to provide pH control, which consequently affects drug stability, Esomeprazole batches, produced in the same way, were kept in partially closed vials for 3 h at temperatures of 20 °C and -30 °C, after which they were lyophilized and stored for long-term stability for 36 months. The aim of the presented study was to apply a deep-learning algorithm for the prediction of the Esomeprazole stability profile and to determine the pH limit for the reconstituted solution of the final freeze-dried product that would assure a quality product profile over a storage period of 36 months. Multilayer perceptron (MLP) as a deep learning tool, with four layers, was used. The pH value of Esomeprazole solution and time of storage (months) were inputs for the network, while Esomeprazole assay and four main impurities were outputs of the network. In order to keep all related substances and Esomeprazole assay in accordance with specifications for the whole shelf life, the pH value for the reconstituted finish product should be set in the range of 10.4-10.6.

Polypseudorotaxane-based supramolecular hydrogels consisting of cyclodextrins and Pluronics as stabilizing agents for antibody drugs

Recently, antibody drugs have been used worldwide, and based on worldwide sales, 7 of the top 10 pharmaceutical products in 2019 were antibody-based drugs. However, antibody drugs often form aggregates upon thermal and shaking stresses with few efficient stabilizing agents against both stresses. Herein, we developed polypseudorotaxane (PpRX) hydrogels consisting of cyclodextrins (CyDs) and polyethylene glycol (PEG)-polypropylene glycol (PPG)-PEG block copolymers (Pluronics F108, F87, F68, and L44), and evaluated their utility as antibody stabilizing agents. α- and γ-CyDs formed PpRX hydrogels with Pluronics, where CyD/F108 gels showed remarkable stabilizing effects for human immunoglobulin G (IgG) against both thermal and shaking stresses beyond CyD/PEG gels or generic gels. The effects were probably due to the interaction between IgG and the free PPG block of Pluronic F108, resulting in the strong IgG retention in the gels. These findings suggest the great potential of CyD/Pluronic gels as pharmaceutical materials for antibody formulations.

Formulation strategies in immunotherapeutic pharmaceutical products

Development of immunologic-based biopharmaceutical products have strikingly increased in recent years and have made evident contributions to human health. Antibodies are the leading entity in immunotherapy, while chimeric antigen receptor T cells therapies are the advent of a novel strategy in this area. In order to enable antibody candidates or cells available as products, formulation is critical in terms of stabilize molecules or cells to achieve practical shelf life, storage and handling conditions. Here we provide a concise and contemporary review of ongoing formulation strategies and excipients used in approved antibodies and cellular therapeutic products. Excipients are categorized, and their function in formulations are discussed.

Binding of excipients is a poor predictor for aggregation kinetics of biopharmaceutical proteins

One of the major challenges in formulation development of biopharmaceuticals is improving long-term storage stability, which is often achieved by addition of excipients to the final formulation. Finding the optimal excipient for a given protein is usually done using a trial-and-error approach, due to the lack of general understanding of how excipients work for a particular protein. Previously, preferential interactions (binding or exclusion) of excipients with proteins were postulated as a mechanism explaining diversity in the stabilisation effects. Weak preferential binding is however difficult to quantify experimentally, and the question remains whether the formulation process should seek excipients which preferentially bind with proteins, or not. Here, we apply solution NMR spectroscopy to comprehensively evaluate protein-excipient interactions between therapeutically relevant proteins and commonly used excipients. Additionally, we evaluate the effect of excipients on thermal and colloidal protein stability, on aggregation kinetics and protein storage stability at elevated temperatures. We show that there is a weak negative correlation between the strength of protein-excipient interactions and effect on enhancing protein thermal stability. We found that the overall protein-excipient binding per se can be a poor criterion for choosing excipients enhancing formulation stability. Experiments on a diverse set of excipients and test proteins reveal that while excipients affect all of the different aspects of protein stability, the effects are very much protein specific, and care must be taken to avoid apparent generalisations if a smaller dataset is being used.

Evaluation of Laboratory Application of Camelid Sera Containing Heavy-Chain Polyclonal Antibody Against Recombinant Cytotoxic T-Lymphocyte-Associated Protein-4

Cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) is a critical negative immunomodulatory receptor that is normally expressed in activated T cells and noticeably, in many cancerous cells. Indeed, molecular detection of CTLA-4 protein is crucial in basic research. In this work, the extracellular domain of the human CTLA-4 (hCTLA-4) protein was cloned, expressed, and purified. Subsequently, this protein was used as an antigen for camel (Camelus dromedarius) immunization to obtain polyclonal camelid sera against this protein. Furthermore, we evaluated the benefits of applying camelid hyperimmune sera containing heavy-chain antibodies in different antibody-based techniques. Our results indicated that hCTLA-4 protein was successfully expressed in the prokaryotic system. The polyclonal antibody (pAb) that raised against recombinant hCTLA-4 protein was able to detect the CTLA-4 protein in antibody-based techniques, such as enzyme-linked immunosorbent assay, western blotting, flow cytometry and immunohistochemistry (IHC) staining. This study shows that, due to the advantages such as multi-epitope-binding ability, camelid pAbs are potent to efficiently apply for molecular detection of CTLA-4 receptors in fundamental antibody-based researches such as IHC.

Self-diffusion of a highly concentrated monoclonal antibody by fluorescence correlation spectroscopy: insight into protein-protein interactions and self-association

The dynamic behavior of monoclonal antibodies (mAbs) at high concentration provides insight into protein microstructure and protein-protein interactions (PPI) that influence solution viscosity and protein stability. At high concentration, interpretation of the collective-diffusion coefficient Dc, as determined by dynamic light scattering (DLS), is highly challenging given the complex hydrodynamics and PPI at close spacings. In contrast, self-diffusion of a tracer particle by Brownian motion is simpler to understand. Herein, we develop fluorescence correlation spectroscopy (FCS) for the measurement of the long-time self-diffusion of mAb2 over a wide range of concentrations and viscosities in multiple co-solute formulations with varying PPI. The normalized self-diffusion coefficient D0/Ds (equal to the microscopic relative viscosity ηeff/η0) was found to be smaller than η/η0. Smaller ratios of the microscopic to macroscopic viscosity (ηeff/η) are attributed to a combination of weaker PPI and less self-association. The interaction parameters extracted from fits of D0/Ds with a length scale dependent viscosity model agree with previous measurements of PPI by SLS and SAXS. Trends in the degree of self-association, estimated from ηeff/η with a microviscosity model, are consistent with oligomer sizes measured by SLS. Finally, measurements of collective diffusion and osmotic compressibility were combined with FCS data to demonstrate that the changes in self-diffusion between formulations are due primarily to changes in the protein-protein friction in these systems, and not to protein-solvent friction. Thus, FCS is a robust and accessible technique for measuring mAb self-diffusion, and, by extension, microviscosity, PPI and self-association that govern mAb solution dynamics.

Counteracting Effect of Charged Amino Acids Against the Destabilization of Proteins by Arginine

Studies on osmolyte-induced effects on proteins help in enhancing protein stability under stressed conditions for various applications. Using mixtures of osmolytes could indeed widen their applications. The combinatorial effects of osmolytes with methylamines are majorly found in the literature; however, such studies are limited on the amino acid class of osmolytes. The present study examines the effect of charged amino acids Arg, Asp, and Lys on the stability of RNase A and α-LA. The thermal stabilities of the proteins in the presence of osmolytes are monitored by absorption changes, and the structural changes are analyzed using fluorescence quenching and near-UV circular dichroism (CD). These results are compared with our previous report on the effect of Glu. Arg destabilizes both the proteins whereas Asp, Lys, and Glu stabilize the proteins. The extent of stability provided by Asp and Glu is almost same and higher than Lys in RNase A. However, the stability acquired in the presence of Asp and Lys is comparable for α-LA and Glu provides higher stability. Further, the quenching and CD results suggest that the addition of amino acids do not alter the structure of the proteins significantly. The counteracting abilities of the stabilizing amino acids (stAAs) against Arg are then investigated. The results show that Glu could counteract Arg at the lowest fraction in the mixture. Lys requires nearly equimolar concentration whereas Asp needs almost double the concentration to counteract Arg induced destabilization of the proteins. At higher concentrations, the counteracting ability of Asp and Lys is similar for both the proteins. The counteracting ratio might slightly vary among the proteins, and it is not necessary that the amino acid providing higher stability to the protein could more effectively counteract Arg. This could be due to the change in the extent of preferential hydration of the proteins by stAAs in the presence of Arg. The results suggest that the addition of stAAs could be an effective strategy to increase the protein stability in biotechnology and biopharma applications.

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

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

FTIR Spectroscopic Study of the Secondary Structure of Globular Proteins in Aqueous Protic Ionic Liquids

Protein misfolding is a detrimental effect which can lead to the inactivation of enzymes, aggregation, and the formation of insoluble protein fibrils called Amyloids. Consequently, it is important to understand the mechanism of protein folding, and under which conditions it can be avoided or mitigated. Ionic liquids (ILs) have previously been shown as capable of increasing or decreasing protein stability, depending on the specific IL, IL concentration and which protein. However, a greater range of IL-proteins need to be systematically explored to enable the development of structure-property relationships. In this work, the secondary structure of four proteins, lysozyme, trypsin, β-lactoglobulin and α-amylase, were studied in aqueous solutions of 10 protic ionic liquids (PILs) with 0-50 mol% PIL present. The PILs consisted of ethyl-, ethanol-, diethanol- and triethanolammonium cations paired with nitrate, formate, acetate or glycolate anions. The secondary structure was obtained using ATR-FTIR spectroscopy. It was found that lysozyme and trypsin retained its secondary structure, consistent with a native folded state, for many of the aqueous IL solutions which contained a formate or nitrate anion at the most dilute concentrations. In contrast, α-amylase and β-lactoglobulin generally had poor stability and solubility in the IL solutions. This may be due to the isoelectric point of α-amylase and β-lactoglobulin being closer to the pH of the solvents. All four proteins were insoluble in ethyl-, ethanol- and diethanolammonium acetate, though α-amylase and trypsin retained their secondary structure in up to 20 and 30 mol% of triethanolammonium acetate, respectively. It was evident that the protein stability varied substantially depending on the protein-IL combination, and the IL concentration in water. Overall, the findings indicated that some ions and some ILs were in general better for protein solubility and stability than others, such as acetate leading to poor solubility, and EAN and EAF generally leading to better protein stability than the other PILs. This study of four proteins in 10 aqueous PILs clearly showed that there are many complexities in their interactions and no clear general trend, despite the similarities between the PIL structures. This highlights the need for more and larger studies to enable the selection and optimization of PIL solvents used with biomolecules.

An Evaluation of the Potential of NMR Spectroscopy and Computational Modelling Methods to Inform Biopharmaceutical Formulations

Protein-based therapeutics are considered to be one of the most important classes of pharmaceuticals on the market. The growing need to prolong stability of high protein concentrations in liquid form has proven to be challenging. Therefore, significant effort is being made to design formulations which can enable the storage of these highly concentrated protein therapies for up to 2 years. Currently, the excipient selection approach involves empirical high-throughput screening, but does not reveal details on aggregation mechanisms or the molecular-level effects of the formulations under storage conditions. Computational modelling approaches have the potential to elucidate such mechanisms, and rapidly screen in silico prior to experimental testing. Nuclear Magnetic Resonance (NMR) spectroscopy can also provide complementary insights into excipient–protein interactions. This review will highlight the underpinning principles of molecular modelling and NMR spectroscopy. It will also discuss the advancements in the applications of computational and NMR approaches in investigating excipient–protein interactions.

Overlooked benefits of using polyclonal antibodies

The benefits of polyclonal antibodies as tools for assay-specific target discovery and detection are numerous. As the future of basic research, diagnostics and biomarker discovery is dependent on high-quality reproducible data, there is a need to understand the importance and benefits of these valuable tools. All antibody forms - polyclonal, hybridoma-based monoclonal and recombinant monoclonal - have pros and cons for development, validation and use. Yet, polyclonal antibodies are embroiled in a firestorm of controversy concerning data reproducibility. We address best practices for developing and using polyclonal antibodies, pitfalls to their use and how to avoid them, and benefits to the life science community. Eliminating their use risks overlooking the unique benefits of polyclonal antibodies as 'fit-for-purpose' life science tools.

19F NMR as a Tool for Monitoring Individual Differentially Labeled Proteins in Complex Mixtures

The ability to monitor the behavior of individual proteins in complex mixtures has many potential uses, ranging from analysis of protein interactions in highly concentrated solutions, modeling biological fluids or the intracellular environment, to optimizing biopharmaceutical co-formulations. Differential labeling NMR approaches, which traditionally use ¹⁵N or ¹³C isotope incorporation during recombinant expression, are not always practical in cases when endogenous proteins are obtained from an organism, or where the expression system does not allow for efficient labeling, especially for larger proteins. This study proposes differential labeling of proteins by covalent attachment of ¹⁹F groups with distinct chemical shifts, giving each protein a unique spectral signature which can be monitored by ¹⁹F NMR without signal overlap, even in complex mixtures, and without any interfering signals from the buffer or other unlabeled components. Parameters, such as signal intensities, translational diffusion coefficients, and transverse relaxation rates, which report on the behavior of individual proteins in the mixture, can be recorded even for proteins as large as antibodies at a wide range of concentrations.

Efficient and easily scalable protein folding strong anion exchange chromatography for renaturation and simultaneous purification of recombinant human asparaginase from E. coli

Recombinant proteins are revolutionizing present day therapeutics. They are generally expressed as insoluble inclusion bodies in the E. coli and mis-folding, loss of protein, and high cost of down streaming are the hurdles in their recovery. For the first time, we are reporting the refolding with simultaneous purification of rhASP in E. coli using a single step utilizing protein folding-strong anion exchange chromatography (PF-SAX). The purification method is also standardized for optimal concentration of solution additives, pH, and mobile phase composition. The results showed purification of rhASP with anion exchange chromatography was effective. Phosphate buffer and slightly alkaline pH produced significant recovery yields and purity profiles. The effect of solution additives such as arginine, glycerol, TMAO, sorbitol, dextran, glutamate, and fructose on rhASP renaturation is also investigated. Significant results were achieved using arginine-TMAO combination in terms of purity, recovery yield and specific activity of 99%, 78%, and 210 IU/mg, respectively. The work concludes that PF-SAX refolding method is superior to other conventional methods and it can be applied to large scale purification of rhASP produced in E. coli. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1036-1044, 2018.

Synthetic glycopolymers as modulators of protein aggregation: influences of chemical composition, topology and concentration

Synthetic glycopolymers with a variable macromolecular architecture and carbohydrate moieties are utilised to modulate stress-induced aggregation of monoclonal antibodies.

Viscosity Control of Protein Solution by Small Solutes: A Review

Viscosity of protein solution is one of the most troublesome issues for the high-concentration formulation of protein drugs. In this review, we summarize the practical methods that suppress the viscosity of protein solution using small molecular additives. The small amount of salts decreases the viscosity that results from electrostatic repulsion and attraction. The chaotrope suppresses the hydrophobic attraction and cluster formation, which can lower the solution viscosity. Arginine hydrochloride (ArgHCl) also suppresses the solution viscosity due to the hydrophobic and aromatic interactions between protein molecules. The small molecular additives are the simplest resolution of the high viscosity of protein solution as well as understanding of the primary cause in complex phenomena of protein interactions.

Structural Basis of Enhanced Crystallizability Induced by a Molecular Chaperone for Antibody Antigen-Binding Fragments

Monoclonal antibodies constitute one of the largest groups of drugs to treat cancers and immune disorders, and are guiding the design of vaccines against infectious diseases. Fragments antigen-binding (Fabs) have been preferred over monoclonal antibodies for the structural characterization of antibody-antigen complexes due to their relatively low flexibility. Nonetheless, Fabs often remain challenging to crystallize because of the surface characteristics of complementary determining regions and the residual flexibility in the hinge region between the variable and constant domains. Here, we used a variable heavy-chain (V_HH) domain specific for the human kappa light chain to assist in the structure determination of three therapeutic Fabs that were recalcitrant to crystallization on their own. We show that this ligand alters the surface properties of the antibody-ligand complex and lowers its aggregation temperature to favor crystallization. The V_HH crystallization chaperone also restricts the flexible hinge of Fabs to a narrow range of angles, and so independently of the variable region. Our findings contribute a valuable approach to antibody structure determination and provide biophysical insight into the principles that govern the crystallization of macromolecules.

Biophysical and Sequence-Based Methods for Identifying Monovalent and Bivalent Antibodies with High Colloidal Stability

In vitro antibody discovery and/or affinity maturation are often performed using antibody fragments (Fabs), but most monovalent Fabs are reformatted as bivalent IgGs (monoclonal antibodies, mAbs) for therapeutic applications. One problem related to reformatting antibodies is that the bivalency of mAbs can lead to increased antibody self-association and poor biophysical properties (e.g., reduced antibody solubility and increased viscosity). Therefore, it is important to identify monovalent Fabs early in the discovery and/or optimization process that will display favorable biophysical properties when reformatted as bivalent mAbs. Here we demonstrate a facile approach for evaluating Fab self-association in a multivalent assay format that is capable of identifying antibodies with low self-association and favorable colloidal properties when reformatted as bivalent mAbs. Our approach (self-interaction nanoparticle spectroscopy, SINS) involves immobilizing Fabs on gold nanoparticles in a multivalent format (multiple Fabs per nanoparticle) and evaluating their self-association behavior via shifts in the plasmon wavelength or changes in the absorbance values. Importantly, we find that SINS measurements of Fab self-association are correlated with self-interaction measurements of bivalent mAbs and are useful for identifying antibodies with favorable biophysical properties. Moreover, the significant differences in the levels of self-association detected for Fabs and mAbs with similar frameworks can be largely explained by the physicochemical properties of the complementarity-determining regions (CDRs). Comparison of the properties of the CDRs in this study relative to those of approved therapeutic antibodies reveals several key factors (net charge, fraction of charged residues, and presence of self-interaction motifs) that strongly influence antibody self-association behavior. Increased positive charge in the CDRs was observed to correlate with increased risk of high self-association for the mAbs in this study and clinical-stage antibodies. We expect that these findings will be useful for improving the development of therapeutic antibodies that are well suited for high concentration applications.

Dipicolinic acid as a novel spore-inspired excipient for antibody formulation

Ionic excipients are commonly used in aqueous therapeutic monoclonal antibody (mAb) formulations. Novel excipients are of industrial interest, with a recent focus on Arg salt forms and their application as viscosity reducing and stabilizing additives. Here, we report that the calcium salt of dipicolinic acid (DPA, pyridine-2,6-dicarboxylic acid), uniquely present in nature in the core of certain bacterial spores, reduces the viscosity of a mAb formulated at 150mg/mL, below that achieved by Arg hydrochloride at the same concentration (10mM). DPA also reduced the reversible phase separation of the same formulation, which characteristically occurs for this mAb upon cooling to 4°C. Differential scanning calorimetry and differential scanning fluorimetry did not reveal a conformation destabilisation of the mAb in the presence of 10mM DPA, or by the related quinolinic acid (QA, pyridine-2,3-dicarboxylic acid). However, fluorescence spectrophotometry did reveal localised (aromatic) conformational changes to the mAb attributed to DPA, dependent on the salt form. While precise mechanisms of action remain to be identified, our preliminary data suggest that these DPA salts are worthy of further investigation as novel ionic excipient for biologics formulation.

A Formulation Development Approach to Identify and Select Stable Ultra-High-Concentration Monoclonal Antibody Formulations With Reduced Viscosities

High protein concentration formulations are required for low-volume administration of therapeutic antibodies targeted for subcutaneous, self-administration by patients. Ultra-high concentrations (≥150 mg/mL) can lead to dramatically increased solution viscosities, which in turn can lead to stability, manufacturing, and delivery challenges. In this study, various categories and individual types of pharmaceutical excipients and other additives (56 in total) were screened for their viscosity reducing effects on 2 different mAbs. The physicochemical stability profile, as well as viscosity ranges, of several candidate antibody formulations, identified and designed based on the results of the excipient screening, were evaluated over a 6-month time period under accelerated and real-time storage conditions. In addition to reducing the solution viscosities to acceptable levels for parenteral administration (using currently available and acceptable delivery devices), the candidate formulations did not result in notable losses of physicochemical stability of the 2 antibodies on storage for 6 months at 25°C. The experiments described here demonstrate the feasibility of a formulation development and selection approach to identify candidate high-concentration antibody formulations with viscosities within pharmaceutically acceptable ranges that do not adversely affect their physicochemical storage stability.

In vitro gene expression-coupled bacterial cell chip for screening species-specific antimicrobial enzymes

Targeting infectious bacterial pathogens is important for reducing the evolution of antibiotic-resistant bacteria and preserving the endogenous human microbiome. Cell lytic enzymes including bacteriophage endolysins, bacterial autolysins, and other bacteriolysins are useful antibiotic alternatives due to their exceptional target selectivity, which may be used to lysins rapidly kill target bacteria and their high specificity permit the normal commensal microflora to be left undisturbed. Genetic information of numerous lysins is currently available, but the identification of their antimicrobial function and specificity has been limited because most lysins are often poorly expressed and exhibit low solubilities. Here, we report the development of bacterial cell chip for rapidly accessing the function of diverse genes that are suggestive of encoding lysins. This approach can be used to evaluate rapidly the species-specific antimicrobial activity of diverse lysins synthesized from in vitro transcription and translation (TNT) of plasmid DNA. In addition, new potent lysins can be assessed that are not expressed in hosts and display low solubility. As a result of evaluating the species-specific antimicrobial function of 11 (un)known lysins with an in vitro TNT-coupled bacterial cell chip, a potent recombinant lysin against Staphylococcus strains, SA1, was identified. The SA1 was highly potent against not only S. aureus, but also both lysostaphin-resistant S. simulans and S. epidermidis cells. To this end, the SA1 may be applicable to treat both methicillin-resistant S. aureus (MRSA) and lysostaphin-resistant MRSA mutants. Biotechnol. Bioeng. 2017;114: 1648-1657. © 2017 Wiley Periodicals, Inc.

Characterizing monoclonal antibody formulations in arginine glutamate solutions using 1H NMR spectroscopy

Assessing how excipients affect the self-association of monoclonal antibodies (mAbs) requires informative and direct in situ measurements for highly concentrated solutions, without sample dilution or perturbation. This study explores the application of solution nuclear magnetic resonance (NMR) spectroscopy for characterization of typical mAb behavior in formulations containing arginine glutamate. The data show that the analysis of signal intensities in 1D ¹H NMR spectra, when compensated for changes in buffer viscosity, is invaluable for identifying conditions where protein-protein interactions are minimized. NMR-derived molecular translational diffusion rates for concentrated solutions are less useful than transverse relaxation rates as parameters defining optimal formulation. Furthermore, NMR reports on the solution viscosity and mAb aggregation during accelerated stability study assessment, generating data consistent with that acquired by size-exclusion chromatography. The methodology developed here offers NMR spectroscopy as a new tool providing complementary information useful to formulation development of mAbs and other large therapeutic proteins.