Potential inaccurate quantitation and sizing of protein aggregates by size exclusion chromatography: Essential need to use orthogonal methods to assure the quality of therapeutic protein products

What is the role of current mass spectrometry in pharmaceutical analysis?

The role of mass spectrometry (MS) has become more important in most application domains in recent years. Pharmaceutical analysis is specific due to its stringent regulation procedures, the need for good laboratory/manufacturing practices, and a large number of routine quality control analyses to be carried out. The role of MS is, therefore, very different throughout the whole drug development cycle. While it dominates within the drug discovery and development phase, in routine quality control, the role of MS is minor and indispensable only for selected applications. Moreover, its role is very different in the case of analysis of small molecule pharmaceuticals and biopharmaceuticals. Our review explains the role of current MS in the analysis of both small-molecule chemical drugs and biopharmaceuticals. Important features of MS-based technologies being implemented, method requirements, and related challenges are discussed. The differences in analytical procedures for small molecule pharmaceuticals and biopharmaceuticals are pointed out. While a single method or a small set of methods is usually sufficient for quality control in the case of small molecule pharmaceuticals and MS is often not indispensable, a large panel of methods including extensive use of MS must be used for quality control of biopharmaceuticals. Finally, expected development and future trends are outlined.

Field-Flow Fractionation in Molecular Biology and Biotechnology

Field-flow fractionation (FFF) is a family of single-phase separative techniques exploited to gently separate and characterize nano- and microsystems in suspension. These techniques cover an extremely wide dynamic range and are able to separate analytes in an interval between a few nm to 100 µm size-wise (over 15 orders of magnitude mass-wise). They are flexible in terms of mobile phase and can separate the analytes in native conditions, preserving their original structures/properties as much as possible. Molecular biology is the branch of biology that studies the molecular basis of biological activity, while biotechnology deals with the technological applications of biology. The areas where biotechnologies are required include industrial, agri-food, environmental, and pharmaceutical. Many species of biological interest belong to the operational range of FFF techniques, and their application to the analysis of such samples has steadily grown in the last 30 years. This work aims to summarize the main features, milestones, and results provided by the application of FFF in the field of molecular biology and biotechnology, with a focus on the years from 2000 to 2022. After a theoretical background overview of FFF and its methodologies, the results are reported based on the nature of the samples analyzed.

Micro-flow size-exclusion chromatography for enhanced native mass spectrometry of proteins and protein complexes

Size-exclusion chromatography (SEC) employing aqueous mobile phases with volatile salts at neutral pH combined with native mass spectrometry (nMS) is a valuable tool to characterize proteins and protein aggregates in their native state. However, the liquid-phase conditions (high salt concentrations) frequently used in SEC-nMS hinder the analysis of labile protein complexes in the gas phase, necessitating higher desolvation-gas flow and source temperature, leading to protein fragmentation/dissociation. To overcome this issue, we investigated narrow SEC columns (1.0 mm internal diameter, I.D.) operated at 15-μL/min flow rates and their coupling to nMS for the characterization of proteins, protein complexes and higher-order structures (HOS). The reduced flow rate resulted in a significant increase in the protein-ionization efficiency, facilitating the detection of low-abundant impurities and HOS up to 230 kDa (i.e., the upper limit of the Orbitrap-MS instrument used). More-efficient solvent evaporation and lower desolvation energies allowed for softer ionization conditions (e.g., lower gas temperatures), ensuring little or no structural alterations of proteins and their HOS during transfer into the gas phase. Furthermore, ionization suppression by eluent salts was decreased, permitting the use of volatile-salt concentrations up to 400 mM. Band broadening and loss of resolution resulting from the introduction of injection volumes exceeding 3% of the column volume could be circumvented by incorporating an online trap-column containing a mixed-bed ion-exchange (IEX) material. The online IEX-based solid-phase extraction (SPE) or "trap-and-elute" set-up provided on-column focusing (sample preconcentration). This allowed the injection of large sample volumes on the 1-mm I.D. SEC column without compromising the separation. The enhanced sensitivity attained by the micro-flow SEC-MS, along with the on-column focusing achieved by the IEX precolumn, provided picogram detection limits for proteins.

Rapid Estimation of Size-Based Heterogeneity in Monoclonal Antibodies by Machine Learning-Enhanced Dynamic Light Scattering

Aggregation of monoclonal antibody therapeutics is a serious concern that is believed to impact product safety and efficacy. There is a need for analytical approaches that enable rapid estimation of mAb aggregates. Dynamic light scattering (DLS) is a well-established technique for estimating the average size of protein aggregates or for evaluating sample stability. It is usually used to measure the size and size distribution over a wide range of nano- to micro-sized particles using time-dependent fluctuations in the intensity of scattered light arising from the Brownian motion of particles. In this study, we present a novel DLS-based approach that allows us to quantify the relative percentage of multimers (monomer, dimer, trimer, and tetramer) in a monoclonal antibody (mAb) therapeutic product. The proposed approach uses a machine learning (ML) algorithm and regression to model the system and predict the amount of relevant species such as monomer, dimer, trimer, and tetramer of a mAb in the size range of 10-100 nm. The proposed DLS-ML technique compares favorably to all potential alternatives with respect to the key method attributes, including per sample cost of analysis, per sample time of data acquisition along with ML-based aggregate prediction (<2 min), sample requirements (<3 μg), and user-friendliness of analysis. The proposed rapid method can serve as an orthogonal tool to size exclusion chromatography, which is the current industry workhorse for aggregate assessment.

Evaluation of a Raman Chemometric Method for Detecting Protein Structural Conformational Changes in Solution

Raman scattering shows promise as a powerful routine tool, to determine both secondary and the smaller tertiary structural changes that precede aggregation in both solutions and solids. A method was developed utilizing principal component analysis (PCA) of Raman spectra for detection of small, but meaningful, pH induced changes in tertiary protein structure linked to aggregate formation using α-lactalbumin solutions as a model. The sample preparation and spectral parameters, were optimized for a bulk Raman probe. Analysis of large regions (600-1850 cm^-1) yielded principal component (PC) scores useful for semi-quantitative comparison of protein conformation between formulations. PC loadings corresponded to specific structural peaks known to change with solution pH. PCA of circular dichroism (CD) spectra of dilute solutions yielded similar results. Sucrose is a common formulation excipient with a Raman spectrum that overlaps many protein peaks. With sucrose in the protein solution, the ability of PCA to discern protein structural changes from the Raman spectra was somewhat reduced. Analysis of a more limited spectral region (1530-1780 cm^-1) with negligible sucrose spectral contribution improved the discrimination of protein conformational states. The new Raman method accurately distinguished differences in protein structure in concentrated solutions. The long-term goal is to explore Raman characterization as a routine monitoring tool of protein stability in both solution and solid states.

Application of Af4-Multidetection to Liraglutide in Its Formulation: Preserving and Representing Native Aggregation

Aggregation is among the most critical parameters affecting the pharmacological and safety profile of peptide Active Pharmaceutical Ingredients (APIs). For this reason, it is of utmost importance to define the exact aggregation state of peptide drugs, particularly when the API is marketed as a ready-to-use solution. Consequently, appropriate non-destructive techniques able to replicate the peptide environment must be employed. In our work, we exploited Asymmetrical Flow Field-Flow Fractionation (AF4), connected to UV, dRI, fluorescence, and MALS detectors, to fully characterize the aggregation state of Liraglutide, a peptide API used for the treatment of diabetes type 2 and chronic obesity. In previous studies, Liraglutide was hypothesized to assemble into hexa-octamers in phosphate buffer, but no information on its behavior in the formulation medium was provided up to now. The method used allowed researchers to work using formulation as the mobile phase with excellent recoveries and LoQ/LoD, discerning between stable and degraded samples, and detecting, when present, aggregates up to 108 Da. The native state of Liraglutide was assessed and found to be an association into pentamers, with a non-spherical conformation. Combined to benchmark analyses, the sameness study was complete and descriptive, also giving insight on the aggregation process and covalent/non-covalent aggregate types.

Failure mode identification of Insulin drug products - Impact of relevant stress conditions on the quality of the drug

Fast-acting insulin drug products (DPs) are carried and administered by diabetic patients to maintain their blood glucose level throughout the day, exposing the DPs to stress conditions. Apidra, Novolog, and Humalog insulin DPs were tested under various stress conditions. Dynamic light scattering (DLS), and size exclusion chromatography (SEC) were used to monitor the stability and aggregation. Thermal stress alone did not influence the stability. However, 24 hr exposure to vigorous mechanical stress shifted the DLS size peaks of Novolog and Humalog from 5 ± 1 nm to > 50.9 ± 25.6 nm, and the SEC native protein peak areas decreased 52% for Novolog and 18.4% for Humalog. Combined stress accelerated protein aggregation more drastically. Novolog and Humalog size shifted (>75 nm) after 3 hr and the peak area decreased > 97.9% after 6 hr exposure, indicating that high temperature accelerated the aggregation triggered by agitation. Soluble aggregates were captured by DLS early on compared to SEC. Apidra was comparably stable indicating DP formulation plays a critical role in stability. Our study provides a greater understanding of potential failure modes patients and care givers may encounter while handling insulin DPs.

Best Practices for Aggregate Quantitation of Antibody Therapeutics by Sedimentation Velocity Analytical Ultracentrifugation

Analytical ultracentrifugation (AUC) is a critical analytical tool supporting the development and manufacture of protein therapeutics. AUC is routinely used as an assay orthogonal to size exclusion chromatography for aggregate quantitation. This article distills the experimental and analysis procedures used by the authors for sedimentation velocity AUC into a series of best-practices considerations. The goal of this distillation is to help harmonize aggregate quantitation approaches across the biopharmaceutical industry. We review key considerations for sample and instrument suitability, experimental design, and data analysis best practices and conversely, highlight potential pitfalls to accurate aggregate analysis. Our goal is to provide experienced users benchmarks against which they can standardize their analyses and to provide guidance for new AUC analysts that will aid them to become proficient in this fundamental technique.

Analysis of Proteins, Biologics, and Nanoparticles in Biological Fluids Using Asymmetrical Flow Field-Flow Fractionation

With the increasing interest in biopharmaceuticals such as proteins, antibodies, and nucleic acids, there is a corresponding increase in the need for characterizing such components. Much effort is spent on characterization in the early drug development phases as well as during formulation development and quality control. One parameter that is commonly investigated is the size distribution of the macromolecular components to deduce if there is aggregation or degradation occurring, if conformational changes occur, or if there are interactions with excipients. While the properties of the protein drug in the buffer system or in the pharmaceutical formulation are important, possibly even more interesting are the properties of the drug once it enters the body. Size characterization of macromolecules in biological fluids has traditionally been an area hampered by the complexity of the matrix. The large amount of indigenous components can interfere with commonly applied analytical techniques for size characterization. However, the separation technique asymmetrical flow field-flow fractionation (AF4) has recently shown increasing applicability for the characterization of components in blood plasma and serum. This article reviews some aspects of applying AF4 to plasma, serum, milk, and cerebrospinal fluid in the field of analysis and characterization of proteins, biologics, and nanoparticles in biological fluids.

Physicochemical and functional characterization of HS016, a biosimilar of adalimumab (Humira)

The characterization of a biosimilar drug HS016, the reference product adalimumab (Humira), and their biosimilarities were determined using physical chemistry and functional similarity tests. The primary and higher order structures, size and charge variants, glycosylation profiles, and in vitro potency of both antibodies were characterized both for unstressed and stability samples. Slight differences were observed in the relative levels of methionine oxidation, low molecular weight components, terminal lysine variant, high mannoses and galactosylated glycans between HS016 and Humira. However, no differences in antigen binding activity, Fc receptor affinity, antibody-dependent cell-mediated cytotoxicity or complemented-dependent cytotoxicity were found. The primary and higher order structures, physicochemical properties, and biological activity of HS016 and adalimumab were similar.

The importance of being metal-free: The critical choice of column hardware for size exclusion chromatography coupled to high resolution mass spectrometry

The goal of the study was to evaluate the possibilities offered by a new generation of metal-free SEC column to perform direct SEC-MS of protein biopharmaceuticals using ammonium acetate as the main mobile phase additive. The prototype metal-free SEC column hardware used in this work was a polyether ether ketone (PEEK) infused stainless steel tube including PEEK frits. This PEEK-lined column provides a fully bioinert and metal-free fluidic path, while maintaining the stability of the metal hardware, and could be a good solution to limit possible undesired interactions between proteins and column wall/frits. This prototype metal-free SEC column was systematically compared with a conventional stainless-steel SEC column hardware packed with the same stationary phase material. Four different mAb products, namely trastuzumab, palivizumab, bevacizumab and NISTmAb, and one antibody drug conjugate (ADC), trastuzumab emtansine, were selected as test samples. It appears that peak symmetry, separation of low molecular weight species (LMWS), and the recovery of high molecular weight species (HMWS) were significantly improved for the different biopharmaceutical products on the metal-free SEC column. It has also been demonstrated that the largest differences between standard and metal-free SEC columns were observed for the most basic mAbs (high pI), which confirms that electrostatic interactions between the mAb and the metallic parts of the column (frits and inlet tube) could be responsible for the issues observed when performing SEC analysis with volatile mobile phase. Finally, it was feasible to perform SEC-MS analysis for a wide range of biopharmaceutical products using volatile mobile phase. Our results also highlight that an inappropriate column could bias the quantification of size variants when using MS-compatible mobile phases. Therefore, metal-free column, such as the PEEK-lined column, should be preferentially selected for SEC-MS analysis.

Analysis of Peptides using Asymmetrical Flow Field-flow Fractionation (AF4)

While asymmetrical flow field-flow fractionation (AF4) has been widely used for separation of high molecular weight species and even particles, its ability to resolve lower molecular weight species has rarely been explored. Over the course of many projects, we have discovered that AF4 can be an effective analytical method for separating peptides from oligomers and higher molecular weight aggregates. The methodology can be used even for peptides as small as 2 kD in molecular weight. Using multi-angle laser light scattering (MALLS) detection, accurate masses of the parent peptide can be obtained, provided accurate extinction coefficients are provided. It was shown that AF4 can be stability-indicating, suggesting that AF4-MALLS may be a suitable alternative to the use of SEC to monitor the aggregation of peptides.

Plate Reader-Based Analytical Method for the Size Distribution of Submicron-Sized Protein Aggregates Using Three-Dimensional Homodyne Light Detection

The assessment of aggregates is essential in biopharmaceutical development. Although submicron-sized aggregates are considered to have a potential immunogenicity risk, analytical techniques are limited. In this study, we present a new analytical technique using three-dimensional homodyne light detection (3D-HLD). In this system, submicron-sized particles are quantified by combining the reflected light detection of each particle by high-speed 3D scan and then enhancing the amplitude of the reflected light using HLD. The particle concentrations and size distributions of human tetanus immune globulin (TIG) aggregates generated by stirring were measured using 3D-HLD. Both concentrations and distributions were comparable to those obtained via resonant mass measurement (RMM), a technique commonly used for submicron-sized particle measurement. Aiming at feasibility assessment of 3D-HLD for the high-through-put formulation development, 30 formulations of TIG and rituximab under agitation stress were analyzed by 3D-HLD. The results showed that 3D-HLD can automatically and simultaneously assess the aggregate concentrations and size distributions of at least 90 samples. This study demonstrates that 3D-HLD can be used for submicron-sized aggregate analysis as an orthogonal method to RMM and also as a screening tool during formulation development.

Size-based Degradation of Therapeutic Proteins - Mechanisms, Modelling and Control

Protein therapeutics are in great demand due to their effectiveness towards hard-to-treat diseases. Despite their high demand, these bio-therapeutics are very susceptible to degradation via aggregation, fragmentation, oxidation, and reduction, all of which are very likely to affect the quality and efficacy of the product. Mechanisms and modelling of these degradation (aggregation and fragmentation) pathways is critical for gaining a deeper understanding of stability of these products. This review aims to provide a summary of major developments that have occurred towards unravelling the mechanisms of size-based protein degradation (particularly aggregation and fragmentation), modelling of these size-based degradation pathways, and their control. Major caveats that remain in our understanding and control of size-based protein degradation have also been presented and discussed.

Interest of flow injection spectrophotometry as an orthogonal method for analyzing biomolecule aggregates: Application to stressed monoclonal antibody study

This study aimed to explore the suitability of flow injection spectrophotometry (FIS) to analyze three degraded therapeutic monoclonal antibodies (bevacizumab, nivolumab, and rituximab). For this purpose, aggregates were generated with stirring, freeze-thaw, and heat stresses. The intact and stressed mab samples were filtered with 0.22 µm hydrophilic filters and analyzed by size exclusion chromatography (SEC), cation-exchange chromatography (CEX), and FIS. In terms of quantitative and qualitative analysis, protein loss and structural changes were assessed. Various aggregates profiles were obtained according to the mabs and the stresses. FIS allowed performing very satisfactory quantifications for each mab with intermediate precision RSD < 3.0 % and recovery between 97.9 and 102.0 %. From the protein loss measurements, it appears that SEC underestimates the mab aggregate proportions up to two times less as compared with FIS since the latter avoids any non-specific interactions (electrostatic or hydrophobic interactions). Using second derivative spectroscopy and multivariate data analysis, we noticed apparent structural differences, located in the regions 245-265 nm for rituximab and nivolumab and 280-300 nm for bevacizumab, depending on the stress. The FIS complementarity with the other techniques used in this study allowed us to demonstrate that the three mabs behave differently for a given stress condition. While extreme mechanical stress formed large aggregates irrespective of the mabs, rituximab showed to be less stable and more sensitive than the two other mabs under freeze-thaw and heat stresses, generating large aggregates (>200 nm) and partial unfolding. Nivolumab tends to form small aggregates less than 50 nm when heated and freeze-thawed. Moreover, freeze-thaw seems to generate native IgG-1 aggregates with rituximab. Similarly, bevacizumab showed to form these IgG-1 aggregates and was resistant to freeze-thaw, likely thanks to trehalose cryoprotectant from its formulation. Finally, FIS associated with multivariate analysis can provide rich information in one single run and appears to be a fast, simple, and reliable method to set complementary and orthogonal approaches for protein aggregates monitoring.

High-Throughput Screening for Colloidal Stability of Peptide Formulations Using Dynamic and Static Light Scattering

Selection of an appropriate formulation to stabilize therapeutic proteins against aggregation is one of the most challenging tasks in early-stage drug product development. The amount of aggregates is more difficult to quantify in the case of peptides due to their small molecular size. Here, we investigated the suitability of diffusion self-interaction parameters (k_D) and osmotic second virial coefficients (B₂₂) for high-throughput (HT) screening of peptide formulations regarding their aggregation risk. These parameters were compared to the effect of thermal stress on colloidal stability. The formulation matrix comprised six buffering systems at two selected pH values, four tonicity agents, and a common preservative. The results revealed that electrostatic interactions are the main driver to control colloidal stability. Preferred formulations consisted of acetate and succinate buffer at pH 4.5 combined with glycerol or mannitol and optional m-cresol. k_D proved to be a suitable surrogate for B₂₂ as an indicator of high colloidal stability in the case of peptides as was previously described for globular proteins and antibodies. Formulation assessment solely based on k_D obtained by HT methods offers important insights into the optimization of colloidal stability during the early development of peptide-based liquid formulations and can be performed with a limited amount of peptide (∼360 mg).

Analytical methods for process and product characterization of recombinant adeno-associated virus-based gene therapies

The optimization of upstream and downstream processes for production of recombinant adeno-associated virus (rAAV) with consistent quality depends on the ability to rapidly characterize critical quality attributes (CQAs). In the context of rAAV production, the virus titer, capsid content, and aggregation are identified as potential CQAs, affecting the potency, purity, and safety of rAAV-mediated gene therapy products. Analytical methods to measure these attributes commonly suffer from long turnaround times or low throughput for process development, although rapid, high-throughput methods are beginning to be developed and commercialized. These methods are not yet well established in academic or industrial practice, and supportive data are scarce. Here, we review both established and upcoming analytical methods for the quantification of rAAV quality attributes. In assessing each method, we highlight the progress toward rapid, at-line characterization of rAAV. Furthermore, we identify that a key challenge for transitioning from traditional to newer methods is the scarcity of academic and industrial experience with the latter. This literature review serves as a guide for the selection of analytical methods targeting quality attributes for rapid, high-throughput process characterization during process development of rAAV-mediated gene therapies.

Instability of therapeutic proteins - An overview of stresses, stabilization mechanisms and analytical techniques involved in lyophilized proteins

Solid-state is the preferred choice for storage of protein therapeutics to improve stability and preserve the biological activity by decreasing the physical and chemical degradation associated with liquid protein formulations. Lyophilization or freeze-drying is an effective drying method to overcome the instability problems of proteins. However, the processing steps (freezing, primary drying and secondary drying) involved in the lyophilization process can expose the proteins to various stress and harsh conditions, leading to denaturation, aggregation often a loss in activity of protein therapeutics. Stabilizers such as sugars and surfactants are often added to protect the proteins against physical stress associated with lyophilization process and storage conditions. Another way to curtail the degradation of proteins due to process related stress is by modification of the lyophilization process. Slow freezing, high nucleation temperature, decreasing the extent of supercooling, and annealing can minimize the formation of the interface (ice-water) by producing large ice crystals with less surface area, thereby preserving the native structure and stability of the proteins. Hence, a thorough understanding of formulation composition, lyophilization process parameters and the choice of analytical methods to characterize and monitor the protein instability is crucial for development of stable therapeutic protein products. This review provides an overview of various stress conditions that proteins might encounter during lyophilization process, mechanisms to improve the stability and analytical techniques to tackle the proteins instability during both freeze-drying and storage.

Asymmetrical flow field-flow fractionation to probe the dynamic association equilibria of β-D-galactosidase

Protein dynamics play a significant role in many aspects of enzyme activity. Monitoring of structural changes and aggregation of biotechnological enzymes under native conditions is important to safeguard their properties and function. In this work, the potential of asymmetrical flow field-flow fractionation (AF4) to study the dynamic association equilibria of the enzyme β-D-galactosidase (β-D-Gal) was evaluated. Three commercial products of β-D-Gal were investigated using carrier liquids containing sodium chloride or ammonium acetate, and the effect of adding magnesium (II) chloride to the carrier liquid was assessed. Preservation of protein structural integrity during AF4 analysis was essential and the influence of several parameters, such as the focusing step (including use of frit-inlet), cross flow, and injected amount, was studied. Size-exclusion chromatography (SEC) and dynamic light scattering (DLS) were used to corroborate the in-solution enzyme oligomerization observed with AF4. In contrast to SEC, AF4 provided sufficiently mild separation conditions to monitor protein conformations without disturbing the dynamic association equilibria. AF4 analysis showed that ammonium acetate concentrations above 40 mM led to further association of the dimers ("tetramerization") of β-D-Gal. Magnesium ions, which are needed to activate β-D-Gal, appeared to induce dimer association, raising justifiable questions about the role of divalent metal ions in protein oligomerization and on whether tetramers or dimers are the most active form of β-D-Gal.

Sedimentation Velocity Analytical Ultracentrifugation Analysis of Marketed Rituximab Drug Product Size Distribution

PURPOSE

Analytical methods suitable for intact drug products are often necessary to evaluate the equivalence in physicochemical properties between two drug products (DP) containing the same drug substance (DS), e.g., an innovator biologic drug and its proposed biosimilar. Analytical Ultracentrifugation (AUC) is a biophysics technique applied to the analysis of size and shape of biomolecules. However, the application of AUC to formulated monoclonal antibody (mAb) DP at high concentration has not been reported.

METHODS

A sedimentation velocity (SV) AUC procedure with a short-pathlength centerpiece was applied to two marketed rituximab DPs, Rituxan® (US) and Reditux® (India), without any buffer exchange or dilution. Detailed precision analysis was performed.

RESULTS

Highly reproducible sedimentation coefficient values (S) and peak areas were obtained for the dominant (> 84%) monomeric rituximab peak. The minor mAb fragment peaks had large variation in both S values and peak areas (3-12%). The identification of oligomer peaks was only reproducible once the abundance was higher than 2%.

CONCLUSIONS

SV-AUC provides an orthogonal characterization tool for protein size distribution, composition and assay, which could be informative for biosimilar drug developers who mostly only have access to formulated mAb. However, AUC needs thorough validation on its accuracy, precision and sensitivity.

Quantitative analysis of weakly bound insulin oligomers in solution using polarized multidimensional fluorescence spectroscopy

Being able to measure the size and distribution of oligomers in solution is a critical issue in the manufacture and stability of insulin and other protein formulations. Measuring oligomers reliably can however be complicated, due to their fragile self-assembled structures, which are held together by weak forces. This can cause issues in chromatographic based methods, where dissociation or re-equilibration of oligomer populations can occur e.g. upon dilution in a different eluting buffer, but also for light scattering based methods like dynamic light scattering (DLS) where the size difference involved (often less than a factor 3) does not allow mixtures of oligomers to be resolved. Intrinsic fluorescence offers an attractive alternative as it is non-invasive, sensitive but also because it contains scattered light when implemented via excitation emission matrix (EEM) measurements, that is sensitive to changes in particle size. Here, using insulin at formulation level concentrations, we show for the first time how EEM can both discriminate and quantify the proportion of oligomeric states in solution. This was achieved by using the Rayleigh scatter (RS) band and the fluorescence signal contained in EEM. After validating size changes with DLS, we show in particular how the volume under the RS band correlated linearly with protein/oligomer molecular weight, in agreement with the Debye-Zimm relationship. This was true for the RS data from both EEM and polarized EEM (pEEM) measurements, the latter providing a stronger scatter signal, more sensitive to particle size changes. The fluorescence signal was then used with multivariate curve resolution (MCR) to quantify more precisely the soluble oligomer composition of insulin solutions. In conditions that promoted the formation of mainly one type of oligomer (monomer, dimer, or hexamer), pEEM-MCR helped identify the presence of small amounts of other oligomeric forms, while in conditions that were previously said to favour the insulin tetramer, we show that in the presence of zinc, these insulin samples were instead a heterogenous mixture composed of mostly dimers and hexamers. These MCR results correlated in all cases with the observed discrimination by principal component analysis (PCA), and deviations observed in the RS data. In conclusion, using pEEM scatter and emission components with chemometric data analysis provides a unique analytical method for characterising and monitoring changes in the soluble oligomeric state of proteins.

High Performance Size Exclusion Chromatography and High-Throughput Dynamic Light Scattering as Orthogonal Methods to Screen for Aggregation and Stability of Monoclonal Antibody Drug Products

The presence of aggregates in monoclonal antibody (mAb) drug product (DP) formulations can present product quality challenges. Here we show that use of High Performance Size Exclusion Chromatography (HP-SEC), in conjunction with high-throughput dynamic light scattering (HT-DLS) analyses of mAb DPs can be a useful strategy to determine monomer content and the presence of aggregates under simulated stress conditions. This analytical approach was used to evaluate four commercially available mAb DPs under different conditions i.e.; original formulations, diluted, and thermo-mechanical stressed condition. Due to particle size limitations of HP-SEC columns, resulting in particles accumulating in the column frits prior to reaching the detector for analysis, there is a possibility that large mAb aggregates may not be detected. Both HP-SEC and HT-DLS were able to detect and resolve the mAb monomer (~10-12 nm) of the DPs in their recommended storage conditions. However, the ability to detect large aggregates (>40 nm) by both analytical methods differed, and HT-DLS was able to detect aggregates between 60 nm and 1400 nm under stress conditions. Our data indicates that HP-SEC, in conjunction with HT-DLS, may be beneficial to detect both mAb DP monomer content and multiple aggregate species (1-1000 nm) in the submicron size range.

Electron microscopy-based semi-automated characterization of aggregation in monoclonal antibody products

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Size-based quantification of small heterogeneous proteins using electron microscopy.

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Electron microscopy as an orthogonal tool for characterizing protein aggregates.

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Quick assessment of small heterogeneous proteins via softEM, a GUI-based algorithm.

Aggregation is a critical parameter for protein-based therapeutics, due to its impact on the immunogenicity of the product. The traditional approach towards characterization of such products is to use a collection of orthogonal tools. However, the fact that none of these tools is able to completely classify the distribution and physical characteristics of aggregates, implies that there exists a need for additional analytical methods. We report one such method for characterization of heterogeneous population of proteins using transmission electron microscopy. The method involves semi-automated, size-based clustering of different protein species from micrographs. This method can be utilized for quantitative characterization of heterogeneous populations of antibody/protein aggregates from TEM images of proteins, and may also be applicable towards other instances of protein aggregation.

Characterization and Control of Dynamic Rearrangement in a Self-Assembled Antibody Carrier

Thorough characterization of protein assemblies is required for the control of structure and robust performance in any given application, especially for the safety and stability of protein therapeutics. Here, we report the use of multiple, orthogonal characterization techniques to enable control over the structure of a multivalent antibody carrier for future use in drug delivery applications. The carrier, known as Hex, contains six antibody binding domains that bind the Fc region of antibodies. Using size exclusion chromatography, analytical ultracentrifugation, and dynamic light scattering, we identified the stoichiometry of assembled Hex-antibody complexes and observed changes in the stoichiometry of nanocarriers when incubated at higher temperatures over time. The characterization data informed the modification of Hex to achieve tighter control over the protein assembly structure for future therapeutic applications. This work demonstrates the importance of using orthogonal characterization techniques and observing protein assembly in different conditions over time to fully understand and control structure and dynamics.

Evaluation of Nanoparticle Tracking Analysis for the Detection of Rod-Shaped Particles and Protein Aggregates

Nanoparticle tracking analysis (NTA) is an important technique for measuring hydrodynamic size of globular biological particles including liposomes and viruses. Less attention has been paid to NTA of rod-like particles, despite their considerable interest. For example, amyloid fibrils and protofibrils are protein aggregates with rod-like morphology, diameters of 2-15 nm, and lengths from 50 nm to 1 μm, and linked to diseases including Alzheimer's and Parkinson's. We used NTA to measure the concentration and hydrodynamic size of gold nanorods (10 nm diameter, 35-250 nm length) and myosin (2 nm diameter, 160 nm length), as models of rod-like particles. Measured hydrodynamic diameters of gold nanorods were consistent with theoretical calculations, as long as particle concentration and solution conditions were controlled. Myosin monomers were invisible by NTA, but a small population of aggregates was detected. We combined NTA results with other light scattering data to gain insight into number and size distribution of protein solutions containing both monomer and aggregates. Finally, we demonstrated the utility of NTA and its limitations by characterizing aggregates of alpha-synuclein. Of note is the use of NTA to detect a change in morphology from compact to elongated by analyzing the ratio of hydrodynamic size to intensity.

Shifting Paradigms Revisited: Biotechnology and the Pharmaceutical Sciences

In 2003, Crommelin et al. published an article titled: "Shifting paradigms: biopharmaceuticals versus low molecular weight drugs" (https://doi.org/10.1016/S0378-5173(03)00376-4). In the present commentary, 16 years later, we discuss pharmaceutically relevant aspects of the evolution of biologics since then. First, we discuss the increasing repertoire of biologics, in particular, the rapidly growing monoclonal antibody family and the advent of advanced therapy medicinal products. Next, we discuss trends in formulation and characterization as well as summarize our current insights into immunogenicity of biologics. We spend a separate section on new product(ion) paradigms for biologics, such as cell-free production systems, production of advanced therapy medicinal products, and downscaled production approaches. Furthermore, we share our views on issues related to reaching the patient, including routes and techniques of administration, alternative development models for affordable biologics, biosimilars, and handling of biologics. In the concluding section, we outline outstanding issues and make some suggestions for resolving those.

Transient Incomplete Separation Facilitates Finding Accurate Equilibrium Dissociation Constant of Protein-Small Molecule Complex

Current practical methods for finding the equilibrium dissociation constant, K_d , of protein-small molecule complexes have inherent sources of inaccuracy. Introduced here is "accurate constant via transient incomplete separation" (ACTIS), which appears to be free of inherent sources of inaccuracy. Conceptually, a short plug of the pre-equilibrated protein-small molecule mixture is pressure-propagated in a capillary, causing fast transient incomplete separation of the complex from the unbound small molecule. A superposition of signals from these two components is measured near the capillary exit and used to calculate a fraction of unbound small molecule, which, in turn, is used to calculate K_d . Herein the validity of ACTIS is proven theoretically, its accuracy is verified by computer simulation, and its practical use is demonstrated. ACTIS has the potential to become a reference-standard method for determining K_d  values of protein-small molecule complexes.

Physicochemical and functional assessments demonstrating analytical similarity between rituximab biosimilar HLX01 and the MabThera®

Development of bio-therapeutics has exhibited exponential growth in China over the past decade. However, no biosimilar drug has been approved in China (CN) due to the lack of a national biosimilar regulatory guidance. HLX01, a rituximab biosimilar developed in China under European Medicines Agency biosimilar guidelines and requirements, was the first such drug submitted for regulatory review in China, and it is expected to receive approval there as a biosimilar product. To demonstrate the analytical similarities of HLX01, CN-rituximab (sourced in China but manufactured in Europe) and EU-rituximab (sourced and manufactured in Europe), an extensive 3-way physicochemical and functional similarity assessment using a series of orthogonal and state-of-the-art techniques was conducted, following the similarity requirement guidelines recently published by China's Center for Drug Evaluation. The results of the similarity study showed an identical protein amino acid sequence and highly similar primary structures between HLX01 and the reference product (RP) MabThera®, along with high similarities in higher order structures, potency, integrity, purity and impurity profiles, biological and immunological binding functions, as well as degradation behaviors under stress conditions. In addition, HLX01 presented slightly lower aggregates and better photostability compared with the RP. Despite slight changes in relative abundance of glycan moieties and heavy chain C-terminal lysine modification, no differences in biological activities and immunological properties were observed between the RP and HLX01. In conclusion, HLX01 is highly similar to CN- and EU-sourced RP in terms of physicochemical properties and biological activities, suggesting similar product quality, efficacy, and safety. The regulatory requirements interpreted and applied towards the HLX01 marketing application sets a precedent for analytical similarity assessment of biosimilar products in China.

Resolving protein mixtures using microfluidic diffusional sizing combined with synchrotron radiation circular dichroism

Circular dichroism spectroscopy has become a powerful tool to characterise proteins and other biomolecules. For heterogeneous samples such as those present for interacting proteins, typically only average spectroscopic features can be resolved. Here we overcome this limitation by using free-flow microfluidic size separation in-line with synchrotron radiation circular dichroism to resolve the secondary structure of each component of a model protein mixture containing monomers and fibrils. To enable this objective, we have integrated far-UV compatible measurement chambers into PDMS-based microfluidic devices. Two architectures are proposed so as to accommodate for a wide range of concentrations. The approach, which can be used in combination with other bulk measurement techniques, paves the way to the study of complex mixtures such as the ones associated with protein misfolding and aggregation diseases including Alzheimer's and Parkinson's diseases.

Proteins and antibodies in serum, plasma, and whole blood-size characterization using asymmetrical flow field-flow fractionation (AF4)

The analysis of aggregates of therapeutic proteins is crucial in order to ensure efficacy and patient safety. Typically, the analysis is performed in the finished formulation to ensure that aggregates are not present. An important question is, however, what happens to therapeutic proteins, with regard to oligomerization and aggregation, after they have been administrated (i.e., in the blood). In this paper, the separation of whole blood, plasma, and serum is shown using asymmetric flow field-flow fractionation (AF4) with a minimum of sample pre-treatment. Furthermore, the analysis and size characterization of a fluorescent antibody in blood plasma using AF4 are demonstrated. The results show the suitability and strength of AF4 for blood analysis and open new important routes for the analysis and characterization of therapeutic proteins in the blood.

Sedimentation velocity analytical ultracentrifugation for characterization of therapeutic antibodies

Sedimentation velocity analytical ultracentrifugation (SV-AUC) coupled with direct computational fitting of the observed concentration profiles (sedimentating boundary) have been developed and widely used for the characterization of macromolecules and nanoparticles in solution. In particular, size distribution analysis by SV-AUC has become a reliable and essential approach for the characterization of biopharmaceuticals including therapeutic antibodies. In this review, we describe the importance and advantages of SV-AUC for studying biopharmaceuticals, with an emphasis on strategies for sample preparation, data acquisition, and data analysis. Recent discoveries enabled by AUC with a fluorescence detection system and potential future applications are also discussed.

Biosimilarity under stress: A forced degradation study of Remicade® and Remsima™

Remsima™ (infliximab) is the first biosimilar monoclonal antibody (mAb) approved by the European Medical Agency and the US Food and Drug Administration. Remsima™ is highly similar to its reference product, Remicade®, with identical formulation components. The 2 products, however, are not identical; Remsima™ has higher levels of soluble aggregates, C-terminal lysine truncation, and fucosylated glycans. To understand if these attribute differences could be amplified during forced degradation, solutions and lyophilized powders of the 2 products were subjected to stress at elevated temperature (40-60°C) and humidity (dry-97% relative humidity). Stress-induced aggregation and degradation profiles were similar for the 2 products and resulted in loss of infliximab binding to tumor necrosis factor and FcγRIIIa. Appearances of protein aggregates and hydrolysis products were time- and humidity-dependent, with similar degradation rates observed for the reference and biosimilar products. Protein powder incubations at 40°C/97% relative humidity resulted in partial mAb unfolding and increased asparagine deamidation. Minor differences in heat capacity, fluorescence, levels of subvisible particulates, deamidation and protein fragments were observed in the 2 stressed products, but these differences were not statistically significant. The protein solution instability at 60°C, although quite significant, was also similar for both products. Despite the small initial analytical differences, Remicade® and Remsima™ displayed similar degradation mechanisms and kinetics. Thus, our results show that the 2 products are highly similar and infliximab's primary sequence largely defines their protein instabilities compared with the limited influence of small initial purity and glycosylation differences in the 2 products.

Visual Detection of Denatured Glutathione Peptides: A Facile Method to Visibly Detect Heat Stressed Biomolecules

Every year pharmaceutical companies use significant resources to mitigate aggregation of pharmaceutical drug products. Specifically, peptides and proteins that have been denatured or degraded can lead to adverse patient reactions such as undesired immune responses. Current methods to detect aggregation of biological molecules are limited to costly and time consuming processes such as high pressure liquid chromatography, ultrahigh pressure liquid chromatography and SDS-PAGE gels. Aggregation of pharmaceutical drug products can occur during manufacturing, processing, packaging, shipment and storage. Therefore, a facile in solution detection method was evaluated to visually detect denatured glutathione peptides, utilizing gold nanoparticle aggregation via 3-Aminopropyltreithoxysilane. Glutathione was denatured using a 70 °C water bath to create an accelerated heat stressed environment. The peptide, gold nanoparticle and aminosilane solution was then characterized via, UV-Vis spectroscopy, FTIR spectroscopy, dynamic light scattering and scanning electron microscopy. Captured images and resulting absorbance spectra of the gold nanoparticle, glutathione, and aminosilane complex demonstrated visual color changes detectable with the human eye as a function of the denaturation time. This work serves as an extended proof of concept for fast in solution detection methods for glutathione peptides that have experienced heat stress.