Characterization of therapeutic monoclonal antibodies reveals differences between in vitro and in vivo time-course studies

Assessing Physicochemical Stability of Monoclonal Antibodies in a Simulated Subcutaneous Environment

Monoclonal antibodies (mAbs) are being increasingly administered by the subcutaneous (SC) route compared to the traditional intravenous route. Despite the growing popularity of the subcutaneous route, our current knowledge regarding the intricate mechanistic changes happening in the formulation after injection in the subcutaneous space, as well as the in vivo stability of administered mAbs, remains quite limited. Changes in the protein environment as it transitions from a stabilized, formulated drug product in an appropriate container closure to the SC tissue environment can drastically impact the structural stability and integrity of the injected protein. Interactions of the protein with components of the extracellular matrix can lead to changes in its structure, potentially impacting both safety and efficacy. Investigating protein stability in the SC space can enable early assessment of risk and performance of subcutaneously administered proteins influencing clinical decisions and formulation development strategies. The Subcutaneous Injection Site Simulator (SCISSOR) is a novel in vitro system that mimics the subcutaneous injection site and models the events that a protein goes through as it transitions from a stabilized formulation environment to the dynamic physiological space. In this paper, we utilize the SCISSOR to probe for biophysical and chemical changes in seven mAbs post SC injection using a variety of analytical techniques. After 24 h, all mAbs demonstrated a relative decrease in conformational stability, an increase in fragmentation, and elevated acidic species. Higher order structure analysis revealed a deviation in the secondary structure from the standard and an increase in the number of unordered species. Our findings suggest an overall reduced stability of mAbs after subcutaneous administration. This reduced stability could have a potential impact on safety and efficacy. In vitro systems such as the SCISSOR combined with downstream analyses have potential to provide valuable information for assessing the suitability of lead molecules and aid in formulation design optimized for administration in the intended body compartment, thus improving chances of clinical success.

Does Aggregation of Therapeutic IgGs in PBS Offer a True Picture of What Happens in Models Derived from Human Body Fluids?

Therapeutic proteins such as monoclonal antibodies (mAb) are known to form aggregates due to various factors. Phosphate buffered saline (PBS), human serum, and human serum filtrate (HSF) are some of the models used to analyze mAb stability in physiologically relevant in-vitro conditions. In this study, aggregation of mAb in PBS and models derived from body fluids seeded with mAb samples subjected to various stresses were compared. Samples containing mAb subjected to pH, temperature, UV light, stirring, and interfacial agitation stress were seeded into different models for 2 case studies. In the first case study, %HMW (high molecular weight species) of mAb in PBS and HSF were compared using size exclusion chromatography. It was found that change in %HMW was higher in PBS compared to HSF. For example, PBS containing mAb that was subjected to UV light stress showed change in HMW by >10 % over 72 h, but the change was <5 % in HSF. In second case study, aggregates particles of FITC tagged mAb were monitored in PBS and serum using fluorescence microscope image processing. It was found that PBS and serum containing mAb subjected to stirring and interfacial agitation resulted in aggregates of >2 µm size, and average size and percentage number of particles having >10 µm size was higher in serum compared to PBS at all analysis time point. Overall, it was found that aggregation of mAb in PBS was different from that in human body fluids. Second case study also showed the importance of advanced strategies for further characterization of mAb in serum.

Protein Stability After Administration: A Physiologic Consideration

Regulatory authorities and the scientific community have identified the need to monitor the in vivo stability of therapeutic proteins (TPs). Due to the unique physiologic conditions in patients, the stability of TPs after administration can deviate largely from their stability under drug product (DP) conditions. TPs can degrade at substantial rates once immersed in the in vivo milieu. Changes in protein stability upon administration to patients are critical as they can have implications on patient safety and clinical effectiveness of DPs. Physiologic conditions are challenging to simulate and require dedicated in vitro models for specific routes of administration. Advancements of in vitro models enable to simulate the exposure to physiologic conditions prior to resource demanding pre-clinical and clinical studies. This enables to evaluate the in vivo stability and thus may allow to improve the safety/efficacy profile of DPs. While in vitro-in vivo correlations are challenging, benchmarking DP candidates enables to identify liabilities and optimize molecules. The in vivo stability should be an integral part of holistic stability assessments during early development. Such assessments can accelerate development timelines and lead to more stable DPs for patients.

Quantifying methionine sulfoxide in therapeutic protein formulation excipients as sensitive oxidation marker

Methionine is a common excipient used in therapeutic protein liquid formulations as stabilizer and antioxidant. The oxidation of methionine to methionine sulfoxide can be regarded as a sensitive marker of oxidative stress for drug product storage conditions. In this study, a sensitive HPLC method for the quantification of methionine sulfoxide in formulated protein product was developed and qualified according to regulatory requirements using a SIELC® Primesep 100 column with UV detection. The separation involves a mixed-mode mechanism including reversed phase and cationic exchange modalities. The operating range of the method was established between 1 µM and 35 µM of methionine sulfoxide. In this testing range, the method was shown to be linear (R² > 0.99), accurate (Recovery 92.9 - 103.6%, average recovery = 99.8 ± 1.4%) and precise (intermediate precision at LoQ, CV = 2.9%). The developed test system was successfully applied to study the effects of temperature and storage conditions on methionine sulfoxide formation in complex therapeutic antibody formulations.

Fate of Antibody and Polysorbate Particles in a Human Serum Model

Monoclonal antibodies (mAbs) and excipients can degrade owing to different stress factors they encounter during their life cycle or after administration in human body. This can result in the formation of aggregates and particulates. As particles can evoke an immune response in patients, it becomes increasingly important to monitor their fate after administration. In this study, we used a protein-free serum model to assess the fate of mAb and polysorbate (PS) particles under physiologic conditions. Commonly encountered stress conditions such as pH, temperature, extrusion, and shaking were chosen to generate mAb particles. Alkaline hydrolysis was used to generate PS particles. The fate of aggregates and particles was evaluated in serum and histidine buffer. We observed that depending on the nature of stress and the environment particles are subjected to, the fate of particles can differ substantially. The mAb aggregates generated by pH stress, showed reduction in HMWS from 26% to 6% over 14days in human serum filtrate. PS particles dissolved at 37°C but remained unaltered in Histidine at 5°C. Our results reinforce the need to track the fate of particles generated during drug product development upon exposure to physiologic conditions.

Characterization of N-Terminal Glutamate Cyclization in Monoclonal Antibody and Bispecific Antibody Using Charge Heterogeneity Assays and Hydrophobic Interaction Chromatography

N-terminal glutamate (E) cyclization to form pyroglutamate (pE) generates charge heterogeneities for mAbs and proteins. Thus far, pE formation rate in lyophilized formulation as compared to in liquid formulation has not been reported. Impact of pE on antibody biological activity has only been predicted or assessed using stressed samples that may contain other confounding degradations besides pE. Additionally, application of hydrophobic interaction chromatography (HIC) to separate pE has not been reported. In our study, N-terminal E cyclization was identified as the major degradation pathway in lyophilized formulation at elevated temperature for both monoclonal antibody (mAb-A) and IgG-like bispecific antibody (bsAb-A). pE was enriched in salt-gradient ion exchange chromatography (IEC) as pre-peak and in HIC as post-peak for both mAb-A and bsAb-A. Structure-function studies with pE-enriched IEC and HIC fractions confirmed that pE did not affect binding activities for mAb-A and bsAb-A. In vitro incubation of bsAb-A in serum and PBS revealed that the serum matrix may play a role in pE conversion in human serum, in contrast to the chemical reaction mechanism reported. These techniques can help in characterization of N-terminal E-to-pE cyclization and quality attribute severity assessment during therapeutic protein product 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.

Assessment of Antibody Stability in a Novel Protein-Free Serum Model

Therapeutic proteins can degrade upon administration as they are subjected to a variety of stresses in human body compartments. In vivo degradation may cause undesirable pharmacokinetic/pharmacodynamic profiles. Pre-clinical in vitro models have gained scientific interest as they enable one to evaluate the in vivo stability of monoclonal antibodies (mAbs) and ultimately can improve patient safety. We used a novel approach by stripping serum of endogenous proteins, which interfere with analytical test methods. This enabled the direct analysis of the target protein without laborious sample work-up procedures. The developed model retained the osmolality, conductivity, temperature, and pH of serum. We compared the impact of human, bovine, and artificial serum to accelerated stability conditions in histidine buffer. Target mAbs were assessed in regard to visible and sub-visible particles, as well as protein aggregation and fragmentation. Both mAbs degraded to a higher extent under physiological conditions compared to accelerated stability conditions. No relevant stability differences between the tested mAbs were observed. Our results reinforced the importance of monitoring protein stability in biological fluids or fluids emulating these conditions closely. Models enabling analysis in fluids directly allow high throughput testing in early pre-clinical stages and help in selecting molecules with increased in vivo stability.

Analytical Challenges Assessing Protein Aggregation and Fragmentation Under Physiologic Conditions

Therapeutic proteins are administered by injection or infusion. After administration, the physiologic environment in the desired body compartment - fluid or tissue - can impact protein stability and lead to changes in the safety and/or efficacy profile. For example, protein aggregation and fragmentation are critical quality attributes of the drug product and can occur after administration to patients. In this context, the in vivo stability of therapeutic proteins has gained increasing attention. However, in vivo protein aggregation and fragmentation are difficult to assess and have been rarely investigated. This mini-review summarizes analytical approaches to assess the stability of therapeutic proteins using simulated physiologic conditions. Furthermore, we discuss factors potentially causing in vivo protein aggregation, precipitation, and fragmentation in complex biological fluids. Different analytical approaches are evaluated with respect to their applicability and possible shortcomings when it comes to these degradation events in biological fluids. Tracking protein stability in biological fluids typically requires purifying or labeling the protein of interest to circumvent matrix interference of biological fluids. Improved analytical methods are strongly needed to gain knowledge on in vivo protein aggregation and fragmentation. In vitro models can support the selection of lead candidates and accelerate the pre-clinical development of therapeutic proteins.

Stability of monoclonal antibodies after simulated subcutaneous administration

Changes in the environment from the drug product to the human physiology might lead to physical and/or chemical modifications of the protein drug, such as in vivo aggregation and fragmentation. Although subcutaneous (SC) injection is a common route of administration for therapeutic proteins, knowledge on in vivo stability in the SC tissue is limited. In this study, we developed a physiologic in vitro model simulating the SC environment in patients. We assessed the stability of two monoclonal antibodies (mAbs) in four different protein-free fluids under physiologic conditions. We monitored protein stability over two weeks using a range of analytical methods, in analogy to testing purposes of a drug product. Both mAbs showed an increase of protein aggregates, fragments, and acidic species. mAb1 was consistently more stable in this in vitro model than mAb2, highlighting the importance of comparing the stability of different mAbs under physiologic conditions. Throughout the study, both mAbs were substantially less stable in bicarbonate buffers as compared to phosphate-buffered saline. In summary, our developed model was able to differentiate stability between molecules. Bicarbonate buffers were more suitable compared to phosphate-buffered saline in regards to simulating the in vivo conditions and evaluating protein liabilities.

Assessing Particle Formation of Biotherapeutics in Biological Fluids

The stability of therapeutic proteins can be impacted in vivo after administration, which may affect patient safety or treatment efficacy, or both. Stability testing of therapeutic proteins using models representing physiologic conditions may guide preclinical development strategy; however, to date only a few studies assessing the physical stability are available in the public domain. In this manuscript, the stability of seven fluorescently labeled monoclonal antibodies (mAbs) was evaluated in human serum and phosphate-buffered saline, two models often discussed to be representative of the situation in humans after intravenous administration. Subvisible particles were analyzed using light obscuration, flow imaging, and imaging flow cytometry. All methods showed that serum itself formed particles under in vitro conditions. Imaging flow cytometry demonstrated that mean particle size and counts of mAbs increased substantially in serum over five days; however, particle formation in phosphate-buffered saline was comparably low. Stability differences were observed across the mAbs evaluated, and imaging flow cytometry data indicated that fluorescently labeled mAbs primarily interacted with serum components. The results indicate that serum may be more suitable as in vitro model to simulate physiologic intravenous conditions in patients closely and evaluate the in vivo stability of therapeutic proteins. Fluorescence labeling and detection methods may be applied to differentiate particles containing therapeutic protein from high amounts of serum particles that form over time.

Micro-Heterogeneity of Antibody Molecules

Therapeutic monoclonal antibodies (mAbs) are mostly of the IgG class and constitute highly efficacious biopharmaceuticals for a wide range of clinical indications. Full-length IgG mAbs are large proteins that are subject to multiple posttranslational modifications (PTMs) during biosynthesis, purification, or storage, resulting in micro-heterogeneity. The production of recombinant mAbs in nonhuman cell lines may result in loss of structural fidelity and the generation of variants having altered stability, biological activities, and/or immunogenic potential. Additionally, even fully human therapeutic mAbs are of unique specificity, by design, and, consequently, of unique structure; therefore, structural elements may be recognized as non-self by individuals within an outbred human population to provoke an anti-therapeutic/anti-drug antibody (ATA/ADA) response. Consequently, regulatory authorities require that the structure of a potential mAb drug product is comprehensively characterized employing state-of-the-art orthogonal analytical technologies; the PTM profile may define a set of critical quality attributes (CQAs) for the drug product that must be maintained, employing quality by design parameters, throughout the lifetime of the drug. Glycosylation of IgG-Fc, at Asn297 on each heavy chain, is an established CQA since its presence and fine structure can have a profound impact on efficacy and safety. The glycoform profile of serum-derived IgG is highly heterogeneous while mAbs produced in mammalian cells in vitro is less heterogeneous and can be "orchestrated" depending on the cell line employed and the culture conditions adopted. Thus, the gross structure and PTM profile of a given mAb, established for the drug substance gaining regulatory approval, have to be maintained for the lifespan of the drug. This review outlines our current understanding of common PTMs detected in mAbs and endogenous IgG and the relationship between a variant's structural attribute and its impact on clinical performance.

Antibody Structure and Function: The Basis for Engineering Therapeutics

Antibodies and antibody-derived macromolecules have established themselves as the mainstay in protein-based therapeutic molecules (biologics). Our knowledge of the structure–function relationships of antibodies provides a platform for protein engineering that has been exploited to generate a wide range of biologics for a host of therapeutic indications. In this review, our basic understanding of the antibody structure is described along with how that knowledge has leveraged the engineering of antibody and antibody-related therapeutics having the appropriate antigen affinity, effector function, and biophysical properties. The platforms examined include the development of antibodies, antibody fragments, bispecific antibody, and antibody fusion products, whose efficacy and manufacturability can be improved via humanization, affinity modulation, and stability enhancement. We also review the design and selection of binding arms, and avidity modulation. Different strategies of preparing bispecific and multispecific molecules for an array of therapeutic applications are included.

Quantitation and modeling of post-translational modifications in a therapeutic monoclonal antibody from single- and multiple-dose monkey pharmacokinetic studies using mass spectrometry

Post-translational modifications (PTMs) of therapeutic monoclonal antibodies (mAbs) are important product quality attributes (PQAs) that can potentially impact drug stability, safety, and efficacy. The PTMs of a mAb may change remarkably in the bloodstream after drug administration compared to in vitro conditions. Thus, monitoring in vivo PTM changes of mAbs helps evaluate the criticality of PQAs during the product risk assessment. In addition, quantitation of the subject exposures to PTM variants helps assess the impact of PTMs on the safety and efficacy of therapeutic mAbs. Here, we developed an immunocapture-liquid chromatography/mass spectrometry (LC/MS) method to quantify in vivo PTM changes a therapeutic mAb overtime in single- and multiple-dose monkey pharmacokinetic (PK) studies. We also built mathematical models to predict the in vivo serum concentrations of PQAs, the subject exposures to PQAs, and the relative abundance of PQAs in single- and multiple-dose regimens. The model predictions are in good agreement with the experimental results. The immunocapture-LC/MS method and mathematical models enable bioanalytical chemists to quantitatively assess the criticality of PQAs during drug development.

Advances in capillary electrophoresis for the life sciences

Capillary electrophoresis (CE) played an important role in developments in the life sciences. The technique is nowadays used for the analysis of both large and small molecules in applications where it performs better than or is complementary to liquid chromatographic techniques. In this review, principles of different electromigration techniques, especially capillary isoelectric focusing (CIEF), capillary gel (CGE) and capillary zone electrophoresis (CZE), are described and recent developments in instrumentation, with an emphasis on mass spectrometry (MS) coupling and microchip CE, are discussed. The role of CE in the life sciences is shown with applications in which it had a high impact over the past few decades. In this context, current practice for the characterization of biopharmaceuticals (therapeutic proteins) is shown with CIEF, CGE and CZE using different detection techniques, including MS. Subsequently, the application of CGE and CZE, in combination with laser induced fluorescence detection and CZE-MS are demonstrated for the analysis of protein-released glycans in the characterization of biopharmaceuticals and glycan biomarker discovery in biological samples. Special attention is paid to developments in capillary coatings and derivatization strategies for glycans. Finally, routine CE analysis in clinical chemistry and latest developments in metabolomics approaches for the profiling of small molecules in biological samples are discussed. The large number of CE applications published for these topics in recent years clearly demonstrates the established role of CE in life sciences.

In Vivo Stability Profiles of Anti-factor D Molecules Support Long-Acting Delivery Approaches

The collection of aqueous humor (phase 1 b/2 Mahalo study) from patients dosed intravitreally with anti-factor D (AFD; FCFD4514S, lampalizumab), a humanized antibody fragment previously under investigation to treat geographic atrophy (GA) secondary to age-related macular degeneration, presented a unique opportunity to examine AFD properties in clinical samples. We investigated AFD stability and target-binding characteristics to set up strategies for engineering and evaluating optimized molecules that enable less frequent dosing. Two variants, AFD.v8 and AFD.v14, were evaluated as alternatives to AFD for longer-acting treatments. Mass spectrometry, surface plasmon resonance, and immunoassay were used to assess AFD stability and binding activity in aqueous humor samples from Mahalo patients. In vitro stability and binding activity of AFD, AFD.v8, and AFD.v14 were assessed in human vitreous humor versus buffer at 37 °C over 16 weeks and in vivo in rabbits over 28 days along with pharmacokinetic determinations. In human aqueous humor, AFD specific binding was >85% through 30 days, and deamidation was <3% through 60 days, consistent with the AFD stability and binding activity in vitreous humor from humans in vitro and rabbits in vivo. Target binding, stability, and rabbit pharmacokinetic parameters of AFD.v8 and AFD.v14 were similar to those of AFD. Physiological stability and activity of AFD translated across in vitro and in vivo studies in humans and rabbits. The two variants AFD.v8 and AFD.v14 demonstrated comparable potency and pharmacokinetics. These findings, along with previously demonstrated improved solubility of AFD.v8 and AFD.v14, provide proof-of-concept for developing other similar long-acting therapeutic variants.

Review of approaches and examples for monitoring biotransformation in protein and peptide therapeutics by MS

Biotherapeutic drugs have emerged in quantity in pharmaceutical pipelines, and increasingly diverse biomolecules are progressed through preclinical and clinical development. As purification, separation, mass spectrometer detection and data processing capabilities improve, there is opportunity to monitor drug concentration by traditional ligand-binding assay or MS measurement and to monitor metabolism, catabolism or other biomolecular mass variants present in circulation. This review highlights approaches and examples of monitoring biotransformation of biotherapeutics by MS as these techniques are poised to add value to drug development in years to come. The increased use of such approaches, and the successful quantitation of biotherapeutic structural modifications, will provide insightful data for the benefit of both researchers and patients.

Antibody characterization using novel ERLIC-MS/MS-based peptide mapping

Electrostatic repulsion hydrophilic interaction chromatography (ERLIC) coupled with mass spectrometry (MS) is a technique that is increasingly being used as a trapping/enrichment tool for glycopeptides/phosphorylated peptides or sample fractionation in proteomics research. Here, we describe a novel ERLIC-MS/MS-based peptide mapping method that was successfully used for the characterization of denosumab, in particular the analysis of sequence coverage, terminal peptides, methionine oxidation, asparagine deamidation and glycopeptides. Compared to reversed phase liquid chromatography (RPLC)-MS/MS methods, ERLIC demonstrated unique advantages in the retention of small peptides, resulting in 100% sequence coverage for both the light and heavy chains. It also demonstrated superior performance in the separation and characterization of asparagine deamidated peptides, which is known to be challenging by RPLC-MS/MS. The developed method can be used alone for peptide mapping-based characterization of monoclonal antibodies, or as an orthogonal method to complement the RPLC-MS/MS method. This study extends the applications of ERLIC from that of a trapping/fractioning column to biologic therapeutics characterization. The ERLIC-MS/MS method can enhance biologic therapeutics analysis with more reliability and confidence for bottom-up peptide mapping-based characterization.

Automated Affinity Capture and On-Tip Digestion to Accurately Quantitate in Vivo Deamidation of Therapeutic Antibodies

Deamidation of therapeutic antibodies may result in decreased drug activity and undesirable changes in pharmacokinetics and immunogenicity. Therefore, it is necessary to monitor the deamidation levels [during storage] and after in vivo administration. Because of the complexity of in vivo samples, immuno-affinity capture is widely used for specific enrichment of the target antibody prior to LC-MS. However, the conventional use of bead-based methods requires large sample volumes and extensive processing steps. Furthermore, with automation difficulties and extended sample preparation time, bead-based approaches may increase artificial deamidation. To overcome these challenges, we developed an automated platform to perform tip-based affinity capture of antibodies from complex matrixes with rapid digestion and peptide elution into 96-well microtiter plates followed by LC-MS analysis. Detailed analyses showed that the new method presents high repeatability and reproducibility with both intra and inter assay CVs < 8%. Using the automated platform, we successfully quantified the levels of deamidation of a humanized monoclonal antibody in cynomolgus monkeys over a time period of 12 weeks after administration. Moreover, we found that deamidation kinetics between in vivo samples and samples stressed in vitro at neutral pH were consistent, suggesting that the in vitro stress test may be used as a method to predict the liability to deamidation of therapeutic antibodies in vivo.

Quantitation and pharmacokinetic modeling of therapeutic antibody quality attributes in human studies

A thorough understanding of drug metabolism and disposition can aid in the assessment of efficacy and safety. However, analytical methods used in pharmacokinetics (PK) studies of protein therapeutics are usually based on ELISA, and therefore can provide a limited perspective on the quality of the drug in concentration measurements. Individual post-translational modifications (PTMs) of protein therapeutics are rarely considered for PK analysis, partly because it is technically difficult to recover and quantify individual protein variants from biological fluids. Meanwhile, PTMs may be directly linked to variations in drug efficacy and safety, and therefore understanding of clearance and metabolism of biopharmaceutical protein variants during clinical studies is an important consideration. To address such challenges, we developed an affinity-purification procedure followed by peptide mapping with mass spectrometric detection, which can profile multiple quality attributes of therapeutic antibodies recovered from patient sera. The obtained data enable quantitative modeling, which allows for simulation of the PK of different individual PTMs or attribute levels in vivo and thus facilitate the assessment of quality attributes impact in vivo. Such information can contribute to the product quality attribute risk assessment during manufacturing process development and inform appropriate process control strategy.

Cutting-edge capillary electrophoresis characterization of monoclonal antibodies and related products

Out of all categories, monoclonal antibodies (mAbs), biosimilar, antibody-drug conjugates (ADCs) and Fc-fusion proteins attract the most interest due to their strong therapeutic potency and specificity. Because of their intrinsic complexity due to a large number of micro-heterogeneities, there is a crucial need of analytical methods to provide comprehensive in-depth characterization of these molecules. CE presents some obvious benefits as high resolution separation and miniaturized format to be widely applied to the analysis of biopharmaceuticals. CE is an effective method for the separation of proteins at different levels. capillary gel electrophoresis (CGE), capillary isoelectric focusing (cIEF) and capillary zone electrophoresis (CZE) have been particularly relevant for the characterization of size and charge variants of intact and reduced mAbs, while CE-MS appears to be a promising analytical tool to assess the primary structure of mAbs and related products. This review will be dedicated to detail the current and state-of-the-art CE-based methods for the characterization of mAbs and related products.

Posttranslational Modifications and the Immunogenicity of Biotherapeutics

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

Assessing in vivo dynamics of multiple quality attributes from a therapeutic IgG4 monoclonal antibody circulating in cynomolgus monkey

Characterization of biopharmaceutical proteins and assessment and understanding of the critical quality attributes (CQAs) is a significant part of biopharmaceutical product development and is routinely performed in vitro. In contrast, systematic analysis of the quality attributes in vivo is not as widespread, although metabolism and clearance of multiple variants of therapeutic proteins administered to non-human primates and human subjects may have a different impact on safety, efficacy and exposure. The major hurdles of such studies are usually sample availability and technical capability. In this study, we used affinity purification coupled with liquid chromatography and mass spectrometric analysis of the digested protein for consistent and simultaneous detection of the full amino acid sequence of a therapeutic IgG4 monoclonal antibody, MAB1. This methodology allowed us to assess in vivo changes of all sequence-related modifications and quality attributes of MAB1 over the duration of a preclinical pharmacokinetic study in cynomolgus monkeys.

Capillary ion-exchange chromatography with nanogram sensitivity for the analysis of monoclonal antibodies

Ion-exchange chromatography (IEC) is widely used for profiling the charge heterogeneity of proteins, including monoclonal antibodies (mAbs). Despite good resolving power and robustness, ionic strength-based ion-exchange separations are generally product specific and can be time consuming to develop. In addition, conventional analytical scale ion-exchange separations require tens of micrograms of mAbs for each injection, amounts that are often unavailable in sample-limited applications. We report the development of a capillary IEC (c-IEC) methodology for the analysis of nanogram amounts of mAb charge variants. Several key modifications were made to a commercially available liquid chromatography system to perform c-IEC for charge variant analysis of mAbs with nanogram sensitivity. We demonstrate the method for multiple monoclonal antibodies, including antibody fragments, on different columns from different manufacturers. Relative standard deviations of <10% were achieved for relative peak areas of main peak, acidic and basic regions, which are common regions of interest for quantifying monoclonal antibody charge variants using IEC. The results herein demonstrate the excellent sensitivity of this c-IEC characterization method, which can be used for analyzing charge variants in sample-limited applications, such as early-stage candidate screening and in vivo studies.

Characterization of asparagine 330 deamidation in an Fc-fragment of IgG1 using cation exchange chromatography and peptide mapping

Deamidation is one of the most common degradation pathways for proteins and frequently occurs at "hot spots" with Asn-Gly, Asn-Ser or Asn-Thr sequences. Occasionally, deamidation may occur at other motifs if the local protein structure can participate or assist in the formation of the succinimide intermediate. Here we report the use of a chymotryptic peptide mapping method to identify and characterize a deamidated form of an IgG1 which was observed as an acidic peak in the cation exchange chromatography (CEX). The antibody was formulated in sodium acetate buffer, pH 5.3 and this deamidated form was observed mainly under thermal stress conditions. It was found that the IgG1 molecule with deamidation in the Fc region at asparagine residue 330 (in a Val-Ser-Asn-Lys motif) is the predominant form in this CEX peak, and was missed by tryptic mapping because the peptides are hydrophilic and elute near the void volume. In addition, a domain-based CEX method using papain digestion was developed to monitor the Asn 330 deamidation. These methods revealed that the Fc deamidation occurs mainly at Asn 330 in the VSNK motif at pH 5.3, whereas at pH 7.5, deamidation occurs predominantly at Asn 389 and Asn 394 in the NGQPENNYK motif.

Effect of ambient light on monoclonal antibody product quality during small-scale mammalian cell culture process in clear glass bioreactors

During a small-scale cell culture process producing a monoclonal antibody, a larger than expected difference was observed in the charge variants profile of the harvested cell culture fluid (HCCF) between the 2 L and larger scales (e.g., 400 L and 12 kL). Small-scale studies performed at the 2 L scale consistently showed an increase in acidic species when compared with the material made at larger scale. Since the 2 L bioreactors were made of clear transparent glass while the larger scale reactors are made of stainless steel, the effect of ambient laboratory light on cell culture process in 2 L bioreactors as well as handling the HCCF was carefully evaluated. Photoreactions in the 2 L glass bioreactors including light mediated increase in acidic variants in HCCF and formulation buffers were identified and carefully analyzed. While the acidic variants comprised of a mixture of sialylated, reduced disulfide, crosslinked (nonreducible), glycated, and deamidated forms, an increase in the nonreducible forms, deamidation and Met oxidation was predominantly observed under light stress. The monoclonal antibody produced in glass bioreactors that were protected from light behaved similar to the one produced in the larger scale. Our data clearly indicate that care should be taken when glass bioreactors are used in cell culture studies during monoclonal antibody production.

Applications of capillary electrophoresis in characterizing recombinant protein therapeutics

The use of recombinant protein for therapeutic applications has increased significantly in the last three decades. The heterogeneity of these proteins, often caused by the complex biosynthesis pathways and the subsequent PTMs, poses a challenge for drug characterization to ensure its safety, quality, integrity, and efficacy. CE, with its simple instrumentation, superior separation efficiency, small sample consumption, and short analysis time, is a well-suited analytical tool for therapeutic protein characterization. Different separation modes, including CIEF, SDS-CGE, CZE, and CE-MS, provide complementary information of the proteins. The CE applications for recombinant therapeutic proteins from the year 2000 to June 2013 are reviewed and technical concerns are discussed in this article.

IgG1 thioether bond formation in vivo

During either production or storage, the LC214-HC220 disulfide in therapeutic antibodies can convert to a thioether bond. Here we report that a thioether forms at the same position on antibodies in vivo. An IgG1κ therapeutic antibody dosed in humans formed a thioether at this position at a rate of about 0.1%/day while circulating in blood. Thioether modifications were also found at this position in endogenous antibodies isolated from healthy human subjects, at levels consistent with this conversion rate. For both endogenous antibodies and recombinant antibodies studied in vivo, thioether conversion rates were faster for IgG1 antibodies containing λ light chains than those containing κ light chains. These light chain reaction rate differences were replicated in vitro. Additional mechanistic studies showed that base-catalyzed thioether formation through the light chain dehydrogenation was more preferred on antibodies with λ light chains, which may help explain the observed reaction rate differences.

Comparison of the in vitro and in vivo stability of a succinimide intermediate observed on a therapeutic IgG1 molecule

Deamidation of asparagine residues, a post-translational modification observed in proteins, is a common degradation pathway in monoclonal antibodies (mAbs). The kinetics of deamidation is influenced by primary sequence as well as secondary and tertiary folding. Analytical hydrophobic interaction chromatography (HIC) is used to evaluate hydrophobicity of candidate mAbs and uncover post-translational modifications. Using HIC, we discovered atypical heterogeneity in a highly hydrophobic molecule (mAb-1). Characterization of the different HIC fractions using LC/MS/MS revealed a stable succinimide intermediate species localized to an asparagine-glycine motif in the heavy chain binding region. The succinimide intermediate was stable in vitro at pH 7 and below and increased on storage at 25°C and 40°C. Biacore evaluation showed a decrease in binding affinity of the succinimide intermediate compared with the native asparagine molecule. In vivo studies of mAb-1 recovered from a pharmacokinetic study in cynomolgus monkeys revealed an unstable succinimide species and rapid conversion to aspartic/iso-aspartic acid. Mutation from asparagine to aspartic acid led to little loss in affinity. This study illustrates the importance of evaluating modifications of therapeutic mAbs both in vitro and in serum, the intended environment of the molecule. Potential mechanisms that stabilize the succinimide intermediate in vitro are discussed.