Characterization of the stability of a fully human monoclonal IgG after prolonged incubation at elevated temperature

Stability of Opened Durvalumab (IMFINZI) Vials. The Beginning of the End of Costly Product Wastage?

Durvalumab is a monoclonal antibody approved for the treatment of lung, urothelial and biliary tract cancers. Durvalumab is supplied in vials as a solution containing no preservatives. Monographs recommend single use of durvalumab vials, and that any leftovers be discarded within 24 h. Thus, significant portions of unused product from opened vials are wasted on a daily basis, generating considerable financial losses. The objective of the present study was to assess the physicochemical and microbiological stability of durvalumab vials kept at 4 °C or room temperature, at 7 and 14 days after opening. Following pH and osmolality measurements, turbidity and submicronic aggregation of durvalumab solution were evaluated by spectrophotometry and dynamic light scattering, respectively. Moreover, steric exclusion high performance liquid chromatography (SE-HPLC), ion exchange HPLC (IEX-HPLC) and peptide mapping HPLC were used to respectively assess aggregation/fragmentation, charge distribution and primary structure of durvalumab. Microbiological stability of durvalumab was evaluated by incubation of vial leftovers on blood agar. All experiments showed physicochemical and microbiological stability of durvalumab vial leftovers for at least 14 days when aseptically handled and kept at either 4 °C or at room temperature. These results suggest the possible extension of utilization of durvalumab vial leftovers well beyond 24 h.

Characterization of bispecific antigen-binding biotherapeutic fragmentation sites using microfluidic capillary electrophoresis coupled to mass spectrometry (mCZE-MS)

Fragmentation of therapeutic proteins is a potential critical quality attribute (CQA) that can occur in vivo or during manufacturing or storage due to enzymatic and non-enzymatic degradation pathways, such as hydrolysis, peroxide mediation, and acid/metal catalysis. Characterization of the fragmentation pattern of a therapeutic protein is traditionally accomplished using capillary gel electrophoresis with UV detection under both non-reducing and reducing conditions (nrCGE and rCGE). However, such methods are incompatible with direct coupling to mass spectrometry (MS) due to the use of anionic surfactants, e.g., sodium dodecyl sulfate (SDS). Here, we present a novel method to characterize size-based fragmentation variants of a new biotherapeutic kind using microfluidic ZipChip® capillary zone electrophoresis (mCZE) system interfaced with mass spectrometry (MS) to determine the molecular masses of fragments. A new modality of immuno-oncology therapy, bispecific antigen-binding biotherapeutic, was chosen to investigate its fragmentation pattern using mCZE-MS for the first time, according to our knowledge. Bispecific antigen-binding biotherapeutic samples from different stages of downstream column purification and forced degradation conditions were analyzed. The results were cross-validated with denaturing size-exclusion chromatography-mass spectrometry and conventional rSDS-CGE. In this study, we demonstrated that mCZE-MS could separate and characterize 12-40 kDa bispecific antigen-binding biotherapeutic fragments rapidly (within ≤12 minutes), with higher resolution and better sensitivity than traditional LC-MS methods.

Risk-Based Control Strategies of Recombinant Monoclonal Antibody Charge Variants

Since the first approval of the anti-CD3 recombinant monoclonal antibody (mAb), muromonab-CD3, a mouse antibody for the prevention of transplant rejection, by the US Food and Drug Administration (FDA) in 1986, mAb therapeutics have become increasingly important to medical care. A wealth of information about mAbs regarding their structure, stability, post-translation modifications, and the relationship between modification and function has been reported. Yet, substantial resources are still required throughout development and commercialization to have appropriate control strategies to maintain consistent product quality, safety, and efficacy. A typical feature of mAbs is charge heterogeneity, which stems from a variety of modifications, including modifications that are common to many mAbs or unique to a specific molecule or process. Charge heterogeneity is highly sensitive to process changes and thus a good indicator of a robust process. It is a high-risk quality attribute that could potentially fail the specification and comparability required for batch disposition. Failure to meet product specifications or comparability can substantially affect clinical development timelines. To mitigate these risks, the general rule is to maintain a comparable charge profile when process changes are inevitably introduced during development and even after commercialization. Otherwise, new peaks or varied levels of acidic and basic species must be justified based on scientific knowledge and clinical experience for a specific molecule. Here, we summarize the current understanding of mAb charge variants and outline risk-based control strategies to support process development and ultimately commercialization.

How neutron scattering techniques benefit investigating structures and dynamics of monoclonal antibody

Over the past several decades, great progresses have been made for the pharmaceutical industry of monoclonal antibody (mAb). More and more mAb products were approved for human therapeutics. This review describes the state of art of utilizing neutron scattering to investigate mAbs, in the aspects of structures, dynamics, physicochemical stability, functionality, etc. Firstly, brief histories of mAbs and neutron scattering, as well as some basic knowledges and principles of neutron scattering were introduced. Then specific examples were demonstrated. For the structure and structural evolution investigation of in dilute and concentrated mAbs solution, in situ small angle neutron scattering (SANS) was frequently utilized. Neutron reflectometry (NR) is powerful to probe the absorption behaviors of mAbs on various surfaces and interfaces. While for dynamic investigation, quasi-elastic scattering techniques such as neutron spin echo (NSE) demonstrate the capabilities. With this review, how to utilize and take advantages of neutron scattering on investigating structures and dynamics of mAbs were demonstrated and discussed.

Shelf-Life Extension of Fc-Fused Single Chain Fragment Variable Antibodies by Lyophilization

Generation of sequence defined antibodies from universal libraries by phage display has been established over the past three decades as a robust method to cope with the increasing market demand in therapy, diagnostics and research. For applications requiring the bivalent antigen binding and an Fc part for detection, phage display generated single chain Fv (scFv) antibody fragments can rapidly be genetically fused to the Fc moiety of an IgG for the production in eukaryotic cells of antibodies with IgG-like properties. In contrast to conversion of scFv into IgG format, the conversion to scFv-Fc requires only a single cloning step, and provides significantly higher yields in transient cell culture production than IgG. ScFv-Fcs can be effective as neutralizing antibodies in vivo against a panel of pathogens and toxins. However, different scFv fragments are more heterologous in respect of stability than Fab fragments. While some scFv fragments can be made extremely stable, this may change due to few mutations, and is not predictable from the sequence of a newly selected antibody. To mitigate the necessity to assess the stability for every scFv-Fc antibody, we developed a generic lyophilization protocol to improve their shelf life. We compared long-term stability and binding activity of phage display-derived antibodies in the scFv-Fc and IgG format, either stored in liquid or lyophilized state. Conversion of scFv-Fcs into the full IgG format reduced protein degradation and aggregation, but in some cases compromised binding activity. Comparably to IgG conversion, lyophilization of scFv-Fc resulted in the preservation of the antibodies' initial properties after storage, without any drop in affinity for any of the tested antibody clones.

Effect of 'pH' on the Rate of Pyroglutamate Formation in Solution and Lyophilized Solids

N-terminal glutamate can cyclize to form pyroglutamate (pGlu) in pharmaceutically relevant peptides and proteins. The reaction occurs nonenzymatically during storage for monoclonal antibodies and shows a strong 'pH' dependence in solution, but the solid-state reaction has not been studied in detail. This work investigates the effect of 'pH' and buffer species on pGlu formation for a model peptide (EVQLVESGGGLVQPGGSLR) in lyophilized solids and in solution. The model peptide was formulated from 'pH' 4 to 'pH' 9 in citrate, citrate-phosphate, phosphate, and carbonate buffers and stored at 50 °C for at least 10 weeks. pGlu formation and loss of the parent peptide were monitored by reversed-phase high-performance liquid chromatography. The apparent 'pH' dependence of the reaction rate in the solid state differed markedly from that in solution. Interestingly, in the 'pH' range often used to formulate mAbs ('pH' 5.5-6), the rate of pGlu formation in the solid state was greater than that in solution. The results have implications for the rational design of stable formulations of peptides and proteins, and for the transition from solid to solution formulations during development.

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.

Computational Studies on the Mechanisms of Nonenzymatic Intramolecular Cyclization of the Glutamine Residues Located at N-Termini Catalyzed by Inorganic Phosphate Species

Glutamine (Gln) residues located at N-termini undergo spontaneous intramolecular cyclization, causing the formation of pyroglutamic acid (pGlu) residues. pGlu residues have been detected at the N-termini in various peptides and proteins. The formation of pGlu residues during the fermentation and purification processes of antibody drugs is one of the concerns in the design and formulation of these drugs and has been reported to proceed rapidly in a phosphate buffer. In this study, we have examined the phosphate-catalyzed mechanisms of the pGlu residue formation from N-terminal Gln residues via quantum chemical calculations using B3LYP density functional methods. Single-point energies were calculated using the second-order Møller-Plesset perturbation theory. We performed the calculations for the model compound in which an uncharged N-terminal Gln residue is capped with a methyl amino group on the C-terminal. The activation energy of the formation of pGlu residues was calculated as 83.8 kJ mol^-1, which was lower than that of the typical nonenzymatic reaction of amino acid residues. In addition, the computational results indicate that the flexibility of the main and side chains in N-terminal Gln residues was necessary for the formation of pGlu residues to proceed. In the obtained pathway, inorganic phosphate species act as the catalyst by mediating the proton transfer.

Characterization of IgG1 Fc Deamidation at Asparagine 325 and Its Impact on Antibody-dependent Cell-mediated Cytotoxicity and FcγRIIIa Binding

Antibody-dependent cell-mediated cytotoxicity (ADCC) is an important mechanism of action for many therapeutic antibodies. A therapeutic immunoglobulin (Ig) G₁ monoclonal antibody lost more than half of its ADCC activity after heat stress at 40 °C for 4 months. Size-exclusion and ion-exchange chromatography were used to fractionate various size and charge variants from the stressed IgG₁. Physicochemical characterization of these fractions revealed that a rarely seen crystallizable fragment (Fc) modification, N325 deamidation, exhibited a positive correlation with the loss of ADCC activity. A further surface plasmon resonance study showed that this modification disrupted the binding between the IgG₁ Fc and Fcγ receptor IIIa, resulting in decreased ADCC activity of the IgG₁ antibody. Mutants of N325/D and N325/Q were made to confirm the effect of N325 deamidation on ADCC. We hypothesize that N325 deamidation altered the local three-dimensional structure, which might interfere with the binding and interaction with the effector cell. Because of its impact on biological activity, N325 deamidation is a critical quality attribute for products whose mechanism of action includes ADCC. A thorough understanding of the criticality of N325 deamidation and appropriate monitoring can help ensure the safety and efficacy of IgG₁ or Fc-fusion products.

Unambiguous Identification of Pyroglutamate in Full-Length Biopharmaceutical Monoclonal Antibodies by NMR Spectroscopy

Biotherapeutic proteins are an indispensable class of pharmaceuticals that present a high degree of structural complexity and are prone to chemical modifications during production, processing, and storage, which have to be tightly controlled. Pyroglutamate (pGlu), a cyclization product of N-terminal Gln or Glu residues, is a widespread post-translational modification in proteins, including monoclonal antibodies (mAbs). The unambiguous identification and quantification of this modification in proteins is challenging, since the mass difference of -17 Da or -18 Da, when formed from Gln or Glu, respectively, is not unique. Moreover, deamidation and dehydration occur not only during cyclization to pGlu, but also during other reactions leading to different types of modifications, like succinimide or isopeptide bond moieties due to cross-linking between Asn or Gln and Lys side chains. Here we report the unambiguous identification and quantification of pGlu in intact mAbs with natural isotope distribution by NMR spectroscopy. The assignment of all ¹H, ¹³C and ¹⁵N random coil chemical shifts of pGlu in short reference peptides led to the identification of unique chemical shift pairs that are distinct from the random coil chemical shifts of the natural amino-acid residues. These characteristic correlations are suited for the detection of pGlu in denatured proteins. We achieved complete denaturation of mAbs using a straightforward protocol, and could detect and quantify pGlu, in agreement with available mass spectrometric data. The application to the mAbs rituximab and adalimumab illustrates the potential of our approach for the characterization of biotherapeutics containing isotopes at natural abundance.

Native peptide mapping - A simple method to routinely monitor higher order structure changes and relation to functional activity

In the biopharmaceutical environment, controlling the Critical Quality Attributes (CQA) of a product is essential to prevent changes that affect its safety or efficacy. Physico-chemical techniques and bioassays are used to screen and monitor these CQAs. The higher order structure (HOS) is a CQA that is typically studied using techniques that are not commonly considered amenable to quality control laboratories. Here, we propose a peptide mapping-based method, named native peptide mapping, which could be considered as straightforward for HOS analysis and applicable for IgG4 and IgG1 antibodies. The method was demonstrated to be fit-for-purpose as a stability-indicating assay by showing differences at the peptide level between stressed and unstressed material. The unfolding pathway induced by a heat stress was also studied via native peptide mapping assay. Furthermore, we demonstrated the structure–activity relationship between HOS and biological activity by analyzing different types of stressed samples with a cell-based assay and the native peptide mapping. The correlation between both sets of results was highlighted by monitoring peptides located in the complementary-determining regions and the relative potency of the biotherapeutic product. This relationship represents a useful approach to interrogate the criticality of HOS as a CQA of a drug.

A rapid and quantitative technique for assessing IgG monomeric purity, calibrated with the NISTmAb reference material

The fraction of intact monomer in a sample (moles/moles), the monomeric purity, is measured as a quality control in therapeutic monoclonal antibodies but is often unknown in research samples and remains a major source of variation in quantitative antibody-based techniques such as immunoassay development. Here, we describe a novel multiplex technique for estimating the monomeric purity and antigen affinity of research grade antibody samples. Light scattering was used to simultaneously observe the mass of antibody binding to biosensor surfaces functionalised with antigen (revealing Fab binding kinetics) or protein A/G (PAG). Initial estimates of monomeric purity in 7 antibody samples including a therapeutic infliximab biosimilar were estimated by observing a mass deficit on the PAG surface compared to the NISTmAb standard of high monomeric purity. Monomeric purity estimates were improved in a second step by observing the mass of antigen binding to the mass of antibody on the PAG surface. The NISTmAb and infliximab biosimilar displayed tightly controlled stoichiometries for antigen binding of 1.31 ± 0.57 and 1.71 ± 0.16 (95% confidence interval)—within the theoretical limit of 1–2 antigens per antibody depending on avidity. The other antibodies in the panel displayed antigen binding stoichiometries in the range 0.06–1.15, attributed to lower monomeric purity. The monomeric purity estimates were verified by electrospray ionization mass spectrometry (ESI), the gold standard technique for structural characterization of antibodies. ESI data indicated that the NISTmAb and infliximab biosimilar samples had monomeric purity values of 93.5% and 94.7%, respectively, whilst the research grade samples were significantly lower (54–89%). Our results demonstrate rapid quality control testing for monomeric purity of antibody samples (< 15 min) which could improve the reproducibility of antibody-based experiments.

The impact of standard accelerated stability conditions on antibody higher order structure as assessed by mass spectrometry

Protein therapeutic higher order structure (HOS) is a quality attribute that can be assessed to help predict shelf life. To model product shelf-life values, possible sample-dependent pathways of degradation that may affect drug efficacy or safety need to be evaluated. As changes in drug thermal stability over time can be correlated with an increased risk of HOS perturbations, the effect of long-term storage on the product should be measured as a function of temperature. Here, complementary high-resolution mass spectrometry methods for HOS analysis were used to identify storage-dependent changes of biotherapeutics (bevacizumab (Avastin), trastuzumab (Herceptin), rituximab (Rituxan), and the NIST reference material 8671 (NISTmAb)) under accelerated or manufacturer-recommended storage conditions. Collision-induced unfolding ion mobility-mass spectrometry data showed changes in monoclonal antibody folded stability profiles that were consistent with the appearance of a characteristic unfolded population. Orthogonal hydrogen-deuterium exchange-mass spectrometry data revealed that the observed changes in unfolding occurred in parallel to changes in HOS localized to the periphery of the hinge region. Using intact reverse-phase liquid chromatography-mass spectrometry, we identified several mass species indicative of peptide backbone hydrolysis, located between the variable and constant domains of the heavy chain of bevacizumab. Taken together, our data highlighted the capability of these approaches to identify age- or temperature-dependent changes in biotherapeutic HOS.

Structure, heterogeneity and developability assessment of therapeutic antibodies

Increasing attention has been paid to developability assessment with the understanding that thorough evaluation of monoclonal antibody lead candidates at an early stage can avoid delays during late-stage development. The concept of developability is based on the knowledge gained from the successful development of approximately 80 marketed antibody and Fc-fusion protein drug products and from the lessons learned from many failed development programs over the last three decades. Here, we reviewed antibody quality attributes that are critical to development and traditional and state-of-the-art analytical methods to monitor those attributes. Based on our collective experiences, a practical workflow is proposed as a best practice for developability assessment including in silico evaluation, extended characterization and forced degradation using appropriate analytical methods that allow characterization with limited material consumption and fast turnaround time.

Recent advancements, challenges, and practical considerations in the mass spectrometry-based analytics of protein biotherapeutics: A viewpoint from the biosimilar industry

The extensive analytical characterization of protein biotherapeutics, especially of biosimilars, is a critical part of the product development and registration. High-resolution mass spectrometry became the primary analytical tool used for the structural characterization of biotherapeutics. Its high instrumental sensitivity and methodological versatility made it possible to use this technique to characterize both the primary and higher-order structure of these proteins. However, even by using high-end instrumentation, analysts face several challenges with regard to how to cope with industrial and regulatory requirements, that is, how to obtain accurate and reliable analytical data in a time- and cost-efficient way. New sample preparation approaches, measurement techniques and data evaluation strategies are available to meet those requirements. The practical considerations of these methods are discussed in the present review article focusing on hot topics, such as reliable and efficient sequencing strategies, minimization of artefact formation during sample preparation, quantitative peptide mapping, the potential of multi-attribute methodology, the increasing role of mass spectrometry in higher-order structure characterization and the challenges of MS-based identification of host cell proteins. On the basis of the opportunities in new instrumental techniques, methodological advancements and software-driven data evaluation approaches, for the future one can envision an even wider application area for mass spectrometry in the biopharmaceutical industry.

Analytical comparability study of recombinant monoclonal antibody therapeutics

Process changes are inevitable in the life cycle of recombinant monoclonal antibody therapeutics. Products made using pre- and post-change processes are required to be comparable as demonstrated by comparability studies to qualify for continuous development and commercial supply. Establishment of comparability is a systematic process of gathering and evaluating data based on scientific understanding and clinical experience of the relationship between product quality attributes and their impact on safety and efficacy. This review summarizes the current understanding of various modifications of recombinant monoclonal antibodies. It further outlines the critical steps in designing and executing successful comparability studies to support process changes at different stages of a product's lifecycle.

Development of an LC-MS/MS peptide mapping protocol for the NISTmAb

Peptide mapping is a component of the analytical toolbox used within the biopharmaceutical industry to aid in the identity confirmation of a protein therapeutic and to monitor degradative events such as oxidation or deamidation. These methods offer the advantage of providing site-specific information regarding post-translational and chemical modifications that may arise during production, processing or storage. A number of such variations may also be induced by the sample preparation methods themselves which may confound the ability to accurately evaluate the true modification levels. One important focus when developing a peptide mapping method should therefore be the use of sample preparation conditions that will minimize the degree of artificial modifications induced. Unfortunately, the conditions that are amenable to effective reduction, alkylation and digestion are often the same conditions that promote unwanted modifications. Here we describe the optimization of a tryptic digestion protocol used for peptide mapping of the NISTmAb IgG1κ which addresses the challenge of balancing maximum digestion efficiency with minimum artificial modifications. The parameters on which we focused include buffer concentration, digestion time and temperature, as well as the source and type of trypsin (recombinant vs. pancreatic; bovine vs porcine) used. Using the optimized protocol we generated a peptide map of the NISTmAb which allowed us to confirm its identity at the level of primary structure. Graphical abstract Peptide map of the NISTmAb RM 8671 monoclonal antibody. Tryptic digestion was performed using an optimized protocol and followed by LC-UV-MS analysis. The trace represents the total ion chromatogram. Each peak was mapped to peptides identified using mass spectrometry data.

The importance of handling high-value biologicals: Physico-chemical instability and immunogenicity of monoclonal antibodies

The present review specifies the various chemical and physical factors that can influence drug stability and immunogenicity, and the treatment outcomes of antibody biologicals. Although monoclonal antibodies (mAbs) are known to be more resistant to environmental changes compared with other proteins, the molecules themselves can be subjected to chemical and physical processes that promote their degradation and transformation into their specific amino-acid moieties. With increasing use of medicinal products that contain mAbs, and their self-administration by the patients, the issue of the correct manipulation of these drugs is of increasing importance. This review summarises the correct handling of mAb biologicals from the point of view of the pharmacist, clinical biochemist and patient, as is supported by relevant cases from the literature and our own data and experience. In particular, if there is a break in the cold chain, both healthcare professionals and patients need to be aware of the potential pharmacokinetics and pharmacodynamics alterations to these biologicals. Furthermore, any alterations in the protein structure can induce harmful immune reactions, including anaphylaxis and cytokine storms, or result in the production of neutralising or blocking Abs. Overall, considering also that treatment costs usually remain high, drug stability can have a tremendous effect on the clinical, humanistic and economic outcomes of such treatments.

Assessment of structural and functional similarity of biosimilar products: Rituximab as a case study

Biosimilars are products that are similar in terms of quality, safety, and efficacy to an already licensed reference/ innovator product and are expected to offer improved affordability. The most significant source of reduction in the cost of development of a biosimilar is the reduced clinical examination that it is expected to undergo as compared to the innovator product. However, this clinical relief is predicated on the assumption that there is analytical similarity between the biosimilar and the innovator product. As a result, establishing analytical similarity is arguably the most important step towards successful development of a biosimilar. Here, we present results from an analytical similarity exercise that was performed with five biosimilars of rituximab (Ristova®, Roche), a chimeric mouse/ human monoclonal antibody biotherapeutic, that are available on the Indian market. The results show that, while the biosimilars exhibited similarity with respect to protein structure and function, there were significant differences with respect to size heterogeneity, charge heterogeneity and glycosylation pattern.

The state-of-play and future of antibody therapeutics

It has been over four decades since the development of monoclonal antibodies (mAbs) using a hybridoma cell line was first reported. Since then more than thirty therapeutic antibodies have been marketed, mostly as oncology, autoimmune and inflammatory therapeutics. While antibodies are very efficient, their cost-effectiveness has always been discussed owing to their high costs, accumulating to more than one billion dollars from preclinical development through to market approval. Because of this, therapeutic antibodies are inaccessible to some patients in both developed and developing countries. The growing interest in biosimilar antibodies as affordable versions of therapeutic antibodies may provide alternative treatment options as well potentially decreasing costs. As certain markets begin to capitalize on this opportunity, regulatory authorities continue to refine the requirements for demonstrating quality, efficacy and safety of biosimilar compared to originator products. In addition to biosimilars, innovations in antibody engineering are providing the opportunity to design biobetter antibodies with improved properties to maximize efficacy. Enhancing effector function, antibody drug conjugates (ADC) or targeting multiple disease pathways via multi-specific antibodies are being explored. The manufacturing process of antibodies is also moving forward with advancements relating to host cell production and purification processes. Studies into the physical and chemical degradation pathways of antibodies are contributing to the design of more stable proteins guided by computational tools. Moreover, the delivery and pharmacokinetics of antibody-based therapeutics are improving as optimized formulations are pursued through the implementation of recent innovations in the field.

Forced degradation of recombinant monoclonal antibodies: A practical guide

Forced degradation studies have become integral to the development of recombinant monoclonal antibody therapeutics by serving a variety of objectives from early stage manufacturability evaluation to supporting comparability assessments both pre- and post- marketing approval. This review summarizes the regulatory guidance scattered throughout different documents to highlight the expectations from various agencies such as the Food and Drug Administration and European Medicines Agency. The various purposes for forced degradation studies, commonly used conditions and the major degradation pathways under each condition are also discussed.

Investigating the Degradation Behaviors of a Therapeutic Monoclonal Antibody Associated with pH and Buffer Species

This study aimed in understanding the degradation behaviors of an IgG 1 subtype therapeutic monoclonal antibody A (mAb-A) associated with pH and buffer species. The information obtained in this study can augment conventional, stability-based screening paradigms by providing the direction necessary for efficient experimental design. Differential scanning calorimetry (DSC) was used for studying conformational stability. Dynamic light scattering (DLS) was utilized to generate B ₂₂*, a modified second virial coefficient for the character of protein-protein interaction. Size-exclusion chromatography (SEC) and hydrophobic interaction chromatography (HIC) were employed to separate degradation products. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used for determining the molecular size and liquid chromatography mass spectrometry (LC-MS) were used for identifying the sequence of the separated fragments. The results showed that both pH and buffer species played the roles in controlling the degradation behaviors of mAb-A, but the pH was more significant. In particular, pH 4.5 induced additional thermal transition peaks occurring at a low temperature compared with pH 6.5. A continual temperature-stress study illustrated that the additional thermal transition peaks related to the least stable structure and a greater fragmentation. Although mAb-A showed the comparable conformational structures and an identical amount of aggregates at time zero between the different types of buffer species at pH 6.5, the aggregation formation rate showed a buffer species-dependent discrepancy over a temperature-stress period. It was found that the levels of aggregations associated with the magnitudes of protein-protein interaction forces.

Activity-based assessment of an engineered hyperthermophilic protein as a capture agent in paper-based diagnostic tests

Antibodies have traditionally served as the affinity reagents of choice in point-of-care diagnostic biosensors. However, this class of proteins is not ideally suited for this use, being poorly characterized and prone to thermal denaturation. Here, we present an activity-based assessment of an alternative engineered binding protein in a cellulose-based assay.

Silk-based stabilization of biomacromolecules

Silk fibroin is a high molecular weight amphiphilic protein that self-assembles into robust biomaterials with remarkable properties including stabilization of biologicals and tunable release kinetics correlated to processing conditions. Cells, antibiotics,monoclonal antibodies and peptides, among other biologics, have been encapsulated in silk using various processing approaches and material formats. The mechanistic basis for the entrapment and stabilization features, along with insights into the modulation of release of the entrained compounds from silks will be reviewed with a focus on stabilization of bioactive molecules.

In vitro and in vivo modifications of recombinant and human IgG antibodies

Tremendous knowledge has been gained in the understanding of various modifications of IgG antibodies, driven mainly by the fact that antibodies are one of the most important groups of therapeutic molecules and because of the development of advanced analytical techniques. Recombinant monoclonal antibody (mAb) therapeutics expressed in mammalian cell lines and endogenous IgG molecules secreted by B cells in the human body share some modifications, but each have some unique modifications. Modifications that are common to recombinant mAb and endogenous IgG molecules are considered to pose a lower risk of immunogenicity. On the other hand, modifications that are unique to recombinant mAbs could potentially pose higher risk. The focus of this review is the comparison of frequently observed modifications of recombinant monoclonal antibodies to those of endogenous IgG molecules.

Structure-based prediction of asparagine and aspartate degradation sites in antibody variable regions

Monoclonal antibodies (mAbs) and proteins containing antibody domains are the most prevalent class of biotherapeutics in diverse indication areas. Today, established techniques such as immunization or phage display allow for an efficient generation of new mAbs. Besides functional properties, the stability of future therapeutic mAbs is a key selection criterion which is essential for the development of a drug candidate into a marketed product. Therapeutic proteins may degrade via asparagine (Asn) deamidation and aspartate (Asp) isomerization, but the factors responsible for such degradation remain poorly understood. We studied the structural properties of a large, uniform dataset of Asn and Asp residues in the variable domains of antibodies. Their structural parameters were correlated with the degradation propensities measured by mass spectrometry. We show that degradation hotspots can be characterized by their conformational flexibility, the size of the C-terminally flanking amino acid residue, and secondary structural parameters. From these results we derive an accurate in silico prediction method for the degradation propensity of both Asn and Asp residues in the complementarity-determining regions (CDRs) of mAbs.

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.

Separate mechanisms for age-related truncation and racemisation of peptide-bound serine

Some amino acids are particularly susceptible to degradation in long-lived proteins. Foremost among these are asparagine, aspartic acid and serine. In the case of serine residues, cleavage of the peptide bond on the N-terminal side, as well as racemisation, has been observed. To investigate the role of the hydroxyl group, and whether cleavage and racemisation are linked by a common mechanism, serine peptides with a free hydroxyl group were compared to analogous peptides where the serine hydroxyl group was methylated. Peptide bond cleavage adjacent to serine was increased when the hydroxyl group was present, and this was particularly noticeable when it was present as the hydroxide ion. Adjacent amino acid residues also had a pronounced affect on cleavage at basic pH, with the SerPro motif being especially susceptible to scission. Methylation of the serine hydroxyl group abolished truncation, as did insertion of a bulky amino acid on the N-terminal side of serine. By contrast, racemisation of serine occurred to a similar extent in both O-methylated and unmodified peptides. On the basis of these data, it appears that racemisation of Ser, and cleavage adjacent to serine, occur via separate mechanisms. Addition of water across the double bond of dehydroalanine was not detected, suggesting that this mechanism was unlikely to be responsible for conversion of L-serine to D-serine. Abstraction of the alpha proton may account for the majority of racemisation of serine in proteins.

Mechanisms of monoclonal antibody stabilization and release from silk biomaterials

The availability of stabilization and sustained delivery systems for antibody therapeutics remains a major clinical challenge, despite the growing development of antibodies for a wide range of therapeutic applications due to their specificity and efficacy. A mechanistic understanding of protein-matrix interactions is critical for the development of such systems and is currently lacking as a mode to guide the field. We report mechanistic insight to address this need by using well-defined matrices based on silk gels, in combination with a monoclonal antibody. Variables including antibody loading, matrix density, charge interactions, hydrophobicity and water access were assessed to clarify mechanisms involved in the release of antibody from the biomaterial matrix. The results indicate that antibody release is primarily governed by hydrophobic interactions and hydration resistance, which are controlled by silk matrix chemistry, peptide domain distribution and protein density. Secondary ionic repulsions are also critical in antibody stabilization and release. Matrix modification by free methionine incorporation was found to be an effective strategy for mitigating encapsulation induced antibody oxidation. Additionally, these studies highlight a characterization approach to improve the understanding and development of other protein sustained delivery systems, with broad applicability to the rapidly developing monoclonal antibody field.