Specific Racemization of Heavy-Chain Cysteine-220 in the Hinge Region of Immunoglobulin Gamma 1 as a Possible Cause of Degradation during Storage

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Development of Plant-Derived Bispecific Monoclonal Antibody Targeting PD-L1 and CTLA-4 against Mouse Colorectal Cancer

Checkpoint blockade immunotherapy has revolutionized cancer treatment, with monoclonal antibodies targeting immune checkpoints, yielding promising clinical benefits. However, with the advent of resistance to immune checkpoint inhibitor treatment in clinical trials, developing next-generation antibodies with potentially increased efficacy is critical. Here, we aimed to generate a recombinant bispecific monoclonal antibody for dual inhibition of programmed cell death protein 1/programmed cell death ligand 1 and cytotoxic T-lymphocyte-associated protein 4 axes. The plant system was used as an alternative platform for bispecific monoclonal antibody production. Dual variable domain immunoglobulin atezolizumab × 2C8 is a plant-derived bispecific monoclonal antibody that combines both programmed cell death ligand 1 and cytotoxic T-lymphocyte-associated protein 4 blockade into a single molecule. Dual variable domain immunoglobulin atezolizumab × 2C8 was transiently expressed in Nicotiana benthamiana and the expression level was determined to be the highest after 4 days of infiltration. The size and assembly of the purified bispecific monoclonal antibody were determined, and its function was investigated in vitro and in vivo. The molecular structures of plant-produced dual variable domain immunoglobulin atezolizumab × 2C8 are as expected, and it was mostly present as a monomer. The plant-produced dual variable domain immunoglobulin atezolizumab × 2C8 showed in vitro binding to programmed cell death ligand 1 and cytotoxic T-lymphocyte-associated protein 4 proteins. The antitumor activity of plant-produced bispecific monoclonal antibody was tested in vivo by treating humanized Balb/c mice bearing a CT26 colorectal tumor. Plant-produced dual variable domain immunoglobulin atezolizumab × 2C8 significantly inhibited tumor growth by reducing tumor volume and weight. Body weight changes indicated that the plant-produced bispecific monoclonal antibody was safe and tolerable. Overall, this proof of concept study demonstrated the viability of plants to produce functional plant-based bispecific immunotherapy.

Mapping Isomeric Peptides Derived from Biopharmaceuticals Using High-Resolution Ion Mobility Mass Spectrometry

The identification and localization of isomeric peptide modifications is a critical requirement of the biopharmaceutical industry. Despite the ability of liquid chromatography-mass spectrometry to identify many of the common post translational modifications, the identification of isobaric or racemized peptides is confounded by modern mass spectrometry-based techniques. Here, we present a novel approach combining liquid chromatography with a high-resolution ion mobility mass spectrometry system to differentiate peptide and peptide fragments based upon their mobility and mass.

Stability testing in monoclonal antibodies

Monoclonal antibodies are proteinaceous in nature and are subject to instability issues. Stability testing of monoclonal antibodies is a critical regulatory requirement in their development and commercialization as therapeutic biological molecules. This article reviews the numerous drug manufacturing processes such as: upstream processing, downstream purification and aseptic filling along with physical and chemical factors such as protein concentration, structure, pH, temperature, light, agitation, deamidation, oxidation, glycation leading to instabilities in monoclonal antibodies and it spotlights the variety of analytical techniques employed to investigate and generate information on stability studies and henceforth, helps in developing the stability-indicating methods. In addition, this paper aims to discuss the ICH regulatory guideline (s) for the stability assessment of biological products (Drug Substance and Drug Product).

Macro- and Micro-Heterogeneity of Natural and Recombinant IgG Antibodies

Recombinant monoclonal antibodies (mAbs) intended for therapeutic usage are required to be thoroughly characterized, which has promoted an extensive effort towards the understanding of the structures and heterogeneity of this major class of molecules. Batch consistency and comparability are highly relevant to the successful pharmaceutical development of mAbs and related products. Small structural modifications that contribute to molecule variants (or proteoforms) differing in size, charge or hydrophobicity have been identified. These modifications may impact (or not) the stability, pharmacokinetics, and efficacy of mAbs. The presence of the same type of modifications as found in endogenous immunoglobulin G (IgG) can substantially lower the safety risks of mAbs. The knowledge of modifications is also critical to the ranking of critical quality attributes (CQAs) of the drug and define the Quality Target Product Profile (QTPP). This review provides a summary of the current understanding of post-translational and physico-chemical modifications identified in recombinant mAbs and endogenous IgGs at physiological conditions.

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.

Identification of D-Amino Acids in Light Exposed mAb Formulations

PURPOSE

We previously demonstrated that D-amino acids can form as a result of photo-irradiation of a monoclonal antibody (mAb) at both λ = 254 nm and λ > 295 nm (λ_max = 305 nm), likely via reversible hydrogen transfer reactions of intermediary thiyl radicals. Here, we investigate the role of various excipients (sucrose, glucose, L-Arg, L-Met and L-Leu) on D-amino acid formation, and specifically the distribution of D-amino acids in mAb monomers and aggregates present after light exposure.

METHODS

The mAb-containing formulations were photo-irradiated at λ = 254 nm and λ_max = 305 nm, followed by fractionation of aggregate and monomer fractions using size exclusion chromatography. These aggregate and monomer fractions were subjected to hydrolysis and subsequent amino acid analysis.

RESULTS

Both aggregate and monomer fractions collected from all formulations showed the formation of D-Glu and D-Val, whereas the formation of D-Ala was limited to the aggregate fraction collected from an L-Arg-containing formulation. Interestingly, quantitative analysis revealed higher yields of D-amino acids in the L-Arg-containing formulation.

CONCLUSIONS

Generally, D-amino acids accumulated to similar extents in monomers and aggregates.

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.

Challenges and new frontiers in analytical characterization of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a growing class of biotherapeutics in which a potent small molecule is linked to an antibody. ADCs are highly complex and structurally heterogeneous, typically containing numerous product-related species. One of the most impactful steps in ADC development is the identification of critical quality attributes to determine product characteristics that may affect safety and efficacy. However, due to the additional complexity of ADCs relative to the parent antibodies, establishing a solid understanding of the major quality attributes and determining their criticality are a major undertaking in ADC development. Here, we review the development challenges, especially for reliable detection of quality attributes, citing literature and new data from our laboratories, highlight recent improvements in major analytical techniques for ADC characterization and control, and discuss newer techniques, such as two-dimensional liquid chromatography, that have potential to be included in analytical control strategies.

Strategies for analysis of isomeric peptides

This review presents an overview and recent progress of strategies for detecting isomerism in peptides, with focus on d/l epimerization and the various isomers that the presence of an aspartic acid residue may yield in a protein or peptide. While mass spectrometry has become a majorly used method of choice within proteomics, isomerism is inherently difficult to analyze because it is a modification that does not yield any change in mass of the analyte. Here, several techniques used for analysis of peptide isomerism are discussed, including enzymatic assays, liquid chromatography, and capillary electrophoresis. Recent progress in method development using mass spectrometry is also discussed, including labeling strategies, fragmentation techniques, and ion-mobility spectrometry.

Assessment of disulfide and hinge modifications in monoclonal antibodies

During the last years there was a substantial increase in the use of antibodies and related proteins as therapeutics. The emphasis of the pharmaceutical industry is on IgG1, IgG2, and IgG4 antibodies, which are therefore in the focus of this article. In order to ensure appropriate quality control of such biopharmaceuticals, deep understanding of their chemical degradation pathways and the resulting impact on potency, pharmacokinetics, and safety is required. Criticality of modifications may be specific for individual antibodies and has to be assessed for each molecule. However, some modifications of conserved structure elements occur in all or at least most IgGs. In these cases, criticality assessment may be applicable to related molecules or molecule formats. The relatively low dissociation energy of disulfide bonds and the high flexibility of the hinge region frequently lead to modifications and cleavages. Therefore, the hinge region and disulfide bonds require specific consideration during quality assessment of mAbs. In this review, available literature knowledge on underlying chemical reaction pathways of modifications, analytical methods for quantification and criticality are discussed. The hinge region is prone to cleavage and is involved in pathways that lead to thioether bond formation, cysteine racemization, and iso‐Asp (Asp, aspartic acid) formation. Disulfide or sulfhydryl groups were found to be prone to reductive cleavage, trisulfide formation, cysteinylation, glutathionylation, disulfide bridging to further light chains, and disulfide scrambling. With regard to potency, disulfide cleavage, hinge cleavage, disulfide bridging to further light chains, and cysteinylation were found to influence antigen binding and fragment crystallizable (Fc) effector functionalities. Renal clearance of small fragments may be faster, whereas clearance of larger fragments appears to depend on their neonatal Fc receptor (FcRn) functionality, which in turn may be impeded by disulfide bond cleavage. Certain modifications such as disulfide induced aggregation and heterodimers from different antibodies are generally regarded critical with respect to safety. However, the detection of some modifications in endogenous antibodies isolated from human blood and the possibility of in vivo repair mechanisms may reduce some safety concerns.

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.

Sequence-specific formation of d-amino acids in a monoclonal antibody during light exposure

The photoirradiation of a monoclonal antibody 1 (mAb1) at λ = 254 nm and λmax = 305 nm resulted in the sequence-specific generation of d-Val, d-Tyr, and potentially d-Ala and d-Arg, in the heavy chain sequence [95-101] YCARVVY. d-Amino acid formation is most likely the product of reversible intermediary carbon-centered radical formation at the (α)C-positions of the respective amino acids ((α)C(•) radicals) through the action of Cys thiyl radicals (CysS(•)). The latter can be generated photochemically either through direct homolysis of cystine or through photoinduced electron transfer from Trp and/or Tyr residues. The potential of mAb1 sequences to undergo epimerization was first evaluated through covalent H/D exchange during photoirradiation in D2O, and proteolytic peptides exhibiting deuterium incorporation were monitored by HPLC-MS/MS analysis. Subsequently, mAb1 was photoirradiated in H2O, and peptides, for which deuterium incorporation in D2O had been documented, were purified by HPLC and subjected to hydrolysis and amino acid analysis. Importantly, not all peptide sequences which incorporated deuterium during photoirradiation in D2O also exhibited photoinduced d-amino acid formation. For example, the heavy chain sequence [12-18] VQPGGSL showed significant deuterium incorporation during photoirradiation in D2O, but no photoinduced formation of d-amino acids was detected. Instead this sequence contained ca. 22% d-Val in both a photoirradiated and a control sample. This observation could indicate that d-Val may have been generated either during production and/or storage or during sample preparation. While sample preparation did not lead to the formation of d-Val or other d-amino acids in the control sample for the heavy chain sequence [95-101] YCARVVY, we may have to consider that during hydrolysis N-terminal residues (such as in VQPGGSL) may be more prone to epimerization. We conclude that the photoinduced, radical-dependent formation of d-amino acids requires not only the intermediary formation of a (α)C(•) radical but also sufficient flexibility of the protein domain to allow both pro-chiral faces of the (α)C(•) radical to accept a hydrogen atom.

Mutational and structural study of RipA, a key enzyme in Mycobacterium tuberculosis cell division: evidence for the L-to-D inversion of configuration of the catalytic cysteine

RipA is a key cysteine protease of Mycobacterium tuberculosis as it is responsible for bacterial daughter-cell separation. Although it is an important target for antimicrobial development, its mechanism of action and its interaction pattern with its substrate are hitherto unknown. By combining crystallographic and mutational studies with functional assays and molecular modelling, it is shown that the catalytic activity of the enzyme relies on a Cys-His-Glu triad and the impact of the mutation of each residue of the triad on the structure and function of RipA is analysed. Unexpectedly, the crystallographic analyses reveal that mutation of the glutamic acid to alanine results in inversion of the configuration of the catalytic cysteine. The consequent burial of the catalytic cysteine side chain explains the enzyme inactivation upon mutation. These data point to a novel role of the acidic residue often present in the triad of cysteine proteases as a supervisor of cysteine configuration through preservation of the local structural integrity.

Cysteine racemization on IgG heavy and light chains

Under basic pH conditions, the heavy chain 220-light chain 214 (H220-L214) disulfide bond, found in the flexible hinge region of an IgG1, can convert to a thioether. Similar conditions also result in racemization of the H220 cysteine. Here, we report that racemization occurs on both H220 and L214 on an IgG1 with a λ light chain (IgG1λ) but almost entirely on H220 of an IgGl with a κ light chain (IgG1κ) under similar conditions. Likewise, racemization was detected at significant levels on H220 and L214 on endogenous human IgG1λ but only at the H220 position on IgG1κ. Low but measurable levels of D-cysteines were found on IgG2 cysteines in the hinge region, both with monoclonal antibodies incubated under basic pH conditions and on antibodies isolated from human serum. A simplified reaction mechanism involving reversible β-elimination on the cysteine is presented that accounts for both base-catalyzed racemization and thioether formation at the hinge disulfide.

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.

Isomerization of Asp-Asp motif in model peptides and a monoclonal antibody Fab fragment

Isomerization of aspartyl (Asp or D) residues is a critical degradation route to consider for stable monoclonal antibody formulations. Among the known hotspot sequences, the DD motif is relatively understudied. To gain mechanistic insights, we used model hexapeptides, YADXFK, YADDXK, and DIDDDM, as surrogates for the hotspots in a Fab protein (YADDFK and DIDDDM), to characterize the rate-pH profile of Asp isomerization. Compared with the YADGFK peptide, isomerization of D3 (the first D in the DD pair) in YADDFK was highly pH dependent. Comparison of rate-pH profiles of YADDFK, YADNFK, and YADHFK revealed a charge effect of the n + 1 residue-isomerization rate is accelerated by the positive side chain and reduced by negative side chain at n + 1 residue. Studies on YADDFK, YADDAK, and YADDGK indicated a mutual impact of D3 and D4 on their respective isomerization rates through charge effect. Comparison of rate-pH profile of DIDDDM sequence in peptide models with that in the complementary determining region of the Fab showed a faster rate in the Fab than in peptides, presumably because of contribution from structural factors in the former.

Effects of rotational speed on the hydrodynamic properties of pharmaceutical antibodies measured by analytical ultracentrifugation sedimentation velocity

Analytical ultracentrifugation sedimentation velocity (AUC-SV) has recently become one of the most important tools for the measurement of hydrodynamic properties of proteins. Although a number of studies using AUC-SV as applied to pharmaceutical antibodies have been conducted, the effect of rotational speed on molecular properties has not been systematically examined. The present study aimed to elucidate the influence of rotational speed on the hydrodynamic parameters of pharmaceutical antibodies. A monoclonal and a polyclonal antibody were studied by using AUC-SV at 5 different rotor speeds, and the acquired data were analyzed either by using the computer programs SEDFIT or UltraScan. The frictional ratio of the studied antibodies decreased at high rotor speeds, resulting in underestimation of molecular weight. The frictional ratio value of the monoclonal antibody measured at the low rotor speed was consistent with that of human immunoglobulin G1 computed from its three-dimensional structure. The best agreement between the measured molecular weight and the value calculated from the antibody sequence was achieved at the lower rotor speed. Similar to the results obtained using antibodies, AUC-SV analysis of human serum albumin revealed that the frictional ratio and apparent molecular weight behave in a speed-dependent manner. We deduced that the findings were mainly attributable to the hydrostatic pressure in the analytical ultracentrifuge. The current study implies that rotor speed should be carefully considered in antibody studies using AUC-SV.