Investigation of monoclonal antibody fragmentation artifacts in non-reducing SDS-PAGE

Characterization of mAb size heterogeneity originating from a cysteine to tyrosine substitution using denaturing and native LC-MS

Upon assessing the comparability between a biosimilar mAb and its reference product by non-reducing CE-SDS, increased levels of a heavy-heavy-light chain (HHL) variant, present as a low molecular weight (LMW) peak, were observed. RPLC-MS applied at top, middle-up and bottom-up level revealed the existence of Cys-to-Tyr substitutions, predominantly at position HC226 involved in connecting LC and HC, explaining the abundant HHL levels. Antigen binding was not impacted by the presence of this size variant suggesting a non-covalent association of Tyr substituted HHL and LC. The latter complex is not maintained in the denaturing conditions associated with CE-SDS and RPLC-MS. Its existence could, nevertheless, be confirmed by native SEC-MS which preserves non-covalent protein interactions during separation and electrospray ionization. Amino acid analysis furthermore demonstrated a depletion of Cys during the fed-batch process indicating that the observed size/sequence variant is not of genetic but rather of metabolic origin. Native SEC-MS showed that supplementing the cell culture medium with Cys halts misincorporation of Tyr and promotes the formation of the desired mAb structure. To the best of our knowledge, Cys-to-Tyr substitutions preventing interchain disulfide bridge formation have not been described earlier. This observation adds to the impressive structural heterogeneity reported to date for mAbs.

Aerosolization Performance of Immunoglobulin G by Jet and Mesh Nebulizers

Recently, many preclinical and clinical studies have been conducted on the delivery of therapeutic antibodies to the lungs using nebulizers, but standard treatment guidelines have not yet been established. Our objective was to compare nebulization performance according to the low temperature and concentration of immunoglobulin G (IgG) solutions in different types of nebulizers, and to evaluate the stability of IgG aerosols and the amount delivered to the lungs. The output rate of the mesh nebulizers decreased according to the low temperature and high concentration of IgG solution, whereas the jet nebulizer was unaffected by the temperature and concentration of IgG. An impedance change of the piezoelectric vibrating element in the mesh nebulizers was observed because of the lower temperature and higher viscosity of IgG solution. This affected the resonance frequency of the piezoelectric element and lowered the output rate of the mesh nebulizers. Aggregation assays using a fluorescent probe revealed aggregates in IgG aerosols from all nebulizers. The delivered dose of IgG to the lungs in mice was highest at 95 ng/mL in the jet nebulizer with the smallest droplet size. Evaluation of the performance of IgG solution delivered to the lungs by three types of nebulizers could provide valuable parameter information for determination on dose of therapeutic antibody by nebulizers.

Visible Light Induces Site-Specific Oxidative Heavy Chain Fragmentation of a Monoclonal Antibody (IgG1) Mediated by an Iron(III)-Containing Histidine Buffer

Fragmentation of therapeutic monoclonal antibodies represents a critical quality attribute. Here, we report a novel visible light-induced heavy chain fragmentation of IgG1 mediated by an Fe(III)-containing histidine (His) buffer. Based on non-reducing sodium dodecylsulfate-polyacrylamide gel electrophoresis and mass spectrometry analysis, IgG1 fragments with apparent molecular weights of ∼130, ∼110, and ∼22 kDa were detected in photo-irradiated samples and were mechanistically rationalized with an oxidative cleavage at Thr²⁵⁹. Specifically, the reactions are proposed to involve the generation of an intermediary alkoxyl radical, which undergoes β-cleavage to yield a glycyl radical. The latter either converts into Gly or adds oxygen and follows a peroxyl radical chemistry. The cleavage process requires the presence of His, while only negligible yields of cleavage products are formed when His is replaced by acetate, succinate, or phosphate buffer. Importantly, the fragmentation can be prevented by ethylenediaminetetraacetic acid (EDTA) only when the EDTA concentrations are in significant excess over the concentrations of Fe(III) and proteins, suggesting a strong binding between Fe(III) and IgG1.

Affinity-controlled capture and release of engineered monoclonal antibodies by macroporous dextran hydrogels using coiled-coil interactions

Long-term delivery is a successful strategy used to reduce the adverse effects of monoclonal antibody (mAb)-based treatments. Macroporous hydrogels and affinity-based strategies have shown promising results in sustained and localized delivery of the mAbs. Among the potential tools for affinity-based delivery systems, the de novo designed Ecoil and Kcoil peptides are engineered to form a high-affinity, heterodimeric coiled-coil complex under physiological conditions. In this study, we created a set of trastuzumab molecules tagged with various Ecoil peptides and evaluated their manufacturability and characteristics. Our data show that addition of an Ecoil tag at the C-termini of the antibody chains (light chains, heavy chains, or both) does not hinder the production of chimeric trastuzumab in CHO cells or affect antibody binding to its antigen. We also evaluated the influence of the number, length, and position of the Ecoil tags on the capture and release of Ecoil-tagged trastuzumab from macroporous dextran hydrogels functionalized with Kcoil peptide (the Ecoil peptide-binding partner). Notably, our data show that antibodies are released from the macroporous hydrogels in a biphasic manner; the first phase corresponding to the rapid release of residual, unbound trastuzumab from the macropores, followed by the affinity-controlled, slow-rate release of antibodies from the Kcoil-functionalized macropore surface.

Elimination of light chain tailing in reducing capillary electrophoresis with sodium dodecyl sulfate analysis of a monoclonal antibody

Capillary electrophoresis with sodium dodecyl sulfate (CE-SDS) is a common analytical technique for investigating the purity and molecular size heterogeneity of monoclonal antibody (mAb) drugs. In reducing CE-SDS analysis of mAb-A, the light chain (LC) peak exhibited severe tailing, seriously affecting the purity analysis. The purposes of this investigation are to clarify the source of tailing and develop a more appropriate CE-SDS method to eliminate LC tailing. The degree of LC tailing was closely related to the mAb concentration, SDS concentration, and injection amount, and more hydrophobic detergents, such as sodium hexadecyl sulfate (SHS) and sodium tetradecyl sulfate (STS), could be used instead of SDS to obtain better peak shapes. The results also indicated that the tailing was caused by the binding problem associated with SDS, and SHS/STS could provide a more stable and uniform complexation for the LC. In summary, the method we developed successfully eliminated the LC tailing and provided a robust characterization of mAb-A in reducing CE-SDS analysis.

Investigation of an artifact during non-reduced capillary electrophoresis with sodium dodecyl sulfate analysis utilizing N-ethylmaleimide as an alkylation reagent

This manuscript describes the formation of an artifact shoulder peak with a slightly larger retention time than the main peak under the standard non-reduced capillary electrophoresis with sodium dodecyl sulfate (nrCE-SDS) analysis of a therapeutic recombinant protein X, and clarifies the formation mechanism of the artifact caused by N-ethylmaleimide (NEM) during the sample preparation procedure. A design of experiment (DoE) approach was used to investigate the impact of the factors on the formation of the impurity. Additionally, orthogonal analytical experiments were performed to study the root cause of this phenomenon. The results consistently suggested that the Michael addition reaction between NEM and lysine residues in protein X, and decreased electrophoretic mobility due to increased molecular weight, was the root cause for the artifact, which could be partially inhibited by modifications of incubation conditions. Thus, before performing the nrCE-SDS method, the effects of alkylation reagents and sample preparation procedure on analytical results need to be considered seriously.

Production of an anti-TNFα antibody in murine myeloma cells by perfusion culture

Infliximab is a mouse/human chimeric IgG1 monoclonal antibody which recognizes the proinflammatory cytokine, tumor necrosis factor α (TNFα), and inhibits receptor interactions, thereby decreasing inflammation and autoimmune response in patients. This monoclonal antibody has been successfully used to treat rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis. However, the high treatment cost limits patient access to this biotherapy. One alternative to this problem is the use of biosimilars. In this work, we describe the stable expression and physicochemical characterization of an anti-TNFα antibody. While infliximab is produced in recombinant murine SP2/0 cells, our anti-TNFα IgG antibody was expressed in recombinant murine NS0 myeloma cells. The best anti-TNFα antibody-expressing clone was selected from three clone candidates based on the stability of IgG expression levels, specific productivity as well as TNFα-binding activity compared to commercial infliximab. Our results indicate that the selected cell clone, culture medium, and fermentation mode allowed for the production of an anti-TNFα antibody with similar characteristics to the reference commercially available product. An optimization of the selected culture medium by metabolomics may increase the volumetric productivity of the process to satisfy the demand for this product. Further experiments should be performed to evaluate the biological properties of this anti-TNFα antibody. KEY POINTS: • An anti-TNFα antibody was produced in NS0 cells using perfusion culture. • A proprietary chemically defined culture medium was used to replace commercially available protein-free medium. • The purified anti-TNFα antibody was comparable to the reference marketed product.

Elucidating chemical and disulfide heterogeneities in rituximab using reduced and non-reduced peptide mapping

Peptide mapping by liquid chromatography-mass spectrometry is the gold standard to characterize post-translational modifications and disulfide bonds. The structural integrity, heterogeneity, and quality of biotherapeutic proteins are evaluated via reduced and non-reduced peptide mapping methods. However, non-enzymatic artifacts are often induced during sample preparation when alkaline pH conditions are used. To minimize these artifacts, methods using various acidic pH conditions have been developed by multiple researchers. However, these may lead to missed and non-specific cleavages during the analysis. In this study, improved reduced and non-reduced peptide mapping method has been proposed to characterize endogenous chemical modifications and native disulfide bonds of monoclonal antibody -based products. Solubilization has been carried out at acidic pH conditions under high temperature, followed by the addition of tris (2-carboxyethyl) phosphine as a reducing agent and a low alkylating agent. It was observed that the non-enzymatic post-translational modifications and non-native disulfide scrambled peptides significantly reduced under trypsin plus Lys-C digestion conditions at acidic pH as compared to the traditional methods. The results demonstrate that the proposed peptide mapping method using trypsin plus Lys-C could identify and quantify various chemical and disulfide heterogeneities with minimal artifacts. This article is protected by copyright. All rights reserved.

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.

Mass spectrometry for quality control of bispecific antibodies after SDS-PAGE in-gel digestion

Recombinant bispecific antibodies (bsAbs) are increasingly included in regimens for cancer therapy. Strict good manufacturing practice (GMP) compliant quality control measures are required to ensure quality and safety of these innovative biologicals. Gel electrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]) and size exclusion chromatography (SEC) are the cornerstones of quality control methods. BsAbs are often prone to aggregation or incomplete synthesis due to their artificial nature. In addition, host cell proteins and host cell DNA as well as impurities from the purification process itself constitute potential contaminants. Such impurities may then appear as additional, unexpected bands or peaks on SDS-PAGE gels and SEC, respectively. Here we describe a standardized protocol for rapid analysis of recombinant antibodies by mass spectrometry (MS) after tryptic digestion of bands excised from SDS-PAGE gels. We have used this protocol to characterize unexpected "contaminating bands" that were observed during the clinical development of a novel bsAb with PSMAxCD3 specificity, either during the production of the protein itself or during the development of a surrogate molecule for evaluation in syngeneic mouse models. MS analysis allowed us to precisely determine the origin of these bands, which resulted from artifacts or from incomplete protein synthesis. The combined utilization of SDS-PAGE und MS can therefore substantially support GMP-compliant production of recombinant proteins.

Four-step approach to efficiently develop capillary gel electrophoresis methods for viral vaccine protein analysis

Vaccines against infectious diseases are urgently needed. Therefore, modern analytical method development should be as efficient as possible to speed up vaccine development. The objectives of the study were to identify critical method parameters (CMPs) and to establish a set of steps to efficiently develop and validate a CE‐SDS method for vaccine protein analysis based on a commercially available gel buffer. The CMPs were obtained from reviewing the literature and testing the effects of gel buffer dilution. A four‐step approach, including two multivariate DoE (design of experiments) steps, was proposed, based on CMPs and was verified by CE‐SDS method development for: (i) the determination of influenza group 1 mini‐hemagglutinin glycoprotein; and (ii) the determination of polio virus particle proteins from an inactivated polio vaccine (IPV). The CMPs for sample preparation were incubation temperature(s) and time(s), pH, and reagent(s) concentration(s), and the detection wavelength. The effects of gel buffer dilution revealed the CMPs for CE‐SDS separation to be the effective length, the gel buffer concentration, and the capillary temperature. The four‐step approach based on the CMPs was efficient for the development of the two CE methods. A four‐step approach to efficiently develop capillary gel electrophoresis methods for viral vaccine protein analysis was successfully established.

Major cause of antibody artifact bands on non-reducing SDS-PAGE and methods for minimizing artifacts

When monoclonal antibodies (mAbs) are analysed by non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), method-induced artifacts are a frequent phenomenon. Previous studies suggested that incomplete denaturation and disulfide-bond scrambling are two main causes of artifact bands. Thus, in practice samples are normally heated and treated with alkylating agent iodoacetamide (IAM) before loading to promote denaturation and block free sulfhydryl groups, respectively. In this work, we further studied the major cause of artifact bands on non-reducing SDS-PAGE and ways of eliminating artifacts with two purified mAbs. In both cases, it was found that artifact bands on non-gradient Tris-glycine gels are mainly caused by incomplete denaturation under typical gel conditions. In general, heating minimizes artifact bands due to incomplete denaturation but it also generates some extra bands. Combining heating with IAM treatment achieved slightly better results than heating alone. As an alternative to heating, treating the samples with 8 M urea also allows close to complete denaturation of samples and thus minimizes artifact bands. In addition, we learned that untreated samples (samples that are not heated or treated with urea) may look different on Bis-Tris gel depending on gel composition (non-gradient vs. gradient) and the buffer used (MES vs. MOPS). In certain case, the apparent lack of artifact bands on gradient Bis-Tris gel may be in fact due to insufficient resolution. In conclusion, this study further confirmed that full-denaturation of sample is critical for minimizing/avoiding artifact bands on non-reducing SDS-PAGE.

Fragmentation of a Monoclonal Antibody by Peroxotungstate

PURPOSE

Tungsten and tungsten oxide leachates found in glass pre-filled syringes were identified to initiate protein precipitation and aggregation. Here, we tested the possibility of tungsten and tungsten oxide to induce the chemical degradation of proteins via reaction with hydrogen peroxide, a possible impurity present in protein formulations, to yield peroxotungstate.

METHODS

A monoclonal antibody (mAb) was incubated with various concentrations of peroxotungstate and the reaction mixtures analyzed by SDS-PAGE and mass spectrometry.

RESULTS

Exposure of a mAb to 1.07-1070 ppm peroxotungstate (based on tungsten content) at temperatures of 4°C and 22°C (pH 5-7) induced protein fragmentation. The extent of fragmentation increased with higher temperatures, lower pH and higher peroxotungstate concentrations. The mAb fragments were identified to contain different combinations of heavy chains (H) and light chains (L). Analogous mAb fragments were generated when the protein was exposed to H₂O₂ and orthotungstate at levels as low as 5 ppm. In addition, extracts from tungsten pins used to manufacture glass pre-filled syringes, in combination with H₂O₂ caused comparable fragmentation of the mAb. Mass spectrometric identification of the fragments suggests fragment generation by oxidative disulfide bond cleavage between the heavy and light chains, confirmed by mass spectrometry data on product formation. The mechanism of oxidative fragmentation was separately confirmed with insulin.

CONCLUSION

Fragmentation of the mAb by peroxotungstate is proposed to occur through inter-chain disulfide bond oxidation to form thiosulfinate (CyS(═O)SCy) and thiosulfonate [CyS(═O)₂SCy], followed by hydrolysis.

Kinetics and Characterization of Non-enzymatic Fragmentation of Monoclonal Antibody Therapeutics

PURPOSE

To understand non-enzymatic hydrolytic fragmentation of a monoclonal antibody therapeutic under temperature stressed conditions and investigating possible mechanism for the same.

METHODS

The mAb therapeutic was incubated at 50°C in phosphate buffer at pH 6.5 and fragmentation was monitored at different ionic strengths under stressed conditions. The incubated mAb was sampled at regular time intervals by analytical Size Exclusion Chromatography (SEC).

RESULTS

It was observed that 57% of the mAb product fragmented over 4 days into two fragment species - Fc-Fab and Fab with molecular weights of 97 KDa and 47 KDa, respectively, as measured by mass spectrometry (MS) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The fragmentation rate was slow initially and then accelerated with time. No change in % aggregate level was observed in this duration, implying that degradation was primarily via fragmentation at high temperature. Kinetics of hydrolytic fragmentation was hypothesized and SEC data was fitted to estimate the kinetic rate constants. While degradation of the monomer into fragment species was non-Arrhenius with a negative activation energy, further degradation of Fab-Fc fragments into Fab or Fc fragments followed Arrhenius Law with an activation energy of 2.1 and 15.38 kcal/mol, respectively.

CONCLUSION

High temperature (50°C) causes mAb to cleave at the hinge region to form Fab-Fc and Fab/Fc, as confirmed by dynamic light scattering, SDS-PAGE, SEC, and MS. A kinetic model for hydrolytic fragmentation has been proposed. The results are expected to assist end users in formulation development as well as in monitoring stability of biotherapeutic products.

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

Background

The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014–2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.

Results

In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.

Conclusions

This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0745-2) contains supplementary material, which is available to authorized users.

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

BACKGROUND

The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014-2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.

RESULTS

In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.

CONCLUSIONS

This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Controlled release of an anthrax toxin-neutralizing antibody from hydrolytically degradable polyethylene glycol hydrogels

In this study, hydrophilic and hydrolytically degradable poly (ethylene glycol) (PEG) hydrogels were formed via Michael-type addition and employed for sustained delivery of a monoclonal antibody against the protective antigen of anthrax. Taking advantage of the PEG-induced precipitation of the antibody, burst release from the matrix was avoided. These hydrogels were able to release active antibodies in a controlled manner from 14 days to as long as 56 days in vitro by varying the polymer architectures and molecular weights of the precursors. Analysis of the secondary and tertiary structure and the in vitro activity of the released antibody showed that the encapsulation and release did not affect the protein conformation or functionality. The results suggest the promise for developing PEG-based carriers for sustained release of therapeutic antibodies against toxins in various applications.

Purification and characterization of a novel lectin from Chinese leek seeds

A novel lectin, CLSL, was purified from Chinese leek seeds by ion exchange chromatography on SP Sephadex C-25 and gel filtration chromatography on Sephadex G50. The lectin had a molecular weight of 23.6 kDa and was composed of two identical subunits linked by disulfide bonds, a conclusion based on SDS-PAGE under reducing and nonreducing conditions. CLSL was a glycoprotein with a carbohydrate content of 3.6%. It exerted potent agglutinating activity against rat red blood cells at a concentration of 8.9 μg/mL. Hemagglutination of rat erythrocytes was inhibited by d-fructose, mannitol, and sorbose at the concentration of 20 mM. The hemagglutinating activity of CLSL was maintained at 100 °C for 60 min and under acidic pH conditions but was lost at neutral and alkaline pH conditions. The hemagglutinating activity was stimulated by Ca(2+), Fe(2+), and Cu(2+) but inactivated by Ba(2+) at a concentration of 10 mM. Ba(2+)-mediated inactivation of CLSL was caused by CLSL conformational change induced by barium ions, according to the results of circular dichroism and fluorescence spectroscopy. Deconvolution of the CLSL circular dichroism indicated that it was an α-helical lectin with α-helix and β-fold contents of 35.8% and 8.6%, respectively. CLSL could also selectively inhibit cell proliferation.

Pulsed electric field (PEF)-induced aggregation between lysozyme, ovalbumin and ovotransferrin in multi-protein system

The aggregation of multi-proteins is of great interest in food processing and a good understanding of the formation of aggregates during PEF processing is needed for the application of the process to pasteurize protein-based foods. The aggregates formation of a multi-protein system (containing ovalbumin, ovotransferrin and lysozyme) was studied through turbidity, size exclusion chromatography and SDS-PAGE patterns for interaction studies and binding forces. Results from size exclusion chromatography indicated that there was no soluble aggregates formed during PEF processing. The existence of lysozyme was important to form insoluble aggregates in the chosen ovalbumin solution. The results of SDS-PAGE patterns indicated that lysozyme was prone to precipitate, and was relatively the higher component of aggregates. Citric acid could be effective in inhibiting lysozyme from interacting with other proteins during PEF processing. Blocking the free sulphydryl by N-ethylmaleimide (NEM) did not affect aggregation inhibition.

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis

Since the introduction about 30 years ago, CE techniques have gained a significant impact in pharmaceutical analysis. The present review covers recent advances and applications of CE for the analysis of pharmaceuticals. Both small molecules and biomolecules such as proteins are considered. The applications range from the determination of drug-related substances to the analysis of counterions and the determination of physicochemical parameters. Furthermore, general considerations of CE methods in pharmaceutical analysis are described.