Isolation and Characterization of Monoclonal Antibody Charge Variants by Free Flow Isoelectric Focusing

Chemical Mobilization-Based Capillary Isoelectric Focusing-Mass Spectrometry Using the nanoCEasy Interface for Pharmaceutical Protein Analysis

Capillary isoelectric focusing (CIEF) coupled with electrospray ionization mass spectrometry (ESI-MS) is regarded as an outstanding approach for protein and proteoform analysis, combining a high-resolution separation technique and an enhanced detection technique. The few so-far developed CIEF-ESI-MS approaches exhibit limitations regarding sensitivity and separation performance. Here, we report a new generic methodology for CIEF-ESI-MS based on chemical mobilization, leading to highly efficient separation. This new integrated methodology relies on exchanging catholyte, initially introduced in the nanoCEasy interface in the focusing step, with sheath liquid (SL) in order to chemically mobilize the analytes into the ESI-MS system. The CIEF-MS method is evaluated by separation of a peptide set, model proteins, and monoclonal antibody charge variants. The effect of various parameters including master mixture composition, field strength, catholyte, SL composition, focusing time, and capillary conditions is optimized and discussed. Excellent separation performance can be achieved with a pI resolution down to 0.1 pH unit. The mobilization reproducibility is demonstrated with "migration time" RSDs below 10%. Additionally, the chemical mobilization is compared with the pressure assistance-chemical mobilization method, demonstrating that even a small pressure causes a strong decrease in separation performance, which clearly indicates the benefit of the chemical mobilization-based method. The applicability and separation power of the developed method are further exhibited by separation of Fc-conjugated insulins (mass = 62 kDa) differing in only one amino acid.

Isolation and characterization of rabies monoclonal antibody charge variants

Current postexposure prophylaxis of rabies includes vaccines, human rabies immunoglobulin (RIG), equine RIG, and recombinant monoclonal antibodies (mAb). In the manufacturing of rabies recombinant mAb, charge variants are the most common source of heterogeneity. Charge variants of rabies mAb were isolated by salt gradient cation exchange chromatography (CEX) to separate acidic and basic and main charge variants. Separated variants were further extensively characterized using orthogonal analytical techniques, which include secondary and tertiary structure determination by far and near ultraviolet circular dichroism spectroscopy. Charge and size heterogeneity were evaluated using CEX, isoelectric focusing (IEF), capillary-IEF, size exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blotting. Antigen binding affinity was assessed by enzyme linked immuno-sorbent assay and rapid florescence foci inhibition test. Results from structural and physicochemical characterizations concluded that charge variants are formed due to posttranslational modification demonstrating that the charge heterogeneity, these charge variants did neither show any considerable physicochemical change nor affect its biological function. This study shows that charge variants are effective components of mAb and there is no need of deliberate removal, until biological functions of rabies mAb will get affected.

Identification of structural origins of complex charge heterogeneity in therapeutic ACE2Fc fusion protein facilitated by free-flow isoelectric focusing

Fc Fusion protein represents a versatile molecular platform with considerable potential as protein therapeutics of which the charge heterogeneity should be well characterized according to regulatory guidelines. Angiotensin-converting enzyme 2 Fc fusion protein (ACE2Fc) has been investigated as a potential neutralizing agent to various coronaviruses, including the lingering SARS-CoV-2, as this coronavirus must bind to ACE2 to allow for its entry into host cells. ACE2Fc, an investigational new drug developed by Henlius (Shanghai China), has passed the Phase I clinical trial, but its huge amount of charge isoforms and complicated charge heterogeneity posed a challenge to charge variant investigation in pharmaceutical development. We employed offline free-flow isoelectric focusing (FF-IEF) fractionation, followed by detailed characterization of enriched ACE2Fc fractions, to unveil the structural origins of charge heterogeneity in ACE2Fc expressed by recombinant CHO cells. We adopted a well-tuned 3-component separation medium for ACE2Fc fractionation, the highest allowable voltage to maximize the FF-IEF separation window and a mild Protein A elution method for preservation of protein structural integrity. Through peptide mapping and other characterizations, we revealed that the intricate profiles of ACE2Fc charge heterogeneity are mainly caused by highly sialylated multi-antenna N-glycosylation. In addition, based on fraction characterization and in silico glycoprotein model analysis, we discovered that the large acidic glycans at N36, N73, and N305 of ACE2Fc were able to decrease the binding activity towards Spike (S) protein of SARS-CoV-2. Our study exemplifies the value of FF-IEF in highly complex fusion protein characterization and revealed a quantitative sialylation-activity relationship in ACE2Fc.

Combination of On-Line and Off-Line Two-Dimensional Liquid Chromatography-Mass Spectrometry for Comprehensive Characterization of mAb Charge Variants and Precise Instructions for Rapid Process Development

Charge variants, as an important quality attribute of mAbs, must be comprehensively characterized and monitored during development. However, due to their complex structure, the characterization of charge variants is challenging, labor-intensive, and time-consuming when using traditional approaches. This work combines on-line and off-line 2D-LC-MS to comprehensively characterize mAb charge variants and quickly offer precise instructions for process development. Six charge variant peaks of mAb 1 were identified using the developed platform. Off-line 2D-LC-MS analysis at the peptide level showed that the acidic peak P1 and the basic peaks P4 and P5 were caused by the deamidation of asparagine, the oxidation of methionine, and incomplete C-terminal K loss, respectively. On-line 2D-LC-MS at the intact protein level was used to identify the root causes, and it was found that the acidic peak P2 and the basic peak P6 were due to the glutathionylation of cysteine and succinimidation of aspartic acid, respectively, which were not found in off-line 2D-LC-MS because of the loss occurring during pre-treatment. These results suggest that process development could focus on cell culture for adjustment of glutathionylation. In this paper, we propose the concept of precision process development based on on-line 2D-LC-MS, which could quickly offer useful data with only 0.6 mg mAb within 6 h for precise instructions for process development. Overall, the combination of on-line and off-line 2D-LC-MS can characterize mAb charge variants more comprehensively, precisely, and quickly than other approaches. This is a very effective platform with routine operations that provides precise instructions for process development within hours, and will help to accelerate the development of innovative therapeutics.

Imaged capillary isoelectric focusing (icIEF) tandem high resolution mass spectrometry for charged heterogeneity of protein drugs in biopharmaceutical discovery

Since the first commercial imaged capillary isoelectric focusing (icIEF) instrument was developed twenty years ago, the technology has become the gold standard of quality and manufacturing process control in the biopharmaceutical industry. This is owing to its high-resolution and high-throughput characterization of protein charge heterogeneity. In addition to a charge variant profiling, mass spectrometry (MS) analyses are also desirable to obtain an in-tact molecular weight (MW) and further identification of these charged species. While offline fractionation technologies including isoelectric focusing (IEF) and free flow electrophoresis (FFE) followed by liquid chromatography (LC)-mass spectrometry (MS) coupling have been employed for this purpose, there have been much fewer reported applications of icIEF-based MS connection and fraction collection. Factors that have impeded the development of these icIEF applications include difficulties with a direct connection to the MS interface as well as high background signal of carrier ampholytes and incompatible coated capillary cartridges. In this work, we developed a robust and flexible icIEF-MS platform which overcomes these challenges to achieve both the rapid icIEF separation and high-resolution MS (HRMS) identification of protein charged variants simultaneously. We demonstrate how this methodology proves highly-sensitive and highly reliable for the characterization of commercial monoclonal antibodies (mAbs) and antibody-drug-conjugates (ADCs). The whole workflow of icIEF-MS for protein heterogeneity is straight forward and accurate and can be performed within 45 min. Furthermore, the developed icIEF-MS configuration can flexibly switch to icIEF-based fraction collection model allowing the user to perform additional in-depth characterization such as peptide mapping by high performance liquid chromatography (HPLC) tandem mass spectrometry (LC-MS/MS).

Fractionation and online mass spectrometry based on imaged capillary isoelectric focusing (icIEF) for characterizing charge heterogeneity of therapeutic antibody

Imaged capillary isoelectric focusing (icIEF) technology has been proved to be robust for the characterization of protein charge heterogeneity due to its high-resolution pI discrimination and high-throughput. Although high performance liquid chromatography (HPLC) tandem mass spectrometry (MS) and offline fraction collection technologies including isoelectric focusing (IEF), ion exchange chromatography (IEX) and free flow electrophoresis (FFE) have been widely utilized for protein charge variant characterization, there are a few applications of MS coupling with icIEF as a front-separation technique and related fractionation technologies for protein charge heterogeneity. However, the application of icIEF-MS has been much less frequent due to difficulties in MS interface, compatible ampholyte and coated capillary cartridge designation, ultimately impeding the breadth of icIEF applications in protein charge heterogeneity. In this study, a therapeutic monoclonal antibody (mAb-M-AT) was used for its charge variant characterization on an integrated icIEF platform with functions including analytical profiling, MS online coupling and fraction collection for charge heterogeneities. The main protein component and its four charge variants were identified using direct icIEF-MS coupling. Additionally, the two major acidic and basic charge variants were collected using preparative fractionation after the protein focused in the separation capillary. The identity of the fractions was confirmed by LC-MS at intact protein level and the results were consistent with those using icIEF-MS online coupling. The multiple operation modes of the icIEF platform described above can be rapidly and flexibly switched just by changing customized capillary separation cartridges without drastically altering instrument configuration. The whole workflow of icIEF-based profiling, fractionation and MS online coupling for protein heterogeneity is straightforward, reliable, and accurate, thus providing comprehensive solutions for in-depth protein heterogeneity characterization.

Cutting-edge mass spectrometry strategy based on imaged capillary isoelectric focusing (icIEF) technology for characterizing charge heterogeneity of monoclonal antibody

Imaging capillary isoelectric focusing (icIEF) technology has been becoming the gold criteria of monitoring monoclonal antibody (mAb) charge heterogeneity that is one of the major product-related variants in recombinant biopharmaceuticals, since the first commercial instrument developed twenty years ago. However, the protein identification in icIEF separation is just based on isoelectric point (pI) measurement of protein. Although high resolution mass spectrometry (HRMS) is currently the most powerful means of qualitative protein analysis, traditional icIEF cannot compatibly be used in conjunction with MS due to the use of less volatile reagents. In addition, protein heterogeneity characterization in depth such as peptide mapping by high performance liquid chromatography (HPLC) requires the focused protein bands to be collected as fractions after the icIEF separation, which is a great challenge in biopharmaceutical discovery. In this work, pembrolizumab was employed as targeting mAb (a highly selective anti-PD-1 humanized mAb), an integrated icIEF platform was developed including analytical profiling, MS coupling and fraction collections for charged variant preparation. Multiple operation modes can be rapidly and flexibly switched just by changing customized capillary separation cartridges without more configurations. Main component, four acidic variants (A1-A4) and three basic variants (B1-B3) were baseline separated then directly detected by icIEF-HRMS online coupling for rapid screening of intact protein heterogeneity where reliable and accurate molecular weight of protein charged variants were obtained. Next, by installing preparative capillary separation cartridge, fractions of major charge variants (A2-3 and B1-2) and main component were collected for following LC-MS peptide mapping characterization. The whole workflow of icIEF-based MS strategy for protein heterogeneity is straight forward, reliable and accurate, which provides a comprehensive and revolutionary technology for protein drug quality control (QC) monitoring, MS coupling for fingerprinting intact protein and HPLC-MS peptide mapping in depth.

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.

In-Depth Metaproteomics Analysis of Oral Microbiome for Lung Cancer

The human oral microbiome correlates with numerous diseases, including lung cancer. Identifying the functional changes by metaproteomics helps understand the disease-related dysbiosis, yet characterizing low-abundant bacteria is challenging. Here, we developed a free-flow isoelectric focusing electrophoresis-mass spectrometry- (FFIEF-MS-) based metaproteomics strategy to reduce host interferences and enrich low-abundant bacteria for in-depth interpretation of the oral microbiome. With our method, the number of interfering peptides decreased by 52.87%, whereas the bacterial peptides and species increased by 94.97% and 44.90%, respectively, compared to the conventional metaproteomics approach. We identified 3647 bacterial proteins, which is the most comprehensive oral metaproteomics study to date. Lung cancer-associated bacteria were validated among an independent cohort. The imbalanced Fusobacterium nucleatum and Prevotella histicola and their dysregulated functions in inhibiting immune response and maintaining cell redox homeostasis were revealed. The FFIEF-MS may serve as a valuable strategy to study the mechanisms between human diseases and microbiomes with broader applications.

Structural and Functional Analysis of CEX Fractions Collected from a Novel Avastin® Biosimilar Candidate and Its Innovator: A Comparative Study

Avastin^® is a humanized recombinant monoclonal antibody used to treat cancer by targeting VEGF-A to inhibit angiogenesis. SIMAB054, an Avastin^® biosimilar candidate developed in this study, showed a different charge variant profile than its innovator. Thus, it is fractionated into acidic, main, and basic isoforms and collected physically by Cation Exchange Chromatography (CEX) for a comprehensive structural and functional analysis. The innovator product, fractionated into the same species and collected by the same method, is used as a reference for comparative analysis. Ultra-Performance Liquid Chromatography (UPLC) ESI-QToF was used to analyze the modifications leading to charge heterogeneities at intact protein and peptide levels. The C-terminal lysine clipping and glycosylation profiles of the samples were monitored by intact mAb analysis. The post-translational modifications, including oxidation, deamidation, and N-terminal pyroglutamic acid formation, were determined by peptide mapping analysis in the selected signal peptides. The relative binding affinities of the fractionated charge isoforms against the antigen, VEGF-A, and the neonatal receptor, FcRn, were revealed by Surface Plasmon Resonance (SPR) studies. The results show that all CEX fractions from the innovator product and the SIMAB054 shared the same structural variants, albeit in different ratios. Common glycoforms and post-translational modifications were the same, but at different percentages for some samples. The dissimilarities were mostly originating from the presence of extra C-term Lysin residues, which are prone to enzymatic degradation in the body, and thus they were previously assessed as clinically irrelevant. Another critical finding was the presence of different glyco proteoforms in different charge species, such as increased galactosylation in the acidic and afucosylation in the basic species. SPR characterization of the isolated charge variants further confirmed that basic species found in the CEX analyses of the biosimilar candidate were also present in the innovator product, although at lower amounts. The charge variants’ in vitro antigen- and neonatal receptor-binding activities varied amongst the samples, which could be further investigated in vivo with a larger sample set to reveal the impact on the pharmacokinetics of drug candidates. Minor structural differences may explain antigen-binding differences in the isolated charge variants, which is a key parameter in a comparability exercise. Consequently, such a biosimilar candidate may not comply with high regulatory standards unless the binding differences observed are justified and demonstrated not to have any clinical impact.

Investigating peak dispersion in free-flow counterflow gradient focusing

Free-flow electrophoresis (FFE) enables the continuous separation and collection of charged solutes, and as a result, it has drawn interest as both a preparative and an analytical tool for biological applications. Recently, a free-flow counterflow gradient focusing (FF-CGF) mechanism has been proposed with the goal of improving the resolution and versatility of FFE. To realize this potential, the factors that influence solute dispersion deserve further attention, including the gradient strength and the parabolic profile of the counterflow. Therefore, the goal of this work is to develop a theoretical model to study the interplay between these factors and molecular diffusion. Overall, an asymmetric solute distribution emerges for a wide range of parameters, and this behavior can be characterized with an exponentially modified Gaussian function. Results show that FF-CGF can achieve high-resolution separations, with the potential for high-throughput protein purification. Moreover, this work provides a practical guide for optimizing experimental conditions, as well as a strong framework for understanding and developing FF-CGF further.

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

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

Preparative continuous flow electrophoretic instrumentation for purification of biological samples

We constructed preparative instrumentation and developed the method that are based on separation of the samples by bidirectional isotachophoresis/moving boundary electrophoresis in continuous divergent flow. The described instrumentation can be used for variety of the samples, however, it can be easily optimized and tailored for the specific sample. The trapezoid separation bed from non-woven textile exhibited minimum adsorption effect for sample and it can be used repeatedly. By addition of different spacers via separation space inlets, the sections of pH gradient can be modified to enhance the separation. The liquid flow from two inlets positioned on each side of the sample inlet prevented the contact of the sample with anolyte and catholyte at the analysis beginning. One pair of thin electrodes (graphite and stainless-steel) was placed at the separation space output. The electrode products were washed out into drains without disturbing the focusing process. The influence of EOF was managed by tilting the separation bed in direction from cathodic to anodic side. The components of spirulina supernatant and color pI markers were separated in the pH gradient from 3.9 to 10.1. pH gradient was stable for at least 4.5 hours and spirulina supernatant from about 0.12 g of dry powder was processed. Compared to other preparative methods used for spirulina separation, the presented method/instrumentation working with continuous divergent flow had essential advantages. The efficient separation was fast, and no intermediate steps were necessary to obtain liquid fractions with separated components compatible with further biological experiments. This article is protected by copyright. All rights reserved.

Fractionated charge variants of biosimilars: A review of separation methods, structural and functional analysis

The similarity between originator and biosimilar monoclonal antibody candidates are rigorously assessed based on primary, secondary, tertiary, quaternary structures, and biological functions. Minor differences in such parameters may alter target-binding, potency, efficacy, or half-life of the molecule. The charge heterogeneity analysis is a prerequisite for all biotherapeutics. Monoclonal antibodies are prone to enzymatic or non-enzymatic structural modifications during or after the production processes, leading to the formation of fragments or aggregates, various glycoforms, oxidized, deamidated, and other degraded residues, reduced Fab region binding activity or altered FcR binding activity. Therefore, the charge variant profiles of the monoclonal antibodies must be regularly and thoroughly evaluated. Comparative structural and functional analysis of physically separated or fractioned charged variants of monoclonal antibodies has gained significant attention in the last few years. The fraction-based charge variant analysis has proved very useful for the biosimilar candidates comprising of unexpected charge isoforms. In this report, the key methods for the physical separation of monoclonal antibody charge variants, structural and functional analyses by liquid chromatography-mass spectrometry, and surface plasmon resonance techniques were reviewed.

Separation of Bioactive Small Molecules, Peptides from Natural Sources and Proteins from Microbes by Preparative Isoelectric Focusing (IEF) Method

Natural products derived from plants and microbes are a rich source of bioactive molecules. Prior to their use, the active molecules from complex extracts must be purified for downstream applications. There are various chromatographic methods available for this purpose yet not all labs can afford high performance methods and isolation from complex biological samples can be difficult. Here we demonstrate that preparative liquid-phase isoelectric focusing (IEF) can separate molecules, including small molecules and peptides from complex plant extracts, based on their isoelectric points (pI). We have used the method for complex biological sample fractionation and characterization. As a proof of concept, we fractionated a Gymnema sylvestre plant extract, isolating a family of terpenoid saponin small molecules and a peptide. We also demonstrated effective microbial protein separation using the Candida albicans fungus as a model system.

Purification of low-abundance lysozyme in egg white via free-flow electrophoresis with gel-filtration chromatography

As an effective separation tool, free-flow electrophoresis has not been used for purification of low-abundance protein in complex sample matrix. Herein, lysozyme in complex egg white matrix was chosen as the model protein for demonstrating the purification of low-content peptide via an FFE coupled with gel fitration chromatography (GFC). The crude lysozyme in egg while was first separated via free-flow zone electrophoresis (FFZE). After that, the fractions with lysozyme activity were condensed via lyophilization. Thereafter, the condensed fractions were further purified via a GFC of Sephadex G50. In all of the experiments, a special poly(acrylamide- co-acrylic acid) (P(AM-co-AA)) gel electrophoresis and a mass spectrometry were used for identification of lysozyme. The conditions of FFZE were optimized as follows: 130 μL/min sample flow rate, 4.9 mL/min background buffer of 20 mM pH 5.5 Tris-Acetic acid, 350 V, and 14 °C as well as 2 mg/mL protein content of crude sample. It was found that the purified lysozyme had the purity of 80% and high activity as compared with its crude sample with only 1.4% content and undetectable activity. The recoveries in the first and second separative steps were 65% and 82%, respectively, and the total recovery was about 53.3%. The reasons of low recovery might be induced by diffusion of lysozyme out off P(AM-co-AA) gel and co-removing of high-abundance egg ovalbumin. All these results indicated FFE could be used as alternative tool for purification of target solute with low abundance.

Thread-based isoelectric focusing coupled with desorption electrospray ionization mass spectrometry

Efficient ‘on-thread’ isoelectric focusing of proteins, with direct on-thread detection using desorption electrospray ionisation mass spectrometry.

Continuous flow electrophoretic separation - Recent developments and applications to biological sample analysis

Continuous flow electrophoretic separation with continuous sample loading provides the advantage of processing volumes of any sizes, as well as the benefit of a real-time monitoring and optimization of the separation process. In addition, the spatial separation of the sample enables collecting multiple separated components simultaneously and in a continuous manner. The separation is usually performed in mild buffers without organic solvents and detergents (sample biological activity is retained) and it is carried out without usage of a solid support in the separation space preventing the interaction of the sample with it (high sample recovery). The method is used for the separation of proteins/peptides in proteomic applications, and its great applicability is to the separation of the cells, cellular organelles, vesicles, membrane fragments, and DNA. This review focuses on the electrophoretic separation performed in a continuous flow and it describes various electrophoretic modes and instrumental setups. Recent developments in methodology and instrumentation, the integration with other techniques, and the application to the biological sample analysis are discussed as well.

Advances in liquid formulations of parenteral therapeutic proteins

Liquid formulation of therapeutic proteins is a maturing technology. Demand for products that are easy to use in the clinic or that are amenable to self-administration make a ready to use liquid formulation desirable. Most modern liquid formulations have a simple composition; comprising a buffer, a tonicity modifier, a surfactant, sometimes a stabiliser, the therapeutic protein and water. Recent formulations of monoclonal antibodies often use histidine or acetate as the buffer, sucrose or trehalose as the tonicity modifier and polysorbate 20 or 80 as the surfactant with a pH of 5.7 +/- 0.4. The mechanisms for the behaviour of excipients is still debated by academics so formulation design is still a black art. Fortunately, a statistical approach like design of experiment is suitable for formulation development and has been successful when combined with accelerated stability experimentation. The development of prefilled syringes and pens has added low viscosity and shear resistance to the quality attributes for a successful formulation. To achieve patient compliance for self-administration, formulations that cause minimal pain and tissue damage is also desirable.

Carrier ampholyte-free free-flow isoelectric focusing for separation of protein

Free-flow isoelectric focusing (FFIEF) has the merits of mild separation conditions, high recovery and resolution, but suffers from the issues of ampholytes interference and high cost due to expensive carrier ampholytes. In this paper, a home-made carrier ampholyte-free FFIEF system was constructed via orientated migration of H⁺ and OH^- provided by electrode solutions. When applying an electric field, a linear pH gradient from pH 4 to 9 (R² = 0.994) was automatically formed by the electromigration of protons and hydroxyl ions in the separation chamber. The carrier ampholyte-free FFIEF system not only avoids interference of ampholyte to detection but also guarantees high separation resolution by establishing stable pH gradient. The separation selectivity was conveniently adjusted by controlling operating voltage and optimizing the composition, concentration and flow rate of the carrier buffer. The constructed system was applied to separation of proteins in egg white, followed by MADLI-TOF-MS identification. Three major proteins, ovomucoid, ovalbumin and ovotransferrin, were successfully separated according to their pI values with 15 mmol/L Tris-acetic acid (pH = 6.5) as carrier buffer at a flow rate of 12.9 mL/min.

Characterization of recombinant monoclonal antibody charge variants using WCX chromatography, icIEF and LC-MS/MS

Charge heterogeneity is an important aspect of research into the development of monoclonal antibody drugs. In the present study, charge variants were separated into four fractions using weak cation exchange chromatography and were thoroughly analyzed using liquid chromatography-mass spectrometry at multiple levels. Molecular weight analysis of intact antibody and subunits confirmed the presence of heavy-chain leader sequences, light-chain leader sequences, dehydration, and cysteinylation. Peptide mapping of the fractions using different enzymes further localized the modified sites. Modified proportions identified at peptide level were compared with the purity detected by imaged capillary isoelectric focusing, the results showed that basic variant 1 consisted of cysteinylation and dehydration of asparagine, and basic variant 2 fully accounted for the N-terminal leader sequence of the heavy chain. About 14.8% of the acidic variant can be explained by N-terminal leader sequences in the light chain, and 18% of the acidic variant was demonstrated to be deamidation of asparagine in the heavy chain. There was approximately 54.2% of the acidic variant still cannot be explained. It was hypothesized that those acidic variants that have not yet been identified are an ensemble of molecules with slight molecular weight differences or the same molecular weight but different structures.

Differential gene expression of a feed-spiked super-producing CHO cell line

Feed supplements are concentrated cell culture media that contain a variety of nutrients, which can be added during a bioprocess. During fed-batch cultivation, feed media are typically added to a growing cell culture to maximize cell and product concentrations. In this study, only a single shot of feed medium was added on day 0 to a basal cell culture medium and compared to non-supplemented basal medium (feed-spiked at day 0 versus control experiments) by cultivation of a recombinant mAb expressing CHO cell line in batch mode under controlled conditions in a bioreactor. Since the feed-spike at day 0 was based on existing medium components without introducing additional supplements, a desirable process with decreased complexity was generated. Unlike cells in basal medium, feed-spiked cultures reached almost 2× higher peak cell concentrations (10 × 10⁶ c/mL vs. 18 × 10⁶ c/mL) and 3× higher antibody concentrations (0.8 g/L vs. 2.4 g/L). Batch process time and the integral over the viable cell count were similar for both process types. Constantly high cell-specific production rates in feed-spiked cultures (70 pg/cell/day) compared to continuously declining rates in basal medium (from 70 to 10 pg/cell/day) were responsible for an overall 70% higher cell-specific production rate and the higher product concentrations. To associate gene expression patterns to different process proceedings, transcriptome analysis was performed using microarrays. Several transcripts that are involved with glutamine de novo synthesis and citric acid cycle were significantly upregulated on several days in feed-spiked cultures. The top identified gene ontology (GO) terms related well to cell cycle and primary metabolism, cellular division as well as nucleobase formation or regulation, which indicated a more active proliferative state for feed-spiked cultures. KEGG biochemical pathway analysis and Gene set enrichment analysis (GSEA) further confirmed these findings from a complementary perspective. Moreover, several interesting gene targets, which have not yet been associated with recombinant protein expression, were identified that related to a higher proliferative state, growth, protein synthesis, cell-size control, metabolism, cell survival as well as genes that are associated with the control of the mammalian target of rapamycin (mTOR) in feed-spiked cultures. Analysis of critical product quality attributes (i.e. glycosylation, charge variants and size distribution) showed that feed-spiking did not change antibody quality.

Combining Affinity Selection and Specific Ion Mobility for Microchip Protein Sensing

The sensitive detection of proteins is a key objective in many areas of biomolecular science, ranging from biophysics to diagnostics. However, sensing in complex biological fluids is hindered by nonspecific interactions with off-target species. Here, we describe and demonstrate an assay that utilizes both the chemical and physical properties of the target species to achieve high selectivity in a manner not possible by chemical complementarity alone, in complex media. We achieve this objective through a combinatorial strategy, by simultaneously exploiting free-flow electrophoresis for target selection, on the basis of electrophoretic mobility, and conventional affinity-based selection. In addition, we demonstrate amplification of the resultant signal by a catalytic DNA nanocircuit. This approach brings together the inherent solution-phase advantages of microfluidic sample handling with isothermal, enzyme-free signal amplification. With this method, no surface immobilization or washing steps are required, and our assay is well suited to monoepitopic targets, presenting advantages over conventional ELISA techniques.

Qualification of NISTmAb charge heterogeneity control assays

The NISTmAb is a monoclonal antibody Reference Material from the National Institute of Standards and Technology; it is a class-representative IgG1κ intended serve as a pre-competitive platform for harmonization and technology development in the biopharmaceutical industry. The publication series of which this paper is a part describes NIST's overall control strategy to ensure NISTmAb quality and availability over its lifecycle. In this paper, the development and qualification of methods for monitoring NISTmAb charge heterogeneity are described. Capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF) assays were optimized and evaluated as candidate assays for NISTmAb quality control. CIEF was found to be suitable as a structural characterization assay yielding information on the apparent pI of the NISTmAb. CZE was found to be better suited for routine monitoring of NISTmAb charge heterogeneity and was qualified for this purpose. This paper is intended to provide relevant details of NIST's charge heterogeneity control strategy to facilitate implementation of the NISTmAb as a test molecule in the end user's laboratory. Graphical Abstract Representative capillary zone electropherogram of the NIST monoclonal antibody (NISTmAb). The NISTmAb is a publicly available research tool intended to facilitate advancement of biopharmaceutical analytics.

Correlating charge heterogeneity data generated by agarose gel isoelectric focusing and ion exchange chromatography methods

An isoelectric focusing method (IEF) has been used to assess the charge heterogeneity profile of a monoclonal antibody during the early stages of product development. A more precise and sensitive ion exchange chromatography (IEC/CEX) method was developed and implemented as development progressed and was used concurrently with IEF for lot release and to monitor charge heterogeneity. Charge variants resolved by both methods (IEC and IEF) were purified and characterized. Tryptic peptide mapping and N- linked oligosaccharide profile analyses of the IEC and IEF fractions indicated a structural correlation between the charge variants separated by these two methods. The major sources of molecular heterogeneity were due to the variation in the sialyated carbohydrate structure and heavy chain C-terminal lysine truncation. By monitoring the rates of change in the charge heterogeneity profiles of the monoclonal antibody stored at elevated temperatures by the IEC and IEF methods, a positive correlation between the two methods was established. This approach enabled replacement of the IEF method with the more precise IEC method.