Charge heterogeneity: Basic antibody charge variants with increased binding to Fc receptors

Coupling cation and anion exchange chromatography for fast separation of monoclonal antibody charge variants

A design procedure for the separation of charge variants of a monoclonal antibody (mAb) was developed, which was based on the coupling of cation-exchange chromatography (CEX) and anion-exchange chromatography (AEX) under high loading conditions. The design of the coupled process was supported by a dynamic model. The model was calibrated on the basis of band profiles of variants determined experimentally for the mAb materials of different variant compositions. The numerical simulations were used to select the coupling configuration and the loading conditions that allowed for efficient separation of the mAb materials into three products enriched with each individual variant: the acidic (av), main (mv) and basic (bv) one. In the CEX section, a two-step pH gradient was used to split the loaded mass of mAb into a weakly bound fraction enriched with av and mv, and a strongly bound fraction containing the bv-rich product. The weakly bound fraction was further processed in the AEX section, where the mv-rich product was eluted in flowthrough, while the av-rich product was collected by a step change in pH. The choice of flow distribution and the number of columns in the CEX and AEX sections depended on the variant composition of the mAb material. For the selected configurations, the optimized mAb loading density in the CEX columns ranged from 10 to 26 mg mL-1, while in the AEX columns it was as high as 300 or 600 mg mL-1, depending on the variant composition of the mAb material. By proper selection of the loading condition, a trade-off between yield and purity of the products could be reached.

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.

Leveraging bioanalytical characterization of fractionated monoclonal antibody pools to identify aggregation-prone and less filterable proteoforms during virus filtration

Monoclonal antibodies (mAbs) are an essential class of biotherapeutics. A platform process is used for mAb development to ensure clinically safe and stable molecules. Regulatory authorities ensure that mAb production processes include sufficient viral clearance steps to achieve less than one virus particle per million doses of product. Virus filtration is used for size-based removal of enveloped and nonenveloped viruses during downstream processing of mAbs. Process development in mAb purification relies on empirical approaches and often includes adsorptive prefiltration to mitigate virus filter fouling. Opportunities for molecular-level prediction of mAb filterability are needed to plug the existing knowledge gap in downstream processing. A molecular-level approach to understanding the factors influencing mAb filterability may reduce process development time, material loss, and processing costs due to oversized virus filters. In this work, pH step gradient fractionation was applied on polished bulk mAb feed to obtain concentrated pools of fractionated mAb variants. Biophysical properties and quality attributes of fractionated pools, including oligomeric state (size), isoelectric point profile, diffusion interaction parameters, and glycoform profile, were determined using bioanalytical methods. Filterability (loading and throughput) of fractionated pools were evaluated. Statistical methods were used to obtain correlations between quality attributes of mAb fractions and filterability on the Viresolve Pro virus filter.

Demonstration of a robust high cell density transient CHO platform yielding mAb titers of up to 2 g/L without medium exchange

Biopharmaceuticals like therapeutic monoclonal antibodies (mAbs) and other derived proteins are popular for treating various diseases. Transient gene expression (TGE) is typically used as a fast yet efficient method to generate moderate amounts of material. It has been used to support early stage research and discovery processes. Introduction of a robust high yielding and predictive TGE platform in Chinese hamster ovary (CHO) is crucial. It maintains the consistency in cell lines and processes throughout the early drug discovery and downstream manufacturing processes. This helps researchers to identify the issues at an early stage for timely resolution. In this study, we have demonstrated a simple high-titer platform for TGE in CHO based on a dilution process of seeding cells. We achieved titers ranging from 0.8 to 1.9 g/L for eight model mAbs at three scales (1, 30, 100 mL) in 10 days using our new platform. The ability to seed by dilution significantly streamlined the process and dramatically enhanced platform throughput. We observed a modest reduction in titer ranging from 11% to 28% when cells were seeded using dilution compared to when cells were seeded using medium exchange. Further studies revealed that carry over of spent medium into transfection negatively affected the DNA uptake and transcription processes, while the translation and secretion was minimally impacted. In summary, our transient CHO platform using cells prepared by dilution at high densities can achieve high titers of up to 1.9 g/L, which can be further improved by targeting the bottlenecks of transfection and transcription.

LC-MS Characterization and Stability Assessment Elucidate Correlation Between Charge Variant Composition and Degradation of Monoclonal Antibody Therapeutics

Aggregation stability of monoclonal antibody (mAb) therapeutics is influenced by many critical quality attributes (CQA) such as charge and hydrophobic variants in addition to environmental factors. In this study, correlation between charge heterogeneity and stability of mAbs for bevacizumab and trastuzumab has been investigated under a variety of stresses including thermal stress at 40 °C, thermal stress at 55 °C, shaking (mechanical), and low pH. Size- and charge-based heterogeneities were monitored using analytical size exclusion chromatography (SEC) and cation exchange chromatography (CEX), respectively, while dynamic light scattering was used to assess changes in hydrodynamic size. CEX analysis revealed an increase in cumulative acidic content for all variants of both mAbs post-stress treatment attributed to increased deamidation. Higher charge heterogeneity was observed in variants eluting close to the main peak than the ones eluting further away (25-fold and 42-fold increase in acidic content for main and B1 of bevacizumab and 19-fold for main of trastuzumab, respectively, under thermal stress; 50-fold increase in acidic for main and B1 of bevacizumab and 10% rise in basic content of main of trastuzumab under pH stress). Conversely, variants eluting far away from main exhibit greater aggregation as compared to close-eluting ones. Aggregation kinetics of variants followed different order for the different stresses for both mAbs (2nd order for thermal and pH stresses and 0th order for shaking stress). Half-life of terminal charge variants of both mAbs was 2- to 8-fold less than main indicating increased degradation propensity.

Effect of Annealing on Visible-Bubble Formation and Stability Profiles of Freeze-Dried High Concentration Omalizumab Formulations

In the clinical application of freeze-dried highly concentrated omalizumab formulations, extensive visible bubbles (VBs) can be generated and remain for a long period of time in the reconstitution process, which greatly reduces the clinical use efficiency. It is necessary to understand the forming and breaking mechanism of VBs in the reconstitution process, which is a key factor for efficient and safe administration of biopharmaceutical injection. The effects of different thermal treatments on the volume of VBs and stability of omalizumab, mAb-1, and mAb-2 were investigated. The internal microvoids of the cake were characterized by scanning electron microscopy and mercury intrusion porosimetry. Electron paramagnetic resonance was applied to obtain the molecular mobility of the protein during annealing. A large number of VBs were generated in the reconstitution process of unannealed omalizumab and remained for a long period of time. When annealing steps were added, the volume of VBs was dramatically reduced. When annealed at an aggressive temperature (i.e., -6 °C), although the volume of VBs decreased, the aggregation and acidic species increased significantly. Thus, our observations highlight the importance of setting an additional annealing step with a suitable temperature, which contributes to reducing the VBs while maintaining the stability of the high concentration freeze-dried protein formulation.

Convolutional Neural Networks Guided Raman Spectroscopy as a Process Analytical Technology (PAT) Tool for Monitoring and Simultaneous Prediction of Monoclonal Antibody Charge Variants

BACKGROUND

Charge related heterogeneities of monoclonal antibody (mAb) based therapeutic products are increasingly being considered as a critical quality attribute (CQA). They are typically estimated using analytical cation exchange chromatography (CEX), which is time consuming and not suitable for real time control. Raman spectroscopy coupled with artificial intelligence (AI) tools offers an opportunity for real time monitoring and control of charge variants.

OBJECTIVE

We present a process analytical technology (PAT) tool for on-line and real-time charge variant determination during process scale CEX based on Raman spectroscopy employing machine learning techniques.

METHOD

Raman spectra are collected from a reference library of samples with distribution of acidic, main, and basic species from 0-100% in a mAb concentration range of 0-20 g/L generated from process-scale CEX. The performance of different machine learning techniques for spectral processing is compared for predicting different charge variant species.

RESULT

A convolutional neural network (CNN) based model was successfully calibrated for quantification of acidic species, main species, basic species, and total protein concentration with R2 values of 0.94, 0.99, 0.96 and 0.99, respectively, and the Root Mean Squared Error (RMSE) of 0.1846, 0.1627, and 0.1029 g/L, respectively, and 0.2483 g/L for the total protein concentration.

CONCLUSION

We demonstrate that Raman spectroscopy combined with AI-ML frameworks can deliver rapid and accurate determination of product related impurities. This approach can be used for real time CEX pooling decisions in mAb production processes, thus enabling consistent charge variant profiles to be achieved.

In-Depth Structure and Function Characterization of Heterogeneous Interchain Cysteine-Conjugated Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs), integrating high specificity of antigen-targeting antibodies and high potency of cell-killing chemical drugs, have become one of the most rapidly expanding therapeutic biologics in oncology. Although ADCs were widely studied from multiple aspects, overall structural elucidation with comprehensive understanding of variants is scarcely reported. Here, for the first time, we present a holistic and in-depth characterization of an interchain cysteine-conjugated ADC, focusing on conjugation and charge heterogeneity, and in vitro biological activities. Conjugation mapping utilized a bottom-up approach, unraveled positional isomer composition, provided insights into the conjugation process, and elucidated how conjugation affects the physicochemical and biological properties of an ADC. Charge profiling combined bottom-up and top-down approaches to interrogate the origin of charge heterogeneity, its impact on function, and best practice for characterization. Specifically, we pioneered the utilization of capillary isoelectric focusing-mass spectrometry to decode not only critical post-translational modifications but also drug load and positional isomer distribution. The study design provides general guidance for in-depth characterization of ADCs, and the analytical findings in turn benefit the discovery and development of future ADCs.

Purification and Quality Control of Recombinant Proteins Expressed in Mammalian Cells: A Practical Review

In the recent years, there has been a rapid development of new technologies and strategies when it comes to protein purification and quality control (QC), but the basic technologies for these processes go back a long way, with many improvements over the past few decades. The purpose of this chapter is to review these approaches, as well as some other topics such as the advantages and disadvantages of various purification methods for intracellular or extracellular proteins, the most effective and widely used genetically engineered affinity tags, solubility-enhancing tags, and specific proteases for removal of nontarget sequences. Affinity chromatography (AC), like Protein A or G resins for the recovery of antibodies or Fc fusion proteins or immobilized metals for the recovery of histidine-tagged proteins, will be discussed along with other conventional chromatography techniques: ion exchange (IEC), hydrophobic exchange (HEC), mixed mode (MMC), size exclusion (SEC), and ultrafiltration (UF) systems. How to select and combine these different technologies for the purification of any given protein and the minimal criteria for QC characterization of the purity, homogeneity, identity, and integrity of the final product will be presented.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

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.

Optimization of the Imaged cIEF Method for Monitoring the Charge Heterogeneity of Antibody-Maytansine Conjugate

The aim of this study was to develop a whole-column imaging-detection capillary isoelectric focusing (icIEF) method for the analytical characterization of charge heterogeneity of a novel humanized anti-EphA2 antibody conjugated to a maytansine derivative. In addition to focusing time, sample composition was optimized: pH range, percent of carrier ampholytes, conjugated antibody concentration, and urea concentration. A good separation of charge isoforms was obtained with 4% carrier ampholytes of a large (3-10) and narrow pH range (8-10.5) (1 : 1 ratio), conjugated antibody concentration (0.3-1 mg/ml) with a good linearity (R²: 0.9905), 2 M of urea concentration, and 12 minute for focusing. The optimized icIEF method demonstrated a good interday repeatability with RSD values: <1% (pI), <8% (% peak area), and 7% (total peak areas). The optimized icIEF was useful as an analytical characterization tool to assess the charged isoform profile of a discovery batch of the studied maytansinoid-antibody conjugate in comparison to its naked antibody. It exhibited a large pI range (7.5-9.0), while its naked antibody showed a narrow pI range (8.9-9.0). In the discovery batch of maytansinoid-antibody conjugate, 2% of charge isoforms had the same pI as the pI of naked antibody isoforms.

Coupling of chromatography and precipitation for adjusting acidic variant content in a monoclonal antibody pool

The acidic charge variants (av) of monoclonal antibodies (mAb) are often reported to have reduced therapeutic potency compared with the main (mv) and basic variants (bv), therefore reduction in the av content in mAb pools is often prioritized over reduction in the bv content. In previous studies we described two different methods for reducing the av content, which were based on either ion exchange chromatography or selective precipitation in polyethylene glycol (PEG) solutions. In this study, we have developed a coupled process, in which advantages of simplicity and ease in realization of PEG-aided precipitation and high separation selectivity of anion exchange chromatography (AEX) were exploited. The design of AEX was supported by the kinetic-dispersive model, which was supplemented with the colloidal particle adsorption isotherm, whereas the precipitation process and its coupling with AEX was quantified by simple mass balance equations and underlying thermodynamic dependencies. The model was used to assess the performance of the coupling of AEX and precipitation under different operating conditions. The advantage of the coupled process over the stand-alone AEX depended on the demand for the av reduction as well as the initial variant composition of the mAb pool, e.g., the improvement in the throughput provided by the optimized sequence of AEX and PREC varied from 70 to 600% for the initial av content changed from 35 to 50% w/w, and the reduction demand changed from 30 to 60%.

Demonstrating analytical similarity of a biosimilar HLX04 to bevacizumab with a panel of state-of-the-art methods and tiering of quality attributes

Therapeutical monoclonal antibodies are structurally and functionally complex, whereas the innovator's manufacturing processes are proprietary. With respect to the similarity assessment, a proposed biosimilar product needs to demonstrate a side-by-side comparison between the reference product (RP) and candidate product in terms of physicochemical properties and biological activities, as well as nonclinical and clinical outcomes. Here, a comprehensive analytical similarity assessment was performed for in-depth comparison of HLX04, China-sourced Avastin^® (CN-Avastin^®), and Europe-sourced Avastin^® (EU-Avastin^®) following a tier-based quality attribute (QA) evaluation. A series of orthogonal and state-of-the-art analytical techniques were developed for the assessment. Ten lots of HLX04 were compared with 29 lots bevacizumab RP. Referred to the characterization results, HLX04 is highly similar to the RPs with respect to physicochemical properties and biological functions. In addition, HLX04 was found with similar stability and degradation behaviors upon multiple stressed conditions to bevacizumab. Minor differences were observed in glycosylation, aggregates, FcγRIIIa(F), and FcγRIIIa(V) binding activities; nevertheless, they were evaluated and demonstrated not to impact clinical outcomes. According to the reported clinical results, the totality of evidence, including the pharmacokinetic, efficacy, safety, and immunogenicity, further shows that HLX04 is similar to CN-/EU-Avastin^®.

Long term culturing of CHO cells: phenotypic drift and quality attributes of the expressed monoclonal antibody

OBJECTIVE

Establishing cell lines with enhanced protein production requires a deep understanding of the cellular dynamics and cell line stability. The aim of the study is to investigate the impact of long term culturing (LTC) on cell morphology and altered cellular functions possibly leading to phenotypic drift, impacting product yield and quality. Study highlights the orthogonal cellular and analytical assay toolbox to define cell line stability for optimal culture performance and product quality.

METHODS

We investigated recombinant monoclonal antibody (mAb) expressing CHO cells for 60 passages or 180 generations and assessed the cell growth characteristics and morphology by confocal and scanning electron microscopy. Quality attributes of expressed mAb is accessed by performing charge variants, glycan, and host cell protein analysis.

RESULTS

We observed a 1.65-fold increase in viable cell population and 1.3-fold increase in cell specific growth rate. A 2.5-fold decrease in antibody titer and abatement of actin filament indicate cellular phenotypic drift. Mitochondrial membrane potential (∆ΨM) signified cell health and metabolic activity during LTC. Host cell protein production is reduced by 1.8-fold. Charge heterogeneity was perturbed with 12.5% and 43% reduction in abundance of acidic and basic charge variants respectively. Glycan profile indicated a decline in fucosylation with 17% increase in galactosylated species as compared with early passaged cells.

CONCLUSION

LTC impinges on cellular phenotype as well as the quality of the expressed antibody, suggesting a defined subculturing limit to retain stable protein expression and cell morphology to achieve consistent product quality. Study signifies the changes in cellular and metabolic markers, suggesting cellular and analytical toolbox which could play a significant role in defining cell characteristics and ensured product quality.

Trastuzumab Charge Variants: a Study on Physicochemical and Pharmacokinetic Properties

Background

Post-translational modifications in bioprocessing and storage of recombinant mAbs are the main sources of charge variants. While the profile of these kinds of variants is considered an important attribute for the therapeutic mAbs, there is controversy about their direct role in safety and efficacy. In this study, the physicochemical and pharmacokinetic (PK) properties of the separated charge variants belonging to a trastuzumab potential biosimilar, were examined.

Methods

The acidic peaks, basic peaks, and main variants of trastuzumab were separated and enriched by semi-preparative weak cation exchange. A panel of analytical techniques was utilized to characterize the physicochemical properties of these variants. The binding affinity to HER2 and FcγRs and the PK parameters were evaluated for each variant.

Results

Based on the results, the charge variants of the proposed biosimilar had no significant influence on the examined efficacy and PK parameters.

Conclusion

During the development and production of biosimilar monoclonal antibodies, evaluating the effect of their charge variants on efficacy and PK parameters is needed.

Pertuzumab Charge Variant Analysis and Complementarity-Determining Region Stability Assessment to Deamidation

Pertuzumab is a monoclonal antibody used for the treatment of HER2-positive breast cancer in combination with trastuzumab. Charge variants of trastuzumab have been extensively described in the literature; however, little is known about the charge heterogeneity of pertuzumab. Here, changes in the ion-exchange profile of pertuzumab were evaluated by pH gradient cation-exchange chromatography after stressing it for up to 3 weeks at physiological and elevated pH and 37 °C. Isolated charge variants arising under stress conditions were characterized by peptide mapping. The results of peptide mapping showed that deamidation in the Fc domain and N-terminal pyroglutamate formation in the heavy chain are the main contributors to charge heterogeneity. The heavy chain CDR2, which is the only CDR containing asparagine residues, was quite resistant to deamidation under stress conditions according to peptide mapping results. Using surface plasmon resonance, it was shown that the affinity of pertuzumab for the HER2 target receptor does not change under stress conditions. Peptide mapping analysis of clinical samples showed an average of 2-3% deamidation in the heavy chain CDR2, 20-25% deamidation in the Fc domain, and 10-15% N-terminal pyroglutamate formation in the heavy chain. These findings suggest that in vitro stress studies are able to predict in vivo modifications.

Continuous manufacturing of monoclonal antibodies: Dynamic control of multiple integrated polishing chromatography steps using BioSMB

We propose a strategy for automation and control of multi-step polishing chromatography in integrated continuous manufacturing of monoclonal antibodies. The strategy is demonstrated for a multi-step polishing process consisting of cation exchange chromatography in bind-and-elute mode followed by mixed-mode chromatography in flowthrough mode. A BioSMB system with a customized Python control layer is used for automation and scheduling of both the chromatography steps. Further, the BioSMB valve manifold is leveraged for in-line conditioning between the two steps, as tight control of pH and conductivity is essential when operating with multimodal resins because even slight fluctuations in load conditions adversely affect the chromatography performance. The pH and conductivity of the load to the multimodal chromatography columns is consistent, despite the elution gradient of the preceding cation exchange chromatography step. Inputs from the BioSMB pH and conductivity sensors are used for real-time control of the 7 pumps and 240 valves to achieve in-line conditioning inside the BioSMB manifold in a fully automated manner. This is confirmed by showcasing different elution strategies in cation exchange chromatography, including linear gradient, step gradient and process deviations like tubing leakage. In all the above cases, the model was able to maintain the pH and conductivity of multimodal chromatography load within the range of 6 ± 0.1 pH and 7 ± 0.3 mS/cm conductivity. The strategy eliminates the need for using multiple BioSMB units or integrating external pumps, valves, mixers, surge tanks, or sensors between the two steps as is currently the standard approach, thus offering a simple and robust structure for integrating multiple polishing chromatography steps in continuous downstream monoclonal antibody purification trains.

Enhancing and stabilizing monoclonal antibody production by Chinese hamster ovary (CHO) cells with optimized perfusion culture strategies

The perfusion medium is critical in maintaining high cell concentration in cultures for the production of monoclonal antibody by Chinese hamster ovary cells. In this study, the effects of perfusion culture strategies when using different media on the process stability, product titer, and product quality were investigated in 3-L bioreactor. The results indicated that continuous perfusion could maintain higher levels of cell density, product titer, and quality in comparison with those of the intermittent perfusion culture. Next, the perfusion culture conditions with different perfusion rates and temperature reduction methods were further optimized. When combining the high perfusion rates and delayed reduction of culture temperature at day 6, the product titer reached a higher level of 16.19 g/L with the monomer relative abundant of 97.6%. In this case, the main peak of the product reached 56.3% and the total N-glycans ratio was 95.2%. To verify the effectiveness of the optimized perfusion culture in a larger scale, a 200-L bioreactor was used to perform and the final product titer reached the highest level of 16.79 g/L at day 16. Meanwhile, the product quality (monomer abundant of 97.6%, main peak of 56.3%, and N-glycans ratio of 96.5%) could also be well maintained. This study provided some guidance for the high-efficient production of monoclonal antibody by CHO cells via optimized perfusion culture strategy.

Preferential precipitation of acidic variants from monoclonal antibody pools

Microheterogeneity of monoclonal antibodies (mAbs) can impact their activity and stability. Formation of charge variants is considered as the most important source of the microheterogeneity. In particular, controlling the content of the acidic species is often of major importance for the production process and regulatory approval of therapeutic proteins. In this study, the preferential precipitation process was developed for reducing the content of acidic variants in mAb downstream pools. The process design was preceded by the determination of phase behavior of mAb variants in the presence of different precipitants. It was shown that the presence of polyethylene glycol (PEG) in protein solutions favored precipitation of acidic variants of mAbs. Precipitation yield was influenced by the variant composition in the mAb feed solutions, the concentration of the precipitant and the protein, and the ionic strength of the solutions. To improve yield, multistage precipitation was employed, where the precipitate was recycled to the precipitation process. The final product was a mixture of supernatants pooled together from the recycling steps. Such an approach can be potentially used either instead or in a combination with chromatography for adjusting the acidic variant content of mAbs, which can benefit in improvement in throughput and reduction in manufacturing costs.

Negative interference with antibody-dependent cellular cytotoxicity mediated by rituximab from its interactions with human serum proteins

Although interactions of small molecular drugs with serum proteins have been widely studied from pharmacokinetic and pharmacodynamic perspectives, there have been few reports on the effects of serum components on therapeutic antibody functions. This study reports the effect of abundant serum proteins on antibody-dependent cellular cytotoxicity (ADCC) mediated by rituximab and Fcγ receptor III (FcγRIII). Human serum albumin (HSA) and the Fab fragment from the pooled serum polyclonal IgG were found to compromise ADCC as non-competitive inhibitors. Our nuclear magnetic resonance data provided direct evidence for the interactions of HSA with both the Fab and Fc regions of rituximab and also with the extracellular region of FcγRIII (sFcγRIII). The degree of involvement in the interaction decreased in the order of rituximab-Fab > rituximab-Fc > sFcγRIII, suggesting preferential binding of HSA to net positively charged proteins. Although much less pronounced than the effect of HSA, polyclonal IgG-Fab specifically interacted with rituximab-Fc. The NMR data also showed that the serum protein interactions cover the Fc surface extensively, suggesting that they can act as pan-inhibitors against various Fc receptor-mediated functions and pharmacokinetics. Our findings highlight the importance of considering serum-protein interactions in the design and application of antibody-based drugs with increased efficacy and safety.

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.

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.

Design and optimization of membrane chromatography for monoclonal antibody charge variant separation

The manufacturing scale implementation of membrane chromatography to purify monoclonal antibodies has gradually increased with the shift in industry focus towards flexible manufacturing and disposable technologies. Membrane chromatography are used to remove process-related impurities such as host cell proteins and DNA, leachates and endotoxins, with improved productivity and process flexibility. However, application of membrane chromatography to separate product-related variants such as charge variants has not gained major traction due to low binding capacity. The work reported here demonstrates that a holistic process development strategy to optimize static binding (pH and salt concentration) and dynamic process (membrane loading, flowrate, and gradient length) parameters can alleviate the capacity limitations. The study employed high throughput screening tools and scale-down membranes for intermediate and polishing purification of the model monoclonal antibody. An optimized process consisting of anion exchange and cation exchange membrane chromatography reduced the acidic variants present in Protein A eluate from 89.5 % to 19.2 % with 71 % recovery of the target protein. The membrane chromatography process also cleared host cell protein to below limit of detection with 6 to 30-fold higher membrane loading, compared to earlier reported values. The results confirm that membrane chromatography is effective in separating closely related product variants when supported by a well-defined process development strategy.

[Quality Evaluation of Therapeutic Antibodies by Multi-attribute Method]

In the development of therapeutic monoclonal antibodies (mAbs), it is essential to characterize the modifications causing structural heterogeneity because certain modifications are associated with safety and efficacy. However, the rapid structural analysis of mAbs remains challenging due to their structural complexity. The multi-attribute method (MAM) is a structural analytical method based on peptide mapping using LC/MS, and has drawn attention as a new quality control method for therapeutic mAbs instead of conventional structural heterogeneity analyses using several chromatographic techniques. Peptide mapping, which is regarded as an identification test method, is used to confirm that the amino acid sequence corresponds to that deduced from the gene sequence for the desired product. In contrast, MAM is used for simultaneously monitoring the modification rates of individual amino acid residues of therapeutic mAbs, indicating that MAM is used as quantitative test rather than identification test. In this review, we summarized the typical structural heterogeneities of mAbs and the general scheme of MAM. We also introduced our optimized sample preparation method for MAM, and examples of simultaneous monitoring of several modifications including deamidation, oxidation, N-terminal pyroglutamination, C-terminal clipping and glycosylation by our MAM system.

Targeting tau only extracellularly is likely to be less efficacious than targeting it both intra- and extracellularly

Aggregation of the tau protein is thought to be responsible for the neurodegeneration and subsequent functional impairments in diseases that are collectively named tauopathies. Alzheimer's disease is the most common tauopathy, but the group consists of over 20 different diseases, many of which have tau pathology as their primary feature. The development of tau therapies has mainly focused on preventing the formation of and/or clearing these aggregates. Of these, immunotherapies that aim to either elicit endogenous tau antibodies or deliver exogenous ones are the most common approach in clinical trials. While their mechanism of action can involve several pathways, both extra- and intracellular, pharmaceutical companies have primarily focused on antibody-mediated clearance of extracellular tau. As we have pointed out over the years, this is rather surprising because it is well known that most of pathological tau protein is found intracellularly. It has been repeatedly shown by several groups over the past decades that antibodies can enter neurons and that their cellular uptake can be enhanced by various means, particularly by altering their charge. Here, we will briefly describe the potential extra- and intracellular mechanisms involved in antibody-mediated clearance of tau pathology, discuss these in the context of recent failures of some of the tau antibody trials, and finally provide a brief overview of how the intracellular efficacy of tau antibodies can potentially be further improved by certain modifications that aim to enhance tau clearance via specific intracellular degradation pathways.

Optimized Methods for Analytical and Functional Comparison of Biosimilar mAb Drugs: A Case Study for Avastin, Mvasi, and Zirabev

Bevacizumab is a humanized therapeutic monoclonal antibody used to reduce angiogenesis, a hallmark of cancer, by binding to VEGF-A. Many pharmaceutical companies have developed biosimilars of Bevacizumab in the last decade. The official reports provided by the FDA and EMA summarize the analytical performance of biosimilars as compared to the originators without giving detailed analytical procedures. In the current study, several key methods were optimized and reported for analytical and functional comparison of bevacizumab originators (Avastin, Altuzan) and approved commercial biosimilars (Zirabev and Mvasi). This case study presents a comparative analysis of a set of biosimilars under optimized analytical conditions for the first time in the literature. The chemical structure of all products was analyzed at intact protein and peptide levels by high-resolution mass spectrometry; the major glycoforms and posttranslational modifications, including oxidation, deamidation, N-terminal PyroGlu addition, and C-terminal Lys clipping, were compared. The SPR technique was used to reveal antigen and some receptor binding kinetics of all products, and the ELISA technique was used for C1q binding affinity analysis. Finally, the inhibition performance of the samples was evaluated by an MTS-based proliferation assay in vitro. Major glycoforms were similar, with minor differences among the samples. Posttranslational modifications, except C-terminal Lys, were determined similarly, while unclipped Lys percentage was higher in Zirabev. The binding kinetics for VEGF, FcRn, FcγRIa, and C1q were similar or in the value range of originators. The anti-proliferative effect of Zirabev was slightly higher than the originators and Mvasi. The analysis of biosimilars under the same conditions could provide a new aspect to the literature in terms of the applied analytical techniques. Further studies in this field would be helpful to better understand the inter-comparability of the biosimilars.

Antibody charge variant modulation by in vitro enzymatic treatment in different CHO cell cultures

Charge variants represent a critical quality attribute that must be controlled during the development and manufacturing of monoclonal antibodies (mAb). Previously, we reported the development of a cost-effective enzymatic treatment capable of removing the C-terminal lysine from a mAb produced by a Chinese hamster ovary (CHO) GS cell line. This treatment resulted in a significant decrease in basic charge variants and a corresponding improvement in the main peak, enabling a longer cell culture production duration for titer improvement. Here, we describe this enzymatic treatment protocol in detail and demonstrate its applicability to two additional mAbs produced by distinct industrial cell lines. The simple addition of carboxypeptidase B (CpB) at a ratio of 1:10,000 (w/w) to whole cell cultures significantly improved the main peaks for both mAbs without affecting other critical quality attributes, including size exclusion chromatography impurities and N-glycans. Our results demonstrate that this in vitro CpB treatment protocol can be used as a platform strategy to improve main peak for mAbs that exhibit high levels of basic variants attributable to C-terminal lysines. An in vitro enzymatic treatment in general may be another good addition to existing in vivo CHO cell culture strategies for titer improvement and control of critical quality attributes. This article is protected by copyright. All rights reserved.

Chromatographic characterization of the fusion protein SARS-CoV-2 S protein (RBD)-hFc

At the Center of Molecular Immunology (Havana, Cuba), the fusion protein SARS-CoV-2 S protein (RBD)-hFc was synthesized linking the receptor-binding domain (RBD) of the SARS-CoV-2 virus and the crystallizable fragment of a human immunoglobulin. This fusion protein was used in the construction of a diagnostic device for COVID-19 called UMELISA SARS-CoV-2-IgG. Given the relevance of this protein, the characterization of three batches (A1, A2 and A3) was carried out. The molecular weight of the protein was determined to be 120 kDa, using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Its isoelectric point was estimated between 8.3 and 9 by isoelectric focusing. The molecular integrity was evaluated by size exclusion liquid chromatography and SDS-PAGE after one year of the production of the protein; the presence of aggregates and fragments was detected. Batches A1 and A2 have a purity percentage higher than 95% and they can be used for the construction of new diagnostic devices.

A Charge Variant of Bevacizumab Offers Enhanced FcRn-Dependent Pharmacokinetic Half-Life and Efficacy

BACKGROUND

Lysine variants of monoclonal antibodies (mAbs) result from incomplete clipping of the C-terminal lysine residues of the heavy chain. Although the structure of the lysine variants has been determined for several mAb products, a detailed study that investigates the impact of lysine charge variants on PK/PD and preclinical safety is yet to be published.

OBJECTIVE

An in-depth investigation of the impact of C- terminal lysine clipping of mAbs on safety and efficacy for bevacizumab charge variants.

METHOD

Charge variant isolation using semi-preparative chromatography is followed by a comparative analysis of FcRn binding, pharmacokinetics, and pharmacodynamics in relevant animal models.

RESULTS

K1 variant exhibited improved FcRn binding affinity (4-fold), half-life (1.3-fold), and anti-tumor activity (1.3-fold) as compared to the K0 (main) product. However, the K2 variant, even though exhibited higher FcRn affinity (2-fold), displayed lower half-life (1.6-fold) and anti-tumor activity at medium and low doses. Differential proteomic analysis revealed that seven pathways (such as glycolysis, gluconeogenesis, carbon metabolism, synthesis of amino acids) were significantly enriched. Higher efficacy of the K1 variant is likely due to higher bioavailability of the drug, leading to complete downregulation of the pathways that facilitate catering of the energy requirements of the proliferating tumor cells. On the contrary, the K2 variant exhibits a shorter half-life, resulting only in partial reduction in the metabolic/energy requirements of the growing tumor cells.

CONCLUSION

Overall, we conclude that the mAb half-life, dosage, and efficacy of a biotherapeutic product are significantly impacted by the charge variant profile of a biotherapeutic product.

Studying protein structure and function by native separation–mass spectrometry

Alterations in protein structure may have profound effects on biological function. Analytical techniques that permit characterization of proteins while maintaining their conformational and functional state are crucial for studying changes in the higher order structure of proteins and for establishing structure-function relationships. Coupling of native protein separations with mass spectrometry is emerging rapidly as a powerful approach to study these aspects in a reliable, fast and straightforward way. This Review presents the available native separation modes for proteins, covers practical considerations on the hyphenation of these separations with mass spectrometry and highlights the involvement of affinity-based separations to simultaneously obtain structural and functional information of proteins. The impact of these approaches is emphasized by selected applications addressing biomedical and biopharmaceutical research questions.

Rapid monitoring of high-mannose glycans during cell culture process of therapeutic monoclonal antibodies using lectin affinity chromatography

We developed a simple high‐performance liquid chromatography assay to monitor high‐mannose glycans in monoclonal antibodies by monitoring terminal alpha‐mannose as a surrogate marker. Analysis of glycan data of therapeutic monoclonal antibodies by 2‐aminobenzamide assay showed a linear relationship between high mannose and terminal mannose of Fc glycans. Concanavalin A has a strong affinity to alpha‐mannose in glycans of typical therapeutic monoclonal antibodies. To show that terminal mannose binds specifically to Concanavalin A column, exoglycosidase‐treated monoclonal antibodies were serially blended with untreated monoclonal antibodies. Linear responses of terminal‐mannose binding to the column and comparable data trending with high mannose levels by 2‐aminobenzamide assay confirmed that terminal‐mannose levels measured by the Concanavalin A column can be used as a surrogate for the prediction of high‐mannose levels in monoclonal antibodies. The assay offers a simple, fast, and specific capability for the prediction of high‐mannose content in samples compared with traditional glycan profiling by 2‐aminobenzamide or mass spectrometry‐based methods. When the Concanavalin A column was coupled with protein A column for purification of antibodies from cell culture samples in a fully automated two‐dimensional analysis, high‐mannose data could be relayed to the manufacturing team in less than 30 min, allowing near‐real‐time monitoring of high‐mannose levels in the cell culture process.

Eliminating protein oxidation artifacts during High Performance Liquid Chromatography peak fractionation processes

Therapeutic monoclonal antibodies (mAbs) are inherently heterogeneous and hence generally studied and controlled by an array of orthogonal separation methods. During drug candidate development, fractionation by HPLC is regularly employed to assist peak identification and product understanding. One overlooked challenge is the protein oxidation introduced by the fractionation process. In this study, we report the extent of fractionation-induced protein oxidation, which tends to complicate data interpretation and peak assignments. Higher-energy detectors such as fluorescence detectors and lower fraction concentration were found to exacerbate the oxidation artifacts. Other contributing factors than the detector-induced photostress were also found to contribute significantly to protein oxidation. Furthermore, our study showed that collecting fractions into a solution with oxidation scavengers, such as histidine and methionine, was effective in eliminating the oxidation artifacts introduced by detector exposure and fraction processing steps. Through an example, we demonstrate that the modified fractionation workflow improves the accuracy of peak assignments.

Assessment of Functional Characterization and Comparability of Biotherapeutics: a Review

The development of monoclonal antibody (mAb) biosimilars is a complex process. The key to their successful development and commercialization is an in-depth understanding of the key product attributes that impact safety and efficacy and the strategies to control them. Functional assessment of mAb is a crucial part of the comparability of biopharmaceutical drugs. The development of a relevant and robust functional assay requires an interdisciplinary approach and sufficient flexibility to balance regulatory concerns as well as dynamics and variability during the manufacturing process. Although many advanced tools are available to study and compare the potency and bioactivity of the protein, most of these techniques suffer from major shortcomings that limit their routine use. These include the complexity of the task, establishment of the relevance of the chosen method with the mechanism of action (MOA) of the biosimilar, cost and extended time of analysis, and often the ambiguity in interpretation of the resulting data. To overcome or to address these challenges, the use of multiple orthogonal state-of-the-art techniques is a necessary prerequisite.

Physicochemical and functional characterization of HS016, a biosimilar of adalimumab (Humira)

The characterization of a biosimilar drug HS016, the reference product adalimumab (Humira), and their biosimilarities were determined using physical chemistry and functional similarity tests. The primary and higher order structures, size and charge variants, glycosylation profiles, and in vitro potency of both antibodies were characterized both for unstressed and stability samples. Slight differences were observed in the relative levels of methionine oxidation, low molecular weight components, terminal lysine variant, high mannoses and galactosylated glycans between HS016 and Humira. However, no differences in antigen binding activity, Fc receptor affinity, antibody-dependent cell-mediated cytotoxicity or complemented-dependent cytotoxicity were found. The primary and higher order structures, physicochemical properties, and biological activity of HS016 and adalimumab were similar.

Separation of charge variants of a monoclonal antibody by overloaded ion exchange chromatography

A procedure for adjusting the content of charge variants of monoclonal antibody by ion exchange chromatography has been developed. The band splitting phenomenon was utilized to split the protein load into two parts, i.e., the flowthrough and bound fractions, which were either enriched or depleted with some of variants. The phenomenon was triggered by thermodynamic effects resulting from oversaturation of the resin binding sites at high column loadings as well as from kinetic effects arising from limited rates of mass transport. Cation exchange chromatography (CEX) and anion exchange chromatography (AEX) separations were examined, with the reverse order of the variant elution: acidic, main, basic in CEX, and basic, main, acidic in AEX, and the corresponding reverse enrichment tendency in the collected fractions. The separations were performed by pH gradient, whose course was simplified to two stages: isocratic loading and washing at mild pH to load and partly elute the protein, followed by a rapid pH change towards non-binding conditions to desorb the remains of the protein load. To improve yield of the operation, possibility of recycling of waste fractions was considered. To predict the process performance, a dynamic model was developed, which accounted for both adsorption kinetics and thermodynamics.

Similarity demonstrated between isolated charge variants of MB02, a biosimilar of bevacizumab, and Avastin® following extended physicochemical and functional characterization

The majority of recombinant mAb products contain heterogeneous charge variants, commonly the result of post-translational modifications occurring during cell culture and accumulated during production, formulation and storage. MB02 is a biosimilar mAb to bevacizumab. Similarity data of charge variants for biosimilars against its reference products must be generated to demonstrate consistency in product quality and to ensure efficacy and safety. The goal of this work was to isolate seven charge variants of MB02 and Avastin® by semi-preparative cation exchange chromatography followed by purity test and extended analytical characterization to prove similarity. Although poor purity obtained for minor variants complicated data interpretation, an in-depth insight into the charge variants pattern of MB02 compared to Avastin® was obtained, contributing to a better understanding of modifications associated to microheterogeneity. To our knowledge, this is the first comparative analytical study of individual charge variants of a bevacizumab biosimilar following a head-to head approach and the most comprehensive N-glycosylation assessment of IgG1 charge variants. Although modifications related to N- and C-terminal, N-glycans, size heterogeneity or deamidation were specifically enriched among low abundant charge variants, they did not affect binding affinity to VEGF or FcRn and in vitro potency compared with the main species or unfractionated material.

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.

Ion Exchange Chromatographic Methods for Purification of Therapeutic Antibodies

Ion Exchange Chromatography has been a critical unit operation for manufacturing of therapeutic antibodies. Cation and anion exchange chromatography are used extensively to remove process-related as well as product-related impurities to obtain the final product. In this chapter, we describe the methods for separating and purifying charge variants and aggregates for manufacturing of monoclonal antibodies. The methods related to removal of host cell impurities such as host cell DNA and host cell proteins are also described. With minimal modifications, the protocols described here can be employed to purify any monoclonal antibody.

Multi-omics profiling of a CHO cell culture system unravels the effect of culture pH on cell growth, antibody titer, and product quality

A robust monoclonal antibody (mAb) bioprocess requires physiological parameters such as temperature, pH, or dissolved oxygen to be well-controlled as even small variations in them could potentially impact the final product quality. For instance, pH substantially affects N-glycosylation, protein aggregation, and charge variant profiles, as well as mAb productivity. However, relatively less is known about how pH jointly influences product quality and titer. In this study, we investigated the effect of pH on culture performance, product titer, and quality profiles by applying longitudinal multi-omics profiling, including transcriptomics, proteomics, metabolomics, and glycomics, at three different culture pH set points. The subsequent systematic analysis of multi-omics data showed that pH set points differentially regulated various intracellular pathways including intracellular vesicular trafficking, cell cycle, and apoptosis, thereby resulting in differences in specific productivity, product titer, and quality profiles. In addition, a time-dependent variation in mAb N-glycosylation profiles, independent of pH, was identified to be mainly due to the accumulation of mAb proteins in the endoplasmic reticulum disrupting cellular homeostasis over culture time. Overall, this multi-omics-based study provides an in-depth understanding of the intracellular processes in mAb-producing CHO cell line under varied pH conditions, and could serve as a baseline for enabling the quality optimization and control of mAb production.

Technology transfer of a monitoring system to predict product concentration and purity of biopharmaceuticals in real-time during chromatographic separation

Technological developments require the transfer to their location of application to make use of them. We describe the transfer of a real-time monitoring system for lab-scale preparative chromatography to two new sites where it will be used and developed further. Equivalent equipment was used. The capture of a biopharmaceutical model protein, human fibroblast growth factor 2 (FGF-2) was used to evaluate the system transfer. Predictive models for five quality attributes based on partial least squares regression were transferred. Six out of seven online sensors (UV/VIS, pH, conductivity, IR, RI, and MALS) showed comparable signals between the sites while one sensor (fluorescence) showed different signal profiles. A direct transfer of the models for real-time monitoring was not possible, mainly due to differences in sensor signals. Adaptation of the models was necessary. Then, among five prediction models, the prediction errors of the test run at the new sites were on average twice as high as at the training site (model-wise 0.9-5.7 times). Additionally, new prediction models for different products were trained at each new site. These allowed monitoring the critical quality attributes of two new biopharmaceutical products during their purification processes with mean relative deviations between 1% and 33%.

Effect of vitamins and metal ions on productivity and charge heterogeneity of IgG1 expressed in CHO cells

Recombinant monoclonal antibodies have emerged as the most successful modality of biotherapeutics. They are primarily expressed in Chinese Hamster Ovary (CHO) cells. It is well known that post-translational modifications (PTM) contribute significantly to heterogeneity with respect to charge, glycosylation, and size. These attributes in turn impact stability, pharmacokinetics, and pharmacodynamics of the biotherapeutic product. Cell culture media components are known to significantly contribute to both cellular productivity as well as post-translational modifications. Thus, it is highly desirable to understand how media components affect product quality. This study aims to explore the impact of vitamins and metal ions on protein expression and post-translational modifications specifically charge heterogeneity. Biotin, choline chloride, D-calcium pantothenate, folic acid, pyridoxine hydrochloride, thiamine hydrochloride vitamins and Fe, Cu, Mg, Co, Zn, Mn, Ni metal ions were examined in this study. The results indicate that pyridoxine enhances productivity while Zn, Cu, Fe, Mn, and biotin impact charge heterogeneity. While, Fe, Mn and Ni enhance production of the acidic variants, Cu and biotin inhibit it. Zn reduces formation of basic variants while biotin enhances it. The results from this investigation could be used for process control so as to get consistent charge variant profile, in particular for biosimilars.

C-terminal lysine clipping of IgG1: impact on binding to human FcγRIIIa and neonatal Fc receptors

Monoclonal antibodies (mAbs) display numerous structural attributes, some of them may impact their safety and/or efficacy profiles. C-terminal lysine clipping is a common phenomenon occurring during the bioproduction of mAbs and leads to variable amounts of final process-related charge variants. If Fc-glycosylation has been by far the most documented critical quality attribute (CQA), the potential impacts of mAb C-terminal lysine content is far less reported, particularly on the ability of these basic variants to bind human Fc receptors. To address this question, three charge variant species having zero (K0), one (K1) and two (K2) C-terminal lysine(s) were isolated with high purity from an in-house human IgG1 by preparative strong-cation exchange (SCX) chromatography. A comprehensive biophysical characterization of these three fractions was undertaken, demonstrating their high similarity in terms of structural homogeneity, with a particular attention paid on their respective N-glycosylation profiles. The binding affinity of the fractions to human FcγRIIIa-Val¹⁷⁶ was assessed both by affinity chromatography and surface plasmon resonance (SPR), and to human neonatal Fc receptor (FcRn) by affinity chromatography. Results demonstrate that the three charge variants did not show any significant binding difference for the two tested human Fc receptors, translating certainly to comparable biological properties. As a consequence, C-terminal lysine clipping of the present therapeutic IgG1 should not impact both FcRn-dependent pharmacokinetic profiles and FcγRIIIa-driven cytotoxic activities. The methods used in this study can be widely applied to other IgG1 to define criticality of the C-terminal lysine clipping as a CQA.

Productivity improvement and charge variant modulation for intensified cell culture processes by adding a carboxypeptidase B (CpB) treatment step

The goal of cell culture process intensification is to improve productivity while maintaining acceptable quality attributes. In this report, four processes, namely a conventional manufacturing Process A, and processes intensified by enriched N-1 seed (Process B), by perfusion N-1 seed (Process C), and by perfusion production (Process D) were developed for the production of a monoclonal antibody. The three intensified processes substantially improved productivity, however, the product either failed to meet the specification for charge variant species (main peak) for Process D or the production process required early harvest to meet the specification for charge variant species, Day 10 or Day 6 for Processes B and C, respectively. The lower main peak for the intensified processes was due to higher basic species resulting from higher C-terminal lysine. To resolve this product quality issue, we developed an enzyme treatment method by introducing carboxypeptidase B (CpB) to clip the C-terminal lysine, leading to significantly increased main peak and an acceptable and more homogenous product quality for all the intensified processes. Additionally, Processes B and C with CpB treatment extended bioreactor durations to Day 14 increasing titer by 38% and 108%, respectively. This simple yet effective enzyme treatment strategy could be applicable to other processes that have similar product quality issues.

LC-MS based case-by-case analysis of the impact of acidic and basic charge variants of bevacizumab on stability and biological activity

The present study investigates the impact of charge variants on bevacizumab's structure, stability, and biological activity. Five basic and one acidic charge variants were separated using semi-preparative cation exchange chromatography using linear pH gradient elution with purity > 85%. Based on the commercial biosimilar product's composition, two basic variants, one acidic and the main bevacizumab product, were chosen for further investigation. Intact mass analysis and tryptic peptide mapping established the basic variants' identity as those originating from an incomplete clipping of either one or both C-terminal lysine residues in the heavy chain of bevacizumab. Based on peptide mapping data, the acidic variant formation was attributed to deamidation of asparagine residue (N84), oxidation of M258, and preservation of C-terminal lysine residue, located on the heavy chain of bevacizumab. None of the observed charge heterogeneities in bevacizumab were due to differences in glycosylation among the variants. The basic (lysine) variants exhibited similar structural, functional, and stability profiles as the bevacizumab main product. But it was also noted that both the variants did not improve bevacizumab's therapeutic utility when pooled in different proportions with the main product. The acidic variant was found to have an equivalent secondary structure with subtle differences in the tertiary structure. The conformational difference also translated into a ~ 62% decrease in biological activity. Based on these data, it can be concluded that different charge variants behave differently with respect to their structure and bioactivity. Hence, biopharmaceutical manufacturers need to incorporate this understanding into their process and product development guidelines to maintain consistency in product quality.

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.