Low glucose depletes glycan precursors, reduces site occupancy and galactosylation of a monoclonal antibody in CHO cell culture

Electron-Activated Dissociation and Collision-Induced Dissociation Glycopeptide Fragmentation for Improved Glycoproteomics

Tandem mass spectrometry coupled with liquid chromatography (LC-MS/MS) has proven a versatile tool for the identification and quantification of proteins and their post-translational modifications (PTMs). Protein glycosylation is a critical PTM for the stability and biological function of many proteins, but full characterization of site-specific glycosylation of proteins remains analytically challenging. Collision-induced dissociation (CID) is the most common fragmentation method used in LC-MS/MS workflows, but the loss of labile modifications renders CID inappropriate for detailed characterization of site-specific glycosylation. Electron-based dissociation methods provide alternatives that retain intact glycopeptide fragments for unambiguous site localization, but these methods often underperform CID due to increased reaction times and reduced efficiency. Electron-activated dissociation (EAD) is another strategy for glycopeptide fragmentation. Here, we use a ZenoTOF 7600 SCIEX instrument to compare the performance of various fragmentation techniques for the analysis of a complex mixture of mammalian O- and N-glycopeptides. We found CID fragmentation identified the most glycopeptides and generally produced higher quality spectra, but EAD provided improved confidence in glycosylation site localization. Supplementing EAD with CID fragmentation (EAciD) further increased the number and quality of glycopeptide identifications, while retaining localization confidence. These methods will be useful for glycoproteomics workflows for either optimal glycopeptide identification or characterization.

Tumor glucose metabolism and the T cell glycocalyx: implication for T cell function

The T cell is an immune cell subset highly effective in eliminating cancer cells. Cancer immunotherapy empowers T cells and occupies a solid position in cancer treatment. The response rate, however, remains relatively low (<30%). The efficacy of immunotherapy is highly dependent on T cell infiltration into the tumor microenvironment (TME) and the ability of these infiltrated T cells to sustain their function within the TME. A better understanding of the inhibitory impact of the TME on T cells is crucial to improve cancer immunotherapy. Tumor cells are well described for their switch into aerobic glycolysis (Warburg effect), resulting in high glucose consumption and a metabolically distinct TME. Conversely, glycosylation, a predominant posttranslational modification of proteins, also relies on glucose molecules. Proper glycosylation of T cell receptors influences the immunological synapse between T cells and tumor cells, thereby affecting T cell effector functions including their cytolytic and cytostatic activities. This review delves into the complex interplay between tumor glucose metabolism and the glycocalyx of T cells, shedding light on how the TME can induce alterations in the T cell glycocalyx, which can subsequently influence the T cell's ability to target and eliminate tumor cells.

Sodium chloride impacts glycosylation and N- and O-glycan site occupancy of an Fc-fusion protein

Fc-fusion proteins are highly complex molecules, difficult to manufacture at scale. In this work, undesired proteoforms were detected during the manufacture of a therapeutic fusion protein produced in CHO cells. These species were characterized using gel electrophoresis, size exclusion chromatography and liquid chromatography-mass spectrometry leading to the identification of low molecular weight proteoforms presenting low N- and O-glycan site occupancy, as well as a low sialylation content. Upstream process parameters were investigated, and fusion protein quality was shown to be linked to the sodium chloride content of the medium. A mitigation strategy was developed to avoid formation of unwanted glyco-variants, resulting in an increased yield of highly glycosylated Fc-fusion protein. The effect of sodium chloride was shown to be independent of the osmolality increase and was hypothesized to be linked to a modulation of Golgi acidity, which is required for the correct localization and function of glycosyltransferases. Altogether, this study highlights the importance of the salt balance in cell culture media used to produce highly sialylated and occupied glycoproteins, helping to maximize the yield and increase robustness of processes aiming at producing biopharmaceutical complex therapeutic molecules.

Features, modulation and analysis of glycosylation patterns of therapeutic recombinant immunoglobulin A

Increasing the production of recombinant antibodies while ensuring high and stable protein quality remains a challenge in mammalian cell culture. This review is devoted to advances in the field of obtaining stable and optimal glycosylation of therapeutic antibodies based on IgA, as well as the subsequent issues of glycosylation control of glycoproteins during their production. Current studies also demonstrate a general need for a more fundamental understanding of the use of CHO cell-based producer cell lines, through which the glycoprofile of therapeutic IgA antibodies is produced and the dependence of glycosylation on culture conditions could be controlled. Optimization of glycosylation improves the therapeutic efficacy and can expand the possibilities for the creation of highly effective glycoprotein therapeutic drugs. Current status and trends in glycan analysis of therapeutic IgA, dominantly based on mass spectrometry and lectin microarrays are herein summarised as well.

Post-Translational Modification of Cav1.2 and its Role in Neurodegenerative Diseases

Cav1.2 plays an essential role in learning and memory, drug addiction, and neuronal development. Intracellular calcium homeostasis is disrupted in neurodegenerative diseases because of abnormal Cav1.2 channel activity and modification of downstream Ca²⁺ signaling pathways. Multiple post-translational modifications of Cav1.2 have been observed and seem to be closely related to the pathogenesis of neurodegenerative diseases. The specific molecular mechanisms by which Cav1.2 channel activity is regulated remain incompletely understood. Dihydropyridines (DHPs), which are commonly used for hypertension and myocardial ischemia, have been repurposed to treat PD and AD and show protective effects. However, further studies are needed to improve delivery strategies and drug selectivity. Better knowledge of channel modulation and more specific methods for altering Cav1.2 channel function may lead to better therapeutic strategies for neurodegenerative diseases.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Continuous optical in-line glucose monitoring and control in CHO cultures contributes to enhanced metabolic efficiency while maintaining darbepoetin alfa product quality

Great efforts are directed towards improving productivity, consistency and quality of biopharmaceutical processes and products. One particular area is the development of new sensors for continuous monitoring of critical bioprocess parameters by using online or in-line monitoring systems. Recently, we developed a glucose biosensor applicable in single-use, in-line and long-term glucose monitoring in mammalian cell bioreactors. Now, we integrated this sensor in an automated glucose monitoring and feeding system capable of maintaining stable glucose levels, even at very low concentrations. We compared this fed-batch feedback system at both low (< 1 mM) and high (40 mM) glucose levels with traditional batch culture methods, focusing on glycosylation and glycation of the recombinant protein darbepoetin alfa (DPO) produced by a CHO cell line. We evaluated cell growth, metabolite and product concentration under different glucose feeding strategies and show that continuous feeding, even at low glucose levels, has no harmful effects on DPO quantity and quality. We conclude that our system is capable of tight glucose level control throughout extended bioprocesses and has the potential to improve performance where constant maintenance of glucose levels is critical.

Towards rational glyco-engineering in CHO: from data to predictive models

Metabolic modelling strives to develop modelling approaches that are robust and highly predictive. To achieve this, various modelling designs, including hybrid models, and parameter estimation methods that define the type and number of parameters used in the model, are adapted. Accurate input data play an important role so that the selection of experimental methods that provide input data of the required precision with low measurement errors is crucial. For the biopharmaceutically relevant protein glycosylation, the most prominent available models are kinetic models which are able to capture the dynamic nature of protein N-glycosylation. In this review we focus on how to choose the most suitable model for a specific research question, as well as on parameters and considerations to take into account before planning relevant experiments.

Probabilistic model by Bayesian network for the prediction of antibody glycosylation in perfusion and fed-batch cell cultures

Glycosylation is a critical quality attribute of therapeutic monoclonal antibodies (mAbs). The glycan pattern can have a large impact on the immunological functions, serum half-life and stability. The medium components and cultivation parameters are known to potentially influence the glycosylation profile. Mathematical modelling provides a strategy for rational design and control of the upstream bioprocess. However, the kinetic models usually contain a very large number of unknown parameters, which limit their practical applications. In this article, we consider the metabolic network of N-linked glycosylation as a Bayesian network (BN) and calculate the fluxes of the glycosylation process as joint probability using the culture parameters as inputs. The modelling approach is validated with data of different Chinese hamster ovary cell cultures in pseudo perfusion, perfusion, and fed batch cultures, all showing very good predictive capacities. In cases where a large number of cultivation parameters is available, it is shown here that principal components analysis can efficiently be employed for a dimension reduction of the inputs compared to Pearson correlation analysis and feature importance by decision tree. The present study demonstrates that BN model can be a powerful tool in upstream process and medium development for glycoprotein productions.

Strategic feeding of NS0 and CHO cell cultures to control glycan profiles and immunogenic epitopes of monoclonal antibodies

The control of glycosylation profiles is essential to the consistent manufacture of therapeutic monoclonal antibodies that may be produced from a variety of cell lines including CHO and NS0. Of particular concern is the potential for generating non-human epitopes such as N-glycolylneuraminic acid (Neu5Gc) and Galα1-3 Gal that may be immunogenic. We have looked at the effects of a commonly used media supplements of manganese, galactose and uridine (MGU) on Mab production from CHO and NS0 cells in enhancing galactosylation and sialylation as well as the generation of these non-human glycan epitopes. In the absence of the MGU supplement, the humanized IgG1 antibody (Hu1D10) produced from NS0 cells showed a low level of mono- and di-sialylated structures (SI:0.09) of which 75 % of sialic acid was Neu5Gc. The chimeric human-llama Mab (EG2-hFc) produced from CHO cells showed an equally low level of sialylation (SI: 0.12) but the Neu5Gc content of sialic acid was negligible (<3%). Combinations of the MGU supplements added to the production cultures resulted in a substantial increase in the galactosylation of both Mabs (up to GI:0.78 in Hu1D10 and 0.81 in EG2-hFc). However, the effects on sialylation differed between the two Mabs. We observed a slight increase in sialylation of the EG2-hFc Mab by a combination of MG but it appeared that one of the components (uridine) was inhibitory to sialylation. On the other hand, MG or MGU increased sialylation of Hu1D10 substantially (SI:0.72) with an increase that could be attributed predominantly to the formation of Neu5Ac rather than Neu5Gc. The increased level of galactosylation observed with MG or MGU was attributed to an activation of the galactosyl transferase enzymes through enhanced intracellular levels of UDP-Gal and the availability of Mn²⁺ as an enzymic co-factor. However, this effect not only increased the desirable beta 1-4 Gal linkage to GlcNAc but unfortunately in NS0 cells increased the formation of Galα1-3 Gal which was shown to increase x3 in the presence of combinations of the MGU supplements. Supplementation of media with fetal bovine serum (FBS) increased the availability of free Neu5Ac which resulted in a significant increase in the sialylation of Hu1D10 from NS0 cells. This also resulted in a significant decrease in the proportion of Neu5Gc in the measured sialic acid from the Mab.

The role of protein hydrolysates in prolonging viability and enhancing antibody production of CHO cells

Four independent mAb-producing CHO cell lines were grown in media supplemented with one of seven protein hydrolysates of animal and plant origin. This generated a 7x4 matrix of replicate cultures which was analysed for viable cell density and mAb productivity. In all cultures, a consistent growth rate was shown in batch culture up to 4 to 5 days. Differences between cultures appeared in the decline phase which was followed up to 7 days beyond the start of the cultures. There was a marginal but significant overall increase (x1.1) in the integral viable cell density (IVCD) in the presence of hydrolysate but a more substantial increase in the cell-specific mAb (qMab) productivity (x1.5). There were individual differences between hydrolysates in terms of enhancement of mAb productivity, the highest being a 166% increase of mAb titre (to 117 mg/L) in batch cultures of CHO-EG2 supplemented with UPcotton hydrolysate. The effect of one of the most active hydrolysates (HP7504) on antibody glycosylation was investigated. This showed no change in the predominant seven glycans produced but a significant increase in the galactosylation and sialylation of some but not all the antibodies. Overall, the animal hydrolysate, Primatone and two cotton-derived hydrolysates provided the most substantial benefit for enhanced productivity. The cotton-based hydrolysates can be viewed as valuable supplements for animal-derived component-free (ADCF) media and as a source for the investigation of chemically defined bioactive components. KEY POINTS: • Protein hydrolysates enhanced both IVCD & qMab; the effect on qMab being consistently greater. • Cotton-based hydrolysates showed high bioactivity and potential for use in serum-free media. • Enhanced galactosylation and sialylation was shown for some of the Mabs tested.

N-Glycosylation of IgG and IgG-Like Recombinant Therapeutic Proteins: Why Is It Important and How Can We Control It?

Regulatory bodies worldwide consider N-glycosylation to be a critical quality attribute for immunoglobulin G (IgG) and IgG-like therapeutics. This consideration is due to the importance of posttranslational modifications in determining the efficacy, safety, and pharmacokinetic properties of biologics. Given its critical role in protein therapeutic production, we review N-glycosylation beginning with an overview of the myriad interactions of N-glycans with other biological factors. We examine the mechanism and drivers for N-glycosylation during biotherapeutic production and the several competing factors that impact glycan formation, including the abundance of precursor nucleotide sugars, transporters, glycosidases, glycosyltransferases, and process conditions. We explore the role of these factors with a focus on the analytical approaches used to characterize glycosylation and associated processes, followed by the current state of advanced glycosylation modeling techniques. This combination of disciplines allows for a deeper understanding of N-glycosylation and will lead to more rational glycan control.

Mass spectrometric analysis of core fucosylation and sequence variation in a human-camelid monoclonal antibody

Electrospray mass spectrometry (ESI-MS) was used to measure the masses of an intact dimeric monoclonal antibody (Mab) and assess the fucosylation level. The Mab under study was EG2-hFc, a chimeric human-camelid antibody of about 80 kDa (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90). It was obtained from cell culture with and without a fucosylation inhibitor, and treated with EndoS which cleaves between the two core N-acetyl glucosamine (GlcNAc) residues. It is the first time that this combined approach with a unique mass spectrometer was used to measure 146 Da differences as part of a large intact dimeric antibody. Results showed that in the dimer, both heavy chains were fucosylated on the core GlcNAc of the Fc Asn site equivalent to Asn297. In the presence of the fucosylation inhibitor, fucosylation was lost on both subunits. Following reduction, monomers were analyzed and the masses obtained corroborated the dimer results. Dimeric EG2-hFc Mab treated with PNGase F, to deglycosylate the protein, was also measured by MS for mass comparison. In spite of the success of fucosylation level measurements, the experimental masses of deglycosylated dimers and GlcNAc-Fuc bearing dimers did not correspond to masses of our sequence of reference (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90; ; ), which prompted experiments to determine the protein backbone sequence. Digest mixtures from trypsin, GluC, as well as trypsin + GluC proteolysis were analyzed by matrix-assisted laser desorption/ionization (MALDI) MS and MS/MS. A few variations were found relative to the reference sequence, which are discussed in detail herein. These measurements allowed us to build a new "experimental" sequence for the EG2-hFc samples investigated in this work, although there are still ambiguities to be resolved in this new sequence. MALDI-MS/MS also confirmed the fucosylation pattern in the Fc tryptic peptide EEQYNSTYR.

Impacts on product quality attributes of monoclonal antibodies produced in CHO cell bioreactor cultures during intentional mycoplasma contamination events

A mycoplasma contamination event in a biomanufacturing facility can result in costly cleanups and potential drug shortages. Mycoplasma may survive in mammalian cell cultures with only subtle changes to the culture and penetrate the standard 0.2‐µm filters used in the clarification of harvested cell culture fluid. Previously, we reported a study regarding the ability of Mycoplasma arginini to persist in a single‐use, perfusion rocking bioreactor system containing a Chinese hamster ovary (CHO) DG44 cell line expressing a model monoclonal immunoglobulin G 1 (IgG1) antibody. Our previous work showed that M. arginini affects CHO cell growth profile, viability, nutrient consumption, oxygen use, and waste production at varying timepoints after M. arginini introduction to the culture. Careful evaluation of certain identified process parameters over time may be used to indicate mycoplasma contamination in CHO cell cultures in a bioreactor before detection from a traditional method. In this report, we studied the changes in the IgG1 product quality produced by CHO cells considered to be induced by the M. arginini contamination events. We observed changes in critical quality attributes correlated with the duration of contamination, including increased acidic charge variants and high mannose species, which were further modeled using principal component analysis to explore the relationships among M. arginini contamination, CHO cell growth and metabolites, and IgG1 product quality attributes. Finally, partial least square models using NIR spectral data were used to establish predictions of high levels (≥10⁴ colony‐forming unit [CFU/ml]) of M. arginini contamination, but prediction of levels below 10⁴ CFU/ml were not reliable. Contamination of CHO cells with M. arginini resulted in significant reduction of antibody product quality, highlighting the importance of rapid microbiological testing and mycoplasma testing during particularly long upstream bioprocesses to ensure product safety and quality.

Combining lipoic acid to methylene blue reduces the Warburg effect in CHO cells: From TCA cycle activation to enhancing monoclonal antibody production

The Warburg effect, a hallmark of cancer, has recently been identified as a metabolic limitation of Chinese Hamster Ovary (CHO) cells, the primary platform for the production of monoclonal antibodies (mAb). Metabolic engineering approaches, including genetic modifications and feeding strategies, have been attempted to impose the metabolic prevalence of respiration over aerobic glycolysis. Their main objective lies in decreasing lactate production while improving energy efficiency. Although yielding promising increases in productivity, such strategies require long development phases and alter entangled metabolic pathways which singular roles remain unclear. We propose to apply drugs used for the metabolic therapy of cancer to target the Warburg effect at different levels, on CHO cells. The use of α-lipoic acid, a pyruvate dehydrogenase activator, replenished the Krebs cycle through increased anaplerosis but resulted in mitochondrial saturation. The electron shuttle function of a second drug, methylene blue, enhanced the mitochondrial capacity. It pulled on anaplerotic pathways while reducing stress signals and resulted in a 24% increase of the maximum mAb production. Finally, the combination of both drugs proved to be promising for stimulating Krebs cycle activity and mitochondrial respiration. Therefore, drugs used in metabolic therapy are valuable candidates to understand and improve the metabolic limitations of CHO-based bioproduction.

Glycan Residues Balance Analysis - GReBA: A novel model for the N-linked glycosylation of IgG produced by CHO cells

The structure of N-linked glycosylation is a very important quality attribute for therapeutic monoclonal antibodies. Different carbon sources in cell culture media, such as mannose and galactose, have been reported to have different influences on the glycosylation patterns. Accurate prediction and control of the glycosylation profile are important for the process development of mammalian cell cultures. In this study, a mathematical model, that we named Glycan Residues Balance Analysis (GReBA), was developed based on the concept of Elementary Flux Mode (EFM), and used to predict the glycosylation profile for steady state cell cultures. Experiments were carried out in pseudo-perfusion cultivation of antibody producing Chinese Hamster Ovary (CHO) cells with various concentrations and combinations of glucose, mannose and galactose. Cultivation of CHO cells with mannose or the combinations of mannose and galactose resulted in decreased lactate and ammonium production, and more matured glycosylation patterns compared to the cultures with glucose. Furthermore, the growth rate and IgG productivity were similar in all the conditions. When the cells were cultured with galactose alone, lactate was fed as well to be used as complementary carbon source, leading to cell growth rate and IgG productivity comparable to feeding the other sugars. The data of the glycoprofiles were used for training the model, and then to simulate the glycosylation changes with varying the concentrations of mannose and galactose. In this study we showed that the GReBA model had a good predictive capacity of the N-linked glycosylation. The GReBA can be used as a guidance for development of glycoprotein cultivation processes.

Multivariate data analysis of growth medium trends affecting antibody glycosylation

Use of multivariate data analysis for the manufacturing of biologics has been increasing due to more widespread use of data-generating process analytical technologies (PAT) promoted by the US FDA. To generate a large dataset on which to apply these principles, we used an in-house model CHO DG44 cell line cultured in automated micro bioreactors alongside PAT with four commercial growth media focusing on antibody quality through N-glycosylation profiles. Using univariate analyses, we determined that different media resulted in diverse amounts of terminal galactosylation, high mannose glycoforms, and aglycosylation. Due to the amount of in-process data generated by PAT instrumentation, multivariate data analysis was necessary to ascertain which variables best modeled our glycan profile findings. Our principal component analysis revealed components that represent the development of glycoforms into terminally galacotosylated forms (G1F and G2F), and another that encompasses maturation out of high mannose glycoforms. The partial least squares model additionally incorporated metabolic values to link these processes to glycan outcomes, especially involving the consumption of glutamine. Overall, these approaches indicated a tradeoff between cellular productivity and product quality in terms of the glycosylation. This work illustrates the use of multivariate analytical approaches that can be applied to complex bioprocessing problems for identifying potential solutions.

Lectin bio-layer interferometry for assessing product quality of Fc- glycosylated immunoglobulin G

Glycosylation, as the most prominent posttranslational modification, is recognized as an important quality attribute of monoclonal antibodies affected by various bioprocess parameters and cellular physiology. A method of lectin‐based bio‐layer interferometry (LBLI) to relatively rank galactosylation and fucosylation levels was developed. For this purpose, Fc‐glycosylated immunoglobulin G (IgG) was recombinantly produced with varying bioprocess conditions in 15 L bioreactor and accumulated IgG was harvested. The reliability, the robustness and the applicability of LBLI to different samples has been proven. Data obtained from LC–MS analysis served as reference and were compared to the LBLI results. The introduced method is based on non‐fluidic bio‐layer interferometry (BLI), which becomes recently a standard tool for determining biomolecular interactions in a label‐free, real‐time and high‐throughput manner. For the intended purpose, biotinylated lectins were immobilized on disposable optical fiber streptavidin (SA) biosensor tips. Aleuria aurantia lectin (AAL) was used to detect the core fucose and Ricinus communis agglutinin 120 (RCA120) to determine galactosylation levels. In our case study it could be shown that fucosylation was not affected by variations in glucose feed concentration and cultivation temperature. However, the galactosylation could be correlated with the ratio of mean specific productivity (q_P) and ammonium (q_NH4+) but was unrelated to the ratio of mean q_P and the specific glucose consumption (q_gluc). This presented method strengthens the applicability of the BLI platform, which already enables measurement of several product related characteristics, such as product quantity as well as kinetic rates (k_d,k_on) and affinity constants (k_D) analysis.

Process development for an inducible rituximab-expressing Chinese hamster ovary cell line

Inducible mammalian expression systems are becoming increasingly available and are not only useful for the production of cytotoxic/cytostatic products, but also confer the unique ability to uncouple the growth and production phases. In this work, we have specifically investigated how the cell culture state at the time of induction influences the cumate-inducible expression of recombinant rituximab by a GS-CHO cell line. To this end, cells grown in batch and fed-batch cultures were induced at increasing cell densities (1 to 10 × 10 ⁶ cells/mL). In batch, the cell specific productivity and the product yield were found to reduce with increasing cell density at induction. A dynamic feeding strategy using a concentrated nutrient solution applied prior and postinduction allowed to significantly increase the integral of viable cells and led to a 3-fold increase in the volumetric productivity (1.2 g/L). The highest product yields were achieved for intermediate cell densities at induction, as cultures induced during the late exponential phase (10 × 10 ⁶ cells/mL) were associated with a shortened production phase. The final glycosylation patterns remained however similar, irrespective of the cell density at induction. The kinetics of growth and production in a 2 L bioreactor were largely comparable to shake flasks for a similar cell density at induction. The degree of galactosylation was found to decrease over time, but the final glycan distribution at harvest was consistent to that of the shake flasks cultures. Taken together, our results provide useful insights for the rational development of fed-batch cell culture processes involving inducible CHO cells. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2742, 2019.

Absolute Quantitation of Glycoforms of Two Human IgG Subclasses Using Synthetic Fc Peptides and Glycopeptides

Immunoglobulins, such as immunoglobulin G (IgG), are of prime importance in the immune system. Polyclonal human IgG comprises four subclasses, of which IgG1 and IgG2 are the most abundant in healthy individuals. In an effort to develop an absolute MALDI-ToF-MS quantitative method for these subclasses and their Fc N-glycoforms, (glyco)peptides were synthesized using a solid-phase approach and used as internal standards. Tryptic digest glycopeptides from monoclonal IgG1 and IgG2 samples were first quantified using EEQYN(GlcNAc)STYR and EEQFN(GlcNAc)STFR standards, respectively. For IgG1, a similar glycopeptide where tyrosine (Y) was isotopically labelled was used to quantify monoclonal IgG1 that had been treated with the enzyme Endo-F2, i.e., yielding tryptic glycopeptide EEQYN(GlcNAc)STYR. The next step was to quantify single subclasses within polyclonal human IgG samples. Although ion abundances in the MALDI spectra often showed higher signals for IgG2 than IgG1, depending on the spotting solvent used, determination of amounts using the newly developed quantitative method allowed to obtain accurate concentrations where IgG1 species were predominant. It was observed that simultaneous analysis of IgG1 and IgG2 yielded non-quantitative results and that more success was obtained when subclasses were quantified one by one. More experiments served to assess the respective extraction and ionization efficiencies of EEQYNSTYR/EEQFNSTFR and EEQYN(GlcNAc)STYR/EEQFN(GlcNAc)STFR mixtures under different solvent and concentration conditions. Graphical Abstract ᅟ.

Real-time monitoring of antibody glycosylation site occupancy by in situ Raman spectroscopy during bioreactor CHO cell cultures

The glycosylation of therapeutic monoclonal antibodies (mAbs), a known critical quality attribute, is often greatly modified during the production process by animal cells. It is essential for biopharmaceutical industries to monitor and control this glycosylation. However, current glycosylation characterization techniques involve time- and labor-intensive analyses, often carried out at the end of the culture when the product is already synthesized. This study proposes a novel methodology for real-time monitoring of antibody glycosylation site occupancy using Raman spectroscopy. It was first observed in CHO cell batch culture that when low nutrient concentrations were reached, a decrease in mAb glycosylation was induced, which made it essential to rapidly detect this loss of product quality. By combining in situ Raman spectroscopy with chemometric tools, efficient prediction models were then developed for both glycosylated and nonglycosylated mAbs. By comparing variable importance in projection profiles of the prediction models, it was confirmed that Raman spectroscopy is a powerful method to distinguish extremely similar molecules, despite the high complexity of the culture medium. Finally, the Raman prediction models were used to monitor batch and feed-harvest cultures in situ. For the first time, it was demonstrated that the concentrations of glycosylated and nonglycosylated mAbs could be successfully and simultaneously estimated in real time with high accuracy, including their sudden variations due to medium exchanges. Raman spectroscopy can thus be considered as a promising PAT tool for feedback process control dedicated to on-line optimization of mAb quality. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:486-493, 2018.

Solid-Phase Enzymatic Remodeling Produces High Yields of Single Glycoform Antibodies

Antibodies are synthesized in mammalian cell culture as heterogeneous mixtures of glycoforms. Production of single glycoforms remains a challenge despite their value as therapeutics. The authors report a method of sequential enzymatic-based changes to antibodies while immobilized on an affinity column. Various antibodies (monoclonal and polyclonal) are isolated on Protein A or G columns and their glycans modified by sequential addition of enzymes for a desired transformation. Galactosylated antibodies (>90% yield) are produced by a one stage reaction process with sialidase to remove any sialic acid residues and addition of galactose with galactosyltransferase and UDP-Gal. Sialylated antibodies (>90%) are produced by a 2 stage conversion involving α(2,3) sialidase and galactosyltransferase followed by treatment with α(2,6) sialyltransferase in the presence of CMP-NANA. By this method, >90% of a disialylated human-llama antibody (EG2-hFc) and equimolar quantities of monosialylated and disialylated forms of human antibodies (αIL8-hFc and human polyclonal) are produced. Such high levels of sialylation are very difficult to obtain by typical cell culture methods. This method of transformation while the antibody is held on a solid-phase column is superior to previous methods because it allows a series of enzymatic steps without the need for intermediate purification. This is an efficient and rapid method to generate therapeutic antibodies with predefined glycosylation profiles. This should also assist in investigating the structure-function relationship of antibody glycans to find the desired glycosylation profile for high functional activity. With further optimization the method can be used to modify antibodies in large-scale manufacturing.

Microheterogeneity of Recombinant Antibodies: Analytics and Functional Impact

Antibodies are typical examples of biopharmaceuticals which are composed of numerous, almost infinite numbers of potential molecular entities called variants or isoforms, which constitute the microheterogeneity of these molecules. These variants are generated during biosynthesis by so-called posttranslational modification, during purification or upon storage. The variants differ in biological properties such as pharmacodynamic properties, for example, Antibody Dependent Cellular Cytotoxicity, complement activation, and pharmacokinetic properties, for example, serum half-life and safety. Recent progress in analytical technologies such as various modes of liquid chromatography and mass spectrometry has helped to elucidate the structure of a lot of these variants and their biological properties. In this review the most important modifications (glycosylation, terminal modifications, amino acid side chain modifications, glycation, disulfide bond variants and aggregation) are reviewed and an attempt is made to give an overview on the biological properties, for which the reports are often contradictory. Even though there is a deep understanding of cellular and molecular mechanism of antibody modification and their consequences, the clinical proof of the effects observed in vitro and in vivo is still not fully rendered. For some modifications such as core-fucosylation of the N-glycan and aggregation the effects are clear and should be monitored, but with others such as C-terminal lysine clipping the reports are contradictory. As a consequence it seems too early to tell if any modification can be safely ignored.

Glycosylation of voltage-gated calcium channels in health and disease

Voltage-gated calcium channels (VGCCs) are transmembrane proteins that translate electrical activities into intracellular calcium elevations and downstream signaling pathways. They serve essential physiological functions including communication between nerve cells, muscle contraction, cardiac activity, and release of hormones and neurotransmitters. Asparagine-linked glycosylation has emerged as an essential post-translational modification to control the number of channels embedded in the plasma membrane but also their functional gating properties. This review provides a comprehensive overview about the current state of knowledge on the role of glycosylation in the expression and functioning of VGCCs, and discusses how variations in the glycosylation of the channel proteins can contribute to pathological conditions.

Predictive glycoengineering of biosimilars using a Markov chain glycosylation model

Biosimilar drugs must closely resemble the pharmacological attributes of innovator products to ensure safety and efficacy to obtain regulatory approval. Glycosylation is one critical quality attribute that must be matched, but it is inherently difficult to control due to the complexity of its biogenesis. This usually implies that costly and time-consuming experimentation is required for clone identification and optimization of biosimilar glycosylation. Here, a computational method that utilizes a Markov model of glycosylation to predict optimal glycoengineering strategies to obtain a specific glycosylation profile with desired properties is described. The approach uses a genetic algorithm to find the required quantities to perturb glycosylation reaction rates that lead to the best possible match with a given glycosylation profile. Furthermore, the approach can be used to identify cell lines and clones that will require minimal intervention while achieving a glycoprofile that is most similar to the desired profile. Thus, this approach can facilitate biosimilar design by providing computational glycoengineering guidelines that can be generated with a minimal time and cost.

Altering the central carbon metabolism of HEK293 cells: Impact on recombinant glycoprotein quality

The accumulation of metabolic by-products remains a critical challenge in the development of mammalian cells culture processes as it impacts cellular growth, productivity and product quality. Although the overexpression of the PYC2 gene was shown to significantly improve the nutrient metabolism efficiency of mammalian cells, its impact on recombinant protein quality has not been investigated yet. In this study, we assess the effect of this metabolic engineering strategy on the quality of a recombinant therapeutic glycoprotein, the human interferon α2b (IFNα2b). As inferred from densitometry analysis of SDS-PAGE gels, PYC2-overexpressing cells sustained a higher percentage of intact glycosylated IFNα2b at the late stage of batch cultures, which was correlated with prolonged viability and reduced accumulation of waste metabolites. Contrarily to the IFNα2b produced by the PYC2 cells, LC-MS analysis confirmed the presence of less glycosylated IFNα2b as well as the occurrence of proteolytic cleavage in the IFNα2b produced in the parental cells. Taken together, these results indicate that PYC2-overexpression in mammalian cells leads to extended favorable conditions for glycosylation and offer an attractive approach to mass-produce high-quality recombinant proteins.

Glycan-Based Cell Targeting To Modulate Immune Responses

Glycosylation is an integral post-translational modification present in more than half of all eukaryotic proteins. It affects key protein functions, including folding, stability, and immunogenicity. Glycoengineering approaches, such as the use of bacterial N-glycosylation systems, or expression systems, including yeasts, insect cells, and mammalian cells, have enabled access to defined and homogenous glycoproteins. Given that glycan structures on proteins can be recognized by host lectin receptors, they may facilitate cell-specific targeting and immune modulation. Myeloid C-type lectin receptors (CLRs) expressed by antigen-presenting cells are attractive targets to shape immune responses. Multivalent glycan display on nanoparticles, liposomes, or dendrimers has successfully enabled CLR targeting. In this review, we discuss novel strategies to access defined glycan structures and highlight CLR targeting approaches for immune modulation.