An investigation of intracellular glycosylation activities in CHO cells: effects of nucleotide sugar precursor feeding

Effects of autophagy-inhibiting chemicals on sialylation of Fc-fusion glycoprotein in recombinant CHO cells

The occurrence of autophagy in recombinant Chinese hamster ovary (rCHO) cell culture has attracted attention due to its effects on therapeutic protein production. Given the significance of glycosylation in therapeutic proteins, this study examined the effects of autophagy-inhibiting chemicals on sialylation of Fc-fusion glycoproteins in rCHO cells. Three chemical autophagy inhibitors known to inhibit different stages were separately treated with two rCHO cell lines that produce the same Fc-fusion glycoprotein derived from DUKX-B11 and DG44. All autophagy inhibitors significantly decreased the sialylation of Fc-fusion glycoprotein in both cell lines. The decrease in sialylation of Fc-fusion glycoprotein is unlikely to be attributed to the release of intracellular enzymes, given the high cell viability and low activity of extracellular sialidases. Interestingly, the five intracellular nucleotide sugars remained abundant in cells treated with autophagy inhibitors. In the mRNA expression profiles of 27 N-glycosylation-related genes using the NanoString nCounter system, no significant differences in gene expression were noted. With the positive effect of supplementing nucleotide sugar precursors on sialylation, attempts were made to enhance the levels of intracellular nucleotide sugars by supplying these precursors. The addition of nucleotide sugar precursors to cultures treated with inhibitors successfully enhanced the sialylation of Fc-fusion glycoproteins compared to the control culture. This was particularly evident under mild stress conditions and not under relatively severe stress conditions, which were characterized by a high decrease in sialylation. These results suggest that inhibiting autophagy in rCHO cell culture decreases sialylation of Fc-fusion glycoprotein by constraining the availability of intracellular nucleotide sugars. KEY POINTS: •  The autophagy inhibition in rCHO cell culture leads to a significant reduction in the sialylation of Fc-fusion glycoprotein. •  The pool of five intracellular nucleotide sugars remained highly abundant in cells treated with autophagy inhibitors. •  Supplementation of nucleotide sugar precursors effectively restores decreased sialylation, particularly under mild stress conditions but not in relatively severe stress conditions.

NAD+ supplementation improves mAb productivity in CHO cells via a glucose metabolic shift

Aerobic glycolysis and its by-product lactate accumulation are usually associated with adverse culture phenotypes such as poor cell viability and productivity. Due to the lack of knowledge on underlying mechanisms and accompanying biological processes, the regulation of aerobic glycolysis has been an ongoing challenge in culture process development for therapeutic protein productivity. Nicotinamide adenine dinucleotide (NAD⁺ ), a coenzyme and co-substrate in energy metabolism, promotes the conversion of inefficient glycolysis into an efficient oxidative phosphorylation (OXPHOS) pathway. However, the effect of NAD⁺ on Chinese hamster ovary (CHO) cells for biopharmaceutical production has not been reported yet. In this work, we aimed to elucidate the influence of NAD⁺ on cell culture performance by examining metabolic shifts and mAb productivity. The supplementation of NAD⁺ increased the intracellular concentration of NAD⁺ and promoted SIRT3 expression. Antibody titer and the specific productivity in the growth phase were improved by up to 1.82- and 1.88-fold, respectively, with marginal restrictions on cell growth. NAD⁺ significantly reduced the accumulation of reactive oxygen species (ROS) and the lactate yield from glucose, determined by lactate accumulation versus glucose consumption (Y_LAC/GLC ). In contrast, OXPHOS capacity and amino acid consumption rate increased substantially. Collectively, these results suggest that NAD⁺ contributes to improving therapeutic protein productivity in bioprocessing via inducing an energy metabolic shift.

Advanced strategies in glycosylation prediction and control during biopharmaceutical development: Avenues toward Industry 4.0

Glycosylation has been shown to define the safety and efficacy of biopharmaceuticals, thus classified as a critical quality attribute. However, controlling glycan heterogeneity has always been a major challenge owing to the multi-variate factors that govern the glycosylation process. Conventional approaches for controlling glycosylation such as gene editing and metabolic control have succeeded in obtaining desired glycan profiles in accordance with the Quality by Design paradigm. Nonetheless, the development of smart algorithms and omics-enabled complete cell characterization have made it possible to predict glycan profiles beforehand, and manipulate process variables accordingly. This review thus discusses the various approaches available for control and prediction of glycosylation in biopharmaceuticals. Further, the futuristic goal of integrating such technologies is discussed in order to attain an automated and digitized continuous bioprocess for control of glycosylation. Given, control of a process as complex as glycosylation requires intense monitoring intervention, we examine the current technologies that enable automation. Finally, we discuss the challenges and the technological gap that currently limits incorporation of an automated process in routine bio-manufacturing, with a glimpse into the economic bearing. This article is protected by copyright. All rights reserved.

Glycoproteomic Characterization of FUT8 Knock-Out CHO Cells Reveals Roles of FUT8 in the Glycosylation

The α1,6-fucosyltransferase (encoded by FUT8 gene) is the key enzyme transferring fucose to the innermost GlcNAc residue on an N-glycan through an α-1,6 linkage in the mammalian cells. The presence of core fucose on antibody Fc region can inhibit antibody-dependent cellular cytotoxicity (ADCC) and reduce antibody therapeutic efficiency in vivo. Chinese hamster ovary (CHO) cells are the predominant production platform in biopharmaceutical manufacturing. Therefore, the generation of FUT8 knock-out (FUT8KO) CHO cell line is favorable and can be applied to produce completely non-fucosylated antibodies. The characterization of monoclonal antibodies as well as host cell glycoprotein impurities are required for quality control purposes under regulation rules. To understand the role of FUT8 in the glycosylation of CHO cells, we generated a FUT8 knock-out CHO cell line and performed a large-scale glycoproteomics to characterize the FUT8KO and wild-type (WT) CHO cells. The glycopeptides were enriched by hydrophilic chromatography and fractionated 25 fractions by bRPLC followed by analysis using high-resolution liquid chromatography mass spectrometry (LC-MS). A total of 7,127 unique N-linked glycosite-containing intact glycopeptides (IGPs), 928 glycosites, and 442 glycoproteins were identified from FUT8KO and WT CHO cells. Moreover, 28.62% in 442 identified glycoproteins and 26.69% in 928 identified glycosites were significantly changed in the FUT8KO CHO compared to wild-type CHO cells. The relative abundance of all the three N-glycan types (high-mannose, hybrid, and complex) was determined in FUT8KO comparing to wild-type CHO cells. Furthermore, a decrease in fucosylation content was observed in FUT8KO cells, in which core-fucosylated glycans almost disappeared as an effect of FUT8 gene knockout. Meantime, a total of 51 glycosylation-related enzymes were also quantified in these two cell types and 16 of them were significantly altered in the FUT8KO cells, in which sialyltransferases and glucosyltransferases were sharply decreased. These glycoproteomic results revealed that the knock-out of FUT8 not only influenced the core-fucosylation of proteins but also altered other glycosylation synthesis processes and changed the relative abundance of protein glycosylation.

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.

Quantifying the impact of cell culture media on CHO cell growth and protein production

In recombinant protein production, cell culture media development and optimization is typically seen as a useful strategy to increase titer and cell density, reduce by-products, as well as improve product quality (with cell density and titer often serving as the primary reported outcome of media studies). However, despite the large number of media optimization studies, there have been few attempts to comprehensively assess the overall effectiveness of media additives. The aim of this review is therefore both to document published media optimization studies over the last twenty years (in the context of Chinese hamster ovary cell recombinant production) and quantitatively estimate the impact of this media optimization on cell culture performance. In considering 78 studies, we have identified 238 unique media components that have been supplemented over the last 20 years. Among these additives, trace elements stood out as having a positive impact on cell density while nucleotides show potential for increasing titer, with commercial supplements benefiting both. However, we also identified that the impact of specific additives is far more variable than often perceived. With relatively few media studies considering multiple cell lines or multiple basal media, teasing out consistent and general trends becomes a considerable challenge. By extracting cell density and titer values from all of the reviewed studies, we were able to build a mixed-effect model capable of estimating the relative impact of additives, cell line, product type, basal medium, cultivation method (flask or reactor), and feeding strategy (batch or fed-batch). Overall, additives only accounted for 3% of the variation in cell density and 1% of the variation in titer. Similarly, the impact of basal media was also relatively modest, at 10% for cell density and 0% for titer. Cell line, product type, and feeding strategy were all found to have more impact. These results emphasize the need for media studies to consider more factors to ensure that reported observations can be generalized and further developed.

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.

Big-Data Glycomics: Tools to Connect Glycan Biosynthesis to Extracellular Communication

Characteristically, cells must sense and respond to environmental cues. Despite the importance of cell-cell communication, our understanding remains limited and often lacks glycans. Glycans decorate proteins and cell membranes at the cell-environment interface, and modulate intercellular communication, from development to pathogenesis. Providing further challenges, glycan biosynthesis and cellular behavior are co-regulating systems. Here, we discuss how glycosylation contributes to extracellular responses and signaling. We further organize approaches for disentangling the roles of glycans in multicellular interactions using newly available datasets and tools, including glycan biosynthesis models, omics datasets, and systems-level analyses. Thus, emerging tools in big data analytics and systems biology are facilitating novel insights on glycans and their relationship with multicellular behavior.

Serum-Free Medium for Recombinant Protein Expression in Chinese Hamster Ovary Cells

At present, nearly 70% of recombinant therapeutic proteins (RTPs) are produced by Chinese hamster ovary (CHO) cells, and serum-free medium (SFM) is necessary for their culture to produce RTPs. In this review, the history and key components of SFM are first summarized, and its preparation and experimental design are described. Some small molecule compound additives can improve the yield and quality of RTP. The function and possible mechanisms of these additives are also reviewed here. Finally, the future perspectives of SFM use with CHO cells for RTP production are discussed.

Understanding the effect of increased cell specific productivity on galactosylation of monoclonal antibodies produced using Chinese hamster ovary cells

Achieving optimal productivity and desired product quality of the therapeutic monoclonal antibody (mAb) is one of the primary goals of process development. Across the various mAb programs at our company, we observed that increasing the specific productivity (q_p) results in a decrease in the % galactosylation (%Gal) level on the protein. In order to gain further insight into this correlation, cells were cultured under different process conditions such as pH or media osmolality or in the presence of supplements such as sodium butyrate. A range of q_p and N-glycan profiles were obtained with the greatest changes observed under high pH (lower q_p, higher %Gal), higher osmolality (higher q_p, lower %Gal) or sodium butyrate (moderately higher q_p, moderately lower %Gal) conditions. Abundance of individual glycan species highlighted different bottlenecks in the N-glycosylation pathway depending on the treatment condition. Transcriptomics analysis was performed to identify changes in gene expression profiles that correlate with the inverse relationship between q_p and %Gal. Results showed downregulation of Beta-1,4-galactosyltransferase 1 (B4GalT1), UDP-GlcNAc and Mn²⁺ transporter (slc35a3 and slc39a8 respectively) for the high osmolality conditions. Significant downregulation of slc39a8 (Mn²⁺ transporter) was observed for the sodium butyrate condition. No significant differences were observed for any of the genes in the N-glycosylation pathway under the high pH condition even though this condition showed highest %Gal. Together, data suggests that different treatments have distinct complex mechanisms by which the overall glycan levels of a mAb are influenced. Further studies based on these results will help build the knowledge necessary to design strategies to obtain the desired productivity and product quality of mAbs.

Control of IgG glycosylation in CHO cell perfusion cultures by GReBA mathematical model supported by a novel targeted feed, TAFE

The N-linked glycosylation pattern is an important quality attribute of therapeutic glycoproteins. It has been reported by our group and by others that different carbon sources, such as glucose, mannose and galactose, can differently impact the glycosylation profile of glycoproteins in mammalian cell culture. Acting on the sugar feeding is thus an attractive strategy to tune the glycan pattern. However, in case of feeding of more than one carbon source simultaneously, the cells give priority to the one with the highest uptake rate, which limits the usage of this tuning, e.g. the cells favor consuming glucose in comparison to galactose. We present here a new feeding strategy (named 'TAFE' for targeted feeding) for perfusion culture to adjust the concentrations of fed sugars influencing the glycosylation. The strategy consists in setting the sugar feeding such that the cells are forced to consume these substrates at a target cell specific consumption rate decided by the operator and taking into account the cell specific perfusion rate (CSPR). This strategy is applied in perfusion cultures of Chinese hamster ovary (CHO) cells, illustrated by ten different regimes of sugar feeding, including glucose, galactose and mannose. Applying the TAFE strategy, different glycan profiles were obtained using the different feeding regimes. Furthermore, we successfully forced the cells to consume higher proportions of non-glucose sugars, which have lower transport rates than glucose in presence of this latter, in a controlled way. In previous work, a mathematical model named Glycan Residues Balance Analysis (GReBA) was developed to model the glycosylation profile based on the fed carbon sources. The present data were applied to the GReBA to design a feeding regime targeting a given glycosylation profile. The ability of the model to achieve this objective was confirmed by a multi-round of leave-one-out cross-validation (LOOCV), leading to the conclusion that the GReBA model can be used to design the feeding regime of a perfusion cell culture to obtain a desired glycosylation profile.

A class of low-cost alternatives to kifunensine for increasing high mannose N-linked glycosylation for monoclonal antibody production in Chinese hamster ovary cells

N-linked glycosylation of therapeutic monoclonal antibodies is an important product quality attribute for drug safety and efficacy. An increase in the percent of high mannose N-linked glycosylation may be required for drug efficacy or to match the glycosylation profile of the innovator drug during the development of a biosimilar. In this study, the addition of several chemical additives to a cell culture process resulted in high mannose N-glycans on monoclonal antibodies produced by Chinese hamster ovary (CHO) cells without impacting cell culture performance. The additives, which include known mannosidase inhibitors (kifunensine and deoxymannojirimycin) as well as novel inhibitors (tris, bis-tris, and 1-amino-1-methyl-1,3-propanediol), contain one similar molecular structure: 2-amino-1,3-propanediol, commonly referred to as serinol. The shared chemical structure provides insight into the binding and inhibition of mannosidase in CHO cells. One of the novel inhibitors, tris, is safer compared to kifunensine, 35x as cost-effective, and stable at room temperature. In addition, tris and bis-tris provide multiple low-cost alternatives to kifunensine for manipulating glycosylation in monoclonal antibody production in a cell culture process with minimal impact to productivity or cell health.

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.

Harnessing the potential of artificial neural networks for predicting protein glycosylation

Kinetic models offer incomparable insight on cellular mechanisms controlling protein glycosylation. However, their ability to reproduce site-specific glycoform distributions depends on accurate estimation of a large number of protein-specific kinetic parameters and prior knowledge of enzyme and transport protein levels in the Golgi membrane. Herein we propose an artificial neural network (ANN) for protein glycosylation and apply this to four recombinant glycoproteins produced in Chinese hamster ovary (CHO) cells, two monoclonal antibodies and two fusion proteins. We demonstrate that the ANN model accurately predicts site-specific glycoform distributions of up to eighteen glycan species with an average absolute error of 1.1%, correctly reproducing the effect of metabolic perturbations as part of a hybrid, kinetic/ANN, glycosylation model (HyGlycoM), as well as the impact of manganese supplementation and glycosyltransferase knock out experiments as a stand-alone machine learning algorithm. These results showcase the potential of machine learning and hybrid approaches for rapidly developing performance-driven models of protein glycosylation.

A high-resolution measurement of nucleotide sugars by using ion-pair reverse chromatography and tandem columns

N-Linked glycosylation is a cellular process transferring sugars from glycosyl donors to proteins or lipids. Biopharmaceutical products widely produced by culturing mammalian cells such as Chinese hamster ovary (CHO) cells are typically glycosylated during biosynthesis. For some biologics, the N-linked glycan is a critical quality attribute of the drugs. Nucleotide sugars are the glycan donors and impact the intracellular glycosylation process. In current analytical methods, robust separation of nucleotide sugar isomers such as UDP glucose and UDP galactose remains a challenge because of their structural similarity. In this study, we developed a strategy to resolve the separation of major nucleotide sugars including challenging isomers based on the use of ion-pair reverse phase (IP-RP) chromatography. The strategy applies core-shell columns and connects multiple columns in tandem to increase separation power and ultimately enables high-resolution detection of nucleotide sugars from cell extracts. The key parameters in the IP-RP method, including temperature, mobile phase, and flow rates, have been systematically evaluated in this work and the theoretical mechanisms of the chromatographic behavior were proposed. Graphical abstract.

Influence of media composition on recombinant monoclonal IgA1 glycosylation analysed by lectin-based protein microarray and MALDI-MS

Glycosylation of therapeutic glycoproteins significantly affects their physico-chemical properties, bioactivity and immunogenicity. The determination of glycan composition is highly important regarding their development and production. Therefore, there is a demand for analytical techniques enabling rapid and reliable glycoprofiling of therapeutic proteins. For the investigation of changes in glycan structures, we have employed two platforms: lectin-based protein microarray, and MALDI-MS. In lectin-based microarray analysis, the samples of IgA were printed on the microarray slide, incubated with the set of lectins with various specificity and evaluation of changes in glycosylation was based on differences in reactivity of samples with lectins. MALDI-MS was used for N-glycan analysis of IgA1 samples. IgAs are effective as therapeutic agents in defense against viruses that use sialic acid as a receptor. Dimeric IgA1 antibodies were produced by stable cell line IgA1/2G9 on the basal medium at different conditions (different supplementation and feeding) and we also evaluated the effect of different conditions on lactate production, which correlates with IgA productivity. Decrease of lactate levels was observed during supplementation with succinic acid, asparagine, or with mannose feeding. We found by lectin-based microarray analysis that the metabolic shift from glutamine to asparagine or feeding with glucose caused increase of high mannose type glycans what was confirmed also by MALDI-MS. Among other changes in IgA glycosylation determined by lectin-based protein microarray were, for example, reduced galactosylation after supplementation with succinic acid and increase of both sialylation and galactosylation after supplementation with glutamine and feeding with mannose. The elucidation of mechanism of determined changes requires further investigation, but the described analytical approach represent effective platform for determination, screening and evaluation of glycosylation of therapeutic proteins.

Enhancement of sialylation in rIgG in glyco-engineered Chinese hamster ovary cells

Since about 70% of commercial biopharmaceutical products have been produced in Chinese hamster ovary (CHO) cells, this cell line is undeniably a workhorse for biopharmaceuticals production. Meanwhile, sialic acid terminals were reported to affect anti-inflammatory activity, antibody-dependent cellular cytotoxicity efficacy of IgG antibodies. Taking these findings together, we aimed to establish CHO cell lines that highly produce sialic acid terminals by overexpressing two N-acetylneuraminic acid-based key enzymes, α(2,6)-sialyltransferase and UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase using dihydrofolate reductase/methotrexate gene amplification method. Indeed, the number of total sialic acid terminal glycan structures increased tremendously, by 12-fold compared to the wild type in total protein extracts. With the methotrexate supplementation, a targeted cell line, CHOmt17-100, showed up to 1.4 times more sialylated structures of glycoforms in total proteins. Interestingly, immunoglobulin G, used as the model protein in CHOmt17-100, showed about 53% sialylated structures in its glycoforms. These resultant sialylated glycans exhibited more than approximately 14.5 times increase as compared to that of the wild type. Moreover, the resultant glycan structures mostly had N-acetylneuraminic acid terminals, while N-glycolylneuraminic acid terminal composition remained less than 5% as compared to the wild type. Engineered antibodies derived from CHO cell lines that produce high levels of sialic acid will contribute to the examination of glycoforms' efficacy and usefulness toward bio-better products.

Bovine serum albumin affects N-glycoforms of murine IgG monoclonal antibody purified from hybridoma supernatants

Immunoglobulin G (IgG) is a class of monoclonal antibodies (mAbs) commonly produced in mammalian cell lines. These cell lines are grown in finely adjusted culture media, which contain components that may impact glycoforms. As variation of N-glycoforms can impact the biological properties of IgGs, medium composition should be controlled. Here, we studied the effects on IgG N-glycoforms of different components in hybridoma culture media, specifically compared bovine serum albumin (BSA) with other small molecules, using a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight multistage mass spectrometry (MALDI-QIT-TOF MSⁿ)-based approach. We show that small molecular additives caused little change in glycan species, though a number of these reagents, especially glutamine, affected levels of glycosylation. In comparison, the addition of macromolecular protein BSA significantly changed IgG N-glycan patterns, not only in species but also in glycosylation levels. Together, our finding suggests that BSA increases the complexity of IgG N-glycoforms, thus raising the difficulty in maintaining glycoforms consistency during antibody production. Therefore, the effect of BSA on IgG N-glycans should be considered when designing optimal medium formulations for IgG production. KEY POINTS: • Small molecular medium additives only affect glycosylation levels of IgG N-glycans. • BSA significantly changes IgG N-glycoforms as a medium additive. • BSA's skewing of IgG N-glycoforms should be considered in IgG production.

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.

Exploiting metabolic glycoengineering to advance healthcare

Metabolic glycoengineering (MGE) is a technique for manipulating cellular metabolism to modulate glycosylation. MGE is used to increase the levels of natural glycans and, more importantly, to install non-natural monosaccharides into glycoconjugates. In this Review, we summarize the chemistry underlying MGE that has been developed over the past three decades and highlight several recent advances that have set the stage for clinical translation. In anticipation of near-term application to human healthcare, we describe emerging efforts to deploy MGE in diverse applications, ranging from the glycoengineering of biotherapeutic proteins and the diagnosis and treatment of complex diseases such as cancer to the development of new immunotherapies.

Monitoring of antibody glycosylation pattern based on microarray MALDI-TOF mass spectrometry

Biologically manufactured monoclonal antibodies (mAb) can strongly vary in their efficacy and affinity. Therefore, engineering and production of the mAb is highly regulated and requires product monitoring, especially in terms of N-glycosylation patterns. In this work, we present a high-throughput matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) method based on a microarray technology to monitor N-glycopeptides of IgG1 produced in a perfusion cell culture. A bottom-up approach combined with zwitterionic-hydrophilic interaction liquid chromatography for sample purification was used to determine the day-by-day variation of the terminal galactose within two major N-glycoforms. Our results show that microarrays for mass spectrometry (MAMS) are a robust platform for the rapid determination of the carbohydrate distribution. The spectral repeatability is characterized by a low coefficient of variations (1.7% and 7.1% for the FA2 and FA2G1 structures, respectively) and allows to detect the N-glycosylation variability resulting from operating conditions during the bioreactor process. The observed trend of released N-glycans was confirmed using capillary gel electrophoresis with laser-induced fluorescence detection. Therefore, the microarray technology is a promising analytical tool for glycosylation control during the production process of recombinant proteins.

Innovation in Cell Banking, Expansion, and Production Culture

Cell culture-based production processes enable the development and commercial supply of recombinant protein products. Such processes consist of the following elements: thaw and initiation of culture, seed expansion, and production culture. A robust cell source storage system in the form of a cell bank is developed and cells are thawed to initiate the cell culture process. Seed culture expansion generates sufficient cell mass to initiate the production culture. The production culture provides an environment where the cells can synthesize the product and is optimized to deliver the highest possible product concentration with acceptable product quality. This chapter describes the significant innovations made in these process elements and the resulting improvements in the overall efficiency, robustness, and safety of the processes and products.

Prediction of N-linked Glycoform Profiles of Monoclonal Antibody with Extracellular Metabolites and Two-Step Intracellular Models

Monoclonal antibodies (mAbs) are commonly glycosylated and show varying levels of galactose attachment. A set of experiments in our work showed that the galactosylation level of mAbs was altered by the culture conditions of hybridoma cells. The uridine diphosphate galactose (UDP-Gal) is one of the substrates of galactosylation. Based on that, we proposed a two-step model to predict N-linked glycoform profiles by solely using extracellular metabolites from cell culture. At the first step, the flux level of UDP-Gal in each culture was estimated based on a computational flux balance analysis (FBA); its level was found to be linear with the galactosylation degree on mAbs. At the second step, the glycoform profiles especially for G0F (agalactosylated), G1F (monogalactosylated) and G2F (digalactosylated) were predicted by a kinetic model. The model outputs well matched with the experimental data. Our study demonstrated that the integrated mathematical approach combining FBA and kinetic model is a promising strategy to predict glycoform profiles for mAbs during cell culture processes.

Model-based optimization of antibody galactosylation in CHO cell culture

Exerting control over the glycan moieties of antibody therapeutics is highly desirable from a product safety and batch-to-batch consistency perspective. Strategies to improve antibody productivity may compromise quality, while interventions for improving glycoform distribution can adversely affect cell growth and productivity. Process design therefore needs to consider the trade-off between preserving cellular health and productivity while enhancing antibody quality. In this work, we present a modeling platform that quantifies the impact of glycosylation precursor feeding - specifically that of galactose and uridine - on cellular growth, metabolism as well as antibody productivity and glycoform distribution. The platform has been parameterized using an initial training data set yielding an accuracy of ±5% with respect to glycoform distribution. It was then used to design an optimized feeding strategy that enhances the final concentration of galactosylated antibody in the supernatant by over 90% compared with the control without compromising the integral of viable cell density or final antibody titer. This work supports the implementation of Quality by Design towards higher-performing bioprocesses.

Improving Immunotherapy Through Glycodesign

Immunotherapy is revolutionizing health care, with the majority of high impact "drugs" approved in the past decade falling into this category of therapy. Despite considerable success, glycosylation-a key design parameter that ensures safety, optimizes biological response, and influences the pharmacokinetic properties of an immunotherapeutic-has slowed the development of this class of drugs in the past and remains challenging at present. This article describes how optimizing glycosylation through a variety of glycoengineering strategies provides enticing opportunities to not only avoid past pitfalls, but also to substantially improve immunotherapies including antibodies and recombinant proteins, and cell-based therapies. We cover design principles important for early stage pre-clinical development and also discuss how various glycoengineering strategies can augment the biomanufacturing process to ensure the overall effectiveness of immunotherapeutics.

Comprehensive manipulation of glycosylation profiles across development scales

The extent and pattern of glycosylation on therapeutic antibodies can influence their circulatory half-life, engagement of effector functions, and immunogenicity, with direct consequences to efficacy and patient safety. Hence, controlling glycosylation patterns is central to any drug development program, yet poses a formidable challenge to the bio-manufacturing industry. Process changes, which can affect glycosylation patterns, range from manufacturing at different scales or sites, to switching production process mode, all the way to using alternative host cell lines. In the emerging space of biosimilars development, often times all of these aspects apply. Gaining a deep understanding of the direction and extent to which glycosylation quality attributes can be modulated is key for efficient fine-tuning of glycan profiles in a stage appropriate manner, but establishment of such platform knowledge is time consuming and resource intensive. Here we report an inexpensive and highly adaptable screening system for comprehensive modulation of glycans on antibodies expressed in CHO cells. We characterize 10 media additives in univariable studies and in combination, using a design of experiments approach to map the design space for tuning glycosylation profile attributes. We introduce a robust workflow that does not require automation, yet enables rapid process optimization. We demonstrate scalability across deep wells, shake flasks, AMBR-15 cell culture system, and 2 L single-use bioreactors. Further, we show that it is broadly applicable to different molecules and host cell lineages. This universal approach permits fine-tuned modulation of glycan product quality, reduces development costs, and enables agile implementation of process changes throughout the product lifecycle.

Metabolic engineering of CHO cells to prepare glycoproteins

As a complex and common post-translational modification, N-linked glycosylation affects a recombinant glycoprotein's biological activity and efficacy. For example, the α1,6-fucosylation significantly affects antibody-dependent cellular cytotoxicity and α2,6-sialylation is critical for antibody anti-inflammatory activity. Terminal sialylation is important for a glycoprotein's circulatory half-life. Chinese hamster ovary (CHO) cells are currently the predominant recombinant protein production platform, and, in this review, the characteristics of CHO glycosylation are summarized. Moreover, recent and current metabolic engineering strategies for tailoring glycoprotein fucosylation and sialylation in CHO cells, intensely investigated in the past decades, are described. One approach for reducing α1,6-fucosylation is through inhibiting fucosyltransferase (FUT8) expression by knockdown and knockout methods. Another approach to modulate fucosylation is through inhibition of multiple genes in the fucosylation biosynthesis pathway or through chemical inhibitors. To modulate antibody sialylation of the fragment crystallizable region, expressions of sialyltransferase and galactotransferase individually or together with amino acid mutations can affect antibody glycoforms and further influence antibody effector functions. The inhibition of sialidase expression and chemical supplementations are also effective and complementary approaches to improve the sialylation levels on recombinant glycoproteins. The engineering of CHO cells or protein sequence to control glycoforms to produce more homogenous glycans is an emerging topic. For modulating the glycosylation metabolic pathways, the interplay of multiple glyco-gene knockouts and knockins and the combination of multiple approaches, including genetic manipulation, protein engineering and chemical supplementation, are detailed in order to achieve specific glycan profiles on recombinant glycoproteins for superior biological function and effectiveness.

Nickel and cobalt affect galactosylation of recombinant IgG expressed in CHO cells

Glycosylation is an important product quality attribute of antibody biopharmaceuticals. It involves enzymatic addition of oligosaccharides on proteins by sequential action of glycosyltransferases and glycosidases in the endoplasmic reticulum and golgi. Some of these enzymes like galactosyltransferase and N-acetylglucosaminyltransferase-I require trace metal cofactors. Variations in trace metal availability during production can thus affect glycosylation of recombinant glycoproteins such as monoclonal antibodies. Variability in trace metal concentrations can be introduced at multiple stages during production such as due to impurities in raw materials for culture medium and leachables from bioreactors. Knowledge of the effect of various trace metals on glycosylation can help in root-cause analysis of unintended variability in glycosylation. In this study, we investigated the effect of nickel and cobalt on glycosylation of recombinant IgG expressed in Chinese hamster ovary cells. Nickel concentrations below 500 µM did not affect glycosylation, but above 500 µM it significantly decreases galactosylation of IgG. Cobalt at 50 µM concentration causes slight increase in G1F glycans (mono galactosylated) as previously reported. However, higher concentrations result in a small increase in G0F (non galactosylated) glycans. This effect of nickel and cobalt on galactosylation of recombinant IgG can be reversed by supplementation of uridine and galactose which are precursors to UDP-Galactose, a substrate for the enzymatic galactosylation reaction.

Supplementing glycosylation: A review of applying nucleotide-sugar precursors to growth medium to affect therapeutic recombinant protein glycoform distributions

Glycosylation is a critical quality attribute (CQA) of many therapeutic proteins, particularly monoclonal antibodies (mAbs), and is a major consideration in the approval of biosimilar biologics due to its effects to therapeutic efficacy. Glycosylation generates a distribution of glycoforms, resulting in glycoproteins with inherent molecule-to-molecule heterogeneity, capable of activating (or failing to activate) different effector functions of the immune system. Glycoforms can be affected by the supplementation of nucleotide-sugar precursors, and related components, to culture growth medium, affecting the metabolism of glycosylation. These supplementations has been demonstrated to increase nucleotide-sugar intracellular pools, and impact glycoform distributions, but with varied results. These variations can be attributed to five key factors: Differences between cell platforms (enzyme/transporter expression levels); differences between recombinant proteins produced (glycan-site accessibility); the fermentation and sampling timeline (glucose availability and exoglycosidase accumulation); glutamine levels (affecting ammonia levels, which impact Golgi pH, as well as UDP-GlcNAc pools); and finally, a lack of standardized metrics for observing shifts in glycoform distributions (glycosylation indices) across different experiments. The purpose of this review is to provide detail and clarity on the state of the art of supplementation strategies for nucleotide-sugar precursors for affecting glycosylation in cell culture processes, and to apply glycosylation indices for standardized comparisons across the field.

Zinc supplementation decreases galactosylation of recombinant IgG in CHO cells

Trace element composition of culture medium can be altered to modulate glycoform of recombinant glycoproteins. In this study, we show that Zn²⁺ supplementation at or above 100 μM decreases galactosylation of recombinant IgG expressed in Chinese Hamster Ovary cells. This decrease in galactosylation is not due to reduced galactosyltransferase expression. This effect persists upon supplementation of galactose and uridine to the culture, indicating that it may not be due to reduced UDP-Gal availability. Measurements of galactosyltransferase activity in the cell lysate show that activity decreases with increasing Zn²⁺/Mn²⁺ ratio. This suggests that one possible explanation of the effect of Zn²⁺ may be reduced intracellular galactosyltransferase activity due to increase in Zn²⁺/Mn²⁺ ratio. Consistent with this, the decrease in galactosylation of IgG could be reversed by supplementation of Mn²⁺ (a cofactor of galactosyltransferase) which increases intracellular Mn²⁺ content. Measurement of total intracellular Zn²⁺ content, however, indicates no significant upregulation of total intracellular Zn²⁺ content and no significant downregulation of intracellular Mn²⁺ content with Zn²⁺ supplementation. One possible explanation could be that cellular detoxification response to higher extracellular Zn²⁺ concentration might lead to changes in intracellular distribution of Mn²⁺. In this case, Zn²⁺ supplementation would be expected to interfere with other known effects of Mn²⁺. Indeed, the previously reported increase in high mannose glycans upon Mn²⁺ supplementation in the absence of glucose is reversed by Zn²⁺ supplementation. This study also suggests the use of Mn²⁺ supplementation as a strategy to overcome the effect of lot-to-lot variability in trace element concentrations on galactosylation.

Glycoengineering in CHO Cells: Advances in Systems Biology

For several decades, glycoprotein biologics have been successfully produced from Chinese hamster ovary (CHO) cells. The therapeutic efficacy and potency of glycoprotein biologics are often dictated by their post-translational modifications, particularly glycosylation, which unlike protein synthesis, is a non-templated process. Consequently, both native and recombinant glycoprotein production generate heterogeneous mixtures containing variable amounts of different glycoforms. Stability, potency, plasma half-life, and immunogenicity of the glycoprotein biologic are directly influenced by the glycoforms. Recently, CHO cells have also been explored for production of therapeutic glycosaminoglycans (e.g., heparin), which presents similar challenges as producing glycoproteins biologics. Approaches to controlling heterogeneity in CHO cells and directing the biosynthetic process toward desired glycoforms are not well understood. A systems biology approach combining different technologies is needed for complete understanding of the molecular processes accounting for this variability and to open up new venues in cell line development. In this review, we describe several advances in genetic manipulation, modeling, and glycan and glycoprotein analysis that together will provide new strategies for glycoengineering of CHO cells with desired or enhanced glycosylation capabilities.

Enhancement of glycosylation by stable co-expression of two sialylation-related enzymes on Chinese hamster ovary cells

Sialic acid plays important roles in stabilization and modulation of the interaction of molecules and membranes in organisms. Due to its high electronegativity, sialic acid can promote binding effects of molecules and support the transportation of drugs and ions in cells. This also strengthens cells against degradation from glycosidases and proteases. Hence sialic acid helps glycoproteins extend their half-lives and bioactivity. On the other hand, Chinese hamster ovary (CHO) cells have been widely used as a workhorse in biopharmaceutical fields in part due to the similarity between their glycan properties and those in humans. Thus, a high sialylation produced by CHO host cell line is strongly desired. In this study, we simultaneously overexpressed two key sialylated-based enzymes human β-galactoside α(2,6) sialyltransferase I and UDP-GlcNAc 2-epimerase/ManNAc kinase to achieve greater sialylation pattern produced host cells. The single-cell line thus-generated produced an approximately 41.6% higher level of total free sialic acid, and the glycan profiles showed a significant increase of more than 7-fold in the relative amount of total sialylated N-glycan as compared to the wild-type. These results demonstrated that co-expression of these two sialylated-based key enzymes yielded a cell line that effectively produced glycoproteins with superior sialylation and achievable human-like glycoforms.

Controlling the Glycosylation Profile in mAbs Using Time-Dependent Media Supplementation

In order to meet desired drug product quality targets, the glycosylation profile of biotherapeutics such as monoclonal antibodies (mAbs) must be maintained consistently during manufacturing. Achieving consistent glycan distribution profiles requires identifying factors that influence glycosylation, and manipulating them appropriately via well-designed control strategies. Now, the cell culture media supplement, MnCl2, is known to alter the glycosylation profile in mAbs generally, but its effect, particularly when introduced at different stages during cell growth, has yet to be investigated and quantified. In this study, we evaluate the effect of time-dependent addition of MnCl2 on the glycan profile quantitatively, using factorial design experiments. Our results show that MnCl2 addition during the lag and exponential phases affects the glycan profile significantly more than stationary phase supplementation does. Also, using a novel computational technique, we identify various combinations of glycan species that are affected by this dynamic media supplementation scheme, and quantify the effects mathematically. Our experiments demonstrate the importance of taking into consideration the time of addition of these trace supplements, not just their concentrations, and our computational analysis provides insight into what supplements to add, when, and how much, in order to induce desired changes.

Combining metabolic and process engineering strategies to improve recombinant glycoprotein production and quality

Increasing recombinant protein production while ensuring a high and consistent protein quality remains a challenge in mammalian cell culture process development. In this work, we combined a nutrient substitution approach with a metabolic engineering strategy that improves glucose utilization efficiency. This combination allowed us to tackle both lactate and ammonia accumulation and investigate on potential synergistic effects on protein production and quality. To this end, HEK293 cells overexpressing the pyruvate yeast carboxylase (PYC2) and their parental cells, both stably producing the therapeutic glycoprotein interferon α2b (IFNα2b), were cultured in media deprived of glutamine but containing chosen substitutes. Among the tested substitutes, pyruvate led to the best improvement in growth (integral of viable cell density) for both cell lines in batch cultures, whereas the culture of PYC2 cells without neither glutamine nor any substitute displayed surprisingly enhanced IFNα2b production. The drastic reduction in both lactate and ammonia in the cultures translated into extended high viability conditions and an increase in recombinant protein titer by up to 47% for the parental cells and the PYC2 cells. Product characterization performed by surface plasmon resonance biosensing using Sambucus nigra (SNA) lectin revealed that the increase in yield was however accompanied by a reduction in the degree of sialylation of the product. Supplementing cultures with glycosylation precursors and a cofactor were effective at counterbalancing the lack of glutamine and allowed improvement in IFNα2b quality as evaluated by lectin affinity. Our study provides a strategy to reconcile protein productivity and quality and highlights the advantages of PYC2-overexpressing cells in glutamine-free conditions.

A novel sugar analog enhances sialic acid production and biotherapeutic sialylation in CHO cells

A desirable feature of many therapeutic glycoprotein production processes is to maximize the final sialic acid content. In this study, the effect of applying a novel chemical analog of the sialic acid precursor N-acetylmannosamine (ManNAc) on the sialic acid content of cellular proteins and a model recombinant glycoprotein, erythropoietin (EPO), was investigated in CHO-K1 cells. By introducing the 1,3,4-O-Bu₃ ManNAc analog at 200-300 µM into cell culture media, the intracellular sialic acid content of EPO-expressing cells increased ∼8-fold over untreated controls while the level of cellular sialylated glycoconjugates increased significantly as well. For example, addition of 200-300 µM 1,3,4-O-Bu₃ ManNAc resulted in >40% increase in final sialic acid content of recombinant EPO, while natural ManNAc at ∼100 times higher concentration of 20 mM produced a less profound change in EPO sialylation. Collectively, these results indicate that butyrate-derivatization of ManNAc improves the capacity of cells to incorporate exogenous ManNAc into the sialic acid biosynthetic pathway and thereby increase sialylation of recombinant EPO and other glycoproteins. This study establishes 1,3,4-O-Bu₃ ManNAc as a novel chemical supplement to improve glycoprotein quality and sialylation levels at concentrations orders of magnitude lower than alternative approaches. Biotechnol. Bioeng. 2017;114: 1899-1902. © 2017 Wiley Periodicals, Inc.

Main Quality Attributes of Monoclonal Antibodies and Effect of Cell Culture Components

The culture media optimization is an inevitable part of upstream process development in therapeutic monoclonal antibodies (mAbs) production. The quality by design (QbD) approach defines the assured quality of the final product through the development stage. An important step in QbD is determination of the main quality attributes. During the media optimization, some of the main quality attributes such as glycosylation pattern, charge variants, aggregates, and low-molecular-weight species, could be significantly altered. Here, we provide an overview of how cell culture medium components affects the main quality attributes of the mAbs. Knowing the relationship between the culture media components and the main quality attributes could be successfully utilized for a rational optimization of mammalian cell culture media for industrial mAbs production.

Understanding of decreased sialylation of Fc-fusion protein in hyperosmotic recombinant Chinese hamster ovary cell culture: N-glycosylation gene expression and N-linked glycan antennary profile

To understand the effects of hyperosmolality on protein glycosylation, recombinant Chinese hamster ovary (rCHO) cells producing the Fc-fusion protein were cultivated in hyperosmolar medium resulting from adding NaCl (415 mOsm/kg). The hyperosmotic culture showed increased specific Fc-fusion protein productivity (q_Fc ) but a decreased proportion of acidic isoforms and sialic acid content of the Fc-fusion protein. The intracellular and extracellular sialidase activities in the hyperosmotic cultures were similar to those in the control culture (314 mOsm/kg), indicating that reduced sialylation of Fc-fusion protein at hyperosmolality was not due to elevated sialidase activity. Expression of 52 N-glycosylation-related genes was assessed by the NanoString nCounter system, which provides a direct digital readout using custom-designed color-coded probes. After 3 days of hyperosmotic culture, nine genes (ugp, slc35a3, slc35d2, gcs1, manea, mgat2, mgat5b, b4galt3, and b4galt4) were differentially expressed over 1.5-fold of the control, and all these genes were down-regulated. N-linked glycan analysis by anion exchange and hydrophilic interaction HPLC showed that the proportion of highly sialylated (di-, tri-, tetra-) and tetra-antennary N-linked glycans was significantly decreased upon hyperosmotic culture. Addition of betaine, an osmoprotectant, to the hyperosmotic culture significantly increased the proportion of highly sialylated and tetra-antennary N-linked glycans (P ≤ 0.05), while it increased the expression of the N-glycan branching/antennary genes (mgat2 and mgat4b). Thus, decreased expression of the genes with roles in the N-glycan biosynthesis pathway correlated with reduced sialic acid content of Fc-fusion protein caused by hyperosmolar conditions. Taken together, the results obtained in this study provide a better understanding of the detrimental effects of hyperosmolality on N-glycosylation, especially sialylation, in rCHO cells. Biotechnol. Bioeng. 2017;114: 1721-1732. © 2017 Wiley Periodicals, Inc.