Culture pH affects expression rates and glycosylation of recombinant mouse placental lactogen proteins by Chinese hamster ovary (CHO) cells

A novel approach to noninvasive monitoring of dissolved carbon dioxide in small-scale cell culture processes

Disposable small-scale vessels are commonly used in cell culture studies in academia as well as early stages of bioprocess development. These types of research are crucial for our understanding about cells and bioprocesses as they provide important information regarding different parameters affecting cells. Dissolved carbon dioxide (DCO₂) is one main parameter affecting cell metabolism. It is also an indicator of cell culture well-being. Despite CO₂ being a critical process parameter, there is a lack of appropriate monitoring system for CO₂ in small-scale vessels. Here, we present a membrane-based noninvasive method for measuring DCO₂ in cell culture medium. The idea was achieved by modifying a T-flask and replacing a small area of it with CO₂ permeable silicone membrane. In the proposed method, the concentration of CO₂ dissolved in the cell culture medium is determined by measuring the initial diffusion rate of CO₂ through a silicone membrane attached to the bottom wall of the T-flask. The measurement method was validated previously, and the efficacy of the noninvasive method was evaluated by growing E.coli, Pichia pastoris, and CHO cells in the proposed prototype. The results obtained from this method were verified with other quantitative data obtained from the process such as optical density (OD), cell density, dissolved oxygen (DO) and pH. The results show that the proposed membrane-based method is an effective way for completely noninvasive monitoring of DCO₂ in small-scale cell culture processes. Additional diffusing species such as oxygen could also be measured using the same approach.

Sialic Acid Conjugated Chitosan Nanoparticles: Modulation to Target Tumour Cells and Therapeutic Opportunities

Targeted delivery of therapeutics forestalls the dreadful delocalized effects, drug toxicities and needless immunosuppression. Cancer cells are bounteous with sialic acid and the differential expression of glycosyl transferase, glycosidase and monosaccharide transporter compared to healthy tissues. The current study entails the development and characterisation of sialic acid (SA)-labelled chitosan nanoparticles encapsulating gemcitabine (GEM). Chitosan (CS) was conjugated with SA using coupling reaction and characterised spectroscopically. Furthermore, different concentrations of chitosan and tripolyphosphate (TPP) were optimised to fabricate surface modified chitosan nanoparticles. SA conjugated chitosan nanoparticles encapsulating GEM (SA-CS_GEM NPs) of 232 ± 9.69 nm with narrow distribution (PDI < 0.5) and zeta potential of - 19 ± 0.97 mV was fabricated. GEM was successfully loaded in the SA-CS NPs, depicting prolonged and biphasic drug release pattern more elated at low pH. Pronounced cellular uptake (FITC tagged) and cytotoxicity (IC₅₀ 487.4 nM) was observed in SA-CS_GEM NPs against A549 cells. IC₅₀ for SA-CS_GEM NPs plunged with an increase in the time points from 24 to 72 h. Concentration-dependent haemolytic study confirmed significant haemocompatibility of SA-CS_GEM NPs. Pharmacokinetic study was performed on Sprague-Dawley rats and the kinetic parameters were calculated using PKSolver 2.0. Results demonstrated a consequential refinement of 2.98 times in modified SA-CS_GEM NPs with a significant increase in retention time, bioavailability and elimination half-life, and decrease in elimination rate constant and volume of distribution in comparison to CS_GEM NPs. Therefore, SA-CS shell core nanoparticles could be a beneficial approach to target and treat NSCLC (non-small cell lung cancer) and direct for research possibilities to target the other tumour cells.

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.

A Reliable Automated Sampling System for On-Line and Real-Time Monitoring of CHO Cultures

Timely monitoring and control of critical process parameters and product attributes are still the basic tasks in bioprocess development. The current trend of automation and digitization in bioprocess technology targets an improvement of these tasks by reducing human error and increasing through-put. The gaps in such automation procedures are still the sampling procedure, sample preparation, sample transfer to analyzers, and the alignment of process and sample data. In this study, an automated sampling system and the respective data management software were evaluated for system performance; applicability with HPLC for measurement of vitamins, product and amino acids; and applicability with a biochemical analyzer. The focus was especially directed towards the adaptation and assessment of an appropriate amino acid method, as these substances are critical in cell culture processes. Application of automated sampling in a CHO fed-batch revealed its potential with regard to data evaluation. The higher sampling frequency compared to manual sampling increases the generated information content, which allows easier interpretation of the metabolism, extraction of e.g., ks values, application of smoothing algorithms, and more accurate detection of process events. A comparison with sensor technology shows the advantages and disadvantages in terms of measurement errors and measurement frequency.

Development of a pre-glycoengineered CHO-K1 host cell line for the expression of antibodies with enhanced Fc mediated effector function

Novel biotherapeutic glycoproteins, like recombinant monoclonal antibodies (mAbs) are widely used for the treatment of numerous diseases. The N-glycans attached to the constant region of an antibody have been demonstrated to be crucial for the biological efficacy. Even minor modifications of the N-glycan structure can dictate the potency of IgG effector functions such as the antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC).

Here, we present the development of a glycoengineered CHO-K1 host cell line (HCL), stably expressing β1,4-N-Acetylglucoseaminyltransferase III (GnT-III) and α-mannosidase II (Man-II), for the expression of a-fucosylated antibodies with enhanced Fc-mediated effector function. Glycoengineered HCLs were generated in a two-step strategy, starting with generating parental HCLs by stable transfection of CHO-K1 cells with GnT-III and Man-II. In a second step, parental HCLs were stably transfected a second time with these two transgenes to increase their copy number in the genetic background. Generated glycoengineered CHO-K1 cell lines expressing two different mAbs deliver antibody products with a content of more than 60% a-fucosylated glycans. In-depth analysis of the N-glycan structure revealed that the majority of the Fc-attached glycans of the obtained mAbs were of complex bisected type. Furthermore, we showed the efficient use of FcγRIIIa affinity chromatography as a novel method for the fast assessment of the mAbs a-fucosylation level. By testing different cultivation conditions for the pre-glycoengineered recombinant CHO-K1 clones, we identified key components essential for the production of a-fucosylated mAbs. The prevalent effect could be attributed to the trace element manganese, which leads to a strong increase of a-fucosylated complex- and hybrid-type glycans. In conclusion, the novel pre-glycoengineered CHO-K1 HCL can be used for the production of antibodies with high ratios of a-fucosylated Fc-attached N-glycans. Application of our newly developed FcγRIIIa affinity chromatography method during cell line development and use of optimized cultivation conditions can ultimately support the efficient development of a-fucosylated mAbs.

Advanced multivariate data analysis to determine the root cause of trisulfide bond formation in a novel antibody-peptide fusion

Product quality heterogeneities, such as a trisulfide bond (TSB) formation, can be influenced by multiple interacting process parameters. Identifying their root cause is a major challenge in biopharmaceutical production. To address this issue, this paper describes the novel application of advanced multivariate data analysis (MVDA) techniques to identify the process parameters influencing TSB formation in a novel recombinant antibody-peptide fusion expressed in mammalian cell culture. The screening dataset was generated with a high-throughput (HT) micro-bioreactor system (AmbrTM 15) using a design of experiments (DoE) approach. The complex dataset was firstly analyzed through the development of a multiple linear regression model focusing solely on the DoE inputs and identified the temperature, pH and initial nutrient feed day as important process parameters influencing this quality attribute. To further scrutinize the dataset, a partial least squares model was subsequently built incorporating both on-line and off-line process parameters and enabled accurate predictions of the TSB concentration at harvest. Process parameters identified by the models to promote and suppress TSB formation were implemented on five 7 L bioreactors and the resultant TSB concentrations were comparable to the model predictions. This study demonstrates the ability of MVDA to enable predictions of the key performance drivers influencing TSB formation that are valid also upon scale-up. Biotechnol. Bioeng. 2017;114: 2222-2234. © 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Investigation of O-glycosylation heterogeneity of recombinant coagulation factor IX using LC–MS/MS

Aim: Recombinant coagulation factor IX (rFIX) has extraordinarily multiple post-translational modifications including N-glycosylation and O-glycosylation which have a drastic effect on biological functions and in vivo recovery. Unlike N-glycosylation extensively characterized, there are a few studies on O-glycosylation due to its intrinsic complexity. In-depth O-glycosylation analysis is necessary to better understand and assess pharmacological activity of rFIX. Results: We determined unusual O-glycosylations including O-fucosylation and O-glucosylation which were located at Serine 53 and 61, respectively in EGF domain. Other O-glycosylations bearing core 1 glycan moiety were found on activation peptide. Conclusion: This is the first comprehensive study to characterize O-glycosylation of rFIX using MS-based glycomic and glycoproteomic approaches. Site-specific profiling will be a powerful platform to determine bioequivalence of biosimilars.

Engineer Medium and Feed for Modulating N-Glycosylation of Recombinant Protein Production in CHO Cell Culture

Chinese hamster ovary (CHO) cells have become the primary expression system for the production of complex recombinant proteins due to their long-term success in industrial scale production and generating appropriate protein N-glycans similar to that of humans. Control and optimization of protein N-glycosylation is crucial, as the structure of N-glycans can largely influence both biological and physicochemical properties of recombinant proteins. Protein N-glycosylation in CHO cell culture can be controlled and tuned by engineering medium, feed, culture process, as well as genetic elements of the cell. In this chapter, we will focus on how to carry out experiments for N-glycosylation modulation through medium and feed optimization. The workflow and typical methods involved in the experiment process will be presented.

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

Controlled feeding of glucose has been employed previously to enhance the productivity of recombinant glycoproteins but there is a concern that low concentrations of glucose could limit the synthesis of precursors of glycosylation. Here we investigate the effect of glucose depletion on the metabolism, productivity and glycosylation of a chimeric human-llama monoclonal antibody secreted by CHO cells. The cells were inoculated into media containing varying concentrations of glucose. Glucose depletion occurred in cultures with an initial glucose ≤5.5 mM and seeded at low density (2.5 × 10(5) cells/mL) or at high cell inoculum (≥2.5 × 10(6) cells/mL) at higher glucose concentration (up to 25 mM). Glucose-depleted cultures produced non-glycosylated Mabs (up to 51%), lower galactosylation index (GI <0.43) and decreased sialylation (by 85%) as measured by mass spectrometry and HPLC. At low glucose a reduced intracellular pool of nucleotides (0.03-0.23 fmoles/cell) was measured as well as a low adenylate energy charge (<0.57). Low glucose also reduced GDP-sugars (by 77%) and UDP-hexosamines (by 90%). The data indicate that under glucose deprivation, low levels of intracellular nucleotides and nucleotide sugars reduced the availability of the immediate precursors of glycosylation. These results are important when applied to the design of fed-batch cultures.

Cyclin and DNA distributed cell cycle model for GS-NS0 cells

Mammalian cell cultures are intrinsically heterogeneous at different scales (molecular to bioreactor). The cell cycle is at the centre of capturing heterogeneity since it plays a critical role in the growth, death, and productivity of mammalian cell cultures. Current cell cycle models use biological variables (mass/volume/age) that are non-mechanistic, and difficult to experimentally determine, to describe cell cycle transition and capture culture heterogeneity. To address this problem, cyclins-key molecules that regulate cell cycle transition-have been utilized. Herein, a novel integrated experimental-modelling platform is presented whereby experimental quantification of key cell cycle metrics (cell cycle timings, cell cycle fractions, and cyclin expression determined by flow cytometry) is used to develop a cyclin and DNA distributed model for the industrially relevant cell line, GS-NS0. Cyclins/DNA synthesis rates were linked to stimulatory/inhibitory factors in the culture medium, which ultimately affect cell growth. Cell antibody productivity was characterized using cell cycle-specific production rates. The solution method delivered fast computational time that renders the model's use suitable for model-based applications. Model structure was studied by global sensitivity analysis (GSA), which identified parameters with a significant effect on the model output, followed by re-estimation of its significant parameters from a control set of batch experiments. A good model fit to the experimental data, both at the cell cycle and viable cell density levels, was observed. The cell population heterogeneity of disturbed (after cell arrest) and undisturbed cell growth was captured proving the versatility of the modelling approach. Cell cycle models able to capture population heterogeneity facilitate in depth understanding of these complex systems and enable systematic formulation of culture strategies to improve growth and productivity. It is envisaged that this modelling approach will pave the model-based development of industrial cell lines and clinical studies.

Effects of nutrient levels and average culture pH on the glycosylation pattern of camelid-humanized monoclonal antibody

The impact of operating conditions on the glycosylation pattern of humanized camelid monoclonal antibody, EG2-hFc produced by Chinese hamster ovary (CHO) cells has been evaluated by a combination of experiments and modeling. Cells were cultivated under different levels of glucose and glutamine concentrations with the goal of investigating the effect of nutrient depletion levels and ammonia build up on the cell growth and the glycoprofiles of the monoclonal antibody (Mab). The effect of average pH reduction on glycosylation level during the entire culture time or during a specific time span was also investigated. The relative abundance of glycan structures was quantified by hydrophilic interaction liquid chromatography (HILIC) and the galactosylation index (GI) and the sialylation index (SI) were determined. Lower initial concentrations of glutamine resulted in lower glucose consumption and lower cell yield but increased GI and SI levels when compared to cultures started with higher initial glutamine levels. Similarly, reducing the average pH of culture resulted in lower growth but higher SI and GI levels. These findings indicate that there is a tradeoff between cell growth, resulting Mab productivity and the achievement of desirable higher glycosylation levels. A dynamic model, based on a metabolic flux analysis (MFA), is proposed to describe the metabolism of nutrients, cell growth and Mab productivity. Finally, existing software (GLYCOVIS) that describes the glycosylation pathways was used to illustrate the impact of extracellular species on the glycoprofiles.

Control of galactosylated glycoforms distribution in cell culture system

Cell culture process conditions including media components and bioreactor operation conditions have a profound impact on recombinant protein quality attributes. Considerable changes in the distribution of galactosylated glycoforms (G0F, G1F, and G2F) were observed across multiple CHO derived recombinant proteins in development at Eli Lilly and Company when switching to a new chemically defined (CD) media platform condition. In the new CD platform, significantly lower G0F percentages and higher G1F and G2F were observed. These changes were of interest as glycosylation heterogeneity can impact the effectiveness of a protein. A systematic investigation was done to understand the root cause of the change and control strategy for galactosylated glycoforms distribution. It was found that changes in asparagine concentration could result in a corresponding change in G0F, G1F, and G2F distribution. A follow-up study examined a wider range of asparagine concentration and it was found that G0F, G1F, and G2F percentage could be titrated by adjusting asparagine concentration. The observed changes in heterogeneity from changing asparagine concentration are due to resulting changes in ammonium metabolism. Further study ascertained that different integrated ammonium level during the cell culture process could control G0F, G1F, and G2F percentage distribution. A mechanism hypothesis is proposed that integrated ammonium level impacts intracellular pH, which further regulates β-1, 4 galactosyltransferase activity.

The availability of glucose to CHO cells affects the intracellular lipid-linked oligosaccharide distribution, site occupancy and the N-glycosylation profile of a monoclonal antibody

The glycosylation pattern of a chimeric heavy chain antibody (EG2) produced from CHO cells was affected by the glucose concentration (0-25mM) of cultures established at high density (>10(6)ml(-1)) over 24h. The resulting proportion of non-glycosylated Mab was directly correlated to the exposure time of cells to media depleted of glucose. Deprivation of glucose for the full 24h resulted in a 45% non-glycosylated Mab fraction. Analysis of steady state levels of intracellular lipid-linked oligosaccharides (LLOs) showed that under glucose limitation there was a reduction in the amount of full length LLO (Glc3Man9GlcNac2), with a concomitant increase in the smaller mannosyl-glycans (Man2-5GlcNAc2). Glycan microheterogeneity was quantified by galactosylation and sialylation indices (GI and SI) which showed a direct correlation to the cell specific glucose uptake. The GI increased to 0.83 following media supplementation with a cocktail of uridine, manganese and galactose. This is significantly higher than for a fully humanized antibody (DP12) produced under the similar conditions or for similar antibodies reported in the literature. The high GI of the chimeric antibody (EG2) may be due to its low molecular weight and unusual structure. These findings are important in relation to the low substrate that may occur in fed-batch cultures for Mab production.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

Application of a nonradioactive method of measuring protein synthesis in industrially relevant Chinese hamster ovary cells

Due to the high medical and commercial value of recombinant proteins for clinical and diagnostic purposes, the protein synthesis machinery of mammalian host cells is the subject of extensive research by the biopharmaceutical industry. RNA translation and protein synthesis are steps that may determine the extent of growth and productivity of host cells. To address the problems of utilization of current radioisotope methods with proprietary media, we have focused on the application of an alternative method of measuring protein synthesis in recombinant Chinese hamster ovary (CHO) cells. This method employs puromycin as a nonradioactive label which incorporates into nascent polypeptide chains and is detectable by western blotting. This method, which is referred to as SUnSET, successfully demonstrated the expected changes in protein synthesis in conditions that inhibit and restore translation activity and was reproducibly quantifiable. The study of the effects of feed and sodium butyrate addition on protein synthesis by SUnSET revealed an increase following 1 h feed supplementation while a high concentration of sodium butyrate was able to decrease translation during the same treatment period. Finally, SUnSET was used to compare protein synthesis activity during batch culture of the CHO cell line in relation to growth. The results indicate that as the cells approached the end of batch culture, the global rate of protein synthesis declined in parallel with the decreasing growth rate. In conclusion, this method can be used as a "snapshot" to directly monitor the effects of different culture conditions and treatments on translation in recombinant host cells.

Effect of culture temperature on a recombinant CHO cell line producing a C-terminal α-amidating enzyme

In order to seek an efficient method for producing a recombinant protein by using animal cell culture, we investigated various effects of the culture temperature on a recombinant CHO cell line (3µ-1S), producing a C-terminal α-amidating enzyme (799BglIIα-AE) originating from Xenopus laevis. The results revealed that a low culture temperature (below 37 °C) led to the following phenomena: [1] inhibited cell growth, [2] enhanced cellular productivity of the recombinant protein, [3] maintained high cell viability, [4] suppressed medium consumption, and [5] suppressed release of impurities from the cells. These findings indicate that a quite simple method, the culture at low temperature, will contribute to the total improvement of the industrial process for the production of the recombinant protein, 799BglIIα-AE.

Synergizing metabolic flux analysis and nucleotide sugar metabolism to understand the control of glycosylation of recombinant protein in CHO cells

BACKGROUND

The glycosylation of recombinant proteins can be altered by a range of parameters including cellular metabolism, metabolic flux and the efficiency of the glycosylation process. We present an experimental set-up that allows determination of these key processes associated with the control of N-linked glycosylation of recombinant proteins.

RESULTS

Chinese hamster ovary cells (CHO) were cultivated in shake flasks at 0 mM glutamine and displayed a reduced growth rate, glucose metabolism and a slower decrease in pH, when compared to other glutamine-supplemented cultures. The N-linked glycosylation of recombinant human chorionic gonadotrophin (HCG) was also altered under these conditions; the sialylation, fucosylation and antennarity decreased, while the proportion of neutral structures increased. A continuous culture set-up was subsequently used to understand the control of HCG glycosylation in the presence of varied glutamine concentrations; when glycolytic flux was reduced in the absence of glutamine, the glycosylation changes that were observed in shake flask culture were similarly detected. The intracellular content of UDP-GlcNAc was also reduced, which correlated with a decrease in sialylation and antennarity of the N-linked glycans attached to HCG.

CONCLUSIONS

The use of metabolic flux analysis illustrated a case of steady state multiplicity, where use of the same operating conditions at each steady state resulted in altered flux through glycolysis and the TCA cycle. This study clearly demonstrated that the control of glycoprotein microheterogeneity may be examined by use of a continuous culture system, metabolic flux analysis and assay of intracellular nucleotides. This system advances our knowledge of the relationship between metabolic flux and the glycosylation of biotherapeutics in CHO cells and will be of benefit to the bioprocessing industry.

Enhanced erythropoietin heterogeneity in a CHO culture is caused by proteolytic degradation and can be eliminated by a high glutamine level

The molecular heterogeneity of recombinant humanerythropoietin (EPO) increased during the course of abatch culture of transfected Chinese hamster ovary(CHO) cells grown in serum-free medium. This wasshown by both an increased molecular weight and pIrange of the isolated EPO at the end of the culture. However, analysis of the N-glycan structures of themolecule by fluorophore-assisted carbohydrateelectrophoresis (FACE) and HPLC anion exchangechromatography indicated a consistent pattern ofglycosylation. Seven glycoforms were identified, thepredominant structure being a fully sialylatedtetra-antennary glycan. The degree of sialylationwas maintained throughout the culture. Analysis ofthe secreted EPO indicated a time-dependent increasein the molecular weight band width of the peptideconsistent with proteolytic degradation. A highglutamine concentration (16-20 mM) in the culturedecreased the apparent degradation of the EPO.

Effects of culture temperature and pH on flag-tagged COMP angiopoietin-1 (FCA1) production from recombinant CHO cells: FCA1 aggregation

To maximize the production of flag-tagged cartilage oligomeric matrix protein angiopoietin-1 (FCA1) from Chinese hamster ovary (CHO) cells, the effects of culture pH and temperature on cell growth and FCA1 production were investigated. Cells were cultivated in a bioreactor at different culture pH (6.7, 6.9, 7.2, and 7.5) and temperatures (33 and 37 °C). Lowering the culture temperature suppressed cell growth while allowing maintenance of high cell viability for a longer culture period. The specific FCA1 productivity (q (FCA1)) was increased at low culture temperature. Accordingly, the highest FCA1 concentration was obtained at pH 7.2 and 33 °C, and was approximately 4.0-fold higher than that at pH 7.2 and 37 °C. However, aggregates and a monomeric form of FCA1, which are undesirable due to reduced biological activity or immunogenicity, were significant at pH 7.2 and 33 °C. It was also found that the expression pattern of FCA1 was affected more significantly by culture pH than by the culture temperature. FCA1 aggregation dramatically decreased at culture pH 7.5 regardless of the culture temperature. Furthermore, the monomeric form of FCA1 was not observed. Taken together, optimization of culture temperature and culture pH (33 °C and pH 7.5) significantly improves the production of biologically active FCA1 with tetrameric or pentameric forms from CHO cells.

Effect of surfactant pluronic F-68 on CHO cell growth, metabolism, production, and glycosylation of human recombinant IFN-γ in mild operating conditions

The control of glycosylation to satisfy regulatory requirements and quality consistency of recombinant proteins produced by different processes has become an important issue. With two N-glycosylation sites, γ-interferon (IFN-γ) can be seen as a prototype of a recombinant therapeutic glycoprotein for this purpose. The effect of the nonionic surfactant Pluronic F-68 (PF-68) on cell growth and death was investigated, as well as production and glycosylation of recombinant IFN-γ produced by a CHO cell line that was maintained in a rich protein-free medium in the absence or presence of low agitation. Under these conditions, a dose-dependent effect of PF-68 (0-0.1%) was shown not only to significantly enhance growth but also to reduce cell lysis. Interestingly, supplementing the culture medium with PF-68 led to increased IFN-γ production as a result of both higher cell densities and a higher specific production rate of IFN-γ. If cells were grown with agitation, lack of PF-68 in the culture medium decreased the fraction of the fully glycosylated IFN-γ glycoform (2N) from 80% to 65-70% during the initial period. This effect appeared to be due to a lag phase in cell growth observed during this period. Finally, a global kinetic study of CHO cell metabolism indicated higher efficiency in the utilization of the two major carbon substrates when cultures were supplemented with PF-68. Therefore, these results highlight the importance of understanding how media surfactant can affect cell growth as well as cell death and the product quality of a recombinant glycoprotein expressed in CHO cell cultures.

Comparisons of optically monitored small-scale stirred tank vessels to optically controlled disposable bag bioreactors

Background

Upstream bioprocesses are extremely complex since living organisms are used to generate active pharmaceutical ingredients (APIs). Cells in culture behave uniquely in response to their environment, thus culture conditions must be precisely defined and controlled in order for productivity and product quality to be reproducible. Thus, development culturing platforms are needed where many experiments can be carried out at once and pertinent scale-up information can be obtained.

Results

Here we have tested a High Throughput Bioreactor (HTBR) as a scale-down model for a lab-scale wave-type bioreactor (CultiBag). Mass transfer was characterized in both systems and scaling based on volumetric oxygen mass transfer coefficient (k_La) was sufficient to give similar DO trends. HTBR and CultiBag cell growth and mAb production were highly comparable in the first experiment where DO and pH were allowed to vary freely. In the second experiment, growth and mAb production rates were lower in the HTBR as compared to the CultiBag, where pH was controlled. The differences in magnitude were not considered significant for biological systems.

Conclusion

Similar oxygen delivery rates were achieved in both systems, leading to comparable culture performance (growth and mAb production) across scales and mode of mixing. HTBR model was most fitting when neither system was pH-controlled, providing an information-rich alternative to typically non-monitored mL-scale platforms.

Mass spectrometric quantification of neutral and sialylated N-glycans from a recombinant therapeutic glycoprotein produced in the two Chinese hamster ovary cell lines

Quality control and assurance of glycan profiles of a recombinant glycoprotein from lot to lot is a critical issue in the pharmaceutical industry. To develop an easy and simple quantitative and qualitative glycan profile method based on matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), the modification with Girard's reagent T (GT) was exploited. Because GT-derivatized quantification of oligosaccharides using MALDI-TOF MS is possible only with neutral glycans, sialylated glycans are not subjected to quantitative analysis with MALDI-TOF MS. To solve this problem, mild methyl esterification and subsequent GT derivatization were employed, enabling us to perform rapid qualitative and quantitative analysis of sialylated and neutral N-linked oligosaccharides using MALDI-TOF MS. This modified method was used in the comparative quantification of N-glycans from the recombinant therapeutic glycoprotein expressed in two different Chinese hamster ovary (CHO) cell lines. The percentages of sialylated N-glycans to total were 22.5 and 5.2% in CHO-I and CHO-II cells, respectively, resulting in a significant difference in the biological activity of the recombinant glycoprotein.

GDP-mannose pyrophosphorylase is a genetic determinant of ammonium sensitivity in Arabidopsis thaliana

Higher plant species differ widely in their growth responses to ammonium (NH(4)(+)). However, the molecular genetic mechanisms underlying NH(4)(+) sensitivity in plants remain unknown. Here, we report that mutations in the Arabidopsis gene encoding GDP-mannose pyrophosphorylase (GMPase) essential for synthesizing GDP-mannose confer hypersensitivity to NH(4)(+). The in planta activities of WT and mutant GMPases all were inhibited by NH(4)(+), but the magnitude of the inhibition was significantly larger in the mutant. Despite the involvement of GDP-mannose in both l-ascorbic acid (AsA) and N-glycoprotein biosynthesis, defective protein glycosylation in the roots, rather than decreased AsA content, was linked to the hypersensitivity of GMPase mutants to NH(4)(+). We conclude that NH(4)(+) inhibits GMPase activity and that the level of GMPase activity regulates Arabidopsis sensitivity to NH(4)(+). Further analysis showed that defective N-glycosylation of proteins, unfolded protein response, and cell death in the roots are likely important downstream molecular events involved in the growth inhibition of Arabidopsis by NH(4)(+).

Living with heterogeneities in bioreactors: understanding the effects of environmental gradients on cells

The presence of spatial gradients in fundamental culture parameters, such as dissolved gases, pH, concentration of substrates, and shear rate, among others, is an important problem that frequently occurs in large-scale bioreactors. This problem is caused by a deficient mixing that results from limitations inherent to traditional scale-up methods and practical constraints during large-scale bioreactor design and operation. When cultured in a heterogeneous environment, cells are continuously exposed to fluctuating conditions as they travel through the various zones of a bioreactor. Such fluctuations can affect cell metabolism, yields, and quality of the products of interest. In this review, the theoretical analyses that predict the existence of environmental gradients in bioreactors and their experimental confirmation are reviewed. The origins of gradients in common culture parameters and their effects on various organisms of biotechnological importance are discussed. In particular, studies based on the scale-down methodology, a convenient tool for assessing the effect of environmental heterogeneities, are surveyed.

Comparisons of optical pH and dissolved oxygen sensors with traditional electrochemical probes during mammalian cell culture

Small-scale upstream bioprocess development often occurs in flasks and multi-well plates. These culturing platforms are often not equipped to accurately monitor and control critical process parameters; thus they may not yield conditions representative of manufacturing. In response, we and others have developed optical sensors that enable small-scale process monitoring. Here we have compared two parameters critical to control in industrial cell culture, pH and dissolved oxygen (DO), measured with our optical sensors versus industrially accepted electrochemical probes. For both optical sensors, agreement with the corresponding electrochemical probe was excellent. The Pearson Correlations between the optical sensors and electrochemical probes were 98.7% and 99.7%, for DO and pH, respectively. Also, we have compared optical pH sensor performance in regular (320 mOsm/kg) and high-osmolality (450 mOsm/kg) cell culture media to simulate the increase in osmolality in pH-controlled cultures. Over a pH range of 6.38-7.98 the average difference in pH readings in the two media was 0.04 pH units. In summary, we have demonstrated that these optical sensors agree well with standard electrochemical probes. The accuracy of the optical probes demonstrates their ability to detect potential parameter drift that could have significant impact on growth, production kinetics, and protein product quality. We have also shown that an increase in osmolality that could result from controlling pH or operating the reactor in fed-batch mode has an insignificant impact on the functionality of the pH patches.

Down-regulation of cold-inducible RNA-binding protein does not improve hypothermic growth of Chinese hamster ovary cells producing erythropoietin

Discovery of the cold-inducible RNA-binding protein (CIRP) in mouse fibroblasts suggests that growth suppression at hypothermic conditions is due to an active response by the cell rather than due to passive thermal effects. To determine the effect of down-regulated CIRP expression on cell growth and erythropoietin (EPO) production in recombinant Chinese hamster ovary (rCHO) cells at low culture temperature, stable CHO cell clones with reduced CIRP expression level were established by transfecting (rCHO) cells with the CIRP siRNA vector with a target sequence of TCGTCCTTCCATGGCTGTA. For comparison of the degree of specific growth rate (micro) reduction at low culture temperature, three CIRP-reduced clones with different mu and three control clones transfected with null vector were cultivated at two different temperatures, 32 degrees C and 37 degrees C. Unlike mouse fibroblasts, alleviation of hypothermic growth arrest of rCHO cells by CIRP down-regulation was insignificant, as shown by statistical analysis using the t-test (P<0.18, n=3). The ratios of mu at 32 degrees C to micro at 37 degrees C of CIRP-reduced clones and control clones were 0.29+/-0.03 and 0.25+/-0.03 on an average, respectively. Furthermore, it was also found that overexpression of CIRP did not inhibit rCHO cell growth significantly at 37 degrees C. Taken together, the data obtained show that down-regulation of only CIRP in rCHO cells, unlike mouse fibroblasts, is not sufficient to recover growth arrest at low-temperature culture (32 degrees C).

Optimisation of the cellular metabolism of glycosylation for recombinant proteins produced by Mammalian cell systems

Many biopharmaceuticals are now produced as secreted glycoproteins from mammalian cell culture. The glycosylation profile of these proteins is essential to ensure structural stability and biological and clinical activity. However, the ability to control the glycosylation is limited by our understanding of the parameters that affect the heterogeneity of added glycan structures. It is clear that the glycosylation process is affected by a number of factors including the 3-dimensional structure of the protein, the enzyme repertoire of the host cell, the transit time in the Golgi and the availability of intracellular sugar-nucleotide donors. From a process development perspective there are many culture parameters that can be controlled to enable a consistent glycosylation profile to emerge from each batch culture. A further, but more difficult goal is to control the culture conditions to enable the enrichment of specific glycoforms identified with desirable biological activities. The purpose of this paper is to discuss the cellular metabolism associated with protein glycosylation and review the attempts to manipulate, control or engineer this metabolism to allow the expression of human glycosylation profiles in producer lines such as genetically engineered Chinese hamster ovary (CHO) cells.