Engineering of a mammalian cell line for reduction of lactate formation and high monoclonal antibody production

High-Titer Recombinant Adenovirus 26 Vector GMP Manufacturing in HEK 293 Cells with a Stirred Single-Use Bioreactor for COVID-19 Vaccination Purposes

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 virus) pandemic has shown the importance of pursuing various vaccine manufacturing strategies. In the present study, the HEK 293 cells were infected with recombinant adenovirus serotype 26 (rAd26), and the effects of critical process parameters (CPPs) including viable cell density (VCD) at infection time (0.5 × 106, 0.8 × 106, 1.4 × 106, 1.8 × 106, and 2.5 × 106 cells/mL), the multiplicity of infection (MOI) = 3, 6, 9, 12, and 15, and two aeration strategies (high-speed agitation with a sparging system and low-speed agitation with an overlay system) were investigated experimentally. The results of small-scale experiments in 2 L shake flasks (SF 2L) demonstrated that the initial VCD and MOI could affect the cell proliferation and viability. The results at these experiments showed that VCD = 1.4 × 106 cells/mL and MOI = 9 yielded TCID50 /mL = 108.9, at 72 h post-infection (hpi), while the virus titer at VCD = 0.5 × 106 and 0.8 × 106 cells/mL was lower compared to that of VCD = 1.4 × 106 cells/mL. Moreover, our findings showed that VCDs > 1.8 × 106 cells/m with MOI = 9 did not have a positive effect on TCID50 /mL and MOI = 3 and 6 were less efficient, whereas MOI > 12 decreased the viability drastically. In the next step, the optimized CPPs in a small scale were exploited in a 200 L single-use bioreactor (SUB), with good manufacturing practice (GMP) conditions, at RPM = 25 with an overlay system, yielding high-titer rAd26 manufacturing, i.e., TCID50/mL = 108.9, at 72 hpi.

Novel cell line development strategy for monoclonal antibody manufacturing using translational enhancing technology

Chinese hamster ovary (CHO) cells are widely used for constructing expression systems to produce therapeutic proteins. However, the establishment of high-producer clones remains a laborious and time-consuming process, despite various progresses having been made in cell line development. We previously developed a new strategy for screening high monoclonal antibody (mAb)-producing cells using flow cytometry (FCM). We also reported that p180 and SF3b4 play key roles in active translation on the endoplasmic reticulum, and that the productivity of secreted alkaline phosphatase was enhanced by the overexpression of p180 and SF3b4. Here, we attempted to apply the translational enhancing technology to high mAb-producing cells obtained after high-producer cell sorting. A high mAb-producing CHO clone, L003, which showed an mAb production level of >3 g/L in fed-batch culture, was established from a high mAb-producing cell pool fractionated by FCM. Clones generated by the overexpression of p180 and SF3b4 in L003 cells were evaluated by fed-batch culture. The specific productivity of clones overexpressing these two factors was ∼3.1-fold higher than that of parental L003 cells in the early phase of the culture period. Furthermore, the final mAb concentration was increased to 9.5 g/L during 17 days of fed-batch culture after optimizing the medium and culture process. These results indicate that the overexpression of p180 and SF3b4 would be promising for establishing high-producer cell lines applicable to industrial production.

Identification of novel inhibitory metabolites and impact verification on growth and protein synthesis in mammalian cells

Mammalian cells consume large amount of nutrients during growth and production. However, endogenous metabolic inefficiencies often prevent cells to fully utilize nutrients to support growth and protein production. Instead, significant fraction of fed nutrients is diverted into extracellular accumulation of waste by-products and metabolites, further inhibiting proliferation and protein synthesis. In this study, an LC-MS/MS based metabolomics pipeline was used to screen Chinese hamster ovary (CHO) extracellular metabolites. Six out of eight identified inhibitory metabolites, caused by the inefficient cell metabolism, were not previously studied in CHO cells: aconitic acid, 2-hydroxyisocaproic acid, methylsuccinic acid, cytidine monophosphate, trigonelline, and n-acetyl putrescine. When supplemented back into a fed-batch culture, significant reduction in cellular growth was observed in the presence of each metabolite and all the identified metabolites were shown to impact the glycosylation of a model secreted antibody, with seven of these also reducing CHO cellular productivity (titer) and all eight inhibiting the formation of mono-galactosylated biantennary (G1F) and biantennary galactosylated (G2F) N-glycans. These inhibitory metabolites further impact the metabolism of cells, leading to a significant reduction in CHO cellular growth and specific productivity in fed-batch culture (maximum reductions of 27.2% and 40.6% respectively). In-depth pathway analysis revealed that these metabolites are produced when cells utilize major energy sources such as glucose and select amino acids (tryptophan, arginine, isoleucine, and leucine) for growth, maintenance, and protein production. Furthermore, these novel inhibitory metabolites were observed to accumulate in multiple CHO cell lines (CHO–K1 and CHO-GS) as well as HEK293 cell line. This study provides a robust and holistic methodology to incorporate global metabolomic analysis into cell culture studies for elucidation and structural verification of novel metabolites that participate in key metabolic pathways to growth, production, and post-translational modification in biopharmaceutical production.

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Mammalian metabolic inefficiencies lead to accumulation of waste by-products.

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Untargeted and targeted metabolomics for identification of novel metabolites.

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Identified six CHO metabolic inhibitors negatively impact growth and titer production.

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Inhibitors were shown to accumulate across different mammalian cell lines.

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A holistic methodology incorporating metabolomics analysis into cell culture studies.

Preventing pyruvate kinase muscle expression in Chinese hamster ovary cells curbs lactogenic behavior by altering glycolysis, gating pyruvate generation, and increasing pyruvate flux into the TCA cycle

Deletion of the pyruvate kinase muscle (PKM) gene, which is involved in conversion of phosphoenolpyruvate to pyruvate, has been shown to curb lactogenic behavior in Chinese hamster ovary (CHO) cells. This study describes the generation of pyruvate kinase muscle isoforms 1 and 2 knockout (PKM-KO) and pyruvate kinase muscle isoform-1 knockout (PKM1-KO) CHO host cells to understand metabolic shifts that reduce lactate secretion in these cells. Glucose and amino acids uptake levels in wild-type (WT), PKM-KO, and PKM1-KO stable cell lines, expressing two different antibodies, were analyzed in 14-day fed-batch production assays using different vessels. PKM-KO and PKM1-KO cells consumed more glucose per cell, altered amino acids metabolism, had higher flux of pyruvate into the tricarboxylic acid (TCA) cycle, and as previously shown reduced lactate secretion levels compared with the WT cells. Additionally, both PKM-KO and PKM1-KO cells had higher specific productivity and lower cell growth rates compared with the WT cells. Our findings suggest that rewiring the flux of pyruvate to the TCA cycle by deletion of PKM or PKM1 reduced cell growth and increased specific productivity in CHO cells. Overall, PKM1-KO cells had similar product quality and comparable or better titers relative to the WT cells, hence, targeted deletion of this isoform for curbing lactogenic behavior in CHO cells is suggested.

Proteomic Profiling of IgG1 Producing CHO Cells Using LC/LC-SPS-MS3: The Effects of Bioprocessing Conditions on Productivity and Product Quality

The biopharmaceutical market is dominated by monoclonal antibodies, the majority of which are produced in Chinese hamster ovary (CHO) cell lines. Intense cell engineering, in combination with optimization of various process parameters results in increasing product titers. To enable further improvements in manufacturing processes, detailed information about how certain parameters affect cellular mechanisms in the production cells, and thereby also the expressed drug substance, is required. Therefore, in this study the effects of commonly applied changes in bioprocessing parameters on an anti-IL8 IgG1 producing CHO DP-12 cell line were investigated on the level of host cell proteome expression combined with product quality assessment of the expressed IgG1 monoclonal antibody. Applying shifts in temperature, pH and dissolved oxygen concentration, respectively, resulted in altered productivity and product quality. Furthermore, analysis of the cells using two-dimensional liquid chromatography-mass spectrometry employing tandem mass tag based isotopic quantitation and synchronous precursor selection-MS³ detection revealed substantial changes in the protein expression profiles of CHO cells. Pathway analysis indicated that applied bioprocessing conditions resulted in differential activation of oxidative phosphorylation. Additionally, activation of ERK5 and TNFR1 signaling suggested an affected cell cycle. Moreover, in-depth product characterization by means of charge variant analysis, peptide mapping, as well as structural and functional analysis, revealed posttranslational and structural changes in the expressed drug substance. Taken together, the present study allows the conclusion that, in anti-IL8 IgG1 producing CHO DP-12 cells, an improved energy metabolism achieved by lowering the cell culture pH is favorable when aiming towards high antibody production rates while maintaining product quality.

Hepatocytes and Endothelial Networks in a Fluid-Based In Vitro Model of Liver Drug Metabolism

Drug-induced liver toxicity remains a major cause of drug withdrawal from animal testing and human clinical trials. A functional liver culture model corresponding to the liver is urgently required; however, in previous liver models, it has proven difficult to stably maintain multiple liver functions. Previously reported fluid-based systems have some advantages for hepatocyte culture, but have insufficient liver-specific functions because they simply involve moving conventional hepatocyte cultures from a dish into a fluid-based system. Importantly, these cultures have no liver tissue-specific structures that construct liver-specific cellular polarities, such as apical, basolateral, and basal faces. In this study, we developed a fluid-based system for our liver tissue culture models. The liver tissues that were constructed in our originally designed fluid-based systems represent a tissue culture model for studying hepatic functions. Together, our findings show that by mimicking the structure of the liver in the body, our system effectively maintains multiple liver-specific functions. Impact statement A functional liver culture model corresponding to the liver is urgently required; however, in previous liver models, it has proven difficult to stably maintain multiple liver functions. In this study, we developed a fluid-based system for our liver tissue culture models. The liver tissues that were constructed in our originally designed fluid-based systems represent a tissue culture model for studying hepatic functions. Together, our findings show that by mimicking the structure of the liver in the body, our system effectively maintains multiple liver-specific functions.

Optimization of recombinant Zika virus NS1 protein secretion from HEK293 cells

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Stable recombinant ZIKV NS1-His-expressing HEK293 cells were generated.

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Rapamycin treatment followed by serum starvation leads to a 29-fold increase in recombinant ZIKV NS1 protein secretion.

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The purified recombinant ZIKV NS1 hexamer is a reliable biological tool for clinical diagnosis and surveillance purposes.

Sensitive, accurate and cost-effective diagnostic tests are urgently needed to detect Zika virus (ZIKV) infection. Nonstructural 1 (NS1) glycoprotein is an excellent diagnostic marker since it is released in a hexameric conformation from infected cells into the patient's bloodstream early in the course of the infection. We established a stable rZNS1-His-expression system in HEK293 cells through lentiviral transduction. A novel optimization approach to enhance rZNS1-His protein secretion in the mammalian expression system was accomplished through 50 nM rapamycin incubation followed by serum-free media incubation for 9 days, reaching protein yields of ∼10 mg/l of culture medium. Purified rZNS1-His hexamer was recognized by anti-NS1 antibodies in ZIKV patient's serum, and showed the ability to induce a humoral response in immunized mice. The obtained recombinant protein is a reliable biological tool that can potentially be applied in the development of diagnostic tests to detect ZIKV in infected patients during the acute phase.

Kinetic model optimization and its application to mitigating the Warburg effect through multiple enzyme alterations

Pathway engineering is a powerful tool in biotechnological and clinical applications. However, many phenomena cannot be rewired with a single enzyme change, and in a complex network like energy metabolism, the selection of combinations of targets to engineer is a daunting task. To facilitate this process, we have developed an optimization framework and applied it to a mechanistic kinetic model of energy metabolism. We then identified combinations of enzyme alternations that led to the elimination of the Warburg effect seen in the metabolism of cancer cells and cell lines, a phenomenon coupling rapid proliferation to lactate production. Typically, optimization approaches use integer variables to achieve the desired flux redistribution with a minimum number of altered genes. This framework uses convex penalty terms to replace these integer variables and improve computational tractability. Optimal solutions are identified which substantially reduce or eliminate lactate production while maintaining the requirements for cellular proliferation using three or more enzymes.

Engineering CHO cells galactose metabolism to reduce lactate synthesis

OBJECTIVE

Over-express galactokinase (Galk1) in tissue plasminogen activator (tPA) producing CHO cells as a potential strategy to improve cell growth and product synthesis.

RESULTS

tPA producing CHO cells were transfected with the galactokinase (Galk1) gene. CHO-Galk1 cells showed a 39% increase of the specific growth rate in galactose. Moreover, clones were able to use this hexose as their main carbon source to sustain growth contrary to their parental cell line. Metabolic Flux Analysis revealed that the CHO-Galk1 selected clone shows an active metabolism towards biomass and product synthesis, characterized by higher fluxes in the TCA cycle, which is consistent with increased cellular densities and final product concentration.

CONCLUSION

This cellular engineering strategy, where modifications of key points of alternative carbon sources metabolism lead to an improved metabolism of these sugars, is a starting point towards the generation of new cell lines with reduced lactate synthesis and increased cell growth and productivity.

High glucose and low specific cell growth but not mild hypothermia improve specific r-protein productivity in chemostat culture of CHO cells

In the biopharmaceutical sector, Chinese hamster ovary (CHO) cells have become the host of choice to produce recombinant proteins (r-proteins) due to their capacity for correct protein folding, assembly, and posttranslational modification. However, the production of therapeutic r-proteins in CHO cells is expensive and presents insufficient production yields for certain proteins. Effective culture strategies to increase productivity (q_p) include a high glucose concentration in the medium and mild hypothermia (28–34 °C), but these changes lead to a reduced specific growth rate. To study the individual and combined impacts of glucose concentration, specific growth rate and mild hypothermia on culture performance and cell metabolism, we analyzed chemostat cultures of recombinant human tissue plasminogen activator (rh-tPA)-producing CHO cell lines fed with three glucose concentrations in feeding media (20, 30 and 40 mM), at two dilution rates (0.01 and 0.018 1/h) and two temperatures (33 and 37 °C). The results indicated significant changes in cell growth, cell cycle distribution, metabolism, and rh-tPA productivity in response to the varying environmental culture conditions. High glucose feed led to constrained cell growth, increased specific rh-tPA productivity and a higher number of cells in the G2/M phase. Low specific growth rate and temperature (33 °C) reduced glucose consumption and lactate production rates. Our findings indicated that a reduced specific growth rate coupled with high feed glucose significantly improves r-protein productivity in CHO cells. We also observed that low temperature significantly reduced q_p, but not cell growth when dilution rate was manipulated, regardless of the glucose concentration or dilution rate. In contrast, we determined that feed glucose concentration and consumption rate were the dominant aspects of the growth and productivity in CHO cells by using multivariate analysis.

Mechanisms driving the lactate switch in Chinese hamster ovary cells

The metabolism of Chinese Hamster Ovary (CHO) cells in a production environment has been extensively investigated. However, a key metabolic transition, the switch from lactate production to lactate consumption, remains enigmatic. Though commonly observed in CHO cultures, the mechanism(s) by which this metabolic shift is triggered is unknown. Despite this, efforts to control the switch have emerged due to the association of lactate consumption with improved cell growth and productivity. This review aims to consolidate current theories surrounding the lactate switch. The influence of pH, NAD⁺ /NADH, pyruvate availability and mitochondrial function on lactate consumption are explored. A hypothesis based on the cellular redox state is put forward to explain the onset of lactate consumption. Various techniques implemented to control the lactate switch, including manipulation of the culture environment, genetic engineering, and cell line selection are also discussed.

All-trans retinoic acid in combination with sodium butyrate enhances specific monoclonal antibody productivity in recombinant CHO cell line

The effects of all-trans retinoic acid (RA) and sodium butyrate (NaBu) on growth, viability and antibody production of two types of transfected Chinese hamster ovary cell lines (CHO-K1 and CHO-S) were investigated using a batch mode cell culture. By adding 0.5 mM NaBu in the CHO-K1 cell culture, the cell specific productivity (Q_p) and antibody concentration increased by five- and threefold, respectively. The optimal concentration of RA was 100 nM which resulted in twofold increase in antibody production. In a combination model, RA applied at early growth phase of CHO-K1 cells followed by addition of NaBu with lowering culture temperature at the end of stationary phase resulted in two- and threefold increase in Q_p and final antibody concentration, respectively. The latter strategy was also applied on suspended CHO-S cells with enhanced Q_p and antibody concentration, but to a lesser extent than the CHO-K1 cells. In conclusion, our results demonstrate that the addition of RA and NaBu along with lowering the culture temperature can increase cell culture period as well as Q_p and the final concentration of recombinant monoclonal antibody in both CHO-K1 and CHO-S cells without any significant change in binding affinity of the mAb.

Metabolic engineering of CHO cells for the development of a robust protein production platform

Chinese hamster ovary (CHO) cells are the most preferred mammalian host used for the bio-pharmaceutical production. A major challenge in metabolic engineering is to balance the flux of the tuned heterogonous metabolic pathway and achieve efficient metabolic response in a mammalian cellular system. Pyruvate carboxylase is an important network element for the cytoplasmic and mitochondrial metabolic pathway and efficiently contributes in enhancing the energy metabolism. The lactate accumulation in cell culture can be reduced by re-wiring of the pyruvate flux in engineered cells. In the present work, we over-expressed the yeast cytosolic pyruvate carboxylase (PYC2) enzyme in CHO cells to augment pyruvate flux towards the TCA cycle. The dual selection strategy is adopted for the screening and isolation of CHO clones containing varying number of PYC2 gene load and studied their cellular kinetics. The enhanced PYC2 expression has led to enhanced pyruvate flux which, thus, allowed reduced lactate accumulation up to 4 folds and significant increase in the cell density and culture longevity. With this result, engineered cells have shown a significant enhanced antibody expression up to 70% with improved product quality (~3 fold) as compared to the parental cells. The PYC2 engineering allowed overall improved cell performance with various advantages over parent cells in terms of pyruvate, glucose, lactate and cellular energy metabolism. This study provides a potential expression platform for a bio-therapeutic protein production in a controlled culture environment.

Improvements in protein production in mammalian cells from targeted metabolic engineering

Bioprocess optimization has yielded powerful clones for biotherapeutic production. However, new genomic technologies allow more targeted approaches to cell line development. Here we review efforts to enhance protein production in mammalian cells through metabolic engineering. Most efforts aimed to reduce toxic byproducts accumulation to enhance protein productivity. However, recent work highlights the possibility of regulating other desirable traits (e.g., apoptosis and glycosylation) by targeting central metabolism since these processes are interconnected. Therefore, as we further detail the pathways underlying cell growth and protein production and deploy diverse algorithms for their analysis, opportunities will arise to move beyond simple cell line designs and facilitate cell engineering strategies with complex combinations of genes that together underlie a phenotype of interest.

Understanding central carbon metabolism of rapidly proliferating mammalian cells based on analysis of key enzymatic activities in GS-CHO cell lines

The central carbon metabolism (glycolysis, the pentose phosphate pathway [PPP], and the tricarboxylic acid [TCA] cycle) plays an essential role in the supply of biosynthetic precursors and energy. How the central carbon metabolism changes with the varying growth rates in the in vitro cultivation of rapidly proliferating mammalian cells, such as cancer cells and continuous cell lines for recombinant protein production, remains elusive. Based on relationships between the growth rate and the activity of seven key enzymes from six cell clones, this work reports finding an important metabolic characteristic in rapidly proliferating glutamine synthetase-Chinese hamster ovary cells. The key enzymatic activity involved in the TCA cycle that is responsible for the supply of energy became elevated as the growth rate exhibited increases, while the activity of key enzymes in metabolic pathways (glycolysis and the PPP), responsible for the supply of biosynthetic precursors, tended to decrease-suggesting that rapidly proliferating cells still depended predominantly on the TCA cycle rather than on aerobic glycolysis for their energetic demands. Meanwhile, the growth-limiting resource was most likely biosynthetic substrates rather than energy provision. In addition, the multifaceted role of glucose-6-phosphate isomerase (PGI) was confirmed, based on a significant correlation between PGI activity and the percentage of G2/M-phase cells.

Metabolic engineering of CHO cells to alter lactate metabolism during fed-batch cultures

Recombinant yeast pyruvate carboxylase (PYC2) expression was previously shown to be an effective metabolic engineering strategy for reducing lactate formation in a number of relevant mammalian cell lines, but, in the case of CHO cells, did not consistently lead to significant improvement in terms of cell growth, product titer and energy metabolism efficiency. In the present study, we report on the establishment of a PYC2-expressing CHO cell line producing a monoclonal antibody and displaying a significantly altered lactate metabolism compared to its parental line. All clones exhibiting strong PYC2 expression were shown to experience a significant and systematic metabolic shift toward lactate consumption, as well as a prolonged exponential growth phase leading to an increased maximum cell concentration and volumetric product titer. Of salient interest, PYC2-expressing CHO cells were shown to maintain a highly efficient metabolism in fed-batch cultures, even when exposed to high glucose levels, thereby alleviating the need of controlling nutrient at low levels and the potential negative impact of such strategy on product glycosylation. In bioreactor operated in fed-batch mode, the higher maximum cell density achieved with the PYC2 clone led to a net gain (20%) in final volumetric productivity.

Cell line development for biomanufacturing processes: recent advances and an outlook

At the core of a biomanufacturing process for recombinant proteins is the production cell line. It influences the productivity and product quality. Its characteristics also dictate process development, as the process is optimized to complement the producing cell to achieve the target productivity and quality. Advances in the past decade, from vector design to cell line screening, have greatly expanded our capability to attain producing cell lines with certain desired traits. Increasing availability of genomic and transcriptomic resources for industrially important cell lines coupled with advances in genome editing technology have opened new avenues for cell line development. These developments are poised to help biosimilar manufacturing, which requires targeting pre-defined product quality attributes, e.g., glycoform, to match the innovator's range. This review summarizes recent advances and discusses future possibilities in this area.

A quantitative proteomic analysis of cellular responses to high glucose media in Chinese hamster ovary cells

A goal in recombinant protein production using Chinese hamster ovary (CHO) cells is to achieve both high specific productivity and high cell density. Addition of glucose to the culture media is necessary to maintain both cell growth and viability. We varied the glucose concentration in the media from 5 to 16 g/L and found that although specific productivity of CHO-DG44 cells increased with the glucose level, the integrated viable cell density decreased. To examine the biological basis of these results, we conducted a discovery proteomic study of CHO-DG44 cells grown under batch conditions in normal (5 g/L) or high (15 g/L) glucose over 3, 6, and 9 days. Approximately 5,000 proteins were confidently identified against an mRNA-based CHO-DG44 specific proteome database, with 2,800 proteins quantified with at least two peptides. A self-organizing map algorithm was used to deconvolute temporal expression profiles of quantitated proteins. Functional analysis of altered proteins suggested that differences in growth between the two glucose levels resulted from changes in crosstalk between glucose metabolism, recombinant protein expression, and cell death, providing an overall picture of the responses to high glucose environment. The high glucose environment may enhance recombinant dihydrofolate reductase in CHO cells by up-regulating NCK1 and down-regulating PRKRA, and may lower integrated viable cell density by activating mitochondrial- and endoplasmic reticulum-mediated cell death pathways by up-regulating HtrA2 and calpains. These proteins are suggested as potential targets for bioengineering to enhance recombinant protein production.

Insights into pH-induced metabolic switch by flux balance analysis

Lactate accumulation in mammalian cell culture is known to impede cellular growth and productivity. The control of lactate formation and consumption in a hybridoma cell line was achieved by pH alteration during the early exponential growth phase. In particular, lactate consumption was induced even at high glucose concentrations at pH 6.8, whereas highly increased production of lactate was obtained at pH 7.8. Consequently, constraint-based metabolic flux analysis was used to examine pH-induced metabolic states in the same growth state. We demonstrated that lactate influx at pH 6.8 led cells to maintain high fluxes in the TCA cycle and malate-aspartate shuttle resulting in a high ATP production rate. In contrast, under increased pH conditions, less ATP was generated and different ATP sources were utilized. Gene expression analysis led to the conclusion that lactate formation at high pH was enabled by gluconeogenic pathways in addition to facilitated glucose uptake. The obtained results provide new insights into the influence of pH on cellular metabolism, and are of importance when considering pH heterogeneities typically present in large scale industrial bioreactors.

Enhancement of monoclonal antibody production in CHO cells by exposure to He-Ne laser radiation

This study tested the effectiveness of laser biostimulation in small-scale cultures in vitro. We investigated the response of recombinant CHO cells, which are used for the production of monoclonal antibody, to low level laser radiation. The cells were irradiated using a 632.8 nm He-Ne laser in a continuous wave mode at different energy doses. We incubated the irradiated cells in small batch cultures and assessed their proliferation and productivity at various time intervals. Compared to untreated cells, the irradiated cells showed a significant increase in antibody production. Moreover, the results showed that laser irradiation did not affect viability and slightly enhanced proliferation rate.

Trends in Upstream and Downstream Process Development for Antibody Manufacturing

A steady increase of product titers and the corresponding change in impurity composition represent a challenge for development and optimization of antibody production processes. Additionally, increasing demands on product quality result in higher complexity of processes and analytics, thereby increasing the costs for product work-up. Concentration and composition of impurities are critical for efficient process development. These impurities can show significant variations, which primarily depend on culture conditions. They have a major impact on the work-up strategy and costs. The resulting "bottleneck" in downstream processing requires new optimization, technology and development approaches. These include the optimization and adaptation of existing unit operations respective to the new separation task, the assessment of alternative separation technologies and the search for new methods in process development. This review presents an overview of existing methods for process optimization and integration and indicates new approaches for future developments.

Applications of low-intensity pulsed ultrasound to increase monoclonal antibody production in CHO cells using shake flasks or wavebags

Many technologies, such as cell line screening and host cell engineering, culture media optimization and bioprocess optimization, have been proposed to increase monoclonal antibody (mAb) production in Chinese Hamster Ovary (CHO) cells. Unlike the existing biochemical approaches, we investigated stimulation using low-intensity pulsed ultrasound (LIPUS) as a purely physical approach, offering enhanced scalability, contamination control and cost-efficiency, while demonstrating significantly increased cell growth and antibody production. It was found that daily ultrasound treatments at 40 mW/cm(2) for 5 min during cell culture increased the production of human anti-IL-8 antibody by more than 30% using 10 or 30 mL shake flasks. Further increasing the ultrasound dosage (either intensities or the treatment duration) did not appreciably increase cell growth or antibody production, however feeding the culture with additional highly-concentrated nutrients, glucose and amino acids (glutamine in this case), did further increase cell growth and antibody titer to 35%. Similar ultrasound treatments (40 mW/cm(2), 5 min per day) when scaled up to larger volume wavebags, resulted in a 25% increase in antibody production. Increased antibody production can be attributed to both elevated cell count and the ultrasound stimulation. Theoretical study of underlying mechanisms was performed through the simulations of molecular dynamics using the AMBER software package, with results showing that LIPUS increases cell permeability. The significance of this study is that LIPUS, as a physical-based stimulation approach, can be externally applied to the cell culture without worrying about contamination. By combining with the existing technologies in antibody production, LIPUS can achieve additional mAb yields. Because it can be easily integrated with existing cell culture apparatuses, the technology is expected to be more acceptable by the end users.

Evaluation of butyrate-induced production of a mannose-6-phosphorylated therapeutic enzyme using parallel bioreactors

Bioreactor process changes can have a profound effect on the yield and quality of biotechnology products. Mannose-6-phosphate (M6P) glycan content and the enzymatic catalytic kinetic parameters are critical quality attributes (CQAs) of many therapeutic enzymes used to treat lysosomal storage diseases (LSDs). Here, we have evaluated the effect of adding butyrate to bioreactor production cultures of human recombinant β-glucuronidase produced from CHO-K1 cells, with an emphasis on CQAs. The β-glucuronidase produced in parallel bioreactors was quantified by capillary electrophoresis, the catalytic kinetic parameters were measured using steady-state analysis, and mannose-6-phosphorylation status was assessed using an M6P-specific single-chain antibody fragment. Using this approach, we found that butyrate treatment increased β-glucuronidase production up to approximately threefold without significantly affecting the catalytic properties of the enzyme. However, M6P content in β-glucuronidase was inversely correlated with the increased enzyme production induced by butyrate treatment. This assessment demonstrated that although butyrate dramatically increased β-glucuronidase production in bioreactors, it adversely impacted the mannose-6-phosphorylation of this LSD therapeutic enzyme. This strategy may have utility in evaluating manufacturing process changes to improve therapeutic enzyme yields and CQAs.

Dynamics of unfolded protein response in recombinant CHO cells

Genes in the protein secretion pathway have been targeted to increase productivity of monoclonal antibodies in Chinese hamster ovary cells. The results have been highly variable depending on the cell type and the relative amount of recombinant and target proteins. This paper presents a comprehensive study encompassing major components of the protein processing pathway in the endoplasmic reticulum (ER) to elucidate its role in recombinant cells. mRNA profiles of all major ER chaperones and unfolded protein response (UPR) pathway genes are measured at a series of time points in a high-producing cell line under the dynamic environment of a batch culture. An initial increase in IgG heavy chain mRNA levels correlates with an increase in productivity. We observe a parallel increase in the expression levels of majority of chaperones. The chaperone levels continue to increase until the end of the batch culture. In contrast, calreticulin and ERO1-L alpha, two of the lowest expressed genes exhibit transient time profiles, with peak induction on day 3. In response to increased ER stress, both the GCN2/PKR-like ER kinase and inositol-requiring enzyme-1alpha (Ire1α) signalling branch of the UPR are upregulated. Interestingly, spliced X-Box binding protein 1 (XBP1s) transcription factor from Ire1α pathway is detected from the beginning of the batch culture. Comparison with the expression levels in a low producer, show much lower induction at the end of the exponential growth phase. Thus, the unfolded protein response strongly correlates with the magnitude and timing of stress in the course of the batch culture.

Characterization of lentiviral vector production using microwell suspension cultures of HEK293T-derived producer cells

ProSavin(®) is a lentiviral vector (LV)-based gene therapy for Parkinson's disease. ProSavin(®) is currently in a Phase I/II clinical trial using material that was generated by transient transfection of adherent human embryonic kidney (HEK)293T cells. For future large-scale productions of ProSavin(®), we have previously reported the development and characterization of two inducible producer cell lines, termed PS5.8 and PS46.2. PS46.2 has been successfully adapted to grow in suspension cultures. The present study describes the creation of a small-scale (<2 ml) microwell-based experimental platform for the parallel investigation of ProSavin(®) production using suspension-adapted PS46.2. This is combined with statistical design of experiments (DoE) techniques to enable rapid characterization of the process conditions that impact cell growth and LV production. The effects of postinduction period, microwell liquid fill volume, and concentration of inducer (doxycycline) on ProSavin(®) titer and the particle:infectivity (P:I) ratio was investigated using three rounds of DoE, in order to identify appropriate factor ranges and optimize production conditions. We identified an optimal "harvest window" between approximately 26-46 hr within which maximal titers of around 6×10(4) transducing units (TU)/ml were obtained (an approximately 30-fold improvement compared to starting microwell conditions), providing that the fill volume was maintained at or below 1 ml and the doxycycline concentration was at least 1.0 μg/ml. Insights from the microwell studies were subsequently used to rapidly establish operating conditions for ProSavin(®) production in a 0.5-L wave bioreactor culture. The information presented herein thus aids the design and evaluation of scalable production processes for LVs.

Effect of Bcl-x(L) overexpression on lactate metabolism in chinese hamster ovary cells producing antibody

Previously, overexpression of anti-apoptotic proteins, such as E1B-19K and Aven, was reported to alter lactate metabolism of CHO cells in culture. To investigate the effect of Bcl-xL , a well-known anti-apoptotic protein, on lactate metabolism of recombinant CHO (rCHO) cells, two antibody-producing rCHO cell lines with regulated Bcl-xL overexpression (CS13*-0.02-off-Bcl-xL and CS13*-1.00-off-Bcl-xL ) were established using the Tet-off system. When cells were cultivated without Bcl-xL overexpression, the specific lactate production rate (qLac ) of CS13*-0.02-off-Bcl-xL and CS13*-1.00-off-Bcl-xL were 7.32 ± 0.37 and 6.78 ± 0.56 pmol/cell/day, respectively. Bcl-xL overexpression, in the absence of doxycycline, did not affect the qLac of either cell line, though it enhanced the viability during cultures. Furthermore, activities of the enzymes related to glucose and lactate metabolism, such as hexokinase, glucose-6-phosphate dehydrogenase, lactate dehydrogenases, and alanine aminotransferase, were not affected by Bcl-xL overexpression either. Taken together, Bcl-xL overexpression showed no significant effect on the lactate metabolism of rCHO cells.

Metabolic flux rewiring in mammalian cell cultures

Continuous cell lines (CCLs) engage in 'wasteful' glucose and glutamine metabolism that leads to accumulation of inhibitory byproducts, primarily lactate and ammonium. Advances in techniques for mapping intracellular carbon fluxes and profiling global changes in enzyme expression have led to a deeper understanding of the molecular drivers underlying these metabolic alterations. However, recent studies have revealed that CCLs are not necessarily entrenched in a glycolytic or glutaminolytic phenotype, but instead can shift their metabolism toward increased oxidative metabolism as nutrients become depleted and/or growth rate slows. Progress to understand dynamic flux regulation in CCLs has enabled the development of novel strategies to force cultures into desirable metabolic phenotypes, by combining fed-batch feeding strategies with direct metabolic engineering of host cells.