Temperature shift as a process optimization step for the production of pro-urokinase by a recombinant Chinese hamster ovary cell line in high-density perfusion culture

Harnessing metabolic plasticity in CHO cells for enhanced perfusion cultivation

Chinese Hamster Ovary (CHO) cells have rapidly become a cornerstone in biopharmaceutical production. Recently, a reinvigoration of perfusion culture mode in CHO cell cultivation has been observed. However, most cell lines currently in use have been engineered and adapted for fed-batch culture methods, and may not perform optimally under perfusion conditions. To improve the cell's resilience and viability during perfusion culture, we cultured a triple knockout CHO cell line, deficient in three apoptosis related genes BAX, BAK, and BOK in a perfusion system. After 20 days of culture, the cells exhibited a halt in cell proliferation. Interestingly, following this phase of growth arrest, the cells entered a second growth phase. During this phase, the cell numbers nearly doubled, but cell specific productivity decreased. We performed a proteomics investigation, elucidating a distinct correlation between growth arrest and cell cycle arrest and showing an upregulation of the central carbon metabolism and oxidative phosphorylation. The upregulation was partially reverted during the second growth phase, likely caused by intragenerational adaptations to stresses encountered. A phase-dependent response to oxidative stress was noted, indicating glutathione has only a secondary role during cell cycle arrest. Our data provides evidence of metabolic regulation under high cell density culturing conditions and demonstrates that cell growth arrest can be overcome. The acquired insights have the potential to not only enhance our understanding of cellular metabolism but also contribute to the development of superior cell lines for perfusion cultivation.

High-density adherent culture of CHO cells using rolled scaffold bioreactor

Rapid expansion of biopharmaceutical market calls for more efficient and reliable platforms to culture mammalian cells on a large scale. Stirred-tank bioreactors have been widely used for large-scale cell culture. However, it requires months of trials and errors to optimize culture conditions for each cell line. In this article, we extend our earlier studies on rolled scaffold (RS) bioreactors for high-density adherent cell culture and report two new implementations of RSs with greatly enhanced mass-manufacturability, termed as Mesh-RS and Fiber-RS. CHO-K1 cells were successfully expanded in Mesh-RS and Fiber-RS bioreactors with an average growth rate of 1.09 ± 0.04 1/day and 0.95 ± 0.07 1/day, which were higher than those reported in similar studies. Fiber-RS bioreactor exhibited a very high cell density of 72.8 × 10⁶  cells/ml. Besides, a dialyzer was integrated into the RS bioreactor to remove cellular waste and to replenish nutrients without disturbing the cells. By collecting the dialyzed media separately, the dialysis efficiency was significantly improved. In conclusion, the developed RS bioreactor has a strong potential to provide a highly reliable and easily scalable platform for large-scale cell culture in the biopharmaceutical industry.

Perfusion culture of Chinese Hamster Ovary cells for bioprocessing applications

Much of the biopharmaceutical industry's success over the past 30 years has relied on products derived from Chinese Hamster Ovary (CHO) cell lines. During this time, improvements in mammalian cell cultures have come from cell line development and process optimization suited for large-scale fed-batch processes. Originally developed for high cell densities and sensitive products, perfusion processes have a long history. Driven by high volumetric titers and a small footprint, perfusion-based bioprocess research has regained an interest from academia and industry. The recent pandemic has further highlighted the need for such intensified biomanufacturing options. In this review, we outline the technical history of research in this field as it applies to biologics production in CHO cells. We demonstrate a number of emerging trends in the literature and corroborate these with underlying drivers in the commercial space. From these trends, we speculate that the future of perfusion bioprocesses is bright and that the fields of media optimization, continuous processing, and cell line engineering hold the greatest potential. Aligning in its continuous setup with the demands for Industry 4.0, perfusion biomanufacturing is likely to be a hot topic in the years to come.

Multivariate analysis of metabolic parameters and optimization of antibody production using high cell density hybridoma in hollow fiber bioreactors

OBJECTIVES

The relationships of manipulation of culture temperature and medium circulation rate on the metabolic parameters were regressed by multiple linear regression analysis in hollow fiber bioreactors (HFB).

RESULTS

The high circulation rate could significantly enhance the oxygen consumption of the hybridoma cells and the medium's oxidation-reduction potential. A mildly hypothermic condition of 36 °C and a circulation rate of 182.5 mL/min could support the hybridoma had the maximal antibody titer of 60.75 μg/mL for 20 days. When the ammonium ion was 65 ppm or lactate close to 2.6 g/L, the medium was replaced to maintain the stable and healthy cells at the high cell concentration of 3.33 × 10⁸/mL for continuous antibody production. Two serum-free media could be successfully applied to this perfusion system and maintain hybridoma growth and antibody production.

CONCLUSION

The single-use HFBs could provide the advantages including high cell density, low shear stress, and continuous antibody production.

Screening Naturally Occurring Phenolic Antioxidants for Their Suitability as Additives to CHO Cell Culture Media Used to Produce Monoclonal Antibodies

This study identified several antioxidants that could be used in Chinese hamster ovary (CHO)cell culture media and benefit monoclonal antibody production. The flavan-3-ols, catechin, epicatechin, epigallocatechin gallate and gallocatechin gallate all had no detrimental effect on cell viability at the concentrations tested, and they reduced the final viable cell count with a resulting rise in the cell specific productivity. The flavone, luteolin behave similarly to the flavan-3-ols. Resveratrol at 50 μM concentration resulted in the most pronounced reduction in viable cell density with minimal decrease in IgG synthesis and the largest increase in cell specific productivity. Low concentrations of α-tocopherol (35 μM) reduced viable cell density and raised cell specific productivity, but at higher concentration it had little additional effect. As high concentrations of α-tocopherol are not toxic to CHO cells, its addition as an anti-oxidant has great potential. Kaempferol up to 50 μM, curcumin up to 20 μM and piceid up to 100 μM showed little effect on growth or IgG synthesis and could be useful as antioxidants. Caffeic acid phenethyl ester was toxic to CHO cell and of no interest. Seven of the phenolic compounds tested are potential cell cycle inhibitors as well as having intrinsic antioxidant properties.

Revealing Key Determinants of Clonal Variation in Transgene Expression in Recombinant CHO Cells Using Targeted Genome Editing

Generation of recombinant Chinese hamster ovary (rCHO) cell lines is critical for the production of therapeutic proteins. However, the high degree of phenotypic heterogeneity among generated clones, referred to as clonal variation, makes the rCHO cell line development process inefficient and unpredictable. Here, we investigated the major genomic causes of clonal variation. We found the following: (1) consistent with previous studies, a strong variation in rCHO clones in response to hypothermia (33 vs 37 °C) after random transgene integration; (2) altered DNA sequence of randomly integrated cassettes, which occurred during the integration process, affecting the transgene expression level in response to hypothermia; (3) contrary to random integration, targeted integration of the same expression cassette, without any DNA alteration, into three identified integration sites showed the similar response of transgene expression in response to hypothermia, irrespective of integration site; (4) switching the promoter from CMV to EF1α eliminated the hypothermia response; and (5) deleting the enhancer part of the CMV promoter altered the hypothermia response. Thus, we have revealed the effects of integration methods and cassette design on transgene expression levels, implying that rCHO cell line generation can be standardized through detailed genomic understanding. Further elucidation of such understanding is likely to have a broad impact on diverse fields that use transgene integration, from gene therapy to generation of production cell lines.

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.

Industrial Production of Therapeutic Proteins: Cell Lines, Cell Culture, and Purification

A central pillar of the biotechnology and pharmaceutical industries continues to be the development of biological drug products manufactured from engineered mammalian cell lines. Since the hugely successful launch of human tissue plasminogen activator in 1987 and erythropoietin in 1988, the biopharmaceutical market has grown immensely. In 2014, biotherapeutics made up a significant portion of global drug sales as 7 of the top 10 and 21 of top 50 selling pharmaceuticals in the world were biologics with over US$100 billion in global sales (Table 1, [1]).

Bioreactor process parameter screening utilizing a Plackett-Burman design for a model monoclonal antibody

Consistent high-quality antibody yield is a key goal for cell culture bioprocessing. This endpoint is typically achieved in commercial settings through product and process engineering of bioreactor parameters during development. When the process is complex and not optimized, small changes in composition and control may yield a finished product of less desirable quality. Therefore, changes proposed to currently validated processes usually require justification and are reported to the US FDA for approval. Recently, design-of-experiments-based approaches have been explored to rapidly and efficiently achieve this goal of optimized yield with a better understanding of product and process variables that affect a product's critical quality attributes. Here, we present a laboratory-scale model culture where we apply a Plackett-Burman screening design to parallel cultures to study the main effects of 11 process variables. This exercise allowed us to determine the relative importance of these variables and identify the most important factors to be further optimized in order to control both desirable and undesirable glycan profiles. We found engineering changes relating to culture temperature and nonessential amino acid supplementation significantly impacted glycan profiles associated with fucosylation, β-galactosylation, and sialylation. All of these are important for monoclonal antibody product quality.

Approaches to optimizing animal cell culture process: substrate metabolism regulation and protein expression improvement

Some high value proteins and vaccines for medical and veterinary applications by animal cell culture have an increasing market in China. In order to meet the demands of large-scale productions of proteins and vaccines, animal cell culture technology has been widely developed. In general, an animal cell culture process can be divided into two stages in a batch culture. In cell growth stage a high specific growth rate is expected to achieve a high cell density. In production stage a high specific production rate is stressed for the expression and secretion of qualified protein or replication of virus. It is always critical to maintain high cell viability in fed-batch and perfusion cultures. More concern has been focused on two points by the researchers in China. First, the cell metabolism of substrates is analyzed and the accumulation of toxic by-products is decreased through regulating cell metabolism in the culture process. Second, some important factors effecting protein expression are understood at the molecular level and the production ability of protein is improved. In pace with the rapid development of large-scale cell culture for the production of vaccines, antibodies and other recombinant proteins in China, the medium design and process optimization based on cell metabolism regulation and protein expression improvement will play an important role. The chapter outlines the main advances in metabolic regulation of cell and expression improvement of protein in animal cell culture in recent years.

Effect of low culture temperature on urokinase production in hollow fiber reactor

The effect of culture temperature on urokinase production by HT-1080 cell line was studied in batch culture and hollow fiber reactor. Small-scale t-flask experiments revealed that urokinase production could be enhanced and media utilization could be reduced by lowering the culture temperature in production phase. Urokinase production was scaled up using a hollow fiber perfusion reactor system. Temperature of culture was maintained at the physiological 37 °C during growth phase that extended up to 12 days in hollow fiber bioreactor. Subsequently, in the production phase, culture temperature was lowered to 34 °C. Decrease in culture temperature resulted in a significant increase in urokinase production. Proteolytic degradation and inhibition was also minimized. The medium utilization rate was decreased at lower temperature, and hence, a higher economy of production could be obtained.

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.

External modulation of HT-1080 human fibrosarcoma cells improves urokinase production

Urokinase was produced in a hollow fiber reactor using HT-1080 human fibrosarcoma cells. External modulation comprised replenishing of the medium in the extracapillary space, reducing the serum concentration in the extracapillary space from 10% to 2% and increasing flow rate of the circulating medium in the intracapillary space from 20 to 80 mL/min, each according to a specific protocol. More than sixfold increase was observed in the cumulative urokinase production for two and three medium replenishing modulations of the extracapillary space. After 15 days of continuous operation, the highest cumulative urokinase obtained was 1.63 x 10(6) PU/mL. SDS-PAGE and zymogram study established that the urokinase obtained was in the high molecular weight range of 54 kDa. The effect of external modulation on cumulative urokinase production was visualized as trajectories with respect to the ratio of lactic acid production rate (LPR) to the glucose uptake rate (GUR). The collective external modulation data showed two separate physiological regions in the cumulative urokinase vs. LPR/GUR plane. The HT-1080 cells exhibited two distinct morphologies in these regions that may be related to acidosis and metastasis. These regions also correspond to low and high urokinase productivity.

Effect of culture temperature on erythropoietin production and glycosylation in a perfusion culture of recombinant CHO cells

To investigate the effect of culture temperature on erythropoietin (EPO) production and glycosylation in recombinant Chinese hamster ovary (CHO) cells, we cultivated CHO cells using a perfusion bioreactor. Cells were cultivated at 37 degrees C until viable cell concentration reached 1 x 10(7) cells/mL, and then culture temperature was shifted to 25 degrees C, 28 degrees C, 30 degrees C, 32 degrees C, 37 degrees C (control), respectively. Lowering culture temperature suppressed cell growth but was beneficial to maintain high cell viability for a longer period. In a control culture at 37 degrees C, cell viability gradually decreased and fell below 80% on day 18 while it remained over 90% throughout the culture at low culture temperature. The cumulative EPO production and specific EPO productivity, q(EPO), increased at low culture temperature and were the highest at 32 degrees C and 30 degrees C, respectively. Interestingly, the cumulative EPO production at culture temperature below 32 degrees C was not as high as the cumulative EPO production at 32 degrees C although the q(EPO) at culture temperature below 32 degrees C was comparable or even higher than the q(EPO) at 32 degrees C. This implies that the beneficial effect of lowering culture temperature below 32 degrees C on q(EPO) is outweighed by its detrimental effect on the integral of viable cells. The glycosylation of EPO was evaluated by isoelectric focusing, normal phase HPLC and anion exchange chromatography analyses. The quality of EPO at 32 degrees C in regard to acidic isoforms, antennary structures and sialylated N-linked glycans was comparable to that at 37 degrees C. However, at culture temperatures below 32 degrees C, the proportions of acidic isoforms, tetra-antennary structures and tetra-sialylated N-linked glycans were further reduced, suggesting that lowering culture temperature below 32 degrees C negatively affect the quality of EPO. Thus, taken together, cell culture at 32 degrees C turned out to be the most satisfactory since it showed the highest cumulative EPO production, and moreover, EPO quality at 32 degrees C was not deteriorated as obtained at 37 degrees C.

Promotion of recombinant macrophage colony stimulating factor production by dimethyl sulfoxide addition in Chinese hamster ovary cells

A Chinese hamster ovary (CHO) cell line is the primary choice for the production of recombinant protein drugs with glycosylation modification. Recombinant protein productivity was enhanced by the addition of dimethyl sulfoxide (DMSO) in CHO cells. However, DMSO induced G0/G1 phase growth arrest and reduced cell growth rate. A two-stage process was developed to utilize the stimulatory effect of DMSO on recombinant protein production and mitigate the problem of growth inhibition in this study. In the first stage, cells are cultured without DMSO for a certain period in order to obtain a high cell density. Sequentially, DMSO is added to achieve a high specific productivity in the second stage. Using this approach, we found that by adding 1% DMSO after 24 h of growth, macrophage colony-stimulating factor (M-CSF) volumetric productivity is increased by 57% compared with the value obtained without the addition of DMSO.

Synthesis, regulation and production of urokinase using mammalian cell culture: a comprehensive review

Urokinase, a serine protease, catalyzes the conversion of plasminogen to plasmin, which is responsible for dissolution of clots in blood vessels. It is an important drug for treatment of thromboembolic disease. Production of urokinase by mammalian cell culture has the following important steps: synthesis, regulation and secretion. Production and accumulation of this product in a bioreactor is a real challenge for biochemical engineers. Considerable information at molecular level needs to be understood for production of urokinase in order to correlate different parameters, which in turn can maximize the productivity. This information will be highlighted in this review. Moreover, urokinase production is a product-inhibited process. Therefore, in situ urokinase separation strategy is required to operate a bioreactor at its maximum urokinase formation rate. Integrated urokinase production and isolation processes developed recently will also be discussed briefly in this review.