Bcl-x(L) mediates increased production of humanized monoclonal antibodies in Chinese hamster ovary cells

Overexpression of Tgm2 in Chinese Hamster Ovary Cells Enhances Recombinant Monoclonal Antibody Expression and Promotes Cell Proliferation through Reduction of Apoptosis

Chinese hamster ovary (CHO) cells are the preferred host system for producing protein-based (antibody) therapeutics. However, recombinant CHO cells undergo substantial apoptosis during prolonged cultivation, impairing cell growth and ultimately compromising product yield and quality. Transglutaminase 2 (Tgm2), which mediates post-translational modifications of substrate proteins, regulates critical biological processes including cellular differentiation, apoptosis, cell cycle progression, and extracellular matrix assembly. In this study, we examined the effects of Tgm2 overexpression and knockdown on CHO cell growth and recombinant antibody production. Stable Tgm2 overexpression enhanced CHO cell proliferation while reducing apoptotic rates, resulting in significantly increased recombinant adalimumab expression (2.09 ± 0.08-fold) and specific productivity (1.88 ± 0.08-fold) compared to controls. In contrast, Tgm2 knockdown promoted apoptosis and induced cell cycle arrest. Mechanistically, elevated Tgm2 upregulated antiapoptotic genes (Bcl-2, Bcl-xL, and Mcl-1) while suppressing caspase-3 activity and BAX expression. These effects were associated with PI3K/AKT/mTOR pathway activation. Our findings demonstrate that Tgm2 overexpression enhances proliferation, bolsters antiapoptotic capacity, and improves monoclonal antibody production efficiency in CHO cells, establishing it as a viable strategy for increasing recombinant protein yields.

From Efficiency to Yield: Exploring Recent Advances in CHO Cell Line Development for Monoclonal Antibodies

The increasing demand for biosimilar monoclonal antibodies (mAbs) has prompted the development of stable high-producing cell lines while simultaneously decreasing the time required for screening. Existing platforms have proven inefficient, resulting in inconsistencies in yields, growth characteristics, and quality features in the final mAb products. Selecting a suitable expression host, designing an effective gene expression system, developing a streamlined cell line generation approach, optimizing culture conditions, and defining scaling-up and purification strategies are all critical steps in the production of recombinant proteins, particularly monoclonal antibodies, in mammalian cells. As a result, an active area of study is dedicated to expression and optimizing recombinant protein production. This review explores recent breakthroughs and approaches targeted at accelerating cell line development to attain efficiency and consistency in the synthesis of therapeutic proteins, specifically monoclonal antibodies. The primary goal is to bridge the gap between rising demand and consistent, high-quality mAb production, thereby benefiting the healthcare and pharmaceutical industries.

Molecular biomarkers identification and applications in CHO bioprocessing

Biomarkers are valuable tools in clinical research where they allow to predict susceptibility to diseases, or response to specific treatments. Likewise, biomarkers can be extremely useful in the biomanufacturing of therapeutic proteins. Indeed, constraints such as short timelines and the need to find hyper-productive cells could benefit from a data-driven approach during cell line and process development. Many companies still rely on large screening capacities to develop productive cell lines, but as they reach a limit of production, there is a need to go from empirical to rationale procedures. Similarly, during bioprocessing runs, substrate consumption and metabolism wastes are commonly monitored. None of them possess the ability to predict the culture behavior in the bioreactor. Big data driven approaches are being adapted to the study of industrial mammalian cell lines, enabled by the publication of Chinese hamster and CHO genome assemblies which allowed the use of next-generation sequencing with these cells, as well as continuous proteome and metabolome annotation. However, if these different -omics technologies contributed to the characterization of CHO cells, there is a significant effort remaining to apply this knowledge to biomanufacturing methods. The correlation of a complex phenotype such as high productivity or rapid growth to the presence or expression level of a specific biomarker could save time and effort in the screening of manufacturing cell lines or culture conditions. In this review we will first discuss the different biological molecules that can be identified and quantified in cells, their detection techniques, and associated challenges. We will then review how these markers are used during the different steps of cell line and bioprocess development, and the inherent limitations of this strategy.

Insights into the Impact of Rosmarinic Acid on CHO Cell Culture Improvement through Transcriptomics Analysis

The use of antioxidants in Chinese hamster ovary (CHO) cell cultures to improve monoclonal antibody production has been a topic of great interest. Nevertheless, the antioxidants do not have consistent benefits of production improvement, which might be cell line specific and/or process specific. In this work, we investigated how treatment with the antioxidant rosmarinic acid (RA) improved cell growth and titer in CHO cell cultures using transcriptomics. In particular, transcriptomics analysis indicated that RA treatment modified gene expression and strongly affected the MAPK and PI3K/Akt signaling pathways, which regulate cell survival and cell death. Moreover, it was observed that these signaling pathways, which had been identified to be up-regulated on day 2 and day 6 by RA, were also up-regulated over time (from initial growth phase day 2 to slow growth or protein production phase day 6) in both conditions. In summary, this transcriptomics analysis provides insights into the role of the antioxidant RA in industrial cell culture processes. The current study also represents an example in the industry of how omics can be applied to gain an in-depth understanding of CHO cell biology and to identify critical pathways that can contribute to cell culture process improvement and cell line engineering.

A Review on the Current Methods of Chinese Hamster Ovary (CHO) Cells Cultivation for the Production of Therapeutic Protein

Most of the clinical approved protein-based drugs or under clinical trials have a profound impact on the treatment of critical diseases. The mammalian eukaryotic cells culture approaches, particularly the CHO (Chinese Hamster Ovary) cells are mainly used in the biopharmaceutical industry for the mass-production of the therapeutic protein. Recent advances in CHO cell bioprocessing to yield recombinant proteins and monoclonal antibodies have enabled the expression of quality protein. The developments of cell lines are possible to enhance specific productivity. As a result, it holds an interesting area for academic as well as industrial researchers around the world. This review will focus on the recent progress of the mammalian CHO cells culture technology and the future scope of further development for the mass-production of protein therapeutics.

Apoptosis: A mammalian cell bioprocessing perspective

Apoptosis is a form of programmed and controlled cell death that accounts for the majority of cellular death in bioprocesses. Cell death affects culture longevity and product quality; it is instigated by several stresses experienced by the cells within a bioreactor. Understanding the factors that cause apoptosis as well as developing strategies that can protect cells is crucial for robust bioprocess development. This review aims to a) address apoptosis from a bioprocess perspective; b) describe the significant apoptotic mechanisms linking them to the most relevant stresses encountered in bioreactors; c) discuss the design of operating conditions in order to avoid cell death; d) focus on industrially relevant cell lines; and e) present anti-apoptosis strategies including cell engineering and model-based optimization of bioprocesses. In addition, the importance of apoptosis in quality-by-design bioprocess development from clone screening to production scale are highlighted.

Quantitative Proteomic Analysis of Cellular Responses to a Designed Amino Acid Feed in a Monoclonal Antibody Producing Chinese Hamster Ovary Cell Line

Background:

Chinese hamster ovary (CHO) cell line is considered as the most common cell line in the biopharmaceutical industry because of its capability in performing efficient post-translational modifications and producing the recombinant proteins, which are similar to natural human proteins. The optimization of the upstream process via different feed strategies has a great impact on the target molecule expression and yield.

Methods:

To determine and understand the molecular events beneath the feed effects on the CHO cell, a label-free quantitative proteomic analysis was applied. The proteome changes followed by the addition of a designed amino acid feed to the monoclonal antibody producing CHO cell line culture medium were investigated.

Results:

The glutathione synthesis, the negative regulation of the programmed cell death, proteasomal catabolic process, and the endosomal transport pathway were up-regulated in the group fed with a designed amino acid feed compared to the control group.

Conclusion:

Our findings could be helpful to identify new targets for metabolic engineering.

Enhanced production of anti-PD1 antibody in CHO cells through transient co-transfection with anti-apoptotic genes Bcl-x L and Mcl-1

Apoptosis has a negative impact on the cell survival state during cell cultivation. To optimize mammalian cell culture for production of biopharmaceuticals, one of the important approaches is to extend cell life through over-expression of anti-apoptotic genes. Here, we reported a cost-effective process to enhance cell survival and production of an antibody through transient co-transfection with anti-apoptotic genes Bcl-x _L or Mcl-1 in Chinese hamster ovary (CHO) cells with polyethylenimine (PEI). Under the optimal conditions, it showed reduced levels of apoptosis and improved cell viability after co-transfected with Bcl-x _L or Mcl-1. The overall production yield of the antibody anti-PD1 increased approximately 82% in CHO cells co-transfected with Bcl-x _L , and 34% in CHO cells co-transfected with Mcl-1. This work provides an effective way to increase viability of host cells through delaying apoptosis onset, thus, raise production yield of biopharmaceuticals without the process of generating stable cell lines and subsequent screening.

A BioDesign Approach to Obtain High Yields of Biosimilars by Anti-apoptotic Cell Engineering: a Case Study to Increase the Production Yield of Anti-TNF Alpha Producing Recombinant CHO Cells

Recent developments in medical biotechnology have facilitated to enhance the production of monoclonal antibodies (mAbs) and recombinant proteins in mammalian cells. Human mAbs for clinical applications have focused on three areas, particularly cancer, immunological disorders, and infectious diseases. Tumor necrosis factor alpha (TNF-α), which has both proinflammatory and immunoregulatory functions, is an important target in biopharmaceutical industry. In this study, a humanized anti-TNF-α mAb producing stable CHO cell line which produces a biosimilar of Humira (adalimumab) was used. Adalimumab is a fully human anti-TNF mAb among the top-selling mAb products in recent years as a biosimilar. Products from mammalian cell bioprocesses are a derivative of cell viability and metabolism, which is mainly disrupted by cell death in bioreactors. Thus, different strategies are used to increase the product yield. Suppression of apoptosis, also called anti-apoptotic cell engineering, is the most remarkable strategy to enhance lifetime of cells for a longer production period. In fact, using anti-apoptotic cell engineering as a BioDesign approach was inspired by nature; nature gives prolonged life span to some cells like stem cells, tumor cells, and memory B and T cells, and researchers have been using this strategy for different purposes. In this study, as a biomimicry approach, anti-apoptotic cell engineering was used to increase the anti-TNF-α mAb production from the humanized anti-TNF-α mAb producing stable CHO cell line by Bcl-xL anti-apoptotic protein. It was shown that transient transfection of CHO cells by the Bcl-xL anti-apoptotic protein expressing plasmid prolonged the cell survival rate and protected cells from apoptosis. The transient expression of Bcl-xL using CHO cells enhanced the anti-TNF-α production. The production of anti-TNF-α in CHO cells was increased up to 215 mg/L with an increase of 160% after cells were transfected with Bcl-xL expressing plasmid with polyethylenimine (PEI) reagent at the ratio of 1:6 (DNA:PEI). In conclusion, the anti-apoptotic efficacy of the Bcl-xL expressing plasmid in humanized anti-TNF-α MAb producing stable CHO cells is compatible with curative effect for high efficiency recombinant protein production. Thus, this model can be used for large-scale production of biosimilars through transient Bcl-xL gene expression as a cost-effective method.

The non-apoptotic action of Bcl-xL: regulating Ca(2+) signaling and bioenergetics at the ER-mitochondrion interface

Bcl-2 family proteins are known to competitively regulate Ca(2+); however, the specific inter-organelle signaling pathways and related cellular functions are not fully elucidated. In this study, a portion of Bcl-xL was detected at the ER-mitochondrion interface or MAM (mitochondria-associated ER membrane) in association with type 3 inositol 1,4,5-trisphosphate receptors (IP3R3); an association facilitated by the BH4 and transmembrane domains of Bcl-xL. Moreover, increasing Bcl-xL expression enhanced transient mitochondrial Ca(2+) levels upon ER Ca(2+) depletion induced by short-term, non-apoptotic incubation with thapsigargin (Tg), while concomitantly reducing cytosolic Ca(2+) release. These mitochondrial changes appear to be IP3R3-dependent and resulted in decreased NAD/NADH ratios and higher electron transport chain oxidase activity. Interestingly, extended Tg exposure stimulated ER stress, but not apoptosis, and further enhanced TCA cycling. Indeed, confocal analysis indicated that Bcl-xL translocated to the MAM and increased its interaction with IP3R3 following extended Tg treatment. Thus, the MAM is a critical cell-signaling junction whereby Bcl-xL dynamically interacts with IP3R3 to coordinate mitochondrial Ca(2+) transfer and alters cellular metabolism in order to increase the cells' bioenergetic capacity, particularly during periods of stress.

Bcl-2 family in inter-organelle modulation of calcium signaling; roles in bioenergetics and cell survival

Bcl-2 family proteins, known for their apoptosis functioning at the mitochondria, have been shown to localize to other cellular compartments to mediate calcium (Ca2+) signals. Since the proper supply of Ca2+ in cells serves as an important mechanism for cellular survival and bioenergetics, we propose an integrating role for Bcl-2 family proteins in modulating Ca2+ signaling. The endoplasmic reticulum (ER) is the main Ca2+ storage for the cell and Bcl-2 family proteins competitively regulate its Ca2+ concentration. Bcl-2 family proteins also regulate the flux of Ca2+ from the ER by physically interacting with inositol 1,4,5-trisphosphate receptors (IP3Rs) to mediate their opening. Type 1 IP3Rs reside at the bulk ER to coordinate cytosolic Ca2+ signals, while type 3 IP3Rs reside at mitochondria-associated ER membrane (MAM) to facilitate mitochondrial Ca2+ uptake. In healthy cells, mitochondrial Ca2+ drives pyruvate into the citric acid (TCA) cycle to facilitate ATP production, while a continuous accumulation of Ca2+ can trigger the release of cytochrome c, thus initiating apoptosis. Since multiple organelles and Bcl-2 family proteins are involved in Ca2+ signaling, we aim to clarify the role that Bcl-2 family proteins play in facilitating Ca2+ signaling and how mitochondrial Ca2+ is relevant in both bioenergetics and apoptosis. We also explore how these insights could be useful in controlling bioenergetics in apoptosis-resistant cell lines.

Enhanced transient recombinant protein production in CHO cells through the co-transfection of the product gene with Bcl-xL

Transient gene expression is gaining popularity as a method to rapidly produce recombinant proteins in mammalian cells. Although significant improvements have been made, in terms of expression, more improvements are needed to compete with the yields achievable in stable gene expression. Much progress has come from optimization of transfection media and parameters, as well as altering culturing conditions to enhance productivity. Recent studies have included cell lines engineered for apoptosis resistance through the constitutive expression of an anti-apoptotic protein, Bcl-xL. In this study, we examine an alternative method of using the benefits of anti-apoptotic gene expression to enhance the transient expression of biotherapeutics, namely, through the co-transfection of Bcl-xL and the product-coding gene. CHO-S cells were co-transfected with the product-coding gene and a vector containing Bcl-xL using polyethylenimine. Cells co-transfected with Bcl-xL showed reduced levels of apoptosis, increased specific productivity, and an overall increase in product yield of approximately 100%. Similar results were produced by employing another anti-apoptotic protein, Bcl-2 delta, in CHO cells, or through the co-transfection with Bcl-xL using HEK-293E cells. This work provides an alternative method for increasing yields of therapeutic proteins in TGE applications without generating a stable cell line and subsequent screening, which are both time- and resource-consuming. See accompanying commentary by Matthias Hackl and Nicole Borth DOI: 10.1002/biot.201400104.

Proteins improving recombinant antibody production in mammalian cells

Mammalian cells have been successfully used for the industrial manufacture of antibodies due to their ability to synthesize antibodies correctly. Nascent polypeptides must be subjected to protein folding and assembly in the ER and the Golgi to be secreted as mature proteins. If these reactions do not proceed appropriately, unfolded or misfolded proteins are degraded by the ER-associated degradation (ERAD) pathway. The accumulation of unfolded proteins or intracellular antibody crystals accompanied by this failure triggers the unfolded protein response (UPR), which can considerably attenuate the levels of translation, folding, assembly, and secretion, resulting in reduction of antibody productivity. Accumulating studies by omics-based analysis of recombinant mammalian cells suggest that not only protein secretion processes including protein folding and assembly but also translation are likely to be the rate-limiting factors for increasing antibody production. Here, this review describes the mechanism of antibody folding and assembly and recent advantages which could improve recombinant antibody production in mammalian cells by utilizing proteins such as ER chaperones or UPR-related proteins.

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.

Stable inhibition of mmu-miR-466h-5p improves apoptosis resistance and protein production in CHO cells

MiRNAs have been shown to be involved in regulation of multiple cellular processes including apoptosis. Since a single miRNA can affect the expression of several genes, the utilization of miRNAs for apoptosis engineering in mammalian cells can be more efficient than the conventional approach of manipulating a single gene. Mmu-miR-466h-5p was previously shown to have a pro-apoptotic role in CHO cells by reducing the expression of several anti-apoptotic genes and its transient inhibition delayed both the activation of Caspase-3/7 and the loss of cell viability. The present study evaluates the effect of stable inhibition of mmu-miR-466h-5p in CHO cells on their ability to resist apoptosis onset and their production properties. The expression of mmu-miR-466h-5p in the engineered anti-miR-466h CHO cell line was significantly lower than in the negative control and the parental CHO cells. These engineered cells reached higher maximum viable cell density and extended viability compared with negative control and parental CHO cells in batch cell cultures which resulted in the 53.8% and 41.6% increase of integral viable cells. The extended viability of anti-miR-466h CHO cells was the result of delayed Caspase-3/7 activation by more than 35h, and the increased levels of its anti-apoptotic gene targets (smo, stat5a, dad1, birc6, and bcl2l2) to between 2.1- and 12.5-fold compared with the negative control CHO in apoptotic conditions. The expression of secreted alkaline phosphatase (SEAP) increased 43% and the cell-specific productivity increased 11% in the stable pools of anti-miR-466h CHO compared with the stable pools of negative control CHO cells. The above results demonstrate the potential of this novel approach to create more productive cell lines through stable manipulation of specific miRNA expression.

Large-scale screening identifies a novel microRNA, miR-15a-3p, which induces apoptosis in human cancer cell lines

MicroRNAs (miRNAs) have been found to be involved in cancer initiation, progression and metastasis and, as such, have been suggested as tools for cancer detection and therapy. In this work, a large-scale screening of the complete miRNA mimics library demonstrated that hsa-miR-15a-3p had a pro-apoptotic role in the following human cancer cells: HeLa, AsPc-1, MDA-MB-231, KB3, ME180, HCT-116 and A549. MiR-15a-3p is a novel member of the pro-apoptotic miRNA cluster, miR-15a/16, which was found to activate Caspase-3/7 and to cause viability loss in B/CMBA.Ov cells during preliminary screening. Subsequent microarrays and bioinformatics analyses identified the following four anti-apoptotic genes: bcl2l1, naip5, fgfr2 and mybl2 as possible targets for the mmu-miR-15a-3p in B/CMBA.Ov cells. Follow-up studies confirmed the pro-apoptotic role of hsa-miR-15a-3p in human cells by its ability to activate Caspase-3/7, to reduce cell viability and to inhibit the expression of bcl2l1 (bcl-xL) in HeLa and AsPc-1 cells. MiR-15-3p was also found to reduce viability in HEK293, MDA-MB-231, KB3, ME180, HCT-116 and A549 cell lines and, therefore, may be considered for apoptosis modulating therapies in cancers associated with high Bcl-xL expression (cervical, pancreatic, breast, lung and colorectal carcinomas). The capability of hsa-miR-15a-3p to induce apoptosis in these carcinomas may be dependent on the levels of Bcl-xL expression. The use of endogenous inhibitors of bcl-xL and other anti-apoptotic genes such as hsa-miR-15a-3p may provide improved options for apoptosis-modulating therapies in cancer treatment compared with the use of artificial antisense oligonucleotides.

Controlling trisulfide modification in recombinant monoclonal antibody produced in fed-batch cell culture

Molecular heterogeneity was detected in a recombinant monoclonal antibody (IgG1 mAb) due to the presence of a trisulfide linkage generated by the post-translational insertion of a sulfur atom into disulfide bonds at the heavy-heavy and heavy-light junctions. This molecular heterogeneity had no observable effect on antibody function. Nevertheless, to minimize the heterogeneity of the IgG1 mAb from run-to-run, an understanding of the impact of cell culture process conditions on trisulfide versus disulfide linkage formation was desirable. To investigate variables that might impact trisulfide formation, cell culture parameters were varied in bench-scale bioreactor studies. Trisulfide analysis of the samples from these runs revealed that the trisulfide content in the bond between heavy and light chains varied considerably from <1% to 39%. Optimizing the culture duration and feeding strategy resulted in more consistent trisulfide levels. Cysteine concentration in the feed medium had a direct correlation with the trisulfide level in the product. Systematic studies revealed that cysteine in the feed and the bioreactor media was contributing hydrogen sulfide which reacted with the IgG1 mAb in the supernatant leading to the insertion of sulfur atom and formation of a trisulfide bond. Cysteine feed strategies were developed to control the trisulfide modification in the recombinant monoclonal antibody.

Increased expression of the integral membrane proteins EGFR and FGFR3 in anti-apoptotic Chinese hamster ovary cell lines

Membrane proteins such as receptor tyrosine kinases (RTKs) have a vital role in many cellular functions, making them potential targets for therapeutic research. In this study, we investigated the coexpression of the anti-apoptosis gene Bcl-x(L) with model membrane proteins as a means of increasing membrane protein expression in mammalian cells. Chinese hamster ovary (CHO) cells expressing heterologous Bcl-x(L) and wild-type CHO cells were transfected with either epidermal growth factor receptor or fibroblast growth factor receptor 3. The CHO-Bcl-x(L) cell lines showed increased expression of both RTK proteins as compared with the wild-type CHO cell lines in transient expression analysis, as detected by Western blot and flow cytometry after 15 days of antibiotic selection in stable expression pools. Increased expression was also seen in clonal isolates from the CHO-Bcl-x(L) cell lines, whereas the clonal cell line expression was minimal in wild-type CHO cell lines. Our results demonstrate that application of the anti-apoptosis gene Bcl-x(L) can increase expression of RTK proteins in CHO cells. This approach may be applied to improve stable expression of other membrane proteins in the future using mammalian cell lines with Bcl-x(L) or perhaps other anti-apoptotic genes.

Controlling apoptosis to optimize yields of proteins from mammalian cells

Apoptosis is the foremost method of cell death in bioreactors and can be caused by nutrient limitation, toxin accumulation, and growth factor withdrawal. By delaying the onset of this form of programmed cell death, one can achieve longer sustained viabilities in culture, thereby increasing product yield. Described here is a genetic-based, step-by-step method to generate an apoptosis-resistant cell line. This cell line, then, can be used as a platform for biotherapeutic protein production. The key steps include antiapoptotic transgene selection and transfection followed by clonal isolation and screening. With the proper screening methods, one can obtain a robust cell line that resists the harsh conditions of late-stage and/or high-density culture.

Directed evolution of mammalian anti-apoptosis proteins by somatic hypermutation

Recently, researchers have created novel fluorescent proteins by harnessing the somatic hypermutation ability of B cells. In this study, we examined if this approach could be used to evolve a non-fluorescent protein, namely the anti-apoptosis protein Bcl-x(L), using the Ramos B-cell line. After demonstrating that Ramos cells were capable of mutating a heterologous bcl-x(L) transgene, the cells were exposed to multiple rounds of the chemical apoptosis inducer staurosporine followed by rounds of recovery in fresh medium. The engineered B cells expressing Bcl-x(L) exhibited progressively lower increases in apoptosis activation as measured by caspase-3 activity after successive rounds of selective pressure with staurosporine treatment. Within the B-cell genome, a number of mutated bcl-x(L) transgene variants were identified after three rounds of evolution, including a mutation of Bcl-x(L) Asp29 to either Asn or His, in 8 out of 23 evaluated constructs that represented at least five distinct Ramos subpopulations. Subsequently, Chinese hamster ovary (CHO) cells engineered to overexpress the Bcl-x(L) Asp29Asn variant showed enhanced apoptosis resistance against an orthogonal apoptosis insult, Sindbis virus infection, when compared with cells expressing the wild-type Bcl-x(L) protein. These findings provide, to our knowledge, the first demonstration of evolution of a recombinant mammalian protein in a mammalian expression system.

Combinatorial engineering of ldh-a and bcl-2 for reducing lactate production and improving cell growth in dihydrofolate reductase-deficient Chinese hamster ovary cells

In Chinese hamster ovary (CHO) cells, rapid glucose metabolism normally leads to inefficient use of glucose, most of which is converted to lactate during cell cultures. Since lactate accumulation during the culture often exerts a negative effect on cell growth and valuable product formation, several genetic engineering approaches have been developed to suppress lactate dehydrogenase-A (LDH-A), the enzyme converting pyruvate into lactate. However, despite the reduced lactate accumulation, such cell cultures are eventually terminated in the late period of the culture, mainly due to apoptosis. Therefore, we developed an apoptosis-resistant, less lactate-producing dhfr(-) CHO cell line (CHO-Bcl2-LDHAsi) by overexpressing Bcl-2, one of the most well-known anti-apoptotic proteins, and by downregulating LDH-A in a dhfr(-) CHO cell line. When the dhfr(-) CHO-Bcl2-LDHAsi cell line was used as a host cell line for the development of recombinant CHO (rCHO) cells producing an Fc-fusion protein, the culture longevity of the rCHO cells was extended without any detrimental effect of genetic engineering on specific protein productivity. Simultaneously, the specific lactate production rate and apparent yield of lactate from glucose were reduced to 21-65% and 37-78% of the control cells, respectively. Taken together, these results show that the use of an apoptosis-resistant, less lactate-producing dhfr(-) CHO cell line as a host cell line saves the time and the effort of establishing an apoptosis-resistant, less lactate-producing rCHO cells for producing therapeutic proteins.

Effect of constitutively active Ras overexpression on cell growth in recombinant Chinese hamster ovary cells

Constitutively active Ras (CA-Ras) is known to enhance cell growth through the induction of various signaling cascades including the phosphoinositide 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/ERK signaling pathways, although the cellular response is highly dependent on the cell type. To evaluate the effect of CA-Ras overexpression on cell growth in recombinant Chinese hamster ovary (rCHO) cells, an erythropoietin (EPO)-producing rCHO cell line with regulated CA-Ras overexpression (EPO-off-CA-Ras) was established using the Tet-off system. The CA-Ras expression level in EPO-off-CA-Ras cells was tightly regulated by doxycycline addition. Although CA-Ras overexpression slightly increased the viable cell concentration during the late exponential phase, it did not increase the maximum viable cell concentration or specific growth rate to a significant degree. Unexpectedly, CA-Ras overexpression in rCHO cells led only to the enhancement in the activation of the MAPK/ERK signaling pathway and not the PI3K/Akt signaling pathway. Taken together, CA-Ras overexpression in rCHO cells did not significantly affect cell growth; it also had no critical impact on viable cell concentration or EPO production, possibly due to a failure to activate the PI3K/Akt signaling pathway.

A novel microRNA mmu-miR-466h affects apoptosis regulation in mammalian cells

This study determined the changes in microRNA (miRs) expression in mammalian Chinese hamster ovary (CHO) cells undergoing apoptosis induced by exposing the cells to nutrient-depleted media. The apoptosis onset was confirmed by reduced cell viability and Caspase-3/7 activation. Microarray comparison of known mouse and rat miRs in CHO cells exposed to fresh or depleted media revealed up-regulation of the mouse miR-297-669 cluster in CHO cells subjected to depleted media. The mmu-miR-466h was chosen for further analysis as the member of this cluster with the highest overexpression and its up-regulation in depleted media was confirmed with qRT-PCR. Since miRs suppress mRNA translation, we hypothesized that up-regulated mmu-miR-466h inhibits anti-apoptotic genes and induces apoptosis. A combination of bioinformatics and experimental tools was used to predict and verify mmu-miR-466h anti-apoptotic targets. 8708 predicted targets were obtained from miRecords database and narrowed to 38 anti-apoptotic genes with DAVID NCBI annotation tool. Several genes were selected from this anti-apoptotic subset based on nucleotide pairing complimentarity between the mmu-miR-466h seed region and 3' UTR of the target mRNAs. The qRT-PCR analysis revealed reduced mRNA levels of bcl2l2, dad1, birc6, stat5a, and smo genes in CHO cells exposed to depleted media. The inhibition of the mmu-miR-466h increased the expression levels of those genes and resulted in increased cell viability and decreased Caspase-3/7 activation. The up-regulation of mmu-miR-466h in response to nutrients depletion causes the inhibition of several anti-apoptotic genes in unison. This suggests the pro-apoptotic role of mmu-miR-466h and its capability to modulate the apoptotic pathway in mammalian cells.

Simultaneous targeting of Requiem & Alg-2 in Chinese hamster ovary cells for improved recombinant protein production

Apoptosis is known to be the main cause of cell death in the bioreactor environment, leading to the loss of recombinant protein productivity. In a previous study, transcriptional profiling was used to identify and target four early apoptosis-signaling genes: FADD, FAIM, Alg-2, and Requiem. The resulting cell lines had increased viable cell numbers and extended culture viability, which translated to increased protein productivity. Combinatorial targeting of two genes simultaneously has previously been shown to be more effective than targeting one gene alone. In this study, we sought to determine if targeting Requiem and Alg-2 was more effective than targeting Requiem alone. We found that targeting Requiem and Alg-2 did not result in extended culture viability, but resulted in an increase in maximum viable cell numbers and cumulative IVCD under fed-batch conditions. This in turn led to an approximately 1.5-fold increase in recombinant protein productivity.

Combining high-throughput screening of caspase activity with anti-apoptosis genes for development of robust CHO production cell lines

A set of anti-apoptotic genes were over-expressed, either singly or in combination, in an effort to develop robust Chinese Hamster Ovary host cell lines suitable for manufacturing biotherapeutics. High-throughput screening of caspase 3/7 activity enabled a rapid selection of transfectants with reduced caspase activity relative to the host cell line. Transfectants with reduced caspase 3/7 activity were then tested for improved integrated viable cell count (IVCC), a function of peak viable cell density and longevity. The maximal level of improvement in IVCC could be achieved by over-expression of either single anti-apoptotic genes, e.g., Bcl-2Δ (a mutated variant of Bcl-2) or Bcl-XL, or a combination of two or three anti-apoptotic genes, e.g., E1B-19K, Aven, and XIAPΔ. These cell lines yielded higher transient antibody production and a greater number of stable clones with high antibody yields. In a 5 L fed-batch bioreactor system, BΔ31-1, a stable clone expressing Bcl-2Δ, had a product titer that was 180% as compared to an optimal clone (Con-1) from the control cell line. Although lactate accumulated to more than 5 g/L in the control culture, its concentration was reduced in the anti-apoptotic BΔ31-1 cultures to below 1 g/L, confirming our earlier findings that cells over-expressing anti-apoptotic genes consume the lactate that would otherwise accumulate as a by-product in the culture medium. To the best of our knowledge, this is the first study to use the high throughput caspase screening method to identify CHO host cell lines with superior anti-apoptotic characteristics.

Cell death in mammalian cell culture: molecular mechanisms and cell line engineering strategies

Cell death is a fundamentally important problem in cell lines used by the biopharmaceutical industry. Environmental stress, which can result from nutrient depletion, by-product accumulation and chemical agents, activates through signalling cascades regulators that promote death. The best known key regulators of death process are the Bcl-2 family proteins which constitute a critical intracellular checkpoint of apoptosis cell death within a common death pathway. Engineering of several members of the anti-apoptosis Bcl-2 family genes in several cell types has extended the knowledge of their molecular function and interaction with other proteins, and their regulation of cell death. In this review, we describe the various modes of cell death and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of anti-apoptotic engineering strategies to inhibit cell death and increase productivity in mammalian cell culture.

Engineering mammalian cells in bioprocessing - current achievements and future perspectives

Over the past 20 years, we have seen significant improvements in product titres from 50 mg/l to 5-10 g/l, a more than 100-fold increase. The main methods that have been employed to achieve this increase in product titre have been through the manipulation of culture media and process control strategies, such as the optimization of fed-batch processes. An alternative means to increase productivity has been through the engineering of host cells by altering cellular processes. Recombinant DNA technology has been used to over-express or suppress specific genes to endow particular phenotypes. Cellular processes that have been altered in host cells include metabolism, cell cycle, protein secretion and apoptosis. Cell engineering has also been employed to improve post-translational modifications such as glycosylation. In this article, an overview of the main cell engineering strategies previously employed and the impact of these strategies are presented. Many of these strategies focus on engineering cell lines with more efficient carbon metabolism towards reducing waste metabolites, achieving a biphasic production system by engineering cell cycle control, increasing protein secretion by targeting specific endoplasmic reticulum stress chaperones, delaying cell death by targeting anti-apoptosis genes, and engineering glycosylation by enhancing recombinant protein sialylation and antibody glycosylation. Future perspectives for host cell engineering, and possible areas of research, are also discussed in this review.

[Producing several hundred of kilograms of monoclonal antibodies for therapy: a constant challenge]

Discovering and designing novel therapeutic monoclonal antibodies (mAb) is just the beginning. In order to support clinical evaluations and to reach the market place, rapid and cost effective production platforms are needed. Process development and production efficiency play a crucial role in this space since they influence the cost of good and ultimately wide access to these life-saving medications. Due to their therapeutic dosages and repeated uses, the yearly need for certain mAb, especially those used in the treatments of cancer and inflammation, amounts to several hundred of kilograms. Consequently, significant technological investments are needed to support these extraordinary large needs for such complex proteins, and the industry is constantly aiming at reducing production costs while maintaining product quality to high levels. This review discusses some of the critical scientific and engineering decisions, which span from the selection of cell-line expression platforms to choices of technologies, which influence mAbs cost of goods that need to be made along the development path of a therapeutic mAb.