Bcl-xL overexpression does not enhance specific erythropoietin productivity of recombinant CHO cells grown at 33°C and 37°C

Co-amplification of EBNA-1 and PyLT through dhfr-mediated gene amplification for improving foreign protein production in transient gene expression in CHO cells

Despite the relatively low transfection efficiency and low specific foreign protein productivity (q_p) of Chinese hamster ovary (CHO) cell-based transient gene expression (TGE) systems, TGE-based recombinant protein production technology predominantly employs CHO cells for pre-clinical research and development purposes. To improve TGE in CHO cells, Epstein-Barr virus nuclear antigen-1 (EBNA-1)/polyoma virus large T antigen (PyLT)-co-amplified recombinant CHO (rCHO) cells stably expressing EBNA-1 and PyLT were established using dihydrofolate reductase/methotrexate-mediated gene amplification. The level of transiently expressed Fc-fusion protein was significantly higher in the EBNA-1/PyLT-co-amplified pools compared to control cultures. Increased Fc-fusion protein production by EBNA-1/PyLT-co-amplification resulted from a higher q_p attributable to EBNA-1 but not PyLT expression. The q_p for TGE-based production with EBNA-1/PyLT-co-amplified rCHO cells (EP-amp-20) was approximately 22.9-fold that of the control culture with CHO-DG44 cells. Rather than improved transfection efficiency, this cell line demonstrated increased levels of mRNA expression and replicated DNA, contributing to an increased q_p. Furthermore, there was no significant difference in N-glycan profiles in Fc-fusion proteins produced in the TGE system. Taken together, these results showed that the use of rCHO cells with co-amplified expression of the viral elements EBNA-1 and PyLT improves TGE-based therapeutic protein production dramatically. Therefore, EBNA-1/PyLT-co-amplified rCHO cells will likely be useful as host cells in CHO cell-based TGE systems.

A Consensus Genome-scale Reconstruction of Chinese Hamster Ovary Cell Metabolism

Chinese hamster ovary (CHO) cells dominate biotherapeutic protein production and are widely used in mammalian cell line engineering research. To elucidate metabolic bottlenecks in protein production and to guide cell engineering and bioprocess optimization, we reconstructed the metabolic pathways in CHO and associated them with >1,700 genes in the Cricetulus griseus genome. The genome-scale metabolic model based on this reconstruction, iCHO1766, and cell-line-specific models for CHO-K1, CHO-S, and CHO-DG44 cells provide the biochemical basis of growth and recombinant protein production. The models accurately predict growth phenotypes and known auxotrophies in CHO cells. With the models, we quantify the protein synthesis capacity of CHO cells and demonstrate that common bioprocess treatments, such as histone deacetylase inhibitors, inefficiently increase product yield. However, our simulations show that the metabolic resources in CHO are more than three times more efficiently utilized for growth or recombinant protein synthesis following targeted efforts to engineer the CHO secretory pathway. This model will further accelerate CHO cell engineering and help optimize bioprocesses.

Multi-omic profiling -of EPO-producing Chinese hamster ovary cell panel reveals metabolic adaptation to heterologous protein production

Chinese hamster ovary (CHO) cells are the preferred production host for many therapeutic proteins. The production of heterologous proteins in CHO cells imposes a burden on the host cell metabolism and impact cellular physiology on a global scale. In this work, a multi‐omics approach was applied to study the production of erythropoietin (EPO) in a panel of CHO‐K1 cells under growth‐limited and unlimited conditions in batch and chemostat cultures. Physiological characterization of the EPO‐producing cells included global transcriptome analysis, targeted metabolome analysis, including intracellular pools of glycolytic intermediates, NAD(P)H/NAD(P)⁺, adenine nucleotide phosphates (ANP), and extracellular concentrations of sugars, organic acids, and amino acids. Potential impact of EPO expression on the protein secretory pathway was assessed at multiple stages using quantitative PCR (qPCR), reverse transcription PCR (qRT‐PCR), Western blots (WB), and global gene expression analysis to assess EPO gene copy numbers, EPO gene expression, intracellular EPO retention, and differentially expressed genes functionally related to secretory protein processing, respectively. We found no evidence supporting the existence of production bottlenecks in energy metabolism (i.e., glycolytic metabolites, NAD(P)H/NAD(P)⁺ and ANPs) in batch culture or in the secretory protein production pathway (i.e., gene dosage, transcription and post‐translational processing of EPO) in chemostat culture at specific productivities up to 5 pg/cell/day. Time‐course analysis of high‐ and low‐producing clones in chemostat culture revealed rapid adaptation of transcription levels of amino acid catabolic genes in favor of EPO production within nine generations. Interestingly, the adaptation was followed by an increase in specific EPO productivity. Biotechnol. Bioeng. 2015;112: 2373–2387. © 2015 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

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.

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.

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.

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.

A proteomic approach for identifying cellular proteins interacting with erythropoietin in recombinant Chinese hamster ovary cells

Identification of the cellular proteins interacting with incompletely folded and unfolded forms of erythropoietin (EPO) in recombinant CHO (rCHO) cells leads to better insight into the possible genetic manipulation approaches for increasing EPO production. To do so, a pull-down assay was performed with dual-tagged (N-terminal GST- and C-terminal hexahistidine-tagged) EPO expressed in E. coli as bait proteins and cell lysates of rCHO cells (DG44) as prey proteins. Cellular proteins interacting with dual-tagged EPO were then resolved by two-dimensional gel electrophoresis (2DE) and identified by MALDI-TOF MS/MS. A total of 27 protein spots including glucose-regulated protein 78 (GRP78) were successfully identified. Western blot analysis of GRP78 confirmed the results of the MS analyses. Taken together, a pull-down assay followed by a proteomic approach is found to be an efficient means to identify cellular proteins interacting with foreign protein in rCHO cells.