High zinc ion supplementation of more than 30 μM can increase monoclonal antibody production in recombinant Chinese hamster ovary DG44 cell culture

ZnSO4 Protects against premature ovarian failure through PI3K/AKT/GSK3β signaling pathway

Zinc (Zn) is an essential trace element with anti-inflammatory and antioxidant effects and plays a crucial role in the female reproductive system. We aimed to investigate the protective effect of ZnSO4 on premature ovarian failure (POF) in SD rats and granulosa cells (GCs) treated with cisplatin. We also explored the underlying mechanisms. In vivo experiments showed that ZnSO4 increased the serum levels of Zn2+, increased estrogen (E2) secretion, and decreased follicle-stimulating hormone (FSH) secretion in rats. ZnSO4 increased ovarian index, protected ovarian tissues and blood vessels, reduced excessive follicular atresia, and maintained follicular development. At the same time, ZnSO4 inhibited apoptosis in the ovaries. In vitro experiments showed that ZnSO4 combination treatment restored the intracellular levels of Zn2+ and inhibited the apoptosis of GCs. ZnSO4 inhibited cisplatin-induced reactive oxygen species (ROS) production and preserved mitochondrial membrane potential (MMP). We also found that ZnSO4 protected against POF by activating the PI3K/AKT/GSK3β signaling pathway and reducing apoptosis of GCs. These data suggest that ZnSO4 may be a potential therapeutic agent for protecting the ovaries and preserving fertility during chemotherapy.

Effects and mechanism of small molecule additives on recombinant protein in CHO cells

Chinese hamster ovary (CHO) cells can produce proteins with complex structures and post-translational modifications which are similar to human-derived cells, and they have been the ideal host cells for the production of recombinant therapy proteins (RTPs). Nearly 70% of approved RTPs are produced by CHO cells. In recent years, a series of measures have been developed to increase the expression of RTPs to achieve the lower production cost during the process of large-scale industrial production of recombinant protein in CHO cells. Among of them, the addition of small molecule additives in the culture medium can improve the expression and production efficiency of recombinant proteins, and has become an effective and simple method. In this paper, the characteristics of CHO cells, the effect and mechanism of small molecule additives are reviewed. KEY POINTS: • Small molecular additives on the expression of RTPs in CHO cells are reviewed • Small molecular additives improve the yield of RTPs • Small molecular additives provide methods for the optimization of serum-free medium.

Rapid metal speciation of cell culture media using reversed-phase separations and inductively coupled plasma optical emission spectrometry

Cell culture media metal content is critical in mammalian cell growth and monoclonal antibody productivity. The variability in metal concentrations has multiple sources of origin. As such, there is a need to analyze media before, during, and after production. Furthermore, it is not the simple presence of a given metal that can impact processes, but also their chemical form that is, speciation. To a first approximation, it is instructive to simply and quickly ascertain if the metals exist as inorganic (free metal) ions or are part of an organometallic complex (ligated). Here we present a simple workflow involving the capture of ligated metals on a fiber stationary phase with passage of the free ions to an inductively coupled plasma optical emission spectrometry for quantification; the captured species are subsequently eluted for quantification. This first level of speciation (free vs. ligated) can be informative towards sources of contaminant metal species and means to assess bioreactor processes.

Metal Ion Interactions with mAbs: Part 2. Zinc-Mediated Aggregation of IgG1 Monoclonal Antibodies

PURPOSE

To evaluate the physical and chemical degradation of monoclonal antibodies in the presence of Zn²⁺.

METHODS

A full length IgG1 monoclonal antibody (mAb1) was formulated with various amounts of Zn²⁺. The resulting mixture was incubated for several weeks at room temperature and analyzed using a variety of biochemical techniques to look for various physical (e.g. aggregation) and chemical (e.g. fragmentation) degradation pathways.

RESULTS

mAb1 of the IgG1 subclass undergoes aggregation in the presence of Zn²⁺ in a concentration dependent manner. Up to hexamers were characterized using SEC-MALS. No fragmentation was noticed in the presence of Zn²⁺ as opposed to that found in our previous report when IgG1 mAbs were incubated in the presence of Cu²⁺ ions. Site directed mutagenesis indicated the involvement of Fc histidine (His 310) in Zn²⁺ mediated aggregation.

CONCLUSIONS

A novel metal ion mediated isodesmic aggregation mechanism was found in IgG1 class of monoclonal antibodies. Histidine residues in the Fc region were determined to be the binding site and implicated in Zn²⁺ mediated aggregation.

Effect of iron addition on mAb productivity and oxidative stress in Chinese hamster ovary culture

Trace metals play a critical role in the development of culture media used for the production of therapeutic proteins. Iron has been shown to enhance the productivity of monoclonal antibodies during Chinese hamster ovary (CHO) cell culture. However, the redox activity and pro-oxidant behavior of iron may also contribute toward the production of reactive oxygen species (ROS). In this work, we aim to clarify the influence of trace iron by examining the relationship between iron supplementation to culture media, mAb productivity and glycosylation, and oxidative stress interplay within the cell. Specifically, we assessed the impacts of iron supplementation on (a) mAb production and glycosylation; (b) mitochondria-generated free hydroxyl radicals (ROS); (c) the cells ability to store energy during oxidative phosphorylation; and (d) mitochondrial iron concentration. Upon the increase of iron at inoculation, CHO cells maintained a capacity to rebound from iron-induced viability lapses during exponential growth phase and improved mAb productivity and increased mAb galactosylation. Fluorescent labeling of the mitochondrial hydroxyl radical showed enhanced environments of oxidative stress upon iron supplementation. Additional labeling of active mitochondria indicated that, despite the enhanced production of ROS in the mitochondria, mitochondrial membrane potential was minimally impacted. By replicating iron treatments during seed train passaging, the CHO cells were observed to adapt to the shock of iron supplementation prior to inoculation. Results from these experiments demonstrate that CHO cells have the capacity to adapt to enhanced environments of oxidative stress and improve mAb productivity and mAb galactosylation with minimal perturbations to cell culture.

Quantifying the impact of cell culture media on CHO cell growth and protein production

In recombinant protein production, cell culture media development and optimization is typically seen as a useful strategy to increase titer and cell density, reduce by-products, as well as improve product quality (with cell density and titer often serving as the primary reported outcome of media studies). However, despite the large number of media optimization studies, there have been few attempts to comprehensively assess the overall effectiveness of media additives. The aim of this review is therefore both to document published media optimization studies over the last twenty years (in the context of Chinese hamster ovary cell recombinant production) and quantitatively estimate the impact of this media optimization on cell culture performance. In considering 78 studies, we have identified 238 unique media components that have been supplemented over the last 20 years. Among these additives, trace elements stood out as having a positive impact on cell density while nucleotides show potential for increasing titer, with commercial supplements benefiting both. However, we also identified that the impact of specific additives is far more variable than often perceived. With relatively few media studies considering multiple cell lines or multiple basal media, teasing out consistent and general trends becomes a considerable challenge. By extracting cell density and titer values from all of the reviewed studies, we were able to build a mixed-effect model capable of estimating the relative impact of additives, cell line, product type, basal medium, cultivation method (flask or reactor), and feeding strategy (batch or fed-batch). Overall, additives only accounted for 3% of the variation in cell density and 1% of the variation in titer. Similarly, the impact of basal media was also relatively modest, at 10% for cell density and 0% for titer. Cell line, product type, and feeding strategy were all found to have more impact. These results emphasize the need for media studies to consider more factors to ensure that reported observations can be generalized and further developed.

Quantitative trace metal determinations in cell culture media using LS-APGD-MS and ICP-OES with free/bound species differentiation following polymer fiber separations

Liquid sampling-atmospheric pressure glow discharge-mass spectrometry (LS-APGD-MS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) were employed for the quantification of trace metals in cell culture media and their capabilities compared. The LS-APGD is interfaced here to a compact mass spectrometer (Advion CMS) towards the development of an at-bioreactor process monitoring strategy. Both techniques have been previously employed for the quantification of trace metals in samples of various complexities, making them a natural choice for this application. They have also demonstrated comparable analytical figures of merit including limits of detection (LOD), matrix tolerance, etc. While cell culture media is a complex sample, the ICP-OES technique was unaffected by the matrix. However, the LS-APGD-MS suffered from increases in spectral background. Despite this, both techniques achieved appropriate LODs for all metals analyzed in this work (Cu, Fe, Zn, Co, Mn, Ni; LOD < 100 ng mL^-1), except for Mn and Ni via LS-APGD-MS. To overcome the increased background seen on the LS-APGD-MS, a capillary channeled polymer (C-CP) polypropylene (PPY) fiber stationary phase was employed as an on-line separation for the removal of organic components prior to sample introduction into the plasma. It was further determined that Ni was retained on the column, preventing the detection of this element via LS-APGD-MS, and insights into metal speciation were discussed. Following implementation of this on-line separation strategy, the agreement between the techniques was acceptable for all analytes, and was excellent for Cu, Fe, and Zn.

Serum-Free Medium for Recombinant Protein Expression in Chinese Hamster Ovary Cells

At present, nearly 70% of recombinant therapeutic proteins (RTPs) are produced by Chinese hamster ovary (CHO) cells, and serum-free medium (SFM) is necessary for their culture to produce RTPs. In this review, the history and key components of SFM are first summarized, and its preparation and experimental design are described. Some small molecule compound additives can improve the yield and quality of RTP. The function and possible mechanisms of these additives are also reviewed here. Finally, the future perspectives of SFM use with CHO cells for RTP production are discussed.

Zinc supplementation increases protein titer of recombinant CHO cells

In order to study the impact of zinc and copper on the titer levels of mAb and recombinant protein in CHO cells, the IgG-expressing (DP12) and EPO-expressing (SK15) cell lines were cultured in chemically defined media with increasing concentrations of either metal. Supplementation with 25 mg/l in CDM media resulted in a significant increase in EPO (1.7-fold) and IgG (2.6-fold) titers compared to control (no added zinc). Titers at this Zn concentration in CDM containing the insulin replacing agent aurintricarboxylic acid (ATA) (CDM + A) showed a 1.8-fold (EPO) and 1.2-fold (IgG) titers increase compared to control. ATA appeared to also reduce the specific productivity (Qp) enhancement induced by Zn-25, with up to 4.9-fold (DP12) and 1.9-fold (SK15) Qp increase in CDM compared to the 1.6-fold (DP12) and 1.5-fold (SK15) Qp increase observed in CDM + A. A 31% reduced Viable Cell Density (VCD) in DP12 was observed in both Zn-supplemented media (3 × 106 cells/ml vs 4.2 × 106 cells/ml, day 5), whereas SK15 Zn-25 cultures displayed a 24% lower peak only in CDM + A (2.2 × 106 cells/ml vs 3.2 × 106 cells/ml, day 5). Supplementation with copper at 13.7-20 mg/l resulted in less significant cell line/product-type dependent effects on titer, VCD and Viability. Analysis of the energetic phenotype of both cell lines in 25 mg/l Zn-supplemented CDM media revealed a twofold increase in the oxygen consumption rate (OCR) compared to non-supplemented cells. Together, these data suggest that high zinc supplementation may induce an increase in oxidative respiration metabolism that results in increased Qp and titers in suspension CHO cultures.

Consequences of trace metal variability and supplementation on Chinese hamster ovary (CHO) cell culture performance: A review of key mechanisms and considerations

Trace metals are supplied to chemically-defined media (CDM) for optimal Chinese hamster ovary (CHO) cell culture performance during the production of monoclonal antibodies and other therapeutic proteins. However, lot-to-lot and vendor-to-vendor variability in raw materials consequently leads to an imbalance of trace metals that are supplied to CDM. This imbalance can yield detrimental effects rooted in several primary mechanisms and pathways including oxidative stress, apoptosis, lactate accumulation, and unfavorable glycan synthesis. Recent research endeavors involve supplying zinc, copper, and manganese to CDM in excess to further maximize culture productivity and product quality. These treatments significantly impact critical quality attributes and furthermore highlight the degree to which trace metal availability can affect CHO cell culture performance. This review highlights the role of trace metal variability, supplementation, and interplay on key cellular mechanisms responsible for overall culture performance and the production and quality of therapeutic proteins.

Purity by design: Reducing impurities in bioproduction by stimulus-controlled global translational downregulation of non-product proteins

Capitalizing on the ability of mammalian cells to conduct complex post-translational modifications, most protein therapeutics are currently produced in cell culture systems. Addition of a signal peptide to the product protein enables its accumulation in the cell culture supernatant, but separation of the product from endogenously secreted proteins remains costly and labor-intensive. We considered that global downregulation of translation of non-product proteins would be an efficient strategy to minimize downstream processing requirements. Therefore, taking advantage of the ability of mammalian protein kinase R (PKR) to switch off most cellular translation processes in response to infection by viruses, we fused a caffeine-inducible dimerization domain to the catalytic domain of PKR. Addition of caffeine to this construct results in homodimerization and activation of PKR, effectively rewiring rapid global translational downregulation to the addition of the stimulus in a dose-dependent manner. Then, to protect translation of the target therapeutic, we screened viral and cellular internal ribosomal entry sites (IRESes) known or suspected to be resistant to PKR-induced translational stress. After choosing the best-in-class Seneca valley virus (SVV) IRES, we additionally screened for IRES transactivation factors (ITAFs) as well as for supplementary small molecules to further boost the production titer of the product protein under conditions of global translational downregulation. Importantly, the residual global translation activity of roughly 10% under maximal downregulation is sufficient to maintain cellular viability during a production timeframe of at least five days. Standard industrially used adherent as well as suspension-adapted cell lines transfected with this synthetic biology-inspired Protein Kinase R-Enhanced Protein Production (PREPP) system could produce several medicinally relevant protein therapeutics, such as the blockbuster drug rituximab, in substantial quantities and with significantly higher purity than previous culture technologies. We believe incorporation of such purity-by-design technology in the production process will alleviate downstream processing bottlenecks in future biopharmaceutical manufacturing.

Zinc supplementation decreases galactosylation of recombinant IgG in CHO cells

Trace element composition of culture medium can be altered to modulate glycoform of recombinant glycoproteins. In this study, we show that Zn²⁺ supplementation at or above 100 μM decreases galactosylation of recombinant IgG expressed in Chinese Hamster Ovary cells. This decrease in galactosylation is not due to reduced galactosyltransferase expression. This effect persists upon supplementation of galactose and uridine to the culture, indicating that it may not be due to reduced UDP-Gal availability. Measurements of galactosyltransferase activity in the cell lysate show that activity decreases with increasing Zn²⁺/Mn²⁺ ratio. This suggests that one possible explanation of the effect of Zn²⁺ may be reduced intracellular galactosyltransferase activity due to increase in Zn²⁺/Mn²⁺ ratio. Consistent with this, the decrease in galactosylation of IgG could be reversed by supplementation of Mn²⁺ (a cofactor of galactosyltransferase) which increases intracellular Mn²⁺ content. Measurement of total intracellular Zn²⁺ content, however, indicates no significant upregulation of total intracellular Zn²⁺ content and no significant downregulation of intracellular Mn²⁺ content with Zn²⁺ supplementation. One possible explanation could be that cellular detoxification response to higher extracellular Zn²⁺ concentration might lead to changes in intracellular distribution of Mn²⁺. In this case, Zn²⁺ supplementation would be expected to interfere with other known effects of Mn²⁺. Indeed, the previously reported increase in high mannose glycans upon Mn²⁺ supplementation in the absence of glucose is reversed by Zn²⁺ supplementation. This study also suggests the use of Mn²⁺ supplementation as a strategy to overcome the effect of lot-to-lot variability in trace element concentrations on galactosylation.

Zinc enhances the cellular energy supply to improve cell motility and restore impaired energetic metabolism in a toxic environment induced by OTA

Exogenous nutrient elements modulate the energetic metabolism responses that are prerequisites for cellular homeostasis and metabolic physiology. Although zinc is important in oxidative stress and cytoprotection processes, its role in the regulation of energetic metabolism remains largely unknown. In this study, we found that zinc stimulated aspect in cell motility and was essential in restoring the Ochratoxin A (OTA)-induced energetic metabolism damage in HEK293 cells. Moreover, using zinc supplementation and zinc deficiency models, we observed that zinc is conducive to mitochondrial pyruvate transport, oxidative phosphorylation, carbohydrate metabolism, lipid metabolism and ultimate energy metabolism in both normal and toxic-induced oxidative stress conditions in vitro, and it plays an important role in restoring impaired energetic metabolism. This zinc-mediated energetic metabolism regulation could also be helpful for DNA maintenance, cytoprotection and hereditary cancer traceability. Therefore, zinc can widely adjust energetic metabolism and is essential in restoring the impaired energetic metabolism of cellular physiology.

Tetrahydrofolate increases suspension growth of dihydrofolate reductase-deficient chinese hamster ovary DG44 cells in chemically defined media

Adaptation of dihydrofolate reductase (DHFR)-deficient Chinese hamster ovary (CHO) DG44 cells to chemically defined suspension culture conditions is a time-consuming and labor-intensive process because nonadapted DHFR-deficient CHO DG44 cells normally show poor growth in chemically defined medium (CDM). We examined the effects of folate derivatives, ribonucleotides, and nucleobases on the growth of suspension-adapted DHFR-deficient CHO DG44 cells in CDM. Among the tested additives, tetrahydrofolate (THF) was identified as an effective component for increasing cell growth. THF supplementation in the range of 0.2-359 μM enhanced cell growth in in-house CDM. Addition of 3.6 μM THF to in-house CDM resulted in a more than 2.5-fold increase in maximum viable cell density. Moreover, supplementation of six different commercial CDMs with 3.6 μM THF yielded up to 2.9-fold enhancement of maximum viable cell density. An anchorage- and serum-dependent DHFR-deficient CHO DG44 cell line was adapted within two consecutive passages to suspension growth in in-house CDM supplemented with 3.6 μM THF. These data indicate that supplementation of chemically defined cell culture media with greater than 0.2 μM THF can help achieve a high density of suspension-adapted DHFR-deficient CHO DG44 cells and may facilitate rapid adaptation of nonadapted DHFR-deficient CHO DG44 cells to suspension culture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1539-1546, 2016.