Altering the central carbon metabolism of HEK293 cells: Impact on recombinant glycoprotein quality

Sodium acetate increases the productivity of HEK293 cells expressing the ECD-Her1 protein in batch cultures: experimental results and metabolic flux analysis

Human Embryonic Kidney cells (HEK293) are a popular host for recombinant protein expression and production in the biotechnological industry. This has driven within both, the scientific and the engineering communities, the search for strategies to increase their protein productivity. The present work is inserted into this search exploring the impact of adding sodium acetate (NaAc) into a batch culture of HEK293 cells. We monitored, as a function of time, the cell density, many external metabolites, and the supernatant concentration of the heterologous extra-cellular domain ECD-Her1 protein, a protein used to produce a candidate prostate cancer vaccine. We observed that by adding different concentrations of NaAc (0, 4, 6 and 8 mM), the production of ECD-Her1 protein increases consistently with increasing concentration, whereas the carrying capacity of the medium decreases. To understand these results we exploited a combination of experimental and computational techniques. Metabolic Flux Analysis (MFA) was used to infer intracellular metabolic fluxes from the concentration of external metabolites. Moreover, we measured independently the extracellular acidification rate and oxygen consumption rate of the cells. Both approaches support the idea that the addition of NaAc to the culture has a significant impact on the metabolism of the HEK293 cells and that, if properly tuned, enhances the productivity of the heterologous ECD-Her1 protein.

Use of single analytic tool to quantify both absolute N-glycosylation and glycan distribution in monoclonal antibodies

Recombinant proteins represent almost half of the top selling therapeutics-with over a hundred billion dollars in global sales-and their efficacy and safety strongly depend on glycosylation. In this study, we showcase a simple method to simultaneously analyze N-glycan micro- and macroheterogeneity of an immunoglobulin G (IgG) by quantifying glycan occupancy and distribution. Our approach is linear over a wide range of glycan and glycoprotein concentrations down to 25 ng/mL. Additionally, we present a case study demonstrating the effect of small molecule metabolic regulators on glycan heterogeneity using this approach. In particular, sodium oxamate (SOD) decreased Chinese hamster ovary (CHO) glucose metabolism and reduced IgG glycosylation by 40% through upregulating reactive oxygen species (ROS) and reducing the UDP-GlcNAc pool, while maintaining a similar glycan profile to control cultures. Here, we suggest glycan macroheterogeneity as an attribute should be included in bioprocess screening to identify process parameters that optimize culture performance without compromising antibody quality.

Homogenous overexpression of the extracellular matrix protein Netrin-1 in a hollow fiber bioreactor

The production of recombinant proteins for functional and biophysical studies, especially in the field of structural determination, still represents a challenge as high quality and quantities are needed to adequately perform experiments. This is in part solved by optimizing protein constructs and expression conditions to maximize the yields in regular flask expression systems. Still, work flow and effort can be substantial with no guarantee to obtain improvements. This study presents a combination of workflows that can be used to dramatically increase protein production and improve processing results, specifically for the extracellular matrix protein Netrin-1. This proteoglycan is an axon guidance cue which interacts with various receptors to initiate downstream signaling cascades affecting cell differentiation, proliferation, metabolism, and survival. We were able to produce large glycoprotein quantities in mammalian cells, which were engineered for protein overexpression and secretion into the media using the controlled environment provided by a hollow fiber bioreactor. Close monitoring of the internal bioreactor conditions allowed for stable production over an extended period of time. In addition to this, Netrin-1 concentrations were monitored in expression media through biolayer interferometry which allowed us to increase Netrin-1 media concentrations tenfold over our current flask systems while preserving excellent protein quality and in solution behavior. Our particular combination of genetic engineering, cell culture system, protein purification, and biophysical characterization permitted us to establish an efficient and continuous production of high-quality protein suitable for structural biology studies that can be translated to various biological systems. KEY POINTS: • Hollow fiber bioreactor produces substantial yields of homogenous Netrin-1 • Biolayer interferometry allows target protein quantitation in expression media • High production yields in the bioreactor do not impair Netrin-1 proteoglycan quality.

Affecting HEK293 Cell Growth and Production Performance by Modifying the Expression of Specific Genes

The HEK293 cell line has earned its place as a producer of biotherapeutics. In addition to its ease of growth in serum-free suspension culture and its amenability to transfection, this cell line’s most important attribute is its human origin, which makes it suitable to produce biologics intended for human use. At the present time, the growth and production properties of the HEK293 cell line are inferior to those of non-human cell lines, such as the Chinese hamster ovary (CHO) and the murine myeloma NSO cell lines. However, the modification of genes involved in cellular processes, such as cell proliferation, apoptosis, metabolism, glycosylation, secretion, and protein folding, in addition to bioprocess, media, and vector optimization, have greatly improved the performance of this cell line. This review provides a comprehensive summary of important achievements in HEK293 cell line engineering and on the global engineering approaches and functional genomic tools that have been employed to identify relevant genes for targeted engineering.

Regulation of the pyruvate metabolism node by monogene and polygene engineering of HEK-293 cells

HEK-293 cells are increasingly being used in the production of human adenovirus (HAdV) vaccines. However, the production of HAdV vaccine has not met the requirements of industrial production. Recently, we investigated the effects of various regulatory genes of the pyruvate metabolism node on the substance and energy metabolism and adenovirus reproduction in HEK-293 cells. Initially, single regulatory genes, including pkm2, pdhα, pyc2, mpc3, aralar1, ldha and pdk1, were studied. We found that metabolic performance and adenovirus reproduction capacity in HEK-293 cells were improved, and maximum adenovirus titre was increased approximately 15-fold. Next, we co-overexpressed the key genes, including pkm2, pyc2 and aralar1. The PYC2-A-P-L cells that had the appropriate co-overexpression levels of three genes had the most pronounced regulatory effect. The maximum cell density and maximum specific growth rate were increased by 21% compared with that in the control. The ΔLac/ΔGlc and ΔNH₃/ΔGln were decreased by 26% and 27%, respectively. The ATP production rate and the ATP/O₂ ratio were increased by 110% and 20%, respectively. The level of reactive oxygen species (ROS) was reduced by 60%. The adenovirus reproductive ability of the PYC2-A-P-L cells was approximately 30-fold higher than that of the control. The results showed that proper overexpression of the aralar1, pkm2 and pyc2 genes can significantly improve the substance and energy metabolism efficiency in HEK-293 cells, maximize the metabolic balance of pyruvate, and ultimately improve HAdV reproduction. This study provides a method of regulation of pyruvate metabolism and polygenic metabolic engineering in mammalian cells cultured in vitro and suggests an effective method for efficient HAdV production.

HEK-293 cells are increasingly being used in the production of human adenovirus (HAdV) vaccines.

Combining metabolic and process engineering strategies to improve recombinant glycoprotein production and quality

Increasing recombinant protein production while ensuring a high and consistent protein quality remains a challenge in mammalian cell culture process development. In this work, we combined a nutrient substitution approach with a metabolic engineering strategy that improves glucose utilization efficiency. This combination allowed us to tackle both lactate and ammonia accumulation and investigate on potential synergistic effects on protein production and quality. To this end, HEK293 cells overexpressing the pyruvate yeast carboxylase (PYC2) and their parental cells, both stably producing the therapeutic glycoprotein interferon α2b (IFNα2b), were cultured in media deprived of glutamine but containing chosen substitutes. Among the tested substitutes, pyruvate led to the best improvement in growth (integral of viable cell density) for both cell lines in batch cultures, whereas the culture of PYC2 cells without neither glutamine nor any substitute displayed surprisingly enhanced IFNα2b production. The drastic reduction in both lactate and ammonia in the cultures translated into extended high viability conditions and an increase in recombinant protein titer by up to 47% for the parental cells and the PYC2 cells. Product characterization performed by surface plasmon resonance biosensing using Sambucus nigra (SNA) lectin revealed that the increase in yield was however accompanied by a reduction in the degree of sialylation of the product. Supplementing cultures with glycosylation precursors and a cofactor were effective at counterbalancing the lack of glutamine and allowed improvement in IFNα2b quality as evaluated by lectin affinity. Our study provides a strategy to reconcile protein productivity and quality and highlights the advantages of PYC2-overexpressing cells in glutamine-free conditions.