Large scale production of recombinant mouse and rat growth hormone by fed-batch GS-NSO cell cultures

Transcriptome and proteome analysis of Chinese hamster ovary cells under low temperature and butyrate treatment

Recombinant Chinese hamster ovary (CHO) cells selected for high productivity are capable of secreting immunoglobulin G (IgG) molecules at a level that rivals plasma cells in vivo. Following butyrate treatment at 33 degrees C, further increases in productivity are observed. To better understand the mechanisms by which this increased productivity is incurred, the transcriptional response of an antibody-producing cell line undergoing these treatments was investigated using oligo-DNA microarrays. Using distance calculations, more than 900 genes were identified as kinetically differentially expressed between the butyrate-treated 33 degrees C culture and the untreated culture. Furthermore, transcript levels of the heavy and light chain IgG genes increased following treatment. Using stable isotope labeling (SILAC), the secretion rate of IgG was investigated by tracking the decay of the isotope label upon switching to unlabeled medium. Both treated and untreated cultures exhibited very similar IgG secretion kinetics. In contrast, the intracellular IgG content was found to be elevated following treatment. This result suggests that increased productivity under treatment is attributable to elevated cellular secretory capacity, rather than shorter holding times in the secretory pathway. This hypothesis is further supported by the results of gene set enrichment analysis (GSEA), which revealed that elements of the secretory pathway, including Golgi apparatus, cytoskeleton protein binding and small GTPase-mediated signal transduction are enriched and thus may play a role in the increased recombinant protein production observed under butyrate treatment at 33 degrees C.

Recombinant Rat and Mouse Growth Hormones: Risk Assessment of Carcinogenic Potential in 2-Year Bioassays in Rats and Mice

Recombinant rat growth hormone (rrGH) and recombinant mouse growth hormone (rmGH) were developed to evaluate the potential carcinogenicity of each biologically active growth hormone (GH) as assessed in the respective species. Biological activities of rrGH and rmGH were demonstrated by showing an increase in body weight gain and serum levels of insulin-like growth factor-1 (IGF-1) in hypophysectomized rats receiving daily sc injections for 6 days. With the exception of pharmacologically mediated weight gain, rrGH and rmGH had no adverse effects in 5-week oral toxicity studies and no production of anti-recombinant GH antibodies. The high doses selected for the carcinogenicity studies provided systemic exposures of GH up to approximately 10-fold over basal levels. In the 105-week mouse carcinogenicity study, daily sc injections of rmGH at 0.1, 0.2, or 0.5 mg/kg/day were well tolerated and had no effects on survival or incidence of tumors. In the 106-week rat carcinogenicity study, daily sc injections of rrGH at 0.2, 0.4, or 0.8 mg/kg/day had a favorable effect on longevity in female rats administered 0.4 or 0.8 mg/kg/day, an increased weight gain in females and males, and no increase in the incidence of tumors. The absence of carcinogenic effects of recombinant GH administered daily for 2 years to rodents was consistent with publications of clinical experience, indicating a lack of convincing evidence for an increased risk of cancer in children receiving human recombinant GH replacement therapy.

Development of a fed-batch culture process for enhanced production of recombinant human antithrombin by Chinese hamster ovary cells

Antithrombin is a serine protease inhibitor that inactivates several coagulation proteases, primarily thrombin and factor Xa. The Chinese hamster ovary (CHO) cell line transfected with a vector expressing recombinant human antithrombin (rAT) and a selectable marker, glutamine synthetase (GS), was cultivated in a 2-l fed-batch culture process using serum-free, glutamine-free medium. To maximize the rAT yield, effects of culture pH, balanced amino acid feeding, and an increased glutamate concentration on cell metabolism and rAT production were investigated. When cells were grown at pH values of 6.6, 6.8, 7.0, and 7.2, the maximum cell density and maximum lactate concentration decreased with decreasing pH. The highest production level of rAT was obtained at culture pH 6.8 due to the extended culture lifetime. Compared to the imbalanced amino acid feeding at culture pH 6.8, the balanced amino acid feeding increased the amount of rAT activity by 30% as a result of an increased viable cell number. A decrease in the specific glucose consumption rate (q(Glc)) with increasing culture time was observed in all the above-mentioned experiments, while the glucose concentration was maintained above 0.7 g l(-1). In addition, a decrease in the specific rAT production rate (q(rAT)) was observed after the depletion of lactate in the late cultivation stage. Taken together, these results suggest that the reduced availability of cellular energy caused by the decrease in q(Glc) and depletion of lactate led to the decrease in q(rAT). This decrease in q(rAT) was partially prevented by increasing the residual glutamate concentration from 1 mM to 7 mM, thus resulting in an additional 30% increase in the amount of rAT activity. The optimized fed-batch culture process yielded 1.0 g l(-1) rAT at 287 h of cultivation.

Large-scale gene expression analysis of cholesterol dependence in NS0 cells

NS0, a nonsecreting mouse myeloma cell, is a major host line used for recombinant antibody production. These cells have a cholesterol-dependent phenotype and rely on an exogenous supply of cholesterol for their survival and growth. To better understand the physiology underlying cholesterol dependence, we compared NS0 cells, cultivated under standard cholesterol-dependent growth conditions (NS0), to cells adapted to cholesterol-independent conditions (NS0 revertant, NS0_r). Large-scale transcriptional analyses were done using the Affymetrix GeneChip array, MG-U74Av2. The transcripts expressed differentially across the two cell lines were identified. Additionally, proteomic tools were employed to analyze cell lysates from these two cell lines. Cellular proteins from both NS0 and NS0_r were subjected to 2D gel electrophoresis. MALDI-TOF mass spectrometry was performed to determine the identity of the differentially expressed spots. We examined the expression level of mouse genes directly involved in cholesterol biosynthesis, lipid metabolism, and central energy metabolism. Most of these genes were downregulated in the revertant cell type, NS0_r, compared to NS0. Overall, a large number of genes are expressed differentially, indicating that the reversal of cholesterol dependency has a profound effect on cell physiology. It is probable that a single gene mutation, activation, or inactivation is responsible for cholesterol auxotrophy. However, the wide-ranging changes in gene expression point to the distinct possibility of a regulatory event affecting the reversibility of auxotrophy, either directly or indirectly.

The response of GS-NS0 myeloma cells to pH shifts and pH perturbations

The perceived sensitivity of animal cells to hydrodynamic shear has limited agitation and aeration at large-scale. This makes it difficult to ensure adequate mixing of the vessel contents and may lead to inhomogeneities in operational parameters such as temperature, dissolved oxygen concentration, and especially pH. The effect of pH shifts and pH perturbations on the cellular responses, in batch culture, of a GS-NS0 mouse myeloma cell line, expressing a recombinant antibody, was investigated. In addition, the effect of extreme pH on the structure of the purified antibody product was studied using isoelectric focusing. The fermentation pH value was shifted abruptly from pH 7.3 to pH values ranging from 6.5 to 9.0. Culture pH was maintained at this new value for the remainder of the fermentation. All pH shifts of above 0.2 units caused a transient increase in apoptosis. However, cultures shifted to pH values between 7.0 and 8.0 continued to grow and the apoptotic fraction returned to initial levels. Cultures shifted to pH values above pH 8.0 and below pH 7.0 did not recover resulting in culture death. For example, a shift to pH 8.5 caused accumulation of cells in the G(2)/M phase of the cell cycle followed by apoptotic death. After the pH shift, maximum specific growth rate was observed over the range pH 7.3 to 7.5 and maximum viable cell number was seen at pH 7.3. Maximum volumetric antibody production, resulting from increased culture longevity, was seen at pH 7.0. It was also observed that glucose consumption increased with increasing pH. In a separate set of experiments cells were subjected to a single pH perturbation ranging in duration from 0 to 600 minutes. Exposure of cells to a pH value greater than 8.5 for more than 10 minutes caused a decrease in the proportion of viable cells and induced a lag in cell growth. At very low pH (6.5) similar effects were seen, but only for extended perturbations (600 min). However, after recovery from the pH perturbation, growth, product secretion and metabolism all returned to original levels. Incubation of the antibody, at the range of pH values investigated, indicated no alterations in the structure of the antibody as determined by the isoelectric focusing pattern.

Advances in animal cell recombinant protein production: GS-NS0 expression system

The production of recombinant proteins using mammalian cell expression systems is of growing importance within biotechnology, largely due to the ability of specific mammalian cells to carry out post-translational modifications of the correct fidelity. The Glutamine Synthetase-NS0 system is now one such industrially important expression system.Glutamine synthetase catalyses the formation ofglutamine from glutamate and ammonia. NS0 cellscontain extremely low levels of endogenous glutaminesynthetase activity, therefore exogenous glutaminesynthetase can be used efficiently as a selectablemarker to identify successful transfectants in theabsence of glutamine in the media. In addition, theinclusion of methionine sulphoximine, an inhibitor ofglutamine synthetase activity, enables furtherselection of those clones producing relatively highlevels of transfected glutamine synthetase and henceany heterologous gene which is coupled to it. Theglutamine synthetase system technology has been usedfor research and development purposes during thisdecade and its importance is clearly demonstrated nowthat two therapeutic products produced using thissystem have reached the market place.

Reactor design for large scale suspension animal cell culture

The scale of operation of freely suspended animal cell culture has been increasing and in order to meet the demand for recombinant therapeutic products, this increase is likely to continue. The most common reactor types used are stirred tanks. Air lift fermenters are also used, albeit less commonly. No specific guidelines have been published for large scale (>/=10 000 L) animal cell culture and reactor designs are often based on those used for microbial systems. However, due to the large difference in energy inputs used for microbial and animal cell systems such designs may be far from optimal. In this review the importance of achieving a balance between mixing, mass transfer and shear effects is emphasised. The implications that meeting this balance has on design of vessels and operation, particularly in terms of strategies to ensure adequate mixing to achieve homogeneity in pH and dissolved gas concentrations are discussed.