Application of a statistical design to the optimization of culture medium for recombinant interferon-gamma production by Chinese hamster ovary cells

Addressing amino acid-derived inhibitory metabolites and enhancing CHO cell culture performance through DOE-guided media modifications

Previously, we identified six inhibitory metabolites (IMs) accumulating in Chinese hamster ovary (CHO) cultures using AMBIC 1.0 community reference medium that negatively impacted culture performance. The goal of the current study was to modify the medium to control IM accumulation through design of experiments (DOE). Initial over-supplementation of precursor amino acids (AAs) by 100% to 200% in the culture medium revealed positive correlations between initial AA concentrations and IM levels. A screening design identified 5 AA targets, Lys, Ile, Trp, Leu, Arg, as key contributors to IMs. Response surface design analysis was used to reduce initial AA levels between 13% and 33%, and these were then evaluated in batch and fed-batch cultures. Lowering AAs in basal and feed medium and reducing feed rate from 10% to 5% reduced inhibitory metabolites HICA and NAP by up to 50%, MSA by 30%, and CMP by 15%. These reductions were accompanied by a 13% to 40% improvement in peak viable cell densities and 7% to 50% enhancement in IgG production in batch and fed-batch processes, respectively. This study demonstrates the value of tuning specific AA levels in reference basal and feed media using statistical design methodologies to lower problematic IMs.

Employing active learning in the optimization of culture medium for mammalian cells

Medium optimization is a crucial step during cell culture for biopharmaceutics and regenerative medicine; however, this step remains challenging, as both media and cells are highly complex systems. Here, we addressed this issue by employing active learning. Specifically, we introduced machine learning to cell culture experiments to optimize culture medium. The cell line HeLa-S3 and the gradient-boosting decision tree algorithm were used to find optimized media as pilot studies. To acquire the training data, cell culture was performed in a large variety of medium combinations. The cellular NAD(P)H abundance, represented as A450, was used to indicate the goodness of culture media. In active learning, regular and time-saving modes were developed using culture data at 168 h and 96 h, respectively. Both modes successfully fine-tuned 29 components to generate a medium for improved cell culture. Intriguingly, the two modes provided different predictions for the concentrations of vitamins and amino acids, and a significant decrease was commonly predicted for fetal bovine serum (FBS) compared to the commercial medium. In addition, active learning-assisted medium optimization significantly increased the cellular concentration of NAD(P)H, an active chemical with a constant abundance in living cells. Our study demonstrated the efficiency and practicality of active learning for medium optimization and provided valuable information for employing machine learning technology in cell biology experiments.

Biopharmaceutical Manufacturing: Historical Perspectives and Future Directions

This review describes key milestones related to the production of biopharmaceuticals-therapies manufactured using recombinant DNA technology. The market for biopharmaceuticals has grown significantly since the first biopharmaceutical approval in 1982, and the scientific maturity of the technologies used in their manufacturing processes has grown concomitantly. Early processes relied on established unit operations, with research focused on process scale-up and improved culture productivity. In the early 2000s, changes in regulatory frameworks and the introduction of Quality by Design emphasized the importance of developing manufacturing processes to deliver a desired product quality profile. As a result, companies adopted platform processes and focused on understanding the dynamic interplay between product quality and processing conditions. The consistent and reproducible manufacturing processes of today's biopharmaceutical industry have set high standards for product efficacy, quality, and safety, and as the industry continues to evolve in the coming decade, intensified processing capabilities for an expanded range of therapeutic modalities will likely become routine. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Clever Experimental Designs: Shortcuts for Better iPSC Differentiation

For practical use of pluripotent stem cells (PSCs) for disease modelling, drug screening, and regenerative medicine, the cell differentiation process needs to be properly refined to generate end products with consistent and high quality. To construct and optimize a robust cell-induction process, a myriad of cell culture conditions should be considered. In contrast to inefficient brute-force screening, statistical design of experiments (DOE) approaches, such as factorial design, orthogonal array design, response surface methodology (RSM), definitive screening design (DSD), and mixture design, enable efficient and strategic screening of conditions in smaller experimental runs through multifactorial screening and/or quantitative modeling. Although DOE has become routinely utilized in the bioengineering and pharmaceutical fields, the imminent need of more detailed cell-lineage specification, complex organoid construction, and a stable supply of qualified cell-derived material requires expedition of DOE utilization in stem cell bioprocessing. This review summarizes DOE-based cell culture optimizations of PSCs, mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), and Chinese hamster ovary (CHO) cells, which guide effective research and development of PSC-derived materials for academic and industrial applications.

Current insights into the microbial degradation for pyrethroids: strain safety, biochemical pathway, and genetic engineering

As a biologically inspired insecticide, pyrethroids (PYRs) exert evident toxic side effects on non-target organisms. PYRs and their general toxic intermediate 3-phenoxybenzoic acid (3-PBA) have shown high detection rates/levels in human beings recently, for which diet was identified as the major exposure route. Microbial mineralization has emerged as a versatile strategy in addressing such escalating concern. Herein, PYRs and 3-PBA biodegradation with regards to strain safety, application and surfactant were summarized. Numerous PYRs-degrading microbes have been reported yet with a minority focused on 3-PBA. Most isolates were from contaminated sites while several microbial food cultures (MFCs) have been investigated. MFCs such as Bacillus spp. and Aspergillus spp. that dominate in PYRs-degrading microbial pools are applicable candidates for agricultural by-products detoxification during the postharvest process. Subsequently, we discussed committed degradation steps, wherein hydrolase responsible for PYRs ester linkage cleavage and oxygenase for 3-PBA diphenyl ether bond rupture play vital roles. Finally, comprehensive information of the key enzyme genes is outlined along with methodologies concerning gene cloning. Cytochrome P450 monooxygenases (CYP) is competent for diphenyl ether scission. Newly-developed omics has become a feasible gene and enzyme mining technology. To achieve PYRs mineralization in feed and food commodities, the screening of MFCs rich in related enzymes and the construction of MFCs-derived genetically modified microbes (GMMs) exhibit great potential considering the safety issues.

One-Time Optimization of Advanced T Cell Culture Media Using a Machine Learning Pipeline

The growing application of cell and gene therapies in humans leads to a need for cell type-optimized culture media. Design of Experiments (DoE) is a successful and well known tool for the development and optimization of cell culture media for bioprocessing. When optimizing culture media for primary cells used in cell and gene therapy, traditional DoE approaches that depend on interpretable models will not always provide reliable predictions due to high donor variability. Here we present the implementation of a machine learning pipeline into the DoE-based design of cell culture media to optimize T cell cultures in one experimental step (one-time optimization). We applied a definitive screening design from the DoE toolbox to screen 12 major media components, resulting in 25 (2k + 1) media formulations. T cells purified from a set of four human donors were cultured for 6 days and cell viability on day 3 and cell expansion on day 6 were recorded as response variables. These data were used as a training set in the machine learning pipeline. In the first step, individual models were created for each donor, evaluated and selected for each response variable, resulting in eight final statistical models (R² > 0.92, RMSE < 1.5). These statistical models were used to predict T cell viability and expansion for 10⁵ random in silico-generated media formulations for each donor in a grid search approach. With the aim of identifying similar formulations in all donors, the 40 best performing media formulations of each response variable were pooled from all donors (n = 320) and subjected to unsupervised clustering using the k-means algorithm. The median of each media component in each cluster was defined as the cluster media formulation. When these formulations were tested in a new set of donor cells, they not only showed a higher T cell expansion than the reference medium, but also precisely matched the average expansion predicted from the donor models of the training set. In summary, we have shown that the introduction of a machine learning pipeline resulted in a one-time optimized T cell culture medium and is advantageous when working with heterogeneous biological material.

Evidence for co-translational misincorporation of non-canonical amino acid hydroxyproline in recombinant antibodies produced in Chinese Hamster Ovary (CHO) cell lines

With the advent of highly sensitive technologies such as tandem mass spectrometry and next-generation sequencing, recombinant antibodies are now routinely analyzed for the presence of low-level sequence variants including amino acid misincorporations. During mAb cell culture process development, we found that proline was replaced with the non-canonical amino acid, hydroxyproline, in the protein sequence. We investigated the relationship between proline content in the cell culture media and proline sequence variants and found that the proline concentration was inversely correlated with the amount of sequence variants detected in the protein sequence. Hydroxyproline incorporation has been previously reported in recombinant proteins produced in mammalian expression systems as a post-translational modification. Given the dependency on proline levels, the mechanism was then investigated. To address the possibility of co-translational misincorporation of hydroxyproline, we used tandem mass spectrometry to measure incorporation of stable-isotope labelled hydroxyproline added to the feed of a production bioreactor. We discovered co-translational misincorporation of labelled hydroxyproline in the recombinant antibody. These findings are significant, since they underscore the need to track non-canonical amino acid incorporation as a co-translational event in CHO cells. Understanding the mechanism of hydroxyproline incorporation is crucial in developing an appropriate control strategy during biologics production.

Efficient Optimization of Process Strategies with Model-Assisted Design of Experiments

Conventional design of experiments (DoE) methods require expert knowledge about the investigated factors and their boundary values and mostly lead to multiple rounds of time-consuming and costly experiments. The combination of DoE with mathematical process modeling in model-assisted DoE (mDoE) can be used to increase the mechanistic understanding of the process. Furthermore, it is aimed to optimize the processes with respect to a target (e.g., amount of cells, product titer), which also provides new insights into the process. In this chapter, the workflow of mDoE is explained stepwise including corresponding protocols. Firstly, a mathematical process model is adapted to cultivation data of first experimental data or existing knowledge. Secondly, model-assisted simulations are treated in the same way as experimentally derived data and included as responses in statistical DoEs. The DoEs are then evaluated based on the simulated data, and a constrained-based optimization of the experimental space can be conducted. This loop can be repeated several times and significantly reduces the number of experiments in process development.

Use of High-Throughput Automated Microbioreactor System for Production of Model IgG1 in CHO Cells

Automated microscale bioreactors (15 mL) can be a useful tool for cell culture engineers. They facilitate the simultaneous execution of a wide variety of experimental conditions while minimizing potential process variability. Applications of this approach include: clone screening, temperature and pH shifts, media and supplement optimization. Furthermore, the small reactor volumes are conducive to large Design of Experiments that investigate a wide range of conditions. This allows upstream processes to be significantly optimized before scale-up where experimentation is more limited in scope due to time and economic constraints. Automated microscale bioreactor systems offer various advantages over traditional small scale cell culture units, such as shake flasks or spinner flasks. However, during pilot scale process development significant care must be taken to ensure that these advantages are realized. When run with care, the system can enable high level automation, can be programmed to run DOE's with a higher number of variables and can reduce sampling time when integrated with a nutrient analyzer or cell counter. Integration of the expert-derived heuristics presented here, with current automated microscale bioreactor experiments can minimize common pitfalls that hinder meaningful results. In the extreme, failure to adhere to the principles laid out here can lead to equipment damage that requires expensive repairs. Furthermore, the microbioreactor systems have small culture volumes making characterization of cell culture conditions difficult. The number and amount of samples taken in-process in batch mode culture is limited as operating volumes cannot fall below 10 mL. This method will discuss the benefits and drawbacks of microscale bioreactor systems.

13 C Flux Analysis Reveals that Rebalancing Medium Amino Acid Composition can Reduce Ammonia Production while Preserving Central Carbon Metabolism of CHO Cell Cultures

¹³ C metabolic flux analysis (MFA) provides a rigorous approach to quantify intracellular metabolism of industrial cell lines. In this study, ¹³ C MFA was used to characterize the metabolic response of Chinese hamster ovary (CHO) cells to a novel medium variant designed to reduce ammonia production. Ammonia inhibits growth and viability of CHO cell cultures, alters glycosylation of recombinant proteins, and enhances product degradation. Ammonia production was reduced by manipulating the amino acid composition of the culture medium; specifically, glutamine, glutamate, asparagine, aspartate, and serine levels were adjusted. Parallel ¹³ C flux analysis experiments determined that, while ammonia production decreased by roughly 40%, CHO cell metabolic phenotype, growth, viability, and monoclonal antibody (mAb) titer were not significantly altered by the changes in media composition. This study illustrates how ¹³ C flux analysis can be applied to assess the metabolic effects of media manipulations on mammalian cell cultures. The analysis revealed that adjusting the amino acid composition of CHO cell culture media can effectively reduce ammonia production while preserving fluxes throughout central carbon metabolism.

Applications of a metabolic network model of mesenchymal stem cells for controlling cell proliferation and differentiation

Mesenchymal stem cells (MSCs) can be isolated from several tissues of adults. In addition, MSCs have the potential of differentiation into several cell types. Therefore, MSCs are very useful in stem cell therapy and regenerative medicine. MSCs have also been used as gene or protein carriers. As a result, maintaining MSCs in a desirable metabolic state has been the subject of several studies. Here, we used a genome scale metabolic network model of bone marrow derived MSCs for exploring the metabolism of these cells. We analyzed metabolic fluxes of the model in order to find ways of increasing stem cell proliferation and differentiation. Consequently, the experimental results were in consistency with computational results. Therefore, analyzing metabolic models was proven to be a promising field in biomedical researches of stem cells.

Strategies for Fermentation Medium Optimization: An In-Depth Review

Optimization of production medium is required to maximize the metabolite yield. This can be achieved by using a wide range of techniques from classical “one-factor-at-a-time” to modern statistical and mathematical techniques, viz. artificial neural network (ANN), genetic algorithm (GA) etc. Every technique comes with its own advantages and disadvantages, and despite drawbacks some techniques are applied to obtain best results. Use of various optimization techniques in combination also provides the desirable results. In this article an attempt has been made to review the currently used media optimization techniques applied during fermentation process of metabolite production. Comparative analysis of the merits and demerits of various conventional as well as modern optimization techniques have been done and logical selection basis for the designing of fermentation medium has been given in the present review. Overall, this review will provide the rationale for the selection of suitable optimization technique for media designing employed during the fermentation process of metabolite production.

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.

Establishment of a fully automated microtiter plate-based system for suspension cell culture and its application for enhanced process optimization

We developed an automated microtiter plate (MTP)-based system for suspension cell culture to meet the increased demands for miniaturized high throughput applications in biopharmaceutical process development. The generic system is based on off-the-shelf commercial laboratory automation equipment and is able to utilize MTPs of different configurations (6-24 wells per plate) in orbital shaken mode. The shaking conditions were optimized by Computational Fluid Dynamics simulations. The fully automated system handles plate transport, seeding and feeding of cells, daily sampling, and preparation of analytical assays. The integration of all required analytical instrumentation into the system enables a hands-off operation which prevents bottlenecks in sample processing. The modular set-up makes the system flexible and adaptable for a continuous extension of analytical parameters and add-on components. The system proved suitable as screening tool for process development by verifying the comparability of results for the MTP-based system and bioreactors regarding profiles of viable cell density, lactate, and product concentration of CHO cell lines. These studies confirmed that 6 well MTPs as well as 24 deepwell MTPs were predictive for a scale up to a 1000 L stirred tank reactor (scale factor 1:200,000). Applying the established cell culture system for automated media blend screening in late stage development, a 22% increase in product yield was achieved in comparison to the reference process. The predicted product increase was subsequently confirmed in 2 L bioreactors. Thus, we demonstrated the feasibility of the automated MTP-based cell culture system for enhanced screening and optimization applications in process development and identified further application areas such as process robustness. The system offers a great potential to accelerate time-to-market for new biopharmaceuticals. Biotechnol. Bioeng. 2017;114: 113-121. © 2016 Wiley Periodicals, Inc.

A Single Dynamic Metabolic Model Can Describe mAb Producing CHO Cell Batch and Fed-Batch Cultures on Different Culture Media

CHO cell culture high productivity relies on optimized culture medium management under fed-batch or perfused chemostat strategies enabling high cell densities. In this work, a dynamic metabolic model for CHO cells was further developed, calibrated and challenged using datasets obtained under four different culture conditions, including two batch and two fed-batch cultures comparing two different culture media. The recombinant CHO-DXB11 cell line producing the EG2-hFc monoclonal antibody was studied. Quantification of extracellular substrates and metabolites concentration, viable cell density, monoclonal antibody concentration and intracellular concentration of metabolite intermediates of glycolysis, pentose-phosphate and TCA cycle, as well as of energetic nucleotides, were obtained for model calibration. Results suggest that a single model structure with a single set of kinetic parameter values is efficient at simulating viable cell behavior in all cases under study, estimating the time course of measured and non-measured intracellular and extracellular metabolites. Model simulations also allowed performing dynamic metabolic flux analysis, showing that the culture media and the fed-batch strategies tested had little impact on flux distribution. This work thus paves the way to an in silico platform allowing to assess the performance of different culture media and fed-batch strategies.

Trends in Upstream and Downstream Process Development for Antibody Manufacturing

A steady increase of product titers and the corresponding change in impurity composition represent a challenge for development and optimization of antibody production processes. Additionally, increasing demands on product quality result in higher complexity of processes and analytics, thereby increasing the costs for product work-up. Concentration and composition of impurities are critical for efficient process development. These impurities can show significant variations, which primarily depend on culture conditions. They have a major impact on the work-up strategy and costs. The resulting "bottleneck" in downstream processing requires new optimization, technology and development approaches. These include the optimization and adaptation of existing unit operations respective to the new separation task, the assessment of alternative separation technologies and the search for new methods in process development. This review presents an overview of existing methods for process optimization and integration and indicates new approaches for future developments.

Amino acid consumption in naïve and recombinant CHO cell cultures: producers of a monoclonal antibody

Most commercial media for mammalian cell culture are designed to satisfy the amino acid requirements for cell growth, but not necessarily those for recombinant protein production. In this study, we analyze the amino acid consumption pattern in naïve and recombinant Chinese hamster ovary (CHO) cell cultures. The recombinant model we chose was a CHO-S cell line engineered to produce a monoclonal antibody. We report the cell concentration, product concentration, and amino acid concentration profiles in naïve and recombinant cell cultures growing in CD OptiCHO™ medium with or without amino acid supplementation with a commercial supplement (CHO CD EfficientFeed™ B). We quantify and discuss the amino acid demands due to cell growth and recombinant protein production during long term fed batch cultivation protocols. We confirmed that a group of five amino acids, constituting the highest mass fraction of the product, shows the highest depletion rates and could become limiting for product expression. In our experiments, alanine, a non-important mass constituent of the product, is in high demand during recombinant protein production. Evaluation of specific amino acid demands could be of great help in the design of feeding/supplementation strategies for recombinant mammalian cell cultures.

Multifactorial interaction of growth factors on Penaeus monodon lymphoid cells and the impact of IGFs in DNA synthesis and metabolic activity in vitro

Development of continuous cell lines from shrimp is essential to investigate viral pathogens. Unfortunately, there is no valid cell line developed from crustaceans in general and shrimps in particular to address this issue. Lack of information on the requirements of cells in vitro limits the success of developing a cell line, where the microenvironment of a cell culture, provided by the growth medium, is of prime importance. Screening and optimization of growth medium components based on statistical experimental designs have been widely used for improving the efficacy of cell culture media. Accordingly, we applied Plackett-Burman design and response surface methodology to study multifactorial interactions between the growth factors in shrimp cell culture medium and to identify the most important ones for growth of lymphoid cell culture from Penaeus monodon. The statistical screening and optimization indicated that insulin like growth factor-I (IGF-I) and insulin like growth factor-II (IGF-II) at concentrations of 100 and 150 ng ml(-1), respectively, could significantly influence the metabolic activity and DNA synthesis of the lymphoid cells. An increase of 53 % metabolic activity and 24.8 % DNA synthesis could be obtained, which suggested that IGF-I and IGF-II had critical roles in metabolic activity and DNA synthesis of shrimp lymphoid cells.

Serum-free media for the production of human mesenchymal stromal cells: a review

The regenerative potential of mesenchymal stromal cells (MSC) holds great promise in using them for treatment of a wide range of debilitating diseases. Several types of culture media and systems have been used for large-scale expansion of MSCs in vitro; however, the majority of them rely heavily on using foetal bovine serum (FBS)-supplement for optimal cell proliferation. FBS-based cultures pose the potential threat of spread of transmissible spongiform encephalopathy and bovine spongiform encephalopathy to MSCs and then to their recipients. A recent trend in cell culture is to change from serum-use to serum-free media (SFM). In this context, the current review focuses specifically on employment of various SFM for MSCs and discusses existences of various options with which to substitute FBS. In addition, we analyse MSC population growth kinetic patterns using various SFM for large-scale production of MSCs.

Application of statistical techniques for elucidating flow cytometric data of batch and fed-batch cultures

The objective of this work is to develop structured, segregated stochastic models for bioprocesses using time-series flow cytometric (FC) data. To this end, mammalian CHO cells were grown in both batch and fed-batch cultures, and their viable cell numbers (VCDs), monoclonal antibody (MAb), cell cycle phases, mitochondria membrane potential/mitochondria mass, Golgi apparatus, and endoplasmic reticulum (ER) were analyzed. For the fed-batch mode, soy hydrolysate was introduced at 24-H intervals. The cytometric data were analyzed for early indicators of growth and productivity by multiple linear regression analysis, which involved taking into account multicollinearity diagnostics, Durbin-Watson statistics, and Houston tests to determine and refine statistically significant correlations between categorical variables (FC parameters) and response variables (yield parameters). The results indicate that the percentage of G1 cells and ER was significantly correlated with VCD and MAb in the case of batch culture, whereas for fed-batch culture, the percentage of G2 cells and ER was correlated significantly. There was a significant difference between cells in the batch and fed-batch cultures in their ER content, suggesting that the increase in protein synthesis as reflected by the ER content and consequent increase in growth rate and MAb productivity both can be monitored at the cellular level by FC analysis of ER content.

Production and partial characterization of extracellular amylase enzyme from Bacillus amyloliquefaciens P-001

Amylases are one of the most important enzymes in present-day biotechnology. The present study was concerned with the production and partial characterization of extracellular amylase from Bacillus amyloliquefaciens P-001. The effect of various fermentation conditions on amylase production through shake-flask culture was investigated. Enzyme production was induced by a variety of starchy substrate but corn flour was found to be a suitable natural source for maximum production. Tryptone and ammonium nitrate (0.2%) as nitrogen sources gave higher yield compared to other nitrogen sources. Maximum enzyme production was obtained after 48 hrs of incubation in a fermentation medium with initial pH 9.0 at 42°C under continuous agitation at 150 rpm. The size of inoculum was also optimized which was found to be 1% (v/v). Enzyme production was 2.43 times higher after optimizing the production conditions as compared to the basal media. Studies on crude amylase revealed that optimum pH, temperature and reaction time of enzyme activity was 6.5, 60°C and 40 minutes respectively. About 73% of the activity retained after heating the crude enzyme solution at 50°C for 30 min. The enzyme was activated by Ca²⁺ (relative activity 146.25%). It was strongly inhibited by Mn²⁺, Zn²⁺ and Cu²⁺, but less affected by Mg²⁺ and Fe²⁺.

Rational development of a serum-free medium and fed-batch process for a GS-CHO cell line expressing recombinant antibody

A serum-free medium (CHO-SFM) together with a fed-batch process was developed for the cultivation of a recombinant GS-CHO cell line producing TNFR-Fc. According to the metabolic characteristics of GS-CHO cell, a basal medium was prepared by supplementing DMEM:F12:RPMI1640 (2:1:1) with amino acids, insulin, transferrin, Pluronic F68 and some other ingredients. Statistical optimization approaches based on Plackett-Burman and central composite designs were then adopted to identify additional positive determinants and determine their optimal concentrations, which resulted in the final CHO-SFM medium formulations. The maximum antibody titer reached was 90.95 mg/l in the developed CHO-SFM, which was a 18 % and 10 fold higher than that observed in the commercial EX-CELL™ 302 medium (76.95 mg/l) and basal medium (8.28 mg/l), respectively. Subsequently, a reliable, reproducible and robust fed-batch strategy was designed according to the offline measurement of glucose, giving a final antibody yield of 378 mg/l, which was a threefold improvement over that in conventional batch culture (122 mg/l) using CHO-SFM. In conclusion, the use of design of experiment (DoE) method facilitated the development of CHO-SFM medium and fed-batch process for the production of recombinant antibody using GS-CHO cells.

Cell culture medium improvement by rigorous shuffling of components using media blending

A novel high-throughput methodology for the simultaneous optimization of many cell culture media components is presented. The method is based on the media blending approach which has several advantages as it works with ready-to-use media. In particular it allows precise pH and osmolarity adjustments and eliminates the need of concentrated stock solutions, a frequent source of serious solubility issues. In addition, media blending easily generates a large number of new compositions providing a remarkable screening tool. However, media blending designs usually do not provide information on distinct factors or components that are causing the desired improvements. This paper addresses this last point by considering the concentration of individual medium components to fix the experimental design and for the interpretation of the results. The extended blending strategy was used to reshuffle the 20 amino acids in one round of experiments. A small set of 10 media was specifically designed to generate a large number of mixtures. 192 mixtures were then prepared by media blending and tested on a recombinant CHO cell line expressing a monoclonal antibody. A wide range of performances (titers and viable cell density) was achieved from the different mixtures with top titers significantly above our previous results seen with this cell line. In addition, information about major effects of key amino acids on cell densities and titers could be extracted from the experimental results. This demonstrates that the extended blending approach is a powerful experimental tool which allows systematic and simultaneous reshuffling of multiple medium components.

On-line heat flux measurements improve the culture medium for the growth and productivity of genetically engineered CHO cells

With the increasingly competitive commercial production of target proteins by hybridoma and genetically engineered cells, there is an urgent requirement for biosensors to monitor and control on-line and in real time the growth of cultured cells. Since growth is accompanied by an enthalpy change, heat dissipation measured by calorimetry could act as an index for metabolic flow rate. Recombinant CHO cell suspensions producing interferon-gamma were pumped to an on-line flow calorimeter. The results showed that an early reflection of metabolic change is size-specific heat flux obtained from dividing heat flow rate by the capacitance change of the cell suspension, using the on-line probe of a dielectric spectroscope. Comparison of heat flux with glucose and glutamine fluxes indicated that the former most accurately reflected decreased metabolic activity. Possibly this was due to accumulation of lactate and ammonia resulting from catabolic substrates being used as biosynthetic precursors. Thus, the heat flux probe is an ideal on-line biosensor for fed-batch culture. A stoichiometric growth reaction was formulated and data for material and heat fluxes incorporated into it. This showed that cell demand for glucose and glutamine was in the stoichiometric ratio of approximately 3:1 rather than the approximately 5:1 in the medium. It was demonstrated that the set of stoichiometric coefficients in the reaction were related through the extent of reaction (advancement) to overall metabolic activity (flux). The fact that this approach can be used for medium optimisation is the basis for an amino-acid-enriched medium which improved cell growth while decreasing catabolic fluxes.

Plant protein hydrolysates support CHO-320 cells proliferation and recombinant IFN-gamma production in suspension and inside microcarriers in protein-free media

We have recently developed a protein-free medium (PFS) able to support the growth of Chinese hamster ovary (CHO) cells in suspension. Upon further supplementation with some plant protein hydrolysates, medium performances reached what could be observed in serum-containing media [Burteau et al. In Vitro Cell. Dev. Biol.-Anim. 39 (2003) 291]. Now, we describe the use of rice and wheat protein hydrolysates, as non-nutritional additives to the culture medium to support productivity and cell growth in suspension or in microcarriers. When CHO-320 cells secreting recombinant interferon-gamma (IFN-gamma) were cultivated in suspension in a bioreactor with our PFS supplemented with wheat hydrolysates, the maximum cell density increased by 25% and the IFN-gamma secretion by 60% compared to the control PFS. A small-scale perfusion system consisting of CHO-320 cells growing on and inside fibrous microcarriers under discontinuous operation was first developed. Under these conditions, rice protein hydrolysates stimulated recombinant IFN-gamma secretion by 30% compared to the control PFS. At the bioreactorscale, similar results were obtained but when compared to shake-flasks studies, nutrients, oxygen or toxic by-products gradients inside the microcarriers seemed to be the main limitation of the system. An increase of the perfusion rate to maintain glucose concentration over 5.5 mM and dissolved oxygen (DO) at 60% was able to stimulate the production of IFN-gamma to a level of 6.6 mug h(-1) g(-1) of microcarriers after 160 h when a cellular density of about 4 x 10(8) cell g(-1) of carriers was reached.

Cell culture processes for monoclonal antibody production

Animal cell culture technology has advanced significantly over the last few decades and is now generally considered a reliable, robust and relatively mature technology. A range of biotherapeutics are currently synthesized using cell culture methods in large scale manufacturing facilities that produce products for both commercial use and clinical studies. The robust implementation of this technology requires optimization of a number of variables, including 1) cell lines capable of synthesizing the required molecules at high productivities that ensure low operating cost; 2) culture media and bioreactor culture conditions that achieve both the requisite productivity and meet product quality specifications; 3) appropriate on-line and off-line sensors capable of providing information that enhances process knowledge; and 4) good understanding of culture performance at different scales to ensure smooth scale-up. Successful implementation also requires appropriate strategies for process development, scale-up and process characterization and validation that enable robust operation that is compliant with current regulations. This review provides an overview of the state-of-the art technology in key aspects of cell culture, e.g., engineering of highly productive cell lines and optimization of cell culture process conditions. We also summarize the current thinking on appropriate process development strategies and process advances that might affect process development.

Novel chemometric strategy based on the application of artificial neural networks to crossed mixture design for the improvement of recombinant protein production in continuous culture

The optimal blends of six compounds that should be present in culture media used in recombinant protein production were determined by means of artificial neural networks (ANN) coupled with crossed mixture experimental design. This combination constitutes a novel approach to develop a medium for cultivating genetically engineered mammalian cells. The compounds were collected in two mixtures of three elements each, and the experimental space was determined by a crossed mixture design. Empirical data from 51 experimental units were used in a multiresponse analysis to train artificial neural networks which satisfy different requirements, in order to define two new culture media (Medium 1 and Medium 2) to be used in a continuous biopharmaceutical production process. These media were tested in a bioreactor to produce a recombinant protein in CHO cells. Remarkably, for both predicted media all responses satisfied the predefined goals pursued during the analysis, except in the case of the specific growth rate (mu) observed for Medium 1. ANN analysis proved to be a suitable methodology to be used when dealing with complex experimental designs, as frequently occurs in the optimization of production processes in the biotechnology area. The present work is a new example of the use of ANN for the resolution of a complex, real life system, successfully employed in the context of a biopharmaceutical production process.

Optimization of actinomycin V production by Streptomyces triostinicus using artificial neural network and genetic algorithm

Artificial neural network (ANN) and genetic algorithm (GA) were applied to optimize the medium components for the production of actinomycin V from a newly isolated strain of Streptomyces triostinicus which is not reported to produce this class of antibiotics. Experiments were conducted using the central composite design (CCD), and the data generated was used to build an artificial neural network model. The concentrations of five medium components (MgSO(4), NaCl, glucose, soybean meal and CaCO(3)) served as inputs to the neural network model, and the antibiotic yield served as outputs of the model. Using the genetic algorithm, the input space of the neural network model was optimized to find out the optimum values for maximum antibiotic yield. Maximum antibiotic yield of 452.0 mg l(-1) was obtained at the GA-optimized concentrations of medium components (MgSO(4) 3.657; NaCl 1.9012; glucose 8.836; soybean meal 20.1976 and CaCO(3) 13.0842 gl(-1)). The antibiotic yield obtained by the ANN/GA was 36.7% higher than the yield obtained with the response surface methodology (RSM).

Optimization of critical medium components using response surface methodology for phenazine-1-carboxylic acid production by Pseudomonas sp. M-18Q

The optimal flask-shaking batch fermentation medium for phenazine-1-carboxylic acid (PCA) production by Pseudomonas sp. M-18Q, a qscR chromosomal inactivated mutant of the strain M18 was studied using statistical experimental design and analysis. The Plackett-Burman design (PBD) was used to evaluate the effects of eight medium components on the production of PCA, which showed that glucose and soytone were the most significant ingredients (P<0.05). The steepest ascent experiment was adopted to determine the optimal region of the medium composition. The optimum composition of the fermentation medium for maximum PCA yield, as determined on the basis of a five-level two-factor central composite design (CCD), was obtained by response surface methodology (RSM). The high correlation between the predicted and observed values indicated the validity of the model. A maximum PCA yield of 1240 mg/l was obtained at 17.81 g/l glucose and 11.47 g/l soytone, and the production was increased by 65.3% compared with that using the original medium, which was at 750 mg/l.

Developement of serum-free media in CHO-DG44 cells using a central composite statistical design

A serum free medium was developed for the production of recombinant antibody against Botulinum A (BoNTA) using dihydrofolate reductase deficient Chinese Hamster Ovary Cells (CHO-DG44) in suspension culture. An initial control basal medium was prepared, which was similar in composition to HAM's F12: IMDM (1:1) supplemented with insulin, transeferrin, selenium and a lipid mixture. The vitamin concentration of the basal medium was twice that of HAM's F12: IMDM (1:1). CHO-DG44 cells expressing S25 antibody grew from 2 x 10(5) cells to maximum cell density of 1.04 x 10(6) cells/ml after 5 days in this control medium. A central composite design was used to identify optimal levels and interaction among five groups of medium components. These five groups were glutamine, Essential Amino Acids (EAA), Non Essential Amino Acids (NEAA), Insulin, Transferrin, Selenium (ITS), and lipids. Fifty experiments were carried out in four batches, with two controls in each batch. There was little effect of ITS and Lipid concentrations over the range studied, and glutamine concentration showed a strong interaction with EAA. The optimal concentrations of the variables studied were 2.5 mM Glutamine, 7.4 mM (2x) EAA, 1.4 mM (0.5x) NEAA, 1x ITS supplement, 0.7x Lipids supplement. The maximum viable cell density attained in the optimized medium was 1.4 x 10(6) cells/ml, a 35% improvement over the control culture, while the final antibody titer attained was 22 +/- 3.4 mug/mL, a 50% improvement.

Related effects of cell adaptation to serum-free conditions on murine EPO production and glycosylation by CHO cells

The necessity to perform serum-free cultures to produce recombinant glycoproteins generally requires an adaptation procedure of the cell line to new environmental conditions, which may therefore induce quantitative and qualitative effects on the product, particularly on its glycosylation. In previous studies, desialylation of EPO produced by CHO cells was shown to be dependent on the presence of serum in the medium. In this paper, to discriminate between the effects of the adaptation procedure to serum-free medium and the effects of the absence of serum on EPO production and glycosylation, adapted and non-adapted CHO cells were grown in serum-free and serum-containing media. The main kinetics of CHO cells were determined over batch processes as well as the glycosylation patterns of produced EPO by HPCE-LIF. A reversible decrease in EPO production was observed when cells were adapted to SFX-CHO(TM) medium, as the same cells partially recovered their production capacity when cultivated in serum-containing medium or in the enriched SFM(TM) serum-free medium. More interestingly, EPO desialylation that was not observed in both serum-free media was restored if the serum-independent cells were recultured in presence of serum. In the same way, while the serum-independent cells did not release a sialidase activity in both serum-free media, a significant activity was recovered when serum was added. In fact, the cell adaptation process to serum-free conditions did not specifically affect the sialidase release and the cellular mechanism of protein desialylation, which appeared to be mainly related to the presence of serum for both adapted and non-adapted cells.

Microplates with integrated oxygen sensing for medium optimization in animal cell culture

A new approach using microtiter plate cultivation with on-line measurement of dissolved oxygen (DO) was applied for medium optimization of mammalian cell culture. Applying dynamic liquid phase balance, oxygen uptake rates were calculated from the DO level and used as an indicator for culture viability. The developed method was successfully applied to optimization of the concentration of glucose, glutamine and inorganic salts for cultivation of a Chinese Hamster Ovary (CHO) cell line. Using 2(3) full factorial central composite design, the optimum medium composition could be identified in one single run. The concentration of inorganic salts had a significant influence on cultivation. The developed method exhibits high potential to improve procedures of medium optimization for animal cell cultivation by allowing the investigation of large sets of potentially important variables in short time and with reduced effort.