CHO synthetic promoters improve expression and product quality of biotherapeutic proteins.

When expressing complex biotherapeutic proteins, traditional expression plasmids and methods may not always yield sufficient levels of high-quality product. High-strength viral promoters commonly used for recombinant protein (rProtein) production in mammalian cells allow for maximal expression, but provide limited scope to alter their transcription dynamics. However, synthetic promoters designed to provide tunable transcriptional activity offer a plasmid engineering approach to more precisely regulate product quality, yield or to reduce product related contaminants. We substituted the viral promoter CMV with synthetic promoters that offer different transcriptional activities to express our gene of interest in Chinese hamster ovary (CHO) cells. Stable pools were established and the benefits of regulating transgene transcription on the quality of biotherapeutics were examined in stable pool fed-batch overgrow experiments. Specific control of gene expression of the heavy chain (HC):light chain (LC) of a Fab, and the ratio between the two HCs in a Duet mAb reduced levels of aberrant protein contaminants; and the controlled expression of the helper gene XBP-1s improved expression of a difficult-to-express mAb. This synthetic promoter technology benefits applications that require custom activity. Our work highlights the advantages of employing synthetic promoters for production of more complex rProteins.

A novel hydrogen peroxide evolved CHO host can improve the expression of difficult to express bispecific antibodies.

The manufacture of bispecific antibodies by Chinese hamster ovary (CHO) cells is often hindered by lower product yields compared to monoclonal antibodies. Recently, reactive oxygen species have been shown to negatively impact antibody production. By contrast, strategies to boost cellular antioxidant capacity appear to be beneficial for recombinant protein expression. With this in mind, we generated a novel hydrogen peroxide evolved host using directed host cell evolution. Here we demonstrate that this host has heritable resistance to hydrogen peroxide over many generations, displays enhanced antioxidant capacity through the upregulation of several, diverse antioxidant defense genes such as those involved in glutathione synthesis and turnover, and has improved glutathione content. Additionally, we show that this host has significantly improved transfection recovery times, improved growth and viability properties in a fed-batch production process, and elevated expression of two industrially relevant difficult to express bispecific antibodies compared to unevolved CHO control host cells. These findings demonstrate that host cell evolution represents a powerful methodology for improving specific host cell characteristics that can positively impact the expression of difficult to express biotherapeutics.

Model-based optimization of antibody galactosylation in CHO cell culture.

Exerting control over the glycan moieties of antibody therapeutics is highly desirable from a product safety and batch-to-batch consistency perspective. Strategies to improve antibody productivity may compromise quality, while interventions for improving glycoform distribution can adversely affect cell growth and productivity. Process design therefore needs to consider the trade-off between preserving cellular health and productivity while enhancing antibody quality. In this work, we present a modeling platform that quantifies the impact of glycosylation precursor feeding - specifically that of galactose and uridine - on cellular growth, metabolism as well as antibody productivity and glycoform distribution. The platform has been parameterized using an initial training data set yielding an accuracy of ±5% with respect to glycoform distribution. It was then used to design an optimized feeding strategy that enhances the final concentration of galactosylated antibody in the supernatant by over 90% compared with the control without compromising the integral of viable cell density or final antibody titer. This work supports the implementation of Quality by Design towards higher-performing bioprocesses.

Model-based investigation of intracellular processes determining antibody Fc-glycosylation under mild hypothermia.

Despite the positive effects of mild hypothermic conditions on monoclonal antibody (mAb) productivity (qmAb ) during mammalian cell culture, the impact of reduced culture temperature on mAb Fc-glycosylation and the mechanism behind changes in the glycan composition are not fully established. The lack of knowledge about the regulation of dynamic intracellular processes under mild hypothermia restricts bioprocess optimization. To address this issue, a mathematical model that quantitatively describes Chinese hamster ovary (CHO) cell behavior and metabolism, mAb synthesis and mAb N-linked glycosylation profile before and after the induction of mild hypothermia is constructed. Results from this study show that the model is capable of representing experimental results well in all of the aspects mentioned above, including the N-linked glycosylation profile of mAb produced under mild hypothermia. Most importantly, comparison between model simulation results for different culture temperatures suggests the reduced rates of nucleotide sugar donor production and galactosyltransferase (GalT) expression to be critical contributing factors that determine the variation in Fc-glycan profiles between physiological and mild hypothermic conditions in stable CHO transfectants. This is then confirmed using experimental measurements of GalT expression levels, thereby closing the loop between the experimental and the computational system. The identification of bottlenecks within CHO cell metabolism under mild hypothermic conditions will aid bioprocess optimization, for example, by tailoring feeding strategies to improve NSD production, or manipulating the expression of specific glycosyltransferases through cell line engineering. Biotechnol. Bioeng. 2017;114: 1570-1582. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals Inc.

How does mild hypothermia affect monoclonal antibody glycosylation?

The application of mild hypothermic conditions to cell culture is a routine industrial practice used to improve recombinant protein production. However, a thorough understanding of the regulation of dynamic cellular processes at lower temperatures is necessary to enhance bioprocess design and optimization. In this study, we investigated the impact of mild hypothermia on protein glycosylation. Chinese hamster ovary (CHO) cells expressing a monoclonal antibody (mAb) were cultured at 36.5°C and with a temperature shift to 32°C during late exponential/early stationary phase. Experimental results showed higher cell viability with decreased metabolic rates. The specific antibody productivity increased by 25% at 32°C and was accompanied by a reduction in intracellular nucleotide sugar donor (NSD) concentrations and a decreased proportion of the more processed glycan structures on the mAb constant region. To better understand CHO cell metabolism at 32°C, flux balance analysis (FBA) was carried out and constrained with exometabolite data from stationary phase of cultures with or without a temperature shift. Estimated fluxomes suggested reduced fluxes of carbon species towards nucleotide and NSD synthesis and more energy was used for product formation. Expression of the glycosyltransferases that are responsible for N-linked glycan branching and elongation were significantly lower at 32°C. As a result of mild hypothermia, mAb glycosylation was shown to be affected by both NSD availability and glycosyltransferase expression. The combined experimental/FBA approach generated insight as to how product glycosylation can be impacted by changes in culture temperature. Better feeding strategies can be developed based on the understanding of the metabolic flux distribution.

Binding of human BiP to the ER stress transducers IRE1 and PERK requires ATP.

ER stress is activated in a number of important diseases such as diabetes, cancer, and neurodegeneration, but the molecular interactions governing the response are still being elucidated. In the absence of stress, protein complexes exist between the ER-resident chaperone BiP and three transmembrane signalling molecules which are responsible for signal transmission. Previous results suggested that cofactors might participate in these interactions, but the molecular details are not well understood. We coexpressed BiP and the lumenal domains of each of the three ER stress transducers and copurified the complexes in the presence of ATP and ADP in order to better understand how the complex is formed. ATP, but not ADP, was required to isolate the BiP-IRE1 and the BiP-PERK complexes, but the BiP-ATF6 complex was purified in all conditions tested. Based on the results, we hypothesize that in contrast to its mode of binding ATF6 and unfolded proteins, BiP binds to IRE1 and PERK in a different manner.