Improved recombinant protein production by regulation of transcription and protein transport in Chinese hamster ovary cells

STEP® vectors for rapid generation of stable transfected CHO cell pools and clones with high expression levels and product quality homogeneity of difficult-to-express proteins

Many proteins produced in CHO cells need evaluation for their clinical and commercial potential. Traditional methods based on stable clone generation are slow and unsuitable for screening larger numbers of proteins, while transient expression technologies are fast but unpredictable regarding product quality and lacking an optional path to subcloning. The STEP® vector technology introduced here combines the best properties of both methods. STEP® vectors contain a strong transcriptional cassette driving expression of a bicistronic mRNA. The gene-of-interest (GOI) is cloned upstream of a functionally impaired zeocin resistance gene (FI-Zeo) whose translation is coupled to that of the GOI through an IRES. Stable transfected cells surviving zeocin selection produce high levels of FI-Zeo and thus, high levels of the GOI-encoded protein. By using different spacers, the translational coupling efficiency and selection strength can be controlled allowing maximization of expression of any GOI. Production of laronidase and factor VII (FVII) is presented as examples of unrelated, difficult-to-express (DTE) proteins. First step is rapid generation of transfected pools with the STEP® vectors. All high expressing surviving pools showed high product quality homogeneity as did monoclonal cell lines obtained from the top pools. Up to 500 μg/mL laronidase was obtained with virtually identical glycosylation profile as reference product. For FVII, cell specific productivity of 0.45 pg/cell/day with 50 IU/μg protein matched highest reported levels of reference product even before process development. Taken together, STEP® vector technology is ideally suited for rapid, small to large-scale production of DTE proteins compared to traditional methods.

Methylthioadenosine (MTA) boosts cell-specific productivities of Chinese hamster ovary cultures: dosage effects on proliferation, cell cycle and gene expression

A major goal for process and cell engineering in the biopharmaceutical industry is enhancing production through increasing volumetric and cell‐specific productivities (CSP). Here, we present 5′‐deoxy‐5′‐(methylthio)adenosine (MTA), the degradation product of S‐(5′‐adenosyl)‐L‐methionine (SAM), as a highly attractive native additive which can boost CSP by 79% when added to exponentially growing cells at a concentration of 250–300 μm. Notably, cell viability and cell size remain higher than in non‐treated cultures. In addition, cell cycle arrests first in S‐, then in G2‐phase before levelling out compared to non‐treated cultivations. Intensive differential gene analysis reveals that expression of genes for cytoskeleton mediated proteins and vesicle transport is amplified by treatment. Furthermore, the interaction of MTA with cell proliferation additionally stimulated recombinant protein formation. The results may serve as a promising starting point for further developments in process and cell engineering to boost productivity.

Random epigenetic modulation of CHO cells by repeated knockdown of DNA methyltransferases increases population diversity and enables sorting of cells with higher production capacities

Chinese hamster ovary (CHO) cells produce a large share of today's biopharmaceuticals. Still, the generation of satisfactory producer cell lines is a tedious undertaking. Recently, it was found that CHO cells, when exposed to new environmental conditions, modify their epigenome, suggesting that cells adapt their gene expression pattern to handle new challenges. The major aim of the present study was to employ artificially induced, random changes in the DNA-methylation pattern of CHO cells to diversify cell populations and consequently increase the finding of cell lines with improved cellular characteristics. To achieve this, DNA methyltransferases and/or the ten-eleven translocation enzymes were downregulated by RNA interference over a time span of ∼16 days. Methylation analysis of the resulting cell pools revealed that the knockdown of DNA methyltransferases was highly effective in randomly demethylating the genome. The same approach, when applied to stable CHO producer cells resulted in (a) an increased productivity diversity in the cell population, and (b) a higher number of outliers within the population, which resulted in higher specific productivity and titer in the sorted cells. These findings suggest that epigenetics play a previously underestimated, but actually important role in defining the overall cellular behavior of production clones.