MicroRNAs as Engineering Targets: Pathway Manipulation to Impact Bioprocess Phenotypes - MicroRNAs as Tools in Biopharmaceutical Production - page 66

5.1 Introduction

5.1.1 Potential Role of MicroRNAs in Improving CHO Cells

Suitable for Large-Scale Production of Biologicals

Chinese hamster ovary cells are the primary mammalian culture system used for
production of biopharmaceuticals. This is attributed to their robustness in a bioreactor
and their ability to produce properly folded recombinant proteins with human-like
posttranslational-modifications which is important for maintaining their biological
activity (Barron et al. 2011b ; Druz et al. 2011 ; Kramer et al. 2010 ; Muller et al. 2008 ).
Mammalian-based systems for biological production are required to produce
high quantities of product and therefore need to meet process-related requirements
that place high demands on CHO cells to generate suitable product titers and
quality (Dinnis and James 2005 ). Improving and predicting the performance of
CHO cells in bioreactors is important for enhancement of cell specific productivity
(Clarke et al. 2011 ).
Limited growth capacities and low tolerance to different environmental con-
ditions in bioreactors (nutrient and growth factor depletion, shear and oxidative
stresses, metabolite accumulation, pH, osmolality and hypoxia) affect cell produc-
tivity. It is possible that these conditions cause apoptosis, reducing the yield and
the quality of the produced proteins (Lim et al. 2010 ). Generation of stress-resistant
CHO cell lines suitable for efficient production of various biologicals is therefore
important for the biopharmaceutical industry. Additional desired characteristics of
high-producing CHO cells are rapid growth, long term genomic stability and protein
secretion capacity.
The discovery of microRNAs (miRNAs) offers an opportunity to improve the
performance of CHO cells in an industrial-scale bioprocess. It is predicted that nearly
half of the proteins may be affected by miRNAs (Lewis et al. 2005 ) which are more
abundant than transcription factors. miRNAs have been shown to be global regulators
of gene expression affecting almost all essential cellular processes and functions. So
far, it has been found that miRNAs are involved in cell development, differentiation,
metabolism and proliferation. miRNA expression profiles can also be explored as
biomarkers for desired properties such as resistance to various stresses, growth and
clonal stability and/or engineering targets (Barron et al. 2011a ; Druz et al. 2011 ).
The potential of miRNAs utilization for mammalian cell engineering was high-
lighted by analyzing miR expression profiles under various physiological conditions
(Druz et al. 2011 ; Gammell 2007 ). Each miRNA has the potential to post-
trascriptionally affect more than 100 targets and concurrently influence several
interlinked pathways or multiple points of the same pathway in the cell, which
may facilitate creating industrially-relevant phenotypes (Barron et al. 2011a ).
One of the key advantages for utilizing miRNAs rather than regulatory proteins
such as transcriptional factors or kinases is the fact that they do not burden the
translational machinery and therefore reduce the metabolic load on the host cells.
As a result, cellular metabolic resources will be better allocated to the production of