Enhancing titers and productivity of rCHO clones with a combination of an optimized fed-batch process and ER-stress adaptation.

To increase the productivity of rCHO cells, many cell engineering approaches have been demonstrated that over-express or knockout a specific gene to achieve increased titers. In this work, we present an alternate approach, based on the concept of evolutionary adaptation, to achieve cells with higher titers. rCHO cells, producing a monoclonal antibody, are adapted to ER-stress, by continuous culturing under increasing concentration of tunicamycin. A sustained higher productivity of at-least 2-fold was achieved in all the clones, in a concentration-dependent manner. Similarly, a 1.5-2 fold increase in final titers was also achieved in the batch culture. Based on metabolic analysis of the adapted cells, a fed-batch process was designed where significantly higher titersare achieved as compared to control. Metabolic flux analysis is employed in addition with gene expression analysis of key genes to understand the basis of increased performance of the adapted cells. Overall, this work illustrates how process modifications and cellular adaptation can be used in synergy to drive up product titers.

The Familial α-Synuclein A53E Mutation Enhances Cell Death in Response to Environmental Toxins Due to a Larger Population of Oligomers.

Amyloid formation of α-synuclein (α-Syn) and its familial mutations are directly linked with Parkinson's disease (PD) pathogenesis. Recently, a new familial α-Syn mutation (A53E) was discovered, associated with an early onset aggressive form of PD, which delays α-Syn aggregation. When we overexpressed wild-type (WT) and A53E proteins in cells, showed neither toxicity nor aggregate formation, suggesting merely overexpression may not recapitulate the PD phenotype in cell models. We hypothesized that cells expressing the A53E mutant might possess enhanced susceptibility to PD-associated toxicants compared to that of the WT. When cells were treated with PD toxicants (dopamine and rotenone), cells expressing A53E showed more susceptibility to cell death along with compromised mitochondrial potential and an increased production of reactive oxygen species. The higher toxicity of A53E could be due to more oligomers being formed in cells as confirmed by a dot blot assay using amyloid specific OC and A11 antibody and using an  in vitro aggregation study. The cellular model presented here suggests that along with familial mutation, environmental and other cellular factors might play a crucial role in dictating PD pathogenesis.

Activation of unfolded protein response pathway is important for valproic acid mediated increase in immunoglobulin G productivity in recombinant Chinese hamster ovary cells.

Process engineering to improve product quality and titers is gaining importance at late-stage cell culture process development. Valproic acid, a US Food and Drug Administration-approved histone deacetylase (HDAC) inhibitor, has been shown to improve cell culture performance with higher productivities and minimal effect on the product quality. However, the wider physiological impact of valproic acid on recombinant cells has not been investigated till date. In this study, we investigate the role of unfolded protein response pathway when immunoglobulin G (IgG)-secreting Chinese hamster ovary (CHO) cells are treated with valproic acid, resulting in a 3-fold increase in product titers and productivity. It is found that cells undergo an early transient endoplasmic reticulum (ER) stress on treatment with valproic acid, and subsequently adapt to perform as high producers. Induction of chaperones through enhanced XBP1 splicing activity and ATF6 activation suggests an increase in protein processing activity in these cells. We show that in addition to the enhanced recombinant mRNA expression of IgG heavy chain and light chain, the activation of unfolded protein response (UPR) pathway is critical to the increase in productivity of cells on valproic acid treatment. Further, upregulation of the UPR pathway is not through HDAC inhibition alone. To our knowledge, this is the first attempt to arrive at a phenotype-genotype mechanistic understanding of how valproic acid treatment enhances productivity in recombinant CHO cells.