Biotechnology and Bioengineering, Vol.115, No.6, 1531-1541, 2018
Butyrated ManNAc analog improves protein expression in Chinese hamster ovary cells
The chemical additive sodium butyrate (NaBu) has been applied in cell culture media as a direct and convenient method to increase the protein expression in Chinese hamster ovary (CHO) and other mammalian cells. In this study, we examined an alternative chemical additive, 1,3,4-O-Bu(3)ManNAc, for its effect on recombinant protein production in CHO. Supplementation with 1,3,4-O-Bu(3)ManNAc for two stable CHO cell lines, expressing human erythropoietin or IgG, enhanced protein expression for both products with negligible impact on cell growth, viability, glucose utilization, and lactate accumulation. In contrast, sodium butyrate treatment resulted in a approximate to 20% decrease in maximal viable cell density and approximate to 30% decrease in cell viability at the end of cell cultures compared to untreated or 1,3,4-O-Bu(3)ManNAc treated CHO cell lines for both products. While NaBu treatment enhanced product yields more than the 1,3,4-O-Bu(3)ManNAc treatment, the NaBu treated cells also exhibited higher levels of caspase 3 positive cells using microscopy analysis. Furthermore, the mRNA levels of four cell apoptosis genes (Cul2, BAK, BAX, and BCL2L11) were up-regulated more in sodium butyrate treated wild-type, erythropoietin, or IgG expressing CHO-K1 cell lines while most of the mRNA levels of apoptosis genes in 1,3,4-O-Bu(3)ManNAc treated cell lines remained equal or increased only slightly compared to the levels in untreated CHO cell lines. Finally, lectin blot analysis revealed that the 1,3,4-O-Bu(3)ManNAc-treated cells displayed higher relative sialylation levels on recombinant EPO, consistent with the effect of the ManNAc component of this additive, compared to control while NaBu treatment led to lower sialylation levels than control, or 1,3,4-O-Bu(3)ManNAc-treatment. These findings demonstrate that 1,3,4-O-Bu(3)ManNAc has fewer negative effects on cell cytotoxicity and apoptosis, perhaps as a result of a more deliberate uptake and release of the butyrate compounds, while simultaneously increasing the expression of multiple recombinant proteins, and improving the glycosylation characteristics when applied at comparable molarity levels to NaBu. Thus, 1,3,4-O-Bu(3)ManNAc represents a highly promising media additive alternative in cell culture for improving protein yields without sacrificing cell mass and product quality in future bioproduction processes.