Gene overexpression reduces inhibitory metabolites to enhance CHO cell growth and IgG1 production

Controlling the generation of toxic by-products in mammalian bioprocess to maximize therapeutic protein production and glycosylation patterns is a challenge. Intracellular metabolism is often not well-regulated and known to secrete toxic intermediate by-products which hampers cellular performance and negatively impacts critical quality attributes (CQA) of cells. Previous studies have identified trigonelline (TRI), n-acetyl putrescine (NAP), aconitic acid (AA), and cytidine monophosphate (CMP) generated through CHO cell metabolism and verified their negative impacts on growth and antibody production. In this approach, a genetic engineering strategy was developed to control downstream accumulation of inhibitory metabolites. The study successfully identified four different metabolic genes in CHO cells, including Cat (nicotinate and nicotinamide metabolism) to control the generation of TRI, Got1 and Hoga1 (proline metabolism) to control the generation of NAP, Got1 (TCA cycle) to control the generation of AA, and Slc35a1 (n-glycan biosynthesis) to control the generation of CMP. Each target gene-of-interest (GOI) was cloned from CHO genomic library, inserted into linearized vector plasmid, and subsequently transfected into cells. CQA of the bioprocess realized 22-30% increase in peak cell density, 16-22% increase overall IVCD, with an improving growth rate during cellular expansion phase when comparing engineered cells against control cells. The study also conducted a follow-up quadruple transfection study where all four GOIs were co-transfected into cells at ¼ of the total DNA concentration per GOI. An increase in cellular performance was also realized, as increases in peak VCD (17% increase), cumulative IVCD (17% increase), and growth rate were achieved. Both studies also found higher IgG1 antibody synthesis when cell metabolism was better regulated, as the studies measured 4% to 40% titer increase across all engineered cells when compared against control cells. The study also measured higher levels of G1F and G2F glycans with decreased level of G0F across all transfected cells, further indicating improvement in bioprocess, as cells were able to produce a higher fraction of semi-complex and complex versus simple glycoforms. Further investigation revealed that Cat and Slc35a1 exhibited comparable expression levels in the MG condition to their single-gene conditions (within 1% and 10% difference, respectively), corresponding to modest titer improvements closest to the control. These findings suggest that when all four genes are co-expressed, Cat and Got1 may act as rate-limiting factors influencing both cellular phenotypes and titer production. In both studies, the concentrations of downstream metabolic inhibitors were measured to be significantly decreased when comparing engineered cells against control cells, further demonstrating that overexpression of genes to re-allocate metabolic fluxes away from synthesizing toxic by-products can significantly improve cellular growth and protein synthesis.