Elucidating the Impact of CHO Cell Culture Media on Tryptophan Oxidation of a Monoclonal Antibody Through Gene Expression Analyses.

Oxidation of monoclonal antibodies (mAb) is a common chemical modification with potential impact on a therapeutic protein's activity and immunogenicity. In a previous study, it was found that tryptophan oxidation (Trp-ox) levels of two mAb produced in Chinese hamster ovary (CHO) cells were significantly lowered by modifying cell culture medium/feed. In this study, transcriptome analysis by RNA-Seq is applied to further elucidate the underlying mechanism of those changes in lowering the Trp-ox levels. Cell samples from the 5L fed-batch conditions are harvested and subjected to RNA-Seq analysis. The results showed that the cell culture changes had little impact on neither the expression of the mAb transgenes nor genes related to glycosylation. However, those changes did significantly alter the expression of multiple genes (p-value ≤0.05 and absolute fold change ≥1.5 or adjusted p-value ≤0.1) involved in transport of copper, regulation of glutathione, iron storage, heme reduction, oxidative phosphorylation, and Nrf2-mediated antioxidative response. These findings suggest a key underlying mechanism in lowering Trp-ox levels by CDM was likely to be collectively controlling ROS levels through regulation of those genes' expression. This is the first example, to our knowledge, applying transcriptomic analysis to mechanistically understand the impact of cell culture on mAb oxidation.