Insight into the roles of tyrosine on rCHO cell performance in fed-batch cultures

Tyrosine (Tyr), as one of the least soluble amino acids, is essential to monoclonal antibody (mAb) production in recombinant Chinese hamster ovary (rCHO) cell cultures since its roles on maintaining the specific productivity (q_mAb) and avoiding Tyr sequence variants. To understand the effects of Tyr on cell performance and its underlying mechanisms, rCHO cell-producing mAbs were cultivated at various cumulative Tyr addition concentrations (0.6 to 5.5 mM) in fed-batch processes. Low Tyr concentrations gave a much lower peak viable cell density (VCD) during the growth phase and also induced rapid cell death and pH decrease during the production phase, resulting in a low efficient fed-batch process. Autophagy was initiated following the inhibition of mTOR under the Tyr starvation condition. Excessive autophagy subsequently induced autophagic cell death, which was found as the major type of cell death in this study. Additionally, the results obtained here demonstrate that the decrease in culture pH under the Tyr starvation condition was associated with the autophagy and such pH drop might be attributed to the lysosome acidification and cell lysis.