Production of tPA in recombinant CHO cells under oxygen‐limited conditions

Animal cell bioreactors are often limited by the oxygen supply. The reduction in oxygen consumption per cell that occurs under hypoxic conditions may be exploited as a method for increasing reactor capacity if additional glucose is provided to offset increased glycolytic activity. The effects of oxygen deprivation on recombinant tPA (tissue‐type plasminogen activator) production were investigated using midexponential and slowly growing CHO cells. The specific oxygen consumption rate can be reduced by at least 50% (mild hypoxic conditions) without affecting the cell growth rate, maximum cell concentration, tPA production rate, or tPA quality (as characterized by the tPA‐specific activity and SDS‐PAGE analysis). This suggests that mild‐hypoxic conditions (with sufficient glucose) can be used to double the cell concentration and volumetric tPA production rate (at a constant volumetric oxygen supply rate) without sacrificing product quality. However, anoxic conditions should be avoided. When slowly growing cultures were exposed to anoxia, the tPA production rate decreased by 80% without affecting tPA quality. However, when midexponential cultures were exposed to anoxia, the drop in tPA production was accompanied by a decrease in tPA quality that ranged from a 40% decrease in tPA specific activity to extensive tPA degradation. © 1993 John Wiley & Sons, Inc.