PRODUCTION OF TPA IN RECOMBINANT CHO CELLS UNDER OXYGEN-LIMITED CONDITIONS

Animal cell bioreactors are often limited by the oxygen supply. The re duction in oxygen consumption per cell that occurs under hypoxic condi tions 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 pl asminogen activator) production were investigated using midexponential and slowly growing CHO cells. The specific oxygen consumption rate ca n be reduced by at least 50% (mild hypoxic conditions) without affecti ng the cell growth rate, maximum cell concentration, tPA production ra te, or tPA quality (as characterized by the tPA-specific activity and SDS-PAGE analysis). This suggests that mild-hypoxic conditions (with s ufficient glucose) can be used to double the cell concentration and vo lumetric tPA production rate (at a constant volumetric oxygen supply r ate) without sacrificing product quality. However, anoxic conditions s hould be avoided. When slowly growing cultures were exposed to anoxia, the tPA production rate decreased by 80% without affecting tPA qualit y. However, when midexponential cultures were exposed to anoxia, the d rop in tPA production was accompanied by a decrease in tPA quality tha t ranged from a 40% decrease in tPA specific activity to extensive tPA degradation.