Pyruvate Kinase Muscle‐1 Expression Appears to Drive Lactogenic Behavior in CHO Cell Lines, Triggering Lower Viability and Productivity: A Case Study

Chinese hamster ovary (CHO) cell lines are used to express a variety of therapeutic proteins. However, lactogenic behavior displayed by some CHO cell lines during manufacturing processes may result in a decline in viability, productivity, and possible alterations in product quality. In cultured cells, lactate is produced during glycolysis through irreversible conversion of phosphoenolpyruvate to pyruvate and then lactate via sequential function of pyruvate kinase and lactate dehydrogenase (LDH) enzymes. In the process of cell line development (CLD), two lactogenic cell lines expressing different antibody molecules are identified. The lactogenic behaviors of these cell lines can be differentially mitigated through optimization of either nutrient feeds or culture pH, depending on the cell line. Analysis of various proteins involved in the glycolysis pathway reveal a direct correlation between the pyruvate kinase muscle‐1 (PKM‐1) isoform levels and lactogenic behavior. CRISPR mediated knockout of the PKM‐1 isoform abolishes lactate accumulation even under lactogenic conditions. Furthermore, a cell line lacking expression of both PKM‐1 and PKM‐2 enzymes capable of maintaining productivity, viability, and growth without displaying lactogenic behavior is identified. Targeted deletion of PKM in CHO cells may be tolerated due to expression of PKL (liver) and PKR (red blood cell) isoforms of pyruvate kinase. All together, these findings suggest that PKM‐1 up‐regulation during antibody production could trigger lactogenic behavior and that this enzyme is dispensable for CHO cell survival.