Coexpression of CMP‐sialic acid transporter reduces N‐glycolylneuraminic acid levels of recombinant glycoproteins in Chinese hamster ovary cells

Abstract Recombinant glycoproteins expressed in Chinese hamster ovary (CHO) cells contain two forms of sialic acids; N ‐acetylneuraminic acid (Neu5Ac) as a major type and N ‐glycolylneuraminic acid (Neu5Gc) as a minor type. The Neu5Gc glycan moieties in therapeutic glycoproteins can elicit immune responses because they do not exist in human. In the present work, to reduce Neu5Gc levels of recombinant glycoproteins from CHO cell cultures, we coexpressed cytidine‐5′‐monophosphate‐sialic acid transporter (CMP‐SAT) that is an antiporter and transports cytosolic CMP‐sialic acids (both forms) into Golgi lumen. When human erythropoietin was used as a target human glycoprotein, coexpression of CMP‐SAT resulted in a significant decrease of Neu5Gc level by 41.4% and a notable increase of Neu5Ac level by 21.2%. This result could be reasonably explained by our hypothesis that the turnover rate of Neu5Ac to Neu5Gc catalyzed by CMP‐Neu5Ac hydroxylase would be reduced through facilitated transportation of Neu5Ac into Golgi apparatus by coexpression of CMP‐SAT. We confirmed the effects of CMP‐SAT coexpression on the decrease of Neu5Gc level and the increase of Neu5Ac level using another glycoprotein human DNase I. Therefore, CMP‐SAT coexpression might be an effective strategy to reduce the levels of undesired Neu5Gc in recombinant therapeutic glycoproteins from CHO cell cultures.