The application of N-acetylmannosamine to the mammalian cell culture production of recombinant human glycoproteins

Introduction Sialic acid (N-acetylneuraminic acid, NeuAc, Neu5Ac) is an essential terminal sugar on the glycan moieties of many functional and structural human glycoproteins. A key intermediate in the biochemical process to form sialic acid is the monosaccharide, ManNAc, which is formed by the bifunctional enzyme UDPN-acetylglucosamine / Nacetylmannosamine epimerase kinase (GNE). ManNAc is an intermediate in the formation of the final product of the GNE enzymatic transformation, ManNAc-6-phosphate, which is subsequently condensed with pyruvate to form the 9-phosphate of sialic acid. At this point the sialic acid is either modified to form other sialic acids or is activated in the cell nucleus to form the nucleotide CMP-sialic acid prior to bonding to galactose (the intermediate terminal sugar of the glycan in glycoprotein formation, by means of a sialyl transferase,1 Fig. 1). This is normally the last step in the biosynthesis of a wide range of glycoproteins which are found in all human tissues.