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Characterization and minimization of sialic acid degradation in an Fc-fusion protein-producing CHO cell bioprocess

Chen, Xinning, Liu, Jintao, Liu, Xuping, Fan, Li, Zhao, Liang, Tan, Wen-Song
Process biochemistry 2018 v.73 pp. 162-169
bioactive properties, bioprocessing, bioreactors, cell culture, glycoproteins, half life, monosaccharides, pH, polysaccharides, process control, protein synthesis, sialic acid, sialidase, therapeutics
Sialic acid content generally affects many biochemical properties of therapeutic glycoproteins. More specific properties, such as charge distribution, circulating half-life and bioactivity, are directly impacted by sialic acid content. Undesirable loss of protein sialylation is commonly observed in CHO bioprocesses, and sialic acid degradation is one of the root causes. In this work, sialic acid degradation by extracellular sialidase was investigated in an Fc-fusion protein production bioprocess. First, cell-free incubation with the cell culture supernatant (CCS) collected at the end of culture revealed a 12.46% drop in sialic acid content by sialidase after 6 days of incubation, while other monosaccharides on the glycans remained stable. Then, potential factors that could affect the action of sialidase were studied, and a pH of over 7.05 was found to have a strong inhibitory effect on the degradation of sialic acid in the CCS. The results were further validated in bioreactors with different pH controls to demonstrate that a minimization of sialic acid loss could be achieved by controlling pH at higher values. Our work provides a simple and effective way to alleviate the decrease in sialic acid content and improves the understanding of the relationship between process control and product sialylation in CHO bioprocesses.