Mammalian cell-produced therapeutic proteins: heterogeneity derived from protein degradation

Therapeutic glycoproteins, for example, antibodies (Abs) and Fc fusion proteins when produced in mammalian cells, such as Chinese hamster ovary (CHO) cells generally exhibit heterogeneity. Both the oligosaccharide moiety and the protein moiety contribute to this phenomenon. Non-enzymatic and enzymatic pathways of protein fragmentation generate heterogeneity in the polypeptide backbone. In the non-enzymatic pathway, physical and chemical events such as light, oxidation, and others can cause the protein moiety to become unstable leading to its fragmentation. Intracellular and secreted proteases are involved in the enzymatic degradation of proteins. This degradative process is modulated by the oligosaccharide moiety of the glycoprotein as well as glycosidases, including sialidases that are secreted in the culture medium. This review focuses on the factors that modulate heterogeneity of the protein moiety especially by the enzymatic methods. Availability of the CHO genome database will facilitate the development of host cell lines with minimal degradative properties.