Monitoring biodistribution of glycoproteins with modified sugar chains

Natural human interferon (hIFN)-gamma has mainly biantennary complex-type sugar chains. Previously, we successfully remodeled its sugar chain structure into: (a) highly branched types; or (b) highly sialylated types, by overexpression of: (a) N-acetylglucosaminyltransferase (GnT)-IV and/or GnT-V; or (b) sialyltransferases, in Chinese hamster ovary (CHO) cells. In addition, we prepared asialo hIFN-gammas by treatment with sialidase in vitro. In the present study, we assessed the bioactivity of remodeled hIFN-gamma in terms of antiviral activity, anticellular activity, and biodistribution. Structural changes to the sugar chains did not have a significant influence on the antiviral and anticellular activities of hIFN-gamma, although the attachment of the sugar chain itself affected both activities. However, the biodistribution differed significantly; the number of exposed galactose residues was the major determinant of the specific distribution to the liver and blood clearance rate of hIFN-gamma. This phenomenon was considered to be mediated by the hepatic asialoglycoprotein receptor (ASGP-R), and we showed a linear, not exponential, enhancement of the distribution to the liver with an increase in the number of exposed galactose residues. We also confirmed this tendency using fibroblast growth factor (FGF). Our observation is not the same as the "glycoside cluster effect." We thus provide important information on the character of modified recombinant glycoproteins.