Selective clearance of glycoforms of a complex glycoprotein pharmaceutical caused by terminal N-acetylglucosamine is similar in humans and cynomolgus monkeys

To understand how the carbohydrate moieties of a recombinant glycoprotein affected its pharmacokinetic (PK) properties, the glycan distribution was directly assessed from serial blood samples taken during PK studies in cynomolgus monkeys and humans. The protein studied was an immunoadhesin (lenercept), containing an Fc domain from human immunoglobulin G (IgG-1) and two copies of the extensively glycosylated extra cellular domain of tumor necrosis factor receptor p55. The protein was recovered in pure form using a dual column, immunoaffinity-reversed-phase high-performance liquid chromatography method. The glycans were released and analyzed by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Alternatively, trypsin was used to obtain glycopeptides, and these were analyzed by MALDI-TOF. The composition versus time profiles show that the distribution of glycans in the Fc domain was not altered over 10 days of circulation, consistent with their sequestration in the interior of the protein. However, the glycan composition in the receptor domain was changed dramatically in the first 24 h and then remained relatively constant. Analysis of the acidic glycans (derived exclusively from the receptor domain) showed that, in the rapid initial phase of clearance, glycans carrying terminal N-acetylglucosamine (tGlcNAc) were selectively cleared from the circulation. This phenomenon occurred similarly in humans and cynomolgus monkeys. Sialic acid content and terminal galactose showed only small changes. These data confirm the correlation of tGlcNAc and half-life of the molecule, and support the hypothesis that the mannose receptor (which can also bind tGlcNAc) causes the variable clearance of this molecule.