Pharmacokinetics and Excretion of 14C-Labeled Polyethylene Glycol (60 kDa) in Rats

Introduction: Although there is no evidence for PEG-related safety issues with PEGylated proteins in the clinic, questions relating to the pharmacokinetics including disposition and excretion of PEG are being raised more frequently by health authorities nowadays, particularly for PEGylated proteins used chronically and/or in the pediatric population (http://www.ema.europa.eu/docs/en_GB/document_library/Scientific_guideline/2012/11/WC500135123.pdf).BAY 94-9027, a B-domain–deleted recombinant FVIII with a 60-kDa branched PEG molecule attached via a maleimide linker to an amino acid using site-specific PEGylation, is in clinical development for acute and prophylactic intravenous treatment of hemophilia A. The objective of this study was to investigate the pharmacokinetics and excretion of radioactivity (unchanged compound and radioactive metabolites) after single intravenous administration of ¹⁴C-labeled BAY 1025662 (cysteine linker-[60-kDa] PEG part of BAY 94-9027 with the ¹⁴C label covalently integrated in the linker) in male Wistar rats.

Methods: The administered dose was 11 mg/kg body weight related to BAY 1025662 (approximated human lifetime dose of PEG 60 kDa resulting from treatment with BAY 94-9027). The concentrations and amounts of radioactivity in urine, feces, blood, plasma, and selected organs and tissues were investigated in order to determine the excretion via urine and feces, and the pharmacokinetics of total radioactivity and radioactive residues in the animal body.

Results: After single intravenous administration of ¹⁴C-BAY 1025662 to rats, a fast initial elimination of ¹⁴C radioactivity was observed; 63.2% of administered radioactivity was excreted within the first 24 hours (51.4% in urine, 11.8% in feces). Up to day 7, 75.6% of administered radioactivity was excreted predominantly via urine. The balance/recovery of radioactivity on day 7 amounted to 99.0% in relation to the administered radioactive dose. The radioactive residue in the animals amounted to 23.4% of administered dose. The majority of the residual radioactivity was recovered in the carcass and skin, followed by liver and kidneys. The excretion of radioactivity continued at steadily decreasing levels until the end of the study. The daily radioactivity excretion decreased from 2.1% at 72 hours to 0.013% of dose at 6 months after administration of ¹⁴C-BAY 1025662. The cumulative excretion of radioactivity via urine and feces was calculated (partly interpolated) to 92.2% of the administered radioactive dose by the end of the experiment on day 168 (74.5% via urine, 17.4% via feces, and 0.294% recovered in the cage wash). The radioactivity was continuously albeit slowly eliminated from the investigated organs and tissues. The elimination half-life of radioactivity was 26 and 23 days in blood and plasma, respectively. The corresponding elimination half-lives of radioactivity were 35, 41, and 31 days in the liver, carcass, and skin, respectively. Radioactivity elimination from kidneys was biphasic with a terminal half-life of 92 days. The radioactive residues in the animals excluding the gastrointestinal tract decreased during the study from 22.5% on day 7 to 1.79% of dose at the end of the study on day 168. There was no indication for any retention or irreversible binding of radioactivity in the animal body. The total recovery of radioactivity (cumulative excretion plus residues in the animals) was 94% in relation to the administered dose at the end of the experiment on day 168.

Conclusions: In this study, nearly complete excretion of the 60-kDa PEG molecule (measured as total radioactivity) could be observed, with a fast initial elimination in the first few days and a subsequent considerably slower process until the end of the observation period (6 months). These results are in agreement with recently proposed fast and slow processes for the renal excretion of large PEG and PEG proteins (Baumann, A. et al. Drug Discov Today. 2014:[Epub ahead of print, http://dx.doi.org/10.1016/j.drudis.2014.06.002]).