Covalent modification of therapeutic proteins by polyethylene glycol derivatives is an established method for improving pharmacokinetic properties of therapeutic proteins.
Highly purified rVWF expressed in CHO cells, was chemically modified via PEGylation of lysine residues at mild alkaline pH with PEG succinimidyl succinate (linear 5 kDa PEG). Increasing the amount of PEG used in the coupling procedure, the molecular size of VWF increased, as demonstrated in SDS-PAGE and by agarose gel electrophoreses indicating an increase in size of the bands resembling the VWF multimers.
PEGylation of rVWF reduced platelet-aggregating and collagen-binding functions by 60% (VWF:RCo activity) and 40% (VWF:CB activity). While FVIII-binding capacity, measured by a FVIII binding ELISA, was reduced and reduction correlated with the amount of PEG bound to VWF, there was almost no effect on FVIII binding affinity which remained in the same order of magnitude as measured with non-PEGylated VWF. Similar results were obtained when rVWF was PEGylated via carbohydrate moieties after oxidation and subsequent derivatization with monomethoxy-PEG hydrazide.
PEGylated rVWF was applied to VWF-deficient mice at a dose of 40 VWF:Ag U/kg and plasma levels were monitored for up to 24 hours. As a control, non-modified rVWF was applied to the animals. PEGylated VWF had substantially prolonged survival in the circulation compared with non-modified rVWF with an increase of the AUC by a factor of >10. VWD mice substituted with human VWF show a secondary rise in FVIII bringing them into the FVIII levels measured in C57Bl/6 control mice. This secondary rise was sustained after treatment with PEGylated rVWF where FVIII levels above the starting level were measurable even 48 hours after injection while in the control group base line FVIII levels were reached already after 24 hours.
rVWF is the largest protein ever PEGylated and PEGylation results in prolonged survival in the circulation while maintaining FVIII stabilizing functions of the VWF molecule in vivo.
Disclosures: All authors are employees of Baxter AG.; Authors have options to Baxter stock.