Evaluation of bioactivity and pharmacokinetic characteristics of PEGylated P.pastoris-expressed erythropoietin.

High costs of production and relatively short serum half-life of mammalian cell-derived recombinant human erythropoietin (rHuEpo) necessitate finding and developing superior hosts/technologies for more efficient production of longer-acting erythropoietic agents. With these aims, we provide the first report on reductive alkylation of low-cost P.pastoris-expressed rHuEpo (PPEpo) with PEG-aldehyde. The PCR-amplified cDNA of native rHuEpo was cloned into the pPICZαA vector and transformed into the yeast Pichia pastoris. The best expressing transformant was selected and employed for secreted-expression of PPEpo using the standard protocols. Purified PPEpo was N-terminally PEGylated with 20-kDa mPEG-propionaldehyde in a low pH (5) condition. The in vitro and in vivo biological activities of purified mono-PEGylated PPEpo was evaluated by the UT-7 cells proliferation assay and normocythaemic mice assay, respectively. Pharmacokinetic parameters were determined following intravenous administration of Epo proteins in rabbits. While PPEpo showed a higher in vitro bioactivity compared to rHuEpo, no in vivo efficiency was determined for PPEpo. However, the in vivo activity of PEG-PPEpo conjugate was comparable to that of rHuEpo. Pharmacokinetic studies showed that the terminal half-life and mean residence time of PEG-PPEpo were increased approximately 4-fold and 6.5-fold respectively, compared with those of PPEpo. The results indicate that N-terminal PEGylation of Pichia-expressed Epo could be considered as a promising approach for generating cost-effective and long-acting erythropoiesis-stimulating agents.