Erythropoietin, or Epo, is a hematopoietic cytokine that promotes erythropoiesis, and recombinant human Epo has been used in the treatment of anemia in various chronic diseases. Here. we have constructed novel Epo derivatives with prolonged half-lives by adding peptides to the carboxy terminus of Epo without using linkers. The fused peptides were selected from the carboxy terminal region of human chorionic gonadotropin (hCG) or human thrombopoietin (hTpo), which promote the proper folding, secretion, and stabilization of bioactive glycoproteins. Addition of these peptides did not interfere with secretion or receptor binding, and significantly increased the in vivo half-life Of human Epo, as measured by intravenous administration in rats. The plasma half-life of the Epo constructs was longest when the carboxy terminal 28 aa of the beta subunit of hCG was added (Epo-CGC), a half-life that was slightly longer than NESP (Ara-nesp), which is the most effective Epo product in current clinical use. The transformation of four Ser glycosylation sites to Ala on the CGC sequence also lengthened the plasma half-life of Epo, indicating that the in vivo stabilizing effect of the hCG peptide was due to both structures within the peptide itself and its O-glycosylations. The application of the carboxy terminal half of hTpo also resulted in remarkably reduced elimination of the Epo chimera (Epo-TpC), possibly due to protection by the TpC sequence. The in vivo hematopoietic activity of Epo derivatives in mice was consistent with their pharmacokinetic profiles. Therefore, these derivatives with prolonged half-lives may provide opportunities for developing new Epo therapeutics With less frequent administration. (c) 2005 Elsevier Inc. All rights reserved.