Erythropoietin Fusion Proteins Comprised of Identical Head-to-Tail Repeats with Enhanced Biological Activity.

Recombinant human erythropoietin (EPO, epoetin) is used widely for treatment of chronic anemia due to renal failure, cancer, and other causes. However, considerably high and frequent doses of EPO are required to maintain therapeutic effectiveness, since it has a relatively short in vivo half-life. Thus, alternatives with higher efficacy and/or longer half-life are being developed. We have shown previously that EPO-dimers, either produced by chemical cross-linking of monomeric EPO or expressed as a recombinant fusion protein from COS cells, exhibit enhanced biological properties in vitro and in vivo (Sytkowski, et.al. Proc. Natl. Acad. Sci. USA 95, 1184; Sytkowski, et.al. J. Biol. Chem. 274, 24773). We now report increased activities of EPO-dimer fusion protein and EPO-trimer fusion protein comprised of identical head-to-tail repeats and a 15 or 20-amino acid linker (for dimer), or 17-amino acid linkers (for trimer) produced from stably transfected CHO cells. EPO-fusion proteins were expressed under a CMV promoter with a signal peptide present on the first monomer coding sequence. The EPO-dimer fusion protein was connected with either three or four repeats of Gly-Gly-Gly-Gly-Ser as a 15 or 20-amino acid linker sequence, respectively. The expression levels of EPO-dimer fusion protein from cloned CHO cells to supernatant of protein-free medium ranged from 4 to 40 mg/L determined by EPO-ELISA, and from 2.0×10⁵ to 4.5×10⁶ IU/L determined by in vitro bioassay. We selected clones producing EPO-dimer fusion protein with the greatest extent of glycosylation, as indicated by SDS-PAGE and isoelectric focusing. Subcutaneous injection of mice with three doses of EPO-dimer fusion protein resulted in percent increases in mean hematocrit of 32.6% (300 IU/kg) or 18.2% (100 IU/kg), while equivalent unit doses of EPO-monomer increased mean hematocrit by 12.5% (300 IU/kg) or 6.4% (100 IU/kg). Moreover, a single dose of EPO-dimer fusion protein (100 IU/kg) increased their mean hematocrit by 4.3% within 7 days, while an equivalent unit dose of EPO-monomer had no effect. Importantly, three doses of EPO-trimer fusion protein increased their mean hematocrit by 8.83% per IU injected, which was much greater than that observed with EPO-monomer (0.69%) or EPO-dimer fusion protein (1.81%). The results show that EPO-fusion proteins exhibit biological activities superior to those of EPO-monomer, suggesting important therapeutic advantages.