Dimeric erythropoietin fusion protein with enhanced erythropoietic activity in vitro and in vivo

High doses of recombinant human erythropoietin (rhEpo) are required for the treatment of chronic anemia. Thus, it is clear that therapy for chronic an emia would greatly benefit from an erythropoietin derivative with increased erythropoietic activity rather than the native endogenous hormone. In this report, the activity of a human Epo-Epo dimer protein, obtained by recombi nant technology, is described and compared with its Epo monomer counterpart produced under identical conditions. Although monomer Epo and dimer Epo-Ep o had similar pharmacokinetics in normal mice, the increase in hematocrit v alue was greater with the dimer than with the monomer, Moreover, in clonoge nic assays using CD34(+) human hematopoietic cells, the human dimer induced a 3- to 4-fold-greater proliferation of erythroid cells than the monomer, Controlled secretion of dimeric erythropoietin was achieved in beta -thalas semic mice by in vivo intramuscular electrotransfer of a mouse Epo-Epo plas mid containing the tetO element and of a plasmid encoding the tetracycline controlled transactivator tTA, Administration of tetracycline completely in hibited the expression of the mEpo dimer, On tetracycline withdrawal, expre ssion of the Epo-Epo dimer resumed, thereby resulting in a large and sustai ned hematocrit increase in beta -thalassemic mice. No immunologic response against the dimer was apparent in mice because the duration of the hematocr it increase was similar to that observed with the monomeric form of mouse e rythropoietin. (C) 2001 by The American Society of Hematology.