Comparative Erythropoietin Receptor Binding Kinetics of C.E.R.A. and Epoetin-β Determined by Surface Plasmon Resonance and Competition Binding Assay

C.E.R.A., a continuous erythropoietin (EPO) receptor activator, has been developed to provide stable maintenance of hemoglobin levels at once-monthly dosing intervals and smooth and steady anemia correction. The comparative EPO receptor binding properties of C.E.R.A. and epoetin-β were assessed by surface plasmon resonance using soluble recombinant EPO receptors and by competition binding on cultured UT-7 cells. Calculated equilibrium dissociation constants (surface plasmon resonance assay) for C.E.R.A. and epoetin-β were 140 and 2.9 nmol/l, respectively. Respective IC₅₀ values (competition binding assay) were 200 and 1.5 nmol/l. Compared with epoetin-β, C.E.R.A. has ∼50- to 100-fold lower affinity for EPO receptor binding sites. Analysis of the equilibrium binding curves indicates that the difference in affinity is mainly due to slower association. The different receptor binding properties of C.E.R.A. may enable continuous stimulation of erythropoiesis and, combined with a long half-life and slow systemic clearance, permit administration at extended intervals.