EPOETIN-ALFA AND EPOETIN-BETA DIFFER IN THEIR ERYTHROPOIETIN ISOFORM COMPOSITIONS AND BIOLOGICAL PROPERTIES

Epoetin alfa and beta are the two forms of recombinant DNA-derived ery thropoietin (rEPO), both synthesized in Chinese hamster ovary cells, w hich are used for the treatment of erythropoietin (EPO)-responsive ana emias. Several batches of each of these rEPOs were compared for differ ences in their EPO isoform compositions by isoelectric focusing (IEF) and in a range of lectin-binding assays, and for differences in their EPO activities by in-vivo and in-vitro mouse bioassays and by immunoas say. Epoetin beta was found to differ from epoetin alfa in containing: (a) a greater proportion of more basic isoforms, (b) a greater propor tion of EPO binding to Erythrina cristagalli agglutinin (which binds N -glycans with non-sialylated outer Gal beta 1-4GlcNAc moieties), and ( c) isoforms with higher in-vivo:in-vitro bioactivity ratios, Epoetin b eta also contained slightly more than epoetin alfa of EPO binding to L ycopersicon esculentum agglutinin (which binds N-glycans containing re peating Gal beta 1-4GlcNAc sequences), to the leucoagglutinin of Phase olus vulgaris (which binds tetra-antennary and 2,6-branched triantenna ry N-glycans) and to Agaricus bisporus agglutinin (which binds Gal bet a 1-3GalNAc containing O-glycans). No differences were found between t he two rEPOs in their binding to a further five lectins. The differenc es between the isoform composition of epoetin alfa and beta, and the s maller inter-batch differences appear to be due to differences in glyc osylation. The higher murine in-vivo:in-vitro bioactivity ratio of epo etin beta compared to epoetin alfa could not be explained in terms of differences in their degrees of sialylation, but was consistent with d ifferences in their pharmacokinetics and pharmacodynamics observed in human subjects, There have been no reports that epoetin alfa differs f rom epoetin beta in its clinical efficacy, but the differences between epoetin alfa and beta in some analytical systems suggest that there m ight be a need for separate international standards for these two type s of rEPO.