CNTO 530 FUNCTIONS AS A POTENT EPO MIMETIC VIA UNIQUE SUSTAINED EFFECTS ON BONE MARROW PROERYTHROBLAST POOLS Running title: EPO mimetic CNTO 530 action modes

Anemia as associated with numerous clinical conditions can be debilitating, but frequently can be treated via administration of epoetin-alfa, darbepoietin-alfa or methoxy-PEG epoetin-beta. Despite the complexity of EPO-EPO receptor interactions, the development of interesting EPO mimetic peptides (EMPs) also has been possible. CNTO 530 is one such novel MIMETIBODY TM Fc-domain dimeric EMP fusion protein. In a mouse model, single-dose CNTO 530 (unlike epoetin-alfa or darbepoietin-alfa) bolstered red cell production for up to one month. In 5-fluorouracil and carboplatin-paclitaxel models, CNTO 530 also protected against anemia with unique efficiency. These actions were not fully accounted for by half-life estimates, and CNTO 530 signaling events therefore were studied. Within primary bone marrow erythroblasts, kinetics of STAT5, ERK, and AKT activation were similar for CNTO 530 and epoietin-alfa. p70S6K activation by CNTO 530, however, was selectively sustained. In vivo, CNTO 530 uniquely stimulated the enhanced formation of PODXL high CD71 high (pro)erythroblasts at frequencies multi-fold above epoetin-alfa or darbepoietin-alfa. CNTO 530 moreover supported the sustained expansion of a bone marrow-resident Kit neg CD71 high Ter119 neg progenitor pool. Based on these distinct erythropoietic and EPOR signaling properties, CNTO 530 holds excellent promise as a new EPO mimetic.