Introduction: Recombinant human erythropoietin (rHuEPO) has become a standard treatment for the alleviation of anemia resulting from chronic renal failure and chemotherapy induced anemia. Treatment with rHuEPO corrects anemia, resulting in a broad range of clinical benefits including improved quality of life. Darbepoetin alfa (DA), a super-sialylated erythropoietic stimulating protein (ESP) with a 3-fold longer serum half-life than rHuEPO, is approved for use in the treatment of anemia. Another ESP investigated was a hyperglycosylated analog of DA having a greater number of carbohydrate chains and sialic acids (AMG205).

Objective: Our intention was to develop and characterize new ESPs and examine their relative activity and ability to maintain normal hemoglobin levels in a mouse model with stable anemia (hemoglobin 2g/dL below initial levels, > 98 days).

Methods and Results: Clearance of ESPs was reduced and in vivo potency was increased in proportion to number of carbohydrate chains; AMG205 was cleared the slowest and was the most potent of the 3 test molecules. A regimen of repeated low dose exposure to cisplatin (CDDP) was established that resulted in a stable reduction of hemoglobin levels by 2–3 g/dL (12.23±0.75g/dL). The hemoglobin range in control animals not treated with CDDP in this experiment was (14.53±0.57g/dL). Animals made anemic by repeated administration of CDDP were treated with rHuEPO (20μg/kg), DA (10μg/kg) or AMG205 (10μg/kg). Each group consisted of 15 mice. Following the initial injection, hemoglobin was measured every 2–3 days, and subsequent injections were administered when hemoglobin values were < 13 g/dL. Animals were so treated for 98 days. In this manner the number of injections of each ESP required to maintain normal hemoglobin was determined. Mice treated for 98 days required more injections of rHuEPO to maintain normal Hb levels than DA (13 vs.7 injections), while mice treated with AMG205 required 5 injections.

Conclusion: Normal hemoglobin levels were maintained over a 3 month period with repeated administration of the ESPs investigated. The ESPs with increased carbohydrate content had reduced clearance, increased in vivo potency and could maintain hemoglobin within a normal range with fewer injections than rHuEPO.

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