We administered recombinant human erythropoietin to 25 anemic patients with end-stage renal disease who were undergoing hemodialysis. The recombinant human erythropoietin was given intravenously three times weekly after dialysis, and transfusion requirements, hematocrit, ferrokinetics, and reticulocyte responses were monitored. Over a range of doses between 15 and 500 units per kilogram of body weight, dose-dependent increases in effective erythropoiesis were noted. At 500 units per kilogram, changes in the hematocrit of as much as 10 percentage points were seen within three weeks, and increases in ferrokinetics of three to four times basal values, as measured by erythron transferrin uptake, were observed. Of 18 patients receiving effective doses of recombinant human erythropoietin, 12 who had required transfusions no longer needed them, and in 11 the hematocrit increased to 35 percent or more. Along with the rise in hematocrit, four patients had an increase in blood pressure, and a majority had increases in serum creatinine and potassium levels. No organ dysfunction or other toxic effects were observed, and no antibodies to the recombinant hormone were formed. These results demonstrate that recombinant human erythropoietin is effective, can eliminate the need for transfusions with their risks of immunologic sensitization, infection, and iron overload, and can restore the hematocrit to normal in many patients with the anemia of end-stage renal disease.

Human erythropoietin is a haematopoietic cytokine required for the differentiation and proliferation of precursor cells into red blood cells. It activates cells by binding and orientating two cell-surface erythropoietin receptors (EPORs) which trigger an intracellular phosphorylation cascade. The half-maximal response in a cellular proliferation assay is evoked at an erythropoietin concentration of 10 pM, 10(-2) of its Kd value for erythropoietin-EPOR binding site 1 (Kd approximately equal to nM), and 10(-5) of the Kd for erythropoietin-EPOR binding site 2 (Kd approximately equal to 1 microM). Overall half-maximal binding (IC50) of cell-surface receptors is produced with approximately 0.18 nM erythropoietin, indicating that only approximately 6% of the receptors would be bound in the presence of 10 pM erythropoietin. Other effective erythropoietin-mimetic ligands that dimerize receptors can evoke the same cellular responses but much less efficiently, requiring concentrations close to their Kd values (approximately 0.1 microM). The crystal structure of erythropoietin complexed to the extracellular ligand-binding domains of the erythropoietin receptor, determined at 1.9 A from two crystal forms, shows that erythropoietin imposes a unique 120 degrees angular relationship and orientation that is responsible for optimal signalling through intracellular kinase pathways.

The human erythropoietin gene has been isolated from a genomric phage library by using mixed 20-mer and 17-mer oligonucleotide probes. Construction of Oligonucleotide Probes. Purified human urinary Epo'isolated from the urine of patients with aplastic anemia (16) was subjected to tryptic digestion. The resulting fragments were isolated and sequenced by using an Applied Biosystems gas-phase microsequencer (unpublished data). A hexapeptide and a heptapeptide containing the least codon degeneracy were selected for oligodeoxyribonucleotide probe synthesis. The phosphoramidite method was l4sed for oligonucleotide synthesis (19,20). Each' probe mixture contained a pool of 128-oligonucleotide sequences. The probe mixtures were Probe mixture EpV = Val-Asn-Phe-Tyr-Ala-Trp-Lys 3' CAA TTG AAG ATG CGA ACC TT 5'Probe mixture EpQ= Gln-Pro-Trp-Glu-Pro-Leu 3' GTT GGA ACC CTT GGA GA 5'The probe mixtures were labeled at the 5' end with [-32P]ATP, 7500-8000 Ci/mmol (ICN) (1 Ci = 37 GBq), by using T4 polynucleotide kinase (21). Hybridization Procedures. Phage plaques were amplified according to the procedures of Woo (22) except that GeneScreenPlus filters and NZYAM plates [NaCl, 5 g; MgCl2-6H2O, 2 g; NZ-Amine A, 10 g; yeast extract, 5 g; Casamino acids, 2 g; maltose, 2 g; and agar, 15 g (per liter)] were utilized. Phage particles were disrupted and the DNAs were fixed on filters (50,000 plaques per 8.4 x 8.4 cm filter). The air-dried filters were baked at 80'C for 1 hr and then subjected to proteinase K digestion [50 ,ug ofproteinase 'K per ml of buffer solution containing 0.1 M Tris HCl (pH 8.0), 0.15 M NaCl, 10 mM EDTA, and 0.2% NaDodSO4] for 30 min at 550C. Prehybridization with a 1 M NaCl/1% NaDodSO4 solution was carried out at 550C for 4 hr or longer.The hybridization buffer contained 0.025 pmol/ml of each of the 128 probe sequences in 0.9 M NaCl/5 mM EDTA/50 mM sodium phosphate, pH 6.5/0.5% NaDodSO4/100 jg of yeast tRNA per ml. Hybridization was carried out at 480C'for 20 hr by using the EpV probe mixture. This is 2TC below the lowest calculated dissociation temperature (td) (23) for members of the mixture. At the completion of hybridization, the filters were washed three times with 0.9 M NaCl/90 mM sodium citrate, pH 7.0/0. 1% NaDodSO4 at room temperature Abbreviations: Epo, erythropoietin; CHO, Chinese hamster ovary; DHFR, dihydrofolate reductase; kb, kilobase(s); bp, base pair(s); nt, nucleotide(s); SV40, simian virus 40; td, dissociation temperature. 7580The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Studies on human erythropoietin (EPO) demonstrated that there is a direct relationship between the sialic acid-containing carbohydrate content of the molecule and its serum half-life and in vivo biological activity, but an inverse relationship with its receptor-binding affinity. These observations led to the hypothesis that increasing the carbohydrate content, beyond that found naturally, would lead to a molecule with enhanced biological activity. Hyperglycosylated recombinant human EPO (rHuEPO) analogues were developed to test this hypothesis. Darbepoetin alfa (novel erythropoiesis stimulating protein, NESP, ARANESP TM , Amgen Inc, Thousand Oaks, CA), which was engineered to contain 5 N-linked carbohydrate chains (two more than rHuEPO), has been evaluated in preclinical animal studies. Due to its increased sialic acid-containing carbohydrate content, NESP is biochemically distinct from rHuEPO, having an increased molecular weight and greater negative charge. Compared with rHuEPO, it has an approximate 3-fold longer serum half-life, greater in vivo potency, and can be administered less frequently to obtain the same biological response. NESP is currently being evaluated in human clinical trials for treatment of anaemia and reduction in its incidence.© 2001 Cance Cance Cancer Research Campaign

Delivery of protein therapeutics often requires frequent injections because of low activity or rapid clearance, thereby placing a burden on patients and caregivers. Using glycoengineering, we have increased and prolonged the activity of proteins, thus allowing reduced frequency of administration. Glycosylation analogs with new N-linked glycosylation consensus sequences introduced into the protein were screened for the presence of additional N-linked carbohydrates and retention of in vitro activity. Suitable consensus sequences were combined in one molecule, resulting in glycosylation analogs of rHuEPO, leptin, and Mpl ligand. All three molecules had substantially increased in vivo activity and prolonged duration of action. Because these proteins were of three different classes (rHuEPO is an N-linked glycoprotein, Mpl ligand an O-linked glycoprotein, and leptin contains no carbohydrate), glycoengineering may be generally applicable as a strategy for increasing the in vivo activity and duration of action of proteins. This strategy has been validated clinically for glycoengineered rHuEPO (darbopoetin alfa).

No abstract

Studies on human erythropoietin (EPO) demonstrated that there is a direct relationship between the sialic acid-containing carbohydrate content of the molecule and its serum half-life and in vivo biological activity, but an inverse relationship with its receptor binding affinity. These observations led to the hypothesis that increasing the carbohydrate content, beyond that found naturally, would lead to a molecule with enhanced biological activity. Hyperglycosylated recombinant human EPO (rHuEPO) analogues were developed to test this hypothesis. Darbepoetin alfa (novel erythropoiesis stimulating protein, NESP), which was engineered to contain five N-linked carbohydrate chains (two more than rHuEPO), has been evaluated in preclinical animal studies. Due to its increased sialic acid-containing carbohydrate content, NESP is biochemically distinct from rHuEPO, having an increased molecular weight and greater negative charge. Compared with rHuEPO, it has an approximately 3-fold longer serum half-life, greater in vivo potency, and can be administered less frequently to obtain the same biological response. NESP is currently being evaluated in human clinical trials for treatment of anaemia and reduction in its incidence.

No abstract