Collaborative study for the establishment of erythropoietin BRP batch 5

The European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for erythropoietin (EPO) is used as a working standard for potency determination of EPO preparations by in vivo bioassay as prescribed in Ph. Eur. monograph 1316 'Erythropoietin concentrated solution'. BRP batch 4 (BRP4) was calibrated in 2014 and its stocks are depleted. The European Directorate for the Quality of Medicines and HealthCare (EDQM) thus endorsed a project (BSP147) to calibrate a replacement batch in International Units against the 3rd WHO International Standard (IS) for erythropoietin, recombinant, for bioassay (11/170). The amount of material contained in the vial of BRP4 greatly exceeded the amount needed for one bioassay, sometimes leading to considerable waste. It was thus decided to prepare a candidate material with a lower EPO content. The collaborative study involved eight laboratories in Europe, the USA and Australia. Based on the outcome of the study, the Ph. Eur. Commission adopted the proposed standard as Erythropoietin BRP batch 5 in June 2018 for use as a reference preparation solely for the polycythaemic and normocythaemic mouse bioassays, with an assigned potency of 2000 IU/ampoule. Furthermore, the potency of BRP batch 4 was confirmed during the study thus warranting a good continuity of the International Unit.

Chemical synthesis of erythropoietin glycoforms for insights into the relationship between glycosylation pattern and bioactivity

The role of sialyloligosaccharides on the surface of secreted glycoproteins is still unclear because of the difficulty in the preparation of sialylglycoproteins in a homogeneous form. We selected erythropoietin (EPO) as a target molecule and designed an efficient synthetic strategy for the chemical synthesis of a homogeneous form of five EPO glycoforms varying in glycosylation position and the number of human-type biantennary sialyloligosaccharides. A segment coupling strategy performed by native chemical ligation using six peptide segments including glycopeptides yielded homogeneous EPO glycopeptides, and folding experiments of these glycopeptides afforded the correctly folded EPO glycoforms. In an in vivo erythropoiesis assay in mice, all of the EPO glycoforms displayed biological activity, in particular the EPO bearing three sialyloligosaccharides, which exhibited the highest activity. Furthermore, we observed that the hydrophilicity and biological activity of the EPO glycoforms varied depending on the glycosylation pattern. This knowledge will pave the way for the development of homogeneous biologics by chemical synthesis.

The winding pathway to erythropoietin along the chemistry-biology frontier: a success at last

The total synthesis of a homogeneous erythropoietin (EPO), possessing the native amino acid sequence and chitobiose glycans at each of the three wild-type sites of N glycosylation, has been accomplished in our laboratory. We provide herein an account of our decade-long research effort en route to this formidable target compound. The optimization of the synergy of the two bedrock sciences we now call biology and chemistry was central to the success of the synthesis of EPO.

Advances in proline ligation

Application of native chemical ligation logic to the case of an N-terminal proline is described. Two approaches were studied. One involved incorporation of a 3R-substituted thiyl-proline derivative. Improved results were obtained from a 3R-substituted selenol function, incorporated in the context of an oxidized dimer.

Toward homogeneous erythropoietin: non-NCL-based chemical synthesis of the Gln78-Arg166 glycopeptide domain

Single erythropoietin (EPO) glycoforms with defined mature oligosaccharide structures and amino acid sequences are essential to elucidate the molecular mechanisms by which carbohydrates exert various physiological and metabolic functions and to explore the possible links between carbohydrates and the prevention or management of diseases. To demonstrate that it is possible to generate EPO even without recourse to cysteine-based native chemical ligation, a concise synthesis of the partially protected EPO fragment (78-166) bearing fully mature N- and O-glycans is described.

Toward homogeneous erythropoietin: fine tuning of the C-terminal acyl donor in the chemical synthesis of the Cys29-Gly77 glycopeptide domain

Described herein is the chemical synthesis of the Cys(29)-Gly(77) glycopeptide domain (22) of erythropoietin. Our initial ligation strategy targeted a C --> N termini condensation between glycopeptide 3 and peptide 4. However, the reaction was hindered by the "unattainable" reactivity, mismatched polarity, and severe aggregation of the (glyco)peptide substrates. In contrast, by tuning the C-terminal acyl donor and using smaller peptide fragments, the Cys(29)-Gly(77) glycopeptide domain of erythropoietin was prepared through unconventional N --> C termini condensation reactions. The use of a p-cyanonitrophenyl ester and the development of a masked thiophenyl ester as acyl donors enabled us to promptly access glycopeptides bearing complex carbohydrates and offer potential synthetic applications beyond our current work.

Toward homogeneous erythropoietin: chemical synthesis of the Ala1-Gly28 glycopeptide domain by "alanine" ligation

The Ala(1)-Gly(28) glycopeptide fragment (28) of EPO was prepared by chemical synthesis as a single glycoform. Key steps in the synthesis include attachment of a complex dodecasaccharide (7) to a seven amino acid peptide via Lansbury aspartylation, native chemical ligation to join peptide 19 with the glycopeptide domain 18, and a selective desulfurization at the ligation site to reveal the natural Ala(19). This glycopeptide fragment (28) contains both the requisite N-linked dodecasaccharide and a C-terminal (alpha)thioester handle, the latter feature permitting direct coupling with a glycopeptide fragment bearing N-terminal Cys(29) without further functionalization.

Optimisation of chemical protein cleavage for erythropoietin semi-synthesis using native chemical ligation

Selective protein cleavage at methionine residues is a useful method for the production of bacterially derived protein fragments containing an N-terminal cysteine residue required for native chemical ligation. Here we describe an optimised procedure for cyanogen bromide-mediated protein cleavage, and ligation of the resulting fragments to afford biologically active proteins.

Synthetic Erythropoietic Proteins: Tuning Biological Performance by Site-Specific Polymer Attachment

Chemical synthesis in combination with precision polymer modification allows the systematic exploration of the effect of protein properties, such as charge and hydrodynamic radius, on potency using defined, homogeneous conjugates. A series of polymer-modified synthetic erythropoiesis proteins were constructed that had a polypeptide chain similar to the amino acid sequence of human erythropoietin but differed significantly in the number and type of attached polymers. The analogs differed in charge from +5 to -26 at neutral pH and varied in molecular weight from 30 to 54 kDa. All were active in an in vitro cell proliferation assay. However, in vivo potency was found to be strongly dependent on overall charge and size. The trends observed in this study may serve as starting points for the construction of more potent synthetic EPO analogs in the future.

Cyanogen Bromide Cleavage Generates Fragments Suitable for Expressed Protein and Glycoprotein Ligation

Herein cyanogen bromide is employed for the efficient production of N-terminal cysteine containing protein fragments for expressed protein ligation (EPL) from polyhistidine-tagged precursors. We provide three examples of efficient CNBr cleavage of fragments of the glycoprotein erythropoietin that can be ligated with peptides or glycopeptide mimetics potentially giving rise to semisynthetic glycoprotein therapeutics.

Expression of recombinant cytoplasmic yeast pyruvate carboxylase for the improvement of the production of human erythropoietin by recombinant BHK-21 cells

Recently, a recombinant yeast pyruvate carboxylase expressed in the cytoplasm of BHK-21 cells was shown to reconstitute the missing link between glycolysis and TCA, thus increasing the flux of glucose into the TCA and resulting in a higher intracellular ATP content. Now, these metabolically engineered cells have been additionally transfected with a plasmid bearing the gene for human erythropoietin. EPO yield and substrate-specific productivity of the recombinant BHK-21 cells have been compared to control cells without the PYC2-gene but transfected with the plasmid coding for the expression of the selection genes and EPO. PYC2-expressing clones showed a 2-fold higher glucose-specific productivity and a 2-fold higher product concentration in a continuously perfused bioreactor. Moreover, the PYC2 expression enabled the cells to become more resistant to low glucose concentrations in the culture medium. They could produce at nearly maximum productivity under glucose-limiting conditions of 0.05-1 gl(-1) that guaranteed a reduced accumulation of lactate in fed-batch production systems. Due to the fact that PYC2-expressing cells are characterized by reduced glucose consumption, a prolonged production phase in bioreactors can be maintained. Based on the demand not to fall short of 80% cell viability for the production, EPO could be produced for 2 days (30%) longer compared to the control due to a more economic exploitation of glucose, and the prolonged viability period of the cells using a batch cultivation driven by glutamine limitation.

Darbepoetin alfa. Amgen

Amgen has launched darbepoetin alfa, synthetic recombinant novel erythropoiesis stimulating protein (NESP), for the treatment of anemia associated with renal disease. The drug was approved by the European Commission in June 2001, under the tradename Aranesp, for the treatment of anemia in chronic kidney failure including patients on and not yet on dialysis. The company launched the drug on day one of its approval in the following countries: Germany, Sweden, Denmark, Portugal, the Netherlands, the UK and Austria. Roll out of the drug in Italy, Greece and France will follow as soon as pricing and reimbursement issues are resolved [412240], [412357]. By January 2001, the product was still under review and the company anticipated approval during the first half of 2001 in both the US and Europe [396802]. Launch in the US had originally been scheduled for 2000 [387293], [396802] and Japanese launch is planned for 2004 or 2005 [405915]. In January 2001, Amgen reported that the first pivotal trial of darbepoetin alfa in treating oncology patients with anemia was successful [396526], [396802]. The company anticipated a phase III trial in US patients in 2001 for the oncology indication 13977941. In the fourth quarter of 2000, darbepoetin alfa entered phase I trials in Japan. Japanese development of darbepoetin alfa was being conducted by Kirin Brewery (under the research code KRN-321) [396653]. In January 2001, Genesis Pharma licensed the rights to distribute, market and sell darbepoetin alfa for the treatment of anemia, in Greece and Cyprus [396437]. MegaPharm Ltd signed an agreement with Amgen in February 2001, granting MegaPharm certain exclusive rights to distribute, market and sell darbepoetin alfa in Israel [398897]. In February 2000, Merrill Lynch predicted that darbepoetin alfa sales will be in excess of $1.4 billion at maturity [355817]. In October 2000, darbepoetin alfa annual sales were predicted to hit $3 billion [387293].

Selective in vitro glycosylation of recombinant proteins: semi-synthesis of novel homogeneous glycoforms of human erythropoietin

BACKGROUND

A natural glycoprotein usually exists as a spectrum of glycosylated forms, where each protein molecule may be associated with an array of oligosaccharide structures. The overall range of glycoforms can have a variety of different biophysical and biochemical properties, although details of structure-function relationships are poorly understood, because of the microheterogeneity of biological samples. Hence, there is clearly a need for synthetic methods that give access to natural and unnatural homogeneously glycosylated proteins. The synthesis of novel glycoproteins through the selective reaction of glycosyl iodoacetamides with the thiol groups of cysteine residues, placed by site-directed mutagenesis at desired glycosylation sites has been developed. This provides a general method for the synthesis of homogeneously glycosylated proteins that carry saccharide side chains at natural or unnatural glycosylation sites. Here, we have shown that the approach can be applied to the glycoprotein hormone erythropoietin, an important therapeutic glycoprotein with three sites of N-glycosylation that are essential for in vivo biological activity.

RESULTS

Wild-type recombinant erythropoietin and three mutants in which glycosylation site asparagine residues had been changed to cysteines (His(10)-WThEPO, His(10)-Asn24Cys, His(10)-Asn38Cys, His(10)-Asn83CyshEPO) were overexpressed and purified in yields of 13 mg l(-1) from Escherichia coli. Chemical glycosylation with glycosyl-beta-N-iodoacetamides could be monitored by electrospray MS. Both in the wild-type and in the mutant proteins, the potential side reaction of the other four cysteine residues (all involved in disulfide bonds) were not observed. Yield of glycosylation was generally about 50% and purification of glycosylated protein from non-glycosylated protein was readily carried out using lectin affinity chromatography. Dynamic light scattering analysis of the purified glycoproteins suggested that the glycoforms produced were monomeric and folded identically to the wild-type protein.

CONCLUSIONS

Erythropoietin expressed in E. coli bearing specific Asn-->Cys mutations at natural glycosylation sites can be glycosylated using beta-N-glycosyl iodoacetamides even in the presence of two disulfide bonds. The findings provide the basis for further elaboration of the glycan structures and development of this general methodology for the synthesis of semi-synthetic glycoproteins.

Mimicry of erythropoietin by a nonpeptide molecule

Erythropoietin (EPO) controls the proliferation and differentiation of erythroid progenitor cells into red blood cells. EPO induces these effects by dimerization of the EPO receptors (EPOR) present on these cells. To discover nonpeptide molecules capable of mimicking the effects of EPO, we identified a small molecule capable of binding to one chain of EPOR and used it to synthesize molecules capable of inducing dimerization of the EPOR. We first identified compound 1 (N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester) by screening the in-house chemical collection for inhibitors of EPO binding to human EPOR and then prepared compound 5, which contains eight copies of compound 1 held together by a central core. Although both compounds inhibited EPO binding of EPOR, only compound 5 induced dimerization of soluble EPOR. Binding of EPO to its receptor in cells results in activation of many intracellular signaling molecules, including transcription factors like signal transducer and activator of transcription (STAT) proteins, leading to growth and differentiation of these cells. Consistent with its ability to induce dimerization of EPOR in solution, compound 5 exhibited much of the same biological activities as EPO, such as (i) the activation of a STAT-dependent luciferase reporter gene in BAF3 cells expressing human EPOR, (ii) supporting the proliferation of several tumor cell lines expressing the human or mouse EPOR, and (iii) the in vitro differentiation of human progenitor cells into colonies of erythrocytic lineage. These data demonstrate that a nonpeptide molecule is capable of inducing EPOR dimerization and mimicking the biological activities of EPO.

Identification of a 13 amino acid peptide mimetic of erythropoietin and description of amino acids critical for the mimetic activity of EMP1

To obtain information about the functional importance of amino acids required for effective erythropoietin (EPO) mimetic action, the conserved residues of a peptide mimetic of EPO, recently discovered by phage display, were subjected to an alanine replacement strategy. Further, to identify a minimal mimetic peptide sequence, a series of truncation peptides has been generated. One EPO mimetic peptide sequence, EMP1, was targeted and more than 25 derivatives of this sequence were evaluated for their ability to compete with [125I]EPO for receptor binding and for their ability to support the proliferation of two EPO-responsive cell lines. Two hydrophobic amino acids, Tyr4 and Trp13, appear essential for mimetic action, and aromatic residues appear to be important at these sites. These findings are consistent with the previously reported X-ray crystal structure of EMP1 complexed with the extracellular domain of the EPO receptor (EPO binding protein; EBP). In our efforts to define the structural elements required for EPO mimetic action, a 13 amino acid peptide was identified which possesses mimetic properties and contains a minimal agonist epitope. The ability of this peptide to effectively serve as a mimetic capable of the induction of EPO-responsive cell proliferation appears to reside within a single residue, equivalent to position Tyr4 of EMP1, when present in a sequence that includes the cyclic core peptide structure. Although these peptides are less potent than EPO, they should serve as an excellent starting point for the design of compounds with EPO mimetic activity.

Human erythropoietin dimers with markedly enhanced in vivo activity

Human erythropoietin, a widely used and important therapeutic glycoprotein, has a relatively short plasma half-life due to clearance by glomerular filtration as well as by other mechanisms. We hypothesized that an erythropoietin species with a larger molecular size would exhibit an increased plasma half-life and, potentially, an enhanced biological activity. We now report the production of biologically active erythropoietin dimers and trimers by chemical crosslinking of the conventional monomeric form. We imparted free sulfhydryl residues to a pool of erythropoietin monomer by chemical modification. A second pool was reacted with another modifying reagent to yield monomer with maleimido groups. Upon mixing these two pools, covalently linked dimers and trimers were formed that were biologically active in vitro. The plasma half-life of erythropoietin dimers in rabbits was >24 h compared with 4 h for the monomers. Importantly, erythropoietin dimers were biologically active in vivo as shown by their ability to increase the hematocrits of mice when injected subcutaneously. In addition, the dimers exhibited >26-fold higher activity in vivo than did the monomers and were very effective after only one dose. Dimeric and other oligomeric forms of Epo may have an important role in therapy.

Effects of recombinant human erythropoietin on fetal and adult hemoglobin in preterm infants

In the present study we assess the effect of recombinant human erythropoietin (r-HuEpo) upon levels of fetal Hb (HbF) and adult Hb (HbA) in preterm infants. Twenty-eight "healthy," appropriate for gestational age infants with birth weights 900-1400 g entered the study at 3 wk of age. Fourteen infants were randomized to receive r-HuEpo, and 14 infants served as controls. Four controls and six r-HuEpo treated infants had been transfused before study start, whereas four control infants were transfused in the course of the study. The untransfused infants showed a high HbF/Hb ratio during the study with only a weak tendency to decline toward the expected time of delivery. The total Hb mass increased (p < 0.05) more in the r-HuEpo-treated infants than in the untreated, whereas the rise in HbF mass was similar in the two groups. After each transfusion, the HbF/Hb ratio reverted gradually to the ratio expected at the infant's postconceptional age. There was no difference in the production rate of HbF between r-HuEpo-treated infants and controls. The present data indicate that the HbF/HbA ratio in preterm infants is subject to the same programmed mechanisms which govern intrauterine erythropoiesis until term and that exogenous r-HuEpo does not influence this pattern significantly.

[Synthesis and cloning of the whole human erythropoietin (EPO) gene]

A 600 bp synthetic erythropoietin (EPO) gene encoding all 166 amino acids of the EPO protein and 27 amino acids of the signal peptide has been constructed. The whole gene was divided into three large fragments consisting of a total of 32 oligonucleotides. These oligonucleotides were synthesized by the solid-phase phosphor-amidite method and ligated into three large fragments. These latter three were separately cloned into vector M13mp19 and then transformed into E. coli JM 103. Positive clones were screened with 32P-labeled probes. The sequences of the fragments were confirmed by DNA sequencing, and the sequence of the whole synthetic EPO gene was confirmed by enzymatic digestion and sequencing. The results indicated that the nucleotide sequence of the synthetic EPO gene is identical to that of the original.

Recombinant human erythropoietin

Erythropoietin is produced mainly by the kidneys and stimulates erythropoiesis in the bone marrow. Chronic renal failure is characterized by anemia, which is principally caused by erythropoietin deficiency. Recombinant human erythropoietin (r-hEPO) corrects the anemia of chronic renal disease and improves patient well-being, exercise tolerance, and cognitive function. The clinical pharmacology, efficacy, safety, and tolerance of r-hEPO are presented. Four major studies attest to r-hEPO's efficacy in the treatment of anemia of chronic renal disease and document potential toxicities of hypertension, iron deficiency, thrombosis, and bone pain. Careful attention to the extent of correction of the hematocrit, increased heparinization during hemodialysis therapy, and compliance with dietary restrictions may minimize the incidence and severity of adverse reactions. Resistance to r-hEPO may be due to iron deficiency, aluminum toxicity, or inflammation, including infection. Potential future uses of r-hEPO include the treatment of various other anemias, such as those seen in sickle cell anemia, rheumatoid arthritis, and autologous blood donation. Controlled clinical studies in these areas have not been reported.