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American Journal of Kidney Diseases

New Treatment Approaches for the Anemia of CKD

Published:September 12, 2015DOI:https://doi.org/10.1053/j.ajkd.2015.06.030
      Normocytic normochromic anemia is a common complication in chronic kidney disease and is associated with many adverse clinical consequences. Erythropoiesis-stimulating agents (ESAs) and adjuvant iron therapy represent the primary treatment for anemia in chronic kidney disease. The introduction of ESAs into clinical practice was a success story, mediating an increase in hemoglobin concentrations without the risk for recurrent blood transfusions and improving quality of life substantially. However, recombinant ESAs are still expensive and require a parenteral route of administration. Moreover, concern has arisen following randomized clinical trials showing that higher hemoglobin targets and/or high ESA doses may cause significant harm. This, together with changes in ESA reimbursement policy in some countries, has resulted in a significant reduction in ESA prescribing and the hemoglobin level targeted during therapy. Several attempts are being made to develop new drugs with improved characteristics and/or easier manufacturing processes compared with currently available ESAs, including new treatment approaches that may indirectly improve erythropoiesis. We give an update on the new investigational strategies for increasing erythropoiesis, examining in depth their characteristics and possible advantages in the clinical setting and the caveats to be aware of at the present stage of development.

      Index Words

      Normocytic normochromic anemia is one of the hallmarks of progressive chronic kidney disease (CKD).
      • Kausz A.T.
      • Levey A.S.
      The care of patients with chronic kidney disease.
      It is mainly due to an absolute or relative decrease in erythropoietin (EPO) production by the failing kidney. However, its pathogenesis is much more complex. Several other factors (iron and vitamin deficiency, infection, inflammation, occult blood loss, oxidative stress, inadequate dialysis, and hyperparathyroidism) often contribute to anemia development and reduce response to treatment.
      The introduction of erythropoiesis-stimulating agents (ESAs) has revolutionized the care of anemic patients with CKD and almost completely eradicated the severe anemia of end-stage renal disease (ESRD).
      • Winearls C.G.
      • Oliver D.O.
      • Pippard M.J.
      • Reid C.
      • Downing M.R.
      • Cotes P.M.
      Effect of human erythropoietin derived from recombinant DNA on the anaemia of patients maintained by chronic haemodialysis.
      Moreover, ESAs decrease the risk for recurrent blood transfusions and iron overload and may improve quality of life. The first-generation ESAs were human recombinant EPOs (epoetin alfa and epoetin beta). Subsequently, 2 second-generation ESAs with a longer duration of action were developed; darbepoetin alfa and methoxy-polyethylene glycol-epoetin beta. Biosimilar epoetins, together with epoetin theta, have also received marketing authorization in many countries.
      • Jelkmann W.
      The ESA scenario gets complex: from biosimilar epoetins to activin traps.
      Today, ESAs and adjuvant iron therapy are the main tools for treating the anemia associated with CKD. Available ESAs are very effective drugs, usually obtaining significant hemoglobin (Hb) level increases. However, recombinant ESAs are still expensive and require cold storage. In addition, they are administered by the parenteral route. Especially with frequent subcutaneous administrations, this may be cumbersome for long-term treatment in non–dialysis-dependent patients with CKD. In hemodialysis (HD) patients, the issue is more complex because intravenous administration increases nurse workload but improves treatment adherence. In addition, in the past several years, clinical trials
      • Singh A.K.
      • Szczech L.
      • Tang K.L.
      • et al.
      Correction of anemia with epoetin alfa in chronic kidney disease.
      • Drüeke T.B.
      • Locatelli F.
      • Clyne N.
      • et al.
      Normalization of hemoglobin level in patients with chronic kidney disease and anemia.
      • Pfeffer M.A.
      • Burdmann E.A.
      • Chen C.Y.
      • et al.
      A trial of darbepoetin alfa in type 2 diabetes and chronic kidney disease.
      have shown that higher Hb targets and/or application of high ESA doses may increase cardiovascular risk. This, together with changes in ESA reimbursement policy in some countries, has led to reductions in prescribed ESA dose
      • Pisoni R.L.
      • Fuller D.S.
      • Bieber B.A.
      • et al.
      The DOPPS Practice Monitor for US dialysis care: trends through August 2011.
      and target Hb levels.
      KDIGO Anemia Work Group
      KDIGO clinical practice guideline for anemia in chronic kidney disease.
      • Locatelli F.
      • Bárány P.
      • Covic A.
      • et al.
      ERA-EDTA ERBP Advisory Board
      Kidney Disease: Improving Global Outcomes guidelines on anaemia management in chronic kidney disease: a European Renal Best Practice position statement.
      Hence, an increase in blood transfusion requirements and intravenous iron dosing has occurred. Blood transfusions cannot be considered as an alternative strategy to ESAs because they still have some risks, expose patients to large Hb-level fluctuations, and by definition have limited availability. Moreover, they may enhance the synthesis of alloantigenic antibodies, reducing the likelihood of patients subsequently receiving a kidney transplant. Excessive iron use may cause harm as well.
      • Hung S.C.
      • Tarng D.C.
      ESA and iron therapy in chronic kidney disease: a balance between patient safety and hemoglobin target.
      In the last 2 decades, recombinant forms of EPO have been engineered to have structural modifications that increase half-life and accommodate a wider administration schedule. However, health systems cannot afford to pay more for a secondary advantage, as attested by the limited success of methoxy-polyethylene glycol-epoetin beta in the European market (though this may have been compounded by a several-month shortage of the drug). Moreover, the experience with peginesatide (discussed later) has highlighted that unexpected adverse events may abruptly halt either the development or commercialization of a given molecule after years of investment. The task is becoming increasingly difficult because regulatory authorities rightly require more and more data for safety and hard end points following the concerns surrounding the safety of existing ESAs with regard to cardiovascular events and cancer worsening.
      Despite this, the ESA market is huge and still very appealing from an economic standpoint. Attempts are being made to develop new molecules with improved characteristics and/or easier manufacturing processes than those currently available. Their success when entering the ESA market will depend on the balance among price, advantages, and possible risks. There remains the general sentiment that new treatment strategies are needed with a better safety profile than existing ESAs.
      In this review, we provide an update on the new treatment approaches for increasing erythropoiesis (Box 1). We report in particular on the new erythropoietic strategies currently in clinical development. Agents that have not yet reached this phase are described in Table 1.
      • Sathyanarayana P.
      • Houde E.
      • Marshall D.
      • et al.
      CNTO 530 functions as a potent EPO mimetic via unique sustained effects on bone marrow proerythroblast pools.
      • Bugelski P.J.
      • Makropoulos D.
      • Spinka-Doms T.
      • et al.
      Differential effects of long-lived erythropoietin receptor agonists in rats.
      • Greindl A.
      • Kessler C.
      • Breuer B.
      • et al.
      AGEM400(HES), a novel erythropoietin mimetic peptide conjugated to hydroxyethyl starch with excellent in vitro efficacy.
      • Kessler C.
      • Greindl A.
      • Breuer B.
      • et al.
      Erythropoietin mimetic compound AGEM400(HES) binds to the same receptor as erythropoietin but displays a different spectrum of activities.
      • Dalle B.
      • Henri A.
      • Rouyer-Fessard P.
      • et al.
      Dimeric erythropoietin fusion protein with enhanced erythropoietic activity in vitro and in vivo.
      • Sytkowski A.J.
      • Lunn E.D.
      • Risinger M.A.
      • Davis K.L.
      An erythropoietin fusion protein comprised of identical repeating domains exhibits enhanced biological properties.
      • Fares F.A.
      • Ganem S.
      • Hajouj T.
      • Agai E.
      Development of a long-acting erythropoietin by fusing the carboxyl-terminal peptide of human chorionic gonadotropin beta-subunit to the coding sequence of human erythropoietin.
      • Fares F.
      • Havron A.
      • Fima E.
      Designing a long acting erythropoietin by fusing three carboxyl-terminal peptides of human chorionic gonadotropin β subunit to the n-terminal coding sequence.
      • Schriebl K.
      • Trummer E.
      • Lattenmayer C.
      • et al.
      Biochemical characterization of rhEPO-Fc fusion protein expressed in CHO cells.
      • Penno C.A.
      • Kawabe Y.
      • Ito A.
      • Kamihita M.
      Production of recombinant human erythropoietin/Fc fusion protein by genetically manipulated chickens.
      • Joung C.H.
      • Shin J.Y.
      • Koo J.K.
      • et al.
      Production and characterization of long-acting recombinant human albumin-EPO fusion protein expressed in CHO cell.
      • Schneider H.
      • Chaovapong W.
      • Matthews D.J.
      • et al.
      Homodimerization of erythropoietin receptor by a bivalent monoclonal antibody triggers cell proliferation and differentiation of erythroid precursors.
      • Elliott S.
      • Lorenzini T.
      • Yanagihara D.
      • Chang D.
      • Elliott G.
      Activation of the erythropoietin (EPO) receptor by bivalent anti-EPO receptor antibodies.
      • Lacy S.E.
      • DeVries P.J.
      • Xie N.
      • Fung E.
      • Lesniewski R.R.
      • Reilly E.B.
      The potency of erythropoietin-mimic antibodies correlates inversely with affinity.
      • Suzuki N.
      • Mukai H.Y.
      • Yamamoto M.
      In vivo regulation of erythropoiesis by chemically inducible dimerization of the erythropoietin receptor intracellular domain.
      New Strategies Under Development to Stimulate Erythropoiesis
      Not Directly Targeting the EPO Receptor
      • HIF stabilizers
        • FG-4592 (Roxadustat)
        • AKB-6548
        • GSK1278863
        • BAY 85-3934 (Molidustat)
        • JTZ-951
        • DS-1093a
      • Activin traps
        • Sotatercept (ACE-011)
        • Luspatercept (ACE-536)
        • LY2157299
      Targeting the EPO Receptor
      • EPO mimetic peptides
        • Centocor molecules: CNTO 528, CNTO 530, CNTO 531
        • AplaGen GmbH: AGEM400(HES)
        • Peginesatidea
      • EPO fusion proteins
        • EPO-EPO dimers
        • EPO-CPT
        • EPO-(CPT)3
        • Albumin-EPO
        • EPO-hyFc (Genexine GX-E2)
      • Antibody agonists to EPO receptor
        • Mouse monoclonal IgG
        • Ab12 molecule
        • Ab12.6 (Abbott Laboratories ABT-007) molecule
      • EPO gene therapy (TARGT EPO)
      • Dimerization of EPO receptor intracellular domain with a CID
      Abbreviations: CID, chemical inducer of dimerization; CPT, carboxyl-terminal peptide; EPO, erythropoietin; HES, hydroxyethyl starch; HIF, hypoxia-inducible factor; IgG, immunoglobulin G; TARGT, transducer autologous regenerative gene therapy.
      aWithdrawn from the market.
      Table 1New Erythropoiesis-Stimulating Agents Not in Clinical Development
      AgentsDrugsMechanism of ActionSummary of Preclinical DataReference
      EPO mimetic peptidesAGEM400(HES), CNTO 530, CNTO 531EPO receptor activationEfficient stimulation of hematopoietic progenitor cells
      • Sathyanarayana P.
      • Houde E.
      • Marshall D.
      • et al.
      CNTO 530 functions as a potent EPO mimetic via unique sustained effects on bone marrow proerythroblast pools.
      ,
      • Bugelski P.J.
      • Makropoulos D.
      • Spinka-Doms T.
      • et al.
      Differential effects of long-lived erythropoietin receptor agonists in rats.
      ,
      • Greindl A.
      • Kessler C.
      • Breuer B.
      • et al.
      AGEM400(HES), a novel erythropoietin mimetic peptide conjugated to hydroxyethyl starch with excellent in vitro efficacy.
      ,
      • Kessler C.
      • Greindl A.
      • Breuer B.
      • et al.
      Erythropoietin mimetic compound AGEM400(HES) binds to the same receptor as erythropoietin but displays a different spectrum of activities.
      EPO fusion proteinsEPO-EPO dimers, EPO-CPT, EPO-(CPT)3, albumin-EPOEPO receptor activationIncreased erythropoietic activity and half-life compared to the native endogenous hormone in vitro and in mice
      • Dalle B.
      • Henri A.
      • Rouyer-Fessard P.
      • et al.
      Dimeric erythropoietin fusion protein with enhanced erythropoietic activity in vitro and in vivo.
      ,
      • Sytkowski A.J.
      • Lunn E.D.
      • Risinger M.A.
      • Davis K.L.
      An erythropoietin fusion protein comprised of identical repeating domains exhibits enhanced biological properties.
      ,
      • Fares F.A.
      • Ganem S.
      • Hajouj T.
      • Agai E.
      Development of a long-acting erythropoietin by fusing the carboxyl-terminal peptide of human chorionic gonadotropin beta-subunit to the coding sequence of human erythropoietin.
      ,
      • Fares F.
      • Havron A.
      • Fima E.
      Designing a long acting erythropoietin by fusing three carboxyl-terminal peptides of human chorionic gonadotropin β subunit to the n-terminal coding sequence.
      ,
      • Schriebl K.
      • Trummer E.
      • Lattenmayer C.
      • et al.
      Biochemical characterization of rhEPO-Fc fusion protein expressed in CHO cells.
      ,
      • Penno C.A.
      • Kawabe Y.
      • Ito A.
      • Kamihita M.
      Production of recombinant human erythropoietin/Fc fusion protein by genetically manipulated chickens.
      ,
      • Joung C.H.
      • Shin J.Y.
      • Koo J.K.
      • et al.
      Production and characterization of long-acting recombinant human albumin-EPO fusion protein expressed in CHO cell.
      Agonistic antibodies to the EPO receptorMouse IgG, Ab12, Ab12.6 (ABT-007)EPO receptor activationRelatively poor EPO receptor activation by mouse monoclonal antibodies; in vitro potency and in vivo erythropoietic efficacy in mice by human agonistic antibodies Ab12 and Ab12.6
      • Schneider H.
      • Chaovapong W.
      • Matthews D.J.
      • et al.
      Homodimerization of erythropoietin receptor by a bivalent monoclonal antibody triggers cell proliferation and differentiation of erythroid precursors.
      ,
      • Elliott S.
      • Lorenzini T.
      • Yanagihara D.
      • Chang D.
      • Elliott G.
      Activation of the erythropoietin (EPO) receptor by bivalent anti-EPO receptor antibodies.
      ,
      • Lacy S.E.
      • DeVries P.J.
      • Xie N.
      • Fung E.
      • Lesniewski R.R.
      • Reilly E.B.
      The potency of erythropoietin-mimic antibodies correlates inversely with affinity.
      Inducers of dimerization of EPO receptor intracellular domainChemical inducer of dimerization (CID)EPO receptor activationExclusive stimulation of erythroid cells upon perioral administration to transgenic mice
      • Suzuki N.
      • Mukai H.Y.
      • Yamamoto M.
      In vivo regulation of erythropoiesis by chemically inducible dimerization of the erythropoietin receptor intracellular domain.
      Note: See Box 1 for expansions of abbreviations.

      New Erythropoietic Strategies Not Directly Targeting the EPO Receptor

      Hypoxia-Inducible Factor Stabilizers

      Hypoxia-inducible factors (HIFs) coordinate the physiologic response to systemic hypoxia by altering gene expression in certain cell types, leading to an increase in EPO production in the kidney and liver, improved uptake and use of iron, and changes to the bone marrow microenvironment that encourage erythroid progenitor maturation and proliferation.
      • Haase V.H.
      Regulation of erythropoiesis by hypoxia-inducible factors.
      HIFs are heterodimers consisting of an oxygen-sensitive α subunit and a constitutively expressed β subunit. There are 3 HIF α subunits in mammals. HIF1-α is ubiquitous and together with HIF2-α facilitates oxygen delivery and cellular adaptation to hypoxia by stimulating a number of biological processes.
      • Semenza G.L.
      Hypoxia-inducible factors in physiology and medicine.
      HIF2-α is expressed in a cell-restricted manner and is the key regulator of EPO synthesis and iron metabolism.
      • Kapitsinou P.P.
      • Liu Q.
      • Unger T.L.
      • et al.
      Hepatic HIF-2 regulates erythropoietic responses to hypoxia in renal anemia.
      • Scortegagna M.
      • Ding K.
      • Zhang Q.
      • et al.
      HIF-2alpha regulates murine hematopoietic development in an erythropoietin-dependent manner.
      • Mastrogiannaki M.
      • Matak P.
      • Keith B.
      • Simon M.C.
      • Vaulont S.
      • Peyssonnaux C.
      HIF-2alpha, but not HIF-1alpha, promotes iron absorption in mice.
      Under normal oxygen conditions, HIF-α subunits are prolyl hydroxylated by PHD1, PHD2, and PHD3 (2-oxoglutarate-dependent oxygenases that contain a prolyl-4-hydroxylase domain [PHD]). By contrast, under hypoxia, PHD activity decreases and HIF-α accumulates. HIF-α can then bind to the HIF-β subunit, resulting in the activation of a large array of target hypoxia-responsive genes.
      • Majmundar A.J.
      • Wong W.J.
      • Simon M.C.
      Hypoxia-inducible factors and the response to hypoxic stress.
      HIF stabilizers are 2-oxoglutarate competitors that are designed to prevent HIF-α degradation. Thus, HIF stabilizers primarily function by mimicking the hypoxia-driven expression of endogenous EPO in the kidney.
      • Rabinowitz M.H.
      Inhibition of hypoxia-inducible factor prolyl hydroxylase domain oxygen sensors: tricking the body into mounting orchestrated survival and repair responses.
      Note that in response to a hypoxic stimulus, damaged kidneys are still able to produce EPO, as shown in patients with CKD
      • Kato A.
      • Hishida A.
      • Kumagai H.
      • Furuya R.
      • Nakajima T.
      • Honda N.
      Erythropoietin production in patients with chronic renal failure.
      and in experimental models.
      • Shimizu S.
      • Enoki Y.
      • Sakata S.
      • Kohzuki H.
      • Ohga Y.
      • Matsumura K.
      Erythropoietin response to acute hypobaric or anaemic hypoxia in gentamicin-administered rats.
      In addition, pharmacologic HIF activation in adults stimulates the liver to retain its ability to produce EPO.
      • Shimizu S.
      • Enoki Y.
      • Sakata S.
      • Kohzuki H.
      • Ohga Y.
      • Matsumura K.
      Erythropoietin response to acute hypobaric or anaemic hypoxia in gentamicin-administered rats.
      • Priyadarshi A.
      • Periyasamy S.
      • Burke T.J.
      • Britton S.L.
      • Malhotra D.
      • Shapiro J.I.
      Effects of reduction of renal mass on renal oxygen tension and erythropoietin production in the rat.
      A feature unique to HIF stabilizers is that they are orally administered, which may be particularly helpful in non–dialysis-dependent patients with CKD and those treated with peritoneal dialysis. Moreover, these agents induce physiologic EPO levels, unlike the abnormally high peak concentrations usually observed with standard ESA therapy, which may be harmful.
      • Unger E.F.
      • Thompson A.M.
      • Blank M.J.
      • Temple R.
      Erythropoiesis stimulating agents—time for a reevaluation.
      The first promising molecule of this class was FG-2216 (FibroGen Inc), which was withdrawn following a case of fatal hepatitis. The same company then developed roxadustat (FG-4592). In 117 non–dialysis-dependent patients with CKD, those who were randomly assigned to roxadustat (4 doses escalating from 0.7 to 2.0 mg/kg administered 2 or 3 times weekly) had a higher Hb response rate than those receiving placebo. Roxadustat also achieved good anemia correction (Hb increased on average by 2 g/dL in 3 months) in ESA-naive HD patients who had severe anemia and were iron deficient in many cases.
      • Besarab A.
      • Chernyavskaya E.N.
      • Motylev I.
      • et al.
      FG-4592, an oral hypoxia-inducible factor propyl hydroxylase inhibitor, corrects anemia without iron supplementation in incident dialysis patients.
      According to the interim analysis of another phase 2 study of HD patients, FG-4592 produced an increase in mean Hb levels of ∼1 g/dL from baseline in the 2 cohorts receiving the highest doses (1.5 and 2.0 mg/kg). Conversely, those randomly assigned to recombinant human EPO experienced a slight decrease in Hb levels during the 6-week follow-up period.

      Provenzano R, Goodkin D, Klaus S, et al. Evaluation of FG-4592, a novel oral hypoxia-inducible factor prolyl hydroxylase inhibitor, to treat anemia in hemodialysis patients [abstract 188]. Presented at: National Kidney Foundation Conference; April 26-30, 2011; Las Vegas, NV.

      In FG-4592–treated patients, the improvement in erythropoiesis accompanied a reduction in serum hepcidin levels. It is still unknown whether this is a direct or indirect effect related to HIF stabilization. Excess hepcidin is the main cause of functional iron deficiency and iron-restricted erythropoiesis in patients with CKD.
      • Finberg K.E.
      Regulation of systemic iron homeostasis.
      • Sun C.C.
      • Vaja V.
      • Babitt J.L.
      • Lin H.Y.
      Targeting the hepcidin-ferroportin axis to develop new treatment strategies for anemia of chronic disease and anemia of inflammation.
      Whatever the underlying mechanism(s), the possibility that HIF stabilization may decrease hepcidin levels and possibly improve iron utilization is promising. In both the above studies, no liver toxicity was reported.
      More recently, data were presented about another phase 2 double-blind placebo-controlled trial in China
      • Qian J.Q.
      • Chen N.
      • Chen J.
      • et al.
      A randomized, double-blind, placebo controlled trial of FG-4592 for correction of anemia in subjects with chronic kidney disease in China.
      in which 91 non–dialysis-dependent patients with CKD with Hb levels < 10 g/dL were randomly assigned 1:1:1 to FG-4592 low or high dose or placebo. At the end of the 8-week treatment period, participants showed mean maximum Hb level increases from baseline of 2.6 g/dL in the high-dose cohort and 1.8 g/dL in the low-dose cohort, compared to 0.7 g/dL in the placebo group. The percentage of patients achieving Hb levels ≥ 11 g/dL was higher in those receiving the active drug than placebo. Interestingly, patients who received roxadustat showed small decreases in blood pressure similar to the placebo group. In still another study, FG-4592 was found effective in achieving anemia correction in ESA-naive patients receiving peritoneal dialysis, with a safety profile similar to the HD population.
      • Besarab A.
      • Tak Mao Chan D.
      • Dua S.L.
      • et al.
      Hypoxia inducing factor propyl hydroxylase inhibitor FG-4592 corrects anemia in peritoneal dialysis.
      Akebia Therapeutics is developing another prolyl hydroxylase inhibitor, AKB-6548. After successfully undergoing phase 2a clinical development in CKD stages 3 and 4, the drug has recently been evaluated in a phase 2b, randomized, double-blind, placebo-controlled study.

      Akebia announces positive top-line results from its phase 2b study of AKB-6548 in non-dialysis patients with anemia related to chronic kidney disease. http://ir.akebia.com/releasedetail.cfm?ReleaseID=878191. Accessed March 2, 2015.

      This 20-week study enrolled 209 non–dialysis-dependent patients with CKD stages 3 to 5 who were randomly assigned 2:1 to active treatment or placebo. The initial dose was 450 mg once daily, with dose adjusted in accordance to the patient’s Hb level response based on the AKB-6548 titration algorithm. Preliminary results showed that the primary end point, defined as achieving or maintaining mean Hb levels ≥ 11 g/dL or increasing Hb ≥ 1.2 g/dL above the pretreatment value, was met in 54.9% who received AKB-6548 compared with 10.3% in the placebo group. The drug was generally well tolerated. A phase 2 open-label study designed to examine the efficacy, safety, and tolerability of AKB-6548 in HD patients is ongoing (ClinicalTrials.gov identifier NCT02260193).
      GlaxoSmithKline are also developing an HIF prolyl hydroxylase inhibitor (GSK1278863). In 2011, they concluded a phase 2a, randomized, single-blind, placebo-controlled, parallel-group study aiming to evaluate the safety, efficacy, and pharmacokinetics of GSK1278863 administered in 28-day oral repeat doses of 10 to 100 mg to 70 anemic non–dialysis-dependent patients with CKD and 37 HD patients.

      A phase IIa, randomized, single-blind, placebo-controlled, parallel-group study to evaluate the safety, pharmacokinetics, and efficacy of 28-day repeat oral doses of GSK 1278863A in anemic pre-dialysis and hemodialysis-dependent patients. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/study/112844#rs. Accessed March 2, 2015.

      Hb levels increased in all dose groups, though the increase in Hb level was excessive in a number of participants and led to drug treatment being discontinued. Dose-dependent increases in endogenous EPO were found, the highest levels occurring in the 100-mg group. Following GSK1278863 administration, significant decreases in hepcidin and ferritin levels were also observed. Probably due to the excessive increase in Hb levels observed in some patients in the previous trial, an open-label parallel-group study has been carried out to evaluate the pharmacokinetics of GSK1278863 (at the lower dose of 5 mg) and its metabolites (predominant metabolites may contribute to the clinical pharmacology of the parent drug and may accumulate upon repeat-dose administration in CKD) in healthy individuals and patients with decreased kidney function.

      A repeat-dose, open-label, parallel-group study to assess the pharmacokinetics of GSK1278863 and metabolites in normal subjects and subjects with impaired renal function. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/study/115573#rs. Accessed March 2, 2015.

      The drug was administered once daily for 14 days (healthy individuals and patients with CKD stages 3 and 4) or 15 days (HD patients). Results showed that the area under the curve (a measure of the drug concentration in plasma) of the parent compound is similar in healthy individuals and patients with CKD; the steady-state metabolite area under the curve was 1.6- to 2.9-fold higher (depending on the metabolite) in patients with CKD, further increasing (2.7- to 6.2-fold higher) in HD patients on a nondialysis day. Though the parent drug was not cleared by HD, exposure to all metabolites was 55% lower on GSK1278863 administration on a dialysis day than a nondialysis day.

      A repeat-dose, open-label, parallel-group study to assess the pharmacokinetics of GSK1278863 and metabolites in normal subjects and subjects with impaired renal function. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/study/115573#rs. Accessed March 2, 2015.

      Phase 2b studies with GSK1278863 are active but not yet recruiting.

      Studies filtered by compound GSK 1278863. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/compounds/gsk1278863#ps. Accessed March 2, 2015.

      Molidustat (BAY 85-3934; Bayer Pharma) is another novel HIF prolyl hydroxylase inhibitor. A recent comprehensive pharmacologic characterization showed the compound to be effective in reversing anemia in animal models of kidney and inflammatory anemia.
      • Flamme I.
      • Oehme F.
      • Ellinghaus P.
      • Jeske M.
      • Keldenich J.
      • Thuss U.
      Mimicking hypoxia to treat anemia: HIF-stabilizer BAY 85-3934 (Molidustat) stimulates erythropoietin production without hypertensive effects.
      No dose-related changes were found in kidney and liver samples in the expression of hypoxia-responsive genes other than EPO. In addition, BAY 85-3934 displayed antihypertensive effects in a CKD model.
      • Flamme I.
      • Oehme F.
      • Ellinghaus P.
      • Jeske M.
      • Keldenich J.
      • Thuss U.
      Mimicking hypoxia to treat anemia: HIF-stabilizer BAY 85-3934 (Molidustat) stimulates erythropoietin production without hypertensive effects.
      Preliminary results of a randomized, single-blind, placebo-controlled, dose-escalation study of single oral doses (5, 12.5, 25, 37.5, and 50 mg) of BAY 85-3934 in healthy men showed rapid absorption (mean terminal half-life, 4.6-10.4 hours), a dose-dependent increase in endogenous EPO, and an increase in reticulocyte count after 37.5- and 50-mg dose administration.
      • Boettcher M.F.
      • Lentini S.
      • Kaiser A.
      • Flamme I.
      • Kubitza D.
      • Wensing G.
      First-in-man study with BAY 85-3934—a new oral selective HIF-PH inhibitor for the treatment of renal anemia.
      Phase 2b studies in patients with anemia of CKD are ongoing.
      At least 2 further HIF stabilizers are currently being developed. JTZ-951 (Akros Pharma Inc) has completed a randomized, single-blind, placebo-controlled, multiple-ascending-dose, phase 1 study, designed to determine the safety, tolerability, pharmacokinetics, and pharmacodynamics of daily administration for 15 days to HD patients.

      Safety, tolerability, PK and PD study of JTZ-951 in anemic subjects with end-stage renal disease. U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show?term=jtz-951&rank=2. Accessed March 2, 2015.

      DS-1093a (Daiichi Sankyo Inc) is undergoing evaluation in a phase 1 study of patients with CKD stage 3b or 4, an open noncontrolled parallel-group investigation of 3 single doses (6 participants per dose; dose allocation being randomly assigned), which is currently recruiting participants.

      Pilot PK/PD study of DS-1093a in patients with chronic kidney disease. U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show?term=ds-1093a&rank=1. Accessed March 2, 2015.

      A potential downside to prolyl hydroxylase inhibition is that HIF transcription factors are involved in the regulation of various biological processes. Intermittent HIF activation over prolonged periods may have adverse effects, including changes in glucose levels, fat and cholesterol metabolism, and angiogenesis promotion.
      • Cheng K.
      • Ho K.
      • Stokes R.
      • et al.
      Hypoxia-inducible factor-1alpha regulates beta cell function in mouse and human islets.
      • Rankin E.B.
      • Rha J.
      • Selak M.A.
      • et al.
      Hypoxia-inducible factor 2 regulates hepatic lipid metabolism.
      • Zehetner J.
      • Danzer C.
      • Collins S.
      • et al.
      PVHL is a regulator of glucose metabolism and insulin secretion in pancreatic beta cells.
      • Krishnan J.
      • Suter M.
      • Windak R.
      • et al.
      Activation of a HIF1alpha-PPARgamma axis underlies the integration of glycolytic and lipid anabolic pathways in pathologic cardiac hypertrophy.
      The primary fear is promotion of tumor growth.
      • Semenza G.L.
      HIF-1: upstream and downstream of cancer metabolism.
      • Ratcliffe P.J.
      Oxygen sensing and hypoxia signalling pathways in animals: the implications of physiology for cancer.
      In particular, careful evaluation is being applied to possible treatment-related increases in vascular endothelial growth factor (VEGF). This is a hypoxia-induced angiogenic protein that exhibits a broad range of biological and pathologic effects, ranging from neoangiogenesis promoting tumor growth to macular degeneration and worsening of proliferative diabetic retinopathy. At present, preliminary data do not suggest that VEGF level increases following treatment with HIF stabilizers. Another possible concern is that HIF inhibitors simulate a chronic hypoxic state, as occurs in people living at high altitude. The long-term consequence of this is unknown, but patients with CKD receiving HIF inhibitors are unlikely to develop symptoms of chronic mountain sickness because those symptoms are mainly driven by excessive erythrocytosis. Conversely, HIF inhibitors may cause ongoing enhancement of several pathways, including VEGF, that might cause systemic vascular dysfunction and predispose to increased systemic cardiovascular morbidity.
      • Rimoldi S.F.
      • Rexhaj E.
      • Pratali L.
      • et al.
      Systemic vascular dysfunction in patients with chronic mountain sickness.
      The fact that patients with heart disease may go safely to high altitudes for intermittent periods is reassuring.
      • Schmid J.P.
      • Nobel D.
      • Brugger N.
      • et al.
      Short-term high altitude exposure at 3454m is well tolerated in patients with stable heart failure.
      An intermittent hypoxic state may be even an advantage, as suggested by experimental studies showing improved recovery of post–myocardial infarction function with intermittent hypobaric hypoxia.
      • Ma H.J.
      • Li Q.
      • Ma H.J.
      • et al.
      Chronic intermittent hypobaric hypoxia ameliorates ischemia/reperfusion-induced calcium overload in heart via Na/Ca2+ exchanger in developing rats.
      The outlook for these molecules is still unclear. They may be an alternative option to treat anemia when used alone or in combination with ESA and/or iron. Their main advantage could be that of stimulating erythropoiesis with EPO at physiologic concentrations. However, it will need to be proved that they are as safe or even safer than existing ESAs. Accordingly, phase 3 studies will require the enrollment of thousands of patients to be adequately powered to test safety.
      HIF stabilizers are much further along in clinical development than most other new therapeutic strategies to increase erythropoiesis (Table 2), although data regarding the use of HIF prolyl hydroxylase inhibitors in kidney anemia come only from abstracts. Despite the promise of a new class of erythropoietic compounds, careful development is still required due to the wide range of biological pathways in which HIF transcription factors are involved.
      Table 2Hypoxia-Inducible Factor Stabilizers Under Clinical Development
      DrugCompanyStage of Clinical Development
      FG-4592 (Roxadustat)Fibrogen
      Collaboration with Astra Zeneca in the United States and China and with Astellas Pharma for Europe, Japan, the Middle East, and South Africa.
      Phase 2 studies completed (NDD CKD, HD, PD); phase 3 studies ongoing (NDD CKD, HD, PD)
      AKB-6548Akebia TherapeuticsPhase 2 studies completed (NDD CKD) or ongoing but not recruiting (HD)
      GSK1278863Glaxo Smith KlinePhase 2a studies completed (NDD-CKD, HD); phase 2b studies ongoing, but not recruiting (NDD CKD)
      BAY 85-3934 (Molidustat)Bayer PharmaceuticalsPhase 2b studies ongoing (NDD CKD, HD)
      JTZ-951Akros PharmaceuticalsPhase 1 study completed (HD)
      DS-1093aDaiichi SankyoPhase 1 study ongoing (CKD 3b-4)
      Abbreviations: CKD, chronic kidney disease; HD, hemodialysis; NDD, non–dialysis-dependent; PD, peritoneal dialysis.
      a Collaboration with Astra Zeneca in the United States and China and with Astellas Pharma for Europe, Japan, the Middle East, and South Africa.

      Activin Traps

      Activins are dimers of inhibin β-type chains and belong to the transforming growth factor β (TGFβ) superfamily. They trigger growth and differentiation by binding to type I and type II serine-threonine kinase receptors, which are transmembrane proteins.
      • Maguer-Satta V.
      • Bartholin L.
      • Jeanpierre S.
      • et al.
      Regulation of human erythropoiesis by activin A, BMP2, and BMP4, members of the TGFbeta family.
      Activin, bone morphogenic proteins, and several other members of the TGFβ family contribute to regulation of erythropoiesis either by directly affecting erythroid progenitor or precursor cells or by altering the behavior of bone marrow accessory cells.
      • Maguer-Satta V.
      • Bartholin L.
      • Jeanpierre S.
      • et al.
      Regulation of human erythropoiesis by activin A, BMP2, and BMP4, members of the TGFbeta family.
      • Yu J.
      • Maderazo L.
      • Shao L.E.
      • et al.
      Specific roles of activin/inhibin in human erythropoiesis in vitro.
      • Zermati Y.
      • Fichelson S.
      • Valensi F.
      • et al.
      Transforming growth factor inhibits erythropoiesis by blocking proliferation and accelerating differentiation of erythroid progenitors.
      These actions seem to be mediated by a signaling pathway involving the SMAD proteins.
      • Maguer-Satta V.
      • Bartholin L.
      • Jeanpierre S.
      • et al.
      Regulation of human erythropoiesis by activin A, BMP2, and BMP4, members of the TGFbeta family.
      Note that activin A is identical to the “erythroid differentiation factor,” which is able to cause differentiation of immature erythropoietic progenitors into mature cells.
      • Murata M.
      • Eto Y.
      • Shibai H.
      • Sakai M.
      • Muramatsu M.
      Erythroid differentiation factor is encoded by the same mRNA as that of the inhibin beta A chain.
      Sotatercept (ACE-011; Acceleron and Celgene Corp) is a dimeric fusion protein in which the extracellular domain of the activin receptor type IIA (ACTRIIA) is linked to the Fc portion of the human immunoglobulin G1 (IgG1) antibody. Sotatercept traps circulating activin and other members of the TGFβ superfamily that signal through ACTRIIA.
      • Raje N.
      • Vallet S.
      Sotatercept, a soluble activin receptor type 2A IgG-Fc fusion protein for the treatment of anemia and bone loss.
      In a double-blind phase 1 trial of healthy postmenopausal women, treatment with a single intravenous injection of sotatercept was accompanied by enhanced bone formation and decreased bone resorption.
      • Ruckle J.
      • Jacobs M.
      • Kramer W.
      • et al.
      Single-dose, randomized, double-blind, placebo-controlled study of ACE-011 (ActRIIA-IgG1) in postmenopausal women.
      Surprisingly, this trial showed an unanticipated increase in Hb level, red blood cell number, and hematocrit.
      • Ruckle J.
      • Jacobs M.
      • Kramer W.
      • et al.
      Single-dose, randomized, double-blind, placebo-controlled study of ACE-011 (ActRIIA-IgG1) in postmenopausal women.
      Treatment with sotatercept also increased Hb and hematocrit levels in a phase 2 trial of patients with multiple myeloma in parallel with improvement in bone lesions.
      • Abdulkadyrov K.
      • Salogub G.
      • Khuazheva N.
      • et al.
      ACE-011, a soluble activin receptor type IIa IgG-FC fusion protein, increases hemoglobin (Hb) and improves bone lesions in multiple myeloma patients receiving myelosuppressive chemotherapy: preliminary analysis.
      The clinical observation that an activin-sequestering agent such as sotatercept stimulates erythropoiesis is hard to reconcile with the reported ability of activin to induce erythroid differentiation.
      • Yu J.
      • Shao L.
      • Vaughan J.
      • Vale W.
      • Yu A.L.
      Characterization of the potentiation effect of activin on human erythroid colony formation in vitro.
      • Shao l
      • Frigon Jr., N.L.
      • Young A.L.
      • et al.
      Effect of activin A on globin gene expression in purified human erythroid progenitors.
      Two potential nonexclusive indirect mechanisms have been proposed for the effects of sotatercept on human erythropoiesis.
      • Iancu-Rubin C.
      • Mosoyan G.
      • Wang J.
      • Kraus T.
      • Sung V.
      • Hoffman R.
      Stromal cell-mediated inhibition of erythropoiesis can be attenuated by sotatercept (ACE-011), an activin receptor type II ligand trap.
      The first relates to the binding of ACTRIIA ligands, resulting in modulation of their function regarding erythroid development. As a second possible mechanism, by neutralizing TGFβ family members, sotatercept can modulate the SMAD signaling pathway in stromal cells, leading to changes in the transcription of SMAD target genes that encode proteins affecting erythroid development.
      • Blank U.
      • Karlsson S.
      The role of Smad signaling in hematopoiesis and translational hematology.
      For example, the expression of angiotensin II, which can stimulate erythropoiesis directly and indirectly by EPO production, is increased, whereas the expression of VEGF, considered an inhibitor of erythropoiesis, is suppressed.
      • Iancu-Rubin C.
      • Mosoyan G.
      • Wang J.
      • Kraus T.
      • Sung V.
      • Hoffman R.
      Stromal cell-mediated inhibition of erythropoiesis can be attenuated by sotatercept (ACE-011), an activin receptor type II ligand trap.
      Sotatercept is currently being evaluated in patients with CKD 5D (ClinicalTrials.gov identifier NCT01146574) in a phase 2a, randomized, double-blind, placebo-controlled, single-dose (0.1 mg/kg subcutaneously) study, followed by a double-blind, placebo-controlled, multiple-dose, dose-escalation study (starting doses of 0.3, 0.5, or 0.7 mg/kg subcutaneously every 28 days in a sequential design for up to 8 doses). The first results of part 2 of this study have recently been presented.
      • El-Shahawy M.
      • Cotton J.
      • Kaupke J.
      • Kopyt N.
      • Choi S.
      • Smith W.T.
      Safety and hemoglobin effects of the first 28-day dose cycle of sotatercept 0.7 mg/kg compared with lower doses and placebo for correction of anemia in hemodialysis subjects: interim analysis.
      At each dose, sotatercept was well tolerated and showed a safety profile comparable to placebo, with a mean elimination half-life of 21 to 26 days. The mean peak Hb response in the first 28 days was dose related, the highest response (1.0 g/dL) being observed in the group treated with sotatercept at a 0.7-mg/kg dose. Based on observed changes in Hb levels, drug administration once every 2 weeks instead of once every 4 weeks has been suggested.
      • Besson-Fournier C.
      • Latour C.
      • Kautz L.
      • et al.
      Induction of activin B by inflammatory stimuli up-regulates expression of the iron-regulatory peptide hepcidin through Smad1/5/8 signaling.
      This is currently being investigated in a phase 2 study (ClinicalTrials.gov identifier; NCT01999582), entailing intravenous and subcutaneous administration of escalating doses of sotatercept every 2 weeks in HD patients.
      Sotatercept also has other activities that are of potential relevance in the CKD setting. The drug can inhibit hepcidin transcription in hepatocytes
      • Finberg K.E.
      • Whittlesey R.L.
      • Fleming M.D.
      • Andrews N.C.
      Down-regulation of Bmp/Smad signaling by Tmprss6 is required for maintenance of systemic iron homeostasis.
      because the hepcidin promoter contains bone morphogenic protein–responsive SMAD-binding elements.
      • Truksa J.
      • Lee P.
      • Beutler E.
      Two BMP responsive elements, STAT, and bZIP/HNF4/COUP motifs of the hepcidin promoter are critical for BMP, SMAD1, and HJV responsiveness.
      Activin B has been shown to play a critical role in hepcidin induction by inflammation
      • Ganz T.
      Systemic iron homeostasis.
      and therefore represents a specific target for treatment of anemia due to inflammation.
      • Besson-Fournier C.
      • Latour C.
      • Kautz L.
      • et al.
      Induction of activin B by inflammatory stimuli up-regulates expression of the iron-regulatory peptide hepcidin through Smad1/5/8 signaling.
      Sotatercept has demonstrated stimulating effects on bone formation,
      • Raje N.
      • Vallet S.
      Sotatercept, a soluble activin receptor type 2A IgG-Fc fusion protein for the treatment of anemia and bone loss.
      which are believed to be mediated through its interaction with activin.
      • Lotinun S.
      • Pearsall R.S.
      • Horne W.C.
      • Baron R.
      Activin receptor signaling: a potential therapeutic target for osteoporosis.
      The administration of ACE-011 and its murine counterpart RAP-011 cause bone loss and osteoporosis to be reversed in various animal models.
      • Lotinun S.
      • Pearsall R.S.
      • Davies M.V.
      • et al.
      A soluble activin receptor type IIA fusion protein (ACE-011) increases bone mass via a dual anabolic-antiresorptive effect in Cynomolgus monkeys.
      • Pearsall R.S.
      • Canalis E.
      • Cornwall-Brady M.
      • et al.
      A soluble activin type IIA receptor induces bone formation and improves skeletal integrity.
      In CKD mouse models for vascular calcification, RAP-011 inhibits SMAD-dependent signaling, blocks aortic osteoblastic transition, increases vascular smooth muscle function, and decreases CKD-stimulated vascular calcification.
      • Fang Y.
      • Agapova O.A.
      • Sugatani T.
      • Malluche H.
      • Hruska K.A.
      Treatment of the CKD-MBD with a ligand trap for the activin receptor type 2A.
      • Hruska K.A.
      • Agapova O.A.
      • Fang Y.
      • Sugatani T.
      • Seifert M.E.
      • Sung V.
      Chronic kidney disease (CKD) stimulates activin and endothelial to mesenchymal transition (EnMT), which causes vascular calcification and is inhibited by an activin ligand trap.
      The effects of sotatercept on bone mineral density and vascular calcification were evaluated by using quantitative computed tomography
      • Leonard M.B.
      A structural approach to skeletal fragility in chronic kidney disease.
      in the above mentioned study in HD patients.
      • El-Shahawy M.
      • Cotton J.
      • Kaupke J.
      • Kopyt N.
      • Choi S.
      • Smith W.T.
      Safety and hemoglobin effects of the first 28-day dose cycle of sotatercept 0.7 mg/kg compared with lower doses and placebo for correction of anemia in hemodialysis subjects: interim analysis.
      A small interim data set showed an apparent dose effect on multiple parameters of CKD–mineral bone disorder, including increasing femoral neck cortical bone mass, decreasing lumbar spine bone mass, and slowing progression of vascular calcification.
      • Malluche H.
      • Hurska K.
      • Singh H.N.
      • Smith W.T.
      Sotatercept: initial signal-seeking quantitative computed tomography results for bone mass and vascular calcification in hemodialysis patients treated with escalating doses: interim analysis of ACE-011-REN-001.
      Considerable differences in baseline characteristics of patients may influence these results, and the number of participants was small. Thus, though sotatercept may address unmet needs in ESRD with favorable effects on CKD–mineral bone disorder, these results need to be confirmed in larger populations.
      Another investigational ligand-trapping fusion protein (Luspatercept; ACE-536; Acceleron/Celgene Corp) containing the extracellular domain of human activin receptor type IIB (ACTRIIB) modified to reduce activin binding shows erythropoietic activity and promotes the maturation of late-stage erythroid precursors in vivo.
      • Suragani R.N.
      • Cadena S.M.
      • Cawley S.M.
      • et al.
      Transforming growth factor-β superfamily ligand trap ACE-536 corrects anemia by promoting late-stage erythropoiesis.
      Interestingly, treatment with EPO and ACE-536 produces a synergistic erythropoietic response.
      • Suragani R.N.
      • Cadena S.M.
      • Cawley S.M.
      • et al.
      Transforming growth factor-β superfamily ligand trap ACE-536 corrects anemia by promoting late-stage erythropoiesis.
      A phase 1, ascending-dose, randomized, double-blind, placebo-controlled, clinical trial of ACE-536 in healthy volunteers has recently been completed.
      • Attie K.M.
      • Allison M.J.
      • McClure T.
      • et al.
      A phase 1 study of ACE-536, a regulator of erythroid differentiation, in healthy volunteers.
      Thirty-two postmenopausal women were randomly assigned in sequential cohorts of 8 participants each to receive up to 2 doses of ACE-536 (0.0625-0.25 mg/kg) or placebo (3:1 randomization) administered subcutaneously every 2 weeks. ACE-536 was well tolerated and no serious or severe adverse events occurred. Hb levels increased dose dependently, beginning 7 days after treatment initiation, and were maintained for several weeks following treatment.
      • Attie K.M.
      • Allison M.J.
      • McClure T.
      • et al.
      A phase 1 study of ACE-536, a regulator of erythroid differentiation, in healthy volunteers.
      These findings support ongoing phase 2 clinical trials of ACE-536 in patients with β-thalassemia and myelodysplastic syndromes.

      New Erythropoietic Strategies Targeting the EPO Receptor

      EPO Mimetic Peptides

      EPO mimetic peptides (EMPs) are a group of synthetic cyclic peptides capable of stimulating the EPO receptor though their amino acid sequence is completely different from the hormone.
      • Livnah O.
      • Stura E.A.
      • Johnson D.L.
      Functional mimicry of a protein hormone by a peptide agonist: the EPO receptor complex at 2.8 A.
      • Wrighton N.C.
      • Farrell F.X.
      • Chang R.
      • et al.
      Small peptides as potent mimetics of the protein hormone erythropoietin.
      EMP-1, an oligopeptide containing 20 amino acids joined by a disulfide bridge between 2 cysteine residues, was synthesized in 1998.
      • Johnson D.L.
      • Farrell F.X.
      • Barbone F.P.
      • et al.
      Identification of a 13 amino acid peptide mimetic of erythropoietin and description of amino acids critical for the mimetic activity of EMP1.
      However, its short in vivo half-life and relatively weak binding to the EPO receptor hampered its clinical use.
      In order to increase effectiveness, peptide dimers that use either chemical linkers or polymeric polyethylene glycol linkers have been constructed. The CNTO molecules (Centocor) were developed by using the MIMETIBODY platform, in which a given active peptide is connected with an amino acid linker to an immunoglobulin Fc domain. The peptide remains capable of interacting with its receptor, while extended pharmacologic properties are provided by the Fc fragment. Fc fusion technology has been introduced to generate long-acting antagonistic drugs, such as those targeting TNFR (tumor necrosis factor receptor) and CTLA-4 (cytotoxic T-lymphocyte–associated antigen 4).
      • Huang C.
      Receptor-Fc fusion therapeutics, traps, and MIMETIBODY technology.
      CNTO 528, obtained by fusion of 2 EMP-1 molecules with a human IgG1 Fc domain, stimulated erythropoiesis after a single intravenous administration at ascending doses in phase 1 studies in healthy volunteers.
      • Bouman-Thio E.
      • Franson K.
      • Miller B.
      • et al.
      A phase I, single and fractionated, ascending-dose study evaluating the safety, pharmacokinetics, pharmacodynamics, and immunogenicity of an erythropoietin mimetic antibody fusion protein (CNTO 528) in healthy male subjects.
      • Perez-Ruixo J.J.
      • Krzyzanski W.
      • Bouman-Thio E.
      • et al.
      Pharmacokinetics and pharmacodynamics of the erythropoietin Mimetibody construct CNTO 528 in healthy subjects.
      Peginesatide (originally named Hematide; Affymax/Takeda), a small dimeric peptide conjugated to a pegylated moiety, was approved by the US Food and Drug Administration in 2012 for treatment of anemic adult patients receiving dialysis. It is a long-acting ESA, with dose requirements irrespective of the administration route. The drug corrected anemia effectively in large studies carried out in both non–dialysis-dependent patients with CKD
      • Macdougall I.C.
      • Provenzano R.
      • Sharma A.
      • et al.
      Peginesatide for anemia in patients with chronic kidney disease not receiving dialysis.
      and those with chronic kidney failure treated by dialysis.
      • Fishbane S.
      • Schiller B.
      • Locatelli F.
      • et al.
      Peginesatide in patients with anemia undergoing hemodialysis.
      Concerns about cardiovascular safety were raised in view of higher incidences of death, unstable angina, and arrhythmia in non–dialysis-dependent patients with CKD treated with peginesatide.
      • Macdougall I.C.
      • Provenzano R.
      • Sharma A.
      • et al.
      Peginesatide for anemia in patients with chronic kidney disease not receiving dialysis.
      However, they were not confirmed by a prespecified combined analysis of the dialysis and nondialysis trials. Given its EPO-unrelated structure, the drug was also used for the treatment of EPO-related pure red cell aplasia.
      • Macdougall I.C.
      • Rossert J.
      • Casadevall N.
      • et al.
      A peptide-based erythropoietin-receptor agonist for pure red-cell aplasia.
      Just one year after commercialization, Affymax and Takeda instituted a voluntary recall of the drug following postmarketing reports of serious acute hypersensitivity reactions that could be life-threatening or fatal.

      Affimax and Takeda announce a nationwide voluntary recall of all lots of OMONTYSR (peginesatide) Injection. http://www.takeda.com/news/2013/20130224_5664.html. Accessed February 8, 2015.

      Approximately 0.02% of patients receiving the first dose of the drug intravenously died. The cause of the hypersensitivity reactions has not been clarified.

      Epoetin Fusion Proteins

      A number of attempts have been made to create EPO fusion molecules with enhanced erythropoietic activity (Box 1). The sole compound in clinical development is GX-E2 (EPO-hyFc; Genexine), in which EPO is fused with a novel hybrid Fc (hyFc) consisting of human IgG4 plus the hinge and the amino-terminus of the IgD heavy chain isotype 2, which replace the corresponding regions of IgG4 without linker amino acids being added.
      • Im S.J.
      • Yang S.I.
      • Yang S.H.
      • et al.
      Natural form of noncytolytic flexible human Fc as a long-acting carrier of agonistic ligand, erythropoietin.
      Of note, IgD has the highest hinge-fold flexibility among human immunoglobulins.
      • Roux K.H.
      • Strelets L.
      • Brekke O.H.
      • Sandlie I.
      • Michaelsen T.E.
      Comparisons of the ability of human IgG3 hinge mutants, IgM, IgE, and IgA2, to form small immune complexes: a role for flexibility and geometry.
      HyFc is nonimmunogenic, noncytolytic, and flexible,
      • Im S.J.
      • Yang S.I.
      • Yang S.H.
      • et al.
      Natural form of noncytolytic flexible human Fc as a long-acting carrier of agonistic ligand, erythropoietin.
      thus overcoming shortcomings of both IgG1 Fc (antibody-dependent cellular cytotoxicity or complement-dependent cytotoxicity of target cells
      • Idusogie E.E.
      • Wong P.Y.
      • Presta L.G.
      • et al.
      Engineered antibodies with increased activity to recruit complement.
      ) and IgG4 Fc (generation of monovalent half-molecules by formation of 2 intrachain disulfide bonds
      • Schuurman J.
      • Perdok G.J.
      • Gorter A.D.
      • Aalberse R.G.
      The inter-heavy chain disulfide bonds of IgG4 are in equilibrium with intra-chain disulfide bonds.
      ). In vitro and in rats, GX-E2 shows higher bioactivity than darbepoetin.
      • Yang S.H.
      • Yang S.I.
      • Chung Y.-K.
      A long-acting erythropoietin fused with noncytolytic human Fc for the treatment of anemia.
      The safety, tolerability, pharmacokinetics, and pharmacodynamics of GX-E2 were examined in a randomized, double-blind, placebo-controlled, phase 1 study recently completed.

      Study to evaluate safety, tolerability, and pharmacokinetics/pharmacodynamics of GX-E2 in healthy subjects (GX-E2-P1). U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show/study/NCT02291991?term=GX-E2&rank=.1 Accessed March 2, 2015.

      The drug is currently under evaluation in a phase 2 randomized study, darbepoetin being the active comparator, aiming to explore the optimal starting dose and dosing interval (as well as safety) in anemic dialysis patients.

      Study to evaluate the efficacy and safety of GX-E2 in the anemic patients diagnosed with chronic kidney disease (CKD). U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show/study/NCT02044653?term=GX-E2&rank=2. Accessed March 2, 2015.

      EPO Gene Therapy

      Medgenics has developed a novel technology for the sustained production and delivery of therapeutic proteins (like EPO) using ex vivo gene therapy and the patient’s own tissue. The technology is based on taking a small tissue explant from the patient’s skin, transducing the cells with a viral vector for ongoing production of EPO, and subcutaneously implanting this dermal pump back into the patient. Following initial favorable observations in severe combined immunodeficiency mice
      • Brill-Almon E.
      • Stern B.
      • Afik D.
      • et al.
      Ex vivo transduction of human dermal tissue structures for autologous implantation production and delivery of therapeutic proteins.
      and technical improvements (preparation of the second-generation viral vector and development of a new implantation protocol), the TARGT (Transducer Autologous Regenerative Gene Therapy) system (formerly known as BioPump) was produced. An open-label phase 1/2 clinical trial (ClinicalTrials.gov identifier NCT02117427) to examine the safety and efficacy of EPO delivered by the pump in 3 cohorts (18-25, 35-45, or 55-65 IU/kg/d) of patients with ESRD is ongoing; follow-up is one year. Interim results of the study, including 3 patients who underwent implantation, were presented in late 2014.

      Neil G. Prolonged secretion of physiological levels of autologous EPO by TARGT. Presented at: XXII Annual Congress of the European Society of Gene and Cell Therapy; The Hague, the Netherlands; October 23-26, 2014.

      The platform delivered sustained physiologically appropriate levels of endogenous EPO, in turn maintaining Hb levels in the desired range. Further clinical studies have been planned in patients with ESRD who respond poorly to conventional ESA treatment, as well as in anemic transplant recipients and peritoneal dialysis patients.

      Conclusions

      The development of new strategies to treat anemia is still an evolving and fascinating area of experimental and clinical research. At present, the most promising class of agents seems to be HIF stabilizers, as evident in the number of molecules currently under development. This class of drug stimulates erythropoiesis by physiologic concentrations of endogenous EPO, which may translate into a clinical advantage because concerns for ESA safety are higher at the high doses. However, these theoretical advantages will need to be demonstrated clinically in large trials. Conversely, the class needs to be proved safe in light of the potential risks for increases in levels of VEGF and related factors and the possibility of widespread stimulation of complex pathways leading to unexpected side effects. The final judgment of benefit/risks of these agents will be possible only after the completion of large long-term safety studies testing hard end points.
      EMPs were a promising class. They had the advantages of long-acting ESAs with the potential of being less expensive than short-acting ESAs. Unfortunately, the experience with peginesatide and the fact that the cause of these adverse events has not yet been discovered seems to be halting development of the molecule and seriously endangering further development of other agents in that class. Sotatercept, which traps circulating activin, is another interesting drug given its potential for not only correcting anemia but also checking osteoporosis. This may be of importance considering that the CKD population is becoming older and frailer.

      Acknowledgements

      Support: None.
      Financial Disclosure: Dr Del Vecchio has served on the advisory board of Astellas. Dr Locatelli has served on the advisory boards of Akebia, Amgen, Astellas, Fibrogen, Genzyme, GSK, Fresenius Medical Care, Janssen Cilag, Pharmacosmos, Keryx, and ZS Pharma and has been a speaker at a meeting supported by Amgen, Asahi Casei, Roche, and ZS Pharma. The remaining authors declare that they have no relevant financial interests.

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      3. A phase IIa, randomized, single-blind, placebo-controlled, parallel-group study to evaluate the safety, pharmacokinetics, and efficacy of 28-day repeat oral doses of GSK 1278863A in anemic pre-dialysis and hemodialysis-dependent patients. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/study/112844#rs. Accessed March 2, 2015.

      4. A repeat-dose, open-label, parallel-group study to assess the pharmacokinetics of GSK1278863 and metabolites in normal subjects and subjects with impaired renal function. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/study/115573#rs. Accessed March 2, 2015.

      5. Studies filtered by compound GSK 1278863. GlaxoSmithKline website www.gsk-clinicalstudyregister.com/compounds/gsk1278863#ps. Accessed March 2, 2015.

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      6. Safety, tolerability, PK and PD study of JTZ-951 in anemic subjects with end-stage renal disease. U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show?term=jtz-951&rank=2. Accessed March 2, 2015.

      7. Pilot PK/PD study of DS-1093a in patients with chronic kidney disease. U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show?term=ds-1093a&rank=1. Accessed March 2, 2015.

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      9. Study to evaluate safety, tolerability, and pharmacokinetics/pharmacodynamics of GX-E2 in healthy subjects (GX-E2-P1). U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show/study/NCT02291991?term=GX-E2&rank=.1 Accessed March 2, 2015.

      10. Study to evaluate the efficacy and safety of GX-E2 in the anemic patients diagnosed with chronic kidney disease (CKD). U.S. National Institutes of Health website https://clinicaltrials.gov/ct2/show/study/NCT02044653?term=GX-E2&rank=2. Accessed March 2, 2015.

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