A dimeric peptide with erythropoiesis-stimulating activity uniquely affects erythropoietin receptor ligation and cell surface expression.

Erythropoiesis-stimulating agents (ESAs) that exert long-acting antianemia effects have been developed recently, but their mechanisms are poorly understood. Analyses reveal unique erythropoietin receptor (EPOR)-binding properties for one such ESA, the synthetic EPOR agonist peginesatide. Compared with recombinant human EPO and darbepoietin, peginesatide exhibited a slow on rate, but sustained EPOR residency and resistant displacement. In EPO-dependent human erythroid progenitor UT7epo cells, culture in peginesatide unexpectedly upmodulated endogenous cell surface EPOR levels with parallel increases in full-length EPOR-68K levels. These unique properties are suggested to contribute to the durable activity of this (and perhaps additional) dimeric peptide hematopoietic growth factor receptor agonist.

RHEX, a novel regulator of human erythroid progenitor cell expansion and erythroblast development.

Ligation of erythropoietin (EPO) receptor (EPOR) JAK2 kinase complexes propagates signals within erythroid progenitor cells (EPCs) that are essential for red blood cell production. To reveal hypothesized novel EPOR/JAK2 targets, a phosphotyrosine (PY) phosphoproteomics approach was applied. Beyond known signal transduction factors, 32 new targets of EPO-modulated tyrosine phosphorylation were defined. Molecular adaptors comprised one major set including growth factor receptor-bound protein 2 (GRB2)-associated binding proteins 1-3 (GAB1-3), insulin receptor substrate 2 (IRS2), docking protein 1 (DOK1), Src homology 2 domain containing transforming protein 1 (SHC1), and sprouty homologue 1 (SPRY1) as validating targets, and SPRY2, SH2 domain containing 2A (SH2D2A), and signal transducing adaptor molecule 2 (STAM2) as novel candidate adaptors together with an ORF factor designated as regulator of human erythroid cell expansion (RHEX). RHEX is well conserved in Homo sapiens and primates but absent from mouse, rat, and lower vertebrate genomes. Among tissues and lineages, RHEX was elevated in EPCs, occurred as a plasma membrane protein, was rapidly PY-phosphorylated >20-fold upon EPO exposure, and coimmunoprecipitated with the EPOR. In UT7epo cells, knockdown of RHEX inhibited EPO-dependent growth. This was associated with extracellular signal-regulated kinase 1,2 (ERK1,2) modulation, and RHEX coupling to GRB2. In primary human EPCs, shRNA knockdown studies confirmed RHEX regulation of erythroid progenitor expansion and further revealed roles in promoting the formation of hemoglobinizing erythroblasts. RHEX therefore comprises a new EPO/EPOR target and regulator of human erythroid cell expansion that additionally acts to support late-stage erythroblast development.

Peginesatide and erythropoietin stimulate similar erythropoietin receptor-mediated signal transduction and gene induction events.

Peginesatide is a synthetic, PEGylated, peptide-based erythropoiesis-stimulating agent that is designed and engineered to stimulate specifically the erythropoietin receptor dimer that governs erythropoiesis. Peginesatide has a unique structure that consists of a synthetic peptide dimer (with no sequence similarity to erythropoietin) conjugated to a 40-kDa PEG moiety. Peginesatide is being developed for the treatment of anemia associated with chronic kidney disease in dialysis patients. To compare signaling effects of peginesatide to recombinant human erythropoietin (rHuEPO), dose-dependent effects on protein phosphorylation and gene expression were evaluated using phosphoproteomics, quantitative signal transduction analyses, and gene profiling. After stimulation with peginesatide or rHuEPO, cell lysates were prepared from UT-7/EPO cells. Liquid chromatography-tandem mass spectrometry and MesoScale arrays were used to quantify phosphorylation events. Transcriptional changes were analyzed using microarrays and quantitative reverse transcription polymerase chain reaction. Peginesatide and rHuEPO were found to regulate the tyrosine phosphorylation of an essentially equivalent set of protein substrates, and modulate the expression of a similar set of target genes. Consistent with their roles in stimulating erythropoiesis, peginesatide and rHuEPO regulate similar cellular pathways.

Dynamic ligand modulation of EPO receptor pools, and dysregulation by polycythemia-associated EPOR alleles.

Erythropoietin (EPO) and its cell surface receptor (EPOR) are essential for erythropoiesis; can modulate non-erythroid target tissues; and have been reported to affect the progression of certain cancers. Basic studies of EPOR expression and trafficking, however, have been hindered by low-level EPOR occurrence, and the limited specificity of anti-EPOR antibodies. Consequently, these aspects of EPOR biology are not well defined, nor are actions of polycythemia- associated mutated EPOR alleles. Using novel rabbit monoclonal antibodies to intracellular, PY- activated and extracellular EPOR domains, the following properties of the endogenous hEPOR in erythroid progenitors first are unambiguously defined. 1) High- Mr EPOR forms become obviously expressed only when EPO is limited. 2) EPOR-68K plus -70K species sequentially accumulate, and EPOR-70K comprises an apparent cell surface EPOR population. 3) Brefeldin A, N-glycanase and associated analyses point to EPOR-68K as a core-glycosylated intracellular EPOR pool (of modest size). 4) In contrast to recent reports, EPOR inward trafficking is shown (in UT7epo cells, and primary proerythroblasts) to be sharply ligand-dependent. Beyond this, when C-terminal truncated hEPOR-T mutant alleles as harbored by polycythemia patients are co-expressed with the wild-type EPOR in EPO-dependent erythroid progenitors, several specific events become altered. First, EPOR-T alleles are persistently activated upon EPO- challenge, yet are also subject to apparent turn-over (to low-Mr EPOR products). Furthermore, during exponential cell growth EPOR-T species become both over-represented, and hyper-activated. Interestingly, EPOR-T expression also results in an EPO dose-dependent loss of endogenous wild-type EPOR's (and, therefore, a squelching of EPOR C-terminal- mediated negative feedback effects). New knowledge concerning regulated EPOR expression and trafficking therefore is provided, together with new insight into mechanisms via which mutated EPOR-T polycythemia alleles dysregulate the erythron. Notably, specific new tools also are characterized for studies of EPOR expression, activation, action and metabolism.

Dose-finding study of peginesatide for anemia correction in chronic kidney disease patients.

BACKGROUND AND OBJECTIVES: Peginesatide is a synthetic, PEGylated, investigational, peptide-based erythropoiesis-stimulating agent. We report the first assessment of its efficacy and safety in correcting renal anemia in a population of 139 nondialysis chronic kidney disease patients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Chronic kidney disease patients who were not on dialysis and not receiving treatment with erythropoiesis-stimulating agents in the 12 weeks before study drug administration were sequentially assigned to one of 10 cohorts; cohorts differed in starting peginesatide dose (different body weight-based or absolute doses), route of administration (intravenous or subcutaneous), and frequency of administration (every 4 or 2 weeks). RESULTS: Across all cohorts, 96% of patients achieved a hemoglobin response. A dose-response relationship was evident for hemoglobin increase. Comparable subcutaneous and intravenous peginesatide doses produced similar hemoglobin responses. Rapid rates of hemoglobin rise and hemoglobin excursions >13 g/dl tended to occur more frequently with every-2-weeks dosing than they did with every-4-weeks dosing. The range of final median doses in the every-4-weeks dosing groups was 0.019 to 0.043 mg/kg. Across all cohorts, 20% of patients reported serious adverse events (one patient had a possibly drug-related serious event) and 81% reported adverse events (11.5% reported possibly drug-related events); these events were consistent with those routinely observed in this patient population. CONCLUSIONS: This study suggests that peginesatide administered every 4 weeks can increase and maintain hemoglobin in nondialysis chronic kidney disease patients. Additional long-term data in larger groups of patients are required to further elucidate the efficacy and safety of this peptide-based erythropoiesis-stimulating agent.

Methods for detection and confirmation of Hematide™/peginesatide in anti-doping samples.

Since the 1990's, cheating athletes have abused substances to increase their oxygen transport capabilities; among these substances, recombinant EPO is the most well known. Currently, other investigational pharmaceutical products are able to produce an effect similar to EPO but without having chemical structures related to EPO; these are the synthetic erythropoiesis stimulating agents (ESAs). Peginesatide (also known as Hematide™) is being developed by Affymax and Takeda and, if approved by regulatory authorities, could soon be released on the international market. To detect potential athletic abuse of this product and deter athletes who consider cheating, we initiated a collaboration to implement a detection test for anti-doping purposes. Peginesatide is a synthetic, PEGylated, investigational, peptide-based erythropoiesis-stimulating agent that is designed and engineered to stimulate specifically the erythropoietin receptor dimer that governs erythropoiesis. It is undetectable using current anti-doping tests due to its lack of sequence homology to EPO. To detect and deter potential abuse of peginesatide, we initiated an industry/antidoping laboratory collaboration to develop and validate screening and confirmation assays so that they would be available before peginesatide reaches the market. We describe a screening ELISA and a confirmation assay consisting of immune-purification followed by separation with SDS-PAGE and revelation with Western double blotting. Both assays can detect 0.5 ng/mL concentrations of peginesatide in blood samples, enabling detection for several days after administration of a physiologically relevant dose. This initial report describes experimental characterization of these assays, including testing with a blinded set of samples from a clinical study conducted in healthy volunteers.

Genotoxic assessment and toxicity evaluation of peginesatide in CByB6F1 hybrid mice.

Peginesatide is a PEGylated, investigational, peptide-based erythropoiesis-stimulating agent (ESA) that was designed and engineered to stimulate specifically the erythropoietin receptor dimer that governs erythropoiesis. Clinical use of peginesatide is anticipated to result in chronic dosing in chronic kidney disease (CKD) patients, and the nonclinical data to support development should include an evaluation of carcinogenic potential evaluation. Peginesatide was not mutagenic or clastogenic in a standard genotoxicity battery of tests. Doses for a rasH2 transgenic mouse carcinogenicity assay were defined in a 28-day study in the wild-type littermates of the rasH2 transgenic mouse strain, using intravenous doses of 1-25 mg/kg on days 1 and 22. The findings were consistent with exaggerated pharmacology, including polycythemia, with associated increases in hemoglobin level and extramedullary hematopoiesis and bone marrow hypercellularity.

Peri- and postnatal rodent development of Hematide, an erythropoiesis-stimulating agent.

BACKGROUND: Aperi- and postnatal reproduction toxicity study was conducted in rats treated with Hematide, a synthetic PEGylated peptidic erythropoiesis stimulating agent (ESA). METHODS: Hematide, at IV doses of 0, 0.5, 3, and 15 mg/kg, was administered from implantation through lactation on gestation days (GDs) 5 and 18 and lactation day (LD) 13. RESULTS: Hematide induced pronounced polycythemia in all Hematide-treated dams. On LDs 2 and 21, hemoglobin (Hgb) increases above control levels were 3.1, 5.2, and 5.0 g/dL and 4.1, 5.1, and 5.5 g/dL at the 0.5, 3, and 15 mg/kg/dose, respectively. There were no effects on parturition, lactation, or maternal behavior in the F0 generation female rats. A slight decrease in pup viability on postpartum days 2-4 and lower body weights and/or body weight gain for the F1 generation were associated with pronounced polycythemia and decreases in maternal body weight gain and/or food consumption at > or =3 mg/kg/dose. Hematide fetal exposure was negligible. No Hematide effect, other than on growth and survival, was noted on developmental, functional, mating, and fertility end points in the F1 generation rats, and no effect on litter or fetal parameters was observed in the F2 generation. The maternal no-observed-adverse-effect level (NOAEL) for Hematide was 0.5 mg/kg, and the NOAEL for parturition and maternal behavior was 15 mg/kg. The NOAEL for F1 pup viability and growth was 0.5 mg/kg/dose. CONCLUSIONS: In conclusion, the Hematide-associated adverse findings were attributed to exaggerated erythropoiesis (pronounced and prolonged polycythemia) resulting from administration of an ESA to pregnant animals.

A subchronic murine intravenous pharmacokinetic and toxicity study of Hematide™, a PEGylated peptidic erythropoiesis-stimulating agent.

The subchronic toxicity of Hematide™, a synthetic PEGylated peptidic erythropoiesis-stimulating agent (ESA), was evaluated in CD-1 mice at intravenous doses of 0, 1, 5, 25, and 125 mg/kg administered once every 3 weeks for 3 months. Hematide displayed sustained plasma levels with reduced clearance and prolonged half-lives up to 59.4 hours that translated into sustained, pronounced polycythemia, bone marrow hyperplasia, and splenic and liver extramedullary hematopoiesis. Toxicological findings were considered to be secondary to exaggerated pharmacology, rather than a direct drug effect, and included mortality at ≥25 mg/kg/dose. The no-observed-adverse-effect-level was determined to be 5 mg/kg.

Chronic pharmacological and safety evaluation of Hematide, a PEGylated peptidic erythropoiesis-stimulating agent, in rodents.

Hematide is a synthetic peptide-based, PEGylated erythropoiesis-stimulating agent, which is being developed for the chronic treatment of anaemia associated with chronic renal failure. To support the safety of long-term dosing of chronic renal failure patients, a comprehensive toxicology programme was implemented including rat subchronic and chronic studies. Rats were administered 0, 0.1, 1 and 10 mg/kg of Hematide every 3 weeks for 3 months via subcutaneous injection or for 6 months via intravenous injection. The dosing period was followed by a 6-week follow-up period. The primary pharmacology of Hematide resulted in erythroid polycythemia as measured by elevated haemoglobin levels that were time- and dose-dependent. The pharmacology profiles were similar regardless of administration route. For example, for male rats at Day 90, subcutaneous dosing resulted in haemoglobin increases of 2.7, 4.5 and 6.9 g/dl for 0.1, 1 and 10 mg Hematide/kg respectively, compared to 2.8, 5.7 and 7.4 g/dl increases for intravenous dosing. Histopathological changes were related to the prolonged severe polycythemia induced in normocythemic animals administered an erythropoiesis-stimulating agent. The findings included extramedullary haematopoiesis in the spleen and liver, bone marrow hypercellularity and organ congestion. Microscopic findings were reversible, demonstrating a return towards control findings within 6 weeks following cessation of dosing. Systemic exposures, based on both area under the curve (AUC) and maximum concentration (C(max)), were substantially greater for intravenous than subcutaneous administration. No Hematide-specific antibodies were detected. In conclusion, Hematide is a potent erythropoiesis-stimulating agent, and the studies provide support for the safety of clinical development, including chronic dosing, for the treatment of anaemia associated with chronic renal failure.

Chronic preclinical safety evaluation of Hematide, a pegylated peptidic erythropoiesis stimulating agent in monkeys.

Hematide is a synthetic peptide-based, pegylated erythropoiesis stimulating agent in clinical development for treatment of anemia. To support chronic clinical dosing requirements, a 9-month repeat dose IV monkey safety study was undertaken. Animals received 0, 0.2, 2 or 20 mg/kg hematide IV every three weeks for nine months followed by a 14-week recovery. Hematide administration was associated with time and dose-dependent polycythemia. Histological findings were related to exaggerated pharmacology that was secondary to the administration of an erythropoiesis stimulating agent to a normocythemic animal. In conclusion, these results support the use of repeated administration of hematide for the correction of anemia.

Preclinical safety and pharmacology of Hematide, a peptidic erythropoiesis stimulating agent (ESA), in rats and monkeys.

The pharmacology, toxicokinetics, and safety of Hematide, a synthetic peptidic erythropoiesis-stimulating agent (ESA), were characterized. Hematide was given intravenously (0, 0.5, 5, and 50 mg/kg) weekly for five weeks with a 6- (rat) and 12-week (monkey) recovery period. The pharmacological action of Hematide resulted in polycythemia. Histopathology consistent with drug-induced exaggerated pharmacology was observed primarily in rats. Secondary sequelae resulting from pronounced polycythemia was considered the cause of deaths in rats and a single high-dose monkey. Toxicokinetic analysis indicated prolonged exposure. In conclusion, Hematide is a potent ESA and the safety and efficacy profile support clinical development.

Hematide is immunologically distinct from erythropoietin and corrects anemia induced by antierythropoietin antibodies in a rat pure red cell aplasia model.

OBJECTIVE: To evaluate the potential of Hematide, a PEGylated, synthetic peptide-based erythropoiesis-stimulating agent that is in clinical development for the treatment of anemia associated with chronic kidney disease and cancer, to correct antierythropoietin antibody-associated pure red cell aplasia (PRCA). MATERIALS AND METHODS: The binding of anti-Hematide antibodies (mouse, rabbit, and monkey) to recombinant human erythropoietin (rHuEPO) and of anti-rHuEPO antibodies (mouse, goat, rat, and human) to Hematide were evaluated. An anti-EPO antibody-mediated anemia rat model was developed by subcutaneously administering rHuEPO to rats three times weekly for 4 weeks. Sixty percent of the animals developed PRCA as characterized by severe anemia, reduced reticulocytes, anti-EPO antibodies, and limited bone marrow erythroid precursors. The effect of Hematide administration on the PRCA rats was evaluated. RESULTS: Antibodies to EPO do not cross react with Hematide and, conversely, antibodies to Hematide do not cross react with EPO. Hematide corrected antibody-induced anemia in a rat PRCA model. CONCLUSIONS: The data support the potential of Hematide to correct anti-EPO antibody-associated PRCA in humans. In addition, the data suggest a negligible risk for development of anti-EPO antibody-induced PRCA secondary to Hematide administration.

Preclinical evaluation of Hematide, a novel erythropoiesis stimulating agent, for the treatment of anemia.

OBJECTIVE: To evaluate the preclinical erythropoiesis stimulating properties of Hematide, a novel, PEGylated, synthetic peptide for the treatment of anemia associated with chronic kidney disease and cancer. METHODS: The in vitro activity of Hematide was assessed in competitive binding, proliferation, signal transduction, and apoptosis assays, and in erythroid colony-forming assays with CD34(+) cells purified from human bone marrow. Erythropoiesis and pharmacokinetics were evaluated in rat, monkey, and a rat chronic renal insufficiency (CRI) model following single administration. Erythropoiesis and immunogenicity were also evaluated following repeat administration in rats. RESULTS: Hematide binds and activates the erythropoietin receptor and causes proliferation and differentiation of erythroid progenitor cells. Sustained circulatory persistence of Hematide is observed in rats and monkeys. In a rat CRI model, Hematide exhibited twofold lower clearance than in the normal rat, with hypothesis consistent with Hematide being cleared, at least partially, via the kidney. A dose-dependent rise in hemoglobin (Hgb) and duration of response was observed following single administration in rats and monkeys. Hematide was able to alleviate anemia in an experimental CRI rodent model. Repeat intravenous (IV) and subcutaneous (SC) administration in rats yielded similar erythrogenic responses, with no anti-Hematide antibodies being detected. CONCLUSIONS: Hematide is a potent erythropoiesis stimulating agent with a prolonged half-life and slow clearance times. It is anticipated that similar prolonged clearance and activity will be observed in the clinic, potentially enabling dosing intervals of 3 to 4 weeks that may translate into improved patient convenience for the treatment of anemia.

Evaluation of the safety and pharmacodynamics of Hematide, a novel erythropoietic agent, in a phase 1, double-blind, placebo-controlled, dose-escalation study in healthy volunteers.

Hematide is an investigational pegylated synthetic peptide that stimulates erythropoiesis in animal models and is being developed for the treatment of anemia associated with chronic renal failure and cancer. This study evaluated the safety and pharmacodynamics of single, intravenous doses (0.025, 0.05, and 0.1 mg/kg) of Hematide in 28 healthy male volunteers. All doses of Hematide were well tolerated, with safety profiles similar to those of placebo. Hematide showed a dose-dependent increase in reticulocytes. The 0.1-mg/kg dose was associated with a statistically significant increase in hemoglobin (Hgb) from baseline compared to the placebo group (13.6 +/- 3.9 g/L [1.36 +/- 0.39 g/dL] versus 3.9 +/- 3.8 g/L [0.39 +/- 0.38 g/dL]; P < .001) that was sustained for longer than 1 month. These results support phase 2 studies in patients with anemia associated with chronic kidney disease or cancer and suggest that Hematide administered as infrequently as once a month may result in a sustained elevation of Hgb levels. (Please note that Hematide is a proposed trade name; the compound does not yet have a nonproprietary name.).