Comparison of epoetin alfa and darbepoetin alfa biological activity under different administration schedules in normal mice

Structure-Function Relationships for Recombinant Erythropoietins: A Case Study From a Proposed Manufacturing Change With Implications for Erythropoietin Biosimilar Study Designs

Comparability studies used to assess a proposed manufacturing change for a biological product include sensitive analytical studies to confirm there are no significant differences in structural or functional attributes that may contribute to clinically meaningful changes in efficacy or safety. When a proposed change is relatively complex or when clinically relevant differences between the product before and after the change cannot be ruled out based on analytical studies, nonclinical and clinical bridging studies are generally required to confirm overall comparability. In this study, we report findings from a comparability assessment of epoetin alfa before and after a proposed manufacturing process change. Although differences in glycosylation attributes were observed, these were initially believed to be irrelevant to the product's pharmacology. This assumption was initially supported via nonclinical and clinical pharmacology studies, but a clinically meaningful difference in potency was ultimately observed in a phase 3 clinical study conducted in a sensitive patient population using a sensitive study design. These results indicate that the nonclinical assessments of structure-function relationships were insufficiently sensitive to identify clinically relevant differences resulting from differences in the glycosylation profile. This case study highlights important findings that may be relevant in the development of biosimilar epoetin alfa products.

Erythropoietin and diabetes mellitus

Erythropoietin (EPO) is a 30.4 kDa growth factor and cytokine that governs cell proliferation, immune modulation, metabolic homeostasis, vascular function, and cytoprotection. EPO is under investigation for the treatment of variety of diseases, but appears especially suited for the treatment of disorders of metabolism that include diabetes mellitus (DM). DM and the complications of this disease impact a significant portion of the global population leading to disability and death with currently limited therapeutic options. In addition to its utility for the treatment of anemia, EPO can improve cardiac function, reduce fatigue, and improve cognition in patients with DM as well as regulate cellular energy metabolism, obesity, tissue repair and regeneration, apoptosis, and autophagy in experimental models of DM. Yet, EPO can have adverse effects that involve the vasculature system and unchecked cellular proliferation. Critical to the cytoprotective capacity and the potential for a positive clinical outcome with EPO are the control of signal transduction pathways that include protein kinase B, the mechanistic target of rapamycin, Wnt signaling, mammalian forkhead transcription factors of the O class, silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae), and AMP activated protein kinase. Therapeutic strategies that can specifically target and control EPO and its signaling pathways hold great promise for the development of new and effective clinical treatments for DM and the complications of this disorder.

Clinical pharmacokinetics and pharmacodynamics of erythropoiesis-stimulating agents

The cloning of the EPO gene in the early 1980s allowed for the development of recombinant erythropoietins and analogues [erythropoiesis-stimulating agents (ESAs)], offering an alternative to transfusion as a method of raising haemoglobin (Hb) levels, which have been used for more than 20 years to treat anaemia in millions of anaemic patients. There are now a number of ESAs available worldwide for the treatment of anaemia, approved for different routes of administration (intravenous and subcutaneous) and dosing intervals (three times weekly, weekly, biweekly and monthly). In this review, we discuss the pharmacokinetic characteristics, including absorption, distribution and elimination processes, across the different ESAs. Incomplete and slow lymphatic absorption, with limited extravascular distribution, and minor contributions of the target-mediated drug disposition to the overall elimination are the common characteristics across the marketed ESA. Additionally, we assess the similarities and differences of ESAs related to pharmacodynamics in the context of the different biomarkers used to monitor the magnitude and duration of the effect, and introduce the concept of the minimum effective concentration of the ESA. The relationship between the minimum effective concentration and the half-life suggests that the time during which drug concentrations are above the minimum effective concentration is the main determinant of ESA efficacy in increasing Hb levels. The tolerance phenomenon and its physiological mechanism and implications for ESA dosing are discussed. Finally, the areas of future clinical pharmacology research are envisioned.

A fully human anti-hepcidin antibody modulates iron metabolism in both mice and nonhuman primates

Fully human anti-hepcidin Abs have been generated for use as a potential therapeutic to treat AI. The mechanism of action was shown to be due to an increase in available serum iron leading to enhanced red cell hemoglobinization.

Erythropoiesis stimulating agents: approaches to modulate activity

Recombinant human erythropoietin (rHuEPO), such as the approved agents epoetin alfa and epoetin beta, has been used successfully for over 20 years to treat anemia in millions of patients. However, due to the relatively short half-life of the molecule (approximately 8 hours), frequent dosing may be required to achieve required hemoglobin levels. Therefore, a need was identified in some anemic patient populations for erythropoiesis stimulating agents with longer half-lives that required less frequent dosing. This need led to the development of second generation molecules which are modified versions of rHuEPO with improved pharma-cokinetic and pharmacodynamic properties such as darbepoetin alfa, a hyperglycosylated analog of rHuEPO, and pegzyrepoetin, a pegylated rHuEPO. Third generation molecules, such as peginesatide, which are peptide mimetics that have no sequence homology to rHuEPO have also recently been developed. The various molecular, pharmacokinetic, and pharmacodynamic properties of these and other erythropoiesis stimulating agents will be discussed in this review.

Darbepoetin-α inhibits the perpetuation of necro-inflammation and delays the progression of cholestatic fibrosis in mice

Biliary obstruction and cholestasis result in hepatocellular necro-inflammation and lead to the development of liver fibrosis. The objective of this study was to analyze whether the multiple tissue-protective properties of erythropoietin are salutary in an experimental model of liver fibrosis. For this purpose, C57BL/6J mice underwent common bile duct ligation (BDL) and were treated with either darbepoetin-α (10 μg/kg i.p.) or physiological saline every third day, beginning 24 h after BDL. Mice were killed at 2, 5, 14, and 28 days after BDL. Beside hematological parameters, markers of inflammation and fibrosis were assessed histomorphometrically and immunohistochemically as well as by quantitative real-time PCR. In addition, a 7-week survival study was performed. BDL provoked cholestatic hepatitis characterized by biliary infarcts with accumulation of macrophages followed by marked collagen deposition and increased expression of profibrotic gene transcripts. Darbepoetin-α treatment significantly diminished the area of focal necrosis, reduced the infiltration of macrophages, decreased levels of profibrotic genes, and lowered collagen deposition. Moreover, darbepoetin-α significantly reduced systemic anemia caused by BDL. Finally, darbepoetin-α treatment significantly prolonged the survival time after BDL. This study suggests that darbepoetin-α, which is a clinically well-established substance, might be used as an efficient therapeutic option for patients with chronic cholestatic liver disease.

Erythropoietin elevates VO2,max but not voluntary wheel running in mice

Voluntary activity is a complex trait, comprising both behavioral (motivation, reward) and anatomical/physiological (ability) elements. In the present study, oxygen transport was investigated as a possible limitation to further increases in running by four replicate lines of mice that have been selectively bred for high voluntary wheel running and have reached an apparent selection limit. To increase oxygen transport capacity, erythrocyte density was elevated by the administration of an erythropoietin (EPO) analogue. Mice were given two EPO injections, two days apart, at one of two dose levels (100 or 300 microg kg(-1)). Hemoglobin concentration ([Hb]), maximal aerobic capacity during forced treadmill exercise (VO2,max) and voluntary wheel running were measured. [Hb] did not differ between high runner (HR) and non-selected control (C) lines without EPO treatment. Both doses of EPO significantly (P<0.0001) increased [Hb] as compared with sham-injected animals, with no difference in [Hb] between the 100 microg kg(-1) and 300 microg kg(-1) dose levels (overall mean of 4.5 g dl(-1) increase). EPO treatment significantly increased VO2,max by approximately 5% in both the HR and C lines, with no dosexline type interaction. However, wheel running (revolutions per day) did not increase with EPO treatment in either the HR or C lines, and in fact significantly decreased at the higher dose in both line types. These results suggest that neither [Hb] per se nor VO2,max is limiting voluntary wheel running in the HR lines. Moreover, we hypothesize that the decrease in wheel running at the higher dose of EPO may reflect direct action on the reward pathway of the brain.

Discovery and basic pharmacology of erythropoiesis-stimulating agents (ESAs), including the hyperglycosylated ESA, darbepoetin alfa: an update of the rationale and clinical impact

Cloning of the human erythropoietin (EPO) gene and development of the first recombinant human erythropoietin (rHuEPO) drug were truly breakthroughs. This allowed a deeper understanding of the structure and pharmacology of rHuEpo, which in turn inspired the discovery and development of additional erythropoiesis-stimulating agents (ESAs). In vivo specific activity and serum half-life of rHuEPO are influenced by the amount and structure of the attached carbohydrate. Increased numbers of sialic acids on carbohydrate attached to rHuEPO correlated with a relative increase in in-vivo-specific activity and increased serum half-life. The effect of increasing the number of sialic-acid-containing carbohydrates on in-vivo-specific activity was explored. Initial research focused on solving the problem of how the protein backbone could be engineered so a cell would add more carbohydrate to it. Additional work resulted in darbepoetin alfa, a longer-acting molecule with two additional carbohydrate chains.

Antihepcidin antibody treatment modulates iron metabolism and is effective in a mouse model of inflammation-induced anemia

Iron maldistribution has been implicated in multiple diseases, including the anemia of inflammation (AI), atherosclerosis, diabetes, and neurodegenerative disorders. Iron metabolism is controlled by hepcidin, a 25-amino acid peptide. Hepcidin is induced by inflammation, causes iron to be sequestered, and thus, potentially contributes to AI. Human hepcidin (hHepc) overexpression in mice caused an iron-deficient phenotype, including stunted growth, hair loss, and iron-deficient erythropoiesis. It also caused resistance to supraphysiologic levels of erythropoiesis-stimulating agent, supporting the hypothesis that hepcidin may influence response to treatment in AI. To explore the role of hepcidin in inflammatory anemia, a mouse AI model was developed with heat-killed Brucella abortus treatment. Suppression of hepcidin mRNA was a successful anemia treatment in this model. High-affinity antibodies specific for hHepc were generated, and hHepc knock-in mice were produced to enable antibody testing. Antibody treatment neutralized hHepc in vitro and in vivo and facilitated anemia treatment in hHepc knock-in mice with AI. These data indicate that antihepcidin antibodies may be an effective treatment for patients with inflammatory anemia. The ability to manipulate iron metabolism in vivo may also allow investigation of the role of iron in a number of other pathologic conditions.

Use and cost of erythropoiesis-stimulating agents in patients with cancer

OBJECTIVE

To compare the baseline characteristics, episodes of care, and cost of erythropoiesis-stimulating agents among cancer patients in a US managed-care population.

RESEARCH DESIGN AND METHODS

Retrospective analysis of administrative claims data. Episodes of care for patients with cancer receiving erythropoiesis-stimulating agents between January 1, 2004 and January 17, 2006 included all claims for erythropoiesis-stimulating agents with < or = 42 days' gap between claims, plus the duration of therapeutic benefit based on median days between consecutive doses.

MAIN OUTCOME MEASURES

Main outcome measures were average weekly dose of erythropoiesis-stimulating agents and costs of therapy.

RESULTS

A total of 15,007 eligible episodes of care (darbepoetin alfa, 7769 episodes [5587 patients]; epoetin alfa 7238 episodes [5157 patients]) were identified. Fewer claims were observed per episode of care for darbepoetin alfa than for epoetin alfa (mean [SD] 3.7 [4.1] vs. 5.3 [6.4]). The median time between consecutive claims was 15 days (darbepoetin alfa) and 8 days (epoetin alfa). The mean (SD) weekly doses were 105 (56) microg (darbepoetin alfa) and 34,242 (28173) U (epoetin alfa), a dose-comparison ratio of 326 : 1. Dose-comparison ratios were sensitive to assumptions about duration of clinical benefit. The mean (95% CI) weekly costs were significantly lower for darbepoetin alfa ($560 [553-567]) than for epoetin alfa ($645 [630-659], p < 0.0001) when duration of clinical benefit was considered.

CONCLUSIONS

Significant differences characterize patterns of use of erythropoiesis-stimulating agents. Duration of therapeutic benefit is an important variable in comparing darbepoetin alfa with epoetin alfa; incorporation of this variable in analyses of costs of therapy may have notable effects on calculated treatment costs. Limitations of the study include the potential for database errors or omissions, lack of detailed disease data, and lack of adjustment for differences in the ages and comorbidities of patients.

Synergistic effect of erythropoietin but not G-CSF in combination with curcumin on impaired liver regeneration in rats

INTRODUCTION

The effect of erythropoietin (Epo) and granulocyte colony-stimulating factor (G-CSF) alone or in combination with the hepatoprotective antioxidant curcumin (Cur) was evaluated in a model of delayed liver regeneration.

MATERIALS AND METHODS

Sprague Dawley rats underwent 70% liver resection with simultaneous cecal ligation and puncture and were randomised to five groups: no treatment, G-CSF (100 microg/kg), Epo (1,000 IU/kg), each alone or in combination with Cur (100mg/kg). Twenty-four hours after surgery, blood and tissue samples were collected. Markers of liver regeneration (liver weight, mitotic index, Ki-67 index), function (bilirubin, bile flow) and hepatocellular damage (liver enzymes, histomorphology) were determined. In addition, cytokine expression and hepatic glutathione concentrations were measured.

RESULTS

Liver regeneration was not improved by G-CSF or Epo monotherapy. Epo more effectively increased liver weight and regeneration markers, but the difference was not significant. Whereas liver regeneration was slightly inhibited in the G-CSF plus Cur group, Epo plus Cur significantly improved liver regeneration. This was accompanied by reduced oxidative stress. Liver function and the expression of pro-inflammatory cytokines were comparable in all treatment groups.

CONCLUSION

In the present model, Epo, at a relatively low dosage, did not improve liver regeneration. However, the combination of Epo and Cur showed a synergistic effect with highly significant stimulation of liver regeneration.