Pure red-cell aplasia and antierythropoietin antibodies in patients treated with recombinant erythropoietin

A new principle suggested for detection of darbepoetin-alpha (NESP) doping

Doping with darbepoetin-alpha, also termed novel erythropoiesis stimulating protein (NESP), a hypersialylated, very effective analogue of erythropoietin, is a serious threat in sport. We report here on a new principle for the detection of darbepoetin-alpha in serum based upon increase in immunoactivity after desialylation with neuraminidase. The method is evaluated on sera from patients taken 2-14 days after last injection of darbepoetin-alpha. Thirty-two venous blood samples and 3 capillary samples taken from finger tips were obtained from 13 patients with end stage renal disease treated with intravenous or subcutaneous injections of Aranesp, 0.45 to 2.60 microg*kg(-1). Blood samples from 37 individuals with endogenous erythropoietin were used as controls. The sera were diluted 1:2 with acetate buffer pH 5.6 with or without neuraminidase and incubated at 37 degrees C for 1 or 24 h before immunoassay. The erythropoietin immunoactivity in serum volumes of 12.5-50 microL was measured with ELISA-kits from R&D Systems Inc and medac GmbH. The relative increase in immunoactivity after desialylation was in all cases higher for the darbepoetin-alpha samples than for any of the control samples assayed in parallel, varying incubation time with the enzyme, serum volumes and batches of both ELISA-kits. The mean relative increase in immunoactivity of endogenous erythropoietin after neuraminidase was 42% with the medac-kit and 117% with R&D-kit while the corresponding figures for darbepoetin-alpha were 282% and 231% with 1 h and 299% and 256% with 24 h enzyme incubation, respectively. Endogenous and recombinant human erythropoietin showed similar relative increase after desialylation. The method to detect darbepoetin-alpha in serum is simple to perform, robust, sensitive and requires a small amount of blood. The drug was detected in all patient sera taken 2-14 days after last injection. We suggest that the method should be evaluated for the detection of darbepoetin-alpha doping in sport.

Erythropoietin: physiology and pharmacology update

This minireview is an update of a 1997 review on erythropoietin (EPO) in this journal. EPO is a 30,400-dalton glycoprotein that regulates red cell production. In the human, EPO is produced by peritubular cells in the kidneys of the adult and in hepatocytes in the fetus. Small amounts of extra-renal EPO are produced by the liver in adult human subjects. EPO binds to an erythroid progenitor cell surface receptor that includes a p66 chain, and, when activated, the p66 protein becomes dimerized. EPO receptor activation induces a JAK2 tyrosine kinase, which leads to tyrosine phosphorylation of the EPO receptor and several proteins. EPO receptor binding leads to intracellular activation of the Ras/mitogen-activated kinase pathway, which is involved with cell proliferation, phosphatidylinositol 3-kinase, and STATS 1, 3, 5A, and 5B transcriptional factors. EPO acts primarily to rescue erythroid cells from apoptosis (programmed cell death) to increase their survival. EPO acts synergistically with several growth factors (SCF, GM-CSF, 1L-3, and IGF-1) to cause maturation and proliferation of erythroid progenitor cells (primarily colony-forming unit-E). Oxygen-dependent regulation of EPO gene expression is postulated to be controlled by a hypoxia-inducible transcription factor (HIF-1alpha). Hypoxia-inducible EPO production is controlled by a 50-bp hypoxia-inducible enhancer that is approximately 120 bp 3' to the polyadenylation site. Hypoxia signal transduction pathways involve kinases A and C, phospholipase A(2), and transcription factors ATF-1 and CREB-1. A model has been proposed for adenosine activation of EPO production that involves protein kinases A and C and the phospholipase A(2) pathway. Other effects of EPO include a hematocrit-independent, vasoconstriction-dependent hypertension, increased endothelin production, upregulation of tissue renin, change in vascular tissue prostaglandins production, stimulation of angiogenesis, and stimulation of endothelial and vascular smooth muscle cell proliferation. Recombinant human EPO (rHuEPO) is currently being used to treat patients with anemias associated with chronic renal failure, AIDS patients with anemia due to treatment with zidovudine, nonmyeloid malignancies in patients treated with chemotherapeutic agents, perioperative surgical patients, and autologous blood donation. A novel erythropoiesis-stimulating factor (NESP, darbepoetin) has been synthesized and when compared with rHuEPO, NESP has a higher carbohydrate content (52% vs 40%), a longer plasma half-life, the amino acid sequence differs from that of native human EPO at five positions, and has been reported to maintain hemoglobin levels just as effectively in patients with chronic renal failure as rHuEPO at less frequent dosing. The use of rHuEPO and darbepoetin to enhance athletic performance is officially banned by most sports-governing bodies because the excessive erythrocytosis can lead to increased thrombogenicity and can cause deep vein, coronary, and cerebral thromboses.

Validation of the BIACORE 3000 platform for detection of antibodies against erythropoietic agents in human serum samples

OBJECTIVE

To develop a validated BIACORE immunoassay for the detection and characterization of serum antibodies with specificity for erythropoietic molecules (e.g. darbepoetin alfa).

METHODS

New Zealand White rabbits (n = 8) were immunized by an intramuscular injection of darbepoetin alfa/adjuvant at 0, 4, 6, and 8 weeks. Serum was collected for 6 weeks after final injection and pooled for affinity purification. Antibody immunoassay measurements were performed using a BIACORE 3000 with darbepoetin alfa immobilized to the biosensor surface. Human serum samples were spiked with the affinity-purified rabbit antibody to develop and validate the BIACORE immunoassay.

RESULTS

The assay was shown to be stable through 180 sample/regeneration cycles and had a threshold of 45.8 response units. The validated limit of detection was 0.40 microg/ml in 100% human serum. The method was robust, with variability not exceeding a 20% coefficient of variation, well within acceptable limits for typical immunoassays.

CONCLUSION

All protein-based therapeutics have a potential for immunogenicity, and antibodies raised against these molecules may have important clinical sequelae. The biotechnology and pharmaceutical industries are challenged to address this potential by developing robust analytical platforms to detect and characterize antibodies directed against therapeutic proteins in clinical specimens. Traditionally, radioimmune precipitation assays and/or enzyme-linked immunoassays (ELISAs) are used for primary detection of host immune response; however, the BIACORE platform may be better suited for this purpose in many instances. This platform represents a robust tool that should be considered for the detection and characterization of antibodies directed against protein-based therapeutics.

Advances in Anemia Management in Chronic Kidney Disease

The prevalence of chronic kidney disease (CKD) is increasing in the United States. Efforts to promote earlier intervention to screen for CKD and manage secondary complications are of paramount importance to improve overall care of this population. Anemia is a secondary complication of CKD that develops as kidney function declines. Historically, anemia management efforts have been primarily emphasized in patients with end-stage renal disease; however, early detection and treatment of anemia in the early stages of the disease are essential to prevent negative consequences of anemia such as reduced quality of life, left ventricular hypertrophy and mortality. With the increased prevalence of CKD and efforts focused on identifying this disorder early in its course, it is likely that more pharmacists will be involved in the management of CKD and secondary complications such as anemia. Treatment approaches must also be based on the more recently advocated guidelines from the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI). This article reviews therapeutic issues of anemia of CKD, new agents for management, and the NKF-K/DOQI anemia management guidelines from a clinical perspective that will assist pharmacists involved in the care of these patients.

Pharmacologic and cytokine treatment of commonly encountered anemias

Anemia has multiple etiologies: it may be caused by nutritional deficiencies or congenital abnormalities, or it may be associated with a number of conditions, such as chronic kidney disease, cancer, or human immunodeficiency virus (HIV) infection. Anemia is associated with an increase in morbidity and mortality in patients with endstage renal disease, cancer, or HIV infection. Each case of anemia is different, with different causes, clinical consequences, and treatment strategies. Identifying the most appropriate treatment requires an understanding of the etiology of the anemia and investigation of the nature of the causative medical condition. In some cases, such as anemia associated with chronic kidney disease, treatment is well defined and consists of administration of erythropoiesis-stimulating agents, accompanied by iron supplementation where appropriate. In other instances, such as megaloblastic anemia, which may be caused by vitamin or folate deficiency, vitamin supplementation alone may be a clinically appropriate treatment. This article gives an overview of the etiologies and current therapies of the most commonly encountered types of anemia, highlighting both the diverse nature of the condition, and the equally diverse pharmacologic and supportive treatment approaches.

Darbepoetin alfa: a new therapy for the management of anaemia associated with chronic kidney disease

Darbepoetin alfa (Aranesp, Amgen, Inc., Thousand Oaks, California) is a new erythropoietic protein that corrects anaemia associated with chronic kidney disease (CKD) in the majority of patients. Darbepoetin alfa contains five N-linked carbohydrate chains compared with three in recombinant human erythropoietin (rHuEPO). The two additional sialic acid-containing carbohydrate chains prolong the serum half-life of darbepoetin alfa, resulting in greater biological activity and a reduced dosing frequency compared with rHuEPO. Clinical studies in patients with CKD have demonstrated that darbepoetin alfa is effective in correcting anaemia in rHuEPO-naive patients and in patients who have been converted from rHuEPO therapy. Darbepoetin alfa provides long-term maintenance of haemoglobin levels when administered once weekly or once every other week, with the possibility of once-monthly dosing in some patients. Darbepoetin alfa is well tolerated and has a safety profile similar to that of rHuEPO. Owing to its half-life being three times longer than rHuEPO, darbepoetin alfa can be administered at an extended dosing interval, without compromising efficacy. Lessfrequent dosing has potential benefits for both patients with CKD and healthcare providers. These benefits include reduced visits to the clinic, fewer injections and a reduced demand on staff and treatment facilities.

The enigma of the metabolic fate of circulating erythropoietin (Epo) in view of the pharmacokinetics of the recombinant drugs rhEpo and NESP

Recombinant human erythropoietin (rhEpo) is a mainstay in the treatment of anaemia, primarily in renal failure. Because the half-life of circulating rhEpo is relatively short (4-8 h), the drug is usually administered 2-3 times weekly. Recently, a novel erythropoiesis-stimulating protein (NESP) with a longer half-life (24-26 h) has been approved. NESP possesses two additional N-glycans compared to endogenous Epo or rhEpo. The pharmacokinetics of rhEpo and NESP in humans have been investigated in detail. The composition of the N-glycans is clearly important in determining the biological activity and the velocity of the degradation of Epo and its analogues. However, due to the lack of knowledge of the main site and mechanism of the removal of Epo from circulation, the difference in survival of rhEpo and NESP has remained phenomenological. Investigators have implicated the liver, kidneys, and bone marrow as possible sites of the catabolism of Epo. However, while hepatocytes take up desialylated Epo, the liver does not appear to play a major role in the degradation of intact Epo. Likewise, renal Epo clearance is apparently of secondary importance. Studies showing non-linear pharmacokinetics of Epo suggest that Epo is eliminated by saturable mechanisms. The hormone, as well as the recombinant drugs, can be incorporated by erythrocytic progenitors and other tissues expressing the Epo receptor. The affinity of the Epo receptor for rhEpo is 4.3-fold higher than for NESP. Taken together, it seems most likely that native Epo, rhEpo and NESP are degraded following Epo receptor-mediated uptake, mainly in bone marrow.

Immunogenicity of therapeutic proteins: clinical implications and future prospects

BACKGROUND

Therapeutic proteins have revolutionized the treatment of many diseases. In the near future, many more therapeutic proteins are likely to become available for an increasingly wide range of indications.

OBJECTIVES

This article reviews the incidence, causes, and consequences of formation of antibodies to therapeutic proteins and suggests ways to address issues surrounding immunogenicity.

METHODS

Searches of MEDLINE and EMBASE databases were performed, covering the period 1990 to May 2002. Search terms included immunogenicity, antibodies, and the names of specific therapeutic proteins and classes of therapeutic proteins. Bibliographies of retrieved articles were not searched.

RESULTS

All exogenous proteins, including therapeutic ones, have the potential to cause antibody formation. The reported incidence of antibody formation with therapeutic proteins varies widely between proteins and between studies (depending on the assay techniques used). The clinical consequences of antibody formation vary with the type of antibody present; for example, neutralizing antibodies are more likely to cause loss of efficacy than nonneutralizing antibodies. The immunogenicity of therapeutic proteins can be influenced by many factors, including the genetic background of the patient, the type of disease, the type of protein (human or nonhuman), the presence of conjugates or fragments, the route of administration, dose frequency, and duration of treatment. Manufacturing, handling, and storage can introduce contaminants, or alter the 3-dimensional structure of the protein via oxidation or aggregate formation. Various means have been suggested by which therapeutic proteins might be modified to reduce their immunogenicity, including PEGylation, site-specific mutagenesis, exon shuffling, and humanization of monoclonal antibodies. In the future, it may even be possible to predict the immunogenicity of new therapeutic proteins more accurately, using specifically designed animal models, including nonhuman primates and transgenic mice.

CONCLUSIONS

Scientists and clinicians are becoming increasingly aware of the importance of assessing the immunogenicity of new molecules as they are introduced, and of existing molecules whenever they are modified or their manufacturing process is changed. Immune responses to therapeutic proteins are usually only of clinical significance if they are associated with the development of treatment resistance. Although various means to reduce the immunogenicity of therapeutic proteins have been suggested, monitoring for antibodies during clinical trials and postmarketing surveillance remains an important issue for all therapeutic proteins.

Use of epoetin in patients with cancer: evidence-based clinical practice guidelines of the American Society of Clinical Oncology and the American Society of Hematology

Anemia resulting from cancer, or its treatment, is an important clinical problem increasingly treated with the recombinant hematopoietic growth factor erythropoietin. To address uncertainties regarding indications and efficacy, the American Society of Clinical Oncology and the American Society of Hematology developed an evidence-based clinical practice guideline for the use of epoetin in patients with cancer. The guideline panel found good evidence to recommend use of epoetin as a treatment option for patients with chemotherapy-associated anemia with a hemoglobin level less than 10 g/dL. Use of epoetin for patients with less severe anemia (hemoglobin < 12 g/dL but never below 10 g/dL) should be determined by clinical circumstances. Good evidence from clinical trials supports the use of subcutaneous epoetin thrice weekly (150 U/kg tiw) for a minimum of 4 weeks. Less strong evidence supports an alternative weekly (40,000 U/wk) dosing regimen, based on common clinical practice. With either administration schedule, dose escalation should be considered for those not responding to the initial dose. In the absence of response, continuing epoetin beyond 6 to 8 weeks does not appear to be beneficial. Epoetin should be titrated once the hemoglobin concentration reaches 12 g/dL. Evidence from one randomized controlled trial supports use of epoetin for patients with anemia associated with low-risk myelodysplasia not receiving chemotherapy; however, there are no published high-quality studies to support its use for anemia in other hematologic malignancies in the absence of chemotherapy. Therefore, for anemic patients with hematologic malignancies, it is recommended that physicians initiate conventional therapy and observe hematologic response before considering use of epoetin.

Management options for cancer therapy-related anaemia

Anaemia is common in patients with haematological malignancy, occurring in the majority of patients with malignant disease who are treated with chemotherapy. Most patients will have their anaemia attributed to the cytokine-mediated anaemia of chronic disease. Many of these patients with anaemia will be symptomatic with fatigue, which is the single most important symptom reported. Data from many studies indicate that treatment of patients with anaemia with recombinant human erythropoietin (rHuEpo) will increase their haemoglobin level, decrease transfusion need and also improve their quality of life. Recent clinical and experimental work suggest that improving the haemoglobin level may improve the patients' prognosis but this finding needs to be confirmed. Treatment of anaemia with rHuEpo in patients with cancer may produce many benefits. Unfortunately, rHuEpo is effective in only around 60% of patients, is slow acting and is expensive. These drawbacks have restricted its use in many healthcare systems. However, a failure to treat anaemia may have important adverse effects for the patient both in terms of their quality of life and, just possibly, in terms of their life expectancy.

Allergic skin and systemic reactions in a patient with pure red cell aplasia and anti-erythropoietin antibodies challenged with different epoetins

Recent concern has arisen about the development of neutralizing anti-erythropoietin (EPO) antibodies during the course of treatment with recombinant EPO. The underlying mechanisms are poorly understood. A patient was observed who developed wheals at the sites of subcutaneous injections of epoetin-alpha before the manifestation of pure red cell aplasia (PRCA). Intravenous application of different epoetins evoked skin reactions at the sites of former subcutaneous injections, indicating local persistence of sensitized cells, and eventually a systemic anaphylactoid response. Anti-EPO antibodies crossreactive with epoetin-beta and darbepoetin-alpha were demonstrated in patient serum. PRCA gradually improved after treatment with prednisolone.

Darbepoetin alfa given every 1 or 2 weeks alleviates anaemia associated with cancer chemotherapy

In part A of this study, patients were randomised to cohorts receiving darbepoetin alfa at doses of 0.5 to 8.0 m.c.g x kg(-1) x wk(-1) or to a control group receiving epoetin alfa at an initial dose of 150 U x kg(-1) three times weekly. In part B, the cohorts were darbepoetin alfa 3.0 to 9.0 m.c.g x kg(-1) every 2 weeks or epoetin alfa, initial dose 40 000 U x wk(-1). Safety was assessed by adverse events, changes in blood pressure, and formation of antibodies to darbepoetin alfa. Efficacy was assessed by several haematologic endpoints, including change in haemoglobin from baseline. The adverse event profile of darbepoetin alfa was similar to that of epoetin alfa. No relationship between the rapidity of haemoglobin response and any adverse event was observed. No antibodies to darbepoetin alfa were detected. Higher doses of darbepoetin alfa increased the proportion of patients with a haemoglobin response and decreased the median time to response. The overall dose of darbepoetin alfa required to produce a mean increase in haemoglobin does not increase when the dosing interval is increased from 1 to 2 weeks. Therapy with darbepoetin alfa is safe and effective in producing a dose-related increase in haemoglobin levels in patients with cancer receiving chemotherapy.

Bioequivalence and the immunogenicity of biopharmaceuticals

The expiry of the first patents for recombinant-DNA-derived biopharmaceuticals will open the possibility of marketing generics, if they can be shown to be essentially similar to the innovator product. However, as shown by the problem of immunogenicity, the properties of biopharmaceuticals are dependent on many factors, including downstream processing and formulation. Products from different sources cannot be assumed to be bioequivalent, even if identical genes are expressed in the same host cells and similar production methods are used. Some of the influencing factors are still unknown, which makes it impossible to completely predict biological behaviour, such as immunogenicity, which can sometimes lead to serious side effects.

Hematopoietic factor erythropoietin fosters neuroprotection through novel signal transduction cascades

In addition to promoting the survival, proliferation, and differentiation of immature erythroid cells, erythropoietin and the erythropoietin receptor have recently been shown to modulate cellular signal transduction pathways that extend beyond the erythropoietic function of erythropoietin. In particular, erythropoietin has been linked to the prevention of programmed cell death in neuronal systems. Although this work is intriguing, the underlying molecular mechanisms that serve to mediate neuroprotection by erythropoietin are not well understood. Further analysis illustrates that erythropoietin modulates two distinct components of programmed cell death that involve the degradation of DNA and the externalization of cellular membrane phosphatidylserine residues. Initiation of the cascades that modulate protection by erythropoietin and its receptor may begin with the activation of the Janus tyrosine kinase 2 protein. Subsequent downstream mechanisms appear to lead to the activation of multiple signal transduction pathways that include transcription factor STAT5 (signal transducers and activators of transcription), Bcl-2, protein kinase B, cysteine proteases, mitogen-activated protein kinases, protein-tyrosine phosphatases, and nuclear factor-kappaB. New knowledge of the cellular pathways regulated by erythropoietin in neuronal environments will potentially solidify the development and initiation of therapeutic strategies against nervous system disorders.