Oprelvekin

Oprelvekin is a recombinant human interleukin-11. Its predominant haemopoietic activity is stimulation of megakaryocytopoiesis. Oprelvekin is indicated for the prevention of severe thrombocytopenia and the reduction of platelet transfusion requirements following myelosuppressive chemotherapy in patients with nonmyeloid malignancies at high risk of severe thrombocytopenia. It is the first available pharmacological alternative to platelet transfusions for these patients. Oprelvekin stimulates platelet progenitor cells (megakaryoblasts and colony-forming unit megakaryocytes). The drug also increases megakaryocyte size and ploidy. The recommended adult dosage of subcutaneous oprelvekin is 50 microg/kg once daily, administered until the platelet count is >/=50 000/microl after the expected nadir, but for not more than 21 days per chemotherapy cycle. Three placebo-controlled trials involving patients with cancer (mostly breast cancer) undergoing dose-intensive cancer chemotherapy, with or without autologous bone marrow transplantation (n = 75 to 82), have been conducted. Compared with placebo, oprelvekin 50 microg/kg/day was associated with significantly fewer patients requiring platelet transfusions and a trend towards a lower median number of platelet transfusions. There was also at least a trend towards reduced time to platelet recovery in oprelvekin recipients. The efficacy of oprelvekin is unaffected by previous platelet transfusion requirements and/or chemotherapy. To date the drug has not been shown to ameliorate chemotherapy-induced leucopenia or neutropenia or to have effects on time to neutrophil engraftment or red blood cell transfusion requirements in clinical trials. The most common adverse events with this agent (oedema and dyspnoea) are considered attributable to drug-induced fluid retention and increased plasma volume; these events are usually mild to moderate, reversible on drug discontinuation and dose related. Cardiovascular events including atrial arrhythmias are also considered attributable to increased plasma volume. CONCLUSIONS: Evidence suggests that oprelvekin reduces severe thrombocytopenia, accelerates platelet recovery and reduces the need for platelet transfusions in patients with nonmyeloid malignancies receiving chemotherapy regimens associated with severe thrombocytopenia. If further studies confirm these findings, oprelvekin is likely to be a valuable means of allowing patients to receive their full planned chemotherapy course.     

Physiologic role of TPO in thrombopoiesis

Recombinant human thrombopoietin (rHuTPO) serves as a megakaryocyte colony-stimulating factor and predominantly acts on GPIIb/IIIa+ rat late megakaryocyte progenitor cells, colony forming units-megakaryocyte (CFU-MK). The GPIIb/IIIa+ fraction of CFU-MK differentiates into mature megakaryocytes and further into proplatelets in liquid culture containing rHuTPO. rHuTPO stimulates cultured megakaryocytes generated from rat GPIIb/IIIa+ CFU-MK to enhance proplatelet formation and to increase megakaryocyte size. rHuTPO also induces a big size of megakaryocyte colonies from human cord blood CD34+ cells. rHuTPO does not cause aggregation of platelets from normal mice and mice made thrombocytotic by consecutive administration of rHuTPO, but preincubation with rHuTPO enhances adenosine diphosphate-induced aggregation, suggesting that platelets induced by rHuTPO administration may have a normal function. Administration of rHuTPO to normal mice daily for five days causes a dose-dependent thrombocytosis. On the other hand, rHuTPO induces a significant decrease in hemoglobin concentration and does not affect white blood cell counts. rHuTPO increases the size and number of marrow megakaryocytes and the number of marrow CFU-MK, and also influences the development of other hematopoietic progenitor cells. The effects of rHuTPO on thrombocytopenia associated with myelosuppression were examined in animal models. Following treatment with mitomycin C, mice received daily injections of various doses of rHuTPO. rHuTPO reduced the severity of thrombocytopenia, accelerated the recovery of platelets and improved neutropenia. Similar therapeutic efficacy was observed in cynomolgus monkeys treated with nimustine. These results suggest the clinical usefulness of rHuTPO for the treatment of thrombocytopenia.     

The clinical development of recombinant human interleukin 11 (NEUMEGA rhIL-11 growth factor)

Completed phase I and II studies of recombinant human interleukin 11 (rhIL-11) demonstrate its potential as a treatment for chemotherapy-induced thrombocytopenia. In a phase I study, 16 women with breast cancer received rhIL-11 (10, 25, 50, 75 or 100 microg/kg s.c. once daily) before and during cycles of moderately dose-intensive chemotherapy. Platelet counts increased in all patients before chemotherapy. During chemotherapy, the mean platelet count nadirs were 67,000 cells/microl (rhIL-11 10 microg/kg) and greater than 150,000 cells/microl (25, 50 and 75 microg/kg). Thus, doses of 25 microg/kg and higher appeared to prevent chemotherapy-induced thrombocytopenia in this study. In a randomized, placebo-controlled study, rhIL-11 (50 microg/kg) prevented the need for platelet transfusions during a subsequent chemotherapy cycle in patients who had already experienced severe chemotherapy-induced thrombocytopenia. Among 82 evaluable patients, 8 (30%) of 27 patients administered rhIL-11 50 microg/kg avoided platelet transfusions versus one (4%) of 28 who received placebo (p < 0.05). rhIL-11-treated patients received approximately two-thirds the number of platelet transfusions that placebo-treated patients received. The median duration of thrombocytopenia (<50,000 cells/microl) was seven days in rhIL-11-treated patients compared to 10 days among patients given placebo. This is the first study in which patients with a history of severe chemotherapy-induced thrombocytopenia who were receiving a variety of chemotherapy regimens have been shown to avoid platelet transfusions following the administration of a thrombopoietic growth factor. This activity of rhIL-11, and the demonstration in preclinical models that it ameliorates chemotherapy-induced mucositis, have promoted its further clinical development as a supportive therapy in patients receiving chemotherapy.     

Effects of Mpl ligands on platelet production and function in nonhuman primates

Endogenous thrombopoietin (TPO) stimulates platelet production in nonhuman primates dose-dependentbyinducing megakaryocyte development from early marrow hematopoietic progenitors and subsequent proliferation and endoreduplication. Recombinant human TPO, nonpegylated or pegylated recombinant human megakaryocyte growth and development factor produce log-linear responses in peak peripheral platelet counts (or peripheral platelet mass turnover), platelet TPO receptor density, and marrow megakaryocyte volume, ploidy, number and mass. Mpl ligand therapy sustains normal peripheral platelet concentrations following myelosuppressive chemotherapy in baboons and corrects peripheral platelet counts in HIV-infected chimpanzees with severe thrombocytopenia. Whereas Mpl ligands do not directly induce platelet aggregation in vitro, they enhance aggregatory responsiveness of platelets to physiologic agonists both in vitro and transiently ex vivo following treatment with Mpl ligands. However, platelet recruitment into forming thrombus is not augmented by these agents when evaluated in quantitative rabbit or baboon models of platelet-dependent thrombus formation, except for the direct effect of platelet concentration per se. These findings indicate that appropriate dosing of these agents prevents thrombocytopenia without increasing the risk of platelet-dependent thrombo-occlusive complications.     

Thrombopoietin administered during induction chemotherapy to patients with acute myeloid leukemia induces transient morphologic changes that may resemble chronic myeloproliferative disorders

Thrombopoietin (TPO), a potent stimulator of megakaryocyte and platelet production, has been used in clinical trials to reduce thrombocytopenia after chemotherapy in patients with acute myeloid leukemia (AML). We report that TPO therapy is associated with peripheral blood and bone marrow findings that can mimic myeloproliferative disorders. Peripheral blood and bone marrow samples of 13 patients with AML who received TPO were examined. A subset of bone marrow samples exhibited hypercellularity, megakaryocytic hyperplasia, and reticulin fibrosis after TPO administration. Cases demonstrated as many as 58.4 megakaryocytes per high-powerfield (MHPF) compared with 3.7 MHPF in the control group. Megakaryocytic atypia, increased mitoses, emperipolesis, intrasinusoidal megakaryocytes, and thickened trabeculae also were seen. Peripheral blood findings included leukoerythroblastosis, leukocytosis, thrombocytosis, and circulating megakaryocyte nuclei. Changes resolved within 3 months after discontinuation of TPO. This rapid resolution of the morphologic abnormalities induced by TPO distinguishes these findings from those seen in true chronic myeloproliferative disorders.     

Immunogenicity of thrombopoietin mimetic peptide GW395058 in BALB/c mice and New Zealand white rabbits: evaluation of the potential for thrombopoietin neutralizing antibody production in man.

Administration of exogenous proteins and peptides as therapeutics carries with it the potential for immune system recognition and the development of neutralizing antibodies to endogenous regulatory proteins. PEGylation of proteins typically reduces their immunogenicity in vivo. GW395058 is a PEGylated peptide thrombopoietin receptor (TPOr) agonist being evaluated for the treatment of chemotherapy-induced thrombocytopenia. Although GW395058 shares no homology with TPO, it does compete with TPO for binding to a common receptor, and a similarity in local structure could result in shared epitopes. Thus GW395058 could elicit TPO-neutralizing antibodies. In this study, we evaluated the immunogenicity of GW395058 in mice, the potential of rabbit antibodies elicited by immunizations with the non-PEGylated parent peptide AF15705 to cross-react with recombinant human (rHu) TPO, and the potential of mouse anti-rHuTPO antibodies elicited by repeated dosing with rHuTPO to cross-react with AF15705. GW395058-dosed mice failed to produce antibodies to AF15705 or rHuTPO. Mouse anti-rHuTPO did not cross-react with AF15705 and rabbit anti-AF15705 antibodies failed to cross-react with rHuTPO. GW395058 caused no immune-mediated lesions in mice, but rHuTPO suppressed megakaryocytopoiesis and caused B-lymphocyte hyperplasia in lymphoid tissues consistent with antigenic stimulation. These data suggest that the potential for an immune response to GW395058 in man would be low.     

A Phase 1 Trial of Eltrombopag in Patients Undergoing Stem Cell Transplantation after Total Body Irradiation

Stem cell transplantation can be associated with significant periods of thrombocytopenia, necessitating platelet transfusions and contributing to the risk of bleeding. Thrombopoietin receptor agonists have been shown to enhance platelet counts in other clinical settings, and so a phase 1 clinical trial was conducted to assess the safety, pharmacokinetics, and maximum tolerated dose of once-daily eltrombopag in patients undergoing stem cell transplantation with conditioning regimens containing total body irradiation ≥400 cGy. Eltrombopag was examined at dosage levels of 75, 150, 225, and 300 mg given orally once daily for 27 days, starting at 24 to 48 hours post-transplantation. Pharmacokinetic sampling was performed over a 24-hour period after the first dose of eltrombopag, as well as during the second week of treatment (steady-state). Nineteen patients were enrolled, 15 of whom completed protocol treatments. Three patients completed each dose level up to 225 mg, and 6 completed treatment at the highest dose of 300 mg. Four patients were replaced because drug compliance was <75% of planned doses. No dose-limiting toxicities were observed in this heterogeneous post-transplantation patient population. Common adverse events were related to standard stem cell transplantation. One episode of pulmonary embolus occurred 9 days after discontinuation of eltrombopag, and the only other thromboembolic episode was a grade 2 catheter-related clot. We conclude that up to 27 days of once-daily dosing of eltrombopag after stem cell transplantation is well tolerated.     

Defective c-Mpl signaling in the syndrome of thrombocytopenia with absent radii

Thrombocytopenia with absent radii (TAR) syndrome is a rare congenital defect with severe hypomegakaryocytic thrombocytopenia and bilateral radial aplasia. To elucidate a possible relationship between thrombocytopenia in TAR and defects in the thrombopoietin (TPO)/c-Mpl system, we examined TPO activity in sera from six patients and in vitro reactivity of the patients' platelets to recombinant human TPO. We found elevated TPO serum levels in all patients, excluding a TPO production defect as a pathomechanism for the thrombocytopenia. In contrast to healthy controls, however, platelets of TAR patients failed to respond to recombinant TPO as measured by testing TPO synergism to suboptimal concentration of platelet activators. Most interestingly, TPO-induced tyrosine phosphorylation of platelet proteins was completely absent (four out of five) or markedly decreased (one out of five). More detailed investigations of the signal cascades of c-Mpl demonstrated the absence of Jak2 phosphorylation after TPO stimulation in a TAR patient's platelets. A defect in the early events of c-Mpl signal transduction might be the reason for impaired megakaryocytopoiesis in TAR syndrome.     

Two Cases of Refractory Thrombocytopenia in Systemic Lupus Erythematosus that Responded to Intravenous Low-Dose Cyclophosphamide

Treatment of thrombocytopenia in systemic lupus erythematosus (SLE) is considered in cases of current bleeding, severe bruising, or a platelet count below 50,000/µL. Corticosteroid is the first choice of medication for inducing remission, and immunosuppressive agents can be added when thrombocytopenia is refractory to corticosteroid or recurs despite it. We presented two SLE patients with thrombocytopenia who successfully induced remission after intravenous administration of low-dose cyclophosphamide (CYC) (500 mg fixed dose, biweekly for 3 months), followed by azathioprine (AZA) or mycophenolate mofetil (MMF). Both patients developed severe thrombocytopenia in SLE that did not respond to pulsed methylprednisolone therapy, and started the intravenous low-dose CYC therapy. In case 1, the platelet count increased to 50,000/µL after the first CYC infusion, and remission was maintained with low dose prednisolone and AZA. The case 2 achieved remission after three cycles of CYC, and the remission continued with low dose prednisolone and MMF.     

The physiology of platelet production

The production of platelets from the bone marrow megakaryocytes is a well-regulated process. Nearly 100 years ago, James Homer Wright described how platelets formed from megakaryocytes and entered the circulation. Subsequent clinical and animal studies have enumerated a number of principles of platelet physiology: the platelet count is constant in any one individual but varies greatly between individuals; an inverse relationship exists between the platelet count and platelet size; the body conserves the mass, not the number, of platelets; and megakaryocyte number, size and ploidy vary in response to changing demands for platelets. With the discovery of thrombopoietin (TPO), a number of additional physiological principles have emerged: TPO takes 24 h to rise maximally and has a maximal half-life of 45 min; TPO levels are inversely and exponentially proportional to the platelet mass; platelets bind and clear TPO from the circulation; and hepatic TPO product on is not altered by changes in the platelet mass. Using these principles, a model for the regulation of platelet production by TPO has been proposed in which the constitutive hepatic TPO produced is removed from the circulation by the platelet mass. Changes in the platelet mass or its ability to clear TPO produce changes in TPO levels resulting in an altered platelet production rate. Using this model, a number of pathological disorders of platelet production, such as essential thrombocythemia and idiopathic thrombocytopenic purpura, are analyzed.     

Impact of conditioning regimen intensity on outcome of allogeneic hematopoietic cell transplantation for advanced acute myelogenous leukemia and myelodysplastic syndrome.

We reviewed 136 patients with advanced acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) undergoing allogeneic transplantation to assess the impact of conditioning regimen intensity on outcome. Thirty-nine patients receiving nonmyeloablative stem cell transplantation (NST) were compared with 97 patients receiving myeloablative transplantation. Patients receiving NST were at high risk for treatment-related complications given that they were older, 57 vs 43 years (P < .001), and more likely had received previous or myeloablative transplantation (54% vs 2%; P < .0001). The cumulative risk of relapse was higher for patients after NST (61% vs 38%; P = .02). The 100-day mortality was less after NST (15% vs 32%) Overall survival (OS) at 2 years was 28% for NST and 34% for myeloablative transplantation (P = .89). Progression-free survival (PFS) at 2 years was 20% for NST and 31% for myeloablative transplantation (P = .31). Cox regression analysis showed that the intensity of the conditioning regimen had no effect on either OS or PFS. Despite the high-risk features of patients with advanced AML or MDS undergoing NST, OS and PFS in these patients was similar to those in patients receiving myeloablative transplantation. These results demonstrate that dose intensity plays a significant role in control of disease after transplantation, but that this benefit is negated by increasing treatment-related mortality. These results suggest that NST is a reasonable alternative for patients with advanced AML and MDS at high risk for complications after myeloablative transplantation.     

The role of platelet growth factors in cancer therapy

The use of myeloid growth factors has markedly reduced the complications of chemotherapy-induced neutropenia, however, abrogation of severe thrombocytopenia remains a major clinical problem. Platelet transfusions remain the standard method of preventing or treating thrombocytopenia but are associated with a variety of complications and are a limited resource. A number of cytokines have been clinically investigated for their thrombopoietic activity, the most promising of which is the recently cloned ligand to the hematopoietic growth factor receptor, c-Mpl. The c-Mpl ligand, also referred to as thrombopoietin, megakaryocyte growth and development factor (MGDF) and megapoietin, is a potent lineage-specific agent that promotes growth and maturation of megakaryocytes and their progenitors. It holds promise for clinical use in the treatment of iatrogenic or disease-associated bone marrow failure states and possibly in syndromes of excessive platelet consumption. Early clinical trials assessing the safety and activity of recombinant human MGDF are now underway.     

Immunofluorescence Microphotometry for the Detection of Platelet Antibodies

After a survey of the literature dealing with the demonstration of platelet autoantibodies by immunofluorescence techniques, the results are given of a study in which immunofluorescence microphotometry was used for this purpose. The serum of 58, the platelets of 34, and the megakaryocytes of. 2 patients -with thrombocytopenia were investigated. In 21 of 52 sera (40%) in which the presence of platelet autoantibodies could be expected, positive results were obtained that could not be due to isoantibodies, either because the patients had not been pregnant and had not received blood transfusions or because the reactivity of the serum with the patient's own platelets was demonstrated. The platelets of 28 patients with thrombocytopenia not due to a platelet defect or decreased thrombopoiesis were investigated. In the platelets of 15 (54%) of these, significant differences in fluorescence were'found with anti-immunoglobulin conjugate as well as with anti-IgG, -IgA, -IgM, or -complement reagents. It was concluded that in these patients in vivo sensitization of the platelets with autoantibody was demonstrated. In two patients an indication of the in vivo sensitization of the megakaryocytes was also obtained.     

Novel platelet products, substitutes and alternatives.

Despite the many advances in the safety, processing, and storage of conventional 22 degrees C liquid-stored allogeneic platelet concentrates, there still are significant drawbacks to the use of such products. Efforts to overcome these shortcomings have resulted in an array of novel platelet products, substitutes, and alternatives; which are currently at various stages of development. This review summarizes the recent developments in the frozen and cold storage of platelets; their pathogen inactivation; as well as the status of lyophilized platelets, infusible platelet membranes (IPMs), red cells bearing arginine-glycine-aspartic acid (RGD) ligands, fibrinogen-coated albumin microcapsules, and liposome-based agents; as potential alternatives to the use of conventional platelet transfusions. Pre-clinical studies have been encouraging for several of these novel products; however, to date, very few have entered human trials. Nonetheless, with the ongoing development of diverse products, those properties that may be necessary for their hemostatic effectiveness will become apparent. However, safety and efficacy must be demonstrated in pre-clinical and phase I to III clinical trials before these novel agents, substitutes and alternatives can be used clinically for patients with thrombocytopenia.     

Synthetic cytokines containing interleukin-3 exert potent megakaryopoietic activity

The shared properties of haematopoietic cytokines and their receptors have enabled the genetically engineered construction of several synthetic cytokines with increased haematopoietic activity and/or more desirable pharmacological characteristics. Thrombocytopenia remains a significant cause of morbidity in cancer patients undergoing allogeneic or autologous bone marrow/blood stem cell transplantation after myeloablative therapy including total body irradiation. Several in vitro, in vivo and preliminary clinical studies have demonstrated the efficacy of synthetic cytokines containing interleukin-3 in accelerating platelet recovery after radiotherapy-induced myelosuppression, enhancing G-CSF-mobilisation of CD34 positive cells for transplantation and increasing the ex-vivo expansion of myeloid and megakaryocytic progenitor cells. More randomised controlled clinical trials are needed to study the efficacy of the pre-transplant platelet mobilisation and the acceleration of the post-transplant platelet recovery. This also applies to cohort in vitro studies for expanding the production of CD41+ megakaryocytes from human bone marrow, mobilised peripheral blood and cord blood CD34 positive cells using myelopoietin as the only accepted synthetic cytokine containing interleukin-3.     

血小板生成素的研究及临床应用

本世纪初化疗的应用，为恶性肿瘤的治疗增加了新的希望，但骨髓抑制是提高疗效的剂量限制性因素的关键问题。经几十年的探索，克隆技术的发展，先后发现了粒细胞集落刺激因子（ｇｒａｎｕｌｏｃｙｔｅ－ｃｏｌｏｎｙｓｔｉｍｕｌａｔｉｎｇ ｆａｃｔｏｒ， Ｇ－ＣＳＦ）及粒巨核细胞集落刺激因子（ ｇｒａｎｕｌｏｃｙｔｅ ａｎｄ ｍｅｇａｋａｒｙｏｃｙｔｅ－ｃｏｌｏｆｌｙ ｓｔｉｍｕｌａｔｉｎｇｆａｃｔｏｒ， ＧＭ－ＣＳＦ），并应用于临床，取得了瞩目的成效，血小板生成素（ｔｈｒｏｍｂｏｐｏｉｅｔｉｎ，ＴＰＯ）的研究成功则晚…     

新生儿血小板减少症46例临床分析

目的分析新生儿血小板减少的临床特点及可能原因,探讨其预防和治疗措施。方法回顾性分析本院2008年1月～2009年7月诊断新生儿血小板减少症所有患儿的临床资料。结果早发型血小板减少患儿临床上多无特殊表现,预后较好;迟发型血小板减少症多发生于早产儿,小于胎龄儿,通常由于合并严重感染所致,病情严重,需要输注血小板来治疗。结论围产期有高危因素母亲,其新生儿出生后要常规监测血常规,对于宫内发育不良或低出生体质量儿生后一旦合并感染要警惕血小板减少,甚至DIC的发生。     

FDA licensure of NEUMEGA to prevent severe chemotherapy-induced thrombocytopenia

This paper discusses background information and the body of clinical data that has been accumulated to demonstrate the efficacy and safety of NEUMEGA (recombinant human interleukin 11) when used to prevent severe chemotherapy-induced thrombocytopenia and reduce the need for platelet transfusions in patients with nonmyeloid malignancies. NEUMEGA is recommended to be used at a dose of 50 microg/kg s.c. once daily starting the day after chemotherapy ends until a platelet count of 50,000 cells/microl is achieved after the expected nadir.     

系统性红斑狼疮重症血小板减少患者血清对巨核祖细胞的影响

研究系统性红斑狼疮(SLE)合并重症血小板患者的血清对正常人巨核祖细胞增殖分化的影响。以12例SLE重症血小板减少患者为研究对象,12份正常骨髓单个核细胞,培养中分别加入患者血清或灭活补体的患者血清,免疫化学染色检测巨核细胞克隆形成单位(CFU-MK),流式细胞仪检测CD41+细胞数。结果是正常对照组骨髓CFU-MK集落数为(61.22±29.71)个/片,加入SLE重症血小板减少患者血清后减少为(29.44±23.35)个/片,P<0.05;加灭活补体血清后减少为(22.56±15.21)个/片,与正常对照相比P<0.05;灭活补体与否差异不显著,P>0.05。加入患者血清或灭活补体的血清后,CD41+细胞数由正常(2.30%±1.63%)分别减少为(1.15%±0.85%)和(1.07%±0.76%),与正常对照相比P<0.05;灭活补体与否差异不显著。SLE血小板正常但活动期病人的血清对正常人CFU-MK和CD41+细胞的生成均无显著抑制。提示SLE重症血小板减少患者血清能抑制正常人骨髓巨核祖细胞的增殖分化,这种抑制作用是非补体依赖性的。     

Passive neonatal thrombocytopenia. A case study of factors predicting the response to i.v. IgG therapy

A term male infant was noted at birth to have petechiae over the face and trunk and a platelet count of 3 x 10(9) per L. Maternal immune thrombocytopenia (ITP) was suspected from the clinical data and confirmed by the presence of antiplatelet antibody (both in the mother and infant) detected by recently described flow cytometry method. Initial treatment with exchange transfusions, platelet transfusions, steroids, failed to correct thrombocytopenia and, hence, seven doses of high-dose gamma globulin (IV-IgG) were given intravascularly. Initiation of IV-IgG was followed by stabilization of platelet counts with marked reduction in the need for platelet transfusions. In this case of passive ITP, the therapeutic efficiency of high dose IV-IgG seems to depend upon maintaining a certain critical level of serum IgG (which in turn may depend upon the serum antiplatelet antibody titers).