Emerging treatments for thrombocytopenia: Increasing platelet production

A Review on Romiplostim Mechanism of Action and the Expressive Approach in E. coli

Immune thrombocytopenic purpura (ITP) is an autoimmune disorder determined by immune-mediated platelet demolition and reduction of platelet production. Romiplostim is a new thrombopoiesis motivating peptibody that binds and stimulates the human thrombopoietin receptor the patent of which was registered in 2008. It is used to treat thrombocytopenia in patients with chronic immune thrombocytopenic purpura. Romiplostim is a 60 kDa peptibody designed to inhibit cross-reacting immune responses. It consists of four high-affinity TPO-receptor binding domains for the Mpl receptor and one human IgG1 Fc domain. Escherichia coli is a good host for the fabrication of recombinant proteins such as romiplostim. The expression of a gene intended in E. coli is dependent on many factors such as a protein's inherent ability to fold, mRNA's secondary structure, its solubility, its toxicity preferential codon use, and its need for post-translational modification (PTM). This review focuses on the structure, function, mechanism of action, and expressive approach to romiplostim in E. coli.

Zebrafish Cancer Predisposition Models

Cancer predisposition syndromes are rare, typically monogenic disorders that result from germline mutations that increase the likelihood of developing cancer. Although these disorders are individually rare, resulting cancers collectively represent 5-10% of all malignancies. In addition to a greater incidence of cancer, affected individuals have an earlier tumor onset and are frequently subjected to long-term multi-modal cancer screening protocols for earlier detection and initiation of treatment. In vivo models are needed to better understand tumor-driving mechanisms, tailor patient screening approaches and develop targeted therapies to improve patient care and disease prognosis. The zebrafish (Danio rerio) has emerged as a robust model for cancer research due to its high fecundity, time- and cost-efficient genetic manipulation and real-time high-resolution imaging. Tumors developing in zebrafish cancer models are histologically and molecularly similar to their human counterparts, confirming the validity of these models. The zebrafish platform supports both large-scale random mutagenesis screens to identify potential candidate/modifier genes and recently optimized genome editing strategies. These techniques have greatly increased our ability to investigate the impact of certain mutations and how these lesions impact tumorigenesis and disease phenotype. These unique characteristics position the zebrafish as a powerful in vivo tool to model cancer predisposition syndromes and as such, several have already been created, including those recapitulating Li-Fraumeni syndrome, familial adenomatous polyposis, RASopathies, inherited bone marrow failure syndromes, and several other pathogenic mutations in cancer predisposition genes. In addition, the zebrafish platform supports medium- to high-throughput preclinical drug screening to identify compounds that may represent novel treatment paradigms or even prevent cancer evolution. This review will highlight and synthesize the findings from zebrafish cancer predisposition models created to date. We will discuss emerging trends in how these zebrafish cancer models can improve our understanding of the genetic mechanisms driving cancer predisposition and their potential to discover therapeutic and/or preventative compounds that change the natural history of disease for these vulnerable children, youth and adults.

Arachidonic acid and Docosahexanoic acid enhance platelet formation from human apheresis-derived CD34+ cells

An Aberration in megakaryopoiesis and thrombopoiesis, 2 important processes that maintain hemostasis, leads to thrombocytopenia. Though platelet transfusions are used to treat this condition, blood banks frequently face a shortage of platelets. Therefore, methods to generate platelets on a large scale are strongly desirable. However, to generate megakaryocytes (MKs) and platelets (PLTs) in numbers sufficient for clinical application, it is essential to understand the mechanism of platelet production and explore efficient strategies accordingly. We have earlier reported that the N-6 and N-3 poly-unsaturated fatty acids (PUFAs), Arachidonic acid (AA)/Docosahexanoic acid (DHA) have beneficial effect on the generation of MKs and PLTs from umbilical cord blood derived CD34⁺ cells. Here we tested if a similar effect is observed with peripheral blood derived CD34⁺ cells, which are more commonly used in transplantation settings. We found a significant enhancement in cell numbers, surface marker expression, cellular ploidy and expression of cytoskeletal components during PLT biogenesis in cultures exposed to media containing AA/DHA than control cultures that were not exposed to these PUFAs. The test cells engrafted more efficiently in NOD/SCID mice than control cells. AA/DHA appears to have enhanced MK/PLT generation through upregulation of the NOTCH and AKT pathways. Our data show that PUFAs could be valuable additives in the culture system for large scale production of platelets for clinical applications.

Production and characterization of genetically modified human IL-11 variants

Interleukin-11 (IL-11) has been expected as a drug on severe thrombocytopenia caused by myelo-suppressive chemotherapy. Whereas, development of IL-11 inhibitor is also expected for a treatment against IL-11 related cancer progression. Here, we will demonstrate the creation of various kinds of genetically modified hIL-11s. Modified vectors were constructed by introducing N- or O-glycosylation site on the region of hIL-11 that does not belong to the core α-helical motif based on the predicted secondary structure. N-terminal (N: between 22 to 23 aa), the first loop (M1:70 to 71 aa), the second loop (M2:114-115 aa), the third loop (M3:160-161 aa) and C-terminal (C: 200- aa) were selected for modification. A large scale production system was established and the characteristics of modified hIL-11s were evaluated. The structure was analyzed by amino acid sequence and composition analysis and CD-spectra. Glycan was assessed by monosaccharide composition analysis. Growth promoting activity and biological stability were analyzed by proliferation of T1165 cells. N-terminal modified proteins were well glycosylated and produced. Growth activity of 3NN with NASNASNAS sequence on N-terminal was about tenfold higher than wild type (WT). Structural and biological stabilities of 3NN were also better than WT and residence time in mouse blood was longer than WT. M1 variants lacked growth activity though they are well glycosylated and secondary structure is very stable. Both of 3NN and OM1 with AAATPAPG on M1 associated with hIL-11R strongly. These results indicate N-terminal and M1 variants will be expected for practical use as potent agonists or antagonists of hIL-11.

Alternatives, and adjuncts, to prophylactic platelet transfusion for people with haematological malignancies undergoing intensive chemotherapy or stem cell transplantation

BACKGROUND

Platelet transfusions are used in modern clinical practice to prevent and treat bleeding in people with thrombocytopenia. Although considerable advances have been made in platelet transfusion therapy since the mid-1970s, some areas continue to provoke debate especially concerning the use of prophylactic platelet transfusions for the prevention of thrombocytopenic bleeding.

OBJECTIVES

To determine whether agents that can be used as alternatives, or adjuncts, to platelet transfusions for people with haematological malignancies undergoing intensive chemotherapy or stem cell transplantation are safe and effective at preventing bleeding.

SEARCH METHODS

We searched 11 bibliographic databases and four ongoing trials databases including the Cochrane Central Register of Controlled Trials (CENTRAL, 2016, Issue 4), MEDLINE (OvidSP, 1946 to 19 May 2016), Embase (OvidSP, 1974 to 19 May 2016), PubMed (e-publications only: searched 19 May 2016), ClinicalTrials.gov, World Health Organization (WHO) ICTRP and the ISRCTN Register (searched 19 May 2016).

SELECTION CRITERIA

We included randomised controlled trials in people with haematological malignancies undergoing intensive chemotherapy or stem cell transplantation who were allocated to either an alternative to platelet transfusion (artificial platelet substitutes, platelet-poor plasma, fibrinogen concentrate, recombinant activated factor VII, desmopressin (DDAVP), or thrombopoietin (TPO) mimetics) or a comparator (placebo, standard care or platelet transfusion). We excluded studies of antifibrinolytic drugs, as they were the focus of another review.

DATA COLLECTION AND ANALYSIS

Two review authors screened all electronically derived citations and abstracts of papers identified by the review search strategy. Two review authors assessed risk of bias in the included studies and extracted data independently.

MAIN RESULTS

We identified 16 eligible trials. Four trials are ongoing and two have been completed but the results have not yet been published (trial completion dates: April 2012 to February 2017). Therefore, the review included 10 trials in eight references with 554 participants. Six trials (336 participants) only included participants with acute myeloid leukaemia undergoing intensive chemotherapy, two trials (38 participants) included participants with lymphoma undergoing intensive chemotherapy and two trials (180 participants) reported participants undergoing allogeneic stem cell transplantation. Men and women were equally well represented in the trials. The age range of participants included in the trials was from 16 years to 81 years. All trials took place in high-income countries. The manufacturers of the agent sponsored eight trials that were under investigation, and two trials did not report their source of funding.No trials assessed artificial platelet substitutes, fibrinogen concentrate, recombinant activated factor VII or desmopressin.Nine trials compared a TPO mimetic to placebo or standard care; seven of these used pegylated recombinant human megakaryocyte growth and differentiation factor (PEG-rHuMGDF) and two used recombinant human thrombopoietin (rhTPO).One trial compared platelet-poor plasma to platelet transfusion.We considered that all the trials included in this review were at high risk of bias and meta-analysis was not possible in seven trials due to problems with the way data were reported.We are very uncertain whether TPO mimetics reduce the number of participants with any bleeding episode (odds ratio (OR) 0.40, 95% confidence interval (CI) 0.10 to 1.62, one trial, 120 participants, very low quality evidence). We are very uncertain whether TPO mimetics reduce the risk of a life-threatening bleed after 30 days (OR 1.46, 95% CI 0.06 to 33.14, three trials, 209 participants, very low quality evidence); or after 90 days (OR 1.00, 95% CI 0.06 to 16.37, one trial, 120 participants, very low quality evidence). We are very uncertain whether TPO mimetics reduce platelet transfusion requirements after 30 days (mean difference -3.00 units, 95% CI -5.39 to -0.61, one trial, 120 participants, very low quality evidence). No deaths occurred in either group after 30 days (one trial, 120 participants, very low quality evidence). We are very uncertain whether TPO mimetics reduce all-cause mortality at 90 days (OR 1.00, 95% CI 0.24 to 4.20, one trial, 120 participants, very low quality evidence). No thromboembolic events occurred for participants treated with TPO mimetics or control at 30 days (two trials, 209 participants, very low quality evidence). We found no trials that looked at: number of days on which bleeding occurred, time from randomisation to first bleed or quality of life.One trial with 18 participants compared platelet-poor plasma transfusion with platelet transfusion. We are very uncertain whether platelet-poor plasma reduces the number of participants with any bleeding episode (OR 16.00, 95% CI 1.32 to 194.62, one trial, 18 participants, very low quality evidence). We are very uncertain whether platelet-poor plasma reduces the number of participants with severe or life-threatening bleeding (OR 4.00, 95% CI 0.56 to 28.40, one trial, 18 participants, very low quality evidence). We found no trials that looked at: number of days on which bleeding occurred, time from randomisation to first bleed, number of platelet transfusions, all-cause mortality, thromboembolic events or quality of life.

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine if platelet-poor plasma or TPO mimetics reduce bleeding for participants with haematological malignancies undergoing intensive chemotherapy or stem cell transplantation. To detect a decrease in the proportion of participants with clinically significant bleeding from 12 in 100 to 6 in 100 would require a trial containing at least 708 participants (80% power, 5% significance). The six ongoing trials will provide additional information about the TPO mimetic comparison (424 participants) but this will still be underpowered to demonstrate this level of reduction in bleeding. None of the included or ongoing trials include children. There are no completed or ongoing trials assessing artificial platelet substitutes, fibrinogen concentrate, recombinant activated factor VII or desmopressin in people undergoing intensive chemotherapy or stem cell transplantation for haematological malignancies.

Effects of Designer Hyper-Interleukin 11 (H11) on Hematopoiesis in Myelosuppressed Mice

The incidence of cancer is constantly increasing. Chemo/radiotherapy is one of major methods of treating cancer. Although adverse chemo/radiotherapy events, such as anemia and neutropenia, can be successfully cured, thrombocytopenia is still problematic. We constructed the Hyper-IL11 (H11) cytokine by linking soluble interleukin 11 receptor alpha (sIL-11Ralpha) with IL-11. In vivo H11 activity was examined in myelosuppressed mice. Myelosuppression was induced by either i) sublethal irradiation and carboplatin administration or ii) sublethal irradiation. A dose of 100 μg/kg of H11 or IL-11 was administered subcutaneously for 7 days. IL-11 and H11 accelerated leukocyte, hematocrit and platelet recovery. The effect on the attenuation of thrombocytopenia was significant. Moreover, both cytokines increased the cellularity and numbers of megakaryocyte, erythroid, and granulocyte/macrophage progenitors in the bone morrow and spleen compared with the control. Although H11 was administered at a molar concentration that was three times lower, its effects were comparable with or better than those of IL-11; thus, the activity of H11 was superior to that of IL-11. Because no toxicity was observed after the intravenous administration of H11, this hyper-cytokine may be potentially useful for treatment of thrombocytopenia and other IL-11-dependent disorders.

The Eltrombopag antitumor effect on hepatocellular carcinoma

Currently, sorafenib is the only available chemotherapeutic agent for advanced hepatocellular carcinoma (HCC), but it cannot be used in patients with liver cirrhosis (LC) or thrombocytopenia. In these cases, sorafenib is likely effective if given in combination with treatments that increase the number of platelets, such as thrombopoietin (TPO) receptor agonists. Increasing the platelet count via TPO treatment resulted in reduction of LC. Eltrombopag (EP), a TPO receptor agonist, has been reported to have antitumor effects against certain cancers, despite their lack of TPO receptor expression. We hypothesized that EP may possess antitumor activity against HCC in addition to its ability to suppress hepatic fibrosis by increasing the platelet count. In the present study, the antitumor activity of EP was examined by assessing the inhibition of cell proliferation and then ascertaining the ability of iron supplementation to reverse these effects in HepG2, Hep3B and Huh7 cells. In addition, a cell cycle assay was performed using flow cytometry, and signal transduction was evaluated by analyzing cell cycle-related protein expression. The results of EP were compared with those of the most common iron chelator, deferoxamine (DFO). The combined effect of EP and sorafenib was also assessed. The results revealed that EP exerts antitumor activity in HCC that is mediated by the modulation of intracellular iron content. EP suppressed the expression of the cell cycle-related protein cyclin D1 and elicited cell cycle arrest in the G0/G1 phase. The activity of EP was comparable to that of DFO in HCC, and EP did not compete with sorafenib at low concentrations. In conclusion, our findings suggest that EP is a good candidate chemotherapeutic agent for the treatment of HCC in patients with LC and thrombocytopenia.

Single thrombopoietin dose alleviates hematopoietic stem cells intrinsic short- and long-term ionizing radiation damage. In vivo identification of anatomical cell expansion sites

Hematopoietic stem cells (HSC) are essential for maintaining the integrity of complex and long-lived organisms. HSC, which are self-renewing, reconstitute the hematopoietic system through out life and facilitate long-term repopulation of myeloablated recipients. We have previously demonstrated that when mice are exposed to sublethal doses of ionizing radiation, subsets of the stem/progenitor compartment are affected. In this study we examine the role of thrombopoietin (TPO) on the regenerative capacities of HSC after irradiation and report the first demonstration of efficacy of a single injection of TPO shortly after in vivo exposure to ionizing radiation for reducing HSC injury and improving their functional outcome. Our results demonstrate that TPO treatment not only reduced the number of apoptotic cells but also induced a significant modification of their intrinsic characteristics. These findings were supported by transplantation assays with long-term HSC that were irradiated or unirradiated, TPO treated or untreated, in CD45.1/CD45.2 systems and by using luciferase-labeled HSC for direct bioluminescence imaging in living animals. Of particular importance, our data demonstrate the skull to be a highly favorable site for the TPO-induced emergence of hematopoietic cells after irradiation, suggesting a TPO-mediated relationship of primitive hematopoietic cells to an anatomical component. Together, the data presented here: provide novel findings about aspects of TPO action on stem cells, open new areas of investigation for therapeutic options in patients who are treated with radiation therapy, and show that early administration of a clinically suitable TPO-agonist counteracts the previously observed adverse effects.

ROS-mediated platelet generation: a microenvironment-dependent manner for megakaryocyte proliferation, differentiation, and maturation

Platelets have an important role in the body because of their manifold functions in haemostasis, thrombosis, and inflammation. Platelets are produced by megakaryocytes (MKs) that are differentiated from haematopoietic stem cells via several consecutive stages, including MK lineage commitment, MK progenitor proliferation, MK differentiation and maturation, cell apoptosis, and platelet release. During differentiation, the cells migrate from the osteoblastic niche to the vascular niche in the bone marrow, which is accompanied by reactive oxygen species (ROS)-dependent oxidation state changes in the microenvironment, suggesting that ROS can distinctly influence platelet generation and function in a microenvironment-dependent manner. The objective of this review is to reveal the role of ROS in regulating MK proliferation, differentiation, maturation, and platelet activation, thereby providing new insight into the mechanism of platelet generation, which may lead to the development of new therapeutic agents for thrombocytopenia and/or thrombosis.

Designer cytokine hyper interleukin 11 (H11) is a megakaryopoietic factor

Interleukin-11 (IL-11) displays megakaryopoietic activity. We constructed super-cytokine Hyper- IL11 (H11) by linking soluble IL-11 receptor α (sIL-11Rα) with IL-11, which directly targets β-receptor (gp130) signal transducing subunit. The effects of H11 on hematopoiesis with a focus on megakaryopoiesis were studied. The expansion, differentiation and type of colony formation of cord blood progenitor Lin-CD34+ cells were analyzed. H11 was more effective than recombinant human IL-11 (rhIL-11) in enhancement of the Lin-CD34+ cells expansion and differentiation into megakaryocytes (Mk). It induced higher expression of CD41a and CD61 antigens, resulting in a substantially larger population of CD34-CD41a(high)CD61(high) cells. H11 treatment led to increased number of small and mainly medium megakaryocyte colony formation (Mk-CFU). Moreover, it induced the formation of a small number of large colonies, which were not observed following rhIL-11 treatment. Significantly higher number of H11 derived Mk colonies released platelets-like particles (PLP). Furthermore, H11 was considerably more potent than rhIL-11 in promoting differentiation of Lin-CD43+ cells toward erythrocytes. Our results indicate that H11 is more effective than rhIL-11 in enhancing expansion of early progenitors and directing them to megakaryocyte and erythroid cells and in inducing maturation of Mk. Thus, H11 may prove beneficial for thrombocytopenia treatment and/or an ex vivo expansion of megakaryocytes.

Low or undetectable TPO receptor expression in malignant tissue and cell lines derived from breast, lung, and ovarian tumors

BACKGROUND

Numerous efficacious chemotherapy regimens may cause thrombocytopenia. Thrombopoietin receptor (TPO-R) agonists, such as eltrombopag, represent a novel approach for the treatment of chemotherapy-induced thrombocytopenia. The TPO-R MPL is expressed on megakaryocytes and megakaryocyte precursors, although little is known about its expression on other tissues.

METHODS

Breast, lung, and ovarian tumor samples were analyzed for MPL expression by microarray and/or quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and for TPO-R protein expression by immunohistochemistry (IHC). Cell line proliferation assays were used to analyze the in vitro effect of eltrombopag on breast, lung, and ovarian tumor cell proliferation. The lung carcinoma cell lines were also analyzed for TPO-R protein expression by Western blot.

RESULTS

MPL mRNA was not detectable in 118 breast tumors and was detectable at only very low levels in 48% of 29 lung tumors studied by microarray analysis. By qRT-PCR, low but detectable levels of MPL mRNA were detectable in some normal (14-43%) and malignant (3-17%) breast, lung, and ovarian tissues. A comparison of MPL to EPOR, ERBB2, and IGF1R mRNA demonstrates that MPL mRNA levels were far lower than those of EPOR and ERBB2 mRNA in the same tissues. IHC analysis showed negligible TPO-R protein expression in tumor tissues, confirming mRNA analysis. Culture of breast, lung, and ovarian carcinoma cell lines showed no increase, and in fact, showed a decrease in proliferation following incubation with eltrombopag. Western blot analyses revealed no detectable TPO-R protein expression in the lung carcinoma cell lines.

CONCLUSIONS

Multiple analyses of breast, lung, and ovarian tumor samples and/or cell lines show no evidence of MPL mRNA or TPO-R protein expression. Eltrombopag does not stimulate growth of breast, lung, or ovarian tumor cell lines at doses likely to exert their actions on megakaryocytes and megakaryocyte precursors.

Use of the novel thrombopoietin receptor-agonist romiplostim, in combination with steroids and immunoglobulins for the increase of platelets prior to splenectomy, in refractory immune thrombocytopenia: a case report

This case report describes a patient with relapsed primary immune thrombocytopenic purpura (ITP), in which splenectomy was not possible due to the persistence of a low platelet count despite treatment with corticosteroids, intravenous immunoglobulins (IVIG) and platelet transfusion treatment. As an attempt to increase platelet count prior to performing splenectomy, the thrombopoietin receptor agonist, romiplostim, was administered in combination with steroids and IVIG. A single administration of romiplostim was found to be markedly effective, allowing a rapid and notable platelet increase, required for a well tolerated splenectomy. This case confirms the potent activity of romiplostim in ITP, and indicates that patients with recurrent primary ITP who are unresponsive to conventional immunosuppressive therapy may benefit from the addition of a short course of romiplostim.

Vascular effects of glycoprotein130 ligands--part II: biomarkers and therapeutic targets

Glycoprotein130 (gp130) ligands are defined by the use of the common receptor subunit gp130 and comprise interleukin (IL)-6, oncostatin M (OSM), IL-11, leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), ciliary neurotrophic factor (CNTF), IL-27 and neuropoietin (NP). In part I of this review we addressed the pathophysiological functions of gp130 ligands with respect to the vascular wall. In part II of this review on the vascular effects of gp130 ligands we will discuss data about possible use of these molecules as biomarkers to predict development or progression of cardiovascular diseases. Furthermore, the possibility to modulate circulating levels of gp130 ligands or their tissue expression by specific antibodies, soluble gp130 protein, renin-angiotensin-aldosterone system (RASS) inhibitors, statins, agonists of peroxisome proliferator-activated receptors (PPAR), hormone replacement therapy, nonsteroidal anti-inflammatory drugs (NSAID) or lifestyle modulating strategies are presented. Recent knowledge about the application of recombinant cytokines from the gp130 cytokine family as therapeutic agents in obesity or atherosclerosis is also summarized. Thus the purpose of this review is to cover a possible usefulness of gp130 ligands as biomarkers and targets for therapy in cardiovascular pathologies.

Novel targets for platelet inhibition

Atherothrombosis often underlies coronary artery disease, stroke, and peripheral arterial disease. Antiplatelet drugs have come to the forefront of prophylactic treatment of atherothrombotic disease. Dual antiplatelet therapy of aspirin plus clopidogrel-the current standard-has benefits, but it also has limitations with regard to pharmacologic properties and adverse effects with often severe bleeding complications. For these reasons, within the last decade or so, the investigation of novel antiplatelet targets has prospered. Target identification can be the result of large-scale genomic or proteomic studies, functional genomics in animal models, the genetic analysis of patients with inherited bleeding disorders, or a combination of these techniques.

Potential use of G protein-coupled receptor-blocking monoclonal antibodies as therapeutic agents for cancers

The therapeutic use of monoclonal antibodies (mAbs) is the fastest growing area of pharmaceutical development and has enjoyed significant clinical success since approval of the first mAb drug in1984. However, despite significant effort, there are still no approved therapeutic mAbs directed against the largest and most attractive family of drug targets: G protein-coupled receptors (GPCRs). GPCRs regulate essentially all cellular processes, including those that are fundamental to cancer pathology, such as proliferation, survival/drug resistance, migration, differentiation, tissue invasion, and angiogenesis. Many different GPCR isoforms are enhanced or dysregulated in multiple tumor types, and several GPCRs have known oncogenic activity. With approximately 350 distinct GPCRs in the genome, these receptors provide a rich landscape for the design of effective, targeted therapies for cancer, a uniquely heterogeneous disease family. While the generation of selective, efficacious mAbs has been problematic for these structurally complex integral membrane proteins, progress in the development of immunotherapeutics has been made by several independent groups. This chapter provides an overview of the roles of GPCRs in cancer and describes the current state of the art of GPCR-targeted mAb drugs.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) impairs the regulation of apoptosis in megakaryocytes by activating NF-κB: a proteomic study

We previously showed that the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and its receptor VPAC1 are negative regulators of megakaryopoiesis and platelet function, but their downstream signaling pathway that inhibits this process still remained unknown. A combined proteomic, transcriptomic, and bioinformatic approach was here used to elucidate the molecular mechanisms underlying PACAP signaling via VPAC1 in megakaryocytes. Two-dimensional difference gel electrophoresis and tandem MS were applied to detect differentially expressed proteins in megakaryocytic CHRF cells stimulated with PACAP. The majority of the 120 proteins modulated by PACAP belong to the class of "cell cycle and apoptosis" proteins. The up- or down-regulated expression of some proteins was confirmed by immunoblot and immunohistochemical analysis. A meta-analysis of our data and 12 other published studies was performed to evaluate signaling pathways involved in different cellular models of PACAP response. From 2384 differentially expressed genes/proteins, 83 were modulated by PACAP in at least three independent studies and Ingenuity Pathway Analysis further identified apoptosis as the highest scored network with NF-κB as a key-player. PACAP inhibited serum depletion-induced apoptosis of CHRF cells via VPAC1 stimulation. In addition, PACAP switched on NF-κB dependent gene expression since higher nuclear levels of the active NF-κB p50/p65 heterodimer were found in CHRF cells treated with PACAP. Finally, a quantitative real time PCR apoptosis array was used to study RNA from in vitro differentiated megakaryocytes from a PACAP overexpressing patient, leading to the identification of 15 apoptotic genes with a 4-fold change in expression and Ingenuity Pathway Analysis again revealed NF-κB as the central player. In conclusion, our findings suggest that PACAP interferes with the regulation of apoptosis in megakaryocytes, probably via stimulation of the NF-κB pathway.

Thrombopoietin receptor levels in tumor cell lines and primary tumors

Thrombopoietin (TPO) receptor agonists represent a new approach for the treatment of thrombocytopenia, which may develop as a consequence of immune thrombocytopenia, chemotherapy treatment, chronic hepatitis C infection, or myelodysplastic syndromes. There are concerns that use of certain growth factors can hasten disease progression in some types of hematologic malignancies and solid tumors. In this study, expression of MPL (TPO-R) mRNA was examined in tumor cell lines, patient tumor samples (renal cell carcinoma, prostatic carcinoma, soft tissue and bony/cartilage sarcoma, colon cancer, and lymphoma), and normal tissues using microarray analysis and qRT-PCR. MPL mRNA is expressed at very low or undetectable levels compared with erythropoietin receptor (EPOR), human epidermal growth factor (ERBB2; HER2), and insulin-like growth factor-1 receptor (IGF1R) in these patient samples. These data suggest TPO-R agonists will likely preferentially stimulate proliferation and differentiation of cells of megakaryocytic lineage, potentially demonstrating their utility for correcting thrombocytopenia in clinical settings.

Non-core region modulates interleukin-11 signaling activity: generation of agonist and antagonist variants

Human interleukin-11 (hIL-11) is a pleiotropic cytokine administered to patients with low platelet counts. From a structural point of view hIL-11 belongs to the long-helix cytokine superfamily, which is characterized by a conserved core motif consisting of four α-helices. We have investigated the region of hIL-11 that does not belong to the α-helical bundle motif, and that for the purpose of brevity we have termed "non-core region." The primary sequence of the interleukin was altered at various locations within the non-core region by introducing glycosylation sites. Functional consequences of these modifications were examined in cell-based as well as biophysical assays. Overall, the data indicated that the non-core region modulates the function of hIL-11 in two ways. First, the majority of muteins displayed enhanced cell-stimulatory properties (superagonist behavior) in a glycosylation-dependent manner, suggesting that the non-core region is biologically designed to limit the full potential of hIL-11. Second, specific modification of a predicted mini α-helix led to cytokine inactivation, demonstrating that this putative structural element belongs to site III engaging a second copy of cell-receptor gp130. These findings have unveiled new and unexpected elements modulating the biological activity of hIL-11, which may be exploited to develop more versatile medications based on this important cytokine.

Zinc is not required for activity of TPO agonists acting at the c-Mpl receptor transmembrane domain

Molecules that mimic the cytokine thrombopoietin that act by an atypical mechanism of binding to a receptor transmembrane (TM) domain are widely understood to require zinc for their biological activity. We investigated potent thrombopoietin mimetics from three chemical classes including the recently registered drug Eltrombopag, which operate via this novel mechanism, to determine whether zinc is essential for inducing cell proliferation. Using addition of zinc and a potent metal chelator, we show that the existing paradigm is incorrect and the compounds exhibit excellent thrombopoietin-mimetic activity even in the presence of high concentrations of EDTA. The implications of these findings for the mechanism of action are discussed.

Eltrombopag (Promacta), a thrombopoietin receptor agonist for the treatment of thrombocytopenia: current and future considerations

Thrombocytopenia, a decreased platelet count, is a common clinical feature that may be caused by decreased platelet production or accelerated platelet removal. Accelerated platelet removal may result from various immunologic mechanisms, excessive consumption, or sequestration of platelets in the spleen. Thrombocytopenia can range from a transient, isolated finding to a severe, life-threatening condition. Eltrombopag (SB497115) is a novel, orally bioavailable, small-molecule thrombopoetin receptor agonist that induces differentiation and proliferation of megakaryocytes. Preclinical testing on healthy volunteers shows high drug bioavailability and efficacy in raising platelet counts. The 10-day treatment with eltrombopag increased platelet count up to 1.5 times. The drug is usually tolerated well and serious adverse events and discontinuation are rare. There is an unmet need for this agent, and probably eltrombopag is indeed the "drug of choice" for some limited categories of patients; however, its long-term safety profile is unknown. To evaluate the potential drug development, careful analysis of thrombocytopenia morbidity and prevalence of the applicable for treatment with eltrombopag clinical scenarios is highly warranted. Lack of vascular outcome data with regard to potential excessive activity of these next-generation novel platelets may result in increased thrombotic risks and cause worsened cardiovascular and stroke outcomes may be the major obstacle to the success of this promising agent.