Gene Summary

Gene:MPL; MPL proto-oncogene, thrombopoietin receptor
Aliases: MPLV, TPOR, C-MPL, CD110, THCYT2
Summary:In 1990 an oncogene, v-mpl, was identified from the murine myeloproliferative leukemia virus that was capable of immortalizing bone marrow hematopoietic cells from different lineages. In 1992 the human homologue, named, c-mpl, was cloned. Sequence data revealed that c-mpl encoded a protein that was homologous with members of the hematopoietic receptor superfamily. Presence of anti-sense oligodeoxynucleotides of c-mpl inhibited megakaryocyte colony formation. The ligand for c-mpl, thrombopoietin, was cloned in 1994. Thrombopoietin was shown to be the major regulator of megakaryocytopoiesis and platelet formation. The protein encoded by the c-mpl gene, CD110, is a 635 amino acid transmembrane domain, with two extracellular cytokine receptor domains and two intracellular cytokine receptor box motifs . TPO-R deficient mice were severely thrombocytopenic, emphasizing the important role of CD110 and thrombopoietin in megakaryocyte and platelet formation. Upon binding of thrombopoietin CD110 is dimerized and the JAK family of non-receptor tyrosine kinases, as well as the STAT family, the MAPK family, the adaptor protein Shc and the receptors themselves become tyrosine phosphorylated. [provided by RefSeq, Jul 2008]
Databases:OMIM, HGNC, GeneCard, Gene
Protein:thrombopoietin receptor
Source:NCBIAccessed: 06 August, 2015


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 06 August 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Thrombocythemia, Essential
  • Leukemia, Megakaryoblastic, Acute
  • Uniparental Disomy
  • Signal Transduction
  • DNA-Binding Proteins
  • Cancer Gene Expression Regulation
  • Reference Standards
  • Protein Kinase Inhibitors
  • Thrombocytosis
  • Thrombosis
  • Receptors, Cytokine
  • Base Sequence
  • Neoplasm Proteins
  • Molecular Sequence Data
  • Hematopoietic Stem Cells
  • Myeloid Leukemia
  • Trans-Activators
  • Genetic Predisposition
  • Cell Differentiation
  • Neoplastic Cell Transformation
  • src-Family Kinases
  • Mutation
  • Cell Proliferation
  • DNA Mutational Analysis
  • Leukemic Gene Expression Regulation
  • Childhood Cancer
  • Proto-Oncogene Proteins
  • JAK2
  • Adolescents
  • Primary Myelofibrosis
  • ras Proteins
  • Messenger RNA
  • Exons
  • Bone Marrow Neoplasms
  • Haematological Malignancies
  • Leukaemia
  • World Health Organization
  • Acute Myeloid Leukaemia
  • Myeloproliferative Disorders
  • Chromosome 1
Tag cloud generated 06 August, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: MPL (cancer-related)

Tefferi A, Barbui T
Polycythemia vera and essential thrombocythemia: 2015 update on diagnosis, risk-stratification and management.
Am J Hematol. 2015; 90(2):162-73 [PubMed] Related Publications
DISEASE OVERVIEW: Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms, respectively characterized by erythrocytosis and thrombocytosis. Other disease features include leukocytosis, splenomegaly, thrombosis, bleeding, microcirculatory symptoms, pruritus, and risk of leukemic or fibrotic transformation.
DIAGNOSIS: PV is defined by a JAK2 mutation, whose absence, combined with normal or increased serum erythropoietin level, makes the diagnosis unlikely. Differential diagnosis in ET includes reactive thrombocytosis, chronic myeloid leukemia, and prefibrotic myelofibrosis. Janus kinase 2 (JAK2), calreticulin (CALR), or myeloproliferative leukemia virus oncogene (MPL) mutations occur in approximately 55%, 25%, and 3% of ET patients, respectively. The same molecular markers are also present in prefibrotic myelofibrosis, which needs to be morphologically distinguished from ET. Survival and leukemic/fibrotic transformation: Median survivals are ∼14 years for PV and 20 years for ET; the corresponding values for younger patients are 24 and 33 years. Life-expectancy in ET is inferior to the control population. JAK2/CALR mutational status does not affect survival in ET. Risk factors for survival in ET and PV include advanced age, leukocytosis, and thrombosis. Leukemic transformation rates at 20 years are estimated at <10% for PV and 5% for ET; fibrotic transformation rates are slightly higher. Thrombosis risk stratification: Current risk stratification in PV and ET is designed to estimate the likelihood of recurrent thrombosis: high-risk is defined by the presence of age >60 years or presence of thrombosis history; low-risk is defined by the absence of both of these two risk factors. Recent data consider JAK2V617F and cardiovascular risk factors as additional risk factors. Presence of extreme thrombocytosis might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding.
RISK-ADAPTED THERAPY: The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. In low risk patients, this is accomplished by the use of low-dose aspirin and phlebotomy (hematocrit target <45%) in PV. In high risk (for thrombosis) patients, treatment with hydroxyurea is additionally recommended. Treatment with busulfan or interferon-α is usually effective in hydroxyurea failures and the additional value of JAK inhibitor therapy in such cases is limited. Screening for AvWS is recommended before administrating aspirin, in the presence of extreme thrombocytosis.

Bussel JB
The new thrombopoietic agenda: impact on leukemias and MDS.
Best Pract Res Clin Haematol. 2014 Sep-Dec; 27(3-4):288-92 [PubMed] Related Publications
The two generations of thrombopoietin (TPO) receptor (R) agonists have had utility in a number of hematologic conditions. However their use has often been surprisingly complex and drawbacks have been revealed in certain conditions more than in others. The first-generation megakaryocyte growth and development factor (MGDF) was discontinued due to the production of antibodies against it that cross-reacted with native TPO. Nonetheless it was tested in a wide variety of thrombocytopenic conditions and showed unequivocal efficacy in increasing the number of platelets in certain ones. As a result of lessons learned with MGDF, second-generation TPO-R agonists romiplostim and eltrombopag were initially tested and have been approved for the treatment of chronic immune thrombocytopenia (ITP), thrombocytopenia in hepatitis C, and recently aplastic anemia. These agents have had more mixed outcomes in diseases such as acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). Results of several studies will be discussed.

Tao J, Zhang X, Lancet J, et al.
Concurrence of B-lymphoblastic leukemia and myeloproliferative neoplasm with copy neutral loss of heterozygosity at chromosome 1p harboring a MPL W515S mutation.
Cancer Genet. 2014 Oct-Dec; 207(10-12):489-94 [PubMed] Related Publications
B-lymphoblastic leukemia (B-ALL) is a neoplasm of precursors committed to B-cell lineage, whereas myeloproliferative neoplasm (MPN) is a clonal proliferation derived from myeloid stem cells. Concurrent B-ALL with MPN is uncommon except in the presence of abnormalities of the PDGFRA, PDGFRB, or FGFR1 genes or the BCR-ABL1 fusion gene. Herein, we describe a rare concurrence, B-ALL with MPN without the aforementioned genetic aberrations, in a 64-year-old male patient. The patient was initially diagnosed with B-ALL with normal karyotype and responded well to aggressive chemotherapy but had sustained leukocytosis and splenomegaly. The posttreatment restaging bone marrow was free of B-ALL but remained hypercellular with myeloid predominance. Using a single nucleotide polymorphism microarray study, we identified a copy neutral loss of heterozygosity at the terminus of 1p in the bone marrow samples taken at diagnosis and again at remission, 49% and 100%, respectively. Several additional genetic abnormalities were present in the initial marrow sample but not in the remission marrow samples. Retrospective molecular studies detected a MPL W515S homozygous mutation in both the initial and remission marrows for B-ALL, at 30-40% and 80% dosage effect, respectively. In summary, we present a case of concurrent B-ALL and MPN and demonstrate a stepwise cytogenetic and molecular approach to the final diagnosis.

Prica A, Sholzberg M, Buckstein R
Safety and efficacy of thrombopoietin-receptor agonists in myelodysplastic syndromes: a systematic review and meta-analysis of randomized controlled trials.
Br J Haematol. 2014; 167(5):626-38 [PubMed] Related Publications
Thrombocytopenia is common (40-65%) and potentially serious in myelodysplastic syndromes (MDS). A systematic review was conducted to determine the safety and efficacy of adding a thrombopoietin-receptor (THPO-R) agonist to standard MDS treatment. MEDLINE, EMBASE and CENTRAL databases were searched. We included randomized controlled trials comparing a THPO-R agonist to placebo. A meta-analysis of the effects was performed. Endpoints included bleeding and platelet transfusion rates, risk of progression to acute myeloid leukaemia (AML) and mortality. Three hundred and eighty four patients from five trials were included, four using romiplostim and one using eltrombopag. Overall, the relative risk (RR) of bleeding with romiplostim versus placebo was 0·84 [95% confidence interval (CI): 0·57-1·24]. However, compared to placebo, romiplostim significantly decreased the exposure-adjusted bleeding rate (RR 0·92; 95% CI: 0·86-0·99), as well as the exposure-adjusted platelet transfusion rate (RR 0·69; 95% CI: 0·53-0·88). The RR of AML progression with romiplostim was 1·36 (95% CI: 0·54-3·40), however the outcome data were judged as higher risk of bias. Romiplostim is promising in its ability to decrease patient-important outcomes: bleeding and platelet transfusion need. Although the risk of AML progression was not increased, due to unclear risk of bias in the data, this safety concern is difficult to assess. Therefore, romiplostim cannot yet be routinely recommended. Early eltrombopag data is promising.

Langabeer SE, Haslam K, Linders J, et al.
Molecular heterogeneity of familial myeloproliferative neoplasms revealed by analysis of the commonly acquired JAK2, CALR and MPL mutations.
Fam Cancer. 2014; 13(4):659-63 [PubMed] Related Publications
The myeloproliferative neoplasms (MPN) are clonal, hematological malignancies that include polycythemia vera, essential thrombocythemia and primary myelofibrosis. While most cases of MPN are sporadic in nature, a familial pattern of inheritance is well recognised. The phenotype and status of the commonly acquired JAK2 V617F, CALR exon 9 and MPL W515L/K mutations in affected individuals from a consecutive series of ten familial MPN (FMPN) kindred are described. Affected individuals display the classical MPN phenotypes together with one kindred identified suggestive of hereditary thrombocytosis. In affected patients the JAK2 V617F mutation is the most commonly acquired followed by CALR exon nine mutations with no MPL W515L/K mutations detected. The JAK2 V617F and CALR exon 9 mutations appear to occur at approximately the same frequency in FMPN as in the sporadic forms of these diseases. The familial nature of MPN may often be overlooked and accordingly more common than previously considered. Characterisation of these FMPN kindred may allow for the investigation of molecular events that contribute to this inheritance.

Sakashita K, Kato I, Daifu T, et al.
In vitro expansion of CD34(+)CD38(-) cells under stimulation with hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia.
Leukemia. 2015; 29(3):606-14 [PubMed] Related Publications
Using serum-containing culture, we examined whether AGM-S3 stromal cells, alone or in combination with hematopoietic growth factor(s), stimulated the proliferation of CD34(+) cells from patients with juvenile myelomonocytic leukemia (JMML). AGM-S3 cells in concert with stem cell factor plus thrombopoietin increased the numbers of peripheral blood CD34(+) cells to approximately 20-fold of the input value after 2 weeks in nine JMML patients with either PTPN11 mutations or RAS mutations, who received allogeneic hematopoietic transplantation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) also augmented the proliferation of JMML CD34(+) cells on AGM-S3 cells. The expansion potential of CD34(+) cells was markedly low in four patients who achieved spontaneous hematological improvement. A large proportion of day-14-cultured CD34(+) cells were negative for CD38 and cryopreservable. Cultured JMML CD34(+)CD38(-) cells expressed CD117, CD116, c-mpl, CD123, CD90, but not CXCR4, and formed GM and erythroid colonies. Day-7-cultured CD34(+) cells from two of three JMML patients injected intrafemorally into immunodeficient mice stimulated with human GM-CSF after transplantation displayed significant hematopoietic reconstitution. The abilities of OP9 cells and MS-5 cells were one-third and one-tenth, respectively, of the value obtained with AGM-S3 cells. Our culture system may provide a useful tool for elucidating leukemogenesis and for therapeutic approaches in JMML.

Rumi E, Pietra D, Pascutto C, et al.
Clinical effect of driver mutations of JAK2, CALR, or MPL in primary myelofibrosis.
Blood. 2014; 124(7):1062-9 [PubMed] Free Access to Full Article Related Publications
We studied the impact of driver mutations of JAK2, CALR, (calreticulin gene) or MPL on clinical course, leukemic transformation, and survival of patients with primary myelofibrosis (PMF). Of the 617 subjects studied, 399 (64.7%) carried JAK2 (V617F), 140 (22.7%) had a CALR exon 9 indel, 25 (4.0%) carried an MPL (W515) mutation, and 53 (8.6%) had nonmutated JAK2, CALR, and MPL (so-called triple-negative PMF). Patients with CALR mutation had a lower risk of developing anemia, thrombocytopenia, and marked leukocytosis compared with other subtypes. They also had a lower risk of thrombosis compared with patients carrying JAK2 (V617F). At the opposite, triple-negative patients had higher incidence of leukemic transformation compared with either CALR-mutant or JAK2-mutant patients. Median overall survival was 17.7 years in CALR-mutant, 9.2 years in JAK2-mutant, 9.1 years in MPL-mutant, and 3.2 years in triple-negative patients. In multivariate analysis corrected for age, CALR-mutant patients had better overall survival than either JAK2-mutant or triple-negative patients. The impact of genetic lesions on survival was independent of current prognostic scoring systems. These observations indicate that driver mutations define distinct disease entities within PMF. Accounting for them is not only relevant to clinical decision-making, but should also be considered in designing clinical trials.

Langabeer SE, Haslam K, McMahon C
The molecular landscape of childhood myeloproliferative neoplasms.
Leuk Res. 2014; 38(8):997-8 [PubMed] Related Publications
The classical myeloproliferative neoplasms (MPN) are comparatively uncommon in children and display a degree of mutational naivety if considering the high frequency of known MPN driver events observed in the corresponding adult diseases. Whole exome sequencing has unravelled much of the underlying molecular complexity of MPN in adult patients yet less is known of the pathogenetic mechanisms when these diseases occur in childhood. It is proposed that such methodological approaches will contribute significant insights into the molecular landscape of childhood MPN that may in turn impact on understanding the pathophysiology of disease in their adult counterparts.

Cazzola M, Kralovics R
From Janus kinase 2 to calreticulin: the clinically relevant genomic landscape of myeloproliferative neoplasms.
Blood. 2014; 123(24):3714-9 [PubMed] Related Publications
Our understanding of the genetic basis of myeloproliferative neoplasms began in 2005, when the JAK2 (V617F) mutation was identified in polycythemia vera, essential thrombocythemia, and primary myelofibrosis. JAK2 exon 12 and MPL exon 10 mutations were then detected in subsets of patients, and subclonal driver mutations in other genes were found to be associated with disease progression. Recently, somatic mutations in the gene CALR, encoding calreticulin, have been found in most patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 and MPL. The JAK-STAT pathway appears to be activated in all myeloproliferative neoplasms, regardless of founding driver mutations. These latter, however, have different effects on clinical course and outcomes. Thus, evaluation of JAK2, MPL, and CALR mutation status is important not only for diagnosis but also for prognostication. These genetic data should now also be considered in designing clinical trials.

Wu Z, Zhang Y, Zhang X, et al.
A multiplex snapback primer system for the enrichment and detection of JAK2 V617F and MPL W515L/K mutations in Philadelphia-negative myeloproliferative neoplasms.
Biomed Res Int. 2014; 2014:458457 [PubMed] Free Access to Full Article Related Publications
A multiplex snapback primer system was developed for the simultaneous detection of JAK2 V617F and MPL W515L/K mutations in Philadelphia chromosome- (Ph-) negative myeloproliferative neoplasms (MPNs). The multiplex system comprises two snapback versus limiting primer sets for JAK2 and MPL mutation enrichment and detection, respectively. Linear-After exponential (LATE) PCR strategy was employed for the primer design to maximize the amplification efficiency of the system. Low ionic strength buffer and rapid PCR protocol allowed for selective amplification of the mutant alleles. Amplification products were analyzed by melting curve analysis for mutation identification. The multiplex system archived 0.1% mutation load sensitivity and <5% coefficient of variation inter-/intra-assay reproducibility. 120 clinical samples were tested by the multiplex snapback primer assay, and verified with amplification refractory system (ARMS), quantitative PCR (qPCR) and Sanger sequencing method. The multiplex system, with a favored versatility, provided the molecular diagnosis of Ph-negative MPNs with a suitable implement and simplified the genetic test process.

Bhagwat N, Koppikar P, Keller M, et al.
Improved targeting of JAK2 leads to increased therapeutic efficacy in myeloproliferative neoplasms.
Blood. 2014; 123(13):2075-83 [PubMed] Free Access to Full Article Related Publications
The discovery of JAK2/MPL mutations in patients with myeloproliferative neoplasms (MPN) led to clinical development of Janus kinase (JAK) inhibitors for treatment of MPN. These inhibitors improve constitutional symptoms and splenomegaly but do not significantly reduce mutant allele burden in patients. We recently showed that chronic exposure to JAK inhibitors results in inhibitor persistence via JAK2 transactivation and persistent JAK-signal transducer and activator of transcription signaling. We performed genetic and pharmacologic studies to determine whether improved JAK2 inhibition would show increased efficacy in MPN models and primary samples. Jak2 deletion in vivo led to profound reduction in disease burden not seen with JAK inhibitors, and deletion of Jak2 following chronic ruxolitinib therapy markedly reduced mutant allele burden. This demonstrates that JAK2 remains an essential target in MPN cells that survive in the setting of chronic JAK inhibition. Combination therapy with the heat shock protein 90 (HSP90) inhibitor PU-H71 and ruxolitinib reduced total and phospho-JAK2 and achieved more potent inhibition of downstream signaling than ruxolitinib monotherapy. Combination treatment improved blood counts, spleen weights, and reduced bone marrow fibrosis compared with ruxolitinib alone. These data suggest alternate approaches that increase JAK2 targeting, including combination JAK/HSP90 inhibitor therapy, are warranted in the clinical setting.

Rumi E, Pietra D, Ferretti V, et al.
JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes.
Blood. 2014; 123(10):1544-51 [PubMed] Free Access to Full Article Related Publications
Patients with essential thrombocythemia may carry JAK2 (V617F), an MPL substitution, or a calreticulin gene (CALR) mutation. We studied biologic and clinical features of essential thrombocythemia according to JAK2 or CALR mutation status and in relation to those of polycythemia vera. The mutant allele burden was lower in JAK2-mutated than in CALR-mutated essential thrombocythemia. Patients with JAK2 (V617F) were older, had a higher hemoglobin level and white blood cell count, and lower platelet count and serum erythropoietin than those with CALR mutation. Hematologic parameters of patients with JAK2-mutated essential thrombocythemia or polycythemia vera were related to the mutant allele burden. While no polycythemic transformation was observed in CALR-mutated patients, the cumulative risk was 29% at 15 years in those with JAK2-mutated essential thrombocythemia. There was no significant difference in myelofibrotic transformation between the 2 subtypes of essential thrombocythemia. Patients with JAK2-mutated essential thrombocythemia and those with polycythemia vera had a similar risk of thrombosis, which was twice that of patients with the CALR mutation. These observations are consistent with the notion that JAK2-mutated essential thrombocythemia and polycythemia vera represent different phenotypes of a single myeloproliferative neoplasm, whereas CALR-mutated essential thrombocythemia is a distinct disease entity.

Klampfl T, Gisslinger H, Harutyunyan AS, et al.
Somatic mutations of calreticulin in myeloproliferative neoplasms.
N Engl J Med. 2013; 369(25):2379-90 [PubMed] Related Publications
BACKGROUND: Approximately 50 to 60% of patients with essential thrombocythemia or primary myelofibrosis carry a mutation in the Janus kinase 2 gene (JAK2), and an additional 5 to 10% have activating mutations in the thrombopoietin receptor gene (MPL). So far, no specific molecular marker has been identified in the remaining 30 to 45% of patients.
METHODS: We performed whole-exome sequencing to identify somatically acquired mutations in six patients who had primary myelofibrosis without mutations in JAK2 or MPL. Resequencing of CALR, encoding calreticulin, was then performed in cohorts of patients with myeloid neoplasms.
RESULTS: Somatic insertions or deletions in exon 9 of CALR were detected in all patients who underwent whole-exome sequencing. Resequencing in 1107 samples from patients with myeloproliferative neoplasms showed that CALR mutations were absent in polycythemia vera. In essential thrombocythemia and primary myelofibrosis, CALR mutations and JAK2 and MPL mutations were mutually exclusive. Among patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 or MPL, CALR mutations were detected in 67% of those with essential thrombocythemia and 88% of those with primary myelofibrosis. A total of 36 types of insertions or deletions were identified that all cause a frameshift to the same alternative reading frame and generate a novel C-terminal peptide in the mutant calreticulin. Overexpression of the most frequent CALR deletion caused cytokine-independent growth in vitro owing to the activation of signal transducer and activator of transcription 5 (STAT5) by means of an unknown mechanism. Patients with mutated CALR had a lower risk of thrombosis and longer overall survival than patients with mutated JAK2.
CONCLUSIONS: Most patients with essential thrombocythemia or primary myelofibrosis that was not associated with a JAK2 or MPL alteration carried a somatic mutation in CALR. The clinical course in these patients was more indolent than that in patients with the JAK2 V617F mutation. (Funded by the MPN Research Foundation and Associazione Italiana per la Ricerca sul Cancro.).

Pathak S, Roth M, Verma A, Steidl U
Eltrombopag for the treatment of thrombocytopenia in patients with malignant and non-malignant hematologic disorders.
Expert Opin Drug Metab Toxicol. 2013; 9(12):1667-75 [PubMed] Related Publications
INTRODUCTION: Eltrombopag (EP) is an orally bioavailable, non-peptide, thrombopoietin receptor (TPO-R) agonist developed to stimulate platelet production. EP is a small hydrazone molecule which interacts with the transmembrane domain of TPO-R and promotes megakaryopoiesis, and a subsequent increase in platelet number. To date, multiple large clinical trials have demonstrated the ability of EP to reduce the burden of thrombocytopenia and its associated side effects in patients with chronic immune thrombocytopenia purpura and patients with hepatitis-C related thrombocytopenia. Given these promising results and the morbidity associated with thrombocytopenia in cancer patients, there is significant interest in investigating the role of EP for thrombocytopenia secondary to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML).
AREAS COVERED: In this review, the authors address the potential utility of EP for patients with AML and MDS with thrombocytopenia. The review provides an overview of the rationale for the development of EP in AML and MDS, and the mechanism(s) of action of EP. The authors focus on preclinical data describing the effectiveness of EP as both a platelet-stimulating, and an anti-leukemia agent and describe the use of EP in clinical trials.
EXPERT OPINION: EP has the potential to be an effective supportive care agent, improving platelet counts and decreasing thrombocytopenia-related morbidity, in patients with AML and MDS. Large, randomized clinical trials are needed to assess the efficacy of EP in reducing the duration and severity of thrombocytopenia, as well assess the clinical utility of EP as an anti-leukemia agent.

Oshima Y, Yuji K, Tanimoto T, et al.
Association between acute myelogenous leukemia and thrombopoietin receptor agonists in patients with immune thrombocytopenia.
Intern Med. 2013; 52(19):2193-201 [PubMed] Related Publications
OBJECTIVE: The development of myeloid malignancies is a concern when administering thrombopoietin receptor (or the myeloproliferative leukemia virus proto-oncogene product, MPL) agonists. Progression from myelodysplastic syndrome (MDS) to acute myelogenous leukemia [AML, 9 (6.12%) AML patients among 147 MDS subjects] was reported in a clinical trial. However, only one (0.15%) case of AML among 653 immune thrombocytopenic purpura (ITP) subjects was reported. Our objective was to determine whether there is currently a safety signal in the FDA files termed Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) for AML in ITP patients who receive MPL agonists.
METHODS: We conducted a case-controlled study using the FAERS as a source of case and control data. We compared demographic characteristics, such as gender, age and exposure to MPL agonists between AML patients and others among ITP subjects registered between 2002 and 2011.
RESULTS: Total of 4,821 ITP subjects were identified, including 62 AML patients. The number of patients treated with romiplostim and eltrombopag was 54 (1.74%) AML patients among 3,102 ITP subjects and nine (1.52%) AML patients among 594 ITP subjects, respectively. It should be noted that all AML patients were exposed to one or more MPL agonists. Another factor associated with AML was male gender.
CONCLUSION: We herein report an association between AML and MPL agonist use in ITP subjects. Due to various biases and the incompleteness of the FAERS data, further studies are warranted to determine whether the detected signal is a real risk. Physicians should not alter their prescribing behaviors based on this single preliminary analysis.

Gong JZ, Cook JR, Greiner TC, et al.
Laboratory practice guidelines for detecting and reporting JAK2 and MPL mutations in myeloproliferative neoplasms: a report of the Association for Molecular Pathology.
J Mol Diagn. 2013; 15(6):733-44 [PubMed] Related Publications
Recurrent mutations in JAK2 and MPL genes are genetic hallmarks of BCR-ABL1-negative myeloproliferative neoplasms. Detection of JAK2 and MPL mutations has been incorporated into routine diagnostic algorithms for these diseases. This Special Article summarizes results from a nationwide laboratory survey of JAK2 and MPL mutation analysis. Based on the current practice pattern and the literature, this Special Article provides recommendations and guidelines for laboratory practice for detection of mutations in the JAK2 and MPL genes, including clinical manifestations for prompting the mutation analysis, current and recommended methodologies for testing the mutations, and standardization for reporting the test results. This Special Article also points to future directions for genomic testing in BCR-ABL1-negative myeloproliferative neoplasms.

Zhan J, Felder B, Ellison AR, et al.
Novel anti-c-Mpl monoclonal antibodies identified multiple differentially glycosylated human c-Mpl proteins in megakaryocytic cells but not in human solid tumors.
Monoclon Antib Immunodiagn Immunother. 2013; 32(3):149-61 [PubMed] Related Publications
Thrombopoietin and its cognate receptor, c-Mpl, are the primary molecular regulators of megakaryocytopoiesis and platelet production. To date the pattern of c-Mpl expression in human solid tumors and the distribution and biochemical properties of c-Mpl proteins in hematopoietic tissues are largely unknown. We have recently developed highly specific mouse monoclonal antibodies (MAb) against human c-Mpl. In this study we used these antibodies to demonstrate the presence of full-length and truncated human c-Mpl proteins in various megakaryocytic cell types, and their absence in over 100 solid tumor cell lines and in the 12 most common primary human tumor types. Quantitative assays showed a cell context-dependent distribution of full-length and truncated c-Mpl proteins. All forms of human c-Mpl protein were found to be modified with extensive N-linked glycosylation but different degrees of sialylation and O-linked glycosylation. Of note, different variants of full-length c-Mpl protein exhibiting differential glycosylation were expressed in erythromegakaryocytic leukemic cell lines and in platelets from healthy human donors. This work provides a comprehensive analysis of human c-Mpl mRNA and protein expression on normal and malignant hematopoietic and non-hematopoietic cells and demonstrates the multiple applications of several novel anti-c-Mpl antibodies.

Gao W, Chen L, Ma Z, et al.
Isolation and phenotypic characterization of colorectal cancer stem cells with organ-specific metastatic potential.
Gastroenterology. 2013; 145(3):636-46.e5 [PubMed] Related Publications
BACKGROUND & AIMS: Migrating cancer stem cells (MCSCs) are believed to form metastases. We sought to identify markers of MCSCs from human colorectal cancers (CRCs) and determine their roles in organ-specific metastasis.
METHODS: To identify colorectal MCSCs that contribute to organ-specific metastasis, we developed a model of liver or lung metastasis using primary tumor cells from patients with CRC who had liver and lung metastases. Distinct organ-specific metastatic cells were isolated by 6 cycles of selecting for cells that formed liver and lung tumors after subcutaneous injection into mice. Microarray analysis was used to identify markers of the organ-specific MCSCs. We then measured levels of these markers in CRC cell lines and 128 CRC samples. We characterized the functional roles of these markers in organ-specific metastasis.
RESULTS: We identified CD110 and CDCP1 as cell surface markers of MCSCs from human colorectal tumors that metastasized to liver and lung. We observed a distinct pattern of CD110 and CDCP1 in a panel of primary colorectal tumor samples and their matched liver or pulmonary metastases, indicating that these proteins might serve as biomarkers of organ-specific metastasis. Functional studies showed that thrombopoietin attracts CD110(+) CSCs and increases their self-renewal to promote formation of liver metastases. CDCP1 promoted adhesion of CRC cells to the lung endothelium.
CONCLUSIONS: We isolated MCSCs from primary human CRCs and found that the CD110(+) and CDCP1(+) subpopulations mediate organ-specific metastasis. These findings might be used to aid in selection of patients for postoperative adjuvant therapy.

Sunohara M, Morikawa S, Fuse A, Sato I
Role of promoter element in c-mpl gene expression induced by TPO.
Okajimas Folia Anat Jpn. 2013; 89(4):131-5 [PubMed] Related Publications
Thrombopoietin (TPO) and its receptor, c-Mpl, play the crucial role for the development of megakaryocyte and considered to regulate megakaryocytopoiesis. Previously we reported that TPO increased the c-mpl promoter activity determined by a transient expression system using a vector containing the luciferase gene as a reporter and the expression of the c-mpl gene is modulated by transcription through a protein kinase C (PKC)-dependent pathway in the megakaryoblastic cells. In this research, to elucidate the required elements in c-mpl promoter, the promoter activity of the deletion constructs and site-directed mutagenesis were measured by a transient transfection assay system. Destruction of -77GATA in c-mpl promoter decreased the activity by 22.8%. Our study elucidated that -77GATA involved in TPO-induced c-mpl gene expression in a human megakaryoblastic cell line, CMK.

Hayes S, Mudd PN, Ouellet D, et al.
Population PK/PD modeling of eltrombopag in subjects with advanced solid tumors with chemotherapy-induced thrombocytopenia.
Cancer Chemother Pharmacol. 2013; 71(6):1507-20 [PubMed] Related Publications
PURPOSE: Eltrombopag, a thrombopoietin receptor agonist, is being evaluated for the treatment of chemotherapy-induced thrombocytopenia. Due to the delay in platelet response after the administration of eltrombopag or chemotherapy, a modeling and simulation approach was used to optimize the eltrombopag dosing regimen.
METHODS: Pharmacokinetic (PK) data from 2 studies in healthy subjects and PK and platelet data from a Phase II study in subjects with cancer receiving carboplatin/paclitaxel (where eltrombopag was given 10 days after chemotherapy) were used to develop a nonlinear mixed-effects PK/PD model. Alternative eltrombopag dosing regimens were then simulated.
RESULTS: The PK model was a linear two-compartment model with first-order absorption. Being Asian, female, and >50 years of age were associated with higher eltrombopag exposure. The time course of platelet counts was described by a four-compartment transit model. Carboplatin inhibited platelet precursor production linearly with dose, with increased effect with each cycle of chemotherapy. Eltrombopag stimulated platelet precursor production, proportional to plasma eltrombopag concentration, and stimulation (slope of the concentration effect) was attenuated with each cycle of chemotherapy.
CONCLUSIONS: Simulations indicated that eltrombopag administered 5 days before and 5 days after chemotherapy minimizes the decrease and fluctuations in platelet counts relative to other evaluated dosing regimens.

Sugita M, Kalota A, Gewirtz AM, Carroll M
Eltrombopag inhibition of acute myeloid leukemia cell survival does not depend on c-Mpl expression.
Leukemia. 2013; 27(5):1207-10 [PubMed] Free Access to Full Article Related Publications

Saleh MN, Bussel JB, Cheng G, et al.
Safety and efficacy of eltrombopag for treatment of chronic immune thrombocytopenia: results of the long-term, open-label EXTEND study.
Blood. 2013; 121(3):537-45 [PubMed] Related Publications
Patients with chronic immune thrombocytopenia may have bleeding resulting from low platelet counts. Eltrombopag increases and maintains hemostatic platelet counts; however, to date, outcome has been reported only for treatment lasting ≤ 6 months. This interim analysis of the ongoing open-label EXTEND (Eltrombopag eXTENded Dosing) study evaluates the safety and efficacy of eltrombopag in 299 patients treated up to 3 years. Splenectomized and nonsplenectomized patients achieved platelets ≥ 50 000/μL at least once (80% and 88%, respectively). Platelets ≥ 50 000/μL and 2 × baseline were maintained for a median of 73 of 104 and 109 of 156 cumulative study weeks, respectively. Bleeding symptoms (World Health Organization Grades 1-4) decreased from 56% of patients at baseline to 20% at 2 years and 11% at 3 years. One hundred (33%) patients were receiving concomitant treatments at study entry, 69 of whom attempted to reduce them; 65% (45 of 69) had a sustained reduction or permanently stopped ≥ 1 concomitant treatment. Thirty-eight patients (13%) experienced ≥ 1 adverse events leading to study withdrawal, including patients meeting protocol-defined withdrawal criteria (11 [4%] thromboembolic events, 5 [2%] exceeding liver enzyme thresholds). No new or increased incidence of safety issues was identified. Long-term treatment with eltrombopag was generally safe, well tolerated, and effective in maintaining platelet counts in the desired range.

Yu P, Qiu SW, Rao Q, et al.
[Expression of c-MPL in leukemic stem cells from acute myeloid leukemia patients].
Zhongguo Shi Yan Xue Ye Xue Za Zhi. 2012; 20(5):1052-5 [PubMed] Related Publications
This study was aimed to investigate the expression of c-MPL in acute myeloid leukemia (AML) and the correlation of the c-MPL expression with CD34 and CD38, so as to define the expression of c-MPL in leukemic stem cells. The expression levels of CD34, CD38 and c-MPL were detected by flow cytometry in bone marrow cells from 29 newly diagnosed AML patients. The relationship of c-MPL positive cell ratio with clinical parameters and correlation of c-MPL with CD34 and CD38 expression in AML patients were analyzed. The results showed that expression level of c-MPL in AML patients was significantly higher than that of normal controls (P < 0.05), and the expression level of c-MPL did not correlate with age, sex, white blood cell count, AML1-ETO fusion gene and remission after chemotherapy, but the expression of c-MPL in M2 and M5 patients was higher than that of normal control (P < 0.05). Expression of c-MPL in CD34 positive AML patients was obviously higher than that in CD34 negative AML patients (P < 0.01). c-MPL was significantly higher expressed in CD34(+) cells than that in CD34(-) cells (P < 0.001), while c-MPL expression was not significantly different between CD34(+)CD38(-) and CD34(+)CD38(-) cell groups. Positive correlation between c-MPL and CD34 expression was observed (r = 0.380, P = 0.042). It is concluded that expression of c-MPL is higher in AML patients, and positively correlates with the expression level of CD34. The c-MPL expresses in leukemic stem cells.

Rancea M, Skoetz N, Monsef I, et al.
Fourteenth biannual report of the Cochrane Haematological Malignancies Group--focus on autologous stem cell transplantation in hematological malignancies.
J Natl Cancer Inst. 2012; 104(14):NP [PubMed] Related Publications

Pulikkan JA, Madera D, Xue L, et al.
Thrombopoietin/MPL participates in initiating and maintaining RUNX1-ETO acute myeloid leukemia via PI3K/AKT signaling.
Blood. 2012; 120(4):868-79 [PubMed] Free Access to Full Article Related Publications
Oncogenic mutations in components of cytokine signaling pathways elicit ligand-independent activation of downstream signaling, enhancing proliferation and survival in acute myeloid leukemia (AML). The myeloproliferative leukemia virus oncogene, MPL, a homodimeric receptor activated by thrombopoietin (THPO), is mutated in myeloproliferative disorders but rarely in AML. Here we show that wild-type MPL expression is increased in a fraction of human AML samples expressing RUNX1-ETO, a fusion protein created by chromosome translocation t(8;21), and that up-regulation of Mpl expression in mice induces AML when coexpressed with RUNX1-ETO. The leukemic cells are sensitive to THPO, activating survival and proliferative responses. Mpl expression is not regulated by RUNX1-ETO in mouse hematopoietic progenitors or leukemic cells. Moreover, we find that activation of PI3K/AKT but not ERK/MEK pathway is a critical mediator of the MPL-directed antiapoptotic function in leukemic cells. Hence, this study provides evidence that up-regulation of wild-type MPL levels promotes leukemia development and maintenance through activation of the PI3K/AKT axis, and suggests that inhibitors of this axis could be effective for treatment of MPL-positive AML.

Stockklausner C, Echner N, Klotter AC, et al.
Hereditary thrombocythemia caused by a thrombopoietin (THPO) gain-of-function mutation associated with multiple myeloma and congenital limb defects.
Ann Hematol. 2012; 91(7):1129-33 [PubMed] Related Publications
Hereditary thrombocythemia (HT) has been described as a rare benign disorder caused by mutations in the thrombopoietin (THPO) or the c-Mpl receptor genes. Here we report two families with HT resulting from a THPO c.13+1 G>C mutation in the splice donor of intron 3. In one family there were coexisting distal limb defects, whereas in the other one member developed early-onset multiple myeloma. These observations, together with previously reported patients, suggest that THPO gain of function may dysregulate the hemangioblast and disturb vasculogenesis and hematopoietic development. Overstimulation of the THPO pathway might therefore predispose to clonal hematopoietic disease and to congenital abnormalities.

Chou FS, Griesinger A, Wunderlich M, et al.
The thrombopoietin/MPL/Bcl-xL pathway is essential for survival and self-renewal in human preleukemia induced by AML1-ETO.
Blood. 2012; 120(4):709-19 [PubMed] Free Access to Full Article Related Publications
AML1-ETO (AE) is a fusion product of translocation (8;21) that accounts for 40% of M2 type acute myeloid leukemia (AML). In addition to its role in promoting preleukemic hematopoietic cell self-renewal, AE represses DNA repair genes, which leads to DNA damage and increased mutation frequency. Although this latter function may promote leukemogenesis, concurrent p53 activation also leads to an increased baseline apoptotic rate. It is unclear how AE expression is able to counterbalance this intrinsic apoptotic conditioning by p53 to promote survival and self-renewal. In this report, we show that Bcl-xL is up-regulated in AE cells and plays an essential role in their survival and self-renewal. Further investigation revealed that Bcl-xL expression is regulated by thrombopoietin (THPO)/MPL-signaling induced by AE expression. THPO/MPL-signaling also controls cell cycle reentry and mediates AE-induced self-renewal. Analysis of primary AML patient samples revealed a correlation between MPL and Bcl-xL expression specifically in t(8;21) blasts. Taken together, we propose that survival signaling through Bcl-xL is a critical and intrinsic component of a broader self-renewal signaling pathway downstream of AML1-ETO-induced MPL.

Gudbrandsdottir S, Frederiksen H, Hasselbalch H
Thrombopoietin-receptor agonists in haematological disorders: the Danish experience.
Platelets. 2012; 23(6):423-9 [PubMed] Related Publications
The objective of this study was to investigate the use of thrombopoietin-receptor agonists (TPO-ra) in patients with refractory primary immune thrombocytopenia (ITP) as well as off-label use of TPO-ra in Danish haematology departments. Hospital medical records from 32 of the 39 patients having received TPO-ra from 2009 to 1 May 2011 were available for data collection and included in the study. Of these patients, 15 received TPO-ra for refractory primary ITP, 7 for secondary ITP (chronic lymphatic leukaemia, systemic lupus erythematosus, Evans syndrome, human immunodeficiency virus and celiac disease) and 10 were treated for non-ITP (chemotherapy-induced, acute myeloid leukaemia, myelodysplastic syndrome, hereditary spherocytosis and suspected chemically induced thrombocytopenia). Initial response to TPO-ra defined as platelet counts >30 × 10(9)/l after 4 weeks of treatment was found in 59% of primary ITP patients, 57% of patients with secondary ITP and 40% of patients with non-ITP. There were four deaths in the cohort, three of which were related to pre-existing medical conditions. Otherwise adverse effects were in general mild. This Danish retrospective registration study has demonstrated that in the off-protocol setting, the use of TPO-ra is associated with response rates largely similar to those seen in previous protocol-monitored studies and no new adverse events were reported.

Rumi E, Harutyunyan A, Elena C, et al.
Identification of genomic aberrations associated with disease transformation by means of high-resolution SNP array analysis in patients with myeloproliferative neoplasm.
Am J Hematol. 2011; 86(12):974-9 [PubMed] Related Publications
Myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). These disorders may undergo phenotypic shifts, and may specifically evolve into secondary myelofibrosis (MF) or acute myeloid leukemia (AML). We studied genomic changes associated with these transformations in 29 patients who had serial samples collected in different phases of disease. Genomic DNA from granulocytes, i.e., the myeloproliferative genome, was processed and hybridized to genome-wide human SNP 6.0 arrays. Most patients in chronic phase had chromosomal regions with uniparental disomy (UPD) and/or copy number changes. Disease progression to secondary MF or AML was associated with the acquisition of additional chromosomal aberrations in granulocytes (P = 0.002). A close relationship was observed between aberrations of chromosome 9p (UPD and/or gain) and progression from PV to post-PV MF (P = 0.002). The acquisition of one or more aberrations involving chromosome 5, 7, or 17p was specifically associated with progression to AML (OR 5.9, 95% CI 1.2-27.7, P = 0.006), and significantly affected overall survival (HR 18, 95% CI 1.9-164, P = 0.01). These observations indicate that disease progression from chronic-phase MPN to secondary MF or AML is associated with specific chromosomal aberrations that can be detected by means of high-resolution SNP array analysis of granulocyte DNA.

Tefferi A, Jimma T, Sulai NH, et al.
IDH mutations in primary myelofibrosis predict leukemic transformation and shortened survival: clinical evidence for leukemogenic collaboration with JAK2V617F.
Leukemia. 2012; 26(3):475-80 [PubMed] Free Access to Full Article Related Publications
Isocitrate dehydrogenase (IDH) mutations are frequent in blast-phase myeloproliferative neoplasms and might therefore contribute to leukemic transformation. We examined this possibility in 301 consecutive patients with chronic-phase primary myelofibrosis (PMF). The mutant IDH was detected in 12 patients (4%): 7 IDH2 (5 R140Q, 1 R140W and 1 R172G) and 5 IDH1 (3 R132S and 2 R132C). In all, 6 (50%) of the 12 IDH-mutated patients also expressed JAK2V617F. Overall, 18 (6%) patients displayed only MPL and 164 (54.3%) only JAK2 mutations. Multivariable analysis that accounted for conventional risk factors disclosed inferior overall survival (OS; P=0.03) and leukemia-free survival (LFS; P=0.003) in IDH-mutated patients: OS hazard ratio (HR) was 0.39 (95% confidence interval (95% CI) 0.2-0.75), 0.50 (95% CI 0.27-0.95) and 0.53 (95% CI 0.23-1.2) for patients with no, JAK2 or MPL mutations, respectively. Further analysis disclosed a more pronounced effect for the mutant IDH on OS and LFS in the presence (P=0.0002 and P<0.0001, respectively) as opposed to the absence (P=0.34 and P=0.64) of concomitant JAK2V617F. Analysis of paired samples obtained during chronic- and blast-phase disease revealed the presence of both IDH and JAK2 mutations at both time points. Our observations suggest that IDH mutations in PMF are independent predictors of leukemic transformation and raise the possibility of leukemogenic collaboration with JAK2V617F.

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