Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1

Whole-blood transcriptional profiling of interferon-inducible genes identifies highly upregulated IFI27 in primary myelofibrosis

Gene expression profiling studies have unraveled deregulation of several genes that might be of pathogenetic importance for the development and phenotype of the Philadelphia-negative chronic myeloproliferative neoplasms. In the context of interferon-alpha2 as a promising therapeutic agent, we focused upon the transcriptional profiling of interferon-associated genes in patients with essential thrombocythemia (ET) (n = 19), polycythemia vera (PV) (n = 41), and primary myelofibrosis (PMF) (n = 9). Using whole-blood transcriptional profiling and accordingly obtaining an integrated signature of genes expressed in several immune cells (granulocytes, monocytes, B cells, T cells, platelets), we have identified a number of interferon-associated genes to be significantly deregulated but with a highly significant deregulation of interferon-inducible gene 27 (IFI27) (ET, PV, and PMF, fold change 8, 16, and 30, respectively). The striking deregulation of IFI genes may reflect a hyperstimulated but insufficient immune system being most enhanced in patients with advanced myelofibrosis, in whom the IFI27 gene displayed an exceedingly high expression. The interferon signature may reflect primary myelofibrosis as the burn-out phase of chronic inflammation which ultimately elicits clonal evolution and expansion owing to an exaggerated but incompetent antitumor immune response. Finally, IFI27 may be a novel biomarker of disease activity and tumor burden in patients with CMPNs.

Ten-Eleven-Translocation 2 (TET2) negatively regulates homeostasis and differentiation of hematopoietic stem cells in mice

The Ten-Eleven-Translocation 2 (TET2) gene encodes a member of TET family enzymes that alters the epigenetic status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Somatic loss-of-function mutations of TET2 are frequently observed in patients with diverse myeloid malignancies, including myelodysplastic syndromes, myeloproliferative neoplasms, and chronic myelomonocytic leukemia. By analyzing mice with targeted disruption of the Tet2 catalytic domain, we show here that Tet2 is a critical regulator of self-renewal and differentiation of hematopoietic stem cells (HSCs). Tet2 deficiency led to decreased genomic levels of 5hmC and augmented the size of the hematopoietic stem/progenitor cell pool in a cell-autonomous manner. In competitive transplantation assays, Tet2-deficient HSCs were capable of multilineage reconstitution and possessed a competitive advantage over wild-type HSCs, resulting in enhanced hematopoiesis into both lymphoid and myeloid lineages. In vitro, Tet2 deficiency delayed HSC differentiation and skewed development toward the monocyte/macrophage lineage. Our data indicate that Tet2 has a critical role in regulating the expansion and function of HSCs, presumably by controlling 5hmC levels at genes important for the self-renewal, proliferation, and differentiation of HSCs.

New mutations and pathogenesis of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clonal disorders characterized by excessive production of mature blood cells. In the majority of classic MPN—polycythemia vera, essential thrombocythemia, and primitive myelofibrosis—driver oncogenic mutations affecting Janus kinase 2 (JAK2) or MPL lead to constitutive activation of cytokine-regulated intracellular signaling pathways. LNK, c-CBL, or SOCSs (all negative regulators of signaling pathways), although infrequently targeted, may either drive the disease or synergize with JAK2 and MPL mutations. IZF1 deletions or TP53 mutations are mainly found at transformation phases and are present at greater frequency than in de novo acute myeloid leukemias. Loss-of-function mutations in 3 genes involved in epigenetic regulation, TET2, ASXL1, and EZH2, may be early events preceding JAK2V617F but may also occur late during disease progression. They are more frequently observed in PMF than PV and ET and are also present in other types of malignant myeloid diseases. A likely hypothesis is that they facilitate clonal selection, allowing the dominance of the JAK2V617F subclone during the chronic phase and, together with cooperating mutations, promote blast crisis. Their precise roles in hematopoiesis and in the pathogenesis of MPN, as well as their prognostic impact and potential as a therapeutic target, are currently under investigation.

Decreased TET2 gene expression during chronic myeloid leukemia progression

Recently it has been demonstrated that ten-eleven-translocation-2 (TET2) gene alterations may represent a crucial event in the pathogenesis of various myeloid malignancies. To date, the loss of TET2 function has been solely ascribed to mutations in the gene coding region. In this study, we report a chronic myeloid leukemia (CML) case showing a TET2 single copy partial deletion associated to a t(4;6;11) rearrangement, appearing during the progression of the disease and responsible for a decreased TET2 gene expression. A putative role for TET2 haploinsufficiency in this patient's CML progression is discussed.

JAK inhibitors in myeloproliferative neoplasms: rationale, current data and perspective

JAK-STAT is an appealing but also problematic drug target in BCR-ABL1-negative myeloproliferative neoplasms (MPN) - it is appealing because the majority of patients with MPN harbor gain-of-function JAK2 or MPL mutations - it is problematic because currently available JAK inhibitors do not distinguish between oncogenic and physiologic JAK-STAT activation. Furthermore, JAK-STAT-relevant mutations in MPN do not always constitute the predominant or ancestral mutant clone. Such complexities undermine the value of JAK-STAT as a robust drug target in MPN and partly explain the hitherto lack of histologic or molecular remissions associated with currently available JAK inhibitors. Most of these drugs were, however, effective in alleviating constitutional symptoms and reducing spleen size; the mechanism of action in this instance includes drug-induced down-regulation of inflammatory cytokine activity. In addition, non-specific myelosuppression contributes to both their salutary and detrimental effects on peripheral blood count. Non-hematologic side effects include gastrointestinal disturbances, asymptomatic elevation of liver and pancreatic enzymes, peripheral neuropathy and hyperacute relapse of symptoms during treatment interruption. It is our impression that many more JAK inhibitors need to be evaluated in order to identify the best-in-class in terms of efficacy, toxicity and suitability for future combination treatment programs.

Isocitrate dehydrogenase mutations in diffuse gliomas: clinical and aetiological implications

The discovery of isocitrate dehydrogenase (IDH) mutations in gliomas is one example of the large impact that next-generation sequencing is having on the understanding of tumour biology and human disease in general. IDH mutations are early and common events in the development of astrocytomas, oligodendrogliomas and oligoastrocytomas. IDH mutations are also found in some myeloid malignancies and soft tissue tumours, but are rare in other malignancies. IDH mutation detection can be incorporated into routine pathology practice via immunohistochemistry and/or standard sequencing techniques and has great diagnostic value. An emerging theme is that IDH mutation status in gliomas is of great prognostic relevance, and there are proposals to include IDH mutation status in the next iteration of the WHO classification of gliomas. The mechanisms of action(s) of mutant IDH are not fully understood, but the understanding is progressing rapidly, and may provide a mechanism to link diverse proneoplastic processes such as oxidative damage and epigenetic dysregulation. There are exciting prospects of novel therapies for glioma patients emerging from the elucidation of these mechanisms. Given the diagnostic and prognostic implications of IDH mutation, and the potential for new therapies, all gliomas should be assessed for IDH mutation status in the future.

Tet2 loss leads to increased hematopoietic stem cell self-renewal and myeloid transformation

Somatic loss-of-function mutations in the ten-eleven translocation 2 (TET2) gene occur in a significant proportion of patients with myeloid malignancies. Although there are extensive genetic data implicating TET2 mutations in myeloid transformation, the consequences of Tet2 loss in hematopoietic development have not been delineated. We report here an animal model of conditional Tet2 loss in the hematopoietic compartment that leads to increased stem cell self-renewal in vivo as assessed by competitive transplant assays. Tet2 loss leads to a progressive enlargement of the hematopoietic stem cell compartment and eventual myeloproliferation in vivo, including splenomegaly, monocytosis, and extramedullary hematopoiesis. In addition, Tet2(+/-) mice also displayed increased stem cell self-renewal and extramedullary hematopoiesis, suggesting that Tet2 haploinsufficiency contributes to hematopoietic transformation in vivo.

Safety and efficacy of everolimus, a mTOR inhibitor, as single agent in a phase 1/2 study in patients with myelofibrosis

In addition to dysregulated JAK/STAT signaling, activation of the AKT/mTOR pathway occurs in myelofibrosis, a myeloproliferative neoplasm with no approved therapies. We conducted a phase 1/2 study with everolimus, an mTOR inhibitor, in 39 high- or intermediate-risk primary or postpolycythemia vera/postessential thrombocythemia myelofibrosis subjects. Responses were evaluated in 30 patients of phase 2. No dose-limiting toxicity was observed in phase 1 up to 10 mg/d. When this dose was used in phase 2, grade ≥ 3 toxicities were infrequent; the commonest toxicity was grade 1-2 stomatitis. Rapid and sustained splenomegaly reduction of > 50% and > 30% occurred in 20% and 44% of subjects, respectively. A total of 69% and 80% experienced complete resolution of systemic symptoms and pruritus. Response in leukocytosis, anemia, and thrombocytosis occurred in 15%-25%. Clinical responses were not associated with reduced JAK2V617F burden, circulating CD34(+) cells, or cytokine levels, whereas CCDN1 mRNA and phospho-p70S6K level, known targets of mTOR, and WT1 mRNA were identified as possible biomarkers associated with response. Response rate was 60% when European Network for Myelofibrosis criteria were used (8 major, 7 moderate, 3 minor responses) or 23% when IWG-MRT criteria (1 partial response, 6 clinical improvements) were used. These results provide proof-of-concept that targeting mTOR pathway in myelofibrosis may be clinically relevant.

Uses and abuses of JAK2 and MPL mutation tests in myeloproliferative neoplasms a paper from the 2010 William Beaumont hospital symposium on molecular pathology

JAK2V617F is sufficiently prevalent in BCR-ABL1-negative myeloproliferative neoplasms (MPNs) to be useful as a clonal marker. JAK2V617F mutation screening is indicated for the evaluation of erythrocytosis, thrombocytosis, splanchnic vein thrombosis, and otherwise unexplained BCR-ABL1-negative granulocytosis. However, the mutation does not provide additional value in the presence of unequivocal morphologic diagnosis, and its presence does not necessarily distinguish one MPN from another or provide useful prognostic information. In general, quantitative cell-based JAK2V617F mutation assays are preferred because the additional information obtained on mutant allele burden enhances diagnostic certainty and facilitates monitoring of response to treatment. JAK2 exon 12 mutation screening is indicated only in the presence of JAK2V617F-negative erythrocytosis that is associated with a subnormal serum erythropoietin level. MPL mutations are neither frequent nor specific enough to warrant their routine use for MPN diagnosis, but they may be useful in resolving specific diagnostic problems. The practice of en bloc screening for JAK2V617F, JAK2 exon 12, and MPL mutations is scientifically irrational and economically irresponsible.

Sensitive detection and quantification of the JAK2V617F allele by real-time PCR blocking wild-type amplification by using a peptide nucleic acid oligonucleotide

A single G-to-T missense mutation in the gene for the JAK2 tyrosine kinase, leading to a V617F amino acid substitution, is commonly found in several myeloproliferative neoplasms. Reliable quantification of this mutant allele is of increasing clinical and therapeutic interest in predicting and diagnosing this group of neoplasms. Because JAK2V617F is somatically acquired and may be followed by loss of heterozygosity, the percentage of mutant versus wild-type DNA in blood can vary between 0% and almost 100%. Therefore, we developed a real-time PCR assay for detection and quantification of the low-to-high range of the JAK2V617F allele burden. To allow the assay to meet these criteria, amplification of the wild-type JAK2 was blocked with a peptide nucleic acid oligonucleotide. JAK2V617F patient DNA diluted in JAK2 wild-type DNA could be amplified linearly from 0.05% to 100%, with acceptable reproducibility of quantification. The sensitivity of the assay was 0.05% (n = 3 of 3). In 9 of 100 healthy blood donors, a weak positive/background signal was observed in DNA isolated from blood, corresponding to approximately 0.01% JAK2V617F allele. In one healthy individual, we observed this signal in duplicate. The clinical relevance of this finding is not clear. By inhibiting amplification of the wild-type allele, we developed a sensitive and linear real-time PCR assay to detect and quantify JAK2V617F.

What is the role of JAK2(V617F) mutation in leukemic transformation of myeloproliferative neoplasms?

BACKGROUND AND OBJECTIVES

The role of the Janus kinase 2 V617F (JAK2(V617F)) mutation in the pathogenesis of the various BCR-ABL1-negative myeloproliferative neoplasms (MPNs) remains unclear. Its significance in leukemic transformation is a matter of even greater controversy. The aim of this study was to evaluate both the JAK2(V617F) mutational status of the rare cases in which blast crisis occurred in our institution and the response after intensive treatment.

MATERIALS AND METHODS

Between 1999 and 2009, 778 patients received diagnoses of BCR-ABL1-negative MPNs in our center (395 polycythemia vera, 329 essential thrombocythemia, and 45 primary myelofibrosis cases, as well as 9 MPN cases not otherwise classifiable). Of these patients, 7 developed leukemic transformation. The genotyping of the JAK2(V617F) mutation was performed by the amplification-refractory mutation system.

RESULTS

Six of the 7 patients were tested for JAK2(V617F) in the chronic phase of their disease, and 3 of these patients were positive for JAK2(V617F). These patients, 2 with polycythemia vera and 1 with essential thrombocythemia, also harbored JAK2(V617F) in the heterozygous state during blast crisis and even after intensive treatment in one of these patients. The other cases that evolved to blast crisis did not harbor the JAK2(V617F) mutation before and after transformation. All 7 patients died despite conventional or supportive treatment.

CONCLUSIONS

The transformation of MPNs into acute leukemia is by itself a very rare phenomenon, and so is the persistence of the JAK2(V617F) mutation after blast crisis. In our series, all JAK2(V617F)-positive patients remained positive for this mutation after leukemic transformation, although in the heterozygous state, suggesting that JAK2(V617F) is not essential for transformation in these cases. The fact that all JAK2(V617F)-negative cases remained negative after blast crisis reinforces the theory that other molecular event(s) may play a role in the clonal heterogeneity of MPNs. Owing to the poor outcome of acute myeloid leukemia secondary to MPN, patients should be included in clinical trials of the novel JAK2 inhibitors.

Regulator of myeloid differentiation and function: The secret life of Ikaros

Ikaros (also known as Lyf-1) was initially described as a lymphoid-specific transcription factor. Although Ikaros has been shown to regulate hematopoietic stem cell renewal, as well as the development and function of cells from multiple hematopoietic lineages, including the myeloid lineage, Ikaros has primarily been studied in context of lymphoid development and malignancy. This review focuses on the role of Ikaros in myeloid cells. We address the importance of post-transcriptional regulation of Ikaros function; the emerging role of Ikaros in myeloid malignancy; Ikaros as a regulator of myeloid differentiation and function; and the selective expression of Ikaros isoform-x in cells with myeloid potential. We highlight the challenges of dissecting Ikaros function in lineage commitment decisions among lymphoid-myeloid progenitors that have emerged as a major myeloid differentiation pathway in recent studies, which leads to reconstruction of the traditional map of murine and human hematopoiesis.

Primary myelofibrosis with or without mutant MPL: comparison of survival and clinical features involving 603 patients

MPL and JAK2V617F mutation analysis was performed in 603 patients with primary myelofibrosis (PMF) seen at the Mayo Clinic, USA (n=329) or University of Florence, Italy (n=274). Mutant MPL was detected in 49 (8.1%) patients and JAK2V617F in 350 (58%); 4 patients showed both mutations. MPLW515L/K was the commonest mutation; 2 patients showed novel mutations (L513ins and Q516-P518insAAAA). The US and Italy patient cohorts were separately analyzed for comparison of survival and clinical features between MPL-mutated, JAK2-mutated and JAK2/MPL-unmutated cases. JAK2/MPL-unmutated patients were significantly younger than their JAK2-mutated counterparts, in both patient cohorts (P<0.01). In the Florence only cohort, the presence of mutant MPL was associated with older age (P<0.01) and constitutional symptoms (P=0.04) and JAK2V617F with higher hemoglobin (P<0.01) and leukocyte (P=0.03) count; neither patient cohort showed significant associations with platelet count, hemoglobin <10 g/dl, abnormal/unfavorable karyotype, spleen size or prognostic score distribution. To date, 240 deaths and 79 leukemic transformations have been documented among all 603 study patients. Multivariable analysis disclosed no significant difference in overall or leukemia-free survival between the three molecular subgroups. We conclude that the presence of mutant MPL has narrow and inconsistent phenotypic effect in PMF and does not influence overall or leukemia-free survival.

Myeloproliferative neoplasms: new translational therapies

The myeloproliferative neoplasms represent a diverse group of hematologic malignancies that have been the subject of intense investigation over the last decade. Although clinical trials of the much anticipated small molecule inhibitors of Janus kinase 2 have shown that these experimental agents are successful in palliating many of the symptoms associated with the myeloproliferative neoplasms, they have not been reported to affect the disease initiating hematopoietic stem cell population or to alter the natural history of these disorders. Investigators remain optimistic that new information about the genetic and cellular origins gained from the efforts of numerous laboratories will ultimately translate in to the identification of new drug targets and more effective therapies. We hypothesize that ultimately, the use of combinations of drugs including chromatin modifying agents, immunomodulatory agents, anti-apoptotic agents, cellular therapies and monoclonal antibodies will be required to effectively treat patients with myeloproliferative neoplasms.

3'UTR-truncated Hmga2 cDNA causes MPN-like hematopoiesis by conferring a clonal growth advantage at the level of HSC in mice

Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors, including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs), and recently in hematopoietic cell clones resulting from gene therapy procedures. In nearly all these cases overexpression is because of deletions or translocations that remove the 3' untranslated region (UTR) which contains binding sites for the regulatory micro RNA let-7. We were therefore interested in the effect of HMGA2 overexpression in hematopoietic tissues in transgenic mice (ΔHmga2 mice) carrying a 3'UTR-truncated Hmga2 cDNA. ΔHmga2 mice expressed increased levels of HMGA2 protein in various tissues including hematopoietic cells and showed proliferative hematopoiesis with increased numbers in all lineages of peripheral blood cells, hypercellular bone marrow (BM), splenomegaly with extramedullary erythropoiesis and erythropoietin-independent erythroid colony formation. ΔHmga2-derived BM cells had a growth advantage over wild-type cells in competitive repopulation and serial transplantation experiments. Thus overexpression of HMGA2 leads to proliferative hematopoiesis with clonal expansion at the stem cell and progenitor levels and may account for the clonal expansion in PNH and MPNs and in gene therapy patients after vector insertion disrupts the HMGA2 locus.

Recurring mutations in myeloproliferative neoplasms alter epigenetic regulation of gene expression

The prevalence of activating JAK2 mutations in myeloproliferative neoplasms (MPNs) suggests that aberrant gene expression due to deregulated signaling of the JAK2/STAT pathway plays an important role in the etiology of these diseases. While likely true, recent work has uncovered some fascinating new insights into both the function of mutationally-activated JAK2 as well as other mutated gene products in MPNs, and how these mutations may affect gene expression. In addition to being a cytoplasmic tyrosine kinase that relays signals from cytokine receptors, activated JAK2 can also function in the nucleus where it phosphorylates histones and deregulates binding of the transcriptional repressor HP1α. In addition, MPN-associated JAK2 mutants phosphorylate PRMT5 and inhibit its histone methyltransferase activity. Thus, in addition to the classical JAK/STAT pathway, JAK2 activating mutations in MPNs may deregulate gene expression by altering epigenetic mechanisms. Studies aimed at identifying the biochemical ramifications of other recurring MPN mutations also suggest deregulated epigenetic modifications may be important in MPN formation. Mutant TET2, as well as IDH1/2, impairs the hydroxylation of methylcytosine, thus affecting DNA methylation. Likewise, mutations in EZH2, a histone methyl transferase, ASXL1, which functions in chromatin modifier complexes, and the DNA methyltransferase DNMT3A, appear to inactivate the functions of these proteins toward regulating the epigenetic state of genes. Thus, it is likely that the control of gene expression by epigenetic mechanisms plays an important role in MPNs, since multiple recurring mutations in MPNs alter normal epigenetic regulatory mechanisms.

A novel tumour-suppressor function for the Notch pathway in myeloid leukaemia

Notch signaling is a central regulator of differentiation in a variety of organisms and tissue types¹. Its activity is controlled by the multi-subunit γ–secretase complex (γSE) complex². Although Notch signaling can play both oncogenic and tumor suppressor roles in solid tumors, in the hematopoietic system, it is exclusively oncogenic, notably in T cell acute lymphoblastic leukemia (T-ALL), a disease characterized by Notch1 activating mutations³. Here we identify novel somatic inactivating Notch pathway mutations in a fraction of chronic myelomonocytic leukemia (CMML) patients. Inactivation of Notch signaling in mouse hematopoietic stem cells (HSC) resulted in an aberrant accumulation of granulocyte/monocyte progenitors (GMP), extramedullary hematopoieisis and the induction of CMML-like disease. Transcriptome analysis revealed that Notch signaling regulates an extensive myelomonocytic-specific gene signature, through the direct suppression of gene transcription by the Notch target Hes1. Our studies identify a novel role for Notch signaling during early hematopoietic stem cell differentiation and suggest that the Notch pathway can play both tumor-promoting and suppressive roles within the same tissue.

Novel multiplex bead-based assay with LNA-modified probes for detection of MPL exon 10 mutations

MPL exon 10 mutations were the second class of mutations shown to be associated with the pathogenesis of some Philadelphia chromosome - negative myeloproliferative neoplasms (MPNs). Recently, their identification gained wide recognition in the diagnostic work-up for suspected cases of JAK2 V617F negative MPNs. Various molecular approaches have been applied, yet universally accepted method is still lacking. We aimed at development and validation of a novel bead-based liquid assay using Locked nucleic acids (LNA)-modified oligonucleotide probes for multiplexed detection of the following MPL mutations: W515L/K/A/R. Testing on both artificial plasmid constructs and on clinical samples revealed that the method was comparable in terms of specificity to direct sequencing and had a much higher sensitivity of 1% mutant alleles. This method could be successfully implemented in the diagnostic work-up for MPNs. Furthermore, this system allows further multiplexing for single-tube identification of different mutations associated with MPNs.

Mouse models of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are hematopoietic malignancies characterized by peripheral cytopenias in the face of normo- or hypercellular, dysplastic bone marrow that arise from mutations in the hematopoietic stem/progenitor cell (HSPC). The disease is characterized by multiple cytogenetic and molecular defects, which result in an extremely heterogeneous phenotype. Recently, significant efforts have been made to develop appropriate mouse models to study this complex disease. Because of the heterogeneity of MDS, no single model is able to capture the MDS phenotype in its entirety. In this review, we describe several MDS mouse models and discuss the advances made in our understanding of the different disease mechanisms within the malignant clone and the marrow microenvironment. In addition, we describe progress in xenotransplantation models of MDS and discuss questions that remain to be answered.

3'UTR-truncated Hmga2 cDNA causes MPN-like hematopoiesis by conferring a clonal growth advantage at the level of HSC in mice

Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors, including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs), and recently in hematopoietic cell clones resulting from gene therapy procedures. In nearly all these cases overexpression is because of deletions or translocations that remove the 3' untranslated region (UTR) which contains binding sites for the regulatory micro RNA let-7. We were therefore interested in the effect of HMGA2 overexpression in hematopoietic tissues in transgenic mice (ΔHmga2 mice) carrying a 3'UTR-truncated Hmga2 cDNA. ΔHmga2 mice expressed increased levels of HMGA2 protein in various tissues including hematopoietic cells and showed proliferative hematopoiesis with increased numbers in all lineages of peripheral blood cells, hypercellular bone marrow (BM), splenomegaly with extramedullary erythropoiesis and erythropoietin-independent erythroid colony formation. ΔHmga2-derived BM cells had a growth advantage over wild-type cells in competitive repopulation and serial transplantation experiments. Thus overexpression of HMGA2 leads to proliferative hematopoiesis with clonal expansion at the stem cell and progenitor levels and may account for the clonal expansion in PNH and MPNs and in gene therapy patients after vector insertion disrupts the HMGA2 locus.

Mutations with epigenetic effects in myeloproliferative neoplasms and recent progress in treatment: Proceedings from the 5th International Post-ASH Symposium

Immediately following the 2010 annual American Society of Hematology (ASH) meeting, the 5th International Post-ASH Symposium on Chronic Myelogenous Leukemia and BCR-ABL1-Negative Myeloproliferative Neoplasms (MPNs) took place on 7–8 December 2010 in Orlando, Florida, USA. During this meeting, the most recent advances in laboratory research and clinical practice, including those that were presented at the 2010 ASH meeting, were discussed among recognized authorities in the field. The current paper summarizes the proceedings of this meeting in BCR-ABL1-negative MPN. We provide a detailed overview of new mutations with putative epigenetic effects (TET oncogene family member 2 (TET2), additional sex comb-like 1 (ASXL1), isocitrate dehydrogenase (IDH) and enhancer of zeste homolog 2 (EZH2)) and an update on treatment with Janus kinase (JAK) inhibitors, pomalidomide, everolimus, interferon-α, midostaurin and cladribine. In addition, the new ‘Dynamic International Prognostic Scoring System (DIPSS)-plus' prognostic model for primary myelofibrosis (PMF) and the clinical relevance of distinguishing essential thrombocythemia from prefibrotic PMF are discussed.

Annual Clinical Updates in Hematological Malignancies: a continuing medical education series: polycythemia vera and essential thrombocythemia: 2011 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus, and a small risk of disease progression into acute leukemia or myelofibrosis.

DIAGNOSIS

Diagnosis is based on JAK2 mutation status (PV and ET), serum erythropoietin (Epo) level (PV), and bone marrow histopathology (ET). The presence of a JAK2 mutation and subnormal serum Epo level confirm a diagnosis of PV. Differential diagnosis in ET should include chronic myelogenous leukemia and prefibrotic myelofibrosis.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk-age > 60 years or presence of thrombosis history; low-risk-absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count > 1,000 x 10⁹/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include age > 60 years, leukocytosis, history of thrombosis, and anemia.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is < 1%/1% in ET and < 5%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV), and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-a is usually effective in hydroxyurea failures.

CBL, CBLB, TET2, ASXL1, and IDH1/2 mutations and additional chromosomal aberrations constitute molecular events in chronic myelogenous leukemia

Progression of chronic myelogenous leukemia (CML) to accelerated (AP) and blast phase (BP) is because of secondary molecular events, as well as additional cytogenetic abnormalities. On the basis of the detection of JAK2, CBL, CBLB, TET2, ASXL1, and IDH1/2 mutations in myelodysplastic/myeloproliferative neoplasms, we hypothesized that they may also contribute to progression in CML. We screened these genes for mutations in 54 cases with CML (14 with chronic phase, 14 with AP, 20 with myeloid, and 6 with nonmyeloid BP). We identified 1 CBLB and 2 TET2 mutations in AP, and 1 CBL, 1 CBLB, 4 TET2, 2 ASXL1, and 2 IDH family mutations in myeloid BP. However, none of these mutations were found in chronic phase. No cases with JAK2V617F mutations were found. In 2 cases, TET2 mutations were found concomitant with CBLB mutations. By single nucleotide polymorphism arrays, uniparental disomy on chromosome 5q, 8q, 11p, and 17p was found in AP and BP but not involving 4q24 (TET2) or 11q23 (CBL). Microdeletions on chromosomes 17q11.2 and 21q22.12 involved tumor associated genes NF1 and RUNX1, respectively. Our results indicate that CBL family, TET2, ASXL1, and IDH family mutations and additional cryptic karyotypic abnormalities can occur in advanced phase CML.

Pomalidomide therapy for multiple myeloma and myelofibrosis: an update

Thalidomide possesses potent anti-inflammatory, immunomodulatory, and antiangiogenic properties. Thalidomide combined with corticosteroids is therapeutically active in multiple myeloma and myelofibrosis (MF). Lenalidomide and pomalidomide are second-generation immunomodulatory drugs (IMiDs) that were created by chemical modification of thalidomide with the intent to reduce toxicity and enhance therapeutic activity. Both drugs have also been shown to be active in the treatment of myeloma and MF. Thalidomide is US Food and Drug Administration (FDA)-approved for use in acute erythema nodosum leprosum and, in combination with dexamethasone, in newly diagnosed myeloma. Lenalidomide is approved for use in low/intermediate-1 risk myelodysplastic syndromes associated with transfusion-dependent anemia and a deletion 5q cytogenetic abnormality and, in combination with dexamethasone, in relapsed myeloma. Pomalidomide is currently not FDA-approved. Herein, we summarize what is currently known about the biologic and therapeutic effects of pomalidomide.

Circulating interleukin (IL)-8, IL-2R, IL-12, and IL-15 levels are independently prognostic in primary myelofibrosis: a comprehensive cytokine profiling study

PURPOSE

Abnormal cytokine expression accompanies myelofibrosis and might be a therapeutic target for Janus-associated kinase (JAK) inhibitor drugs. This study describes the spectrum of plasma cytokine abnormalities in primary myelofibrosis (PMF) and examines their phenotypic correlates and prognostic significance.

PATIENTS AND METHODS

Patients included in this study were required to have archived plasma, bone marrow biopsy, and cytogenetic information available at the time of first referral to the Mayo Clinic. Multiplex biometric sandwich immunoassay was used to measure plasma levels of 30 cytokines.

RESULTS

In total, 127 PMF patients were studied; comparison with normal controls (n = 35) revealed significantly increased interleukin-1β (IL-1β), IL-1RA, IL-2R, IL-6, IL-8, IL-10, IL-12, IL-13, IL-15, tumor necrosis factor α (TNF-α), granulocyte colony-stimulating factor (G-CSF), interferon alfa (IFN-α), macrophage inflammatory protein 1α (MIP-1α), MIP-1β, hepatocyte growth factor (HGF), IFN-γ-inducible protein 10 (IP-10), monokine induced by IFN-γ (MIG), monocyte chemotactic protein 1 (MCP-1), and vascular endothelial growth factor (VEGF) levels and decreased IFN-γ levels. In treatment-naive patients (n = 90), increased levels of IL-8 (P < .001), IL-2R (P < .001), IL-12 (P < .001), IL-15 (P = .001), and IP-10 (P = .003) were independently predictive of inferior survival. A similar multivariable analysis that included all 127 study patients confirmed the prognostic value of these five cytokines, and IL-8, IL-2R, IL-12, and IL-15 remained significant when risk stratification, according to the recently revised Dynamic International Prognostic Scoring System (DIPSS plus), was added to the multivariable model. Leukemia-free survival was predicted by IL-8, which was also the only cytokine associated with ≥ 1% circulating blasts. Other cytokine-phenotype associations included increased IL-8 and constitutional symptoms; IL-2R, IL-12, and transfusion need; IL-2R, IL-8, and leukocytosis; IP-10 and thrombocytopenia; HGF, MIG, IL-1RA, and marked splenomegaly; and IL-1RA, IL-2R, IP-10, MIP-1β, and JAK2V617F. A two-cytokine (IL-8/IL-2R) -based risk categorization delineated prognostically different groups within specific DIPSS plus risk categories.

CONCLUSION

This study signifies the presence of specific cytokine-phenotype associations in PMF and a prognostically relevant plasma cytokine signature that might prove useful as a laboratory tool for predicting and monitoring treatment response.

DIPSS Plus: A Refined Dynamic International Prognostic Scoring System for Primary Myelofibrosis That Incorporates Prognostic Information From Karyotype, Platelet Count, and Transfusion Status

Purpose

The Dynamic International Prognostic Scoring System (DIPSS) for primary myelofibrosis (PMF) uses five risk factors to predict survival: age older than 65 years, hemoglobin lower than 10 g/dL, leukocytes higher than 25 × 109/L, circulating blasts ≥ 1%, and constitutional symptoms. The main objective of this study was to refine DIPSS by incorporating prognostic information from karyotype, platelet count, and transfusion status.

Patients and Methods

Mayo Clinic databases for PMF were used to identify patients with available bone marrow histologic and cytogenetic information.

Results

Seven hundred ninety-three consecutive patients were selected and divided into two groups based on whether or not their referral occurred within (n = 428; training set) or after (n = 365; test set) 1 year of diagnosis. Multivariable analysis identified DIPSS, unfavorable karyotype, platelets lower than 100 × 109/L, and transfusion need as independent predictors of inferior survival. Hazard ratio (HR) –weighted adverse points were assigned to these variables to develop a composite prognostic model using the training set. The model was subsequently validated in the test set, and its application to all 793 patients resulted in median survivals of 185, 78, 35, and 16 months for low, intermediate-1 (HR, 2.2; 95% CI, 1.4 to 3.6), intermediate-2 (HR, 4.9; 95% CI, 3.2 to 7.7), and high-risk groups (HR, 10.7; 95% CI, 6.8 to 16.9), respectively (P < .001). Leukemia-free survival was predicted by the presence of thrombocytopenia or unfavorable karyotype (10-year risk of 31% v 12%; HR, 3.3; 95% CI, 1.9 to 5.6).

Conclusion

DIPSS plus effectively combines prognostic information from DIPSS, karyotype, platelet count, and transfusion status to predict overall survival in PMF. In addition, unfavorable karyotype or thrombocytopenia predicts inferior leukemia-free survival.

Janus kinase inhibitors for the treatment of myeloproliferative neoplasias and beyond

Recent advances in our understanding of the pathogenesis of the Philadelphia chromosome-negative myeloproliferative neoplasms, polycythaemia vera, essential thrombocythaemia and myelofibrosis have led to the identification of the mutation V617F in Janus kinase (JAK) as a potential therapeutic target. This information has prompted the development of ATP-competitive JAK2 inhibitors. Therapy with JAK2 inhibitors may induce rapid and marked reductions in spleen size and can lead to remarkable improvements in constitutional symptoms and overall quality of life. Because JAKs are involved in the pathogenesis of inflammatory and immune-mediated disorders, JAK inhibitors are also being tested in clinical trials in patients with rheumatoid arthritis and psoriasis, as well as for the treatment of other autoimmune diseases and for the prevention of allograft rejection. Preliminary results indicate that these agents hold great promise for the treatment of JAK-driven disorders.

Relevance of JAK2V617F positivity to hematological diseases--survey of samples from a clinical genetics laboratory

Background

JAK2V617F is found in the majority of patients with Ph- myeloproliferative neoplasms (MPNs) and has become a valuable marker for diagnosis of MPNs. However, it has also been found in many other hematological diseases, and some studies even detected the presence of JAK2V617F in normal blood samples. This casts doubt on the primary role of JAK2V617F in the pathogenesis of MPNs and its diagnostic value.

Methods

In the present study, we analyzed JAK2V617F positivity with 232 normal blood samples and 2663 patient blood, bone marrow, and amniotic fluid specimens obtained from a clinical genetics laboratory by using a simple DNA extraction method and a sensitive nested allele-specific PCR strategy.

Results

We found JAK2V617F present in the majority (78%) of MPN patients and in a small fraction (1.8-8.7%) of patients with other specific hematological diseases but not at all in normal healthy donors or patients with non-hematological diseases. We also revealed associations of JAK2V617F with novel as well as known chromosomal abnormalities.

Conclusions

Our study suggests that JAK2V617F positivity is associated with specific hematological malignancies and is an excellent diagnostic marker for MPNs. The data also indicate that the nested allele-specific PCR method provides clinically relevant information and should be conducted for all cases suspected of having MPNs as well as for other related diseases.

Myeloproliferative neoplasms: molecular pathophysiology, essential clinical understanding, and treatment strategies

To update oncologists on pathogenesis, contemporary diagnosis, risk stratification, and treatment strategies in BCR-ABL1-negative myeloproliferative neoplasms, including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Recent literature was reviewed and interpreted in the context of the authors' own experience and expertise. Pathogenetic mechanisms in PV, ET, and PMF include stem cell-derived clonal myeloproliferation and secondary stromal changes in the bone marrow and spleen. Most patients carry an activating JAK2 or MPL mutation and a smaller subset also harbors LNK, CBL, TET2, ASXL1, IDH, IKZF1, or EZH2 mutations; the precise pathogenetic contribution of these mutations is under investigation. JAK2 mutation analysis is now a formal component of diagnostic criteria for PV, ET, and PMF, but its prognostic utility is limited. Life expectancy in the majority of patients with PV or ET is near-normal and disease complications are effectively (and safely) managed by treatment with low-dose aspirin, phlebotomy, or hydroxyurea. In PMF, survival and quality of life are significantly worse and current therapy is inadequate. In ET and PV, controlled studies are needed to show added value and justify the risk of unknown long-term health effects associated with nonconventional therapeutic approaches (eg, interferon-alfa). The unmet need for treatment in PMF dictates a different approach for assessing the therapeutic value of new drugs (eg, JAK inhibitors, pomalidomide) or allogeneic stem-cell transplantation.

How I treat myelofibrosis

It is currently assumed that myelofibrosis (MF) originates from acquired mutations that target the hematopoietic stem cell and induce dysregulation of kinase signaling, clonal myeloproliferation, and abnormal cytokine expression. These pathogenetic processes are interdependent and also individually contributory to disease phenotype-bone marrow stromal changes, extramedullary hematopoiesis, ineffective erythropoiesis, and constitutional symptoms. Molecular pathogenesis of MF is poorly understood despite a growing list of resident somatic mutations that are either functionally linked to Janus kinase (JAK)-signal transducer and activator of transcription hyperactivation (eg JAK2, MPL, and LNK mutations) or possibly involved in epigenetic dysregulation of transcription (TET2, ASXL1, or EZH2 mutations). Current prognostication in primary MF is based on the Dynamic International Prognostic Scoring System-plus model, which uses 8 independent predictors of inferior survival to classify patients into low, intermediate 1, intermediate 2, and high-risk disease groups; corresponding median survivals are estimated at 15.4, 6.5, 2.9, and 1.3 years. Such information is used to plan a risk-adapted treatment strategy for the individual patient, which might include observation alone, conventional or investigational (eg, JAK inhibitors, pomalidomide) drug therapy, allogenic stem cell transplantation with reduced- or conventional-intensity conditioning, splenectomy, or radiotherapy. I discuss these treatment approaches in the context of who should get what and when.

Management of myelofibrosis

Myelofibrosis (MF), either primary or arising from previous polycythemia vera (PV) or essential thrombocythemia (ET), is the worst among the chronic myeloproliferative neoplasms in terms of survival and quality of life. Patients with MF have to face several clinical issues that, because of the poor effectiveness of medical therapy, surgery or radiotherapy, represent largely unmet clinical needs. Powerful risk stratification systems, applicable either at diagnosis using the International Prognostic Scoring System (IPSS) or during the variable course of illness using the Dynamic International Prognostic Scoring System (DIPSS) and DIPSS Plus, allow recognition of categories of patients with survival times ranging from decades to < 2 years. These scores are especially important for therapeutic decisions that include allogeneic stem cell transplantation (allogeneic SCT), the only curative approach that still carries a nonnegligible risk of morbidity and mortality even with newest reduced intensity conditioning (RIC) regimens. Discovery of JAK2V617F mutation prompted the development of clinical trials using JAK2 inhibitors; these agents overall have resulted in meaningful symptomatic improvement and reduction of splenomegaly that were otherwise not achievable with conventional therapy. Intriguing differences in the efficacy and tolerability of JAK2 inhibitors are being recognized, which could lead to a nonoverlapping spectrum of activity/safety. Other agents that do not directly target JAK2 and have shown symptomatic efficacy in MF are represented by inhibitors of the mammalian target of rapamycin (mTOR) and histone deacetylases (HDACs). Pomalidomide appears to be particularly active against MF-associated anemia. However, because these agents are all poorly effective in reducing the burden of mutated cells, further advancements are needed to move from enhancing our ability to palliate the disease to arriving at an actual cure for MF.

Rational therapeutic options for patients with myeloproliferative neoplasms

Patients with advanced forms of primary myelofibrosis (PMF) have an average survival of 4 to 5 years. At present, the standard of care for these patients is largely palliative, including supportive measures and the use of a variety of therapeutic agents, each of which's directed toward reducing transfusion requirements or decreasing the degree of splenomegaly. Currently, allogeneic stem-cell transplantation remains the only potentially curative approach for PMF. Although the administration of Janus Kinase 2 (JAK2) inhibitors to patients with PMF often dramatically reduces the degree of splenomegaly and improves in systemic symptoms, these drugs do not correct the cytopenias associated with PMF, nor do they reverse abnormalities of BM architecture or substantially influence the JAK2V617F allele burden. Furthermore, the effects of such small-molecule therapy on the natural history of PMF and the rate of its evolution to acute myeloid leukemia (AML) remain uncertain. Recently, additional genetic alterations that precede or accompany JAK2V617F in PMF have been documented. These findings indicate that therapies directed against a single genetic lesion such as JAK2V617F are unlikely to be curative of PMF. These observations have led us to consider alternative therapeutic targets for drug development. The dysregulation of the hematopoietic microenvironment in PMF provides an attractive therapeutic target. Novel agents capable of correcting the abnormalities seen in PMF would probably be used in combination with the currently available therapeutic armamentarium, including the JAK2 inhibitors, to treat patients with PMF, which would represent a paradigm shift in the management of such patients.

JAK2 inhibitors: what's the true therapeutic potential?

Physicians treating patients with the classic Philadelphia-negative myeloproliferative neoplasms (Ph-negative MPNs) (polycythemia vera [PV], essential thrombocythemia [ET] and primary myelofibrosis [PMF]) traditionally had few therapeutic drugs available. Spurred by the discovery of activating mutation of the JAK2 tyrosine kinase (JAK2 V617F mutation) in patients with Ph-negative MPNs several years ago, several JAK2 inhibitors were synthesized and are currently undergoing clinical trials in patients with PMF, PV and ET. Initial results from these studies have shown that these drugs can markedly reduce spleen size and alleviate constitutional symptoms, increase weight and improve exercise capacity in MF patients, thus improve quality of their life, which is significant clinical benefit. In ET and PV JAK2 inhibitor therapy may efficiently control blood cell count, as well as improve splenomegaly and control disease related symptoms. JAK2 inhibitors are a novel class of agents with promising results for treating patients with MF, PV and ET. In this article we will review the current evidence regarding the role of JAK2 mutations in the pathogenesis of Ph-negative MPNs and summarize results from the most recent clinical trials with JAK2 inhibitors in these disorders. JAK2 inhibitors are a novel class of agents with promising results for treating patients with MF, PV and ET.