Advances in the molecular characterization of Philadelphia-negative chronic myeloproliferative disorders

PURPOSE OF REVIEW: The identification and characterization of somatic disease alleles have greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies investigating the role of activated tyrosine kinase signaling in the Philadelphia chromosome negative myeloproliferative disorders. RECENT FINDINGS: Previously identified tyrosine kinase mutations in chronic myeloid leukemia and other myeloproliferative disorders suggested the possibility that polycythemia vera, essential thrombocythemia and primary myelofibrosis are also caused by activated tyrosine kinases. Recent studies identified an activating mutation in the JAK2 tyrosine kinase (JAK2V617F) in most patients with polycythemia vera and in approximately half of those with essential thrombocythemia and primary myelofibrosis. More recently, activating mutations in the thrombopoietin receptor and in JAK2 exon 12 have been identified in JAK2V617F negative myeloproliferative disorders. SUMMARY: The discovery of activated tyrosine kinases in the majority of patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis has diagnostic and pathogenetic implications. Subsequent studies are needed to elucidate the cause of myeloproliferative disorders without known disease alleles and to determine if inhibition of JAK2 signaling has therapeutic efficacy in the treatment of polycythemia vera, essential thrombocythemia and primary myelofibrosis.     

bcr-abl阴性骨髓增生性疾病患者JAK2V617F点突变检测的临床意义

目的 探索Janus Kinase 2V617F基因突变(JAK2V617F)在bcr-abl阴性骨髓增生性疾病(MPD)的发生率和临床意义.方法 基因组DNA从患者骨髓或外周血粒细胞中提取.采用等位基因特异性PCR(AS-PCR)、限制性内切酶消化和PCR产物测序的方法检测JAK2V617F突变.共检测患者110例,其中bcr-abl阴性MPD 41例、bcr-abl阳性慢性粒细胞白血病(CML)25例和急性白血病44例.结果 JAK2V617F阳性结果分别为真性红细胞增多症(PV)11例(91.7%)、原发性血小板增多症(ET)8例(53.3%)、特发性骨髓纤维化(IMF)4例(57.1%),而高嗜酸粒细胞增多症(HES)7例、bcr-abl阳性CML 25例和急性白血病44例[包括急性髓细胞白血病(AML)24例、急性淋巴细胞白血病(ALL)18例、急性混合细胞白血病2例1均未检测到JAK2V617F基因突变.在所有JAK2V617F阳性的标本和10份阴性标本中,AS-PCR和限制性内切酶消化方法的测定结果都可经测序进一步证实.结论 90%以上的PV、50%以上的ET和IMF可检测到JAK2V617F基因突变;JAK2V617F基因突变在PV、ET和IMF的诊断和鉴别诊断中有重要意义,可以作为诊断的分子标志,也可能是治疗的新靶点.     

JAK2 allele burden in polycythemia vera correlates with grade of myelofibrosis, but is not substantially affected by therapy

In a series of 105 patients with polycythemia vera, we retrospectively determined whether the JAK2^V617F mutation correlated with severity of disease phenotype. Higher JAK2^V617F allele burden correlated with more advanced myelofibrosis, greater splenomegaly, and higher white blood cell count, but not with age, gender, hematocrit level, or frequency of phlebotomy prior to cytoreductive therapy. Although a subgroup at increased risk for thrombosis was not clearly defined, there was a suggestion that frequency of thrombosis increased as the JAK2^V617F allele burden increased. The JAK2^V617F allele burden did not change significantly in treated patients with serial JAK2 analyses.     

Bim and Mcl-1 exert key roles in regulating JAK2<Superscript>V617F</Superscript>cell survival

Background  

The JAK2^V617F mutation plays a major role in the pathogenesis of myeloproliferative neoplasms and is found in the vast majority of patients suffering from polycythemia vera and in roughly every second patient suffering from essential thrombocythemia or from primary myelofibrosis. The V617F mutation is thought to provide hematopoietic stem cells and myeloid progenitors with a survival and proliferation advantage. It has previously been shown that activated JAK2 promotes cell survival by upregulating the anti-apoptotic STAT5 target gene Bcl-xL. In this study, we have investigated the role of additional apoptotic players, the pro-apoptotic protein Bim as well as the anti-apoptotic protein Mcl-1.     

JAK2, CALR,and MPL Mutations in Egyptian Patients With Classic Philadelphia-negative Myeloproliferative Neoplasms

BackgroundGenetic mutations have been proven to be one of the major criteria in the diagnosis and distinction of different myeloproliferative neoplasm (MPN) subtypes. Therefore, the aim of this study was to determine the molecular profile of Egyptian patients with MPN subtypes and correlate with clinicopathological status.MethodsA series of 200 patients with MPNs (92 polycythemia vera, 68 essential thrombocythemia, and 40 primary myelofibrosis) were included in this study. DNA from each sample was amplified using polymerase chain reaction to detect Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) mutations. Sanger sequencing was used to determine the mutation types.ResultsOf the 200 samples, 44% had JAK2V617F and 10% were carrying CALR mutation with type 2 being the most frequent type in this study (55%). No MPL or JAK2 exon 12 mutations were detected. All clinical and hematological data had no differences with other populations except that our CALR-positive patients showed a decrease in the platelet count compared with JAK2V617F-positive patients.ConclusionOur study on Egyptian patients shows a specific molecular profile of JAK2 mutation, and CALR mutation type 2 was higher than type 1.     

Chronic myeloproliferative disorders: a tyrosine kinase tale.

Chronic myeloproliferative diseases (CMPDs) are characterized by the abnormal proliferation and survival of one or more myeloid cell types. The archetype of this class of hematological diseases is chronic myeloid leukemia (CML), characterized by the presence of the Philadelphia (Ph) chromosome, the result of t(9;22)(q34;q11), and the associated BCR-ABL1 oncogene. Some of the Ph-negative myeloproliferative diseases are characterized by other chromosomal translocations involving a variety of tyrosine kinase genes, including ABL1, ABL2, PDGFRA, PDGFRB, FGFR1, and JAK2. The majority of Ph-negative CMPDs, however, such as chronic eosinophilic leukemia, polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis are not characterized by the presence of recurrent chromosomal abnormalities. Recent studies have identified the FIP1L1-PDGFRA fusion gene, generated due to a small cryptic deletion on chromosome 4q12, and the activating V617F mutation in JAK2 in a significant fraction of Ph-negative CMPDs. These results show that abnormalities in tyrosine kinase genes are central to the molecular pathogenesis of CMPDs. Genome-wide screenings to identify novel tyrosine kinase abnormalities in CMPDs may contribute to further improvement of the diagnosis and the treatment of these diseases.     

Efficacy of NS-018, a potent and selective JAK2/Src inhibitor, in primary cells and mouse models of myeloproliferative neoplasms

Aberrant activation of Janus kinase 2 (JAK2) caused by somatic mutation of JAK2 (JAK2V617F) or the thrombopoietin receptor (MPLW515L) plays an essential role in the pathogenesis of myeloproliferative neoplasms (MPNs), suggesting that inhibition of aberrant JAK2 activation would have a therapeutic benefit. Our novel JAK2 inhibitor, NS-018, was highly active against JAK2 with a 50% inhibition (IC₅₀) of <1 n, and had 30–50-fold greater selectivity for JAK2 over other JAK-family kinases, such as JAK1, JAK3 and tyrosine kinase 2. In addition to JAK2, NS-018 inhibited Src-family kinases. NS-018 showed potent antiproliferative activity against cell lines expressing a constitutively activated JAK2 (the JAK2V617F or MPLW515L mutations or the TEL–JAK2 fusion gene; IC₅₀=11–120 n), but showed only minimal cytotoxicity against most other hematopoietic cell lines without a constitutively activated JAK2. Furthermore, NS-018 preferentially suppressed in vitro erythropoietin-independent endogenous colony formation from polycythemia vera patients. NS-018 also markedly reduced splenomegaly and prolonged the survival of mice inoculated with Ba/F3 cells harboring JAK2V617F. In addition, NS-018 significantly reduced leukocytosis, hepatosplenomegaly and extramedullary hematopoiesis, improved nutritional status, and prolonged survival in JAK2V617F transgenic mice. These results suggest that NS-018 will be a promising candidate for the treatment of MPNs.     

New and old prognostic factors in polycythemia vera

Polycythemia vera is a chronic myeloproliferative disorder affecting people in the sixth decade of life. The disease is considered long-lasting; median survival exceeds 18 years. As thrombosis is the main complication during follow-up, scoring systems have focused on the risk of thrombosis. Age over 60 years and prior thrombosis are considered the standard risk factors for thrombosis and represent the state of the art for risk stratification in decision making regarding treatment. However, new disease-based risk factors—leukocytosis and the JAK2V617F mutation burden—seem to be emerging as indicators of prognosis in polycythemia vera. Leukocytosis, as a marker of disease proliferation, seems to have an impact on thrombosis, post-polycythemia vera myelofibrosis, leukemia, and survival. The role of the JAK2V617F mutation as a prognostic factor requires further validation, but it may have a dominant role in disease progression and in the activation of platelets and leukocytes.     

Molecular heterogeneity of familial myeloproliferative neoplasms revealed by analysis of the commonly acquired JAK2, CALR and MPL mutations

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.     

Mutation screening for JAK2V617F: when to order the test and how to interpret the results

With the application of adequately sensitive tests, it is now becoming evident that more than 90% of patients with conventionally-defined polycythemia vera (PV) carry the somatic JAK2V617F mutation in their granulocytes. However, the specific mutation is also found in other classic and atypical myeloproliferative disorders (MPD), albeit at a lesser frequency. In contrast, JAK2V617F has not been reported in patients with either reactive myeloproliferation or lymphoid disorders. Therefore, mutation screening for JAK2V617F can be considered as a myeloid-specific clonality assay and it is diagnostically most useful in the evaluation of "polycythemia".     

Prevalence of JAK2 V617F mutation in west algerian population with chronic myeloproliferative neoplasms: A multicenter study

JAK2 V617F point mutation is now well recognized in patients with chronic myeloproliferative neoplasms (MPNs). However, its frequency in Algerian patients is still unknown. We determined the JAK2 V617F mutation in blood samples from 344 patients from five hematology departments across West Algeria, using amplification refractory mutation system-polymerase chain reaction (ARMSPCR). The JAK2 V617F mutation was identified in 157/344 patients (45.63%), 80/98 polycythemia vera patients (81.6%), 44/75 essential thrombocythemia patients (58.6%), 6/13 primary myelofibrosis patients (46.2%), 21/87 with suspected MPN (12.9%), and 2/32 secondary thrombocytosis patients (6.2%), but was not detected in 28 patients with secondary erythrocytosis. Detection of JAK2 V617F mutation is an essential molecular tool to establish myeloproliferative neoplasm diagnosis, which allowed us to adjust the diagnosis for 6 patients and should be systematically included into the initial evaluation of patients suspected of MPNs in Algeria.     

Spleen deflation and beyond: The pros and cons of Janus kinase 2 inhibitor therapy for patients with myeloproliferative neoplasms

The myeloproliferative neoplasms (MPNs) essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (MF) are malignancies that frequently harbor the recurrent somatic point mutation JAK2^V617F. The discovery of this mutation has fueled the development of Janus kinase 2 (JAK2) inhibitors. Available results have indicated that JAK2 inhibitors are particularly effective at reducing spleen size. However, the activity of these agents is multifaceted and also involves a marked improvement of systemic symptoms and, for those agents with dual JAK1 and JAK2 inhibitory activity, a marked reduction in the levels of circulating cytokines involved in the pathogenesis of the disease. Because JAK2 inhibitors are not specific for JAK2^V617F, responses have also been observed in JAK2^V617F‐negative MPNs because of the inhibition of wild‐type JAK2, which is also likely responsible for the induction of cytopenias in patients with MF and for the normalization of peripheral blood counts observed in patients with ET or PV. Given the distinct mortality and morbidity associated with ET, PV, and MF, the use of JAK2 inhibitors appears reasonable for patients with MF as well as for those with ET or PV who have become resistant or intolerant to hydroxyurea. Ongoing randomized, placebo‐controlled, phase 3 trials will further delineate the role of these agents in the management of patients with MPNs. The pros and cons of JAK2 kinase inhibitor therapy are herein discussed. Cancer 2012;. © 2011 American Cancer Society.     

A sensitive and reliable semi-quantitative real-time PCR assay to detect JAK2 V617F in blood

Diagnosis of the myeloproliferative disorders, polycythemia vera (PV), essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF) is difficult due to lack of diagnostic markers. Recently, the acquisition of a mutation in the Janus kinase 2 (JAK2) gene by hemopoietic cells has been described as a genetic defect underlying myeloproliferative disorders. The mutation leads to constitutive activation of JAK2, a tyrosine kinase involved in cytokine receptor signalling. Because of the clinical importance of this mutation (JAK2 V617F) in diagnosing myeloproliferative disorders and its relevance for disease progression, we developed a semi-quantitative real-time PCR test to detect JAK2 V617F. With this assay, quantities down to 0.8% JAK2 V617F amongst wild-type DNA could reliably be detected. For quantification purposes, low intra- and inter-assay variabilities ensure good reproducibility of the assay. Thus the JAK2 V617F qPCR assay described here is quick, robust, simple and more sensitive than direct sequencing, RFLP, ARMS assay and other methods published so far to detect JAK2 V617F. We therefore believe that the assay will contribute to early diagnosis of myeloproliferative disorders and to disease management, especially when JAK2-specific inhibitors have become available for therapeutic use.     

Diagnostic Performance of Erythropoietin Levels in Polycythemia Vera: Experience at a Comprehensive Cancer Center

IntroductionConsidering the evolving diagnostic criteria of polycythemia vera (PV), we analyzed the utility of serum erythropoietin (EPO) as a predictive marker for differentiating polycythemia vera (PV) from other etiologies of erythrocytosis.Patients and MethodsWe conducted a retrospective study after a review of electronical medical records from January 2005 to December 2016 with diagnosis of erythrocytosis using International Classification of Disease–specific codes. To evaluate the diagnostic performance of EPO levels and JAK2-V617F mutation, we constructed a receiver-operated characteristic curve of sensitivity versus 1-specificity for serum EPO levels and JAK2-V617F mutation as predictive markers for differentiating PV from other causes of erythrocytosis.ResultsWe surveyed 577 patients with erythrocytosis. Median patient age was 59.2 years, 57.72% (n = 329) were male, 86.3% (n = 491) were white, and only 3.3% (n = 19) were African American. A total of 80.88% (n = 351) of those diagnosed with PV had a JAK2-V617F mutation compared to only 1.47% (n = 2) whose primary diagnosis was secondary polycythemia. When comparing JAK2-V617 mutation to the EPO level, the area under the curve of JAK2-V617 (0.8970) was statistically larger than that of EPO test (0.6765). Therefore, the PV diagnostic methodology using JAK2-V617 is better than the EPO test. An EPO level of < 2 mIU/mL was > 99% specific to predict PV but was only 12% sensitive.ConclusionIn the appropriate clinical setting, cytogenetic and molecular studies such as JAK2 mutation status prevail as the most useful tools for PV case identification. The use of isolated EPO to screen patients with erythrocytosis is not a good diagnostic approach.     

Interferon α-2b gains high sustained response therapy for advanced essential thrombocythemia and polycythemia vera with JAK2V617F positive mutation

Objective

This open-label, prospective, observational study aimed to evaluate treatment response, efficacy therapy and safety to IFN α-2b for the essential thrombocythemia (ET) and polycythemia vera (PV) with JAK2V617F positive mutation.

Method

A total of 123 ET patients received IFNα-2b therapy with JAK2V617F positive or negative mutation; and 136 PV patients with JAK2V617F⁺ received IFNα-2b or hydroxyurea (HU) therapy according to random number assignment (ages 18–65 years old).

Result

ET patients receiving IFN α-2b with JAK2V617F⁺ had a greater advantage in overall hematologic response (OHR) than JAK2V617F⁻ (83.3% versus 61.4%, P < 0.01). For PV patients with JAK2V617F⁺, IFN had no OHR superiority to HU (70.3% versus 70.8%, P > 0.05), but which gained a greater satisfactory molecular response than HU (54.7% versus 19.4%, P < 0.01). IFN significantly decreased the phlebotomy rate, which was better than HU for MPDs patients with OHR than HU (3.6% versus 65.7%, P < 0.01). Furthermore, ET patients with JAK2V617F⁺ demonstrated a definite advantage over JAK2V617F⁻ in five-year PFS (75.9% versus 47.6%, P < 0.05). For PV patients with JAK2V617F⁺, IFN α-2b was superior to HU in five-year PFS (66.3% versus 46.7%, P < 0.01). Moreover, IFN α-2b also contributed to improved vasomotor symptoms in MPDs, and especially significantly decreased the incidence of distal paresthesias (14.1% versus 37.5%) and erythromelalgia (9.4% versus 29.2%) better than HU (P < 0.01). Meanwhile, IFN did not observe the severe hematological adverse events in patients with PV or ET.

Conclusion

The data confirmed that IFN α-2b benefited the patients with ET or PV, particularly for JAK2V617F⁺ mutation.     

A refined diagnostic algorithm for polycythemia vera that incorporates mutation screening for JAK2V617F

Historically, red cell mass (RCM) measurement has been promoted as an accurate indicator of the body’s red cell content. Both the Polycythemia Vera Study Group and a committee sponsored by the World Health Organization have endorsed its inclusion in their diagnostic criteria without supporting evidence of diagnostic accuracy from a systematic study. Over the years, it has become evident that RCM measurement is a cumbersome and costly test and, as a result, it has been abandoned by many hematologists in practice. The recent discovery that a somatic JAK2-activating mutation, JAK2^V617F, is almost invariably associated with polycythemia vera further supports the use of diagnostic algorithms that are based on biologic parameters in place of traditional diagnostic criteria that are based on RCM measurement. Therefore, a contemporary approach to the diagnosis of polycythemia vera starts with peripheral blood mutation screening for JAK2^V617F as well as measurement of serum erythropoietin. The results of these tests, along with the clinical scenario, determine the need for further investigation, including bone marrow examination.     

JAK2 (V617F) as an acquired somatic mutation and a secondary genetic event associated with disease progression in familial myeloproliferative disorders

BACKGROUND: A somatic gain-of-function mutation of the Janus kinase 2 (JAK2) gene has been identified in chronic myeloproliferative disorders, which appear to have a sporadic occurrence in most individuals. The authors studied the biologic significance of the JAK2 (V617F) mutation in familial myeloproliferative disorders. METHODS: Twenty pedigrees with familial chronic myeloproliferative disorders were identified through an investigation of family history in 264 patients with sporadic myeloproliferative disorders. A quantitative real-time polymerase chain reaction (qRT-PCR)-based allelic discrimination assay was employed for the detection of the V617F mutation in circulating granulocytes and T lymphocytes. An analysis of X-chromosome inactivation pattern was performed in female patients. RESULTS: Fourteen families had homogeneous phenotypes, and 6 families had mixed phenotypes. By using a qRT-PCR-based allelic discrimination assay, the JAK2 (V617F) mutation was detected in circulating granulocytes from 20 of 31 patients, but the mutation was not detected in T lymphocytes. Granulocyte mutant alleles ranged from 2.1% to 91.5% and, on average, increased with time. Discordant distribution of the JAK2 (V617F) mutation was observed in siblings with polycythemia vera. The proportion of granulocytes that carried the JAK2 (V617F) mutation was lower than the proportion of clonal granulocytes, as determined in an analysis of X-chromosome inactivation patterns in female patients. CONCLUSIONS: The current findings indicated that the JAK2 (V617F) mutation represents an acquired somatic mutation in patients with familial chronic myeloproliferative disorders and probably occurs as a secondary genetic event in the background of preexisting clonal hematopoiesis. Thus, a genetic predisposition to acquisition of JAK2 (V617F) is inherited in families with myeloproliferative disorders.