Multiomic profiling reveals metabolic alterations mediating aberrant platelet activity and inflammation in myeloproliferative neoplasms.

Platelets from patients with myeloproliferative neoplasms (MPNs) exhibit a hyperreactive phenotype. Here, we found elevated P-selectin exposure and platelet-leukocyte aggregates indicating activation of platelets from essential thrombocythemia (ET) patients. Single-cell RNA-seq analysis of primary samples revealed significant enrichment of transcripts related to platelet activation, mTOR, and oxidative phosphorylation in ET patient platelets. These observations were validated via proteomic profiling. Platelet metabolomics revealed distinct metabolic phenotypes consisting of elevated ATP generation accompanied by increases in the levels of multiple intermediates of the tricarboxylic acid cycle, but lower α-ketoglutarate (α-KG) in MPN patients. Inhibition of PI3K/AKT/mTOR signaling significantly reduced metabolic responses and hyperreactivity in MPN patient platelets, while α-KG supplementation markedly reduced oxygen consumption and ATP generation. Ex vivo incubation of platelets from both MPN patients and Jak2 V617F-knockin mice with α-KG supplementation significantly reduced platelet activation responses. Oral α-KG supplementation of Jak2 V617F mice decreased splenomegaly and reduced hematocrit, monocyte, and platelet counts. Finally, α-KG treatment significantly decreased proinflammatory cytokine secretion from MPN CD14+ monocytes. Our results reveal a previously unrecognized metabolic disorder in conjunction with aberrant PI3K/AKT/mTOR signaling that contributes to platelet hyperreactivity in MPN patients.

Synergetic effect of Azacitidine and Sorafenib in treatment of a case of myeloid neoplasm with sole chromosomal abnormality t(8;22)(p11.2;q11.2)/BCR-FGFR1 rearrangement.

The sole t(8;22)(p11.2;q11.2)/BCR- FGFR1 chromosomal abnormality formerly known as aCML is an extremely rare disease entity with a history of rapid progression. Though patients resemble phenotypically chronic myeloid leukemia, the treatment of patients with sole BCR-FGFR1 rearrangement are still challenging for clinicians due to rapid progressive nature and unavailability of uniform treatment guidelines. In present case study, we describe a case of myeloid neoplasm with sole chromosomal abnormality of t(8;22)(p11.2;q11.2)/BCR-FGFR1 rearrangement which is successfully managed by Sorafenib with Azacitidine. Hence our case report suggests that combination of Sorafenib and Azacitidine treatment is effective in sole BCR-FGFR1 rearrangement, however this combination therapy should be studied in large clinical trials.

Clinical and molecular characteristics associated with Vitamin C deficiency in myeloid malignancies; real world data from a prospective cohort.

Vitamin C is an essential vitamin that acts as a co-factor for many enzymes involved in epigenetic regulation in humans. Low vitamin C levels in hematopoietic stem cells (HSC) promote self-renewal and vitamin C supplementation retards leukaemogenesis in vitamin C-deficient mouse models. Studies on vitamin C levels in patients with myeloid malignancies are limited. We thus conducted a retrospective analysis on a prospective cohort of patients with myeloid malignancies on whom plasma vitamin C levels were measured serially at diagnosis and during treatment. Baseline characteristics including hematological indices, cytogenetics, and molecular mutations are described in this cohort. Among 64 patients included in our study, 11 patients (17%) had low vitamin C levels. We noted a younger age at diagnosis for patients with myeloid malignancies who had low plasma vitamin C levels. Patients with low plasma vitamin C levels were more likely to have acute myeloid leukemia compared to other myeloid malignancies. Low vitamin C levels were associated with ASXL1 mutations. Our study calls for further multi-institutional studies to understand the relevance of low plasma vitamin C level in myeloid neoplasms, the role of vitamin C deficiency in leukemogenesis, and the potential benefit of vitamin C supplementation.

Intratumoral heterogeneity of c-KIT mutations in a feline splenic mast cell tumor and their functional effects on cell proliferation.

A cat was presented with mast cell tumors (MCTs) of the skin and spleen. During the initial diagnosis, the exon 8 mutation of c-KIT was detected in the masses from skin and spleen by a commercial laboratory test. Consequently, treatment with toceranib was started. After complete remission, because of recurrence on day 117, the spleen and skin tumors were removed, but the cat eventually died on day 191. The analysis of ten cDNA clones of the c-KIT gene cloned from the surgically removed spleen revealed that seven different cDNA patterns were included, indicating the heterogeneity of this gene in the splenic MCT. The seven cDNA nucleotide patterns can be classified into four protein sequence patterns. In addition to the previously known mutations in exon 8, we identified novel mutations in exons 9, 10, and 18; four amino acids deletion in exon 9, and a point mutation in exons 10 and 18. Mouse IL-3-dependent cell line, Ba/F3, was transduced with these mutant clones, and c-KIT phosphorylation and proliferation assays were performed. We found that certain mutations affected the c-KIT phosphorylation status and cell proliferation. This suggests that heterogeneity among the population of tumor cells exists in MCTs, and that the dominant clones of this heterogeneity may contribute to the subsequent tumor cell growth.

RAPID LOW-COST DETECTION OF TYPE 2CALR MUTATION BY ALLELE-SPECIFIC RT-PCR FOR DIAGNOSIS OF MYELOPROLIFERATIVE NEOPLASMS.

BACKGROUND: Approximately 15% to 24% of essential thrombocythemia (ET) and 25-35% of primary myelofibrosis cases carry a mutation in the calreticulin (CALR) gene. Sanger sequencing, qPCR, high resolution melt or targeted next generation sequencing usually used to detect these mutations are expensive and require costly equipment. Nevertheless, type 1 CALR mutations are detectable by using polymerase chain reaction (PCR) and agarose gel electrophoresis. AIM: To offer the use of the allele-specific reverse transcription (RT) PCR for rapid low-cost detection of the type 2 mutation in the CALR gene. MATERIALS AND METHODS: Allele-specific primers designed for detecting type 2 mutation (5-bp insertion; c.1154_1155 ins TTGTC) of the CALR gene were used for allele-specific RT-PCR analysis of cDNA of the patient with JAK2-, MPL-negative ET, whose mutation in CALR gene has been identified by Sanger sequencing. RT-PCR samples were analyzed by agarose gel electrophoresis. RESULTS: The type 2 mutation (K385fs*47 ins5) in CALR gene was detected by Sanger sequencing in JAK2- and MPL-negative ET patient. The cDNA obtained was then re-analyzed by using allele-specific RT-PCR with newly designed primers. Normal and type 2 mutation alleles of the CALR gene were detected by gel electrophoresis. The results of allele-specific RT-PCR were consistent with the data of Sanger sequencing. CONCLUSION: Allele-specific RT-PCR analysis may be used for the fast low-cost detection of the major type 2 mutation (ins 5) of the CALR gene in patients with MPNs.

Inferring the dynamics of mutated hematopoietic stem and progenitor cells induced by IFNα in myeloproliferative neoplasms.

Classical BCR-ABL-negative myeloproliferative neoplasms (MPNs) are clonal disorders of hematopoietic stem cells (HSCs) caused mainly by recurrent mutations in genes encoding JAK2 (JAK2), calreticulin (CALR), or the thrombopoietin receptor (MPL). Interferon α (IFNα) has demonstrated some efficacy in inducing molecular remission in MPNs. To determine factors that influence molecular response rate, we evaluated the long-term molecular efficacy of IFNα in patients with MPN by monitoring the fate of cells carrying driver mutations in a prospective observational and longitudinal study of 48 patients over more than 5 years. We measured the clonal architecture of early and late hematopoietic progenitors (84 845 measurements) and the global variant allele frequency in mature cells (409 measurements) several times per year. Using mathematical modeling and hierarchical Bayesian inference, we further inferred the dynamics of IFNα-targeted mutated HSCs. Our data support the hypothesis that IFNα targets JAK2V617F HSCs by inducing their exit from quiescence and differentiation into progenitors. Our observations indicate that treatment efficacy is higher in homozygous than heterozygous JAK2V617F HSCs and increases with high IFNα dose in heterozygous JAK2V617F HSCs. We also found that the molecular responses of CALRm HSCs to IFNα were heterogeneous, varying between type 1 and type 2 CALRm, and a high dose of IFNα correlates with worse outcomes. Our work indicates that the long-term molecular efficacy of IFNα implies an HSC exhaustion mechanism and depends on both the driver mutation type and IFNα dose.

Discovery and evaluation of ZT55, a novel highly-selective tyrosine kinase inhibitor of JAK2V617F against myeloproliferative neoplasms.

BACKGROUND: The JAK2-STAT signaling pathway plays a critical role in myeloproliferative neoplasms (MPN). An activating mutation in JAK2 (V617F) is present in ~ 95% of polycythemia vera, essential thrombocythemia, and primary myelofibrosis cases. This study aims to explore the selective JAK2V617F inhibitor, evaluate the efficacy and possible mechanism of ZT55 on MPN. METHODS: HTRF assays were conducted to evaluate the selective inhibition of ZT55 for JAKs. Cell apoptosis, proliferation, and cycle arrest assays were performed to examine the effect of ZT55 on HEL cell line with JAK2V617F mutation in vitro. Western analysis was used to monitor the expression and activity of proteins on JAK2/STAT pathway. A mice xenograft model was established to evaluate the antitumor efficacy of ZT55 in vivo. Peripheral blood samples from patients with the JAK2V617F mutation were collected to estimate the effect of ZT55 on erythroid colony formation by colony-forming assay. RESULTS: We found that ZT55 showed a selective inhibition of a 0.031 µM IC50 value against JAK2. It exhibited potent effects on the cellular JAK-STAT pathway, inhibiting tyrosine phosphorylation in JAK2V617F and downstream STAT3/5 transcription factors. ZT55 inhibited the proliferation of the JAK2V617F-expressing HEL cell line, leading to cell cycle arrest at the G2/M phase and induction of caspase-dependent apoptosis. Notably, ZT55 also significantly suppressed the growth of HEL xenograft tumors in vivo. Further evaluation indicated that ZT55 blocked erythroid colony formation of peripheral blood hematopoietic progenitors from patients carrying the JAK2V617F mutation. CONCLUSION: These results suggest that ZT55 is a highly-selective JAK2 inhibitor that can induce apoptosis of human erythroleukemia cells by inhibiting the JAK2-STAT signaling.

Epigenetic Modifiers in Myeloid Malignancies: The Role of Histone Deacetylase Inhibitors.

Myeloid hematological malignancies are clonal bone marrow neoplasms, comprising of acute myeloid leukemia (AML), the myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML), the myeloproliferative neoplasms (MPN) and systemic mastocytosis (SM). The field of epigenetic regulation of normal and malignant hematopoiesis is rapidly growing. In recent years, heterozygous somatic mutations in genes encoding epigenetic regulators have been found in all subtypes of myeloid malignancies, supporting the rationale for treatment with epigenetic modifiers. Histone deacetylase inhibitors (HDACi) are epigenetic modifiers that, in vitro, have been shown to induce growth arrest, apoptotic or autophagic cell death, and terminal differentiation of myeloid tumor cells. These effects were observed both at the bulk tumor level and in the most immature CD34⁺38- cell compartments containing the leukemic stem cells. Thus, there is a strong rationale supporting HDACi therapy in myeloid malignancies. However, despite initial promising results in phase I trials, HDACi in monotherapy as well as in combination with other drugs, have failed to improve responses or survival. This review provides an overview of the rationale for HDACi in myeloid malignancies, clinical results and speculations on why clinical trials have thus far not met the expectations, and how this may be improved in the future.

Diagnostic, Prognostic, and Predictive Utility of Recurrent Somatic Mutations in Myeloid Neoplasms.

The classification and risk stratification of myeloid neoplasms, including acute myeloid leukemia, myelodysplastic syndromes, myelodysplastic syndromes/myeloproliferative neoplasms, and myeloproliferative neoplasms, have increasingly been guided by molecular genetic abnormalities. Gene expression analysis and next-generation sequencing have led to the ever increasing discovery of somatic gene mutations in myeloid neoplasms. Mutations have been identified in genes involved in epigenetic modification, RNA splicing, transcription factors, DNA repair, and the cohesin complex. These new somatic/acquired gene mutations have refined the classification of myeloid neoplasms and have been incorporated into the 2016 update of the World Health Organization (WHO) classification and the National Comprehensive Cancer Network guidelines. They have also been helpful in the development of new targeted therapeutic agents. In the present review, we describe the clinical utility of recently identified, clinically important gene mutations in myeloid neoplasms, including those incorporated in the 2016 update of the WHO classification.

The Development and Use of Janus Kinase 2 Inhibitors for the Treatment of Myeloproliferative Neoplasms.

Following the discovery of the JAK2V617F mutation, Janus kinase (JAK) 2 inhibitors were developed as rationally designed therapy in myeloproliferative neoplasms (MPNs). Although JAK2 inhibitors have clinical efficacy in MPN, they are not clonally selective for the JAK2V617F-mutant cells. Because activated JAK-signal transducer and activator of transcription (STAT) signaling is a common feature of MPN, JAK2 inhibitors are efficacious regardless of the specific MPN phenotypic driver mutation. The Food and Drug Administration approved the JAK1/JAK2 inhibitor, ruxolitinib, for the treatment of myelofibrosis and polycythemia vera. Additional JAK2 inhibitors are currently in advanced phased clinical trials.

Targeted next-generation sequencing identified novel mutations in triple-negative myeloproliferative neoplasms.

Mutations in JAK2, MPL and CALR genes have been identified in the majority of myeloproliferative neoplasm (MPN) patients, and patients negative for these three mutations are the so-called triple-negative (TN) MPN. In this study, we examined the mutational profiles of 16 triple-negative MPN patients including 7 essential thrombocythemia (ET), 1 primary myelofibrosis and 8 polycythemia vera (PV). Targeted next-generation sequencing was performed using the ACTOnco Comprehensive Cancer Panel (Ion AmpliSeq Comprehensive Cancer Panel, Life Technologies) to target all coding exons of 409 cancer-related genes. Overall, 30 nonsynonymous somatic mutations were detected in 12 (75%) patients with a range of 1-5 mutations per sample. Notably, one ET patient was found to have JAK2V617F and KITP551L mutations at very low allele frequency. One MPLP70L and 1 MPLM602T mutations were identified each in 1 ET and 1 PV, respectively. Other recurrent mutations were also identified including KMT2C, KMT2D, IRS2, SYNE1, PDE4DIP, SETD2, ATM, TNFAIP3 and CCND2. In addition, germline mutations were also found in some cancer-related genes. Copy number changes were rare in this cohort of TN MPNs. In conclusion, both somatic and germline mutations can be detected in TN MPN patients.

Screening of drugs to treat 8p11 myeloproliferative syndrome using patient-derived induced pluripotent stem cells with fusion gene CEP110-FGFR1.

Induced pluripotent stem (iPS) cells provide powerful tools for studying disease mechanisms and developing therapies for diseases. The 8p11 myeloproliferative syndrome (EMS) is an aggressive chronic myeloproliferative disorder (MPD) that is caused by constitutive activation of fibroblast growth factor receptor 1. EMS is rare and, consequently, effective treatment for this disease has not been established. Here, iPS cells were generated from an EMS patient (EMS-iPS cells) to assist the development of effective therapies for EMS. When iPS cells were co-cultured with murine embryonic stromal cells, EMS-iPS cells produced more hematopoietic progenitor and hematopoietic cells, and CD34+ cells derived from EMS-iPS cells exhibited 3.2-7.2-fold more macrophage and erythroid colony forming units (CFUs) than those derived from control iPS cells. These data indicate that EMS-iPS cells have an increased hematopoietic differentiation capacity, which is characteristic of MPDs. To determine whether a tyrosine kinase inhibitor (TKI) could suppress the increased number of CFUs formed by EMS-iPS-induced CD34+ cells, cells were treated with one of four TKIs (CHIR258, PKC 412, ponatinib, and imatinib). CHIR258, PKC 412, and ponatinib reduced the number of CFUs formed by EMS-iPS-induced CD34+ cells in a dose-dependent manner, whereas imatinib did not. Similar effects were observed on primary peripheral blood cells (more than 90% of which were blasts) isolated from the patient. This study provides evidence that the EMS-iPS cell line is a useful tool for the screening of drugs to treat EMS and to investigate the mechanism underlying this disease.

Janus kinase inhibitors for the treatment of myeloproliferative neoplasms.

INTRODUCTION: Disordered signaling through the JAK/STAT pathway is a hallmark of myeloproliferative neoplasms (MPNs). Targeted therapies that inhibit and regulate this pathway are reasonable strategies for disease management. Only one JAK1/JAK2 inhibitor has gained FDA approval for treatment of myelofibrosis. Despite significant reductions in splenomegaly and disease-associated symptoms, additional agents are necessary to manage disease in those that do not respond. AREAS COVERED: A review of the currently available literature and meeting abstracts for JAK inhibitors in myeloproliferative neoplasms identified studies aimed at improving outcomes and establishing alternative therapies in MPNs. Development of specific JAK inhibitors and ongoing trials involving ruxolitinib, CYT387, SAR302503, CEP701, SB 1518, XL-019, LY2784544, BMS-911453, NS-018, AZD1480 and INCB039110 are reviewed. EXPERT OPINION: The identification of JAK2V617F mutation and its link to MPNs has revolutionized treatment options. Resultant research in targeting the JAK/STAT pathway led to the approval of ruxolitinib, a JAK1/JAK2 inhibitor with activity in MPNs. While ruxolitinib produces durable reductions in splenomegaly and improvement of symptoms, and prolongs survival, there is room for new and more specific agents to be developed. Minimizing toxicity and avoiding drug resistance are challenges that lie ahead. Combining agents with different mechanisms seems to be a rational strategy.

The Jak2 inhibitor, G6, alleviates Jak2-V617F-mediated myeloproliferative neoplasia by providing significant therapeutic efficacy to the bone marrow.

We recently developed a Janus kinase 2 (Jak2) small-molecule inhibitor called G6 and found that it inhibits Jak2-V617F-mediated pathologic cell growth in vitro, ex vivo, and in vivo. However, its ability to inhibit Jak2-V617F-mediated myeloproliferative neoplasia, with particular emphasis in the bone marrow, has not previously been examined. Here, we investigated the efficacy of G6 in a transgenic mouse model of Jak2-V617F-mediated myeloproliferative neoplasia. We found that G6 provided therapeutic benefit to the peripheral blood as determined by elimination of leukocytosis, thrombocytosis, and erythrocytosis. G6 normalized the pathologically high plasma concentrations of interleukin 6 (IL-6). In the liver, G6 eliminated Jak2-V617F-driven extramedullary hematopoiesis. With respect to the spleen, G6 significantly reduced both the splenomegaly and megakaryocytic hyperplasia. In the critically important bone marrow, G6 normalized the pathologically high levels of phospho-Jak2 and phospho-signal transducer and activator of transcription 5 (STAT5). It significantly reduced the megakaryocytic hyperplasia in the marrow and completely normalized the M/E ratio. Most importantly, G6 selectively reduced the mutant Jak2 burden by 67%on average, with virtual elimination of mutant Jak2 cells in one third of all treated mice. Lastly, clonogenic assays using marrow stem cells from the myeloproliferative neoplasm mice revealed a time-dependent elimination of the clonogenic growth potential of these cells by G6. Collectively, these data indicate that G6 exhibits exceptional efficacy in the peripheral blood, liver, spleen, and, most importantly, in the bone marrow, thereby raising the possibility that this compound may alter the natural history of Jak2-V617F-mediated myeloproliferative neoplasia.

Temozolomide-induced severe myelosuppression: analysis of clinically associated polymorphisms in two patients.

Genotyping of putative determinants of temozolomide (TMZ)-induced life-threatening bone marrow suppression was performed in two patients with glioma treated with adjuvant TMZ and radiation therapy. DNA was extracted from the patients' mononuclear cells and genotyping of O-methylguanine-DNA-methyltransferase (MGMT), multidrug resistance (MDR1; also known as ABCB1), NQO1, and GSTP1 genes and analysis for the epigenetic silencing of specific MGMT gene promoters were carried out to evaluate the possible genetic determinants of increased risk of severe TMZ-induced myelosuppression. Although both patients were heterozygous for all ABCB1 single nucleotide polymorphisms and for rs12917 and rs1803965 in the MGMT gene, patient 1 was heterozygous for rs1695 in GSTP1 and rs2308327 in the MGMT gene. This patient also exhibited GG genotype for the MGMT single nucleotide polymorphisms, rs2308321, which is noteworthy for its 0.7% frequency globally. Epigenetic silencing of MGMT gene was not detected in either patient. Two single nucleotide polymorphisms identified in patient 1 (missense I143V and K178R polymorphisms; rs2308321 and rs2308327, respectively) have recently been shown to correlate with an increased risk of severe TMZ-induced myelosuppression. The polymorphisms identified in patient 2 have not been associated with an increased risk of severe TMZ-induced myelosuppression. Genotyping analyses of larger patient populations administered TMZ are required to validate the genetic determinants of severe TMZ-induced myelosuppression.

AT9283, a potent inhibitor of the Aurora kinases and Jak2, has therapeutic potential in myeloproliferative disorders.

Constitutive activation of Janus kinase (Jak) 2 is the most prevalent pathogenic event observed in the myeloproliferative disorders (MPD), suggesting that inhibitors of Jak2 may prove valuable in their management. Inhibition of the Aurora kinases has also proven to be an effective therapeutic strategy in a number of haematological malignancies. AT9283 is a multi-targeted kinase inhibitor with potent activity against Jak2 and Aurora kinases A and B, and is currently being evaluated in clinical trials. To investigate the therapeutic potential of AT9283 in the MPD we studied its activity in a number of Jak2-dependent systems. AT9283 potently inhibited proliferation and Jak2-related signalling in Jak2-dependent cell lines as well as inhibiting the formation of erythroid colonies from haematopoietic progenitors isolated from MPD patients with Jak2 mutations. The compound also demonstrated significant therapeutic potential in vivo in an ETV6-JAK2 (TEL-JAK2) murine leukaemia model. Inhibition of both Jak2 and Aurora B was observed in the model systems used, indicating a dual mechanism of action. Our results suggest that AT9283 may be a valuable therapy in patients with MPD and that the dual inhibition of Jak2 and the Aurora kinases may potentially offer combinatorial efficacy in the treatment of these diseases.

Therapeutic potential of JAK2 inhibitors.

The discovery of an activating tyrosine kinase mutation JAK2V617F in myeloproliferative neoplasms (MPNs), polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) has resulted in the development of JAK2 inhibitors, of which several are being evaluated in phase I/II clinical studies. It is important to recognize that because the V617F mutation is localized in a region outside the adenosine triphosphate (ATP)-binding pocket of JAK2 enzyme, ATP-competitive inhibitors of JAK2 kinase (like the current JAK2 inhibitors in the clinic) are not likely to discriminate between wild-type and mutant JAK2 enzymes. Therefore, JAK2 inhibitors, by virtue of their near equipotent activity against wild-type JAK2 that is important for normal hematopoiesis, may have adverse myelosuppression as an expected side effect, if administered at doses that aim to completely inhibit the mutant JAK2 enzyme. While they may prove to be effective in controlling hyperproliferation of hematopoietic cells in PV and ET, they may not be able to eliminate mutant clones. On the other hand, JAK inhibitors may have great therapeutic benefit by controlling the disease for patients with MPNs who suffer from debilitating signs (eg, splenomegaly) or constitutional symptoms (which presumably result from high levels of circulating cytokines that signal through JAK enzymes). Indeed, the primary clinical benefits observed so far in MF patients have been significant reduction is splenomegaly, elimination of debilitating disease-related symptoms, and weight gain. Most importantly, patients with and without the JAK2V617F mutation appear to benefit to the same extent. In this review we summarize current clinical experience with JAK2 inhibitors in MPNs.

Epigenetic alterations complement mutation of JAK2 tyrosine kinase in patients with BCR/ABL-negative myeloproliferative disorders.

An acquired autoactivating mutation with a V617F amino-acid substitution in the JAK2 tyrosine kinase is frequently found in BCR/ABL-negative myeloproliferative disorders (MPD). Hypermethylation of CpG islands within gene promoter regions is associated with transcriptional inactivation and represents an important mechanism of gene silencing in the pathogenesis of hematopoietic malignancies. In this study, we determined the DNA methylation status of 13 cancer-related genes in the context of JAK2 mutations in 39 patients with MPD. Genes analyzed for hypermethylation were SOCS-1, SHP-1, E-cadherin, MGMT, TIMP-2, TIMP-3, p15, p16, p73, DAPK1, RASSF1A, RARbeta2 and hMLH1. We found at least one hypermethylated gene in 15/39 MPD patient specimens, and in 6/39 samples aberrant methylation of the negative cytokine regulator SOCS-1 was present. The JAK2V617F mutation was found in 21/39 patients as determined by allele-specific polymerase chain reaction. Hypermethylation of SOCS-1 was observed in 3/21 patients with an autoactivating JAK2 mutation and in 3/18 patients with wild-type JAK2. Our results suggest that epigenetic inactivation of SOCS-1 may be a complementary mechanism to the JAK2V617F mutation in the pathogenesis of MPD that leads to dysregulation of JAK-STAT signal transduction and thus contributes to growth factor hypersensitivity.