Hydroxyurea does not appreciably reduce JAK2 V617F allele burden in patients with polycythemia vera or essential thrombocythemia

Moving toward disease modification in polycythemia vera

Polycythemia vera (PV) belongs to the BCR-ABL1-negative myeloproliferative neoplasms and is characterized by activating mutations in JAK2 and clinically presents with erythrocytosis, variable degrees of systemic and vasomotor symptoms, and an increased risk of both thromboembolic events and progression to myelofibrosis and acute myeloid leukemia (AML). Treatment selection is based on a patient's age and a history of thrombosis in patients with low-risk PV treated with therapeutic phlebotomy and aspirin alone, whereas cytoreductive therapy with either hydroxyurea or interferon alfa (IFN-α) is added for high-risk disease. However, other disease features such as significant disease-related symptoms and splenomegaly, concurrent thrombocytosis and leukocytosis, or intolerance of phlebotomy can constitute an indication for cytoreductive therapy in patients with otherwise low-risk disease. Additionally, recent studies demonstrating the safety and efficacy (ie, reduction in phlebotomy requirements and molecular responses) of ropegylated IFN-α2b support its use for patients with low-risk PV. Additionally, emerging data suggest that early treatment is associated with higher rates of molecular responses, which might eventually enable time-limited therapy. Nonetheless, longer follow-up is needed to assess whether molecular responses associate with clinically meaningful outcome measures such as thrombosis and progression to myelofibrosis or AML. In this article, we provide an overview of the current and evolving treatment landscape of PV and outline our vision for a patient-centered, phlebotomy-free, treatment approach using time-limited, disease-modifying treatment modalities early in the disease course, which could ultimately affect the natural history of the disease.

Treatment of hydroxyurea-resistant/intolerant polycythemia vera: a discussion of best practices

Polycythemia vera (PV) is a burdensome, chronic myeloproliferative neoplasm characterized by activating mutations in Janus kinase 2, erythrocytosis, and bone marrow hypercellularity. The goals of treatment are to achieve hematocrit and blood count control to ultimately reduce the risk of thrombohemorrhagic events and improve PV-related symptoms. Treatment is risk-stratified and typically includes cytoreduction with hydroxyurea or interferon formulations in first line for high-risk disease. However, inadequate response, resistance, or intolerance to first-line cytoreductive therapies may warrant introduction of second-line treatments, such as ruxolitinib. In this review, I detail preferred treatment and patient management approaches following inadequate response to or intolerance of first-line treatment for PV.

MDM2 antagonist idasanutlin in patients with polycythemia vera: results from a single-arm phase 2 study

Idasanutlin showed clinical activity in patients with HU-resistant/-intolerant PV, but chronic toxicity led to a high discontinuation rate.

Significant reductions in JAK2 allele burden occurred after 3 treatment cycles and were greatest in patients with clinical response.

Idasanutlin, an MDM2 antagonist, showed clinical activity and a rapid reduction in JAK2 V617F allele burden in patients with polycythemia vera (PV) in a phase 1 study. This open-label phase 2 study evaluated idasanutlin in patients with hydroxyurea (HU)-resistant/-intolerant PV, per the European LeukemiaNet criteria, and phlebotomy dependence; prior ruxolitinib exposure was permitted. Idasanutlin was administered once daily on days 1 through 5 of each 28-day cycle. The primary end point was composite response (hematocrit control and spleen volume reduction > 35%) in patients with splenomegaly and hematocrit control in patients without splenomegaly at week 32. Key secondary end points included safety, complete hematologic response (CHR), patient-reported outcomes, and molecular responses. All patients (n = 27) received idasanutlin; 16 had response assessment (week 32). Among responders with baseline splenomegaly (n = 13), 9 (69%) attained any spleen volume reduction, and 1 achieved composite response. Nine patients (56%) achieved hematocrit control, and 8 patients (50%) achieved CHR. Overall, 43% of evaluable patients (6/14) showed a ≥50% reduction in the Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (week 32). Nausea (93%), diarrhea (78%), and vomiting (41%) were the most common adverse events, with grade ≥ 3 nausea or vomiting experienced by 3 patients (11%) and 1 patient (4%), respectively. Reduced JAK2 V617F allele burden occurred early (after 3 cycles), with a median reduction of 76%, and was associated with achieving CHR and hematocrit control. Overall, the idasanutlin dosing regimen showed clinical activity and rapidly reduced JAK2 allele burden in patients with HU-resistant/- intolerant PV but was associated with low-grade gastrointestinal toxicity, leading to poor long-term tolerability. This trial was registered at www.clinincaltrials.gov as #NCT03287245.

Genomic Profiling of a Randomized Trial of Interferon-α versus Hydroxyurea in MPN Reveals Mutation-Specific Responses

Treatment with IFNα was associated with distinct molecular responses in patients with JAK2-mutated MPN compared with CALR-mutated MPN.

Among patients treated with IFNα who did not achieve CHR, DNMT3A mutations emerged more frequently than non-DNMT3A mutations.

Although somatic mutations influence the pathogenesis, phenotype, and outcome of myeloproliferative neoplasms (MPNs), little is known about their impact on molecular response to cytoreductive treatment. We performed targeted next-generation sequencing (NGS) on 202 pretreatment samples obtained from patients with MPN enrolled in the DALIAH trial (A Study of Low Dose Interferon Alpha Versus Hydroxyurea in Treatment of Chronic Myeloid Neoplasms; #NCT01387763), a randomized controlled phase 3 clinical trial, and 135 samples obtained after 24 months of therapy with recombinant interferon-alpha (IFNα) or hydroxyurea. The primary aim was to evaluate the association between complete clinicohematologic response (CHR) at 24 months and molecular response through sequential assessment of 120 genes using NGS. Among JAK2-mutated patients treated with IFNα, those with CHR had a greater reduction in the JAK2 variant allele frequency (median, 0.29 to 0.07; P < .0001) compared with those not achieving CHR (median, 0.27 to 0.14; P < .0001). In contrast, the CALR variant allele frequency did not significantly decline in those achieving CHR or in those not achieving CHR. Treatment-emergent mutations in DNMT3A were observed more commonly in patients treated with IFNα compared with hydroxyurea (P = .04). Furthermore, treatment-emergent DNMT3A mutations were significantly enriched in IFNα–treated patients not attaining CHR (P = .02). A mutation in TET2, DNMT3A, or ASXL1 was significantly associated with prior stroke (age-adjusted odds ratio, 5.29; 95% confidence interval, 1.59-17.54; P = .007), as was a mutation in TET2 alone (age-adjusted odds ratio, 3.03; 95% confidence interval, 1.03-9.01; P = .044). At 24 months, we found mutation-specific response patterns to IFNα: (1) JAK2- and CALR-mutated MPN exhibited distinct molecular responses; and (2) DNMT3A-mutated clones/subclones emerged on treatment.

Data-driven analysis of the kinetics of the JAK2V617F allele burden and blood cell counts during hydroxyurea treatment of patients with polycythemia vera, essential thrombocythemia, and primary myelofibrosis

BACKGROUND

Hydroxyurea (HU) treatment of patients with essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) (MPNs) normalizes elevated blood cell counts within weeks in the large majority of patients. Studies on the impact of HU upon the kinetics of the JAK2V617F allele burden, leukocyte, and platelet counts over time are scarce.

PURPOSE

Using data-driven analysis as a novel tool to model the kinetics of the JAK2V617F allele burden and blood cell counts over time during treatment with HU.

MATERIAL AND METHODS

Using serial measurements of JAK2V617F and correlation analysis of routine hematological values (the Hb-concentration, leukocyte count, platelet count, and lactic dehydrogenase), we present a detailed description and analysis of the kinetics of the JAK2V617F, leukocyte, and platelet counts and lactic dehydrogenase in 27 patients (PV = 18; ET = 7; PMF = 2), who were followed in the Danish randomized trial (DALIAH). To further analyze the JAK2V617F kinetics, we use a machine learning clustering algorithm to group the response patterns.

RESULTS

Response patterns were highly heterogeneous, with clustering resulting in 3 groups and 3 outliers. In the large majority of patients, HU treatment was initially associated with a modest decline in the JAK2V617F allele burden in concert with a decline in leukocyte and platelet counts. However, HU did not induce a sustained and continuous decrease in the JAK2V617F allele burden.

CONCLUSION

Using data-driven analysis of the JAK2V617F allele burden, leukocyte, and platelet kinetics during treatment with HU, we have shown that HU does not induce a sustained decrease in the JAK2V617F allele burden and neither induces sustained normalization of elevated cell counts in MPN patients. Our results may explain why MPN patients during treatment with HU still have a substantially increased risk of thrombosis.

IRF4 and IRF8 expression are associated with clinical phenotype and clinico-hematological response to hydroxyurea in essential thrombocythemia

The morbidity and mortality of myeloproliferative neoplasms (MPNs) are primarily caused by arterial and venous complications, progression to myelofibrosis, and transformation to acute leukemia. However, identifying molecular-based biomarkers for risk stratification of patients with MPNs remains a challenge. We have previously shown that interferon regulatory factor-8 (IRF8) and IRF4 serve as tumor suppressors in myeloid cells. In this study, we evaluated the expression of IRF4 and IRF8 and the JAK2V617F mutant allele burden in patients with MPNs. Patients with decreased IRF4 expression were correlated with a more developed MPN phenotype in myelofibrosis (MF) and secondary AML (sAML) transformed from MPNs versus essential thrombocythemia (ET). Negative correlations between the JAK2V617F allele burden and the expression of IRF8 (P < 0.05) and IRF4 (P < 0.001) and between white blood cell (WBC) count and IRF4 expression (P < 0.05) were found in ET patients. IRF8 expression was negatively correlated with the JAK2V617F allele burden (P < 0.05) in polycythemia vera patients. Complete response (CR), partial response (PR), and no response (NR) were observed in 67.5%,10%, and 22.5% of ET patients treated with hydroxyurea (HU), respectively, in 12 months. At 3 months, patients in the CR group showed high IRF4 and IRF8 expression compared with patients in the PR and NR groups. In the 12-month therapy period, low IRF4 and IRF8 expression were independently associated with the unfavorable response to HU and high WBC count. Our data indicate that the expression of IRF4 and IRF8 was associated with the MPN phenotype, which may serve as biomarkers for the response to HU in ET.

Hydroxycarbamide effects on DNA methylation and gene expression in myeloproliferative neoplasms

Hydroxycarbamide (HC, hydroxyurea) is a cytoreductive drug inducing cell cycle blockade. However, emerging evidence suggests that HC plays a role in the modulation of transcription through the activity of transcription factors and DNA methylation. Examining the global mechanism of action of HC in the context of myeloproliferative neoplasms (MPNs), for which HC is the first-line treatment, will provide a better understanding of its molecular effects. To explore the effects of HC genome-wide, transcriptomic analyses were performed on two clinically relevant cell types at different stages of differentiation treated with HC in a murine MPN model. This study was replicated in MPN patients by profiling genome-wide gene expression and DNA methylation using patient blood samples collected longitudinally, before and following HC exposure. The effects of HC on the transcriptome were not only associated with cell cycle interruption but also with hematopoietic functions. Moreover, a group of genes were restored to normal expression levels in murine hematopoietic stem cells (HSCs) following drug treatment, including the master regulator of hematopoiesis, RUNX1. In humans, HC significantly modifies DNA methylation levels in HSCs at several distal regulatory regions, which we show to be associated with SPI1 binding sites and at the SPI1 locus itself. We have identified novel targets of HC that include pivotal transcription factors involved in hematopoiesis, and for the first time we report abnormal methylation patterns in MPN patients at the master regulator gene SPI1 and its distal binding sites, which HC is able to restore to normal levels.

Interferon alpha therapy in essential thrombocythemia and polycythemia vera-a systematic review and meta-analysis

Data on the efficacy and safety of interferon (IFN)-α for the treatment of essential thrombocythemia (ET) and polycythemia vera (PV) are inconsistent. We conducted a systematic review and meta-analysis and searched MEDLINE and EMBASE via Ovid, Scopus, COCHRANE registry of clinical trials, and Web of Science from inception through 03/2019 for studies of pegylated IFN (peg-IFN) and non-pegylated IFN (non-peg-IFN) in PV and ET patients. Random-effects models were used to pool response rates for the primary outcome of overall response rate (ORR) defined as a composite of complete response, partial response, complete hematologic response (CHR) and partial hematologic response. Peg-IFN and non-peg-IFN were compared by meta-regression analyses. In total, 44 studies with 1359 patients (730 ET, 629 PV) were included. ORR were 80.6% (95% confidence interval: 76.6-84.1%, CHR: 59.0% [51.5%-66.1%]) and 76.7% (67.4-84.0%; CHR: 48.5% [37.8-59.4%]) for ET and PV patients, respectively. In meta-regression analyses results did not differ significantly for non-peg-IFN vs. peg-IFN. Annualized rates of thromboembolic complications and treatment discontinuation due to adverse events were low at 1.2% and 8.8% for ET and 0.5% and 6.5% for PV patients, respectively. Both peg-IFN and non-peg-IFN can be effective and safe long-term treatments for ET and PV.

A case of JAK2V617F-positive essential thrombocythemia where allele burden was reduced by a PD-1 inhibitor

The Janus kinase/signal transducers and activators of transcription signaling pathway induces programmed death ligand-1 (PD-L1) expression. JAK2 mutation at position 617 (JAK2V617) is a frequent driver of myeloproliferative neoplasms (MPN) through PD-L1 expression. Although PD-1 inhibitors should be effective against MPN with JAK2V617F mutation, this has not yet been reported in humans. Thus, we assessed the efficacy of a PD-1 inhibitor in a lung cancer patient with JAK2V617F-positive essential thrombocythemia (ET). A 71-year-old man was diagnosed with ET, and with lung carcinoma 3 years later. After right lobectomy and postoperative chemotherapy, pembrolizumab [a PD-1 inhibitor (200 mg, every 3 weeks)] was initiated for refractory lung carcinoma. Lung cancer progression did not occur for 1.5 years under treatment. Most megakaryocytes were PD-L1-positive, and after pembrolizumab initiation, platelet count remained below 45 × 10⁴/μL without the need for other cytoreductive therapies for ET. The JAK2V617F allele burden gradually decreased from 11.5% at diagnosis to 2.9% after 17 months of pembrolizumab treatment. Other peripheral blood lineages did not decrease, and pembrolizumab treatment was continued without any adverse events. This is the first report demonstrating the effectiveness of pembrolizumab in an MPN patient with JAK2V617F mutation.

Interferon Therapy in Myelofibrosis: Systematic Review and Meta-analysis

BACKGROUND

Myelofibrosis (MF) is a Philadelphia chromosome-negative myeloproliferative neoplasm characterized by progressive bone marrow failure, increased risk of progression to acute myeloid leukemia, and constitutional symptoms. For over 3 decades, various formulations of interferon (IFN) have been used for the treatment of MF, with variable results, and the role of IFN in the treatment of MF is evolving.

PATIENTS AND METHODS

For this systematic review and meta-analysis, Medline and Embase via Ovid, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science were searched from inception through March 2019 for studies of pegylated IFN (peg-IFN) and non-peg-IFN in MF patients. The primary outcome of overall response rate was defined as a composite of complete response, partial response, complete hematologic response, and partial hematologic response. Random-effects models were used to pool overall response rate, and metaregression analyses were performed to compare peg-IFN and non--peg-IFN formulations.

RESULTS

Among the 10 studies with 141 MF patients included, the overall response rate was 49.9% (95% confidence interval [CI], 30.4-69.3), and there was no statistically significant difference (P = .99) between peg-IFN (50.0%; 95% CI, 26.2-73.9; I2 = 76.9%) and non-peg-IFN (49.6%; 95% CI, 20.5-79.0; I2 = 56.7%). Treatment discontinuation resulting from adverse events was common with non-peg-IFN at 35.8% (95% CI, 3.5-68.1) per year, and less in the one study on peg-IFN (0.5% per year).

CONCLUSION

IFN can lead to hematologic improvements in a subset of MF patients, but study quality is limited and heterogenous. Biomarkers predicting response to IFN and formulations with improved tolerability are needed.

Next Generation Sequencing in MPNs. Lessons from the Past and Prospects for Use as Predictors of Prognosis and Treatment Responses

The myeloproliferative neoplasms (MPNs) are acquired hematological stem cell neoplasms characterized by driver mutations in JAK2, CALR, or MPL. Additive mutations may appear in predominantly epigenetic regulator, RNA splicing and signaling pathway genes. These molecular mutations are a hallmark of diagnostic, prognostic, and therapeutic assessment in patients with MPNs. Over the past decade, next generation sequencing (NGS) has identified multiple somatic mutations in MPNs and has contributed substantially to our understanding of the disease pathogenesis highlighting the role of clonal evolution in disease progression. In addition, disease prognostication has expanded from encompassing only clinical decision making to include genomics in prognostic scoring systems. Taking into account the decreasing costs and increasing speed and availability of high throughput technologies, the integration of NGS into a diagnostic, prognostic and therapeutic pipeline is within reach. In this review, these aspects will be discussed highlighting their role regarding disease outcome and treatment modalities in patients with MPNs.

How I treat polycythemia vera

Since its discovery, polycythemia vera (PV) has challenged clinicians responsible for its diagnosis and management and scientists investigating its pathogenesis. As a clonal hematopoietic stem cell (HSC) disorder, PV is a neoplasm but its driver mutations result in overproduction of morphologically and functionally normal blood cells. PV arises in an HSC but it can present initially as isolated erythrocytosis, leukocytosis, thrombocytosis, or any combination of these together with splenomegaly or myelofibrosis, and it can take years for a true panmyelopathy to appear. PV shares the same JAK2 mutation as essential thrombocytosis and primary myelofibrosis, but erythrocytosis only occurs in PV. However, unlike secondary causes of erythrocytosis, in PV, the plasma volume is frequently expanded, masking the erythrocytosis and making diagnosis difficult if this essential fact is ignored. PV is not a monolithic disorder: female patients deregulate fewer genes and clinically behave differently than their male counterparts, while some PV patients are genetically predisposed to an aggressive clinical course. Nevertheless, based on what we have learned over the past century, most PV patients can lead long and productive lives. In this review, using clinical examples, I describe how I diagnose and manage PV in an evidence-based manner without relying on chemotherapy.

Safety and efficacy of combination therapy of interferon-α2 and ruxolitinib in polycythemia vera and myelofibrosis

Interferon‐α2 reduces elevated blood cell counts and splenomegaly in patients with myeloproliferative neoplasms (MPN) and may restore polyclonal hematopoiesis. Its use is limited by inflammation‐mediated toxicity, leading to treatment discontinuation in 10‐30% of patients. Ruxolitinib, a potent anti‐inflammatory agent, has demonstrated benefit in myelofibrosis (MF) and polycythemia vera (PV) patients. Combination therapy (CT) with these two agents may be more efficacious than monotherapy with either, potentially improving tolerability of interferon‐α2 as well. We report the preliminary results from a phase II study of CT with pegylated interferon‐α2 and ruxolitinib in 50 MPN patients (PV, n = 32; low‐/intermediate‐1‐risk MF, n = 18), the majority (n = 47) being resistant and/or intolerant to interferon‐α2 monotherapy. Objectives included remission (2013 revised criteria encompassing histologic, hematologic, and clinical responses), complete hematologic response (CHR), molecular response, and toxicity. Follow‐up was 12 months. Partial remission (PR) and sustained CHR were achieved in 9% and 44% of PV patients, respectively. In MF patients, complete or partial remission was achieved in 39%, and sustained CHR in 58%. The median JAK2V617F allele burden declined significantly in both groups. Hematologic toxicity was the most common adverse event and was managed by dose reduction. Thirty‐seven serious adverse events were recorded in 23 patients; the discontinuation rate was 20%. We conclude that CT with interferon‐α2 and ruxolitinib is efficacious in patients with low‐/intermediate‐1‐risk MF and, to a lesser extent, in patients with PV. These preliminary results encourage phase III studies as well as a study with CT in newly diagnosed MPN patients.

Assessment of the interlaboratory variability and robustness of JAK2V617F mutation assays: A study involving a consortium of 19 Italian laboratories

To date, a plenty of techniques for the detection of JAK2^V617F is used over different laboratories, with substantial differences in specificity and sensitivity. Therefore, to provide reliable and comparable results, the standardization of molecular techniques is mandatory.

A network of 19 centers was established to 1) evaluate the inter- and intra-laboratory variability in JAK2^V617F quantification, 2) identify the most robust assay for the standardization of the molecular test and 3) allow consistent interpretation of individual patient analysis results. The study was conceived in 3 different rounds, in which all centers had to blindly test DNA samples with different JAK2^V617F allele burden (AB) using both quantitative and qualitative assays.

The positivity of samples with an AB < 1% was not detected by qualitative assays. Conversely, laboratories performing the quantitative approach were able to determine the expected JAK2^V617F AB. Quantitative results were reliable across all mutation loads with moderate variability at low AB (0.1 and 1%; CV = 0.46 and 0.77, respectively). Remarkably, all laboratories clearly distinguished between the 0.1 and 1% mutated samples.

In conclusion, a qualitative approach is not sensitive enough to detect the JAK2^V617F mutation, especially at low AB. On the contrary, the ipsogen JAK2 MutaQuant CE-IVD kit resulted in a high, efficient and sensitive quantification detection of all mutation loads. This study sets the basis for the standardization of molecular techniques for JAK2^V617F determination, which will require the employment of approved operating procedures and the use of certificated standards, such as the recent WHO 1st International Reference Panel for Genomic JAK2^V617F.

Impact of hydroxycarbamide and interferon-α on red cell adhesion and membrane protein expression in polycythemia vera

Polycythemia vera is a chronic myeloproliferative neoplasm characterized by the JAK2V617F mutation, elevated blood cell counts and a high risk of thrombosis. Although the red cell lineage is primarily affected by JAK2V617F, the impact of mutated JAK2 on circulating red blood cells is poorly documented. Recently, we showed that in polycythemia vera, erythrocytes had abnormal expression of several proteins including Lu/BCAM adhesion molecule and proteins from the endoplasmic reticulum, mainly calreticulin and calnexin. Here we investigated the effects of hydroxycarbamide and interferon-α treatments on the expression of erythroid membrane proteins in a cohort of 53 patients. Surprisingly, while both drugs tended to normalize calreticulin expression, proteomics analysis showed that hydroxycarbamide deregulated the expression of 53 proteins in red cell ghosts, with overexpression and downregulation of 37 and 16 proteins, respectively. Within over-expressed proteins, hydroxycarbamide was found to enhance the expression of adhesion molecules such as Lu/BCAM and CD147, while interferon-α did not. In addition, we found that hydroxycarbamide increased Lu/BCAM phosphorylation and exacerbated red cell adhesion to its ligand laminin. Our study reveals unexpected adverse effects of hydroxycarbamide on red cell physiology in polycythemia vera and provides new insights into the effects of this molecule on gene regulation and protein recycling or maturation during erythroid differentiation. Furthermore, our study shows deregulation of Lu/BCAM and CD147 that are two ubiquitously expressed proteins linked to progression of solid tumors, paving the way for future studies to address the role of hydroxycarbamide in tissues other than blood cells in myeloproliferative neoplasms.

Recommendations for molecular testing in classical Ph1-neg myeloproliferative disorders-A consensus project of the Italian Society of Hematology

The discovery that Philadelphia-negative classical myeloproliferative neoplasms (MPNs) present with several molecular abnormalities, including the mostly represented JAK2V617F mutation, opened new horizons in the diagnosis, prognosis, and monitoring of these disorders. However, the great strides in the knowledge on molecular genetics need parallel progresses on the best approach to methods for detecting and reporting disease-associated mutations, and to shape the most effective and rationale testing pathway in the diagnosis, prognosis and monitoring of MPNs. The MPN taskforce of the Italian Society of Hematology (SIE) assessed the scientific literature and composed a framework of the best, possibly evidence-based, recommendations for optimal molecular methods as well as insights about the applicability and interpretation of those tests in the clinical practice, and clinical decision for testing MPNs patients. The issues dealt with: source of samples and nucleic acid template, the most appropriate molecular abnormalities and related detection methods required for diagnosis, prognosis, and monitoring of MPNs, how to report a diagnostic molecular test, calibration and quality control. For each of these issues, practice recommendations were provided.

Monitoring Minimal Residual Disease in the Myeloproliferative Neoplasms: Current Applications and Emerging Approaches

The presence of acquired mutations within the JAK2, CALR, and MPL genes in the majority of patients with myeloproliferative neoplasms (MPN) affords the opportunity to utilise these mutations as markers of minimal residual disease (MRD). Reduction of the mutated allele burden has been reported in response to a number of therapeutic modalities including interferon, JAK inhibitors, and allogeneic stem cell transplantation; novel therapies in development will also require assessment of efficacy. Real-time quantitative PCR has been widely adopted for recurrent point mutations with assays demonstrating the specificity, sensitivity, and reproducibility required for clinical utility. More recently, approaches such as digital PCR have demonstrated comparable, if not improved, assay characteristics and are likely to play an increasing role in MRD monitoring. While next-generation sequencing is increasingly valuable as a tool for diagnosis of MPN, its role in the assessment of MRD requires further evaluation.

JAK2V617F Allele Burden Measurement in Peripheral Blood of Iranian Patients with Myeloproliferative Neoplasms and Effect of Hydroxyurea on JAK2V617F Allele Burden

BACKGROUND

Myeloproliferative neoplasms (MPNs) are clonal malignant diseases that represent a group of conditions including polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The aim of this study was to evaluate possible correlations between JAK2V617F allele burden and clinicohematologic characteristics in Iranian patients with MPNs. We also aimed at determining the correlation between JAK2V617F allele burden and use of cyto reductive treatment (hydroxyurea).

MATERIALS AND METHODS

We performed ARMS-PCR for all MPNs samples and subsequently performed real-time quantitative polymerase chain reaction (qRT-PCR) for JAK2V617F allele burden measurement using DNA from peripheral blood leukocytes.

RESULTS

Two distinct groups of patients were examined at a single time point: group A (n=40; 20 PV, 20 ET) was examined at the time of diagnosis; group B (n=85; 40 PV, 30 ET and 15 PMF) while under treatment with hydroxyurea (HU). The median allele burden of the JAK2 V617F was 72% for PV and 49% for ET patients at the time of diagnosis (p=0.01). For patients with HU treatment, we determined the median JAK2V617F allele burden to be 43%, 40%, and 46.5 % in PV, ET and PMF patients; respectively. HU-treated PV patients had a significant lower %JAK2V617F than PV patients at the time of diagnosis (43% vs. 72%, p=0.005). In ET group, the relationship between the JAK2 V617F allele burden and leukocyte count was significant (p=0.02 and p=0.01 in untreated and treated patients, respectively).

CONCLUSIONS

Our results showed that patients with PV have a higher JAK2V617F allele burden. Moreover, our study demonstrated that the JAK2V617F allele burden correlates with clinical features in ET group. We also showed hydroxyurea can affect the JAK2V617F allele burden in PV patients.

RECQL5 Suppresses Oncogenic JAK2-Induced Replication Stress and Genomic Instability

JAK2V617F is the most common oncogenic lesion in patients with myeloproliferative neoplasms (MPNs). Despite the ability of JAK2V617F to instigate DNA damage in vitro, MPNs are nevertheless characterized by genomic stability. In this study, we address this paradox by identifying the DNA helicase RECQL5 as a suppressor of genomic instability in MPNs. We report increased RECQL5 expression in JAK2V617F-expressing cells and demonstrate that RECQL5 is required to counteract JAK2V617F-induced replication stress. Moreover, RECQL5 depletion sensitizes JAK2V617F mutant cells to hydroxyurea (HU), a pharmacological inducer of replication stress and the most common treatment for MPNs. Using single-fiber chromosome combing, we show that RECQL5 depletion in JAK2V617F mutant cells impairs replication dynamics following HU treatment, resulting in increased double-stranded breaks and apoptosis. Cumulatively, these findings identify RECQL5 as a critical regulator of genome stability in MPNs and demonstrate that replication stress-associated cytotoxicity can be amplified specifically in JAK2V617F mutant cells through RECQL5-targeted synthetic lethality.

The JAK2 V617F mutational status and allele burden may be related with the risk of venous thromboembolic events in patients with Philadelphia-negative myeloproliferative neoplasms

INTRODUCTION

Patients with Philadelphia-negative myeloproliferative neoplasms (Ph(-) MPNs) are at increased risk of thromboembolic and hemorrhagic complications. The aim of the study was to determine the relationship between JAK2 V617F mutational status, JAK2 V617F allele burden and the risk of vascular complications occurrence.

MATERIALS AND METHODS

Analysis was performed in a cohort of 186 patients diagnosed with polycythemia vera (53), essential thrombocythemia (114), primary myelofibrosis (11), and unclassified MPN (8). The risk of vascular complications development was analyzed in 126 JAK2 V617F-positive patients with respect to allele burden assessed with allele-specific 'real-time' quantitative polymerase chain reaction (AS RQ-PCR).

RESULTS

Overall prevalence of any vascular complications was 44.6%. Arterial thrombosis occurred in 20.4%, venous thromboembolism (VTE) in 11.3%, bleeding episodes in 24.7% of patients. Individuals harboring JAK2 V617F mutation, regardless of MPN type, were at higher risk of VTE (OR=5.15, 95%CI: 1.16-22.90, P=0.024), mainly deep vein thrombosis (DVT). JAK2 allele burden higher than 20% identified patients with 7.4-fold increased risk of VTE (95%CI: 1.6-33.7, P=0.004), but not of arterial thrombosis, neither of bleeding complications, and remained the only significant VTE risk factor in multivariate logistic regression. High allele burdens (over 50%) were strikingly associated with proximal DVT cases, but not with distal DVT.

CONCLUSIONS

The group of MPN patients with JAK2 V617F allele burden higher than 20% may benefit the most from vigilant monitoring and appropriate prophylaxis against vascular events. Inclusion of JAK2 V617F mutant allele burden in new risk stratifications seems to be justified and requires controlled prospective trials.

X chromosome inactivation analysis reveals a difference in the biology of ET patients with JAK2 and CALR mutations

Calreticulin mutations (CALR(MUT)) are found in a significant proportion of patients with essential thrombocythemia (ET) lacking JAK2(V617F) or MPL mutations. They are associated with substantially different hematological and clinical features and define a distinct subtype of ET. We show here that their presence is significantly correlated with a clonal X chromosome inactivation pattern (XCIP). Of 105 female ET patients investigated, 61 had an interpretable XCIP, and a clonal pattern was observed in 88% of CALR(MUT) patients compared with 26% of JAK2(V617F) (P = .0002) and 9% of JAK2(V617F)/MPL/CALR wild-type patients (P < .0001). Neutrophil CALR(MUT) level was significantly higher than JAK2(V617F) level (median, 50% vs 18%; P < .0001), and wild-type myelopoiesis was suppressed in CALR(MUT) but not JAK2(V617F) patients. These data are suggestive of truly monoclonal hematopoiesis in CALR(MUT) patients and provide further evidence that the biology associated with CALR mutations is markedly different from that of JAK2(V617F) mutations.

Emerging drugs for polycythemia vera

INTRODUCTION

Polycythemia vera (PV) patients suffer from disease-related constitutional symptoms, cardiovascular complications and risk of transformation into myelofibrosis and acute leukemia.

AREAS COVERED

Clinical and molecular aspects and current therapies will be described to provide clinical and molecular background to understand the natural history and treatment strategies in PV. Pertinent ongoing research questions, challenges arising out of the specific disease course and biology of PV as well as challenges and opportunities for new agents in PV are addressed. A focus is placed on pegylated interferon-α formulations (PEG-INFa2a) and JAK2 inhibitors. Newest data on symptom burden and incidence and prevalence of PV and MPNs are highlighted in the context of development of PV therapies.

EXPERT OPINION

Therapeutic goals in PV are to prevent vascular events, reduce symptoms and for future therapies delay/prevent disease progression. Currently available treatments such as phlebotomy, antiplatelet therapy, managing risk factors and cytoreductive therapies such as hydroxyurea (HU) and PEG-INFa2a are effective. JAK2 inhibitors recently have shown promising activity in reducing PV symptoms and spleen size and improving blood counts. Yet the influence of long-term outcome and delaying disease progression is unknown. Thus, there still remains an unmet medical need for improved therapy and symptom management in PV.

Differential effects of hydroxyurea and INC424 on mutant allele burden and myeloproliferative phenotype in a JAK2-V617F polycythemia vera mouse model

JAK2-V617F cells show a competitive advantage over wild-type cells in BM transplantation assays. A preclinical mouse model allows the examination of the effects of therapeutic agents on blood parameters and JAK2-V617F mutant allele burden.

BCR-ABL1-negative chronic myeloid neoplasms: an update on management techniques

Recent discoveries concerning mutations associated with chronic myeloproliferative neoplasms have modified our understanding of the biology of these incurable diseases and guided us to the development of inhibitors active on the constitutively activated JAK-STAT pathway. Concurrently, numerous studies dealt with clinical issues; it led to a revised WHO classification; clarified the role of mutated JAK2 and leukocytosis in the pathogenesis of cardiovascular events; allowed the development of risk prognostic scores and tools for monitoring response to therapy; and resulted in completion of Phase III trials with JAK2 inhibitor in myelofibrosis. All these results hold the promise of improving patient prognostication and therapeutic approach, with the aim of efficiently preventing disease-associated complications and, hopefully, to improve the dismal survival associated with myelofibrosis. This review discusses how to manage, according to current clinical practice, the steps of diagnosis, prognostication and therapeutic choices in myeloproliferative neoplasm patients.

A novel, highly sensitive and rapid allele-specific loop-mediated amplification assay for the detection of the JAK2V617F mutation in chronic myeloproliferative neoplasms

BACKGROUND

The identification of the JAK2V617F mutation is mandatory in the diagnostic work-up of Philadelphia chromosome-negative myeloproliferative neoplasms. Several molecular techniques to detect this mutation are currently available, but each of them has some limits.

DESIGN AND METHODS

We set up a novel molecular method for the identification of the JAK2V617F mutation based on an allele-specific loop-mediated amplification, not polymerase chain reaction analysis. This innovative technique amplifies DNA targets under isothermal conditions with high specificity, efficiency and rapidity. The method does not require either a thermal cycler or gel separation and the DNA amplification reaction is visible to the naked eye and can be monitored by turbidimetry. This method was validated on DNA from cell lines as well as from patients with myeloproliferative neoplasms. The results were compared with those obtained by conventional polymerase chain reaction methods.

RESULTS

This assay detects, within 1 hour, the JAK2V617F mutation down to an allele burden of 0.1-0.01%. All samples positive by polymerase chain reaction (n=146) proved positive when tested by allele-specific loop-mediated amplification and none of the 80 negative controls gave false positive results. In addition, six patients with essential thrombocythemia previously diagnosed as being JAK2V617F negative by polymerase chain reaction analysis were found to be positive (at a low level) by allele-specific loop-mediated amplification. Furthermore, this assay discriminated the amount of JAK2V617F tumor allele within intervals of positivity, above 50%, between 50% and 10% and below 10%.

CONCLUSIONS

Allele-specific loop-mediated amplification is a simple, robust and easily applicable method for the molecular diagnosis and monitoring of JAK2V617F mutation in patients with chronic myeloproliferative neoplasms.

Decrease in JAK2 V617F allele burden is not a prerequisite to clinical response in patients with polycythemia vera

BACKGROUND

Although reduction in the JAK2(V617F) allele burden (%V617F) has been suggested as a criterion for defining disease response to cytoreductive therapy in polycythemia vera, its value as a response monitor is unclear. The purpose of this study is to determine whether a reduction in %V617F in polycythemia vera is a prerequisite to achieving hematologic remission in response to cytoreductive therapy.

DESIGN AND METHODS

We compared the clinical and hematologic responses to change in %V617F (molecular response) in 73 patients with polycythemia vera treated with either interferon (rIFNα-2b: 28, Peg-rIFNα-2a: 18) or non-interferon drugs (n=27), which included hydroxyurea (n=8), imatinib (n=12), dasatinib (n=5), busulfan (n=1), and radioactive phosphorus (n=1). Hematologic response evaluation employed Polycythemia Vera Study Group criteria, and molecular response evaluation, European Leukemia Net criteria.

RESULTS

Of the 46 treated with interferon, 41 (89.1%) had a hematologic response, whereas only 7 (15.2%) had a partial molecular response. Of the 27 who received non-interferon treatments, 16 (59.3%) had a hematologic response, but only 2 (7.4%) had a molecular response. Median duration of follow up was 2.8 years. Statistical agreement between hematologic response and molecular response was poor in all treatment groups.

CONCLUSIONS

Generally, hematologic response was not accompanied by molecular response. Therefore, a quantitative change in %V617F is not required for clinical response in patients with polycythemia vera.

Modulation of JAK2 V617F allele burden dynamics by hydroxycarbamide in polycythaemia vera and essential thrombocythaemia patients

The modulation of JAK2 V617F allele burden dynamics was prospectively analysed in 47 patients (26 polycythaemia vera [PV] and 21 essential thrombocythaemia [ET]) treated with first-line hydroxyurea (HU) and compared with the JAK2 V617F dynamics of a control group of 45 PV and ET patients. A partial molecular response (PMR), according to European Leukaemia Net criteria, was observed in 27/47 (57%) patients. Median time to PMR was 14 months (3-66) with a probability of PMR at 3 years of 57%. A significant decrease in JAK2 V617F allele load was observed at 36 months both in PV and ET patients, being the reduction in PV higher than in ET patients (P = 0·01). A haematocrit ≥0·45 L/L was associated with a higher probability of attaining a PMR (HR:3·4; 95%CI:1·02-11·6, P = 0·04). Control group showed a slight increase of JAK2 V617F allele burden over time. The reduction in the mutated allele load comparing treated patients versus controls was highly significant both in PV and ET, demonstrating a clear effect of HU on the JAK2 V617F allele burden. In conclusion, first-line HU can attain PMR in more than 50% of newly diagnosed PV and ET patients, with a continuous decrease of the JAK2 V617F allele burden in PV patients during treatment.

Differences in the JAK2 and MPL mutation status in the cell lineages of the bcr/abl-negative chronic myeloproliferative neoplasm subtypes

OBJECTIVE

While the somatic mutation of Janus Kinase 2 (JAK2) and the thrombopoietin receptor (c-MPL) gene are thought to affect the pathogenesis of bcr/abl negative chronic myeloproliferative neoplasm (MPN), the relationship between the mutation and the clinical features remain obscure.

METHODS

The mutation status of these genes in granulocytes, platelets, T-cells, and erythroid colonies (BFU-E) was obtained from 115 MPN patients, and then the clinical features of the MPN subtypes were compared.

RESULTS

The JAK2-V617F mutation was observed in three lineages of granulocytes, platelets, and BFU-E in almost all polycythemia vera (PV) and primary myelofibrosis (PMF) patients. In contrast, 68% of essential thrombocythemia (ET) patients have the JAK2-V617F mutation in at least one of the lineages, of which 70% of these patients have the JAK2-V617F mutation in three lineages; the remaining ET patients with the JAK2-V617F mutation only exhibited the mutation in one or two lineages. Further, the ET patients that exhibited the JAK2-V617F mutation in three lineages had higher WBC and granulocyte counts as compared to the ET patients that did not have the JAK2-V617F mutation or only had the mutation in one or two lineages. Concerning the MPL gene, two ET patients had the MPL-W515L gene mutation in their platelets, although the lineage of the JAK2-V617F mutation involved differed from case to case.

CONCLUSION

The progenitor cells that are involved with the JAK2-V617F mutation in MPNs are different in each subtype and this difference may also affect the clinical features of MPNs.

A prospective study of 338 patients with polycythemia vera: the impact of JAK2 (V617F) allele burden and leukocytosis on fibrotic or leukemic disease transformation and vascular complications

We studied the relationship between JAK2 (V617F) mutant allele burden and clinical phenotype, disease progression and survival in patients with polycythemia vera (PV). The percentage of granulocyte mutant alleles was evaluated using a quantitative real-time polymerase chain reaction-based allelic discrimination assay. Of the 338 patients enrolled in this prospective study, 320 (94.7%) carried the JAK2 (V617F) mutation. Direct relationships were found between mutant allele burden and hemoglobin concentration (P=0.001), white blood cell count (P=0.001), spleen size (P=0.001) and age-adjusted bone marrow cellularity (P=0.002), while an inverse relationship was found with platelet count (P<0.001). During the study period, eight patients progressed to post-PV myelofibrosis (MF) (all carrying >50% mutant alleles), while 10 patients developed acute myeloid leukemia (AML). The mutant allele burden was significantly related to the risk of developing myelofibrosis (P=0.029) and retained its significant effect also in multivariable analysis (P=0.03). By contrast, the risk of developing AML as well as that of thrombosis was not significantly related to mutant allele burden. Leukocytosis did not affect thrombosis, MF, leukemia or survival. In conclusion, a JAK2 (V617F) allele burden >50% represents a risk factor for progression to MF in PV.