Since its approval in 2011, the Janus kinase 1/2 (JAK1/2) inhibitor ruxolitinib has evolved to become the centerpiece of therapy for myelofibrosis (MF), and its use in patients with hydroxyurea ...resistant or intolerant polycythemia vera (PV) is steadily increasing. Several other JAK2 inhibitors have entered clinical testing, but none have been approved and many have been discontinued. Importantly, the activity of these agents is not restricted to patients with JAK2 V617F or exon 12 mutations. Although JAK2 inhibitors provide substantial clinical benefit, their disease-modifying activity is limited, and rational combinations with other targeted agents are needed, particularly in MF, in which survival is short. Many such combinations are being explored, as are other novel agents, some of which could successfully be combined with JAK2 inhibitors in the future. In addition, new JAK2 inhibitors with the potential for less myelosuppression continue to be investigated. Given the proven safety and efficacy of ruxolitinib, it is likely that ruxolitinib-based combinations will be a major way forward in drug development for MF. If approved, less myelosuppressive JAK2 inhibitors such as pacritinib or NS-018 could prove to be very useful additions to the therapeutic armamentarium in MF. In PV, inhibitors of histone deacetylases and human double minute 2 have activity, but their role, if any, in the future treatment algorithm is uncertain, given the availability of ruxolitinib and renewed interest in interferons. Ruxolitinib is in late-phase clinical trials in essential thrombocythemia, in which it could fill an important void for patients with troublesome symptoms.
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.
Aberrant activation of the JAK/STAT pathway has been reported in a variety of disease states, including inflammatory conditions, hematologic malignancies, and solid tumors. For instance, a large ...proportion of patients with myeloproliferative neoplasms (MPN) carry the acquired gain-of-function JAK2 V617F somatic mutation. This knowledge has dramatically improved our understanding of the pathogenesis of MPNs and has facilitated the development of therapeutics capable of suppressing the constitutive activation of the JAK/STAT pathway, now recognized as a common underlying biologic abnormality in MPNs. Ruxolitinib is an oral JAK1 and JAK2 inhibitor that has recently been approved for the treatment of myelofibrosis and has been tested against other hematologic malignancies. A series of agents with different specificities against different members of the JAK family of proteins is currently undergoing evaluation in clinical trials for patients with MPNs, lymphoma, and solid tumors such as breast or pancreatic cancer. Despite the significant clinical activity exhibited by these agents in myelofibrosis, some patients fail to respond or progress during JAK kinase inhibitor therapy. Recent reports have shed light into the mechanisms of resistance to JAK inhibitor therapy. Several approaches hold promise to overcome such resistance.
Ruxolitinib, an oral inhibitor of Janus kinase (JAK) 1 and 2, was associated with hematocrit control and spleen size reduction in 21% of patients with polycythemia vera who had an inadequate response ...to or unacceptable side effects from hydroxyurea.
Polycythemia vera is a chronic clonal myeloproliferative neoplasm characterized by increased red-cell mass; elevated white-cell and platelet counts are also common.
1
Patients have an increased risk of thrombotic and cardiovascular events
2
and a substantial symptom burden that includes pruritus, fatigue, and night sweats.
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Splenomegaly often develops as the disease progresses.
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The main goal of therapy is to prevent thrombotic events while avoiding iatrogenic harm and minimizing the risk of transformation to post–polycythemia vera myelofibrosis or acute myeloid leukemia (AML).
5
,
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Most patients receive low-dose aspirin and undergo phlebotomy,
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with a goal of maintaining hematocrit values of less than 45%. Aggressive . . .
This trial showed clinically significant responses in spleen size and quality of life among patients with myelofibrosis receiving ruxolitinib, a JAK1 and JAK2 inhibitor. The agent has some ...myelotoxicity, but this study showed a survival advantage with ruxolitinib.
Myelofibrosis, a myeloproliferative neoplasm, is manifested by abnormal blood counts (anemia, thrombocytosis or thrombocytopenia, and leukocytosis or leukopenia), splenomegaly, and debilitating symptoms (e.g., fatigue, weakness, abdominal pain, cachexia, weight loss, pruritus, night sweats, and bone pain), which are thought to be caused by the combined effects of massive splenomegaly and elevated levels of proinflammatory cytokines.
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Survival ranges from approximately 2 to 11 years, depending on defined prognostic factors.
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Traditional therapeutic options, including splenectomy, have limited benefit.
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Although allogeneic stem-cell transplantation may cure myelofibrosis, few patients are eligible for this treatment.
Although the gain-of-function mutation in the gene encoding Janus kinase . . .
The 2011 approval of ruxolitinib ushered in the Janus kinase (JAK) inhibitor era in the treatment of myelofibrosis (MF), and 2019 saw the US approval of fedratinib. The first therapeutic agents ...approved by regulatory authorities for MF, these drugs attenuate the overactive JAK‐signal transducer and activator of transcription (STAT) signaling universally present in these patients, translating into major clinical benefits in terms of spleen shrinkage and symptom improvement. These, in turn, confer a survival advantage on patients with advanced disease, demonstrated in the case of ruxolitinib, for which long‐term follow‐up data are available. However, JAK inhibitors do not improve cytopenias in most patients, have relatively modest effects on bone marrow fibrosis and driver mutation allele burden, and clinical resistance eventually develops. Furthermore, they do not modify the risk of transformation to blast phase; indeed, their mechanism of action may be more anti‐inflammatory than truly disease‐modifying. This has spurred interest in rational combinations of JAK inhibitors with other agents that may improve cytopenias and drugs that could potentially modify the natural history of MF. Newer JAK inhibitors that are distinguished from ruxolitinib and fedratinib by their ability to improve anemia (eg, momelotinib) or safety and efficacy in severely thrombocytopenic patients (eg, pacritinib) are in phase 3 clinical trials. There is also interest in developing inhibitors that are highly selective for mutant JAK2, as well as “type II” JAK2 inhibitors. Overall, although current JAK inhibitors have limitations, they will likely continue to form the backbone of MF therapy for the foreseeable future.
The suite of marked anemia benefits that momelotinib has consistently conferred on myelofibrosis (MF) patients stem from its unique inhibitory activity on the BMP6/ACVR1/SMAD and IL-6/JAK/STAT3 ...pathways, resulting in decreased hepcidin (master iron regulator) expression, higher serum iron and hemoglobin levels, and restored erythropoiesis. Clinical data on momelotinib from the phase 2 and the two phase 3 SIMPLIFY trials consistently demonstrated high rates of sustained transfusion-independence. In a recent phase 2 translational study, 41% of the patients achieved transfusion independence for ≥ 12 weeks. In the phase 3 trials SIMPLIFY-1 and SIMPLIFY-2, 17% more JAK inhibitor-naïve patients and two-fold more JAK inhibitor-treated patients achieved or maintained transfusion independence with momelotinib versus ruxolitinib and best available therapy (89% ruxolitinib), respectively. Anemia is present in approximately a third of MF patients at diagnosis, eventually developing in nearly all patients. The need for red blood cell transfusions is an independent adverse risk factor for both overall survival and leukemic transformation. Presently, FDA-approved medications to address anemia are lacking. Momelotinib is one of the prime candidates to durably address the critical unmet needs of MF patients with moderate/severe anemia. Importantly, momelotinib may have overall survival benefits in frontline and second-line MF patients. MOMENTUM is an international registration-track phase 3 trial further assessing momelotinib's unique constellation of anemia and other benefits in second-line MF patients; the results of the MOMENTUM trial are keenly awaited and may lead to regulatory approval of momelotinib.
This document updates the recommendations on the management of Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-neg MPNs) published in 2011 by the European LeukemiaNet (ELN) ...consortium. Recommendations were produced by multiple-step formalized procedures of group discussion. A critical appraisal of evidence by using Grades of Recommendation, Assessment, Development and Evaluation (GRADE) methodology was performed in the areas where at least one randomized clinical trial was published. Seven randomized controlled trials provided the evidence base; earlier phase trials also informed recommendation development. Key differences from the 2011 diagnostic recommendations included: lower threshold values for hemoglobin and hematocrit and bone marrow examination for diagnosis of polycythemia vera (PV), according to the revised WHO criteria; the search for complementary clonal markers, such as ASXL1, EZH2, IDH1/IDH2, and SRSF2 for the diagnosis of myelofibrosis (MF) in patients who test negative for JAK2V617, CALR or MPL driver mutations. Regarding key differences of therapy recommendations, both recombinant interferon alpha and the JAK1/JAK2 inhibitor ruxolitinib are recommended as second-line therapies for PV patients who are intolerant or have inadequate response to hydroxyurea. Ruxolitinib is recommended as first-line approach for MF-associated splenomegaly in patients with intermediate-2 or high-risk disease; in case of intermediate-1 disease, ruxolitinib is recommended in highly symptomatic splenomegaly. Allogeneic stem cell transplantation is recommended for transplant-eligible MF patients with high or intermediate-2 risk score. Allogeneic stem cell transplantation is also recommended for transplant-eligible MF patients with intermediate-1 risk score who present with either refractory, transfusion-dependent anemia, blasts in peripheral blood > 2%, adverse cytogenetics, or high-risk mutations. In these situations, the transplant procedure should be performed in a controlled setting.
The Janus kinase inhibitor ruxolitinib is approved for the treatment of myelofibrosis (MF) and improved overall survival (OS) versus control therapy in the phase 3 COMFORT trials. The aim of this ...retrospective analysis was to examine the real-world impact of ruxolitinib on OS in patients with MF. The US Medicare Fee-for-Service claims database (parts A/B/D) was used to identify patients with ≥ 1 inpatient or ≥ 2 outpatient claims with an MF diagnosis (January 2010–December 2017). Eligible patients with MF were ≥ 65 years old (intermediate-1 or higher risk based on age). Patients were divided into 3 groups based on ruxolitinib approval status at diagnosis and ruxolitinib exposure: (1) preapproval, ruxolitinib-unexposed; (2) post-approval, ruxolitinib-unexposed; and (3) post-approval, ruxolitinib-exposed. In total, 1677 patients with MF were included (preapproval all ruxolitinib-unexposed,
n
= 278; post-approval,
n
= 1399 ruxolitinib-unexposed,
n
= 1127; ruxolitinib-exposed,
n
= 272). Overall, median age was 78 years, and 39.8% were male. Among patients with valid death dates (preapproval,
n
= 119 42.8%; post-approval, ruxolitinib-unexposed,
n
= 382 33.9%; post-approval ruxolitinib-exposed,
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= 54 19.9%), 1-year survival rates were 55.6%, 72.5%, and 82.3%, and median OS was 13.2 months, 44.4 months, and not reached, respectively. Risk of mortality was significantly lower post- versus preapproval regardless of exposure to ruxolitinib (ruxolitinib-unexposed: adjusted hazard ratio HR, 0.67; ruxolitinib-exposed: adjusted HR, 0.36;
P
< 0.001 for both); post-approval, mortality risk was significantly lower in ruxolitinib-exposed versus ruxolitinib-unexposed patients (adjusted HR, 0.61;
P
= 0.002). Findings from this study complement clinical data of ruxolitinib in MF by demonstrating a survival benefit in a real-world setting.
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