Janus kinase-1 and Janus kinase-2 inhibitors for treating myelofibrosis

BACKGROUND

Myelofibrosis is a bone marrow disorder characterized by excessive production of reticulin and collagen fiber deposition caused by hematological and non-hematological disorders. The prognosis of myelofibrosis is poor and treatment is mainly palliative. Janus kinase inhibitors are a novel strategy to treat people with myelofibrosis.

OBJECTIVES

To determine the clinical benefits and harms of Janus kinase-1 and Janus kinase-2 inhibitors for treating myelofibrosis secondary to hematological or non-hematological conditions.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, the Cochrane Library 2014, Issue 11), Ovid MEDLINE (from 1946 to 13 November 2014), EMBASE (from 1980 to 12 January 2013), and LILACS (from 1982 to 20 November 2014). We searched WHO International Clinical Trials Registry Platform and The metaRegister of Controlled Trials. We also searched for conference proceedings of the American Society of Hematology (from 2009 to October 2013), European Hematology Association (from 2009 to October 2013), American Society of Clinical Oncology (from 2009 to October 2013), and European Society of Medical Oncology (from 2009 to October 2013). We included searches in FDA, European Medicines Agency, and Epistemonikos. We handsearched the references of all identified included trials, and relevant review articles. We did not apply any language restrictions. Two review authors independently screened search results.

SELECTION CRITERIA

We included randomized clinical trials comparing Janus kinase-1 and Janus kinase-2 inhibitors with placebo or other treatments. Both previously treated and treatment naive patients were included.

DATA COLLECTION AND ANALYSIS

We used the hazard ratio (HR) and 95% confidence interval (95% CI) for overall survival, progression-free survival and leukemia-free survival, risk ratio (RR) and 95% CI for reduction in spleen size and adverse events binary data, and standardized mean differences (SMD) and 95% CI for continuous data (health-related quality of life). Two review authors independently extracted data and assessed the risk of bias of included trials. Primary outcomes were overall survival, progression-free survival and adverse events.

MAIN RESULTS

We included two trials involving 528 participants, comparing ruxolitinib with placebo or best available therapy (BAT). As the two included trials had different comparators we did not pool the data. The confidence in the results estimates of these trials was low due to the bias in their design, and their limited sample sizes that resulted in imprecise results.There is low quality evidence for the effect of ruxolitinib on survival when compared with placebo at 51 weeks of follow-up (HR 0.51, 95% CI 0.27 to 0.98) and compared with BAT at 48 weeks of follow-up (HR 0.70, 95% CI 0.20 to 2.47). Similarly there was very low quality evidence for the effect of ruxolitinib on progression free survival compared with BAT (HR 0.81, 95% CI 0.47 to 1.39).There is low quality evidence for the effect of ruxolitinib in terms of quality of life. Compared with placebo, the drug achieved a greater proportion of patients with a significant reduction of symptom scores (RR 8.82, 95% CI 4.40 to 17.69), and treated patients with ruxolitinib obtained greater MFSAF scores at the end of follow-up (MD -87.90, 95% CI -139.58 to -36.22). An additional trial showed significant differences in EORTC QLQ-C30 scores when compared ruxolitinib with best available therapy (MD 7.60, 95% CI 0.35 to 14.85).The effect of ruxolitinib on reduction in the spleen size of participants compared with placebo or BAT was uncertain (versus placebo: RR 64.58, 95% CI 9.08 to 459.56, low quality evidence; versus BAT: RR 41.78, 95% CI 2.61 to 669.75, low quality evidence).There is low quality evidence for the effect of the drug compared with placebo on anemia (RR 2.35, 95% CI 1.62 to 3.41), neutropenia (RR 3.57, 95% CI 1.02 to 12.55) and thrombocytopenia (RR 9.74, 95% CI 2.32 to 40.96). Ruxolitinib did not result in differences versus BAT in the risk of anemia (RR 1.35, 95% CI 0.91 to 1.99, low quality evidence) or thrombocytopenia (RR 1.20; 95% CI 0.44 to 3.28, low quality evidence). The risk of non-hematologic grade 3 or 4 adverse events (including fatigue, arthralgia, nausea, diarrhea, extremity pain and pyrexia) was similar when ruxolitinib was compared with placebo or BAT. The rate of neutropenia comparing ruxolitinib with standard medical treatment was not reported by the trial.

AUTHORS' CONCLUSIONS

Currently, there is insufficient evidence to allow any conclusions regarding the efficacy and safety of ruxolitinib for treating myelofibrosis. The findings of this Cochrane review should be interpreted with caution as they are based on trials sponsored by industry, and include a small number of patients. Unless powered randomized clinical trials provide strong evidence of a treatment effect, and the trade-off between potential benefits and harms is established, clinicians should be cautious when administering ruxolitinib for treating patients with myelofibrosis.

Ruxolitinib: an oral Janus kinase 1 and Janus kinase 2 inhibitor in the management of myelofibrosis

Myelofibrosis (MF), polycythemia vera (PV), and essential thrombocythemia (ET) are referred to as the classic Philadelphia chromosome (BCR-ABL1)-negative myeloproliferative neoplasms. Although each has distinct pathologic features, all 3 display alterations in Janus kinase (JAK) signal transduction activator of transcription signaling. Myelofibrosis is the most serious of the 3, associated with shortened survival (median survival, 5-7 years); bone marrow failure with anemia; progressive splenomegaly; and chronic, burdensome symptoms, including fatigue, night sweats, itching, abdominal discomfort, loss of appetite/early satiety, unintentional weight loss, and bone, chest, and abdominal pain. Treatments for MF have been mainly palliative, with the exception of allogeneic stem cell transplantation, which, although potentially curative, is feasible only in a small subpopulation of patients. In November 2011, ruxolitinib, an inhibitor of JAK1 and JAK2, was approved by the US Food and Drug Administration for the treatment of intermediate- or high-risk MF, including primary MF, post-PV MF, and post-ET MF. In clinical trials, ruxolitinib was shown to reduce spleen volume and improve MF-related symptoms and quality-of-life measures. Evidence also suggests that ruxolitinib therapy has a survival advantage over placebo and best available therapy. Thrombocytopenia and anemia were the most common adverse events with treatment. Ongoing trials are assessing the efficacy and safety of ruxolitinib therapy in patients with PV and ET.

The evolving treatment paradigm in myelofibrosis

Myelofibrosis (MF) is a BCR-ABL1-negative myeloproliferative neoplasm diagnosed de novo or developed from essential thrombocythemia (ET) or polycythemia vera (PV). Average survival of a patient with MF is 5-7 years. Disease complications include fatigue, early satiety, pruritus, painful splenic infarcts, infections and leukemic transformation. Allogeneic hematopoietic stem cell transplant (HSCT) is the only potentially curative option for MF, but carries a risk of treatment-related mortality and is reserved for the few high-risk patients fit enough to endure the procedure. Other traditional therapies are palliative and supported by few randomized, controlled trials; thus, novel treatment strategies are needed. Discovery of the Janus kinase 2 (JAK2) gain-of-function mutation, JAK2V617F, in the majority (50-60%) of patients with MF led to increased understanding of the biology underlying MF and the development of JAK2 inhibitors to treat MF. Recent Food and Drug Administration (FDA) approval of the first JAK2 inhibitor, ruxolitinib, signaled a new era for treatment of MF. Additional JAK2 inhibitors, such as SAR302503, may become commercially available in the near future, and their distinct pharmacologic and efficacy profiles will help determine their use across the patient population. Data on JAK2 inhibitors, their role in an evolving treatment paradigm, and future directions for treatment of MF are discussed.

Emerging drugs for myelofibrosis

INTRODUCTION

Myelofibrosis (MF), a Philadelphia chromosome-negative myeloproliferative neoplasm, is a life-threatening heterogeneous disorder characterized by dysregulation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling network. The clinical hallmarks of MF are progressive splenomegaly, anemia and debilitating symptoms attributable to ineffective hematopoiesis and excessive production of proinflammatory cytokines.

AREAS COVERED

This review describes the pathogenesis, clinical features and current treatment of MF, clinical data for ruxolitinib, a potent oral JAK1/JAK2 inhibitor and the only therapy approved for the treatment of MF, and agents in development for the treatment of MF. Information was derived from relevant MF articles identified in the published literature and abstracts of recent congresses.

EXPERT OPINION

Ruxolitinib reduces spleen size and alleviates MF-related symptoms, thereby improving quality of life. Ruxolitinib may increase the risk of anemia and thrombocytopenia and does not appear to reverse bone marrow fibrosis. Studies are exploring ruxolitinib dosing strategies for patients with low platelet counts and combination therapies. Several other JAK inhibitors and other agents (i.e., immunomodulators, antifibrotic agents, anti-anemia agents, mammalian target of rapamycin [mTOR] inhibitors, epigenetic modifiers, pegylated interferon-α2a) to treat various aspects of MF (i.e., to improve blood counts or forestall marrow fibrosis) are in early clinical development.

Assessing efficacy in myelofibrosis treatment: a focus on JAK inhibition

Myelofibrosis (MF) is characterized by splenomegaly, anemia and a debilitating symptom burden (e.g., fatigue, night sweats, pruritus, bone and muscle pain, undesired weight loss). Moreover, these symptoms impair activities of daily living and quality of life. Until recently, there have been no approved therapies for MF, and management of MF has been predominantly palliative. Dysregulated JAK-STAT signaling is associated with the pathologic MF disease state. A novel class of therapies, the JAK inhibitors, offers the potential to abrogate this pathologic signaling pathway. In clinical trials of patients with intermediate- and high-risk MF, JAK inhibitors have demonstrated efficacy in reducing splenomegaly and MF-associated symptoms. Evidence from ruxolitinib trials also suggests that JAK inhibitors may improve survival outcomes.

Ruxolitinib, an oral JAK1 and JAK2 inhibitor, in myelofibrosis

INTRODUCTION

Myelofibrosis (MF) is a debilitating hematologic malignancy characterized by progressive splenomegaly, burdensome symptoms, cytopenias and shortened survival. Chronic alterations in Janus-associated kinase-signal transducer and activator of transcription (JAK-STAT) signaling have been identified in the pathogenesis of MF, making this pathway a target for drug development. Ruxolitinib is the first JAK1 and JAK2 inhibitor to be approved by the US Food and Drug Administration.

AREAS COVERED

This review describes the characteristics of MF, the current therapeutic options and need for effective therapies, the contribution of aberrant JAK-STAT signaling to various disease-specific manifestations and the pharmacodynamics, pharmacokinetics, efficacy and tolerability of ruxolitinib. Articles describing MF disease burden and results of ruxolitinib pre-clinical and clinical trials were identified and summarized.

EXPERT OPINION

Conventional MF treatments alleviate some MF symptoms but have limited efficacy, do not modify the natural history of the disease and are not approved for MF. The JAK1 and JAK2 inhibitor ruxolitinib has shown promising results in pre-clinical and clinical trials. In Phase III trials, ruxolitinib was shown to reduce splenomegaly and improve MF-related symptoms. Recent evidence also suggests that ruxolitinib may improve survival. The most common adverse events were anemia and thrombocytopenia, which were managed with dose adjustments (or red blood cell transfusions for anemia).