New insights into the pathogenesis and drug treatment of myelofibrosis

The Treatment Landscape of Myelofibrosis Before and After Ruxolitinib Approval

INTRODUCTION/BACKGROUND

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm that presents with a heterogeneous clinical phenotype and prognosis. Before the US Food and Drug Administration approval of ruxolitinib, treatment options were varied and had limited effect. The increased use of ruxolitinib has drastically altered the MF treatment landscape. In this study, we aimed to clarify the clinical situations in which ruxolitinib is being used and analyze its effect on this landscape.

PATIENTS AND METHODS

We retrospectively assessed treatment choices for MF patients treated at our institution (n = 309). This population was divided into 2 cohorts on the basis of a diagnosis before (cohort BR: n = 174) or after (cohort AR: n = 135) ruxolitinib approval. Cohorts were further stratified for comparison according to presenting clinical factors.

RESULTS

Expectedly, the first-line use of ruxolitinib markedly increased after its approval. AR patients were less likely to receive erythropoiesis-stimulating agents (ESAs; P = .0003) and thalidomide (P = .003) than BR patients. In patients with MF-related symptoms and/or splenomegaly, increased use of ruxolitinib was associated with decreased use of first-line ESA (P = .03) or thalidomide (P = .03). In anemic patients, increased use of first-line ruxolitinib was associated with a decreased use of thalidomide (P = .007). In patients with severe leukocytosis, ruxolitinib use did not significantly increase and hydroxyurea was the preferred first-line agent.

CONCLUSION

Overall, the increased use of ruxolitinib appears to have come predominantly at the expense of thalidomide and ESAs, while not having a large effect on the first-line use of hydroxyurea.

Fibrogenesis in Primary Myelofibrosis: Diagnostic, Clinical, and Therapeutic Implications

Primary myelofibrosis is a stem cell-derived clonal malignancy characterized by unchecked proliferation of myeloid cells, resulting in bone marrow fibrosis, osteosclerosis, and pathologic angiogenesis. Bone marrow fibrosis (BMF) plays a central role in the pathophysiology of the disease. This review describes current issues regarding BMF in primary myelofibrosis, including the pathophysiology and impact of abnormal deposition of excess collagen and reticulin fibers in bone marrow spaces, the modified Bauermeister and the European Consensus grading systems of BMF, and the prognostic impact of BMF on the overall outcome of patients with primary myelofibrosis. The impact of novel therapeutic strategies, including JAK-STAT inhibitors and allogeneic stem cell transplant, on BMF is discussed.

Symptom burden and splenomegaly in patients with myelofibrosis in the United States: a retrospective medical record review

Myelofibrosis (MF) is a clonal hematopoietic malignancy characterized by constitutional and localized symptoms, progressive splenomegaly, bone marrow fibrosis, and cytopenias. Although MF is well studied, few studies exist regarding its symptomatic burden in routine clinical practice. This study aimed to characterize symptoms and other clinical features of MF among patients in the United States. We conducted a retrospective medical record review of adult patients with an MF diagnosis between 1 January 2005 and 31 March 2010, stratified by the presence of palpable splenomegaly. Eligible patients had 12 months or more of follow-up after diagnosis (or after detection of splenomegaly, if present) unless death occurred. Demographic and clinical characteristics, MF-related symptoms, and treatments were reported by treating physicians. We report on 180 MF patients: 102 with splenomegaly, 78 without. Median age was 66 years, 63% were male, and 82% had intermediate-2 or high-risk MF (International Prognostic Scoring System). Fatigue was reported by ~85% of patients; weight loss, night sweats, and fever (any grade) were each reported by 50% or more of patients. Generalized abdominal pain, left subcostal pain, and early satiety occurred more frequently among patients with splenomegaly. Multiple symptoms were reported by 95% of patients. Common comorbidities were hypertension, diabetes, and chronic pulmonary disease. Symptoms are common in MF patients, regardless of the presence of palpable splenomegaly. Careful assessment of symptom burden is an important aspect of the clinical evaluation of patients with MF.

The Association Between JAK2V617F Mutation and Bone Marrow Fibrosis at Diagnosis in Patients with Philadelphia-Negative Chronic Myeloproliferative Neoplasms

Objective: Bone marrow fibrosis is the second most common complication that causes morbidity and mortality inpatients with Philadelphia-negative myeloproliferative neoplasms (MPNs). The aim of this study was to investigate theassociation between JAK2V617F mutation and bone marrow fibrosis at diagnosis in patients with MPNs.

Material and Methods: In total, 149 patients with MPNs were retrospectively evaluated to determine if there was anassociation between the histological grade of bone marrow fibrosis and JAK2V617F mutation.

Results: In all, 67.7% of the patients carried the mutated JAK2 gene. The presence of JAK2V617F mutation was notassociated with the occurrence of bone marrow fibrosis (P=0.55) or its grade at diagnosis (P=0.65).

Conclusion: Molecular mechanisms or genetic defects other than JAK2V617F may underlie the occurrence of bonemarrow fibrosis in patients with MPNs.

The European Consensus on grading of bone marrow fibrosis allows a better prognostication of patients with primary myelofibrosis

We investigated the relationship between the International Prognostic Scoring System of the International Working Group for Myelofibrosis Research and Treatment and the European Consensus on grading of bone marrow fibrosis (MF) in patients with primary myelofibrosis. We compared them in 196 consecutive primary myelofibrosis patients (median follow-up 45.7 months; range 7.4-159). International Prognostic Scoring System classified 42 cases as low risk, 73 as intermediate risk-1, 69 as intermediate risk-2, and 12 as high risk; European Consensus on grading of bone marrow fibrosis classified 83 cases as MF-0, 58 as MF-1, 41 as MF-2, and 14 as MF-3. By the time of the analysis, 30 patients (15.3%) had died. Overall median survival was 3.8 years (95% confidence interval: 3.3-4.3). Multivariate analysis confirmed that both scoring systems independently predicted survival, with hazard ratios similar to those provided by univariate analysis (respectively, 2.40 (95% confidence interval: 1.47-3.91) and 2.58 (95% confidence interval: 1.72-3.89) but the likelihood ratio increased from 19.6 of the International Prognostic Scoring System or 29.0 of the European Consensus on grading of bone MF to 42.3 when both measures were considered together. Analysis of the overall survival curves documented that patients classified as having the most favourable rate with both prognostic scores (ie low risk and MF-0) survive longer than those with only one favourable score (ie low risk but MF >0 or MF-0, but International Prognostic Scoring System >low risk). In contrast, those patients classified as having the most unfavourable rate for both scores (high risk and MF-3) have a shorter survival than those with only one unfavourable score (ie high risk but MF<3 or MF-3, but International Prognostic Scoring System <high risk). In conclusion, our analysis suggests that better prognostication can be achieved in primary myelofibrosis patients when both systems are used together.

HSP90 is a therapeutic target in JAK2-dependent myeloproliferative neoplasms in mice and humans

JAK2 kinase inhibitors were developed for the treatment of myeloproliferative neoplasms (MPNs), following the discovery of activating JAK2 mutations in the majority of patients with MPN. However, to date JAK2 inhibitor treatment has shown limited efficacy and apparent toxicities in clinical trials. We report here that an HSP90 inhibitor, PU-H71, demonstrated efficacy in cell line and mouse models of the MPN polycythemia vera (PV) and essential thrombocytosis (ET) by disrupting JAK2 protein stability. JAK2 physically associated with both HSP90 and PU-H71 and was degraded by PU-H71 treatment in vitro and in vivo, demonstrating that JAK2 is an HSP90 chaperone client. PU-H71 treatment caused potent, dose-dependent inhibition of cell growth and signaling in JAK2 mutant cell lines and in primary MPN patient samples. PU-H71 treatment of mice resulted in JAK2 degradation, inhibition of JAK-STAT signaling, normalization of peripheral blood counts, and improved survival in MPN models at doses that did not degrade JAK2 in normal tissues or cause substantial toxicity. Importantly, PU-H71 treatment also reduced the mutant allele burden in mice. These data establish what we believe to be a novel therapeutic rationale for HSP90 inhibition in the treatment of JAK2-dependent MPN.

Safety and efficacy of INCB018424, a JAK1 and JAK2 inhibitor, in myelofibrosis

BACKGROUND

Myelofibrosis is a Philadelphia chromosome–negative myeloproliferative neoplasm associated with cytopenias, splenomegaly, poor quality of life, and shortened survival. About half of patients with myelofibrosis carry a gain-of-function mutation in the Janus kinase 2 gene (JAK2 V617F) that contributes to the pathophysiology of the disease. INCB018424 is a potent and selective Janus kinase 1 (JAK1) and JAK2 inhibitor.

METHODS

We conducted a phase 1−2 trial of INCB018424 in patients with JAK2 V617F−positive or JAK2 V617F−negative primary myelofibrosis, post–essential thrombocythemia myelofibrosis, or post–polycythemia vera myelofibrosis.

RESULTS

A total of 153 patients received INCB018424 for a median duration of more than 14.7 months. The initial dose-escalation phase established 25 mg twice daily or 100 mg once daily as maximum tolerated doses, on the basis of reversible thrombocytopenia. A dose-dependent suppression of phosphorylated signal transducer and activator of transcription 3 (STAT3), a marker of JAK signaling, was demonstrated in patients with wild-type JAK2 and in patients with the JAK2 V617F mutation. We studied additional doses and established that a 15-mg twice-daily starting dose, followed by individualized dose titration, was the most effective and safest dosing regimen. At this dose, 17 of 33 patients (52%) had a rapid objective response (≥50% reduction of splenomegaly) lasting for 12 months or more, and this therapy was associated with grade 3 or grade 4 adverse events (mainly myelosuppression) in less than 10% of patients. Patients with debilitating symptoms, including weight loss, fatigue, night sweats, and pruritus, had rapid improvement. Clinical benefits were associated with a marked diminution of levels of circulating inflammatory cytokines that are commonly elevated in myelofibrosis.

CONCLUSIONS

INCB018424 was associated with marked and durable clinical benefits in patients with myelofibrosis for whom no approved therapies existed. (Funded by Incyte; ClinicalTrials.gov number, NCT00509899.)

Essential thrombocythemia, polycythemia vera, and myelofibrosis: current management and the prospect of targeted therapy

The recent discovery of JAK2 and/or MPL mutations in polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) has had a major impact on how we diagnose and treat these disorders. For instance, the presence of a JAK2 mutation is now considered conditio sine qua non for the diagnosis of PV and the World Health Organization classification system has recently revised its diagnostic criteria for PV, ET, and PMF to include JAK2 and MPL mutations as clonal markers. From the standpoint of treatment, JAK-STAT is now identified as a legitimate target pathway for drug development in myeloproliferative neoplasms. Herein, I will first outline my views regarding current management in ET, PV, and PMF and then discuss emerging data on preclinical and clinical activity of anti-JAK2 small molecule drugs. Am. J. Hematol., 2008. (c) 2008 Wiley-Liss, Inc.

The presence of JAK2V617F in primary myelofibrosis or its allele burden in polycythemia vera predicts chemosensitivity to hydroxyurea

JAK2V617F-positive patients with essential thrombocythemia, as opposed to their mutation-negative counterparts, require lower doses of hydroxyurea (HU) for control of their platelet count. In the current study, we looked for predictors of HU response in 69 patients with primary myelofibrosis (PMF) and 56 with polycythemia vera (PV). JAK2V617F analysis was performed on bone marrow-derived DNA obtained at or near the time of diagnosis. HU response in PMF was associated with a shorter disease duration (P = 0.008), absence of previous therapy (P = 0.01), older age at diagnosis (P = 0.009), and presence of JAK2V617F (P = 0.02). On multivariable analysis, only the latter retained its significance (48% vs. 8% response in mutation positive vs. negative cases). In PV, JAK2V617F allele burden correlated directly with HU response (P = 0.05) and inversely with daily HU dose in responding patients (P = 0.02). The current study suggests that JAK2V617F presence identifies PMF patients who are likely to respond to HU therapy, and information on its allele burden helps in assigning the optimal starting dose in individual patients with PV.

From palliation to epigenetic therapy in myelofibrosis

Myelofibrosis shows a progressive clinical course and usually a poor, lethal prognosis. The molecular pathogenesis of this disease largely remains to be fully understood but the identification of the JAK2V617F mutation in more than half of patients was a major improvement in our understanding of the disease biology and may represent the first biologic marker useful for risk stratification, independently from conventional clinical predictors. After many elusive efforts, new effective treatment strategies are becoming available for this disease. Allogeneic transplantation following reduced-intensity conditioning programs, at least in some patients, may induce not only a hematologic response but also a molecular remission, thus supporting the hope of a possible, definitive eradication of the disease. Moreover, new innovative drugs, targeting either the JAK2V617F mutation or more general oncogenic mechanisms, may provide widely applicable, effective treatments to many patients for whom allogeneic transplantation is not feasible.

Prognostic implications of the European consensus for grading of bone marrow fibrosis in chronic idiopathic myelofibrosis

Various clinical prognostic scoring systems (PSSs) have been suggested as means of selecting high-risk chronic idiopathic myelofibrosis (CIMF) patients at diagnosis. The WHO has recently proposed strict diagnostic criteria for CIMF, and the European consensus for bone marrow fibrosis (BMF) grading recommends 4 classes. It has been suggested that BMF grading may play a prognostic role in CIMF, but it has never been compared with the other PSSs in the same patients. We tested a prognostic model for overall survival (OS) based on the WHO criteria and BMF grading in 113 consecutive patients with chronic myeloproliferative disorders (98 with CIMF and 15 with postpolycythemic myelofibrosis), and compared the findings with those of PSSs. The results showed that our model is significantly associated with different OSs and, unlike the other PSSs, clearly discriminates the OS of intermediate- and high-risk patients.

Cytogenetic and molecular aspects of Philadelphia negative chronic myeloproliferative disorders: clinical implications

Chronic myeloproliferative disorders (CMPD) are clonal disorders of the hematopoietic stem cell. The myeloid lineage shows increased proliferation with effective maturation, while peripheral leukocytosis, thrombocytosis or elevated red blood cell mass are found. In Philadelphia negative CMPD recurrent cytogenetic abnormalities occur, but no specific abnormality has been defined to date. The spectrum of cytogenetic aberrations is heterogeneous ranging from numerical gains and losses to structural changes including unbalanced translocations. The most common chromosomal abnormalities are 20q-, 13q-, 12p-, +8, +9, partial duplication of 1q, balanced translocations involving 8p11 and gains in 9p. Cytogenetic analysis of CMPD by conventional or molecular techniques has an important role in establishing the diagnosis of a malignant disease, adding also more information for disease outcome. Molecular studies may detect the possible role of candidate genes implicated in the neoplastic process, addressing new molecular target therapies. FIP1L1/PDGFRalpha rearrangements, as well as alterations of PDGFRbeta or FGFR1 gene have been found to be associated with specific types of CMPD. Recently, a novel somatic mutation, JAK2V617F, has been reported in most of the polycthemia vera (PV) patients, as well as in a lower percentage in essential thrombocythemia (ET) or idiopathic myelofibrosis (IMF) patients. This finding represents the most important advance in understanding of the molecular mechanisms underlined the pathogenesis of CMPD, contributing to the classification and management of patients.

Expression of bone morphogenetic proteins and their receptors in the bone marrow megakaryocytes of GATA-1(low) mice: a possible role in osteosclerosis

The mechanism of osteosclerosis associated with myelofibrosis in megakaryocyte (MK)-related myeloproliferative disorders is largely unknown. However, growth factors released from the bone marrow cells, including from MKs, have been implicated in myelofibrosis, osteosclerosis, and angiogenesis. GATA-1 is a transcription factor required for normal MK development. GATA-1 deficiency in mice (GATA-1(low)) leads to increased megakaryocytic proliferation, followed by osteosclerosis and myelofibrosis. In this study we investigated the expression of bone morphogenetic proteins (BMPs) and BMP receptors and their possible role in the development of osteosclerosis in the MKs of 12-month-old GATA-1(low) mice by immunohistochemistry, cytomorphometry, and quantitative real-time PCR. Marrow MKs from both wild-type and GATA-1(low) mice showed moderate to intense staining for BMP-2, -4, and -6 and BMPR-IA and BMPR-II, whereas splenic MKs showed no BMP immunostaining. Presence of BMP protein in the bone marrow of GATA-1(low) mice was more than that seen in controls, owing to an increased number of MKs and osteoblasts. The osteosclerosis seen in GATA-1(low) mice appeared not to be due to a reduced number of functional osteoclasts because the number of tartrate-resistant acid phosphatase-positive osteoclasts was greater in GATA-1(low) mice than in controls. Our findings demonstrate the presence of significant amounts of BMP-2, -4, and -6 along with their receptors in bone marrow MKs of WT and GATA-1(low) mice. The increased levels of BMPs appear to be a result of increased numbers of MKs in GATA-1(low) mice and may, in part, account for the stimulation of osteoblastic activity and resulting osteosclerosis.

The evolving role of lenalidomide in the treatment of hematologic malignancies

Lenalidomide is an immunomodulatory drug, structurally related to thalidomide, which has pleotropic activity, including antiangiogenic and antineoplastic properties. This agent is the product of advances in the understanding of the biology of neoplastic cells, their interaction with the microenvironment and of the underlying molecular pathways. Lenalidomide has shown significant activity in refractory/resistant multiple myeloma, and further studies have shown its activity in other hematologic malignancies with some very encouraging results, especially in subsets of patients with myelodysplastic syndromes. This article reviews the data on lenalidomide use in patients with multiple myeloma, as well as in myelodysplastic syndromes, chronic lymphocytic leukemia and myelofibrosis with myeloid metaplasia.