Long-term findings from COMFORT-II, a phase 3 study of ruxolitinib vs best available therapy for myelofibrosis

Recommendations for the use of pegylated interferon-α in the treatment of classical myeloproliferative neoplasms

The classical myeloproliferative neoplasms (MPN) are uncommon clonal haemopoietic malignancies characterised by excessive production of mature blood cells. Clinically, they are associated with thrombosis, haemorrhage, varying degrees of constitutional disturbance and a risk of progression to myelofibrosis or acute myeloid leukaemia. Many of the disease manifestations may be ameliorated by treatment with interferon-α (IFN), but its use in Australian MPN patients has been limited due to the inconvenience of frequent injections and side-effects. The pegylated form of IFN is a long-acting preparation, which is better tolerated, and its Pharmaceutical Benefits Scheme listing is likely to lead to increased usage. We review the literature on risks and benefits of IFN treatment for MPN, suggest criteria for patient selection in each of these diseases and discuss strategies to manage the side-effects of pegylated IFN.

Patterns of Ruxolitinib Therapy Failure and Its Management in Myelofibrosis: Perspectives of the Canadian Myeloproliferative Neoplasm Group

Ruxolitinib improves splenomegaly and other disease-related symptoms in patients with myelofibrosis, but over time, many patients lose this benefit. It is difficult to determine whether this is due to resistance or intolerance to the drug; thus, we have used the more inclusive term of ruxolitinib failure. The survival of patients with myelofibrosis after ruxolitinib failure is poor but varies significantly by the pattern of the failure, underlining the need for a clinically appropriate classification. In this review, we propose diagnostic guidance for early recognition of the pattern of ruxolitinib failure and we recommend treatment options. The most frequent patterns of ruxolitinib failure are loss or failure to obtain a significant reduction in splenomegaly or symptom response, and the development or persistence of clinically significant cytopenias. Ruxolitinib dose modification and other ancillary therapies are sometimes helpful, and splenectomy is a palliative option in selected cases. Stem-cell transplantation is the only curative option for these patterns of failure, but its restricted applicability due to toxicity highlights the importance of ongoing clinical trials in this area. Recent approval of fedratinib by the US Food and Drug Administration provides an alternative option for patients with suboptimal or loss of spleen response. The transformation of myelofibrosis to accelerated or blast phase is an infrequent form of failure with an extremely poor prognosis, whereby patients who are ineligible for transplantation have limited treatment options.

A case report of cryptococcal meningitis associated with ruxolitinib

We herein report a 76-year-old Japanese man with myelofibrosis who developed cryptococcal meningitis. After treatment for 5 months with ruxolitinib, the patient presented with fever and disturbance of consciousness. Marked nuchal stiffness was noted. The magnetic resonance imaging results of the brain were normal. Lumbar puncture showed an opening cerebrospinal fluid (CSF) pressure of 110 mm H2O, pleocytosis (85 mononuclear cells and 222 polymorphonuclear cells/μL), decreased CSF/serum glucose ratio (43%), and elevated protein (194 mg/dL). Blood and CSF cultures grew no bacteria or fungi. However, cryptococcal antigen was detected in the blood and CSF samples. We discontinued ruxolitinib and started administration of amphotericin B. His condition improved gradually 1 week after initiation of treatment. There have been only a few reports on cryptococcal meningitis associated with ruxolitinib. Physicians should consider the possibility of cryptococcal meningitis in patients receiving ruxolitinib.

Primary analysis of JUMP, a phase 3b, expanded-access study evaluating the safety and efficacy of ruxolitinib in patients with myelofibrosis, including those with low platelet counts

Ruxolitinib is a potent Janus kinase (JAK) 1/JAK2 inhibitor approved for the treatment of myelofibrosis (MF). Ruxolitinib was assessed in JUMP, a large (N = 2233), phase 3b, expanded-access study in MF in countries without access to ruxolitinib outside a clinical trial, which included patients with low platelet counts (<100 × 10⁹ /l) and patients without splenomegaly - populations that have not been extensively studied. The most common adverse events (AEs) were anaemia and thrombocytopenia, but they rarely led to discontinuation (overall, 5·4%; low-platelet cohort, 12·3%). As expected, rates of worsening thrombocytopenia were higher in the low-platelet cohort (all grades, 73·2% vs. 53·5% overall); rates of anaemia were similar (all grades, 52·9% vs. 59·5%). Non-haematologic AEs, including infections, were mainly grade 1/2. Overall, ruxolitinib led to meaningful reductions in spleen length and symptoms, including in patients with low platelet counts, and symptom improvements in patients without splenomegaly. In this trial, the largest study of ruxolitinib in patients with MF to date, the safety profile was consistent with previous reports, with no new safety concerns identified. This study confirms findings from the COMFORT studies and supports the use of ruxolitinib in patients with platelet counts of 50-100 × 10⁹ /l. (ClinicalTrials.gov identifier NCT01493414).

Ruxolitinib Alleviates Renal Interstitial Fibrosis in UUO Mice

Ruxolitinib is a selective inhibitor of Jak1/2. Downstream signaling pathways of Jak, such as Stat3 and Akt/mTOR, are overactivated and contribute to renal interstitial fibrosis. Therefore, we explored the effect of Ruxolitinib on this pathological process. Unilateral ureteral obstruction (UUO) models and TGF-β1-treated fibroblasts and renal tubular epithelial cells were adopted in this study. Ruxolitinib was administered to UUO mice and TGF-β1-treated cells. Kidneys from UUO mice with Ruxolitinib treatment displayed less tubular injuries compared with those without Ruxolitinib treatment. Ruxolitinib treatment suppressed fibroblast activation and extracellular matrix (ECM) production in UUO kidneys and TGF-β1-treated fibroblasts. Ruxolitinib treatment also blocked epithelial-mesenchymal transition (EMT) in UUO kidneys and TGF-β 1-treated renal tubular epithelial cells. Moreover, Ruxolitinib treatment alleviated UUO-induced inflammation, oxidative stress and apoptosis. Mechanistically, Ruxolitinib treatment attenuated activation of both Stat3 and Akt/mTOR/Yap pathways. In conclusion, Ruxolitinib treatment can ameliorate UUO-induced renal interstitial fibrosis, suggesting that Ruxolitinib may be potentially used to treat fibrotic kidney disease.

Life after ruxolitinib: Reasons for discontinuation, impact of disease phase, and outcomes in 218 patients with myelofibrosis

BACKGROUND

After discontinuing ruxolitinib, the outcome of patients with myelofibrosis reportedly has been poor. The authors investigated whether disease characteristics before the receipt of ruxolitinib may predict drug discontinuation in patients with myelofibrosis and whether reasons for drug discontinuation, disease phase at discontinuation, and salvage therapies may influence the outcome.

METHODS

A centralized electronic clinical database was created in 20 European hematology centers, including clinical and laboratory data for 524 patients who received ruxolitinib for myelofibrosis.

RESULTS

At 3 years, 40.8% of patients had stopped ruxolitinib. Baseline predictors of drug discontinuation were: intermediate-2-risk/high-risk category (Dynamic International Prognostic Score System), a platelet count <100 ×10⁹ per liter, transfusion dependency, and unfavorable karyotype. At last contact, 268 patients (51.1%) had discontinued therapy, and the median drug exposure was 17.5 months. Fifty patients (18.7%) died while taking ruxolitinib. The reasons for discontinuation in the remaining 218 patients were the lack (22.9%) or loss (11.9%) of a spleen response, ruxolitinib-related adverse events (27.5%), progression to blast phase (23.4%), ruxolitinib-unrelated adverse events (9.2%), and allogeneic transplantation during response (5.1%). The median survival after ruxolitinib was 13.2 months and was significantly better in the 167 patients who discontinued ruxolitinib in chronic phase (27.5 vs 3.9 months for those who discontinued in blast phase; P < .001). No survival differences were observed among patients who discontinued ruxolitinib in chronic phase because of lack of response, loss of response, or ruxolitinib-related adverse events. The use of investigational agents and/or ruxolitinib rechallenge were associated with improved outcome.

CONCLUSIONS

The survival of patients with myelofibrosis after discontinuation of ruxolitinib is poor, particularly for those who discontinue in blast phase. Salvage therapies can improve outcome, emphasizing the need for novel therapies.

Beyond JAK-STAT: novel therapeutic targets in Ph-negative MPN

The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) share a common pathobiology of constitutive activation of the JAK and STAT pathway, despite having the 3 distinct phenotypes of essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Targeting the JAK-STAT pathway has led to remarkable clinical benefit, including reduction in splenomegaly, amelioration of cytokine-driven symptoms, improvement in quality of life, and even some improvement in survival. However, targeting this pathway has not resulted in consistent disease modification by current metrics, including a reduction in mutant allele burden or reversal of fibrosis. Moreover, targeting JAK-STAT can lead to limiting treatment-emergent side effects, such as anemia and thrombocytopenia. Continued discovery points to a complex system of pathogenesis beyond JAK-STAT driving the formation and evolution of MPNs. This article reviews the successes and limitations of JAK-STAT inhibition, surveys the strategies behind emerging therapies, and discusses the challenges that are present in moving beyond JAK-STAT.

The pan-PIM inhibitor INCB053914 displays potent synergy in combination with ruxolitinib in models of MPN

Aberrant JAK2 tyrosine kinase signaling drives the development of Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis. However, JAK2 kinase inhibitors have failed to significantly reduce allele burden in MPN patients, underscoring the need for improved therapeutic strategies. Members of the PIM family of serine/threonine kinases promote cellular proliferation by regulating a variety of cellular processes, including protein synthesis and the balance of signaling that regulates apoptosis. Overexpression of PIM family members is oncogenic, exemplified by their ability to induce lymphomas in collaboration with c-Myc. Thus, PIM kinases are potential therapeutic targets for several malignancies such as solid tumors and blood cancers. We and others have shown that PIM inhibitors augment the efficacy of JAK2 inhibitors by using in vitro models of MPNs. Here we report that the recently developed pan-PIM inhibitor INCB053914 augments the efficacy of the US Food and Drug Administration-approved JAK1/2 inhibitor ruxolitinib in both in vitro and in vivo MPN models. INCB053914 synergizes with ruxolitinib to inhibit cell growth in JAK2-driven MPN models and induce apoptosis. Significantly, low nanomolar INCB053914 enhances the efficacy of ruxolitinib to inhibit the neoplastic growth of primary MPN patient cells, and INCB053914 antagonizes ruxolitinib persistent myeloproliferation in vivo. These findings support the notion that INCB053914, which is currently in clinical trials in patients with advanced hematologic malignancies, in combination with ruxolitinib may be effective in MPN patients, and they support the clinical testing of this combination in MPN patients.

Distinct effects of ruxolitinib and interferon-alpha on murine JAK2V617F myeloproliferative neoplasm hematopoietic stem cell populations

JAK2V617F is the most common mutation in patients with BCR-ABL negative myeloproliferative neoplasms (MPNs). The eradication of JAK2V617F hematopoietic stem cells (HSCs) is critical for achieving molecular remissions and cure. We investigate the distinct effects of two therapies, ruxolitinib (JAK1/2 inhibitor) and interferon-alpha (IFN-α), on the disease-initiating HSC population. Whereas ruxolitinib inhibits Stat5 activation in erythroid progenitor populations, it fails to inhibit this same pathway in HSCs. In contrast, IFN-α has direct effects on HSCs. Furthermore, STAT1 phosphorylation and pathway activation is greater after IFN-α stimulation in Jak2V617F murine HSCs with increased induction of reactive oxygen species, DNA damage and reduction in quiescence after chronic IFN-α treatment. Interestingly, ruxolitinib does not block IFN-α induced reactive oxygen species and DNA damage in Jak2V617F murine HSCs in vivo. This work provides a mechanistic rationale informing how pegylated IFN-α reduces JAK2V617F allelic burden in the clinical setting and may inform future clinical efforts to combine ruxolitinib with pegylated IFN-α in patients with MPN.

Risk factors for infections and secondary malignancies in patients with a myeloproliferative neoplasm treated with ruxolitinib: a dual-center, propensity score-matched analysis

Ruxolitinib is a JAK1/2 inhibitor approved for the treatment of myelofibrosis (MF) and polycythemia vera (PV). Recent data have suggested the possibility of increased infectious and secondary malignancy rates in patients treated with ruxolitinib. We conducted a dual-center, retrospective study of 202 myeloproliferative neoplasm (MPN) patients receiving ruxolitinib and a control cohort of 73 ruxolitinib-naïve MPN patients. We utilized propensity score matching to analyze the primary outcome of development of any grade infection. Infections occurred in 38.4% of ruxolitinib-naïve patients and 42.6% of ruxolitinib-treated patients and were primarily grade 1/2. After propensity score weighting, there was no difference in risk of infection between ruxolitinib-treated and -naïve patients with MF (HR 1.15 [95% CI 0.80-1.65], p = .466) and non-MF MPNs (HR = 0.52 [95% CI 0.21-1.28, p = .152). These results suggest that there is not an increased risk of infection with ruxolitinib therapy.

Mechanisms Underlying the Anti-inflammatory and Immunosuppressive Activity of Ruxolitinib

The JAK-STAT signaling pathway plays a central role in signal transduction in hematopoietic cells, as well as in cells of the immune system. The occurrence in most patients affected by myeloproliferative neoplasms (MPNs) of driver mutations resulting in the constitutive activation of JAK2-dependent signaling identified the deregulated JAK-STAT signal transduction pathway as the major pathogenic mechanism of MPNs. It also prompted the development of targeted drugs for MPNs. Ruxolitinib is a potent and selective oral inhibitor of both JAK2 and JAK1 protein kinases. Its use in patients with myelofibrosis is associated with a substantial reduction in spleen volume, attenuation of symptoms and decreased mortality. With growing clinical experience, concerns about infectious complications, and increased risk of B-cell lymphoma, presumably caused by the effects of JAK1/2 inhibition on immune response and immunosurveillance, have been raised. Evidence shows that ruxolitinib exerts potent anti-inflammatory and immunosuppressive effects. Cellular targets of ruxolitinib include various components of both the innate and adaptive immune system, such as natural killer cells, dendritic cells, T helper, and regulatory T cells. On the other hand, immunomodulatory properties have proven beneficial in some instances, as highlighted by the successful use of ruxolitinib in corticosteroid-resistant graft vs. host disease. The objective of this article is to provide an overview of published evidence addressing the key question of the mechanisms underlying ruxolitinib-induced immunosuppression.

Platelet-derived growth factor receptor β activation and regulation in murine myelofibrosis

There is prevailing evidence to suggest a decisive role for platelet-derived growth factors (PDGF) and their receptors in primary myelofibrosis. While PDGF receptor β (PDGFRβ) expression is increased in bone marrow stromal cells of patients correlating with the grade of myelofibrosis, knowledge on the precise role of PDGFRβ signaling in myelofibrosis is sparse. Using the Gata-1^low mouse model for myelofibrosis, we applied RNA sequencing, protein expression analyses, multispectral imaging and, as a novel approach in bone marrow tissue, an in situ proximity ligation assay to provide a detailed characterization of PDGFRβ signaling and regulation during development of myelofibrosis. We observed an increase in PDGFRβ and PDGF-B protein expression in overt fibrotic bone marrow, along with an increase in PDGFRβ–PDGF-B interaction, analyzed by proximity ligation assay. However, PDGFRβ tyrosine phosphorylation levels were not increased. We therefore focused on regulation of PDGFRβ by protein tyrosine phosphatases as endogenous PDGFRβ antagonists. Gene expression analyses showed distinct expression dynamics among PDGFRβ-targeting phosphatases. In particular, we observed enhanced T-cell protein tyrosine phosphatase protein expression and PDGFRβ–T-cell protein tyrosine phosphatase interaction in early and overt fibrotic bone marrow of Gata-1^low mice. In vitro, T-cell protein tyrosine phosphatase (Ptpn2) knockdown increased PDGFRβ phosphorylation at Y⁷⁵¹ and Y¹⁰²¹, leading to enhanced downstream signaling in fibroblasts. Furthermore, Ptpn2 knockdown cells showed increased growth rates when exposed to low-serum growth medium. Taken together, PDGF signaling is differentially regulated during myelofibrosis. Protein tyrosine phosphatases, which have so far not been examined during disease progression, are novel and hitherto unrecognized components in myelofibrosis.

Standard care and investigational drugs in the treatment of myelofibrosis

Myelofibrosis (MF) is a heterogeneous disorder characterized by splenomegaly, constitutional symptoms, ineffective hematopoiesis, and an increased risk of leukemic transformation. The ongoing research in understanding the pathophysiology of the disease has allowed for the development of targeted drugs optimizing patient management. Furthermore, disease prognostication has significantly improved. Current therapeutic interventions are only partially effective with only allogeneic stem cell transplant potentially curative. Ruxolitinib is the only approved therapy for MF by the US Food and Drug Administration. However, despite efficacy in reducing splenomegaly and controlling symptomatology, it is not associated with consistent molecular or pathologic responses. Drug discontinuation is associated with a dismal outcome. The therapeutic landscape in MF has significantly improved, and emerging drugs with different target pathways, alone or in combination with ruxolitinib, seem promising.

Advances in potential treatment options for myeloproliferative neoplasm associated myelofibrosis

INTRODUCTION

The Janus kinase (JAK)1/2 inhibitor ruxolitinib provides rapid, sustained and often dramatic benefits to patients with myelofibrosis, inducing spleen shrinkage and ameliorating symptoms, and improves survival. However, the drug has little effect on the underlying bone marrow fibrosis or on mutant allele burden, and clinical resistance eventually develops. Furthermore, ruxolitinib-induced cytopenias can be challenging in everyday practice.

AREAS COVERED

The developmental therapeutics landscape in MF is discussed. This includes potential partners for ruxolitinib being developed with an aim to improve cytopenias, or to enhance its disease-modifying effects. The development of other JAK inhibitors with efficacy post-ruxolitinib or other unique attributes is being pursued in earnest. Agents with novel mechanisms of action are being studied in patients whose disease responds sub-optimally to, is refractory to or progresses after ruxolitinib.

EXPERT OPINION

The JAK inhibitors fedratinib, pacritinib and momelotinib are clearly active, and it is expected that one or more of these will become licensed in the future. The activin receptor ligand traps are promising as treatments for anemia. Imetelstat has shown interesting activity post-ruxolitinib, and azactidine may be a useful partner for ruxolitinib in some patients. Appropriately, multiple pre-clinical and clinical leads are being pursued in this difficult therapeutic area.

Myelofibrosis in 2019: moving beyond JAK2 inhibition

Myelofibrosis (MF) is a myeloproliferative neoplasm characterized by ineffective clonal hematopoiesis, splenomegaly, bone marrow fibrosis, and the propensity for transformation to acute myeloid leukemia. The discovery of mutations in JAK2, CALR, and MPL have uncovered activated JAK-STAT signaling as a primary driver of MF, supporting a rationale for JAK inhibition. However, JAK inhibition alone is insufficient for long-term remission and offers modest, if any, disease-modifying effects. Given this, there is great interest in identifying mechanisms that cooperate with JAK-STAT signaling to predict disease progression and rationally guide the development of novel therapies. This review outlines the latest discoveries in the biology of MF, discusses current clinical management of patients with MF, and summarizes the ongoing clinical trials that hope to change the landscape of MF treatment.

Hematological malignancies and molecular targeting therapy

Recent genetic analysis using next-generation sequencing (NGS) vastly improved the understanding of molecular mechanism of hematological malignancies. Many molecular targeting drugs have since been used in the clinic, which is timely as clinical outcomes using conventional chemotherapy and hematopoietic stem cell transplantation (HSCT) reached a plateau. The first memorable success in this field was imatinib, a first-generation tyrosine kinase inhibitor (TKI), which has been applied in chronic myeloid leukemia (CML) since 2001. Imatinib drastically changed CML treatment and many CML patients no longer require HSCT. Recently, the second generation TKIs, dasatinib, nilotinib, and ponatinib, have also been available for CML patients. Acute lymphoblastic leukemia (ALL) is sub-categorized based on cytogenetic or molecular genetic abnormalities. Chemotherapy and HSCT combined with TKI improved the event-free survival rate from 20% to 80% in Philadelphia (Ph) chromosome-positive ALL. Reportedly, another Ph-like ALL subgroup with poor prognosis can also be treated by TKIs; additionally, cell therapies that include bispecific T-cell engagers or chimeric antigen receptor (CAR)-T therapy are emerging. Acute myeloid leukemia (AML) is a heterogenous disease and FMS-like related tyrosine kinase-3 (FLT3)-internal tandem duplication, is the most robust marker for poor prognosis. Several first-generation TKIs have been studied for clinical use. Notably, chemotherapy plus midostaurin improved survival compared with chemotherapy alone. Therefore, midostaurin was approved to treat adult AML patients with FLT3-ITD in 2017. Gemtuzumab ozogamicin, a selective anti-CD33 antibody-calicheamicin conjugate, is approved for clinical practice. Many molecular targeting agents are now being used for hematological malignancies.

A journey through infectious risk associated with ruxolitinib

Ruxolitinib has proved to be effective for the treatment of patients with myelofibrosis (either primary or secondary) and polycythaemia vera, and its approval led to a significant change in the current treatment algorithm. Despite its efficacy and beyond its well described haematological toxicity, a peculiar immunosuppressive effect emerged as our clinical experience grew, both within and outside of a clinical trial setting. Definite and negative interactions with multiple pathways of the immune system of patients have been reported so far, involving both adaptive and innate immune responses. These pathophysiological mechanisms may contribute to the increased risk of reactivation of silent infections (e.g., tuberculosis, hepatitis B virus and varicella zoster virus) that have been associated with the drug. Even though such infectious events may be fatal or may lead to significant impairment of organ function, compromising the eligibility of patients for an allotransplant procedure, there are no dedicated guidelines that may help us in assessing and managing the risk of developing serious infections. On this basis, our aim for the present work was to review the current knowledge on the pathophysiological mechanisms through which ruxolitinib may exert its immunosuppressive effect, and to illustrate our personal approach to the management of three peculiar clinical scenarios, for which a risk-based algorithm is suggested.

Aurora Kinase A Inhibition: A Mega-Hit for Myelofibrosis Therapy?

The positive but limited efficacy of JAK inhibitors has sparked the need for alternative therapeutic targets in the treatment of myelofibrosis. The discovery of novel targets, like Aurora Kinase A, may provide new avenues of single-agent and combinatorial therapy for myelofibrosis and restoration of normal bone marrow function.See related article by Gangat et al., p. 4898.

Roles of JAK2 in Aging, Inflammation, Hematopoiesis and Malignant Transformation

Clonal alterations in hematopoietic cells occur during aging and are often associated with the establishment of a subclinical inflammatory environment. Several age-related conditions and diseases may be initiated or promoted by these alterations. JAK2 mutations are among the most frequently mutated genes in blood cells during aging. The most common mutation within the JAK2 gene is JAK2-V617F that leads to constitutive activation of the kinase and thereby aberrant engagement of downstream signaling pathways. JAK2 mutations can act as central drivers of myeloproliferative neoplasia, a pre-leukemic and age-related malignancy. Likewise, hyperactive JAK-signaling is a hallmark of immune diseases and critically influences inflammation, coagulation and thrombosis. In this review we aim to summarize the current knowledge on JAK2 in clonal hematopoiesis during aging, the role of JAK-signaling in inflammation and lymphocyte biology and JAK2 function in age-related diseases and malignant transformation.

Targeted therapies for myeloproliferative neoplasms

The discovery of JAK2V617F and the demonstration that BCR-ABL-negative myeloproliferative neoplasms (MPNs) are driven by abnormal JAK2 activation have led to advances in diagnostic algorithms, prognosis and ultimately also treatment strategies. The JAK 1/2 inhibitor ruxolitinib was a pivotal moment in the treatment of MPNs, representing the first targeted treatment in this field. Despite a weak effect on the cause of the disease itself in MPNs, ruxolitinib improves the clinical state of patients and increases survival in myelofibrosis. In parallel, other JAK inhibitors with potential for pathologic and molecular remissions, less myelosuppression, and with greater selectivity for JAK1 or JAK2, and the ability to overcome JAK inhibitor persistence are in various stages of development. Moreover, many novel classes of targeted agents continue to be investigated in efforts to build on the progress made with ruxolitinib. This article will discuss some of the advances in the targeted therapy in this field in recent years and explore in greater detail some of the most advanced emerging agents as well as those with greatest potential.

A phase 2 study of pracinostat combined with ruxolitinib in patients with myelofibrosis

Although ruxolitinib improves symptoms and splenomegaly in patients with advanced myelofibrosis, whether this agent is truly disease-modifying remains unclear. Histone deacetylase inhibitors (HDACi) downregulate JAK2 via interference with chaperone function. Pracinostat, a pan-HDACi, has modest single-agent activity in myelofibrosis. We conducted a single-institution, phase 2, investigator-initiated trial of ruxolitinib plus pracinostat (begun after 12 weeks of ruxolitinib) in 25 patients with myelofibrosis, of whom 20 received both agents. Sixteen (80%) patients had objective responses (all 'clinical improvement'). The rate of spleen response (by palpation) was 74%, and that of symptom response 80%. Most responses occurred prior to pracinostat initiation. Three patients experienced improvement in bone marrow fibrosis, and one a near-complete molecular response after two years on study treatment. All patients discontinued pracinostat and are currently off-study. Pracinostat interruptions and dose reductions were frequent, often due to worsening anemia. These findings do not support continued development of pracinostat in myelofibrosis.

Cotargeting the JAK/STAT signaling pathway and histone deacetylase by ruxolitinib and vorinostat elicits synergistic effects against myeloproliferative neoplasms

The majority of patients with Philadelphia-negative myeloproliferative neoplasms (MPNs) harbor a gain of function mutation V617F in Janus kinase (JAK) 2. Although JAK2 inhibitors such as ruxolitinib have been shown to be clinically efficacious, the hematological toxicity and eventual drug resistance limit its use as monotherapy. Other gene mutations or dysregulation correlated with the disease phenotype and prognosis have been found to contribute to the complexity and heterogeneity of MPNs, giving rise to an increasing demand for combination therapies. Here, we combine ruxolitinib and the histone deacetylase inhibitor vorinostat as a rational combination strategy for MPNs. We tested the combination of ruxolitinib and vorinostat in cells with the JAK2V617F mutation, such as HEL cells, c-Kit⁺ cells from JAK2V617F transgenic mice and bone marrow mononuclear cells (BMMNCs) from patients with MPN. Our results showed significant synergistic effects of this combination strategy. Cotreatment with ruxolitinib and vorinostat synergistically induced apoptosis, cell cycle arrest and inhibition of the colony-forming capacity of HEL cells by attenuating the JAK/signal transducer and activator of transcription (STAT) and protein kinase-B (AKT) signaling pathways. In particular, cotreatment with ruxolitinib and vorinostat prevented the formation of large colonies of colony-forming unit-granulocyte/erythroid/macrophage/megakaryocytes (CFU-GEMMs) and colony-forming unit-granulocyte/macrophages (CFU-GMs) derived from the BMMNCs of patients with MPN. Taken together, these data provided preclinical evidence that the combination of ruxolitinib and vorinostat is a potential dual-target therapy for patients with MPN.

Emerging translational science discoveries, clonal approaches, and treatment trends in chronic myeloproliferative neoplasms

The 60th American Society of Hematology (ASH) held in San Diego in December 2018 was followed by the 13th Post-ASH chronic myeloproliferative neoplasms (MPNs) workshop on December 4 and 5, 2018. This closed annual workshop, first introduced in 2006 by Goldman and Mughal, was organized in collaboration with Alpine Oncology Foundation and allowed experts in preclinical and clinical research in the chronic MPNs to discuss the current scenario, including relevant presentations at ASH, and address pivotal open questions that impact translational research and clinical management. This review is based on the presentations and deliberations at this workshop, and rather than provide a resume of the proceedings, we have selected some of the important translational science and treatment issues that require clarity. We discuss the experimental and observational evidence to support the intimate interaction between aging, inflammation, and clonal evolution of MPNs, the clinical impact of the unfolding mutational landscape on the emerging targets and treatment of MPNs, new methods to detect clonal heterogeneity, the challenges in managing childhood and adolescent MPN, and reflect on the treatment of systemic mastocytosis (SM) following the licensing of midostaurin.

Efficacy and safety of ruxolitinib and hydroxyurea combination in patients with hyperproliferative myelofibrosis

Ruxolitinib is the only commercially available JAK1/2 inhibitor approved for the treatment of myelofibrosis-related splenomegaly and symptoms. During treatment, as rare conditions, leukocytosis and/or thrombocytosis could develop and the management of these situations is not well established. We report here 53 myelofibrosis patients that received a combination of hydroxyurea and ruxolitinib because of uncontrolled myeloproliferation. Both drugs were administered outside clinical trials. At 48 weeks, a significant reduction in leucocyte and platelet counts was observed (p = 0.02 and p = 0.04, respectively). Additionally, the spleen volume decreased from a median value of 10 cm below the left costal margin (range, 0-10) to 6 cm (range, 0-15). The rate of spleen response increased from 14% at the start of the combination to 45% after 48 weeks. The safety profile of the combination was consistent with that observed with ruxolitinib single agent. These data require further confirmation in large cohorts of patients prospectively assessed.

Overview of the Mutational Landscape in Primary Myelofibrosis and Advances in Novel Therapeutics

Primary Myelofibrosis is a BCR-ABL negative myeloproliferative neoplasm with a variety of hematological presentations, including thrombosis, bleeding diathesis and marrow fibrosis. It is estimated to have an incidence of 1.5 per 100,000 people each year. Although JAK2 or MPL mutations are seen in PMF, several other mutations have recently been documented, including mutations in CALR, epigenetic regulators like TET, ASXL1, and 13q deletions. The identification of these mutations has improved the ability to develop novel treatment options. These include JAK inhibitors like ruxolitinib, heat shock protein-90 inhibitors like ganetespib, histone deacetylase inhibitors including panobinostat, pracinostat, vorinostat and givinostat, hypomethylating agents like decitabine, hedgehog inhibitors like glasdegib, PI3K, AKT and mTOR inhibitors like everolimus as well as telomerase inhibitors like imtelstat. Research on novel therapeutic options is being actively pursued in order to expand treatment options for primary myelofibrosis however currently, there is no curative therapy other than allogenic hematopoietic stem cell transplantation (ASCT) which is possible in select patients.

SOHO State of the Art Updates and Next Questions: Myelofibrosis

The discovery of a mutation in the Janus Kinase 2 gene in 2005 spurred significant progress in the field of myeloproliferative neoplasms. A comprehensive description of genomic factors at play in the malignant clone in myeloproliferative neoplasms, particularly myelofibrosis (MF), have recently led to more precise, personalized prognostic tools. Despite this, understanding of the disease pathogenesis remains relatively limited. We continue to lack a detailed description of the interaction between the hematopoietic stem cell clone, abnormal bone marrow niche cells, and circulating signaling molecules and an understanding of how they cooperate to promote cell proliferation, fibrogenesis, and extramedullary hematopoiesis. Despite our knowledge gaps, recent research in MF has led to promising clinical translation. In this article, we summarize recent insights into MF pathophysiology, progress in the development of novel therapeutics, and opportunities for further advancement of the field.

Adding hydroxyurea in combination with ruxolitinib improves clinical responses in hyperproliferative forms of myelofibrosis

Ruxolitinib, an orally bioavailable and selective inhibitor of Janus kinase 1 (JAK1) and JAK2, significantly reduces splenomegaly and disease‐related symptoms in patients with myelofibrosis (MF). However, no clear survival benefit has been demonstrated, which may in part reflect suboptimal drug exposure related to lower dosages needed to minimize hematological toxicity, specifically cytopenias. Furthermore, the optimal management of specific conditions such as leukocytosis or thrombocytosis in patients under ruxolitinib therapy is still undefined. In these cases, combining ruxolitinib with a cytoreductive agent like hydroxyurea might improve hematological response. This observational multi‐center study enrolled 20 adult patients with intermediate‐ or high‐risk primary MF, post‐ polycythemia vera MF, or postessential thrombocythemia MF with hyperproliferative manifestations of the disease and WBC and/or platelet counts not controlled by ruxolitinib therapy. The patients received treatment with a combination of ruxolitinib and hydroxyurea. A clinical response of any type was obtained in 8 patients (40%) during ruxolitinib monotherapy and in 17 patients (85%) during ruxolitinib‐hydroxyurea combination (P = 0.003). After a median duration of 12.4 months of combination therapy, 16/20 patients had a hematological response; 14/17 patients who had started combination therapy to control WBC count and 2/3 who started in order to reduce platelets count. The number of patients requiring ruxolitinib dosage reduction or discontinuations was lower during combination therapy and, at the end of follow‐up the median ruxolitinib dose was increased in 50% of patients. In conclusion, the combination of hydroxyurea with ruxolitinib yielded a high clinical response rate and increased ruxolitinib exposure in patients with hyperproliferative forms of MF.

Pharmacotherapy of Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm that is pathologically characterized by bone marrow myeloproliferation, reticulin and collagen fibrosis, and extramedullary hematopoiesis. Constitutive activation of the Janus associated kinase (JAK)-signal transducers and activators of transcription signaling pathway with resultant elevation in pro-inflammatory cytokine levels is the pathogenic hallmark of MF. JAK inhibitors, namely ruxolitinib, have been successful in alleviating symptoms and reducing splenomegaly, but therapy-related myelosuppression has led to the further development of highly selective JAK2 inhibitors. Additionally, ruxolitinib does not appear to affect the malignant hematopoietic clone substantially, evidenced by lack of molecular remissions, bone marrow histopathologic responses, and a proportion of treated patients developing progressive disease and leukemic transformation while receiving therapy. A number of other pharmacotherapeutic strategies are currently being explored in the clinic. Non-JAK inhibitor strategies being evaluated in MF include non-JAK signaling pathway inhibitors, epigenetic-directed therapies, immune-modulating agents, anti-fibrotic agents, and telomerase inhibitors. This review highlights the current landscape of MF pharmacotherapy and explores therapeutic advances underway.

Infections associated with immunotherapeutic and molecular targeted agents in hematology and oncology. A position paper by the European Conference on Infections in Leukemia (ECIL)

A multitude of new agents for the treatment of hematologic malignancies has been introduced over the past decade. Hematologists, infectious disease specialists, stem cell transplant experts, pulmonologists and radiologists have met within the framework of the European Conference on Infections in Leukemia (ECIL) to provide a critical state-of-the-art on infectious complications associated with immunotherapeutic and molecular targeted agents used in clinical routine. For brentuximab vedotin, blinatumomab, CTLA4- and PD-1/PD-L1-inhibitors as well as for ibrutinib, idelalisib, HDAC inhibitors, mTOR inhibitors, ruxolitinib, and venetoclax, a detailed review of data available until August 2018 has been conducted, and specific recommendations for prophylaxis, diagnostic and differential diagnostic procedures as well as for clinical management have been developed.

A case report of disseminated histoplasmosis and concurrent cryptococcal meningitis in a patient treated with ruxolitinib

Background

Ruxolitinib is a highly potent janus kinase inhibitor that places its users at risk for various bacterial infections and viral reactivation. However new reports are also emerging that suggest greater immunosuppression and risk for fungal disease.

Case presentation

We report the case of a 51 year-old veteran from Guam, treated with ruxolitinib for polycythemia vera, who developed disseminated histoplasmosis and concurrent cryptococcal meningitis.

Conclusion

This case draws attention to the degree of immunosuppression that may be seen with this drug and the need for heightened vigilance for opportunistic infections in those treated with inhibitors of janus kinase/signal transducers and activators of transcription (JAK/STAT) such as ruxolitinib.

Next-Generation Sequencing-Based Assessment of JAK2, PD-L1, and PD-L2 Copy Number Alterations at 9p24.1 in Breast Cancer: Potential Implications for Clinical Management

Genomic amplification at 9p24.1, including the loci for JAK2, PD-L1, and PD-L2, has recently been described as a mechanism of resistance in postchemotherapy, triple-negative breast cancer. This genomic signature holds significant promise as a prognostic biomarker and has implications for targeted therapy with JAK2 inhibitors, as well as with immunotherapy. To guide future screening strategies, the frequency of these alterations was determined. A total of 5399 cases were included in the study. This encompassed 2890 institutional cases tested by the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets assay and 2509 cases from The Cancer Genome Atlas (TCGA). The combined incidence of 9p24.1 amplifications in both the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets and TCGA cohorts was 1.0% (56/5399 cases) and showed a >10-fold higher incidence in triple-negative breast cancer (triple-negative: 5.1%; non-triple-negative: 0.5%). Tumor mutation burden and stromal tumor infiltrating lymphocytes, parameters used to assess response to immunotherapy, were not significantly higher for these cases. The significance of genomic losses at 9p24.1 is unclear, and further studies are needed. Herein, we studied the spectrum of copy number alterations in breast cancer cases within our institutional clinical sequencing cohort and those profiled by TCGA to determine the frequency of genomic alterations that may predict response or resistance to JAK2 inhibitors and/or immunotherapy.

Vaccination of patients with haematological malignancies who did not have transplantations: guidelines from the 2017 European Conference on Infections in Leukaemia (ECIL 7)

Patients with haematological malignancies are at high risk of infection because of various mechanisms of humoral and cell-mediated immune deficiencies, which mainly depend on underlying disease and specific therapies. Some of these infections are vaccine preventable. However, these malignancies are different from each other, and the treatment approaches are diverse and rapidly evolving, so it is difficult to have a common programme for vaccination in a haematology ward. Additionally, because of insufficient training about the topic, vaccination is an area often neglected by haematologists, and influenced by cultural differences, even among health-care workers, in compliance to vaccines. Several issues are encountered when addressing vaccination in haematology: the small size of the cohorts that makes it difficult to show the clinical benefits of vaccination, the subsequent need to rely on biological parameters, their clinical pertinence not being established in immunocompromised patients, scarcity of clarity on the optimal timing of vaccination in complex treatment schedules, and the scarcity of data on long-term protection in patients receiving treatments. Moreover, the risk of vaccine-induced disease with live-attenuated vaccines strongly limits their use. Here we summarise guidelines for patients without transplantations, and address the issue by the haematological group-myeloid and lymphoid-of diseases, with a special consideration for children with acute leukaemia.

New Concepts of Treatment for Patients with Myelofibrosis

OPINION STATEMENT

Seven years after the approval of the Janus kinase 1/2 (JAK1/2) inhibitor ruxolitinib, it remains the only drug licensed for the treatment of myelofibrosis. Patients who discontinue ruxolitinib have a dismal outcome, and this is, therefore, an area of significant unmet need. Given the central role that JAK-signal transducer and activator of transcription (STAT) activation plays in disease pathogenesis, there have been many other JAK inhibitors tested, but most have been abandoned, for a variety of reasons. The JAK2-selective inhibitor fedratinib has recently been resurrected, and there has been a resurgence of interest in the failed JAK1/2 inhibitor momelotinib, which possibly improves anemia. Pacritinib, a non-myelosuppressive JAK2-selective inhibitor, is currently in a dose-ranging study mandated by regulatory authorities. A plethora of other targeted agents, most backed by preclinical data, are in various stages of investigation. These include epigenetic and immune therapies, agents targeting cellular survival, metabolic and apoptotic pathways, the cell cycle, DNA repair, and protein folding and degradation, among others. However, at this time, none of these is close to registration or even in a pivotal trial, illustrating the difficulties in recapitulating the clinical disease in preclinical models. Most current clinical trials are testing the addition of a novel agent to ruxolitinib, either in the frontline setting or in the context of an insufficient response to ruxolitinib, or attempting to study new drugs in the second-line, "ruxolitinib failure" setting. Emerging data supports the addition of azacitidine to ruxolitinib in some patients. Other strategies have focused on improving cytopenias, through amelioration of bone marrow fibrosis or other mechanisms. This is important, because cytopenias are the commonest reason for ruxolitinib interruption and/or dose reduction, and dose optimization of ruxolitinib is tied to its survival benefit. The activin receptor ligand trap, sotatercept, and the anti-fibrotic agent, PRM-151, have shown promise in this regard.

Busulfan- or Thiotepa-Based Conditioning in Myelofibrosis: A Phase II Multicenter Randomized Study from the GITMO Group

We report a randomized study comparing fludarabine in combination with busulfan (FB) or thiotepa (FT), as conditioning regimen for hematopoietic stem cell transplantation (HSCT) in patients with myelofibrosis. The primary study endpoint was progression-free survival (PFS). Sixty patients were enrolled with a median age of 56 years and an intermediate-2 or high-risk score in 65%, according to the Dynamic International Prognostic Staging System (DIPSS). Donors were HLA-identical sibling (n = 25), matched unrelated (n = 25) or single allele mismatched unrelated (n = 10). With a median follow-up of 22 months (range, 1 to 68 months), outcomes at 2 years after HSCT in the FB arm versus the FT arm were as follows: PFS, 43% versus 55% (P = .28); overall survival (OS), 54% versus 70% (P = .17); relapse/progression, 36% versus 24% (P = .24); nonrelapse mortality (NRM), 21% in both arms (P = .99); and graft failure, 14% versus 10% (P = .96). A better PFS was observed in patients with intermediate-1 DIPSS score (P = .03). Both neutrophil engraftment and platelet engraftment were significantly influenced by previous splenectomy (hazard ratio [HR], 2.28; 95% confidence interval [CI], 1.16 to 4.51; P = .02) and splenomegaly at transplantation (HR, 0.51; 95% CI, 0.27 to 0.94; P = .03). In conclusion, the clinical outcome after HSCT was comparable when using either a busulfan or thiotepa based conditioning regimen.

Management of Myelofibrosis-Related Cytopenias

PURPOSE OF REVIEW

Cytopenias, particularly anemia, are frequently encountered in patients with myelofibrosis. Management of cytopenias in myelofibrosis can be very challenging because current therapeutic interventions are only of modest efficacy and ruxolitinib, the only approved drug for myelofibrosis, is myelosuppressive. Yet, dose optimization of ruxolitinib is important for its survival benefit in patients with advanced disease. We sought to summarize the data on treatments for cytopenias available at present and review promising agents in development and emerging strategies.

RECENT FINDINGS

The activin receptor ligand traps hold considerable promise for the treatment of anemia and could represent an attractive combination strategy with ruxolitinib. Low-dose thalidomide, which could offset both anemia and thrombocytopenia caused by ruxolitinib, represents another potential partner for ruxolitinib. The anti-fibrotic agent PRM-151 produced sustained improvements in cytopenias in some patients, and further data on this drug are eagerly awaited. Finally, several preclinical leads with translational potential are worthy of clinical investigation as strategies to halt/reverse bone marrow fibrosis and thereby improve cytopenias. Cytopenias remain a significant hurdle in myelofibrosis management, but several novel investigational agents hold considerable promise for the future.

Nuclear-Cytoplasmic Transport Is a Therapeutic Target in Myelofibrosis

PURPOSE

Myelofibrosis is a hematopoietic stem cell neoplasm characterized by bone marrow reticulin fibrosis, extramedullary hematopoiesis, and frequent transformation to acute myeloid leukemia. Constitutive activation of JAK/STAT signaling through mutations in JAK2, CALR, or MPL is central to myelofibrosis pathogenesis. JAK inhibitors such as ruxolitinib reduce symptoms and improve quality of life, but are not curative and do not prevent leukemic transformation, defining a need to identify better therapeutic targets in myelofibrosis.

EXPERIMENTAL DESIGN

A short hairpin RNA library screening was performed on JAK2^V617F-mutant HEL cells. Nuclear-cytoplasmic transport (NCT) genes including RAN and RANBP2 were among top candidates. JAK2^V617F-mutant cell lines, human primary myelofibrosis CD34⁺ cells, and a retroviral JAK2^V617F-driven myeloproliferative neoplasms mouse model were used to determine the effects of inhibiting NCT with selective inhibitors of nuclear export compounds KPT-330 (selinexor) or KPT-8602 (eltanexor).

RESULTS

JAK2^V617F-mutant HEL, SET-2, and HEL cells resistant to JAK inhibition are exquisitely sensitive to RAN knockdown or pharmacologic inhibition by KPT-330 or KPT-8602. Inhibition of NCT selectively decreased viable cells and colony formation by myelofibrosis compared with cord blood CD34⁺ cells and enhanced ruxolitinib-mediated growth inhibition and apoptosis, both in newly diagnosed and ruxolitinib-exposed myelofibrosis cells. Inhibition of NCT in myelofibrosis CD34⁺ cells led to nuclear accumulation of p53. KPT-330 in combination with ruxolitinib-normalized white blood cells, hematocrit, spleen size, and architecture, and selectively reduced JAK2^V617F-mutant cells in vivo.

CONCLUSIONS

Our data implicate NCT as a potential therapeutic target in myelofibrosis and provide a rationale for clinical evaluation in ruxolitinib-exposed patients with myelofibrosis.

The ruxolitinib effect: understanding how molecular pathogenesis and epigenetic dysregulation impact therapeutic efficacy in myeloproliferative neoplasms

The myeloproliferative neoplasms (MPN), polycythaemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) are linked by a propensity to thrombosis formation and a risk of leukaemic transformation. Activation of cytokine independent signalling through the JAK/STAT cascade is a feature of these disorders. A point mutation in exon 14 of the JAK2 gene resulting in the formation of the JAK2 V617F transcript occurs in 95% of PV patients and around 50% of ET and PMF patients driving constitutive activation of the JAK/STAT pathway. Mutations in CALR or MPL are present as driving mutations in the majority of remaining ET and PMF patients. Ruxolitinib is a tyrosine kinase inhibitor which inhibits JAK1 and JAK2. It is approved for use in intermediate and high risk PMF, and in PV patients who are resistant or intolerant to hydroxycarbamide. In randomised controlled trials it has demonstrated efficacy in spleen volume reduction and symptom burden reduction with a moderate improvement in overall survival in PMF. In PV, there is demonstrated benefit in haematocrit control and spleen volume. Despite these benefits, there is limited impact to induce complete haematological remission with normalisation of blood counts, reduce the mutant allele burden or reverse bone marrow fibrosis. Clonal evolution has been observed on ruxolitinib therapy and transformation to acute leukaemia can still occur. This review will concentrate on understanding the clinical and molecular effects of ruxolitinib in MPN. We will focus on understanding the limitations of JAK inhibition and the challenges to improving therapeutic efficacy in these disorders. We will explore the demonstrated benefits and disadvantages of ruxolitinib in the clinic, the role of genomic and clonal variability in pathogenesis and response to JAK inhibition, epigenetic changes which impact on response to therapy, the role of DNA damage and the role of inflammation in these disorders. Finally, we will summarise the future prospects for improving therapy in MPN in the JAK inhibition era.

JAK2 (and other genes) be nimble with MPN diagnosis, prognosis, and therapy

Now that the spectrum of somatic mutations that initiate, propagate, and drive the progression of myeloproliferative neoplasms (MPNs) has largely been defined, recent efforts have focused on integrating this information into clinical decision making. In this regard, the greatest progress has been made in myelofibrosis, in which high-molecular-risk mutations have been identified and incorporated into prognostic models to help guide treatment decisions. In this chapter, we focus on advances in 4 main areas: (1) What are the MPN phenotypic driver mutations? (2) What constitutes high molecular risk in MPN (focusing on ASXL1)? (3) How do we risk-stratify patients with MPN? And (4) What is the significance of molecular genetics for MPN treatment? Although substantial progress has been made, we still have an incomplete understanding of the molecular basis for phenotypic diversity in MPN, and few rationally designed therapeutic approaches to target high-risk mutations are available. Ongoing research efforts in these areas are critical to understanding the biological consequences of genetic heterogeneity in MPN and to improving outcomes for patients.