A phase 2 study of ruxolitinib in combination with azacitidine in patients with myelofibrosis

When and how to transplant in myelofibrosis - recent trends

Allogeneic hematopoietic stem cell transplantation (AHSCT) is currently the only treatment modality that is capable of curing myelofibrosis (MF). Although outcomes of AHSCT have improved vastly in recent years owing to advancements in HLA typing, conditioning regimens, and supportive care, it remains a procedure with a considerable risk in MF patients due to conditioning regimen related toxicity, higher rates of graft failure, infections, and graft versus host disease (GVHD). Recent progress in the treatment and prevention of GVHD with post-transplant cyclophosphamide has also rendered transplantation from alternative donors feasible and safer, thus improving access to patients without HLA-identical donors. Accordingly, all patients with intermediate or high-risk MF today should be referred for potential transplant evaluation to consider the pros and cons of an early versus a delayed transplant strategy. Individual risk assessment in MF is best facilitated by contemporary prognostic models that incorporate both clinical and genetic risk factors. The current review highlights new information regarding risk stratification in MF, anchored by practical algorithms that facilitate patient selection for specific treatment actions, including AHSCT.

Janus kinase inhibitor monotherapy and combination therapies for myelofibrosis: what's the current standard of care?

INTRODUCTION

JAK inhibitors (JAKi) have changed the treatment paradigm of myelofibrosis (MF). Currently, 4 JAKis are approved in the US as monotherapy (mono) to treat patients with MF. JAKis are also being studied in combination (combo) with novel agents. Herein, we review some of the key studies that evaluated JAKi as mono and combo in MF.

AREAS COVERED

We performed a Pubmed search for 'JAK inhibitors' and 'myelofibrosis' from 1/2010 to 12/2023. For mono, we included only the unique phase II/III studies of the approved JAKi. Selective studies that evaluated JAKi in combo with the novel agents were also included.

EXPERT OPINION

JAKis aim to provide clinical benefit to patients via spleen size reduction and MPN symptom improvement. In order to potentially increase clinical benefit for patients with MF, several novel agents are being partnered with ruxolitinib (RUX) with the ongoing hypothesis to augment greater measures of MF disease modification. The novel agents are either 'added-on' to RUX or as a combo in JAKi naïve patients. Also, the mutant-targeting era of therapies is now beginning with novel CALR-mutated, novel JAK2 V617F mutation-specific and type II JAK2i in the initial stages of drug development, representing a new approach to treatment.

Advances in pharmacotherapy for myelofibrosis: what is the current state of play?

INTRODUCTION

The introduction of the first JAK inhibitor (JAKi) ruxolitinib 10 years ago represented a pivotal advancement in myelofibrosis (MF) treatment, mostly in terms of spleen and symptoms response. Nowadays three more JAKi, fedratinib, pacritinib, and momelotinib, are available for both ruxolitinib-resistant and naïve patients. Moreover, many drugs are currently being investigated, both alone and in combination with JAKi.

AREAS COVERED

In this review we discuss the long-term data of ruxolitinib and more recent evidence coming from clinical trials of fedratinib, pacritinib, and momelotinib, used as first- or second-line MF therapy. More, focus is set on data from non-JAKi drugs, such as the quite extensively studied BET-inhibitors (pelabresib) and BCL-inhibitors (navitoclax), novel target therapies, and drugs aimed to improve anemia, still representing a major determinant of reduced survival in MF.

EXPERT OPINION

It's now evident that JAKi monotherapy, though clinically effective, is rarely able to change MF natural history; novel drugs are promising but long-term data are inevitably lacking. We feel that soon MF treatment will require clinicians to select the most appropriate JAKi inhibitor, based on patient characteristics, associating either front-line or in case of early suboptimal response, non-JAKi drugs with the aim to pursue disease modification.

Evolving landscape of JAK inhibition in myelofibrosis: monotherapy and combinations

Myeloproliferative neoplasms (MPNs) are characterized by clonal myeloproliferation in 1 or more of the hematopoietic stem cell lineages. Primary myelofibrosis (MF), post-polycythemia vera MF, and post-essential thrombocythemia MF have the worst prognosis and are characterized by the presence of cytokine-mediated symptom complex, splenomegaly, progressive marrow failure, and clonal instability, leading to leukemic transformation. The key therapeutic aims encompass the management of symptoms, splenomegaly, and anemia and the improvement of survivals. These therapeutic aims have evolved with the availability of Jak inhibitors and novel agents, making disease modification potentially achievable. Novel agents may potentially target MPN stem cells, epigenetic alterations, signaling pathways, and apoptotic pathways. In this case-based review, we outline our approach to the management of MF and discuss the therapeutic landscape of MF, highlighting the utility of Jak inhibitors and novel Jak inhibitor-based combinations.

Management of classical Philadelphia chromosome-negative myeloproliferative neoplasms in Asia: consensus of the Asian Myeloid Working Group

Myeloproliferative neoplasms (MPN) are a heterogeneous group of clonal hematopoietic stem cell disorders characterized clinically by the proliferation of one or more hematopoietic lineage(s). The classical Philadelphia-chromosome (Ph)-negative MPNs include polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The Asian Myeloid Working Group (AMWG) comprises representatives from fifteen Asian centers experienced in the management of MPN. This consensus from the AMWG aims to review the current evidence in the risk stratification and treatment of Ph-negative MPN, to identify management gaps for future improvement, and to offer pragmatic approaches for treatment commensurate with different levels of resources, drug availabilities and reimbursement policies in its constituent regions. The management of MPN should be patient-specific and based on accurate diagnostic and prognostic tools. In patients with PV, ET and early/prefibrotic PMF, symptoms and risk stratification will guide the need for early cytoreduction. In younger patients requiring cytoreduction and in those experiencing resistance or intolerance to hydroxyurea, recombinant interferon-α preparations (pegylated interferon-α 2A or ropeginterferon-α 2b) should be considered. In myelofibrosis, continuous risk assessment and symptom burden assessment are essential in guiding treatment selection. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) in MF should always be based on accurate risk stratification for disease-risk and post-HSCT outcome. Management of classical Ph-negative MPN entails accurate diagnosis, cytogenetic and molecular evaluation, risk stratification, and treatment strategies that are outcome-oriented (curative, disease modification, improvement of quality-of-life).

Ten years after ruxolitinib approval for myelofibrosis: a review of clinical efficacy

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterized by splenomegaly, abnormal cytokine expression, cytopenias, and progressive bone marrow fibrosis. The disease often manifests with burdensome symptoms and is associated with reduced survival. Ruxolitinib, an oral Janus kinase (JAK) 1 and JAK2 inhibitor, was the first agent approved for MF. As a first-in-class targeted treatment, ruxolitinib approval transformed the MF treatment approach and remains standard of care. In addition, targeted inhibition of JAK1/JAK2 signaling, a key molecular pathway underlying MF pathogenesis, and the large volume of literature evaluating ruxolitinib, have led to a better understanding of the disease and improved management in general. Here we review ruxolitinib efficacy in patients with MF in the 10 years following approval, including demonstration of clinical benefit in the phase 3 COMFORT-I/II trials, real-world evidence, translational studies, and expanded access data. Lastly, future directions for MF treatment are discussed, including ruxolitinib-based combination therapies.

Pharmacotherapeutic advances for splenomegaly in myelofibrosis

INTRODUCTION

Myelofibrosis is a hematologic malignancy with a variety of clinical manifestations including splenomegaly, which is present in approximately 80% of newly diagnosed patients. JAK inhibitors are the mainstay of pharmacologic treatment for splenomegaly in myelofibrosis, although spleen size reduction is not universal, and the duration of benefit is only moderately durable.

AREAS COVERED

We first discuss the pathobiology of splenomegaly in myelofibrosis before detailing approved and novel pharmacotherapies that can reduce spleen size while also highlighting non-pharmacologic approaches. In this review, efficacy of these treatments is measured solely by spleen volume reduction, acknowledging that other outcome measures such as symptom improvement and survival are also critical.

EXPERT OPINION

Currently, ruxolitinib can be administered to the majority of frontline patients although those with severe thrombocytopenia should receive pacritinib to address spleen burden. Momelotinib may be particularly well suited for patients with significant anemia and novel combination treatments in clinical development may improve the depth and duration of spleen responses. After frontline treatment failure, fedratinib, or pacritinib are commercial options for patients with persistent symptomatic splenomegaly. Novel agents given alone or in combination with a JAK inhibitor are being explored in trials, which may ameliorate splenomegaly and ultimately improve disease progression.

The ABNL-MARRO 001 study: a phase 1-2 study of randomly allocated active myeloid target compound combinations in MDS/MPN overlap syndromes

BACKGROUND

Myelodysplastic/myeloproliferative neoplasms (MDS/MPN) comprise several rare hematologic malignancies with shared concomitant dysplastic and proliferative clinicopathologic features of bone marrow failure and propensity of acute leukemic transformation, and have significant impact on patient quality of life. The only approved disease-modifying therapies for any of the MDS/MPN are DNA methyltransferase inhibitors (DNMTi) for patients with dysplastic CMML, and still, outcomes are generally poor, making this an important area of unmet clinical need. Due to both the rarity and the heterogeneous nature of MDS/MPN, they have been challenging to study in dedicated prospective studies. Thus, refining first-line treatment strategies has been difficult, and optimal salvage treatments following DNMTi failure have also not been rigorously studied. ABNL-MARRO (A Basket study of Novel therapy for untreated MDS/MPN and Relapsed/Refractory Overlap Syndromes) is an international cooperation that leverages the expertise of the MDS/MPN International Working Group (IWG) and provides the framework for collaborative studies to advance treatment of MDS/MPN and to explore clinical and pathologic markers of disease severity, prognosis, and treatment response.

METHODS

ABNL MARRO 001 (AM-001) is an open label, randomly allocated phase 1/2 study that will test novel treatment combinations in MDS/MPNs, beginning with the novel targeted agent itacitinib, a selective JAK1 inhibitor, combined with ASTX727, a fixed dose oral combination of the DNMTi decitabine and the cytidine deaminase inhibitor cedazuridine to improve decitabine bioavailability.

DISCUSSION

Beyond the primary objectives of the study to evaluate the safety and efficacy of novel treatment combinations in MDS/MPN, the study will (i) Establish the ABNL MARRO infrastructure for future prospective studies, (ii) Forge innovative scientific research that will improve our understanding of pathogenetic mechanisms of disease, and (iii) Inform the clinical application of diagnostic criteria, risk stratification and prognostication tools, as well as response assessments in this heterogeneous patient population.

TRIAL REGISTRATION

This trial was registered with ClinicalTrials.gov on August 19, 2019 (Registration No. NCT04061421).

Lysine-Specific Demethylase 1 (LSD1/KDM1A) Inhibition as a Target for Disease Modification in Myelofibrosis

Myelofibrosis (MF) is the most symptomatic form of myeloproliferative neoplasm and carries the worst outcome. Allogeneic hematopoietic stem cell transplantation is the only therapy with potential for cure at present, but is limited by significant mortality and morbidity. JAK inhibition is the mainstay of treatment for intermediate- and high-risk MF. Ruxolitinib is the most widely used JAK1/2 inhibitor and provides durable effects in controlling symptom burden and spleen volumes. Nevertheless, ruxolitinib may not adequately address the underlying disease biology. Its effects on mutant allele burden, bone marrow fibrosis, and the prevention of leukemic transformation are minimal. Multiple small molecules are being tested in multiple phase 2 and 3 studies as either monotherapy or in combination with JAK2 inhibitors. In this review, the role of LSD1/KDM1A inhibition as a potential disease-modification strategy in patients with myelofibrosis is described and discussed.

Thrombocytopenia in Patients With Myelofibrosis: Pathogenesis, Prevalence, Prognostic Impact, and Treatment

Myelofibrosis (MF) is a clonal hematopoietic stem cell neoplasm, characterized by pathologic myeloproliferation associated with inflammatory and pro-angiogenic cytokine release, that results in functional compromise of the bone marrow. Thrombocytopenia is a disease-related feature of MF, which portends a poor prognosis impacting overall survival (OS) and leukemia free survival. Thrombocytopenia in MF has multiple causes including ineffective hematopoiesis, splenic sequestration, and treatment-related effects. Presently, allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curable treatment for MF, which, unfortunately, is only a viable option for a minority of patients. All other currently available therapies are either focused on improving cytopenias or the alleviating systemic symptoms and burdensome splenomegaly. While JAK2 inhibitors have moved to the forefront of MF therapy, available JAK inhibitors are advised against in patients with severe thrombocytopenia (platelets < 50 × 10⁹/L). In this review, we describe the pathogenesis, prevalence, and prognostic significance of thrombocytopenia in MF. We also explore the value and limitations of treatments directed at addressing cytopenias, splenomegaly and symptom burden, and those with potential disease modification. We conclude by proposing a treatment algorithm for patients with MF and severe thrombocytopenia.

Mutational landscape of blast phase myeloproliferative neoplasms (MPN-BP) and antecedent MPN

Myeloproliferative neoplasms (MPN) have an inherent tendency to evolve to the blast phase (BP), characterized by ≥20% myeloblasts in the blood or bone marrow. MPN-BP portends a dismal prognosis and currently, effective treatment modalities are scarce, except for allogeneic hematopoietic stem cell transplantation (allo-HSCT) in selected patients, particularly those who achieve complete/partial remission. The mutational landscape of MPN-BP differs from de novo acute myeloid leukemia (AML) in several key aspects, such as significantly lower frequencies of FLT3 and DNMT3A mutations, and higher incidence of IDH1/2 and TP53 in MPN-BP. Herein, we comprehensively review the impact of the three signaling driver mutations (JAK2 V617F, CALR exon 9 indels, MPL W515K/L) that constitutively activate the JAK/STAT pathway, and of the other somatic non-driver mutations (epigenetic, mRNA splicing, transcriptional regulators, and mutations in signal transduction genes) that cooperatively or independently promote MPN progression and leukemic transformation. The MPN subtype, harboring two or more high-molecular risk (HMR) mutations (epigenetic regulators and mRNA splicing factors) and "triple-negative" PMF are among the critical factors that increase risk of leukemic transformation and shorten survival. Primary myelofibrosis (PMF) is the most aggressive MPN; and polycythemia vera (PV) and essential thrombocythemia (ET) are relatively indolent subtypes. In PV and ET, mutations in splicing factor genes are associated with progression to myelofibrosis (MF), and in ET, TP53 mutations predict risk for leukemic transformation. The advent of targeted next-generation sequencing and improved prognostic scoring systems for PMF inform decisions regarding allo-HSCT. The emergence of treatments targeting mutant enzymes (e.g., IDH1/2 inhibitors) or epigenetic pathways (BET and LSD1 inhibitors) along with new insights into the mechanisms of leukemogenesis will hopefully lead the way to superior management strategies and outcomes of MPN-BP patients.

Post-Transplantation Cyclophosphamide-Based Graft- versus-Host Disease Prophylaxis with Nonmyeloablative Conditioning for Blood or Marrow Transplantation for Myelofibrosis

We describe outcomes after post-transplantation cyclophosphamide and nonmyeloablative conditioning-based allogeneic blood or marrow transplantation for myelofibrosis using matched or mismatched related or unrelated donors. The conditioning regimen consisted of fludarabine, cyclophosphamide, and total body irradiation. Forty-two patients were included, with a median age of 63 years, of whom 19% had Dynamic International Prognostic Scoring System (DIPSS)-plus intermediate-1 risk, 60% had intermediate-2 risk, and 21% had high-risk disease, and 60% had at least 1 high-risk somatic mutation. More than 90% of patients engrafted neutrophils, at a median of 19.5 days, and 7% experienced graft failure. At 1 year and 3 years, respectively, overall survival was 65% and 60%, relapse-free survival was 65% and 31%, relapse was 5% and 40%, and nonrelapse mortality was 30% and 30%. Acute graft-versus-host disease grade 3-4 was seen in 17% of patients at 1 year, and chronic graft-versus-host disease requiring systemic therapy in occurred in 12% patients. Spleen size ≥17 cm or prior splenectomy was associated with inferior relapse-free survival (hazard ratio [HR], 3.50; 95% confidence interval [CI], 1.18 to 10.37; P = .02) and higher relapse rate (subdistribution HR [SDHR] not calculable; P = .01). Age >60 years (SDHR, 0.26; 95% CI, 0.08 to 0.80, P = .02) and receipt of peripheral blood grafts (SDHR, 0.34; 95% CI, 0.11 to 0.99; P = .05) were associated with a lower risk of relapse. In our limited sample, the presence of a high-risk mutation was not statistically significantly associated with an inferior outcome, although ASXL1 was suggestive of inferior survival (SDHR, 2.36; 95% CI, 0.85 to 6.6; P = .09). Overall, this approach shows outcomes comparable those of to previously reported approaches and underscores the importance of spleen size in the evaluation of transplantation candidates.

SOHO State of the Art Updates and Next Questions: Novel Therapies in Development for Myelofibrosis

Myeloproliferative neoplasms research has entered a dynamic and exciting era as we witness exponential growth of novel agents in advanced/early phase clinical trials for myelofibrosis (MF). Building on the success and pivotal role of ruxolitinib, many novel agents, spanning a wide range of mechanisms/targets (epigenetic regulation, apoptotic/intracellular signaling pathways, telomerase, bone marrow fibrosis) are in clinical development; several are studied in registrational trials and hold great potential to expand the therapeutic arsenal/shift the treatment paradigm if regulatory approval is granted. Insight into MF pathogenesis and its molecular underpinnings, preclinical studies demonstrating synergism of ruxolitinib with investigational agents, urgent unmet clinical needs (cytopenias, loss of response to JAK inhibitors); and progressive disease fueled the rapid rise of innovative therapeutics. New strategies include pairing ruxolitinib with erythroid maturation agents to manage anemia (luspatercept), designing rational combinations with ruxolitinib to boost responses in both the frontline and suboptimal response settings (pelabresib, navitoclax, parsaclisib), treatment with non-JAK inhibitor monotherapy in the second-line setting (navtemadlin, imetelstat), novel JAK inhibitors tailored to subgroups with challenging unmet needs (momelotinib and pacritinib for anemia and thrombocytopenia, respectively); and agents potentially enhancing longevity (imetelstat). Beyond typical endpoints evaluated in MF clinical trials (spleen volume reduction ≥ 35%, total symptom score reduction ≥ 50%) thus far, emerging endpoints include overall survival, progression-free survival, transfusion independence, anemia benefits, bone marrow fibrosis and driver mutation allele burden reduction. Novel biomarkers and additional clinical features are being sought to assess new agents and tailor emerging therapies to appropriate patients. New strategies are needed to optimize the design of clinical trials comparing novel combinations to standard agent monotherapy.

Role of JAK inhibitors in myeloproliferative neoplasms: current point of view and perspectives

Classic Philadelphia-negative myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF), classified as primary (PMF), or secondary to PV or ET. All MPN, regardless of the underlying driver mutation in JAK2/CALR/MPL, are invariably associated with dysregulation of JAK/STAT pathway. The discovery of JAK2V617F point mutation prompted the development of small molecules inhibitors of JAK tyrosine kinases (JAK inhibitors-JAKi). To date, among JAKi, ruxolitinib (RUX) and fedratinib (FEDR) are approved for intermediate and high-risk MF, and RUX is also an option for high-risk PV patients inadequately controlled by or intolerant to hydroxyurea. While not yet registered, pacritinib (PAC) and momelotinib (MMB), proved to be effective particularly in thrombocytopenic and anemic MF patients, respectively. In most cases, JAKi are effective in reducing splenomegaly and alleviating disease-related symptoms. However, almost 50% lose response by three years and dose-dependent toxicities may lead to suboptimal dosing or treatment discontinuation. To date, although not being disease-modifying agents, JAKi represent the therapeutic backbone particularly in MF patient. To optimize therapeutic strategies, many trials with drug combinations of JAKi with novel molecules are ongoing. This review critically discusses the role of JAKi in the modern management of patients with MPN.

Novel strategies for challenging scenarios encountered in managing myelofibrosis

Given its rarity, multi-faceted clinical presentation and the relative paucity of approved therapies, the management of myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF) can be challenging. Janus kinase (JAK) inhibitors, the only approved agents at present, have brought many clinical benefits to patients, with prolongation of survival also demonstrated for ruxolitinib. However, these agents have clear limitations. Optimal management of anemia in MF remains a major unmet need. Neither ruxolitinib nor fedratinib is recommended for use in patients with severe thrombocytopenia, i.e. platelets <50 × 10⁹/L, who have a particularly poor prognosis. The search for the optimal partner for JAK inhibitors to address some of the shortcomings of these agents (e.g. limited ability to improve bone marrow fibrosis, cytopenias and induce molecular responses) and achieve meaningful 'disease modification' continues. This has led to the development of a number of rational, preclinically synergistic combinations for use either upfront or in the setting of sub-optimal response to JAK inhibition. Finally, the outlook for patients whose disease progresses on JAK inhibitor therapy continues to be grim, and agents with alternative mechanisms of action may be needed in this setting. In this article, we use a case-based approach to illustrate challenges commonly encountered in clinical practice and our management of the same. Fortunately, there has been enormous growth in drug development efforts in the MF space in the last few years, some of which appear poised to bear fruit in the very near future.

Allogeneic blood or marrow transplantation with haploidentical donor and post-transplantation cyclophosphamide in patients with myelofibrosis: a multicenter study

We report the results from a multicenter retrospective study of 69 adult patients who underwent haploidentical blood or marrow transplantation (haplo-BMT) with post-transplantation cyclophosphamide (PTCy) for chronic phase myelofibrosis. The median age at BMT was 63 years (range, 41-74). Conditioning regimens were reduced intensity in 54% and nonmyeloablative in 39%. Peripheral blood grafts were used in 86%. The median follow-up was 23.1 months (range, 1.6-75.7). At 3 years, the overall survival, relapse-free survival (RFS), and graft-versus-host-disease (GVHD)-free-RFS were 72% (95% CI 59-81), 44% (95% CI 29-59), and 30% (95% CI 17-43). Cumulative incidences of non-relapse mortality and relapse were 23% (95% CI 14-34) and 31% (95% CI 17-47) at 3 years. Spleen size ≥22 cm or prior splenectomy (HR 6.37, 95% CI 2.02-20.1, P = 0.002), and bone marrow grafts (HR 4.92, 95% CI 1.68-14.4, P = 0.004) were associated with increased incidence of relapse. Cumulative incidence of acute GVHD grade 3-4 was 10% at 3 months and extensive chronic GVHD was 8%. Neutrophil engraftment was reported in 94% patients, at a median of 20 days (range, 14-70). In conclusion, haplo-BMT with PTCy is feasible in patients with myelofibrosis. Splenomegaly ≥22 cm and bone marrow grafts were associated with a higher incidence of relapse in this study.

Recent Advances in Molecular Diagnostics and Targeted Therapy of Myeloproliferative Neoplasms

Simple Summary

Myeloproliferative neoplasms (MPN) are clonal hematologic malignancies with dysregulated myeloid blood cell production driven by JAK2, calreticulin, and MPL gene mutations. Technological advances have revealed a heterogeneous genomic landscape with additional mutations mainly in epigenetic regulators and splicing factors, which are of diagnostic and prognostic value and may inform treatment decisions. Thus, genetic testing has become an integral part of the state-of-the-art work-up for MPN. The finding that JAK2, CALR, and MPL mutations activate JAK2 signaling has promoted the development of targeted JAK2 inhibitor therapies. However, their disease-modifying potential remains limited and investigations of additional molecular vulnerabilities in MPN are imperative to advance the development of new therapeutic options. Here, we summarize the current insights into the genetic basis of MPN, its use as diagnostic and prognostic tool in clinical settings, and recent advances in targeted therapies for MPN.

Abstract

Somatic mutations in JAK2, calreticulin, and MPL genes drive myeloproliferative neoplasms (MPN), and recent technological advances have revealed a heterogeneous genomic landscape with additional mutations in MPN. These mainly affect genes involved in epigenetic regulation and splicing and are of diagnostic and prognostic value, predicting the risk of progression and informing decisions on therapeutic management. Thus, genetic testing has become an integral part of the current state-of-the-art laboratory work-up for MPN patients and has been implemented in current guidelines for disease classification, tools for prognostic risk assessment, and recommendations for therapy. The finding that JAK2, CALR, and MPL driver mutations activate JAK2 signaling has provided a rational basis for the development of targeted JAK2 inhibitor therapies and has fueled their translation into clinical practice. However, the disease-modifying potential of JAK2 inhibitors remains limited and is further impeded by loss of therapeutic responses in a substantial proportion of patients over time. Therefore, the investigation of additional molecular vulnerabilities involved in MPN pathogenesis is imperative to advance the development of new therapeutic options. Combination of novel compounds with JAK2 inhibitors are of specific interest to enhance therapeutic efficacy of molecularly targeted treatment approaches. Here, we summarize the current insights into the genetic basis of MPN, its use as a diagnostic and prognostic tool in clinical settings, and the most recent advances in targeted therapies for MPN.

AXL Inhibition Represents a Novel Therapeutic Approach in BCR-ABL Negative Myeloproliferative Neoplasms

BCR-ABL negative myeloproliferative neoplasms (MPNs) consist of essential thrombocythemia, polycythemia vera, and myelofibrosis. The majority of patients harbor the JAK2-activating mutation V617F. JAK2 inhibitors were shown to reduce symptom burden and splenomegaly in MPN patients. However, treatment options are limited after failure of JAK2 inhibitors. AXL, a member of the TAM family of receptor tyrosine kinases, mediates survival and therapy resistance of different myeloid cancers including acute myeloid leukemia and chronic myeloid leukemia. We studied the relevance of AXL as a target in MPN using primary patient cells and preclinical disease models. We found that AXL is abundantly activated in MPN cells and that its ligand growth arrest-specific gene 6 is upregulated in MPN patients. Pharmacologic and genetic blockade of AXL impaired viability, decreased proliferation and increased apoptosis of MPN cells. Interestingly, ruxolitinib treatment induced increased phosphorylation of AXL indicating that activation of AXL might mediate resistance to ruxolitinib. Consistently, the AXL inhibitor bemcentinib exerted additive effects with ruxolitinib via impaired STAT3, STAT5, and AKT signaling. Both agents had activity when employed alone and exerted an additive effect on survival and splenomegaly in vivo. Moreover, bemcentinib treatment normalized red blood cell count and hemoglobin levels in vivo. Thus, our data indicate that AXL inhibition represents a novel treatment option in MPN warranting clinical investigation.

A case of a primary myelofibrosis with progression and related literature review of progression phase genetics

Philadelphia (BCR-ABL)-negative myeloproliferative neoplasms (MPNs) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). MPN can transform into an accelerated or a blast phase, which is associated with poor response to standard therapy and low overall median survival. We present an interesting case of a patient with a history of PMF and progression and summarize the current studies on genetic features of myeloproliferative neoplasms in blast phase (MPN-BP) with an emphasis on PMF. Although MPN-BP show ≥20% blasts in peripheral blood or bone marrow, it is not considered as acute myeloid leukemia (AML) according to the WHO classification. While MPNs-BP typically lack genetic mutations seen in de novo AML, they commonly harbor IDH1/2, SRSF2, ASXL1, and TP53 mutations, similar to the genetic profiles of acute myeloid leukemia with myelodysplasia-related changes (AML-MRC).

Improving symptom burden and quality of life in patients with myelofibrosis: current strategies and future directions

INTRODUCTION

Myelofibrosis (MF) is a complex and aggressive hematologic malignancy resulting from JAK/STAT-driven myeloproliferation and abnormal fibrogenesis. The clinical manifestations are heterogeneous and negatively impact quality of life and survival. JAK inhibitors improve symptoms and splenomegaly to a variable degree in a proportion of patients, but the effects for many patients are insufficient or short-lived.

AREAS COVERED

This review examines the constellation of symptoms that befall patients with MF, describes methods to quantify and serially monitor these symptoms, and evaluates pharmacologic and non-pharmacologic interventions for disease-related symptoms. The review also includes a discussion of areas of unmet medical need, and proposes future methods for meeting this need.

EXPERT OPINION

The treatment landscape for MF is evolving rapidly. The most effective therapies or combinations of therapies will likely simultaneously impact both the malignant hematopoietic stem cell and mechanisms of aberrant fibrogenesis that drive this disease. The goals of treatment for patients with myelofibrosis should be to improve length and quality of life. Clinical trials must be designed with these goals in mind, with endpoints focused on overall survival and symptom reduction, as opposed to surrogate endpoints such as spleen volume reduction.

Novel Therapies in Myeloproliferative Neoplasms: Beyond JAK Inhibitor Monotherapy

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic disorders that consist classically of polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). Janus kinase (JAK) inhibitors have become the standard of therapy in treating patients with intermediate- to higher-risk MF. However, JAK inhibitor (JAKi) treatment can be associated with development of resistance, suboptimal response, relapse, or treatment-related adverse effects. With no approved therapies beyond the JAKi class, the estimated median survival, post JAKi failure, is approximately two years or less; therefore, novel therapies are urgently needed in the MF field. In this review, we discuss ruxolitinib use in MPNs as well as causes of ruxolitinib failure or discontinuation. In addition, we review novel therapies being investigated alone or in combination with JAKi administration. We summarize concepts and mechanisms behind emerging novel therapies being studied for MPNs. This review of emerging novel therapies outlines several novel mechanisms of agents, including via promotion of apoptosis, alteration of the microenvironment, activation or inactivation of various pathways, targeting fibrosis, and telomerase inhibition.

Spleen Stiffness Measurement by Using Shear-Wave Elastography as a Predictor of Progression to Secondary Myelofibrosis

OBJECTIVE

Polycythemia vera (PV) and essential thrombocythemia (ET) are chronic myeloproliferative diseases that can transform to secondary myelofibrosis (SMF). In this study, we evaluated spleen stiffness using shear-wave elastography (SWE) as a predictor of progression to SMF.

METHODS

Participants were grouped as healthy volunteers (HVs), PV/ET patients, and SMF patients. Participants' spleen sizes, spleen stiffness values, bone marrow fibrosis degrees, and the other parameters were evaluated. Spleen stiffness values and spleen sizes were compared between groups.

RESULTS

Of the 121 participants included in this study, 52 patients were HVs, 52 patients were PV and/or ET patients, and 17 patients were SMF patients. In terms of age and sex, there was no difference between groups. Splenic parenchymal stiffness median values by using SWE were found to be 0.82 m/s in HVs, 1.41 m/s in PV/ET patients, and 2.32 m/s in SMF patients (P < 0.001). In terms of median length of the spleen, the difference between groups was significant (P < 0.001). In addition, we found a significant positive correlation between spleen stiffness and bone marrow fibrosis degree (P < 0.001, r = 0.757). However, in multivariate analysis, there was no strong independent risk factor for spleen stiffness.

CONCLUSION

In this study, we showed that measurement of spleen stiffness using SWE can distinguish SMF from PV/ET patients and HVs. Therefore, we believe that SWE may be used as a noninvasive and easily accessible method to check the fibrotic progression of bone marrow in PV and ET patients to monitor the transformation to SMF, and enables to detect fibrosis in early phase.

Outcome of patients with IDH1/2-mutated post-myeloproliferative neoplasm AML in the era of IDH inhibitors

IDH1/2-inhibitor–based combinations conferred significant clinical responses in patients with IDH1/2-mutated post–MPN AML. Complete remission was achieved in 3/7 patients (1 attaining MRD–) with new IDH1/2-mutated post–MPN AML treated with IDH1/2-i combinations.

Accelerated Phase of Myeloproliferative Neoplasms

BACKGROUND

Myeloproliferative neoplasms (MPNs) can transform into blast phase MPN (leukemic transformation; MPN-BP), typically via accelerated phase MPN (MPN-AP), in ∼20-25% of the cases. MPN-AP and MPN-BP are characterized by 10-19% and ≥20% blasts, respectively. MPN-AP/BP portend a dismal prognosis with no established conventional treatment. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the sole modality associated with long-term survival.

SUMMARY

MPN-AP/BP has a markedly different mutational profile from de novo acute myeloid leukemia (AML). In MPN-AP/BP, TP53 and IDH1/2 are more frequent, whereas FLT3 and DNMT3A are rare. Higher incidence of leukemic transformation has been associated with the most aggressive MPN subtype, myelofibrosis (MF); other risk factors for leukemic transformation include rising blast counts above 3-5%, advanced age, severe anemia, thrombocytopenia, leukocytosis, increasing bone marrow fibrosis, type 1 CALR-unmutated status, lack of driver mutations (negative for JAK2, CALR, or MPL genes), adverse cytogenetics, and acquisition of ≥2 high-molecular risk mutations (ASXL1, EZH2, IDH1/2, SRSF2, and U2AF1Q157). The aforementioned factors have been incorporated in several novel prognostic scoring systems for MF. Currently, elderly/unfit patients with MPN-AP/BP are treated with hypomethylating agents with/without ruxolitinib; these regimens appear to confer comparable benefit to intensive chemotherapy but with lower toxicity. Retrospective studies in patients who acquired actionable mutations during MPN-AP/BP showed positive outcomes with targeted AML treatments, such as IDH1/2 inhibitors, and require further evaluation in clinical trials. Key Messages: Therapy for MPN-AP patients represents an unmet medical need. MF patients, in particular, should be appropriately stratified regarding their prognosis and the risk for transformation. Higher-risk patients should be monitored regularly and treated prior to progression to MPN-BP. MPN-AP patients may be treated with hypomethylating agents alone or in combination with ruxolitinib; also, patients can be provided with the option to enroll in rationally designed clinical trials exploring combination regimens, including novel targeted drugs, with an ultimate goal to transition to transplant.

Myelofibrosis: challenges for preclinical models and emerging therapeutic targets

Introduction: Myelofibrosis (MF) is characterized by anemia, splenomegaly, constitutional symptoms and bone marrow fibrosis. MF has no curative treatment to date, except for a small subset of patients that are eligible for allogeneic hematopoietic stem cell transplant. The discovery in recent years of the MF mutational landscape and the role of bone marrow microenvironment in disease pathogenesis has led to further insights into disease biology and consequentially rationally derived therapies.Areas covered: We searched PubMed/Medline/American Society of Hematology (ASH) abstracts until November 2020 using the following terms: myelofibrosis, mouse models, pre-clinical studies and clinical trials. The development of targeted therapies is aimed to modify the history of the disease. Although JAK inhibitors showed encouraging results in terms of spleen and symptoms response, long term remissions and disease modifying ability is lacking. Beyond JAK inhibitors, a range of agents targeting proliferative, metabolic, apoptotic pathways, the microenvironment, epigenetic modification and immunomodulation are in various stages of investigations. We review pre-clinical data, preliminary clinical results of these agents, and finally offer insights on the management of MF patients.Expert opinion: MF patients refractory or with suboptimal response to JAK inhibitors, may be managed by addition of agents with differing mechanisms, such as bromodomain (BET), lysine demethylase 1 (LSD1), MDM2, or Bcl-Xl inhibitors which could prevent emergence of resistance. Immunotherapies as long-acting interferons, and calreticulin directed antibodies or peptide vaccination are eagerly awaited. Historically, therapeutic challenges in MF have arisen due to the fact that rationally derived therapies that are based on murine models have limited impact on fibrosis and underlying disease biology in human studies, the latter illustrates the complex multi-faceted disease pathogenesis of MF. Together, we not only suggest individualized therapy in MF that is guided by genomic signature but also its early implementation potentially in prefibrotic MF.

Recent developments in epigenetic cancer therapeutics: clinical advancement and emerging trends

Epigenetic drug discovery field has evidenced significant advancement in the recent times. A plethora of small molecule inhibitors have progressed to clinical stage investigations and are being explored exhaustively to ascertain conclusive benefits in diverse malignancies. Literature precedents indicates that substantial amount of efforts were directed towards the use of epigenetic tools in monotherapy as well as in combination regimens at the clinical level, however, the preclinical/preliminary explorations were inclined towards the identification of prudent approaches that can leverage the anticancer potential of small molecule epigenetic inhibitors as single agents only. This review article presents an update of FDA approved epigenetic drugs along with the epigenetic inhibitors undergoing clinical stage investigations in different cancer types. A detailed discussion of the pragmatic strategies that are expected to steer the progress of the epigenetic therapy through the implementation of emerging approaches such as PROTACS and CRISPR/Cas9 along with logical ways for scaffold fabrication to selectively approach the enzyme isoforms in pursuit of garnering amplified antitumor effects has been covered. In addition, the compilation also presents the rational strategies for the construction of multi-targeting scaffold assemblages employing previously identified pharmacophores as potential alternatives to the combination therapy.

Epigenetic Dysregulation of Myeloproliferative Neoplasms

This article reviews the genetic data on epigenetic modifying mutations in myeloproliferative neoplasms and their clinical implications, preclinical studies exploring our current understanding of how mutations in epigenetic modifying proteins cooperate with myeloproliferative neoplasms drivers to promote disease progression, and recent advances in novel therapeutics supporting the role of targeting epigenetic pathways to treat fibrotic progression.

Current Clinical Investigations in Myelofibrosis

The US Food and Drug Administration (FDA) approval of Janus kinase 2 inhibitors, ruxolitinib and fedratinib for the treatment of intermediate-2 or high-risk primary or secondary myelofibrosis (MF) has revolutionized the management of MF. Nevertheless, these drugs do not reliably alter the natural history of disease. Burgeoning understanding of the molecular pathogenesis and the bone marrow microenvironment in MF has galvanized the development of targeted therapeutics. This review provides insight into the novel therapies under clinical evaluation.

Accelerated and Blast Phase Myeloproliferative Neoplasms

Accelerated and blast phase myeloproliferative neoplasms are advanced stages of the disease with historically a poor prognosis and little improvement in outcomes thus far. The lack of responses to standard treatments likely results from the more aggressive biology reflected by the higher incidence of complex karyotype and high-risk somatic mutations, which are enriched at the time of transformation. Treatment options include induction chemotherapy (7 + 3) as that used on de novo acute myeloid leukemia or hypomethylating agent-based therapy, which has shown similar outcomes. Allogeneic stem cell transplantation remains the only potential for cure.

Genetics of Myeloproliferative Neoplasms

Myeloproliferative neoplasms are hematopoietic stem cell disorders based on somatic mutations in JAK2, calreticulin, or MPL activating JAK-STAT signaling. Modern sequencing efforts have revealed the genomic landscape of myeloproliferative neoplasms with additional genetic alterations mainly in epigenetic modifiers and splicing factors. High molecular risk mutations with adverse outcomes have been identified and clonal evolution may promote progression to fibrosis and acute myeloid leukemia. JAK2V617F is recurrently detected in clonal hematopoiesis of indeterminate potential with increased risk for vascular events. Insights into the genetics of myeloproliferative neoplasms has facilitated diagnosis and prognostication and poses novel candidates for targeted therapeutic intervention.

Janus Kinases in Leukemia

Janus kinases (JAKs) transduce signals from dozens of extracellular cytokines and function as critical regulators of cell growth, differentiation, gene expression, and immune responses. Deregulation of JAK/STAT signaling is a central component in several human diseases including various types of leukemia and other malignancies and autoimmune diseases. Different types of leukemia harbor genomic aberrations in all four JAKs (JAK1, JAK2, JAK3, and TYK2), most of which are activating somatic mutations and less frequently translocations resulting in constitutively active JAK fusion proteins. JAKs have become important therapeutic targets and currently, six JAK inhibitors have been approved by the FDA for the treatment of both autoimmune diseases and hematological malignancies. However, the efficacy of the current drugs is not optimal and the full potential of JAK modulators in leukemia is yet to be harnessed. This review discusses the deregulation of JAK-STAT signaling that underlie the pathogenesis of leukemia, i.e., mutations and other mechanisms causing hyperactive cytokine signaling, as well as JAK inhibitors used in clinic and under clinical development.

COVID-19: High-JAKing of the Inflammatory "Flight" by Ruxolitinib to Avoid the Cytokine Storm

Since SARS-CoV-2 outbreak in December 2019, world health-system has been severely impacted with increased hospitalization, Intensive-Care-Unit (ICU) access and high mortality rates, mostly due to severe acute respiratory failure and multi-organ failure. Excessive and uncontrolled release of proinflammatory cytokines (cytokine release/storm syndrome, CRS) have been linked to the development of these events. The recent advancements of immunotherapy for the treatment of hematologic and solid tumors shed light on many of the molecular mechanisms underlying this phenomenon, thus rendering desirable a multidisciplinary approach to improve COVID-19 patients' outcome. Indeed, currently available therapeutic-strategies to overcome CRS, should be urgently evaluated for their capability of reducing COVID-19 mortality. Notably, COVID-19 shares different pathogenic aspects with acute graft-versus-host-disease (aGVHD), hemophagocytic-lymphohistiocytosis (HLH), myelofibrosis, and CAR-T-associated CRS. Specifically, similarly to aGVHD, an induced tissue damage (caused by the virus) leads to increased cytokine release (TNFα and IL-6) which in turn leads to exaggerated dendritic cells, macrophages (like in HLH) and lymphocytes (as in CAR-T) activation, immune-cells migration, and tissue-damage (including late-stage fibrosis, similar to myelofibrosis). Janus Kinase (JAK) signaling represents a molecular hub linking all these events, rendering JAK-inhibitors suitable to limit deleterious effects of an overwhelming inflammatory-response. Accordingly, ruxolitinib is the only selective JAK1 and JAK2-inhibitor approved for the treatment of myelofibrosis and aGVHD. Here, we discuss, from a molecular and hematological point of view, the rationale for targeting JAK signaling in the management of COVID-19 patients and report the clinical results of a patient admitted to ICU among the firsts to be treated with ruxolitinib in Italy.

Challenges and Perspectives for Therapeutic Targeting of Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders with dysregulated myeloid blood cell production and propensity for transformation to acute myeloid leukemia, thrombosis, and bleeding. Acquired mutations in JAK2, MPL, and CALR converge on hyperactivation of Janus kinase 2 (JAK2) signaling as a central feature of MPN. Accordingly, JAK2 inhibitors have held promise for therapeutic targeting. After the JAK1/2 inhibitor ruxolitinib, similar JAK2 inhibitors as fedratinib are entering clinical use. While patients benefit with reduced splenomegaly and symptoms, disease-modifying effects on MPN clone size and clonal evolution are modest. Importantly, response to ruxolitinib may be lost upon treatment suggesting the MPN clone acquires resistance. Resistance mutations, as seen with other tyrosine kinase inhibitors, have not been described in MPN patients suggesting that functional processes reactivate JAK2 signaling. Compensatory signaling, which bypasses JAK2 inhibition, and other processes contribute to intrinsic resistance of MPN cells restricting efficacy of JAK2 inhibition overall. Combinations of JAK2 inhibition with pegylated interferon-α, a well-established therapy of MPN, B-cell lymphoma 2 inhibition, and others are in clinical development with the potential to enhance therapeutic efficacy. Novel single-agent approaches targeting other molecules than JAK2 are being investigated clinically. Special focus should be placed on myelofibrosis patients with anemia and thrombocytopenia, a delicate patient population at high need for options. The extending range of new treatment approaches will increase the therapeutic options for MPN patients. This calls for concomitant improvement of our insight into MPN biology to inform tailored therapeutic strategies for individual MPN patients.

The safety of JAK kinase inhibitors for the treatment of myelofibrosis

INTRODUCTION

During the last decade, the development of small molecule inhibitors of Janus kinases (JAKi) contributed to revolutionize the therapeutic landscape of myelofibrosis (MF). JAKi proved to be effective in controlling disease-related symptoms and splenomegaly with remarkable inter-drug variability. However, in some cases the border between clinical efficacy of JAKi and dose-dependent toxicities is narrow leading to sub-optimal dose modifications and/or treatment discontinuation.

AREAS COVERED

In the current review, the authors aimed at providing a comprehensive review of the safety profile of JAKi that are currently approved or in advanced clinical development. Also, a short discussion of promising JAKi in early clinical evaluation and molecules 'lost' early in clinical development is provided. Finally, we discuss the possible strategies aimed at strengthening the safety of JAKi while improving the therapeutic efficacy.

EXPERT OPINION

Overall, JAKi display a satisfactory risk-benefit ratio, with main toxicities being gastrointestinal or related to the myelo/immunosuppressive effects, generally mild and easily manageable. However, JAKi may be associated with potentially life-threatening toxicities, such as neurological and infectious events. Thus, many efforts are needed in order to optimize JAKi-based therapeutic strategies without burdening patient safety. This could be attempted through drug combinations or the development of more selective molecules.

Novel therapeutics in myeloproliferative neoplasms

Hyperactive signaling of the Janus-Associated Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) pathway is central to the pathogenesis of Philadelphia-chromosome-negative myeloproliferative neoplasms (MPN), i.e., polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) which are characterized by inherent biological and clinical heterogeneity. Patients with MPNs suffer from substantial symptom burden and curtailed longevity due to thrombohemorrhagic complications or progression to myelofibrosis or acute myeloid leukemia. Therefore, the management strategies focus on thrombosis risk mitigation in PV/ET, alleviation of symptom burden and improvement in cytopenias and red blood cell transfusion requirements, and disease course alteration in PMF. The United States Food and Drug Administration's (USFDA) approval of two JAK inhibitors (ruxolitinib, fedratinib) has transformed the therapeutic landscape of MPNs in assuaging the need for frequent therapeutic phlebotomy (PV) and reduction in spleen and symptom burden (PV and PMF). Despite improving biological understanding of these complex clonal hematopoietic stem/progenitor cell neoplasms, none of the currently available therapies appear to modify the proclivity of the disease per se, thereby remaining an urgent unmet clinical need and an ongoing area of intense clinical investigation. This review will highlight the evolving targeted therapeutic agents that are in early- and late-stage MPN clinical development.

Finding a Jill for JAK: Assessing Past, Present, and Future JAK Inhibitor Combination Approaches in Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm hallmarked by the upregulation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway with associated extramedullary hematopoiesis and a high burden of disease-related symptoms. While JAK inhibitor therapy is central to the management of MF, it is not without limitations. In an effort to improve treatment for MF patients, there have been significant efforts to identify combination strategies that build upon the substantial benefits of JAK inhibition. Early efforts to combine agents with additive therapeutic profiles have given way to rationally designed combinations hoping to demonstrate clinical synergism and modify the underlying disease. In this article, we review the preclinical basis and existing clinical data for JAK inhibitor combination strategies while highlighting emerging strategies of particular interest.

JAK Inhibition for the Treatment of Myelofibrosis: Limitations and Future Perspectives

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 Rationale for Immunotherapy in Myeloproliferative Neoplasms

PURPOSE OF REVIEW

The classic, chronic Philadelphia chromosome negative myeloproliferative neoplasms (MPN)-essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF)-are clonal malignancies of hematopoietic stem cells and are associated with myeloproliferation, organomegaly, and constitutional symptoms. Expanding knowledge that chronic inflammation and a dysregulated immune system are central to the pathogenesis and progression of MPNs serves as a driving force for the development of agents affecting the immune system as therapy for MPN. This review describes the rationale and potential impact of anti-inflammatory, immunomodulatory, and targeted agents in MPNs.

RECENT FINDINGS

The advances in molecular insights, especially the discovery of the Janus kinase 2 (JAK2) V617F mutation and its role in JAK-STAT pathway dysregulation, led to the development of the JAK inhibitor ruxolitinib, which currently represents the cornerstone of medical therapy in MF and hydroxyurea-resistant/intolerant PV. However, there remain significant unmet needs in the treatment of these patients, and many agents continue to be investigated. Novel, more selective JAK inhibitors might offer reduced myelosuppression or even improvement of blood counts. The recent approval of a novel, long-acting interferon for PV patients in Europe, might eventually lead to its broader clinical use in all MPNs. Targeted immunotherapy involving monoclonal antibodies, checkpoint inhibitors, or therapeutic vaccines against selected MPN epitopes could further enhance tumor-specific immune responses. Immunotherapeutic approaches are expanding and hopefully will extend the therapeutic armamentarium in patients with myeloproliferative neoplasms.

Ruxolitinib-based combinations in the treatment of myelofibrosis: worth looking forward to

Ruxolitinib is a targeted drug to treat myelofibrosis (MF). Ruxolitinib has significant advantages in spleen reduction and increasing 5-year overall survival (OS), and ruxolitinib-based combinations might provide more benefits than ruxolitinib monotherapy. In this review, we focus on the data of ruxolitinib-based combinations therapies and treatment-related adverse events (AEs) and safety. We analyzed and summarized the data of ruxolitinib-based combinations. Ruxolitinib combined with prednisone + thalidomide + danazol (TPD), panobinostat, pracinostat, azacytidine, or hydroxyurea has well reduced spleen. Ruxolitinib combined with danazol or TPD had well therapies in improvement of hemoglobin (Hgb) and platelets (PLT). Most ruxolitinib-based combinations therapies showed a superior benefit on reduced treatment-related AEs than ruxolitinib monotherapy. Treatment-related AEs and dose modification affect the safety and tolerability of ruxolitinib-based combinations. Genetic testing before treatment is recommended. To provide better clinical guidance, comparisons of these randomized controlled trials with the trials of ruxolitinib alone are necessary. This review suggests that the clinical application of ruxolitinib-based combinations is worth waiting for.

Bone marrow niche dysregulation in myeloproliferative neoplasms

The bone marrow niche is a complex and dynamic structure composed of a multitude of cell types which functionally create an interactive network facilitating hematopoietic stem cell development and maintenance. Its specific role in the pathogenesis, response to therapy, and transformation of myeloproliferative neoplasms has only recently been explored. Niche functionality is likely affected not only by the genomic background of the myeloproliferative neoplasm-associated mutated hematopoietic stem cells, but also by disease-associated 'chronic inflammation', and subsequent adaptive and innate immune responses. 'Cross-talk' between mutated hematopoietic stem cells and multiple niche components may contribute to propagating disease progression and mediating drug resistance. In this timely article, we will review current knowledge surrounding the deregulated bone marrow niche in myeloproliferative neoplasms and suggest how this may be targeted, either directly or indirectly, potentially influencing therapeutic choices both now and in the future.

Investigational non-JAK inhibitors for chronic phase myelofibrosis

INTRODUCTION

Patients with myelofibrosis (MF) have no effective treatment option after the failure of approved JAK inhibitor (JAKi) therapy. Non-JAK inhibitors (non-JAKi) that target non-canonical molecular pathways are undergoing clinical evaluations to optimize efficacy and/or to reduce hematological toxicity of JAKi.

AREA COVERED

This article reviews the efficacy data from completed and ongoing early phase clinical trials of non-JAKi agents for chronic phase MF. The article also illuminates some of the challenges of myelofibrosis drug development.

EXPERT OPINION

Most non-JAKi agents tested so far have shown modest benefit in improving the efficacy of ruxolitinib. Several novel agents such as BET inhibitor- CPI-0610, activin receptor ligand trap- luspatercept, recombinant pentraxin-PRM-151, telomerase inhibitor- imetelstat and bcl-2 inhibitor- navitoclax, have shown promising activity; however, they require vigorous evaluation in randomized controlled trials to understand the clinical benefit. Drugs that target new molecular pathways (MDM2, p-selectin, TIM-3, TGF-β, aurora kinase) and immune-based strategies (CALR vaccine, anti-PD-1, allogeneic cord blood regulatory T cells) are in early phase trials. Further translational studies to target leukemic stem cells, improvement in trial designs by incorporating control arm and survival endpoints, and patient-focused collaborations among all stakeholders could pave a way for future success in MF drug development.

A provider's guide to primary myelofibrosis: pathophysiology, diagnosis, and management

Although understanding of the pathogenesis and molecular biology of primary myelofibrosis continues to improve, treatment options are limited, and several biological features remain unexplained. With an appropriate clinical history, exam, laboratory evaluation, and bone marrow biopsy, the diagnosis can often be established. Recent studies have better characterized prognostic factors and driver mutations in myelofibrosis, facilitated by use of next-generation sequencing. These advances have facilitated development of a management strategy that is based on both risk factors and clinical phenotype. For low-risk patients, treatment will depend on symptom severity. For patients with higher-risk disease, several treatments are available including JAK inhibitors, allogeneic hematopoietic stem cell transplant, and clinical trials using novel molecularly targeted therapies and rational drug combinations. In this review, we outline what is known about the disease pathogenesis, discuss an approach to reaching the diagnosis, review the prognosis of myelofibrosis, and detail current therapeutic strategies.

Myelofibrosis biology and contemporary management

Myelofibrosis is an enigmatic myeloproliferative neoplasm, despite noteworthy strides in understanding its genetic underpinnings. Driver mutations involving JAK2, CALR or MPL in 90% of patients mediate constitutive JAK-STAT signaling which, in concert with epigenetic alterations (ASXL1, DNMT3A, SRSF2, EZH2, IDH1/2 mutations), play a fundamental role in disease pathogenesis. Aberrant immature megakaryocytes are a quintessential feature, exhibiting reduced GATA1 protein expression and secreting a plethora of pro-inflammatory cytokines (IL-1 ß, TGF-ß), growth factors (b-FGF, PDGF, VEGF) in addition to extra cellular matrix components (fibronectin, laminin, collagens). The ensuing disrupted interactions amongst the megakaryocytes, osteoblasts, endothelium, stromal cells and myofibroblasts within the bone marrow culminate in the development of fibrosis and osteosclerosis. Presently, prognostic assessment tools for primary myelofibrosis (PMF) are centered on genetics, with incorporation of cytogenetic and molecular information into the mutation-enhanced (MIPSS 70-plus version 2.0) and genetically-inspired (GIPSS) prognostic scoring systems. Both models illustrate substantial clinical heterogeneity in PMF and serve as the crux for risk-adapted therapeutic decisions. A major challenge remains the dearth of disease-modifying drugs, whereas allogeneic transplant offers the chance of long-term remission for some patients. Our review serves to synopsise current appreciation of the pathogenesis of myelofibrosis together with emerging management strategies.

Forging ahead or moving back: dilemmas and disappointments of novel agents for myeloproliferative neoplasms

The common 'Philadelphia chromosome'-negative myeloproliferative neoplasms (MPN) comprise essential thrombocythaemia, polycythaemia vera and myelofibrosis. These are clinically diverse disorders and present many challenges during their course, ranging from the management of very indolent, chronic-phase disease through to very aggressive stages frequently associated with poor quality of life, heavy symptom burdens and potentially life expectancies of <18 months. Their management also requires expertise in thrombosis and haemostasis in addition to marrow failure, debilitating symptom control and balancing the 'pros and cons' of intensive therapy such as allogeneic stem cell transplant versus novel and established therapies. In the past 15 years this field has seen rapid advances following an understanding of the pivotal importance of constitutive Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling, the interplay of the wider genomic landscape and the development of updated diagnostic criteria, prognostic scores and targeted therapies. In this article, we review the successes and failures of novel agents and approaches to MPN management.

Beyond Ruxolitinib: Fedratinib and Other Emergent Treatment Options for Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm characterized by clonal proliferation of differentiated myeloid cells leading to bone marrow fibrosis, cytopenias and extramedullary hematopoiesis. In late 2019, the FDA approved the highly selective JAK2 inhibitor, fedratinib, for intermediate-2 or high-risk primary or secondary MF, making it the second drug approved for MF after ruxolitinib, a JAK1/2 inhibitor, which was approved for MF in 2011. The approval of fedratinib was based on phase II trials and the phase III JAKARTA trial, in which the drug significantly reduced splenomegaly and symptom burden compared to placebo, including some patients previously treated with ruxolitinib. The main side effects of fedratinib include anemia, gastrointestinal symptoms, and elevations in liver transaminases. Fedratinib also has ablack box warning for encephalopathy, although this occurred only in about 1% of the treated patients, most of which were ultimately felt not to represent Wernicke’s encephalopathy. Nonetheless, monitoring of thiamine levels and supplementation are recommended especially in high-risk patients. This concern has led to a prolonged clinical hold and delayed the drug approval by several years during which the drug exchanged manufacturers, highlighting the need for meticulous investigation and adjudication of serious, but rare, adverse events in drug development that could end up preventing drugs with favorable risk/benefit ratio from being approved. In this review, we discuss the pharmacokinetic data and efficacy, as well as the toxicity results of clinical trials of fedratinib. We also review ongoing trials of JAK inhibitors in MF and explore future treatment options for MF patients who are refractory to ruxolitinib.

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.

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.