ACVR1/JAK1/JAK2 inhibitor momelotinib reverses transfusion dependency and suppresses hepcidin in myelofibrosis phase 2 trial

JAK inhibitor selectivity: new opportunities, better drugs?

Cytokines function as communication tools of the immune system, serving critical functions in many biological responses and shaping the immune response. When cytokine production or their biological activity goes awry, the homeostatic balance of the immune response is altered, leading to the development of several pathologies such as autoimmune and inflammatory disorders. Cytokines bind to specific receptors on cells, triggering the activation of intracellular enzymes known as Janus kinases (JAKs). The JAK family comprises four members, JAK1, JAK2, JAK3 and tyrosine kinase 2, which are critical for intracellular cytokine signalling. Since the mid-2010s multiple JAK inhibitors have been approved for inflammatory and haematological indications. Currently, approved JAK inhibitors have demonstrated clinical efficacy; however, improved selectivity for specific JAKs is likely to enhance safety profiles, and different strategies have been used to accomplish enhanced JAK selectivity. In this update, we discuss the background of JAK inhibitors, current approved indications and adverse effects, along with new developments in this field. We address the issue of JAK selectivity and its relevance in terms of efficacy, and describe new modalities of JAK targeting, as well as new aspects of JAK inhibitor action.

Momelotinib versus Continued Ruxolitinib or Best Available Therapy in JAK Inhibitor-Experienced Patients with Myelofibrosis and Anemia: Subgroup Analysis of SIMPLIFY-2

INTRODUCTION

Some Janus kinase (JAK) inhibitors such as ruxolitinib and fedratinib do not address and may worsen anemia in patients with myelofibrosis. In these cases, the JAK inhibitor may be continued at a reduced dose in an effort to maintain splenic and symptom control, with supportive therapy and/or red blood cell (RBC) transfusions added to manage anemia. This post hoc descriptive analysis of the phase 3 SIMPLIFY-2 trial evaluated the relative benefits of this approach versus switching to the JAK1/JAK2/activin A receptor type 1 inhibitor momelotinib in patients for whom anemia management is a key consideration.

METHODS

SIMPLIFY-2 was a randomized (2:1), open-label, phase 3 trial of momelotinib versus best available therapy (BAT; 88.5% continued ruxolitinib) in JAK inhibitor-experienced patients with myelofibrosis (n = 156). Patient subgroups (n = 105 each) were defined by either baseline (1) hemoglobin (Hb) of < 100 g/L or (2) non-transfusion independence (not meeting the criteria of no transfusions and no Hb of < 80 g/L for the previous 12 weeks); outcomes have been summarized descriptively.

RESULTS

In both subgroups of interest, week 24 transfusion independence rates were higher with momelotinib versus BAT/ruxolitinib: baseline Hb of < 100 g/L, 22 (33.3%) versus 5 (12.8%); baseline non-transfusion independent, 25 (34.7%) versus 1 (3.0%). Mean Hb levels over time were also generally higher in both subgroups with momelotinib, despite median transfusion rates through week 24 with momelotinib being comparable to or lower than with BAT/ruxolitinib. Spleen and symptom response rates with momelotinib in these subgroups were comparable to the intent-to-treat population, while rates with BAT/ruxolitinib were lower.

CONCLUSION

In patients with moderate-to-severe anemia and/or in need of RBC transfusions, outcomes were improved by switching to momelotinib rather than continuing ruxolitinib and using anemia supportive therapies.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02101268.

Treatment of myelofibrosis with refractory anemia with luspatercept: a multicenter Chinese study

Myelofibrosis is a rare and often fatal hematological neoplasm, and the treatment of myelofibrosis-associated anemia remains suboptimal, with no improved therapies. Luspatercept was shown to display some efficacy in a phase 2 clinical trial for Myelofibrosis with anemia, yet relevant research are limited. Threrfore, data from patients diagnosed with refractory anemic primary or post-essential thrombocythemia/polycythemia vera myelofibrosis, who were treated with luspatercept for at least 9 weeks, were retrospectively collected. Eighteen patients with myelofibrosis treated with luspatercept were enrolled. Median age was 68 years (range, 44-80 years), and 27.8% were males. Ten (55.6%) were transfusion-dependent. Ten (55.6%) were Dynamic International Prognostic Scoring System intermediate-1, and eight (44.4%) were intermediate-2. The median follow-up was 7 (4-16) months. Erythroid response occurred in eight patients (44.4%) at week 12, four patients (30.8%) at week 24, and nine (50%) at the end of follow-up. Patients who were transfusion-dependent and not transfusion-dependent had similar HI-E responses, at different time points (P > 0.05). Patients had a significantly higher hemoglobin level at 12 weeks, 24 weeks, and at the end of follow-up, than at baseline (P = 0.001, P = 0.021, and P = 0.005, respectively). Treatment-related adverse events occurred in five (16.7%) patients, with no serious adverse events. Two (11.1%) patients relapsed at weeks 15 and 31. One patient progressed to acute myeloid leukemia. No patients had died by the end of follow-up. Luspatercept induced a good response in patients with anemic myelofibrosis, with a low relapse rate and good tolerance.

Momelotinib versus ruxolitinib in JAK inhibitor-naïve patients with myelofibrosis: an efficacy/safety analysis in the Japanese subgroup of the phase 3 randomized SIMPLIFY-1 trial

Momelotinib, an oral Janus kinase (JAK) 1/2 and activin A receptor type 1 inhibitor, improved symptoms, splenomegaly, and anemia in patients with myelofibrosis (MF). This sub-analysis of SIMPLIFY-1 evaluated the efficacy and safety of momelotinib versus ruxolitinib in Japanese patients with JAK inhibitor (JAKi)-naïve MF. Patients were randomized 1:1 to receive momelotinib 200 mg once daily or ruxolitinib 20 mg twice daily (or modified based on label) for 24 weeks, after which patients could receive open-label momelotinib. The primary endpoint was splenic response rate (SRR; ≥ 35% reduction in spleen volume) at 24 weeks; main secondary endpoints were total symptom score (TSS) response (≥ 50% reduction) and transfusion independence (TI) rates. Fifteen Japanese patients (momelotinib, n = 6; ruxolitinib, n = 9) were enrolled; all completed treatment. At Week 24, SRR was 50.0% with momelotinib and 44.4% with ruxolitinib. TSS response rates were 33.3% and 0%, and TI rates were 83.3% and 44.4%. Any-grade treatment-related adverse event (TRAE) rates were 83.3% with momelotinib and 88.9% with ruxolitinib. Grade 3/4 TRAE rates were 0% and 55.6%, with specific events being anemia (55.6%) and vertigo (11.1%) with ruxolitinib. Momelotinib was well tolerated, improved spleen and symptom responses, and reduced transfusion requirements in Japanese patients with JAKi-naïve MF.

Targeting anemia in myeloid neoplasms

Anemia-directed therapeutic approaches targeting the TGF-β-SMAD and HIF-PH pathways.

Iron biology

Iron is a fundamental element for biological life, from bacteria to humans. Iron is essential for cell function and survival, energy production and metabolism, whereas increased levels cause oxidative stress. It is also a constituent of haemoglobin and thus it is necessary for oxygen transportation through the body. Given these multiple functions, the regulation of iron metabolism is complex and tight coupled with oxygen homeostasis at tissue and cellular levels, thanks to the interaction with the hypoxia inducible factor system. In patients with chronic kidney disease (CKD), iron deficiency significantly contributes to anaemia development. This frequently overlaps with chronic inflammation, causing iron- restricted erythropoiesis. To add further complexity, metabolic hyperferritinemia may, on one hand, increase the risk for CKD and, on the other, overlaps with functional iron deficiency. Excessive intracellular iron in certain cell types during CKD can also mediate cellular death (called ferroptosis), and contribute to the pathogenesis of kidney damage, atherosclerosis and vascular calcifications. This review is aimed at broadening the perspective of iron metabolism in the setting of CKD not just as a contributor to anaemia in CKD patients, but also as an important player with an impact on cell metabolism, renal fibrosis and the cardiovascular system.

Comparative efficacy and hematologic safety of different dosages of JAK inhibitors in the treatment of myelofibrosis: a network meta-analysis

Background

Myelofibrosis (MF) is a myeloproliferative neoplasm characterized by bone marrow fibrosis associated with substantial morbidity and mortality. The therapeutic landscape for MF has advanced with the development of Janus kinase inhibitors (JAKis) like ruxolitinib (RUX), fedratinib (FED), pacritinib (PAC), and momelotinib (MMB), aiming to alleviate symptoms and enhance patient comfort.

Methods

A network meta-analysis was conducted to assess the efficacy and safety of eleven JAKi treatment regimens across nine randomized controlled trials (RCTs) with a total of 2340 participants. Outcomes were evaluated in terms of spleen volume reduction (SVR), total symptom score reduction (TSSR), hematological safety profiles, and overall survival (OS).

Results

RUX and MMB were superior in achieving SVR and TSSR, with significant dose-response relationships observed. PAC and MMB were associated with a decreased risk of grade 3/4 anemia and thrombocytopenia compared to other JAKis. However, no substantial benefits in OS were observed with newer JAKis compared to RUX. The poorer OS outcomes with certain PAC dosages were likely influenced by baseline patient characteristics, particularly severe cytopenias.

Conclusion

The introduction of JAKis significantly changed the treatment of MF. This meta-analysis reaffirms the core role of RUX and positions MMB as a potentially powerful alternative for treating symptoms and reducing spleen size. Meanwhile, MMB and PAC have a positive effect on anemia in MF while FED is more tolerable for patients with thrombocytopenia. However, it should be noted that these results are influenced by baseline patient characteristics, particularly cytopenias, which affects both management and overall survival. Therefore, there is an urgent need for personalized dosing strategies to optimize the balance between efficacy and safety, with careful consideration of patient-specific factors.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42023424179.

Momelotinib in myelofibrosis and beyond: a comprehensive review of therapeutic insights in hematologic malignancies

Myelofibrosis (MF), a complex hematological malignancy, presents a diverse array of symptoms, including anemia, constitutional symptoms, bone marrow insufficiency, and splenomegaly. The latter, often necessitating blood transfusions, poses an essential obstacle to MF management. While conventional approaches predominantly involve the use of JAK inhibitors, the potential for exacerbating anemia introduces complexity to the treatment. Nonetheless, Momelotinib stands out as a promising pharmaceutical compound with the potential to revolutionize the field. Momelotinib is an ACVR1 antagonist and a dual inhibitor of the JAK1 and JAK2 enzymes. By targeting MF's hematological and fibrotic aspects, Momelotinib influences iron metabolism by regulating hepcidin. This results in reduced hepcidin expression and increased iron availability, ultimately leading to improved anemia and reduced dependency on blood transfusion. This study aims to provide a concise overview of the pathogenesis of MF and elucidate the mechanism of action of Momelotinib. Subsequently, our review offers a practical summary encompassing the effects of Momelotinib in monotherapy, combined comparative drug therapy, and its associated side effects. Additionally, we explore the application of Momelotinib in other cancer types and investigate predictors for treatment success. Furthermore, we examine the utilization of Momelotinib in patients with liver and kidney failure.

Momelotinib for the treatment of myelofibrosis

ABSTRACT

In September 2023, the US Food and Drug Administration approved momelotinib for the treatment of myelofibrosis (MF) with anemia, marking the fourth US regulatory approval of a Janus kinase inhibitor for MF. A positive opinion from the European Medicines Agency followed in November 2023. Momelotinib's ability to address splenomegaly, symptoms, and anemia, including in patients with thrombocytopenia (with platelet counts of ≥25 × 109/L), the ease of switching from ruxolitinib, and good tolerability uniquely position it to substantially impact the MF treatment landscape.

Momelotinib: Mechanism of action, clinical, and translational science

Myelofibrosis is a chronic myeloproliferative disorder characterized by bone marrow fibrosis, splenomegaly, anemia, and constitutional symptoms, with a median survival of ≈6 years from diagnosis. While currently approved Janus kinase (JAK) inhibitors (ruxolitinib, fedratinib) improve splenomegaly and symptoms, most can exacerbate myelofibrosis-related anemia, a negative prognostic factor for survival. Momelotinib is a novel JAK1/JAK2/activin A receptor type 1 (ACVR1) inhibitor approved in the US, European Union, and the UK and is the first JAK inhibitor indicated specifically for patients with myelofibrosis with anemia. Momelotinib not only addresses the splenomegaly and symptoms associated with myelofibrosis by suppressing the hyperactive JAK-STAT (signal transducer and activator of transcription) pathway but also improves anemia and reduces transfusion dependency through ACVR1 inhibition. The recommended dose of momelotinib is 200 mg orally once daily, which was established after review of safety, efficacy, pharmacokinetic, and pharmacodynamic data. Momelotinib is metabolized primarily by CYP3A4 and excreted as metabolites in feces and urine. Steady-state maximum concentration is 479 ng/mL (CV%, 61%), with a mean AUCtau of 3288 ng.h/mL (CV%, 60%); its major metabolite, M21, is active (≈40% of pharmacological activity of parent), with a metabolite-to-parent AUC ratio of 1.4-2.1. This review describes momelotinib's mechanism of action, detailing how the JAK-STAT pathway is involved in myelofibrosis pathogenesis and ACVR1 inhibition decreases hepcidin, leading to improved erythropoiesis. Additionally, it summarizes the pivotal studies and data that informed the recommended dosage and risk/benefit assessment.

Transfusion-related cost offsets and time burden in patients with myelofibrosis on momelotinib vs. danazol from MOMENTUM

Aim: To estimate projected US-based cost and time burden for patients with myelofibrosis and anemia treated with momelotinib compared with danazol. Methods: Cost and time burden were calculated based on the transfusion status of patients in the MOMENTUM trial and estimates extracted from previous studies. Results: Reductions in transfusion associated with momelotinib are projected to result in cost and time savings compared with danazol in transfusion-dependent and transfusion-independent/requiring patients with myelofibrosis, respectively: annual medical costs ($53,143 and $46,455 per person), outpatient transfusion costs ($42,021 and $8,370 per person) and annual time savings (173 and 35 h per person). Conclusion: Fewer transfusions with momelotinib are projected to result in cost and time savings in patients with myelofibrosis and anemia compared with danazol.

Advances with janus kinase inhibitors for the treatment of myeloproliferative neoplasms: an update of the literature

INTRODUCTION

The hallmark discovery of hyperactivation of the janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway was a sentinel moment in the history of myeloproliferative neoplasms (MPNs). This finding paved the way for the development of JAK inhibitors, which now represent the foundation of myelofibrosis therapy. With four JAK inhibitors now approved for myelofibrosis, awareness of their clinical efficacy and safety data and recognition of their unique pharmacologic attributes are of critical importance. Additionally, ruxolitinib represents an integral part of the therapeutic arsenal for polycythemia vera.

AREAS COVERED

This review provides a broad overview of the published literature supporting JAK inhibitor therapy for MPNs. Primarily focusing on myelofibrosis, each of the four available JAK inhibitors is reviewed in detail, including pharmacology, efficacy, and safety data. Failure of JAK inhibitors and future directions in JAK inhibitor therapy are also discussed.

EXPERT OPINION

JAK inhibitors revolutionized the treatment of MPNs and have dramatically improved patient outcomes. However, data informing selection between currently available JAK inhibitors is limited. These agents are not curative and eventually fail most patients with myelofibrosis. Combining JAK inhibitors with novel targeted agents appears to be the most promising path to further improve outcomes.

Momelotinib vs. ruxolitinib in myelofibrosis patient subgroups by baseline hemoglobin levels in the SIMPLIFY-1 trial

A key hallmark of myelofibrosis is anemia, which ranges from mild to severe based on hemoglobin levels. To more clearly define outcomes with the Janus kinase (JAK) 1/JAK2/activin A receptor type 1 inhibitor momelotinib by anemia severity, we performed a descriptive post hoc exploratory analysis of the double-blind, randomized, phase 3 SIMPLIFY-1 study (NCT01969838; N = 432, JAK inhibitor naive, momelotinib vs. ruxolitinib); subgroups were defined by baseline hemoglobin: <10 (moderate/severe), ≥10 to <12 (mild), or ≥12 g/dL (nonanemic). Spleen and symptom results were generally consistent with those previously reported for the intent-to-treat population. In anemic subgroups, momelotinib was associated with higher rates of transfusion independence and reduced/stable transfusion intensity vs. ruxolitinib. No new or unexpected safety signals were identified. Overall, momelotinib provides spleen, symptom, and anemia benefits to JAK inhibitor-naive patients with myelofibrosis regardless of baseline hemoglobin level, and greater anemia-related benefits vs. ruxolitinib in patients with hemoglobin <12 g/dL.

Functional and Structural Characterization of Clinical-Stage Janus Kinase 2 Inhibitors Identifies Determinants for Drug Selectivity

Janus kinase 2 (JAK2) plays a critical role in orchestrating hematopoiesis, and its deregulation leads to various blood disorders, most importantly myeloproliferative neoplasms (MPNs). Ruxolitinib, fedratinib, momelotinib, and pacritinib are FDA-/EMA-approved JAK inhibitors effective in relieving symptoms in MPN patients but show variable clinical profiles due to poor JAK selectivity. The development of next-generation JAK2 inhibitors is hampered by the lack of comparative functional analysis and knowledge of the molecular basis of their selectivity. Here, we provide mechanistic profiling of the four approved and six clinical-stage JAK2 inhibitors and connect selectivity data with high-resolution structural and thermodynamic analyses. All of the JAK inhibitors potently inhibited JAK2 activity. Inhibitors differed in their JAK isoform selectivity and potency for erythropoietin signaling, but their general cytokine inhibition signatures in blood cells were comparable. Structural data indicate that high potency and moderate JAK2 selectivity can be obtained by targeting the front pocket of the adenosine 5'-triphosphate-binding site.

Novel drugs approved by the EMA, the FDA, and the MHRA in 2023: A year in review

In 2023, seventy novel drugs received market authorization for the first time in either Europe (by the EMA and the MHRA) or in the United States (by the FDA). Confirming a steady recent trend, more than half of these drugs target rare diseases or intractable forms of cancer. Thirty drugs are categorized as "first-in-class" (FIC), illustrating the quality of research and innovation that drives new chemical entity discovery and development. We succinctly describe the mechanism of action of most of these FIC drugs and discuss the therapeutic areas covered, as well as the chemical category to which these drugs belong. The 2023 novel drug list also demonstrates an unabated emphasis on polypeptides (recombinant proteins and antibodies), Advanced Therapy Medicinal Products (gene and cell therapies) and RNA therapeutics, including the first-ever approval of a CRISPR-Cas9-based gene-editing cell therapy.

Clinical assessment of momelotinib drug-drug interactions via CYP3A metabolism and transporters

Momelotinib-approved for treatment of myelofibrosis in adults with anemia-and its major active metabolite, M21, were assessed as drug-drug interaction (DDI) victims with a strong cytochrome P450 (CYP) 3A4 inhibitor (multiple-dose ritonavir), an organic anion transporting polypeptide (OATP) 1B1/1B3 inhibitor (single-dose rifampin), and a strong CYP3A4 inducer (multiple-dose rifampin). Momelotinib DDI perpetrator potential (multiple-dose) was evaluated with CYP3A4 and breast cancer resistance protein (BCRP) substrates (midazolam and rosuvastatin, respectively). DDI was assessed from changes in maximum plasma concentration (Cmax), area under the concentration-time curve (AUC), time to reach Cmax, and half-life. The increase in momelotinib (23% Cmax, 14% AUC) or M21 (30% Cmax, 24% AUC) exposure with ritonavir coadministration was not clinically relevant. A moderate increase in momelotinib (40% Cmax, 57% AUC) and minimal change in M21 was observed with single-dose rifampin. A moderate decrease in momelotinib (29% Cmax, 46% AUC) and increase in M21 (31% Cmax, 15% AUC) were observed with multiple-dose rifampin compared with single-dose rifampin. Due to potentially counteracting effects of OATP1B1/1B3 inhibition and CYP3A4 induction, multiple-dose rifampin did not significantly change momelotinib pharmacokinetics compared with momelotinib alone (Cmax no change, 15% AUC decrease). Momelotinib did not alter the pharmacokinetics of midazolam (8% Cmax, 16% AUC decreases) or 1'-hydroxymidazolam (14% Cmax, 16% AUC decreases) but increased rosuvastatin Cmax by 220% and AUC by 170%. Safety findings were mild in this short-term study in healthy volunteers. This analysis suggests that momelotinib interactions with OATP1B1/1B3 inhibitors and BCRP substrates may warrant monitoring for adverse reactions or dose adjustments.

Anemia-related response end points in myelofibrosis clinical trials: current trends and need for renewed consensus

JAK inhibitors are the current standard of care in myelofibrosis, but many do not address and may worsen anemia; thus, anemia-related responses have traditionally been overlooked as efficacy end points in pivotal clinical trials, leading to a lack of consistency and analytic detail in their reporting. Here we apply our experiences in the phase III trials of momelotinib, a JAK1/JAK2/ACVR1 inhibitor and the first therapy indicated by the US FDA for myelofibrosis patients with anemia, to highlight how application of different criteria impacts the anemia-related benefits reported for any potential treatment in myelofibrosis. We advocate for a convention of a new expert consensus panel to bring consistency and transparency to the definition of anemia-related response in myelofibrosis.

Momelotinib in myelofibrosis

INTRODUCTION

Myelofibrosis (MF) is a hematologic disease characterized by bone marrow fibrosis, cytopenias, splenomegaly, and constitutional symptoms. Recent years have seen the emergence of novel therapeutic agents, notably ruxolitinib and fedratinib, which target the Janus kinases (JAK) pathway. However, their myelosuppressive effect coupled with the persistence, and even worsening anemia remains a significant challenge, leading usually to treatment discontinuation.

AREAS COVERED

This review focuses on Momelotinib (MMB), a unique JAK inhibitor that has shown promise in MF treatment, particularly in improving anemia. MMB inhibits type 1 kinase activin A receptor or activin receptor-like kinase-2 (ACVR1/ALK2), with consequent rebalancing of the SMAD pathways and reduced transcription of hepcidin. Moreover, it seems that MMB could reduce the serum levels of several inflammatory cytokines responsible for anemia. Clinical trials have demonstrated MMB's efficacy in reducing spleen size, alleviating symptoms, and improving anemia, with a favorable safety profile compared to other JAK inhibitors, both in treatment-naïve and in pre-treated patients.

EXPERT OPINION

Due to its mechanism of action, MMB represents a valuable therapeutic option in MF, addressing the clinical challenge of anemia and potentially improving outcomes for patients with hematologic malignancies. Ongoing research explores MMB's potential in acute myeloid leukemia and combination therapies.

A phase I trial of pevonedistat in combination with ruxolitinib for the treatment of myelofibrosis

Janus kinase 2 (JAK2) inhibitors such as ruxolitinib have become standard-of-care therapy for patients with myeloproliferative neoplasms (MPNs); however, activation of alternate oncogenic pathways including nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) has limited durable response as single-agent therapy. With the rationale of targeting both pathways, we conducted a phase I dose escalation trial of pevonedistat in combination with ruxolitinib for the treatment of patients with myelofibrosis (NCT03386214). The primary objective was to assess the safety and tolerability of combination therapy with additional objectives of treatment efficacy and alterations of biomarkers. There were no dose-limiting toxicities observed with most adverse events being limited to grades 1/2. In secondary measures, anemia response was observed in two patients. Pro-inflammatory cytokines and iron parameters were longitudinally assessed, which revealed suppression of interleukin-6 and interferon-gamma in a dose-dependent manner across a subset of patients. These results suggest that combination therapy targeting both JAK2 and NFκB may hold clinical merit for MPN patients.

Changes in bone marrow fibrosis during momelotinib or ruxolitinib therapy do not correlate with efficacy outcomes in patients with myelofibrosis

Bone marrow fibrosis (BMF) is a pathological feature of myelofibrosis, with higher grades associated with poor prognosis. Limited data exist on the association between outcomes and BMF changes. We present BMF data from Janus kinase (JAK) inhibitor-naive patients from SIMPLIFY-1 (NCT01969838), a double-blind, randomized, phase 3 study of momelotinib vs ruxolitinib. Baseline and week 24 bone marrow biopsies were graded from 0 to 3 as per World Health Organization criteria. Other assessments included Total Symptom Score, spleen volume, transfusion independence status, and hemoglobin levels. Paired samples were available from 144 and 160 patients randomized to momelotinib and ruxolitinib. With momelotinib and ruxolitinib, transfusion independence was achieved by 87% and 44% of patients with BMF improvement of ≥1 grade and 76% and 56% of those with stable/worsening BMF; there was no association between BMF changes and transfusion independence for either arm (momelotinib, p = .350; ruxolitinib, p = .096). Regardless of BMF changes, hemoglobin levels also generally increased on momelotinib but decreased on ruxolitinib. In addition, no associations between BMF changes and spleen (momelotinib, p = .126; ruxolitinib, p = .407)/symptom (momelotinib, p = .617; ruxolitinib, p = .833) outcomes were noted, and no improvement in overall survival was observed with ≥1-grade BMF improvement (momelotinib, p = .395; ruxolitinib, p = .407). These data suggest that the anemia benefit of momelotinib is not linked to BMF changes, and question the use of BMF assessment as a surrogate marker for clinical benefit with JAK inhibitors.

Momelotinib expands the therapeutic armamentarium for myelofibrosis: Impact on hierarchy of treatment choices

The primary objective of treatment in myelofibrosis (MF) is prolongation of life, which is currently accomplished only by allogeneic hematopoietic stem cell transplantation (AHSCT). Determination of optimal timing for AHSCT is facilitated by molecular risk stratification. Non-transplant treatment options in MF are palliative in scope and include Janus kinase 2 (JAK2) inhibitors (JAKi): momelotinib (FDA approved on September 15, 2023), ruxolitinib (November 16, 2011), fedratinib (August 16, 2019), and pacritinib (February 28, 2022); all four JAKi are effective in reducing spleen size and alleviating symptoms, considered a drug class effect and attributed to their canonical JAK-STAT inhibitory mechanism of action. In addition, momelotinib exhibits erythropoietic effect, attributed to alleviation of ineffective erythropoiesis through inhibition of activin A receptor type-I (ACVR1). In transplant-ineligible or deferred patients, the order of treatment preference is based on specific symptoms and individual assessment of risk tolerance. Because of drug-induced immunosuppression and other toxicities attributed to JAKi, we prefer non-JAKi drugs as initial treatment for MF-associated anemia that is not accompanied by treatment-requiring splenomegaly or constitutional symptoms. Otherwise, it is reasonable to consider momelotinib as the first-line JAKi treatment of choice, in order to target the triad of quality-of-life offenders in MF: anemia, splenomegaly, and constitutional symptoms/cachexia. For second-line therapy, we favor ruxolitinib, over fedratinib, based on toxicity profile. Pacritinib and fedratinib provide alternative options in the presence of severe thrombocytopenia or ruxolitinib-resistance/intolerance, respectively. Splenectomy remains a viable option for drug-resistant symptomatic splenomegaly and cytopenia.

Treatment of anemia in myelofibrosis: focusing on novel therapeutic options

INTRODUCTION

Myelofibrosis is a clonal myeloproliferative neoplasm associated with the proliferation of hematopoietic stem cells, increased bone marrow fibrosis, extramedullary hematopoiesis, hepatosplenomegaly, abnormal cytokine production, and constitutional symptoms. These and many other factors contribute to the development of anemia in myelofibrosis patients.

AREAS COVERED

This review summarizes novel and promising treatments for anemia in myelofibrosis including transforming growth factor-β inhibitors luspatercept and KER-050, JAK inhibitors momelotinib, pacritinib, and jaktinib, BET inhibitors pelabresib and ABBV-744, antifibrotic PRM-151, BCL2/BCL-XL inhibitor navitoclax, and telomerase inhibitor imetelstat.

EXPERT OPINION

Standard approaches to treat myelofibrosis-related anemia have limited efficacy and are associated with toxicity. New drugs have shown positive results in myelofibrosis-associated anemia when used alone or in combination.

ACVR1: A Novel Therapeutic Target to Treat Anemia in Myelofibrosis

Activin receptor type I (ACVR1) is a transmembrane kinase receptor belonging to bone morphogenic protein receptors (BMPs). ACVR1 plays an important role in hematopoiesis and anemia via the BMP6/ACVR1/SMAD pathway, which regulates expression of hepcidin, the master regulator of iron homeostasis. Elevated hepcidin levels are inversely associated with plasma iron levels, and chronic hepcidin expression leads to iron-restricted anemia. Anemia is one of the hallmarks of myelofibrosis (MF), a bone marrow (BM) malignancy characterized by BM scarring resulting in impaired hematopoiesis, splenomegaly, and systemic symptoms. Anemia and red blood cell transfusions negatively impact MF prognosis. Among the approved JAK inhibitors (ruxolitinib, fedratinib, momelotinib, and pacritinib) for MF, momelotinib and pacritinib are preferably used in cytopenic patients; both agents are potent ACVR1 inhibitors that suppress hepcidin expression via the BMP6/ACVR1/SMAD pathway and restore iron homeostasis/erythropoiesis. In September 2023, momelotinib was approved as a treatment for patients with MF and anemia. Zilurgisertib (ACVR1 inhibitor) and DISC-0974 (anti-hemojuvelin monoclonal antibody) are evaluated in early phase clinical trials in patients with MF and anemia. Luspatercept (ACVR2B ligand trap) is assessed in transfusion-dependent MF patients in a registrational phase 3 trial. Approved ACVR1 inhibitors and novel agents in development are poised to improve the outcomes of anemic MF patients.

Momelotinib: First Approval

Momelotinib (OJJAARA) is an oral Janus kinase 1 and 2 (JAK1/JAK2) and activin A receptor, type I (ACVR1) inhibitor that has been developed for the treatment of myelofibrosis (MF). In September 2023, momelotinib was approved in the USA for the treatment of intermediate or high-risk MF, including primary MF or secondary MF [post-polycythemia vera (PV) and post-essential thrombocythemia (ET)], in adults with anemia. This article summarizes the milestones in the development of momelotinib leading to this first approval for MF.

Top advances of the year: Myeloproliferative neoplasms

The rapid pace of drug development in hematology has led to multiple approvals for myelofibrosis (MF) and polycythemia vera (PV) in recent years. Moreover, there are many innovative agents and combinations being explored for myeloproliferative neoplasms (MPNs). In the past year, there have been several advances in MF, PV, and essential thrombocythemia. In MF, investigational approaches are focusing on strategies to optimize inhibition of signal transduction (including JAK inhibition), modify epigenetics, enhance apoptosis, target DNA replication, transform host immunity, and/or alter the tumor microenvironment. In PV, ropeginterferon alfa-2b has been introduced to the market in the United States, and data continue to accumulate to support the safety and efficacy of this treatment. Hepcidin mimesis is also emerging as a novel way to treat erythrocytosis. In essential thrombocythemia, ropeginterferon alfa-2b is being evaluated, as are therapies to modify epigenetics and inhibit CALR. The enhanced focus on MPNs brings hope that our field can improve morbidity and mortality in this group of diseases.

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).

Momelotinib (JAK1/JAK2/ACVR1 inhibitor): mechanism of action, clinical trial reports, and therapeutic prospects beyond myelofibrosis

Janus kinase (JAK) 2 inhibitors are now part of the therapeutic armamentarium for primary and secondary myelofibrosis (MF). Patients with MF endure shortened survival and poor quality of life. Allogeneic stem cell transplantation (ASCT) is currently the only treatment modality in MF with the potential to cure the disease or prolong survival. By contrast, current drug therapy in MF targets quality of life and does not modify the natural history of the disease. The discovery of JAK2 and other JAK-STAT activating mutations (i.e., CALR and MPL) in myeloproliferative neoplasms, including MF, has facilitated the development of several JAK inhibitors that are not necessarily specific to the oncogenic mutations themselves but have proven effective in countering JAK-STAT signaling, resulting in suppression of inflammatory cytokines and myeloproliferation. This non-specific activity resulted in clinically favorable effects on constitutional symptoms and splenomegaly and, consequently, approval by the Food and Drug Administration (FDA) of three small molecule JAK inhibitors: ruxolitinib, fedratinib, and pacritinib. A fourth JAK inhibitor, momelotinib, is poised for FDA approval soon and has been shown to provide additional benefit in alleviating transfusion-dependent anemia in MF. The salutary effect of momelotinib on anemia has been attributed to inhibition of activin A receptor, type 1 (ACVR1) and recent information suggests a similar effect from pacritinib. ACRV1 mediates SMAD2/3 signaling which contributes to upregulation of hepcidin production and iron-restricted erythropoiesis. Targeting ACRV1 raises therapeutic prospects in other myeloid neoplasms associated with ineffective erythropoiesis, such as myelodysplastic syndromes with ring sideroblasts or SF3B1 mutation, especially those with co-expression of a JAK2 mutation and thrombocytosis.

Momelotinib in Myelofibrosis Patients With Thrombocytopenia: Post Hoc Analysis From Three Randomized Phase 3 Trials

The oral activin A receptor type I, Janus kinase 1 (JAK1), and JAK2 inhibitor momelotinib demonstrated symptom, spleen, and anemia benefits in intermediate- and high-risk myelofibrosis (MF). Post hoc analyses herein evaluated the efficacy and safety of momelotinib in patients with MF and thrombocytopenia (platelet counts <100 × 109/L) from randomized phase 3 studies: MOMENTUM (momelotinib versus danazol; JAK inhibitor experienced); SIMPLIFY-1 (momelotinib versus ruxolitinib; JAK inhibitor naïve); and SIMPLIFY-2 (momelotinib versus best available therapy; JAK inhibitor experienced); these studies were not statistically powered to assess differences in thrombocytopenic subgroups, and these analyses are descriptive. The treatment effect of momelotinib versus ruxolitinib on week 24 response rates (spleen volume reduction ≥35%/Total Symptom Score reduction ≥50%/transfusion independence) was numerically comparable or better in thrombocytopenic patients versus the overall JAK inhibitor naive population; rates were preserved with momelotinib in thrombocytopenic patients but attenuated with ruxolitinib (momelotinib: 27%/28%/67% overall versus 39%/35%/61% in thrombocytopenic group; ruxolitinib: 29%/42%/49% overall versus 0%/22%/39% in thrombocytopenic group, respectively). In contrast to ruxolitinib, momelotinib maintained high dose intensity throughout the treatment. In the JAK inhibitor experienced population, thrombocytopenic patients had the following: (1) numerically higher symptom and transfusion independence response rates with momelotinib than in control arms; and (2) preserved spleen, symptom, and transfusion independence response rates with momelotinib relative to the overall study populations. The safety profile of momelotinib in thrombocytopenic patients was also consistent with the overall study population. In summary, momelotinib represents a safe and effective treatment option for patients with MF and moderate-to-severe thrombocytopenia.

Patient-reported Outcomes and Quality of Life in Anemic and Symptomatic Patients With Myelofibrosis: Results From the MOMENTUM Study

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm that typically manifests with debilitating symptoms that progressively worsen, negatively impacting patients' quality of life. Fatigue is a multifactorial and burdensome MF-related symptom due to its severity, persistence, and prevalence, with anemia a contributing factor and major unmet need. Clinical trials of the Janus kinase (JAK)1/JAK2/activin A receptor type 1 inhibitor momelotinib have shown consistent anemia benefits, in addition to improvements in MF-related symptoms. The phase 3 MOMENTUM trial in symptomatic and anemic patients met its primary end point, with a greater proportion having a Myelofibrosis Symptom Assessment Form (MFSAF) Total Symptom Score (TSS) reduction ≥50% at week 24 with momelotinib versus danazol. To support the positive primary end point result, we conducted longitudinal, responder, and time-to-event analyses of patient-reported outcomes from MOMENTUM, as measured by the MFSAF, European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30), and Patient-Reported Outcomes Measurement Information System (PROMIS) assessments. These analyses demonstrated rapid and durable response benefits with momelotinib, with achievement of first TSS response by day 29 and continued improvement over time. Improvements favored momelotinib versus danazol for each MFSAF individual item, and greater improvements were observed for disease- and cancer-related fatigue and physical functioning at week 24, with significant results for multiple items/domains across the 3 assessments. These findings are consistent in demonstrating that momelotinib provides substantial symptom benefit.

Pacritinib is a potent ACVR1 inhibitor with significant anemia benefit in patients with myelofibrosis

In patients with cytopenic myelofibrosis, treatment with the JAK2/IRAK1 inhibitor pacritinib was associated with anemia benefit in the phase 3 PERSIST-2 study. The impact of pacritinib on transfusion independence (TI) has not been previously described, nor has the mechanism by which pacritinib improves anemia been elucidated. Because it has been previously postulated that inhibition of activin A receptor, type 1 (ACVR1)/activin receptor-like kinase-2 improves anemia in patients with myelofibrosis via suppression of hepcidin production, we assessed the relative inhibitory potency of pacritinib compared with other JAK2 inhibitors against ACVR1. Pacritinib inhibited ACVR1 with greater potency (half-maximal inhibitory concentration [IC50] = 16.7 nM; Cmax:IC50 = 12.7) than momelotinib (IC50 = 52.5 nM; Cmax:IC50 = 3.2), fedratinib (IC50 = 273 nM; Cmax:IC50 = 1.0), or ruxolitinib (IC50 > 1000; Cmax:IC50 < 0.01). Pacritinib's inhibitory activity against ACVR1 was corroborated via inhibition of downstream SMAD signaling in conjunction with marked suppression of hepcidin production. Among patients on PERSIST-2 who were not transfusion independent at baseline based on Gale criteria, a significantly greater proportion achieved TI on pacritinib compared with those treated on best available therapy (37% vs 7%, P = .001), and significantly more had a ≥50% reduction in transfusion burden (49% vs 9%, P < .0001). These data indicate that the anemia benefit of the JAK2/IRAK1 inhibitor pacritinib may be a function of potent ACVR1 inhibition.

A Journey Through JAK Inhibitors for the Treatment of Myeloproliferative Diseases

PURPOSE OF REVIEW

Chronic myeloproliferative neoplasms (MPN) represent a group of diseases characterised by constitutive activation of the JAK/STAT pathway in a clonal myeloid precursor. The therapeutic approach aims to treat the symptom burden (headache, itching, debilitation), splenomegaly, slow down the fibrotic proliferation in the bone marrow and reduce the risk of thrombosis/bleeding whilst avoiding leukaemic transformation.

RECENT FINDINGS

In recent years, the advent of JAK inhibitors (JAKi) has significantly broadened treatment options for these patients. In myelofibrosis, symptom control and splenomegaly reduction can improve quality of life with improved overall survival, not impacting progression into acute leukaemia. Several JAKi are available and used worldwide, and combination approaches are now being explored. In this chapter, we review the approved JAKi, highlighting its strengths, exploring potential guidelines in choosing which one to use and reasoning towards future perspectives, where the combinations of therapies seem to promise the best results.

Next-Generation JAK2 Inhibitors for the Treatment of Myeloproliferative Neoplasms: Lessons from Structure-Based Drug Discovery Approaches

Selective inhibitors of Janus kinase (JAK) 2 have been in demand since the discovery of the JAK2 V617F mutation present in patients with myeloproliferative neoplasms (MPN); however, the structural basis of V617F oncogenicity has only recently been elucidated. New structural studies reveal a role for other JAK2 domains, beyond the kinase domain, that contribute to pathogenic signaling. Here we evaluate the structure-based approaches that led to recently-approved type I JAK2 inhibitors (fedratinib and pacritinib), as well as type II (BBT594 and CHZ868) and pseudokinase inhibitors under development (JNJ7706621). With full-length JAK homodimeric structures now available, superior selective and mutation-specific JAK2 inhibitors are foreseeable.

SIGNIFICANCE

The JAK inhibitors currently used for the treatment of MPNs are effective for symptom management but not for disease eradication, primarily because they are not strongly selective for the mutant clone. The rise of computational and structure-based drug discovery approaches together with the knowledge of full-length JAK dimer complexes provides a unique opportunity to develop better targeted therapies for a range of conditions driven by pathologic JAK2 signaling.

The pharmacotherapeutic management of patients with myelofibrosis: looking beyond JAK inhibitors

INTRODUCTION

The approach to myelofibrosis (MF) has been revolutionized in recent years, overcoming the traditional therapies, often not very effective. Janus kinase inhibitors (JAKi - from ruxolitinib up to momelotinib) were the first class of drugs with considerable results.

AREAS COVERED

Ongoing, new molecules are being tested that promise to give hope even to those patients not eligible for bone marrow transplants who become intolerant or are refractory to JAKi, for which therapeutic hopes are currently limited. Telomerase, murine double minute 2 (MDM2), phosphatidylinositol 3-kinase δ (PI3Kδ), BCL-2/xL, and bromodomain and extra-terminal motif (BET) inhibitors are the drugs with promising results in clinical trials and close to closure with consequent placing on the market, finally allowing JAK to look beyond. The novelty of the MF field was searched in the PubMed database, and the recently completed/ongoing trials are extrapolated from the ClinicalTrial website.

EXPERT OPINION

From this point of view, the use of new molecules widely described in this review, probably in association with JAKi, will represent the future treatment of choice in MF, leaving, in any case, the potential new approaches actually in an early stage of development, such as the use of immunotherapy in targeting CALR, which is coming soon.

Momelotinib versus danazol in symptomatic patients with anaemia and myelofibrosis previously treated with a JAK inhibitor (MOMENTUM): an updated analysis of an international, double-blind, randomised phase 3 study

BACKGROUND

The MOMENTUM study met all key endpoints at week 24, demonstrating symptom, spleen, and anaemia benefits with momelotinib versus danazol in patients with myelofibrosis. In this updated analysis, we report duration of week 24 responses and new responses with momelotinib through week 48.

METHODS

MOMENTUM is an international, double-blind, randomised, phase 3 study done at 107 sites across 21 countries. Patients were 18 years or older with primary, post-polycythaemia vera, or post-essential thrombocythaemia myelofibrosis, previously treated with an approved Janus kinase (JAK) inhibitor for 90 days or more (≥28 days with haematological complications), and had an Eastern Cooperative Oncology Group performance status of 2 or less. Patients were randomly assigned (2:1) to either the momelotinib group (200 mg orally once per day) or danazol group (300 mg orally twice per day) through week 24 via non-deterministic biased coin minimisation and an interactive response system. Stratification factors were Total Symptom Score (TSS; <22 vs ≥22), spleen size (<12 cm vs ≥12 cm), transfusion burden (0 units vs 1-4 units vs ≥5 units), and study site. After week 24, all patients initially randomly assigned to either group who remained on the study received open-label momelotinib. The primary endpoint, which has already been reported, was Myelofibrosis Symptom Assessment Form TSS response rate at week 24. Predefined secondary endpoints were duration of week 24 TSS and transfusion independence responses, safety, and survival, which are summarised post hoc at the week 48 data cutoff (May 17, 2022). TSS, transfusion independence, and splenic responses at week 48 were defined post hoc and assessed in all evaluable patients who entered the open-label period and provided sufficient data. The timing of this updated analysis was defined post hoc after all patients had the opportunity to complete their week 48 assessments, as most patients entered an extended access study (NCT03441113) after week 48. This study is registered with ClinicalTrials.gov, number NCT04173494, and is now complete.

FINDINGS

Between April 24, 2020, and Dec 3, 2021, a total of 195 patients were randomised (130 [67%] in the momelotinib group and 65 [33%] in the danazol group). 93 (72%) of 130 patients in the momelotinib group and 41 (63%) of 65 in the danazol group entered the momelotinib open-label extension period. Median follow-up was 48·4 weeks (IQR 40·6-55·7). Among TSS-evaluable patients at week 48, 30 (45%) of 67 patients in the momelotinib group who continued treatment and 15 (50%) of 30 in the danazol group who crossed over were responders. TSS responders at any time during the open-label period by week 48 were 46 (61%) of 75 evaluable patients in the momelotinib group who continued and 19 (59%) of 32 in the danazol group who crossed over, including most week 24 responders plus new responders after week 24. No new safety signals emerged with long-term follow-up. The most common non-haematological treatment-emergent adverse events in momelotinib-treated patients over the entire study period as of the data cutoff were diarrhoea (45 [26%] of 171) and asthenia (28 [16%]); the most common grades 3-4 treatment-emergent adverse events were thrombocytopenia (33 [19%]) and anaemia (19 [11%]). Serious treatment-emergent adverse events were reported in 79 (46%) of 171 patients, and fatal treatment-emergent adverse events were reported in 30 (18%); two fatal treatment-emergent adverse events were considered possibly related to momelotinib (rotaviral enteritis and Staphylococcus pneumonia).

INTERPRETATION

Momelotinib was associated with durable symptom, spleen, and anaemia benefits, late responses after week 24, and favourable safety through week 48. These results highlight the potential benefits of treatment with momelotinib in patients with myelofibrosis, particularly those with anaemia.

FUNDING

Sierra Oncology, a GSK company.

Momelotinib long-term safety and survival in myelofibrosis: integrated analysis of phase 3 randomized controlled trials

Momelotinib is the first inhibitor of Janus kinase 1 (JAK1) and JAK2 shown to also inhibit activin A receptor type 1 (ACVR1), a key regulator of iron homeostasis, and has demonstrated improvements in splenomegaly, constitutional symptoms, and anemia in myelofibrosis (MF). This long-term analysis pooled data from 3 randomized phase 3 studies of momelotinib (MOMENTUM, SIMPLIFY-1, and SIMPLIFY-2), representing MF disease from early (JAK inhibitor-naive) to late (JAK inhibitor-experienced) stages. Patients in the control arms (danazol in MOMENTUM, ruxolitinib in SIMPLIFY-1, and best available therapy in SIMPLIFY-2) could cross over to receive momelotinib at the end of the 24-week randomized period, and all patients could continue momelotinib treatment after the completion of these studies via an extended access protocol (XAP). Across these studies, 725 patients with MF received momelotinib; 12% remained on therapy for ≥5 years, with a median treatment exposure of 11.3 months (range, 0.1-90.4 months). The most common nonhematologic treatment-emergent adverse event (AE) occurring in ≥20% of patients was diarrhea (any grade, 27% and grade ≥3, 3%). Any-grade thrombocytopenia, anemia, and neutropenia occurred in 25%, 23%, and 7% of patients, respectively. The most common reason for momelotinib discontinuation was thrombocytopenia (4% discontinuation rate). The incidence of AEs of clinical importance (eg, infections, malignant transformation, peripheral neuropathy, and hemorrhage) did not increase over time. This analysis of one of the largest randomized trial databases for a JAK inhibitor to date in MF demonstrated a consistent safety profile of momelotinib without long-term or cumulative toxicity. These trials were registered at www.clinicaltrials.gov as: MOMENTUM (#NCT04173494), SIMPLIFY-1 (#NCT01969838), SIMPLIFY-2 (#NCT02101268), and XAP (#NCT03441113).

Comprehensive profiling of clinical JAK inhibitors in myeloproliferative neoplasms

Small molecule inhibitors targeting JAK2 provide symptomatic benefits for myeloproliferative neoplasm (MPN) patients and are among first-line therapeutic agents. However, despite all having potent capacity to suppress JAK-STAT signaling, they demonstrate distinct clinical profiles suggesting contributory effects in targeting other ancillary pathways. Here, we performed comprehensive profiling on four JAK2 inhibitors either FDA-approved (ruxolitinib, fedratinib, and pacritinib) or undergoing phase 3 studies (momelotinib) to better outline mechanistic and therapeutic efficacy. Across JAK2-mutant in vitro models, all four inhibitors demonstrated similar anti-proliferative phenotypes, whereas pacritinib yielded greatest potency on suppressing colony formation in primary samples, while momelotinib exhibited unique erythroid colony formation sparing. All inhibitors reduced leukemic engraftment, disease burden, and extended survival across patient-derived xenograft (PDX) models, with strongest effects elicited by pacritinib. Through RNA-sequencing and gene set enrichment analyses, differential suppressive degrees of JAK-STAT and inflammatory response signatures were revealed, which we validated with signaling and cytokine suspension mass cytometry across primary samples. Lastly, we assessed the capacity of JAK2 inhibitors to modulate iron regulation, uncovering potent suppression of hepcidin and SMAD signaling by pacritinib. These comparative findings provide insight into the differential and beneficial effects of ancillary targeting beyond JAK2 and may help guide the use of specific inhibitors in personalized therapy.

Emerging Treatment Options for Myelofibrosis: Focus on Anemia

Myelofibrosis (MF) is a hematologic malignancy characterized by abnormal proliferation of myeloid cells and the release of pro-inflammatory cytokines, leading to progressive bone marrow dysfunction. The introduction of ruxolitinib just over a decade ago marked a significant advancement in MF therapy, with JAK inhibitors now being the first-line treatment for reducing spleen size and managing symptoms. However, early JAK inhibitors (ruxolitinib and fedratinib) are often associated with cytopenias, particularly thrombocytopenia and anemia, which limit their tolerability. To address these complications, pacritinib has been developed and recently approved for patients with thrombocytopenia, while momelotinib is in development for those with anemia. Although JAK inhibitors have significantly improved the quality of life of MF patients, they have not demonstrated the ability to reduce leukemic transformation and their impact on survival is debated. Numerous drugs are currently being developed and investigated in clinical trials, both as standalone therapy and in combination with JAK inhibitors, with promising results enhancing the benefits of JAK inhibitors. In the near future, MF treatment strategies will involve selecting the most suitable JAK inhibitor based on individual patient characteristics and prior therapy. Ongoing and future clinical trials are crucial for advancing the field and expanding therapeutic options for MF patients.

Association of Myelofibrosis Phenotypes with Clinical Manifestations, Molecular Profiles, and Treatments

Myelofibrosis (MF) presents an array of clinical manifestations and molecular profiles. The two distinct phenotypes- myeloproliferative and myelodepletive or cytopenic- are situated at the two poles of the disease spectrum and are largely defined by different degrees of cytopenias, splenomegaly, and distinct molecular profiles. The myeloproliferative phenotype is characterized by normal/higher peripheral blood counts or mildly decreased hemoglobin, progressive splenomegaly, and constitutional symptoms. The myeloproliferative phenotype is typically associated with secondary MF, higher JAK2 V617F burden, fewer mutations, and superior overall survival (OS). The myelodepletive phenotype is usually associated with primary MF, ≥2 cytopenias, modest splenomegaly, lower JAK2 V617F burden, higher fibrosis, greater genomic complexity, and inferior OS. Cytopenias are associated with mutations in epigenetic regulators/splicing factors, clonal evolution, disease progression, and shorter OS. Clinical variables, in conjunction with the molecular profiles, inform integrated prognostication and disease management. Ruxolitinib/fedratinib and pacritinib/momelotinib may be more suitable to treat patients with the myeloproliferative and myelodepletive phenotypes, respectively. Appreciation of MF heterogeneity and two distinct phenotypes, the different clinical manifestations and molecular profiles associated with each phenotype alongside the growing treatment expertise, the development of non-myelosuppressive JAK inhibitors, and integrated prognostication are leading to a new era in patient management. Physicians can increasingly tailor personalized treatments that will address the unique unmet needs of MF patients, including those presenting with the myelodepletive phenotype, to elicit optimal outcomes and extended OS across the disease spectrum.

Moving Beyond Ruxolitinib Failure in Myelofibrosis: Evolving Strategies for Second Line Therapy

Ruxolitinib has been the cornerstone of pharmacologic therapy for myelofibrosis for over a decade. However, the last several years have witnessed the regulatory approval of other Janus kinase (JAK) inhibitors for myelofibrosis, i.e. fedratinib, pacritinib, and US approval of momelotinib is widely anticipated in 2023. Due to the multifaceted clinical presentation of myelofibrosis, a watertight definition of ruxolitinib failure has remained elusive, as "progression" on ruxolitinib can take many forms and management is highly nuanced. Yet, the availability of other JAK inhibitors and potential future availability of non-JAK inhibitor agents for myelofibrosis make a consensus on management of ruxolitinib failure critically important. This consensus paper summarizes a discussion between multiple academic and community physician experts, a pharmacist and an advanced practice provider around the issues to be considered for the optimal care of patients with myelofibrosis whose disease is refractory to or does not respond adequately to ruxolitinib, or who exhibit intolerance to ruxolitinib. The panel identified several areas of consensus, as well as some areas where more data to inform evidence-based practice are needed. In some situations, maintaining ruxolitinib while adding another agent, e.g. to address anemia, is appropriate, whereas in others, switching to a different drug has merit.

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.

Biology and therapeutic targeting of molecular mechanisms in MPNs

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by activated Janus kinase (JAK)-signal transducer and activator of transcription signaling. As a result, JAK inhibitors have been the standard therapy for treatment of patients with myelofibrosis (MF). Although currently approved JAK inhibitors successfully ameliorate MPN-related symptoms, they are not known to substantially alter the MF disease course. Similarly, in essential thrombocythemia and polycythemia vera, treatments are primarily aimed at reducing the risk of cardiovascular and thromboembolic complications, with a watchful waiting approach often used in patients who are considered to be at a lower risk for thrombosis. However, better understanding of MPN biology has led to the development of rationally designed therapies, with the goal of not only addressing disease complications but also potentially modifying disease course. We review the most recent data elucidating mechanisms of disease pathogenesis and highlight emerging therapies that target MPN on several biologic levels, including JAK2-mutant MPN stem cells, JAK and non-JAK signaling pathways, mutant calreticulin, and the inflammatory bone marrow microenvironment.

JAK inhibition in myelofibrosis: how to sequence treatment in this new era of multiple options

The management of myelofibrosis has improved following approval of the JAK1/JAK2 inhibitor, ruxolitinib. This agent laid the foundation for JAK inhibitor therapy, yet limitations have included myelosuppression and other adverse events (skin cancer, weight gain, and infection), as well as loss of response. Recently, two additional JAK inhibitors were approved for use in myelofibrosis. Fedratinib can be used front-line and has demonstrated impressive responses as a salvage option after ruxolitinib loss of response. Previously, patients with severe thrombocytopenia had limited treatment options; approval of pacritinib offers an option to address splenomegaly and/or symptoms in these patients. A significant unmet need has been the treatment of anemia; momelotinib (not approved at the time of writing) has demonstrated spleen, symptom, and anemia responses. The possibility of having four approved options for myelofibrosis may be soon realized. This speaks to progress in the past decade, though achieving clinical and molecular remissions remain paramount.

Predictors of anemia response to momelotinib therapy in myelofibrosis and impact on survival

We retrospectively reviewed 72 anemic patients with myelofibrosis (MF; median age 68 years), who were JAK2 inhibitor-naïve at the time of study entry to a phase-1/2 momelotinib clinical trial. Driver mutation profile included JAK2 69%, CALR 17%, MPL 8%, and triple-negative 6%; other mutations included ASXL1 39% and SRSF2 17%. Momelotinib was administered at a median dose of 300 mg daily. Anemia response was assessed by formal criteria and documented in 44% of all patients with hemoglobin levels below the sex-adjusted reference range (n = 72), 48% of those with hemoglobin <10 g/dl (n = 54), and 46% of those who were transfusion-dependent at the time of study entry (n = 28). Anemia response was more likely with post-essential thrombocythemia MF (83% vs 37%; p = .001), lower serum ferritin (p = .003), and shorter time from diagnosis to momelotinib therapy (p = .001); the first two variables were also predictive in transfusion-dependent patients. Post-momelotinib median survival was 3.2 years; in univariate analysis, survival was superior in anemia responders (median 3.8 vs. 2.8 years; p = .14) and in the presence of type 1/like CALR mutation and inferior in the presence of age > 65 years, ASXL1/SRSF2 mutation, unfavorable karyotype, DIPSS-plus high risk, red cell transfusion need and higher serum ferritin. Multivariable analysis confirmed the favorable impact of anemia response on survival (p = .02; HR 0.5, 3/5/10-year survival; 69%/38%/25%). This survival advantage was also noted in transfusion-dependent patients (3.7 vs. 1.9 years; p = .01; HR 0.3) and appeared to be restricted to patients with an unfavorable genetic profile. The current study suggests a short-term survival benefit associated with anemia response in momelotinib-treated patients with MF.

Momelotinib versus danazol in symptomatic patients with anaemia and myelofibrosis (MOMENTUM): results from an international, double-blind, randomised, controlled, phase 3 study

BACKGROUND

Janus kinase (JAK) inhibitors approved for myelofibrosis provide spleen and symptom improvements but do not meaningfully improve anaemia. Momelotinib, a first-in-class inhibitor of activin A receptor type 1 as well as JAK1 and JAK2, has shown symptom, spleen, and anaemia benefits in myelofibrosis. We aimed to confirm the differentiated clinical benefits of momelotinib versus the active comparator danazol in JAK-inhibitor-exposed, symptomatic patients with anaemia and intermediate-risk or high-risk myelofibrosis.

METHODS

MOMENTUM is an international, double-blind, randomised, controlled, phase 3 study that enrolled patients at 107 sites across 21 countries worldwide. Eligible patients were 18 years or older with a confirmed diagnosis of primary myelofibrosis or post-polycythaemia vera or post-essential thrombocythaemia myelofibrosis. Patients were randomly assigned (2:1) to receive momelotinib (200 mg orally once per day) plus danazol placebo (ie, the momelotinib group) or danazol (300 mg orally twice per day) plus momelotinib placebo (ie, the danazol group), stratified by total symptom score (TSS; <22 vs ≥22), spleen size (<12 cm vs ≥12 cm), red blood cell or whole blood units transfused in the 8 weeks before randomisation (0 units vs 1-4 units vs ≥5 units), and study site. The primary endpoint was the Myelofibrosis Symptom Assessment Form (MFSAF) TSS response rate at week 24 (defined as ≥50% reduction in mean MFSAF TSS over the 28 days immediately before the end of week 24 compared with baseline). MOMENTUM is registered with ClinicalTrials.gov, number NCT04173494, and is active but not recruiting.

FINDINGS

195 patients were randomly assigned to either the momelotinib group (130 [67%]) or danazol group (65 [33%]) and received study treatment in the 24-week randomised treatment period between April 24, 2020, and Dec 3, 2021. A significantly greater proportion of patients in the momelotinib group reported a 50% or more reduction in TSS than in the danazol group (32 [25%] of 130 vs six [9%] of 65; proportion difference 16% [95% CI 6-26], p=0·0095). The most frequent grade 3 or higher treatment-emergent adverse events with momelotinib and danazol were haematological abnormalities by laboratory values: anaemia (79 [61%] of 130 vs 49 [75%] of 65) and thrombocytopenia (36 [28%] vs 17 [26%]). The most frequent non-haematological grade 3 or higher treatment-emergent adverse events with momelotinib and danazol were acute kidney injury (four [3%] of 130 vs six [9%] of 65) and pneumonia (three [2%] vs six [9%]).

INTERPRETATION

Treatment with momelotinib, compared with danazol, resulted in clinically significant improvements in myelofibrosis-associated symptoms, anaemia measures, and spleen response, with favourable safety. These findings support the future use of momelotinib as an effective treatment in patients with myelofibrosis, especially in those with anaemia.

FUNDING

Sierra Oncology.