Myelofibrosis-Related Anemia: Current and Emerging Therapeutic Strategies

Red cell distribution width and prognosis in myelofibrosis patients treated with ruxolitinib

We evaluated RDW in a single-center series of 61 consecutive patients with primary and secondary MF at diagnosis and during treatment with ruxolitinib (RUX) and examined any possible prognostic impact. Elevated RDW values were present in all but 4 patients at diagnosis with a median RDW of 18.9%. RDW was higher in subjects with palpable splenomegaly (p = 0.02), higher ferritin, as well as among those cases who did not receive any cytoreduction before RUX (p = 0.04). Interestingly, higher RDW at diagnosis also correlated with a shorter time from MF diagnosis to RUX start (-4.1 months per one RDW unit; p = 0.03). We observed a modest increase (< 1%) in RDW during the first 6 months of RUX treatment. In a multivariable random-intercept model that considered all time points and contained the covariates time and RUX dose, we also observed a clear decrease in RDW with increasing hemoglobin (Hb) during RUX (slope: -0.4% per g/dL of Hb; p < 0.001). The median RDW at diagnosis of 18.9% was used as a cut-off to identify two subgroups of patients [Group 1: RDW 19.0-25.7%; Group 2: RDW 13.1-18.7%], showing a difference in mortality [Group 1 vs. 2: crude HR 2.88; p = 0.01]. Using continuous RDW at diagnosis, the crude HR was 1.21 per RDW unit (p = 0.002). In a Cox model adjusted for gender, age and Hb at diagnosis, the HR was 1.13 per RDW unit (p = 0.07). RDW may have prognostic significance at MF diagnosis and during RUX, helping in the rapid detection of patients with poor prognosis.

A randomized, double-blind study of zinpentraxin alfa in patients with myelofibrosis who were previously treated with or ineligible for ruxolitinib: stage 2 of a phase II trial

Not available.

Incidence of blast phase in myelofibrosis patients according to anemia severity at ruxolitinib start and during therapy

BACKGROUND

Anemia is frequently present in patients with myelofibrosis (MF), and it may be exacerbated by treatment with the JAK2-inhibitor ruxolitinib (RUX). Recently, a relevant blast phase (BP) incidence has been reported in anemic MF patients unexposed to RUX.

METHODS

The authors investigated the incidence of BP in 886 RUX-treated MF patients, included in the "RUX-MF" retrospective study.

RESULTS

The BP incidence rate ratio (IRR) was 3.74 per 100 patient-years (3.74 %p-y). At therapy start, Common Terminology Criteria for Adverse Events grade 3-4 anemia (hemoglobin [Hb] <8 g/dL) and severe sex/severity-adjusted anemia (Hb <8/<9 g/dL in women/men) were present in 22.5% and 25% patients, respectively. IRR of BP was 2.34 in patients with no baseline anemia and reached respectively 4.22, 4.89, and 4.93 %p-y in patients with grade 1, 2, and 3-4 anemia. Considering the sex/severity-adjusted Hb thresholds, IRR of BP was 2.85, 4.97, and 4.89 %p-y in patients with mild/no anemia, moderate, and severe anemia. Transfusion-dependent patients had the highest IRR (5.03 %p-y). Progression-free survival at 5 years was 70%, 52%, 43%, and 27% in patients with no, grade 1, 2, and 3-4 anemia, respectively (p < .001). At 6 months, 260 of 289 patients with no baseline anemia were receiving ruxolitinib, and 9.2% had developed a grade 3-4 anemia. By 6-month landmark analysis, BP-free survival was significantly worse in patients acquiring grade 3-4 anemia (69.3% vs. 88.1% at 5 years, p < .001).

CONCLUSIONS

This study highlights that anemia correlates with an increased risk of evolution into BP, both when present at baseline and when acquired during RUX monotherapy. Innovative anemia therapies and disease-modifying agents are warranted in these patients.

Results from phase 1 of the MANIFEST clinical trial to evaluate the safety and tolerability of pelabresib in patients with myeloid malignancies

Pelabresib (CPI-0610), a BET protein inhibitor, is in clinical development for hematologic malignancies, given its ability to target NF-κB gene expression. The MANIFEST phase 1 study assessed pelabresib in patients with acute leukemia, high-risk myelodysplastic (MDS) syndrome, or MDS/myeloproliferative neoplasms (MDS/MPNs) (NCT02158858). Forty-four patients received pelabresib orally once daily (QD) at various doses (24-400 mg capsule or 225-275 mg tablet) on cycles of 14 d on and 7 d off. The most frequent drug-related adverse events were nausea, decreased appetite, and fatigue. The maximum tolerated dose (MTD) was 225 mg tablet QD. One patient with chronic myelomonocytic leukemia (CMML) showed partial remission. In total, 25.8% of acute myeloid leukemia (AML) patients and 38.5% of high-risk MDS patients had stable disease. One AML patient and one CMML patient showed peripheral hematologic response. The favorable safety profile supports the ongoing pivotal study of pelabresib in patients with myelofibrosis using the recommended phase 2 dose of 125 mg tablet QD.CLINICAL TRIAL REGISTRATION: NCT02158858.

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.

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.

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.

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).

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.

Advances in management of primary myelofibrosis and polycythaemia vera: Implications in clinical practice

Primary myelofibrosis (PMF) and polycythaemia vera (PV) are rare BCR-ABL1-negative myeloproliferative neoplasms, associated with an increased risk of thrombosis, haemorrhagic complications and progression to fibrosis or leukaemia or fibrosis for PV. Both diseases are characterised by biological and clinical heterogeneity, leading to great variability in their management in routine clinical practice. In this review, we present an updated overview of the diagnosis, prognosis and treatment of PMF and PV, and we discuss how our multidisciplinary expert group based across France translates this evidence-based knowledge into routine clinical practice.

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).

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.

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

Development of myelofibrosis (MF) therapeutics has reached fruition as the transformative impact of JAK2 inhibitors in the MPN landscape is complemented/expanded by a profusion of novel monotherapies and rational combinations in the frontline and second line settings. Agents in advanced clinical development span various mechanisms of action (eg, epigenetic or apoptotic regulation), may address urgent unmet clinical needs (cytopenias), increase the depth/duration of spleen and symptom responses elicited by ruxolitinib, improve other aspects of the disease besides splenomegaly/constitutional symptoms (eg, resistance to ruxolitinib, bone marrow fibrosis or disease course), provide personalized strategies, and extend overall survival (OS). Ruxolitinib had a dramatic impact on the quality of life and OS of MF patients. Recently, pacritinib received regulatory approval for severely thrombocytopenic MF patients. Momelotinib is advantageously poised among JAK inhibitors given its differentiated mode of action (suppression of hepcidin expression). Momelotinib demonstrated significant improvements in anemia measures, spleen responses, and MF-associated symptoms in MF patients with anemia; and will likely receive regulatory approval in 2023. An array of other novel agents combined with ruxolitinib, such as pelabresib, navitoclax, parsaclisib, or as monotherapies (navtemadlin) are evaluated in pivotal phase 3 trials. Imetelstat (telomerase inhibitor) is currently evaluated in the second line setting; OS was set as the primary endpoint, marking an unprecedented goal in MF trials, wherein SVR35 and TSS50 at 24 weeks have been typical endpoints heretofore. Transfusion independence may be considered another clinically meaningful endpoint in MF trials given its correlation with OS. Overall, therapeutics are at the cusp of an exponential expansion and advancements that will likely lead to the golden era in treatment of MF.

New Treatments for Myelofibrosis

OPINION STATEMENT

Currently approved therapies for myelofibrosis (MF) consist of JAK inhibitors, which produce meaningful improvements in spleen size and symptom burden but do not significantly impact leukemic progression. In addition, many patients develop resistance or intolerance to existing therapies and are left without meaningful therapeutic options. There has been recent rapid development of agents in MF that may be able to fill these unmet needs. Importantly, most treatments currently in clinical development have targets outside the JAK-STAT pathway, including BET, BCL-2/BCL-xL, PI3k, HDM2, PIM-1, SINE, telomerase, LSD1, and CD123. These therapies are being tested in combination with JAK inhibitors in the front-line setting and in patients with a suboptimal response, as well as a single agent after JAK inhibitor failure. This next generation of agents is likely to produce a paradigm shift in MF treatment with a focus on combination treatment targeting multiple areas of MF pathophysiology.

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.

Thrombocytopenia in Patients With Myelofibrosis: A Practical Management Guide

Patients with myelofibrosis (MF) frequently develop thrombocytopenia as a consequence of bone marrow fibrosis, splenic sequestration, and myelosuppression from an inflammatory microenvironmental milieu. Thrombocytopenia occurs frequently at diagnosis, worsens with disease progression, is an independent adverse prognostic factor, and limits effective dosing of JAK2 inhibitors. Recently, pacritinib was approved for patients with MF and extreme thrombocytopenia. However, this JAK2/IRAK1 inhibitor is not primarily used to attain improvement in platelet count. In this narrative review, we discuss strategies to specifically address thrombocytopenia in MF patients including immunomodulatory drugs, synthetic androgens, hypomethylating agents and splenectomy, all of which have only modest efficacy in alleviating thrombocytopenia. We also detail transfusion approaches, including diagnostic and therapeutic consideration for platelet transfusion refractoriness. We end by discussing novel therapies, including TGFβ traps and recombinant pentraxin-2, which may increase platelet counts in MF patients. Despite recent therapeutic advancements in MF, there remains a near paucity of agents that can effectively alleviate thrombocytopenia.

Pacritinib for the treatment of patients with myelofibrosis and thrombocytopenia

INTRODUCTION

: Myelofibrosis (MF) is a rare myeloproliferative neoplasm characterized by a complex symptom profile, cytopenias, splenomegaly, and potential for leukemic progression. Severe thrombocytopenia is common in patients with MF and correlates with poor prognosis; however, until recently, treatment options for these patients were limited. Pacritinib, a potent Janus kinase (JAK) 2/interleukin-1 receptor-associated kinase 1 (IRAK1) inhibitor, has demonstrated significant reduction in splenomegaly, improved symptom control, and a manageable safety profile in patients with MF regardless of the severity of thrombocytopenia.

AREAS COVERED

: This review will outline the pacritinib drug profile and summarize key efficacy and safety data, focusing on the 200 mg twice daily dose from phase 2 and 3 studies that formed the basis for the recent US Food and Drug Administration approval of pacritinib in patients with MF and severe thrombocytopenia (platelet counts <50 x 10⁹/L).

EXPERT OPINION

Pacritinib, with its unique mechanism of action targeting both JAK2 and IRAK1, offers patients with MF and severe thrombocytopenia a new treatment option, providing consistent disease and symptom control. Adverse events are easily manageable. Further analyses to identify ideal patient characteristics for pacritinib and other JAK inhibitors along with studies of pacritinib combinations are warranted, including in related myeloid malignancies.

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.

Momelotinib for the treatment of myelofibrosis with anemia

Myelofibrosis is a myeloproliferative neoplasm characterized by splenomegaly, debilitating constitutional symptoms and bone marrow failure. Disease-related anemia is common and associated with an inferior quality of life and survival. Unfortunately, few therapies exist to improve hemoglobin in myelofibrosis patients. Momelotinib is a JAK1/JAK2 inhibitor that also antagonizes ACVR1, leading to downregulation of hepcidin expression and increased availability of iron for erythropoiesis. In clinical testing, momelotinib has demonstrated a unique ability to improve hemoglobin and reduce transfusion burden in myelofibrosis patients with baseline anemia, while producing reductions in spleen size and symptom burden. This review explores the preclinical rationale, clinical trial data and future role of momelotinib in the evolving therapeutic landscape of myelofibrosis.

Novel Usefulness of Krebs von den Lungen 6 (KL-6) with Hemoglobin and Lactate Dehydrogenase for Assessing Bone Marrow Fibrosis

Bone marrow fibrosis (BMF) is manually assessed by reticulin and trichrome stain of bone marrow (BM) biopsy and graded on a semi-quantitative scale. Krebs von den Lungen 6 (KL-6) and Mac-2 binding protein glycosylation isomer (M₂BPGi) are known to be associated with lung and liver fibrosis, respectively. We explored the usefulness of KL-6 and M₂BPGi to assess BMF. A total of 250 patients who underwent BM biopsy with hematologic or non-hematologic diseases were included, and 42 patients with lung and liver diseases were excluded. The patients’ data, including age, sex, diagnosis, white blood cell, hemoglobin (Hb), platelet, and lactate dehydrogenase (LDH) were collected. Measured KL-6 and M₂BPGi levels were compared with reticulin grade (RG) (grade 0–3). KL-6 levels were significantly elevated with an increase in RG, but M₂BPGi did not show a significant difference. Hb, LDH, or KL-6 were independent predictors for BMF (odds ratio: 1.96, 2.26, 2.91, respectively), but showed poor predictive ability (area under the curve [AUC] 0.62, 0.61, 0.60, respectively). The combination of Hb, LDH, and KL-6 showed a significantly improved predictive ability for BMF (AUC 0.73; integrated discrimination improvement 0.057; category-free net reclassification improvement 0.625). This is the first study to evaluate the usefulness of KL-6 for assessing BMF. The combination of Hb, LDH, and KL-6 would be an objective and relevant biomarker approach and be applied to risk stratification for BMF.

Momelotinib: an emerging treatment for myelofibrosis patients with anemia

The suite of marked anemia benefits that momelotinib has consistently conferred on myelofibrosis (MF) patients stem from its unique inhibitory activity on the BMP6/ACVR1/SMAD and IL-6/JAK/STAT3 pathways, resulting in decreased hepcidin (master iron regulator) expression, higher serum iron and hemoglobin levels, and restored erythropoiesis. Clinical data on momelotinib from the phase 2 and the two phase 3 SIMPLIFY trials consistently demonstrated high rates of sustained transfusion-independence. In a recent phase 2 translational study, 41% of the patients achieved transfusion independence for ≥ 12 weeks. In the phase 3 trials SIMPLIFY-1 and SIMPLIFY-2, 17% more JAK inhibitor-naïve patients and two-fold more JAK inhibitor-treated patients achieved or maintained transfusion independence with momelotinib versus ruxolitinib and best available therapy (89% ruxolitinib), respectively. Anemia is present in approximately a third of MF patients at diagnosis, eventually developing in nearly all patients. The need for red blood cell transfusions is an independent adverse risk factor for both overall survival and leukemic transformation. Presently, FDA-approved medications to address anemia are lacking. Momelotinib is one of the prime candidates to durably address the critical unmet needs of MF patients with moderate/severe anemia. Importantly, momelotinib may have overall survival benefits in frontline and second-line MF patients. MOMENTUM is an international registration-track phase 3 trial further assessing momelotinib’s unique constellation of anemia and other benefits in second-line MF patients; the results of the MOMENTUM trial are keenly awaited and may lead to regulatory approval of momelotinib.

Emerging drugs for the treatment of myelofibrosis: phase II & III clinical trials

INTRODUCTION

Myelofibrosis is a clonal hematologic malignancy with clinical manifestations that include cytopenias, debilitating constitutional symptoms, splenomegaly, bone marrow fibrosis and a propensity toward leukemic progression. While allogeneic hematopoietic stem cell transplantation can be curative, this therapy is not available for the majority of patients. Ruxolitinib and fedratinib are approved JAK2 inhibitors that have produced meaningful benefits in terms of spleen reduction and symptom improvement, but there remain several unmet needs.

AREAS COVERED

We discuss novel therapies based upon published data from phase II or III clinical trials. Specifically, we cover novel JAK inhibitors (momelotinib and pacritinib), and agents that target bromodomain and extra-terminal domain (pelabresib), the antiapoptotic proteins BCL-2/BCL-xL (navitoclax), MDM2 (navtemadlin), phosphatidylinositol 3-kinase (parsaclisib), or telomerase (imetelstat).

EXPERT OPINION

Patients with disease related cytopenias are ineligible for currently approved JAK2 inhibitors. However, momelotinib and pacritinib may be able to fill this void. Novel therapies are being evaluated in the upfront setting to improve the depth and duration of responses with ruxolitinib. Future evaluation of agents must be judged on their potential to modify disease progression, which current JAK2 inhibitors lack. Combination therapy, possibly with an immunotherapeutic agent might serve as key components of future myelofibrosis treatment options.

From Biology to Clinical Practice: Iron Chelation Therapy With Deferasirox

Iron chelation therapy (ICT) has become a mainstay in heavily transfused hematological patients, with the aim to reduce iron overload (IOL) and prevent organ damage. This therapeutic approach is already widely used in thalassemic patients and in low-risk Myelodysplastic Syndrome (MDS) patients. More recently, ICT has been proposed for high-risk MDS, especially when an allogeneic bone marrow transplantation has been planned. Furthermore, other hematological and hereditary disorders, characterized by considerable transfusion support to manage anemia, could benefit from this therapy. Meanwhile, data accumulated on how iron toxicity could exacerbate anemia and other clinical comorbidities due to oxidative stress radical oxygen species (ROS) mediated by free iron species. Taking all into consideration, together with the availability of approved oral iron chelators, we envision a larger use of ICT in the near future. The aim of this review is to better identify those non-thalassemic patients who can benefit from ICT and give practical tips for management of this therapeutic strategy.

Inflammation in Myeloid Malignancies: From Bench to Bedside

Myeloid malignancies, stemming from a somatically mutated hematopoietic clone, can cause a wide variety of clinical consequences, including pancytopenia in myelodysplastic syndrome, overproduction of three myeloid lineages in myeloproliferative neoplasm, and the rapid growth of immature hematopoietic cells in acute myeloid leukemia (AML). It is becoming clear that inflammation is a hallmark feature of clonal myeloid conditions, ranging from clonal hematopoiesis of indeterminate potential to AML. Fundamental findings from laboratory research on inflammation in myeloid malignancies has potential implications for diagnosis, prognostication, and treatment in these diseases. In this review, we highlighted some pertinent basic science findings regarding the role of inflammation in myeloid malignancies and speculated how these findings could impact the clinical care of patients.

MOMENTUM: momelotinib vs danazol in patients with myelofibrosis previously treated with JAKi who are symptomatic and anemic

Hallmark features of myelofibrosis (MF) are cytopenias, constitutional symptoms and splenomegaly. Anemia and transfusion dependency are among the most important negative prognostic factors and are exacerbated by many JAK inhibitors (JAKi). Momelotinib (MMB) has been investigated in over 820 patients with MF and possesses a pharmacological and clinical profile differentiated from other JAKi by inhibition of JAK1, JAK2 and ACVR1. MMB is designed to address the complex drivers of iron-restricted anemia and chronic inflammation in MF and should improve constitutional symptoms and splenomegaly while maintaining or improving hemoglobin in JAKi-naive and previously JAKi-treated patients. The MOMENTUM Phase III study is designed to confirm and extend observations of safety and clinical activity of MMB.

Inflammatory Microenvironment and Specific T Cells in Myeloproliferative Neoplasms: Immunopathogenesis and Novel Immunotherapies

The Philadelphia-negative myeloproliferative neoplasms (MPNs) are malignancies of the hematopoietic stem cell (HSC) arising as a consequence of clonal proliferation driven by somatically acquired driver mutations in discrete genes (JAK2, CALR, MPL). In recent years, along with the advances in molecular characterization, the role of immune dysregulation has been achieving increasing relevance in the pathogenesis and evolution of MPNs. In particular, a growing number of studies have shown that MPNs are often associated with detrimental cytokine milieu, expansion of the monocyte/macrophage compartment and myeloid-derived suppressor cells, as well as altered functions of T cells, dendritic cells and NK cells. Moreover, akin to solid tumors and other hematological malignancies, MPNs are able to evade T cell immune surveillance by engaging the PD-1/PD-L1 axis, whose pharmacological blockade with checkpoint inhibitors can successfully restore effective antitumor responses. A further interesting cue is provided by the recent discovery of the high immunogenic potential of JAK2V617F and CALR exon 9 mutations, that could be harnessed as intriguing targets for innovative adoptive immunotherapies. This review focuses on the recent insights in the immunological dysfunctions contributing to the pathogenesis of MPNs and outlines the potential impact of related immunotherapeutic approaches.

Inflammatory Microenvironment and Specific T Cells in Myeloproliferative Neoplasms: Immunopathogenesis and Novel Immunotherapies

The Philadelphia-negative myeloproliferative neoplasms (MPNs) are malignancies of the hematopoietic stem cell (HSC) arising as a consequence of clonal proliferation driven by somatically acquired driver mutations in discrete genes (JAK2, CALR, MPL). In recent years, along with the advances in molecular characterization, the role of immune dysregulation has been achieving increasing relevance in the pathogenesis and evolution of MPNs. In particular, a growing number of studies have shown that MPNs are often associated with detrimental cytokine milieu, expansion of the monocyte/macrophage compartment and myeloid-derived suppressor cells, as well as altered functions of T cells, dendritic cells and NK cells. Moreover, akin to solid tumors and other hematological malignancies, MPNs are able to evade T cell immune surveillance by engaging the PD-1/PD-L1 axis, whose pharmacological blockade with checkpoint inhibitors can successfully restore effective antitumor responses. A further interesting cue is provided by the recent discovery of the high immunogenic potential of JAK2V617F and CALR exon 9 mutations, that could be harnessed as intriguing targets for innovative adoptive immunotherapies. This review focuses on the recent insights in the immunological dysfunctions contributing to the pathogenesis of MPNs and outlines the potential impact of related immunotherapeutic approaches.

The relationship between serum ferritin level and fibrosis and splenomegaly in myelofibrosis

INTRODUCTION

Myelofibrosis (MF) is a disease in which the grade of bone marrow fibrosis increases in proportion to the degree of extramedullary hematopoiesis and splenomegaly. Associated with increased cytokines and inflammation, anemia deepens and an increase in serum ferritin levels is also expected. There are no studies addressing the relationship between ferritin and splenomegaly or fibrosis. In this study, the relationship between serum ferritin level and splenomegaly and bone marrow fibrosis was examined.

MATERIAL AND METHOD

The study was performed retrospectively in 46 MF cases diagnosed between 2012 and 2020. MF was divided into 3 separate subgroups: Primary myelofibrosis, secondary myelofibrosis and myeloproliferative neoplasms (MDS/MPN) with myelodsplastic syndrome.

RESULTS

Thirty (28.3%) of cases were PMF, 26 (56.5%) were SMF and 7 (15.2%) were MDS/MPN. There was no relation found between serum ferritin and splenomegaly in none of the cases or subgroup analysis (for PMF p: 0.564, for SMF p: 0.192, for MDS/MPN p: 0.364). There was a statistically significant relationship between serum ferritin and marrow fibrosis within the group of ages 60 years and older (p: 0.016).

DISCUSSION AND CONCLUSION

Disruption of hematopoiesis and progressive splenomegaly causes an increase in iron stores associated with an increased need for transfusion. This causes iron-related organ toxicity and bone marrow hematopoiesis disruption, leading to an increase in morbidity. We see that a significant relationship between ferritin and fibrosis has been revealed in the group aged 60 years and older. It is an unprecedented study in the literature in terms of both examining the relationship ferritin and fibrosis or splenomegaly and its results.

Evaluating the Safety, Efficacy, and Therapeutic Potential of Momelotinib in the Treatment of Intermediate/High-Risk Myelofibrosis: Evidence to Date

Myelofibrosis is a heterogeneous disorder with regard to both molecular pathogenesis and clinical phenotype, ranging from an initial fairly indolent condition in some through to an aggressive and debilitating scenario with profound constitutional symptoms, cytopenia frequently requiring transfusional support, and massive splenomegaly. Many advances have been made within the therapeutic arena, and an increasing array of novel agents are now available for disease management. Within this review, we focus on the current and predicted role of the JAK inhibitor momelotinib (Sierra Oncology) in myelofibrosis, with an emphasis on clinical trial evaluation, drug efficacyand safety, and discuss the suggested place in the therapeutic paradigm of myelofibrosis in 2020 and beyond.