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

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 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.

Safety and efficacy of jaktinib (a novel JAK inhibitor) in patients with myelofibrosis who are relapsed or refractory to ruxolitinib: A single-arm, open-label, phase 2, multicenter study

Ruxolitinib has demonstrated efficacy in patients with myelofibrosis (MF). However, substantial number of patients may not respond after 3-6 months of treatment or develop resistance over time. In this phase 2 trial, patients with a current diagnosis of intermediate or high-risk MF who either had an inadequate splenic response or spleen regrowth after ruxolitinib treatment were enrolled. All patients received jaktinib 100 mg Bid. The primary endpoint was the proportion of patients with ≥35% reduction in spleen volume (SVR 35) at week 24. The secondary endpoints included change of MF-related symptoms, anemic response, and safety profile. From July 6, 2021, to January 24, 2022, 34 ruxolitinib-refractory or relapsed patients were enrolled, 52.9% (18 of 34) were DIPSS intermediate 2 or high risk. SVR 35 at week 24 was 32.4% (11 of 34, 95% CI 19.1%-49.2%) in all patients and 33.3% (6 of 18, 95% CI 16.3%-56.3%) in the intermediate 2 or high-risk group. A total of 50% (8 of 16) transfusion-independent patients with hemoglobin (HGB) <100 g/L at baseline had HGB elevation ≥20 g/L within 24 weeks. Furthermore, 46.4% (13 of 28) of patients had a ≥ 50% decrease in the total symptom score (TSS 50) at week 24. The most common grade ≥3 treatment-emergent adverse events (TEAEs) were thrombocytopenia (32.4%), anemia (32.4%), and leukocytosis (20.6%). In total, 13 (38.2%) of 34 patients had serious adverse events (SAE), of which drug-related SAEs were found in 5 patients (14.7%). These results indicate that jaktinib can be a promising treatment option for patients with MF who have either become refractory to or relapsed after ruxolitinib treatment.

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.

Safety and efficacy of jaktinib (a novel JAK inhibitor) in patients with myelofibrosis who are intolerant to ruxolitinib: A single-arm, open-label, phase 2, multicenter study

Although ruxolitinib improves splenomegaly and constitutional symptoms in patients with myelofibrosis (MF), a substantial proportion of patients discontinue ruxolitinib because of intolerance. This phase 2 trial investigated the safety and efficacy of jaktinib, a novel JAK inhibitor in patients with ruxolitinib-intolerant MF. The primary endpoint was the proportion of patients with ≥35% reduction in spleen volume (SVR35) at week 24. The secondary endpoints included change of MF-related symptoms, anemic response, and safety profiles. Between December 18, 2019, and November 24, 2021, 51 patients were enrolled, 45 treated with jaktinib 100 mg bid (100 mg bid group) and six received non-100 mg bid doses (non-100 mg bid group). The SVR35 at week 24 in the 100 mg bid group was 43.2% (19/44, 95% CI 29.7%-57.8%). There were 41.9% (13/31) of transfusion-independent patients with hemoglobin (HGB) ≤100 g/L who had HGB elevation ≥20 g/L within 24 weeks. The proportion of patients with a ≥50% decrease in the total symptom score (TSS 50) at week 24 was 61.8% (21/34). The most commonly reported grade ≥3 treatment-emergent adverse events (TEAEs) in the 100 mg bid group were anemia 31.1%, thrombocytopenia 22.2%, and infectious pneumonia 17.8%. A total of 16 (35.6%) in the 100 mg bid group had serious adverse events, and 4 (8.9%) were considered possibly drug related. These results indicate jaktinib can provide a treatment option for patients with MF who are intolerant to ruxolitinib.

Polycythemia vera: 2024 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) is a JAK2-mutated myeloproliferative neoplasm characterized by clonal erythrocytosis; other features include leukocytosis, thrombocytosis, splenomegaly, pruritus, constitutional symptoms, microcirculatory disturbances, and increased risk of thrombosis and progression into myelofibrosis (post-PV MF) or acute myeloid leukemia (AML).

DIAGNOSIS

A working diagnosis is considered in the presence of a JAK2 mutation associated with hemoglobin/hematocrit levels of >16.5 g/dL/49% in men or 16 g/dL/48% in women; morphologic confirmation by bone marrow examination is advised but not mandated.

CYTOGENETICS

Abnormal karyotype is seen in 15%-20% of patients with the most frequent sole abnormalities being +9 (5%), loss of chromosome Y (4%), +8 (3%), and 20q- (3%).

MUTATIONS

Over 50% of patients harbor DNA sequence variants/mutations other than JAK2, with the most frequent being TET2 (18%) and ASXL1 (15%). Prognostically adverse mutations include SRSF2, IDH2, RUNX1, and U2AF1, with a combined incidence of 5%-10%.

SURVIVAL AND PROGNOSIS

Median survival is ⁓15 years but exceeds 35 years for patients aged ≤40 years. Risk factors for survival include older age, leukocytosis, abnormal karyotype, and the presence of adverse mutations. Twenty-year risk for thrombosis, post-PV MF, or AML are ⁓26%, 16% and 4%, respectively.

RISK FACTORS FOR THROMBOSIS

Two risk categories are considered: high (age >60 years or thrombosis history) and low (absence of both risk factors). Additional predictors for arterial thrombosis include cardiovascular risk factors and for venous thrombosis higher absolute neutrophil count and JAK2V617F allele burden.

TREATMENT

Current goal of therapy is to prevent thrombosis. Periodic phlebotomy, with a hematocrit target of <45%, combined with once- or twice-daily aspirin (81 mg) therapy, absent contraindications, is the backbone of treatment in all patients, regardless of risk category. Cytoreductive therapy is reserved for high-risk disease with first-line drugs of choice being hydroxyurea and pegylated interferon-α and second-line busulfan and ruxolitinib. In addition, systemic anticoagulation is advised in patients with venous thrombosis history.

ADDITIONAL TREATMENT CONSIDERATIONS

At the present time, we do not consider a drug-induced reduction in JAK2V617F allele burden, which is often incomplete and seen not only with peg-IFN but also with ruxolitinib and busulfan, as an indicator of disease-modifying activity, unless accompanied by cytogenetic and independently-verified morphologic remission. Accordingly, we do not use the specific parameter to influence treatment choices. The current review also includes specific treatment strategies in the context of pregnancy, splanchnic vein thrombosis, pruritus, perioperative care, and post-PV MF.

Novel Janus-kinase (JAK) Inhibitors in Myelofibrosis

INTRODUCTION

JAK inhibitors (JAKis), used in the treatment of myelofibrosis, have entered standard treatment, providing significant improvements in spleen size and symptom burden. Although splenomegaly provides a reduction and some improvement in cytopenia, there is still a way to go. Novel JAKis are being investigated to overcome barriers to treatment access, such as therapeutic challenges, intolerance, and unresponsiveness.

AREAS COVERED

This review includes the current status of JAKi treatment for myelofibrosis, mainly focusing on investigational JAKis; jaktinib, lestaurtinib, itacitinib, gandotinib, BMS-911543, ilginatinib, TQ05105, and flonoltinib maleate. MEDLINE and clinicaltrials.gov were screened to identify all completed or active studies on this topic. The outcomes of the preclinical studies and clinical trials are presented and discussed for each drug.

EXPERT OPINION

In patients with myelofibrosis, momelotinib was effective in treating anemia, whereas jaktinib was effective in both anemia and Total Symptom Score (TSS). More phase 3 studies are needed to provide more precise evidence. The increasing variety of JAKis will allow for more personalized treatment options for myelofibrosis in the future. The potential impact on disease progression, molecular responses, and the duration of this response will become important parameters for future evaluations of these drugs.

Determinants of survival and retrospective comparisons of 183 clinical trial patients with myelofibrosis treated with momelotinib, ruxolitinib, fedratinib or BMS- 911543 JAK2 inhibitor

Between October 2007 and July 2013, 183 Mayo Clinic patients (median age 65 years; 58% males) with high/intermediate risk myelofibrosis (MF) were enrolled in consecutive phase 1/2 JAK2 inhibitor (JAKi) clinical trials with momelotinib (n = 79), ruxolitinib (n = 50), fedratinib (n = 23) and BMS-911543 (n = 31). Using conventional criteria, the respective response rates for spleen and "transfusion-dependent anemia" were 47%, 32%, 83%, 62% and 51%, 30%, 10%, 44%, respectively, favoring momelotinib for anemia response (p = 0.02) and fedratinib for spleen response (p < 0.01). All study patients were followed to death or 2022, during which time 177 (97%) drug discontinuations, 27 (15%) leukemic transformations, and 22 (12%) allogeneic stem cell transplants (ASCT) were recorded. 5/10-year survival rate for all 183 patients was 41%/16% and not significantly different across the four drug cohorts (p = 0.33). Multivariable analysis of pre-treatment variables identified age >65 years (HR 3.5), absence of type 1/like CALR mutation (HR 2.8), baseline transfusion need (HR 2.1), and presence of ASXL1/SRSF2 mutation (HR 1.6) as risk factors for overall survival; subsequent HR-based modeling segregated three risk categories with 5/10-year survival rates of 84%/60%, 44%/14%, and 21%/5% (p < 0.01). In addition, spleen (p < 0.01) and anemia (p = 0.01) responses were independently associated with improved short-term survival while long-term survival was secured only by ASCT (5/10-year survival rate 91%/45% vs 47%/19% in non-transplanted patients; p < 0.01). The current retrospective study suggests the value of specific pre-treatment variables in identifying long-lived MF patients receiving JAKi and also confirms recent observations on the favorable impact of treatment response on short-term and of ASCT on long-term survival.