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

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.

Novel therapeutic agents for myelofibrosis after failure or suboptimal response to JAK2 inhbitors

PURPOSE OF REVIEW

JAK2 inhibitors have changed the therapeutic strategies for the management of primary and secondary myelofibrosis. Ruxolitinib, the first available agent, improved disease-related symptoms, spleen volume, and overall survival compared to conventional chemotherapy. It has been revealed that after 3 years of treatment, about 50% of patients discontinued ruxolitinib for resistance and/or intolerance and should be candidate to a second line of treatment.

RECENT FINDINGS

Second-generation tyrosine kinase inhibitors have been tested in this setting, but all these new drugs do not significantly impact on disease progression. Novel agents are in developments that target on different pathways, alone or in combination with JAK2 inhibitors.

SUMMARY

In this review, we summarize all the clinical efficacy and safety data of these drugs providing a vision of the possible future.

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, arising from immature lymphocytes that show uncontrolled proliferation and arrested differentiation. Genomic alterations affecting Janus kinase 2 (JAK2) correlate with some of the poorest outcomes within the Philadelphia-like subtype of ALL. Given the success of kinase inhibitors in the treatment of chronic myeloid leukemia, the discovery of activating JAK2 point mutations and JAK2 fusion genes in ALL, was a breakthrough for potential targeted therapies. However, the molecular mechanisms by which these alterations activate JAK2 and promote downstream signaling is poorly understood. Furthermore, as clinical data regarding the limitations of approved JAK inhibitors in myeloproliferative disorders matures, there is a growing awareness of the need for alternative precision medicine approaches for specific JAK2 lesions. This review focuses on the molecular mechanisms behind ALL-associated JAK2 mutations and JAK2 fusion genes, known and potential causes of JAK-inhibitor resistance, and how JAK2 alterations could be targeted using alternative and novel rationally designed therapies to guide precision medicine approaches for these high-risk subtypes of ALL.

Deferasirox in the management of iron overload in patients with myelofibrosis treated with ruxolitinib: The multicentre retrospective RUX-IOL study

Deferasirox (DFX) is used for the management of iron overload (IOL) in many haematological malignancies including myelofibrosis (MF). The 'RUX-IOL' study retrospectively collected 69 MF patients treated with ruxolitinib (RUX) and DFX for IOL to assess: safety, efficacy in term of iron chelation response (ICR) and erythroid response (ER), and impact on overall survival of the combination therapy. The RUX-DFX therapy was administered for a median time of 12.4 months (interquartile range 3.1-71.2). During treatment, 36 (52.2%) and 34 (49.3%) patients required RUX and DFX dose reductions, while eight (11.6%) and nine (13.1%) patients discontinued due to RUX- or DFX-related adverse events; no unexpected toxicity was reported. ICR and ER were achieved by 33 (47.8%) and 32 patients (46.4%) respectively. Thirteen (18.9%) patients became transfusion-independent. Median time to ICR and ER was 6.2 and 2 months respectively. Patients achieving an ER were more likely to obtain an ICR also (p = 0.04). In multivariable analysis, the absence of leukocytosis at baseline (p = 0.02) and achievement of an ICR at any time (p = 0.02) predicted improved survival. In many MF patients, the RUX-DFX combination provided ICR and ER responses that correlated with improved outcome in the absence of unexpected toxicities. This strategy deserves further clinical investigation.

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.

Next Generation Therapeutics for the Treatment of Myelofibrosis

Myelofibrosis is a myeloproliferative neoplasm characterized by splenomegaly, constitutional symptoms, bone marrow fibrosis, and a propensity towards transformation to acute leukemia. JAK inhibitors are the only approved therapy for myelofibrosis and have been successful in reducing spleen and symptom burden. However, they do not significantly impact disease progression and many patients are ineligible due to coexisting cytopenias. Patients who are refractory to JAK inhibition also have a dismal survival. Therefore, non-JAK inhibitor-based therapies are being explored in pre-clinical and clinical settings. In this review, we discuss novel treatments in development for myelofibrosis with targets outside of the JAK-STAT pathway. We focus on the mechanism, preclinical rationale, and available clinical efficacy and safety information of relevant agents including those that target apoptosis (navitoclax, KRT-232, LCL-161, imetelstat), epigenetic modulation (CPI-0610, bomedemstat), the bone marrow microenvironment (PRM-151, AVID-200, alisertib), signal transduction pathways (parsaclisib), and miscellaneous agents (tagraxofusp. luspatercept). We also provide commentary on the future of therapeutic development in myelofibrosis.

Ruxolitinib rechallenge in resistant or intolerant patients with myelofibrosis: Frequency, therapeutic effects, and impact on outcome

BACKGROUND

After ruxolitinib discontinuation, the outcome of patients with myelofibrosis (MF) is poor with scarce therapeutic possibilities.

METHODS

The authors performed a subanalysis of an observational, retrospective study (RUX-MF) that included 703 MF patients treated with ruxolitinib to investigate 1) the frequency and reasons for ruxolitinib rechallenge, 2) its therapeutic effects, and 3) its impact on overall survival.

RESULTS

A total of 219 patients (31.2%) discontinued ruxolitinib for ≥14 days and survived for ≥30 days. In 60 patients (27.4%), ruxolitinib was rechallenged for ≥14 days (RUX-again patients), whereas 159 patients (72.6%) discontinued it permanently (RUX-stop patients). The baseline characteristics of the 2 cohorts were comparable, but discontinuation due to a lack/loss of spleen response was lower in RUX-again patients (P = .004). In comparison with the disease status at the first ruxolitinib stop, at its restart, there was a significant increase in patients with large splenomegaly (P < .001) and a high Total Symptom Score (TSS; P < .001). During the rechallenge, 44.6% and 48.3% of the patients had spleen and symptom improvements, respectively, with a significant increase in the number of patients with a TSS reduction (P = .01). Although the use of a ruxolitinib dose > 10 mg twice daily predicted better spleen (P = .05) and symptom improvements (P = .02), the reasons for/duration of ruxolitinib discontinuation and the use of other therapies before rechallenge were not associated with rechallenge efficacy. At 1 and 2 years, 33.3% and 48.3% of RUX-again patients, respectively, had permanently discontinued ruxolitinib. The median overall survival was 27.9 months, and it was significantly longer for RUX-again patients (P = .004).

CONCLUSIONS

Ruxolitinib rechallenge was mainly used in intolerant patients; there were clinical improvements and a possible survival advantage in many cases, but there was a substantial rate of permanent discontinuation. Ruxolitinib rechallenge should be balanced against newer therapeutic possibilities.