Current treatment algorithm for the management of patients with myelofibrosis, JAK inhibitors, and beyond

Impact of Individual Comorbidities on Survival of Patients with Myelofibrosis

The comorbidity burden is an important risk factor for overall survival (OS) in several hematological malignancies. This observational prospective study was conducted to evaluate the impact of individual comorbidities on survival in a multicenter series of 668 patients with primary myelofibrosis (PMF) or MF secondary to polycythemia vera (PPV-MF) or essential thrombocythemia (PET-MF). Hypertension (hazard ratio (HR) = 4.96, p < 0.001), smoking (HR = 5.08, p < 0.001), dyslipidemia (HR = 4.65, p < 0.001) and hepatitis C virus (HCV) (HR = 4.26, p = 0.015) were most adversely associated with OS. Diabetes (HR = 3.01, p < 0.001), pulmonary disease (HR = 3.13, p < 0.001) and renal dysfunction (HR = 1.82, p = 0.037) were also associated with an increased risk of death. Multivariate analysis showed that pulmonary disease (HR = 2.69, p = 0.001), smoking (HR = 3.34, p < 0.001), renal dysfunction (HR = 2.08, p = 0.043) and HCV (HR = 11.49, p = 0.001) had a negative impact on OS. When ruxolitinib exposure was included in the model, the effect of each comorbidity on survival was modified. Therefore, individual comorbidities should be taken into account in determining the survival prognosis for patients with MF.

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.

OUP accepted manuscript

Background

This study analyses treatment patterns, health care resource utilization (HCRU), and costs in patients with myelofibrosis (MF) and a subgroup treated with ruxolitinib (RUX).

Materials and Methods

Treatment patterns, all-cause and MF-related HCRU, and costs were analyzed in adults with MF with continuous enrollment in a commercial or the Medicare Advantage health plan in the pre-index period, defined as the 12 months immediately prior to the index date (date of primary or secondary MF diagnosis), and the post-index period, defined as ≥6 months following the index date. In a subgroup analysis, outcomes were analyzed in patients treated with optimal RUX (OPT RUX, ≥30 mg) and suboptimal RUX (SUB RUX, <30 mg) in the pre-index RUX period, defined as the 3 months immediately prior to the index RUX date (first date for an RUX claim), and the post-index RUX period, defined as ≥6 months following the index RUX date.

Results

Of 2830 patients with an MF diagnosis, 1191 met eligibility requirements. The median age of patients was 72 years, 54% were male, and comorbidities were frequent. Sixty percent of patients received ≥1 line of therapy (LOT), of which 46% (n = 331) had ≥2 LOTs during the post-index MF period. Costs increased considerably 6-month pre-index to 6-month post-index (all-cause: cause ($24,216 to $48,966) and MF-related ($16,502 to $39,383), driven by inpatient stays and pharmacy costs. In the subgroup analysis, patients treated with RUX (n = 495) experienced significant disease burden and high costs, regardless of dose. A shorter duration of therapy and a higher rate of discontinuation were observed in patients treated with SUB RUX (n = 191) versus OPT RUX (n = 304).

Conclusion

These findings suggest a significant disease and economic impacts associated with MF patients that persists with RUX therapy, highlighting the need for additional therapeutic options for MF.

Trends in allogeneic haematopoietic cell transplantation for myelofibrosis in Europe between 1995 and 2018: a CMWP of EBMT retrospective analysis

We performed a retrospective assessment of patient- and transplant-specific characteristics and outcomes for 4142 patients undergoing allogeneic haematopoietic cell transplant for myelofibrosis between 1995 and 2018 across 278 centres. Activity increased steadily across the four analysed eras (<2006, 2006-2010, 2011-2014 and 2015-2018). Median recipient age increased over time between the earliest and most recent cohort (49.4 years (range, 20.1-68) versus 59.3 years (range, 18.1-78.1). Increasing number of patients with a Karnofsky performance status <90 underwent transplant over time. Increased utilisation of matched unrelated donors was apparent (<2006, 22.5% versus 2015-18, 45.2%; p < 0.001). Decreased use of myeloablative conditioning, increased use of busulphan-based platforms and anti-thymocyte globulin was evident. Of note, rates of acute (a)GVHD grade II-IV by day +100 decreased over time (p = 0.027) as did rates of chronic (c) GVHD, predominantly extensive cGVHD (<2006, 36% (31-41%) versus 2015-18, 23% (21-25%); p = 0.001). Overall, significant factors associated with worse overall survival and non-relapse mortality (NRM) remained older age, use of donors other than matched sibling, recipient CMV seropositivity and a lower Karnofsky performance status (<90). Multivariable analysis demonstrated improvements in overall survival and reductions in relapse risk over time with stable NRM rates despite increasing numbers of older, less fit patients and use of unrelated donors.

Current and future status of JAK inhibitors

An enhanced understanding of the importance of Janus kinase (JAK) and signal transducer and activator of transcription (STAT) signalling in multiple disease states has led to an increasing applicability of therapeutic intervention with JAK inhibitors. These agents have revolutionised treatments for a heterogeneous group of disorders, such as myeloproliferative neoplasms, rheumatoid arthritis, inflammatory bowel disease, and multiple immune-driven dermatological diseases, exemplifying rapid bench-to-bedside translation. In this Therapeutics paper, we summarise the currently available data concerning the successes and safety of an array of JAK inhibitors and hypothesise on how these fields could develop.

Fedratinib in myelofibrosis

Following the discovery of the JAK2V617F mutation in myeloproliferative neoplasms in 2005, fedratinib was developed as a small molecular inhibitor of JAK2. It was optimized to yield low-nanomolar activity against JAK2 (50% inhibitory concentration = 3 nM) and was identified to be selective for JAK2 relative to other JAK family members (eg, JAK1, JAK3, and TYK2). It quickly moved into clinical development with a phase 1 clinical trial opening in 2008, where a favorable impact on spleen and myelofibrosis (MF) symptom responses was reported. A phase 3 trial in JAK2 inhibitor treatment-naive MF patients followed in 2011 (JAKARTA); a phase 2 trial in MF patients resistant or intolerant to ruxolitinib followed in 2012 (JAKARTA-2). Clinical development suffered a major setback between 2013 and 2017 when the US Food and Drug Administration (FDA) placed fedratinib on clinical hold due to the development of symptoms concerning for Wernicke encephalopathy (WE) in 8 of 608 subjects (1.3%) who had received the drug. It was ultimately concluded that there was no evidence that fedratinib directly induces WE, but clear risk factors (eg, poor nutrition, uncontrolled gastrointestinal toxicity) were identified. In August 2019, the FDA approved fedratinib for the treatment of adults with intermediate-2 or high-risk MF. Notably, approval includes a "black box warning" on the risk of serious and fatal encephalopathy, including WE. FDA approval was granted on the basis of the JAKARTA studies in which the primary end points (ie, spleen and MF symptom responses) were met in ∼35% to 40% of patients (JAKARTA) and 25% to 30% of patients (JAKARTA-2), respectively.

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.

Fedratinib, a newly approved treatment for patients with myeloproliferative neoplasm-associated myelofibrosis

Myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF) is characterized by cytopenias, marrow fibrosis, constitutional symptoms, extramedullary hematopoiesis, splenomegaly, and shortened survival. Constitutive activation of the janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in MF leads to cell proliferation, inhibition of cell death, and clonal expansion of myeloproliferative malignant cells. Fedratinib is a selective oral JAK2 inhibitor recently approved in the United States for treatment of adult patients with intermediate-2 or high-risk MF. In mouse models of JAK2V617F-driven myeloproliferative disease, fedratinib blocked phosphorylation of STAT5, increased survival, and improved MF-associated disease features, including reduction of white blood cell counts, hematocrit, splenomegaly, and fibrosis. Fedratinib exerts off-target inhibitory activity against bromodomain-containing protein 4 (BRD4); combination JAK/STAT and BRD4 inhibition was shown to synergistically block NF-kB hyperactivation and inflammatory cytokine production, attenuating disease burden and reversing bone marrow fibrosis in animal models of MPNs. In patients, fedratinib is rapidly absorbed and dosed once daily (effective half-life 41 h). Fedratinib showed robust clinical activity in JAK-inhibitor-naïve patients and in patients with MF who were relapsed, refractory, or intolerant to prior ruxolitinib therapy. Fedratinib is effective regardless of JAK2 mutation status. Onset of spleen and symptom responses are typically seen within the first 1–2 months of treatment. The most common adverse events (AEs) with fedratinib are grades 1–2 gastrointestinal events, which are most frequent during early treatment and decrease over time. Treatment discontinuation due to hematologic AEs in clinical trials was uncommon (~3%). Suspected cases of Wernicke’s encephalopathy were reported during fedratinib trials in ~1% of patients; thiamine levels should be monitored before and during fedratinib treatment as medically indicated. Phase III trials are ongoing to assess fedratinib effects on long-term safety, efficacy, and overall survival. The recent approval of fedratinib provides a much-needed addition to the limited therapeutic options available for patients with MF.

Bone marrow niche dysregulation in myeloproliferative neoplasms

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

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.

Current and future role of fedratinib in the treatment of myelofibrosis

Fedratinib (INREBIC^® [fedratinib] capsules, Impact Biomedicines, Inc., a wholly owned subsidiary of Celgene Corporation), is a potent JAK2 inhibitor that has been approved for use in myelofibrosis, both as a first-line agent and also in second line following ruxolitinib (Novartis Pharmaceuticals, Basel, Switzerland) failure or intolerance. Within this article, we will review relevant preclinical and early/late clinical trial data concerning the use of fedratinib to treat myeloproliferative neoplasms. Moreover, we will review in detail the assumed safety issues that led to temporary cessation of all programs with the agent in 2013 which subsequently re-entered the clinical arena in 2017. We will discuss how physicians may safely transition a patient across from ruxolitinib to fedratinib following intolerance or lack of efficacy. At last, we will discuss potential future applications of this agent within the field.

Beyond JAK-STAT: novel therapeutic targets in Ph-negative MPN

The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) share a common pathobiology of constitutive activation of the JAK and STAT pathway, despite having the 3 distinct phenotypes of essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Targeting the JAK-STAT pathway has led to remarkable clinical benefit, including reduction in splenomegaly, amelioration of cytokine-driven symptoms, improvement in quality of life, and even some improvement in survival. However, targeting this pathway has not resulted in consistent disease modification by current metrics, including a reduction in mutant allele burden or reversal of fibrosis. Moreover, targeting JAK-STAT can lead to limiting treatment-emergent side effects, such as anemia and thrombocytopenia. Continued discovery points to a complex system of pathogenesis beyond JAK-STAT driving the formation and evolution of MPNs. This article reviews the successes and limitations of JAK-STAT inhibition, surveys the strategies behind emerging therapies, and discusses the challenges that are present in moving beyond JAK-STAT.

Myeloablative and Reduced-Intensity Conditioned Allogeneic Hematopoietic Stem Cell Transplantation in Myelofibrosis: A Retrospective Study by the Chronic Malignancies Working Party of the European Society for Blood and Marrow Transplantation

This retrospective study by the European Society for Blood and Marrow Transplantation analyzed the outcome of 2224 patients with myelofibrosis (MF) who underwent allogeneic stem cell transplantation (allo-SCT) between 2000 and 2014; 781 (35%) underwent myeloablative conditioning (MAC) and 1443 (65%) reduced-intensity conditioning (RIC). Median patient age was 52.9 years (range, 18 to 74 years) and 57.5 years (range, 21 to 76 years) in the MAC and RIC cohorts, respectively. Donor type was similar: matched sibling donors (MAC, 317 [41%]; RIC, 552 [38%]) and unrelated donors (MAC, 464 [59%]; RIC, 891 [62%]). Median time to both neutrophil and platelet (>20 × 10⁹/L) engraftment did not differ between cohorts. Rates of grade II to IV acute GVHD were 28% (MAC) and 31% (RIC; P = NS). Cumulative chronic GVHD rates (limited/extensive) were 22%/27% (MAC) and 19%/31% (RIC; P = .10). Cumulative incidences of nonrelapse mortality (NRM) at 1, 3, and 5 years were 25.5%, 32.2%, and 34.6% (MAC) and 26.3%, 32.8%, and 34.4% (RIC), respectively. There was a trend toward a higher relapse rate with RIC regimens compared with MAC (P = .08); rates at 1, 3, and 5 years were 10.9%, 17.2%, and 20.1% (MAC) and 14%, 19.7%, and 23.2% (RIC), respectively. No significant difference in 5-year probabilities of overall survival (OS) was noted: MAC (53.0%; 95% confidence interval [CI], 49.1% to 56.9%) and RIC (51.0%; 95% CI, 48.3% to 53.7%); P = .78. Regarding the composite end point of GVHD-free/relapse-free survival (GRFS), the unadjusted Kaplan-Meier estimate of 5-year GRFS was 32.4% (95% CI, 29.0% to 36.1%) in the MAC group and 26.1% (95% CI, 23.9% to 28.2%) in the RIC group (P = .001). In the MAC cohort, multivariable analysis confirmed worse OS and NRM with older age (>50 years), using an unrelated donor and a Karnofsky Performance Status of 80 or less. For the RIC cohort, worse OS and NRM were associated with age 60 to 70 years compared with younger recipients, use of a mismatched donor, and poor performance status. In conclusion, although similar OS rates existed for both cohorts overall, this study suggests that MAC should still be used for younger individuals suitable for such an approach due to a trend toward less relapse and an overall suggested advantage of improved GRFS, albeit this should be examined in a more homogeneous cohort. RIC allo-SCT still offers significant survival advantage in the older, fitter MF allograft patient, and optimization to reduce significant relapse and NRM rates is required.

Comprehensive clinical-molecular transplant scoring system for myelofibrosis undergoing stem cell transplantation

Allogeneic hematopoietic stem cell transplantation is curative in myelofibrosis, and current prognostic scoring systems aim to select patients for transplantation. Here, we aimed to develop a prognostic score to determine prognosis after transplantation itself, using clinical, molecular, and transplant-specific information from a total of 361 patients with myelofibrosis. Of these, 205 patients were used as a training cohort to create a clinical-molecular myelofibrosis transplant scoring system (MTSS), which was then externally validated in a cohort of 156 patients. Multivariable analysis on survival identified age at least 57 years, Karnofsky performance status lower than 90%, platelet count lower than 150 × 10⁹/L, leukocyte count higher than 25 × 10⁹/L before transplantation, HLA-mismatched unrelated donor, ASXL1 mutation, and non-CALR/MPL driver mutation genotype being independent predictors of outcome. The uncorrected concordance index for the final survival model was 0.723, and bias-corrected indices were similar. Risk factors were incorporated into a 4-level MTSS: low (score, 0-2), intermediate (score, 3-4), high (score, 5), and very high (score, >5). The 5-year survival according to risk groups in the validation cohort was 83% (95% confidence interval [CI], 71%-95%), 64% (95% CI, 53%-75%), 37% (95% CI, 17%-57%), and 22% (95% CI, 4%-39%), respectively (P < .001). Increasing score was predictive of nonrelapse mortality (P < .001) and remained applicable to primary (0.718) and post-essential thrombocythemia (ET)/polycythemia vera (PV) myelofibrosis (0.701) improving prognostic ability in comparison with all currently available disease-specific systems. In conclusion, this MTSS predicts outcome of patients with primary and post-ET/PV myelofibrosis undergoing allogeneic stem cell transplantation.

Recent advances in the diagnosis and management of primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) in which dysregulation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathways is the major pathogenic mechanism. Most patients with PMF carry a driver mutation in the JAK2, MPL (myeloproliferative leukemia), or CALR (calreticulin) genes. Mutations in epigenetic regulators and RNA splicing genes may also occur, and play critical roles in PMF disease progression. Based on revised World Health Organization diagnostic criteria for MPNs, both screening for driver mutations and bone marrow biopsy are required for a specific diagnosis. Clinical trials of JAK2 inhibitors for PMF have revealed significant efficacy for improving splenomegaly and constitutional symptoms. However, the currently available drug therapies for PMF do not improve survival. Although allogeneic stem cell transplantation is potentially curative, it is associated with substantial treatment-related morbidity and mortality. PMF is a heterogeneous disorder and decisions regarding treatments are often complicated, necessitating the use of prognostic models to determine the management of treatments for individual patients. This review focuses on the clinical aspects and outcomes of a cohort of Japanese patients with PMF, including discussion of recent advances in the management of PMF.

The identification of fibrosis-driving myofibroblast precursors reveals new therapeutic avenues in myelofibrosis

Myofibroblasts are fibrosis-driving cells and are well characterized in solid organ fibrosis, but their role and cellular origin in bone marrow fibrosis remains obscure. Recent work has demonstrated that Gli1⁺ and LepR⁺ mesenchymal stromal cells (MSCs) are progenitors of fibrosis-causing myofibroblasts in the bone marrow. Genetic ablation of Gli1⁺ MSCs or pharmacologic targeting of hedgehog (Hh)-Gli signaling ameliorated fibrosis in mouse models of myelofibrosis (MF). Moreover, pharmacologic or genetic intervention in platelet-derived growth factor receptor α (Pdgfrα) signaling in Lepr⁺ stromal cells suppressed their expansion and ameliorated MF. Improved understanding of cellular and molecular mechanisms in the hematopoietic stem cell niche that govern the transition of MSCs to myofibroblasts and myofibroblast expansion in MF has led to new paradigms in the pathogenesis and treatment of MF. Here, we highlight the central role of malignant hematopoietic clone-derived megakaryocytes in reprogramming the hematopoietic stem cell niche in MF with potential detrimental consequences for hematopoietic reconstitution after allogenic stem cell transplantation, so far the only therapeutic approach in MF considered to be curative. We and others have reported that targeting Hh-Gli signaling is a therapeutic strategy in solid organ fibrosis. Data indicate that targeting Gli proteins directly inhibits Gli1⁺ cell proliferation and myofibroblast differentiation, which results in reduced fibrosis severity and improved organ function. Although canonical Hh inhibition (eg, smoothened [Smo] inhibition) failed to improve pulmonary fibrosis, kidney fibrosis, or MF, the direct inhibition of Gli proteins ameliorated fibrosis. Therefore, targeting Gli proteins directly might be an interesting and novel therapeutic approach in MF.