Emerging drugs for the treatment of Myelofibrosis

New Markers of Disease Progression in Myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm due to the clonal proliferation of a hematopoietic stem cell. The vast majority of patients harbor a somatic gain of function mutation either of JAK2 or MPL or CALR genes in their hematopoietic cells, resulting in the activation of the JAK/STAT pathway. Patients display variable clinical and laboratoristic features, including anemia, thrombocytopenia, splenomegaly, thrombotic complications, systemic symptoms, and curtailed survival due to infections, thrombo-hemorrhagic events, or progression to leukemic transformation. New drugs have been developed in the last decade for the treatment of PMF-associated symptoms; however, the only curative option is currently represented by allogeneic hematopoietic cell transplantation, which can only be offered to a small percentage of patients. Disease prognosis is based at diagnosis on the classical International Prognostic Scoring System (IPSS) and Dynamic-IPSS (during disease course), which comprehend clinical parameters; recently, new prognostic scoring systems, including genetic and molecular parameters, have been proposed as meaningful tools for a better patient stratification. Moreover, new biological markers predicting clinical evolution and patient survival have been associated with the disease. This review summarizes basic concepts of PMF pathogenesis, clinics, and therapy, focusing on classical prognostic scoring systems and new biological markers of the disease.

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

Momelotinib (MMB) is a JAK1/2 and ACVR1 inhibitor with demonstrated clinical activity in all 3 hallmarks of myelofibrosis (MF): anemia, constitutional symptoms, and splenomegaly. In this phase 2 open-label translational biology study (NCT02515630) of 41 transfusion-dependent patients with MF, we explored mechanisms underlying the favorable activity of MMB on MF-associated iron-restricted anemia, including its impact on serum hepcidin levels, and markers of iron storage and availability, erythropoiesis, and inflammation. A transfusion-independent response (TI-R), defined as red blood cell transfusion independence (TI) ≥12 weeks at any time on study, occurred in 17 patients (41%; 95% confidence interval [CI], 26%-58%), including 14 patients (34%; 95% CI, 20%-51%) who achieved TI-R by week 24. In addition, 78% of TI nonresponse (TI-NR) patients achieved a ≥50% decrease in transfusion requirement for ≥8 weeks. Adverse events (AEs) were consistent with previous studies of MMB in MF, with cough, diarrhea, and nausea as the most common. Twenty-one patients experienced grade ≥3 AEs, most commonly anemia and neutropenia. Consistent with preclinical data, daily MMB treatment led to an acute and persistent decrease in blood hepcidin associated with increased iron availability and markers of erythropoiesis. Baseline characteristics associated with TI-R were lower inflammation and hepcidin as well as increased markers of erythropoiesis and bone marrow function. Overall, the study demonstrates that MMB treatment decreases hepcidin in conjunction with improving iron metabolism and erythropoiesis, suggesting a mechanistic explanation for the reduced transfusion dependency observed in transfusion-dependent MF patients treated with MMB, thereby addressing the key unmet medical need in the MF population.

Shifting the paradigm in treating multi-factorial diseases: polypharmacological co-inhibitors of HDAC6

Multi-factorial diseases are illnesses that exploit multiple cellular processes, or stages within one process, and thus highly targeted therapies often succumb to the disease, losing efficacy as resistance sets in. Combination therapies have become a mainstay to battle these diseases, however these regimens are plagued with caveats. An emerging avenue to treat multi-factorial diseases is polypharmacology, wherein a single drug is rationally designed to bind multiple targets, and is widely touted to be superior to combination therapy by inherently addressing the latter's shortcomings, which include poor patient compliance, narrow therapeutic windows and spiraling healthcare costs. Through its roles in intracellular trafficking, cell motility, mitosis, protein folding and as a back-up to the proteasome pathway, HDAC6 has rapidly become an exciting new target for therapeutics, particularly in the discovery of new drugs to treat Alzheimer's disease and cancer. Herein, we describe recent efforts to marry together HDAC pharmacophores, with a particular emphasis on HDAC6 selectivity, with those of other targets towards the discovery of potent therapeutics to treat these evasive diseases. Such polypharmacological agents may supercede combination therapies through inherent synergism, permitting reduced dosing, wider therapeutic windows and improved compliance.

Ruxolitinib-based combinations in the treatment of myelofibrosis: worth looking forward to

Ruxolitinib is a targeted drug to treat myelofibrosis (MF). Ruxolitinib has significant advantages in spleen reduction and increasing 5-year overall survival (OS), and ruxolitinib-based combinations might provide more benefits than ruxolitinib monotherapy. In this review, we focus on the data of ruxolitinib-based combinations therapies and treatment-related adverse events (AEs) and safety. We analyzed and summarized the data of ruxolitinib-based combinations. Ruxolitinib combined with prednisone + thalidomide + danazol (TPD), panobinostat, pracinostat, azacytidine, or hydroxyurea has well reduced spleen. Ruxolitinib combined with danazol or TPD had well therapies in improvement of hemoglobin (Hgb) and platelets (PLT). Most ruxolitinib-based combinations therapies showed a superior benefit on reduced treatment-related AEs than ruxolitinib monotherapy. Treatment-related AEs and dose modification affect the safety and tolerability of ruxolitinib-based combinations. Genetic testing before treatment is recommended. To provide better clinical guidance, comparisons of these randomized controlled trials with the trials of ruxolitinib alone are necessary. This review suggests that the clinical application of ruxolitinib-based combinations is worth waiting for.

Therapeutic targeting of JAKs: from hematology to rheumatology and from the first to the second generation of JAK inhibitors

Several cytokines and growth factors, as well as their downstream signalling pathways, are implicated in the pathogenesis of haematological and immune-mediated diseases. These mediators act through binding to their cognate receptor and activation of one or more of the four Janus family tyrosine kinases (JAKs). Gene knock-out studies together with evidence from patients carrying activating mutant forms of JAKs (eg, JAK2 V617F in myeloproliferative disorders) provided strong rationale for the development of JAK inhibitors. Based on encouraging preclinical data showing the capacity of JAK inhibitors to suppress the signalling from multiple cytokines, an extensive drug development program was set out, with the initial successful introduction of tofacitinib, baricitinib and ruxolitinib in various chronic rheumatic and myeloproliferative diseases, respectively. Importantly, advancements with the design of next-generation, hyper-selective JAK inhibitors hold promise for the better control of inflammation, while reducing the risk for harms, in an expanding spectrum of medical disorders.

Recommendations for the use of pegylated interferon-α in the treatment of classical myeloproliferative neoplasms

The classical myeloproliferative neoplasms (MPN) are uncommon clonal haemopoietic malignancies characterised by excessive production of mature blood cells. Clinically, they are associated with thrombosis, haemorrhage, varying degrees of constitutional disturbance and a risk of progression to myelofibrosis or acute myeloid leukaemia. Many of the disease manifestations may be ameliorated by treatment with interferon-α (IFN), but its use in Australian MPN patients has been limited due to the inconvenience of frequent injections and side-effects. The pegylated form of IFN is a long-acting preparation, which is better tolerated, and its Pharmaceutical Benefits Scheme listing is likely to lead to increased usage. We review the literature on risks and benefits of IFN treatment for MPN, suggest criteria for patient selection in each of these diseases and discuss strategies to manage the side-effects of pegylated IFN.

Novel strategies for the treatment of myelofibrosis driven by recent advances in understanding the role of the microenvironment in its etiology

Myelofibrosis is the advanced stage of the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), characterized by systemic inflammation, hematopoietic failure in the bone marrow, and development of extramedullary hematopoiesis, mainly in the spleen. The only potentially curative therapy for this disease is hematopoietic stem cell transplantation, an option that may be offered only to those patients with a compatible donor and with an age and functional status that may face its toxicity. By contrast, with the Philadelphia-positive MPNs that can be dramatically modified by inhibitors of the novel BCR-ABL fusion-protein generated by its genetic lesion, the identification of the molecular lesions that lead to the development of myelofibrosis has not yet translated into a treatment that can modify the natural history of the disease. Therefore, the cure of myelofibrosis remains an unmet clinical need. However, the excitement raised by the discovery of the genetic lesions has inspired additional studies aimed at elucidating the mechanisms driving these neoplasms towards their final stage. These studies have generated the feeling that the cure of myelofibrosis will require targeting both the malignant stem cell clone and its supportive microenvironment. We will summarize here some of the biochemical alterations recently identified in MPNs and the novel therapeutic approaches currently under investigation inspired by these discoveries.

Novel treatments to tackle myelofibrosis

INTRODUCTION

Despite the dramatic progress made in the treatment of patients with myelofibrosis since the introduction of the JAK1/2 inhibitor ruxolitinib, a therapeutic option that can modify the natural history of the disease and prevent evolution to blast-phase is still lacking. Recent investigational treatments including immunomodulatory drugs and histone deacetylase inhibitors benefit some patients but these effects have proven modest at best. Several novel agents do show promising activity in preclinical studies and early-phase clinical trials. We will illustrate a snapshot view of where the management of myelofibrosis is evolving, in an era of personalized medicine and advanced molecular diagnostics. Areas covered: A literature search using MEDLINE and recent meeting abstracts was performed using the keywords below. It focused on therapies in active phases of development based on their scientific and preclinical rationale with the intent to highlight agents that have novel biological effects. Expert commentary: The most mature advances in treatment of myelofibrosis are the development of second-generation JAK1/2 inhibitors and improvements in expanding access to donors for transplantation. In addition, there are efforts to identify drugs that target pathways other than JAK/STAT signaling that might improve the survival of myelofibrosis patients, and limit the need for stem-cell transplantation.

Design and synthesis of potent dual inhibitors of JAK2 and HDAC based on fusing the pharmacophores of XL019 and vorinostat

Specifically blocking more than one oncogenic pathway simultaneously in a cancer cell with a combination of different drugs is the mainstay of the majority of cancer treatments. Being able to do this via two targeted pathways without inducing side effects through a general mechanism, such as chemotherapy, could bring benefit to patients. In this work we describe a new dual inhibitor of the JAK-STAT and HDAC pathways through designing and developing two types of molecule based on the JAK2 selective inhibitor XL019 and the pan-HDAC inhibitor, vorinostat. Both series of compounds had examples with low nanomolar JAK2 and HDAC1/6 inhibition. In some cases good HDAC1 selectivity was achieved while retaining HDAC6 activity. The observed potency is explained through molecular docking studies of all three enzymes. One example, 69c had 16-25 fold selectivity against the three other JAK-family proteins JAK1, JAK3 and TYK2. A number of compounds had sub-micromolar potencies against a panel of 4 solid tumor cell lines and 4 hematological cell lines with the most potent compound, 45h, having a cellular IC₅₀ of 70 nM against the multiple myeloma cell line KMS-12-BM. Evidence of both JAK and HDAC pathway inhibition is presented in Hela cells showing that both pathways are modulated. Evidence of apoptosis with two compounds in 4 sold tumor cell lines is also presented.