Evolving Therapeutic Strategies for the Classic Philadelphia-Negative Myeloproliferative Neoplasms

A Broad Overview of Signaling in Ph-Negative Classic Myeloproliferative Neoplasms

Simple Summary

There is growing evidence that Ph-negative myeloproliferative neoplasms are disorders in which multiple signaling pathways are significantly disturbed. The heterogeneous phenotypes observed among patients have highlighted the importance of having a comprehensive knowledge of the molecular mechanisms behind these diseases. This review aims to show a broad overview of the signaling involved in myeloproliferative neoplasms (MPNs) and other processes that can modify them, which could be helpful to better understand these diseases and develop more effective targeted treatments.

Abstract

Ph-negative myeloproliferative neoplasms (polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF)) are infrequent blood cancers characterized by signaling aberrations. Shortly after the discovery of the somatic mutations in JAK2, MPL, and CALR that cause these diseases, researchers extensively studied the aberrant functions of their mutant products. In all three cases, the main pathogenic mechanism appears to be the constitutive activation of JAK2/STAT signaling and JAK2-related pathways (MAPK/ERK, PI3K/AKT). However, some other non-canonical aberrant mechanisms derived from mutant JAK2 and CALR have also been described. Moreover, additional somatic mutations have been identified in other genes that affect epigenetic regulation, tumor suppression, transcription regulation, splicing and other signaling pathways, leading to the modification of some disease features and adding a layer of complexity to their molecular pathogenesis. All of these factors have highlighted the wide variety of cellular processes and pathways involved in the pathogenesis of MPNs. This review presents an overview of the complex signaling behind these diseases which could explain, at least in part, their phenotypic heterogeneity.

HDAC8 overexpression in mesenchymal stromal cells from JAK2+ myeloproliferative neoplasms: a new therapeutic target?

Histone deacetylases (HDACs) are involved in epigenetic modulation and their aberrant expression has been demonstrated in myeloproliferative neoplasms (MPN). HDAC8 inhibition has been shown to inhibit JAK2/STAT5 signaling in hematopoietic cells from MPN. Nevertheless, the role of HDAC8 expression in bone marrow-mesenchymal stromal cells (BM-MSC) has not been assessed. In the current work we describe that HDAC8 is significantly over-expressed in MSC from in JAK-2 positive MPN compared to those from healthy-donors (HD-MSC). Using a selective HDAC8 inhibitor (PCI34051), we verified that the subsequent decrease in the protein and mRNA expression of HDAC8 is linked with an increased apoptosis of malignant MSC whereas it has no effects on normal MSC. In addition, HDAC8 inhibition in MPN-MSC also decreased their capacity to maintain neoplastic hematopoiesis, by increasing the apoptosis, cell-cycle arrest and colony formation of JAK2⁺-hematopoietic cells. Mechanistic studies using different MPN cell lines revealed that PCI34051 induced their apoptosis, which is enhanced when were co-cultured with JAK2V617F-MSC, decreased their colony formation and the phosphorylation of STAT3 and STAT5. In summary, we show for the first time that the inhibition of HDAC8 in MSC from JAK2⁺ MPN patients selectively decreases their hematopoietic-supporting ability, suggesting that HDAC8 may be a potential therapeutic target in this setting by acting not only on hematopoietic cells but also on the malignant microenvironment.

The BCR-ABL1-negative myeloproliferative neoplasms: a review of JAK inhibitors in the therapeutic armamentarium

INTRODUCTION

The classical BCR-ABL1-negative myeloproliferative neoplasms (MPN) include primary myelofibrosis (PMF), polycythemia vera (PV) and essential thrombocythemia (ET). They are characterized by stem cell-derived clonal proliferation, harbor Janus kinase 2 (JAK2), or calreticulin (CALR), or myeloproliferative leukemia virus oncogene (MPL) driver mutations and exert an over activated JAK-signal transducer and activator of transcription (STAT) pathway. Therefore JAK inhibiting strategies have been successfully investigated in MPN clinical trials. Areas covered: The present review aims to provide a concise overview of the current and future role of JAK inhibitors in the therapeutic armamentarium of MPN. Expert opinion: The JAK1/JAK2 inhibitor ruxolitinib has clearly enriched the therapeutic armamentarium of MPN and is now licenced for more than five years in MF and over three years as second line in PV. Momelotinib, although of limited activity in MPN trials, demonstrated unique property of improving MF associated anemia. Less myelosuppressive or more selective JAK inhibitors like pacritinib, NS-01872 or Itacitinib are new promising agents tested in MF. JAK inhibition has become a cornerstone of MPN therapy and future efforts focus on ruxolitinib-based combinations and new JAK inhibitors.

The impact of myeloproliferative neoplasms (MPNs) on patient quality of life and productivity: results from the international MPN Landmark survey

Myelofibrosis (MF), polycythemia vera (PV), and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPNs) associated with high disease burden, reduced quality of life (QOL), and shortened survival. To assess how MPNs affect patients, we conducted a global MPN Landmark survey. This online survey of patients with MPNs and physicians was conducted in Australia, Canada, Germany, Japan, Italy, and the United Kingdom. The survey measured MPN-related symptoms and the impact of MPNs on QOL and the ability to work as well as disease-management strategies. Overall, 219 physicians and 699 patients (MF, n = 174; PV, n = 223; ET, n = 302) completed the survey; 90% of patients experienced MPN-related symptoms. The most frequent and severe symptom was fatigue. Most patients experienced a reduction in QOL, including those with low symptom burden or low-risk scores. A substantial proportion of patients reported impairment at work and in overall activity. Interestingly, physician feedback and blood counts were the most important indicators of treatment success among patients, with improvements in symptoms and QOL being less important. Regarding disease management, our study revealed a lack of alignment between physician and patient perceptions relating to communication and disease management, with patients often having different treatment goals than physicians. Overall, our study suggested that therapies that reduce symptom burden and improve QOL in patients with MPNs are crucial in minimizing disease impact on patient daily lives. Additionally, our findings showed a need for improved patient-physician communication, standardized monitoring of symptoms, and agreement on treatment goals.