AKT is a therapeutic target in myeloproliferative neoplasms

Gadd45g insufficiency drives the pathogenesis of myeloproliferative neoplasms

Despite the identification of driver mutations leading to the initiation of myeloproliferative neoplasms (MPNs), the molecular pathogenesis of MPNs remains incompletely understood. Here, we demonstrate that growth arrest and DNA damage inducible gamma (GADD45g) is expressed at significantly lower levels in patients with MPNs, and JAK2V617F mutation and histone deacetylation contribute to its reduced expression. Downregulation of GADD45g plays a tumor-promoting role in human MPN cells. Gadd45g insufficiency in the murine hematopoietic system alone leads to significantly enhanced growth and self-renewal capacity of myeloid-biased hematopoietic stem cells, and the development of phenotypes resembling MPNs. Mechanistically, the pathogenic role of GADD45g insufficiency is mediated through a cascade of activations of RAC2, PAK1 and PI3K-AKT signaling pathways. These data characterize GADD45g deficiency as a novel pathogenic factor in MPNs.

Phase 2 study of add-on parsaclisib for patients with myelofibrosis and suboptimal response to ruxolitinib: final results

ABSTRACT

Ruxolitinib reduces spleen volume, improves symptoms, and increases survival in patients with intermediate- or high-risk myelofibrosis. However, suboptimal response may occur, potentially because of signaling via the phosphoinositide 3-kinase (PI3K)/protein kinase B pathway. This phase 2 study evaluated dosing, efficacy, and safety of add-on PI3Kδ inhibitor parsaclisib for patients with primary or secondary myelofibrosis with suboptimal response to ruxolitinib. Eligible patients remained on a stable ruxolitinib dose and received add-on parsaclisib 10 or 20 mg, once daily for 8 weeks, and once weekly thereafter (daily-to-weekly dosing; n = 32); or parsaclisib 5 or 20 mg, once daily for 8 weeks, then 5 mg once daily thereafter (all-daily dosing; n = 42). Proportion of patients achieving a ≥10% decrease in spleen volume at 12 weeks was 28% for daily-to-weekly dosing and 59.5% for all-daily dosing. Proportions of patients achieving ≥50% decrease at week 12 in Myelofibrosis Symptom Assessment Form and Myeloproliferative Neoplasms Symptom Assessment Form symptom scores were 14% and 18% for daily-to-weekly dosing, and 28% and 32% for all-daily dosing, respectively. Most common nonhematologic treatment-emergent adverse events were nausea (23%), diarrhea (22%), abdominal pain and fatigue (each 19%), and cough and dyspnea (each 18%). New-onset grade 3 and 4 thrombocytopenia were observed in 19% of patients, each dosed daily-to-weekly, and in 26% and 7% of patients dosed all-daily, respectively, managed with dose interruptions. Hemoglobin levels remained steady. The addition of parsaclisib to stable-dose ruxolitinib can reduce splenomegaly and improve symptoms, with manageable toxicity in patients with myelofibrosis with suboptimal response to ruxolitinib. This trial was registered at www.clinicaltrials.gov as #NCT02718300.

Danggui Jixueteng decoction for the treatment of myelosuppression after chemotherapy: A combined metabolomics and network pharmacology analysis

Objective

This study aimed to explore the mechanism of the Danggui Jixueteng decoction (DJD) in treating Myelosuppression after chemotherapy (MAC) through network pharmacology and metabolomics.

Methods

We obtained the chemical structures of DJD compounds from TCMSP and PubMed. SwissTargetPrediction, STITCH, CTD, GeneCards, and OMIM were utilized to acquire component targets and MAC-related targets. We identified the key compounds, core targets, main biological processes, and signaling pathways related to DJD by constructing and analyzing related networks. The main active compounds and key proteins of DJD in treating AA were confirmed by molecular docking. A MAC rat model was established through intraperitoneal injection of cyclophosphamide to confirm DJD's effect on the bone marrow hematopoietic system. Untargeted metabolomics analyzed serum metabolite differences between MAC rats and the control group, and before and after DJD treatment, to explore DJD's mechanism in treating MAC.

Results

Of the 93 active compounds identified under screening conditions, 275 compound targets and 3113 MAC-related targets were obtained, including 95 intersecting targets; AKT1, STAT3, CASP3, and JUN were key proteins in MAC treatment. The phosphatidylinositol-3-kinase/RAC-alpha serine/threonine-protein kinase (PI3K/AKT) signaling pathway may play a crucial role in MAC treatment with DJD. Molecular docking results showed good docking effects of key protein AKT1 with luteolin, β-sitosterol, kaempferol, and glycyrrhizal chalcone A. In vivo experiments indicated that, compared to the model group, in the DJD group, levels of WBCs, RBCs, HGB, and PLTs in peripheral blood cells, thymus index increased, spleen index decreased, serum IL-3, GM-CSF levels increased, and IL-6, TNF-α, and VEGF levels decreased (p < 0.01); the pathological morphology of femoral bone marrow improved. Eleven differential metabolites were identified as differential serum metabolites, mainly concentrated in phenylalanine, tyrosine, and tryptophan biosynthesis pathways, phenylalanine metabolism, and arachidonic acid metabolism.

Conclusion

This study revealed that DJD's therapeutic effects are due to multiple ingredients, targets, and pathways. DJD may activate the PI3K/AKT signaling pathway, promote hematopoietic-related cytokine production, regulate related metabolic pathways, and effectively alleviate cyclophosphamide-induced myelosuppression after chemotherapy in rats.

Multiomic profiling reveals metabolic alterations mediating aberrant platelet activity and inflammation in myeloproliferative neoplasms

Platelets from patients with myeloproliferative neoplasms (MPNs) exhibit a hyperreactive phenotype. Here, we found elevated P-selectin exposure and platelet-leukocyte aggregates indicating activation of platelets from essential thrombocythemia (ET) patients. Single-cell RNA-seq analysis of primary samples revealed significant enrichment of transcripts related to platelet activation, mTOR, and oxidative phosphorylation in ET patient platelets. These observations were validated via proteomic profiling. Platelet metabolomics revealed distinct metabolic phenotypes consisting of elevated ATP generation accompanied by increases in the levels of multiple intermediates of the tricarboxylic acid cycle, but lower α-ketoglutarate (α-KG) in MPN patients. Inhibition of PI3K/AKT/mTOR signaling significantly reduced metabolic responses and hyperreactivity in MPN patient platelets, while α-KG supplementation markedly reduced oxygen consumption and ATP generation. Ex vivo incubation of platelets from both MPN patients and Jak2 V617F-knockin mice with α-KG supplementation significantly reduced platelet activation responses. Oral α-KG supplementation of Jak2 V617F mice decreased splenomegaly and reduced hematocrit, monocyte, and platelet counts. Finally, α-KG treatment significantly decreased proinflammatory cytokine secretion from MPN CD14+ monocytes. Our results reveal a previously unrecognized metabolic disorder in conjunction with aberrant PI3K/AKT/mTOR signaling that contributes to platelet hyperreactivity in MPN patients.

Assessment of intestinal status in MPLW515L mutant myeloproliferative neoplasms mice model

The MPLW515L mutation is a prevalent genetic mutation in patients with myeloproliferative neoplasms (MPN), and utilizing this mutation in mice model can provide important insights into the disease. However, the relationship between intestinal homeostasis and MPN mice model remains elusive. In this study, we utilized a retroviral vector to transfect hematopoietic stem cells with the MPLW515L mutation, creating mutated MPN mice model to investigate their intestinal status. Our results revealed that the MPLW515L in MPN mice model aggravated inflammation in the intestines, decreased the levels of tight junction proteins and receptors for bacteria metabolites. Additionally, there was increased activation of the caspase1/IL-1β signaling pathway and a significant reduction in phos-p38 levels in the intestinal tissue in MPN mice. The MPLW515L mutation also led to up-expression of anti-microbial genes in the intestinal tract. Though the mutation had no impact on the alpha diversity and dominant bacterial taxa, it did influence the rare bacterial taxa/sub-communities and consequently impacted intestinal homeostasis. Our findings demonstrate the significance of MPLW515L mice model for studying MPN disease and highlight the mutation's influence on intestinal homeostasis, including inflammation, activation of the IL-1β signaling pathway, and the composition of gut microbial communities.

JAK2 inhibitors for the treatment of Philadelphia-negative myeloproliferative neoplasms: current status and future directions

The overactivation of Janus kinases 2 (JAK2) by gain-of-function mutations in the JAK2, Myeloproliferative leukemia virus oncogene, or Calreticulin genes are the most important factor in the development of Philadelphia-negative myeloproliferative neoplasms (MPNs). The discovery of the JAK2V617F mutation is a significant breakthrough in understanding the pathogenesis of MPNs, and inhibition of JAK2 abnormal activation has become one of the most effective strategies against MPNs. Currently, three JAK2 inhibitors for treating MPNs have been approved, and several are being evaluated in clinical trials. However, persistent challenges in terms of drug resistance and off-target effects remain unresolved. In this review, we introduce and classify the available JAK2 inhibitors in terms of their mechanisms and clinical considerations. Additionally, through an analysis of target points, binding modes, and structure-activity inhibitor relationships, we propose strategies such as combination therapy and allosteric inhibitors to overcome specific challenges. This review offers valuable insights into current trends and future directions for optimal management of MPNs using JAK2 inhibitors.

Enkurin: a novel marker for myeloproliferative neoplasms from platelet, megakaryocyte, and whole blood specimens

Impaired protein homeostasis, though well established in age-related disorders, has been recently linked with the pathogenesis of myeloproliferative neoplasms (MPNs). However, little is known about MPN-specific modulators of proteostasis, thus impeding our ability for increased mechanistic understanding and discovery of additional therapeutic targets. Loss of proteostasis, in itself, is traced to dysregulated mechanisms in protein folding and intracellular calcium signaling at the endoplasmic reticulum (ER). Here, using ex vivo and in vitro systems (including CD34+ cultures from patient bone marrow and healthy cord/peripheral blood specimens), we extend our prior data from platelet RNA sequencing in patients with MPN and discover select proteostasis-associated markers at RNA and/or protein levels in each of platelet, parent megakaryocyte, and whole blood specimens. Importantly, we identify a novel role in MPNs for enkurin (ENKUR), a calcium mediator protein originally implicated only in spermatogenesis. Our data reveal consistent ENKUR downregulation at both RNA and protein levels across specimens from patients with MPN and experimental models (including upon treatment with thapsigargin, an agent that causes protein misfolding in the ER by selective loss of calcium), with a concomitant upregulation of a cell cycle marker, CDC20. Silencing of ENKUR using short hairpin RNA in CD34+-derived megakaryocytes further confirms this association with CDC20 at both RNA and protein levels and indicates a likely role for the PI3K/Akt pathway. Together, our work sheds light on enkurin as a novel marker of MPN pathogenesis and indicates further mechanistic investigation into a role for dysregulated calcium homeostasis and ER and protein folding stress in MPN transformation.

Recent advances in therapies for primary myelofibrosis

Primary myelofibrosis (PMF), polycythemia vera (PV) and essential thrombocythemia (ET) form the classical BCR-ABL1-negative myeloproliferative neoplasms (MPNs) that are driven by a constitutive activation of JAK2 signaling. PMF as well as secondary MF (post-ET and post-PV MF) are the most aggressive MPNs. Presently, there is no curative treatment, except allogenic hematopoietic stem cell transplantation. JAK inhibitors, essentially ruxolitinib, are the therapy of reference for intermediate and high-risk MF. However, presently the current JAK inhibitors behave mainly as anti-inflammatory drugs, improving general symptoms and spleen size without major impact on disease progression. A better understanding of the genetics of MF, the biology of its leukemic stem cells (LSCs), the mechanisms of fibrosis and of cytopenia and the role of inflammatory cytokines has led to new approaches with the development of numerous therapeutic agents that target epigenetic regulation, telomerase, apoptosis, cell cycle, cytokines and signaling. Furthermore, the use of a new less toxic form of interferon-α has been revived, as it is presently one of the only molecules that targets the mutated clone. These new approaches have different aims: (a) to provide alternative therapy to JAK inhibition; (b) to correct cytopenia; and (c) to inhibit fibrosis development. However, the main important goal is to find new disease modifier treatments, which will profoundly modify the progression of the disease without major toxicity. Presently the most promising approaches consist of the inhibition of telomerase and the combination of JAK2 inhibitors (ruxolitinib) with either a BCL2/BCL-xL or BET inhibitor. Yet, the most straightforward future approaches can be considered to be the development of and/or selective inhibition of JAK2V617F and the targeting MPL and calreticulin mutants by immunotherapy. It can be expected that the therapy of MF will be significantly improved in the coming years.

Enkurin: A novel marker for myeloproliferative neoplasms from platelet, megakaryocyte, and whole blood specimens

Impaired protein homeostasis, though well established in age-related disorders, has been linked in recent research with the pathogenesis of myeloproliferative neoplasms (MPNs). As yet, however, little is known about MPN-specific modulators of proteostasis, thus impeding our ability for increased mechanistic understanding and discovery of additional therapeutic targets. Loss of proteostasis, in itself, is traced to dysregulated mechanisms in protein folding and intracellular calcium signaling at the endoplasmic reticulum (ER). Here, using ex vivo and in vitro systems (including CD34 + cultures from patient bone marrow, and healthy cord/peripheral blood specimens), we extend our prior data from MPN patient platelet RNA sequencing, and discover select proteostasis-associated markers at RNA and/or protein levels in each of platelets, parent megakaryocytes, and whole blood specimens. Importantly, we identify a novel role in MPNs for enkurin ( ENKUR ), a calcium mediator protein, implicated originally only in spermatogenesis. Our data reveal consistent ENKUR downregulation at both RNA and protein levels across MPN patient specimens and experimental models, with a concomitant upregulation of a cell cycle marker, CDC20 . Silencing of ENKUR by shRNA in CD34 + derived megakaryocytes further confirm this association with CDC20 at both RNA and protein levels; and indicate a likely role for the PI3K/Akt pathway. The inverse association of ENKUR and CDC20 expression was further confirmed upon treatment with thapsigargin (an agent that causes protein misfolding in the ER by selective loss of calcium) in both megakaryocyte and platelet fractions at RNA and protein levels. Together, our work sheds light on enkurin as a novel marker of MPN pathogenesis beyond the genetic alterations; and indicates further mechanistic investigation into a role for dysregulated calcium homeostasis, and ER and protein folding stress in MPN transformation.

VISUAL ABSTRACT

Key Points

Enkurin, a calcium adaptor protein, is identified as a novel marker of pathogenesis in MPNs.MPN megakaryocyte and platelet expression of enkurin at RNA and protein levels is inversely associated with a cell differentiation cycle gene, CDC20.Likely role for dysregulated calcium homeostasis, and ER and protein folding stress in MPN transformation.

Combined treatment with ruxolitinib and MK-2206 inhibits the JAK2/STAT5 and PI3K/AKT pathways via apoptosis in MDA-MB-231 breast cancer cell line

BACKGROUND

Due to deficiencies in the expression of hormone receptors, such as PR, ER and HER2, it is challenging to treat triple-negative breast cancer, which does not respond to single targeted therapy. Ruxolitinib is a Janus kinase (JAK)1/JAK2 inhibitor. MK-2206 is an allosteric AKT inhibitor. Due to the limited activities of ruxolitinib and MK-2206 for monotherapy, the need for cotreatment with other drugs has emerged. This study is the first to examine the effects of ruxolitinib and MK-2206 cotreatment on apoptosis and JAK2/STAT5 and PI3K/AKT signaling in MDA-MB-231 breast cancer cells. Additionally, this work aimed to decrease the side effects of ruxolitinib and increase its anticancer effects with MK-2206 cotreatment.

METHODS AND RESULTS

Cell viability was reduced in a dose- and time-dependent manner after exposure to ruxolitinib, MK-2206 or both for 48 h, as shown by MTT assay. Ruxolitinib had a synergistic antiproliferative effect, as demonstrated by colony formation and wound healing assays. The effects of ruxolitinib, MK-2206 and their combination on apoptosis, as well as PI3K/AKT and JAK/STAT signaling, were examined by western blot analyses. Cotreatment with ruxolitinib and MK-2206 reduced proliferation with the dual inhibition of JAK2/STAT5 and PI3K/AKT signaling by decreasing PI3K, AKT, JAK2, STAT5, Caspase-9, Caspase-7, PARP, c-Myc, and Bcl-2 and increasing P53 and PTEN protein expression.

CONCLUSIONS

Our results revealed the roles of P53 and PTEN in the regulation of apoptosis and the PI3K/AKT and JAK2/STAT5 signaling pathways. The dual inhibition of JAK2/STAT5 and PI3K/AKT may reduce metastasis by decreasing tumor cell survival.

Targeting the PI3K pathway in myeloproliferative neoplasms

INTRODUCTION

Decreasing efficacy over time and initial suboptimal response to Janus kinase (JAK) inhibitors such as ruxolitinib in a subset of patients are critical clinical challenges associated with myeloproliferative neoplasms (MPNs), primarily myelofibrosis.

AREAS COVERED

The role of phosphatidylinositol-3 kinase (PI3K) in MPN disease progression and treatment resistance and as a potential therapeutic target in patients who experience loss of response to JAK inhibition is discussed. Understanding the complex signaling networks involved in the pathogenesis of MPNs has identified potentially novel therapeutic targets and treatment strategies, such as inhibiting other signaling pathways in addition to the JAK/signal transducer and activator of transcription (STAT) pathway. PI3K plays a crucial role downstream of JAK signaling in rescuing tumor cell proliferation, with PI3Kδ being particularly important in hematologic malignancies. Concurrent targeting of both PI3K and JAK/STAT pathways may offer an innovative therapeutic strategy to maximize efficacy.

EXPERT OPINION

Based on our understanding of the underlying mechanisms and the role of PI3K pathway signaling in the loss of response or resistance to JAK inhibitor treatment and initial results from clinical studies, the combination of parsaclisib (PI3Kδ inhibitor) and ruxolitinib holds great clinical potential. If confirmed in larger clinical trials, parsaclisib may provide more treatment options and improve clinical outcomes for patients with MPNs.

JAK2-V617F is a negative regulation factor of SHIP1 protein and thus influences the AKT signaling pathway in patients with Myeloproliferative Neoplasm (MPN)

BACKGROUND

Myeloproliferative neoplasms (MPN) are a group of chronic haematological disorders. At the molecular level of MPN cells, the gain-of-function mutation V617F of the Janus kinase 2 (JAK2) leads to a constitutive activation of the downstream signaling cascade and is a conventional criteria for diagnosis. Here, the functional role of the tumor suppressor SHIP1 (SH2 domain containing inositol-5 phosphatase 1) in the pathogenesis of MPNs was investigated.

METHODS

Primary blood samples of MPN-patients were analysed using Western Blot technique regarding the level of SHIP1 expression. Moreover, SHIP1 and SHIP1-mutations were lentivirally transduced in the JAK2-V617F-positive UKE-1 cell line and expression was monitored over time. In addition, we examined SHIP1 reconstitution by inhibition of JAK2-V617F. Furthermore, we transfected SHIP1-expressing cells with a JAK2-V617F respectively a BCR-ABL construct and investigated changes in SHIP1 expression.

RESULTS

Four out of five MPN-patient samples showed a loss or a reduction in SHIP1 expression. We identified JAK2 as a negative regulator of SHIP1 expression in MPN cells and inhibition of JAK2-V617F implicates a reconstituted SHIP1 expression. This is significant because SHIP1 negatively regulates the AKT signaling pathway and in consequence the reconstitution of SHIP1 expression leads to a decreased cell growth. Moreover, we examined the impact of SHIP1 and patient-derived SHIP1-mutations on AKT phosphorylation and show the benefit of a combined therapy in MPN cells with inhibitors of the AKT/mTOR pathway.

CONCLUSION

In summary, the data suggest that SHIP1 may play a role during the development of MPNs and could be the basis for establishing a targeted therapy.

JAK2 inhibitor persistence in MPN: uncovering a central role of ERK activation

The Philadelphia chromosome negative myeloproliferative neoplasms, including polycythemia vera, essential thrombocytosis, and myelofibrosis, are driven by hyper activation of the JAK2 tyrosine kinase, the result of mutations in three MPN driving genes: JAK2, MPL, and CALR. While the anti-inflammatory effects of JAK2 inhibitors can provide improved quality of life for many MPN patients, the upfront and persistent survival of disease-driving cells in MPN patients undergoing JAK2 inhibitor therapy thwarts potential for remission. Early studies indicated JAK2 inhibitor therapy induces heterodimeric complex formation of JAK2 with other JAK family members leading to sustained JAK2-dependent signaling. Recent work has described novel cell intrinsic details as well as cell extrinsic mechanisms that may contribute to why JAK2 inhibition may be ineffective at targeting MPN driving cells. Diverse experimental strategies aimed at uncovering mechanistic details that contribute to JAK2 inhibitor persistence have each highlighted the role of MEK/ERK activation. These approaches include, among others, phosphoproteomic analyses of JAK2 signaling as well as detailed assessment of JAK2 inhibition in mouse models of MPN. In this focused review, we highlight these and other studies that collectively suggest targeting MEK/ERK in combination with JAK2 inhibition has the potential to improve the efficacy of JAK2 inhibitors in MPN patients. As MPN patients patiently wait for improved therapies, such studies should further strengthen optimism that pre-clinical research is continuing to uncover mechanistic insights regarding the ineffectiveness of JAK2 inhibitors, which may lead to development of improved therapeutic strategies.

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.

The Synergistic Inhibitory Effect of Combining MK-2206 and AZD 6244 in MARIMO Cells Harboring a Calreticulin Gene Mutation

INTRODUCTION

Somatic mutations in the calreticulin (CALR) gene occur in most myeloproliferative neoplasm (MPN) patients who lack Janus kinase 2 or thrombopoietin receptor (MPL) mutations, but the molecular pathogenesis of MPN with mutated CALR is unclear, which limited the further treatment for CALR gene mutant patients.

OBJECTIVES

Previous studies showed that CALR mutations not only activated serine/threonine protein kinase (AKT) in primary mouse bone marrow cells but also mitogen-activated protein kinases (MAPKs) in MARIMO cells harboring a heterozygous 61-bp deletion in CALR exon 9, which were responsible for mutant CALR cell survival, respectively. Hence, we aimed to initially explore the mechanism of AKT activation and observe the synergistic inhibitory effect of combining AKT (MK-2206) and MAPK kinase (AZD 6244) inhibitors in MARIMO cells.

METHODS

We detected the expression of phosphorylated AKT in MARIMO cells treated with inhibitors for 24 or 48 h by western blotting and analyzed cell proliferation, cell cycle, and apoptosis by flow cytometry. We further examined the synergistic inhibitory effect of combining MK-2206 and AZD 6244 in MARIMO cells using the median effect principle of Chou and Talalay.

RESULTS

We found that the AKT was activated in MARIMO cells, and blocking its activity significantly inhibited MARIMO cell growth with downregulation of cyclin D and E, and accelerated cell apoptosis by decreasing Bcl-2 but increasing Bax and cleaved caspase-3 levels in a dose-dependent manner. Further analysis showed that AKT activation was dependent on mammalian target of rapamycin but not on the JAK signaling pathway in MARIMO cells, displaying that inhibition of JAK activity by ruxolitinib (RUX) did not decrease the AKT phosphorylation. Furthermore, the combination of MK-2206 and AZD 6244 produced a significantly synergistic inhibitory effect on MARIMO cells.

CONCLUSIONS

AKT activation is a feature of MARIMO cells and co-targeting of AKT and MAPKs signaling pathways synergistically inhibits MARIMO cell growth.

JAK-STAT signaling in human disease: From genetic syndromes to clinical inhibition

Since its discovery, the Janus kinase-signal transduction and activation of transcription (JAK-STAT) pathway has become recognized as a central mediator of widespread and varied human physiological processes. The field of JAK-STAT biology, particularly its clinical relevance, continues to be shaped by 2 important advances. First, the increased use of genomic sequencing has led to the discovery of novel clinical syndromes caused by mutations in JAK and STAT genes. This has provided insights regarding the consequences of aberrant JAK-STAT signaling for immunity, lymphoproliferation, and malignancy. In addition, since the approval of ruxolitinib and tofacitinib, the therapeutic use of JAK inhibitors (jakinibs) has expanded to include a large spectrum of diseases. Efficacy and safety data from over a decade of clinical studies have provided additional mechanistic insights while improving the care of patients with inflammatory and neoplastic conditions. This review discusses major advances in the field, focusing on updates in genetic diseases and in studies of clinical jakinibs in human disease.

The Next Generation of JAK Inhibitors: an Update on Fedratinib, Momelotonib, and Pacritinib

PURPOSE OF REVIEW

Ruxolitinib is the first FDA-approved JAK inhibitor for the treatment of myeloproliferative neoplasms and is an effective means of controlling symptom burden and improving splenomegaly. However, a majority of patients will develop disease progression with long-term use. Fedratinib, momelotinib, and pacritinib are three newer-generation JAK inhibitors being prospectively evaluated and we will discuss their roles in the treatment of myeloproliferative neoplasms.

RECENT FINDINGS

Fedratinib has a role in both JAK-inhibitor naive intermediate-/high-risk myelofibrosis patients and in patients that have previously received ruxolitinib. It has recently received FDA approval for these indications as well. Momelotinib does not appear to have an advantage over ruxolitinib with regards to improving splenomegaly in intermediate-/high-risk JAK-inhibitor naive myelofibrosis. However, increased rates of transfusion independence have been noted with momelotinib. Pacritinib has been studied in myelofibrosis patients with significant baseline anemia and thrombocytopenia; these trials support the use of pacritinib in myelofibrosis patients with significant thrombocytopenia. While ruxolitinib is effective in reducing the symptom burden and splenomegaly of patients with myeloproliferative neoplasms, a majority of patients will ultimately progress on therapy. Newer-generation JAK inhibitors including fedratinib, momelotinib, and pacritinib are being prospectively evaluated to determine their appropriate roles in the management of myeloproliferative neoplasms. In addition, both combination therapies with JAK inhibitors and novel investigational therapies are being actively explored.

MAPK14 over-expression is a transcriptomic feature of polycythemia vera and correlates with adverse clinical outcomes

Background

The transcriptomic signature has not been fully elucidated in PV, as well as mRNA markers for clinical variables (thrombosis, leukemic transformation, survival, etc.). We attempted to reveal and validate crucial co-expression modules and marker mRNAs correlating with polycythemia vera (PV) by weighted gene co-expression network analysis (WGCNA).

Material and methods

The GSE57793/26014/61629 datasets were downloaded from Gene Expression Omnibus (GEO) database and integrated into one fused dataset. By R software and ‘WGCNA’ package, the PV-specific co-expression module was identified, the pathway enrichment profile of which was obtained by over-representation analysis (ORA). Protein–protein interaction (PPI) network and hub gene analysis identified MAPK14 as our target gene. Then the distribution of MAPK14 expression in different disease/mutation types, were depicted based on external independent datasets. Genome-scale correlation analysis revealed the association of MAPK14 and JAK/STAT family genes. Then gene set enrichment analysis (GSEA) was performed to detect the activated and suppressed pathways associating with MAPK14 expression. Moreover, GSE47018 dataset was utilized to compare clinical variables (thrombosis, leukemic transformation, survival, etc.) between MAPK14-high and MAPK14-low groups.

Results

An integrated dataset including 177 samples (83 PV, 35 ET, 17 PMF and 42 normal donors) were inputted into WGCNA. The ‘tan’ module was identified as the PV-specific module (R² = 0.56, p = 8e−16), the genes of which were dominantly enriched in pro-inflammatory pathways (Toll-like receptor (TLR)/TNF signaling, etc.). MAPK14 is identified as the top hub gene in PV-related PPI network with the highest betweenness. External datasets validated that the MAPK14 expression was significantly higher in PV than that of essential thrombocytosis (ET)/primary myelofibrosis (PMF) patients and normal donors. JAK2 homozygous mutation carriers have higher level of MAPK14 than that of other mutation types. The expression of JAK/STAT family genes significantly correlated with MAPK14, which also contributed to the activation of oxidated phosphorylation, interferon-alpha (IFNα) response and PI3K-Akt-mTOR signaling, etc. Moreover, MAPK14-high group have more adverse clinical outcomes (splenectomy, thrombosis, disease aggressiveness) and inferior survival than MAPK14-low group.

Conclusion

MAPK14 over-expression was identified as a transcriptomic feature of PV, which was also related to inferior clinical outcomes. The results provided novel insights for biomarkers and therapeutic targets for PV.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02913-3.

RAS/CBL mutations predict resistance to JAK inhibitors in myelofibrosis and are associated with poor prognostic features

The dysregulation of the JAK/STAT pathway drives the pathogenesis of myelofibrosis (MF). Recently, several JAK inhibitors (JAKis) have been developed for treating MF. Select mutations (MTs) have been associated with impaired outcomes and are currently incorporated in molecularly annotated prognostic models. Mutations of RAS/MAPK pathway genes are frequently reported in cancer and at low frequencies in MF. In this study, we investigated the phenotypic, prognostic, and therapeutic implications of NRASMTs, KRASMTs, and CBLMTs (RAS/CBLMTs) in 464 consecutive MF patients. A total of 59 (12.7%) patients had RAS/CBLMTs: NRASMTs, n = 25 (5.4%); KRASMTs, n = 13 (2.8%); and CBLMTs, n = 26 (5.6%). Patients with RAS/CBLMTs were more likely to present with high-risk clinical and molecular features. RAS/CBLMTs were associated with inferior overall survival compared with patients without MTs and retained significance in a multivariate model, including the Mutation-Enhanced International Prognostic Score System (MIPSS70) risk factors and cytogenetics; however, inclusion of RAS/CBLMTs in molecularly annotated prognostic models did not improve the predictive power of the latter. The 5-year cumulative incidence of leukemic transformation was notably higher in the RAS/CBLMT cohort. Among 61 patients treated with JAKis and observed for a median time of 30 months, the rate of symptoms and spleen response at 6 months was significantly lower in the RAS/CBLMT cohort. Logistic regression analysis disclosed a significant inverse correlation between RAS/CBLMTs and the probability of achieving a symptom or spleen response that was retained in multivariate analysis. In summary, our study showed that RAS/CBLMTs are associated with adverse phenotypic features and survival outcomes and, more important, may predict reduced response to JAKis.

Disease modifying agents of myeloproliferative neoplasms: a review

The identification of driver mutations in Janus kinase (JAK) 2, calreticulin (CALR), and myeloproliferative leukemia (MPL) has contributed to a better understanding of disease pathogenesis by highlighting the importance of JAK signal transducer and activator of transcription (STAT) signaling in classical myeloproliferative neoplasms (MPNs). This has led to the therapeutic use of novel targeted treatments, such as JAK2 inhibitors. More recently, with the development of next-generation sequencing, additional somatic mutations, which are not restricted to MPNs, have been elucidated. Treatment decisions for MPN patients are influenced by the MPN subtype, symptom burden, and risk classification. Although prevention of vascular events is the main objective of therapy for essential thrombocythemia (ET) and polycythemia vera (PV) patients, disease-modifying drugs are needed to eradicate clonal hematopoiesis and prevent progression to more aggressive myeloid neoplasms. JAK inhibitors are a valuable therapeutic strategy for patients with myelofibrosis (MF) who have splenomegaly and/or disease-related symptoms, but intolerance, refractory, resistance, and disease progression still present challenges. Currently, allogeneic stem cell transplantation remains the only curative treatment for MF, but it is typically limited by age-related comorbidities and high treatment-related mortality. Therefore, a better understanding of the molecular pathogenesis and potential new therapies with the aim of modifying the natural history of the disease is important. In this article, I review the current understanding of the molecular basis of MPNs and clinical studies on potential disease-modifying agents.

Focus on Osteosclerotic Progression in Primary Myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by hematopoietic stem-cell-derived clonal proliferation, leading to bone marrow (BM) fibrosis. Hematopoiesis alterations are closely associated with modifications of the BM microenvironment, characterized by defective interactions between vascular and endosteal niches. As such, neoangiogenesis, megakaryocytes hyperplasia and extensive bone marrow fibrosis, followed by osteosclerosis and bone damage, are the most relevant consequences of PMF. Moreover, bone tissue deposition, together with progressive fibrosis, represents crucial mechanisms of disabilities in patients. Although the underlying mechanisms of bone damage observed in PMF are still unclear, the involvement of cytokines, growth factors and bone marrow microenvironment resident cells have been linked to disease progression. Herein, we focused on the role of megakaryocytes and their alterations, associated with cytokines and chemokines release, in modulating functions of most of the bone marrow cell populations and in creating a complex network where impaired signaling strongly contributes to progression and disabilities.

Focus on Osteosclerotic Progression in Primary Myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by hematopoietic stem-cell-derived clonal proliferation, leading to bone marrow (BM) fibrosis. Hematopoiesis alterations are closely associated with modifications of the BM microenvironment, characterized by defective interactions between vascular and endosteal niches. As such, neoangiogenesis, megakaryocytes hyperplasia and extensive bone marrow fibrosis, followed by osteosclerosis and bone damage, are the most relevant consequences of PMF. Moreover, bone tissue deposition, together with progressive fibrosis, represents crucial mechanisms of disabilities in patients. Although the underlying mechanisms of bone damage observed in PMF are still unclear, the involvement of cytokines, growth factors and bone marrow microenvironment resident cells have been linked to disease progression. Herein, we focused on the role of megakaryocytes and their alterations, associated with cytokines and chemokines release, in modulating functions of most of the bone marrow cell populations and in creating a complex network where impaired signaling strongly contributes to progression and disabilities.

Challenges and Perspectives for Therapeutic Targeting of Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders with dysregulated myeloid blood cell production and propensity for transformation to acute myeloid leukemia, thrombosis, and bleeding. Acquired mutations in JAK2, MPL, and CALR converge on hyperactivation of Janus kinase 2 (JAK2) signaling as a central feature of MPN. Accordingly, JAK2 inhibitors have held promise for therapeutic targeting. After the JAK1/2 inhibitor ruxolitinib, similar JAK2 inhibitors as fedratinib are entering clinical use. While patients benefit with reduced splenomegaly and symptoms, disease-modifying effects on MPN clone size and clonal evolution are modest. Importantly, response to ruxolitinib may be lost upon treatment suggesting the MPN clone acquires resistance. Resistance mutations, as seen with other tyrosine kinase inhibitors, have not been described in MPN patients suggesting that functional processes reactivate JAK2 signaling. Compensatory signaling, which bypasses JAK2 inhibition, and other processes contribute to intrinsic resistance of MPN cells restricting efficacy of JAK2 inhibition overall. Combinations of JAK2 inhibition with pegylated interferon-α, a well-established therapy of MPN, B-cell lymphoma 2 inhibition, and others are in clinical development with the potential to enhance therapeutic efficacy. Novel single-agent approaches targeting other molecules than JAK2 are being investigated clinically. Special focus should be placed on myelofibrosis patients with anemia and thrombocytopenia, a delicate patient population at high need for options. The extending range of new treatment approaches will increase the therapeutic options for MPN patients. This calls for concomitant improvement of our insight into MPN biology to inform tailored therapeutic strategies for individual MPN patients.

Metabolic Vulnerabilities and Epigenetic Dysregulation in Myeloproliferative Neoplasms

The Janus kinase 2 (JAK2)-driven myeloproliferative neoplasms (MPNs) are associated with clonal myelopoiesis, elevated risk of death due to thrombotic complications, and transformation to acute myeloid leukemia (AML). JAK2 inhibitors improve the quality of life for MPN patients, but these approved therapeutics do not readily reduce the natural course of disease or antagonize the neoplastic clone. An understanding of the molecular and cellular changes requisite for MPN development and progression are needed to develop improved therapies. Recently, murine MPN models were demonstrated to exhibit metabolic vulnerabilities due to a high dependence on glucose. Neoplastic hematopoietic progenitor cells in these mice express elevated levels of glycolytic enzymes and exhibit enhanced levels of glycolysis and oxidative phosphorylation, and the disease phenotype of these MPN model mice is antagonized by glycolytic inhibition. While all MPN-driving mutations lead to aberrant JAK2 activation, these mutations often co-exist with mutations in genes that encode epigenetic regulators, including loss of function mutations known to enhance MPN progression. In this perspective we discuss how altered activity of epigenetic regulators (e.g., methylation and acetylation) in MPN-driving stem and progenitor cells may alter cellular metabolism and contribute to the MPN phenotype and progression of disease. Specific metabolic changes associated with epigenetic deregulation may identify patient populations that exhibit specific metabolic vulnerabilities that are absent in normal hematopoietic cells, and thus provide a potential basis for the development of more effective personalized therapeutic approaches.

Finding a Jill for JAK: Assessing Past, Present, and Future JAK Inhibitor Combination Approaches in Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm hallmarked by the upregulation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway with associated extramedullary hematopoiesis and a high burden of disease-related symptoms. While JAK inhibitor therapy is central to the management of MF, it is not without limitations. In an effort to improve treatment for MF patients, there have been significant efforts to identify combination strategies that build upon the substantial benefits of JAK inhibition. Early efforts to combine agents with additive therapeutic profiles have given way to rationally designed combinations hoping to demonstrate clinical synergism and modify the underlying disease. In this article, we review the preclinical basis and existing clinical data for JAK inhibitor combination strategies while highlighting emerging strategies of particular interest.

RAS/CBL mutations predict resistance to JAK inhibitors in myelofibrosis and are associated with poor prognostic features

The dysregulation of the JAK/STAT pathway drives the pathogenesis of myelofibrosis (MF). Recently, several JAK inhibitors (JAKis) have been developed for treating MF. Select mutations (MTs) have been associated with impaired outcomes and are currently incorporated in molecularly annotated prognostic models. Mutations of RAS/MAPK pathway genes are frequently reported in cancer and at low frequencies in MF. In this study, we investigated the phenotypic, prognostic, and therapeutic implications of NRASMTs, KRASMTs, and CBLMTs (RAS/CBLMTs) in 464 consecutive MF patients. A total of 59 (12.7%) patients had RAS/CBLMTs: NRASMTs, n = 25 (5.4%); KRASMTs, n = 13 (2.8%); and CBLMTs, n = 26 (5.6%). Patients with RAS/CBLMTs were more likely to present with high-risk clinical and molecular features. RAS/CBLMTs were associated with inferior overall survival compared with patients without MTs and retained significance in a multivariate model, including the Mutation-Enhanced International Prognostic Score System (MIPSS70) risk factors and cytogenetics; however, inclusion of RAS/CBLMTs in molecularly annotated prognostic models did not improve the predictive power of the latter. The 5-year cumulative incidence of leukemic transformation was notably higher in the RAS/CBLMT cohort. Among 61 patients treated with JAKis and observed for a median time of 30 months, the rate of symptoms and spleen response at 6 months was significantly lower in the RAS/CBLMT cohort. Logistic regression analysis disclosed a significant inverse correlation between RAS/CBLMTs and the probability of achieving a symptom or spleen response that was retained in multivariate analysis. In summary, our study showed that RAS/CBLMTs are associated with adverse phenotypic features and survival outcomes and, more important, may predict reduced response to JAKis.

Investigational non-JAK inhibitors for chronic phase myelofibrosis

INTRODUCTION

Patients with myelofibrosis (MF) have no effective treatment option after the failure of approved JAK inhibitor (JAKi) therapy. Non-JAK inhibitors (non-JAKi) that target non-canonical molecular pathways are undergoing clinical evaluations to optimize efficacy and/or to reduce hematological toxicity of JAKi.

AREA COVERED

This article reviews the efficacy data from completed and ongoing early phase clinical trials of non-JAKi agents for chronic phase MF. The article also illuminates some of the challenges of myelofibrosis drug development.

EXPERT OPINION

Most non-JAKi agents tested so far have shown modest benefit in improving the efficacy of ruxolitinib. Several novel agents such as BET inhibitor- CPI-0610, activin receptor ligand trap- luspatercept, recombinant pentraxin-PRM-151, telomerase inhibitor- imetelstat and bcl-2 inhibitor- navitoclax, have shown promising activity; however, they require vigorous evaluation in randomized controlled trials to understand the clinical benefit. Drugs that target new molecular pathways (MDM2, p-selectin, TIM-3, TGF-β, aurora kinase) and immune-based strategies (CALR vaccine, anti-PD-1, allogeneic cord blood regulatory T cells) are in early phase trials. Further translational studies to target leukemic stem cells, improvement in trial designs by incorporating control arm and survival endpoints, and patient-focused collaborations among all stakeholders could pave a way for future success in MF drug development.

Myelofibrosis biology and contemporary management

Myelofibrosis is an enigmatic myeloproliferative neoplasm, despite noteworthy strides in understanding its genetic underpinnings. Driver mutations involving JAK2, CALR or MPL in 90% of patients mediate constitutive JAK-STAT signaling which, in concert with epigenetic alterations (ASXL1, DNMT3A, SRSF2, EZH2, IDH1/2 mutations), play a fundamental role in disease pathogenesis. Aberrant immature megakaryocytes are a quintessential feature, exhibiting reduced GATA1 protein expression and secreting a plethora of pro-inflammatory cytokines (IL-1 ß, TGF-ß), growth factors (b-FGF, PDGF, VEGF) in addition to extra cellular matrix components (fibronectin, laminin, collagens). The ensuing disrupted interactions amongst the megakaryocytes, osteoblasts, endothelium, stromal cells and myofibroblasts within the bone marrow culminate in the development of fibrosis and osteosclerosis. Presently, prognostic assessment tools for primary myelofibrosis (PMF) are centered on genetics, with incorporation of cytogenetic and molecular information into the mutation-enhanced (MIPSS 70-plus version 2.0) and genetically-inspired (GIPSS) prognostic scoring systems. Both models illustrate substantial clinical heterogeneity in PMF and serve as the crux for risk-adapted therapeutic decisions. A major challenge remains the dearth of disease-modifying drugs, whereas allogeneic transplant offers the chance of long-term remission for some patients. Our review serves to synopsise current appreciation of the pathogenesis of myelofibrosis together with emerging management strategies.

Overview of the Mutational Landscape in Primary Myelofibrosis and Advances in Novel Therapeutics

Primary Myelofibrosis is a BCR-ABL negative myeloproliferative neoplasm with a variety of hematological presentations, including thrombosis, bleeding diathesis and marrow fibrosis. It is estimated to have an incidence of 1.5 per 100,000 people each year. Although JAK2 or MPL mutations are seen in PMF, several other mutations have recently been documented, including mutations in CALR, epigenetic regulators like TET, ASXL1, and 13q deletions. The identification of these mutations has improved the ability to develop novel treatment options. These include JAK inhibitors like ruxolitinib, heat shock protein-90 inhibitors like ganetespib, histone deacetylase inhibitors including panobinostat, pracinostat, vorinostat and givinostat, hypomethylating agents like decitabine, hedgehog inhibitors like glasdegib, PI3K, AKT and mTOR inhibitors like everolimus as well as telomerase inhibitors like imtelstat. Research on novel therapeutic options is being actively pursued in order to expand treatment options for primary myelofibrosis however currently, there is no curative therapy other than allogenic hematopoietic stem cell transplantation (ASCT) which is possible in select patients.

New Concepts of Treatment for Patients with Myelofibrosis

OPINION STATEMENT

Seven years after the approval of the Janus kinase 1/2 (JAK1/2) inhibitor ruxolitinib, it remains the only drug licensed for the treatment of myelofibrosis. Patients who discontinue ruxolitinib have a dismal outcome, and this is, therefore, an area of significant unmet need. Given the central role that JAK-signal transducer and activator of transcription (STAT) activation plays in disease pathogenesis, there have been many other JAK inhibitors tested, but most have been abandoned, for a variety of reasons. The JAK2-selective inhibitor fedratinib has recently been resurrected, and there has been a resurgence of interest in the failed JAK1/2 inhibitor momelotinib, which possibly improves anemia. Pacritinib, a non-myelosuppressive JAK2-selective inhibitor, is currently in a dose-ranging study mandated by regulatory authorities. A plethora of other targeted agents, most backed by preclinical data, are in various stages of investigation. These include epigenetic and immune therapies, agents targeting cellular survival, metabolic and apoptotic pathways, the cell cycle, DNA repair, and protein folding and degradation, among others. However, at this time, none of these is close to registration or even in a pivotal trial, illustrating the difficulties in recapitulating the clinical disease in preclinical models. Most current clinical trials are testing the addition of a novel agent to ruxolitinib, either in the frontline setting or in the context of an insufficient response to ruxolitinib, or attempting to study new drugs in the second-line, "ruxolitinib failure" setting. Emerging data supports the addition of azacitidine to ruxolitinib in some patients. Other strategies have focused on improving cytopenias, through amelioration of bone marrow fibrosis or other mechanisms. This is important, because cytopenias are the commonest reason for ruxolitinib interruption and/or dose reduction, and dose optimization of ruxolitinib is tied to its survival benefit. The activin receptor ligand trap, sotatercept, and the anti-fibrotic agent, PRM-151, have shown promise in this regard.

IL-6 stimulation of DNA replication is JAK1/2 mediated in cross-talk with hyperactivated ERK1/2 signaling

Myeloproliferative neoplasms (MPNs) are developing resistance to therapy by JAK1/2 inhibitor ruxolitinib. To explore the mechanism of ruxolitinib's limited effect, we examined the JAK1/2 mediated induction of proliferation related ERK1/2 and AKT signaling by proinflammatory interleukin-6 (IL-6) in MPN granulocytes and JAK2V617F mutated human erythroleukemia (HEL) cells. We found that JAK1/2 or JAK2 inhibition prevented the IL-6 activation of STAT3 and AKT pathways in polycythemia vera and HEL cells. Further, we showed that these inhibitors also blocked the IL-6 activation of the AKT pathway in primary myelofibrosis (PMF). Only JAK1/2 inhibitor ruxolitinib largely activated ERK1/2 signaling in essential thrombocythemia and PMF (up to 4.6 fold), with a more prominent activation in JAK2V617F positive granulocytes. Regarding a cell cycle, we found that IL-6 reduction of HEL cells percentage in G2M phase was reversed by ruxolitinib (2.6 fold). Moreover, ruxolitinib potentiated apoptosis of PMF granulocytes (1.6 fold). Regarding DNA replication, we found that ruxolitinib prevented the IL-6 augmentation of MPN granulocytes frequency in the S phase of the cell cycle (up to 2.9 fold). The inflammatory stimulation induces a cross-talk between the proliferation linked pathways, where JAK1/2 inhibition is compensated by the activation of the ERK1/2 pathway during IL-6 stimulation of DNA replication.

Bone marrow-specific loss of ABI1 induces myeloproliferative neoplasm with features resembling human myelofibrosis

Although the pathogenesis of primary myelofibrosis (PMF) and other myeloproliferative neoplasms (MPNs) is linked to constitutive activation of the JAK-STAT pathway, JAK inhibitors have neither curative nor MPN-stem cell-eradicating potential, indicating that other targetable mechanisms are contributing to the pathophysiology of MPNs. We previously demonstrated that Abelson interactor 1 (Abi-1), a negative regulator of Abelson kinase 1, functions as a tumor suppressor. Here we present data showing that bone marrow-specific deletion of Abi1 in a novel mouse model leads to development of an MPN-like phenotype resembling human PMF. Abi1 loss resulted in a significant increase in the activity of the Src family kinases (SFKs), STAT3, and NF-κB signaling. We also observed impairment of hematopoietic stem cell self-renewal and fitness, as evidenced in noncompetitive and competitive bone marrow transplant experiments. CD34⁺ hematopoietic progenitors and granulocytes from patients with PMF showed decreased levels of ABI1 transcript as well as increased activity of SFKs, STAT3, and NF-κB. In aggregate, our data link the loss of Abi-1 function to hyperactive SFKs/STAT3/NF-κB signaling and suggest that this signaling axis may represent a regulatory module involved in the molecular pathophysiology of PMF.

Application of kinomic array analysis to screen for altered kinases in atrial fibrillation remodeling

BACKGROUND

Dysregulation of protein kinase-mediated signaling is an early event in many diseases, including the most common clinical cardiac arrhythmia, atrial fibrillation (AF). Kinomic profiling represents a promising technique to identify candidate kinases.

OBJECTIVE

In this study we used kinomic profiling to identify kinases altered in AF remodeling using atrial tissue from a canine model of AF (atrial tachypacing).

METHODS

Left atrial tissue obtained in a previous canine study was used for kinomic array (containing 1024 kinase pseudosubstrates) analysis. Three groups of dogs were included: nonpaced controls and atrial tachypaced dogs, which were contrasted with geranylgeranylacetone-treated dogs with AF, which are protected from AF promotion, to enhance specificity of detection of putative kinases.

RESULTS

While tachypacing changed activity of 50 kinases, 40 of these were prevented by geranylgeranylacetone and involved in differentiation and proliferation (SRC), contraction, metabolism, immunity, development, cell cycle (CDK4), and survival (Akt). Inhibitors of Akt (MK2206) and CDK4 (PD0332991) and overexpression of a dominant-negative CDK4 phosphorylation mutant protected against tachypacing-induced contractile dysfunction in HL-1 cardiomyocytes. Moreover, patients with AF show down- and upregulation of SRC and Akt phosphorylation, respectively, similar to findings of the kinome array.

CONCLUSION

Contrasting kinomic array analyses of controls and treated subjects offer a versatile tool to identify kinases altered in atrial remodeling owing to tachypacing, which include Akt, CDK4, and SRC. Ultimately, pharmacological targeting of altered kinases may offer novel therapeutic possibilities to treat clinical AF.

Targeting few to help hundreds: JAK, MAPK and ROCK pathways as druggable targets in atypical chronic myeloid leukemia

Atypical Chronic Myeloid Leukemia (aCML) is a myeloproliferative neoplasm characterized by neutrophilic leukocytosis and dysgranulopoiesis. From a genetic point of view, aCML shows a heterogeneous mutational landscape with mutations affecting signal transduction proteins but also broad genetic modifiers and chromatin remodelers, making difficult to understand the molecular mechanisms causing the onset of the disease. The JAK-STAT, MAPK and ROCK pathways are known to be responsible for myeloproliferation in physiological conditions and to be aberrantly activated in myeloproliferative diseases. Furthermore, experimental evidences suggest the efficacy of inhibitors targeting these pathways in repressing myeloproliferation, opening the way to deep clinical investigations. However, the activation status of these pathways is rarely analyzed when genetic mutations do not occur in a component of the signaling cascade. Given that mutations in functionally unrelated genes give rise to the same pathology, it is tempting to speculate that alteration in the few signaling pathways mentioned above might be a common feature of pathological myeloproliferation. If so, targeted therapy would be an option to be considered for aCML patients.

Xist reduction in breast cancer upregulates AKT phosphorylation via HDAC3-mediated repression of PHLPP1 expression

Long noncoding RNAs (lncRNAs) dysregulated in cancer potentially play oncogenic or tumor-suppressive roles. While the X inactivate-specific transcript (Xist) lncRNA is important for X-chromosome inactivation in female cells, very little is known about the role of Xist in human breast cancer in modulating cellular pathway(s). Here, we show that Xist expression is significantly reduced in breast tumor samples and cancer cell lines. Xist knockdown or overexpression resulted in increased or decreased levels, respectively, of AKT phosphorylation and cell viability. Further studies revealed an inverse correlation between Xist and phospho-AKT levels in breast cancer samples. Additionally, Xist knockdown-elicited increase of cell viability was attenuated by AKT inhibitor. These results suggest that Xist negatively regulates cell viability via inhibition of AKT activation. Interestingly, decreased Xist expression in breast cancer samples was associated with reduced levels of Jpx RNA, an lncRNA that positively regulates Xist promoter activity. Accordingly, Jpx knockdown enhanced AKT activation and cell viability. We also demonstrate that knockdown of Xist or SPEN, an intermediator protein to link Xist, SMRT co-repressor and HDAC3 complexes for X-chromosome inactivation, decreased expression of PHLPP1, a phosphatase to remove AKT phosphorylation, via increased HDAC3 recruitment to the PHLPP1 promoter, correlating with increased AKT phosphorylation. Our findings elucidate the tumor suppressor role of Xist in breast cancer and provide the molecular basis of Xist in downregulating AKT activation.

Novel Therapies for Myelofibrosis

PURPOSE OF REVIEW

The purpose of the review was to provide a contemporary update of novel agents and targets under investigation in myelofibrosis in the Janus kinase (JAK) inhibitor era.

RECENT FINDINGS

Myelofibrosis (MF) is a clonal stem cell disease characterized by marrow fibrosis and a heterogeneous disease phenotype with a variable degree of splenomegaly, cytopenias, and constitutional symptoms that significantly impact quality of life and survival. Overactive JAK/STAT signaling is a hallmark of MF. The only approved therapy for MF, JAK1/2 inhibitor ruxolitinib, can ameliorate splenomegaly, improve symptoms, and prolong survival in some patients. Therapeutic challenges remain, however. Myelosuppression limits the use of ruxolitinib in some patients, eventual drug resistance is common, and the underlying malignant clone persists despite therapy. A deeper understanding of the pathogenesis of MF has informed the development of additional agents. Promising targets under investigation include JAK1 and JAK2 and downstream intermediates in related signaling pathways, epigenetic modifiers, pro-inflammatory cytokines, and immune regulators.

Developmental Therapeutics in Myeloproliferative Neoplasms

The unprecedented success of the Janus kinase (JAK) 1/2 inhibitor ruxolitinib in myelofibrosis (MF) provided much-needed impetus for clinical drug development for the Philadelphia chromosome-negative myeloproliferative neoplasms. The survival benefit conferred by this agent, along with its marked efficacy with regard to spleen volume and symptom reduction, have made ruxolitinib the cornerstone of drug therapy in MF. However, there remain significant unmet needs in the treatment of patients with MF, and many novel classes of agents continue to be investigated in efforts to build on the progress made with ruxolitinib. These include inhibitors of histone deacetylases (HDACs) and DNA methyltransferases, phosphatidylinositol-3-kinase isoforms, heat shock protein 90, cyclin-dependent kinases 4/6, and Hedgehog signaling, among others. In parallel, other JAK inhibitors with potential for less myelosuppression or even improvement of anemia, greater selectivity for JAK1 or JAK2, and the ability to overcome JAK inhibitor persistence are in various stages of development. First-in-class agents such as the activin receptor IIA ligand trap sotatercept (for anemia of MF), the telomerase inhibitor imetelstat, and the antifibrotic agent PRM-151 (recombinant human pentraxin-2) are also in clinical trials. In polycythemia vera, a novel interferon administered every 2 weeks is being developed for front-line therapy in high-risk individuals, and inhibitors of human double minute 2 (HDM2) have shown promise in preclinical studies, as have HDAC inhibitors such as givinostat (both in the laboratory and in the clinic). Ruxolitinib is approved for second-line therapy of polycythemia vera and is being developed for essential thrombocythemia.

Inhibitors of the PI3K/mTOR pathway prevent STAT5 phosphorylation in JAK2V617F mutated cells through PP2A/CIP2A axis

Inhibition of the constitutively activated JAK/STAT pathway in JAK2V617F mutated cells by the JAK1/JAK2 inhibitor ruxolitinib resulted in clinical benefits in patients with myeloproliferative neoplasms. However, evidence of disease-modifying effects remains scanty; furthermore, some patients do not respond adequately to ruxolitinib, or have transient responses, thus novel treatment strategies are needed. Here we demonstrate that ruxolitinib causes incomplete inhibition of STAT5 in JAK2V617F mutated cells due to persistence of phosphorylated serine residues of STAT5b, that conversely are targeted by PI3K and mTORC1 inhibitors. We found that PI3K/mTOR-dependent phosphorylation of STAT5b serine residues involves Protein Phosphatase 2A and its repressor CIP2A. The levels of CIP2A were found increased in cells harboring the JAK2V617F mutation, and we provide evidence of a correlation between clinical responses and the extent of CIP2A downregulation in myelofibrosis patients receiving the mTOR inhibitor RAD001 in a phase II clinical trial. To achieve maximal inhibition of STAT5 phosphorylation, we combined ruxolitinib with BKM120, a PI3K inhibitor, and RAD001, an mTOR inhibitor, obtaining improved efficacy in JAK2V617F mutated cell lines, primary patients’ cells, and JAK2V617F knock-in mice. These findings contribute to understanding the effectiveness of PI3K/mTOR inhibitors in MPN and argue for the rationale to develop combination clinical trials.

Mechanisms of Resistance to JAK2 Inhibitors in Myeloproliferative Neoplasms

Myeloproliferative neoplasms are driven by activated JAK2 signaling due to somatic mutations in JAK2, the thrombopoietin receptor MPL or the chaperone calreticulin in hematopoietic stem/progenitor cells. JAK2 inhibitors have been developed, but despite clinical benefits, they do not signficantly reduce the mutant clone. Loss of response to JAK2 inhibitors occurs and several mechanisms of resistance, genetic and functional, have been identified. Resistance mutations have not been reported in MPN patients suggesting incomplete target inhibition. Alternative targeting of JAK2 by HSP90 inhibitors or type II JAK2 inhibition overcomes resistance to current JAK2 inhibitors. Additional combined therapy approaches are currently being evaluated.

Kinase signaling and targeted therapy for primary myelofibrosis

The myeloproliferative neoplasms (MPNs) are somatic mutation-driven hematologic malignancies characterized by bone marrow fibrosis and the accumulation of atypical megakaryocytes with reduced polyploidization in the primary myelofibrosis subtype of the MPNs. Increasing evidence points to a dominant role of abnormal megakaryocytes in disease initiation and progression. Here we review the literature related to kinase signaling pathways relevant to megakaryocyte differentiation and proliferation, including Aurora A kinase, RhoA/ROCK, and JAK/STAT, as well as the activities of their targeted inhibitors in models of the disease. Some of these pathway inhibitors selectively induce megakaryocyte differentiation, suppress malignant proliferation, and promote polyploidization and proplatelet formation. Moreover, combining sets of these inhibitors may be an effective approach to treat and potentially cure MPN patients. For example, preclinical studies reported significant synergistic effects of the combination of an Aurora A inhibitor and JAK1/2 inhibitor, in a murine model of the primary myelofibrosis. Future basic and clinical research into the contributions of these signaling pathways to aberrant megakaryopoiesis may lead to novel effective treatments for MPN patients.

Myeloproliferative Neoplasms: Molecular Drivers and Therapeutics

Activating mutations in genes that drive neoplastic cell growth are numerous and widespread in cancer, and specific genetic alterations are associated with certain types of cancer. For example, classic myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders that affect cells of the myeloid lineage, including erythrocytes, platelets, and granulocytes. An activating mutation in the JAK2 tyrosine kinase is prevalent in these diseases. In MPN patients that lack such a mutation, other genetic changes that lead to activation of the JAK2 signaling pathway are present, indicating deregulation of JAK2 signaling plays an etiological driving role in MPNs, a concept supported by significant evidence from in vivo experimental MPN systems. Thus, small molecules that inhibit JAK2 activity are ideal drugs to impede the progression of disease in MPN patients. However, even though JAK inhibitors provide significant symptomatic relief, they have failed as a remission-inducing therapy. Nonetheless, the progress made understanding the molecular etiology of MPNs since 2005 is significant and has provided insight for the development and testing of novel molecular targeted therapeutic approaches. The current understanding of driver mutations in MPNs and an overview of current and potential therapeutic strategies for MPN patients will be discussed.

The PIM inhibitor AZD1208 synergizes with ruxolitinib to induce apoptosis of ruxolitinib sensitive and resistant JAK2-V617F-driven cells and inhibit colony formation of primary MPN cells

Classical myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders that exhibit excess mature myeloid cells, bone marrow fibrosis, and risk of leukemic transformation. Aberrant JAK2 signaling plays an etiological role in MPN formation. Because neoplastic cells in patients are largely insensitive to current anti-JAK2 therapies, effective therapies remain needed. Members of the PIM family of serine/threonine kinases are induced by JAK/STAT signaling, regulate hematopoietic stem cell growth, protect hematopoietic cells from apoptosis, and exhibit hematopoietic cell transforming properties. We hypothesized that PIM kinases may offer a therapeutic target for MPNs. We treated JAK2-V617F-dependent MPN model cells as well as primary MPN patient cells with the PIM kinase inhibitors SGI-1776 and AZD1208 and the JAK2 inhibitor ruxolitinib. While MPN model cells were rather insensitive to PIM inhibitors, combination of PIM inhibitors with ruxolitinib led to a synergistic effect on MPN cell growth due to enhanced apoptosis. Importantly, PIM inhibitor mono-therapy inhibited, and AZD1208/ruxolitinib combination therapy synergistically suppressed, colony formation of primary MPN cells. Enhanced apoptosis by combination therapy was associated with activation of BAD, inhibition of downstream components of the mTOR pathway, including p70S6K and S6 protein, and activation of 4EBP1. Importantly, PIM inhibitors re-sensitized ruxolitinib-resistant MPN cells to ruxolitinib by inducing apoptosis. Finally, exogenous expression of PIM1 induced ruxolitinib resistance in MPN model cells. These data indicate that PIMs may play a role in MPNs and that combining PIM and JAK2 kinase inhibitors may offer a more efficacious therapeutic approach for MPNs over JAK2 inhibitor mono-therapy.

Angiogenic factors are increased in circulating granulocytes and CD34+ cells of myeloproliferative neoplasms

It has been shown that angiogenesis and inflammation play an important role in development of most hematological malignancies including the myeloproliferative neoplasm (MPN). The aim of this study was to investigate and correlate the levels of key angiogenic molecules such as hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) in peripheral blood and bone marrow cells of MPN patients, along with JAK2V617F mutation allele burden and effects of therapy. HIF-1α and VEGF gene expression were decreased, while eNOS mRNA levels were increased in granulocytes of MPN patients. Furthermore, positively correlated and increased VEGF and eNOS protein levels were in negative correlation with HIF-1α levels in granulocytes of MPN patients. According to immunoblotting, the generally augmented angiogenic factors demonstrated JAK2V617F allele burden dependence only in granulocytes of PMF. The angiogenic factors were largely reduced after hydroxyurea therapy in granulocytes of MPN patients. Levels of eNOS protein expression were stimulated by Calreticulin mutations in granulocytes of essential thrombocythemia. Immunocytochemical analyses of CD34⁺ cells showed a more pronounced enhancement of angiogenic factors than in granulocytes. Increased gene expression linked to the proinflammatory TGFβ and MAPK signaling pathways were detected in CD34⁺ cells of MPN patients. In conclusion, the angiogenesis is increased in several cell types of MPN patients supported by the transcriptional activation of inflammation-related target genes, and is not limited to bone marrow stroma cells. It also appears that some of the benefit of hydroxyurea therapy of the MPN is mediated by effects on angiogenic factors. © 2016 Wiley Periodicals, Inc.

Tyrosine 625 plays a key role and cooperates with tyrosine 630 in MPL W515L-induced signaling and myeloproliferative neoplasms

BACKGROUND

Myeloproliferative neoplasms (MPN) are a group of blood cancers that boost normal blood cell production in the bone marrow. Abnormal mutations in stem cells were found accompanying with the occurrence of MPN. It has been shown that MPL mutations (MPL W515L or MPL W515K) were involved in patients with MPN. Since tyrosine residues 625 and 630 mediate normal MPL signaling, whether them affect MPL W515L-induced myeloproliferative neoplasms (MPNs) is unknown.

RESULTS

In this study, we further tested their functions in MPL W515L-induced myeloproliferative neoplasms (MPNs) by substituting either or both of them with phenylalanine in MPL W515L (termed as MPL515/625, MPL515/630 and MPL515/625/630, respectively). In vitro, MPL515/630 but not MPL515/625 or MPL515/625/630 retained the ability to induce TPO-independent proliferation and increase colony-forming unit megakaryocytes (CFU-Mk). Accordingly, differential activation of the downstream signaling by four mutants was observed and constitutively active STAT5 or AKT instead of STAT3 partially compensated MPL515/625/630 function. Further support this, STAT5-deficiency impaired MPL W515L-induced CFU-Mk expansion. In vivo, MPL515/630 but not MPL515/625 or MPL515/625/630 induced typical features of MPNs with high WBC and platelet counts, splenomegaly, hepatomegaly and hypercellularity in the bone marrow. Surprisingly, MPL515/625 also caused hypercellularity of bone marrow and splenomegaly without any other significant features. We also observed differential effects of the four mutants on progenitors, myeloid cells and megakaryocytes.

CONCLUSIONS

Our studies have revealed distinct features of tyrosine sites 625 and 630 in mediating MPL W515L-induced megakaryocyte hyperproliferation and MPNs. Our study also suggests that MPL cytosolic phosphorylated Y625 and flanking amino acids could become targets for pharmacologic inhibition in MPNs.

Pathogenesis of myeloproliferative neoplasms

Major progress has been recently made in understanding the molecular pathogenesis of myeloproliferative neoplasms (MPN). Mutations in one of four genes-JAK2, MPL, CALR, and CSF3R-can be found in the vast majority of patients with MPN and represent driver mutations that can induce the MPN phenotype. Hyperactive JAK/STAT signaling appears to be the common denominator of MPN, even in patients with CALR mutations and the so-called "triple-negative" MPN, where the driver gene mutation is still unknown. Mutations in epigenetic regulators, transcription factors, and signaling components modify the course of the disease and can contribute to disease initiation and/or progression. The central role of JAK2 in MPN allowed development of small molecular inhibitors that are in clinical use and are active in almost all patients with MPN. Advances in understanding the mechanism of JAK2 activation open new perspectives of developing the next generation of inhibitors that will be selective for the mutated forms of JAK2.