Myeloid malignancies are heterogenous disorders characterized by distinct molecular drivers but share convergence of oncogenic signaling pathways and propagation by ripe pro-inflammatory niches. Here, we establish a comprehensive transcriptional atlas across the spectrum of myeloproliferative neoplasms (MPN) and secondary acute myeloid leukemia (sAML) through RNA-sequencing of 158 primary samples encompassing CD34+ hematopoietic stem/progenitor cells and CD14+ monocytes. Supported by mass cytometry (CyTOF) profiling, we reveal aberrant networks of PI3K/AKT/mTOR signalling and NFκB-mediated hyper-inflammation. Combining ATAC-Seq, CUT Tag, RNA-seq, and CyTOF, we demonstrate that targeting of ribosomal protein S6 kinase A1 (RSK1) suppresses NFκB activation and diminishes pro-inflammatory mediators including tumor necrosis factor (TNF) associated with MPN disease severity and transformation. We further evaluate a therapeutic approach utilizing a first-in-class RSK inhibitor, PMD-026, currently in Phase 2 development for breast cancer, for use in myeloid malignancies. Treatment with PMD-026 suppressed disease burden across seven syngeneic and patient-derived xenograft leukemia mouse models spanning the spectrum of driver and disease-modifying mutations. These findings uncover a therapeutic avenue for a conserved dependency across MPN and sAML. Secondary acute myeloid leukemias (sAMLs) evolving from myeloproliferative neoplasms (MPNs) associate with poor prognosis. Here authors identify RSK1 as a vulnerability for MPN and sAML and show the efficacy of a first-in-class RSK inhibitor, PMD-026, against these types of myeloid malignancies.

FH, SL and BG equal contributors Myeloproliferative neoplasms (MPN) and acute myeloid leukemia (AML) exhibit shared hallmarks of hyperinflammation and aberrant clonal expansion. Chronic MPNs exhibit a propensity for transformation to secondary AML (sAML), which imparts a dismal prognosis with limited treatment options. However, the pathogenesis of leukemia transition for MPN and the bidirectional relationship between MPN and AML remain incompletely understood. In this study, we investigated commonly-featured genes and pathways of these two diseases to explore novel therapeutic strategies. To dissect the causal association between MPN and AML, we first performed two-sample bidirectional mendelian randomization (MR) analysis which revealed that MPN predicts the risk of AML across multiple statistical methods with consistent directionality and significance. Heterogeneity, pleiotropy, or outlier effects were ruled out by sensitivity analyses with no reverse causality from AML to MPN. To identify a potential myeloid signature, we estimated causal effects of 2,940 plasma proteins on MPN via a two-sample MR framework and identified 55 candidates significantly associated with increased risk of MPN (P < 0.05, OR > 1). Utilizing data from the BEAT-AML cohort, we further screened the prognostic value of these candidates using Cox and log-rank test survival analyses and identified a 4-gene myeloid signature comprising MPO, CDCP1, CRISP3 and DXCR, with each conferring prognostic significance individually. Our scRNA-seq results confirmed enrichment of myeloid signature genes in myeloid progenitor cells, with further elevation in MPN. Of note, expression of myeloid signature genes was induced by Jak2V617F and MPLW515L in Ba/F3 cells. We then investigated the combined prognostic significance of these four genes by constructing a risk score via LASSO regression modeling and divided patients into high- and low-risk groups accordingly. Cox analysis validated the risk score as an independent prognostic factor (HR: 3.01 (1.2 - 7.6), P = 0.019) and Kaplan-Meier survival analysis demonstrated that low-risk AML patients had a significantly better survival than high-risk AML patients with median survival of 21.9 months vs. 11.9 months (P < 0.0001). The prediction accuracy of the myeloid signature was successfully validated in the TCGA-LAML cohort. The risk score significantly correlated with several key clinical parameters, including age, platelet count, ELN2017 staging, monocyte percentage and bone marrow cellularity. To interrogate the underlying mechanism of the myeloid signature, we performed gene set enrichment analysis (GSEA) and observed enrichment of several inflammatory pathways in high-risk AML patients. A similar enrichment of inflammatory pathways in MPN samples compared to healthy donors observed in our previous scRNA-seq results reinforced hyperinflammation as a shared etiology of myeloid malignancies. To explore potential therapeutic strategies, we performed in silico drug sensitivity screening which predicted specific vulnerability of high-risk AML to compounds targeting PI3K/AKT/mTOR pathway signaling. Activation of PI3K/AKT/mTOR signaling in both MPN and AML samples observed across multiple single cell and bulk RNA-seq datasets further prompted us to evaluate targeted therapies against this pathway in myeloid malignancies. MPN and AML cells exhibited sensitivity to mTOR inhibitors as indicated by suppression of cellular proliferation, metabolism, colony formation, and inflammatory cytokine secretion in conjunction with induction of apoptosis. We further evaluated the therapeutic effects of mTOR inhibition in vivo via administration of omipalisib, a potent dual PI3K/mTOR inhibitor, to JAK2V617F knock-in mice. Omipalisib treatment significantly ameliorated features of myeloid malignancies including splenomegaly and leukocytosis which were both significantly reduced following 4 weeks of treatment, without affecting body weight. In summary, our MR analyses reveal that MPN predicts the risk of AML and enabled the construction of a novel myeloid signature which risk stratified AML patients across two different cohorts. We further demonstrate shared activation of PI3K/AKT/mTOR pathway across myeloid malignancies, with in vitro and in vivo data providing a rationale for therapeutic targeting of PI3K/AKT/mTOR pathway in these diseases.

Hyperactivation of the NFκB cascade propagates oncogenic signaling and pro-inflammation, which together augments disease burden in myeloproliferative neoplasms (MPNs). Here, we systematically ablate NFκB signaling effectors to identify core dependencies using a series of primary samples and syngeneic and patient-derived xenograft (PDX) mouse models. Conditional knockout of Rela attenuated Jak2V617F and MPLW515L-driven onset of polycythemia vera and myelofibrosis disease hallmarks, respectively. In PDXs, RELA-knockout diminished leukemic engraftment and bone marrow fibrosis while extending survival. Knock-out of upstream effector Myd88 also alleviated disease burden; conversely, perturbation of negative regulator miR-146a microRNA induced earlier lethality and exacerbated disease. Perturbation of NFκB effectors further skewed the abundance and distribution of hematopoietic multipotent progenitors. Finally, pharmacological targeting of interleukin-1 receptor-associated kinase 4 (IRAK4) with inhibitor CA-4948 suppressed disease burden and inflammatory cytokines specifically in MPN without inducing toxicity in non-diseased models. These findings highlight vulnerabilities in MPN that are exploitable with emerging therapeutic approaches.

Activating mutations in the calcium sensor STIM1 underlie Stormorken Syndrome (SS), a rare congenital disorder that causes thrombocytopenia and tubular aggregate myopathy. We recently identified two patients with SS and confirmed mutations in STIM1 (R304W and S88G), who were found to have features consistent with myelofibrosis (MF), as indicated by bone marrow biopsies demonstrating megakaryocyte hyperplasia and atypia in conjunction with marked reticulin fibrosis. The unusual MF findings in these two patients raised the hypothesis that altered calcium signaling represents a shared hallmark of congenital platelet disorders such as Stormorken Syndrome and myeloproliferative neoplasms (MPNs) including MF. Analyzing gene expression data from public datasets, we found increased expression of STIM1 in megakaryocyte progenitors and platelets, as well as CD34+ hematopoietic stem/progenitor cells (HSPCs), from MPN patients (including those with CALR or JAK2 mutations) vs healthy controls. These findings led us to hypothesize that dysregulation of STIM1 and store operated calcium entry (SOCE) signaling may contribute to altered megakaryopoiesis and development of fibrosis in both SS and MPNs. To further delineate these processes, we analyzed samples from our two SS patients, demonstrating constitutive activation of SOCE causing increased calcium flux, as well as decreased aggregation in mature platelets. We also performed transmission electron microscopy (TEM) and identified platelets with abnormal granularity in dense and alpha granules. We also performed single cell RNA-seq on SS patient peripheral blood mononuclear cells, which revealed enhanced NFkB inflammatory signaling, suggesting that altered signaling driven by STIM1 mutations may drive aberrant inflammation to contribute to MF development. To corroborate these initial observations, we identified a separate family cohort of 9 individuals in Italy with SS and confirmed STIM1 mutation (L92V). In ex vivo megakaryocytic differentiation assays, cells derived from these patients demonstrated a defect in thrombopoiesis with significantly decreased pro-platelet formation and adhesion to extracellular matrix. To further characterize the effects of the gain of function STIM1 mutations seen in our patients, we developed a novel, conditional knock-in mouse model of the heterozygous R304W mutation in the coiled coil (CC) domain of Stim1. Induction of hematopoietic-specific expression of mutant Stim1 via Vav-Cre resulted in recapitulation of hematological features of SS, including thrombocytopenia and a mild bleeding tendency, with confirmation of increased SOCE activity and calcium flux. Notably, we confirmed the development of bone marrow fibrosis, as well as findings of severe osteosclerosis, in these mice. TEM imaging confirmed that platelets from Stim1R304W/+Vav-Cre mice exhibit abnormal granularity, similar to what we observed from our SS patients. Noting that we identified increased STIM1 expression in samples from MPN patients harboring either JAK2 or CALR mutations, we further characterized the role of STIM1 in MPN disease development. NSGS mice were engrafted with CALR-mutant CD34+ cells subjected to CRISPR ablation of STIM1. Recipient mice exhibited decreased human CD45+ cell engraftment in conjunction with prolonged survival. In contrast, targeting of STIM1 in JAK2-mutant CD34+ cells led to exacerbated disease phenotypes, as manifested by enhanced human CD45+ cell engraftment, worsened splenomegaly, and early lethality. Taken together, these findings suggest a striking, differential relationship between mutant JAK2 and CALR and STIM1 activity and their relationship to MF development. Altogether, this study represents the first demonstration of MF development in patients with Stormorken Syndrome, and reveals a previously unrecognized hallmark of altered calcium signaling via aberrant STIM1 activation underlying SS and MPNs. We further demonstrate recapitulation of these hematologic features in a novel knock-in Stim1R304W/+Vav-Cre mouse model. These findings implicate an important role for STIM1and SOCE activity in MF development, and further uncover important distinctions between JAK2 vs CALR mutations and their interaction with altered STIM1 activity. These studies may contribute to the development of novel therapeutic approaches for these disorders.

JDP and STO co-corresponding authors Previous studies by our group and others have elucidated a key role for monocytes in driving hyperinflammation in myeloproliferative neoplasms (MPNs). To further interrogate the cellular landscape of aberrant inflammation in MPNs, we subjected MPN patient samples to single cell RNA-seq (scRNA-seq) analysis and found significant enrichment of inflammation-related genes, including galectins, in MPN patient monocytes. Cell-cell communication networks inferred from expression of ligands and receptors predicted monocytes as a pivotal mediator of cell interactions and galectin signaling as one of the most robust input/output pathways for monocytes. Galectins are a class of proteins that bind to glycosylated proteins and mediate broad biological functions, including cell proliferation, apoptosis, adhesion, and inflammation. Dysregulation of galectins and global protein glycosylation has been reported in various cancers, but its role in MPN has remained incompletely understood. To validate our scRNA-seq findings, we performed flow cytometry analysis which demonstrated elevated expression of galectin-1 (Gal-1) in MPN patient CD14+ monocytes. Increased plasma levels of Gal-1 were also identified in MPN patients compared to healthy individuals. We also observed enrichment of Gal-1 in mouse CD11b+ myeloid cells, with further elevation in JAK2V617F knock-in mice compared to wild-type controls. Additionally, Gal-1 expression was induced by MPLW515L and JAK2V617F and inhibited by ruxolitinib, a JAK inhibitor, in Ba/F3 cells. Thus, our results confirm enrichment of Gal-1 in MPN monocytes, with evidence of direct contribution from specific MPN driver mutations. To comprehensively characterize functional effects of Gal-1, we performed mass cytometry (CyTOF) analysis of MPN samples which demonstrated that Gal-1 stimulation induced multiple inflammatory cytokines, including TNF and IL-6, in monocytes specifically without affecting other types of cells. We further incubated CD14+ monocytes from MPN patients with recombinant Gal-1 (rGal-1) and observed markedly stimulated transcription and secretion of inflammatory cytokines, such as IL-1α, IL-1β, IL-6, IL-8 and TNF. Pharmacologic inhibition of Gal-1 by OTX008 suppressed the expression and secretion of inflammatory cytokines in MPN monocytes and monocytic cell lines. Furthermore, we observed crosstalk between LPS-TLR4 and Gal-1 signaling pathways. Using protein 3D structure prediction and co-immunoprecipitation, we confirmed interaction of Gal-1 with TLR4. Notably, targeting TLR4 via both neutralizing antibody and pharmacologic inhibition (TAK-242) abrogated the proinflammatory effects of Gal-1 on monocytes. Taken together, these findings uncover a monocyte-specific pro-inflammatory effect of Gal-1 mediated by TLR4 in MPN. To explore molecular mechanisms underlying its proinflammatory functions, we performed gene co-expression analysis for Gal-1 in monocytes and identified OXPHOS and PI3K-AKT-mTOR signaling pathways as top candidates. Both genetic and pharmacologic inhibition of Gal-1 reduced cellular ATP levels and oxygen consumption rate, suggesting a metabolic reprogramming by Gal-1 in MPN. Incubation of monocytic cell lines and MPN monocytes with rGal-1 stimulated PI3K-AKT-mTOR signaling, represented by increased levels of phosphorylated mTOR, AKT and S6. Consistently, genetic and pharmacologic inhibition of Gal-1 inhibited activation of the PI3K-AKT-mTOR pathway. Across in vivo models, both Gal-1 knockout and OTX008 ameliorated key MPN disease features, including leukocytosis and splenomegaly, driven by MPLW515L and JAK2V617F. Gal-1 inhibition also suppressed carrageenan-induced thrombosis and inflammation in mice. We further evaluated therapeutic effects of targeting global glycosylation in MPN via 2-Deoxy-D-glucose (2-DG), a global glycosylation inhibitor, which decreased splenomegaly and reduced elevated platelets and hematocrit in JAK2V617F knock-in mice. In summary, we identify enrichment of Gal-1 in MPN monocytes, potentially due to activation of JAK2-driven signaling. We further demonstrate that Gal-1 fuels monocyte inflammation by interacting with TLR4 and activation of OXPHOS and PI3K-AKT-mTOR signaling pathways. Our results uncover a novel therapeutic avenue for targeting aberrant Gal-1 and global glycosylation in MPNs.

Myeloproliferative neoplasms (MPNs) are driven by hyperactivation of JAK-STAT signaling but can demonstrate skewed hematopoiesis upon acquisition of additional somatic mutations. Here, using primary MPN samples and engineered embryonic stem cells, we demonstrate that mutations in JAK2 induced a significant increase in erythroid colony formation, whereas mutations in additional sex combs-like 1 (ASXL1) led to an erythroid colony defect. RNA-sequencing revealed upregulation of protein arginine methyltransferase 6 (PRMT6) induced by mutant ASXL1. Furthermore, genetic perturbation of PRMT6 exacerbated the MPN disease burden, including leukemic engraftment and splenomegaly, in patient-derived xenograft models, highlighting a novel tumor-suppressive function of PRMT6. However, augmented erythroid potential and bone marrow human CD71+ cells following PRMT6 knockdown were reserved only for primary MPN samples harboring ASXL1 mutations. Last, treatment of CD34+ hematopoietic/stem progenitor cells with the PRMT6 inhibitor EPZ020411 induced expression of genes involved in heme metabolism, hemoglobin, and erythropoiesis. These findings highlight interactions between JAK2 and ASXL1 mutations and a unique erythroid regulatory network in the context of mutant ASXL1.

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 (OXPHOS) 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 (TCA) cycle, but lower alpha-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 mice with α-KG 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 incubation 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, contributing to platelet hyperreactivity in MPN patients.

Hyperactivation of JAK2 kinase is a unifying feature of human Ph- myeloproliferative neoplasms (MPNs), most commonly due to the JAK2 V617F mutation. Mice harboring a homologous mutation in the Jak2 locus exhibit a phenotype resembling polycythemia vera. NFκB pathway hyperactivation is present in myeloid neoplasms, including MPNs, despite scarcity of mutations in NFκB pathway genes. To determine the impact of NFκB pathway hyperactivation in conjunction with Jak2 V617F, we utilized Ikk2 (Ikk2-CA) mice. Pan-hematopoietic Ikk2-CA alone produced depletion of hematopoietic stem cells and B cells. When combined with the Jak2 V617F mutation, Ikk2-CA rescued the polycythemia vera phenotype of Jak2 V617F. Likewise, Jak2 V617F ameliorated defects in hematopoiesis produced by Ikk2-CA. Single-cell RNA sequencing of hematopoietic stem and progenitor cells revealed multiple genes antagonistically regulated by Jak2 and Ikk2, including subsets whose expression was altered by Jak2 V617F and/or Ikk2-CA but partly or fully rectified in the double mutant. We hypothesize that Jak2 promotes hematopoietic stem cell population self-renewal, whereas Ikk2 promotes myeloid lineage differentiation, and biases cell fates at several branch points in hematopoiesis. Jak2 and Ikk2 both regulate multiple genes affecting myeloid maturation and cell death. Therefore, the presence of dual Jak2 and NFκB hyperactivation may present neomorphic therapeutic vulnerabilities in myeloid neoplasms.

MB and VA equal contributors AB and STO co-corresponding authors This study was initiated following evaluation of a 32 year-old woman who presented with a history of thrombocytopenia identified in childhood who subsequently developed features of myelofibrosis (MF). A bone marrow biopsy demonstrated hypercellularity in conjunction with megakaryocyte hyperplasia and marked reticulin fibrosis. Molecular testing for JAK2, CALR, and MPL mutations was negative. Given the unusual association between congenital thrombocytopenia and MF in this patient, exome sequencing was performed, revealing a heterozygous R304W mutation in the coiled coil (CC) domain of STIM1. Activating mutations in the CC and EF hand domains of STIM1 have been associated with Stormorken syndrome, a rare congenital platelet disorder associated with abnormal store operated calcium entry (SOCE). We subsequently identified a second patient with MF associated with a STIM1 activating mutation. This individual was found to have severe thrombocytopenia at birth, and exome sequencing revealed a heterozygous S88G mutation in the EF hand of STIM1. A bone marrow biopsy obtained at 6 months of age revealed atypical megakaryocytes and grade 1-2 MF. A repeat biopsy at age 2 showed persistence of stable MF. The unusual finding of MF in these two patients suggested the possibility of altered calcium signaling as a shared mechanism driving congenital platelet disorders such as Stormorken syndrome and myeloproliferative neoplasms (MPNs) including MF. In support of this notion, we identified elevated STIM1 expression in MF vs normal megakaryocyte progenitors, as well as in platelets from patients with essential thrombocythemia (ET) vs healthy controls. Additionally, we found that STIM1 expression was significantly elevated in CD34+ hematopoietic stem/progenitor cells (HSPCs) from both ET and MF patients vs healthy controls. Notably, STIM1 expression was increased in both JAK2 and CALR-mutant MF patients. Collectively, these findings provide evidence of aberrant STIM1 expression in MPN patient cells. To determine the functional role of STIM1 in MPN disease development, colony assays and patient-derived xenograft (PDX) experiments were performed with MF patient CD34+ cells subjected to CRISPR ablation of STIM1. Strikingly discordant results were observed with JAK2 vs CALR-mutant patient samples. Abrogation of STIM1 in CALR-mutant CD34+ cells led to decreased colony formation, and NSGS mice engrafted in parallel with STIM1-targeted cells exhibited decreased human CD45+ cell engraftment in conjunction with prolonged survival. These findings suggest an important role for STIM1 in CALR-mutant MPN disease phenotypes. In contrast, targeting of STIM1 in JAK2-mutant CD34+ cells led to increased colony formation and exacerbated disease phenotypes in vivo as manifested by enhanced human CD45+ cell engraftment, worsened splenomegaly, and early lethality. Similar results were obtained in experiments utilizing pharmacologic inhibitors of SOCE activity. Taken together, these findings indicate that the consequences of aberrant STIM1 activity may be context-dependent relating to specific MPN driver mutations. To expand these observations, we identified a separate cohort of 9 family members in Italy with Stormorken syndrome and confirmed STIM1 EF hand mutations. In ex vivo megakaryocytic differentiation assays, cells from affected individuals exhibited a defect in proplatelet formation. These observations were corroborated by initial analyses of a newly generated Stim1 R304W conditional knock-in mouse which recapitulated the characteristic thrombocytopenia found in patients with Stormorken syndrome. In summary, this study represents the first demonstration of MF development in patients with Stormorken syndrome, thereby uncovering a previously unrecognized hallmark of altered calcium signaling via aberrant STIM1 activation underlying Stormorken syndrome and MPNs. Our findings suggest distinct mechanisms relating to the interaction between JAK2 vs CALR mutation and altered STIM1 activity. Further studies of these relationships may have important ramifications for potential therapeutic approaches targeting these pathways.

Myeloid malignancies harbor distinct molecular drivers but share convergence of oncogenic signaling pathways and propagation by ripe pro-inflammatory niches. To delineate these hallmarks across the spectrum of myeloid disease states, we established the largest comprehensive atlas of myeloproliferative neoplasms (MPN) and secondary acute myeloid leukemia (sAML) through RNA-sequencing and mass cytometry (CyTOF) of 370 primary samples encompassing CD34+ hematopoietic stem/progenitor cells and CD14+ monocytes, revealing aberrant of PI3K/AKT/mTOR signalling and NFκB-mediated hyper-inflammation. As a central mediator of these hyperactive signaling pathways, ribosomal S6 kinases (RSKs) represent potentially attractive novel therapeutic targets warranting further evaluation. Using both genetic approaches and a first-in-class oral RSK inhibitor, PMD-026, that is currently being evaluated in phase 1/1b clinical trials (NCT04115306) in metastatic and triple negative breast cancer, we found that RSK1 ( RPS6KA1) inhibition potently induced apoptosis and G2/M arrest in leukemia models in conjunction with suppression of PI3K/AKT/mTOR and NFκB signaling. Further NFκB cascade profiling following RSK1 perturbation revealed reduced phosphorylation of IKKα/β and p65/RELA and prevention of p65/RELA nuclear translocation. Using RNA-seq, ATAC-seq and H3K27ac CUT&Tag, we found that PMD-026 treatment altered chromatin accessibility and inhibited NFKB1, TNF, and cell cycle regulators CCNA1/2 and CDK1/2. In cytokine CyTOF, PMD-026 nearly abrogated all induction of inflammatory cytokines including TNF, IL-6, IL-8, CCL3, and CCL4 in primary MPN monocytes to levels substantially below basal conditions. We further extended our findings to de novo AML harboring FLT3 internal tandem duplication ( FLT3-ITD), where FLT3-ITD patients exhibited elevated RPS6KA1 expression and those who developed resistance to gilteritinib demonstrated progressively increased RPS6KA1 expression. FLT3-ITD cells exhibited preferentially sensitivity to RSK1 inhibition, where we uncovered bi-directional regulation. Through cycloheximide, MG-132, and ubiquitination assays, we found that RSK1 regulates FLT3-ITD activity and protein stability through deubiqutinase USP1, and where either RPS6KA1 or USP1 inhibition resulted in concomitant downregulation of FLT3 protein and cell lethality. Multivariate analysis of the TCGA and BeatAML cohorts (n= 568 patients) revealed high median USP1 or RPS6KA1 expression to be significantly associated with poor survival, thus defining a RSK1-USP1-FLT3 axis with prognostic relevance. Across in vivo models, PMD-026 ameliorated MPN disease features driven by MPL W515L including leukocytosis, splenomegaly, and bone marrow fibrosis, while prolonging survival, in conjunction with suppression of inflammatory cytokines including TNF, IL-6 and IL-1b. We then evaluated PMD-026 across five patient-derived xenograft (PDX) models spanning the spectrum of myeloid malignancies including myelofibrosis (MF), sAML, and chronic myelomonocytic leukemia (CMML) encompassing various driver and multiple high-risk mutations. Treatment in MF PDX mice decelerated disease progression, extended survival, and reduced splenomegaly, while in CMML/sAML PDXs, PMD-026 led to a 67 to 96 percent reduction in human CD45+ cells engraftment. Finally, PMD-026 treatment in both mice xenografted with MV4-11 cells and syngeneic Flt3ITDTet2KO mice significantly reduced leukemic cell engraftment and prolonged survival. These data indicate potent efficacy of RSK inhibition across diverse models of chronic and acute myeloid malignancies. Lastly, we investigated the impact of PMD-026 on hematological parameters from 41 breast cancer patients enrolled in the phase 1/1b clinical trial. Overall, there was no sustained suppressive effect on hematological parameters and there were no hematological PMD-026-related toxicities meeting criteria for dose modification during the trial period. These clinical data demonstrate that PMD-026 did not cause myelosuppression. Our findings uncover a novel therapeutic avenue for a conserved RSK1 dependency across chronic and acute myeloid neoplasms. The potent and consistent disease-ameliorating effects across numerous leukemia mouse models demonstrates promise for repurposing PMD-026 for the treatment of myeloid malignancies.

JDP and STO co-corresponding authors Previous studies by our group and others have demonstrated that monocytes play a key role in driving hyperinflammation in myeloproliferative neoplasms (MPNs), and that aberrant inflammatory cytokine signaling contributes to disease progression and poor prognosis in MPNs. To interrogate relationships between cellular sources and targets of inflammatory cytokines, we performed single cell RNA-seq (scRNA-seq) in PBMCs and progenitor cells from MPN patients and healthy controls. Monocytes from MPN patients displayed significant enrichment of inflammation-relevant genes as expected. Cell-cell communication networks inferred from expression of ligands and receptors predicted monocytes as a pivotal mediator of cell interactions. Further analysis revealed galectin signaling as one of the most robust input/output pathways for monocytes and significant enrichment of LGALS1 (galectin-1) expression in MPN monocytes. Galectins are a class of proteins that bind specifically to β-galactoside carbohydrates, such as N-linked or O-linked glycosylated proteins. Abnormal expression of galectins in various cancers has been found to mediate broad biological functions, including cell proliferation, apoptosis, adhesion, and inflammation. However, the mechanisms by which galectins contribute to MPN pathogenesis remain incompletely understood. To corroborate our sRNA-seq findings, we performed flow cytometry analysis which demonstrated elevated expression of galectin-1 in MPN patient CD14+ monocytes. Increased plasma levels of galectin-1 were also identified in MPN patients compared to healthy individuals. Higher galectin-1 protein levels in both Kit+ progenitor cells and CD11b+ myeloid cells from Jak2 V617F knock-in mice were also observed when compared to wild type mice. Additionally, galectin-1 expression was induced by MPL W515L and JAK2 V617F and inhibited by ruxolitinib in Ba/F3 cells. Thus, our results show enrichment of galectin-1 in both MPN patients and mouse models, with evidence of direct contribution from specific MPN driver mutations. Our scRNA-seq dataset analysis showed significant correlations of galectin-1 expression with inflammatory and oxidative phosphorylation (OXPHOS) genes in MPN patient monocytes. To investigate the effects of galectin-1 in monocyte activation, we incubated CD14+ monocytes from MPN patients with recombinant galectin-1 (rGal-1) and observed markedly stimulated secretion of inflammatory cytokines, such as IL-1α, IL-1β, IL-6, IL-8 and TNF-α. Furthermore, OTX008, a galectin-1 inhibitor, inhibited the transcription and secretion of inflammatory cytokines in MPN patient CD14+ monocytes and monocytic cell lines. Notably, both genetic and pharmacologic inhibition of galectin-1 reduced cellular ATP level and oxygen consumption rate, suggesting a metabolic reprogramming in MPNs. Although galectin-1 mediates broad biological functions, the molecular mechanisms by which galectin-1 regulates signaling pathways and transcription in MPN cells had not been delineated. Our scRNA-seq heterogeneity analysis suggested that genes in the PI3K-AKT-mTOR pathway were differentially expressed between galectin-1 high- and low-expressing monocytes. We therefore incubated both monocytic cell lines and monocytes from MPN patients with rGal-1 and observed stimulation of the PI3K-AKT-mTOR pathway, represented by increased levels of phosphorylated mTOR, AKT and S6. Consistently, genetic and pharmacologic inhibition of galectin-1 inhibited activation of the PI3K-AKT-mTOR pathway. In summary, our results demonstrate upregulation of galectin-1 in MPN monocytes, potentially due to activation of JAK2-driven signaling. We further demonstrate that galectin-1 fuels inflammation potentially via metabolic reprogramming of monocytes and activation of PI3K-AKT-mTOR signaling. Our data also suggest galectin-1 as a putative therapeutic target in MPNs.

The British Journal of Haematology publishes original research papers in clinical, laboratory and experimental haematology. The Journal also features annotations, reviews, short reports, images in haematology and Letters to the Editor.

Myeloproliferative neoplasms (MPNs) exhibit a propensity for transformation to secondary acute myeloid leukemia (sAML), for which the underlying mechanisms remain poorly understood, resulting in limited treatment options and dismal clinical outcomes. Here, we performed single-cell RNA sequencing on serial MPN and sAML patient stem and progenitor cells, identifying aberrantly increased expression of DUSP6 underlying disease transformation. Pharmacologic dual-specificity phosphatase (DUSP)6 targeting led to inhibition of S6 and Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling while also reducing inflammatory cytokine production. DUSP6 perturbation further inhibited ribosomal S6 kinase (RSK)1, which we identified as a second indispensable candidate associated with poor clinical outcome. Ectopic expression of DUSP6 mediated JAK2-inhibitor resistance and exacerbated disease severity in patient-derived xenograft (PDX) models. Contrastingly, DUSP6 inhibition potently suppressed disease development across Jak2(V617F) and MPLW515L MPN mouse models and sAML PDXs without inducing toxicity in healthy controls. These findings underscore DUSP6 in driving disease transformation and highlight the DUSP6-RSK1 axis as a vulnerable, druggable pathway in myeloid malignancies.

Prior studies by our group and others have demonstrated that platelets from patients with myeloproliferative neoplasms (MPNs) exhibit a hyperreactive phenotype. However, a complete understanding of platelet alterations in MPNs remains lacking, and the mechanisms by which platelets contribute to MPN-related thrombosis, as well as other MPN disease features, are incompletely understood. In this study, utilizing multiomic approaches to interrogate platelet phenotypes in patient samples, in conjunction with relevant MPN animal models (Figure 1A), we aim to investigate mechanisms of dysregulated platelet activity in MPNs, and explore how these findings may be leveraged to uncover novel therapeutic strategies. We initially studied platelet activation in peripheral blood from patients with essential thromobocythemia (ET) and compared to age-, sex-matched healthy controls. We found significantly increased P-selectin exposure in conjunction with increased platelet-leukocyte aggregates indicating activation of platelets from ET patients. To investigate the transcriptional signature of PBMCs and platelets at the single cell level, we performed single cell RNA-seq (scRNA-seq) in PBMCs from ET patients and healthy controls. Monocytes were increased in ET patients and displayed the highest inflammation index, implicating monocytes as the primary source of inflammation in ET. GSEA analysis revealed enrichment of platelet activation and oxidative phosphorylation (OXPHOS) genes in platelets from ET patients. Liquid chromatography-mass spectrometry (LC-MS) metabolomics analysis showed distinct metabolic phenotypes consisting of elevated tricarboxylic acid (TCA) cycle components, ATP generation and lower alpha-ketoglutarate (α-KG), in platelets from ET patients, all consistent with increased OXPHOS. α-KG is a key TCA cycle intermediate, which inhibits ATP generation via the suppression of ATP synthase. Extracellular flux analysis by Seahorse analysis confirmed bioenergetic alterations in MPN patient platelets. Enhanced mitochondrial respiration at both baseline and after ex vivo stimulation with the platelet agonist thrombin receptor activator peptide (TRAP6) was also observed from MPN patient platelets. Notably, α-KG supplementation drastically reduced oxygen consumption and ATP generation in platelets from MPN patients. We further investigated the effects of α-KG on MPN platelet activation. Ex vivo incubation of platelets from both MPN patients and Jak2 V617F knock-in mice with α-KG significantly reduced platelet surface P-selectin and integrin a2bb3 activation. Additionally, α-KG inhibited the spreading and adhesion of platelets from Jak2 V617F knock-in mice to fibrinogen-coated surfaces. Platelet phosphoblots demonstrated significant downregulation of p-STAT3, p-AKT and p-ERK after treatment with α-KG, suggesting these signaling pathways may be responsible for the inhibitory effects of α-KG on platelet activation. Thus, α-KG inhibited platelet activities in both human and mouse MPN samples. To test the therapeutic impact of α-KG on MPN disease features, we treated Jak2 V617F knock-in mice with α-KG for 6 weeks. Oral α-KG supplementation decreased splenomegaly and reduced elevated platelets and hematocrit. Additionally, monocytes were significantly decreased as early as 2 weeks after α-KG treatment in Jak2 V617F knock-in mice. In ex vivo studies with MPN patient CD34+ cells, α-KG treatment for 10 days led to a decrease in CD41+ CD61+ cells, suggesting decreased megakaryocyte commitment. We further observed that α-KG incubation significantly decreased the secretion of proinflammatory cytokines from sorted CD14+ human monocytes. Mass cytometry analysis of whole blood from MPN patients demonstrated inhibition of MAPK pathway signaling after α-KG treatment. Taken together, these results suggest that α-KG supplementation may exert therapeutic effects through both direct inhibition of MPN platelet activity and via quenching of monocyte hyper-inflammation (Figure 1B). In summary, these studies reveal a previously unrecognized metabolic disorder in platelets from MPN patients and highlight a prominent role for α-KG in aberrant MPN platelet activity and monocyte-driven inflammation. These findings have potential relevance for novel therapeutic approaches for MPN patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

AbstractTargeted inhibitors of JAK2 (eg ruxolitinib) often provide symptomatic relief for myeloproliferative neoplasm (MPN) patients, but the malignant clone persists and remains susceptible to disease transformation. These observations suggest that targeting alternative dysregulated signaling pathways may provide therapeutic benefit. Previous studies identified NFκB pathway hyperactivation in myelofibrosis (MF) and secondary acute myeloid leukemia (sAML) that was insensitive to JAK2 inhibition. Here, we provide evidence that NFκB pathway inhibition via pevonedistat targets malignant cells in MPN patient samples as well as in MPN and patient-derived xenograft mouse models that are nonredundant with ruxolitinib. Colony forming assays revealed preferential inhibition of MF colony growth compared with normal colony formation. In mass cytometry studies, pevonedistat blunted canonical TNFα responses in MF and sAML patient CD34+ cells. Pevonedistat also inhibited hyperproduction of inflammatory cytokines more effectively than ruxolitinib. Upon pevonedistat treatment alone or in combination with ruxolitinib, MPN mouse models exhibited reduced disease burden and improved survival. These studies demonstrating efficacy of pevonedistat in MPN cells in vitro as well as in vivo provide a rationale for therapeutic inhibition of NFκB signaling for MF treatment. Based on these findings, a Phase 1 clinical trial combining pevonedistat with ruxolitinib has been initiated.

Introduction: Hepcidin, a peptide-hormone produced by hepatocytes, is a key regulator of iron homeostasis in mammals. Hepcidin levels are affected by several factors including inflammation, iron concentration, and erythropoietic signaling, and elevated hepcidin levels can lead to anemia. Inflammatory cytokines such as IL-6 induce hepcidin mRNA transcription via JAK/STAT signaling, whereas high serum iron levels and high erythropoietic drive via erythroferrone (ERFE) suppress hepcidin transcription via BMP/SMAD signaling. Anemia is a common problem in patients with myelofibrosis (MF). In a previous study of primary myelofibrosis (PMF) patients, serum hepcidin levels were found to be elevated compared to normal controls and were associated with increased RBC transfusion requirement and reduced survival (Pardanani et al. Am J Hematol 2013;88(4):312-316). Ruxolitinib is a JAK1/2 inhibitor approved for treatment of patients with MF. Treatment with ruxolitinib reduces spleen volume, constitutional symptoms, and inflammatory cytokines, but does not lead to anemia improvement in MF (Verstovsek et al. NEJM 2012;366:799-807). To further assess the relationship between hepcidin and anemia in MF, we measured hepcidin levels in 99 MF patients including 49 PMF and 50 secondary MF (sMF) patients, as well as 24 patients treated with ruxolitinib. We also evaluated the relationship between hepcidin and hemoglobin levels, inflammatory cytokines, and serum iron markers.

Myeloproliferative neoplasms (MPNs) feature a malignant clone containing the JAK2 V617F mutation, or another mutation causing dysregulated JAK2 kinase activity. The multiple disease phenotypes of MPNs, and their tendency to transform phenotypically, suggest pathophysiologic heterogeneities beyond a common phenomenon of JAK2 hyperactivation. JAK2 has the potential to activate multiple other signaling molecules, either directly through downstream effectors, or indirectly through induction of target gene expression. We have interrogated myeloproliferative signaling in myelofibrosis (MF) and secondary acute myeloid leukemia (sAML) patient samples using mass cytometry, which allows the quantitative measurement of multiple signaling molecules simultaneously at the single-cell level, in cell populations representing a nearly complete spectrum of hematopoiesis. MF and sAML malignant cells demonstrated a high prevalence of hyperactivation of the JAK-STAT, MAP kinase, PI3 kinase and NFκB signaling pathways. Constitutive NFκB signaling was evident across MF and sAML patients. A supporting gene set enrichment analysis (GSEA) of MF showed many NFκB target genes to be expressed above normal levels in MF patient CD34+ cells. NFκB inhibition suppressed colony formation from MF CD34+ cells. This study indicates that NFκB signaling contributes to human myeloproliferative disease and is abnormally activated in MF and sAML.

A 77 year-old man initially presented in July 2013 with anemia, splenomegaly, and constitutional symptoms. A bone marrow biopsy revealed a hypercellular marrow with megakaryocytic hyperplasia and atypia and mild reticulin fibrosis, consistent with a diagnosis of primary myelofibrosis (PMF). Cytogenetics revealed a normal karyotype. JAK2 V617F testing was negative. Initiation of treatment with the JAK inhibitor ruxolitinib led to marked symptomatic improvement. The patient was then enrolled in a Phase 2 study with the anti-lysyl oxidase-like-2 (LOXL2) monoclonal antibody simtuzumab, administered via IV infusion every two weeks (while continuing ruxolitinib). He tolerated the simtuzumab infusions well initially, but with the 11th and 12th infusions experienced rigors, hypotension, and hypoxia. This occurred ~8 months after his initial PMF diagnosis. A repeat bone marrow biopsy revealed large aggregates of mast cells comprising 30-40% of the marrow cellularity (with 16% mast cells enumerated on the aspirate). A subset of the mast cells exhibited spindled morphology, and CD25 co-expression was demonstrated by flow cytometry in a subset of CD117-positive cells. Testing for the KITD816V mutation was positive. Tryptase levels were significantly elevated (375 ng/mL). These findings were consistent with a diagnosis of aggressive systemic mastocytosis with an associated hematologic non-mast cell lineage disorder (ASM-AHNMD).

We developed Split DamID (SpDamID), a protein complementation version of DamID, to mark genomic DNA bound in vivo by interacting or juxta-positioned transcription factors. Inactive halves of DAM (DNA adenine methyltransferase) were fused to protein pairs to be queried. Either direct interaction between proteins or proximity enabled DAM reconstitution and methylation of adenine in GATC. Inducible SpDamID was used to analyze Notch-mediated transcriptional activation. We demonstrate that Notch complexes label RBP sites broadly across the genome and show that a subset of these complexes that recruit MAML and p300 undergo changes in chromatin accessibility in response to Notch signaling. SpDamID differentiates between monomeric and dimeric binding, thereby allowing for identification of half-site motifs used by Notch dimers. Motif enrichment of Notch enhancers coupled with SpDamID reveals co-targeting of regulatory sequences by Notch and Runx1. SpDamID represents a sensitive and powerful tool that enables dynamic analysis of combinatorial protein-DNA transactions at a genome-wide level.

Myeloproliferative neoplasms (MPNs) including myelofibrosis (MF) are characterized by chronic hyperactivation of a signaling axis downstream of the JAK2 kinase. Pharmacologic inhibitors of JAK2 ameliorate constitutional symptoms and splenomegaly in MF patients. However, these agents do not appear to be capable of eradicating the malignant clone, nor have they have been shown to prevent transformation to secondary acute myeloid leukemia (sAML). These findings suggest that aberrant activation of additional signaling pathways, either downstream of JAK2, or via alternative mechanisms, may contribute to MPN pathogenesis. To develop more effective therapeutic strategies, a fuller understanding of these altered signaling pathways in MPNs is needed.