The role of ribosome biogenesis in erythroid development is supported by the recognition of erythroid defects in ribosomopathies in both Diamond-Blackfan anemia and 5q- syndrome. Whether ribosome ...biogenesis exerts a regulatory function on normal erythroid development is still unknown. In the present study, a detailed characterization of ribosome biogenesis dynamics during human and murine erythropoiesis showed that ribosome biogenesis is abruptly interrupted by the decline in ribosomal DNA transcription and the collapse of ribosomal protein neosynthesis. Its premature arrest by the RNA Pol I inhibitor CX-5461 targeted the proliferation of immature erythroblasts. p53 was activated spontaneously or in response to CX-5461, concomitant to ribosome biogenesis arrest, and drove a transcriptional program in which genes involved in cell cycle-arrested, negative regulation of apoptosis, and DNA damage response were upregulated. RNA Pol I transcriptional stress resulted in nucleolar disruption and activation of the ATR-CHK1-p53 pathway. Our results imply that the timing of ribosome biogenesis extinction and p53 activation is crucial for erythroid development. In ribosomopathies in which ribosome availability is altered by unbalanced production of ribosomal proteins, the threshold downregulation of ribosome biogenesis could be prematurely reached and, together with pathological p53 activation, prevents a normal expansion of erythroid progenitors.
Summary
The effectiveness of tyrosine kinase inhibitors (TKIs) has made it possible to consider treatment discontinuation in chronic myeloid leukaemia (CML) patients that achieve an excellent ...response. However, a few of the patients included in the Europe Stop Tyrosine Kinase Inhibitors (EURO‐SKI) trial reported musculoskeletal pain shortly after stopping TKIs, considered as a withdrawal syndrome (WS). To identify factors that may predispose to TKI WS, we analysed the pharmacovigilance declarations for the 6 months after stopping TKIs in a large cohort of CML (n = 427) that combined the French patients included in the STop IMatinib 2 (STIM2; n = 224) and EURO‐SKI (n = 203) trials. Among these patients, 23% (99/427) developed TKI WS after stopping imatinib (77/373; 20·4%), nilotinib (12/29; 41·4%) or dasatinib (10/25; 40%). WS concerned mainly the upper body joints, and required multiple symptomatic treatments in 30% of patients. Univariate and multivariate analyses identified two risk factors: duration of TKI treatment risk ratio (RR) = 1·68 (1·02–2·74) with a 93‐month cut‐off time, and history of osteoarticular symptoms RR = 1·84 (1·04–3·28). These findings confirm that WS is a TKI class effect. CML patients should be carefully screened before treatment initiation to identify pre‐existent osteoarticular symptoms. Moreover, before TKI discontinuation, patients should be informed of the possibility of WS, particularly after a long treatment period.
Background Following a clinical evaluation of deferasirox (Exjade) it was concluded that, in addition to baseline body iron burden, ongoing transfusional iron intake should be considered when ...selecting doses. The 1-year EPIC study, the largest ever investigation conducted for an iron chelator, is the first to evaluate whether fixed starting doses of deferasirox, based on transfusional iron intake, with dose titration guided by serum ferritin trends and safety markers, provides clinically acceptable chelation in patients (aged >or=2 years) with transfusional hemosiderosis from various types of anemia.
The recommended initial dose was 20 mg/kg/day for patients receiving 2-4 packed red blood cell units/month and 10 or 30 mg/kg/day was recommended for patients receiving less or more frequent transfusions, respectively. Dose adjustments were based on 3-month serum ferritin trends and continuous assessment of safety markers. The primary efficacy end-point was change in serum ferritin after 52 weeks compared with baseline.
The 1744 patients enrolled had the following conditions; thalassemia (n=1115), myelodysplastic syndromes (n=341), aplastic anemia (n=116), sickle cell disease (n=80), rare anemias (n=43) and other transfused anemias (n=49). Overall, there was a significant reduction in serum ferritin from baseline (-264 ng/mL; P<0.0001), reflecting dosage adjustments and ongoing iron intake. The most common (>5%) adverse events were gastrointestinal disturbances (28%) and skin rash (10%). Conclusions Analysis of this large, prospectively collected data set confirms the response to chelation therapy across various anemias, supporting initial deferasirox doses based on transfusional iron intake, with subsequent dose titration guided by trends in serum ferritin and safety markers (clinicaltrials.gov identifier: NCT00171821).
Myeloproliferative diseases (MPDs) represent the commonest cause of splanchnic vein thrombosis (SVT), including Budd-Chiari syndrome (BCS) and portal vein thrombosis (PVT), but their diagnosis is ...hampered by changes secondary to portal hypertension, while their influence in the outcome of SVT remains unclear. We assessed the diagnostic and prognostic value of JAK2 and MPL515 mutations in 241 SVT patients (104 BCS, 137 PVT). JAK2V617F was found in 45% of BCS and 34% of PVT, while JAK2 exon 12 and MPL515 mutations were not detected. JAK2V617F was found in 96.5% of patients with bone marrow (BM) changes specific for MPD and endogenous erythoid colonies, but also in 58% of those with only one feature and in 7% of those with neither feature. Stratifying MPD diagnosis first on JAK2V617F detection would have avoided BM investigations in 40% of the patients. In BCS, presence of MPD carried significantly poorer baseline prognostic features, required hepatic decompression procedures earlier, but had no impact on 5-year survival. Our results suggest that JAK2V617F testing should replace BM investigations as initial test for MPD in patients with SVT. Underlying MPD is associated with severe forms of BCS, but current therapy appears to offset deleterious effects of MPD on the medium-term outcome.
Megakaryopoiesis is a 2-step differentiation process, regulated by thrombopoietin (TPO), on binding to its cognate receptor myeloproliferative leukemia (MPL). This receptor associates with ...intracytoplasmic tyrosine kinases, essentially janus kinase 2 (JAK2), which regulates MPL stability and cell-surface expression, and mediates TPO-induced signal transduction. We demonstrate that JAK2 and MPL mediate TPO-induced proliferation arrest and megakaryocytic differentiation of the human megakaryoblastic leukemia cell line UT7-MPL. A decrease in JAK2 or MPL protein expression, and JAK2 chemical inhibition, suppress this antiproliferative action of TPO. The expression of JAK2 and MPL, which progressively increases along normal human megakaryopoiesis, is decreased in platelets of patients diagnosed with JAK2- or MPL-mutated essential thrombocytemia and primary myelofibrosis, 2 myeloproliferative neoplasms in which megakaryocytes (MKs) proliferate excessively. Finally, low doses of JAK2 chemical inhibitors are shown to induce a paradoxical increase in MK production, both in vitro and in vivo. We propose that JAK2 and MPL expression levels regulate megakaryocytic proliferation vs differentiation in both normal and pathological conditions, and that JAK2 chemical inhibitors could promote a paradoxical thrombocytosis when used at suboptimal doses.
•We propose that megakaryopoiesis is regulated by the expression levels of the TPO receptor MPL and the associated tyrosine kinase JAK2.•This model could explain why suboptimal doses of JAK2 inhibitors can induce a paradoxical increase in platelet production.
Summary
Superior rates of deep molecular response (DMR) have been reported with the combination of tyrosine kinase inhibitors and pegylated‐interferon‐alpha (Peg‐IFN) in patients with newly diagnosed ...chronic phase‐chronic myeloid leukaemia (CP‐CML). In this setting, this study investigated the efficacy and safety of dasatinib combined to Peg‐IFN‐α2b (Dasa‐PegIFN, NCT01872442). A total of 79 patients (age ≤65 years) started dasatinib; 61 were eligible for Peg‐IFNα‐2b add‐on therapy at month 3 for a maximum 21‐months duration. Dasatinib was continued thereafter. The primary endpoint was the cumulative rate of molecular response 4.5 log (MR4.5) by 12 months. The results are reported for the 5‐year duration of the study. Grade 3 neutropenia was frequent with the combination but did not induce severe infection (one of grade 3). Other adverse events were generally low grade (4% of grade 3–4) and expected. Seventy‐nine per cent and 61% of patients continued the Peg‐IFN until months 12 and 24, respectively. Overall, at these time points, MR4.5 rates were 25% and 38%, respectively. Thereafter, 32% and 46% of patients achieved a sustained (≥2 years) MR4.5 or MR4, respectively. This work established the feasibility and high rates of achievement of early and sustained DMR (a prerequisite for treatment‐free‐remission) with dasatinib and Peg‐IFNα‐2b combination as initial therapy.
Several studies suggest an implication of transforming growth factor-β1 (TGF-β1) in the promotion of myelofibrosis associated with hematopoietic malignancies, but the involvement of this cytokine is ...not fully investigated. To test directly the impact of TGF-β1 in the pathogenesis of myelofibrosis, bone marrow stem cells from homozygous TGF-β1 null (TGF-β1−/−) and wild-type (WT) littermates were infected with a retrovirus encoding the murine thrombopoietin (TPO) protein and engrafted into lethally irradiated wild-type hosts for long-term reconstitution. Over the 4 months of follow-up, TPO levels in plasma were markedly elevated in both groups of mice, and animals typically developed a myeloproliferative syndrome characterized by thrombocytosis, leukocytosis, splenomegaly, increased numbers of progenitors in blood, and extramedullary hematopoiesis. Severe fibrosis was observed in spleen and marrow from all the mice engrafted with WT cells. In contrast, none of the mice repopulated with TGF-β1−/− cells (chimerism > 70%) showed deposition of reticulin fibers at any time during the follow-up. In accordance with the development of fibrosis, latent TGF-β1 levels in plasma and extracellular fluid of the spleen from mice engrafted with WT cells were increased 6-fold and 4-fold, respectively, over levels found in normal hosts, whereas no increase over baseline levels could be demonstrated in animals undergoing transplantation with TGF-β1−/− cells. These data provide evidence that TGF-β1 produced by hematopoietic cells is pivotal for the pathogenesis of myelofibrosis that develops in mice with TPO overexpression.
The purpose of this study was to identify the incidence, causes and impact of non-adherence to oral and subcutaneous chronic treatments for patients with polycythemia vera or essential ...thrombocythemia. Patients receiving cytoreductive drugs for polycythemia vera or essential thrombocythemia were recruited at our institution (
registry). They completed a one-shot questionnaire designed by investigators (
study). Data about complications (thrombosis, transformation and death) at any time in the patient's life (before diagnosis, up until consultation and after the completion of the questionnaire) were collected. Sixty-five (22.7%) of 286 patients reported poor adherence (<90%) to their treatment with cytoreductive drugs and 46/255/18%) also declared non-adherence to antithrombotic drugs. In total, 85/286 patients (29.7%) declared they did not adhere to their treatment. Missing an intake was rare and was mostly due to forgetfulness especially during occupational travel and holidays. Patients who did not adhere to their treatment were characterized by younger age, living alone, having few medications but a high numbers of pills and determining their own schedule of drug intake. Having experienced thrombosis or hematologic evolution did not influence the adherence rate. Non-adherence to oral therapy was associated with a higher risk of phenotypic evolution (7.3
1.8%,
=0.05). For patients treated for polycythemia vera or essential thrombocythemia, non-adherence to cytoreductive and/or antithrombotic therapies is frequent and is influenced by age, habitus and concomitant treatments, but not by disease history or treatment side effects. Phenotypic evolution seems to be more frequent in the non-adherent group.
Constitutively active JAK2V617F and thrombopoietin receptor (TpoR) W515L/K mutants are major determinants of human myeloproliferative neoplasms (MPNs). We show that a TpoRW515 mutation (W515A), which ...we detected in 2 myelofibrosis patients, and the Δ5TpoR active mutant, where the juxtamembrane R/KW515QFP motif is deleted, induce a myeloproliferative phenotype in mouse bone marrow reconstitution experiments. This phenotype required cytosolic Y112 of the TpoR. Phosphotyrosine immunoprofiling detected phosphorylated cytosolic TpoR Y78 and Y112 in cells expressing TpoRW515A. Mutation of cytosolic Y112 to phenylalanine prevented establishment of the in vivo phenotype and decreased constitutive active signaling by Δ5TpoR and TpoRW515A, especially via the mitogen-activated protein (MAP)–kinase pathway, without decreasing Janus kinase 2 (JAK2) activation. In contrast, mutation of cytosolic Y78 to phenylalanine enhanced the myeloproliferative syndrome induced by the TpoRW515 mutants, by enhancing receptor-induced JAK2 activation. We propose that TpoR cytosolic phosphorylated Y112 and flanking sequences could become targets for pharmacologic inhibition in MPNs.
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