Thrombopoietin-independent Megakaryocyte Differentiation of Hematopoietic Progenitor Cells from Patients with Myeloproliferative Neoplasms.

Primary hematopoietic stem and progenitor cell (HSPC)-derived megakaryocytes are a valuable tool for translational research interrogating disease pathogenesis and developing new therapeutic avenues for patients with hematologic disorders including myeloproliferative neoplasms (MPNs). Thrombopoietin (TPO)-independent proliferation and megakaryocyte differentiation play a central role in the pathogenesis of essential thrombocythemia and myelofibrosis, two MPN subtypes that are characterized by increased numbers of bone marrow megakaryocytes and somatic mutations in either , or . However, current culture strategies generally use healthy HSPCs for megakaryocyte production and are not optimized for the investigation of TPO-independent or TPO-hypersensitive growth and megakaryocyte-directed differentiation of primary patient-derived HSPCs.

Dysregulated Lipid Synthesis by Oncogenic IDH1 Mutation Is a Targetable Synthetic Lethal Vulnerability.

Unlabelled: Isocitrate dehydrogenase 1 and 2 (IDH) are mutated in multiple cancers and drive production of (R)-2-hydroxyglutarate (2HG). We identified a lipid synthesis enzyme [acetyl CoA carboxylase 1 (ACC1)] as a synthetic lethal target in mutant IDH1 (mIDH1), but not mIDH2, cancers. Here, we analyzed the metabolome of primary acute myeloid leukemia (AML) blasts and identified an mIDH1-specific reduction in fatty acids.

Ceramide-induced integrated stress response overcomes Bcl-2 inhibitor resistance in acute myeloid leukemia.

Inducing cell death by the sphingolipid ceramide is a potential anticancer strategy, but the underlying mechanisms remain poorly defined. In this study, triggering an accumulation of ceramide in acute myeloid leukemia (AML) cells by inhibition of sphingosine kinase induced an apoptotic integrated stress response (ISR) through protein kinase R-mediated activation of the master transcription factor ATF4. This effect led to transcription of the BH3-only protein Noxa and degradation of the prosurvival Mcl-1 protein on which AML cells are highly dependent for survival.

Targeting human CALR-mutated MPN progenitors with a neoepitope-directed monoclonal antibody.

Calreticulin (CALR) is recurrently mutated in myelofibrosis via a frameshift that removes an endoplasmic reticulum retention signal, creating a neoepitope potentially targetable by immunotherapeutic approaches. We developed a specific rat monoclonal IgG2α antibody, 4D7, directed against the common sequence encoded by both insertion and deletion mutations. 4D7 selectively bound to cells co-expressing mutant CALR and thrombopoietin receptor (TpoR) and blocked JAK-STAT signalling, TPO-independent proliferation and megakaryocyte differentiation of mutant CALR myelofibrosis progenitors by disrupting the binding of CALR dimers to TpoR.