Summary Specific combinations of Acute Myeloid Leukemia (AML) disease alleles, including FLT3 and TET2 mutations, confer distinct biologic features and adverse outcome. We generated mice with mutations in Tet2 and Flt3, which resulted in fully penetrant, lethal AML. Multipotent Tet2−/−;Flt3ITD progenitors (LSK CD48+CD150−) propagate disease in secondary recipients and were refractory to standard AML chemotherapy and FLT3-targeted therapy. Flt3ITD mutations and Tet2 loss cooperatively remodeled DNA methylation and gene expression to an extent not seen with either mutant allele alone, including at the Gata2 locus. Re-expression of Gata2 induced differentiation in AML stem cells and attenuated leukemogenesis. TET2 and FLT3 mutations cooperatively induce AML, with a defined leukemia stem cell population characterized by site-specific changes in DNA methylation and gene expression.

Even though hematopoietic stem cell (HSC) dysfunction is presumed in myelodysplastic syndrome (MDS), the exact nature of quantitative and qualitative alterations is unknown. We conducted a study of phenotypic and molecular alterations in highly fractionated stem and progenitor populations in a variety of MDS subtypes. We observed an expansion of the phenotypically primitive long-term HSCs (lineage ؊ /CD34 ؉ /CD38 ؊ /CD90 ؉ ) in MDS, which was most pronounced in higher-risk cases. These MDS HSCs demonstrated dysplastic clonogenic activity. Examination of progenitors revealed that lower-risk MDS is

Neomorphic mutations in isocitrate dehydrogenase 1 (IDH1) are driver mutations in acute myeloid leukemia (AML) and other cancers. We report the development of new allosteric inhibitors of mutant IDH1. Crystallographic and biochemical results demonstrated that compounds of this chemical series bind to an allosteric site and lock the enzyme in a catalytically inactive conformation, thereby enabling inhibition of different clinically relevant IDH1 mutants. Treatment of IDH1 mutant primary AML cells uniformly led to a decrease in intracellular 2-HG, abrogation of the myeloid differentiation block and induction of granulocytic differentiation at the level of leukemic blasts and more immature stem-like cells, in vitro and in vivo. Molecularly, treatment with the inhibitors led to a reversal of the DNA cytosine hypermethylation patterns caused by mutant IDH1 in AML patients’ cells. Our study provides proof-of-concept for the molecular and biological activity of novel allosteric inhibitors for targeting different mutant forms of IDH1 in leukemia.

IntroductionAcute myeloid leukemia (AML) and myelodysplastic syndromes (MDSs) are heterogeneous neoplastic diseases, and most subtypes have poor clinical outcomes. Despite the established use of poly-chemotherapy and the development of new agents that transiently reduce the tumor burden, relapse or failure to achieve durable remission continues to be the most common causes of death in most subtypes of AML and MDS. Recent experimental evidence suggests that AML arises from transformed immature hematopoietic cells after the accumulation of multiple stepwise genetic and epigenetic changes in hematopoietic stem cells (HSCs) and committed progenitors. 1 The series of transforming events are thought to initially give rise to preleukemia stem cells (pre-LSCs), preceding the formation of fully transformed LSCs. Defining the characteristics of LSCs, and also of pre-LSCs, is critical to understanding the genesis of leukemia and to developing strategies by which these cells can be eradicated. AML is characterized by a cellular heterogeneous tumor bulk, with LSCs at the top of the hierarchy and a differentiation block at various stages during myeloid maturation. 2 To address the problem of cellular heterogeneity within the tumor and to identify relevant molecular pathways effective in LSCs and pre-LSCs, novel experimental approaches other than the examination of bulk tumor cells need to be established. Recent findings have suggested that human LSCs are contained within different phenotypic compartments and at relatively low frequencies. [3][4][5] Several surface molecules were reported to permit enrichment of LSCs in AML. 4,[6][7][8][9][10][11] However, reliable markers for human LSCs at the single-cell level have yet to be identified; and because of the challenges associated with the use of xenograft models, the search for such markers remains difficult. Moreover, although there is clear evidence for the involvement of HSCs in AML pathogenesis, studies from murine models suggest that fully transformed and transplantable LSCs may reside at a committed progenitor stage. 12-15 Here we applied a novel approach of parallel transcriptional analysis of multiple, highly fractionated stem and progenitor populations in individual patients. We isolated phenotypic long-term HSCs (LT-HSCs), short-term HSCs (ST-HSCs), The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use only. on May 11, 2018. by guest www.bloodjournal.org From and committed granulocyte-monocyte progenitors (GMP) from individual patients with AML, and compared gene expression profiles of each population with their phenotypic counterparts from age-matched healthy controls (HCs). Subsequent intersection of differentially expressed genes in the different cellular compartments allowed us to identify candidate genes that are consistently...

Chronic innate immune signaling in hematopoietic cells is widely described in myelodysplastic syndromes (MDS), and innate immune pathway activation, predominantly via pattern recognition receptors, increases the risk of developing MDS. An inflammatory component to MDS has been reported for many years, but only recently has evidence supported a more direct role of chronic innate immune signaling and associated inflammatory pathways in the pathogenesis of MDS. Here we review recent findings and discuss relevant questions related to chronic immune response dysregulation in MDS.