Npm1 haploinsufficiency in collaboration with MEIS1 is sufficient to induce AML in mice.

NPM1 is among the most frequently mutated genes in acute myeloid leukemia (AML). Mutations in the NPM1 gene result in the increased export of NPM1 to the cytoplasm (NPM1c) and are associated with multiple transforming events including the aberrant upregulation of MEIS1 that maintains stem cell and cell cycle-associated pathways in NPM1c AML. However, another consequence of the NPM1c mutation is the inadequate levels of NPM1 wild-type in the nucleus and nucleolus, caused by the loss of one wild-type allele in addition to enforced NPM1 nuclear export. The contribution of NPM1 haploinsufficiency independently of the NPM1 mutation to AML development and its relationship with MEIS1 function is poorly understood. Using mouse models, our study shows that NPM1 haploinsufficiency paired with MEIS1 overexpression is sufficient to induce a fully penetrant AML in mice that transcriptionally resembles human NPM1c AML. NPM1 haploinsufficiency alters MEIS1-binding occupancies such that it binds the promoter of the oncogene structural maintenance of chromosome protein 4 (SMC4) in NPM1 haploinsufficient AML cells but not in NPM1 wild-type-harboring Hoxa9/Meis1-transformed cells. SMC4 is higher expressed in haploinsufficient and NPM1c+ AML cells, which are more vulnerable to the disruption of the MEIS1-SMC4 axis compared with AML cells with nonmutated NPM1. Taken together, our study underlines that NPM1 haploinsufficiency on its own is a key factor of myeloid leukemogenesis and characterizes the MEIS1-SMC4 axis as a potential therapeutic target in this AML subtype.

Alberta Spinal Muscular Atrophy Newborn Screening-Results from Year 1 Pilot Project.

Spinal muscular atrophy (SMA) is a progressive neuromuscular disease caused by biallelic pathogenic/likely pathogenic variants of the survival motor neuron 1 (SMN1) gene. Early diagnosis via newborn screening (NBS) and pre-symptomatic treatment are essential to optimize health outcomes for affected individuals. We developed a multiplex quantitative polymerase chain reaction (qPCR) assay using dried blood spot (DBS) samples for the detection of homozygous absence of exon 7 of the SMN1 gene. Newborns who screened positive were seen urgently for clinical evaluation. Confirmatory testing by multiplex ligation-dependent probe amplification (MLPA) revealed SMN1 and SMN2 gene copy numbers. Six newborns had abnormal screen results among 47,005 newborns screened during the first year and five were subsequently confirmed to have SMA. Four of the infants received SMN1 gene replacement therapy under 30 days of age. One infant received an SMN2 splicing modulator due to high maternally transferred AAV9 neutralizing antibodies (NAb), followed by gene therapy at 3 months of age when the NAb returned negative in the infant. Early data show that all five infants made excellent developmental progress. Based on one year of data, the incidence of SMA in Alberta was estimated to be 1 per 9401 live births.

Linkage of the potent leukemogenic activity of Meis1 to cell-cycle entry and transcriptional regulation of cyclin D3.

MEIS1 is a three-amino acid loop extension class homeodomain-containing homeobox (HOX) cofactor that plays key roles in normal hematopoiesis and leukemogenesis. Expression of Meis1 is rate-limiting in MLL-associated leukemias and potently interacts with Hox and NUP98-HOX genes in leukemic transformation to promote self-renewal and proliferation of hematopoietic progenitors. The oncogenicity of MEIS1 has been linked to its transcriptional activation properties. To further reveal the pathways triggered by Meis1, we assessed the function of a novel engineered fusion form of Meis1, M33-MEIS1, designed to confer transcriptional repression to Meis1 target genes that are otherwise up-regulated in normal and malignant hematopoiesis. Retroviral overexpression of M33-Meis1 resulted in the rapid and complete eradication of M33-Meis1-transduced normal and leukemic cells in vivo. Cell-cycle analysis showed that M33-Meis1 impeded the progression of cells from G(1)-to-S phase, which correlated with significant reduction of cyclin D3 levels and the inhibition of retinoblastoma (pRb) hyperphosphorylation. We identified cyclin D3 as a direct downstream target of MEIS1 and M33-MEIS1 and showed that the G(1)-phase accumulation and growth suppression induced by M33-Meis1 was partially relieved by overexpression of cyclin D3. This study provides strong evidence linking the growth-promoting activities of Meis1 to the cyclin D-pRb cell-cycle control pathway.

MicroRNA-223 dose levels fine tune proliferation and differentiation in human cord blood progenitors and acute myeloid leukemia.

A precise understanding of the role of miR-223 in human hematopoiesis and in the pathogenesis of acute myeloid leukemia (AML) is still lacking. By measuring miR-223 expression in blasts from 115 AML patients, we found significantly higher miR-223 levels in patients with favorable prognosis, whereas patients with low miR-223 expression levels were associated with worse outcome. Furthermore, miR-223 was hierarchically expressed in AML subpopulations, with lower expression in leukemic stem cell-containing fractions. Genetic depletion of miR-223 decreased the leukemia initiating cell (LIC) frequency in a myelomonocytic AML mouse model, but it was not mandatory for rapid-onset AML. To relate these observations to physiologic myeloid differentiation, we knocked down or ectopically expressed miR-223 in cord-blood CD34⁺ cells using lentiviral vectors. Although miR-223 knockdown delayed myeloerythroid precursor differentiation in vitro, it increased myeloid progenitors in vivo following serial xenotransplantation. Ectopic miR-223 expression increased erythropoiesis, T lymphopoiesis, and early B lymphopoiesis in vivo. These findings broaden the role of miR-223 as a regulator of the expansion/differentiation equilibrium in hematopoietic stem and progenitor cells where its impact is dose- and differentiation-stage-dependent. This also explains the complex yet minor role of miR-223 in AML, a heterogeneous disease with variable degree of myeloid differentiation.

Targeting integrin linked kinase and FMS-like tyrosine kinase-3 is cytotoxic to acute myeloid leukemia stem cells but spares normal progenitors.

Acute myeloid leukemia (AML) is maintained by rare leukemia-initiating cells (L-ICs). FLT3 and/or PI3K pathways are often dysregulated in AML and may be important for L-IC survival. The presence of PI3K pathway intermediate integrin linked kinase (ILK), and FLT3 was confirmed in five L-IC-enriched AML patient samples. Treatment of AML cells with QLT0267, an inhibitor of ILK and FLT3, decreased survival of long-term suspension culture-initiating cells and NOD/SCID mouse L-IC. In contrast, little toxicity toward normal bone marrow progenitors was observed, demonstrating that candidate leukemic stem cells can be eliminated by inhibition of these targets while normal hematopoietic counterparts are spared.

Identification of miR-145 and miR-146a as mediators of the 5q- syndrome phenotype.

5q- syndrome is a subtype of myelodysplastic syndrome characterized by severe anemia and variable neutropenia but normal or high platelet counts with dysplastic megakaryocytes. We examined expression of microRNAs (miRNAs) encoded on chromosome 5q as a possible cause of haploinsufficiency. We show that deletion of chromosome 5q correlates with loss of two miRNAs that are abundant in hematopoietic stem/progenitor cells (HSPCs), miR-145 and miR-146a, and we identify Toll-interleukin-1 receptor domain-containing adaptor protein (TIRAP) and tumor necrosis factor receptor-associated factor-6 (TRAF6) as respective targets of these miRNAs. TIRAP is known to lie upstream of TRAF6 in innate immune signaling. Knockdown of miR-145 and miR-146a together or enforced expression of TRAF6 in mouse HSPCs resulted in thrombocytosis, mild neutropenia and megakaryocytic dysplasia. A subset of mice transplanted with TRAF6-expressing marrow progressed either to marrow failure or acute myeloid leukemia. Thus, inappropriate activation of innate immune signals in HSPCs phenocopies several clinical features of 5q- syndrome.

Combined inhibition of integrin linked kinase and FMS-like tyrosine kinase 3 is cytotoxic to acute myeloid leukemia progenitor cells.

OBJECTIVE: Dysregulation of signaling pathways leading to enhanced cell proliferation and resistance to apoptosis is frequent in acute myeloid leukemia (AML). The effectiveness of inhibiting two such pathways, the phosphatidylinosityl-3-kinase pathway via the intermediate integrin-linked kinase (ILK), and FMS-like tyrosine kinase-3 (FLT-3) signaling pathway in killing AML cells was studied. MATERIALS AND METHODS: AML colony-forming cell (CFC) assays were used to determine the effects of a small molecule inhibitor of both ILK and FLT-3 (QLT0267) on poor prognosis primary AML sample viability. Kinase assays and Western blots were used to analyze effects of the compound on target molecules. RESULTS: In 31/36 AML blast samples p-Akt was detected indicating phosphatidylinosityl-3-kinase activation. ILK was ubiquitously and FLT-3 abundantly expressed. Downregulation of ILK in the AML cell line TF-1 using small interfering RNA caused >or= 50% CFC death, suggesting ILK inhibition might also be toxic to primary AML cells. In vitro kinase assays on three AML samples showed inhibition of both ILK and FLT-3 by QLT0267. Treatment of AML patient blast cells (n=27) with QLT0267, caused a dose- and time-dependent downregulation of p-Akt and kill of AML-CFC with AML samples containing FLT-3 mutations being more sensitive to QLT0267 than those without. AML samples were more sensitive to QLT0267 killing than normal bone marrow (IC(50)=3 microM, vs 10 microM for AML-CFC and normal CFC, respectively, n=5). CONCLUSION: Combined inhibition of ILK and FLT-3 with a small molecule kinase inhibitor can achieve selective targeting of AML rather than normal hematopoietic progenitors.