Project description:Heterozygous mutations in FLT3ITD, TET2, and DNMT3A are associated with hematologic malignancies in humans. In patients, cooccurrence of mutations in FLT3ITD combined with TET2 (TF) or FLT3ITD combined with DNMT3A (DF) are frequent. However, in some rare complex acute myeloid leukemia (AML), all 3 mutations cooccur - i.e., FLT3ITD, TET2, and DNMT3A (TFD). Whether the presence of these mutations in combination result in quantitative or qualitative differences in disease manifestation has not been investigated. We generated mice expressing heterozygous Flt3ITD and concomitant for either heterozygous loss of Tet2 (TF) or Dnmt3a (DF) or both (TFD). TF and DF mice did not induce disease early on, in spite of similar changes in gene expression; during the same time frame, an aggressive form of transplantable leukemia was observed in TFD mice, which was mostly associated with quantitative but not qualitative differences in gene expression relative to TF or DF mice. The gene expression signature of TFD mice showed remarkable similarity to the human TFD gene signature at the single-cell RNA level. Importantly, TFD-driven AML responded to a combination of drugs that target Flt3ITD, inflammation, and methylation in a mouse model, as well as in a PDX model of AML bearing 3 mutations.
Project description:Acute myeloid leukemia (AML) with FLT3-ITD mutations (FLT3-ITDmut) remains a therapeutic challenge, with a still high relapse rate, despite targeted treatment with tyrosine kinase inhibitors. In this disease, the CD34/CD123/CD25/CD99+ leukemic precursor cells (LPCs) phenotype predicts for FLT3-ITD-positivity. The aim of this study was to characterize the distribution of FLT3-ITD mutation in different progenitor cell subsets to shed light on the subclonal architecture of FLT3-ITDmut AML. Using high-speed cell sorting, we sequentially purified LPCs and CD34+ progenitors in samples from patients with FLT3-ITDmut AML (n = 12). A higher FLT3-ITDmut load was observed within CD34/CD123/CD25/CD99+ LPCs, as compared to CD34+ progenitors (CD123+/-,CD25-,CD99low/-) (p = 0.0005) and mononuclear cells (MNCs) (p < 0.0001). This was associated with significantly increased CD99 mean fluorescence intensity in LPCs. Significantly higher FLT3-ITDmut burden was also observed in LPCs of AML patients with a small FLT3-ITDmut clones at diagnosis. On the contrary, the mutation burden of other myeloid genes was similar in MNCs, highly purified LPCs and/or CD34+ progenitors. Treatment with an anti-CD99 mAb was cytotoxic on LPCs in two patients, whereas there was no effect on CD34+ cells from healthy donors. Our study shows that FLT3-ITD mutations occur early in LPCs, which represent the leukemic reservoir. CD99 may represent a new therapeutic target in FLT3-ITDmut AML.
Project description:DNMT3A, the gene encoding the de novo DNA methyltransferase 3A, is among the most frequently mutated genes in hematologic malignancies. However, the mechanisms through which DNMT3A normally suppresses malignancy development are unknown. Here, we show that DNMT3A loss synergizes with the FLT3 internal tandem duplication in a dose-influenced fashion to generate rapid lethal lymphoid or myeloid leukemias similar to their human counterparts. Loss of DNMT3A leads to reduced DNA methylation, predominantly at hematopoietic enhancer regions in both mouse and human samples. Myeloid and lymphoid diseases arise from transformed murine hematopoietic stem cells. Broadly, our findings support a role for DNMT3A as a guardian of the epigenetic state at enhancer regions, critical for inhibition of leukemic transformation.
Project description:Acute myeloid leukemia (AML) is an aggressive hematologic malignancy which is cured in a minority of patients. A FLT3-internal tandem duplication (ITD) mutation, found in approximately a quarter of patients with de novo AML, imparts a particularly poor prognosis. Patients with FLT3-ITD AML often present with more aggressive disease and have a significantly higher propensity for relapse after remission. The therapeutic approach for these patients has traditionally included intensive induction chemotherapy, followed by consolidative chemotherapy or hematopoietic cell transplantation (HCT). In recent years, multiple small molecule inhibitors of the FLT3 tyrosine kinase have been studied preclinically and in clinical trials. The earlier generation of these agents, often non-specific and impacting a variety of tyrosine kinases, produced at best transient peripheral blood responses in early clinical trials. Additionally, the combination of FLT3 inhibitors with cytotoxic regimens has not, as of yet, demonstrated an improvement in overall survival. Nevertheless, multiple current trials, including those with sorafenib, lestaurtinib, and midostaurin, continue to study the combination of FLT3 inhibitors with standard chemotherapy. Factors such as sustained FLT3 inhibition, protein binding, pharmacokinetics, and the presence of elevated FLT3-ligand levels appear to significantly impact the potency of these agents in vivo. In recent years, the development of more specific and potent agents has generated hope that FLT3 inhibitors may play a more prominent role in the treatment of FLT3-ITD AML in the near future. Nevertheless, questions remain regarding the optimal timing and schedule for incorporation of FLT3 inhibitors. The suitability, type, and timing of allogeneic HCT in the therapeutic approach for these patients are also issues which require further study and definition. Recent retrospective data appears to support the efficacy of allogeneic HCT in first complete remission, possibly due to a graft versus leukemia effect. However, larger prospective studies are necessary to further elucidate the role of HCT and its potential combination with FLT3 inhibitor therapy. We are hopeful that current clinical investigation will lead to an optimization and improvement of outcomes for these patients.
Project description:FLT3 kinase internal tandem duplication (ITD) mutations are common in acute myeloid leukemia (AML) and are associated with poor clinical outcomes. Although initial responses to FLT3 tyrosine kinase inhibitors (TKIs) are observed in FLT3-ITD-positive patients, subsequent relapse often occurs upon acquisition of secondary FLT3 kinase domain (KD) mutations, primarily at residues D835 and F691. Using biochemical assays, we determined that crenolanib, a novel TKI, demonstrates type I properties and is active against FLT3 containing ITD and/or D835- or F691-activating mutations. Potent activity was observed in FLT3-ITD-positive AML cell lines. Crenolanib delayed the outgrowth of MV4-11 cells in a xenograft mouse model, whereas in combination with the type II TKI sorafenib, a significant decrease in leukemic burden (P < .001) and prolonged survival (P < .01) was observed compared with either type I or II TKI alone. Crenolanib was active against Ba/F3 cells harboring FLT3-ITD and secondary KD mutations and sorafenib-resistant MOLM-13 cells containing FLT3-ITD/D835Y both in vitro and in vivo. In addition, crenolanib inhibited drug-resistant AML primary blasts with FLT3-ITD and D835H/Y mutations. These preclinical data demonstrate that crenolanib is effective against FLT3-ITD containing secondary KD mutations, suggesting that crenolanib may be a useful therapeutic agent for TKI-naive and drug-resistant FLT3-ITD-positive AML.
Project description:MiR-126 and miR-155 are key microRNAs (miRNAs) that regulate, respectively, hematopoietic cell quiescence and proliferation. Herein we showed that in acute myeloid leukemia (AML), the biogenesis of these two miRNAs is interconnected through a network of regulatory loops driven by the FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD). In fact, FLT3-ITD induces the expression of miR-155 through a noncanonical mechanism of miRNA biogenesis that implicates cytoplasmic Drosha ribonuclease III (DROSHA). In turn, miR-155 down-regulates SH2-containing inositol phosphatase 1 (SHIP1), thereby increasing phosphor-protein kinase B (AKT) that in turn serine-phosphorylates, stabilizes, and activates Sprouty related EVH1 domain containing 1 (SPRED1). Activated SPRED1 inhibits the RAN/XPO5 complex and blocks the nucleus-to-cytoplasm transport of pre-miR-126, which cannot then complete the last steps of biogenesis. The net result is aberrantly low levels of mature miR-126 that allow quiescent leukemia blasts to be recruited into the cell cycle and proliferate. Thus, miR-126 down-regulation in proliferating AML blasts is downstream of FLT3-ITD–dependent miR-155 expression that initiates a complex circuit of concatenated regulatory feedback (i.e., miR-126/SPRED1, miR-155/human dead-box protein 3 [DDX3X]) and feed-forward (i.e., miR-155/SHIP1/AKT/miR-126) regulatory loops that eventually converge into an output signal for leukemic growth.