The FLT3-ITD mutation is frequently observed in acute myeloid leukemia (AML) and is associated with poor prognosis. In such patients, FLT3 tyrosine kinase inhibitors (TKIs) are only partially effective and do not eliminate the leukemia stem cells (LSCs) that are assumed to be the source of treatment failure. Here, we show that the NAD-dependent SIRT1 deacetylase is selectively overexpressed in primary human FLT3-ITD AML LSCs. This SIRT1 overexpression is related to enhanced expression of the USP22 deubiquitinase induced by c-MYC, leading to reduced SIRT1 ubiquitination and enhanced stability. Inhibition of SIRT1 expression or activity reduced the growth of FLT3-ITD AML LSCs and significantly enhanced TKI-mediated killing of the cells. Therefore, these results identify a c-MYC-related network that enhances SIRT1 protein expression in human FLT3-ITD AML LSCs and contributes to their maintenance. Inhibition of this oncogenic network could be an attractive approach for targeting FLT3-ITD AML LSCs to improve treatment outcomes.
Signal transducer and activator of transcription 3 (STAT3) is an oncogene and immune checkpoint commonly activated in cancer cells and in tumor-associated immune cells. We previously developed an immunostimulatory strategy based on targeted Stat3 silencing in Toll-like receptor 9 (TLR9)-positive hematopoietic cells using CpG-small interfering RNA (siRNA) conjugates. Here, we assessed the therapeutic effect of systemic STAT3 blocking/TLR9 triggering in disseminated acute myeloid leukemia (AML). We used mouse Cbfb-MYH11/Mpl-induced leukemia model, which mimics human inv(16) AML. Our results demonstrate that intravenously delivered CpG-Stat3 siRNA, but not control oligonucleotides, can eradicate established AML and impair leukemia-initiating potential. These antitumor effects require hosts effector T cells but not TLR9-positive antigen-presenting cells. Instead, CpG-Stat3 siRNA has direct immunogenic effect on AML cells in vivo upregulating major histocompatibility complex class-II, costimulatory and proinflammatory mediators, such as interleukin-12, while downregulating coinhibitory PD-L1 molecule. Systemic injections of CpG-Stat3 siRNA generate potent tumor antigen-specific immune responses, increase the ratio of tumor-infiltrating CD8(+) T cells to regulatory T cells in various organs, and result in CD8(+) T-cell-dependent regression of leukemia. Our findings underscore the potential of using targeted STAT3 inhibition/TLR9 triggering to break tumor tolerance and induce immunity against AML and potentially other TLR9-positive blood cancers.
Induction treatments for acute myeloid leukemia (AML) have remained largely unchanged for nearly 50 years, and AML remains a disease of poor prognosis. Allogeneic hematopoietic cell transplantation can achieve cures in select patients and highlights the susceptibility of AML to donor-derived immunotherapy. The interleukin-3 receptor ? chain (CD123) has been identified as a potential immunotherapeutic target because it is overexpressed in AML compared with normal hematopoietic stem cells. Therefore, we developed 2 chimeric antigen receptors (CARs) containing a CD123-specific single-chain variable fragment, in combination with a CD28 costimulatory domain and CD3-? signaling domain, targeting different epitopes on CD123. CD123-CAR-redirected T cells mediated potent effector activity against CD123+ cell lines as well as primary AML patient samples. CD123 CAR T cells did not eliminate granulocyte/macrophage and erythroid colony formation in vitro. Additionally, T cells obtained from patients with active AML can be modified to express CD123 CARs and are able to lyse autologous AML blasts in vitro. Finally, CD123 CAR T cells exhibited antileukemic activity in vivo against a xenogeneic model of disseminated AML. These results suggest that CD123 CAR T cells are a promising immunotherapy for the treatment of high-risk AML.
The SRC family kinases (SFKs) and the receptor tyrosine kinase c-Kit are activated in human acute myeloid leukemia (AML) cells. We show here that the SFKs LYN, HCK, or FGR are overexpressed and activated in AML progenitor cells. Treatment with the SFK and c-KIT inhibitor dasatinib selectively inhibits human AML stem/progenitor cell growth in vitro. Importantly, dasatinib markedly increases the elimination of AML stem cells capable of engrafting immunodeficient mice by chemotherapeutic agents. In vivo dasatinib treatment enhances chemotherapy-induced targeting of primary murine AML stem cells capable of regenerating leukemia in secondary recipients. Our studies suggest that enhanced targeting of AML cells by the combination of dasatinib with daunorubicin may be related to inhibition of AKT-mediated human mouse double minute 2 homolog phosphorylation, resulting in enhanced p53 activity in AML cells. Combined treatment using dasatinib and chemotherapy provides a novel approach to increasing p53 activity and enhancing targeting of AML stem cells.
Polo like kinase-1 is a key effector of cell division and its overexpression in several cancers is often linked with negative prognostic. We recently described that Plk1 is overexpressed in acute myeloid leukemia, and that its inhibition selectively reduces the proliferation of leukemic cells. Here, we report that Plk1 inhibition or depletion using pharmacological and siRNA approaches decreased the phosphorylation of two mTOR substrates in AML cells. In HCT116 cells, inducible expression of a constitutively active form of Plk1 leads to activation of mTOR, as shown by increased phosphorylation of its 4E-BP1 and RPS6 down-stream targets. In addition, cells overexpressing the active form of Plk1 were characterized by abnormal growth that could be reversed by rapamycin, a specific inhibitor of the TORC1 complex. Altogether these data suggest the existence of a molecular and functional link between the Plk1 mitotic kinase and the mTOR pathway. Given the different established functions of Plk1 and mTOR during the cell cycle, we will discuss the possible meaning of this functional relationship.
Polo-like kinase 1 (Plk1) is a major mitotic regulator overexpressed in many solid tumors. Its role in hematopoietic malignancies is still poorly characterized. In this study, we demonstrate that Plk1 is highly expressed in leukemic cell lines, and overexpressed in a majority of samples from patients with acute myeloid leukemia compared with normal progenitors. A pharmacologic inhibitor, BI2536, blocks proliferation in established cell lines, and dramatically inhibits the clonogenic potential of leukemic cells from patients. Plk1 knockdown by small interfering RNA also blocked proliferation of leukemic cell lines and the clonogenic potential of primary cells from patients. Interestingly, normal primary hematopoietic progenitors are less sensitive to Plk1 inhibition than leukemic cells, whose proliferation is dramatically decreased by the inhibitor. These results highlight Plk1 as a potentially interesting therapeutic target for the treatment of acute myeloid leukemia.
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