SU11652 Inhibits tyrosine kinase activity of FLT3 and growth of MV-4-11 cells

FLT3 inhibitors induce p53 instability, driven by STAT5/MDM2/p53 competitive interactions in acute myeloid leukemia

FLT3 mutations are present in one third of patients with Acute myeloid leukemia (AML) and stand as an attractive therapeutic target. Although FLT3 inhibitors demonstrate clinical efficacy, the drug resistance remains challenging attributed to multiple mechanisms. In this study, we found that tyrosine kinase inhibitors (TKIs) targeting FLT3 prompt p53 degradation in AML cells with FLT3-ITD through ubiquitination. STAT5 phosphorylation facilitates its nuclear localization, leading to competitive interactions among STAT5, MDM2, and p53. TKIs blocked STAT5 nuclear entry, amplifying MDM2/p53 binding and subsequent p53 degradation. Additionally, STAT5 overexpression inhibited MDM2-mediated p53 ubiquitination, whereas knock-down of STAT5 destabilizes p53. Co-administration of MDM2 inhibitors stabilizes p53 ubiquitination induced by TKIs, enhancing pro-apoptotic effects on AML cells. Moreover, in mice engrafted with AML cells, gilteritinib treatment results in decreased p53 protein levels and the transcriptional repression of downstream genes in leukemia cells, which are mitigated by the co-administration of MDM2 inhibitors. In conclusion, our study shows that FLT3 TKIs impede STAT5 nuclear translocation, strengthening p53/MDM2 interaction and consequent p53 degradation. This finding reveals a novel mechanism of TKIs resistance and indicates a combination of MDM2 inhibitors with TKIs for AML therapy, offering new insights into effective treatment strategies.

miR-221/222 induce instability of p53 By downregulating deubiquitinase YOD1 in acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematological malignancy characterized by the impaired differentiation and uncontrolled proliferation of myeloid blasts. Tumor suppressor p53 is often downregulated in AML cells via ubiquitination-mediated degradation. While the role of E3 ligase MDM2 in p53 ubiquitination is well-accepted, little is known about the involvement of deubiquitinases (DUBs). Herein, we found that the expression of YOD1, among several DUBs, is substantially reduced in blood cells from AML patients. We identified that YOD1 deubiqutinated and stabilized p53 through interaction via N-terminus of p53 and OTU domain of YOD1. In addition, expression levels of YOD1 were suppressed by elevated miR-221/222 in AML cells through binding to the 3' untranslated region of YOD1, as verified by reporter gene assays. Treatment of cells with miR-221/222 mimics and inhibitors yielded the expected effects on YOD1 expressions, in agreement with the negative correlation observed between the expression levels of miR-221/222 and YOD1 in AML cells. Finally, overexpression of YOD1 stabilized p53, upregulated pro-apoptotic p53 downstream genes, and increased the sensitivity of AML cells to FLT3 inhibitors remarkably. Collectively, our study identified a pathway connecting miR-221/222, YOD1, and p53 in AML. Targeting miR-221/222 and stimulating YOD1 activity may improve the therapeutic effects of FLT3 inhibitors in patients with AML.

Sunitinib selectively targets leukemogenic signaling of mutant SHP2 in juvenile myelomonocytic leukemia

Leukemogenic SHP2 mutations occur in 35% of patients with juvenile myelomonocytic leukemia (JMML), a hematopoietic malignancy with poor response to cytotoxic chemotherapy. Novel therapeutic strategies are urgently needed for patients with JMML. Previously, we established a novel cell model of JMML with HCD-57, a murine erythroleukemia cell line that depends on EPO for survival. SHP2-D61Y or -E76K drove the survival and proliferation of HCD-57 in absence of EPO. In this study, we identified sunitinib as a potent compound to inhibit SHP2-mutant cells by screening a kinase inhibitor library with our model. We used cell viability assay, colony formation assay, flow cytometry, immunoblotting, and a xenograft model to evaluate the effect of sunitinib against SHP2-mutant leukemia cells in vitro and in vivo. The treatment of sunitinib selectively induced apoptosis and cell cycle arrest in mutant SHP2-transformed HCD-57, but not parental cells. It also inhibited cell viability and colony formation of primary JMML cells with mutant SHP2, but not bone marrow mononuclear cells from healthy donors. Immunoblotting showed that the treatment of sunitinib blocked the aberrantly activated signals of mutant SHP2 with deceased phosphorylation levels of SHP2, ERK, and AKT. Furthermore, sunitinib effectively reduced tumor burdens of immune-deficient mice engrafted with mutant-SHP2 transformed HCD-57. Our data demonstrated that sunitinib selectively inhibited SHP2-mutant leukemia cells, which could serve as an effective therapeutic strategy for SHP2-mutant JMML in the future.

Identification of New Purpuroine Analogues from the Arctic Echinodermata Pteraster militaris That Inhibit FLT3-ITD+ AML Cell Lines

Isolation of bioactive products from the marine environment is considered a very promising approach to identify new compounds that can be used for further drug development. In this work we have isolated three new compounds from the purpuroine family by mass-guided preparative HPLC; purpuroine K-M. These compounds where screened for antibacterial- and antifungal activity, antibiofilm formation and anti-cell proliferation activity. Additionally, apoptosis-, cell cycle-, kinase binding- and docking studies were performed to evaluate the mechanism-of-action. None of the compounds showed activity in antibacterial-, antibiofilm- or antifungal assays. However, one of the isolated compounds, purpuroine K, showed activity against two cell lines, MV-4-11 and MOLM-13, two AML cell lines both carrying the FTL3-ITD mutation. In MV-4-11 cells, purpuroine K was found to increase apoptosis and arrest cells cycle in G1/G0, which is a common feature of FLT3 inhibitors. Interactions between purpuroine K and the FLT3 wild type or FLT3 ITD mutant proteins could however not be elucidated in our kinase binding and docking studies. In conclusion, we have isolated three novel molecules, purpuroine K-M, one of which (purpuroine K) shows a potent activity against FLT3-ITD mutated AML cell lines, however, the molecular target(s) of purpuroine K still need to be further investigated.

Vorolanib, a novel tyrosine receptor kinase receptor inhibitor with potent preclinical anti-angiogenic and anti-tumor activity

Vorolanib (CM082) is a multi-targeted tyrosine kinase receptor inhibitor with a short half-life and limited tissue accumulation that has been shown to reduce choroidal neovascularization in rats. In this preclinical study, vorolanib demonstrated competitive binding and inhibitory activities with KDR, PDGFRβ, FLT3, and C-Kit, and inhibited RET and AMPKα1 more weakly than sunitinib, indicating more stringent kinase selectivity. Vorolanib inhibited vascular endothelial growth factor (VEGF)-induced proliferation of human umbilical vein endothelial cells (HUVECs) and HUVEC tube formation in vitro. In mouse xenograft models, vorolanib inhibited tumor growth of MV-4-11, A549, 786-O, HT-29, BxPC-3, and A375 cells in a dose-dependent fashion. Complete tumor regression was achieved in the MV-4-11 xenograft model. No significant toxicities were observed in vorolanib groups, whereas a significant negative impact on body weights was observed in the sunitinib group at a dose of 40 mg/kg qd. Overall, vorolanib is a novel multi-kinase receptor inhibitor with potent preclinical anti-angiogenic and anti-tumor activity that is potentially less toxic than other similar kinase inhibitors.

Aberrantly expressed Wnt5a in nurse-like cells drives resistance to Venetoclax in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of neoplastic B lymphocytes with high levels of Wnt5a in the plasma. Currently, the cell source of Wnt5a remains controversial. The receptor of Wnt5a is ROR1, whose expression is associated with disease progression and resistance to venetoclax, a BCL-2 inhibitor approved for the treatment of CLL. In this study, we found that the levels of Wnt5a in the plasma of CLL patients were positively correlated with absolute monocyte counts, but not lymphocyte counts. We cultured monocyte-derived nurse-like cells (NLCs) from patients with CLL, and detected Wnt5a expressed in NLCs. Flow cytometry and transwell assays showed that the antibody neutralizing Wnt5a inhibited the enhanced survival and migration in CLL cells co-cultured with NLCs. Furthermore, we performed a drug screening with CLL cells cultured with or without NLCs with a library containing 133 FDA-approved oncology drugs by using high-throughput flow cytometry. We observed a significant resistance to venetoclax in CLL cells co-cultured with NLCs. Immunoblot revealed the activation of NF-κB with enhanced expression of MCL-1 and BCL-XL in CLL cells co-cultured with NLCs. Neutralizing Wnt5a or blocking NF-κB pathway significantly decreased the expression of MCL-1 and BCL-XL, which leads to enhanced sensitivity to venetoclax in CLL cells co-cultured with NLCs. In conclusion, our data showed that NLCs could be one of the sources of Wnt5a detected in patients with CLL, and Wnt5a-induced NF-κB activation in the CLL microenvironment results in resistance to venetoclax in CLL cells.

FLT3-specific curcumin micelles enhance activity of curcumin on FLT3-ITD overexpressing MV4-11 leukemic cells

Curcumin, a major active compound in the turmeric rhizome, has many biological properties, especially anti-leukemia activity. The overexpression of FMS-like tyrosine kinase 3 protein with internal tandem duplication (FLT3-ITD) mutation protein was related to the poor prognosis and disease progression of leukemia. In this study, the cytotoxicity and inhibitory effect of curcumin on cell cycle of FLT3-ITD overexpressing MV4-11 leukemic cells were evaluated. Moreover, curcumin polymeric micelles conjugated with FLT3-specific peptide (FLT3-Cur-micelles) were prepared using a film hydration method to increase curcumin solubility and the inhibitory effect on MV4-11 cells was evaluated. Cytotoxicity and cell cycle analysis were performed using an MTT assay and flow cytometry, respectively. Physical properties of FLT3-Cur-micelles, including particle size, size distribution, morphology, and entrapment efficiency (EE), were evaluated. Cellular uptake of the micelles on MV4-11 cells was determined by flow cytometry and fluorescence microscopy. FLT3-Cur-micelles were observed with size less than 50 nm and high EE of >75%. In addition, FLT3-Cur-micelles demonstrated excellent internalization and increased curcumin accumulation in leukemic cells when compared to free curcumin. Furthermore, FLT3-Cur-micelles exhibited a strong cytotoxic effect on MV4-11 cells with IC₅₀ value of 1.1 µM, whereas the blank micelles showed no effect. Furthermore, FLT3-Cur-micelles showed no significant effect on normal human PBMCs with IC₅₀ value >25 µM. In summary, FLT3-Cur-micelles are a promising nanocarrier system for enhancing anti-leukemic activity of curcumin and suitable for further preclinical studies.

Tyrosine kinase inhibitors targeting FLT3 in the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a cancer of the myeloid lineage of blood cells. Although significant progress has been made in treating many types of cancers during recent years, AML remains a deadly disease with survival rate lagging behind other blood cancers. A combination of toxic chemotherapies has been the standard AML treatment for more than 40 years. With intensive efforts to define the pathogenesis of AML, novel therapeutic drugs targeting key molecular defects in AML are being developed. Mutated in nearly 30% of AML, FMS-like tyrosine kinase 3 (FLT3) represents one of the most attractive targets. FLT3 mutants resulted from either internal tandem duplication (ITD) or point mutations possess enhanced kinase activity and cause constitutive activation of signaling. To date, several small molecule inhibitors of FLT3 have been developed but their clinical efficacy is limited due to a lack of potency and the generation of drug resistance. Therefore, next-generation FLT3 inhibitors overcoming these limitations are urgently in need. This review focuses on the pathological role of mutant FLT3 in the development of AML, the current status of FLT3 inhibitor development, and mechanisms underlining the development of resistance to existing FLT3 inhibitors.

Integrin alphavbeta3 enhances β-catenin signaling in acute myeloid leukemia harboring Fms-like tyrosine kinase-3 internal tandem duplication mutations: implications for microenvironment influence on sorafenib sensitivity

Binding of leukemia cells to the bone marrow extracellular matrix (ECM) through integrins might influence drug response and the survival of acute myeloid leukemia (AML). However, the functions of integrin in AML are needed to be clarified. Data from The Cancer Genome Atlas (TCGA) were retrieved and integrin β3 (ITGB3) expression and prognostic significance for AML were analyzed. Integrin alphavbeta3 (αvβ3) in sorafenib sensitivity and signaling pathway of FLT3-ITD AML cells was evaluated in vitro. The level of ITGB3 expression was positively correlated with risk stratification and prognosis of AML patients, especially in cytogenetic-normal patients with Fms-like tyrosine kinase-3 internal tandem duplication (FLT3-ITD) mutation. Integrin αvβ3 decreased sorafenib sensitivity when co-culture of MV4-11 cells and bone marrow stromal cells (BMSCs), and it is crucial for osteopontin (OPN) induced sorafenib insensitivity in FLT3-ITD mutated AML cells. Mechanically, αvβ3 enhance β-catenin activation through phosphatidylinositol 3-kinase (PI3K)/Akt/Glycogen synthase kinase-3 beta (GSK3β) pathway. Moreover, genetic inhibition of β-catenin by shRNA could increase sorafenib sensitivity in MV4-11 cells. Taken together, our study revealed a novel mechanism in microenvironment influence on sorafenib sensitivity in AML with FLT3-ITD mutation that was caused by activating integrin αvβ3/PI3K/Akt/GSK3β/β-catenin pathway. Integrin αvβ3/β-catenin could be considered as a new therapeutic target for AML especially for FLT3-ITD mutated AML.

Identification of an orally available compound with potent and broad FLT3 inhibition activity

FLT3 internal tandem duplication (FLT3-ITD) is an activating mutation found in 20%-30% of patients with acute myeloid leukemia (AML), which makes FLT3 an attractive target for the treatment of AML. Although FLT3-mutant patients respond to current FLT3 inhibitors, relapse usually happens due to the acquisition of resistant secondary mutations at the FLT3 catalytic domain, which is mainly on D835. In the search for compounds with broad FLT3 inhibition activities, we screened a kinase inhibitor library by using our unique FLT3 substrate and identified JAK3 inhibitor VI (designated JI6 hereafter) as a novel FLT3 inhibitor, which selectively targets FLT3 D835 mutants as well as FLT3-ITD. JI6 effectively inhibited FLT3-ITD-containing MV4-11 cells and HCD-57 cells transformed with FLT3-ITD and D835 mutants. Furthermore, administration of JI6 effectively targeted FLT3 signaling in vivo and suppressed the myeloproliferative phenotypes in FLT3-ITD knock-in mice and significantly prolonged the survival of immunodeficient mice implanted with the transformed HCD-57 cells. Therefore, JI6 is a promising candidate for development of next generation anti-AML drugs.

Generation and characterization of a JAK2V617F-containing erythroleukemia cell line

The JAK2V617F mutation is found in the majority of patients with myeloproliferative neoplasms (MPNs). Transgenic expression of the mutant gene causes MPN-like phenotypes in mice. We have produced JAK2V617F mice with p53 null background. Some of these mice developed acute erythroleukemia. From one of these mice, we derived a cell line designated J53Z1. J53Z1 cells were stained positive for surface markers CD71 and CD117 but negative for Sca-1, TER-119, CD11b, Gr-1, F4/80, CD11c, CD317, CD4, CD8a, CD3e, B220, CD19, CD41, CD42d, NK-1.1, and FceR1. Real time PCR analyses demonstrated expressions of erythropoietin receptor EpoR, GATA1, and GATA2 in these cells. J53Z1 cells grew rapidly in suspension culture containing fetal bovine serum with a doubling time of ∼18 hours. When transplanted into C57Bl/6 mice, J53Z1 cells induced acute erythroleukemia with massive infiltration of tumor cells in the spleen and liver. J53Z1 cells were responsive to stimulation with erythropoietin and stem cell factor and were selectively inhibited by JAK2 inhibitors which induced apoptosis of the cells. Together, J53Z1 cells belong to the erythroid lineage, and they may be useful for studying the role of JAK2V617F in proliferation and differentiation of erythroid cells and for identifying potential therapeutic drugs targeting JAK2.

Elevated levels of mast cells are involved in pruritus associated with polycythemia vera in JAK2V617F transgenic mice

Pruritus occurs frequently in patients with polycythemia vera (PV), and the pathophysiology of PV-associated pruritus is unclear. We have previously demonstrated that transgenic mice expressing JAK2V617F displayed clear PV-like phenotypes. In the current study, we found frequent occurrence of pruritus with aged JAK2V617F transgenic mice and further investigated the underlying mechanisms by studying mast cells, key players in allergic reactions and anaphylaxis. Massive accumulations of mast cells were observed in the skin of pruritic JAK2V617F transgenic mice. In vitro culture yielded much higher mast cell counts from the bone marrow, spleen, peripheral blood, and peritoneal cavity of JAK2V617F transgenic mice than from controls. Cultured mast cells from JAK2V617F transgenic mice exhibited enhanced proliferative signals, relative resistance to cell death upon growth factor deprivation, and a growth advantage over control cells under suboptimal growth conditions. However, these mast cells displayed normal morphology and contained normal levels of mast cell proteases before and after degranulation. Finally, the JAK2 inhibitor G6 effectively reduced mast cell numbers and alleviated pruritus in JAK2V617F transgenic mice. Collectively, these data demonstrate that mast cells are involved in PV-associated pruritogenesis and that JAK2 inhibitors are potential antipruritus drugs.

Inhibitory effect of turmeric curcuminoids on FLT3 expression and cell cycle arrest in the FLT3-overexpressing EoL-1 leukemic cell line

Leukemia is a hematologic malignancy with a frequent incidence and high mortality rate. Previous studies have shown that the FLT3 gene is overexpressed in leukemic blast cells, especially in acute myeloid leukemia. In this study, a commercially available curcuminoid mixture (1), pure curcumin (2), pure demethoxycurcumin (3), and pure bisdemethoxycurcumin (4) were investigated for their inhibitory effects on cell growth, FLT3 expression, and cell cycle progression in an FLT3-overexpressing EoL-1 leukemic cell line using an MTT assay, Western blotting, and flow cytometry, respectively. The mixture (1) and compounds 2-4 demonstrated cytotoxic effects with IC50 values ranging from 6.5 to 22.5 μM. A significant decrease in FLT3 protein levels was found after curcuminoid treatment with IC20 doses, especially with mixture 1 and compound 2. In addition, mixture 1 and curcumin (2) showed activity on cell cycle arrest at the G0/G1 phase and decreased the FLT3 and STAT5A protein levels in a dose-dependent manner. Compound 2 demonstrated the greatest potential for inhibiting cell growth, cell cycle progression, and FLT3 expression in EoL-1 cells. This investigation has provided new findings regarding the effect of turmeric curcuminoids on FLT3 expression in leukemic cells.

Silvestrol exhibits significant in vivo and in vitro antileukemic activities and inhibits FLT3 and miR-155 expressions in acute myeloid leukemia

Background

Activating mutations [internal tandem duplication (ITD)] or overexpression of the FMS-like tyrosine kinase receptor-3 (FLT3) gene are associated with poor outcome in acute myeloid leukemia (AML) patients, underscoring the need for novel therapeutic approaches. The natural product silvestrol has potent antitumor activity in several malignancies, but its therapeutic impact on distinct molecular high-risk AML subsets remains to be fully investigated. We examined here the preclinical activity of silvestrol in FLT3-ITD and FLT3 wild-type (wt) AML.

Methods

Silvestrol in vitro anti-leukemic activity was examined by colorimetric cell viability assay, colony-forming and flow cytometry assays assessing growth inhibition and apoptosis, respectively. Pharmacological activity of silvestrol on FLT3 mRNA translation, mRNA and protein expression was determined by RNA-immunoprecipitation, qRT-PCR and immunoblot analyses, respectively. Silvestrol in vivo efficacy was investigated using MV4-11 leukemia-engrafted mice.

Results

Silvestrol shows antileukemia activity at nanomolar concentrations both in FLT3-wt overexpressing (THP-1) and FLT3-ITD (MV4-11) expressing AML cell lines (IC₅₀ = 3.8 and 2.7 nM, respectively) and patients’ primary blasts [IC₅₀ = ~12 nM (FLT3-wt) and ~5 nM (FLT3-ITD)]. Silvestrol increased apoptosis (~4fold, P = 0.0001), and inhibited colony-formation (100%, P < 0.0001) in primary blasts. Silvestrol efficiently inhibited FLT3 translation reducing FLT3 protein expression by 80–90% and decreased miR-155 levels (~60%), a frequently co-regulated onco-miR in FLT3-ITD-positive AML. The median survival of silvestrol-treated vs vehicle-treated mice was 63 vs 29 days post-engraftment, respectively (P < 0.0001).

Conclusions

Silvestrol exhibits significant in vivo and in vitro antileukemic activities in AML through a novel mechanism resulting in inhibition of FLT3 and miR-155 expression. These encouraging results warrant a rapid translation of silvestrol for clinical testing in AML.

Synergistic effect of paclitaxel and epigenetic agent phenethyl isothiocyanate on growth inhibition, cell cycle arrest and apoptosis in breast cancer cells

This study examined whether combining paclitaxel (taxol) with a novel epigenetic agent phenethyl isothiocyanate (PEITC) will yield a synergistic effect on inhibiting breast cancer cells. Two drug-resistant breast cancer cell lines, MCF7 and MDA-MB-231, were treated with PEITC and taxol. Cell growth, cell cycle, and apoptosis were examined. The combination of PEITC and taxol significantly decreased the IC₅₀ of PEITC and taxol over each agent alone. The combination also increased apoptosis by more than two fold over each single agent in both cell lines. A significant increase of cells in the G2/M phases was detected. In conclusion, the combination of PEITC and taxol exhibits a synergistic effect on growth inhibition in breast cancer cells. This combination deserves further study in vivo.