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Background: Acute lymphoblastic leukemia (ALL) is a heterogeneous group of malignant disorders derived from B- or T-cell lymphoid progenitor cells. ALL often is refractory to or relapses after treatment; thus, novel targeted therapy for ALL is urgently needed. In the present study, we initially found that the level of SIRT1, a class III histone deacetylase, was higher in primary ALL cells from patients than in peripheral blood mononuclear cells from healthy individuals. But it is not clear whether inhibition of SIRT1 by its selective small molecule inhibitor Tenovin-6 is effective against ALL cells. Methods: We tested the effect of Tenovin-6 on ALL cell lines (REH and NALM-6) and primary cells from 41 children with ALL and 2 adult patients with ALL. The effects of Tenovin-6 on cell viability were determined by MTS assay; colony-forming assays were determined by soft agar in ALL cell lines and methylcellulose medium in normal bone marrow cells and primary ALL blast cells; cell apoptosis and cell cycling were examined by flow cytometry; the signaling pathway was determined by Western blotting; ALL stem/progenitor cells were separated by using MACS MicroBead kit. Results: The results showed that Tenovin-6 treatment activated p53, potently inhibited the growth of pre-B ALL cells and primary ALL cells, and sensitized ALL cells to frontline chemotherapeutic agents etoposide and cytarabine. Tenovin-6 induced apoptosis in REH and NALM-6 cells and primary ALL cells and diminished expression of Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP) in such cells. Furthermore, inhibition of SIRT1 by Tenovin-6 inhibited the Wnt/β-catenin signaling pathway and eliminated ALL stem/progenitor (CD133 + CD19-) cells. Conclusion: Our results indicate that Tenovin-6 may be a promising targeted therapy for ALL and clinical trials are warranted to investigate its efficacy in ALL patients. [ABSTRACT FROM AUTHOR]

Background T674I FIP1L1-PDGFRα in a subset of chronic eosinophilic leukemia (CEL) is a gatekeeper mutation that is resistant to many tyrosine kinase inhibitors (TKIs) (e.g., imatinib, nilotinib and dasatinib), similar to T315I Bcr-Abl. Therefore, novel TKIs effective against T674I FIP1L1-PDGFRα are needed. Ponatinib (AP24534) is a novel orally bioavailable TKI against T315I Bcr-Abl, but it is not clear whether ponatinib is effective against T674I FIP1L1- PDGFRα. The purpose of this study was to examine the effect of ponatinib on T674I FIP1L1- PDGFRα. Methods Molecular docking analysis in silico was performed. The effects of ponatinib on PDGFRα signaling pathways, apoptosis and cell cycling were examined in EOL-1, BaF3 cells expressing either wild type (WT) or T674I FIP1L1-PDGFRα. The in vivo antitumor activity of ponatinib was evaluated with xenografted BaF3-T674I FIP1L1-PDGFRα cells in nude mice models. Results Molecular docking analysis revealed that ponatinib could bind to the DFG (Asp-Phe-Gly)-out state of T674I PDGFRα. Ponatinib potently inhibited the phosphorylation of WT and T674I FIP1L1-PDGFRα and their downstream signaling molecules (e.g., Stat3, Stat5). Ponatinib strikingly inhibited the growth of both WT and T674I FIP1L1-PDGFRα-carrying CEL cells (IC50: 0.004-2.5 nM). It induced apoptosis in CEL cells with caspase-3-dependent cleavage of Mcl-1, and inhibited tyrosine phosphorylation of β-catenin to decrease its stability and prosurvival functions. In vivo, ponatinib abrogated the growth of xenografted BaF3-T674I FIP1L1-PDGFRα cells in nude mice. Conclusions Ponatinib is a pan-FIP1L1-PDGFRα inhibitor, and clinical trials are warranted to investigate its efficacy in imatinib-resistant CEL. [ABSTRACT FROM AUTHOR]

Background: Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. Bcr-Abl- T315I is the notorious point mutation that causes resistance to imatinib and the second generation tyrosine kinase inhibitors, leading to poor prognosis. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML that may also be effective against CML cells with Bcr-Abl- T315I. Results: In this report, we discovered that pristimerin, a quinonemethide triterpenoid isolated from Celastraceae and Hippocrateaceae, inhibited growth and induced apoptosis in CML cells, including the cells harboring Bcr-Abl-T315I mutation. Additionally, pristimerin inhibited the growth of imatinib-resistant Bcr-Abl-T315I xenografts in nude mice. Pristimerin blocked the TNFα-induced IκBa phosphorylation, translocation of p65, and expression of NF-κB-regulated genes. Pristimerin inhibited two steps in NF-κB signaling: TAK1TIKK and IKKTIκBa. Pristimerin potently inhibited two pairs of CML cell lines (KBM5 versus KBM5-T315I, 32D-Bcr-Abl versus 32D-Bcr-Abl-T315I) and primary cells from a CML patient with acquired resistance to imatinib. The mRNA and protein levels of Bcr-Abl in imatinib-sensitive (KBM5) or imatinib-resistant (KBM5-T315I) CML cells were reduced after pristimerin treatment. Further, inactivation of Bcr-Abl by imatinib pretreatment did not abrogate the TNFα-induced NF-κB activation while silencing p65 by siRNA did not affect the levels of Bcr-Abl, both results together indicating that NF-κB inactivation and Bcr-Abl inhibition may be parallel independent pathways. Conclusion: To our knowledge, this is the first report to show that pristimerin is effective in vitro and in vivo against CML cells, including those with the T315I mutation. The mechanisms may involve inhibition of NF-κB and Bcr-Abl. We concluded that pristimerin could be a lead compound for further drug development to overcome imatinib resistance in CML patients. [ABSTRACT FROM AUTHOR]