scholarly journals Mapping nonapoptotic caspase activity with a transgenic reporter in mice

2017 ◽  
Author(s):  
P. J. Nicholls ◽  
Thomas F. Pack ◽  
Nikhil M. Urs ◽  
Sunil Kumar ◽  
Gabor Turu ◽  
...  
Keyword(s):  
Cell Death ◽  
Neural Plasticity ◽  
Structural Changes ◽  
Caspase 3 ◽  
Neuronal Firing ◽  
Caspase Activity ◽  
Live Animal ◽  
Simple Method ◽  
Fluorescent Reporter

AbstractThe protease caspase-3 is a key mediator of apoptotic programmed cell death. But weak or transient caspase activity can contribute to neuronal differentiation, axonal pathfinding, and synaptic long-term depression. Despite the importance of sublethal, or nonapoptotic, caspase activity in neurodevelopment and neural plasticity, there has been no simple method for mapping and quantifying nonapoptotic caspase activity in rodent brains. We therefore generated a transgenic mouse expressing a highly sensitive and specific fluorescent reporter of caspase activity, with peak signal localized to the nucleus. Surprisingly, nonapoptotic caspase activity was prevalent in healthy adult brains and influenced neuronal functional connectivity. We quantified the relationship between caspase activity and cell firing and morphology. We also notably observed a sex-specific persistent elevation in amygdalar caspase activity in females after restraint stress. This simple in vivo caspase activity reporter will facilitate systems-level studies of apoptotic and nonapoptotic phenomena in behavioral and pathological models.Significance StatementCaspase-3 is an enzyme that can cause cell death when highly active but can also perform important cellular functions, such as maturation and structural changes, when only weakly or transiently active. Despite the importance of this nonlethal type of caspase activity, there is no straightforward method to measure it in live rodents. We therefore developed mice that have a fluorescent reporter that is sensitive enough to detect nonlethal caspase activity. Surprisingly, we found that weak caspase activity is widespread in healthy brains and influences the synchrony of neuronal firing across different brain regions. We also observed increased caspase activity in female mice after severe stress. This simple, live-animal caspase activity reporter can subserve multiple applications in behavior and pathology research.

The Bcr-Abl Kinase Inhibitor INNO-406 Induces Autophagy and Different Modes of Cell Death Execution in Bcr-Abl-Positive Leukemias.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 2951-2951
Author(s):  
Yuri Kamitsuji ◽  
Junya Kuroda ◽  
Shinya Kimura ◽  
Ken-ichiro Watanabe ◽  
Eishi Ashihara ◽  
...  
Keyword(s):  
Cell Death ◽  
Dna Fragmentation ◽  
Cell Lines ◽  
Caspase 3 ◽  
Kinase Inhibitor ◽  
Cellular Growth ◽  
Mitochondrial Outer Membrane ◽  
Caspase Activity ◽  
Cell Death Pathway

Abstract The blockade of Bcr-Abl signaling suppresses cellular growth and induces cell death in Bcr-Abl+ cells. While they are known to promote caspase-mediated apoptosis, it remains unclear whether caspase-independent cell death-inducing mechanisms are also triggered. Here we assessed the regulatory mechanisms for cellular survival and death of Bcr-Abl+ leukemias more precisely, using a novel Bcr-Abl tyrosine kinase inhibitor, INNO-406 (formerly NS-187) which is more selective and 25-55-fold more active than imatinib (Kimura S, Blood 2005), in four CML-derived Bcr-Abl+ cell lines (K562, KT-1, BV173 and MYL), Ba/F3 harboring wild type bcr-abl (Ba/F3/wt bcr-abl), and in vivo CML mouse model. INNO-406 induces apoptosis in all lines examined, as were demonstrated by typical apoptotic morphology, loss of mitochondrial outer membrane potential (reduction of DiOC6 uptake), increase of cells in subG1 fraction by propidium iodide (PI) staining, DNA fragmentation and caspase-3 activation. However, when we inhibit caspase activity by zVAD-fmk (zVAD), a pan-caspase inhibitor, two modes of cell death execution were observed. In K562, KT-1 and BV173 cells treated with INNO-406, zVAD almost completely prevented apoptosis (i.e. showing atypical feature for apoptosis, no DNA fragmentation and no accumulation of subG1 fraction), with cell death resulting from morphologically non-apoptotic, so-called caspase-independent necrosis-like cell death (CIND). While, in MYL and Ba/F3/wt bcr-abl cells, despite the sufficient inhibition of caspases’ activity, the inhibition of the cell death by zVAD was only partial and these cell lines still underwent apoptosis (i.e. showing DNA fragmentation and the accumulation of subG1 population), suggesting the presence of alter cell death pathway which is caspase-independent apoptosis (CIA) in MYL and Ba/F3/wt bcr-abl. The propensity towards CIND or CIA in cells was strongly associated with cellular dependency on apoptosome-mediated caspase activity, that is CIND with a high apoptosome activity potential while CIA with low. Freshly isolated leukemic cell samples from Bcr-Abl+ leukemia patients also had either low or high apoptosome activity potential. Moreover, cells undergoing CIND exhibited hallmarks of autophagy (i.e. the autophagosome formation, punctate formations of LC3 and the accumulation of LC3-II isoform), suggested the participation of autophagy in response to Bcr-Abl blockade. Inhibition of autophagy with chloroquine enhanced INNO-406-induced cell death, which indicates that the autophagic response of the tumor cells is protective. While, in vivo CML model, INNO-406 treatment increased apoptotic cells regardless of the caspase-3 activation, further implicating the involvement of caspase-independent cell death regulatory pathway in vivo in primary Bcr-Abl+ leukemic cells. These findings suggest new insights into the biology and therapy of Bcr-Abl+ leukemias.

scholarly journals Effectiveness of Vitamin C and Vitamin E Antioxidant Combination on Caspase-3 Expression in Wistar White Rat Pulmonum Contusion

2020 ◽  
Vol 3 (1) ◽  
pp. 31-44
Author(s):  
Bermansyah ◽  
Gama Satria ◽  
Ahmad Umar
Keyword(s):  
Cell Death ◽  
Vitamin E ◽  
Vitamin C ◽  
Wistar Rats ◽  
Caspase 3 ◽  
Cell Function ◽  
Pulmonary Contusion ◽  
Tnf Α ◽  
Male Wistar Rats

Introduction.Pulmonary contusions can cause a progressive inflammatory response. Activation of TNF-α cytokines and reactive oxygen species (ROS) can cause pulmonary cell death. Antioxidants can have the potential to neutralize ROS. The purpose of this study is to determine the effectiveness of antioxidant administration in maintaining pulmonary cell function in wistar rats that have been induced to experience pulmonary contusions through caspase-3 levels. Methods.This study was an in vivo experimental study conducted on thirty male wistar rats and divided into five groups (n = 6): control, pulmonary contusion + asthaxanthine 5 mg/kgBW, pulmonary contusion + vitamin C and E 50 mg/kgBW, pulmonary contusion + vitamin C and E 100 mg/kgBW, pulmonary contusion + vitamin C and E 200 mg/kgBW. The value of Caspase-3 is evaluated by the IHC. All data analyzes used SPSS 18. Results. Low doses of antioxidants have the potential to reduce pulmonary cell death in wistar rats induced by pulmonary contusions.Conclussion. Vitamin C and E effective to reduce polmonary cell death in pulmonary contusion.Keywords: antioxidants, vitamin C, vitamin E, pulmonary contusions animal model, apoptosis, caspase-3

Epicatechin and its in vivo metabolite, 3′-O-methyl epicatechin, protect human fibroblasts from oxidative-stress-induced cell death involving caspase-3 activation

2001 ◽  
Vol 354 (3) ◽  
pp. 493-500 ◽  
Author(s):  
Jeremy P. E. SPENCER ◽  
Hagen SCHROETER ◽  
Gunter KUHNLE ◽  
S. Kaila S. SRAI ◽  
Rex M. TYRRELL ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Hydrogen Peroxide ◽  
Cell Death ◽  
Caspase 3 ◽  
Cell Damage ◽  
Protective Action ◽  
Human Fibroblasts ◽  
Membrane Damage ◽  
Antioxidant Properties

There is considerable current interest in the cytoprotective effects of natural antioxidants against oxidative stress. In particular, epicatechin, a major member of the flavanol family of polyphenols with powerful antioxidant properties in vitro, has been investigated to determine its ability to attenuate oxidative-stress-induced cell damage and to understand the mechanism of its protective action. We have induced oxidative stress in cultured human fibroblasts using hydrogen peroxide and examined the cellular responses in the form of mitochondrial function, cell-membrane damage, annexin-V binding and caspase-3 activation. Since one of the major metabolites of epicatechin in vivo is 3′-O-methyl epicatechin, we have compared its protective effects with that of epicatechin. The results provide the first evidence that 3′-O-methyl epicatechin inhibits cell death induced by hydrogen peroxide and that the mechanism involves suppression of caspase-3 activity as a marker for apoptosis. Furthermore, the protection elicited by 3′-O-methyl epicatechin is not significantly different from that of epicatechin, suggesting that hydrogen-donating antioxidant activity is not the primary mechanism of protection.

scholarly journals Nitric Oxide Inhibits Caspase Activation and Apoptotic Morphology but Does Not Rescue Neuronal Death

2005 ◽  
Vol 25 (3) ◽  
pp. 348-357 ◽  
Author(s):  
Ping Zhou ◽  
Liping Qian ◽  
Costantino Iadecola
Keyword(s):  
Nitric Oxide ◽  
Cell Death ◽  
Cell Viability ◽  
Cell Survival ◽  
Caspase 3 ◽  
Apoptotic Cell ◽  
Cysteine Residue ◽  
Caspase Activity ◽  
No Donors ◽  
Apoptotic Morphology

Nitric oxide (NO) has been shown to inhibit apoptotic cell death by S-nitrosylation of the catalytic-site cysteine residue of caspases. However, it is not clear whether in neurons NO-mediated caspase inactivation leads to improved cell survival. To address this issue, we studied the effect of NO donors on caspase activity and cell survival in cortical neuronal culture treated with the apoptosis inducer staurosporine (STS) and camptothecin. In parallel, cell viability was assessed by the MTS assay and MAP2 staining. We found that NO donors ((±)- S-nitroso- N-acetylpenicillamine, S-nitrosoglutathione, and NONOates) dose-dependently inhibited caspase-3 and -9 activity induced by STS and camptothecin. The reduction in caspase-3 activity was, in large part, because of the blockage of the proteolytic conversion of pro-caspase-3 to active caspase-3. NO donors also inhibited the appearance of the classical apoptotic nuclear morphology. However, inhibition of both caspase activity and apoptotic morphology was not associated with enhancement of cell viability. Thus, inhibition of caspase and apoptotic morphology by NO donors does not improve neuronal survival. The data suggest that inhibition of caspase by NO unmasks a caspase-independent form of cell death. A better understanding of this form of cell death may provide new strategies for neuroprotection in neuropathologies, such as ischemic brain injury, associated with apoptosis.

scholarly journals Caspase levels and execution efficiencies determine the apoptotic potential of the cell

2012 ◽  
Vol 196 (4) ◽  
pp. 513-527 ◽  
Author(s):  
Anat Florentin ◽  
Eli Arama
Keyword(s):  
Cell Death ◽  
Drosophila Melanogaster ◽  
Activity Levels ◽  
Caspase Activity ◽  
Intrinsic Properties ◽  
Functional Differences ◽  
Effector Caspases ◽  
Set Up

Essentially, all metazoan cells can undergo apoptosis, but some cells are more sensitive than others to apoptotic stimuli. To date, it is unclear what determines the apoptotic potential of the cell. We set up an in vivo system for monitoring and comparing the activity levels of the two main effector caspases in Drosophila melanogaster, Drice and Dcp-1. Both caspases were activated by the apoptosome after irradiation. However, whereas each caspase alone could induce apoptosis, Drice was a more effective inducer of apoptosis than Dcp-1, which instead had a role in establishing the rate of cell death. These functional differences are attributed to their intrinsic properties rather than merely their tissue specificities. Significantly, the levels of the procaspases are directly proportional to their activity levels and play a key role in determining the cell’s sensitivity to apoptosis. Finally, we provide evidence for the existence of a cellular execution threshold of caspase activity, which must be reached to induce apoptosis.

Intracellular NAD+ Depletion Enhances Bortezomib-Induced Myeloma Cytotoxicity

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 330-330
Author(s):  
Antonia Cagnetta ◽  
Michele Cea ◽  
Chirag Acharya ◽  
Teresa Calimeri ◽  
Yu-Tzu Tai ◽  
...  
Keyword(s):  
Cell Death ◽  
Synergistic Effect ◽  
Cell Lines ◽  
Caspase 3 ◽  
Statistical Significance ◽  
Caspase 8 ◽  
Caspase 9 ◽  
Nicotinamide Phosphoribosyltransferase

Abstract Abstract 330 Background: Our previous study demonstrated that inhibition of nicotinamide phosphoribosyltransferase (Nampt) acts by severely depleting intracellular NAD+ content and thus eliciting mitochondrial dysfunction and autophagic MM cell death. The proteasome inhibitor Bortezomib induces anti-MM activity by affecting a variety of signaling pathways. However, as with other agents, dose-limiting toxicities and the development of resistance limit its long-term utility. Here, we demonstrate that combining Nampt inhibitor and bortezomb induces synergistic anti-MM cell death both in vitro using MM cell lines or patient CD138+ MM cells and in vivo in a human plasmacytoma xenograft mouse model. Material and Methods: We utilized MM.1S, MM.1R, RPMI-8226, and U266 human MM cell lines, as well as purified tumor cells from patients relapsing after prior therapies. Cell viability and apoptosis assays were performed using Annexin V/PI staining. Intracellular NAD+ level and proteasome activity were quantified after 12, 24, and 48h exposure to single/combination drugs by specific assays. In vitro angiogenesis was assessed by Matrigel capillary-like tube structure formation assay. Immunoblot analysis was performed using antibodies to caspase-8, caspase-9, caspase-3, PARP, Bcl-2, and tubulin. CB-17 SCID male mice (n = 28; 7 mice/EA group) were subcutaneously inoculated with 5.0 × 106 MM.1S cells in 100 microliters of serum free RPMI-1640 medium. When tumors were measurable (3 weeks after MM cell injection), mice were treated for three weeks with vehicle alone, FK866 (30mg/kg 4 days weekly), Bortezomib (0.5 mg/kg twice weekly), or FK866 (30 mg/kg) plus Bortezomib (0.5 mg/kg). Statistical significance of differences observed in FK866, Bortezomib or combination-treated mice was determined using a Student t test. Isobologram analysis was performed using “CalcuSyn” software program. A combination index < 1.0 indicates synergism. Results/Discussion: Combining FK866 and Bortezomib induces synergistic anti-MM activity in vitro against MM cell lines (P<0.005, CI < 1) or patient CD138-positive MM cells (P< 0.004). FK866 plus Bortezomib-induced synergistic effect is associated with: 1)activation of caspase-8, caspase-9, caspase-3, and PARP; 2) improved intracellular NAD+ dissipation; 3) suppression of chymotrypsin-like, caspase-like, and trypsin-like proteolytic activities; 4) inhibition of NF-kappa B signaling; and 5) inhibition of angiogenesis. Importantly, the ectopic overexpression of Nampt rescues this observed synergistic effect; conversely, Nampt knockdown by RNAi significantly enhances the anti-MM effect of bortezomib. In the murine xenograft MM model, low dose combination FK866 (30 mg/kg) and Bortezomib (0.5 mg/kg) is well tolerated, significantly inhibits tumor growth (P < 0.001), and prolongs host survival (2–2.5 months in mice receiving combined drugs, P = 0.001). These findings demonstrate that intracellular NAD+ levels represent a major determinant in the ability of bortezomib to induce apoptosis of MM cells, providing the rationale for clinical protocols evaluating FK866 together with Bortezomib to improve patient outcome in MM. Disclosures: Munshi: Celgene: Consultancy; Millenium: Consultancy; Merck: Consultancy; Onyx: Consultancy.

Interfering with Arginine Metabolism As a New Treatment Strategy for Multiple Myeloma

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 3005-3005
Author(s):  
Bjoern Jacobi ◽  
Lea Stroeher ◽  
Nadine Leuchtner ◽  
Hakim Echchannaoui ◽  
Alexander Desuki ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Cell Death ◽  
Cell Lines ◽  
Caspase 3 ◽  
Xenograft Model ◽  
Myeloma Cell ◽  
Intracellular Protein ◽  
Myeloma Cells ◽  
Induction Of Apoptosis

Abstract Introduction Starvation of tumor cells from the amino acid arginine has recently gained particular interest because of the downregulation of the rate-limiting enzyme argininosuccinate synthethase 1 (ASS1) in various cancer entities. ASS1-deficient cells cannot resynthesize arginine from citrulline and are therefore considered arginine auxotrophic. The arginine depleting enzyme arginine deiminase (ADI-PEG20, Polaris Pharmaceuticals) is currently tested in phase I-III clinical trials for different arginine auxotrophic cancers. The natural arginine analogue canavanine can compete with arginine for arginyl-tRNA-binding sites and consequently be incorporated into nascent proteins instead of arginine. Canavanine could therefore potentially further disturb intracellular protein homeostasis, especially under arginine deprivation. The sensitivity of myeloma cells towards arginine depletion strategies has not been analyzed so far. Methods Human myeloma cell lines and CD138-sorted primary human myeloma cells from patient bone marrow were screened for ASS1 expression by western blotting (WB). The cells were cultured in arginine free medium and assessed for proliferation and metabolic activity (CFSE/MTT assays), apoptosis (caspase-3 cleavage) and cell death (annexinV/propidium iodide). Canavanine was supplied in both arginine-sufficient and -deficient conditions. The level of intracellular protein stress was determined by WB and/or flow cytometry analysis for ubiquitinated proteins, phosphorylated eukaryotic initiation factor 2α (peIF2α) and the spliced isoform of the X-Box binding protein 1 (Xbp1s). Repetitive ADI-PEG20 ± canavanine application i.p. were tested in vivo in an U266 myeloma xenograft model in NOD/SCID/IL2Rcg-/- (NSG) mice. Arginine and canavanine levels in plasma were determined by HPLC. Tumor growth was measured, mice were assessed for survival, weight and side effects. Tumor tissues were analyzed for caspase-3 cleavage and Ki67 expression by immunohistochemistry. Results 5 of 6 myeloma cell lines were negative for ASS1. Also, ASS1 was either not or only weakly expressed in the majority of primary CD138+ myeloma patient samples. Arginine starvation induced an arrest of cell proliferation and/or metabolic activity of primary myeloma cells and myeloma cell lines after 18-24 h. Addition of citrulline could only rescue ASS1 positive myeloma cells due to the intracellular resynthesis of arginine. Arginine starvation alone led to delayed induction of apoptosis (e.g. 35% cell death of NCI-H929 cells after 72 h of treatment). Addition of 100 mM canavanine strongly increased cell death specifically in the context of arginine deficiency (e.g. cell death in NCI-H929 cells: 87% after 24 h, 100 % after 48h) while it was non-toxic and had no effect on cell viability under physiological arginine conditions. Co-application of canavanine induced ubiquitination of cellular proteins and led to the prolongation of a fatal unfolded protein response (UPR) as measured by markedly elevated Xbp1s levels. Prolonged UPR ultimately led to the induction of apoptosis as reflected by annexin V binding and caspase-3 cleavage. In an U266 myeloma NSG xenograft model, systemic arginine depletion by ADI-PEG20 suppressed tumor growth in vivo and significantly prolonged median survival of mice when compared with the control group (22±3 vs. 15±3 days). Canavanine treatment alone had no influence on viability (13±0 days). However, the combination of ADI-PEG20 and canavanine demonstrated the longest median survival (27±7 days). Histological examination of explanted tumors showed the highest rates of caspase-3 cleavage in the ADI-PEG20/canavanine group. Conclusion Myeloma cells are mostly arginine auxotrophic and can be selectively targeted by arginine starvation. Combination of arginine depletion with the arginine analogue canavanine leads to a highly efficient and specific tumor cell eradication and should be further optimized in multiple myeloma preclinical models. Disclosures Bomalaski: Polaris Pharmaceuticals Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Expression of caspase-3 and structural changes associated with apoptotic cell death of keratinocytes in oral lichen planus

Oral Diseases ◽  
2004 ◽  
Vol 10 (3) ◽  
pp. 173-178 ◽  
Author(s):  
SI Tobon-Arroyave ◽  
FA Villegas-Acosta ◽  
SM Ruiz-Restrepo ◽  
B Vieco-Duran ◽  
M Restrepo-Misas ◽  
...  
Keyword(s):  
Cell Death ◽  
Lichen Planus ◽  
Oral Lichen Planus ◽  
Structural Changes ◽  
Caspase 3 ◽  
Apoptotic Cell ◽  
Apoptotic Cell Death ◽  
Oral Lichen

Abstract 1950: Role of Superoxide, Nitric Oxide and Peroxynitrite in Doxorubicin-induced Cell Death in vitro and in vivo

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Partha Mukhopadhyay ◽  
Mohanraj Rajesh ◽  
Sandor Bátkai ◽  
György Haskó ◽  
Csaba Szabo ◽  
...  
Keyword(s):  
Cell Death ◽  
Caspase 3 ◽  
Superoxide Generation ◽  
Cytochrome C Release ◽  
Mitochondrial Superoxide ◽  
Induced Apoptosis ◽  
Peroxynitrite Scavengers

Although doxorubicin (DOX) is one of the most potent antitumor agents available, its clinical use is limited because of the risk of severe cardiotoxicity often leading to irreversible congestive heart failure. Apoptotic cell death is a key component in DOX-induced cardiotoxicity, but its trigger(s) and mechanisms are poorly understood. Here, we explore the role of peroxynitrite (a reactive oxidant produced from the diffusion-controlled reaction between nitric oxide and superoxide anion) in DOX-induced cell death. Using a well-established in vivo mouse model of DOX-induced acute heart failure, we demonstrate marked increases in myocardial apoptosis (caspase-3 and 9 gene expression, caspase 3 activity, cytochrome-c release, and TUNEL), iNOS but not eNOS and nNOS expression, 3-nitrotyrosine formation and a decrease in myocardial contractility following DOX treatment. Pre-treatment of mice with peroxynitrite scavengers markedly attenuated DOX-induced myocardial cell death and dysfunction without affecting iNOS expression. DOX induced increased superoxide generation and nitrotyrosine formation in the mitochondria, dissipation of mitochondrial membrane potential, apoptosis (cytochrome-C release, annexin V staining, caspase activation, nuclear fragmentation), and disruption of actin cytoskeleton structure in cardiac-derived H9c2 cells. Selective iNOS inhibitors attenuated DOX-induced apoptosis, without affecting increased mitochondrial superoxide generation, whereas NO donors increased DOX-induced cell death in vitro . The peroxynitrite scavengers FeTMPyP and MnTMPyP markedly reduced both DOX- or peroxynitrite-induced nitrotyrosine formation and cell death in vitro , without affecting DOX-induced increased mitochondrial superoxide formation. Thus, peroxynitrite is a major trigger of DOX-induced apoptosis, and its effective neutralization can be of significant therapeutic benefit.

Anti-Acute Myeloid Leukemia Activity of Chaetocin, a Novel Epigenetic Drug Inhibitor Inducing Oxidative Stress.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 889-889
Author(s):  
Hassiba Chaib ◽  
Thomas Prebet ◽  
Audrey Restouin ◽  
Remy Castellano ◽  
Sandrine Opi ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Cell Death ◽  
Acute Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Caspase 3 ◽  
Hdac Inhibitors ◽  
Oxidative Species ◽  
Acute Myeloid

Abstract Recent studies have highlighted the importance of epigenetic modifications in the pathogenesis of Acute Myeloid Leukemia (AML). This results have been confirmed by the activity of new drug like DNA demethylating agents and histone deacetylase (HDAC) inhibitors in both in vivo and in vitro studies. Recently, Chaetocin, a natural fungal compound, has been identified as the first specific inhibitor of the histone methyltransferase SU(VAR)3–9 which plays a role in heterochromatin gene silencing. In this study, we decided to evaluate Chaetocin as a therapeutic agent in AML in vitro and to explore the related mechanisms. We show that Chaetocin induce dramatic cell death at nanomolar concentrations in U937 and HL60 (97.2% ± 0.4 and 91.6% ± 9 cell death at 100 nM chaetocin, respectively), and to a lesser extend in K562 (67.3% ± 1.6 cell death at 100 nM chaetocin), cell cultures. Cell death occurred at 24 h incubation time which correlated with induction of apoptosis as assessed by Annexin V/7-AAD staining and activation of downstream executioner caspase-3/7. Using transcription low-density array and quantitative RT- PCR, Chaetocin was showed to up-regulate gene transcription such as of the cell cycle inhibitor p21/WAF1 consistent with a role for the targeted SU(VAR)3–9 in heterochromatin gene silencing. In agreement with the recent report of Chaetocin being a promising new antimyeloma agent acting via imposition of oxidative stress, intracellular levels of oxidative species were increased in Chaetocin treated U937 cells in a time- and dose-dependent manner that correlated with induction of cell death. Furthermore, incubation of cells with N-acetyl cysteine, a cell-permeable precursor of intracellular glutathione reductant, prevented chaetocin-induced accumulation of oxidative species, transcription of selected genes (e.g. p21/WAF1), activation of caspase-3, and cell death. Finally, Chaetocin was found to increase the antileukemia activity of HDAC inhibitors and Aracytin, and thus appears as a promising agent for further study as a potential anti-AML therapeutic. Preliminary results obtained in vivo in xenograft models and ex vivo, using blasts of a panel of patients with AML, will be presented.

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