Phenylarsine Oxide Blocks Interleukin-1β–Induced Activation of the Nuclear Transcription Factor NF-κB, Inhibits Proliferation, and Induces Apoptosis of Acute Myelogenous Leukemia Cells

Research progress on arsenic, arsenic-containing medicinal materials, and arsenic-containing preparations: clinical application, pharmacological effects, and toxicity

Introduction: The toxicity of arsenic is widely recognized globally, mainly harming human health by polluting water, soil, and food. However, its formulations can also be used for the clinical treatment of diseases such as leukemia and tumors. Arsenic has been used as a drug in China for over 2,400 years, with examples such as the arsenic-containing drug realgar mentioned in Shennong's Herbal Classic. We have reviewed references on arsenic over the past thirty years and found that research has mainly focused on clinical, pharmacological, and toxicological aspects. Results and Discussion: The finding showed that in clinical practice, arsenic trioxide is mainly used in combination with all-trans retinoic acid (ATRA) at a dose of 10 mg/d for the treatment of acute promyelocytic leukemia (APL); realgar can be used to treat acute promyelocytic leukemia, myelodysplastic syndrome, and lymphoma. In terms of pharmacology, arsenic mainly exerts anti-tumor effects. The dosage range of the action is 0.01-80 μmol/L, and the concentration of arsenic in most studies does not exceed 20 μmol/L. The pharmacological effects of realgar include antiviral activity, inhibition of overactivated lactate dehydrogenase, and resistance to malaria parasites. In terms of toxicity, arsenic is toxic to multiple systems in a dose-dependent manner. For example, 5 μmol/L sodium arsenite can induce liver oxidative damage and promote the expression of pro-inflammatory factors, and 15 μmol/L sodium arsenite induces myocardial injury; when the concentration is higher, it is more likely to cause toxic damage.

NF-κB: A Druggable Target in Acute Myeloid Leukemia

Acute Myeloid Leukemia (AML) is an aggressive hematological malignancy that relies on highly heterogeneous cytogenetic alterations. Although in the last few years new agents have been developed for AML treatment, the overall survival prospects for AML patients are still gloomy and new therapeutic options are still urgently needed. Constitutive NF-κB activation has been reported in around 40% of AML patients, where it sustains AML cell survival and chemoresistance. Given the central role of NF-κB in AML, targeting the NF-κB pathway represents an attractive strategy to treat AML. This review focuses on current knowledge of NF-κB's roles in AML pathogenesis and summarizes the main therapeutic approaches used to treat NF-κB-driven AML.

Oroxylin A, a natural compound, mitigates the negative effects of TNFα-treated acute myelogenous leukemia cells

Tumor necrosis factor alpha (TNFα) is a complicated cytokine which is involved in proliferation and differentiation of acute myelogenous leukemia (AML) cells through a poorly understood mechanism. Mechanistic studies indicate that TNFα induced binding of PI3K subunit p85α to N-terminal truncated nuclear receptor RXRα (tRXRα) proteins, and activated AKT. The activated PI3K/AKT pathway negatively regulated differentiation of AML cells through the upregulation of c-Myc. In addition, TNFα also induced activation of nuclear factor κB (NF-κB), a nuclear transcription factor which was shown to promote cell proliferation. The present study demonstrates that oroxylin A, a natural compound isolated from Scutellariae radix, sensitizes leukemia cells to TNFα and markedly enhances TNFα-induced growth inhibition and differentiation of AML cell including human leukemia cell lines and primary AML cells. Activation of PI3K/AKT pathway could be inhibited by oroxylin A through inhibiting expression of tRXRα in NB4 and HL-60-resistant cells. Furthermore, we found that oroxylin A inhibited the activation of NF-κB and the DNA binding activity by TNFα proved by EMSA in these two AML cell lines. Moreover, in vivo studies showed that treatment with oroxylin A in combination with TNFα decreased AML cell population and prolonged survival in NOD/SCID mice with xenografts of primary AML cells. Overall, our results indicate that oroxylin A is able to inhibit the negative effects of TNFα for AML therapy, suggesting that combination of oroxylin A and TNFα have the potential to delay growth or eliminate the abnormal leukemic cells, thus representing a promising strategy for AML treatment.

Deferasirox selectively induces cell death in the clinically relevant population of leukemic CD34+CD38- cells through iron chelation, induction of ROS, and inhibition of HIF1α expression

Despite a high remission rate after therapy, only 40-50% of acute myeloid leukemia (AML) patients survive 5 years after diagnosis. The main cause of treatment failure is thought to be insufficient eradication of CD34⁺CD38^- AML cells. In order to induce preferential cell death in CD34⁺CD38^- AML cells, two separate events may be necessary: (1) inhibition of survival signals such as nuclear factor kappa-beta (NF-κB) and (2) induction of stress responses such as the oxidative stress response. Therefore, regimens that mediate both effects may be favorable. Deferasirox is a rationally designed oral iron chelator mainly used to reduce chronic iron overload in patients who receive long-term blood transfusions. Our study revealed that clinically relevant concentrations of deferasirox are cytotoxic in vitro to AML progenitor cells, but even more potent against the more primitive CD34⁺CD38^- cell population. In addition, we found that deferasirox exerts its effect, at least in part, by inhibiting the NF-κB/hypoxia-induced factor 1-alpha (HIF1α) pathway and by elevating reactive oxygen species levels. We believe that, pending further characterization, deferasirox can be considered as a potential therapeutic agent for eradicating CD34⁺CD38^- AML cells.

The cytokine network in acute myeloid leukemia (AML): A focus on pro- and anti-inflammatory mediators

Cytokines exert profound effects on the progression of hematopoietic malignancies such as acute myeloid leukemia (AML). Critical roles of cytokines in the context of inflammation have gained special interest. While pro-inflammatory mediators such as IL-1β, TNF-α and IL-6 tend to increase AML aggressiveness, anti-inflammatory mediators such as TGF-β and IL-10 appear to impede AML progression. Dysregulation of the complex interactions between pro- and anti-inflammatory cytokines in AML may create a pro-tumorigenic microenvironment with effects on leukemic cell proliferation, survival and drug-resistance. This article summarizes current knowledge about the functions of pro- and anti-inflammatory cytokines in AML, their modes of action, and therapeutic interventions with potential to improve clinical outcomes for AML patients.

Phenylarsine oxide (PAO) induces apoptosis in HepG2 cells via ROS-mediated mitochondria and ER-stress dependent signaling pathways

Arsenic trioxide (As₂O₃) is an old drug that has recently been reintroduced as a therapeutic agent for acute promyelocytic leukemia (APL). Although As₂O₃ is also applied to treat other types of cancer in vitro and in vivo, it has been reported that single agent As₂O₃ has poor efficacy against non-hematologic malignant cancers in clinical trials. Recently, a few reports have indicated that organic arsenic compounds can be a possible alternative for the treatment of As₂O₃-resistant cancers. In this study, we aimed to investigate whether the organic arsenic compound phenylarsine oxide (PAO) has potent cytotoxic effects against human hepatocellular carcinoma (HCC) HepG2 cells. Our results showed that PAO not only had a potent inhibitory effect on the proliferation of HepG2 cells but also activated apoptosis-related proteins (e.g., caspase-3 and -9 and poly-ADP ribose polymerase) in a dose- and time-dependent manner. Furthermore, intracellular ROS were specifically accumulated in the mitochondria and endoplasmic reticulum (ER) after exposure to PAO, implying that they are the target organelles for PAO-induced cytotoxicity. Additionally, when the cells were pretreated with antioxidant N-acetylcysteine (NAC), apoptosis and ER-stress were attenuated significantly, suggesting that induction of apoptosis and cell death probably occurs through the ROS-mediated mitochondria and ER-stress dependent signaling pathways.

Phenylarsine Oxide Can Induce the Arsenite-Resistance Mutant PML Protein Solubility Changes

Arsenic trioxide (As₂O₃) has recently become one of the most effective drugs for treatment of patient with acute promyelocytic leukemia (APL), and its molecular mechanism has also been largely investigated. However, it has been reported that As₂O₃ resistant patients are frequently found in relapsed APL after consolidation therapy, which is due to the point mutations in B-box type 2 motifs of promyelocytic leukemia (PML) gene. In the present study, we for the first time establish whether organic arsenic species phenylarsine oxide (PAO) could induce the mutant PML-IV (A216V) protein solubility changes and degradation. Here, three different PML protein variants (i.e., PML-IV, PML-V and mutant PML-A216V) were overexpressed in HEK293T cells and then exposed to PAO in time- and dose-dependent manners. Interestingly, PAO is found to have potential effect on induction of mutant PML-IV (A216V) protein solubility changes and degradation, but no appreciable effects were found following exposure to high concentrations of iAs^III, dimethylarsinous acid (DMA^III) and adriamycin (doxorubicin), even though they cause cell death. Our current data strongly indicate that PAO has good effects on the mutant PML protein solubility changes, and it may be helpful for improving the therapeutic strategies for arsenic-resistant APL treatments in the near future.

Glutathione transferase P1-1 as an arsenic drug-sequestering enzyme

Arsenic-based compounds are paradoxically both poisons and drugs. Glutathione transferase (GSTP1-1) is a major factor in resistance to such drugs. Here we describe using crystallography, X-ray absorption spectroscopy, mutagenesis, mass spectrometry, and kinetic studies how GSTP1-1 recognizes the drug phenylarsine oxide (PAO). In conditions of cellular stress where glutathione (GSH) levels are low, PAO crosslinks C47 to C101 of the opposing monomer, a distance of 19.9 Å, and causes a dramatic widening of the dimer interface by approximately 10 Å. The GSH conjugate of PAO, which forms rapidly in cancerous cells, is a potent inhibitor (K_i  = 90 nM) and binds as a di-GSH complex in the active site forming part of a continuous network of interactions from one active site to the other. In summary, GSTP1-1 can detoxify arsenic-based drugs by sequestration at the active site and at the dimer interface, in situations where there is a plentiful supply of GSH, and at the reactive cysteines in conditions of low GSH.

Identifying and Tackling Emergent Vulnerability in Drug-Resistant Mycobacteria

The global mechanisms and associated molecular alterations that occur in drug-resistant mycobacteria are poorly understood. To address this, we obtain genomics data and then construct a genome-scale response network in isoniazid-resistant Mycobacterium smegmatis and apply a network-mining algorithm. Through this, we decipher global alterations in an unbiased manner and identify emergent vulnerabilities in resistant bacilli, of which redox response was prominent. Using phenotypic profiling, we find that resistant bacilli exhibit collateral sensitivity to several compounds that block antioxidant responses. We find that nanogram/milliliter concentrations of ebselen, vancomycin, and phenylarsine oxide, in combination with isoniazid, are highly effective against Mycobacterium tuberculosis H37Rv and three clinical drug-resistant strains. Dynamic measurements of cytoplasmic redox potential revealed a surprisingly diminished capacity of clinical drug-resistant strains to counteract oxidative stress, providing a mechanistic basis for efficient and synergistic mycobactericidal activity of the drug combinations. Ebselen and vancomycin appear to be promising repurposable drugs.

GATA Factor-Dependent Positive-Feedback Circuit in Acute Myeloid Leukemia Cells

The master regulatory transcription factor GATA-2 triggers hematopoietic stem and progenitor cell generation. GATA2 haploinsufficiency is implicated in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), and GATA2 overexpression portends a poor prognosis for AML. However, the constituents of the GATA-2-dependent genetic network mediating pathogenesis are unknown. We described a p38-dependent mechanism that phosphorylates GATA-2 and increases GATA-2 target gene activation. We demonstrate that this mechanism establishes a growth-promoting chemokine/cytokine circuit in AML cells. p38/ERK-dependent GATA-2 phosphorylation facilitated positive autoregulation of GATA2 transcription and expression of target genes, including IL1B and CXCL2. IL-1β and CXCL2 enhanced GATA-2 phosphorylation, which increased GATA-2-mediated transcriptional activation. p38/ERK-GATA-2 stimulated AML cell proliferation via CXCL2 induction. As GATA2 mRNA correlated with IL1B and CXCL2 mRNAs in AML-M5 and high expression of these genes predicted poor prognosis of cytogenetically normal AML, we propose that the circuit is functionally important in specific AML contexts.

Inhibition of Setaria cervi protein tyrosine phosphatases by Phenylarsine oxide: A proteomic and biochemical study

Phenylarsine oxide (PAO), a specific protein tyrosine phosphatase (PTP) inhibitor significantly decreased the motility and viability of Setaria cervi ultimately leading to its death. The PTP activity present in the cytosolic and detergent soluble fractions as well as on surface of these parasites was significantly inhibited by PAO. A marked alteration in protein spots abundance after proteomic analysis showed 14 down-regulated and 9 upregulated spots in the treated parasites as compared to the control. The PTP inhibition led to increase in the cytosolic and mitochondrial calpain activity in these parasites. PAO also blocked the ATP generation in the parasite depicted by reduced activity of phosphoglycerate kinase and expression of enolase. An increased ROS level, induced lipid peroxidation/protein carbonyl formation and decreased activity of different antioxidant enzymes like thioredoxin reductase, glutathione reductase and glutathione transferases was also observed in the PAO treated parasites. PAO, thus disturbs the overall homeostasis of the filarial parasite by inhibiting PTPs. Thereby suggesting that these molecules could be used as a good chemotherapeutic target for lymphatic filariasis.

Balsalazide Potentiates Parthenolide-Mediated Inhibition of Nuclear Factor-κB Signaling in HCT116 Human Colorectal Cancer Cells

BACKGROUND/AIMS

Balsalazide is an anti-inflammatory drug used in the treatment of inflammatory bowel disease. Balsalazide can reduce inflammatory responses via several mechanisms, including inhibition of nuclear factor-κB (NF-κB) activity. Parthenolide (PT) inhibits NF-κB and exerts promising anticancer effects by promoting apoptosis. The present investigated the antitumor effects of balsalazide, combined with PT, on NF-κB in a representative human colorectal carcinoma cell line, HCT116.

METHODS

We counted cells and conducted annexin-V assays and cell cycle analysis to measure apoptotic cell death. Western blotting was used investigate the levels of proteins involved in apoptosis.

RESULTS

PT and balsalazide produced synergistic anti-proliferative effects and induced apoptotic cell death. The combination of balsalazide and PT markedly suppressed nuclear translocation of the NF-κB p65 subunit and the phosphorylation of inhibitor of NF-κB. Moreover, PT and balsalazide dramatically enhanced NF-κB p65 phosphorylation. Apoptosis, through the mitochondrial pathway, was confirmed by detecting effects on Bcl-2 family members, cytochrome c release, and activation of caspase-3 and -8.

CONCLUSIONS

Combination treatment with PT and balsalazide may offer an effective strategy for the induction of apoptosis in HCT116 cells.

IKK-dependent activation of NF-κB contributes to myeloid and lymphoid leukemogenesis by BCR-ABL1

The product of the Ph chromosome, the BCR-ABL1 tyrosine kinase activates diverse signaling pathways in leukemic cells from patients with chronic myeloid leukemia (CML) and Ph(+) B-cell acute lymphoblastic leukemia (B-ALL). Previous studies showed that nuclear factor κB (NF-κB) is activated in BCR-ABL1-expressing cells, but the mechanism of activation and importance of NF-κB to the pathogenesis of BCR-ABL1-positive myeloid and lymphoid leukemias are unknown. Coexpression of BCR-ABL1 and a superrepressor mutant of inhibitory NF-κB α (IκBαSR) blocked nuclear p65/RelA expression and inhibited the proliferation of Ba/F3 cells and primary BCR-ABL1-transformed B lymphoblasts without affecting cell survival. In retroviral mouse models of CML and B-ALL, coexpression of IκBαSR attenuated leukemogenesis, prolonged survival, and reduced myeloid leukemic stem cells. Coexpression of dominant-negative mutants of IκB kinase α (IKKα)/IKK1 or IKKβ/IKK2 also inhibited lymphoid and myeloid leukemogenesis by BCR-ABL1. Blockade of NF-κB decreased expression of the NF-κB targets c-MYC and BCL-X and increased the sensitivity of BCR-ABL1-transformed lymphoblasts to ABL1 kinase inhibitors. These results demonstrate that NF-κB is activated through the canonical IKK pathway and plays distinct roles in the pathogenesis of myeloid and lymphoid leukemias induced by BCR-ABL1, validating NF-κB and IKKs as targets for therapy of Ph(+) leukemias.

Modulation of apoptosis-related cell signalling pathways by curcumin as a strategy to inhibit tumor progression

A hallmark of cancer is resistance to apoptosis, with both the loss of proapoptotic signals and the gain of anti-apoptotic mechanisms contributing to tumorigenesis. As inducing apoptosis in malignant cells is one of the most challenging tasks regarding cancer, researchers increasingly focus on natural products to regulate apoptotic signaling pathways. Curcumin, a polyphenolic derivative of turmeric, is a natural compound derived from Curcuma longa, has attracted great interest in the research of cancer during the last half century. Extensive studies revealed that curcumin has chemopreventive properties, which are mainly due to its ability to arrest cell cycle and to induce apoptosis in cancer cells either alone or in combination with chemotherapeutic agents or radiation. The underlying action mechanisms of curcumin are diverse and has not been elucidated so far. By regulating multiple important cellular signalling pathways including NF-κB, TRAIL, PI3 K/Akt, JAK/STAT, Notch-1, JNK, etc., curcumin are known to activate cell death signals and induce apoptosis in pre-cancerous or cancer cells without affecting normal cells, thereby inhibiting tumor progression. Several phase I and phase II clinical trials indicate that curcumin is quite safe and may exhibit therapeutic efficacy. This article reviews the main effects of curcumin on the different apoptotic signaling pathways involved in curcumin induced apoptosis in cancer cells via cellular transduction pathways and provides an in depth assessment of its pharmacological activity in the management of tumor progression.

The role of inflammation in leukaemia

Acute leukaemias are a group of malignancies characterised by the invasion of the bone marrow by immature haematopoietic precursors and differentiation arrest at various maturation steps. Multiplicity of intrinsic and extrinsic factors influences the transformation and progression of leukaemia. The intrinsic factors encompass genetic alterations of cellular pathways leading to the activation of, among others, inflammatory pathways (such as nuclear factor kappa B). The extrinsic components include, among others, the inflammatory pathways activated by the bone marrow microenvironment and include chemokines, cytokines and adhesion molecules. In this chapter, we review the role of inflammatory processes in the transformation, survival and proliferation of leukaemias, particularly the role of nuclear factor kappa B and its downstream signalling in leukaemias and the novel therapeutic strategies that exploit potentially unique properties of inflammatory signalling that offer interesting options for future therapeutic interventions.

Digitoflavone inhibits IκBα kinase and enhances apoptosis induced by TNFα through downregulation of expression of nuclear factor κB-regulated gene products in human pancreatic cancer cells

Tumor necrosis factor-α (TNFα) activates both cell death and cell survival pathways. The activation of survival pathway renders most cancer cells resistant to TNF-induced cytotoxicity. We found that pretreatment with digitoflavone, a plant flavonoid, greatly sensitized TNFα-induced apoptotic cell death in several human pancreatic cancer cells. In search of the molecular basis of the sensitization effect of digitoflavone, digitoflavone was found to inhibit TNFα-induced activation of nuclear transcription factor-kappa B (NF-κB) which is the main survival factor in TNFα signaling. NF-κB suppression occurred through inhibition of IκBα kinase activation, IκBα phosphorylation, IκBα degradation, and NF-κB nuclear translocation. This inhibition correlated with suppression of NF-κB-dependent genes involved in antiapoptosis (mcl-1, bcl-2, bcl-xl, c-iap1, c-iap2, flip, and survivin), proliferation (c-myc, cyclin d1), and angiogenesis (vegf, cox-2, and mmp-9). In addition, digitoflavone can activate JNK through inhibition of NF-κB signaling, provide a continuous blockade of the feed-back inhibitory mechanism by JNK-induced NF-κB activation. This study found a novel function of digitoflavone and enhanced the value of digitoflavone as an anticancer agent.

Darinaparsin: solid tumor hypoxic cytotoxin and radiosensitizer

PURPOSE

Hypoxia is an important characteristic of the solid tumor microenvironment and constitutes a barrier for effective radiotherapy. Here, we studied the effects of darinaparsin (an arsenic cytotoxin) on survival and radiosensitivity of tumor cells in vitro under normoxia and hypoxia and in vivo using xenograft models, compared to effects on normal tissues.

EXPERIMENTAL DESIGN

The cytotoxicity and radiosensitization of darinaparsin were first tested in vitro in a variety of solid tumor cell lines under both normoxia and hypoxia and compared with arsenic trioxide (ATO, an arsenical with reported cytotoxic and radiosensitizing activities on tumor cells). The effects were then tested in mouse models of xenograft tumors derived from tumor cell lines and clinical tumor specimens. The potential mechanisms of darinaparsin effects, including reactive oxygen species (ROS) generation, cellular damage, and changes in global gene expression, were also investigated.

RESULTS

In comparison with ATO, darinaparsin had significantly higher in vitro cytotoxic and radiosensitizing activities against solid tumor cells under both normoxia and hypoxia. In vivo experiments confirmed these activities at doses that had no systemic toxicities. Importantly, darinaparsin did not radiosensitize normal bone marrow and actually radioprotected normal intestinal crypts. The darinaparsin-mediated antitumor effects under hypoxia were not dependent on ROS generation and oxidative damage, but were associated with inhibition of oncogene (RAS and MYC)-dependent gene expression.

CONCLUSION

Darinaparsin has significant and preferential cytotoxic and radiosensitizing effects on solid tumors as compared with normal cells. Darinaparsin may therefore increase the therapeutic index of radiation therapy and has near term translational potential.

Anti-cancer effect of bee venom in prostate cancer cells through activation of caspase pathway via inactivation of NF-κB

BACKGROUND

Bee venom has been used as a traditional medicine to treat arthritis, rheumatism, back pain, cancerous tumors, and skin diseases. However, the effects of bee venom on the prostate cancer and their action mechanisms have not been reported yet.

METHODS

To determine the effect of bee venom and its major component, melittin on the prostate cancer cells, apoptosis is analyzed by tunnel assay and apoptotic gene expression. For xenograft studies, bee venom was administrated intraperitoneally twice per week for 4 weeks, and the tumor growth was measured and the tumor were analyzed by immunohistochemistry. To investigate whether bee venom and melittin can inactivate nuclear factor kappa B (NF-κB), we assessed NF-κB activity in vitro and in vivo.

RESULTS AND CONCLUSIONS

Bee venom (1-10 µg/ml) and melittin (0.5-2.5 µg/ml) inhibited cancer cell growth through induction of apoptotic cell death in LNCaP, DU145, and PC-3 human prostate cancer cells. These effects were mediated by the suppression of constitutively activated NF-κB. Bee venom and melittin decreased anti-apoptotic proteins but induced pro-apoptotic proteins. However, pan caspase inhibitor abolished bee venom and melittin-induced apoptotic cell death and NF-κB inactivation. Bee venom (3-6 mg/kg) administration to nude mice implanted with PC-3 cells resulted in inhibition of tumor growth and activity of NF-κB accompanied with apoptotic cell death. Therefore, these results indicated that bee venom and melittin could inhibit prostate cancer in in vitro and in vivo, and these effects may be related to NF-κB/caspase signal mediated induction of apoptotic cell death.

NF-κB as a potential therapeutic target in myelodysplastic syndromes and acute myeloid leukemia

IMPORTANCE OF THE FIELD

The inactive NF-κB-inhibitor of NF-κB (IκB) complex is activated by stimuli including pro-inflammatory cytokines, mitogens, growth factors and stress-inducing agents. The release of NF-κB facilitates its translocation to the nucleus, where it promotes cell survival by initiating transcription of genes encoding stress-response enzymes, cell-adhesion molecules, pro-inflammatory cytokines and anti-apoptotic proteins. NF-κB and associated regulatory factors (IκB kinase subunits and bcl-3) are implicated in hematological and solid tumour malignancies. NF-κB appears to be involved in cell proliferation control, apoptosis control, angiogenesis promotion and possibly regulation of diffusion of metastases. There are several reports that inhibition of NF-κB as a therapeutic target may have a role in tumour cell death or growth inhibition.

AREA COVERED IN THIS REVIEW

We review data about inhibition of NF-κB in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). We describe the molecular mechanisms underlying NF-κB deregulation in these haematological malignancies.

WHAT THE READER WILL GAIN

Constitutive activation of NF-κB in the nucleus has been reported in some varieties of MDS/AML. The in vitro and in vivo results of NF-κB inhibition in myeloid malignancies are highlighted.

TAKE HOME MESSAGE

NF-κB selective inhibitory drugs may be useful, either as single agents or associated with conventional chemotherapy.

The synthetic heat shock protein 90 (Hsp90) inhibitor EC141 induces degradation of Bcr-Abl p190 protein and apoptosis of Ph-positive acute lymphoblastic leukemia cells

The prognosis of patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) is poor. Chemotherapy is rarely curative and tyrosine kinase inhibitors (TKIs) induce only transient responses. Heat shock protein 90 (Hsp90) is a chaperone protein that is important in signal transduction, cell cycle control, and transcription regulation in both normal and leukemia cells. In the current study, we tested the growth inhibitory and apoptotic effects of a novel Hsp90 inhibitor, EC141 on the Ph+ ALL lines Z-119, Z-181, and Z-33, as well as primary bone marrow-derived blasts from patients with newly diagnosed Ph+ ALL. We found that EC141 inhibited the growth of Ph+ ALL cells in a concentration-dependent manner with IC(50) ranged from 1 to 10 nM. EC141 also inhibited the proliferation of primary bone marrow-derived blasts using the ALL blast colony assay. EC141 down-regulated Hsp90 and up-regulated Hsp70 protein levels, inhibited CrkL phosphorylation, and induced degradation of Bcr-Abl p190 protein through ubiquitin-dependent proteasomal pathway. Furthermore, exposure of Ph+ ALL cells to EC141 resulted in activation of caspase-3, cleavage of poly (ADP-ribose) polymerase (PARP), and induction of apoptosis. In conclusion, our data suggest that EC141 is a potent Hsp90 inhibitor with activity against Ph+ ALL. Further studies to investigate the anticancer effect of EC141 either as a single agent, or in combination in Ph+ ALL and other hematological malignancies are warranted.

Kit inhibitor APcK110 induces apoptosis and inhibits proliferation of acute myeloid leukemia cells

Kit is a membrane-bound tyrosine kinase and receptor for stem cell factor (SCF) with a crucial role in hematopoiesis. Mutations of KIT occur in almost half of patients with core-binding factor leukemias, in which they have been associated with worse outcome. Development of new compounds targeting Kit may therefore hold promise for therapy. We investigated the activity and mechanism of action of APcK110, a novel Kit inhibitor, in the mastocytosis cell line HMC1.2 (KITV560G and KITD816V), acute myeloid leukemia (AML) lines OCIM2 and OCI/AML3 (both wild-type), and primary samples from patients with AML. We show that (a) APcK110 inhibits proliferation of the mastocytosis cell line HMC1.2 and the SCF-responsive cell line OCI/AML3 in a dose-dependent manner; (b) APcK110 is a more potent inhibitor of OCI/AML3 proliferation than the clinically used Kit inhibitors imatinib and dasatinib and at least as potent as cytarabine; (c) APcK110 inhibits the phosphorylation of Kit, Stat3, Stat5, and Akt in a dose-dependent fashion, showing activity of APcK110 on Kit and its downstream signaling pathways; (d) APcK110 induces apoptosis by cleavage of caspase-3 and poly(ADP-ribose) polymerase; and (e) APcK110 inhibits proliferation of primary AML blasts in a clonogenic assay but does not affect proliferation of normal colony-forming cells. Although APcK110 activity may partly depend on cytokine responsiveness (e.g., SCF) and not exclusively KIT mutation status, it remains a potent inhibitor of AML and mastocytosis cell lines and primary AML samples. APcK110 and similar compounds should be evaluated in clinical trials of patients with AML.

Nuclear factor-kappaB as a potential therapeutic target for the novel cytotoxic agent LC-1 in acute myeloid leukaemia

Nuclear factor-kappaB (NF-kappaB) has been implicated in a number of malignancies and has been suggested to be a potential molecular target in the treatment of leukaemia. This study demonstrated the constitutive activation of NF-kappaB in human myeloid blasts and a clear correlation between NF-kappaB expression and in vitro cytoprotection. High NF-kappaB expression was found in many of the poor prognostic acute myeloid leukaemia (AML) subtypes, such as French-American-British classification M0 and M7, and the poor cytogenetic risk group. The in vitro effects of LC-1, a novel dimethylamino-parthenolide analogue, were assessed in 62 primary untreated AML samples. LC-1 was found to be cytotoxic to AML cells in a dose-dependent manner, mediated through the induction of apoptosis. The median drug concentration necessary to kill 50% of the cells was 4.5 micromol/l for AML cells, compared with 12.8 micromol/l for normal marrow cells. LC-1 was shown to reduce the five individual human NF-kappaB Rel proteins in a dose-dependent manner. The subsequent inhibition of many NF-kappaB-regulated cytokines was also demonstrated. Importantly, sensitivity to LC-1 was correlated with the basal NF-kappaB activity. Consequently, LC-1 treatment provides a proof of principle for the use of NF-kappaB inhibitors in the treatment of AML.

Sulforaphane suppresses TNF-alpha-mediated activation of NF-kappaB and induces apoptosis through activation of reactive oxygen species-dependent caspase-3

Sulforaphane (SFN) is a biologically active compound extracted from cruciferous vegetables, and possessing potent anti-cancer and anti-inflammatory activities. Here, we show that tumor necrosis factor-alpha (TNF-alpha), in combination with a sub-toxic dose of SFN, significantly triggered apoptosis in TNF-alpha-resistant leukemia cells (THP-1, HL60, U937, and K562), which was associated with caspase activity and poly (ADP-ribose)-polymerase cleavage. We also report that SFN non-specifically inhibited TNF-alpha-induced NF-kappaB activation through the inhibition of IkappaBalpha phosphorylation, IkappaBalpha degradation, and p65 nuclear translocation. This inhibition correlated with the suppression of NF-kappaB-dependent genes involved in anti-apoptosis (IAP-1, IAP-2, XIAP, Bcl-2, and Bcl-xL), cell proliferation (c-Myc, COX-2, and cyclin D1), and metastasis (VEGF and MMP-9). These effects suggest that SFN inhibits TNF-alpha-induced NF-kappaB activation through the suppression of IkappaBalpha degradation, leading to reduced expression of NF-kappaB-regulated gene products. Combined treatment with SFN and TNF-alpha was also accompanied by the generation of reactive oxygen species (ROS). Pre-treatment with N-acetyl-l-cysteine significantly attenuated the combined treatment-induced ROS generation and caspase-3-dependent apoptosis, implying the involvement of ROS in this type of cell death. In conclusion, the results of the present study indicate that SFN suppresses TNF-alpha-induced NF-kappaB activity and induces apoptosis through activation of ROS-dependent caspase-3.

MicroRNA expression in cytogenetically normal acute myeloid leukemia

BACKGROUND

A role of microRNAs in cancer has recently been recognized. However, little is known about the role of microRNAs in acute myeloid leukemia (AML).

METHODS

Using microRNA expression profiling, we studied samples of leukemia cells from adults under the age of 60 years who had cytogenetically normal AML and high-risk molecular features--that is, an internal tandem duplication in the fms-related tyrosine kinase 3 gene (FLT3-ITD), a wild-type nucleophosmin (NPM1), or both. A microRNA signature that was associated with event-free survival was derived from a training group of 64 patients and tested in a validation group of 55 patients. For the latter, a microRNA compound covariate predictor (called a microRNA summary value) was computed on the basis of weighted levels of the microRNAs forming the outcome signature.

RESULTS

Of 305 microRNA probes, 12 (including 5 representing microRNA-181 family members) were associated with event-free survival in the training group (P<0.005). In the validation group, the microRNA summary value was inversely associated with event-free survival (P=0.03). In multivariable analysis, the microRNA summary value remained associated with event-free survival (P=0.04) after adjustment for the allelic ratio of FLT3-ITD to wild-type FLT3 and for the white-cell count. Using results of gene-expression microarray analysis, we found that expression levels of the microRNA-181 family were inversely correlated with expression levels of predicted target genes encoding proteins involved in pathways of innate immunity mediated by toll-like receptors and interleukin-1beta.

CONCLUSIONS

A microRNA signature in molecularly defined, high-risk, cytogenetically normal AML is associated with the clinical outcome and with target genes encoding proteins involved in specific innate-immunity pathways.

Nuclear factor-kappaB activation: from bench to bedside

Nuclear factor-kappaB (NF-kappaB) is a proinflammatory transcription factor that has emerged as an important player in the development and progression of malignant cancers. NF-kappaB targets genes that promote tumor cell proliferation, survival, metastasis, inflammation, invasion, and angiogenesis. Constitutive or aberrant activation of NF-kappa is frequently encountered in many human tumors and is associated with a resistant phenotype and poor prognosis. The mechanism of such persistent NF-kappaB activation is not clear but may involve defects in signaling pathways, mutations, or chromosomal rearrangements. Suppression of constitutive NF-kappaB activation inhibits the oncogenic potential of transformed cells and thus makes NF-kappaB an interesting new therapeutic target in cancer.

WP1066 disrupts Janus kinase-2 and induces caspase-dependent apoptosis in acute myelogenous leukemia cells

Several cytokines and growth factors that stimulate the proliferation of acute myelogenous leukemia (AML) cells transduce their signals by activating the transcription factor Janus-activated kinase 2 (JAK2). Accordingly, the inhibition of JAK2 or of its downstream signaling pathways suppresses the proliferation of AML cells. Because (E)-3(6-bromopyridin-2-yl)-2-cyano-N-((S0-1-phenylethyl)acrylamide) (WP1066) is a novel analogue of the JAK2 inhibitor AG490, we tested its activity in AML cells and investigated its mechanism of action. Using clonogenic assays, we found that although WP1066 had a marginal effect on normal marrow progenitors, it inhibited the proliferation of AML colony-forming cells obtained from patients with newly diagnosed AML and that of the AML cell lines OCIM2 and K562. WP1066 inhibited OCIM2 cell multiplication by inducing accumulation of cells at the G(0)-G(1) phase of the cell cycle. Similar to its parent compound AG490, WP1066 inhibited the phosphorylation of JAK2, but unlike AG490, WP1066 also degraded JAK2 protein, thereby blocking its downstream signal transducer and activator of transcription (STAT) and phosphoinositide-3-kinase pathways. These effects resulted in the activation of the caspase pathway. Incubation of both OCIM2 and K562 cells with WP1066 activated caspase-3, induced cleavage of poly(ADP-ribose) polymerase, and caused caspase-dependent apoptotic cell death. Thus, WP1066 is a potent JAK2 inhibitor whose effects in AML and other hematologic malignancies merit further investigation.

Arsenic derivatives in hematologic malignancies: a role beyond acute promyelocytic leukemia?

The importance of arsenic trioxide (As2O3) has been underscored over the last decade due to its efficacy against acute promyelocytic leukemia (APL), a disease in which this agent has been associated with complete hematologic and molecular remission rates of 87% and 83%, respectively. The different molecular mechanisms of action of As2O3 suggest its applicability in hematologic malignancies other than APL. However, responses obtained thus far have consisted of improvements in signs and symptoms without the elimination of a given disease. Toxicities derived from As2O3 are significant but manageable and reversible. However, the risk/benefit ratio of As2O3 in hematologic malignancies other than APL is still unclear. The development of new generations of orally bioavailable inorganic, as well as new organic, arsenic compounds with improved toxicity profiles may bolster the therapeutic application of arsenic derivatives in hematologic malignancies such as leukemia, multiple myeloma and myelodysplastic syndromes.

A synthetic triterpenoid, CDDO-Me, inhibits IkappaBalpha kinase and enhances apoptosis induced by TNF and chemotherapeutic agents through down-regulation of expression of nuclear factor kappaB-regulated gene products in human leukemic cells

The C-28 methyl ester of 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO-Me), a synthetic triterpenoid based on naturally occurring ursolic and oleanolic acids, induces apoptosis in tumor cells, induces differentiation, and inhibits inflammatory response through a poorly understood mechanism. Because the nuclear transcription factor nuclear factor kappaB (NF-kappaB) has been shown to suppress apoptosis and promote proliferation and is linked with inflammation and differentiation, we postulated that CDDO-Me modulates NF-kappaB activity and NF-kappaB-regulated gene expression. Using human leukemia cell lines and patient samples, we show that CDDO-Me potently inhibits both constitutive and inducible NF-kappaB activated by tumor necrosis factor (TNF), interleukin (IL)-1beta, phorbol ester, okadaic acid, hydrogen peroxide, lipopolysaccharide, and cigarette smoke. CDDO-Me was more potent than CDDO and its imidazole derivative. NF-kappaB suppression occurred through inhibition of IkappaBalpha kinase activation, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation, p65 nuclear translocation, and NF-kappaB-mediated reporter gene transcription. This inhibition correlated with suppression of NF-kappaB-dependent genes involved in antiapoptosis (IAP2, cFLIP, TRAF1, survivin, and bcl-2), proliferation (cyclin d1 and c-myc), and angiogenesis (VEGF, cox-2, and mmp-9). CDDO-Me also potentiated the cytotoxic effects of TNF and chemotherapeutic agents. Overall, our results suggest that CDDO-Me inhibits NF-kappaB through inhibition of IkappaBalpha kinase, leading to the suppression of expression of NF-kappaB-regulated gene products and enhancement of apoptosis induced by TNF and chemotherapeutic agents.

Distinct biological impact of dephosphorylation vs. downregulation of p210Bcr-Abl: implications for imatinib mesylate response and resistance

Imatinib mesylate suppresses phosphorylation of its kinase target, Bcr-Abl. We hypothesized that loss of p210Bcr-Abl (the kinase target) may lead to imatinib mesylate resistance. We studied K562 cells [chronic myelogenous leukemia (CML) blast crisis line] and MO7E/MBA-1 cells (with MBA-1 cells representing MO7E cells stably transfected with BCR-ABL). Imatinib mesylate resistance developed when p210Bcr-Abl expression was abolished. Furthermore, K562 cells were significantly more growth suppressed after imatinib mesylate exposure than after downregulation of Bcr-Abl expression. Signaling pathways which were functional in the absence of Bcr-Abl expression (NF-kappaB and mitogen-activated protein kinase activation or the growth factor pathway) were disrupted when p210Bcr-Abl was present but dephosphorylated, suggesting that an intact, but enzymatically inactive Bcr-Abl, may interfere with critical growth/signaling pathways. Downregulation of p210Bcr-Abl may be a mechanism by which imatinib mesylate resistance emerges. Samples from three of 15 patients with imatinib mesylate-resistant CML blast crisis had undetectable levels of p210Bcr-Abl. We conclude that retention of a dephosphorylated p210Bcr-Abl has a biologic impact distinct from that of downregulation/loss of p210Bcr-Abl and, in a subset of patients, loss of the target of the kinase inhibitor may lead to imatinib mesylate resistance.

Effect of ICAM-1 and LFA-1 in hyperleukocytic acute myeloid leukaemia

Acute hyperleukocytic leukemia [AHL; WBC count >100 x 10(9)/l] is associated with a life-threatening complication. The mechanisms of hyperleukocytosis in acute myeloid leukaemia (AML) remain unclear. However, the interaction of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) plays an important role in the adhesion and migration of normal leukocytes and AML cells. Therefore, effects of ICAM-1 and LFA-1 were studied in hyperleukocytic AML. The adhesion of hyperleukocytic AML blasts and human umbilical vein endothelial cells (HUVECs) was significantly increased compared with that of blasts from non-hyperleukocytic AML (WBC < 100 x 10(9)/l). The adhesion of normal neutrophils and HUVECs treated with hyperleukocytic AML blast supernatant was increased significantly. Finally, we determined the ICAM-1 on the surface of HUVECs treated with the supernatant of hyperleukocytic AML blasts and LFA-1 on hyperleukocytic AML blasts by flow cytometry. It showed that the ICAM-1 expression on the surface of the HUVECs treated with hyperleukocytic AML blast supernatant for 24 h could be increased, and the expression of LFA-1 on hyperleukocytic AML was also increased significantly. Our data show that hyperleukocytic AML blasts stimulate the endothelium to secrete more ICAM-1 and promote their own adhesion to vascular endothelium, suggesting that ICAM-1 and LFA-1 may have a role in hyperleukocytic AML.

Production and upregulation of granulocyte chemotactic protein-2/CXCL6 by IL-1beta and hypoxia in small cell lung cancer

Small cell lung cancer (SCLC) is characterised by early and widespread metastasis. However, SCLC cells have so far been found to produce low levels of known pro-angiogenic factors. We speculated that SCLC cells might produce alternative pro-angiogenic factors. Here, we report that a panel of SCLC cell lines constitutively secrete granulocyte chemotactic protein-2 (GCP-2)/CXCL6, a CXC ELR+ chemokine. In contrast, none of the three tested NSCLC cell lines secreted GCP-2. Production of GCP-2 in vivo was also confirmed in seven out of nine specimens with SCLC. We demonstrate that expression of GCP-2 is mediated by NF-kappaB as ALLN, an NF-kappaB pathway inhibitor, almost completely abolished GCP-2 production in SCLC cell lines. We also demonstrate that GCP-2 can be significantly upregulated by IL-1beta and hypoxia in SCLC cell lines. This result suggests a role for GCP-2 in promoting tumour progression in vivo under unfavourable conditions such as oxygen deprivation. As SCLC cells express both GCP-2 and its receptors CXCR1 and CXCR2, their biological significance in SCLC progression was further studied. We demonstrate that GCP-2 is an autocrine growth factor. Cell proliferation was significantly inhibited by anti-GCP-2 neutralising antibody in two high-GCP-2-producing cell lines. In addition, expression of the proliferation marker PCNA was upregulated by exogenous GCP-2 in two low-GCP-2-producing cell lines. Taken together, these results suggest an important role for GCP-2 as an autocrine mitogen in the growth and metastasis of SCLC.

Targeting NF-κB in hematologic malignancies

The transcription factor nuclear factor kappa B (NF-kappaB) can intervene in oncogenesis by virtue of its capacity to regulate the expression of a plethora of genes that modulate apoptosis, and cell survival as well as proliferation, inflammation, tumor metastasis and angiogenesis. Different reports demonstrate the intrinsic activation of NF-kappaB in lymphoid and myeloid malignancies, including preneoplastic conditions such as myelodysplastic syndromes, underscoring its implication in malignant transformation. Targeting intrinsic NF-kappaB activation, as well as its upstream and downstream regulators, may hence constitute an additional approach to the oncologist's armamentarium. Several small inhibitors of the NF-kappaB-activatory kinase IkappaB kinase, of the proteasome, or of the DNA binding of NF-kappaB subunits are under intensive investigation. Currently used cytotoxic agents can induce NF-kappaB activation as an unwarranted side effect, which confers apoptosis suppression and hence resistance to these drugs. Thus, NF-kappaB inhibitory molecules may be clinically useful, either as single therapeutic agents or in combination with classical chemotherapeutic agents, for the treatment of hematological malignancies.

Atiprimod blocks STAT3 phosphorylation and induces apoptosis in multiple myeloma cells

Multiple myeloma (MM) accounts for 1 % of all cancer deaths. Although treated aggressively, almost all myelomas eventually recur and become resistant to treatment. Atiprimod (2-(3-Diethylaminopropyl)-8,8-dipropyl-2-azaspiro[4,5] decane dimaleate) has exerted anti-inflammatory activities and inhibited oeteoclast-induced bone resorption in animal models and been well tolerated in patients with rheumatoid arthritis in phase I clinical trials. Therefore, we investigated its activity in MM cells and its mechanism of action. We found that Atiprimod inhibited proliferation of the myeloma cell lines U266-B1, OCI-MY5, MM-1, and MM-1R in a time- and dose-dependent manner. Atiprimod blocked U266-B1 myeloma cells in the G₀/G₁ phase, preventing cell cycle progression. Furthermore, Atiprimod inhibited signal transducer and activator of transcription (STAT) 3 activation, blocking the signalling pathway of interleukin-6, which contributes to myeloma cell proliferation and survival, and downregulated the antiapoptotic proteins Bcl-2, Bcl-X_L, and Mcl-1. Incubation of U266-B1 myeloma cells with Atiprimod induced apoptosis through the activation of caspase 3 and subsequent cleavage of the DNA repair enzyme poly(adenosine diphosphate-ribose) polymerase. Finally, Atiprimod suppressed myeloma colony-forming cell proliferation in fresh marrow cells from five patients with newly diagnosed MM in a dose-dependent fashion. These data suggest that Atiprimod has a role in future therapies for MM.

Curcumin (diferuloylmethane) inhibits constitutive NF-kappaB activation, induces G1/S arrest, suppresses proliferation, and induces apoptosis in mantle cell lymphoma

Human mantle cell lymphoma (MCL), an aggressive B cell non-Hodgkin's lymphoma, is characterized by the overexpression of cyclin D1 which plays an essential role in the survival and proliferation of MCL. Because of MCL's resistance to current chemotherapy, novel approaches are needed. Since MCL cells are known to overexpress NF-kappaB regulated gene products (including cyclin D1), we used curcumin, a pharmacologically safe agent, to target NF-kappaB in a variety of MCL cell lines. All four MCL cell lines examined had overexpression of cyclin D1, constitutive active NF-kappaB and IkappaB kinase and phosphorylated forms of IkappaBalpha and p65. This correlated with expression of TNF, IkappaBalpha, Bcl-2, Bcl-xl, COX-2 and IL-6, all regulated by NF-kappaB. On treatment of cells with curcumin, however, downregulated constitutive active NF-kappaB and inhibited the consitutively active IkappaBalpha kinase (IKK), and phosphorylation of IkappaBalpha and p65. Curcumin also inhibited constitutive activation of Akt, needed for IKK activation. Consequently, the expression of all NF-kappaB-regulated gene products, were downregulated by the polyphenol leading to the suppression of proliferation, cell cycle arrest at the G1/S phase of the cell cycle and induction of apoptosis as indicated by caspase activation, PARP cleavage, and annexin V staining. That NF-kappaB activation is directly linked to the proliferation of cells, is also indicated by the observation that peptide derived from the IKK/NEMO-binding domain and p65 suppressed the constitutive active NF-kappaB complex and inhibited the proliferation of MCL cells. Constitutive NF-kappaB activation was found to be due to TNF, as anti-TNF antibodies inhibited both NF-kappaB activation and proliferation of cells. Overall, our results indicate that curcumin inhibits the constitutive NF-kappaB and IKK leading to suppression of expression of NF-kappaB-regulated gene products that results in the suppression of proliferation, cell cycle arrest, and induction of apoptosis in MCL.

NF-kappaB and FLIP in arsenic trioxide (ATO)-induced apoptosis in myelodysplastic syndromes (MDSs)

Tumor necrosis factor (TNF)-alpha, a potent stimulus of nuclear factor-kappaB (NF-kappaB), is up-regulated in myelodysplastic syndrome (MDS). Here, we show that bone marrow mononuclear cells (BMMCs) and purified CD34+ cells from patients with low-grade/early-stage MDS (refractory anemia/refractory anemia with ring sideroblasts [RA/RARS]) have low levels of NF-kappaB activity in nuclear extracts comparable with normal marrow, while patients with RA with excess blasts (RAEB) show significantly increased levels of activity (P = .008). Exogenous TNF-alpha enhanced NF-kappaB nuclear translocation in MDS BMMCs above baseline levels. Treatment with arsenic trioxide (ATO; 2-200 microM) inhibited NF-kappaB activity in normal marrow, primary MDS, and ML1 cells, even in the presence of exogenous TNF-alpha (20 ng/mL), and down-regulated NF-kappaB-dependent antiapoptotic proteins, B-cell leukemia XL (Bcl-XL), Bcl-2, X-linked inhibitor of apoptosis (XIAP), and Fas-associated death domain (FADD)-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP), leading to apoptosis. However, overexpression of FLIP resulted in increased NF-kappaB activity and rendered ML1 cells resistant to ATO-induced apoptosis. These data are consistent with the observed up-regulation of FLIP and resistance to apoptosis with advanced MDS, where ATO as a single agent may show only limited efficacy. However, the data also suggest that combinations of ATO with agents that interfere with other pathways, such as FLIP autoamplification via NF-kappaB, may have considerable therapeutic activity.

Microarrays of small molecules embedded in biodegradable polymers for use in mammalian cell-based screens

We developed a microarray-based system for screening small molecules in mammalian cells. This system is compatible with image-based screens and requires fewer than 100 cells per compound. Each compound is impregnated in a 200-microm-diameter disc composed of biodegradable poly-(D),(L)-lactide/glycolide copolymer. Cells are seeded on top of these discs, and compounds slowly diffuse out, affecting proximal cells. In contrast with microtiter-based screening, this system does not involve the use of wells or walls between each compound-treated group of cells. We demonstrate detection of the effects of a single compound in a large microarray, that diverse compounds can be released in this format, and that extended release over several days is feasible. We performed a small synthetic lethal screen and identified a compound (macbecin II) that has reduced activity in cells with RNA interference-mediated decrease in the expression of tuberous sclerosis 2. Thus, we have developed a microarray-based screening system for testing the effects of small molecules on mammalian cells by using an imaging-based readout. This method will be useful to those performing small-molecule screens to discover new chemical tools and potential therapeutic agents.

Interleukin-1beta maintains an apoptosis-resistant phenotype in the blast cells of acute myeloid leukaemia via multiple pathways

Blast cell survival in suspension culture is associated with chemoresistance in acute myeloid leukaemia (AML). Autonomous production of IL-1beta by AML blasts is linked with a proliferative response, although its role in survival and hence apoptosis-resistance has not been examined in this disease. Cells that secreted more than 19.7 pg/ml IL-1beta were significantly more resistant to spontaneous apoptosis in 48-h culture than those that produced less than 19.7 pg/ml IL-1beta (P=0.008). Exogenous rhIL-1beta significantly enhanced 48-h survival in 25/29 blast cell samples (P=0.0001). IL-1 receptor ligation is known to activate at least three survival pathways: those mediated by PI-3 kinase, IL-1 receptor-associated kinase (IRAK) and ceramidase. In apoptosis-sensitive AML blasts with a strong survival response to rhIL-1beta, inhibitors of all three pathways down-modulated an IL-1beta-mediated increase in blast survival, but only the inhibition of all three pathways totally eliminated viable blasts. In apoptosis-resistant and apoptosis-sensitive primary AML samples, the three inhibitors all increased apoptosis in vitro after 48 h. Exogenous rhIL-1beta induced the hyperphosphorylation of Bcl-2. It also increased the activation of NF-kappaB in 5/15 blast samples. IL-1beta-mediated survival pathways may be a factor in apoptosis-resistance in primary AML blasts, and may therefore contribute to chemoresistance.

Phase II trial of arsenic trioxide in relapsed and refractory acute myeloid leukemia, secondary leukemia and/or newly diagnosed patients at least 65 years old

The prognosis for patients with relapsed/refractory AML, secondary leukemia and AML in older adults is extremely poor. An appealing alternative approach to intensive cytotoxic chemotherapy is to induce apoptosis with a novel agent. There is in vitro evidence that arsenic trioxide (ATO) has anti-proliferative and pro-apoptotic effects on myeloid leukemia cell lines. To evaluate efficacy and toxicities of ATO, we conducted a phase II trial including subjects with relapsed/refractory or secondary AML or age > or = 65 years with de novo disease. Eleven subjects were entered with a median age of 77 years (56-90) and a median total dose of ATO of 415.55 mg (91.5-793) with a daily dose of 0.25 mg/kg. Median survival following the first dose of ATO was 2.25 months (0.4-19). Myelosuppression was the major adverse effect, most likely due to disease progression rather than drug-related. All subjects had progressive disease. There was no direct treatment-related mortality. Based on this study, we do not recommend single agent ATO as a treatment option for AML.

Guggulsterone inhibits NF-kappaB and IkappaBalpha kinase activation, suppresses expression of anti-apoptotic gene products, and enhances apoptosis

Guggulsterone, derived from Commiphora mukul and used to treat obesity, diabetes, hyperlipidemia, atherosclerosis, and osteoarthritis, has been recently shown to antagonize the farnesoid X receptor and decrease the expression of bile acid-activated genes. Because activation of NF-kappaB has been closely linked with inflammatory diseases affected by guggulsterone, we postulated that it must modulate NF-kappaB activation. In the present study, we tested this hypothesis by investigating the effect of this steroid on the activation of NF-kappaB induced by inflammatory agents and carcinogens. Guggulsterone suppressed DNA binding of NF-kappaB induced by tumor necrosis factor (TNF), phorbol ester, okadaic acid, cigarette smoke condensate, hydrogen peroxide, and interleukin-1. NF-kappaB activation was not cell type-specific, because both epithelial and leukemia cells were inhibited. Guggulsterone also suppressed constitutive NF-kappaB activation expressed in most tumor cells. Through inhibition of IkappaB kinase activation, this steroid blocked IkappaBalpha phosphorylation and degradation, thus suppressing p65 phosphorylation and nuclear translocation. NF-kappaB-dependent reporter gene transcription induced by TNF, TNFR1, TRADD, TRAF2, NIK, and IKK was also blocked by guggulsterone but without affecting p65-mediated gene transcription. In addition, guggulsterone decreased the expression of gene products involved in anti-apoptosis (IAP1, xIAP, Bfl-1/A1, Bcl-2, cFLIP, and survivin), proliferation (cyclin D1 and c-Myc), and metastasis (MMP-9, COX-2, and VEGF); this correlated with enhancement of apoptosis induced by TNF and chemotherapeutic agents. Overall, our results indicate that guggulsterone suppresses NF-kappaB and NF-kappaB-regulated gene products, which may explain its anti-inflammatory activities.

Endothelial Cell Surface ATP Synthase-Triggered Caspase-Apoptotic Pathway Is Essential for K1-5-Induced Antiangiogenesis

We have recently reported the identification of kringle 1-5 (K1-5) of plasminogen as a potent and specific inhibitor of angiogenesis and tumor growth. Here, we show that K1-5 bound to endothelial cell surface ATP synthase and triggered caspase-mediated endothelial cell apoptosis. Induction of endothelial apoptosis involved sequential activation of caspases-8, -9, and -3. Administration of neutralizing antibodies directed against the alpha- and beta-subunits of ATP synthase to endothelial cells attenuated activation of these caspases. Furthermore, inhibitors of caspases-3, -8, and -9 also remarkably blocked K1-5-induced endothelial cell apoptosis and antiangiogenic responses. In a mouse tumor model, we show that caspase-3 inhibitors abolished the antitumor activity of K1-5 by protecting the tumor vasculature undergoing apoptosis. These results suggest that the specificity of the antiendothelial effect of K1-5 is attributable, at least in part, to its interaction with the endothelial cell surface ATP synthase and that the caspase-mediated endothelial apoptosis is essential for the angiostatic activity of K1-5. Thus, our findings provide a mechanistic insight with respect to the angiostatic action and signaling pathway of K1-5 and angiostatin.

Expression of constitutively active nuclear-kappa B RelA transcription factor in blasts of acute myeloid leukemia

The nuclear transcription factor NF-kappa B regulates cell survival, proliferation, and differentiation. Little is known about NF-kappa B in myeloid malignancies. In this report, we assessed NF-kappa B in a group of myeloid neoplasms by using an electrophoretic mobility shift assay (EMSA) and immunofluorescence methods in freshly isolated leukemia cells. We analyzed 30 cases of acute myeloid leukemia (AML), 5 cases of myelodysplastic syndrome (MDS), 3 cases of chronic myelomonocytic leukemia (CMML), 15 cases of chronic myeloid leukemia in chronic phase (CML-CP), and 2 cases of chronic myeloid leukemia in blast crisis (CML-BC). Unstimulated cells (bone marrow and peripheral blood) from 17 normal donors and apheresis samples from 6 peripheral blood stem cell donors treated with granulocyte colony-stimulating factor (G-CSF) were used as controls. When EMSA was used, NF-kappa B was elevated in 14 of 30 (47%) cases of AML, in both cases of CML-BC, and in all reference donors treated with G-CSF, but it was at basal levels in all cases of MDS and CML-CP and in normal donors (P = <.01). Immunofluorescence analysis confirmed strong nuclear RelA/NF-kappa B immunoreactivity in AML blasts but not in normal bone marrow. Bcl-2, a downstream molecule, was expressed in cases with elevated NF-kappa B, but not in cases with basal levels of NF-kappa B, suggesting that NF-kappa B is active and provides the cells with survival advantages in vivo. These results suggest that suppression of NF-kappa B may be a useful therapeutic strategy for a subset of patients with AML.

The human herpes virus 8-encoded viral FLICE-inhibitory protein induces cellular transformation via NF-kappaB activation

Infection with human herpes virus 8 (HHV8) has been associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. HHV8 encodes for a viral FLICE-inhibitory protein (vFLIP), designated K13, which resembles the prodomain of caspase-8 in structure and has been shown to protect cells against death receptor-induced apoptosis in vitro and in vivo. In this report, we present evidence that HHV8 vFLIP also possesses the unique ability of transforming Rat-1 and Balb/3T3 fibroblast cells, which is not shared by other vFLIPs. Rat-1 cells expressing HHV8 vFLIP form colonies in soft agar and form tumors in nude mice. The transforming ability of HHV8 vFLIP is associated with the activation of the NF-kappaB pathway and is blocked by molecular and chemical inhibitors of this pathway. Our results suggest that vFLIP K13 has activity beyond its role as an inhibitor of death receptor signaling and may play a causative role in the pathogenesis of HHV8-associated malignancies. Furthermore, inhibitors of the NF-kappaB pathway may have a role in the treatment of malignancies linked to HHV8 infection.

Molecular genetic analysis of human herpes virus 8-encoded viral FLICE inhibitory protein-induced NF-kappaB activation

The human herpes virus 8 (HHV8)-encoded viral FLICE inhibitory protein (vFLIP), also known as K13, is known to activate the NF-kappaB pathway, a property not shared by other vFLIPs. Previous studies have demonstrated that HHV8 vFLIP K13 interacts with several cellular signaling proteins involved in NF-kappaB activation, such as receptor-interacting protein, NF-kappaB-inducing kinase, IkappaB kinase (IKK) 1, IKK2, and NF-kappaB essential modulator (NEMO). In this report we have used cell lines deficient in the above proteins to investigate the mechanism of NF-kappaB activation via HHV8 vFLIP K13. We demonstrate that receptor-interacting protein and NF-kappaB-inducing kinase are dispensable for vFLIP K13-induced NF-kappaB DNA binding and transcriptional activation. On the other hand, vFLIP K13-induced NF-kappaB DNA binding activity is significantly reduced, although not absent, in cells deficient in IKK1, IKK2, and NEMO. Furthermore, vFLIP K13-induced NF-kappaB transcriptional activity is only weakly present in IKK1-deficient cells and almost completely absent in those deficient in IKK2 and NEMO. HHV8 vFLIP K13-induced NF-kappaB activation in IKK1- and IKK2-deficient fibroblasts could be rescued by wild type but not by the kinase-inactive mutants of IKK1 and IKK2, respectively. Consistent with the above results, vFLIP K13-induced NF-kappaB activation could be effectively blocked by chemical inhibitors of the kinase activity of IKK1 and IKK2. Thus, a cooperative interaction of all three subunits of the IKK complex is required for maximal NF-kappaB activation via HHV8 vFLIP K13. Selective inhibitors of the IKK1 kinase activity may have a role in the treatment of disorders caused by abnormal NF-kappaB activation by HHV8 vFLIP K13.

Resveratrol blocks interleukin-1beta-induced activation of the nuclear transcription factor NF-kappaB, inhibits proliferation, causes S-phase arrest, and induces apoptosis of acute myeloid leukemia cells

Resveratrol, an edible polyphenolic stilbene, has been reported to possess substantial antileukemic activities in different leukemia cell lines. We investigated whether resveratrol is active against fresh acute myeloid leukemia (AML) cells and its mechanism of action. Because interleukin 1beta(IL-1beta) plays a key role in proliferation of AML cells, we first tested the effect of resveratrol on the AML cell lines OCIM2 and OCI/AML3, both of which produce IL-1beta and proliferate in response to it. Resveratrol inhibited proliferation of both cell lines in a dose-dependent fashion (5-75 microM) by arresting the cells at S phase, thus preventing their progression through the cell cycle; IL-1beta partially reversed this inhibitory effect. Resveratrol significantly reduced production of IL-1beta in OCIM2 cells. It also suppressed the IL-1beta-induced activation of transcription factor nuclear factor kappaB (NF-kappaB), which modulates an array of signals controlling cellular survival, proliferation, and cytokine production. Indeed, incubation of OCIM2 cells with resveratrol resulted in apoptotic cell death. Because caspase inhibitors Ac-DEVD-CHO or z-DEVD-FMK partially reversed the antiproliferative effect of resveratrol, we tested its effect on the caspase pathway and found that resveratrol induced the activation of the cysteine protease caspase 3 and subsequent cleavage of the DNA repair enzyme poly (adenosine diphosphate [ADP]-ribose) polymerase. Finally, resveratrol suppressed colony-forming cell proliferation of fresh AML marrow cells from 5 patients with newly diagnosed AML in a dose-dependent fashion. Taken together, our data showing that resveratrol is an effective in vitro inhibitor of AML cells suggest that this compound may have a role in future therapies for AML.

Opportunities for Trisenox (arsenic trioxide) in the treatment of myelodysplastic syndromes

Arsenic trioxide (ATO) has a long history of efficacy as an antileukemic agent. However, with the advent of modern therapy, it had been relegated to a historical footnote. In the 1990s, investigators in China reported that ATO was safe and had dramatic efficacy in patients with acute promyelocytic leukemia (APL). Preclinical investigations indicate that the biological targets of this novel drug extend to a variety of malignancies other than APL and include induction of apoptosis, nonterminal differentiation, and suppression of proliferation and angiogenesis. The myelodysplastic syndromes (MDSs) present a particular therapeutic challenge. Ineffective hematopoiesis predominates in patients with low-grade prognostic scores. The survival of those patients with high-grade disease is compromised by a high risk of leukemia transformation. Although a number of therapeutic options have been investigated, none has emerged as being broadly efficacious and having an acceptable toxicity profile. No drug has yet received approval by the Food and Drug Administration for this indication. Biologic features of MDS, which include accelerated apoptotic potential, limited maturation capacity, and medullary neovascularity, create a strong scientific rationale for the investigation of ATO in MDS. This report describes the history and scientific basis for ATO treatment of hematologic malignancies, enumerates the potential benefits of ATO in MDS, and discusses the direction of ongoing trials of this novel antineoplastic agent.