In vitro susceptibility to TRAIL-induced apoptosis of acute leukemia cells in the context of TRAIL receptor gene expression and constitutive NF-kappa B activity

Emerging Therapies for Acute Myelogenus Leukemia Patients Targeting Apoptosis and Mitochondrial Metabolism

Acute Myelogenous Leukemia (AML) is a malignant disease of the hematopoietic cells, characterized by impaired differentiation and uncontrolled clonal expansion of myeloid progenitors/precursors, resulting in bone marrow failure and impaired normal hematopoiesis. AML comprises a heterogeneous group of malignancies, characterized by a combination of different somatic genetic abnormalities, some of which act as events driving leukemic development. Studies carried out in the last years have shown that AML cells invariably have abnormalities in one or more apoptotic pathways and have identified some components of the apoptotic pathway that can be targeted by specific drugs. Clinical results deriving from studies using B-cell lymphoma 2 (BCL-2) inhibitors in combination with standard AML agents, such as azacytidine, decitabine, low-dose cytarabine, provided promising results and strongly support the use of these agents in the treatment of AML patients, particularly of elderly patients. TNF-related apoptosis-inducing ligand (TRAIL) and its receptors are frequently deregulated in AML patients and their targeting may represent a promising strategy for development of new treatments. Altered mitochondrial metabolism is a common feature of AML cells, as supported through the discovery of mutations in the isocitrate dehydrogenase gene and in mitochondrial electron transport chain and of numerous abnormalities of oxidative metabolism existing in AML subgroups. Overall, these observations strongly support the view that the targeting of mitochondrial apoptotic or metabolic machinery is an appealing new therapeutic perspective in AML.

The role of XIAP in resistance to TNF-related apoptosis-inducing ligand (TRAIL) in Leukemia

The treatment for leukemic malignancies remains a challenge despite the wide use of conventional chemotherapies. Therefore, new therapeutic approaches are highly demanded. TNF-related apoptosis-inducing ligand (TRAIL) represents a targeted therapy against cancer because it induces apoptosis only in tumor cells. TRAIL is currently under investigation for the treatment of leukemia. Preclinical studies evaluated the potential therapeutic efficacy of TRAIL on cell lines and clinical samples and showed promising results. However, like most anti-cancer drugs, resistance to TRAIL-induced apoptosis may limit its clinical efficacy. It is critical to understand the molecular mechanisms of TRAIL. Therefore, rational therapeutic drug combinations for clinical trials of TRAIL-based therapies might be achieved. In a variety of leukemic cells, overexpression of X-linked inhibitor of apoptosis protein (XIAP), a negative regulator of apoptosis pathway, has been discovered. Implication of XIAP in the ineffective induction of cell death by TRAIL in leukemia has been explored in several resistant cell lines. XIAP inhibitors restored TRAIL sensitivity in resistant cells and primary leukemic blasts. Moreover, TRAIL resistance in leukemic cells could be overcome by the effects of several anti-leukemic agents via the mechanisms of XIAP downregulation. Here, we discuss targeting XIAP, a strategy to restore TRAIL sensitivity in leukemia to acquire more insights into the mechanisms of TRAIL resistance. The concluding remarks may lead to identify putative ways to resensitize tumors.

Effects of Decitabine on the proliferation of K562 cells and the expression of DR4 gene

Objective

To investigate the role of DR4 gene in the occurrence, development and prognosis of acute myeloid leukemia (AML), find a new regulatory gene of Decitabine for the treatment of AML, namely DR4 gene, and explore the molecular mechanism of AML in the treatment of AML.

Methods

The methylation level and the mRNA expression level of DR4 gene promoters of bone marrow mononuclear cells in 122 patients with newly diagnosed AML and 24 patients with iron deficiency anemia (IDA) were detected using Methylation specific PCR (MS-PCR) and Q-RT-PCR, respectively, and a correlation analysis of them was conducted. The effects of Decitabine on the proliferation of K562 cells were detected using CCK-8 assay. Then, the effects of Decitabine on the methylation level and the mRNA expression level of DR4 genes of K562 cells treated with Decitabine were detected using MS-PCR and Q-RT-PCR, respectively. The effects of Decitabine on the cell cycle and apoptosis of K562 cells were detected using flow cytometry.

Results

Compared with the control group, the methylation level (P = .002) of DR4 genes of bone marrow mononuclear cells in patients with newly diagnosed AML was high. The methylation level (P = .01) of DR4 genes of bone marrow mononuclear cells in patients of the positive group of enlargement of liver, spleen and lymph node was lower than that of the negative group, and the methylation level (P = .006) of DR4 genes in patients of the high risk group of clinical stage was lower than that of the low risk group, and the methylation level (P = .03) of DR4 genes in patients of the group where patients did not achieve complete remission (CR1) after a course of induction chemotherapy was lower than that of the group where patients achieved complete remission (CR1) after a course of induction chemotherapy. There was a significant negative correlation (P < .01) between the methylation level and the mRNA expression level of DR4 genes of bone marrow mononuclear cells in 122 patients with newly diagnosed AML. After the K562 cells were treated with Decitabine for 48 h, the methylation level of DR4 gene promoters gradually decreased, while the mRNA expression level of DR4 genes gradually increased, both of which showed a concentration-dependent relationship. After the K562 cells were treated with 5 µmol/L Decitabine for 48 h, the K562 cells in G0/G1 phase and G2/M phase increased significantly, and the K562 cells in S phase decreased significantly.

Conclusion

DR4 gene played an important role in the occurrence and development of AML. Decitabine can effectively inhibit the proliferation of K562 cells, which probably partly because it can terminate the methylation effect of DR4 gene promoters and restore the mRNA expression of DR4 genes.

Synergistic activity of bortezomib and HDACi in preclinical models of B-cell precursor acute lymphoblastic leukemia via modulation of p53, PI3K/AKT, and NF-κB

PURPOSE

Relapse of disease and subsequent resistance to established therapies remains a major challenge in the treatment of childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). New therapeutic options, such as proteasome and histone deacetylase inhibitors (HDACi) with a toxicity profile differing from that of conventional cytotoxic agents, are needed for these extensively pretreated patients.

EXPERIMENTAL DESIGN

Antiproliferative and proapoptotic effects of combined HDACi/proteasome inhibitor treatments were analyzed using BCP-ALL monocultures, cocultures with primary mesenchymal stroma cells from patients with ALL, and xenograft mouse models. The underlying molecular mechanisms associated with combined treatment were determined by gene expression profiling and protein validation.

RESULTS

We identified the proteasome inhibitor bortezomib as a promising combination partner for HDACi due to the substantial synergistic antileukemic activity in BCP-ALL cells after concomitant application. This effect was maintained or even increased in the presence of chemotherapeutic agents. The synergistic effect of combined HDACi/BTZ treatment was associated with the regulation of genes involved in cell cycle, JUN/MAPK, PI3K/AKT, p53, ubiquitin/proteasome, and NF-κB pathways. We observed an activation of NF-κB after bortezomib treatment and the induction of apoptosis-related NF-κB target genes such as TNFαRs after concomitant treatment, indicating a possible involvement of NF-κB as proapoptotic mediator. In this context, significantly lower NF-κB subunits gene expression was detected in leukemia cells from patients who developed a relapse during frontline chemotherapy, compared with those who relapsed after cessation of frontline therapy.

CONCLUSION

These results provide a rationale for the integration of HDACi/BTZ combinations into current childhood BCP-ALL treatment protocols.

Leukemia-initiating cells of patient-derived acute lymphoblastic leukemia xenografts are sensitive toward TRAIL

Cancer stem cells represent the most important target cells for antitumor therapy. TRAIL (TNF-related apoptosis-inducing ligand) is a potential anticancer agent that induces apoptosis in a wide variety of tumor cells, but its ability to target cancer stem cells is currently unknown. Here we investigated whether TRAIL targets leukemia-initiating cells. Limiting dilution transplantation assays were performed on xenografts from pediatric patients with precursor B-cell acute lymphoblastic leukemia (pre-B ALL) in NSG mice. In vitro treatment of xenograft cells with TRAIL significantly reduced and delayed their engraftment and procrastinated animal death from leukemia. Systemic TRAIL treatment of mice injected with patient-derived pre-B ALL xenograft cells abrogated leukemia in 3 of 5 mice in 1 sample. In conclusion, our data suggest that TRAIL targets leukemia-initiating cells derived from pre-B ALL xenografts in vitro and in vivo, and hence constitutes an attractive candidate drug for treatment of ALL.

Wogonin and related natural flavones overcome tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein resistance of tumors by down-regulation of c-FLIP protein and up-regulation of TRAIL receptor 2 expression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent that kills various tumor cells without damaging normal tissues. However, many cancers remain resistant to TRAIL. To overcome TRAIL resistance, combination therapies using sensitizers of the TRAIL pathway would be an efficacious approach. To investigate potential sensitizers of TRAIL-induced apoptosis, we used TRAIL-resistant human T cell leukemia virus type 1 (HTLV-1)-associated adult T cell leukemia/lymphoma (ATL) cells as a model system. So far, HTLV-1-associated ATL is incurable by presently known therapies. Here, we show that wogonin and the structurally related natural flavones apigenin and chrysin break TRAIL resistance in HTLV-1-associated ATL by transcriptional down-regulation of c-FLIP, a key inhibitor of death receptor signaling, and by up-regulation of TRAIL receptor 2 (TRAIL-R2). This effect is mediated through transcriptional inhibition of the p53 antagonist murine double minute 2 (Mdm2), leading to an increase in p53 levels and, consequently, to up-regulation of the p53 target gene TRAIL-R2. We also show that these flavones can sensitize to TNFα- and CD95-mediated cell death. Furthermore, we show that wogonin, apigenin, and chrysin also enhance TRAIL-mediated apoptosis in other human cancer cell lines including breast cancer cell line MDA-MB-231, colon cancer cell line HT-29, hepatocellular carcinoma cell line HepG2, melanoma cell line SK-MEL-37, and pancreatic carcinoma cell line Capan-1 by the same mechanism. Thus, our study suggests the potential use of these flavones as an adjuvant for TRAIL-mediated anticancer therapy.

Rocaglamide breaks TRAIL resistance in HTLV-1-associated adult T-cell leukemia/lymphoma by translational suppression of c-FLIP expression

The human T-cell leukemia virus type-1 (HTLV-1)-associated adult T-cell leukemia/lymphoma (ATL) is incurable by currently known therapies. ATL samples and cell lines derived from ATL patients show restricted sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and CD95 ligand (CD95L). We have recently shown that HTLV-1-infected cells express elevated levels of cellular caspase-8 FLICE-inhibitory protein (c-FLIP) conferring resistance to receptor-mediated apoptosis. This finding underscores the demand to develop new strategies for treatment of ATL. In this study, we show that the naturally occurring herbal compound Rocaglamide (Roc) sensitizes CD95L- and TRAIL-induced apoptosis in HTLV-1-infected cells by downregulation of c-FLIP expression. Investigation of the molecular mechanism of Roc-mediated downregulation of c-FLIP revealed that it inhibits phosphorylation of the translation initiation factor 4E (eIF4E), a key factor that controls the rate-limiting step of translation, through inhibition of the MEK-ERK-MNK1 signaling pathway. This event prevents de novo synthesis of short-lived proteins such as c-FLIP in HTLV-1-infected cells. Our data suggest that Roc may serve as an adjuvant for TRAIL-based anticancer therapy.

Apoptosis in leukemias: regulation and therapeutic targeting

Nearly 25 years after the seminal publication of John Foxton Kerr that first described apoptosis, the process of regulated cell death, our understanding of this basic physiological phenomenon is far from complete [39]. From cardiovascular disease to cancer, apoptosis has assumed a central role with broad ranging therapeutic implications that depend on a complete understanding of this process, yet have also identified an incredibly complex regulatory system that is critical for development and is at the core of many diseases, challenging scientist and clinicians to step into its molecular realm and modulate its circuitry for therapeutic purposes. This chapter will review our understanding of the molecular circuitry that controls apoptosis in leukemia and the pharmacological manipulations of this pathway that may yield therapeutic benefit.

TRAIL, caspases and maturation of normal and leukemic myeloid precursors

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) is a membrane-bound cytokine molecule that belongs to the family of tumor necrosis factor (TNF). Members of this family share diverse biological effects, including induction of apoptosis and/or promotion of cell survival. Identification of TRAIL has generated considerable enthusiasm for its ability to induce apoptotic cell death in a variety of tumor cells, by engaging the death receptors TRAIL-R1/DR4 and TRAIL-R2/DR5, while sparing most normal cells. Beside its anticancer activity, several studies have suggested a role for endogenously expressed TRAIL in hemopoiesis. In this review, we summarize the knowledge about the different lineage-specific roles of TRAIL and its receptors in hemopoiesis regulation. Moreover, the complex interplay among the signaling pathways triggered by TRAIL/TRAIL-receptors in myeloid cells is discussed in some detail.

Fragment-based design of small molecule X-linked inhibitor of apoptosis protein inhibitors

We report on a general structure- and NMR-based approach to derive druglike small molecule inhibitors of protein-protein interactions in a rapid and efficient manner. We demonstrate the utility of the approach by deriving novel and effective SMAC mimetics targeting the antiapoptotic protein X-linked inhibitor of apoptosis protein (XIAP). The XIAP baculovirus IAP repeat 3 (Bir3) domain binds directly to the N-terminal of caspase-9, thus inhibiting programmed cell death. It has been shown that in the cell this interaction can be displaced by the protein second mitochondrial activator of caspases (SMAC) and that its N-terminal tetrapeptide region (NH2-AVPI, Ala-Val-Pro-Ile) is responsible for this activity. However, because of their limited cell permeability, synthetic SMAC peptides are inefficient when tested in cultured cells, limiting their use as potential chemical tools or drug candidates against cancer cells. Hence, as an application, we report on the derivation of novel, selective, druglike, cell permeable SMAC mimics with cellular activity.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced chemokine release in both TRAIL-resistant and TRAIL-sensitive cells via nuclear factor kappa B

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a variety of tumour cells, but not in most normal cells, and has attracted considerable attention for its potential use in cancer therapy. Recently, increasing evidence has shown that TRAIL is involved in inflammation, although much of this evidence is controversial. In this article, it is shown that TRAIL induces CXCL2, CCL4 and CCL20 secretion in a nuclear factor kappa B-dependent manner. The dominant negative constructs of tumour necrosis factor receptor-associated death domain protein (TRADD) and tumour necrosis factor receptor-associated factor 2 are unable to block TRAIL-induced chemokine up-regulation, and the dominant negative construct of TRADD may even enhance TRAIL-triggered signals. Using small interfering RNA, receptor interacting protein has been demonstrated to be essential for TRAIL-induced chemokine release. Furthermore, it has been demonstrated that p38 mitogen-activated protein kinase is involved in TRAIL-induced chemokine release without any effects on nuclear factor kappa B activation, suggesting that some unknown transcription factors may be activated by TRAIL. Using a xenograft tumour model, it has been illustrated that TRAIL can also induce chemokine release in vivo. Although these chemokines induced by TRAIL are inflammatory chemokines, their functions are not restricted to inflammation and require further examination. Our results indicate that attention should be paid to the side-effects of TRAIL treatment, not only in TRAIL-resistant but also in TRAIL-sensitive tumour cells.

The TRAIL apoptotic pathway in cancer onset, progression and therapy

Triggering of tumour cell apoptosis is the foundation of many cancer therapies. Death receptors of the tumour necrosis factor (TNF) superfamily have been largely characterized, as have the signals that are generated when these receptors are activated. TNF-related apoptosis-inducing ligand (TRAIL) receptors (TRAILR1 and TRAILR2) are promising targets for cancer therapy. Herein we review what is known about the molecular control of TRAIL-mediated apoptosis, the role of TRAIL in carcinogenesis and the potential therapeutic utility of recombinant TRAIL and agonistic antibodies against TRAILR1 and TRAILR2.

Triptolide sensitizes AML cells to TRAIL-induced apoptosis via decrease of XIAP and p53-mediated increase of DR5

Acute myeloid leukemia (AML) cells are relatively resistant to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL). We previously reported that triptolide, a potent anticancer agent from a Chinese herb, decreases XIAP in leukemic cells. We evaluated the combination of triptolide and TRAIL and found synergistic promotion of apoptosis in AML cells. XIAP-overexpressing U937 cells (U937XIAP) were more resistant to TRAIL than U937neo cells, and inhibition of XIAP with the small-molecule inhibitor 1396-11 enhanced TRAIL-induced apoptosis, implying XIAP as a resistance factor in AML. Furthermore, triptolide increased DR5 levels in OCI-AML3, while the DR5 increase was blunted in p53-knockdown OCI-AML3 and p53-mutated U937 cells, confirming a role for p53 in the regulation of DR5. In support of this finding, disruption of MDM2-p53 binding with subsequent increase in p53 levels by nutlin3a increased DR5 levels and sensitized OCI-AML3 cells to TRAIL. The combination of 1396-11 plus nutlin3a plus TRAIL was more effective than either the 1396-11 and TRAIL or nutlin3a and TRAIL combinations in OCI-AML3 cells, further supporting the role of triptolide as a sensitizer to TRAIL-induced apoptosis in part by independent modulation of XIAP expression and p53 signaling. Thus, the combination of triptolide and TRAIL may provide a novel strategy for treating AML by overcoming critical mechanisms of apoptosis resistance.

Novel therapies targeting the apoptosis pathway for the treatment of acute myeloid leukemia

Defects in the core regulators of the apoptosis pathway contribute to chemoresistance and poor outcomes in patients with acute myeloid leukemia (AML). To overcome these defects, novel molecules that target key proteins in the mitochondrial, death receptor, and convergence pathways of caspase activation are being developed. This review will highlight selected molecules including Bcl-2 and XIAP inhibitors that are advanced stages of development and have entered clinical trial for AML. In addition, this review will discuss how these novel therapies are being used as chemical probes to better understand the biology of the apoptosis pathway.

Molecular mechanisms of drug resistance in acute myeloid leukaemia

Resistance to chemotherapy in acute myeloid leukaemia is a major obstacle to a successful outcome for many patients. Often, there is resistance against a broad range of drugs due to multiple, simultaneously active processes. These mechanisms include effects on drug influx and efflux, drug activation/inactivation, DNA repair mechanisms, altered response of end targets, an altered haematopoietic microenvironment and dysfunctional apoptotic pathways. This article reviews the factors that determine leukaemic cell chemosensitivity and discusses the potential for rationally guided therapy.

Antitumor activity of human CD34+ cells expressing membrane-bound tumor necrosis factor-related apoptosis-inducing ligand

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in a variety of transformed cells while sparing normal cells. To enhance the therapeutic index of soluble (s)TRAIL, we used CD34+ cells transduced with a replication-deficient adenovirus encoding the human TRAIL gene (CD34-TRAIL+) for the systemic delivery of membrane-bound (m)TRAIL to lymphoid tumors. CD34-TRAIL+ cells were evaluated for their activity in vitro and in vivo in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice xenografted with sTRAIL-sensitive and -resistant tumors. In vitro, coculturing CD34-TRAIL+ cells with sTRAIL-sensitive or -resistant lymphoma cell lines induced significant levels of caspase-dependent tumor cell death. In vivo, CD34-TRAIL+ cells significantly increased the survival of NOD/SCID mice bearing sTRAIL-sensitive or -resistant lymphoid tumors at an early or advanced stage of disease. No obvious toxicity was observed on administration of CD34-TRAIL+ cells. Histological analysis revealed high-level expression of the agonistic receptor TRAIL-R2 by tumor endothelial cells, and efficient tumor homing of transduced cells. Injection of CD34-TRAIL+ cells resulted in extensive damage of tumor vasculature followed by hemorrhagic necrosis exhibiting a perivascular distribution. These results show that CD34-TRAIL+ cells might be an efficient vehicle for mTRAIL delivery to tumors, where they exert a potent antitumor effect possibly mediated by both direct tumor cell killing and indirect vascular-disrupting mechanisms.

New molecular therapy targets in acute myeloid leukemia

Despite improvements to acute myelogenous leukemia (AML) therapy during the last 25 years, the majority of patients still succumb to the disease. Thus, there remains an urgent need for further improvements in this field. The present chapter focuses on exciting areas of research in the field of AML therapy, including promising results with regards to recent improvements in our understanding of angiogenesis, tyrosine kinase signaling, farnesylation, cell cycling, modulation of gene expression, protein degradation, modulation of intracellular proteins, apoptosis, metabolism, and the possible retargeting of oncogenic proteins.

Multiple mechanisms underlie resistance of leukemia cells to Apo2 Ligand/TRAIL

Targeting death receptors with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has the remarkable potential to selectively kill malignant cells whereas normal cells are largely unaffected by this treatment. However, some tumor cells, including leukemia cells, exhibit resistance to this molecule. To investigate the basis for resistance of leukemia cells to the zinc-bound form of Apo2 ligand (Apo2L)/TRAIL, which is currently being evaluated in clinical trial, we isolated several resistant HL60 clones from parental HL60 cells by selection using the recombinant Apo2L/TRAIL. Differing resistance mechanisms were identified and characterized in these Apo2L/TRAIL-resistant clones. In one case, the level of the cell-surface death receptor DR4, but not DR5, was significantly decreased. However, these cells did undergo apoptosis in response to another form of recombinant TRAIL, histidine-tagged TRAIL, suggesting differing contributions of DR4 and DR5 in the response to these two forms of TRAIL. In the case of other clones, expression of procaspase-8 protein was lost and this was associated with a novel Leu(22)-->Phe(22) point mutation in CASP-8 gene. These results show that cells within a given tumor can have widely distinct mechanisms underlying resistance to Apo2L/TRAIL.

The sesquiterpene lactone parthenolide induces selective apoptosis of B-chronic lymphocytic leukemia cells in vitro

We have studied the in vitro actions of the sesquiterpene lactone parthenolide (PTL) on cells isolated from patients with chronic lymphocytic leukemia (CLL). Dye reduction viability assays showed that the median LD(50) for PTL was 6.2 muM (n=78). Fifteen of these isolates were relatively resistant to the conventional agent chlorambucil but retained sensitivity to PTL. Brief exposures to PTL (1-3 h) were sufficient to induce caspase activation and commitment to cell death. Chronic lymphocytic leukemia cells were more sensitive towards PTL than were normal T lymphocytes or CD34(+) haematopoietic progenitor cells. The mechanism of cell killing was via PTL-induced generation of reactive oxygen species, resulting in turn in a proapoptotic Bax conformational change, release of mitochondrial cytochrome c and caspase activation. Parthenolide also decreased nuclear levels of the antiapoptotic transcription factor nuclear factor-kappa B and diminished phosphorylation of its negative regulator IkappaB. Killing of CLL cells by PTL was apparently independent of p53 induction. This is the first report showing the relative selectivity of PTL towards CLL cells. The data here warrant further investigation of this class of natural product as potential therapeutic agents for CLL.

Identification of small molecules that sensitize resistant tumor cells to tumor necrosis factor-family death receptors

Two major pathways for apoptosis have been identified, involving either mitochondria (intrinsic) or tumor necrosis factor (TNF)-family death receptors (extrinsic) as initiators of caspase protease activation and cell death. Because tumor resistance to TNF-family death receptor ligands is a common problem, helping malignant cells evade host immune defenses, we sought to identify compounds that selectively sensitize resistant tumor cells to death receptor ligands. We screened a 50,000-compound library for agents that enhanced anti-FAS antibody-mediated killing of FAS-resistant PPC-1 prostate cancer cell, then did additional analysis of the resulting hits to arrive at eight compounds that selectively sensitized PPC-1 cells to anti-FAS antibody (extrinsic pathway agonist) without altering sensitivity to staurosporine and etoposide (VP-16; intrinsic pathway agonists). These eight compounds did not increase Fas surface levels and also sensitized PPC-1 cells to apoptosis induced by TNF-family member TNF-related apoptosis-inducing ligand, consistent with a post-receptor mechanism. Of these, two reduced expression of c-FLIP, an intracellular antagonist of the extrinsic pathway. Characterization of the effects of the eight compounds on a panel of 10 solid tumor cell lines revealed two structurally distinct compounds that frequently sensitize to extrinsic pathway agonists. Structure-activity relation studies of one of these compounds revealed a pharmacophore from which it should be possible to generate analogues with improved potency. Altogether, these findings show the feasibility of identifying compounds that selectively enhance apoptosis via the extrinsic pathway, thus providing research tools for uncovering resistance mechanisms and a starting point for novel therapeutics aimed at restoring sensitivity of tumor cells to immune effector mechanisms.

Renewed interest in cancer immunotherapy with the tumor necrosis factor superfamily molecules

Molecules belonging to the Tumor Necrosis Factor (TNF) and TNF receptor superfamilies have explosively expanded through the era of genomics and bioinformatics. Biological investigations of these molecules have explored their potency as attractive targets for cancer therapy. Anti-tumor mechanisms mediated by TNF superfamily molecules (TNFSF) could be classified into direct actions onto tumor cells and indirect effects through immune or non-immune components of tumor-bearing host. In this review, we focus on TRAIL, CD40, 4-1BB (CD137), and LIGHT as promising molecules to mediate powerful and selective anti-tumor responses, and summarize their unique effector mechanisms. In addition, optimal approaches to manipulate these molecules for cancer therapy are also discussed. We try to provide an insight into a role of TNFSF in cancer therapeutics and highlight each of their potency to be an important player in anti-cancer strategies.

Cytochrome c-related caspase-3 activation determines treatment response and relapse in childhood precursor B-cell ALL

Deficient activation of apoptosis signaling pathways may be responsible for treatment failure in acute leukemia. Here, we address the impact of intact apoptosis signaling in 78 patients with pediatric precursor B-cell acute lymphoblastic leukemia (ALL) by analysis of 2 key apoptogenic events: caspase-3 activation and cytochrome c release in leukemia cells cultured in vitro. Both events correlated only in the group of patients who had a good response and patients in continuous remission, suggesting that intact apoptosis signaling is a characteristic for favorable outcome. By combining both parameters, we identified a novel indicator, cytochrome c-related activation of caspase-3 (CRAC). CRAC directly connects the extent of caspase-3 activation to cytochrome c release in single cells in an individual patient sample. In CRAC-positive patients, indicating proficient apoptosis signaling, the number of persisting leukemia cells on day 15 was significantly lower than in the CRAC-negative patient group (n = 27, mean 6.0% versus n = 36, mean 22.6%; P = .003). At a median follow-up of 31 months, disease-free survival was 84 months (95% CI = 76 to 91 months) and 66 months (95% CI = 52 to 80 months) for patients with positive and negative CRAC, respectively (P = .019). CRAC may serve as a functionally defined risk factor for treatment stratification.

17-Allylamino-17-Demethoxygeldanamycin Synergistically Potentiates Tumor Necrosis Factor–Induced Lung Cancer Cell Death by Blocking the Nuclear Factor-κB Pathway

Nuclear factor-κB (NF-κB), a survival signal induced by tumor necrosis factor (TNF), contributes substantially to the resistance to TNF-induced cell death. Previous studies suggest that heat shock protein 90 (Hsp90) regulates the stability and function of receptor-interaction proteins (RIP) and IκB kinase β (IKKβ), the key components of the TNF-induced NF-κB activation pathway. In this study, we showed that the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG) was synergistic with TNF to induce apoptotic cell death in a panel of lung tumor-derived cell lines. Treatment with 17AAG caused degradation of RIP and IKKβ that, in turn, blocked TNF-induced NF-κB activation and antiapoptotic gene expression. The synergistic cytotoxicity was detected only when TNF treatment followed 17AAG preexposure. Importantly, the potentiation of cell death was abolished in NF-κB-disabled cells that express a nondegradable IκBα mutant (IκBαAA). These results suggest that the cytotoxicity seen with 17AAG and TNF treatment results from blocking TNF-induced NF-κB activation. The other components of the TNF receptor I signaling cascade were not altered, whereas TNF-induced c-Jun NH2-terminal kinase activation and apoptosis were potentiated. A similar synergism for inducing apoptosis was also observed in 17AAG-treated and TNF-related apoptosis-inducing ligand (TRAIL)–treated cancer cells. Our results suggest that NF-κB plays a key role in the resistance of lung cancer cells to TNF and TRAIL and that disabling this survival signal with 17AAG followed by TNF or TRAIL treatment could be an effective new therapeutic strategy for lung cancer. (Cancer Res 2006; 66(2): 1089-95)

Quantitative PCR on 5 genes reliably identifies CTCL patients with 5% to 99% circulating tumor cells with 90% accuracy

We previously identified a small number of genes using cDNA arrays that accurately diagnosed patients with Sézary Syndrome (SS), the erythrodermic and leukemic form of cutaneous T-cell lymphoma (CTCL). We now report the development of a quantitative real-time polymerase chain reaction (qRT-PCR) assay that uses expression values for just 5 of those genes: STAT4, GATA-3, PLS3, CD1D, and TRAIL. qRT-PCR data from peripheral blood mononuclear cells (PBMCs) accurately classified 88% of 17 patients with high blood tumor burden and 100% of 12 healthy controls in the training set using Fisher linear discriminant analysis (FLDA). The same 5 genes were then assayed on 56 new samples from 49 SS patients with blood tumor burdens of 5% to 99% and 69 samples from 65 new healthy controls. The average accuracy over 1000 resamplings was 90% using FLDA and 88% using support vector machine (SVM). We also tested the classifier on 14 samples from patients with CTCL with no detectable peripheral involvement and 3 patients with atopic dermatitis with severe erythroderma. The accuracy was 100% in identifying these samples as non-SS patients. These results are the first to demonstrate that gene expression profiling by quantitative PCR on a selected number of critical genes can be employed to molecularly diagnosis SS.

On the TRAIL of a new therapy for leukemia

The cytokine TRAIL (tumor necrosis factor alpha-related apoptosis-inducing ligand) as well as agonistic antibodies that bind to the TRAIL receptors, death receptor 4 (DR4) and DR5, are undergoing preclinical and early clinical evaluation as potential therapeutic agents for a variety of hematological and nonhematological malignancies. Here, we briefly review the normal biological function of TRAIL, the mechanism of cytotoxicity of TRAIL receptor ligands, and their effects on normal myeloid progenitors, myelodysplastic marrow and leukemic cells, including acute myelogenous leukemia (AML) and chronic lymphocytic leukemia (CLL), in vitro. Recent observations suggesting that DR4 is the predominant receptor for the cytotoxic effects of TRAIL in CLL and that histone deacetylase inhibitors synergize with TRAIL in CLL in vitro are described and discussed. Collectively, the reviewed studies not only illustrate the potential therapeutic usefulness of TRAIL and the agonistic antibodies, but also highlight the need for additional preclinical evaluation of these agents.

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.

Death to the bad guys: targeting cancer via Apo2L/TRAIL

All higher organisms consist of an ordered society of individual cells that must communicate to maintain and regulate their functions. This is achieved through a complex but highly regulated network of hormones, chemical mediators, chemokines and other cytokines, acting as ligands for intra or extra-cellular receptors. Ligands and receptors of the tumor necrosis factor (TNF) superfamilies are examples of signal transducers, whose integrated actions influence the development, homeostasis and adaptive responses of many cells and tissue types. Apo2L/TRAIL is one of several members of the tumour necrosis factor superfamily that induce apoptosis through the engagement of death receptors. Apo2L/TRAIL interacts with an unusually complex receptor system, which in humans comprises two death receptors and three decoy receptors. This molecule has received considerable attention recently because of the finding that many cancer cell types are sensitive to Apo2L/TRAIL-induced apoptosis, while most normal cells appear to be resistant to this action of Apo2L/TRAIL. In this review, we specifically emphasise on the actions of Apo2L/TRAIL with respect to its apoptotic signaling pathways and summarise what is known about its physiological role. The potential therapeutic usefulness of Apo2L/TRAIL, especially in combination with chemotherapeutic agents, is also discussed in some detail.

Absence of gene mutation in TRAIL receptor 1 (TRAIL-R1) and TRAIL receptor 2 (TRAIL-R2) in chronic myelogenous leukemia and myelodysplastic syndrome, and analysis of mRNA Expressions of TRAIL and TRAIL-related genes in chronic myelogenous leukemia

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an interferon (IFN)-induced molecule with apoptotic activity. We examined gene mutations in the death domains of TRAIL receptor 1 (TRAIL-R1) and TRAIL receptor 2 (TRAIL-R2), and in the TRAIL gene promoter in 46 chronic myelogenous leukemia (CML) patients. In 23 of the 46 patients, all the coding regions of TRAIL-R2 were also examined. However, no mutation or loss of heterozygosity was found. Furthermore, no mutation in the death domains of TRAIL-R1 and TRAIL-R2 genes, which causes amino acid change, was found in 18 myelodysplastic syndrome (MDS) patients. Ribonuclease protection assay (RPA) and real-time quantitative polymerase chain reaction using polymorphonuclear neutrophils of five new CML patients showed that the TRAIL mRNA expression was very low before in vitro IFN-alpha stimulation and markedly upregulated after IFN-alpha stimulation. FAS mRNA was also upregulated with IFN-alpha stimulation but the fold induction was far lower than that of TRAIL mRNA. In addition, RPA revealed that the ratio of (TRAIL-R1 plus TRAIL-R2) to TRAIL-R3 was also increased after IFN-alpha stimulation. Taken together, gene mutations of TRAIL-R1, TRAIL-R2 are infrequent in patients with CML and MDS. And so is the TRAIL promoter for CML. These mutations seem unrelated to tumorigenesis, disease progression, and response to IFN-alpha therapy in CML. A markedly high induction of TRAIL mRNA by IFN-alpha may have some relevance to IFN-alpha action in CML patients.

Following a TRAIL: update on a ligand and its five receptors

Identification of tumour necrosis factor apoptosis inducing ligand (TRAIL), a TNF family ligand, sparked a torrent of research, following an initial observation that it could kill tumour cells, but spare normal cells. Almost a decade after its discovery, and with five known receptors, the true physiological role of TRAIL is still debated and its anti-tumorigenic properties limited by potential toxicity. This review takes a comprehensive look at the story of this enigmatic ligand, addressing its remaining potential as a therapeutic and providing an overview of the TRAIL receptors themselves.

Sensitivity of adult T-cell leukaemia lymphoma cells to tumour necrosis factor-related apoptosis-inducing ligand

Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis in many transformed cells, but not in normal cells, and hence TRAIL has recently emerged as a novel anti-cancer agent. Adult T-cell leukaemia lymphoma (ATLL) is a neoplasm of T-lymphocyte origin aetiologically associated with human T-lymphotropic virus type 1 (HTLV-I), and is resistant to standard anti-cancer therapy. We thus characterized the sensitivity of ATLL cells to TRAIL in this study. Although most primary ATLL cells and cell lines expressed TRAIL death receptors on their surface, they showed only restricted sensitivity to TRAIL. Among the 10 ATLL cell lines examined, one was sensitive, but two had insufficient death-receptor expression, two had an unknown resistant mechanism with abrogation of the death signal upstream of caspase-8, and the remaining five showed attenuation of the signal in both extrinsic and intrinsic pathways by X-linked inhibitor of apoptosis and Bcl-2/Bcl-xL respectively. Furthermore, the level of HTLV-I tax expression was significantly correlated to TRAIL resistance. Interestingly, ATLL cells themselves expressed TRAIL on the cell surface. Constitutive production of TRAIL may offer resistance, thus allowing the development of TRAIL-resistant ATLL cells. Consequently, the resistant mechanism in ATLL cells against TRAIL was assigned to multiple factors and was not explained by a definitive single agent.

Functional expression of TRAIL and TRAIL-R2 during human megakaryocytic development

The expression and function of surface TRAIL and TRAIL receptors were investigated in primary megakaryocytic cells, generated in serum-free liquid phase from peripheral human CD34(+) cells. The surface expression of both TRAIL and "death receptor" TRAIL-R2 became detectable starting from the early phase of megakaryocytic differentiation (day 6 of culture) and persisted at later (days10-14) culture times. On the other hand, "death receptor" TRAIL-R1, "decoy receptors" TRAIL-R3, and TRAIL-R4 were barely detectable or undetectable at any time point examined. Addition of recombinant TRAIL at day 6 of culture increased the rate of spontaneous apoptosis of CD34(+)/CD41(dim) megakaryoblasts and it significantly decreased the total output of mature megakaryocytic cells evaluated after additional 4-8 days of culture. Conversely, addition in culture of TRAIL-R2-Fc chimera, which blocked the interaction between endogenous TRAIL and TRAIL-R2 on the surface of cultured megakaryocytic cells, increased the total megakaryocytic cell count. In addition, recombinant TRAIL promoted a small but reproducible increase of maturation in the surviving megakaryocytic cell population, evaluated by both phenotypic analysis and morphology. A similar pro-maturation effect was observed when TRAIL was added to bone marrow-derived CD61(+) megakaryocytic cells. Thus, our data suggest a role of TRAIL as a regulator of megakaryocytopoiesis.

Functional analysis of apoptosis induction in acute myeloid leukaemia-relevance of karyotype and clinical treatment response

Deficiencies or structural defects of the apoptotic machinery have been postulated as a potential mechanism for a broad resistance of acute myeloid leukaemia (AML) blasts towards cytotoxic therapy comprising chemotherapeutic agents with diverse pharmacodynamic principles but also cell-mediated cytotoxicity of the graft-versus-leukaemia effect, for example, in the setting of allogeneic transplantation. This hypothesis was systematically tested by functionally analysing the early, intermediate and late events of the apoptotic process in primary AML (n = 31) blasts following activation of the intrinsic and extrinsic pathway of apoptosis (etoposide and cytarabine as DNA damaging agents, FAS-ligand as an activator of the death receptor pathway). Activation of the extrinsic pathway by FAS-ligand did not induce apoptosis in primary AML, instead the proapoptotic signal was shown to 'fade', even in the early phase of the apoptotic sequence. However, activation of the intrinsic pathway induced severe cytotoxicity in all samples that showed the characteristic features of typical apoptosis, with a prominent apoptotic volume decrease (blebbing) in the early phase, significant increases in caspase 3 activity (intermediate or effector phase) and breakdown of cellular energy production in the late phase of apoptosis. These characteristics did not differ between prognostically favourable versus unfavourable AML karyotypes or between clinically responding versus refractory AML--indicating that a functional apoptotic apparatus is present even in the unfavourable AML subgroups. Our data indicate that the mechanism for a broad clinical resistance is not a dysfunctional apparatus per se but rather the consequence of anti-apoptotic regulation impeding otherwise functional apoptotic machinery.

Apoptosis in acute leukemia

In leukemias and malignant tumors the balance between apoptosis and cell proliferation is dysregulated. This review deals with the apoptosis in acute leukemia. There are several publications about the molecular basis of decreased apoptosis in acute lymphoid leukemia (ALL) and AML. However, there have been contradictory results. Different results are published about the correlation of the spontaneous and induced apoptosis in leukemia with prognosis. The potential causes of these contradictions are discussed.

Geldanamycin and herbimycin A induce apoptotic killing of B chronic lymphocytic leukemia cells and augment the cells' sensitivity to cytotoxic drugs

We studied the actions of geldanamycin (GA) and herbimycin A (HMA), inhibitors of the chaperone proteins Hsp90 and GRP94, on B chronic lymphocytic leukemia (CLL) cells in vitro. Both drugs induced apoptosis of the majority of CLL isolates studied. Whereas exposure to 4-hour pulses of 30 to 100 nM GA killed normal B lymphocytes and CLL cells with similar dose responses, T lymphocytes from healthy donors as well as those present in the CLL isolates were relatively resistant. GA, but not HMA, showed a modest cytoprotective effect toward CD34+ hematopoietic progenitors from normal bone marrow. The ability of bone marrow progenitors to form hematopoietic colonies was unaffected by pulse exposures to GA. Both GA and HMA synergized with chlorambucil and fludarabine in killing a subset of CLL isolates. GA- and HMA-induced apoptosis was preceded by the up-regulation of the stress-responsive chaperones Hsp70 and BiP. Both ansamycins also resulted in down-regulation of Akt protein kinase, a modulator of cell survival. The relative resistance of T lymphocytes and of CD34+ bone marrow progenitors to GA coupled with its ability to induce apoptosis following brief exposures and to synergize with cytotoxic drugs warrant further investigation of ansamycins as potential therapeutic agents in CLL.

TRAIL regulates normal erythroid maturation through an ERK-dependent pathway

In order to investigate the biologic activity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on human erythropoiesis, glycophorin A (GPA)+ erythroid cells were generated in serum-free liquid phase from human cord blood (CB) CD34+ progenitor cells. The surface expression of TRAIL-R1 was weakly detectable in the early-intermediate phase of erythroid differentiation (days 4-6; dim-intermediate GPA expression), whereas a clear-cut expression of TRAIL-R2 was observed through the entire course of erythroid differentiation (up to days 12-14; bright GPA expression). On the other hand, surface TRAIL-R3 and -R4 were not detected at any culture time. Besides inducing a rapid but small increase of apoptotic cell death, which was abrogated by the pan-caspase inhibitor z-VAD-fmk, the addition of recombinant TRAIL at day 6 of culture inhibited the generation of morphologically mature erythroblasts. Among the intracellular pathways investigated, TRAIL significantly stimulated the extracellular signal-regulated kinase 1/2 (ERK1/2) but not the p38/mitogen-activated protein kinase (MAPK) or the c-Jun NH2-terminal kinase (JNK) pathway. Consistently with a key role of ERK1/2 in mediating the negative effects of TRAIL on erythroid maturation, PD98059, a pharmacologic inhibitor of the ERK pathway, but not z-VAD-fmk or SB203580, a pharmacologic inhibitor of p38/MAPK, reverted the antidifferentiative effect of TRAIL on CB-derived erythroblasts.

Synthetic triterpenoids activate a pathway for apoptosis in AML cells involving downregulation of FLIP and sensitization to TRAIL

Acute myelogenous leukemia (AML) remains a deadly disease for most adult patients, due primarily to the emergence of chemoresistant cells. Defects in apoptosis pathways make important contributions to chemoresistance, suggesting a need to restore apoptosis sensitivity or to identify alternative pathways for apoptosis induction. Triterpenoids represent a class of naturally occurring and synthetic compounds with demonstrated antitumor activity, including 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) and its methyl ester (CDDO-m). We explored the effects of CDDO and CDDO-m in vitro on established AML cell lines (HL-60, U937, AML-2) and on freshly isolated AML blasts. CDDO and CDDO-m reduced the viability of all AML cell lines tested in a dose-dependent manner, with effective doses for killing 50% of cells (ED(50)) within 48 h of approximately 1 and 0.5 muM, respectively. CDDO or CDDO-m also induced substantial increases in cell death in five out of 10 samples of primary AML blasts. Cell death induced by CDDO and CDDO-m was attributed to apoptosis, based on characteristic cell morphology and evidence of caspase activation. Immunoblot analysis demonstrated proteolytic processing of caspase-3, -7, and -8, but not caspase-9, suggesting the involvement of the 'extrinsic' pathway, linked to apoptosis induction by TNF-family death receptors. Accordingly, CDDO and CDDO-m induced concentration-dependent reductions in the levels of FLIP protein, an endogenous antagonist of caspase-8, without altering the levels of several other apoptosis-relevant proteins. Reductions in FLIP were rapid, detectable within 3 h after exposure of AML cell lines to CDDO or CDDO-m. CDDO and CDDO-m also sensitized two of four leukemia lines to TRAIL, a TNF-family death ligand. The findings suggest that synthetic triterpenoids warrant further investigation in the treatment of AML, alone or in combination with TRAIL or other immune-based therapies.

NF-κB/Rel-mediated regulation of apoptosis in hematologic malignancies and normal hematopoietic progenitors

The activity of NF-kappaB/Rel transcription factors can downmodulate apoptosis in normal and neoplastic cells of the hematologic and other compartments, contributing in maintaining neoplastic clone survival and impairing response to therapy. Alterations in nfkappab or ikappaB genes are documented in some hematologic neoplasias, while in others dysfunction in NF-kappaB/Rel-activating signaling pathways can be recognized. The prosurvival properties of NF-kappaB/Rel appear to rely on the induced expression of molecules (caspase inhibitors, Bcl2 protein family members, etc.), which interfere with the apoptosis pathway. Constitutive NF-kappaB/Rel activity in some hematologic malignancies could be advantageous for neoplastic clone expansion by counteracting stress stimuli (consumption of growth factors and metabolites) and immune system-triggered apoptosis; it is furthermore likely to play a central role in determining resistance to therapy. Based on this evidence, NF-kappaB/Rel-blocking approaches have been introduced in antineoplastic strategies. The identification of NF-kappaB/Rel target genes relevant for survival in specific neoplasias is required in order to address tailored therapies and avoid possible detrimental effects due to widespread NF-kappaB/Rel inhibition. Moreover, comparative analyses of normal hematopoietic progenitors and neoplastic cell sensitivities to inhibitors of NF-kappaB/Rel and their target genes will allow to evaluate the impact of these tools on normal bone marrow.

Tracking death dealing by Fas and TRAIL in lymphatic neoplastic disorders: pathways, targets, and therapeutic tools

In the past decade, it was concluded from a number of investigations that death domain-containing members of the tumor necrosis factor-receptor (TNF-R) family and their ligands such as Fas/FasL and TNF-related apoptosis-inducing ligand (TRAIL)-R/TRAIL are essential for maintaining an intact immune system for surveillance against infection and cancer development and that nondeath domain-containing members such as CD30 or CD40 are involved in the fine tuning of this system during the selection process of the lymphatic system. In line with this conclusion are the observations that alterations in structure, function, and regulation of these molecules contribute to autoimmunity and cancer development of the lymphoid system. Besides controlling size and function of the lymphoid cell pool, Fas/FasL and TRAIL-R/TRAIL regulate myelopoiesis and the dendritic cell functions, and severe alterations of these lineages during the outgrowth and expansion of the lymphoid tumors have been reported. It is the aim of this review to summarize what is currently known about the complex role of these two death receptor/ligand systems in normal, disturbed, and neoplastic hemato-/lymphopoiesis and to point out how such knowledge can be used in developing novel, therapeutic options and the problems that will have to be faced along the way.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and TNF-alpha promote the NF-kappaB-dependent maturation of normal and leukemic myeloid cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and TNF-alpha induced monocytic maturation of primary normal CD34-derived myeloid precursors and of the M2/M3-type acute myeloid leukemia HL-60 cell line, associated to increased nuclear factor (NF)-kappaB activity and nuclear translocation of p75, p65, and p50 NF-kappaB family members. Consistently, both cytokines also induced the degradation of the NF-kappaB inhibitors, IkappaBalpha and IkappaB epsilon, and up-regulated the surface expression of TRAIL-R3, a known NF-kappaB target. However, NF-kappaB activation and IkappaB degradation occurred with different time-courses, since TNF-alpha was more potent, rapid, and transient than TRAIL. Of the two TRAIL receptors constitutively expressed by HL-60 (TRAIL-R1 and TRAIL-R2), only the former was involved in IkappaB degradation, as demonstrated by using agonistic anti-TRAIL receptor antibodies. Moreover, NF-kappaB nuclear translocation induced by TRAIL but not by TNF-alpha was abrogated by z-IETD-fmk, a caspase-8-specific inhibitor. The key role of NF-kappaB in mediating the biological effects of TNF-alpha and TRAIL was demonstrated by the ability of unrelated pharmacological inhibitors of the NF-kappaB pathway (parthenolide and MG-132) to abrogate TNF-alpha- and TRAIL-induced monocytic maturation. These findings demonstrate that NF-kappaB is essential for monocytic maturation and is activated via distinct pathways, involving or not involving caspases, by the related cytokines TRAIL and TNF-alpha.

Cytotoxic drugs enhance the ex vivo sensitivity of malignant cells from a subset of acute myeloid leukaemia patients to apoptosis induction by tumour necrosis factor receptor-related apoptosis-inducing ligand

We have studied the actions of tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) on cells isolated from patients with acute myeloid leukaemia (AML). Apoptosis induction was initially assessed by quantitative morphological analysis. Only 2/19 isolates showed a > 10% increase in apoptotic cells following TRAIL treatment. However, incubation with TRAIL combined with fludarabine, cytosine arabinoside or daunorubicin resulted in additive or super-additive apoptosis induction in approximately half of the isolates. Molecular evidence of super-additive apoptosis induction by TRAIL and cytotoxic agents was obtained by quantification of caspase 3 activation, detected by Western blot analysis of poly (ADP ribose) polymerase cleavage. The ability of TRAIL and daunorubicin to induce super-additive apoptosis correlated with the ability of these agents to activate caspase 8 and to augment cellular levels of the truncated pro-apoptotic form of the BCL-2 family member BID. Our data suggest that co-administration of TRAIL with conventional cytotoxic drugs may be of therapeutic value in some patients with AML.

TRAIL-beta and TRAIL-gamma: two novel splice variants of the human TNF-related apoptosis-inducing ligand (TRAIL) without apoptotic potential

Tumour necrosis factor (TNF) related apoptosis-inducing ligand (TRAIL/APO2L) is a recently identified member of the TNF family, which induces programmed cell death in a variety of neoplastic cell types, but not in most nonneoplastic cells. In this study, we report on the identification of two novel alternative splice variants of TRAIL in neoplastic and non-neoplastic human cells lacking either exon 3 (TRAIL-beta) or exons 2 and 3 (TRAIL-gamma). In both splice variants, loss of exon 3 resulted in a frame shift generating a stop codon with consecutive extensive truncation in the extracellular domain. Ectopic expression revealed a loss of proapoptotic potential for both alternative splice variants. In contrast to the predominantly cytoplasmatic localisation of GFP-tagged TRAIL-alpha and TRAIL-beta, TRAIL-gamma showed an additional association with the cell surface and nuclear membrane. In conclusion, alternative splicing might be involved in fine tuning of TRAIL-induced apoptosis and underlines the complexity of the TRAIL system.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Nature's TRAIL--on a path to cancer immunotherapy

The TNF-related apoptosis-inducing ligand (TRAIL) offers great promise as a cancer therapeutic. Initially, soluble recombinant versions of the TRAIL molecule have exhibited specific tumoricidal activity against a variety of tumors alone, or in combination with other cancer treatments, and much anticipation awaits the outcomes from early clinical trials. More recently, the natural role of TRAIL has been explored in tumor and allogeneic bone marrow transplantation models in the mouse. Strikingly, the TRAIL effector pathway appears a vital component of immunosurveillance of spontaneous or resident tumor cells by both T cells and NK cells, stimulating more hope that manipulating TRAIL activity is a natural path to improved cancer immunotherapy.