Up-regulation of XIAP by M-CSF is associated with resistance of myeloid leukemia cells to apoptosis

Targeting apoptosis in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a molecularly and clinically heterogeneous disease, and its incidence is increasing as the populations in Western countries age. Despite major advances in understanding the genetic landscape of AML and its impact on the biology of the disease, standard therapy has not changed significantly in the last three decades. Allogeneic haematopoietic stem cell transplantation remains the best chance for cure, but can only be offered to a minority of younger fit patients. Molecularly targeted drugs aiming at restoring apoptosis in leukaemic cells have shown encouraging activity in early clinical trials and some of these drugs are currently being evaluated in randomised controlled trials. In this review, we discuss the current development of drugs designed to trigger cell death in AML.

Anti-tumor activity of the X-linked inhibitor of apoptosis (XIAP) inhibitor embelin in gastric cancer cells

This study investigated the anticancer effects of embelin in human gastric cancer cells and the underlying molecular mechanisms. Gastric cancer cells were treated with embelin and 5-FU for methyl-thiazolyl-tetrazolium bromide cell viability assay and flow cytometric detection of cell viability and apoptosis. Protein pathway array (PPA) and Western blot were used to investigate differentially expressed proteins in embelin-treated gastric cancer cells. Embelin reduced gastric cancer cell viability, induced apoptosis, and enhanced 5-FU antitumor activity in gastric cancer cells. Mechanistically, embelin induced cell cycle arrest at the S and G2/M phases. Molecularly, embelin downregulated expression of X-linked inhibitor of apoptosis and cell cycle-regulatory proteins, such as CDK1, CDC25B, CDC25C, cyclinB1, and CDK2. PPA analysis showed that embelin modulated several pathways that are associated with cell growth and apoptosis, such as PI3K/AKT, JAK/STAT, p38 MAPK, and p53. The data from the current study implied that reduction of gastric cancer cell viability after treatment with embelin was through cell cycle arrest at the S and G2/M phases and apoptosis.

TNF-α up-regulates cellular inhibitor of apoptosis protein 2 (c-IAP2) via c-Jun N-terminal kinase (JNK) pathway in nasopharyngeal carcinoma

Inhibitor of apoptosis proteins (IAPs) contribute to both tumor progression and tumor metastasis. Here, we show that pro-inflammatory cytokine TNF-α induced the up-regulation of c-IAP2 in the potential metastatic nasopharyngeal carcinoma (NPC) cells in a dose- and time-dependent manner. This up-regulation is tolerant, as the pre-treatment of NPC cells with TNF-α reversed the up-regulation of c-IAP2 induced by TNF-α re-stimulation. TNF-α activated MAKP signals, including ERK, JNK and p38, and NF-κB signal, but only inhibition of JNK signal transduction reversed the induction of c-IAP2, suggesting that JNK signaling contributed to the c-IAP2 induction. The results from in vitro scratch wound-healing assays showed that TNF-α promoted cell invasion, which was reversed by the inhibition of JNK signaling. Taken together, these studies suggested that pro-inflammation cytokine TNF-α may be a promoter for NPC metastasis, and the anti-inflammatory therapy may be of benefit to the prevention of NPC metastasis.

Human cytomegalovirus stimulates monocyte-to-macrophage differentiation via the temporal regulation of caspase 3

Monocytes are primary targets for human cytomegalovirus (HCMV) infection and are proposed to be responsible for hematogenous dissemination of the virus. Biologically, monocytes have a short life span of 48 h in the circulation, a period of time during which monocytes must make a cell fate decision on whether to undergo apoptosis or differentiate into a macrophage. We have previously shown that HCMV infection stimulates monocyte-to-macrophage differentiation; however, the mechanism(s) by which HCMV-infected monocytes simultaneously navigate the 48-h "viability gate" and undergo macrophagic differentiation has remained elusive. Studies have demonstrated that the level of caspase 3 and 8 activities in monocytes may mediate the delicate balance between apoptosis and macrophage colony-stimulating factor (M-CSF)-induced myeloid differentiation. Here, we show that HCMV infection, unlike M-CSF treatment, does not induce caspase 8 activity to promote myeloid differentiation. However, HCMV infection does induce a temporal activation of caspase 3, with only a low level of active caspase 3 being observed after the 48-h viability checkpoint. Consistent with the role of a time-dependent activation of caspase 3 in promoting myeloid differentiation, the inhibition of caspase 3 blocked HCMV-induced monocyte-to-macrophage differentiation. Temporal transcriptome and functional analyses identified heat shock protein 27 (HSP27) and Mcl-1, two known regulators of caspase 3 activation, as being upregulated prior to the 48-h viability gate following HCMV infection. Using small interfering RNAs (siRNAs), we demonstrate that HCMV targets the rapid induction of HSP27 and Mcl-1, which cooperatively function to precisely control caspase 3 activity in order to allow for HCMV-infected monocytes to successfully traverse the 48-h cell fate decision checkpoint and commence macrophage maturation. Overall, this study highlights a unique regulatory mechanism employed by HCMV to tightly modulate the caspase 3 activity needed to promote myeloid differentiation, a key process in the viral dissemination and persistence strategy.

Ex vivo detection of primary leukemia cells resistant to granule cytotoxin-induced cell death: a rapid isolation method to study granzyme-B-mediated cell death

Cytotoxic T lymphocytes and natural killer cells (CTL/NK) induce cell death in leukemia cells by the granzyme B (grB)-dependent granule cytotoxin (GC) pathway. Resistance to GC may be involved in immune evasion of leukemia cells. The delivery of active grB into the cytoplasma is dependent on the presence of perforin (PFN) and grB complexes. We developed a rapid method for the isolation of GC to investigate GC-mediated cell death in primary leukemia cells. We isolated GC containing grB, grB complexes and PFN by detergent free hypotonic lysis of the human NK cell leukemia line YT. The GC induce grB-mediated, caspase-dependent apoptosis in live cells. The human leukemia cell lines KG-1, U937, K562 (myeloid leukemia), Jurkat, Daudi, and BV173 (lymphoblastic leukemia) treated with GC internalized grB and underwent cell death. In primary leukemia cells analyzed ex vivo, we found GC-resistant leukemia cells in three out of seven patients with acute myeloid leukemia and one out of six patients with acute lymphoblastic leukemia. We conclude that our method is fast (approximately 1 h) and yields active GC that induce grB-dependent cell death. Furthermore, resistance to GC can be observed in acute leukemias and may be an important mechanism contributing to leukemia cell immune evasion.

IKK antagonizes CD95 ligation-mediated apoptosis by regulating NF-κB activity

The CD95 (Apo1/Fas)/CD95 ligand system plays pivotal roles in various aspects of immune regulation and function by triggering apoptosis. Besides the apoptosis signaling pathway, CD95 ligation also induces the activation of NF-kappaB. Previous studies suggest that IkappaB kinase (IKK) may be a key player in cell survival by mediating NF-kappaB activation. However, the roles of IKK in CD95 ligation-mediated apoptosis and NF-kappaB activation are still not clear. In this report, we show that expression of the caspase-resistant uncleavable IKKbeta (UCIKKbeta) mutant suppressed CD95 ligation-mediated cell death in HeLa cells. Furthermore, CD95 ligation induced much more cell death in IKKbeta-/- murine embryonic fibroblasts (MEFs) than in wild type MEFs, despite that IKK was only marginally activated upon CD95 ligation. Pretreatment of HeLa cells with a specific IKK inhibitor NEMO-binding domain (NBD) peptide blocked CD95 ligation-induced NF-kappaB transcriptional activity. And UCIKKbeta enhanced the basal NF-kappaB activity, and consequently led to higher NF-kappaB activity upon CD95 ligation in HeLa cells. Therefore, IKK antagonizes CD95 ligation-mediated apoptosis by regulating NF-kappaB activity.

Method validation and preliminary qualification of pharmacodynamic biomarkers employed to evaluate the clinical efficacy of an antisense compound (AEG35156) targeted to the X-linked inhibitor of apoptosis protein XIAP

Data are presented on pharmacodynamic (PD) method validation and preliminary clinical qualification of three PD biomarker assays. M65 Elisa, which quantitates different forms of circulating cytokeratin 18 (CK18) as putative surrogate markers of both apoptotic and nonapoptotic tumour cell death, was shown to be highly reproducible: calibration curve linearity r2 = 0.996, mean accuracy > 91% and mean precision < 3%, n = 27. Employing recombinant (r) CK18 and caspase cleaved CK18 (CK18 Asp396 neo-epitope) as external standards, kit to kit reproducibly was < 6% (n = 19). rCK18 was stable in plasma for 4 months at -20 degrees C and -80 degrees C, for 4 weeks at 4 degrees C and had a half-life of 2.3 days at 37 degrees C. Cytokeratin 18 Asp396 NE, the M30 Apoptosense Elisa assay antigen, was stable in plasma for 6 months at -20 degrees C and -80 degrees C, for 3 months at 4 degrees C, while its half-life at 37 degrees C was 3.8 days. Within-day variations in endogenous plasma concentrations of the M30 and M65 antigens were assessed in two predose blood samples collected from a cohort of 15 ovarian cancer patients receiving carboplatin chemotherapy and were shown to be no greater than the variability associated with methods themselves. Between-day fluctuations in circulating levels of the M30 and M65 antigens and in XIAP mRNA levels measured in peripheral blood mononuclear cells by quantitative (q) RT-PCR were evaluated in two predose blood samples collected with a 5- to 7-day gap from 23 patients with advanced cancer enrolled in a phase I trial. The mean variation between the two pretreatment values ranged from 13 to 14 to 25%, respectively, for M65, M30 and qRT-PCR. These data suggest that the M30 and M65 Elisa's and qRT-PCR as PD biomarker assays have favourable performance characteristics for further investigation in clinical trials of anticancer agents which induce tumour apoptosis/necrosis or knockdown of the anti-apoptotic protein XIAP.

Inhibitor of apoptosis proteins: new therapeutic targets in hematological cancer?

Apoptosis is an essential process for the selection and survival of lymphocytes. Resistance to apoptosis can promote malignant transformation of hematopoietic cells. Proteins that regulate apoptosis may therefore be critically involved in the development of hematological cancer. A delicate balance between pro- and antiapoptotic mechanisms determines whether a cell death signal can activate the execution of the apoptotic cell death program. The family of inhibitor of apoptosis (IAP) proteins is a recently identified, novel category of apoptosis-regulatory proteins. IAPs can inhibit the activation of caspases that are the executioners of apoptosis, activated by both the extrinsic and intrinsic pathway. IAPs may thereby set the threshold for apoptosis-activation and play a key role in the regulation of apoptotic cell death. IAPs themselves are also subject to strict regulation through feedback mechanisms. This paper focuses on the role of IAP family proteins in the regulation of apoptosis and discusses implications for their involvement in cancer and possible use for cancer therapy, especially in leukemias and lymphomas.

Apoptosis: targets in pancreatic cancer

Pancreatic adenocarcinoma is characterized by poor prognosis, because of late diagnosis and lack of response to chemo- and/or radiation therapies. Resistance to apoptosis mainly causes this insensitivity to conventional therapies. Apoptosis or programmed cell death is a central regulator of tissue homeostasis. Certain genetic disturbances of apoptotic signaling pathways have been found in carcinomas leading to tumor development and progression. In the past few years, the knowledge about the complex pathways of apoptosis has strongly increased and new therapeutic approaches based on this knowledge are being developed. This review will focus on the role of apoptotic proteins contributing to pancreatic cancer development and progression and will demonstrate possible targets to influence this deadly disease.