Endogenously released Smac is insufficient to mediate cell death of human lung carcinoma in response to etoposide

Lipopolysaccharide sensitizes the therapeutic response of breast cancer to IAP antagonist

Inhibitor of apoptosis protein (IAP) is a class of E3 ubiquitin ligases functioning to support cancer survival and growth. Many small-molecule IAP antagonists have been developed, aiming to degrade IAP proteins to kill cancer. We have evaluated the effect of lipopolysaccharide (LPS), a component of the bacterial outer membrane, on IAP antagonists in treating breast cancer in a mouse model to guide future clinical trials. We show that LPS promotes IAP antagonist-induced regression of triple-negative breast cancer (TNBC) from MDA-MB-231 cells in immunodeficient mice. IAP antagonists such as SM-164, AT-406, and BV6, do not kill MDA-MB-231 cells alone, but allow LPS to induce cancer cell apoptosis rapidly. The apoptosis caused by LPS plus SM-164 is blocked by toll-like receptor 4 (TLR4) or MyD88 inhibitor, which inhibits LPS-induced TNFα production by the cancer cells. Consistent with this, MDA-MB-231 cell apoptosis induced by LPS plus SM-164 is also blocked by the TNF inhibitor. LPS alone does not kill MDA-MB-231 cells because it markedly increases the protein level of cIAP1/2, which is directly associated with and stabilized by MyD88, an adaptor protein of TLR4. ER⁺ MCF7 breast cancer cells expressing low levels of cIAP1/2 undergo apoptosis in response to SM-164 combined with TNFα but not with LPS. Furthermore, TNFα but not LPS alone inhibits MCF7 cell growth in vitro. Consistent with these, LPS combined with SM-164, but not either of them alone, causes regression of ER⁺ breast cancer from MCF7 cells in immunodeficient mice. In summary, LPS sensitizes the therapeutic response of both triple-negative and ER⁺ breast cancer to IAP antagonist therapy by inducing rapid apoptosis of the cancer cells through TLR4- and MyD88-mediated production of TNFα. We conclude that antibiotics that can reduce microbiota-derived LPS should not be used together with an IAP antagonist for cancer therapy.

ILP-2: A New Bane and Therapeutic Target for Human Cancers

Inhibitor of apoptosis protein-related-like protein-2 (ILP-2), also known as BIRC-8, is a member of the inhibitor of apoptosis protein (IAPs) family, which mainly encodes the negative regulator of apoptosis. It is selectively overexpressed in a variety of human tumors and can help tumor cells evade apoptosis, promote tumor cell growth, increase tumor cell aggressiveness, and appears to be involved in tumor cell resistance to chemotherapeutic drugs. Several studies have shown that downregulation of ILP-2 expression increases apoptosis, inhibits metastasis, reduces cell growth potential, and sensitizes tumor cells to chemotherapeutic drugs. In addition, ILP-2 inhibits apoptosis in a unique manner; it does not directly inhibit the activity of caspases but induces apoptosis by cooperating with other apoptosis-related proteins. Here, we review the current understanding of the various roles of ILP-2 in the apoptotic cascade and explore the use of interfering ILP-2, and the combination of related anti-tumor agents, as a novel strategy for cancer therapy.

Tudor staphylococcal nuclease drives chemoresistance of non-small cell lung carcinoma cells by regulating S100A11

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC), the major lung cancer subtype, is characterized by high resistance to chemotherapy. Here we demonstrate that Tudor staphylococcal nuclease (SND1 or TSN) is overexpressed in NSCLC cell lines and tissues, and is important for maintaining NSCLC chemoresistance. Downregulation of TSN by RNAi in NSCLC cells led to strong potentiation of cell death in response to cisplatin. Silencing of TSN was accompanied by a significant decrease in S100A11 expression at both mRNA and protein level. Downregulation of S100A11 by RNAi resulted in enhanced sensitivity of NSCLC cells to cisplatin, oxaliplatin and 5-fluouracil. AACOCF₃, a phospholipase A₂ (PLA₂) inhibitor, strongly abrogated chemosensitization upon silencing of S100A11 suggesting that PLA₂ inhibition by S100A11 governs the chemoresistance of NSCLC. Moreover, silencing of S100A11 stimulated mitochondrial superoxide production, which was decreased by AACOCF₃, as well as N-acetyl-L-cysteine, which also mimicked the effect of PLA₂ inhibitor on NSCLC chemosensitization upon S100A11 silencing. Thus, we present the novel TSN-S100A11-PLA₂ axis regulating superoxide-dependent apoptosis, triggered by platinum-based chemotherapeutic agents in NSCLC that may be targeted by innovative cancer therapies.

Differential sensitivity to apoptosome apparatus activation in non-small cell lung carcinoma and the lung

The intrinsic apoptosis pathway represents an important mechanism of stress-induced death of cancer cells. To gain insight into the functional status of the apoptosome apparatus in non-small cell lung carcinoma (NSCLC), we studied its sensitivity to activation, the assembly of apoptosome complexes and stability of their precursors, and the importance of X-linked inhibitor of apoptosis (XIAP) in the regulation of apoptosome activity, using cell-free cytosols from NSCLC cell lines and NSCLC tumours and lungs from 62 surgically treated patients. Treatment of cytosol samples with cytochrome c (cyt-c) and dATP induced proteolytic processing of procaspase-9 to caspase-9, which was followed by procaspase-3 processing to caspase-3, and by generation of caspase-3-like activity in 5 of 7 studied NSCLC cell lines. Further analysis demonstrated formation of high-M_r Apaf-1 complexes associated with cleaved caspase-9 in the (cyt-c + dATP)-responsive COLO-699 and CALU-1 cells. By contrast, in A549 cells, Apaf-1 and procaspase-9 co-eluted in the high-M_r fractions, indicating formation of an apoptosome complex unable of procaspase-9 processing. Thermal pre-treatment of cell-free cytosols in the absence of exogenous cyt-c and dATP lead to formation of Apaf-1 aggregates, unable to recruit and activate procaspase-9 in the presence of cyt-c and dATP, and to generate caspase-3-like activity. Further studies showed that the treatment with cyt-c and dATP induced a substantially higher increase of caspase-3-like activity in cytosol samples from NSCLC tumours compared to matched lungs. Tumour histology, grade and stage had no significant impact on the endogenous and the (cyt-c + dATP)-induced caspase-3-like activity. Upon addition into the cytosol, the XIAP-neutralizing peptides AVPIAQK and ATPFQEG only moderately heightened the (cyt-c + dATP)-induced caspase-3-like activity in some NSCLC tumours. Taken together, the present study provides evidence that the apoptosome apparatus is functional in the majority of NSCLCs and that its sensitivity to the (cyt-c + dATP)-mediated activation is often enhanced in NSCLCs compared to lungs. They also indicate that XIAP does not frequently and effectively suppress the activity of apoptosome apparatus in NSCLCs.

Smac: Its role in apoptosis induction and use in lung cancer diagnosis and treatment

Apoptosis is a conserved and regulated cell suicide process, the malfunction of which is closely linked with carcinogenesis. Caspases control the induction of apoptosis through an enzymatic cascade that can be activated by both the mitochondrial and death receptor pathways. Smac is a mitochondrial protein that interacts with Inhibitor of Apoptosis Proteins (IAPs) and, upon apoptotic stimuli, is released into the cytoplasm to inhibit the capase-binding activity of IAPs. Smac plays key roles in both the diagnosis and treatment of cancer, especially lung cancer. Our review will focus on the roles of Smac in lung carcinogenesis and cancer progression and its relevance in lung cancer treatment.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

Differential regulation of Smac/DIABLO and Hsp-70 during brain maturation

The heat shock protein (Hsp) system is a cell defense mechanism constitutively expressed at the basal state and essential for cell survival in response to damaging stimuli. Apoptosis is a physiological cell death program that preserves tissue homeostasis. We investigated the intrinsic pathway of apoptosis at various stages of brain maturation in CD-1 mice, triggered by two mitochondrial proapoptotic proteins, cytochrome c and Smac/DIABLO, and the pathway's regulation by Hsp-70. Smac/DIABLO and Hsp-70 proteins were upregulated 2-fold and 1.5-3-fold, respectively, after birth. In contrast, in the presence of cytochrome c/2'-deoxyadenosine 5'-triphosphate (dATP), caspase activity in mouse brain cell-free extracts increased 90-fold and 61-fold, at fetal and neonatal stages, whereas no activation was detected 15 days postnatally or at any subsequent times. These results indicate that the activation pattern of the intrinsic pathway of apoptosis undergoes a marked shift during postnatal maturation.

Overcoming chemoresistance of non-small cell lung carcinoma through restoration of an AIF-dependent apoptotic pathway

Non-small cell lung carcinomas (NSCLCs) are typically resistant against apoptosis induced by standard chemotherapy. We evaluated the effects of the two potential antitumor agents of the lamellarin class on a highly apoptosis-resistant NSCLC cell line. Both the marine alkaloid lamellarin-D and its synthetic amino derivative PM031379 induced the activation of Bax, the mitochondrial release of cytochrome c and apoptosis-inducing factor (AIF), as well as the activation of caspase-3. However, only PM031379 triggered cell death and sign of nuclear apoptosis coupled to the nuclear translocation of AIF. Depletion of AIF with small interfering RNA or microinjection of a neutralizing anti-AIF antibody largely prevented PM031379-induced cytotoxicity, underscoring the essential contribution of AIF to NSCLC killing. Using NSCLC cells lacking mitochondrial DNA, we showed that the generation of mitochondrial reactive oxygen species (ROS) was crucial for the PM031379-induced translocation of AIF to the nucleus and subsequently cell death. Pretreatment of NSCLC cells with menadione, a mitochondrial ROS generator, was able to restore the deficient chemotherapy-induced apoptosis of NSCLC cells. Altogether, these data suggest that mitochondrial ROS generation is crucial for overriding the chemoresistance of NSCLC cells. Moreover, this study delineates the unique mechanism of action of lamellarins as potential anticancer agents.

Extrinsic versus intrinsic apoptosis pathways in anticancer chemotherapy

Apoptosis or programmed cell death is a key regulator of physiological growth control and regulation of tissue homeostasis. One of the most important advances in cancer research in recent years is the recognition that cell death mostly by apoptosis is crucially involved in the regulation of tumor formation and also critically determines treatment response. Killing of tumor cells by most anticancer strategies currently used in clinical oncology, for example, chemotherapy, gamma-irradiation, suicide gene therapy or immunotherapy, has been linked to activation of apoptosis signal transduction pathways in cancer cells such as the intrinsic and/or extrinsic pathway. Thus, failure to undergo apoptosis may result in treatment resistance. Understanding the molecular events that regulate apoptosis in response to anticancer chemotherapy, and how cancer cells evade apoptotic death, provides novel opportunities for a more rational approach to develop molecular-targeted therapies for combating cancer.

Metaphase arrest and cell death induced by etoposide on HeLa cells

DNA damage, cell cycle and apoptosis form a network with important implications for cancer chemotherapy. Dysfunctions of the cycle checkpoints can allow cancer cells to acquire drug resistance. Etoposide is a well-known inducer of apoptosis, which is widely used in cell biology and in clinical practice. In this work we report that a pulse of 50 microM etoposide (incubation for only 3h) on HeLa cells causes a sequence of events that leads to abnormal mitotic figures that could be followed either by cell death or, more commonly, by interphase restitution and endocycle. The endocycling polyploid cells enter immediately into mitosis and suffer metaphase blockage with multiple spindle poles, which were generally followed by a direct triggering of apoptosis from metaphase (mitotic catastrophe), or by a new process of endocycling, until surviving cells finally became apoptotic (96 h after the treatment).

Peroxiredoxin V is essential for protection against apoptosis in human lung carcinoma cells

Sensitivity of tumor cells to treatment with anticancer drugs depends on expression and function of antiapoptotic and antioxidant proteins. The goal of our study was to determine the functional role of the novel antioxidant protein Peroxiredoxin V (PrxV), in protection of human lung carcinoma cell lines against apoptosis. Analysis of expression of PrxV in multiple lung carcinoma cell lines revealed a positive correlation between the expression of PrxV and radioresistance in vitro. Clones of the lung carcinoma cells U1810 with down-regulated expression of PrxV, or with its impaired enzymatic function (expression of redox-negative PrxV), demonstrated increased sensitivity to treatment with anticancer drugs etoposide and adriamycin. Pre-treatment of these clones with antioxidant N-acetyl-cysteine did not change their sensitivity to adriamycin, suggesting the involvement of a non-redox activity of PrxV. Expression of the redox-negative PrxV mainly affected the mitochondrial pathway of apoptosis, as assessed by cytochrome c release assay. Impairment of the PrxV enzymatic function also affected transmembrane potential and calcium loading capacity of mitochondria, as well as mitochondrial morphology. Altogether, these findings suggest that PrxV is a multifunctional protein, which is essential for protection against apoptosis induced by anticancer drugs.

Relative timing of redistribution of cytochrome c and Smac/DIABLO from mitochondria during apoptosis assessed by double immunocytochemistry on mammalian cells

Redistribution of cytochrome c and Smac/DIABLO from mitochondria occurs during apoptosis, although the relative timing of their release is not well characterized. Double immunocytochemistry was utilized here to study quantitatively the patterns of release of cytochrome c and Smac/DIABLO from mitochondria in single cells. Human osteosarcoma cells and murine embryonic cortical neurons were analyzed during apoptosis induced by staurosporine. In osteosarcoma cells treated with staurosporine for 24 h, a substantial proportion of cells (36%) released cytochrome c from the mitochondria before Smac/DIABLO. In contrast, these proteins were released mostly concordantly in neurons; only a minority of cells (< or = 15%) released cytochrome c without Smac/DIABLO (or vice versa) from mitochondria. Patterns of release in either cell type were unaltered by addition of the caspase inhibitor, zVAD-fmk. The double immunocytochemistry procedure facilitated clear definition of the temporal release of cytochrome c and Smac/DIABLO from mitochondria in intact apoptotic cells, enabling us to demonstrate for the first time that their mutual redistribution during apoptosis varies between different cell types.

Synthetic Smac peptide enhances the effect of etoposide-induced apoptosis in human glioblastoma cell lines

Smac/DIABLO is a mitochondrial protein released into cytosol during the progression of apoptosis. Smac/DIABLO promotes apoptosis by neutralizing the inhibitory effect of the inhibitor of apoptosis proteins (IAPs) on the processing and activity of the effecter of caspase. Here, we generated synthetic Smac peptide which possesses an IAP-binding domain and Drosophila antennapaedia penetration sequence, and examined whether it enhances the effect of the chemotherapeutic agent etoposide in the human glioblastoma cell line. Cellular uptake of Smac peptide in several glioma cell lines was most prominent at 6-12 h after addition. Caspase activity assay showed that our peptide successfully increased the activity of caspase-3 and caspase-9 in etoposide-induced apoptosis. In addition, Smac peptide increased the amount of cleaved PARP (poly ADP-ribose polymerase), but control peptides did not. Moreover, the addition of z-VAD-fmk, a caspase inhibitor, counterbalanced the effect of Smac peptide. Finally, we demonstrated that Smac peptide could enhance the growth inhibition effect of etoposide compared with control peptides. These results suggest that synthetic Smac peptide may be a new molecular targeting anti-tumor therapy for human glioblastoma.

Expression of apoptosome pathway-related transcripts in non-small cell lung cancer

PURPOSE

Tumour cells killing by cytotoxic therapies largely depends on triggering the intrinsic apoptosome-mediated caspase activation pathway but it had never been evaluated whether the expression of transcripts encoding the core components of apoptosome pathway is altered in non-small cell lung carcinoma (NSCLC).

METHODS

We investigated the expression status of several apoptosome pathway-related transcripts including Apaf-1, procaspase-9, -3, -6, -7 and Smac in tumour and lung tissue samples from 65 surgically treated NSCLC patients and in 10 NSCLC cell lines with using real time RT-PCR.

RESULTS

NSCLC tissues and cell lines showed significantly increased expression of procaspase-9, -3, -6 and Smac mRNAs as compared to the lungs and expression of these transcripts was simultaneously upregulated in a subset of NSCLCs belonging to different histopathological type, grade and stage categories. The expression of procaspase-7 mRNA in NSCLC tissues and cell lines and lungs was not significantly different. By contrast, the expression of Apaf-1 mRNA was frequently downregulated in the tumours as compared to matched lungs. Nevertheless, the examined NSCLC cell lines showed significantly higher expression of Apaf-1 mRNA than the lungs. The expression of Apaf-1, procaspase-9 and -6 mRNAs was higher in lung adenocarcinomas as compared to squamous cell lung carcinomas but the expression levels of the studied apoptosome pathway-related transcripts in the tumours were independent of tumour's grade and stage.

CONCLUSIONS

The results of the present study suggest that there is a subgroup of NSCLCs, which may be intrinsically primed for apoptosis through upregulated expression of transcripts encoding the apoptosome pathway components.

Proliferative stimulus of lung fibroblasts on lung cancer cells is impaired by the receptor for advanced glycation end-products

The receptor for advanced glycation end-products (RAGE) is highly expressed in lung tissue, especially at the site of the alveolar epithelium, but its expression is reduced in lung carcinomas. Because epithelial-mesenchymal interactions are suggested to contribute to cancer progression, we investigated the RAGE-dependent impact of fibroblasts on tumor cell growth. Cocultivation of human lung cancer cells (H358) with lung fibroblasts (WI-38) improved their proliferation in monolayer and spheroid culture models, the number of H358 cells in the S/G2 cell cycle phase increased, and there was less spontaneous cell death. Overexpression of full-length human RAGE reduced the proliferative stimulus of fibroblasts as seen in monolayers (cell number, cell cycle), spheroid cultures (spheroid size), and in a colony-forming assay compared with mock-transfected cells. Comparable results were observed by culturing H358 cells with and without RAGE overexpression in the presence of conditioned medium taken from WI-38 cells, or in response to selected growth factors, such as basic fibroblast growth factor. Moreover, we clearly showed that the fibroblast-induced proliferation correlates with activation of the p42/44 mitogen-activated protein kinase, but not with Akt kinase activation. On the basis of lung cancer as an age-related disease, we additionally proved the impact of senescent WI-38 fibroblasts. Here, we show that senescent fibroblasts improve H358 cell proliferation to the same extent as do presenescent fibroblasts. From our data, we conclude that re-expression of RAGE in lung cancer cells impairs the proliferative stimulus mediated by fibroblasts. Therefore, lung cancer progression may be enhanced by the RAGE downregulation in human lung carcinomas.

Recent advances in understanding the cell death pathways activated by anticancer therapy

Over the past two decades, the role of apoptosis in the cytotoxicity of anticancer drugs has become clear. Apoptosis may occur via a death receptor-dependent (extrinsic) or independent (intrinsic or mitochondrial) pathway. Mitochondria play a central role in cell death in response to DNA damage, and mediate the interaction(s) of various cytoplasmic organelles, including the endoplasmic reticulum, Golgi apparatus, and lysosomes. The mitochondrial pathway of cell death is mediated by Bcl-2 family proteins, a group of antiapoptotic and proapoptotic proteins that regulate the passage of small molecules, such as cytochrome c, Smac/Diablo, and apoptosis-inducing factor, which activates caspase cascades, through the mitochondrial transition pore. In addition, apoptosis can induce autophagic cell death via crosstalk between the two pathways upon treatment with anticancer drugs. The current review focused on recent advances surrounding the mechanism(s) of cell death induced by anticancer agents and discussed potential molecular targets for enhancing the chemotherapeutic effect(s) of anticancer agents.