Alterations in the apoptotic machinery and their potential role in anticancer drug resistance

Oxymatrine reverses multidrug resistance of human hepatocellular carcinoma HepG2/ADM cells

AIM: To investigate whether oxymatrine (OM) reverses the multidrug resistance of hepatocellular carcinoma cell line HepG2/adriamycin (ADM) in vitro and to explore the potential mechanisms involved.

METHODS: MTT assay was used to test the sensitivity of HepG2 cells, HepG2/ADM cells and oxymatrine-treated HepG2/ADM cells to chemotherapeutics and oxymatrine. Flow cytometry was used to detect the apoptosis and the protein levels of p-glycoprotein (P-gp) in HepG2 cells, HepG2/ADM cells and oxymatrine-treated HepG2/ADM cells. Real-time fluorescence quantitative PCR was used to determine the expression of multidrug resistance related gene ATP-binding cassette, sub-family B member 1 (ABCB1) in HepG2/ADM cells and oxymatrine-treated HepG2/ADM cells.

RESULTS: Oxymatrine at concentrations lower than 0.5 mg/mL had no apparent cytotoxic effects on HepG2/ADM cells. HepG2/ADM cells showed cross-resistance to ADM, cisplatin (CDDP), and 5-fluorouracil (5-FU), and the resistance indexes were 27.52, 5.50 and 4.39, respectively. Oxymatrine could partly reverse the resistance of HepG2/ADM cells to ADM, CDDP and 5-FU by 3.68, 2.82 and 2.03 times, respectively. After addition of oxymatrine for 24, 48 and 72 h, the rates of early apoptosis of HepG2/ADM cells were increased gradually compared with the control group (1.77% ± 0.25% vs 0.50% ± 0.10%, 2.53% ± 0.15% vs 0.63% ± 0.06%, 3.83% ± 0.42% vs 0.66% ± 0.06%, P < 0.05 for all). Oxymatrine down-regulated the expression levels of multidrug resistance-related genes ABCB1 and P-gp compared with the control group (21.50% ± 1.08% vs 40.83% ± 0.35%, P < 0.01).

CONCLUSION: Oxymatrine can reverse multidrug resistance of HepG2/ADM cells in vitro possibly via mechanisms related to down-regulation of ABCB1 and P-gp and promotion of cell apoptosis.

Interaction of translationally controlled tumor protein with Apaf-1 is involved in the development of chemoresistance in HeLa cells

Background

Translationally controlled tumor protein (TCTP), alternatively called fortilin, is believed to be involved in the development of the chemoresistance of tumor cells against anticancer drugs such as etoposide, taxol, and oxaliplatin, the underlying mechanisms of which still remain elusive.

Methods

Cell death analysis of TCTP-overexpressing HeLa cells was performed following etoposide treatment to assess the mitochondria-dependent apoptosis. Apoptotic pathway was analyzed through measuring the cleavage of epidermal growth factor receptor (EGFR) and phospholipase C-γ (PLC-γ), caspase activation, mitochondrial membrane perturbation, and cytochrome c release by flow cytometry and western blotting. To clarify the role of TCTP in the inhibition of apoptosome, in vitro apoptosome reconstitution and immunoprecipitation was used. Pull-down assay and silver staining using the variants of Apaf-1 protein was applied to identify the domain that is responsible for its interaction with TCTP.

Results

In the present study, we confirmed that adenoviral overexpression of TCTP protects HeLa cells from cell death induced by cytotoxic drugs such as taxol and etoposide. TCTP antagonized the mitochondria-dependent apoptotic pathway following etoposide treatment, including mitochondrial membrane damage and resultant cytochrome c release, activation of caspase-9, and -3, and eventually, the cleavage of EGFR and PLC-γ. More importantly, TCTP interacts with the caspase recruitment domain (CARD) of Apaf-1 and is incorporated into the heptameric Apaf-1 complex, and that C-terminal cleaved TCTP specifically associates with Apaf-1 of apoptosome in apoptosome-forming condition thereby inhibiting the amplification of caspase cascade.

Conclusions

TCTP protects the cancer cells from etoposide-induced cell death by inhibiting the mitochondria-mediated apoptotic pathway. Interaction of TCTP with Apaf-1 in apoptosome is involved in the molecular mechanism of TCTP-induced chemoresistance. These findings suggest that TCTP may serve as a therapeutic target for chemoresistance in cancer treatment.

Kaempferol promotes apoptosis in human bladder cancer cells by inducing the tumor suppressor, PTEN

Kaempferol (Kae), a natural flavonoid, is widely distributed in fruits and vegetables. Previous studies have identified Kae as a possible cancer preventive and therapeutic agent. We found Kae to exhibit potent antiproliferation and anti-migration effects in human bladder cancer EJ cells. Kaempferol robustly induced apoptosis in EJ cells in a dose-dependent manner, as evidenced by increased cleavage of caspase-3. Furthermore, we found Kae-induced apoptosis in EJ cells to be associated with phosphatase and the tensin homolog deleted on the chromosome 10 (PTEN)/PI3K/Akt pathway. Kae significantly increased PTEN and decreased Akt phosphorylation. Kae-induced apoptosis was partially attenuated in PTEN-knockdown cells. Our findings indicate that Kae could be an alternative medicine for bladder cancer, based on a PTEN activation mechanism.

Catalase abrogates β-lapachone-induced PARP1 hyperactivation-directed programmed necrosis in NQO1-positive breast cancers

Improving patient outcome by personalized therapy involves a thorough understanding of an agent's mechanism of action. β-Lapachone (clinical forms, Arq501/Arq761) has been developed to exploit dramatic cancer-specific elevations in the phase II detoxifying enzyme NAD(P)H:quinone oxidoreductase (NQO1). NQO1 is dramatically elevated in solid cancers, including primary and metastatic [e.g., triple-negative (ER-, PR-, Her2/Neu-)] breast cancers. To define cellular factors that influence the efficacy of β-lapachone using knowledge of its mechanism of action, we confirmed that NQO1 was required for lethality and mediated a futile redox cycle where ∼120 moles of superoxide were formed per mole of β-lapachone in 2 minutes. β-Lapachone induced reactive oxygen species (ROS), stimulated DNA single-strand break-dependent poly(ADP-ribose) polymerase-1 (PARP1) hyperactivation, caused dramatic loss of essential nucleotides (NAD(+)/ATP), and elicited programmed necrosis in breast cancer cells. Although PARP1 hyperactivation and NQO1 expression were major determinants of β-lapachone-induced lethality, alterations in catalase expression, including treatment with exogenous enzyme, caused marked cytoprotection. Thus, catalase is an important resistance factor and highlights H2O2 as an obligate ROS for cell death from this agent. Exogenous superoxide dismutase enhanced catalase-induced cytoprotection. β-Lapachone-induced cell death included apoptosis-inducing factor (AIF) translocation from mitochondria to nuclei, TUNEL+ staining, atypical PARP1 cleavage, and glyceraldehyde 3-phosphate dehydrogenase S-nitrosylation, which were abrogated by catalase. We predict that the ratio of NQO1:catalase activities in breast cancer versus associated normal tissue are likely to be the major determinants affecting the therapeutic window of β-lapachone and other NQO1 bioactivatable drugs.

Activation of executioner caspases is a predictor of progression-free survival in glioblastoma patients: a systems medicine approach

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults. GBM cells are highly resistant to apoptosis induced by antitumor drugs and radiotherapy resulting in cancer progression. We assessed whether a systems medicine approach, analysing the ability of tumor cells to execute apoptosis could be utilized to predict the response of GBM patients to treatment. Concentrations of the key proapoptotic proteins procaspase-3, procaspase-9, Smac and Apaf-1 and the antiapopotic protein XIAP were determined in a panel of GBM cell lines and GBM patient tumor resections. These values were used as input for APOPTO-CELL, a systems biological based mathematical model built to predict cellular susceptibility to undergo caspase activation. The modeling was capable of accurately distinguishing between GBM cells that die or survive in response to treatment with temozolomide in 10 of the 11 lines analysed. Importantly the results obtained using GBM patient samples show that APOPTO-CELL was capable of stratifying patients according to their progression-free survival times and predicted the ability of tumor cells to support caspase activation in 16 of the 21 GBM patients analysed. Calculating the susceptibility to apoptosis execution may be a potent tool in predicting GBM patient therapy responsiveness and may allow for the use of APOPTO-CELL in a clinical setting.

XIAP antisense therapy with AEG 35156 in acute myeloid leukemia

INTRODUCTION

AEG 35156 is an antisense oligonucleotide to X-linked inhibitor of apoptosis protein (XIAP). Overexpression of XIAP is common in acute myeloid leukemia (AML) and other cancers and is thought to cause resistance to cancer therapy. Effective treatment options for patients with relapsed or refractory AML are limited and survival continues to be poor. Targeting resistance mechanisms is expected to improve results in relapsed as well as front-line settings.

AREAS COVERED

Role of XIAP in apoptosis pathways, structure of AEG 35156, mechanism of action, pharmacokinetics and pharmacodynamics, clinical efficacy and review of clinical trials in AML.

EXPERT OPINION

AEG 35156 in combination with standard chemotherapy was generally very well-tolerated and had shown some evidence of anti-leukemic activity in AML. The target knock down was transient and has not always correlated with response. Future studies may be done with variations in dose scheduling and with more emphasis on comprehensive pharmacodynamic studies simultaneously analyzing other inhibitor of apoptosis proteins (IAPs) and various XIAP regulators. Use of small molecule mimetics of second mitochondria derived activator of caspases (Smac) simultaneously targeting other IAPs appears to be an attractive option.

Label-free recognition of drug resistance via impedimetric screening of breast cancer cells

We present a novel study on label-free recognition and distinction of drug resistant breast cancer cells (MCF-7 DOX) from their parental cells (MCF-7 WT) via impedimetric measurements. Drug resistant cells exhibited significant differences in their dielectric properties compared to wild-type cells, exerting much higher extracellular resistance (Rextra ). Immunostaining revealed that MCF-7 DOX cells gained a much denser F-actin network upon acquiring drug resistance indicating that remodeling of actin cytoskeleton is probably the reason behind higher Rextra , providing stronger cell architecture. Moreover, having exposed both cell types to doxorubicin, we were able to distinguish these two phenotypes based on their substantially different drug response. Interestingly, impedimetric measurements identified a concentration-dependent and reversible increase in cell stiffness in the presence of low non-lethal drug doses. Combined with a profound frequency analysis, these findings enabled distinguishing distinct cellular responses during drug exposure within four concentration ranges without using any labeling. Overall, this study highlights the possibility to differentiate drug resistant phenotypes from their parental cells and to assess their drug response by using microelectrodes, offering direct, real-time and noninvasive measurements of cell dependent parameters under drug exposure, hence providing a promising step for personalized medicine applications such as evaluation of the disease progress and optimization of the drug treatment of a patient during chemotherapy.

Liposomes decorated with Apo2L/TRAIL overcome chemoresistance of human hematologic tumor cells

Human Apo2-ligand/TRAIL is a member of the TNF cytokine superfamily capable of inducing apoptosis on tumor cells while sparing normal cells. Besides its antitumor activity, Apo2L/TRAIL is also implicated in immune regulation. Apo2L/TRAIL is stored inside activated T cells in cytoplasmic multivesicular bodies and is physiologically released to the extracellular medium inserted in the internal membrane vesicles, known as exosomes. In this study we have generated artificial lipid vesicles coated with bioactive Apo2L/TRAIL, which resemble natural exosomes, to analyze their apoptosis-inducing ability on cell lines from hematological tumors. We have tethered Apo2L/TRAIL to lipid vesicles by using a novel Ni(2+)-(N-5-amino-1-carboxylpentyl)-iminodiacetic acid, NTA)-containing liposomal system. This lipidic framework (LUVs-Apo2L/TRAIL) greatly improves Apo2L/TRAIL activity, decreasing by around 14-fold the LC50 on the T-cell leukemia Jurkat. This increase in bioactivity correlated with the greater ability of LUVs-Apo2L/TRAIL to induce caspase-3 activation and is probably due to the increase in local concentration of Apo2L/TRAIL, improving its receptor cross-linking efficiency. More important, liposome-bound Apo2L/TRAIL overcame the resistance to soluble recombinant Apo2L/TRAIL exhibited by tumor cell mutants overexpressing Bcl-xL or by a Bax and Bak-defective Jurkat cell mutant (Jurkat-shBak) and are also effective against other hematologic tumor cells. Jurkat-Bcl-xL and Jurkat-shBak cells are resistant to most chemotherapeutic drugs currently used in cancer treatment, and their sensitivity to LUVs-Apo2L/TRAIL could have potential clinical applications.

Effect of Ottoman Viper (Montivipera xanthina (Gray, 1849)) Venom on Various Cancer Cells and on Microorganisms

Cytotoxic and antimicrobial effects of Montivipera xanthina venom against LNCaP, MCF-7, HT-29, Saos-2, Hep3B, Vero cells and antimicrobial activity against selected bacterial and fungal species: Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, E. coli O157H7, Enterococcus faecalis 29212, Enterococcus faecium DSM 13590, Staphylococcus epidermidis ATCC 12228, S. typhimirium CCM 5445, Proteus vulgaris ATCC 6957 and Candida albicans ATCC 10239 were studied for evaluating the potential medical benefit of this snake venom. Cytotoxicity of venom was determined using MTT assay. Snake venom cytotoxicity was expressed as the venom dose that killed 50 % of the cells (IC50). The antimicrobial activity of venom was studied by minimal inhibitory concentration (MIC) and disc diffusion assay. MIC was determined using broth dilution method. The estimated IC50 values of venom varied from 3.8 to 12.7 or from 1.9 to 7.2 μg/ml after treatment with crude venom for 24 or 48 h for LNCaP, MCF-7, HT-29 and Saos-2 cells. There was no observable cytotoxic effect on Hep3B and Vero cells. Venom exhibited the most potent activity against C. albicans (MIC, 7.8 μg/ml and minimal fungicidal concentration, 62.5 μg/ml) and S. aureus (MIC, 31.25 μg/ml). This study is the first report showing the potential of M. xanthina venom as an alternative therapeutic approach due to its cytotoxic and antimicrobial effects.

Manumycin A inhibits triple-negative breast cancer growth through LC3-mediated cytoplasmic vacuolation death

Therapy resistance can be attributed to acquisition of anti-apoptotic mechanisms by the cancer cells. Therefore, developing approaches that trigger non-apoptotic cell death in cancer cells to compensate for apoptosis resistance will help to treat cancer effectively. Triple-negative breast cancers (TNBC) are among the most aggressive and therapy resistant to breast tumors. Here we report that manumycin A (Man A), an inhibitor of farnesyl protein transferase, reduces cancer cell viability through induction of non-apoptotic, non-autophagic cytoplasmic vacuolation death in TNBC cells. Man A persistently induced cytoplasmic vacuolation and cell death through the expression of microtubule-associated protein 1 light chain 3 (LC3) and p62 proteins along with endoplasmic reticulum (ER) stress markers, Bip and CHOP, and accumulation of ubiquitinated proteins. As inhibitors of apoptosis and autophagy failed to block cytoplasmic vacuolation and its associated protein expression or cell death, it appears that these processes are not involved in the death induced by Man A. Ability of thiol antioxidant, NAC in blocking Man A-induced vacuolation, death and its related protein expression suggests that sulfhydryl homeostasis may be the target of Man A. Surprisingly, normal human mammary epithelial cells failed to undergo cytoplasmic vacuolation and cell death, and grew normally in presence of Man A. In conjunction with its in vitro effects, Man A also reduced tumor burden in vivo in xenograft models that showed extensive cytoplasmic vacuoles and condensed nuclei with remarkable increase in the vacuolation-associated protein expression together with increase of p21, p27, PTEN and decrease of pAkt. Interestingly, Man A-mediated upregulation of p21, p27 and PTEN and downregulation of pAkt and tumor growth suppression were also mimicked by LC3 knockdown in MDA-MB-231 cells. Overall, these results suggest novel therapeutic actions by Man A through the induction of non-apoptotic and non-autophagic cytoplasmic vacuolation death by probably affecting ER stress, LC3 and p62 pathways in TNBC but not in normal mammary epithelial cells.

Induction of apoptosis by a potent caffeic acid derivative, caffeic acid undecyl ester, is mediated by mitochondrial damage in NALM-6 human B cell leukemia cells

Caffeic acid esters have various biological activities, and we previously reported that undecyl caffeate (caffeic acid undecyl ester, CAUE), a new caffeic acid derivative, has strong pharmacological activity. The present study investigated the cytotoxicity of both CAUE and its parent compound, caffeic acid phenethyl ester (CAPE), and characterized the mechanisms by which they induce apoptosis in the human B cell leukemia cell line NALM-6. Treatment with CAUE reduced cell survival in NALM-6 cells but had no significant effect on the survival of normal lymphocytes. When assessing the 50% inhibitory concentration (IC(50)) for cytotoxicity, CAUE had 10-fold higher activity than CAPE in NALM-6 cells. CAUE treatment resulted in induction of apoptotic features in NALM-6 cells, including cleaved poly (ADP-ribose) polymerase and activated caspase-3. A caspase inhibitor completely blocked CAUE-induced apoptosis. CAUE treatment resulted in a concentration- and time-dependent decrease in both mitochondrial membrane potential and downregulation of Bcl-2 expression. Moreover, CAUE-induced apoptosis was enhanced in the Bcl-2 knockdown condition induced by small interfering RNA. These data suggest that CAUE-induced apoptosis was mediated via an apoptotic intrinsic pathway including mitochondrial damage and was caspase-dependent. These data also suggest that CAUE is a powerful anti-leukemic agent that acts via induction of apoptosis by mitochondrial damage and selective action in leukemia cells.

Snake venom toxin from Vipera lebetina turanica induces apoptosis of colon cancer cells via upregulation of ROS- and JNK-mediated death receptor expression

BACKGROUND

Abundant research suggested that the cancer cells avoid destruction by the immune system through down-regulation or mutation of death receptors. Therefore, it is very important that finding the agents that increase the death receptors of cancer cells. In this study, we demonstrated that the snake venom toxin from Vipera lebetina turanica induce the apoptosis of colon cancer cells through reactive oxygen species (ROS) and c-Jun N-terminal kinases (JNK) dependent death receptor (DR4 and DR5) expression.

METHODS

We used cell viability assays, DAPI/TUNEL assays, as well as western blot for detection of apoptosis related proteins and DRs to demonstrate that snake venom toxin-induced apoptosis is DR4 and DR5 dependent. We carried out transient siRNA knockdowns of DR4 and DR5 in colon cancer cells.

RESULTS

We showed that snake venom toxin inhibited growth of colon cancer cells through induction of apoptosis. We also showed that the expression of DR4 and DR5 was increased by treatment of snake venom toxin. Moreover, knockdown of DR4 or DR5 reversed the effect of snake venom toxin. Snake venom toxin also induced JNK phosphorylation and ROS generation, however, pretreatment of JNK inhibitor and ROS scavenger reversed the inhibitory effect of snake venom toxin on cancer cell proliferation, and reduced the snake venom toxin-induced upregulation of DR4 and DR5 expression.

CONCLUSIONS

Our results indicated that snake venom toxin could inhibit human colon cancer cell growth, and these effects may be related to ROS and JNK mediated activation of death receptor (DR4 and DR5) signals.

Silencing of X-linked inhibitor of apoptosis decreases resistance to cisplatin and paclitaxel but not gemcitabine in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a highly lethal malignancy that often becomes resistant to chemotherapy. The effect of silencing the X-linked inhibitor of apoptosis gene (XIAP) on resistance to cisplatin, paclitaxel and gemcitabine was studied in the NSCLC cell lines A549 and H460. Transfection of these cells with small interfering RNA (siRNA) for XIAP blocked overexpression of the gene, suppressed cell proliferation, increased apoptosis and increased the cells' sensitivity to cisplatin and paclitaxel by preventing the binding of XIAP to caspase3 and increasing the activity of this enzyme. There was no significant difference in resistance to gemcitabine between XIAP-silenced cells and non-transfected cells. Changes in chemoresistance were independent of the activity of caspase-9. Silencing XIAP with siRNA can decrease chemoresistance in NSCLC and may have a potential role in the treatment of this disease.

Biomarkers of cell death applicable to early clinical trials

The development of biomarkers of cell death to reflect tumor biology and drug-induced response has garnered interest with the development of several classes of drugs aimed at decreasing the cellular threshold for apoptosis and exploiting pre-existing oncogenic stresses. These novel anticancer drugs, directly targeted to the apoptosis regulatory machinery and aimed at abrogating survival signaling pathways, are entering early clinical trials provoking the question of how to monitor their impact on cancer patients. The parallel development of drugs with predictive biomarkers and their incorporation into early clinical trials are anticipated to support the pharmacological audit trail, to speed the development and reduce the attrition rate of novel drugs whose objective is to provoke tumor cell death. Tumor biopsies are an ideal matrix to measure apoptosis, but surrogate less invasive biomarkers such as blood samples and functional imaging are less challenging to acquire clinically. Archetypal and exploratory examples illustrating the importance of biomarkers to drug development are given. This review explores the substantive challenges associated with the validation, deployment, interpretation and utility of biomarkers of cell death and reviews recent advances in their incorporation in preclinical and early clinical trial contexts.

Synergistic anticancer effect of rAd/P53 combined with 5-fluorouracil or iodized oil in the early therapeutic response of human colon cancer in vivo

Exogenous wild-type p53 (wt-p53) tumor suppression increases the sensitivity of tumor cells to radiotherapy and chemotherapy. An iodized oil emulsion was used as a p53 vector for intra-arterial gene delivery to treat hepatic tumors. Whether the chemotherapeutic agent or the iodized oil affects exogenous wt-p53 activity remains poorly understood. In the present study, the early therapeutic response of rAd/p53, combined with 5-fluorouracil (5-FU) or with iodized oil, was observed in a human colon cancer model. Allograft models in 82 nude mice with human colon carcinoma SW480 were divided randomly into four groups and administered with physiologic saline, rAd/p53, rAd/p53+5-FU, and rAd/p53+iodized oil by intratumoral injection. At 24, 48, 72, 120, and 168 h after treatment, p53 expression, the Ki-67 index (KI), and the degree of tumor necrosis were assessed. The p53 expression and tumor necrosis in the therapeutic groups were higher than those in the control group. p53 expression reached its peak at 120 h in the rAd/p53 group, at 72 h in the rAd/p53+5-FU group, and at 48 h in the rAd/p53+iodized oil group. The p53 expression in the rAd/P53+5-FU group and the iodized oil group was significantly higher than those in the rAd/P53 group at 24 and 48 h. The results revealed that tumor necrosis is positively correlated with p53 expression. The KI of the rAd/p53+5-FU group increased significantly at 24 h. 5-FU and iodized oil increase the anticancer effect of rAd/p53, and 5-FU combined with rAd/p53 has a synergistic anticancer effect.

An agonistic antibody to human death receptor 4 induces apoptotic cell death in head and neck cancer cells through mitochondrial ROS generation

The proapoptotic death receptor 4 (DR4), along with DR5, is currently regarded as a promising target for development of agonistic anti-cancer agents due to its tumor-selective apoptosis-inducing ability with no significant cytotoxicity to normal cells. In this study, we examine susceptibility of various head and neck cancer (HNC) cells and mechanism of cell death to an anti-DR4 agonistic monoclonal antibody (mAb), AY4. AY4 as a single agent induced caspase-dependent apoptotic cell death of KB and HN9, but not in SNU899 and FaDu cell lines. AY4 treatment resulted in accumulation of intracellular reactive oxygen species (ROS) generated from mitochondria in AY4-sensitive cells. Blockade of ROS production by N-acetyl-l-cysteine (NAC) resulted in protection of AY4-sensitive cells against AY4-induced apoptosis. ROS generation induced by AY4 treatment triggered down-regulation of anti-apoptotic molecules of Bcl-xL and X-linked inhibitor of apoptosis (XIAP) without affecting the expression levels of DR4, Mcl-1, and survivin. AY4 also inhibited growth of pre-established HN9 tumors in a nude mouse xenograft model and did not show noticeable cytotoxicity in a zebrafish model. Our results provide further insight into the mechanism of DR4-mediated cell death and potential use of AY4 mAb as an anti-cancer therapeutic agent in AY4-sensitive HNC types.

Histone deacetylase inhibitors in the generation of the anti-tumour immune response

Acetylation of lysine residues acts to modify the function of a wide range of proteins. In histones, it affects chromatin structure, which can impact gene transcription, whereas acetylation of transcription factors and heat-shock proteins affect their activity. Deacetylase inhibitors block the dynamic turnover of acetylation resulting in hyperacetylation of target proteins. This can affect a wide range of cellular functions, and in a wide range of tumour cell types promote cytostatic and cytotoxic effects, but has little effect on normal cells. The inhibitors are being used clinically as anti-cancer agents. Although direct effects of the histone deacetylase (HDAC) inhibitors on cancers are beginning to be elucidated, the prospect of concurrent stimulation of the immune response raises hopes for immune attack of the tumour as part of the initial anti-cancer therapy and long-term immune-surveillance of residual or recurrent tumour. This review will examine the evidence for the generation of anti-tumour immunity after treatment of cancers with HDAC inhibitors.

Inhibitor of apoptosis proteins: fascinating biology leads to attractive tumor therapeutic targets

Cell death inhibition is a very successful strategy that cancer cells employ to combat the immune system and various anticancer therapies. Inhibitor of apoptosis (IAP) proteins possess a wide range of biological activities that promote cancer survival and proliferation. One of them, X-chromosome-linked IAP is a direct inhibitor of proapoptotic executioners, caspases. Cellular IAP proteins regulate expression of antiapoptotic molecules and prevent assembly of proapoptotic protein signaling complexes, while survivin regulates cell division. In addition, amplifications, mutations and chromosomal translocations of IAP genes are associated with various malignancies. Several therapeutic strategies have been designed to target IAP proteins, including a small-molecule approach that is based on mimicking the IAP-binding motif of an endogenous IAP antagonist - the second mitochondrial activator of caspases. Other strategies involve antisense nucleotides and transcriptional repression. The main focus of this article is to provide an update on IAP protein biology and perspectives on the development of IAP-targeting therapeutics.

Metabolic approaches to overcoming chemoresistance in ovarian cancer

The poor prognosis in the treatment of ovarian cancer is mainly attributed to chemoresistance. The development of new strategies is urgently necessary to overcome chemoresistance because of the low efficacy of the current standard chemotherapy in ovarian cancer. Metabolic alterations have been suggested to have a crucial role in cancer development. The key metabolic changes in cancer include aerobic glycolysis and macromolecular synthesis, causing antiapoptosis in cancer cells. Therefore, the manipulation of the metabolic derangement could be an effective strategy to overcome chemoresistance in ovarian cancer. In this review, we will discuss metabolic interventions as promising anticancer strategies in ovarian cancer, focusing on the glycolytic, mitochondrial apoptotic, and necrotic pathways. In addition, the role of p53 in relation to metabolic alterations in cancer will be mentioned.

A whole-genome RNAi screen identifies an 8q22 gene cluster that inhibits death receptor-mediated apoptosis

Deregulation of apoptosis is a common occurrence in cancer, for which emerging oncology therapeutic agents designed to engage this pathway are undergoing clinical trials. With the aim of uncovering strategies to activate apoptosis in cancer cells, we used a pooled shRNA screen to interrogate death receptor signaling. This screening approach identified 16 genes that modulate the sensitivity to ligand induced apoptosis, with several genes exhibiting frequent overexpression and/or copy number gain in cancer. Interestingly, two of the top hits, EDD1 and GRHL2, are found 50 kb apart on chromosome 8q22, a region that is frequently amplified in many cancers. By using a series of silencing and overexpression studies, we show that EDD1 and GRHL2 suppress death-receptor expression, and that EDD1 expression is elevated in breast, pancreas, and lung cancer cell lines resistant to death receptor-mediated apoptosis. Supporting the relevance of EDD1 and GRHL2 as therapeutic candidates to engage apoptosis in cancer cells, silencing the expression of either gene sensitizes 8q22-amplified breast cancer cell lines to death receptor induced apoptosis. Our findings highlight a mechanism by which cancer cells may evade apoptosis, and therefore provide insight in the search for new targets and functional biomarkers for this pathway.

High cell surface death receptor expression determines type I versus type II signaling

Previous studies have suggested that there are two signaling pathways leading from ligation of the Fas receptor to induction of apoptosis. Type I signaling involves Fas ligand-induced recruitment of large amounts of FADD (FAS-associated death domain protein) and procaspase 8, leading to direct activation of caspase 3, whereas type II signaling involves Bid-mediated mitochondrial perturbation to amplify a more modest death receptor-initiated signal. The biochemical basis for this dichotomy has previously been unclear. Here we show that type I cells have a longer half-life for Fas message and express higher amounts of cell surface Fas, explaining the increased recruitment of FADD and subsequent signaling. Moreover, we demonstrate that cells with type II Fas signaling (Jurkat or HCT-15) can signal through a type I pathway upon forced receptor overexpression and that shRNA-mediated Fas down-regulation converts cells with type I signaling (A498) to type II signaling. Importantly, the same cells can exhibit type I signaling for Fas and type II signaling for TRAIL (TNF-α-related apoptosis-inducing ligand), indicating that the choice of signaling pathway is related to the specific receptor, not some other cellular feature. Additional experiments revealed that up-regulation of cell surface death receptor 5 levels by treatment with 7-ethyl-10-hydroxy-camptothecin converted TRAIL signaling in HCT116 cells from type II to type I. Collectively, these results suggest that the type I/type II dichotomy reflects differences in cell surface death receptor expression.

Monitoring a nuclear factor-κB signature of drug resistance in multiple myeloma

The emergence of acquired drug resistance results from multiple compensatory mechanisms acting to prevent cell death. Simultaneous monitoring of proteins involved in drug resistance is a major challenge for both elucidation of the underlying biology and development of candidate biomarkers for assessment of personalized cancer therapy. Here, we have utilized an integrated analytical platform based on SDS-PAGE protein fractionation prior to liquid chromatography coupled to multiple reaction monitoring mass spectrometry, a versatile and powerful tool for targeted quantification of proteins in complex matrices, to evaluate a well-characterized model system of melphalan resistance in multiple myeloma (MM). Quantitative assays were developed to measure protein expression related to signaling events and biological processes relevant to melphalan resistance in multiple myeloma, specifically: nuclear factor-κB subunits, members of the Bcl-2 family of apoptosis-regulating proteins, and Fanconi Anemia DNA repair components. SDS-PAGE protein fractionation prior to liquid chromatography coupled to multiple reaction monitoring methods were developed for quantification of these selected target proteins in amounts of material compatible with direct translation to clinical specimens (i.e. less than 50,000 cells). As proof of principle, both relative and absolute quantification were performed on cell line models of MM to compare protein expression before and after drug treatment in naïve cells and in drug resistant cells; these liquid chromatography-multiple reaction monitoring results are compared with existing literature and Western blots. The initial stage of a systems biology platform for examining drug resistance in MM has been implemented in cell line models and has been translated to MM cells isolated from a patient. The ultimate application of this platform could assist in clinical decision-making for individualized patient treatment. Although these specific assays have been developed to monitor MM, these techniques are expected to have broad applicability in cancer and other types of disease.

Effects of lapatinib monotherapy: results of a randomised phase II study in therapy-naive patients with locally advanced squamous cell carcinoma of the head and neck

BACKGROUND

Lapatinib is a dual inhibitor of epidermal growth factor receptor (EGFR) and human EGFR-2 (HER-2) tyrosine kinases. This study investigated the pharmacodynamic and clinical effects of lapatinib in patients with locally advanced squamous cell carcinoma of the head and neck (SCCHN).

METHODS

In total, 107 therapy-naive patients with locally advanced SCCHN were randomised (2 : 1) to receive lapatinib or placebo for 2-6 weeks before chemoradiation therapy (CRT). Endpoints included apoptosis and proliferation rates, clinical response, and toxicity.

RESULTS

Versus placebo, lapatinib monotherapy did not significantly increase apoptosis detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labelling or caspase-3 assays. A statistically significant decrease in proliferation using Ki67 assay was observed (P=0.030). In a subset of 40 patients that received 4 weeks of lapatinib or placebo, objective response rate (ORR) was 17% (n=4/24) vs 0% (n=0/16). In the lapatinib single-agent responders, all had EGFR overexpression, 50% had EGFR amplification, and 50% had HER2 expression by immunohistochemistry (including one patient with HER2 amplification). However, these patients showed variable modulation of apoptosis, proliferation, and phosphorylated EGFR on drug treatment. Following CRT, there was a statistically non-significant difference in ORR between lapatinib (70%) and placebo (53%). There was no clear correlation between changes in apoptosis or proliferation and response to chemoradiation. Mucosal inflammation, asthenia, odynophagia, and dysphagia were the most commonly reported adverse events with lapatinib.

CONCLUSION

Short-term lapatinib monotherapy did not demonstrate apoptotic changes, but provided evidence of clinical activity in locally advanced SCCHN, and warrants further investigation in this disease.

Targeting inhibitor of apoptosis proteins for therapeutic intervention

The inhibitors of apoptosis (IAP) proteins have emerged over the last decade as important targets for therapeutic intervention in human malignancies. Overexpression of IAPs has been implicated in cell survival and resistance against stress-induced apoptosis brought on by radiation and/or chemotherapeutics (currently the standard-of-care in a variety of different cancer diseases). In addition, evasion from death receptor-mediated apoptosis and regulation of NF-κB pathways and cell division have also been associated with IAP proteins. Efforts to target IAP proteins in tumors have focused mainly on designing small molecules that mimic the IAP-binding motif of the endogenous IAP antagonist, second mitochondrial activator of caspases. In addition, several other IAP-targeting strategies, including antisense oligonucleotides and transcriptional repression, have also been initiated, with the hope of providing therapeutic benefit to cancer patients.

Ubiquitylation in apoptosis: a post-translational modification at the edge of life and death

The proper regulation of apoptosis is essential for the survival of multicellular organisms. Furthermore, excessive apoptosis can contribute to neurodegenerative diseases, anaemia and graft rejection, and diminished apoptosis can lead to autoimmune diseases and cancer. It has become clear that the post-translational modification of apoptotic proteins by ubiquitylation regulates key components in cell death signalling cascades. For example, ubiquitin E3 ligases, such as MDM2 (which ubiquitylates p53) and inhibitor of apoptosis (IAP) proteins, and deubiquitinases, such as A20 and ubiquitin-specific protease 9X (USP9X) (which regulate the ubiquitylation and degradation of receptor-interacting protein 1 (RIP1) and myeloid leukaemia cell differentiation 1 (MCL1), respectively), have important roles in apoptosis. Therapeutic agents that target apoptotic regulatory proteins, including those that are part of the ubiquitin-proteasome system, might afford clinical benefits.

The molecular mechanisms of glucocorticoids-mediated neutrophil survival

Neutrophil-dominated inflammation plays an important role in many airway diseases including asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis and cystic fibrosis. In cases of asthma where neutrophil-dominated inflammation is a major contributing factor to the disease, treatment with corticosteroids can be problematic as corticosteroids have been shown to promote neutrophil survival which, in turn, accentuates neutrophilic inflammation. In light of such cases, novel targeted medications must be developed that could control neutrophilic inflammation while still maintaining their antibacterial/anti-fungal properties, thus allowing individuals to maintain effective innate immune responses to invading pathogens. The aim of this review is to describe the molecular mechanisms of neutrophil apoptosis and how these pathways are modulated by glucocorticoids. These new findings are of potential clinical value and provide further insight into treatment of neutrophilic inflammation in lung disease.

The connections between neural crest development and neuroblastoma

Neuroblastoma (NB), the most common extracranial solid tumor in childhood, is an extremely heterogeneous disease both biologically and clinically. Although significant progress has been made in identifying molecular and genetic markers for NB, this disease remains an enigmatic challenge. Since NB is thought to be an embryonal tumor that is derived from precursor cells of the peripheral (sympathetic) nervous system, understanding the development of normal sympathetic nervous system may highlight abnormal events that contribute to NB initiation. Therefore, this review focuses on the development of the peripheral trunk neural crest, the current understanding of how developmental factors may contribute to NB and on recent advances in the identification of important genetic lesions and signaling pathways involved in NB tumorigenesis and metastasis. Finally, we discuss how future advances in identification of molecular alterations in NB may lead to more effective, less toxic therapies, and improve the prognosis for NB patients.

Low-dose valproic acid enhances radiosensitivity of prostate cancer through acetylated p53-dependent modulation of mitochondrial membrane potential and apoptosis

Histone deacetylase inhibitors (HDI) have shown promise as candidate radiosensitizers for many types of cancers, including prostate cancer. However, the mechanisms of action are not well understood. In this study, we show in prostate cancer cells that valproic acid (VPA) at low concentrations has minimal cytotoxic effects yet can significantly increase radiation-induced apoptosis. VPA seems to stabilize a specific acetyl modification (lysine 120) of the p53 tumor suppressor protein, resulting in an increase in its proapoptotic function at the mitochondrial membrane. These effects of VPA are independent of any action of the p53 protein as a transcription factor in the nucleus, since these effects were also observed in native and engineered prostate cancer cells containing mutant forms of p53 protein having no transcription factor activity. Transcription levels of p53-related or Bcl-2 family member proapoptotic proteins were not affected by VPA exposure. The results of this study suggest that, in addition to nuclear-based pathways previously reported, HDIs may also result in radiosensitization at lower concentrations via a specific p53 acetylation and its mitochondrial-based pathway(s).

Presence of ecotoxicologically relevant Pgp and MRP transcripts and proteins in Cyprinid fish

One of the most intriguing defence strategies which aquatic organisms developed through evolution is multixenobiotic resistance (MXR). The key mediators of MXR activity are ATP-binding cassette (ABC) transport proteins. They provide resistance of aquatic organisms by binding xenobiotics and extruding them from cells in an energy-dependent manner. Since Cyprinid fish species are common target in freshwater biomonitoring programs, we have studied the presence of two main MDR/MXR efflux transporters P-glycoprotein (Pgp, Abcb1) and MRP-like protein(s) (Abcc) in the liver of five Cyprinid species: common carp, European chub, sneep, barbel, and silver prussian carp. Their presence was evaluated on the mRNA and protein level. Various pairs of primers were designed to clone homologous fragments of MXR-related genes. At the protein level, we used Western blotting with specific monoclonal antibodies against human Pgp (Abcb1, Ab C219), MRP1 (Abcc1; Ab MRPm6) or MRP2 (Abcc2; Ab M2I-4). Transcripts of both key types of MXR transporters were identified in all species examined and here we provide the phylogenetic analysis of new partial sequences. Immunochemical determinations with mammalian antibodies failed to identify the presence of MRP(s), but Pgp expression was found in all five Cyprinid species. These results support that MXR is a defence system mediated by both Pgp and MRP types of ABC transport proteins.

Identification and characterization of a novel agonistic anti-DR4 human monoclonal antibody

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its functional receptors, DR4 and DR5, have been established as promising targets for cancer treatment. Therapeutics targeting TRAIL and its receptors are not only effective in killing many types of tumors, but they also synergize with traditional therapies and show efficacy against tumors that are otherwise resistant to conventional treatments. We describe here the identification and characterization of two human monoclonal antibodies, m921 and m922, that are specific for human DR4. Both antibodies competed with TRAIL for binding to DR4, but only m921 recognized cell surface-associated DR4 and inhibited the growth of ST486 cells. This antibody may have potential for further development as a candidate therapeutic and research tool.

Utilization of cytokeratin-based biomarkers for pharmacodynamic studies

Cytokeratin (CK)18 is a useful serum biomarker for the determination of cell death of epithelial-derived tumors (carcinomas). ELISAs are available for caspase-cleaved CK18 (M30) released from apoptotic cells, or total CK18 (M65) released by cells undergoing cell death by any cause. These assays have been demonstrated to have prognostic or predictive utility in various types of carcinomas. Encouraging data have been reported by different investigators with regard to the potential use of CK18 as a serum efficacy biomarker for monitoring therapy efficiency in carcinoma patients. The ratio of caspase-cleaved to total CK18 can be determined conveniently in serum or plasma using commercially available ELISA kits (M30-Apoptosense and M65 ELISA, Peviva AB, Bromma, Sweden). M30:M65 ratios potentially provide information as to whether tumor cells undergo apoptosis or necrosis. However, as discussed in this review, M30:M65 ratios should be interpreted with caution and, preferably, only be applied to samples that contain significant levels of CK18. We conclude that M30 and M65 biomarkers provide both quantitative and qualitative information on carcinoma cell death.

Tumor suppressor XIAP-Associated factor 1 (XAF1) cooperates with tumor necrosis factor-related apoptosis-inducing ligand to suppress colon cancer growth and trigger tumor regression

BACKGROUND

XIAP-associated factor 1 (XAF1) antagonizes the anticaspase activity of XIAP (X-linked inhibitor of apoptosis) and functions as a tumor suppressor in colon cancer. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known as a potential anticancer agent. In this study, the synergistic effect of XAF1 and TRAIL on colon cancer growth was investigated.

METHODS

Adeno-XAF1 virus was generated and purified. Cell apoptosis was detected by flow-cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Protein expression of the different genes was determined by Western blot analysis. Tumorigenesis and tumor growth were assessed in subcutaneous nude mouse xenograft experiments.

RESULTS

Stable overexpression of XAF1-sensitized colon cancer cells to TRAIL-induced apoptosis significantly increased the activity of caspase 3, 7, 8, and 9; released cytochrome c; and down-regulated XIAP, survivin, and c-IAP-2. The restoration of XAF1 expression mediated by adenovirus (adeno-XAF1) directly induced apoptosis, and synergized TRAIL-induced apoptosis in colon cancer cells. Ex vivo transduction of adeno-XAF1 suppressed colon cancer formation in vivo. Furthermore, adeno-XAF1 treatment of mice significantly inhibited tumor growth, strongly enhanced TRAIL-induced apoptosis and antitumor activity in colon cancer xenograft models in vivo, and markedly prolonged the survival. Notably, the combined treatment with adeno-XAF1 and TRAIL completely eradicated the established tumors without detectable toxicity in normal tissue.

CONCLUSIONS

The combined restoration of XAF1 expression and TRAIL treatment may be a potent strategy for colon cancer therapy.

High temperature requirement A3 (HtrA3) promotes etoposide- and cisplatin-induced cytotoxicity in lung cancer cell lines

Lung cancer is the leading cause of cancer-related deaths worldwide. Here we show for the first time that HtrA3 is a mitochondrial stress-response factor that promotes cytotoxicity to etoposide and cisplatin in lung cancer cell lines. Exogenous expression of wild type HtrA3 domain variants significantly attenuated cell survival with etoposide and cisplatin treatment in lung cancer cell lines H157 and A549 compared with expression of protease inactive mutants (S305A) or vector control. Conversely, HtrA3 suppression promoted cell survival with etoposide and cisplatin treatment in lung cancer cell lines Hop62 and HCC827. Survival was attenuated by re-expression of wild type HtrA3 variants during treatment but not by protease inactive mutants or vector control. HtrA3 also co-fractionated and co-localized with mitochondrial markers with both endogenous and exogenous expression in normal lung and lung cancer cell lines but was translocated from mitochondria following etoposide treatment. Moreover, HtrA3 translocation from mitochondria correlated with an increase in cell death that was attenuated by either HtrA3 suppression or Bcl-2 overexpression. Taken together, these results suggest that HtrA3 may be a previously uncharacterized mitochondrial cell death effector whose serine protease function may be crucial to modulating etoposide- and cisplatin-induced cytotoxicity in lung cancer cell lines.

Noninvasive molecular imaging of apoptosis in vivo using a modified firefly luciferase substrate, Z-DEVD-aminoluciferin

Apoptosis is a highly regulated process of programmed cell death essential for normal physiology. Dysregulation of apoptosis contributes to the development and progression of various diseases, including cancer, neurodegenerative disorders, and chronic heart failure. Quantitative noninvasive imaging of apoptosis in preclinical models would allow for dynamic longitudinal screening of compounds and facilitates a more rapid determination of therapeutic efficacy. In this study, we report the in vivo characterization of Z-DEVD-aminoluciferin, a modified firefly luciferase substrate that in apoptotic cells is cleaved by caspase-3 to liberate aminoluciferin, which can be consumed by luciferase to generate a luminescent signal. In two oncology models, namely SKOV3-luc and MDA-MB-231-luc-LN, at 24, 48, and 72 h after treatment with docetaxel, animals were injected with Z-DEVD-aminoluciferin and bioluminescent images were acquired. Significantly more light was detected at 24 (P<0.05), 48 (P<0.01), and 72 h (P<0.01) in the docetaxel-treated group compared with the vehicle-treated group, with caspase-3 activation at these time points confirmed using immunohistochemistry. Importantly, whereas significant differences between groups were detected as early as 24 h after treatment by molecular imaging, caliper measurements were unable to detect a difference for 4-5 additional days. Taken together, these data show that in vivo imaging of apoptosis using Z-DEVD-aminoluciferin could provide a sensitive and rapid method for early detection of drug efficacy, which could potentially be used by numerous therapeutic programs.

DcR1 expression in endometrial carcinomas

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family, which mediates apoptosis by the extrinsic pathway. Up-regulation of decoy receptors, DcR1 and DcR2, may result in diminished binding of TRAIL to their functional receptors. DcR1 expression was assessed in normal endometrial tissue (NE) and endometrial carcinoma (EC) samples by immunohistochemistry (IHC) and quantitative real-time polymerase chain reaction (PCR). IHC was performed in two tissue microarrays; one composed of 80 samples of NE and a second one constructed from paraffin-embedded blocks of 62 EC. For quantitative real-time RT-PCR analysis, RNA was obtained from 19 NE and 28 EC samples using Trizol. mRNA expression of DcR1 was assessed with Taqman-based assays in an Abi-Prism 700 SDS. Results were correlated with stage, histological type, and grade. By IHC, cytoplasmic expression of DcR1 was frequently seen in NE (79.6%) and varied according to the menstrual cycle. Positive DcR1 immunostaining was also detected in EC (98.1% of the cases) without any specific statistical association with histological type, grade, and stage. By quantitative real-time PCR, all NE had similar levels of DcR1expression (0.8-1.7 RQ), which were considered the basal levels of DcR1 expression in NE. Increased DcR1 expression (> or =5-fold higher than the basal levels) was detected in 13 of 28 EC (46.4%). High DcR1 expression levels were found in ECs of different stages: IA, four of 12 (33%); IB, two of four (50%); IC, four of six (66%); and IIA and IIB three of six (50%). Results suggest that DcR1 expression occurs in a subset of EC and may contribute to resistance to TRAIL-induced apoptosis.

X chromosome-linked inhibitor of apoptosis regulates cell death induction by proapoptotic receptor agonists

Proapoptotic receptor agonists cause cellular demise through the activation of the extrinsic and intrinsic apoptotic pathways. Inhibitor of apoptosis (IAP) proteins block apoptosis induced by diverse stimuli. Here, we demonstrate that IAP antagonists in combination with Fas ligand (FasL) or the death receptor 5 (DR5) agonist antibody synergistically stimulate death in cancer cells and inhibit tumor growth. Single-agent activity of IAP antagonists relies on tumor necrosis factor-alpha signaling. By contrast, blockade of tumor necrosis factor-alpha does not affect the synergistic activity of IAP antagonists with FasL or DR5 agonist antibody. In most cancer cells, proapoptotic receptor agonist-induced cell death depends on amplifying the apoptotic signal via caspase-8-mediated activation of Bid and subsequent activation of the caspase-9-dependent mitochondrial apoptotic pathway. In the investigated cancer cell lines, induction of apoptosis by FasL or DR5 agonist antibody can be inhibited by knockdown of Bid. However, knockdown of X chromosome-linked IAP (XIAP) or antagonism of XIAP allows FasL or DR5 agonist antibody to induce activation of effector caspases efficiently without the need for mitochondrial amplification of the apoptotic signal and thus rescues the effect of Bid knockdown in these cells.

Blockade of MGMT expression by O6 benzyl guanine leads to inhibition of pancreatic cancer growth and induction of apoptosis

PURPOSE

We sought to determine whether administration of a MGMT blocker, O(6)-benzyl guanine (O(6)BG), at an optimal biological dose alone or in combination with gemcitabine inhibits human pancreatic cancer cell growth.

EXPERIMENTAL DESIGN

Human pancreatic cancer L3.6pl and PANC1 cells were treated with O(6)BG, either alone or in combination with gemcitabine, and the therapeutic efficacy and biological activity of these drug combinations were investigated.

RESULTS

O(6)BG sensitized pancreatic cancer cells to gemcitabine. Protein and mRNA expression of MGMT, cyclin B1, cyclin B2, cyclin A, and ki-67 were significantly decreased in the presence of O(6)BG. In sharp contrast, protein expression and mRNA message of p21(cip1) were significantly increased. Interestingly, O(6)BG increases p53-mediated p21(cip1) transcriptional activity and suppresses cyclin B1. In addition, our results indicate that p53 is recruited to p21 promoter. Furthermore, an increase in p21(cip1) and a decrease in cyclin transcription are p53 dependent. The volume of pancreatic tumors was reduced by 27% in mice treated with gemcitabine alone, by 47% in those treated with O(6)BG alone, and by 65% in those mice given combination. Immunohistochemical analysis showed that O(6)BG inhibited expression of MGMT and cyclins, and increased expression of p21(cip1). Furthermore, there was a significant decrease in tumor cell proliferation and an increase in tumor cell apoptosis.

CONCLUSIONS

Collectively, our results show that decreased MGMT expression is correlated with p53 activation, and significantly reduced primary pancreatic tumor growth. These findings suggest that O(6)BG either alone or in combination with gemcitabine may provide a novel and effective approach for the treatment of human pancreatic cancer.

Restoration of XAF1 expression induces apoptosis and inhibits tumor growth in gastric cancer

XAF1 (XIAP-associated factor 1) is a novel XIAP binding protein that can antagonize XIAP and sensitize cells to other cell death triggers. Our previous results have shown that aberrant hypermethylation of the CpG sites in XAF1 promoter is strongly associated with lower expression of XAF1 in gastric cancers. In our study, we investigated the effect of restoration of XAF1 expression on growth of gastric cancers. We found that the restoration of XAF1 expression suppressed anchorage-dependent and -independent growth and increased sensitivity to TRAIL and drug-induced apoptosis. Stable cell clones expressing XAF1 exhibited delayed tumor initiation in nude mice. Restoration of XAF1 expression mediated by adenovirus vector greatly increased apoptosis in gastric cancer cell lines in a time- and dose-dependent manner and sensitized cancer cells to TRAIL and drugs-induced apoptosis. Adeno-XAF1 transduction induced cell cycle G2/M arrest and upregulated the expression of p21 and downregulated the expression of cyclin B1 and cdc2. Notably, adeno-XAF1 treatment significantly inhibited tumor growth, strongly enhanced the antitumor activity of TRAIL in a gastric cancer xenograft model in vivo, and significantly prolonged the survival time of animals bearing tumor xenografts. Complete eradication of established tumors was achieved on combined treatment with adeno-XAF1 and TRAIL. Our results document that the restoration of XAF1 inhibits gastric tumorigenesis and tumor growth and that XAF1 is a promising candidate for cancer gene therapy.

Bullatacin triggered ABCB1-overexpressing cell apoptosis via the mitochondrial-dependent pathway

This paper was to explore bullatacin-mediated multidrug-resistant cell apoptosis at extremely low concentration. To investigate its precise mechanisms, the pathway of cell apoptosis induced by bullatacin was examined. Bullatacin causes an upregulation of ROS and a downregulation of ΔΨ_m in a concentration-dependent manner in ABCB1-overexpressing KBv200 cells. In addition, cleavers of caspase-9, caspase-3, and PARP were observed following the release of cytochrome c from mitochondria after bullatacin treatment. However, neither cleavage of caspase-8 nor change of expression level of bcl-2, bax and Fas was observed by the same treatment. Pretreating KBv200 cells with N-acetylcysteine, an antioxidant modulator, resulted in a significant reduction of ROS generation and cell apoptosis induced by bullatacin. Bullatacin-induced apoptosis was antagonized by z-LEHD-fmk, a caspase-9 inhibitor, but not by z-IETD-fmk, a caspase-8 inhibitor. These implied that apoptosis of KBv200 cells induced by bullatacin was associated with the mitochondria-dependent pathway that was limited to activation of apical caspase-9.

MLH1 expression sensitises ovarian cancer cells to cell death mediated by XIAP inhibition

BACKGROUND

The X-linked inhibitor of apoptosis protein (XIAP), an endogenous apoptosis suppressor, can determine the level of caspase accumulation and the resultant response to apoptosis-inducing agents such as cisplatin in epithelial ovarian cancer (EOC). In addition, the mismatch repair protein, hMLH1, has been linked to DNA damage-induced apoptosis by cisplatin by both p53-dependent and -independent mechanisms.

METHODS

In this study, hMLH1 expression was correlated with clinical response to platinum drugs and survival in advanced stage (III-IV) EOC patients. We then investigated whether MLH1 loss was a determinant in anti-apoptosis response to cisplatin mediated by XIAP in isogenic and established EOC cell lines with differential p53 status.

RESULTS

The percentage of cells undergoing cisplatin-induced cell killing was higher in MLH1-proficient cells than in MLH1-defective cells. In addition, the presence of wild-type hMLH1 or hMLH1 re-expression significantly increased sensitivity to 6-thioguanine, a MMR-dependent agent. Cell-death response to 6-thioguanine and cisplatin was associated with significant proteolysis of MLH1, with XIAP destabilisation and increased caspase-3 activity. The siRNA-mediated inhibition of XIAP increased MLH1 proteolysis and cell death in MLH1-proficient cells but not in MLH1-defective cells.

CONCLUSION

These data suggest that XIAP inhibitors may prove to be an effective means of sensitising EOC to MLH1-dependent apoptosis.

Antagonism of c-IAP and XIAP proteins is required for efficient induction of cell death by small-molecule IAP antagonists

The inhibitor of apoptosis (IAP) proteins are critical regulators of cancer cell survival, which makes them attractive targets for therapeutic intervention in cancers. Herein, we describe the structure-based design of IAP antagonists with high affinities and selectivity (>2000-fold) for c-IAP1 over XIAP and their functional characterization as activators of apoptosis in tumor cells. Although capable of inducing cell death and preventing clonogenic survival, c-IAP-selective antagonists are significantly less potent in promoting apoptosis when compared to pan-selective compounds. However, both pan-IAP- and c-IAP-selective antagonists stimulate c-IAP1 and c-IAP2 degradation and activation of NF-kappaB pathways with comparable potencies. Therefore, although compounds that specifically target c-IAP1 and c-IAP2 are capable of inducing apoptosis, antagonism of the c-IAP proteins and XIAP is required for efficient induction of cancer cell death by IAP antagonists.

A novel role for MAP1 LC3 in nonautophagic cytoplasmic vacuolation death of cancer cells

Thiol reactive cyclopentenone prostaglandin, 15-deoxy-Δ^{12, 14}-Prostaglandin J₂, induced a novel, non-apoptotic and Map1 LC3 dependent but non-autophagic form of cell death in colon, breast and prostate cancer cell lines, characterized by extensive cytoplasmic vacuolation with dilatation of endoplasmic reticulum. Disruption of sulfhydryl homeostasis, which resulted in ER stress, accumulation of ubiquitinated proteins and subsequent ER dilation, contributed to PPARγ independent cell death by 15d-PGJ2. Absence of intracellular organelles in these vacuoles, shown by Electron Microscopy and unique fragmentation of Lamin B, suggested this form of cell death to be different from autophagy and apoptosis. Cell death induced by 15d-PGJ2 is prevented by cycloheximide and actinomycin D, suggesting a requirement of new protein synthesis for death with cytoplasmic vacuolation. Here, we report for the first time that upregulation and processing of autophagy marker LC3 is an important event in non-autophagic cytoplasmic vacuolation and cell death. Notably, knockdown of LC3 conferred significant protection against 15d-PGJ2 induced cytoplasmic vacuolation and cell death suggesting a novel role of LC3 in a death process other than autophagy.

Epigallocatechin-gallate modulates chemotherapy-induced apoptosis in human cholangiocarcinoma cells

BACKGROUND

Green tea polyphenols are chemopreventive in several cancer models but their use as adjunctive therapeutic agents for cancer is unknown.

AIMS

Cholangiocarcinomas respond poorly to chemotherapeutic agents and our aims were to assess the utility of green tea polyphenols as adjuncts to chemotherapy for cholangiocarcinoma.

MATERIALS AND METHODS

We assessed the effect of purified green tea catechins on chemotherapy-induced apoptosis in KMCH, CC-LP-1 and Mz-ChA-1 human cholangiocarcinoma cells, and on chemosensitivity of Mz-ChA-1 cell xenografts in nude mice.

RESULTS

Epigallocatechin-gallate (EGCG), but not the structurally related catechin epigallocatechin, sensitized cells to apoptosis induced by gemcitabine (GEM), mitomycin C or 5-fluorouracil in vitro. Mitochondrial membrane depolarization, cytosolic cytochrome c expression and apoptosis were increased in cells incubated with EGCG and GEM compared with either agent alone. Furthermore, EGCG decreased in vivo growth and increased the sensitivity to GEM of Mz-ChA-1 cell xenografts in nude mice.

CONCLUSIONS

The green tea polyphenol EGCG sensitizes human cholangiocarcinoma cells to chemotherapy-induced apoptosis and warrants evaluation as an adjunct to chemotherapy for the treatment of human cholangiocarcinoma.