17-Allylamino-17-demethoxygeldanamycin overcomes TRAIL resistance in colon cancer cell lines

Combination effects of capecitabine, irinotecan and 17-AAG on colorectal cancer cell line (HT-29)

Objevtive

Evasion of apoptosis is a major feature of cancer cells, therefore designing treatment strategies to target apoptotic pathways seems effective. In this study, we investigate the effect of 17-AAG (17-allylaminogeldanamycin) alone and in double and triple combination with capecitabine (Cap) and irinotecan (IR) on HT-29 colon cancer cell line apoptosis.

Methods

Capase-3, 8, 9, p53 and NF-κB genes expression were analyzed by Real-time PCR. DNA laddering assay was performed to confirm Real-time PCR results.

Results

Our results showed that all single treatment groups elevated expression of caspase-3, 8, and 9 significantly and IR/Cap was the only double combination group that could upregulate caspase-8 and -9. NF-κB was down-regulated in single treatment and IR/Cap double combination group, significantly. 17-AAG mono-treatment and IR/Cap and Cap/17-AAG double combination group significantly upregulated p53 gene expression.

Conclusion

Our findings showed proapoptotic effects of 17-AAG alone and in combination with Cap and IR. These findings propose 17-AAG in combination with routine chemotherapy, as a new protocol for colorectal cancer combination therapy.

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Targeted therapy of apoptosis is the main effective way against of cancer cells.

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17-AAG alone and in combination with Cap and IR can regulate the pro-apoptotic factors.

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Combination therapy has more effective than single therapy.

DCZ5248, a novel dual inhibitor of Hsp90 and autophagy, exerts antitumor activity against colon cancer

Hsp90 is a potential therapeutic target for tumor, as it maintains the stability of a variety of proteins related to tumor development and progression. Autophagy is a self-degradation process to maintain cellular homeostasis and autophagy inhibitors can suppress tumor growth. In this study, we identified DCZ5248, a triazine derivative, was a dual inhibitor of both Hsp90 and late-autophagy with potent antitumor activity against colon cancer cells in vitro and in vivo. We showed that DCZ5248 (0.1-10 μM) induced dose-dependent degradation of Hsp90 client proteins (AKT, CDK4, CDK6 and RAF-1) in HCT 116 colon cancer cells through a proteasome-dependent pathway. Meanwhile, DCZ5248 (0.3 μM) induced cytoplasmic vacuole formation, LC3 II conversion, p62 protein upregulation, and inhibited autophagy at the late stage in the colon cancer cell lines tested. We further revealed that the inhibition of autophagy was achieved by impairing lysosomal functions through induction of lysosomal acidification and attenuation of lysosomal cathepsin activity. The modulation of autophagy by DCZ5248 was independent of Hsp90 inhibition as the autophagy inhibition was not blocked by Hsp90 knockdown. Importantly, inhibition of both Hsp90 function and autophagy by DCZ5248 induced G1-phase cell cycle arrest, apoptosis, and exerted potent antitumor activity against colon cancer cells both in vitro and in vivo. These findings demonstrate that DCZ5248 is a novel dual inhibitor of Hsp90 and autophagy with potential for colon cancer therapy.

Hsp90 Inhibitor SNX-2112 Enhances TRAIL-Induced Apoptosis of Human Cervical Cancer Cells via the ROS-Mediated JNK-p53-Autophagy-DR5 Pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent cancer cell apoptosis-inducing factor that can induce apoptosis in a variety of cancer cells. However, resistance to TRAIL in cancer cells is a huge obstacle in creating effective TRAIL-targeted clinical therapies. Thus, agents that can either enhance the effect of TRAIL or overcome its resistance are needed. In this study, we combined TRAIL with SNX-2112, an Hsp90 inhibitor we previously developed, to explore the effect and mechanism that SNX-2112 enhanced TRAIL-induced apoptosis in cervical cancer cells. Our results showed that SNX-2112 markedly enhanced TRAIL-induced cytotoxicity in HeLa cells, and this combination was found to be synergistic. Additionally, we found that SNX-2112 sensitized TRAIL-mediated apoptosis caspase-dependently in TRAIL-resistant HeLa cells. Mechanismly, SNX-2112 downregulated antiapoptosis proteins, including Bcl-2, Bcl-XL, and FLIP, promoted the accumulation of reactive oxygen species (ROS), and increased the expression levels of p-JNK and p53. ROS scavenger NAC rescued SNX-2112/TRAIL-induced apoptosis and suppressed SNX-2112-induced p-JNK and p53. Moreover, SNX-2112 induced the upregulation of death-receptor DR5 in HeLa cells. The silencing of DR5 by siRNA significantly decreased cell apoptosis by the combined effect of SNX-2112 and TRAIL. In addition, SNX-2112 inhibited the Akt/mTOR signaling pathway and induced autophagy in HeLa cells. The blockage of autophagy by bafilomycin A1 or Atg7 siRNA abolished SNX-2112-induced upregulation of DR5. Meanwhile, ROS scavenger NAC, JNK inhibitor SP600125, and p53 inhibitor PFTα were used to verify that autophagy-mediated upregulation of DR5 was regulated by the SNX-2112-stimulated activation of the ROS-JNK-p53 signaling pathway. Thus, the combination of SNX-2112 and TRAIL may provide a novel strategy for the treatment of human cervical cancer by overcoming cellular mechanisms of apoptosis resistance.

Spotlight on 17-AAG as an Hsp90 inhibitor for molecular targeted cancer treatment

Hsp90 is a ubiquitous chaperone with important roles in the organization and maturation of client proteins that are involved in the progression and survival of cancer cells. Multiple oncogenic pathways can be affected by inhibition of Hsp90 function through degradation of its client proteins. That makes Hsp90 a therapeutic target for cancer treatment. 17-allylamino-17-demethoxy-geldanamycin (17-AAG) is a potent Hsp90 inhibitor that binds to Hsp90 and inhibits its chaperoning function, which results in the degradation of Hsp90's client proteins. There have been several preclinical studies of 17-AAG as a single agent or in combination with other anticancer agents for a wide range of human cancers. Data from various phases of clinical trials show that 17-AAG can be given safely at biologically active dosages with mild toxicity. Even though 17-AAG has suitable pharmacological potency, its low water solubility and high hepatotoxicity could significantly restrict its clinical use. Nanomaterials-based drug delivery carriers may overcome these drawbacks. In this paper, we review preclinical and clinical research on 17-AAG as a single agent and in combination with other anticancer agents. In addition, we highlight the potential of using nanocarriers and nanocombination therapy to improve therapeutic effects of 17-AAG.

c-FLIP is a target of the E3 ligase deltex1 in gastric cancer

The ubiquitin E3 ligase DELTEX1 (DTX1) is specifically downregulated in gastric cancer tissues, and expression of DTX1 is linked to better prognoses and survival in gastric cancer. Cellular FLICE inhibitory protein (c-FLIP) is known for its pivotal role in the resistance of cancer cells to death receptor-induced cell death. Here, we show that DTX1 is an E3 ligase for c-FLIP in gastric cancer cells. DTX1 promoted c-FLIP downregulation. Overexpression of DTX1 sensitized gastric cancer cells to TRAIL-induced apoptosis, whereas DTX1-knockdown attenuated apoptosis induction. DTX1 binds c-FLIP_L and directs it into the endosome-lysosomal pathway for proteasome-independent degradation. Moreover, induction of DTX1 in AGS cells by geldanamycin conferred susceptibility of those cells to TRAIL-induced apoptosis. Our results reveal a tumor-suppressive role for DTX1 and suggest a new approach to increasing TRAIL efficacy by raising DTX1 levels in gastric cancer therapy. DTX1 also enhanced c-FLIP degradation and FasL-induced and TRAIL-induced apoptosis in T cells, suggesting that DTX1 constitutes one of the physiological mechanisms regulating c-FLIP stability.

Polymeric mechanical amplifiers of immune cytokine-mediated apoptosis

Physical forces affect tumour growth, progression and metastasis. Here, we develop polymeric mechanical amplifiers that exploit in vitro and in vivo physical forces to increase immune cytokine-mediated tumour cell apoptosis. Mechanical amplifiers, consisting of biodegradable polymeric particles tethered to the tumour cell surface via polyethylene glycol linkers, increase the apoptotic effect of an immune cytokine on tumour cells under fluid shear exposure by as much as 50% compared with treatment under static conditions. We show that targeted polymeric particles delivered to tumour cells in vivo amplify the apoptotic effect of a subsequent treatment of immune cytokine, reduce circulating tumour cells in blood and overall tumour cell burden by over 90% and reduce solid tumour growth in combination with the antioxidant resveratrol. The work introduces a potentially new application for a broad range of micro- and nanoparticles to maximize receptor-mediated signalling and function in the presence of physical forces.

Fluid shear stress plays a critical role in receptor-mediated signalling and has been shown to sensitize cancer cells to apoptosis. Here, Mitchell et al. introduce polymer micro- and nanoparticles tethered to tumour cells to amplify fluid shear stress effects, and find that they can enhance immune cytokine-mediated apoptosis of tumour cells in vitro and in vivo.

Effects of 17-AAG on the cell cycle and apoptosis of H446 cells and the associated mechanisms

As a heat shock protein 90 inhibitor, 17-allyl-amino-17-demethoxygeldanamycin (17-AAG) has been studied in numerous types of cancer, however the effects of 17-AAG on apoptosis and the cell cycle of H446 cells remain unclear. In the current study, the MTT method was used to evaluate the inhibitory effects of different durations and doses of 17-AAG treatment on the proliferation of H446 cells. The cells were stained with Annexin-fluorescein isothiocyanate/propidium iodide and measured by flow cytometry, and the gene and protein expression levels of signal transducer and activator of transcription 3 (STAT3), survivin, cyclin D1, cyt-C, caspase 9 and caspase 3 were determined by reverse transcription-quantitative polymerase chain reaction and western blot analysis. The results indicated that with treatment with 1.25–20 mg/l 17-AAG for 24 and 48 h, significant inhibition of H446 cell proliferation was observed in a time- and dose-dependent manner. With treatment of 3.125, 6.25 and 12.5 mg/l 17-AAG for 48 h, significant apoptosis and cell cycle arrest was observed. The results indicated that the gene and protein expression levels of STAT3, survivin and cyclin D1 were downregulated, and cyt-C, caspase 9 and caspase 3 were upregulated by 17-AAG in a dose-dependent manner when the cells were treated with 3.125 and 6.25 mg/l 17-AAG for 48 h. The results indicated that 17-AAG is able to inhibit the cell proliferation, induce apoptosis and G₂/M arrest and downregulate the gene and protein expression levels of STAT3, survivin and cyclin D1, and upregulate gene and protein expression of cyt-C, caspase 9, caspase 3.

Hsp90: A New Player in DNA Repair?

Heat shock protein 90 (Hsp90) is an evolutionary conserved molecular chaperone that, together with Hsp70 and co-chaperones makes up the Hsp90 chaperone machinery, stabilizing and activating more than 200 proteins, involved in protein homeostasis (i.e., proteostasis), transcriptional regulation, chromatin remodeling, and DNA repair. Cells respond to DNA damage by activating complex DNA damage response (DDR) pathways that include: (i) cell cycle arrest; (ii) transcriptional and post-translational activation of a subset of genes, including those associated with DNA repair; and (iii) triggering of programmed cell death. The efficacy of the DDR pathways is influenced by the nuclear levels of DNA repair proteins, which are regulated by balancing between protein synthesis and degradation as well as by nuclear import and export. The inability to respond properly to either DNA damage or to DNA repair leads to genetic instability, which in turn may enhance the rate of cancer development. Multiple components of the DNA double strand breaks repair machinery, including BRCA1, BRCA2, CHK1, DNA-PKcs, FANCA, and the MRE11/RAD50/NBN complex, have been described to be client proteins of Hsp90, which acts as a regulator of the diverse DDR pathways. Inhibition of Hsp90 actions leads to the altered localization and stabilization of DDR proteins after DNA damage and may represent a cell-specific and tumor-selective radiosensibilizer. Here, the role of Hsp90-dependent molecular mechanisms involved in cancer onset and in the maintenance of the genome integrity is discussed and highlighted.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Hsp90 inhibitor as a sensitizer of cancer cells to different therapies (review)

Hsp90 is a molecular chaperone that maintains the structural and functional integrity of various client proteins involved in signaling and many other functions of cancer cells. The natural inhibitors, ansamycins influence the Hsp90 chaperone function by preventing its binding to client proteins and resulting in their proteasomal degradation. N- and C-terminal inhibitors of Hsp90 and their analogues are widely tested as potential anticancer agents in vitro, in vivo as well as in clinical trials. It seems that Hsp90 competitive inhibitors target different tumor types at nanomolar concentrations and might have therapeutic benefit. On the contrary, some Hsp90 inhibitors increased toxicity and resistance of cancer cells induced by heat shock response, and through the interaction of survival signals, that occured as side effects of treatments, could be very effectively limited via combination of therapies. The aim of our review was to collect the data from experimental and clinical trials where Hsp90 inhibitor was combined with other therapies in order to prevent resistance as well as to potentiate the cytotoxic and/or antiproliferative effects.

Combining trail with PI3 kinase or HSP90 inhibitors enhances apoptosis in colorectal cancer cells via suppression of survival signaling

TRAIL has been shown to induce apoptosis in cancer cells, but in some cases they fail to respond to this ligand. We explored the ability of representative phosphatidylinositol-3-kinase (PI3 Kinase)/mTOR and HSP90 inhibitors to overcome TRAIL resistance by increasing apoptosis in colorectal cancer models. We determined the sensitivity of 27 human colorectal cancer and 2 non-transformed colon epithelial cell lines to TRAIL treatment. A subset of the cancer cell lines with a range of responses to TRAIL was selected from the panel for treatment with TRAIL combined with the PI3 Kinase/mTOR inhibitor PI-103 or the HSP90 inhibitor 17-AAG (tanespimycin). Two TRAIL-resistant cell lines were selected for in vivo combination studies with TRAIL and 17-AAG. We found that 13 colorectal cancer cell lines and the 2 non-transformed colon epithelial cell lines were resistant to TRAIL. We demonstrated that co-treatment of TRAIL and PI-103 or 17-AAG was synergistic or additive and significantly enhanced apoptosis in colorectal cancer cells. This was associated with decreased expression or activity of survival protein biomarkers such as ERBB2, AKT, IKKα and XIAP. In contrast, the effect of the combination treatments in non-transformed colon cells was minimal. We show here for the first time that co-treatment in vivo with TRAIL and 17-AAG in two TRAIL-resistant human colorectal cancer xenograft models resulted in significantly greater tumor growth inhibition compared to single treatments. We propose that combining TRAIL with PI3 Kinase/mTOR or HSP90 inhibitors has therapeutic potential in the treatment of TRAIL-resistant colorectal cancers.

The TRAIL of oncogenes to apoptosis

Despite the significant advances in clinical research, surgical resection, radiotherapy and chemotherapy are still used as the primary method for cancer treatment. As compared to conventional therapies that often induce systemic toxicity and eventually contribute to tumor resistance, the TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent that selectively triggers apoptosis in various cancer cells by interacting with its proapoptotic receptors DR4 and KILLER/DR5, while sparing the normal surrounding tissue. The intensive studies of TRAIL signaling pathways over the past decade have provided clues for understanding the molecular mechanisms of TRAIL-induced apoptosis in carcinogenesis and identified an array of therapeutic responses elicited by TRAIL and its receptor agonists. Analysis of its activity at the molecular level has shown that TRAIL improves survival either as monotherapies or combinatorial therapies with other mediators of apoptosis or anticancer chemotherapy. Combinatorial treatments amplify the activities of anticancer agents and widen the therapeutic window by overcoming tumor resistance to apoptosis and driving cancer cells to self-destruction. Although TRAIL sensitivity varies widely depending on the cell type, nontransformed cells are largely resistant to death mediated by TRAIL Death Receptors (DRs). Genetic alterations in cancer can contribute in tumor progression and often play an important role in evasion of apoptosis by tumor cells. Remarkably, RAS, MYC and HER2 oncogenes have been shown to sensitise tumor cells to TRAIL induced cell death. Here, we summarise the cross-talk of oncogenic and apoptotic pathways and how they can be exploited toward efficient combinatorial therapeutic protocols.

Novel antineoplastics targeting genetic changes in colorectal cancer

Cytotoxic chemotherapy remains the mainstay of the medical -management of colorectal cancer (CRC). Research over the last two decades has led to a molecular understanding of the oncogenic mechanisms involved in CRC and has contributed to the rational development of antineoplastics that target these mechanisms. During carcinogenesis, genetic changes often occur in molecules that play key functional roles in cancer such as cell proliferation, angiogenesis, apoptosis, cell death and immune-mediated destruction of cancer cells. Here, we review novel antineoplastics that are approved or in development for CRC that target molecules associated with genetic aberrations in CRC. Some of these targeted antineoplastics have proven effective against other solid tumors and hold promise in treating CRC whereas others are now routinely used in combination with cytotoxic agents. This article reviews antineoplastics that target genetic changes in CRC, their antitumor mechanisms, and their stage of development.

Heat shock protein 90α (HSP90α), a substrate and chaperone of DNA-PK necessary for the apoptotic response

The "apoptotic ring" is characterized by the phosphorylation of histone H2AX at serine 139 (γ-H2AX) by DNA-dependent protein kinase (DNA-PK). The γ-H2AX apoptotic ring differs from the nuclear foci patterns observed in response to DNA-damaging agents. It contains phosphorylated DNA damage response proteins including activated Chk2, activated ATM, and activated DNA-PK itself but lacks MDC1 and 53BP1, which are required to initiate DNA repair. Because DNA-PK can phosphorylate heat shock protein 90α (HSP90α) in biochemical assays, we investigated whether HSP90α is involved in the apoptotic ring. Here we show that HSP90α is phosphorylated by DNA-PK on threonines 5 and 7 early during apoptosis and that both phosphorylated HSP90α and DNA-PK colocalize in the apoptotic ring. We also show that DNA-PK is a client of HSP90α and that HSP90α is required for full DNA-PK activation, γ-H2AX formation, DNA fragmentation, and apoptotic body formation. In contrast, HSP90 inhibition by geldanamycin markedly enhances TRAIL-induced DNA-PK and H2AX activation. Together, our results reveal that HSP90α is a substrate and chaperone of DNA-PK in the apoptotic response. The response of phosphorylated HSP90α to TRAIL and its localization to the γ-H2AX ring represent epigenetic features of apoptosis that offer insights for studying and monitoring nuclear apoptosis.

Molecular targets of TRAIL-sensitizing agents in colorectal cancer

Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily, interacts with its functional death receptors (DRs) and induces apoptosis in a wide range of cancer cell types. Therefore, TRAIL has been considered as an attractive agent for cancer therapy. However, many cancers are resistant to TRAIL-based therapies mainly due to the reduced expression of DRs and/or up-regulation of TRAIL pathway-related anti-apoptotic proteins. Compounds that revert such defects restore the sensitivity of cancer cells to TRAIL, suggesting that combined therapies could help manage neoplastic patients. In this article, we will focus on the TRAIL-sensitizing effects of natural products and synthetic compounds in colorectal cancer (CRC) cells and discuss the molecular mechanisms by which such agents enhance the response of CRC cells to TRAIL.

Hsp90 inhibitors and drug resistance in cancer: the potential benefits of combination therapies of Hsp90 inhibitors and other anti-cancer drugs

Hsp90 is a chaperone protein that interacts with client proteins that are known to be in the cell cycle, signaling and chromatin-remodeling pathways. Hsp90 inhibitors act additively or synergistically with many other drugs in the treatment of both solid tumors and leukemias in murine tumor models and humans. Hsp90 inhibitors potentiate the actions of anti-cancer drugs that target Hsp90 client proteins, including trastuzumab (Herceptin™) which targets Her2/Erb2B, as Hsp90 inhibition elicits the drug effects in cancer cell lines that are otherwise resistant to the drug. A phase II study of the Hsp90 inhibitor 17-AAG and trastuzumab showed that this combination therapy has anticancer activity in patients with HER2-positive metastatic breast cancer progressing on trastuzumab. In this review, we discuss the results of Hsp90 inhibitors in combination with trastuzumab and other cancer drugs. We also discuss recent results from yeast focused on the genetics of drug resistance when Hsp90 is inhibited and the implications that this might have in understanding the effects of genetic variation in treating cancer in humans.

Selective BRAFV600E inhibitor PLX4720, requires TRAIL assistance to overcome oncogenic PIK3CA resistance

Documented sensitivity of melanoma cells to PLX4720, a selective BRAFV600E inhibitor, is based on the presence of mutant BRAF(V600E) alone, while wt-BRAF or mutated KRAS result in cell proliferation. In colon cancer appearance of oncogenic alterations is complex , since BRAF, like KRAS mutations, tend to co-exist with those in PIK3CA and mutated PI3K has been shown to interfere with the successful application of MEK inhibitors. When PLX4720 was used to treat colon tumours, results were not encouraging and herein we attempt to understand the cause of this recorded resistance and discover rational therapeutic combinations to resensitize oncogene driven tumours to apoptosis. Treatment of two genetically different BRAF(V600E) mutant colon cancer cell lines with PLX4720 conferred complete resistance to cell death. Even though p-MAPK/ ERK kinase (MEK) suppression was achieved, TRAIL, an apoptosis inducing agent, was used synergistically in order to achieve cell death by apoptosis in RKO(BRAFV600E/PIK3CAH1047) cells. In contrast, for the same level of apoptosis in HT29(BRAFV600E/PIK3CAP449T) cells, TRAIL was combined with 17-AAG, an Hsp90 inhibitor. For cells where PLX4720 was completely ineffective, 17-AAG was alternatively used to target mutant BRAF(V600E). TRAIL dependence on the constitutive activation of BRAF(V600E) is emphasised through the overexpression of BRAF(V600E) in the permissive genetic background of colon adenocarcinoma Caco-2 cells. Pharmacological suppression of the PI3K pathway further enhances the synergistic effect between TRAIL and PLX4720 in RKO cells, indicating the presence of PIK3CA(MT) as the inhibitory factor. Another rational combination includes 17-AAG synergism with TRAIL in a BRAF(V600E) mutant dependent manner to commit cells to apoptosis, through DR5 and the amplification of the apoptotic pathway. We have successfully utilised combinations of two chemically unrelated BRAF(V600E) inhibitors in combination with TRAIL in a BRAF(V600E) mutated background and provided insight for new anti-cancer strategies where the activated PI3KCA mutation oncogene should be suppressed.

Prognostic significance of TRAIL signaling molecules in stage II and III colorectal cancer

PURPOSE

We previously found that cellular FLICE-inhibitory protein (c-FLIP), caspase 8, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2 (DR5) are major regulators of cell viability and chemotherapy-induced apoptosis in colorectal cancer. In this study, we determined the prognostic significance of c-FLIP, caspase 8, TRAIL and DR5 expression in tissues from patients with stage II and III colorectal cancer.

EXPERIMENTAL DESIGN

Tissue microarrays were constructed from matched normal and tumor tissue derived from patients (n = 253) enrolled in a phase III trial of adjuvant 5-fluorouracil-based chemotherapy versus postoperative observation alone. TRAIL, DR5, caspase 8, and c-FLIP expression levels were determined by immunohistochemistry.

RESULTS

Colorectal tumors displayed significantly higher expression levels of c-FLIP (P < 0.001), caspase 8 (P = 0.01), and DR5 (P < 0.001), but lower levels of TRAIL (P < 0.001) compared with matched normal tissue. In univariate analysis, higher TRAIL expression in the tumor was associated with worse overall survival (P = 0.026), with a trend to decreased relapse-free survival (RFS; P = 0.06), and higher tumor c-FLIP expression was associated with a significantly decreased RFS (P = 0.015). Using multivariate predictive modeling for RFS in all patients and including all biomarkers, age, treatment, and stage, we found that the model was significant when the mean tumor c-FLIP expression score and disease stage were included (P < 0.001). As regards overall survival, the overall model was predictive when both TRAIL expression and disease stage were included (P < 0.001).

CONCLUSIONS

High c-FLIP and TRAIL expression may be independent adverse prognostic markers in stage II and III colorectal cancer and might identify patients most at risk of relapse.

Inhibition of constitutive and cxc-chemokine-induced NF-kappaB activity potentiates ansamycin-based HSP90-inhibitor cytotoxicity in castrate-resistant prostate cancer cells

Background:

We determined how CXC-chemokine signalling and necrosis factor-κB (NF-κB) activity affected heat-shock protein 90 (Hsp90) inhibitor (geldanamycin (GA) and 17-allylamino-demethoxygeldanamycin (17-AAG)) cytotoxicity in castrate-resistant prostate cancer (CRPC).

Methods:

Geldanamycin and 17-AAG toxicity, together with the CXCR2 antagonist AZ10397767 or NF-κB inhibitor BAY11-7082, was assessed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay in two CRPC lines, DU145 and PC3. Flow cytometry quantified apoptotic or necrosis profiles. Necrosis factor-κB activity was determined by luciferase readouts or indirectly by quantitative PCR and ELISA-based determination of CXCL8 expression.

Results:

Geldanamycin and 17-AAG reduced PC3 and DU145 cell viability, although PC3 cells were less sensitive. Addition of AZ10397767 increased GA (e.g., PC3 IC₂₀: from 1.67±0.4 to 0.18±0.2 nM) and 17-AAG (PC3 IC₂₀: 43.7±7.8 to 0.64±1.8 nM) potency in PC3 but not DU145 cells. Similarly, BAY11-7082 increased the potency of 17-AAG in PC3 but not in DU145 cells, correlating with the elevated constitutive NF-κB activity in PC3 cells. AZ10397767 increased 17-AAG-induced apoptosis and necrosis and decreased NF-κB activity/CXCL8 expression in 17-AAG-treated PC3 cells.

Conclusion:

Ansamycin cytotoxicity is enhanced by inhibiting NF-κB activity and/or CXC-chemokine signalling in CRPC cells. Detecting and/or inhibiting NF-κB activity may aid the selection and treatment response of CRPC patients to Hsp90 inhibitors.

S-Adenosylmethionine and methylthioadenosine inhibit cellular FLICE inhibitory protein expression and induce apoptosis in colon cancer cells

S-Adenosylmethionine (SAMe) and its metabolite 5'-methylthioadenosine (MTA) inhibit mitogen-induced proliferative response in liver and colon cancer cells. SAMe and MTA are also proapoptotic in liver cancer cells by selectively inducing Bcl-x(S) expression. The aims of this work were to assess whether these agents are proapoptotic in colon cancer cells, and if so, to elucidate the molecular mechanisms. We found that both SAMe and MTA are proapoptotic in HT-29 and RKO cells in a dose- and time-dependent manner. Gene microarray uncovered down-regulation of cellular FLICE inhibitory protein (cFLIP). SAMe and MTA treatment led to a decrease in the mRNA and protein levels of both the long and short cFLIP isoforms. This required de novo RNA synthesis and was associated with activation of procaspase-8, Bid cleavage, and release of cytochrome c from the mitochondria. Inhibiting caspase 8 activity or overexpression of cFLIP protected against apoptosis, whereas supplementing with polyamines did not. SAMe and MTA treatment sensitized RKO cells to tumor necrosis factor alpha-related apoptosis-inducing ligand-induced apoptosis. Although SAMe and MTA are proapoptotic in colon cancer cells, they have no toxic effects in NCM460 cells, a normal colon epithelial cell line. In contrast to liver cancer cells, SAMe and MTA had no effect on Bcl-x(S) expression in colon cancer cells. In conclusion, SAMe and MTA are proapoptotic in colon cancer cells but not normal colon epithelial cells. One molecular mechanism identified is the inhibition of cFLIP expression. SAMe and MTA may be attractive agents in the chemoprevention and treatment of colon cancer.

TRAIL receptor signalling and modulation: Are we on the right TRAIL?

Tumour necrosis factor-related apoptosis-inducing ligand or Apo2 ligand (TRAIL/Apo2L) is a member of the tumour necrosis factor (TNF) superfamily of cytokines that induces apoptosis upon binding to its death domain-containing transmembrane receptors, death receptors 4 and 5 (DR4, DR5). Importantly, TRAIL preferentially induces apoptosis in cancer cells while exhibiting little or no toxicity in normal cells. To date, research has focused on the mechanism of apoptosis induced by TRAIL and the processes involved in the development of TRAIL resistance. TRAIL-resistant tumours can be re-sensitized to TRAIL by a combination of TRAIL with chemotherapeutics or irradiation. Studies suggest that in many cancer cells only one of the two death-inducing TRAIL receptors is functional. These findings as well as the aim to avoid decoy receptor-mediated neutralization of TRAIL led to the development of receptor-specific TRAIL variants and agonistic antibodies. These molecules are predicted to be more potent than native TRAIL in vivo and may be suitable for targeted treatment of particular tumours. This review focuses on the current status of TRAIL receptor-targeting for cancer therapy, the apoptotic signalling pathway induced by TRAIL receptors, the prognostic implications of TRAIL receptor expression and modulation of TRAIL sensitivity of tumour cells by combination therapies. The mechanisms of TRAIL resistance and the potential measures that can be taken to overcome them are also addressed. Finally, the status of clinical trials of recombinant TRAIL and DR4-/DR5-specific agonistic antibodies as well as the pre-clinical studies of receptor-selective TRAIL variants is discussed including the obstacles facing the use of these molecules as anti-cancer therapeutics.

Lupulone, a hop bitter acid, activates different death pathways involving apoptotic TRAIL-receptors, in human colon tumor cells and in their derived metastatic cells

Our study aimed to compare death signalling pathways triggered by lupulone in TRAIL-sensitive human colon cancer cells (SW480) and in their derived TRAIL-resistant metastatic cells (SW620). Lupulone (40 microg/ml) up-regulated expression of TRAIL DR4/DR5 death receptors at the cell surface of both cell lines, even in the absence of exogenous TRAIL ligand. Cell death induced by lupulone was inhibited in SW480 and SW620 cells exposed to blocking anti-DR4/DR5 antibodies. In SW480 cells, lupulone triggered cell death through a cross-talk between TRAIL-DR4/DR5 and the mitochondrial (intrinsic) pathways involving caspase-8 activation and Bid protein cleavage. As a consequence mitochondrial cytochrome c was released into the cytosol and activation of caspases-9 and -3 was observed. In the metastatic SW620 cells, lupulone restored the sensibility of these cells to TRAIL ligand and activated the extrinsic apoptotic pathway via DR4/DR5 death receptors and the involvement of the caspase-8/caspase-3 cascade. The demonstration that lupulone is able to activate TRAIL-death signalling pathways even in TRAIL resistant cancer cells highlights the potential of this natural compound for cancer prevention and therapy.

17-AAG sensitized malignant glioma cells to death-receptor mediated apoptosis

17-AAG is a selective HSP90-inhibitor that exhibited therapeutic activity in cancer. In this study three glioblastoma cell lines (U87, LN229 and U251) were treated with 17-AAG, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or the combination of both. Treatment with subtoxic doses of 17-AAG in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces rapid apoptosis in TRAIL-resistant glioma cells, suggesting that this combined treatment may offer an attractive strategy for treating gliomas. 17-AAG treatment down-regulated survivin through proteasomal degradation. In addition, over-expression of survivin attenuated cytotoxicity induced by the combination of 17-AAG and TRAIL. In summary, survivin is a key regulator of TRAIL-17-AAG mediated cell death in malignant glioma.

Heat shock proteins in animal neoplasms and human tumours--a comparison

Heat shock proteins (HSPs) are implicated in all phases of cancer from proliferation, impaired apoptosis and sustained angiogenesis to invasion and metastasis. The presence of abnormal HSP levels in several human tumours suggests that these proteins could be used as diagnostic and/or prognostic markers, whilst the direct correlation between HSP expression and drug resistance in neoplastic tissues means they could also be used to predict cancer response to specific treatment. HSPs have also been successfully targeted in clinical trials modifying their expression or chaperone activity. Preliminary studies in veterinary medicine have also demonstrated the presence of altered HSP expression in neoplasms, and the study of carcinogenesis and the role of HSPs in animal models will surely be an additional source of information for clinical cancer research.

Death receptor-4 (DR4) expression is regulated by transcription factor NF-kappaB in response to etoposide treatment

Tumour necrosis factor related apoptosis inducing ligand (TRAIL) binds to death receptor 4 (DR4) activating the apoptotic signalling pathway. DNA damaging agents (genotoxins) such as etoposide increase DR4 expression and when combined with TRAIL induce a synergistic apoptotic response. The mechanism for up-regulation of DR4 expression following genotoxin treatment is not well understood. Herein, we determined that transcription factor NF-kappaB plays a role in genotoxin induced DR4 expression. Increased expression of DR4 following etoposide treatment is blocked by inhibition of the NF-kappaB pathway. Moreover, expression of the p65 subunit of NF-kappaB is sufficient to increase DR4 protein levels. Indeed, knockdown of p65 by RNA interference blocked etoposide up-regulation of DR4. We further identified a functional NF-kappaB binding site located in the DR4 promoter. Mutation of this site abrogates the induction of luciferase activity after p65 over-expression. Furthermore, electromobility shift assays and chromatin immunoprecipitaton suggest that NF-kappaB binds to this site upon etoposide treatment. MEK kinase 1 (MEKK1) is a serine threonine kinase that is activated following etoposide treatment and activates NF-kappaB. Expression of the kinase inactive MEKK1 (MEKK1-KM) abrogates the up-regulation of DR4 after etoposide treatment. Taken together, NF-kappaB plays a role in up-regulation of DR4 following etoposide treatment.

TRAIL in cancer therapy: present and future challenges

Since its identification in 1995, TNF-related apoptosis-inducing ligand (TRAIL) has sparked growing interest in oncology due to its reported ability to selectively trigger cancer cell death. In contrast to other members of the TNF superfamily, TRAIL administration in vivo is safe. The relative absence of toxic side effects of this naturally occurring cytokine, in addition to its antitumoural properties, has led to its preclinical evaluation. However, despite intensive investigations, little is known in regards to the mechanisms underlying TRAIL selectivity or efficiency. An appropriate understanding of its physiological relevance, and of the mechanisms controlling cancer cells escape from TRAIL-induced cell death, will be required to optimally use the cytokine in clinics. The present review focuses on recent advances in the understanding of TRAIL signal transduction and discusses the existing and future challenges of TRAIL-based cancer therapy development.

Sensitization of Mesothelioma Cells to Tumor Necrosis Factor–Related Apoptosis–Inducing Ligand–Induced Apoptosis by Heat Stress via the Inhibition of the 3-Phosphoinositide-Dependent Kinase 1/Akt Pathway

Heat stress may enhance the effect of apoptosis-inducing agents in resistant tumor cells. One such agent is the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which has attracted intense interest for its ability to induce apoptosis in tumors without affecting nonmalignant cells. We therefore tested whether heat stress potentiates TRAIL-induced apoptosis in mesothelioma cells, its cell type being resistant to TRAIL alone. We found that heat stress enhanced the apoptosis caused by TRAIL but not by chemotherapy. To explain this potentiation, we found that heat stress decreased Akt phosphorylation via the dissociation of heat shock protein 90 (Hsp90) from its client protein 3-phosphoinositide-dependent kinase 1 (PDK-1), a major Akt kinase. The role of Hsp90 and the Akt pathway was confirmed by showing that inhibitors of Hsp90 and the phosphatidyilinositol-3 kinase/Akt pathway reproduced the effect of heat stress on TRAIL-induced apoptosis and that the effect of inhibiting Hsp90 on TRAIL-induced apoptosis could be overcome by activating the Akt pathway with a constitutively active construct of the Akt kinase PDK-1. The effect of heat stress involved multiple steps of the apoptotic machinery. Heat stress potentiated the death receptor pathway, as shown by an increase in TRAIL-induced caspase 8 cleavage. Nonetheless, knockdown of Bid, the main intermediary molecule from the death receptor pathway to the mitochondria, inhibited the effect of heat stress, showing that mitochondrial amplification was required for potentiation by heat stress. In summary, these results support the novel concept that heat stress inhibits the Akt pathway by dissociating PDK-1 from its chaperone Hsp90, leading to potentiation of TRAIL-induced apoptosis in resistant malignant cells.

Mithramycin A sensitizes cancer cells to TRAIL-mediated apoptosis by down-regulation of XIAP gene promoter through Sp1 sites

Mithramycin A is a DNA-binding antitumor agent, which has been clinically used in the therapies of several types of cancer and Paget's disease. In this study, we investigated the combined effect of mithramycin A and tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) on apoptosis of cancer cells. In Caki renal cancer cells, which are resistant to TRAIL, cotreatment with subtoxic doses of mithramycin A and TRAIL resulted in a marked increase in apoptosis. This combined treatment was also cytotoxic to Caki cells overexpressing Bcl-2 but not to normal mesengial cells. Moreover, apoptosis by the combined treatment with mithramycin A and TRAIL was dramatically induced in various cancer cell types, thus offering an attractive strategy for safely treating malignant tumors. Mithramycin A-stimulated TRAIL-induced apoptosis was blocked by pretreatment with the broad caspase inhibitor zVAD-fmk or Crm-A overexpression, showing its dependence on caspases. We found that mithramycin A selectively down-regulated XIAP protein levels in various cancer cells. Luciferase reporter assay and the chromatin immunoprecipitation assay using the XIAP promoter constructs show that mithramycin A down-regulates the transcription of XIAP gene through inhibition of Sp1 binding to its promoter. Although XIAP overexpression significantly attenuated apoptosis induced by mithramycin A plus TRAIL, suppression of XIAP expression by transfection with its small interfering RNA prominently enhanced TRAIL-induced apoptosis. We present here for the first time that mithramycin A-induced suppression of XIAP transcription plays a critical role in the recovery of TRAIL sensitivity in various cancer cells.