Phenethyl isothiocyanate sensitizes glioma cells to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is a promising antitumor therapy. However, many cancer cells, including malignant glioma cells, tend to be resistant to TRAIL, highlighting the need for strategies to overcome TRAIL resistance. Here we show that in combination with phenethyl isothiocyanate (PEITC), exposure to TRAIL induced apoptosis in TRAIL-resistant glioma cells. Subtoxic concentrations of PEITC significantly potentiated TRAIL-induced cytotoxicity and apoptosis in glioma cells. PEITC dramatically upregulated DR5 receptor expression but had no effects on DR4 receptor. PEITC enhances TRAIL-induced apoptosis through the downregulation of cell survival proteins and the upregulation of DR5 receptors through actions on the ROS-induced-p53.     

Lithium enhances TRAIL-induced apoptosis in human lung carcinoma A549 cells

Non-small cell lung cancer (NSCLC) A549 cells are resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Therefore, combination therapy using sensitizing agents to overcome TRAIL resistance may provide new strategies for treatment of NSCLC. Here, we investigated whether lithium chloride (LiCl), a drug for mental illness, could sensitize A549 cells to TRAIL-induced apoptosis. We observed that LiCl significantly enhanced A549 cells apoptosis through up-regulation of death receptors DR4 and DR5 and activation of caspase cascades. In addition, G2/M arrest induced by LiCl also contributed to TRAIL-induced apoptosis. Concomitantly, LiCl strongly inhibited the activity of c-Jun N-terminal kinases (JNKs), and the inhibition of JNKs by SP600125 also induced G2/M arrest and augmented cell death caused by TRAIL or TRAIL plus LiCl. However, glycogen synthase kinase-3β (GSK3β) inhibition was not involved in TRAIL sensitization induced by LiCl. Collectively, these findings indicated that LiCl sensitized A549 cells to TRAIL-induced apoptosis through caspases-dependent apoptotic pathway via death receptors signaling and G2/M arrest induced by inhibition of JNK activation, but independent of GSK3β.     

Rosiglitazone promotes tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by reactive oxygen species-mediated up-regulation of death receptor 5 and down-regulation of c-FLIP

Death receptor 5 (DR5/TRAIL-R2) is an apoptosis-inducing membrane receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). In this study, we show that rosiglitazone sensitizes human renal cancer cells to TRAIL-mediated apoptosis, but not normal human mesangial cells. Furthermore, because rosiglitazone-enhanced TRAIL-mediated apoptosis is induced in various types of cancer cells but is not interrupted by Bcl-2 overexpression, this combinatory treatment may provide an attractive strategy for cancer treatment. We found that treatment with rosiglitazone significantly induces DR5 expression at both its mRNA and its protein levels, accompanying the generation of reactive oxygen species (ROS). Both treatment with DR5/Fc chimeric protein and silencing of DR5 expression using small interfering RNAs attenuated rosiglitazone plus TRAIL-induced apoptosis, showing the critical role of DR5 in this cell death. Pretreatment with GSH significantly inhibited rosiglitazone-induced DR5 up-regulation and the cell death induced by the combined treatment with rosiglitazone and TRAIL, suggesting that ROS mediate rosiglitazone-induced DR5 up-regulation, contributing to TRAIL-mediated apoptosis. However, both DR5 up-regulation and sensitization of TRAIL-mediated apoptosis induced by rosiglitazone are likely PPARgamma-independent, because a dominant-negative mutant of PPARgamma and a potent PPARgamma inhibitor, GW9662, failed to block DR5 induction and apoptosis. Interestingly, we also found that rosiglitazone treatment induced down-regulation of cellular FLICE-inhibitory protein (c-FLIPs), and ectopic expression of c-FLIPs attenuated rosiglitazone plus TRAIL-mediated apoptosis, demonstrating the involvement of c-FLIPs in this apoptosis. Taken together, the results of this study demonstrate that rosiglitazone enhances TRAIL-induced apoptosis in various cancer cells by ROS-mediated DR5 up-regulation and down-regulation of c-FLIPs.     

Gossypol Induces Death Receptor-5 through Activation of the ROS-ERK-CHOP Pathway and Sensitizes Colon Cancer Cells to TRAIL

Development of resistance to TRAIL, an apoptosis-inducing cytokine, is one of the major problems in its development for cancer treatment. Thus, pharmacological agents that are safe and can sensitize the tumor cells to TRAIL are urgently needed. We investigated whether gossypol, a BH3 mimetic that is currently in the clinic, can potentiate TRAIL-induced apoptosis. Intracellular esterase activity, sub-G₁ cell cycle arrest, and caspase-8, -9, and -3 activity assays revealed that gossypol potentiated TRAIL-induced apoptosis in human colon cancer cells. Gossypol also down-regulated cell survival proteins (Bcl-x_L, Bcl-2, survivin, XIAP, and cFLIP) and dramatically up-regulated TRAIL death receptor (DR)-5 expression but had no effect on DR4 and decoy receptors. Gossypol-induced receptor induction was not cell type-specific, as DR5 induction was observed in other cell types. Deletion of DR5 by siRNA significantly reduced the apoptosis induced by TRAIL and gossypol. Gossypol induction of the death receptor required the induction of CHOP, and thus, gene silencing of CHOP abolished gossypol-induced DR5 expression and associated potentiation of apoptosis. ERK1/2 (but not p38 MAPK or JNK) activation was also required for gossypol-induced TRAIL receptor induction; gene silencing of ERK abolished both DR5 induction and potentiation of apoptosis by TRAIL. We also found that reactive oxygen species produced by gossypol treatment was critical for TRAIL receptor induction and apoptosis potentiation. Overall, our results show that gossypol enhances TRAIL-induced apoptosis through the down-regulation of cell survival proteins and the up-regulation of TRAIL death receptors through the ROS-ERK-CHOP-DR5 pathway.     

Acrolein sensitizes human renal cancer Caki cells to TRAIL-induced apoptosis via ROS-mediated up-regulation of death receptor-5 (DR5) and down-regulation of Bcl-2

TRAIL resistance in many cancer cells is one of the major problems in TRAIL-based cancer therapy. Thus, the agents that can sensitize the tumor cells to TRAIL-mediated apoptosis are strictly needed for the improvement of anti-cancer effect of TRAIL. Acrolein is a byproduct of lipid peroxidation, which has been involved in pulmonary, cardiac and neurodegenerative diseases. We investigated whether acrolein, an α,β-unsaturated aldehyde, can potentiate TRAIL-induced apoptosis in human renal cancer cells. The combined treatment with acrolein and TRAIL significantly induced apoptosis, and stimulated of caspase-3 activity, DNA fragmentation, and cleavage of PARP. We found that acrolein down-regulated the protein level of Bcl-2 and Bcl-2 overexpression inhibited the cell death induced by the combined treatment with acrolein and TRAIL. In addition, acrolein up-regulated C/EBP homologous protein (CHOP) and TRAIL death receptor 5 (DR5) and down-regulation of CHOP or DR5 expression using the respective small interfering RNA significantly attenuated the apoptosis induced by acrolein plus TRAIL. Interestingly, pretreatment with an antioxidant, N-acetylcysteine (NAC), inhibited not only CHOP and DR5 up-regulation but also the cell death induced by acrolein plus TRAIL. Taken together, our results demonstrated that acrolein enhances TRAIL-induced apoptosis in Caki cells through down-regulation of Bcl-2 and ROS dependent up-regulation of DR5.     

The flavonolignan silibinin potentiates TRAIL-induced apoptosis in human colon adenocarcinoma and in derived TRAIL-resistant metastatic cells

Silibinin, a flavonolignan, is the major active component of the milk thistle plant (Silybum marianum) and has been shown to possess anti-neoplastic properties. TNF-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent which selectively induces apoptosis in cancer cells. However, resistance to TRAIL-induced apoptosis is an important and frequent problem in cancer treatment. In this study, we investigated the effect of silibinin and TRAIL in an in vitro model of human colon cancer progression, consisting of primary colon tumor cells (SW480) and their derived TRAIL-resistant metastatic cells (SW620). We showed by flow cytometry that silibinin and TRAIL synergistically induced cell death in the two cell lines. Up-regulation of death receptor 4 (DR4) and DR5 by silibinin was shown by RT-PCR and by flow cytometry. Human recombinant DR5/Fc chimera protein that has a dominant-negative effect by competing with the endogenous receptors abrogated cell death induced by silibinin and TRAIL, demonstrating the activation of the death receptor pathway. Synergistic activation of caspase-3, -8, and -9 by silibinin and TRAIL was shown by colorimetric assays. When caspase inhibitors were used, cell death was blocked. Furthermore, silibinin and TRAIL potentiated activation of the mitochondrial apoptotic pathway and down-regulated the anti-apoptotic proteins Mcl-1 and XIAP. The involvement of XIAP in sensitization of the two cell lines to TRAIL was demonstrated using the XIAP inhibitor embelin. These findings demonstrate the synergistic action of silibinin and TRAIL, suggesting chemopreventive and therapeutic potential which should be further explored.     

The combination of TRAIL and luteolin enhances apoptosis in human cervical cancer HeLa cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for cancer therapeutics. However, some tumor cells are resistant to TRAIL-induced apoptosis. Our previous studies have shown that luteolin, a naturally occurring flavonoid, induces the up-regulation of death receptor 5 (DR5), which is a receptor for TRAIL. Here, we show for the first time that luteolin synergistically acts with exogenous soluble recombinant human TRAIL to induce apoptosis in HeLa cells, but not in normal human peripheral blood mononuclear cells. The combined use of luteolin and TRAIL induced Bid cleavage and the activation of caspase-8. Also, human recombinant DR5/Fc chimera protein, caspase inhibitors, and DR5 siRNA efficiently reduced apoptosis induced by co-treatment with luteolin and TRAIL. These results raise the possibility that this combined treatment with luteolin and TRAIL might be promising as a new therapy against cancer.     

Gefitinib enhances human colon cancer cells to TRAIL-induced apoptosis of via autophagy- and JNK-mediated death receptors upregulation

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a potent cancer cell-specific apoptosis-inducing cytokine with little toxicity to most normal cells. Here, we report that gefitinib and TRAIL in combination produce a potent synergistic effect on TRAIL-sensitive human colon cancer HCT116 cells and an additive effect on TRAIL-resistant HT-29 cells. Interestingly, gefitinib increases the expression of cell surface receptors DR4 and DR5, possibly explaining the synergistic effect. Knockdown of DR4 and DR5 by siRNA significantly decreases gefitinib- and TRAIL-mediated cell apoptosis, supporting this idea. Because the inhibition of gefitinib-induced autophagy by 3-MA significantly decreases DR4 and DR5 upregulation, as well as reduces gefitinib- and TRAIL-induced apoptosis, we conclude that death receptor upregulation is autophagy mediated. Furthermore, our results indicate that death receptor expression may also be regulated by JNK activation, because pre-treatment of cells with JNK inhibitor SP600125 significantly decreases gefitinib-induced death receptor upregulation. Interestingly, SP600125 also inhibits the expression CHOP, yet CHOP has no impact on death receptor expressions. We also find here that phosphorylation of Akt and ERK might also be required for TRAIL sensitization. In summary, our results indicate that gefitinib effectively enhances TRAIL-induced apoptosis, likely via autophagy and JNK- mediated death receptor expression and phosphorylation of Akt and ERK.     

Oxaliplatin enhances TRAIL-induced apoptosis in gastric cancer cells by CBL-regulated death receptor redistribution in lipid rafts

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor family that selectively induces apoptosis in cancer cells. However, gastric cancer cells are insensitive to TRAIL. In the present study, we show that oxaliplatin enhanced TRAIL-induced apoptosis of MGC803, BGC823, and SGC7901 cells. Oxaliplatin promoted death receptor 4 (DR4) and death receptor 5 (DR5) clustering into aggregated lipid rafts, while the cholesterol-sequestering agent nystatin partially prevented lipid raft aggregation, DR4 and DR5 clustering, and reduced apoptosis. Furthermore, the expression of the casitas B-lineage lymphoma (Cbl) family was downregulated by oxaliplatin. Transfection of c-Cbl or Cbl-b partially reversed oxaliplatin-induced lipid raft aggregation. These results indicated that oxaliplatin enhanced TRAIL-induced gastric cancer cell apoptosis at least partially through Cbl-regulated death receptor redistribution in lipid rafts.     

Transformation by oncogenic RAS sensitizes human colon cells to TRAIL-induced apoptosis by up-regulating death receptor 4 and death receptor 5 through a MEK-dependent pathway

RAS oncogenes play a major role in cancer development by activating an array of signaling pathways, most notably mitogen-activated protein kinases, resulting in aberrant proliferation and inhibition of apoptotic signaling cascades, rendering transformed cells resistant to extrinsic death stimuli. However, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is able to kill specific tumor cells through the engagement of its receptors, death receptor 4 (DR4) and death receptor 5 (DR5), and the activation of apoptotic pathways, providing promising targets for anticancer therapies. In this study, we show that TRAIL induces cell death in human colon adenocarcinoma cells in a MEK-dependent manner. We also report a prolonged MEK-dependent activation of ERK1/2 and increased c-FOS expression induced by TRAIL in this system. Our study reveals that transformation of the colon cell line Caco-2 by Ki- and mainly by Ha-ras oncogenes sensitizes these cells to TRAIL-induced apoptosis by causing specific MEK-dependent up-regulation of DR4 and DR5. These observations taken together reveal that RAS-MEK-ERK1/2 signaling pathway can sensitize cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 and overall imply that TRAIL-based therapeutic strategies using TRAIL agonists could be used in cases of human colon cancers bearing RAS mutations.     

The Herbal Compound Cryptotanshinone Restores Sensitivity in Cancer Cells That Are Resistant to the Tumor Necrosis Factor-related Apoptosis-inducing Ligand

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis and kills cancer cells but not normal cells. However, TRAIL resistance due to low level of TRAIL receptor expression is widely found in cancer cells and hampers its development for cancer treatment. Thus, the agents that can sensitize the tumor cells to TRAIL-mediated apoptosis are urgently needed. We investigated whether tanshinones, the major bioactive compounds of Salvia miltiorrhiza (danshen), can up-regulate TRAIL receptor expression. Among the major tanshinones being tested, cryptotanshinone (CT) showed the best ability to induce TRAIL receptor 2 (DR5) expression. We further showed that CT was capable of promoting TRAIL-induced cell death and apoptosis in A375 melanoma cells. CT-induced DR5 induction was not cell type-specific, as DR5 induction was observed in other cancer cell types. DR5 knockdown abolished the enhancing effect of CT on TRAIL responses. Mechanistically, induction of the DR5 by CT was found to be p53-independent but dependent on the induction of CCAAT/enhancer-binding protein-homologous protein (CHOP). Knockdown of CHOP abolished CT-induced DR5 expression and the associated potentiation of TRAIL-mediated cell death. In addition, CT-induced ROS production preceded up-regulation of CHOP and DR5 and consequent sensitization of cells to TRAIL. Interestingly, CT also converted TRAIL-resistant lung A549 cancer cells into TRAIL-sensitive cells. Taken together, our results indicate that CT can potentiate TRAIL-induced apoptosis through up-regulation of DR5.     

Mitomycin C potentiates TRAIL-induced apoptosis through p53-independent upregulation of death receptors

The discovery of the molecular targets of chemotherapeutic medicines and their chemical footprints can validate and improve the use of such medicines. In the present report, we investigated the effect of mitomycin C (MMC), a classical chemotherapeutic agent on cancer cell apoptosis induced by TRAIL. We found that MMC not only potentiated TRAIL-induced apoptosis in HCT116 (p53?/?) colon cancer cells but also sensitized TRAIL-resistant colon cancer cells HT-29 to the cytokine both in vitro and in vivo. MMC also augmented the pro-apoptotic effects of two TRAIL receptor agonist antibodies, mapatumumab and lexatumumab. At a mechanistic level, MMC downregulated cell survival proteins, including Bcl2, Mcl-1 and Bcl-XL, and upregulated pro-apoptotic proteins including Bax, Bim and the cell surface expression of TRAIL death receptors DR4 and DR5. Gene silencing of DR5 by short hairpin RNA reduced the apoptosis induced by combination treatment of MMC and TRAIL. Induction of DR4 and DR5 was independent of p53, Bax and Bim but was dependent on c-Jun N terminal kinase (JNK) as JNK pharmacological inhibition and siRNA abolished the induction of the TRAIL receptors by MMC.     

Celastrol, a Triterpene, Enhances TRAIL-induced Apoptosis through the Down-regulation of Cell Survival Proteins and Up-regulation of Death Receptors

Whether celastrol, a triterpene from traditional Chinese medicine, can modulate the anticancer effects of TRAIL, the cytokine that is currently in clinical trial, was investigated. As indicated by assays that measure plasma membrane integrity, phosphatidylserine exposure, mitochondrial activity, and activation of caspase-8, caspase-9, and caspase-3, celastrol potentiated the TRAIL-induced apoptosis in human breast cancer cells, and converted TRAIL-resistant cells to TRAIL-sensitive cells. When examined for its mechanism, we found that the triterpene down-regulated the expression of cell survival proteins including cFLIP, IAP-1, Bcl-2, Bcl-xL, survivin, and XIAP and up-regulated Bax expression. In addition, we found that celastrol induced the cell surface expression of both the TRAIL receptors DR4 and DR5. This increase in receptors was noted in a wide variety of cancer cells including breast, lung, colorectal, prostate, esophageal, and pancreatic cancer cells, and myeloid and leukemia cells. Gene silencing of the death receptor abolished the effect of celastrol on TRAIL-induced apoptosis. Induction of the death receptor by the triterpenoid was found to be p53-independent but required the induction of CAAT/enhancer-binding protein homologous protein (CHOP), inasmuch as gene silencing of CHOP abolished the induction of DR5 expression by celastrol and associated enhancement of TRAIL-induced apoptosis. We found that celastrol also induced reactive oxygen species (ROS) generation, and ROS sequestration inhibited celastrol-induced expression of CHOP and DR5, and consequent sensitization to TRAIL. Overall, our results demonstrate that celastrol can potentiate the apoptotic effects of TRAIL through down-regulation of cell survival proteins and up-regulation of death receptors via the ROS-mediated up-regulation of CHOP pathway.     

Combination of TRAIL with Bortezomib Shifted Apoptotic Signaling from DR4 to DR5 Death Receptor by Selective Internalization and Degradation of DR4

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) mediates apoptosis in cancer cells through death receptors DR4 and DR5 preferring often one receptor over another in the cells expressing both receptors. Receptor selective mutant variants of TRAIL and agonistic antibodies against DR4 and DR5 are highly promising anticancer agents. Here using DR5 specific mutant variant of TRAIL - DR5-B we have demonstrated for the first time that the sensitivity of cancer cells can be shifted from one TRAIL death receptor to another during co-treatment with anticancer drugs. First we have studied the contribution of DR4 and DR5 in HCT116 p53+/+ and HCT116 p53−/− cells and demonstrated that in HCT116 p53+/+ cells the both death receptors are involved in TRAIL-induced cell death while in HCT116 p53−/− cells prevailed DR4 signaling. The expression of death (DR4 and DR5) as well as decoy (DcR1 and DcR2) receptors was upregulated in the both cell lines either by TRAIL or by bortezomib. However, combined treatment of cells with two drugs induced strong time-dependent and p53-independent internalization and further lysosomal degradation of DR4 receptor. Interestingly DR5-B variant of TRAIL which do not bind with DR4 receptor also induced elimination of DR4 from cell surface in combination with bortezomib indicating the ligand-independent mechanism of the receptor internalization. Eliminatory internalization of DR4 resulted in activation of DR5 receptor thus DR4-dependent HCT116 p53−/− cells became highly sensitive to DR5-B in time-dependent manner. Internalization and degradation of DR4 receptor depended on activation of caspases as well as of lysosomal activity as it was completely inhibited by Z-VAD-FMK, E-64 and Baf-A1. In light of our findings, it is important to explore carefully which of the death receptors is active, when sensitizing drugs are combined with agonistic antibodies to the death receptors or receptor selective variants of TRAIL to enhance cancer treatment efficiency.     

Mitomycin C potentiates TRAIL-induced apoptosis through p53-independent upregulation of death receptors: Evidence for the role of c-Jun N-terminal kinase activation

The discovery of the molecular targets of chemotherapeutic medicines and their chemical footprints can validate and improve the use of such medicines. In the present report, we investigated the effect of mitomycin C (MMC), a classical chemotherapeutic agent on cancer cell apoptosis induced by TRAIL. We found that MMC not only potentiated TRAIL-induced apoptosis in HCT116 (p53−/−) colon cancer cells but also sensitized TRAIL-resistant colon cancer cells HT-29 to the cytokine both in vitro and in vivo. MMC also augmented the pro-apoptotic effects of two TRAIL receptor agonist antibodies, mapatumumab and lexatumumab. At a mechanistic level, MMC downregulated cell survival proteins, including Bcl2, Mcl-1 and Bcl-XL, and upregulated pro-apoptotic proteins including Bax, Bim and the cell surface expression of TRAIL death receptors DR4 and DR5. Gene silencing of DR5 by short hairpin RNA reduced the apoptosis induced by combination treatment of MMC and TRAIL. Induction of DR4 and DR5 was independent of p53, Bax and Bim but was dependent on c-Jun N terminal kinase (JNK) as JNK pharmacological inhibition and siRNA abolished the induction of the TRAIL receptors by MMC.     

Snake venom toxin from Vipera lebetina turanica sensitizes cancer cells to TRAIL through ROS- and JNK-mediated upregulation of death receptors and downregulation of survival proteins

We investigated whether snake venom toxin (SVT) from Vipera lebetina turanica enhances the apoptosis ability of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in cancer cells. TRAIL inhibited HCT116 cell growth in a dose-dependent manner; however, this reduction did not occur in TRAIL resistant HT-29, A549 and HepG2 cells with an even higher dose of TRAIL. SVT, but not TRAIL enhanced expression of cell death receptor (DR) in TRAIL resistant cancer cells in a dose-dependent manner. A combination of SVT with TRAIL significantly inhibited cell growth of TRAIL resistant HT-29, A549 and HepG2 cells. Consistent with cell growth inhibition, the expression of TRAIL receptors; DR4 and DR5 was significantly increased as well as apoptosis related proteins such as cleaved caspase-3, -8, -9 and Bax. However, the expression of survival proteins (e.g., cFLIP, survivin, XIAP and Bcl2) was suppressed by the combination treatment of SVT and TRAIL. Depletion of DR4 or DR5 by small interfering RNA significantly reversed the cell growth inhibitory and apoptosis blocking effects of SVT in HCT116 and HT-29 cells. Pretreatment with the c-Jun N-terminal kinase (JNK) inhibitor SP600125 and the reactive oxygen species (ROS) scavenger N-acetylcysteine reduced the SVT and TRAIL-induced upregulation of DR4 and DR5 expression, expression of the apoptosis related protein such as caspase-3 and-9, as well as cell growth inhibitory effects. The collective results suggest that SVT facilitates TRAIL-induced apoptosis in cancer cells through up-regulation of the TRAIL receptors; DR4 and DR5 via ROS/JNK pathway signals.