Apigenin Sensitizes Huh-7 Human Hepatocellular Carcinoma Cells to TRAIL-induced Apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) is a promising agent for management of cancer because of its selective cytotoxicity to cancer cells. However, some cancer cells have resistance to TRAIL. Accordingly, novel treatment strategies are required to overcome TRAIL resistance. Here, we examined the synergistic apoptotic effect of apigenin in combination with TRAIL in Huh-7 cells. We found that combined treatment of TRAIL and apigenin markedly inhibited Huh-7 cell growth compared to either agent alone by inducing apoptosis. Combined treatment with apigenin and TRAIL induced chromatin condensation and the cleavage of poly (ADP-ribose) polymerase (PARP). In addition, enhanced apoptosis by TRAIL/apigenin combination was quantified by annexin V/PI flow cytometry analysis. Western blot analysis suggested that apigenin sensitizes cells to TRAIL-induced apoptosis by activating both intrinsic and extrinsic apoptotic pathway-related caspases. The augmented apoptotic effect by TRAIL/apigenin combination was accompanied by triggering mitochondria-dependent signaling pathway, as indicated by Bax/Bcl-2 ratio up-regulation. Our results demonstrate that combination of TRAIL and apigenin facilitates apoptosis in Huh-7 cells.     

活性氧介导5, 7- 二甲氧基黄酮增敏TRAIL 诱导肺癌细胞凋亡

目的研究5,7-二甲氧基黄酮(5,7-DMF)是否能增强肿瘤坏死因子相关凋亡诱导配体(TRAIL)诱导的人肺癌细胞凋亡及其作用机制。方法体外培养人肺癌A549细胞。MTT法测定细胞增殖活性;碘化丙啶(PI)染色流式细胞术(FCM)和ELISA试剂盒检测细胞凋亡;DCFH-DA荧光标记FCM检测细胞内活性氧(ROS)水平。结果 5,7-DMF能增强TRAIL诱导的A549细胞凋亡和ROS生成。N-乙酰半胱氨酸能有效阻断5,7-DMF与TRAIL所诱导的A549细胞凋亡及ROS生成。结论 5,7-DMF通过促进A549细胞内活性氧生成从而增强TRAIL诱导的凋亡。     

培美曲塞联合顺铂通过TRAIL诱导非小细胞肺癌A549细胞凋亡发挥抗癌效果的研究

目的：初步探讨培美曲塞联合顺铂通过TRAIL诱导非小细胞肺癌A549细胞凋亡发挥的抗癌效果。方法：将肺癌细胞株A549做4种处理并分为4组：空白组（Blank组）、顺铂处理组（CDPP组）、培美曲塞处理组（MTA组）、培美曲塞联合顺铂处理组（MTA+CDPP组），应用CCK-8和流式细胞术检测4种处理细胞的细胞活性和细胞凋亡变化；qPCR检测顺铂单药治疗组和培美曲塞联合顺铂治疗组的细胞肿瘤坏死因子相关凋亡诱导配体（TRAIL）表达差异；干扰TRAIL后再次检测各处理组细胞的细胞活性和细胞凋亡变化；qPCR和WB检测干扰TRAIL后BCL-2转录水平和蛋白表达。结果：培美曲塞联合顺铂（CDDP）在非小细胞肺癌细胞中起到降低细胞活性和诱导细胞凋亡的作用，二者协同发挥抗肿瘤效果；培美曲塞联合顺铂治疗组TRAIL转录表达显著高于顺铂处理组；干扰TRAIL后，顺铂与培美曲塞联合诱导的细胞活力的降低作用被抑制，并逆转了顺铂与培美曲塞联合对细胞凋亡的促进作用；培美曲塞联合顺铂通过TRAIL降低Bcl-2的转录水平和蛋白表达来发挥促进肿瘤细胞凋亡的作用。结论：培美曲塞可联合顺铂（CDDP）在非小细胞肺癌细胞中发挥抗肿瘤效果，其通过TRAIL降低Bcl-2的表达来诱导肿瘤细胞凋亡，从而发挥抗肿瘤作用。     

Inostamycin enhanced TRAIL-induced apoptosis through DR5 upregulation on the cell surface

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been considered as a possible therapeutic agent for cancer treatment. This is because of its selective cytotoxicity against various cancer cells without a detrimental effect on normal cells. However, recent studies have reported that the potential application of TRAIL in cancer therapy is limited, as many cancer cells have been found to be resistant to TRAIL. Therefore, small molecule compounds that potentiate the cytotoxicity of TRAIL would be strategic candidates for therapeutic applications in combination with TRAIL. Here we found that a combined treatment of inostamycin and TRAIL synergistically induced caspase-dependent apoptosis in HCT116 cells. Inostamycin upregulated DR5, and a knockdown of DR5 suppressed the apoptosis that was synergistically induced by co-treatment with inostamycin and TRAIL. Moreover, inostamycin increased the expression of DR5 on the cell surface. Therefore, inostamycin-increased cell surface expression of DR5 may have contributed to the enhancement of TRAIL-induced apoptosis. Our study suggests that combined treatment with inostamycin and TRAIL may offer a strategy to overcome TRAIL resistance in tumor cells.     

A multicomponent microemulsion using rational combination strategy improves lung cancer treatment through synergistic effects and deep tumor penetration

Previously, we have developed a multicomponent-based microemulsion composed of etoposide, coix seed oil, and ginsenoside Rh2 (ECG-MEs). In this study, our goal was to validate the feasibility of ECG-MEs in lung cancer treatment and explore the mechanism underling the enhanced antitumor efficacy. The optimal weight ratio of ginsenoside Rh2 (G-Rh2) in ECG-MEs was determined as 3% (wt%), that was capable of forming the microemulsion readily with small particle size and high drug encapsulation efficiency. In cellular studies, the intracellular fluorescence of human non-small cell lung cancer (A549) cells treated with fluorescein isothiocyanate-labeled ECG-MEs (FITC/ECG-MEs) was significantly higher than that of various controls, leading to the obviously synergistic anticancer activities in cytotoxicity and in vitro cell apoptosis induction. The anticancer efficacy in vivo results showed that ECG-MEs markedly inhibited the growth of A549 tumor xenografts, potently induced tumor cells apoptosis, and obviously prolonged the survival time of mice. Of note, the mechanisms of enhanced anticancer efficiency were connected with the small size-mediated deep tumor penetration and increase in serum concentration of T helper 1 (Th1) cytokines. In summary, ECG-MEs exerting the rational drug combination strategy offers a solid evidence for lung cancer treatment, and has a promising potential for clinical application.     

The action and mechanism of myrislignan on A549 cells in vitro and in vivo

Myrislignan is a natural compound with little pharmacological study. In our investigation, we investigated the effect of myrislignan in the induction of apoptosis in A549 cells in vitro and in vivo. Myrislignan inhibited the proliferation of A549 cells in a dose- and time-dependent manner assayed by MTT. In addition, Hoechst flow cytometry showed that myrislignan significantly induced apoptosis and cell cycle arrest in A549 cells. The apoptosis and anti-cell proliferation was mediated by the activation of mitogen-activated protein kinase and the inhibition of epidermal growth factor receptor signal pathway, change of mitochondrial membrane potential, the releasing of c-Myc, the downregulation of the level of the anti-apoptotic protein Bcl-2, and the upregulation of the level of the pro-apoptotic protein Bax. In conclusion, those results reveal a potential mechanism for the anti-cancer effect of myrislignan on human lung cancer, while suggesting that myrislignan may be a promising compound for the treatment of lung cancer.     

Targeting androgen receptor and trail:a novel treatment paradigm for breast cancer

OBJECTIVE TNF-related apoptosis-inducing ligand(TRAIL)is a promising cancer therapeutic agent due to its minimal toxicity to normal tissues and remarkable apoptotic activity in tumors.However,most breast cancer cells are resistant to TRAIL-induced apoptosis.Our objectives are to investigate the underlying molecular mechanisms and to develop strategies to overcome such resistance.METHODS To identify modulators of TRAIL-induced apoptosis,we carried out a genome wide si RNA screen.To validate the screening result,we either silenced or overexpressed the identified genes in various breast cancer cells and changes in growth and TRAIL-induced cell apoptosis were determined in vitro and in an orthotopic xenograft mouse model.Finally,we investigated whether small molecules targeting the identified genes improve the effectiveness of TRAIL-therapy.RESULTS We unexpectedly identified androgen receptor(AR)to be responsible for TRAIL resistance.While AR is classically viewed as the key factor in prostate cancer progression,we found that AR expression levels were markedly elevated in human invasive breast cancer specimens including triple-negative breast cancers(TNBC)that are highly aggressive with poor prognosis.Importantly,breast cancer cell lines express different levels of AR that correlated with their TRAIL resistance.AR overexpression in MDA-MB-231 and MDA-MB-436 cells suppressed the TRAIL sensitivity whereas knockdown of AR rendered MCF-7 and MDA-MB-453 cells sensitive to TRAIL-induced apoptosis.AR overexpression also induced TRAIL resistance in breast tumors in vivo.Further,we observed an upregulation of the TRAIL receptor,death receptor 5(DR5)in breast cancer cells,following the removal or inhibition of AR by its antagonists Casodex and MDV3100.Treatment with AR antagonists also enhanced TRAIL-induced breast cancer cell apoptosis.CONCLUSION AR signaling suppresses TRAIL-induced breast cancer cell apoptosis,in part,by suppressing DR5 expression,and a combination of AR antagonists together with TRAIL may be a novel and effective therapy for TNBC.     

Bortezomib treatment of ovarian cancer cells mediates endoplasmic reticulum stress,cell cycle arrest,and apoptosis

Bortezomib, an approved drug for the treatment of certain haematological neoplasms, is currently being tested in clinical trials as a potential therapeutic agent against several types of solid cancer, including ovarian cancer. We have analyzed the effect of bortezomib on ovarian cancer cells and tissue explants either as a single agent or in combination with carboplatin, taxol, or TRAIL (tumor necrosis factor-related apoptosis-inducing ligand). Bortezomib alone efficiently induced apoptosis in ovarian cancer cells. Apoptosis was preceded by an upregulation of the endoplasmic reticulum stress sensor ATF3, and increased the expression of cytoplasmic heat shock proteins. Bortezomib enhanced the sensitivity of ovarian cancer cells and tissue explants to an apoptosis-inducing TRAIL receptor antibody by upregulating the TRAIL receptor DR5. In contrast to the synergistic effect observed for TRAIL, the efficacy of the taxol treatment was reduced by bortezomib, and bortezomib inhibited the G2/M phase accumulation of ovarian cancer cells treated with taxol. Bortezomib alone or in combination with taxol induced a cell cycle arrest within the S phase, and downregulation of cdk1, a cyclin-dependent kinase that is necessary for the entry into the M phase. Thus, bortezomib can be regarded as a promising agent for the treatment of ovarian cancer and could either be administered as a single agent or in combination with TRAIL. However, a combination treatment with taxanes may not be beneficial and may even be less effective.     

Myriocin induces apoptotic lung cancer cell death via activation of DR4 pathway

It has been known that myriocin inhibits melanoma growth. However, the effects and action mechanisms of myriocin on lung cancer cell growth have not been reported. In this study, we examined whether myriocin isolated from Mycelia sterilia inhibits cell growth of lung cancer cells (A549 and NCI-H460) as well as possible signaling pathways involved in cell growth inhibition. Different concentrations of myriocin inhibited the growth of lung cancer cells through the induction of apoptotic cell death. Consistent with cancer cell growth inhibition, myriocin induced the expression of death receptors (DRs) as well as p-JNK and p-p38 in both cell lines. Moreover, the combination of myriocin with DR4 ligand TRAIL, and other well known anti-tumor drugs (docetaxel and cisplatin) synergistically inhibited cancer cell growth, and induced DR4 expression. These results showed that myriocin inhibits lung cancer cells growth through apoptosis via the activation of DR4 pathways, and enhanced anti-cancer effects with well known drugs. Thus, our study indicates that myriocin could be effective for lung cancer cells as an anti-cancer drug and/or a conjunction agent with well known anti-cancers.     

Down-Regulation of Survivin by Nemadipine-A Sensitizes Cancer Cells to TRAIL-Induced Apoptosis

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor family of cytokines. TRAIL selectively induces apoptotic cell death in various tumors and cancer cells, but it has little or no toxicity in normal cells. Agonism of TRAIL receptors has been considered to be a valuable cancer-therapeutic strategy. However, more than 85% of primary tumors are resistant to TRAIL, emphasizing the importance of investigating how to overcome TRAIL resistance. In this report, we have found that nemadipine-A, a cell-permeable L-type calcium channel inhibitor, sensitizes TRAIL-resistant cancer cells to this ligand. Combination treatments using TRAIL with nemadipine-A synergistically induced both the caspase cascade and apoptotic cell death, which were blocked by a pan caspase inhibitor (zVAD) but not by autophagy or a necrosis inhibitor. We further found that nemadipine-A, either alone or in combination with TRAIL, notably reduced the expression of survivin, an inhibitor of the apoptosis protein (IAP) family of proteins. Depletion of survivin by small RNA interference (siRNA) resulted in increased cell death and caspase activation by TRAIL treatment. These results suggest that nemadipine-A potentiates TRAIL-induced apoptosis by down-regulation of survivin expression in TRAIL resistant cells. Thus, combination of TRAIL with nemadipine-A may serve a new therapeutic scheme for the treatment of TRAIL resistant cancer cells, suggesting that a detailed study of this combination would be useful.     

山楂酸与顺铂合用对肺癌A549细胞增殖、凋亡的影响

目的探讨山楂酸与顺铂合用对肺癌细胞A549增殖及凋亡产生的影响。方法将人的肺癌细胞系A549经过药物干预(山楂酸、顺铂),并将干预后的肺癌细胞通过MTT实验,分析细胞增殖能力变化,通过流式细胞技术,分析细胞的凋亡水平变化。通过Western blot分析细胞中XIAP、Survivin的表达水平变化。结果山楂酸和顺铂合用后,A549细胞的增殖率显著降低,凋亡水平显著提高;荧光电子显微镜下观察到凋亡细胞明显增加,核碎裂明显,细胞大片脱落;Western blot结果显示,山楂酸和顺铂合用,显著下调XIAP、Survivin的蛋白表达量。结论山楂酸和顺铂合用抑制肺癌细胞的增殖,促进肺癌细胞的凋亡,并下调细胞中凋亡抑制相关指标XIAP、Survivin的表达水平。     

Histone deacetylase inhibitors interact synergistically with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to induce apoptosis in carcinoma cell lines

Summary Both tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and histone deacetylase inhibitors (HDIs) show promise for the treatment of cancer. However, in a number of reports they have been proven ineffective to induce cell death when applied as single agents. In this study, we show that A549 lung carcinoma cells and PC-3 prostate carcinoma cells underwent substantial apoptosis when coexposed to TRAIL and either suberoylanilide hydroxamic acid, sodium butyrate or trichostatin A. HDIs and TRAIL synergized in activation of capase-3, induction of internucleosomal DNA fragmentation and promoting mitochondrial damage. Significantly, cotreatment with minimally toxic doses of HDIs and TRAIL resulted in a marked apoptotic response in both cell lines. These data provide a rationale for a more in-depth exploration into the potential of combining TRAIL and HDIs as a valuable anticancer strategy.     

Targeting TRAIL towards the clinic

Tumor necrosis factor-related apoptosis-inducing ligand or Apo2 ligand (TRAIL/Apo2L) is a member of the tumor necrosis factor (TNF) superfamily that induces apoptosis upon binding to its death domain-containing transmembrane receptors. The preferential toxicity of TRAIL to cancer cells and the sparing of normal cells make it an ideal cancer therapeutic agent. TRAIL induces apoptosis via the extrinsic death receptor apoptotic pathway and activates the JNK, ERK, Akt and NF-κB signaling cascades. However, not all cancer cells are sensitive to TRAIL therapy. This may limit its efficacy in the clinic, although ways have already been identified to overcome resistance by combining TRAIL with chemotherapeutic and other biological agents. This review focuses on TRAIL receptor-targeting as anticancer therapy, the apoptotic signaling pathways induced by TRAIL receptors, the prognostic implications of TRAIL receptor expression and modulation by combination therapies. The mechanisms of TRAIL resistance and strategies to overcome drug resistance will also be addressed. Finally, the progress of TRAIL and DR4/DR5-specific agonistic antibodies in clinical trials and the development of new receptor-selective TRAIL variants are discussed including future directions for apoptosis inducing therapy.     

Trichostatin A sensitizes human ovarian cancer cells to TRAIL-induced apoptosis by down-regulation of c-FLIPL via inhibition of EGFR pathway

TRAIL-resistant cancer cells can be sensitized to TRAIL by combination therapy. In this study, we investigated the effect of trichostatin A (TSA), a histone deacetylase inhibitor, to overcome the TRAIL resistance in human ovarian cancer cells. Co-treatment of human ovarian cancer cells with TSA and TRAIL synergistically inhibited cell proliferation and induced apoptosis. The combined treatment of ovarian cancer SKOV3 cells with TSA and TRAIL significantly activated caspase-8 and truncated Bid, resulting in the cytosolic accumulation of cytochrome c as well as the activation of caspase-9 and -3. Moreover, we found that down-regulation of c-FLIP_L might contribute to TSA-mediated sensitization to TRAIL-induced apoptosis in SKOV3 cells, and this result was supported by showing that down- or up-regulation of c-FLIP_L with transfection of siRNA or plasmid sensitized or made SKOV3 cells resistant to TRAIL-induced apoptosis, respectively. TSA or co-treatment with TSA alone and TRAIL also resulted in down-regulation of EGFR1/2 and dephosphorylation of its downstream targets, AKT and ERK. Treatment of SKOV3 cells with PKI-166 (EGFR1/2 inhibitor), LY294002 (AKT inhibitor), and PD98059 (ERK inhibitor) decreased c-FLIP_L expression and co-treatment with TRAIL further reduced the level of c-FLIP_L, respectively, as did TSA. Collectively, our data suggest that TSA-mediated sensitization of ovarian cancer cells to TRAIL is closely correlated with down-regulation of c-FLIP_L via inhibition of EGFR pathway, involving caspase-dependent mitochondrial apoptosis, and combination of TSA and TRAIL may be an effective strategy for treating TRAIL-resistant human ovarian cancer cells.     

Potential and caveats of TRAIL in cancer therapy.

Induction of apoptosis in tumor cells is a major goal for chemotherapy and radiation treatment strategies. However, disordered gene expression often leads to apoptosis resistance rendering tumor cells insensitive to various conventional treatments. TNF-related apoptosis-inducing ligand (TRAIL) is a recently identified cytokine of the TNF superfamily that induces apoptosis in tumor cells upon binding to different receptors. Remarkably, the majority of tumor cell lines are sensitive to TRAIL-induced apoptosis, while most nontransformed cell types are TRAIL-resistant. Furthermore, a combination treatment of TRAIL with ionizing irradiation or chemotherapeutic agents induces apoptosis in a highly synergistic manner, particularly in those cells that are otherwise resistant to a sole treatment. In contrast to other TNF members, TRAIL apparently does not exert overt systemic toxicity in murine and primate models, although unexpected concerns about a potential hepatotoxicity of TRAIL have been recently raised. While the molecular mechanisms of TRAIL sensitivity and resistance are poorly understood, TRAIL seems to be a promising biological agent for combination therapy with chemotherapeutic drugs or irradiation.     

姜黄素诱导人肺腺癌A549细胞脱落凋亡作用的研究

目的检测姜黄素诱导人肺腺癌细胞(A549)脱落凋亡的作用。方法采用DNA ladder法,流式细胞仪(FCM)技术结合PI及AnnexinV-FITC双标记染色试验方法及W estern-b lot法观察姜黄素是否能诱导A549脱落凋亡。结果A549细胞具有抗脱落凋亡的特性,而10μmol.L-1的姜黄素即可引起悬浮培养的A549细胞发生脱落凋亡。结论姜黄素可诱导人肺腺癌细胞(A549)脱落凋亡。     

Itch/AIP4-independent proteasomal degradation of cFLIP induced by the histone deacetylase inhibitor SAHA sensitizes breast tumour cells to TRAIL

The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA, vorinostat) is undergoing clinical trials as an antitumor drug and has received regulatory approval for cancer treatment. Here, we show that pre-treatment of human breast cancer cells with SAHA makes them susceptible to apoptosis induced by TRAIL (tumour necrosis factor-related apoptosis-inducing ligand). The apoptosis of breast tumour cells induced by TRAIL is blocked at the level of apical activation of caspase-8 and SAHA enhances the TRAIL-induced processing of procaspase-8. Consequently, a TRAIL associated pathway of apoptosis operated via mitochondria is activated in cells treated with SAHA. Interestingly, degradation of cellular FLICE-inhibitory proteins (cFLIP_L and cFLIP_S) by an ubiquitin/proteasome-dependent Itch/AIP4-independent mechanism is observed upon exposure to SAHA. Targeting cFLIP_L directly with siRNA oligonucleotides also sensitizes human breast tumour cells to TRAIL-induced apoptosis. Furthermore, cFLIP_L over-expression significantly inhibits the apoptosis elicited through the combined effects of SAHA and TRAIL. Together, these results indicate that SAHA sensitizes breast cancer cells to TRAIL-induced apoptosis by facilitating the activation of early events in the apoptotic TRAIL pathway. Therefore, the combination of TRAIL and SAHA may represent a therapeutic tool to combat breast tumours.     

Molecular crosstalk between TRAIL and natural antioxidants in the treatment of cancer

The endogenous protein, tumour necrosis factor receptor apoptosis-inducing ligand (TRAIL), induces apoptosis in a wide variety of transformed and cancer cells but has little or no effect on normal cells. Therefore, TRAIL is considered to be a tumour-selective, apoptosis-inducing cytokine and a promising new candidate for cancer prevention and treatment. Some cancer cells are however resistant to TRAIL-induced apoptosis, but treatment in combination with conventional chemotherapeutic drugs or radiation generally restores TRAIL sensitivity in those cells. A novel class of molecules exhibiting synergy with TRAIL but devoid of major side effects are emerging as alternative approaches to treat resistant cancer cells, including natural antioxidants such as sulphoraphane or the flavonoids curcumin, quercetin, resveratrol, baicalein and wogonin. In this issue of the BJP, Lee et al. demonstrate that treatment of TRAIL-resistant cancer cells with wogonin restores TRAIL-induced cell death in a reactive oxygen species-dependent manner through up-regulation of p53 and Puma.     

和厚朴酚及厚朴酚抗肺癌药理作用及机制的研究进展

和厚朴酚及厚朴酚是疏水性烯丙基联苯酚类结构的同分异构体,均有抗肺癌药理作用。和厚朴酚能抑制肺癌A549细胞、H1299细胞和Lewis细胞移植瘤在小鼠体内的生长和转移,而厚朴酚能预防乌拉坦诱导小鼠发生肺癌和抑制A549细胞移植瘤在小鼠体内生长。和厚朴酚及厚朴酚在体外能浓度相关地抑制人小细胞肺癌N446细胞、H446细胞,非小细胞肺癌中的肺腺癌A549、H1299、H441、H1975、Calu3、A2、PC、SPC-A-1、95D细胞,大细胞肺癌H460细胞,人肺鳞癌H226、H520、CH27细胞以及小鼠肺癌Lewis细胞增殖,并诱导其凋亡和坏死。和厚朴酚及厚朴酚抑制肺癌的主要机制是：（1）抑制I型去乙酰化酶的表达和酶活性,上调死亡受体-5（DR5）的表达,激活肿瘤坏死因子相关的凋亡诱导配体（TRAIL）信号通路;（2）激活与半胱天冬酶无关的凋亡通路;（3）阻滞癌细胞中的微管聚合,破坏微管结构;（4）阻滞蛋白激酶B（AKT）/哺乳动物雷帕霉素靶蛋白（mTOR）信号通路,诱导癌细胞自噬;（5）阻滞磷脂酰肌醇-3激酶（PI3K）/AKT信号通路而抑制癌细胞转移。     

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

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) is a promising candidate for treatment of cancer, but displays variable cytotoxicity in cell lines. The mechanisms of sensitivity and resistance have not been fully elucidated; both AKT and NF-kappaB pathways may modulate cytotoxic responses. We have shown that the Hsp90 inhibitor 17-AAG enhances the cytotoxicity of oxaliplatin in colon cancer cell lines through inhibition of NF-kappaB. We analyzed the effects of TRAIL and 17-AAG in combination in a series of nine colon cancer cell lines and characterized activation of the pathways to apoptosis. IC(50) values for a 72 h exposure to TRAIL ranged from 30 to 4000 ng/ml. Cytotoxicity assays demonstrated additivity or synergism of the TRAIL/17-AAG combination in all cell lines, with combination indices at IC(50) ranging from 0.53 to 1. The sensitizing effect of 17-AAG was greater in the TRAIL-resistant cell lines. In TRAIL-resistant cell lines, the combination of 17-AAG and TRAIL resulted in activation of both extrinsic and intrinsic apoptotic pathways, though with quantitative differences between HT29 and RKO cells: differential effects of 17-AAG on AKT and NF-kappaB characterized these cell lines. In both cell lines, the combination also led to down-regulation of X-linked inhibitor of apoptosis protein (XIAP) and enhanced activation of caspase-3. We conclude that either AKT or NF-kappaB may promote resistance to TRAIL in colon cancer cells, and that the ability of 17-AAG to target multiple putative determinants of TRAIL sensitivity warrants their further investigation in combination.