Sulindac sulfide-induced apoptosis is enhanced by a small-molecule Bcl-2 inhibitor and by TRAIL in human colon cancer cells overexpressing Bcl-2

Sulindac is a nonsteroidal anti-inflammatory drug (NSAID) that induces apoptosis in cultured colon cancer cells and in intestinal epithelia in association with its chemopreventive efficacy. Resistance to sulindac is well documented in patients with familial adenomatous polyposis; however, the molecular mechanisms underlying such resistance remain unknown. We determined the effect of ectopic Bcl-2 expression upon sulindac-induced apoptotic signaling in SW480 human colon cancer cells. Sulindac sulfide activated both the caspase-8-dependent and mitochondrial apoptotic pathways. Ectopic Bcl-2 attenuated cytochrome c release and apoptosis induction compared with SW480/neo cells. Coadministration of sulindac sulfide and the small-molecule Bcl-2 inhibitor HA14-1 increased apoptosis induction and enhanced caspase-8 and caspase-9 cleavage, Bax redistribution, and cytochrome c and second mitochondria-derived activator of caspase release. Given that sulindac sulfide activated caspase-8 and increased membrane death receptor (DR4 and DR5) protein levels, we evaluated its combination with the endogenous death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Coadministration of sulindac sulfide and TRAIL cooperatively enhanced apoptotic signaling as effectively as did HA14-1. Together, these data indicate that HA14-1 or TRAIL can enhance sulindac sulfide-induced apoptosis and represent novel strategies for circumventing Bcl-2-mediated apoptosis resistance in human colon cancer cells.     

5-Aminoimidazole-4-carboxamide riboside sensitizes TRAIL- and TNF{alpha}-induced cytotoxicity in colon cancer cells through AMP-activated protein kinase signaling

Death receptor-mediated tumor cell death, either alone or in combination with other anticancer drugs, is considered as a new strategy for anticancer therapy. In this study, we have investigated the effects and molecular mechanisms of 5-aminoimidazole-4-carboxamide riboside [AICAR; a pharmacologic activator of AMP-activated protein kinase (AMPK)] in sensitizing tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)- and TNFalpha-induced apoptosis of human colon cancer HCT116 cells. The cytotoxic action of AICAR requires AMPK activation and may occur at various stages of apoptotic pathways. AICAR cotreatment with either TRAIL or TNFalpha enhances activities of caspase-8, caspase-9, and caspase-3; down-regulates the antiapoptotic protein Bcl-2; increases the cleavage of Bid and results in the decrease of mitochondrial membrane potential; potentiates activation of p38 and c-Jun NH(2)-terminal kinase; and inhibits nuclear factor-kappaB activity. In addition, this sensitized cell apoptosis was neither observed in p53-null HCT116 cells nor affected by the cotreatment with mevalonate. In summary, we have developed a novel strategy of combining AICAR with TRAIL for the treatment of colon cancer cells. The sensitization effect of AICAR in cell apoptosis was mediated through AMPK pathway, requires p53 activity, and involves mitochondria-dependent apoptotic cascades, p38 and c-Jun NH(2)-terminal kinase.     

The alkylphospholipid perifosine induces apoptosis of human lung cancer cells requiring inhibition of Akt and activation of the extrinsic apoptotic pathway

The Akt inhibitor, perifosine, is an alkylphospholipid exhibiting antitumor properties and is currently in phase II clinical trials for various types of cancer. The mechanisms by which perifosine exerts its antitumor effects, including the induction of apoptosis, are not well understood. The current study focused on the effects of perifosine on the induction of apoptosis and its underlying mechanisms in human non-small cell lung cancer (NSCLC) cells. Perifosine, at clinically achievable concentration ranges of 10 to 15 micromol/L, effectively inhibited the growth and induced apoptosis of NSCLC cells. Perifosine inhibited Akt phosphorylation and reduced the levels of total Akt. Importantly, enforced activation of Akt attenuated perifosine-induced apoptosis. These results indicate that Akt inhibition is necessary for perifosine-induced apoptosis. Despite the activation of both caspase-8 and caspase-9, perifosine strikingly induced the expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor, death receptor 5, and down-regulated cellular FLICE-inhibitory protein (c-FLIP), an endogenous inhibitor of the extrinsic apoptotic pathway, with limited modulatory effects on the expression of other genes including Bcl-2, Bcl-X(L), PUMA, and survivin. Silencing of either caspase-8 or death receptor 5 attenuated perifosine-induced apoptosis. Consistently, further down-regulation of c-FLIP expression with c-FLIP small interfering RNA sensitized cells to perifosine-induced apoptosis, whereas enforced overexpression of ectopic c-FLIP conferred resistance to perifosine. Collectively, these data indicate that activation of the extrinsic apoptotic pathway plays a critical role in perifosine-induced apoptosis. Moreover, perifosine cooperates with TRAIL to enhance the induction of apoptosis in human NSCLC cells, thus warranting future in vivo and clinical evaluation of perifosine in combination with TRAIL in the treatment of NSCLC.     

TRAIL联合Res对乳腺癌MDA-MB-231细胞DR和Caspase表达的影响

目的研究TRAIL联合白藜芦醇（Res）对乳腺癌MDA-MB-231细胞DR和caspase表达的影响。方法MTT法检测细胞增殖;流式细胞术检测细胞凋亡及细胞表面DR4、DR5蛋白的表达;分光光度法检测caspase-3、caspase-8相对活性;荧光定量PCR检测DR4、DR5及caspase-3、caspase-8 mRNA的表达。结果50μmol／L和100μmo/L,Res分别与50ng／mL TRAIL联合作用后,对MDA-MB-231细胞增殖的抑制率及细胞凋亡率分别与单独应用相应浓度的Res和TRAIL比较,均存在显著差异（P〈0．01）。50μmol／L和100μmol／LRes分别与50ng／mLT RAIL联合作用后,caspase-3、caspase-8的相对活性与对照组及单用TRAIL、Res比较均明显增强,差异显著（P〈0．01）。Res作用后,细胞表面DR4、DR5荧光指数与对照组比较明显增强。荧光定量PCR结果显示与对照组比较．Res作用后DR4、DR5mRNA表达上调;与单独用药比较,TRAIL联合Resetcagpase-3、easpase-8 mRNA表达上调。结论TRAIL和Res联合应用对诱导乳腺癌MDA-MB-231细胞凋亡具有明显的协同效果,其作用机制可能与增加DR和caspase活性有关。     

The dietary flavonoid apigenin sensitizes malignant tumor cells to tumor necrosis factor-related apoptosis-inducing ligand

Dietary flavonoid apigenin is expected to have preventive and therapeutic potential against malignant tumors. In this report, we show for the first time that apigenin markedly induces the expression of death receptor 5 (DR5) and synergistically acts with exogenous soluble recombinant human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to induce apoptosis in malignant tumor cells. TRAIL is a promising candidate for cancer therapeutics due to its ability to selectively induce apoptosis in cancer cells. The combined use of apigenin and TRAIL at suboptimal concentrations induces Bcl-2-interacting domain cleavage and the activation of caspases-8, -10, -9, and -3. Furthermore, human recombinant DR5/Fc chimera protein and caspase inhibitors dramatically inhibit apoptosis induced by the combination of apigenin and TRAIL. On the other hand, apigenin-mediated induction of DR5 expression is not observed in normal human peripheral blood mononuclear cells. Moreover, apigenin does not sensitize normal human peripheral blood mononuclear cells to TRAIL-induced apoptosis. These results suggest that this combined treatment with apigenin and TRAIL might be promising as a new therapy against malignant tumors.     

Inorganic selenium sensitizes prostate cancer cells to TRAIL-induced apoptosis through superoxide/p53/Bax-mediated activation of mitochondrial pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in prostate cancer cells through DR4 and DR5 death receptors, but not in normal prostate cells, which do not express these receptors. Therefore, TRAIL has excellent potential to be a selective prostate cancer therapeutic agent with minimal toxic side effects. However, prostate cancer cells, as many other cancer types, develop resistance to TRAIL, and the underlying molecular mechanisms require further investigation. We hypothesize that selenium may sensitize TRAIL-resistant cells to undergo caspase-mediated apoptosis and increase therapeutic efficacy. Here, we report that TRAIL signaling in LNCaP prostate cancer cells stalled at downstream of caspase-8 and BID cleavage, as indicated by the lack of Bax translocation into mitochondria, and no subsequent activation of the caspase-9 cascade. Selenite induced a rapid generation of superoxide and p53 Ser(15) phosphorylation and increased Bax abundance and translocation into the mitochondria. Selenite and TRAIL combined treatment led to synergistic increases of Bax abundance and translocation into mitochondria, loss of mitochondrial membrane potential, cytochrome c release, and cleavage activation of caspase-9 and caspase-3. Inactivating p53 with a dominant-negative mutant abolished apoptosis without affecting superoxide generation, whereas a superoxide dismutase mimetic agent blocked p53 activation, Bax translocation to mitochondria, cytochrome c release, and apoptosis induced by selenite/TRAIL. In support of Bax as a crucial target for cross-talk between selenite and TRAIL pathways, introduction of Bax into p53 mutant DU145 cells enabled selenite to sensitize these cells for TRAIL-induced apoptosis. Taken together, the results indicate that selenite induces a rapid superoxide burst and p53 activation, leading to Bax up-regulation and translocation into mitochondria, which restores the cross-talk with stalled TRAIL signaling for a synergistic caspase-9/3 cascade-mediated apoptosis execution.     

Glycogen synthase kinase-3beta suppression eliminates tumor necrosis factor-related apoptosis-inducing ligand resistance in prostate cancer

Prostate cancer is a major health threat for American men. Therefore, the development of effective therapeutic options is an urgent issue for prostate cancer treatment. In this study, we evaluated the effect of glycogen synthase kinase-3beta (GSK-3beta) suppression on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human prostate cancer cell lines. In the presence of lithium chloride (LiCl) or SB216763, the GSK-3beta inhibitors, TRAIL-induced cell death was dramatically enhanced, and the enhanced cell death was an augmented apoptotic response evidenced by increased Annexin V labeling and caspase-3 activation. GSK-3beta gene silencing mediated by a small interference RNA (siRNA) duplex also sensitized the cells to TRAIL, confirming the specificity of GSK-3beta suppression. Importantly, TRAIL stimulation increased GSK-3beta tyrosine phosphorylation at Y216, suggesting that GSK-3beta is activated by TRAIL. Furthermore, TRAIL sensitization was associated with increased proteolytic procession of caspase-8 and its downstream target BID, and z-IETD-FMK, the inhibitor specific to active caspase-8 totally blocked LiCl-induced TRAIL sensitization. Finally, Trichodion, a potent nuclear factor-kappaB (NF-kappaB) inhibitor, could not affect LiCl-induced TRAIL sensitization, although GSK-3beta inhibitors significantly blocked TRAIL-reduced NF-kappaB activity in prostate cancer cells. These results indicate that GSK-3beta suppression sensitizes prostate cancer cells to TRAIL-induced apoptosis that is dependent on caspase-8 activities but independent of NF-kappaB activation, and suggest that a mechanism involving GSK-3beta activation may be responsible for TRAIL resistance in prostate cancer cells.     

Enhancement of Apo2L/TRAIL-mediated cytotoxicity in esophageal cancer cells by cisplatin

Although expressing adequate levels of functional tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR4/DR5, significant proportion of cancer cells exhibit resistance to the cytotoxic effect of this ligand. Exposure of Apo2L/TRAIL-refractory cancer cells to cytotoxic chemotherapeutic agents enhances their sensitivity to Apo2L/TRAIL cytotoxicity. This study aims to elucidate the molecular mechanism responsible for the cisplatin-mediated enhancement of Apo2L/TRAIL sensitivity in cultured esophageal cancer cells. Exposure of cancer cells to sublethal concentrations of cisplatin resulted in profound potentiation of their susceptibility to Apo2L/TRAIL cytotoxicity as indicated by 2- to >20-fold reduction in Apo2L/TRAIL IC50 values. Significant activation of caspase-8, caspase-9, and caspase-3 was observed only in cells treated with cisplatin/Apo2L/TRAIL combination and not in those exposed to either agent alone. More importantly, activation of these key caspases was significantly abrogated by overexpression of Bcl2 or by the selective caspase-9 inhibitor. This observation strongly suggested that caspase-8 activation in cells treated with the cisplatin/Apo2L/TRAIL combination was secondary to the mitochondria-mediated amplification feedback loop and activation of the executioner caspase-3 was dependent on the recruitment of the intrinsic pathway characteristic of the type II cell. Profound combination-mediated cytotoxicity and induction of apoptosis was completely suppressed either by Bcl2 overexpression or by inhibition of caspase-9 activity, which conclusively pointed to the essential role of the mitochondria-dependent death signaling cascade in this process. Cisplatin sensitizes esophageal cancer cells to Apo2L/TRAIL cytotoxicity by potentiation of the mitochondria-dependent death signaling pathway that leads to amplification of caspase activation, particularly caspase-8, by the feedback loop to efficiently induce apoptosis.     

2-methoxy-5-amino-N-hydroxybenzamide sensitizes colon cancer cells to TRAIL-induced apoptosis by regulating death receptor 5 and survivin expression

TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis is a crucial event in the control of tumor growth. However, many cancer cells, including colon cancer cells, are resistant to TRAIL-driven cell death. We have recently shown that 2-methoxy-5-amino-N-hydroxybenzamide (herein termed 2-14), a novel derivative of mesalamine, induces endoplasmic reticulum stress in colon cancer cells. Because endoplasmic reticulum stress-induced signals regulate the expression of molecules involved in TRAIL-driven apoptosis, we examined whether 2-14 makes colon cancer cells sensitive to TRAIL. Colon cancer cells were cultured with 2-14 and/or TRAIL. Death receptor (DR) 4/DR5 were analyzed by real-time PCR and flow cytometry. TRAIL pathway-associated proteins and extracellular signal-regulated kinase (ERK) were assessed by Western blotting. The in vivo capability of 2-14 to sensitize colon cancer cells to TRAIL-induced apoptosis was evaluated in a syngenic colon cancer model in which CT26-derived grafts were induced in mice. 2-14 promoted ERK-dependent induction of DR5, thereby enhancing TRAIL-mediated caspase-8 activation and apoptosis. Analysis of TRAIL-related pro- and antiapoptotic factors and functional studies revealed that survivin is involved in the protection of colon cancer cells against TRAIL-driven apoptosis. Notably, 2-14 enhanced ubiquitination and proteasome-mediated degradation of survivin. These data were confirmed in a murine model of TRAIL-resistant colon cancer in which 2-14 upregulated DR5, reduced survivin expression, and synergized with TRAIL in inhibiting tumor growth. Similarly, intraperitoneal administration of 2-14 to mice upregulated DR5 and downregulated survivin in a model of colitis-associated colon cancer. These findings indicate that 2-14 acts as a sensitizer for TRAIL-induced apoptosis and suggest that 2-14 can be useful in the therapy for TRAIL-resistant colon cancer.     

Curcumin suppresses constitutive activation of nuclear factor-kappa B and requires functional Bax to induce apoptosis in Burkitt's lymphoma cell lines

We provide evidence that curcumin, a natural compound isolated from rhizomes of plant Curcuma longa, induces apoptosis in several Burkitt's lymphoma cell lines expressing Bax protein (AS283A, KK124, and Pa682PB), whereas it has no effects in cell lines with no Bax expression (BML895 and CA46). Our data show that curcumin treatment results in down-regulation of constitutive activation of nuclear factor-kappaB (NF-kappaB) via generation of reactive oxygen species where it causes conformational changes in Bax protein leading to loss of mitochondrial membrane potential and release of cytochrome c to the cytosol. This leads to activation of caspase-9, caspase-3, and poly(ADP)-ribose polymerase cleavage leading to caspase-dependent apoptosis. In addition, curcumin treatment of Burkitt's lymphoma cell lines also causes up-regulation of DR5; however, this up-regulation does not result in apoptosis. Importantly, cotreatment with curcumin and TRAIL induces apoptosis in Bax-deficient cell lines. Taken together, our findings suggest that curcumin is able to induce apoptosis in Bax-positive cell lines, whereas combinations with TRAIL result in apoptosis in Bax-negative cell lines. These findings also raise the possibility that incorporation of curcumin in treatment regimens may provide a novel approach for the treatment of Burkitt's lymphomas and provide the molecular basis for such future translational efforts.     

AAV-encoded expression of TRAIL in experimental human colorectal cancer leads to tumor regression

Gene transfer vectors based on the adeno-associated virus (AAV) are used for various experimental and clinical therapeutic approaches. In the present study, we demonstrate the utility of rAAV as a tumoricidal agent in human colorectal cancer. We constructed an rAAV vector that expresses tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) and used it to transduce human colorectal cancer cells. TRAIL belongs to the TNF superfamily of cytokines that are involved in various immune responses and apoptotic processes. It has been shown to induce cell death specifically in cancer cells. Transduction with AAV.TRAIL gave rise to rapid expression of TRAIL, followed by induction of apoptosis, which could be inhibited by the caspase inhibitor z-VAD.fmk, in several human colon cancer cell lines. The apoptotic mechanism included activation of caspase-3, as well as cytochrome c release from mitochondria. The outgrowth of human colorectal tumors grown in mice was completely blocked by transduction with AAV.TRAIL in vitro, while in vivo transduction significantly inhibited the growth of established tumors. AAV vectors could provide a safe method of gene delivery and offer a novel method of using TRAIL as a therapeutic protein.     

Down-regulation of X-linked inhibitor of apoptosis synergistically enhanced peroxisome proliferator-activated receptor gamma ligand-induced growth inhibition in colon cancer

We found previously that X-linked inhibitor of apoptosis protein (XIAP), a potent endogenous inhibitor of apoptosis, is overexpressed in colon cancer. Ligand-induced activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to exert proapoptotic and antiproliferative effects in many cancer cell types. However, neither XIAP down-regulation alone nor monotherapy using PPARgamma ligands is potent enough to control colon cancer. We explored whether XIAP inhibition and PPARgamma activation offer a synergistic anticancer effect in colon cancer. HCT116-XIAP(+/+) and HCT116-XIAP(-/-) cells were treated with troglitazone or 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-PGJ(2)). Cell growth and apoptosis were measured. Nude mice were s.c. inoculated with HCT116 cells with or without oral troglitazone. Tumor growth, angiogenesis, and apoptosis were measured. Troglitazone- and 15-PGJ(2)-induced growth inhibition and apoptosis were more prominent in HCT116-XIAP(-/-) cells. Troglitazone- and 15-PGJ(2)-induced apoptosis correlated with enhanced cleavage of caspases and poly(ADP-ribose) polymerase, which were more profound in HCT116-XIAP(-/-) cells. Pretreatment of cells with XIAP inhibitor 1396-12 also sensitized HCT116-XIAP(+/+) cells to PPARgamma ligand-induced apoptosis. Troglitazone significantly retarded the growth of xenograft tumors, more significantly so in HCT116-XIAP(-/-) cell-derived tumors. Reduction of tumor size was associated with reduced expression of Ki-67, vascular endothelial growth factor, and CD31 as well as increased apoptosis. Loss of XIAP significantly sensitized colorectal cancer cells to PPARgamma ligand-induced apoptosis and inhibition of cell proliferation. Thus, simultaneous inhibition of XIAP and activation of PPARgamma may have a synergistic antitumor effect against colon cancer.     

Overcoming acquired resistance to TRAIL by chemotherapeutic agents and calpain inhibitor I through distinct mechanisms.

We recently found that repeated application of adenovectors expressing the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or recombinant TRAIL proteins to TRAIL-susceptible cancer cells resulted in selection and expansion of TRAIL-resistant cells. Overcoming this acquired resistance to TRAIL is desirable for TRAIL-mediated cancer therapy. Here we demonstrate that several chemotherapeutic agents, including 5-fluorouracil (5-FU) and mitomycin, and calpain inhibitor I, an NFkappaB inhibitor, can overcome acquired resistance to TRAIL in DLD1 colon cancer cells. The combination of TRAIL (approved gene symbol TNFSF10) gene therapy and 5-FU enhanced tumor suppression in vivo in nude mice bearing subcutaneous tumors established from TRAIL-resistant colon cancer cells. Whereas treatment with the combination of TRAIL and 5-FU or mitomycin led to enhanced activation of caspase-3, the combination of TRAIL and calpain inhibitor I resulted in enhanced activation of both caspase-8 and caspase-3. Moreover, mitomycin, but not 5-FU or calpain inhibitor I, induced overexpression of the BAX gene, which was correlated with enhanced TRAIL-induced cell killing in TRAIL-resistant DLD1 cells. Together, these results suggest that acquired resistance to TRAIL can be overcome by different mechanisms and that combinations of TRAIL gene therapy and chemotherapy may be a useful approach for cancer treatment.