Sensitization of human colon cancer cells to trail-mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the tumor necrosis factor (TMF) family, is thought to induce apoptosis preferentially in cancer cells; however, increasing evidence suggests that a number of cancers are resistant to TRAIL treatment. FLICE-like inhibitory protein (FLIP), which structurally resembles caspase-8, can act as an inhibitor of apoptosis when expressed at high levels in certain cancer cells. The purpose of our present study was to determine whether human colon cancer cells are sensitive to TRAIL treatment and, if not, to identify potential mechanisms of resistance. Colon cancer cells of different metastatic potential (KMlZC, KML4A, and KM20) were found to be resistant to the effects of TRAIL when used as a single agent. FLIP expression levels were increased in all three KM cell lines. Treatment with either actinomycin D (Act D;10 μ/ml) or cycloheximide (CHX; 10 μg/ml) decreased FLIP expression levels in all three cell lines. The decrease in cellular levels of FLIP was associated with sensitization to TRAIL-mediated apoptosis, as demonstrated by enhanced cell death and caspase-3 activity compared with either Act D or CHX alone. Our findings suggest that reduction of FLIP levels by Act D or CHX renders TRAIL-resistant human colon cancer cells sensitive to TRAIL-mediated apoptosis. The combination of TRAIL along with agents such as Act D or CHX, which target proteins that prevent cell death, may provide a more effective and less toxic regimen for treatment of resistant colon cancers. Presented at the Forty-First Annual Meeting of The Society for Surgery of the Alimentary Tract, San Diego, Calif., May 2l–24, 2000, and published as an abstract in Gastroentmolog 118:A1025, 2000. Supported by grants R01 AG10885, R01 DK48498, PO1 DK35608, and T32 DK07639 from the National Institutes of Health, Bethesda, Md.     

Targeted RNA interference of PI3K pathway components sensitizes colon cancer cells to TNF-related apoptosis-inducing ligand (TRAIL)

BACKGROUND: The phosphoinositide 3-kinase (PI3K/Akt) pathway transduces signals initiated from growth factors. Previously, we identified an important role for PI3K/Akt in colon cancer progression. The purpose of this study was to determine (1) whether short interfering RNA (siRNA) directed to PI3K/Akt components can render colon cancer cells sensitive to treatment with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and (2) the cellular mechanisms contributing to the enhanced sensitivity. METHODS: Human colon cancer cells KM20 and KM12C (both TRAIL resistant) were transfected with siRNA directed against the PI3K p85alpha regulatory subunit Akt1 or nontargeting control sequence and then treated with TRAIL (100 ng/mL) or vehicle. A ribonuclease protection assay was performed to assess changes in TRAIL receptor expression. Protein was extracted and analyzed by Western blot for expression of cleavage of TRAIL receptors (death receptor (DR) 4 and 5), caspase-3, caspase-8, and BID. Apoptosis was measured by enzyme-linked immunosorbent assay of DNA fragmentation. RESULTS: Combination treatment with p85alpha or Akt1 siRNA and TRAIL increased apoptosis in KM20 and KM12C cells, compared with TRAIL alone; these results were corroborated further by complete inhibition of apoptosis by Z-acetyl-Asp-Glu-Val-Asp-(DEVD)-fmk, a caspase-3 inhibitor. Furthermore, siRNA-mediated PI3K pathway inhibition resulted in increased expression of the TRAIL death receptors 4 and 5. CONCLUSIONS: Inhibition of PI3K/Akt by RNA interference sensitizes resistant colon cancer cells to TRAIL-induced cell death through the induction of TRAIL receptors and activation of caspase-3 and caspase-8. Agents that selectively target the PI3K/Akt pathway may enhance the effects of chemotherapeutic agents and provide novel adjuvant treatment for selected colon cancers.     

Effect of the XIAP inhibitor Embelin on TRAIL-induced apoptosis of pancreatic cancer cells

BACKGROUND: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in a wide variety of tumor cells, while it has no toxicity for the majority of normal cells.Therefore, TRAIL may be a suitable agent for anticancer therapy. We previously reported that a number of pancreatic cancer cell lines show resistance to TRAIL-induced apoptosis via overexpression of XIAP and FLIP. The present study was conducted to further examine TRAIL-based therapeutic strategies by aiming to restore functional apoptotic pathways in resistant pancreatic cancer cells. METHODS: In various pancreatic cancer cell lines, TRAIL-induced apoptosis was evaluated in the presence or absence of an XIAP-inhibitor (Smac peptide). Second, TRAIL-induced apoptosis was evaluated in TRAIL-resistant AsPC-1 cells with or without FLIP antisense. Third, the combined effect of Smac peptide and FLIP antisense was tested, and the activation of apoptosis-related caspases and poly (ADP-ribose) polymerase was evaluated. Finally, TRAIL-induced apoptosis was evaluated in the presence or absence of FLIP antisense and an XIAP inhibitor (embelin). RESULTS: Smac peptide enhanced TRAIL-induced apoptosis in a dose-dependent manner for several pancreatic cancer cell lines, but showed no effect on TRAIL-resistant AsPC-1 cells. Smac peptide alone had no influence on cell viability. TRAIL-induced apoptosis was restored in TRAIL-resistant AsPC-1 cells by exposure to FLIP antisense, which suppressed the expression of FLIP. The effect of TRAIL was augmented by the combination of FLIP antisense and Smac peptide. Similarly, TRAIL-induced apoptosis was restored by the combination of FLIP antisense and embelin. Activation of apoptotic caspases and cleavage of poly (ADP-ribose) polymerase was observed after sensitization of TRAIL-resistant pancreatic cancer cells. CONCLUSIONS: Pancreatic cancer cells gain resistance to TRAIL-induced apoptosis via expression of the antiapoptotic proteins XIAP and FLIP. Smac peptide and FLIP antisense could restore the apoptotic effect of TRAIL. An XIAP inhibitor, embelin, enhanced the effect of TRAIL in the presence of FLIP antisense. These findings may provide useful information for the development of TRAIL-based therapeutic strategies by restoring functional apoptotic pathways in resistant pancreatic cancer cells. In addition, a low molecular weight XIAP inhibitor like embelin could be a lead compound for the development of effective XIAP inhibitors.     

Regulation of the resistance to TRAIL-induced apoptosis as a new strategy for pancreatic cancer

BACKGROUND: Tumor necrosis factor-related, apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in a wide variety of tumor cells, but it does not cause toxicity in the majority of normal cells. Therefore, TRAIL could become a suitable agent for anticancer therapies. However, a number of tumor cell lines are known to be resistant to TRAIL-induced apoptosis. The purpose of this study was to determine the mechanisms of resistance to TRAIL in pancreatic cancer cells. METHODS: In human pancreatic cancer cell lines, the sensitivity to TRAIL-induced apoptosis was tested. The expression of TRAIL receptors (DR4, DR5, DcR1, and DcR2) and the expression of death signal-transducing proteins were investigated. In the TRAIL-resistant pancreatic cancer cells, effects of cycloheximide, a protein synthesis inhibitor, on death signal-transducing proteins were tested. Finally, the effects of the combined treatment with cycloheximide and TRAIL on the induction of apoptosis and on the expression of death signal-transducing proteins were examined. RESULTS: Pancreatic cancer cells responded to TRAIL in a different way. Resistant cell lines, AsPC-1, Suit-2, and CFPAC-1, expressed higher levels of FLIP-S protein, one of the splice variants of FLIP. Cycloheximide reduced the expression of FLIP in the resistant cells. Combined treatment with cycloheximide and TRAIL induced cleaved forms of caspases and simultaneously restored the sensitivity to TRAIL-induced apoptosis in the resistant cells. CONCLUSIONS: Pancreatic cancer cells are resistant to TRAIL-induced apoptosis via strong expression of the anti-apoptotic protein FLIP-S. Suppression of FLIP-S by cycloheximide restored sensitivity to TRAIL-induced apoptosis in resistant cancer cells. These findings may provide useful information for the development of TRAIL-based therapeutic strategies aimed at restoring the functionality of apoptotic pathways in pancreatic cancer cells.     

肿瘤坏死因子相关凋亡诱导配体诱导结肠癌HCT-116细胞凋亡和炎性反应相关基因表达的研究

目的探讨肿瘤坏死因子相关凋亡诱导配体（TRAIL）对结肠癌细胞凋亡和炎性反应相关基因表达的影响。方法HCT-116细胞经10μg／L和100μg／L重组人类TRAIL蛋白处理后,应用荧光实时定量PCR和试剂盒测定凋亡相关基因（Bcl-2、Bad、caspase-3和-8）和炎性反应相关基因（TNF—α,IL-1β,COX-2）的表达水平。结果经10μg几和100μg／L重组人类TRAIL蛋白孵育处理24h后．HCT-116细胞的凋亡率分别为27．4％和45．9％。同时抗凋亡基因Bcl-2、促凋亡基因Bad以及凋亡指示基因caspase-3和caspase-8的表达均显著上调。且100μg／L组的上调幅度均高于10μg／L组（P〈0．05）。TRAIL蛋白处理后,炎性反应相关基因TNF-α,IL-1β,COX-2的表达亦显著上升．且100μg／L处理组的上升幅度均高于10μg／L组（P〈0．05）。结论TRAIL重组蛋白能够诱导结肠癌细胞凋亡以及炎性反应的发生。     

Ionizing radiation enhances the therapeutic potential of TRAIL in prostate cancer in vitro and in vivo: Intracellular mechanisms

BACKGROUND: We assessed the influence of sequential treatment of ionizing radiation followed by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) on intracellular mechanisms of apoptosis of prostate tumor cells in vitro and in vivo. METHODS: Prostate normal and cancer cells were exposed to irradiation and TRAIL. Four- to 6-week-old athymic nude mice were injected s.c. with PC-3 tumor cells. Tumor bearing mice were exposed to irradiation and TRAIL, either alone or in combination (TRAIL after 24 hr of irradiation), and tumor growth, apoptosis, and survival of mice were examined. Expressions of death receptors, Bcl-2 family members, and caspase were measured by Western blotting, ELISA, and ribonuclease protection assay; tumor cellularity was assessed by H&E staining; inhibition of p53 was performed by RNA interference (RNAi) technology, and apoptosis was measured by annexin V/propidium iodide staining, and terminal deoxynucleotidyltransferase-mediated nick end labeling assay. RESULTS: Irradiation significantly augmented TRAIL-induced apoptosis in prostate cancer cells through upregulation of DR5, Bax, and Bak, and induction of caspase activation. Dominant negative FADD and p53 siRNA inhibited the synergistic interaction between irradiation and TRAIL. The pretreatment of cells with irradiation followed by TRAIL significantly enhanced more apoptosis than single agent alone or concurrent treatment. Furthermore, irradiation sensitized TRAIL-resistant LNCaP cells to undergo apoptosis. The sequential treatment of xenografted mice with irradiation followed by TRAIL-induced apoptosis through activation of caspase-3, induction of Bax and Bak, and inhibition of Bcl-2, and completely eradicated the established tumors with enhanced survival of nude mice. CONCLUSION: The sequential treatment with irradiation followed by TRAIL can be used as a viable option to enhance the therapeutic potential of TRAIL in prostate cancer.     

Caspase-8 activation is necessary but not sufficient for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in the prostatic carcinoma cell line LNCaP

BACKGROUND: The differential sensitivity of tumor cells to TRAIL-induced apoptosis may be mediated by different intracellular inhibitors of apoptosis, and only a few reports have described the pathway(s) that are activated in response to TRAIL in prostate cells. METHODS: LNCaP was transfected with a dominant-negative form of FADD (FADD-DN) and cells were selected in the presence of hygromycin. Cell viability was estimated by calcein assay. Apoptosis was estimated by caspase activation using both fluorogenic substrates and Western blot analysis of activated caspases. To detect cytochrome c release, mitochondria-free cytosol was prepared and Western blot analysis was performed. RESULTS: LNCaP is resistant to TRAIL but TRAIL transiently induces DEVDase activity and activation of caspase-8; caspase-2, -3, -7, and -9 were not activated. Wortmannin, an inhibitor of the PI3K/Akt pathway, converted the phenotype of LNCaP from TRAIL-resistant to -sensitive. In the presence of wortmannin TRAIL induced activation of caspase-2, -3, -7, -8, and -9, as well as dissipation of mitochondrial transmembrane potential and release of cyto-chrome c from mitochondria into the cytosol. In addition, combined TRAIL and wortmannin treatment resulted in cleavage of several proteins: PARP, Akt, p21/WAF1, and MDM2 as well as dephosphorylation of Akt. The proteolysis of p21/WAFI and Akt, which are known survival factors, presumably amplify the apoptotic cascade in LNCaP. Transfection of FADD-DN in LNCaP resulted in inhibition of caspase activation as well as in resistance to combined treatment with TRAIL and wortmannin. CONCLUSIONS: These results suggest that caspase-8 activation is necessary but not sufficient for TRAIL-mediated apoptosis and is presumably blocked downstream of caspase-8 by the PI3K/Akt pathway.     

Valproic Acid Sensitizes TRAIL-Resistant Anaplastic Thyroid Carcinoma Cells to Apoptotic Cell Death

Background

Anaplastic thyroid carcinoma (ATC) is an aggressive human tumor associated with a median survival of 2–6 months. TRAIL, as a ligand of death receptors, is known to induce apoptotic cell death in several cancer cells. However, TRAIL treatment alone is not effective against TRAIL-resistant cancer cells. This study was designed to investigate whether valproic acid (VPA) enhances apoptotic cell death of TRAIL-resistant ATC cells and to identify the mechanism of cell death of ATC cells by combination treatment with VPA and TRAIL.

Methods

To evaluate the cytotoxic effect of TRAIL and/or VPA on ATC cells, we used the MTT assay. The effects of VPA and TRAIL on apoptosis were assessed using FACS analysis (Annexin-V/PI stain) and Western blotting.

Results

The combination of VPA with TRAIL significantly induced apoptotic cell death compared with 8505C and ARO cells treated with TRAIL alone. The protein levels of cleaved caspase-8, -3, and PARP were increased in VPA and TRAIL co-treated ARO cells. The combination induced the activation of JNK and the phosphorylation of FADD and c-Jun but not p38. However, pretreatment with caspase inhibitors reduced the expression of cleaved caspase-8, -3, and PARP in co-treated ARO cells. SP600125 remarkably reduced the expression of cleaved caspase-8, -3, and PARP and the phosphorylation of FADD and c-Jun, as well as apoptotic cell death.

Conclusions

VPA sensitized TRAIL-resistant ATC cells to apoptotic cell death through involvement of the JNK pathway. Thus, the combination of VPA and TRAIL may be a promising therapy for ATC.

     

Enhanced sensitivity of bladder cancer cells to tumor necrosis factor related apoptosis inducing ligand mediated apoptosis by cisplatin and carboplatin

PURPOSE: The development and acquisition of multiple drug resistance in cancer cells are a consequence of cancer chemotherapy and remain a major obstacle in treatment. Therefore, there is an obvious need for alternative approaches, such as immunotherapy and gene therapy. Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is one of the tumor necrosis factor ligand families and it selectively induces apoptosis against cancer cells. Several cytotoxic anticancer drugs also mediate apoptosis and may share the common intracellular pathways leading to apoptosis. We reasoned that combination treatment of cancer cells with TRAIL and drugs may overcome this resistance. We evaluated whether bladder cancer cells are sensitive to TRAIL mediated cytotoxicity and whether TRAIL may synergize with anticancer agents in cytotoxicity and apoptosis against bladder cancer cells. MATERIALS AND METHODS: Cytotoxicity was determined by a 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis. RESULTS: Human T24 bladder cancer line was relatively resistant to TRAIL and TRAIL was not cytotoxic against normal bladder cells. Treatment of T24 cells with TRAIL in combination with 5-fluorouracil or mitomycin C did not overcome resistance to these agents. However, treatment of T24 cells with a combination of TRAIL and cisplatin resulted in a synergistic cytotoxic effect. Synergy was also achieved in the cisplatin resistant T24 line (T24/CDDP), 2 other bladder cancer lines and 3 freshly derived bladder cancer cells. The combination of TRAIL and carboplatin resulted in a synergistic cytotoxic effect on T24 cells. However, the combination of TRAIL and trans-diamminedichloroplatinum (II) resulted in an antagonistic cytotoxic effect. The synergy achieved in cytotoxicity with TRAIL and cisplatin was also achieved in apoptosis. Treating T24 cells with cisplatin enhanced the expression of bax but not bcl-2. Incubation of T24 cells with TRAIL increased the intracellular accumulation of cisplatin. CONCLUSIONS: This study demonstrates that combination treatment of bladder cancer cells with TRAIL and cisplatin overcomes their resistance. The sensitization obtained with established cisplatin resistant and freshly isolated bladder cancer cells required low subtoxic concentrations of cisplatin, supporting the in vivo potential application of a combination of TRAIL and cisplatin for treating TRAIL resistant and cisplatin resistant bladder cancer.     

Sensitivity of prostate cells to TRAIL-induced apoptosis increases with tumor progression: DR5 and caspase 8 are key players

BACKGROUND: As advanced prostate cancers are resistant to currently available chemotherapies, we evaluated the cytotoxic effect of TNF-related apoptosis-inducing ligand (TRAIL) and characterized the involvement of its five receptors DR4, DR5, DcR1, DcR2, and osteoprotegerin (OPG) and of the death-inducing signaling complex (DISC)-forming proteins caspase 8 and c-FLIP in prostate cell lines. METHODS: We used six prostate cell lines, each corresponding to a particular stage in prostate tumorigenesis, and analyzed TRAIL sensitivity in relation to TRAIL receptors' expression. RESULTS: TRAIL sensitivity was correlated with tumor progression and DR5 expression levels and apoptosis was exclusively mediated by DR5. DcR2 was significantly more abundant in tumor cells than in non-neoplastic ones and may contribute to partial resistance to TRAIL in some prostate tumor cells. Conversely, non-tumoral cells secreted high levels of OPG, which can protect them from apoptosis. Finally, caspase 8 expression levels were as DR5 directly correlated to TRAIL sensitivity in prostate tumor cells. CONCLUSION: TRAIL-induced apoptosis is closely related to the balanced expression of its different receptors in prostate cancer cells and their modulation could be of potential clinical value for advanced tumor treatment.     

MicroRNA-221 silencing predisposed human bladder cancer cells to undergo apoptosis induced by TRAIL

ObjectivesBladder cancer is the most common type of urologic cancer in Chinese males. The 5-year survival rate of advanced bladder cancer is approximately 20%–40%. There is an obvious urgent need for novel and effective therapies against bladder cancer. MicroRNAs (miRNAs) are a recently discovered class of noncoding RNAs; suppressing miRNA-221 might prove beneficial in several cancers. To explore novel and effective therapies against bladder cancer, we explored the effects of miRNA-221 silencing on the survival of bladder cancer cells.Materials and methodsNorthern blot analysis was used to determine miRNA-221 expression levels in bladder cancer T24 cells, RT4 cells and human normal urothelial cells. miRNA-221 was silenced with antisense oligonucleotides in T24 cells and pro-apoptotic effect of necrosis factor related apoptosis-inducing ligand (TRAIL) on miRNA-221-silenced cells was assessed with flow cytometry. The p27^kip1 protein expression in miRNA-221-silenced cells exposed to TRAIL was detected by Western blotting. The role of miRNA-221 silencing on T24 cell cycle phase distribution was investigated through flow cytometric analysis.ResultsHuman miRNA-221 was significantly up-regulated in bladder cancer T24 cells and RT4 cells compared to human normal urothelial cells. T24 cell was TRAIL-resistant cell line. MiRNA-221 silencing predisposed T24 cells to undergo apoptosis induced by TRAIL and resulted in an up-modulation of cyclin-dependent kinase inhibitor p27Kip1. MiRNA-221 suppression promoted the activation of caspase 3 induced by TRAIL in T24 cells.ConclusionsMiRNA-221 silencing rendered human bladder cancer T24 cells to undergo apoptosis induced by TRAIL. Our findings suggest a potential role of suppressing miRNA-221 in human bladder cancer therapy.     

Subtoxic concentration of doxorubicin enhances TRAIL-induced apoptosis in human prostate cancer cell line LNCaP

Most tumor cells are sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis but sparing to normal cells, thus providing therapeutic potential for clinical use. Some tumor cells are resistant to TRAIL-induced cell death while the sensitivity could be recruited with the existence of some chemical agents. In this study, human prostatic cancer cell line LNCaP was found to be resistant to TRAIL-induced apoptosis while it could be restored to TRAIL sensitivity with combination treatment of low concentration of doxorubicin. TRAIL receptor-1 (DR4) and TRAIL receptor-2 (DR5) were upregulated under the treatment of doxorubicin and verified to be responsible for TRAIL-mediated signal transduction. Furthermore, caspase-8 and caspase-3 were activated and drove their autocleavage into programmed cell death. Interestingly, apoptosis-inhibitory protein c-FLIP, but not Bcl-2 and XIAP was downregulated after doxorubicin treatment. Taken together, these findings suggested that the pathway of cell apoptosis induced by TRAIL was intact but under negative control. Subtoxic concentration of doxorubicin effectively boosted TRAIL sensitivity via depletion of antiapoptotic protein. These findings support the new strategies for killing tumors with TRAIL and chemical agents.     

Enhancement of Apo2L/TRAIL (tumor necrosis factor-related apoptosis-inducing ligand)-induced apoptosis in non-small cell lung cancer cell lines by chemotherapeutic agents without correlation to the expression level of cellular protease caspase-8 inhibitory protein.

OBJECTIVE: Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potential anticancer drug that promotes apoptosis specifically in tumor cells. Because not all cancer cells are susceptible to Apo2L/TRAIL, the aim of our study was to determine whether non-small cell lung cancer cells can be sensitized by chemotherapeutic agents for Apo2L/TRAIL-induced apoptosis. In addition, endogenous expression levels of the caspase-inhibiting cellular protease caspase-8 inhibitory protein (C-FLIP) were measured to investigate partial resistance to Apo2L/TRAIL. METHODS: Six human lung cancer cell lines (A549, NCI-H358, Calu1, Calu6, SkMes1, and SkLu1) were incubated with soluble Apo2L/TRAIL and two different concentrations each of cisplatin, paclitaxel, doxorubicin, 5-fluorouracil, and camptothecin. After 24 hours the rate of apoptosis was measured by annexin V/propidium iodide staining followed by FACScan analysis. Expression levels of C-FLIP in cell lines and lung cancer biopsy specimens were determined by Western blotting. RESULTS: Treatment of lung cancer cells with Apo2L/TRAIL alone resulted in apoptotic cell death in four cell lines (P <.001). Combining Apo2L/TRAIL and chemotherapeutic agents enhanced the rate of apoptosis significantly. Statistical analysis revealed a synergistic effect of Apo2L/TRAIL in combination with 1.8 mmol/L camptothecin and 100 micromol/L cisplatin, each in four of the six cell lines (P <.002). Western blot analysis showed that sensitization to Apo2L/TRAIL did not correlate with the expression of cellular protease caspase-8 inhibitory protein. Furthermore, no increased cellular protease caspase-8 inhibitory protein levels relative to those in normal lung tissue could be found in non-small cell lung cancer specimens from 12 patients. CONCLUSION: Apo2L/TRAIL-induced apoptosis in non-small cell lung cancer cell lines is significantly enhanced by chemotherapeutic agents. Resistance and sensitization to Apo2L/TRAIL are not correlated with the endogenous expression level of cellular protease caspase-8 inhibitory protein, implying that in non-small cell lung cancer other mechanisms are responsible for inhibition of the Apo2L/TRAIL pathway. Even though the molecular mechanism remains unclear, the combination of Apo2L/TRAIL with chemotherapy may be a promising treatment modality for non-small cell lung cancer.     

Proteasome inhibition blocks caspase-8 degradation and sensitizes prostate cancer cells to death receptor-mediated apoptosis

BACKGROUND: Proteasome inhibition through the administration of Velcade is a viable chemotherapeutic strategy that is approved to treat multiple myeloma and is being evaluated for efficacy against prostate cancer. Currently, the apoptotic pathways that contribute to this anticancer response are poorly understood. Our goal is to test the extent to which proteasome inhibition modulates apoptosis through death receptor pathways. METHODS: Several prostate cancer cell lines and primary prostate epithelial cells (PrECs) were used as models. The death receptor pathway was activated by the expression of Fas ligand (FasL) or addition of TNF-related apoptosis-inducing ligand (TRAIL) in the presence or absence of proteasome inhibitors. The apoptotic response was quantified by annexin V, TUNEL and nuclear condensation assays. Western blot analysis was conducted to quantify protein levels and enzyme assays were used to measure caspase activity. RESULTS: Proteasome inhibition markedly sensitized prostate cancer cells to apoptosis initiated by Fas ligand (FasL) or TRAIL. In the presence of either death ligand, procaspase-8 processing occurred, but led to minimal amounts of active caspase-8. The addition of Velcade, however, led to robust active caspase-8 protein abundance and activity. In the presence of Velcade the caspase-8 p18 subunit half-life increased from 22 min to over 2 hr. CONCLUSIONS: These findings demonstrate that proteasome inhibition can sensitize cells to apoptosis elicited by tumor necrosis factor ligands and retarding caspase-8 degradation provides one explanation for this activity. This study suggests that the clinical efficacy of Velcade may result, at least in part, from the activity of death ligands.     

Increased resistance to trail-induced apoptosis in prostate cancer cells selected in the presence of bicalutamide

BACKGROUND: Following prolonged treatment with the non-steroidal anti-androgen bicalutamide (Casodex), LNCaP cells have become resistant to this drug. Previously, we found that the bicalutamide-refractory subline LNCaP-Bic acquires a growth advantage and does not respond to androgenic stimulation. In the present study, we have asked whether changes in response to the tumor-selective apoptosis inducer TNF-related apoptosis-inducing ligand (TRAIL) occur in LNCaP-Bic cells. METHODS: LNCaP and LNCaP-Bic cells were incubated with increasing concentrations of TRAIL and apoptosis rate was analyzed using FACS. Expression of death receptors (DR), adaptor protein Fas-associated death domain (FADD), members of the Bcl-2 family, and caspases were investigated by Western blot. RESULTS: The percentage of cells undergoing apoptosis was lower in LNCaP-Bic in comparison to LNCaP cells. There were no major differences in death receptor expression between control LNCaP and bicalutamide-selected cells. Surprisingly, treatment with TRAIL increased the levels of Bcl-2 by 50% in LNCaP-Bic cells. The ratio cleaved caspase/procaspase-8 was substantially lower in LNCaP-Bic cells. CONCLUSIONS: Reduced sensitivity to TRAIL-induced apoptosis is a novel mechanism relevant to resistance to bicalutamide in prostate cancer. Inability of TRAIL to cause programmed cell death might be caused by multiple perturbations in the TRAIL-signaling pathway.     

Targeted induction of apoptosis via TRAIL and cryoablation: a novel strategy for the treatment of prostate cancer

Adjuvant therapies contribute to the successful treatment of cancer. Our previous reports have shown that combining cryoablation with cytotoxic agents enhances cell death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Human prostate cancer cells (PC-3) are resistant to many cytodestructive agents, including cryoablation and TRAIL. Here, we evaluated the effects of TRAIL combined with cryoablation on PC-3 and normal prostate (RWPE-1) cell death. Exposure of PC-3 cells to freezing (-10 degrees C) or TRAIL (500 ng/ml) results in minimal cell death, whereas a complete loss of viability is observed with the simultaneous combination. The synergistic effect was found to be due to a marked increase in apoptosis. Western blot analysis revealed a significant level of caspase-8 and -3 cleavage between 12 and 24 h post-exposure. Caspase activation assays provided similar results and also indicated a role for caspase-9. Inhibitors to caspase-8 and -9 along with a pan-caspase inhibitor were incorporated to determine which pathway was necessary for the combined efficacy. Inhibition of caspase-8 significantly blocked the combination-induced cell death compared to cells that did not receive the inhibitor (63% compared to 10% viable). The addition of the caspase-9 inhibitor resulted in only a minimal protection. Importantly, the combination was not effective when applied to normal prostate cells. The results describe a novel therapeutic model for the treatment of prostate cancer and provide support for future in vivo studies.