Expression of TRAIL and death receptor DR4 in Palmer type 2 TFCC lesions

Introduction

Degenerative articular disc perforations of the triangular fibrocartilage (TFC) of the wrist are characterized by fibrocartilage cell loss and are often associated with ulna-plus situations. Apoptosis has been found to play a crucial role in fibrocartilage cell loss, however, the molecular mechanism and mediators are still poorly understood.

Aim

The purpose of this study was to identify receptors to apoptosis in degenerative disc lesions.

Patients

Included in the study were 17 patients with degenerative articular disc tears of the TFC (Palmer type 2C). Following arthroscopic debridement of the TFC, histological sections were examined to assess the presence of apoptosis. Apoptosis was determined using TRAIL and death receptor DR4 agonists for immunohistochemical analyses. The number of cells positive for apoptosis was then correlated with ulna length.

Results

Cells positive for TRAIL and DR4 were found in all specimens. The number of cells positive for TRAIL was significantly increased in specimens of patients with an ulna positive variance (P = 0.040). However, DR4 was not significantly increased in ulna plus (P > 0.05). Both, TRAIL and DR4 positive cells were found to be evenly distributed throughout each specimen. There was no accumulation of any type of cells in any particular zone of the biopsies.

Conclusion

This is the first study that shows that TFCC cells express TRAIL and DR4, which suggests that apoptosis, as well as, mechanical trauma are involved in the development of disc perforation. The TRAIL/DR4 receptor system is a molecular mediator of apoptosis induction in TFC cells and therefore plays a role in cell loss in degenerative disc lesions.     

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.     

Expression of TRAIL, DR4, and DR5 in kidney and serum from patients receiving renal transplantation

Renal transplantation is the best treatment of some end-stage renal diseases. Unfortunately, not every transplant is successful due to the rejection or dysfunction of the transplanted kidney. Many cytokines participate in rejection by inducing inflammation or apoptosis. In this study, the expressions of TRAIL, DR4, and DR5 in rejected renal tissue and of serum soluble TRAIL (sTRAIL) in patients with kidney rejection were investigated by immunohistochemical staining and sandwich enzyme-linked immunosorbent assay, respectively. The results showed that the expression of TRAIL, DR4 and DR5, and serum sTRAIL levels were markedly upregulated among renal transplant patients. Since both membrane and soluble forms of TRAIL can induce apoptosis of DR4/DR5-expressing cells via recruiting FADD and caspase 8, elevated TRAIL and its receptors may participate in renal graft rejection.     

Chemotherapeutic agents sensitize sarcoma cell lines to tumor necrosis factor-related apoptosis-inducing ligand-induced caspase-8 activation, apoptosis and loss of mitochondrial membrane potential.

Chemotherapeutic agents have been used for the treatment of patients with osteosarcoma (OS). However, inherent or acquired resistance to these agents is a serious problem in the management of OS patients. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered to induce apoptosis in a variety of cancer cells but not normal cells. In the present study, we examined whether chemotherapeutic agents enhance TRAIL-induced apoptosis in the sarcoma cell lines MG-63 and SaOS-2. Pretreatment with sub-toxic or slightly toxic concentrations of chemotherapeutic agents (cis-diammine dichloroplatinum, CDDP and doxorubicin, DXR) sensitized both cell lines to TRAIL-induced apoptosis, as assessed by the propidium iodide or Annexin V-Cy5 staining method. These cell lines expressed death receptors TRAIL-receptor 1 (TRAIL-R1) and TRAIL-R2, which were unaltered by treatment with CDDP, as assessed by flow cytometry. The decoy receptors TRAIL-R3 and -R4 were barely detected in both cell lines. CDDP down-regulated c-FLIP, tending to lower the activation threshold required for TRAIL-induced caspase-8 activation. The CDDP-pretreated cells indeed demonstrated more increased TRAIL-mediated caspase-8 activation, loss of mitochondrial membrane potential (DeltaPsi(m)), and apoptosis than untreated cells. Consequently, the activated caspase-8 might lead to either activation of effector caspases such as caspase-3 or loss in DeltaPsi(m). Both the increased caspase activation and mitochondrial dysfunction induced by combination of CDDP and TRAIL would contribute to enhanced apoptotic cell death. The results of the present study would be valuable for the design of novel treatment modalities for patients with OS.     

化疗药上调DR4、DR5表达体外逆转人骨肉瘤对TRAIL的耐受

目的研究肿瘤坏死因子相关凋亡诱导配体（TRAIL）与化疗药对人骨肉瘤的联合作用及其受体（TRAILR）在人骨肉瘤中的表达间的关系。方法应用细胞计数、AO／EB染色、流式细胞术等方法比较检测阿霉素、顺铂、甲氨喋呤、紫杉醇单独作用和与TRAIL联合作用于MG-63及骨肉瘤组织的细胞毒效应；应用原位杂交、Western Blot方法检测人骨肉瘤细胞系MG-63及新鲜骨肉瘤组织用药前后TRAILR的表达。结果阿霉素、顺铂和紫杉醇增强死亡受体的表达，且与TRAIL联合作用诱导人骨肉瘤细胞凋亡的效率显著强于单用。结论阿霉素、顺铂、紫杉醇通过上调DR4、DR5表达逆转人骨肉瘤对TRAIL的耐受。     

Lack of death receptor 4 (<Emphasis Type="Italic">DR4</Emphasis>) expression through gene promoter methylation in gastric carcinoma

Background and aims  To determine the underlying mechanism for the differential expression, the extent of promoter methylation in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-related genes acting downstream of TRAIL was examined in early and advanced gastric carcinomas. Methods  The extent of promoter methylation in the DR4, DR5, DcR1, DcR2, and CASP8 genes was quantified using bisulfite modification and methylation-specific polymerase chain reaction. Results  The promoters for DcR1, DcR2, and CASP8 were largely unmethylated in early gastric carcinoma, advanced gastric carcinoma, and controls, with no significant difference among them. Protein levels of DR4, DcR1, and DcR2 as revealed by immunohistochemistry correlated with the extent of the respective promoter methylation (P < 0.05 in all cases). Hypomethylation, rather than hypermethylation, of the DR4 promoter was noted in invasive gastric malignancies, with statistical significance (P = 0.003). Conclusion  The promoter methylation status of TRAIL receptors in gastric carcinoma may have clinical implications for improving therapeutic strategies in patients with gastric carcinoma.     

Sensitization of human renal cell carcinoma cell lines to TRAIL-induced apoptosis by anthracyclines

BACKGROUND: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a new member of the tumor necrosis factor family. The present study investigated whether anthracyclines enhance TRAIL-induced apoptosis and cytotoxicity in renal cell carcinoma (RCC) cells. METHODS: Cytotoxicity was measured using the microtiter assay. Apoptosis was monitored using DNA ladder analysis. Caspase activity was determined using a quantitative colorimetric assay. RESULTS: Treatment of ACHN and Caki-1 human RCC lines with TRAIL, in combination with subtoxic concentrations of epirubicin (EPI) or pirarubicin (THP), enhanced induction of apoptosis and cytotoxicity. Sequential treatment with EPI followed by TRAIL induced significantly more cytotoxicity than the inverse treatment. The combined cytotoxicity of TRAIL and EPI was significantly inhibited by the TRAIL-neutralizing fusion protein DR5:Fc, although EPI did not affect the mRNA expression of DR4, DR5, DcR1 or DcR2. The combination treatment with TRAIL and EPI activated caspase-6 and -3, which were downstream molecules of the death receptor. Furthermore, the combined cytotoxicity of TRAIL and EPI was almost completely inhibited by Z-VAD-FMK, and partly inhibited by Ac-DMQD-CHO. CONCLUSION: These findings indicate that anthracyclines sensitize RCC cells to TRAIL-induced apoptosis and cytotoxicity through activation of caspases, suggesting that TRAIL, in combination with anthracyclines, has a therapeutic potential in the treatment of RCC.     

TRAIL受体在人骨肉瘤组织中的表达

目的 研究肿瘤坏死因子相关凋亡诱导配体(TRAIL)受体在骨肉瘤细胞中的表达情况。方法 应用逆转录—聚合酶链反应(RT—PCR)对22例骨肉瘤组织标本、MG—63骨肉瘤细胞株、U251脑胶质瘤细胞株以及正常人外周血淋巴细胞TRAILR1—R4 mRNA表达进行检测。结果 22例骨肉瘤组织标本中15例同时表达TRAILR1、-R2和-R3，4例同时表达TRAIL-R1和-R2，只表达TRAIL-R1或-R2者3例，所有标本中均未检测到TRAIL，-R4表达；MG-63骨肉瘤细胞株、U251脑胶质瘤细胞株以及正常人外周血淋巴细胞则均检测到TRAILR1、-R2和-R3的联合表达。结论 死亡受体TRAIL-R1，R2在骨肉瘤中的普遍表达，是TRAIL诱导骨肉瘤细胞凋亡的分子基础；死亡受体和诱骗受体的差异性分布，并非TRAIL对选择性杀伤肿瘤细胞的关键性因素，可能还受其它因子调控。     

Causative agents of osteomyelitis induce death domain-containing TNF-related apoptosis-inducing ligand receptor expression on osteoblasts

Bacteria and their products are potent inducers of bone destruction. While inflammatory damage during conditions such as osteomyelitis is associated with increased formation and activity of bone-resorbing osteoclasts, it is likely that bone loss also results from the elimination of the cells responsible for matrix deposition. Consistent with this notion, we have previously demonstrated that bone-forming osteoblasts undergo apoptosis following bacterial challenge and that this cell death is due, at least in part, to the actions of TNF-related apoptosis-inducing ligand (TRAIL). In the present study, we demonstrate that primary osteoblasts constitutively express death domain containing TRAIL receptors. Importantly, we show that cell surface expression of the death-inducing receptors DR4 and DR5 on murine and human osteoblasts is restricted to cells infected with the principle causative agents of osteomyelitis, Staphylococcus aureus and Salmonella. In addition, we show that the robust constitutive production by osteoblasts of the decoy TRAIL receptor, OPG, is inhibited following bacterial infection. Finally, we report that while exogenous administration of TRAIL fails to activate apoptosis signaling pathways in uninfected osteoblasts, acute bacterial exposure sensitizes these cells to this ligand. Based upon these findings we suggest a model in which bacterially challenged osteoblasts express TRAIL while concomitantly decreasing the production of the decoy receptor OPG and upregulating cell surface death receptor expression. Such an increase in TRAIL bioavailability and induced sensitivity of infected osteoblasts to this ligand would result in apoptotic cell death of this bone-forming population, providing an additional mechanism underlying inflammatory bone loss during diseases such as osteomyelitis.     

Activation of signal transducer and activator of transcription 3 (Stat3) pathway in osteosarcoma cells and overexpression of phosphorylated‐Stat3 correlates with poor prognosis

Stat3 expression in cancer may have important prognostic and therapeutic value, but there has been no reports correlating Stat3 expression with prognosis in patients with osteosarcoma. The goal of this study is to correlate patient prognosis with the expression of Stat3 in osteosarcoma tissue and determine the effectiveness of blocking this pathway in osteosarcoma cell lines by Stat3 inhibitor, CDDO‐Me. We examine the expression levels of Stat3 and pStat3 in osteosarcoma cell lines and primary tissues by Western blot analysis. We also evaluate the levels of pStat3 expression in osteosarcoma tissue microarray (TMA) by immunohistochemistry. We use clinical data to determine the impact of levels of Stat3 expression on patient prognosis. Finally, we evaluated the effect of CDDO‐Me on the inhibition of activated Stat3 pathway in osteosarcoma cell lines using MTT assay and Western blot analysis. Stat3 is observed to be activated in osteosarcoma tissues as well as in cultured cell lines. Overexpression of pStat3 is associated with poor prognosis. CDDO‐Me inhibits the growth of osteosarcoma cell lines and induces apoptosis as well. Our results suggest that Stat3 may be a prognostic indicator and potential therapeutic target for osteosarcoma. Blocking the pathway of Stat3 may lead to develop new therapeutic strategies against osteosarcoma. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:971–978, 2010     

ROCK1 as a potential therapeutic target in osteosarcoma

Osteosarcoma is the most common primary malignancy of bone. Patients with localized disease are routinely treated with surgery and chemotherapy. Unfortunately, many of these patients eventually relapse even after high‐dose pre‐ and postoperative chemotherapy. Upon recurrence of the tumor locally or distantly, they have limited treatment options that are usually unsuccessful. Our prior studies screening lentiviral shRNA libraries, searching for kinases involved in osteosarcoma cell growth and proliferation have identified the Rho‐associated coiled‐coil containing protein kinase 1 (ROCK1) as a possible hit. We show in this study that ROCK1 is highly expressed in various tumor cell lines and tumor tissues from osteosarcoma patients. ROCK1 knockdown by synthetic siRNA decreases cell proliferation, viability and induces apoptosis in osteosarcoma cell lines KHOS and U‐2OS. Finally, we established the relationship between expression levels of ROCK1 and clinical prognosis in osteosarcoma patients by using immunohistochemistry. There were significant differences in overall survival between cohorts of patients with ROCK1 levels categorized as high‐staining, moderate‐staining, and low‐staining. High levels of ROCK1 were associated with poor outcomes in clinical osteosarcoma. These findings suggest that knockdown of ROCK1 inhibits proliferation and induces apoptosis in osteosarcoma cell lines. ROCK1 may be a promising therapeutic target for the treatment of osteosarcoma patients. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1259–1266, 2011     

Targeting Cdk11 in osteosarcoma cells using the CRISPR‐cas9 system

Osteosarcoma is the most common type primary malignant tumor of bone. Patients with regional osteosarcoma are routinely treated with surgery and chemotherapy. In addition, many patients with metastatic or recurrent osteosarcoma show poor prognosis with current chemotherapy agents. Therefore, it is important to improve the general condition and the overall survival rate of patients with osteosarcoma by identifying novel therapeutic strategies. Recent studies have revealed that CDK11 is essential in osteosarcoma cell growth and survival by inhibiting CDK11 mRNA expression with RNAi. Here, we apply the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)‐Cas9 system, a robust and highly efficient novel genome editing tool, to determine the effect of targeting endogenous CDK11 gene at the DNA level in osteosarcoma cell lines. We show that CDK11 can be efficiently silenced by CRISPR‐Cas9. Inhibition of CDK11 is associated with decreased cell proliferation and viability, and induces cell death in osteosarcoma cell lines KHOS and U‐2OS. Furthermore, the migration and invasion activities are also markedly reduced by CDK11 knockout. These results demonstrate that CRISPR‐Cas9 system is a useful tool for the modification of endogenous CDK11 gene expression, and CRISPR‐Cas9 targeted CDK11 knockout may be a promising therapeutic regimen for the treatment of osteosarcoma. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:199–207, 2015.

     

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.     

白细胞介素12通过抑制survivin表达加强肿瘤坏死因子相关凋亡诱导配体诱导的肝癌细胞凋亡

目的 探讨肿瘤坏死因子相关凋亡诱导配体(TRAIL)对肝细胞癌(HCC)的治疗作用,以及TRAIL耐药的可能机制和逆转耐药方案。方法 采用原位杂交方法观察HCC与正常肝组织中TRAIL的表达差异。采用不同浓度的sTRAIL(可溶性)处理HCC细胞株及真核表达质粒pIRES-EGFP-sTRAIL转染HCC细胞株,观察sTRAIL的抑癌疗效。建立裸鼠肝癌模型,观察sTRAIL的体内抑癌作用。进一步,检测HCC中survivin的表达并采用反义寡核苷酸封闭治疗。最后,观测sTRAIL和IL-12联合抗癌效果。结果 肝癌组织DR表达量显著强于正常肝组织DR表达量。60例肝癌组织中54例不表达诱捕受体DcRl,25例不表达DcR2,而20例正常肝组织均表达DcR。两种．HCC细胞株中DcR1表达缺失。经sTRAIL(100ng/ml)处理24h,HCC细胞凋亡发生率约10％,而Jurkat细胞凋亡率达70％以上。体外pIRES-EGFP-sTRAIL转染对肝癌细胞杀伤作用不敏感。体内直接瘤体注射pIRES-EGFP-sTRAIL可对裸鼠肝癌无明显抑制作用。HCC高表达survivin,反义寡核苷酸封闭可部分逆转TRAIL耐药。IL-12使survivin表达明显下调,显著加强TRAIL对HCC细胞的杀伤作用。结论 HCC对TRAIL诱导的凋亡有耐药现象。survivin参与HCC对TRAIL的耐药机制,反义寡核苷酸封闭可部分逆转TRAIL耐药。IL-12可通过抑制siurvivin表达增强TRAIL对HCC杀癌作用。联合基因治疗(如TRAIL和IL-12基因)可能成为一种有前途HCC治疗方案。     

Antitumor effects of telomerase inhibitor TMPyP4 in osteosarcoma cell lines

Telomere studies in carcinomas have been extensively reported for prognostic utility and effective methods for targeting telomerase therapy has been described, but efficacy of telomerase inhibitor remained unknown in sarcoma cells. In this study, we investigated the effects of telomerase inhibitor cationic porphyrin TMPyP4 on telomerase activity, telomere length, cell growth, and apoptosis in osteosarcoma cell lines. TMPyP4 significantly inhibited telomerase activity in telomerase positive HOS and Saos‐2, but not in MG‐63. TMPyP4 significantly induced telomere shortening, and inhibition of the cell growth in HOS and Saos‐2 with over 17% apoptosis rates. In terms of MG‐63, TMPyP4 did not induce inhibition of both telomerase activity and cell growth, although it induced significant telomere shortening. Telomere length after treatment was 5.60 kb in HOS, 4.00 kb in Saos‐2, and 9.89 kb in MG‐63. These results may suggest that both telomerase activity loss and sufficient telomere shortening are necessary to inhibit cell growth in telomerase positive osteosarcoma cells. TMPyP4 did not induced telomere shortening but significantly inhibited the growth with 22.6% apoptosis rate in telomerase negative with extremely longer telomere‐U2OS, may indicating the antitumor effect of TMPyP4 may be related to DNA damage including telomere dysfunction through G‐quadruplex stabilization, independent on telomere length. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:1707–1711, 2011     

Enhanced proapoptotic effects of tumor necrosis factor-related apoptosis-inducing ligand on temozolomide-resistant glioma cells

OBJECT: Death receptor targeting is an attractive approach in experimental treatment for tumors such as malignant gliomas, which are resistant to radiation and chemotherapy. Among the family of cytokines referred to as death li gands, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted clinical interest. The aim of this study was to assess whether TRAIL can be used as an adjuvant to temozolomide (TMZ) for apoptosis induction in malignant glioma cell lines. METHODS: Six human malignant glioma cell lines (A172, U87, U251, T98, U343, and U373) were exposed to human (h)TRAIL, TMZ, or an hTRAIL/TMZ combined treatment. Cell viability was assayed using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide and phase-contrast microscopy. Cell apoptosis was detected using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique and quantified using flow cytometric analysis. The apoptosis signaling cascade was studied with Western blotting. The additive effects of hTRAIL and TMZ resulted in a significant decrease in cell viability and an increased apoptotic rate. Expression of the death receptors DR5 and DR4 in two cell lines (A172 and U251) upregulated significantly when they were used in combination hTRAIL/TMZ treatment (p < 0.05 compared with baseline control), leading to activation of caspase-8 and caspase-3 (p < 0.05 compared with baseline control) and confirming an extrinsic apoptotic pathway. A cell intrinsic pathway through mitochondrial cytochrome c was not activated. CONCLUSIONS: Based on this work, one may infer that hTRAIL should be considered as an adjuvant treatment for TMZ-resistant human malignant gliomas.     

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.