siRNA沉默c-FLIP基因表达与表柔比星联合应用对MCF-7细胞凋亡的影响

目的 探讨RNA干扰技术沉默c-FLIP基因表达联合应用表柔比星对人乳腺癌细胞MCF-7凋亡的影响。方法 体外化学合成c-FLIP序列特异性双链小干扰RNA(siRNA),转染MCF-7细胞,应用Western blot方法检测c-FLIP蛋白的抑制水平、检测Caspase-8的表达差异;应用流式细胞术检测细胞凋亡的变化及表柔比星与c-FLIP-siRNA联合应用对细胞凋亡的影响。结果 c-FLIP-siRNA能有效地抑制c-FLIP蛋白的表达(P＜0.05),促进细胞的凋亡(P＜0.05)。c-FLIP-siRNA和表柔比星联合应用较单用表柔比星能明显促进MCF-7细胞的凋亡(P＜0.05)。结论 c-FLIP-siRNA能够促进MCF-7细胞的凋亡,并且能够增强表柔比星的抗肿瘤作用。     

c-FLIP与凋亡、信号转导途径

c-FLIP是一种凋亡抑制蛋白,能强效抑制Fas(CD95/APO-1)、TRAIL(肿瘤坏死因子相关凋亡诱导配体)-R1/R2(DR4/5)、TNFR1(肿瘤坏死因子受体)等死亡受体(DR)诱导的细胞凋亡,近年来发现其在多种凋亡、信号转导途径中发挥了凋亡抑制的作用.     

骨髓增生异常综合征造血细胞bcl-2 VEGF抗原表达及原位凋亡的研究

  目的  研究骨髓增生异常综合征(MDS)bcl-2、VEGF抗原表达及造血细胞原位凋亡之间的关系, 探讨MDS发病机理。  方法  对MDS患者骨髓活检标本光镜下观察骨髓增生程度、各系造血细胞形态异常情况、不成熟前体细胞异常定位(ALJP)等组织病理学改变, 免疫组织化学染色观测bcl-2及VEGF抗原的表达, TUNEL法检测造血细胞原位凋亡。  结果  13例患者骨髓均有不同程度的异常造血, 异常造血主要累及的细胞系列不尽相同, RA、RAEB两组患者异常造血未见明显区别; 有6例患者检出ALIP现象, 其中RA 3例(3/8, 37.50%), RAEB 3例(3/5, 60.00%); VEGF阳性者占9例(9/13, 69.23%), 其中RA 6例(6/8, 75.00%), RAEB 3例(3/5, 60.00%); bcl-2阳性者占7例, 其中RA4例(4/8, 50.00%), RAEB 3例(3/5, 60.00%); TUNEL检测13例患者均为阳性, 检出ALIP现象者, 其造血细胞发生原位调亡明显, 而bcl-2、VEGF与TUNEL结果之间未见明显关联。  结论  MDS患者均存在不同程度的细胞凋亡异常, 而TUNEL法提供了简便、实用、敏感、快速特异的检测MDS细胞原位凋亡的方法结果初步显示MDS患者ALlP现象明显者其细胞凋亡也明显, 提示调控MDS患者细胞凋亡和恶性克隆增殖可能是两种完全不同的机制。      

去甲斑蝥素诱导人食管癌Eca-109细胞凋亡及其作用机制

目的:探讨去甲斑蝥素诱导人食管癌Eca-109细胞的凋亡及其可能的作用机制.方法:去甲斑蝥素作用食管癌Eca-109细胞后,应用MTT法检测其对细胞的生长抑制作用, 透射电子显微镜下观察细胞超微结构的变化,琼脂糖凝胶电泳观察其对细胞凋亡的诱导作用,RT-PCR法检测caspase 8和caspase 3 mRNA的表达,Western 印迹法检测Fas、细胞型含死亡域的Fas结合蛋白样白介素-1β转换酶抑制蛋白(cellular FADD-like interleukin-1β converting enzyme inhibitory protein,c-FLIP) 、caspase 8和caspase 3蛋白的表达.结果:去甲斑蝥素对人食管癌Eca-109细胞具有生长抑制作用,并呈时效和量效依赖关系.电子显微镜下观察发现, 食管癌Eca-109细胞趋于凋亡.DNA琼脂糖凝胶电泳可见典型的DNA梯状条带.RT-PCR检测显示,caspase 8和caspase 3 mRNA的表达水平明显上升 (P<0.01).Western 印迹法检测结果显示,与阴性对照组比较,去甲斑蝥素作用后,食管癌Eca-109细胞中Fas、caspase 3和caspase 8蛋白的表达明显上升(P<0.05),c-FLIP蛋白的表达水平明显下降(P<0.05).结论:去甲斑蝥素能够抑制食管癌Eca-109细胞的生长并诱导其凋亡,其机制可能是通过上调Fas、caspase 8、caspase 3的表达和下调c-FLIP的表达来实现的.     

c-FLIP在凋亡增殖中的双向调节作用及与肿瘤预后和治疗关系的研究

细胞型Fas相关死亡域样白介素-1β转换酶抑制蛋白(c-FLIP) 在细胞凋亡和增殖信号通路中具有重要的调节作用。一方面通过与Caspase-8竞争性结合上游信号阻断凋亡通路, 另一方面经酶切释放出p43-FLIP和p22-FLIP片段促进NF-κΒ、Erk等增殖信号通路, 最终引发肿瘤发生发展、浸润转移。c-FLIP的双向调节作用与蛋白表达量、底物的亲和力和亚细胞定位密切相关。恶性肿瘤中c-FLIP高表达使细胞逃逸机体免疫监视、耐受化疗药物杀伤以及抵抗TRAIL、FasL诱导的凋亡。本文初步阐释c-FLIP在不同的细胞微环境中对凋亡-增殖通路的双向调节作用及其分子机制, 并对c-FLIP与恶性肿瘤预后、化疗和TRAIL生物治疗相关性进行综述, 为肿瘤化疗耐药和TRAIL抵抗提供理论基础。 < /span >      

骨髓增生异常综合征bcl-2蛋白表达与细胞凋亡及增殖的关系

目的 :研究骨髓增生异常综合征 (MDS)中 bcl- 2蛋白表达与细胞凋亡及增殖的关系。方法 :以 2 0例 MDS患者、4例急性髓细胞白血病 (AML )患者、4例正常人的骨髓组织为研究对象 ,用免疫组织化学技术 SABC法分别检测 bcl- 2蛋白和增殖细胞核抗原 (PCNA )的表达 ,用 d U TP缺口末端标记 (TU NEL )技术检测细胞凋亡。结果 :MDS、AML、正常人 bcl- 2蛋白表达半定量积分值分别为 2 5 .35± 16 .6 8、6 6 .31± 10 .36、8.2 2± 2 .45 ;MDS、AML与正常对照组凋亡率依次递减 ;AML、MDS与正常对照组 PCNA阳性率依次递减 ;bcl- 2蛋白表达与凋亡负相关 (r=- 0 .6 76 1,P<0 .0 5 )。结论 :bcl- 2蛋白过度表达与细胞凋亡抑制、增殖失控关系密切 ,在 MDS向 AML转化过程中起重要作用     

凋亡相关基因Survivin、bcl-2和bax表达在高三尖杉酯碱诱导骨髓增生异常综合征MUTZ-1细胞凋亡中的作用

目的：研究骨髓增生异常综合征(MDS)细胞株MUTZ—1凋亡相关基因Survivin、bcl—2和bax的表达及高三尖杉酯碱(HHT)诱导其凋亡的作用机制。方法：用MDS—RAEB细胞系MUTZ—1为体外模型，采用透射电镜和流式细胞仪Annexin-V^FITC/PI双染分析细胞凋亡，PI染色分析细胞周期变化，RT—PCR技术检测抗凋亡基因Survivin、bcl—2和促凋亡基因bax的表达。结果：HHT能诱导MUTZ—1细胞凋亡，凋亡率与作用浓度和时间成正相关，细胞被阻滞在G2期。HHT作用MUTZ—1细胞6小时后细胞内抗凋亡基因Survivin表达明显下降，而抗凋亡基因bcl—2和促凋亡基因bax表达无明显变化。结论：HHT能诱导MUTZ—1细胞凋亡，抗凋亡基因Survivin mRNA下调可能是MUTZ—1细胞凋亡的机制之一。     

阿克拉霉素影响骨髓增生异常综合征细胞株细胞增殖及其机制的初步研究

目的　探讨阿克拉霉素 ( aclacinomycin,ACM)对骨髓增生异常综合征 ( myelodysplastic syndrome,MDS)细胞株 ( MUTZ- 1)细胞的体外作用及其机制 ,以期为进展期 MDS的治疗提供理论基础。方法　采用 MTT比色法、流式细胞术、DNA凝胶电泳法研究 ACM对 MU TZ- 1细胞生长的影响。结果　 ( 1) ACM对 MUTZ- 1细胞的生长具有抑制作用 ,其 4 8小时 IC50 为 0 .4 6μmol。( 2 ) ACM对 MUTZ- 1细胞的作用主要为诱导凋亡。( 3 ) ACM诱导 MUTZ- 1细胞凋亡 ,阻滞细胞于细胞周期的 G2 / M期。结论　 ACM可诱导 MDS细胞株细胞凋亡 ,作用靶点位于 G2 / M期。提示诱导细胞凋亡疗法治疗进展期 MDS的可行性     

Fas/Fasl系统及凋亡与骨髓增生异常综合征关系的研究

目的 :研究 F as/Fasl系统及凋亡与骨髓增生异常综合征 ( myelodysplastic syndrome,MDS)发生发展的关系。方法 :分别用 TU NEL方法和免疫组化标记方法检测凋亡细胞和 Fas、Fasl表达细胞。而后在光镜下计数相应的阳性细胞并计算其百分率。另外 ,还以 EL ISA方法检测患者血清中的 s Fas的含量。结果 :( 1) MDS组BMMNC中的凋亡细胞百分率 [( 2 2 .83± 10 .14 ) % ]高于正常对照组 [( 2 .2 7± 0 .74) % ] ( P<0 .0 5 ) ;( 2 ) MDS组BMMNC中的 F as表达细胞百分率 [( 2 4.37± 6 .42 ) % ]高于正常对照组 [( 1.93± 0 .32 ) % ] ( P<0 .0 5 ) ;( 3) MDS组BMMNC中的 Fasl表达细胞百分率 [( 2 2 .2 7± 10 .5 0 ) % ]高于正常对照组 [( 4 .18± 1.0 2 ) % ] ( P<0 .0 5 ) ;( 4 ) MDS组血清 s Fas的含量 [( 9.2 4± 10 .5 0 ) μg/L]高于正常对照组 [( 7.5 5± 0 .79) μg/L] ( P<0 .0 5 ) ;( 5 ) MDS组凋亡细胞百分率与 Fas+细胞或 Fasl+细胞百分率之间无直线相关关系 ( P>0 .0 5 )。结论 :实验结果表明 Fas/Fasl系统介导的凋亡以及机体对其调控的失常参与了 MDS骨髓无效造血的病理生理过程。但体内可能还存在另外的机制可引起MDS患者 BMMNC凋亡增加     

骨髓增生异常综合征患者来源的异种基因移植小鼠模型的研究进展

骨髓增生异常综合征(myelodysplastic syndromes,MDS)是一种恶性克隆性血液疾病,其发病机制至今仍不明确.基因工程小鼠在研究MDS发病机制方面发挥了重要作用,但随着对发病机制的不断探究,基因工程小鼠也显示出一定的不足.为了更好地研究MDS患者的临床特征和发病机制,十分有必要建立MDS患者异种移植...     

Immunohistopathological Study of c-FLIP Protein in Mycosis Fungoides

Background: Mycosis fungoides (MF) is the commonest variant of primary cutaneous T cell lymphoma with several clinicopathologic variants. Defective apoptotic mechanism may be important in the pathogenesis and progression of MF. c-FLIP protein is an important anti-apoptotic marker and chemotherapeutic resistant factor. This study aimed to evaluate the c-FLIP expression in MF and its role in the pathogenesis of MF. Methods: Twenty patients of MF and ten normal persons were included in this study. Skin biopsies were obtained from both patients and controls. They were studied and examined immunohistochemically for the expression of CD4 and c-FLIP. Results: c-FLIP expression was significantly increased in patients when compared to controls in both epidermis and dermis. There were positive correlations between c-FLIP expression and CD4+ expression in both epidermal and dermal lesions of patients group. There were statistically significant positive correlations between c-FLIP expression (in both dermal and epidermal lesions) and the age of patients. c-FLIP expression increased with the tumor progression but with no statistical significance. Conclusion: Defective regulation of apoptosis has been considered as a main cause for accumulation of clonal T cells, and it was related to an increased expression of c-FLIP which may have a role in the pathogenesis of MF. Also, c-FLIP may have prognostic information in MF as its level increased with both age of the patients and tumor progression.     

Short hairpin RNA targeting c-FLIP sensitizes human cervical adenocarcinoma Hela cells to chemotherapy and radiotherapy

c-FLIP inhibits caspase-8 activation and cell apoptosis mediated by death receptors. The present study aims at determining the effects of c-FLIP targeted vector-based short hairpin RNA (shRNA) on cell growth and evaluating its modulation of responsiveness to drugs and radiotherapy in cervical adenocarcinoma Hela cells. cFLIP expression of the cells transfected with shRNA against c-FLIP was significantly down-regulated after 72 h. c-FLIP silencing markedly suppressed cell proliferation and increased cell apoptosis. The activation of caspase-8 and caspase-3 was induced with shRNA targeting cFLIP with the passage of time after transfection. Furthermore, Vector-based shRNA against c-FLIP subsequently increased the sensitivity to cisplatin, iritican and Co60 radiotherapy by about 4- to 6-folds in Hela cells. Our data suggest that vector-based shRNA effectively inhibited c-FLIP expression, enhanced the expression level of caspase-8 and caspase-3 to induce cell apoptosis, probably with the higher efficacy in combination therapies with conventional chemotherapy and radiotherapy in cervical adenocarcinoma.     

Persistent c-FLIP(L) expression is necessary and sufficient to maintain resistance to tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis in prostate cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in a variety of tumorigenic and transformed cell lines but not in many normal cells. Hence, TRAIL has the potential to be an ideal cancer therapeutic agent with minimal cytotoxicity. FLICE inhibitory protein (c-FLIP) is an important regulator of TRAIL-induced apoptosis. Here, we show that persistent expression of c-FLIP(Long) [c-FLIP(L)] is inversely correlated with the ability of TRAIL to induce apoptosis in prostate cancer cells. In contrast to TRAIL-sensitive cells, TRAIL-resistant LNCaP and PC3-TR (a TRAIL-resistant subpopulation of PC3) cells showed increased c-FLIP(L) mRNA levels and maintained steady protein expression of c-FLIP(L) after treatment with TRAIL. Ectopic expression of c-FLIP(L) in TRAIL-sensitive PC3 cells changed their phenotype from TRAIL sensitive to TRAIL resistant. Conversely, silencing of c-FLIP(L) expression by small interfering RNA in PC3-TR cells reversed their phenotype from TRAIL resistant to TRAIL sensitive. Therefore, persistent expression of c-FLIP(L) is necessary and sufficient to regulate sensitivity to TRAIL-mediated apoptosis in prostate cancer cells.     

Over-expression of Reticulon 3 (RTN3) enhances TRAIL-mediated apoptosis via up-regulation of death receptor 5 (DR5) and down-regulation of c-FLIP

Reticulons (RTNs) are a group of integral membrane proteins that have no homology to other known apoptosis-related domains. Herein, we found that RTN3 overexpressing Caki cells were sensitive to TRAIL-mediated apoptosis. RTN3-induced down-regulation of c-FLIP was recovered by pan-caspase inhibitor, z-VAD to basal levels in TRAIL-treated cells. The forced expression of c-FLIP attenuated the TRAIL-mediated apoptosis in RTN3 over-expressing cells. In addition, RTN3 over-expression provoked the enhanced protein levels in DR4 and DR5 as well as levels in DR5 surface protein but slight increase in DR4 surface protein. RTN3-mediated enhancement of TRAIL-induced apoptosis was markedly blocked by the DR5/Fc chimera or DR5 siRNA, indicating that the sensitization by RTN3 was mainly mediated through interactions of TRAIL with its receptors, DR5. Over-expression of RTN3 also enhanced TNF-α and Fas-mediated apoptosis. Taken together, over-expression of RTN3 might increase DR5 surface protein and concomitantly more activate caspase pathways, which cause the c-FLIP cleavage and enhancement of TRAIL-mediated apoptosis.     

Cellular FLICE-inhibitory protein down-regulation contributes to celecoxib-induced apoptosis in human lung cancer cells

The cyclooxygenase-2 (COX-2) inhibitor celecoxib is an approved drug in the clinic for colon cancer chemoprevention and has been tested for its chemopreventive and therapeutic efficacy in various clinical trials. Celecoxib induces apoptosis in a variety of human cancer cells including lung cancer cells. Our previous work has shown that celecoxib induces death receptor 5 expression, resulting in induction of apoptosis and enhancement of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human lung cancer cells. In the current study, we further show that celecoxib down-regulated the expression of cellular FLICE-inhibitory protein (c-FLIP), a major negative regulator of the death receptor-mediated extrinsic apoptotic pathway, through a ubiquitin/proteasome-dependent mechanism independent of COX-2 in human lung cancer cells. Overexpression of c-FLIP, particularly FLIP(L), inhibited not only celecoxib-induced apoptosis but also apoptosis induced by the combination of celecoxib and TRAIL. These results thus indicate that c-FLIP down-regulation also contributes to celecoxib-induced apoptosis and enhancement of TRAIL-induced apoptosis, which complements our previous finding that the extrinsic apoptotic pathway plays a critical role in celecoxib-induced apoptosis in human lung cancer cells. Collectively, we conclude that celecoxib induces apoptosis in human lung cancer cells through activation of the extrinsic apoptotic pathway, primarily by induction of death receptor 5 and down-regulation of c-FLIP.     

Targeting c-FLIP in cancer

Cellular-FLICE inhibitory protein (c-FLIP) is a key anti-apoptotic regulator that inhibits cell death mediated by the death receptors Fas, DR4, DR5, and TNF-R1. Three splice variants of c-FLIP function at the DISC level by blocking the processing and activation of procaspase-8 and -10. Overexpression of c-FLIP has been identified in many different tumour types, and its downregulation in vitro has been shown to restore apoptosis mediated by CD95L and TRAIL. c-FLIP therefore represents a promising target for cancer therapy. This review focuses on the molecular mechanisms that control c-FLIP expression and current research into inhibitors of the protein. Increasing evidence supports the investigation of c-FLIP as a therapeutic target to restore an apoptotic response in cancer cells.     

The proteasome inhibitor PS-341 (bortezomib) up-regulates DR5 expression leading to induction of apoptosis and enhancement of TRAIL-induced apoptosis despite up-regulation of c-FLIP and survivin expression in human NSCLC cells

The proteasome inhibitor PS-341 (bortezomib or Velcade), an approved drug for treatment of patients with multiple myeloma, is currently being tested in clinical trials against various malignancies, including lung cancer. Preclinical studies have shown that PS-341 induces apoptosis and enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human cancer cells with undefined mechanisms. In the present study, we show that PS-341 induced caspase-8-dependent apoptosis, cooperated with TRAIL to induce apoptosis, and up-regulated death receptor 5 (DR5) expression in human non-small cell lung cancer (NSCLC) cells. DR5 induction correlated with the ability of PS-341 to induce apoptosis. Blockage of PS-341-induced DR5 up-regulation using DR5 small interfering RNA (siRNA) rendered cells less sensitive to apoptosis induced by either PS-341 or its combination with TRAIL, indicating that DR5 up-regulation mediates PS-341-induced apoptosis and enhancement of TRAIL-induced apoptosis in human NSCLC cells. We exclude the involvement of c-FLIP and survivin in mediating these events because c-FLIP (i.e., FLIP(S)) and survivin protein levels were actually elevated on exposure to PS-341. Reduction of c-FLIP with c-FLIP siRNA sensitized cells to PS-341-induced apoptosis, suggesting that c-FLIP elevation protects cells from PS-341-induced apoptosis. Thus, the present study highlights the important role of DR5 up-regulation in PS-341-induced apoptosis and enhancement of TRAIL-induced apoptosis in human NSCLC cells.     

Apoptosis and its role in the myelodysplastic syndromes: implications for disease natural history and treatment

Apoptosis (programmed cell death) is an active cellular process which regulates cell population size by decreasing cell survival. In this review the underlying cellular and molecular mechanisms of apoptosis in hemopoietic and non-hemopoietic cells are described, with specific focus on these issues in the myelodysplastic syndrome (MDS), a myeloid clonal hemopathy. Apoptosis-regulating genes exist as families whose protein products are either anti-apoptotic or pro-apoptotic. Numerous stimuli can serve as initiators of the cell death pathway, including essentially all chemotherapeutic drugs, irradiation, certain inhibitory cytokines and deprivation of relevant growth factors. Morphological evidence of increased apoptosis in marrow hemopoietic cells has been demonstrated in patients with MDS. The reviewed data provide support for the hypothesis that early in MDS, increased apoptosis is associated with ineffective progenitor and maturing hemopoietic cell survival, and occurs concomitant with cytopenias/ineffective hemopoiesis; conversely, the progression of MDS toward AML occurs in concert with decreased apoptosis and an increased degree of neoplastic cell survival, leading to subsequent expansion of the abnormal precursor cells. These processes are associated with alterations in the balance between pro- and anti-apoptotic oncoprotein expression within the hemopoietic precursors, which may be modified by cytokine treatment. Investigations evaluating apoptotic events in MDS have improved our understanding of the biology of hemopoietic cell survival as related to pathogenetic features of this disease. By modifying levels of apoptosis, such studies provide a framework for future potentially beneficial therapeutic approaches to treat patients with MDS.     

The novel Akt inhibitor API-1 induces c-FLIP degradation and synergizes with TRAIL to augment apoptosis independent of Akt inhibition

API-1 (pyrido[2,3-d]pyrimidines) is a novel small-molecule inhibitor of Akt, which acts by binding to Akt and preventing its membrane translocation and has promising preclinical antitumor activity. In this study, we reveal a novel function of API-1 in regulation of cellular FLICE-inhibitory protein (c-FLIP) levels and TRAIL-induced apoptosis, independent of Akt inhibition. API-1 effectively induced apoptosis in tested cancer cell lines including activation of caspase-8 and caspase-9. It reduced the levels of c-FLIP without increasing the expression of death receptor 4 (DR4) or DR5. Accordingly, it synergized with TRAIL to induce apoptosis. Enforced expression of ectopic c-FLIP did not attenuate API-1-induced apoptosis but inhibited its ability to enhance TRAIL-induced apoptosis. These data indicate that downregulation of c-FLIP mediates enhancement of TRAIL-induced apoptosis by API-1 but is not sufficient for API-1-induced apoptosis. API-1-induced reduction of c-FLIP could be blocked by the proteasome inhibitor MG132. Moreover, API-1 increased c-FLIP ubiquitination and decreased c-FLIP stability. These data together suggest that API-1 downregulates c-FLIP by facilitating its ubiquitination and proteasome-mediated degradation. Because other Akt inhibitors including API-2 and MK2206 had minimal effects on reducing c-FLIP and enhancement of TRAIL-induced apoptosis, it is likely that API-1 reduces c-FLIP and enhances TRAIL-induced apoptosis independent of its Akt-inhibitory activity.     

c-FLIP: a key regulator of colorectal cancer cell death

c-FLIP is an inhibitor of apoptosis mediated by the death receptors Fas, DR4, and DR5 and is expressed as long (c-FLIP(L)) and short (c-FLIP(S)) splice forms. We found that small interfering RNA (siRNA)-mediated silencing of c-FLIP induced spontaneous apoptosis in a panel of p53 wild-type, mutant, and null colorectal cancer cell lines and that this apoptosis was mediated by caspase-8 and Fas-associated death domain. Further analyses indicated the involvement of DR5 and/or Fas (but not DR4) in regulating apoptosis induced by c-FLIP siRNA. Interestingly, these effects were not dependent on activation of DR5 or Fas by their ligands tumor necrosis factor-related apoptosis-inducing ligand and FasL. Overexpression of c-FLIP(L), but not c-FLIP(S), significantly decreased spontaneous and chemotherapy-induced apoptosis in HCT116 cells. Further analyses with splice form-specific siRNAs indicated that c-FLIP(L) was the more important splice form in regulating apoptosis in HCT116, H630, and LoVo cells, although specific knockdown of c-FLIP(S) induced more apoptosis in the HT29 cell line. Importantly, intratumoral delivery of c-FLIP-targeted siRNA duplexes induced apoptosis and inhibited the growth of HCT116 xenografts in BALB/c severe combined immunodeficient mice. In addition, the growth of c-FLIP(L)-overexpressing colorectal cancer xenografts was more rapid than control xenografts, an effect that was significantly enhanced in the presence of chemotherapy. These results indicate that c-FLIP inhibits spontaneous death ligand-independent, death receptor-mediated apoptosis in colorectal cancer cells and that targeting c-FLIP may have therapeutic potential for the treatment of colorectal cancer.