TRAIL耐药的研究进展

肿瘤坏死因子相关凋亡诱导配体(tumor necrosis factor-related apoptosis-inducing ligand,TRAIL)能选择性地诱导肿瘤细胞凋亡,因此作为抗肿瘤药物备受瞩目,现已进入II期临床试验,尽管有报道称部分肿瘤细胞对TRAIL耐药,导致治疗效果不如预期,但TRAIL用于肿瘤治疗的前景依旧被人们看好。通过对TRAIL耐药机理的研究将有助于寻找逆转肿瘤细胞耐药的靶点,并通过联合用药来调节相关的信号分子以获得更好的抗肿瘤效应。该文将介绍TRAIL及其介导的细胞凋亡通路并总结近年来TRAIL耐药机理及逆转其耐药方面的研究进展。     

基于TRAIL的肿瘤治疗策略进展

肿瘤坏死因子相关凋亡诱导配体(TRAIL)能选择性诱导肿瘤细胞凋亡,且对机体正常组织细胞无毒副作用,被认为是一种非常有潜力的抗癌药物。我们简要介绍TRAIL及其配体诱导细胞凋亡的机制、肿瘤细胞对TRAIL的耐受机制及其克服策略。     

c-FLIP的siRNA促进TRAIL诱导的癌细胞凋亡的研究

肿瘤凋亡因子TRAIL(TNF-related apoptosis-inducing ligand)是TNF家族的成员之一,其不论在体内还是体外均可选择性诱导癌细胞凋亡。初期临床试验已经证实TRAIL或死亡受体激动剂抗体在癌症治疗中的安全性。另外,也有研究表明,许多癌细胞对TRAIL有耐受性,究其原因是凋亡通路中抗凋亡蛋白c-FLIP和IAP等的阻遏。更多研究发现,si RNA靶向抑制c-FLIP的同时结合广谱IAP拮抗剂AT406,进一步提高了TRAIL诱导的癌细胞凋亡,因此联合使用c-FLIP抑制剂或拮抗剂、IAP拮抗剂以及TRAIL或死亡受体激动剂抗体这三类药物可能是理想的抗癌新方法。综述了c-FLIP的发现、结构、功能和其参与死亡受体介导的信号通路,以及多种si RNA应用于c-FLIP以提高癌细胞对TRAIL敏感性和si RNA条件优化中的一些进展,并讨论了目前癌症临床治疗中si RNA的应用前景及存在的问题,最后提出较安全有效的基于TRAIL介导的癌症治疗新方法。     

肿瘤细胞死亡受体的调控

肿瘤坏死因子相关凋亡诱导配体(tumor necrosis factor related apoptosis inducing ligand,TRAIL)只有与细胞膜上死亡受体结合才能促使癌细胞凋亡,一旦细胞膜上的死亡受体发生缺失或失去活性,将使癌细胞对TRAIL极为耐受。近年来,对死亡受体的研究发现,死亡受体异常表达可能是死亡受体在细胞膜上发生功能性缺失的最主要原因。该文主要探究肿瘤细胞中死亡受体在转录调控、翻译后修饰、转运和内化过程中的异常情况,期望为今后研发克服TRAIL耐受的联合药物及癌症治疗提供参考。     

以TRAIL为靶点的肿瘤治疗研究进展

肿瘤坏死因子相关凋亡配体（tumor necrosis factor-related apoptosis-inducing ligand,TRAIL）是肿瘤坏死因子（tumor necrosis factor,TNF）超家族成员。TRAIL与其受体结合后启动凋亡信号转导,选择性地诱导肿瘤细胞凋亡,而对正常组织细胞没有明显的伤害,而且一些药物和细胞因子可协同TRAIL诱导肿瘤细胞凋亡。本文就TRAIL及其受体、TRAIL诱导凋亡的机制以及影响凋亡的因素和途径,以TRAIL为靶点的肿瘤治疗的研究现状作一综述。     

TRAIL诱导肿瘤细胞凋亡的分子机制及其在肿瘤生物治疗中的应用前景

肿瘤坏死因子相关的凋亡诱导配体(tumor necrosis factor related apoptosis-inducingligand,TRAIL)是肿瘤坏死因子超家族成员之一,由于它能特异性诱导肿瘤细胞的凋亡而对正常细胞无毒性,因此具有被开发成治疗肿瘤的蛋白质药物的可能性。目前已经有5个与TRAIL相关的受体被鉴定出,其中,TRAILR1和TRAILR2是与诱导细胞凋亡最直接相关的受体,也是最具有前景的药物设计靶点。本文基于TRAIL蛋白及其受体复合物的三维结构分析,阐述TRAIL诱导肿瘤细胞凋亡的机制以及影响凋亡的因素和途径,对以TRAIL为靶点的肿瘤治疗的研究现状作全面综述,为探索肿瘤生物治疗的新方法和途径提供帮助。     

Procaspase-8失调与肿瘤细胞对TRAIL的耐受

肿瘤坏死因子相关凋亡诱导配体(TRAIL)可激活胱天蛋白酶（caspase）家族蛋白系列级联反应,最终诱导细胞凋亡. TRAIL选择性地诱导肿瘤细胞凋亡而不损伤正常细胞,使其成为治疗癌症的潜在药物靶点. 目前已知,细胞型FADD样白介素-1-β转换酶抑制蛋白(c FLIP)和凋亡抑制蛋白(IAPs)是肿瘤细胞对TRAIL耐受的主要原因.胱天蛋白酶原-8（procaspase-8）是TRAIL凋亡信号途径中的凋亡起始蛋白. 然而近年发现,在某些肿瘤细胞中procaspase-8功能失调常会阻碍凋亡信号传导,使肿瘤细胞对TRAIL诱导的凋亡产生耐受. 本文就其机制进行概述.     

XIAP在胰腺癌化疗耐药及治疗中的研究进展

X连锁的凋亡抑制蛋白(X-linked inhibitor of apoptosis protein,XIAP)是凋亡抑制蛋白家族中的一员,具有抗凋亡作用.研究发现XIAP在胰腺癌中呈高表达,并且能诱导胰腺癌细胞及组织对化疗耐药.通过在基因水平及蛋白水平降低XIAP的表达对胰腺癌的治疗具有重要意义.AEG 35156是针对XIAP的反义寡核苷酸分子,能够抑制胰腺癌细胞及组织生长.RNAi能够稳定下调胰腺癌细胞中XIAP水平,从而加强TRAIL诱导的细胞凋亡,并能提高胰腺癌细胞对化疗的敏感性.针对XIAP的小分化合物能够抑制XIAP的功能,释放被XIAP抑制的凋亡起始和效应分子以及XIAP抑制的其他促凋亡蛋白,提高多种肿瘤细胞的凋亡指数及对放化疗的敏感性.XAFl能抑制XIAP的抗凋亡作用.本文就XIAP在胰腺癌化疗耐药及治疗中的研究进展做一综述.     

肿瘤细胞抗TRAIL凋亡诱导的分子机制

肿瘤坏死因子相关的凋亡诱导配体(tumornecrosisfactor-relatedapoptosis-inducingligand,TRAIL)是肿瘤坏死因子(tumornecrosisfactor,TNF)超家族的成员之一,它能选择性诱导肿瘤细胞凋亡,对大多数正常细胞无杀伤作用。研究表明,某些恶性肿瘤抵抗TRAIL诱导的凋亡,且TRAIL重复作用使一些TRAIL敏感的细胞产生获得性抗性,这是TRAIL应用于肿瘤治疗的重大障碍。现对与TRAIL凋亡诱导通路直接相关的抗TRAIL机制及由Akt等途径介导的抗性分子机制进行综述。     

CCN1对食管癌细胞凋亡的作用及其机制研究

为了研究TRAIL的诸多受体能否触发细胞凋亡以及其通过诱导凋亡治疗食管癌的原因治疗食管癌的原因,本研究利用单分类单因素方差分析对采用pCMV6:CCN1、TRAIL、TRAILR2、TRAILR3、TRAILR4和OPG,以及其中每一种shRNA的pRS转染的细胞进行细胞凋亡分析、实时RT-PCR和阵列分析、Western印迹分析采集的数据进行分析。同时观察其免疫荧光和免疫组织化学。研究结果表明CCN1在患有胃食管反流病的患者的食管上皮中高度表达,但随着情况恶化为腺癌而消失。用CCN1处理肿瘤细胞导致细胞凋亡,而对正常细胞的相同处理则会滋养细胞生长。CCN1改变了TRAIL及其受体在肿瘤细胞中的表达谱,即激活TRAIL及其死亡受体并关闭其诱饵受体,而TRAIL是该过程的介导。本研究结论初步表明,CCN1和TRAIL都不能单独使癌细胞凋亡,但它们联合可以将癌细胞致死。     

Activation of the Akt Survival Pathway Contributes to TRAIL Resistance in Cancer Cells

The mechanism of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance in cancer cells is not fully understood. Here, we show that the Akt survival pathway plays an important role in TRAIL resistance in human cancer cells. Specifically, we found that TRAIL treatment activates the Akt survival pathway and that inhibition of this pathway by the PI3K inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 or knockdown of Akt sensitizes resistant cancer cells to TRAIL. Since Akt is negatively regulated by the tumor suppressor PTEN, we examined the TRAIL sensitivity in PTEN knockdown mouse prostate epithelial cells and found that PTEN^−/− cells are more resistant than PTEN^+/+ cells while the sensitivity of PTEN^+/− cells fell in between. Further, we showed that overexpression of a mutant PTEN confers TRAIL resistance in PTEN^+/+ cells, supporting a role of PTEN in TRAIL sensitivity. In TRAIL resistant breast T47D cells, overexpression of the mutant PTEN further increased their resistance to TRAIL. Taken together, our data indicate that inactivation of functional PTEN and the consequent activation of the Akt pathway prevents TRAIL-induced apoptosis, leading to TRAIL resistance. Therefore, our results suggest that TRAIL resistance can be overcome by targeting PTEN or the Akt survival pathway in cancer cells.     

Plasminogen activator urokinase expression reveals TRAIL responsiveness and supports fractional survival of cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/TNFSF10/Apo2L) holds promise for cancer therapy as it induces apoptosis in a large variety of cancer cells while exerting negligible toxicity in normal ones. However, TRAIL can also induce proliferative and migratory signaling in cancer cells resistant to apoptosis induced by this cytokine. In that regard, the molecular mechanisms underlying the tumor selectivity of TRAIL and those balancing apoptosis versus survival remain largely elusive. We show here that high mRNA levels of PLAU, which encodes urokinase plasminogen activator (uPA), are characteristic of cancer cells with functional TRAIL signaling. Notably, decreasing uPA levels sensitized cancer cells to TRAIL, leading to markedly increased apoptosis. Mechanistic analyses revealed three molecular events taking place in uPA-depleted cells: reduced basal ERK1/2 prosurvival signaling, decreased preligand decoy receptor 2 (DcR2)-death receptor 5 (DR5) interaction and attenuated recruitment of DcR2 to the death-inducing signaling complex upon TRAIL challenge. These phenomena were accompanied by increased FADD and procaspase-8 recruitment and processing, thus guiding cells toward a caspase-dependent cell death that is largely independent of the intrinsic apoptosis pathway. Collectively, our results unveil PLAU mRNA levels as marker for the identification of TRAIL-responsive tumor cells and highlight a key role of uPA signaling in ‘apoptosis versus survival'' decision-making processes upon TRAIL challenge.     

Resistance of cancer cells to the TRAIL-induced apoptosis in confluent cultures

TRAIL (TNF-alpha Related Apoptosis-Inducing Ligand) is an attractive candidate for anticancer therapy. TRAIL selectively kills tumor cells, without damaging normal cells. It is known that cancer cells can acquire resistance to chemotherapeutic drugs, oxidative stress in high density culture. This phenomenon appears as a multi-cell resistance, cell adhesion-dependent resistance, or density-dependent resistance of tumor cells. However, it is unclear whether such resistance appears in TRAIL-induced apoptosis. We observed that the resistance to izTRAIL of all tumor cell lines used was considerably increased in confluent cultures. The increase in tumor cell resistance in dense populations is not related to their proliferative status. It was shown that the dissociation of calcium-dependent cell-cell contacts with EGTA did not suppress tumor cell resistance to izTRAIL in confluent cultures. This phenomenon of cancer cells resistance to TRAIL-induced apoptosis should be considered in the development of methods of anticancer therapy.     

Involvement of protective autophagy in TRAIL resistance of apoptosis-defective tumor cells

Targeting TRAIL receptors with either recombinant TRAIL or agonistic DR4- or DR5-specific antibodies has been considered a promising treatment for cancer, particularly due to the preferential apoptotic susceptibility of tumor cells over normal cells to TRAIL. However, the realization that many tumors are unresponsive to TRAIL treatment has stimulated interest in identifying apoptotic agents that when used in combination with TRAIL can sensitize tumor cells to TRAIL-mediated apoptosis. Our studies suggest that various apoptosis defects that block TRAIL-mediated cell death at different points along the apoptotic signaling pathway shift the signaling cascade from default apoptosis toward cytoprotective autophagy. We also obtained evidence that inhibition of such a TRAIL-mediated autophagic response by specific knockdown of autophagic genes initiates an effective mitochondrial apoptotic response that is caspase-8-dependent. Currently, the molecular mechanisms linking disabled autophagy to mitochondrial apoptosis are not known. Our analysis of the molecular mechanisms involved in the shift from protective autophagy to apoptosis in response to TRAIL sheds new light on the negative regulation of apoptosis by the autophagic process and by some of its individual components.     

A cell-based high-throughput screen to identify synergistic TRAIL sensitizers

We have developed a high-throughput screen (HTS) to search for novel molecules that can synergize with TRAIL, thus promoting apoptosis of ACHN renal tumor cells in a combinatorial fashion. The HTS detects synthetic compounds and pure natural products that can pre-sensitize the cancer cells to TRAIL-mediated apoptosis, yet have limited toxicity on their own. We have taken into account the individual effects of the single agents, versus the combination, and have identified hits that are synergistic, synergistic-toxic, or additive when combined with TRAIL in promoting tumor cell death. Preliminary mechanistic studies indicate that a subset of the synergistic TRAIL sensitizers act very rapidly to promote cleavage and activation of caspase-8 following TRAIL binding. Caspase-8 is an apical enzyme that initiates programmed cell death via the extrinsic apoptotic pathway. Thus, these TRAIL sensitizers may potentially reduce resistance of tumor cells to TRAIL-mediated apoptosis. Two representative sensitizers were found to increase levels of p53 but did not inhibit the proteasome, suggesting that early DNA damage-sensing pathways may be involved in their mechanisms of action.     

Specific resistance upon lentiviral TRAIL transfer by intracellular retention of TRAIL receptors

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in many transformed cells, suggesting TRAIL as an ideal candidate for cancer gene therapy. A main obstacle in cancer therapy is intrinsic or acquired therapy resistance of malignant cells. To study induction of resistance against TRAIL, we generated lentiviral vectors allowing efficient TRAIL expression and apoptosis induction in a variety of human cancer cell lines. Within days upon TRAIL overexpression, cells became resistant towards TRAIL, but not to CD95 ligation or DNA damage by cisplatin. Cell surface expression of TRAIL receptors 1 and 2 was completely abrogated in resistant cells due to intracellular retention of the receptors by TRAIL. SiRNA directed against TRAIL resensitized the resistant cells by restoring cell surface expression of TRAIL receptors. These findings represent a novel resistance mechanism towards TRAIL, specifically caused by TRAIL overexpression, and question the use of TRAIL expression in tumor-cell targeting gene therapy.