凋亡抑制蛋白XIAP和促凋亡因子Smac在胰腺癌化疗抵抗中的调控作用

目的探讨凋亡抑制蛋白XIAP和促凋亡因子Smac在胰腺癌细胞化疗抵抗中的作用及其分子机制。方法应用流式细胞术检测顺铂、5-FU介导的Panc-1、BXPC-3的凋亡率及胞浆染色分析细胞XIAP表达变化,Western-blot分析XIAP、Smac、Caspase-3表达水平；构建pEGFP-N1／Smac真核表达载体并转染胰腺癌Panc-1细胞,流式细胞术检测转染胞浆表达型 Smac基因对Panc-1细胞凋亡敏感性的作用。结果与BXPC-3细胞相比,Panc-1对顺铂或5-FU介导的凋亡具有较强抵抗性,Western blot分析显示Panc-1细胞高表达XIAP,在化疗药物作用下化疗敏感细胞BXPC-3胞浆内XIAP水平下降明显多于Panc-1细胞,而且凋亡的BXPC-3细胞释放入胞浆内的成熟 Smac蛋白水平明显高于Panc-1细胞。转染胞浆表达型Smac基因至化疗抵抗Panc-1细胞,可明显下调其XIAP表达水平,促进效应 Caspase-3分子活化,显著提高顺铂、5-FU诱导的细胞凋亡率。结论在化疗药物诱导的凋亡中,线粒体释放Smac下调XIAP是胰腺癌化疗敏感性的重要决定因素,而上调Smac活性蛋白的胞浆表达作为一种有效调节信号,通过拮抗XIAP的凋亡抑制作用协同化疗药物促进胰腺癌细胞凋亡。     

人工合成拟Smac多肽增强膀胱癌细胞化疗敏感性的实验研究

背景与目的: Smac是目前发现的惟一能直接同时抑制多个IAPs家族成员活性的凋亡相关蛋白,其N端的4个氨基酸残基AVPI(Ala-Val-Pro-Ile)是重要的促凋亡结构域,我们通过人工合成可穿透细胞的促凋亡融合多肽SmacN7,探讨其对膀胱痛化疗药物敏感性的促进作用.方法: 噻唑蓝(MTT)检测SmacN7融合多肽对低剂量丝裂霉素C(MMC)诱导的膀胱癌T24细胞的相对存活率的影响;Annexin V/PI双标流式细胞术检测T24细胞的凋亡:Western印迹检测SmacN7融合多肽与MMC联用后T24细胞内XIAP、Caspase-3的表达;同时检测Caspase-3活性及SmacN7融合多肽与MMC联用对T24细胞的杀伤作用.结果: SmacN7融合多肽能穿透细胞并与内源性XIAP结合,增加低剂量MMC诱导的T24细胞凋亡并呈时间和浓度依赖性;并能显著降低细胞内xlAP的表达水平,增强Caspase-3的表达及活性;在24 h和48 h,SmacN7 MMC组与单用MMC组相比,T24细胞的存活率分别降低55%和72.7%.结论: 人工合成可穿透细胞的促凋亡融合多肽SmacNT能促进化疗药物诱导的膀胱癌T24细胞凋亡,抑制细胞增殖,增强膀胱癌细胞对MMC的化疗药物敏感性.     

蛋白激酶B抑制线粒体Smac释放与卵巢癌顺铂耐药的关系

目的 探讨蛋白激酶B(Akt)和线粒体促凋亡蛋白(Smac)在顺铂诱导的卵巢癌细胞凋亡中的关系及Akt在卵巢癌顺铂耐药中的分子机制.方法 应用Western blot检测顺铂作用前后卵巢癌顺铂敏感细胞OV2008、A2780s和顺铂耐药细胞C13*、A2780cp中Smac含量.将Smac siRNA和Smac N7多肽分别导人0V2008和C13*细胞中,应用流式细胞仪测定细胞的凋亡率,观察稳定转染Akt2的A2780s(A2780s-AAkt2)细胞和转染Akt1/2siRNA的C13*细胞对顺铂耐药性的改变.结果顺铂能导致OV2008、A2780s细胞线粒体释放Smac,并引起细胞凋亡(P＜0.05);但在C13*和A2780cp细胞中无此反应(P＞0.05).转染Smac siRNA后的0V2008细胞,其Smac表达降低,对顺铂的耐药性增加;转染Smac N7多肽能增加C13*细胞对顺铂的敏感性;Akt2过度表达可抑制A2780s细胞Smac释放,并对顺铂产生了耐药性;应用Akt1/2 siRNA后可下调C13*细胞中Akt1/2的表达,使C13*细胞对顺铂的敏感性增加.结论 顺铂对卵巢癌细胞的杀伤在一定程度上是通过线粒体释放Smac所致;Akt抑制了线粒体Smac释放与卵巢癌化疗耐药部分相关.     

DNMT3a通过STAT3及RAD51影响胰腺癌细胞对奥沙利铂敏感性的研究

目的:检测DNMT3a在胰腺癌细胞中的表达及对奥沙利铂（oxaliplatin，OXA）敏感性的影响，探讨DNMT3a对胰腺癌细胞奥沙利铂敏感性影响的机制。方法:MTT法检测奥沙利铂对人胰腺癌Panc-1细胞的增殖影响，及下调DNMT3a对Panc-1细胞奥沙利铂敏感性的影响。Western blot检测siDNMT3a对DNMT3a蛋白表达的影响，检测奥沙利铂及下调DNMT3a对γ-H2AX、RAD51、p-STAT3和STAT3蛋白表达的影响。流式细胞仪检测奥沙利铂及联合下调DNMT3a对Panc-1细胞凋亡的影响。结果:奥沙利铂能够以浓度依赖方式抑制胰腺癌Panc-1细胞的增殖。奥沙利铂能够引起DNA损伤、γ-H2AX上调及RAD51增高，同时引起STAT3通路的一过性活化。下调DNMT3a表达能够明显增加Panc-1细胞对奥沙利铂的敏感性，抑制STAT3一过性活化，并抑制RAD51表达，促进DNA损伤，进而增加奥沙利铂诱导Panc-1细胞的凋亡。结论:下调DNMT3a表达能够通过抑制STAT3活化及增加DNA损伤增加胰腺癌细胞对奥沙利铂的敏感性，DNMT3a有望成为胰腺癌新的治疗靶点。     

HIF-1α反义寡核苷酸增强胃癌细胞对顺铂的敏感性

目的研究缺氧诱导因子-1α(hypoxia inducible factor1α,HIF-1α)反义寡核苷酸(antisense ol-igodexynucleotide,ASODN)对人胃癌细胞凋亡及化疗药物敏感性的影响。方法人工合成HIF-1αASODN经阳离子脂质体包裹后瞬时转染人胃癌SGC-7901细胞系。采用RT-PCR和免疫细胞化学检测转染后HIF-1α基因表达情况,MTT法观察化疗药物敏感性的变化,AO/EB染色及TUNEL检测SGC-7901细胞转染后顺铂诱导的凋亡。结果经HIF-1αASODN处理的SGC-7901细胞HIF-1α基因表达明显下调,HIF-1αASODN处理的SGC-7901细胞加顺铂作用后与对照组比较,细胞凋亡率明显增加,化疗药物敏感性增强。结论阳离子脂质体转染HIF-1αASODN具有促进化疗药物诱导胃癌SGC-7901细胞凋亡及增强化疗药物敏感性作用。     

顺铂对人鼻咽癌CNE-2Z细胞端粒酶活性和细胞周期及凋亡的影响

目的研究顺铂对人鼻咽癌CNE-2Z细胞端粒酶活性、细胞周期及凋亡的影响,以探讨顺铂诱导CNE-2Z细胞凋亡与端粒酶活性水平的关系以及顺铂诱导鼻咽癌细胞凋亡的可能机制。方法分别以不同的药物浓度作用于体外培养的CNE-2Z细胞不同的时间,用TRAP-ELISA的方法定量检测CNE-2Z细胞在顺铂处理前后的端粒酶活性水平,同步进行细胞形态观察,流式细胞仪分析细胞周期的改变并检测凋亡。结果CNE-2Z细胞端粒酶呈阳性。用不同浓度的顺铂不同的时间作用于CNE-2Z细胞,结果细胞周期被阻滞在G1期,出现细胞凋亡,下调端粒酶活性,且呈时间依赖性及剂量依赖性。结论化疗药物顺铂可能是通过改变细胞周期分布(G1期阻滞)并同时诱导细胞凋亡、下调其端粒酶活性而发挥抗癌作用的,故可将化疗前后细胞端粒酶活性的变化作为鼻咽癌化疗敏感性指标之一。     

拟Smac促凋亡多肽的合成及其生物活性的初步研究

目的探讨拟Smac多肽的合成及其对膀胱癌细胞的促凋亡生物活性。方法应用固相多肽合成技术,合成具有细胞膜穿透性SmacN7融合多肽,经RP-HPLC纯化、纯度分析,用质谱仪定性鉴定;通过荧光显微镜观察细胞凋亡形态、细胞增殖抑制率测定及流式细胞仪分析,研究其对低剂量丝裂霉素C诱导的膀胱癌T24细胞的凋亡促进作用。结果 可穿透性融合多肽SmacN7产物峰纯度达95％以上,分子量为3278．08,质谱鉴定结果与合成预期结果完全一致;50-500 μg／L SmacN7作用12-48h,肿瘤细胞出现典型的凋亡形态学改变;随着SmacN7浓度的增加或作用时间的延长,细胞增殖抑制率出现明显增加,药物作用12h、24h、48h后增殖抑制率分别为（9．62±1．07）％～（61．48±1．15）％、（24．17±1．02）％～（72．86±1．68）％、（43．24±1．15）％～（84．91±1．74）％;肿瘤细胞凋亡率也明显增加,分别为（6．12±1．16）％～（49．81±2．11）％、（13．47±1．15）％～（64．54±2．27）％、（28．91±1．08）％～（82．36±2．19）％。结论 固相合成的拟Smac融合多肽SmacN7为高纯度的目的肽,能够稳定地转入细胞内且利用率高,并有明显促进低剂量丝裂霉素C诱导的膀胱癌T24细胞凋亡的生物活性,为进一步研究膀胱肿瘤的生物治疗积累了有价值的资料。     

凋亡抑制蛋白XIAP基因对A549细胞凋亡和化疗敏感性的影响

背景与目的X连锁凋亡抑制蛋白(X-linked inhibitor of apoptosis protein,XIAP)是新发现的一个IAP家族中的主要成员,是IAP家族中最强的凋亡抑制因子,它可直接抑制caspases并可多途径调节细胞凋亡。XIAP基因在大多数的肿瘤细胞株中过表达,其表达与肿瘤的进展、复发、预后以及肿瘤化疗的耐药密切相关。研究通过RNAi方法下调非小细胞肺癌(NSCLC)细胞NIC-A549的XIAP基因表达后,研究XIAP siRNA特异序列在NSCLC细胞凋亡和化疗敏感性方面的作用。方法应用半定量RT-PCR法检测A549细胞中XIAP mRNA基因的表达,设计并构建XIAP干扰性小RNA(small interfering RNA,siRNA)序列的表达载体,转染siRNA载体至A549中。荧光纤维镜确定转染效率,MTT法测定细胞增殖率及化疗药物对细胞杀伤率,流式细胞仪测定细胞凋亡率。结果酶切和DNA测序证实XIAP siRNA构建成功。荧光纤维镜显示阳性转染组及阴性转染组的细胞转染效率无差异。半定量RT-PCR法示阳性转染组较阴性转染组、未转染组细胞XIAP mRNA表达明显降低;与对照组相比,顺铂对阳性转染组XIAP mRNA表达的抑制作用明显增强、阳性转染组细胞增殖在24h、48h、72h、96h明显受抑制;细胞杀伤率、凋亡率明显增加。结论XIAP基因在NSCLC中表达增高,可抑制NSCLC细胞凋亡,导致NSCLC化疗耐药。XIAP siRNA序列可特异性地抑制NSCLC细胞增长,下调XIAP基因的表达,促进细胞凋亡,增加NSCLC化疗敏感性。XIAP siRNA序列有可能成为NSCLC治疗的靶标。     

奥曲肽逆转人胰腺癌细胞多药耐药机制的初步研究

目的:探讨生长抑素类似物奥曲肽对人胰腺癌细胞BxPC-3多药耐药现象的逆转作用及其机理,为临床应用奥曲肽提高胰腺癌化疗疗效提供实验依据.方法:应用不同浓度的奥曲肽(0-1.6 μg/ml)联合化疗药物顺铂、表阿霉素、氟尿嘧啶、吉西他滨共同处理稳定表达SSTR2的胰腺癌细胞BxPC-3-SSTR2,CCK-8比色法测定奥曲肽处理前后各化疗药物的IC50值,判断奥曲肽对胰腺癌多药耐药的逆转.Real-time PCR法检测SSTR2基因转染前后及奥曲肽处理前后的胰腺癌细胞中MDR1、MRP2、LRP基因表达.结果:奥曲肽可以显著降低顺铂、表阿霉素、氟尿嘧啶和吉西他滨的IC50值(P<0.05),并且这种作用呈剂最依赖性.胰腺癌细胞株BxPC-3在转染SSTR2基因后,细胞中MDR1、MRP2、LRP基因的表达分别下调57%、47%和56%(P<0.01);而转染后的胰腺癌细胞经过1.6 μg/ml奥曲肽作用48h后,其所表达的MDR1、MRP2、LRP基因出现进一步的下调,分别下降88%、73%和87%(P<0.01).结论:生长抑素类似物奥曲肽可逆转胰腺癌细胞的多药耐药,其机制可能与降低胰腺癌细胞中MDR1、MRP、LRP基因的表达,使胰腺癌细胞内细胞毒性药物浓度增加有关.     

Smac基因过表达对胃癌细胞株 MKN-45 化疗敏感性的影响

背景与目的:细胞凋亡异常是肿瘤细胞产生耐药性的关键因素之一. Smac(second mitochondria-derived activator of caspases,Smac或称 DIABLO)是新近发现的一种凋亡调节基因,在介导化疗药物诱导肿瘤细胞凋亡中起重要作用.本研究旨在观察 Smac基因过表达对胃癌细胞株化疗敏感性的影响.方法:采用脂质体 GeneSHUTTLE-40介导的方法,将 Smac基因转入胃癌细胞 MKN-45, RT-PCR和 Western blot法检测癌细胞中 Smac的表达;选用顺铂 (1、 5、 10 μ g/ml)、丝裂霉素 (0.1、 1、 10 μ g/ml)和姜黄素 (10、 20、 40 μ mol/L)分别处理转染前后的胃癌细胞,四甲基偶氮唑蓝( MTT)比色法检测细胞增殖活性,倒置显微镜下观察细胞形态变化并摄影, Annexin V-FITC和碘化丙啶双染色,流式细胞仪检测细胞凋亡.结果:同未转染对照组比较,转染外源性 Smac基因后 MKN-45细胞 Smac mRNA和蛋白表达水平显著增高( P< 0.01);各浓度顺铂、丝裂霉素和姜黄素处理 24 h后,细胞生长抑制率分别 增加 10.10%～ 23.80%( P< 0.01)、 10.01%～ 15.86%( P< 0.01)、 11.28%～ 22.12%( P< 0.01),细胞明显变圆、折光增强、漂浮细胞增多,细胞凋亡率分别增加 6.7%～ 20.2%( P< 0.01)、 5.4%～ 13.2%( P< 0.01)、 10.6%～ 20.1%( P< 0.01).结论:转染外源性 Smac基因并使其在胃癌细胞中过表达,能提高 MKN-45对化疗药物的敏感性.     

凋亡抑制蛋白XIAP和促凋亡因子Smac在胰腺癌化疗抵抗中的调控作用

Objective： To investigate the relation of X-linked inhibitor of apoptosis （XIAP） and second mitochondria-derived activator of caspase （Smac） signaling pathway to chemoresistance in human pancreatic cancer Panc-1 and BXPC-3 cells. Methods： Apoptosis and the changes of XIAP expression in permeabilized cells induced by cisplatin and 5-fluorouracil （FU） were measured by flow cytometry. The cytosolic expression of XIAP, Smac and caspase-3 was detected by Western blot. A recombinant plasmid vector pEGFP-N1/Smac was constructed and transfected into of Pancol cells. The effect of cytosolic overexpression of Smac on apoptosis of Panc-1 cells was evaluated by flow cytometry. Results： Panc-1 was more resistant to cisplatin or 5-FU induced apoptosis than BXPC-3. Western blot revealed that chemoresistant Panc-1 highly expressed XIAP, and increased cytosolic expression of Smac might be responsible for the marked down-regulation of XIAP in chemo-sensitive BXPC-3 cells after exposure to cisplatin or 5-FU. Furthermore, cytosolic overexpression of Smac could significantly down-regulate the levels of XIAP and promote the activity of caspase-3, as well as sensitize Panc-1 cells to anticancer drug-induced apoptosis. Conclusion： Anticancer drug-induced apoptosis requires mitochondrial release of Smac and downregulation of XIAP, which may be an important determinant of chemo-sensitivity in pancreatic cancer cells. Up-regulation of cytosolic expression of Smac may act as an effective modifying signal to overcome apoptosis resistance to chemotherapy in pancreatic cancer cells.     

Predominant suppression of apoptosome by inhibitor of apoptosis protein in non-small cell lung cancer H460 cells: therapeutic effect of a novel polyarginine-conjugated Smac peptide

The inhibitor of apoptosis proteins (IAPs) plays a central role in repressing caspase-mediated cell death. However, little is known about the actual role of endogenously expressed IAPs in cancer cells. We found that the cytochrome c/apoptotic protease-activating factor-1 (apoptosome)-dependent caspase activation is deficient in human non-small cell lung cancer (NSCLC) NCI-H460 cells. This dysfunctional apoptosome activity was not correlated with any decrease of apoptosome component factors, but it was linked to an increased X-linked inhibitor of apoptosis protein (XIAP). In H460 cells, the overexpressed XIAP, but not c-IAP1, bound to the processed form of caspase-9 and suppressed the activation of downstream effector caspases. Moreover, the defect in apoptosome activity in H460 cells was dramatically restored by the IAP-targeting SmacN7 peptide, which disrupted XIAP-caspase-9 binding, indicating an essential role of the IAP in the apoptosome inhibition. However, the SmacN7 did not show any striking effect on the apoptosome activity of normal lung fibroblast cells, although these cells also expressed modest amounts of IAP. To explore the therapeutic approach, we additionally developed SmacN7(R)8, a newly designed cell permeable peptide. The SmacN7(R)8 selectively reversed the apoptosis resistance of H460 cells, and when in combination with chemotherapy, regressed the tumor growth in vivo with little toxicity to the mice. Our results indicate that IAP-dependent suppression of apoptosome predominantly occurs in IAP-overexpressing tumor, and the IAP-targeting Smac peptide is an effective molecule to increase tumor cell death induced by chemotherapy in vitro and in vivo.     

Two peptides derived from ras-p21 induce either phenotypic reversion or tumor cell necrosis of ras-transformed human cancer cells

PURPOSE: We investigated the effects of two peptides from the ras-p21 protein, corresponding to residues 35-47 (PNC-7) and 96-110 (PNC-2), on two ras-transformed human cancer cell lines, HT1080 fibrosarcoma and MIAPaCa-2 pancreatic cancer cell lines. In prior studies, we found that both peptides block oncogenic, but not insulin-activated wild-type, ras-p21-induced oocyte maturation. When linked to a transporter penetratin peptide, these peptides induce reversion of ras-transformed rat pancreatic cancer cells (TUC-3) to the untransformed phenotype. METHODS: These peptides and a control peptide, linked to a penetratin peptide, were incubated with each cell lines. Cell counts were obtained over several weeks. The cause of cell death was determined by measuring caspase as an indicator of apoptosis and lactate dehydrogenase (LDH) as marker of necrosis. Since both peptides block the phosphorylation of jun-N-terminal kinase (JNK) in oocytes, we blotted cell lysates of the two cancer cell lines for the levels of phosphorylated JNK to determine if the peptides reduced these levels. RESULTS: We find that both peptides, but not control peptides linked to the penetratin sequence, induce phenotypic reversion of the HT-1080 cell line but cause tumor cell necrosis of the MIA-PaCa-2 cell line. On the other hand, neither peptide has any effect on the viability of an untransformed pancreatic acinar cell line, BMRPA1. We find that, while total JNK levels remain constant during peptide treatment, phosphorylated JNK levels decrease dramatically, consistent with the mechanisms of action of these peptides. CONCLUSION: We conclude that these peptides block tumor but not normal cell growth likely by blocking oncogenic ras-p21-induced phosphorylation of JNK, an essential step on the oncogenic ras-p21-protein pathway. These peptides are therefore promising as possible anti-tumor agents.     

Oleanolic acid potentiates the antitumor activity of 5-fluorouracil in pancreatic cancer cells

The antitumor activity of oleanolic (OA) has attracted attention due to its marked antitumor effects and pharmacological safety. In the present study, the effects of the combination of OA and 5-fluorouracil (5-FU) on Panc-28 human pancreatic cells were studied. The results showed that combined use of OA and 5-FU synergistically potentiated cell death effects on Panc-28 cells, and the pro-apoptotic effects were also increased. Further study revealed that the combined treatment could enhance mitochondrial depolarization, lysosomal membrane permeabilization (LMP) and leakage of cathepin D, while the release of cytochrome C did not display significant changes. The expression of apoptosis related proteins was also affected in cells treated with the combination of OA and 5-FU, including activation of caspases-3 and the expression of Bcl-2/Bax, survivin and NF-κB. Our results provide evidence that combination of OA and 5-FU may serve as a novel strategy for the treatment of pancreatic cancer.     

Overexpression of neuropilin-1 promotes constitutive MAPK signalling and chemoresistance in pancreatic cancer cells

Neuropilin-1 (NRP-1) is a novel co-receptor for vascular endothelial growth factor (VEGF). Neuropilin-1 is expressed in pancreatic cancer, but not in nonmalignant pancreatic tissue. We hypothesised that NRP-1 expression by pancreatic cancer cells contributes to the malignant phenotype. To determine the role of NRP-1 in pancreatic cancer, NRP-1 was stably transfected into the human pancreatic cancer cell line FG. Signal transduction was assessed by Western blot analysis. Susceptibility to anoikis (detachment induced apoptosis) was evaluated by colony formation after growth in suspension. Chemosensitivity to gemcitabine or 5-fluorouracil (5-FU) was assessed by MTT assay in pancreatic cancer cells following NRP-1 overexpression or siRNA-induced downregulation of NRP-1. Differential expression of apoptosis-related genes was determined by gene array and further evaluated by Western blot analysis. Neuropilin-1 overexpression increased constitutive mitogen activated protein kinase (MAPK) signalling, possibly via an autocrine loop. Neuropilin-1 overexpression in FG cells enhanced anoikis resistance and increased survival of cells by > 30% after exposure to clinically relevant levels of gemcitabine and 5-FU. In contrast, downregulation of NRP-1 expression in Panc-1 cells markedly increased chemosensitivity, inducing > 50% more cell death at clinically relevant concentrations of gemcitabine. Neuropilin-1 overexpression also increased expression of the antiapoptotic regulator, MCL-1. Neuropilin-1 overexpression in pancreatic cancer cell lines is associated with (a) increased constitutive MAPK signalling, (b) inhibition of anoikis, and (c) chemoresistance. Targeting NRP-1 in pancreatic cancer cells may downregulate survival signalling pathways and increase sensitivity to chemotherapy.     

Gelsolin regulates cisplatin sensitivity in human head‐and‐neck cancer

Chemoresistance is a major challenge in cancer therapy. Cisplatin is commonly used for chemotherapy in patients with head‐and‐neck cancer (HNC), but it increases control of the disease by only 10–15%. Downregulation of proapoptotic pathways is a key determinant for chemoresistance in which gelsolin (GSN) is critically involved. We analyzed the association between GSN expression and cisplatin resistance in HNC cell lines, animals with HNC and cancer tissue samples from 58 cisplatin‐treated patients with HNC. GSN expression levels were positively associated with chemoresistance in vitro and in vivo. Cisplatin‐induced GSN downregulation was associated with the cleavage of GSN and the promotion of apoptosis. GSN silencing facilitated cisplatin‐induced apoptosis in chemoresistant cells. In contrast, intact gelsolin was prosurvival in the presence of cisplatin by interacting with X‐linked inhibitor of apoptosis protein (XIAP). In chemosensitive cells, cisplatin suppressed GSN–XIAP interaction, promoted translocation of XIAP from the perinuclear region to the nucleus and induced apoptosis. In chemoresistant cells, GSN was highly expressed, and cisplatin had no significant effect on GSN–XIAP interaction and apoptosis. We conclude that GSN is important for chemoresistance in HNC and may be an appropriate therapeutic target in chemoresistant cancers.     

Coexistence of high levels of apoptotic signaling and inhibitor of apoptosis proteins in human tumor cells: implication for cancer specific therapy

It is well known that dysfunction of the apoptotic pathway confers apoptosis resistance and results in a low sensitivity of human cancer cells to therapeutic agents. A novel strategy to overcome the resistance is to target the apoptotic pathway directly. To identify molecular targets in the apoptotic pathway that are differentially regulated in cancer and normal cells, we have examined the levels of apoptotic effectors and inhibitors in human tumor and normal cell lines as well as in cancer and normal tissues. These include three pancreatic cancer lines (BXPC-3, MIA PaCa-2, and Panc-1), four breast cancer cell lines (MDA-MB-231, MDA-MB-435, MDA-MB-361, and MCF-7), and colon carcinoma line (SW620). Additionally, breast carcinoma tissue specimens were examined. Compared with normal human fibroblast and mammary epithelial cell lines, we detected high basal levels of caspase-3 and caspase-8 activities and active caspase-3 fragments in the tumor cell lines and cancer tissues in the absence of apoptotic stimuli. Furthermore, the tumor cells expressed high levels of survivin and XIAP, two members of the inhibitor of apoptosis (IAP) protein family. When the activity of these IAPs was blocked by expression of dominant-negative mutant survivin (survivinT34A) and XIAP-associated factor 1, respectively, apoptosis was induced in tumor but not normal cell lines. Moreover, down-regulation of both survivin and XIAP significantly enhanced tumor-cell apoptosis as compared with inhibition of either survivin or XIAP alone. These results suggest that up-regulated IAP expression counteracts the high basal caspase-3 activity observed in these tumor cells and that apoptosis in tumor cells but not normal cells can be induced by blocking IAP activity. Therefore, IAPs are important molecular targets for the development of cancer-specific therapeutic approaches.