Hammerhead ribozyme-mediated inactivation of mutant RET in medullary thyroid carcinoma.

Activating mutations of the RET proto-oncogene cause hereditary medullary thyroid carcinoma. To examine whether selective inactivation of mutant RET could prevent transformation, a hammerhead ribozyme was designed to cleave RET mRNA containing a transforming mutation of codon 634 TGC --> TAC (Cys634Tyr). In vitro RNA cleavage assay demonstrated that the ribozyme selectively cleaved RET RNA with a Cys634Tyr but not Cys634Arg or the normal sequence. Expression of ribozyme in NIH/3T3 cells prevented RET-mediated colony formation in soft agar. This inhibition required catalytically active ribozyme and was specific for the TAC mutation. Therefore, ribozymes designed to selectively target mutant RET RNA may provide an effective therapeutic in the treatment of this syndrome.     

抑制VEGF表达的锤头状核酶系统

目的:建立和评估抑制血管内皮生长因子(VEGF)表达的锤头状核酶(hammerhead ribozyme)技术系统.方法:对VEGF121基因RNA序列进行二级结构分析,选择靶点;设计并构建针对VEGF的分泌肽RNA的可表达锤头状核酶(14)载体系统和VEGF-荧光色素酶融合基因报告质粒;通过试管内切割实验等方法评估核酶对于试管内转录得到的VEGF RNA切割特异性和效率;通过瞬时共转染实验和稳定转染实验评估核酶在细胞内对于VEGF RNA的切割效率.结果:设计和构建了对VEGF RNA二级结构水平上的暴露区( 8, 36和 71位点:核酶1,3和4)和非暴露区( 17位点:核酶2)4个锤头状核酶(14)的两套质粒;试管内切割检测表明,针对 8, 36和 71位点的核酶(1,3和4)可以有效地在试管内对VEGFRNA进行特异性切割,使其水平分别降至对照的61.7%,27.6%和44.8%(荧光色素酶活性)或66.3%,27.0%和30.0%(蛋白质水平);将核酶表达质粒与VEGF-LUC模板质粒瞬时共转染人SMMC-7721肝癌细胞,核酶1,3和4 VEGF-LUC水平分别降低到对照的81.4%,56.6%和69.1%;稳定表达针对VEGF的核酶1,3或4的SMMC-7721细胞株中,内源性VEGF RNA的水平降至对照水平的5%以下.对照未转染的、转染空载体的和转染了核酶2( 17)的SMMC-7721细胞.结论:分别针对VEGF 8, 36和 71位点锤头状核酶可有效地抑制VEGF的RNA水平.     

Ribozyme对癌基因Ki-ras~(G12V) mRNA的剪切及其特异性

目的 :设计切割ki-rasG12V mRNA的特异性ribozyme(Rz2 17) ,明确其对癌基因ki-rasG12VmRNA的细胞内外切割活性 ,为以ki-rasG12VmRNA为特异性靶分子的基因治疗及癌基因ki-ras的功能研究提拱一种新的途径。方法 :依Symons总结的“锤头结构”原理 ,设计一种能特异性切割ki-rasG12VmRNA的ribozyme ,利用DNA重组技术构建ki-rasG12V外显子 1和ri-bozymeRz2l7的体外转录质粒及ribozymeRz2 17的真核表达质粒 ,体外转录获得ribozymeRz2 17及ki-rasG12V外显子 1mRNA ,在含Mg2 溶液中ribozymeRz2 17对其靶RNA分子进行切割。以RT -PCR对转染ribozymeRz2 17真核表达质粒的细胞ki-rasG12VmRNA进行半定量分析。结果 :ki-rasG12V外显子 1体外转录mRNA分子 ,能被ribozymeRz2 17定点切割而野生型ki-ras外显子 1体外转录mRNA则不被切割 ;转染ribozymeRz2 17的胰癌细胞ki-rasG12VmRNA含量减少 ,而转染ri bozymeRz2 17的肝癌细胞其内源性ki-rasmRNA含量无明显变化。结论 :ribozymeRz2 17无论在细胞内外均能剪切突变型ki-rasmRNA(G12V)而且其切割作用为突变型ki-rasG12VmRNA特异性的。     

Modulation of c-fms proto-oncogene in an ovarian carcinoma cell line by a hammerhead ribozyme.

Co-expression of macrophage colony-stimulating factor (M-CSF) and its receptor (c-fms) is often found in ovarian epithelial carcinoma, suggesting the existence of autocrine regulation of cell growth by M-CSF. To block this autocrine loop, we have developed hammerhead ribozymes against c-fms mRNA. As target sites of the ribozyme, we chose the GUC sequence in codon 18 and codon 27 of c-fms mRNA. Two kinds of ribozymes were able to cleave an artificial c-fms RNA substrate in a cell-free system, although the ribozyme against codon 18 was much more efficient than that against codon 27. We next constructed an expression vector carrying a ribozyme sequence that targeted the GUC sequence in codon 18 of c-fms mRNA. It was introduced into TYK-nu cells that expressed M-CSF and its receptor. Its transfectant showed a reduced growth potential. The expression levels of c-fms protein and mRNA in the transfectant were clearly decreased with the expression of ribozyme RNA compared with that of an untransfected control or a transfectant with the vector without the ribozyme sequence. These results suggest that the ribozyme against GUC in codon 18 of c-fms mRNA is a promising tool for blocking the autocrine loop of M-CSF in ovarian epithelial carcinoma.     

Attenuation of telomerase activity by hammerhead ribozyme targeting human telomerase RNA induces growth retardation and apoptosis in human breast tumor cells

Ribozyme possesses specific endoribonuclease activity and catalyzes the hydrolysis of specific phosphodiester bonds, which results in the cleavage of target RNA sequences. Here, we evaluated the ability of hammerhead ribozymes targeting human telomerase RNA (hTR) to inhibit the catalytic activity of telomerase and the proliferation of cancer cells. Hammerhead ribozymes were designed against 7 NUX sequences located in open loops of the hTR secondary structure. We verified the ribozyme specificity by in vitro cleavage assay by using a synthetic RNA substrate. Subsequently, we introduced ribozyme expression vector into human breast tumor MCF-7 cells and assessed the biologic effects of ribozyme. Hammerhead ribozyme R1 targeting the template region of hTR efficiently cleaved hTR in vitro, and stable transfectants of this ribozyme induced the degradation of target hTR RNA and attenuated telomerase activity in MCF-7 cells. Moreover, the ribozyme R1 transfectant displayed a significant telomere shortening and a lower proliferation rate than parental cells. Clones with reduced proliferation capacity showed enlarged senescence-like shapes or highly differentiated dendritic morphologies of apoptosis. In conclusion, the inhibition of telomerase activity by hammerhead ribozyme targeting the template region of the hTR presents a promising strategy for inhibiting the growth of human breast cancer cells.     

Reversal of drug resistance using hammerhead ribozymes against multidrug resistance-associated protein and multidrug resistance 1 gene

We examined the effects of suppressing multidrug resistance-associated protein (MRP) and multidrug resistance 1 (MDR1) gene expression in HCT-8DDP human colon cancer cell lines, which showed both cisplatin and multidrug resistance. Hammerhead ribozymes, designed to cleave MRP mRNA (anti-MRP Rz) and MDR1 mRNA (anti-MDR1 Rz), were transfected into the HCT-8DDP cells. Drug sensitivity was estimated by MTT assay in vitro. The HCT-8DDP/anti-MRP Rz cells were more sensitive to doxorubicin (DOX) and etoposide (VP-16) by 2.5- and 4.1-fold, respectively, compared with HCT-8DDP cells. The HCT-8DDP/anti-MDR Rz cells were more sensitive to DOX and VP-16 by 2.3- and 3.8-fold, respectively. The anti-MRP Rz and anti-MDR1 Rz significantly down-regulated resistance to DOX and VP-16, while anti-MRP Rz and anti-MDR1 Rz did not affect resistance to cisplatin, methotrexate and 5-fluorouracil. The hammerhead ribozyme-mediated specific suppression of MRP or MDR1 was sufficient to reverse multidrug resistance in the human colon cancer cell line.     

抗肿瘤细胞多药抗性核酶的合成及其活性的研究

目的 研究抗肿瘤细胞多药抗性（ＭＤＲ）核酶的生物学活性及其稳定性。方法 构建表达抗ＭＤＲ１核酶的逆转录病毒载体（Ｎ２Ａ＋ｔＲＮＡ＾ｅｍｔｉ－１９６ＭＤＲ１－Ｒｚ、Ｎ２Ａ＋ｔＲＮＡ＾ｍｅｔｉ－１９６ＭＤＲ１－ｓＲｚ、Ｎ２Ａ＋ｔＲＮＡ＾ｍｅｔｉ－ｌｉＭＤＲ１－ｓＲｚ）和合成了裸核酶ｃＤＮＡ。利用体外转录反应合成５种ａｎｔｉ－ＭＤＲ１核酶（ｔＮＲＡ－１９６ＭＤＲ１－Ｒｚ、ｔＲＮＡ－１９６ＭＤＲ１－ｓＲｚ     

Downregulation of bcl-2 expression in lymphoma cells by bcl-2 ARE-targeted modified,synthetic ribozyme

Synthetic ribozymes are catalytic RNA molecules designed to inhibit gene expression by cleaving specific mRNA sequences. We investigated the potential of synthetic ribozymes to inhibit bcl-2 expression in apoptosis defective bcl-2 overexpressing tumors. A chemically stabilized hammerhead ribozyme has been targeted to the A+U-rich regulative element of bcl-2 mRNA that is involved in bcl-2 gene switch-off during apoptosis. The design of the ribozyme was based on the results of probing accessibility of the RNA target in cellular extracts with antisense DNA. The ribozyme was lipotransfected to a bcl-2 overexpressing human lymphoma cell line (Raji). The cellular uptake of this ribozyme resulted in a marked reduction of both bcl-2 mRNA and BCL-2 protein levels and dramatically increased cellular death by apoptosis. Our results suggest a potential therapeutic application of such ribozyme for the treatment of bcl-2 overexpressing tumors.     

Ribozyme-mediated cleavage of the human survivin mRNA and inhibition of antiapoptotic function of survivin in MCF-7 cells

Survivin is a new member of the inhibitor of apoptosis protein (IAP) family that is implicated in the control of cell proliferation and the regulation of cell life span. This protein is selectively expressed in most human carcinomas but not in normal adult tissues. To down-regulate a human survivin expression as a strategy for cancer gene therapy, we designed two hammerhead ribozymes (RZ-1, RZ-2) targeting human survivin mRNA. RZ-1 and RZ-2 efficiently cleaved the human survivin mRNA at nucleotide positions +279 and +289, which was identified by in vitro cleavage assay using in vitro transcribed ribozymes and truncated survivin mRNA substrate. To investigate the function of the ribozymes in cells, the sequences of the ribozymes were cloned into replication-deficient adenoviral vector and transferred to breast cancer cell, MCF-7. The infection with adenovirus encoding the ribozymes resulted in a significant reduction of survivin mRNA (74% and 73%, respectively) and protein. As revealed by nuclear condensation/ fragmentation and flow cytometry analysis, inhibition of survivin gene by ribozymes increased apoptosis and sensitivity induced by etoposide or serum starvation. Our results suggest that the designed hammerhead ribozymes against survivin mRNA are good candidates for feasible gene therapy in the treatment of cancer.     

Antitumor and antimetastatic activity of ribozymes targeting the messenger RNA of vascular endothelial growth factor receptors.

Chemically stabilized hammerhead ribozymes are nuclease-resistant, RNA-based oligonucleotides that selectively bind and cleave specific target RNAs. Due to their potential for specifically inhibiting gene expression, ribozymes are being investigated for therapeutic applications as well as for the elucidation of gene function. In particular, we have investigated ribozymes that target the mRNA of the vascular endothelial growth factor (VEGF) receptors because VEGF signaling is an important mediator of tumor angiogenesis and metastasis. Here we report pharmacodynamic studies testing anti-Flt-1 (VEGFR-1) and anti-KDR (VEGFR-2) ribozymes in animal models of solid tumor growth and metastasis. Ribozymes targeting either Flt-1 or KDR significantly inhibited primary tumor growth in a highly metastatic variant of Lewis lung carcinoma. However, only treatment with the anti-Flt-1 ribozyme resulted in a statistically significant and dose-dependent inhibition of lung metastasis in this model. The anti-Flt-1 ribozyme was then tested in a xenograft model of human metastatic colorectal cancer in which significant inhibition of liver metastasis was observed. Taken together, these data represent the first demonstration that synthetic ribozymes targeting VEGF receptor mRNA reduced the growth and metastasis of solid tumors in vivo.     

Hammerhead ribozyme specifically inhibits vascular endothelial growth factor gene expression in a human hepatocellular carcinoma cell line

Hammerhead-type ribozymes are often utilized to suppress the expression of target genes. We evaluated the efficacy of an anti-vascular endothelial growth factor (VEGF) hammerhead-type ribozyme against GUC at exon 1 of the VEGF gene in a cell-free system (in vitro) as well as in the hepatocellular carcinoma cell line HLF (in vivo). The anti-VEGF ribozyme (alphaVRz) specifically cleaved synthetic VEGF RNA substrate, but not other triplet sequences of VEGF RNA substrate in vitro. When the alphaVRz was introduced into HLF cells, the ribozyme suppressed not only VEGF mRNA level but also that of VEGF protein. These results suggest that this ribozyme selectively inhibits VEGF gene expression in human hepatocellular carcinoma cells.     

切割MDR1 RNA的核酶(Ribozyme)对肝癌多药耐药细胞株BEL-7402/DOX化疗耐药性的逆转作用

为逆转肿瘤多药耐药基因(MDR1)产物P-gp蛋白所介导的肿瘤细胞对多种化疗药物的耐受性,设计合成了一种能切割MDR1 mRNA第196密码子GUC序列的锤头状核酶(Ribozlyme)并定向克隆于转录病毒载体pDOR-neo的BamH Ⅰ位点.经病毒包装细胞PA317包装后感染人肝癌多药耐药细胞株BEL-7402/DOX细胞,经G418筛选得到稳定的转化细胞株.Northem Blot杂交证实包装细胞PA317及转化的BEL-7402/DOX细胞中均有病毒的高表达,RT-PCR证实转化细胞中MDR1 mRNA与未转化细胞相比明显减少甚至不能扩增出来,流式细胞技术检测转化细胞P-gp的表达与非转化细胞的93.4～97.5%相比下降至8.2～14.6%.MTT法检测证实转化细胞对多种化疗药物重新产生较高的敏感性.结果表明,表达Ribozyme的逆转录病毒载体转化肝癌多药耐药细胞BEL-7402/DOX后能有效抑制MDR1的表达和翻译,使已产生耐药的肿瘤细胞的多药耐药表型发生逆转.     

抗VEGF165核酶对人肺腺癌细胞生物学特性的影响

目的 探讨抗血管内皮生长冈子165(VEGF165)核酶对人肺腺癌细胞生物学特性的影响。方法设计合成针对VEGF165 212位点的锤头状核酶(vascular endothelial growth factor ribozyme，VRZ)及其突变体(mutant VRz，mVRz)，体外检测核酶的剪切活性。采用亚克隆技术，构建腺病毒介导的抗VEGF165核酶真核表达载体pAdVRz，用重组腺病毒感染人肺腺癌细胞A549，分别采用Northern blot印迹杂交、流式细胞仪、透射电镜和激光共聚焦等技术，观察感染前后A549细胞的生物学性状的改变。结果成功地合成了具有明显剪切活性的抗VEGF165核酶VRz及其重组腺病毒表达载体rpAdVRz，并在A549细胞中获得表达。重组腺病毒感染细胞的VEGF165表达减少了87％，而生物学性状不受外源基因表达的影响。结论抗VEGF165核酶能够显著抑制人肺腺癌细胞内VEGF165的表达，为进一步进行肺癌的抗血管治疗提供了实验基础。     

核酶对食管癌EC9706细胞端粒酶活性及凋亡的影响

目的 :观察针对人端粒酶RNA模板区的核酶对食管癌细胞端粒酶活性和细胞凋亡的影响。方法 :利用脂质体Lipofectamine介导 ,将已构建好的带有端粒酶核酶基因的重组质粒pBBS2 12Rz及空载质粒pBBS2 12转染食管癌EC970 6细胞 ,采用TRAP ELISA法检测端粒酶活性 ,用倒置相差显微镜及流式细胞仪观察细胞生长和凋亡情况。结果 :重组质粒pBBS2 12Rz转染的食管癌EC970 6细胞的端粒酶活性明显下降 ,细胞生长速度明显变慢 ,凋亡加速。结论 :端粒酶核酶对食管癌细胞端粒酶活性和细胞生长有抑制作用 ,可望成为食管癌基因治疗的新方法