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.     

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     

Attenuation of telomerase activity does not increase sensitivity of human melanoma cells to anticancer agents

In tumour cells, replicative immortality is attained through stabilisation of telomeres by telomerase. Recent evidence suggests that telomerase plays an anti-apoptotic role. Since apoptosis is the primary mode of cell death induced by several drugs, telomerase could be involved in determining the chemosensitivity profile of tumour cells. We investigated whether inhibition of telomerase activity through a hammerhead ribozyme targeting the RNA template of telomerase influences the susceptibility of human melanoma cells to a variety of anticancer agents (platinum compounds, taxanes, topoisomerase I inhibitors). The ribozyme sequence was inserted into an expression vector and the JR8 human melanoma cell line was transfected with it. The cell clones obtained showed a reduced telomerase activity. Growth inhibition curves generated after exposure of ribozyme-transfectant clones to individual drugs were superimposable to those obtained from parental cells. Moreover, telomerase inhibition did not promote apoptosis as a cellular response to drug treatment. Overall, our results indicate that downregulation of telomerase activity does not increase the sensitivity of melanoma cells to anticancer drugs.     

抗端粒酶核酶质粒的构建筛选及其对CNE-2Z细胞增殖与凋亡的影响

背景与目的:已证实端粒酶(telomerase,TLMA)对肿瘤的进展和肿瘤细胞的无限增殖起着重要的决定作用。核酶是具有特殊核酸内切酶活性的反义RNA,可序列特异性地与靶RNA分子配对并切割靶基因RNA。有报道人低分化鼻咽癌CNE-2Z细胞端粒酶阳性,本实验目的是构建抗端粒酶RNA模板区特异性核酶的真核表达载体并用电穿孔法将其导入人低分化鼻咽癌CNE-2Z细胞,研究该核酶对CNE-2Z细胞增殖、凋亡的影响。方法:设计合成针对端粒酶RNA模板区的锤头状核酶基因teloRZ作为端粒酶抑制剂,构建3种带有绿色荧光蛋白(greenfluorescentprotein,GFP)报道基因和嘌呤霉素(puromycin)抗性基因的teloRZ真核表达质粒pGFPuro-teloRZ2.1、pGFPuro-teloRZ7.1、pGFPuro-teloRZ7.7,这3种质粒的不同点在于teloRZ基因和puromycin抗性基因按3种不同方向设计,然后将上述3种质粒及载体质粒pPAT-GFP电转染CNE-2Z细胞,用荧光显微镜检测GFP表达情况;用流式细胞仪、荧光染色法检测细胞增殖指数及凋亡等指标。结果:CNE-2ZGTR7.1细胞(转染目的基因质粒pGFPuro-teloRZ7.1的CNE-2Z细胞)增殖指数(25.100±0.141)%明显低于CNE-2Z细胞(未转染质粒的细胞)的(53.663±16.981)%、CNE-2ZG细胞(转染空载质粒pPAT-GFP的CNE-2Z细胞)的(61.575±5.166)%、CNE-2ZGTR2.1     

Targeting the c-Met pathway potentiates glioblastoma responses to gamma-radiation.

PURPOSE: Resistance to current cytotoxic therapies limits the treatment of most solid malignancies. This results, in part, from the overactivation of receptor tyrosine kinases and their downstream pathways in tumor cells and their associated vasculature. In this report, we ask if targeting the multifunctional mitogenic, cytoprotective, and angiogenic scatter factor/hepatocyte growth factor (SF/HGF)/c-Met pathway potentiates antitumor responses to gamma-radiation. EXPERIMENTAL DESIGN: Endogenous expression of SF/HGF and c-Met was targeted in U87 MG human malignant glioma cells and xenografts using chimeric U1/ribozymes. The effects of U1/ribozymes +/- gamma-radiation on glioma cell proliferation, apoptosis, xenograft growth, and animal survival were examined. RESULTS: U1/ribozymes knocked down SF/HGF and c-Met mRNA and protein levels, sensitized cells to gamma-radiation (P < 0.005), and enhanced radiation-induced caspase-dependent cytotoxicity in vitro (P < 0.005). Intravenous U1/ribozyme therapy as liposome/DNA complexes or radiation alone modestly and transiently inhibited the growth of s.c. U87 xenografts. Combining the therapies caused tumor regression and a 40% tumor cure rate. In animals bearing intracranial xenografts, long-term survival was 0% in response to radiation, 20% in response to intratumoral adenoviral-based U1/ribozyme delivery, and 80% (P < 0.0005) in response to combining U1/ribozymes with radiation. This apparent synergistic antitumor response was associated with a approximately 70% decrease in cell proliferation (P < 0.001) and a approximately 14- to 40-fold increase in apoptosis (P < 0.0001) within xenografts. CONCLUSIONS: Targeting the SF/HGF/c-Met pathway markedly potentiates the anti-glioma response to gamma-radiation. Clinical trials using novel SF/HGF/c-Met pathway inhibitors in glioma and other malignancies associated with c-Met activation should ultimate include concurrent radiation and potentially other cytotoxic therapeutics.     

端粒酶特异性核酶抑制宫颈癌细胞的作用

目的 :研究端粒酶RNA特异性核酶对宫颈癌细胞活性的影响。方法 :通过脂质体将核酶转染至宫颈癌Hela细胞 ,以G4 18筛选细胞 ,经斑点杂交提示转染成功后 ,检测细胞活力及细胞周期变化 ,测定细胞端粒酶活性 ,观察细胞的增殖情况。结果 :试验组细胞的活力较对照组明显减弱。转染后细胞受阻于G1期的细胞明显增多 ,S期细胞比例明显降低 ,P <0 0 1。转核酶细胞端粒酶活性较对照组明显减低 ,转染空载体的细胞端粒酶活性与未转染细胞比较则无明显变化。结论 :端粒酶RNA特异性核酶可抑制宫颈癌细胞端粒酶活性 ,抑制细胞增殖 ,为核酶用于恶性肿瘤基因治疗提供了试验依据     

Ribozyme cleavage of telomerase mRNA sensitizes breast epithelial cells to inhibitors of topoisomerase

Telomerase activity is necessary and sufficient for immortality in many cells and hence represents a prime target for antitumor strategies. Here, we show that a hammerhead ribozyme cleaves human telomerase (hTERT) mRNA in vitro. Stable transfection in clones of the human breast tumor line MCF-7 and the immortal breast cell line HBL-100 results in expression of the ribozyme, diminishes the abundance of hTERT mRNA, and inhibits telomerase activity. This led to shortened telomeres, inhibition of net growth, and induction of apoptosis. In HBL-100 mass cultures infected with a ribozyme-expressing adenovirus diminution of hTERT mRNA, attenuation of telomerase activity, inhibition of net growth, and induction of apoptosis was found as well. Attenuation of telomerase activity increased the sensitivity of HBL-100 and MCF-7 clones specifically to inhibitors of topoisomerase. Likewise, expression of exogenous telomerase in originally telomerase-negative human fibroblasts decreased their sensitivity to topoisomerase poisons but not to a number of other cytotoxic drugs. The data validate a ribozyme approach for telomerase inhibition therapy in cancer and suggest that it might be combined advantageously with topoisomerase-directed chemotherapy.     

Efficient inducation of local and systemic antitumor immune response by liposome-mediated intratumoral co-transfer of interleukin-2 gene and interleukin-6 gene.

Interleukin 2 (IL-2) expressing plasmid and interleukin 6 (IL-6)-expressing plasmid were encapsulated in liposome and administrated intratumoraly into tumor-bearing mice 4 days after subcutaneous inoculation of B16F10 melanoma cells. The results showed that treatment of tumor-bearing mice with IL-2 gene or IL-6 gene transfer inhibited the growth of subcutaneous tumor and prolonged the survival of tumor-bearing mice significantly when compared with the treatment of PBS or control gene transfer mediated by liposome (P < 0.01). Combined transfer of IL-2 gene and IL-6 gene was found to elicit inhibitory effects on the growth of B16F10 tumor more significantly and prolonged the survival period of tumor-bearing mice more obviously. We investigated the local immunity in tumor microenvironment and found that IL-2 and IL-6 gene transfer could significantly increase the expression of lymphocyte function-associated antigen-1 on tumor infiltrating lymphocytes (TIL) and MHC-I molecule on tumor cells freshly isolated from the tumor mass. The NK and CTL activity of TIL increased markedly after the combined transfer of these two cytokine genes. We also observed the systemic antitumor immune response in the tumor-bearing mice and demonstrated that NK and CTL activity of splenocytes and the production of IL-2, tumor necrosis factor and interferon-gamma from splenocytes increased obviously in mice after the combined transfer of IL-2 and IL-6 gene. In conclusion, local and systemic antitumor immunity of the tumor-bearing host could be induced efficiently after the combined gene transfer. The enhanced specific and non-specific antitumor immunity might be responsible for the more potent antitumor effects of the combined gene therapy.     

Ribozyme-mediated down-regulation of survivin expression sensitizes human melanoma cells to topotecan in vitro and in vivo

The ability of melanoma cells to evade engagement of apoptosis plays a significant role in their resistance to chemotherapy. In an attempt to lower the apoptotic threshold of melanoma cells as a possible strategy to increase their drug sensitivity, we generated a hammerhead ribozyme to down-regulate the expression of the anti-apoptotic protein survivin. The JR8 human melanoma cell line was stably transfected with the active ribozyme RZsurv (targeting the 3' end of the GUC294 triplet in the exon 3 of the survivin mRNA) or the catalytically inactive ribozyme mutRZsurv (carrying a mutation in the catalytic core of RZsurv). Two polyclonal cell populations expressing the active (JR8/RZsurv) or the mutant (JR8/mutRZsurv) ribozyme were selected for the study. JR8/RZsurv cells were characterized by a markedly lower survivin protein level than JR8 parental cells, whereas a negligible reduction in survivin expression was observed in JR8/mutRZsurv cells. JR8/RZsurv cells showed a significantly increased sensitivity to the topoisomerase-I inhibitor topotecan (as detected by clonogenic cell survival) compared with JR8/mutRZsurv cells. Moreover, the extent of drug-induced apoptosis (in terms of percentage of apoptotic nuclei and level of caspase-9 and caspase-3 catalytic activity) was significantly greater in JR8/RZsurv than in JR8/mutRZsurv cells. Finally, an increased antitumor activity of oral topotecan was observed in JR8/RZsurv cells grown as xenograft tumors in athymic nude mice compared with JR8/mutRZsurv cells. These results demonstrate that attenuation of survivin expression renders human melanoma cells more susceptible to topotecan-induced apoptosis and more responsive to in vivo treatment, and support the concept that survivin is an attractive target for new therapeutic interventions in melanoma.     

GFP报道基因在鼻咽癌细胞系CNE-2Z中的表达

目的　观察GFP报道基因在鼻咽癌细胞系CNE 2Z中的表达。方法　将带有GFP报道基因的载体质粒pPAT GFP和 3种带有GFP报道基因及目的基因抗端粒酶核酶基因teloRZ的不同质粒 pGFPuro teloRZ 2 .1、pGFPuro teloRZ 7.1、pGFPuro teloRZ 7.7,转染到鼻咽癌CNE 2Z细胞系中 ,用荧光显微镜及流式细胞仪检测转染细胞在固定后的活细胞中GFP基因的表达情况。结果　GFP基因在活细胞中有表达 ,而在固定后无表达 ,且目的基因的插入影响GFP基因的表达。结论　GFP基因在转染了含目的基因质粒的鼻咽癌CNE 2Z细胞中稳定表达 ,可以在CNE 2Z细胞株和抗端粒酶模板区核酶的研究中作为质粒转染和基因表达的报道基因     

The influence of oral tumor cell proliferation activity and membrane potential on the transfection efficiency of a cationic liposome

The transfection efficiency of cationic liposomes varies according to cell type, but the specific cellular characteristics that affect transfection efficiency have not yet been defined. We investigated whether the transfection efficiency of cationic liposomes correlates with cell proliferation activity or cell membrane potential in oral malignant melanoma (HMG) and oral osteosarcoma cell lines (HOSM-1 and HOSM-2). The cell membrane potential was assessed by uptake of a cationic probe. Three oral tumor cell lines were exposed to a cationic liposome complexed with a beta-galactosidase expression plasmid, and beta-galactosidase expression was compared. Cell proliferation was about 2-fold higher in HOSM-1 cells than in HMG cells. The cell membrane potential in HMG and HOSM-1 cells was comparable, while the membrane potential in HOSM-2 cells was 1.6-fold higher. beta-galactosidase expression was measured by X-Gal staining in 7.0% of HMG, 17.0% of HOSM-1 and 11.5% of HOSM-2 cells. The present study demonstrates that gene therapy with cationic liposomes may be a promising new strategy for treatment of oral malignant melanoma and osteosarcoma. In addition, the transfection efficiency of cationic liposomes appears to be influenced by cell proliferation activity, but not cell membrane potential.     

Aerosol delivery of PEI-p53 complexes inhibits B16-F10 lung metastases through regulation of angiogenesis

Inhibition of pulmonary metastases poses a difficult clinical challenge for current therapeutic regimens. We have developed an aerosol system utilizing a cationic polymer, polyethyleneimine (PEI), for topical gene delivery to the lungs as a novel approach for treatment of lung cancer. Using a B16-F10 murine melanoma model in C57BL/6 mice, we previously demonstrated that aerosol delivery of PEI-p53 DNA resulted in highly significant reductions in the tumor burden (P < .001) in treated animals, and also lead to about 50% increase in the mean length of survival of the mice-bearing B16-F10 lung tumors. The mechanisms of this antitumor effect of p53 are investigated in this report. Here, we demonstrate that the p53 transfection leads to an up-regulation of the antiangiogenic factor thrombospondin-1 (TSP-1) in the lung tissue and the serum of the mice. Furthermore, there is a down-regulation of vascular endothelial growth factor (VEGF) in the lung tissue and serum of the B16-F10 tumor-bearing mice treated with PEI-p53 DNA complexes, compared with untreated tumor-bearing animals. In addition, staining for von Willebrand factor (vWF), a marker for the angiogenic blood vessels, revealed that p53 treatment leads to a decrease in the angiogenic phenotype of the B16-F10 tumors. Immunohistochemistry for transgene expression reveals that the PEI-p53 aerosol complexes transfect mainly the epithelial cells lining the airways, with diffuse transfection in the alveolar lining cells, as well as, the tumor foci in the lung tissue. There was also some evidence of apoptosis in the lung tumor foci of animals treated with p53. The data suggest that aerosol delivery of PEI-p53 complexes leads to inhibition of B16-F10 lung metastases, in part by suppression of angiogenesis.     

pEgr-Endostatin-EGFP抑制黑色素瘤生长及血管生成

目的 检测pEgr-Endostatin-EGFP质粒的表达特性和pEgr-Endostatin-EGFP基因-放射治疗小鼠黑色素瘤的作用。方法pEgr-Endostatin-EGFP重组质粒用脂质体方法转染B16细胞,采用Western blot方法检测Endostatin表达。建立小鼠荷瘤模型,注射质粒并给予5Gy X射线照射,共3次,18天观察肿瘤生长情况,并采用免疫组织化学方法检测肿瘤血管生成。结果 转染了pEgr-Endostatin-EGFP质粒的B16细胞和转染并接受照射的B16细胞组可以检测到Endostatin蛋白表达。C57BL/6J小鼠给予pEgr-Endostatin-EGFP质粒注射并接受肿瘤X射线照射,可以显著抑制肿瘤生长(P<0.01),而且肿瘤局部血管生成明显降低(P<0.01)。结论 本研究数据为肿瘤基因-放射治疗提供了新的治疗方案。     

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.     

An <Emphasis Type="Italic">in vitro</Emphasis> Study on the Suppressive Effect of Glioma Cell Growth Induced by Plasmid-Based Small Interference RNA (siRNA) Targeting Human Epidermal Growth Factor Receptor

Summary Objectives:To study the inhibitory effects of plasmid-based siRNA targeting human epidermal growth factor receptor (EGFR) on tumor proliferation and invasion of TJ905 glioblastoma cells. Methods: Two siRNA expression constructs targeting human EGFR extracellular domain (516–536) and catalytic domain (2400–2420) were transfected into TJ905 cell as mediated by Lipofectamine. Immunofluorescence assay and Western blotting were used to detect EGFR expression. Cell cycle was analyzed by flow cytometry, cell proliferative activity was measured by MTT assay. The expression and enzymatic activity of MMP9 were measured by Western blotting and gelatin zymography. Cell invasive capability was evaluated by Transwell method. Results: The expression of EGFR was knocked-down by 90 and 92, respectively in siRNA constructs transfected groups as indicated by immunofluorescence assay and Western blotting. The flow cytometric analysis showed that the S phase fraction (SPF) was lowered in both siRNAs transfected cells than that in parental cells and the cells transfected with empty vector. Compared to parental cells and the cells transfected with empty vector, the survival rates of glioma cells transfected with the siRNAs dramatically dropped down from the first day after implantation (P<0.05) as indicated by MTT assay. Meanwhile, the expression and enzymatic activity of MMP9 decreased significantly in siRNAs transfected in TJ905 cells, and cell invasive potential was also greatly inhibited in the Transwell study. Conclusion: The siRNA expression constructs targeting EGFR could specifically suppress EGFR expression, inhibit cell growth, induce cell cycle arrest and suppress invasion. The plasmid-based siRNA targeting human EGFR approach should be a new strategy for gene therapy of malignant gliomas.     

应用脂质体及直接注射法在小鼠体内表达人生长激素的研究

本文以构建的含人生长激素(hGH)cDNA的重组真核表达质粒为外源靶基因,研究了直接注射质粒及脂质体与质粒复合物后hGH在小鼠体内表达的情况.用RT-PCR技术检测hGH转录产物,用免疫放射检测分析法(IRMA)检测hGH蛋白质表达水平.结果发现,注射质粒与脂质体复合物组的表达效率高于单纯质粒组,Lipofectamine的作用强于Lipofectin,表明应用脂质体及直接注射法是使外源靶基因在小鼠体内表达的简便、有效途径.     

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。