缺氧/辐射双敏感性启动子调控HSV-TK表达对肺癌移植瘤的作用

背景与目的放射-基因治疗是近年来国际上肿瘤治疗的新策略,由于实体瘤常处于缺氧状态而对放射敏感性低,放射-基因治疗尚未达理想疗效。本研究拟构建缺氧/辐射双敏感性启动子,增强缺氧条件下放射诱导的HSV-TK表达水平,提高肺癌放射-基因治疗效果。方法利用基因重组构建HRE-Egr启动子及其调控的HSV-TK表达载体;脂质体介导重组质粒转染肺癌A549细胞,分为对照组、放射组(6Gy)、缺氧组(1%氧浓度)和放射合并缺氧组,Northernblot法检测转染细胞中HSV-TK表达,四甲基偶氮唑蓝(MTT)法检测放射、缺氧和GCV处理后的细胞存活率。建立BALB/c裸鼠肺癌移植瘤模型,检测放射合并质粒转染后移植瘤体积变化并计算抑瘤率。结果对照组细胞仅可检测到HyTK的低水平表达(21U),放射组和缺氧组HyTK基因表达水平均显著升高(分别为227U和94U),放射合并缺氧组(769U)显著高于放射组。在缺氧条件下,放射合并GCV处理后细胞存活率为(7.2±1.8)%,显著低于常氧组的(32.7±4.6)%。放射联合GCV可明显抑制HRE-Egr启动子转染肺癌移植瘤,抑瘤率达91.2%。结论HRE-Egr启动子具有辐射/缺氧双重敏感性,并使放射后的HSV-TK表达水平在缺氧下得到显著增强。放射联合HRE-Egr启动子可显著抑制肺癌移植瘤的生长。     

Enhancement of gene expression under hypoxic conditions using fragments of the human vascular endothelial growth factor and the erythropoietin genes

Purpose: Selective gene expression in response to tumor hypoxia may provide new avenues, not only for radiotherapy and chemotherapy, but also for gene therapy. In this study, we have assessed the extent of hypoxia responsiveness of various DNA constructs by the luciferase assay to help design vectors suitable for cancer therapy.Materials and Methods: Reporter plasmids were constructed with fragments of the human vascular endothelial growth factor (VEGF) and the erythropoietin (Epo) genes encompassing the putative hypoxia-responsive elements (HRE) and the pGL3 promoter vector. Test plasmids and the control pRL-CMV plasmid were cotransfected into tumor cells by the calcium phosphate method. After 6 h hypoxic treatment, the reporter assay was performed.Results: The construct pGL3/VEGF containing the 385 bp fragment of the 5’ flanking region in human VEGF gene showed significant increases in luciferase activity in response to hypoxia. The hypoxic/aerobic ratios were about 3–4, and 8–12 for murine and human tumor cells, respectively. Despite the very high degree of conservation among the HREs of mammalian VEGF genes, murine cells showed lower responsiveness than human cells. We next tested the construct pGL3/Epo containing the 150 bp fragment of the 3’ flanking region in the Epo gene. Luciferase activity of pGL3/Epo was increased with hypoxia only in human cell lines. The insertion of 5 copies of the 35-bp fragments derived from the VEGF HREs and 32 bp of the E1b minimal promoter resulted in maximal enhancement of hypoxia responsiveness.Conclusions: The constructs with VEGF or Epo fragments containing HRE may be useful for inducing specific gene expression in hypoxic cells. Especially, the application of multiple copies of the HREs and an E1b minimal promoter appears to have the advantage of great improvement in hypoxia responsiveness.     

缺氧对血管内皮生长因子启动子-胸苷激酶系统杀伤肝癌细胞系的增强作用

目的：探讨缺氧对腺病毒介导的血管内皮生长因子启动子－胸苷激酶系统（AdVEGF-tk)对肝癌细胞系HepG2选择性杀伤活性的增强作用。方法：采用AdEasy system构建重组腺病毒载体AdVEGF-tk和AdVEGF-GFP,在293细胞中包装,扩增后,分别感染L02（正常肝细胞系）和HepG2,A VEGF-GFP感染细胞经正常培养24h后,在荧光显微镜下观察其荧光蛋白表达情况;AdVEGF-tk感染细胞在缺氧或不缺氧条件下培养,并给予不同浓度的丙氧鸟苷（GCV）处理,用MTT法检测感染细胞的增殖情况,结果：AdVEGF-GFP感染的L02细胞仅见稀散的荧光,而AdVEGF-GFP感染的HepG2细胞则出现大量荧光,感染AdVEGF-tk后,当感染指数（MOI）为100目GCV浓度为10ug/ml时,L02细胞在不缺氧条件下对GCV几乎不敏感,但在缺氧条件下,70％以上的细胞被杀死,而HepG2细胞即便在不缺氧培养条件下也有60％以上的细胞被杀死,缺氧则使80％以上细胞被杀死,结论：缺氧可加强腺病毒介导的AdVEGF-tk系统对体外培养肝癌细胞的选择性杀伤作用。     

Enhanced efficacy of radiation-induced gene therapy in mice bearing lung adenocarcinoma xenografts using hypoxia responsive elements

The aim of the present study was to investigate whether the hypoxia responsive element (HRE) could be used to enhance suicide gene (HSV-tk) expression and tumoricidal activity in radiation-controlled gene therapy of human lung adenocarcinoma xenografts. A chimeric promoter, HRE-Egr, was generated by directly linking a 0.3-kb fragment of HRE to a 0.6-kb human Egr-1 promoter. Retroviral vectors containing luciferase or the HSV-tk gene driven by Egr-1 or HRE-Egr were constructed. A human adenocarcinoma cell line (A549) was stably transfected with the above vectors using the lipofectamine method. The sensitivity of transfected cells to prodrug ganciclovir (GCV) and cell survival rates were analyzed after exposure to a dose of 2 Gy radiation and hypoxia (1%). In vivo, tumor xenografts in BALB/c mice were transfected with the constructed retroviruses and irradiated to a total dose of 6 Gy, followed by GCV treatment (20 mg/kg for 14 days). When the HSV-tk gene controlled by the HRE-Egr promoter was introduced into A549 cells by a retroviral vector, the exposure to 1% O(2) and 2 Gy radiation induced significant enhancement of GCV cytotoxicity to the cells. Moreover, in nude mice bearing solid tumor xenografts, only the tumors infected with the hybrid promoter-containing virus gradually disappeared after GCV administration and radiation. These results indicate that HRE can enhance transgene expression and tumoricidal activity in HSV-tk gene therapy controlled by ionizing radiation in hypoxic human lung adenocarcinoma.     

HIF1A induces expression of the WASF3 metastasis-associated gene under hypoxic conditions

The WASF3 (WAVE3) gene is an important mediator of cell motility, invasion and metastasis and is expressed at high levels in some advanced stage tumors. In our survey of breast cancer cells, we now demonstrate that exposure to hypoxic conditions increases WASF3 expression levels in MDA231, SKBR3 and MCF7 cells. The WASF3 promoter region contains HIF1A response elements (HRE). ChIP assays demonstrate that HIF1A binds to these HRE elements in the promoter region, and luciferase reporter assays using the WASF3 gene minimal promoter shows that hypoxia results in its upregulation. Phosphorylation of WASF3 is required for its ability to affect invasion and increased phosphoactivation of WASF3 is also seen in cells challenged with hypoxia. These cells also show increased motility in the scratch wound assay. Cells in which WASF3 has been knocked down show no response to hypoxia as expected, implicating the specificity of the hypoxic response to WASF3. Overall, these experiments demonstrate WASF3 is a HIF1A-regulated gene and suggests a mechanism to explain the observation of elevated expression of WASF3 in advanced stage tumors.     

Development of a flexible and potent hypoxia-inducible promoter for tumor-targeted gene expression in attenuated Salmonella

To increase the potential of attenuated Salmonella as gene delivery vectors for cancer treatment, we developed a hypoxia-inducible promoter system to limit gene expression specifically to the tumor. This approach is envisaged to not only increase tumor specificity, but also to target those cells that are most resistant to conventional therapies. We demonstrate that the exponential growth of the attenuated bacteria is identical under normoxia and hypoxia. A hypoxia-inducible promoter (HIP-1) was created from a portion of the endogenous Salmonella pepT promoter and was shown to drive reporter gene expression under both acute and chronic hypoxia, but not under normoxia. Genetic engineering of the TATA- and FNR-box within HIP-1 allowed fine-tuning of gene induction, resulting in hypoxic induction factors of up to 200-fold. Finally, we demonstrate that HIP-1 can drive hypoxia-mediated gene expression in bacteria which have colonized human tumor xenografts in mouse models. Expression of both GFP and RFP under control of HIP-1 demonstrated an approximately 15-fold increase relative to a constitutive promoter when tumors were made hypoxic. Moreover, the use of a constitutive promoter resulted in reporter gene expression in both tumors and normal tissues, whereas reporter gene expressing using HIP-1 was confined to the tumor.     

Killing of brain tumor cells by hypoxia-responsive element mediated expression of BAX

The presence of radioresistant hypoxic cells in human brain tumors limits the overall effectiveness of conventional fractionated radiation therapy. Tumor-specific therapies that target hypoxic cells are clearly needed. We have investigated the expression of suicide genes under hypoxia by a hypoxia-responsive element (HRE), which can be activated through hypoxia-inducible factor-1 (HIF-1). We transfected plasmids containing multiple copies of HRE into U-87 MG and U-251 MG-NCI human brain tumor cells and tested their ability to induce LacZ gene expression under anoxia. Gene expression under anoxia versus oxia was increased about 12-fold for U-87 MG cells and about fourfold for U-251 MG-NCI cells. At intermediate hypoxic conditions, increased LacZ gene expression in U-87 MG cells was induced by the plasmid that contained three HREs, but not by the plasmid with two HREs. Lastly, when we placed a suicide gene BAX under the control of HREs, cells transfected with the BAX plasmids were preferentially killed through apoptosis under anoxia. Our studies demonstrate that HRE-regulated gene expression is active in brain tumor cells, and that the amount of increased gene expression obtained is dependent on the cell line, the HRE copy number, and the degree of hypoxia.     

Hypoxia regulates choline kinase expression through hypoxia-inducible factor-1 alpha signaling in a human prostate cancer model

The intensity of the total choline (tCho) signal in spectroscopic images of tumors is spatially heterogeneous. The likewise heterogeneous physiologic tumor microenvironment may contribute to this heterogeneity. We therefore investigated the relationship between hypoxia, choline metabolites, and choline kinase (Chk) in a human prostate cancer model. Human PC-3 prostate cancer cells were engineered to express enhanced green fluorescent protein (EGFP) under hypoxic conditions. These PC-3-5HRE-EGFP cells were characterized in culture and as tumors transplanted in mice using (1)H magnetic resonance spectroscopy (MRS) and MRS imaging (MRSI) combined with EGFP fluorescence microscopy and imaging. Hypoxic EGFP-fluorescing tumor regions colocalized with regions of high tCho in combined MRSI and optical imaging studies. Cellular phosphocholine (PC) and tCho concentrations as well as Chk expression levels significantly increased following exposure of PC-3 cells to hypoxia. A putative promoter region located 5' of the translation start site of the human chk-alpha gene was cloned and luciferase (Luc)-based reporter vector constructs were generated. Luc reporter assays provided evidence that some of the putative hypoxia response elements (HRE) within this putative chk-alpha promoter region functioned in vitro. Chromatin immunoprecipitation assays using an antibody against hypoxia-inducible factor (HIF)-1 alpha showed that HIF-1 can directly bind this region of the endogenous chk-alpha promoter in hypoxic PC-3-5HRE-EGFP cells. These data suggest that HIF-1 activation of HREs within the putative chk-alpha promoter region can increase Chk-alpha expression within hypoxic environments, consequently increasing cellular PC and tCho levels within these environments.     

Development of a hypoxia-inducible cytosine deaminase expression vector for gene-directed prodrug cancer therapy

One important feature of human solid tumors is the presence of a hypoxic microenvironment. Under hypoxia, genes that contain a hypoxia-response element (HRE) can be activated by the binding of hypoxia-inducible factor-1. To reach the goal of selectively killing tumor cells in a hypoxic microenvironment using a gene therapy approach, we developed a cytosine deaminase (CD) gene construct (pH9YCD2) that contains an HRE gene enhancer. CD is an enzyme that catalyzes the conversion of noncytotoxic 5-fluorocytosine (5-FC) to the cytotoxic and radiosensitizing drug 5-fluorouracil (5-FU). Yeast CD was cloned into an SV40 promoter-based mammalian expression vector, and an HRE enhancer was inserted in front of the promoter. Human glioblastoma U-87 MG cells were transfected with pH9YCD2. Western blots revealed that CD was strongly expressed under hypoxic conditions (0.3-1% O2), whereas only minor CD expression was seen under normoxic conditions. To confirm that the expressed CD enzyme retains catalytic activity, we performed a 5-FC/5-FU-conversion assay in which 5-FC was incubated with the lysates of pH9YCD2-transfected cells. The percentage of conversion from 5-FC to 5-FU was 63% under hypoxia versus 13% under normoxia. In vitro, cell viability and colony-forming efficiency assays demonstrated that the gene construct was able to significantly kill glioblastoma cells in a hypoxia-dependent manner. In addition, 5-FC treatment of hypoxic pH9YCD2-transfected cells produced a marked bystander effect, which could be a distinct advantage for gene therapy. If this construct exhibits antitumor efficacy in vivo, it may have promise as an antitumor agent in humans.     

HSVTK/GCV自杀基因系统治疗乳腺癌的研究

 目的　探讨HSV TK/GCV自杀基因系统对小鼠乳腺癌细胞系MA782 / 5S 810 2体外及体内杀伤作用及其产生的旁观者效应。方法　采用脂质体转染法将GINaTK载体转入包装细胞PA317。取病毒上清液感染小鼠乳腺癌细胞MA782 / 5S 810 2 ,得到带有HSV TK基因的MA782 / 5S 810 2 /TK细胞 ,并将其分别用于体外和体内实验。结果　载体HSV TK导入了PA317细胞。体外实验结果显示 ,当MA782 / 5S 810 2 /TK细胞数占混合细胞 10 %时 ,低浓度 (10 μg/ml)的GCV就可将 5 0 %左右的肿瘤细胞杀死。体内实验结果显示GCV可明显抑制MA782 / 5S 810 2 /TK细胞在BALB/C小鼠体内的肿瘤形成。实验组肿瘤组织与对照组相比存在明显的病理学改变。结论　逆转录病毒可介导HSV TK基因转入小鼠乳腺癌细胞MA782 / 5S 810 2并获稳定表达 ,HSV TK/GCV自杀基因系统在体内外对乳腺癌细胞均有杀伤作用 ,且存在明显的旁观者效应。     

Optimization of radiation controlled gene expression by adenoviral vectors in vitro

The radiation-inducible EGR-1-promoter has been used in different gene therapy approaches in order to enhance and locally restrict therapeutic efficacy. The aim of this study was to reduce nonspecific gene expression in the absence of irradiation (IR) in an adenoviral vector. Rat rhabdomyosarcoma R1H tumor cells were infected with adenoviral vectors expressing either EGFP or HSV-TK under control of the murine EGR-1 promoter/enhancer. Cells were irradiated at 0-6 Gy. Gene expression was determined by FACS-analysis (EGFP), or crystal violet staining (HSV-TK). The bovine growth hormone polyadenylation signal (BGH pA) was used as insulating sequence and was introduced upstream or upstream and downstream of the expression cassette. Infected R1H cells displayed IR dose-dependent EGFP expression. Cells treated with IR, AdEGR.TK and ganciclovir displayed a survival of 17.3% (6 Gy). However, significant gene expression was observed in the absence of IR with EGR.TK and EGR.EGFP constructs. Introduction of BGHpA upstream or upstream and downstream of expression cassette resulted in decreased nonspecific cytotoxicity by a factor of 1.6-2.3 with minor influence on the induced level of cytotoxicity. Introduction of insulating sequences in adenoviral vectors might allow tighter temporospatial control of gene expression by the radiation-inducible EGR-1 promoter.     

Hypoxia-regulated expression of attenuated diphtheria toxin A fused with hypoxia-inducible factor-1alpha oxygen-dependent degradation domain preferentially induces apoptosis of hypoxic cells in solid tumor

Tumor cells in hypoxic areas of solid tumors are resistant to conventional chemotherapy and radiotherapy and thus are obstacles of cancer therapy. We report here the feasibility of applying hypoxia-regulated expression of diphtheria toxin A (DT-A) for killing hypoxic tumor cells. The expression vector was constructed to express DT-A fused with hypoxia-inducible factor-1alpha (HIF-1alpha) oxygen-dependent degradation (ODD) domain under the control of vascular endothelial growth factor gene promoter and contain erythropoietin mRNA-binding protein (ERBP)-binding sequence downstream of the DT-A/ODD sequence. In vitro ubiquitination assay showed that DT-A/ODD, but not DT-A, was ubiquitinated as efficient as HIF-1alpha under normoxic conditions in a von Hippel-Lindau- and oxygen-dependent manner. DT-A/ODD exhibited a comparable translation inhibitory activity to DT-A. ERBP-binding sequence was effective in stabilizing mRNA under hypoxic conditions in various cell types. Transfection of the vector expressing DT-A/ODD into high-metastatic Lewis lung carcinoma (3LL) A11 cells resulted in induction of apoptosis independently of hypoxia, probably due to its extreme toxicity. However, transfection of the vector expressing attenuated DT-A(W153F)/ODD or DT-A(H21A)/ODD resulted in a hypoxia-dependent induction of apoptosis. Liposomal gene transfer of the vector encoding DT-A(W153F)/ODD induced apoptosis in hypoxic, but not in normoxic, areas of solid tumors established by A11 variant cells with higher resistance to hypoxia-induced apoptosis and inhibited the growth of hypoxic tumors established by 3LL-P29 cells. These results suggest that hypoxia-regulated expression of attenuated DT-A(W153F)/ODD fusion protein is potentially of use for killing hypoxic tumor cells with minimizing the damage to normoxic normal tissues.     

靶向治疗肺癌双自杀基因HSV-TK/CD真核表达载体的构建

背景与目的：本研究构建CEA启动子和CMV增强子调控表达的HSV-TK和CD基因双顺反子真核表达载体CMVE—pCEA—TK—IRES—CD。方法：根据特异性引物PCR扩增获得CEA启动子（pCEA），巨细胞病毒的早期基因增强子（CMVE）序列，用基因重组的方法替换载体PIRES-EGFP通用启动子pCMV，得到重组质粒CMVE-PCEA-IRES-EGFP，转染重组质粒到表达CEA的肺癌细胞株中进行绿色荧光蛋白检测，确定启动子能有效启动报告基因在CEA阳性的肺癌细胞中的表达。用PCR扩增得到目的基因HSV—TK和CD，将目的基因HSV-TK和CD亚克隆到载体CMVE-pCEA-IRES-EGFP上，得到自杀基因HSV-TK／CD双表达载体CMVE-pCEA-TK-IRES-CD。结果：经酶切、PCR及DNA测序鉴定，双自杀基因真核表达载体CMVE-pCEA-TK-IRES-CD已成功构建，嵌合启动子CMVE-pCEA调控下能启动下游报告基因在CEA阳性的肺癌细胞株的表达。结论：成功构建了嵌合启动子CMVE-pCEA启动的双自杀基因HSV—TK／CD真核表达载体，为下一步研究双自杀基因对于CEA阳性表达的肺癌的治疗奠定了基础。     

Efficacy of suicide gene therapy in hypoxic rat 9L glioma cells

Viral vector mediated suicide gene therapy (SGT) involving thymidine kinase (TK) or cytosine deaminase (CD) have considerable promise in the treatment of malignant brain tumors. An unresolved issue is to what extent tumor hypoxia influences the outcome of SGT since brain tumors characterized by regions of hypoxia have potentially reduced cellular metabolism and SGT's cytotoxicity is manifest through cellular metabolism. We studied in vitro and in vivo, the effect of hypoxia on the cytotoxicity of SGT in rat 9L glioma cells. Neither acute nor chronic hypoxia affected the cell killing of SGT by TK or CD. In vivo confirmation that SGT efficacy was not adversely affected by tumor hypoxia using the hypoxic cell marker pimonidazole was shown by the absence of a change in tumor hypoxia by SGT. These studies support the use of SGT utilizing either TK or CD gene strategies even when tumors are characterized by a hypoxic microenvironment.