5-氟胞嘧啶对表达胞嘧啶脱氨酶的人肾母细胞瘤裸鼠异种移植瘤的疗效

目的　以人肾母细胞瘤裸鼠异种移植瘤模型 ,研究 5 氟胞嘧啶 (5 FC)作为原药对表达胞嘧啶脱氨酶 (CD)的肾母细胞瘤治疗 (以下简称CD/ 5 FC)的作用。方法　 1例低分化肾母细胞瘤组织 ,移植于无胸腺BALB/c裸鼠 ,经连续传代 ,建立了人肾母细胞瘤异种移植瘤模型。以腺病毒为载体 ,分别建立CD基因 (Ad/CMV CD)和lac基因 (Ad/CMV lac)的表达载体。瘤内注射基因表达载体 ,使基因转导入肿瘤细胞。用RT PCR检测转导基因在瘤细胞内的表达。腹腔注射 5 FC ,5 0 0mg·kg-1·d-1,连续 10d ,观察移植瘤生长情况。结果　经 5 FC治疗的小鼠 ,表达lac基因的移植瘤生长情况与未转导基因的移植瘤并无两样 ;表达CD基因的移植瘤生长则受到显著抑制。根据接种肿瘤后 8周的肿瘤重量 ,5 FC治疗对CD基因转导的移植瘤生长抑制率为 6 5 %。病理检查可见瘤细胞坏死 ,细胞器出现空泡。结论　在瘤内转导CD基因的基础上施以 5 FC治疗 ,对人肾母细胞瘤裸鼠移植瘤有明显疗效。     

胞嘧啶脱氨酶/氟胞嘧啶体系对人乳腺癌基因的实验治疗作用

目的：研究胞嘧啶脱氨酶（ＣＤ）／氟胞嘧啶（５－ＦＣ）体系对人乳腺癌的实验治疗作用。方法：应用ＭＴＴ法测定人乳腺细胞对５－ＦＣ的敏感性。结果：５－ＦＣ对导入ＣＤ基因的人乳腺癌细胞有明显的细胞毒作用,而对未导入ＣＤ基因的人乳腺癌细胞的毒性较低,５－ＦＣ对导入ＣＤ基因的人乳腺癌细胞的ＩＣ５０分别为４１８μｇ／ｍｌ和１４２９μｇ／ｍｌ。结论：ＣＤ／４－ＦＣ体系对体外转基因的人乳腺癌细胞具有抗肿瘤作用。     

体内复制缺陷型腺病毒载体介导的胞嘧啶脱氨酶基因转染胶质瘤细胞对5-氟胞嘧啶敏感

病毒介导的化学敏感基因的转染,为肿瘤的治疗提供了一条有希望的新途径,目前脑肿瘤的基因治疗集中在将包装携带TK基因的逆转录病毒的细胞系植入肿瘤,其主要局限性是逆转录病毒在体内的转染几乎无效,即只有和包装细胞非常接近的胶质瘤细胞才易被转染,且TK基因疗法所产生的旁观者效应需依赖细胞间的直接接触。本文介绍通过复制缺陷的腺病毒载体介导将细菌胞嘧啶脱氨酶(cd)基因转染至大鼠9L胶质瘤细胞,使其对在正常细胞没有毒性的核苷-5-氟胞嘧啶(5-Fc)敏感。     

肾母细胞瘤和神经母细胞瘤术前化疗及超微结构改变

目的了解术前化疗对小儿恶性肿瘤组织结构的改变及应用价值。方法对７例肾母细胞瘤和５例神经母细胞瘤进行光镜和透镜检查，比较前化疗对其组织结构的影响及疗效。术前化疗可造成肿瘤组织不同程度的破坏，肿瘤缩小，肿瘤的切除率有提高。结果术前化疗对不能一期切除的肿瘤有实际应用价值，在神经母细胞瘤尤为明显。     

婴儿双歧杆菌/胞嘧啶脱氨酶肿瘤靶向性基因治疗系统的构建

目的 构建婴儿双歧杆菌/胞嘧啶脱氨酶肿瘤靶向性基因治疗系统。方法 PCR扩增胞嘧啶脱氨酶(CD)基因，TSS法在大肠杆菌，M109中扩增pGEX-1LambdaT质粒。EcoRⅠ和BamHⅠ对CD基因和pGEX-1LambdaT质粒分别进行双酶酶切。琼脂糖电泳凝胶分离并切取其中4．9kb和1．3kb两个片段长度的凝胶。凝胶DNA提取试剂盒提取其中所含的DNA片段，T4DNA连接酶连接这两个片段，最后用电穿孔法将重组片段转染婴儿双歧杆菌，并挑选阳性菌落，提取质粒双酶切后进行琼脂糖凝胶电泳检测。结果 应用电穿孔法转染婴儿双歧杆菌，获得含6．2kbp重组质粒的阳性转染婴儿双歧杆菌。结论 成功构建婴儿双歧杆菌/胞嘧啶脱氨酶肿瘤靶向性基因治疗系统。     

胞嘧啶脱氨酶基因重组逆转录病毒载体构建及对PA317细胞的转移表达

逆转录病毒载体是向真核细胞中进行基因转移的高效载体之一,是比较成熟和应用范围最广的基因转移和基因治疗载体。胞嘧啶脱氨酶（ｃｙｔｏｓｉｎｅｄｅａｍｉｎｅｓｅ,ＣＤ）基因是一重要的自杀性基因,我们研究的目的是克隆构建含有ＣＤ基因的重组逆转录病毒载体,并将该基因导入ＰＡ３１７包装细胞,建立完整的和安全高效的逆转录病毒表达载体系统,为开展ＣＤ基因与前体药物５氟胞嘧啶（５ｆｌｕｏｒｏｃｙｔｏｓｉｎｅ,５Ｆｃ）联合用于肿瘤的实验治疗研究奠定基础。材料与方法　１－主要试剂：限制性内切酶、Ｔ４ＤＮＡ连接酶…     

大肠杆菌胞嘧啶脱氨酶基因的克隆及其真核表达载体的构建

目的 克隆大肠杆菌胞嘧啶脱氨酶(CD)基因，构建真核表达载体，本研究拟探索该基因在肿瘤基因治疗中的应用基础。方法 根据GenBank数据库提供的CD基因核苷酸序列，设计并合成一对引物，采用PCR方法，从大肠杆菌基因组DNA中扩增出CD基因，并与pcDNA3．1定向连接，构建受控于人巨细胞病毒启动子的重组真核载体pcDNA3．1-CD，并用限制性内切酶、PCR和DNA测序进行鉴定。结果克隆了大肠杆菌CD基因，并构建了真核表达载体，经限制性内切酶酶切、PCR扩增和DNA测序证实了其正确性。结论 pcDNA3．1-CD真核表达载体构建成功。     

人生长抑素受体-2和大肠杆菌胞嘧啶脱氨酶共表达细胞系的建立及其对5-氟胞嘧啶杀伤的敏感性

目的建立共表达人生长抑素受体2(SSTR2)和大肠杆菌胞嘧啶脱氨酶(CD)的细胞系,为"自杀基因"/前体药物系统联合SSTR2介导的放射性免疫杀伤和显像治疗肿瘤提供细胞模型.方法应用反转录PCR方法从人胚肾293细胞中克隆人sstr2基因,通过基因重叠延伸拼接(SOE)结合PCR方法将CD、内部核糖体进入位点(IRES2)和sstr2连接,并构建表达载体.体外转染人乳腺癌SKBr3细胞并筛选,通过间接免疫荧光检测SSTR2的表达,并研究前体药物5-氟胞嘧啶(5-FC)对上述细胞的杀伤作用.结果成功克隆了人sstr2基因,并构建了CD和sstr2基因的双顺反子表达载体,进一步建立了稳定转染上述表达载体的SKBr3细胞系,间接免疫荧光证实了SSTR2的表达,同时建系细胞能够被前体药物5-FC高效杀伤.结论本研究建立的人乳腺癌细胞系可以共表达sstr2和CD基因,为在体内研究放射性核素标记的SSTR2配体显像和免疫杀伤,并协同CD/5-FC治疗肿瘤奠定基础.     

氟胞嘧啶/胞嘧啶脱氨酶自杀基因疗法结合热休克蛋白-多肽复合物治疗小鼠胃癌

目的；研究氟胞嘧啶／胞嘧啶脱氨酶（5－FC／CD）基因疗法与热休克蛋白－多肽复合物（FSP70－PC）免疫疗法联合抗肿瘤效果。方法；将携带CD基因的重组腺病毒注射到小鼠MFC瘤体内，腹腔注射5－FC，同时皮下接种HSP70－PC。结果；经联合治疗后，70％荷瘤小鼠肿瘤体答缩小，消退，小鼠存活期延长，细胞毒T淋巴细胞（CTL）杀伤活性增高，CD4^ 及CD^8 T细胞浸润明显。结论：5－FC／CD基因疗法结合HSP－PC免疫疗法抗小鼠MFC瘤作用显著，具有临床应用前景。     

胞嘧啶脱氨酶基因联合5-Fc治疗结肠癌的实验研究

目的研究胞嘧啶脱氨酶基因(CD)联合前体药物5-氟胞嘧啶(5-Fc)对结肠癌细胞的生长抑制作用。方法应用逆转录病毒介导的方法,将逆转录病毒载体pLXSN中含有大肠杆菌CD基因的重组质粒pCD2转染到病毒包装细胞PA317后,感染人结肠癌细胞株SW1116。对转基因的细胞进行RT-PCR检测和体内外药物敏感实验。结果获得了稳定表达EC—CD基因的结肠癌细胞株SWCD2,与野生型SW1116细胞相比,SWCD2细胞对基本无毒性的原药5-Fc的敏感性增加,50％细胞生长抑制率(IC50)浓度由野生型SW1116细胞的16000μmol／L降低到SWCD2的66μmol／L。经5-Fc治疗后,SWCD2细胞的裸鼠移植瘤生长明显缩小。结论CD基因联合5-Fc对人结肠癌细胞具有实验性基因治疗作用。     

Hypoxia imaging predicts success of hypoxia-induced cytosine deaminase/5-fluorocytosine gene therapy in a murine lung tumor model

Tc-99m-HL91 is a hypoxia imaging biomarker. The aim of this study was to investigate the value of Tc-99m-HL91 imaging for hypoxia-induced cytosine deaminase (CD)/5-fluorocytosine (5-FC) gene therapy in a murine lung tumor model. C57BL/6 mice were implanted with Lewis lung carcinoma cells transduced with the hypoxia-inducible promoter-driven CD gene (LL2/CD) or luciferase gene (LL2/Luc) serving as the control. When tumor volumes reached 100?mm(3), pretreatment images were acquired after injection of Tc-99m-HL91. The mice were divided into low and high hypoxic groups based on the tumor-to-non-tumor ratio of Tc-99m-HL91. They were injected daily with 5-FC (500?mg?kg(-1)) or the vehicle for 1 week. When tumor volumes reached 1000?mm(3), autoradiography and histological examinations were performed. Treatment with 5-FC delayed tumor growth and enhanced the survival of mice bearing high hypoxic LL2/CD tumors. The therapeutic effect of hypoxia-induced CD/5-FC gene therapy was more pronounced in high hypoxic tumors than in low hypoxic tumors. This study provides the first evidence that Tc-99m-HL91 can serve as an imaging biomarker for predicting the treatment responses of hypoxia-regulated CD/5-FC gene therapy in animal tumor models. Our results suggest that hypoxia imaging using Tc-99m-HL91 has the predictive value for the success of hypoxia-directed treatment regimens.     

Transduction of cytosine deaminase gene makes rat glioma cells highly sensitive to 5-fluorocytosine

To investigate the potential use of E. coli cytosine deaminase (CD) gene instead of the commonly used HSV-TK gene in the gene therapy of brain tumors, we constructed a retrovirus vector carrying the CD gene. We then transduced a rat glioma cell line C6 with CD gene by the retrovirus vector. Transduction of the CD gene made C6 cells become highly sensitive to the anti-fungi drug 5-fluorocytosine (5FC). IC₅₀ for 5FC was 6,000 μM in CD-negative cells, while it was 3 μM in Cd -positive cells. Mixed cellular assay showed that CD-positive cells had a strong “bystander effect” on CD-negative cells when exposed to 5FC. Significant anti-tumor effects were observed in nude mice bearing s.c. tumors derived from CD-positive cells when these animals were given 250 mg/kg 5FC twice a day for 20 consecutive days. A marked decrease in tumor weight occurred when a mixture containing 50% CD-positive and 50% CD-negative C6 cells was injected s.c., followed by 5FC treatment, suggesting the bystander effect in vivo. Concerning the pharmacokinetics of 5FC, especially its high oral bio-availability and good penetration into cerebrospinal fluid, we suppose that the combination of CD-gene transfer and 5FC oral administration may have potential use in the gene therapy of brain tumors. Int. J. Cancer 71:675-679, 1997. © 1997 Wiley-Liss, Inc.     

Selective in vivo radiosensitization by 5-fluorocytosine of human colorectal carcinoma cells transduced with the E. coli cytosine deaminase (CD) gene

Purpose: The E. coli cytosine deaminase (CD) gene encodes an enzyme capable of converting the nontoxic prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), a known radiosensitizer. Having previously shown that combined CD suicide gene therapy and radiation (RT) results in pronounced radiosensitization in vitro, we progressed to in vivo studies of combined therapy.Methods and Materials: WiDr human colon cancer cells were transduced in vitro with the CD gene and cells expressing CD were selected for use as xenografts in a nude mouse model. After administration of 5-FC, tumors received 10–30 Gy local field radiation (RT) and tumor growth delay was compared to control animals receiving either 5-FU, 5-FC, or RT alone.Results: Maximal growth delay was seen in mice treated with 5-FC for 6 consecutive days prior to RT. Combined treatment with 15 Gy radiation resulted in a dose-modifying factor (DMF) of 1.50, and a greater DMF was observed with higher doses of radiation. There was no appreciable toxicity using this new approach. In contrast, a similar treatment of combined 5-FU and radiation resulted in considerable toxicity and no appreciable radiosensitization.Conclusion: The present results show that combined suicide gene therapy and RT results in pronounced antitumor effect without any notable toxicity. This indicates that the CD gene may be useful in the development of novel treatment strategies combining radiation and gene therapy in the treatment of locally advanced cancers.     

Interaction of endothelial progenitor cells expressing cytosine deaminase in tumor tissues and 5-fluorocytosine administration suppresses growth of 5-fluorouracil-sensitive liver cancer in mice

The drug delivery system to tumors is a critical factor in upregulating the effect of anticancer drugs and reducing adverse events. Recent studies indicated selective migration of bone marrow-derived endothelial progenitor cells (EPC) into tumor tissues. Cytosine deaminase (CD) transforms nontoxic 5-fluorocytosine (5-FC) into the highly toxic 5-fluorouracil (5-FU). We investigated the antitumor effect of a new CD/5-FC system with CD cDNA transfected EPC for hepatocellular carcinoma (HCC) in mice. We used human hepatoma cell lines (HuH-7, HLF, HAK1-B, KYN-2, KIM-1) and a rat EPC cell line (TR-BME-2). Escherichia coli CD cDNA was transfected into TR-BME-2 (CD-TR-BME). The inhibitory effect of 5-FU on the proliferation of hepatoma cell lines and the inhibitory effect of 5-FU secreted by CD-TR-BME and 5-FC on the proliferation of co-cultured hepatoma cells were evaluated by a tetrazolium-based assay. In mouse subcutaneous xenograft models of KYN-2 and HuH-7, CD-TR-BME was transplanted intravenously followed by 5-FC injection intraperitoneally. HuH-7 cells were the most sensitive to 5-FU and KYN-2 cells were the most resistant. CD-TR-BME secreted 5-FU and inhibited HuH-7 proliferation in a 5-FC dose-dependent manner. CD-TR-BME were recruited into the tumor tissues and some were incorporated into tumor vessels. Tumor growth of HuH-7 was significantly suppressed during 5-FC administration. No bodyweight loss, ALT abnormality or bone marrow suppression was observed. These findings suggest that our new CD/5-FC system with CD cDNA transfected EPC could be an effective and safe treatment for suppression of 5-FU-sensitive HCC growth.     

Antineoplastic effects in rats of 5-fluorocytosine in combination with cytosine deaminase capsules

5-Fluorocytosine (5-FC) lacks antineoplastic activity in human subjects because of the absence of cytosine deaminase (CDase) in mammalian cells. Intratumoral conversion of 5-FC into 5-fluorouracil (5-FUra) by locally implanted capsules containing CDase followed by systemic administration of 5-FC can be expected to induce antineoplastic activity at a local site with minimal systemic toxicity. In vitro and in vivo experiments were performed to evaluate this hypothesis. Spectrophotometric analysis confirmed the deamination of 5-FC to 5-FUra by CDase extracted from cultivated Escherichia coli. In vitro studies showed that 5-FC combined with CDase induced significant growth-inhibitory effects on the cultured glioma cells. An active CDase capsule, made of cellulose tubing, was newly designed for local implantation. 5-FC concentrations in the s.c. tumors of the rats given these CDase capsules, followed by 5-FC administration, showed a sufficient amount of delivery of 5-FC to the tumor tissue. 5-FUra appearing in the tumor reached the level of 8.0 micrograms/g at 2 h and stayed at more than 1.0 microgram/g at between 1 and 6 h. Significant reduction of the tumor growth and cytotoxic changes were observed. The passive cutaneous anaphylaxis reaction demonstrated no allergic reaction to the host due to the capsule. These results suggest that this chemotherapeutic method is effective for human brain tumors.     

Yeast cytosine deaminase improves radiosensitization and bystander effect by 5-fluorocytosine of human colorectal cancer xenografts

The efficacy of cancer gene therapy using bacterial cytosine deaminase (bCD)/5-fluorocytosine (5-FC) enzyme/prodrug strategy is limited by the inefficiency of cytosine deaminase (CD)-catalyzed conversion of 5-FC into 5-fluorouracil (5-FU). We have shown previously that yeast CD (yCD) is more efficient at the conversion of 5-FC than bCD. In the current study, we hypothesized that the increased production of 5-FU by yCD would enhance the efficacy of the CD/5-FC treatment strategy by increasing the bystander effect as well as the efficacy of radiotherapy because of the radiosensitizing capacity of 5-FU. To test this hypothesis, we generated stable HT29 human colon cancer cell lines expressing either bCD (HT29/bCD) or yCD (HT29/yCD). The amount of 5-FU produced in HT29/yCD tumors after a single injection of 5-FC (1000 mg/kg, i.p.) was 15-fold higher than that produced in HT29/bCD tumors. In tumor-bearing nude mice, the average minimum relative tumor size (compared with pretreatment values) of HT29/bCD tumors treated with 5-FC and radiation (500 mg/kg i.p. and 3 Gy, 5 days a week for 2 weeks) was 0.55+/-0.1, compared with 0.01+/-0.01 in HT29/yCD tumors (P = 0.002). Moreover, an increased cytotoxic and radiosensitizing effect of 5-FC on bystander cells was observed in vitro and in vivo when yCD was expressed in HT29 cells instead of bCD. In mice bearing HT29 tumors containing 10% HT29/yCD cells, the combined treatment resulted in a minimum tumor size of 0.20+/-0.07 compared with 0.60+/-0.1 in 10% HT29/bCD cells (P < 0.001). These results demonstrate that the use of yCD in the CD/5-FC strategy has a high potential to improve the therapeutic outcome of combined gene therapy and radiotherapy in cancer patients.     

Intratumoral 5-fluorouracil produced by cytosine deaminase/5-fluorocytosine gene therapy is effective for experimental human glioblastomas

5-Fluorouracil (5-FU) is a potent antimetabolite used for chemotherapy of gastrointestinal (GI), breast, and head and neck malignancies. Although clinical trials have been conducted, the poor therapeutic index of 5-FU has precluded its clinical use for a number of other tumor types. It is unclear whether this lack of utility is due to problems with drug delivery or inherent insensitivity. Adenovirus (Ad) vector-mediated cytosine deaminase (CD)/5-fluorocytosine (5-FC) gene therapy has the potential to overcome pharmacokinetic issues associated with systemic 5-FU and is particularly well suited to use with tumors in which local control is paramount, such as recurrent, localized prostate cancer and malignant gliomas. In this study, the in vitro response by a panel of human tumor cell lines derived from both GI (colon, pancreas) and non-GI (prostate, glioma) tumors to 5-FU and to AdCMVCD (an Ad encoding Escherichia coli CD)/5-FC was examined. Whereas the sensitivity (IC(50)) of individual cell lines to these agents varied, no significant difference in median IC(50) for either 5-FU or AdCMVCD/5-FC was evident for the four tumor types tested (P > 0.1). The relevant contributions of Ad gene transfer efficiency and inherent 5-FU sensitivity in determining response to AdCMVCD/5-FC were then assessed. Multiple linear regression analysis revealed that whereas both factors significantly contribute to the response, inherent 5-FU sensitivity was substantially more important (beta= 0.78 versus 0.48; P < 0.001). Finally, the therapeutic efficacy of a single intratumoral injection of AdCMVCD followed by systemic 5-FC was assessed in three intracranial C.B17 severe combined immunodeficient mouse models of human glioma. AdCMVCD/5-FC efficacy was specific, virus dose-dependent, and closely paralleled in vitro 5-FU and CD/5-FC sensitivity in two of three models tested. These results reveal that glioma cells are as sensitive as GI tumor cells to the antineoplastic effects of 5-FU, identify inherent 5-FU sensitivity as an important factor in determining CD/5-FC efficacy, and confirm previous findings in rat models that demonstrate the potential clinical utility of AdCMVCD/5-FC gene therapy for gliomas.     

Annexin V-targeted enzyme prodrug therapy using cytosine deaminase in combination with 5-fluorocytosine

A fusion protein, consisting of cytosine deaminase (CD) linked to human annexin V, was created for use in an enzyme prodrug therapy targeted to the tumor vasculature and associated cancer cells in the primary tumor and distant metastases. The major finding of this study is that the CD-annexin V fusion protein in combination with the prodrug 5-fluorocytosine has significant cytotoxic activity against endothelial cells and two breast cancer cells lines in vitro that expose phosphatidylserine on their surface. The cytotoxicity experiments verified this novel enzyme prodrug system has the ability to produce therapeutic levels of 5-fluorouracil and thus appears promising.     

Cytosine deaminase/5-fluorocytosine gene therapy can induce efficient anti-tumor effects and protective immunity in immunocompetent mice but not in athymic nude mice

Murine hepatocellular carcinoma cells were retrovirally transduced with the bacterial cytosine deaminase (CD) gene. CD-transduced cells exhibited more than 120-fold higher sensitivity to 5-fluorocytosine (5-FC) compared with parental cells. When syngeneic immunocompetent mice were inoculated s.c. with parental hepatocellular carcinoma cells containing as little as 5% CD-transduced cells, significant inhibition of tumor formation was induced by 5-FC treatment. Furthermore, established solid tumors in immunocompetent mice containing only 5% CD-transduced cells were infiltrated markedly with CD4- and CD8+ T lymphocytes and macrophages by 5-FC treatment, such that significant reduction or even complete regression of tumors was observed. These tumor-free mice resisted subsequent rechallenge with wild-type tumor. Conversely, when athymic nude mice were inoculated with a cell mixture containing CD-transduced cells and parental cells at a ratio of 40:60, all developed tumors despite 5-FC treatment. Our results indicate that gene therapy using the CD/5-FC system can induce efficient anti-tumor effects and protective immunity in immunocompetent mice but not in athymic immunodeficient mice, suggesting that the host's immunocompetence may be a critical factor for achieving successful gene therapy against cancer.