Killing effects of cytosine deaminase gene mediated by adenovirus vector on human pancreatic cancer cell lines in vitro

OBJECTIVE: To evaluate the killing effects of the cytosine deaminase (CD) gene mediated by adenovirus vector on human pancreatic cancer cell lines in vitro. METHODS: The CD gene was cloned into pAdTrack-CMV-CD, and pAdTrack-CMV-CD and pAdEasy-l were recombinated in bacteria. The newly recombinated Ad-CD containing green fluoreseent protein (GFP) was propagated in 293 cells and purified by cesium chloride gradient centrifugation. Human pancreatic cancer cell lines Patu8988 and SW1990 were infected with this virus, then 5-FC was added. XTT assay was used to estimate relative numbers of viable cells. RESULTS: The positive clones were selected by using endonuclease to digest the combinatants and the concentration of viral liquids containing the CD gene was 2×1O^(11) pfu/ml. It was found that significant cytotoxic activities were possesscd by 5-FC for the CD gene transduced pancreatic cell lines, but little effects exerted on the nontransduced pancreatic carcinoma cells. CONCLUSIONS: The CD gene mediated by adenovirus with a high infectivity is efficient for gene therapy of pancreatic carcinoma cell lines. These data demonstrate the therapeutic efficacy of an enzyme prodrug strategy in experimental pancreatic cancer.

Specific CEA-producing colorectal carcinoma cell killing with recombinant adenoviral vector containing cytosine deaminase gene

AIM: To kill CEA positive colorectal carcinoma cells specifically using the E coli cytosine deaminase (CD) suicide gene, a new replication-deficient recombinant adenoviral vector was constructed in which CD gene was controlled under CEA promoter and its in vitro cytotoxic effects were evaluated. METHODS: Shuttle plasmid containing CD gene and regulatory sequence of the CEA gene was constructed and recombined with the right arm of adenovirus genome DNA in 293 cell strain. Dot blotting and PCR were used to identify positive plaques. The purification of adenovirus was performed with ultra-concentration in CsCl step gradients and the titration was measured with plaque formation assay. Cytotoxic effects were assayed with MTT method, The fifty percent inhibition concentration (IC(50)) of 5-FC was calculated using a curve-fitting parameter. The human colorectal carcinoma cell line, which was CEA-producing, and the CEA-nonproducing Hela cell line were applied in cytological tests. An established recombinant adenovirus vector AdCMVCD, in which the CD gene was controlled under CMV promoter, was used as virus control. Quantitative results were expressed as the mean +/- SD of the mean. Statistical analysis was performed using ANOVA test. RESULTS: The desired recombinant adenovirus vector was named AdCEACD. The results of dot blotting and PCR showed that the recombinant adenovirus contained CEA promoter and CD gene. Virus titer was about 5.0 X 10(14)pfu/L(-1) after purification. The CEA-producing Lovo cells were sensitive to 5-FC and had the same cytotoxic effect after infection with AdCEACD and AdCMVCD (The IC(50) values of 5-FC in parent Lovo cells, Lovo cells infected with 100 M.O.I AdCEACD and Lovo cells infected with 10 M.O.I AdCMVCD were 】15000, 216.5+/-38.1 and 128.8+/-25.4 micromol.L(-1), P【0.001, respectively), and the cytotoxicity of 5-FC increased accordingly when the m.o.i of adenoviruses were enhanced (The value of IC(50) of 5-FC was reduced to 27.9+/-4.2 micromol.L(-1) in 1000 M.O.I AdCEACD infected Lovo cells and 24.8+/-7.1 micromol.L(-1) in 100 M.O.I AdCMVCD infected Lovo cells, P【0.05, P【0.01, respectively). The CEA-nonproducing Hela cells had no effect after infection with AdCEACD, but Hela cells had the cytotoxic sensitivity to 5-FC after infection with AdCMVCD (The IC(50) of 5-FC in parent Hele cells and Hela cells infected with AdCMVCD at 10 M.O.I was 】15000 and 214.5+/-31.3 micromol.L(-1), P【0.001). AdCEACD/5-FC system also had bystander effect, and the viability was about 30 percent when the proportion of transfected cells was only 10 percent. CONCLUSION: The recombinant adenovirus vector AdCEACD has the character of cell type-specific gene delivery. The AdCEACD/5-FC system may become a new, potent and specific approach for the gene therapy of CEA-positive neoplasms, especially colon carcinoma.

N-terminal and C-terminal cytosine deaminase domain of APOBEC3G inhibit hepatitis B virus replication

AIM: To investigate the effect of human apolipoprotein B mRNA-editing enzyme catalytic-polypeptide 3G (APOBEC3G) and its N-terminal or C-terminal cytosine deaminase domain-mediated antiviral activity against hepatitis B virus (HBV) in vitro and in vivo. METHODS: The mammalian hepatoma cells HepG2 and HuH7 were cotransfected with APOBEC3G and its N-terminal or C-terminal cytosine deaminase domain expression vector and 1.3-fold-overlength HBV DNA as well as the linear monomeric HBV of genotype B and C. For in vivo study, an HBV vector-based mouse model was used in which APOBEC3G and its N-terminal or C-terminal cytosine deaminase domain expression vectors were co-delivered with 1.3-fold-overlength HBV DNA via high-volume tail vein injection. Levels of hepatitis B virus surface antigen (HBsAg) and hepatitis B virus e antigen (HBeAg) in the media of the transfected cells and in the sera of mice were determined by ELISA.The expression of hepatitis B virus core antigen (HBcAg) in the transfected cells was determined by Western blot analysis. Core-associated HBV DNA was examined by Southern blot analysis. Levels of HBV DNA in the sera of mice as well as HBV core-associated RNA in the liver of mice were determined by quantitative PCR and quantitative RT-PCR analysis, respectively. RESULTS: Human APOBEC3G exerted an anti-HBV activity in a dose-dependent manner in HepG2 cells, and comparable suppressive effects were observed on genotype B and C as that of genotype A. Interestingly, the N-terminal or C-terminal cytosine deaminase domain alone could also inhibit HBV replication in HepG2 cells as well as Huh7 cells. Consistent with in vitro results, the levels of HBsAg in the sera of mice were dramatically decreased, with more than 50 times decrease in the levels of serum HBV DNA and core-associated RNA in the liver of mice treated with APOBEC3G and its N-terminal or C-terminal cytosine deaminase domain as compared to the controls. CONCLUSION: Our findings provide probably the first evidence showing that APOBEC3G and its N-terminal or C-terminal cytosine deaminase domain could suppress HBV replication in vitro and in vivo.

Migration to gliomas of bone mesenchymal stem cells transfected with cytosine deaminase gene following transplantation in vivo

This experiment sought to observe the migration and distribution of bone mesenchymal stem cells transfected with the cytosine deaminase gone （BMSCs-CD/eGFP） after transplantation in vivo through three pathways. In addition, we examined the tropism of these cells to glioma. Intracranial C6 glioma models were established in Sprague-Dawley rats using an intracranial stereotactic inoculation method. When tumors were 7 days old, rats were inoculated with lx106 BMSCs-CD/eGFP cells via the tumor-bearing internal carotid artery, the contralateral hemisphere and the tumor-bearing glioma. Fluorescence microscopy revealed that BMSCs-CD/eGFP exhibited a strong capacity for migration to tumors. BMSCs-CD/eGFP transplanted via the tumor-bearing intemal carotid artery were observed to distribute in glioma tissues. BMSCs-CD/eGFP inoculated via the ipsilateral glioma mainly located within and at the edge of glioma tissues. BMSCs-CD/eGFP inoculated via the contralateral hemisphere mainly distributed at the proximal end of the tumor at the incubation site.

Inhibitory effects of cytosine deaminase gene-transfected bone marrow mesenchymal stem cells on glioma cell proliferation

Bone marrow mesenchymal stem cells were isolated from C57BL mice, transfected with the cytosine deaminase （CD） gene using a lentivirus vector and co-cultured with C6 glioma cells to verify anti-tumor effects of bone marrow mesenchymal stem cells carrying CD genes. C57MSC-CD/eGFP cells converted 5-fluorocytosine to 5-fluorouracil and exhibited significant inhibition of proliferation and apoptosis in C6 glioma cells. C57MSC-CD/eGFP cells were then implanted into rat models of brain C6 glioma. Rats were also intraperitoneally injected with 5-fluorocytosine after 7 days. MSC-CD/eGFP cells were irregularly distributed at the margin of the glioma, as well as encased and reduced the volume of the glioma. CD-transfected bone marrow mesenchymal stem cells inhibit the in vivo growth and in vitro proliferation of glioma.

Adenovirus-mediated tissue specific cytosine deaminase gene therapy for human hepatocellular carcinoma with different AFP expression level

Hepatocellular carcinoma (HCC) is one of the mostcommon cancers in the world, especially in East Asia.There is no standardized or effective strategy could beadapted routinely except of some early diagnosedpatients, and the prognosis is poor. In recent years, genetherapy has become a standard experimental approach fortreating cancers that have escaped conventionaltherapies. One such an approach is to confer the tumorcells with sensitivity to chemical reagents through

Purification and characterization of <i>Aspergillus parasiticus</i>cytosine deaminase for possible deployment in suicide gene therapy

Cytosine Deaminase (CD) from Aspergillus parasiticus was purified and characterized. Time course for maximal CD production (50 μmol/min/mg) was at 72 hrs. The enzyme was purified 387.73 folds with an overall yield of 13%. The CD had pH optimum of 7.2, a temperature optimum of 40℃ - 45℃, activation of energy (Ea) of 8.4 KJ/mol and a t1/2 of 1.10 hr. A. parasiticus CD stoichiometrically deaminated Cyto-sine and 5-fluorocytosine (5-FC) with the KM values of 0.19mM and 0.30 mM respectively. Studies on the effect of pH on KM and Vmax gave pKa1 of 5.8 and pKa2 of 6.3 with enthalpy of ionization of 43.01 KJ/mole suggesting histidine in the active site. The enzyme was strongly inhibited by Ca2+, Co2+, Zn2+ and Hg2+ and completely inhibited by Cu2+ and Fe2+ at 50 mM. Therefore, A. parasiticus CD can be compared with CDs from other sources that are used in suicide gene therapy.

Killing effect of adenoviral mediated cytosine deaminase gene on human pancreatic cancer cell line PaTu8988

Objective:To evaluatethein vitro killingeffectsof cytosinedeaminasegene mediatedby adenovirusvector on humanpancreaticcarcinoma.Methods:CytosineDeaminase(CD)genewas clonedintopAdTrack-CMV-CD,pAd-Track-CMV-CDandpAdEasy-1wererecombinedinbacteria,andtheproductscontaininggreenfluorescentprotein(GFP)werepropagatedin293cellsandpurifiedby cesiumchloridegradientcentrifugation.Humanpancreaticcarcinomacellline8988wereinfectedwiththisvirus,then5-FCwasadded;XTTassaywasusedto estimatetherelativenumbersof viable cells.Results:Thepositivecloneswereconfirmedby usingendonucleasedigestion,andthetiterof theviruscontaining CD genewas2×10 11 pfu/ml.Itwasfoundthat5-FCpossessedsignificantcytotoxicactivitiesforCD genetransfected8988cellline,buthadlittleeffectson non-transfectedpancreaticcarcinomacells.Conclusion:CD genemediatedby adenovirus hasa highinfectivityandis efficientforkillingculturedpancreaticcarcinomacells,indicatingsuicidegenemaybe effec-tiveforpancreaticcancerinfuture.

In situ transduction of cytosine deaminase gene followed by systemic use of 5-fluorocytosine inhibits tumor growth and metastasis in orthotopic prostate cancer mouse models

OBJECTIVE: To investigate the antitumor and anti-metastatic effect of in situ transduction of adenovirus encoding cytosine deaminase (AdCD) followed by the systemic use of 5-fluorocytosine (5-FC) in the orthotopic (o.t.) prostate cancer mouse model. METHODS: The o.t. prostate cancer model of C57BL/6 mouse was developed by o.t. inoculation of RM-1 cells to the subcapsular area of the prostate gland. In situ transduction of the CD gene, followed by systemic use of 5-FC at a daily dosage of 300 mg/kg for 14 days, was performed two days later. RESULTS: Compared with mice treated with Adbeta-gal/5-FC, 5-FC and PBS, mice of the o.t. model receiving in situ treatment of AdCD/5-FC had significant prolongation of survival and suppression of local tumor growth. More importantly, pathological observations showed that metastatic activity occurred in all mice of the PBS, 5-FC and Adbeta-gal groups including metastasis to the iliac lymph node (10/10, 10/10, 10/10) and the lung (8/10, 7/10, 7/10). However, only two out of ten had iliac lymphatic metastasis in the AdCD/5-FC group with no systemic or preaotic lymphatic metastasis, suggesting a strong metastatic inhibitory effect. CONCLUSIONS: In situ transduction of AdCD followed by systemic use of 5-FC leads to the inhibitory effect on tumor growth and metastatic activity in the o.t. mouse model of prostate cancer. Clinically, it may be possible to treat metastatic or recurrent prostate cancer with a novel gene therapy using in situ injection techniques in future.

Cloning, construction of prokaryotic expression vector and expression of Escherichia coli cytosine deaminase gene

Cytosine deaminase gene of Escherichia coli strain H30 was cloned, and its initiation codon of ’GTG’ was mutated to ’ATG’ by PCR. Prokaryotic recombinant expression vector pBV220CD was constructed. Clone with high enzyme activity were selected by detecting their specific activity of cytosine deaminase. 5FC（5FC, 5fluorocytosine） could induce the lethal toxicity to cells containing active CD gene. DNA sequence analysis indicated that there were 16 altered bases and 5 of them resulted in the alteration of amino acids in predicted peptide by comparing DNA sequence of the clone H30CD11 with high enzyme activity with CD gene reported in Gene Bank.

Construction of Bifidobacterium Infantis/CD Targeting Gene Therapy System

Objective： To construct Bifidobacterium Infantis/CD targeting gene therapy system. Methods： CD gene was amplified from E. Coli K12λ using PCR method, pGEX-1LamdaT plasmid and CD gene were digested with dual restriction endonucleas of EcoR Ⅰ and BamH Ⅰ and two segments of 4.9 kb and 1.3 kb were obtained. T4 DNA ligase was added to these two segments to make a recombinant CD/pGEX-1LamdaT plasmid. Then the recombinant plasmid was transfected into Bifidobacterium Infantis by electroporation. The recombinant plasmid was extracted from the positively transfected Bifidobacterium Infantis and digested with dual restriction endonucleases. Then the size of digested fragments was detected and sequencing of the gene segment inserted in extracted recombinant plasmid was performed according to the method of Sanger dideoxynucleotide triphosphate chain termination. Results： 6.2 kb recombinant plasmid was obtained from the positively transfected bacterial colony of Bifidobacterium Infantis. After being digested with dual restriction endonucleases, two segments of approximate 4.9 kb and 1.3 kb were gained from the extracted recombinant plasmid, which were equal to the size of pGEX-1LamdaT plasmid and CD gene, respectively. The full length and sequence of nucleotide acid of the inserted gene in extracted recombinant plasmid was completely identical to the CD gene. Conclusion： The foreign gene, CD gene was correctly inserted into pGEX-1LambdaT plasmid and transferred into Bifidobacterium Infantis. Bifidobacterium Infantis/CD targeting gene therapy system was successfully constructed.

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JM 10 9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。

YCD基因修饰对小鼠P388白血病的体内治疗作用研究

目的 :以P388/DBA小鼠白血病模型 ,探讨新型自杀基因YCD的体内治疗作用。方法 :用逆转录病毒载体将YCD基因导入 ,筛选P388 YCD eGFP细胞克隆 ,以P388 eGFP和野生性 (wt)P388细胞为对照。 (1) 3组细胞腹腔接种给DBA小鼠 (n =5 ) ,5× 10 6/只 (下同 ) ,观察致病性 ;(2 ) 3组细胞腹腔接种给DBA小鼠 (n =5 ) ,分别以 5 FC治疗 2周 ,观察疗效 ;(3) 2组× 5只小鼠腹腔接种P388 YCD eGFP ,5 FC 5 μmol/L·d-1× 2d或PBS治疗 ,根据小鼠存活时间推算杀伤效率。以流式细胞仪、冰冻切片和HE切片检测各脏器中白血病细胞的分布和变化。结果 :基因导入对细胞的生物学特性影响不显著 ;5 FC治疗 2周 ,YCD组小鼠存活 (17.8± 1.89)d ,而eGFP组和wtP388组分别存活 (7.8± 1.10 )d和 (7.7± 1.15 )d (P <0 0 5 ) ;5 FC治疗 2d的杀伤率达 99.6 %。结论 :YCD转基因细胞在体内可被 5 FC有效杀灭 ,该系统具有应用前景。

婴儿双歧杆菌介导的CD和UPRT联合5-FC基因疗法对黑色素瘤的体外治疗实验研究

目的采用婴儿双歧杆菌为载体,探讨尿嘧啶磷酸核糖转移酶基因(UPRT)对胞嘧啶脱氨酶/5-氟胞嘧啶(CD/5-FC)自杀基因系统抗瘤作用的增强效应。方法构建原核表达质粒pGEX-UPRT,以电穿孔法将该质粒转化入婴儿双歧杆菌,筛选阳性重组菌并鉴定。采用M TT法检测表达的U PRT是否可以与CD产生抗瘤协同作用,并观察细胞形态学改变。结果重组婴儿双歧杆菌可以正确表达UPRT。体外M TT检测显示CD+UPRT组细胞存活率低于对照组(P<0.01),且可使B 16-F 10鼠黑色素瘤细胞对5-FC的杀伤敏感性(IC50=0.015μm o l/mL)提高,是CD组(IC50=0.127μm o l/mL)的8.5倍。形态学观察CD+UPRT组肿瘤细胞显示出明显的损伤性改变,细胞生长受到明显抑制,而UPRT组和CD组变化明显不如前者。结论婴儿双歧杆菌联合转导UPRT基因可明显增强CD/5-FC自杀基因系统对鼠黑色素瘤细胞B 16-F 10的杀伤作用。

甲胎蛋白特异启动元件介导的肝癌靶向性基因治疗的体外实验研究

目的采用体外培养的肿瘤细胞系探讨甲胎蛋白特异启动元件介导的靶向性肝癌基因治疗。方法将２．２ｋｂ的重组人甲胎蛋白（ＡＦＰ）基因顺式调控元件克隆于胞嘧啶脱氨酶（ＣＤ）基因的上游，构建逆转录病毒载体ＬＸ２．２ＣＤ。再以此载体和另一不含ＡＦＰ基因调控元件的逆转录病毒载体ｐＣＤ２分别转染３种肝癌细胞系和１种肺腺癌细胞系，筛选出整合ＣＤ基因的抗Ｇ４１８克隆，并进行细胞生长抑制实验。结果５氟胞嘧啶（５ＦＣ）对用ＬＸ２．２ＣＤ转染的ＡＦＰ阳性肝癌细胞具有特异杀伤作用，而对ＡＦＰ阴性的肝癌细胞和非肝癌细胞无杀伤作用。结论在细胞水平实现了对ＡＦＰ阳性肝癌细胞的靶向性基因治疗。

组织特异性CD/5-FC系统对大肠癌的原位基因治疗

目的 探讨癌胚抗原(carcinoembryonic antigen,CEA)组织特异性胞嘧啶脱氨基酶基因对不同分泌CEA大肠癌组织的靶向杀伤作用。方法 脂质体法将CEA 组织特异性逆转录病毒载体G1CEACDNa在PA317细胞中进行包装,大肠癌细胞LoVo和SW480分别接种到BALB/c裸鼠大腿皮下,成瘤2周后,瘤内多点注射法行原位基因转染,每天腹腔注射500mg/kg的5 FC(5 fluorocytosine),观察治疗效果。结果 病毒滴度为5.6×106CFU/L。经多次注射法转染,目的基因在肿瘤组织中能有效表达,治疗21天后,基因治疗组有明显的抑瘤作用,但对LoVo 细胞肿瘤的抑瘤作用明显大于对SW480细胞肿瘤。结论 CEA组织特异性CD/5 FC系统对LoVo细胞肿瘤的抑瘤作用更明显。

婴儿双歧杆菌介导的CD/5-FC自杀基因系统对黑色素瘤的抑瘤实验

目的 观察婴儿双歧杆菌介导的胞嘧啶脱氨酶 / 5 -氟胞嘧啶 (CD/ 5 - FC)自杀基因系统对黑色素瘤的体内、外抑瘤效果。方法 含重组 CD基因的婴儿双歧杆菌中加入 5 - FC,厌氧条件下培养 2 4 h后取其上清液 ,加到黑色素瘤 B16 - F10细胞上 ,观察其对细胞形态及细胞生长抑制率的影响 ;建立小鼠黑色素瘤动物模型 ,尾静脉注入含重组 CD基因的婴儿双歧杆菌 ,腹腔注入 5 - FC,观察携带重组 CD基因的婴儿双歧杆菌联合 5 - FC对黑色素瘤肿瘤体积及肿瘤体积倍增时间的影响。结果 1体外实验 :实验组肿瘤细胞形态显示出显著的损伤性改变 ,细胞生长受到明显抑制 ,而对照组肿瘤细胞影响不大。 2小鼠黑色素瘤动物模型实验结果显示 ,经重组婴儿双歧杆菌联合 5 -FC治疗 2 1d,实验组肿瘤倍增时间明显长于对照组 ,其肿瘤体积明显小于对照组 ,且随着观察时间的延长 ,这种差异越显著。结论 婴儿双歧杆菌介导的 CD/ 5 - FC自杀基因系统对黑色素瘤具有明显的抑瘤效果。

双自杀基因融合基因重组腺病毒的制备与鉴定

目的 :制备含胞嘧啶脱氨酶 (CD)基因、胸苷激酶 (TK )基因的融合基因重组腺病毒 ,为恶性肿瘤的基因治疗研究作准备。方法 :构建含有 CD、TK融合基因的重组粘粒 ,将其与腺病毒 DNA末端肽复合物混合后以磷酸钙共沉淀法转染人胚肾2 93细胞株细胞 ,获取重组腺病毒 ,并进行鉴定。结果 :酶切结果及 PCR结果显示 ,重组粘粒中 CD、TK融合基因插入正确 ,经鉴定所获重组腺病毒带有融合基因 ,并且无具有复制能力的腺病毒存在。 结论 :所获重组腺病毒为 E1、E3缺陷型 ,含有所需的双自杀基因 。

高效化学转化菌内同源重组法构建重组腺病毒

目的:对细菌内同源重组法构建重组腺病毒AdEasy系统加以改进,为制备具有更高抗肿瘤疗效的生物治疗制剂奠定基础。方法:将自杀基因CD和HSV-TK插入穿梭质粒pAdTrack-CMV中,PmeⅠ酶切后,用酚∶氯仿抽提、乙醇沉淀或切胶回收纯化;分别采用电穿孔转化法和化学转化法将线性穿梭质粒(pAdTrackCMV-CDglyTK)与腺病毒骨架质粒pAdEasy-1在细菌内实现同源重组;将重组腺病毒质粒rpAdEasyGFP-CDglyTK以脂质体介导至293细胞中进行包装、扩增。结果:采用切胶回收化学转化法获得阳性重组率最高(100%)。经PCR、酶切以及测序等方法鉴定,证实融合自杀基因已成功插入腺病毒中。结论:对细菌内同源重组法构建重组腺病毒的方法进行了改进,在降低实验成本的同时获得了较原法更高的阳性重组率,并成功构建了复制缺陷性重组腺病毒rAd-CDglyTK。

CEA启动子启动双自杀基因与单自杀基因对Lovo细胞杀伤作用的比较

【目的】探讨CEA启动子(CEApromoter,Cp)启动的双自杀基因胞嘧啶脱氨酶(cytosinedeaminase,CD)与胸苷激酶(thymidinekinase,TK)组织特异性对Lovo结肠癌细胞杀伤作用是否优于单一自杀基因。【方法】以带有Cp、CD与TK的重组腺病毒转染的Lovo细胞作为实验组,未转染者为对照组,5鄄氟胞嘧啶(5鄄fluorocytosine,5鄄Fc)组系列质量浓度:10、8、6、4、2、0滋g/mL;更昔洛韦(ganciclovir,GCV)组系列质量浓度:5、4、3、2、1、0滋g/mL;两药联合应用的系列质量浓度:(10+5)、(8+4)、(6+3)、(4+2)、(2+1)、0滋g/mL。光镜观察细胞形态,噻唑蓝法测定细胞生长抑制率(growthinhibitionrate,GIR)及半数抑制浓度(IC50)。病毒转染的Lovo细胞与未转染的Lovo细胞按不同比例混合培养,给予5鄄Fc5滋g/mL或/和GCV10滋g/mL,噻唑蓝法测定细胞GIR。【结果】对照组5鄄Fc与GCV对细胞的生长抑制作用极低,5鄄Fc组IC50为2400滋g/mL,GCV组为3500滋g/mL。实验组随5鄄Fc与GCV剂量增加,对细胞的杀伤作用明显增加,5鄄Fc组IC50为5.75滋g/mL,GCV组为3.50滋g/mL,两者同时应用相当于5鄄Fc1.90滋g/mL+GCV0.95滋g/mL,细胞对5鄄Fc的敏感性提高417.4倍,对GCV的敏感性提高1000倍。病毒杀伤Lovo细胞具有明显的“旁观者”效应,联合应药组的“旁观者”效应明显高于单独应用组。【结论】双自杀基因细胞毒效应以及“旁观者”效应均高于单一自杀基因。