Abstract:
A method for reconstructing a replication-selective oncolytic adenovirus using a subgroup B recombinant human adenovirus vector Ad11-5EP. The method includes: 1) deleting E1A CR2 gene and/or anti-apoptotic gene E1B 21K that is necessary for viability of an adenovirus in normal cells but not necessary in tumor cells; 2) inserting a tumor-specific promoter to drive the expression of E1A gene; 3) re-directing a cellular tropism of Ad11-5EP according to receptors on a tumor cell surface; or 4) allowing adenovirus to selectively replicate in tumor cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/093,078, filed on Nov. 29, 2013, now pending, which is a continuation-in-part of International Patent Application No. PCT/CN2012/071757 with an international filing date of Feb. 29, 2012, designating the United States, now pending, and further claims priority benefits to Chinese Patent Application No. 201110143385.3 filed May 31, 2011. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P. C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18th Floor, Cambridge, Mass. 02142. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a subgroup B recombinant human adenovirus vectors Ad11-5EP and Ad11-5ETel-GFP and methods for constructing and for using the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Adenovirus 11 (Ad11) is a serotype of the subgroup B human adenovirus and is obviously superior to Ad 5 in oncolytic virotherapy. Ad11 is able to combine other cell surface receptor X besides the CD46 receptor. Tuve has reported that Ad11 is the only virus in the B subgroup adenovirus that is able to combine CD46 as well as the surface receptor X, which indicated that Ad11 is capable of infecting a much wider spectrum of tumor cells, thereby solving the problem of low infection rate in the application of Ad5 due to downregulation of virus acceptor. Ad11 is also superior to Ad5 in that the content of neutralizing antibodies of Ad11 is relatively low, being 10-31%, compared with 45-90% of that of Ad5, and the neutralizing antibodies of Ad11 have no cross-reactivity. When Ad11 is intravenously injected to transgenic mice expressing CD46, no obvious intrahepatic transduction or hepatotoxicity occurs. Furthermore, Ad11 is able to effectively transduce dendritic cells, allows tumor-specific antigens to express, and enhances the immune response to benefit the cancer therapy. 
         [0006]    Studies on other adenovirus serotypes except Ad5 used as a vaccine or gene conversion vector have been reported, but the use of the adenovirus serotype used as an oncolytic virus has been rarely conducted. In vitro and in vivo studies from Sandberg indicated that transduction, replication, and lysis of Ad11 effectively undergo in prostate cancer cell line PC-3, but the comparison between Ad5 was not conducted by Sandberg. Shashakova et al. have compared oncolytic efficacy among Ad5, Ad6, Ad11, and Ad35 based on in vitro studies on human tumor cell lines and in vivo studies on human prostate cancer cell lines DC145, and found that Ad5, Ad6, and Ad11 have similar antitumoral efficacy whereas Ad35 has no antitumoral efficacy. The most important is that only Ad5 has hepatotoxicity. After that, chimeric oncolytic Ad5 (by substituting cilium of Ad5 by that of the B subgroup adenovirus) was constructed for allowing the chimeric oncolytic Ad5 to combine with membrane receptor CD46 to improve the antitumoral efficacy. However, compared with a whole B subgroup adenovirus, this method is not able to overcome the neutralizing ability of hexon antigen of Ad5. 
         [0007]    The number of circulating tumor cells (CTCs) is in relation to the clinical stage, treatment effect, and short survival rate. CTCs level in peripheral blood in tumor patient is taken as the basis for monitoring, adjusting the treatment, and anticipating the results. Thus, a specific and sensitive method for detecting these cells is necessitated. In recent years, immune cells counting analysis and quantitative PCR have been applied by which a small amount of CTCs were detected, however, the application of these methods were restricted because of a high testing cost and the lack of specific biological markers. 
         [0008]    Replication-selective oncolytic adenovirus is a new kind of medicine for treating tumors. To be noted, it has been reported recently that the replication-selective oncolytic adenovirus expressing GFP has been used to detect CTCs among more than hundred million of peripheral blood cells. However, genetic variation of tumor cells is a very important factor affecting the infection ability of adenovirus. A low expression of CAR in tumor cells significantly decreases the infection ability of Ad5, which further influences the positive rate of tumor cells. Besides the known influence mechanism of the low expression of CAR, it has also been found that other tumor related genes like CEACAM6 influences Ad5 from entering the nuclear, thereby decreasing the infection ability of Ad5 on tumor cells. These data indicate that methods for testing CTCs using Ad5 have a low sensitivity in some tumor cells. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above-described problems, it is one objective of the invention to provide an adenovirus vector Ad11-5EP that is more effective in cancer therapy, and to provide a subgroup B recombinant human adenovirus vector Ad11-5ETel-GFP for treating tumor or detecting tumor cells in circulating blood. 
         [0010]    Inventors have first compared the anti-tumor potencies of Ad11 and Ad5 in human cancer cell lines in vitro, and found that only 9 among 25 cell lines being tested are Ad11-sensitive, in which, PC-3 is insensitive to Ad5 and sensitive to Ad11. Compared with Ad5, Ad11 obviously inhibits the growth of subcutaneous tumors of PC-3 cells in vivo, and further improves the survival of tumor-bearing animals. When the above experiment is conducted on Ad5-sensitive and Ad11-insensitive MIAPaCa-2 cell line, the antitumoral efficacy of Ad11 is obviously reduced. 
         [0011]    Although Ad11 receptors are often highly expressed within human tumor cells, the wild-type Ad11 is not able to effectively kill the tumor cells. The inventors have conducted extensive studies and proved that more Ad11 than Ad5 are attached to the membrane of tumor cells by using two different methods. The attached Ad11 virus particles are capable of entering the nucleus, which means a relatively high level of Ad11 exists in the nucleus in early stage of the virus infection compared with Ad5. The inventors have studied expressions of two viruses in early stage of tumor cells infection, and levels of mRNA of E1A are tested by using specific primers for quantitative PCR. After 2 hours of virus infection in all cell lines, it was found that in cell lines that had a high level of Ad11, E1AmRNA was highly expressed. Expression of E1AmRNA of Ad11 in Ad11-insensitive cell lines (MIAPaCa-2 and LNCaP) after 2 hours of the infection is obviously decreased. Ad11-sensitive Capan-2 and PC-3 cells have a high level of Ad11E1 AmRNA. Ad11E1 AmRNA directly influences the replication of virus, so that the decrease of the level of Ad11E1AmRNA in MIAPaCa-2 and LNCaP cell lines will decrease the replication level of the virus, and correspondingly decrease the synthesis of hexon protein. Such result is in accordance with the production of low level of Ad11 virus particles and the cytotoxicity from the initial observation. These results indicate that the replication and cell killing of Ad11 have no relationship with its infectivity, but are associated with the activity of the enhancer and the promoter of early gene E1A. 
         [0012]    To solve the above problem, one objective of the invention is to construct a tumor targeting adenoviral vector (Ad11-5EP) where the original enhancer and promoter of Ad11 E1A gene was replaced by the counterpart of Ad5. Experiments indicate that Ad11-5EP is a very useful backbone vector capable of developing replication-selective oncolytic adenovirus for treating a wider spectrum of human cancers. 
         [0013]    To explore the application of the new adenovirus vector and improve the sensitivity to detect circulating tumor cells in the blood using replication-selective adenovirus, the Ad5 promoter of Ad11-5EP is substituted by a promoter of human telomerase gene, a reporter gene GFP was inserted into E3gp18.5 K of Ad11, and a replication-selective adenovirus (Ad11-5ETel-GFP) capable of expressing reporter genes was created by homologous recombination. As telomerase is highly expressed in 95% of human tumor cells, Ad11-5ETel-GFP selectively replicates and expresses GFP in tumor cells but has no activity in normal epithelial cells. 
         [0014]    To achieve the above objective, in accordance with one embodiment of the invention, there is provided a method for constructing a subgroup B recombinant human adenovirus vector Ad11-5EP (SEQ ID NO: 1), comprises substituting a 365 bp fragment comprising an enhancer and a promoter of an upstream coding sequence of Ad5 E1A (SEQ ID NO: 2) for a corresponding region of a serotype Ad11 (SEQ ID NO: 3) of the subgroup B human adenovirus vector by homologous recombination to construct the subgroup B recombinant human adenovirus vector Ad11-5EP. 
         [0015]    In a class of this embodiment, the homologous recombination comprises: amplifying a 329 bp fragment in the front of the Ad11 genome as a left arm sequence, providing a fragment formed by ligating a 195-559 bp fragment of Ad5 E1A comprising the enhancer and the promoter and a 568-1125 bp fragment of Ad11 E1A (SEQ ID NO: 4) as a right arm sequence, and ligating the left arm sequence and the right arm sequence to multi-cloning sites arranged on two sides of pSS-ChI (SEQ ID NO: 12), respectively, to construct a shuttle vector pSS-A1A7 (SEQ ID NO: 5); digesting and purifying the pSS-A1A7 by PmeI while performing homologous recombination between a PmeI digested segment and pAd11 (SEQ ID NO: 6) plasmid within BJ5183 cells, and screening positive clones using agar plates comprising ampicillin and chloramphenicol; and digesting the positive clones by SwaI, and deleting a chloramphenicol-resistance gene expression cassette to yield pAd11-Ad5EP (SEQ ID NO: 7), digesting and linearizing the pAd11-Ad5EP by NotI, and transfecting 293 cells to yield the adenovirus vector Ad11-5EP. 
         [0016]    In a class of this embodiment, the concentrations of ampicillin and chloramphenicol are 100 mg/mL and 25 mg/mL, respectively. 
         [0017]    A method for reconstructing replication-selective oncolytic adenovirus using the subgroup B recombinant human adenovirus vector Ad11-5EP, the method comprises one of the following steps:
       1) deleting E1A CR2 gene (SEQ ID NO: 8) and/or anti-apoptotic gene E1B 21K (SEQ ID NO: 9) that are necessary for viability of the adenovirus in normal cells but not necessary in tumor cells;   2) inserting a tumor-specific promoter to drive the expression of E1A gene;   3) re-directing a cellular tropism of Ad11-5EP according to receptors on a tumor cell surface; or   4) allowing adenovirus to selectively replicate in tumor cells combining with MicroRNA technology.       
 
         [0022]    A method for constructing a subgroup B recombinant human adenovirus vector Ad11-5ETel-GFP (SEQ ID NO: 10), the method comprises:
       1) constructing vectors pSS-ChI and pSS-kna (SEQ ID NO: 13) by using two different antibiotics-resistance cassettes, introducing SwaI restriction sites to two flanks of a chloramphenicol-resistance gene sequence cassette, and introducing sbfI restriction sites to two flanks of a kanamycin-resistance gene sequence cassette;   2) cloning an initiation sequence for replication of pBR322 (SEQ ID NO: 14) by pUC18 (SEQ ID NO: 15), ligating a first synthetic nucleotide sequence comprising multi-cloning sites to the chloramphenicol-resistance gene sequence cassette to yield pSS-ChI, homologously recombining an upstream of a left arm sequence and a downstream of a right arm sequence of the chloramphenicol-resistance gene sequence cassette, and inserting the upstream of the left arm sequence of the chloramphenicol-resistance gene sequence cassette and the downstream of the right arm sequence of the chloramphenicol-resistance gene sequence cassette into the multi-cloning sites on two sides of pSS-ChI by blunt end insertion or cohesive end insertion, respectively, to construct a shuttle vector pSSENTel (SEQ ID NO: 16) for recombination;   3) cloning an initiation sequence for replication of pBR322 by pUC18, ligating a second synthetic nucleotide sequence comprising multi-cloning sites to the kanamycin-resistance gene sequence cassette to yield pSS-kna, homologously recombining an upstream of a left arm sequence and a downstream of a right arm sequence of the kanamycin-resistance gene sequence cassette, and inserting the upstream of the left arm sequence of the kanamycin-resistance gene sequence cassette and the downstream of the right arm sequence of the kanamycin-resistance gene sequence cassette into the multi-cloning sites on two sides of pSS-kna by blunt end insertion or cohesive end insertion, respectively, to construct a shuttle vector pSSGFP (SEQ ID NO: 17) for recombination;   4) constructing pSSENTe comprising: amplifying a 329 bp in the front of Ad11 genome as a left arm sequence, providing a fragment formed by ligating 195-378 bp of Ad5 E1A enhancer, −714-0 bp of human TERT promoter, and 568-1125 bp of Ad11 E1A in order as a right arm sequence, introducing two restriction enzyme sites XbaI and NcoI to two sides of the human TERT promoter, and inserting the left arm sequence and the right arm sequence into Snabl and EcoRV arranged on two sides of pSS-ChI, respectively, by blunt end insertion, to yield pSSENTel;   5) constructing pSSGFP comprising: providing a left arm being a product by ligating 27301-27837 bp of DNA segment of Ad11 genome with EGFP gene via NcoI, and introducing a SnaBI site to 3′ terminal of EGFP; providing a right arm being 28337-28920 bp of DNA segment of Ad11 genome; and inserting the left arm and the right arm into Snabl and EcoRV sites arranged on two sides of pSS-kna by blunt end insertion, to yield pSSGFP; and   6) digesting and purifying the pSSENTel and pSSGFP by PmeI, to yield two PmeI digested segments, performing homogenous recombination synchronously between the two PmeI digested segments and pAd11 plasmid, respectively, in BJ5183 cells; screening positive clones using agar plates comprising ampicillin, kanamycin, and chloramphenicol; digesting the positive clones by SwaI and SbfI, and deleting chloramphenicol-resistance gene expression cassette and kanamycin-resistance gene expression cassette to yield pAd11-5ETel-GFP (SEQ ID NO: 11); and digesting and linearizing the pAd11-5ETel-GFP by NotI, and transfecting 293 cells to produce adenovirs vector Ad11-5ETel-GFP.       
 
         [0029]    In a class of this embodiment, the concentrations of ampicillin, kanamycin, and chloramphenicol are 100 mg/mL, 50 μg/mL, and 25 mg/mL, respectively. 
         [0030]    In a class of this embodiment, Tel sequence of pSSENTel is substitutable by promoters of other tumor specific genes to yield a tumor-specific oncolytic adenovirus; and GFP sequence of pSSGFP is substitutable by a signal gene or therapeutic gene. 
         [0031]    In a class of this embodiment, Ad11 18.5 K gene promoter of pSSGFP is substitutable by a tumor-specific promoter. 
         [0032]    A method for treatment of tumor comprises applying a subgroup B recombinant human adenovirus vector Ad11-5EP. 
         [0033]    A method for treatment of tumor or detection of tumor cells in circulating blood comprises applying a subgroup B adenovirus vector Ad11-5ETel-GFP. 
         [0034]    Advantages of the invention are as follows: 
         [0035]    1) The tumor targeting adenovirus vector Ad11-5EP is acquired by substituting the enhancer and the promoter of E1A by the enhancer and the promoter of Ad5E1A based on the wild type Ad11. Such a vector has stronger oncolytic efficacy than the wild type Ad11, thereby enhancing the potency on the tumor cells. 
         [0036]    2) The tumor targeting adenovirus vector Ad11-5EP has tumor targeting and antitumoral efficacy. Experiments from oncolytic potency have indicated that Ad11-5EP has stronger potency on tumor cells than Ad5 and stronger cell toxicity than Ad11. Measurements of tumor growth and tumor clearance indicate that Ad11-5EP significantly reduces the tumor growth, and the non-tumor ratio of the tumor-bearing mice is significantly better than Ad11. 
         [0037]    3) The tumor targeting adenovirus vector Ad11-5EP can be used as a tumor-targeting genetic engineering drug for treating cancer, thereby producing social and economic benefits. 
         [0038]    4) The method for constructing subgroup B human recombinant adenovirus vector Ad11-5ETel-GFP of the invention features that homogeneous recombination is performed synchronously between Ad11-5EP genome and shutter vectors of pSSENTel and pSSGFP to produce recombinant virus vector Ad11-5ETel-GFP. Ad11-5ETel-GFP can be used in cancer therapy or detection of cancer cells in circulating blood. Expression tests of GFP of Ad11-5ETel-GFP in human normal epithelial cells and cancer cells and CTCs tests demonstrated that Ad11-5ETel-GFP is very sensitive to cancer cells and is capable of infecting a wide spectrum of cancer cells, thereby being specific, sensitive, and economic to apply in cancer cells detection in circulating blood. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a diagram showing a method of construction of a subgroup B recombinant human adenovirus vector Ad11-5EP; 
           [0040]      FIG. 2  is a diagram showing oncolytic potency of Ad5, Ad11 and Ad11-5EP in human cancer cells sensitive to Ad11; 
           [0041]      FIG. 3  is a diagram showing oncolytic potency of Ad5, Ad11 and Ad11-5EP in human cancer cells less sensitive to Ad11; in  FIGS. 2 and 3 , white columns represent Ad5, black columns represents Ad11, grid columns represent Ad11-5EP; 
           [0042]      FIG. 4  is a curve chart showing mean tumor volume after treatment of Ad5, Ad11, and Ad11-5EP in MIAPaCa-2 subcutaneous xenograft model; 
           [0043]      FIG. 5  is a chart showing percentage of progression-free mice after treatment with Ad5, Ad11, and Ad11-5EP in MIAPaCa-2 subcutaneous xenograft model; in  FIGS. 4-5 , 1 represents PBS, 2 represents Ad11, 3 represents Ad11-5EP, and 4 represents Ad5; 
           [0044]      FIG. 6  is a procedure diagram of construction of shutter vectors pSSENTel and pSSGFP and replication-selective oncolytic adenovirus plasmid pAd11-5ETel-GFP; 
           [0045]      FIG. 7  is a comparison chart of GFP expression after Ad11-5ETel-GFP infection in human normal epithelial cells and cancer cells; 
           [0046]      FIG. 8  is a histogram of detected tumor cells in blood by Ad11-5ETel-GFP in number; and 
           [0047]      FIG. 9  is a fluorescent image showing detected tumor cells in blood by Ad11-5ETel-GFP in fluorescent image. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0048]    The invention is further described by the following embodiments but not to limit the protection scope of the invention. It will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. 
       Example 1 
     Method for Constructing a Subgroup B Recombinant Human Adenovirus Vector Ad11-5EP 
       [0049]    A 365 bp fragment comprising an enhancer and a promoter of an upstream coding sequence of Ad5 E1A was substituted for a corresponding region of a serotype Ad11 of the subgroup B human adenovirus vector by homologous recombination to construct the subgroup B recombinant human adenovirus vector Ad11-5EP. 
         [0050]    A 329 bp fragment in the front of the Ad11 genome was provided as a left arm sequence, and a fragment formed by ligating a 195-559 bp fragment of Ad5 E1A comprising the enhancer and the promoter and a 568-1125 bp fragment of Ad11 E1A was provided as a right arm sequence. The left arm sequence and the right arm sequence were connected to multi-cloning sites arranged on two sides of pSS-ChI, respectively, to construct a shuttle vector pSS-A1A7. The pSS-A1A7 was digested and purified by PmeI while performing homologous recombination between a PmeI digested segment and pAd11 plasmid within BJ5183 cells. Positive clones were screened using agar plates comprising ampicillin and chloramphenicol. The positive clones were digested by SwaI, and a chloramphenicol-resistance gene expression cassette was deleted to yield pAd11-Ad5EP. The pAd11-Ad5EP was and linearized by NotI, and 293 cells were transfected to yield the adenovirus vector Ad11-5EP (as shown in  FIG. 1 ). 
       Example 2 
     Oncolytic Potencies of Ad5, Ad11, and Ad11-5EP in Ad11-Sensitive and -Insensitive Human Cancer Cell Lines 
       [0051]    Oncolytic potencies of Ad5, Ad11, and Ad11-5EP were tested on Ad11-sensitive human tumor cell lines Capan-2, PaTu8988s, PC-3m MCF7, HT-29 and Ad11-insensitive human tumor cell lines MIAPaCa-2, MDA-MB-231, HCT116, LNCaP, and A549 in vitro. 2% of fetal bovine serum (FBS) medium was employed to prepare cell suspensions of the above 10 cell lines, respectively, and were inoculated to a 96-well plate. After 14-18 h, virus was diluted by a serious dilution. An original concentration was 1×104 pt/cell, and the viral solution was then diluted by a ten-fold series dilution. The diluted solution was added to different cell lines of the 96-well plate at an addition of 10 μl/hole, and the oncolytic potencies of Ad5, Ad11, and Ad11-5EP were tested by MTS on a 6 th  day after the infection. 
         [0052]    Results showed that: in all Ad11-sensitive cell lines, Ad11-5EP has better oncolytic potency than Ad5, and Ad11 produced stronger cytotoxicity (as shown in  FIG. 2 ) whereas in Ad11-insensitive cell lines, performance of Ad11-5EP was significantly improved (as shown in  FIG. 3 ). Ad11-5EP showed a high sensitivity in 90% ( 9/10) cell lines, which indicated that Ad5 and Ad11 has better cancer killing efficacy, and Ad11-5EP was capable of killing a wide spectrum of cancer cells. 
       Example 3 
     Antitumoral Efficacy of Ad5, Ad11, and Ad11-5EP in a MIAPaCa-2 Subcutaneous Xenograft Model 
       [0053]    MIAPaCa-2 cells (as MIAPaCa-2 is Ad11-insensitve and Ad5-sensitive) were subcutaneously grafted to right backs of BALA/c nude mice (n=8/group), respectively, to construct subcutaneous xenograft models. When a volume of the tumor reached 180 mm 3 , PBS or viruses (Ad5, Ad11, and Ad11-5EP, 1×1010 viral particles/injection) were injected at a 1 st , 3 rd , and 5 th  days, tumor growth and tumor clearance rate were observed. Results showed that Ad11-5EP was as effective as Ad5 in reducing tumor growth (as shown in  FIG. 4 ), and non-tumor ratio of tumor-bearing mice was significantly better than Ad11-treated group (as shown in  FIG. 5 ). 
       Example 4 
     Method for Constructing a Subgroup B Recombinant Human Adenovirus Vector Ad11-5ETel-GFP 
       [0054]    1) Vectors pSS-ChI and pSS-kna were constructed by using two different antibiotics-resistance cassettes, SwaI restriction sites were introduced to two flanks of a chloramphenicol-resistance gene sequence cassette, and sbfI restriction sites were introduced to two flanks of a kanamycin-resistance gene sequence cassette. 
         [0055]    2) An initiation sequence for replication of pBR32 was cloned by pUC18, and a first synthetic nucleotide sequence comprising multi-cloning sites was connected to the chloramphenicol-resistance gene sequence cassette to yield pSS-ChI. Homologously recombination between an upstream of a left arm sequence and a downstream of a right arm sequence of the chloramphenicol-resistance gene sequence cassette was performed, and the upstream of the left arm sequence of the chloramphenicol-resistance gene sequence cassette and the downstream of the right arm sequence of the chloramphenicol-resistance gene sequence cassette were inserted into the multi-cloning sites on two sides of pSS-ChI by blunt end insertion or cohesive end insertion, respectively, to construct a shuttle vector pSSENTel for recombination. 
         [0056]    3) An initiation sequence for replication of pBR32 was cloned by pUC18, and a second synthetic nucleotide sequence comprising multi-cloning sites was connected to the kanamycin-resistance gene sequence cassette to yield pSS-kna. Homologously recombination was performed between an upstream of a left arm sequence and a downstream of a right arm sequence of the kanamycin-resistance gene sequence cassette, and the upstream of the left arm sequence of the kanamycin-resistance gene sequence cassette and the downstream of the right arm sequence of the kanamycin-resistance gene sequence cassette were inserted into the multi-cloning sites on two sides of pSS-kna by blunt end insertion or cohesive end insertion, respectively, to construct a shuttle vector pSSGFP for recombination. 
         [0057]    4) pSSENTe was constructed, and the construction of pSSENTe comprised: amplifying a 329 bp in the front of Ad11 genome as a left arm sequence, providing a fragment formed by ligating 195-378 bp of Ad5 E1A enhancer, −714-0 bp of human TERT promoter, and 568-1125 bp of Ad11 E1A in order as a right arm sequence, introducing two restriction enzyme sites XbaI and NcoI to two sides of the human TERT promoter, and inserting the left arm sequence and the right arm sequence into Snabl and EcoRV arranged on two sides of pSS-ChI, respectively, by blunt end insertion, to yield pSSENTel. 
         [0058]    5) pSSGFP was constructed and the construction of pSSGFP comprised: providing a left arm being a product by ligating 27301-27837 bp of DNA segment of Ad11 genome with EGFP gene via NcoI, and introducing a SnaBI site to 3′ terminal of EGFP; providing a right arm being 28337-28920 bp of DNA segment of Ad11 genome; and inserting the left arm and the right arm into Snabl and EcoRV sites arranged on two sides of pSS-kna by blunt end insertion, to yield pSSGFP. 
         [0059]    6) pSSENTel and pSSGFP were digested and purified by PmeI to yield two PmeI digested segments, homogenous recombination was synchronously performed between the two PmeI digested segments and pAd11 plasmid, respectively, in BJ5183 cells. Positive clones were screened using agar plates comprising ampicillin, kanamycin, and chloramphenicol. The positive clones were digested by SwaI and SbfI, and chloramphenicol-resistance gene expression cassette and kanamycin-resistance gene expression cassette were deleted to yield pAd11-5ETel-GFP (as shown in  FIG. 6 ). 
         [0060]    The pAd11-5ETel-GFP was and linearized by NotI, and 293 cells were transfected to produce adenovirus vector Ad11-5ETel-GFP. 
       Example 5 
     Expression of GFP of Ad11-5ETel-GFP in Human Normal Epithelial Cells and Cancer Cells 
       [0061]    Ad11-5ETel-GFP was used to infect human pancreatic cancer cell line SUIT-2 and human normal bronchial epithelial cell line NHBE (an infection concentration of 100 pfu/cell), expression of GFP was observed under immunofluorescence microscope after 24 h. It has been found that GFP had a high expression in cancer cell line SUIT-2, and relatively low expression in normal cells NHBE (as shown in  FIG. 7 ), which indicated that the cancer cell line SUIT-2 is Ad11-5ETel-GFP-sensitive. 
       Example 6 
     Circulation Tumor Cells (CTCs) Detection Using Ad11-5ETel-GFP 
       [0062]    10, 25, 50, 100, and 200 human pancreatic cancer cell line SUIT-2 were respectively mixed with 3 mL of blood, nucleated cells were collected by centrifugation after red blood cells were lysised. Thereafter, the nucleated cells were resuspended in 900 μL of DMEM medium, added with 1×104 pfu of Ad11-5ETel-GFP, and cultured for 24 h. GFP positive cells were counted under an immunofluorescence microscope (as shown in  FIG. 8 ). Peripheral blood cells were mixed with 0, 10, 100, and 1000 human pancreatic cancer cell line SUIT-2, respectively (an infection concentration of 100 pfu/cell). The samples were processed as described above. GFP positive cells were observed under the immunofluorescence microscope after 24 h of culturing and it demonstrated that the cancer cell line SUIT-2 is Ad11-5ETel-GFP-sensitive. The GFP-positive cells were correlated to the number of tumor cells mixed with the blood cells. 
         [0063]    While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.