Cloning of Thymidine Kinase Gene of Duck Plague Virus Using Degenerate PCR

The DNA of duck plague virus （DPV） thymidine kinase （TK） gene was cloned and sequenced from a vaccine virus in the study. Degenerate oligonucleotide primers for the consensus site of herpesvirus UL24, TK, and glycoprotein H（gH） gene were used in the polymerase chain reaction （PCR） to amplify DNA product with 3 741-base-pairs （bp） in size. DNA sequence analysis revealed a 1 077-base-pairs （bp） open reading frame （ORF） encoding a 358 amino acid polypeptide homologous to herpesvirus TK proteins. The predicted TK protein shared 31.2, 41.3, 35.7, 37.4, and 28.4% identity with herpes simplex virus typel, equine herpesvirus type 4, Marek＇s disease virus 2, herpesvirus turkey, and infectious laryngotracheitis virus, respectively. Comparison of the amino acid sequences of other herpesvirus TK proteins showed that these proteins were not conserved on the whole, otherwise the portion of the TK proteins corresponding to the nucleotide binding domain and the nucleoside binding site were highly conserved among herpesvirus. Comparison with the amino acid sequences of the conserved nucleotide and nucleoside binding domains of other eleven herpesvirus TK proteins to the predicted DPV peptide confirmed its identity as the DPV TK protein.

Cooperative Therapeutic Effects of Herpes Simplex Virus Thymidine Kinase Gene/Ganciclovir System and Chemotherapeutic Agents on Prostate Cancer in vitro

The killing effects of herpes simplex virus thymidine kinase gene/ganciclovir （HSV-tk/GCV） approach by the addition of several commonly clinical chemotherapeutic agents on hormone refractory prostate cancer （HRPC） cells PC-3m were investigated. After transferring of the HSV-tk gene into PC-3m cells, mRNA and protein expression of HSV-tk was detected by reverse-transcript polymerase chain reaction （RT-PCR） and strept avidin-biotin complex （SABC） im- munohistochemical method. The killing effect of GCV, cisplatin （CDDP）, etoposide （VP-16）, vincristine （VCR）, methotrexate （MTX）, 5-fluorouracil （5-Fu）, and suramin on PC-3m cells was evaluated by morphological assessment analysis, trypan blue exclusion assay and MTT assay respectively. Additionally, the cooperative effect of HSV-tk/GCV system combined with the above agents on the target cancer cells was determined by MTT. Furthermore, apoptosis and necrosis induced by GCV plus 5-Fu or suramin was analyzed by flow cytometry （FCM）. The results showed that that there was HSV-tk mRNA and protein expression in pDR2-tk plasmid transduced PC-3m cell. Combination of GCV with VP-16, VCR, 5-Fu or suramin led to an enhanced cellular killing effect, but with CDDP resulted in a reduced one and with MTX in an approximate one. FCM revealed that synergistic use of GCV and 5-fu or suramin resulted in a rather large proportion of apoptosis and necrosis with the apoptosis index being 36.38 % and 35.51%, and the proportion of necrosis being 33.05 % and 28.87 %, respectively. In conclusion, HSV-tk/CGV approach by addition of certain clinical available chemotherapeutic drugs brings on statistically significant enhanced cell killing over single-agent treatment. Our results highlight the potential for such new combination therapies for future treatments of HRPC.

Vascular damage and anti-angiogenic effects of tumor vessel-targeted adenovirus-mediated herpes simplex virus thymidine kinase gene

AIM： To explore the therapeutic efficacy and mechanism of herpes simplex virus-thymidine kinase （HSV-tk） targeting angiogenesis against hepatocellular carcinoma in vivio and in vitro. METHODS： Recombinant adenovirus containing kinase domain insert with receptor （KDR） or cytomegalovirus （CMV） promoter-controlled HSV-tk gene （AdKDR-tk and AdCMV-tk） was constructed using pAdeasy system. The expression of KDR antigen in human umbilical venous endothelial cells （HUVEC） and HepG2 was detected with histological analysis of cells. The virus was used to infect HUVEC and HepG2. Following administration of ganciclovir （GCV）, the survival rate of gene-transfected HUVEC and HepG2 was evaluated by MTT method. To develop hepatocarcinomas in 32 Balb/C mice with HepG2 cells, the mice were divided into four groups： ganciclovir group （Ⅰ）, Ad group （Ⅱ）, AdCMV-tk group （Ⅲ） and AdKDR-tk group （Ⅳ）. Then selective administration of recombinant adenovirus or Ad via the intratumorial was given to all rats. Ganciclovir （GCV） was given at a dose of 100 mg·kg^-1·d^-1 （ip） started on the following day and lasted 10 d. Microvessel density （MVD） of tumor in all the treated animals were examined by the immunohistochemical methods and tumor burden was evaluated 10 d before and alter the last GCV dose.RESULTS： Immunocytochemical staining indicated the expression of KDR antigen in HUVEC. Under adenovirus infection index of 100, with increasing GCV concentration from 0 up to 50 mg/L, the survival rate of AdKDR-tk- transfected HUVEC and HepG2 decreased from 100% to （28.94 ± 5.67）% and （75.45 ± 2.91）% at proper order, respectively （P 〈 0.01）, while the survival rate of AdCMV- tk-transfected HUVEC and HepG2 declined from 100% to （17.56 ± 2.48）% and （23.15± 5.72）%, respectively （P 〉 0.05）. Compared with group I, there was a decrease of tumor weight by 14.7% in group Ⅲ and by 23.6% in group Ⅳ. And there was a distinct difference between group M and Ⅳ （P 〈 0.05）. The median MVD for all groups was 37.4 ± 8.6, 30.6 ± 7.8, 27.6 ± 7.1, and 10.7 ± 4.1 （microvessels/mm^2） in group Ⅰ, Ⅱ, M and IV, respectively. And there was a marked difference between group M and Ⅱ （P 〈 0.05）, Ⅳ and Ⅱ （P 〈 0.01）, and Ⅳ and M （P 〈 0.01）. CONCLUSION： KDR promoter-HSV-tk gene may effectually restrain the growth of tumor via targeting angiogenesis for hepatocellular carcinoma with treatment of GCV.

HSVTK Gene Therapy for CarcinoembryonicAntigen-Producing Human Lung Cancer Cells

The long-term success of gene therapy for cancer relies heavily on the development of effective targeting systems. We investigate the possibility of targeted gene therapy using promoter of carcinoembryonic antigen (CEA) gene. By using luciferase reporter gene, we found that CEA promoter exhibit 16 times high activity in CEA-producing lung cancer cells, A549 than in nonproducing cells, Hela. We also constructed a recombinant expression plasmid pCEATK, in which CEA promoter drives the effector gene, thymidine kinase gene of Herpes Simplex Virus (HSVTK). A549 cells transfected with pCEATK became 865 times more sensitive to ganciclovir (GCV) than the control cells. However, Hela cells transfected with this plasmid remained resistant to GCV. These data indicate the potential for targeted gene therapy using the CEA promoter against CEA-producing tumor cells, such as lung cancer cells.

Altered Expression of Connexin-43 and Impaired Capacity of Gap Junctional Intercellular Communication in Prostate Cancer Cells

Connexin-43 (Cx43) expression in prostate cancer (PCa) cells and the potency of gap junctional intercellular communication (GJIC) in the cells were investigated, with an attempt to elu- cidate the reason why the so-called 'bystander effect' mediated by thymidine kinase (TK) suicide gene therapy on PCa cells is not of significance and to explore the role of GJIC in PCa carcinogenesis. mRNA and protein expression of Cx43 in a PCa cell line PC-3m was detected by re- verse-transcription polymerase chain reaction (RT-PCR) and strapt-avidin-biotin-enzyme complex (SABC) immunohistochemical staining, and inherent GJIC of PC-3m cells was assayed by scrape-loading and dye transfer (SLDT) assay. The expression of Cx43 in human normal and malig- nant prostate tissues was determined by SABC immunohistochemistry as well. It was found that Cx43 mRNA and protein expression in PC-3m cells was slightly reduced as compared with positive controls and the location of Cx43 protein was aberrant in cytoplasm rather than on membrane. As- sessment of paraffin sections demonstrated that the expression of Cx43 protein in PCa cells was ab- normally located and markedly diminished as compared with normal prostatic epithelial ones, dis- playing a negative correlation to the pathological grade (χ2=4.025, P<0.05). Additionally, capacity of inherent GJIC in PC-3m cells was disrupted, which was semi-quantified as (+) or (-). It was indi- cated that both down-regulated expression of Cx43 mRNA and aberrant location of Cx43 protein par- ticipated in the mechanisms leading to deficient GJIC in PC-3m cells. Lack of efficient GJIC is a molecular event, which may contribute not only to limited extent of 'bystander effect', but also to initiation and progression of prostatic neoplasm.

Characteristics of ovarian cancer cells transduced by the bicistronic retroviral vector containing GM-CSF and HSV-TK genes

Objectives To explore whether HSV-TK (herpes simplex virus thymidine kinase) and GM-CSF (granulocyte-macrophage colony-stimulating factor) genes could be linked by internal ribosome entry site (IRES) in one retroviral vector and expressed by ovarian cancer cells following transfection, and to observe the characteristics of the transduced cells.Methods Retroviral vector pLGM-I-TK was constructed by linking the HSV-TK gene and GM-CSF gene with the IRES sequence. By using the “ping-pong' technique, pLGM-I-TK was transfected into the packaging cell line, PA317, to produce a PA317/TK-GM cell line. Using the resulting viral supernatant to infect the ovarian cancer cell line SKOV3, PCR and RT-PCR were used to explore the integration and transcription of HSV-TK and GM-CSF genes. The cytotoxicity of GCV (gancyclovir) on SKOV3/TK-GM was determined by MTT assay and the bystander effect of the HSV-TK/GCV system was also assessed. ELISA was used to measure the expression of GM-CSF by the transgene cells.Results The bicistronic retroviral vector constructed could be successfully transduced into PA317 and the titer of the retroviral vector was about 8.6×105?cfu/ml. PCR and RT-PCR demonstrated the successful integration and transcription of HSV-TK and GM-CSF genes transduced into the SKOV3 cell. SKOV3/TK-GM cells could be killed by GCV, and the IC50 was 0.7?μg/ml. The bystander effect was demonstrated. The expression level of GM-CSF in SKOV3/TK-GM was 60.4?ng*ml-1*106 cells-1*2 days-1.Conclusion The IRES sequence can be used to construct retroviral vectors to facilitate co-transfection of two genes. SKOV3/TK-GM cells can simultaneously express the HSV-TK and GM-CSF genes with biological activities which could be useful for enhancing the function of immune cells on the basis of suicide gene therapy.