Expression of thymidine kinase driven by an endothelial-specific promoter inhibits tumor growth of Lewis lung carcinoma cells in transgenic mice

Gene Therapy Using Neural Stem/Progenitor Cells Derived from Human Induced Pluripotent Stem Cells: Visualization of Migration and Bystander Killing Effect

Glioblastoma is the most aggressive brain tumor characterized by diffuse infiltration into the normal brain parenchyma. Neural stem cells are known to possess the tumor-tropic migratory capacity and thus can be used as cellular vehicles for targeted delivery of therapeutic agents. In the present study, we evaluated the efficacy of herpes simplex virus thymidine kinase (HSV-TK) suicide gene therapy for glioblastoma using neural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs). Although transduction of hiPSCs is preferable for a safe and stable supply in the clinical setting, high-level and/or constitutive HSV-TK expression was highly cytotoxic to hiPSCs. To overcome this problem, we used the tetracycline-inducible system to control the expression of HSV-TK. hiPSC-derived NS/PCs expressing HSV-TK were transplanted in an orthotopic xenograft mouse model of human glioblastoma. Glioblastoma cell growth in mice was dramatically inhibited following ganciclovir (GCV) administration. Survival of the mice was significantly prolonged with administration of GCV compared with control groups. Time-lapse imaging of organotypic brain slice cultures first demonstrated the directional migration of NS/PCs toward glioblastoma cells and the bystander killing effect upon GCV treatment. hiPSC-derived NS/PCs with HSV-TK/GCV suicide gene system may have considerable therapeutic potential for the treatment of glioblastoma. Color images are available online.

Development of Endothelial-Specific Single Inducible Lentiviral Vectors for Genetic Engineering of Endothelial Progenitor Cells

Endothelial progenitor cells (EPC) are able to migrate to tumor vasculature. These cells, if genetically modified, can be used as vehicles to deliver toxic material to, or express anticancer proteins in tumor. To test this hypothesis, we developed several single, endothelial-specific, and doxycycline-inducible self-inactivating (SIN) lentiviral vectors. Two distinct expression cassettes were inserted into a SIN-vector: one controlled by an endothelial lineage-specific, murine vascular endothelial cadherin (mVEcad) promoter for the expression of a transactivator, rtTA2S-M2; and the other driven by an inducible promoter, TREalb, for a firefly luciferase reporter gene. We compared the expression levels of luciferase in different vector constructs, containing either the same or opposite orientation with respect to the vector sequence. The results showed that the vector with these two expression cassettes placed in opposite directions was optimal, characterized by a robust induction of the transgene expression (17.7- to 73-fold) in the presence of doxycycline in several endothelial cell lines, but without leakiness when uninduced. In conclusion, an endothelial lineage-specific single inducible SIN lentiviral vector has been developed. Such a lentiviral vector can be used to endow endothelial progenitor cells with anti-tumor properties.

Endoglin (CD105) Silencing Mediated by shRNA Under the Control of Endothelin-1 Promoter for Targeted Gene Therapy of Melanoma

Endoglin (CD105), a transforming growth factor (TGF)-β coreceptor, and endothelin-1, a vasoconstrictor peptide, are both overexpressed in tumor endothelial and melanoma cells. Their targeting is therefore a promising therapeutic approach for melanoma tumors. The aim of our study was to construct a eukaryotic expression plasmid encoding the shRNA molecules against CD105 under the control of endothelin-1 promoter and to evaluate its therapeutic potential both in vitro in murine B16F10-luc melanoma and SVEC4-10 endothelial cells and in vivo in mice bearing highly metastatic B16F10-luc tumors. Plasmid encoding shRNA against CD105 under the control of the constitutive U6 promoter was used as a control. We demonstrated the antiproliferative and antiangiogenic effects of both plasmids in SVEC4-10 cells, as well as a moderate antitumor and pronounced antimetastatic effect in B16F10-luc tumors in vivo. Our results provide evidence that targeting melanoma with shRNA molecules against CD105 under the control of endothelin-1 promoter is a feasible and effective treatment, especially for the reduction of metastatic spread.

Gene Electrotransfer of Plasmid with Tissue Specific Promoter Encoding shRNA against Endoglin Exerts Antitumor Efficacy against Murine TS/A Tumors by Vascular Targeted Effects

Vascular targeted therapies, targeting specific endothelial cell markers, are promising approaches for the treatment of cancer. One of the targets is endoglin, transforming growth factor-β (TGF-β) co-receptor, which mediates proliferation, differentiation and migration of endothelial cells forming neovasculature. However, its specific, safe and long-lasting targeting remains the challenge. Therefore, in our study we evaluated the transfection efficacy, vascular targeted effects and therapeutic potential of the plasmid silencing endoglin with the tissue specific promoter, specific for endothelial cells marker endothelin-1 (ET) (TS plasmid), in comparison to the plasmid with constitutive promoter (CON plasmid), in vitro and in vivo. Tissue specificity of TS plasmid was demonstrated in vitro on several cell lines, and its antiangiogenic efficacy was demonstrated by reducing tube formation of 2H11 endothelial cells. In vivo, on a murine mammary TS/A tumor model, we demonstrated good antitumor effect of gene electrotransfer (GET) of either of both plasmids in treatment of smaller tumors still in avascular phase of growth, as well as on bigger tumors, already well vascularized. In support to the observations on predominantly vascular targeted effects of endoglin, histological analysis has demonstrated an increase in necrosis and a decrease in the number of blood vessels in therapeutic groups. A significant antitumor effect was observed in tumors in avascular and vascular phase of growth, possibly due to both, the antiangiogenic and the vascular disrupting effect. Furthermore, the study indicates on the potential use of TS plasmid in cancer gene therapy since the same efficacy as of CON plasmid was determined.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

Expression of thymidine kinase mediated by a novel non-viral delivery system under the control of vascular endothelial growth factor receptor 2 promoter selectively kills human umbilical vein endothelial cells

AIM: To investigate the killing efficiency of a recombinant plasmid containing a thymidine kinase (TK) domain insert driven by the vascular endothelial growth factor receptor 2 (VEGFR2) promoter (KDR) on vascular endothelial cells.

METHODS: The KDR-TK fragment was extracted from pBluescript II KDR-TK plasmid by enzymatic digestion with XhoI and SalI. The enhanced green fluorescence protein (EGFP) carrier was extracted from pEGFP by the same procedure. The KDR-TK was inserted into the pEGFP carrier to construct pEGFP-KDR-TK. Using ultrasound irradiation and microbubble, pEGFP-KDR-TK was transferred into human umbilical vein endothelial cells (HUVECs). The transient infection rate was estimated by green fluorescent protein (GFP) expression. Transfected HUVECs, non-transfected HUVECs, and HepG2 cells were cultured in the presence of different concentrations of ganciclovir (GCV), and the killing efficacy of HSV-TK/GCV was analyzed by 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide (MTT) assay.

RESULTS: The recombinant pEGFP-KDR-TK was successfully constructed by inserting the KDR-TK fragment into the pEGFP carrier. Transfected HUVECs showed cytoplasmic green fluorescence, and the transient transfection rate was about 20.3%. Pools of G418-resistant cells exhibited a higher sensitivity to the prodrug/GCV compared to non-transfected HUVECs or non-transfected HepG2 cells, respectively.

CONCLUSION: KDR promoter and the suicide gene/prodrug system mediated by diagnostic ultrasound combined with microbubble can significantly kill HUVECs. Such therapy may present a novel and attractive approach to target gene therapy on tumor vessels.

VE-cadherin: the major endothelial adhesion molecule controlling cellular junctions and blood vessel formation

Vascular endothelial (VE)-cadherin is a strictly endothelial specific adhesion molecule located at junctions between endothelial cells. In analogy of the role of E-cadherin as major determinant for epithelial cell contact integrity, VE-cadherin is of vital importance for the maintenance and control of endothelial cell contacts. Mechanisms that regulate VE-cadherin-mediated adhesion are important for the control of vascular permeability and leukocyte extravasation. In addition to its adhesive functions, VE-cadherin regulates various cellular processes such as cell proliferation and apoptosis and modulates vascular endothelial growth factor receptor functions. Consequently, VE-cadherin is essential during embryonic angiogenesis. This review will focus on recent new developments in understanding the role of VE-cadherin in controlling endothelial cell contacts and influencing endothelial cell behavior by various outside-in signaling processes.

Gene therapy targeting to tumor endothelium

Tumor-associated vasculature is a relatively accessible component of solid cancers that is essential for tumor survival and growth, providing a vulnerable target for cancer gene therapy administered by intravenous injection. Several features of tumor-associated vasculature are different from normal vasculature, including overexpression of receptors for angiogenic growth factors, markers of vasculogenesis, upregulation of coagulation cascades, aberrant expression of adhesion molecules and molecular consequences of hypoxia. Many of these differences provide candidate targets for tumor-selective 'transductional targeting' of genetically- or chemically modified vectors and upregulated gene expression can also enable 'transcriptional targeting', regulating tumor endothelia-selective expression of transgenes following nonspecific gene delivery. Tumor vasculature also represents an important site of therapeutic action by the secreted products of antiangiogenic gene therapies that are expressed in non-endothelial cells. In this review we assess the challenges faced and the vectors that may be suitable for gene delivery to exploit these targets. We also overview some of the strategies that have been developed to date and highlight the most promising areas of research.

In vivo efficacy of HSV-TK transcriptionally targeted to the tumour vasculature is augmented by combination with cytotoxic chemotherapy

BACKGROUND

Retroviral vectors are suitable for targeting endothelial cells in the tumour neovasculature because of their intrinsic selectivity for proliferating cells. Previously, we inserted regulatory elements of the endothelial-specific prepro-endothelin-1 (ppET1) promoter in retroviral vectors to generate high-titre, replication-defective recombinant retroviruses that restricted gene expression to the vascular compartment of tumours.

METHODS

A retroviral vector was generated in which expression of herpes simplex virus thymidine kinase (HSV-TK) was transcriptionally restricted to endothelial cells, under the control of a hybrid ppET-1 LTR. Xenograft tumour models were used to determine the efficacy of targeting HSV-TK to the tumour vasculature. Subsequently, vascular-targeted gene therapy was combined with chemotherapeutic agents.

RESULTS

Breast or colorectal xenograft tumour growth was reduced and survival was increased in response to ganciclovir treatment. Treatment resulted in widespread vascular disruption and tumour cell apoptosis. In colorectal tumours, combination with irinotecan, a cytotoxic drug used to treat colorectal cancer, significantly increased survival compared to drug alone. No beneficial effect on survival was observed when combined with cisplatin, a cytotoxic drug not in clinical use for this tumour type. On the basis of their relative efficacies in vitro against tumour and endothelial cells, co-operativity with irinotecan likely derives from additionally targeting the peripheral tumour cells that survive the anti-vascular treatment.

CONCLUSIONS

We show that the ppET1-targeted vector is efficacious for therapeutic gene expression in vivo, validating a strategy targeted to tumour vasculature, and demonstrate that vascular targeting combined with appropriate chemotherapy is more effective than either therapy alone.

The human VE-cadherin promoter is subjected to organ-specific regulation and is activated in tumour angiogenesis

Vascular endothelial (VE)-cadherin is exclusively expressed at interendothelial junctions of normal and tumour vessels. In this report, we characterized the transcriptional activity of the human VE-cadherin promoter. Transient transfection assays revealed that sequences at positions --1135/-744 and -166/-5 base pairs are critical for promoter activity in endothelial cells. We show that specific sequences in the proximal region interact with Ets and Sp1 family members. Transgenic mice were created and the human VE-cadherin promoter was able to confer correct temporal and spatial expression on the LacZ gene in embryos. In adults, the transgene was specifically and strongly expressed in the lung, heart, ovary, spleen and kidney glomeruli, whereas expression was weak or absent in the vasculature of other organs, including the brain, thymus, liver and skeletal muscle. Neovessels in tumour grafts and Matrigel implants harboured strong stainings, indicating that promoter activity is enhanced in angiogenic situations. Furthermore, Matrigel and transfection assays showed that VE-cadherin promoter is subjected to bFGF induction. Transgene expression was also noticed in extravascular sites of the central nervous system, suggesting that silencer elements may be located elsewhere in the gene. These results are a first step towards addressing the organ- and tumour-specific regulation of the VE-cadherin gene.

Vascular-targeted cancer gene therapy

As a consequence of the dramatic progress that has been made in recent years towards elucidating the diverse molecular events involved in the development and pathogenesis of malignant disease, there is now no shortage of genes that can be exploited or targeted in the context of cancer gene therapy. Many of these have been shown to be effective both in vitro and in various animal models, and a number have progressed to the clinic. The results of these later studies, although generally encouraging, are perhaps less dramatic than one might have hoped. Although a number of factors undoubtedly contribute to this finding, it is evident that a major reason relates to the difficulties implicit in achieving efficient in vivo gene transfer, particularly in a clinical context. Targeting gene therapy, not to the malignant population, but instead to the vasculature upon which the survival and growth of a tumour depends constitutes an alternative approach that overcomes some of the delivery problems associated with established tumour cell-directed strategies.

Spying on cancer: molecular imaging in vivo with genetically encoded reporters

Genetically encoded imaging reporters introduced into cells and transgenic animals enable noninvasive, longitudinal studies of dynamic biological processes in vivo. The most common reporters include firefly luciferase (bioluminescence imaging), green fluorescence protein (fluorescence imaging), herpes simplex virus-1 thymidine kinase (positron emission tomography), and variants with enhanced spectral and kinetic properties. When cloned into promoter/enhancer sequences or engineered into fusion proteins, imaging reporters allow transcriptional regulation, signal transduction, protein-protein interactions, oncogenic transformation, cell trafficking, and targeted drug action to be spatiotemporally resolved in vivo. Spying on cancer with genetically encoded imaging reporters provides insight into cancer-specific molecular machinery within the context of the whole animal.

Use of suicide genes for cancer gene therapy: study of the different approaches

Cancer is a disease of high incidence for which conventional treatments are not necessarily effective. There is a need for the development of new alternative strategies. Among them, suicide gene therapy has been developed. In this approach, a gene encoding for a protein toxic under particular conditions is delivered to the target cells, resulting in their death. Although this approach has been in development for a long time, new combinations with other gene therapy areas, such as selective replicative viruses, tumour targeting, or conventional treatments such as chemo- or radiotherapy, are currently being tested. This review will summarise some of these approaches.

Construction of the vector that harbors self-restricted system for hepatitis B virus clearance in gene therapy

AIM

To construct the vector that harbors self-restricted system for clearing hepatitis B virus, eliminating infected hepatic cells and inhibiting hepatitis B recurrence in gene therapy.

METHODS

After amplifying hepatitis C virus (HCV) internal ribosome entry sites (IRES) by reverse-transcription PCR (RT-PCR), the products were cloned into pcDNA3. A biscistronic vector was obtained. A part of sequence in HBV anti-surface gene and part of sequence in HCV core gene were cloned into the vector before IRES site in turn and thymidine kinase (TK) was also cloned into it following the IRES site. After determination by PCR and sequencing, we acquired the vector containing HBV anti-S, HCV-C gene, HCV IRES and thymidine kinase gene, which was named the vector pcDNA3-SCITK. The vectors were separately transfected into HepG2 cells and 2.2.15 cells and all the media contained ganciclovir.

RESULTS

The novel vector was transfected into 2.2.15 and hepG2 cells, the expressed protein could destroy the former, but had no effect on HepG2 cells if all the media contained ganciclovir. Apoptosis cells in the former accounted for 15 per cent of all cells by fluorescence (FACS) detection. There was obvious difference between the two types of cells (the later was only 6 per cent).

CONCLUSION

The function of genes that pcDNA3-SCITK carried with self-restricted system could be ego-controlled, and it might be used as gene therapy vector for HBV clearance if taking HBV S gene as target gene and TK gene as objective gene.