Gene therapy for hepatocellular carcinoma based on tumour-selective suicide gene expression using the alpha-fetoprotein (AFP) enhancer and a housekeeping gene promoter

Neomorphic DNA-binding enables tumor-specific therapeutic gene expression in fusion-addicted childhood sarcoma

Chimeric fusion transcription factors are oncogenic hallmarks of several devastating cancer entities including pediatric sarcomas, such as Ewing sarcoma (EwS) and alveolar rhabdomyosarcoma (ARMS). Despite their exquisite specificity, these driver oncogenes have been considered largely undruggable due to their lack of enzymatic activity.

Here, we show in the EwS model that – capitalizing on neomorphic DNA-binding preferences – the addiction to the respective fusion transcription factor EWSR1-FLI1 can be leveraged to express therapeutic genes.

We genetically engineered a de novo enhancer-based, synthetic and highly potent expression cassette that can elicit EWSR1-FLI1-dependent expression of a therapeutic payload as evidenced by episomal and CRISPR-edited genomic reporter assays. Combining in silico screens and immunohistochemistry, we identified GPR64 as a highly specific cell surface antigen for targeted transduction strategies in EwS. Functional experiments demonstrated that anti-GPR64-pseudotyped lentivirus harboring our expression cassette can specifically transduce EwS cells to promote the expression of viral thymidine kinase sensitizing EwS for treatment to otherwise relatively non-toxic (Val)ganciclovir and leading to strong anti-tumorigenic, but no adverse effects in vivo. Further, we prove that similar vector designs can be applied in PAX3-FOXO1-driven ARMS, and to express immunomodulatory cytokines, such as IL-15 and XCL1, in tumor entities typically considered to be immunologically ‘cold’.

Collectively, these results generated in pediatric sarcomas indicate that exploiting, rather than suppressing, the neomorphic functions of chimeric transcription factors may open inroads to innovative and personalized therapies, and that our highly versatile approach may be translatable to other cancers addicted to oncogenic transcription factors with unique DNA-binding properties.

PEGylation potentiates hepatoma cell targeted liposome-mediated in vitro gene delivery via the asialoglycoprotein receptor

Hepatocellular carcinoma is a burgeoning health issue in sub-Saharan Africa and East Asia where it is most prevalent. The search for gene medicine treatment modalities for this condition represents a novel departure from current treatment options and is gaining momentum. Here we report on nonPEGylated and on sterically stabilized PEGylated cationic liposomes decorated with D-galacto moieties linked to 24.1 Å spacers for asialoglycoprotein receptor (ASGP-R)-targeted vehiculation of pCMV-luc plasmid DNA. Cargo DNA is fully liposome associated at N/P ratio=3:1 and is partially protected from the effects of serum nucleases. Moreover, at this ratio, lipoplex dimensions (89-97 nm) are compatible with the requirements for extravasation in vivo. Ethidium displacement assays show that the reporter DNA is in a less condensed state when bound to PEGylated liposomes than with nonPEGylated liposomes. PEGylated lipoplexes were well tolerated by both HEK293 (ASGP-R-negative) and HepG2 (ASGP-R-positive) cell lines and delivered DNA to the human hepatoma cell line HepG2 by ASGP-R mediation at levels three-fold greater than nonPEGylated lipoplexes. PEGylated ASGP-R-targeted liposomes reported in this study possess the required characteristics for hepatotropic gene delivery and may be considered for further application in vivo.

Peptide micelle-mediated delivery of tissue-specific suicide gene and combined therapy with avastin in a glioblastoma model

Bevacizumab (Avastin) is an angiogenesis inhibitor used as a treatment for various cancers. In this study, the combination therapy of Avastin and glioblastoma-specific thymidine kinase gene [pEpo-NI2-SV-herpes simplex virus thymidine kinase(HSVtk)] was evaluated in a glioblastoma animal model. The R7L10 peptide was used as a gene carrier of pEpo-NI2-SV-HSVtk. Gel retardation assays confirmed that R7L10 formed stable complexes with pEpo-NI2-SV-HSVtk. R7L10 protected DNA from nuclease digestion. R7L10 had lower transfection efficiency than polyethylenimine (PEI; 25 kDa). However, the in vitro and in vivo toxicity assays showed that R7L10 had lower cytotoxicity than PEI, suggesting that R7L10 is safer than PEI. For the combination therapy, Avastin was injected intravenously and the pEpo-NI2-SV-HSVtk/R7L10 complexes were injected intratumorally in the glioblastoma animal model. Tumor growth was most effectively inhibited by the combination therapy of Avastin and the gene. The immunostaining results confirmed that the HSVtk genes were expressed in the groups with the pEpo-NI2-SV-HSVtk/R7L10 complex. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed a higher level of apoptotic cells in the combination group than the pEpo-NI2-SV-HSVtk/R7L10 complex or Avastin group. In conclusion, the combination of Avastin and the glioblastoma-specific HSVtk gene has a higher antitumor effect than single therapy of Avastin or HSVtk after intratumoral administration in glioblastoma animal model.

Combination of hepatocyte specific delivery and transformation dependent expression of shRNA inducing transcriptional gene silencing of c-Myc promoter in hepatocellular carcinoma cells

Background

A specific targeting modality for hepatocellular carcinoma (HCC) could ideally encompass a liver cell specific delivery system of a transcriptional unit that is active only in neoplastic cells. Sendai virosomes, derived from Sendai viral envelopes, home to hepatocytes based on the liver specific expression of asialoglycoprotein receptors (ASGPRs) which are recognized by the Sendai virosomal fusion (F) proteins. As reported earlier by us and other groups, transcriptional gene silencing (TGS) does not require continuous presence of the effector siRNA/shRNA molecule and is heritable, involving epigenetic modifications, leading to long term transcriptional repression. This could be advantageous over conventional gene therapy approaches, since continuous c-Myc inactivation is required to suppress hepatocarcinoma cells.

Methods

Exploiting such virosomal delivery, the alpha-fetoprotein (AFP) promoter, in combination with various tumour specific enhancers, was used to drive the expression of shRNA directed against ME1a1 binding site of the proto-oncogene c-Myc P2 promoter, in order to induce TGS in neoplastic liver cells.

Results

The dual specificity achieved by the Sendai virosomal delivery system and the promoter/enhancer guided expression ensured that the shRNA inducing TGS was active only in liver cells that had undergone malignant transformation. Our results indicate that such a bimodal therapeutic system induced specific activation of apoptosis in hepatocarcinoma cells due to heterochromatization and increased DNA methylation of the CpG islands around the target loci.

Conclusions

The Sendai virosomal delivery system, combined with AFP promoter/enhancer expression machinery, could serve as a generalized mechanism for the expression of genes deleterious to transformed hepatocarcinoma cells. In this system, the epigenetic suppression of c-Myc could have an added advantage for inducing cell death in the targeted cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-582) contains supplementary material, which is available to authorized users.

A preliminary step of a novel strategy in suicide gene therapy with lentiviral vector

Background:

One of the challenges in lentiviral vector–based suicide gene therapy by toxin or apoptosis-inducing genes is death of packaging cells. Therefore, the process of production of these lentiviral particles would be stopped in this step. We proposed that insertion of a reverse promoter between R and U5 regions of 5′ long terminal repeat (LTR) in transfer plasmid could be considered as a solution for this problem. But it is not known, whether the insertion of RΔU3 sequence between the promoter and target gene in proviral genome during the life-cycle of lentivirus may interfere whit gene expression in target cells.

Materials and Methods:

These following methods were performed in this study: insertion of RΔU3 sequence in pEGFP-N1 plasmid, evaluation of the expression of eGFP gene after calcium phosphate co-precipitation transfection of pCMV-RΔU3-GFP construction in 293T cells, and quantitative assay of eGFP gene by flow cytometry technique.

Results:

Our results from flow cytometry technique analysis showed that there was no significant difference between the expression of eGFP gene in transfected cells with pEGFP-N1 and pCMV-RΔU3-GFP plasmids (P > 0.05).

Conclusion:

In this step of our strategy, we demonstrated that modification of orientation and location of promoter may overcome some issues in lentiviral suicide gene therapy, especially when toxin or apoptosis-inducing genes are used.

Post-translational regulation of gene expression using the ATF4 oxygen-dependent degradation domain for hypoxia-specific gene therapy

Solid tumors have hypoxic regions in their cores, due to low blood supply levels. Therefore, hypoxia-specific gene regulation systems have been developed for tumor-specific gene therapy. In this study, the oxygen-dependent degradation (ODD) domain on activating transcription factor-4 (ATF4) was evaluated for post-translational regulation of proteins. The ATF4 ODD cDNA was amplified by RT-PCR, and a luciferase plasmid containing the ATF4 ODD domain, pSV-Luc-ATF4-ODD, was constructed. Luciferase expression was induced under hypoxia by the ATF4 ODD domain in transfection assays into N2A neuroblastoma cells, C6 glioblastoma cells, and U87 glioblastoma cells. In the transfection assay with pSV-Luc-ATF4-ODD, RT-PCR results showed that the mRNA level did not change under hypoxia. This suggests that the induction of luciferase under hypoxia was mediated by post-translational regulation. A plasmid expressing thymidine kinase from herpes simplex virus (HSV-tk), pSV-HSVtk-ATF4-ODD, was constructed with the ATF4 ODD cDNA. The transfection assay with pSV-TK-ATF4-ODD showed that the ATF4 ODD domain induced HSV-tk expression under hypoxia and facilitated the death of C6 cells in the presence of ganciclovir (GCV). Furthermore, pSV-HSVtk-ATF4-ODD induced caspase-3 activity in the hypoxic cells. In conclusion, the ATF4 ODD may be useful for hypoxia-specific gene therapy by post-translational regulation of gene expression.

Development of a gene therapy strategy to target hepatocellular carcinoma based inhibition of protein phosphatase 2A using the α-fetoprotein promoter enhancer and pgk promoter: an in vitro and in vivo study

Background

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. Current therapies are insufficient, making HCC an intractable disease. Our previous studies confirmed that inhibition of protein phosphatase 2A (PP2A) may provide a promising therapeutic strategy for cancer. Unfortunately, constitutive expression of PP2A in normal tissues limits the application of PP2A inhibition. Thus, a HCC-specific gene delivery system should be developed. The α-fetoprotein (AFP) promoter is commonly used in HCC-specific gene therapy strategies; however, the utility of this approach is limited due to the weak activity of the AFP promoter. It has been shown that linking the AFP enhancer with the promoter of the non-tissue-specific, human housekeeping phosphoglycerate kinase (pgk) gene can generate a strong and HCC-selective promoter.

Methods

We constructed a HCC-specific gene therapy system to target PP2A using the AFP enhancer/pgk promoter, and evaluated the efficiency and specificity of this system both in vitro and in vivo.

Results

AFP enhancer/pgk promoter-driven expression of the dominant negative form of the PP2A catalytic subunit α (DN-PP2Acα) exerted cytotoxic effects against an AFP-positive human hepatoma cell lines (HepG2 and Hep3B), but did not affect AFP-negative human hepatoma cells (SK-HEP-1) or normal human liver cells (L-02). Moreover, AFP enhancer/pgk promoter driven expression of DN-PP2Acα inhibited the growth of AFP-positive HepG2 tumors in nude mice bearing solid tumor xenografts, but did not affect AFP-negative SK-HEP-1 tumors.

Conclusions

The novel approach of AFP enhancer/pgk promoter-driven expression of DN-PP2Acα may provide a useful cancer gene therapy strategy to selectively target HCC.

Current advances in retroviral gene therapy

There have been major changes since the incidents of leukemia development in X-SCID patients after the treatments using retroviral gene therapy. Due to the risk of oncogenesis caused by retroviral insertional activation of host genes, most of the efforts focused on the lentiviral therapies. However, a relative clonal dominance was detected in a patient with β-thalassemia Major, two years after the subject received genetically modified hematopoietic stem cells using lentiviral vectors. This disappointing result of the recent clinical trial using lentiviral vector tells us that the current and most advanced vector systems does not have enough safety. In this review, various safety features that have been tried for the retroviral gene therapy are introduced and the possible new ways of improvements are discussed. Additional feature of chromatin insulators, co-transduction of a suicidal gene under the control of an inducible promoter, conditional expression of the transgene only in appropriate target cells, targeted transduction, cell type-specific expression, targeted local administration, splitting of the viral genome, and site specific insertion of retroviral vector are discussed here.

AFP promoter enhancer increased specific expression of the human sodium iodide symporter (hNIS) for targeted radioiodine therapy of hepatocellular carcinoma

The sodium iodide symporter (NIS) present in the membranes of thyroid cells is responsible for the capacity of the thyroid to concentrate iodide. This allows treatment of thyroid cancers with (131)I. We propose to enlarge the therapeutic strategy to hepatocellular carcinomas by using hepatoma-specific promoter and enhancer for targeted radiotherapy. We constructed a recombinant adenovirus encoding hNIS gene under the control of AFP promoter and enhancer (AdPLEN). After being infected with AdPLEN, HepG2 cells (high AFP-expression hepatoma cells) showed 6 times greater perchlorate-sensitive (125)I uptake than did SMMC7721 cells (low/no AFP-expression hepatoma cells), 30 times higher than Hela (human cervix tumor cells), and noninfected HepG2 cells. These results demonstrate that the AdPLEN vector can function in high AFP expression hepatoma cells. In addition, AdPLEN-infected tumor cells were selectively killed by exposure to (131)I, as revealed by clonogenic assays. To assess the efficiency of this target gene therapy strategy in vivo, we injected the AdPLEN vector in human tumors (HepG2 cells) established in nude mice. Western blotting analysis confirmed the expression of the NIS protein in the tumor. Two days after intratumoral injection, AdPLEN-treated tumors could specifically accumulate (131)I, as revealed by imaging experiments. Altogether, these data indicate that AdPLEN is very efficient in triggering and enlarging significant iodide uptake by hepatocellular carcinomas, outlining the potential of this novel cancer gene therapy approach for a targeted radiotherapy.

Anti-angiogenic gene therapy for hepatocellular carcinoma mediated by microbubble-enhanced ultrasound exposure: an in vivo experimental study

OBJECTIVE

The aim of this study was to assess the effect of anti-angiogenic gene therapy for hepatocelluar carcinoma (HCC) treated by microbubble-enhanced ultrasound exposure.

METHODS

Forty C57BL/6J female mice were inoculated s.c. with Hepa1-6 tumor cell line. Herpes simplex virus thymidine kinase under the control of kinase domain-containing receptor (KDR, angiogenic growth factor's corresponding receptor) promoter was used. Plasmid DNA with or without microbubble contrast agent of SonoVuetrade mark was i.v. injected. Ultrasound (1 MHz, 2 W/cm(2), 5 min) was delivered to hepatic carcinomas in mice. The KDR-tk gene transfer was followed by ganciclovir (GCV) injection for 10 days and then the diameters of tumors were measured every 4 days till 28 days. The survivals of tumor-bearing mice were observed. PCR analysis and immunohistochemistry measurements revealed expression of the transfected gene. Transferase-mediated dUTP nick end labeling staining was used to detect apoptotic cells.

RESULTS

Compared with the group treated by ultrasound alone, KDR-tk gene treatment treated by ultrasound combined with SonoVue restrained tumor growth and increased survival time of tumor-bearing mice; microvessel density in group mediated by ultrasound and SonoVue was significantly lower than that in group ultrasound alone (12.3 +/- 1.4 vs. 27.4 +/- 3.2, P < 0.05). An apoptosis index increased in the group treated by ultrasound and SonoVue compared with the group treated by ultrasound alone (25 +/- 3.6 vs. 36 +/- 3.8, P < 0.05), whereas there was no significant difference between group mediated by SonoVue alone and group phosphate-buffered saline alone (17 +/- 1.8 vs. 14 +/- 1.2, P>0.05).

CONCLUSIONS

Gene therapy mediated by ultrasound exposure enhanced by a microbubble contrast agent may become a new treatment option for persistent HCC.

Retroviral vectors encoding a reverse transcription-activated transgene efficiently limit expression of the gene to target cells

Recombinant retroviral vectors are indispensable tools for the study of gene function and for therapeutic gene transfer owing to their ability to transfer and stably express foreign genes in target cells. A limitation of these vectors, however, is the difficulty in generating stable vector producer cell (VPC) lines when the vectors encode cytotoxic proteins. We developed a series of Moloney murine leukemia virus-based vectors encoding a reverse transcription-activated transgene. These vectors preclude gene expression in the producer cells, yet allow lines for transgene expression in target cells. The vectors were generated by cloning the gene of interest in reverse orientation either just upstream of the viral 3' long terminal repeat (LTR) or in the U3 region of the 3'LTR. An exogenous promoter was inserted, also in reverse orientation, at the R-U5 border of the viral 5'LTR. Upon transduction of target cells, the inserted promoter is copied to the 3'LTR during reverse transcription of the vector genomic RNA, where it then drives transgene expression. We tested this system using a green fluorescent protein (GFP) gene and the SV40 promoter. Reverse transcription-activated retroviral vectors may allow for the generation of stable retroviral VPC lines encoding cytotoxic or inhibitory genes.

Gene- and immunotherapy for hepatocellular carcinoma

For the minority of patients with hepatocellular carcinoma (HCC), surgical or locally ablative therapies may offer the prospect of cure. However, the majority of patients present with advanced disease, such that treatment with curative intent is no longer possible. For some of these patients, with good hepatic reserve and a patent portal venous system, chemoembolisation may afford a modest survival benefit. The remainder of patients are frequently treated with systemic therapies with palliative intent. However, no drug treatment has yet clearly demonstrated a significant beneficial effect on survival or quality of life. Thus, there is an urgent need for novel approaches. Gene- and immunotherapy approaches using a variety of strategies are in development at present. HCC possesses several characteristics that make it an attractive target for these therapies. This review aims to summarise the approaches to gene- and immunotherapy for HCC, with particular reference to strategies that are entering clinical trials. It will then describe some of the obstacles to the success of these new approaches and provide opinion regarding ongoing and future developments. The challenge remains to design clinical trials to optimally evaluate these agents and allow feedback to the laboratory for their ongoing development.

Enhanced efficacy of radiation-induced gene therapy in mice bearing lung adenocarcinoma xenografts using hypoxia responsive elements

The aim of the present study was to investigate whether the hypoxia responsive element (HRE) could be used to enhance suicide gene (HSV-tk) expression and tumoricidal activity in radiation-controlled gene therapy of human lung adenocarcinoma xenografts. A chimeric promoter, HRE-Egr, was generated by directly linking a 0.3-kb fragment of HRE to a 0.6-kb human Egr-1 promoter. Retroviral vectors containing luciferase or the HSV-tk gene driven by Egr-1 or HRE-Egr were constructed. A human adenocarcinoma cell line (A549) was stably transfected with the above vectors using the lipofectamine method. The sensitivity of transfected cells to prodrug ganciclovir (GCV) and cell survival rates were analyzed after exposure to a dose of 2 Gy radiation and hypoxia (1%). In vivo, tumor xenografts in BALB/c mice were transfected with the constructed retroviruses and irradiated to a total dose of 6 Gy, followed by GCV treatment (20 mg/kg for 14 days). When the HSV-tk gene controlled by the HRE-Egr promoter was introduced into A549 cells by a retroviral vector, the exposure to 1% O(2) and 2 Gy radiation induced significant enhancement of GCV cytotoxicity to the cells. Moreover, in nude mice bearing solid tumor xenografts, only the tumors infected with the hybrid promoter-containing virus gradually disappeared after GCV administration and radiation. These results indicate that HRE can enhance transgene expression and tumoricidal activity in HSV-tk gene therapy controlled by ionizing radiation in hypoxic human lung adenocarcinoma.

Preparation and characteristics of DNA-nanoparticles targeting to hepatocarcinoma cells

AIM: To prepare thymidine kinase gene (TK gene) nanoparticles and to investigate the expression of TK gene.

METHODS: Poly(D,L-lactic-co-glycolic acid) (PLGA), a biodegradable and biocompatible polymer, was used to prepare recombinant plasmid P^EGFP-AFP nanoparticles by a double-emulsion evaporation technique. Characteristics of the nanoparticles were investigated in this study, including morphology, entrapment efficiency, and tissue distribution. The expression of TK gene was also investigated by MTT assay, by which the viable cells were determined after the addition of ganciclovir (GCV). The enhanced green fluorescent protein (EGFP) expression in human hepatocellular carcinoma SMMC-7721 cells and normal parenchymal Chang liver cells were assessed by flow cytometry.

RESULTS: The prepared plasmid-nanoparticles had regular spherical surface and narrow particle size span with a mean diameter of 72 ± 12 nm. The mean entrapment efficiency was 91.25%. A total of 80.14% DNA was found to be localized in the livers after 1-h injection with ³²P-DNA-PLGA nanoparticles in mouse caudal vein. The expression of DNA encapsulated in nanoparticles was much higher than that in naked DNA, and human hepatocellular carcinoma SMMC-7721 cells were more sensitive to GCV than human normal parenchymal Chang liver cells.

CONCLUSION: The enhanced transfection efficiency and stronger ability to protect plasmid DNA from being degraded by nucleases are due to nanoparticles encapsulation.

Construction of a targeting adenoviral vector carrying AFP promoter for expressing EGFP gene in AFP producing hepatocarcinoma cell

AIM: To construct a recombinant adenoviral vector carrying AFP promoter and EGFP gene for specific expression of EGFP gene in AFP producing hepatocellular carcinoma (HCC) HepG2 cells.

METHODS: Based on the Adeno-X^TM expression system, the human immediate early cytomegalovirus promoter (P_{CMV IE}) was removed from the plasmid, pshuttle, and replaced by a 0.3 kb α-fetoprotein (AFP) promoter that was synthesized by polymerase chain reaction (PCR). The enhanced green fluorescent protein (EGFP) gene was inserted into the multi-clone site (MCS), and then the recombinant adenovirus vector carrying the 0.3 kb AFP promoter and EGFP gene was constructed. Cells of a normal liver cell line (LO2), a hepatocarcinoma cell line (HepG2) and a cervical cancer cell line (HeLa) were transfected with the adenovirus. Northern blot and fluorescence microscopy were used to detect the expression of the EGFP gene at mRNA or protein level in three different cell lines.

RESULTS: The 0.3 kb AFP promoter was synthesized through PCR from the human genome. The AFP promoter and EGFP gene were directly inserted into the plasmid pshuttle as confirmed by restriction digestion and DNA sequencing. Northern blot showed that EGFP gene was markedly transcribed in HepG2 cells, but only slightly in LO2 and HeLa cells. In addition, strong green fluorescence was observed in HepG2 cells under a fluorescence microscopy, but fluorescence was very weak LO2 and HeLa cells.

CONCLUSION: Under control of the 0.3 kb human AFP promoter, the recombinant adenovirus vector carrying EGFP gene can be specially expressed in AFP-producing HepG2 cells. Therefore, this adenovirus system can be used as a novel, potent and specific tool for gene-targeting therapy for the AFP positive primary hepatocellular carcinoma.

Gene therapy of hepatocarcinoma: a long way from the concept to the therapeutical impact

Hepatocellular carcinoma (HCC), the most prevalent histological form of primary liver cancer is one of the most frequent cancer worldwide. This pathology still requires the development of new therapeutical approaches. Gene therapy strategies focusing on the genetic manipulation of accessory cells involved in the immune reaction against cancer cells, or on the direct transduction of tumor cells with transgenes able to "suicide" cancer cells have been largely developed for more than ten years.

Where do we stand with hepatoblastoma? A review

Hepatoblastoma (HB) is the most common pediatric liver malignancy, comprising approximately 1% of all pediatric cancers. The disparate clinical staging systems and histologic classifications that were developed during the last decades, nevertheless, reflect the remaining difficulties and uncertainties in characterizing HB. Furthermore, the combination of surgery and (neo)adjuvant chemotherapy has improved patient outcomes dramatically. A poor prognosis is associated with large tumor size, multifocality, extrahepatic disease, and metastatic spread. The exact etiology of HB remains unknown, but the cytogenetic alterations, phenotypic features, and biologic aspects that accompany this neoplasm yield more and more insight into its pathogenesis. New cell-biologic and molecular-biologic insights may lead to the development of new treatment modalities, especially for patients with a bad prognosis. This review summarizes the different aspects of this intriguing tumor and discusses the current status of research and treatment for patients with HB.

Insulation from viral transcriptional regulatory elements enables improvement to hepatoma-specific gene expression from adenovirus vectors

We previously reported that the HS-4 insulator, derived from the chicken beta-globin locus, was able to shield a downstream inducible promoter from viral enhancers or silencers present in the genome of adenovirus vectors. In this study, we constructed two recombinant adenoviruses (Ad) that express an alkaline phosphatase (AP) reporter gene driven by an alpha-fetoprotein (AFP) enhancer/promoter with and without HS-4 insulator (Ad.HS4.AFP-AP and Ad.AFP-AP). The insulated vector, Ad.HS4.AFP-AP, conferred significantly higher AP expression than Ad.AFP-AP in all AFP-producing hepatocellular carcinoma cell lines (HepG2, Hep3B, and HuH7) examined. AP expression from Ad.HS4.AFP-AP was specific to hepatoma cells and barely detectable in AFP-negative tumor cell lines and normal human cells, including human hepatocytes. Intravenous infusion of viral vectors into mice with liver metastasis derived from Hep3B hepatoma cells resulted in AP expression exclusively localized to tumor cells. The number of tumor cells with detectable AP expression was significantly higher in mice infused with Ad.HS4.AFP-AP than in mice that received the non-insulated vector. This study demonstrates that the HS-4 insulator in the context of an Ad vector can increase the activity of the AFP promoter, while maintaining its tumor-specificity in vitro and in vivo. Considering that the anti-tumor activity of oncolytic vectors often depends on the level of pro-apoptotic or suicide gene expression, insulators might be a useful tool to improve the efficacy and specificity of these vectors.