Gene transfer and therapy with adenoviral vector in rats with diethylnitrosamine-induced hepatocellular carcinoma

Preferential targeting of disseminated liver tumors using a recombinant adeno-associated viral vector

A novel selectively targeting gene delivery approach has been developed for advanced hepatocellular carcinoma (HCC), a leading cause of cancer mortality whose prognosis remains poor. We combine the strong liver tropism of serotype-8 capsid-pseudotyped adeno-associated viral vectors (AAV8) with a liver-specific promoter (HLP) and microRNA-122a (miR-122a)-mediated posttranscriptional regulation. Systemic administration of our AAV8 construct resulted in preferential transduction of the liver and encouragingly of HCC at heterotopic sites, a finding that could be exploited to target disseminated disease. Tumor selectivity was enhanced by inclusion of miR-122a-binding sequences (ssAAV8-HLP-TK-122aT4) in the expression cassette, resulting in abrogation of transgene expression in normal murine liver but not in HCC. Systemic administration of our tumor-selective vector encoding herpes simplex virus-thymidine kinase (TK) suicide gene resulted in a sevenfold reduction in HCC growth in a syngeneic murine model without toxicity. In summary, we have developed a systemically deliverable gene transfer approach that enables high-level expression of therapeutic genes in HCC but not normal tissues, thus improving the prospects of safe and effective treatment for advanced HCC.

Evaluation of miR-122-regulated suicide gene therapy for hepatocellular carcinoma in an orthotopic mouse model

OBJECTIVE

Intratumoral administration of adenoviral vector encoding herpes simplex virus (HSV) thymidine kinase (TK) gene (Ad-TK) followed by systemic ganciclovir (GCV) is an effective approach in treating experimental hepatocellular carcinoma (HCC). However, hepatotoxicity due to unwanted vector spread and suicide gene expression limited the application of this therapy. miR-122 is an abundant, liver-specific microRNA whose expression is decreased in human primary HCC and HCC-derived cell lines. These different expression profiles provide an opportunity to induce tumor-specific gene expression by miR-122 regulation.

METHODS

By inserting miR-122 target sequences (miR-122T) in the 3' untranslated region (UTR) of TK gene, we constructed adenovirus (Ad) vectors expressing miR-122-regulated TK (Ad-TK-122T) and report genes. After intratumoral administration of Ad vectors into an orthotopic miR-122-deficient HCC mouse model, we observed the miR-122-regulated transgene expression and assessed the antitumor activity and safety of Ad-TK-122T.

RESULTS

Insertion of miR-122T specifically down-regulated transgene expression in vitro and selectively protected the miR-122-positive cells from killing by TK/GCV treatment. Insertion of miR-122T led to significant reduction of tansgene expression in the liver without inhibition of its expression in tumors in vivo, resulting in an 11-fold improvement of tumor-specific transgene expression. Intratumoral injection of Ad vectors mediated TK/GCV system led to a vector dosage-dependent regression of tumor. The insertion of miR-122T does not influence the antitumor effects of suicide gene therapy. Whereas mice administrated with Ad-TK showed severe lethal hepatotoxicity at the effective therapeutic dose, no liver damage was found in Ad-TK-122T group.

CONCLUSIONS

miR-122-regulated TK expression achieved effective anti-tumor effects and increased the safety of intratumoral delivery of adenovirus-mediated TK/GCV gene therapy for miR-122-deficient HCC.

Engineering a waste management enzyme to overcome cancer resistance to apoptosis: adding DNase1 to the anti-cancer toolbox

Cancer treatment is often complicated by resistance to conventional anti-cancer treatment and to more recently developed immunotherapy and gene therapy. These therapeutic modalities aim at activating death pathways within cancer cells. Attempts to activate the apoptotic death pathway, by overexpressing proapoptotic signals, are compromised by cancer defense mechanisms, which disrupt the apoptotic-signaling cascade downstream of the overexpressed component. Here, we describe a therapeutic option of triggering apoptosis without activating the apoptotic-signaling cascade or using the native apoptosis executioner nuclease. We have engineered Deoxyribonuclease-1 (DNase1), a waste-management enzyme, by deleting its signal peptide, adding a nuclear localization signal, and mutating its actin-binding site. Apoptosis studies and colony-forming assay for assessing cell viability were conducted in apoptosis-resistant Mel-Juso human melanoma cells. The modified DNase1 reduced cell viability by 77% relative to controls. It also induced typical microscopic features of cellular apoptosis, such as Terminal Transferase dUTP Nick-End Labeling-positive cells and DNA fragmentation. Quantification of apoptosis by Laser scanning cytometry demonstrated high-killing efficiency of 70-100%. The results suggest that this modified DNase1 can efficiently eliminate apoptosis-resistant cancer cells through apoptosis. Coupled to different tissue-specific gene expression elements, this recombinant DNase1 may serve as a platform for eliminating a variety of cancer types.

Efficient recovery of HLA class I expression in human tumor cells after beta2-microglobulin gene transfer using adenoviral vector: implications for cancer immunotherapy

Here we report a successful use of a non-replicating adenovirus expressing the wild-type human beta2m gene in recovery of normal human leucocyte antigen (HLA) class I expression in beta2m-null cancer cells. Total loss of HLA class I expression in these cell lines is caused by a mutation in beta2m gene and a loss of heterozygosity in chromosome 15 carrying another copy of that gene. Normal HLA class I expression on the tumour cell surface is critical for the successful outcome of cancer immunotherapy as T cells can only recognize tumour-derived peptides in a complex with self-HLA class I molecules. In this report we characterize the newly generated adenoviral vector AdCMVbeta2m and demonstrate an efficient beta2m gene transfer in tumour cell lines of different histological origin, including melanoma, prostate and colorectal carcinoma. The beta2m re-expression lasted for an extended period of time both in vitro and in vivo in human tumour xenograft transplants. We propose that in a subset of cancer patients with structural defect in beta2m gene or chromosome 15, the adenoviral-mediated recovery (or even increase) of HLA class I expression on tumour cells in combination with vaccination or adoptive T-cell therapy can provide a complementary approach to improve the clinical efficacy of cancer immunotherapy.

Gene therapy of liver cancer

The application of gene transfer technologies to the treatment of cancer has led to the development of new experimental approaches like gene directed enzyme/pro-drug therapy (GDEPT), inhibition of oncogenes and restoration of tumor-suppressor genes. In addition, gene therapy has a big impact on other fields like cancer immunotherapy, anti-angiogenic therapy and virotherapy. These strategies are being evaluated for the treatment of primary and metastatic liver cancer and some of them have reached clinical phases. We present a review on the basis and the actual status of gene therapy approaches applied to liver cancer.

Cancer-selective induction of cytotoxicity by tissue-specific expression of targetedtrans-splicing ribozyme

For suicide gene therapy to be successfully applied for clinical settings, cancer-restricted expression of such suicide gene should be required. We previously showed that group I intron from Tetrahymena can induce new RNA that exerts anti-cancer activity through RNA replacement by trans-splicing reaction with high fidelity and specificity onto targeted human telomerase reverse transcriptase (hTERT) RNA in cancer cells, and hence the ribozyme can selectively retard growth of the cells in vivo as well as in vitro. However, the shortage of complete tumor-selectivity due to telomerase expression of highly proliferating normal cells can limit therapeutic applicability of the hTERT-targeting approach. In this study, to explore the possibility of improving specificity of cancer therapy, we have attempted to stimulate anticancer gene activity specifically in liver cancer cells by tissue-specific expression of the hTERT-targeting trans-splicing ribozyme using liver-specific promoters. Transient transfection experiments demonstrated that the expression of transgene such as luciferase gene was specifically and highly triggered from hTERT-expressing liver cancer cells transfected with the ribozyme. Moreover, liver-specific expression of the ribozyme with diphtheria toxin A or herpes simplex virus thymidine kinase gene as 3' exon could specifically and highly retard the growth of the hTERT-expressing liver cancer cells. In conclusion, we can greatly improve specificity of cancer cytotoxicity by combination of transcriptional targeting for tissue-specific transgene expression with RNA replacement for cancer-specific anticancer gene induction.

Adenovirus vector-mediated gene transfer using degradable starch microspheres for hepatocellular carcinoma in rats

BACKGROUND

When gene therapy is performed for malignant tumors, gene transfer efficiency and selectivity are extremely important. The delivery of anticancer agents and embolic agents through tumor feeding artery is known as transarterial embolization. We speculated that genes might be efficiently and selectively transferred to hepatocellular carcinomas (HCCs) by degradable starch microspheres (DSM) as the embolic agent, which could be trapped within the tumor and release a gene vector. Therefore, we studied the use of DSM for adenovirus vector-mediated gene transfer to HCC in vivo.

MATERIAL AND METHODS

HCC was induced in rats with diethylnitrosamine and phenobarbital, after which either AxCALacZ and DSM or AxCALacZ alone was injected through the hepatic artery.

RESULTS

Histological examination revealed that beta-galactosidase expression was greater (P < 0.001), and more selective (P < 0.001) in tumors after injection of AxCALacZ and DSM, than after injection of the vector alone.

CONCLUSION

Injection of DSM together with an adenovirus vector through the hepatic artery can result in efficient and cancer-selective transfer of genes to HCC.

Gene therapy strategies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent cancers worldwide. Effective therapy to this cancer is currently lacking, creating an urgent need for new therapeutic strategies for HCC. Gene therapy approach that relies on the transduction of cells with genetic materials, such as apoptotic genes, suicide genes, genes coding for antiangiogenic factors or immunomodulatory molecules, small interfering RNA (siRNA), or oncolytic viral vectors, may provide a promising strategy. The aforementioned strategies have been largely evaluated in the animal models with HCC or liver metastasis. Due to the diversity of vectors and therapeutic genes, being used alone or in combination, gene therapy approach may generate great beneficial effects to control the growth of tumors within the liver.

Gene therapy of liver diseases

Many liver diseases lack satisfactory treatment and alternative therapeutic options are urgently needed. Gene therapy is a new mode of treatment for both inherited and acquired diseases, based on the transfer of genetic material to the tissues. Genes are incorporated into appropriate vectors in order to facilitate their entrance and function inside the target cells. Gene therapy vectors can be constructed on the basis of viral or non-viral molecular structures. Viral vectors are frequently used, due to their higher transduction efficiency. Both the type of vector and the expression cassette determine the duration, specificity and inducibility of gene expression. A considerable number of preclinical studies indicate that a great variety of liver diseases, including inherited metabolic defects, chronic viral hepatitis, liver cirrhosis and primary and metastatic liver cancer, are amenable to gene therapy. Gene transfer to the liver can also be used to convert this organ into a factory of secreted proteins needed to treat conditions that do not affect the liver itself. Clinical trials of gene therapy for the treatment of inherited diseases and liver cancer have been initiated but human gene therapy is still in its infancy. Recent progress in vector technology and imaging techniques, allowing in vivo assessment of gene expression, will facilitate the development of clinical applications of gene therapy.

Future therapies for hepatocellular carcinoma

A large proportion of patients with advanced hepatocellular carcinoma (HCC) lack effective therapy. Due to chemoresistance, hope has focused on other approaches including targeted therapies, immune stimulants, and the emerging area of gene therapy. Increasing efforts in basic and clinical development of these approaches will hopefully result in more efficient therapies against HCC.

The prospects of hepatic drug delivery and gene therapy

Liver targeted therapy is designed to deliver a substance preferentially to the organ in order to increase the accumulation, improve the therapeutic effect and reduce toxicity to other organs. The aim of selective targeting is to deliver a substance to a specific cell type in the liver. A variety of vehicles have been designed and further modified for selective targeting of therapeutics to the liver. The targeting properties and strategies of commonly used agents, such as liposomes, microspheres and recombinant chylomicrons, are discussed. Viral and non-viral vectors, such as cationic liposomes, reconstituted chylomicron remnants, adenoviruses, adeno-associated viruses, retroviruses, and SV-40, are currently being evaluated for the delivery of DNA to the liver. New developments in improving the targeting efficiency of the available vectors while avoiding their disadvantages have made their use in clinical trials of various genetic disorders possible. For viral hepatitis, antisense and ribozyme techniques are being employed with selective targeting approaches. A commonly employed current strategy for targeting hepatocellular carcinoma cells is to make the tumour cells convert non-toxic 'prodrugs' to toxic metabolites in situ, achieving a high concentration of the toxic product in the local milieu, while avoiding systemic toxicity. Although gene therapy itself is in its infancy, some encouraging results have been developed in studies of familial hypercholesterolaemia, haemophilia, alpha1-antitrypsin deficiency and Crigler-Najjar syndrome. The potential strengths as well as the problems with these studies are discussed.

Increased Expression of Metallothionein Is Associated with Irinotecan Resistance in Gastric Cancer

To gain insight into clinically relevant mechanisms of irinotecan resistance, we undertook oligonucleotide microarray analyses on paired malignant effusion samples obtained from eight gastric cancer patients treated with weekly irinotecan. Pretreatment and posttreatment (48 h) effusion samples were obtained for each patient, and the change in expression profile was compared between clinical responders and nonresponders. When differences in the expression of genes were examined using SAM (Significance Analysis of Microarrays) software, five isoforms of the metallothionein family were identified to have significantly higher signal log ratios in five nonresponders, compared with three responders. Compared with control cells, metallothionein 1X (MT1X)-transfected AGS cells showed a 1.4-fold higher irinotecan IC(50) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and tended to form more colonies. These findings collectively suggest that irinotecan-induced up-regulation of metallothionein might be associated with irinotecan resistance in patients with gastric cancer, although it remains to be confirmed in a larger data set.

Biologic therapy of liver tumors

Nonresectable primary and metastatic liver tumors are common malignancies that lack therapies allowing substantial prolongation of survival. Recent progress in molecular and cell biology has opened the way to novel therapies based on biological modifiers, gene transfer, and autologous stem cells. It is now possible to transfer therapeutic genes to the tumor or pericancerous tissue, and to control their expression for long periods of time. It is also feasible to generate autologous endothelial progenitor cells that can be recruited by tumoral vessels acting as vehicles to convey therapeutic genes to the interior of the tumor mass. Combination of biological modifiers, gene therapy, and cell therapy will hopefully provide efficient means to combat inoperable neoplasms in a not-very-distant future.

Herpes simplex virus thymidine kinase-mediated suicide gene therapy for hepatocellular carcinoma using HIV-1-derived lentiviral vectors

BACKGROUND/AIMS

Gene therapy is a promising approach for treatment of hepatocellular carcinoma (HCC). However, transduction of non-tumoral hepatocytes may lead to severe hepatitis when using suicide gene therapy approaches. The aim of our study was to evaluate the gene transfer efficiency into HCC cells and normal hepatocytes using human immunodeficiency virus (HIV)-derived lentiviral vectors in vitro and in vivo.

METHODS

Lentiviral vectors encoding for the LacZ gene or the fusion gene HSV-Tk/GFP were tested in vitro in human HCC cells and human hepatocytes in primary culture and in vivo in a chemically induced rat model of HCC.

RESULTS

We show that HIV-1-derived lentiviral vectors are efficient in transducing HCC cells in vitro and in vivo. No significant transduction of non-tumorous hepatocytes was observed in vivo whatever the route of administration used. Measurement of tumor growth following direct intratumoral injection of a lentiviral vector containing the HSV-Tk gene and GCV treatment showed a strong antitumoral efficacy in the absence of normal liver toxicity.

CONCLUSIONS

These observations suggest that lentiviral vectors allow an antitumoral effect with low liver toxicity when using suicide gene therapy approach and could be efficient tools for HCC gene therapy.

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.

Gene therapy for hepatocellular carcinoma using non-viral vectors composed of bis guanidinium-tren-cholesterol and plasmids encoding the tissue inhibitors of metalloproteinases TIMP-2 and TIMP-3

Metalloproteinases (MMPs) and their natural inhibitors (TIMPs) contribute to the regulation of tumor microenvironment. Their expressions are deregulated in almost all human cancers. We report a novel approach to gene therapy of hepatocellular carcinoma (HCC), using repeated injections of DNA plasmids encoding the tissue inhibitors of metalloproteinases (TIMPs) TIMP-2 or TIMP-3, and a novel competent formulation of gene transfer based on nontoxic cationic cholesterol derivatives. The new gene delivery system was efficient in demonstrating the antitumor efficiency of TIMP-2 or TIMP-3 in inhibiting tumor growth of human HuH7 HCC cells xenografted into nude mice. We show, for the first time, an in vivo effect of TIMP-3 in delaying HCC tumor growth. No treatment-related toxicity was noted. An inhibition of angiogenesis and tumor necrosis accompanied the inhibitory effects of TIMP-2 or TIMP-3 on tumor expansion and invasion. We also report a bystander effect produced by transfected HuH7 tumor cells mixed with untransfected cells in 1:1 ratio in culture that resulted in killing 98% of cells within 96 h. In addition, the soluble forms of TIMP-2 and TIMP-3 expressed by transfected cells exerted a cytotoxic effect on untransfected HuH7 cell cultures. Taken together, these results demonstrate the potential efficacy of repeated treatment of secreted TIMP-2 and TIMP-3 for the design of nonviral gene therapy for hepatocarcinoma.

Construction of a regulable gene therapy vector targeting for hepatocellular carcinoma

AIM: To construct a gene modified hepatocellular carcinoma (HCC) specific EGFP expression vector regulated by abbreviated cis-acting element of AFP gene.

METHODS: The minimal essential DNA segments of AFP gene enhancer and promoter were synthesized through PCR from Genome DNA of HepG2 cells. Gene fragments were then cloned into the multiple cloning site of non-promoter EGFP vector pEGFP-1. Recombinant plasmid was transferred into positive or negative AFP cell lines by means of lipofectamine. The expression of EGFP was tested by fluorescence microscope and flow cytometry. The effect of all-trans retinoic acid (ATRA) on the expression of EGFP was tested in different concentrations.

RESULTS: By the methods of restriction digestion and sequence analyses we confirmed that the length, position and orientation of inserted genes of cis-acting element of AFP were all correct. The transcription of EGFP was under the control of AFP cis-acting element. The expressing EGFP can only been detected in AFP producing hepatoma cells. The expression rate of EGFP in G418 screened cell line was 34.9% ± 4.1%. 48 h after adding 1 × 10^-7 M retinoic acid, EGFP expression rate was 14.7% ± 3.5%. The activity of AFP gene promoter was significantly suppressed by addition of 1 × 10^-7 M retinoic acid (P < 0.05, P = 0.003, t = 6.488).

CONCLUSION: This recombinant expression vector can be used as a gene therapy vector for HCC. The expression of tumor killing gene will be confined within the site of tumor and the activity of which can be regulated by retinoic acid.

Liver failure caused by herpes simplex virus thymidine kinase plus ganciclovir therapy is associated with mitochondrial dysfunction and mitochondrial DNA depletion

Herpes simplex virus thymidine kinase (HSV-tk) converts ganciclovir (GCV) into an active compound, which can be incorporated into DNA molecules and terminate DNA synthesis. Gene transfer of HSV-tk followed by GCV administration has been used with success to treat experimental cancer and this strategy has entered into clinical trials. Although it is thought that the cytotoxic effect occurs mainly in tumoral dividing cells, where mitotic activity favors integration of the genotoxic compound into nuclear DNA, there are concerns of potential damage to normal nondividing cells. In the present work we have explored the mechanisms of HSV-tk/GCV toxicity and in particular whether this therapy may cause lesions of mitochondrial DNA (mtDNA) and mitochondrial dysfunction. We found that the administration of GCV to rats injected with adenovirus encoding HSV-tk induced hepatocellular damage characterized by the presence of apoptotic bodies, ballooning of hepatocytes, and severe hepatic steatosis with mitochondria enlargement and cristae dissolution at the ultrastructural level. Remarkably, Southern blot analysis showed substantial reduction in the amount of mtDNA in the liver. Using radiolabeled GCV we could demonstrate incorporation of this compound into both nuclear and mtDNA in HSV-tk-transduced rat hepatocytic cell line MCA-RH7777 and subsequent alteration of mitochondrial function. Our observations confirm that GCV can damage both nuclear and mtDNA in cells transduced with HSV-tk and that this effect could be responsible for severe mitochondrial dysfunction and toxicity in normal nondividing cells. These data are relevant for the design of clinical trials using adenoviral vectors encoding HSV-tk.

Gene therapy of neoplastic liver diseases

Since advanced liver cancer lacks effective therapy in most cases, a considerable interest has been drawn towards gene therapy. Natural or chimerical genes can be transferred to the tumour itself, the non-tumoral liver, or even distant tissues using a variety of vectors administered by intratumoral or intravascular routes. The desired selectivity in gene expression can be achieved by increasing the specificity of gene delivery or by controlling gene expression with tumour-specific promoters, such as alpha-fetoprotein or carcinoembryonic antigen. There are two main approaches to gene therapy of liver cancer aiming at killing directly malignant cells or at improving the host's defensive systems, respectively. The former include replacing the lost function of tumour suppressor genes, inhibiting the action of activated oncogenes, sensitising tumour cells to prodrugs, or infecting the tumoral tissue with viruses that replicate selectively in cancer cells. Host defences can be improved by stimulating the antitumoral immune response, or by interfering with tumour vessel formation. Progress in gene therapy of liver cancer depends very much on information collected from well-designed clinical trials. This information includes knowledge of whether an efficient gene transfer has been achieved and what is the duration and magnitude of gene expression in the transduced tissues. Hopefully, magnetic resonance or positron emission tomography (PET) may turn out to be reliable procedures for tracing transgene expression in humans. Pre-clinical evidence and early clinical trials strongly suggest that there is a place for gene therapy of liver malignancies.

Inhibition of rat hepatocellular carcinoma tumor growth after multiple infusions of recombinant Ad.AFPtk followed by ganciclovir treatment

BACKGROUND/AIMS

The antitumor efficiency of thymidine kinase (tk) in Herpes Simplex virus-tk-based gene therapy of rat hepatocellular carcinoma (HCC) was examined by specific transcriptional targeting of tk to tumor cells by the alpha-fetoprotein (AFP) gene promoter and by multiple infusions of recombinant adenovirus Ad.AFPtk.

METHODS

We developed a surgical procedure that allows efficient, non-invasive delivery (during 2 months) of recombinant Ad via the intra-hepatic artery (IHA) route.

RESULTS

Treatment of tumor-bearing rats with either three or five doses of 5x10(9)pfu Ad.AFPtk, administered every 3 days, and followed by intra-peritoneal treatment with ganciclovir (GCV), resulted in tumor growth inhibition and apoptosis, when compared to untreated tumor-bearing rats or animals treated with Ad.AFPlacZ or buffered saline. No treatment-related toxicity was noted. Antitumor efficacy, based on tumor size and number of tumors, was demonstrated in more than 50% of Ad.AFPtk+GCV-treated rats, as compared to control rats (P<0.0005).

CONCLUSIONS

Our results demonstrate the safety and potential of multiple Ad.AFPtk administrations by the IHA route to inhibit HCC tumor growth, and support further clinical investigation of Ad.AFPtk gene therapy for treatment of multifocal tumor lesions in most primary liver cancers.

VP22-mediated intercellular transport of p53 in hepatoma cells in vitro and in vivo

The capacity of VP22 chimeric proteins to spread from the primary transduced cell to surrounding cells could improve gene therapy approaches, especially in cancer therapy. However, there are conflicting data about VP22-mediated intercellular trafficking in different studies. To assess the role of VP22 in gene therapy of hepatocellular carcinomas (HCCs) we constructed expression vectors for N- and C-terminal versions of VP22-p53 fusion proteins and investigated the VP22-mediated shuttle effect in hepatoma cells by cotransfection experiments. VP22-mediated trafficking was not detectable in hepatoma cells in vitro by fluorescence microscopy, but reporter gene transactivation assays demonstrated intercellular trafficking of functional VP22-p53 in vitro. For in vivo experiments, the recombinant adenoviruses Ad5CMVp53 and Ad5CMVp53-VP22 were constructed. In contrast to the in vitro experiments intercellular trafficking of VP22-p53 could be observed in subcutaneous tumors of hepatoma cells by fluorescence microscopy, indicating a stronger shuttle effect in solid tumors compared to cell culture experiments. Because spread of p53-VP22 in liver tumors was correlated with enhanced apoptosis of hepatoma cells VP22-mediated trafficking of potential therapeutic proteins may improve the results of gene therapy of HCCs.

Gene therapy of hepatocellular carcinoma and gastrointestinal tumors

Primary liver cancer and liver metastases from gastrointestinal tumors lack effective therapy. Gene therapy is a promising therapeutic approach and is based on the introduction of genetic material into cells to generate a curative biological effect. Adenoviral vectors can very efficiently transduce a wide variety of malignant epithelial cells both in vitro and in vivo. A variety of gene therapy-based anticancer strategies have been effective in animal tumor models, including replacement of tumor suppressor genes, selective activation of prodrugs, genetic immunotherapy, and antiangiogenic actions. Enzymes used for genetic activation include viral thymidine kinase (tk), which may activate nucleoside analogs such as ganciclovir. We and others have demonstrated the efficacy of the tk/ganciclovir system in the treatment of hepatocellular carcinoma and metastatic colorectal cancer in experimental models. Also, this strategy can be safely applied to patients with liver tumors. Interleukin-12 (IL-12) is among the most potent cytokines in stimulating antitumor immunity. In models of primary and metastatic liver cancer we showed that intratumoral administration of recombinant adenovirus encoding IL-12 activates natural killer cells, induces specific antitumor immunity, and displays a powerful antiangiogenic effect, resulting in tumor regression. There is a synergistic effect with the gene transfer of the chemokine IP-10. Also, intratumoral injection of either dendritic cells transfected ex vivo with recombinant adenovirus encoding IL-12 (Ad.IL-12) or an adenovirus coding for the CD40 ligand have shown an intense antitumor effect against experimental colorectal cancer. In summary, a variety of gene therapy strategies have been effective against animal models of gastrointestinal tumors. Clinical trials should determine whether human patients can be treated safely and effectively by such strategies.

Tumor-specific transcriptional targeting of suicide gene therapy

Transcriptional targeting of gene expression has been plagued by the weakness of tissue-specific promoters. Thus, to increase promoter strength while maintaining tissue specificity, we constructed a recombinant adenovirus containing a binary promoter system with a tumor-specific promoter (CEA; carcinoembryonic antigen) driving a transcription transactivator, which then activates a minimal promoter to express a suicide gene (HSV-tk; herpes simplex virus thymidine kinase). This ADV/binary-tk induced equal or greater cell killing in a CEA-specific manner in vitro compared with the CEA-independent killing of a vector with a constitutive viral promoter driving HSV-tk (ADV/RSV-tk). To monitor adenovirus-mediated HSV-tk gene expression in vivo, we employed noninvasive nuclear imaging using a radioiodinated nucleoside analog ([((1)31)I]-FIAU) serving as a substrate for HSV-tk. [((1)31)I]-FIAU-derived radioactivity accumulated after intratumoral injection of ADV/binary-tk only in the area of CEA-positive tumors with significantly less spread to the adjacent liver tissue than after administration of the universally expressed ADV/RSV-tk. Both viruses exhibited similar antitumor efficacy upon injection of liver metastases. Importantly, in vivo dose escalation studies demonstrated significantly reduced toxicity after intravenous administration of ADV/binary-tk versus ADV/RSV-tk. In summary, the increased therapeutic index of this novel, amplified CEA-driven suicide gene therapy vector is a proof of principle for the powerful enhancement of a weak tissue-specific promoter for effective tumor restricted gene expression.

Gene therapy for malignant liver disease

For most patients with advanced or multifocal hepatocellular carcinoma (HCC) or with metastatic malignant liver disease treatment options are limited, resulting in a poor prognosis. Novel therapeutic strategies such as gene therapy are therefore urgently required. Gene therapeutic approaches use gene delivery systems (vectors) to introduce DNA constructs as therapeutic agents into living cells. Antitumour strategies include the reintroduction of tumour suppressor genes into tumour cells, the expression of foreign enzymes to render tumours susceptible to treatment with chemotherapeutic agents and the enhancement of tumour immunogenicity by expressing immunomodulatory genes or by genetic vaccination with tumour antigens. Furthermore, gene therapy may be also used for anti-angiogenesis to reduce tumour growth and metastatic potential. Other novel approaches aim at the development of genetically altered replication competent viruses, which selectively replicate in tumour cells inducing cell lysis. Although most clinical trials of antitumour gene therapy so far have failed to induce strong therapeutic effects, further improvement of antitumour gene therapy may finally result in potent clinical treatment options for patients with malignant liver tumours.

Efficient and cancer-selective gene transfer to hepatocellular carcinoma in a rat using adenovirus vector with iodized oil esters

Gene therapy for cancer requires efficient, selective gene transfer to cancer cells. In gene therapy for hepatocellular carcinoma (HCC), gene transfer is efficient for small tumors, but not for large tumors. The delivery of anticancer agents and of iodized oil esters as embolic agents through tumor-feeding arteries is known as transarterial embolization. We speculate that genes may be efficiently and selectively transferred for HCC using iodized oil esters because these esters may remain together with a genetic vector within HCC selectively. Hence, we have studied the effect of iodized oil esters on adenovirus vector-mediated gene transfer for HCC in vivo. A rat model of HCC induced with diethylnitrosamine and phenobarbital was injected with either AxCALacZ, which expresses the beta-galactosidase of Escherichia coli, or AxCALacZ and iodized oil esters into the hepatic artery. Histological comparisons revealed that the beta-galactosidase expression in the rats with HCC injected with AxCALacZ and iodized oil esters was greater (P<.0001) in small tumors (P=.0046) and large tumors (P=.0023), and more selective (P=.0229) than in only AxCALacZ-injected rats. These results suggest that iodized oil esters are injected into hepatic artery together with adenovirus vector, and that genes may be efficiently and cancer-selectively transferred to HCC.

Hepatic intra-arterial delivery of a retroviral vector expressing the cytosine deaminase gene, controlled by the CEA promoter and intraperitoneal treatment with 5-fluorocytosine suppresses growth of colorectal liver metastases

Targeting of colorectal liver metastases by regional gene therapy was tested in a clinically relevant syngeneic model. First, the CEA-CD-113 retroviral vector containing the cytosine deaminase gene controlled by the CEA specific tumour cell promoter, was shown in vitro to convert 5-fluorocytosine to 5-fluorouracil, resulting in cancer cell killing with a large bystander effect. Second, 10 days after the establishment of liver metastases, retroviral vectors were delivered to the liver by hepatic artery injection. After 5-fluorocytosine administration for 7 days, most surface metastases disappeared and tumour volumes were suppressed up to 8.2-fold. The results support the development of this approach for patient treatment.

Adenovirus-mediated gene transfer to orthotopic hepatocellular carcinomas in athymic nude mice

Gene therapy may become an option for the treatment of malignant tumors such as hepatocellular carcinoma (HCC), once safe and efficient vector systems have been established. Due to their stability in vivo, recombinant adenoviral vectors are promising vectors for gene delivery to HCC. To study the characteristics of gene delivery into HCCs by recombinant adenoviral vectors in vivo, we established an in situ HCC model in the livers of athymic nude mice by intrahepatic injection of human HCC cells. Recombinant adenovirus vectors expressing beta-galactosidase (Ad2CMV beta gal) were injected via the tail vein of mice bearing HCC or directly into intrahepatic tumors. Levels of beta-galactosidase expression in tumor tissue and surrounding normal liver were analyzed by histochemistry or for quantification by a chemiluminescence assay in tissue homogenates. Following tail vein injection, high levels of beta-galactosidase expression were found in the liver, but virtually no gene expression could be detected in the tumor tissue. In contrast, after direct injection of Ad2CMV beta gal into intrahepatic HCCs, high levels of beta-galactosidase expression were detected in the tumor tissue. However, single transduced hepatocytes scattered throughout the normal liver could also be identified. These results indicate that barriers such as the endothelial lining of the tumor vasculature impair the efficiency of adenoviral vectors for gene delivery into HCCs by intravenous administration, which can be overcome by direct injection into the tumor tissue. However, due to the observed transduction of disseminated hepatocytes following intratumoral administration, additional HCC-specific targeting to further enhance the safety of adenoviral vectors may be required.

Intra-arterial delivery of a recombinant adenovirus does not increase gene transfer to tumor cells in a rat model of metastatic colorectal carcinoma

Hepatic artery infusion of adenoviral vectors has been shown to increase transduction of certain hepatocellular malignancies in preclinical studies. In addition, clinical trials have begun evaluating the efficacy of gene transfer of cytotoxic genes to metastatic colorectal tumors through hepatic artery infusion. Here we evaluate the extent of gene expression and therapeutic effect following various routes of administration of recombinant adenovirus in a rat model of metastatic colorectal carcinoma. We administered adenovirus (AdCMVlacZ) to rats with established colorectal metastases through infusion into the hepatic artery, intravenous infusion, or direct injection into a tumor. Intravenous administration resulted in transduction of hepatocytes, but not tumor cells. Hepatic arterial administration failed to substantially increase transduction of tumor cells. In addition, ligation of the hepatic artery following infusion of adenovirus or the addition of lipiodol infusion had no effect on the transduction of tumor cells. We administered AdCMVp53 by direct injection into tumors, intravenous administration, or hepatic artery infusion to evaluate the delivery of a therapeutic gene. Direct injection of AdCMVp53 into established hepatic colorectal metastases resulted in a therapeutic response in comparison with both hepatic arterial and intravenous infusion of vector. These preclinical studies fail to support a strategy of infusion through the hepatic artery of recombinant adenovirus targeting tumor cells in the treatment of colorectal cancer liver metastases.

Sequential histopathological changes in vivo after suicide gene therapy of gastric cancer induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats

Gastrointestinal cancer is the most important clinical target of gene therapy. Suicide gene therapy, such as with the herpes simplex virus type 1 thymidine kinase (HSV-TK) gene, has been shown to exert antitumor efficacy in various cancer models in vitro. We previously reported in situ gene transfer and gene therapy for gastric cancer induced by N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) in dogs. Here, we describe the sequential histopathological changes after suicide gene therapy of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced gastric cancer in rats. Gastric tumors were induced by MNNG in 38 / 73 (52%) of Wistar strain rats. The suicide gene therapy group (14 rats) was subjected to in situ gene transfer with a recombinant adenovirus vector carrying the HSV-TK gene driven by CAG promoter (Ad.CAGHSV-TK) in gastric tumor, followed by the antiviral drug ganciclovir (GCV). To observe the histopathological changes at various times after HSV-TK / GCV gene therapy, groups of animals were sacrificed at 3, 8, and 30 days after gene transfer. Apoptosis in the gastric tumors was detected by the TUNEL method to assess the efficacy of HSV-TK / GCV gene therapy, and it was marked in the 8- and 30-day treatment groups compared to the sham operation controls (P < 0.001). Various histopathological changes, degeneration of cancer tissue and fibrosis after necrosis and apoptosis were significantly greater in the 30-day treatment group. The HSV-TK gene was detectable in peripheral blood by PCR until 30 days after gene transfer. These results may be useful in devising a method of suicide gene therapy for humans.

Cationic liposome-mediated gene delivery to the liver and to hepatocellular carcinomas in mice

The potential of cationic liposomes as nonviral vectors for in vivo gene delivery to the liver and to intrahepatic hepatocellular carcinoma (HCC) was investigated. Mice were injected via the tail vein or portal vein with a cationic lipid complexed to plasmid DNA (pDNA) encoding the chloramphenicol acetyltransferase (CAT) reporter gene at various cationic lipid:pDNA molar ratios to analyze the efficiency of gene delivery after intravenous administration. Tail vein injection resulted in high CAT expression levels in lung and spleen and low levels in the liver. Portal vein injection, by comparison, significantly enhanced hepatic reporter gene expression but also resulted in pronounced hepatic toxicity. Gene delivery to intrahepatic tumors produced by intrahepatic injection of human HCC cells was analyzed in nude mice. Tail vein injection as well as portal vein injection resulted in low levels of gene expression in intrahepatic tumors. By comparison, high levels of gene expression were achieved by direct, intratumoral injection of liposome-pDNA complexes, with only minimal expression in the surrounding normal liver. Therefore, direct liposome-pDNA complex injection appears far superior to systemic or portal intravenous administration for gene therapy of localized intrahepatic tumors, and may be a useful adjunct in the treatment of human HCCs.

Robust prostate-specific expression for targeted gene therapy based on the human kallikrein 2 promoter

Tissue-specific transcriptional regulatory elements can increase the safety of gene therapy vectors. Unlike prostate-specific antigen (PSA/hK3), whose expression displays an inverse correlation with prostate cancer grade and stage, human glandular kallikrein 2 (hK2) is upregulated in higher grade and stage disease. Therefore, our goal was to develop a strong and prostate-specific hK2-based promoter for targeted gene therapy. We identified the minimum "full-strength" hK2 enhancer and built transcriptional regulatory elements composed of multiple tandem copies of this 1.2-kb enhancer, fused to the hK2 minimal promoter. Relative to the weak induction of the minimal hK2 promoter by androgen analog (R1881) in androgen receptor (AR)-positive LNCaP cells, transcriptional activity was increased by 25-, 44-, 81-, and 114-fold when one to four enhancers were spliced to the hK2 promoter, respectively. In contrast, the enhancer/promoter elements were inactive in the AR(-) prostate cancer line PC-3 and in a panel of nonprostate lines, including 293, U87, MCF-7, HuH-7, and HeLa cells. Furthermore, we generated a recombinant adenovirus, ADV.hK2-E3/P-EGFP, expressing enhanced green fluorescent protein (EGFP) under the control of the hK2 triplicate enhancer/promoter, and compared its properties with ADV.CMV-EGFP expressing EGFP under the control of the cytomegalovirus (CMV) enhancer/promoter. Unlike the CMV promoter, the hK2-E3/P promoter was at least 100-fold inducible by R1881 in the adenoviral backbone. Compared with in situ injection of subcutaneous LNCaP tumors with ADV.CMV-EGFP, which led to detectable EGFP expression in tumor, liver, and brain tissue, ADV.hK2-E3/P-EGFP injection led to robust but tumor-restricted EGFP expression. These results suggest that the hk2 multienhancer/promoter should be a powerful novel reagent for safer targeted gene therapy of prostate cancer.

Genetic heterogeneity in the toxicity to systemic adenoviral gene transfer of interleukin-12

Despite the efficacy of IL-12 in cancer experimental models, clinical trials with systemic recombinant IL-12 showed unacceptable toxicity related to endogenous IFNgamma production. We report that systemic administration of a recombinant adenovirus encoding IL-12 (AdCMVmIL-12) has a dramatically different survival outcome in a number of mouse pure strains over a wide range of doses. For instance at 2.5 x 10(9) p.f.u., systemic AdCMVmIL-12 killed all C57BL/6 mice but spared all BALB/c mice. Much higher IFNgamma concentrations in serum samples of C57BL/6 than in those from identically treated BALB/c were found. Causes for heterogeneous toxicity can be traced to differences among murine strains in the levels of gene transduction achieved in the liver, as assessed with adenovirus coding for reporter genes. In accordance, IL-12 serum concentrations are higher in susceptible mice. In addition, sera from C57BL/6 mice treated with AdCMVmIL-12 showed higher levels of IL-18, a well-known IFNgamma inducer. Interestingly, lethal toxicity in C57BL/6 mice was abolished by administration of blocking anti-IFNgamma mAbs and also by simultaneous depletion of T cells, NK cells, and macrophages. These observations together with the great dispersion of IFNgamma produced by human PBMCs upon in vitro stimulation with IL-12, or infection with recombinant adenovirus encoding IL-12, suggest that patients might also show heterogeneous degrees of toxicity in response to IL-12 gene transfer.

Hepatocyte targeting with Gd-EOB-DTPA: potential application for gene therapy

RATIONALE AND OBJECTIVES

To evaluate the suitability of the liver-specific MRI contrast agent Gd-EOB-DTPA as a nonviral vector for gene therapy of hepatocellular carcinoma.

METHODS

Specific uptake of Gd-EOB-DTPA was quantified by relaxometry in rat cultured hepatocytes and the hepatoma cells HepG2 and Huh7. Nonviral vectors for gene transfer were synthesized by coupling Gd-EOB-DTPA to polyethyleneimine or polylysine as DNA condensing agents, and their efficiency was studied using beta-galactosidase (lacZ) as the reporter gene.

RESULTS

Gd-EOB-DTPA was specifically taken up by rat cultured hepatocytes (4.32 vs. 1.08 mmol/L in nonhepatocyte control cells) but not by the hepatoma cells; this uptake was concentration-dependently inhibited by Bromsulphtalein. Polycation linkages were achieved with yields of 0.9 Gd-EOB-DTPA molecule per polyethyleneimine molecule and 10 Gd-EOB-DTPA molecules per polylysine molecule. Incubating the cells with plasmids containing lacZ reporter gene and polyethyleneimine-Gd-EOB-DTPA resulted in a few blue (transfected) cells, whereas no blue cells were observed on incubation with polylysine-Gd-EOB-DTPA.

CONCLUSIONS

Gd-EOB-DTPA is taken up by normal hepatocytes but not by HepG2 and Huh7 cells, probably because of the lack of the organic anion transporter in these hepatoma cells. The Gd-EOB-DTPA polycation conjugates, such as polyethyleneimine-Gd-EOB-DTPA, could serve as transfer vectors of interest for gene targeting imagery at the early stage of hepatocarcinogenesis. However, the transfer efficiency of such conjugates is low and requires improvement.

A blood-tumor barrier limits gene transfer to experimental liver cancer: the effect of vasoactive compounds

We have evaluated gene transfer efficiency to tumor nodules in diethylnitrosoamine (DENA)-induced hepatocellular carcinoma (HCC) in rats using adenoviral vectors administered by three different routes: intraportal, intra-arterial and intratumoral injection. Our results showed that intraportal infusion could not transduce tumor nodules greater than 1 mm in diameter while the intra-arterial route allowed transduction of nodules up to 2-5 mm in diameter. Tumors greater than this size were resistant to transduction by intravascular route, but could be transduced by direct intratumoral injection, indicating that the obstacle preventing gene transfer to tumor cells was mainly at the level of tumor vasculature and not at the level of neoplastic cells. We have studied the extracellular matrix in tumoral lesions to assess whether nodules with different size and histological pattern have different profiles in relation to transduction efficacy. Immunohistochemical detection showed a high expression of fibronectin (FN), laminin (LN) and alpha-smooth muscle actin (alpha-SMA) in those large HCC, which were resistant to adenoviral infection. Intra-arterial infusion of vasoactive compounds (histamine, angiotensin II or nitric oxide donor nitroglycerin) before vector administration enhanced gene transfer to tumor nodules that were poorly transduced without pre-treatment. Nitroglycerin was active to enhance transduction of large tumors with trabecular or pseudoglandular histological pattern, which were impermeable to adenoviral vectors even after histamine or angiotensin treatments. Our data indicate the presence of a physical barrier between blood and neoplastic cells, which prevents transduction of the tumor by vectors given by the intravascular route. The thickness and impermeability of the barrier increases as the tumor nodule grows. Vasoactive compounds may be of value in gene therapy of liver cancer by increasing transduction efficiency by intravascularly administered vectors.

Liver damage using suicide genes. A model for oval cell activation

Liver regeneration from the facultative hepatic stem cells, the oval cells, takes place in situations in which liver regeneration from pre-existing hepatocytes is prevented. Different models have been used to stimulate oval cell response. Many of them involve the use of carcinogenic agents with or without partial hepatectomy. In this study we show that adenovirus-mediated gene transfer of the suicide gene thymidine kinase followed by ganciclovir administration caused hepatotoxicity of variable intensity. Rats with moderate elevation in serum transaminases recovered normal liver architecture few weeks after adenovirus injection. In contrast, rats with severe liver damage exhibited a marked and persisting activation of oval cells accompanied by ductular hyperplasia. In some rats, such lesion eventually evolved to cholangiofibrosis and in one rat to cholangiocarcinoma. Deposition of fibronectin and increased number of hepatic stellate cells were found in association with oval cells and cholangiofibrotic lesions. Hepatocyte growth factor was hyperexpressed in the livers with intense oval cell response or ductular proliferation, suggesting a participation of this factor in those lesions. In summary, our data demonstrate activation of oval cell response after gene transfer of thymidine kinase followed by ganciclovir administration. These findings indicate that high doses of this therapy causes liver damage together with an impairment in hepatocellular regeneration.

Targeting a recombinant adenovirus vector to HCC cells using a bifunctional Fab-antibody conjugate

We developed a specific adenoviral gene delivery system with monoclonal antibody (mAb) AF-20 that binds to a 180 kDa antigen highly expressed on human hepatocellular carcinoma (HCC) cells. A bifunctional Fab-antibody conjugate (2Hx-2-AF-20) was generated through AF-20 mAb crosslinkage to an anti-hexon antibody Fab fragment. Uptake of adenoviral particles and gene expression was examined in FOCUS HCC and NIH 3T3 cells by immunofluorescence; beta-galactosidase expression levels were determined following competitive inhibition of adenoviral CAR receptor by excess fibre knob protein. The chimeric complex was rapidly internalized at 37 degrees C, and enhanced levels of reporter gene expression was observed in AF-20 antigen positive HCC cells, but not in AF-20 antigen negative NIH 3T3 control cells. Targeting of recombinant adenoviral vectors to a tumor associated antigen by a bifunctional Fab-antibody conjugate is a promising approach to enhance specificity and efficiency of gene delivery to HCC.

Transduction of hepatocellular carcinoma (HCC) using recombinant adeno-associated virus (rAAV): in vitro and in vivo effects of genotoxic agents

BACKGROUND/AIMS

Adeno-associated virus (AAV) is an attractive tool for gene therapy. Here we investigated the in vitro and in vivo transduction of hepatocellular carcinoma (HCC) cells by an AAV vector and the efficacy of different strategies to enhance the transduction of the tumor.

METHODS

Transduction efficiency was determined by analyzing AAV-mediated beta-galactosidase gene (rAAV/lacZ) expression.

RESULTS

Adenovirus help or pretreatment of HCC cells with y-irradiation or with the topoisomerase inhibitor etoposide resulted in marked enhancement of cell transduction in vitro. In vivo studies in nude mice with subcutaneous HCC tumors showed that HCC cells were not transduced by AAV vector alone. However, co-infection of the tumor with adenovirus allowed an efficient expression of the reporter gene but only at the sites of vector injection. Previous gamma-irradiation of subcutaneous tumors with 1800 rad was able to improve transduction of HCC cells (up to 30%) using recombinant AAV. Continuous i.p. infusion of etoposide in buffalo rats harboring HCC tumors in the liver resulted in transduction of normal liver tissue and also of very small neoplastic lesions (<2 mm) but no transduction was observed in tumors bigger than 2 mm. To analyze this phenomenon we determined etoposide concentration in hepatic tissue. Our results revealed high concentrations of the drug in non-tumoral tissue but almost undetectable levels in big tumor nodules.

CONCLUSIONS

Our results indicate that while both radiotherapy and etoposide enhance transduction of tumor cells by rAAV in vitro, only radiotherapy increases tumor transduction in vivo. Our data suggest the existence of a barrier which limits in vivo the diffusion of chemotherapeutic agents to well-established HCC nodules.

Intratumoral coinjection of two adenoviruses, one encoding the chemokine IFN-gamma-inducible protein-10 and another encoding IL-12, results in marked antitumoral synergy

We have constructed a recombinant defective adenovirus that expresses functional murine IFN-gamma-inducible protein-10 (IP-10) chemokine (AdCMVIP-10). Injection of AdCMVIP-10 into s.c. tumor nodules derived from the CT26 murine colorectal adenocarcinoma cell line displayed some antitumor activity but it was not curative in most cases. Previous studies have shown that injection of similar s. c. CT26 tumor nodules with adenovirus-encoding IL-12 (AdCMVIL-12) induces tumor regression in nearly 70% of cases in association with generation of antitumor CTL activity. AdCMVIP-10 synergizes with the antitumor effect of suboptimal doses of AdCMVIL-12, reaching 100% of tumor eradication not only against injected, but also against distant noninjected tumor nodules. Colocalization of both adenoviruses at the same tumor nodule was required for the local and distant therapeutic effects. Importantly, intratumoral gene transfer with IL-12 and IP-10 generated a powerful tumor-specific CTL response in a synergistic fashion, while both CD4 and CD8 T cells appeared in the infiltrate of regressing tumors. Moreover, the antitumor activity of IP-10 plus IL-12 combined gene therapy was greatly diminished by simultaneous in vivo depletion of CD4+ and CD8+ T cells but was largely unaffected by single depletion of each T cell subset. An important role for NK cells was also suggested by asialo GM1 depletion experiments. From a clinical point of view, the effects of IP-10 permit one to lower the required gene transfer level of IL-12, thus preventing dose-dependent IL-12-mediated toxicity while improving the therapeutic efficacy of the elicited antitumor response.

Gene therapy of hepatocellular carcinoma in vitro and in vivo in nude mice by adenoviral transfer of the Escherichia coli purine nucleoside phosphorylase gene

Expression of viral or bacterial enzymes in tumor cells to convert nontoxic prodrugs into highly toxic metabolites is an attractive gene-therapeutic approach for the treatment of hepatocellular carcinoma (HCC). The Escherichia coli purine nucleoside phosphorylase (PNP) converts purine analogs into freely diffusible metabolites, which are highly toxic to dividing and nondividing cells. We investigated the antitumor effects of PNP in the human HCC cell lines, HepG2, Hep3B, and HuH-7, and performed a comparison with herpes simplex thymidine kinase (TK). The genes for PNP, TK, and enhanced green fluorescent protein (EGFP) were delivered to HCC cells by identical adenoviral vectors. Fludarabine and ganciclovir (GCV) served as prodrugs for PNP and TK, respectively. Expression of PNP highly sensitized HCC cells to fludarabine treatment. Fludarabine concentrations between 0.5 and 1 microg/mL killed 100% of the cells expressing PNP with no detectable toxicity in control cells expressing EGFP. Expression of PNP in as few as 10% of HCC cells induced efficient killing of most bystander cells. Expression of TK followed by GCV treatment produced a potent growth inhibition but failed to kill all TK-expressing HCC cells. More importantly, the TK system exhibited a lower degree of bystander effect. Adenoviral delivery of PNP followed by fludarabine administration prevented subcutaneous and intrahepatic tumor formation in nude mice and was also effective for the treatment of established tumors. These results demonstrate the potential of the PNP/fludarabine system for the treatment of HCC.

Combined gene therapy with suicide gene and interleukin-12 is more efficient than therapy with one gene alone in a murine model of hepatocellular carcinoma

BACKGROUND/AIMS

Gene therapy has emerged as a new form of treatment for unresectable hepatocellular carcinoma (HCC). We evaluate here the effect of IL-12 and the suicide gene thymidine kinase as single agents and in combination to treat experimental liver cancer.

METHODS

Recombinant adenoviruses expressing mouse interleukin-12 (AdCMVIL-12) or thymidine kinase of herpes simplex virus (AdCMVtk) or lacZ reporter gene (AdCMVlacZ) were constructed. The efficacy of the treatment was evaluated in a murine HCC model based on subcutaneous implantation of liver tumor cells (BNL).

RESULTS

Transduction of BNL cells after in vitro infection with AdCMVlacZ was very low at multiplicity of infection (moi) of 100, whereas 10-15% of cells were transduced when using moi 1,000. Similarly, production of IL-12 was detectable only in BNL cells infected with AdCMVIL-12 at moi 1,000. In vitro infection of BNL cells with AdCMVIL-12 at moi 100 did not abrogate tumorigenicity, whereas moi 1,000 resulted in inhibition of tumor growth in all mice as well as in abrogation of tumor formation in 3 out of 8 animals. In vivo studies showed that intratumor injection of AdCMVIL-12 induced a dose-dependent effect on tumor regression. However, none of the animals exhibited complete tumor elimination with this treatment. We observed that suppression of tumor growth was more intense in animals treated with the combination of AdCMVIL-12 plus AdCMVtk than in animals which received AdCMVtk or AdCMVIL-12 alone. The combined treatment resulted in a significant increase in animal survival, and 25% of treated animals were free of tumor for over 100 days without recurrence of the disease.

CONCLUSIONS

Combination of AdCMVIL-12 and AdCMVtk is more efficient than either of the two vectors alone for the treatment of the murine model of HCC used in this study.

Adenoviral gene transfer of interleukin 12 into tumors synergizes with adoptive T cell therapy both at the induction and effector level

Tumors infected with a recombinant defective adenovirus expressing interleukin 12 (IL-12) undergo regression, associated with a cytotoxic T lymphocyte (CTL)-mediated antitumor immune response. In the present study we generated anti-CT26 CTLs by short-term coculture of CT26 cells and lymph node cells obtained from mice harboring subcutaneous CT26 tumors injected with an adenoviral vector expressing IL-12 (AdCMVIL-12), control adenovirus (AdCMVlacZ), or saline. Regression of small intrahepatic CT26 tumors in unrelated syngeneic animals was achieved with CTLs derived from mice whose subcutaneous tumors had been injected with AdCMVIL-12 but not with CTLs from the other two control groups. The necessary and sufficient effector cell population for adoptive transfer consisted of CD8+ T cells that showed anti-CT26 specificity partly directed against the AH1 epitope presented by H-2Ld. Interestingly, treatment of a subcutaneous tumor nodule with AdCMVIL-12, combined with intravenous adoptive T cell therapy with short-term CTL cultures, had a marked synergistic effect against large, concomitant live tumors. Expression of IL-12 in the liver in the vicinity of the hepatic tumor nodules, owing to spillover of the vector into the systemic circulation, appeared to be involved in the increased in vivo antitumor activity of injected CTLs. In addition, adoptive T cell therapy improved the outcome of tumor nodules transduced with suboptimal doses of AdCMVIL-12. Our data provide evidence of a strong synergy between gene transfer of IL-12 and adoptive T cell therapy. This synergy operates both at the induction and effector phases of the CTL response, thus providing a rationale for combined therapeutic strategies for human malignancies.