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

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Recent progress in the immunotherapy of hepatocellular carcinoma: Non-coding RNA-based immunotherapy may improve the outcome

Hepatocellular carcinoma (HCC) is the second most lethal cancer and a leading cause of cancer-related mortality worldwide. Immune checkpoint inhibitors (ICIs) significantly improved the prognosis of HCC; however, the therapeutic response remains unsatisfactory in a substantial proportion of patients or needs to be further improved in responders. Herein, other methods of immunotherapy, including vaccine-based immunotherapy, adoptive cell therapy, cytokine delivery, kynurenine pathway inhibition, and gene delivery, have been adopted in clinical trials. Although the results were not encouraging enough to expedite their marketing. A major proportion of human genome is transcribed into non-coding RNAs (ncRNAs). Preclinical studies have extensively investigated the roles of ncRNAs in different aspects of HCC biology. HCC cells reprogram the expression pattern of numerous ncRNAs to decrease the immunogenicity of HCC, exhaust the cytotoxic and anti-cancer function of CD8 + T cells, natural killer (NK) cells, dendritic cells (DCs), and M1 macrophages, and promote the immunosuppressive function of T Reg cells, M2 macrophages, and myeloid-derived suppressor cells (MDSCs). Mechanistically, cancer cells recruit ncRNAs to interact with immune cells, thereby regulating the expression of immune checkpoints, functional receptors of immune cells, cytotoxic enzymes, and inflammatory and anti-inflammatory cytokines. Interestingly, prediction models based on the tissue expression or even serum levels of ncRNAs could predict response to immunotherapy in HCC. Moreover, ncRNAs markedly potentiated the efficacy of ICIs in murine models of HCC. This review article first discusses recent advances in the immunotherapy of HCC, then dissects the involvement and potential application of ncRNAs in the immunotherapy of HCC.

Nitroglycerine use in transcatheter arterial (chemo) embolization in patients with hepatocellular carcinoma: Five-year retrospective study

BACKGROUND

Addition of nitroglycerine (NTG) to transcatheter arterial embolization/transarterial chemoembolization (TAE/TACE) has been shown to increase deposition of Lipiodol emulsion in hepatocellular carcinoma (HCC) tumors. The aim of this retrospective study was to evaluate if the addition of nitroglycerin (NTG) to TAE/TACE improved treatment response in HCC.

METHODS

Patients with HCC either received (n=42) or did not receive (non-NTG) (n=111) NTG and an emulsion of Lipiodol with or without doxorubicin, followed by embolization with Gelfoam pledgets. Treatment response was monitored using dual-energy computer tomography (CT). Disease progression and overall survival (OS) were monitored.

RESULTS

The rate of disease progression in the NTG group was 86.5% and in the non-NTG group was 88.6%. Median time to disease progression was 12 months (95% CI; 9.0, 15.0) for the NTG group and 12 months (95% CI; 10.4, 13.6) for the non-NTG groups (P=0.040). No difference was observed in OS between the NTG (60 months) and the non-NTG groups (41 months) (P=0.117). Multivariate analysis found that in the NTG group, OS was associated with Cancer of the Liver Italian Program (CLIP) stage I and Barcelona Clinic Liver Cancer (BCLC) stage B.

CONCLUSIONS

Addition of NTG to TAE/TACE did not result in improved OS or disease progression.

Angiotensin II increases gene expression after selective intra-arterial adenovirus delivery in a rabbit model assessed using in vivo SSTR2-based reporter imaging

Background

Gene therapy has been hampered by low expression upon in vivo delivery. Using a somatostatin receptor type 2 (SSTR2)-based reporter, we assessed whether angiotensin II (AII) can improve gene expression by adenovirus upon intra-arterial (IA) delivery in a large animal model.

Methods

A SSTR2-based reporter that can be imaged by a clinically approved radiopharmaceutical was used to assess gene expression. Eight rabbits bearing VX2 tumors in each thigh were randomly injected IA with adenovirus containing a human SSTR2 (Ad-CMV-HA-SSTR2) gene chimera ± AII or control adenovirus containing green fluorescent protein (Ad-CMV-GFP). Three days later, ¹¹¹In-octreotide was given IV after computed tomography (CT) imaging using a clinical CT scanner and intravenous contrast. Tumor uptake of ¹¹¹In-octreotide was evaluated the next day using a clinical gamma camera. Gene expression was normalized to tumor weight and morphology from CT to obtain in vivo biodistribution.

Results

SSTR2-based expression was readily visualized. VX2 tumors infected with Ad-CMV-HA-SSTR2 upon intra-arterial delivery with AII had greater in vivo biodistribution, thus greater gene expression, than those without AII (p < 0.01, n = 6). VX2 tumors infected with Ad-CMV-HA-SSTR2 upon IA delivery had greater biodistribution, thus greater gene expression, than those with the negative control Ad-CMV-GFP (p < 0.02). Similarly, VX2 tumors infected with Ad-CMV-HA-SSTR2 upon IA delivery with AII had greater biodistribution, thus greater gene expression, than those with the negative control Ad-CMV-GFP (p < 0.01).

Conclusions

Angiotensin II improves in vivo gene expression by adenovirus upon intra-arterial delivery and thus may improve gene therapy efficacy. In vivo SSTR2-based reporter imaging can be used to compare methodologies for improving gene expression.

Cancer immunotherapy via combining oncolytic virotherapy with chemotherapy: recent advances

Oncolytic viruses are multifunctional anticancer agents with huge clinical potential, and have recently passed the randomized Phase III clinical trial hurdle. Both wild-type and engineered viruses have been selected for targeting of specific cancers, to elicit cytotoxicity, and also to generate antitumor immunity. Single-agent oncolytic virotherapy treatments have resulted in modest effects in the clinic. There is increasing interest in their combination with cytotoxic agents, radiotherapy and immune-checkpoint inhibitors. Similarly to oncolytic viruses, the benefits of chemotherapeutic agents may be that they induce systemic antitumor immunity through the induction of immunogenic cell death of cancer cells. Combining these two treatment modalities has to date resulted in significant potential in vitro and in vivo synergies through various mechanisms without any apparent additional toxicities. Chemotherapy has been and will continue to be integral to the management of advanced cancers. This review therefore focuses on the potential for a number of common cytotoxic agents to be combined with clinically relevant oncolytic viruses. In many cases, this combined approach has already advanced to the clinical trial arena.

Oncolytic viruses: a new class of immunotherapy drugs

Oncolytic viruses represent a new class of therapeutic agents that promote anti-tumour responses through a dual mechanism of action that is dependent on selective tumour cell killing and the induction of systemic anti-tumour immunity. The molecular and cellular mechanisms of action are not fully elucidated but are likely to depend on viral replication within transformed cells, induction of primary cell death, interaction with tumour cell antiviral elements and initiation of innate and adaptive anti-tumour immunity. A variety of native and genetically modified viruses have been developed as oncolytic agents, and the approval of the first oncolytic virus by the US Food and Drug Administration (FDA) is anticipated in the near future. This Review provides a comprehensive overview of the basic biology supporting oncolytic viruses as cancer therapeutic agents, describes oncolytic viruses in advanced clinical trials and discusses the unique challenges in the development of oncolytic viruses as a new class of drugs for the treatment of cancer.

Oncolytic adenoviruses: A thorny path to glioma cure

Glioblastoma Multiforme (GBM) is a rapidly progressing brain tumor. Despite the relatively low percentage of cancer patients with glioma diagnoses, recent statistics indicate that the number of glioma patients may have increased over the past decade. Current therapeutic options for glioma patients include tumor resection, chemotherapy, and concomitant radiation therapy with an average survival of approximately 16 months. The rapid progression of gliomas has spurred the development of novel treatment options, such as cancer gene therapy and oncolytic virotherapy. Preclinical testing of oncolytic adenoviruses using glioma models revealed both positive and negative sides of the virotherapy approach. Here we present a detailed overview of the glioma virotherapy field and discuss auxiliary therapeutic strategies with the potential for augmenting clinical efficacy of GBM virotherapy treatment.

Chemotherapy and Oncolytic Virotherapy: Advanced Tactics in the War against Cancer

Cancer is a traitorous archenemy that threatens our survival. Its ability to evade detection and adapt to various cancer therapies means that it is a moving target that becomes increasingly difficult to attack. Through technological advancements, we have developed sophisticated weapons to fight off tumor growth and invasion. However, if we are to stand a chance in this war against cancer, advanced tactics will be required to maximize the use of our available resources. Oncolytic viruses (OVs) are multi-functional cancer-fighters that can be engineered to suit many different strategies; in particular, their retooling can facilitate increased capacity for direct tumor killing (oncolytic virotherapy) and elicit adaptive antitumor immune responses (oncolytic immunotherapy). However, administration of these modified OVs alone, rarely induces successful regression of established tumors. This may be attributed to host antiviral immunity that acts to eliminate viral particles, as well as the capacity for tumors to adapt to therapeutic selective pressure. It has been shown that various chemotherapeutic drugs with distinct functional properties can potentiate the antitumor efficacy of OVs. In this review, we summarize the chemotherapeutic combinatorial strategies used to optimize virally induced destruction of tumors. With a particular focus on pharmaceutical immunomodulators, we discuss how specific therapeutic contexts may alter the effects of these synergistic combinations and their implications for future clinical use.

Trial Watch:: Oncolytic viruses for cancer therapy

Oncolytic viruses are natural or genetically modified viral species that selectively infect and kill neoplastic cells. Such an innate or exogenously conferred specificity has generated considerable interest around the possibility to employ oncolytic viruses as highly targeted agents that would mediate cancer cell-autonomous anticancer effects. Accumulating evidence, however, suggests that the therapeutic potential of oncolytic virotherapy is not a simple consequence of the cytopathic effect, but strongly relies on the induction of an endogenous immune response against transformed cells. In line with this notion, superior anticancer effects are being observed when oncolytic viruses are engineered to express (or co-administered with) immunostimulatory molecules. Although multiple studies have shown that oncolytic viruses are well tolerated by cancer patients, the full-blown therapeutic potential of oncolytic virotherapy, especially when implemented in the absence of immunostimulatory interventions, remains unclear. Here, we cover the latest advances in this active area of translational investigation, summarizing high-impact studies that have been published during the last 12 months and discussing clinical trials that have been initiated in the same period to assess the therapeutic potential of oncolytic virotherapy in oncological indications.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.

Trial watch: Oncolytic viruses for cancer therapy

Oncolytic virotherapy is emerging as a promising approach for the treatment of several neoplasms. The term "oncolytic viruses" is generally employed to indicate naturally occurring or genetically engineered attenuated viral particles that cause the demise of malignant cells while sparing their non-transformed counterparts. From a conceptual standpoint, oncolytic viruses differ from so-called "oncotropic viruses" in that only the former are able to kill cancer cells, even though both display a preferential tropism for malignant tissues. Of note, such a specificity can originate at several different steps of the viral cycle, including the entry of virions (transductional specificity) as well as their intracellular survival and replication (post-transcriptional and transcriptional specificity). During the past two decades, a large array of replication-competent and replication-incompetent oncolytic viruses has been developed and engineered to express gene products that would specifically promote the death of infected (cancer) cells. However, contrarily to long-standing beliefs, the antineoplastic activity of oncolytic viruses is not a mere consequence of the cytopathic effect, i.e., the lethal outcome of an intense, productive viral infection, but rather involves the elicitation of an antitumor immune response. In line with this notion, oncolytic viruses genetically modified to drive the local production of immunostimulatory cytokines exert more robust therapeutic effects than their non-engineered counterparts. Moreover, the efficacy of oncolytic virotherapy is significantly improved by some extent of initial immunosuppression (facilitating viral replication and spread) followed by the administration of immunostimulatory molecules (boosting antitumor immune responses). In this Trial Watch, we will discuss the results of recent clinical trials that have evaluated/are evaluating the safety and antineoplastic potential of oncolytic virotherapy.

Systemic TNFα gene therapy synergizes with liposomal doxorubicine in the treatment of metastatic cancer

Tumor necrosis factor alpha (TNFα) is a potent antitumoral cytokine, either killing tumor cells directly or affecting the tumor vasculature leading to enhanced accumulation of macromolecular drugs. Due to dose limiting side effects systemic administration of TNFα protein at therapeutically active doses is precluded. With gene vectors, tumor restricted TNFα expression can be achieved and in principle synergize with chemotherapy. Synthetic gene carriers based on polyamines were intravenously injected, which either passively accumulate within the tumor or specifically target the epidermal growth factor receptor. A single intravenous injection of TNFα gene vector promoted accumulation of liposomal doxorubicine (Doxil) in murine neuroblastoma and human hepatoma by enhancing tumor endothelium permeability. The expression of transgenic TNFα was restricted to tumor tissue. Three treatment cycles with TNFα gene vectors and Doxil significantly delayed tumor growth in subcutaneous murine Neuro2A neuroblastoma. Also tumors re-growing after initial treatment were successfully treated in a fourth cycle pointing at the absence of resistance mechanisms. Systemic Neuro2A metastases or human LS174T colon carcinoma metastases in liver were also successfully treated with this combined approach. In conclusion, this schedule opens the possibility for the efficient treatment of tumors metastases otherwise not accessible for macromolecular drug carriers.

Nitroglycerine use in transcatheter arterial (chemo)embolization in patients with hepatocellular carcinoma and dual-energy CT assessment of Lipiodol retention

OBJECTIVES

To investigate whether the addition of nitroglycerine to transcatheter arterial (chemo)embolization (TAE/TACE) can increase the delivery and effectiveness of TAE/TACE in patients with hepatocellular carcinoma (HCC) by dual-energy CT.

METHODS

HCC patients (BCLC stage A or B) were randomized to (n = 51) or not to (n = 50) receive nitroglycerine and an emulsion of Lipiodol with or without doxorubicin, followed by embolization with Gelfoam pledgets. Dual-energy CT was performed pre- and 1 to 3 months post-embolization to assess changes in tumour diameter and Lipiodol levels in tumours.

RESULTS

Median tumour diameter decreased from baseline in both groups with and without nitroglycerine (7.11 % vs. 12.5 %, respectively), and was statistically significant in the group receiving nitroglycerine (P = 0.023). There was no difference between the two groups in disease response (P = 0.237). The concentration and percentage of Lipiodol retained in tumours were significantly greater in patients treated with nitroglycerine compared to those without (median concentration 15.05 mg/mL vs. 4.40 mg/mL, respectively, P < 0.001; median percentage 82.01 % vs. 36.75 %, respectively, P < 0.001).

CONCLUSIONS

Nitroglycerine increased delivery of the Lipiodol emulsion via TAE/TACE to HCC tumours with significant tumour reduction. Dual-energy CT can accurately quantify the amount of Lipiodol deposited in tumours.

KEY POINTS

• Nitroglycerine improves delivery of tumour-targeted therapy via enhanced permeability and retention. • In hepatocellular carcinoma, nitroglycerine added to TAE/TACE showed greater tumour reduction. • Dual-energy CT can reliably quantify the amount of Lipiodol in TAE/TACE.

Oncolytic adenovirus based on serotype 3

Oncolytic adenoviruses have been safe in clinical trials but the efficacy has been mostly limited. All published trials have been performed with serotype 5 based viruses. The expression level of the Ad5 receptor CAR may be variable in advanced tumors. In contrast, the Ad3 receptor remains unclear, but is known to be abundantly expressed in most tumors. Therefore, we hypothesized that a fully serotype 3 oncolytic adenovirus might be useful for treating cancer. Patients exposed to adenoviruses develop high titers of serotype-specific neutralizing antibodies, which might compromise re-administration. Thus, having different serotype oncolytic viruses available might facilitate repeated dosing in humans. Ad3-hTERT-E1A is a fully serotype 3 oncolytic adenovirus controlled by the promoter of the catalytic domain of human telomerase. It was effective in vitro on cell lines representing seven major cancer types, although low toxicity was seen in non-malignant cells. In vivo, the virus had anti-tumor efficacy in three different animal models. Although in vitro oncolysis mediated by Ad3-hTERT-E1A and wild-type Ad3 occurred more slowly than with Ad5 or Ad5/3 (Ad3 fiber knob in Ad5) based viruses, in vivo the virus was at least as potent as controls. Anti-tumor efficacy was retained in presence of neutralizing anti-Ad5 antibodies whereas Ad5 based controls were blocked. In summary, we report generation of a non-Ad5 based oncolytic adenovirus, which might be useful for testing in cancer patients, especially in the context of high anti-Ad5 neutralizing antibodies.

Transient increase in intrahepatic pressure mediates successful treatment of the Gunn rat with reduced doses of lentiviral vector

Lentiviral vectors can stably transduce hepatocytes and are promising tools for gene therapy of hepatic diseases. Although hepatocytes are accessible to blood-borne viral vectors through fenestrations of the hepatic endothelium, improved liver transduction after delivery of vectors to the blood stream is needed. As the normal endothelial fenestration and lentiviral vectors are similar in size (150 nm), we hypothesized that a transient increase in hepatic blood pressure may enhance in vivo gene transfer to hepatocytes. We designed a simple surgical procedure, by which the liver is temporarily excluded from blood flow. Lentiviral vectors were injected in a large volume to increase intrahepatic pressure. We demonstrated that in the Gunn rat, a model of Crigler-Najjar disease, the administration of low vector doses (corresponding to a multiplicity of infection of 0.2) by this procedure resulted in therapeutic correction of hyperbilirubinemia, without toxicity. The correction was sustained for 10 months (end of study). The same vector amounts yielded only partial correction after intraportal delivery. We believe that this new and clinically applicable strategy may broaden the range of genetic liver diseases accessible to gene therapy.

Dendrimer-based nanoparticles for cancer therapy

Recent work has suggested that nanoparticles in the form of dendrimers may be a keystone in the future of therapeutics. The field of oncology could soon be revolutionized by novel strategies for diagnosis and therapy employing dendrimer-based nanotherapeutics. Several aspects of cancer therapy would be involved. Diagnosis using imaging techniques such as MRI will be improved by the incorporation of dendrimers as advanced contrast agents. This might involve novel contrast agents targeted specifically to cancer cells. Dendrimers can also be being applied to a variety of cancer therapies to improve their safety and efficacy. A strategy, somewhat akin to the "Trojan horse," involves targeting anti-metabolite drugs via vitamins or hormones that tumors need for growth. Further applications of dendrimers in photodynamic therapy, boron neutron capture therapy, and gene therapy for cancer are being examined. This presentation will cover the fundamentals of research utilizing dendrimers for cancer diagnosis and therapy. An evaluation of this new technologies will detail what advantage dendrimer based therapeutics might have over conventional cancer drugs.

Bevacizumab increases viral distribution in human anaplastic thyroid carcinoma xenografts and enhances the effects of E1A-defective adenovirus dl922-947

PURPOSE

Anaplastic thyroid carcinoma is a prime target for innovative therapy because it represents one of the most lethal human neoplasms and is refractory to conventional treatments such as chemotherapy and radiotherapy. We have evaluated a novel therapeutic approach based on the oncolytic replication-selective adenovirus dl922-947.

EXPERIMENTAL DESIGN

The antitumor efficacies of the E1ADeltaCR2 (dl922-947) and DeltaE1B55K (dl1520) mutants were compared in human thyroid anaplastic carcinoma cells in culture and in xenografts in vivo. To enhance the effects of dl922-947, anaplastic thyroid carcinoma tumor xenografts were treated with dl922-947 in combination with bevacizumab.

RESULTS

We showed that the efficacy of dl922-947 exceeded that of dl1520 in all tested anaplastic thyroid carcinoma cells in vitro and in vivo. Furthermore, bevacizumab in combination with dl922-947 significantly reduced tumor growth compared with single treatments alone. Bevacizumab treatment significantly improved viral distribution in neoplastic tissues.

CONCLUSIONS

Our data showed that dl922-947 had a higher oncolytic activity compared with dl1520 in anaplastic thyroid carcinoma cell lines and might represent a better option for virotherapy of anaplastic thyroid carcinoma. Moreover, bevacizumab increased the oncolytic effects of dl922-947 by enhancing viral distribution in tumors. The results described herein encourage the use of the dl922-947 virus in combination with bevacizumab.

Replication competent Semliki Forest virus prolongs survival in experimental lung cancer

We evaluated the therapeutic potential of the replication competent vector VA7-EGFP, which is based on the avirulent Semliki Forest virus (SFV) strain A7 (74) carrying the EGFP marker gene in an orthotopic lung cancer tumor model in nude mice. We have previously shown that this oncolytic vector destroys tumor cells efficiently in vitro and in vivo (in subcutaneous tumor model). Tumor growth in animals with orthotopically implanted adenocarcinoma cells (A549) were monitored during the study with small animal CT. We show that locally administered virotherapy with VA7-EGFP increased survival rate in experimental lung cancer significantly (p < 0.001) comparable to results obtained with the second generation conditionally replicating adenoviral vector Ad5-Delta24TK-GFP, used for comparison. The limited efficacy in systemically administered oncolytic viruses is the essential problem in oncolytic virotherapy and also in this study we were not able to elicit significant response with systemic administration route. Despite the fact that tumor microenvironment in orthotopic lung cancer is more optimal, viruses failed to home to the tumors and were unable to initiate efficient intratumoral replication. Clearly, the efficacy of virotherapy is influenced by many factors such as the route of virus administration, immunological and physiological barriers and cancer cell-specific features (IFN-responsiveness).

A quantitative proteomic approach for identification of potential biomarkers in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. In this study, our objective was to identify differentially regulated proteins in HCC through a quantitative proteomic approach using iTRAQ. More than 600 proteins were quantitated of which 59 proteins were overexpressed and 92 proteins were underexpressed in HCC as compared to adjacent normal tissue. Several differentially expressed proteins were not implicated previously in HCC. A subset of these proteins (six each from upregulated and downregulated groups) was further validated using immunoblotting and immunohistochemical labeling. Some of the overexpressed proteins with no previous description in the context of HCC include fibroleukin, interferon induced 56 kDa protein, milk fat globule-EGF factor 8, and myeloid-associated differentiation marker. Interestingly, all the enzymes of urea metabolic pathway were dramatically downregulated. Immunohistochemical labeling confirmed differential expression of fibroleukin, myeloid associated differentiation marker and ornithine carbamoyl transferase in majority of HCC samples analyzed. Our results demonstrate quantitative proteomics as a robust discovery tool for the identification of differentially regulated proteins in cancers.

Tumor associated stromal cells play a critical role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses

The clinical efficacy of conditionally replicative oncolytic adenoviruses (CRAd) is still limited by the inefficient infection of the tumor mass. Since tumor growth is essentially the result of a continuous cross-talk between malignant and tumor-associated stromal cells, targeting both cell compartments may profoundly influence viral efficacy. Therefore, we developed SPARC promoter-based CRAds since the SPARC gene is expressed both in malignant cells and in tumor-associated stromal cells. These CRAds, expressing or not the Herpes Simplex thymidine kinase gene (Ad-F512 and Ad(I)-F512-TK, respectively) exerted a lytic effect on a panel of human melanoma cells expressing SPARC; but they were completely attenuated in normal cells of different origins, including fresh melanocytes, regardless of whether cells expressed or not SPARC. Interestingly, both CRAds displayed cytotoxic activity on SPARC positive-transformed human microendothelial HMEC-1 cells and WI-38 fetal fibroblasts. Both CRAds were therapeutically effective on SPARC positive-human melanoma tumors growing in nude mice but exhibited restricted efficacy in the presence of co-administered HMEC-1 or WI-38 cells. Conversely, co-administration of HMEC-1 cells enhanced the oncolytic efficacy of Ad(I)-F512-TK on SPARC-negative MIA PaCa-2 pancreatic cancer cells in vivo. Moreover, conditioned media produced by stromal cells pre-infected with the CRAds enhanced the in vitro viral oncolytic activity on pancreatic cancer cells, but not on melanoma cells. The whole data indicate that stromal cells might play an important role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses.

Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

The liver is the site of numerous metabolic inherited diseases. It has unique features that make it compliant to various gene therapy approaches. Many vector types and gene delivery strategies have been evaluated during the past 20 years in a number of animal models of metabolic liver diseases. However, the complete cure of inherited liver deficiencies by gene therapy in relevant animal models were only reported recently. These successes were achieved thanks to major advances in vector technology. In this review, we will focus on Crigler-Najjar disease and hereditary tyrosinemia, two paradigmatic examples of the two categories of enzymatic liver deficiencies: type I, in which the genetic defect does not affect liver histology; and type II, in which liver lesions are present.

Oncolytic viruses in cancer therapy

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature’s own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.

High volume hydrodynamic injection of plasmid DNA via the hepatic artery results in a high level of gene expression in rat hepatocellular carcinoma induced by diethylnitrosamine

BACKGROUND

Hydrodynamic injection of naked plasmid DNA (pDNA) via the tail vein is a safe and effective method of gene transfer to the liver. However, successful gene transfer has yet to be shown for hepatocellular carcinoma (HCC); therefore, we investigated the feasibility and efficacy of hydrodynamic injection via the tail vein and hepatic artery in a diethylnitrosamine (DEN)-induced HCC model in rats.

METHODS

HCC was induced in Sprague-Dawley rats by 100 ppm DEN in drinking water. pCMV-SPORT-beta-galactosidase (beta-gal, 400 microg) was injected (i) via the tail vein in a volume of 0.1 ml/g in 30 s or (ii) via the hepatic artery in a volume of 5 or 10 ml at 1 ml/s, either with or without temporary occlusion of the inferior vena cava (IVC) and portal vein (PV). The liver was harvested 24 h after administration, and beta-gal expression was evaluated with X-gal staining and measurement of enzymatic activity in tissue homogenates.

RESULTS

Hydrodynamic injection via the tail vein achieved transgene expression only in non-cancerous tissue (tumor: 0.16 +/- 0.04%, non-tumor: 5.07 +/- 1.66%). Hydrodynamic injection via the hepatic artery was tolerated, but failed to produce efficient transgene expression in tumor and non-tumor cells. On the other hand, concomitant use of temporary IVC/PV occlusion with hydrodynamic injection via the hepatic artery dramatically increased transgene expression in cancer cells, but tumor-selective gene transfer was not achieved with this procedure (tumor: 7.38 +/- 3.66%, non-tumor: 7.77 +/- 1.06%).

CONCLUSIONS

High-volume hydrodynamic injection of a pDNA solution via the hepatic artery with IVC/PV occlusion achieved a high level of gene expression in a HCC rat model. This gene transfer technique may have potential in clinical gene therapy for HCC.

Oncolytic capacity of attenuated replicative semliki forest virus in human melanoma xenografts in severe combined immunodeficient mice

Oncolytic viruses have gained attention as a novel form of cancer treatment. Many viral vectors in use today have been rendered safe by deletion of genes encoding viral structural proteins, thus making them unable to spread beyond the first infected cells. Hence, such replication-deficient constructs may lack efficacy. Here, we analyzed the oncolytic potential of the replication-competent vector VA7-EGFP, based on the avirulent Semliki Forest virus (SFV) strain A7(74), to kill cancer cells in culture as well as to target s.c. human melanoma xenografts in severe combined immunodeficient (SCID) mice. VA7-EGFP was able to infect most cancer cell lines studied, leading to complete lysis of the cells within 72 hours after infection. In SCID mice grafted with A2058 human melanoma, marked regression of the xenografts was observed following a single injection of 10(6) plaque-forming units of virus given either i.p., i.v., or intratumorally. Histologic analysis revealed the presence of virus not only in all treated tumors but also in the brains of the treated mice, causing progressing neuropathology beginning at day 16 after infection. Following initial oncolysis, clusters of viable tumor cells were observed embedded in connective tissue, and at later stages, encapsulated tumor nodules had formed. Infection of melanoma cells from explant cultures of these nodules revealed that a portion of the cells were resistant to virus. To be eligible for use in virotherapy, the ability of avirulent SFV to spread within tumor tissue may have to be improved and the biological safety of the virus may have to be addressed thoroughly in higher animals.

Melanoma cultures show different susceptibility towards E1A-, E1B-19 kDa- and fiber-modified replication-competent adenoviruses

Replicating adenovirus (Ad) vectors with tumour tissue specificity hold great promise for treatment of cancer. We have recently constructed a conditionally replicating Ad5 AdDeltaEP-TETP inducing tumour regression in a xenograft mouse model. For further improvement of this vector, we introduced four genetic modifications and analysed the viral cytotoxicity in a large panel of melanoma cell lines and patient-derived melanoma cells. (1) The antiapoptotic gene E1B-19 kDa (Delta19 mutant) was deleted increasing the cytolytic activity in 18 of 21 melanoma cells. (2) Introduction of the E1A 122-129 deletion (Delta24 mutant), suggested to attenuate viral replication in cell cycle-arrested cells, did not abrogate this activity and increased the cytolytic activity in two of 21 melanoma cells. (3) We inserted an RGD sequence into the fiber to extend viral tropism to alphav integrin-expressing cells, and (4) swapped the fiber with the Ad35 fiber (F35) enhancing the tropism to malignant melanoma cells expressing CD46. The RGD-fiber modification strongly increased cytolysis in all of the 11 CAR-low melanoma cells. The F35 fiber-chimeric vector boosted the cytotoxicity in nine of 11 cells. Our results show that rational engineering additively enhances the cytolytic potential of Ad vectors, a prerequisite for the development of patient-customized viral therapies.

Intra-arterial adenoviral mediated tumor transfection in a novel model of cancer gene therapy

Background

The aim of the present study was to develop and characterize a novel in vivo cancer gene therapy model in which intra-arterial adenoviral gene delivery can be characterized. In this model, the rat cremaster muscle serves as the site for tumor growth and provides convenient and isolated access to the tumor parenchyma with discrete control of arterial and venous access for delivery of agents.

Results

Utilizing adenovirus encoding the green fluorescent protein we demonstrated broad tumor transfection. We also observed a dose dependant increment in luciferase activity at the tumor site using an adenovirus encoding the luciferase reporter gene. Finally, we tested the intra-arterial adenovirus dwelling time required to achieve optimal tumor transfection and observed a minimum time of 30 minutes.

Conclusion

We conclude that adenovirus mediated tumor transfection grown in the cremaster muscle of athymic nude rats via an intra-arterial route could be achieved. This model allows definition of the variables that affect intra-arterial tumor transfection. This particular study suggests that allowing a defined intra-tumor dwelling time by controlling the blood flow of the affected organ during vector infusion can optimize intra-arterial adenoviral delivery.

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.

Bifunctional chimeric SuperCD suicide gene -YCD: YUPRT fusion is highly effective in a rat hepatoma model

AIM

To investigate the effects of catalytically superior gene-directed enzyme prodrug therapy systems on a rat hepatoma model.

METHODS

To increase hepatoma cell chemosensitivity for the prodrug 5-fluorocytosine (5-FC), we generated a chimeric bifunctional SuperCD suicide gene, a fusion of the yeast cytosine deaminase (YCD) and the yeast uracil phosphoribosyltransferase (YUPRT) gene.

RESULTS

In vitro stably transduced Morris rat hepatoma cells (MH) expressing the bifunctional SuperCD suicide gene (MH SuperCD) showed a clearly marked enhancement in cell killing when incubated with 5-FC as compared with MH cells stably expressing YCD solely (MH YCD) or the cytosine deaminase gene of bacterial origin (MH BCD), respectively. In vivo, MH SuperCD tumors implanted both subcutaneously as well as orthotopically into the livers of syngeneic ACI rats demonstrated significant tumor regressions (P<0.01) under both high dose as well as low dose systemic 5-FC application, whereas MH tumors without transgene expression (MH naive) showed rapid progression. For the first time, an order of in vivo suicide gene effectiveness (SuperCD>> YCD>>BCD>>>negative control) was defined as a result of a direct in vivo comparison of all three suicide genes.

CONCLUSION

Bifunctional SuperCD suicide gene expression is highly effective in a rat hepatoma model, thereby significantly improving both the therapeutic index and the efficacy of hepatocellular carcinoma killing by fluorocytosine.

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.

Treatment of multi-focal colorectal carcinoma metastatic to the liver of immune-competent and syngeneic rats by hepatic artery infusion of oncolytic vesicular stomatitis virus

Viruses that replicate selectively in cancer cells hold considerable promise as novel therapeutic agents for the treatment of malignancy. We report an orthotopic model of multi-focal colorectal cancer (CRC) metastases in the livers of syngeneic and immune-competent rats, which permitted rigorous testing of oncolytic virus vectors as novel therapeutic agents through hepatic arterial infusion for efficacy and safety. Vesicular stomatitis virus (VSV) is a negative-strand RNA virus with intrinsic oncolytic specificity due to attenuated anti-viral responses in many tumors. After administration at the maximum tolerated dose, the recombinant VSV vector gained access to multi-focal hepatic CRC lesions that led to tumor-selective viral replication and oncolysis. No relevant vector-associated toxicities were noted and in particular, no damage to the hepatic parenchyma was seen. Moreover, the survival rate of vector-treated rats was significantly improved over that of animals in the control treatment group (p = 0.015). Our results demonstrate that hepatic arterial administration of oncolytic VSV is both effective and safe in an immune-competent and syngeneic rat model of multi-focal CRC liver metastasis, suggesting that it can be developed into an effective therapeutic modality in patients in the future.

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.

Eradication of advanced hepatocellular carcinoma in rats via repeated hepatic arterial infusions of recombinant VSV

Viruses that replicate selectively in cancer cells hold considerable promise as novel therapeutic agents for the treatment of malignancy. Vesicular stomatitis virus (VSV) is a nonpathogenic RNA virus with intrinsic oncolytic specificity due to attenuated antiviral responses in many tumors. We report that repeated hepatic arterial infusion of recombinant syncytia-forming VSV vector in advanced multifocal hepatocellular carcinoma (HCC)-bearing rats at a 10-fold reduced vector dose resulted in sustained tumor-selective virus replication until the onset of high-titer neutralizing antibodies in blood. No significant elevations in serum transaminases and liver pathology were noted, indicating a lack of hepatotoxicity. Substantially improved tumor response was achieved with completely necrotic tumor nodules surrounded by mononuclear phagocytic cells, followed by fibrosis and calcification of the lesions, angiogenesis, and regeneration of normal hepatic parenchyma. Survival of tumor-bearing rats treated with repeated vector infusions was not only significantly improved over that of animals after a single injection at 10 times the vector dose (P = .001), but 18% of animals in the former treatment group also achieved long-term and tumor-free survival compared with 0% of animals in the latter treatment group. In conclusion, this treatment regimen will be very useful in the future development of VSV-mediated virotherapy as a novel therapeutic modality for patients with advanced HCC.

Xenograft models for liver metastasis: Relationship between tumor morphology and adenovirus vector transduction

The improvement of initial tumor cell transduction with viral vectors is a major task in tumor gene therapy. We have developed mouse tumor models with hepatic metastases to study transduction of tumor cells after systemic adenovirus vector application. The tumor models were established by intraportal transplantation of human tumor cell lines into immunodeficient mice. Liver metastases derived from cervix, colon, breast, and liver cancer lines were analyzed for distribution of extracellular matrix, vascularization, and transgene expression after tail vein injection of adenovirus vectors. Overall, xenografts resembled the morphology of corresponding tumors in cancer patients. Adenovirus-mediated gene delivery depended on tumor vascularization and direct contact between blood vessels and tumor cells. These models represent important tools for studying and improving tumor gene therapy approaches.

Liver gene therapy: advances and hurdles

Liver gene therapy is being developed as an alternative to orthotopic liver transplantation, which is the only effective therapy for many liver diseases. The liver has unique features that make it attractive for in vivo and ex vivo gene transfer. In vivo approach is far less invasive than ex vivo approach, although in most cases, host immune response directed against the transgene product and/or vector particles severely impairs the efficiency of gene transfer, and precludes long-term transgene expression after in vivo gene delivery. Ex vivo approach allows for an elective targeting of the hepatocytes, avoiding that the transgene be expressed in professional antigen-presenting, but is faced with the low in vitro proliferative ability of hepatocytes, and to the low in vivo liver repopulating ability of transplanted cells. In some specific situations where immune response was controlled or transplanted cells had a strong growth advantage over host hepatocytes, gene transfer resulted in long-term and complete correction of a liver genetic defect. In this review, we will outline the liver diseases that may benefit from gene therapy, the vector technology under investigation, the advances and the problems to be overcome.

Liposomal enhancement of the antitumor activity of conditionally replication-competent adenoviral plasmids

Many human tumors have a functional deficiency in p53. Numerous studies have taken advantage of this phenomenon to use a conditionally replication-competent adenovirus (Ad dl1520) that will grow in and lyse tumor cells while sparing normal tissues. However, success has been limited, in part due to difficulties in reaching a sufficiently high proportion of tumor cells. Preexisting or developing immune responses directed toward viral proteins further decrease the efficacy of the approach. We have developed a liposome-encapsulated conditionally replication-competent plasmid based on the dl1520 virus. Like the parent virus, this plasmid generates infectious particles following transfection of p53-defective, but not p53-wild-type tumor cells, but unlike the parent virus it is able to infect CAR-negative tumor cells. The antitumor efficacy of this infectious plasmid was demonstrated in mice with xenografted human tumors, in which it was active after both local and intravenous administration for subcutaneous tumors and following intravenous administration for disseminated malignancy. Activity was retained systemically, even in the presence of neutralizing antibody. Such liposomally encapsulated conditionally replication-competent plasmids may complement the use of conventional viral particles, particularly in settings in which liver uptake of adenoviral vector is undesirable or there are problematic inhibitory effects from humoral immune responses.

A tumor-targeted and conditionally replicating oncolytic adenovirus vector expressing TRAIL for treatment of liver metastases

We have constructed a new capsid-modified adenovirus (Ad) vector that specifically replicates in tumor cells and expresses TNF-related apoptosis-inducing ligand (TRAIL). The Ad capsid contains short-shafted fibers derived from Ad serotype 35, which allow for efficient infection of malignant tumor cells, and largely avoids innate toxicity after intravenous application. Replication-dependent homologous recombination in Ad genomes was used to achieve tumor-specific expression of Ad E1a (to mediate viral replication) and TRAIL (to mediate apoptosis and enhance release of progeny virus from infected cells). We demonstrated that our oncolytic vector (Ad5/35.IR-E1A/TRAIL) induced apoptosis in human tumor cell lines derived from colorectal, lung, prostate, and liver cancer. Both in vitro and in vivo tumor models showed efficient intratumoral spread of this vector. In a model for metastatic colon cancer, tail vein infusion of Ad5/35.IR-E1A/TRAIL resulted in elimination of preestablished liver metastases. Intravenous injection of this vector caused a transient elevation of serum glutamic pyruvic transaminase in tumor-bearing mice, which we attributed to factors released from apoptotic tumor cells. Liver histology analyzed at day 14 after virus injection did not show signs of hepatocellular damage. This new oncolytic vector represents a potentially efficient means for gene therapy of metastatic cancer.

Antibody-directed therapy for human hepatocellular carcinoma

The goals of our research are to develop high-affinity and high-stability antibodies and fragments thereof for targeting tumor-specific antigens in an attempt to develop new therapeutic agents for human hepatocellular carcinoma (HCC). Tumor-associated antigens are excellent targets for drug and gene delivery, and offer the advantage of high cellular specificity. We have explored the use of a monoclonal antibody (Mab) AF-20 raised against a human hepatoma cell line (FOCUS) as a model system. This antibody binds to a 180-kDa homodimeric cell surface glycoprotein with high affinity. The antigen is uniformly expressed in HCC-derived cell lines and human tumors, including those with distant metastasis. There is minimal expression in nontumor tissues, and none detectable in normal liver. Because the AF-20 antigen antibody interactions on the cell surface is rapidly internalized at 37 degrees C, there is an opportunity to deliver cytotoxic payloads to tumor cells. In addition, high-affinity single-chain monoclonal antibody fragments (scFv) have been created using a novel yeast display system. Drug conjugates with AF-20 monoclonal antibodies have been prepared for gene targeting of HCC both in vitro and in vivo using preclinical animal model systems. These studies show that it is possible to generate high-affinity intact scFv antibody fragments that will allow specific tumor targeting of adenoviruses containing suicide genes, chemotherapeutic agents such as methotrexate, and cytotoxic peptides to produce antitumor effects. Therefore, specific antibody targeting of antitumor agents to HCC cells has the potential for therapeutic application in this devastating disease.

Oncolysis of multifocal hepatocellular carcinoma in the rat liver by hepatic artery infusion of vesicular stomatitis virus

Hepatocellular carcinoma (HCC) is a lethal malignancy with poor prognosis and few effective treatments, as well as ever-increasing frequencies in the Western world. Viruses that replicate selectively in cancer cells hold considerable promise as novel therapeutic agents for the treatment of malignancy. Vesicular stomatitis virus (VSV) is a negative-strand RNA virus with intrinsic oncolytic specificity due to significantly attenuated antiviral responses in many tumor cells. The aim of this study was to evaluate the potential of VSV, administered via the hepatic artery, as an effective and safe therapeutic agent for treating "multifocal" HCC in the rat liver. Recombinant VSV vector expressing beta-galactosidase (rVSV-beta-gal) was generated by reverse genetics and infused into the hepatic artery of Buffalo rats bearing orthotopically implanted multifocal HCC. Access by the virus to multifocal HCC lesions in the liver, as well as the kinetic profiles of intratumoral viral replication and spread, was established by X-gal staining of liver and tumor sections. Plaque assays were also performed to determine the infectious viral yields in tumor and normal liver tissues. Pharmacotoxicology studies, including serum chemistries and proinflammatory cytokine production, as well as organ histopathology, were performed. Buffer- or vector-treated tumor-bearing rats were followed for survival and the results were analyzed by the Kaplan-Meier method and the log-rank test. Hepatic arterial infusion of rVSV-beta-gal at the maximum tolerated dose in tumor-bearing rats resulted in efficient viral transduction of multifocal HCC lesions in their livers, tumor-selective viral replication, and extensive oncolysis. Importantly, no significant vector-associated toxicities were noted and, in particular, no damage to the hepatic parenchyma was seen. Finally, survival of vector-treated rats was substantially prolonged over that of animals in the control treatment group (p < 0.028). Thus, hepatic arterial administration of VSV is both effective and safe in an orthotopic animal model of multifocal HCC. The results suggest that oncolytic VSV can be developed into an effective and safe therapeutic modality for patients with multifocal HCC in the future.

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.

Targeted delivery of adenoviral vectors by cytotoxic T cells

Effective targeting of vectors to tumor cells that have metastasized to multiple different tissue sites remains a major challenge for gene therapy. Tumor-specific cytotoxic T lymphocytes (CTLs) have been shown in animal models and in humans to be able to cross tissue barriers and traffic to tumor cells. However, their capacity to eliminate malignancy has been limited by tumor immune evasion strategies. We now use a model of Epstein-Barr virus-mediated malignancy to show that human CTLs themselves may be modified to release therapeutic vectors following engagement of their antigen-specific receptors and that these vectors will effectively transduce and destroy tumor targets. We generated EBV-specific CTLs that were transgenic for the adenoviral E1 gene under the control of the cell activation-dependent CD40 ligand (CD40L) promoter. Following transduction with E1-deficient adenoviral vectors, these CTLs produced infectious virus when exposed to HLA-matched EBV-expressing targets, but not on exposure to major histocompatibility complex (MHC)-mismatched or otherwise irrelevant cells. This approach provides a means of delivering oncolytic/therapeutic vectors not only to locally accessible macroscopic tumors as is presently the case, but also to disseminated metastatic disease, while avoiding the risks associated with systemic administration of large doses of adenoviral vectors.

Biocompatibility of adenoviral vectors in poly(vinyl chloride) tubing catheters with presence or absence of plasticizer di-2-ethylhexyl phthalate

Adenoviral (Ad) vectors feature attractive characteristics for gene therapy of a wide variety of diseases. In many cases, the Ad vector must be administered using catheters and other plastic medical devices. Although poly(vinyl chloride) is one of the most frequently used catheter materials, it is relatively rigid and requires the addition of a plasticizer such as di-2-ethylhexyl phthalate (DEHP) to increase its flexibility. In this study, we demonstrated that exposure to a DEHP-containing catheter decreased the infectivity of Ad vectors but not the total particle number of the vector. Loss of Ad vector infectivity was directly related to the time of exposure to the DEHP-containing catheter, but it was not due to simple leaching of the chemical from the plastic. The loss of Ad vector infectivity could be prevented by preflushing the tube with albumin. Careful consideration of the compatibility between gene therapy vectors and medical delivery devices will be critical to the success of human gene therapy applications.

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 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.

Specific systemic nonviral gene delivery to human hepatocellular carcinoma xenografts in SCID mice

Systemic tumor-targeted gene delivery is attracting increasing attention as a promising alternative to conventional therapeutical strategies. To be considered as a viable option, however, the respective transgene has to be administered with high tumor specificity. Here, we describe novel polyethylenimine (PEI)-based DNA complexes, shielded by covalent attachment of polyethylene glycol (PEG), that make use of epidermal growth factor (EGF) as a ligand for targeting gene delivery to EGF receptor-expressing human hepatocellular carcinoma (HCC) cells. In vitro transfection of luciferase reporter DNA resulted in high levels of gene expression in the human HCC cell lines Huh-7 and HepG2. An excess of free EGF during transfection clearly reduced expression levels, indicating a specific EGF receptor-mediated uptake of the DNA particles. Following intravenous injection into human HCC xenograft-bearing SCID mice, luciferase expression was predominantly found in the tumor, with levels up to 2 logs higher than in the liver, which was the highest expressing major organ. Histologic investigation showed reporter gene expression (beta-galactosidase) localized to tumor cells. Assessing DNA distribution within the tumor by immunofluorescence microscopy, rhodamine-labelled transgene DNA was found to be mainly associated with HCC cells. In the liver, DNA was taken up almost exclusively by Kupffer cells and, as indicated by the low expression, subsequently degraded. In conclusion, we have shown that intravenous injection of PEGylated EGF-containing DNA/PEI complexes allows for highly specific expression of a transgene in human HCC tumors.

Developments in medical oncology and their implications for interventional radiology

Although surgery and radiation therapy have always been spatially targeted, chemotherapy as administered by oncologists has remained steadfastly committed to non-targeted systemic delivery. Decades of pharmaceutical research have yielded agents appropriate for intravenous use, but countless potentially efficacious agents have been discarded because of pharmacokinetic and toxicity profiles unsuitable for systemic delivery. With the emerging technology of biological agents comes a new series of challenges. These agents tend to be larger, less long-lived, and antigenic when compared with the agents of the past. Meanwhile, interventional radiologists have shown that targeted methods of delivery can have substantial impact on the efficacy and toxicity of agents. Laboratory scientists have developed new bullets; we interventional radiologists have developed new guns. It is time we take advantage of potential synergies.