A Conditionally Replicating Adenovirus for Nasopharyngeal Carcinoma Gene Therapy

Pathogenesis and therapeutic implications of EBV-associated epithelial cancers

Epstein-Barr virus (EBV), one of the most common human viruses, has been associated with both lymphoid and epithelial cancers. Undifferentiated nasopharyngeal carcinoma (NPC), EBV associated gastric cancer (EBVaGC) and lymphoepithelioma-like carcinoma (LELC) are amongst the few common epithelial cancers that EBV has been associated with. The pathogenesis of EBV-associated NPC has been well described, however, the same cannot be said for primary pulmonary LELC (PPLELC) owing to the rarity of the cancer. In this review, we outline the pathogenesis of EBV-associated NPC and EBVaGCs and their recent advances. By drawing on similarities between NPC and PPLELC, we then also postulated the pathogenesis of PPLELC. A deeper understanding about the pathogenesis of EBV enables us to postulate the pathogenesis of other EBV associated cancers such as PPLELC.

Targeting Epstein-Barr Virus in Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is consistently associated with Epstein-Barr virus (EBV) infection in regions in which it is endemic, including Southern China and Southeast Asia. The high mortality rates of NPC patients with advanced and recurrent disease highlight the urgent need for effective treatments. While recent genomic studies have revealed few druggable targets, the unique interaction between the EBV infection and host cells in NPC strongly implies that targeting EBV may be an efficient approach to cure this virus-associated cancer. Key features of EBV-associated NPC are the persistence of an episomal EBV genome and the requirement for multiple viral latent gene products to enable malignant transformation. Many translational studies have been conducted to exploit these unique features to develop pharmaceutical agents and therapeutic strategies that target EBV latent proteins and induce lytic reactivation in NPC. In particular, inhibitors of the EBV latent protein EBNA1 have been intensively explored, because of this protein's essential roles in maintaining EBV latency and viral genome replication in NPC cells. In addition, recent advances in chemical bioengineering are driving the development of therapeutic agents targeting the critical functional regions of EBNA1. Promising therapeutic effects of the resulting EBNA1-specific inhibitors have been shown in EBV-positive NPC tumors. The efficacy of multiple classes of EBV lytic inducers for NPC cytolytic therapy has also been long investigated. However, the lytic-induction efficiency of these compounds varies among different EBV-positive NPC models in a cell-context-dependent manner. In each tumor, NPC cells can evolve and acquire somatic changes to maintain EBV latency during cancer progression. Unfortunately, the poor understanding of the cellular mechanisms regulating EBV latency-to-lytic switching in NPC cells limits the clinical application of EBV cytolytic treatment. In this review, we discuss the potential approaches for improvement of the above-mentioned EBV-targeting strategies.

Radiogenic Therapy: Novel Approaches for Enhancing Tumor Radiosensitivity

Radiotherapy (RT) is a well established modality for treating many forms of cancer. However, despite many improvements in treatment planning and delivery, the total radiation dose is often too low for tumor cure, because of the risk of normal tissue damage. Gene therapy provides a new adjunctive strategy to enhance the effectiveness of RT, offering the potential for preferential killing of cancer cells and sparing of normal tissues. This specificity can be achieved at several levels including restricted vector delivery, transcriptional targeting and specificity of the transgene product. This review will focus on those gene therapy strategies that are currently being evaluated in combination with RT, including the use of radiation sensitive promoters to control the timing and location of gene expression specifically within tumors. Therapeutic transgenes chosen for their radiosensitizing properties will also be reviewed, these include:

gene correction therapy, in which normal copies of genes responsible for radiation-induced apoptosis are transfected to compensate for the deletions or mutated variants in tumor cells (p53 is the most widely studied example). enzymes that synergize the radiation effect, by generation of a toxic species from endogenous precursors ( e.g., inducible nitric oxide synthase) or by activation of non toxic prodrugs to toxic species ( e.g., herpes simplex virus thymidine kinase/ganciclovir) within the target tissue. conditionally replicating oncolytic adenoviruses that synergize the radiation effect. membrane transport proteins ( e.g., sodium iodide symporter) to facilitate uptake of cytotoxic radionuclides.

The evidence indicates that many of these approaches are successful for augmenting radiation induced tumor cell killing with clinical trials currently underway.

Evaluation of apoptogenic adenovirus type 5 oncolytic vectors in a Syrian hamster head and neck cancer model

Human adenovirus (HAdV) vectors are intensely investigated for virotherapy of a wide variety of human cancers. Here, we have evaluated the effect of two apoptogenic HAdV5 vectors in an immunocompetent Syrian hamster animal model of head and neck cancer. We established two cell lines of hamster cheek pouch squamous cell carcinomas, induced by treatment with 9, 10-dimethyl-1, 2-benzanthracene (DMBA). These cell lines, when infected with HAdV5 mutants lp11w and lp11w/Δ55K (which are defective in the expression of either E1B-19K alone or both E1B-19K and E1B-55K proteins) exhibited enhanced apoptotic and cytotoxic responses. The cheek pouch tumor cells transplanted either subcutaneously at the flanks or in the cheek pouches of hamsters readily formed tumors. Intra-tumoral administration of HAdV5 E1B mutants efficiently suppressed the growth of tumors at both sites. Histological examination of orthotopic tumors revealed reduced vascularity and the expression of the viral fiber antigen in virus-administered cheek pouch tumors. These tumors also exhibited increased caspase-3 levels, suggesting virus-induced apoptosis may contribute to tumor growth suppression. Our results suggest that the apoptogenic HAdV5 vectors may have utility for the treatment of human head and neck cancers.

Chapter seven--Cancer treatment with gene therapy and radiation therapy

Radiation therapy methods have evolved remarkably in recent years which have resulted in more effective local tumor control with negligible toxicity of surrounding normal tissues. However, local recurrence and distant metastasis often occur following radiation therapy mostly due to the development of radioresistance through the deregulation of the cell cycle, apoptosis, and inhibition of DNA damage repair mechanisms. Over the last decade, extensive progress in radiotherapy and gene therapy combinatorial approaches has been achieved to overcome resistance of tumor cells to radiation. In this review, we summarize the results from experimental cancer therapy studies on the combination of radiation therapy and gene therapy.

Minicircle-oriP-IFNγ: a novel targeted gene therapeutic system for EBV positive human nasopharyngeal carcinoma

Background

Nonviral vectors are attractively used for gene therapy owing to their distinctive advantages. Our previous study has demonstrated that transfer of human IFNγ gene into nasopharyngeal carcinoma (NPC) by using a novel nonviral vector, minicircle (mc), under the control of cytomegalovirus (CMV) promoter was effective to inhibit tumor growth. However, therapies based on CMV promoter cannot express the targeted genes in cancer tissues. Previous studies indicated that the development of human NPC was closely associated with Epstein-Barr virus (EBV) and demonstrated the transcriptional enhancer function of oriP when bound by EBV protein. Therefore, the present study is to explore the targeted gene expression and the anti-tumor effect of a novel tumor-specific gene therapeutic system (mc-oriP-IFNγ) in which the transgene expression was under the transcriptional regulation of oriP promoter.

Methodology/Principal Findings

Dual-luciferase reporter assay and ELISA were used to assess the expression of luciferase and IFNγ. WST assay was used to assess the cell proliferation. RT-PCR was used to detect the mRNA level of EBNA1. RNAi was used to knockdown the expression of EBNA1. NPC xenograft models in nude mice were used to investigate the targeted antitumor efficacy of mc-oriP-IFNγ. Immunohistochemistry was used to detect the expression and the activity of the IFNγ in tumor sections. Our results demonstrated that mc-oriP vectors mediated comparable gene expression and anti-proliferative effect in the EBV-positive NPC cell line C666-1 compared to mc-CMV vectors. Furthermore, mc-oriP vectors exhibited much lower killing effects on EBV-negative cell lines compared to mc-CMV vectors. The targeted expression of mc-oriP vectors was inhibited by EBNA1-siRNA in C666-1. This selective expression was corroborated in EBV-positive and -negative tumor models.

Conclusions/Significance

This study demonstrates the feasibility of mc-oriP-IFNγ as a safe and highly effective targeted gene therapeutic system for the treatment of EBV positive NPC.

Down-regulation of multiple cell survival proteins in head and neck cancer cells by an apoptogenic mutant of adenovirus type 5

Head and neck squamous cell carcinomas (HNSCC) are one of the leading causes of cancer deaths world wide. Up-regulation of the epidermal growth factor receptor (EGFR) and BCL-2 family anti-apoptosis proteins in these cancers is linked to aggressive tumor growth, metastasis and chemoresistance. Infection of two HNSCC cell lines, SCC25 and CAL27 by an Ad5 mutant (lp11w) defective in coding for the viral anti-apoptosis protein, E1B-19K efficiently induced apoptotic cell death. In cells infected with lp11w there was a dramatic down-regulation of EGFR by apoptosis-dependent and -independent mechanisms. The levels of the anti-apoptotic proteins BCL-2, BCL-xL and MCL-1 were also down-regulated in lp11w-infected cells compared to uninfected or Ad5-RM infected cells. Infection with lp11w also enhanced sensitivity of the HNSCC cells to the chemotherapeutic drug cisplatin. Our results suggest that adenoviral vectors defective in E1B-19K would be valuable for efficient down-regulation of cell survival proteins and EGFR in epithelial cancers and could be exploited as oncolytic agents to treat HNSCCs.

Therapeutic efficacy of seliciclib in combination with ionizing radiation for human nasopharyngeal carcinoma

PURPOSE

Seliciclib is a small-molecule cyclin-dependent kinase inhibitor, which has been reported to induce apoptosis and cell cycle arrest in EBV-negative nasopharyngeal carcinoma cell lines. Because most nasopharyngeal carcinoma patients harbor EBV, we proceeded to evaluate the cytotoxic effects of seliciclib in EBV-positive nasopharyngeal carcinoma models.

EXPERIMENTAL DESIGN

Cytotoxicity of seliciclib was investigated in the EBV-positive cell line C666-1 and the C666-1 and C15 xenograft models. Caspase activities and cell cycle analyses were measured by flow cytometry. Efficacy of combined treatment of seliciclib with radiation therapy was also evaluated.

RESULTS

Seliciclib caused significant cytotoxicity in the C666-1 cells in a time- and dose-dependent manner, with accumulation of cells in both sub-G(1) and G(2)-M phases, indicative of apoptosis and cell cycle arrest, respectively. Caspase-2, -3, -8, and -9 activities were all increased, with caspase-3 being the most significantly activated at 48 h after treatment. These cells also showed a reduction of Mcl-1 mRNA and protein levels. Combined treatment of seliciclib with radiation therapy showed a synergistic interaction with enhanced cytotoxicity in C666-1 cells and delayed repair of double-strand DNA breaks. For in vivo models, significant delays in tumor growth were observed for both C666-1 and C15 tumors, which were associated with enhanced apoptosis as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and immunohistochemistry analyses.

CONCLUSIONS

Seliciclib enhanced the antitumor efficacy of radiation therapy in EBV-positive nasopharyngeal carcinoma, characterized by G(2)-M arrest, and apoptosis, associated with an induction in caspase activity. This process is mediated by reduction in Mcl-1 expression and by attenuation of double-strand DNA break repair.

Efficacy of systemically administered mutant vesicular stomatitis virus (VSVDelta51) combined with radiation for nasopharyngeal carcinoma

PURPOSE

Nasopharyngeal carcinoma (NPC) is a malignancy of the head and neck region that is associated with EBV latency. Curative treatments for NPC achieve modest survival rates, underscoring a need to develop novel therapies. We evaluated the therapeutic potential of a mutant vesicular stomatitis virus (VSVDelta51) as single treatment modality or in combination with ionizing radiation (RT) in NPC.

EXPERIMENTAL DESIGN

MTS assay was used to assess cell viability in vitro; apoptosis was measured using propidium iodide staining and caspase activation. In vivo experiments were conducted using tumor-bearing nude mice with or without local RT (4 Gy). Apoptosis was assessed in excised tumor sections with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining.

RESULTS

Our data showed that NPC cells are exquisitely sensitive to VSVDelta51 oncolysis, which correlated with the presence of EBV. Efficacy of VSVDelta51 against NPC cells was further augmented when combined with RT. A single systemic injection of VSVDelta51 achieved 50% survival in treated mice, which increased to 83% when combined with local tumor RT. In addition to induction of apoptosis, an antiangiogenic effect of VSVDelta51 was observed in vivo, suggesting a novel tumoricidal mechanism for VSVDelta51. This virus also prevented growth of NPC sphere-forming cells in vitro, showing potential utility in targeting NPC-initiating cells.

CONCLUSIONS

Our data represent the first report showing that EBV-positive NPC cells are exquisitely sensitive to VSVDelta51 oncolysis and documenting the successful utilization of this combinatorial regimen as a novel curative therapeutic strategy for NPC.

Cellular genetic tools to control oncolytic adenoviruses for virotherapy of cancer

Key challenges facing cancer therapy are the development of tumor-specific drugs and the implementation of potent multimodal treatment regimens. Oncolytic adenoviruses, featuring cancer-selective viral cell lysis and spread, constitute a particularly interesting drug platform towards both goals. First, as complex biological agents, adenoviruses allow for rational drug development by genetic incorporation of targeting mechanisms that exert their function at different stages of the viral replication cycle. Secondly, therapeutic genes implementing diverse cancer cell-killing activities can be inserted into the oncolytic adenovirus genome without loss of replication potential, thus deriving a "one-agent combination therapy". This article reviews an intriguing approach to derive oncolytic adenoviruses, which is to insert cellular genetic regulatory elements into adenovirus genomes for control of virus replication and therapeutic gene expression. This approach has been thoroughly investigated and optimized during the last decade for transcriptional targeting of adenovirus replication and gene expression to a wide panel of tumor types. More recently, further cellular regulatory mechanisms, such as mRNA stability and translation regulation, have been reported as tools for virus control. Consequently, oncolytic adenoviruses with a remarkable specificity profile for prostate cancer, gastrointestinal cancers, liver cancer, breast cancer, lung cancer, melanoma, and other cancers were derived. Such specificity profiles allow for the engineering of new generations of oncolytic adenoviruses with improved potency by enhancing viral cell binding and entry or by expressing therapeutic genes. Clearly, genetic engineering of viruses has great potential for the development of innovative antitumor drugs--towards targeted and multimodal cancer therapy.

Nasopharyngeal carcinoma: molecular pathogenesis and therapeutic developments

Nasopharyngeal carcinoma (NPC) is a prevalent tumour in southern China and southeast Asia, particularly in the Cantonese population, where its incidence has remained high for decades. Recent studies have demonstrated that the aetiology of NPC is complex, involving multiple factors including genetic susceptibility, infection with the Epstein-Barr virus (EBV) and exposure to chemical carcinogens. During development of the disease, viral infection and multiple somatic genetic and epigenetic changes synergistically disrupt normal cell function, thus contributing to NPC pathogenesis. NPC is highly radiosensitive and chemosensitive, but treatment of patients with locoregionally advanced disease remains problematic. New biomarkers for NPC, including EBV DNA copy number or methylation of multiple tumour suppressor genes, which can be detected in serum and nasopharyngeal brushings, have been developed for the molecular diagnosis of this tumour. Meanwhile, new therapeutic strategies such as intensity-modulated radiation therapy and immuno- and epigenetic therapies might lead to more specific and effective treatments.

Imaging the modulation of adenoviral kinetics and biodistribution for cancer gene therapy

To explore systemic utilization of Epstein-Barr virus (EBV)-specific transcriptionally targeted adenoviruses, three vectors were constructed to examine kinetics, specificity, and biodistribution: adv.oriP.luc, expressing luciferase under EBV-specific control; adv.SV40luc, expressing luciferase constitutively; and adv.oriP.E1A.oriP.luc, a conditionally replicating adenovirus, expressing both luciferase and E1A. Bioluminescence imaging (BLI) was conducted on tumor-bearing severe combined immunodeficient (SCID) mice (C666-1, EBV-positive human nasopharyngeal cancer) treated intravenously (i.v.) with 3 x 10(8) infectious units (ifu) of the adenoviral vectors. At 72 hours, adv.oriPluc demonstrated an 8.4-fold higher tumor signal than adv.SV40luc; adv.oriP.E1A.oriP.luc was 26.7-fold higher; however, a significant liver signal was also observed, necessitating further action to improve biodistribution. Several compounds were examined to this end, including norepinephrine, serotonin, clodronate liposomes, and STI571, to determine whether any of these measures could improve adenoviral biodistribution. Each of these interventions was assessed using BLI in mice i.v. injected with adv.oriP.luc. STI571 achieved the highest increase in tumor-to-liver ratio (TLR; 6.6-fold), which was associated with a 59% reduction in tumor interstitial fluid pressure (IFP) along with a decrease in platelet-derived growth factor-beta receptor (PDGF beta R) activation. This study reports the favorable modulation by STI571 of the biodistribution of adenoviral vectors, providing a potential approach to improving therapeutic outcome.

Head and neck cancer cells are efficiently infected by Ad5/35 hybrid virus

BACKGROUND

Clinical gene therapy trials using standard Ad5-based vectors have thus far demonstrated limited efficacy, most likely due to low expression levels of adenoviral receptors on tumor cells. We sought to analyze adenoviral receptor expression levels on primary head and neck squamous cell carcinoma (HNSCC) cells and to determine whether adenoviral retargeting to the CD46 receptor via the Ad5/35 system would increase therapeutic potential for HNSCC.

METHODS

We used flow cytometric analyses to determine adenoviral receptor expression levels on nine primary HNSCC cells collected from cancer patients. Adenoviruses Ad5.LacZ and Ad5/35.LacZ were used to analyze the differences in viral transduction both in vitro and in a HNSCC tumor mouse model.

RESULTS

Flow cytometric analyses demonstrated uniformly high CD46 expression in all cells studied (85-99%). In contrast, coxsackievirus and adenovirus receptor (CAR) expression was substantially lower and highly variable (1.6-62%). Alpha(v) integrin expression was between 39-98%. In situ stainings for beta-galactosidase gene expression demonstrated that Ad5/35.LacZ was clearly more effective than Ad5.LacZ in transducing primary HNSCC cells. Quantification of beta-galactosidase expression revealed up to 65 times higher transgene expression from Ad5/35.LacZ than Ad5.LacZ. In vivo, beta-galactosidase expression was detected in a substantial area after a single intratumoral injection of Ad5/35.LacZ, whereas injection with Ad5.LacZ resulted in gene expression only in a few cells.

CONCLUSIONS

Our results demonstrate that the low and variable CAR expression levels limit the therapeutic efficacy of Ad5-based strategies for HNSCC. In contrast, the effective in vivo transduction capacity of Ad5/35 warrants further development of this vector for the treatment of head and neck cancer.

Potential use of alexidine dihydrochloride as an apoptosis-promoting anticancer agent

Despite advances in surgery, radiation, and chemotherapy, novel therapeutics are needed for head and neck cancer treatment. The objective of this current study was to evaluate alexidine dihydrochloride as a novel compound lead for head and neck cancers. Using a tetrazolium-based assay, the dose required to reduce cell viability by 50% (ED50) was found to be approximately 1.8 micromol/L in FaDu (human hypopharyngeal squamous cancer) and approximately 2.6 micromol/L in C666-1 (human undifferentiated nasopharyngeal cancer) cells. In contrast, the ED50 values were much higher in untransformed cells, specifically at approximately 8.8 micromol/L in GM05757 (primary normal human fibroblast), approximately 8.9 micromol/L in HNEpC (primary normal human nasal epithelial), and approximately 19.6 micromol/L in NIH/3T3 (mouse embryonic fibroblast) cells. Alexidine dihydrochloride did not interfere with the activities of cisplatin, 5-fluorouracil, or radiation, and interacted in a less-than-additive manner. DNA content analyses and Hoechst 33342 staining revealed that this compound induced apoptosis. Alexidine dihydrochloride-induced mitochondrial damage was visualized using transmission electron microscopy. Mitochondrial membrane potential (DeltaPsiM) depolarization was detectable after only 3 hours of treatment, and was followed by cytosolic Ca2+ increase along with loss of membrane integrity/cell death. Caspase-2 and caspase-9 activities were detectable at 12 hours, caspase-8 at 24 hours, and caspase-3 at 48 hours. FaDu cell clonogenic survival was reduced to < 5% with 1 micromol/L alexidine dihydrochloride, and, correspondingly, this compound decreased the in vivo tumor-forming potential of FaDu cells. Thus, we have identified alexidine dihydrochloride as the first bisbiguanide compound with anticancer specificity.

Benzethonium chloride: a novel anticancer agent identified by using a cell-based small-molecule screen

PURPOSE

This study aims to identify a novel therapeutic agent for head and neck cancer and to evaluate its antitumor efficacy.

EXPERIMENTAL DESIGN

A cell-based and phenotype-driven high-throughput screening of approximately 2,400 biologically active or clinically used compounds was done using a tetrazolium-based assay on FaDu (hypopharyngeal squamous cancer) and NIH 3T3 (untransformed mouse embryonic fibroblast) cells, with secondary screening done on C666-1 (nasopharyngeal cancer) and GM05757 (primary normal human fibroblast) lines. The "hit" compound was assayed for efficacy in combination with standard therapeutics on a panel of human cancer cell lines. Furthermore, its mode of action (using transmission electron microscopy and flow cytometry) and its in vivo efficacy (using xenograft models) were evaluated.

RESULTS

Benzethonium chloride was identified as a novel cancer-specific compound. For benzethonium (48-hour incubation), the dose required to reduce cell viability by 50% was 3.8 micromol/L in FaDu, 42.2 micromol/L in NIH 3T3, 5.3 micromol/L in C666-1, and 17.0 micromol/L in GM05757. In vitro, this compound did not interfere with the effects of cisplatin, 5-fluorouracil, or gamma-irradiation. Benzethonium chloride induced apoptosis and activated caspases after 12 hours. Loss of mitochondrial membrane potential (DeltaPsiM) preceded cytosolic Ca2+ increase and cell death. In vivo, benzethonium chloride ablated the tumor-forming ability of FaDu cells, delayed the growth of xenograft tumors, and combined additively with local tumor radiation therapy. Evaluation of benzethonium chloride on the National Cancer Institute/NIH Developmental Therapeutics Program 60 human cancer cell lines revealed broad-range antitumor activity.

CONCLUSIONS

This high-throughput screening identified a novel antimicrobial compound with significant broad-spectrum anticancer activity.

Multiple dysregulated pathways in nasopharyngeal carcinoma revealed by gene expression profiling

Gene expression profiling was conducted using primary human nasopharyngeal carcinoma (NPC) biopsy samples to improve the understanding of the molecular pathways defining NPC and to identify novel potential therapeutic targets. RNA samples were extracted from 36 patients suspected to have NPC and hybridized onto the Affymetrix U133A chip. NPC was diagnosed in 19 patients, 11 had lymphoid hyperplasia (LH), and 6 were "normal" biopsies. Clinical stages for these NPC patients ranged from I-IV, including one M1. All NPC patients (except the M1) were treated with curative intent, which included radiotherapy alone (4 patients), or combined with chemotherapy (14 patients). Unsupervised clustering demonstrated a distinct NPC expression pattern, compared to normal biopsies. Subsequent Significance Analysis of Microarrays (SAM) derived from 14 NPC and 6 normal samples discovered 1,089 differentially regulated genes. Pathway analyses revealed novel insights into the mechanisms leading to NPC, whereby upregulation of NFkappaB2 and survivin play central roles in increasing resistance to apoptosis, and changes in integrin and WNT/beta-catenin signaling leading to uncontrolled proliferation. The role of survivin in resisting apoptosis in NPC was confirmed by RNA interference. Our data provide novel insights into the development and progression of NPC, and suggest survivin as a novel therapeutic target for NPC.

Potential utility of BimS as a novel apoptotic therapeutic molecule

We have previously demonstrated a 1000-fold induction of gene expression exclusive to Epstein-Barr virus (EBV)-positive nasopharyngeal carcinoma (NPC) cells using an adenoviral vector (ad5.oriP). This platform allows us to explore tumor-specific gene therapy with BimS (ad5.oriP.BimS), a potent proapoptotic Bcl-2 family member. Ad5.oriP.BimS (25 infectious units (ifu)/cell) reduced C666-1 viability in a time- and dose-dependent manner to 15% survival. The effect was enhanced with radiation (6 Gy). Three days after infection, the proportion of apoptotic cells increased from 3.5% (control) to 47.5% (25 ifu/cell). Confocal microscopy demonstrated Bim colocalization to the mitochondria within 18 h of ad5.oriP.BimS infection. Ad5.oriP.BimS induced a 2.8-, 2.1-, and 1.85-fold increase in caspase-3, -8, and -9 activities, respectively. When C666-1 cells were infected with ad5.oriP.BimS (20 ifu/cell), no tumors formed in 7/9 mice followed for 100 days. Six intratumoral injections of ad5.oriP.BimS (1.5 x 10(9) ifu/dose) in combination with radiation were sufficient to cause almost complete disappearance of established C666-1 or C15 xenograft tumors. Intravenous injections of ad5.oriP.BimS (10(9) ifu) induced mild perturbation in liver function tests, associated with hepatocyte apoptoses and mitoses. This vector appears to be safe and effectively cytotoxic to EBV-positive NPC cells both in vitro and in vivo, mediated primarily through the induction of apoptosis.

EBV-associated nasopharyngeal carcinomas: from epidemiology to virus-targeting strategies

Nasopharyngeal carcinoma is a human malignancy consistently associated with the Epstein-Barr virus. Exposure to non-viral carcinogens and genetic predisposition are other crucial etiologic factors. Tumor development appears to require the expression of a small subset of transforming viral RNAs and proteins with concomitant silencing of most other viral genes. Impairment of the interactions of viral proteins with cellular partners or disruption of viral latency might prove to be useful for novel therapeutic strategies.