Transcriptional targeting of herpes simplex virus for cell-specific replication

The evaluation expression of non-coding RNAs in response to HSV-G47∆ oncolytic virus infection in glioblastoma multiforme cancer stem cells

Glioblastoma multiforme is the most aggressive astrocytes brain tumor. Glioblastoma cancer stem cells and hypoxia conditions are well-known major obstacles in treatment. Studies have revealed that non-coding RNAs serve a critical role in glioblastoma progression, invasion, and resistance to chemo-radiotherapy. The present study examined the expression levels of microRNAs (in normoxic condition) and long non-coding RNAs (in normoxic and hypoxic conditions) in glioblastoma stem cells treated with the HSV-G47∆. The expression levels of 43 miRNAs and 8 lncRNAs isolated from U251-GBM-CSCs were analyzed using a miRCURY LNA custom PCR array and a quantitative PCR assay, respectively. The data revealed that out of 43 miRNAs that only were checked in normoxic condition, the only 8 miRNAs, including miR-7-1, miR-let-7b, miR-130a, miR-137, miR-200b, miR-221, miR-222, and miR-874, were markedly upregulated. The expression levels of lncRNAs, including LEF1 antisense RNA 1 (LEF1-AS1), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), long intergenic non-protein coding RNA 470 (LINC00470), tumor suppressor candidate 7 (TUSC7), HOX transcript antisense RNA (HOTAIR), nuclear paraspeckle assembly transcript 1 (NEAT1), and X inactive specific transcript (XIST), were markedly downregulated in the hypoxic microenvironment, and H19-imprinted maternally expressed transcript (H19) was not observed to be dysregulated in this environment. Under normoxic conditions, LEF1-AS1, MALAT1, LINC00470, H19, HOTAIR, NEAT1, and XIST were downregulated and TUSC7 was not targeted by HSV-G47∆. Overall, the present data shows HSVG47Δ treatment deregulates non-coding RNA expression in GBM-CSC tumor microenvironments.

The discovery and development of oncolytic viruses: are they the future of cancer immunotherapy?

Introduction: Despite diverse treatment modalities and novel therapies, many cancers and patients are not effectively treated. Cancer immunotherapy has recently achieved breakthrough status yet is not effective in all cancer types or patients and can generate serious adverse effects. Oncolytic viruses (OVs) are a promising new therapeutic modality that harnesses virus biology and host interactions to treat cancer. OVs, genetically engineered or natural, preferentially replicate in and kill cancer cells, sparing normal cells/tissues, and mediating anti-tumor immunity.Areas covered: This review focuses on OVs as cancer therapeutic agents from a historical perspective, especially strategies to boost their immunotherapeutic activities. OVs offer a multifaceted platform, whose activities are modulated based on the parental virus and genetic alterations. In addition to direct viral effects, many OVs can be armed with therapeutic transgenes to also act as gene therapy vectors, and/or combined with other drugs or therapies.Expert opinion: OVs are an amazingly versatile and malleable class of cancer therapies. They tend to target cellular and host physiology as opposed to specific genetic alterations, which potentially enables broad responsiveness. The biological complexity of OVs have hindered their translation; however, the recent approval of talimogene laherparepvec (T-Vec) has invigorated the field.

Oncolytic virotherapy using herpes simplex virus: how far have we come?

Oncolytic virotherapy exploits the properties of human viruses to naturally cytolysis of cancer cells. The human pathogen herpes simplex virus (HSV) has proven particularly amenable for use in oncolytic virotherapy. The relative safety of HSV coupled with extensive knowledge on how HSV interacts with the host has provided a platform for manipulating HSV to enhance the targeting and killing of human cancer cells. This has culminated in the approval of talimogene laherparepvec for the treatment of melanoma. This review focuses on the development of HSV as an oncolytic virus and where the field is likely to head in the future.

A novel oHSV-1 targeting telomerase reverse transcriptase-positive cancer cells via tumor-specific promoters regulating the expression of ICP4

Virotherapy is a promising strategy for cancer treatment. Using the human telomerase reverse transcriptase promoter, we developed a novel tumor-selective replication oncolytic HSV-1. Here we showed that oHSV1-hTERT virus was cytopathic in telomerase-positive cancer cell lines but not in telomerase-negative cell lines. In intra-venous injection in mice, oHSV1-hTERT was safer than its parental oHSV1-17+. In human blood cell transduction assays, both viruses transduced few blood cells and the transduction rate for oHSV1-hTERT was even less than that for its parental virus. In vivo, oHSV1-hTERT inhibited growth of tumors and prolong survival in telomerase-positive xenograft tumor models. Therefore, we concluded that this virus may be a safe and effective therapeutic agent for cancer treatment, warranting clinical trials in humans.

Designing Herpes Viruses as Oncolytics

Oncolytic herpes simplex virus (oHSV) was one of the first genetically-engineered oncolytic viruses. Because herpes simplex virus (HSV) is a natural human pathogen that can cause serious disease, it is incumbent that it be genetically-engineered or significantly attenuated for safety. Here we present a detailed explanation of the functions of HSV-1 genes frequently mutated to endow oncolytic activity. These genes are non-essential for growth in tissue culture cells but are important for growth in post-mitotic cells, interfering with intrinsic antiviral and innate immune responses or causing pathology, functions dispensable for replication in cancer cells. Understanding the function of these genes leads to informed creation of new oHSVs with better therapeutic efficacy. Virus infection and replication can also be directed to cancer cells through tumor-selective receptor binding and transcriptional- or post-transcriptional miRNA-targeting, respectively. In addition to the direct effects of oHSV on infected cancer cells and tumors, oHSV can be 'armed' with transgenes that are: reporters, to track virus replication and spread; cytotoxic, to kill uninfected tumor cells; immune modulatory, to stimulate anti-tumor immunity; or tumor microenvironment altering, to enhance virus spread or to inhibit tumor growth. In addition to HSV-1, other alphaherpesviruses are also discussed for their oncolytic activity.

Bacteriophage-derived vectors for targeted cancer gene therapy

Cancer gene therapy expanded and reached its pinnacle in research in the last decade. Both viral and non-viral vectors have entered clinical trials, and significant successes have been achieved. However, a systemic administration of a vector, illustrating safe, efficient, and targeted gene delivery to solid tumors has proven to be a major challenge. In this review, we summarize the current progress and challenges in the targeted gene therapy of cancer. Moreover, we highlight the recent developments of bacteriophage-derived vectors and their contributions in targeting cancer with therapeutic genes following systemic administration.

MicroRNA-145 regulates oncolytic herpes simplex virus-1 for selective killing of human non-small cell lung cancer cells

BACKGROUND

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality worldwide, and novel treatment modalities to improve the prognosis of patients with advanced disease are highly desirable. Oncolytic virotherapy is a promising approach for the treatment of advanced NSCLC. MicroRNAs (miRNAs) may be a factor in the regulation of tumor-specific viral replication. The purpose of this study was to investigate whether miRNA-145 regulated oncolytic herpes simplex virus-1 (HSV-1) can selectively kill NSCLC cells with reduced collateral damage to normal cells.

METHODS

We incorporated 4 copies of miRNA-145 target sequences into the 3'-untranslated region of an HSV-1 essential viral gene, ICP27, to create AP27i145 amplicon viruses and tested their target specificity and toxicity on normal cells and lung cancer cells in vitro.

RESULTS

miRNA-145 expression in normal cells was higher than that in NSCLC cells. AP27i145 replication was inversely correlated with the expression of miRNA-145 in infected cells. This oncolytic HSV-1 selectively reduced cell proliferation and prevented the colony formation of NSCLC cells. The combination of radiotherapy and AP27i145 infection was significantly more potent in killing cancer cells than each therapy alone.

CONCLUSIONS

miRNA-145-regulated oncolytic HSV-1 is a promising agent for the treatment of NSCLC.

Antiglioma oncolytic virotherapy: unattainable goal or a success story in the making?

Initial observations from as early as the mid-1800s suggested that patients suffering from hematological malignancies would transiently go into remission upon naturally contracting viral infections laid the foundation for the oncolytic virotherapy research field. Since then, research focusing on anticancer oncolytic virotherapy has rapidly evolved. Today, oncolytic viral vectors have been engineered to stimulate and manipulate the host immune system, selectively targeting tumor tissues while sparing non-neoplastic cells. Glioblastoma multiforme, the most common adult primary brain tumor, has a disasterous history. It is one of the most deadly cancers known to humankind. Over the last century our understanding of this disease has grown exponentially. However, the median survival of patients suffering from this disease has only been extended by a few months. Even with the best, most aggressive modern therapeutic approaches available, malignant gliomas are still virtually 100% fatal. Motivated by the desperate need to find effective treatment strategies, more investments have been applied to oncolytic virotherapy preclinical and clinical studies. In this review we will discuss the antiglioma oncolytic virotherapy research field. We will survey its history and the principles laid down to serve as basis for preclinical works. We will also debate the variety of viral vectors used, their clinical applications, the lessons learned from clinical trials and possible future directions.

HSV-1 as a Model for Emerging Gene Delivery Vehicles

The majority of viral vectors currently used possess modest cargo capability (up to 40 kb) being based on retroviruses, lentiviruses, adenoviruses, and adenoassociated viruses. These vectors have made the most rapid transition from laboratory to clinic because their small genomes have simplified their characterization and modification. However, there is now an increasing need both in research and therapy to complement this repertoire with larger capacity vectors able to deliver multiple transgenes or to encode complex regulatory regions, constructs which can easily span more than 100 kb. Herpes Simplex Virus Type I (HSV-1) is a well-characterized human virus which is able to package about 150 kb of DNA, and several vector systems are currently in development for gene transfer applications, particularly in neurons where other systems have low efficiency. However, to reach the same level of versatility and ease of use as that of smaller genome viral vectors, simple systems for high-titer production must be developed. This paper reviews the major HSV-1 vector systems and analyses the common elements which may be most important to manipulate to achieve this goal.

Oncolytic virotherapy

Oncolytic virotherapy is an emerging treatment modality that uses replication-competent viruses to destroy cancers. Recent advances include preclinical proof of feasibility for a single-shot virotherapy cure, identification of drugs that accelerate intratumoral virus propagation, strategies to maximize the immunotherapeutic action of oncolytic viruses and clinical confirmation of a critical viremic threshold for vascular delivery and intratumoral virus replication. The primary clinical milestone has been completion of accrual in a phase 3 trial of intratumoral herpes simplex virus therapy using talimogene laherparepvec for metastatic melanoma. Key challenges for the field are to select 'winners' from a burgeoning number of oncolytic platforms and engineered derivatives, to transiently suppress but then unleash the power of the immune system to maximize both virus spread and anticancer immunity, to develop more meaningful preclinical virotherapy models and to manufacture viruses with orders-of-magnitude higher yields than is currently possible.

Characterization of herpes simplex virus 1 strains as platforms for the development of oncolytic viruses against liver cancer

BACKGROUND

Diverse oncolytic viruses (OV) are being designed for the treatment of cancer. The characteristics of the parental virus strains may influence the properties of these agents.

AIMS

To characterize two herpes simplex virus 1 strains (HSV-1 17syn(+) and HFEM) as platforms for virotherapy against liver cancer.

METHODS

The luciferase reporter gene was introduced in the intergenic region 20 locus of both HSV-1 strains, giving rise to the Cgal-Luc and H6-Luc viruses. Their properties were studied in hepatocellular carcinoma (HCC) cells in vitro. Biodistribution was monitored by bioluminescence imaging (BLI) in athymic mice and immune-competent Balb/c mice. Immunogenicity was studied by MHC-tetramer staining, in vivo killing assays and determination of specific antibody production. Intratumoural transgene expression and oncolytic effect were studied in HuH-7 xenografts.

RESULTS

The H6-Luc virus displayed a syncytial phenotype and showed higher cytolytic effect on some HCC cells. Upon intravenous or intrahepatic injection in mice, both viruses showed a transient transduction of the liver with rapid relocalization of bioluminescence in adrenal glands, spinal cord, uterus and ovaries. No significant differences were observed in the immunogenicity of these viruses. Local intratumoural administration caused progressive increase in transgene expression during the first 5 days and persisted for at least 2 weeks. H6-Luc achieved faster amplification of transgene expression and stronger inhibition of tumour growth than Cgal-Luc, although toxicity of these non-attenuated viruses should be reduced to obtain a therapeutic effect.

CONCLUSIONS

The syncytial H6-Luc virus has a strong oncolytic potential on human HCC xenografts and could be the basis for potent OV.

Novel tumour-specific promoters for transcriptional targeting of hepatocellular carcinoma by herpes simplex virus vectors

BACKGROUND

Hepatocellular carcinoma (HCC) is a cancer of poor prognosis, with limited success in patient treatment, which it makes an excellent target for gene therapy and viral oncolysis. Accordingly, herpes virus simplex type-1 (HSV-1) is one of the most promising viral platforms for transferring therapeutic genes and the development of oncolytic vectors that can target, multiply in, and eradicate hepatoma cells via their lytic cycle. Enhanced efficacy and specificity of HSV-1-based vectors towards HCC may be achieved by using HCC-specific gene promoters to drive selective viral gene expression and accomplish conditional replication and/or to control the expression of therapeutic genes. However, careful verification of promoter function in the context of the replication-competent HSV-1 vectors is required. The present study aimed to identify novel HCC-specific promoters that could efficiently direct transgene expression to HCC cells and maintain their activity during active viral replication.

METHODS

Publicly available microarray data from human HCC biopsies were analysed in order to detect novel candidate genes induced primarily in HCC compared to normal liver. HCC specificity and promoter activity were evaluated by RT-PCR and chromatin immunoprecipitation. Additionally, transcriptional activity of promoters was further evaluated in the context of HSV-1 genome, using luciferase assays in cultured cells and animal models.

RESULTS

Eight HCC-specific genes were characterised in this study: Angiopoietin-like-3, Cytochrome P450, family 2, subfamily C, polypeptide 8, Vitronectin, Alcohol dehydrogenase 6-class V, Apolipoprotein B, Fibrinogen beta chain, Inter-alpha-globulin-inhibitor H3 and Inter-alpha-globulin-inhibitor H1. Specific HCC expression and active gene transcription were confirmed in human liver and non-liver cell lines and further evaluated in primary neoplastic cells from hepatitis C and B virus (HCV- and HBV)-associated HCC patients. High promoter activity and specificity in the presence of HSV-1 infection and from within the viral genome, was validated, both in vitro and in vivo.

CONCLUSIONS

We identified and experimentally characterized novel hepatoma-specific promoters, which were valuable for cancer-specific gene therapy, using HSV-1 vectors.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Development of an oncolytic herpes simplex virus using a tumor-specific HIF-responsive promoter

We exploited the differential activation of hypoxia-inducible factor (HIF)-dependent gene expression in tumors versus normal tissue for the design of a targeted oncolytic Herpes simplex virus type-1 (HSV-1). A gene that is essential for viral replication, ICP4, was placed under the regulation of a HIF-responsive promoter and then introduced into the thymidine kinase locus (U_L23) of HSV d120 which contains partial deletions in the two endogenous ICP4 genes. Recombinant HIF-HSV were isolated and their derivation from d120 was verified by expression of a truncated, nonfunctional form of ICP4 protein. Disruption of the U_L23 locus was confirmed by loss of thymidine kinase expression and resistance to acyclovir. Unexpectedly, HIF-HSV expressed ICP4 and induced tumor cell lysis at similar levels under normoxia and hypoxia. The lack of HIF-dependent ICP4 transgene expression by HIF-HSV was due to two factors that have not previously been reported- reversion of the ICP4 gene region to its wild-type configuration and increased HIF-transcriptional activity under normoxia when cells were infected with any strain of HSV-1. The findings that an oncolytic HSV-1 is genetically unstable and can activate a tumor-related promoter in a non-specific manner have important implications for any proposed use of this virus in cancer therapy.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Development of a regulatable oncolytic herpes simplex virus type 1 recombinant virus for tumor therapy

Oncolytic viruses are genetically modified viruses that preferentially replicate in host cancer cells, leading to the production of new viruses and, ultimately, cell death. Currently, no oncolytic viruses that are able to kill only tumor cells while leaving normal cells intact are available. Using T-REx (Invitrogen, Carlsbad, CA) gene switch technology and a self-cleaving ribozyme, we have constructed a novel oncolytic HSV-1 recombinant, KTR27, whose replication can be tightly controlled and regulated by tetracycline in a dose-dependent manner. Infection of normal replicating cells as well as multiple human cancer cell types with KTR27 in the presence of tetracycline led to 1,000- to 250,000-fold-higher progeny virus production than in the absence of tetracycline, while little viral replication and virus-associated cytotoxicity was observed in infected growth-arrested normal human cells. We show that intratumoral inoculation with KTR27 markedly inhibits tumor growth in a xenograft model of human non-small-cell lung cancer in nude mice. It is shown further that replication of KTR27 in the inoculated tumors can be efficiently controlled by local codelivery of tetracycline to the target tumors at the time of KTR27 inoculation. Collectively, KTR27 possesses a unique pharmacological feature that can limit its replication to the targeted tumor microenvironment with localized tetracycline delivery, thus minimizing unwanted viral replication in distant tissues following local virotherapy. This regulatory mechanism would also allow the replication of the virus to be quickly shut down should adverse effects be detected.

Targeting cancer by transcriptional control in cancer gene therapy and viral oncolysis

Cancer-specificity is the key requirement for a drug or treatment regimen to be effective against malignant disease--and has rarely been achieved adequately to date. Therefore, targeting strategies need to be implemented for future therapies to ensure efficient activity at the site of patients' tumors or metastases without causing intolerable side-effects. Gene therapy and viral oncolysis represent treatment modalities that offer unique opportunities for tumor targeting. This is because both the transfer of genes with anti-cancer activity and viral replication-induced cell killing, respectively, facilitate the incorporation of multiple mechanisms restricting their activity to cancer. To this end, cellular mechanisms of gene regulation have been successfully exploited to direct therapeutic gene expression and viral cell lysis to cancer cells. Here, transcriptional targeting has been the role model and most widely investigated. This approach exploits cellular gene regulatory elements that mediate cell type-specific transcription to restrict the expression of therapeutic genes or essential viral genes, ideally to cancer cells. In this review, we first discuss the rationale for such promoter targeting and its limitations. We then give an overview how tissue-/tumor-specific promoters are being identified and characterized. Strategies to apply and optimize such promoters for the engineering of targeted viral gene transfer vectors and oncolytic viruses-with respect to promoter size, selectivity and activity in the context of viral genomes-are described. Finally, we discuss in more detail individual examples for transcriptionally targeted virus drugs. First highlighting oncolytic viruses targeted by prostate-specific promoters and by the telomerase promoter as representatives of tissue-targeted and pan-cancer-specific virus drugs respectively, and secondly recent developments of the last two years.

Gene therapy: the end of the rainbow?

The increased understanding of the molecular basis of oral cancer has led to expectations that correction of the genetic defects will lead to improved treatments. Nevertheless, the first clinical trials for gene therapy of oral cancer occurred 20 years ago, and routine treatment is still not available. The major difficulty is that genes are usually delivered by virus vectors whose effects are weak and temporary. Viruses that replicate would be better, and the field includes many approaches in that direction. If any of these are effective in patients, then gene therapy will become available in the next few years. Without significant advances, however, the treatment of oral cancer by gene therapy will remain as remote as the legendary pot of gold at the end of the rainbow.

[Oncolytic virotherapy: new strategies in oncology]

The introduction of new therapeutical approaches to the medical practice has never been an easy task. On the one hand, modern therapies have to fulfil the strict requirements of the industry, on the other, patients and therapists have usually high expectations towards them. Thus, the public's initial euphoric emotions can quickly turn into pessimism following the experience of the first complications and difficulties of the new therapeutic method. Regarding oncolytic virotherapy, the emerging troubles and the lack of complete success upon the first clinical trials also led to the rejection of this promising new approach to the treatment of cancer. In the last few decades, however, due to the advances in molecular and cell biology, oncolytic virotherapy has been put in the lime-light again, and some of the newly developed virotherapeutic agents have been tested in various clinical trials all around the world. This review focuses on the current situation of the field and summarizes the available results.

An oncolytic mutant of herpes simplex virus type-1 in which replication is governed by a promoter/enhancer of human papillomavirus type-16

Although herpes simplex virus type-1 (HSV-1) can be used as an oncolytic virus it has the undesirable side effect of neurotoxicity. To create a virus with improved specificity for oral cancer we used a fragment of human papillomavirus type-16, which is frequently found in oral and cervical cancers, but not elsewhere. The upstream regulatory region, URR16, was shown to have a high level of transcriptional activity in three of four oral cancer cell lines but low activity in three cell lines derived from brain cancers. URR16 was therefore placed in HSV-1, replacing the promoter of the essential gene ICP4, and the resulting virus was named HSPV-1. When cells were infected with HSPV-1, ICP4 was expressed at levels that were not associated with the level of activity of URR16. The virus replicated in each type of cell to a final titer that showed a correlation with the level of expression of ICP4, but with no correlation to either the tumor of origin or the presence of HPV sequences in the cells. To find if some function of HSV-1 was affecting the activity of URR16, oral cancer cells were transfected with a URR-reporter construct and were then infected with virus. This induced transcription, which was attributed to immediate-early viral genes other than ICP4. A promoter/enhancer from a papillomavirus therefore has the potential to regulate the functions of an oncolytic strain of HSV-1, and is affected by functions of both the host cell and of HSV-1 itself.

Effective Treatment of Tumors with Strong β-Catenin/T-Cell Factor Activity by Transcriptionally Targeted Oncolytic Herpes Simplex Virus Vector

The Wnt/beta-catenin/T-cell factor (Tcf) pathway is aberrantly up-regulated in the majority of colorectal cancers (CRC) and hepatoblastomas due to either an APC or beta-catenin gene mutation. We constructed synthetic promoters, T and TE, which contain tandem repeats of a Tcf responsive element without and with the human 4F2 gene intronic enhancer, respectively. Although the T and TE promoters showed higher transcriptional activity than a control promoter in all CRC and hepatoblastoma cell lines tested, with low activities in most other tumor cell lines, the level of transcription varied considerably among the CRC and hepatoblastoma cell lines. In some CRC cell lines, the TE promoter displayed higher levels of transcription than even the human CMV(IE) promoter. In those CRC cells, the APC gene mutations were located within a small segment between the first and second 20-amino-acid repeats in the mutation cluster region of the APC protein. We created a transcriptionally targeted oncolytic herpes simplex virus vector (bM24-TE) in which replication is driven by the TE promoter. This vector efficiently and specifically replicated in and killed tumor cells with strong beta-catenin/Tcf signaling. Intratumoral injection of bM24-TE significantly reduced the growth of highly beta-catenin active SW480 CRC tumors and induced a complete response in half of them, whereas it had no effect on the growth of beta-catenin-inactive A549 tumors. Our results suggest that a transcriptionally regulated oncolytic herpes vector targeting beta-catenin/Tcf signal is very efficacious against CRC tumors carrying an APC gene mutation between the first and second 20-amino-acid repeats.

Flip-Flop HSV-BAC: bacterial artificial chromosome based system for rapid generation of recombinant herpes simplex virus vectors using two independent site-specific recombinases

BACKGROUND

Oncolytic herpes simplex virus (HSV) vectors that specifically replicate in and kill tumor cells sparing normal cells are a promising cancer therapy. Traditionally, recombinant HSV vectors have been generated through homologous recombination between the HSV genome and a recombination plasmid, which usually requires laborious screening or selection and can take several months. Recent advances in bacterial artificial chromosome (BAC) technology have enabled cloning of the whole HSV genome as a BAC plasmid and subsequent manipulation in E. coli. Thus, we sought a method to generate recombinant oncolytic HSV vectors more easily and quickly using BAC technology.

RESULTS

We have developed an HSV-BAC system, termed the Flip-Flop HSV-BAC system, for the rapid generation of oncolytic HSV vectors. This system has the following features: (i) two site-specific recombinases, Cre and FLPe, are used sequentially to integrate desired sequences and to excise the BAC sequences, respectively; and (ii) the size of the HSV-BAC-insert genome exceeds the packaging limit of HSV so only correctly recombined virus grows efficiently. We applied this to the construction of an HSV-BAC plasmid that can be used for the generation of transcriptionally-targeted HSV vectors. BAC sequences were recombined into the UL39 gene of HSV ICP4-deletion mutant d120 to generate M24-BAC virus, from which HSV-BAC plasmid pM24-BAC was isolated. An ICP4 expression cassette driven by an exogenous promoter was re-introduced to pM24-BAC by Cre-mediated recombination and nearly pure preparations of recombinant virus were obtained typically in two weeks. Insertion of the ICP4 coding sequence alone did not restore viral replication and was only minimally better than an ICP4-null construct, whereas insertion of a CMVIE promoter-ICP4 transgene (bM24-CMV) efficiently drove viral replication. The levels of bM24-CMV replication in tumor cells varied considerably compared to hrR3 (UL39 mutant).

CONCLUSION

Our Flip-Flop HSV-BAC system enables rapid generation of HSV vectors carrying transgene inserts. By introducing a tumor-specific-promoter-driven ICP4 cassette into pM24-BAC using this system, one should be able to generate transcriptionally-targeted oncolytic HSV vectors. We believe this system will greatly facilitate the screening of a plethora of clinically useful tumor-specific promoters in the context of oncolytic HSV vectors.

Herpes simplex virus 1 (HSV-1) for cancer treatment

Cancer remains a serious threat to human health, causing over 500 000 deaths each year in US alone, exceeded only by heart diseases. Many new technologies are being developed to fight cancer, among which are gene therapies and oncolytic virotherapies. Herpes simplex virus type 1 (HSV-1) is a neurotropic DNA virus with many favorable properties both as a delivery vector for cancer therapeutic genes and as a backbone for oncolytic viruses. Herpes simplex virus type 1 is highly infectious, so HSV-1 vectors are efficient vehicles for the delivery of exogenous genetic materials to cells. The inherent cytotoxicity of this virus, if harnessed and made to be selective by genetic manipulations, makes this virus a good candidate for developing viral oncolytic approach. Furthermore, its large genome size, ability to infect cells with a high degree of efficiency, and the presence of an inherent replication controlling mechanism, the thymidine kinase gene, add to its potential capabilities. This review briefly summarizes the biology of HSV-1, examines various strategies that have been used to genetically modify the virus, and discusses preclinical as well as clinical results of the HSV-1-derived vectors in cancer treatment.

Triple combination of oncolytic herpes simplex virus-1 vectors armed with interleukin-12, interleukin-18, or soluble B7-1 results in enhanced antitumor efficacy

Conditionally replicating herpes simplex virus-1 (HSV-1) vectors are promising therapeutic agents for cancer. Insertion of therapeutic transgenes into the viral genome should confer desired anticancer functions in addition to oncolytic activities. Herein, using bacterial artificial chromosome and two recombinase-mediated recombinations, we simultaneously created four "armed" oncolytic HSV-1, designated vHsv-B7.1-Ig, vHsv-interleukin (IL)-12, vHsv-IL-18, and vHsv-null, which express murine soluble B7.1 (B7.1-Ig), murine IL-12, murine IL-18, and no transgene, respectively. These vHsv vectors possess deletions in the gamma34.5 genes and contain the green fluorescent protein gene as a histochemical marker and the immunostimulatory transgene inserted in the deleted ICP6 locus. The vHsv showed similar replicative capabilities in vitro. The in vivo efficacy was tested in A/J mice harboring s.c. tumors of syngeneic and poorly immunogenic Neuro2a neuroblastoma. The triple combination of vHsv-B7.1-Ig, vHsv-IL-12, and vHsv-IL-18 exhibited the highest efficacy among all single vHsv or combinations of two viruses. Combining 1 x 10(5) plaque-forming units each of the three armed viruses showed stronger antitumor activities than any single armed virus at 3 x 10(5) plaque-forming units in inoculated tumors as well as in noninoculated remote tumors. Studies using athymic mice indicated that this enhancement of antitumor efficacy was likely mediated by T-cell immune responses. The combined use of multiple oncolytic HSV-1 armed with different immunostimulatory genes may be a useful strategy for cancer therapy.

Replication-competent herpes simplex vectors: design and applications

Replication-competent vectors are derived from attenuated viruses whose genes, that are nonessential for replication in cultured cells in vitro, are either mutated or deleted. The removal of one or more nonessential genes may reduce pathogenicity without requiring a cell line to complement growth. Herpes simplex viruses (HSV) are potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. This review highlights the progress in creating attenuated genetically engineered HSV vectors.

Cancer gene therapy

The prognosis of patients with some kinds of cancers whose patients are often found unresectable upon diagnosis is still dismal. In these fields, development of a new therapeutic modality is needed and gene therapy represents one promising strategy. So far, numerous cancer gene therapy clinical trials based on these principles have been carried out and have shown the safety of such modalities, but have fallen short of the initial expectations to cure cancers. In this review, we would like to make a problem-oriented discussion of current status of cancer gene therapy research by using mainly gastrointestinal cancers as an example. In order to overcome obstacles for full realization of cancer gene therapy, numerous researches have been conducted by many researchers. Various cancer-selective and non-selective genes, as well as lytic viruses themselves have been employed for gene therapy. In the context of gene delivery method, different kinds of viral and non-viral strategies have been utilized. In addition, surrogate assays, such as soluble markers and imaging, have been developed for safer and more informative clinical trials. Many experiments and clinical trials to date have figured out current obstacles for the realization of an effective cancer gene therapy modality. Tireless efforts to overcome such hurdles and continuous infusion of novel concepts into this field should lead to break through technologies and the cure of the patients.

Effective gene-virotherapy for complete eradication of tumor mediated by the combination of hTRAIL (TNFSF10) and plasminogen k5

Virotherapy with oncolytic viruses is a highly promising approach for cancer therapy. To improve further the therapeutic effect of oncolytic viruses, therapeutic genes have been incorporated into these types of vectors. In this study, we have inserted hTRAIL (approved gene symbol TNFSF10) into the ZD55 vector, which was based on deletion of the adenoviral E1B 55-kDa gene and could replicate in and lyse p53-deficient tumors. Our data shows that infection of colorectal carcinoma cells with ZD55-hTRAIL resulted in tumor cell death that was much greater than that induced by ZD55 vector or replication-defective adenovirus expressing hTRAIL. In contrast to these, ZD55-hTRAIL did not induce any cytopathic effect in normal cells. Treatment of established tumor with ZD55-hTRAIL resulted in dramatic inhibition of tumor growth in an animal model of colorectal carcinoma. However, when the established tumors were treated by coadministration of ZD55-hTRAIL and Ad-k5, we observed complete eradication of the established tumors in all animals treated with the combined therapy. This strong anti-tumor activity was due to the fact that two genes may act with compensative (or synergic) effect through different mechanisms to kill tumors. Therefore, targeting dual gene-virotherapy may be one of the best strategies for cancer therapy if two suitable genes are chosen.

Enhanced efficacy of conditionally replicating herpes simplex virus (G207) combined with 5-fluorouracil and surgical resection in peritoneal cancer dissemination models

BACKGROUND

The therapeutic efficacy of G207, a replication-competent herpes simplex virus, for malignancies is increased when combined with certain chemotherapies, but the mechanism is unclear and the interaction between G207 and surgical resection has not been extensively studied. The goals of the current study were to examine the performance of combination treatments for peritoneal disseminated cancers and to explore the mechanism of effective combinations.

METHODS

Hamsters and SCID and BALB/c mice harboring peritoneal dissemination of gallbladder, gastric or colon cancer cells were treated with G207, 5-fluorouracil (5FU), or surgical resection alone, or G207 combined with 5FU or surgery. Animal survival, antiviral immunity, intratumoral ribonucleotide reductase activity, and viral spread were compared between the groups.

RESULTS

The combination of G207 and 5FU prolonged the survival of hamsters bearing peritoneal dissemination of gallbladder cancer compared with the controls, G207 alone and 5FU alone. 5FU did not suppress the production of neutralizing antibodies against G207, but increased ribonucleotide reductase activity and viral spread in subcutaneous gallbladder tumors. The enhanced efficacy of the combination treatment was also observed in immunodeficient mice with disseminated gastric cancer. Although surgical resection did not significantly prolong animal survival or increase the intratumoral activity of ribonucleotide reductase, long-term survivors emerged from groups of animals treated with surgical resection and G207 for gallbladder and colon disseminated cancers.

CONCLUSIONS

These results indicate that the increased activity of ribonucleotide reductase in tumors mediated by 5FU and the decreased tumor burden resulting from surgical resection may enhance the therapeutic efficacy of oncolytic herpes virus for peritoneal disseminated cancer.

Replication-selective oncolytic viruses in the treatment of cancer

In the search for novel strategies, oncolytic virotherapy has recently emerged as a viable approach to specifically kill tumor cells. Unlike conventional gene therapy, it uses replication competent viruses that are able to spread through tumor tissue by virtue of viral replication and concomitant cell lysis. Recent advances in molecular biology have allowed the design of several genetically modified viruses, such as adenovirus and herpes simplex virus that specifically replicate in, and kill tumor cells. On the other hand, viruses with intrinsic oncolytic capacity are also being evaluated for therapeutic purposes. In this review, an overview is given of the general mechanisms and genetic modifications by which these viruses achieve tumor cell-specific replication and antitumor efficacy. However, although generally the oncolytic efficacy of these approaches has been demonstrated in preclinical studies the therapeutic efficacy in clinical trails is still not optimal. Therefore, strategies are evaluated that could further enhance the oncolytic potential of conditionally replicating viruses. In this respect, the use of tumor-selective viruses in conjunction with other standard therapies seems most promising. However, still several hurdles regarding clinical limitations and safety issues should be overcome before this mode of therapy can become of clinical relevance.

Oncolytic viruses for cancer therapy II. Cell-internal factors for conditional growth in neoplastic cells

Recent advances in our understanding of virus-host interactions have fueled new studies in the field of oncolytic viruses. The first part of this review explained how cell-external factors, such as cellular receptors, influence tumor tropism and specificity of oncolytic virus candidates. In the second part of this review, we focus on cellinternal factors that mediate tumor-specific virus growth. An oncolytic virus must be able to replicate within cancerous cells and kill them without collateral damage to healthy surrounding cells. This desirable property is inherent to some proposed oncolytic viral agents or has been achieved by genetic manipulation in others.

Oncolytic viral therapies

Molecular research has vastly advanced our understanding of the mechanism of cancer growth and spread. Targeted approaches utilizing molecular science have yielded provocative results in the treatment of cancer. Oncolytic viruses genetically programmed to replicate within cancer cells and directly induce toxic effect via cell lysis or apoptosis are currently being explored in the clinic. Safety has been confirmed and despite variable efficacy results several dramatic responses have been observed with some oncolytic viruses. This review summarizes results of clinical trials with oncolytic viruses in cancer.

Herpes simplex virus-induced, death receptor-dependent apoptosis and regression of transplanted human cancers

Inoculation of a live attenuated herpes simplex virus (HSV) vector, betaH1, into human U87MG glioblastoma cells transplanted into athymic nude mice induced complete regression of tumors. The infected cells underwent histochemically confirmed apoptosis without lymphocyte infiltration after expressing CD30, CD30 ligand (CD30L), tumor necrosis factor (TNF)-alpha, TNF receptor 1 (TNF-R1), FAS, and FAS ligand (FAS-L) with activation of caspases 3 and 8. Induction of the transcripts of these receptors and ligands in inoculated tumors was confirmed by quantitative RT-PCR. To examine the specificity of apoptosis in the transplanted tumor, we inoculated betaH1 into transplanted human lung, breast, gastric, and colon cancer tumors, and similar tumor regression with apoptosis was observed in all tumors. We analyzed the roles of expression of CD30, CD30L, TNF-alpha, TNF-R1, FAS, and FAS-L in the tumors, and found that HSV-induced apoptosis was suppressed by the respective antibodies. These findings indicate that the CD30/CD30L, TNF-alpha/TNF-R1, and FAS/FAS-L interactions resulted in apoptosis and tumor regression in immunocompromised mice. In addition to the death receptor-dependent apoptosis induced by HSV, the expressed ligands and receptors might enhance the susceptibility of tumor cells to cell-mediated cyto-toxicity and augment the activation of tumor-killing lymphocytes in immunocompetent models.

Novel tracing paradigms--genetically engineered herpesviruses as tools for mapping functional circuits within the CNS: present status and future prospects

The mammalian CNS is composed of an extremely complex meshwork of highly ordered interconnections among billions of neurons. To understand the diverse functions of this neuronal network we need to differentiate between functionally related and nonrelated elements. A powerful labeling method for defining intricate neural circuits is based on the utilization of neurotropic herpesviruses, including pseudorabies virus and herpes simplex virus type 1. The recent development of genetically engineered tracing viruses can open the way toward the conception of novel tract-tracing paradigms. These new-generation tracing viruses may facilitate the clarification of problems, which were inaccessible to earlier approaches. This article first presents a concise review of the general aspects of neuroanatomical tracing protocols. Subsequently, it discusses the molecular biology of alpha-herpesviruses, and the genetic manipulation and gene expression techniques that are utilized for the construction of virus-based tracers. Finally, it describes the current utilization of genetically modified herpesviruses for circuit analysis, and the future directions in their potential applications.

Selectivity of an oncolytic herpes simplex virus for cells expressing the DF3/MUC1 antigen

Replication-conditional viruses destroy tumors in a process referred to as viral oncolysis. An important prerequisite for this cancer therapy strategy is use of viruses that replicate preferentially in neoplastic cells. In this study the DF3/MUC1 promoter/enhancer sequence is used to regulate expression of gamma(1)34.5 to drive replication of a Herpes simplex virus 1 (HSV-1) mutant (DF3gamma34.5) preferentially in DF3/MUC1-positive cells. HSV-1 gamma(1)34.5 functions to dephosphorylate elongation initiation factor 2alpha, which is an important step for robust HSV-1 replication. After DF3gamma34.5 infection of cells, elongation initiation factor 2alpha phosphatase activity and viral replication were observed preferentially in DF3/MUC1-positive cells but not in DF3/MUC1-negative cells. Regulation of gamma(1)34.5 function results in preferential replication in cancer cells that express DF3/MUC1, restricted biodistribution in vivo, and less toxicity as assessed by LD(50). Preferential replication of DF3gamma34.5 was observed in DF3/MUC1-positive liver tumors after intravascular perfusion of human liver specimens. DF3gamma34.5 was effective against carcinoma xenografts in nude mice. Regulation of gamma(1)34.5 by the DF3/MUC1 promoter is a promising strategy for development of HSV-1 mutants for viral oncolysis.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

Herpes simplex virus type-1 infection upregulates cellular promoters and telomerase activity in both tumor and nontumor human cells

Targeted gene expression through viral vectors has been a promising approach for gene therapy. However, the effects of viral gene products expressed from virus vectors on the expression of the host gene are not well known. In the present study, we examined the activities of cellular promoters, including the promoter for genes of human telomerase reverse transcriptase (hTERT), tyrosinase and probasin, in both tumor and normal cells after infection with herpes simplex virus type 1 (HSV-1) vectors. Our results showed that infection with replication-defective HSV-1 vectors significantly upregulated the activity of all three cellular promoters in a nonsequence specific fashion in all cell types tested. Furthermore, viral infection upregulated activities of the hTERT promoter and endogenous telomerase in nontumoral cells. Additional experiments suggested that the viral immediate-early gene product, infected cell protein 0, might be responsible for the deregulation of cellular promoter activity and activation of telomerase. Our study alerts to the potential risk of oncogenesis through deregulation of host gene expression, such as the telomerase by viral vectors in normal cells.

Myoglobin gene expression attenuates hepatic ischemia reperfusion injury

BACKGROUND

Cellular functions are maintained by a continuous supply of ATP, which is supplied efficiently by mitochondrial oxidative phosphorylation. Since myoglobin, found in cardiac myocytes and red skeletal muscle, but not in the liver, facilitates oxygen diffusion under low oxygen conditions and enhances oxidative phosphorylation, this study seeks to enhance hepatic ATP levels and attenuate ischemia-reperfusion injury in rodent livers by adenovirus-mediated myoglobin expression.

MATERIAL AND METHODS

After infecting Hep3B and rodent livers with adenovirus carrying CMV promoter sequences linked to the human myoglobin gene (AdCMVMyo), reverse transcriptase-PCR and immunodetection for myoglobin, and cellular and hepatic ATP levels were examined. The effect of myoglobin was evaluated in a hepatic ischemia-reperfusion model in the rat.

RESULTS

Myoglobin expression was confirmed in Hep3B and rat livers after AdCMVMyo infection. The ATP levels in Hep3B cells and C57BL/6 mice livers 72 h after AdCMVMyo transfection were significantly higher than control levels and those after adenovirus-mediated beta-galactosidase transfection. Finally, expression of myoglobin attenuated ischemia-reperfusion injury in the rat liver.

CONCLUSION

These results indicate that myoglobin gene transfer to the liver enhanced ATP levels both in vitro and in vivo and might be a novel strategy to reduce ischemia-reperfusion injury.

Armed therapeutic viruses: strategies and challenges to arming oncolytic viruses with therapeutic genes

Oncolytic viruses are attractive therapeutics for cancer because they selectively amplify, through replication and spread, the input dose of virus in the target tumor. To date, clinical trials have demonstrated marked safety but have not realized their theoretical efficacy potential. In this review, we consider the potential of armed therapeutic viruses, whose lytic potential is enhanced by genetically engineered therapeutic transgene expression from the virus, as potential vehicles to increase the potency of these agents. Several classes of therapeutic genes are outlined, and potential synergies and hurdles to their delivery from replicating viruses are discussed.

Oncolytic herpes simplex virus vectors for cancer virotherapy

Oncolytic herpes simplex virus type 1 (HSV-1) vectors are emerging as an effective and powerful therapeutic approach for cancer. Replication-competent HSV-1 vectors with mutations in genes that affect viral replication, neuropathogenicity, and immune evasiveness have been developed and tested for their safety and efficacy in a variety of mouse models. Evidence to-date following administration into the brain attests to their safety, an important observation in light of the neuropathogenicity of the virus. Phase I clinical traits of three vectors, G207, 1716, and NV1020, are either ongoing or completed, with no adverse events attributed to the virus. These and other HSV-1 vectors are effective against a myriad of solid tumors in mice, including glioma, melanoma, breast, prostate, colon, ovarian, and pancreatic cancer. Enhancement of activity was observed when HSV-1 vectors were used in combination with traditional therapies such as radiotherapy and chemotherapy, providing an attractive strategy to pursue in the clinic. Oncolytic HSV-1 vectors expressing "suicide" genes (thymidine kinase, cytosine deaminase, rat cytochrome P450) or immunostimulatory genes (IL-12, GM-CSF, etc.) have been constructed to maximize tumor destruction through multimodal therapeutic mechanisms. Further advances in virus delivery and tumor specificity should improve the likelihood for successful translation to the clinic.

The oncolytic virotherapy treatment platform for cancer: unique biological and biosafety points to consider

The field of replication-selective oncolytic viruses (virotherapy) has exploded over the last 10 years. As with many novel therapeutic approaches, initial overexuberance has been tempered by clinical trial results with first-generation agents. Although a number of significant hurdles to this approach have now been identified, novel solutions have been proposed and improvements are being made at a furious rate. This article seeks to initiate a discussion of these hurdles, approaches to overcome them, and unique safety and regulatory issues to consider.

Regulation of herpes simplex virus 1 replication using tumor-associated promoters

OBJECTIVE

To investigate use of transcriptional regulatory elements (promoters) for tumor-associated antigens to achieve HSV-1 replication preferentially in cells that overexpress the tumor-associated antigens.

SUMMARY BACKGROUND DATA

An important advantage of replicating viruses for cancer therapy is their ability to simultaneously destroy tumor cells by replication and release progeny virion to infect and destroy adjacent cancer cells. This strategy requires regulation of the viral life cycle to obtain robust replication in neoplastic cells and minimize replication in nonneoplastic cells.

METHODS

Promoters for the human carcinoembryonic antigen (CEA) and MUC1/DF3 tumor-associated antigens were characterized and cloned into HSV-1 mutants as heterologous promoters regulating expression of two different HSV-1 genes. Viral replication in tumor cells and cytotoxicity was quantified with in vitro assays. Antineoplastic efficacy was characterized in a flank tumor xenograft model.

RESULTS

Several CEA promoters were cloned and characterized using luciferase reporter assays. The most specific promoter was used to construct and isolate two different HSV-1 mutants in which critical genes are regulated by this promoter (ICP4 and gamma(1) 34.5). Similarly, the promoter for the DF3/MUC1 tumor-associated antigen was cloned into a third HSV-1 mutant such that it regulates expression of gamma(1) 34.5. Regulation of ICP4 expression by the CEA promoter during HSV-1 infection overly attenuates viral replication. Regulation of gamma(1) 34.5 expression by either the CEA promoter or the MUC1/DF3 promoter during HSV-1 infection modulates viral replication, with preferential replication in cells that overexpress the corresponding tumor-associated antigen. A single intratumoral inoculation of an HSV-1 mutant with the MUC1/DF3 promoter regulating gamma(1) 34.5 expression results in significant antineoplastic activity in MUC1-positive pancreatic carcinoma xenografts as compared to mock inoculation.

CONCLUSIONS

Promoters for tumor-associated antigens may be incorporated into the HSV-1 genome to regulate HSV-1 replication. The choices of HSV-1 gene and tumor-associated promoter are important determinants of success of this strategy. Because of its preferential replication in MUC1-positive tumors, an HSV-1 mutant with the MUC1/DF3 promoter regulating gamma(1) 34.5 expression will undergo further examination as a novel cancer therapy agent.

Gene therapy using tissue-specific replication competent HSV

Tissue- or cell-specific targeting of vectors is critical to the success of gene therapy. I describe a novel approach to viral-mediated gene therapy, where viral replication and associated cytotoxicity are limited to a specific cell-type by the regulated expression of an essential immediate-early viral gene product. This is illustrated with two herpes simplex virus type 1 vectors (G92A and d12.CALP) whose growth are restricted to albumin- or calponin-expressing cells, respectively. G92A was constructed by inserting an albumin enhancer/promoter--ICP4 transgene into the thymidine kinase gene of mutant herpes simplex virus type 1 d120, deleted for both copies of the ICP4 gene. This vector also contains the Escherichia coli lacZ gene under control of the thymidine kinase promoter, a viral early promoter, to permit easy detection of infected cells containing replicating vector. In the adult, albumin is expressed uniquely in the liver and in hepatocellular carcinoma and is transcriptionally regulated. G92A efficiently replicated in vitro in two human hepatoma cell lines expressing albumin, but not in three human non-hepatoma, albumin-non-expressing tumor cell lines, while all cell lines were equally susceptible to a tissue non-specific HSV recombinant, hrR3. In vivo, G92A replicated well in subcutaneous xenografts of human hepatoma cells (Hep3B) in athymic mice, but not in non-hepatoma subcutaneous tumors (PC3 and HeLa), whereas, hrR3 replicated well in both tumor types. Intratumoral inoculation of G92A inhibited the growth of established subcutaneous hepatoma tumors in nude mice, but not prostate tumors. D12CALP also revealed the cell-specific replication to leiomyosarcoma in which calponin expression was augmented. Using hrR3, we demonstrated inhibition of re-stenosis of rat carotid arteries caused by balloon injury. The antiproliferative effects of this virus was marked in the proliferating smooth muscle cells, however, there still remained the fear for the injury of the endothelial cells. Confining a productive, cytotoxic viral infection to a specific cell-type should be useful for tumor therapy and the ablation of specific cell-types for the generation of animal models of disease. Further experiments using d12CALP will be focused on the arteriosclerosis due to balloon angioplasty or organ transplantation.

Friendly fire: redirecting herpes simplex virus-1 for therapeutic applications

Herpes simplex virus-1 (HSV-1) is a relatively large double-stranded DNA virus encoding at least 89 proteins with well characterized disease pathology. An understanding of the functions of viral proteins together with the ability to genetically engineer specific viral mutants has led to the development of attenuated HSV-1 for gene therapy. This review highlights the progress in creating attenuated genetically engineered HSV-1 mutants that are either replication competent (viral non-essential gene deleted) or replication defective (viral essential gene deleted). The choice between a replication-competent or -defective virus is based on the end-goal of the therapeutic intervention. Replication-competent HSV-1 mutants have primarily been employed as antitumor oncolytic viruses, with the lytic nature of the virus harnessed to destroy tumor cells selectively. In replacement gene therapy, replication-defective viruses have been utilized as delivery vectors. The advantages of HSV-1 vectors are that they infect quiescent and dividing cells efficiently and can encode for relatively large transgenes.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.

Viral oncolysis

The concept of using replicating viruses as anticancer agents is not a new one, but the ability to genetically modify these viruses into increasingly potent and tumor-specific vectors is a recent phenomenon. As more is learned about the functions of viral gene products in controlling the mammalian cell cycle and in disabling cellular defense mechanisms, specific viral functions can be augmented or eliminated to enhance antineoplastic efficacy. In this article, general mechanisms by which oncolytic viruses achieve their antitumor efficacy and specificity are reviewed. The paradoxical roles of the immune response are addressed with respect to oncolytic viral therapy, as it, on one hand, impedes the spread of viral infection, and on the other, augments tumor cell destruction through the recruitment of T cells "vaccinated" against tumor antigens. The most commonly used oncolytic viruses are each reviewed in turn, including adenoviruses, herpes simplex viruses, vaccinia viruses, reoviruses, and Newcastle disease viruses. Special attention is focused on the unique biology of each of these viruses as well as the status of several of these mutants in clinical trials.