Gene therapy progress and prospects cancer: oncolytic viruses

Hypoxia-regulated overexpression of soluble VEGFR2 controls angiogenesis and inhibits tumor growth

VEGFs are found at high levels in hypoxic tumors. As major components directing pathologic neovascularization, they regulate stromal reactions. Consequently, novel strategies targeting and inhibiting VEGF overproduction upon hypoxia offer considerable potential for modern anticancer therapies controlling rather than destroying tumor angiogenesis. Here, we report the design of a vector expressing the soluble form of VEGF receptor-2 (sVEGFR2) driven by a hypoxia-responsive element (HRE)-regulated promoter. To enable in vivo imaging by infrared visualization, mCherry and IFP1.4 coding sequences were built into the vector. Plasmid construction was validated through transfection into embryonic human kidney HEK293 and murine B16F10 melanoma cells. sVEGFR2 was expressed in hypoxic conditions only, confirming that the gene was regulated by the HRE promoter. sVEGFR2 was found to bind efficiently and specifically to murine and human VEGF-A, reducing the growth of tumor and endothelial cells as well as impacting angiogenesis in vitro. The hypoxia-conditioned sVEGFR2 expression was shown to be functional in vivo: Tumor angiogenesis was inhibited and, on stable transfection of B16F10 melanoma cells, tumor growth was reduced. Enhanced expression of sVEGFR2 was accompanied by a modulation in levels of VEGF-A. The resulting balance reflected the effect on tumor growth and on control of angiogenesis. A concomitant increase of intratumor oxygen tension also suggested an influence on vessel normalization. The possibility to express an angiogenesis regulator as sVEGFR2, in a hypoxia-conditioned manner, significantly opens new strategies for tumor vessel-controlled normalization and the design of adjuvants for combined cancer therapies.

Anti-tumor activity of a miR-199-dependent oncolytic adenovirus

The down-regulation of miR-199 occurs in nearly all primary hepatocellular carcinomas (HCCs) and HCC cell lines in comparison with normal liver. We exploited this miR-199 differential expression to develop a conditionally replication-competent oncolytic adenovirus, Ad-199T, and achieve tumor-specific viral expression and replication. To this aim, we introduced four copies of miR-199 target sites within the 3’ UTR of E1A gene, essential for viral replication. As consequence, E1A expression from Ad-199T virus was tightly regulated both at RNA and protein levels in HCC derived cell lines, and replication controlled by the level of miR-199 expression. Various approaches were used to asses in vivo properties of Ad-199T. Ad-199T replication was inhibited in normal, miR-199 positive, liver parenchyma, thus resulting in reduced hepatotoxicity. Conversely, the intrahepatic delivery of Ad-199T in newborn mice led to virus replication and fast removal of implanted HepG2 liver cancer cells. The ability of Ad-199T to control tumor growth was also shown in a subcutaneous xenograft model in nude mice and in HCCs arising in immune-competent mice. In summary, we developed a novel oncolytic adenovirus, Ad-199T, which could demonstrate a therapeutic potential against liver cancer without causing significant hepatotoxicity.

Update on oncolytic viral therapy - targeting angiogenesis

Oncolytic viruses (OVs) have the ability to selectively replicate in and lyse cancer cells. Angiogenesis is an essential requirement for tumor growth. Like OVs, the therapeutic effect of many angiogenesis inhibitors has been limited, leading to the development of more effective approaches to combine antiangiogenic therapy with OVs. Angiogenesis can be targeted either directly by OV infection of vascular endothelial cells, or by arming OVs with antiangiogenic transgenes, which are subsequently expressed locally in the tumor microenvironment. In this review, we describe the development and targeting of OVs, the role of angiogenesis in cancer, and the progress made in arming viruses with antiangiogenic transgenes. Future developments required to optimize this approach are addressed.

Viral vectors for vaccine applications

Traditional approach of inactivated or live-attenuated vaccine immunization has resulted in impressive success in the reduction and control of infectious disease outbreaks. However, many pathogens remain less amenable to deal with the traditional vaccine strategies, and more appropriate vaccine strategy is in need. Recent discoveries that led to increased understanding of viral molecular biology and genetics has rendered the used of viruses as vaccine platforms and as potential anti-cancer agents. Due to their ability to effectively induce both humoral and cell-mediated immune responses, viral vectors are deemed as an attractive alternative to the traditional platforms to deliver vaccine antigens as well as to specifically target and kill tumor cells. With potential targets ranging from cancers to a vast number of infectious diseases, the benefits resulting from successful application of viral vectors to prevent and treat human diseases can be immense.

An armed oncolytic measles vaccine virus eliminates human hepatoma cells independently of apoptosis

Due to late diagnosis and a pronounced chemoresistance, most patients with hepatocellular carcinoma (HCC) have an overall poor prognosis. Measles vaccine viruses (MeV) have been shown to possess anti-tumor properties and their efficacy has been enhanced by arming with suicide genes. To test armed MeV for the treatment of HCC, we equipped it with the suicide gene Super-cytosine deaminase (SCD) and tested the efficacy in cell culture and in a mouse xenograft model of human HCC. Prodrug conversion was investigated in cell culture and quantified by high-performance liquid chromatography. We observed a strong oncolytic activity of MeV-SCD against human HCC in vitro and in vivo. The prodrug was efficiently converted in infected cells leading to a significant enhancement of the cytotoxic effect. Treatment of HCC xenografts with MeV caused long-term virus replication in tumor tissue. We show that the suicide gene therapy induces an apoptosis-like cell death but is not dependent on intact apoptosis pathways. These results demonstrate that MeV-based suicide gene therapy is a promising novel therapy regimen for HCC overcoming resistance towards conventional therapy. The independence from apoptosis raises hopes for the treatment of patients whose tumor cells exert defects in this cell death mechanism.

Bugs and drugs: oncolytic virotherapy in combination with chemotherapy

Single agent therapies are rarely successful in treating cancer, particularly at metastatic or end stages, and survival rates with monotherapies alone are generally poor. The combination of multiple therapies to treat cancer has already driven significant improvements in the standard of care treatments for many types of cancers. The first combination treatments exploited for cancer therapy involved the use of several cytotoxic chemotherapy agents. Later, with the development of more targeted agents, the use of novel, less toxic drugs, in combination with the more classic cytotoxic drugs has proven advantageous for certain cancer types. Recently, the combination of oncolytic virotherapy with chemotherapy has shown that the use of these two therapies with very distinct anti-tumor mechanisms may also lead to synergistic interactions that ultimately result in increased therapeutic effects not achievable by either therapy alone. The mechanisms of synergy between oncolytic viruses (OVs) and chemotherapeutic agents are just starting to be elucidated. It is evident, however, that the success of these OV-drug combinations depends greatly on the particular OV, the drug(s) selected, and the cancer type targeted. This review summarizes the different OV-drug combinations investigated to date, including the use of second generation armed OVs, which have been studied with the specific purpose of generating synergistic interactions with particular chemotherapy agents. The known mechanisms of synergy between these OV-drug combinations are also summarized. The importance of further investigating these mechanisms of synergy will be critical in order to maximize the therapeutic efficacy of OV-drug combination therapies in the future.

Creation and screening of a multi-family bacterial oxidoreductase library to discover novel nitroreductases that efficiently activate the bioreductive prodrugs CB1954 and PR-104A

Two potentially complementary approaches to improve the anti-cancer strategy gene-directed enzyme prodrug therapy (GDEPT) are discovery of more efficient prodrug-activating enzymes, and development of more effective prodrugs. Here we demonstrate the utility of a flexible screening system based on the Escherichia coli SOS response to evaluate novel nitroreductase enzymes and prodrugs in concert. To achieve this, a library of 47 candidate genes representing 11 different oxidoreductase families was created and screened to identify the most efficient activators of two different nitroaromatic prodrugs, CB1954 and PR-104A. The most catalytically efficient nitroreductases were found in the NfsA and NfsB enzyme families, with NfsA homologues generally more active than NfsB. Some members of the AzoR, NemA and MdaB families also exhibited low-level activity with one or both prodrugs. The results of SOS screening in our optimised E. coli reporter strain SOS-R2 were generally predictive of the ability of nitroreductase candidates to sensitise E. coli to CB1954, and of the kcat/Km for each prodrug substrate at a purified protein level. However, we also found that not all nitroreductases express stably in human (HCT-116 colon carcinoma) cells, and that activity at a purified protein level did not necessarily predict activity in stably transfected HCT-116. These results highlight a need for all enzyme-prodrug partners for GDEPT to be assessed in the specific context of the vector and cell line that they are intended to target. Nonetheless, our oxidoreductase library and optimised screens provide valuable tools to identify preferred nitroreductase-prodrug combinations to advance to preclinical evaluation.

TRAIL and Noxa are selectively upregulated in prostate cancer cells downstream of the RIG-I/MAVS signaling pathway by nonreplicating Sendai virus particles

PURPOSE

The treatment of cancer with oncolytic viruses primarily depends on the selective viral replication in cancer cells. However, a replication-incompetent hemagglutinating virus of Japan (HVJ; Sendai virus) envelope (HVJ-E) suppresses the growth of human cancer cells as effectively as replication-competent live HVJ without producing toxic effects in nonmalignant cells. Here, we analyze the molecular mechanism of the oncolytic activity of HVJ-E.

EXPERIMENTAL DESIGN

The molecules responsible for HVJ-E-induced cancer cell death were elucidated in prostate cancer cell lines, and the effect of HVJ-E on orthotopic prostate cancers was evaluated in nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice.

RESULTS

The liposome-mediated transfer of viral RNA genome fragments from HVJ-E suppressed the viability of prostate cancer cells but not the viability of the noncancerous prostate epithelium. Knockdown experiments using siRNAs showed that the cancer cell-selective killing induced by HVJ-E was mediated by retinoic acid-inducible gene I (RIG-I) and mitochondrial antiviral signaling protein (MAVS). Downstream of the RIG-I/MAVS pathway, both TNF-related apoptosis-inducing ligand (TRAIL) and Noxa were upregulated by HVJ-E in the castration-resistant prostate cancer cell line PC3 but not in the noncancerous prostate epithelial cell line PNT2. TRAIL siRNA but not Noxa siRNA significantly inhibited HVJ-E-induced cell death in PC3 cells. However, Noxa siRNA effectively suppressed HVJ-E-induced cell death in DU145 cells, another castration-resistant prostate cancer cell line, in which Noxa but not TRAIL was upregulated by HVJ-E. Furthermore, the orthotopic prostate cancers were dramatically eradicated in immunodeficient mice injected with HVJ-E.

CONCLUSION

The RIG-I/MAVS signaling pathway represents an attractive target for cancer therapy.

Potent antitumoral effects of targeted promoter-driven oncolytic adenovirus armed with Dm-dNK for breast cancer in vitro and in vivo

Currently, no curative treatments are available for late-stage metastatic or recurrent breast cancer, because the cancer tolerates both chemotherapy and endocrine therapy. In this study, we investigated the feasibility of a dual-regulated oncolytic adenoviral vector with a novel suicide gene to treat breast cancer. Following targeted gene virotherapy of conditionally replicating adenoviruses (CRAds), the novel suicide gene of multisubstrate deoxyribonucleoside kinase of Drosophila melanogaster (Dm-DNK) was inserted into the double-regulated oncolytic adenovirus SG500 to ensure more safety and enhanced antitumor activity against breast cancer both in vitro and in vivo. Selective replication, cell-killing efficacy, and cytotoxicity, combined with chemotherapeutics were investigated in several breast cell lines (MDA-MB-231 and MCF-7), normal cells (WI-38 and MRC-5), and human (MDA-MB-231) tumor models in vivo. The double-regulated SG500-dNK had high cell-killing activity in breast cancer. Replication was similar to wild-type in breast cells and was attenuated in normal cells. SG500-dNK combined with the chemotherapeutics (E)-5-(2-bromovinyl)-2'-deoxyuridine (Bvdu) and 2',2'-difluoro-deoxycytidine (dFdC) resulted in synergistically enhanced cell killing and greatly improved antitumor efficacy in vitro or in breast xenografts in vivo. These data suggest that the novel oncolytic variant SG500-dNK is a promising candidate for targeting breast tumors specifically when combined with chemotherapeutics.

Receptors and tropisms of envelope viruses

Envelope virus replication begins with receptor binding, followed by fusion of the viral envelope with the cell membrane. The binding and fusion steps are usually mediated by envelope proteins. The ability of envelope proteins of a particular virus to bind and fuse with target cells defines the host range of the virus, known as 'viral tropism'. The mechanism(s) of fusion by the viral envelope is largely categorized as either pH-dependent or pH-independent. By redirecting the binding specificities of envelope proteins to desired target molecules while maintaining fusion activity, it is possible to redirect the tropisms of virus and viral vectors, enabling specific killing and/or transduction of desired cells in vivo. Recently, a lipid, phosphatidylserine, was also shown to mediate binding of virus, which affects the tropisms of viruses and viral vectors.

Systemic delivery of oncolytic adenoviruses targeting transforming growth factor-β inhibits established bone metastasis in a prostate cancer mouse model

We have examined whether Ad.sTβRFc and TAd.sTβRFc, two oncolytic viruses expressing soluble transforming growth factor-β receptor II fused with human Fc (sTGFβRIIFc), can be developed to treat bone metastasis of prostate cancer. Incubation of PC-3 and DU-145 prostate tumor cells with Ad.sTβRFc and TAd.sTβRFc produced sTGFβRIIFc and viral replication; sTGFβRIIFc caused inhibition of TGF-β-mediated SMAD2 and SMAD3 phosphorylation. Ad(E1-).sTβRFc, an E1(-) adenovirus, produced sTGFβRIIFc but failed to replicate in tumor cells. To examine the antitumor response of adenoviral vectors, PC-3-luc cells were injected into the left heart ventricle of nude mice. On day 9, mice were subjected to whole-body bioluminescence imaging (BLI). Mice bearing hind-limb tumors were administered viral vectors via the tail vein on days 10, 13, and 17 (2.5×10(10) viral particles per injection per mouse, each injection in a 0.1-ml volume), and subjected to BLI and X-ray radiography weekly until day 53. Ad.sTβRFc, TAd.sTβRFc, and Ad(E1-).sTβRFc caused significant inhibition of tumor growth; however, Ad.sTβRFc was the most effective among all the vectors. Only Ad.sTβRFc and TAd.sTβRFc inhibited tumor-induced hypercalcemia. Histomorphometric and synchrotron micro-computed tomographic analysis of isolated bones indicated that Ad.sTβRFc induced significant reduction in tumor burden, osteoclast number, and trabecular and cortical bone destruction. These studies suggest that Ad.sTβRFc and TAd.sTβRFc can be developed as potential new therapies for prostate cancer bone metastasis.

Virosome: a novel vector to enable multi-modal strategies for cancer therapy

Despite advancements in treatments, cancer remains a life-threatening disease that is resistant to therapy. Single-modal cancer therapy is often insufficient to provide complete remission. A revolution in cancer therapy may someday be provided by vector-based gene and drug delivery systems. However, it remains difficult to achieve this aim because viral and non-viral vectors have their own advantages and limitations. To overcome these limitations, virosomes have been constructed by combining viral components with non-viral vectors or by using pseudovirions without viral genome replication. Viruses, such as influenza virus, HVJ (hemagglutinating virus of Japan; Sendai virus) and hepatitis B virus, have been used in the construction of virosomes. The HVJ-derived vector is particularly promising due to its highly efficient delivery of DNA, siRNA, proteins and anti-cancer drugs. Furthermore, the HVJ envelope (HVJ-E) vector has intrinsic anti-tumor activities including the activation of multiple anti-tumor immunities and the induction of cancer-selective apoptosis. HVJ-E is currently being clinically used for the treatment of melanoma. A promising multi-modal cancer therapy will be achieved when virosomes with intrinsic anti-tumor activities are utilized as vectors for the delivery of anti-tumor drugs and genes.

Engineering of Brome mosaic virus for biomedical applications

Viral nanoparticles (VNPs) are becoming versatile tools in platform technology development. Their well-defined structures as well as their programmability through chemical and genetic modification allow VNPs to be engineered for potential imaging and therapeutic applications. In this article, we report the application of a variety of bioconjugation chemistries to the plant VNP Brome mosaic virus (BMV). Functional BMV nanoparticles displaying multiple copies of fluorescent dyes, PEG molecules, chemotherapeutic drug moieties, targeting proteins and cell penetrating peptides were formulated. This opens the door for the application of BMV in nanomedicine.

Virus-mediated gene delivery for human gene therapy

After over 20 years from the first application of gene transfer in humans, gene therapy is now a mature discipline, which has progressively overcome several of the hurdles that prevented clinical success in the early stages of application. So far, the vast majority of gene therapy clinical trials have exploited viral vectors as very efficient nucleic acid delivery vehicles both in vivo and ex vivo. Here we summarize the current status of viral gene transfer for clinical applications, with special emphasis on the molecular properties of the major classes of viral vectors and the information so far obtained from gene therapy clinical trials.

Oncolytic measles virus encoding thyroidal sodium iodide symporter for squamous cell cancer of the head and neck radiovirotherapy

Oncolytic measles virus (MV) encoding the human thyroidal sodium iodide symporter (MV-NIS) has proved to be safe after intraperitoneal or intravenous administration in patients with ovarian cancer or multiple myeloma, respectively, but it has not yet been administered through intratumoral injection in humans. Squamous cell carcinoma (SCC) of the head and neck (SCCHN) usually is locally invasive and spreads to the cervical lymph nodes, which are suitable for the intratumoral administration of oncolytic viruses. To test whether oncolytic MV is an effective treatment for SCCHN, we used oncolytic MV-NIS to infect SCCHN in vitro and in vivo. The data show that SCCHN cells were infected and killed by MV-NIS in vitro. Permissiveness of the tumor cells to MV infection was not affected by irradiation after viral addition. Monitored noninvasively through radioiodine-based single-photon emission computed tomography/computed tomography, intratumorally virus-delivered NIS has concentrated the radioiodine in the MV-NIS-treated tumors in the FaDu mouse xenograft model of human SCCHN, and the antitumor effect could be boosted significantly (p<0.05) either with concomitant cyclophosphamide therapy or with appropriately timed administration of radioiodine (131)I. MV-NIS could be a promising new anticancer agent that may substantially enhance the outcomes of standard therapy after intratumoral administration in patients with locally advanced SCCHN.

Infection

This chapter provides an overview of the numerous patterns of different virus infections from the perspective of host organisms, and describes the major responses of plants and animals to virus infections. The scientific basis for prevention and treatment of virus diseases are also explained. Virus infection is a complex, multistage interaction between the virus and the host organism. The patterns of virus infection can be divided into these types: abortive, acute, chronic, pertinent, and latent. The course and eventual outcome of any infection are the results of a balance between host and virus processes. The host factors involved include exposure to different routes of virus transmission and the control of virus replication by the immune response. Virus processes include the initial infection of the host, its spread throughout the host, and the regulation of gene expression to evade the immune response. The chapter also discusses the virus infections of plants, immune responses to virus infections in animals, apoptosis (programmed cell death), interferons (the blocking of virus infection), and evasion of immune responses. Medical intervention against virus infections includes the use of vaccines to stimulate the immune response and drugs to inhibit virus replication. Molecular biology is stimulating the production of a new generation of antiviral drugs and vaccines.

Early infection and spread of a conditionally replicating adenovirus under conditions of plaque formation

Conditionally-replicating adenoviruses (CRAds) and other oncolytic viruses replicate selectively in tumor cells, presenting a potential cancer treatment approach. To optimize application of these viruses, understanding of early spread of these viruses in target cells is important. Here we used a recombinant adenovirus expressing enhanced jellyfish green fluorescent protein (EGFP) in place of the EIA and EIB genes (AdEGFPuci). Infection of susceptible cells (AD-293) under plaque formation conditions (MOI<<1) on gridded culture dishes and daily monitoring allowed visualization of initially infected cells, as well as spread to neighboring cells. We determined key parameters of early infection, including the rate and efficiency of spread from the initially infected cell to other cells. It was noteworthy that a minority of initially infected cells ultimately resulted in plaques. The approaches elucidated here will be useful for determining early infection parameters for CRAds of therapeutic interest.

Effective oncolytic vaccinia therapy for human sarcomas

BACKGROUND

Approximately one fourth of bone and soft-tissue sarcomas recur after prior treatment. GLV-1h68 is a recombinant, replication-competent vaccinia virus that has been shown to have oncolytic effects against many human cancer types. We sought to determine whether GLV-1h68 could selectively target and lyse a panel of human bone and soft-tissue sarcoma cell lines in vitro and in vivo.

METHODS

GLV-1h68 was tested in a panel of four cell lines including: fibrosarcoma HT-1080, osteosarcoma U-2OS, fibrohistiocytoma M-805, and rhabdomyosarcoma HTB-82. Gene expression, infectivity, viral proliferation, and cytotoxicity were characterized in vitro. HT-1080 xenograft flank tumors grown in vivo were injected intratumorally with a single dose of GLV-1h68.

RESULTS

All four cell lines supported robust viral transgene expression in vitro. At a multiplicity of infection (MOI) of five, GLV-1h68 was cytotoxic to three cell lines, resulting in >80% cytotoxicity over 7 d. In vivo, a single injection of GLV-1h68 into HT-1080 xenografts exhibited localized intratumoral luciferase activity peaking at d 2-4, with gradual resolution over 8 d and no evidence of spread to normal tissues. Treated animals exhibited near-complete tumor regression over a 28-d period without observed toxicity.

CONCLUSION

GLV-1h68 has potent direct oncolytic effects against human sarcoma in vitro and in vivo. Recombinant vaccinia oncolytic virotherapy could provide a new platform for the treatment of patients with bone and soft tissue sarcomas. Future clinical trials investigating oncolytic vaccinia as a therapy for sarcomas are warranted.

Questing for an optimal, universal viral agent for oncolytic virotherapy

One of the most promising strategies to treat cancer is attacking it with viruses designed to exploit specific altered pathways. Here, the effects of oncolytic virotherapy on tumors having compact, papillary, and disconnected morphologies are investigated through computer simulations of a multiscale model coupling macroscopic reaction-diffusion equations for the nutrients with microscopic stochastic rules for the actions of individual cells and viruses. The interaction among viruses and tumor cells involves cell infection, intracellular virus replication, and the release of new viruses in the tissue after cell lysis. The evolution over time of both the viral load and cancer cell population, as well as the probabilities for tumor eradication, were evaluated for a range of multiplicities of infection, viral entries, and burst sizes. It was found that in immunosuppressed hosts, the antitumor efficacy of a virus is primarily determined by its entry efficiency, its replicative capacity within the tumor, and its ability to spread over the tissue. However, the optimal traits for oncolytic viruses depend critically on the tumor growth dynamics and do not necessarily include rapid replication, cytolysis, or spreading, currently assumed as necessary conditions for a successful therapeutic outcome. Our findings have potential implications on the design of new vectors for the viral therapy of cancer.

Emerging cancer vaccines: the promise of genetic vectors

Therapeutic vaccination against cancer is an important approach which, when combined with other therapies, can improve long-term control of cancer. In fact, the induction of adaptive immune responses against Tumor Associated Antigens (TAAs) as well as innate immunity are important factors for tumor stabilization/eradication. A variety of immunization technologies have been explored in last decades and are currently under active evaluation, such as cell-based, protein, peptide and heat-shock protein-based cancer vaccines. Genetic vaccines are emerging as promising methodologies to elicit immune responses against a wide variety of antigens, including TAAs. Amongst these, Adenovirus (Ad)-based vectors show excellent immunogenicity profile and have achieved immunological proof of concept in humans. In vivo electroporation of plasmid DNA (DNA-EP) is also a desirable vaccine technology for cancer vaccines, as it is repeatable several times, a parameter required for the long-term maintenance of anti-tumor immunity. Recent findings show that combinations of different modalities of immunization (heterologous prime/boost) are able to induce superior immune reactions as compared to single-modality vaccines. In this review, we will discuss the challenges and requirements of emerging cancer vaccines, particularly focusing on the genetic cancer vaccines currently under active development and the promise shown by Ad and DNA-EP heterologous prime-boost.

Oncolytic virotherapy of breast cancer

The use of replication competent viruses that selectively target and destroy cancer cells has rapidly evolved over the past decade and numerous innovative oncolytic viruses have been created. Many of these promising anti-cancer agents have recently entered into clinical trials (including those on breast cancer) and demonstrated encouraging safety and efficacy. Virotherapeutic strategies are thus of considerable interest to combat breast cancer in both (i) the primary disease situation in which relapse should be avoided as good as possible and (ii) in the metastatic situation which remains incurable to date. Here, we summarize data from preclinical and clinical trials using oncolytic virotherapy to treat breast cancer. This includes strategies to specifically target breast cancer cells, to arm oncolytic viruses with additional therapeutic transgenes and an outlining of future challenges when translating these promising therapeutics "from bench to bedside".

Vesicular stomatitis virus has extensive oncolytic activity against human sarcomas: rare resistance is overcome by blocking interferon pathways

Oncolytic viruses have been tested against many carcinomas of ectodermal and endodermal origin; however, sarcomas, arising from mesoderm, have received relatively little attention. Using 13 human sarcomas representing seven tumor types, we assessed the efficiency of infection, cytolysis, and replication of green fluorescent protein (GFP)-expressing vesicular stomatitis virus (VSV) and its oncolytically enhanced mutant VSV-rp30a. Both viruses efficiently infected and killed 12 of 13 sarcomas. VSV-rp30a showed a faster rate of infection and replication. In vitro and in vivo, VSV was selective for sarcomas compared with normal mesoderm. A single intravenous injection of VSV-rp30a selectively infected all subcutaneous human sarcomas tested in mice and arrested the growth of tumors that otherwise grew 11-fold. In contrast to other sarcomas, synovial sarcoma SW982 demonstrated remarkable resistance, even to high titers of virus (multiplicity of infection [MOI] of 100). We found no dysfunction in VSV binding or internalization. SW982 also resisted infection by human cytomegalovirus and Sindbis virus, suggesting a virus resistance mechanism based on an altered antiviral state. Quantitative reverse transcriptase (qRT)-PCR analysis revealed a heightened basal expression of interferon-stimulated genes (ISGs). Pretreatment, but not cotreatment, with interferon attenuators valproate, Jak1 inhibitor, or vaccinia virus B18R protein rendered SW982 highly susceptible, and this correlated with downregulation of ISG expression. Jak1 inhibitor pretreatment also enhanced susceptibility in moderately VSV-resistant liposarcoma and bladder carcinoma. Overall, we find that the potential efficacy of VSV as an oncolytic agent extends to nonhematologic mesodermal tumors and that unusually strong resistance to VSV oncolysis can be overcome with interferon attenuators.

Replication-competent retrovirus vector-mediated prodrug activator gene therapy in experimental models of human malignant mesothelioma

Replication-competent retrovirus (RCR) vectors have been shown to achieve significantly enhanced tumor transduction efficiency and therapeutic efficacy in various cancer models. In the present study, we investigated RCR vector-mediated prodrug activator gene therapy for the treatment of malignant mesothelioma, a highly aggressive tumor with poor prognosis. RCR-GFP vector expressing the green fluorescent protein marker gene successfully infected and efficiently replicated in human malignant mesothelioma cell lines, as compared with non-malignant mesothelial cells in vitro. In mice with pre-established subcutaneous tumor xenografts, RCR-GFP vector showed robust spread throughout entire tumor masses after intratumoral administration. Next, RCR-cytosine deaminase (RCR-CD), expressing the yeast CD prodrug activator gene, showed efficient transmission of the prodrug activator gene associated with replicative spread of the virus, resulting in efficient killing of malignant mesothelioma cells in a prodrug 5-fluorocytosine (5FC)-dose dependent manner in vitro. After a single intratumoral injection of RCR-CD followed by intraperitoneal administration of 5FC, RCR vector-mediated prodrug activator gene therapy achieved significant inhibition of subcutaneous tumor growth, and significantly prolonged survival in the disseminated peritoneal model of malignant mesothelioma. These data indicate the potential utility of RCR vector-mediated prodrug activator gene therapy in the treatment of malignant mesothelioma.

Oncolytic viruses in radiation oncology

Oncolytic viruses are investigational cancer treatments. They are currently being assessed as single agents or in combination with standard therapies such as external beam radiotherapy - a DNA damaging agent that is a standard of care for many tumour types. Preclinical data indicate that combinations of oncolytic viruses and radiation therapy are promising, showing additional or synergistic antitumour effects in in vitro and in vivo studies. This interaction has the potential to be multifaceted: viruses may act as radiosensitizing agents, but radiation may also enhance viral oncolysis by increasing viral uptake, replication, gene expression and cell death (apoptosis, autophagy or necrosis) in irradiated cells. Phase I and II clinical trials investigating combinations of viruses and radiation therapy have been completed, paving the way for ongoing phase III studies. The aim of this review is to focus on the therapeutic potential of these combinations and to highlight their mechanistic bases, with particular emphasis on the role of the DNA damage response.

A non-replicating oncolytic vector as a novel therapeutic tool against cancer

Cancers are still difficult targets despite recent advances in cancer therapy. Due to the heterogeneity of cancer, a single-treatment modality is insufficient for the complete elimination of cancer cells. Therapeutic strategies from various aspects are needed. Gene therapy has been expected to bring a breakthrough to cancer therapy, but it has not yet been successful. Gene therapy also should be combined with other treatments to enhance multiple therapeutic pathways. In this view, gene delivery vector itself should be equipped with intrinsic anti-cancer activities. HVJ (hemagglutinating virus of Japan; Sendai virus) envelope vector (HVJ-E) was developed to deliver therapeutic molecules. HVJ-E itself possessed anti-tumor activities such as the generation of anti-tumor immunities and the induction of cancer-selective apoptosis. In addition to the intrinsic anti-tumor activities, therapeutic molecules incorporated into HVJ-E enabled to achieve multi-modal therapeutic strategies in cancer treatment. Tumor-targeting HVJ-E was also developed. Thus, HVJ-E will be a novel promising tool for cancer treatment.

A hypoxia- and {alpha}-fetoprotein-dependent oncolytic adenovirus exhibits specific killing of hepatocellular carcinomas

PURPOSE

Oncolytic adenoviruses (Ad) constitute a new promising modality of cancer gene therapy that displays improved efficacy over nonreplicating Ads. We have previously shown that an E1B 19-kDa-deleted oncolytic Ad exhibits a strong cell-killing effect but lacks tumor selectivity. To achieve hepatoma-restricted cytotoxicity and enhance replication of Ad within the context of tumor microenvironment, we used a modified human α-fetoprotein (hAFP) promoter to control the replication of Ad with a hypoxia response element (HRE).

EXPERIMENTAL DESIGN

We constructed Ad-HRE(6)/hAFPΔ19 and Ad-HRE(12)/hAFPΔ19 that incorporated either 6 or 12 copies of HRE upstream of promoter. The promoter activity and specificity to hepatoma were examined by luciferase assay and fluorescence-activated cell sorting analysis. In addition, the AFP expression- and hypoxia-dependent in vitro cytotoxicity of Ad-HRE(6)/hAFPΔ19 and Ad-HRE(12)/hAFPΔ19 was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cytopathic effect assay. In vivo tumoricidal activity on subcutaneous and liver orthotopic model was monitored by noninvasive molecular imaging.

RESULTS

Ad-HRE(12)/hAFPΔ19 exhibited enhanced tumor selectivity and cell-killing activity when compared with Ad-hAFPΔ19. The tumoricidal activity of Ad-HRE(12)/hAFPΔ19 resulted in significant inhibition of tumor growth in both subcutaneous and orthotopic models. Histologic examination of the primary tumor after treatment confirmed accumulation of viral particles near hypoxic areas. Furthermore, Ad-HRE(12)/hAFPΔ19 did not cause severe inflammatory immune response and toxicity after systemic injection.

CONCLUSIONS

The results presented here show the advantages of incorporating HREs into a hAFP promoter-driven oncolytic virus. This system is unique in that it acts in both a tissue-specific and tumor environment-selective manner. The greatly enhanced selectivity and tumoricidal activity of Ad-HRE(12)/hAFPΔ19 make it a promising therapeutic agent in the treatment of liver cancers.

The good viruses: viral mutualistic symbioses

Although viruses are most often studied as pathogens, many are beneficial to their hosts, providing essential functions in some cases and conditionally beneficial functions in others. Beneficial viruses have been discovered in many different hosts, including bacteria, insects, plants, fungi and animals. How these beneficial interactions evolve is still a mystery in many cases but, as discussed in this Review, the mechanisms of these interactions are beginning to be understood in more detail.

Complete regression of human malignant mesothelioma xenografts following local injection of midkine promoter-driven oncolytic adenovirus

BACKGROUND

Malignant mesothelioma is a highly aggressive tumor with poor prognosis. We hypothesized that the tumor-specific midkine (Mdk) promoter could confer transcriptional targeting to oncolytic adenoviruses for effective treatment of malignant mesothelioma.

METHODS

We analysed Mdk expression by quantitative reverse transcription-polymerase chain reaction in six human mesothelioma cell lines, and tested Mdk promoter activity by luciferase reporter assay. On the basis of these data, we constructed a replication-selective oncolytic adenovirus designated AdMdk-E1-iresTK. This virus contains a Mdk promoter-driven adenoviral E1 gene and herpes simplex virus-thymidine kinase (TK) suicide gene and cytomagalovirus promoter-driven enhanced green fluorescent protein marker gene. Selectivity of viral replication and cytolysis were characterized in normal versus mesothelioma cells in vitro, and intratumoral spread and antitumor efficacy were investigated in vivo.

RESULTS

Mdk promoter activity was restricted in normal cells, but highly activated in mesothelioma cell lines. AdMdk-E1-iresTK was seen to efficiently replicate, produce viral progeny and spread in multiple mesothelioma cell lines. Lytic spread of AdMdk-E1-iresTK mediated the efficient killing of these mesothelioma cells, and its in vitro cytocidal effect was significantly enhanced by treatment with the prodrug, ganciclovir. Intratumoral injection of AdMdk-E1-iresTK caused complete regression of MESO4 and MSTO human mesothelioma xenografts in athymic mice. In vivo fluorescence imaging demonstrated intratumoral spread of AdMdk-E1-iresTK-derived signals, which vanished after tumor eradication.

CONCLUSIONS

These data indicate that transcriptional targeting of viral replication by the Mdk promoter represents a promising general strategy for oncolytic virotherapy of cancers with up-regulated Mdk expression, including malignant mesothelioma.

Evaluating vaccinia virus cytokine co-expression in TLR GKO mice

Using Toll-like receptor (TLR) and MyD88 gene knock-out (GKO) mice the effect of TLRs and MyD88 on virus replication, interferon (IFN)-β production, natural killer (NK) cell and CD8T cell responses were assessed following ectromelia virus (ECTV) and recombinant vaccinia virus (rVV) infection. The capacity for rVVs encoding cytokines to restore immune function in MyD88(-/-) mice was clearly demonstrated. Results showed that TLR2(-/-), TLR4(-/-)and TLR7(-/-) mice survived ECTV infection whereas MyD88(-/-) and TLR9(-/-)mice, in contrast, were highly susceptible. Next, following infection with rVV, MyD88(-/-) mice elicited reduced serum IFN-β, NK cell and CD8T cell responses compared with wild-type mice, whereas TLR9(-/-) mice showed elevated CD8T cell responses. When MyD88(-/-)mice were infected with rVV co-expressing IFN-β these mice were able to restore IFN-β levels and CD8T cell responses but not NK cell activation. Interestingly, even though rVV co-expressing interleukin (IL)-2 enhanced NK cell activation in MyD88(-/-) mice, this was not associated with an antiviral effect, as observed in normal mice. Surprisingly, co-infection with rVV IL-2/rVV IL-12, but not rVV IL-2/rVV IFN-β, restored the attenuated phenotype of rVV IL-2 in MyD88(-/-) mice indicating that the IL-2/IL-12 combination promotes antiviral responses. Our results clearly show that the CD8T cell defect observed in MyD88(-/-) mice to vaccinia virus infection can be restored by rVV-encoding IFN-β demonstrating the critical role of this cytokine in T cell mediated immunity and illustrates that the model can provide an effective platform for the elucidation of cytokine immunobiology.

Development of a selective biopharmaceutical from Herpes simplex virus type 1 glycoproteins E and I for blocking antibody mediated neutralization of oncolytic viruses

Future cancer therapies will be molecular cures. They will correct, block or destroy cancer cells by targeting molecular changes that lead to carcinogenesis. Destroying cancer cells can be done using oncolytic viruses. By blocking antibody mediated neutralization of oncolytic viruses, Herpes simplex virus type 1 glycoproteins E and I could be used in the adjuvant treatment of cancer for improving the chances of oncolytic viruses to kill cancer cells in vivo.

Update on non-viral delivery methods for cancer therapy: possibilities of a drug delivery system with anticancer activities beyond delivery as a new therapeutic tool

IMPORTANCE OF THE FIELD

Cancer is the most formidable human disease. Owing to the heterogeneity of cancer, a single-treatment modality is insufficient for the complete elimination of cancer cells. Therapeutic strategies from various aspects are needed for cancer therapy. These therapeutic agents should be carefully selected to enhance multiple therapeutic pathways. Non-viral delivery methods have been utilized to enhance the tumor-selective delivery of therapeutic molecules, including proteins, synthetic oligonucleotides, small compounds and genes.

AREAS COVERED IN THIS REVIEW

As non-viral delivery methods, liposomes and polymer-based delivery materials to target tumors mainly by systemic delivery, physical methods including electroporation, sonoporation, and so on, to locally inject therapeutic molecules, and virosomes to use the viral infectious machinery for the delivery of therapeutic molecules are summarized.

WHAT THE READER WILL GAIN

This article aims to provide an overview of the characteristic properties of each non-viral vector. It will be beneficial to utilize appropriately the vector for cancer treatment.

TAKE HOME MESSAGE

Efficient and minimally invasive vectors are generally considered to be the ideal drug delivery system (DDS). However, against cancer, DDS equipped with antitumor activities may be a therapeutic choice. By combining therapeutic molecules with DDS having antitumor activities, enhancement of the multiple therapeutic pathways may be achieved.

A single intravenous injection of oncolytic picornavirus SVV-001 eliminates medulloblastomas in primary tumor-based orthotopic xenograft mouse models

Difficulties of drug delivery across the blood-brain barrier (BBB) and failure to eliminate cancer stem cells (CSCs) are believed to be the major causes of tumor recurrences in children with medulloblastoma (MB). Seneca Valley virus-001 (SVV-001) is a naturally occurring oncolytic picornavirus that can be systemically administered. Here, we report its antitumor activities against MB cells in a panel of 10 primary tumor-based orthotopic xenograft mouse models. We found that SVV-001 killed the primary cultured xenograft cells, infected and replicated in tumor cells expressing CSC surface marker CD133, and eliminated tumor cells capable of forming neurospheres in vitro in 5 of the 10 xenograft models. We confirmed that SVV-001 could pass through BBB in vivo. A single i.v. injection of SVV-001 in 2 anaplastic MB models led to widespread infection of the preformed intracerebellar (ICb) xenografts, resulting in significant increase in survival (2.2-5.9-fold) in both models and complete elimination of ICb xenografts in 8 of the 10 long-term survivors. Mechanistically, we showed that the intracellular replication of SVV-001 is mediated through a subverted autophagy that is different from the bona fide autophagic process induced by rapamycin. Our data suggest that SVV-001 is well suited for MB treatment. This work expands the current views in the oncolytic therapy field regarding the utility of oncolytic viruses in simultaneous targeting of stem and nonstem tumor cells.

Review article: gene therapy, recent developments and future prospects in gastrointestinal oncology

BACKGROUND

Gene therapy consists of the introduction of genetic material into cells for a therapeutic purpose. A wide range of gene therapy vectors have been developed and used for applications in gastrointestinal oncology.

AIM

To review recent developments and published clinical trials concerning the application of gene therapy in the treatment of liver, colon and pancreatic cancers.

METHODS

Search of the literature published in English using the PubMed database.

RESULTS

A large variety of therapeutic genes are under investigation, such as tumour suppressor, suicide, antiangiogenesis, inflammatory cytokine and micro-RNA genes. Recent progress concerns new vectors, such as oncolytic viruses, and the synergy between viral gene therapy, chemotherapy and radiation therapy. As evidence of these basic developments, recently published phase I and II clinical trials, using both single agents and combination strategies, in adjuvant or advanced disease settings, have shown encouraging results and good safety records.

CONCLUSIONS

Cancer gene therapy is not yet indicated in clinical practice. However, basic and clinical advances have been reported and gene therapy is a promising, new therapeutic approach for the treatment of gastrointestinal tumours.

Sodium iodide symporter (NIS)-mediated radiovirotherapy for pancreatic cancer

OBJECTIVE

We have previously shown the therapeutic efficacy of an engineered oncolytic measles virus expressing the sodium iodide symporter reporter gene (MV-NIS) in mice with human pancreatic cancer xenografts. The goal of this study was to determine the synergy between MV-NIS-induced oncolysis and NIS-mediated (131)I radiotherapy in this tumor model.

MATERIALS AND METHODS

Subcutaneous human BxPC-3 pancreatic tumors were injected twice with MV-NIS. Viral infection, NIS expression, and intratumoral iodide uptake were quantitated with (123)I micro-SPECT/CT. Mice with MV-NIS-infected tumors were treated with 0, 37, or 74 MBq (131)I and monitored for tumor progression and survival. Additional studies were performed with stable NIS-expressing tumors (BxPC-3-NIS) treated with 0, 3.7, 18.5, 37, or 74 MBq of (131)I.

RESULTS

Mice treated with intratumoral MV-NIS exhibited significant tumor growth delay (p < 0.01) and prolonged survival (p = 0.02) compared with untreated mice. Synergy between MV-NIS-induced oncolysis and NIS-mediated (131)I ablation was not seen; however, a significant correlation was observed between NIS-mediated intratumoral iodide localization (% ID/g) and peak tumor volume reduction (p = 0.04) with combination MV-NIS and (131)I therapy. Stably transduced NIS-expressing BxPC-3 tumors exhibited rapid regression with > or = 18.5 MBq (131)I.

CONCLUSION

Delivery of (131)I radiotherapy to NIS-expressing tumors can be optimized using micro-SPECT/CT imaging guidance. Significant hurdles exist for NIS as a therapeutic gene for combined radiovirotherapy in this human pancreatic cancer model. The lack of synergy observed with MV-NIS and (131)I in this model was not due to a lack of radiosensitivity but rather to a nonuniform intratumoral distribution of MV-NIS infection.

Adenovirus-retrovirus hybrid vectors achieve highly enhanced tumor transduction and antitumor efficacy in vivo

Murine leukemia virus (MLV)-based replication-competent retrovirus (RCR) vectors have been shown to mediate efficient, selective, and persistent tumor transduction, thereby achieving significant therapeutic benefit in a wide variety of cancer models. To further augment the efficiency of this strategy, we have developed a delivery method employing a gutted adenovirus encoding an RCR vector (AdRCR); thus, tumor cells transduced with the adenoviral vector transiently become RCR vector producer cells in situ. As expected, high-titer AdRCR achieved significantly higher initial transduction levels in human cancer cells both in vitro and in vivo, as compared to the original RCR vector itself. Notably, even at equivalent initial transduction levels, more secondary RCR progeny were produced from AdRCR-transduced cells as compared to RCR-transduced cells, resulting in further acceleration of subsequent RCR replication kinetics. In pre-established tumor models in vivo, prodrug activator gene therapy with high-titer AdRCR could achieve enhanced efficacy compared to RCR alone, in a dose-dependent manner. Thus, AdRCR hybrid vectors offer the advantages of high production titers characteristic of adenovirus and secondary production of RCR in situ, which not only accelerates subsequent vector spread and progressive tumor transduction, but can also significantly enhance the therapeutic efficacy of RCR-mediated prodrug activator gene therapy.

Mechanisms of cell death in canine parvovirus-infected cells provide intuitive insights to developing nanotools for medicine

Viruses have great potential as nanotools in medicine for gene transfer, targeted gene delivery, and oncolytic cancer virotherapy. Here we have studied cell death mechanisms of canine parvovirus (CPV) to increase the knowledge on the CPV life cycle in order to facilitate the development of better parvovirus vectors. Morphological studies of CPV-infected Norden laboratory feline kidney (NLFK) cells and canine fibroma cells (A72) displayed characteristic apoptotic events. Apoptosis was further confirmed by activation of caspases and cellular DNA damage. However, results from annexin V-propidium iodide (PI) labeling and membrane polarization assays indicated disruption of the plasma membrane uncommon to apoptosis. These results provide evidence that secondary necrosis followed apoptosis. In addition, two human cancer cell lines were found to be infected by CPV. This necrotic event over apoptotic cell death and infection in human cells provide insightful information when developing CPV as a nanotool for cancer treatments.

Analysis of adenovirus trans-complementation-mediated gene expression controlled by melanoma-specific TETP promoter in vitro

BACKGROUND

Human adenoviruses (Ads) have substantial potential for clinical applications in cancer patients. Conditionally replicating adenoviruses (CRAds) include oncolytic adenoviruses in which expression of the immediate early viral transactivator protein E1A is controlled by a cancer cell-selective promoter. To enhance efficacy, CRAds are further armed to contain therapeutic genes. Due to size constraints of the capsid geometry, the capacity for packaging transgenes into Ads is, however, limited. To overcome this limitation, the employment of E1A-deleted replication-deficient viruses carrying therapeutic genes in combination with replication-competent CRAd vectors expressing E1A in trans has been proposed. Most trans-complementing studies involved transgene expressions from strong ubiquitous promoters, and thereby relied entirely on the cancer cell specificity of the CRAd vector.

RESULTS

Here we tested the trans-complementation of a CRAd and a replication-deficient transgene vector containing the same cancer cell-selective promoter. Hereto, we generated two new vectors expressing IL-2 and CD40L from a bicistronic expression cassette under the control of the melanoma/melanocyte-specific tyrosinase enhancer tyrosinase promoter (TETP), which we previously described for the melanoma-specific CRAd vector AdDeltaEP-TETP. These vectors gave rise to tightly controlled melanoma-specific transgene expression levels, which were only 5 to 40-fold lower than those from vectors controlled by the nonselective CMV promoter. Reporter analyses using Ad-CMV-eGFP in combination with AdDeltaEP-TETP revealed a high level of trans-complementation in melanoma cells (up to about 30-fold), but not in non-melanoma cells, unlike the AdCMV-eGFP/wtAd5 binary vector system, which was equally efficient in melanoma and non-melanoma cells. Similar findings were obtained when replacing the transgene vector AdCMV-eGFP with AdCMV-IL-2 or AdCMV-CD40L. However, the combination of the novel AdTETP-CD40L/IL-2 vector with AdDeltaEP-TETP or wtAd5 gave reproducible moderate 3-fold enhancements of IL-2 by trans-complementation only.

CONCLUSIONS

The cancer cell-selective TETP tested here did not give the expected enforceable transgene expression typically achieved in the Ad trans-complementing system. Reasons for this could include virus-mediated down regulation of limiting transcription factors, and/or competition for such factors by different promoters. Whether this finding is unique to the particular promoter system tested here, or also occurs with other promoters warrants further investigations.

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.

Possible applications for replicating HIV 1 vectors

Since its discovery some 25 years ago, much has been learned about HIV type 1 and the molecular details of its replication cycle. This insight has been used to develop lentiviral vector systems that have advantages over conventional retroviral vector systems. For safety reasons, the lentiviral vector systems are replication incompetent and the risk of generating a replication competent virus has been minimized. Nevertheless, there may be certain applications for replication competent HIV based vector systems, and we will review our activities in this particular field. This includes the generation of a conditionally replicating HIV 1 variant as a safe live attenuated virus vaccine, the construction of mini HIV variants as cancer selective viruses for virotherapy against leukemia, and the use of a conditionally live anti HIV gene therapy vector. Although safety concerns will undoubtedly remain for the use of replication competent HIV based vector systems, some of the results in cell culture systems are very promising and warrant further testing in appropriate animal models.

Antiangiogenic cancer therapy combined with oncolytic virotherapy leads to regression of established tumors in mice

Clinical trials of oncolytic virotherapy have shown low toxicity and encouraging signs of efficacy. However, it remains critically important to develop methods for systemic viral delivery if such therapies are to be clinically implemented to treat established tumors. In this respect, much effort is being focused on combining oncolytic viruses with standard treatment modalities such as inhibitors of VEGF165 (an alternatively spliced isoform of VEGF-A) signaling, which are widely used to treat several different cancers. Here, we have demonstrated that combining VEGF165 inhibitors with systemic delivery of oncolytic viruses leads to substantial regression and cure of established tumors in immunocompetent mice. We have shown that manipulating VEGF165-mediated signaling by administering VEGF165 to mice harboring mouse melanoma cells that do not express VEGF165 and by administering a VEGF inhibitor and then withdrawing treatment to allow VEGF levels to rebound in mice harboring mouse melanoma cells expressing VEGF165 allows tumor-associated endothelial cells transiently to support viral replication. This approach led to direct tumor cell lysis and triggered innate immune-mediated attack on the tumor vasculature. It also resulted in long-term antitumor effects, even against tumors in which viral replication is poorly supported. Since this combinatorial approach targets the tumor endothelium, we believe these data have direct, wide-ranging, and immediate clinical applicability across a broad range of tumor types.

Gene Therapy and its Implications in Dentistry

Background

The concept of transferring genes to tissues for clinical applications has been discussed for nearly half a century. The exponential increase in our ability to manipulate the genetic material of a cell via recombinant DNA technology has brought this goal closer to realization. The original perception that gene therapy should be considered only for a few major organs as a means of treating life-threatening disorders that are refractory to conventional treatment has changed. There are many non-life-threatening conditions that adversely affect a patient’s quality of life, for which there are no effective treatments. The lack of suitable treatment has permitted morbidity to become a rational basis for extending the scope of gene therapy. In the past few years, remarkable progress has been made in the field of gene therapy. While considerable problems remain, thus impeding the routine clinical use of gene transfer, gene therapy will have a pervasive and significant impact on areas that are based on biological science.

Aim

The purpose of this review is to examine the progress made in addressing gene transfer strategies for correcting various diseases and problems that are relevant to dental practice.

Gene therapy in Alzheimer's disease - potential for disease modification

Alzheimer's disease (AD) is the major cause of dementia in the elderly, leading to memory loss and cognitive decline. The mechanism underlying onset of the disease has not been fully elucidated. However, characteristic pathological manifestations include extracellular accumulation and aggregation of the amyloid beta-peptide (Abeta) into plaques and intracellular accumulation and aggregation of hyperphosphorylated tau, forming neurofibrillary tangles. Despite extensive research worldwide, no disease modifying treatment is yet available. In this review, we focus on gene therapy as a potential treatment for AD, and summarize recent work in the field, ranging from proof-of-concept studies in animal models to clinical trials. The multifactorial causes of AD offer a variety of possible targets for gene therapy, including two neurotrophic growth factors, nerve growth factor and brain-derived neurotrophic factor, Abeta-degrading enzymes, such as neprilysin, endothelin-converting enzyme and cathepsin B, and AD associated apolipoprotein E. This review also discusses advantages and drawbacks of various rapidly developing virus-mediated gene delivery techniques for gene therapy. Finally, approaches aiming at down-regulating amyloid precursor protein (APP) and beta-site APP cleaving enzyme 1 levels by means of siRNA-mediated knockdown are briefly summarized. Overall, the prospects appear hopeful that gene therapy has the potential to be a disease modifying treatment for AD.

Bioengineered viral vectors for targeting and killing prostate cancer cells

Enabling the transduction of therapeutic gene expression exclusively in diseased sites is the key to developing more effective treatments for advanced prostate cancer using viral-based therapy. While prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by lentiviruses with envelope proteins engineered to bind to this therapeutic antibody. More importantly, after intravenous injection, this trastuzumab-bound lentivirus is able to target castration-resistant prostate tumor xenografts, albeit with low efficiency. This proof of principle opens up multiple possibilities for the prevention and treatment of prostate cancer using a viral-based therapy. However, to be safe and more effective, the viral vectors must target prostate cancer cells more selectively and efficiently. A higher degree of specificity and efficiency of cancer cell targeting can be achieved by engineering viral vectors to bind to a specific cell surface marker and by controlling the expression of the therapeutic payload at transcriptional level, with a tissue-specific promoter, and at the translational level, with a regulatory sequences inserted into either the 5'UTR or 3'UTR regions of the therapeutic gene(s). The latter would be designed to ensure that translation of this mRNA occurs exclusively in malignant cells. Furthermore, in order to obtain a potent anti-tumor effect, viral vectors would be engineered to express pro-apoptotic genes, intra-cellar antibodies/nucleotide aptamers to block critical proteins, or siRNAs to knockdown essential cellular mRNAs. Alternatively, controlled expression of an essential viral gene would restore replication competence to the virus and enable selective oncolysis of tumor cells. Successful delivery of such bioengineered viruses may provide a more effective way to treat advanced prostate cancer.

Enhanced antitumor effects of an engineered measles virus Edmonston strain expressing the wild-type N, P, L genes on human renal cell carcinoma

Measles virus Edmonston strain (MV-Edm) is thought to have remarkable oncolytic activity that selectively destroys human tumor cells. The P/V/C protein of wild-type MV was shown to resist the antiviral effects of interferon (IFN)-alpha. Here, we engineered new MVs by arming MV-Edm tag strain (a V-defective vaccine-lineage strain, MV-Etag) with the P or N, P, and L genes of wild-type MV (MV-P and MV-NPL, respectively). The oncolytic activities of the MVs were determined in human renal cell carcinoma (RCC) cell lines and primary human RCC cells by the MTT assay. The antitumor efficacy of the MVs was evaluated in A-498 xenografts in nude mice. IFN-alpha effectively inhibited the replication of MV-Etag and MV-P, but not MV-NPL. MV-NPL more efficiently induced cytopathic effects (CPEs) in OS-RC-2 cells, even in the presence of human IFN-alpha. MV-NPL replicated more rapidly than MV-P and MV-Etag in A-498 cells. Apoptosis was induced earlier in A-498 cells by MV-NPL than MV-Etag and MV-P. MV-NPL showed more significant antitumoral effects and had prolonged replication compared to MV-Etag and MV-P. In this study, we demonstrated that the newly engineered MV-NPL has more effective oncolytic activity and may help establish an innovative cancer therapy.

Molecular and traditional chemotherapy: a united front against prostate cancer

Castrate resistant prostate cancer (CRPC) is essentially incurable. Recently though, chemotherapy demonstrated a survival benefit ( approximately 2months) in the treatment of CRPC. While this was a landmark finding, suboptimal efficacy and systemic toxicities at the therapeutic doses warranted further development. Smart combination therapies, acting through multiple mechanisms to target the heterogeneous cell populations of PC and with potential for reduction in individual dosing, need to be developed. In that, targeted molecular chemotherapy has generated significant interest with the potential for localized treatment to generate systemic efficacy. This can be further enhanced through the use of oncolytic conditionally replicative adenoviruses (CRAds) to deliver molecular chemotherapy. The prospects of chemotherapy and molecular-chemotherapy as single and as components of combination therapies are discussed.

In vitro dynamic visualization analysis of fluorescently labeled minor capsid protein IX and core protein V by simultaneous detection

Oncolytic adenoviruses represent a promising therapeutic medicine for human cancer therapy, but successful translation into human clinical trials requires careful evaluation of their viral characteristics. While the function of adenovirus proteins has been analyzed in detail, the dynamics of adenovirus infection remain largely unknown due to technological constraints that prevent adequate tracking of adenovirus particles after infection. Fluorescence labeling of adenoviral particles is one new strategy designed to directly analyze the dynamic processes of viral infection in virus-host cell interactions. We hypothesized that the double labeling of an adenovirus with fluorescent proteins would allow us to properly analyze intracellular viruses and the fate of viral proteins in a live analysis of an adenovirus as compared to single labeling. Thus, we generated a fluorescently labeled adenovirus with both a red fluorescent minor capsid protein IX (pIX) [pIX monomeric red fluorescent protein 1 (mRFP1)] and a green fluorescent minor core protein V (pV) [pV enhanced green fluorescent protein (EGFP)], resulting in Ad5-IX-mRFP1-E3-V-EGFP. The fluorescent signals for pIX-mRFP1 and pV-EGFP were detected within 10 min in living cells. However, a growth curve analysis of Ad5-IX-mRFP1-E3-V-EGFP showed an approximately 150-fold reduced production of the viral progeny at 48 h postinfection as compared to adenovirus type 5. Interestingly, pIX-mRFP1 and pV-EGFP were initially localized in the cytoplasm and nucleolus, respectively, at 18 h postinfection. These proteins were observed in the nucleus during the late stage of infection, and relocalization of the proteins was observed in an adenoviral-replication-dependent manner. These results indicate that simultaneous detection of adenoviruses using dual-fluorescent proteins is suitable for real-time analysis, including identification of infected cells and monitoring of viral spread, which will be required for a complete evaluation of oncolytic adenoviruses.