Targeted Measles Virus Vector Displaying Echistatin Infects Endothelial Cells via αvβ3 and Leads to Tumor Regression

Prospects for Using Expression Patterns of Paramyxovirus Receptors as Biomarkers for Oncolytic Virotherapy

Simple Summary

Some non-pathogenic viruses that do not cause serious illness in humans can efficiently target and kill cancer cells and may be considered candidates for cancer treatment with virotherapy. However, many cancer cells are protected from viruses. An important goal of personalized cancer treatment is to identify viruses that can kill a certain type of cancer cells. To this end, researchers investigate expression patterns of cell entry receptors, which viruses use to bind to and enter host cells. We summarized and analyzed the receptor expression patterns of two paramyxoviruses: The non-pathogenic measles and the Sendai viruses. The receptors for these viruses are different and can be proteins or lipids with attached carbohydrates. This review discusses the prospects for using these paramyxovirus receptors as biomarkers for successful personalized virotherapy for certain types of cancer.

Abstract

The effectiveness of oncolytic virotherapy in cancer treatment depends on several factors, including successful virus delivery to the tumor, ability of the virus to enter the target malignant cell, virus replication, and the release of progeny virions from infected cells. The multi-stage process is influenced by the efficiency with which the virus enters host cells via specific receptors. This review describes natural and artificial receptors for two oncolytic paramyxoviruses, nonpathogenic measles, and Sendai viruses. Cell entry receptors are proteins for measles virus (MV) and sialylated glycans (sialylated glycoproteins or glycolipids/gangliosides) for Sendai virus (SeV). Accumulated published data reviewed here show different levels of expression of cell surface receptors for both viruses in different malignancies. Patients whose tumor cells have low or no expression of receptors for a specific oncolytic virus cannot be successfully treated with the virus. Recent published studies have revealed that an expression signature for immune genes is another important factor that determines the vulnerability of tumor cells to viral infection. In the future, a combination of expression signatures of immune and receptor genes could be used to find a set of oncolytic viruses that are more effective for specific malignancies.

Tumour vasculature: Friend or foe of oncolytic viruses?

In the past two decades there have been substantial advances in understanding the anti-cancer mechanisms of oncolytic viruses (OVs). OVs can mediate their effects directly, by preferentially infecting and killing tumour cells. Additionally, OVs can indirectly generate anti-tumour immune responses. These differing mechanisms have led to a paradoxical divergence in strategies employed to further increase the potency of oncolytic virotherapies. On one hand, the tumour neovasculature is seen as a vital lifeline to the survival of the tumour, leading some to use OVs to target the tumour vasculature in hopes to starve cancers. Therapeutics causing vascular collapse can potentiate tumour hypoxia, nutrient restriction and pro-inflammatory cytokine release, which has shown promise in oncological studies. On the other hand, the same vasculature plays an important role for the dissemination of OVs, trafficking of effector cells and other therapeutics, which has prompted researchers to find ways of normalizing the vasculature to enhance infiltration of leukocytes and delivery of therapeutic agents. This article describes the recent developments of therapies aimed to shut down versus normalize tumour vasculature in order to inform researchers striving to optimize OV-based therapies.

Measles virus in cancer therapy

Over the last years, the development of viruses to treat cancer patients has re-gained considerable attention. A genetically modified herpesvirus, Talimogene laherparepvec, has already been authorized for the treatment of melanoma patients. Also recombinant measles virus (MeV) is developed as an oncolytic virus. Because of its high genetic flexibility, a number of different MeV strains have been the basis for the generation of targeted, armed, or shielded viruses that are highly specific for a given tumor target, more effective, or protected against serum neutralization. Such MeV have been extensively tested in vitro and in vivo, whereby remarkable oncolytic potency is accompanied by safety also in non-human primates. Therefore, MeV has been introduced into 19 different clinical trials and has reached phase II against two different tumor entities, multiple myeloma and ovarian carcinoma. Remarkably, one patient with advanced stage myeloma experienced long-term remission after treatment, visualizing the potency of this approach.

Viral Pathogenesis, Recombinant Vaccines, and Oncolytic Virotherapy: Applications of the Canine Distemper Virus Reverse Genetics System

Canine distemper virus (CDV) is a highly contagious pathogen transmissible to a broad range of terrestrial and aquatic carnivores. Despite the availability of attenuated vaccines against CDV, the virus remains responsible for outbreaks of canine distemper (CD) with significant morbidity and mortality in domesticated and wild carnivores worldwide. CDV uses the signaling lymphocytic activation molecule (SLAM, or CD150) and nectin-4 (PVRL4) as entry receptors, well-known tumor-associated markers for several lymphadenomas and adenocarcinomas, which are also responsible for the lysis of tumor cells and apparent tumor regression. Thus, CDV vaccine strains have emerged as a promising platform of oncolytic viruses for use in animal cancer therapy. Recent advances have revealed that use of the CDV reverse genetic system (RGS) has helped increase the understanding of viral pathogenesis and explore the development of recombinant CDV vaccines. In addition, genetic engineering of CDV based on RGS approaches also has the potential of enhancing oncolytic activity and selectively targeting tumors. Here, we reviewed the host tropism and pathogenesis of CDV, and current development of recombinant CDV-based vaccines as well as their use as oncolytic viruses against cancers.

Clinical Trials with Oncolytic Measles Virus: Current Status and Future Prospects

Attenuated Edmonston lineage measles virus (MV-Edm) vaccine strains can preferentially infect and lyse a wide variety of cancer cells. Oncolytic MV-Edm derivatives are genetically engineered to express the human carcinoembryonic antigen (MV-CEA virus) or the human sodium iodide symporter (MV-NIS virus) and are currently being tested in clinical trials against ovarian cancer, glioblastoma multiforme, multiple myeloma, mesothelioma, head and neck cancer, breast cancer and malignant peripheral nerve sheath tumors. This review describes the basic and preclinical data that facilitated the clinical translation of MV-Edm strains, and summarizes the clinical results of this oncolytic platform to date. Furthermore, we discuss the latest clinically relevant MV-Edm vector developments and creative strategies for future translational steps.

Oncolytic Viruses for Multiple Myeloma Therapy

Although recent treatment advances have improved outcomes for patients with multiple myeloma (MM), the disease frequently becomes refractory to current therapies. MM thus remains incurable for most patients and new therapies are urgently needed. Oncolytic viruses are a promising new class of therapeutics that provide tumor-targeted therapy by specifically infecting and replicating within cancerous cells. Oncolytic therapy yields results from both direct killing of malignant cells and induction of an anti-tumor immune response. In this review, we will describe oncolytic viruses that are being tested for MM therapy with a focus on those agents that have advanced into clinical trials.

Potential of oncolytic viruses in the treatment of multiple myeloma

Multiple myeloma (MM) is a clonal malignancy of plasma cells that is newly diagnosed in ~30,000 patients in the US each year. While recently developed therapies have improved the prognosis for MM patients, relapse rates remain unacceptably high. To overcome this challenge, researchers have begun to investigate the therapeutic potential of oncolytic viruses as a novel treatment option for MM. Preclinical work with these viruses has demonstrated that their infection can be highly specific for MM cells and results in impressive therapeutic efficacy in a variety of preclinical models. This has led to the recent initiation of several human trials. This review summarizes the current state of oncolytic therapy as a therapeutic option for MM and highlights a variety of areas that need to be addressed as the field moves forward.

The disintegrin echistatin in combination with doxorubicin targets high-metastatic human osteosarcoma overexpressing ανβ3 integrin in chick embryo and nude mouse models

Echistatin, a cyclic RGD peptide, which is an antagonist of αvβ3 integrin (disintegrin), inhibited human osteosarcoma in the chick chorioallontoic membrane (CAM) model and tumor growth and pulmonary metastases in a nude mouse orthotopic model. A high-metastatic variant of human osteosarcoma, 143B-LM4, overexpressing αvβ3 integrin was used. Tumor angiogenesis by high-metastatic variant 143B-LM4 cells in the CAM was significantly inhibited by echistatin (P<0.05) as was overall growth. A doxorubicin (DOX)-echistatin combination inhibited orthotopic tumor growth compared to untreated control (P<0.01) or DOX alone (P<0.05) in nude mice. Tumor-bearing mice treated with the DOX-echistatin combination survived longer than those treated with DOX alone or control PBS (P<0.01 and P<0.01, respectively). Echistatin also inhibited experimental lung metastasis of 143B-LM4 cells in nude mice. These results suggest that DOX in combination with a disintegrin has potential to treat osteosarcoma and that αvβ3 integrin may be a target for osteosarcoma.

Using Cystine Knot Proteins as a Novel Approach to Retarget Oncolytic Measles Virus

Modified measles virus (MV) has effective oncolytic activity preclinically and is currently being investigated in clinical trials for various types of cancer. We investigated the use of cystine knot proteins (CKPs) to direct MV activity. CKPs are short polypeptides that bind their targets with high affinity. We used a CKP that binds αvβ3, αvβ5, and α5β1 integrins with single-digit nanomolar affinity to retarget MV to the integrins (MV-CKPint). MV-CKPint infected, replicated in, and killed human glioblastoma, medulloblastoma, diffuse intrinsic pontine glioma (DIPG), and melanoma cancer cells in vitro, all of which express the target integrins. MV-CKPint activity was competitively blocked by echistatin, an integrin binding peptide. When the CKP was cleaved from the viral H protein at an included protease site, virus activity was abrogated. When delivered intravenously (i.v.), the retargeted virus reached a subcutaneous glioblastoma tumor bed and produced cytopathic effects similar to that shown by intratumoral injection of the virus. Because these target integrins are overexpressed by tumor vascular endothelium, MV-CKPint may allow for effective therapy with i.v. injection. These results indicate for the first time that CKPs can be used to retarget MV for a receptor of choice. In addition, MV-CKPint provides proof of principle for the use of a CKP of interest to retarget any enveloped virus for both oncolytic and gene therapy purposes.

Efficient method for site-directed mutagenesis in large plasmids without subcloning

Commonly used methods for site-directed DNA mutagenesis require copying the entire target plasmid. These methods allow relatively easy modification of DNA sequences in small plasmids but become less efficient and faithful for large plasmids, necessitating full sequence verification. Introduction of mutations in larger plasmids requires subcloning, a slow and labor-intensive process, especially for multiple mutations. We have developed an efficient DNA mutagenesis technique, UnRestricted Mutagenesis and Cloning (URMAC) that replaces subcloning steps with quick biochemical reactions. URMAC does not suffer from plasmid size constraints and allows simultaneous introduction of multiple mutations. URMAC involves manipulation of only the mutagenesis target site(s), not the entire plasmid being mutagenized, therefore only partial sequence verification is required. Basic URMAC requires two PCR reactions, each followed by a ligation reaction to circularize the product, with an optional third enrichment PCR step followed by a traditional cloning step that requires two restriction sites. Here, we demonstrate URMAC’s speed, accuracy, and efficiency through several examples, creating insertions, deletions or substitutions in plasmids ranging from 2.6 kb to 17 kb without subcloning.

Designing and building oncolytic viruses

Oncolytic viruses (OVs) are engineered and/or evolved to propagate selectively in cancerous tissues. They have a dual mechanism of action; direct killing of infected cancer cells cross-primes anticancer immunity to boost the killing of uninfected cancer cells. The goal of the field is to develop OVs that are easily manufactured, efficiently delivered to disseminated sites of cancer growth, undergo rapid intratumoral spread, selectively kill tumor cells, cause no collateral damage and pose no risk of transmission in the population. Here we discuss the many virus engineering strategies that are being pursued to optimize delivery, intratumoral spread and safety of OVs derived from different virus families. With continued progress, OVs have the potential to transform the paradigm of cancer care.

Measles to the Rescue: A Review of Oncolytic Measles Virus

Oncolytic virotherapeutic agents are likely to become serious contenders in cancer treatment. The vaccine strain of measles virus is an agent with an impressive range of oncolytic activity in pre-clinical trials with increasing evidence of safety and efficacy in early clinical trials. This paramyxovirus vaccine has a proven safety record and is amenable to careful genetic modification in the laboratory. Overexpression of the measles virus (MV) receptor CD46 in many tumour cells may direct the virus to preferentially enter transformed cells and there is increasing awareness of the importance of nectin-4 and signaling lymphocytic activation molecule (SLAM) in oncolysis. Successful attempts to retarget MV by inserting genes for tumour-specific ligands to antigens such as carcinoembryonic antigen (CEA), CD20, CD38, and by engineering the virus to express synthetic microRNA targeting sequences, and "blinding" the virus to the natural viral receptors are exciting measures to increase viral specificity and enhance the oncolytic effect. Sodium iodine symporter (NIS) can also be expressed by MV, which enables in vivo tracking of MV infection. Radiovirotherapy using MV-NIS, chemo-virotherapy to convert prodrugs to their toxic metabolites, and immune-virotherapy including incorporating antibodies against immune checkpoint inhibitors can also increase the oncolytic potential. Anti-viral host immune responses are a recognized barrier to the success of MV, and approaches such as transporting MV to the tumour sites by carrier cells, are showing promise. MV Clinical trials are producing encouraging preliminary results in ovarian cancer, myeloma and cutaneous non-Hodgkin lymphoma, and the outcome of currently open trials in glioblastoma multiforme, mesothelioma and squamous cell carcinoma are eagerly anticipated.

Enhanced lysis by bispecific oncolytic measles viruses simultaneously using HER2/neu or EpCAM as target receptors

To target oncolytic measles viruses (MV) to tumors, we exploit the binding specificity of designed ankyrin repeat proteins (DARPins). These DARPin-MVs have high tumor selectivity while maintaining excellent oncolytic potency. Stability, small size, and efficacy of DARPins allowed the generation of MVs simultaneously targeted to tumor marker HER2/neu and cancer stem cell (CSC) marker EpCAM. For optimization, the linker connecting both DARPins was varied in flexibility and length. Flexibility had no impact on fusion helper activity whereas length had. MVs with bispecific MV-H are genetically stable and revealed the desired double-target specificity. In vitro, the cytolytic activity of bispecific MVs was superior or comparable to mono-targeted viruses depending on the target cells. In vivo, therapeutic efficacy of the bispecific viruses was validated in an orthotopic ovarian carcinoma model revealing an effective reduction of tumor mass. Finally, the power of bispecific targeting was demonstrated on cocultures of different tumor cells thereby mimicking tumor heterogeneity in vitro, more closely reflecting real tumors. Here, bispecific excelled monospecific viruses in efficacy. DARPin-based targeting domains thus allow the generation of efficacious oncolytic viruses with double specificity, with the potential to handle intratumoral variation of antigen expression and to simultaneously target CSCs and the bulk tumor mass.

Biosafety considerations for attenuated measles virus vectors used in virotherapy and vaccination

Attenuated measles virus (MV) is one of the most effective and safe vaccines available, making it attractive candidate vector to prevent infectious diseases. Attenuated MV have acquired the ability to use the complement regulator CD46 as a major receptor to mediate virus entry and intercellular fusion. Therefore, attenuated MV strains preferentially infect and destroy a wide variety of cancer cells making them also attractive oncolytic vectors. The use of recombinant MV vector has to comply with various regulatory requirements, particularly relating to the assessment of potential risks for human health and the environment. The present article highlights the main characteristics of MV and recombinant MV vectors used for vaccination and virotherapy and discusses these features from a biosafety point of view.

Targeting tumor vasculature through oncolytic virotherapy: recent advances

The oncolytic virotherapy field has made significant advances in the last decade, with a rapidly increasing number of early- and late-stage clinical trials, some of them showing safety and promising therapeutic efficacy. Targeting tumor vasculature by oncolytic viruses (OVs) is an attractive strategy that offers several advantages over nontargeted viruses, including improved tumor viral entry, direct antivascular effects, and enhanced antitumor efficacy. Current understanding of the biological mechanisms of tumor neovascularization, novel vascular targets, and mechanisms of resistance has allowed the development of oncolytic viral vectors designed to target tumor neovessels. While some OVs (such as vaccinia and vesicular stomatitis virus) can intrinsically target tumor vasculature and induce vascular disruption, the majority of reported vascular-targeted viruses are the result of genetic manipulation of their viral genomes. Such strategies include transcriptional or transductional endothelial targeting, "armed" viruses able to downregulate angiogenic factors, or to express antiangiogenic molecules. The above strategies have shown preclinical safety and improved antitumor efficacy, either alone, or in combination with standard or targeted agents. This review focuses on the recent efforts toward the development of vascular-targeted OVs for cancer treatment and provides a translational/clinical perspective into the future development of new generation biological agents for human cancers.

Oncolysis by paramyxoviruses: multiple mechanisms contribute to therapeutic efficiency

Oncolytic paramyxoviruses include some strains of Measles, Mumps, Newcastle disease, and Sendai viruses. All these viruses are well equipped for promoting highly specific and efficient malignant cell death, which can be direct and/or immuno-mediated. A number of proteins that serve as natural receptors for oncolytic paramyxoviruses are frequently overexpressed in malignant cells. Therefore, the preferential interaction of paramyxoviruses with malignant cells rather than with normal cells is promoted. Due to specific genetic defects of cancer cells in the interferon (IFN) and apoptotic pathways, viral replication has the potential to be promoted specifically in tumors. Viral mediation of syncytium formation (a polykaryonic structure) promotes intratumoral paramyxo-virus replication and spreading, without exposure to host neutralizing antibodies. So, two related processes: efficient intratumoral infection spread as well as the consequent mass malignant cell death, both are enhanced. In general, the paramyxoviruses elicit strong anticancer innate and adaptive immune responses by triggering multiple danger signals. The paramyxoviruses are powerful inducers of IFN and other immuno-stimulating cytokines. These viruses efficiently promote anticancer activity of natural killer cells, dendritic cells, and cytotoxic T lymphocytes. Moreover, a neuraminidase (sialidase), a component of the viral envelope of Newcastle Disease, Mumps, and Sendai viruses, can cleave sialic acids on the surface of malignant cells thereby unmasking cancer antigens and exposing them to the immune system. These multiple mechanisms contribute to therapeutic efficacy of oncolytic paramyxovi-ruses and are responsible for encouraging results in preclinical and clinical studies.

Viral oncolysis - can insights from measles be transferred to canine distemper virus?

Neoplastic diseases represent one of the most common causes of death among humans and animals. Currently available and applied therapeutic options often remain insufficient and unsatisfactory, therefore new and innovative strategies and approaches are highly needed. Periodically, oncolytic viruses have been in the center of interest since the first anecdotal description of their potential usefulness as an anti-tumor treatment concept. Though first reports referred to an incidental measles virus infection causing tumor regression in a patient suffering from lymphoma several decades ago, no final treatment concept has been developed since then. However, numerous viruses, such as herpes-, adeno- and paramyxoviruses, have been investigated, characterized, and modified with the aim to generate a new anti-cancer treatment option. Among the different viruses, measles virus still represents a highly interesting candidate for such an approach. Numerous different tumors of humans including malignant lymphoma, lung and colorectal adenocarcinoma, mesothelioma, and ovarian cancer, have been studied in vitro and in vivo as potential targets. Moreover, several concepts using different virus preparations are now in clinical trials in humans and may proceed to a new treatment option. Surprisingly, only few studies have investigated viral oncolysis in veterinary medicine. The close relationship between measles virus (MV) and canine distemper virus (CDV), both are morbilliviruses, and the fact that numerous tumors in dogs exhibit similarities to their human counterpart, indicates that both the virus and species dog represent a highly interesting translational model for future research in viral oncolysis. Several recent studies support such an assumption. It is therefore the aim of the present communication to outline the mechanisms of morbillivirus-mediated oncolysis and to stimulate further research in this potentially expanding field of viral oncolysis in a highly suitable translational animal model for the benefit of humans and dogs.

Attenuated measles virus controls pediatric acute B-lineage lymphoblastic leukemia in NOD/SCID mice

Novel therapies are needed for pediatric acute lymphoblastic leukemia resistant to conventional therapy. While emerging data suggest leukemias as possible targets of oncolytic attenuated measles virus, it is unknown whether measles virus can eradicate disseminated leukemia, in particular pediatric acute lymphoblastic leukemia. We evaluated the efficacy of attenuated measles virus against a large panel of pediatric xenografted and native primary acute lymphoblastic leukemias ex vivo, and against four different acute lymphoblastic leukemia xenografts of B-lineage in non-obese diabetic/severe combined immunodeficient mice. Ex vivo, attenuated measles virus readily spread among and effectively killed leukemia cells while sparing normal human blood cells and their progenitors. In immunodeficient mice with disseminated acute lymphoblastic leukemia a few intravenous injections of attenuated measles virus sufficed to eradicate leukemic blasts in the hematopoietic system and to control central nervous system disease resulting in long-term survival in three of the four xenografted B-lineage leukemias. Differential sensitivity of leukemia cells did not require increased expression of the measles entry receptors CD150 or CD46 nor absence of the anti-viral retinoic acid-inducible gene I/melanoma differentiation associated gene-5 /interferon pathway. Attenuated oncolytic measles virus is dramatically effective against pediatric B-lineage acute lymphoblastic leukemia in the pre-clinical setting warranting further investigations towards clinical translation.

Antibody neutralization of retargeted measles viruses

The measles virus (MV) vaccine lineage is a promising oncolytic but prior exposure to the measles vaccine or wild-type MV strains limits treatment utility due to the presence of anti-measles antibodies. MV entry can be redirected by displaying a polypeptide ligand on the Hemagglutinin (H) C-terminus. We hypothesized that retargeted MV would escape neutralization by monoclonal antibodies (mAbs) recognizing the H receptor-binding surface and be less susceptible to neutralization by human antisera. Using chimeric H proteins, with and without mutations that ablate MV receptor binding, we show that retargeted MVs escape mAbs that target the H receptor-binding surface by virtue of mutations that ablate infection via SLAM and CD46. However, C-terminally displayed domains do not mediate virus entry in the presence of human antibodies that bind to the underlying H domain. In conclusion, utility of retargeted oncolytic measles viruses does not extend to evasion of human serum neutralization.

Cell carriers for oncolytic viruses: current challenges and future directions

The optimal route for clinical delivery of oncolytic viruses is thought to be systemic intravenous injection; however, the immune system is armed with several highly efficient mechanisms to remove pathogens from the circulatory system. To overcome the challenges faced in trying to delivery oncolytic viruses specifically to tumors via the bloodstream, carrier cells have been investigated to determine their suitability as delivery vehicles for systemic administration of oncolytic viruses. Cell carriers protect viruses from neutralization, one of the most limiting aspects of oncolytic virus interaction with the immune system. Cell carriers can also possess inherent tumor tropism, thus directing the delivery of the virus more specifically to a tumor. With preclinical studies already demonstrating the success and feasibility of this approach with multiple oncolytic viruses, clinical evaluation of cell-mediated delivery of viruses is on the horizon. Meanwhile, ongoing preclinical studies are aimed at identifying new cellular vehicles for oncolytic viruses and improving current promising cell carrier platforms.

Characteristics of oncolytic vesicular stomatitis virus displaying tumor-targeting ligands

We sought proof of principle that tumor-targeting ligands can be displayed on the surface of vesicular stomatitis virus (VSV) by engineering its glycoprotein. Here, we successfully rescued VSVs displaying tumor vasculature-targeting ligands. By using a rational approach, we investigated various feasible insertion sites on the G protein of VSV (VSV-G) for display of tumor vasculature-targeting ligands, cyclic RGD (cRGD) and echistatin. We found seven sites on VSV-G that tolerated insertion of the 9-residue cRGD peptide, two of which could tolerate insertion of the 49-amino acid echistatin domain. All of the ligand-displaying viruses replicated as well as the parental virus. In vitro studies demonstrated that the VSV-echistatin viruses specifically bound to targeted integrins. Since the low-density lipoprotein receptor (LDLR) was recently identified as a major receptor for VSV, we investigated the entry of ligand-displaying viruses after masking LDLR. The experiment showed that the modified viruses can enter the cell independently of LDLR, whereas entry of unmodified virus is significantly blocked by a specific monoclonal antibody against LDLR. Both parental and ligand-displaying viruses displayed equal oncolytic efficacies in a syngeneic mouse myeloma model. We further demonstrated that single-chain antibody fragments against tumor-specific antigens can be inserted at the N terminus of the G protein and that corresponding replication-competent VSVs can be rescued efficiently. Overall, we demonstrated that functional tumor-targeting ligands can be displayed on replication-competent VSVs without perturbing viral growth and oncolytic efficacy. This study provides a rational foundation for the future development of fully retargeted oncolytic VSVs.

Mounting a strategic offense: fighting tumor vasculature with oncolytic viruses

Blood supply within a tumor drives progression and ultimately allows for metastasis. Many anticancer therapies target tumor vasculature, but their individual effectiveness is limited because they induce indirect cell death. Agents that disrupt nascent and/or established tumor vasculature while simultaneously killing cancer cells would certainly have a greater impact. Oncolytic virotherapy utilizes attenuated viruses that replicate specifically within a tumor. They induce cytotoxicity through a combination of direct cell lysis, antitumor immune stimulation, and recently identified antitumor vascular effects. This review summarizes the novel preclinical and clinical evidence regarding the antitumor vascular effects of oncolytic viruses, which include infection and lysis of tumor endothelial cells, natural or genetically engineered antiangiogenic properties, and combination therapy with clinically approved antivascular agents.

Attenuated oncolytic measles virus strains as cancer therapeutics

Attenuated measles virus vaccine strains have emerged as a promising oncolytic vector platform, having shown significant anti-tumor activity against a broad range of malignant neoplasms. Measles virus strains derived from the attenuated Edmonston-B (MV-Edm) vaccine lineage have been shown to selectively infect, replicate in and lyse cancer cells while causing minimal cytopathic effect on normal tissues. This review summarizes the preclinical data that led to the rapid clinical translation of oncolytic measles vaccine strains and provides an overview of early clinical data using this oncolytic platform. Furthermore, novel approaches currently under development to further enhance the oncolytic efficacy of MV-Edm strains, including strategies to circumvent immunity or modulate immune system responses, combinatorial approaches with standard treatment modalities, virus retargeting as well as strategies for in vivo monitoring of viral replication are discussed.

Oncolytic measles virus strains as novel anticancer agents

INTRODUCTION

Replication-competent oncolytic measles virus (MV) strains preferentially infect and destroy a wide variety of cancer tissues. Clinical translation of engineered attenuated MV vaccine derivatives is demonstrating the therapeutic potential and negligible pathogenicity of these strains in humans.

AREAS COVERED

The present review summarizes the mechanisms of MV tumor selectivity and cytopathic activity as well as the current data on the oncolytic efficacy and preclinical testing of MV strains. Investigational strategies to reprogram MV selectivity, escape antiviral immunity and modulate the immune system to enhance viral delivery and tumor oncolysis are also discussed.

EXPERT OPINION

Clinical viral kinetic data derived from noninvasive monitoring of reporter transgene expression will guide future protocols to enhance oncolytic MV efficacy. Anti-measles immunity is a major challenge of measles-based therapeutics and various strategies are being investigated to modulate immunity. These include the combination of MV therapy with immunosuppressive drugs, such as cyclophosphamide, the use of cell carriers and the introduction of immunomodulatory transgenes and wild-type virulence genes. Available MV retargeting technologies can address safety considerations that may arise as more potent oncolytic MV vectors are being developed.

Effect of the disintegrin eristostatin on melanoma-natural killer cell interactions

Malignant melanoma is difficult to treat due to its resistance to chemotherapeutic regimens. Discovery of new pharmaceuticals with inhibitory potential can be helpful in the development of novel treatments. The snake venom disintegrin eristostatin, from the viper Eristicophis macmahoni, caused immunodeficient mice to be significantly protected from development of lung colonization when melanoma cells and the disintegrin were co-injected in vivo into the lateral tail vein compared to vehicle controls. Cytotoxicity assays suggested that eristostatin makes the melanoma cells a better target for lysis by human natural killer cells. Direct binding assays using atomic force microscopy showed eristostatin does specifically bind the surface of the six melanoma cell lines tested. Eristostatin binding was partially inhibited by the addition of soluble RGDS peptide, suggesting an integrin as one likely, but not the sole, binding partner. Studies done with melanoma cells on a culture dish and natural killer cells attached to a cantilever tip in atomic force microscopy showed four major populations of interactions which exhibited altered frequency and unbinding strength in the presence of eristostatin.

Oncolytic measles virus retargeting by ligand display

Despite significant advances in recent years, treatment of metastatic malignancies remains a significant challenge. There is an urgent need for development of novel therapeutic approaches. Virotherapy approaches have considerable potential, and among them measles virus (MV) vaccine strains have emerged as a promising oncolytic platform. Retargeted MV strains deriving from the Edmonston vaccine lineage (MV-Edm) have shown comparable antitumor efficacy to unmodified strains against receptor expressing tumor cells with improved therapeutic index. Here, we describe the construction, rescue, amplification, and titration of fully retargeted MV-Edm derivatives displaying tumor specific receptor binding ligands on the viral surface in combination with H protein CD46 and SLAM entry ablating mutations.

Targeted cell fusion facilitates stable heterokaryon generation in vitro and in vivo

Induced cell fusion has enabled several important discoveries, including the phenomenon of nuclear reprogramming and may yet be applied as a novel therapy for degenerative diseases. However, existing fusogens lack the efficiency required to enable investigation of the epigenetic modifications underlying nuclear reprogramming and the specificity required for clinical application. Here we present a chimeric measles hemagglutinin, Hα7, which specifically and efficiently mediates the fusion of diverse cell types with skeletal muscle both in vitro and in vivo. When compared directly to polyethylene glycol, Hα7 consistently generated a substantial increase in heterokaryon yield and exhibited insignificant levels of toxicity. Moreover, this increased fusion efficiency enabled detection of chromatin modifications associated with nuclear reprogramming following Hα7-mediated fusion of human fibroblasts and mouse myotubes. Finally, Hα7 was also capable of increasing the contribution of transplanted fibroblasts to skeletal muscle repair in vivo, suggesting that this strategy could be used for therapeutic gene delivery.

Strategies to enhance viral penetration of solid tumors

The efficient delivery of viral vectors to tumors is an active area of investigation. A number of barriers exist that must be overcome to achieve good penetration of vectors into tumors and distribution of their effects throughout the tumor mass. Replicating oncolytic viruses have the advantage of being able to amplify the initial dose, but progeny virus are prevented from spreading because of a dense mass of tightly packed cells with a dense extracellular matrix, admixed normal stromal cells, and high interstitial pressure. Although intratumoral injection may ensure initial delivery the distribution achieved by intravenous administration may be superior and come with beneficial bystander damage to the tumor vasculature. Strategies to enhance intravenous delivery and subsequent spread of these vectors within tumors are being developed by a number of groups. Achieving the goal of efficient penetration and spread of viruses within solid tumors is a necessary prerequisite to significant improvements in virus-vectored therapy of solid tumors.

Use of attenuated paramyxoviruses for cancer therapy

Paramyxoviruses, measles virus (MV), mumps virus (MuV) and Newcastle disease virus (NDV), are well known for causing measles and mumps in humans and Newcastle disease in birds. These viruses have been tamed (attenuated) and successfully used as vaccines to immunize their hosts. Remarkably, pathogenic MuV and vaccine strains of MuV, MV and NDV efficiently infect and kill cancer cells and are consequently being investigated as novel cancer therapies (oncolytic virotherapy). Phase I/II clinical trials have shown promise but treatment efficacy needs to be enhanced. Technologies being developed to increase treatment efficacy include: virotherapy in combination with immunosuppressive drugs (cyclophosphamide); retargeting of viruses to specific tumor types or tumor vasculature; using infected cell carriers to protect and deliver the virus to tumors; and genetic manipulation of the virus to increase viral spread and/or express transgenes during viral replication. Transgenes have enabled noninvasive imaging or tracking of viral gene expression and enhancement of tumor destruction.

Double suicide genes selectively kill human umbilical vein endothelial cells

Background

To construct a recombinant adenovirus containing CDglyTK double suicide genes and evaluate the killing effect of the double suicide genes driven by kinase domain insert containing receptor (KDR) promoter on human umbilical vein endothelial cells.

Methods

Human KDR promoter, Escherichia coli (E. coli) cytosine deaminase (CD) gene and the herpes simplex virus-thymidine kinase (TK) gene were cloned using polymerase chain reaction (PCR). Plasmid pKDR-CDglyTK was constructed with the KDR promoter and CDglyTK genes. A recombinant adenoviral plasmid AdKDR-CDglyTK was then constructed and transfected into 293 packaging cells to grow and harvest adenoviruses. KDR-expressing human umbilical vein endothelial cells (ECV304) and KDR-negative liver cancer cell line (HepG2) were infected with the recombinant adenoviruses at different multiplicity of infection (MOI). The infection rate was measured by green fluorescent protein (GFP) expression. The infected cells were cultured in culture media containing different concentrations of prodrugs ganciclovir (GCV) and/or 5-fluorocytosine (5-FC). The killing effects were measured using two different methods, i.e. annexin V-FITC staining and terminal transferase-mediated dUTP nick end-labeling (TUNEL) staining.

Results

Recombinant adenoviruses AdKDR-CDglyTK were successfully constructed and they infected ECV304 and HepG2 cells efficiently. The infection rate was dependent on MOI of recombinant adenoviruses. ECV304 cells infected with AdKDR-CDglyTK were highly sensitive to GCV and 5-FC. The cell survival rate was dependent on both the concentration of the prodrugs and the MOI of recombinant adenoviruses. In contrast, there were no killing effects in the HepG2 cells. The combination of two prodrugs was much more effective in killing ECV304 cells than GCV or 5-FC alone. The growth of transgenic ECV304 cells was suppressed in the presence of prodrugs.

Conclusion

AdKDR-CDglyTK/double prodrog system may be a useful method for suppressing tumor angiogenesis.

The emerging role of viruses in the treatment of solid tumours

There is increasing optimism for the use of non-pathogenic viruses in the treatment of many cancers. Initial interest in oncolytic virotherapy was based on the observation of an occasional clinical resolution of a lymphoma after a systemic viral infection. In many cancers, by comparison with normal tissues, the competency of the cellular anti-viral mechanism is impaired, thus creating an exploitable difference between the tumour and normal cells, as an unimpeded viral proliferation in cancer cells is eventually cytocidal. In addition to their oncolytic capability, these particular viruses may be engineered to facilitate gene delivery to tumour cells to produce therapeutic effects such as cytokine secretion and anti -tumour immune responses prior to the eventual cytolysis. There is now promising clinical experience with these viral strategies, particularly as part of multimodal studies, and already several clinical trials are in progress. The limitations of standard cancer chemotherapies, including their lack of specificity with consequent collateral toxicity and the development of cross-resistance, do not appear to apply to viral-based therapies. Furthermore, virotherapy frequently restores chemoradiosensitivity to resistant tumours and has also demonstrated efficacy against cancers that historically have a dismal prognosis. While there is cause for optimism, through continued improvements in the efficiency and safety of systemic delivery, through the emergence of alternative viral agents and through favourable clinical experiences, clinical trials as part of multimodal protocols will be necessary to define clinical utility. Significant progress has been made and this is now a major research area with an increasing annual bibliography.

Mutations in the stalk region of the measles virus hemagglutinin inhibit syncytium formation but not virus entry

Measles virus (MV) entry requires at least 2 viral proteins, the hemagglutinin (H) and fusion (F) proteins. We describe the rescue and characterization of a measles virus with a specific mutation in the stalk region of H (I98A) that is able to bind normally to cells but infects at a lower rate than the wild type due to a reduction in fusion triggering. The mutant H protein binds to F more avidly than the parent H protein does, and the corresponding virus is more sensitive to inhibition by fusion-inhibitory peptide. We show that after binding of MV to its receptor, H-F dissociation is required for productive infection.

Intravascularly administered RGD-displaying measles viruses bind to and infect neovessel endothelial cells in vivo

Systemically administered vectors must cross the endothelial lining of tumor blood vessels to access cancer cells. Vectors that interact with markers on the lumenal surface of these endothelial cells might have enhanced tumor localization. Here, we generated oncolytic measles viruses (MVs) displaying alpha(v)beta(3) integrin-binding peptides, cyclic arginine-glycine-aspartate (RGD) or echistatin, on the measles hemagglutinin protein. Both viruses had expanded tropisms, and efficiently entered target cells via binding to integrins, but also retained their native tropisms for CD46 and signaling lymphocyte activation molecule (SLAM). When fluorescently labeled and injected intravascularly into chick chorioallantoic membranes (CAMs), in contrast to unmodified viruses, the integrin-binding viral particles bound to the lumenal surface of the developing chick neovessels and infected the CAM vascular endothelial cells. In a mouse model of VEGF-induced angiogenesis in the ear pinna, the integrin-binding viruses, but not the parental virus, infected cells at sites of new blood vessel formation. When given intravenously to mice bearing tumor xenografts, the integrin-binding virus infected endothelial cells of tumor neovessels in addition to tumor parenchyma. To our knowledge, this is the first report demonstrating that oncolytic MVs can be engineered to target the lumenal endothelial surface of newly formed blood vessels when administered intravenously in living animals.

Measles virus glycoprotein complex assembly, receptor attachment, and cell entry

Measles virus (MV) enters cells by membrane fusion at the cell surface at neutral pH. Two glycoproteins mediate this process: the hemagglutinin (H) and fusion (F) proteins. The H-protein binds to receptors, while the F-protein mediates fusion of the viral and cellular membranes. H naturally interacts with at least three different receptors. The wild-type virus primarily uses the signaling lymphocyte activation molecule (SLAM, CD150) expressed on certain lymphatic cells, while the vaccine strain has gained the ability to also use the ubiquitous membrane cofactor protein (MCP, CD46), a regulator of complement activation. Additionally, MV infects polarized epithelial cells through an unidentified receptor (EpR). The footprints of the three receptors on H have been characterized, and the focus of research is shifting to the characterization of receptor-specific conformational changes that occur in the H-protein dimer and how these are transmitted to the F-protein trimer. It was also shown that MV attachment and cell entry can be readily targeted to designated receptors by adding specificity determinants to the H-protein. These studies have contributed to our understanding of membrane fusion by the glycoprotein complex of paramyxoviruses in general.

Tumor and vascular targeting of a novel oncolytic measles virus retargeted against the urokinase receptor

Oncolytic measles virus (MV) induces cell fusion and cytotoxicity in a CD46-dependent manner. Development of fully retargeted oncolytic MVs would improve tumor selectivity. The urokinase-type plasminogen activator receptor (uPAR) is a tumor and stromal target overexpressed in multiple malignancies. MV-H glycoproteins fully retargeted to either human or murine uPAR were engineered and their fusogenic activity was determined. Recombinant human (MV-h-uPA) and murine (MV-m-uPA) uPAR-retargeted MVs expressing enhanced green fluorescent protein (eGFP) were rescued and characterized. Viral expression of chimeric MV-H was shown by reverse transcription-PCR and Western blot. In vitro viral replication was comparable to MV-GFP control. The receptor and species specificity of MV-uPAs was shown in human and murine cells with different levels of uPAR expression. Removal of the NH(2)-terminal fragment ligand from MV-uPA by factor X(a) treatment ablated the MV-uPA functional activity. Cytotoxicity was shown in uPAR-expressing human and murine cells. MV-h-uPA efficiently infected human endothelial cells and capillary tubes in vitro. I.v. administration of MV-h-uPA delayed tumor growth and prolonged survival in the MDA-MB-231 breast cancer xenograft model. Viral tumor targeting was confirmed by immunohistochemistry. MV-m-uPA transduced murine mammary tumors (4T1) in vivo after intratumor administration. MV-m-uPA targeted murine tumor vasculature after systemic administration, as shown by dual (CD31 and MV-N) staining of tumor capillaries in the MDA-MB-231 model. In conclusion, MV-uPA is a novel oncolytic MV associated with potent and specific antitumor effects and tumor vascular targeting. This is the first retargeted oncolytic MV able to replicate in murine cells and target tumor vasculature in a uPAR-dependent manner.

Measles virus for cancer therapy

Measles virus offers an ideal platform from which to build a new generation of safe, effective oncolytic viruses. Occasional so-called spontaneous tumor regressions have occurred during natural measles infections, but common tumors do not express SLAM, the wild-type MV receptor, and are therefore not susceptible to the virus. Serendipitously, attenuated vaccine strains of measles virus have adapted to use CD46, a regulator of complement activation that is expressed in higher abundance on human tumor cells than on their nontransformed counterparts. For this reason, attenuated measles viruses are potent and selective oncolytic agents showing impressive antitumor activity in mouse xenograft models. The viruses can be engineered to enhance their tumor specificity, increase their antitumor potency, and facilitate noninvasive in vivo monitoring of their spread. A major impediment to the successful deployment of oncolytic measles viruses as anticancer agents is the high prevalence of preexisting anti-measles immunity, which impedes bloodstream delivery and curtails intratumoral virus spread. It is hoped that these problems can be addressed by delivering the virus inside measles-infected cell carriers and/or by concomitant administration of immunosuppressive drugs. From a safety perspective, population immunity provides an excellent defense against measles spread from patient to carers and, in 50 years of human experience, reversion of attenuated measles to a wild-type pathogenic phenotype has not been observed. Clinical trials testing oncolytic measles viruses as an experimental cancer therapy are currently underway.

Oncolytic virotherapy for multiple myeloma

BACKGROUND

Current therapies for multiple myeloma (MM) are not curative, thus novel targeted therapeutics are being developed. One such targeted therapy is oncolytic virotherapy, wherein viruses specifically infect and kill the malignant plasma cells, leaving normal cells intact.

OBJECTIVE

This review provides an overview of the mechanisms and results of the oncolytic viruses being used to date and discusses the recent advances in the field of virotherapy for MM.

METHODS

All papers using viruses to treat MM were identified and screened. Only papers describing replicating, oncolytic viruses were reviewed.

RESULTS/CONCLUSIONS

Several viruses are currently being developed preclinically and clinically to treat MM, including measles virus, vesicular stomatitis virus, coxsackievirus A21 and vaccinia virus. Other viruses are being used preclinically to purge myeloma cells from autologous bone marrow transplants. Efforts to improve myeloma-specific targeting, avoid the antiviral immune response and evaluate combination therapies for MM are ongoing.

Taming the Trojan horse: optimizing dynamic carrier cell/oncolytic virus systems for cancer biotherapy

Live cells offer unique advantages as vehicles for systemic oncolytic virus (OV) delivery. Recent studies from our laboratory and others have shown that virus-infected cells can serve as Trojan horse vehicles to evade antiviral mechanisms encountered in the bloodstream, prevent uptake by off-target tissues and act as microscale factories to produce OV upon arrival in tumor beds. However to be employed effectively, OV-infected cells are best viewed as dynamic biological systems rather than static therapeutic agents. The time-dependent processes of infection and in vivo cell trafficking will inevitably vary depending on which particular OV is being delivered, as well as the type of carrier cells (CC) employed. Understanding these parameters with respect to each unique CC/OV combination will therefore be required in order to effectively evaluate and harness their potential in preclinical study. In the following review, we discuss how early studies of OV delivery led us to investigate the use of cell carriers in our laboratory, and the approaches we are currently undertaking to compare the dynamics of different CC/OV systems. On the basis of these studies and others it is apparent that the success of any cell-based system for OV delivery rests upon the coordinated timing of three sequential phases--(1) ex vivo loading, (2) stealth delivery and (3) virus production at the tumor site. While at the current time, the timing of these processes are coupled to the natural cycle of infection and in vivo trafficking properties innate to each cell virus system, a quantitative delineation of their dynamics will lay the foundation for engineering CC/OV biotherapeutic systems that can be clinically deployed in a highly directed and controlled manner.

Targeted release of oncolytic measles virus by blood outgrowth endothelial cells in situ inhibits orthotopic gliomas

Malignant gliomas remain largely incurable despite intensive efforts to develop novel therapies. Replicating oncolytic viruses have shown great promise, among them attenuated measles viruses of the Edmonston B strain (MV-Edm). However, host immune response and the infiltrative nature of gliomas limit their efficacy. We show that human blood outgrowth endothelial cells (BOECs), readily expandable from peripheral blood, are easily infected by MV-Edm and allow replication of MV-Edm while surviving long enough after infection to serve as vehicles for MV-Edm (BOEC/MV-Edm). After intravenous and peritumoral injection, BOEC/MV-Edm deliver the viruses selectively to irradiated orthotopic U87 gliomas in mice. At the tumor, MV-Edm produced by the BOECs infect glioma cells. Subsequent spread from tumor cell to tumor cell leads to focal infection and cytopathic effects that decrease tumor size and, in the case of peritumoral injection, prolong survival of mice. Since MV-Edm within BOECs are not readily neutralized and because BOEC/MV-Edm search and destroy glioma cells, BOEC/MV-Edm constitute a promising novel approach for glioma therapy.

Engineering targeted viral vectors for gene therapy

Translating knowledge of genetic disease mechanisms into gene therapies has been slow with limited clinical success. One major reason is that the transfer vectors, which are most often of viral origin, are not targeted sufficiently towards the cells of interest.

To achieve successful delivery of genetic material, transductional targeting is often essential to enter the target cell and to avoid side effects from the transduction of non-target cells.

Many techniques to target viral vectors to specific cells have been developed. They can be divided into three types: systems that use adaptor proteins from other viruses (pseudotyping); systems that use adaptors to couple the targeting ligand to the vector; and systems that genetically incorporate the targeting moiety into the viral genome.

Whereas systems involving adaptor proteins are highly useful in preclinical evaluations, systems that make use of genetically incorporated targeting ligands are advantageous for clinical applications.

Combinations of several targeting principles (including ablation of natural tropism, pseudotyping and adaptors) and novel combinations (such as the adeno-associated virus (AAV) genome in a phage vector) allow systemic vector application.

An initial clinical study with a targeted retrovirus showed feasibility to transfer laboratory success to patient application, underlining that there are no principal regulatory barriers for targeted vectors.

Systemic vector applications will be facilitated by enabling the vector to move beyond the vascular endothelium at specific sites, using transcytosis or cellular vehicles. The application of existing targeting techniques to new viral vector serotypes and new vector classes is extending the therapeutic capabilities further.

Obstacles to systemic application of vectors are found in the blood as immune reactions against the vector and as binding of blood proteins to the vector. Some targeting approaches might have the potential to circumvent these obstacles.

To preclinically evaluate new targeting strategies, several models that reflect the human situation to varying degrees are available. The use of primary cells, tissue-slice systems and transgenic animals seems to be especially promising.

Imaging technologies provide the ability to monitor the vector in vivo in real time without sacrificing the animal model. These techniques facilitate vector targeting and biodistribution studies.

A key challenge in gene therapy is vector targeting to specific cells, while avoiding effects on other tissues. Several strategies have been developed recently to enable targeting of the main viral vectors, moving them a step closer to clinical use.

To achieve therapeutic success, transfer vehicles for gene therapy must be capable of transducing target cells while avoiding impact on non-target cells. Despite the high transduction efficiency of viral vectors, their tropism frequently does not match the therapeutic need. In the past, this lack of appropriate targeting allowed only partial exploitation of the great potential of gene therapy. Substantial progress in modifying viral vectors using diverse techniques now allows targeting to many cell types in vitro. Although important challenges remain for in vivo applications, the first clinical trials with targeted vectors have already begun to take place.

Viruses as anticancer drugs

Oncolytic viruses are being developed as anticancer drugs. They propagate selectively in tumor tissue and destroy it without causing excessive damage to normal non-cancerous tissues. When used as drugs, they must meet stringent criteria for safety and efficacy and be amenable to pharmacological study in human subjects. Specificity for neoplastic tissue is the key to safety, and this goal can be achieved through a variety of ingenious virus-engineering strategies. Antiviral immunity remains a significant barrier to the clinical efficacy of oncolytic viruses but this is being addressed by using novel immune-evasive delivery strategies and immunosuppressive drugs. Noninvasive pharmacokinetic monitoring is facilitated by engineering marker genes into the viral genome. Clinical data on the pharmacokinetics of oncolytic viruses will be the key to accelerating their development and approval as effective anticancer drugs. This review introduces concepts relevant to the use of viruses as anticancer drugs, emphasizing targeting mechanisms as well as safety and efficacy issues that are currently limiting their clinical success.

Novel challenges in exploring peptide ligands and corresponding tissue-specific endothelial receptors

The structural and molecular diversity of vascular endothelium may depend on the functional state and tissue localisation of its cells. Tumour vasculature expresses a number of molecular markers that distinguish it from normal vasculature. In cancer, the determinant of specific tumour vasculature heterogeneity is, in part, dictated by dysregulated expression of tumour-derived angiogenic factors. The identification of molecular 'addresses' on the surface of tumour vasculature has significantly contributed to the selection of targets, which have been used for delivering therapeutic and imaging agents in cancer. Cytotoxic drug, pro-apoptotic peptides, protease inhibitors, and gene therapy vectors have been successfully linked to peptides and delivered to tumour sites with an improved experimental therapy. Different diagnostic and therapeutic compounds can be efficiently targeted to specific receptors on vascular endothelial cells; the development of ligand-directed vector tools may promote systemic targeted gene delivery. Here, we review the very recent advances in the identification of peptide ligands and their corresponding tissue-specific endothelial receptors through the phage display technology with emphasis on ligand-directed delivery of therapeutic agents and targeted gene therapy.

Cell-based delivery of oncolytic viruses: a new strategic alliance for a biological strike against cancer

Recent years have seen tremendous advances in the development of exquisitely targeted replicating virotherapeutics that can safely destroy malignant cells. Despite this promise, clinical advancement of this powerful and unique approach has been hindered by vulnerability to host defenses and inefficient systemic delivery. However, it now appears that delivery of oncolytic viruses within carrier cells may offer one solution to this critical problem. In this review, we compare the advantages and limitations of the numerous cell lineages that have been investigated as delivery platforms for viral therapeutics, and discuss examples showing how combined cell-virus biotherapeutics can be used to achieve synergistic gains in antitumor activity. Finally, we highlight avenues for future preclinical research that might be taken in order to refine cell-virus biotherapeutics in preparation for human trials.

Inhibition of melanoma cell motility by the snake venom disintegrin eristostatin

Eristostatin, an RGD-containing disintegrin isolated from the venom of Eristicophis macmahoni, inhibits lung or liver colonization of melanoma cells in a mouse model. In this study, transwell migration and in vitro wound closure assays were used to determine the effect of eristostatin on the migration of melanoma cells. Eristostatin significantly impaired the migration of five human melanoma cell lines. Furthermore, it specifically inhibited cell migration on fibronectin in a concentration-dependent manner, but not that on collagen IV or laminin. In contrast, eristostatin was found to have no effect on cell proliferation or angiogenesis. These results indicate that the interaction between eristostatin and melanoma cells may involve fibronectin-binding integrins that mediate cell migration. Mutations to alanine of seven residues within the RGD loop of eristostatin and four residues outside the RGD loop of eristostatin resulted in significantly less potency in both platelet aggregation and wound closure assays. For six of the mutations, however, decreased activity was found only in the latter assay. We conclude that a different mechanism and/or integrin is involved in these two cell activities.

International Society for Cell and Gene Therapy of Cancer: 2005 meeting in Shenzhen, China

The 2005 International Society for Cell and Gene Therapy of Cancer (ISCGT) Congress was held in Shenzhen, China (www.iscgtchina2005.com) from December 9th-11th 2005. Here, we describe a representation of the most seminal presentations providing an overview of the progress in the field of cancer gene therapy including the successful introduction of the first approved gene therapy drug.

Antitumor immune response induced by i.t. injection of vector-activated dendritic cells and chemotherapy suppresses metastatic breast cancer

S.c. injection of the Ad-sig-tumor-associated antigen (TAA)/ecdCD40L vector vaccine has been shown to induce a CD8 immune response against TAA for up to 1 year. The first goal of this article is to test if the injection of autologous dendritic cells infected ex vivo with the Ad-sig-TAA/ecdCD40L can increase the immune response induced against TAA. The second goal is to test the effect of adding local chemotherapy in the form of i.t. injection of the AdCDIRESE1A vector-directed chemotherapy on the immune response induced by i.t. injection of adenoviral vector-activated dendritic cells. The results show that the i.t. injection of the AdCDIRESE1A chemotherapy sensitization vector, which encodes the cytosine deaminase chemotherapy sensitization transcription unit, to the i.t. injection of Ad-sig-ecdCD40L vector-infected dendritic cells increased the level of suppression of the growth of the CCL-51 breast cancer cells. The combination of i.t. injection of the AdCDIRESE1A chemotherapy sensitization vector and Ad-sig-ecdCD40L vector-infected dendritic cells into s.c. CCL-51 breast cancer nodules suppressed the growth of uninjected metastatic tumor nodules in the lung. Finally, adding the i.t. injection of the AdCDIRESE1A chemotherapy sensitization vector to the i.t. administration of dendritic cells infected with a rat HER-2/neu (rH2N)-expressing vector (Ad-sig-rH2N/ecdCD40L) led to the induction of rH2N-specific antitumoral immunity in rH2N transgenic mice (which are anergic to the rH2N antigen). This anti-rH2N immune response suppressed the growth of established H2N-positive NT2 breast cancer more efficiently than did the vector-targeted chemotherapy or Ad-sig-rH2N/ecdCD40L-infected dendritic cell vaccine alone.