Potent oncolytic activity of human enteroviruses against human prostate cancer

A physiologically based pharmacokinetic model for V937 oncolytic virus in mice

Introduction: Oncolytic viruses (OVs) represent a novel therapeutic strategy in oncology due to their capability to selectively infect and replicate in cancer cells, triggering a direct and/or immune-induced tumor lysis. However, the mechanisms governing OV pharmacokinetics are still poorly understood. This work aims to develop a physiologically based pharmacokinetic model of the novel OV, V937, in non-tumor-bearing mice to get a quantitative understanding of its elimination and tissue uptake processes. Materials and methods: Model development was performed using data obtained from 60 mice. Viral levels were quantified from eight tissues after a single intravenous V937 dose. An external dataset was used for model validation. This test set included multiple-dose experiments with different routes of administration. V937 distribution in each organ was described using a physiological structure based on mouse-specific organ blood flows and volumes. Analyses were performed using the non-linear mixed-effects approach with NONMEM 7.4. Results: Viral levels showed a drop from 108 to 105 copies/µg RNA at day 1 in blood, reflected in a high estimate of total clearance (18.2 mL/h). A well-stirred model provided an adequate description for all organs except the muscle and heart, where a saturable uptake process improved data description. The highest numbers of viral copies were observed in the brain, lymph node, kidney, liver, lung, and spleen on the first day after injection. On the other hand, the maximum amount of viral copies in the heart, muscle, and pancreas occurred 3 days after administration. Conclusion: To the best of our knowledge, this is the first physiologically based pharmacokinetic model developed to characterize OV biodistribution, representing a relevant source of quantitative knowledge regarding the in vivo behavior of OVs. This model can be further expanded by adding a tumor compartment, where OVs could replicate.

Oncolyic Virotherapy for Prostate Cancer: Lighting a Fire in Winter

As the most common cancer of the genitourinary system, prostate cancer (PCa) is a global men's health problem whose treatments are an urgent research issue. Treatment options for PCa include active surveillance (AS), surgery, endocrine therapy, chemotherapy, radiation therapy, immunotherapy, etc. However, as the cancer progresses, the effectiveness of treatment options gradually decreases, especially in metastatic castration-resistant prostate cancer (mCRPC), for which there are fewer therapeutic options and which have a shorter survival period and worse prognosis. For this reason, oncolytic viral therapy (PV), with its exceptional properties of selective tumor killing, relatively good safety in humans, and potential for transgenic delivery, has attracted increasing attention as a new form of anti-tumor strategy for PCa. There is growing evidence that OV not only kills tumor cells directly by lysis but can also activate anticancer immunity by acting on the tumor microenvironment (TME), thereby preventing tumor growth. In fact, evidence of the efficacy of this strategy has been observed since the late 19th century. However, subsequently, interest waned. The renewed interest in this therapy was due to advances in biotechnological methods and innovations at the end of the 20th century, which was also the beginning of PCa therapy with OV. Moreover, in combination with chemotherapy, radiotherapy, gene therapy or immunotherapy, OV viruses can have a wide range of applications and can provide an effective therapeutic result in the treatment of PCa.

Cytolytic Properties and Genome Analysis of Rigvir® Oncolytic Virotherapy Virus and Other Echovirus 7 Isolates

Rigvir® is a cell-adapted, oncolytic virotherapy enterovirus, which derives from an echovirus 7 (E7) isolate. While it is claimed that Rigvir® causes cytolytic infection in several cancer cell lines, there is little molecular evidence for its oncolytic and oncotropic potential. Previously, we genome-sequenced Rigvir® and five echovirus 7 isolates, and those sequences are further analyzed in this paper. A phylogenetic analysis of the full-length data suggested that Rigvir® was most distant from the other E7 isolates used in this study, placing Rigvir® in its own clade at the root of the phylogeny. Rigvir® contained nine unique mutations in the viral capsid proteins VP1-VP4 across the whole data set, with a structural analysis showing six of the mutations concerning residues with surface exposure on the cytoplasmic side of the viral capsid. One of these mutations, E/Q/N162G, was located in the region that forms the contact interface between decay-accelerating factor (DAF) and E7. Rigvir® and five other isolates were also subjected to cell infectivity assays performed on eight different cell lines. The used cell lines contained both cancer and non-cancer cell lines for observing Rigvir®'s claimed properties of being both oncolytic and oncotropic. Infectivity assays showed that Rigvir® had no discernable difference in the viruses' oncolytic effect when compared to the Wallace prototype or the four other E7 isolates. Rigvir® was also seen infecting non-cancer cell lines, bringing its claimed effect of being oncotropic into question. Thus, we conclude that Rigvir®'s claim of being an effective treatment against multiple different cancers is not warranted under the evidence presented here. Bioinformatic analyses do not reveal a clear mechanism that could elucidate Rigvir®'s function at a molecular level, and cell infectivity tests do not show a discernable difference in either the oncolytic or oncotropic effect between Rigvir® and other clinical E7 isolates used in the study.

Oncolytic Virotherapy in Peritoneal Metastasis Gastric Cancer: The Challenges and Achievements

Gastric cancer (GC) is the fourth most common cancer and the second leading cause of cancer death globally. Although the mortality rate in some parts of the world, such as East Asia, is still high, new treatments and lifestyle changes have effectively reduced deaths from this type of cancer. One of the main challenges of this type of cancer is its late diagnosis and poor prognosis. GC patients are usually diagnosed in the advanced stages of the disease, which is often associated with peritoneal metastasis (PM) and significantly reduces survival. This type of metastasis in patients with GC poses a serious challenge due to limitations in common therapies such as surgery and tumor resection, as well as failure to respond to systemic chemotherapy. To solve this problem, researchers have used virotherapy such as reovirus-based anticancer therapy in patients with GC along with PM who are resistant to current chemotherapies because this therapeutic approach is able to overcome immune suppression by activating dendritic cells (DCs) and eventually lead to the intrinsic activity of antitumor effector T cells. This review summarizes the immunopathogenesis of peritoneal metastasis of gastric cancer (PMGC) and the details for using virotherapy as an effective anticancer treatment approach, as well as its challenges and opportunities.

Oncolytic Viruses in the Therapy of Lymphoproliferative Diseases

Cancer is a leading causes of death. Despite significant success in the treatment of lymphatic system tumors, the problems of relapse, drug resistance and effectiveness of therapy remain relevant. Oncolytic viruses are able to replicate in tumor cells and destroy them without affecting normal, healthy tissues. By activating antitumor immunity, viruses are effective against malignant neoplasms of various nature. In lymphoproliferative diseases with a drug-resistant phenotype, many cases of remissions have been described after viral therapy. The current level of understanding of viral biology and the discovery of host cell interaction mechanisms made it possible to create unique strains with high oncoselectivity widely used in clinical practice in recent years.

Real-time PCR assay as a simple and efficient tool for viral stability study

Aim: For oncolytic virus trials, regulatory agencies often require pharmaceutical industry to evaluate risks of released viruses from patients to environment. This study was to establish a real-time PCR method to assess viral shedding and viral stability in human urine. Results/methodology: Herein, we describe an incubation of viral drug product in human urine and use of real-time PCR as a simple, efficient and high throughput assay to assess the level and stability of a nonenveloped and single stranded RNA virus. The viral stability issue is critical to the collection, transport, storage and testing of clinical samples. Discussion/conclusion: In summary, this simple method provides useful viral stability information at various temperatures and detergents. A similar approach may apply to other RNA viruses (including SARS-CoV-2).

Viral Vector-Based Melanoma Gene Therapy

Gene therapy applications of oncolytic viruses represent an attractive alternative for cancer treatment. A broad range of oncolytic viruses, including adenoviruses, adeno-associated viruses, alphaviruses, herpes simplex viruses, retroviruses, lentiviruses, rhabdoviruses, reoviruses, measles virus, Newcastle disease virus, picornaviruses and poxviruses, have been used in diverse preclinical and clinical studies for the treatment of various diseases, including colon, head-and-neck, prostate and breast cancer as well as squamous cell carcinoma and glioma. The majority of studies have focused on immunotherapy and several drugs based on viral vectors have been approved. However, gene therapy for malignant melanoma based on viral vectors has not been utilized to its full potential yet. This review represents a summary of the achievements of preclinical and clinical studies using viral vectors, with the focus on malignant melanoma.

Oncolytic Immunotherapy for Bladder Cancer Using Coxsackie A21 Virus: Using a Bladder Tumor Precision-Cut Slice Model System to Assess Viral Efficacy

Oncolytic viruses are anticancer agents that selectively target and kill cancer cells by direct lysis, while at the same time stimulating a tumor antigen-specific adaptive immune response. These promising therapeutic agents target multiple cancers and have already proven to be an effective treatment option for solid malignancies. One such agent, T-Vec (Talimogene laherparepvec) has been licensed and is in routine clinical use for treatment of malignant melanoma.Non-muscle invasive bladder cancer (NMIBC) is an ideal potential target for oncolytic immunotherapy as locally instilled live biological therapy using Bacille Calmette-Guerin (BCG) is already well established in the clinical setting. Coxsackievirus A21 (CVA21) is a novel intercellular adhesion molecule-1 (ICAM-1)-targeted immunotherapeutic virus. We have investigated CVA21-induced cytotoxicity in a panel of human bladder cancer cell lines, revealing a range of sensitivities largely correlating with expression of the viral receptor ICAM-1. CVA21 in combination with low doses of mitomycin-C enhanced CVA21 viral replication and oncolysis by increasing surface expression levels of ICAM-1. In addition to cell lines and an animal model a key component of our studies into oncolytic immunotherapy for bladder cancer was the use of a bladder tumor precision slice preclinical model system which represents tumor architecture, heterogeneity, and the complexity of a tumor in vitro. Results seen in cell lines were reflected in the tumor slice model whereby levels of virus protein expression and induction of apoptosis were enhanced with prior exposure to mitomycin-C. In this chapter we demonstrate the utility of the precision cut tumor slice model as a unique organotypic model to test oncolytic viruses. We will describe how to prepare and slice the tumor using a vibrating microtome together with the optimum culture and conditions for treatment.

Phase I Trial of an ICAM-1-Targeted Immunotherapeutic-Coxsackievirus A21 (CVA21) as an Oncolytic Agent Against Non Muscle-Invasive Bladder Cancer

PURPOSE

The CANON [CAVATAK in NON-muscle-invasive bladder cancer (NMIBC)] study evaluated a novel ICAM-1-targeted immunotherapeutic-coxsackievirus A21 as a novel oncolytic agent against bladder cancer.

PATIENTS AND METHODS

Fifteen patients enrolled in this "window of opportunity" phase I study, exposing primary bladder cancers to CAVATAK prior to surgery. The first 9 patients received intravesical administration of monotherapy CAVATAK; in the second stage, 6 patients received CAVATAK with a subtherapeutic dose of mitomycin C, known to enhance expression of ICAM-1 on bladder cancer cells. The primary endpoint was to determine patient safety and maximum tolerated dose (MTD). Secondary endpoints were evidence of viral replication, induction of inflammatory cytokines, antitumor activity, and viral-induced changes in resected tissue.

RESULTS

Clinical activity of CAVATAK was demonstrated by induction of tumor inflammation and hemorrhage following either single or multiple administrations of CAVATAK in multiple patients, and a complete resolution of tumor in 1 patient. Whether used alone or in combination with mitomycin C, CAVATAK caused marked inflammatory changes within NMIBC tissue biopsies by upregulating IFN-inducible genes, including both immune checkpoint inhibitory genes (PD-L1 and LAG3) and Th1-associated chemokines, as well as the induction of the innate activator RIG-I, compared with bladder cancer tissue from untreated patients. No significant toxicities were reported in any patient, from either virus or combination therapy.

CONCLUSIONS

The acceptable safety profile of CAVATAK, proof of viral targeting, replication, and tumor cell death together with the virus-mediated increases in "immunological heat" within the tumor microenvironment all indicate that CAVATAK may be potentially considered as a novel therapeutic for NMIBC.

Developing Picornaviruses for Cancer Therapy

Oncolytic viruses (OVs) form a group of novel anticancer therapeutic agents which selectively infect and lyse cancer cells. Members of several viral families, including Picornaviridae, have been shown to have anticancer activity. Picornaviruses are small icosahedral non-enveloped, positive-sense, single-stranded RNA viruses infecting a wide range of hosts. They possess several advantages for development for cancer therapy: Their genomes do not integrate into host chromosomes, do not encode oncogenes, and are easily manipulated as cDNA. This review focuses on the picornaviruses investigated for anticancer potential and the mechanisms that underpin this specificity.

RNA Viruses as Tools in Gene Therapy and Vaccine Development

RNA viruses have been subjected to substantial engineering efforts to support gene therapy applications and vaccine development. Typically, retroviruses, lentiviruses, alphaviruses, flaviviruses rhabdoviruses, measles viruses, Newcastle disease viruses, and picornaviruses have been employed as expression vectors for treatment of various diseases including different types of cancers, hemophilia, and infectious diseases. Moreover, vaccination with viral vectors has evaluated immunogenicity against infectious agents and protection against challenges with pathogenic organisms. Several preclinical studies in animal models have confirmed both immune responses and protection against lethal challenges. Similarly, administration of RNA viral vectors in animals implanted with tumor xenografts resulted in tumor regression and prolonged survival, and in some cases complete tumor clearance. Based on preclinical results, clinical trials have been conducted to establish the safety of RNA virus delivery. Moreover, stem cell-based lentiviral therapy provided life-long production of factor VIII potentially generating a cure for hemophilia A. Several clinical trials on cancer patients have generated anti-tumor activity, prolonged survival, and even progression-free survival.

Coxsackievirus B infection induces the extracellular release of miR-590-5p, a proviral microRNA

Coxsackievirus B is a significant human pathogen and is a leading cause of myocarditis. We and others have observed that certain enteroviruses including coxsackievirus B cause infected cells to shed extracellular vesicles containing infectious virus. Recent reports have shown that vesicle-bound virus can infect more efficiently than free virus. Though microRNAs are differentially regulated in cells following infection, few have been associated with the vesicles shed from infected cells. Here we report exclusive trafficking of specific microRNAs into viral vesicles compared to vesicles from non-infected cells. We found that the most highly-expressed unique microRNA in viral vesicles was miR-590-5p, which facilitates prolonged viral replication by blocking apoptotic factors. Cells over-expressing this miR were significantly more susceptible to infection. This may be a mechanism by which coxsackievirus B boosts subsequent rounds of infection by co-packaging virus and a select set of pro-viral microRNAs in extracellular vesicles.

Intralesional Cancer Immunotherapies

Melanoma and other solid cancers with low or absent T-cell inflammation respond poorly to immune checkpoint inhibitors. Tumor infiltration with T cells that are directed against tumor antigens requires the induction of an innate immune response leading to production of type I interferons and maturation and activation of dendritic cells that can cross-present tumor antigens to T cells. Intralesional therapies, including oncolytic viral therapies, inflammatory cytokines, and agonists of Toll-like receptors and stimulator of interferon genes, can provide the necessary stimuli to trigger such an innate immune response.

Oncolytic Immunotherapy for Bladder Cancer Using Coxsackie A21 Virus

As a clinical setting in which local live biological therapy is already well established, non-muscle invasive bladder cancer (NMIBC) presents intriguing opportunities for oncolytic virotherapy. Coxsackievirus A21 (CVA21) is a novel intercellular adhesion molecule-1 (ICAM-1)-targeted immunotherapeutic virus. This study investigated CVA21-induced cytotoxicity in a panel of human bladder cancer cell lines, revealing a range of sensitivities largely correlating with expression of the viral receptor ICAM-1. CVA21 in combination with low doses of mitomycin-C enhanced CVA21 viral replication and oncolysis by increasing surface expression levels of ICAM-1. This was further confirmed using 300-μm precision slices of NMIBC where levels of virus protein expression and induction of apoptosis were enhanced with prior exposure to mitomycin-C. Given the importance of the immunogenicity of dying cancer cells for triggering tumor-specific responses and long-term therapeutic success, the ability of CVA21 to induce immunogenic cell death was investigated. CVA21 induced immunogenic apoptosis in bladder cancer cell lines, as evidenced by expression of the immunogenic cell death (ICD) determinant calreticulin, and HMGB-1 release and the ability to reject MB49 tumors in syngeneic mice after vaccination with MB49 cells undergoing CVA21 induced ICD. Such CVA21 immunotherapy could offer a potentially less toxic, more effective option for the treatment of bladder cancer.

Heparan Sulfate Binding Coxsackievirus B3 Strain PD: A Novel Avirulent Oncolytic Agent Against Human Colorectal Carcinoma

Coxsackievirus B3 (CVB3), a single-stranded RNA virus of the picornavirus family, has been described as a novel oncolytic virus. However, the CVB3 strain used induced hepatitis and myocarditis in vivo. It was hypothesized that oncolytic activity and safety of CVB3 depends on the virus strain and its specific receptor tropism. Different laboratory strains of CVB3 (Nancy, 31-1-93, and H3), which use the coxsackievirus and adenovirus receptor (CAR), and the strain PD, which uses N- and 6-O-sulfated heparan sulfate (HS) for entry into the cells, were investigated for their potential to lyse tumor cells and for their safety profile. The investigations were carried out in colorectal carcinoma. In vitro investigations showed variable infection efficiency and lysis of colorectal carcinoma cell lines by the CVB3 strains. The most efficient strain was PD, which was the only one that could lyse all investigated colorectal carcinoma cell lines. Lytic activity of CAR-dependent CVB3 did not correlate with CAR expression on cells, whereas there was a clear correlation between lytic activity of PD and its ability to bind to HS at the cell surface of colorectal carcinoma cells. Intratumoral injection of Nancy, 31-1-93, or PD into subcutaneous colorectal DLD1 cell tumors in BALB/c nude mice resulted in strong inhibition of tumor growth. The effect was seen in the injected tumor, as well as in a non-injected, contralateral tumor. However, all animals treated with 31-1-93 and Nancy developed systemic infection and died or were moribund and sacrificed within 8 days post virus injection. In contrast, five of the six animals treated with PD showed no signs of a systemic viral infection, and PD was not detected in any organ. The data demonstrate the potential of PD as a new oncolytic virus and HS-binding of PD as a key feature of oncolytic activity and improved safety.

Viral Vectors in Gene Therapy

Applications of viral vectors have found an encouraging new beginning in gene therapy in recent years. Significant improvements in vector engineering, delivery, and safety have placed viral vector-based therapy at the forefront of modern medicine. Viral vectors have been employed for the treatment of various diseases such as metabolic, cardiovascular, muscular, hematologic, ophthalmologic, and infectious diseases and different types of cancer. Recent development in the area of immunotherapy has provided both preventive and therapeutic approaches. Furthermore, gene silencing generating a reversible effect has become an interesting alternative, and is well-suited for delivery by viral vectors. A number of preclinical studies have demonstrated therapeutic and prophylactic efficacy in animal models and furthermore in clinical trials. Several viral vector-based drugs have also been globally approved.

New frontiers in oncolytic viruses: optimizing and selecting for virus strains with improved efficacy

Oncolytic viruses have demonstrated selective replication and killing of tumor cells. Different types of oncolytic viruses – adenoviruses, alphaviruses, herpes simplex viruses, Newcastle disease viruses, rhabdoviruses, Coxsackie viruses, and vaccinia viruses – have been applied as either naturally occurring or engineered vectors. Numerous studies in animal-tumor models have demonstrated substantial tumor regression and prolonged survival rates. Moreover, clinical trials have confirmed good safety profiles and therapeutic efficacy for oncolytic viruses. Most encouragingly, the first cancer gene-therapy drug – Gendicine, based on oncolytic adenovirus type 5 – was approved in China. Likewise, a second-generation oncolytic herpes simplex virus-based drug for the treatment of melanoma has been registered in the US and Europe as talimogene laherparepvec.

Review: Oncolytic virotherapy, updates and future directions

Oncolytic viruses (OVs) are viral strains that can infect and kill malignant cells while spare their normal counterparts. OVs can access cells through binding to receptors on their surface or through fusion with the plasma membrane and establish a lytic cycle in tumors, while leaving normal tissue essentially unharmed. Multiple viruses have been investigated in humans for the past century. IMLYGIC™ (T-VEC/Talimogene Laherparepvec), a genetically engineered Herpes Simplex Virus, is the first OV approved for use in the United States and the European Union for patients with locally advanced or non-resectable melanoma. Although OVs have a favorable toxicity profile and are impressively active anticancer agents in vitro and in vivo the majority of OVs have limited clinical efficacy as a single agent. While a virus-induced antitumor immune response can enhance oncolysis, when OVs are used systemically, the antiviral immune response can prevent the virus reaching the tumor tissue and having a therapeutic effect. Intratumoral administration can provide direct access to tumor tissue and be beneficial in reducing side effects. Immune checkpoint stimulation in tumor tissue has been noted after OV therapy and can be a natural response to viral-induced oncolysis. Also for immune checkpoint inhibition to be effective in treating cancer, an immune response to tumor neoantigens and an inflamed tumor microenvironment are required, both of which treatment with an OV may provide. Therefore, direct and indirect mechanisms of tumor killing provide rationale for clinical trials investigating the combination of OVs other forms of cancer therapy, including immune checkpoint inhibition.

Bioselection of coxsackievirus B6 strain variants with altered tropism to human cancer cell lines

Cancer cells develop increased sensitivity to members of many virus families and, in particular, can be efficiently infected and lysed by many low-pathogenic human enteroviruses. However, because of their great genetic heterogeneity, cancer cells display different levels of sensitivity to particular enterovirus strains, which may substantially limit the chances of a positive clinical response. We show that a non-pathogenic strain of coxsackievirus B6 (LEV15) can efficiently replicate to high titers in the malignant human cell lines C33A, DU145, AsPC-1 and SK-Mel28, although it displays much lower replication efficiency in A431 and A549 cells and very limited replication ability in RD and MCF7 cells, as well as in the normal lung fibroblast cell line MRC-5 and the immortalized mammary epithelial cell line MCF10A. By serial passaging in RD, MCF7 and A431 cells, we obtained LEV15 strain variants that had acquired high replication capacity in the appropriate carcinoma cell lines without losing their high replication capability in the original set of cancer cell lines and had limited replication capability in untransformed cells. The strains demonstrated improved oncolytic properties in nude-mouse xenografts. We identified nucleotide changes responsible for the phenotypes and suggest a bioselection approach for a generation of oncolytic virus strains with a wider spectrum of affected tumors.

Oncolytic immunotherapy: unlocking the potential of viruses to help target cancer

Oncolytic immunotherapy is a research area of cancer immunotherapy investigating the use of modified viruses to target cancer cells. A variety of different viral backbones (e.g., adenovirus, reovirus) with a diverse range of genetic modifications are currently being investigated for the treatment of a variety of cancers. The oncolytic virus that has advanced the furthest in clinical development is talimogene laherparepvec, a recombinant HSV-1 virus expressing granulocyte-macrophage colony-stimulating factor (GM-CSF). In a phase 3 study in patients with unresectable metastatic melanoma, intralesional talimogene laherparepvec treatment resulted in a higher durable response rate compared with subcutaneous GM-CSF treatment (16.3 versus 2.1%; P < 0.001). Notably, responses were observed at uninjected lesions including visceral lesions, indicating a systemic antitumor response had occurred. Studies evaluating combination treatments involving oncolytic viruses and immunologic agents are ongoing. This review focuses on the mechanisms of action for oncolytic viruses and highlights select agents and combinations currently in development.

Oncolytic alphavirus SFV-VA7 efficiently eradicates subcutaneous and orthotopic human prostate tumours in mice

Background:

Despite recent therapeutic and diagnostic advances, prostate cancer remains the second leading cause of cancer-related deaths among men in the Western world. Oncolytic viruses that replicate selectively in tumour cells represent a novel treatment candidate for these malignancies.

Methods:

We analysed infectivity of avirulent Semliki Firest virus SFV-VA7 in human prostate cancer cell lines VCaP, LNCaP and 22Rv1 and in nonmalignant prostate epithelial cell line RWPE-1. Therapeutic potency of SFV-VA7 was evaluated in subcutaneous and orthotopic mouse LNCaP xenograft models.

Results:

SFV-VA7 infected and killed the tested human prostate cancer cell lines irrespective of their hormone response status, while the nonmalignant prostate epithelial cell line RWPE-1 proved highly virus resistant. Notably, a single peritoneal dose of SFV-VA7 was sufficient to eradicate all subcutaneous and orthotopic LNCaP tumours.

Conclusions:

Our results indicate that SFV-VA7 is a novel, promising therapeutic virus against prostate cancer warranting further testing in early clinical trials.

Talimogene Laherparepvec (T-VEC) and Other Oncolytic Viruses for the Treatment of Melanoma

Many mammalian viruses have properties that can be commandeered for the treatment of cancer. These characteristics include preferential infection and replication in tumor cells, the initiation of tumor cell lysis, and the induction of innate and adaptive anti-tumor immunity. Furthermore, viruses can be genetically engineered to reduce pathogenicity and increase immunogenicity resulting in minimally toxic therapeutic agents. Talimogene laherparepvec (T-VEC; Imlygic™), is a genetically modified herpes simplex virus, type 1, and is the first oncolytic virus therapy to be approved for the treatment of advanced melanoma by the US FDA. T-VEC is attenuated by the deletion of the herpes neurovirulence viral genes and enhanced for immunogenicity by the deletion of the viral ICP47 gene. Immunogenicity is further supported by expression of the human granulocyte-macrophage colony-stimulating factor (GM-CSF) gene, which helps promote the priming of T cell responses. T-VEC demonstrated significant improvement in durable response rate, objective response rate, and progression-free survival in a randomized phase III clinical trial for patients with advanced melanoma. This review will discuss the optimal selection of patients for such treatment and describe how therapy is optimally delivered. We will also discuss future directions for oncolytic virus immunotherapy, which will likely include combination T-VEC clinical trials, expansion of T-VEC to other types of non-melanoma skin cancers, and renewed efforts at oncolytic virus drug development with other viruses.

Therapeutic Use of Native and Recombinant Enteroviruses

Research on human enteroviruses has resulted in the identification of more than 100 enterovirus types, which use more than 10 protein receptors and/or attachment factors required in cell binding and initiation of the replication cycle. Many of these “viral” receptors are overexpressed in cancer cells. Receptor binding and the ability to replicate in specific target cells define the tropism and pathogenesis of enterovirus types, because cellular infection often results in cytolytic response, i.e., disruption of the cells. Viral tropism and cytolytic properties thus make native enteroviruses prime candidates for oncolytic virotherapy. Copy DNA cloning and modification of enterovirus genomes have resulted in the generation of enterovirus vectors with properties that are useful in therapy or in vaccine trials where foreign antigenic epitopes are expressed from or on the surface of the vector virus. The small genome size and compact particle structure, however, set limits to enterovirus genome modifications. This review focuses on the therapeutic use of native and recombinant enteroviruses and the methods that have been applied to modify enterovirus genomes for therapy.

A phase I trial of single-agent reolysin in patients with relapsed multiple myeloma

PURPOSE

Reolysin, a proprietary isolate of reovirus type III dearing, enters and preferentially induces apoptosis of malignant cells. RAS pathway activation has been associated with more efficient reoviral infectivity and enhanced oncolysis. Reovirus is currently in advanced solid tumor phase I-II trials; no clinical trials have been conducted in patients with hematologic malignancies.

EXPERIMENTAL DESIGN

A phase I trial treated 12 relapsed myeloma patients at two dose levels. Reolysin was infused daily for 5 days every 28 days. Bone marrow specimens were examined by in situ-based hybridization (ISH) for CD138, p38, caspase-3, reoviral RNA, and capsid protein at screening and cycle 1 day 8. Junctional adhesion molecule 1 (JAM-1) and cancer upregulated gene 2 (CUG2) were evaluated in patient samples and multiple myeloma cell lines. Neutralizing anti-reovirus antibody assay was performed weekly during cycle 1.

RESULTS

There were no dose-limiting toxicities, patients reached the 3 × 10(10) TCID50 daily on days 1 to 5 dose level, and grade 3 laboratory toxicities included neutropenia, thrombocytopenia, and hypophosphatemia. ISH demonstrated reoviral genome confined in multiple myeloma cells. Reoviral capsid protein and caspase-3 were rarely identified within reoviral RNA-positive cells. The longest durations of stable disease were 4, 5, and 8 months.

CONCLUSIONS

Treatment with single-agent Reolysin was well tolerated and associated with avid reoviral RNA myeloma cell entry but only minimal intracellular reoviral protein production within multiple myeloma cells. Our data support that in multiple myeloma cells, Reolysin-induced oncolysis requires combination therapy, similar to other cancers.

Remission of disseminated cancer after systemic oncolytic virotherapy

MV-NIS is an engineered measles virus that is selectively destructive to myeloma plasma cells and can be monitored by noninvasive radioiodine imaging of NIS gene expression. Two measles-seronegative patients with relapsing drug-refractory myeloma and multiple glucose-avid plasmacytomas were treated by intravenous infusion of 10(11) TCID50 (50% tissue culture infectious dose) infectious units of MV-NIS. Both patients responded to therapy with M protein reduction and resolution of bone marrow plasmacytosis. Further, one patient experienced durable complete remission at all disease sites. Tumor targeting was clearly documented by NIS-mediated radioiodine uptake in virus-infected plasmacytomas. Toxicities resolved within the first week after therapy. Oncolytic viruses offer a promising new modality for the targeted infection and destruction of disseminated cancer.

Applications of coxsackievirus A21 in oncology

The clinical management of cancer continues to be dominated by macroscopic surgical resection, radiotherapy, and cytotoxic drugs. The major challenge facing oncology is to achieve more selective, less toxic and effective methods of targeting disseminated tumors, a challenge oncolytic virotherapy may be well-placed to meet. Characterization of coxsackievirus A21 (CVA21) receptor-based mechanism of virus internalization and lysis in the last decade has suggested promise for CVA21 as a virotherapy against malignancies which overexpress those receptors. Preclinical studies have demonstrated proof of principle, and with the results of early clinical trials awaited, CVA21 may be one of the few viruses to demonstrate benefit for patients. This review outlines the potential of CVA21 as an oncolytic agent, describing the therapeutic development of CVA21 in preclinical studies and early stage clinical trials. Preclinical evidence supports the potential use of CVA21 across a range of malignancies. Malignant melanoma is the most intensively studied cancer, and may represent a “test case” for future development of the virus. Although there are theoretical barriers to the clinical utility of oncolytic viruses like CVA21, whether these will block the efficacy of the virus in clinical practice remains to be established, and is a question which can only be answered by appropriate trials. As these data become available, the rapid journey of CVA21 from animal studies to clinical trials may offer a model for the translation of other oncolytic virotherapies from laboratory to clinic.

Oncolytic virus therapy for cancer

The use of oncolytic viruses to treat cancer is based on the selection of tropic tumor viruses or the generation of replication selective vectors that can either directly kill infected tumor cells or increase their susceptibility to cell death and apoptosis through additional exposure to radiation or chemotherapy. In addition, viral vectors can be modified to promote more potent tumor cell death, improve the toxicity profile, and/or generate host antitumor immunity. A variety of viruses have been developed as oncolytic therapeutics, including adenovirus, vaccinia virus, herpesvirus, coxsackie A virus, Newcastle disease virus, and reovirus. The clinical development of oncolytic viral therapy has accelerated in the last few years, with several vectors entering clinical trials for a variety of cancers. In this review, current strategies to optimize the therapeutic effectiveness and safety of the major oncolytic viruses are discussed, and a summary of current clinical trials is provided. Further investigation is needed to characterize better the clinical impact of oncolytic viruses, but there are increasing data demonstrating the potential promise of this approach for the treatment of human and animal cancers.

Cytolytic replication of echoviruses in colon cancer cell lines

BACKGROUND

Colorectal cancer is one of the most common cancers in the world, killing nearly 50% of patients afflicted. Though progress is being made within surgery and other complementary treatments, there is still need for new and more effective treatments. Oncolytic virotherapy, meaning that a cancer is cured by viral infection, is a promising field for finding new and improved treatments. We have investigated the oncolytic potential of several low-pathogenic echoviruses with rare clinical occurrence. Echoviruses are members of the enterovirus genus within the family Picornaviridae.

METHODS

Six colon cancer cell lines (CaCo-2, HT29, LoVo, SW480, SW620 and T84) were infected by the human enterovirus B species echovirus 12, 15, 17, 26 and 29, and cytopathic effects as well as viral replication efficacy were investigated. Infectivity was also tested in spheroids grown from HT29 cells.

RESULTS

Echovirus 12, 17, 26 and 29 replicated efficiently in almost all cell lines and were considered highly cytolytic. The infectivity of these four viruses was further evaluated in artificial tumors (spheroids), where it was found that echovirus 12, 17 and 26 easily infected the spheroids.

CONCLUSIONS

We have found that echovirus 12, 17 and 26 have potential as oncolytic agents against colon cancer, by comparing the cytolytic capacity of five low-pathogenic echoviruses in six colon cancer cell lines and in artificial tumors.

Oncolytic virus therapy for prostate cancer

The use of replication-competent viruses that can selectively replicate in and destroy neoplastic cells is an attractive strategy for treating cancer. Various oncolytic viruses have been taken to clinical trials since a recombinant virus was first applied to cancer patients a decade ago. The concept of the therapy is simple: infectious virus kills the host cancer cells in the course of viral replication. It is important, however, that the virus does not harm the surrounding normal tissue. Oncolytic viruses can be classified largely into two groups: DNA viruses genetically engineered to achieve cancer specificity (e.g. adenovirus, herpes simplex virus and vaccinia) and RNA viruses of which human is not the natural host (e.g. Newcastle disease virus and reovirus). Prostate cancer has always been one of the major targets of oncolytic virus therapy development. The result of six clinical trials for prostate cancer has been published and several trials are now going on. Forty-eight of 83 (58%) patients evaluated in the phase I studies demonstrated a >25% decrease in serum prostate-specific antigen level without evidence of severe toxicities. The result shows the oncolytic virus therapy is promising toward clinical application. Here, we review the recent advances in the field and summarize the results from clinical trials.

Targeting of prostate cancer cells by a cytotoxic lentiviral vector containing a prostate stem cell antigen (PSCA) promoter

BACKGROUND

The efficacy of prostate cancer gene therapy is limited by the inefficiency of prostate-specific promoters as compared to ubiquitous viral promoters. The purpose of this investigation was to evaluate the specificity and efficacy of a lentiviral vector driven by a PSCA promoter.

METHODS

Prostate cancer (LNCap, C42-B, and LAPC-4) and non-prostate cancer (HeLa, MB231, and MCF-7) cells were transduced with a lentiviral vector expressing either the luciferase or the HSV-TK suicide gene and driven by a short PSCA promoter. Specificity and efficacy were evaluated in vitro and in vivo.

RESULTS

Luciferase expression was only detected in prostate cancer cells and was comparable to the universal CMV promoter. Luciferase expression in prostate cancer cells cultured with androgen was higher than that in cells cultured without androgen. In subsequent cytotoxicity experiments in which the luciferase marker gene was replaced with the HSV-TK gene, the lentiviral vector harboring the PSCA promoter induced cytotoxicity in prostate cancer cell lines while demonstrating a minimal effect on non-prostate cells. Cellular toxicity was correlated to increasing concentrations of the prodrug ganciclovir. Androgen had a positive effect on the cytotoxicity of this lentiviral construct. Intratumoral injection of prostate cancer xenografts with the lentiviral construct induced tumor growth inhibition versus saline controls.

CONCLUSION

Our results indicate that a lentiviral gene therapy vector driven by a short PSCA promoter can induce prostate-specific cellular toxicity in vivo and in vitro and may provide a strategy to selectively treat local and advanced metastatic prostate cancer. Prostate 69: 1422-1434, 2009. (c) 2009 Wiley-Liss, Inc.

Intralesional recombinant alpha-interferon for localized prostate cancer: a pilot study with follow-up of >10 years

OBJECTIVE

To report the long-term results of the intralesional administration of an immune modifier, interferon-alpha (IFN-alpha) in men with localized prostate cancer, providing a method for drug delivery within the gland under ultrasonographic control.

PATIENTS AND METHODS

Ten men with localized prostate cancer participated in a study involving the intraprostatic injection of IFN-alpha, weekly for 5 weeks. Prostate biopsies were taken and prostate-specific antigen (PSA) levels were measured bi-annually or until the men had an alternative treatment.

RESULTS

The pretreatment mean Gleason score was 7 and the mean PSA level 11 ng/mL. Biopsies after treatment were negative in three patients. Of the remaining seven, six chose to continue watchful waiting. With time, five went on to alternative treatment; one had radical prostatectomy (at 3 months), two had external beam radiotherapy (at 3 and 6 months), and two had androgen suppression (at 3 and 24 months). Of the three men with initial negative biopsies, one died from unrelated causes 13 years later, with an undetectable PSA level; the second remains asymptomatic 13 years later but has an elevated PSA level. The last patient has a low (<4 ng/mL) PSA level, negative biopsies and had 'no cancer' in a resection specimen, 64 months after treatment. These two men remain under active surveillance with no intervention.

CONCLUSIONS

After delivery of IFN-alpha directly into the prostate gland, and a long follow-up, it appears that there was some antitumour activity in some patients. The doses used were small and the schedule of administration short. Further evaluation of this, and other agents alone and in combination, might be worthwhile.

Human antibodies targeting cell surface antigens overexpressed by the hormone refractory metastatic prostate cancer cells: ICAM-1 is a tumor antigen that mediates prostate cancer cell invasion

Transition from hormone-sensitive to hormone-refractory metastatic tumor types poses a major challenge for prostate cancer treatment. Tumor antigens that are differentially expressed during this transition are likely to play important roles in imparting prostate cancer cells with the ability to grow in a hormone-deprived environment and to metastasize to distal sites such as the bone and thus, are likely targets for therapeutic intervention. To identify those molecules and particularly cell surface antigens that accompany this transition, we studied the changes in cell surface antigenic profiles between a hormone-sensitive prostate cancer line LNCaP and its hormone-refractory derivative C4-2B, using an antibody library-based affinity proteomic approach. We selected a naïve phage antibody display library to identify human single-chain antibodies that bind specifically to C4-2B but not LNCaP. Using mass spectrometry, we identified one of the antibody-targeted antigens as the ICAM-1/CD54/human rhinovirus receptor. Recombinant IgG1 derived from this single-chain antibody binds to a neutralizing epitope of ICAM-1 and blocks C4-2B cell invasion through extracellular matrix in vitro. ICAM-1 is thus differentially expressed during the transition of the hormone-sensitive prostate cancer cell line LNCaP to its hormone-refractory derivative C4-2B, plays an important role in imparting the C4-2B line with the ability to invade, and may therefore be a target for therapeutic intervention.

Regional administration of oncolytic Echovirus 1 as a novel therapy for the peritoneal dissemination of gastric cancer

The dissemination of malignant gastric cells to the peritoneum occurs frequently, usually as an early event in disease, and results in poor patient prognosis. Surgery and chemotherapy offer limited therapeutic success. The low-pathogenic human enterovirus, Echovirus 1 (EV1), is an oncolytic virus that selectively targets and destroys malignant prostate and ovarian cancer xenografts in vivo. Lytic EV1 infection requires the cell surface expression of alpha(2)beta(1), an integrin involved in the dissemination of gastric cancer cells to the peritoneum. Herein, we evaluated the capacity of EV1 for anti-neoplastic cell action in gastric peritoneal carcinomatosis. Flow cytometric analysis demonstrated that alpha(2)beta(1) was abundantly surface expressed on a panel of gastric cancer cell lines, rendering the majority of lines highly susceptible to in vitro lytic EV1 infection and supportive of efficient viral progeny production. A bioluminescent MKN-45-Luc SCID mouse model of peritoneal dissemination was developed to allow real-time non-invasive monitoring of peritoneal tumor burden. Employing this mouse model, we demonstrated a therapeutic dose-response for escalating oncolytic EV1 doses. Taken together, these results emphasize the exciting potential for EV1 as a single or adjunct therapy for the control of the peritoneal dissemination of gastric cancer.