Oncolytic rat parvovirus H-1PV, a candidate for the treatment of human lymphoma: In vitro and in vivo studies

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Stability and safety key factors of the oncolytic protoparvovirus H-1 from manufacturing to human application

The oncolytic rodent protoparvovirus H-1PV has been successfully used in phase I/II clinical trials to treat recurrent glioblastoma multiforme and pancreatic cancer. The present work focuses on the stability and environmental safety of the H-1PV drug product from production up to its use in patients. We identified hold-steps in manufacturing for up to 3 months and showed 7-years stability for the optimal product formulation. Stress testing via UV, temperature, and pH also determined that the drug product is stable. De- and rehydration for lyophilization simulation are possible without infectious virus loss. Furthermore, we prove in-use stability for 4 days at room temperature and show no virus adsorption to injection devices, guaranteeing the correct administration dose. Iodixanol in the formulation, resulting in high viscosity, protects H-1PV against UV and some disinfectants. Nonetheless, H-1PV is depleted with rapid heat deactivation, autoclavation, and nanofiltration. Assessment of chemical disinfectants that are currently recommended by the Robert Koch-Institute demonstrated that ethanol-based hand disinfectants are not effective; however, aldehyde-based disinfectants for surfaces and instruments demonstrate sufficient H-1PV deactivation in aqueous formulations by 4 to 6 log₁₀. With these results, we could establish a specific hygiene plan for all involved facilities from manufacturing to patient application. Overall, using 48% Iodixanol in Visipaque/Ringer as a drug formulation stabilizes H-1PV infectivity over years and protects against virus loss from short-term UV, low pH, and temperature exposure. KEY POINTS: • Optimal formulation of drug product protects the H-1PV protoparvovirus against UV, temperatures up to 50 °C, and low pH (> 1.25), stabilizing the virus during manufacturing, storage, transport, and application. • H-1PV is stable during in-use and does not adsorb to injection devices during patient administration. • Hygiene plan for H-1PV with physicochemical methods has been established.

Best of most possible worlds: Hybrid gene therapy vectors based on parvoviruses and heterologous viruses

Parvoviruses and especially the adeno-associated virus (AAV) species provide an exciting and versatile platform for the rational design or molecular evolution of human gene-therapy vectors, documented by literature from over half a century, hundreds of clinical trials, and the recent commercialization of multiple AAV gene therapeutics. For the last three decades, the power of these vectors has been further potentiated through various types of hybrid vectors created by intra- or inter-genus juxtaposition of viral DNA and protein cis elements or by synergistic complementation of parvoviral features with those of heterologous, prokaryotic, or eukaryotic viruses. Here, we provide an overview of the history and promise of this rapidly expanding field of hybrid parvoviral gene-therapy vectors, starting with early generations of chimeric particles composed of a recombinant AAV genome encapsidated in shells of synthetic AAVs or of adeno-, herpes-, baculo-, or protoparvoviruses. We then dedicate our attention to two newer, highly promising types of hybrid vectors created via (1) pseudotyping of AAV genomes with bocaviral serotypes and capsid mutants or (2) packaging of AAV DNA into, or tethering of entire vector particles to, bacteriophages. Finally, we conclude with an outlook summarizing critical requirements and improvements toward clinical translation of these original concepts.

Upstream process optimization and micro- and macrocarrier screening for large-scale production of the oncolytic H-1 protoparvovirus

Abstract

The oncolytic virus H-1PV is a promising candidate for various cancer treatments. Therefore, production process needs to be optimized and scaled up for future market release. Currently, the virus is produced with minimum essential medium in 10-layer CellSTACK® chambers with limited scalability, requiring a minimum seeding density of 7.9E3 cells/cm². Production also requires a 5% fetal bovine serum (FBS) supplementation and has a virus yield up to 3.1E7 plaque-forming units (PFU)/cm². Using the animal-free cell culture medium VP-SFM™ and a new feeding strategy, we demonstrate a yield boost by a mean of 0.3 log while reducing seeding density to 5.0E3 cells/cm² and cutting FBS supplementation by up to 40% during the production process. Additionally, FBS is completely removed at the time of harvest. Eleven commercial micro- and macrocarriers were screened regarding cell growth, bead-to-bead transfer capability, and virus yield. We present a proof-of-concept study for producing H-1PV on a large scale with the microcarrier Cytodex® 1 in suspension and a macrocarrier for a fixed-bed iCELLis® bioreactor. A carrier-based H-1PV production process combined with an optimized cell culture medium and feeding strategy can facilitate future upscaling to industrial-scale production.

Key points

• Virus yield increase and FBS-free harvest after switching to cell culture medium VP-SFM™.

• We screened carriers for cell growth, bead-to-bead transfer capability, and H-1PV yield.

• High virus yield is achieved with Cytodex® 1 and macrocarrier for iCellis® in Erlenmeyer flasks.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11642-y.

Oncolytic virotherapy in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a curative option for various hematologic malignancies. However, fatal complications, such as relapse and graft-versus-host disease (GVHD) hampered favorable HSCT outcomes. Cancer cells remained in the body following the conditioning regimen, or those contaminating the autologous graft can cause relapse. Although the relapse is much lesser in allogeneic HSCT, GVHD is still a life-threatening complication in this type of HSCT. Researchers are seeking various strategies to reduce relapse and GVHD in HSCT with minimum effects on the engraftment and immune-reconstitution. Oncolytic viruses (OVs) are emerging anti-cancer agents with promising results in battling solid tumors. OVs can selectively replicate in the malignant cells in which the antiviral immune responses have defected. Hence, they could be used as a purging agent to eradicate the tumoral contamination of autologous grafts with no damages to hematopoietic stem cells. Moreover, they have been shown to alleviate GVHD complications through modulating alloreactive T cell responses. Primary results promise using OVs as a strategy to reduce both relapse and GVHD in the HSCT without affecting hematologic and immunologic engraftment. Herein, we provide the latest findings in the field of OV therapy in HSCT and discuss their pros and cons.

A Roadmap for the Success of Oncolytic Parvovirus-Based Anticancer Therapies

Autonomous rodent protoparvoviruses (PVs) are promising anticancer agents due to their excellent safety profile, natural oncotropism, and oncosuppressive activities. Viral infection can trigger immunogenic cell death, activating the immune system against the tumor. However, the efficacy of this treatment in recent clinical trials is moderate compared with results seen in preclinical work. Various strategies have been employed to improve the anticancer activities of oncolytic PVs, including development of second-generation parvoviruses with enhanced oncolytic and immunostimulatory activities and rational combination of PVs with other therapies. Understanding the cellular factors involved in the PV life cycle is another important area of investigation. Indeed, these studies may lead to the identification of biomarkers that would allow a more personalized use of PV-based therapies. This review focuses on this work and the challenges that still need to be overcome to move PVs forward into clinical practice as an effective therapeutic option for cancer patients.

Apoptin as a Tumor-Specific Therapeutic Agent: Current Perspective on Mechanism of Action and Delivery Systems

Cancer remains one of the leading causes of death worldwide in humans and animals. Conventional treatment regimens often fail to produce the desired outcome due to disturbances in cell physiology that arise during the process of transformation. Additionally, development of treatment regimens with no or minimum side-effects is one of the thrust areas of modern cancer research. Oncolytic viral gene therapy employs certain viral genes which on ectopic expression find and selectively destroy malignant cells, thereby achieving tumor cell death without harming the normal cells in the neighborhood. Apoptin, encoded by Chicken Infectious Anemia Virus' VP3 gene, is a proline-rich protein capable of inducing apoptosis in cancer cells in a selective manner. In normal cells, the filamentous Apoptin becomes aggregated toward the cell margins, but is eventually degraded by proteasomes without harming the cells. In malignant cells, after activation by phosphorylation by a cancer cell-specific kinase whose identity is disputed, Apoptin accumulates in the nucleus, undergoes aggregation to form multimers, and prevents the dividing cancer cells from repairing their DNA lesions, thereby forcing them to undergo apoptosis. In this review, we discuss the present knowledge about the structure of Apoptin protein, elaborate on its mechanism of action, and summarize various strategies that have been used to deliver it as an anticancer drug in various cancer models.

Virus-Receptor Interactions and Virus Neutralization: Insights for Oncolytic Virus Development

Oncolytic viruses (OVs) are replication competent agents that selectively target cancer cells. After penetrating the tumor cell, viruses replicate and eventually trigger cell lysis, releasing the new viral progeny, which at their turn will attack and kill neighbouring cells. The ability of OVs to self-amplify within the tumor while sparing normal cells can provide several advantages including the capacity to encode and locally produce therapeutic protein payloads, and to prime the host immune system. OVs targeting of cancer cells is mediated by host factors that are differentially expressed between normal tissue and tumors, including viral receptors and internalization factors. In this review article, we will discuss the evolution of oncolytic viruses that have reached the stage of clinical trials, their mechanisms of oncolysis, cellular receptors, strategies for targeting cancers, viral neutralization and developments to bypass virus neutralization.

Immune System Stimulation by Oncolytic Rodent Protoparvoviruses

Rodent protoparvoviruses (PVs), parvovirus H-1 (H-1PV) in particular, are naturally endowed with oncolytic properties. While being historically described as agents that selectively replicate in and kill cancer cells, recent yet growing evidence demonstrates that these viruses are able to reverse tumor-driven immune suppression through induction of immunogenic tumor cell death, and the establishment of antitumorigenic, proinflammatory milieu within the tumor microenvironment. This review summarizes the most important preclinical proofs of the interplay and the cooperation between PVs and the host immune system. The molecular mechanisms of PV-induced immunostimulation are also discussed. Furthermore, initial encouraging in-human observations from clinical trials and compassionate virus uses are presented, and speak in favor of further H-1PV clinical development as partner drug in combined immunotherapeutic protocols.

Regression of solid breast tumours in mice by Newcastle disease virus is associated with production of apoptosis related-cytokines

Background

Different strains of Newcastle disease virus (NDV) worldwide proved to have tumouricidal activity in several types of cancer cells. However, the possible anti-cancer activity of Malaysian NDV AF2240 strain and its mechanism of action remains unknown. The ability of cytokine-related apoptosis-inducing NDV AF2240 to treat breast cancer was investigated in the current study.

Methods

A total of 90 mice were used and divided into 15 groups, each group comprising of 6 mice. Tumour, body weight and mortality of the mice were determined throughout the experiment, to observe the effect of NDV and NDV + tamoxifen treatments on the mice. In addition, the toxic effect of the treatments was determined through liver function test. In order to elucidate the involvement of cytokine production induced by NDV, a total of six cytokines, i.e. IL-6, IFN-γ, MCP-1, IL-10, IL12p70 and TNF-α were measured using cytometric bead array assay (plasma) and enzyme-linked immunosorbent spot (isolated splenocytes).

Results

The results demonstrated that 4 T1 breast cancer cells in allotransplanted mice treated with AF2240 showed a noticeable inhibition of tumour growth and induce apoptotic-related cytokines.

Conclusions

NDV AF2240 suppression of breast tumour growth is associated with induction of apoptotic-related cytokines. It would be important to further investigate the molecular mechanism underlaying cytokines production by Newcastle disease virus.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5516-5) contains supplementary material, which is available to authorized users.

Making Oncolytic Virotherapy a Clinical Reality: The European Contribution

Oncolytic viruses (OVs) are quickly moving toward the forefront of modern medicines. The reward for the decades of research invested into developing viral platforms that selectively replicate in and lyse tumor cells while sparking anticancer adaptive immunity is presenting in the form of durable therapeutic responses. While this has certainly been a concerted global effort, in this review for the 25th anniversary of the European Society of Gene and Cell Therapy, we focus on the contributions made by European researchers. Research centers across Europe have held central roles in advancing OVs, from the earliest reports of coincidental viral infections leading to antitumor efficacy, to advanced mechanistic studies, and now through Phase I-III trials to imminent regulatory approvals. While challenges still remain, with limitations in preclinical animal models, antiviral immune clearance, and manufacture restrictions enforced by poor viral yields in certain cases, the field has come a very long way in recent years. Thoughtful mechanistic integration of OVs with standard of care strategies and other newly approved therapies should provide potent novel approaches. Combination with immunotherapeutic regimes holds significant promise, and the ability to arm the viral platform with therapeutic proteins for localized expression at the tumor site provides an opportunity for creating highly effective synergistic treatments and brings a new age of targeted cancer therapeutics.

The Oncolytic Virotherapy Era in Cancer Management: Prospects of Applying H-1 Parvovirus to Treat Blood and Solid Cancers

Non-Hodgkin lymphoma (NHL) and leukemia are among the most common cancers worldwide. While the treatment of NHL/leukemia of B-cell origin has much progressed with the introduction of targeted therapies, few treatment standards have been established for T-NHL/leukemia. As presentation in both B- and T-NHL/leukemia patients is often aggressive and as prognosis for relapsed disease is especially dismal, this cancer entity poses major challenges and requires innovative therapeutic approaches. In clinical trials, oncolytic viruses (OVs) have been used against refractory multiple myeloma (MM). In preclinical settings, a number of OVs have demonstrated a remarkable ability to suppress various types of hematological cancers. Most studies dealing with this approach have used MM or B- or myeloid-cell-derived malignancies as models. Only a few describe susceptibility of T-cell lymphoma/leukemia to OV infection and killing. The rat H-1 parvovirus (H-1PV) is an OV with considerable promise as a novel therapeutic agent against both solid tumors (pancreatic cancer and glioblastoma) and hematological malignancies. The present perspective article builds on previous reports of H-1PV-driven regression of Burkitt's lymphoma xenografts and on unpublished observations demonstrating effective killing by H-1PV of cells from CHOP-resistant diffuse large B-cell lymphoma, cutaneous T-cell lymphoma, and T-cell acute lymphoblastic leukemia. On the basis of these studies, H-1PV is proposed for use as an adjuvant to (chemo)therapeutic regimens. Furthermore, in the light of a recently completed first parvovirus clinical trial in glioblastoma patients, the advantages of H-1PV for systemic application are discussed.

Virotherapy of digestive tumors with rodent parvovirus: overview and perspectives

INTRODUCTION

Toolan's H-1 parvovirus (H-1PV) exerts a cytotoxic/oncolytic effect, predominantly mediated by its non-structural protein (NS1). This rat parvovirus is harmless, unlike other parvoviruses, and its antitumor potential may be useful to clinicians as its oncolytic action appears to be true in numerous non-digestive and digestive cancers.

AREAS COVERED

After a brief review of parvovirus genus and biology, we summarize the proposed mechanisms to explain the cytotoxicity of H-1PV to tumors which results in dysregulation of cell transcription, cell-cycle arrest, termination of cell replication, activation of cellular stress response and induction of cell death. Viral oncolysis induces a strong tumor-specific immune response leading to the recognition and elimination of minimal residual disease. As the action of H-1PV is not limited to the digestive tract, we initially analyse studies performed in non-digestive cancers such as glioma (as the virus is able to cross the blood brain barrier), and then focused more particularly on the results in digestive cancers.

EXPERT OPINION

Based on the results of studies showing little H-1PV toxicity to living bodies, we advocate for the use of the parvovirus in cancers such as melanoma, glioma and pancreatic ductal adenocarcinoma in addition to conventional chemotherapy.

Standardized large-scale H-1PV production process with efficient quality and quantity monitoring

The promising anticancer properties of rodent protoparvoviruses, notably H-1PV, have led to their clinical testing. This makes it necessary to produce highly pure, well-characterized virus batches in sufficient quantity. The present work focused on developing standardized production, purification, and characterization procedures as a basis for exploiting H-1PV both preclinically and in clinical trials for anticancer virotherapy. Two infection and two virus purification strategies were tested and the resulting virus preparations compared for their purity and full-, infectious-, and empty-particle contents. The adopted production process, which involves culturing and infecting NB-324K cells in 10-layer CellSTACK(®) chambers (1×10(3) infectious units per infected cell), is simple, scalable, and reproducible. Downstream processing to eliminate contaminating DNA and protein includes DNAse treatment, filtration, and two Iodixanol density-gradient centrifugations, the first gradient being a step gradient and the second, either a step (1×10(10) PFU/ml) or a continuous gradient (3×10(11) PFU/ml). A procedure was also developed for obtaining infectious particle-free preparations of empty virions for research purposes: cesium chloride density gradient centrifugation followed by UV irradiation (1×10(14) physical particles/ml). For quick, sensitive determination of physical particles (and hence, particle-to-infectivity ratios), a "Capsid-ELISA" was developed, based on a novel monoclonal antibody that specifically targets assembled capsids.

Tumor Selectivity of Oncolytic Parvoviruses: From in vitro and Animal Models to Cancer Patients

Oncolytic virotherapy of cancer is among the innovative modalities being under development and especially promising for targeting tumors, which are resistant to conventional treatments. Presently, at least a dozen of viruses, belonging to nine different virus families, are being tested within the frames of various clinical studies in cancer patients. Continuously growing preclinical evidence showing that the autonomous rat parvovirus H-1 (H-1PV) is able to kill tumor cells that resist conventional treatments and to achieve a complete cure of various human tumors in animal models argues for its inclusion in the arsenal of oncolytic viruses with an especially promising bench to bedside translation potential. Oncolytic parvovirus safe administration to humans relies on the intrinsic preference of these agents for quickly proliferating, metabolically, and biochemically disturbed tumor versus normal cells (tumor selectivity or oncotropism). The present review summarizes and discusses (i) preclinical evidence of H-1PV innocuousness for normal cells and healthy tissues in vitro and in animals, respectively, (ii) toxicological assessments of H-1PV mono- or combined therapy in tumor-bearing virus-permissive animal models, as well as (iii) historical results of experimental infection of human cancer patients with H-1PV. Altogether, these data argue against a risk of H-1PV inducing significant toxic effects in human patients. This highly favorable safety profile allowed the translation of H-1PV preclinical research into a Phase I/IIa clinical trial being currently in progress.

Pathology, organ distribution, and immune response after single and repeated intravenous injection of rats with clinical-grade parvovirus H1

Parvovirus H1 (H1PV) is an autonomous parvovirus that is transmitted in rodent populations. Its natural host is rats. H1PV infection is nonpathogenic except in rat and hamster fetuses and newborns. H1PV infection of human cancer cells caused strong oncolytic effects in preclinical models. For a clinical trial of H1PV in patients with brain tumors, clinical-grade H1PV was produced according to Good Manufacturing Practices. This report focuses on results obtained after a single high-dose intravenous injection of highly purified H1PV in 30 rats and multiple (n = 17) intravenous injections at 3 dose levels in 223 rats. In both studies, no virus-related mortality or macroscopic organ changes related to H1PV occurred. Histopathology after multiple virus injections revealed minimal diffuse bile duct hyperplasia in livers of animals of the highest dose group and germinal center development in spleens of animals from the high-dose group. Liver changes were reversible within a 2-wk recovery period after the last injection. Hematology, blood chemistry, and coagulation analyses did not reveal significant toxicologic changes due to H1PV. Virus injection stimulated the production of IgG antibodies but did not alter mononuclear cell function or induce cytokine release. PCR analysis showed dose-dependent levels of viral genomes in all organs tested. The virus was excreted primarily through feces. These data provide important information regarding H1PV infection in its natural host. Due to the confirmation of the favorable safety profile of H1PV in a permissive animal model, a phase I/IIa clinical trial of H1PV in brain tumor patients could be initiated.

Bioavailability, biodistribution, and CNS toxicity of clinical-grade parvovirus H1 after intravenous and intracerebral injection in rats

The autonomous parvovirus H1 (H1PV) is transmitted in rodent populations. The natural host is the rat, in which H1PV infection is pathogenic only in fetuses and newborns. H1PV infection of human cancer cells leads to strong oncolytic effects in preclinical models. In preparation for a clinical trial of H1PV injection in patients with malignant brain tumors, H1PV had to be prepared to Good Manufacturing Practice standards, including extensive toxicology testing in rats. Because the trial involves direct intracerebral injection of H1PV into the tumor and around the resection cavity, possible toxicity to CNS tissue had to be investigated. In addition, quantitative blood levels and the tissue distribution of H1PV after single intracerebral or intravenous injection were measured. Direct injection of H1PV into rat brain at 3 dose levels (maximum, 7.96 × 107 pfu) did not cause any macroscopic or histologic pathology. Furthermore, H1PV infection of the brain did not alter central or autonomous nervous system function. H1PV DNA was detected in almost all organs at 6 h, 48 h, and 14 d after intravenous and intracerebral injection, with the highest levels in liver and spleen. H1PV concentrations in most organs were similar after intravenous and intracerebral injection, indicating high permeability of the blood-brain barrier for this small virus. The current results demonstrate wide organ distribution of H1PV after intravenous or intracerebral injection, confirm that H1PV is nonpathogenic in adult rats even after direct injection into the brain, and form the basis for the ongoing ParvOryx01 clinical trial.

Oncolytic parvoviruses: from basic virology to clinical applications

Accumulated evidence gathered over recent decades demonstrated that some members of the Parvoviridae family, in particular the rodent protoparvoviruses H-1PV, the minute virus of mice and LuIII have natural anticancer activity while being nonpathogenic to humans. These studies have laid the foundations for the launch of a first phase I/IIa clinical trial, in which the rat H-1 parvovirus is presently undergoing evaluation for its safety and first signs of efficacy in patients with glioblastoma multiforme. After a brief overview of the biology of parvoviruses, this review focuses on the studies which unraveled the antineoplastic properties of these agents and supported their clinical use as anticancer therapeutics. Furthermore, the development of novel parvovirus-based anticancer strategies with enhanced specificity and efficacy is discussed, in particular the development of second and third generation vectors and the combination of parvoviruses with other anticancer agents. Lastly, we address the key challenges that remain towards a more rational and efficient use of oncolytic parvoviruses in clinical settings, and discuss how a better understanding of the virus life-cycle and of the cellular factors involved in virus infection, replication and cytotoxicity may promote the further development of parvovirus-based anticancer therapies, open new prospects for treatment and hopefully improve clinical outcome.

The ex vivo purge of cancer cells using oncolytic viruses: recent advances and clinical implications

Hematological malignancies are treated with intensive high-dose chemotherapy, with or without radiation. This is followed by hematopoietic stem cell (HSC) transplantation (HSCT) to rescue or reconstitute hematopoiesis damaged by the anticancer therapy. Autologous HSC grafts may contain cancer cells and purging could further improve treatment outcomes. Similarly, allogeneic HSCT may be improved by selectively purging alloreactive effector cells from the graft rather than wholesale immune cell depletion. Viral agents that selectively replicate in specific cell populations are being studied in experimental models of cancer and immunological diseases and have potential applications in the context of HSC graft engineering. This review describes preclinical studies involving oncolytic virus strains of adenovirus, herpes simplex virus type 1, myxoma virus, and reovirus as ex vivo purging agents for HSC grafts, as well as in vitro and in vivo experimental studies using oncolytic coxsackievirus, measles virus, parvovirus, vaccinia virus, and vesicular stomatitis virus to eradicate hematopoietic malignancies. Alternative ex vivo oncolytic virus strategies are also outlined that aim to reduce the risk of relapse following autologous HSCT and mitigate morbidity and mortality due to graft-versus-host disease in allogeneic HSCT.

Design and development of a robotized system coupled to µCT imaging for intratumoral drug evaluation in a HCC mouse model

Hepatocellular carcinoma (HCC) is one of the most common cancer related deaths worldwide. One of the main challenges in cancer treatment is drug delivery to target cancer cells specifically. Preclinical evaluation of intratumoral drugs in orthotopic liver cancer mouse models is difficult, as percutaneous injection hardly can be precisely performed manually. In the present study we have characterized a hepatoma model developing a single tumor nodule by implantation of Hep55.1C cells in the liver of syngeneic C57BL/6J mice. Tumor evolution was followed up by µCT imaging, and at the histological and molecular levels. This orthotopic, poorly differentiated mouse HCC model expressing fibrosis, inflammation and cancer markers was used to assess the efficacy of drugs. We took advantage of the high precision of a previously developed robotized system for automated, image-guided intratumoral needle insertion, to administer every week in the tumor of the Hep55.1C mouse model. A significant tumor growth inhibition was observed using our robotized system, whereas manual intraperitoneal administration had no effect, by comparison to untreated control mice.

Autonomous parvoviruses neither stimulate nor are inhibited by the type I interferon response in human normal or cancer cells

Members of the genus Parvovirus are small, nonenveloped single-stranded DNA viruses that are nonpathogenic in humans but have potential utility as cancer therapeutics. Because the innate immune response to parvoviruses has received relatively little attention, we compared the response to parvoviruses to that of several other types of viruses in human cells. In normal human glia, fibroblasts, or melanocytes, vesicular stomatitis virus evoked robust beta interferon (IFN-β) responses. Cytomegalovirus, pseudorabies virus, and Sindbis virus all evoked a 2-log-unit or greater upregulation of IFN-β in glia; in contrast, LuIII and MVMp parvoviruses did not evoke a detectable IFN-β or interferon-stimulated gene (ISG; MX1, oligoadenylate synthetase [OAS], IFIT-1) response in the same cell types. The lack of response raised the question of whether parvoviral infection can be attenuated by IFN; interestingly, we found that IFN did not decrease parvovirus (MVMp, LuIII, and H-1) infectivity in normal human glia, fibroblasts, or melanocytes. The same was true in human cancers, including glioma, sarcoma, and melanoma. Similarly, IFN failed to attenuate transduction by the dependovirus vector adeno-associated virus type 2. Progeny production of parvoviruses was also unimpaired by IFN in both glioma and melanoma, whereas vesicular stomatitis virus replication was blocked. Sarcoma cells with upregulated IFN signaling that show high levels of resistance to other viruses showed strong infection by LuIII. Unlike many other oncolytic viruses, we found no evidence that impairment of innate immunity in cancer cells plays a role in the oncoselectivity of parvoviruses in human cells. Parvoviral resistance to the effects of IFN in cancer cells may constitute an advantage in the virotherapy of some tumors.

IMPORTANCE

Understanding the interactions between oncolytic viruses and the innate immune system will facilitate employing these viruses as therapeutic agents in cancer patients. The cancer-selective nature of some oncolytic viruses is based on the impaired innate immunity of many cancer cells. The parvoviruses H-1, LuIII, and MVM target cancer cells; however, their relationship with the innate immune system is relatively uncharacterized. Surprisingly, we found that these parvoviruses do not evoke an interferon response in normal human fibroblasts, glia, or melanocytes. Furthermore, unlike most other types of virus, we found that parvovirus infectivity is unaffected by interferon treatment of human normal or tumor cells. Finally, parvoviral replication was unimpaired by interferon in four human tumor types, including those with residual interferon functionality. We conclude that deficits in the interferon antiviral response of cancer cells do not contribute to parvoviral oncoselectivity in human cells. The interferon-resistant phenotype of parvoviruses may give them an advantage over interferon-sensitive oncolytic viruses in tumors showing residual interferon functionality.

Capacity of wild-type and chemokine-armed parvovirus H-1PV for inhibiting neo-angiogenesis

Anti-angiogenic therapy has been recognized as a powerful potential strategy for impeding the growth of various tumors. However no major therapeutic effects have been observed to date, mainly because of the emergence of several resistance mechanisms. Among novel strategies to target tumor vasculature, some oncolytic viruses open up new prospects. In this context, we addressed the question whether the rodent parvovirus H-1PV can target endothelial cells. We show that cultures of human normal (HUVEC) and immortalized (KS-IMM) endothelial cells sustain an abortive viral cycle upon infection with H-1PV and are sensitive to H-1PV cytotoxicity. H-1PV significantly inhibits infected KS-IMM tumor growth. This effect may be traced back by the virus ability to both kill proliferating endothelial cells and inhibit VEGF production Recombinant H-1PV vectors can also transduce tumor cells with chemokines endowed with anti-angiogenesis properties, and warrant further validation for the treatment of highly vascularized tumors.

Structural characterization of H-1 parvovirus: comparison of infectious virions to empty capsids

The structure of single-stranded DNA (ssDNA) packaging H-1 parvovirus (H-1PV), which is being developed as an antitumor gene delivery vector, has been determined for wild-type (wt) virions and noninfectious (empty) capsids to 2.7- and 3.2-Å resolution, respectively, using X-ray crystallography. The capsid viral protein (VP) structure consists of an α-helix and an eight-stranded anti-parallel β-barrel with large loop regions between the strands. The β-barrel and loops form the capsid core and surface, respectively. In the wt structure, 600 nucleotides are ordered in an interior DNA binding pocket of the capsid. This accounts for ∼12% of the H-1PV genome. The wt structure is identical to the empty capsid structure, except for side chain conformation variations at the nucleotide binding pocket. Comparison of the H-1PV nucleotides to those observed in canine parvovirus and minute virus of mice, two members of the genus Parvovirus, showed both similarity in structure and analogous interactions. This observation suggests a functional role, such as in capsid stability and/or ssDNA genome recognition for encapsulation. The VP structure differs from those of other parvoviruses in surface loop regions that control receptor binding, tissue tropism, pathogenicity, and antibody recognition, including VP sequences reported to determine tumor cell tropism for oncotropic rodent parvoviruses. These structures of H-1PV provide insight into structural features that dictate capsid stabilization following genome packaging and three-dimensional information applicable for rational design of tumor-targeted recombinant gene delivery vectors.

TLR-9 contributes to the antiviral innate immune sensing of rodent parvoviruses MVMp and H-1PV by normal human immune cells

The oncotropism of Minute Virus of Mice (MVMp) is partially related to the stimulation of an antiviral response mediated by type-I interferons (IFNs) in normal but not in transformed mouse cells. The present work was undertaken to assess whether the oncotropism displayed against human cells by MVMp and its rat homolog H-1PV also depends on antiviral mechanisms and to identify the pattern recognition receptor (PRR) involved. Despite their low proliferation rate which represents a drawback for parvovirus multiplication, we used human peripheral blood mononuclear cells (hPBMCs) as normal model specifically because all known PRRs are functional in this mixed cell population and moreover because some of its subsets are among the main IFN producers upon infections in mammals. Human transformed models consisted in lines and tumor cells more or less permissive to both parvoviruses. Our results show that irrespective of their permissiveness, transformed cells do not produce IFNs nor develop an antiviral response upon parvovirus infection. However, MVMp- or H-1PV-infected hPBMCs trigger such defense mechanisms despite an absence of parvovirus replication and protein expression, pointing to the viral genome as the activating element. Substantial reduction of an inhibitory oligodeoxynucleotide (iODN) of the latter IFN production identified TLR-9 as a potential PRR for parvoviruses in hPBMCs. However, neither the iODN treatment nor an antibody-induced neutralization of the IFN-triggered effects restored parvovirus multiplication in these cells as expected by their weak proliferation in culture. Finally, given that a TLR-9 activation could also not be observed in parvovirus-infected human lines reported to be endowed with a functional TLR-9 pathway (Namalwa, Raji, and HEK293-TLR9(+/+)), our data suggest that transformed human cells do not sense MVMp or H-1PV either because of an absence of PRR expression or an intrinsic, or virus-driven defect in the endosomal sensing of the parvovirus genomes by TLR-9.

Proteomic analysis identifies a novel function for galectin-3 in the cell entry of parvovirus

Cellular factors associated with the parvovirus minute virus of mice (MVM) during infection are thought to play important roles in the MVM life cycle but only a few of these have been identified. Here we used a proteomic-based approach in order to identify host-binding partners of MVM. Using purified MVM as bait for immunoprecipitation assays, a total of 150 proteins were identified in MVM immunoprecipitates by quantitative liquid chromatography-tandem mass spectrometry. Galectin-3 was one of six proteins showing a statistically significant enrichment across replicates. Small interfering RNA depletion studies revealed an important role for galectin-3 in MVM endocytosis and infectivity in LA9 mouse fibroblast cells. Galectin-3-depleted cells were less susceptible to MVM infection than control cells and showed a significant reduction of MVM cellular uptake, but not of MVM binding to the cell surface. Our results indicate an important role for galectin-3 in the cellular uptake of MVM. We propose that galectin-3 facilitates the access of MVM to its receptor(s) at the plasma membrane and in this way promotes MVM endocytosis.

Production, purification, crystallization and structure determination of H-1 Parvovirus

Crystals of H-1 Parvovirus (H-1PV), an antitumor gene-delivery vector, were obtained for DNA-containing capsids and diffracted X-rays to 2.7 Å resolution using synchrotron radiation. The crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a=255.4, b=350.4, c=271.6 Å, β=90.34°. The unit cell contained two capsids, with one capsid per crystallographic asymmetric unit. The H-1PV structure has been determined by molecular replacement and is currently being refined.

Activation of the human immune system via toll-like receptors by the oncolytic parvovirus H-1

This study aimed to investigate the function of toll-like receptors (TLRs) during oncolytic parvovirus H-1 (H-1PV)-induced human immune responses. First, the role of TLRs in the activation of the NFκB transcription factor was characterized; second, the immunologic effects of H-1PV-induced tumor cell lysates (TCL) on human antitumor immune responses were evaluated. A human ex vivo model was used to study immune responses with dendritic cells (DCs). Human embryonic kidney cells (HEK293) transfected to stably express TLRs were used as potential human DC equivalents to further investigate the role of specific TLRs during immune activation. TLR3 and TLR9 were activated by H-1PV infection, which correlated with NFκB translocation to the nucleus and a reduced cytoplasmic IκB expression. Using a TLR-signaling reporter plasmid (pNiFty-Luc), NFκB activity was increased following H-1PV infection. In addition, human DCs coincubated with H-1PV-induced TCL demonstrated increased TLR3 and TLR9 expression. These data suggest that H-1PV-induced TCL stimulate human DCs at least in part through TLR-dependent signaling pathways. Thus, DC maturation occurred through exposure to H-1PV-induced TCL through TLR-signaling leading to NFκB-dependent activation of the adaptive immune system as indicated by the increased expression of CD86, TLR3 and TLR9. Furthermore, the transcription of various cytokines indicates the activation of immune response, therefore the production of the proinflammatory cytokine TNF-α was determined. Here, H-1PV-induced TCL significantly enhanced the TNF-α level by DCs after coculture. H-1PV oncolytic virotherapy enhances immune priming by different effects on DCs and generates antitumor immunity. These findings potentially offer a new approach to tumor therapy.

Effect of the parvovirus H-1 non-structural protein NS1 on the tumorigenicity of human gastric cancer cells

OBJECTIVE

To investigate the in vivo oncosuppressive effect of the non-structural protein NS1 of parvovirus H-1 on human gastric cancer cell lines.

METHODS

Recombinant plasmid pcDNA3.1-NS1 containing the complete NS1 gene of parvovirus H-1 was constructed and characterized by restriction enzyme digestion and sequence analysis. The human gastric cancer cell lines MKN28, SGC7901 and MKN45 were stably transfected with empty or recombinant plasmids. NS1 gene transcription and protein expression in the latter transfectants were verified by reverse transcriptase polymerase chain reaction and Western blot, respectively. The oncosuppressive effect of the parvoviral protein NS1 on the gastric cancer cell lines was tested by comparing the tumorigenicity of empty and recombinant vector-transfected cells in nude mice.

RESULTS

Well differentiated gastric cancer cells (MKN28) transfected with either empty plasmid or pcDNA3.1-NS1 were tumorigenic in nude mice. Moderately (SGC7901) and poorly (MKN45) differentiated gastric cancer cells transfected with empty plasmid were also tumorigenic, but no tumor resulted from the injection when they were transfected with pcDNA3.1-NS1. This NS1-associated suppression of SGC7901 and MKN45 tumors correlated with the decreased percentage of CD44 positive cells.

CONCLUSIONS

NS1 expression in poorly differentiated gastric cancer cells prevents them from forming tumors, perhaps by impairing the stem-like phenotype. The parvoviral NS1 protein warrants further investigation for its therapeutic potential against cancer.

Molecular pathways: rodent parvoviruses--mechanisms of oncolysis and prospects for clinical cancer treatment

Rodent parvoviruses (PV) are recognized for their intrinsic oncotropism and oncolytic activity, which contribute to their natural oncosuppressive effects. Although PV uptake occurs in most host cells, some of the subsequent steps leading to expression and amplification of the viral genome and production of progeny particles are upregulated in malignantly transformed cells. By usurping cellular processes such as DNA replication, DNA damage response, and gene expression, and/or by interfering with cellular signaling cascades involved in cytoskeleton dynamics, vesicular integrity, cell survival, and death, PVs can induce cytostasis and cytotoxicity. Although productive PV infections normally culminate in cytolysis, virus spread to neighboring cells and secondary rounds of infection, even abortive infection or the sole expression of the PV nonstructural protein NS1, is sufficient to cause significant tumor cell death, either directly or indirectly (through activation of host immune responses). This review highlights the molecular pathways involved in tumor cell targeting by PVs and in PV-induced cell death. It concludes with a discussion of the relevance of these pathways to the application of PVs in cancer therapy, linking basic knowledge of PV-host cell interactions to preclinical assessment of PV oncosuppression.

Retargeting of rat parvovirus H-1PV to cancer cells through genetic engineering of the viral capsid

The rat parvovirus H-1PV is a promising anticancer agent given its oncosuppressive properties and the absence of known side effects in humans. H-1PV replicates preferentially in transformed cells, but the virus can enter both normal and cancer cells. Uptake by normal cells sequesters a significant portion of the administered viral dose away from the tumor target. Hence, targeting H-1PV entry specifically to tumor cells is important to increase the efficacy of parvovirus-based treatments. In this study, we first found that sialic acid plays a key role in H-1PV entry. We then genetically engineered the H-1PV capsid to improve its affinity for human tumor cells. By analogy with the resolved crystal structure of the closely related parvovirus minute virus of mice, we developed an in silico three-dimensional (3D) model of the H-1PV wild-type capsid. Based on this model, we identified putative amino acids involved in cell membrane recognition and virus entry at the level of the 2-fold axis of symmetry of the capsid, within the so-called dimple region. In situ mutagenesis of these residues significantly reduced the binding and entry of H-1PV into permissive cells. We then engineered an entry-deficient viral capsid and inserted a cyclic RGD-4C peptide at the level of its 3-fold axis spike. This peptide binds α(v)β(3) and α(v)β(5) integrins, which are overexpressed in cancer cells and growing blood vessels. The insertion of the peptide rescued viral infectivity toward cells overexpressing α(v)β(5) integrins, resulting in the efficient killing of these cells by the reengineered virus. This work demonstrates that H-1PV can be genetically retargeted through the modification of its capsid, showing great promise for a more efficient use of this virus in cancer therapy.

Live-attenuated measles virus vaccine confers cell contact loss and apoptosis of ovarian cancer cells via ROS-induced silencing of E-cadherin by methylation

Herein we present a novel molecular mechanism of the antitumor effects of live-attenuated measles virus (MV) vaccine in ovarian cancer. Using a 2-DE/MS-based comparative proteomics strategy, we identified 17 proteins differentially expressed in live-attenuated MV vaccine-treated SKOV-3 ovarian cancer cells, including oxidative stress-associated enzymes and cell contact-related proteins, which indicated that live-attenuated MV vaccine could induce aberrant ROS activation. It further mediated epigenetic silencing of E-cadherin via upregulating DNMT3a that conferred both cell-cell and cell-matrix contact loss and apoptosis of ovarian cancer cells. This process could be reversed through ROS inhibition. Our study lays the theoretical foundation for the clinical application of live-attenuated MV vaccine as a potential oncotherapeutic agent for ovarian cancer treatment.

Oncolytic virotherapy for hematological malignancies

Hematological malignancies such as leukemias, lymphomas, multiple myeloma (MM), and the myelodysplastic syndromes (MDSs) primarily affect adults and are difficult to treat. For high-risk disease, hematopoietic stem cell transplant (HCT) can be used. However, in the setting of autologous HCT, relapse due to contamination of the autograft with cancer cells remains a major challenge. Ex vivo manipulations of the autograft to purge cancer cells using chemotherapies and toxins have been attempted. Because these past strategies lack specificity for malignant cells and often impair the normal hematopoietic stem and progenitor cells, prior efforts to ex vivo purge autografts have resulted in prolonged cytopenias and graft failure. The ideal ex vivo purging agent would selectively target the contaminating cancer cells while spare normal stem and progenitor cells and would be applied quickly without toxicities to the recipient. One agent which meets these criteria is oncolytic viruses. This paper details experimental progress with reovirus, myxoma virus, measles virus, vesicular stomatitis virus, coxsackievirus, and vaccinia virus as well as requirements for translation of these results to the clinic.

Activation of the human immune system by chemotherapeutic or targeted agents combined with the oncolytic parvovirus H-1

Background

Parvovirus H-1 (H-1PV) infects and lyses human tumor cells including melanoma, hepatoma, gastric, colorectal, cervix and pancreatic cancers. We assessed whether the beneficial effects of chemotherapeutic agents or targeted agents could be combined with the oncolytic and immunostimmulatory properties of H-1PV.

Methods

Using human ex vivo models we evaluated the biological and immunological effects of H-1PV-induced tumor cell lysis alone or in combination with chemotherapeutic or targeted agents in human melanoma cells +/- characterized human cytotoxic T-cells (CTL) and HLA-A2-restricted dendritic cells (DC).

Results

H-1PV-infected MZ7-Mel cells showed a clear reduction in cell viability of >50%, which appeared to occur primarily through apoptosis. This correlated with viral NS1 expression levels and was enhanced by combination with chemotherapeutic agents or sunitinib. Tumor cell preparations were phagocytosed by DC whose maturation was measured according to the treatment administered. Immature DC incubated with H-1PV-induced MZ7-Mel lysates significantly increased DC maturation compared with non-infected or necrotic MZ7-Mel cells. Tumor necrosis factor-α and interleukin-6 release was clearly increased by DC incubated with H-1PV-induced SK29-Mel tumor cell lysates (TCL) and was also high with DC-CTL co-cultures incubated with H-1PV-induced TCL. Similarly, DC co-cultures with TCL incubated with H-1PV combined with cytotoxic agents or sunitinib enhanced DC maturation to a greater extent than cytotoxic agents or sunitinib alone. Again, these combinations increased pro-inflammatory responses in DC-CTL co-cultures compared with chemotherapy or sunitinib alone.

Conclusions

In our human models, chemotherapeutic or targeted agents did not only interfere with the pronounced immunomodulatory properties of H-1PV, but also reinforced drug-induced tumor cell killing. H-1PV combined with cisplatin, vincristine or sunitinib induced effective immunostimulation via a pronounced DC maturation, better cytokine release and cytotoxic T-cell activation compared with agents alone. Thus, the clinical assessment of H-1PV oncolytic tumor therapy not only alone but also in combination strategies is warranted.

Translation control by protein kinase R restricts minute virus of mice infection: role in parvovirus oncolysis

The relevance of translational control in the gene expression and oncotropism of the autonomous parvoviruses was investigated with MVMp, the prototype strain of minute virus of mice (MVM), infecting normal and transformed rodent and human cells of different tissue origins. Mouse embryo fibroblasts (MEFs) and NIH 3T3 fibroblasts were resistant to MVMp infection, but 3T3 fibroblasts derived from double-stranded RNA (dsRNA)-dependent protein kinase R (PKR) knockout mice (PKR(o/o)) behaved in a manner that was highly permissive to productive MVMp replication. NIH 3T3 resistance correlated with significant phosphorylation of eukaryotic translation initiation factor 2 (eIF2) occurring at early time points after infection. Permissive PKR(o/o) cells were converted to MVMp-restrictive cells after reintroduction of the PKR gene by transfection. Conversely, regulated expression of the vaccinia virus E3 protein, a PKR inhibitor, in MEFs prevented eIF2alpha phosphorylation and increased MVMp protein synthesis. In vitro-synthesized genome-length R1 mRNA of MVMp was a potent activator of PKR. Virus-resistant primary MEFs and NIH 3T3 cells responded to MVMp infection with significant increases in eIF2alpha phosphorylation. In contrast, virus-permissive mouse (PKR(o/o), BHK21, and A9) and human transformed (NB324K fibroblast, U373 glioma, and HepG2 hepatoma) cells consistently showed no significant increase in the level of eIF2alpha phosphorylation following MVMp infection. The synthesis of the viral NS1 protein was inversely correlated with the steady-state PKR levels. Our results show that the PKR-mediated antiviral response is an important mechanism for control of productive MVMp infection, and its impairment in human transformed cells allowed efficient MVMp gene expression. PKR translational control may therefore contribute to the oncolysis of MVMp and other autonomous parvoviruses.

Viral-based gene delivery and regulated gene expression for targeted cancer therapy

IMPORTANCE OF THE FIELD

Cancer is both a major health concern and a care-cost issue in the US and the rest of the world. It is estimated that there will be a total of 1,479,350 new cancer cases and 562,340 cancer deaths in 2009 within the US alone. One of the major obstacles in cancer therapy is the ability to target specifically cancer cells. Most existing chemotherapies and other routine therapies (such as radiation therapy and hormonal manipulation) use indiscriminate approaches in which both cancer cells and non-cancerous surrounding cells are treated equally by the toxic treatment. As a result, either the cancer cell escapes the toxic dosage necessary for cell death and consequently resumes replication, or an adequate lethal dose that kills the cancer cell also causes the cancer patient to perish. Owing to this dilemma, cancer- or organ/tissue-specific targeting is greatly desired for effective cancer treatment and the reduction of side effect cytotoxicity within the patient.

AREAS COVERED IN THIS REVIEW

In this review, the strategies of targeted cancer therapy are discussed, with an emphasis on viral-based gene delivery and regulated gene expression.

WHAT THE READER WILL GAIN

Numerous approaches and updates in this field are presented for several common cancer types.

TAKE HOME MESSAGE

A summary of existing challenges and future directions is also included.

New perspectives in cancer virotherapy: bringing the immune system into play

Despite constant advances in medically orientated cancer studies, conventional treatments by surgery, chemotherapy or radiotherapy remain partly ineffective against numerous cancers. Oncolytic virotherapy – the use of replication-competent viruses that specifically target tumor cells – has opened up new perspectives for improved treatment of these pathologies. Certain viruses demonstrate a natural, preferential tropism for tumor cells, while others can be genetically modified to show such an effect. Several of these viruses have already been used in preclinical and clinical trials in different tumor models; these studies have provided encouraging results and, thus, confirm the growing interest presented by this therapeutic strategy. The role of the immune system in the efficacy of cancer virotherapy has been poorly documented for a long time; however, several recent reports have presented evidence of synergistic effects between both direct viral oncolysis and the activation of specific, anti-tumor immune responses. These findings offer an exciting outlook for the future of cancer virotherapy.