Oncolytic parvoviruses as cancer therapeutics

Oncolytic Rodent Protoparvoviruses Evade a TLR- and RLR-Independent Antiviral Response in Transformed Cells

The oncolytic rodent protoparvoviruses (PVs) minute virus of mice (MVMp) and H-1 parvovirus (H-1PV) are promising cancer viro-immunotherapy candidates capable of both exhibiting direct oncolytic activities and inducing anticancer immune responses (AIRs). Type-I interferon (IFN) production is instrumental for the activation of an efficient AIR. The present study aims at characterizing the molecular mechanisms underlying PV modulation of IFN induction in host cells. MVMp and H-1PV triggered IFN production in semi-permissive normal mouse embryonic fibroblasts (MEFs) and human peripheral blood mononuclear cells (PBMCs), but not in permissive transformed/tumor cells. IFN production triggered by MVMp in primary MEFs required PV replication and was independent of the pattern recognition receptors (PRRs) Toll-like (TLR) and RIG-like (RLR) receptors. PV infection of (semi-)permissive cells, whether transformed or not, led to nuclear translocation of the transcription factors NFĸB and IRF3, hallmarks of PRR signaling activation. Further evidence showed that PV replication in (semi-)permissive cells resulted in nuclear accumulation of dsRNAs capable of activating mitochondrial antiviral signaling (MAVS)-dependent cytosolic RLR signaling upon transfection into naïve cells. This PRR signaling was aborted in PV-infected neoplastic cells, in which no IFN production was detected. Furthermore, MEF immortalization was sufficient to strongly reduce PV-induced IFN production. Pre-infection of transformed/tumor but not of normal cells with MVMp or H-1PV prevented IFN production by classical RLR ligands. Altogether, our data indicate that natural rodent PVs regulate the antiviral innate immune machinery in infected host cells through a complex mechanism. In particular, while rodent PV replication in (semi-)permissive cells engages a TLR-/RLR-independent PRR pathway, in transformed/tumor cells this process is arrested prior to IFN production. This virus-triggered evasion mechanism involves a viral factor(s), which exert(s) an inhibitory action on IFN production, particularly in transformed/tumor cells. These findings pave the way for the development of second-generation PVs that are defective in this evasion mechanism and therefore endowed with increased immunostimulatory potential through their ability to induce IFN production in infected tumor cells.

Design and Characterization of Mutated Variants of the Oncotoxic Parvoviral Protein NS1

Oncotoxic proteins such as the non-structural protein 1 (NS1), a constituent of the rodent parvovirus H1 (H1-PV), offer a novel approach for treatment of tumors that are refractory to other treatments. In the present study, mutated NS1 variants were designed and tested with respect to their oncotoxic potential in human hepatocellular carcinoma cell lines. We introduced single point mutations of previously described important residues of the wild-type NS1 protein and a deletion of 114 base pairs localized within the N-terminal domain of NS1. Cell-viability screening with HepG2 and Hep3B hepatocarcinoma cells transfected with the constructed NS1-mutants led to identification of the single-amino acid NS1-mutant NS1-T585E, which led to a 30% decrease in cell viability as compared to NS1 wildtype. Using proteomics analysis, we could identify new interaction partners and signaling pathways of NS1. We could thus identify new oncotoxic NS1 variants and gain insight into the modes of action of NS1, which is exclusively toxic to human cancer cells. Our in-vitro studies provide mechanistic explanations for the observed oncolytic effects. Expression of NS1 variants had no effect on cell viability in NS1 unresponsive control HepG2 cells or primary mouse hepatocytes. The availability of new NS1 variants in combination with a better understanding of their modes of action offers new possibilities for the design of innovative cancer treatment strategies.

Immunovirotherapy for Pediatric Solid Tumors: A Promising Treatment That is Becoming a Reality

Immunotherapy has seen tremendous strides in the last decade, acquiring a prominent position at the forefront of cancer treatment since it has been proven to be efficacious for a wide variety of tumors. Nevertheless, while immunotherapy has changed the paradigm of adult tumor treatment, this progress has not yet been translated to the pediatric solid tumor population. For this reason, alternative curative therapies are urgently needed for the most aggressive pediatric tumors. In recent years, oncolytic virotherapy has consolidated as a feasible strategy for cancer treatment, not only for its tumor-specific effects and safety profile but also for its capacity to trigger an antitumor immune response. This review will summarize the current status of immunovirotherapy to treat cancer, focusing on pediatric solid malignancies. We will revisit previous basic, translational, and clinical research and discuss advances in overcoming the existing barriers and limitations to translate this promising therapeutic as an every-day cancer treatment for the pediatric and young adult populations.

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.

Phase 2 Trial of Oncolytic H-1 Parvovirus Therapy Shows Safety and Signs of Immune System Activation in Patients With Metastatic Pancreatic Ductal Adenocarcinoma

PURPOSE

To investigate the safety, clinical efficacy, virus pharmacokinetics, shedding, and immune response after administration of an oncolytic parvovirus (H-1PV, ParvOryx) to patients with metastatic pancreatic ductal adenocarcinoma (PDAC) refractory to first-line therapy.

PATIENTS AND METHODS

This is a noncontrolled, single-arm, open-label, dose-escalating, single-center clinical trial. Seven patients with PDAC and at least one liver metastasis were included. ParvOryx was administered intravenously on 4 consecutive days and as an intralesional injection, 6 to 13 days thereafter. Altogether, three escalating dose levels were investigated. In addition, gemcitabine treatment was initiated on day 28.

RESULTS

ParvOryx showed excellent tolerability with no dose-limiting toxicities. One patient had a confirmed partial response and one patient revealed an unconfirmed partial response according to RECIST criteria. Both patients showed remarkably long surivial of 326 and 555 days, respectively. Investigation of pharmacokinetics and virus shedding revealed dose dependency with no excretion of active virus particles in saliva or urine and very limited excretion in feces. H-1PV nucleic acids were detected in tumor samples of four patients. All patients showed T-cell responses to viral proteins. An interesting immunologic pattern developed in tumor tissues and in blood of both patients with partial response suggesting immune activation after administration of ParvOryx.

CONCLUSIONS

The trial met all primary objectives, revealed no environmental risks, and indicated favorable immune modulation after administration of ParvOryx. It can be considered a good basis for further systematic clinical development alone or in combination with immunomodulatory compounds.

Combinatorial Approaches for Cancer Treatment Using Oncolytic Viruses: Projecting the Perspectives through Clinical Trials Outcomes

Recent cancer immunotherapy breakthroughs have fundamentally changed oncology and revived the fading hope for a cancer cure. The immune checkpoint inhibitors (ICI) became an indispensable tool for the treatment of many malignant tumors. Alongside ICI, the application of oncolytic viruses in clinical trials is demonstrating encouraging outcomes. Dozens of combinations of oncolytic viruses with conventional radiotherapy and chemotherapy are widely used or studied, but it seems quite complicated to highlight the most effective combinations. Our review summarizes the results of clinical trials evaluating oncolytic viruses with or without genetic alterations in combination with immune checkpoint blockade, cytokines, antigens and other oncolytic viruses as well. This review is focused on the efficacy and safety of virotherapy and the most promising combinations based on the published clinical data, rather than presenting all oncolytic virus variations, which are discussed in comprehensive literature reviews. We briefly revise the research landscape of oncolytic viruses and discuss future perspectives in virus immunotherapy, in order to provide an insight for novel strategies of cancer treatment.

Canine Parvovirus and Its Non-Structural Gene 1 as Oncolytic Agents: Mechanism of Action and Induction of Anti-Tumor Immune Response

The exploration into the strategies for the prevention and treatment of cancer is far from complete. Apart from humans, cancer has gained considerable importance in animals because of increased awareness towards animal health and welfare. Current cancer treatment regimens are less specific towards tumor cells and end up harming normal healthy cells. Thus, a highly specific therapeutic strategy with minimal side effects is the need of the hour. Oncolytic viral gene therapy is one such specific approach to target cancer cells without affecting the normal cells of the body. Canine parvovirus (CPV) is an oncolytic virus that specifically targets and kills cancer cells by causing DNA damage, caspase activation, and mitochondrial damage. Non-structural gene 1 (NS1) of CPV, involved in viral DNA replication is a key mediator of cytotoxicity of CPV and can selectively cause tumor cell lysis. In this review, we discuss the oncolytic properties of Canine Parvovirus (CPV or CPV2), the structure of the NS1 protein, the mechanism of oncolytic action as well as role in inducing an antitumor immune response in different tumor models.

Oncolytic viruses as a promising therapeutic strategy for hematological malignancies

The incidence of hematological malignancies such as multiple myeloma, leukemia, and lymphoma has increased over time. Although bone marrow transplantation, immunotherapy and chemotherapy have led to significant improvements in efficacy, poor prognosis in elderly patients, recurrence and high mortality among hematological malignancies remain major challenges, and innovative therapeutic strategies should be explored. Besides directly lyse tumor cells, oncolytic viruses can activate immune responses or be engineered to express therapeutic factors to increase antitumor efficacy, and have gradually been recognized as an appealing approach for fighting cancers. An increasing number of studies have applied oncolytic viruses in hematological malignancies and made progress. In particular, strategies combining immunotherapy and oncolytic virotherapy are emerging. Various phase I clinical trials of oncolytic reovirus with lenalidomide or programmed death 1(PD-1) immune checkpoint inhibitors in multiple myeloma are ongoing. Moreover, preclinical studies of combinations with chimeric antigen receptor T (CAR-T) cells are underway. Thus, oncolytic virotherapy is expected to be a promising approach to cure hematological malignancies. This review summarizes progress in oncolytic virus research in hematological malignancies. After briefly reviewing the development and oncolytic mechanism of oncolytic viruses, we focus on delivery methods of oncolytic viruses, especially systemic delivery that is suitable for hematological tumors. We then discuss the main types of oncolytic viruses applied for hematological malignancies and related clinical trials. In addition, we present several ways to improve the antitumor efficacy of oncolytic viruses. Finally, we discuss current challenges and provide suggestions for future studies.

Parvoviruses-tools to fine-tune anticancer immune responses

Oncolytic virotherapy represents a recent approach to anticancer therapy. Rodent autonomous parvoviruses (PVs) represent naturally oncolytic viruses that are non-pathogenic for humans but possess and extended tropism, being capable of infecting transformed cells of both rodent and human origin. Recent work from our group demonstrate that PVs can act as direct lytic agents and adjuvants, stimulating antitumor immune responses against glioma and pancreatic ductal adenocarcinoma (PDAC).

Parvovirus-Based Combinatorial Immunotherapy: A Reinforced Therapeutic Strategy against Poor-Prognosis Solid Cancers

Resistance to anticancer treatments poses continuing challenges to oncology researchers and clinicians. The underlying mechanisms are complex and multifactorial. However, the immunologically "cold" tumor microenvironment (TME) has recently emerged as one of the critical players in cancer progression and therapeutic resistance. Therefore, TME modulation through induction of an immunological switch towards inflammation ("warming up") is among the leading approaches in modern oncology. Oncolytic viruses (OVs) are seen today not merely as tumor cell-killing (oncolytic) agents, but also as cancer therapeutics with multimodal antitumor action. Due to their intrinsic or engineered capacity for overcoming immune escape mechanisms, warming up the TME and promoting antitumor immune responses, OVs hold the potential for creating a proinflammatory background, which may in turn facilitate the action of other (immunomodulating) drugs. The latter provides the basis for the development of OV-based immunostimulatory anticancer combinations. This review deals with the smallest among all OVs, the H-1 parvovirus (H-1PV), and focuses on H-1PV-based combinatorial approaches, whose efficiency has been proven in preclinical and/or clinical settings. Special focus is given to cancer types with the most devastating impact on life expectancy that urgently call for novel therapies.

Cutavirus DNA in Malignant and Nonmalignant Skin of Cutaneous T-Cell Lymphoma and Organ Transplant Patients but Not of Healthy Adults

BACKGROUND

Three new parvoviruses of Protoparvovirus genus, bufavirus (BuV), tusavirus (TuV), and cutavirus (CuV), have recently been discovered in diarrheal stools. CuV was further detected in a proportion of cutaneous T-cell lymphoma (CTCL)/mycosis fungoides skin samples and in one melanoma.

PATIENTS AND METHODS

With novel multiplex quantitative polymerase chain reaction and antibody assays, we studied 3 patient groups for BuV, TuV, and CuV DNA and immunoglobulin G (IgG): CTCL patients, immunosuppressed solid-organ transplant recipients, and immunocompetent healthy adults.

RESULTS

CuV DNA was detected in skin biopsies of 4/25 (16.0%) CTCL and 4/136 (2.9%) transplant patients but not in any of 159 skin samples of 98 healthy adults. The dermal CuV-DNA prevalence was significantly higher in CTCL patients than in the other subjects. CuV DNA was further detected in healthy skin of 4 organ transplant recipients, 2 of whom also had CuV-positive skin carcinomas. One CTCL patient harbored CuV DNA in both malignant (CTCL, melanoma) and nonmalignant skin and sentinel lymph nodes but not in his prostate. The CuV IgG seroprevalences were among CTCL patients 9.5% (4/42), transplant recipients 6.5% (8/124), and healthy adults 3.8% (3/78). BuV and TuV DNAs were absent and antibodies infrequent in all cohorts. Parvoviral antibodies were shown to persist for ≥20 years and dermal CuV DNA for 4 years. All 3 CuV-DNA-positive patients, with both biopsies and sera available, were CuV-IgG positive.

CONCLUSION

Our results suggest that dermal CuV DNA carriage is associated with CTCL. Any putative roles of CuV in the carcinogenesis must be determined in forthcoming studies.

Oncolytic Virotherapy for Malignant Tumor: Current Clinical Status

Oncolytic viruses, as novel biological anti-tumor agents, provide anti-tumor therapeutic effects by different mechanisms including directly selective tumor cell lysis and secondary systemic anti-tumor immune responses. Some wide-type and genetically engineered oncolytic viruses have been applied in clinical trials. Among them, T-Vec has a significant therapeutic effect on melanoma patients and received the approval of the US Food and Drug Administration (FDA) as the first oncolytic virus to treat cancer in the US. However, the mechanisms of virus interaction with tumor and immune systems have not been clearly elucidated and there are still no "gold standards" for instructions of virotherapy in clinical trials. This Review collected the recent clinical trials data from 2005 to summarize the basic oncolytic viruses biology, describe the application in recent clinical trials, and discuss the challenges in the application of oncolytic viruses in clinical trials.

Cancer Treatment Goes Viral: Using Viral Proteins to Induce Tumour-Specific Cell Death

Cell death is a tightly regulated process which can be exploited in cancer treatment to drive the killing of the tumour. Several conventional cancer therapies including chemotherapeutic agents target pathways involved in cell death, yet they often fail due to the lack of selectivity they have for tumour cells over healthy cells. Over the past decade, research has demonstrated the existence of numerous proteins which have an intrinsic tumour-specific toxicity, several of which originate from viruses. These tumour-selective viral proteins, although from distinct backgrounds, have several similar and interesting properties. Though the mechanism(s) of action of these proteins are not fully understood, it is possible that they can manipulate several cell death modes in cancer exemplifying the intricate interplay between these pathways. This review will discuss our current knowledge on the topic and outstanding questions, as well as deliberate the potential for viral proteins to progress into the clinic as successful cancer therapeutics.

Antiangiogenic Vascular Endothelial Growth Factor-Blocking Peptides Displayed on the Capsid of an Infectious Oncolytic Parvovirus: Assembly and Immune Interactions

As many tumor cells synthetize vascular endothelial growth factors (VEGF) that promote neo-vascularization and metastasis, frontline cancer therapies often administer anti-VEGF (α-VEGF) antibodies. To target the oncolytic parvovirus minute virus of mice (MVM) to the tumor vasculature, we studied the functional tolerance, evasion of neutralization, and induction of α-VEGF antibodies of chimeric viruses in which the footprint of a neutralizing monoclonal antibody within the 3-fold capsid spike was replaced by VEGF-blocking peptides: P6L (PQPRPL) and A7R (ATWLPPR). Both peptides allowed viral genome replication and nuclear translocation of chimeric capsid subunits. MVM-P6L efficiently propagated in culture, exposing the heterologous peptide on the capsid surface, and evaded neutralization by the anti-spike monoclonal antibody. In contrast, MVM-A7R yielded low infectious titers and was poorly recognized by an α-A7R monoclonal antibody. MVM-A7R showed a deficient assembly pattern, suggesting that A7R impaired a transitional configuration that the subunits must undergo in the 3-fold axis to close up the capsid shell. The MVM-A7R chimeric virus consistently evolved in culture into a mutant carrying the P6Q amino acid substitution within the A7R sequence, which restored normal capsid assembly and infectivity. Consistent with this finding, anti-native VEGF antibodies were induced in mice by a single injection of MVM-A7R empty capsids, but not by MVM-A7R virions. This fundamental study provides insights to endow an infectious parvovirus with immune antineovascularization and evasion capacities by replacing an antibody footprint in the capsid 3-fold axis with VEGF-blocking peptides, and it also illustrates the evolutionary capacity of single-stranded DNA (ssDNA) viruses to overcome engineered capsid structural restrictions.IMPORTANCE Targeting the VEGF signaling required for neovascularization by vaccination with chimeric capsids of oncolytic viruses may boost therapy for solid tumors. VEGF-blocking peptides (VEbp) engineered in the capsid 3-fold axis endowed the infectious parvovirus MVM with the ability to induce α-VEGF antibodies without adjuvant and to evade neutralization by MVM-specific antibodies. However, these properties may be compromised by structural restraints that the capsid imposes on the peptide configuration and by misassembly caused by the heterologous peptides. Significantly, chimeric MVM-VEbp resolved the structural restrictions by selecting mutations within the engineered peptides that restored efficient capsid assembly. These data show the promise of antineovascularization vaccines using chimeric VEbp-icosahedral capsids of oncolytic viruses but also raise safety concerns regarding the genetic stability of manipulated infectious parvoviruses in cancer and gene therapies.

Immune Conversion of Tumor Microenvironment by Oncolytic Viruses: The Protoparvovirus H-1PV Case Study

Cancer cells utilize multiple mechanisms to evade and suppress anticancer immune responses creating a “cold” immunosuppressive tumor microenvironment. Oncolytic virotherapy is emerging as a promising approach to revert tumor immunosuppression and enhance the efficacy of other forms of immunotherapy. Growing evidence indicates that oncolytic viruses (OVs) act in a multimodal fashion, inducing immunogenic cell death and thereby eliciting robust anticancer immune responses. In this review, we summarize information about OV-mediated immune conversion of the tumor microenvironment. As a case study we focus on the rodent protoparvovirus H-1PV and its dual role as an oncolytic and immune modulatory agent. Potential strategies to improve H-1PV anticancer efficacy are also discussed.

Viral vector: potential therapeutic for glioblastoma multiforme

Glioblastoma multiforme is a highly malignant primary brain tumour found in adults and is highlighted as the most devastating among all the other grades of glioma. Well-established standard treatment methods, such as chemotherapy, radiation and surgery, have resulted in modest improvement in the survival of patients. Hence, the arduous search for novel treatments backed by advancements in molecular biology still persists. Glioblastoma has many distinctive characteristics, which makes it a potential candidate for gene therapy. Gene therapy involves the delivery of genetic material of therapeutic use into tumour cells, which produces a specific antitumour response. Moreover, viruses stimulate a vigorous cytotoxic effect, they are easily modifiable and the inherent property of horizontal transfer of genetic material makes them valuable tools for genetic engineering. In this review, we have enlisted the various viral vectors employed in gene therapy for glioblastoma.

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.

Immunotherapeutic Potential of Oncolytic H-1 Parvovirus: Hints of Glioblastoma Microenvironment Conversion towards Immunogenicity

Glioblastoma, one of the most aggressive primary brain tumors, is characterized by highly immunosuppressive microenvironment. This contributes to glioblastoma resistance to standard treatment modalities and allows tumor growth and recurrence. Several immune-targeted approaches have been recently developed and are currently under preclinical and clinical investigation. Oncolytic viruses, including the autonomous protoparvovirus H-1 (H-1PV), show great promise as novel immunotherapeutic tools. In a first phase I/IIa clinical trial (ParvOryx01), H-1PV was safe and well tolerated when locally or systemically administered to recurrent glioblastoma patients. The virus was able to cross the blood-brain (tumor) barrier after intravenous infusion. Importantly, H-1PV treatment of glioblastoma patients was associated with immunogenic changes in the tumor microenvironment. Tumor infiltration with activated cytotoxic T cells, induction of cathepsin B and inducible nitric oxide (NO) synthase (iNOS) expression in tumor-associated microglia/macrophages (TAM), and accumulation of activated TAM in cluster of differentiation (CD) 40 ligand (CD40L)-positive glioblastoma regions was detected. These are the first-in-human observations of H-1PV capacity to switch the immunosuppressed tumor microenvironment towards immunogenicity. Based on this pilot study, we present a tentative model of H-1PV-mediated modulation of glioblastoma microenvironment and propose a combinatorial therapeutic approach taking advantage of H-1PV-induced microglia/macrophage activation for further (pre)clinical testing.

Canine Parvovirus ns1 gene and Chicken Anemia vp3 gene induce partial oncolysis of Canine Transmissible Venereal Tumor

The oncolytic effect of Canine Parvovirus ns1 gene and Chicken Anemia vp3 gene in naturally occurring cases of Canine Transmissible Venereal Tumor (CTVT) is being reported. Dogs suffering from CTVT (N = 18) were systematically randomized into three groups viz. A, B, and C (n = 6). Animals of the groups A, B, and C received 100 µg of the ns1 gene, vp3 gene, and ns1  +  vp3 gene combination, respectively, for three weeks intratumorally at weekly intervals; results were normalized against base values before commencement of therapy and after complete remission that were taken as negative and positive controls, respectively. Initiation of oncolytic gene therapy arrested the further progression of the tumor but most of the animals in the study underwent incomplete remission, indicating incomplete activity of ns1 and vp3 genes. The oncolytic effect of the treatments was in the order ns1 > vp3 > ns1 + vp3. Oncolysis was accompanied by decreased mitotic index and AgNOR count, and increased TUNEL positive cells and CD4⁺ lymphocyte counts. Our findings show that Canine Parvovirus ns1 may eventually find an important role as an oncolytic agent.

Atomic Resolution Structure of the Oncolytic Parvovirus LuIII by Electron Microscopy and 3D Image Reconstruction

LuIII, a protoparvovirus pathogenic to rodents, replicates in human mitotic cells, making it applicable for use to kill cancer cells. This virus group includes H-1 parvovirus (H-1PV) and minute virus of mice (MVM). However, LuIII displays enhanced oncolysis compared to H-1PV and MVM, a phenotype mapped to the major capsid viral protein 2 (VP2). This suggests that within LuIII VP2 are determinants for improved tumor lysis. To investigate this, the structure of the LuIII virus-like-particle was determined using single particle cryo-electron microscopy and image reconstruction to 3.17 Å resolution, and compared to the H-1PV and MVM structures. The LuIII VP2 structure, ordered from residue 37 to 587 (C-terminal), had the conserved VP topology and capsid morphology previously reported for other protoparvoviruses. This includes a core β-barrel and α-helix A, a depression at the icosahedral 2-fold and surrounding the 5-fold axes, and a single protrusion at the 3-fold axes. Comparative analysis identified surface loop differences among LuIII, H-1PV, and MVM at or close to the capsid 2- and 5-fold symmetry axes, and the shoulder of the 3-fold protrusions. The 2-fold differences cluster near the previously identified MVM sialic acid receptor binding pocket, and revealed potential determinants of protoparvovirus tumor tropism.

Oncolytic H-1 Parvovirus Shows Safety and Signs of Immunogenic Activity in a First Phase I/IIa Glioblastoma Trial

Oncolytic virotherapy may be a means of improving the dismal prognosis of malignant brain tumors. The rat H-1 parvovirus (H-1PV) suppresses tumors in preclinical glioma models, through both direct oncolysis and stimulation of anticancer immune responses. This was the basis of ParvOryx01, the first phase I/IIa clinical trial of an oncolytic parvovirus in recurrent glioblastoma patients. H-1PV (escalating dose) was administered via intratumoral or intravenous injection. Tumors were resected 9 days after treatment, and virus was re-administered around the resection cavity. Primary endpoints were safety and tolerability, virus distribution, and maximum tolerated dose (MTD). Progression-free and overall survival and levels of viral and immunological markers in the tumor and peripheral blood were also investigated. H-1PV treatment was safe and well tolerated, and no MTD was reached. The virus could cross the blood-brain/tumor barrier and spread widely through the tumor. It showed favorable pharmacokinetics, induced antibody formation in a dose-dependent manner, and triggered specific T cell responses. Markers of virus replication, microglia/macrophage activation, and cytotoxic T cell infiltration were detected in infected tumors, suggesting that H-1PV may trigger an immunogenic stimulus. Median survival was extended in comparison with recent meta-analyses. Altogether, ParvOryx01 results provide an impetus for further H-1PV clinical development.

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.

Oncolytic Virotherapy for the Treatment of Malignant Glioma

Malignant glioma is the most common primary brain tumor and carries a grim prognosis, with a median survival of just over 14 months. Given the poor outcomes with standard-of-care treatments, novel treatment strategies are needed. The concept of virotherapy for the treatment of malignant tumors dates back more than a century and can be divided into replication-competent oncolytic viruses and replication-deficient viral vectors. Oncolytic viruses are designed to selectively target, infect, and replicate in tumor cells, while sparing surrounding normal brain. A host of oncolytic viruses has been evaluated in early phase human trials with promising safety results, but none has progressed to phase III trials. Despite the 25 years that has passed since the initial publication of genetically engineered oncolytic viruses for the treatment of glioma, much remains to be learned about the use of this therapy, including its mechanism of action, optimal treatment paradigm, appropriate targets, and integration with adjuvant agents. Oncolytic viral therapy for glioma remains promising and will undoubtedly impact the future of patient care.

A novel scalable, robust downstream process for oncolytic rat parvovirus: isoelectric point-based elimination of empty particles

The rodent protoparvovirus H-1PV, with its oncolytic and oncosuppressive properties, is a promising anticancer agent currently under testing in clinical trials. This explains the current demand for a scalable, good manufacturing practice-compatible virus purification process yielding high-grade pure infectious particles and overcoming the limitations of the current system based on density gradient centrifugation. We describe here a scalable process offering high purity and recovery. Taking advantage of the isoelectric point difference between full and empty particles, it eliminates most empty particles. Full particles have a significantly higher cationic charge than empty ones, with an isoelectric point of 5.8–6.2 versus 6.3 (as determined by isoelectric focusing and chromatofocusing). Thanks to this difference, infectious full particles can be separated from empty particles and most protein impurities by Convective interaction media^® diethylaminoethyl (DEAE) anion exchange chromatography: applying unpurified H-1PV to the column in 0.15 M NaCl leaves, the former on the column and the latter in the flow through. The full particles are then recovered by elution with 0.25 M NaCl. The whole large-scale purification process involves filtration, single-step DEAE anion exchange chromatography, buffer exchange by cross-flow filtration, and final formulation in Visipaque/Ringer solution. It results in 98% contaminating protein removal and 96% empty particle elimination. The final infectious particle concentration reaches 3.5E10 plaque forming units (PFU)/ml, with a specific activity of 6.8E11 PFU/mg protein. Overall recovery is over 40%. The newly established method is suitable for use in commercial production.

Recombinant Parvoviruses Armed to Deliver CXCL4L1 and CXCL10 Are Impaired in Their Antiangiogenic and Antitumoral Effects in a Kaposi Sarcoma Tumor Model Due To the Chemokines' Interference with the Virus Cycle

Application of oncolytic viruses is a valuable option to broaden the armament of anticancer therapies, as these combine specific cytotoxic effects and immune-stimulating properties. The self-replicating H-1 parvovirus (H-1PV) is a prototypical oncolytic virus that, besides targeting tumor cells, also infects endothelial cells, thus combining oncolytic and angiostatic traits. To increase its therapeutic value, H-1PV can be armed with cytokines or chemokines to enhance the immunological response. Some chemokines-more specifically, the CXCR3 ligands CXCL4L1 and CXCL10-combine immune-stimulating properties with angiostatic activity. This study explores the therapeutic value of recombinant parvoviruses carrying CXCL4L1 or CXCL10 transgenes (Chi-H1/CXCL4L1 or Chi-H1/CXCL10, respectively) to inhibit the growth of the human Kaposi sarcoma cell line KS-IMM. KS-IMM cells infected by Chi-H1/CXCL4L1 or Chi-H1/CXCL10 released the corresponding chemokine and showed reduced migratory capacity. Therefore, the antitumoral capacity of Chi-H1/CXCL4L1 or Chi-H1/CXCL10 was tested in mice. Either in vitro infected KS-IMM cells were injected or subcutaneously growing KS-IMM xenografts were treated by peritumoral injections of the different viruses. Surprisingly, the transgenes did not increase the antitumoral effect of natural H-1PV. Further experiments indicated that CXCL4L1 and CXCL10 interfered with the expression of the viral NS1 protein in KS-IMM cells. These results indicate that the outcome of parvovirus-based delivery of CXCR3 ligands might be tumor cell type dependent, and hence its application must be considered carefully.

A new protoparvovirus in human fecal samples and cutaneous T cell lymphomas (mycosis fungoides)

We genetically characterized seven nearly complete genomes in the protoparvovirus genus from the feces of children with diarrhea. The viruses, provisionally named cutaviruses (CutaV), varied by 1-6% nucleotides and shared ~76% and ~82% amino acid identity with the NS1 and VP1 of human bufaviruses, their closest relatives. Using PCR, cutavirus DNA was found in 1.6% (4/245) and 1% (1/100) of diarrhea samples from Brazil and Botswana respectively. In silico analysis of pre-existing metagenomics datasets then revealed closely related parvovirus genomes in skin biopsies from patients with epidermotropic cutaneous T-cell lymphoma (CTCL or mycosis fungoides). PCR of skin biopsies yielded cutavirus DNA in 4/17 CTCL, 0/10 skin carcinoma, and 0/21 normal or noncancerous skin biopsies. In situ hybridization of CTCL skin biopsies detected viral genome within rare individual cells in regions of neoplastic infiltrations. The influence of cutavirus infection on human enteric functions and possible oncolytic role in CTCL progression remain to be determined.

Replication-Competent Viruses as Cancer Immunotherapeutics: Emerging Clinical Data

Replication-competent (oncolytic) viruses (OV) as cancer immunotherapeutics have gained an increasing level of attention over the last few years while the clinical evidence of virus-mediated antitumor immune responses is still anecdotal. Multiple clinical studies are currently ongoing and more immunomonitoring results are expected within the next five years. All viruses can be recognized by the immune system and are therefore potential candidates for immune therapeutics. However, each virus activates innate immune system by using different combination of recognition receptors/pathways which leads to qualitatively different adaptive immune responses. This review summarizes immunological findings in cancer patients following treatment with replication-competent viruses.

Oncolytic viruses for therapy of malignant glioma

Effective treatment of malignant brain tumors is still an open problem. Location of tumor in vital areas of the brain significantly limits capasities of surgical treatment. The presence of tumor stem cells resistant to radiation and anticancer drugs in brain tumor complicates use of chemoradiotherapy and causes a high rate of disease recurrence. A technological improvement in bioselection and production of recombinant resulted in creation of viruses with potent oncolytic properties against glial tumors. Recent studies, including clinical trials, showed, that majority of oncolytic viruses are safe. Despite the impressive results of the viral therapy in some patients, the treatment of other patients is not effective; therefore, further improvement of the methods of oncolytic virotherapy is necessary. High genetic heterogeneity of glial tumor cells even within a single tumor determines differences in individual sensitivity of tumor cells to oncolytic viruses. This review analyses the most successful oncolytic virus strains, including those which had reached clinical trials, and discusses the prospects for new approaches to virotherapy of gliomas.

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.

Canine parvovirus NS1 induced apoptosis involves mitochondria, accumulation of reactive oxygen species and activation of caspases

The non-structural protein (NS1) of parvoviruses plays an important role in viral replication and is thought to be responsible for inducing cell death. However, the detailed mechanism and the pathways involved in canine parvovirus type 2 NS1 (CPV2.NS1) induced apoptosis are not yet known. In the present study, we report that expression of CPV2.NS1 in HeLa cells arrests cells in G1 phase of the cell cycle and the apoptosis is mitochondria mediated as indicated by mitochondrial depolarization, release of cytochrome-c and activation of caspase 9. Treatment of cells with caspase 9 inhibitor Z-LEHD-FMK reduced the induction of apoptosis significantly. We also report that expression of CPV2.NS1 causes accumulation of reactive oxygen species (ROS) and treatment with an antioxidant reduces the ROS levels and the extent of apoptosis. Our results provide an insight into the mechanism of CPV2.NS1 induced apoptosis, which might prove valuable in developing NS1 protein as an oncolytic agent.

Oncolysis by paramyxoviruses: multiple mechanisms contribute to therapeutic efficiency

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

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.

Viral genes as oncolytic agents for cancer therapy

Many viruses have the ability to modulate the apoptosis, and to accomplish it; viruses encode proteins which specifically interact with the cellular signaling pathways. While some viruses encode proteins, which inhibit the apoptosis or death of the infected cells, there are viruses whose encoded proteins can kill the infected cells by multiple mechanisms, including apoptosis. A particular class of these viruses has specific gene(s) in their genomes which, upon ectopic expression, can kill the tumor cells selectively without affecting the normal cells. These genes and their encoded products have demonstrated great potential to be developed as novel anticancer therapeutic agents which can specifically target and kill the cancer cells leaving the normal cells unharmed. In this review, we will discuss about the viral genes having specific cancer cell killing properties, what is known about their functioning, signaling pathways and their therapeutic applications as anticancer agents.

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.

EXPLORING THE ANTITUMOR EFFECT OF VIRUS IN MALIGNANT GLIOMA

Malignant gliomas are the most common type of primary malignant brain tumor with no effective treatments. Current conventional therapies (surgical resection, radiation therapy, temozolomide (TMZ), and bevacizumab administration) typically fail to eradicate the tumors resulting in the recurrence of treatment-resistant tumors. Therefore, novel approaches are needed to improve therapeutic outcomes. Oncolytic viruses (OVs) are excellent candidates as a more effective therapeutic strategy for aggressive cancers like malignant gliomas since OVs have a natural preference or have been genetically engineered to selectively replicate in and kill cancer cells. OVs have been used in numerous preclinical studies in malignant glioma, and a large number of clinical trials using OVs have been completed or are underway that have demonstrated safety, as well as provided indications of effective antiglioma activity. In this review, we will focus on those OVs that have been used in clinical trials for the treatment of malignant gliomas (herpes simplex virus, adenovirus, parvovirus, reovirus, poliovirus, Newcastle disease virus, measles virus, and retrovirus) and OVs examined preclinically (vesicular stomatitis virus and myxoma virus), and describe how these agents are being used.

Induction of an embryonic mouse innate immune response following inoculation in utero with minute virus of mice

We used an embryonic-infection model system to show that MVMp, the prototypic minute virus of mice (MVM) serotype and a member of the genus Protoparvovirus, triggers a comprehensive innate immune response in the developing mouse embryo. Direct inoculation of the midtrimester embryo in utero with MVMp results in a widespread, productive infection. During a 96-h infection course, embryonic beta interferon (IFN-β) and IFN-γ transcription were induced 90- and 60-fold, respectively. IFN-β levels correlated with the embryo viral burden, while IFN-γ levels first increased and then decreased. Production of proinflammatory cytokines, interleukin 1β (IL-1β) and tumor necrosis factor alpha (TNF-α), also increased, but by smaller amounts, approximately 7-fold each. We observed increased levels of downstream antiviral effector molecules, PKR and phosphorylated STAT2. Finally, we showed that there is an immune cell response to the virus infection. Infected tissues in the embryo exhibited an increased density of mature leukocytes compared to the same tissues in uninfected embryos. The responses we observed were almost completely restricted to the infected embryos. Uninfected littermates routinely exhibited small increases in innate immune components that rarely reached statistical significance compared to negative controls. Similarly, the placentae of infected embryos did not show any significant increase in transcription of innate immune cytokines. Since the placenta has both embryonic and maternal components, we suggest there is minimal involvement of the dam in the response to infection.

IMPORTANCE

Interaction between the small single-stranded vertebrate DNA viruses, the protoparvoviruses, and the host innate immune system has been unclear. The issue is important practically given the potential use of these viruses as oncotherapeutic agents. The data reported here stand in contrast to studies of innate immune response during protoparvovirus infection of adult hosts, which invariably reported no or minimal and sporadic induction of an interferon response during infection. We conclude that under conditions of robust and productive MVM infection, a normal murine host is able to mount a significant and broad innate immune response.

Cell migration is another player of the minute virus of mice infection

The parvovirus minute virus of mice, prototype strain (MVMp), preferentially infects and kills cancer cells. This intrinsic MVMp oncotropism may depend in part on the early stages of MVMp infection. To test this hypothesis, we investigated the early events of MVMp infection in mouse LA9 fibroblasts and a highly invasive mouse mammary tumor cell line derived from polyomavirus middle T antigen-mediated transformation. Using a combination of fluorescence and electron microscopy, we found that various parameters of the cell migration process affect MVMp infection. We show that, after binding to the plasma membrane, MVMp particles rapidly cluster at the leading edge of migrating cells, which exhibit higher levels of MVMp uptake than non-motile cells. Moreover, promoting cell migration on a fibronectin matrix increased MVMp infection, and induction of epithelial-mesenchymal transition allowed MVMp replication in non-permissive epithelial cells. Hence, we propose that cell migration influences the early stages of MVMp infection.

Parvovirus glycan interactions

Members of the Parvoviridae utilize glycan receptors for cellular attachment and subsequent interactions determine transduction efficiency or pathogenic outcome. This review focuses on the identity of the glycan receptors utilized, their capsid binding footprints, and a discussion of the overlap of these sites with tropism, transduction, and pathogenicity determinants. Despite high sequence diversity between the different genera, most parvoviruses bind to negatively charged glycans, such as sialic acid and heparan sulfate, abundant on cell surface membranes. The capsid structure of these viruses exhibit high structural homology enabling common regions to be utilized for glycan binding. At the same time the sequence diversity at the common footprints allows for binding of different glycans or differential binding of the same glycan.

Chemotherapy and Oncolytic Virotherapy: Advanced Tactics in the War against Cancer

Cancer is a traitorous archenemy that threatens our survival. Its ability to evade detection and adapt to various cancer therapies means that it is a moving target that becomes increasingly difficult to attack. Through technological advancements, we have developed sophisticated weapons to fight off tumor growth and invasion. However, if we are to stand a chance in this war against cancer, advanced tactics will be required to maximize the use of our available resources. Oncolytic viruses (OVs) are multi-functional cancer-fighters that can be engineered to suit many different strategies; in particular, their retooling can facilitate increased capacity for direct tumor killing (oncolytic virotherapy) and elicit adaptive antitumor immune responses (oncolytic immunotherapy). However, administration of these modified OVs alone, rarely induces successful regression of established tumors. This may be attributed to host antiviral immunity that acts to eliminate viral particles, as well as the capacity for tumors to adapt to therapeutic selective pressure. It has been shown that various chemotherapeutic drugs with distinct functional properties can potentiate the antitumor efficacy of OVs. In this review, we summarize the chemotherapeutic combinatorial strategies used to optimize virally induced destruction of tumors. With a particular focus on pharmaceutical immunomodulators, we discuss how specific therapeutic contexts may alter the effects of these synergistic combinations and their implications for future clinical use.

Oncolytic virotherapy as emerging immunotherapeutic modality: potential of parvovirus h-1

Human tumors develop multiple strategies to evade recognition and efficient suppression by the immune system. Therefore, a variety of immunotherapeutic strategies have been developed to reactivate and reorganize the human immune system. The recent development of new antibodies against immune check points may help to overcome the immune silencing induced by human tumors. Some of these antibodies have already been approved for treatment of various solid tumor entities. Interestingly, targeting antibodies may be combined with standard chemotherapy or radiation protocols. Furthermore, recent evidence indicates that intratumoral or intravenous injections of replicative oncolytic viruses such as herpes simplex-, pox-, parvo-, or adenoviruses may also reactivate the human immune system. By generating tumor cell lysates in situ, oncolytic viruses overcome cellular tumor resistance mechanisms and induce immunogenic tumor cell death resulting in the recognition of newly released tumor antigens. This is in particular the case of the oncolytic parvovirus H-1 (H-1PV), which is able to kill human tumor cells and stimulate an anti-tumor immune response through increased presentation of tumor-associated antigens, maturation of dendritic cells, and release of pro-inflammatory cytokines. Current research and clinical studies aim to assess the potential of oncolytic virotherapy and its combination with immunotherapeutic agents or conventional treatments to further induce effective antitumoral immune responses.

[New drugs in oncology]

BACKGROUND

Drug development in oncology has seen major innovations in recent years. Based on the molecular changes found in malignant tumors, new drugs are being developed which specifically target these altered signaling pathways.

RESULTS

In addition to the already broadly used inhibitors of growth factor and angiogenic signaling pathways, new and innovative target structures have been identified. Cancer stem cells which are thought to be the reason for drug resistance and tumor recurrence are now being targeted. c-MET signaling has emerged as an important new signaling module which can be influenced pharmacologically. Inhibitors of immune checkpoints like antibodies which target the CTLA4 molecule are leading to impressive results in clinical trials. Drugs which influence the epigenetic changes found in tumor cells are tested specifically for their ability to overcome drug resistance. Finally, treatment with oncolytic viruses has made a comeback in certain tumor entities.

CONCLUSION

Oncological treatments will see a significant addition of new drugs and treatment options in the next few years which will hopefully improve the survival of patients with tumors.

Complementary induction of immunogenic cell death by oncolytic parvovirus H-1PV and gemcitabine in pancreatic cancer

Novel therapies employing oncolytic viruses have emerged as promising anticancer modalities. The cure of particularly aggressive malignancies requires induction of immunogenic cell death (ICD), coupling oncolysis with immune responses via calreticulin, ATP, and high-mobility group box protein B1 (HMGB1) release from dying tumor cells. The present study shows that in human pancreatic cancer cells (pancreatic ductal adenocarcinoma [PDAC] cells n=4), oncolytic parvovirus H-1 (H-1PV) activated multiple interconnected death pathways but failed to induce calreticulin exposure or ATP release. In contrast, H-1PV elevated extracellular HMGB1 levels by 4.0±0.5 times (58%±9% of total content; up to 100 ng/ml) in all infected cultures, whether nondying, necrotic, or apoptotic. An alternative secretory route allowed H-1PV to overcome the failure of gemcitabine to trigger HMGB1 release, without impeding cytotoxicity or other ICD activities of the standard PDAC medication. Such broad resistance of H-1PV-induced HMGB1 release to apoptotic blockage coincided with but was uncoupled from an autocrine interleukin-1β (IL-1β) loop. That and the pattern of viral determinants maintained in gemcitabine-treated cells suggested the activation of an inflammasome/caspase 1 (CASP1) platform alongside DNA detachment and/or nuclear exclusion of HMGB1 during early stages of the viral life cycle. We concluded that H-1PV infection of PDAC cells is signaled through secretion of the alarmin HMGB1 and, besides its own oncolytic effect, might convert drug-induced apoptosis into an ICD process. A transient arrest of cells in the cyclin A1-rich S phase would suffice to support compatibility of proliferation-dependent H-1PV with cytotoxic regimens. These properties warrant incorporation of the oncolytic virus H-1PV, which is not pathogenic in humans, into multimodal anticancer treatments.

IMPORTANCE

The current therapeutic concepts targeting aggressive malignancies require an induction of immunogenic cell death characterized by exposure of calreticulin (CRT) as well as release of ATP and HMGB1 from dying cells. In pancreatic tumor cells (PDAC cells) infected with the oncolytic parvovirus H-1PV, only HMGB1 was released by all infected cells, whether nondying, necrotic, or succumbing to one of the programmed death pathways, including contraproductive apoptosis. Our data suggest that active secretion of HMGB1 from PDAC cells is a sentinel reaction emerging during early stages of the viral life cycle, irrespective of cell death, that is compatible with and complements cytotoxic regimens. Consistent induction of HMGB1 secretion raised the possibility that this reaction might be a general "alarming" phenomenon characteristic of H-1PV's interaction with the host cell; release of IL-1β points to the possible involvement of a danger-sensing inflammasome platform. Both provide a basis for further virus-oriented studies.

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.

Oncolytic viral therapy for pancreatic cancer: current research and future directions

The development of targeted agents and chemotherapies for pancreatic cancer has only modestly affected clinical outcome and not changed 5-year survival. Fortunately the genetic and molecular mechanisms underlying pancreatic cancer are being rapidly uncovered and are providing opportunities for novel targeted therapies. Oncolytic viral therapy is one of the most promising targeted agents for pancreatic cancer. This review will look at the current state of the development of these self-replicating nanoparticles in the treatment of pancreatic cancer.

A systematic review of inhaled intranasal therapy for central nervous system neoplasms: an emerging therapeutic option

The intranasal route for drug delivery is rapidly evolving as a viable means for treating selected central nervous system (CNS) conditions. We aimed to identify studies pertaining to the application of intranasal drug administration for the treatment of primary CNS tumors. A systematic literature review was conducted to identify all studies published in the English language pertaining to intranasal therapy for CNS neoplasms, and/or general mechanisms and pharmacokinetics regarding targeted intranasal CNS drug delivery. A total of 194 abstracts were identified and screened. Thirty-seven studies met inclusion criteria. Of these, 21 focused on intranasal treatment of specific primary CNS tumors, including gliomas (11), meningiomas (1), and pituitary adenomas (4). An additional 16 studies focused on general mechanisms of intranasal therapy and drug delivery to the CNS using copolymer micelles, viral vectors, and nanoparticles. Inhaled compounds/substances investigated included perillyl alcohol, vesicular stomatitis virus, parvovirus, telomerase inhibitors, neural stem and progenitor cells, antimetabolites, somatostatin analogues, and dopamine agonists. Radiolabeling, CSF concentration measurement, imaging studies, and histological examination were utilized to clarify the mechanism and distribution by which drugs were delivered to the CNS. Successful drug delivery and tumor/symptom response was reported in all 21 tumor-specific studies. The intranasal route holds tremendous potential as a viable option for drug delivery for CNS neoplasms. A variety of antitumoral agents may be delivered via this route, thereby potentially offering a more direct delivery approach and ameliorating the adverse effects associated with systemic drug delivery.

[Modern molecular approaches to diagnosis and treatment of high-grade brain gliomas]

The review analyzes the current state of the problem of diagnosis and therapy of high-grade gliomas on the basis of the most promising present-day approaches. The diagnostic and treatment perspectives of the molecular genetic analysis of glioblastoma markers located on the tumor cell surface are considered. Gene therapy and the use of dendritic cells and oncolytic viruses are considered as the most interesting approaches to therapy of high-grade gliomas.