Dose-dependent regression of HeLa cell-derived tumours in SCID mice after parvovirus H-1 infection

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.

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.

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.

The MVMp P4 promoter is a host cell-type range determinant in vivo

The protoparvovirus early promoters, e.g. P4 of Minute Virus of Mice (MVM), play a critical role during infection. Initial P4 activity depends on the host transcription machinery only. Since this is cell-type dependent, it is hypothesized that P4 is a host cell-type range determinant. Yet host range determinants have mapped mostly to capsid, never P4. Here we test the hypothesis using the mouse embryo as a model system. Disruption of the CRE element of P4 drastically decreased infection levels without altering range. However, when we swapped promoter elements of MVM P4 with those from equivalent regions of the closely related H1 virus, we observed elimination of infection in fibroblasts and chondrocytes and the acquisition of infection in skeletal muscle. We conclude that P4 is a host range determinant and a target for modifying the productive infection potential of the virus - an important consideration in adapting these viruses for oncotherapy.

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.

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.

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.

Oncosuppressive suicide gene virotherapy "PVH1-yCD/5-FC" for pancreatic peritoneal carcinomatosis treatment: NFκB and Akt/PI3K involvement

Peritoneal carcinomatosis is common in advanced pancreatic cancer. Despite current standard treatment, patients with this disease until recently were considered incurable. Cancer gene therapy using oncolytic viruses have generated much interest over the past few years. Here, we investigated a new gene directed enzyme prodrug therapy (GDEPT) approach for an oncosuppressive virotherapy strategy using parvovirus H1 (PV-H1) which preferentially replicates and kills malignant cells. Although, PV-H1 is not potent enough to destroy tumors, it represents an attractive vector for cancer gene therapy. We therefore sought to determine whether the suicide gene/prodrug system, yCD/5-FC could be rationally combined to PV-H1 augmenting its intrinsic oncolytic activity for pancreatic cancer prevention and treatment. We showed that the engineered recombinant parvovirus rPVH1-yCD with 5-FC treatment increased significantly the intrinsic cytotoxic effect and resulted in potent induction of apoptosis and tumor growth inhibition in chemosensitive and chemoresistant cells. Additionally, the suicide gene-expressing PV-H1 infection reduced significantly the constitutive activities of NFκB and Akt/PI3K. Combination of their pharmacological inhibitors (MG132 and LY294002) with rPVH1-yCD/5-FC resulted in substantial increase of antitumor activity. In vivo, high and sustained expression of NS1 and yCD was observed in the disseminated tumor nodules and absent in normal tissues. Treatment of mice bearing intraperitoneal pancreatic carcinomatosis with rPVH1-yCD/5-FC resulted in a drastic inhibition of tumor cell spreading and subsequent increase in long-term survival. Together, the presented data show the improved oncolytic activity of wPV-H1 by yCD/5-FC and thus provides valuable effective and promising virotherapy strategy for prevention of tumor recurrence and treatment. In the light of this study, the suicide gene parvovirotherapy approach represents a new weapon in the war against pancreatic cancer. Moreover, these preliminary accomplishments are opening new field for future development of new combined targeted therapies to have a meaningful impact on advanced cancer.

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.

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.

The parvoviral capsid controls an intracellular phase of infection essential for efficient killing of stepwise-transformed human fibroblasts

Members of the rodent subgroup of the genus Parvovirus exhibit lytic replication and spread in many human tumor cells and are therefore attractive candidates for oncolytic virotherapy. However, the significant variation in tumor tropism observed for these viruses remains largely unexplained. We report here that LuIII kills BJ-ELR 'stepwise-transformed' human fibroblasts efficiently, while MVM does not. Using viral chimeras, we mapped this property to the LuIII capsid gene, VP2, which is necessary and sufficient to confer the killer phenotype on MVM. LuIII VP2 facilitates a post-entry, pre-DNA-amplification step early in the life cycle, suggesting the existence of an intracellular moiety whose efficient interaction with the incoming capsid shell is critical to infection. Thus targeting of human cancers of different tissue-type origins will require use of parvoviruses with capsids that effectively make this critical interaction.

SMAD4: a predictive marker of PDAC cell permissiveness for oncolytic infection with parvovirus H-1PV

Pancreatic ductal adenocarcinoma (PDAC) represents the eighth frequent solid tumor and fourth leading cause of cancer death. Because current treatments against PDAC are still unsatisfactory, new anticancer strategies are required, including oncolytic viruses. Among these, autonomous parvoviruses (PV), like MVMp (minute virus of mice) and H-1PV are being explored as candidates for cancer gene therapy. Human PDAC cell lines were identified to display various susceptibilities to an infection with H-1PV. The correlation between the integrity of the transcription factor SMAD4, mutated in 50% of all PDAC, and H-1PV permissiveness was particularly striking. Indeed, mutation or deletion of SMAD4 dramatically reduced the activity of the P4 promoter and, consequently, the accumulation of the pivotal NS1 protein. By means of DNA affinity immunoblotting, novel binding sites for SMAD4 and c-JUN transcription factors could be identified in the P4 promoter of H-1PV. The overexpression of wild-type SMAD4 in deficient cell lines (AsPC-1, Capan-1) stimulated the activity of the P4 promoter, whereas interference of endogenous SMAD4 function with a dominant-negative mutant decreased the viral promoter activity in wild-type SMAD4-expressing cells (Panc-1, MiaPaCa-2) reducing progeny virus production. In conclusion, the importance of members of the SMAD family for H-1PV early promoter P4 activity should guide us to select SMAD4-positive PDACs, which may be possible targets for an H-1PV-based cancer therapy.

Through its nonstructural protein NS1, parvovirus H-1 induces apoptosis via accumulation of reactive oxygen species

The rat parvovirus H-1 (H-1PV) attracts high attention as an anticancer agent, because it is not pathogenic for humans and has oncotropic and oncosuppressive properties. The viral nonstructural NS1 protein is thought to mediate H-1PV cytotoxicity, but its exact contribution to this process remains undefined. In this study, we analyzed the effects of the H-1PV NS1 protein on human cell proliferation and cell viability. We show that NS1 expression is sufficient to induce the accumulation of cells in G(2) phase, apoptosis via caspase 9 and 3 activation, and cell lysis. Similarly, cells infected with wild-type H-1PV arrest in G(2) phase and undergo apoptosis. Furthermore, we also show that both expression of NS1 and H-1PV infection lead to higher levels of intracellular reactive oxygen species (ROS), associated with DNA double-strand breaks. Antioxidant treatment reduces ROS levels and strongly decreases NS1- and virus-induced DNA damage, cell cycle arrest, and apoptosis, indicating that NS1-induced ROS are important mediators of H-1PV cytotoxicity.

Parvovirus H-1 induces cytopathic effects in breast carcinoma-derived cultures

Parvovirus H-1 (H-1 PV) preferentially replicates in malignant cells resulting in their death by cytolysis. It has often been considered a potential candidate for use in novel anticancer therapy. To evaluate its potential in a model of natural tumors, we assayed in vitro the effect exerted by H-1 PV on short-term cultures derived from breast tumor samples freshly excised from patients. Our results show that H-1 PV effectively kills tumor-derived cells, whereas normal tissue-derived cells showed no H-1 PV-induced cytopathic effects (CPE). We also determined that the H-1 PV sensitivity (up to 67% sensitive cultures) is related with the quantities of virus assayed. We further examined the expression and phosphorylation state of the parvoviral nonstructural protein 1 (NS1), known to be associated with parvoviruses-induced CPE. Both appear to be impaired in normal tissue-derived cells and resistant cultures. Finally, we show that H-1 PV sensitivity in cultures correlates significantly with higher tumor grades (Nottingham combined histologic grade 2 or 3). This report confirms that H-1 PV can efficiently induce CPE in primary breast tumor cells in vitro. It identifies tumor characteristics representing potential criteria for recruiting patients for clinical evaluation of H-1 PV antitumor effects.

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

The incidence of lymphomas developing in both immunocompetent and immunosuppressed patients continues to steadily increase worldwide. Current chemotherapy and immunotherapy approaches have several limitations, such as severe side toxicity and selection of resistant cell variants. Autonomous parvoviruses (PVs), in particular the rat parvovirus H-1PV, have emerged as promising anticancer agents. Although it is apathogenic in humans, H-1PV has been shown to infect and suppress various rat and human tumors in animal models. In this study, we demonstrate the capacity of H-1PV for efficiently killing, through necrosis, cell cultures originating from Burkitt's lymphoma (BL), while sparing normal B lymphocytes. The cytotoxic effect was generally accompanied by a productive H-1PV infection. Remarkably, parvovirus-based monotherapy efficiently suppressed established BL at an advanced stage in a severe combined immunodeficient (SCID) mouse model of the disease. The data show for the first time that an oncolytic parvovirus deserves further consideration as a potential tool for the treatment of some non-Hodgkin B-cell lymphomas, including those resistant to apoptosis induction by rituximab.

Effects of red light emitting diode on apoptosis of HeLa cells and suppression of implanted HeLa cells growth in mice

Low intensity irradiation of cells by laser was an effective method of biostimulation. Here, we have extended these actions to evaluate the apoptosis effects in red light emitting diode (RLED) exposure. Through morphological observation, flow cytometric analysis, intracellular calcium measurement and RT-PCR, we found that HeLa cells in 24 h RLED irradiation in in-vitro experiments would significantly affects the induction of cellular apoptosis, and morphological changes such as the loose arrangement of cells, the noticeable development of apoptotic bodies,and the accompaniment of arrested S phase and activated caspases-3,-6,-8. Moreover, intracellular calcium concentrations markedly increased 40.3 +/- 1.3% and 43.1 +/- 0.8% respectively, relative to an extracellular solution containing the Ca(2+) and Ca(2+) free unexposed group. In in-vivo tests, RLED irradiation decreased the growth of tumors on day 50 and attenuated the elevation of vascular endothelial growth factor (VEGF) expression in HeLa cell implanted BALB/c mice. Taken together, our results suggest that RLED could induce HeLa cell apoptosis and convey potential antitumor properties.

Exploring the contribution of distal P4 promoter elements to the oncoselectivity of Minute Virus of Mice

Minute Virus of Mice (MVM) shares inherent oncotropic properties with other members of the genus Parvovirus. Two elements responsible, at least in part, for this oncoselectivity have been mapped to an Ets1 binding site adjacent to the P4 TATA box of the initiating promoter, P4, and to a more distal cyclic AMP responsive element (CRE), located within the telomeric hairpin stem. Here the CRE overlaps one half-site for the binding of parvoviral initiation factor (PIF), which is essential for viral DNA replication. We used a degenerate oligonucleotide selection approach to show that CRE binding protein (CREB) selects the sequence ACGTCAC within this context, rather than its more generally accepted palindromic TGACGTCA recognition site. We have developed strategies for manipulating these sequences directly within the left-end palindrome of the MVM infectious clone and used them to clone mutants whose CRE either matches the symmetric consensus sequence or is scrambled, or in which the PIF binding site is incrementally weakened with respect to the CRE. The panel of mutants were tested for fitness relative to wildtype in normal murine fibroblasts A9 or transformed human fibroblasts 324 K, through multiple rounds of growth in co-infected cultures, using a differential real-time quantitative PCR assay. We confirmed that inactivating the CRE substantially abrogates oncoselectivity, but found that improving its fit to the palindromic consensus is somewhat debilitating in either cell type. We also confirmed that reducing the PIF half-site spacing by one basepair enhances oncoselectivity, but found that a further basepair deletion significantly reduces this effect.

Environmental exposure to bacteria and viruses may provide oncolytic protection against cancers, and declining exposure to infections may contribute to a rising incidence of cancer

Over the past century, the incidence of cancer rose markedly in developed countries. Many underlying factors are known, but not all of them. Over the same century, advances in public health and hygiene practically eradicated many infectious illnesses, and exposure to some untargeted infectious agents has also declined. There are reasons to suspect that these two trends are linked. Although some viruses and one bacterium are known to be oncogenic, a high percentage of infectious agents, 71% of viruses tested in one study, have shown oncolytic properties. Some of these agents have minimal or no clinical consequences, and some are - or were - quite ubiquitous. Many types of cancer are unusually susceptible to several different agents, sometimes 10-1000 times more susceptible than normal cells. When wild-type or attenuated viruses are used to treat cancer, they are often more effective with smaller tumors, and it may be that nascent, undetectable cancers are especially vulnerable. Environmental exposure to bacteria and viruses may provide natural protection from cancer by attacking it at this stage, or inducing the body to do so. Immunity to an infectious agent can attenuate its oncolytic effect, but generally does not stop it, so both initial and repeated exposures may be protective. As more direct evidence, treatment of animals with selected live virus vaccines has provided protection from cancer, and in humans, exposure to two specific infectious agents is known to correlate with a reduced risk of cancer. The significant decline in exposure to infectious agents over the past century may have inadvertently weakened this naturally protective mechanism, driving cancer rates up. There is considerable research on the impact of oncogenic agents, but surprisingly little regarding the impact of oncolytic agents on cancer rates. An understanding of the relationship between natural infections and the suppression of cancer may lead to prophylactic measures against cancer, improved public health policies regarding vaccination programs and hygiene, and greater insight into cancer treatment as well.

Oncolytic potential of rodent parvoviruses for cancer therapy in humans: a brief review

Summary Rodent parvoviruses are promising candidates for oncolytic virotherapy of cancer in humans because of their oncotropism (preferential killing of transformed cells) in the absence of pathogenicity. Here, we give an overview concerning the possible application of parvovirus H-1 for cancer therapy, with specific emphasis on malignant brain tumours in humans.

Parvovirus H-1-induced tumor cell death enhances human immune response in vitro via increased phagocytosis, maturation, and cross-presentation by dendritic cells

Oncotropic and oncolytic viruses have attracted high attention as antitumor agents because they preferentially kill cancer cells in vitro and reduce the incidence of spontaneous, induced, or implanted animal tumors. Some autonomous parvoviruses (H-1, minute virus of mice) and derived recombinant vectors are currently under preclinical evaluation. Still not fully understood, their antitumor properties involve more than just tumor cell killing. Because wild-type parvovirus-mediated tumor cell lysates (TCLs) may trigger antigen-presenting cells (APCs) to augment the host immune repertoire, we analyzed phagocytosis, maturation, and crosspresentation of H-1-induced TCLs by human dendritic cells (DCs). We first established H-1-mediated oncolysis in two HLA-A2(+) and A2(-) variant melanoma cell clones. Monocyte-derived immature DCs phagocytosed H- 1-infected TCLs as well as ultraviolet-induced apoptotic TCLs and better than freeze-thaw-induced necrotic TCLs. Immature DCs incubated with H-1-induced TCLs acquired specific maturation markers comparable to a standard cytokine cocktail. Furthermore, A2(+) DCs pulsed with H-1-infected A2(-) TCLs cross-presented melanoma antigens to specific cytotoxic T lymphocytes (CTLs) and released proinflammatory cytokines. This shows for the first time that tumor cell killing by a wild-type oncolytic virus directly stimulates human APCs and CTLs. Because H-1-infected tumors enhance the immune repertoire, the clinical perspectives of parvoviral vectors are even more promising.

B1 lymphocytes and myeloid dendritic cells in lymphoid organs are preferential extratumoral sites of parvovirus minute virus of mice prototype strain expression

Due to their oncolytic properties and apathogenicity, autonomous parvoviruses have attracted significant interest as possible anticancer agents. Recent preclinical studies provided evidence of the therapeutic potential of minute virus of mice prototype strain (MVMp) and its recombinant derivatives. In a murine model of hemangiosarcoma, positive therapeutic outcome correlated with high intratumoral expression of MVMp-encoded genes in tumors and lymphoid organs, especially in tumor-draining lymph nodes. The source and relevance of this extratumoral expression, which came as a surprise because of the known fibrotropism of MVMp, remained unclear. In the present study, we investigated (i) whether the observed expression pattern occurs in different tumor models, (ii) which cell population is targeted by the virus, and (iii) the immunological consequences of this infection. Significant MVMp gene expression was detected in lymphoid tissues from infected tumor-free as well as melanoma-, lymphoma-, and hemangiosarcoma-bearing mice. This expression was especially marked in lymph nodes draining virus-injected tumors. Fluorescent in situ hybridization analysis, multicolor fluorescence-activated cell sorting, and quantitative reverse transcription-PCR revealed that MVMp was expressed in rare subpopulations of CD11b (Mac1)-positive cells displaying CD11c+ (myeloid dendritic cells [MDC]) or CD45B (B220+ [B1 lymphocytes]) markers. Apart from the late deletion of cytotoxic memory cells (CD8+ CD44+ CD62L-), this infection did not lead to significant alteration of the immunological profile of cells populating lymphoid organs. However, subtle changes were detected in the production of specific proinflammatory cytokines in lymph nodes from virus-treated animals. Considering the role of B1 lymphocytes and MDC in cancer and immunological surveillance, the specific ability of these cell types to sustain parvovirus-driven gene expression may be exploited in gene therapy protocols.

Parvovirus H-1 infection of human glioma cells leads to complete viral replication and efficient cell killing

The extremely poor prognosis of malignant gliomas requires the investigation of other than standard therapies, i.e., the application of oncolytic viruses. In our study, we evaluated the effects of the oncosuppressive parvovirus H-1 on different established glioblastoma cell lines of rat and human origin and on short-term/low-passage cultures of human glioblastoma cells. We observed an efficient and dose-dependent killing of all glioma cell cultures at low multiplicities of infectious particles (MOI) per cell. Southern blot analysis of viral DNA amplification, RT-PCR analysis of viral RNA expression and Western blot analysis of the expression of viral structural (VP-1/VP-2) and nonstructural (NS-1) proteins demonstrated the biosynthesis of these viral macromolecular components in all of the cultures. Moreover, all the glioma cells were proficient for the production of infectious H-1 virus particles. The amount of virus production differed between a several fold increase of the input virus titer in most of the short-term/low-passage cultures up to 1,000-fold in one short-term glioma and in the rat cells. Glioma cells lines and, more importantly, short-term/low-passage cultures of human glioblastomas were found to be highly susceptible target cells for H-1 virus mediated cytotoxicity. The formation of fully infectious progeny particles in infected glioma cells offers the chance for the induction of secondary rounds of infection resulting in an advanced cytotoxic effect. These advantageous characteristics of H-1 virus infection of glioma cells, combined with the known low toxicity of H-1 virus in nontransformed cells, make parvovirus H-1 a promising candidate for oncolytic glioma therapy.

Replicating parvoviruses that target colon cancer cells

The wnt signaling pathway is constitutively activated in colon tumors by mutations in the adenomatous polyposis coli and beta-catenin genes. We have modified the minute virus of mice (MVM) P4 promoter to make it responsive to wnt signaling by inserting binding sites for the heterodimeric beta-catenin/Tcf transcription factor. In luciferase assays we can see up to 20-fold selectivity of Tcf mutant P4 promoters for cells with activated wnt signaling. Hybrid MVM/H-1 viruses containing Tcf mutant promoters were tested for NS1 expression, viral DNA replication, virus replication, and cytopathic effect on colon, lung, kidney, and cervical cancer cell lines. Activation of the wnt pathway by expression of Delta N-beta-catenin increased NS1 expression and viral burst size in 293T and H1299 lung cancer cells, showing that the Tcf mutant P4 promoter can respond to wnt signals in the context of the virus. Compared to the parental virus, the burst size of the Tcf mutant viruses was reduced at least 1,000-fold in H1299, 293T, NB324K, and HeLa cells, which have inactive wnt signaling pathways. The burst size and cytopathic effect of the Tcf viruses was near wild-type levels in SW480 and Isreco1 colon cancer cell lines, which have high Tcf activity. The high specificity of these viruses should permit the development of H-1 virus-based vectors which combine high safety and greater efficacy in cancer therapy.

Chimeric and pseudotyped parvoviruses minimize the contamination of recombinant stocks with replication-competent viruses and identify a DNA sequence that restricts parvovirus H-1 in mouse cells

Recent studies demonstrated the ability of the recombinant autonomous parvoviruses MVMp (fibrotropic variant of the minute virus of mice) and H-1 to transduce therapeutic genes in tumor cells. However, recombinant vector stocks are contaminated by replication-competent viruses (RCVs) generated during the production procedure. To reduce the levels of RCVs, chimeric recombinant vector genomes were designed by replacing the right-hand region of H-1 virus DNA with that of the closely related MVMp virus DNA and conversely. Recombinant H-1 and MVMp virus pseudotypes were also produced with this aim. In both cases, the levels of RCVs contaminating the virus stocks were considerably reduced (virus was not detected in pseudotyped virus stocks, even after two amplification steps), while the yields of vector viruses produced were not affected. H-1 virus could be distinguished from MVMp virus by its restriction in mouse cells at an early stage of infection prior to detectable viral DNA replication and gene expression. The analysis of the composite viruses showed that this restriction could be assigned to a specific genomic determinant(s). Unlike MVMp virus, H-1 virus capsids were found to be a major determinant of the greater permissiveness of various human cell lines for this virus.

The P4 promoter of the parvovirus minute virus of mice is developmentally regulated in transgenic P4-LacZ mice

Activation of the minute virus of mice (MVM) P4 promoter is a key step in the life cycle of the virus and is completely dependent on host transcription factors. Since transcription-factor composition varies widely in different cell types, there is the possibility that only some cell types in the host organism have the capacity to initiate expression from the P4 promoter and therefore that the promoter may be a factor in determining the tropism of MVM. In this study, the ability of various cell types to activate P4, independent of the other virus-host interactions, was examined in transgenic mouse lines bearing a beta-galactosidase reporter sequence driven by the P4 promoter. It was found that lacZ was expressed during embryogenesis and in the adult in a cell-type-specific and differentiation-dependent pattern. The data are consistent with cell-type and stage-specific activation of the P4 promoter having a role in determining the host cell-type range of MVM. The ability of some parvoviruses to replicate in, and kill oncogenically transformed cells, and to destroy induced tumors in laboratory animals is the basis of recent approaches to use MVM-based vectors in cancer gene therapy. Since these vectors rely on the activation of the P4 promoter by the target tissues, understanding the promoter dependence on cell-type and differentiation status is important for their design and potential use.

Suppression of metastatic hemangiosarcoma by a parvovirus MVMp vector transducing the IP-10 chemokine into immunocompetent mice

We have previously shown that the growth of human tumor xenografts in immunodeficient mice can be efficiently suppressed upon infection with the autonomous parvovirus H-1 or with cytokine-transducing derivatives thereof. To further evaluate the benefits of implementing parvoviruses in cancer gene therapy, we have created a new recombinant vector, MVMp/IP-10, transducing the immunoactive, antiangiogenic chemokine IP-10, and used this virus to treat syngeneic tumors grown in immunocompetent mice. Intratumoral/intraperitoneal administration of only 3 x 10(7) replication units of MVMp/IP-10 per animal strongly inhibited the progression of established H5V cell-induced vascular tumors, a highly malignant mouse model for human cavernous hemangioma and Kaposi's sarcoma. Retardation of recurrent tumor growth and suppression of life-threatening metastatic dissemination to internal organs were accompanied by a striking delay in hemangioma-associated mortality. Parental MVMp did not have a significant effect under these conditions up to the dose of 10(10) infectious units/animal, but had strong antihemangiosarcoma activity when used to infect H5V cells ex vivo prior to implantation. In all cases, virus therapy was very well tolerated. Virus-induced suppression of hemangiosarcoma was dependent on host T cells and associated with intratumoral persistence of IFN gamma-expressing cytotoxic lymphocytes, and led to the reduced expression of hepatic plasminogen activator inhibitor-1 (PAI-1), a metastasis-linked marker. This proof of principle study demonstrates that MVMp/IP-10 can aid the treatment of vascular tumors and that autonomous parvovirus-based vectors can be considered potent tools for cancer gene therapy purposes.

Transduction of human MCP-3 by a parvoviral vector induces leukocyte infiltration and reduces growth of human cervical carcinoma cell xenografts

BACKGROUND

The oncosuppressive properties of some autonomous parvoviruses such as H-1 virus, together with their low pathogenicity, make them attractive vectors for tumor-directed gene therapy. Indeed, it was recently shown that these viruses became endowed with an enhanced oncosuppressive activity after they had been engineered to deliver a recognized therapeutic transgene. This prompted us to use a parvoviral vector to analyse the antineoplastic capacity of MCP-3 (monocyte chemotactic protein-3), a CC chemokine which has a broad spectrum of target cells, and can thus be considered to be a promising candidate for cancer treatment.

METHODS

We explored the use of a parvovirus H-1-based vector encoding human MCP-3 for its antitumor potential on human cervical carcinoma cells. HeLa cells were infected in vitro with the recombinant virus hH1/MCP-3 at a low multiplicity [1 replication unit (RU)/cell] and we investigated the effect of parvovirus-mediated MCP-3 transduction on tumor formation and growth upon implantation of HeLa cells in nude mice.

RESULTS

Infection of HeLa cells with hH1/MCP-3 led to secretion of high levels of MCP-3 and to significant retardation of tumor growth in recipient mice, as compared with HeLa cells that were either buffer-treated or infected with a MCP-3-free vector. Tumors from hH1/MCP-3-infected HeLa cells were heavily infiltrated with activated macrophages and showed increased numbers of dendritic cells. In addition, activated natural killer (NK) cells were also recruited into MCP-3-transduced tumors.

CONCLUSION

These observations indicate that parvovirus H-1-transduced MCP-3 is able to exert a significant antitumor activity which is mediated, at least in part, through macrophages and NK cells, under conditions in which activated T cells are lacking.

Highly efficient transduction and expression of cytokine genes in human tumor cells by means of autonomous parvovirus vectors; generation of antitumor responses in recipient mice

The possible use of recombinant autonomous parvoviruses as vectors to efficiently express therapeutic cytokines in human tumor cells was evaluated in vitro and in vivo. The parvovirus H1 was used to generate recombinant viruses (rH1) that carried transgenes encoding either human interleukin 2 (IL-2) or monocyte chemotactic protein 1 (MCP-1), in replacement of part of the capsid genes. Such rH11 viruses have been shown to retain in vitro the intrinsic oncotropic properties of the parental virus. On infection with the recombinant viruses at an input multiplicity of 1 replication unit (RU) per cell, HeLa cultures were induced to release 4-10 microg of cytokine per 10(6) cells over a period of 5 days. The expression of the rH1-transduced human cytokine/chemokine could also be detected in tumor material recovered from nude mice that had been subcutaneously engrafted with in vitro-infected HeLa cells. The formation of tumors from HeLa xenografts was reduced by 90% compared with wild-type or mock-infected cells as a result of cells preinfected with IL2-expressing virus at an input multiplicity as low as 1 RU per cell. Tumors arising from HeLa cells infected with transgene-free or MCP1-expressing vectors or with wild-type H1 virus were not rejected at this virus dose. Tumors infected with rH1/IL-2 virus displayed markers indicative of their infiltration with NK cells in which the cytocidal program was activated, whereas little NK activity was detected in wild-type virus or mock-infected tumors. Altogether, these data show that the IL-2 expressing H1 vector was a more potent antineoplastic agent than the parental virus, and point to the possible application of recombinant autonomous parvoviruses toward therapy of some human tumors.

Parvovirus H-1-induced cell death: influence of intracellular NAD consumption on the regulation of necrosis and apoptosis

The autonomous parvovirus H-1 exerts tumor-suppressive effects in living organisms and has been shown to specifically interfere with the survival of transformed cells in culture. The mechanism(s) by which H-1 virus induces death of transformed cells is not yet well understood. It has recently been reported that H-1 virus induces apoptotic cell death in the human monocytic U937 cell line, as assessed by biochemical and morphological changes of infected cells (Rayet, B., Lopez-Guerrero, J.-A., Rommelaere, J., Dinsart, C., 1998. Induction of programmed cell death by parvovirus H-1 in U937 cells: connection with the TNFalpha signalling pathway. J. Virol. 72, 8893-8903). Here we show that parvovirus H-1 infection induced early biochemical changes pointing to apoptotic events also in the transformed human keratinocyte cell line, HeLa, and the transformed rat fibroblast cell line, P1. Morphologic changes, however, and in particular the early breakdown of plasma membrane integrity, suggested that apoptosis did not go to completion, leading to necrotic cell death as the major result of parvovirus infection of HeLa and P1 cells. Parvovirus infection of these, and to a significantly lesser extent of U937 cells, was accompanied by rapid depletion of intracellular NAD stores. Inhibition of NAD-consuming enzymes interfered with parvovirus-induced NAD depletion and increased the proportion of H-1 virus-infected cells displaying apoptotic features of cell death. In contrast, a similar prevention of NAD depletion through stimulation of NAD production had little influence on the cell death pathway, suggesting that NAD-consuming enzymes may promote necrosis in a direct way rather than through inducing the overall drop of intracellular NAD.