Characterization of a full-length infectious cDNA clone and a GFP reporter derivative of the oncolytic picornavirus SVV-001.

Seneca Valley virus (SVV-001) is an oncolytic picornavirus with selective tropism for a subset of human cancers with neuroendocrine differentiation. To characterize further the specificity of SVV-001 and its patterns and kinetics of intratumoral spread, bacterial plasmids encoding a cDNA clone of the full-length wild-type virus and a derivative virus expressing GFP were generated. The full-length cDNA of the SVV-001 RNA genome was cloned into a bacterial plasmid under the control of the T7 core promoter sequence to create an infectious cDNA clone, pNTX-09. A GFP reporter virus cDNA clone, pNTX-11, was then generated by cloning a fusion protein of GFP and the 2A protein from foot-and-mouth disease virus immediately following the native SVV-001 2A sequence. Recombinant GFP-expressing reporter virus, SVV-GFP, was rescued from cells transfected with in vitro RNA transcripts from pNTX-11 and propagated in cell culture. The proliferation kinetics of SVV-001 and SVV-GFP were indistinguishable. The SVV-GFP reporter virus was used to determine that a subpopulation of permissive cells is present in small-cell lung cancer cell lines previously thought to lack permissivity to SVV-001. Finally, it was shown that SVV-GFP administered to tumour-bearing animals homes in to and infects tumours whilst having no detectable tropism for normal mouse tissues at 1×10(11) viral particles kg(-1), a dose equivalent to that administered in ongoing clinical trials. These infectious clones will be of substantial value in further characterizing the biology of this virus and as a backbone for the generation of additional oncolytic derivatives.

Structural features of the Seneca Valley virus internal ribosome entry site (IRES) element: a picornavirus with a pestivirus-like IRES.

The RNA genome of Seneca Valley virus (SVV), a recently identified picornavirus, contains an internal ribosome entry site (IRES) element which has structural and functional similarity to that from classical swine fever virus (CSFV) and hepatitis C virus, members of the Flaviviridae. The SVV IRES has an absolute requirement for the presence of a short region of virus-coding sequence to allow it to function either in cells or in rabbit reticulocyte lysate. The IRES activity does not require the translation initiation factor eIF4A or intact eIF4G. The predicted secondary structure indicates that the SVV IRES is more closely related to the CSFV IRES, including the presence of a bipartite IIId domain. Mutagenesis of the SVV IRES, coupled to functional assays, support the core elements of the IRES structure model, but surprisingly, deletion of the conserved IIId(2) domain had no effect on IRES activity, including 40S and eIF3 binding. This is the first example of a picornavirus IRES that is most closely related to the CSFV IRES and suggests the possibility of multiple, independent recombination events between the genomes of the Picornaviridae and Flaviviridae to give rise to similar IRES elements.

Structure of Seneca Valley Virus-001: an oncolytic picornavirus representing a new genus.

The crystal structure of Seneca Valley Virus-001 (SVV-001), the representative member of a new genus, Senecavirus, is reported at 2.3A resolution. SVV-001 is the first naturally occurring nonpathogenic picornavirus shown to mediate selective cytotoxicity towards tumor cells with neuroendocrine cancer features. The nonsegmented (+) ssRNA genome of SVV-001 shares closest sequence similarity with the genomes of the members of Cardiovirus. The overall tertiary structure of VP1-VP4 subunits is conserved with the exception of loops, especially those of VP1 that show large deviations relative to the members of the cardioviruses. The surface loops of VP1 and VP2 are predicted to mediate cell tropism of SVV-001. In addition, the organization of the packaged nucleic acid density indicates that certain regions of VP2 and VP4 interact closely with the packaged nucleic acid.

Crystallization and preliminary X-ray diffraction studies of Seneca Valley virus-001, a new member of the Picornaviridae family.

Seneca Valley Virus-001 (SVV-001) is a newly found species in the Picornaviridae family. SVV-001 is the first naturally occurring nonpathogenic picornavirus observed to mediate selective cytotoxicity towards tumor cells with neuroendocrine cancer features. The nonsegmented (+)ssRNA genome of SVV-001 shares closest sequence similarity to the genomes of the members of the Cardiovirus genus. However, based on the distinct characteristics of the genome organization and other biochemical properties, it has been suggested that SVV-001 represents a new genus, namely 'Senecavirus', in the Picornaviridae family. In order to understand the oncolytic properties of SVV-001, the native virus was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group R3, with unit-cell parameters (in the hexagonal setting) a = b = 311.5, c = 1526.4 A. Although the SVV crystals diffracted to better than 2.3 A resolution, the data quality is acceptable [I/sigma(I) > 2.0] to 2.6 A resolution. The unit-cell volume and the locked rotation-function analysis suggest that six particles could be accommodated in the unit cell, with two distinct sets of one third of a particle, each containing 20 protomers, occupying the crystallographic asymmetric unit. (ClinicalTrials.gov identifier NCT00314925)

An oncolytic adenovirus selective for retinoblastoma tumor suppressor protein pathway-defective tumors: dependence on E1A, the E2F-1 promoter, and viral replication for selectivity and efficacy.

The use of oncolytic adenoviruses as a cancer therapeutic is dependent on the lytic properties of the viral life cycle, and the molecular differences between tumor cells and nontumor cells. One strategy for achieving safe and efficacious adenoviral therapies is to control expression of viral early gene(s) required for replication with tumor-selective promoter(s), particularly those active in a broad range of cancer cells. The retinoblastoma tumor suppressor protein (Rb) pathway is dysregulated in a majority of human cancers. The human E2F-1 promoter has been shown to be selectively activated/derepressed in tumor cells with a defect in the Rb pathway. Ar6pAE2fE3F and Ar6pAE2fF are oncolytic adenoviral vectors (with and without the viral E3 region, respectively) that use the tumor-selective E2F-1 promoter to limit expression of the viral E1A transcription unit, and, thus, replication, to tumor cells. We demonstrate that the antitumor activity of Ar6pAE2fF in vitro and in vivo is dependent on the E2F-1 promoter driving E1A expression in Rb pathway-defective cells, and furthermore, that its oncolytic activity is enhanced by viral replication. Selective oncolysis by Ar6pAE2fF was dependent on the presence of functional E2F binding sites in the E2F-1 promoter, thus linking antitumor viral activity to the Rb pathway. Potent antitumor efficacy was demonstrated with Ar6pAE2fF and Ar6pAE2fE3F in a xenograft model following intratumoral administration. Ar6pAE2fF and Ar6pAE2fE3F were compared with Addl1520, which is reported to be molecularly identical to an E1B-55K deleted vector currently in clinical trials. These vectors were compared in in vitro cytotoxicity and virus production assays, after systemic delivery in an in vivo E1A-related hepatotoxicity model, and in a mouse xenograft tumor model after intratumoral administration. Our results support the use of oncolytic adenoviruses using tumor-selective promoter(s) that are activated or derepressed in tumor cells by virtue of a particular defective pathway, such as the Rb pathway.

Antitumor efficacy and tumor-selective replication with a single intravenous injection of OAS403, an oncolytic adenovirus dependent on two prevalent alterations in human cancer.

A potentially promising treatment of metastatic cancer is the systemic delivery of oncolytic adenoviruses. This requires engineering viruses which selectively replicate in tumors. We have constructed such an oncolytic adenovirus, OAS403, in which two early region genes are under the control of tumor-selective promoters that play a role in two key pathways involved in tumorigenesis. The early region E1A is controlled by the promoter for the E2F-1 gene, a transcription factor that primarily upregulates genes for cell growth. The E4 region is under control of the promoter for human telomerase reverse transcriptase, a gene upregulated in most cancer cells. OAS403 was evaluated in vitro on a panel of human cells and found to elicit tumor-selective cell killing. Also, OAS403 was less toxic in human hepatocyte cultures, as well as in vivo when compared to an oncolytic virus that lacked selective E4 control. A single intravenous injection of 3 x 10(12) vp/kg in a Hep3B xenograft mouse tumor model led to significant antitumor efficacy. Additionally, systemic administration in a pre-established LNCaP prostate tumor model resulted in over 80% complete tumor regressions at a tolerable dose. Vector genome copy number was measured in tumors and livers at various times following tail vein injection and showed a selective time-dependent increase in tumors but not livers over 29 days. Furthermore, efficacy was significantly improved when OAS403 treatment was combined with doxorubicin. This virus holds promise for the treatment of a broad range of human cancers including metastatic disease.

Intravenous injection of oncolytic picornavirus SVV-001 prolongs animal survival in a panel of primary tumor-based orthotopic xenograft mouse models of pediatric glioma.

BACKGROUND: Seneca Valley virus (SVV-001) is a nonpathogenic oncolytic virus that can be systemically administered and can pass through the blood-brain barrier. We examined its therapeutic efficacy and the mechanism of tumor cell infection in pediatric malignant gliomas. METHODS: In vitro antitumor activities were examined in primary cultures, preformed neurospheres, and self-renewing glioma cells derived from 6 patient tumor orthotopic xenograft mouse models (1 anaplastic astrocytoma and 5 GBM). In vivo therapeutic efficacy was examined by systemic treatment of preformed xenografts in 3 permissive and 2 resistant models. The functional role of sialic acid in mediating SVV-001 infection was investigated using neuraminidase and lectins that cleave or competitively bind to linkage-specific sialic acids. RESULTS: SVV-001 at a multiplicity of infection of 0.5 to 25 replicated in and effectively killed primary cultures, preformed neurospheres, and self-renewing stemlike single glioma cells derived from 4 of the 6 glioma models in vitro. A single i.v. injection of SVV-001 (5 × 10(12) viral particles/kg) led to the infection of orthotopic xenografts without harming normal mouse brain cells, resulting in significantly prolonged survival in all 3 permissive and 1 resistant mouse models (P < .05). Treatment with neuraminidase and competitive binding using lectins specific for α2,3-linked and/or α2,6-linked sialic acid significantly suppressed SVV-001 infectivity (P < .01). CONCLUSION: SVV-001 possesses strong antitumor activity against pediatric malignant gliomas and utilizes α2,3-linked and α2,6-linked sialic acids as mediators of tumor cell infection. Our findings support the consideration of SVV-001 for clinical trials in children with malignant glioma.

Phase I clinical study of Seneca Valley Virus (SVV-001), a replication-competent picornavirus, in advanced solid tumors with neuroendocrine features.

PURPOSE: Seneca Valley Virus (SVV-001) is a novel naturally occurring replication-competent picornavirus with potent and selective tropism for neuroendocrine cancer cell types, including small cell lung cancer. We conducted a first-in-human, first-in-class phase I clinical trial of this agent in patients with cancers with neuroendocrine features, including small cell lung cancer. EXPERIMENTAL DESIGN: Clinical evaluation of single intravenous doses in patients with cancers with neuroendocrine features was performed across five log-increments from 10(7) to 10(11) vp/kg. Toxicity, viral titers and clearance, neutralizing antibody development, and tumor response were assessed. RESULTS: A total of 30 patients were treated with SVV-001, including six with small cell carcinoma at the lowest dose of 10(7) vp/kg. SVV-001 was well tolerated, with no dose-limiting toxicities observed in any dose cohort. Viral clearance was documented in all subjects and correlated temporally with development of antiviral antibodies. Evidence of in vivo intratumoral viral replication was observed among patients with small cell carcinoma, with peak viral titers estimated to be >10(3)-fold higher than the administered dose. One patient with previously progressive chemorefractory small cell lung cancer remained progression-free for 10 months after SVV-001 administration, and is alive over 3 years after treatment. CONCLUSIONS: Intravenous SVV-001 administration in patients is well tolerated at doses up to 10(11) vp/kg, with predictable viral clearance kinetics, intratumoral viral replication, and evidence of antitumor activity in patients with small cell lung cancer. Phase II clinical evaluation in small cell lung cancer is warranted, and has been initiated.

A single intravenous injection of oncolytic picornavirus SVV-001 eliminates medulloblastomas in primary tumor-based orthotopic xenograft mouse models.

Difficulties of drug delivery across the blood-brain barrier (BBB) and failure to eliminate cancer stem cells (CSCs) are believed to be the major causes of tumor recurrences in children with medulloblastoma (MB). Seneca Valley virus-001 (SVV-001) is a naturally occurring oncolytic picornavirus that can be systemically administered. Here, we report its antitumor activities against MB cells in a panel of 10 primary tumor-based orthotopic xenograft mouse models. We found that SVV-001 killed the primary cultured xenograft cells, infected and replicated in tumor cells expressing CSC surface marker CD133, and eliminated tumor cells capable of forming neurospheres in vitro in 5 of the 10 xenograft models. We confirmed that SVV-001 could pass through BBB in vivo. A single i.v. injection of SVV-001 in 2 anaplastic MB models led to widespread infection of the preformed intracerebellar (ICb) xenografts, resulting in significant increase in survival (2.2-5.9-fold) in both models and complete elimination of ICb xenografts in 8 of the 10 long-term survivors. Mechanistically, we showed that the intracellular replication of SVV-001 is mediated through a subverted autophagy that is different from the bona fide autophagic process induced by rapamycin. Our data suggest that SVV-001 is well suited for MB treatment. This work expands the current views in the oncolytic therapy field regarding the utility of oncolytic viruses in simultaneous targeting of stem and nonstem tumor cells.

Complete genome sequence analysis of Seneca Valley virus-001, a novel oncolytic picornavirus.

The complete genome sequence of Seneca Valley virus-001 (SVV-001), a small RNA virus, was determined and was shown to have typical picornavirus features. The 7280 nt long genome was predicted to contain a 5' untranslated region (UTR) of 666 nt, followed by a single long open reading frame consisting of 6543 nt, which encodes a 2181 aa polyprotein. This polyprotein could potentially be cleaved into 12 polypeptides in the standard picornavirus L-4-3-4 layout. A 3' UTR of 71 nt was followed by a poly(A) tail of unknown length. Comparisons with other picornaviruses showed that the P1, 2C, 3C and 3D polypeptides of SVV-001 were related most closely to those of the cardioviruses, although they were not related as closely to those of encephalomyocarditis virus and Theiler's murine encephalomyelitis virus as the latter were to each other. Most other regions of the polyprotein differed considerably from those of all other known picornaviruses. SVV-001 contains elements of an internal ribosome entry site reminiscent of that found in hepatitis C virus and a number of genetically diverse picornaviruses. SVV-001 is a novel picornavirus and it is proposed that it be classified as the prototype species in a novel genus named 'Senecavirus'.

Seneca Valley virus, a systemically deliverable oncolytic picornavirus, and the treatment of neuroendocrine cancers.

BACKGROUND: Numerous clinical trials have demonstrated that oncolytic viruses can elicit antitumor responses when they are administered directly into localized cancers. However, the treatment of metastatic disease with oncolytic viruses has been challenging due to the inactivation of viruses by components of human blood and/or to inadequate tumor selectivity. METHODS: We determined the cytolytic potential and selectivity of Seneca Valley Virus-001 (SVV-001), a newly discovered native picornavirus, in neuroendocrine and pediatric tumor cell lines and normal cells. Suitability of the virus for intravenous delivery in humans was assessed by blood inactivation assays. Safety was evaluated in vivo using an immune-competent mouse model, and efficacy was evaluated in vivo in athymic mice bearing tumors derived from human small-cell lung cancer and retinoblastoma cell lines. RESULTS: Cell lines derived from small-cell lung cancers and solid pediatric cancers were at least 10,000-fold more sensitive to the cytolytic activity of SVV-001 than were any of the adult normal human cells tested. Viral infectivity was not inhibited by human blood components. Intravenous doses up to 1 x 10(14) virus particles (vp) per kg were well tolerated, and no dose-limiting toxicity was observed in immune-competent mice. A single intravenous dose of 1 x 10(8) vp per kg into athymic mice bearing preestablished small-cell lung or retinoblastoma tumors resulted in complete, durable responses in ten of ten and five of eight mice, respectively. CONCLUSIONS: SVV-001 has potent cytolytic activity and high selectivity for tumor cell lines having neuroendocrine properties versus adult normal cells. Systemically administered SVV-001 has potential for the treatment of metastatic neuroendocrine cancers.