Reovirus-based therapy for cancer

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

Deciphering molecular mechanisms stabilizing the reovirus-binding complex

Mammalian orthoreoviruses (reoviruses) serve as potential triggers of celiac disease and have oncolytic properties, making these viruses potential cancer therapeutics. Primary attachment of reovirus to host cells is mainly mediated by the trimeric viral protein, σ1, which engages cell-surface glycans, followed by high-affinity binding to junctional adhesion molecule-A (JAM-A). This multistep process is thought to be accompanied by major conformational changes in σ1, but direct evidence is lacking. By combining biophysical, molecular, and simulation approaches, we define how viral capsid protein mechanics influence virus-binding capacity and infectivity. Single-virus force spectroscopy experiments corroborated by in silico simulations show that GM2 increases the affinity of σ1 for JAM-A by providing a more stable contact interface. We demonstrate that conformational changes in σ1 that lead to an extended rigid conformation also significantly increase avidity for JAM-A. Although its associated lower flexibility impairs multivalent cell attachment, our findings suggest that diminished σ1 flexibility enhances infectivity, indicating that fine-tuning of σ1 conformational changes is required to successfully initiate infection. Understanding properties underlying the nanomechanics of viral attachment proteins offers perspectives in the development of antiviral drugs and improved oncolytic vectors.

The differential expression of toll like receptors and RIG-1 correlates to the severity of infectious diseases

The toll like receptors (TLRs) and RIG-1 are proteins involved in the initial reaction of the innate immune system to infectious diseases and, thus, can provide much information to the surgical pathologist in terms of the molecular dynamics of the infection. The TLRs (TLR1, 2, 3, 4, 7, 8) and RIG-1 distribution as determined by immunohistochemistry was examined in the following diseases: human papillomavirus (n = 30 including 15 squamous intraepithelial lesions (SIL), 5 cancers, and 10 controls); molluscum contagiosum (n = 8 including 4 controls), SARS-CoV2 (n = 52 including 20 mild, 5 fatal, and 27 controls) and reovirus infection as oncolytic therapy. Mild, regressing infection (molluscum contagiosum, mild SARS-CoV2 and low grade SIL) each showed the same pattern: marked up regulation of at least three of the TLRs/RIG-1 with decreased expression of none compared to the controls. Severe infection (fatal SARS-CoV2, and cervical cancer) each showed marked decrease expression in at least three of the TLRs/RIG-1. We recently documented an equivalent marked decrease expression of the TLRs/RIG-1 in the placenta in fatal in utero infections. The reoviral infected tissues showed an overall pattern of marked increase expression of TLRs/RIG-1, consistent with a strong anti-viral response. Thus, the in situ testing of infectious diseases by a panel of these early infectious disease recognition proteins may allow the surgical pathologist to predict the outcome of the disease which, in turn, may assist in the understanding of the role of the TLRs/RIG-1 in determining the fate of a given infectious process.

Targeting steroid hormone receptors for anti-cancer therapy-A review on small molecules and nanotherapeutic approaches

The steroid hormone receptors (SHRs) among nuclear hormone receptors (NHRs) are steroid ligand-dependent transcription factors that play important roles in the regulation of transcription of genes promoted via hormone responsive elements in our genome. Aberrant expression patterns and context-specific regulation of these receptors in cancer, have been routinely reported by multiple research groups. These gave an window of opportunity to target those receptors in the context of developing novel, targeted anticancer therapeutics. Besides the development of a plethora of SHR-targeting synthetic ligands and the availability of their natural, hormonal ligands, development of many SHR-targeted, anticancer nano-delivery systems and theranostics, especially based on small molecules, have been reported. It is intriguing to realize that these cytoplasmic receptors have become a hot target for cancer selective delivery. This is in spite of the fact that these receptors do not fall in the category of conventional, targetable cell surface bound or transmembrane receptors that enjoy over-expression status. Glucocorticoid receptor (GR) is one such exciting SHR that in spite of it being expressed ubiquitously in all cells, we discovered it to behave differently in cancer cells, thus making it a truly druggable target for treating cancer. This review selectively accumulates the knowledge generated in the field of SHR-targeting as a major focus for cancer treatment with various anticancer small molecules and nanotherapeutics on progesterone receptor, mineralocorticoid receptor, and androgen receptor while selectively emphasizing on GR and estrogen receptor. This review also briefly highlights lipid-modification strategy to convert ligands into SHR-targeted cancer nanotherapeutics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Lipid-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Bluetongue Viruses Act as Novel Oncolytic Viruses to Effectively Inhibit Human Renal Cancer Cell Growth In Vitro and In Vivo

Background

The bluetongue virus (BTV) is the prototype virus in the genus Orbivirus within the family Reoviridae. Recent studies indicate that BTVs are capable of infecting and selectively lysing human hepatic carcinoma cells (Hep-3B) and prostate carcinoma cells (pc-3). This study was designed to evaluate the oncolytic potential of BTV in experimental models of human renal cancer in vitro and in vivo.

Material/Methods

Five human renal cancer cell lines, ACHN, CAKI-1, OS-RC-2, 786-O, and A498, were used in this study to analyze BTV replication. These cells were lysed by oncolysis compared to normal control. Xenograft models were used to assess the efficacy and toxicity of BTVs in vivo. Data were analyzed by one-way ANOVA or two-sided unpaired t tests.

Results

The results showed HPTEC cells to be relatively resistant to cytotoxic effects of BTVs and exhibited normal growth rate even at high dose of BTVs. Nonetheless, the renal cancer cells showed a remarkably higher sensitivity to BTVs. Moreover, the ultramicroscopic subcellular changes were also detected in the renal cells. The viral particles were observed in all the RCC cell lines, but not in HPTEC cells. Intratumoral injections of BTVs significantly decreased the tumor volume as compared to animals that received no virus treatment. Infection with BTVs significantly increased the percentage of apoptotic renal cancer cells but not the HPTEC cells. Moreover, BTV triggered apoptosis in renal cancer cells via a mitochondria-mediated pathway.

Conclusions

This study for the first time demonstrated the oncolytic potential of BTV in experimental models of human renal cancer. BTV exhibits the potential to inhibit human renal cancer cell growth in vitro and in vivo.

Oncolytic viruses: what to expect from their use in cancer treatment

Oncolytic viruses are biologic agents able to selectively infect and destroy cancer cells while sparing the normal ones. Furthermore, they also stimulate the host immune system to combat the tumor growth and to promote tumor removal. This review thoroughly describes different types of viruses developed for targeting specific cancers, as well as the strategies to improve the efficacy and safety of oncolytic virotherapy. It also explores how their potential as anticancer agents may be enhanced through combination with other traditional therapies, such as chemotherapy or more recent approaches, such as checkpoint inhibitors. There are many oncolytic viruses currently being tested in clinical trials for the treatment of various types of cancer, suggesting that this approach could become the near future of the oncology field.

Oncolytic Reovirus Inhibits Immunosuppressive Activity of Myeloid-Derived Suppressor Cells in a TLR3-Dependent Manner

Oncolytic reovirus, which possesses 10 segments of dsRNA genome, mediates antitumor effects via not only virus replication in a tumor cell-specific manner, but also activation of antitumor immunity; however, the mechanism(s) of reovirus-induced activation of antitumor immunity have not been fully elucidated. Recent studies have demonstrated that overcoming an immunosuppressive environment in tumor-bearing hosts is important to achieve efficient activation of antitumor immunity. Among the various types of cells involved in immunosuppression, it has been revealed that myeloid-derived suppressor cells (MDSCs) are significantly increased in tumor-bearing hosts and play crucial roles in the immunosuppression in tumor-bearing hosts. In this study, we examined whether reovirus inhibits the immunosuppressive activity of MDSCs, resulting in efficient activation of immune cells after in vivo administration. The results showed that splenic MDSCs recovered from PBS-treated tumor-bearing mice significantly suppressed the Ag-specific proliferation of CD8⁺ T cells. In contrast, the suppressive activity of MDSCs on T cell proliferation was significantly reduced after reovirus administration. Reovirus also inhibited the immunosuppressive activity of MDSCs in IFN-β promoter stimulator-1 knockout (KO) mice and in wild-type mice. In contrast, the immunosuppressive activity of MDSCs in TLR-3 KO mice was not significantly altered by reovirus treatment. The activation levels of CD4⁺ and CD8⁺ T cells were significantly lower in TLR3 KO mice than in wild-type mice after reovirus administration. These results indicate that reovirus inhibits the immunosuppressive activity of MDSCs in a TLR3, but not IFN-β promoter stimulator-1, signaling-dependent manner.

Multiple proteins differing between laboratory stocks of mammalian orthoreoviruses affect both virus sensitivity to interferon and induction of interferon production during infection

In the course of previous works, it was observed that the virus laboratory stock (T3D^S) differs in sequence from the virus encoded by the ten plasmids currently in use in many laboratories (T3D^K), and derived from a different original virus stock. Seven proteins are affected by these sequence differences. In the present study, replication of T3D^K was shown to be more sensitive to the antiviral effect of interferon. Infection by the T3D^K virus was also shown to induce the production of higher amount of β and α-interferons compared to T3D^S. Two proteins, the μ2 and λ2 proteins, were found to be responsible for increased sensitivity to interferon while both μ2 and λ1 are responsible for increased interferon secretion. Altogether this supports the idea that multiple reovirus proteins are involved in the control of induction of interferon and virus sensitivity to the interferon-induced response. While interrelated, interferon induction and sensitivity can be separated by defined gene combinations. While both μ2 and λ2 were previously suspected of a role in the control of the interferon response, other proteins are also likely involved, as first shown here for λ1. This also further stresses that due caution should be exerted when comparing different virus isolates with different genetic background.

A classical PKA inhibitor increases the oncolytic effect of M1 virus via activation of exchange protein directly activated by cAMP 1

Oncolytic virotherapy is an emerging and promising treatment modality that uses replicating viruses as selective antitumor agents. Here, we report that a classical protein kinase A (PKA) inhibitor, H89, synergizes with oncolytic virus M1 in various cancer cells through activation of Epac1 (exchange protein directly activated by cAMP 1). H89 substantially increases viral replication in refractory cancer cells, leading to unresolvable Endoplasmic Reticulum stress, and cell apoptosis. Microarray analysis indicates that H89 blunts antiviral response in refractory cancer cells through retarding the nuclear translocation of NF-κB. Importantly, in vivo studies show significant antitumor effects during M1/H89 combination treatment. Overall, this study reveals a previously unappreciated role for H89 and demonstrates that activation of the Epac1 activity can improve the responsiveness of biotherapeutic agents for cancer.

Anti-tumor efficacy of oncolytic reovirus against gastrointestinal stromal tumor cells

Imatinib, a multitargeted receptor tyrosine kinase inhibitor, is used as the standard initial therapy against inoperable gastrointestinal stromal tumor (GIST). However, GIST can acquire resistance to imatinib within several years of therapy. The development of oncolytic reovirus as an anticancer agent has expanded to many clinical trials for various tumors. Here, we investigated whether reovirus has antitumor activity against GIST cells in the setting of imatinib sensitivity in vitro and in vivo. Cell proliferation and apoptosis assays were performed using a human GIST cell line, GIST-T1, and imatinib-resistant GIST (GIST-IR) cells that we established. The molecular pathways responsible for cell damage by reovirus were explored using PCR-arrays and Western blots. Reovirus significantly induced apoptotic cell death in GIST-T1 and GIST-IR cells in vitro, despite differences in the activation of receptor tyrosine kinase pathways between GIST-T1 and GIST-IR. Molecular assays indicated the possibility that reovirus induces apoptotic cell death via Fas signaling. Furthermore, in vivo mouse tumor xenograft models demonstrated a significant anti-tumor effect of reovirus on both GIST-T1 and GIST-IR cells. Our results demonstrate the therapeutic potential of reovirus against GIST.

Oncolytic reovirus inhibits angiogenesis through induction of CXCL10/IP-10 and abrogation of HIF activity in soft tissue sarcomas

The tumor-selective viral replication capacity and pro-apoptotic effects of oncolytic reovirus have been reported to be dependent on the presence of an activated RAS pathway in several solid tumor types. However, the mechanisms of selective anticancer efficacy of the reovirus-based formulation for cancer therapy (Reolysin, pelareorep) have not been rigorously studied in soft tissue sarcomas (STS). Here we report that Reolysin triggered a striking induction of the anti-angiogenic chemokine interferon-γ-inducible protein 10 (IP-10)/CXCL10 (CXC chemokine ligand 10) in both wild type and RAS mutant STS cells. Further analysis determined that Reolysin treatment possessed significant anti-angiogenic activity irrespective of RAS status. In addition to CXCL10 induction, Reolysin dramatically downregulated the expression of hypoxia inducible factor (HIF)-1α, HIF-2α and inhibited vascular endothelial growth factor (VEGF) secretion. CXCL10 antagonism significantly diminished the anti-angiogenic effects of Reolysin indicating that it is a key driver of this phenomenon. Xenograft studies demonstrated that Reolysin significantly improved the anticancer activity of the anti-angiogenic agents sunitinib, temsirolimus, and bevacizumab in a manner that was associated with increased CXCL10 levels. This effect was most pronounced following treatment with Reolysin in combination with temsirolimus. Further analysis in additional sarcoma xenograft models confirmed the significant increase in CXCL10 and increased anticancer activity of this combination. Our collective results demonstrate that Reolysin possesses CXCL10-driven anti-angiogenic activity in sarcoma models, which can be harnessed to enhance the anticancer activity of temsirolimus and other agents that target the tumor vasculature.

Junctional adhesion molecule-A is overexpressed in advanced multiple myeloma and determines response to oncolytic reovirus

Despite the development of several new agents for multiple myeloma (MM) therapy over the last decade, drug resistance continues to be a significant problem. Patients with relapsed/refractory disease have high mortality rates and desperately need new precision approaches that directly target specific molecular features that are prevalent in the refractory setting. Reolysin is a proprietary formulation of reovirus for cancer therapy that has demonstrated efficacy in multiple clinical trials. Its selective effects against solid tumors have been largely attributed to RAS-mediated control of reovirus replication. However, the mechanisms regulating its preferential anti-neoplastic effects in MM and other hematological malignancies have not been rigorously studied. Here we report that the reovirus receptor, junctional adhesion molecule-A (JAM-A) is highly expressed in primary cells from patients with MM and the majority of MM cell lines compared to normal controls. A series of experiments demonstrated that JAM-A expression, rather than RAS, was required for Reolysin-induced cell death in MM models. Notably, analysis of paired primary MM specimens revealed that JAM-A expression was significantly increased at relapse compared to diagnosis. Two different models of acquired resistance to bortezomib also displayed both higher JAM-A expression and elevated sensitivity to Reolysin compared to parental cells, suggesting that Reolysin may be an effective agent for patients with relapsed/refractory disease due to their high JAM-A levels. Taken together, these findings support further investigation of Reolysin for the treatment of patients with relapsed/refractory MM and of JAM-A as a predictive biomarker for sensitivity to Reolysin-induced cell death.

Clinical development of reovirus for cancer therapy: An oncolytic virus with immune-mediated antitumor activity

Reovirus is a double-stranded RNA virus with demonstrated oncolysis or preferential replication in cancer cells. The oncolytic properties of reovirus appear to be dependent, in part, on activated Ras signaling. In addition, Ras-transformation promotes reovirus oncolysis by affecting several steps of the viral life cycle. Reovirus-mediated immune responses can present barriers to tumor targeting, serve protective functions against reovirus systemic toxicity, and contribute to therapeutic efficacy through antitumor immune-mediated effects via innate and adaptive responses. Preclinical studies have demonstrated the broad anticancer activity of wild-type, unmodified type 3 Dearing strain reovirus (Reolysin^®) across a spectrum of malignancies. The development of reovirus as an anticancer agent and available clinical data reported from 22 clinical trials will be reviewed.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

The combination of intravenous Reolysin and gemcitabine induces reovirus replication and endoplasmic reticular stress in a patient with KRAS-activated pancreatic cancer

BACKGROUND

Activating mutations in RAS are present in the majority of pancreatic cancer cases and represent an ideal therapeutic target. Reolysin is a proprietary formulation of oncolytic reovirus that is currently being evaluated in multiple clinical trials due to its ability to selectively replicate in cells harboring an activated RAS pathway. Here we report for the first time the presence of reovirus replication and induction of endoplasmic reticular (ER) stress in a primary tumor specimen collected from a pancreatic cancer patient receiving intravenous Reolysin and gemcitabine.

CASE PRESENTATION

We describe the case of a 54-year old patient diagnosed with pancreatic adenocarcinoma in February 2012. Analysis of a tumor biopsy revealed an activating KRAS mutation (G12D) and the patient was started on first-line treatment with Reolysin in combination with gemcitabine in March 2012. Stable disease was achieved with significant improvement in cancer-related pain. Following 25 cycles of treatment over 23 months, a second biopsy was collected and immunohistochemical analyses revealed the presence of reovirus replication and induction of the ER stress-related gene GRP78/BIP and the pro-apoptotic protein NOXA. Importantly, co-localization of reoviral protein and active caspase-3 was also observed in the biopsy specimen.

CONCLUSION

This is the first report of reoviral protein detection in primary tumor biopsies taken from a pancreatic cancer patient receiving intravenous Reolysin therapy. The accumulation of reoviral protein was associated with ER stress induction and caspase-3 processing suggesting that Reolysin and gemcitabine treatment exhibited direct pro-apoptotic activity against the tumor.

A single amino acid substitution in the mRNA capping enzyme λ2 of a mammalian orthoreovirus mutant increases interferon sensitivity

In the last few years, the development of a plasmid-based reverse genetics system for mammalian reovirus has allowed the production and characterization of mutant viruses. This could be especially significant in the optimization of reovirus strains for virotherapeutic applications, either as gene vectors or oncolytic viruses. The genome of a mutant virus exhibiting increased sensitivity to interferon was completely sequenced and compared with its parental virus. Viruses corresponding to either the parental or mutant viruses were then rescued by reverse genetics and shown to exhibit the expected phenotypes. Systematic rescue of different viruses harboring either of the four parental genes in a mutant virus backbone, or reciprocally, indicated that a single amino acid substitution in one of λ2 methyltransferase domains is the major determinant of the difference in interferon sensitivity between these two viruses.

•

An interferon sensitive reovirus harbors amino acids substitutions in four proteins.

•

Wild-type laboratory stock and mutant viruses were reconstructed by reverse genetics.

•

Each mutant gene was substituted by its wild-type counterpart and reciprocally.

•

Interferon sensitivity was assigned to a substitution in mRNA capping protein λ2.

A phase I trial and viral clearance study of reovirus (Reolysin) in children with relapsed or refractory extra-cranial solid tumors: a Children's Oncology Group Phase I Consortium report

BACKGROUND

Reovirus is a naturally occurring human virus that is cytopathic to malignant cells possessing an activated Ras signaling pathway. We conducted a phase I trial of Reolysin, a manufactured, proprietary isolate of purified reovirus, in children with relapsed/refractory extracranial solid tumors to define the recommended phase 2 dose (RP2D), toxicities, and pharmacokinetic properties when administered as a single agent or in combination with cyclophosphamide.

PROCEDURES

Reolysin was administered intravenously for 5 consecutive days, every 28 days. Using a 3 + 3 design, the following dose levels were evaluated: 3 × 10(8) Tissue Culture Inhibitory Dose 50% (TCID50 )/kg; 5 × 10(8) TCID50 /kg (maximum dose was 3 × 10(10) TCID50 ); and 5 × 10(8) TCID50 /kg plus oral cyclophosphamide (50 mg/m(2) /day × 21 days).

RESULTS

Twenty-nine patients were enrolled; 28 were eligible and 24 were evaluable for toxicity and response. There were no hematologic dose-limiting toxicities. Grade 5 respiratory failure and a Grade 5 thromboembolic event were reported, both in the setting of progressive disease. The median time to clear the reovirus viremia was 6.5 days. Eight of 24 patients were viremic beyond the 5 days of therapy, all were negative by day 17. No patient had detectable viral RNA in saliva or stool. There were no objective responses.

CONCLUSIONS

Reolysin at a dose of 5 × 10(8) TCID50 /kg daily for 5 days was well tolerated in children alone and in combination with oral cyclophosphamide. Virus was cleared rapidly from the serum and shedding in stool and saliva was not detectable.

Reovirus double-stranded RNA genomes and polyI:C induce down-regulation of hypoxia-inducible factor 1α

Reovirus has genomes consisting of 10-segmented double-stranded RNAs, and have received much attention as an oncolytic virus. A previous study reported that reovirus down-regulates hypoxia-inducible factor 1α (HIF-1α) protein levels following infection in tumor cells, which contributes to the antitumor effects of reovirus; however, the mechanism remains to be elucidated. In this study, we examined which virus component was involved in reovirus-mediated down-regulation of HIF-1α. Reovirus induced significant down-regulation of HIF-1α protein levels in not only reovirus-permissive tumor cells but also reovirus-resistant tumor cells. UV-inactivated reovirus also induced a reduction in HIF-1α protein levels. These data indicate that reovirus induces HIF-1α down-regulation independently of virus replication. Furthermore, transfection with not only reovirus genomes but also polyI:C efficiently induced HIF-1α down-regulation in a manner similar to reovirus, indicating that double-stranded reovirus RNA genomes are a key component for HIF-1α down-regulation. Reovirus-mediated HIF-1α down-regulation was inhibited when tumor cells were pretreated with inhibitors of cathepsins B and L, which play a crucial role in endo-lysosomal escape of virions to the cytoplasm. These data suggest that endo-lysosomal escape of reovirus genome into the cytoplasm is crucial for HIF-1α down-regulation; however, the retinoic acid-inducible gene-I (RIG-I) or interferon-β promoter stimulator-1 (IPS-1), which are involved in reovirus genome-induced innate immunity in the cytoplasm, did not play a crucial role in reovirus-mediated HIF-1α reduction.

Proteolytic disassembly of viral outer capsid proteins is crucial for reovirus-mediated type-I interferon induction in both reovirus-susceptible and reovirus-refractory tumor cells

Oncolytic reovirus induces innate immune responses, which contribute to the antitumor activity of reovirus, following in vivo application. Reovirus-induced innate immune responses have been relatively well characterized in immune cells and mouse embryonic fibroblasts cells; however, the mechanisms and profiles of reovirus-induced innate immune responses in human tumor cells have not been well understood. In particular, differences in reovirus-induced innate immune responses between reovirus-susceptible and reovirus-refractory tumor cells remain unknown, although the intracellular trafficking of reovirus differs between these tumor cells. In this study, we examined reovirus-induced upregulation of interferon- (IFN-) β and of the proapoptotic gene, Noxa, in reovirus-susceptible and -refractory tumor cells. IFN-β and Noxa were significantly induced by reovirus via the IFN-β promoter stimulator-1 (IPS-1) signaling in both types of tumor cells. Inhibition of cathepsins B and L, which are important for disassembly of reovirus outer capsid proteins and escape into cytoplasm, largely suppressed reovirus-induced upregulation of IFN-β and Noxa expression in not only reovirus-susceptible but also reovirus-refractory tumor cells. These results indicated that in both reovirus-susceptible and reovirus-refractory tumor cells, disassembly of the outer capsid proteins by cathepsins and the escape into the cytoplasm were crucial steps for reovirus-induced innate immunity.

The oncolytic virus, pelareorep, as a novel anticancer agent: a review

Pelareorep (REOLYSIN®) is an investigational new drug, a proprietary formulation consisting of a live, replication-competent, naturally occurring Reovirus Type 3 Dearing strain. Through several preclinical studies it was determined that reovirus can exhibit profound cytotoxic effects on cancer cells predominantly with an activated RAS-signalling pathway. Moreover, it was discovered that reoviruses can "hitchhike" on peripheral blood mononuclear cells and dendritic cells, thereby evading neutralizing antibodies of the host immune system. Cell carriage, targeted delivery, triggering host immune response and other inherent characteristics of the reovirus led to its further advancement into cancer therapy. When injected into Sprague-Dawley rats, the viral routes of clearance, predominantly through the spleen and liver, remained consistent with earlier studies. Toxicology findings were considered incidental and not associated with pelareorep when tested in animal models. Pelareorep demonstrated a high level of homogeneity at the amino acid level and genetic stability when compared to the master and working virus banks. The drug is manufactured in a 100 L bioreactor after which it is purified and formulated for use in pre-clinical, clinical and research studies. Over the past few decades, we have witnessed a paradigm shift from conventional therapy to the conceivable use of oncolytic viruses for the treatment of cancer. This review will detail pre-clinical evidence of anticancer activity of pelareorep that has led to extensive clinical development. Several Phase I-II clinical trials have been completed or are ongoing in cancer patients on a broad spectrum of solid tumors and hematologic malignancies.

Oncolytic reovirus combined with trastuzumab enhances antitumor efficacy through TRAIL signaling in human HER2-positive gastric cancer cells

The human epidermal growth factor receptor 2 (HER2)-targeting agent, trastuzumab, is effective for HER2-overexpressing gastric cancer therapy. As oncolytic reovirus is currently undergoing clinical trials internationally, we wanted to explore whether combination therapy using trastuzumab and reovirus might provide a novel, more effective therapeutic option for gastric cancer. Cell proliferation and cell apoptosis were examined in vitro, while molecular analysis of pathways responsible for cell damage was examined using polymerase chain reaction array. Activation of the proteins related to apoptosis, cell growth and survival was detected by Western blotting. Mouse tumor xenograft models were used to examine antitumor activity in vivo. Reovirus sensitized HER2-overexpressing gastric cancer cells to undergo apoptosis. Both in vitro and in vivo studies provided evidence that the combination therapy is a more powerful modality against HER2-overexpressing gastric cancer cells than treatment using a single agent. Molecular analysis indicated that combination therapy induced significantly higher levels of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in cancer cells. Antibody against TRAIL strongly inhibited cell toxicity caused by the combined treatment. These data suggest that reovirus may augment trastuzumab-induced cytotoxicity in gastric cancer cells.

Amino acids substitutions in σ1 and μ1 outer capsid proteins of a Vero cell-adapted mammalian orthoreovirus are required for optimal virus binding and disassembly

In a recent study, the serotype 3 Dearing strain of mammalian orthoreovirus was adapted to Vero cells; cells that exhibit a limited ability to support the early steps of reovirus uncoating and are unable to produce interferon as an antiviral response upon infection. The Vero cell-adapted virus (VeroAV) exhibits amino acids substitutions in both the σ1 and μ1 outer capsid proteins but no changes in the σ3 protein. Accordingly, the virus was shown not to behave as a classical uncoating mutant. In the present study, an increased ability of the virus to bind at the Vero cell surface was observed and is likely associated with an increased ability to bind onto cell-surface sialic acid residues. In addition, the kinetics of μ1 disassembly from the virions appears to be altered. The plasmid-based reverse genetics approach confirmed the importance of σ1 amino acids substitutions in VeroAV's ability to efficiently infect Vero cells, although μ1 co-adaptation appears necessary to optimize viral infection. This approach of combining in vitro selection of reoviruses with reverse genetics to identify pertinent amino acids substitutions appears promising in the context of eventual reovirus modification to increase its potential as an oncolytic virus.

Bio-distribution study of Reolysin® (pelareorep) through a single intravenous infusion in Sprague-Dawley rats

Numerous pre-clinical and clinical studies on reovirus have generated valuable information which supports the use of this orphan virus as an investigational drug for cancer treatment. Reolysin® (pelareorep) is a clinical formulation of the human Reovirus Type 3 Dearing strain. The clinical safety and efficacy of Reolysin® in humans is being tested on an assortment of cancer indications as a mono and/or combination therapy. Reovirus has many inherent characteristics that make it a potential candidate for virotherapy, including: the rapid and natural spread through the haematogenous route, the ability to overcome immunological barriers thereby reaching tumor sites, and being replication-competent. The purpose of this study was to elucidate the bio-distribution pattern of Reolysin® in healthy Sprague-Dawley rats. Following a single 15-min intravenous infusion via the tail vein in Sprague-Dawley rats, the levels of virus genome were determined in 16 organs/tissues by RT-qPCR (Reverse Transcriptase- Quantitative Polymerase Chain Reaction) over a 336 h (Day 15) incubation regime. Consistent with previous studies, maximal reovirus RNA levels were observed in the spleen; indicating its involvement in viral uptake and clearance, followed by heart, ovaries, tail (infusion site), liver and lungs. All the organs/tissues demonstrated unquantifiable levels of reovirus genome at the end of incubation, suggesting substantial to complete viral clearance. Several studies in the last decade have described the use of reovirus for treating ovarian cancers. An increase of reovirus genome in ovaries at 24 h post infection was noted. The results will aid in the design of additional exploratory clinical trials for Reolysin®.

Activated ras signaling pathways and reovirus oncolysis: an update on the mechanism of preferential reovirus replication in cancer cells

The development of wild-type, unmodified Type 3 Dearing strain reovirus as an anticancer agent has currently expanded to 32 clinical trials (both completed and ongoing) involving reovirus in the treatment of cancer. It has been more than 30 years since the potential of reovirus as an anticancer agent was first identified in studies that demonstrated the preferential replication of reovirus in transformed cell lines but not in normal cells. Later investigations have revealed the involvement of activated Ras signaling pathways (both upstream and downstream) and key steps of the reovirus infectious cycle in promoting preferential replication in cancer cells with reovirus-induced cancer cell death occurring through necrotic, apoptotic, and autophagic pathways. There is increasing evidence that reovirus-induced antitumor immunity involving both innate and adaptive responses also contributes to therapeutic efficacy though this discussion is beyond the scope of this article. Here, we review our current understanding of the mechanism of oncolysis contributing to the broad anticancer activity of reovirus. Further understanding of reovirus oncolysis is critical in enhancing the clinical development and efficacy of reovirus.

Trial Watch:: Oncolytic viruses for cancer therapy

Oncolytic viruses are natural or genetically modified viral species that selectively infect and kill neoplastic cells. Such an innate or exogenously conferred specificity has generated considerable interest around the possibility to employ oncolytic viruses as highly targeted agents that would mediate cancer cell-autonomous anticancer effects. Accumulating evidence, however, suggests that the therapeutic potential of oncolytic virotherapy is not a simple consequence of the cytopathic effect, but strongly relies on the induction of an endogenous immune response against transformed cells. In line with this notion, superior anticancer effects are being observed when oncolytic viruses are engineered to express (or co-administered with) immunostimulatory molecules. Although multiple studies have shown that oncolytic viruses are well tolerated by cancer patients, the full-blown therapeutic potential of oncolytic virotherapy, especially when implemented in the absence of immunostimulatory interventions, remains unclear. Here, we cover the latest advances in this active area of translational investigation, summarizing high-impact studies that have been published during the last 12 months and discussing clinical trials that have been initiated in the same period to assess the therapeutic potential of oncolytic virotherapy in oncological indications.

The interplay of reovirus with autophagy

Autophagy participates in multiple fundamental physiological processes, including survival, differentiation, development, and cellular homeostasis. It eliminates cytoplasmic protein aggregates and damaged organelles by triggering a series of events: sequestering the protein substrates into double-membrane vesicles, fusing the vesicles with lysosomes, and then degrading the autophagic contents. This degradation pathway is also involved in various disorders, for instance, cancers and infectious diseases. This paper provides an overview of modulation of autophagy in the course of reovirus infection and also the interplay of autophagy and reovirus.

Armed therapeutic viruses - a disruptive therapy on the horizon of cancer immunotherapy

For the past 150 years cancer immunotherapy has been largely a theoretical hope that recently has begun to show potential as a highly impactful treatment for various cancers. In particular, the identification and targeting of immune checkpoints have given rise to exciting data suggesting that this strategy has the potential to activate sustained antitumor immunity. It is likely that this approach, like other anti-cancer strategies before it, will benefit from co-administration with an additional therapeutic and that it is this combination therapy that may generate the greatest clinical outcome for the patient. In this regard, oncolytic viruses are a therapeutic moiety that is well suited to deliver and augment these immune-modulating therapies in a highly targeted and economically advantageous way over current treatment. In this review, we discuss the blockade of immune checkpoints, how oncolytic viruses complement and extend these therapies, and speculate on how this combination will uniquely impact the future of cancer immunotherapy.

Model-based rational design of an oncolytic virus with improved therapeutic potential

Oncolytic viruses are complex biological agents that interact at multiple levels with both tumour and normal tissues. Antiviral pathways induced by interferon are known to have a critical role in determining tumour cell sensitivity and normal cell resistance to infection with oncolytic viruses. Here we pursue a synthetic biology approach to identify methods that enhance antitumour activity of oncolytic viruses through suppression of interferon signalling. On the basis of the mathematical analysis of multiple strategies, we hypothesize that a positive feedback loop, established by virus-mediated expression of a soluble interferon-binding decoy receptor, increases tumour cytotoxicity without compromising normal cells. Oncolytic rhabdoviruses engineered to express a secreted interferon antagonist have improved oncolytic potential in cellular cancer models, and display improved therapeutic potential in tumour-bearing mice. Our results demonstrate the potential of this methodology in evaluating potential caveats of viral immune-evasion strategies and improving the design oncolytic viruses.

Reolysin is a novel reovirus-based agent that induces endoplasmic reticular stress-mediated apoptosis in pancreatic cancer

Activating mutation of KRas is a genetic alteration that occurs in the majority of pancreatic tumors and is therefore an ideal therapeutic target. The ability of reoviruses to preferentially replicate and induce cell death in transformed cells that express activated Ras prompted the development of a reovirus-based formulation for cancer therapy called Reolysin. We hypothesized that Reolysin exposure would trigger heavy production of viral products leading to endoplasmic reticular (ER) stress-mediated apoptosis. Here, we report that Reolysin treatment stimulated selective reovirus replication and decreased cell viability in KRas-transformed immortalized human pancreatic duct epithelial cells and pancreatic cancer cell lines. These effects were associated with increased expression of ER stress-related genes, ER swelling, cleavage of caspase-4, and splicing of XBP-1. Treatment with ER stress stimuli including tunicamycin, brefeldin A, and bortezomib (BZ) augmented the anticancer activity of Reolysin. Cotreatment with BZ and Reolysin induced the simultaneous accumulation of ubiquitinated and viral proteins, resulting in enhanced levels of ER stress and apoptosis in both in vitro and in vivo models of pancreatic cancer. Our collective results demonstrate that the abnormal protein accumulation induced by the combination of Reolysin and BZ promotes heightened ER stress and apoptosis in pancreatic cancer cells and provides the rationale for a phase I clinical trial further investigating the safety and efficacy of this novel strategy.

Trial watch: Oncolytic viruses for cancer therapy

Oncolytic virotherapy is emerging as a promising approach for the treatment of several neoplasms. The term "oncolytic viruses" is generally employed to indicate naturally occurring or genetically engineered attenuated viral particles that cause the demise of malignant cells while sparing their non-transformed counterparts. From a conceptual standpoint, oncolytic viruses differ from so-called "oncotropic viruses" in that only the former are able to kill cancer cells, even though both display a preferential tropism for malignant tissues. Of note, such a specificity can originate at several different steps of the viral cycle, including the entry of virions (transductional specificity) as well as their intracellular survival and replication (post-transcriptional and transcriptional specificity). During the past two decades, a large array of replication-competent and replication-incompetent oncolytic viruses has been developed and engineered to express gene products that would specifically promote the death of infected (cancer) cells. However, contrarily to long-standing beliefs, the antineoplastic activity of oncolytic viruses is not a mere consequence of the cytopathic effect, i.e., the lethal outcome of an intense, productive viral infection, but rather involves the elicitation of an antitumor immune response. In line with this notion, oncolytic viruses genetically modified to drive the local production of immunostimulatory cytokines exert more robust therapeutic effects than their non-engineered counterparts. Moreover, the efficacy of oncolytic virotherapy is significantly improved by some extent of initial immunosuppression (facilitating viral replication and spread) followed by the administration of immunostimulatory molecules (boosting antitumor immune responses). In this Trial Watch, we will discuss the results of recent clinical trials that have evaluated/are evaluating the safety and antineoplastic potential of oncolytic virotherapy.

Transient high level mammalian reovirus replication in a bat epithelial cell line occurs without cytopathic effect

Mammalian reoviruses exhibit a large host range and infected cells are generally killed; however, most studies examined only a few cell types and host species, and are probably not representative of all possible interactions between virus and host cell. Many questions thus remain concerning the nature of cellular factors that affect viral replication and cell death. In the present work, it was observed that replication of the classical mammalian reovirus serotype 3 Dearing in a bat epithelial cell line, Tb1.Lu, does not result in cell lysis and is rapidly reduced to very low levels. Prior uncoating of virions by chymotrypsin treatment, to generate infectious subviral particles, increased the initial level of infection but without any significant effect on further viral replication or cell survival. Infected cells remain resistant to virus reinfection and secrete an antiviral factor, most likely interferon, that is protective against the unrelated encephalomyocarditis virus. Although, the transformed status of a cell is believed to promote reovirus replication and viral "oncolysis", resistant Tb1.Lu cells exhibit a classical phenotype of transformed cells by forming colonies in semisolid soft agar medium. Further transduction of Tb.Lu cells with a constitutively active Ras oncogene does not seem to affect cell growth or reovirus effect on these cells. Infected Tb1.Lu cells can produce low-level of infectious virus for a long time without any apparent effect, although these cells are resistant to reinfection. The results suggest that Tb1.Lu cells can mount an unusual antiviral response. Specific properties of bat cells may thus be in part responsible for the ability of the animals to act as reservoirs for viruses in general and for novel reoviruses in particular. Their peculiar resistance to cell lysis also makes Tb1.Lu cells an attractive model to study the cellular and viral factors that determine the ability of reovirus to replicate and destroy infected cells.

Isolation of reovirus T3D mutants capable of infecting human tumor cells independent of junction adhesion molecule-A

Mammalian Reovirus is a double-stranded RNA virus with a distinctive preference to replicate in and lyse transformed cells. On that account, Reovirus type 3 Dearing (T3D) is clinically evaluated as oncolytic agent. The therapeutic efficacy of this approach depends in part on the accessibility of the reovirus receptor Junction Adhesion Molecule-A (JAM-A) on the target cells. Here, we describe the isolation and characterization of reovirus T3D mutants that can infect human tumor cells independent of JAM-A. The JAM-A-independent (jin) mutants were isolated on human U118MG glioblastoma cells, which do not express JAM-A. All jin mutants harbour mutations in the S1 segments close to the region that encodes the sialic acid-binding pocket in the shaft of the spike protein. In addition, two of the jin mutants encode spike proteins with a Q336R substitution in their head domain. The jin mutants can productively infect a wide range of cell lines that resist wt reovirus T3D infection, including chicken LMH cells, hamster CHO cells, murine endothelioma cells, human U2OS and STA-ET2.1 cells, but not primary human fibroblasts. The jin-mutants rely on the presence of sialic-acid residues on the cell surface for productive infection, as is evident from wheat germ agglutinin (WGA) inhibition experiments, and from the jin-reovirus resistance of CHO-Lec2 cells, which have a deficiency of sialic-acids on their glycoproteins. The jin mutants may be useful as oncolytic agents for use in tumors in which JAM-A is absent or inaccessible.

Cell carriage, delivery, and selective replication of an oncolytic virus in tumor in patients

Oncolytic viruses, which preferentially lyse cancer cells and stimulate an antitumor immune response, represent a promising approach to the treatment of cancer. However, how they evade the antiviral immune response and their selective delivery to, and replication in, tumor over normal tissue has not been investigated in humans. Here, we treated patients with a single cycle of intravenous reovirus before planned surgery to resect colorectal cancer metastases in the liver. Tracking the viral genome in the circulation showed that reovirus could be detected in plasma and blood mononuclear, granulocyte, and platelet cell compartments after infusion. Despite the presence of neutralizing antibodies before viral infusion in all patients, replication-competent reovirus that retained cytotoxicity was recovered from blood cells but not plasma, suggesting that transport by cells could protect virus for potential delivery to tumors. Analysis of surgical specimens demonstrated greater, preferential expression of reovirus protein in malignant cells compared to either tumor stroma or surrounding normal liver tissue. There was evidence of viral factories within tumor, and recovery of replicating virus from tumor (but not normal liver) was achieved in all four patients from whom fresh tissue was available. Hence, reovirus could be protected from neutralizing antibodies after systemic administration by immune cell carriage, which delivered reovirus to tumor. These findings suggest new preclinical and clinical scheduling and treatment combination strategies to enhance in vivo immune evasion and effective intravenous delivery of oncolytic viruses to patients in vivo.

REO-001: A phase I trial of percutaneous intralesional administration of reovirus type 3 dearing (Reolysin®) in patients with advanced solid tumors

PURPOSE

This open-labeled, phase I clinical trial was designed to determine the safety and tolerability of percutaneous intralesional administration of wild-type oncolytic revovirus type 3 Dearing (Reolysin®) in cancer patients with accessible and evaluable disease, who had otherwise failed to improve on standard cancer interventions.

EXPERIMENTAL DESIGN

An escalating dose of Reolysin® starting from up to 10(10) plague forming units (PFU) was administered to each cohort of three patients per dose level. Viral shedding, reovirus neutralizing antibody response, toxicity and clinical response were assessed.

RESULTS

Nineteen patients with various advanced solid tumors were treated. The most common toxicities related to treatment were grade 2 (or less) local erythema and transient flu like symptoms. Viral shedding was not seen in cerebral spinal fluid (CSF), urine and stool samples in all patients. Rising viral antibody titres were seen in all patients. In addition, we observed some evidence of local target tumor response activity in 7/19 patients (37 %) at the end of six or more weeks follow-up, with one patient exhibiting a complete response (CR), two a partial response (PR), and four stable disease (SD) to the local injected lesion.

CONCLUSIONS

Reolysin® is well tolerated given intralesionaly, with DLT/MTD not reached at a dose of 10(10) PFU. The favorable toxicity profile, lack of viral shedding and possible therapeutic activity has made this unattenuated oncolytic reovirus an attractive cancer therapeutic agent for ongoing clinical studies, including in the setting of locally advanced accessible disease for palliation of symptoms.

Reovirus variants with mutations in genome segments S1 and L2 exhibit enhanced virion infectivity and superior oncolysis

Reovirus preferentially replicates in transformed cells and is being explored as a cancer therapy. Immunological and physical barriers to virotherapy inspired a quest for reovirus variants with enhanced oncolytic potency. Using a classical genetics approach, we isolated two reovirus variants (T3v1 and T3v2) with superior replication relative to wild-type reovirus serotype 3 Dearing (T3wt) on various human and mouse tumorigenic cell lines. Unique mutations in reovirus λ2 vertex protein and σ1 cell attachment protein were associated with the large plaque-forming phenotype of T3v1 and T3v2, respectively. Both T3v1 and T3v2 exhibited higher infectivity (i.e., a higher PFU-to-particle ratio) than T3wt. A detailed analysis of virus replication revealed that virus cell binding and uncoating were equivalent for variant and wild-type reoviruses. However, T3v1 and T3v2 were significantly more efficient than T3wt in initiating productive infection. Thus, when cells were infected with equivalent input virus particles, T3v1 and T3v2 produced significantly higher levels of early viral RNAs relative to T3wt. Subsequent steps of virus replication (viral RNA and protein synthesis, virus assembly, and cell death) were equivalent for all three viruses. In a syngeneic mouse model of melanoma, both T3v1 and T3v2 prolonged mouse survival compared to wild-type reovirus. Our studies reveal that oncolytic potency of reovirus can be improved through distinct mutations that increase the infectivity of reovirus particles.

A novel classification of lung cancer into molecular subtypes

The remarkably heterogeneous nature of lung cancer has become more apparent over the last decade. In general, advanced lung cancer is an aggressive malignancy with a poor prognosis. The discovery of multiple molecular mechanisms underlying the development, progression, and prognosis of lung cancer, however, has created new opportunities for targeted therapy and improved outcome. In this paper, we define "molecular subtypes" of lung cancer based on specific actionable genetic aberrations. Each subtype is associated with molecular tests that define the subtype and drugs that may potentially treat it. We hope this paper will be a useful guide to clinicians and researchers alike by assisting in therapy decision making and acting as a platform for further study. In this new era of cancer treatment, the 'one-size-fits-all' paradigm is being forcibly pushed aside-allowing for more effective, personalized oncologic care to emerge.

Addition of exogenous polypeptides on the mammalian reovirus outer capsid using reverse genetics

Addition of exogenous peptide sequences on viral capsids is a powerful approach to study the process of viral infection or to retarget viruses toward defined cell types. Until recently, it was not possible to manipulate the genome of mammalian reovirus and this was an obstacle to the addition of exogenous sequence tags onto the capsid of a replicating virus. This obstacle has now been overcome by the availability of the plasmid-based reverse genetics system. In the present study, reverse genetics was used to introduce different exogenous peptides, up to 40 amino acids long, at the carboxyl-terminal end of the σ1 outer capsid protein. The tagged viruses obtained were infectious, produce plaques of similar size, and could be easily propagated at high titers. However, attempts to introduce a 750 nucleotides-long sequence failed, even when it was added after the stop codon, suggesting a possible size limitation at the nucleic acid level.

Reovirus therapy stimulates endoplasmic reticular stress, NOXA induction, and augments bortezomib-mediated apoptosis in multiple myeloma

Oncolytic virotherapy with reovirus has demonstrated anti-cancer activity and minimal toxicity in clinical trials, but the mechanisms underlying these effects have not been fully elucidated. Reolysin, a proprietary formulation of reovirus for cancer therapy, stimulated selective viral replication and apoptosis in multiple myeloma (MM) cells. Reolysin-mediated apoptosis was associated with an induction of endoplasmic reticular (ER) stress-related gene expression, swelling of the endoplasmic reticulum, increases in intracellular calcium levels and a strong induction of the Bcl-2 homology 3 (BH3)-only pro-apoptotic protein NOXA. Knockdown of NOXA expression by short hairpin RNA significantly reduced the pro-apoptotic effects of Reolysin. We next showed that co-administration of Reolysin and bortezomib resulted in the dual accumulation of viral and ubiquitinated proteins, which led to enhanced ER stress, NOXA induction and apoptosis. Importantly, the combination of reovirus infection and proteasomal inhibition significantly decreased tumor burden in a xenograft and syngeneic bone disease model of MM without exhibiting adverse side effects. Our study establishes ER stress stimulation and NOXA induction as novel mediators of reovirus-induced apoptosis. Furthermore, reovirus infection can be used as a promising approach to augment the anti-myeloma activity of bortezomib by promoting additional stress to the endoplasmic reticulum of MM cells.

Oncolytic virus-initiated protective immunity against prostate cancer

Recently reovirus-based oncotherapy has been successfully implemented for the treatment of prostate cancer. In this report, we show that apart from its primary direct cancer-killing activity, reovirus oncotherapy overrides tumor-associated immune evasion strategies and confers protective antiprostate cancer immunity. Prostate cancer represents an ideal target for immunotherapies. However, currently available immune interventions fail to induce clinically significant antiprostate cancer immune responses, owing to the immunosuppressive microenvironment associated with this disease. We show here that during the process of oncolysis, reovirus acts upon prostate cancer cells and initiates proinflammatory cytokines and major histocompatibility complex (MHC) class I molecule expression. In an immunocompetent transgenic adenocarcinoma of mouse prostate (TRAMP) model, reovirus oncotherapy induces the homing of CD8(+) T and NK cells in tumors and the display of tumor-associated antigens (TAAs) on antigen-presenting cells (APCs), and endows dendritic cells (DCs) with a capacity to successfully present TAAs to tumor-specific CD8(+) T cells. These newly generated immunological events lead to the development of strong antiprostate cancer T cell responses, which restrict the growth of subsequently, implanted syngeneic tumor in an antigen-specific, but reovirus-independent manner. Such reovirus-initiated antiprostate cancer immunity represents a clinically valuable entity that can promote long-term cancer-free health even after discontinuation of the primary oncotherapy.

Pancreatic cancer gene therapy: from molecular targets to delivery systems

The continuous identification of molecular changes deregulating critical pathways in pancreatic tumor cells provides us with a large number of novel candidates to engineer gene-targeted approaches for pancreatic cancer treatment. Targets—both protein coding and non-coding—are being exploited in gene therapy to influence the deregulated pathways to facilitate cytotoxicity, enhance the immune response or sensitize to current treatments. Delivery vehicles based on viral or non-viral systems as well as cellular vectors with tumor homing characteristics are a critical part of the design of gene therapy strategies. The different behavior of tumoral versus non-tumoral cells inspires vector engineering with the generation of tumor selective products that can prevent potential toxic-associated effects. In the current review, a detailed analysis of the different targets, the delivery vectors, the preclinical approaches and a descriptive update on the conducted clinical trials are presented. Moreover, future possibilities in pancreatic cancer treatment by gene therapy strategies are discussed.

Initial testing of the replication competent Seneca Valley virus (NTX-010) by the pediatric preclinical testing program

BACKGROUND

Seneca Valley virus (NTX-010) is a non-recombinant, replication competent RNA virus that is undergoing phase 1 clinical trials in adults for tumors with neuroendocrine characteristics. Here we have evaluated the antitumor activity of NTX-010 administered systemically.

PROCEDURES

In vitro NTX-010 was tested against 23 cell lines exposed for 96 hr at 1 x 10(-4) to 10(4) viral particles (vp)/cell. In vivo NTX-010 was administered intravenously once at 3 x 10(12) vp/kg. Three measures of antitumor activity were used: (1) an objective response measure modeled after the clinical setting; (2) a treated to control (T/C) tumor volume measure; and (3) a time to event (fourfold increase in tumor volume for solid tumor models), measure based on the median event-free survival (EFS) of treated and control animals for each xenograft.

RESULTS

In vitro NTX-010 demonstrated a marked cytotoxic effect in a subset of the cell lines from the neuroblastoma, Ewing sarcoma, and rhabdomyosarcoma panels. In vivo the most consistent activity was observed for the rhabdomyosarcoma and the neuroblastoma panels, with all four of the alveolar rhabdomyosarcoma xenografts and four of five neuroblastoma xenografts achieving CR or maintained CR. Objective responses were also observed in the rhabdoid tumor, Wilms tumor, and glioblastoma panels.

CONCLUSIONS

NTX-010 demonstrated a high level of activity both in vitro and in vivo. Further analysis of existing testing and molecular characterization data may help define the biological characteristics of cancer cells that are associated with response to NTX-010.

Modification of mammalian reoviruses for use as oncolytic agents

The Reoviridae are a family of viruses with a non-enveloped icosahedral capsid and a segmented double-stranded RNA genome. Prototypes of the mammalian Orthoreoviruses have been isolated from human respiratory and enteric tracts and are not associated with human disease. One of these, human reovirus type 3 Dearing (T3D), usually serves as a model for the family. In the last decade the mammalian Orthoreoviruses, especially T3D, have been evaluated as oncolytic agents in experimental cancer therapy. This is based on the observation that reoviruses induce cell death and apoptosis in tumor cells, but not in healthy non-transformed cells. Several clinical trials have been initiated in Canada, the USA, and the UK, to study the feasibility and safety of this approach. Due to the segmented structure of their double-stranded RNA genomes genetic modification of Reoviridae has been notoriously difficult. Several techniques have been described recently that facilitate the genetic modification of reovirus genomes. The basis for reverse genetics of reovirus is the discovery in 1990 that reovirus RNA is infectious. Subsequently, it took ten years before a foreign gene was introduced into the reovirus genome. Here we review the methods for reovirus modification and their use for generating new reovirus-derived oncolytic agents.

An improved reverse genetics system for mammalian orthoreoviruses

Mammalian orthoreoviruses (reoviruses) are highly useful models for studies of double-stranded RNA virus replication and pathogenesis. We previously developed a strategy to recover prototype reovirus strain T3D from cloned cDNAs transfected into murine L929 fibroblast cells. Here, we report the development of a second-generation reovirus reverse genetics system featuring several major improvements: (1) the capacity to rescue prototype reovirus strain T1L, (2) reduction of required plasmids from 10 to 4, and (3) isolation of recombinant viruses following transfection of baby hamster kidney cells engineered to express bacteriophage T7 RNA polymerase. The efficiency of virus rescue using the 4-plasmid strategy was substantially increased in comparison to the original 10-plasmid system. We observed full compatibility of T1L and T3D rescue vectors when intermixed to produce a panel of T1LxT3D monoreassortant viruses. Improvements to the reovirus reverse genetics system enhance its applicability for studies of reovirus biology and clinical use.