Replicating poxviruses for human cancer therapy

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

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

A Comparative Study of Oncolytic Vaccinia Viruses Harboring Different Marine Lectins in Breast Cancer Cells

Our previous studies demonstrated that arming vaccinia viruses with marine lectins enhanced the antitumor efficacy in several cancer cells. This study aims to compare the efficacy of oncolytic vaccinia viruses harboring Tachypleus tridentatus lectin (oncoVV-TTL), Aphrocallistes vastus lectin (oncoVV-AVL), white-spotted charr lectin (oncoVV-WCL), and Asterina pectinifera lectin (oncoVV-APL) in breast cancer cells (BC). These results indicated that oncoVV-AVL elicited the highest anti-tumor effect, followed by oncoVV-APL, while oncoVV-TTL and oncoVV-WCL had lower effects in BC. Further studies showed that apoptosis and replication may work together to enhance the cytotoxicity of oncoVV-lectins in a cell-type dependent manner. TTL/AVL/APL/WCL may mediate multiple pathways, including ERK, JNK, Hippo, and PI3K pathways, to promote oncoVV replication in MDA-MB-231 cells. In contrast, these pathways did not affect oncoVV-TTL/AVL/APL/WCL replication in MCF-7 cells, suggesting that the mechanisms of recombinant viruses in MCF-7 (ER⁺, PR⁺) and MDA-MB-231 (TNBC) cells were significantly different. Based on this study, we hypothesized that ER or PR may be responsible for the differences in promoting viral replication and inducing apoptosis between MCF-7 and MDA-MB-231 cells, but the specific mechanism needs to be further explored. In addition, small-molecule drugs targeting key cellular signaling pathways, including MAPK, PI3K/Akt, and Hippo, could be conjunction with oncoVV-AVL to promote breast cancer therapy, and key pathway factors in the JNK and PI3K pathways may be related to the efficacy of oncoVV-APL/TTL/WCL. This study provides a basis for applying oncolytic vaccinia virus in breast carcinoma.

The OH system: A panorama view of the PPV-host interaction

Poxviruses are a family of specialized cytoplasm-parasitic DNA viruses that replicate and assembly in virus factory. In Parapoxvirus (PPV) genus, with the orf virus (ORFV) as a representative species of this genus, their behaviors are significantly different from that of Orthopoxvirus, and the plots of viral practical solutions for evading host immunity are intricate and fascinating, particularly to anti-host and host's antiviral mechanisms. In order to protect the virus factory from immune elimination caused by infection, PPVs attempt to interfere with multiple stress levels of host, mainly by modulating innate immunity response (IIR) and adaptive immunity response (AIR). Given that temporarily constructed by virus infection, ORFV-HOST (OH) system accompanied by viral strategies is carefully managed in the virus factory, thus directing many life-critical events once undergoing the IIR and AIR. Evolutionarily, to reduce the risk of system destruction, ORFV have evolved into a mild-looking mode to avoid overstimulation. Moreover, the current version of development also focus on recognizing and hijacking more than eight antiviral security mechanisms of host cells, such as the 2',5'-oligoadenylate synthetase (OAS)/RNase L and PKR systems, the ubiquitin protease system (UPS), and so on. In summary, this review assessed inescapable pathways as mentioned above, through which viruses compete with their hosts strategically. The OH system provides a panoramic view and a powerful platform for us to study the PPV-Host interaction, as well as the corresponding implications on a great application potential in anti-virus design.

Poxvirus-driven human diseases and emerging therapeutics

Poxviridae have been successful pathogens throughout recorded history, infecting humans among a variety of other hosts. Although eradication of the notorious smallpox has been a globally successful healthcare phenomenon, the recent emergence of Monkeypox virus, also belonging to the Orthopoxvirus genus and causing human disease, albeit milder than smallpox, is a cause of significant public health concern. The ongoing outbreak of monkeypox, demonstrating human-human transmission, in previously nonendemic countries, calls for critical need into further research in the areas of viral biology, ecology, and epidemiology to better understand, prevent and treat human infections. In the wake of these recent events, it becomes important to revisit poxviral infections, their pathogenesis and ability to cause infection across multiple nonhuman hosts and leap to a human host. The poxviruses that cause human diseases include Monkeypox virus, Molluscum contagiosum virus, and Orf virus. In this review, we summarize the current understanding of various poxviruses causing human diseases, provide insights into their replication and pathogenicity, disease progression and symptoms, preventive and treatment options, and their importance in shaping modern medicine through application in gene therapy, oncolytic viral therapies for human cancers, or as poxvirus vectors for vaccines.

Oncolytic Vaccinia Virus Expressing White-Spotted Charr Lectin Regulates Antiviral Response in Tumor Cells and Inhibits Tumor Growth In Vitro and In Vivo

Oncolytic vaccina virus (oncoVV) used for cancer therapy has progressed in recent years. Here, a gene encoding white-spotted charr lectin (WCL) was inserted into an oncoVV vector to form an oncoVV-WCL recombinant virus. OncoVV-WCL induced higher levels of apoptosis and cytotoxicity, and replicated faster than control virus in cancer cells. OncoVV-WCL promoted IRF-3 transcriptional activity to induce higher levels of type I interferons (IFNs) and blocked the IFN-induced antiviral response by inhibiting the activity of IFN-stimulated responsive element (ISRE) and the expression of interferon-stimulated genes (ISGs). The higher levels of viral replication and antitumor activity of oncoVV-WCL were further demonstrated in a mouse xenograft tumor model. Therefore, the engineered oncoVV expressing WCL might provide a new avenue for anticancer gene therapy.

Anti-Tumor Effects of MAPK-Dependent Tumor-Selective Oncolytic Vaccinia Virus Armed with CD/UPRT against Pancreatic Ductal Adenocarcinoma in Mice

Engineered vaccinia virus serves as an oncolytic virus for cancer virotherapy. We evaluated the oncolytic characteristics of VGF- and O1-deleted recombinant mitogen-activated protein kinase (MAPK)-dependent vaccinia virus (MDRVV). We found that compared with viruses with the deletion of either gene alone, MDRVV is more attenuated in normal cells and can replicate in cancer cells that exhibit constitutive ERK1/2 activation in the MAPK pathway. We armed MDRVV with a bifunctional fusion gene encoding cytosine deaminase and uracil phosphoribosyltransferase (CD/UPRT), which converts 5-fluorocytosine (5-FC) into chemotherapeutic agents, and evaluated its oncolytic activity alone or in combination with 5-FC in human pancreatic cancer cell lines, tumor mouse models of peritoneal dissemination and liver metastasis, and ex vivo-infected live pancreatic cancer patient-derived tissues. CD/UPRT-armed MDRVV alone could efficiently eliminate pancreatic cancers, and its antitumor effects were partially enhanced in combination with 5-FC in vitro and in vivo. Moreover, the replication of MDRVV was detected in tumor cells of patient-derived, surgically resected tissues, which showed enlarged nuclei and high expression of pERK1/2 and Ki-67, and not in stromal cells. Our findings suggest that systemic injections of CD/UPRT-armed MDRVV alone or in combination with 5-FC are promising therapeutic strategies for pancreatic ductal adenocarcinoma.

Oncolytic Virotherapy for Malignant Tumor: Current Clinical Status

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

Novel Oncolytic Virus Armed with Cancer Suicide Gene and Normal Vasculogenic Gene for Improved Anti-Tumor Activity

Here, we developed a novel oncolytic vaccinia virus (NOV) with the dual advantages of cancer selectivity and normal vessel reconstructive activity by replacing the viral thymidine kinase (vTk) and vaccinia growth factor (VGF) genes with genes encoding TNF-related apoptosis-inducing ligand (TRAIL) and angiopoietin 1 (Ang1), respectively. The pan-cancer-specific oncolytic potency of NOV was confirmed in various human and mouse cancer cell lines (colon, liver, pancreas, cholangiocarcinoma, cervical cancer, osteosarcoma, and melanoma). Vaccinia virus (VV) treatment directly induced early apoptosis in tumors within 24 h, and this effect was enhanced with further engineering; VGF and Tk deletion with Ang1 and TRAIL insertion. Meanwhile, treatment with the conventional anti-cancer drug cisplatin did not induce apoptosis. A virus-treated CT26 mouse colon cancer syngeneic model showed attenuated tumor growth, which was in accordance with the results of percent survival measurement, CD8 expression analysis, and TUNEL staining with advanced genetic engineering (vAng1 < vTRAIL < NOV). Taken together, our results indicate that NOV induces cancer tissue apoptosis and anti-tumor immunity and may constitute a highly advantageous therapeutic agent for next-generation solid tumor virotherapy with pan-cancer-specific oncolytic activity and high biosafety.

Target Therapy With Vaccinia Virus Harboring IL-24 For Human Breast Cancer

Background: Breast cancer is a heterogeneous disease with high aggression and novel targeted therapeutic strategies are required. Oncolytic vaccinia virus is an attractive candidate for cancer treatment due to its tumor cell-specific replication causing lysis of tumor cells as well as a delivery vector to overexpress therapeutic transgenes. Interleukin-24 (IL-24) is a novel tumor suppressor cytokine that selectively induces apoptosis in a wide variety of tumor types, including breast cancer. In this study, we used vaccinia virus as a delivery vector to express IL-24 gene and antitumor effects were evaluated both in vitro and in vivo. Methods: The vaccinia virus strain Guang9 armed with IL-24 gene (VG9-IL-24) was constructed via disruption of the viral thymidine kinase (TK) gene region. The cytotoxicity of VG9-IL-24 in various breast cancer cell lines was assessed by MTT and cell cycle progression and apoptosis were examined by flow cytometry. In vivo antitumor effects were further observed in MDA-MB-231 xenograft mouse model. Results: In vitro, VG9-IL-24 efficiently infected and selectively killed breast cancer cells with no strong cytotoxicity to normal cells. VG9-IL-24 induced increased number of apoptotic cells and blocked breast cancer cells in the G2/M phase of the cell cycle. Western blotting results indicated that VG9-IL-24-mediated apoptosis was related to PI3K/β-catenin signaling pathway. In vivo, VG9-IL-24 delayed tumor growth and improved survival. Conclusions: Our findings provided documentation that VG9-IL-24 was targeted in vitro and exhibited enhanced antitumor effects, and it may be an innovative therapy for breast cancer.

Poxvirus oncolytic virotherapy

INTRODUCTION

Over the last decade, advances in biological therapies have resulted in remarkable clinical responses for the treatment of some previously incurable cancers. Oncolytic virotherapy is one of these promising novel strategies for cancer therapy. A successful oncolytic virus promotes tumor cell oncolysis and elicits a robust long-term anti-tumor immunity.

AREAS COVERED

Oncolytic poxviruses (Vaccinia virus and Myxoma virus) demonstrated encouraging results in multiple pre-clinical tumor models and some clinical trials for the treatment of various cancers. This review summarizes the advances made on poxvirus oncolytic virotherapy in the last five years.

EXPERT OPINION

Many challenges remain in poxvirus oncolytic virotherapy. Two key goals to achieve are enhancing the efficiency of viral delivery to tumor sites and overcoming local tumor immune-evasion. Additional efforts are necessary to explore the best combination of virotherapy with standard available treatments, particularly immunotherapies. By addressing these issues, this new modality will continue to improve as an adjunct biotherapy to treat malignant diseases.

Viral and metazoan poxins are cGAMP-specific nucleases that restrict cGAS-STING signalling

Cytosolic DNA triggers innate immune responses through the activation of cyclic GMP-AMP synthase (cGAS) and production of the cyclic dinucleotide second messenger 2',3'-cyclic GMP-AMP (cGAMP)1-4. 2',3'-cGAMP is a potent inducer of immune signalling; however, no intracellular nucleases are known to cleave 2',3'-cGAMP and prevent the activation of the receptor stimulator of interferon genes (STING)5-7. Here we develop a biochemical screen to analyse 24 mammalian viruses, and identify poxvirus immune nucleases (poxins) as a family of 2',3'-cGAMP-degrading enzymes. Poxins cleave 2',3'-cGAMP to restrict STING-dependent signalling and deletion of the poxin gene (B2R) attenuates vaccinia virus replication in vivo. Crystal structures of vaccinia virus poxin in pre- and post-reactive states define the mechanism of selective 2',3'-cGAMP degradation through metal-independent cleavage of the 3'-5' bond, converting 2',3'-cGAMP into linear Gp[2'-5']Ap[3']. Poxins are conserved in mammalian poxviruses. In addition, we identify functional poxin homologues in the genomes of moths and butterflies and the baculoviruses that infect these insects. Baculovirus and insect host poxin homologues retain selective 2',3'-cGAMP degradation activity, suggesting an ancient role for poxins in cGAS-STING regulation. Our results define poxins as a family of 2',3'-cGAMP-specific nucleases and demonstrate a mechanism for how viruses evade innate immunity.

Mutagenic repair of double-stranded DNA breaks in vaccinia virus genomes requires cellular DNA ligase IV activity in the cytosol

Poxviruses comprise a group of large dsDNA viruses that include members relevant to human and animal health, such as variola virus, monkeypox virus, cowpox virus and vaccinia virus (VACV). Poxviruses are remarkable for their unique replication cycle, which is restricted to the cytoplasm of infected cells. The independence from the host nucleus requires poxviruses to encode most of the enzymes involved in DNA replication, transcription and processing. Here, we use the CRISPR/Cas9 genome engineering system to induce DNA damage to VACV (strain Western Reserve) genomes. We show that targeting CRISPR/Cas9 to essential viral genes limits virus replication efficiently. Although VACV is a strictly cytoplasmic pathogen, we observed extensive viral genome editing at the target site; this is reminiscent of a non-homologous end-joining DNA repair mechanism. This pathway was not dependent on the viral DNA ligase, but critically involved the cellular DNA ligase IV. Our data show that DNA ligase IV can act outside of the nucleus to allow repair of dsDNA breaks in poxvirus genomes. This pathway might contribute to the introduction of mutations within the genome of poxviruses and may thereby promote the evolution of these viruses.

Development of improved therapeutic mesothelin-based vaccines for pancreatic cancer

Pancreatic cancer is the 5^th leading cause of cancer deaths, and there are no effective treatments. We developed a poxvirus platform vaccine with improved immunogenicity and inserted the mesothelin gene to create an anti-mesothelin cancer vaccine. Mesothelin expression is mostly restricted to tumors in adult mammals and thus may be a good target for cancer treatment. We show here that the modified vaccinia virus Ankara (MVA) virus expressing mesothelin and the enhanced MVA virus missing the immunosuppressive A35 gene and expressing mesothelin were both safe in mice and were able to induce IFN-gamma secreting T cells in response to mesothelin expressing tumor cells. In addition, the MVA virus has oncolytic properties in vitro as it can replicate in and kill Panc02 pancreatic adenocarcinoma cell line tumor cells, even though it is unable to replicate in most mammalian cells. Deletion of the A35 gene in MVA improved T cell responses as expected. However, we were unable to demonstrate inhibition of Panc02 tumor growth in immunocompetent mice with pre-vaccination of mice, boosts, or even intratumoral injections of the recombinant viruses. Vaccine efficacy may be limited by shedding of mesothelin from tumor cells thus creating a protective screen from the immune system.

Intra-tumoral delivery of CXCL11 via a vaccinia virus, but not by modified T cells, enhances the efficacy of adoptive T cell therapy and vaccines

T cell trafficking into tumors depends on a "match" between chemokine receptors on effector cells (e.g., CXCR3 and CCR5) and tumor-secreted chemokines. There is often a chemokine/chemokine receptor "mismatch", with tumors producing minute amounts of chemokines, resulting in inefficient targeting of effectors to tumors. We aimed to alter tumors to produce higher levels of CXCL11, a CXCR3 ligand, to attract more effector cells following immunotherapy. Mice bearing established subcutaneous tumors were studied. In our first approach, we used modified chimeric antigen receptor (CAR)-transduced human T cells to deliver CXCL11 (CAR/CXCL11) into tumors. In our second approach, we intravenously (iv) administered a modified oncolytic vaccinia virus (VV) engineered to produce CXCL11 (VV.CXCL11). The effect of these treatments on T cell trafficking into the tumors and anti-tumor efficacy after subsequent CAR T cell injections or anti-tumor vaccines was determined. CAR/CXCL11 and VV.CXCL11 significantly increased CXCL11 protein levels within tumors. For CAR/CXCL11, injection of a subsequent dose of CAR T cells did not result in increased intra-tumoral trafficking, and appeared to decrease the function of the injected CAR T cells. In contrast, VV.CXCL11 increased the number of total and antigen-specific T cells within tumors after CAR T cell injection or vaccination and significantly enhanced anti-tumor efficacy. Both approaches were successful in increasing CXCL11 levels within the tumors; however, only the vaccinia approach was successful in recruiting T cells and augmenting anti-tumor efficacy. VV.CXCL11 should be considered as a potential approach to augment adoptive T cell transfer or vaccine immunotherapy.

Primary lymphocyte infection models for KSHV and its putative tumorigenesis mechanisms in B cell lymphomas

Kaposi's sarcoma-associated herpesvirus (KSHV) is the latest addition to the human herpesvirus family. Unlike alpha- and beta-herpesvirus subfamily members, gamma-herpesviruses, including Epstein-Barr virus (EBV) and KSHV, cause various tumors in humans. KSHV primarily infects endothelial and B cells in vivo, and is associated with at least three malignancies: Kaposi's sarcoma and two B cell lymphomas, respectively. Although KSHV readily infects endothelial cells in vitro and thus its pathogenic mechanisms have been extensively studied, B cells had been refractory to KSHV infection. As such, functions of KSHV genes have mostly been elucidated in endothelial cells in the context of viral infection but not in B cells. Whether KSHV oncogenes, defined in endothelial cells, play the same roles in the tumorigenesis of B cells remains an open question. Only recently, through a few ground-breaking studies, B cell infection models have been established. In this review, those models will be compared and contrasted and putative mechanisms of KSHV-induced B cell transformation will be discussed.

Oncolytic viruses: emerging options for the treatment of breast cancer

Breast cancer (BC) is the most common type of cancer among women and is the second most common cause of cancer-related deaths, following lung cancer. Severe toxicity associated with a long-term use of BC chemo- and radiotherapy makes it essential to look for newer therapeutics. Additionally, molecular heterogeneity at both intratumoral and intertumoral levels among BC subtypes is known to result in a differential response to standard therapeutics. Oncolytic viruses (OVs) have emerged as one of the most promising treatment options for BC. Many preclinical and clinical studies have shown that OVs are effective in treating BC, both as a single therapeutic agent and as a part of combination therapies. Combination therapies involving multimodal therapeutics including OVs are becoming popular as they allow to achieve the synergistic therapeutic effects, while minimizing the associated toxicities. Here, we review the OVs for BC therapy in preclinical studies and in clinical trials, both as a monotherapy and as part of a combination therapy. We also briefly discuss the potential therapeutic targets for BC, as these are likely to be critical for the development of new OVs.

Single-particle characterization of oncolytic vaccinia virus by flow virometry

Vaccinia virus (VV) is an oncolytic virus that is currently being evaluated as a promising cancer vaccine in several phase I, II and III clinical trials. Although several quality control tests are performed on each new batch of virus, these do not routinely include a systematic characterization of virus particle homogeneity, or relate the infectious titer to the total number of submicron sized particles (SSPs) present in the sample. SSPs are comprised of infectious virus and non-infectious viral particles, but also cell contaminants derived from the virus isolation procedures, such as cellular vesicles and debris. Here we have employed flow virometry (FV) analysis and sorting to isolate and characterize distinct SSP populations in therapeutic oncolytic VV preparations. We show that VV preparations contain SSPs heterogeneous in size and include large numbers of non-infectious VV particles. Furthermore, we used FV to illustrate how VV has a propensity to aggregate over time and under various handling and storage procedures. Accordingly, we find that together the infectious titer, the total number of SSPs, the number of viral genomes and the level of particle aggregation in a sample constitute useful parameters that greatly facilitate inter-sample assessment of physical quality, and also provides a means to monitor sample deterioration over time. Additionally, we have successfully employed FV sorting to further isolate virus from other particles by identifying a lipophilic dye that preferentially stains VV over other SSPs in the sample. Overall, we demonstrate that FV is a fast and effective tool that can be used to perform quality, and consistency control assessments of oncolytic VV vaccine preparations.

Oncolytic virus efficiency inhibited growth of tumour cells with multiple drug resistant phenotype in vivo and in vitro

Background

Tumour resistance to a wide range of drugs (multiple drug resistant, MDR) acquired after intensive chemotherapy is considered to be the main obstacle of the curative treatment of cancer patients. Recent work has shown that oncolytic viruses demonstrated prominent potential for effective treatment of diverse cancers. Here, we evaluated whether genetically modified vaccinia virus (LIVP-GFP) may be effective in treatment of cancers displaying MDR phenotype.

Methods

LIVP-GFP replication, transgene expression and cytopathic effects were analysed in human cervical carcinomas KB-3-1 (MDR−), KB-8-5 (MDR+) and in murine melanoma B-16 (MDR−), murine lymphosarcomas RLS and RLS-40 (MDR+). To investigate the efficacy of this therapy in vivo, we treated immunocompetent mice bearing murine lymphosarcoma RLS-40 (MDR+) (6- to 8-week-old female CBA mice; n = 10/group) or melanoma B-16 (MDR−) (6- to 8-week-old female C57Bl mice; n = 6/group) with LIVP-GFP (5 × 10⁷ PFU of virus in 0.1 mL of IMDM immediately and 4 days after tumour implantation).

Results

We demonstrated that LIVP-GFP replication was effective in human cervical carcinomas KB-3-1 (MDR−) and KB-8-5 (MDR+) and in murine melanoma B-16 (MDR−), whereas active viral production was not detected in murine lymphosarcomas RLS and RLS-40 (MDR+). Additionally, it was found that in tumour models in immunocompetent mice under the optimized regimen intratumoural injections of LIVP-GFP significantly inhibited melanoma B16 (33 % of mice were with complete response after 90 days) and RLS-40 tumour growth (fourfold increase in tumour doubling time) as well as metastasis.

Conclusion

The anti-tumour activity of LIVP-GFP is a result of direct oncolysis of tumour cells in case of melanoma B-16 because the virus effectively replicates and destroys these cells, and virus-mediated activation of the host immune system followed by immunologically mediated destruction of of tumour cells in case of lymphosarcoma RLS-40. Thus, the recombinant vaccinia virus LIVP-GFP is able to inhibit the growth of malignant cells with the MDR phenotype and tumour metastasis when administered in the early stages of tumour development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1002-x) contains supplementary material, which is available to authorized users.

Naturally occurring reoviruses for human cancer therapy

Naturally occurring reoviruses are live replication-proficient viruses that specifically infect human cancer cells while sparing their normal counterpart. Since the discovery of reoviruses in 1950s, they have shown various degrees of safety and efficacy in pre-clinical or clinical applications for human anti-cancer therapeutics. I have recently discovered that cellular tumor suppressor genes are also important in determining reoviral tropism. Carcinogenesis is a multi-step process involving the accumulation of both oncogene and tumor suppressor gene abnormalities. Reoviruses can exploit abnormal cellular tumor suppressor signaling for their oncolytic specificity and efficacy. Many tumor suppressor genes such as p53, ataxia telangiectasia mutated (ATM), and retinoblastoma associated (RB) are known to play important roles in genomic fidelity/maintenance. Thus, a tumor suppressor gene abnormality could affect host genomic integrity and likely disrupt intact antiviral networks due to the accumulation of genetic defects which in turn could result in oncolytic reovirus susceptibility. This review outlines the discovery of oncolytic reovirus strains, recent progresses in elucidating the molecular connection between oncogene/tumor suppressor gene abnormalities and reoviral oncotropism, and their clinical implications. Future directions in the utility of reovirus virotherapy is also proposed in this review.

Oncolytic virotherapy for urological cancers

Oncolytic virotherapy is a cancer treatment in which replication-competent viruses are used that specifically infect, replicate in and lyse malignant tumour cells, while minimizing harm to normal cells. Anecdotal evidence of the effectiveness of this strategy has existed since the late nineteenth century, but advances and innovations in biotechnological methods in the 1980s and 1990s led to a renewed interest in this type of therapy. Multiple clinical trials investigating the use of agents constructed from a wide range of viruses have since been performed, and several of these enrolled patients with urological malignancies. Data from these clinical trials and from preclinical studies revealed a number of challenges to the effectiveness of oncolytic virotherapy that have prompted the development of further sophisticated strategies. Urological cancers have a range of distinctive features, such as specific genetic mutations and cell surface markers, which enable improving both effectiveness and safety of oncolytic virus treatments. The strategies employed in creating advanced oncolytic agents include alteration of the virus tropism, regulating transcription and translation of viral genes, combination with chemotherapy, radiotherapy or gene therapy, arming viruses with factors that stimulate the immune response against tumour cells and delivery technologies to ensure that the viral agent reaches its target tissue.

Use of Reporter Genes in the Generation of Vaccinia Virus-Derived Vectors

Vaccinia virus (VACV) is one of the most extensively-studied viruses of the Poxviridae family. It is easy to genetically modify, so it has become a key tool for many applications. In this context, reporter genes facilitate the study of the role of foreign genes introduced into the genome of VACV. In this review, we describe the type of reporter genes that have been used to generate reporter-expressing VACV and the applications of the recombinant viruses obtained. Reporter-expressing VACV are currently employed in basic and immunology research, in the development of vaccines and cancer treatment.

Features of the Antitumor Effect of Vaccinia Virus Lister Strain

Oncolytic abilities of vaccinia virus (VACV) served as a basis for the development of various recombinants for treating cancer; however, "natural" oncolytic properties of the virus are not examined in detail. Our study was conducted to know how the genetically unmodified L-IVP strain of VACV produces its antitumor effect. Human A431 carcinoma xenografts in nude mice and murine Ehrlich carcinoma in C57Bl mice were used as targets for VACV, which was injected intratumorally. A set of virological methods, immunohistochemistry, light and electron microscopy was used in the study. We found that in mice bearing A431 carcinoma, the L-IVP strain was observed in visceral organs within two weeks, but rapidly disappeared from the blood. The L-IVP strain caused decrease of sizes in both tumors, however, in different ways. Direct cell destruction by replicating virus plays a main role in regression of A431 carcinoma xenografts, while in Ehrlich carcinoma, which poorly supported VACV replication, the virus induced decrease of mitoses by pushing tumor cells into S-phase of cell cycle. Our study showed that genetically unmodified VACV possesses at least two mechanisms of antitumor effect: direct destruction of tumor cells and suppression of mitoses in tumor cells.