Development of a Conditionally Replicating Pseudorabies Virus for HER-2/neu-overexpressing Bladder 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.

Porcine Astrovirus Infection in Brains of Pigs in Korea

Recently, neurological diseases associated with astroviruses (AstVs) have been reported in pigs, ruminants, minks, and humans. In 2017, neuro-invasive porcine astrovirus (Ni-PAstV) 3 was detected in the central nervous system (CNS) of pigs with encephalomyelitis in Hungary and the USA. In the process of diagnosing domestic pigs exhibiting neurological signs, histopathologic lesions of non-suppurative encephalomyelitis with meningitis, neuronal vacuolation, and gliosis were detected, and PAstV was identified using reverse transcriptase PCR in CNS samples of four pigs in three farms from August to September in 2020, South Korea. Subsequently, the ORF2 region was successfully acquired from three brain samples, facilitating subsequent analysis. Four genotypes of PAstV (PAstV1, 3, 4, and 5) were detected, and coinfection of PAstV with multiple genotypes was observed in brain samples. This is the first study to report Ni-PAstV infection in pigs in South Korea.

The potential of swine pseudorabies virus attenuated vaccine for oncolytic therapy against malignant tumors

BACKGROUND

Oncolytic viruses are now well recognized as potential immunotherapeutic agents against cancer. However, the first FDA-approved oncolytic herpes simplex virus 1 (HSV-1), T-VEC, showed limited benefits in some patients in clinical trials. Thus, the identification of novel oncolytic viruses that can strengthen oncolytic virus therapy is warranted. Here, we identified a live-attenuated swine pseudorabies virus (PRV-LAV) as a promising oncolytic agent with broad-spectrum antitumor activity in vitro and in vivo.

METHODS

PRV cytotoxicity against tumor cells and normal cells was tested in vitro using a CCK8 cell viability assay. A cell kinase inhibitor library was used to screen for key targets that affect the proliferation of PRV-LAV. The potential therapeutic efficacy of PRV-LAV was tested against syngeneic tumors in immunocompetent mice, and against subcutaneous xenografts of human cancer cell lines in nude mice. Cytometry by time of flight (CyTOF) and flow cytometry were used to uncover the immunological mechanism of PRV-LAV treatment in regulating the tumor immune microenvironment.

RESULTS

Through various tumor-specific analyses, we show that PRV-LAV infects cancer cells via the NRP1/EGFR signaling pathway, which is commonly overexpressed in cancer. Further, we show that PRV-LAV kills cancer cells by inducing endoplasmic reticulum (ER) stress. Moreover, PRV-LAV is responsible for reprogramming the tumor microenvironment from immunologically naïve ("cold") to inflamed ("hot"), thereby increasing immune cell infiltration and restoring CD8+ T cell function against cancer. When delivered in combination with immune checkpoint inhibitors (ICIs), the anti-tumor response is augmented, suggestive of synergistic activity.

CONCLUSIONS

PRV-LAV can infect cancer cells via NRP1/EGFR signaling and induce cancer cells apoptosis via ER stress. PRV-LAV treatment also restores CD8+ T cell function against cancer. The combination of PRV-LAV and immune checkpoint inhibitors has a significant synergistic effect. Overall, these findings point to PRV-LAV as a serious potential candidate for the treatment of NRP1/EGFR pathway-associated tumors.

A Recombinant Oncolytic Pseudorabies Virus Expressing Interleukin-18, Interferon-Gamma and PH20 Genes Promotes Systemic Antitumor Immunity

Pseudorabies virus (PRV) is considered to be a promising oncolytic virus that has potential as a cancer gene therapy drug. In this study, PRV-DCD-1-70 was used as a vector to carry exogenous genes IL-18, IFN-γ and PH20 to construct novel recombinant PRV, rPRV-PH20 and rPRV-IL-18-γ-PH20, and their tumorolytic effects were evaluated in vitro and in vivo. Our study showed that recombinant PRV lysed all four tumor cell lines, Pan02, EMT-6, CT26 and H446, and rPRV-IL-18-γ-PH20 showed the best tumor lysis effect. Further studies in mice bearing Pan02 tumors showed that recombinant PRV, especially rPRV-IL-18-γ-PH20, were able to inhibit tumor growth. Moreover, an immunohistochemical analysis indicated that the recombinant PRV effectively increased the infiltration of CD4⁺T and CD8⁺T cells and enhanced the anti-tumor immune response of the organism in vivo. Overall, PRV carrying PH20 and IL-18-γ exogenous genes demonstrated anti-tumor effects, providing a foundation for the further development and application of PRV as a novel tumor oncolytic virus vector.

Recent Advances in Molecular Mechanisms of Cancer Immunotherapy

Cancer is among the current leading causes of death worldwide, despite the novel advances that have been made toward its treatment, it is still considered a major public health concern. Considering both the serious impact of cancer on public health and the significant side effects and complications of conventional therapeutic options, the current strategies towards targeted cancer therapy must be enhanced to avoid undesired toxicity. Cancer immunotherapy has become preferable among researchers in recent years compared to conventional therapeutic options, such as chemotherapy, surgery, and radiotherapy. The understanding of how to control immune checkpoints, develop therapeutic cancer vaccines, genetically modify immune cells as well as enhance the activation of antitumor immune response led to the development of novel cancer treatments. In this review, we address recent advances in cancer immunotherapy molecular mechanisms. Different immunotherapeutic approaches are critically discussed, focusing on the challenges, potential risks, and prospects involving their use.

Oncolytic Viruses for the Treatment of Bladder Cancer: Advances, Challenges, and Prospects

Bladder cancer is one of the most prevalent cancers. Despite recent advancements in bladder cancer therapy, new strategies are still required for improving patient outcomes, particularly for those who experienced Bacille Calmette-Guerin failure and those with locally advanced or metastatic bladder cancer. Oncolytic viruses are either naturally occurring or purposefully engineered viruses that have the ability to selectively infect and lyse tumor cells while avoiding harming healthy cells. In light of this, oncolytic viruses serve as a novel and promising immunotherapeutic strategy for bladder cancer. A wide diversity of viruses, including adenoviruses, herpes simplex virus, coxsackievirus, Newcastle disease virus, vesicular stomatitis virus, alphavirus, and vaccinia virus, have been studied in many preclinical and clinical studies for their potential as oncolytic agents for bladder cancer. This review aims to provide an overview of the advances in oncolytic viruses for the treatment of bladder cancer and highlights the challenges and research directions for the future.

The Effects of Oncolytic Pseudorabies Virus Vaccine Strain Inhibited the Growth of Colorectal Cancer HCT-8 Cells In Vitro and In Vivo

Oncolytic viral therapy is a promising treatment approach for a variety of tumor forms. Although a number of studies have demonstrated that the pseudorabies virus (PRV) may be applied as an oncolytic carrier, the anti-colorectal cancer impact of the virus and the mechanism of its cytotoxic effect remain elusive. In this study, the replication capacity and cell activity of PRV attenuated live vaccines Bartha K61 and HB98 in HCT-8 cells in vitro were investigated. Next, the antitumor ability and safety were evaluated in a mouse model of HCT-8 tumor transplantation. Both PRV strains were able to suppress tumor growth and HB98 showed higher safety and efficiency than the Bartha K61 strain. Finally, flow cytometry and immunohistochemistry examination were performed to investigate its possible cytotoxic mechanism. The results showed that PRV inhibited tumor proliferation both in vitro and in vivo by inducing apoptosis. In summary, our study discovered for the first time that the live attenuated PRV has an oncolytic effect on HCT-8 cells with high efficacy and safety.

Structures of pseudorabies virus capsids

Pseudorabies virus (PRV) is a major etiological agent of swine infectious diseases and is responsible for significant economic losses in the swine industry. Recent data points to human viral encephalitis caused by PRV infection, suggesting that PRV may be able to overcome the species barrier to infect humans. To date, there is no available therapeutic for PRV infection. Here, we report the near-atomic structures of the PRV A-capsid and C-capsid, and illustrate the interaction that occurs between these subunits. We show that the C-capsid portal complex is decorated with capsid-associated tegument complexes. The PRV capsid structure is highly reminiscent of other α-herpesviruses, with some additional structural features of β- and γ-herpesviruses. These results illustrate the structure of the PRV capsid and elucidate the underlying assembly mechanism at the molecular level. This knowledge may be useful for the development of oncolytic agents or specific therapeutics against this arm of the herpesvirus family.

Etoposide enhances antitumor efficacy of MDR1-driven oncolytic adenovirus through autoupregulation of the MDR1 promoter activity

Conditionally replicating adenoviruses (CRAds), or oncolytic adenoviruses, such as E1B55K-deleted adenovirus, are attractive anticancer agents. However, the therapeutic efficacy of E1B55K-deleted adenovirus for refractory solid tumors has been limited. Environmental stress conditions may induce nuclear accumulation of YB-1, which occurs in multidrug-resistant and adenovirus-infected cancer cells. Overexpression and nuclear localization of YB-1 are associated with poor prognosis and tumor recurrence in various cancers. Nuclear YB-1 transactivates the multidrug resistance 1 (MDR1) genes through the Y-box. Here, we developed a novel E1B55K-deleted adenovirus driven by the MDR1 promoter, designed Ad5GS3. We tested the feasibility of using YB-1 to transcriptionally regulate Ad5GS3 replication in cancer cells and thereby to enhance antitumor efficacy. We evaluated synergistic antitumor effects of oncolytic virotherapy in combination with chemotherapy. Our results show that adenovirus E1A induced E2F-1 activity to augment YB-1 expression, which shut down host protein synthesis in cancer cells during adenovirus replication. In cancer cells infected with Ad5WS1, an E1B55K-deleted adenovirus driven by the E1 promoter, E1A enhanced YB-1 expression, and then further phosphorylated Akt, which, in turn, triggered nuclear translocation of YB-1. Ad5GS3 in combination with chemotherapeutic agents facilitated nuclear localization of YB-1 and, in turn, upregulated the MDR1 promoter activity and enhanced Ad5GS3 replication in cancer cells. Thus, E1A, YB-1, and the MDR1 promoter form a positive feedback loop to promote Ad5GS3 replication in cancer cells, and this regulation can be further augmented when chemotherapeutic agents are added. In the in vivo study, Ad5GS3 in combination with etoposide synergistically suppressed tumor growth and prolonged survival in NOD/SCID mice bearing human lung tumor xenografts. More importantly, Ad5GS3 exerted potent oncolytic activity against clinical advanced lung adenocarcinoma, which was associated with elevated levels of nuclear YB-1 and cytoplasmic MDR1 expression in the advanced tumors. Therefore, Ad5GS3 may have therapeutic potential for cancer treatment, especially in combination with chemotherapy. Because YB-1 is expressed in a broad spectrum of cancers, this oncolytic adenovirus may be broadly applicable.

Construction of recombinant pseudorabies viruses by using PRV BACs deficient in IE180 or pac sequences: Application of vBAC90D recombinant virus to production of PRV amplicons

We describe a simple and efficient method to obtain recombinant pseudorabies virus (PRV) in mammalian cells by using the PRV BACs, PBAC80 deficient in pac sequences and PBAC90 deficient in the IE180 gene. These essential viral sequences were used as targets to obtain viable recombinant viruses. PBAC80 was constructed, confirmed to encode a copy of the IE180 gene regulated by the inducible Ptet promoter, and used to obtain recombinant attenuated PRV viruses that express the EGFP protein (PRV-BT80GF virus). PBAC90 was used to obtain the vBAC90D virus, deficient in IE180 and free of replication-competent revertants, and which can be used as a helper in the production of PRV amplicons.

Expression of the immediate early IE180 protein under the control of the hTERT and CEA tumor-specific promoters in recombinant pseudorabies viruses: Effects of IE180 protein on promoter activity and apoptosis induction

Since the pseudorabies virus (PRV) genome encodes for a single immediate-early protein, IE180, we reasoned that this strong transactivating protein could represent a key regulatory switch that could be genetically manipulated in order to alter its tropism towards cancer cells. We therefore initiated studies to test whether the human telomerase reverse transcriptase (hTERT) and carcinoembryonic antigen (CEA) tumor promoters could functionally replace the IE180 promoter. We show that both promoters can functionally substitute the IE180 promoter in plasmid constructs and recombinant viruses, and observed that IE180 differentially auto-regulated each promoter tested, with PRV IE180 negatively regulating the hTERT promoter but positively hyper-activating the CEA promoter. Interestingly, we also observed that the recombinant PRV-TER and PRV-CEA viruses preferentially replicated in diverse cancer cell lines compared to control non-cancer cells, and the PRV-CEA was capable of additionally inducing a profound apoptotic phenotype which we correlated to the overexpression of IE180.

In vivo anti-cancer efficacy of magnetite nanocrystal--based system using locoregional hyperthermia combined with 5-fluorouracil chemotherapy

We present an approach for synchronizing hyperthermia and thermal-responsive local drug release. The targeting probe has a magnetite nanocrystal (Fe₃O₄@PSMA) core and a polynucleotide shell that carries 5-fluorouracil (5-FU) and anti-human epidermal growth factor receptor 2 (anti-HER2) antibody for cancer cell-specific targeting. The targeting nanocrystals play as an important role to relay the externally delivered radiofrequency energy for tumor hyperthermia. Locoregional heat then triggers a drug release from the oligonucleotide carrier as it directly damages tumor cells. Cell viability assays and pathological examinations show that this synchronization is significantly more efficacious in both in vitro and in vivo models than hyperthermia or chemotherapy alone. Prominent tumor remission in vivo was achieved through radiofrequency synchronization of hyperthermia and chemotherapy after the nanoparticle had been intravenously injected.

Enhancement of antitumor activity of gammaretrovirus carrying IL-12 gene through genetic modification of envelope targeting HER2 receptor: a promising strategy for bladder cancer therapy

The objective of this study was to develop an HER2-targeted, envelope-modified Moloney murine leukemia virus (MoMLV)-based gammaretroviral vector carrying interleukin (IL)-12 gene for bladder cancer therapy. It displayed a chimeric envelope protein containing a single-chain variable fragment (scFv) antibody to the HER2 receptor and carried the mouse IL-12 gene. The fragment of anti-erbB2scFv was constructed into the proline-rich region of the viral envelope of the packaging vector lacking a transmembrane subunit of the carboxyl terminal region of surface subunit. As compared with envelope-unmodified gammaretroviruses, envelope-modified ones had extended viral tropism to human HER2-expressing bladder cancer cell lines, induced apoptosis, and affected cell cycle progression despite lower viral titers. Moreover, animal studies showed that envelope-modified gammaretroviruses carrying IL-12 gene exerted higher antitumor activity in terms of retarding tumor growth and prolonging the survival of tumor-bearing mice than unmodified ones, which were associated with enhanced tumor cell apoptosis as well as increased intratumoral levels of IL-12, interferon-gamma, IL-1beta, and tumor necrosis factor-alpha proteins. Therefore, the antitumor activity of gammaretroviruses carrying the IL-12 gene was enhanced through genetic modification of the envelope targeting HER2 receptor, which may be a promising strategy for bladder cancer therapy.

Novel strategies to augment genetically delivered immunotoxin molecular therapy for cancer therapy

Immunotoxin therapy is a promising molecular cancer treatment strategy. Its main advantage is seletive cytotoxicity towards tumor cells and minimal toxicity in normal tissues. However, a short half-life and rapid clearance severely hampers its clinical application. We report here a novel genetic approach in which a recombinant adenovirus vector was used to deliver an immunotoxin gene e23(scFv)-PE40 targeted to the oncogene c-erbB-2 (also known as Her2/neu). This vector, when combined with a low dose of a conditionally replicative adenovirus vector (CRAd), has enhanced tumor-killing ability either alone or in combination with the chemotherapeutic agent etoposide. Our data show that low-dose CRAd facilitated the replication of replication-deficient Ad-e23(scFv)-PE40 up to 6-20 times and the transcription of e23(scFv)-PE40 gene up to 12 times. Moreover, etoposide increased the e23(scFv)-PE40 transcription up to 8.5 times. Furthermore, we show that systemic application of Ad-e23(scFv)-PE40 and enhanced expression of the immunotoxin gene was well tolerated as determined by serum biochemical markers and histological examination of most vital organs. Taken together, our data support a novel genetic immunotoxin delivery approach that may yield enhanced efficacy against a variety of Her2/neu-expressing tumors.