Current understanding of reovirus oncolysis mechanisms

The influence of the cytoskeleton on the development and behavior of viral factories in mammalian orthoreovirus

Cytosolic viral factories (VFs) of mammalian orthoreovirus (MRV) are sites for viral genome replication and assembly of virus progeny. Despite advancements in reverse genetics, the formation and dynamics of VFs still need to be clarified. MRV exploits host cytoskeletal components like microtubules (MTs) throughout its life cycle, including cell entry, replication, and release. MRV VFs, membrane-less cytosolic inclusions, rely on the viral proteins μ2 and μNS for formation. Protein μ2 interacts and stabilizes MTs through acetylation, supporting VF formation and viral replication, while scaffold protein μNS influences cellular components to aid VF maturation. The disruption of the MT network reduces viral replication, underscoring its importance. Additionally, μ2 associates with MT-organizing centers, modulating the MT dynamics to favor viral replication. In summary, MRV subverts the cytoskeleton to facilitate VF dynamics and promote viral replication and assembly to promote VF dynamics, replication, and assembly, highlighting the critical role of the cytoskeleton in viral replication.

Viral infections in celiac disease: what should be considered for better management

Following a gluten-free diet (GFD) is known as the main effective therapy available for celiac disease (CD) patients, which in some cases is not enough to heal all patients presentations completely. Accordingly, emerging researchers have focused on finding novel therapeutic/preventive strategies for this disorder. Moreover, previous studies have shown that celiac patients, especially untreated subjects, are at increased risk of developing viral and bacterial infections, which can become a challenge for the clinician. Viruses, such as Rotavirus, Reovirus, Adenovirus, Enterovirus, Rhinovirus, Astrovirus, Hepatitis virus, COVID-19, Norovirus, and Herpesvirus, have been related to CD pathogenesis. Therefore, clinicians need to pay more attention to evaluate CD patients' viral infection history (especially nonresponders to the GFD), to look for effective preventive strategies and educate patients about important risk factors. In addition, there are still viruses whose role in CD pathogenesis has not been fully studied. In this review, current information on the association between CD and various viral infections was gathered to improve knowledge in this subject area and draw researchers'/clinicians' attention to unstudied/less studied viruses in CD pathogenesis, which might guide future prevention approaches.

Human Melanoma and Glioblastoma Cells Express Cathepsins Supporting Reovirus Moscow Strain Infection

This study evaluates the oncolytic potential of the Moscow strain of reovirus against human metastatic melanoma and glioblastoma cells. The Moscow strain effectively infects and replicates within human melanoma cell lines and primary glioblastoma cells, while sparing non-malignant human cells. Infection leads to the selective destruction of neoplastic cells, mediated by functional viral replication. A positive correlation was identified between viral RNA accumulation and tumor cell death, with no replication observed in non-malignant cells. This study highlights the critical roles of cathepsins B, L, and S as mediators of the oncolytic process. The pharmacological inhibition of these enzymes significantly attenuated reovirus-induced cytotoxicity in melanoma and glioblastoma cells. Conversely, PKR production analysis revealed minimal activation in reovirus-infected tumor cells, suggesting that the hyperactivation of the RAS-signaling pathway and subsequent PKR inhibition do not directly contribute to the selective efficacy of reovirus. Moreover, infected tumor cells exhibited features of both apoptotic and non-apoptotic death, emphasizing the intricate mechanisms of reovirus-mediated oncolysis. These findings underscore the therapeutic promise of the Moscow strain of reovirus as a selective and potent oncolytic agent for targeting melanoma and glioblastoma cells.

Combination Therapy with Secretome of Reovirus-Infected Mesenchymal Stem Cells and Metformin Improves Anticancer Effects of Irinotecan on Colorectal Cancer Cells in vitro

INTRODUCTION

Irinotecan, a topoismorase 1 inhibitor, has been used for the treatment of colorectal cancer. It was shown that monotherapy alone is largely ineffective. The combination therapy was used for antitumor activity. The synergistic anticancer effects of oncolytic reovirus-infected secretome in combination with irinotecan and metformin are evaluated in vitro. The aim of research was to assess anticancer impacts of ReoT3D, irinotecan, metformin in combination, against murine colorectal cancer cells (CT26).

METHODS

The L929 and the CT26 colorectal cancerous cell lines were treated in vitro with irinotecan, metformin, the Dearing strain of reovirus serotype 3 (ReoT3D) (V), and the secretome of intact (S) or reovirus-infected murine adipose-derived mesenchymal stem cells (SV). The cell viability was measured by MTT, and the apoptosis rate was analyzed by annexin V-FITC staining and flow cytometry 48 and 72 h after treatment.

RESULTS

We found that cells exposed to a combination of SV+Met+I had significantly lower cell viability and higher apoptosis rates as compared to cells exposed to Met+I, 48 and 72 h. These results suggest that metformin in combination with irinotecan and reovirus produces a synergistic effect on cell death, and adding reovirus-infected secretome (SV) to a Met+I regimen induces a higher apoptosis rate compared to Met+I alone. Based on the results, the combination of SV+Met+I has induced more apoptosis than S, SV, SV+I, and SV+Met. Also, all of the combined treatments induced apoptosis significantly versus secretome alone.

DISCUSSION

In this in vitro study, we found that the combination of T3D reovirus (oncolytic virus) and metformin with the anticancer drug irinotecan resulted in higher rates of growth inhibition and apoptosis induction in the colorectal cancer cell line. This synergistic effect was even more pronounced when using the combination of secretome derived from reovirus-infected AD-MSCs, metformin, and irinotecan.

CONCLUSION

We highlight that the combination of ReoT3D-derived secretome with irinotecan and metformin showed a synergistic anticancer effect on the CT26 cell line, and this strategy may be considered as a new approach against colorectal cancer in the in vitro and in vivo in future studies.

Human umbilical cord mesenchymal stem cell exosomes deliver potent oncolytic reovirus to acute myeloid leukemia cells

In addition to chemotherapy, oncolytic viruses are an efficient treatment for acute myeloid leukemia (AML). Like other oncolytic viruses, the anti-tumor efficacy of reovirus when administered intravenously is reduced due to the presence of neutralizing antibodies. In this study, we evaluated the role of exosomes in human umbilical cord-derived mesenchymal stem cells (UC-MSCs) to deliver reovirus to AML cells. We show that UC-MSCs loaded with reovirus can deliver reovirus to tumor cells without cellular contact. We further demonstrate that the exosome inhibitor, GW4869, inhibits the release of exosomes as well as inhibited the transfer of reovirus from UC-MSCs to tumor cells. Mechanistically, we show that exosomes derived from reovirus-infected UC-MSCs (MSCREO-EXOs) have a tumor lysis effect and transmit reovirus to tumor cells mainly through clathrin-mediated endocytosis (CME) and macropinocytosis. In addition, we demonstrate the feasibility of using MSC-derived exosomes (MSC-EXOs) as a reovirus carrier to exert an anti-tumor effect on AML cells. Collectively, our data indicate that UC-MSCs transfer reovirus to AML cells via exosome release and prompt further study of MSC-EXOs as a potential reovirus carrier to treat AML.

The reovirus variant RP116 is oncolytic in immunocompetent models and generates reduced neutralizing antibodies to Type 3 Dearing

The mammalian reovirus Type 3 Dearing (T3D) is a naturally occurring oncolytic virus. We previously identified a T3D variant isolated from persistently infected cancer cells that has a premature stop codon mutation in the S1 gene, generating a truncated σ1-attachment protein that lacks the globular head. We now report on the molecular characterization of this variant, named RP116, and assess its antitumor potential in human cancer cells and syngeneic mouse models. RP116 replicates efficiently in several cancer cell lines, shows reduced dependency for the JAM-A receptor, significantly decreases tumor growth in syngeneic models when injected either intratumorally or intravenously, and generates long-term cures and immune memory in combination with checkpoint inhibitors. Finally, we demonstrate that RP116 infection in mice leads to reduced production of neutralizing antibodies directed against reovirus T3D, preserving the efficacy of subsequent reovirus treatment. These results establish the value of developing RP116 as an additional oncolytic reovirus platform.

Reovirus infection induces transcriptome-wide unique A-to-I editing changes in the murine fibroblasts

The conversion of Adenosine (A) to Inosine (I), by Adenosine Deaminases Acting on RNA or ADARs, is an essential post-transcriptional modification that contributes to proteome diversity and regulation in metazoans including humans. In addition to its transcriptome-regulating role, ADARs also play a major part in immune response to viral infection, where an interferon response activates interferon-stimulated genes, such as ADARp150, in turn dynamically regulating host-virus interactions. A previous report has shown that infection from reoviruses, despite strong activation of ADARp150, does not influence the editing of some of the major known editing targets, while likely editing others, suggesting a potentially nuanced editing pattern that may depend on different factors. However, the results were based on a handful of selected editing sites and did not cover the entire transcriptome. Thus, to determine whether and how reovirus infection specifically affects host ADAR editing patterns, we analyzed a publicly available deep-sequenced RNA-seq dataset, from murine fibroblasts infected with wild-type and mutant reovirus strains that allowed us to examine changes in editing patterns on a transcriptome-wide scale. To the best of our knowledge, this is the first transcriptome-wide report on host editing changes after reovirus infection. Our results demonstrate that reovirus infection induces unique nuanced editing changes in the host, including introducing sites uniquely edited in infected samples. Genes with edited sites are overrepresented in pathways related to immune regulation, cellular signaling, metabolism, and growth. Moreover, a shift in editing targets has also been observed, where the same genes are edited in infection and control conditions but at different sites, or where the editing rate is increased for some and decreased for other differential targets, supporting the hypothesis of dynamic and condition-specific editing by ADARs.

Targeting Innate Immunity in Glioma Therapy

Currently, there is a lack of effective therapies for the majority of glioblastomas (GBMs), the most common and malignant primary brain tumor. While immunotherapies have shown promise in treating various types of cancers, they have had limited success in improving the overall survival of GBM patients. Therefore, advancing GBM treatment requires a deeper understanding of the molecular and cellular mechanisms that cause resistance to immunotherapy. Further insights into the innate immune response are crucial for developing more potent treatments for brain tumors. Our review provides a brief overview of innate immunity. In addition, we provide a discussion of current therapies aimed at boosting the innate immunity in gliomas. These approaches encompass strategies to activate Toll-like receptors, induce stress responses, enhance the innate immune response, leverage interferon type-I therapy, therapeutic antibodies, immune checkpoint antibodies, natural killer (NK) cells, and oncolytic virotherapy, and manipulate the microbiome. Both preclinical and clinical studies indicate that a better understanding of the mechanisms governing the innate immune response in GBM could enhance immunotherapy and reinforce the effects of chemotherapy and radiotherapy. Consequently, a more comprehensive understanding of the innate immune response against cancer should lead to better prognoses and increased overall survival for GBM patients.

A promising future in cancer immunotherapy: Oncolytic viruses

Alongside the conventional methods, attention has been drawn to the use of immunotherapy-based methods for cancer treatment. Immunotherapy has developed as a therapeutic option that can be more specific with better outcomes in tumor treatment. It can boost or regulate the immune system behind the targeted virotherapy. Virotherapy is a kind of oncolytic immunotherapy that investigated broadly in cancer treatment in recent decades, due to its several advantages. According to recent advance in the field of understanding cancer cell biology and its occurrence, as well as increasing the knowledge about conditionally replicating oncolytic viruses and their destructive function in the tumor cells, nowadays, it is possible to apply this strategy in the treatment of malignancies. Relying on achievements in clinical trials of oncolytic viruses, we can certainly expect that this therapeutic perception can play a more central role in cancer treatment. In cancer treatment, combination therapy using oncolytic viruses alongside standard cancer treatment methods and other immunotherapy-based treatments can expect more promising results in the future.

Reovirus combined with a STING agonist enhances anti-tumor immunity in a mouse model of colorectal cancer

Reovirus, a naturally occurring oncolytic virus, initiates the lysis of tumor cells while simultaneously releasing tumor antigens or proapoptotic cytokines in the tumor microenvironment to augment anticancer immunity. However, reovirus has developed a strategy to evade antiviral immunity via its inhibitory effect on interferon production, which negatively affects the induction of antitumor immune responses. The mammalian adaptor protein Stimulator of Interferon Genes (STING) was identified as a key regulator that orchestrates immune responses by sensing cytosolic DNA derived from pathogens or tumors, resulting in the production of type I interferon. Recent studies reported the role of STING in innate immune responses to RNA viruses leading to the restriction of RNA virus replication. In the current study, we found that reovirus had a reciprocal reaction with a STING agonist regarding type I interferon responses in vitro; however, we found that the combination of reovirus and STING agonist enhanced anti-tumor immunity by enhancing cytotoxic T cell trafficking into tumors, leading to significant tumor regression and survival benefit in a syngeneic colorectal cancer model. Our data indicate the combination of reovirus and a STING agonist to enhance inflammation in the tumor microenvironment might be a strategy to improve oncolytic reovirus immunotherapy.

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.

Intertumoral Differences Dictate the Outcome of TGF-β Blockade on the Efficacy of Viro-Immunotherapy

The absence of T cells in the tumor microenvironment of solid tumors is a major barrier to cancer immunotherapy efficacy. Oncolytic viruses, including reovirus type 3 Dearing (Reo), can recruit CD8⁺ T cells to the tumor and thereby enhance the efficacy of immunotherapeutic strategies that depend on high T-cell density, such as CD3-bispecific antibody (bsAb) therapy. TGF-β signaling might represent another barrier to effective Reo&CD3-bsAb therapy due to its immunoinhibitory characteristics. Here, we investigated the effect of TGF-β blockade on the antitumor efficacy of Reo&CD3-bsAb therapy in the preclinical pancreatic KPC3 and colon MC38 tumor models, where TGF-β signaling is active. TGF-β blockade impaired tumor growth in both KPC3 and MC38 tumors. Furthermore, TGF-β blockade did not affect reovirus replication in both models and significantly enhanced the Reo-induced T-cell influx in MC38 colon tumors. Reo administration decreased TGF-β signaling in MC38 tumors but instead increased TGF-β activity in KPC3 tumors, resulting in the accumulation of α-smooth muscle actin (αSMA⁺) fibroblasts. In KPC3 tumors, TGF-β blockade antagonized the antitumor effect of Reo&CD3-bsAb therapy, even though T-cell influx and activity were not impaired. Moreover, genetic loss of TGF-β signaling in CD8⁺ T cells had no effect on therapeutic responses. In contrast, TGF-β blockade significantly improved therapeutic efficacy of Reo&CD3-bsAb in mice bearing MC38 colon tumors, resulting in a 100% complete response. Further understanding of the factors that determine this intertumor dichotomy is required before TGF-β inhibition can be exploited as part of viroimmunotherapeutic combination strategies to improve their clinical benefit.

Significance

Blockade of the pleiotropic molecule TGF-β can both improve and impair the efficacy of viro-immunotherapy, depending on the tumor model. While TGF-β blockade antagonized Reo&CD3-bsAb combination therapy in the KPC3 model for pancreatic cancer, it resulted in 100% complete responses in the MC38 colon model. Understanding factors underlying this contrast is required to guide therapeutic application.

Reovirus Type 3 Dearing Variants Do Not Induce Necroptosis in RIPK3-Expressing Human Tumor Cell Lines

Reoviruses are used as oncolytic viruses to destroy tumor cells. The concomitant induction of anti-tumor immune responses enhances the efficacy of therapy in tumors with low amounts of immune infiltrates before treatment. The reoviruses should provoke immunogenic cell death (ICD) to stimulate a tumor cell-directed immune response. Necroptosis is considered a major form of ICD, and involves receptor-interacting protein kinase 1 (RIPK1), RIPK3 and phosphorylation of mixed-lineage kinase domain-like protein (MLKL). This leads to cell membrane disintegration and the release of damage-associated molecular patterns that can activate immune responses. Reovirus Type 3 Dearing (T3D) can induce necroptosis in mouse L929 fibroblast cells and mouse embryonic fibroblasts. Most human tumor cell lines have a defect in RIPK3 expression and consequently fail to induce necroptosis as measured by MLKL phosphorylation. We used the human colorectal adenocarcinoma HT29 cell line as a model to study necroptosis in human cells since this cell line has frequently been described in necroptosis-related studies. To stimulate MLKL phosphorylation and induce necroptosis, HT29 cells were treated with a cocktail consisting of TNFα, the SMAC mimetic BV6, and the caspase inhibitor Z-VAD-FMK. While this treatment induced necroptosis, three different reovirus T3D variants, i.e., the plasmid-based reverse genetics generated virus (T3D^K), the wild-type reovirus T3D isolate R124, and the junction adhesion molecule-A-independent reovirus mutant (jin-1) failed to induce necroptosis in HT29 cells. In contrast, these viruses induced MLKL phosphorylation in murine L929 cells, albeit with varying efficiencies. Our study shows that while reoviruses efficiently induce necroptosis in L929 cells, this is not a common phenotype in human cell lines. This study emphasizes the difficulties of translating the results of ICD studies from murine cells to human cells.

Oncolytic viruses as emerging therapy against cancers including Oncovirus-induced cancers

There are several human viruses with known potential for causing cancers including, Hepatitis B virus, Hepatitis C virus, Epstein-Barr virus, Kaposi's sarcoma herpesvirus, Human T-cell lymphotropic virus, Human papillomavirus, and Merkel cell polyomavirus. Cancer is the second leading cause of death that affects humans worldwide, especially in developing countries. Surgery, chemotherapy, and radiotherapy can cure about 60% of humans with cancer but recurrent and metastatic diseases remain a major reason for death. In recent years, understanding the molecular characteristics of cancer cells has led to the improvement of therapeutic strategies using novel emerging therapies. Oncolytic viruses with the potential of lysing cancer cells defined the field of oncolytic virology, hence becoming a biotechnology tool rather than just a cause of disease. This study mainly focused on targeting cell proliferation and death pathways in human tumor-inducing viruses by developing innovative therapies for cancer patients based on the natural oncolytic properties of reovirus. To kill tumor cells efficiently and reduce the chance of recurrence both the direct ability of reovirus infection to lyse the tumor cells and the stimulation of a potent host immune response are applied. Hence, bioengineered stem cells can be used as smart carriers to improve the efficacy of oncolytic reovirus and safety profiles.

Oncolytic Virotherapy

Oncolytic virotherapy opens up avenues for cancer treatment by selectively targeting the cancer cells and destructs them either through direct lysis or by inducing an immune response in the tumor microenvironment. This platform technology utilizes a diverse range naturally existing or genetically modified oncolytic viruses for their immunotherapeutic potential. Due to the limitations associated with the conventional cancer therapies, immunotherapies using oncolytic viruses (OVs) have generated a great deal of interest in the modern era. Currently, several oncolytic viruses have entered clinical trials and have proven successful for a number of different cancers as monotherapies as well as in combination with the standard treatment methods like chemotherapy, radiotherapy, or immunotherapy. Efficacy of OVs can be further enhanced by utilizing several approaches. Efforts of the scientific community for getting better knowledge of individual patient tumor immune responses will enable medical community to treat cancer patients more precisely. In this regard, OV seems to be a part of multimodality cancer treatment option in the near future. In this chapter, the fundamental characteristics and mechanism of actions of oncolytic viruses are initially described and then overview of the important clinical trials of various oncolytic viruses for a number of cancers is presented.

Emerging Nano-/Biotechnology Drives Oncolytic Virus-Activated and Combined Cancer Immunotherapy

Oncolytic viruses (OVs) as one promising antitumor methods have made important contributions to tumor immunotherapy, which arouse increasing attention. They provide the dual mechanisms including direct killing effect toward tumor cells and immune activation for elevating antitumor responses, which have been proved in many preclinical studies. Especially, natural or genetically modified viruses as clinical immune preparations have emerged as a new promising approach objective to oncology treatment. The approval of talimogene laherparepvec (T-VEC) by the U.S. Food and Drug Administration (FDA) for the therapy of advanced melanoma could be considered as a milestone achievement in the clinical translation of OV. In this review, we first discussed the antitumor mechanisms of OVs with an emphasis on targeting, replication, and propagation. We further outlined the state of the art of current OVs in tumor and underlined the activated biological effects especially including immunity. More significantly, the enhanced immune responses based on OVs were systematically discussed from different perspectives such as combination with immunotherapy, genetic engineering of OVs, integration with nanobiotechnology or nanoparticles, and antiviral response counteraction, where their principles were shed light on. The development of OVs in the clinics was also highlighted to analyze the actuality and concerns of different OV applications in clinical trials. At last, the future perspectives and challenges of OVs as an already widely accepted treatment means were discussed. This review will provide a systematic review and deep insight into OV development and also offer new opportunities and guidance pathways to drive the further clinical translation.

Application of Bioinformatics Tools for the Prediction of Helper MicroRNAs for Improvement of Oncolytic Virus Efficacy

Purpose. Oncolytic Reoviruses, as a self-limiting virus, can be used in cancer treatment, because they have the ability to replicate in tumor cells selectively and destroy them. Studies show that some immune response proteins may interfere with the virus life cycle. So, the main aim of this bioinformatic study is to check which microRNA is able to target some reovirus inhibitory proteins. Experimental Design. By use of online bioinformatics software, the microRNAs that could target inhibitory genes were selected. Then, other features like content ++ score and cell type were checked and finally the eligible microRNAs were determined. Results. After choosing 15 inhibitory proteins, analysis was performed and finally 37 microRNAs which could target inhibitory proteins in colorectal cell lines were selected. In the end, by investigation of web-based tools, just two microRNAs were finalized. Conclusions and Clinical Relevance. This bioinformatic study shows that microRNA-140 and microRNA-92a have the potential to target some inhibitory proteins which interfere with oncolytic Reovirus replication and it may help in the optimal use of this virus as a cancer treatment. Because selective reproduction of Reovirus in tumor cells, as a nonchemical therapy, can be a good way to overcome this disease with broad advantages.

Therapeutic potential of phospho-thiadiazole derivatives as anti-glioblastoma agents: synthesis, biological assessment and computational study

In this study, three new phospho thiadiazole compounds (A, F and W) were investigated as possible cytotoxic agents. The compounds were synthesised and characterised by using spectroscopy methods. The crystal structure of compound A was investigated using X-ray crystallography, since the title compounds can exist as different tautomeric forms, their conformational and geometrical aspects were investigated computationally by the DFT method. NBO analysis suggested that these compounds can function as appropriate ligands for the reaction with the nitrogen bases of DNA. All the synthesised compounds were evaluated in vitro for their cytotoxic activities against cancer in the human glioblastoma cell lines (U-251) using the MTT assay. According to the annexin V-FITC/PI results, a combination of synthesised compounds with ReoT3D showed a synergistic effect to increase the percentage of apoptotic cells. Molecular docking study for A (the most toxic compound) showed how it interacts with DNA. Both in vitro and in silico results showed that A has promising inhibitory potential (IC₅₀: 48.1 ± 0.3 μM) and binding energy (-6.67 kcal/mol).

Characterization of replication and variations in genome segments of a bat reovirus, BatMRV/B19-02, by RNA-seq in infected Vero-E6 cells

Mammalian orthoreoviruses (MEVs) that can cause enteric, respiratory, and encephalitic infections have been identified in a wide variety of mammalian species. Here, we report a novel MRV type 1 strain detected in Miniopterus schreibersii that may have resulted from reassortment events. Using next-generation RNA sequencing (RNA-seq), we found that the ratios of the RNA levels of the 10 reovirus segments in infected cells were constant during the late stages of infection. We also discovered that the relative abundance of each segment differed. Notably, the relative abundance of M2 (encoding the µ1 protein) and S4 (encoding the σ3 protein) RNAs was higher than that of the others throughout the infection. Additionally, massive junctions were identified. These results support the hypothesis that defective genome segments are generated and that cross-family recombination occurs. These data may further the study of gene function, viral replication, and virus evolution.

Reovirus Activated Cell Death Pathways

Mammalian orthoreoviruses (ReoV) are non-enveloped viruses with segmented double-stranded RNA genomes. In humans, ReoV are generally considered non-pathogenic, although members of this family have been proven to cause mild gastroenteritis in young children and may contribute to the development of inflammatory conditions, including Celiac disease. Because of its low pathogenic potential and its ability to efficiently infect and kill transformed cells, the ReoV strain Type 3 Dearing (T3D) is clinical trials as an oncolytic agent. ReoV manifests its oncolytic effects in large part by infecting tumor cells and activating programmed cell death pathways (PCDs). It was previously believed that apoptosis was the dominant PCD pathway triggered by ReoV infection. However, new studies suggest that ReoV also activates other PCD pathways, such as autophagy, pyroptosis, and necroptosis. Necroptosis is a caspase-independent form of PCD reliant on receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and its substrate, the pseudokinase mixed-lineage kinase domain-like protein (MLKL). As necroptosis is highly inflammatory, ReoV-induced necroptosis may contribute to the oncolytic potential of this virus, not only by promoting necrotic lysis of the infected cell, but also by inflaming the surrounding tumor microenvironment and provoking beneficial anti-tumor immune responses. In this review, we summarize our current understanding of the ReoV replication cycle, the known and potential mechanisms by which ReoV induces PCD, and discuss the consequences of non-apoptotic cell death—particularly necroptosis—to ReoV pathogenesis and oncolysis.

Comparison of the Effect of Adipose Mesenchymal Stem Cells-Derived Secretome with and without Reovirus in CT26 Cells

Colorectal cancer is the fourth leading cause of cancer-related deaths that has significantly increased over the past three decades. New therapeutic approaches, such as oncolytic viruses, have become very imperative recently to destroy cancer cells. The use of mesenchymal stem cells (MSCs) secretome that is produced in response to variant conditions involves different paracrine molecules secretion that has therapeutic potential in several chronic diseases. Mesenchymal stem cells and their derivatives are employed as regenerative medicine; nevertheless, there is ambiguity in the function of these cells in the control of malignancy. This study aimed to examine the apoptotic effect of secretomes derived from MSCs affected by encompassing oncolytic reoviruses. Mesenchymal stem cells were cultured after separation from abdominal adipose tissue of BALB/c mice. After three passages, the cells were infected by reovirus at the multiplicity of infection of 1 plaque-forming unit per cell. Uninfected and infected secretomes with reovirus were collected separately. The colorectal cancer CT26 cells were confronted with uninfected secretome, infected secretions, reovirus as a positive control, and Dulbecco's Modified Eagle Medium/High Glucose as negative control separately. Finally, apoptosis and necrosis were evaluated by flow cytometry. The infected secretome with reovirus was capable to induce apoptosis more than the uninfected secretome in CT26. However, the supernatant of reovirus infected cells was more capable to induce cell death, in comparison to the infected secretome. Infected MSCs with oncolytic reovirus produced a type of condition media that enhanced apoptosis induction and could have a therapeutic effect on cancer cells. Nonetheless, tumoral cells confronted with the oncolytic reovirus showed more capability in inducing apoptosis in CT26 cells. As a result, the use of oncolytic virus and infected secretome are more effective than uninfected secretome in inducing apoptosis.

Infection of non-cancer cells: A barrier or support for oncolytic virotherapy?

Oncolytic viruses are designed to specifically target cancer cells, sparing normal cells. Although numerous studies demonstrate the ability of oncolytic viruses to infect a wide range of non-tumor cells, the significance of this phenomenon for cancer virotherapy is poorly understood. To fill the gap, we summarize the data on infection of non-cancer targets by oncolytic viruses with a special focus on tumor microenvironment and secondary lymphoid tissues. The review aims to address two major questions: how do attenuated viruses manage to infect normal cells, and whether it is of importance for oncolytic virotherapy.

Oncolytic Viruses in the Therapy of Lymphoproliferative Diseases

Cancer is a leading causes of death. Despite significant success in the treatment of lymphatic system tumors, the problems of relapse, drug resistance and effectiveness of therapy remain relevant. Oncolytic viruses are able to replicate in tumor cells and destroy them without affecting normal, healthy tissues. By activating antitumor immunity, viruses are effective against malignant neoplasms of various nature. In lymphoproliferative diseases with a drug-resistant phenotype, many cases of remissions have been described after viral therapy. The current level of understanding of viral biology and the discovery of host cell interaction mechanisms made it possible to create unique strains with high oncoselectivity widely used in clinical practice in recent years.

Multimodal immune activation abilities and characteristics of reovirus

Reovirus is a ubiquitous, non-pathogenic, double stranded RNA virus with anti-tumor properties. The virus's replicative potential is regulated by phosphorylation of protein kinase receptor (PKR). In cancers with RAS pathway activation which leads to dysregulation of PKR, the virus maintains its protein translational potential and induces oncolysis. Systemic chemotherapy remains the standard of care for metastatic colorectal cancer with the addition of biologic agents in KRAS wildtype subtypes. In KRAS mutant colorectal cancers, there has been no added benefit to biologic agents. The therapeutic potential of reovirus (Reolysin^®, pelareorep, Oncolytic Inc., Calgary, Canada), which induces its oncolysis with RAS activation through multimodal immune mechanisms, has been demonstrated in preclinical and clinical studies. In this review, we outline the specific immune mechanisms of reovirus induced oncolysis and provide both preclinical and clinical data on its applications in metastatic colorectal cancer patients.

Repurposing drugs as novel triple negative breast cancer therapeutics

BACKGROUND

Among all the types of breast cancer (BC), triple negative breast cancer (TNBC) is the most aggressive form having high metastasis and recurrence rate with limited treatment options. Conventional treatments such as chemotherapy and radiotherapy have lots of toxic side effects and also no FDA approved therapies are available till now. Repurposing of old clinically approved drugs towards various targets of TNBC is the new approach with lesser side effects and also leads to successful inexpensive drug development with less time consuming. Medicinal plants containg various phytoconstituents (flavonoids, alkaloids, phenols, essential oils, tanins, glycosides, lactones) plays very crucial role in combating various types of diseases and used in drug development process because of having lesser side effects.

OBJECTIVE

The present review focuses in summarization of various categories of repurposed drugs against multitarget of TNBC and also summarizes the phytochemical categories that targets TNBC singly or in combination with synthetic old drugs.

METHODS

Literature information was collected from various databases such as Pubmed, Web of Science, Scopus and Medline to understand and clarify the role and mechanism of repurposed synthetic drugs and phytoconstituents aginst TNBC by using keywords like "breast cancer", "repurposed drugs", "TNBC" and "phytoconstituents".

RESULTS

Various repurposed drugs and phytochemicals targeting different signaling pathways that exerts their cytotoxic activities on TNBC cells ultimately leads to apoptosis of cells and also lowers the recurrence rate and stops the metastasis process.

CONCLUSION

Inhibitory effects seen in different levels, which provides information and evidences to researchers towards drug developments process and thus further more investigations and researches need to be taken to get the better therapeutic treatment options against TNBC.

Reovirus Nonstructural Protein σNS Recruits Viral RNA to Replication Organelles

The function of the mammalian orthoreovirus (reovirus) σNS nonstructural protein is enigmatic. σNS is an RNA-binding protein that forms oligomers and enhances the stability of bound RNAs, but the mechanisms by which it contributes to reovirus replication are unknown. To determine the function of σNS-RNA binding in reovirus replication, we engineered σNS mutants deficient in RNA-binding capacity. We found that alanine substitutions of positively charged residues in a predicted RNA-binding domain decrease RNA-dependent oligomerization. To define steps in reovirus replication facilitated by the RNA-binding property of σNS, we established a complementation system in which wild-type or mutant forms of σNS could be tested for the capacity to overcome inhibition of σNS expression. Mutations in σNS that disrupt RNA binding also diminish viral replication and σNS distribution to viral factories. Moreover, viral mRNAs only incorporate into viral factories or factory-like structures (formed following expression of nonstructural protein μNS) when σNS is present and capable of binding RNA. Collectively, these findings indicate that σNS requires positively charged residues in a putative RNA-binding domain to recruit viral mRNAs to sites of viral replication and establish a function for σNS in reovirus replication.

Mesenchymal stem cells loaded with oncolytic reovirus enhances antitumor activity in mice models of colorectal cancer

Oncolytic viruses (OVs) are promising alternative biological agents for treating cancer. However, triggered immune responses against viruses and their delivery to tumor sites are their primary limitations in cancer therapy. To address these challenges, mesenchymal stem cells (MSCs) can serve as permissive tools for OVs loading and delivery to tumor sites. Here, we evaluated the in vitro and in vivo antitumor capability of adipose-derived mesenchymal stem cells (AD-MSCs) as a new vehicle for Dearing strain of reovirus (ReoT3D) loading. We first isolated and confirmed the purity of MSCs, and the optimized dose of ReoT3D for MSCs loading was computed by a standard assay. Next, we used murine CT26 cell line to establish the colorectal cancer model in BALB/c mice and demonstrated the antitumor effects of MSCs loaded with reovirus. Our results demonstrated that multiplicity of infection (MOI) 1 pfu/cells of reovirus was the safe dose for loading into purified MSCs. Moreover, our anticancer experiments exhibited that treatment with MSCs loaded with ReoT3D was more effective than ReoT3D and MSCs alone. Higher anticancer impact of MSCs loaded with OV was associated with induction of apoptosis, cell cycle arrests, P53 expression in tumor sections, and reduced tumor growth and size. The present results suggest that MSCs as a permissive shuttle for oncolytic virus (OV) delivery increased the anticancer activity of ReoT3D in mice models of colorectal cancer and these findings should be supported by more preclinical and clinical studies.

MSCs loaded with oncolytic reovirus: migration and in vivo virus delivery potential for evaluating anti-cancer effect in tumor-bearing C57BL/6 mice

Background and aims

Several oncolytic viruses applications have been approved in the clinic or in different phases of clinical trials. However, these methods have some rudimentary problems. Therefore, to enhance the delivery and quality of treatment, considering the advantage of cell carrier-based methods such as Mesenchymal Stem Cells (MSC) have been proposed. This study was designed to evaluate the performance and quality of cancer treatment based on MSCs loaded by oncolytic reovirus in the cancerous C57BL/6 mouse model. Also, we evaluated MSCs migration potency in vitro and in vivo following the oncolytic reovirus infection.

Methods

C57BL/6 mice were inoculated with TC-1 cell lines and tumors were established in the right flank. Mice were systemically treated with reovirus, MSCs-loaded with reovirus, MSCs, and PBS as a control in separated groups. Effects of infected AD-MSCs with reovirus on tumor growth and penetration in the tumor site were monitored. All groups of mice were monitored for two months in order to therapeutic and anticancer potential. After treatments, tumor size alteration and apoptosis rate, as well as cytokine release pattern was assessed.

Results

The results of the current study indicated that the effect of reovirus infection on AD-MSCs is not devastating the migration capacity especially in MOI 1 and 5 while intact cells remain. On the other hand, MSCs play an efficient role as a carrier to deliver oncolytic virus into the tumor site in comparison with systemic administration of reovirus alone. Apoptosis intensity relies on viral titration and passing time. Followed by systemic administration, treatment with oncolytic reovirus-infected AD-MSCs and MSCs alone had shown significant inhibition in tumor growth. Also, treatment by reovirus causes an increase in IFN-γ secretion.

Conclusion

The results of in vitro and in vivo study confirmed the tumor-homing properties of infected AD-MSCs and the significant antitumor activity of this platform. Hence, our results showed that the cell carrier strategy using oncolytic reovirus-loaded AD-MSCs enhanced virus delivery, infiltration, and antitumor activity can be effectively applied in most cancers.

The reovirus μ2 C-terminal loop inversely regulates NTPase and transcription functions versus binding to factory-forming μNS and promotes replication in tumorigenic cells

Wild type reovirus serotype 3 'Dearing PL strain' (T3wt) is being heavily evaluated as an oncolytic and immunotherapeutic treatment for cancers. Mutations that promote reovirus entry into tumor cells were previously reported to enhance oncolysis; herein we aimed to discover mutations that enhance the post-entry steps of reovirus infection in tumor cells. Using directed evolution, we identified that reovirus variant T3v10^M1 exhibited enhanced replication relative to T3wt on a panel of cancer cells. T3v10^M1 contains an alanine-to-valine substitution (A612V) in the core-associated μ2, which was previously found to have NTPase activities in virions and to facilitate virus factory formation by association with μNS. Paradoxically, the A612V mutation in μ2 from T3v10^M1 was discovered to impair NTPase activities and RNA synthesis, leading to five-fold higher probability of abortive infection for T3v10^M1 relative to T3wt. The A612V mutation resides in a previously uncharacterized C-terminal region that juxtaposes the template entry site of the polymerase μ2; our findings thus support an important role for this domain during virus transcription. Despite crippled onset of infection, T3v10^M1 exhibited greater accumulation of viral proteins and progeny during replication, leading to increased overall virus burst size. Both Far-Western and co-immunoprecipitation approaches corroborated that the A612V mutation in μ2 increased association with the non-structural virus protein μNS and enhances burst size. Altogether the data supports that mutations in the C-terminal loop domain of μ2 inversely regulate NTPase and RNA synthesis versus interactions with μNS, but with a net gain of replication in tumorigenic cells.SIGNIFICANCEReovirus is a model system for understanding virus replication but also a clinically relevant virus for cancer therapy. We identified the first mutation that increases reovirus infection in tumorigenic cells by enhancing post-entry stages of reovirus replication. The mutation is in a previously uncharacterized c-terminal region of the M1-derived μ2 protein, which we demonstrated affects multiple functions of μ2; NTPase, RNA synthesis, inhibition of antiviral immune response and association with the virus replication factory-forming μNS protein. These findings promote a mechanistic understanding of viral protein functions. In the future, the benefits of μ2 mutations may be useful for enhancing reovirus potency in tumors.

Oncolytic Virotherapy for Cancer: Clinical Experience

Oncolytic viruses are a new class of therapeutics which are largely in the experimental stage, with just one virus approved by the FDA thus far. While the concept of oncolytic virotherapy is not new, advancements in the fields of molecular biology and virology have renewed the interest in using viruses as oncolytic agents. Backed by robust preclinical data, many oncolytic viruses have entered clinical trials. Oncolytic viruses that have completed some levels of clinical trials or are currently undergoing clinical trials are mostly genetically engineered viruses, with the exception of some RNA viruses. Reolysin, an unmodified RNA virus is clinically the most advanced oncolytic RNA virus that has completed different phases of clinical trials. Other oncolytic viruses that have been studied in clinical trials are mostly DNA viruses that belong to one of the three families: herpesviridae, poxviridae or adenoviridae. In this review work we discuss recent clinical studies with oncolytic viruses, especially herpesvirus, poxvirus, adenovirus and reovirus. In summary, the oncolytic viruses tested so far are well tolerated, even in immune-suppressed patients. For most oncolytic viruses, mild and acceptable toxicities are seen at the currently defined highest feasible doses. However, anti-tumor efficacies of oncolytic viruses have been modest, especially when used as monotherapy. Therefore, the potency of oncolytic viruses needs to be enhanced for more oncolytic viruses to hit the clinic. Aiming to achieve higher therapeutic benefits, oncolytic viruses are currently being studied in combination with other therapies. Here we discuss the currently available clinical data on oncolytic viruses, either as monotherapy or in combination with other treatments.

Mesenchymal stem cell carriers enhance anti-tumor efficacy of oncolytic virotherapy

Oncolytic viruses (OVs) specifically infect, replicate and eventually destroy tumor cells, with no concomitant toxicity to adjacent normal cells. Furthermore, OVs can regulate tumor microenvironments and stimulate anti-tumor immune responses. Mesenchymal stem cells (MSCs) have inherent tumor tropisms and immunosuppressive functions. MSCs carrying OVs not only protect viruses from clearing by the immune system, but they also deliver the virus to tumor lesions. Equally, cytokines released by MSCs enhance anti-tumor immune responses, suggesting that MSCs carrying OVs may be considered as a promising strategy in enhancing the anti-tumor efficacies of virotherapy. In the present review, preclinical and clinical studies were evaluated and discussed, as well as the effectiveness of MSCs carrying OVs for tumor treatment.

Inhibition of HIF-1α accumulation in prostate cancer cells is initiated during early stages of mammalian orthoreovirus infection

Mammalian orthoreovirus (MRV) is a safe and effective cancer killing virus that has completed Phase I-III clinical trials against numerous cancer types. While many patients experience benefit from MRV therapy, pre-defined set points necessary for FDA approval have not been reached. Therefore, additional research into MRV biology and the effect of viral therapy on different tumor genetic subtypes and microenvironments is necessary to identify tumors most amenable to MRV virotherapy. In this work we analyzed the stage of viral infection necessary to inhibit HIF-1α, an aggressive cancer activator induced by hypoxia. We demonstrated that two viral capsid proteins were not necessary and that a step parallel with virus core movement across the endosomal membrane was required for this inhibition. Altogether, this work clarifies the mechanisms of MRV-induced HIF-1α inhibition and provides biological relevance for using MRV to inhibit the devastating effects of tumor hypoxia.

Mesenchymal stem cell carriers enhance antitumor efficacy induced by oncolytic reovirus in acute myeloid leukemia

Chemotherapy is the main treatment for acute myeloid leukemia (AML), but the therapeutic efficacy is modest, and most commonly manifests as relapse from remission. Thus, improving long-term AML survival is a crucial clinical challenge. In recent years, oncolytic virotherapy has provided an alternative approach for AML treatment. The use of oncolytic reoviruses has been explored in more than 30 clinical trials for safety and feasibility issues. However, like other oncolytic viruses, neutralizing antibodies (NAbs) reduce therapeutic efficacy. To tackle this problem, human umbilical cord mesenchymal stem cells (hUC-MSCs) were used to deliver reovirus using in vitro and in vivo models. Human UC-MSCs were successfully loaded with reovirus, without impairing biological function.We also observed in vitro protective effects of hUC-MSCs on reovirus in the presence of NAbs. In the immunocompromised AML mouse model, hUC-MSCs effectively carried reoviruses to tumor lesions and significantly prolonged the survival of AML xenografts in mice in the presence of a high titer anti-reovirus antibody (p = 0.001). However, reovirus-induced activation of AKT, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and NF-κB signaling led to the maintenance of intrinsic migratory properties and secretion of pro-inflammatory cytokines from hUC-MSCs, particularly CXCL10. In immuno-competent AML mice, MSCs carrying reovirus triggered immune responses, and eventually inhibited tumor growth. Therefore, these results suggest that MSCs as carriers of oncolytic reoviruses can enhance the antitumor efficacy of virotherapy.

Reovirus and the Host Integrated Stress Response: On the Frontlines of the Battle to Survive

Cells are continually exposed to stressful events, which are overcome by the activation of a number of genetic pathways. The integrated stress response (ISR) is a large component of the overall cellular response to stress, which ultimately functions through the phosphorylation of the alpha subunit of eukaryotic initiation factor-2 (eIF2α) to inhibit the energy-taxing process of translation. This response is instrumental in the inhibition of viral infection and contributes to evolution in viruses. Mammalian orthoreovirus (MRV), an oncolytic virus that has shown promise in over 30 phase I–III clinical trials, has been shown to induce multiple arms within the ISR pathway, but it successfully evades, modulates, or subverts each cellular attempt to inhibit viral translation. MRV has not yet received Food and Drug Administration (FDA) approval for general use in the clinic; therefore, researchers continue to study virus interactions with host cells to identify circumstances where MRV effectiveness in tumor killing can be improved. In this review, we will discuss the ISR, MRV modulation of the ISR, and discuss ways in which MRV interaction with the ISR may increase the effectiveness of cancer therapeutics whose modes of action are altered by the ISR.

Oncolytic Viruses and Immune Checkpoint Inhibitors: Preclinical Developments to Clinical Trials

Immuno-oncology (IO) has been an active area of oncology research. Following US FDA approval of the first immune checkpoint inhibitor (ICI), ipilimumab (human IgG1 k anti-CTLA-4 monoclonal antibody), in 2011, and of the first oncolytic virus, Imlygic (talimogene laherparepvec), in 2015, there has been renewed interest in IO. In the past decade, ICIs have changed the treatment paradigm for many cancers by enabling better therapeutic control, resuming immune surveillance, suppressing tumor immunosuppression, and restoring antitumor immune function. However, ICI therapies are effective only in a small subset of patients and show limited therapeutic potential due to their inability to demonstrate efficacy in 'cold' or unresponsive tumor microenvironments (TMEs). Relatedly, oncolytic viruses (OVs) have been shown to induce antitumor immune responses, augment the efficacy of existing cancer treatments, and reform unresponsive TME to turn 'cold' tumors 'hot,' increasing their susceptibility to checkpoint blockade immunotherapies. For this reason, OVs serve as ideal complements to ICIs, and multiple preclinical studies and clinical trials are demonstrating their combined therapeutic efficacy. This review will discuss the merits and limitations of OVs and ICIs as monotherapy then progress onto the preclinical rationale and the results of clinical trials of key combination therapies.

Hitting the Target but Missing the Point: Recent Progress towards Adenovirus-Based Precision Virotherapies

More people are surviving longer with cancer. Whilst this can be partially attributed to advances in early detection of cancers, there is little doubt that the improvement in survival statistics is also due to the expansion in the spectrum of treatments available for efficacious treatment. Transformative amongst those are immunotherapies, which have proven effective agents for treating immunogenic forms of cancer, although immunologically "cold" tumour types remain refractive. Oncolytic viruses, such as those based on adenovirus, have great potential as anti-cancer agents and have seen a resurgence of interest in recent years. Amongst their many advantages is their ability to induce immunogenic cell death (ICD) of infected tumour cells, thus providing the alluring potential to synergise with immunotherapies by turning immunologically "cold" tumours "hot". Additionally, enhanced immune mediated cell killing can be promoted through the local overexpression of immunological transgenes, encoded from within the engineered viral genome. To achieve this full potential requires the development of refined, tumour selective "precision virotherapies" that are extensively engineered to prevent off-target up take via native routes of infection and targeted to infect and replicate uniquely within malignantly transformed cells. Here, we review the latest advances towards this holy grail within the adenoviral field.

Noncanonical Cell Death Induction by Reassortant Reovirus

Triple-negative breast cancer (TNBC) constitutes 10 to 15% of all breast cancer and is associated with worse prognosis than other subtypes of breast cancer. Current therapies are limited to cytotoxic chemotherapy, radiation, and surgery, leaving a need for targeted therapeutics to improve outcomes for TNBC patients. Mammalian orthoreovirus (reovirus) is a nonenveloped, segmented, double-stranded RNA virus in the Reoviridae family. Reovirus preferentially kills transformed cells and is in clinical trials to assess its efficacy against several types of cancer. We previously engineered a reassortant reovirus, r2Reovirus, that infects TNBC cells more efficiently and induces cell death with faster kinetics than parental reoviruses. In this study, we sought to understand the mechanisms by which r2Reovirus induces cell death in TNBC cells. We show that r2Reovirus infection of TNBC cells of a mesenchymal stem-like (MSL) lineage downregulates the mitogen-activated protein kinase/extracellular signal-related kinase pathway and induces nonconventional cell death that is caspase-dependent but caspase 3-independent. Infection of different MSL lineage TNBC cells with r2Reovirus results in caspase 3-dependent cell death. We map the enhanced oncolytic properties of r2Reovirus in TNBC to epistatic interactions between the type 3 Dearing M2 gene segment and type 1 Lang genes. These findings suggest that the genetic composition of the host cell impacts the mechanism of reovirus-induced cell death in TNBC. Together, our data show that understanding host and virus determinants of cell death can identify novel properties and interactions between host and viral gene products that can be exploited for the development of improved viral oncolytics.IMPORTANCE TNBC is unresponsive to hormone therapies, leaving patients afflicted with this disease with limited treatment options. We previously engineered an oncolytic reovirus (r2Reovirus) with enhanced infective and cytotoxic properties in TNBC cells. However, how r2Reovirus promotes TNBC cell death is not known. In this study, we show that reassortant r2Reovirus can promote nonconventional caspase-dependent but caspase 3-independent cell death and that the mechanism of cell death depends on the genetic composition of the host cell. We also map the enhanced oncolytic properties of r2Reovirus in TNBC to interactions between a type 3 M2 gene segment and type 1 genes. Our data show that understanding the interplay between the host cell environment and the genetic composition of oncolytic viruses is crucial for the development of efficacious viral oncolytics.

The synergistic anticancer effects of ReoT3D, CPT-11, and BBI608 on murine colorectal cancer cells

BACKGROUND

Many types of oncolytic viruses (OVs) were enrolled in clinical trials. Recently, an OV named Talimogene laherparepvec approved for the treatment of melanoma. This achievement highlighted the clinical application of OVs. Scientists focus on using these anticancer agents in combination with the current or/and new anticancer chemotherapeutics. They aim to increase the oncolytic effect of a new approach for the treatment of cancer cells.

OBJECTIVES

The present study aimed to assess the anticancer impacts of ReoT3D, irinotecan (CPT-11), and napabucasin (BBI608) against murine colorectal cancer cells (CT26). They are assessed alone and in combination with each other.

METHODS

Here, oncolytic reovirus was propagated and titrated. Then MTT assay was carried out to assess the toxicity of this OV and chemotherapeutics effect on CT26 cells. The anticancer effects of ReoT3D, CPT-11, and BBI608, alone and simultaneously, on CT26 cell line, were assessed by the induction of apoptosis, cell cycle arrest, colony-forming, migration, and real-time PCR experiments.

RESULTS

Alone treatment with ReoT3D, CPT-11, and BBI608 led to effectively inducing of apoptosis, cell cycle arrest, and apoptotic genes expression level and significantly reduce of colony-forming, migration, and anti-apoptotic genes expression rate. Importantly, the maximum anticancer effect against CT26 cell line was seen upon combination ReoT3D, CPT-11, and BBI608 treatment.

CONCLUSION

The present study highlights that combination of ReoT3D, CPT-11, and BBI560 showed synergistic anticancer activity against CT26 cell line. This modality might be considered as a new approach against colorectal cancer (CRC) in the in vivo and clinical trial investigations.

Cyclin-dependent kinases and CDK inhibitors in virus-associated cancers

The role of several risk factors, such as pollution, consumption of alcohol, age, sex and obesity in cancer progression is undeniable. Human malignancies are mainly characterized by deregulation of cyclin-dependent kinases (CDK) and cyclin inhibitor kinases (CIK) activities. Viruses express some onco-proteins which could interfere with CDK and CIKs function, and induce some signals to replicate their genome into host's cells. By reviewing some studies about the function of CDK and CIKs in cells infected with oncoviruses, such as HPV, HTLV, HERV, EBV, KSHV, HBV and HCV, we reviewed the mechanisms of different onco-proteins which could deregulate the cell cycle proteins.

In Vitro Anti-cancer Activity of Adipose-Derived Mesenchymal Stem Cells Increased after Infection with Oncolytic Reovirus

Purpose: Reovirus type 3 Dearing (ReoT3D), a wild type oncolytic virus (OV) from the Reoviridae family, kills KRAS mutant cancer cells. However, the use of OVs has faced with some limitations such as immune responses, and delivery of OVs to the tumor sites in systemic therapy. To solve this, and also to increase the anti-cancer effects of these OVs, mesenchymal stem cells (MSCs) might be used as an effective vehicle for OVs delivery. In this study, we examined the anti-cancer effects of human adipose derived-MSCs (AD-MSCs) as a vehicle of ReoT3D against human glioblastoma cells.

Methods: Here, AD-MSCs were characterized and toxicity of ReoT3D on them was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Then, capability of AD-MSCs for virus production was assessed by real-time polymerase chain reaction (PCR), and different in vitro anti-cancer experiments were applied for our anti-cancer purposes.

Results: Our results from toxicity assay revealed that the isolated and provoked AD-MSCs were resistant to nontoxic concentration multiplicity of infection (MOI) >1 pfu/cells of ReoT3D. In addition, the results indicated that AD-MSCs were susceptible for virus life cycle complementation and were capable for production of virus progenies. Furthermore, our results showed that AD-MSCs had oncolysis effects and increased the anti-cancer effects of ReoT3D.

Conclusion: AD-MSCs as a susceptible host for oncolytic reovirus could increase the anti-cancer activity of this OV against glioblastoma multiforme (GBM) cell line.

Elucidation of Pelareorep Pharmacodynamics in A Phase I Trial in Patients with KRAS-Mutated Colorectal Cancer

KRAS mutation is a negative predictive biomarker of anti-EGFR agents in patients with metastatic colorectal cancer (mCRC), and remains an elusive target. Pelareorep, a double-stranded RNA virus selectively replicates in KRAS-mutated cells, and is synergistic with irinotecan. A dose escalation trial of FOLFIRI/bevacizumab [irinotecan (150-180 mg/m²) and pelareorep (1 × 10¹⁰ TCID₅₀-3 × 10¹⁰ TCID₅₀)] was implemented in adult patients with oxaliplatin refractory/intolerant, KRAS-mutant mCRC. Pelareorep was administered intravenously over 1 hour on days 1-5 every 4 weeks. Additional studies included pharmacokinetics, tumor morphology, and immune responses. Among FOLFIRI-naïve patients, the highest dose of FOLFIRI/bevacizumab (180 mg/m² irinotecan) and pelareorep (3 × 10¹⁰ TCID₅₀) was well tolerated, without a dose-limiting toxicity. At the recommended phase II dose, 3 of 6 patients (50%) had a partial response; the median progression-free and overall survival (PFS, OS) were 65.6 weeks and 25.1 months, respectively. Toxicities included myelosuppression, fatigue, and diarrhea. Transmission electron microscopy revealed viral factories (viral collections forming vesicular structures), at various stages of development. Immunogold staining against viral capsid σ-1 protein demonstrated viral "homing" in the tumor cells. The nucleus displayed sufficient euchromatin regions suggestive of active transcription. Flow cytometry revealed rapid dendritic cell maturation (48 hours) with subsequent activation of cytotoxic T cells (7 days). The combination of pelareorep with FOLFIRI/bevacizumab is safe. The PFS and OS data are encouraging and deserve further exploration. Pelareorep leads to a clear recurrent immune stimulatory response with cytotoxic T-cell activation, and homes and replicates in the tumor.

Reovirus uses macropinocytosis-mediated entry and fast axonal transport to infect neurons

Several barriers protect the central nervous system (CNS) from pathogen invasion. Yet viral infections of the CNS are common and often debilitating. Understanding how neurotropic viruses co-opt host machinery to overcome challenges to neuronal entry and transmission is important to combat these infections. Neurotropic reovirus disseminates through neural routes and invades the CNS to cause lethal encephalitis in newborn animals. To define mechanisms of reovirus neuronal entry and directional transport, we used primary neuron cultures, which reproduce in vivo infection patterns displayed by different reovirus serotypes. Treatment of neurons with small-molecule inhibitors of different endocytic uptake pathways allowed us to discover that the cellular machinery mediating macropinocytosis is required for reovirus neuronal entry. This mechanism of reovirus entry differs from clathrin-mediated endocytosis, which is used by reovirus to invade non-neuronal cells. Analysis of reovirus transport and release from isolated soma or axonal termini of neurons cultivated in microfluidic devices indicates that reovirus is capable of retrograde but only limited anterograde neuronal transmission. The dynamics of retrograde reovirus movement are consistent with fast axonal transport coordinated by dynein along microtubules. Further analysis of viral transport revealed that multiple virions are transported together in axons within non-acidified vesicles. Reovirus-containing vesicles acidify after reaching the soma, where disassembly of virions and release of the viral core into the cytoplasm initiates replication. These results define mechanisms of reovirus neuronal entry and transport and establish a foundation to identify common host factors used by neuroinvasive viruses. Furthermore, our findings emphasize consideration of cell type-specific entry mechanisms in the tailored design of neurotropic viruses as tracers, oncolytic agents, and delivery vectors.

Viral infections of the central nervous system (CNS) cause a significant health burden globally and compel a better mechanistic understanding of neural invasion by viruses to develop effective interventions. Neurotropic reovirus disseminates through neural routes to infect the CNS and serves as a tractable model to study neural invasion by viruses. Despite knowledge of reovirus neurotropism for decades, mechanisms mediating reovirus neuronal infection remain undefined. We used primary neurons cultured in microfluidic devices to study entry and directional transport of reovirus. We discovered that reovirus uses macropinocytosis for neuronal entry as opposed to the use of a clathrin-mediated pathway in non-neuronal cells. We are unaware of another virus using macropinocytosis to enter neurons. Following internalization, reovirus spreads in the retrograde direction using dynein-mediated fast axonal transport but exhibits limited anterograde spread. We further demonstrate that reovirus disassembly and replication occur in the neuronal soma subsequent to axonal transport. Remarkably, these entry and transport mechanisms mirror those used by misfolded proteins implicated in neurodegenerative diseases. Our findings establish the mechanics of reovirus neuronal uptake and spread and provide clues about therapeutic targets to limit neuropathology inflicted by pathogens and misfolded proteins.

Enhanced Killing of Triple-Negative Breast Cancer Cells by Reassortant Reovirus and Topoisomerase Inhibitors

Breast cancer is the second leading cause of cancer-related deaths in women in the United States. Triple-negative breast cancer constitutes a subset of breast cancer that is associated with higher rates of relapse, decreased survival, and limited therapeutic options for patients afflicted with this type of breast cancer. Mammalian orthoreovirus (reovirus) selectively infects and kills transformed cells, and a serotype 3 reovirus is in clinical trials to assess its efficacy as an oncolytic agent against several cancers. It is unclear if reovirus serotypes differentially infect and kill triple-negative breast cancer cells and if reovirus-induced cytotoxicity of breast cancer cells can be enhanced by modulating the activity of host molecules and pathways. Here, we generated reassortant reoviruses by forward genetics with enhanced infective and cytotoxic properties in triple-negative breast cancer cells. From a high-throughput screen of small-molecule inhibitors, we identified topoisomerase inhibitors as a class of drugs that enhance reovirus infectivity and cytotoxicity of triple-negative breast cancer cells. Treatment of triple-negative breast cancer cells with topoisomerase inhibitors activates DNA damage response pathways, and reovirus infection induces robust production of type III, but not type I, interferon (IFN). Although type I and type III IFNs can activate STAT1 and STAT2, triple-negative breast cancer cellular proliferation is only negatively affected by type I IFN. Together, these data show that reassortant viruses with a novel genetic composition generated by forward genetics in combination with topoisomerase inhibitors more efficiently infect and kill triple-negative breast cancer cells.IMPORTANCE Patients afflicted by triple-negative breast cancer have decreased survival and limited therapeutic options. Reovirus infection results in cell death of a variety of cancers, but it is unknown if different reovirus types lead to triple-negative breast cancer cell death. In this study, we generated two novel reoviruses that more efficiently infect and kill triple-negative breast cancer cells. We show that infection in the presence of DNA-damaging agents enhances infection and triple-negative breast cancer cell killing by reovirus. These data suggest that a combination of a genetically engineered oncolytic reovirus and topoisomerase inhibitors may provide a potent therapeutic option for patients afflicted with triple-negative breast cancer.

Virus-Receptor Interactions: Structural Insights For Oncolytic Virus Development

Recent advancements in oncolytic virotherapy commend a special attention to developing new strategies for targeting cancer cells with oncolytic viruses (OVs). Modifications of the viral envelope or coat proteins serve as a logical mean of repurposing viruses for cancer treatment. In this review, we discuss how detailed structural knowledge of the interactions between OVs and their natural receptors provide valuable insights into tumor specificity of some viruses and re-targeting of alternate receptors for broad tumor tropism or improved tumor selectivity.

Breast Tumor-Associated Metalloproteases Restrict Reovirus Oncolysis by Cleaving the σ1 Cell Attachment Protein and Can Be Overcome by Mutation of σ1

Reovirus is undergoing clinical testing as an oncolytic therapy for breast cancer. Given that reovirus naturally evolved to thrive in enteric environments, we sought to better understand how breast tumor microenvironments impinge on reovirus infection. Reovirus was treated with extracellular extracts generated from polyomavirus middle T-antigen-derived mouse breast tumors. Unexpectedly, these breast tumor extracellular extracts inactivated reovirus, reducing infectivity of reovirus particles by 100-fold. Mechanistically, inactivation was attributed to proteolytic cleavage of the viral cell attachment protein σ1, which diminished virus binding to sialic acid (SA)-low tumor cells. Among various specific protease class inhibitors and metal ions, EDTA and ZnCl₂ effectively modulated σ1 cleavage, indicating that breast tumor-associated zinc-dependent metalloproteases are responsible for reovirus inactivation. Moreover, media from MCF7, MB468, MD-MB-231, and HS578T breast cancer cell lines recapitulated σ1 cleavage and reovirus inactivation, suggesting that inactivation of reovirus is shared among mouse and human breast cancers and that breast cancer cells by themselves can be a source of reovirus-inactivating proteases. Binding assays and quantification of SA levels on a panel of cancer cells showed that truncated σ1 reduced virus binding to cells with low surface SA. To overcome this restriction, we generated a reovirus mutant with a mutation (T249I) in σ1 that prevents σ1 cleavage and inactivation by breast tumor-associated proteases. The mutant reovirus showed similar replication kinetics in tumorigenic cells, toxicity equivalent to that of wild-type reovirus in a severely compromised mouse model, and increased tumor titers. Overall, the data show that tumor microenvironments have the potential to reduce infectivity of reovirus.IMPORTANCE We demonstrate that metalloproteases in breast tumor microenvironments can inactivate reovirus. Our findings expose that tumor microenvironment proteases could have a negative impact on proteinaceous cancer therapies, such as reovirus, and that modification of such therapies to circumvent inactivation by tumor metalloproteases merits consideration.

Past, Current, and Future of Immunotherapies for Prostate Cancer

Prostate cancer (PCa) is the most common cancer in men, and the second leading cause of cancer related death in men in Western countries. The standard therapy for metastatic PCa is androgen suppression therapy (AST). Men undergoing AST eventually develop metastatic castration-resistant prostate cancer (mCRPC), of which there are limited treatment options available. Immunotherapy has presented substantial benefits for many types of cancer, but only a marginal benefit for mCRPC, at least in part, due to the immunosuppressive tumor microenvironment (TME). Current clinical trials are investigating monotherapies or combination therapies involving adoptive cellular therapy, viral, DNA vaccines, oncolytic viruses, and immune checkpoint inhibitors (ICI). Immunotherapies are also being combined with chemotherapy, radiation, and AST. Additionally, preclinical investigations show promise with the recent description of alternative ways to circumvent the immunosuppressive nature of the prostate tumor microenvironment, including harnessing the immune stimulatory NKG2D pathway, inhibiting myeloid derived suppressor cells, and utilizing immunomodulatory oncolytic viruses. Herein we provide an overview of recent preclinical and clinical developments in cancer immunotherapies and discuss the perspectives for future immunotherapies in PCa.

Novel Function of Bluetongue Virus NS3 Protein in Regulation of the MAPK/ERK Signaling Pathway

Bluetongue virus (BTV) is an arbovirus transmitted by blood-feeding midges to a wide range of wild and domestic ruminants. In this report, we showed that BTV, through its nonstructural protein NS3 (BTV-NS3), is able to activate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway, as assessed by phosphorylation levels of ERK1/2 and the translation initiation factor eukaryotic translation initiation factor 4E (eIF4E). By combining immunoprecipitation of BTV-NS3 and mass spectrometry analysis from both BTV-infected and NS3-transfected cells, we identified the serine/threonine-protein kinase B-Raf (BRAF), a crucial player in the MAPK/ERK pathway, as a new cellular interactor of BTV-NS3. BRAF silencing led to a significant decrease in the MAPK/ERK activation by BTV, supporting a model wherein BTV-NS3 interacts with BRAF to activate this signaling cascade. This positive regulation acts independently of the role of BTV-NS3 in counteracting the induction of the alpha/beta interferon response. Furthermore, the intrinsic ability of BTV-NS3 to bind BRAF and activate the MAPK/ERK pathway is conserved throughout multiple serotypes/strains but appears to be specific to BTV compared to other members of Orbivirus genus. Inhibition of MAPK/ERK pathway with U0126 reduced viral titers, suggesting that BTV manipulates this pathway for its own replication. Altogether, our data provide molecular mechanisms that unravel a new essential function of NS3 during BTV infection.IMPORTANCE Bluetongue virus (BTV) is responsible of the arthropod-borne disease bluetongue (BT) transmitted to ruminants by blood-feeding midges. In this report, we found that BTV, through its nonstructural protein NS3 (BTV-NS3), interacts with BRAF, a key component of the MAPK/ERK pathway. In response to growth factors, this pathway promotes cell survival and increases protein translation. We showed that BTV-NS3 enhances the MAPK/ERK pathway, and this activation is BRAF dependent. Treatment of MAPK/ERK pathway with the pharmacologic inhibitor U0126 impairs viral replication, suggesting that BTV manipulates this pathway for its own benefit. Our results illustrate, at the molecular level, how a single virulence factor has evolved to target a cellular function to increase its viral replication.