Oncolytic adenoviral mutants induce a novel mode of programmed cell death in ovarian cancer

Oncolytic virotherapy for hepatocellular carcinoma: A potent immunotherapeutic landscape

Hepatocellular carcinoma (HCC) is a systemic disease with augmented malignant degree, high mortality and poor prognosis. Since the establishment of the immune mechanism of tumor therapy, people have realized that immunotherapy is an effective means for improvement of HCC patient prognosis. Oncolytic virus is a novel immunotherapy drug, which kills tumor cells and exempts normal cells by directly lysing tumor and inducing anti-tumor immune response, and it has been extensively examined as an HCC therapy. This editorial discusses oncolytic viruses for the treatment of HCC, emphasizing viral immunotherapy strategies and clinical applications related to HCC.

Molecular insights and promise of oncolytic virus based immunotherapy

Discovering a therapeutic that can counteract the aggressiveness of this disease's mechanism is crucial for improving survival rates for cancer patients and for better understanding the most different types of cancer. In recent years, using these viruses as an anticancer therapy has been thought to be successful. They mostly work by directly destroying cancer cells, activating the immune system to fight cancer, and expressing exogenous effector genes. For the treatment of tumors, oncolytic viruses (OVs), which can be modified to reproduce only in tumor tissues and lyse them while preserving the healthy non-neoplastic host cells and reinstating antitumor immunity which present a novel immunotherapeutic strategy. OVs can exist naturally or be created in a lab by altering existing viruses. These changes heralded the beginning of a new era of less harmful virus-based cancer therapy. We discuss three different types of oncolytic viruses that have already received regulatory approval to treat cancer as well as clinical research using oncolytic adenoviruses. The primary therapeutic applications, mechanism of action of oncolytic virus updates, future views of this therapy will be covered in this chapter.

Oncolytic Adenovirus, a New Treatment Strategy for Prostate Cancer

Prostate cancer is the most common cancer and one of the leading causes of cancer mortality in males. Androgen-deprivation therapy (ADT) is an effective strategy to inhibit tumour growth at early stages. However, 10~50% of cases are estimated to progress to metastatic castration-resistant prostate cancer (mCRPC) which currently lacks effective treatments. Clinically, salvage treatment measures, such as endocrine therapy and chemotherapy, are mostly used for advanced prostate cancer, but their clinical outcomes are not ideal. When the existing clinical therapeutic methods can no longer inhibit the development of advanced prostate cancer, human adenovirus (HAdV)-based gene therapy and viral therapy present promising effects. Pre-clinical studies have shown its powerful oncolytic effect, and clinical studies are ongoing to further verify its effect and safety in prostate cancer treatment. Targeting the prostate by HAdV alone or in combination with radiotherapy and chemotherapy sheds light on patients with castration-resistant and advanced prostate cancer. This review summarizes the advantages of oncolytic virus-mediated cancer therapy, strategies of HAdV modification, and existing preclinical and clinical investigations of HAdV-mediated gene therapy to further evaluate the potential of oncolytic adenovirus in prostate cancer treatment.

Biological causes of immunogenic cancer cell death (ICD) and anti-tumor therapy; Combination of Oncolytic virus-based immunotherapy and CAR T-cell therapy for ICD induction

Chimeric antigen receptor (CAR) T-cell therapy is a promising and rapidly expanding therapeutic option for a wide range of human malignancies. Despite the ongoing progress of CAR T-cell therapy in hematologic malignancies, the application of this therapeutic strategy in solid tumors has encountered several challenges due to antigen heterogeneity, suboptimal CAR T-cell trafficking, and the immunosuppressive features of the tumor microenvironment (TME). Oncolytic virotherapy is a novel cancer therapy that employs competent or genetically modified oncolytic viruses (OVs) to preferentially proliferate in tumor cells. OVs in combination with CAR T-cells are promising candidates for overcoming the current drawbacks of CAR T-cell application in tumors through triggering immunogenic cell death (ICD) in cancer cells. ICD is a type of cellular death in which danger-associated molecular patterns (DAMPs) and tumor-specific antigens are released, leading to the stimulation of potent anti-cancer immunity. In the present review, we discuss the biological causes of ICD, different types of ICD, and the synergistic combination of OVs and CAR T-cells to reach potent tumor-specific immunity.

Carvedilol targets β-arrestins to rewire innate immunity and improve oncolytic adenoviral therapy

Oncolytic viruses are being tested in clinical trials, including in women with ovarian cancer. We use a drug-repurposing approach to identify existing drugs that enhance the activity of oncolytic adenoviruses. This reveals that carvedilol, a β-arrestin-biased β-blocker, synergises with both wild-type adenovirus and the E1A-CR2-deleted oncolytic adenovirus, dl922-947. Synergy is not due to β-adrenergic blockade but is dependent on β-arrestins and is reversed by β-arrestin CRISPR gene editing. Co-treatment with dl922-947 and carvedilol causes increased viral DNA replication, greater viral protein expression and higher titres of infectious viral particles. Carvedilol also enhances viral efficacy in orthotopic, intraperitoneal murine models, achieving more rapid tumour clearance than virus alone. Increased anti-cancer activity is associated with an intratumoural inflammatory cell infiltrate and systemic cytokine release. In summary, carvedilol augments the activity of oncolytic adenoviruses via β-arrestins to re-wire cytokine networks and innate immunity and could therefore improve oncolytic viruses for cancer patient treatment.

Autophagy in Tumor Immunity and Viral-Based Immunotherapeutic Approaches in Cancer

Autophagy is a fundamental catabolic process essential for the maintenance of cellular and tissue homeostasis, as well as directly contributing to the control of invading pathogens. Unsurprisingly, this process becomes critical in supporting cellular dysregulation that occurs in cancer, particularly the tumor microenvironments and their immune cell infiltration, ultimately playing a role in responses to cancer therapies. Therefore, understanding "cancer autophagy" could help turn this cellular waste-management service into a powerful ally for specific therapeutics. For instance, numerous regulatory mechanisms of the autophagic machinery can contribute to the anti-tumor properties of oncolytic viruses (OVs), which comprise a diverse class of replication-competent viruses with potential as cancer immunotherapeutics. In that context, autophagy can either: promote OV anti-tumor effects by enhancing infectivity and replication, mediating oncolysis, and inducing autophagic and immunogenic cell death; or reduce OV cytotoxicity by providing survival cues to tumor cells. These properties make the catabolic process of autophagy an attractive target for therapeutic combinations looking to enhance the efficacy of OVs. In this article, we review the complicated role of autophagy in cancer initiation and development, its effect on modulating OVs and immunity, and we discuss recent progress and opportunities/challenges in targeting autophagy to enhance oncolytic viral immunotherapy.

Crosstalk between oncolytic viruses and autophagy in cancer therapy

Oncolytic viruses have attracted attention as a promising strategy in cancer therapy owing to their ability to selectively infect and kill tumor cells, without affecting healthy cells. They also exert their anti-tumor effects by releasing immunostimulatory molecules from dying cancer cells. Several regulatory mechanisms, such as autophagy, contribute to the anti-tumor properties of oncolytic viruses. Autophagy is a conserved catabolic process in responses to various stresses, such as nutrient deprivation, hypoxia, and infection that produces energy by lysosomal degradation of intracellular contents. Autophagy can support infectivity and replication of the oncolytic virus and enhance their anti-tumor effects via mediating oncolysis, autophagic cell death, and immunogenic cell death. On the other hand, autophagy can reduce the cytotoxicity of oncolytic viruses by providing survival nutrients for tumor cells. In his review, we summarize various types of oncolytic viruses in clinical trials, their mechanism of action, and autophagy machinery. Furthermore, we precisely discuss the interaction between oncolytic viruses and autophagy in cancer therapy and their combinational effects on tumor cells.

Oncolytic Adenovirus in Cancer Immunotherapy

Tumor-selective replicating "oncolytic" viruses are novel and promising tools for immunotherapy of cancer. However, despite their first success in clinical trials, previous experience suggests that currently used oncolytic virus monotherapies will not be effective enough to achieve complete tumor responses and long-term cure in a broad spectrum of cancers. Nevertheless, there are reasonable arguments that suggest advanced oncolytic viruses will play an essential role as enablers of multi-stage immunotherapies including established systemic immunotherapies. Oncolytic adenoviruses (oAds) display several features to meet this therapeutic need. oAds potently lyse infected tumor cells and induce a strong immunogenic cell death associated with tumor inflammation and induction of antitumor immune responses. Furthermore, established and versatile platforms of oAds exist, which are well suited for the incorporation of heterologous genes to optimally exploit and amplify the immunostimulatory effect of viral oncolysis. A considerable spectrum of functional genes has already been integrated in oAds to optimize particular aspects of immune stimulation including antigen presentation, T cell priming, engagement of additional effector functions, and interference with immunosuppression. These advanced concepts have the potential to play a promising future role as enablers of multi-stage immunotherapies involving adoptive cell transfer and systemic immunotherapies.

Pharmacological Inhibition of WEE1 Potentiates the Antitumoral Effect of the dl922-947 Oncolytic Virus in Malignant Mesothelioma Cell Lines

Malignant mesothelioma (MM) is a very aggressive asbestos-related cancer, for which no therapy proves to be effective. We have recently shown that the oncolytic adenovirus dl922-947 had antitumor effects in MM cell lines and murine xenografts. Previous studies demonstrated that dl922-947-induced host cell cycle checkpoint deregulation and consequent DNA lesions associated with the virus efficacy. However, the cellular DNA damage response (DDR) can counteract this virus action. Therefore, we assessed whether AZD1775, an inhibitor of the G2/M DNA damage checkpoint kinase WEE1, could enhance MM cell sensitivity to dl922-947. Through cell viability assays, we found that AZD1775 synergized with dl922-947 selectively in MM cell lines and increased dl922-947-induced cell death, which showed hallmarks of apoptosis (annexinV-positivity, caspase-dependency, BCL-XL decrease, chromatin condensation). Predictably, dl922-947 and/or AZD1775 activated the DDR, as indicated by increased levels of three main DDR players: phosphorylated histone H2AX (γ-H2AX), phospho-replication protein A (RPA)32, phospho-checkpoint kinase 1 (CHK1). Dl922-947 also increased inactive Tyr-15-phosphorylated cyclin-dependent kinase 1 (CDK1), a key WEE1 substrate, which is indicative of G2/M checkpoint activation. This increase in phospho-CDK1 was effectively suppressed by AZD1775, thus suggesting that this compound could, indeed, abrogate the dl922-947-induced DNA damage checkpoint in MM cells. Overall, our data suggest that the dl922-947-AZD1775 combination could be a feasible strategy against MM.

Understanding and addressing barriers to successful adenovirus-based virotherapy for ovarian cancer

Ovarian cancer is the leading cause of death among women with gynecological cancer, with an overall 5-year survival rate below 50% due to a lack of specific symptoms, late stage at time of diagnosis and a high rate of recurrence after standard therapy. A better understanding of heterogeneity, genetic mutations, biological behavior and immunosuppression in the tumor microenvironment have allowed the development of more effective therapies based on anti-angiogenic treatments, PARP and immune checkpoint inhibitors, adoptive cell therapies and oncolytic vectors. Oncolytic adenoviruses are commonly used platforms in cancer gene therapy that selectively replicate in tumor cells and at the same time are able to stimulate the immune system. In addition, they can be genetically modified to enhance their potency and overcome physical and immunological barriers. In this review we highlight the challenges of adenovirus-based oncolytic therapies targeting ovarian cancer and outline recent advances to improve their potential in combination with immunotherapies.

Overexpression of Smac by an Armed Vesicular Stomatitis Virus Overcomes Tumor Resistance

Despite reports of successful clinical cases, many tumors appear to resist infection by oncolytic viruses (OVs). To circumvent this problem, an armed vesicular stomatitis virus was constructed by inserting a transgene to express Smac/DIABLO during virus infection (VSV-S). Endogenous Smac in HeLa cells was diminished during wtVSV infection, whereas the Smac level was enhanced during VSV-S infection. Apoptosis was readily induced by VSV-S, but not wtVSV, infection. More importantly, the tumor volume was reduced to a larger extent when xenografts of 4T1 cells in BALB/c mice and OV-resistant T-47D cells in nude mice were intratumorally injected with VSV-S. VSV-S represents a novel mechanism to overcome tumor resistance, resulting in more significant tumor regression due to enhanced apoptosis.

The role of JNK phosphorylation as a molecular target to enhance adenovirus replication, oncolysis and cancer therapeutic efficacy

Oncolytic adenoviruses (Ads) are cancer selective tumoricidal agents; however their mechanism of Ad-mediated cancer cell lysis, or oncolysis, remains undefined. This report focuses upon the autophagy mediator c-JUN n-terminal kinase (JNK) and its effects upon Ad oncolysis and replication. Previously, E1b-deleted Ads have been used to treat several hundred cancer patients with limited clinical efficacy. We hypothesize that by studying the potential interactions between E1b and JNK, mechanisms to improve oncolytic Ad design and cancer therapeutic efficacy may be elucidated. To test this hypothesis, E1b was selectively deleted from the Ad genome. These studies indicated that Ads encoding E1b induced JNK phosphorylation predominately occurred via E1b-19K. The expression of another crucial Ad gene E1a was then overexpressed by the CMV promoter via the replication competent Ad vector Adhz69; these data indicated that E1A also induced JNK phosphorylation. To assess the effects of host cell JNK expression upon Ad oncolysis and replication, siRNA targeting JNK1 and JNK2 (JNK1/2) were utilized. The oncolysis and replication of the E1b-19K wild-type Ads Ad5 and Adhz63 were significantly attenuated following JNK1/2 siRNA transfection. However the oncolytic effects and replication of the E1b-19K deleted Ad Adhz60 were not altered by JNK1/2 siRNA transfection, further implicating the crucial role of E1b-19K for Ad oncolysis and replication via JNK phosphorylation. This study has demonstrated for the first time that JNK is an intriguing molecular marker associated with enhanced Ad virotherapy efficacy, influencing future Ad vector design.

Fowl adenovirus serotype 4-induced apoptosis, autophagy, and a severe inflammatory response in liver

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotrophic virus that causes severe liver diseases. Upon histological examination, the most remarkable findings in the liver are small multifocal areas of necrosis and mononuclear cell infiltration, including basophilic intranuclear inclusion bodies in hepatocytes surrounded by a clear halo or which fill the entire nucleus. Here, we examined the mechanism responsible for FAdV-4-mediated hepatocyte damage in vivo and in vitro. The results showed that FAdV-4 impaired liver integrity and function, which decreased albumin and blood glucose concentrations and increased the plasma activity of aspartate aminotransferase and lactate dehydrogenase, compared with a non-infected control group (P<0.05). FAdV-4 induced hepatocyte apoptosis in a time-dependent manner in vivo and in vitro. Additionally, we found that FAdV-4 also induced the autophagy of hepatocytes, which promoted the conversion of microtubule-associated protein light chain 3 (LC3-I) to LC3-II, which is a hallmarks of autophagy. Furthermore, the mRNA expressions of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in vivo and in vitro showed a statistically significant increase (P<0.05) compared to that of the control group. However, the molecular mechanisms underlying the FAdV-4-induced apoptotic and autophagic cell death remain unclear. In summation, our observations suggested that FAdV-4 induced liver injury via apoptosis, autophagy, and a severe inflammatory response.

Autophagy in glioma cells: An identity crisis with a clinical perspective

Over the last decade, autophagy has emerged as one of the critical cellular systems that control homeostasis. Besides management of normal homeostatic processes, autophagy can also be induced by tissue damage stress or by rapidly progressing tumors. During tumor progression, autophagy mediates a cellular reaction to the changes inside and outside of cells, which leads to tumor adaptation. Even though the regulation of autophagy seems universal and is a well-described process, its dysregulation and role in glioma progression remain an important topic of investigation. In this review, we summarize recent evidence of autophagy regulation in brain tumor tissues and possible interconnection between signaling pathways that govern cellular responses. This perspective may help to assess the qualitative differences and various outcomes in response to autophagy stimulation.

A p53-independent apoptotic mechanism of adenoviral mutant E1A was involved in its selective antitumor activity for human cancer

The conserved regions (CR) of adenoviral E1A had been shown to be necessary for disruption of pRb-E2F transcription factor complexes and induction of the S phase. Here we constructed a mutant adenoviral E1A with Rb-binding ability absent (E1A 30-60aa and 120-127aa deletion, mE1A) and investigated its antitumor capacities in vitro and in vivo. The mE1A suppressed the viability of tumor cells as efficiently as the wild type E1A, and there was no cytotoxic effect on normal cells. Although the mE1A arrested tumor cell cycle with the same manner as E1A, the former played a different role on cell cycle regulation compared with E1A in normal cells, which might contribute to its selective antitumor activity. E1A and mE1A had accumulated inactive p53, decreased the expression of mdm2, Cdkn1a (also named p21), increased p21's nuclear distribution and induced tumor cell apoptosis in a p53-indenpent manner. Further, E1A or mE1A significantly suppressed tumor growth in subcutaneous hepatocellular carcinoma xenograft models. Especially, tumor-bearing mice treated with mE1A had higher survival rate than those treated with E1A. Our data demonstrated that mutant adenoviral E1A significantly induced tumor cell apoptosis in a p53-indenpednt manner and had selective tumor suppressing ability. The observations of adenoviral E1A mutant had provided a novel mechanism for E1A's complex activities during infection.

RIPK3 promotes adenovirus type 5 activity

Oncolytic adenoviral mutants infect human malignant cells and replicate selectively within them. This induces direct cytotoxicity that can also trigger profound innate and adaptive immune responses. However, the mechanism by which adenoviruses produce cell death remains uncertain. We previously suggested that type 5 adenoviruses, including the E1A CR2 deletion mutant dl922-947, might induce a novel form of programmed death resembling necroptosis. Here we have investigated the roles of core necrosis proteins RIPK1, RIPK3 and MLKL in the cytotoxicity of dl922-947 and other adenovirus serotypes. By electron microscopy, we show that dl922-947 induces similar necrotic morphology as TSZ treatment (TNF-α, Smac mimetic, zVAD.fmk). However, dl922-947-mediated death is independent of TNF-α signalling, does not require RIPK1 and does not rely upon the presence of MLKL. However, inhibition of caspases, specifically caspase-8, induces necroptosis that is RIPK3 dependent and significantly enhances dl922-947 cytotoxicity. Moreover, using CRISPR/Cas9 gene editing, we demonstrate that the increase in cytotoxicity seen upon caspase inhibition is also MLKL dependent. Even in the absence of caspase inhibition, RIPK3 expression promotes dl922-947 and wild-type adenovirus type 5 efficacy both in vitro and in vivo. Together, these results suggest that adenovirus induces a form of programmed necrosis that differs from classical TSZ necroptosis.

The E1B19K-deleted oncolytic adenovirus mutant AdΔ19K sensitizes pancreatic cancer cells to drug-induced DNA-damage by down-regulating Claspin and Mre11

Adenovirus-mediated sensitization of cancer cells to cytotoxic drugs depends on simultaneous interactions of early viral genes with cell death and survival pathways. It is unclear what cellular factors mediate these interactions in the presence of DNA-damaging drugs. We found that adenovirus prevents Chk1-mediated checkpoint activation through inactivation of Mre11 and downregulation of the pChk1 adaptor-protein, Claspin, in cells with high levels of DNA-damage induced by the cytotoxic drugs gemcitabine and irinotecan. The mechanisms for Claspin downregulation involve decreased transcription and increased degradation, further attenuating pChk1-mediated signalling. Live cell imaging demonstrated that low doses of gemcitabine caused multiple mitotic aberrations including multipolar spindles, micro- and multi-nucleation and cytokinesis failure. A mutant virus with the anti-apoptotic E1B19K-gene deleted (AdΔ19K) further enhanced cell killing, Claspin downregulation, and potentiated drug-induced DNA damage and mitotic aberrations. Decreased Claspin expression and inactivation of Mre11 contributed to the enhanced cell killing in combination with DNA-damaging drugs. These results reveal novel mechanisms that are utilised by adenovirus to ensure completion of its life cycle in the presence of cellular DNA damage. Taken together, our findings reveal novel cellular targets that may be exploited when developing improved anti-cancer therapeutics.

Oncolytic virus-induced cell death and immunity: a match made in heaven?

Our understanding of the mechanisms responsible for cancer development has increased enormously over the last decades. However, for many cancers, this has not been translated into a significant improvement in overall survival, and overall mortality remains high. Treatment for many malignancies remains based on surgery, chemotherapy, and radiotherapy. Significant progress has been made toward the development of more specific, more potent, and less invasive treatment modalities, but such targeted therapies remain the exception for most cancers. Thus, cancer therapies based on a different mechanism of action should be explored. The immune system plays an important role in keeping tumor growth at bay. However, in many cases, these responses are not strong enough to keep tumor growth under control. Thus, immunotherapy aims to boost the immune system to suppress tumor growth efficiently. This has been demonstrated by the recent successes of immune checkpoint therapy in several cancers. Oncolytic viruses (OVs) are another exciting class of immunotherapy agent. As well as replicating selectively within and killing tumor cells, OVs are able to elicit potent anti-tumor immune responses. Therapeutic vaccination with OVs, also referred to as cancer virotherapy, can thus be tailored to elicit vigorous cellular immune responses and even target individual malignancies in a personalized manner. In this review, we will describe the intricate link among oncolytic virotherapy, tumor immunology, and immunogenic cell death (ICD) and discuss ways to harness optimally their potential for future cancer therapy.

A novel bladder cancer - specific oncolytic adenovirus by CD46 and its effect combined with cisplatin against cancer cells of CAR negative expression

BACKGROUND

Conditionally replicative oncolytic adenoviruses (CRAds) display significant anti-tumor effects. However, the traditional adenovirus of serotype 5 (Ad5) entering cancer cells via coxsackie virus and adenovirus receptor (CAR) can't be utilized for bladder cancer with low expression of CAR, which limits the application of Ad5.

METHODS

We utilized Ad5/F11p containing the chimeric fiber gene encoding the Ad5 fiber tail domain and Ad11p fiber shaft and knob domains to construct bladder cancer-specific chimeric type viruses Ad5/F11p-PSCAE-UPII-E1A, which can infect bladder cancer cells mediated by CD46 molecule. We carried out series of experiments in vitro to research anti-tumor effect of Ad5/F11p-PSCAE-UPII-E1A and the interaction in combination with cisplatin.

RESULTS

The results demonstrated Ad5/F11p-PSCAE-UPII-E1A could infect bladder cancer cells (T24, EJ and 5637) in a CAR-independent way, and exert anti-tumor effect by blocking the cancer cells in G1 phase and inducing apoptosis. Ad5/F11p-PSCAE-UPII-E1A plus cisplatin enhanced the anti-proliferative effect and increased the number of apoptotic cells compared with viruses or cisplatin alone. Ad5/F11p-PSCAE-UPII-E1A plus cisplatin could upregulate the proteins expression of p53, Bax, and cleaved caspase-3, and downregulated Bcl-2 protein expression in T24, EJ and 5637 cells.

CONCLUSION

We constructed a bladder cancer-specific oncolytic adenovirus and provided new combination treatment strategies for bladder cancer.

Oncolytic Group B Adenovirus Enadenotucirev Mediates Non-apoptotic Cell Death with Membrane Disruption and Release of Inflammatory Mediators

Enadenotucirev (EnAd) is a chimeric group B adenovirus isolated by bioselection from a library of adenovirus serotypes. It replicates selectively in and kills a diverse range of carcinoma cells, shows effective anticancer activity in preclinical systems, and is currently undergoing phase I/II clinical trials. EnAd kills cells more quickly than type 5 adenovirus, and speed of cytotoxicity is dose dependent. The EnAd death pathway does not involve p53, is predominantly caspase independent, and appears to involve a rapid fall in cellular ATP. Infected cells show early loss of membrane integrity; increased exposure of calreticulin; extracellular release of ATP, HSP70, and HMGB1; and influx of calcium. The virus also causes an obvious single membrane blister reminiscent of ischemic cell death by oncosis. In human tumor biopsies maintained in ex vivo culture, EnAd mediated release of pro-inflammatory mediators such as TNF-α, IL-6, and HMGB1. In accordance with this, EnAd-infected tumor cells showed potent stimulation of dendritic cells and CD4+ T cells in a mixed tumor-leukocyte reaction in vitro. Whereas many viruses have evolved for efficient propagation with minimal inflammation, bioselection of EnAd for rapid killing has yielded a virus with a short life cycle that combines potent cytotoxicity with a proinflammatory mechanism of cell death.

Targeting Autophagy for Oncolytic Immunotherapy

Oncolytic viruses (OVs) are capable of exerting anti-cancer effects by a variety of mechanisms, including immune-mediated tumor cell death, highlighting their potential use in immunotherapy. Several adaptation mechanisms such as autophagy contribute to OV-mediated anti-tumor properties. Autophagy regulates immunogenic signaling during cancer therapy which can be utilized to design therapeutic combinations using approaches that either induce or block autophagy to potentiate the therapeutic efficacy of OVs. In this article, we review the complicated interplay between autophagy, cancer, immunity, and OV, summarize recent progress in the contribution of OV-perturbed autophagy to oncolytic immunity, and discuss the challenges in targeting autophagy to enhance oncolytic immunotherapy.

Development of an Oncolytic Adenovirus with Enhanced Spread Ability through Repeated UV Irradiation and Cancer Selection

Oncolytic adenoviruses (Ads) have been shown to be safe and have great potential for the treatment of solid tumors. However, the therapeutic efficacy of Ads is antagonized by limited spread within solid tumors. To develop Ads with enhanced spread, viral particles of an E1-wildtype Ad5 dl309 was repeatedly treated with UV type C irradiation and selected for the efficient replication and release from cancer cells. After 72 cycles of treatment and cancer selection, AdUV was isolated. This vector has displayed many favorable characteristics for oncolytic therapy. AdUV was shown to lyse cancer cells more effectively than both E1-deleted and E1-wildtype Ads. This enhanced cancer cell lysis appeared to be related to increased AdUV replication in and release from infected cancer cells. AdUV-treated A549 cells displayed greater expression of the autophagy marker LC3-II during oncolysis and formed larger viral plaques upon cancer cell monolayers, indicating increased virus spread among cancer cells. This study indicates the potential of this approach of irradiation of entire viral particles for the development of oncolytic viruses with designated therapeutic properties.

Oncolytic viruses: finally delivering

Oncolytic viruses can be found at the confluence of virology, genetic engineering and pharmacology where versatile platforms for molecularly targeted anticancer agents can be designed and optimised. Oncolytic viruses offer several important advantages over traditional approaches, including the following. (1) Amplification of the active agent (infectious virus particles) within the tumour. This avoids unnecessary exposure to normal tissues experienced during delivery of traditional stoichiometric chemotherapy and maximises the therapeutic index. (2) The active cell-killing mechanisms, often independent of programmed death mechanisms, should decrease the emergence of acquired drug resistance. (3) Lytic death of cancer cells provides a pro-inflammatory microenvironment and the potential for induction of an anticancer vaccine response. (4) Tumour-selective expression and secretion of encoded anticancer biologics, providing a new realm of potent and cost-effective-targeted therapeutics.

RAD51 and BRCA2 Enhance Oncolytic Adenovirus Type 5 Activity in Ovarian Cancer

Homologous recombination (HR) function is critically important in high-grade serous ovarian cancer (HGSOC). HGSOC with intact HR has a worse prognosis and is less likely to respond to platinum chemotherapy and PARP inhibitors. Oncolytic adenovirus, a novel therapy for human malignancies, stimulates a potent DNA damage response that influences overall antitumor activity. Here, the importance of HR was investigated by determining the efficacy of adenovirus type 5 (Ad5) vectors in ovarian cancer. Using matched BRCA2-mutant and wild-type HGSOC cells, it was demonstrated that intact HR function promotes viral DNA replication and augments overall efficacy, without influencing viral DNA processing. These data were confirmed in a wider panel of HR competent and defective ovarian cancer lines. Mechanistically, both BRCA2 and RAD51 localize to viral replication centers within the infected cell nucleus and that RAD51 localization occurs independently of BRCA2. In addition, a direct interaction was identified between RAD51 and adenovirus E2 DNA binding protein. Finally, using functional assays of HR competence, despite inducing degradation of MRE11, Ad5 infection does not alter cellular ability to repair DNA double-strand break damage via HR. These data reveal that Ad5 redistributes critical HR components to viral replication centers and enhances cytotoxicity.

IMPLICATIONS

Oncolytic adenoviral therapy may be most clinically relevant in tumors with intact HR function.

In vitro screening of clinical drugs identifies sensitizers of oncolytic viral therapy in glioblastoma stem-like cells

Oncolytic viruses (OV) have broad potential as an adjuvant for the treatment of solid tumors. The present study addresses the feasibility of clinically applicable drugs to enhance the oncolytic potential of the OV Delta24-RGD in glioblastoma. In total, 446 drugs were screened for their viral sensitizing properties in glioblastoma stem-like cells (GSCs) in vitro. Validation was done for 10 drugs to determine synergy based on the Chou Talalay assay. Mechanistic studies were undertaken to assess viability, replication efficacy, viral infection enhancement and cell death pathway induction in a selected panel of drugs. Four viral sensitizers (fluphenazine, indirubin, lofepramine and ranolazine) were demonstrated to reproducibly synergize with Delta24-RGD in multiple assays. After validation, we underscored general applicability by testing candidate drugs in a broader context of a panel of different GSCs, various solid tumor models and multiple OVs. Overall, this study identified four viral sensitizers, which synergize with Delta24-RGD and two other strains of OVs. The viral sensitizers interact with infection, replication and cell death pathways to enhance efficacy of the OV.

Combination of bladder cancer-specific oncolytic adenovirus gene therapy with cisplatin on bladder cancer in vitro

Bladder cancer-specific oncolytic adenovirus Ad/PSCAE/UPII/E1A, carrying E1A gene regulated by human Uroplakin II (UPII) promoter and prostate stem cell antigen enhancer (PSCAE), could kill bladder tumor cells preferentially. The aim of this study was to examine the effects of Ad/PSCAE/UPII/E1A combined with cisplatin on human bladder cancer cells and to identify the underlying mechanisms. The combined effects of Ad/PSCAE/UPII/E1A and cisplatin on EJ, 5637, and BIU-87 bladder cancer cells were evaluated by MTT cell proliferation assay. Cell apoptosis was detected by flow cytometry with fluorescein isothiocyanate-conjugated annexin V (annexin V-FITC) and propidium iodide staining. The activation of the caspase pathway and the expression of Bcl-2 family proteins were determined by western blot assay. Ad/PSCAE/UPII/E1A adenovirus vector could infect bladder cancer cell lines selectively and induce growth inhibition effectively. Of note, the combination treatment of cisplatin and Ad/PSCAE/UPII/E1A could inhibit the proliferation of bladder cancer cells significantly compared with the "alone" treatment. Furthermore, Ad/PSCAE/UPII/E1A plus cisplatin combined treatment resulted in enhanced apoptosis in bladder cancer cells. The enhanced antitumor effects in vitro elicited by Ad/PSCAE/UPII/E1A plus cisplatin were closely related to the increased Fas expression and cleavage of caspase-8 and Bid and decrease in the ratio of anti- to pro-apoptotic proteins followed by activation of caspase-9 and caspase-3, which may contribute to the activation of extrinsic and intrinsic apoptotic pathways. Our results indicate that the combination of Ad/PSCAE/UPII/E1A with cisplatin exerts a synergistic antitumor effect on human bladder cancer cells and is a potential combined treatment strategy for bladder cancer.

Oncolytic Immunotherapy: Dying the Right Way is a Key to Eliciting Potent Antitumor Immunity

Oncolytic viruses (OVs) are novel immunotherapeutic agents whose anticancer effects come from both oncolysis and elicited antitumor immunity. OVs induce mostly immunogenic cancer cell death (ICD), including immunogenic apoptosis, necrosis/necroptosis, pyroptosis, and autophagic cell death, leading to exposure of calreticulin and heat-shock proteins to the cell surface, and/or released ATP, high-mobility group box 1, uric acid, and other damage-associated molecular patterns as well as pathogen-associated molecular patterns as danger signals, along with tumor-associated antigens, to activate dendritic cells and elicit adaptive antitumor immunity. Dying the right way may greatly potentiate adaptive antitumor immunity. The mode of cancer cell death may be modulated by individual OVs and cancer cells as they often encode and express genes that inhibit/promote apoptosis, necroptosis, or autophagic cell death. We can genetically engineer OVs with death-pathway-modulating genes and thus skew the infected cancer cells toward certain death pathways for the enhanced immunogenicity. Strategies combining with some standard therapeutic regimens may also change the immunological consequence of cancer cell death. In this review, we discuss recent advances in our understanding of danger signals, modes of cancer cell death induced by OVs, the induced danger signals and functions in eliciting subsequent antitumor immunity. We also discuss potential combination strategies to target cells into specific modes of ICD and enhance cancer immunogenicity, including blockade of immune checkpoints, in order to break immune tolerance, improve antitumor immunity, and thus the overall therapeutic efficacy.

Adenovirus E1B 19-kilodalton protein modulates innate immunity through apoptotic mimicry

Cells that undergo apoptosis in response to chemical or physical stimuli repress inflammatory reactions, but cells that undergo nonapoptotic death in response to such stimuli lack this activity. Whether cells dying from viral infection exhibit a cell death-type modulatory effect on inflammatory reactions is unknown. We compared the effects on macrophage inflammatory responses of cells dying an apoptotic or a nonapoptotic death as a result of adenoviral infection. The results were exactly opposite to the predictions from the conventional paradigm. Cells dying by apoptosis induced by infection with an adenovirus type 5 (Ad5) E1B 19-kilodalton (E1B 19K) gene deletion mutant did not repress macrophage NF-κB activation or cytokine responses to proinflammatory stimuli, whereas cells dying a nonapoptotic death from infection with E1B 19K-competent, wild-type Ad5 repressed these macrophage inflammatory responses as well as cells undergoing classical apoptosis in response to chemical injury. The immunorepressive, E1B 19K-related cell death activity depended upon direct contact of the virally infected corpses with responder macrophages. Replacement of the viral E1B 19K gene with the mammalian Bcl-2 gene in cis restored the nonapoptotic, immunorepressive cell death activity of virally infected cells. These results define a novel function of the antiapoptotic, adenoviral E1B 19K protein that may limit local host innate immune inflammation during accumulation of virally infected cells at sites of infection and suggest that E1B 19K-deleted, replicating adenoviral vectors might induce greater inflammatory responses to virally infected cells than E1B 19K-positive vectors, because of the net effect of their loss-of-function mutation.

IMPORTANCE

We observed that cells dying a nonapoptotic cell death induced by adenovirus infection repressed macrophage proinflammatory responses while cells dying by apoptosis induced by infection with an E1B 19K deletion mutant virus did not repress macrophage proinflammatory responses and enhanced some cytokine responses. Our results define a new function of the antiapoptotic, adenoviral protein E1B 19K, which we have termed "apoptotic mimicry." Our studies suggest the possibility that the presence or absence of this E1B 19K function could alter the immunological outcome of both natural and therapeutic adenoviral infections. For example, emerging, highly immunopathogenic adenovirus serotypes might induce increased host inflammatory responses as a result of altered E1B 19K function or expression. It is also possible that engineered variations in E1B 19K expression/function could be created during adenovirus vector design that would increase the therapeutic efficacy of replicating adenovirus vectors for vaccines or oncolytic viral targeting of neoplastic cells.

Ionizing radiation enhances dl922-947-mediated cell death of anaplastic thyroid carcinoma cells

dl922-947 is an oncolytic adenovirus potentially suitable for the treatment of aggressive localized tumors, such as anaplastic thyroid carcinoma (ATC). In this study, we have analyzed the effects of dl922-947 in combination with ionizing radiations, testing different schedules of administration and observing synergistic effects only when ATC cells were irradiated 24 h prior to viral infection. Cells undergoing combined treatment exhibited a marked increase in cell death and viral replication, suggesting that irradiation blocks cells in a more permissive state for viral life cycle. We also show that dl922-947 triggers a DNA damage response, characterized by mobilization of the MRN complex (composed by Mre11-Rad50-Nbs1), accumulation of γH2AX, and activation of the checkpoint kinases ataxia telangiectasia mutated (ATM) and Chk1. Based on these observations, we speculate that the DNA damage response acts as a cellular protective mechanism to hinder viral infection and replication. To confirm this hypothesis, we demonstrate that the ATM inhibitor KU55933 increased the oncolytic activity of dl922-947 and its replication. Finally, we validate the potential therapeutic use of this approach by showing in vivo that the combined treatment slows tumor xenograft growth more potently than either irradiation or infection alone.

Oncolytic viruses as therapeutic cancer vaccines

Oncolytic viruses (OVs) are tumor-selective, multi-mechanistic antitumor agents. They kill infected cancer and associated endothelial cells via direct oncolysis, and uninfected cells via tumor vasculature targeting and bystander effect. Multimodal immunogenic cell death (ICD) together with autophagy often induced by OVs not only presents potent danger signals to dendritic cells but also efficiently cross-present tumor-associated antigens from cancer cells to dendritic cells to T cells to induce adaptive antitumor immunity. With this favorable immune backdrop, genetic engineering of OVs and rational combinations further potentiate OVs as cancer vaccines. OVs armed with GM-CSF (such as T-VEC and Pexa-Vec) or other immunostimulatory genes, induce potent anti-tumor immunity in both animal models and human patients. Combination with other immunotherapy regimens improve overall therapeutic efficacy. Coadministration with a HDAC inhibitor inhibits innate immunity transiently to promote infection and spread of OVs, and significantly enhances anti-tumor immunity and improves the therapeutic index. Local administration or OV mediated-expression of ligands for Toll-like receptors can rescue the function of tumor-infiltrating CD8⁺ T cells inhibited by the immunosuppressive tumor microenvironment and thus enhances the antitumor effect. Combination with cyclophosphamide further induces ICD, depletes Treg, and thus potentiates antitumor immunity. In summary, OVs properly armed or in rational combinations are potent therapeutic cancer vaccines.

Targeting autophagy to enhance oncolytic virus-based cancer therapy

INTRODUCTION

Autophagy is a conserved catabolic process crucial in maintaining cellular homeostasis. On infection, oncolytic viruses (OVs) perturb the cellular autophagy machinery in infected tumor cells both in vitro and in vivo. Currently, pharmacological modulation of autophagy in OV-infected tumor cells has been shown to augment OV-mediated antitumor effects in preclinical studies. Combination of OVs with autophagy modulators can, therefore, have many potential applications in the future research on targeting autophagy and novel anticancer therapies.

AREAS COVERED

This review provides a detailed description of known interactions between OVs and autophagy and summarizes the roles of autophagy in OV replication and cell lysis. The recent literature on targeting autophagy with either the autophagy inducers, such as rapamycin, or autophagy inhibitors, such as chloroquine, to increase OV-induced cytotoxicity is reviewed to help researchers in further investigations. The major challenge for investigators is to understand the molecular mechanism underlying the interplay between OV and the autophagy machinery and its effect on oncolysis.

EXPERT OPINION

Targeting the cellular autophagy machinery could be explored as a new therapeutic strategy to enhance OV-mediated antitumor effects in the future.

Oncolytic viruses & their specific targeting to tumour cells

Cancer is one of the major causes of death worldwide. In spite of achieving significant successes in medical sciences in the past few decades, the number of deaths due to cancer remains unchecked. The conventional chemotherapy and radiotherapy have limited therapeutic index and a plethora of treatment related side effects. This situation has provided an impetus for search of novel therapeutic strategies that can selectively destroy the tumour cells, leaving the normal cells unharmed. Viral oncotherapy is such a promising treatment modality that offers unique opportunity for tumour targeting. Numerous viruses with inherent anti-cancer activity have been identified and are in different phases of clinical trials. In the era of modern biotechnology and with better understanding of cancer biology and virology, it has become feasible to engineer the oncolytic viruses (OVs) to increase their tumour selectivity and enhance their oncolytic activity. In this review, the mechanisms by which oncolytic viruses kill the tumour cells have been discussed as also the development made in virotherapy for cancer treatment with emphasis on their tumour specific targeting.

Oncolytic virotherapy with modified adenoviruses and novel therapeutic targets

INTRODUCTION

Numerous oncolytic viral mutants derived from a variety of strains have antitumor efficacy with limited or no toxicity to normal tissue. While all modes of administration were determined to be safe in patients with solid cancers refractory to current standard of care, this therapeutic approach requires further improvements to achieve definite efficacy.

AREAS COVERED

We review the most promising clinical developments with several oncolytic viruses. The focus is on preclinical and clinical findings with replication-selective adenoviral mutants including ONYX-015, H101 and Ad5ΔCR mutants that, to date, are the most studied oncolytic viruses. Cellular pathways reported to play a role in virus-induced cell killing are reviewed as potential targets for the development of more effective combinatorial therapies.

EXPERT OPINION

The most promising clinical outcomes for metastatic cancers have been reported for oncolytic vaccinia and herpes virus mutants expressing the cytokine GMCSF. However, highly efficacious and selective adenoviral mutants have been developed that interact synergistically with cytotoxic drugs in model systems. We anticipate that by delineating the cellular targets for synergistic cancer cell killing in response to adenoviral mutants and drugs such as apoptosis and autophagy signaling, greatly improved anticancer therapies will result in the near future.

Failure of translation of human adenovirus mRNA in murine cancer cells can be partially overcome by L4-100K expression in vitro and in vivo

Adaptive immune responses may be vital in the overall efficacy of oncolytic viruses in human malignancies. However, immune responses to oncolytic adenoviruses are poorly understood because these viruses lack activity in murine cells, which precludes evaluation in immunocompetent murine cancer models. We have evaluated human adenovirus activity in murine cells. We show that a panel of murine carcinoma cells, including CMT64, MOVCAR7, and MOSEC/ID8, can readily be infected with human adenovirus. These cells also support viral gene transcription, messenger RNA (mRNA) processing, and genome replication. However, there is a profound failure of adenovirus protein synthesis, especially late structural proteins, both in vitro and in vivo, with reduced loading of late mRNA onto ribosomes. Our data also show that in trans expression of the nonstructural late protein L4-100K increases both the amount of viral mRNA on ribosomes and the synthesis of late proteins, accompanied by reduced phosphorylation of eIF2α and improved anticancer efficacy. These results suggest that murine models that support human adenovirus replication could be generated, thus allowing evaluation of human adenoviruses in immunocompetent mice.

Inhibition of autophagy enhances the effects of E1A-defective oncolytic adenovirus dl922-947 against glioma cells in vitro and in vivo

Oncolytic viruses represent a novel therapeutic approach for aggressive tumors, such as glioblastoma multiforme, which are resistant to available treatments. Autophagy has been observed in cells infected with oncolytic viruses; however, its role in cell death/survival is unclear. To elucidate the potential therapeutic use of autophagy modulators in association with viral therapy, we analyzed autophagy induction in human glioma cell lines U373MG and U87MG infected with the oncolytic adenovirus dl922-947. dl922-947 infection triggered an autophagic cellular response, as shown by the development of acidic vesicular organelles, LC3-I→LC3-II conversion, and reduction of p62 levels. However, on infection, the Akt/mTOR/p70s6k pathway, which negatively regulates autophagy, was activated, whereas the ERK1/2 pathway, a positive regulator of autophagy, was inhibited. Accordingly, MEK inhibition by PD98059 sensitized glioma cells to dl922-947 effects, whereas autophagy induction by rapamycin protected cells from dl922-947-induced death. Treatment with two inhibitors of autophagy, chloroquine and 3-methyladenine, increased the cytotoxic effects of dl922-947 in vitro. In vivo, the growth of U87MG-induced xenografts was further reduced by adding chloroquine to the dl922-947 treatment. In conclusion, autophagy acts as a survival response in glioma cells infected with dl922-947, thus suggesting autophagy inhibitors as adjuvant/neoadjuvant drugs in oncolytic virus-based treatments.

Genetically engineered oncolytic adenovirus induces autophagic cell death through an E2F1-microRNA-7-epidermal growth factor receptor axis

Autophagy is known to have a cytoprotective role under various cellular stresses; however, it also results in robust cell death as an important safeguard mechanism that protects the organism against invading pathogens and unwanted cancer cells. Autophagy is regulated by cell signalling including microRNA (miRNA), a post-transcriptional regulator of gene expression. Here, we show that genetically engineered telomerase-specific oncolytic adenovirus induced miR-7 expression, which is significantly associated with its cytopathic activity in human cancer cells. Virus-mediated miR-7 upregulation depended on enhanced expression of the E2F1 protein. Ectopic expression of miR-7 suppressed cell viability and induced autophagy by inhibiting epidermal growth factor receptor (EGFR) expression. Our results suggest that oncolytic adenovirus induces autophagic cell death through an E2F1-miR-7-EGFR pathway in human cancer cells, providing a novel insight into the molecular mechanism of an anticancer virotherapy.

Proinflammatory characteristics of SMAC/DIABLO-induced cell death in antitumor therapy

Molecular mimetics of the caspase activator second mitochondria-derived activator of caspase (SMAC) are being investigated for use in cancer therapy, but an understanding of in vivo effects remains incomplete. In this study, we offer evidence that SMAC mimetics elicit a proinflammatory cell death in cancer cells that engages an adaptive antitumor immune response. Cancer cells of different histologic origin underwent apoptosis when transduced with lentiviral vectors encoding a cytosolic form of the SMAC mimetic LV-tSMAC. Strikingly, treatment of tumor-bearing mice with LV-tSMAC resulted in the induction of apoptosis, activation of antitumor immunity, and enhanced survival. Antitumor immunity was accompanied by an increase of tumor-infiltrating lymphocytes displaying low PD-1 expression, high lytic capacity, and high levels of IFN-γ when stimulated. We also noted in vivo a decrease in regulatory T cells along with in vitro activation of tumor-specific CD8(+) T cells by dendritic cells (DC) isolated from tumor draining lymph nodes. Last, tumor-specific cytotoxic T cells were also found to be activated in vivo. Mechanistic analyses showed that transduction of cancer cells with LV-tSMAC resulted in exposure of calreticulin but not release of HMGB1 or ATP. Nevertheless, DCs were activated upon engulfment of dying cancer cells. Further validation of these findings was obtained by their extension in a model of human melanoma using transcriptionally targeted LV-tSMAC. Together, our findings suggest that SMAC mimetics can elicit a proinflammatory cell death that is sufficient to activate adaptive antitumor immune responses in cancer.

Downregulation of Mcl-1 synergizes the apoptotic response to combined treatment with cisplatin and a novel fiber chimeric oncolytic adenovirus

The aim of this study was to examine the effects of SG511, a novel fiber chimeric oncolytic adenovirus with E1B 55-kDa deleted, combined with cisplatin on cancer cells and to identify their underlying mechanisms. The combined effect of SG511 and cisplatin on HeLa and HT-29 cells was assessed by a crystal violet assay and an MTT assay, followed by combination index analysis. Cell apoptosis was evaluated by DAPI staining and visualized by fluorescein-mediated signal detection. Mitochondrial membrane potential was detected by flow cytometric analysis of Rhodamine 123 accumulation. The activation of the caspase pathway and the expression of Bcl-2 family proteins were examined by western blotting. Results show that SG511 vector infected various human cancer cell lines and induced growth inhibition effectively. Of note, SG511 synergistically enhanced the anti-proliferative activity of cisplatin, a DNA-damaging agent, against HeLa and HT-29 cells in vitro, concomitantly with increased apoptosis and activation of the mitochondrial pathway. Furthermore, treatment with SG511 alone or in combination with cisplatin resulted in reduced expression the anti-apoptotic Bcl-2 family member Mcl-1 in HeLa and HT-29 cells. Importantly, this combination did not increase the growth inhibitory effects of cisplatin on human normal liver cells. Collectively, SG511, a novel fiber chimeric oncolytic adenovirus, sensitizes cancer cells to apoptosis by reducing anti-apoptotic Mcl-1 protein levels.

The E1B19K oncoprotein complexes with Beclin 1 to regulate autophagy in adenovirus-infected cells

The mechanisms underlying adenovirus-mediated autophagy are currently unknown. Recently, members of the Bcl-2 protein family have been associated with autophagy. It was also reported that the Bcl-2 homology-3 (BH3) domain encompassed by both Beclin 1 and Bcl-2-like proteins is essential for their pro-autophagy or anti-autophagy functions. Here, we report for the first time that E1B19K, the adenovirus BH3 domain protein, interacts with Beclin 1 to initiate autophagy. Using immunoprecipitation assays we showed that expression of E1B19K in the host cell disrupted the physical interactions between Beclin 1 and Bcl-2 proteins. The displacement of Bcl-2 was coincident with the recruitment of PI3KC3 to the Beclin 1/E1B19K complexes. As a result of the changes in the components of the Beclin 1 interactome, there was activation of PI3KC3, as showed by the identification of PI3K-mediated lipid phosphorylation, and subsequent formation of autophagosomes. Importantly, the BH3 functional domain of E1B19K protein was required for the heterodimerization with Beclin 1. We also showed that transfer of E1B19K was sufficient to trigger autophagy in cancer cells. Consistent with these data, mutant adenoviruses encompassing a deletion of the E1B19K gene produced a marked deficiency in the capability of the virus to induce autophagy as showed by examining the lipidation and cleavage of LC3-I as well as the subcellular localization of LC3-II, the decrease in the levels of p62, and the formation of autophagosomes. Our work offers new information on the mechanisms of action of the adenoviral E1B19K protein as partner of Beclin 1 and positive regulator of autophagy.

Anti-tumor function of double-promoter regulated adenovirus carrying SEA gene, in the treatment of bladder cancer

To construct an adenovirus carrying SEA gene and regulated by telomerase reverse transcriptase (hTERT) and hypoxia-inducible factor (HIF) promoters and investigate its anti-tumor function in vitro, as well as its role in lymphocyte production. hTERT and HIF genes were cloned into adenovirus E1A and E1B shuttle plasmids. The control vector for SEA gene expression is under the regulation of CMV and SV40 promoters. Double regulation was obtained through homologous recombination. The positive clones of replicable adenovirus H2-SEA-Ad were selected by plaque assay. The adenovirus was purified, titrated, and DNA was verified by PCR. The obtained virus was used to infect EJ bladder tumor cells and the SEA Mrna, and protein expression was measured by RT-PCR, western blot, and immunofluorescence microscopy, respectively. Co-culture of lymphocytes and tumor cells was observed dynamically under microscope. The construction of shuttle plasmid p315-CSS-SEA was confirmed by PCR and DNA sequencing. Insertion of superantigen SEA gene in adenovirus (H2-SEA-Ad.SEA) was obtained by homologous recombination. In lymphocytes and tumor cell co-culture, the number of viable tumor cells in test groups was significantly lower than that in control group after 12, 24, and 48 h of treatment. Production of interleukin-2, interleukin-4, and tumor necrosis factor were higher in test groups than in control group. Expression of SEA gene in bladder tumor cells by adenoviral vector caused reduced tumor cell proliferation, as well as stimulation of inflammatory cytokine productions in co-cultures with lymphocytes.

Adenovirus, autophagy and lysis: ecstasies and agonies

Evaluation of: Rodriguez-Rocha H, Gomez-Gutierrez JG, Garcia-Garcia A et al. Adenoviruses induce autophagy to promote virus replication and oncolysis. Virology 416(1–2), 9–15 (2011). This publication addresses the potentiating effects of autophagy induction on adenovirus replication and cell lysis. After demonstrating the induction of autophagy during infection in several cancer cell lines, the authors investigated how adenovirus benefits from this phenomenon. By interrogating the differences in autophagy regulation among wild-type adenovirus, the E1B-deleted Adhz60 and AdLacZ, a nonreplicating adenovirus, the authors present evidence that autophagy is only triggered by a replication-competent adenovirus. Moreover, they show that when autophagy is inhibited, it becomes a limiting factor in oncolytic efficacy. The significance of this report is based on the potential of targeting autophagy modulation to enhance oncolytic adenoviral therapy. This paper evaluation will shed light on the context of these studies, by summarizing previous findings and interpreting the data with regard to oncolytic adenovirus-based therapies.

Human dendritic cells efficiently phagocytose adenoviral oncolysate but require additional stimulation to mature

Oncolytic adenoviruses are emerging agents for treatment of cancer by tumor-restricted virus infection and cell lysis. Clinical trials have shown that oncolytic adenoviruses are well tolerated in patients but also that their antitumor activity needs improvement. A promising strategy toward this end is to trigger systemic and prolonged antitumor immunity by adenoviral oncolysis. Antitumor immune activation depends in large part on antigen presentation and T cell activation by dendritic cells (DCs). Thus, it is likely that the interaction of lysed tumor cells with DCs is a key determinant of such "oncolytic vaccination." Our study reveals that human DCs effectively phagocytose melanoma cells at late stages of oncolytic adenovirus infection, when the cells die showing preferentially features of necrotic cell death. Maturation, migration toward CCL19 and T cell stimulatory capacity of DCs, crucial steps for immune induction, were, however, not induced by phagocytosis of oncolysate, but could be triggered by a cytokine maturation cocktail. Therefore, oncolytic adenoviruses and adenoviral oncolysate did not block DC maturation, which is in contrast to reports for other oncolytic viruses. These results represent a rationale for inserting immunostimulatory genes into oncolytic adenovirus genomes to assure critical DC maturation. Indeed, we report here that adenoviral transduction of melanoma cells with CD40L during oncolysis triggers the maturation of human DCs with T cell stimulatory capacity similar to DCs matured by cytokines. We conclude that triggering and shaping DC-induced antitumor immunity by oncolytic adenoviruses "armed" with immunostimulatory genes holds promise for improving the therapeutic outcome of viral oncolysis in patients.

Adenoviruses induce autophagy to promote virus replication and oncolysis

Adenoviruses with deletion of E1b have been used in clinical trials to treat cancers that are resistant to conventional therapies. The efficacy of viral replication within cancer cells determines the results of oncolytic therapy, which remains poorly understood and requires further improvement. In this report, we show that adenoviruses induce autophagy by increasing the conversion of LC3-I to LC3-II and the formation of the Atg12-Atg5 complex. Inhibition of autophagy with 3-methyladenine (3MA) resulted in a decreased synthesis of adenovirus structural proteins, and thereby a poor viral replication; promotion of autophagy with rapamycin increased adenovirus yield. This study indicates that adenovirus-induced autophagy correlates positively with virus replication and oncolytic cell death, and that autophagy may generate nutrients that can be used for building viral progeny particles. These results further suggest that chemotherapeutic agents that increase cancer cell autophagy may improve the efficacy of oncolytic virotherapy.

Efficacy of oncolytic mutants targeting pRb and p53 pathways is synergistically enhanced when combined with cytotoxic drugs in prostate cancer cells and tumor xenografts

Replication-selective oncolytic adenoviruses have proven safety records with promising clinical outcomes. However, strategies to improve efficacy are still required. Here we report greatly improved antitumor efficacy for both attenuated (dl1520) and highly potent (dl922–947) oncolytic mutants in combination with the current standard of care for late-stage hormone-independent prostate cancers, mitoxantrone or docetaxel. In agreement with previous reports, dl922–947 had superior potency compared with dl1520 both as a single agent and in combination with cytotoxic drugs. The dl922–947 mutant caused significant synergistic cell killing in both drug-insensitive and -sensitive prostate cancer cell lines, PC3 and DU145, respectively, when combined with docetaxel or mitoxantrone. The magnitude of the synergistic response was greatest for dl1520 whereas overall efficacy was greatest for dl922–947, and the latter was also more efficacious in vivo in prostate cancer models. In DU145 and PC3 cells increased viral uptake (up to 9- and 8-fold, respectively), E1A expression, and altered cell cycle progression contributed to the synergistic cell killing. A similar trend was also detected in LNCaP cells. Potent E1A expression was essential for the response. In murine xenograft models (DU145 and PC3) tumor growth inhibition was improved when suboptimal doses of docetaxel and viral mutants were combined. These findings demonstrate that the efficacy of highly potent oncolytic mutants such as dl922–947 that target the retinoblastoma protein (pRb) pathway could be further enhanced even with low drug doses, and support the deletion of the E1ACR2 region in future candidate adenoviruses for treatment of hormone-independent prostate cancers.

Genomic DNA damage and ATR-Chk1 signaling determine oncolytic adenoviral efficacy in human ovarian cancer cells

Oncolytic adenoviruses replicate selectively within and lyse malignant cells. As such, they are being developed as anticancer therapeutics. However, the sensitivity of ovarian cancers to adenovirus cytotoxicity varies greatly, even in cells of similar infectivity. Using both the adenovirus E1A-CR2 deletion mutant dl922-947 and WT adenovirus serotype 5 in a panel of human ovarian cancer cell lines that cover a 3-log range of sensitivity, we observed profound overreplication of genomic DNA only in highly sensitive cell lines. This was associated with the presence of extensive genomic DNA damage. Inhibition of ataxia telangiectasia and Rad3-related checkpoint kinase 1 (ATR-Chk1), but not ataxia telangiectasia mutated (ATM), promoted genomic DNA damage and overreplication in resistant and partially sensitive cells. This was accompanied by increased adenovirus cytotoxicity both in vitro and in vivo in tumor-bearing mice. We also demonstrated that Cdc25A was upregulated in highly sensitive ovarian cancer cell lines after adenovirus infection and was stabilized after loss of Chk1 activity. Knockdown of Cdc25A inhibited virus-induced DNA damage in highly sensitive cells and blocked the effects of Chk1 inhibition in resistant cells. Finally, inhibition of Chk1 decreased homologous recombination repair of virus-induced genomic DNA double-strand breaks. Thus, virus-induced host cell DNA damage signaling and repair are key determinants of oncolytic adenoviral activity, and promoting unscheduled DNA synthesis and/or impeding homologous recombination repair could potentiate the effects of oncolytic adenoviruses in the treatment of ovarian cancer.

Inhibition of the inflammatory cytokine TNF-α increases adenovirus activity in ovarian cancer via modulation of cIAP1/2 expression

Oncolytic adenoviruses show promise as a cancer treatment. However, they generate acute inflammatory responses with production of cytokines, including tumor necrosis factor-α (TNF-α). We investigated whether inhibition of TNF-α augments efficacy of the E1A CR2-deleted adenovirus dl922-947 in ovarian cancer. dl922-947 induced transcription of TNF-α and its downstream signaling targets interleukin-6 and -8 (IL-6 and IL-8) in ovarian cancer cells. In vitro, RNAi-mediated knockdown of TNF-α reduced production of multiple inflammatory cytokines after infection and increased ovarian cancer cell sensitivity to virus cytotoxicity, as did treatment with the anti-TNF-α antibody infliximab. In vivo, stable knockdown of TNF-α in IGROV-1 xenografts increased the anticancer activity of dl922-947. In addition, inhibition of TNF-α using monoclonal antibodies also improved dl922-947 efficacy. This increased efficacy resulted from suppression of cellular inhibitor of apoptosis-1 and -2 (cIAP1 and cIAP2) transcription in malignant cells and a consequent increase in caspase-mediated apoptosis. These findings suggest that TNF-α acts as a survival factor in adenovirus-infected cells. Combining TNF-α inhibition with oncolytic adenoviruses could improve antitumor activity in clinical trials.

Low-dose paclitaxel synergizes with oncolytic adenoviruses via mitotic slippage and apoptosis in ovarian cancer

The microtubule-stabilizing drug paclitaxel has activity in relapsed ovarian cancer. dl922-947, an oncolytic adenovirus with a 24-bp deletion in E1A CR2, replicates selectively within and lyses cells with a dysregulated Rb pathway and has efficacy in ovarian cancer. In the aggressive A2780CP xenograft, combination treatment with weekly dl922-947 and paclitaxel has significantly greater efficacy than either treatment alone and can produce complete tumor eradication in some animals. We investigated the mechanisms of paclitaxel's synergy with dl922-947 in ovarian cancer. The host-cell microtubule network is grossly rearranged and stabilized following adenovirus infection, but paclitaxel does not increase this significantly. Paclitaxel does not synergize by increasing infectivity, viral protein expression or virus release. However, destabilizing the microtubule network with nocodazole reduces viral exit, revealing a novel microtubule-dependent pathway for non-lytic adenoviral exit. dl922-947 can override multiple cell cycle checkpoints but induces cell death by a non-apoptotic mechanism. In combination, dl922-947 and low-dose paclitaxel induces aberrant, multipolar mitoses, mitotic slippage and multinucleation, triggering an apoptotic cell death.

p21 Promotes oncolytic adenoviral activity in ovarian cancer and is a potential biomarker

The oncolytic adenovirus dl922-947 replicates selectively within and lyses cells with a dysregulated Rb pathway, a finding seen in > 90% human cancers. dl922-947 is more potent than wild type adenovirus and the E1B-deletion mutant dl1520 (Onyx-015). We wished to determine which host cell factors influence cytotoxicity. SV40 large T-transformed MRC5-VA cells are 3-logs more sensitive to dl922-947 than isogenic parental MRC5 cells, confirming that an abnormal G1/S checkpoint increases viral efficacy. The sensitivity of ovarian cancer cells to dl922-947 varied widely: IC₅₀ values ranged from 51 (SKOV3ip1) to 0.03 pfu/cell (TOV21G). Cells sensitive to dl922-947 had higher S phase populations and supported earlier E1A expression. Cytotoxicity correlated poorly with both infectivity and replication, but well with expression of p21 by microarray and western blot analyses. Matched p21+/+ and -/- Hct116 cells confirmed that p21 influences dl922-947 activity in vitro and in vivo. siRNA-mediated p21 knockdown in sensitive TOV21G cells decreases E1A expression and viral cytotoxicity, whilst expression of p21 in resistant A2780CP cells increases virus activity in vitro and in intraperitoneal xenografts. These results highlight that host cell factors beyond simple infectivity can influence the efficacy of oncolytic adenoviruses. p21 expression may be an important biomarker of response in clinical trials.