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

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

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

Characterization of Pre-Existing Neutralizing Antibody to Human Adenovirus Types 5 and 49 and Simian Type 23 in Chinese Population

Recombinant adenovirus vector has been widely used in vaccine development. Due to the pre-existing immunity of human adenovirus type 5 (HAd5) in humans, a range of rare human and chimpanzee adenovirus vectors have been developed. In the previous study, we constructed novel adenovirus vector Sad23L and Ad49L based on simian adenovirus type 23 (SAd23) and human adenovirus type 49 (HAd49), which were used in the development of ZIKV and COVID-19 vaccines. However, the levels of pre-existing neutralizing antibody (NAb) of HAd49 and SAd23 remain unclear in China. In this study, we measured NAbs titers of HAd5, HAd49, and SAd23 in 600 healthy blood donors from 6 regions across China. NAb titer of HAd49 or SAd23 was significantly lower than that of HAd5 (p < 0.001). There was no significant difference in seroprevalence and NAb titers of three adenoviruses between male and female donors. The seropositive rates of HAd5 and SAd23 increased with age growth in a positive correlation (p < 0.01), while in contrast to HAd5, HAd49, and SAd23 had a low level of pre-existing immunity in Chinese population, which suggested that Ad49L and Sad23L vectors could be used in vaccine development for humans.

Safety and efficacy of the tumor-selective adenovirus enadenotucirev, in combination with nivolumab, in patients with advanced/metastatic epithelial cancer: a phase I clinical trial (SPICE)

BACKGROUND

Novel combination therapies to overcome anti-PD-1 resistance are required. Enadenotucirev, a tumor-selective blood stable adenoviral vector, has demonstrated a manageable safety profile and ability to increase tumor immune-cell infiltration in phase I studies in solid tumors.

METHODS

We conducted a phase I multicenter study of intravenous enadenotucirev plus nivolumab in patients with advanced/metastatic epithelial cancer not responding to standard therapy. Co-primary objectives were safety/tolerability and maximum tolerated dose and/or maximum feasible dose (MTD/MFD) of enadenotucirev plus nivolumab. Additional endpoints included response rate, cytokine responses, and anti-tumor immune responses.

RESULTS

Overall, 51 heavily pre-treated patients were treated, 45/51 (88%) of whom had colorectal cancer (35/35 patients with information available were microsatellite instability-low/microsatellite stable) and 6/51 (12%) had squamous cell carcinoma of the head and neck. The MTD/MFD of enadenotucirev plus nivolumab was not reached, with the highest dose level tested (1×10¹² vp day 1; 6×10¹² vp days 3 and 5) shown to be tolerable. Overall, 31/51 (61%) patients experienced a grade 3-4 treatment-emergent adverse event (TEAE), most frequently anemia (12%), infusion-related reaction (8%), hyponatremia (6%), and large intestinal obstruction (6%). Seven (14%) patients experienced serious TEAEs related to enadenotucirev; the only serious TEAE related to enadenotucirev occurring in >1 patient was infusion-related reaction (n=2). Among the 47 patients included in efficacy analyses, median progression-free survival was 1.6 months, objective response rate was 2% (one partial response for 10 months), and 45% of patients achieved stable disease. Median overall survival was 16.0 months; 69% of patients were alive at 12 months. Persistent increases in Th1 and related cytokines (IFNγ, IL-12p70, IL-17A) were seen from ~day 15 in two patients, one of whom had a partial response. Among the 14 patients with matching pre-tumor and post-tumor biopsies, 12 had an increase in intra-tumoral CD8⁺ T-cell infiltration and 7 had increased markers of CD8 T-cell cytolytic activity.

CONCLUSIONS

Intravenously dosed enadenotucirev plus nivolumab demonstrated manageable tolerability, an encouraging overall survival and induced immune cell infiltration and activation in patients with advanced/metastatic epithelial cancer. Studies of next-generation variants of enadenotucirev (T-SIGn vectors) designed to further re-program the tumor microenvironment by expressing immune-enhancer transgenes are ongoing.

TRIAL REGISTRATION NUMBER

NCT02636036.

Oncolytic Adenoviruses Armed with Co-Stimulatory Molecules for Cancer Treatment

In clinical trials, adenovirus vectors (AdVs) are commonly used platforms for human gene delivery therapy. High genome capacity and flexibility in gene organization make HAdVs suitable for cloning. Recent advancements in molecular techniques have influenced the development of genetically engineered adenovirus vectors showing therapeutic potential. Increased molecular understanding of the benefits and limitations of HAdVs in preclinical research and clinical studies is a crucial point in the engineering of refined oncolytic vectors. This review presents HAdV species (A-G) used in oncotherapy. We describe the adenovirus genome organizations and modifications, the possibilities oncolytic viruses offer, and their current limitations. Ongoing and ended clinical trials based on oncolytic adenoviruses are presented. This review provides a broad overview of the current knowledge of oncolytic therapy. HAdV-based strategies targeting tumors by employing variable immune modifiers or delivering immune stimulatory factors are of great promise in the field of immune oncologyy This approach can change the face of the fight against cancer, supplying the medical tools to defeat tumors more selectively and safely.

Non-human primate adenoviruses of the Human Adenovirus B species are potent and broadly-acting oncolytic vector candidates

The use of human adenoviruses (hAds) as oncolytic agents has demonstrated considerable potential. However, their efficacy in clinical studies is generally moderate and often varies between patients. This may, in part, be attributable to variable pre-existing neutralizing immunity in patients, which can impact the antitumor efficacy and lead to response heterogeneity. Our aim was to isolate new Ads for the development of oncolytic vectors with low prevalence of neutralizing immunity in the human population. To this end, we isolated a collection of new nonhuman primate (nhp) Ads from stool samples of four great ape species held captive. We elected 12 isolates comprising the broadest genetic variability for further characterization. For three new nhpAds, all classified as the human adenovirus B (HAdV-B) species, no neutralizing activity could be detected when exposed to a preparation of immunoglobulins isolated from a pool of >1,000 donors as a surrogate of population immunity. In addition, the nhpAds of the HAdV-B species showed enhanced oncolytic potency compared to nhpAds of the HAdV-C species as well as to human adenovirus type 5 (HAdV-C5) in vitro when tested in a panel of 29 human cancer cell lines. Next-generation sequencing of the viral genomes revealed higher sequence similarity between hAds and nhpAds of HAdV-B compared to HAdV-C, which might underlie the differences in oncolytic ability. As a proof-of-concept, the Rb-binding domain of the E1A protein of the gorilla-derived HAdV-B nhpAd-lumc007 was deleted, thereby creating a new oncolytic derivative, which demonstrated increased oncolytic potential compared to HAdV-C5. Collectively, our data demonstrate that nhpAds of the HAdV-B species can serve as an alternative for the development of potent oncolytic Ad vectors with limited pre-existing neutralizing immunity in humans.

Safety and efficacy of the tumor-selective adenovirus enadenotucirev with or without paclitaxel in platinum-resistant ovarian cancer: a phase 1 clinical trial

BACKGROUND

Treatment outcomes remain poor in recurrent platinum-resistant ovarian cancer. Enadenotucirev, a tumor-selective and blood stable adenoviral vector, has demonstrated a manageable safety profile in phase 1 studies in epithelial solid tumors.

METHODS

We conducted a multicenter, open-label, phase 1 dose-escalation and dose-expansion study (OCTAVE) to assess enadenotucirev plus paclitaxel in patients with platinum-resistant epithelial ovarian cancer. During phase 1a, the maximum tolerated dose of intraperitoneally administered enadenotucirev monotherapy (three doses; days 1, 8 and 15) was assessed using a 3+3 dose-escalation model. Phase 1b included a dose-escalation and an intravenous dosing dose-expansion phase assessing enadenotucirev plus paclitaxel. For phase 1a/b, the primary objective was to determine the maximum tolerated dose of enadenotucirev (with paclitaxel in phase 1b). In the dose-expansion phase, the primary endpoint was progression-free survival (PFS). Additional endpoints included response rate and T-cell infiltration.

RESULTS

Overall, 38 heavily pretreated patients were enrolled and treated. No dose-limiting toxicities were observed at any doses. However, frequent catheter complications led to the discontinuation of intraperitoneal dosing during phase 1b. Intravenous enadenotucirev (1×1012 viral particles; days 1, 3 and 5 every 28-days for two cycles) plus paclitaxel (80 mg/m2; days 9, 16 and 23 of each cycle) was thus selected for dose-expansion. Overall, 24/38 (63%) patients experienced at least 1 Grade ≥3 treatment-emergent adverse event (TEAE); most frequently neutropenia (21%). Six patients discontinued treatment due to TEAEs, including one patient due to a grade 2 treatment-emergent serious AE of catheter site infection (intraperitoneal enadenotucirev monotherapy). Among the 20 patients who received intravenous enadenotucirev plus paclitaxel, 4-month PFS rate was 64% (median 6.2 months), objective response rate was 10%, 35% of patients achieved stable disease and 65% of patients had a reduction in target lesion burden at ≥1 time point. Five out of six patients with matched pre-treatment and post-treatment biopsies treated with intravenous enadenotucirev plus paclitaxel had increased (mean 3.1-fold) infiltration of CD8 +T cells in post-treatment biopsies.

CONCLUSIONS

Intravenously dosed enadenotucirev plus paclitaxel demonstrated manageable tolerability, an encouraging median PFS and increased tumor immune-cell infiltration in platinum-resistant ovarian cancer.

TRIAL REGISTRATION NUMBER

NCT02028117.

Immunomodulatory Arming Factors-The Current Paradigm for Oncolytic Vectors Relies on Immune Stimulating Molecules

The dogma of engineering oncolytic viral vectors has shifted from emphasizing the viral lysis of individual cancer cells to the recruitment and coordination of the adaptive immune system to clear the tumor. To accomplish this, researchers have been adding several classes of transgenes to their preferred viral platforms. The most prevalent of these include antibodies and targeting moieties, interleukins and cytokines, and genes which rely on small molecule co-administration for tumor killing. Most current vectors rely exclusively on one of these types of transgenes to elicit the desired immune response to clear tumors, but are not mutually exclusive, with several larger OVs armed with several of these factors. The common theme of emerging armed vectors is to simply initiate or enhance infiltration of effector CD8+ T cells to clear the tumor locally at OV infection sites, and systemically throughout the body where the OV has not infected tumor cells. The precision of oncolytic vectors to target a cell type or tissue remains its key advantage over small-molecule drugs. Unlike chemo- and other drug therapies, viral vectors can be made to specifically infect and grow within tumor cells. This ensures localized expression of the therapeutic transgene to the diseased tissue, thereby limiting systemic toxicity. This review will examine the immunomodulating transgenes of current OVs, describe their general effect on the immune system, and provide the rationale for each vector's use in clearing its targeted tumor.

In Vitro and In Vivo Evaluation of Human Adenovirus Type 49 as a Vector for Therapeutic Applications

The human adenovirus phylogenetic tree is split across seven species (A-G). Species D adenoviruses offer potential advantages for gene therapy applications, with low rates of pre-existing immunity detected across screened populations. However, many aspects of the basic virology of species D-such as their cellular tropism, receptor usage, and in vivo biodistribution profile-remain unknown. Here, we have characterized human adenovirus type 49 (HAdV-D49)-a relatively understudied species D member. We report that HAdV-D49 does not appear to use a single pathway to gain cell entry, but appears able to interact with various surface molecules for entry. As such, HAdV-D49 can transduce a broad range of cell types in vitro, with variable engagement of blood coagulation FX. Interestingly, when comparing in vivo biodistribution to adenovirus type 5, HAdV-D49 vectors show reduced liver targeting, whilst maintaining transduction of lung and spleen. Overall, this presents HAdV-D49 as a robust viral vector platform for ex vivo manipulation of human cells, and for in vivo applications where the therapeutic goal is to target the lung or gain access to immune cells in the spleen, whilst avoiding liver interactions, such as intravascular vaccine applications.

Tackling HLA Deficiencies Head on with Oncolytic Viruses

Dysregulation of HLA (human leukocyte antigen) function is increasingly recognized as a common escape mechanism for cancers subject to the pressures exerted by immunosurveillance or immunotherapeutic interventions. Oncolytic viruses have the potential to counter this resistance by upregulating HLA expression or encouraging an HLA-independent immunological responses. However, to achieve the best therapeutic outcomes, a prospective understanding of the HLA phenotype of cancer patients is required to match them to the characteristics of different oncolytic strategies. Here, we consider the spectrum of immune competence observed in clinical disease and discuss how it can be best addressed using this novel and powerful treatment approach.

The Fiber Knob Protein of Human Adenovirus Type 49 Mediates Highly Efficient and Promiscuous Infection of Cancer Cell Lines Using a Novel Cell Entry Mechanism

The human adenovirus (HAdV) phylogenetic tree is diverse, divided across seven species and comprising over 100 individual types. Species D HAdV are rarely isolated with low rates of preexisting immunity, making them appealing for therapeutic applications. Several species D vectors have been developed as vaccines against infectious diseases, where they induce robust immunity in preclinical models and early phase clinical trials. However, many aspects of the basic virology of species D HAdV, including their basic receptor usage and means of cell entry, remain understudied. Here, we investigated HAdV-D49, which previously has been studied for vaccine and vascular gene transfer applications. We generated a pseudotyped HAdV-C5 presenting the HAdV-D49 fiber knob protein (HAdV-C5/D49K). This pseudotyped vector was efficient at infecting cells devoid of all known HAdV receptors, indicating HAdV-D49 uses an unidentified cellular receptor. Conversely, a pseudotyped vector presenting the fiber knob protein of the closely related HAdV-D30 (HAdV-C5/D30K), differing in four amino acids from HAdV-D49, failed to demonstrate the same tropism. These four amino acid changes resulted in a change in isoelectric point of the knob protein, with HAdV-D49K possessing a basic apical region compared to a more acidic region in HAdV-D30K. Structurally and biologically we demonstrate that HAdV-D49 knob protein is unable to engage CD46, while potential interaction with coxsackievirus and adenovirus receptor (CAR) is extremely limited by extension of the DG loop. HAdV-C5/49K efficiently transduced cancer cell lines of pancreatic, breast, lung, esophageal, and ovarian origin, indicating it may have potential for oncolytic virotherapy applications, especially for difficult to transduce tumor types.IMPORTANCE Adenoviruses are powerful tools experimentally and clinically. To maximize efficacy, the development of serotypes with low preexisting levels of immunity in the population is desirable. Consequently, attention has focused on those derived from species D, which have proven robust vaccine platforms. This widespread usage is despite limited knowledge in their basic biology and cellular tropism. We investigated the tropism of HAdV-D49, demonstrating that it uses a novel cell entry mechanism that bypasses all known HAdV receptors. We demonstrate, biologically, that a pseudotyped HAdV-C5/D49K vector efficiently transduces a wide range of cell lines, including those presenting no known adenovirus receptor. Structural investigation suggests that this broad tropism is the result of a highly basic electrostatic surface potential, since a homologous pseudotyped vector with a more acidic surface potential, HAdV-C5/D30K, does not display a similar pantropism. Therefore, HAdV-C5/D49K may form a powerful vector for therapeutic applications capable of infecting difficult to transduce cells.

Metabolome-Driven Regulation of Adenovirus-Induced Cell Death

A viral infection that involves virus invasion, protein synthesis, and virion assembly is typically accompanied by sharp fluctuations in the intracellular levels of metabolites. Under certain conditions, dramatic metabolic shifts can result in various types of cell death. Here, we review different types of adenovirus-induced cell death associated with changes in metabolic profiles of the infected cells. As evidenced by experimental data, in most cases changes in the metabolome precede cell death rather than represent its consequence. In our previous study, the induction of autophagic cell death was observed following adenovirus-mediated lactate production, acetyl-CoA accumulation, and ATP release, while apoptosis was demonstrated to be modulated by alterations in acetate and asparagine metabolism. On the other hand, adenovirus-induced ROS production and ATP depletion were demonstrated to play a significant role in the process of necrotic cell death. Interestingly, the accumulation of ceramide compounds was found to contribute to the induction of all the three types of cell death mentioned above. Eventually, the characterization of metabolite analysis could help in uncovering the molecular mechanism of adenovirus-mediated cell death induction and contribute to the development of efficacious oncolytic adenoviral vectors.

Convergent Evolution by Cancer and Viruses in Evading the NKG2D Immune Response

The natural killer group 2 member D (NKG2D) receptor and its family of NKG2D ligands (NKG2DLs) are key components in the innate immune system, triggering NK, γδ and CD8+ T cell-mediated immune responses. While surface NKG2DL are rarely found on healthy cells, expression is significantly increased in response to various types of cellular stress, viral infection, and tumour cell transformation. In order to evade immune-mediated cytotoxicity, both pathogenic viruses and cancer cells have evolved various mechanisms of subverting immune defences and preventing NKG2DL expression. Comparisons of the mechanisms employed following virus infection or malignant transformation reveal a pattern of converging evolution at many of the key regulatory steps involved in NKG2DL expression and subsequent immune responses. Exploring ways to target these shared steps in virus- and cancer-mediated immune evasion may provide new mechanistic insights and therapeutic opportunities, for example, using oncolytic virotherapy to re-engage the innate immune system towards cancer cells.

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.

Non-Human Primate-Derived Adenoviruses for Future Use as Oncolytic Agents?

Non-human primate (NHP)-derived adenoviruses have formed a valuable alternative for the use of human adenoviruses in vaccine development and gene therapy strategies by virtue of the low seroprevalence of neutralizing immunity in the human population. The more recent use of several human adenoviruses as oncolytic agents has exhibited excellent safety profiles and firm evidence of clinical efficacy. This proffers the question whether NHP-derived adenoviruses could also be employed for viral oncolysis in human patients. While vaccine vectors are conventionally made as replication-defective vectors, in oncolytic applications replication-competent viruses are used. The data on NHP-derived adenoviral vectors obtained from vaccination studies can only partially support the suitability of NHP-derived adenoviruses for use in oncolytic virus therapy. In addition, the use of NHP-derived adenoviruses in humans might be received warily given the recent zoonotic infections with influenza viruses and coronaviruses. In this review, we discuss the similarities and differences between human- and NHP-derived adenoviruses in view of their use as oncolytic agents. These include their genome organization, receptor use, replication and cell lysis, modulation of the host’s immune responses, as well as their pathogenicity in humans. Together, the data should facilitate a rational and data-supported decision on the suitability of NHP-derived adenoviruses for prospective use in oncolytic virus therapy.

A phase 1 trial of the safety, tolerability and biological effects of intravenous Enadenotucirev, a novel oncolytic virus, in combination with chemoradiotherapy in locally advanced rectal cancer (CEDAR)

BACKGROUND

Chemoradiotherapy remains the standard of care for locally advanced rectal cancer. Efforts to intensify treatment and increase response rates have yet to yield practice changing results due to increased toxicity and/or absence of increased radiosensitization. Enadenotucirev (EnAd) is a tumour selective, oncolytic adenovirus which can be given intravenously. Pre-clinical evidence of synergy with radiation warrants further clinical testing and assessment of safety with radiation.

METHODS

Eligibility include histology confirmed locally advanced rectal cancer that require chemoradiation. The trial will use a Time-to-Event Continual Reassessment Model-based (TiTE-CRM) approach using toxicity and efficacy as co-primary endpoints to recommend the optimal dose and treatment schedule 30 patients will be recruited. Secondary endpoints include pathological complete response the neoadjuvant rectal score. A translational program will be based on a mandatory biopsy during the second week of treatment for 'proof-of-concept' and exploration of mechanism. The trial opened to recruitment in July 2019, at an expected rate of 1 per month for up to 4 years.

DISCUSSION

Chemoradiation with Enadenotucirev as a radiosensitiser in locally Advanced Rectal cancer (CEDAR) is a prospective multicentre study testing a new paradigm in radiosensitization in rectal cancer. The unique ability of EnAd to selectively infect tumour cells following intravenous delivery is an exciting opportunity with a clear translational goal. The novel statistical design will make efficient use of both toxicity and efficacy data to inform subsequent studies.

TRIAL REGISTRATION

ClinicalTrial.gov, NCT03916510. Registered 16th April 2019.

Combination therapy with oncolytic viruses and immune checkpoint inhibitors

Introduction: Immune checkpoint inhibitors (ICI) have dramatically improved the outcome for cancer patients across multiple tumor types. However the response rates to ICI monotherapy remain relatively low, in part due to some tumors cultivating an inherently 'cold' immune microenvironment. Oncolytic viruses (OV) have the capability to promote a 'hotter' immune microenvironment which can improve the efficacy of ICI.Areas covered: In this article we conducted a literature search through Pubmed/Medline to identify relevant articles in both the pre-clinical and clinical settings for combining OVs with ICIs and discuss the impact of this approach on treatment as well as changes within the tumor microenvironment. We also explore the future directions of this novel combination strategy.Expert opinion: The imminent results of the Phase 3 study combining pembrolizumab with or without T-Vec injection are eagerly awaited. OV/ICI combinations remain one of the most promising avenues to explore in the success of cancer immunotherapy.

Challenges and strategies for next-generation bispecific antibody-based antitumor therapeutics

Bispecific antibodies (bsAbs) refer to a large family of molecules that recognize two different epitopes or antigens. Although a series of challenges, especially immunogenicity and chain mispairing issues, once hindered the development of bsAbs, they have been gradually overcome with the help of rapidly developing technologies in the past 5 decades. In the meantime, an increasing number of bsAb platforms have been designed to satisfy different clinical demands. Currently, numerous preclinical and clinical trials are underway, portraying a promising future for bsAb-based cancer treatment. Nevertheless, bsAb drugs still face enormous challenges in their application as cancer therapeutics, including tumor heterogeneity and mutational burden, intractable tumor microenvironment (TME), insufficient costimulatory signals to activate T cells, the necessity for continuous injection, fatal systemic side effects, and off-target toxicities to adjacent normal cells. Therefore, we provide several strategies as solutions to these issues, which comprise generating multispecific bsAbs, discovering neoantigens, combining bsAbs with other anticancer therapies, exploiting natural killer (NK)-cell-based bsAbs and producing bsAbs in situ. In this review, we mainly discuss previous and current challenges in bsAb development and underscore corresponding strategies, with a brief introduction of several typical bsAb formats.

External Beam Radiation Therapy and Enadenotucirev: Inhibition of the DDR and Mechanisms of Radiation-Mediated Virus Increase

Ionising radiation causes cell death through the induction of DNA damage, particularly double-stranded DNA (dsDNA) breaks. Evidence suggests that adenoviruses inhibit proteins involved in the DNA damage response (DDR) to prevent recognition of double-stranded viral DNA genomes as cellular dsDNA breaks. We hypothesise that combining adenovirus treatment with radiotherapy has the potential for enhancing tumour-specific cytotoxicity through inhibition of the DDR and augmentation of virus production. We show that EnAd, an Ad3/Ad11p chimeric oncolytic adenovirus currently being trialled in colorectal and other cancers, targets the DDR pathway at a number of junctures. Infection is associated with a decrease in irradiation-induced 53BP1 and Rad51 foci formation, and in total DNA ligase IV levels. We also demonstrate a radiation-associated increase in EnAd production in vitro and in a pilot in vivo experiment. Given the current limitations of in vitro techniques in assessing for synergy between these treatments, we adapted the plaque assay to allow monitoring of viral plaque size and growth and utilised the xCELLigence cell adhesion assay to measure cytotoxicity. Our study provides further evidence on the interaction between adenovirus and radiation in vitro and in vivo and suggests these have at least an additive, and possibly a synergistic, impact on cytotoxicity.

Calcium Influx Caused by ER Stress Inducers Enhances Oncolytic Adenovirus Enadenotucirev Replication and Killing through PKCα Activation

Oncolytic viruses represent an emerging approach to cancer therapy. However, better understanding of their interaction with the host cancer cell and approaches to enhance their efficacy are needed. Here, we investigate the effect of chemically induced endoplasmic reticulum (ER) stress on the activity of the chimeric group B adenovirus Enadenotucirev, its closely related parental virus Ad11p, and the archetypal group C oncolytic adenovirus Ad5. We show that treatment of colorectal and ovarian cancer cell lines with thapsigargin or ionomycin caused an influx of Ca2+, leading to an upregulation in E1A transcript and protein levels. Increased E1A protein levels, in turn, increased levels of expression of the E2B viral DNA polymerase, genome replication, late viral protein expression, infectious virus particle production, and cell killing during Enadenotucirev and Ad11p, but not Ad5, infection. This effect was not due to the induction of ER stress, but rather the influx of extracellular Ca2+ and consequent increase in protein kinase C activity. These results underscore the importance of Ca2+ homeostasis during adenoviral infection, indicate a signaling pathway between protein kinase C and E1A, and raise the possibility of using Ca2+ flux-modulating agents in the manufacture and potentiation of oncolytic virotherapies.

Immunology of Adenoviral Vectors in Cancer Therapy

Adenoviruses are a commonly utilized virus for gene therapy platforms worldwide. Since adenovirus components are characterized as highly immunogenic, their immunogenicity inhibits the widespread use of adenoviral vectors to treat genetic disorders. However, stimulation of the immune response can be exploited for cancer immunotherapy platforms, and thus adenoviral vectors are used for therapeutic gene transfer, vaccines, and oncolytic agents in the cancer gene therapy field. It is now accepted that the generation of anti-tumor immune responses induced by oncolytic adenovirus treatments is critical for their anti-tumor efficacy. As such, in cancer immunotherapy with adenoviral vectors, a balance must be struck between induction of anti-adenoviral and anti-tumor immune responses. The recent trend in adenoviral-based cancer gene therapy is the development of adenoviral vectors to enhance immune responses and redirect them toward tumors. This review focuses on anti-adenoviral immunity and how adenovirotherapies skew the immune response toward an anti-tumor response.

Virotherapy: Current Trends and Future Prospects for Treatment of Colon and Rectal Malignancies

Colorectal cancer (CRC) is one of the most common malignancies. In recent decades, early diagnosis and conventional therapies have resulted in a significant reduction in mortality. However, late stage metastatic disease still has very limited effective treatment options. There is a growing interest in using viruses to help target therapies to tumour sites. In recent years the evolution of immunotherapy has emphasised the importance of directing the immune system to eliminate tumour cells; we aim to give a state-of-the-art over-view of the diverse viruses that have been investigated as potential oncolytic agents for the treatment of CRC.

An oncolytic adenovirus 11p vector expressing adenovirus death protein in the E1 region showed significant apoptosis and tumour-killing ability in metastatic prostate cells

The usefulness for cancer therapy of replication-competent adenoviral vectors expressing therapeutic genes from the E3 region has been evaluated, but few reports have described replication-competent adenoviruses with insertions at the E1 region in the full viral genome. We investigated in different prostate cancer cells the oncolytic efficacy of the replication-competent adenovirus 11p vectors expressing adenovirus death (RCAd11pADP) and red fluorescence (RCAd11pRFP) proteins from the upstream E1 region. ADP/RFP gene expression was 2-3 logs higher in PC3 and DU145 cells than in LNCaP and RWPE-1 cells. E1A protein expression in PC3 and DU145 cells was notably increased after infection with the RCAd11pADP or RCAd11pRFP vector compared with the Ad11pwt virus. Toxicity assays revealed 2-5-fold greater oncolytic effects of RCAd11pADP compared to Ad11pwt. Although all three viruses suppressed subcutaneous PC3 tumour growth in nude mice, RCAd11pRFP had greater oncolytic effects than did the Ad11pwt virus, and RCAd11pADP exhibited significant anti-tumour effects via apoptosis in a xenograft model. Interestingly, the apoptosis triggered by RCAd11pADP was markedly enhanced in comparison to that by the vector expressing ADP from E3 region. Taken together, our findings suggest that RCAd11pADP can potentially be used for the treatment of prostate metastases in clinical settings.

Turning cold tumours hot: oncolytic virotherapy gets up close and personal with other therapeutics at the 11th Oncolytic Virus Conference

The 11th International Oncolytic Virus Conference (IOVC) was held from April 9-12, 2018 in Oxford, UK. This is part of the high-profile academic-led series of meetings that was started back in 2002 by Steve Russell and John Bell, with most of the previous meetings being held in North America (often in Banff). The conference brought together many of the major players in oncolytic virotherapy from all over the world, addressing all stages of research and development-from aspects of basic science and cellular immunology all the way through to early- and late-phase clinical trials. The meeting welcomed 352 delegates from 24 countries. The top seven delegate countries, namely, the UK, US, Canada, The Netherlands, Germany, Japan and South Korea, contributed 291 delegates while smaller numbers coming from Australia, Austria, Bulgaria, China, Finland, France, Iraq, Ireland, Israel, Italy, Latvia, Malaysia, Poland, Slovenia, Spain, Sweden and Switzerland. Academics comprised about half of the attendees, industry 30% and students 20%. The next IOVC is scheduled to be held on Vancouver Island in autumn 2019. Here we share brief summaries of the oral presentations from invited speakers and proffered papers in the different subtopics presented at IOVC 2018.

A phase 1 dose escalation study of the oncolytic adenovirus enadenotucirev, administered intravenously to patients with epithelial solid tumors (EVOLVE)

BACKGROUND

Enadenotucirev is a chimeric adenovirus with demonstrated preclinical tumor-selective cytotoxicity and a short half-life. Further clinical mechanism of action data showed that enadenotucirev can gain access to and replicate within different types of epithelial tumors. This phase 1 dose escalation study assessed intravenous (IV) dose escalation with enadenotucirev to establish the maximum tolerated dose (MTD) and subsequently identify a suitable schedule for repeated cycles.

METHODS

Sixty-one patients with advanced epithelial tumors unresponsive to conventional therapy were enrolled and received enadenotucirev monotherapy as part of this study. During the phase 1a dose escalation (n = 22) and expansion (n = 9), delivery of enadenotucirev between 1 × 1010 and 1 × 1013 viral particles (vp) on days 1, 3, and 5 (single cycle) was used to determine an appropriate MTD. Subsequent treatment cohorts (phase 1a, n = 6 and phase 1b, n = 24) examined the feasibility of repeated dosing cycles in either 3-weekly or weekly dosing regimens.

RESULTS

Enadenotucirev displayed a predictable and manageable safety profile at doses up to the MTD of 3 × 1012 vp, irrespective of infusion time or dosing schedule. The most commonly reported treatment-emergent adverse events (TEAEs) of grade 3 or higher were hypoxia, lymphopenia, and neutropenia. The frequency of all TEAEs (notably pyrexia and chills) was highest within 24 h of the first enadenotucirev infusion and decreased upon subsequent dosing. Additionally, delivery of three doses of enadenotucirev over 5 days optimized pharmacokinetic and chemokine profiles in the circulation over time.

CONCLUSIONS

This study provides key clinical data in patients with solid epithelial tumors following treatment with IV enadenotucirev monotherapy and supports further investigation of enadenotucirev in combination with other therapeutic agents at doses up to the MTD of 3 × 1012 vp.

TRIAL REGISTRATION

( ClinicalTrials.gov Identifier: NCT02028442 ). Trial registration date: 07 January 2014 - Retrospectively registered.

Antagonism of Glycolysis and Reductive Carboxylation of Glutamine Potentiates Activity of Oncolytic Adenoviruses in Cancer Cells

Tumor cells exhibiting the Warburg effect rely on aerobic glycolysis for ATP production and have a notable addiction to anaplerotic use of glutamine for macromolecular synthesis. This strategy maximizes cellular biosynthetic potential while avoiding excessive depletion of NAD+ and provides an attractive anabolic environment for viral infection. Here, we evaluate infection of highly permissive and poorly permissive cancer cells with wild-type adenoviruses and the oncolytic chimeric adenovirus enadenotucirev (EnAd). All adenoviruses caused an increase in glucose and glutamine uptake along with increased lactic acid secretion. Counterintuitively, restricting glycolysis using 2-deoxyglucose or by limiting glucose supply strongly improved virus activity in both cell types. Antagonism of glycolysis also boosted EnAd replication and transgene expression within human tumor biopsies and in xenografted tumors in vivo. In contrast, the virus life cycle was critically dependent on exogenous glutamine. Virus activity in glutamine-free cells was rescued with exogenous membrane-permeable α-ketoglutarate, but not pyruvate or oxaloacetate, suggesting an important role for reductive carboxylation in glutamine usage, perhaps for production of biosynthetic intermediates. This overlap between the metabolic phenotypes of adenovirus infection and transformed tumor cells may provide insight into how oncolytic adenoviruses exploit metabolic transformation to augment their selectivity for cancer cells. SIGNIFICANCE: This study describes changes in glucose and glutamine metabolism induced by oncolytic and wild-type adenoviruses in cancer cells, which will be important to consider in the preclinical evaluation of oncolytic viruses.

An Oncolytic Virus Expressing a T-cell Engager Simultaneously Targets Cancer and Immunosuppressive Stromal Cells

: Effective immunotherapy of stromal-rich tumors requires simultaneous targeting of cancer cells and immunosuppressive elements of the microenvironment. Here, we modified the oncolytic group B adenovirus enadenotucirev to express a stroma-targeted bispecific T-cell engager (BiTE). This BiTE bound fibroblast activation protein on cancer-associated fibroblasts (CAF) and CD3ε on T cells, leading to potent T-cell activation and fibroblast death. Treatment of fresh clinical biopsies, including malignant ascites and solid prostate cancer tissue, with FAP-BiTE-encoding virus induced activation of tumor-infiltrating PD1+ T cells to kill CAFs. In ascites, this led to depletion of CAF-associated immunosuppressive factors, upregulation of proinflammatory cytokines, and increased gene expression of markers of antigen presentation, T-cell function, and trafficking. M2-like ascites macrophages exhibited a proinflammatory repolarization, indicating spectrum-wide alteration of the tumor microenvironment. With this approach, we have actively killed both cancer cells and tumor fibroblasts, reversing CAF-mediated immunosuppression and yielding a potent single-agent therapeutic that is ready for clinical assessment. SIGNIFICANCE: An engineered oncolytic adenovirus that encodes a bispecific antibody combines direct virolysis with endogenous T-cell activation to attack stromal fibroblasts, providing a multimodal treatment strategy within a single therapeutic agent.

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors

Oncolytic viruses selectively target and kill cancer cells in an immunogenic fashion, thus supporting the establishment of therapeutically relevant tumor-specific immune responses. In 2015, the US Food and Drug Administration (FDA) approved the oncolytic herpes simplex virus T-VEC for use in advanced melanoma patients. Since then, a plethora of trials has been initiated to assess the safety and efficacy of multiple oncolytic viruses in patients affected with various malignancies. Here, we summarize recent preclinical and clinical progress in the field of oncolytic virotherapy.

Surviving Deadly Lung Infections: Innate Host Tolerance Mechanisms in the Pulmonary System

Much research on infectious diseases focuses on clearing the pathogen through the use of antimicrobial drugs, the immune response, or a combination of both. Rapid clearance of pathogens allows for a quick return to a healthy state and increased survival. Pathogen-targeted approaches to combating infection have inherent limitations, including their pathogen-specific nature, the potential for antimicrobial resistance, and poor vaccine efficacy, among others. Another way to survive an infection is to tolerate the alterations to homeostasis that occur during a disease state through a process called host tolerance or resilience, which is independent from pathogen burden. Alterations in homeostasis during infection are numerous and include tissue damage, increased inflammation, metabolic changes, temperature changes, and changes in respiration. Given its importance and sensitivity, the lung is a good system for understanding host tolerance to infectious disease. Pneumonia is the leading cause of death for children under five worldwide. One reason for this is because when the pulmonary system is altered dramatically it greatly impacts the overall health and survival of a patient. Targeting host pathways involved in maintenance of pulmonary host tolerance during infection could provide an alternative therapeutic avenue that may be broadly applicable across a variety of pathologies. In this review, we will summarize recent findings on tolerance to host lung infection. We will focus on the involvement of innate immune responses in tolerance and how an initial viral lung infection may alter tolerance mechanisms in leukocytic, epithelial, and endothelial compartments to a subsequent bacterial infection. By understanding tolerance mechanisms in the lung we can better address treatment options for deadly pulmonary infections.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Expression of human CD46 and trans-complementation by murine adenovirus 1 fails to allow productive infection by a group B oncolytic adenovirus in murine cancer cells

BACKGROUND

Oncolytic viruses are currently experiencing accelerated development in several laboratories worldwide, with some forty-seven clinical trials currently recruiting. Many oncolytic viruses combine targeted cytotoxicity to cancer cells with a proinflammatory cell lysis. Due to their additional potential to express immunomodulatory transgenes, they are also often known as oncolytic viral vaccines. However, several types of oncolytic viruses are human-specific and the lack of suitable immune-competent animal models complicates biologically relevant evaluation of their vaccine potential. This is a particular challenge for group B adenoviruses, which fail to infect even those immunocompetent animal model systems identified as semi-permissive for type 5 adenovirus. Here, we aim to develop a murine cell line capable of supporting replication of a group B oncolytic adenovirus, enadenotucirev (EnAd), for incorporation into a syngeneic immunocompetent animal model to explore the oncolytic vaccine potential of group B oncolytic viruses.

METHODS

Transgenic murine cell lines were infected with EnAd expressing GFP transgene under replication-independent or -dependent promoters. Virus mRNA expression, genome replication, and late protein expression were determined by qRT-PCR, qPCR, and immunoblotting, respectively. We also use Balb/c immune-competent mice to determine the tumourogenicity and infectivity of transgenic murine cell lines.

RESULTS

Our results show that a broad range of human carcinoma cells will support EnAd replication, but not murine carcinoma cells. Murine cells can be readily modified to express surface human CD46, one of the receptors for group B adenoviruses, allowing receptor-mediated uptake of EnAd particles into the murine cells and expression of CMV promoter-driven transgenes. Although the early E1A mRNA was expressed in murine cells at levels similar to human cells, adenovirus E2B and Fibre mRNA expression levels were hampered and few virus genomes were produced. Unlike previous reports on group C adenoviruses, trans-complementation of group B adenoviruses by co-infection with mouse adenovirus 1 did not rescue replication. A panel of group B adenoviruses expressing individual mouse adenovirus 1 genes were also unable to rescue EnAd replication.

CONCLUSION

Together, these results indicate that there may be major differences in the early stages of replication of group C and B adenoviruses in murine cells, and that the block to the life cycle of B adenoviruses in murine cells occurs in the early stage of virus replication, perhaps reflecting poor activity of Ad11p E1A in murine cells.

In vitro immunotherapy potency assays using real-time cell analysis

A growing understanding of the molecular interactions between immune effector cells and target tumor cells, coupled with refined gene therapy approaches, are giving rise to novel cancer immunotherapeutics with remarkable efficacy in the clinic against both solid and liquid tumors. While immunotherapy holds tremendous promise for treatment of certain cancers, significant challenges remain in the clinical translation to many other types of cancers and also in minimizing adverse effects. Therefore, there is an urgent need for functional potency assays, in vitro and in vivo, that could model the complex interaction of immune cells with tumor cells and can be used to rapidly test the efficacy of different immunotherapy approaches, whether it is small molecule, biologics, cell therapies or combinations thereof. Herein we report the development of an xCELLigence real-time cytolytic in vitro potency assay that uses cellular impedance to continuously monitor the viability of target tumor cells while they are being subjected to different types of treatments. Specialized microtiter plates containing integrated gold microelectrodes enable the number, size, and surface attachment strength of adherent target tumor cells to be selectively monitored within a heterogeneous mixture that includes effector cells, antibodies, small molecules, etc. Through surface-tethering approach, the killing of liquid cancers can also be monitored. Using NK92 effector cells as example, results from RTCA potency assay are very well correlated with end point data from image-based assays as well as flow cytometry. Several effector cells, i.e., PBMC, NK, CAR-T were tested and validated as well as biological molecules such as Bi-specific T cell Engagers (BiTEs) targeting the EpCAM protein expressed on tumor cells and blocking antibodies against the immune checkpoint inhibitor PD-1. Using the specifically designed xCELLigence immunotherapy software, quantitative parameters such as KT₅₀ (the amount of time it takes to kill 50% of the target tumor cells) and % cytolysis are calculated and used for comparing the relative efficacy of different reagents. In summary, our results demonstrate the xCELLigence platform to be well suited for potency assays, providing quantitative assessment with high reproducibility and a greatly simplified work flow.

Solid Tumor Immunotherapy with T Cell Engager-Armed Oncolytic Viruses

Oncolytic viruses (OVs) are novel anticancer agents that combine direct cancer cell killing with the stimulation of antitumor immunity. In addition, OVs can be engineered to deliver biological therapeutics directly to tumors, offering unique opportunities to design multimodal anticancer strategies. Here, a case for arming OVs with bispecific T cell engagers (BiTEs) is put forward. BiTEs redirect the cytotoxicity of polyclonal T cells to target cells of choice, and have demonstrated efficacy against a number of hematological cancers. However, the success of BiTEs in the treatment of solid tumors appears more limited, at least in part due to: (i) poor delivery kinetics and penetration into tumors, and (ii) on-target off-tumor activity, leading to dose-limiting toxicities. Linking the production of BiTEs to OV replication provides an exciting means to restrict production to the tumor site, widen their therapeutic window, and synergize with direct oncolysis. This review summarizes progress thus far in the preclinical development of BiTE-armed OVs, and explores the possibility of cotargeting cancer cells and nontransformed stromal cells.

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.

Making Oncolytic Virotherapy a Clinical Reality: The European Contribution

Oncolytic viruses (OVs) are quickly moving toward the forefront of modern medicines. The reward for the decades of research invested into developing viral platforms that selectively replicate in and lyse tumor cells while sparking anticancer adaptive immunity is presenting in the form of durable therapeutic responses. While this has certainly been a concerted global effort, in this review for the 25th anniversary of the European Society of Gene and Cell Therapy, we focus on the contributions made by European researchers. Research centers across Europe have held central roles in advancing OVs, from the earliest reports of coincidental viral infections leading to antitumor efficacy, to advanced mechanistic studies, and now through Phase I-III trials to imminent regulatory approvals. While challenges still remain, with limitations in preclinical animal models, antiviral immune clearance, and manufacture restrictions enforced by poor viral yields in certain cases, the field has come a very long way in recent years. Thoughtful mechanistic integration of OVs with standard of care strategies and other newly approved therapies should provide potent novel approaches. Combination with immunotherapeutic regimes holds significant promise, and the ability to arm the viral platform with therapeutic proteins for localized expression at the tumor site provides an opportunity for creating highly effective synergistic treatments and brings a new age of targeted cancer therapeutics.

Phase 1 study of intravenous administration of the chimeric adenovirus enadenotucirev in patients undergoing primary tumor resection

BACKGROUND

Enadenotucirev (formerly ColoAd1) is a tumor-selective chimeric adenovirus with demonstrated preclinical activity. This phase 1 Mechanism of Action study assessed intravenous (IV) delivery of enadenotucirev in patients with resectable colorectal cancer (CRC), non-small-cell lung cancer (NSCLC), urothelial cell cancer (UCC), and renal cell cancer (RCC) with a comparator intratumoral (IT) dosed CRC patient cohort.

METHODS

Seventeen patients scheduled for primary tumor resection were enrolled. IT injection of enadenotucirev (CRC only) was administered as a single dose (≤ 3 × 1011 viral particles [vp]) on day 1, followed by resection during days 8-15. IV infusion of enadenotucirev was administered by three separate doses (1 × 1012 vp) on days 1, 3, and 5, followed by resection during days 8-15 (CRC) or days 10-25 (NSCLC, UCC, and RCC). Enadenotucirev activity was measured using immunohistochemical staining of nuclear viral hexon and quantitative polymerase chain reaction for viral genomic DNA.

RESULTS

Delivery of enadenotucirev was observed in most tumor samples following IV infusion, with little or no demonstrable activity in normal tissue. This virus delivery (by both IV and IT dosing) was accompanied by high local CD8+ cell infiltration in 80% of tested tumor samples, suggesting a potential enadenotucirev-driven immune response. Both methods of enadenotucirev delivery were well tolerated, with no treatment-associated serious adverse events.

CONCLUSIONS

This study provides key delivery and feasibility data to support the use of IV infusion of enadenotucirev, or therapeutic transgene-bearing derivatives of it, in clinical trials across a range of epithelial tumors, including the ongoing combination study of enadenotucirev with the checkpoint inhibitor nivolumab. It also provides insights into the potential immune-stimulating properties of enadenotucirev.

TRIAL REGISTRATION

This MOA study was a phase 1, multicenter, non-randomized, open-label study to investigate the administration of enadenotucirev in a preoperative setting (ClinicalTrials.gov: NCT02053220).

Oncolytic adenovirus expressing bispecific antibody targets T-cell cytotoxicity in cancer biopsies

Oncolytic viruses exploit the cancer cell phenotype to complete their lytic life cycle, releasing progeny virus to infect nearby cells and repeat the process. We modified the oncolytic group B adenovirus EnAdenotucirev (EnAd) to express a bispecific single-chain antibody, secreted from infected tumour cells into the microenvironment. This bispecific T-cell engager (BiTE) binds to EpCAM on target cells and cross-links them to CD3 on T cells, leading to clustering and activation of both CD4 and CD8 T cells. BiTE transcription can be controlled by the virus major late promoter, limiting expression to cancer cells that are permissive for virus replication. This approach can potentiate the cytotoxicity of EnAd, and we demonstrate using primary pleural effusions and peritoneal malignant ascites that infection of cancer cells with the BiTE-expressing EnAd leads to activation of endogenous T cells to kill endogenous tumour cells despite the immunosuppressive environment. In this way, we have armed EnAd to combine both direct oncolysis and T cell-mediated killing, yielding a potent therapeutic that should be readily transferred into the clinic.

Combining Oncolytic Adenovirus with Radiation-A Paradigm for the Future of Radiosensitization

Oncolytic viruses and radiotherapy represent two diverse areas of cancer therapy, utilizing quite different treatment modalities and with non-overlapping cytotoxicity profiles. It is, therefore, an intriguing possibility to consider that oncolytic ("cancer-killing") viruses may act as cancer-selective radiosensitizers, enhancing the therapeutic consequences of radiation treatment on tumors while exerting minimal effects on normal tissue. There is a solid mechanistic basis for this potential synergy, with many viruses having developed strategies to inhibit cellular DNA repair pathways in order to protect themselves, during genome replication, from unwanted interference by cell processes that are normally triggered by DNA damage. Exploiting these abilities to inhibit cellular DNA repair following damage by therapeutic irradiation may well augment the anticancer potency of the approach. In this review, we focus on oncolytic adenovirus, the most widely developed and best understood oncolytic virus, and explore its various mechanisms for modulating cellular DNA repair pathways. The most obvious effects of the various adenovirus serotypes are to interfere with activity of the MRE11-Rad50-Nbs1 complex, temporally one of the first sensors of double-stranded DNA damage, and inhibition of DNA ligase IV, a central repair enzyme for healing double-stranded breaks by non-homologous end joining (NHEJ). There have been several preclinical and clinical studies of this approach and we assess the current state of progress. In addition, oncolytic viruses provide the option to promote a localized proinflammatory response, both by mediating immunogenic death of cancer cells by oncosis and also by encoding and expressing proinflammatory biologics within the tumor microenvironment. Both of these approaches provide exciting potential to augment the known immunological consequences of radiotherapy, aiming to develop systems capable of creating a systemic anticancer immune response following localized tumor treatment.