A Phase II Study of Pelareorep (REOLYSIN®) in Combination with Gemcitabine for Patients with Advanced Pancreatic Adenocarcinoma

Pancreatic Cancer: Pathogenesis and Clinical Studies

Pancreatic cancer (PC) is a highly lethal malignancy, with pancreatic ductal adenocarcinoma (PDAC) being the most common and aggressive subtype, characterized by late diagnosis, aggressive progression, and resistance to conventional therapies. Despite advances in understanding its pathogenesis, including the identification of common genetic mutations (e.g., KRAS, TP53, CDKN2A, SMAD4) and dysregulated signaling pathways (e.g., KRAS-MAPK, PI3K-AKT, and TGF-β pathways), effective therapeutic strategies remain limited. Current treatment modalities including chemotherapy, targeted therapy, immunotherapy, radiotherapy, and emerging therapies such as antibody-drug conjugates (ADCs), chimeric antigen receptor T (CAR-T) cells, oncolytic viruses (OVs), cancer vaccines, and bispecific antibodies (BsAbs), face significant challenges. This review comprehensively summarizes these treatment approaches, emphasizing their mechanisms, limitations, and potential solutions, to overcome these bottlenecks. By integrating recent advancements and outlining critical challenges, this review aims to provide insights into future directions and guide the development of more effective treatment strategies for PC, with a specific focus on PDAC. Our work underscores the urgency of addressing the unmet needs in PDAC therapy and highlights promising areas for innovation in this field.

Epigenetic modulation by oncolytic viruses: Implications for cancer therapeutic efficacy

Among various therapeutic agents, Oncolytic Viruses (OVs) are the most promising anticancer therapeutics because of their tumor-specific targeting and capability to mediate an antitumor immune response. In this review, we will discuss how epigenetic reprogramming of both the host and tumor can facilitate increased sensitivity of tumors to OV therapy. OVs infect tumor cells and modulate epigenetic landscapes, including DNA methylation, histone modifications, and chromatin remodeling, as well as non-coding RNA expression that consequently induces immune responses. These epigenetic changes, including hypermethylation of tumor-associated antigen genes and chromatin accessibility alterations, enhance the immunogenicity of tumors to facilitate recognition by the immune system. Here, we provide a general review addressing this question by discussing the potential benefits of combining OVs with epigenetic drugs to combat resistance and promote treatment efficacy. This information illustrates the importance of personalized OV therapy regarding epigenome in individual profiles and transitions. Still, it extends difficulty in inducing with acquisitions of viral-induced changes globally and making translatable steps by creating cancer-specific predictive treatment models.

The Complexity of Malignant Glioma Treatment

Malignant glioma is a highly aggressive, therapeutically non-responsive, and deadly disease with a unique tumor microenvironment (TME). Of the 14 currently recognized and described cancer hallmarks, five are especially implicated in malignant glioma and targetable with repurposed drugs: cancer stem-like cells, in general, and glioma stem-like cells in particular (GSCs), vascularization and hypoxia, metabolic reprogramming, tumor-promoting inflammation and sustained proliferative signaling. Each hallmark drives malignant glioma development, both individually and through interactions with other hallmarks, in which the TME plays a critical role. To combat the aggressive malignant glioma spatio-temporal heterogeneity driven by TME interactions, and to overcome its therapeutic challenges, a combined treatment strategy including anticancer therapies, repurposed drugs and multimodal immunotherapy should be the aim for future treatment approaches.

Threading the Needle: Navigating Novel Immunotherapeutics in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with a poor prognosis. Currently, chemotherapy is the only option for most patients with advanced-stage PDAC. Further, conventional immunotherapies and targeted therapies improve survival outcomes only in rare PDAC patient subgroups. To date, combinatory immunotherapeutic strategies to overcome the immune-hostile PDAC tumor microenvironment (TME) have resulted in limited efficacy in clinical studies. However, efforts are ongoing to develop new treatment strategies for patients with PDAC with the evolving knowledge of the TME, molecular characterization, and immune resistance mechanisms. Further, the growing arsenal of various immunotherapeutic agents, including novel classes of immune checkpoint inhibitors and oncolytic, chimeric antigen receptor T cell, and vaccine therapies, reinforces these efforts. This review will focus on the place of immunotherapy and future possible strategies in PDAC.

Oncolytic Virus Therapy in a New Era of Immunotherapy, Enhanced by Combination with Existing Anticancer Therapies: Turn up the Heat!

Oncolytic viral therapy is a promising treatment for cancer, where 'cold' tumour cells can become 'hot' to the host immune system. However, with few FDA approved therapies, development of new strategies for more cancer types has been slow and relatively unsuccessful in recent years, Combination therapy has been successful for other types of cancer treatment, therefore, may be a viable alternative to improve the efficacy of oncolytic viral therapy which may reduce some of the adverse events of currently used monotherapies, oncolytic virus therapy and chemotherapy being mutually complimentary with each other. Combining oncolytic viruses with immune checkpoint inhibitors provides a significant increase in efficacy when viral therapy was combined with the drug ipilimumab. Phase I and II studies concluded that combination with chemotherapies was safe and effective but did not significantly improve on current monotherapies. Recent experiments suggest that a combination of CAR-T and CAR--M cells is a promising therapeutic approach but needs to advance to clinical testing to observe the human response to the therapy. Viral combination with ipilimumab showed the highest potential for a successful treatment and clinical trials should be advanced to phase III to find conclusive supporting evidence. This review aims to identify and evaluate the potential of currently evolving oncolytic viral therapy with recent advances in genetic engineering providing enhanced oncolytic activity in the tumour, and addressing the lack of host immune responses in 'cold' tumours, with an additional role in enhancing conventional treatment efficacy with combination therapies. The potential of oncolytic viruses to 'turn up the heat' of a tumour microenvironment immunogenicity in combination with other anticancer treatments, provides a promising future for new cancer therapies.

Improving systemic delivery of oncolytic virus by cellular carriers

Oncolytic virotherapy (OVT) is a promising option for cancer treatment. OVT involves selective oncolytic virus (OV) replication within cancer cells, which triggers anti-tumor responses and immunostimulation. Despite promising potential, OVT faces critical challenges, including insufficient tumor-specific targeting, which results in limited tumor penetration and variability in therapeutic efficacy. These challenges are particularly pronounced in solid tumors with complex microenvironments and heterogeneous vascularization. A comprehensive research program is currently underway to develop and refine innovative delivery methods to address these issues to enhance OVT precision and efficacy. A principal area of investigation is the utilization of cellular carriers to enhance the delivery and distribution of OVs within tumor microenvironments, thereby optimizing immune system activation and maximizing anti-tumor effects. This review offers a comprehensive overview of the current strategies that are being used to enhance the delivery of OVs via cellular carriers with the goal of improving the clinical impact of OVT in cancer therapy.

Extracellular matrix re-normalization to improve cold tumor penetration by oncolytic viruses

Immunologically inert or cold tumors pose a substantial challenge to the effectiveness of immunotherapy. The use of oncolytic viruses (OVs) to induce immunogenic cell death (ICD) in tumor cells is a well-established strategy for initiating the cancer immunity cycle (CIC). This process promotes the trafficking and infiltration of CD8+ T cells into tumors, thereby eliciting a tumor-specific immune response. Despite the potential of OVs for handling cold tumors, clinical outcomes have fallen short of expectations. To better understand the obstacles faced by oncolytic virus immunotherapy (OVI), we would like to revisit the OV issue. Growing evidence indicates that limited intratumoral penetration and inadequate intratumoral distribution of OVs are critical factors contributing to the suboptimal response to OVI. Aberrant expressions of matrix proteins by cancer-associated fibroblasts (CAFs) alter the mechanical properties of the tumor extracellular matrix (ECM). This results in increased ECM desmoplasia and elevated intratumoral interstitial fluid pressure (IFP), creating physical barriers that impede the penetration and dissemination of OVs within tumors. This review explores the latest advancements in strategies designed to improve the intratumoral penetration of OVs to facilitate the penetration of tumor-infiltrating lymphocytes (TILs) into cold tumors. Additionally, we investigated current clinical trials and challenges associated with translating these strategies into clinical practice to improve patient outcomes.

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

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

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.

Frontiers and future of immunotherapy for pancreatic cancer: from molecular mechanisms to clinical application

Pancreatic cancer is a highly aggressive malignant tumor, that is becoming increasingly common in recent years. Despite advances in intensive treatment modalities including surgery, radiotherapy, biological therapy, and targeted therapy, the overall survival rate has not significantly improved in patients with pancreatic cancer. This may be attributed to the insidious onset, unknown pathophysiology, and poor prognosis of the disease. It is therefore essential to identify and develop more effective and safer treatments for pancreatic cancer. Tumor immunotherapy is the new and fourth pillar of anti-tumor therapy after surgery, radiotherapy, and chemotherapy. Significant progress has made in the use of immunotherapy for a wide variety of malignant tumors in recent years; a breakthrough has also been made in the treatment of pancreatic cancer. This review describes the advances in immune checkpoint inhibitors, cancer vaccines, adoptive cell therapy, oncolytic virus, and matrix-depletion therapies for the treatment of pancreatic cancer. At the same time, some new potential biomarkers and potential immunotherapy combinations for pancreatic cancer are discussed. The molecular mechanisms of various immunotherapies have also been elucidated, and their clinical applications have been highlighted. The current challenges associated with immunotherapy and proposed strategies that hold promise in overcoming these limitations have also been discussed, with the aim of offering new insights into immunotherapy for pancreatic cancer.

LOAd703, an oncolytic virus-based immunostimulatory gene therapy, combined with chemotherapy for unresectable or metastatic pancreatic cancer (LOKON001): results from arm 1 of a non-randomised, single-centre, phase 1/2 study

BACKGROUND

Pancreatic ductal adenocarcinoma is characterised by low immunogenicity and an immunosuppressive tumour microenvironment. LOAd703, an oncolytic adenovirus with transgenes encoding TMZ-CD40L and 4-1BBL, lyses cancer cells selectively, activates cytotoxic T cells, and induces tumour regression in preclinical models. The aim of this study was to evaluate the safety and feasibility of combining LOAd703 with chemotherapy for advanced pancreatic ductal adenocarcinoma.

METHODS

LOKON001 was a non-randomised, phase 1/2 study conducted at the Dan L Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, USA, and consisted of two arms conducted sequentially; the results of arm 1 are presented here. In arm 1, patients 18 years or older with previously treated or treatment-naive unresectable or metastatic pancreatic ductal adenocarcinoma were treated with standard 28-day cycles of intravenous nab-paclitaxel 125 mg/m2 plus gemcitabine 1000 mg/m2 (up to 12 cycles) and intratumoural injections of LOAd703 every 2 weeks. Patients were assigned using Bayesian optimal interval design to receive 500 μL of LOAd703 at 5 × 1010 (dose 1), 1 × 1011 (dose 2), or 5 × 1011 (dose 3) viral particles per injection, injected endoscopically or percutaneously into the pancreatic tumour or a metastasis for six injections. The primary endpoints were safety and treatment-emergent immune response in patients who received at least one dose of LOAd703, and antitumour activity was a secondary endpoint. This study was registered with ClinicalTrials.gov, NCT02705196, arm 2 is ongoing and open to new participants.

FINDINGS

Between Dec 2, 2016, and Oct 17, 2019, 23 patients were assessed for eligibility, leading to 22 patients being enrolled. One patient withdrew consent, resulting in 21 patients (13 [62%] men and eight [38%] women) assigned to a dose group (three to dose 1, four to dose 2, and 14 to dose 3). 21 patients were evaluable for safety. Median follow-up time was 6 months (IQR 4-10), and data cutoff was Jan 5, 2023. The most common treatment-emergent adverse events overall were anaemia (96 [8%] of 1237 events), lymphopenia (86 [7%] events), hyperglycaemia (70 [6%] events), leukopenia (63 [5%] events), hypertension (62 [5%] events), and hypoalbuminaemia (61 [5%] events). The most common adverse events attributed to LOAd703 were fever (14 [67%] of 21 patients), fatigue (eight [38%]), chills (seven [33%]), and elevated liver enzymes (alanine aminotransferase in five [24%], alkaline phosphatase in four [19%], and aspartate aminotransferase in four [19%]), all of which were grade 1-2, except for a transient grade 3 aminotransferase elevation occurring at dose 3. A maximum tolerated dose was not reached, thereby establishing dose 3 as the highest-evaluated safe dose when combined with nab-paclitaxel plus gemcitabine. Proportions of CD8+ effector memory cells and adenovirus-specific T cells increased after LOAd703 injections in 15 (94%) of 16 patients for whom T-cell assays could be performed. Eight (44%, 95% CI 25-66) of 18 patients evaluable for activity had an objective response.

INTERPRETATION

Combining LOAd703 with nab-paclitaxel plus gemcitabine in patients with advanced pancreatic ductal adenocarcinoma was feasible and safe. To build upon this novel chemoimmunotherapeutic approach, arm 2 of LOKON001, which combines LOAd703, nab-paclitaxel plus gemcitabine, and atezolizumab, is ongoing.

FUNDING

Lokon Pharma, the Swedish Cancer Society, and the Swedish Research Council.

Oncolytic virotherapy in cancer treatment: challenges and optimization prospects

Oncolytic viruses (OVs) are emerging cancer therapeutics that offer a multifaceted therapeutic platform for the benefits of replicating and lysing tumor cells, being engineered to express transgenes, modulating the tumor microenvironment (TME), and having a tolerable safety profile that does not overlap with other cancer therapeutics. The mechanism of OVs combined with other antitumor agents is based on immune-mediated attack resistance and might benefit patients who fail to achieve durable responses after immune checkpoint inhibitor (ICI) treatment. In this Review, we summarize data on the OV mechanism and limitations of monotherapy, which are currently in the process of combination partner development, especially with ICIs. We discuss some of the hurdles that have limited the preclinical and clinical development of OVs. We also describe the available data and provide guidance for optimizing OVs in clinical practice, as well as a summary of approved and promising novel OVs with clinical indications.

Advancements and challenges in oncolytic virus therapy for gastrointestinal tumors

BACKGROUND

Tumors of the gastrointestinal tract impose a substantial healthcare burden due to their prevalence and challenging prognosis.

METHODS

We conducted a review of peer-reviewed scientific literature using reputable databases (PubMed, Scopus, Web of Science) with a focus on oncolytic virus therapy within the context of gastrointestinal tumors. Our search covered the period up to the study's completion in June 2023.

INCLUSION AND EXCLUSION CRITERIA

This study includes articles from peer-reviewed scientific journals, written in English, that specifically address oncolytic virus therapy for gastrointestinal tumors, encompassing genetic engineering advances, combined therapeutic strategies, and safety and efficacy concerns. Excluded are articles not meeting these criteria or focusing on non-primary gastrointestinal metastatic tumors.

RESULTS

Our review revealed the remarkable specificity of oncolytic viruses in targeting tumor cells and their potential to enhance anti-tumor immune responses. However, challenges related to safety and efficacy persist, underscoring the need for ongoing research and improvement.

CONCLUSION

This study highlights the promising role of oncolytic virus therapy in enhancing gastrointestinal tumor treatments. Continued investigation and innovative combination therapies hold the key to reducing the burden of these tumors on patients and healthcare systems.

Effectiveness and safety of pelareorep plus chemotherapy versus chemotherapy alone for advanced solid tumors: a meta-analysis

Background: Pelareorep is an oncolytic virus that causes oncolytic effects in many solid tumors, and it has shown therapeutic benefits. However, few studies have compared pelareorep combined with chemotherapy to traditional chemotherapy alone in advanced solid tumors. Consequently, we intended to evaluate the effectiveness and safety of pelareorep plus chemotherapy in this paper. Methods: We searched four databases including PubMed, Embase, Cochrane Library and Web of Science comprehensively for studies comparing pelareorep combined with chemotherapy to chemotherapy alone in the treatment of advanced solid tumors. The outcomes measures were 1-year overall survival (OS), 2-year OS, 4-month progression-free survival (PFS), 1-year PFS, objective response rate (ORR), any-grade adverse events (any-grade AEs), and severe AEs (grade ≥ 3). Results: There were five studies involving 492 patients included in the study. Combination therapy did not significantly improve clinical outcomes in terms of 1-year OS [RR = 1.02, 95%CI = (0.82-1.25)], 2-year OS [RR = 1.00, 95%CI = (0.67-1.49)], 4-month PFS [RR = 1.00, 95%CI = (0.67-1.49)], 1-year PFS [RR = 0.79, 95%CI = (0.44-1.42)], and ORR [OR = 0.79, 95%CI = (0.49-1.27)] compared to chemotherapy alone, and the subgroup analysis of 2-year OS, 1-year PFS, and ORR based on countries and tumor sites showed similar results. In all grades, the incidence of AEs was greater with combination therapy, including fever [RR = 3.10, 95%CI = (1.48-6.52)], nausea [RR = 1.19, 95%CI = (1.02-1.38)], diarrhea [RR = 1.87, 95%CI = (1.39-2.52)], chills [RR = 4.14, 95%CI = (2.30-7.43)], headache [RR = 1.46, 95%CI = (1.02-2.09)], vomiting [RR = 1.38, 95%CI = (1.06-1.80)] and flu-like symptoms [RR = 4.18, 95%CI = (2.19-7.98)]. However, severe adverse events did not differ significantly between the two arms. Conclusion: Pelareorep addition to traditional chemotherapy did not lead to significant improvements in OS, PFS, or ORR in advanced solid tumor patients, but it did partially increase AEs in all grades, with no discernible differences in serious AEs. Therefore, the combination treatment is not recommended in patients with advanced solid tumors. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=400841, identifier CRD42023400841.

Reovirus infection of tumor cells reduces the expression of NKG2D ligands, leading to impaired NK-cell cytotoxicity and functionality

In recent years, reoviruses have been of major interest in immunotherapy because of their oncolytic properties. Preclinical and clinical trials, in which reovirus was used for the treatment of melanoma and glioblastoma, have paved the way for future clinical use of reovirus. However, little is known about how reovirus infection affects the tumor microenvironment and immune response towards infected tumor cells. Studies have shown that reovirus can directly stimulate natural killer (NK) cells, but how reovirus affects cellular ligands on tumor cells, which are ultimately key to tumor recognition and elimination by NK cells, has not been investigated. We tested how reovirus infection affects the binding of the NK Group-2 member D (NKG2D) receptor, which is a dominant mediator of NK cell anti-tumor activity. Using models of human-derived melanoma and glioblastoma tumors, we demonstrated that NKG2D ligands are downregulated in tumor cells post-reovirus-infection due to the impaired translation of these ligands in reovirus-infected cells. Moreover, we showed that downregulation of NKG2D ligands significantly impaired the binding of NKG2D to infected tumor cells. We further demonstrated that reduced recognition of NKG2D ligands significantly alters NK cell anti-tumor cytotoxicity in human primary NK cells and in the NK cell line NK-92. Thus, this study provides novel insights into reovirus-host interactions and could lead to the development of novel reovirus-based therapeutics that enhance the anti-tumor immune response.

Combination of pembrolizumab and pelareorep promotes anti-tumour immunity in advanced pancreatic adenocarcinoma (PDAC)

BACKGROUND

We previously reported activity of pelareorep, pembrolizumab and chemotherapy. Patients developed new T-cell clones and increased peripheral T-cell clonality, leading to an inflamed tumour. To evaluate a chemotherapy-free regimen, this study assesses if pelareorep and pembrolizumab has efficacy by inducing anti-tumour immunological changes (NCT03723915).

METHODS

PDAC patients who progressed after first-line therapy, received iv pelareorep induction with pembrolizumab every 21-days. Primary objective is overall response rate. Secondary objectives included evaluation of immunological changes within tumour and blood.

RESULTS

Clinical benefit rate (CBR) was 42% amongst 12 patients. One patient achieved partial response (PR) and four stable disease (SD). Seven progressed, deemed non-responders (NR). VDAC1 expression in peripheral CD8+ T cells was higher at baseline in CBR than NR but decreased in CBR upon treatment. On-treatment peripheral CD4+ Treg levels decreased in CBR but not in NR. Analysis of tumour demonstrated PD-L1+ cells touching CD8+ T cells, and NK cells were more abundant post-treatment vs. baseline. A higher intensity of PD-L1 in tumour infiltrates at baseline, particularly in CBR vs. NR. Finally, higher levels of soluble (s)IDO, sLag3, sPD-1 observed at baseline among NR vs. CBR.

CONCLUSION

Pelareorep and pembrolizumab showed modest efficacy in unselected patients, although potential immune and metabolic biomarkers were identified to warrant further evaluation.

The clinical terrain of immunotherapies in heterogeneous pancreatic cancer: unravelling challenges and opportunities

Pancreatic ductal adenocarcinoma (PDAC) is the most common and aggressive type of pancreatic cancer and has abysmal survival rates. In the past two decades, immunotherapeutic agents with success in other cancer types have gradually been trialled against PDACs at different stages of cancer progression, either as a monotherapy or in combination with chemotherapy. Unfortunately, to this day, chemotherapy still prolongs the survival rates the most and is prescribed in clinics despite the severe side effects in other cancer types. The low success rates of immunotherapy against PDAC have been attributed most frequently to its complex and multi-faceted tumour microenvironment (TME) and low mutational burden. In this review, we give a comprehensive overview of the immunotherapies tested in PDAC clinical trials thus far, their limitations, and potential explanations for their failure. We also discuss the existing classification of heterogenous PDACs into cancer, cancer-associated fibroblast, and immune subtypes and their potential opportunity in patient selection as a form of personalisation of PDAC immunotherapy. © 2023 The Pathological Society of Great Britain and Ireland.

Modulation of Reoviral Cytolysis (I): Combination Therapeutics

Patients with stage IV gastric cancer suffer from dismal outcomes, a challenge especially in many Asian populations and for which new therapeutic options are needed. To explore this issue, we used oncolytic reovirus in combination with currently used chemotherapeutic drugs (irinotecan, paclitaxel, and docetaxel) for the treatment of gastric and other gastrointestinal cancer cells in vitro and in a mouse model. Cell viability in vitro was quantified by WST-1 assays in human cancer cell lines treated with reovirus and/or chemotherapeutic agents. The expression of reovirus protein and caspase activity was determined by flow cytometry. For in vivo studies, athymic mice received intratumoral injections of reovirus in combination with irinotecan or paclitaxel, after which tumor size was monitored. In contrast to expectations, we found that reoviral oncolysis was only poorly correlated with Ras pathway activation. Even so, the combination of reovirus with chemotherapeutic agents showed synergistic cytopathic effects in vitro, plus enhanced reovirus replication and apoptosis. In vivo experiments showed that reovirus alone can reduce tumor size and that the combination of reovirus with chemotherapeutic agents enhances this effect. Thus, we find that oncolytic reovirus therapy is effective against gastric cancer. Moreover, the combination of reovirus and chemotherapeutic agents synergistically enhanced cytotoxicity in human gastric cancer cell lines in vitro and in vivo. Our data support the use of reovirus in combination with chemotherapy in further clinical trials, and highlight the need for better biomarkers for reoviral oncolytic responsiveness.

Development and application of oncolytic viruses as the nemesis of tumor cells

Viruses and tumors are two pathologies that negatively impact human health, but what occurs when a virus encounters a tumor? A global consensus among cancer patients suggests that surgical resection, chemotherapy, radiotherapy, and other methods are the primary means to combat cancer. However, with the innovation and development of biomedical technology, tumor biotherapy (immunotherapy, molecular targeted therapy, gene therapy, oncolytic virus therapy, etc.) has emerged as an alternative treatment for malignant tumors. Oncolytic viruses possess numerous anti-tumor properties, such as directly lysing tumor cells, activating anti-tumor immune responses, and improving the tumor microenvironment. Compared to traditional immunotherapy, oncolytic virus therapy offers advantages including high killing efficiency, precise targeting, and minimal side effects. Although oncolytic virus (OV) therapy was introduced as a novel approach to tumor treatment in the 19th century, its efficacy was suboptimal, limiting its widespread application. However, since the U.S. Food and Drug Administration (FDA) approved the first OV therapy drug, T-VEC, in 2015, interest in OV has grown significantly. In recent years, oncolytic virus therapy has shown increasingly promising application prospects and has become a major research focus in the field of cancer treatment. This article reviews the development, classification, and research progress of oncolytic viruses, as well as their mechanisms of action, therapeutic methods, and routes of administration.

Vaccinating against cancer: getting to prime time

Immunotherapies, such as immune checkpoint inhibitors, cellular therapies, and T-cell engagers, have fundamentally changed our approach to treating cancer. However, successes with cancer vaccines have been more difficult to realize. While vaccines against specific viruses have been widely adopted to prevent the development of cancer, only two vaccines can improve survival in advanced disease: sipuleucel-T and talimogene laherparepvec. These represent the two approaches that have the most traction: vaccinating against cognate antigen and priming responses using tumors in situ. Here, we review the challenges and opportunities researchers face in developing therapeutic vaccines for cancer.

Next-Generation Approaches to Immuno-Oncology in GI Cancers

Immunotherapy has only had a modest impact on the treatment of advanced GI malignancies. Microsatellite-stable colorectal cancer and pancreatic adenocarcinoma, the most common GI tumors, have not benefited from treatment with standard immune checkpoint inhibitors. With this huge unmet need, multiple approaches are being tried to overcome barriers to better anticancer outcomes. This article reviews a number of novel approaches to immunotherapy for these tumors. These include the use of novel checkpoint inhibitors such as a modified anti-cytotoxic T lymphocyte-associated antigen-4 antibody and antibodies to lymphocyte-activation gene 3, T cell immunoreceptor with immunoglobulin and ITIM domains, T-cell immunoglobulin-3, CD47, and combinations with signal transduction inhibitors. We will discuss other trials that aim to elicit an antitumor T-cell response using cancer vaccines and oncolytic viruses. Finally, we review attempts to replicate in GI cancers the frequent and durable responses seen in hematologic malignancies with immune cell therapies.

Oncolytic virotherapy: basic principles, recent advances and future directions

Oncolytic viruses (OVs) have attracted growing awareness in the twenty-first century, as they are generally considered to have direct oncolysis and cancer immune effects. With the progress in genetic engineering technology, OVs have been adopted as versatile platforms for developing novel antitumor strategies, used alone or in combination with other therapies. Recent studies have yielded eye-catching results that delineate the promising clinical outcomes that OVs would bring about in the future. In this review, we summarized the basic principles of OVs in terms of their classifications, as well as the recent advances in OV-modification strategies based on their characteristics, biofunctions, and cancer hallmarks. Candidate OVs are expected to be designed as "qualified soldiers" first by improving target fidelity and safety, and then equipped with "cold weapons" for a proper cytocidal effect, "hot weapons" capable of activating cancer immunotherapy, or "auxiliary weapons" by harnessing tactics such as anti-angiogenesis, reversed metabolic reprogramming and decomposing extracellular matrix around tumors. Combinations with other cancer therapeutic agents have also been elaborated to show encouraging antitumor effects. Robust results from clinical trials using OV as a treatment congruously suggested its significance in future application directions and challenges in developing OVs as novel weapons for tactical decisions in cancer treatment.

Therapy with oncolytic viruses: progress and challenges

Oncolytic viruses (OVs) are an emerging class of cancer therapeutics that offer the benefits of selective replication in tumour cells, delivery of multiple eukaryotic transgene payloads, induction of immunogenic cell death and promotion of antitumour immunity, and a tolerable safety profile that largely does not overlap with that of other cancer therapeutics. To date, four OVs and one non-oncolytic virus have been approved for the treatment of cancer globally although talimogene laherparepvec (T-VEC) remains the only widely approved therapy. T-VEC is indicated for the treatment of patients with recurrent melanoma after initial surgery and was initially approved in 2015. An expanding body of data on the clinical experience of patients receiving T-VEC is now becoming available as are data from clinical trials of various other OVs in a range of other cancers. Despite increasing research interest, a better understanding of the underlying biology and pharmacology of OVs is needed to enable the full therapeutic potential of these agents in patients with cancer. In this Review, we summarize the available data and provide guidance on optimizing the use of OVs in clinical practice, with a focus on the clinical experience with T-VEC. We describe data on selected novel OVs that are currently in clinical development, either as monotherapies or as part of combination regimens. We also discuss some of the preclinical, clinical and regulatory hurdles that have thus far limited the development of OVs.

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

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

Significance

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

Exploiting RIG-I-like receptor pathway for cancer immunotherapy

RIG-I-like receptors (RLRs) are intracellular pattern recognition receptors that detect viral or bacterial infection and induce host innate immune responses. The RLRs family comprises retinoic acid-inducible gene 1 (RIG-I), melanoma differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2) that have distinctive features. These receptors not only recognize RNA intermediates from viruses and bacteria, but also interact with endogenous RNA such as the mislocalized mitochondrial RNA, the aberrantly reactivated repetitive or transposable elements in the human genome. Evasion of RLRs-mediated immune response may lead to sustained infection, defective host immunity and carcinogenesis. Therapeutic targeting RLRs may not only provoke anti-infection effects, but also induce anticancer immunity or sensitize "immune-cold" tumors to immune checkpoint blockade. In this review, we summarize the current knowledge of RLRs signaling and discuss the rationale for therapeutic targeting RLRs in cancer. We describe how RLRs can be activated by synthetic RNA, oncolytic viruses, viral mimicry and radio-chemotherapy, and how the RNA agonists of RLRs can be systemically delivered in vivo. The integration of RLRs agonism with RNA interference or CAR-T cells provides new dimensions that complement cancer immunotherapy. Moreover, we update the progress of recent clinical trials for cancer therapy involving RLRs activation and immune modulation. Further studies of the mechanisms underlying RLRs signaling will shed new light on the development of cancer therapeutics. Manipulation of RLRs signaling represents an opportunity for clinically relevant cancer therapy. Addressing the challenges in this field will help develop future generations of cancer immunotherapy.

Radiotherapy/Chemotherapy-Immunotherapy for Cancer Management: From Mechanisms to Clinical Implications

Cancer immunotherapy has drawn much attention because it can restart the recognition and killing function of the immune system to normalize the antitumor immune response. However, the role of radiotherapy and chemotherapy in cancer treatment cannot be ignored. Due to cancer heterogeneity, combined therapy has become a new trend, and its efficacy has been confirmed in many studies. This review discussed the clinical implications and the underlying mechanisms of cancer immunotherapy in combination with radiotherapy or chemotherapy, offering an outline for clinicians as well as inspiration for future research.

Tumour microenvironment and heterotypic interactions in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a disease with a survival rate of 9%; this is due to its chemoresistance and the large tumour stroma that occupies most of the tumour mass. It is composed of a large number of cells of the immune system, such as Treg cells, tumour-associated macrophages (TAMs), myeloid suppressor cells (MDCs) and tumour-associated neutrophiles (TANs) that generate an immunosuppressive environment by the release of inflammatory cytokines. Moreover, cancer-associated fibroblast (CAFs) provide a protective coverage that would difficult the access of chemotherapy to the tumour. According to this, new therapies that could remodel this heterogeneous tumour microenvironment, such as adoptive T cell therapies (ACT), immune checkpoint inhibitors (ICI), and CD40 agonists, should be developed for targeting PDA. This review organizes the different cell populations found in the tumour stroma involved in tumour progression in addition to the different therapies that are being studied to counteract the tumour.

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

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

Repeated dosing improves oncolytic rhabdovirus therapy in mice via interactions with intravascular monocytes

There is debate in the field of oncolytic virus (OV) therapy, whether a single viral dose, or multiple administrations, is better for tumor control. Using intravital microscopy, we describe the fate of vesicular stomatitis virus (VSV) delivered systemically as a first or a second dose. Following primary administration, VSV binds to the endothelium, initiates tumor infection and activates a proinflammatory response. This initial OV dose induces neutrophil migration into the tumor and limits viral replication. OV administered as a second dose fails to infect the tumor and is captured by intravascular monocytes. Despite a lack of direct infection, this second viral dose, in a monocyte-dependent fashion, enhances and sustains infection by the first viral dose, promotes CD8 T cell recruitment, delays tumor growth and improves survival in multi-dosing OV therapy. Thus, repeated VSV dosing engages monocytes to post-condition the tumor microenvironment for improved infection and anticancer T cell responses. Understanding the complex interactions between the subsequent viral doses is crucial for improving the efficiency of OV therapy and virus-based vaccines.

Efficacy and safety of oncolytic virus combined with chemotherapy or immune checkpoint inhibitors in solid tumor patients: A meta-analysis

Background: In recent years, several clinical trials have focused on oncolytic virus (OVs) combined with chemotherapy or immune checkpoint inhibitors (ICIs) in solid tumor patients, which showed encouraging effects. However, few studies have concentrated on the summary on the safety and efficacy of the combined treatments. Therefore, we conducted this meta-analysis to explore the safety and curative effect of the combined therapy. Methods: We searched the PubMed, Cochrane Library, Embase, and Clinicaltrials.gov databases to comprehensively select articles on OVs combined with chemotherapy or ICIs for the solid tumor treatment. Overall survival (OS), progression-free survival (PFS), 1-year survival rate, 2-year survival rate, objective response rate (ORR), and adverse events (AEs) were the outcomes. Results: Fifteen studies with 903 patients were included in this meta-analysis. The pooled ORR was 32% [95% confidence interval (CI): 27-36%, I2 = 24.9%, p = 0.239]. Median OS and median PFS were 6.79 months (CI: 4.29-9.30, I2 = 62.9%, p = 0.044) and 3.40 months (CI: 2.59-4.22, I2 = 0.0%, p = 0.715), respectively. The 1-year survival rate was 38% (CI: 0.29-0.47, I2 = 62.9%, p = 0.044), and the 2-year survival rate was 24% (CI: 12-37%, I2 = 0.0%, p = 0.805). The most common AEs were fever (63%, CI: 57-69%, I2 = 2.3%, p = 0.402), fatigue (58%, CI: 51-65%, I2 = 49.2%, p = 0.096), chill (52%, CI: 43-60%, I2 = 0.0%, p = 0.958), and neutropenia (53%, CI: 47-60%, I2 = 0.0%, p = 0.944). Conclusion: OVs combined with ICIs showed a better efficacy than OVs combined with chemotherapy, which lends support to further clinical trials of OVs combined with ICIs. In addition, OVs combined with pembrolizumab can exert increased safety and efficacy. The toxicity of grades ≥3 should be carefully monitored and observed. However, high-quality, large-scale clinical trials should be completed to further confirm the efficacy and safety of OVs combined with ICIs. Systematic Review Registration: [https://www.crd.york.ac.uk/PROSPERO/login.php], identifier [RD42022348568].

Combination immunotherapy for pancreatic cancer: challenges and future considerations

INTRODUCTION

: Immune checkpoint inhibitors (ICI) have not yielded significant efficacy in pancreatic ductal adenocarcinoma (PDA), despite the role of the innate and adaptive immune systems on progression and survival. However, recently identified pathways have identified new targets and generated promising clinical investigations into promoting an effective immune-mediated antitumor response in PDA.

AREAS COVERED

: We review biological mechanisms associated with immunotherapy resistance and outline strategies for therapeutic combinations with established and novel therapies in PDA.

EXPERT OPINION

: Pancreatic cancers rarely benefits from treatment with ICI due to an immunosuppressive tumor microenvironment (TME). New understandings of factors associated with the suppressive TME, include low and poor quality neoantigens, constrained effector T cells infiltration, and the presence of a dense, suppressive myeloid cell population. These findings have been translated into new clinical investigations evaluating novel therapies in combination with ICI and/or standard systemic chemotherapy and radiotherapy. The epithelial, immune, and stromal compartments are intricately related in PDA, and the framework for successful targeting of this disease requires a comprehensive and personalized approach.

GOBLET: a phase I/II study of pelareorep and atezolizumab +/- chemo in advanced or metastatic gastrointestinal cancers

Most gastrointestinal (GI) cancers have microsatellite-stable (MSS) tumors, which have an immunologically 'cold' phenotype with fewer genetic mutations, reduced immune cell infiltration and downregulated immune checkpoint proteins. These attributes make MSS tumors resistant to conventional immunotherapy including checkpoint blockade therapy. Pelareorep is a naturally occurring, nongenetically modified reovirus. Upon intravenous administration, pelareorep selectively kills tumor cells and promotes several immunologic changes that prime tumors to respond to checkpoint blockade therapy. Given its demonstrated synergy with checkpoint blockade, as well as its encouraging efficacy in prior GI cancer studies, pelareorep plus atezolizumab will be evaluated in the GOBLET study in multiple GI cancer indications.

Preinduced reovirus-specific T-cell immunity enhances the anticancer efficacy of reovirus therapy

BACKGROUND

Many solid tumors do not respond to immunotherapy due to their immunologically cold tumor microenvironment (TME). We and others found that oncolytic viruses (OVs), including reovirus type 3 Dearing, can enhance the efficacy of immunotherapy by recruiting CD8⁺ T cells to the TME. A significant part of the incoming CD8⁺ T cells is directed toward reovirus itself, which may be detrimental to the efficacy of OVs. However, here we aim to exploit these incoming virus-specific T cells as anticancer effector cells.

METHODS

We performed an in-depth characterization of the reovirus-induced T-cell response in immune-competent mice bearing pancreatic KPC3 tumors. The immunodominant CD8⁺ T-cell epitope of reovirus was identified using epitope prediction algorithms and peptide arrays, and the quantity and quality of reovirus-specific T cells after reovirus administration were assessed using high-dimensional flow cytometry. A synthetic long peptide (SLP)-based vaccination strategy was designed to enhance the intratumoral frequency of reovirus-specific CD8⁺ T cells.

RESULTS

Reovirus administration did not induce tumor-specific T cells but rather induced high frequencies of reovirus-specific CD8⁺ T cells directed to the immunodominant epitope. Priming of reovirus-specific T cells required a low-frequent population of cross-presenting dendritic cells which was absent in Batf3^-/- mice. While intratumoral and intravenous reovirus administration induced equal systemic frequencies of reovirus-specific T cells, reovirus-specific T cells were highly enriched in the TME exclusively after intratumoral administration. Here, they displayed characteristics of potent effector cells with high expression of KLRG1, suggesting they may be responsive against local reovirus-infected cells. To exploit these reovirus-specific T cells as anticancer effector cells, we designed an SLP-based vaccination strategy to induce a strong T-cell response before virotherapy. These high frequencies of circulating reovirus-specific T cells were reactivated on intratumoral reovirus administration and significantly delayed tumor growth.

CONCLUSIONS

These findings provide proof of concept that OV-specific T cells, despite not being tumor-specific, can be exploited as potent effector cells for anticancer treatment when primed before virotherapy. This is an attractive strategy for low-immunogenic tumors lacking tumor-specific T cells.

An Extensive Review on Preclinical and Clinical Trials of Oncolytic Viruses Therapy for Pancreatic Cancer

Chemotherapy resistance and peculiar tumor microenvironment, which diminish or mitigate the effects of therapies, make pancreatic cancer one of the deadliest malignancies to manage and treat. Advanced immunotherapies are under consideration intending to ameliorate the overall patient survival rate in pancreatic cancer. Oncolytic viruses therapy is a new type of immunotherapy in which a virus after infecting and lysis the cancer cell induces/activates patients’ immune response by releasing tumor antigen in the blood. The current review covers the pathways and molecular ablation that take place in pancreatic cancer cells. It also unfolds the extensive preclinical and clinical trial studies of oncolytic viruses performed and/or undergoing to design an efficacious therapy against pancreatic cancer.

Oncolytic Viruses: Immunotherapy Drugs for Gastrointestinal Malignant Tumors

Oncolytic virus therapy has advanced rapidly in recent years. Natural or transgenic viruses can target tumor cells and inhibit tumor growth and metastasis in various ways without interfering with normal cell and tissue function. Oncolytic viruses have a high level of specificity and are relatively safe. Malignant tumors in the digestive system continue to have a high incidence and mortality rate. Although existing treatment methods have achieved some curative effects, they still require further improvement due to side effects and a lack of specificity. Many studies have shown that oncolytic viruses can kill various tumor cells, including malignant tumors in the digestive system. This review discusses how oncolytic virus therapy improves malignant tumors in the digestive system from the point-of-view of basic and clinical studies. Also, the oncolytic virus anti-tumor mechanisms underpinning the therapeutic potential of oncolytic viruses are expounded. In all, we argue that oncolytic viruses might eventually provide therapeutic solutions to malignant tumors in the digestive system.

Combination therapy with CAR T cells and oncolytic viruses: a new era in cancer immunotherapy

Chimeric antigen receptor (CAR) T-cell therapy is an encouraging and fast-growing platform used for the treatment of various types of tumors in human body. Despite the recent success of CAR T-cell therapy in hematologic malignancies, especially in B-cell lymphoma and acute lymphoblastic leukemia, the application of this treatment approach in solid tumors faced several obstacles resulted from the heterogeneous expression of antigens as well as the induction of immunosuppressive tumor microenvironment. Oncolytic virotherapy (OV) is a new cancer treatment modality by the use of competent or genetically engineered viruses to replicate in tumor cells selectively. OVs represent potential candidates to synergize the current setbacks of CAR T-cell application in solid tumors and then and overcome them. As well, the application of OVs gives researches the ability to engineer the virus with payloads in the way that it selectively deliver a specific therapeutic agents in tumor milieu to reinforce the cytotoxic activity of CAR T cells. Herein, we made a comprehensive review on the outcomes resulted from the combination of CAR T-cell immunotherapy and oncolytic virotherapy for the treatment of solid cancers. In the current study, we also provided brief details on some challenges that remained in this field and attempted to shed a little light on the future perspectives.

Win or loss? Combination therapy does improve the oncolytic virus therapy to pancreatic cancer

Pancreatic cancer (PC) is a growing global burden, remaining one of the most lethal cancers of the gastrointestinal tract. Moreover, PC is resistant to various treatments such as chemotherapy, radiotherapy, and immunotherapy. New therapies are urgently needed to improve the prognosis of PC. Oncolytic virus (OV) therapy is a promising new treatment option. OV is a genetically modified virus that selectively replicates in tumor cells. It can kill tumor cells without harming normal cells. The activation of tumor-specific T-cells is a unique feature of OV-mediated therapy. However, OV-mediated mono-therapeutic efficacy remains controversial, especially for metastatic or advanced patients who require systemically deliverable therapies. Hence, combination therapies will be critical to improve the therapeutic efficacy of OV-mediated therapy and prevent tumor recurrence. This review aims to investigate novel combinatorial treatments with OV therapy and explore the inner mechanism of those combined therapies, hopefully providing a new direction for a better prognosis of PC.

Protein Cages: From Fundamentals to Advanced Applications

Proteins that self-assemble into polyhedral shell-like structures are useful molecular containers both in nature and in the laboratory. Here we review efforts to repurpose diverse protein cages, including viral capsids, ferritins, bacterial microcompartments, and designed capsules, as vaccines, drug delivery vehicles, targeted imaging agents, nanoreactors, templates for controlled materials synthesis, building blocks for higher-order architectures, and more. A deep understanding of the principles underlying the construction, function, and evolution of natural systems has been key to tailoring selective cargo encapsulation and interactions with both biological systems and synthetic materials through protein engineering and directed evolution. The ability to adapt and design increasingly sophisticated capsid structures and functions stands to benefit the fields of catalysis, materials science, and medicine.

The Combined Use of Orf Virus and PAK4 Inhibitor Exerts Anti-tumor Effect in Breast Cancer

The parapoxvirus Orf virus (ORFV) has long been recognized as one of the valuable vectors in researches of oncolytic virus. In order to develop a potential therapeutic strategy for breast cancer based on the oncolytic virotherapy via ORFV, firstly we explore the oncolytic effects of ORFV. Our research showed that ORFV exerts anti-tumor effects in vitro by inducing breast cancer cell G2/M phase arrest and cell apoptosis. In vivo experiments were carried out, in which we treated 4T1 tumor-bearing BALB/C mice via intratumoral injection of ORFV. ORFV can exert anti-tumor activity by regulating tumor microenvironment (TME) and inducing a host immune response plus directly oncolytic effect. The CRISPR-Cas9 knockout library targeting 507 kinases was used to screen out PAK4, which is beneficial to the anti-tumor effect of ORFV on breast cancer cells. PF-3758309 is a potent PAK4-targeted inhibitor. Co-using of ORFV and PF-3758309 as a combination treatment produces its anti-tumor effects through inhibition of cell viability, induction of apoptosis and suppression of cell migration and invasion in vitro. The results of in vivo experiments showed that the tumor growth of mice in the combination treatment group was significantly inhibited, which proved that the combination treatment exerts an effective anti-tumor effect in vivo. In summary, we have clarified the oncolytic effect of ORFV on breast cancer, and found that the combination of ORFV and PAK4 inhibitor can effectively improve the oncolytic effect of ORFV. We hope our research could provide a new idea for the development of new treatment strategies for breast cancer.

Phase I, multicenter, open-label study of intravenous VCN-01 oncolytic adenovirus with or without nab-paclitaxel plus gemcitabine in patients with advanced solid tumors

BACKGROUND

VCN-01 is an oncolytic adenovirus (Ad5 based) designed to replicate in cancer cells with dysfunctional RB1 pathway, express hyaluronidase to enhance virus intratumoral spread and facilitate chemotherapy and immune cells extravasation into the tumor. This phase I clinical trial was aimed to find the maximum tolerated dose/recommended phase II dose (RP2D) and dose-limiting toxicity (DLT) of the intravenous delivery of the replication-competent VCN-01 adenovirus in patients with advanced cancer.

METHODS

Part I: patients with advanced refractory solid tumors received one single dose of VCN-01. Parts II and III: patients with pancreatic adenocarcinoma received VCN-01 (only in cycle 1) and nab-paclitaxel plus gemcitabine (VCN-concurrent on day 1 in Part II, and 7 days before chemotherapy in Part III). Patients were required to have anti-Ad5 neutralizing antibody (NAbs) titers lower than 1/350 dilution. Pharmacokinetic and pharmacodynamic analyses were performed.

RESULTS

26% of the patients initially screened were excluded based on high NAbs levels. Sixteen and 12 patients were enrolled in Part I and II, respectively: RP2D were 1×1013 viral particles (vp)/patient (Part I), and 3.3×1012 vp/patient (Part II). Fourteen patients were included in Part III: there were no DLTs and the RP2D was 1×1013 vp/patient. Observed DLTs were grade 4 aspartate aminotransferase increase in one patient (Part I, 1×1013 vp), grade 4 febrile neutropenia in one patient and grade 5 thrombocytopenia plus enterocolitis in another patient (Part II, 1×1013 vp). In patients with pancreatic adenocarcinoma overall response rate were 50% (Part II) and 50% (Part III). VCN-01 viral genomes were detected in tumor tissue in five out of six biopsies (day 8). A second viral plasmatic peak and increased hyaluronidase serum levels suggested replication after intravenous injection in all patients. Increased levels of immune biomarkers (interferon-γ, soluble lymphocyte activation gene-3, interleukin (IL)-6, IL-10) were found after VCN-01 administration.

CONCLUSIONS

Treatment with VCN-01 is feasible and has an acceptable safety. Encouraging biological and clinical activity was observed when administered in combination with nab-paclitaxel plus gemcitabine to patients with pancreatic adenocarcinoma.

TRIAL REGISTRATION NUMBER

NCT02045602.

Modulation of the tumor microenvironment by armed vesicular stomatitis virus in a syngeneic pancreatic cancer model

Background

The immunosuppressive microenvironment in pancreatic ductal adenocarcinoma is a major factor that limits the benefits of immunotherapy, especially immune checkpoint blockade. One viable strategy for reverting the immunosuppressive conditions is the use of an oncolytic virus (OV) in combination with other immunotherapy approaches. Infection of PDAC cells with a robust OV can change the tumor microenvironment and increase tumor antigen release by its lytic activities. These changes in the tumor may improve responses to immunotherapy, including immune checkpoint blockade. However, a more potent OV may be required for efficiently infecting pancreatic tumors that may be resistant to OV.

Methods

Vesicular stomatitis virus, a rapid replicating OV, was armed to express the Smac protein during virus infection (VSV-S). Adaptation by limited dilution largely increased the selective infection of pancreatic cancer cells by VSV-S. The engineered OV was propagated to a large quantity and evaluated for their antitumor activities in an animal model.

Results

In a syngeneic KPC model, intratumoral injection of VSV-S inhibited tumor growth, and induced increasing tumor infiltration of neutrophils and elimination of myeloid derived suppressor cells and macrophages in the tumor. More importantly, M2-like macrophages were eliminated preferentially over those with an M1 phenotype. Reduced levels of arginase 1, TGF-β and IL-10 in the tumor also provided evidence for reversion of the immunosuppressive conditions by VSV-S infection. In several cases, tumors were completely cleared by VSV-S treatment, especially when combined with anti-PD-1 therapy. A long-term survival of 44% was achieved.

Conclusions

The improved OV, VSV-S, was shown to drastically alter the immune suppressive tumor microenvironment when intratumorally injected. Our results suggest that the combination of potent OV treatment with immune checkpoint blockade may be a promising strategy to treat pancreatic cancer more effectively.

Oncolytic virotherapy as promising immunotherapy against cancer: mechanisms of resistance to oncolytic viruses

Oncolytic virotherapy has currently emerged as a powerful therapeutic approach in cancer treatment. Although the history of using viruses goes back to the early 20th century, the approval of talimogene laherparepvec (T-VEC) in 2015 increased interest in oncolytic viruses (OVs). OVs are multifaceted biotherapeutic agents because they replicate in and kill tumor cells and augment immune responses by releasing immunostimulatory molecules from lysed cells. Despite promising results, some limitations hinder the efficacy of oncolytic virotherapy. The delivery challenges and the upregulation of checkpoints following oncolytic virotherapy also mediate resistance to OVs by diminishing immune responses. Furthermore, the localization of receptors of viruses in the tight junctions, interferon responses, and the aberrant expression of genes involved in the cell cycle of the virus, including their infection and replication, reduce the efficacy of OVs. In this review, we present different mechanisms of resistance to OVs and strategies to overcome them.

Uncovering key targets of success for immunotherapy in pancreatic cancer

INTRODUCTION

Despite available treatment options, pancreatic ductal adenocarcinoma (PDAC) is frequently lethal. Recent immunotherapy strategies have failed to yield any notable impact. Therefore, research is focussed on unearthing new drug targets and therapeutic strategies to tackle this malignancy and attain more positive outcomes for patients.

AREAS COVERED

In this perspective article, we evaluate the main resistance mechanisms to immune checkpoint inhibitors (ICIs) and the approaches to circumvent them. We also offer an assessment of concluded and ongoing trials of PDAC immunotherapy. Literature research was performed on Pubmed accessible through keywords such as: 'pancreatic ductal adenocarcinoma,' 'immunotherapy,' 'immunotherapy resistance,' 'immune escape,' 'biomarkers.' Papers published between 2000 and 2021 were selected.

EXPERT OPINION

The tumor microenvironment is a critical variable of treatment resistance because of its role as a physical barrier and inhibitory immune signaling. Promising therapeutic strategies appear to be a combination of immunotherapeutics with other targeted treatments. Going forward, predictive biomarkers are required to improve patient selection. Biomarker-driven trials could enhance approaches for assessing the role of immunotherapy in PDAC.

Oncolytic reovirus-mediated killing of mouse cancer-associated fibroblasts

Oncolytic viruses, which mediate tumor cell-specific infection, resulting in efficient tumor cell killing, have attracted much attention as a novel class of anti-cancer biopharmaceutical agents. Cancer-associated fibroblasts (CAFs) are an important component of the tumor microenvironment that strongly supports the growth, survival, and metastasis of tumor cells, suggesting that CAFs would have influence to the antitumor effects of oncolytic viruses; however, it remains to be fully evaluated whether oncolytic viruses affect the viabilities and properties of CAFs following treatment. Oncolytic reovirus, which is a non-enveloped virus that contains 10-segmented double-stranded RNA genome, shows efficient tumor cell lysis without apparent cytotoxicity to normal cells and has been tested worldwide in clinical trials against various types of tumors. In this study, we demonstrated that reovirus exhibited cytotoxicity against mouse primary CAFs isolated from subcutaneous tumors, but not against tail-tip fibroblasts. Infection with reovirus resulted in activation of caspase 3 and up-regulation of apoptosis-related gene expression, indicating that reovirus induced apoptosis of mouse primary CAFs. Intratumoral administration of reovirus induced apoptosis of mouse CAFs in the tumor. Taken together, these results indicate that reovirus has the potential to mediate antitumor effects by killing not only cancer cells but also CAFs.

Targeted Anti-Tumor Immunotherapy Using Tumor Infiltrating Cells

In the tumor microenvironment, T cells, B cells, and many other cells play important and distinct roles in anti-tumor immunotherapy. Although the immune checkpoint blockade and adoptive cell transfer can elicit durable clinical responses, only a few patients benefit from these therapies. Increased understanding of tumor-infiltrating immune cells can provide novel therapies and drugs that induce a highly specific anti-tumor immune response to certain groups of patients. Herein, the recent research progress on tumor-infiltrating B cells and T cells, including CD8+ T cells, CD4+ T cells, and exhausted T cells and their role in anti-tumor immunity, is summarized. Moreover, several anti-tumor therapy approaches are discussed based on different immune cells and their prospects for future applications in cancer treatment.

The Heterogeneity of the Tumor Microenvironment as Essential Determinant of Development, Progression and Therapy Response of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is commonly diagnosed at advanced stages and most anti-cancer therapies have failed to substantially improve prognosis of PDAC patients. As a result, PDAC is still one of the deadliest tumors. Tumor heterogeneity, manifesting at multiple levels, provides a conclusive explanation for divergent survival times and therapy responses of PDAC patients. Besides tumor cell heterogeneity, PDAC is characterized by a pronounced inflammatory stroma comprising various non-neoplastic cells such as myofibroblasts, endothelial cells and different leukocyte populations which enrich in the tumor microenvironment (TME) during pancreatic tumorigenesis. Thus, the stromal compartment also displays a high temporal and spatial heterogeneity accounting for diverse effects on the development, progression and therapy responses of PDAC. Adding to this heterogeneity and the impact of the TME, the microbiome of PDAC patients is considerably altered. Understanding this multi-level heterogeneity and considering it for the development of novel therapeutic concepts might finally improve the dismal situation of PDAC patients. Here, we outline the current knowledge on PDAC cell heterogeneity focusing on different stromal cell populations and outline their impact on PDAC progression and therapy resistance. Based on this information, we propose some novel concepts for treatment of PDAC patients.

The application of oncolytic viruses in cancer therapy

Oncolytic therapy is a treatment method used to directly combat tumor cells by modifying the genes of naturally occurring low pathogenic viruses to form "rhizobia" virus. By taking the advantage of abnormal signal pathways in cancer cells, it selectively replicates in tumor cells leading to tumor cell lysis and death. At present, clinical studies widely employ biomolecular technology to transform oncolytic viruses to exert stronger oncolytic effects and reduce their adverse reactions. This review summarizes the current progresses and the molecular mechanism of oncolytic viruses towards tumor treatment and management.

Challenges and Future Perspectives of Immunotherapy in Pancreatic Cancer

Simple Summary

Immunotherapeutic agents harness the patient’s immune system to fight cancer cells. Especially immune checkpoint inhibitors, a certain group of immunotherapeutic agents, have recently improved treatment options for many cancer types. Unfortunately, clinical trials testing of these agents in pancreatic cancer patients have not confirmed promising results from laboratory experiments. Several characteristics of pancreatic cancer biology, especially the profound tumour microenvironment that inhibits the successful identification and elimination of tumour cells by immune cells seems to be responsible for the lacking efficacy of immunotherapeutics in pancreatic cancer. We summarise recently published clinical trials investigating immunotherapeutic strategies in pancreatic cancer patients and available data on how these treatments influence pancreatic cancer biology. Moreover, we identify potential strategies to improve experimental and clinical studies in order to generate more conclusive data and improve patient outcomes in the future.

Abstract

To date, extensive efforts to harness immunotherapeutic strategies for the treatment of pancreatic ductal adenocarcinoma (PDAC) have yielded disappointing results in clinical trials. These strategies mainly focused on cancer vaccines and immune checkpoint inhibitors alone or in combination with chemotherapeutic or targeted agents. However, the growing preclinical and clinical data sets from these efforts have established valuable insights into the immunological characteristics of PDAC biology. Most notable are the immunosuppressive role of the tumour microenvironment (TME) and PDAC’s characteristically poor immunogenicity resulting from tumour intrinsic features. Moreover, PDAC tumour heterogeneity has been increasingly well characterized and may additionally limit a “one-fits-all” immunotherapeutic strategy. In this review, we first outline mechanisms of immunosuppression and immune evasion in PDAC. Secondly, we summarize recently published data on preclinical and clinical efforts to establish immunotherapeutic strategies for the treatment of PDAC including diverse combinatorial treatment approaches aiming at overcoming this resistance towards immunotherapeutic strategies. Particularly, these combinatorial treatment approaches seek to concomitantly increase PDAC antigenicity, boost PDAC directed T-cell responses, and impair the immunosuppressive character of the TME in order to allow immunotherapeutic agents to unleash their full potential. Eventually, the thorough understanding of the currently available data on immunotherapeutic treatment strategies of PDAC will enable researchers and clinicians to develop improved treatment regimens and to design innovative clinical trials to overcome the pronounced immunosuppression of PDAC.