Relaxin-expressing, fiber chimeric oncolytic adenovirus prolongs survival of tumor-bearing mice

The diverse influences of relaxin-like peptide family on tumor progression: Potential opportunities and emerging challenges

Relaxin-like peptide family exhibit differential expression patterns in various types of cancers and play a role in cancer development. This family participates in tumorigenic processes encompassing proliferation, migration, invasion, tumor microenvironment, immune microenvironment, and anti-cancer resistance, ultimately influencing patient prognosis. In this review, we explore the mechanisms underlying the interaction between the RLN-like peptide family and tumors and provide an overview of therapeutic approaches utilizing this interaction.

Programmed Death-Ligand (PD-L1), Epidermal Growth Factor (EGF), Relaxin, and Matrix Metalloproteinase-3 (MMP3): Potential Biomarkers of Malignancy in Canine Mammary Neoplasia

Gene expression has been suggested as a putative tool for prognosis and diagnosis in canine mammary neoplasia (CMNs). In the present study, 58 formalin-fixed paraffin-embedded (FFPE) paraffined canine mammary neoplasias from 27 different bitches were included. Thirty-seven tumours were classified as benign, whereas thirty-one were classified as different types of canine carcinoma. In addition, mammary samples from three healthy bitches were also included. The gene expression for vascular endothelial growth factor-α (VEGFα), CD20, progesterone receptor (PGR), hyaluronidase-1 (HYAL-1), programmed death-ligand 1 (PD-L1), epidermal growth factor (EGF), relaxin (RLN2), and matrix metalloproteinase-3 (MMP3) was assessed through RT-qPCR. All the assessed genes yielded a higher expression in neoplastic mammary tissue than in healthy tissue. All the evaluated genes were overexpressed in neoplastic mammary tissue, suggesting a role in the process of tumorigenesis. Moreover, PD-L1, EGF, relaxin, and MMP3 were significantly overexpressed in malignant CMNs compared to benign CMNs, suggesting they may be useful as malignancy biomarkers.

Oncolytic Virus Engineering and Utilizations: Cancer Immunotherapy Perspective

Oncolytic viruses have positively impacted cancer immunotherapy over the past 20 years. Both natural and genetically modified viruses have shown promising results in treating various cancers. Various regulatory authorities worldwide have approved four commercial oncolytic viruses, and more are being developed to overcome this limitation and obtain better anti-tumor responses in clinical trials at various stages. Faster advancements in translating research into the commercialization of cancer immunotherapy and a comprehensive understanding of the modification strategies will widen the current knowledge of future technologies related to the development of oncolytic viruses. In this review, we discuss the strategies of virus engineering and the progress of clinical trials to achieve virotherapeutics.

Genetic Modifications That Expand Oncolytic Virus Potency

Oncolytic viruses (OVs) are a promising type of cancer therapy since they selectively replicate in tumor cells without damaging healthy cells. Many oncolytic viruses have progressed to human clinical trials, however, their performance as monotherapy has not been as successful as expected. Importantly, recent literature suggests that the oncolytic potential of these viruses can be further increased by genetically modifying the viruses. In this review, we describe genetic modifications to OVs that improve their ability to kill tumor cells directly, to dismantle the tumor microenvironment, or to alter tumor cell signaling and enhance anti-tumor immunity. These advances are particularly important to increase virus spread and reduce metastasis, as demonstrated in animal models. Since metastasis is the principal cause of mortality in cancer patients, having OVs designed to target metastases could transform cancer therapy. The genetic alterations reported to date are only the beginning of all possible improvements to OVs. Modifications described here could be combined together, targeting multiple processes, or with other non-viral therapies with potential to provide a strong and lasting anti-tumor response in cancer patients.

Delivery of therapeutic oligonucleotides in nanoscale

Therapeutic oligonucleotides (TOs) represent one of the most promising drug candidates in the targeted cancer treatment due to their high specificity and capability of modulating cellular pathways that are not readily druggable. However, efficiently delivering of TOs to cancer cellular targets is still the biggest challenge in promoting their clinical translations. Emerging as a significant drug delivery vector, nanoparticles (NPs) can not only protect TOs from nuclease degradation and enhance their tumor accumulation, but also can improve the cell uptake efficiency of TOs as well as the following endosomal escape to increase the therapeutic index. Furthermore, targeted and on-demand drug release of TOs can also be approached to minimize the risk of toxicity towards normal tissues using stimuli-responsive NPs. In the past decades, remarkable progresses have been made on the TOs delivery based on various NPs with specific purposes. In this review, we will first give a brief introduction on the basis of TOs as well as the action mechanisms of several typical TOs, and then describe the obstacles that prevent the clinical translation of TOs, followed by a comprehensive overview of the recent progresses on TOs delivery based on several various types of nanocarriers containing lipid-based nanoparticles, polymeric nanoparticles, gold nanoparticles, porous nanoparticles, DNA/RNA nanoassembly, extracellular vesicles, and imaging-guided drug delivery nanoparticles.

Antifibrotic Therapy Augments the Antitumor Effects of Vesicular Stomatitis Virus Via Reprogramming Tumor Microenvironment

Solid tumors are characterized by abundant extracellular matrix originating from cancer-associated fibroblasts (CAFs). High collagen content can trigger the collapse of vascular system in the tumor and form physical barrier that eventually impedes the penetration of drug particles and cytotoxic immune cells. Moreover, CAFs is able to promote the enrichment of tumor-associated macrophages (TAMs) and differentiation of myeloid-derived suppressor cells (MDSCs) that work in concert to develop a highly immunosuppressive tumor microenvironment (TME). In this study, we investigated if halofuginone, an antifibrotic drug, can augment the therapeutic effects of oncolytic vesicular stomatitis virus (VSV). The results revealed that halofuginone significantly disrupts the collagen network in tumors and promotes the distribution of VSV and infiltration of CD8⁺ T cells (p < 0.0001). Combined treatment of VSV and halofuginone also modulates the immunosuppressive TME via deletion of TAM, MDSCs, and regulatory T cells (Tregs). Collectively, the combination therapy remarkably inhibits the tumor growth in multiple murine models and prolongs survival of mice. The results demonstrate the clinical potential of halofuginone in combination with oncolytic virus.

Strategies for enhancing intratumoral spread of oncolytic adenoviruses

Oncolytic viruses, effectively replicate viruses within malignant cells to lyse them without affecting normal ones, have recently shown great promise in developing therapeutic options for cancer. Adenoviruses (Ads) are one of the candidates in oncolytic virotheraoy due to its easily manipulated genomic DNA and expression of wide rane of its receptors on the various cancers. Although systematic delivery of oncolytic adenoviruses can target both primary and metastatic tumors, there are some drawbacks in the effective systematic delivery of oncolytic adenoviruses, including pre-existing antibodies and liver tropism. To overcome these limitations, intratumural (IT) administration of oncolytic viruses have been proposed. However, IT injection of Ads leaves much of the tumor mass unaffected and Ads are not able to disperse more in the tumor microenvironment (TME). To this end, various strategies have been developed to enhance the IT spread of oncolytic adenoviruses, such as using extracellular matrix degradation enzymes, junction opening peptides, and fusogenic proteins. In the present paper, we reviewed different oncolytic adenoviruses, their application in the clinical trials, and strategies for enhancing their IT spread.

Antifibrotic therapy to normalize the tumor microenvironment

Most tumors develop abnormal fibrotic regions consisting of fibroblasts, immune cells, and a dense extracellular matrix (ECM) immersed in a viscous interstitial fluid, and an abundant fibrotic tumor microenvironment (TME) is associated with poor outcome of treatment. It has been hypothesized that the treatment of cancer may be improved by interventions aiming to normalize this TME. The approaches used in attempts to normalize the fibrotic TME can be categorized into three strategies of targeted antifibrotic therapy: targeting of components of the ECM, targeting of the producers of the ECM components-the activated cancer-associated fibroblasts (CAFs), and targeting of the signaling pathways activating CAFs. To target the ECM, enzymes against components of the ECM have been used, including collagenase, relaxin, hyaluronidase, and lyxyl oxidase. Targeting of CAFs have been investigated by using agents aiming to eliminate or reprogram CAFs. CAFs are activated primarily by transforming growth factor-β (TGF-β), hedgehog, or focal adhesion kinase signaling, and several agents have been used to target these signaling pathways, including angiotensin II receptor I blockers (e.g., losartan) to inhibit the TGF-β pathway. Taken together, these studies have revealed that antifibrotic therapy is a two-edged sword: while some studies suggest enhanced response to treatment after antifibrotic therapy, others suggest that antifibrotic therapy may lead to increased tumor growth, metastasis, and impaired outcome of treatment. There are several possible explanations of these conflicting observations. Most importantly, tumors contain different subpopulations of CAFs, and while some subpopulations may promote tumor growth and metastasis, others may inhibit malignant progression. Furthermore, the outcome of antifibrotic therapy may depend on stage of disease, duration of treatment, treatment-induced activation of alternative profibrotic signaling pathways, and treatment-induced recruitment of tumor-supporting immune cells. Nevertheless, losartan-induced suppression of TGF-β signaling appears to be a particularly promising strategy. Losartan is a widely prescribed antihypertensive drug and highly advantageous therapeutic effects have been observed after losartan treatment of pancreatic cancer. However, improved understanding of the mechanisms governing the development of fibrosis in tumors is needed before safe antifibrotic treatments can be established.

Effect of Transgene Location, Transcriptional Control Elements and Transgene Features in Armed Oncolytic Adenoviruses

Clinical results with oncolytic adenoviruses (OAds) used as antitumor monotherapies show limited efficacy. To increase OAd potency, transgenes have been inserted into their genome, a strategy known as "arming OAds". Here, we review different parameters that affect the outcome of armed OAds. Recombinant adenovirus used in gene therapy and vaccination have been the basis for the design of armed OAds. Hence, early region 1 (E1) and early region 3 (E3) have been the most commonly used transgene insertion sites, along with partially or complete E3 deletions. Besides transgene location and orientation, transcriptional control elements, transgene function, either virocentric or immunocentric, and even the codons encoding it, greatly impact on transgene levels and virus fitness.

Enhancing oncolytic virotherapy: Observations from a Voronoi Cell-Based model

Oncolytic virotherapy is a promising cancer treatment using genetically modified viruses. Unfortunately, virus particles rapidly decay inside the body, significantly hindering their efficacy. In this article, treatment perturbations that could overcome obstacles to oncolytic virotherapy are investigated through the development of a Voronoi Cell-Based model (VCBM). The VCBM derived captures the interaction between an oncolytic virus and cancer cells in a 2-dimensional setting by using an agent-based model, where cell edges are designated by a Voronoi tessellation. Here, we investigate the sensitivity of treatment efficacy to the configuration of the treatment injections for different tumour shapes: circular, rectangular and irregular. The model predicts that multiple off-centre injections improve treatment efficacy irrespective of tumour shape. Additionally, we investigate delaying the infection of cancer cells by modifying viral particles with a substance such as alginate (a hydrogel polymer used in a range of cancer treatments). Simulations of the VCBM show that delaying the infection of cancer cells, and thus allowing more time for virus dissemination, can improve the efficacy of oncolytic virotherapy. The simulated treatment noticeably decreases the tumour size with no increase in toxicity. Improving oncolytic virotherapy in this way allows for a more effective treatment without changing its fundamental essence.

The oncolytic adenovirus VCN-01 promotes anti-tumor effect in primitive neuroectodermal tumor models

Last advances in the treatment of pediatric tumors has led to an increase of survival rates of children affected by primitive neuroectodermal tumors, however, still a significant amount of the patients do not overcome the disease. In addition, the survivors might suffer from severe side effects caused by the current standard treatments. Oncolytic virotherapy has emerged in the last years as a promising alternative for the treatment of solid tumors. In this work, we study the anti-tumor effect mediated by the oncolytic adenovirus VCN-01 in CNS-PNET models. VCN-01 is able to infect and replicate in PNET cell cultures, leading to a cytotoxicity and immunogenic cell death. In vivo, VCN-01 increased significantly the median survival of mice and led to long-term survivors in two orthotopic models of PNETs. In summary, these results underscore the therapeutic effect of VCN-01 for rare pediatric cancers such as PNETs, and warrants further exploration on the use of this virus to treat them.

Emerging roles for the relaxin/RXFP1 system in cancer therapy

A role for the hormone relaxin in cancer was described well before the receptor was identified. Relaxin predominantly increases the growth and invasive potential in cancers of different origins. However, relaxin was also shown to promote cell differentiation and to act in a dose-and time-dependent manner in different cancer cell models used. Following the discovery of the relaxin like family peptide receptor 1 (RXFP1) as the cellular receptor for RLN1 and RLN2, research has focussed on the ligand interaction with the large extracellular domain of RXFP1 and resulting molecular signaling mechanisms. RXFP1 activation mediates anti-apoptotic functions, angiogenesis and chemoresistance in cancer cells. This minireview summarizes the known biological functions of RXFP1 activation in different cancer entities in-vitro and in-vivo and outlines possible mechanisms to therapeutically address the relaxin-RXFP1 system in cancer cells.

Relaxin gene therapy: A promising new treatment option for various diseases with aberrant fibrosis or irregular angiogenesis

Relaxin (RLX) is an insulin-like polypeptide hormone that was initially introduced for its pregnancy-related function. Subsequent studies revealed that RLX possesses anti-fibrotic functions in tumors and nonreproductive tissues, such as skin, lungs, and others. This aspect of the RLX has been explored for the treatment of various illnesses, such as cardiac fibrosis, liver fibrosis, and solid tumors. With gene therapy coming into age with increasing number of products being approved by regulatory bodies in Europe and United States, we aim to discuss how RLX have been utilized in scope of gene therapy for treatment of various illnesses.

Asiatic acid enhances intratumor delivery and the antitumor effect of pegylated liposomal doxorubicin by reducing tumor-stroma collagen

Tumor-targeted drug delivery systems (Tt-DDSs) are proposed as a promising strategy for cancer care. However, the dense collagen network in tumors stroma significantly reduces the penetration and efficacy of Tt-DDS. In order to investigate the effect of asiatic acid (AA) on antitumor effect of pegylated liposomal doxorubicin (PLD) by attenuating stroma-collagen, colon cancer xenograft mice (SW620 cell line) were treated by PLD, AA, or combined regimes, respectively; the collagen levels were estimated by Sirius red/fast green dual staining and immunohistochemistry (IHC) staining; the intratumor exposure of doxorubicin was visualized by ex vivo fluorescence imaging and quantified by HPLC/MS analysis. In addition, the impact of AA on collagen synthesis of fibroblast cell (HFL-1) and cytotoxic effect of PLD and doxorubicin to cancer cell (SW620) were studied in vitro. In the presence of AA (4 mg/kg), the intratumor collagen level was restricted in vivo (reduced by 22%, from 4.14% ± 0.30% to 3.24% ± 0.25%, P = 0.051) and in vitro. Subsequently, doxorubicin level was increased by ~30%. The antitumor activity of PLD was significantly improved (57.3% inhibition of tumor growth and 44% reduction in tumor weight) by AA combination. Additionally, no significant improvement in cytotoxic effect of PLD or doxorubicin induced by AA was observed. In conclusion, AA is a promising sensitizer for tumor treatment by enhancing intratumor drug exposure via stromal remodeling.

Oncolytic adenoviruses: a game changer approach in the battle between cancer and the immune system

INTRODUCTION

Oncolytic adenoviruses are among the most studied oncolytic viruses because of their tumor selectivity, safety, and transgene-delivery capability. With a growing number of different immunotherapies against cancer, the extraordinary immunogenicity of the adenovirus has emerged as a differentiating strength. Enabling T-cell related therapies with oncolytic adenoviruses appears a promising approach due to its inherent ability to elicit responses from the adaptive immune compartment.

AREAS COVERED

These viruses have successfully enhanced both adoptive T-cell therapies and immune-checkpoint therapies. Oncolytic viruses induce several effects at the tumor and on the systemic level that help to circumvent current limitations of T-cells and related therapies, such as T-cell trafficking, tumor immune suppressivity and antigen spreading

EXPERT OPINION

Taking into account the multitude of possibilities of treating cancer with immunotherapies, learning to optimize the combinations and administration strategies of these drugs, could lead to durable responses in patients with currently incurable cancers.

Synergistic Effects of Bortezomib-OV Therapy and Anti-Invasive Strategies in Glioblastoma: A Mathematical Model

It is well-known that the tumor microenvironment (TME) plays an important role in the regulation of tumor growth and the efficacy of anti-tumor therapies. Recent studies have demonstrated the potential of combination therapies, using oncolytic viruses (OVs) in conjunction with proteosome inhibitors for the treatment of glioblastoma, but the role of the TME in such therapies has not been studied. In this paper, we develop a mathematical model for combination therapies based on the proteosome inhibitor bortezomib and the oncolytic herpes simplex virus (oHSV), with the goal of understanding their roles in bortezomib-induced endoplasmic reticulum (ER) stress, and how the balance between apoptosis and necroptosis is affected by the treatment protocol. We show that the TME plays a significant role in anti-tumor efficacy in OV combination therapy, and illustrate the effect of different spatial patterns of OV injection. The results illustrate a possible phenotypic switch within tumor populations in a given microenvironment, and suggest new anti-invasion therapies.

CAR-T Cells and Oncolytic Viruses: Joining Forces to Overcome the Solid Tumor Challenge

Adoptive transfer of chimeric antigen receptor (CAR)-modified T cells has resulted in unprecedented rates of long-lasting complete responses in patients with leukemia and lymphoma. However, despite the impressive results in patients with hematologic malignancies, CAR-T cells have showed limited effect against solid cancers. New approaches will need to simultaneously overcome the multiple challenges that CAR-T cells encounter in solid tumors, including the immunosuppressive tumor microenvironment and heterogeneity of antigen expression. Oncolytic viruses are lytic and immunogenic anti-cancer agents with the potential to synergize with CAR-T cells for the treatment of solid tumors. In addition, viruses can be further modified to deliver therapeutic transgenes selectively to the tumor microenvironment, which could enhance the effector functions of tumor-specific T cells. This review summarizes the major limitations of CAR-T cells in solid tumors and discusses the potential role for oncolytic viruses as partners for CAR-T cells in the fight against cancer.

Reengineering the Physical Microenvironment of Tumors to Improve Drug Delivery and Efficacy: From Mathematical Modeling to Bench to Bedside

Physical forces have a crucial role in tumor progression and cancer treatment. The application of principles of engineering and physical sciences to oncology has provided powerful insights into the mechanisms by which these forces affect tumor progression and confer resistance to delivery and efficacy of molecular, nano-, cellular, and immuno-medicines. Here, we discuss the mechanics of the solid and fluid components of a tumor, with a focus on how they impede the transport of therapeutic agents and create an abnormal tumor microenvironment (TME) that fuels tumor progression and treatment resistance. We also present strategies to reengineer the TME by normalizing the tumor vasculature and the extracellular matrix (ECM) to improve cancer treatment. Finally, we summarize various mathematical models that have provided insights into the physical barriers to cancer treatment and revealed new strategies to overcome these barriers.

A novel fiber chimeric conditionally replicative adenovirus-Ad5/F35 for tumor therapy

Significant progress has been made in the diagnosis and treatment of cancer; however, significant challenges remain. Conditionally replicating adenoviruses (CRAds), which not only kill cancer cells, but also serve as vectors to express therapeutic genes, are a novel and effective method to treat cancer. However, most adenoviruses are Ad5, which infect cells through the coxsackie and adenovirus receptor (CAR). The transduction efficacy of Ad5 is restricted because of the absent or low expression of CAR on several cancer cells. Ad serotype 35 has a different tropism pattern to Ad5. Ad35 attaches to cells via a non-CAR receptor, CD46, which is expressed widely on most tumor cells. Thus, chimeric adenoviral vectors consisting of the knob and shaft of Ad35 combined with Ad5 have been constructed. The chimeric fiber adenoviral vectors can transduce CAR-positive and CAR-negative cell lines. In this review, we explore the application of the novel fiber chimeric conditionally replicative adenovirus-Ad5/F35 in tumor therapy in terms of safety, mechanism, transduction efficacy, and antitumor effect.

Celecoxib normalizes the tumor microenvironment and enhances small nanotherapeutics delivery to A549 tumors in nude mice

Barriers presented by the tumor microenvironment including the abnormal tumor vasculature and interstitial matrix invariably lead to heterogeneous distribution of nanotherapeutics. Inspired by the close association between cyclooxygenase-2 (COX-2) and tumor-associated angiogenesis, as well as tumor matrix formation, we proposed that tumor microenvironment normalization by COX-2 inhibitors might improve the distribution and efficacy of nanotherapeutics for solid tumors. The present study represents the first time that celecoxib, a special COX-2 inhibitor widely used in clinics, was explored to normalize the tumor microenvironment and to improve tumor nanotherapeutics delivery using a human-derived A549 tumor xenograft as the solid tumor model. Immunofluorescence staining of tumor slices demonstrated that oral celecoxib treatment at a dose of 200 mg/kg for two weeks successfully normalized the tumor microenvironment, including tumor-associated fibroblast reduction, fibronectin bundle disruption, tumor vessel normalization, and tumor perfusion improvement. Furthermore, it also significantly enhanced the in vivo accumulation and deep penetration of 22-nm micelles rather than 100-nm nanoparticles in tumor tissues by in vivo imaging and distribution experiments and improved the therapeutic efficacy of paclitaxel-loaded micelles in tumor xenograft-bearing mouse models in the pharmacodynamics experiment. As celecoxib is widely and safely used in clinics, our findings may have great potential in clinics to improve solid tumor treatment.

Recent advances in oncolytic adenovirus therapies for cancer

Oncolytic adenoviruses (Onc.Ads) selectively replicate in and lyse cancer cells and are therefore commonly used vectors in clinical trials for cancer gene therapy. Building upon the well-characterized adenoviral natural tropism, genetic modification of Onc.Ad can enhance/regulate their transduction and replication within specific cancer cell types. However, Onc.Ad-mediated tumor cell lysis cannot fully eliminate tumors. The hostile tumor microenvironment provides many barriers to efficient oncolytic virotherapy, as tumors develop structure and immune-evasion mechanisms in order to grow and ultimately spread. For these reasons, Onc.Ads modified to deliver structural or immune modulatory molecules (Armed Onc.Ads) have been developed to overcome the physical and immunological barriers of solid tumors. The combination of oncolysis with tumor microenvironment modulation/destruction may provide a promising platform for Ad-based cancer gene therapy.

Actin-resistant DNAse I Expression From Oncolytic Adenovirus Enadenotucirev Enhances Its Intratumoral Spread and Reduces Tumor Growth

Spread of oncolytic viruses through tumor tissue is essential to effective virotherapy. Interstitial matrix is thought to be a significant barrier to virus particle convection between "islands" of tumor cells. One way to address this is to encode matrix-degrading enzymes within oncolytic viruses, for secretion from infected cells. To test the hypothesis that extracellular DNA provides an important barrier, we assessed the ability of DNase to promote virus spread. Nonreplicating Ad5 vectors expressing actin-resistant DNase (aDNAse I), proteinase K (PK), hyaluronidase (rhPH20), and chondroitinase ABC (CABC) were injected into established DLD human colorectal adenocarcinoma xenografts, transcomplemented with a replicating Ad5 virus. Each enzyme improved oncolysis by the replicating adenovirus, with no evidence of tumor cells being shed into the bloodstream. aDNAse I and rhPH20 hyaluronidase were then cloned into conditionally-replicating group B adenovirus, Enadenotucirev (EnAd). EnAd encoding each enzyme showed significantly better antitumor efficacy than the parental virus, with the aDNAse I-expressing virus showing improved spread. Both DNase and hyaluronidase activity was still measurable 32 days postinfection. This is the first time that extracellular DNA has been implicated as a barrier for interstitial virus spread, and suggests that oncolytic viruses expressing aDNAse I may be promising candidates for clinical translation.

Oncolytic viruses for therapy of malignant glioma

Effective treatment of malignant brain tumors is still an open problem. Location of tumor in vital areas of the brain significantly limits capasities of surgical treatment. The presence of tumor stem cells resistant to radiation and anticancer drugs in brain tumor complicates use of chemoradiotherapy and causes a high rate of disease recurrence. A technological improvement in bioselection and production of recombinant resulted in creation of viruses with potent oncolytic properties against glial tumors. Recent studies, including clinical trials, showed, that majority of oncolytic viruses are safe. Despite the impressive results of the viral therapy in some patients, the treatment of other patients is not effective; therefore, further improvement of the methods of oncolytic virotherapy is necessary. High genetic heterogeneity of glial tumor cells even within a single tumor determines differences in individual sensitivity of tumor cells to oncolytic viruses. This review analyses the most successful oncolytic virus strains, including those which had reached clinical trials, and discusses the prospects for new approaches to virotherapy of gliomas.

Oncolytic Immunotherapy for Treatment of Cancer

Immunotherapy entails the treatment of disease by modulation of the immune system. As detailed in the previous chapters, the different modes of achieving immune modulation are many, including the use of small/large molecules, cellular therapy, and radiation. Oncolytic viruses that can specifically attack, replicate within, and destroy tumors represent one of the most promising classes of agents for cancer immunotherapy (recently termed as oncolytic immunotherapy). The notion of oncolytic immunotherapy is considered as the way in which virus-induced tumor cell death (known as immunogenic cancer cell death (ICD)) allows the immune system to recognize tumor cells and provide long-lasting antitumor immunity. Both immune responses toward the virus and ICD together contribute toward successful antitumor efficacy. What is now becoming increasingly clear is that monotherapies, through any of the modalities detailed in this book, are neither sufficient in eradicating tumors nor in providing long-lasting antitumor immune responses and that combination therapies may deliver enhanced efficacy. After the rise of the genetic engineering era, it has been possible to engineer viruses to harbor combination-like characteristics to enhance their potency in cancer immunotherapy. This chapter provides a historical background on oncolytic virotherapy and its future application in cancer immunotherapy, especially as a combination therapy with other treatment modalities.

Exploring the tumor microenvironment with nanoparticles

Recent developments in nanotechnology have brought new approaches to cancer diagnosis and therapy. While enhanced permeability and retention effect (EPR) promotes nanoparticle (NP) extravasation, the abnormal tumor vasculature, high interstitial pressure and dense stroma structure limit homogeneous intratumoral distribution of NP and compromise their imaging and therapeutic effect. Moreover, heterogeneous distribution of NP in nontumor-stroma cells damages the nontumor cells, and interferes with tumor-stroma crosstalk. This can lead to inhibition of tumor progression, but can also paradoxically induce acquired resistance and facilitate tumor cell proliferation and metastasis. Overall, the tumor microenvironment plays a crucial, yet controversial role in regulating NP distribution and their biological effects. In this review, we summarize recent studies on the stroma barriers for NP extravasation, and discuss the consequential effects of NP distribution in stroma cells. We also highlight design considerations to improve NP delivery and propose potential combinatory strategies to overcome acquired resistance induced by damaged stroma cells.

Safety and efficacy of VCN-01, an oncolytic adenovirus combining fiber HSG-binding domain replacement with RGD and hyaluronidase expression

PURPOSE

Tumor targeting upon intravenous administration and subsequent intratumoral virus dissemination are key features to improve oncolytic adenovirus therapy. VCN-01 is a novel oncolytic adenovirus that combines selective replication conditional to pRB pathway deregulation, replacement of the heparan sulfate glycosaminoglycan putative-binding site KKTK of the fiber shaft with an integrin-binding motif RGDK for tumor targeting, and expression of hyaluronidase to degrade the extracellular matrix. In this study, we evaluate the safety and efficacy profile of this novel oncolytic adenovirus.

EXPERIMENTAL DESIGN

VCN-01 replication and potency were assessed in a panel of tumor cell lines. VCN-01 tumor-selective replication was evaluated in human fibroblasts and pancreatic islets. Preclinical toxicity, biodistribution, and efficacy studies were conducted in mice and Syrian hamsters.

RESULTS

Toxicity and biodistribution preclinical studies support the selectivity and safety of VCN-01. Antitumor activity after intravenous or intratumoral administration of the virus was observed in all tumor models tested, including melanoma and pancreatic adenocarcinoma, both in immunodeficient mice and immunocompetent hamsters.

CONCLUSIONS

Oncolytic adenovirus VCN-01 characterized by the expression of hyaluronidase and the RGD shaft retargeting ligand shows an efficacy-toxicity prolife in mice and hamsters by intravenous and intratumoral administration that warrants clinical testing.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.

Cycles of transient high-dose cyclophosphamide administration and intratumoral oncolytic adenovirus vector injection for long-term tumor suppression in Syrian hamsters

Immune responses against oncolytic adenovirus (Ad) vectors are thought to limit vector anti-tumor efficacy. With Syrian hamsters, which are immunocompetent and whose tumors and normal tissues are permissive for replication of Ad5-based oncolytic Ad vectors, treating with high-dose cyclophosphamide (CP) to suppress the immune system and exert chemotherapeutic effects enhances Ad vector anti-tumor efficacy. However, long-term CP treatment and immunosuppression can lead to anemia and vector spread to normal tissues. Here, we employed three cycles of transient high-dose CP administration plus intratumoral injection of the oncolytic Ad vector VRX-007 followed by withdrawal of CP. Each cycle lasted 4-6 weeks. This protocol allowed the hamsters to remain healthy so the study could be continued for ~100 days. The tumors were very well suppressed throughout the study. With immunocompetent hamsters, the vector retarded tumor growth initially, but after 3-4 weeks the tumors resumed rapid growth and further injections of vector were ineffective. Preimmunization of the hamsters with Ad5 prevented vector spillover from the tumor to the liver yet still allowed for effective long-term anti-tumor efficacy. Our results suggest that a clinical protocol might be developed with cycles of transient chemotherapy plus intratumoral vector injection to achieve significant anti-tumor efficacy while minimizing the side effects of cytostatic treatment.

The combination of i-leader truncation and gemcitabine improves oncolytic adenovirus efficacy in an immunocompetent model

Adenovirus (Ad) i-leader protein is a small protein of unknown function. The C-terminus truncation of the i-leader protein increases Ad release from infected cells and cytotoxicity. In the current study, we use the i-leader truncation to enhance the potency of an oncolytic Ad. In vitro, an i-leader truncated oncolytic Ad is released faster to the supernatant of infected cells, generates larger plaques, and is more cytotoxic in both human and Syrian hamster cell lines. In mice bearing human tumor xenografts, the i-leader truncation enhances oncolytic efficacy. However, in a Syrian hamster pancreatic tumor model, which is immunocompetent and less permissive to human Ad, antitumor efficacy is only observed when the i-leader truncated oncolytic Ad, but not the non-truncated version, is combined with gemcitabine. This synergistic effect observed in the Syrian hamster model was not seen in vitro or in immunodeficient mice bearing the same pancreatic hamster tumors, suggesting a role of the immune system in this synergism. These results highlight the interest of the i-leader C-terminus truncation because it enhances the antitumor potency of an oncolytic Ad and provides synergistic effects with gemcitabine in the presence of an immune competent system.

Therapeutic effect of oncolytic adenovirus expressing relaxin in radioresistant oral squamous cell carcinoma

Radioresistance is one of the main determinants of treatment outcome in oral squamous cell carcinoma (OSCC), and treatment of radioresistant OSCC is difficult due to cross resistance to other conventional treatments. We aimed to identify whether genetically modified oncolytic adenovirus expressing relaxin (RLX), which affects collagen metabolism, can effectively inhibit growth of the radioresistant OSCC. Therapeutic effect of oncolytic adenovirus was compared between radiosensitive and radioresistant OSCC cell lines in vitro and in vivo, and spread of adenovirus throughout the tumor mass was verified by immunohistochemistry (IHC). Oncolytic adenovirus effectively killed cancer cells and there was no significant difference in the cytotoxic effect between radiosensitive and radioresistant OSCC cell lines. In animal experiments, the adenovirus significantly reduced the size of tumor, and there was no significant difference between radiosensitive and radioresistant OSCC. In IHC, RLX expressing adenovirus showed better proliferation and eliminated collagens more effectively compared to RLX nonexpressing adenovirus. These findings suggested that genetically modified oncolytic adenovirus can effectively inhibit growth of the radioresistant OSCC and might be a new therapeutic option in radioresistant OSCC.

Strategies to increase drug penetration in solid tumors

Despite significant improvement in modalities for treatment of cancer that led to a longer survival period, the death rate of patients with solid tumors has not changed during the last decades. Emerging studies have identified several physical barriers that limit the therapeutic efficacy of cancer therapeutic agents such as monoclonal antibodies, chemotherapeutic agents, anti-tumor immune cells, and gene therapeutics. Most solid tumors are of epithelial origin and, although malignant cells are de-differentiated, they maintain intercellular junctions, a key feature of epithelial cells, both in the primary tumor as well as in metastatic lesions. Furthermore, nests of malignant epithelial tumor cells are shielded by layers of extracellular matrix (ECM) proteins (e.g., collagen, elastin, fibronectin, laminin) whereby tumor vasculature rarely penetrates into the tumor nests. In this chapter, we will review potential strategies to modulate the ECM and epithelial junctions to enhance the intratumoral diffusion and/or to remove physical masking of target receptors on malignant cells. We will focus on peptides that bind to the junction protein desmoglein 2 and trigger intracellular signaling, resulting in the transient opening of intercellular junctions. Intravenous injection of these junction openers increased the efficacy and safety of therapies with monoclonal antibodies, chemotherapeutics, and T cells in mouse tumor models and was safe in non-human primates. Furthermore, we will summarize approaches to transiently degrade ECM proteins or downregulate their expression. Among these approaches is the intratumoral expression of relaxin or decorin after adenovirus- or stem cell-mediated gene transfer. We will provide examples that relaxin-based approaches increase the anti-tumor efficacy of oncolytic viruses, monoclonal antibodies, and T cells.

Monitoring the initial delivery of an oncolytic measles virus encoding the human sodium iodide symporter to solid tumors using contrast-enhanced computed tomography

BACKGROUND

We aimed to determine the feasibility of monitoring viral delivery and initial distribution to solid tumors using iodinated contrast agent and micro-computed tomography (CT).

METHODS

Human BxPC-3 pancreatic tumor xenografts were established in nude mice. An oncolytic measles virus with an additional transcriptional unit encoding the sodium iodide symporter (NIS), as a reporter for viral infection, was mixed with a 1:10 dilution of Omnipaque 300 (GE Healthcare, Milwaukee, WI, USA) contrast agent and injected directly into tumors. Mice were imaged with micro-CT immediately before and after injection to determine the location of contrast agent/virus mixture. Mice were imaged again on day 3 after injection with micro-single-photon emission CT/CT to determine the location of NIS-mediated (99m) TcO(4) transport.

RESULTS

A 1:10 dilution of Omnipaque had no effect on viral infectivity or cell viability in vitro and was more than adequate for CT imaging of the intratumoral injectate distribution. The volume of tumor coverage with initial CT contrast agent and the 3-day postinfection measurement of virally infected tumor volume were significantly correlated. Additionally, regions of the tumor that did not receive contrast agent from the initial injection were largely devoid of viral infection at early time points.

CONCLUSIONS

Contrast-enhanced viral delivery enables a rapid and accurate prediction of the initial viral distribution within a solid tumor. This technique should enable real-time monitoring of viral propagation from initially infected tumor regions to adjacent tumor regions.

Oncolytic virotherapy for malignant glioma: translating laboratory insights into clinical practice

Glioblastoma multiforme, one of the most common and aggressive brain tumors in adults, is highly resistant to currently available therapies and often recurs. Due to its poor prognosis and difficult management, there is an urgent need for the development and translation of new anti-glioma therapeutic approaches into the clinic. In this context, oncolytic virotherapy arises as an exciting treatment option for glioma patients. These natural or genetically engineered viruses are able to effectively infect cancer cells, inducing a specific anti-tumor cytotoxic effect. In addition, some viruses have been redesigned to modulate glioma microenvironment, to express cytokines to boost a systemic anti-glioma immune response and to incorporate angiostatic genes to decrease glioma vasculature. Although recent clinical trials have confirmed the safety of oncolytic virotherapies in the brain, their moderate clinical efficacy has not yet matched the encouraging preclinical laboratory results. In this review, we will discuss the leading anti-glioma virotherapy approaches that are presently under preclinical and clinical evaluation. We will also review different delivery methods, in vivo virus behavior, fate, replication, intratumoral spread, activation of anti-tumor immune response, and targeting of glioma stem cells. We will focus on the advantages and limitations of each therapeutic approach and how to overcome these hurdles to effectively translate exciting laboratory results into promising clinical trials.

Chapter four--Design of improved oncolytic adenoviruses

During the last decade adenovirus has lost its appeal in gene therapy due to a high immunogenicity that leads to a transient gene expression. However, adenovirus has gained attention as replication-competent vector to treat cancer. Designed for virotherapy, adenovirus has been successfully modified to replicate selectively in tumor cells. After the initial clinical trials with tumor-selective adenoviruses, it has become clear that further improvements on tumor targeting, intratumoral dissemination, and modulation of antiviral and antitumor immune responses are needed to effectively treat cancer. The non-viral delivery of infectious DNA encoding an oncolytic adenovirus armed with extracellular matrix-degrading genes and with genes that regulate the immune system to favor antitumor instead of antiviral immunity are key in the design oncolytic adenovirus.

Vaccinia virus-mediated intra-tumoral expression of matrix metalloproteinase 9 enhances oncolysis of PC-3 xenograft tumors

Background

Oncolytic viruses, including vaccinia virus (VACV), are a promising alternative to classical mono-cancer treatment methods such as surgery, chemo- or radiotherapy. However, combined therapeutic modalities may be more effective than mono-therapies. In this study, we enhanced the effectiveness of oncolytic virotherapy by matrix metalloproteinase (MMP-9)-mediated degradation of proteins of the tumoral extracellular matrix (ECM), leading to increased viral distribution within the tumors.

Methods

For this study, the oncolytic vaccinia virus GLV-1h255, containing the mmp-9 gene, was constructed and used to treat PC-3 tumor-bearing mice, achieving an intra-tumoral over-expression of MMP-9. The intra-tumoral MMP-9 content was quantified by immunohistochemistry in tumor sections. Therapeutic efficacy of GLV-1h255 was evaluated by monitoring tumor growth kinetics and intra-tumoral virus titers. Microenvironmental changes mediated by the intra-tumoral MMP-9 over-expression were investigated by microscopic quantification of the collagen IV content, the blood vessel density (BVD) and the analysis of lymph node metastasis formation.

Results

GLV-1h255-treatment of PC-3 tumors led to a significant over-expression of intra-tumoral MMP-9, accompanied by a marked decrease in collagen IV content in infected tumor areas, when compared to GLV-1h68-infected tumor areas. This led to considerably elevated virus titers in GLV-1h255 infected tumors, and to enhanced tumor regression. The analysis of the BVD, as well as the lumbar and renal lymph node volumes, revealed lower BVD and significantly smaller lymph nodes in both GLV-1h68- and GLV-1h255- injected mice compared to those injected with PBS, indicating that MMP-9 over-expression does not alter the metastasis-reducing effect of oncolytic VACV.

Conclusions

Taken together, these results indicate that a GLV-1h255-mediated intra-tumoral over-expression of MMP-9 leads to a degradation of collagen IV, facilitating intra-tumoral viral dissemination, and resulting in accelerated tumor regression. We propose that approaches which enhance the oncolytic effect by increasing the intra-tumoral viral load, may be an effective way to improve therapeutic outcome.

Anti-angiogenic therapy increases intratumoral adenovirus distribution by inducing collagen degradation

Conditionally replicating adenoviruses (CRAd) are a promising class of gene therapy agents that can overcome already known glioblastoma (GBM) resistance mechanisms but have limited distribution upon direct intratumoral (i.t.) injection. Collagen bundles in the extracellular matrix (ECM) play an important role in inhibiting virus distribution. In fact, ECM pre-treatment with collagenases improves virus distributions to tumor cells. Matrix metalloproteinases (MMPs) are an endogenous class of collagenases secreted by tumor cells whose function can be altered by different drugs including anti-angiogenic agents, such as bevacizumab. In this study we hypothesized that up-regulation of MMP activity during antiangiogenic therapy can improve CRAd-S-pk7 distribution in GBM. We find that MMP-2 activity in human U251 GBM xenografts increases (*p=0.03) and collagen IV content decreases (*p=0.01) during vascular endothelial growth factor (VEGF-A) antibody neutralization. After proving that collagen IV inhibits CRAd-S-pk7 distribution in U251 xenografts (Spearman rho= −0.38; **p=0.003), we show that VEGF blocking antibody treatment followed by CRAd-S-pk7 i.t. injection reduces U251 tumor growth more than each individual agent alone (***p<0.0001). Our data proposes a novel approach to improve virus distribution in tumors by relying on the early effects of anti-angiogenic therapy.

Nanoscale drug delivery systems for enhanced drug penetration into solid tumors: current progress and opportunities

Poor penetration of anticancer drags into solid tumors significantly limits their efficacy. This phenomenon has long been observed for small-molecule chemotherapeutics, and it can be even more pronounced for nanoscale therapies. Nanoparticles have enormous potential for the treatment of cancer due to their wide applicability as drug delivery and imaging vehicles and their size-dependent accumulation into solid tumors by the enhanced permeability and retention (EPR) effect. Further, synthetic nanoparticles can be engineered to overcome barriers to drag delivery. Despite their promise for the treatment of cancer, relatively little work has been done to study and improve their ability to diffuse into solid tumors following passive accumulation in the tumor vasculature. In this review, we present the complex issues governing efficient penetration of nanoscale therapies into solid tumors. The current methods available to researchers to study nanoparticle penetration into malignant tumors are described, and the most recent works studying the penetration of nanoscale materials into solid tumors are summarized. We conclude with an overview of the important nanoparticle design parameters governing their tumor penetration, as well as by highlighting critical directions in this field.

Isolation of more potent oncolytic paramyxovirus by bioselection

Newcastle disease virus (NDV) is an oncolytic paramyxovirus with a nonsegmented single-stranded RNA genome. In this report, a recombinant oncolytic NDV was passaged in human tumor xenografts and reisolated and characterized after two rounds of bioselection. Several isolates could be recovered that differed from the parental virus with respect to virus spread in tumor cells and the ability to form syncytia in human tumor cells. Three isolates were identified that demonstrated superior oncolytic potency compared with the parental virus as measured by increased oncolytic potency in confluent tumor cell monolayers, in tumor cell spheroids and in a mouse xenograft tumor model. The surface proteins F and HN were sequence analyzed and characterized for fusogenicity. The present study demonstrates that in vivo NDV bioselection can enable the isolation of novel, oncolytic NDV and thus represents a powerful methodology for the development of highly potent oncolytic viruses.

Oncolytic virotherapy in veterinary medicine: current status and future prospects for canine patients

Oncolytic viruses refer to those that are able to eliminate malignancies by direct targeting and lysis of cancer cells, leaving non-cancerous tissues unharmed. Several oncolytic viruses including adenovirus strains, canine distemper virus and vaccinia virus strains have been used for canine cancer therapy in preclinical studies. However, in contrast to human studies, clinical trials with oncolytic viruses for canine cancer patients have not been reported. An 'ideal' virus has yet to be identified. This review is focused on the prospective use of oncolytic viruses in the treatment of canine tumors - a knowledge that will undoubtedly contribute to the development of oncolytic viral agents for canine cancer therapy in the future.

GALV expression enhances the therapeutic efficacy of an oncolytic adenovirus by inducing cell fusion and enhancing virus distribution

The limitations of the current oncolytic adenoviruses for cancer therapy include insufficient potency and poor distribution of the virus throughout the tumor mass. To address these problems, we generated an oncolytic adenovirus expressing the hyperfusogenic form of the gibbon-ape leukemia virus (GALV) envelope glycoprotein under the control of the adenovirus major late promoter. The oncolytic properties of the new fusogenic adenovirus, ICOVIR16, were analyzed both in vitro and in vivo, and compared with that of its non-fusogenic counterpart, ICOVIR15. Our results indicate that GALV expression by ICOVIR16 induced extensive syncytia formation and enhanced tumor cell killing in a variety of tumor cell types. When injected intratumorally or intravenously into mice with large pre-established melanoma or pancreatic tumors, ICOVIR16 rapidly reduced tumor burden, and in some cases, resulted in complete eradication of the tumors. Importantly, GALV expression induced tumor cell fusion in vivo and enhanced the spreading of the virus throughout the tumor. Taken together, these results indicate that GALV expression can improve the antitumoral potency of an oncolytic adenovirus and suggest that ICOVIR16 is a promising candidate for clinical evaluation in patients with cancer.

Macrophage metalloelastase (MME) as adjuvant for intra-tumoral injection of oncolytic adenovirus and its influence on metastases development

Oncolytic adenoviruses are a promising treatment alternative for many advanced cancers, including colorectal cancer. However, clinical trials have demonstrated that single-agent therapy in advanced tumor masses is rarely curative. Poor spreading of the virus through tumor tissue is one of the major issues limiting efficacy. As oncolytic viruses kill preferentially cancer cells, high extracellular matrix (ECM) content constitutes potential barriers for viral penetration within tumors. In this study, the ECM-degrading proteases relaxin, hyaluronidase, elastase and macrophage metalloelastase (MME) were tested for their antitumor efficacy alone and in combination with oncolytic adenovirus. MME improved the overall antitumor efficacy of oncolytic adenovirus in subcutaneous HCT116 xenografts. In a liver metastatic colorectal cancer model, intra-tumoral treatment of primary tumors from HT29 cells with MME monotherapy or with oncolytic adenovirus inhibited tumor growth. Combination therapy showed no increased mortality in comparison with either monotherapy alone. Contradictory results of effects of MME on tumorigenesis and metastasis formation have been reported in the literature. This study demonstrates for the first time in a metastatic animal model that MME, as a monotherapy or in combination with oncolytic virus, does not increase tumor invasiveness. Co-administration of MME and oncolytic adenovirus may be a suitable approach for further optimization aiming at clinical applications for metastatic colorectal cancer.

Adenovirus i-leader truncation bioselected against cancer-associated fibroblasts to overcome tumor stromal barriers

Tumor-associated stromal cells constitute a major hurdle in the antitumor efficacy with oncolytic adenoviruses. To overcome this biological barrier, an in vitro bioselection of a mutagenized AdwtRGD stock in human cancer-associated fibroblasts (CAFs) was performed. Several rounds of harvest at early cytopathic effect (CPE) followed by plaque isolation led us to identify one mutant with large plaque phenotype, enhanced release in CAFs and enhanced cytotoxicity in CAF and several tumor cell lines. Whole genome sequencing and functional mapping identified the truncation of the last 17 amino acids in C-terminal end of the i-leader protein as the mutation responsible for this phenotype. Similar mutations have been previously isolated in two independent bioselection processes in tumor cell lines. Importantly, our results establish the enhanced antitumor activity in vivo of the i-leader C-terminal truncated mutants, especially in a desmotic fibroblast-embedded lung carcinoma model in mice. These results indicate that the i-leader truncation represents a promising trait to improve virotherapy with oncolytic adenoviruses.