Targeting HSV-1 virions for specific binding to epidermal growth factor receptor-vIII-bearing tumor cells

Development of a novel, high-efficacy oncolytic herpes simplex virus type 1 platform equipped with two distinct retargeting modalities

To retarget oncolytic herpes simplex virus (oHSV) to cancer-specific antigens, we designed a novel, double-retargeted oHSV platform that uses single-chain antibodies (scFvs) incorporated into both glycoprotein H and a bispecific adapter expressed from the viral genome to mediate infection predominantly via tumor-associated antigens. Successful retargeting was achieved using a nectin-1-detargeted HSV that remains capable of interacting with herpesvirus entry mediator (HVEM), the second canonical HSV entry receptor, and is, therefore, recognized by the adapter consisting of the virus-binding N-terminal 82 residues of HVEM fused to the target-specific scFv. We tested both an epithelial cell adhesion molecule (EpCAM)- and a human epidermal growth factor receptor 2-specific scFv separately and together to target cells expressing one, the other, or both receptors. Our results show not only dose-dependent, target receptor-specific infection in vitro, but also enhanced virus spread compared with single-retargeted virus. In addition, we observed effective infection and spreading of the EpCAM double-retargeted virus in vivo. Remarkably, a single intravenous dose of the EpCAM-specific virus eliminated all detectable tumors in a subcutaneous xenograft model, and the same intravenous dose seemed to be harmless in immunocompetent FVB/N mice. Our findings suggest that our double-retargeted oHSV platform can provide a potent, versatile, and systemically deliverable class of anti-cancer therapeutics that specifically target cancer cells while ensuring safety.

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.

Nanobody-based retargeting of an oncolytic herpesvirus for eliminating CXCR4+ GBM cells: A proof of principle

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, which remains difficult to cure. The very high recurrence rate has been partly attributed to the presence of GBM stem-like cells (GSCs) within the tumors, which have been associated with elevated chemokine receptor 4 (CXCR4) expression. CXCR4 is frequently overexpressed in cancer tissues, including GBM, and usually correlates with a poor prognosis. We have created a CXCR4-retargeted oncolytic herpesvirus (oHSV) by insertion of an anti-human CXCR4 nanobody in glycoprotein D of an attenuated HSV-1 (ΔICP34.5, ΔICP6, and ΔICP47), thereby describing a proof of principle for the use of nanobodies to target oHSVs toward specific cellular entities. Moreover, this virus has been armed with a transgene expressing a soluble form of TRAIL to trigger apoptosis. In vitro, this oHSV infects U87MG CXCR4⁺ and patient-derived GSCs in a CXCR4-dependent manner and, when armed, triggers apoptosis. In a U87MG CXCR4⁺ orthotopic xenograft mouse model, this oHSV slows down tumor growth and significantly improves mice survival. Customizing oHSVs with diverse nanobodies for targeting multiple proteins appears as an interesting approach for tackling the heterogeneity of GBM, especially GSCs. Altogether, our study must be considered as a proof of principle and a first step toward personalized GBM virotherapies to complement current treatments.

Large and small extracellular vesicles released by glioma cells in vitro and in vivo

Tumour cells release diverse populations of extracellular vesicles (EVs) ranging in size, molecular cargo, and function. We sought to characterize mRNA and protein content of EV subpopulations released by human glioblastoma (GBM) cells expressing a mutant form of epidermal growth factor receptor (U87EGFRvIII) in vitro and in vivo with respect to size, morphology and the presence of tumour cargo. The two EV subpopulations purified from GBM U87EGFRvIII cancer cells, non-cancer human umbilical vein endothelial cells (HUVEC; control) and serum of U87EGFRvIII glioma-bearing mice using differential centrifugation (EVs that sediment at 10,000 × g or 100,000 × g are termed large EVs and small EVs, respectively) were characterized using transmission electron microscopy (TEM), confocal microscopy, nanoparticle tracking analysis (NTA), flow cytometry, immunofluorescence (IF), quantitative-polymerase chain reaction (qPCR), droplet digital polymerase chain reaction (ddPCR) and micro-nuclear magnetic resonance (μNMR). We report that both U87EGFRvIII and HUVEC release a similar number of small EVs, but U87EGFRvIII glioma cells alone release a higher number of large EVs compared to non-cancer HUVEC. The EGFRvIII mRNA from the two EV subpopulations from U87EGFRvIII glioma cells was comparable, while the EGFR protein (wild type + vIII) levels are significantly higher in large EVs. Similarly, EGFRvIII mRNA in large and small EVs isolated from the serum of U87EGFRvIII glioma-bearing mice is comparable, while the EGFR protein (wild type + vIII) levels are significantly higher in large EVs. Here we report for the first time a direct comparison of large and small EVs released by glioma U87EGFRvIII cells and from serum of U87EGFRvIII glioma-bearing mice. Both large and small EVs contain tumour-specific EGFRvIII mRNA and proteins and combining these platforms may be beneficial in detecting rare mutant events in circulating biofluids.

Oncolytic herpes simplex virus tumor targeting and neutralization escape by engineering viral envelope glycoproteins

Oncolytic herpes simplex viruses (oHSVs) have been approved for clinical usage and become more and more popular for tumor virotherapy. However, there are still many issues for the oHSVs used in clinics and clinical trials. The main issues are the limited anti-tumor effects, intratumor injection, and some side effects. To overcome such challenges, here we review the genetic engineering of the envelope glycoproteins for oHSVs to target tumors specifically, and at the same time we summarize the many neutralization antibodies against the envelope glycoproteins and align the neutralization epitopes with functional domains of the respective glycoproteins for future identification of new functions of the glycoproteins and future engineering of the epitopes to escape from host neutralization.

Retargeting of herpes simplex virus (HSV) vectors

Gene therapy applications depend on vector delivery and gene expression in the appropriate target cell. Vector infection relies on the distribution of natural virus receptors that may either not be present on the desired target cell or distributed in a manner to give off-target gene expression. Some viruses display a very limited host range, while others, including herpes simplex virus (HSV), can infect almost every cell within the human body. It is often an advantage to retarget virus infectivity to achieve selective target cell infection. Retargeting can be achieved by (i) the inclusion of glycoproteins from other viruses that have a different host-range, (ii) modification of existing viral glycoproteins or coat proteins to incorporate peptide ligands or single-chain antibodies (scFvs) that bind to the desired receptor, or (iii) employing soluble adapters that recognize both the virus and a specific receptor on the target cell. This review summarizes efforts to target HSV using these three strategies.

Recent progress in protein-protein interaction study for EGFR-targeted therapeutics

INTRODUCTION

Epidermal growth factor receptor (EGFR) expression is upregulated in many tumors and its aberrant signaling drives progression of many cancer types. Consequently, EGFR has become a clinically validated target as extracellular tumor marker for antibodies as well as for tyrosine kinase inhibitors. Within the last years, new mechanistic insights were uncovered and, based on clinical experience as well as progress in protein engineering, novel bio-therapeutic approaches were developed and tested.

AREAS COVERED

The potential therapeutic targeting arsenal in the fight against cancer now encompasses bispecific or biparatopic antibodies, DARPins, Adnectins, Affibodies, peptides and combinations of these binding molecules with viral- and nano-particles. We review past and recent binding proteins from the literature and include a brief description of the various targeting approaches. Special attention is given to the binding modes with the EGFR. Expert commentary: Clinical data from the three approved anti EGFR antibodies indicate that there is room for improved therapeutic efficacy. Having choices in size, affinity, avidity and the mode of EGFR binding as well as the possibility to combine various effector functions opens the possibility to rationally design more effective therapeutics.

Oncolytic viruses: From bench to bedside with a focus on safety

Oncolytic viruses are a relatively new class of anti-cancer immunotherapy agents. Several viruses have undergone evaluation in clinical trials in the last decades, and the first agent is about to be approved to be used as a novel cancer therapy modality. In the current review, an overview is presented on recent (pre)clinical developments in the field of oncolytic viruses that have previously been or currently are being evaluated in clinical trials. Special attention is given to possible safety issues like toxicity, environmental shedding, mutation and reversion to wildtype virus.

Designing Herpes Viruses as Oncolytics

Oncolytic herpes simplex virus (oHSV) was one of the first genetically-engineered oncolytic viruses. Because herpes simplex virus (HSV) is a natural human pathogen that can cause serious disease, it is incumbent that it be genetically-engineered or significantly attenuated for safety. Here we present a detailed explanation of the functions of HSV-1 genes frequently mutated to endow oncolytic activity. These genes are non-essential for growth in tissue culture cells but are important for growth in post-mitotic cells, interfering with intrinsic antiviral and innate immune responses or causing pathology, functions dispensable for replication in cancer cells. Understanding the function of these genes leads to informed creation of new oHSVs with better therapeutic efficacy. Virus infection and replication can also be directed to cancer cells through tumor-selective receptor binding and transcriptional- or post-transcriptional miRNA-targeting, respectively. In addition to the direct effects of oHSV on infected cancer cells and tumors, oHSV can be 'armed' with transgenes that are: reporters, to track virus replication and spread; cytotoxic, to kill uninfected tumor cells; immune modulatory, to stimulate anti-tumor immunity; or tumor microenvironment altering, to enhance virus spread or to inhibit tumor growth. In addition to HSV-1, other alphaherpesviruses are also discussed for their oncolytic activity.

Oncolytic herpes simplex virus-based strategies: toward a breakthrough in glioblastoma therapy

Oncolytic viruses (OV) are a class of antitumor agents that selectively kill tumor cells while sparing normal cells. Oncolytic herpes simplex virus (oHSV) has been investigated in clinical trials for patients with the malignant brain tumor glioblastoma for more than a decade. These clinical studies have shown the safety of oHSV administration to the human brain, however, therapeutic efficacy of oHSV as a single treatment remains unsatisfactory. Factors that could hamper the anti-glioblastoma efficacy of oHSV include: attenuated potency of oHSV due to deletion or mutation of viral genes involved in virulence, restricting viral replication and spread within the tumor; suboptimal oHSV delivery associated with intratumoral injection; virus infection-induced inflammatory and cellular immune responses which could inhibit oHSV replication and promote its clearance; lack of effective incorporation of oHSV into standard-of-care, and poor knowledge about the ability of oHSV to target glioblastoma stem cells (GSCs). In an attempt to address these issues, recent research efforts have been directed at: (1) design of new engineered viruses to enhance potency, (2) better understanding of the role of the cellular immunity elicited by oHSV infection of tumors, (3) combinatorial strategies with different antitumor agents with a mechanistic rationale, (4) “armed” viruses expressing therapeutic transgenes, (5) use of GSC-derived models in oHSV evaluation, and (6) combinations of these. In this review, we will describe the current status of oHSV clinical trials for glioblastoma, and discuss recent research advances and future directions toward successful oHSV-based therapy of glioblastoma.

Armed therapeutic viruses - a disruptive therapy on the horizon of cancer immunotherapy

For the past 150 years cancer immunotherapy has been largely a theoretical hope that recently has begun to show potential as a highly impactful treatment for various cancers. In particular, the identification and targeting of immune checkpoints have given rise to exciting data suggesting that this strategy has the potential to activate sustained antitumor immunity. It is likely that this approach, like other anti-cancer strategies before it, will benefit from co-administration with an additional therapeutic and that it is this combination therapy that may generate the greatest clinical outcome for the patient. In this regard, oncolytic viruses are a therapeutic moiety that is well suited to deliver and augment these immune-modulating therapies in a highly targeted and economically advantageous way over current treatment. In this review, we discuss the blockade of immune checkpoints, how oncolytic viruses complement and extend these therapies, and speculate on how this combination will uniquely impact the future of cancer immunotherapy.

New viruses for cancer therapy: meeting clinical needs

Early-stage clinical trials of oncolytic virotherapy have reported the safety of several virus platforms, and viruses from three families have progressed to advanced efficacy trials. In addition, preclinical studies have established proof-of-principle for many new genetic engineering strategies. Thus, the virotherapy field now has available a diverse collection of viruses that are equipped to address unmet clinical needs owing to improved systemic administration, greater tumour specificity and enhanced oncolytic efficacy. The current key challenge for the field is to develop viruses that replicate with greater efficiency within tumours while achieving therapeutic synergy with currently available treatments.

Strategies in gene therapy for glioblastoma

Glioblastoma (GBM) is the most aggressive form of brain cancer, with a dismal prognosis and extremely low percentage of survivors. Novel therapies are in dire need to improve the clinical management of these tumors and extend patient survival. Genetic therapies for GBM have been postulated and attempted for the past twenty years, with variable degrees of success in pre-clinical models and clinical trials. Here we review the most common approaches to treat GBM by gene therapy, including strategies to deliver tumor-suppressor genes, suicide genes, immunomodulatory cytokines to improve immune response, and conditionally-replicating oncolytic viruses. The review focuses on the strategies used for gene delivery, including the most common and widely used vehicles (i.e., replicating and non-replicating viruses) as well as novel therapeutic approaches such as stem cell-mediated therapy and nanotechnologies used for gene delivery. We present an overview of these strategies, their targets, different advantages, and challenges for success. Finally, we discuss the potential of gene therapy-based strategies to effectively attack such a complex genetic target as GBM, alone or in combination with conventional therapy.

Novel therapies in glioblastoma

Conventional treatment of glioblastoma has advanced only incrementally in the last 30 years and still yields poor outcomes. The current strategy of surgery, radiation, and chemotherapy has increased median survival to approximately 15 months. With the advent of molecular biology and consequent improved understanding of basic tumor biology, targeted therapies have become cornerstones for cancer treatment. Many pathways (RTKs, PI3K/AKT/mTOR, angiogenesis, etc.) have been identified in GBM as playing major roles in tumorigenesis, treatment resistance, or natural history of disease. Despite the growing understanding of the complex networks regulating GBM tumors, many targeted therapies have fallen short of expectations. In this paper, we will discuss novel therapies and the successes and failures that have occurred. One clear message is that monotherapies yield minor results, likely due to functionally redundant pathways. A better understanding of underlying tumor biology may yield insights into optimal targeting strategies which could improve the overall therapeutic ratio of conventional treatments.