Oncolytic viruses: smart therapeutics for smart cancers

Design Strategies and Precautions for Using Vaccinia Virus in Tumor Virotherapy

Oncolytic virotherapy has emerged as a novel form of cancer immunotherapy. Oncolytic viruses (OVs) can directly infect and lyse the tumor cells, and modulate the beneficial immune microenvironment. Vaccinia virus (VACV) is a promising oncolytic vector because of its high safety, easy gene editing, and tumor intrinsic selectivity. To further improve the safety, tumor-targeting ability, and OV-induced cancer-specific immune activation, various approaches have been used to modify OVs. The recombinant oncolytic VACVs with deleting viral virulence factors and/or arming various therapeutic genes have displayed better therapeutic effects in multiple tumor models. Moreover, the combination of OVs with other cancer immunotherapeutic approaches, such as immune checkpoint inhibitors and CAR-T cells, has the potential to improve the outcome in cancer patients. This will open up new possibilities for the application of OVs in cancer treatment, especially for personalized cancer therapies.

Viral Proteins as Emerging Cancer Therapeutics

Simple Summary

This review is focused on enlisting viral proteins from different host sources, irrespective of their origin, that may act as future cancer curatives. Unlike the viral proteins that are responsible for tumor progression, these newly emerged viral proteins function as tumor suppressors. Their ability to regulate various cell signaling mechanisms specifically in cancer cells makes them interesting candidates to explore their use in cancer therapy. The discussion about such viral components may provide new insights into cancer treatment in the absence of any adverse effects to normal cells. The study also highlights avian viral proteins as a substitute to human oncolytic viruses for their ability to evade pre-existing immunity.

Abstract

Viruses are obligatory intracellular parasites that originated millions of years ago. Viral elements cover almost half of the human genome sequence and have evolved as genetic blueprints in humans. They have existed as endosymbionts as they are largely dependent on host cell metabolism. Viral proteins are known to regulate different mechanisms in the host cells by hijacking cellular metabolism to benefit viral replication. Amicable viral proteins, on the other hand, from several viruses can participate in mediating growth retardation of cancer cells based on genetic abnormalities while sparing normal cells. These proteins exert discreet yet converging pathways to regulate events like cell cycle and apoptosis in human cancer cells. This property of viral proteins could be harnessed for their use in cancer therapy. In this review, we discuss viral proteins from different sources as potential anticancer therapeutics.

Intravenous injection of the oncolytic virus M1 awakens antitumor T cells and overcomes resistance to checkpoint blockade

Reversing the highly immunosuppressive tumor microenvironment (TME) is essential to achieve long-term efficacy with cancer immunotherapy. Despite the impressive clinical response to checkpoint blockade in multiple types of cancer, only a minority of patients benefit from this approach. Here, we report that the oncolytic virus M1 induces immunogenic tumor cell death and subsequently restores the ability of dendritic cells to prime antitumor T cells. Intravenous injection of M1 disrupts immune tolerance in the privileged TME, reprogramming immune-silent (cold) tumors into immune-inflamed (hot) tumors. M1 elicits potent CD8⁺ T cell-dependent therapeutic effects and establishes long-term antitumor immune memory in poorly immunogenic tumor models. Pretreatment with M1 sensitizes refractory tumors to subsequent checkpoint blockade by boosting T-cell recruitment and upregulating the expression of PD-L1. These findings reveal the antitumor immunological mechanism of the M1 virus and indicated that oncolytic viruses are ideal cotreatments for checkpoint blockade immunotherapy.

Proinflammatory response induced by Newcastle disease virus in tumor and normal cells

Purpose

To investigate the specific role of immune responses induced by lentogenic Newcastle disease virus (NDV) for its antitumor effect.

Materials and methods

NDV LaSota strain was used to infect the following human cells: non-small cell lung carcinoma (A549), glioblastoma (U87MG and T98G), mammary gland adenocarcinoma (MCF7 and MDA-MB-453), hepatocellular carcinoma (Huh7), transformed embryonic kidney cells (HEK293), primary monocytes, lung fibroblast (HF19), skin fibroblast (NB1RGB) and rat astroglia (RCR-1) at 0.001 multiplicity of infection. NDV-induced cytotoxicity and expression of proinflammatory cytokines were analyzed using 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide assay and multiplex enzyme-linked immunosorbent assay, respectively.

Results

Tumor cells (A549, U87MG, T98G, Huh7, MDA-MB-453, and MCF7) showed viability of <44%, while normal cell lines HEK293, NB1RGB, and RCR-1 showed 84%, 73%, and 69% viability at 72 hours postinfection, respectively. Proinflammatory cytokine profiling showed that NDV mainly induced the secretion of interferon (IFN)-α, IFN-β, and IFN-λ in tumor cells and only IFN-λ in normal cells. In addition, NDV infection induced the production of interleukin (IL)-6 in most cells.

Conclusion

Our findings suggest a new perspective regarding the role of IFN-λ and IL-6 in the mechanism of tumor selectivity and oncolysis of NDV.

Enhancing Expression of Functional Human Sodium Iodide Symporter and Somatostatin Receptor in Recombinant Oncolytic Vaccinia Virus for In Vivo Imaging of Tumors

Oncolytic virus (OV) therapy has emerged as a novel tool in our therapeutic arsenals for fighting cancer. As a live biologic agent, OV has the ability to target and selectively amplify at the tumor sites. We have reported that a vaccinia-based OV (Pexa-Vec) has shown good efficacy in preclinical models and in clinical trials. To give an additional tool to clinicians to allow both treatment of the tumor and improved visualization of tumor margins, we developed new viral-based platforms with 2 specific gene reporters.

METHODS

We incorporated the human sodium iodide symporter (hNIS) and the human somatostatin receptor 2 (hSSR2) in the vaccinia-based OV and tested viral constructs for their abilities to track and treat tumor development in vivo.

RESULTS

Early and high-level expression of hNIS is detrimental to the recombinant virus, leading to the aggregation of hNIS protein and early cell death. Putting hNIS under a late synthetic promoter allowed a higher functional expression of the protein and much stronger ¹²³I or ⁹⁹Tc uptake. In vivo, the hNIS-containing virus infected and amplified in the tumor site, showing a better efficacy than the parental virus. The hNIS expression at the tumor site allowed for the imaging of viral infection and tumor regression. Similarly, hSSR2-containing OV vaccinia infected and lysed cancer cells.

CONCLUSION

When tumor-bearing mice were given hNIS- and hSSR2-containing OV, ⁹⁹Tc and ¹¹¹In signals coalesced at the tumor, highlighting the power of using these viruses for tumor diagnosis and treatment.

Oncolytic viral therapy for neuroblastoma cells with Sindbis virus AR339 strain

PURPOSE

With current treatment regimens, high-risk neuroblastoma (NB) remains largely incurable. Oncolytic viral therapy uses replication-competent viruses, like Sindbis virus (SINV), to kill cancers. The SINV AR339 strain is blood borne and relatively non-virulent. We evaluated the feasibility of SINV AR339 for treating human NB.

METHODS

The cytotoxicity and viral growth of SINV AR339 were evaluated for five human NB cell lines, SK-N-SH, IMR-32, LAN-5, GOTO, and RT-BM-1. SINV-induced apoptosis was confirmed by TUNEL assays and PARP-1 cleavage. In vivo effects of SINV on neuroblastoma cell xenografts in nude mice were assessed by intratumoral or intravenous SINV inoculation.

RESULTS

In five human NB cell lines, SINV infections induced remarkable cytotoxicity. The mRNA expressions of anti-apoptotic genes, Bcl-2 and Bcl-xL, in LAN-5 and RT-BM-1, which were less sensitive to SINV infection, increased in response to SINV infection, while the other NB cell lines sensitive to SINV infection failed to respond. In nude mice, intratumoral and intravenous SINV inoculations caused significant regression of NB xenograft tumors.

CONCLUSION

Our results suggested that SINV AR339 was significantly oncolytic against human NB. Thus, SINV showed promise as a novel therapy for treating NB.

Therapy of endocrine disease: the challenges in managing giant prolactinomas

Giant prolactinomas are rare tumours, representing only 2-3% of all prolactin (PRL)-secreting tumours and raising special diagnostic and therapeutic challenges. Based on several considerations developed in this review, their definition should be restricted to pituitary adenomas with a diameter of 40  mm or more, significant extrasellar extension, very high PRL concentrations (usually above 1000  μg/l) and no concomitant GH or ACTH secretion. Giant prolactinomas are much more frequent in young to middle-aged men than in women, with a male to female ratio of about 9:1. Endocrine symptoms are often present but overlooked for a long period of time, and diagnosis is eventually made when neurologic complications arise from massive extension into the surrounding structures, leading to cranial nerve palsies, hydrocephalus, temporal epilepsy or exophthalmos. PRL concentrations are usually in the range of 1000-100,000  μg/l, but may be underestimated by the so-called 'high-dose hook effect'. As in every prolactinoma, dopamine agonists are the first-line treatment allowing rapid alleviation of neurologic symptoms in the majority of the cases, a significant reduction in tumour size in three-fourths of the patients and PRL normalization in 60-70%. These extensive tumours are usually not completely resectable and neurosurgery has significant morbidity and mortality. It should therefore be restricted to acute complications such as apoplexy or leakage of cerebrospinal fluid (often induced by medical treatment) or to patients with insufficient tumoural response or progression. Irradiation and temozolomide are useful adjuvant therapies in a subset of patients with aggressive/invasive tumours, which are not controlled despite combined medical and surgical treatments. Because of these various challenges, we advocate a multidisciplinary management of these giant tumours in expert centres.

[Development of incurable cancer cell targeted agents using viral technology]

The safety and anti-tumor effect of oncolytic virus have been reported in a clinical study conducted in Japan. We have engineered a novel multimutated tumor-specific oncolytic herpes virus, harboring a smooth muscle-specific calponin promoter. Since tumor cells present in a hypoxic environment are known to be resistant to chemotherapy and radiotherapy, we also engineered a novel oncolytic herpes virus targeting a specific tumor microenvironment, which harbors a gene encoding a fusion protein of oxygen-dependent degradation (ODD) domain of HIF1α and ICP4, a master viral transcription factor required for replication. The recombinant virus selectively replicates in and disrupts the target tumor cells, including human sarcoma and malignant mesothelioma cells which are unresponsive to chemotherapy and molecular targeted therapy. We confirmed significant anti-tumor effects of the novel viruses in vivo in an allogeneic experimental model of an undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma; MFH) spontaneously generated in immunocompetent Fischer rats. Our viruses, manufactured in the Master Virus Seed Stock in the Good Manufacturing Practice facility will become novel agents that enable tumor cells unresponsive to conventional treatment to be disrupted.

Functional genomic screening to enhance oncolytic virotherapy

Functional genomic screening has emerged as a powerful approach for understanding complex biological phenomena. Of the available tools, genome-wide RNA interference (RNAi) technology is unquestionably the most incisive, as it directly probes gene function. Recent applications of RNAi screening have been impressive. Notable amongst these are its use in elucidated mechanism(s) for signal transduction, various aspects of cell biology, tumourigenesis and metastasis, resistance to cancer therapeutics, and the host's response to a pathogen. Herein we discuss how recent RNAi screening efforts have helped turn our attention to the targetability of non-oncogene support pathways for cancer treatment, with a particular focus on a recent study that identified a non-oncogene addiction to the ER stress response as a synergist target for oncolytic virus therapy (OVT). Moreover, we give our thoughts on the future of RNAi screening as a tool to enhance OVT and describe recent technical improvements that are poised to make genome-scale RNAi experiments more sensitive, less noisy, more applicable in vivo, and more easily validated in clinically relevant animal models.

The use of oncolytic viruses to overcome lung cancer drug resistance

Intrinsic and acquired drug resistance remains a fundamental obstacle to successful applications of anticancer therapies for lung cancer. Combining conventional therapies with immunotherapeutic approaches is a promising strategy to circumvent lung cancer drug resistance. Genetically modified oncolytic viruses (OVs) kill tumor cells via completely unique mechanisms compared to small molecule chemotherapeutics typically used in lung cancer treatment and can also be used to deliver specific toxic, therapeutic or immunomodulatory genes to tumor cells. Recent pre-clinical and clinical studies with oncolytic vaccine approaches have revealed promising combination strategies that enhance oncolysis of tumor cells and circumvent tumor resistance mechanisms. As clinical trials with oncolytic vaccines progress, and as the knowledge acquired from these studies builds a foundation demonstrating OVs safety and efficacy, novel combination approaches could soon have a major impact on the clinical management of patients diagnosed with lung cancer.

Genetic cancer vaccines: current status and perspectives

INTRODUCTION

The recent approval of the first therapeutic cancer vaccine by the US Regulatory Agency represents a breakthrough event in the history of cancer treatment. The past scepticism towards this type of therapeutic intervention is now replaced by great expectations. The field is now moving towards the development of alternative vaccination technologies, which are capable of generating stronger, more durable and efficient immune responses against specific tumour-associated antigens (TAAs) in combination with cheaper and more standardised manufacturing.

AREAS COVERED

In this context, genetic vaccines are emerging among the most promising methodologies. Several evidences point to combinations of different genetic immunisation modalities (heterologous prime/boost) as a powerful approach to induce superior immune responses and achieve greater clinical efficacy. In this review, we provide an overview of the current status of development of genetic cancer vaccines with particular emphasis on adenoviral vector prime/DNA boost vaccination schedules.

EXPERT OPINION

We believe that therapeutic genetic cancer vaccines have the strong potential to become an established therapeutic modality for cancer in next coming years, in a manner similar to what have now become monoclonal antibodies.